Materials for improving energy storage battery technologies

Resume : A lithium-ion battery is an important energy storage device to effectively store renewable energies such photovoltaic cell and wind-power generation. Nickel, Cobalt, and Manganese are very significant elements for the cathodes of lithium battery. This is because changes in their valences directly affect the battery capacity. Therefore, their valences or electric states are often estimated by operando (in-situ) X-ray Absorption Fine Structure (XAFS) measurement during electrochemical reactions in the battery. Many researchers often use XAFS method to evaluate their valences and to clarify the electrochemical reactions of their target electrodes during electrochemical reactions for its science. There are two approaches to estimate it qualitatively and quantitatively by XAFS measurement. One of their approaches in the XAFS method is a qualitative method to roughly evaluate its valences by the comparing the energy position among the target material and reference materials. This approach is friendly-understanding method to roughly estimate it without difficult analysis [1]. However, it is difficult to estimate absolute values of the valences in detailed during electrochemical reaction by this approach. The other is a quantitative method to estimate relative change of valences in the target electrode materials during electrochemical reaction. Many researchers focus an energy point value in the XANES (X-ray Absorption Near Edge structure) region of XAFS spectrum, which value influences the valences of target element in the target electrode material. They can understand the changes of its valences by tracking a shift of the value such as absorbance value, 0.5 in the spectrum. But this cannot lead to obtaining absolute value of the valences in the target element, Ni2.5+ for instance [2]. We propose a new approach to quantitatively estimate the absolute valences in detailed in order to understand the electrochemical reaction for the electrode in the battery [3]. We used LiNi0.5Co0.2Mn0.3O2 (NCM523) for a modeled cathode of lithium-ion battery. These XAFS spectra of Ni and Co K-edges are obtained at some open-circuit voltages (OCVs) during charge process. These spectra are calculated to correspond the experimental spectra by the good fitting spectra superposition of reference spectra of Ni and Co, respectively. The valences of Ni and Co can be estimated by calculation of reference ratios and the known valences of Ni and Co in the references samples. Valences of not only Ni but also Co are found to change in the NCM523 during charge process between 3.0 V and 4.3 V. Estimated valences of Ni and Co reasonably become lower as OCVs become lower. The proposed approach can lead to estimation of the valences of Ni and Co in NCM523 with high accuracy using all plots in the XANES region of these XAFS spectra. We also applied this approach into degraded NCM523 by a repeats of charge-discharge test, 800 cycles. We can obtain the valences of Ni and Co for the degraded NCM523 at same OCVs between the non-degraded and degraded NCM523. The valences of Ni and Co were found to be lower in the degraded than those in the non-degraded, respectively. We will make our presentation about analysis in detailed and discuss the analysis result. Reference [1] A. Jarry, et al., J. Am. Chem. Soc., 2015, 137, 3533. [2] J. Xu, et al., ACS Appl. Mater. Interfaces, 2016, 8, 31677. [3] T. Kobayashi, et al., submitted.

Resume : Glassy, glass-ceramic and crystalline lithium thiophosphates have attracted interest as solid electrolytes for all-solid-state batteries. Despite similar structural motifs, these materials exhibit a wide range of compositions, structures and ionic conductivities. For the glass-ceramic consisting of crystalline Li4P2S6 and glassy Li4P2S7, for example, contradictory ionic conductivities were reported. In this contribution we present density functional theory (DFT) calculations on the defect thermodynamics and kinetics of crystalline Li4P2S6. [1] Despite the existence of low energy diffusion paths, the overall conductivity is inhibited by high defect formation energies. This supports the hypothesis that the conductivity of the Li4P2S7/Li4P2S6 composite material is determined by the relative amount of glassy and crystalline phases. Furthermore, thermodynamics predict the instability of Li4P2S6 against metallic lithium. Corresponding interface models for different surface terminations of Li4P2S6 show the barrierless formation of an interphase reminiscent of Li2S, which might act as a passivating layer and protect the electrolyte from further decomposition. [1] C. Dietrich, M. Sadowski, S. Sicolo, D. A. Weber, S. J. Sedlmaier, K. S. Weldert, S. Indris, K. Albe, J. Janek, W. G. Zeier, Chem. Mater. DOI:*10.1021/acs.chemmater.6b04175 (2016).

Resume : There is overwhelming demand for the design of new high performance cathode materials for the next generation of rechargeable batteries for both Li and Na ion technology. The olivine structured orthophosphates Li/NaMPO4 (M = Fe, Mn, Ni and Co) have garnered significant interest due to their good thermal stability and high voltage vs Li+/Li / Na+/Na couple. This interest manifested in the relative recent commercialisation of LiFePO4. LiMnPO4 remains a promising alternative candidate to LiFePO4 due to its higher operational voltage (~4.1 V vs Li+/Li), however it has been shown to be less electrochemically active than its iron counterpart, as it specifically exhibits lower ionic diffusion due to its Jahn-Teller activity. Investigating and understanding ionic diffusion at an atomic level is therefore a priority for battery materials innovation. Computational methods continue to provide insight on an atomic level and Molecular Dynamics (MD) simulation remains one of the most powerful tools. For a typical diffusive process, there are numerous energy barriers due to the highly corrugated potential energy surface. Therefore a standard MD simulation will frequently visit probable configurations whilst reactive states of Li/Na particle hopping will be less or not represented. Instead of just increasing the overall temperature of the system, our approach selectively ‘warm up’ the Li/Na ions by transferring a variable amount of kinetic energy from the slower frequencies of framework dynamics (MPO4) to the lighter and more mobile Li/Na ions. The justification of this novel method is based upon the fact that upon activation of Li/Na mobility the Li/Na sublattice behaves resembles a liquid hosted in a solid framework (MPO4), this implies a natural separation of velocities and frequencies between the Li/Na sublattice and framework. Using the ‘Shooter’ algorithm it is possible to simulate and visualise diffusion on a suitable timeframe and analyse the mechanism and dimensionality of the diffusive process. Based on a detailed elucidation of mass transport mechanisms, diffusion coefficients, and subsequently free energies and reaction rates cab be assessed for each cathode candidate material. This step is in propaedeutic to a deep understanding of the coupling of electrochemical redox processes with mass and ion motion within materials.

Resume : The increasing interest in future energy storage technologies has generated the urgent need for alternative ways to improve the classical batteries by enhancing their high reversible capacity, high energy density and good cycle life. DFT-based first principles calculations, including van der Waals interactions, were performed in order to examine the structural properties, binding energies, specific capacities and diffusion barrier energies for the adsorption of Li, Be, Na, Mg, K and Ca on phosphorene. Our results show that all the adatoms are more stably adsorbed on the hollow site with a direct influence of the atomic size on the adsorption properties. We find a strong reinforcement in terms of the interaction between the adatoms and phosphorene with binding energies exceeding those of similar 2D materials such as graphene. After full adsorption, a semiconductor-metal transition is observed. We also find that the diffusion of the metals on phosphorene is a fast and anisotropic process with an extremely low energy barrier of 0.02 eV for K across the open channel (zigzag direction). The comparison on the diffusion barrier energies of the studied adatoms with other classical ion batteries shows that phosphorene could make a good candidate as an anode material in batteries.

Resume : Safe, low-cost, and long-cycle-life rechargeable batteries are key enabling components for grid scale energy storage. Organic redox materials are promising due to the attractive features of high theoretical capacity, potentially low-cost, recyclable, and tunable properties that can be designed by modifying chemical structures. A “π-conjugated redox polymer” (N2200) simultaneously featuring a π-conjugated backbone and integrated redox sites can be stably and reversibly n-doped to a high doping level of 2.0. N2200 delivers 95% of its theoretical capacity at a high rate as well as 96% capacity retention after 3000 cycles of deep discharge−charge. This will be followed by a microscopic understanding of how ions, electrons, solvents interact with polymer chains during electrochemical process through a combined electrochemical, morphology, and charge transport study. Finally, we will demonstrate a class of polymeric electrode materials that enable long-cycle-life aqueous batteries that address the key limitations of current aqueous batteries.

Resume : Recent observation of stable charging and discharging of electrochemical devices using high performance chelating conjugated polymers showed promising evidence that reliable and high power density electrochemical energy storage could be achieved through these materials. We present on spectroelectrochemical measurements used to characterize ionic and electronic transport in polymer electrodes. Our study focusses on sodium and chloride ions dissolved in water penetrating in conjugated polymer thin films deposited on transparent conductive substrates. We consider p and n type polymers and show that engineering of the side chains results in enhancement of the electrode’s energy and power density. We analyse the electrochemical behaviour of the polymers in conjunction with the changes in their spectral features upon charging/discharging. We show that this measurement can be applied to half cells or to full battery devices enabling to access information regarding the two separate electrodes which are not otherwise available from electrical measurements (e.g. EIS). This approach illustrates that designing materials that include optical probes is a promising direction to refine the understanding of the working principle of energy storage systems. Secondly, our study suggests that further fundamental questions on the influence of chemical structure on the transport properties of electronic, ionic or mixed electronic ionic conductors can be addressed via optical techniques.

Resume : Application of silicon (Si) as an anode material for lithium-ion batteries has recently gained significant attention due to the large demand from the off-grid energy storage modules. However, use of Si as the anode material leads to problems arising from its large volume expansion (~400 %) upon lithium (Li) alloying reaction (lithiation) and its low intrinsic electrical conductivity (~ 10-3 S cm-1) that limits its use in cyclic and high-rate performances. Carbon nanofibers (CNF) are highly promising one-dimensional carbon nanostructures as a conductive support for Si nanoparticle, acting as a buffer to suppress the severe volume expansion during lithiation/delithiation reaction and providing a continuous conductive pathway for electron transfer. Most of the reported CNF/Si anodes are developed using commercial Si nanoparticles. In this study, copolymers of acrylonitrile and alkoxysilanes are developed both as CNF and Si precursors. Briefly, both copolymers of vinyltriethoxysilane (VTES) and trimethoxysilylpropylmethacrylate (TMSPMA) with polyacrylonitrile (PAN) and homopolymers of VTES and TMSPMA are synthesized. These newly developed polymers are subjected to electrospinning – a simple and cost-effective method for nanofiber manufacturing – for the production of electrospun silane-containing nanofibers. The resulting fibermats are carbonized under their autogenic pressure for the production of silicon decorated CNF composite structures to be used as freestanding anodes in lithium-ion batteries.

Resume : Recent scientific findings are at the edge of a breakthrough towards novel metal free redox flow battery based on bio-inspired organic molecules. Their environmental friendliness aside, the raw material used is not affected from resource constraints as occurs with metals in conventional batteries (i.e. lithium, cadmium or nickel). Thanks to their non-expensive price, abundance as well as straight forward synthesis, we concentrated our efforts on quinone-based batteries [1]. Benzoquinone molecules were selected for cathode, while anthraquinone for anode in aqueous solution owing to their higher solubility in aqueous conditions as well as compatible redox pair and low cross over trough the membrane due to its large molecular size. Our initial results were obtained with a hybrid anode electrode composed of reduced graphene oxide with a quinone complex (rGO/Q) deposited on a commercial graphite felt. This promising metal free anode electrode complex can not only achieve current densities of 300 mA/cm2 but also remain stable for 1000 cycles at 100 mA/cm2. Besides ~80% of energy efficiency was attained with 0.4 M (anthraquinone 2, 7-disulfonic acid disodium salt) in acidic conditions (3 M methanosulfonic acid). Despite several cycles of charge/discharge under 25 mA/cm2, full cell configuration was successfully implemented with a previously mentioned optimized metal free anode vs. a quinone-cathode (para- and orto-benzoquinone). The self-degradation of the cathode molecule act as a limiting factor for long term stability [2], and both molecules maximum solubility still remain a challenge to build a battery to cope with lithium ion batteries. However, efforts on design and synthesis of a new cathode complex for the complementary reaction have been conducting and will be expanded to overcome this issue and boost it into the market. References [1] B. Huskinson, M.P. Marshak, C. Suh, S. Er, M.R. Gerhardt, C.J. Galvin, X. Chen, A. Aspuru-Guzik, R.G. Gordon, M.J. Aziz, Nature 505 (2014) 195. [2] K. Wedege, E. Drazevic, D. Konya, A. Bentien, Nature Publishing Group (2016) 1.

Resume : Owing to its high surface area and concomitant high theoretical capacity graphene and its derivatives are highly interesting materials for supercapacitors with excellent capacity and cyclability in static devices (C. Liu et al. Nano Lett. 2010, 10, 4863–4868). Recently, reduced graphene oxide nanofluids were applied in an aqueous flow supercapacitor configuration yielding a promising capacity (156 F/g) and over 98% Coulombic efficiency without addition of further conductive carbons (D. P. Dubal, P. Gomez-Romero 2D Mater. 2016, 3, 031004). In aqueous solutions of graphene and its derivatives colloidal stability and capacity on one side and conductivity on the other are antagonistic properties, since a higher degree of functionalisation increases one while reducing the other. For fast charging in a flow configuration the conductivity of the flowable electrode is a crucial factor. For this reason it is desirable to find a compromise that optimises properties of the graphene component in both directions. We examine and discuss the effects of different stabilisation strategies and functionalisation treatments such as heteroatom doping on stability as well as electrolyte conductivity and capacity of aqueous graphene based electrodes in static and flow conditions.

Resume : The present work investigates the electrochemical performance of Fe/Fe2O3 incorporated porous electrospun carbon nanofibers (PCNFs) towards ultra-high charge-discharge supercapacitors. The work will be conveyed into two major sections. Firstly, we will demonstrate our one-step thermal treatment, where diffusion velocities between Fe3 and O2- showed discrepancies which results in-situ pores on CNFs matrix [1]. These in-situ pores and FeOx nanostructures attribute to electric double-layer capacitor (EDLC) and as well as Faradaic behavior, which results in a two-fold increase in charge storage along with high charge retention at high scan rates (retention= C200 mV/s/C5 mV/s; >80%). Secondly, we will show the two paths to further enhance the capacitance, surface area, electrical conductivities and time constant. The two paths were conducted would be varying: (i) precursor concentrations and (ii) precursor anion. A emerging trend was observed in terms of morphology, pore size distribution, surface area and electrical conductivities. For example, HRTEM phase filtered composition shows varation of Fe-Fe2O3 phases in dependence with the precursor anion. Based on these trends, we design a model to achieve ultra-high charge-discharge behavior, which will be also discussed. Using these models, the cyclic voltammograms show quasi-EDLC behavior, even at 12.5 V/s and best ultra-low time constant of 87 ms [3]. These rational tailoring can provide efficient charge storage models which can be a powerful tool the energy storage community to design high power supercapacitors. Acknowledgement: Authors thank Dr. Sònia Abelló (IREC, Tarragona) for N2 sorption measurements. References [1] B.D.A. and J.B. Tracy, Nanoscale. 6 (2014) 12195–12216. doi:10.1039/C4NR02025A. [2] L. Coustan, P. Lannelongue, P. Arcidiacono, F. Favier, Electrochim. Acta. 206 (2016) 479–489. doi:10.1016/j.electacta.2016.01.212. [3] L. Wang, T. Wei, L. Sheng, L. Jiang, X. Wu, Q. Zhou, B. Yuan, J. Yue, Z. Liu, Z. Fan, Nano Energy. 30 (2016) 84–92. doi:10.1016/j.nanoen.2016.09.042.

Resume : Performance and safety monitoring of the batteries is clearly of major importance for most of applications. Usual methods presently embedded in the Battery Management Systems (BMS), based on temperature and electrochemical monitoring, do not provide sufficiently relevant information to detect the mild signs of improper operation that could lead to irreversible degradation of the performance and even safety issues. In view of this fact, we evaluated the use of acoustic methods of characterization and thermal analysis for an advanced monitoring of the batteries. These two in-operando and non-invasive techniques are used to detect discrete phenomena related to material and interfacial modifications inside the batteries under operation. We propose to describe the experimental setup used for commercial batteries and battery packs monitoring, and discuss the capabilities and limitations of these techniques. A few example of experimental results relative to the detection of early warning signs of damaging during abusive operation and to the evolution of thermal behavior of a battery over ageing are presented. Acoustic techniques of characterization are commonly used in materials characterization and monitoring. Two main techniques exist. - The first one, so called acoustic emission (AE), is a passive monitoring technique. Relaxation of mechanical stresses in materials and at interfaces (e.g. due to volume change associated with lithium intercalation, cracks of the SEI, gas evolution during electrolyte degradation, etc…) produce transient elastic waves that propagate through the battery. The acquisition of these propagative elastic waves using piezoelectric sensors sensitive to ultrasonic waves (frequencies throughout the range 50 kHz to 1 MHz) and positioned at the material periphery aims at detecting internal relaxation phenomena. Thereby, the analysis of the emitted acoustic signals (amplitude, frequency, shape, energy) allows monitoring material fatigue or/and aging through non-intrusive, non-destructive and in-operando approach. However, these acoustic phenomena are generally generated as sets of non-coherent acoustic waves. Thereby, the acquired signals need careful data processing and treatment to identify and selectively ascribe acoustic events with specific internal physic-chemical phenomena arising from SEI formation, lithium intercalation or aging mechanisms. - In contrast to AE, Ultrasound characterization (UsC) is an active characterization method in which acoustic waves of a defined wavelength are injected from a transducer within the battery material. The acoustic waves interact with the materials and can be absorbed or reflected by defects. Attributes of the waveforms recorded by the sensor (e.g. Time of Flight, amplitude, frequency, presence of any echoes, etc…) are analyzed to identify physical changes in the battery. Thermal analysis of the batteries is implemented by heat flux sensors arranged on the surface of the system. The electrical signal recorded is directly related to the energy absorbed or dissipated as heat by the battery to the surrounding environment. It is then possible to identify endothermal and exothermal reactions occurring during operation and measure directly the calorific capacity (Cp) of the system. Modelling of the thermal behavior allows a better thermal management of the battery, improving the performance and durability, and improving the safety of the system. Changes in the thermal behavior during ageing has been evidenced on different types of batteries. We recommend to take these changes into account in the thermal management of the battery packs in order to avoid abnormal overheating. Acoustic characterization techniques and thermal analysis are evaluated as non-electrochemical in-operando methods to complement the usual electrochemical monitoring of batteries in order to detect materials and interface changes in commercial-type batteries during operation and ageing. After a description of the experimental setup, we discuss their capability and limitations to be used to improve determine different status indicators such as the State of Charge (SoC) during usual operation, State of Health (SoH) related to aging mechanisms, and the State of Safety (SoS) with the possibility to prevent safety issues, detecting the early warning signs of damaging during abusive operation (thermal runaway, overcharge and overdischarge …).

Resume : Using electron diffraction tomography we solved and refined the changes in the structures of several lithium battery cathode materials after cycling. We obtained the complete crystal structures including the positions of the lithium atoms and the ocupation of these positions. This would not have been possible from bulk diffraction, because of the need to mix the compounds with other phases to enable electrochemical charging, which is not a problem for electron diffraction. For example the refinement of Li2FePO4F after cycling showed massive antisite disorder, which is uncommon in polyanionic cathode materials. Some Li positions contained 40% of Fe and oppositely after only 10 cycles. The same investigation on LiFePO4 did not show such antisite disorder. We propose that the difference is due to the different connectivity of the polyhedra in both compounds. As other examples, on the one hand, for Li1-xFe0.5Mn0.5PO4, a material with improved specific energy and specific power compared to the commercially used LiFePO4, we determined that the structure does not change much during charging and that the introduction of Mn3+ does not lead to a cooperative Jahn Teller distortion. On the other hand, we see very drastic changes in the structure upon cycling for LiRhO2, a layered compound like LiCoO2. During charging up to 3.85 V about half of the Li is removed without significant changes in the structure, but then on full charging, the structure changes drastically. The new structure contains two types of channels: large ramsdellite channels and small rutile channels. In short, in this presentation we will show that electron diffraction tomography is a valuable tool to study degradation upon cycling and support this with several clear examples. Published as: O.M. Karakulina et al. Chem. Mater. 28 (2016) 7578; S.S. Fedotov et al., JSSC 242 (2016) 70; D. Mikhailova et al. Inorg. Chem. 55 (2016) 7079; O.A. Drozhzhin, Electrochim. Acta 191 (2016) 149; S.S. Fedotov, Chem. Mater. 28 (2016) 411

Resume : Ruddlesden-popper phases especially those with K2NiF4-type structure, are of particular interest, as they exhibit high ionic and electronic conductivity already at moderate temperatures. Among them, Pr2NiO4+δ phases have attracted much attention as promising materials, showing a rather wide range of oxygen non-stoichiometric and high oxygen mobility accommodating extra oxygen on interstitial lattice sites, suitable for next generation SOFCs cathode material through the understanding of oxygen diffusion at low temperature. A high oxygen doping level has been shown to induce a special lattice dynamic, allowing the apical oxygen atoms to easily move to vacant interstitial sites on a shallow energy diffusion pathway [1,2]. It is fundamental to understand the mechanism of oxygen diffusion and more importantly, the crystal structure of this kind of oxides w.r.t. complex superstructures. Hole doping in Pr2NiO4, either by substituting Pr with Sr cations or by O2- ion intercalation on interstitial lattice sites modifies the structural (ordering of O2- ions) and electronic/charge ordering in Pr2-xSrxNiO4+δ. High quality single crystals of Pr2-xSrxNiO4+δ were grown by FZT using image furnace. We have investigated the structural evolution of the complex electronic and structural ordering as a function of x, δ, T(K) and P(O2) by scanning the whole reciprocal space using single crystal x-ray diffraction. The average structure changes from orthorhombic Fmmm (x = 0 and 0.125) to tetragonal P42/ncm (x = 0.25) and I4/mmm (x =0.5) in Pr2-xSrxNiO4+δ. Due to oxygen intercalation δ up to 0.25 and long-range ordering of those O2- ions, Pr2NiO4+δ forms complex superstructures with (3+2)D-incommensurate modulation (q1,2 = ±0.83a*+0.49b*) in the (hkl, l=integer) reciprocal plane still present in the doped crystal (x = 0.125) but appears as diffuse scattering. More complex and different modulation exists in (hkl+1/2, l=integer) plane due to ordering along c-axis. Four twin individuals are present in the as grown Pr2NiO4+δ single crystal which also makes the incommensurate modulation more complex whereas this modulation disappear gradually and new p-type superstructure reflections appear when entering to the tetragonal phase of Pr2-xSrxNiO4+δ (x=0.25) with no other superstructures. Changes in the crystal structure as function of temperature have been investigated since the phase stability of Pr2NiO4+δ with temperature becomes an important factor. The evolution of the modulation vectors as function of temperature is not linear rather goes to more incommensurate from nearly commensurate as starting phase and disappears completely at the temperature where LTO to HTT phase transition take place. [1] M. Ceretti, O. Wahyudi, A. Cousson, A. Villesuzanne, M. Meven, B. Pedersen, J. M. Bassat and W. Paulus, J. Mater Chem. A, 3 (42), 21140-21148 (2015). [2] O. Wahyudi, M. Ceretti, I. Weill, A. Cousson, F. Weill, M. Meven, M. Guerre, A. Villesuzanne, J.-M. Bassat and W. Paulus, CrystEngComm, 17, 6278-6285 (2015).

Resume : Polycrystalline ferrites are group of materials, useful for wide range of applications such as high frequency applications, magnetoelectric coupling, magnetic resonance imaging, hyperthermia and drug delivery1–5etc. Among the various ferrites, cobalt ferrite has good chemical stability, high coercivity, moderate saturation magnetization (~80 emu/g), positive anisotropy (~ 106 erg/cm3), while nickel ferrite has remarkably high electrical resistivity (~106 Ωcm) with mechanical hardness and chemical stability 6–8. Mixed phase of Nickel and cobalt ferrite can be useful for multiferroic application and power electronics due to its moderate magnetic properties with high resistivity. In this report, structural and electrical properties of Ni1-xCoxFe2O4 (x= 0.0, 0.5, 1.0) have studied because for the application point of view, structural and electrical properties of ferrites have equally importance. The electrical properties of ferrites are highly influenced by the distribution of cations between the sub-lattices, grain size, grain boundaries, voids, inhomogeneities, etc. The structural, vibrational and electrical studies were performed using x-ray diffraction (XRD), fourier transform infrared (FTIR) and LCR meter. XRD patterns confirm the formation cubic phase ferrites in crystalline nature. The shift in XRD peaks and increased lattice parameter from 8.337 Å (x=0.0) to 8.397 Å (x=1.0 is found with Co2 ions substitution. FTIR spectra show the characteristic peaks of spinel ferrites. The dielectric constant (εꞌ) decreases with frequency and stable at higher frequencies (above 100 KHz) except for x=0. The maximum dielectric constant (εꞌ~ 104 order at 4 Hz) is recorded for x=0.0. The abnormal behavior observed for the tanδ versus frequency curves for all samples in the range of 42 Hz to 1000 Hz with Co2 ions. The maximum ac conductivity was obtain for composition x=0 and x=1.0 at 8MHz which are correlated with hopping of charge carrier. References 1 M. Pardavi-Horvath, J. Magn. Magn. Mater. 215, 171 (2000). 2 B. Sahoo et al., J. Colloid Interface Sci. 431, 31 (2014). 3 A.S. Fawzi et al., J. Alloy. Compd. 502, 231 (2010). 4 X. Fan et al., Eur. J. Inorg. Chem. 419 (2010). 5 Z. Zhou et al., Biomaterials 35, 7470 (2014). 6 J. Bera et al., Acta Phys. Sin. 54, 5764 (2005). 7 J.S. and H.P.J.W. Win, (1959). 8 P.R. Kumar and S. Mitra, 3, 25058 (2013).

Resume : Lithium ion batteries (LIB) have attracted special attention in the scientific and industrial communities due to their durability and high energy density. Graphite is used as commercial anode material in LIBs (theoretical specific capacity of 372 mAhg−1) from past few decades. However, metal disulfide materials are in present consideration as alternate anode materials for graphite. Molybdenum disulfide (MoS2) is one among popular metal disulfide materials with multiple applications1. Even though MoS2 has theoretical capacity over 670 mAhg-1 (which is double the value of Graphite), it has less conductivity which further resists its application in LIBs. So as to overcome this issue making composites with carbonaceous materials like reduced graphene oxide (RGO)2 will help for the enhancement of conductivity, cycling ability and increase in the capacity higher than MoS2theoretical capacity 3. In the present study, a novel synthesis route has been adopted to prepare RGO/MoS2 nanocomposites. The typical synthesis involves two step process. In first step stoichiometric amount of MoS2 powder was well dispersed in 100 ml of N-Methyl Pyrrolidone (NMP) solution via sonication for an hour in a beaker followed by centrifugation to get MoS2 nano flakes4. Product was washed with Ethanol and acetone to obtain dry product. In next step Graphene oxide (GO) and MoS2 nano flakes were taken in different stoichiometric ratios and dispersed in 25 ml of NMP via sonication. Further solution was subjected to micro wave irradiation for three to five minutes. After cooling solution was centrifuged and washed with Ethanol and Acetone to get dry product of RGO/MoS2 nanocomposites. Structural and morphological studies were carried using XRD, XPS, TGA, FT-IR, Raman, BET Surface area analysis, FE-SEM and FE-TEM analysis. Finally, electrochemical performances of the RGO/MoS2 nanocomposites were studied using EIS, CV and galvanostatic charge/discharge measurements by fabricating 2032 type coin cells with Li/Li+ as counter and reference electrode. Key words: MoS2, Lithium ion batteries, anode materials, RGO. References: 1. X. Zhang and Y. Xie, Chemical Society Reviews, 2013, 42, 8187-8199. 2. R. Raccichini, A. Varzi, S. Passerini and B. Scrosati, Nat Mater, 2015, 14, 271-279. 3. D. Kong, H. He, Q. Song, B. Wang, W. Lv, Q.-H. Yang and L. Zhi, Energy & Environmental Science, 2014, 7, 3320-3325. 4. K. Wang, J. Wang, J. Fan, M. Lotya, A. O’Neill, D. Fox, Y. Feng, X. Zhang, B. Jiang, Q. Zhao, H. Zhang, J. N. Coleman, L. Zhang and W. J. Blau, ACS Nano, 2013, 7, 9260-9267.

Resume : Hollow structured particles have attracted great interest in energy storage application due to the typical merits of high electrochemical activities and the capability of buffering large volume change during redox-reaction. But it is still a challenge to fabricate hollow-shaped electrode materials in large scale. In this paper, we report a facile supramolecular gel templating method to mass produce hollow structure CuO. In this strategy, a transparent and stable Cu-chitosan hydrogel was firstly formed via the ultra-fast cross-linking between Cu and chitosan solution at room temperature. Then Cu2+ ions were in-situ reduced by the preexisting ascorbic acid in chitosan solution and self-assembled into chitosan coated Cu/Cu2O composite hollow spheres by the template effect of chitosan supramolecular hydrogel. The chitosan coated Cu/Cu2O composite hollow spheres converted into uniform CuO hollow spheres with C and N doping by annealing at 500 oC in the air. When evaluated as anode materials for Li-ion batteries, the as-produced C and N co-doped CuO hollow spheres exhibited superior electrochemical properties with a good combination of high reversible discharge capacity of 791 mAh g-1 at 100 mA g-1, extremely stable cycling performance with a retention rate higher than 90% after 550 cycles, and excellent high rate capability (delivering a capacity of 430 mAh g-1 at a high current density of 500 mA g-1). This method is energy-efficient, bio-compatible, sustainable, low cost, and scalable that is universal technique for the synthesis of hollow nanostructures in a large number of compounds for energy storage and conversion applications.

Resume : The novel flake NiFe2O4 materials on Ni foam substrate as binder- and conductive-agent-free are prepared by a simple, cost-effective hydrothermal growth followed by sintering. In typical synthesis, nickel foam was firstly ultrasonically cleaned by acetone, HCl solution, deionized water and ethanol. Then Fe, Ni salts were dissolved in mixed solution followed by adding 2 mmol of NH4F stirring for 2 h to obtain well distributed solution. Then the solution and the pretreated Ni foam were transferred into a Teflon-lined stainless steel autoclave and heated at 120°C for 10 h. After cooled down naturally to room temperature, the product on nickel substrate was taken out, washed, vacuum dried and then thermally treated at 350°C in argon for 2 h to obtain the flake NiFe2O4. The flake NiFe2O4 materials are used as anode material for lithium-ion batteries and it exhibits good cycling performance and rate capability. The corresponding anode delivers a reversible capacity of 1138 mA h g-1 after 100 cycles at a current density of 100 mA g-1. Moreover, it exhibits superior rate performance with reversible capacity of 450 mA h g-1 even at the current density of 3200 mA g-1. Such remarkable electrochemical properties could be ascribed to the unique flake morphology with large surface area and porosity that were good for facilitating the diffusion of Li+ and electrolyte into the electrodes, meanwhile preventing volume expansion/contraction during charge-discharge process.

Resume : Lithium ion batteries (LIBs) have attracted lots of interest as outstanding electrical energy sources.1,2 Fe2O3 is a promising anode material for LIBs since it has high theoretical capacity (~ 1007 mAh/g), and it is abundant in nature and environmentally friendly. However, there is a large volume expansion (over 200%) of Fe2O3 anode materials during charging and discharging process, which leads to a quick capacity decrease.3 Therefore, different forms of carbon and Fe2O3 composites are studied to absorb the volume change. Among them, Fe2O3 and reduced graphene oxide (RGO) composites perform outstandingly.1,3 In this work, we investigated the lithium storage capabilities of Fe2O3/Multiwall Carbon Nanotubes/RGO aerogel, Multiwall Carbon Nanotubes/RGO aerogel, Fe2O3/RGO, RGO aerogel and Fe2O3. All materials are synthesized via simple hydrothermal methods, and followed by freeze drying. The morphology and properties are characterized by scanning electron microscope and X-ray diffraction. Fe2O3 content is analyzed by thermogravimetric analysis. The galvanostatic performance is measured by a Xinwei battery test system between 3.0 V and 0.01 V. Electrochemical impedance spectroscopy and cyclic voltammetry measurements are both carried out using a BioLogic VMP3 electrochemical workstation. The cycling performance and its relationship with material morphology will be discussed in detail.

Resume : ABSTRACT Glasses are suitable alternatives for making safe and high energy density batteries for use in automobiles in presence to flammable organic liquid electrolytes [1]. Recently fast lithium ion conduction with conductivity around 10-4 S-cm-1 with activation energy of 0.1 eV has been reported in lithium silicate glasses grown within mesoporous silica template [2]. Sodium ion conductors are now becoming promising choices for solid electrolyte due to low cost, non-toxicity, natural abundance than lithium ion conductors. Sodium ions have chemical similarity with lithium ions and so various works have been done so far upon mobility of sodium ions [3-5]. In this investigation we have explored sodium ion conduction in nanodimensional sodium silicate glasses of composition 30Na2O.70SiO2. The latter were grown within the nanochannels of diameter 5.5 nm of mesoporous silica SBA-15 by heat treatment of suitable sol precursors. Electrical conductivity of the sample was studied by ac impedance spectroscopy. The activation energy for ionic conduction was found to be 0.16 eV which is much smaller than that of the other reported results [3-5] with dc conductivity at room temperature of 10-6 S-cm-1. This is attributed to the creation of oxygen ion vacancies at the interface of mesoporous silica and nanoglass arising out of the presence of Si2+ and Si4+ species in the system. References [1]. K. Bange, H. Jain, C. Pantano, ed. by K. Bange, A. Duran, J. Parker. Functional Glasses: Properties and Applications for Energy and Information. International Commission on Glass (2015) [2]. S. Chatterjee, R. P. Maiti, S. K. Saha and D. Chakravorty, Journal of Physical Chemistry C, 120 (2016), 431 [3]. W. D. Richards, T. Tsujimura, L. J. Miara, Y. Wang, J. C. Kim, S. P. Ong, I. Uechi, N. Suzuki and G. Ceder, Nature Communications (2016) doi:10.1038/ncomms11009 [4]. Z. Zhu, Iek-Heng Chu, Z. Deng and S. P. Ong, Chemistry of materials, 27 (2015), 8318 [5] H. Pan, Yong-Sheng Hu and L. Chen, Energy and Environmental Science, 6 (2013), 2338

Resume : Iron sulfides chalcogenides accommodate lithium ions through conversion reaction, thus their theoretical capacities are two or three times higher than the intercalation graphite anode. Nevertheless, Iron sulfides suffer a large volume expansion during charging and discharging which causes pulverization. To overcome these drawbacks, we have designed a rational three-dimensional hierarchical honey comb-like iron mono-sulfide (FeS) nanoparticles (nps) encapsulated by nitrogen and sulfur co-doped carbon nanostructures (HFSC), using metal organic complex. A series of HFSC composites: compact and free- bound carbon framework, thickness of encapsulated nanolayer carbon (~1.5 to ~3.5 nm) over FeS nps, average size distribution of FeS nps over the carbon surface- and edge- sites, amount of nitrogen (7.18 to 3.26 at.%) and sulfur (6.63 to 4.64 at. %) functionalities, have been easily controlled via synthesis temperature. The optimized material displays a high reversible capacity of ~1116 mAh/g at a low current density of 100 mA/g, and even at a high current density of 1100 mA/g a discharge capacity of ~650 mAh/g is retained; more importantly, moderate cycle life of 50 cycles with a retention capacity of 941 mAh/g and columbic efficiency of 100% at a high current density of 500 mA/g is achieved. Thus, our approach highlights the facts that physicochemically optimized FeS carbon hybrid composite nanostructure has strong influences over high discharge capacity, superior high-rate capability, and enhanced kinetics towards lithium intercalation, making them suitable anode candidates for LIB applications.

Resume : TiO2 nanoparticles with diverse polymorphs such as amorphous, anatase, brookite and rutile forms, have emerged in applications for energy storage devices, exhibiting excellent electrochemical activities. However, employing TiO2 as a catalyst support in Li-O2 batteries has been rarely reported. In this study, amorphous TiO2 supported crystalline RuO2 (a-TiO2/c-RuO2 hybrid) was synthesized as a carbon-free cathode for non-aqueous Li-O2 batteries. The a-TiO2/c-RuO2 hybrid was prepared by a sol-gel method, which provides a simple synthetic route and chemical homogeneity, followed by annealing at relatively low temperature. The TiO2/RuO2 precursors obtained by a hydrolysis reaction of titanium oxysulfate and ruthenium chloride in aqueous solution were annealed at the temperature between 300 and 600℃ for phase transformation from hydroxide to oxide. The electrochemical performance of the prepared a-TiO2/c-RuO2 hybrid was evaluated. The a-TiO2/c-RuO2 hybrid achieved the overpotential of 1.0 V at a specific capacity of 1200 mAhg-1. The enhanced battery performance was attributed to the crystallinity of the TiO2 that amorphous TiO2 is more electrochemically active toward ORR/OER than crystalline TiO2. The reversibility as well as cyclic stability was achieved up to 132 cycles, making it a promising carbon-free cathode material for non-aqueous Li-O2 batteries.

Resume : The next-generation lithium-ion batteries (LIBs) with high efficiency are needed to power future advanced electric vehicles. Therefore numerous efforts have been devoted to meet these demands on LIBs. To advance its performance, MnO2 has been recently employed in Li-ion battery because of its high abundance, low cost and environmental friendliness. In this study, electrodes were fabricated via electrochemical deposition to grow MnO2 nanosheets (NSs) on Au nanothorns (NTs) covered carbon fiber. With proper selecting reaction including solution concentration and voltage, we grow Au NTs on carbon fiber to increase the interior conductivity of the electrode. Then MnO2 was electroplated from Mn(NO3)2(aq) ,growing on the pre-synthesized Au@CF electrode. Scanning electron microscopy (SEM) was used to observe crystals growth of these nanostructure and Electrochemistry Impedance Spectroscopy (EIS) was used to analyze the interior impedance of the electrode. As a result, an as-fabricated anode demonstrated a capacity of 927.14 mAh g-1 after 50 discharge/charge cycles with a current density 100 mA g-1.

Resume : Sn is a promising material as an anode for sodium ion batteries due to its high theoretical capacity of 847 mAh/g by a formation of Na15Sn4 alloy. However, a fast capacity fading, caused by the pulverization of the active material during cycling, limits its practical application. We develop porosity and mechanical strength controlled graphene/reduced graphene oxide (Gr/rGO) composite as a reservoir of Sn via a camera flash reduction method. The porous geometry and robust mechanical property of Gr/rGO composite enable a uniform Sn loading on its surface and an improvement in the cycle performance due to a sufficient free space for accommodating the large volume change of Sn and a mechanical stability of Gr/rGO skeleton framework. With optimal electrode configuration design, such electrode shows a high reversible capacity of 750 mAh/g, stable capacity retention (>74% after 50 cycles) and excellent rate capability. Our electrode design strategy could be extended to other alloy type electrode materials for Na ion batteries as well as Li ion batteries.

Resume : A vanadium redox flow battery (VRFB) have attracted increasing attention as a potential energy-storage system because of their outstanding features such as safety, long cycle life, and design flexibility. Since it was invented by Skyllas-Kazacos research group at the University of New South Wales in 1986, extensive studies have been conducted to improve its performance. However, the performance of VRFBs still suffers from the significant charge-transfer polarization. Here, we report a new fabrication method for a felt electrode on which zeolitic imidazolate frameworks (ZIFs) are uniformly distributed. It is sequentially exposed by the thermal treatment to convert ZIFs to the nitrogen-doped carbon nanotube (NCNT). The felt electrode modified by NCNTs shows the excellent electrocatalytic effect for vanadium redox reaction. It is proved by the cyclic voltammetry and the charge-discharge test using a single flow cell.

Resume : Synthesis and structure design of cathode materials with superior catalytic activity is still major challenge for rechargeable lithium-oxygen batteries. Among many cathode materials, carbons are often used because they help achieve high discharge capacities and good ORR performance. However, most lithium-oxygen batteries containing carbon electrodes suffer from a low round-trip efficiency, low rate capability, a poor cycle life, and electrolyte instability. In this poster, we report a binder- and carbon-free, 3D porous Ru- and RuO2-foam cathode for lithium-oxygen batteries. The cathode was simply fabricated by three-step process; co-electrodeposition, electrochemical dealloying and heat treatment process. Both 3D porous Ru- and RuO2-foams have lots of cavity and pits which provide a large surface area for catalytic sites and buffer spaces for the volume stress by the formation/decomposition of Li2O2 during the cycling process. Moreover, cathodes made of Ru- and RuO2- foam can provide high catalytic activities, short ion diffusion length and channels for rapid transport of oxygen and electrolyte. The hierarchically dendritic cathodes without carbon and binder present low charge/discharge overpotential, remarkable cyclability, good oxygen efficient and reduced irreversible formation form electrolyte decomposition. We systematically investigated the reversibility and cyclability of a lithium-oxygen battery using the 3D porous Ru- and RuO2-foam cathode using scanning electron microscopy (SEM), X-ray diffraction (XRD), selected area electron diffraction (SAED), in-situ Differential Electrochemical Mass Spectrometry (DEMS) and FT-IR spectroscopy. The results using the 3D porous nanostructured electrodes in our study represent a promising approach for high-performance electrodes which are compatible with scaled-up manufacturing process for next-generation lithium- air batteries due to their simple and rapid fabrication process.

Resume : There has been a constant effort to find a replacement to the precious metal Pt as a catalyst in Hydrogen Evolution Reaction (HER). Non-precious Metal phosphides are found to show remarkable catalytic activity as compared to platinum. In this work from our first principle density functional calculations we discuss, how Ni2P surface evolve during electrolysis and assist in Hydrogen evolution. From our calculations we show the most stable termination of Ni2P(0001) surface. We show that Ni2P(0001) surface gets modified under excess phosphorous available. Using our first principle results we show how this modified surface further assists H adsorption on these surfaces. We use ab-initio thermodynamics to approximate and compare the catalytic activity with Pt and other precious metals. Our calculation results successfully explained surface behaviour observed in experiments and also provided further guidelines.

Resume : The effects of different polymer binders on the electrochemical performances of tin-based electrodes for lithium-ion batteries were investigated by using poly(vinylidene fluoride) (PVDF), conventional polyimide (PI-OB), and new polyimide containing amino-quinone (PI-AQOB) as polymer binders for electrodes consisting of commercial powdered Sn particles and Super P. We synthesized a new type of aromatic PI binder having amino-quinones since those groups have been known to be very effective in adhesion between polymer and metal because of their high affinity to the surface of metals. PI-AQOB could be prepared from polyamic acid (PA-AQOB) synthesized from 2,5-bis(4,4'-oxydianiline)-1,4-benzoquinone (AQODA) and 4,4'-biphthalic dianhydride (BPDA) by condensation polymerization, and the thermal conversion was confirmed by Fourier-transform infrared analysis. The effects of the functional groups (amino-quinone) of the PI binders on the electrochemical performance of a Sn particle anode were studied by comparing with the Sn particle anode employing PVDF and conventional PI (PI-OB). Compared to the electrode employing the traditional PVDF binder, those with the PI-AQOB binder exhibited significantly enhanced electrochemical performance in terms of rate capability, specific capacity, and cycling behavior. PI-AQOB provided a high initial charge capacity of 1529 mAh/g at a current density of 50 mAh/g. After 50 cycles, the PI-AQOB electrode maintained a higher specific capacity of 332 mAh/g than the Sn/PVDF electrode (only 65 mAh/g at a current density of 200 mA g-1). Furthermore, we could observe better volume restoration of the Sn/PI-AQOB electrode by scanning electron microscopy, compared to the electrodes with Sn/PVDF and Sn/PI-OB. The amino-quinone group of PI-AQOB binder played a very important role in enhancing the electrochemical performances in tin-based anodes for lithium-ion batteries by increasing the interfacial adhesion between the binder and tin particle during expansion/contraction of Sn particles in the lithiation/delithiation process.

Resume : V2O5 is a promising cathode material for lithium ion batteries boasting a large energy density due to its high capacity as well as abundant source and low cost. Hydrogenated transition metal oxides (TMOs) prepared by H2 thermal treatment have attracted increasing attention as electrodes in LIBs and supercapacitors on account of the improved conductivity and kinetics in the electrochemical reactions. In this presentation, we report the design and fabrication of a hydrogenated V2O5 nanosheets with super Li storage properties. The V2O5 nanosheets with most of O(II) vacancies are fabricated by hydrogenating V2O5 nanosheets at a relatively lower temperature of 200 oC, enabling easier and faster Li ion diffusion. In our work, hydrogen atoms first adsorbed at the oxygen sites forming OH and then H-V2O5 with most oxygen vacancies at O(II) sites could be produced beacuse the formation of the oxygen vacancy in O(II) sites by removing the OH group requires less energy than removing oxygen directly. The H-V2O5 with most oxygen vacancies in O(II) sites has improved conductivity, faster diffusion of Li+, and improved structure stability for Li+ intercalation/deintercalation, resulting in higher capacity, rate capability, and improved cycling stability. The hydrogenated V2O5 (H-V2O5) nanosheets deliver an initial discharge capacity as high as 259 mAh g-1 and it remains at 55% when the current density is increased 20 times from 0.1 to 2 A g-1. The H-V2O5 electrode has excellent cycle stability with only 0.05% capacity decay per cycle after stabilization. The effects of oxygen defects on Li+ diffusion and overall electrochemical lithium storage performance are revealed. Our results reveal a simple and effective strategy to improve the capacity, rate capability, and cycling stability of V2O5 materials which have large potential in energy storage and conversion applications.

Resume : With the increasing demand for clean and sustainable energy, much effort has been put into developing new colossal permittivity (CP) materials. High-performance CP materials exhibiting high dielectric permittivity, low dielectric loss and relatively weak dependence of frequency- and temperature have aroused considerable interest in the areas of device miniaturization and energy storage. A wide range of CP materials are developed but maximizing their performance by fulfilling all the aforementioned requirements remains a barrier. In this work, the rutile TiO2 ceramics co-doped with niobium and erbium, (Er0.5Nb0.5)xTi1-xO2, achieve excellent dielectric properties. The material showed a CP of up to ten thousand to a hundred thousand and a low dielectric loss down to 0.03, which was lower than that of the previously reported co-doped TiO2 CP materials when measured at 1 kHz. Stabilities of frequency and temperature were also accomplished via doping Er and Nb. Valence states of the elements in the material were analyzed using X-ray photoelectron spectroscopy. The Er induced secondary phases were observed using elemental mapping and energy-dispersive spectrometry. As there is a trend towards size reduction of many microelectronic devices, the optimum dielectric properties of the material was selected for fabricating the film. Consequently, doped TiO2 ceramics and films may be attractive for potential fully solid-state capacitor and energy-density storage applications, respectively. The work was supported by the grant from Research Grants Council of Hong Kong (GRF No. PolyU 153004/14P).

Resume : La-Mg-Ni-based alloys with unique superlattice structures were the most promising negative electrode materials for Ni-MHx batteries. In this study, mechanical alloying with subsequent annealing under an argon atmosphere at 700 C for 0.5 h were used to produce La2-xMgxNi7 alloys (x = 0, 0.25, 0.5, 0.75, 1). An objective of the study was to investigate an influence of amount of Mg in alloy on electrochemical and electronic properties of La2-xMgxNi7 materials. The nanocrystalline La1.5Mg0.5Ni7 sample was studied by X-ray photoelectron spectroscopy (XPS). The results for La1.5Mg0.5Ni7 were compared with XPS measurements for pure nanocrystalline La and Mg, and polycrystalline Ni thin films prepared by UHV magnetron sputternig. The experimental efforts were followed by the density functional theory (DFT) calculations. In order to simulate chemical disorder the coherent potential approximation (CPA) and the ordered compound method were used. The modeling of La1.5Mg0.5Ni7 we started from a crystallographic structure of La2Ni7 with space group P63/mmc, with two inequivalent La atoms and five inequivalent Ni atoms in formula, and with four formulas (36 atoms) in a unit cell. We presented results of calculations for three most distinctive inequivalent configurations of Mg dopants (La6Mg2Ni28). Finally, the theoretically determined XPS valence band was compared with experimental results. Work supported by the National Science Centre Poland under the decision DEC-2014/15/B/ST8/00088.

Resume : The energy system with the solar cell, poly-silane-metal catalyst and direct fuel cell is proposed. In this system, the solar energy is stored in the recycled hydrogen carriers, such as, 2-methyl-1, 4-benzoquinone. This method consists of the following steps. First, the water was efficiently decomposed by the electrical power generated using solar cells. The developed high efficiency and low cost solar cells are one of the candidates to generate hydrogen molecules with the low cost enough for the future energy market. The generated hydrogen molecules were catalyzed using the poly-silane Fe catalyst to hydrogenate the carbonyl groups of benzoquinone, resulting in making it hydroquinone. The solar energy was stored as a chemical storage of hydrogen as OH in the molecules. This catalytic reaction occurred at room temperature, and the instrument worked standalone without adding extra heats. Here, the changes were only from the carbonyl groups to the hydroxyl groups of the ring by adding a hydrogen atom and the main structure of the molecule did not change. This storage energy in the molecules was converted to the electrical power using the direct fuel cell, where the hydroquinone was oxidized to benzoquinone. Therefore, the recycle of the hydrogen carrier was realized, and this system will solve the instability problem of renewable energies.

Resume : The 3D battery architecture can be a promising way to extend the application area of the conventional lithium-ion batteries to the miniaturised electronic devices. We will demonstrate the Sn-Ni intermetallic alloys electrodeposited onto nickel foam, as a promising anode material for 3D lithium-sulfur battery. The Sn-Ni intermetallic alloys were successfully electrochemically deposited onto 3D structural nickel foam in an aqueous electrolyte solution. The homogenous deposition of the alloys were confirmed using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (SEM-EDS). Meanwhile, the phase of the alloys was analyzed by X-ray diffractometer. The electrochemical properties were extensively studied using Cyclic Voltammetry and galvanostatic charge-discharge. The Sn-Ni intermetallic alloys demonstrated remarkable electrochemical behavior with high capacity and stable cycle performance.

Resume : A series of new fluorinated sulfonated copolytriazoles (PTHQSH-XX) membranes were synthesized via cuprous ion catalyzed azide-alkyne click polymerization (AACP) reaction between, 1,4-bis(prop-2-ynyloxy)benzene (TH), 4,4ʹ-diazido-2,2ʹ-stilbene disulfonic acid disodium salt (SA) and 4,4-bis[3ʹ-trifluoromethyl-4ʹ(4-azidobenzoxy) benzyl] biphenyl (QAZ). The degree of sulfonation (DS) the copolytriazoles were adjusted by changing the molar ratio of sulfonated monomer (SA) to the non-sulfonated monomer (QAZ). The structures of the copolytriazoles were characterized by FTIR and 1H NMR techniques. These copolytriazoles membranes exhibited high thermal, mechanical properties, low water uptake, and good oxidative and hydrolytic stability. The PTHQSH-XX membranes showed high proton conductivity (19-142 mS/cm at 80 °C, and 22-157 mS/cm at 90 °C), in 100 % RH. Transmission electron microscopy (TEM) confirms the formation of good phase separated morphology with ionic clusters in the range of 15-145 nm.

Resume : The demand for secondary batteries is constantly increasing with the rising trend of connected devices and increasing effort to dramatically reduce fossil fuel consumption in society. Apart from conventional metal based batteries, batteries consisting of naturally occurring organic materials can be envisioned, thus becoming fully sustainable and avoiding the negative environmental impact associated with the production and recycling of conventional metal based batteries. One class of fully organic batteries utilizes conducting redox polymers (CRPs) as electrode materials. CRPs combine the high charge storage capacity of a redox active pendant group (PG) with the conduction properties of a conducting polymer (CP) backbone, both to reduce the need for addition of conductive carbon black and increasing the stability of the PG redox conversion in a battery setup. In the current work a concept and initial results for a metal-free, fully organic battery based on CRP electrode materials are presented. Challenges and possibilities associated with these types of batteries are discussed.

Resume : In order to provide society with sustainable electrical energy storage technologies, organic based batteries is an attractive target. Making batteries with materials from renewable resources would ensure production without the use of non-renewable inorganic materials that have to be acquired through energy consuming mining. To ensure sufficient conductivity, most organic batteries researched on today use conducting additives since organic molecules, in general, are insulating. A different approach is to use conducting redox polymers (CRPs). They utilize a conducting polymer as a backbone for good conductivity and redox active pendant groups to ensure high charge storage capacity and a well-defined redox process. The polymer backbone used in the present work is poly(3,4-ethylenedioxythiophene) while quinones are used as pendant groups. In an all-organic battery the two electrodes will have quinones with different redox potentials, resulting in a voltage difference between the electrodes. This work focuses on characterizing the cathode material in water electrolytes. The CRPs are studied with regard to conductivity and mass transport, by in situ conductance as well as electrochemical quartz crystal microbalance experiments. Redox matching between the conducting polymer and the pendant group is evident from in situ conductance measurements. From EQCM measurements it is evident that during the hydroquinone/quinone redox conversion only protons are cycled in and out of the CRP.

Resume : Lithium ion batteries (LIBs) represent an attractive energy storage technology, especially for mobile applications such as personal electronics and electric vehicles. Compared to graphite, which is used as the negative electrode in commercial LIBs, silicon has a theoretical highest lithium storage capacity 8 to 10 times larger, 4,200 mAh g–1 approximately. However, the use of Si in LIBs has been limited due to the large volume change (>300%) that occurs during charging and discharging, which causes electrode fracture and pulverization, and thereby, a drastic loss of capacity. We present ordered arrays of parallel silicon nanotubes as a novel LIB platform. The tubular shape is designed to allow for volume expansion without damage, and thereby, to minimize electrode pulverization and prevent capacity loss in silicon anodes. Our silicon nanotubes are manufactured by a thermal reduction of silicon oxide nanotubes, generated by atomic layer deposition (ALD) onto the walls of the deep, straight, cylindrical pores of “anodic” aluminum oxide membranes serving as the matrix. Afterwards, the samples are treated with acid to remove the Li2O by-product. After sputtering an electrical contact made of gold, the electrodes are assembled into full lithium ion batteries for electrochemical characterization by cyclic voltammetry, charge-discharge, and electrochemical impedance spectroscopy. The performance of the samples can be optimized based on the tubes' geometry.

Resume : Carbon-coated binder-free flexible porous SnOx nanosheets (SnO/SnO2 heterogeneous structure) were fabricated and tested as anode materials for Na-ion batteries (NIBs). The novel free-standing and binder-free porous C@SnOx nanosheets were first self-assembled on the Cu substrate via a facile, low-cost anodization method followed by the carbonization treatment. Instrument analyses show that the porous C@SnOx nanosheets exhibit a remarkably large surface area of 221 m2 g-1, delivering a reversible discharge capacity of 510 mA h g-1 after 100 cycles at 100 mA g-1, demonstrating great potential for Na+ storage applications. The superior electrochemical performance is ascribed to the unique hierarchical porous architecture which greatly facilitates electrolyte penetration and ion transportation with the carbon coating further increasing the electrode conductivity and alleviating strains generated by volume change upon Na+ ions insertion/extraction.

Resume : In the present work, we will show the influence of Fe2O3 shell thickness in the electrochemical performances of supercapacitor electrodes in aqueous electrolytes. Initially, Fe-Fe2O3 core-shell were incorporated in CNFs matrix by one-step controlled thermal treatment. This one-step thermal treatment provides formation of in-situ pores along with the growth of Fe-Fe2O3 core shell nanostructures, which attributes both EDLC and Faradaic behavior. The formation of these core-shell nanostructures will be explained by the differences in the diffusion velocities between Fe3+ and O2-, which is known as reductive transformation (Kirkendall effect)[1]. Under controlled diffusions, we vary the Fe2O3 shell thickness and characterize them through several materials and electrochemical techniques. For example, the variation in the thickness of Fe2O3 shell was readily observed by HRTEM-EELS mapping. The variation of Fe2O3 thickness shows a trend in the electrical conductivities, BET surface area, the values of capacitances and time constants. In our initial results, we show that the variation of shell thickness influences the values of time constants. We observe that by varying the shell thickness from high to low, the reduction of time constant occurs from 2000 ms to 87 ms, thanks to aforementioned in-situ pores and excellent electrical conductivities. This method of tailoring can provide us a suitable model, will be also discussed, helping the energy community to design high power supercapacitors. References [1] B.D.A. and J.B. Tracy, Nanoparticle conversion chemistry: Kirkendall effect, galvanic exchange, and anion exchange, Nanoscale. 6 (2014) 12195–12216. doi:10.1039/C4NR02025A.

Resume : Traditional inorganic energy storage materials involve high carbon emissions and low renewability. As an alternative battery material, organic conducting redox polymers (CRPs) have caught much attention in recent years due to the sustainable raw materials and low energy consumption used in their production1. CRPs consist of a conducting polymer (CP) backbone, a redox active pendant group (PG), and a linker. The CP contributes to conductivity and hinders dissolution of PGs, while the PGs provide capacity for the polymer2. The present work involves the CP poly(3,4-ethylenedioxythiophene) (PEDOT) and a terephthalate PG in acetonitrile. The CRP is characterized by Electrochemical Quartz Crystal Microbalance and Electron Spin Resonance during the doping process. Temperature-dependence in situ conductances are measured to probe the thermodynamic processes within the CRP. Cyclic voltammetry at different scan rates is employed to investigate the charge transfer kinetic process. The rate constant for electron transport in the polymer is calculated and the rate-limiting step is identified. Based on the results, the electron and ion transport during electrochemical redox conversion is discussed. Cycle stability is also investigated to improve the electrochemical performance in the n-doping potential region, so as to enhance the possibility of full organic battery fabrication. (1) Park, K. S.; Schougaard, S. B.; Goodenough, J. B. Adv. Mater. 2007, 19, 848−851. (2) L. Yang, X. Huang, A. Gogoll, M. Strømme, M. Sjödin. C 119 (2015) 18956–18963.

Resume : Lithium ion batteries are the most popular energy storage systems for portable electronic devices given their high energy density. To meet the requirements for future energy technologies, such as electric mobility, even higher energy densities are required. Among the family of spinel electrodes, LiCoMnO4 (LCMO) offers the highest theoretical energy density, which is 25% higher than that for the commercial LiCoO2 cathode. However, LCMO often suffers from poor reversible capacity and fast capacity fading upon cycling. To enhance its performance, LCMO was fluorinated at 800°C. The desired fluorination degrees of x = 0.05 and x = 0.1 in LiCoMnO4-dFx were confirmed directly by using nuclear reaction analysis. Rietveld analysis and inert gas fusion analysis reveal a stabilizing effect of fluorine on the spinel lattice, leading to enhanced phase purity. The stabilizing effect of fluorine also leads to improved cycling stability, as observed by electrochemical analysis by using a liquid electrolyte setup. Moreover, the fluorinated cathodes demonstrate higher reversible capacity as an effect of their lower activation polarization and ohmic polarization, which facilitates the lithium ion insertion/extraction at a voltage higher than 4.9 V vs. Li/Li . Therefore, we propose fluorinated LiCoMnO4 spinels as promising cathode candidates for next generation lithium batteries.

Resume : Vanadium pentoxide has been attractive due to its relatively high theoretical capacity of 294 mAh/g and layered crystal structure as a host for reversible Li+ intercalation/de-intercalation1. Herein, we show that the reduced graphene oxide/V2O5 nanobelts (rGOVONB) are a promising candidate for cathode material of high performance Li-ion batteries (LIBs). The rGOVONB were synthesized by microwave-assisted hydrothermal method followed by thermal annealing under nitrogen atmosphere at variable temperatures (573, 673, and 773K). One-dimensional V2O5 nanobelts were formed in the presence of graphene oxide (GO), which also enhanced the conductivity of rGOVONB. GO played a significant role as a mild oxidizing agent for the formation of nanobelts. The existence of rGO into the layered V2O5 crystal structure was confirmed by electron energy loss spectroscopy (EELS) analysis. The point EELS spectrum clearly showed the strong carbon signal. The electrochemical properties of rGOVONBs as cathode materials were investigated for LIBs. The rGOVONB annealed at 773 K exhibited a high capacity of 225mAh/g at a current density of 40mA/g and showed better electrochemical performance with a capacity of 137mAh/g after 70cycles at the current density of 800 mA/g in comparison to the other rGOVONBs and the pristine materials. This study provides a simple and efficient route for 1D cathode materials through a microwave-assisted hydrothermal method. [1] Yu, H. et al, Nanoscale, 5, 4937-4943 (2013)

Resume : Advanced energy materials and effective manufacturing facilities of battery cells production are key parameters to overcome the economic barrier to entry into the market. This paper reviews the advances that are obtained on new materials for high energy density thin film electrodes. These new materials have the capability of keeping an excellent performance of energy storage system, e.g. of lithium ion batteries and beyond, for vehicles and stationary applications. Battery materials and devices like an ordered mesoporous Metal/Metal-Silicon anode with integrated current collector, a solid-state air electrode, and Aluminum based battery are addressed. It will be demonstrated how it is possible to develop a Si based anode material with outstanding properties with one order of magnitude higher capacity than the standard of the day, compatible to many variants of lithium cells, solvents free, cost-effective and capable to be integrated on roll-to-roll processing. An important issue of our work was the increase of the oxygen exchange of metal oxide crystalline materials dealing with ion beam doping and ultra-short thermal processing. Finally, the strong development of an aluminum based battery is represented by reporting our research activities in order to fabricate an aluminum battery linked to roll-to-roll manufacturing.

Resume : Sodium ion batteries (SIBs) have recently received attention as a low-cost alternative to lithium ion batteries (LIBs) mainly due to the high availability of sodium sources. Cathode materials for SIBs need to possess the following attributes: low surface resistance, high solid-state ionic diffusion, and high rate of ionic intercalation. This study investigates NaMnO2-based SIB cathodes in terms of energy density and capacitance by selectively controlling the associated oxidation and reduction reactions. NaMnO2 nanopowder was synthesized via the urea-assisted polymeric citrate route. Electrochemical measurements were performed in NaClO4-based aqueous solutions; physicochemical properties were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray analysis (EDAX), and Raman spectroscopy. Our results show that NaMnO2-based cathodes can increase SIB capacity up to 30% by increasing the electrolyte concentration from 1M to 5 M.

Resume : The electrochemical performance of nano-shaped hematite (α-Fe2O3) is successfully enhanced by non-isovalent modification with Ti4+, which supports possible future applications of hematite-based high capacity materials as negative electrodes in LIBs, e.g. as power sources for electric vehicles. The facile and low-cost synthesis procedure consists of hydrothermal approach assisted by 1,2-diaminopropane as shape controlling agent (SCA), followed by an annealing process. The physicochemical characteristics are investigated via XRD, FESEM, EDX and UV-Vis. Phase-pure hematite structure can be preserved even at a Ti4+ substitution level of 10%. Morphology evolution from nanowires (~ 1 µm length, 1% Ti4+ substitution level) towards small elongated nanoparticles (~ 200 nm length, 10% Ti4+ substitution level) is observed. The electrochemical performance is evaluated by cyclic voltammetry, and charge-discharge measurements at various C rates and found to be excellent. A Ti4+ substitution level of 10% leads to a doubled capacity compared to undoped hematite after 40 cycles (~300 mAh g-1 to ~600 mAh g-1). At a high current density of 3 C, the 10% Ti4+ doped nano-shaped hematite delivers a delithiation capacity of 370 mAh g-1, which is three times higher than for unmodified hematite

Resume : Semi-solid flow batteries (SSFBs) consist in anolyte and catholyte flowable suspensions of solid active materials (SAM), increasing the concentration of active redox centres. Using intercalation type active materials such as those typically used in Li (Na)-ion batteries (LIBs), e.g. Li4Ti5O12, the energy densities can reach up to 300 – 500 Wh L-1, which is more than 10 times higher than that of all-vanadium RFBs (40 Wh L-1). Compared to conventional LIBs, power and energy can be scaled independently in SSFBs. Compared with RFB, the current collectors are simpler and become more cost-effective in SSFB. Besides, carbon is used to improve conductivity since it forms a percolating conducting network that ensures fast electron transfer between electroactive particles and the current collector. Despite the fact that the present technology of SSFB is based on the chemistry of well-investigated Li-ion battery materials, the fluid electrodes cannot be assumed to behave as the solid ones. In this framework, a deep analysis of several formulations for anolyte and catholyte suspensions is discussed in terms of electrochemical and rheological properties. Moreover, improved formulations are proposed for the next generation of SSFB, based on: i) new carbon particles with superior electrical properties; ii) innovative high-energy density SAM and iii) alternative electrolyte with higher electrochemical window stability, presented for the first time in the literature (i.e. ionic liquid).

Resume : A flow battery is based on reversible redox couples to transform chemical energy into electricity. However, unlike in conventional batteries where the electrochemical reactants are contained in the solid electrodes, in flow batteries, the reactants are stored in tanks external to the flow battery stack. Flow batteries are emerging as a potential electricity storage technology to support an efficient, reliable and cleaner energy market. Some of the promising applications of flow batteries are related to load management of large-scale electricity supply to the grid (e.g., peak shaving, power quality, spinning reserves). Flow battery technology can also offer solutions to issues associated with the integration of intermittent renewable energy resources (e.g., wind, solar) with the power grid by making these power resources more stable, dependable, and dispachable. The objective of this talk is to provide an overview, status, and challenges of the flow-battery technology with an emphasis on vanadium redox-based system, which will also include an examination of some recent developments that led to a significant improvement in flow battery power density.

Resume : Semi Solid Flow batteries (SSFBs) are interesting energy storage systems (ESSs) for stationary applications because they have several advantages with respect to conventional Li ion batteries. For instance, the chemistry of a SSFB can be adjusted if storage necessities change and, in the same way as in Redox Flow battery (RFBs), the energy and power of the battery are decoupled. Therefore, the energy produced by either solar or wind power may be stored in a SSFB and released, when necessary, to the general grid. SSFBs aim to compete directly with other flowable systems i.e. RFBs, however, they electrochemical performance is still far from optimum. Ideally, SSFBs should operate in continuous flow mode to release the total energy stored in suspensions tanks, however, this has not been the general trend and electrochemical results of SSFB are mostly presented in static mode conditions. In a previous publication, we prepared catholyte suspensions based on LiNi1/3Co1/3Mn1/3O2 (LNCM) as redox-active particles and Ketjenblack as conductive additive and their electrochemical performance were not stable in dynamic flow conditions. In this work, we present a new recipe for a LMCN based catholyte using an alternative conductive additive. Prepared suspensions show comparable electrochemical performance to the ones containing Ketjenblack but with much improved electrochemical stability over time in dynamic flow mode. The new suspensions cycle for up to 15 days with a current density of 1 mAcm-2. The use of electrochemical impedance spectroscopy as well as Scanning Electron Microscopy (SEM) has been crucial to understand the role of the conductive additive to the suspension.

Resume : With the growing efforts to integrate current electricity grid with generation from renewable energy options, energy storage is envisioned to play an important role to bridge the gap between sustainable energy future and current technology in grid utilization, reliability and robustness. Grid energy storage especially for renewable energy mix has been a challenging task due to its costs and the intermittent nature of the energy feeding. Redox Flow Batteries (RFBs) have emerged as an excellent option for large-scale Electrical Energy Storage (EES) by offering many advantages over the conventional batteries (e.g., Li-ion and lead acid batteries). Due to its design flexibility, flow batteries can meet a wide range of EES applications with varying power-to-energy ratios. In addition, flow batteries have excellent energy efficiency and competitive life-cycle cost. Furthermore, as a result of their simple thermal management which is provided by the circulating reactant solutions, and their low sensitivity to crossover (no thermal runaway reactions), flow batteries are considered to be inherently safer compared to conventional sealed batteries. Despite its attractiveness and demonstrated performance, flow battery technology still suffers from high system capital cost which limits its potential deployment into grid storage applications. Also, due to the low energy density of the reactant fluids, flow battery system suffers from large footprint, which makes it impractical for EES applications with confined space. A number of studies have reported an estimated cost of flow battery system at large scale (MW) that exceeds $500/kW.hr. For an energy storage system to be economically feasible, the United States Department of Energy (DOE) set the cost target for its large-scale deployment at $100/kW.hr. Therefore, to deploy flow batteries for EES applications for mass market, the high system cost and the large footprint issues must be addressed. These challenges can only be met if high energy density and cheaper battery materials are developed. An attractive approach has been recently envisaged, where the active materials are mixed with carbon to make the electrode flowable. This system helps to operate flow battery with increased concentration of redox species and as a result the energy density would be significantly improved. In this presentation, a study of flowable electrode, based on carbon and redox systems (e.g., V/Carbon, S/Carbon), focusing in particular on carbon/redox screening, development of slurry with various carbons (e.g., Vulcan Carbon, Acetylene Carbon Black, Black Pearl, CNFs, CNTs, and Modified Carbons), development of slurry composites with various redox systems (such as Sulfur, Iron, Quinone) will be presented and discussed.

Resume : Vanadium redox flow battery (VRFB) [1] offers not only a great promise to provide a robust and constant energy storage system, but also several advantages such as scalability, long cycle life, high efficiency, and besides they are energy independent. Despite all of its merits, the improvements of VRFB[2] performances require a superior reversibility with minimum side reactions i.e hydrogen evolution (HER), and power density output enhancement for a commercial outbreak. VRFBs have reached only a limited market presence after the continuous development during the last 30 years. We tackled those issues with a post-thermal modified r-TiO2 core-shell approach that have been implemented as electrodes for VRFBs [3]. TiO2 hydrogen-treated shell on graphite felt core (GF@TiO2:H) was prepared by a combination of hydrothermal synthesis followed by thermal treatment. Comparatively to commercial electrodes i.e. graphite or carbon felts, GF@TiO2:H performs an abrupt inhibition of HER, which is a critical barrier for operating at high charge/discharge rate in long term cycling. Moreover, outstanding improvements in charge and electron transfer processes towards V3 /V2 redox reaction was achieved using GF@TiO2:H electrodes due to the enhancement in the electron donor properties of TiO2 after hydrogen annealing, which is a consequence of oxygen vacancies formation in the lattice structure. This also gave rise to active sites on behalf of electrolyte-utilization ratio > 80% leading to a remarkable high capability rate of 150 mAcm-2. Besides a 31 WhL-1 of specific discharge capacity and 61% of energy efficiency was observed beyond 120 cycles. Subsequently, nitrogen-doping by ammonia annealing/treatment at high temperature originates a partial TiN phase on the TiO2, enhancing the electrical conductivity and charge transfer for vanadium redox reactions analogously as previously mentioned treatment. Additionally, this superior catalyst has not only improved the catalytic capacity towards the redox reactions of the pairs V3 /V2 and VO2 /VO 2, but also inhibits hydrogen evolution on the negative half-cell. All these qualities has allowed us to work at noteworthy high current density, up to 150 mAcm−2, with low ohmic losses and therefore high energy efficiency (71%) which correspond with a 5% more efficiency than our previously mentioned treatment. Moreover, allowing us to achieve a high power density up to 1500 mW/cm2. Herein proposed two exceptional posts thermal modifications hold a great promise for an ideal anode material which is inexpensive, environmental friendly and scalable synthesis method applicable to the industry. References [1] M. Park, J. Ryu, Y. Kim, and J. Cho, Energy Environ. Sci., 2014, 7, 3727–3735. [2] B. Li, M. Gu, Z. Nie, Y. Shao, Q. Luo, X. Wei, X. Li, J. Xiao, C. Wang, V. Sprenkle, and W. Wang, Nano Lett., 2013,13,1330–5. [3] T.-M. Tseng, R.-H. Huang, C.-Y. Huang, C.-C. Liu, K.-L. Hsueh, and F.-S. Shieu, J. Electrochem. Soc., 2014, 161, A1132–A1138.

Resume : In this work, a practical method is used to optimize vanadium redox flow battery performance. This particular sort of redox flow cells, stores energy in two electrolytes comprised of different oxidation states of Vanadium ions in acidic media. Inside the cell two electrolytes being pumped onto the electrode surface in which electron transfer occurs and are separated by a proton exchange membrane allowing ionic charge balance. Among many parameters affecting the overall performance of the battery, Electrolyte concentration, Flow rate, and current density play important and complicated roles. In fact, battery performance optimization should be performed considering these parameters in correlation with each other. The optimization process is necessary for any parameter involving the cell performance, because all the quantity of energy applied to the cell during charging, is not retrievable while discharging. Some parameters should be just minimized or maximized for optimization (cell resistance should be minimized), but Electrolyte concentration, Flow rate, and current density are parameters which on both sides are not desirable. After optimization besides achieving high current density and high discharge voltage, round-trip efficiency is also improved.

Resume : The Vanadium Redox Flow Batteries (VRFBs) are promising energy storage devices which behavior can be enhanced by modifying electrode properties. In this sense, this work provides useful data about the suitability of several synthesis methods for deposition of g-C3N4 on GF. The physicochemical outcomes show that g-C3N4 species are achieved uniquely by wetness impregnation with melamine as precursor. Indeed, the results do not provide evidence of g-C3N4 formation with any of the other methods or precursors. The surface modification achieved by g-C3N4 incorporation provides enhanced electronic transfer which results on improved electrochemical behavior as electrode materials. So, enhanced reaction rates, diminished charge transfer resistances and improved mass transport phenomena are displayed by the g-C3N4/GF sample. In agreement, boosted battery performances are obtained when g-C3N4/GF is tested on the positive halfcell resulting in superior capacities and electrolyte use. The benefits provided by g-C3N4 species allow diminished overvoltage values leading to superior overall energy efficiencies in battery flow cell. To the best of our knowledge, we present the first study in which the success of several synthesis methods for preparing carbon nitrides over carbon felts is evaluated. Lastly, the reference electrode incorporation allows the demonstration for the first time of positive halfcell data which supports the g-C3N4 benefits in VRFBs.

Resume : Zn-air batteries are promising candidates for large scale energy storage devices due to their larger energy density, cheaper production cost, and better safety than most of battery technologies.[1,2] However, oxygen evolution reaction (OER) which is one of the key reactions in rechargeable Zn-air batteries is kinetically sluggish, leading to high charging voltage and low cycling stability of Zn-air batteries. Thus, high performance catalysts for OER are in demand to improve the re-chargeability of Zn-air batteries.[3] We prepare NiMn layered double hydroxides (NiMn LDH) with an optimum Ni:Mn molar feeding ratio.[4] The optimized sample has good crystallinity, big interlayer spacing, and large surface area which benefit its catalytic activity during OER. It shows an overpotential of 0.35 V, a tafel slope of 40 mV dec-1 and a stable performance during degradation test. Sulfidation of NiMn LDH leads to morphology changes from layered structure into nanoparticles. XRD results indicate the presence of nickel sulfide which further improves its catalytic activity during OER. Sulfidized NiMn LDH shows a smaller overpotential of 0.33 V and a lower tafel slope of 36 mV dec-1 as compared to NiMn LDH. Zn-air batteries with such catalysts have low charging voltage of ≈2 V and good stability during 200 cycles of discharge/charge cycling. They have an enhanced stability than the battery with Ir/C catalyst which exhibit significant degradation after 80 cycles of discharge/charge cycling. References [1] A. Sumboja, X. Ge, G. Zheng, F.W.T. Goh, T.S.A. Hor, Y. Zong and Z. Liu, J Power Sources, 2016,332,330. [2] X. Ge, A. Sumboja, D. Wuu, T. An, B. Li, F.W.T. Goh, T.S.A. Hor, Y. Zong and Z. Liu, ACS Catal., 2015,5,4643. [3] A. Sumboja, X. Ge, F.W.T. Goh, B. Li, D. Geng, T.S.A. Hor, Y. Zong and Z. Liu, ChemPlusChem, 2015,80,1341. [4] A. Sumboja, J. Chen, Y. Zong, P. S. Lee and Z. Liu, Nanoscale, 2017, 9, 774.

Resume : The development of low-cost non-noble metal catalysts for high performance oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is highly sought-after. The co-doping of transition metal and nitrogen into carbon is one such approach that have proven effective. In this work, we report a facile approach to produce porous carbon nanofibers with homogeneously distributed CoFe2O4/CoFe nanoparticles (CoFe2O4/CoFe/C-PDA PNFs) encapsulated within, achieved by a mussel inspired polymerization process followed by an annealing and partial oxidation process. Cobalt and ferric ions were introduced into an aqueous solution of dopamine with poly(styrene) porous nanofibers, resulting in a thin film of transition metal containing polydopamine hybrid coated on the poly(styrene) porous nanofibers. Subsequent annealing and partial oxidation process produced the CoFe2O4/CoFe/C-PDA PNFs, whose morphologies, chemical compositions and electrochemical performances were analyzed. For comparison purpose, polydopamine derived carbon nanospheres with encapsulated CoFe2O4/CoFe nanoparticles (CoFe2O4/CoFe/C-PDA nanospheres) were also prepared and studied. Electrochemical studies suggest that the CoFe2O4/CoFe/C-PDA PNFs electrocatalyst effectively catalyzes ORR via an ideal 4-electron pathway and outdo commercial Pt/C in catalyzing OER. Zinc air batteries based on the CoFe2O4/CoFe/C-PDA PNFs electrocatalyst also showed longer cycling life and higher cycling stability when compared to counterparts based on commercial Pt/C and CoFe2O4/CoFe/C-PDA PNFs nanospheres.