Materials for sustainable energy technologies (M-SET)

Resume : Semiconductor nanowires have demonstrated fascinating properties with application in a wide range of fields, including energy and information technologies. In particular, increasing attention has been focused on SiGe nanowires for application in thermoelectric generation after recent successful implementation in miniaturized devices. In this work, a bottom-up Vapour-Liquid-Solid methodology is optimized to integrate in-situ heavily boron-doped SiGe nanowires on thermoelectric generators. The effect of precursors gases is studied to determine the optimal parameters, and these conditions are then used to obtain fully epitaxially integrated nanowires into silicon-made microdevices. Higly accurate elemental maps obtained with nano-X-ray fluorescence and tip-enhanced Raman spectroscopy sheed light on the mechanisms hindering electric transport and helps heading appropriate processing conditions. The thermoelectrical properties - i.e. the electrical, thermal conductivity, and Seebeck coefficient - of the fabricated nanowires are fully characterized at temperatures ranging from 300 to 600 K, hence, allowing the complete determination of the Figure-of-merit, zT, with values up to 0.4 at 600 K. Likewise, the power harvesting capability of dense packaged microdevices including the described NWs is evaluated. These devices include several thermoelectric elements connected in different electrical configurations - i.e standalone, series or parallel -. Maximum open circuit voltages 3.6 mV in a series configuration and absolute power outputs of 0.11 µW in a parallel configuration were achieved we operating upon natural thermal gradients generated with hot heat sources at 200 °C. Moreover, voltages as high as 13.8 mV in a series configuration and powers of 1.25 µW in a parallel configuration were obtained under improved heat dissipation conditions with air flows of 1.5 m/s.

Resume : With the climate rapidly changing due to humanities excessive use of fossil fuels, the world is looking for sustainable solutions to our energy crisis. Thermoelectric materials play an intriguing role here, since they cannot only be used to convert waste heat into electricity, but also for solid state refrigeration. Their conversion efficiency depends on the Seebeck coefficient S, the electrical conductivity ?, and the thermal conductivity ?. Since these quantities are interconnected, finding a good thermoelectric material with high values of S and ?, but a low ?, is difficult, but there are several promising candidates. Clathrates, for instance, form in cage-like structures that encapsulate heavy guest atoms. The rattling of these guest atoms disrupts the heat carrying phonons, thus leading to a remarkably low lattice thermal conductivity, while keeping a high electrical conductivity. Recently it was discovered that the acoustic phonon modes and the rattling modes of such systems can hybridize in a way that resembles the Kondo effect [1]. Since this phononic Kondo effect strongly suppresses the high-frequency acoustic phonons, the lattice thermal conductivity is dominated by low-frequency, i.e., long-wavelength, phonons. Therefore, the clathrate?s already low thermal conductivity should decrease drastically if the long-wavelength phonons are cut off, for instance through nanostructuring. We set out to prove this by measuring individual type-I clathrate nanowires, fabricated out of carefully selected single crystals using a focused ion beam (FIB). We study the electrical resistivity and thermal conductivity at temperatures between 300 and 80 K, where an influence of crystal defects can be neglected. To avoid measurement uncertainties at such high temperatures, we implement a 3? technique for the thermal conductivity measurement, in which the suspended nanowire itself acts both as a heater and a thermometer, making it one of the most precise methods available. With this, we plan to trace the complex relationship between the size and the transport properties of type-I clathrates. [1] Ikeda, M.S. et al., Nat Commun 10, 887 (2019)

Resume : Most of the currently available commercial grade thermoelectric generators contain expensive and potentially hazardous elements, such as Bi, Pb or Te, which becomes a major hindrance for wide range application of thermoelectric generators. As such alternative materials are being sought, one potential candidate is the p-type semiconductor mineral tetrahedrite (Cu12Sb4S13). Tetrahedrite is a naturally occurring and abundant mineral with low toxicity that displays good electrical and thermal properties, with a figure of merit, zT, of 0,6 at 700K. Comparatively to commercially available thermoelectric materials (zT>1,0), this mineral cannot yet compete, however various studies have reported major improvements of the thermoelectric performance via isovalent doping. [1] In this talk, results of the effect of simultaneous isovalent doping of two elements in the thermoelectric properties of tetrahedrite, with the pair of dopants selenium (Se) and nickel (Ni), are presented. Characterization of the samples, Cu12-xNixSb4S13-ySey, was carried out with Powder X-Ray Diffraction, Raman Spectroscopy and Scanning Electron Microscopy, with Energy Dispersive Spectrometry. After annealing at 723K for 7 days (present stage of the production process), the samples show a main tetrahedrite phase (with the estimated lowest molar content being ≈84%), with minor presence of secondary phases, most frequently covellite and famatinite. Simulations carried out with Wien2K[2] software for calculating electrical band structures and density of states coupled with BoltzTrap[3], for calculating thermoelectric properties, established the optimum stoichiometric content for Ni and Se at x=0,5 and y=0,5. Measurements of the Seebeck coefficient and electrical resistivity of the actual samples, not only suggest that co-doping is improving the power factor, but also are congruent with simulations, with the Cu11,5Ni0,5Sb4S12,5Se0,5 sample achieving the highest power factor with 1277,73 µW/m.K2 at 300K, and after estimating the thermal conductivity with the Friedman-Franz law, a figure of merit zT=0.32 at 300K was obtained. Keywords: Tetrahedrites, annealed materials, thermoelectric materials, power factor References [1] R. Chetty et al., Tetrahedrites as thermoelectric materials: an overview, J Mater Chem C 3, No. 48 (2015) [2] Blaha, P. "WIEN2K, an Augmented Plane Wave Local Orbitals Program for Calculating Crystal Properties Karlheinz Schwarz." Techn. Universität Wien, Austria (2001). [3] Georg K.H. Madsen, David J. Singh, Comput. Phys. Commun., Vol. 175, issue 1 (2006), 67-71, BoltzTraP. A code for calculating band-structure dependent quantities,

Resume : Structural complexity of the unit cell is recognized as an efficient route for reducing the thermal conductivity without impacting on the electronic conduction of crystals.This is precisely the reason for which the so-called “clathrates” structures, guest-host structures, have been widely investigated in the field of thermoelectricity. Clathrates are structurally complex materials composed of covalently bonded cages filled with guest atoms. The very simple binary type I clathrates which contain two types of cages have a thermal conductivity of less than 2 W.m-1.K-1, which is suitable for thermoelectric applications as the large ZT of 1.35 at 900 K for n-type Ba8Ga16Ge30 confirms [1]. Type IX clathrates such as Ba24Ge100 and Ba24Si100 have a cage structure without equivalent in the hydrate and silicate clathrates. They have three different cages in which Ba guest atoms are intercalated. Previous works have shown that Ga substitution on Ge sites of Ba24Ge100 can lead to very low thermal conductivity of less than 1 W/m.K and ZT as high as 1.25 at 950 K [2].Thus the Ga-alloyed Ba24Ge100 clathrate is the clathrate compound with the lowest lattice thermal conductivity (about 0.3 W/m.K). Furthermore, at low temperatures, Ba24Ge100 is superconducting and experiences a structural transition involving significant changes in the charge density of the guest Ba atoms whose microscopic mechanism is not understand yet. All these physical properties are driven or take influence on the lattice dynamics of Ba24Ge100. Thus, the phonon properties require a better understanding, especially the dynamics of the guest Ba atoms. In the present work, we investigate for the first time the effect of the host cage structure on the low energy vibrational dynamics in the type IX germanium clathrate by combining inelastic neutron scattering and ab initio simulations. We report on the guest dynamics in Ba24Ge100 and evidence the existence of guest vibrational modes at about 3 meV, at much lower energy than those in type I clathrate Ba8Ge46-xZnx [3] and in similar energy range as for Ba24Si100 [4].We show a strong anisotropy of the vibrations of Ba guests in the open and very asymmetric Ge20 cages like as in the case of Ba24Si100, which points at a general behavior in the type IX clathrates.We were able to determine the momentum Q dependence of the low energy modes, showing that the dynamics of the Ba guests are correlated.We observe a strong change in the spectral weight of these modes when the compound undergoes a temperature-induced structural transformation in the temperature range 190-230 K. Our DFT calculations successfully approximate the essential features in the dynamics of the high-temperature Ba24Ge100 structure. [1] Saramat et al, J. Appl. Phys. 99, 023708 (2006) [2] Kim et al, Acta Mater. 54, 2057 (2006) [3] M. Koza et al, Phys. Rev. B 82, 214301 (2010) [4] R. Viennois et al, Phys. Rev. B 101, 224302 (2020)

Resume : Tetrahedrite based thermoelectric generators (TTEG’s) are seen as eco-friendly devices with great potential, especially because tetrahedrites are cheap, abundant and do not present the high toxicity observed in the common bismuth telluride and lead -based TEG’s. At the same time, with the crescent challenges to stop the global warming and the industries efforts to become greener, the TEG’s market has a good potential to grow, boosting the needs for more efficient and cheaper materials. Thermoelectric devices are quite attractive since they are able to harvest wasted heat, directly converting-it into electricity, have no moving parts or emit greenhouse gases and almost need no maintenance. Regardless of all these advantages, TTEG’s are still under development, being the fabrication of good electrical contacts between tetrahedrites and electrodes one of the biggest challenges to produce efficient/competitive devices. Since high electrical and thermal resistivities ruin the performance of thermoelectric devices, such problems are also common to other generators. However, and regarding the commercial devices, there are only a few public studies concerning these issues, being many jointing fabrication techniques patented and considered an industrial secret [1]. In this work, several jointing fabrication techniques are explored to evaluate which technique and method is more suitable to connected manganese doped tetrahedrites to copper electrodes. Several Cu11Mn1Sb4S13 tetrahedrite legs were synthesized by solid-state reaction and sintered/densified by hot-pressing. At the end of the synthesis/sintering processes the materials where shaped into small cubes and connected to copper electrodes using three techniques: cold pressing, hot-pressing, and a manual jointing fabrication method. At the same time several solders and paints, such as Zn-Al5 wt%, Ni and Ag water-based paints, were used for jointing, the possibility of contact fabrication without any paint or solder was also explored. The contact resistance between the tetrahedrite legs and the copper electrodes was measured on a custom-made system based on the three points pulsed current method. Computer simulations were made with the COMSOL Multiphysics software to simulate the expected devices performance using the measured contacts resistance. In these studies, we showed how the different fabrication methods and materials used affect the performance of a device and identify some off the biggest difficulties/problems of each of the fabrication methods and the main advantages of the best ones. [1] Z. Ren, Y. Lan, and Q. Zhang, Eds., Advanced Thermoelectrics, Materials, Devices, Contacts and Systems. 2018 by Taylor & Francis Group, LLC, 2017.

Resume : As derived from silicon substrate, meso-porous Si could be a competitive candidate for many thermoelectric applications for micro-systems namely due to the huge decrease of its intrinsic thermal conductivity. As reported in the literature, this can offer a higher figure of merit as well as a more significant efficiency for energy harvesting at the microscale level at room temperature. Also, to consider the electronic transport that is lowered by the fabrication process, a graphenisation step is investigated both on the structural and thermoelectric behavior of the mesoporous complex Si matrix. Porous silicon membrane is obtained by electrochemical etching process from an electrolytic solution of hydrofluoric acid and ethanol. Depending on numerous parameters (porosity, pore size distribution, porous thickness...) the Seebeck coefficient will be experimentally investigated accordingly to key process parameters and correlated to the membrane morphology and structural characteristics. Using a new home-made thermoelectric device specifically designed for porous membranes will make possible to evaluate the Seebeck coefficient in the range of 10 to 70 °C. Systematic investigation of graphenized and non-graphenized membranes is conducted to determine the contribution of the graphene in the enhancement of the thermoelectric properties. In parallel, electrical measurements (Van Der Pauw and Hall effect techniques) and thermal characterization (Pulsed photothermal and pulsed electrothermal methods) are also achieved for the estimation of the ZT coefficient and the power factor.

Resume : TEGs are an elegant way to transform wasted heat into useable electrical power. While downsizing the active thermoelectric legs is an effective strategy for increasing the maximum output power density p_max, still high electrical contact resistances and thermomechanical stresses are two major issues that have prevented a significant reduction in the volume of thermoelectric materials integrated thus far. In this communication, we will show how these limitations can be overcome by employing a non-traditional leg architecture that involves the insertion of thick metallic layers. Several single-couple and multi-couple TEGs with skutterudite layers as thin as 1 mm have been fabricated, generating record p_max values ranging from 3.4 to 7.6 W cm-2 for temperature differences of 450 and 630 K [1], respectively. Compared to conventional legs of 1 cm long, these p_max represent a sixtyfold decrease in the volume of skutterudites used. Thick metallic layers are shown to be a reliable technique for developing high-power-density TEGs. [1] El Oualid, S., Kogut, I., Benyahia, M., Geczi, E., Kruck, U., Kosior, F., Masschelein, P., Candolfi, C., Dauscher, A., Koenig, J. D., Jacquot, A., Caillat, T., Alleno, E., & Lenoir, B. (2021). High Power Density Thermoelectric Generators with Skutterudites. Advanced Energy Materials, 11(19), 2100580. https://doi.org/10.1002/aenm.202100580

Resume : The design and optimization of thermoelectric (TE) materials rely on the intricate balance between thermopower (Seebeck coefficient), electrical resistivity and thermal conductivity; perfecting such a balance is key to improve energy recovery systems and TE cooling devices. Complex copper sulfides can provide an eco-friendly high-performance low-cost alternative by using elements that are abundant in naturally occurring minerals. Most of these materials exhibit low thermal conductivity possibly determined by local structural distortions, rattling phenomena, or strong bond anharmonicity. However, the improvement of the TE performances of these materials remains a challenge, due to the interdependent and contrary effects of their properties. The presence of structural defects, non-stoichiometry, the nature of the chemical bonds, order/disorder phenomena in these complex structures are still a matter of debate, which is of capital importance for the optimization of their TE properties. Our investigations on some thermoelectric complex sulphides derived from natural minerals (colusite, tetrahedrite, gladite, stannoidite, germanite, mohite-derivatives) will be presented.[1] Mechanical alloying, SPS sintering, as well as structural and microstructural features will be reported, together with electrical, thermal properties. Band structure and vibrational dispersions from first principles calculations will be discussed. [1] J. Amer. Chem. Soc. 140 (2018) 2186, Angewandte Chemie Int. Ed. 58 (2019) 15455, Adv. Energy Mater. 9 (2019) 1803249, Phys. Rev. Mater. 4 (2020) 025404, Chem. Mater. 32 (2020) 830, J. Mater. Chem. C 9 (2021) 773 (Review article), Angewandte Chemie Int. Ed. 61 (2022) e202108686 (Review), J. Mater. Chem. A 9 (2021) 10812, Inorg. Chem. 60 (2021) 16273, J. Amer. Chem. Soc. (2022, doi: 10.1021/jacs.1c11998)

Resume : The storage of energy in the form of dihydrogen is attracting growing interest in the scientific community as well as in the energy and transport industries. Proton exchange membrane fuel cells (PEMFC) convert this gas into electricity without harmful emission, at relatively low temperatures. Nowadays, catalysts are mainly made up of platinum nanoparticles, deposited on a microporous carbon material. However, this expensive, rare and unsustainable noble metal is a source of environmental and societal problems, and its supply is subject to geopolitical tensions and vagaries. Nitrogen-doped graphenic materials are investigated as cheap alternative to platinum since nitrogen is able to catalyze oxygen reduction by partially redistributing the electric charges of the neighboring carbon atoms An elaboration method based on a solvothermal reaction between cheap organic molecules, e.g. ethanol, cyclohexanol, ethanolamine or N piperidineethanol and sodium, followed by a pyrolysis treatment, has been developed, yielding N-doped graphenic materials with a pronounced three-dimensional aspect and a very developed porosity with surface area up to 2200 m2.g 1, and electrochemical properties brought by the nitrogen doping (1-3 at.%). Recently, this material has been tested as the cathode material in a complete PEM fuel cell setup under H2-air flows. N-doped graphenic foams have been studied with electrochemical impedance spectroscopy, a powerful technique to characterize and diagnose fuel cells, allowing to extract the contributions from the different processes and from the different components impacting the potential losses of the cells. First tests showed that N-doped graphenic foam as cathode catalyst, allows current density over 30 mA/cm2, a power density of 3.2 mW.cm-2, approximately 50-fold larger than with nitrogen-free graphenic foam. While nitrogen atoms appear essential to catalytic activity, intrinsic carbon defects nature, pore size or oxygen functions content could also play an essential role for catalysis purpose, as currently studied to optimize furthermore our materials.

Resume : Due to the threat posed by climate change, the European Union has agreed to downsize greenhouse emissions by at least 55% by 2030. Among these gasses, carbon dioxide is considered one of the main contributors to global warming. To generate environmentally sustainable energy, not only new and cost-effective energy processes, but also CO2 fixation technologies must be developed. Carbon dioxide can be captured via chemical methods, usually based on the use of amine solutions with several drawbacks such as high sorbent cost and equipment corrosion damage. Simple metal oxides have been studied as viable alternatives since they easily form stable carbonates in the presence of CO2. These carbonates can be decomposed again under high temperatures and/or specific atmospheres, liberating the absorbed gas in the process, and returning to their oxide form. Despite perovskite-type structure oxides exhibiting a wide range of physical properties, they have not been highly studied as materials in the CO2 capture. In this context, we have studied Ba-Ni oxides that can host carbonate groups within their structure. A new oxycarbonate can be obtained through sol gel method and posterior calcination under oxygen atmosphere. This new phase has been compositional and structurally characterized by X-Ray and Neutron Diffraction and atomically-resolved Scanning Transmission Electron Microscopy coupled with Energy Dispersive Spectroscopy and Electron Energy Loss Spectroscopy. In this work, we study its chemical and physical properties focusing on its viability as CO2 sorbent. For this purpose, we have carried out a combined “in situ” High-Temperature X-Ray Diffraction and Thermogravimetric Analysis study.

Resume : Semiconductor-based photocatalysts have attracted a lot of attention owing to their potential use as photocatalysts to convert sunlight into electricity or fuels. Among these materials, TiO2 is considered to be one such promising metal oxide because it possesses excellent physical and chemical properties such as a high oxidative power or a long-term stability. TiO2 has a rather wide band gap lending to this material a use limited to the ultraviolet light region. Furthermore, photoexcited electron–hole pairs tend to recombine relatively easily in TiO2. In order to alleviate these problems, doping TiO2 with noble metal nanoparticles such as Pt, Ag, Pd or Au has been demonstrated to be an effective approach [1]. In order to scrutinize further the interaction of TiO2 with light at the nanoscale, we report a second harmonic (SH) intensity microscopy study performed in retro-reflection from TiO2 and ZnO nanocrystals powders. Such a method has been performed in the past on other type of powders like lithium niobate nanocrystals powders [2]. Depth intensity profiles exhibit first an intensity increase due to the beam focus entering the powder followed by a decrease due to multiple scattering. Besides, the polarization analysis performed at selected depths demonstrates a competition between ballistic and multiply scattered photons. In parallel, a model has been developed to retrieve the main parameters for these SH profiles using a Gaussian beam approach. Wavelength dependence of the SH signals is also reported in order to provide further insights into the role of the resonance enhancement due to the interband transition excitation and light absorption. Single crystals SH microscopy is also studied in order to understand fully the origin of the SH intensity and its principal characteristics.

Resume : Design and development of efficient, economical, and durable electrocatalysts for oxygen ‎evolution reaction (OER) are of key importance for the realization of electrocatalytic water ‎splitting. To date, VB2 and its derivates have not been considered as electrocatalysts for ‎water oxidation. Herein, we developed a series of electrocatalysts with a formal composition ‎of V1-xCoxB2 (x = 0, 0.05, 0.1, and 0.2) and employed them in an oxygen-evolving reaction. ‎The incorporation of Co into the VB2 structure caused a dramatic transformation in the ‎morphology, resulting in a super low overpotential of 200 mV at 10 mA cm-2 for V0.9Co0.1B2 ‎and displaying much greater performance compared to the noble-metal catalyst RuO2 (290 ‎mV). The longevity of the best-performing sample was assessed through the exposure to the ‎current density of 10 mA cm-2, showing relative durability after 12 h under 1 M KOH ‎conditions. The Faradaic efficiency (FE) tests corroborated the initiation of OER at 1.45 V ‎‎(vs. RHE) and suggested a potential region of 1.50 – 1.55 V (vs. RHE) as the practical OER ‎region. The Facile electron transfer between metal(s)-metalloid, high specific surface area, ‎and availability of active oxy-hydroxy species on the surface were identified as the major ‎contributors to this superior OER performance.‎

Resume : Nickel oxyhydroxides (NiOOH) are promising catalysts for the oxygen evolution reaction (OER) in alkaline solutions. The OER is the limiting step for the water-splitting reaction at the anode in electrolyzers that are foreseen for mass-scale production of green hydrogen. Doping with iron increases the OER activity of NiOOH significantly up to 2~3 orders of magnitudes [1]. We applied the state-of-the-art parameter-free DFT+U approach to shed light on the underlying phenomena [2]. Our methodology corrects incorrect prediction of standard DFT+U methods of semi-metallic state, predicting NiOOH as a semiconductor [3]. This was achieved by applying the Wannier functions as more realistic projectors for the occupancy of d states [2]. The resulting band gaps of nickel (oxy)hydroxides are consistent with the measured values. We discuss the maximum solubility of Fe in NiOOH and related enhancement of electrocatalytic activity in terms of electronic structure, thermodynamics of Fe:Ni solid solution, and spin state of cations [3,4]. References: [1] Friebel D., Louie M. W., Bajdich M., J. Am. Chem. Soc., 2015, 137, 1305-1313 [2] Kowalski P. M., He Z.D., Cheong O., Front. Energy Res., 2021, 9, 653542 [3] Zaffran J., Toroker M. C., J. Chem. Theory Comput., 2016, 12, 3807-3812 [4] Mogilevsky P., Phys. Chem. Miner., 2007, 34, 201-214 [5] Hammer B., Nørskov J. K., Surf. Sci., 1995, 343, 211-220

Resume : Korovin A.N.*(1), Humonen I.S.(1), Samtsevich A.I.(1), Eremin R.A. (1), Vasilyev A.I.(1), Lazarev V.D.(1), Budennyy S.A.(1) (1)AIRI, Moscow, Russia, 121170 Boosting heterogeneous catalyst discovery by structurally constrained Machine Learning models. Despite extensive use of heterogeneous catalysts for water splitting and carbon dioxide reduction their development is still going through a trial-and-error approach, they are not efficient with respect to activity and selectivity. Ab-initio computational chemistry can be used to model and evaluate prospective materials. However, the region of interest in configurational space and compositional space is enormously large and quantum mechanical simulations are too computationally expensive so most of potentially existing materials can not be neither tested nor even predicted. Introduction of machine learning approaches can dramatically boost research. Unfortunately, there is a lack of precise models and relevant datasets to train them. Predictions of catalysts are even more challenging as combinations of small-molecules and multiple crystalline surfaces should be considered. Open catalyst challenge, one of recent and aspiring attempts to tackle this task, is an open dataset combining about half a million of DFT models of stable and smallest organic reactants. The main idea of our approach has been to implement a GNN-based model by constructing a graph with edges representing interaction only between directly connected neighbours which mainly contribute energy properties of solids. Such graphs have been calculated via Voronoi tessellation accounting for periodic boundary conditions (PBC) with a cut-off radius of 6Å, in order to avoid any interslab connections (due to PBC in the z-direction). The corresponding contact solid angles and types (direct/indirect) were considered as edges’ features and Voronoi volumes were used to characterise nodes. The auxiliary approach was enriching node representation by intrinsic atomic properties (electronegativity, period, and group position). The level of the mean absolute error of the best model on the validation dataset was 0.651 eV/atom that improved the original model on 0.04 eV/atom. To reach the trade-off between the performance and computational costs, we have used the SpinConv [1] model. It is a graph convolutional neural network with a message passing mechanism and two key peculiarities: Gaussian smearing transformation and trainable element-dependent correction for interatomic distance encoding and a spin convolution in local spherical coordinate systems of each edge of the graph to take into consideration relative atomic positions. These peculiarities determine such physical restrictions as a rotation equivariance and a difference in radii of atoms. We have obtained satisfactory results considering the OCP leaderboard, but all participants’ models still are not able to approximate the DFT calculation from the OCP challenge with accuracy, required for practical application (less than 10% of predictions is acceptable). Nevertheless, we believe that the graph neural network approach is viable: we applied it to more specific, but less complex and artificial data, and achieve two orders of magnitude smaller error References ​(1) Shuaibi, M.; Kolluru, A.; Das, A.; Grover, A.; Sriram, A.; Ulissi, Z.; Zitnick, C. L. Rotation Invariant Graph Neural Networks Using Spin Convolutions. 2021.

Resume : There has been immense interest in hierarchical design of structural composite materials as electrocatalysts with high performance for direct methanol fuel cells (DMFCs). Herein, we rationally designed and prepared a newly hierarchical quaternary nanocomposite composed of carbon nanotube (CNT), polyacrylic acid (PAA), SnO2 layer and PtRu alloy. In this multiple-phase boundary nanostructure, tiny-sized PtRu alloy particles are deposited in a highly dispersed form on the robust CNT support owing to the efficient utilization of covalently grafted PAA brushes and uniformly coated SnO2 layer. The overall electrocatalytic activity of as-prepared CNT-g-PAA@SnO2/PtRu catalysts for methanol oxidation has been thoroughly studied. Amongst, the best CNT-g-PAA@SnO2/PtRu catalyst exhibits well-balanced performance with high mass activity (519.74 mA mg−1 of Pt), low onset potential (0.16 V) and good If/Ib values (1.40). Furthermore, the activities of the CNT-g-PAA@SnO2/PtRu catalysts were evaluated by single-cell DMFC test, which reveals superior performance toward methanol oxidation as compared with the reported catalysts. The outstanding performance of the prepared CNT-g-PAA@SnO2/PtRu catalysts is attributed to the good dispersion and small particle size of PtRu alloy NPs, the high porosity and electrical conductivity of CNT support and the rational synergism with the combined effect (i.e. enhancing the intrinsic activity of PtRu, promoting formation of active OH species from water and improving CO poisoning tolerance). This work provides some guidance for the fabrication of hierarchical composite materials for use in DMFCs.

Resume : When designing new materials for sustainable energy applications, researchers commonly optimise existing materials towards certain desired properties such as a specific bandgap value. Increasingly often computational methods such as genetic algorithms or random searches are combined with human intuition. Machine learning systems have the potential to complement and eventually outperform human intuition. In this talk, I will be explaining the challenges of designing and training such a system based on the latest models from the field of machine learning. In the end, I will also expand on possible extensions of the project towards a system that is not limited to tuning the bandgap but also a number of other properties such as chemical stability, carrier mobility or catalytic activity.

Resume : Multifunctional semiconductor cubic silicon carbide (3C-SiC) is employed for fuel cell electrolyte, which has never been used before. n-type 3C-SiC can be individually employed as the electrolyte in fuel cells, but delivers insufficient open circuit voltage and minuscule current density due to its electronic dominant property. By introducing n-type ZnO to form an n–n 3C-SiC/ZnO heterostructure, significant enhancements in the ionic conductivity of 0.12 S/cm and fuel cell performance of 270 mW cm2 are achieved at 550 C. It is found that the energy band bending and build-in electric field of the heterostructure play the pivotal role in the ionic transport and suppressing the electronic conduction of 3C-SiC, leading to a markable material ionic property and fuel cell performance. These findings suggest that 3C-SiC can be tuned to ionic conducting electrolyte for fuel cell applications through the heterostructure approach and energy band alignment methodology.

Resume : From the proton ceramic cell (PCFC) to the emerging semiconductor ion fuel cell (SIFC)/ semiconductor membrane fuel cell (SMFC), the polarization curve or current-voltage characteristics of fuel cells are vitally important to explore the scientific mechanism of various solid oxide cells aiming at low operational temperatures (below 600◦C). There is no uniform measurement process in cell testing, resulting in small geometrical errors that can cause differences in electrochemical properties. Researchers are pursuing higher peak power density (PPD) at low temperatures, but partial cells may still remain in a transient state (TS) to some extent, which means that they are unable to fulfill the prerequisite of a steady state (SS) characteristic of polarization curve measurement. The reported PPD value can be anywhere between a high transient power density (TPD) and a low stable power density (SPD), depending on the test parameters. Here, we propose a procedure by standardizing the method and process for cell testing and modifying the quasi-steady state (QSS) characterization based on stabilized cell and time-prolonged measurements of common I–V plots. This study shows that the quasi-steady-state power density itself can still better approximate the real performance of fuel cells compared to the steady-state value.

Resume : Proton conducting perovskite oxides are emerging demand for advanced electrochemical energy systems. Herein we develop semiconductor SrCo0.8Fe0.2O3−δ (SCF) with significant proton conductivity by constructing a heterostructure using a guest component Fe3O4 from the bulk on the surface. This process may be called as a self-assembled SCF and Fe3O4 exsolution heterostructure (SCF-Fe3O4) used as a new functional proton electrolyte for semiconductor ionic fuel cell (SIFC). The optimum composition of SCF-Fe3O4 SIFC has reached a power density of 583 mW cm-2 and OCV of 1.01 V at 550 oC. exhibiting the extraordinary ionic conductivity of 0.2 S cm -1. An energy band alignment mechanism based on a p-n heterojunction may explain the suppression of electronic conductivity and promotion of ionic conductivity in the heterostructure due to built-in electric field effect. Our findings reveal that semiconductor SCF can be developed as promising protonic electrolytes by self-assembly SCF-Fe3O4 heterostructure approach.

Resume : Abstract: Global warming caused by the use of fossil energy; new green energy technologies are urgently demanded. Semiconductor membrane fuel cell (SMFC) has become a new energy conversion technology that is very likely to realize the commercialization of low-temperature ceramic fuel cells (CFCs). There are many advantages of the SMFCs over the conventional CFCs, e.g., solid oxide fuel cell (SOFC) and proton ceramic fuel cell (PCFC). Typically, the built-in electric field formed by the semiconductor heterostructure can assist ionic transport and the interface can build up superionic conduction channels resulting in the ion conductivity much higher than that of the traditional CFC. However, the stability of SMFC is still a challenge worthy of study. Therefore, in this work, transition metal elements are used to regulate and optimize the performance of GDC, form heterostructures. We synthesize a new material and construct the SMFC to conduct stability studies, we explore the new ways to improve cell performance and optimize its stability. Keywords: semiconductor membrane fuel cell (SMFC); heterostructure; fuel cell stability; doped ceria, GDC

Resume : Ultra-wide bandgap semiconductor samarium oxide attracts great interest because of its high stability and electronic properties. However, the ionic transport properties of Sm2O3 have rarely been studied. In this work, Ni doping is proposed to be used for electronic structure engineering of Sm2O3. The formation of Ni-doping defects lowers the Fermi level to induce a local electric field, which greatly enhances the proton transport at the surface. Furthermore, ascribed to surface modification, the high concentration of vacancies and lattice disorder on the surface layer promote proton transport. A high-performance of 1438 mW cm–2 and ionic conductivity of 0.34 S cm–1 at 550 °C have been achieved using 3% mol Ni doped Sm2O3 as electrolyte for fuel cells. The well-dispersed Ni doped surface in Sm2O3 builds up continuous surfaces as proton channels for high-speed transport. In this work, a new methodology is presented to develop high-performance, low-temperature ceramic fuel cells.

Resume : Solid oxide fuel cell (SOFC) can transform chemical energy in electric energy efficiently. What’s more, compared with proton exchange membrane fuel cell, SOFC possesses the advantage of needless of precious metal catalyst and low requirement for hydrogen purity. However, high work temperature limits its commercialization. Increase ionic conductivity of electrolyte can effectively decrease the SOFC work temperature. Constructing heterointerface has been an emerging approach for increasing electrolyte materials conductivity. Here this work fabricated WO3-LSCF composite electrolyte which showed excellent ionic conductivity in low temperature. The maximum power density (Pmax) of this fuel cell with WO3-LSCF electrolyte achieved more than 800 mW cm-2 under 550 ℃.

Resume : Among lithium-conducting SSEs, Li7La3Zr2O12 (LLZO) has received much attention due to its high ionic conductivity (∼10-4-10-3 S cm-1) and stability in contact with lithium metal over a wide voltage window (∼0-5 V). [1] While the application of Li metal as anode has been intensively investigated [2], the integration of LLZO with high-energy cathodes such as layered mixed metal oxides is a challenge in the development of SSBs. [3] Chemical reactions occur during cell production, especially at high processing temperatures, which are usually required to obtain conformal contact, and accelerate the kinetics of chemical reactions and diffusion processes that lead to high interface resistances. In this study, the interface between LLZO pellets with LiCoO2 (LCO) as cathode material is modified by depositing different metal oxide interface coatings. Various ternary Li-oxide systems (Nb, Al, Ti, Zr) are deposited on the pellets by RF sputtering and then coated with a thin-film cathode. Co-sintering at high temperatures establishes uniform physical contact between the electrolyte and the cathode. To study the electrochemical performance, we compare electrochemical impedance spectroscopy of full cells (LCO|Li-Nb-O|LLZO|Li) with symmetric cells (LCO|Li-Nb-O|LLZO|Li-Nb-O|LCO, etc.) to describe impedance characteristics specific to the evolution of interfacial dynamics at the cathode interface. By studying the interfacial dynamics between the thin-film LCO cathode, an "artificial" solid electrolyte interface, and LLZO, we systematically investigate the effect of different interlayers of ternary Li-oxides and determine the most promising interlayers for future studies. 1. Wang, C. et al. Chem Rev 120, 4257–4300 (2020). 2. Fu, K. (Kelvin) et al. Sci Adv 3, e1601659 (2017). 3. Xiao, Y. et al. Nat Rev Mater 5, 105–126 (2020).

Resume : High operating temperature resulting in materials and cost limitations and operating complexities has hindered the commercial application of ceramic fuel cells (CFCs) based on an oxide-ion conductor electrolyte, i.e. solid oxide fuel cells (SOFCs). In recent years, much efforts have been devoted to develop advanced CFCs that can operate at low temperature region (300-600 ℃) based on new solid electrolyte materials such as protonic ceramics, thus much attention has been paid on protonic ceramic fuel cells (PCFCs). Instead of perovskite oxide proton conductors, LISICON such as Li13.9Sr0.1Zn(GeO4)4 (LSZG) has been successfully adopted as electrolyte in SOFC due to its high H+ conductivity (0.048 S·cm-1@600 °C) via Li+/H+ ion exchange mechanism. To further improve ionic conductivity at low temperature, a new strategy has been proposed to design electrolyte for low temperature CFCs based on semiconductor-ionic materials (SIMs), which has achieved high ionic conductivity (>0.1 S·cm-1 below 600 °C) via heterostructure field effect. Excellent cell performances have been demonstrated because of the high ionic conductivity and good electrocatalytic activity of SIMs. In this work, SIM was designed by composing a NASICON Na5YSi4O12 (NYS) with a semiconductor Ni0.8Co0.15Al0.05LiO2 (NCAL) and functioned as electrolyte in PCFC. By optimizing the composition of NYS-NCAL heterostructure electrolyte, the symmetric PCFC with a 2 mm thick NYS-NCAL (1:1 in weight ratio) composite electrolyte layer and NCAL coated nickel foam electrode achieved the highest performance, peak power density of 281 mW·cm-2 and an open-circuit voltage of 0.91V at 550 °C. The ionic conductivity of the NYS-NCAL composite electrolyte evaluated from the cell I-V curve was 0.19 S·cm-1 at 550 °C, which is much lower than that (0.41 S·cm-1) obtained from the cell EIS curve under open circuit condition, but much higher than that (0.011 S·cm-1) of pure NYS obtained from the EIS curve of electrolyte pellet in humidified hydrogen atmosphere, indicating that the NYS-NCAL heterostructure greatly improves the proton conductivity of NYS by Na+/H+ ion exchange mechanism, however, this ion exchange process is insufficient and contributes less to cell performance. Thus, Further study should be conducted to the Na+/H+ ion exchange mechanism and it can be expected that excellent cell performance be obtained by reducing the thickness of NYS-NCAL composite electrolyte while maintaining its mechanical strength and gas barrier.

Resume : Indoor organic photovoltaics (OPVs) are the potential niche applications of organic semiconductors due to their strong and well-matched absorption with the emission of indoor lighting. However, due to extremely low photocurrent generation, the device parameters critical for efficient indoor OPVs differ from those under 1 Sun conditions. Herein, we identify these critical device parameters – recombination loss and shunt resistance (Rsh) – and demonstrate that bilayer OPVs are suitable for indoor PV applications. Compared to bulk-heterojunction (BHJ), the open-circuit voltage loss of bilayer devices under low light intensities is much smaller, consistent with a larger surface photovoltage response, indicating suppressed recombination losses. The bilayer devices show a higher fill factor at low light intensities, resulted from high Rsh afforded by the ideal interfacial contacts between the photoactive and the charge transport layers. The high Rsh enables bilayer devices to perform well without a light-soaking process. Finally, the charge carriers are extracted rapidly in bilayers, which we attribute to strongly suppressed trap states possibly induced by isolated domains and non-ideal interfacial contacts in BHJs. This study highlights the excellent suitability of bilayer OPVs for indoor applications and demonstrates the importance of device architecture and interfacial structures for efficient indoor OPVs.

Resume : The growth conditions for a material may have drastic effects on its properties and performance, impacting reliability, storage capacity, and operational kinetics. Additionally, with the fast pace of development for promising new energy storage materials, it is critical to identify the salient features of a new material phase or microstructure for high-throughput screening of materials. While Mg-transition metal hydrides are well-studied materials systems, here we present novel experimental results showing a correlation between the thin film growth method and hydrogenation mechanisms. Thin films of Mg2Ni were grown under two sets of conditions: one yielding an equiaxed microstructure (20-50 nm) and the other a columnar microstructure (20-40 nm width and >300 nm length). The films were then hydrogenated, causing a transformation to the Mg2NiH4 hydride phase. When the equiaxed microstructure is hydrogenated, hydride nucleation is preferred to growth, and the hydrogenation process begins at the exposed surface. On the other hand, for the columnar microstructure, hydride growth is preferred to nucleation, and hydride formation is initiated at the interface between the substrate and the Mg2Ni layer. The change in nucleation and growth rates, as well as nucleation location implies a significant change in overall hydrogenation kinetics. Here we demonstrate a correlative approach to identifying these differences in the hydrogenation pathway, combining TEM imaging and diffraction, X-ray diffraction, SEM backscatter imaging, optical and laser-scanning confocal microscopy (LSCM), and a FIB-SEM platform with attached in-house developed secondary ion mass spectrometer (FIB-SIMS). SIMS is one of the few techniques capable of directly imaging the hydrogen distribution in solid materials, and we present 3D reconstructions of the partially transformed thin films illustrating the size, shape, and location of the hydrogenated phases, which were first identified using TEM bright field and dark field imaging and diffraction analysis. Finally, we find that due to the volume expansion associated with the hydride phase transformation, LSCM can identify the in-plane size and location of the hydrogenated phases, allowing the hydrogenation state of future films to be rapidly assessed. Thus, once the more complex mechanisms of the transformation have been established using intensive techniques like TEM or high-resolution SIMS imaging, the day-to-day characterization of future films may be performed with relative ease using optical microscopy techniques. Acknowledgement: This work was funded by the Luxembourg National Research Fund (FNR) by the grant C18/MS/12661114 (MEMPHIS)

Resume : Given the wide capability of small positive ions (H+ and Li+) intercalation, WO3 represents a promising material for energy storage applications due to its low cost, electrochemical durability, and high stability in an acidic environment. In this scenario, nanostructured WO3 is extremely interesting due to the very high surface available that allows a high rate of charge transfer in supercapacitors. Here we present a low-cost electrode obtained by drop-casting of hexagonal WO3 nanorods synthesized by one-step hydrothermal growth. Careful optimization of the electrode mass and thickness and of WO3 nanostructures morphology is proposed allowing to reach up to 488 F/g at 5 mV/s and 406 F/g at 0.5 A/g. The microscopic mechanism underlying the charge storage process is discussed in terms of surface and diffusion-controlled mechanisms, based on an extensive electrochemical investigation (cyclic voltammetry, galvanostatic charge-discharge analysis, electrochemical impedance spectroscopy). The superior pseudocapacitive performance of WO3 nanorods has been then integrated into a prototypal asymmetric supercapacitor (ASC) demonstrating up to 110 W*h*Kg-1 at 2700 W*Kg-1 and up to 9000 W*Kg-1 at 92.5 W*h*Kg-1.

Resume : Hydrogenated amorphous silicon–carbon alloy Si1-xCx:H is an attractive material for receiver absorber in CSP due to its high strength, high thermal conductivity, low thermal expansion, chemical inertness at high temperatures and high solar absorptance [1]. Si1-xCx:H thin films have a refractive index (n > 2.5 at 630 nm) adapted for the design of Si1-xCx:H/W multilayers selective absorber materials. Si1-xCx:H can also act as diffusion barrier for metals to stabilize selective stacks optical properties, for which metal diffusion is a major source of degradation [2]. However, all the properties listed above are intrinsically linked to the Si1-xCx:H material stoichiometry and connectivity of the silicon carbide network. It is known that the chemical bonding and band structure of Si1-xCx:H thin films depend primarily on the value of carbon content x [3]. Likewise, the optical properties such as refractive index and optical band gap also depend on the degree of microcrystallinity and hydrogen content in the films. Therefore, the control of the carbon and hydrogen contents incorporated into the films during the synthesis is essential to optimize the properties of the selective absorber materials. In this context, the current presentation will concern the contribution of ion beam analyzes through RBS, ERDA and NRA techniques in the exploration and optimization of the deposition parameters in PVD magnetron sputtering for W layers and microwave PECVD for Si1-xCx:H layers. The objective is to produce multilayers films endowed with excellent optical properties and chemical inertness at high temperatures to design multilayer selective absorber materials for CSP. Ion beam analyzes before and after annealing at 500°C are complemented by electron microscopy, XPS and infrared spectroscopy, allowing in-depth analysis of the material network, which can be linked to the materials optical properties measured by ellipsometry and spectrophotometry. [1] C.K Ho et al., Solar Energy, 152, pp.38-56, (2017). [2] A. Soum‐Glaude et al., for the book: Nanotechnology for Energy Sustainability, Wiley-Blackwell, pp.231-248, (2017) [3] I. Solomon et al., Applied Surface Science, 184 pp.3-7, (2001)

Resume : For further developing perovskite solar cells (PSCs), knowledge about the energetic alignment between the key components is required. Photoelectron spectroscopy (PES) has provided valuable information on both chemical and electronic properties of individual layers, buried interfaces and full device stacks. With the study of individual layers, we were able to explain the enhanced efficiency of a PSC based on a 2D/3D hybrid Pb-free perovskite [1]. Addition of phenethyl ammonium bromide on top of CsAgBiBr6 converts the absorber from a 3D to a 2D perovskite structure. Energy levels of 3D and 2D/3D hybrid layers were measured by PES and were compared to those of a Spiro-OMeTAD layer in order to assess the interfacial band alignment. It could be shown that the presence of the 2D layer improves hole transfer from CsAgBiBr to Spiro-OMeTAD and acts as an additional blocking layer for the electrons. This previous approach is limited by the absence of a real interface between the absorber and the hole transport layer. This is why we resorted to so-called interface experiments. Layers are deposited step-by-step and intermittently analyzed by PES to follow the evolution of the energetics at the interface. For the MAPbI3 | Spiro-OMeTAD interface [2], we could demonstrate a band bending of 0.8 eV in the dark and a photovoltage of the same value under illumination. It evidences that the main part of the potential drops at this key interface. Interface experiments also have limitations. They are for instance limited to vacuum-prepared PSCs which are in general less efficient than solution-prepared PSCs. To proceed to the analysis of real, state-of-the-art, high performance mixed ion PSCs, the tapered cross-section PES (TCS-PES) was developed [3]. In TCS-PES, a tapered cross-section is prepared by polishing the PSC at a very low angle. It projects the normal sub-µm cross-section to a length of several millimeters, matching the spatial resolution of the PES system. With this approach, the chemical and electronic properties along the full device stack can be analysed. We measured the electrostatic potential evolution along the PSC and could confirm that the main variation occurs at the perovskite | Spiro-OMeTAD interface. We realize that transferring the knowledge obtained from a TCS device to a realistic working device is not straightforward. The absorber measured at the TCS is few hundreds of µm away from the contacts. The TCS device therefore requires a new physical description, which we in 2D drift-diffusion simulations. For the PSC studied here, the simulated electrostatic potential evolution across the working device and across the TCS matched well. [1] M.T. Sirtl et al., Adv. Energy Mater. n/a (n.d.) 2103215. https://doi.org/10.1002/aenm.202103215 [2] T. Hellmann et al., Adv. Energy Mater. 10 (2020) 2002129. https://doi.org/10.1002/aenm.202002129 [3] C. Das et al., ACS Appl. Mater. Interfaces. 12 (2020) 40949–40957. https://doi.org/10.1021/acsami.0c11484

Resume : Transparent conductive oxide (TCO) thin films play an important role as transparent electrodes (TE) for photovoltaic applications and flexible electronics. Emerging technologies requires long-term stability, high conductivity, and selected high optical transparency for TE to be implemented in the devices. It is extremely important to improve conventional TCOs as Indium Tin Oxide (ITO), the most used TCO, and other Indium-based TE taking advantage of their already consolidate good electrical and optical properties. Reducing the amount of In and optimizing the process parameters to obtain good performance at room temperature and low post-deposition thermal annealing is still one of the major challenges. In this work, we present an ultra-thin, highly conductive, and transparent TCO based on In2O3 doped with low Zr concentration (IZrO). Films with reduced thickness (down to 15nm) compared to those standardly used in solar cells, were deposited by co-sputtering of In2O3 and Zr targets, at room temperature followed by low-temperature thermal annealing (T = 200 °C). Rutherford backscattering spectrometry has been performed to measure the elements at% and film thickness, while SEM and AFM were employed for morphological analysis. Fractal analysis through the Power Spectral Density method was conducted on topographic images to extract fractal dimension and roughness parameters in order to understand how the geometry affects the physical properties of the system. Optical bandgap and work function values were obtained by Tauc analysis and KPFM measurements, while the crystalline structure was detected by XRD technique showing a transition from amorphous to crystalline phase after annealing. The improvement of the crystalline quality leads to very good optical and electrical properties: resistivity as low as 10^(-4)Ωcm and optical transmittance up to 80% in VIS and NIR range. IZrO electrode performances have also been tested through EQE measurements on a semi-finite HJT bi-facial silicon solar cell manufactured by Enel Green Power. The cell was taken from the production line just after the deposition of the n+ and p+ hydrogenated amorphous silicon layers deposited on the front and on the back surfaces respectively, and before the standard ITO deposition. Our studies report EQE comparable to that of standard ITO. Those results suggest that ultra-thin IZrO may successfully be employed to reduce costs and the amount of critical materials for In-based TCO.

Resume : The extensive concerns of limited resources, safety and the environmental issues of current energy storage techniques has fired new research to sustainable battery revolution to satisfy the burgeoning global market. Aqueous zinc-based batteries are able to address these issues but suffer from fast capacity fade and poor ion diffusion kinetics; due to unstable structures and limited performance of cathode materials and electrolytes. The recent progress of cathode materials for zinc-based batteries from my group will be discussed in the talk.

Resume : Hydroxysulfate (AMSO4OH) compounds form a niche class of high-voltage polyanionic battery cathodes with a desirable combination of efficient electrochemical activity along with moisture resistance due to the presence of hydroxyl (OH) group1. Monoclinic FeSO4OH (s.g. C2/c) was the first reported hydroxysulfate cathode exhibiting an Fe3+/Fe2+ redox potential at 3.2 V with capacity over 120 mAh/g involving a two-step biphasic redox reaction2,3. Showcasing its versatility, here we report the first demonstration of reversible Na+ (de)insertion in FeSO4OH via solid solution mechanism at ~2.9 V with a discharge capacity of 85 mAh/g. The size of (de)intercalating ions can trigger varied structural/ electrochemical properties in addition to polymorphism4. In this pursuit, an orthorhombic polymorph of FeSO4OH (s.g. Pnma) has been investigated for the first time focusing on its electrochemical performance. When implemented as cathode for Li-ion battery, it delivered a reversible capacity of 110 mAh/g (0.7 Li+) at C/20 with Fe3+/Fe2+ redox potential centered ~3.2 V (vs Li/Li+). Deviating from monoclinic form, the orthorhombic FeSO4OH underwent a monophasic redox mechanism. This presentation will discuss (i) the first reports of FeSO4OH hydroxysulfate as cathodes for post Li-ion (Na-ion/ K-ion) batteries, (ii) the first demonstration of orthorhombic FeSO4OH as an economic air-stable cathode for Li-ion and Na-ion batteries, and (iii) in-depth mechanistic understanding of the electrochemical redox reaction in both orthorhombic and monoclinic polymorphs of FeSO4OH cathodes. This work will showcase synergistic study of hydroxysulfate cathodes using in-operando analytical tools, electrochemical titration techniques and first-principle (DFT) calculations.

Resume : Lithium phosphorus oxynitride (LiPON) is one of the most stable solid electrolytes against lithium metal anode in all-solid-state batteries (ASSBs). However, LiPON has been proven to react with lithium metal and forms solid electrolyte interphases (SEIs). The SEI formation is self-passivated after a thin layer is formed, and the mechanisms still require deep theoretical understanding. Here, using first-principles defect calculations, we investigated the native charged point defects for all the Li-LiPON SEI components, including Li2O, Li3N, Li3P, and Li3PO4. The defect and net charge carrier concentrations were calculated from the defect thermodynamics. We then predicted the electronic conductivity of the SEI components induced by their charged defects under different chemical conditions, which corresponds to different proximity to the lithium metal anode in the SEI. Our results reveal that the major and uniformly distributed Li2O show negligible electronic conductivity, while the electronically conducting components like Li3N and Li3P show preferential distribution in the SEI in previous experiments. Based on this, we elucidate the self-passivating behavior by the stop of electron transfer due to the insulating nature of the overall Li-LiPON SEIs.

Resume : Rechargeable batteries are aiding the growing use of electric vehicles and renewable energy. Predictions at the system level show that Lithium-ion batteries have a high gravimetric and volumetric energy density. Despite the success of the rechargeable lithium battery, using intercalation compound as the positive electrode has several drawbacks, the most serious of which is the material's relatively high cost and toxicity. As battery researchers go in this new path, it's essential to take a fresh look at Li- systems to grasp the underlying causes of some practical hurdles (i.e., voltage fade, poor kinetics, and voltage hysteresis). Finding novel metal oxide intercalation hosts for lithium that give a good performance as a positive cathode is one of the most difficult tasks in developing better rechargeable lithium batteries. This material must have a high voltage vs. the Li+/Li couple, a large capacity to cycle lithium, and excellent capacity retention when cycling at a fast rate. Metal oxides in the first-row transition series are the only ones that can meet all of the criteria. Our interest in lithium manganese oxides is sustained by the relevance of cost and toxicity in particular. Because we have limited options for changing the composition of the intercalation host, we must be creative in designing novel structures that may outperform the present lithium manganese oxide phases. Because sodium is larger than lithium, it is typically used to stabilize manganese oxides of various structures. The 3D tunnel structure of Na0.44MnO2 is one of these phases. Our major focus has been on substituting lithium for sodium in the compound. Herein, we present an electrochemical and structural analysis of totally exchanged Li0.44MnO2. Structural investigations utilizing powder synchrotron diffraction are integrated with galvanostatic cycling and cyclic voltammetry. Furthermore, we investigated the kinetics of the intercalation of lithium into the compound using PITT. An in-depth understanding using in-situ XRD and ex situ XPS will be described. References: (1) Armstrong, A. R.; Huang, H.; Jennings, R. A.; Bruce, P. G. Li0.44MnO2: An Intercalation Electrode with a Tunnel Structure and Excellent Cyclability. J. Mater. Chem. 1998, 8 (1), 255–259. https://doi.org/10.1039/a705099b. (2) Sauvage, F.; Laffont, L.; Tarascon, J.-M.; Baudrin, E. Study of the Insertion/Deinsertion Mechanism of Sodium into Na0.44MnO2. Inorg. Chem. 2007, 46 (8), 3289–3294. https://doi.org/10.1021/ic0700250.

Resume : Ceramic electrolytes have attracted great attention in battery research as so-called all-solid state devices may take advantage of increased safety. The search for suitable electrolytes with sufficiently high ionic conductivity does also include nanocrystalline materials. Ion conductivity in such materials may benefit from interfacial effects occurring when an ionic conductor is in close contact with an insulating phase [1, 2]. Here, LiBH4 served as a promising Li+ conductor to study such effects in composites with zirconium dioxide (ZrO2), magnesium oxide (MgO), magnesium aluminate (MgAl2O4) or even titanium dioxide (TiO2). Li ions residing near or in the interfacial regions often show increased diffusivity because of structural disorder [3,4] or space charge regions [5]. Nanocomposites were prepared by high-energy ball-milling and structural details were studied by powder X-ray diffraction. We used conductivity spectroscopy and 7Li NMR spectroscopy to study both long-range ion dynamics and local jump processes. It turned out that the dynamic parameters sensitively depend on the annealing history of the samples. If we assume that annealing is expected to be responsible for the healing of defects, this dependence points to a strong impact of structural disorder on interfacial ion dynamics. As an example, for LiBH4:MgO the highest conductivity achieved at room temperature was in the order of 0.6 * 10−4 S/cm. A similar value (0.2 * 10−4 S/cm) was obtained for a sample using ZrO2 as insulating phase. Compared to nanocrystalline, that is, single phase LiBH4 these values reveal an increase of the overall conductivity by three orders of magnitude provided the optimum conductor:insulator ratio was taken into account to prepare the samples. [1] M. Gombotz, K. P. Pree, V. Pregartner, B. Gadermaier, K. Hogrefe, I. Hanzu, and H. M. R. Wilkening, Solid State Ionics 369 (2021) 115726. [2] R. Zettl, K. Hogrefe, B. Gadermaier, I. Hanzu, P. Ngene, P. E. de Jongh, and H. M. R. Wilkening, J. Phys. Chem. C 125 (2021) 27 15052-15060. [3] D. Wohlmuth, V. Epp, P. Bottke, I. Hanzu, B. Bitschnau, I. Letovsky-Papst, M. Kriechbaum, H. Amenitsch, F. Hofer, M. Wilkening, J. Mater. Chem. A 2 (2014) 20295. [4] S. Breuer, M. Uitz, M. Wilkening, J. Phys. Chem. Lett. 9 (2018) 2093. [5] J. Maier, Phys. Chem. Chem. Phys. 11 (2009) 3011.

Resume : Beyond the current state-of-the-art cathodes for Li-ion batteries, the quest for alternate high-voltage polyanionic class of cathode material is vital. Sulfate chemistry aids the identification of high-voltage cathode materials due to the high electronegativity of S6+ ion-based on the inductive effect.1,2 Herein, we have explored the mechanism of anionic redox in LixM(SO4)2 frameworks (M = Mn, Fe, Co, and Ni and 0≤x≤2) using a combination of Hubbard U corrected strongly constrained and appropriately normed (SCAN+U) and generalized gradient approximation (GGA+U) functionals in density functional theory (DFT) framework.3,4 We have investigated the thermodynamic (polymorph stability), electrochemical (intercalation voltage), geometric (bond lengths), and electronic (band gaps, magnetic moments, charge populations, etc.) properties of the bisulfate considered. Specifically, we find anionic redox process is dominant throughout the delithiation reaction in Ni-based bisulfate. On the other hand, in Fe and Co bisulfates, cationic redox dominates the initial delithiation (1≤x≤2), while anionic redox dominates subsequent delithiation (0≤x≤2), as backed by the calculated projected density of state, bond length and on-site magnetic moments. Finally, evaluation of the crystal overlap Hamilton population reveals insignificant bonding between oxidizing O atoms throughout the delithiation process in the Ni bisulfate, indicating robust battery performance that is resistant to irreversible oxygen evolution. References 1. Reynaud, M.; Rousse, G.; Chotard, J.-N.; Rodríguez-Carvajal, J.; Tarascon, J.-M., Marinite Li2M(SO4)2 (M = Co, Fe, Mn) and Li1Fe(SO4)2: Model Compounds for Super-Super-Exchange Magnetic Interactions. Inorg. Chem. 2013, 52, 10456-10466. 2. Singh, S.; Jha, P. K.; Avdeev, M.; Zhang, W.; Jayanthi, K.; Navrotsky, A.; Alshareef, H. N.; Barpanda, P., Marinite Li2Ni(SO4)2 as a new member of the bisulfate family of high-voltage lithium battery cathodes. Chem. Mater. 2021, 33, 6108-6119. 3. Anisimov, V. I.; Zaanen, J.; Andersen, O. K., Band theory and Mott insulators: Hubbard U instead of Stoner I. Phys. Rev. B 1991, 44, 943-954. 4. Sai Gautam, G.; Carter, E. A., Evaluating transition metal oxides within DFT-SCAN and SCAN+U frameworks for solar thermochemical applications. Phys. Rev. Mater. 2018, 2, 095401.

Resume : Li-on battery (LIB) is considered as an important technology for future energy transition. Commercial LIB uses layered oxides (LiCoO2, LiNi1-y-zMnyCozO2…), spinel oxides LiNixMn2-xO4 as well as olivine LiFePO4 as positive electrode materials. In contrast, the choice for negative electrodes is limited to graphite or Li4Ti5O12 (LTO). Graphite is inexpensive and it delivers a large capacity but it suffers from the formation of solid electrolyte interphase (SEI) and the formation of Li dendrites at high rate, leading to low rate capability and security problem [1]. LTO on the other hand [2], is able to circumvent the problems of graphite thanks to its higher working potential (1.5V) and minimal structural change during lithiation. High working potential gives inherent security but results in lower overall voltage in a full cell. Besides, LTO delivers a moderate specific capacity (∼150 mAh g−1 at 1C rate, 120 mAh g−1 at 5C rate) compared to graphite. The gain in security and cycling performance of LTO is therefore at the expense of a lower energy density. Consequently, there is huge motivation to find large-capacity insertion-compounds as negative electrode materials working in the voltage range of 1.0 < V ≤ 1.5 V to design new generation high energy density full cell with inherent security. Lithiated transition-metal nitrides are considered to be among the most promising insertion class of negative electrode materials for LiBs [3]. Within this family, Li7MnN4 (LMN) [4] and Li3FeN2 (LFN)[5], with an anti-fluorite 3D structure, have received great attention due to their large specific capacities (285 mAh g-1, 250 mAh g-1, respectively ), appropriate working potentials ( 1.18 V, 1.25V, respectively) and good cycling performance. Considering LMN, previous study showed by using a crucial post-synthesis ball-milling step to decrease particle size, a better rate capability (250 mAh g−1 at 1C rate and 130 mAh g−1 at 5C rat) can be achieved.[6] In this work, an optimization of the synthesis conditions of LMN is proposed and new key parameters controlling the particle size distribution (PSD) are identified, allowing the suppression of the post-synthesis ball-milling process. Thanks to the specific morphology obtained when using our optimized synthesis conditions, the as-synthesized LMN material is able to deliver larger capacity at higher rate (265 mAh g−1 and 160 mAh g−1 at 1C and 5C rate, respectively). These capacity values are the best to our knowledge and compete with that of benchmark LTO. Furthermore, the lower working potential of LMN (1.2 V, i. e. 0.35 V lower than LTO) is expected to provide larger energy density in a full cell device compared to LTO. The concept of using delithiated LMN and LiNi1/3Mn1/3Co1/3O2 (NMC) to construct the full cell is proposed for the first time and the feasibility of this full cell is demonstrated in both 3-electrode Swagelock cell and 2-electrode coin cell. Remarkably, the maximum energy density of the NMC/LMN full cell, of 256 Wh/kg (based on total active materials mass loading), is 30-50% higher that exhibited by a NMC/LTO full cell. Considering LFN, no previous study reports the performance of this materials probably due to its poor cycling behavior. In this work, the cycling performance is presented for the first time for a newly synthesized LFN material. Good cycling performance is exhibited at high rate (less than 10% capacity fading after 80 cycles at rates larger than C/2). However, moderate cycling performance is observed in low rate (12% capacity fading after 10 cycles at C/5), that could be ascribed to the chemical instability of Fe4+ as shown in our examples. [1] T. Waldmann, B. I. Hogg, and M. Wohlfahrt-Mehrens, “Li plating as unwanted side reaction in commercial Li-ion cells – A review,” J. Power Sources, vol. 384, no. November 2017, pp. 107–124, 2018. [2] T. Ohzuku, A. Ueda, and N. Yamamoto, “Zero‐Strain Insertion Material of Li [ Li1 / 3Ti5 / 3 ] O 4 for Rechargeable Lithium Cells,” J. Electrochem. Soc., vol. 142, no. 5, pp. 1431–1435, 1995. [3] J. M. Tarascon and M. Armand, “Issues and challenges facing rechargeable lithium batteries,” Mater. Sustain. Energy A Collect. Peer-Reviewed Res. Rev. Artic. from Nat. Publ. Gr., vol. 414, no. November, pp. 171–179, 2010. [4] N. Emery et al., “In operando X-ray diffraction study of Li7MnN4 upon electrochemical Li extraction-insertion: A reversible three-phase mechanism,” J. Power Sources, vol. 247, pp. 402–405, 2014. [5] N. Emery et al., “Unidimensional unit cell variation and Fe 3/Fe 4redox activity of Li3FeN2in Li-ion batteries,” J. Alloys Compd., vol. 696, pp. 971–979, 2017. [6] E. Panabière, N. Emery, S. Bach, J. P. Pereira-Ramos, and P. Willmann, “Ball-milled Li7MnN4: An attractive negative electrode material for lithium-ion batteries,” Electrochim. Acta, vol. 97, pp. 393–397, 2013.

Resume : The lifetime of SnO2-based anodes is often limited by high volumetric expansion during cycling. Here, we investigate active and inactive heterostructures: SnO2/ZnO core/shell nanowires and SnO2/Al2O3 core/shell nanowires. The structure of these nanowires is measured using scanning electron microscopy and high-resolution transmission electron microscopy before and after cycling. Comparing the as-prepared and post-mortem nanostructures, we find distinctive structural changes in the two cases even after as few as 5 cycles. Additional analysis by energy-dispersive X-ray spectroscopy and energy-filtered TEM imaging provides more detailed information regarding the various structural changes. The results show that a deep understanding of the properties of the combined materials is crucial for achieving volumetric stability. The combination of both approaches in the form of SnO2 nanowires with active and inactive coatings allows for new insight into the influence of ultra-thin ALD-based coatings for nanowires and the control of structural stability of NW-based heterostructures for battery anodes.

Resume : With the aim of making lithium batteries safer, the scientific community is looking in recent years to replace the liquid solvents used as electrolyte with a solid ionic conductor compound. Several families of materials have been developed, leading to major improvements in this technology (NASICON, perovskites, Garnets). In addition, the thio-phosphate family is widely explored and several compounds have been discovered in the pseudo-binary Li2S-P2S5 diagram such as Li3PS4, Li7P3S11 or Li7PS6. In 2011, R. Kanno and al. had discovered a new phase: Li10GeP2S12 showing ionic conduction of 12 mS/cm. Unfortunately, this structure is unstable towards lithium metal and germanium remains a very expensive element. In order to improve the stability of this structure, a partial substitution of sulfur by oxygen has been successfully obtained and shown better cycling capability. Very recently, the germanium-free phase Li9.6P3S12 has been obtained and exhibits better stability towards lithium despite a lower conductivity. In this context, we explored three different systems to discovered new solid electrolyte. By exploring the Li-P-S-O system, we were able to form new LGPS phases Li3.2PS4-xOx. Structural characterization have confirmed the insertion of oxygen in the structure. Oxygen substitution resulted in lower ionic conductivity but a higher interface is form versus lithium resulting in better performance in all solid-state battery compare to Li10GeP2S12. The effect of halogen doping have been investigate on the compound Li3.2PS3.7O0.3. This doping showed a better interface formation despite a lower ionic conductivity, which resulted in better performance in solid-state battery. Finally, a new LGPS domain of stability were fund in the Li-B-P-S system. The ionic conductivity reach the values of 1.17 10-4 S/cm and a higher stability is observed in versus lithium compare to Li10GeP2S12. These electrochemical characteristics result in better performance in all solid-state battery. However high reactivity of this material versus moisture make it not suitable as solid electrolyte.

Resume : Batteries can broadly cater to two kinds of applications: volume/weight restricted applications like electronic gadgets/ electric automobiles and volume/weight independent usages like stationary grid storage. While lithium-ion batteries (LIBs) are irreplaceable for the former category, the latter can be driven by economic sodium-ion batteries (SIBs).[1] In the quest for high-energy-density sodium insertion materials, polyanionic frameworks can be designed with tunable high-voltage operations stemming from the inductive effect.[2] Alluaudite Na2Fe2(SO4)3 forms one such earth-abundant compound registering the highest Fe3+/Fe2+ redox potential (ca. 3.8 V vs. Na/Na+) reported till date.[3] While this SO4-based system exhibits high voltage operation due to the high electronegativity of S, nonetheless it is prone to thermal decomposition and moisture attack leading to its hydrated derivatives and making its synthesis cumbersome. Also, the Na-Fe-S-O quaternary system is rich with (anhydrous to hydrated) phase transitions. Herein, we demonstrate scalable aqueous-based spray drying synthesis of alluaudite Na2+2xFe2-x(SO4)3 sodium insertion material involving the formation of bloedite Na2Fe(SO4)2.4H2O as an intermediate phase which assured atomic-level mixing and labile ionic diffusion. Moreover, a reversible phase transition from alluaudite to bloedite under controlled conditions of temperature and relative humidity is reported for the first time. Thermochemistry measurements revealed the enthalpies of formation (ΔH°f) of alluaudite and bloedite are exothermic. Hydrated bloedite was found to be significantly more energetically stable than anhydrous alluaudite. Aqueous Spray drying route led to spherical morphology (which increases the surface area) delivering capacity ~80 mAh/g. The synthetic, structural, and electrochemical properties of spray-dried alluaudite cathode will be described. References (1) Yabuuchi, N.; Kubota, K.; Dahbi, M.; Komaba, S. Research development on sodium-ion batteries. Chemical Reviews 2014, 114 (23), 11636. (2) Manthiram, A.; Goodenough, J. B. Lithium insertion into Fe2(SO4)3 frameworks. Journal of Power Sources 1989, 26 (3), 403. (3) Barpanda, P.; Oyama, G.; Nishimura, S.-i.; Chung, S.-C.; Yamada, A. A 3.8-V earth-abundant sodium battery electrode. Nature Communications 2014, 5 (1), 4358.

Resume : Technologies for breeding Tritium as a fission product are actually for developing “green” thermonuclear energy. Lithium compounds are studied due to the reaction of thermal neutron capture 6Li3(n,alpha)3T1. Irradiation of LiF crystals in the reactor core is known to generate dislocations, defect clusters in (100) plane, Li colloids and cavities. Since neutron flux is accompanied by intensive gamma-radiation, many authors ascribe all radiation-induced defects to gamma-radiolysis with F losses, rather than Li fission generating 3T1. However, other possible fission reactions of light nuclei from Li to F generating 3T1 were not considered so far. This work was aimed at revealing the contribution of nuclear reactions into chemical bond radiolysis and structure–phase transformations in LiF:OH crystals exposed to fluencies of fast >0.1 MeV neutrons from 5×10^15 to 5×10^17 cm^-2 and gamma-quanta to 6 MeV from O and other elements in the core of WWR-SM reactor operating at 9 MWt. Samples for irradiations were cleaved from the optical grade crystal. In addition to XRD, local element analysis in vacuum and FTIR spectroscopy were implemented. The cleaved subsurface layer of non-irradiated crystal contains 30%LiF, 37%LiOH, 31%F2 and 2%Li. The irradiation to 5×10^15 сm-2 resulted in disappear of LiOH, Li and F2 phases transformed to 60%LiH, and appear of B2O3 (confirmed by K-line). Orthorhombic LiFB6O9 phase was first detected after fluency 10^16 cm-2 and grew up to 51% after 10^17 cm-2 due to decay of LiH phase; the all phases seem to compete each to other. LiB appears as orthorhombic phase and after fluency 10^16 cm-2 transforms into hexagonal one with a denser lattice than that of LiF. After 10^17 cm-2 a new phase LiBН2 arises at the expense of the others and becomes dominative (74%) at 5×10^17 сm-2, perhaps due to joining of LiB and LiH phases. In the fluency interval the lattice parameter of cubic LiF increases from 4.0270 to 4.0500 Å due to the lattice deformation. While that of cubic LiH decreases significantly from 4.0832 to 4.0150 Å possibly due to accumulation of a long living radioisotope 3T1 causing phase transition LiH to LiT. Such mutual phase transformations can be attributed only to fission of 19F and 16O nuclei at capture of slow < 0.1 MeV neutrons and absorption of > 1 MeV-gamma-quanta by the nuclear reactions of “branching decay” type: 19F9 + 1n0 = 11B5 + 6Li3 + 3H1 or 10B5 + 7Li3 + 3H1 ; 19F9 + gamma = 11B5 + 7Li3 + 1H1 or 10B5 + 6Li3 + 3H1 or 16О8 + 3Н1. These reactions may be convertible under a long term exposure to synergic influence of mixed neutron and gamma-ray fluxes in the nuclear reactor core. Stable nuclei products B, Li and H or T in excited state easily make solid phases. These results are applicable for producing Tritium in WWR and nuclear energy stations, and also neutron-gamma-fluency determination with the use of lithium compounds and other light elements.

Resume : In recent years, all-solid-state batteries have been gaining ever more research attention as they are considered as alternatives to devices based on liquid electrolytes. To increase energy density, while alleviating safety concerns caused by hazardous and flammable liquids, new materials with high ionic conductivity are urgently needed. Many of these are Li-rich compounds such as Li-stuffed garnets as well as Li-rich antiperovskites such as Li3−xOHxCl. Despite the increasing number of studies on Li3-xOHxCl, it remains difficult to reliably synthesize and to characterize these compounds, particularly in a proton-free form (x = 0) [1]. Among these, Li2(OH)Cl, which is accessible via different synthesis routes including, for example, hydrothermal ones, has recently been discussed as a promising electrolyte. However, we still do not fully understand the full dynamic situation in Li2(OH)Cl, which seems to be described by both translational and rotational jump processes. For instance, Dawson et al. suggested the interrelation of Li+ translational dynamics with OH− rotational motions [2]. Here, we used a combination of broadband (10 mHz to 10 MHz) conductivity spectroscopy [1] and charge carrier specific 1H and 7Li nuclear magnetic resonance (NMR) spectroscopy to look at the dynamic properties of Li2(OH)Cl over a broad length scale. Conductivity spectroscopy is able to probe macroscopic transport, while NMR provides insights into the elementary jump processes from the atomic-scale point of view. Against some wishful thinking, our findings clearly show that Li2(OH)Cl is a rather poor Li+ ion conductor. We could clearly resolve the phase transformation at 35 °C at which orthorhombic Li2(OH)Cl transforms into its cubic counterpart. Although this transition is accompanied by a jump in overall electric conductivity, even the cubic polymorph of Li2(OH)Cl must be described as a moderate rather than a fast ion conductor. Most importantly, our high-quality time-domain 1H and 7Li NMR relaxation rate measurements provide a detailed view on the correlation of translational with rotational motions of the OH units, as suggested [2]. [1] Hanghofer, I., Redhammer, G. J., Rohde, S., Hanzu, I., Senyshyn, A., Wilkening, H. M. R., Rettenwander, D., Untangling the Structure and Dynamics of Lithium-Rich Anti-Perovskites Envisaged as Solid Electrolytes for Batteries. Chem. Mater. 30 (2018) 8134. [2] Dawson, J. A., Attari, T. S., Chen, H., Emge, S. P., Johnston, K. E., Islam, S. M., Elucidating lithium-ion and proton dynamics in anti-perovskite solid electrolytes. Energy Environ. Sci. 11 (2018) 2993.

Resume : The abundance in earth crust, high volumetric capacity and low redox potential enable Mg a promising anode material for cost-effective and sustainable high energy batteries. Particularly, primary aqueous Mg batteries, like Mg-air system, exhibit great potential in many applications like maritime equipment and transient bioelectronics. Unfortunately, the state-of-art energy density of aqueous Mg batteries is far below the theoretical value. One major issue is the severe self-discharge of Mg anode in aqueous electrolytes related to detachment of undissolved metallic particles (chunk effect) and fast hydrogen evolution (self-corrosion) due to the well-known negative difference effect (NDE). Therefore, regulating the self-discharge is crucial to the accomplishment of high efficiency anode and, thus, high energy density aqueous Mg batteries. In this work, anode micro-alloying and electrolyte additives are proposed as two effective ways for reducing Mg anode self-discharge. Micro-alloying with proper elements and tailored electrolyte additives are capable of simultaneously reducing anode chunk effect and self-corrosion. Noticeably, the newly designed Mg-0.1Ca-0.6In anode exhibits utilization efficiency of 80% at 5 mA cm–2. Furthermore, high energy density of 3 kWh kg–1 for Mg-air battery is achieved via micro-alloyed anode and citrate additive in NaCl aqueous electrolyte in comparison to 1.5 kWh kg–1 for the additive-free battery based on commercial AZ31 anode.

Resume : K-ion batteries could be a possible alternative to Li-ion systems for the storage of renewable but intermittent energies if abundant and low cost materials are considered. However, their development remains limited as most studies are based on half-cells that rely on highly reactive K metal. Indeed, K metal greatly influences the electrochemical performance due to the high polarization and low coulombic efficiency of its plating/stripping.[1] Also, in contact with K metal, electrolytes form degradation products that contaminate the working electrode (via a cross talking mechanism) leading to difficulties to properly understand the SEI.[2] After a brief introduction of these limiting factors, this presentation will focus on the K metal reactivity in conventional KPF6 (or KFSI) EC:DEC electrolytes.[3] Full electrolyte degradation pathways are obtained by combining gaseous and solid products analysis using gas chromatography/Fourier transform infrared spectroscopy/mass spectrometry and XPS,[4] respectively. Comparison with Li metal reactivity in LiPF6 EC:DEC electrolyte will also be discussed. The impact of the metal and salt cation/anion will be addressed. In particular, with KFSI, the FSI anion drives the degradation and forms an inorganic rich SEI, which can explain the better electrochemical performance often reported in half-cells using this salt. Finally, the understanding of these chemically-driven electrolyte degradation mechanisms will help researchers to design robust carbonate-based electrolyte formulations for KIBs. References [1] J. Touja, V. Gabaudan, F. Farina, S. Cavaliere, L. Caracciolo, L. Madec, H. Martinez, A. Boulaoued, J. Wallenstein, P. Johansson, L. Stievano, and L. Monconduit, Electrochim. Acta, 362, 137125 (2020). [2] L. Madec, V. Gabaudan, G. Gachot, L. Stievano, L. Monconduit, and H. Martinez, ACS Appl. Mater. Interfaces, 10, 34116–34122 (2018). [3] L. Caracciolo, L. Madec, G. Gachot, and H. Martinez, ACS Appl. Mater. Interfaces, 13, 57505–57513 (2021). [4] L. Caracciolo, L. Madec, and H. Martinez, ACS Appl. Energy Mater. 4, 11693–11699 (2021).

Resume : Solid electrolytes with extraordinarily high Li-ionic conductivities are key for high performance all-solid-state batteries. In many sulfide materials nanosizing via ball-milling increases the ionic conductivity. So far, the thiophosphate Li10GeP2S12 (LGPS) belongs to the best Li ion conductors with an ionic conductivity exceeding 10 mS cm–1 at ambient. However, the effect of reducing the grains size to the nm-regime has not been investigated experimentally. Recent molecular dynamics simulations performed by Dawson and Islam predict that the ionic conductivity of LGPS can be further enhanced by a factor of three if the crystallite size is reduced to the nanometer regime. A change in local ion coordination, hence local disorder, has been assumed to facilitate Li diffusion in the ab-plane of LGPS. Here, we synthesized nanocrystalline LGPS by different steps of high-energy ball milling and characterized the structure and Li+ ion transport parameters of the materials. X-ray powder diffraction and high-resolution 31P and 6Li magic angle spinning nuclear magnetic resonance (NMR) spectroscopy helped us to determine morphological changes and local structures upon milling. To precisely follow the changes in Li+ ion dynamics we applied broadband conductivity spectroscopy in combination with electric modulus measurements. Surprisingly and against the behavior of other electrolytes, ionic conductivity turned out to decrease with increasing milling time, finally leading to a reduction of σ20°C by a factor of 25 in the bulk. This decrease affects both, bulk ion dynamics and total conductivity, which also comprises Li+ transport across grain boundary regions in LGPS. As could be shown by NMR, ball-milling leads to a structurally heterogeneous sample with the nm-sized LGPS crystallites embedded in an amorphous matrix. This amorphous phase is also responsible for the reduced performance of the milled LGPS-electrolyte. Importantly, careful separation of the amorphous and (nano)crystalline contributions to the overall ionic conductivity revealed that even in the nanocrystalline regions Li+ ion dynamics is slowed down compared to untreated, coarse-grained LGPS. In conclusion, defects introduced into the LGPS bulk structure via ball milling have a negative impact on ionic transport. We postulate that such kind of structural disorder is detrimental to fast ion transport in materials whose transport properties rely on crystallographically well-defined diffusion pathways.

Resume : Since the advent of the Li-S battery in 1962, it has experienced more than 60 years of development and is gradually moving towards industrialization. However, the problems of the ‘shuttle effect’ and lithium anode corrosion hinder its industrialization process. Here, we prepared three-dimensional interconnected graphene-like carbon and rutile titania to modify the separator of the Li-S battery to solve these two problems at the same time. The modified separator has low charge transfer impedance, a catalytic effect on polysulfides, and a barrier effect on polysulfides, which suppresses the ‘shuttle effect’ and prevents the corrosion of lithium anodes in Li-S batteries. The as-prepared Li-S battery shows good cycling stability for 250 cycles with 0.048% capacity decay per cycle at 1 C. Moreover, the SEM images of the lithium anode after 50 cycles showed that the lithium anode was uncorroded. The simple separator modification can effectively improve the electrochemical performance of the Li-S battery, and we believe this work can effectively promote the industrialization of Li-S battery.

Resume : Using organic redox-active molecules provides a new paradigm for future development of metal-ion batteries. Indeed, organic materials are usually based on light elements (C, H, N, O, S) and, therefore, can enable much higher specific capacities compared to the salts and oxides of heavy transition metals. Most of organic materials are non-toxic and environment friendly, which makes easy their recycling as a common household waste. In contrast to crystalline inorganic cathodes and anodes, organic materials are soft and, therefore, can operate at high charge and discharge rates thus leading to design of ultrafast batteries. Mechanical properties of polymeric cathodes and anodes enable their application in truly bendable batteries for emerging generation of portable electronics. Lithium-ion batteries currently represent one of the mainstream energy storage technologies. However, lithium is a scarce element and the available resources are definitely not matching the rapidly growing demand for energy storage. Therefore, sodium- and potassium-ion batteries (SIBs and PIBs) are now considered as promising scalable metal-ion battery technologies. In that context, organic redox-active materials are particularly important since they can operate efficiently with multiple mobile ions, while most of inorganic cathodes are constrained to only one specific ion matching the crystal lattice. In this talk, we will highlight our recent results on the design of organic and metal-organic cathode and anode materials for potassium batteries. In particular, we will present ultrafast potassium-ion batteries delivering specific capacities of 169 mA h g−1 at an impressive current density of 10 A g−1 (charging/discharging in ca. one minute) and 245 mA h g−1A at a lower current density of 50 mA g−1. Specific energy of ~550-600 W h kg-1 is reached for the best organic cathodes in potassium batteries. The polymer-based devices also demonstrated record-high cycling stability with no capacity decay after 4600 cycles, thus outperforming all previously reported non-aqueous K-ion batteries. The obtained results suggest that organic electrode materials, while being at the infancy of their development, start to show commercially interesting performances thus paving a way to implementation of a new generation of post-lithium metal-ion batteries.

Resume : Silicon anode suffers from poor intrinsic conductivity and dramatic volume change during the discharge/charge process[1, 2], which hinders its commercialization for high energy density lithium-ion batteries(LiBs). This issue can be alleviated by embedding particles of the active material in an adhesive matrix, such as a polymer binder [3], that can accommodate large volume changes during lithiation and delithiation. Several research efforts have aimed at enhancing the adhesive, elastic, electrical, and ionic properties of binders for use in Si anodes [1, 3, 4, 5]. Therefore stable silicon/polymer interfaces[6] are crucial for the performance of high capacity of silicon-based LiBs. In particular, we will focus on silicon and new self-healing polymers as new promising anode material for next-generation high-energy-density LiBs. In this presentation from first-principles calculation based on density functional theory (DFT), some initial challenges of self-healing properties of polymeric binders, B-doped polyaniline (PANI)/ polyvinylalcohol (PVA) polymers have been explored. To simulate the effect that different functionalizing molecules can have on the electronic/mechanical properties of a Si-based anode surface, we started with: 1) different silicon surfaces and their possible reconstructions, 2) different anchoring geometry of the binders on the surfaces before and after lithiation. In this presentation, I will discuss the functionalization of Si(110) surface with B-doped polyaniline (PANI)/ polyvinylalcohol (PVA) followed by lithiation of the surface. The structural evolution and corresponding electronic properties as a function of Li concentration will be discussed. References: 1. S. Huang et al. Int. J. Energy Res. 2018, 42, 919−935 2. M. N. Obrovac et al. Electrochem. Solid-State Lett. 2004, 7, A93−A96. 3. Manav Bhati and Thomas P. Senftle J. Phys. Chem. C 2019, 123, 27036−27047 4. T.-w. Kwon et al. , Chem. Soc. Rev. 2018, 47, 2145−2164 5. Q. Y. Zhang et al. , Adv. Sci. 2020, 7, 2000749 6. Andrea Miranda et al. , Mol. Syst. Des. Eng., 2020, 5, 709 ACKNOWLEDGEMENTS: This research was developed under the framework of the BAT4EVER project that has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 957225.

Resume : Transition metal based compounds are promising electrode materials for electrochemical energy storage devices, and have been attracting intensive research efforts in the past three decades. The recent emerging high-entropy concept enables the transition metal based compounds with new perspectives: superior crystal structure stability and synergistic effect. The chemically complex, single-phase high-entropy materials have demonstrated unexpected and interesting properties. Rock-salt structured (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)O was reported with a stable long-term cycling performance over 900 cycles, with the lithiation potentials of between 0.5-1.0 V vs. Li+/Li. Through a facile mechanochemistry method, lithium and fluorine was introduced into the cationic and anionic lattice, respectively. The obtained high-entropy oxyfluoride exhibited a working potential of 3.4 V vs. Li+/Li, rendering its implementation as cathode active material. The incorporated fluorine further improved the stability of the cathode by improving the resistant against HF etching in the electrolyte. In this work, a similar mechnochemical process of milling spinel oxide (CoCrFeMnNi)3O4 with LiF was introduced, with the final solid solution of lithium oxyfluorides crystallized in rock-salt structure. A switching from spinel high-entropy oxide as anode to rock-salt high-entropy rock-salt as cathode was achieved. Given that spinel and rock-salt structures consist of a common cubic close-packed anion arrangement with cations distributed over various octahedral and tetrahedral sites, the structural evolution has been systematically investigated, with an insight into the entropy-stabilization effect.

Resume : The never-ending quest for facile, non-destructive chemical analysis techniques that can provide microscopic insights into the phase evolution of materials has been the driving force for many successes in the research community within the last decades. Despite this progress, some of the most powerful techniques, such as isotopic ion exchange methods, in situ TEM, and a collection of synchrotron radiation-based techniques, are quite complex, limiting easy access to crucial data for creating high-performance devices for energy harvesting and storage. Raman spectroscopy is a widely used optical technique able to provide quantitative chemical and structural information about the material under investigation in a fast, non-destructive manner. However, conventional Raman microscopy is diffraction-limited and thus, is unable to provide spatial resolution below ~ 1 µm. Tip-Enhanced Raman Spectroscopy (TERS) emerges as the most powerful approach among the strategies that have been proposed in the last decades to overcome the physical limitation of Raman microscopy in terms of spatial resolution. In essence, TERS combines the chemical sensitivity of Raman spectroscopy with high spatial resolution of scanning probe microscopy (SPM) and enables chemical imaging of surfaces at the nanometer length-scale. Since its first implementation 20 years ago, TERS has been generally applied to the study of organic materials – even down to the single-molecule level. However, its application to inorganic compounds in the field of energy remains essentially unexplored. In this talk, we will briefly discuss the fundamentals of TERS, its challenges and our recent advancements in the implementation of the technique in the field of energy with regards to inorganic materials. In particular, we will discuss our latest TERS results regarding Li-ion battery, thermoelectricity and fuel cells applications. Overall, the spatial resolution capabilities of the technique will be highlighted, showing, for instance, phase evolution at grain boundaries in Li-ion battery materials with a resolution < 20 nm. .

Resume : Potassium-ion batteries (KIBs) are considered as possible energy storage systems thanks to the high potassium abundance (2.1 wt.% of the earth’s crust) [1], low standard potential, and low Stokes radius of K+ (3.6 Å compared to 4.8 and 4.6 Å for Li+ and Na+) in propylene carbonate, so that high power KIBs are expected [2]. Also, similarly to Li-ion batteries and unlike to Na-ion ones, the reversible electrochemical intercalation of K+ ions in graphite has been experimentally demonstrated by Komaba et al. [3] in 2015, allowing its use as anode material in KIBs. Parameters that usually govern the electrochemical performance of graphite electrodes are porosity, amounts of carbon black (CB), and binder(s). This presentation will thus focus on the influence of these parameters. First, different CB amounts, as well as compaction pressures (i.e. porosities), were evaluated to ensure an optimum between the electronic and ionic percolation of the electrode. Then, different ratios of carboxymethylcellulose (CMC)/styrene-butadiene rubber (SBR) were used as water-soluble, inexpensive, and non-polluting binders to enhance the electrodes mechanical properties. Indeed, the presence of a binary binder allowed a high elasticity, which absorbs the electrode volume expansion while improving electrochemical performance (capacity retention, power rate, and polarization). For instance, K//graphite cells using SBR deliver up to 256 mAh g-1 at 5C with the capacity retention of 240 mAh g-1 after 55 cycles at C/5-1C potassiation-depotassiation rates. Finally, the interest of SBR as a co-binder of graphite electrodes will be demonstrated in high energy (with high electrodes mass loading) KVPO4F0.5O0.5//graphite full cells. [1] Su, D.; McDonagh, A.; Qiao, S.; Wang, G. High‐Capacity Aqueous Potassium‐Ion Batteries for Large‐Scale Energy Storage. Adv. Mater. 2017, 29 (1), 1604007. https://doi.org/10.1002/adma.201604007. [2] Hosaka, T.; Kubota, K.; Hameed, A. S.; Komaba, S. Research Development on K-Ion Batteries. Chem. Rev. 2020, 120 (14), 6358–6466. https://doi.org/10.1021/acs.chemrev.9b00463. [3] Komaba, S.; Hasegawa, T.; Dahbi, M.; Kubota, K. Potassium Intercalation into Graphite to Realize High-Voltage/High-Power Potassium-Ion Batteries and Potassium-Ion Capacitors. Electrochemistry Communications 2015, 60, 172–175. https://doi.org/10.1016/j.elecom.2015.09.002