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Future optimized lithium-sulfur batteries may promise higher energy densities than the current standard. However, there are many barriers which hinder their commercialization. In this review we describe how ionic liquids (ILs) and their polymers are utilized in different components of the battery to address some of these issues. For example, IL-based electrolytes have the potential to reduce the solubility of polysulfides compared to conventional organic electrolytes. Polymerizing ILs directly on the surface of the Li-metal anode is suggested as an approach to protect the surface of this electrode. Finally, using poly(ionic liquids) (PILs) as binders for the cathode active material may increase the performance of the cathode as compared to polyvinylidene difluoride (PVdF) and could inhibit swelling-induced degradation. These results demonstrate the advantages of ILs and their polymers for improving the performance of Li−S batteries.

Insights into the electrochemical processes occurring at the electrode-electrolyte interface are a crucial step in most electrochemistry domains and in particular in the optimization of the battery technology. However, studying potential-dependent processes at the interface is one of the biggest challenges, both for theoreticians and experimentalists. The challenge is pushed further when stable species also depend on the concentration of specific ligands in the electrolyte, such as chlorides. Herein, we present a general theoretical

Sodium ion batteries (SIB) present one of the most perspective post lithium technology and their progress strongly depends on the development of compounds having the structure which enables fast sodium insertion/deinsertion reactions. Polyanion compounds have been widely investigated as cathode materials for SIBs where they compete effectively to the usually used layered oxides. This survey is focused on the development of specific family of isostructural polyanion phases encompassed by the common chemical formula Na4M3(PO4)2(P2O7). The comprehensive retrospective of their synthesis procedures, the kinetics and mechanism of sodiation/desodiation reactions, based on both experimental and theoretical results, is provided. First, the review summarizes the structural properties of variety of Na4M3(PO4)2(P2O7) compounds in terms of its electrical, vibrational and surface properties. Then, the synthesis methods and sodium/lithium storage performance, of each type of Na4M3(PO4)2(P2O7) compounds, are chronologically presented and discussed. Finally, the strengths and weaknesses of these mixed polyanion cathodes are outlined, with the aim to explain some discrepancies and unclarified issues encountered in the literature. Besides, this survey will make room for future development. It can be very useful for the future design of high-performance mixed polyanionic compounds as cathodes for alkaline-ion rechargeable batteries. This is the peer-reviewed version of the article: Gezović Aleksandra, Vujković Milica, Milović Miloš, Grudić Veselinka, Dominko Robert, Mentus Slavko, "Recent developments of Na4M3(PO4)2(P2O7) as the cathode material for alkaline-ion rechargeable batteries: challenges and outlook" Energy Storage Materials, 37 (2021-05):243-273, [https://doi.org/10.1016/j.ensm.2021.02.011] Supplementary information: [https://hdl.handle.net/21.15107/rcub_dais_11634]

BATTERY 2030+ targets the development of a chemistry neutral platform for accelerating the development of new sustainable high-performance batteries. Here, a description is given of how the AI-assisted toolkits and methodologies developed in BATTERY 2030+ can be transferred and applied to representative examples of future battery chemistries, materials, and concepts. This perspective highlights some of the main scientific and technological challenges facing emerging low-technology readiness level (TRL) battery chemistries and concepts, and specifically how the AI-assisted toolkit developed within BIG-MAP and other BATTERY 2030+ projects can be applied to resolve these. The methodological perspectives and challenges in areas like predictive long time- and length-scale simulations of multi-species systems, dynamic processes at battery interfaces, deep learned multi-scaling and explainable AI, as well as AI-assisted materials characterization, self-driving labs, closed-loop optimization, and AI for advanced sensing and self-healing are introduced. A description is given of tools and modules can be transferred to be applied to a select set of emerging low-TRL battery chemistries and concepts covering multivalent anodes, metal-sulfur/oxygen systems, non-crystalline, nano-structured and disordered systems, organic battery materials, and bulk vs. interface-limited batteries., The authors acknowledge the European Union's Horizon 2020 research and innovation program under grant agreements no. 957189 (BIG-MAP) and no. 957213 (BATTERY 2030+). K.H. acknowledges the Swedish Research Council (Vetenskapsrådet) and the Swedish national Strategic e-Science programme eSSENCE. R.D. acknowledges the financial support from the Slovenian Research Agency (research core funding P2-0393 and Project N2-0214). H.S.S. acknowledges funding from Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy—EXC 2154—Project number 390874152. M.C.-C. acknowledges the Spanish Ministerio de Ciencia, Innovación y Universidades (Project reference number: PID2019-107106RB-C33). M.R.P. acknowledges the Spanish Agencia Estatal de Investigación Severo Ochoa Programme for Centres of Excellence in R&D (CEX2019-000917-S)., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

The high redox activity of polyaniline emeraldine salt (PANI-ES) was revealed in the aqueous solution of Al-salt, which makes this polymer attractive as an electrode material for aqueous aluminum electrochemical storage devices. Its redox behavior in Al(NO3)3, Al(NO3)3+HCl, AlCl3 and HCl was investigated by Cyclic Voltammetry and Chronopotentiometry. While the proton exchange determines PANI's redox behavior in strong acidic solutions, anion doping/dedoping is a more dominant process in less acidic Al-salt solutions. The formation/dissolution of solid-state nitrate complexes is proposed to happen during PANI's redox switching in Al(NO3)3, which causes disappearance and reappearance of grain boundaries, as revealed by AFM. Combined experimental and DFT approaches identify Al-salt as a secondary dopant of protonated PANI-ES (by Lewis acid-base complexation), which causes polaron→bipolaron conversion. The change in the redox mechanism of PANI-ES, caused by the substitution of HCl with Al(NO3)3, did not attenuate its charge storage ability. Moreover, PANI-ES delivers a higher capacitance in Al(NO3)3, amounting to 269 F g−1 at 10 A g−1. Furthermore, the use of Al(NO3)3 results in attenuated electrochemical PANI overoxidation, when compared to HCl, thus providing better capacitance retention upon potentiodynamic cycling. The results open novel perspective of using PANI-based materials for more suitable energy storage devices.

Al metal-organic batteries are a perspective high-energy battery technology based on abundant materials. However, the practical energy density of Al metal-organic batteries is strongly dependent on its electrochemical mechanism. Energy density is mostly governed by the nature of the aluminium complex ion and utilization of redox activity of the organic group. Although organic cathodes have been used before, detailed study of the electrochemical mechanism is typically not the primary focus. In the present work, electrochemical mechanism of Al metal-phenanthrenequinone battery is investigated with a range of different analytical techniques. Firstly, its capacity retention is optimized through the preparation of insoluble cross-coupled polymer, which exemplifies extremely low capacity fade and long-term cycling stability. Ex situ and operando ATR-IR confirm that reduction of phenanthrenequinone group proceeds through the two-electron reduction of carbonyl groups, which was previously believed to exchange only one-electron, severely limiting cathode capacity. Nature of aluminium complex ion interacting with organic cathode is determined through multiprong approach using SEM-EDS, XPS, and solid-state NMR, which all point to the dominant contribution of AlCl 2+ cation. Upon full capacity utilization, Al metal-polyphenanthrenequinone battery utilizing AlCl 2+ offers an energy density of more than 200 Wh/kg making it a viable solution for stationary electrical energy storage.

Open access to research data is increasingly important for accelerating research. Grant authorities therefore request detailed plans for how data is managed in the projects they finance. We have recently developed such a plan for the EU-H2020 BIG-MAP project - a cross-disciplinary project targeting disruptive battery-material discoveries. Essential for reaching the goal is extensive sharing of research data across scales, disciplines and stakeholders, not limited to BIG-MAP and the European BATTERY 2030+ initiative but within the entire battery community. The key challenges faced in developing the data management plan for such a large and complex project were to generate an overview of the enormous amount of data that will be produced, to build an understanding of the data flow within the project and to agree on a roadmap for making all data FAIR. This paper describes the process we followed and how we structured the plan., 12 pages, 4 figures; the full DMP is published as Supporting Information

The development of new batteries has historically been achieved through discovery and development cycles based on the intuition of the researcher, followed by experimental trial and error—often helped along by serendipitous breakthroughs. Meanwhile, it is evident that new strategies are needed to master the ever-growing complexity in the development of battery systems, and to fast-track the transfer of findings from the laboratory into commercially viable products. This review gives an overview over the future needs and the current state-of-the art of five research pillars of the European Large-Scale Research Initiative BATTERY 2030+, namely 1) Battery Interface Genome in combination with a Materials Acceleration Platform (BIG-MAP), progress toward the development of 2) self-healing battery materials, and methods for operando, 3) sensing to monitor battery health. These subjects are complemented by an overview over current and up-coming strategies to optimize 4) manufacturability of batteries and efforts toward development of a circular battery economy through implementation of 5) recyclability aspects in the design of the battery.

We report the synthesis and detailed structural and chemical characterization including electrochemical properties of a lithium vanadium oxy/fluoro-phosphate material. To the best of our knowledge,...

The impact of the solid film deposit (mainly Li2S) on the complex electrochemistry of a Li–S cell is studied in detail. Already a simple, straightforward experiment strongly indicates that this imp...

International audience; Calcium batteries represent a promising alternative to lithium metal batteries. The combination of the low redox potential and low-cost and energy-dense calcium anode (2073 mAh/cm3, similar to 2044 mAh/cm3 for Li) with appropriate low-cost cathode materials such as sulfur, could produce a game-changing technology in several fields of applications. In this work, we present the reversible activity of a proof-of-concept Ca/S battery at room temperature, characterized by a surprising medium-term cycling stability with low polarization, promoted by the use of a simple positive electrode made of sulfur supported on an activated carbon cloth scaffold, and a state-of-the-art fluorinated alkoxyborate-based electrolyte. Insights on the electrochemical mechanism governing the chemistry of the Ca/S system were obtained for the first time by combining X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The mechanism implies the formation of different types of soluble polysulfides species during both charge and discharge at room temperature, and the formation of solid CaS at the end of discharge. The reversible electrochemical activity is proven by the reformation of elemental sulfur at the end of the following charge. These promising results open the way to the comprehension of emerging Ca/S systems which may represent a valid alternative to Mg/S and Li/S batteries.

The effect of Li2S deposition on the impedance response of Li-S battery cells is investigated using a simplified cell design, systematic impedance spectroscopy measurements combined with transmission line modeling, and a complementary microscopy analysis. Glassy carbon cathodes are employed to build and validate the proposed transmission line model, which is later on employed to investigate the effect of various parameters of Li2S deposit (coverage, thickness, porosity) on cell’s impedance. Among others, the model is applied to study the effect of discharge and self-discharge. Finally, the simplified planar cathode is exchanged with a more conventional mesoporous carbon cathode to determine the effect of Li2S deposition on the impedance of a commercially viable cell design. We have found that Li2S deposit has little effect on the impedance response, owing to its porous structure. The most noticeable change stemming from the process of Li2S deposition is due to the depletion of polysulfide species concentration in the electrolyte, which decreases the chemical capacitance and increases the tail height in the low frequency region of the impedance spectra.

International audience; Abundance of Ca, its low redox potential and high specific capacity make Ca metal batteries an attractive energy storage system for the future. Recent demonstration of room temperature calcium plating/stripping opened new avenue of development, but performance of cathode materials is still lagging behind. Due to nature of divalent cations, conversion and coordination electrochemical reactions show better performance compared to insertion. Herein we demonstrate use of anthraquinone based polymer as cathode material for Ca metal‒organic battery. Electrochemical mechanism investigation confirms reversible reduction of carbonyl bond and coordination with Ca 2+ cations in the discharged state opening a pathway toward high energy density battery. Continued performance of 2‐electrode cell is strongly hampered by overpotential increase connected with Ca stripping process on Ca metal anode stating need for further development of Ca electrolytes. Ca metal‒organic battery promise to achieve cells with gravimetric energy density on the practical level compared to state‐of‐the‐art Li‐ion batteries.

Multivalent organic batteries can be considered as sustainable, cheap and environmental friendly batteries with high energy density due to use of metal negative electrodes. Magnesium, calcium, aluminum metals can be successfully combined with redox active polymers after proper selection of electrolytes. Several challenges are facing multivalent batteries and further development is required. Redox mechanism in multivalent organic batteries is based on charge transfer on quinone groups, however depends on the electrolyte, besides multivalent cations (Mg2+, Ca2+, Al3+) also cation complexes or even partially solvated cations can be involved into charge transfer reaction. In this presentation, overview of recent achievements in our group on the field of multivalent batteries will be discussed with a focus on reaction mechanism and how different battery components can influence charge transfer reaction.

Journal of power sources 450, 227672 - (2020). doi:10.1016/j.jpowsour.2019.227672, Development of magnesium sulfur battery is accompanied with all known difficulties present in Li–S batteries, however with even more limited choice of electrolytes. In the present work, the influence of current collector on electrochemical mechanism was investigated in light of different reports where improved behavior was ascribed to electrolyte. Notable differences in cycling behavior are reported when Al current collector is replaced by Cu current collector independent of electrolyte. The initial reduction of sulfur follows similar reaction path no mater of current collector, but formation of MgS can be in competition with formation of CuS in the presence of Cu cations. With the subsequent cycling cells prepared from cathodes deposited on Cu current collector show decrease in the voltage and formation of single plateau during cycling. The change corresponds to the involvement of Cu into the reaction and formation of redox couple Mg/CuS as determined by Cu K-edge XANES measurements. Corrosion of Cu foil is identified by SEM and serves as a source of Cu cations for the chemical reaction between Cu and polysulfides. Mg/CuS redox couple shows improved cycling stability, but theoretical energy density is severely reduced due to substitution of S with CuS as cathode active material., Published by Elsevier, New York, NY [u.a.]

Although a great variety of strategies to suppress Li dendrite have been proposed for lithium metal batteries (LMBs), a deeper understanding of the factors playing a crucial role during extended el...

International audience; Rechargeable magnesium batteries are gaining a lot of interest due to promising electrochemical features, which, at least in theory, are comparable than those of Li-ion batteries. Such performance metrics can be achieved by using thin metal foils or high-capacity alloys coupled with suitable electrolytes enabling a high Coulombic efficiency and use of a high energy density cathode materials. All three components significantly influence electrochemical characteristics and energy density of rechargeable magnesium batteries. Although there are many reports showing progress in the cyclability and stability of different systems, only few cathode materials promise possible commercialization. Remaining issues with efficiency, magnesium anode processing and electrolyte compatibility with cell housing are preventing faster development of technology with high possible impact on the future battery landscape. In the given perspective paper a critical overview on electrolytes, anode materials and three different classes of cathode materials is reported. Different rechargeable magnesium battery configurations were assumed and their dependence of volumetric energy densities on gravimetric energy densities are provided assuming realistic conditions with optimized electrode thicknesses and loadings, electrode porosity and optimized electrolyte quantity. Although calculated values are attractive, further experimental steps are needed in order to prove these numbers on the lab-scale and small prototype cells.

International audience; The electrochemical degradation of two solvent-based electrolytes for Mg-metal batteries is investigated through a Grand canonical DFT approach. Both electrolytes are highly reactive in the double layer region where the solvated species have no direct contact with the Mg-surface, hence emphasising that surface reactions are not the only phenomena responsible for electrolyte degradation. Applied to dimethoxyethane (DME) and ethylene carbonate (EC), the present methodology shows that both solvents should thermodynamically decompose in the double layer prior to the Mg 2+ /Mg 0 reduction, leading to electrochemically inactive reaction products. Based on thermodynamic considerations, Mg 0 deposition should not be possible, which is not in agreement with experiments, at least for DME-based electrolytes. This apparent contradiction is here addressed through the rationalization of the electrochemical mechanism underlying solvent electro-activation. An extended operation potential window (OPW) is defined, in which the Mg 2+ /Mg 0 reduction can compete with electrolyte decomposition, thus enabling battery operation beyond the solvated species thermodynamic stability. The chemical study of the degradation products is in excellent agreement with experiments and it offer rationale for the Mg-battery failure in EC electrolyte and 2 capacity fade in DME electrolyte. Potential-dependent approach proposed herein is thus able to successfully tackle the challenging problem of interface electrochemistry. Being fully transferable to any other electrochemical systems, this methodology should provide rational guidelines for the development of viable electrolytes for multivalent batteries, and more generally, energy conversion and storage devices.

Climate change is the biggest challenge facing the world today. Europe is committed to achieving a climate-neutral society by 2050, as stated in the European Green Deal.1 The transition towards a climate-neutral Europe requires fundamental changes in the way we generate and use energy. If batteries can be made simultaneously more sustainable, safe, ultrahigh performing, and affordable, they will be true enablers, “accelerating the shift towards sustainable and smart mobility; supplying clean, affordable and secure energy; and mobilizing industry for a clean and circular economy” - all of which are important elements of the UN Sustainable Development Goals. In other words, batteries are a key technology for battling carbon dioxide emissions from the transport, power, and industry sectors. However, to reach our sustainability goals, batteries must exhibit ultra-high performance beyond their capabilities today. Ultra-high performance includes energy and power performance approaching theoretical limits, outstanding lifetime and reliability, and enhanced safety and environmental sustainability. Furthermore, to be commercially successful, these batteries must support scalability that enables cost-effective large-scale production. BATTERY 2030+, is the large-scale, long-term European research initiative with the vision of inventing the sustainable batteries of the future, to enable Europe to reach the goals envisaged in the European Green Deal. BATTERY 2030+ is at the heart of a green and connected society. BATTERY 2030+ will contribute to create a vibrant battery research and development (R&D) community in Europe, focusing on long-term research that will continuously feed new knowledge and technologies throughout the value chain, resulting in new products and innovations. In addition, the initiative will attract talent from across Europe and contribute to ensure access to competences needed for ongoing societal transformation. The BATTERY 2030+ aims are:• to invent ultra-high performance batteries that are safe, affordable, and sustainable, witha long lifetime.• to provide new tools and breakthrough technologies to the European battery industrythroughout the value chain.• to enable long-term European leadership in both existing markets (e.g., transport andstationary storage) and future emerging sectors (e.g., robotics, aerospace, medical devices, and Internet of things) With this roadmap, BATTERY 2030+ advocates research directions based on a chemistry-neutral approach that will allow Europe to reach or even surpass its ambitious battery performance targets set in the European Strategic Energy Technology Plan (SET-Plan)3 and foster innovation throughout the battery value chain. Battery 2030+

Transmission line modeling (TLM) has become an important approach for analysis of measured impedance spectra of battery cells. Still, the existing models lack some important features which prevents a full and accurate analysis of measured spectra. Here we present a general physics-based TLM that contains all the processes known from treatments of transport/reaction schemes based on the Newman porous electrode model or the corresponding Poisson-Nernst-Planck framework. Compared to previous TLMs, the present model additionally takes into account the movement of non-active mobile ions in all phases. After detailed description of the individual TLM model elements and their physical background we show, step-by-step, how it can be used to interpret the measured response of NMC cathodes, lithium anodes and full NMC-Li cells. Many details are considered the origin of which is identified by performing carefully designed additional experiments, e.g. electrolytes with variable concentration of salt. Besides identifying all the meaningful impedance features of electrodes and full cells, we also show how various materials parameters such as transport number, diffusion coefficient, conductivity etc can be calculated for various phases appearing in a porous battery electrode system. Finally, we use the findings to analyze the development of impedance response during discharge of a NMC-Li cell.

The search for high Li-ion conducting ceramics has regained tremendous interest triggered by the renaissance of the all-solid-state battery. Within this context we herein reveal the impact of structural polymorphism of lithium copper pyroborate Li6CuB4O10 on its ionic conductivity. Using combined in situ synchrotron X-ray and neutron powder diffraction, a structural and synthetic relationship between α- and β-Li6CuB4O10 could be established and its impact on ionic conductivity evolution was followed using electrochemical impedance spectroscopy. We show that the high temperature form of Li6CuB4O10 exhibits a high Li-ion conductivity (2.7 mS cm–1 at 350 °C) and solve its crystal structure for the first time. Our results emphasize the significant impact of structural phase transitions on ionic conductivity and show possible high Li-ion mobility within borate based compounds.

A magnesium (Mg) battery in the combination with the redox active polymers possesses attractive electrochemical properties as a future battery technology. This concept has been demonstrated by using quinone based polymers and the non-nucleophilic electrolytes, while polyimides were rarely investigated. In this work, a naphthalene-hydrazine diimide polymer (NP) has been tested as a cathode material for Mg organic battery in two different electrolytes. Average discharge voltage of the Mg-NP battery is 1.70 V with Coulombic efficiency above 99% in the TEGDME/DOL based electrolyte. The electrochemical mechanism was studied by in operando ATR IR spectroscopy and confirmed by DFT calculation of the IR spectra. We confirmed redox activity of carbonyl moieties, which undergo reversible reduction to enolate anion. Moreover, in operando IR spectroscopy shows charge delocalization in the reduced form since none of the bonds has pure single/double bond character.

Organic materials are receiving an increasing amount of attention as electrode materials for future post lithium-ion batteries due to their versatility and sustainability. However, their electrochemical reaction mechanism has seldom been investigated. This is a direct consequence of a lack of straightforward and broadly available analytical techniques. Herein, a straightforward in operando attenuated total reflectance infrared spectroscopy method is developed that allows visualization of changes of all infrared active bands that occur as a consequence of reduction/oxidation processes. In operando infrared spectroscopy is applied to the analysis of three different organic polymer materials in lithium batteries. Moreover, this in operando method is further extended to investigation of redox reaction mechanism of poly(anthraquinonyl sulfide) in a magnesium battery, where a reduction of carbonyl bond is demonstrated as a mechanism of electrochemical activity. Conclusions done by the in operando results are complemented by synthesis of model compound and density functional theory calculation of infrared spectra., Metal-organic batteries are gaining traction as versatile, low-cost, and sustainable devices, although there are still few ways to probe internal behavior during use. Here, the authors explore organic-molecule structural changes within several battery systems by in operando infrared spectroscopy.

Magnesium–sulfur batteries are considered as attractive energy-storage devices due to the abundance of electrochemically active materials and high theoretical energy density. Here we report the mechanism of a Mg–S battery operation, which was studied in the presence of simple and commercially available salts dissolved in a mixture of glymes. The electrolyte offers high sulfur conversion into MgS in the first discharge with low polarization. The electrochemical conversion of sulfur with magnesium proceeds through two well-defined plateaus, which correspond to the equilibrium between sulfur and polysulfides (high-voltage plateau) and polysulfides and MgS (low-voltage plateau). As shown by XANES, RIXS (resonant inelastic X-ray scattering), and NMR studies, the end discharge phase involves MgS with Mg atoms in a tetrahedral environment resembling the wurtzite structure, while chemically synthesized MgS crystallizes in the rock-salt structure with octahedral coordination of magnesium.

Electrolyte choice is an important decision on the quest for higher-energy batteries. Besides general guidelines on the required properties of an electrolyte suitable for use in lithium–sulfur batteries, the influence of more specific physicochemical properties on its characteristics is not well understood. For this purpose, binary mixtures based on the [DEME][TFSI] and dioxolane electrolyte system for lithium–sulfur batteries was investigated in this work. Selected physicochemical properties were determined for different mixtures of solvents and lithium salt concentrations. All the electrolytes prepared were also tested in the lithium–sulfur battery system. The capacity, Coulombic efficiency, overpotentials and impedance spectra were analyzed and a connection between them and the determined electrolyte properties elucidated. We show that the electrolyte's conductivity does not have a direct connection to any of the battery system properties measured. The highest specific capacities were obtained with batteries compromising 1.0 M LiTFSI and the highest ratio of dioxolane in the binary solvent mixture. On the other hand, the best Coulombic efficiencies were obtained with batteries having high ratios of ionic liquid. Resistance and overpotential are connected parameters and are a function of the ionic liquid content. None of the monitored parameters prevail, since the best electrochemical performance in terms of specific capacity and stability was obtained with the 1.0 M LiTFSI in X[DEME][TFSI] = 0.199 electrolyte.

In this work a novel pulse combustion reactor method for preparation of Li-ion cathode materials is introduced. Its advantages and potential challenges are demonstrated on two widely studied cathode materials, LiFePO 4 /C and Li-rich NMC. By exploiting the nature of efficiency of pulse combustion we have successfully established a slightly reductive or oxidative environment necessary for synthesis. As a whole, the proposed method is fast, environmentally friendly and easy to scale. An important advantage of the proposed method is that it preferentially yields small-sized powders (in the nanometric range) at a fast production rate of 2 s. A potential disadvantage is the relatively high degree of disorder of synthesized active material which however can be removed using a post-annealing step. This additional step allows a further tuning of materials morphology as shown and commented in some detail.

Polysulfides are central compounds in lithium-sulfur battery cells. However, the fundamental redox and diffusion properties of polysulfides are still poorly understood. We try to fill this gap by performing an accurate impedance spectroscopy investigation using symmetrical cells consisting of two planar glassy carbon electrodes separated with catholyte-soaked separator. The catholyte contains a mixture of selected polysulfides with predetermined nominal concentrations. Impedance measurements reveal textbook shapes of spectra for most polysulfide compounds or their mixtures. This allows reliable and accurate determination of the rate constant (exchange current density) for a given redox reaction as well as the diffusion coefficient and diffusion length for the rate-determining polysulfide species. Further, it is confirmed that polysulfides tend to disproportionate with time, which significantly changes the chemistry and electrochemistry of the system. Two approaches are proposed for identification of the prevailing redox mechanism in the resulting mixtures. The values of kinetic and transport parameters obtained for different cases of interest are commented on in significant detail. The study provides a solid basis for better understanding of the complex processes in polysulfide mixtures.

Dual electrolyte systems based on APC electrolyte mixed with either LiCl or LiTFSI are compared in a hybrid Mg/Li4Ti5O12 battery. Their comparison points to the detrimental effect of TFSI− anions on the battery performance through increase of polarization for Mg stripping and subsequent capacity fade. The effect is further explored through the study of Mg deposition/stripping in a dual electrolyte system and its comparison with conventional Mg electrolyte. Again, the detrimental effect of TFSI− anions is confirmed through the increase of polarization and decrease of the Coulombic efficiency, while Cl− anions have a minor beneficial effect on both. We hypothesize that the passivation of Mg metal in TFSI− anions containing electrolytes is the likely cause. Keywords: Dual electrolyte, TFSI− and Cl− anion, Hybrid Mg/Li4Ti5O12 battery, Mg deposition/stripping

One of the crucial steps for the development of batteries is understanding the interface stability and morphological changes occurring during continuous stripping and deposition. In order to investigate the dependence of morphology evolution on surface orientation, we examine the energetics and growth mechanism on magnesium (0001), (101[combining macron]0), (101[combining macron]1), (112[combining macron]0) and (112[combining macron]1) surface orientations using density functional theory and kinetic Monte Carlo simulations. Workfunctions, surface, adsorption and interaction energies, diffusion barriers and k-rates for diffusion via hopping and exchange mechanisms are studied. The results provide a comprehensive relationship between these properties and morphology evolution. The latter shows strong dependence on the surface orientation, demonstrating the need for all commonly present facets to be studied, instead of focusing only on the most stable surface orientation.

Redox active organic materials can be considered as a suitable host matrix for multivalent cations due to their open structure caused by relatively weak intermolecular forces. Their application in realistic two electrode rechargeable magnesium batteries has been realized after the discovery of non-nucleophilic electrolytes. Different groups have tested and proposed several families of redox active organic materials. Among them, materials based on conjugated carbonyls can be seen as the most promising direction, since practical batteries with an average discharge voltage of 2 V could be obtained and with proper design of redox active organic polymers, a battery with a theoretical energy density close to 700 W h kg−1 could be realized. The mechanism of the redox process of conjugated carbonyl compounds occurs through the reversible reduction of carbonyl bonds. It is proposed that the low volumetric energy density of a cathode based on redox active organic materials is compensated by the high volumetric energy density of metallic magnesium. The remaining problems of redox active organic materials are mainly due to their solubility in electrolytes based on organic solvents, which affects the cycling stability. In addition, reports on water-based electrolytes show much better electrochemical stability. Stability issues, together with the optimization of several battery engineering parameters, such as the content of electron conductive additives, the amount of required electrolyte and areal loadings of both electrodes will in future determine the practical viability of Mg–organic batteries.

The HPLC method including derivatisation was used for the determination of polysulfide species concentration during the operation of lithium-sulfur battery cells. A comparison was made between a glyme based electrolyte, which exhibits high polysulfide solubility, and a fluorinated ether based electrolyte, which was proposed to reduce the dissolution and diffusion of polysulfides. A separate analysis was conducted on porous carbon cathodes and separators obtained from cycled battery cells. The determination of the species concentration trends allowed a deeper understanding of the differences in battery cell operating mechanism. We have determined that polysulfide species are formed in similar concentrations in both examined electrolytes, but they remain trapped in the cathode pores in the fluorinated ether based electrolyte lithium-sulfur battery cells. The polysulfide concentration in the separators of the fluorinated ether cells was below the limit of detection, which indicates that the solubilities of polysulfides in the fluorinated electrolyte are below 50 µM. This results in absence of disproportionation or coproportionation reactions between the polysulfide species in solution. This different mechanism influences the change in length and potential of the voltage plateaus of the battery cells during galvanostatic cycling.

International audience; X-ray absorption spectroscopy is a synchrotron radiation based technique that is able to provide information on both local structure and electronic properties in a chemically selective manner. It can be used to characterize the dynamic processes that govern the electrochemical energy storage in batteries, and to shed light on the redox chemistry and changes in structure during galvanostatic cycling to design cathode materials with improved properties. Operando XAS studies have been performed at beamline XAFS at Elettra on different systems. For Li-ion batteries, a multiedge approach revealed the role of the different cathode components during the charge and discharge of the battery. In addition, Li-S batteries for automotive applications were studied. Operando sulfur K-edge XANES and EXAFS analysis was used to characterize the redox chemistry of sulfur, and to relate the electrochemical mechanism to its local structure.

Herein a novel solvothermal synthesis approach for preparing poly(hydrobenzoquinonyl-benzoquinonyl sulfide) polymer (PHBQS) using sulfur and hydroquinone is presented. We investigate and compare electrochemical activity of this polymer as a cathode in Li and Mg battery systems. In the Li system we retain more than 160 mAh/g after 340 cycles, while in the Mg system a discharge voltage of approximately 2.0 V vs. Mg is achieved. This represents a significant increase in working voltage of Mg organic battery over majority of previously reported Mg organic batteries. The maximum specific capacity of 158 mAh/g is achieved in MgCl2-Mg(TFSI)2 tetraglyme:1,3-dioxolane electrolyte. Keywords: Organic battery, Mg battery, Mg(TFSI)2, Solvothermal synthesis

For the design of light-metal-sulfur batteries and for the understanding of their performance, knowledge on the stable crystalline polysulfides is very important. We confronted experimental and ab initio crystal structure prediction studies on the stability of Na polysulfides. The selected evolutionary-based structure-prediction algorithm was able to quickly and correctly predict the thermodynamically stable crystalline forms of Na polysulfides with small unit cells. For Na polysulfides with large unit cells, the algorithm correctly proposed short unbranched polysulfide chains to be energetically favorite structural motifs, but could not find proper three-dimensional structures in the limited number of generations. Experimentally, the polysulfides were studied by X-ray diffraction and 23 Na solid-state NMR spectroscopy. Complemented by calculations of the isotropic chemical shifts and quadrupolar coupling constants, NMR spectroscopy proved to be an excellent tool for the examination of Na polysulfides, because it allowed easy distinction and quantification of components in the samples.

In the search for new cathode materials for Li-ion batteries, borate (BO33-) based compounds have gained much interest during the last two decades due to the low molecular weight of the borate polyanions which leads to active materials with increased theoretical capacities. In this context we herein report the electrochemical activity versus lithium and the ionic conductivity of a diborate or pyroborate B2O54- based compound, Li6CuB4O10. By combining various electrochemical techniques with in situ X-ray diffraction, we show that this material can reversibly insert/deinsert limited amounts of lithium (~0.3 Li+) in a potential window ranging from 2.5 to 4.5 V vs. Li+/Li0. We demonstrate, via electron paramagnetic resonance (EPR), that such an electrochemical activity centered near 4.25 V vs. Li+/Li0 is associated with the Cu3+/Cu2+ redox couple, confirmed by density functional theory (DFT) calculations. Another specificity of this compound lies in its different electrochemical behavior when cycled down to 1 V vs. Li+/Li0 which leads to the extrusion of elemental copper via a conversion type reaction as deduced by transmission electron microscopy (TEM). Lastly, we probe the ionic conductivity by means of AC and DC impedance measurements as a function of temperature and show that Li6CuB4O10 undergoes a reversible structural transition around 350 °C, leading to a surprisingly high ionic conductivity of ~1.4 mS cm-1 at 500 °C.

Long term stability of LiMnPO 4 particles with a crystallite size between ∼20 and 50 nm covered with a dense native carbon coating (14 wt.%) is demonstrated. More than 500 cycles at a rate of C/20, in the potential window of 2.7–4.5 V and a temperature of 55 °C were achieved. During most of the cycling the average capacity decay was less than 0.06% per cycle. After about 500 cycles a sudden capacity drop was observed. Degradation processes in various stages of cycling were thoroughly examined using a range of techniques. Severe surface film formation, manganese dissolution and degradation of Li x MnPO 4 accompanied by formation of Li 4 P 2 O 7 were clearly identified. The good long term stability seems to be due to dense, protective carbon coating. Decomposition is most likely initiated at local defects in the microstructure of pyrolytic carbon coating around LiMnPO 4 particles. In addition to known degradation mechanisms of LiMnPO 4 we observed pronounced gradual amorphization of the olivine crystallites during long-term cycling at 55 °C. Finally, changes in morphology of the carbon black additive after prolonged cycling are reported and commented.

International audience; We report on the synthesis of fluorinated reduced graphene oxide (F-rGO) by a direct fluorination of reduced graphene oxide (rGO) with F2 or XeF2/BF3 in anhydrous HF. Characterization performed by high-angle annular dark-field (HAADF)-scanning transmission electron microscopy (STEM) and NMR confirmed the formation of C-F bonds, which is also supported by the color change from graphite gray to light yellow. F-rGO has been used as an interlayer additive supported by a glass fiber separator in lithium-sulfur (Li-S) batteries in order to block the diffusion/migration of polysulfides from the porous positive electrode to the metallic lithium electrode and to prevent the redox shuttle effect. Electrochemical cycling of Li-S batteries has confirmed the beneficial role of F-rGO separators, with a more pronounced effect observed for high degrees of fluorination. X-ray photoelectron spectroscopy (XPS) studies have shown a direct effect on the amount of Li2S and polysulfides found on the lithium electrode and evidenced a better reversibility of reduction/oxidation mechanisms of sulfur at the positive electrode upon discharge/charge. © 2015 American Chemical Society.

Aluminum 3D thin film anodes fully integrated with a separator are fabricated by sputtering and enable rechargeable aluminum metal batteries with high power performance. The 3D thin film anodes have an approximately four to eight times larger active surface area than a metal foil, which significantly both reduces the electrochemical overpotential, and improves materials utilization. In full cells with organic cathodes, that is, aluminum metal-organic batteries, the 3D thin film anodes provide 165 mAh g(-1)at 0.5 C rate, with a capacity retention of 81% at 20 C, and 86% after 500 cycles. Post-mortem analysis reveals structural degradation to limit the long-term stability at high rates. As the multivalent charge carrier active here is AlCl2+, the realistic maximal specific energy, and power densities at cell level are approximate to 100 Wh kg(-1)and approximate to 3100 W kg(-1), respectively, which is significantly higher than the state-of-the-art for Al batteries.

The direct reaction of polysulfide species with the Li metal anode causes several issues in the performance of lithium-sulfur batteries, from poor capacity utilization and fast capacity fade to poor Coulombic efficiency. Nevertheless, several reports indicate formation of favorable lithium SEI when allowing for its contact with polysulfides. With cycling tests, impedance spectroscopy measurements and morphology investigation, we have confirmed the beneficial effect of polysulfides on lithium metal stripping and deposition even without LiNO3, which is usually added. Most importantly, highly concentrated catholytes, which are closer to the saturated solutions encountered in lean electrolyte-to-sulfur ratios, were tested. In the 1 M Li2S8 catholyte solution, its effect produced Li electrodes without dendritic growth, but rather a wrinkled surface. To circumvent the issue of viscosity in such solutions, pre-treatment in polysulfide solutions was also tested. The performance of such electrodes showed an increase in cycle life and lower overpotentials, although dendritic growth could not be fully avoided. In order to better understand the effect of pre-treatment on transport/reaction mechanism in Li electrode, a detailed analysis of selected impedance spectra is carried out using physics-based transmission line modelling (TLM).

Disordered lithium-rich transition metal oxyfluorides with a general formula Li1þxMO2Fx (M being a transition metal) are gaining more attention due to their high specific capacity which can be delivered from the facecentered cubic (fcc) structure. The most common synthesis procedure involves use of mechanosynthesis. In this work, ceramic synthesis of lithium rich iron oxyfluoride and lithium rich titanium oxyfluoride are reported. Two ceramic synthesis routes are developed each leading to the different level of doping with Li and F and different levels of cationic disorder in the structure. Three different Li1þxMO2Fx samples (x ¼ 0.25, 0.3 and 1) are compared with a sample prepared by mechanochemical synthesis and non-doped LiFeO2 with fcc structure. The obtained lithium rich iron oxyfluoride are characterized by use of M€ossbauer spectroscopy, X-ray absorption spectroscopy, NMR and TEM. Successful incorporation of Li and F have been confirmed and specific capacity that can be obtained from the samples is in the correlation with the level of disorder introduced with doping, nevertheless oxidation state of iron in all samples is very similar. Conclusions obtained from lithium rich iron oxyfluoride are validated by lithium rich titanium oxyfluoride.

The direct reaction between Li metal surface and polysulfide species that tend to continuously diffuse through the separator and reach the anode, significantly affects the performance of Li-S batteries. Among others, this reaction generally leads to a decrease in the measured capacity, an increased rate of self-discharge and a poorer coulombic efficiency. In order to understand the parameters affecting the rate and nature of this reaction, we have carried out detailed studies employing impedance spectroscopy and UV-Vis spectroscopy in conjunction with variable cell design. Based on the experimental results a simple kinetic model is proposed whereby we take into account both the reaction of polysulfides with lithium as well as the inherent disproportionation reaction of polysulfide species themselves. Despite various unknowns - such as the exact nature of the polysulfide species present in the system or their transport properties - several trends are identified and commented on. The present results may serve as a good framework towards better understanding of the reactivity of polysulfides when in contact with metallic lithium.

Rechargeable magnesium (Mg) batteries are considered as potential post lithium batteries with different application. Due to natural abundance of Mg, batteries based on Mg metal as an anode are considered as sustainable batteries which with high specific theoretical capacity (2205 mAh/g and 3.832 mAh/cm3) and with a reduction potential of −2.356 V versus standard hydrogen electrode (NHE) puts a lot of motivation for their exploration and application. Metallic magnesium is known as a highly passivating metal and it requires a special attention to the electrolyte development. Recent progress in the field of non-nucleophilic electrolytes with high oxidative stability opens the possibility to employ these types of electrolytes with redox active organic materials where weak intermolecular forces enable the reversible electrochemical interaction of Mg cations coupled with fast diffusion. Organic polymers can be considered as a sustainable counterpart in the combination with Mg metal and that represents a robust approach towards sustainable Mg batteries with high power and good cycling properties. Another, even more attractive combination is magnesium sulfur battery, which is a combination of two highly abundant elements and it can provide higher energy density compared to current Li-ion batteries. Finally, problems related to high voltage insertion materials will be discussed within presentation.

Conversion type materials, in particular metal fluorides, have emerged as attractive candidates for positive electrodes in next generation Li-ion batteries (LIBs). However, their practical use is being hindered by issues related to reversibility and large polarization. To minimize these issues, a few approaches enlisting the anionic network have been considered. We herein report the electrochemical properties of bismuth oxyborate Bi

Metallic lithium is considered to be one of the most promising anode materials since it offers high volumetric and gravimetric energy densities when combined with high-voltage or high-capacity cathodes. However, the main impediment to the practical applications of metallic lithium is its unstable solid electrolyte interface (SEI), which results in constant lithium consumption for the formation of fresh SEI, together with lithium dendritic growth during electrochemical cycling. Here we present the electrochemical performance of a fluorinated reduced graphene oxide interlayer (FGI) on the metallic lithium surface, tested in lithium symmetrical cells and in combination with two different cathode materials. The FGI on the metallic lithium exhibit two roles, firstly it acts as a Li-ion conductive layer and electronic insulator and secondly, it effectively suppresses the formation of high surface area lithium (HSAL). An enhanced electrochemical performance of the full cell battery system with two different types of cathodes was shown in the carbonate or in the ether based electrolytes. The presented results indicate a potential application in future secondary Li-metal batteries.