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Development of Mg-ion batteries as advanced electrochemical energy storage systems relies on the design and discovery of high-voltage positive electrode (cathode) materials. To date, a variety of sulfide cathodes have been reported (e.g., MgxMo6S8, MgxTi2S4, etc.), but the voltages of these materials are too low to prepare a high energy density Mg cell. Theoretical computations predicted that MgxCr2S4 operating with the high-voltage Cr3+/4+ redox couple would serve as a suitable cathode candidate, but experimental attempts to extract Mg2+ from the lattice have been largely unsuccessful. We show that reversible electrochemical activity within a thiospinel framework (AB2S4) relies on a redox-active transition metal present in the B site; otherwise, anionic redox activity triggers decomposition of the spinel structure. Since Cr and S states are highly coupled in MgCr2S4, the Cr3+/4+ redox couple is inaccessible so that reversible (de)intercalation of Mg2+ cannot occur and charging leads to dissolution of the active material. These findings point to an insufficiency in the screening criteria previously used to identify MgCr2S4 as a promising Mg cathode. Thus, a computable descriptor based on the electronic structure of the discharged material is proposed to predict the prevalence of cation vs anion redox and improve future surveys of potential candidates. It is unlikely that the high-voltage Cr redox couple will be accessible to oxidation in the presence of sulfur within the restrictions of a spinel framework; however, it is possible that a suitable layered MgxCrS2 structure could serve as a reversible high-voltage Mg cathode.

The ongoing search for high voltage positive electrode materials for Mg batteries has been primarily hampered by poor Mg mobility in bulk oxide frameworks. Motivated by the presence of Mo3 clusters that can facilitate charge redistribution and the presence of Mg in a non-preferred (tetrahedral) coordination environment, we have investigated the Mg (de)intercalation behavior in layered-Mg2Mo3O8, a potential positive electrode. While no electrochemical activity is observed, chemical demagnesiation of Mg2Mo3O8 is successful but leads to amorphization. Subsequent first-principles calculations predict a strong thermodynamic driving force for structure decomposition at low Mg concentrations and high activation barriers for bulk Mg diffusion, in agreement with experimental observations. Further analysis of the Mg diffusion pathway reveals an O-Mg-O dumbbell intermediate site that creates a high Mg2+ migration barrier, indicating the influence of transition states on setting the magnitude of migration barriers.

'Anode-free' or, more fittingly, metal reservoir-free cells could drastically improve current solid-state battery technology by achieving higher energy density, improving safety and simplifying manufacturing. Various strategies have been reported so far to control the morphology of electrodeposited alkali metal films to be homogeneous and dense, but until now, the microstructure of electrodeposited alkali metal is unknown, and a suitable characterization route is yet to be identified. Here we establish a reproducible protocol for characterizing the size and orientation of metal grains in differently processed lithium and sodium samples by a combination of focused ion beam and electron backscatter diffraction. Electrodeposited films at Cu|Li 6.5 Ta 0.5 La 3 Zr 1.5 O 12 , steel|Li 6 PS 5 Cl and Al|Na 3.4 Zr 2 Si 2.4 P 0.6 O 12 interfaces were characterized. The analyses show large grain sizes (>100 µm) within these films and a preferential orientation of grain boundaries. Furthermore, metal growth and dissolution were investigated using in situ electron backscatter diffraction, showing a dynamic grain coarsening during electrodeposition and pore formation within grains during dissolution. Our methodology and results deepen the research field for the improvement of solid-state battery performance through a characterization of the alkali metal microstructure., Competing Interests: Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

Developing solid-state batteries (SSB) with a lithium metal electrode (LME) using only one type of solid electrolyte (SE) is a significant challenge since no SE fits all the requirements imposed by both electrodes. A possible solution is using multilayer SSBs with an LME where the drawbacks of each SE are overcome by using layers of different SEs. However, research on inorganic SE 1 |SE 2 heteroionic interfaces is still quite preliminary, especially regarding oxide|sulfide heteroionic interfaces. This work reports the electrochemical investigation of the heteroionic interface between Li 6.25 Al 0.25 La 3 Zr 2 O 12 (Al-LLZO) and two representative materials for sulfide-based SEs: argyrodite-based Li 6 PS 5 Cl (LPSCl) and glass-like Li 7 P 3 S 11 (LPS711). Through in-depth temperature- and pressure-dependent impedance analyses of multilayer symmetric cells at equilibrium (i.e., no current load), the electrical properties of the heteroionic interfaces are assessed. The pressure-dependent kinetic of the Al-LLZO|LPSCl pair is interpreted with the concept of geometric constriction resistance and show that its resistance is lower than for the Al-LLZO|LPS711 pair. Furthermore, the effect of Al-LLZO surface treatment on the electrical properties of the Al-LLZO|LPSCl heteroionic interface is evaluated. Such investigation shows that the value of the interface activation energy decreases when the Al-LLZO surface is heat treated, revealing a significant influence of the carbonate/hydroxide passivation layer on the heteroionic interface. Additionally, by cycling the symmetric cell for 900 h at 1.0 mAh·cm -2 , it is revealed that the Al-LLZO|LPSCl interface has a lower impedance increase than the Al-LLZO|LPS711 interface, especially if the Al-LLZO is heat treated. With this work, we highlight that the oxide|argyrodite combination can be a promising candidate for multilayer SSBs with an LME. However, we show that an optimized LLZO surface treatment and chemical analysis of the interface are recommended for future research.

Understanding Li-ion transport is key for the rational design of superionic solid electrolytes with exceptional ionic conductivities. LiNbOCl 4 is reported to be one of the most highly conducting materials in the recently realized new class of soft oxyhalide solid electrolytes, exhibiting an ionic conductivity of ∼11 mS·cm -1 . Here, we apply X-ray/neutron diffraction and pair distribution function analysis─coupled with density functional theory/ab initio molecular dynamics (AIMD)─to determine a structural model that provides a rationale for the high conductivity that we observe experimentally in this nanocrystalline solid. We show that it arises from unusually high framework flexibility at room temperature. This is due to isolated 1-D [NbOCl 4 ] - anionic chains that exhibit energetically favorable orientational disorder that is─in turn─correlated to multiple, disordered, and equi-energetic Li + sites in the lattice. As the Li ions sample the 3-D energy landscape with a fast predicted diffusion coefficient of 5.1 × 10 -7 cm 2 /s at room temperature (σ i calc = 17.4 mS·cm -1 ), the inorganic polymer chains can reorient or vice versa. The activation energy barrier for Li migration through the frustrated energy landscape is especially reduced by the elastic nature of the NbO 2 Cl 4 octahedra evident from very widely dispersed Cl-Nb-Cl bond angles in AIMD simulations at 300 K. The phonon spectra are predominantly influenced by Cl vibrations in the low energy range, and there is a strong overlap between the framework (Cl, Nb) and Li partial density of states in the region between 1.2 and 4.0 THz. The framework flexibility is also reflected in a relatively low bulk modulus of 22.7 GPa. Our findings pave the way for the investigation of future "flex-ion" inorganic solids and open up a new direction for the design of high-conductivity, soft solid electrolytes for all-solid-state batteries.

Conventional Li-S batteries rely on liquid electrolytes based on LiNO 3 /DOL/DME mixtures that produce a quasistable interface with the lithium anode. Electron pair donor (EPD) solvents, also known as high donor number solvents, provide much higher polysulfide solubility and close-to-ideal sulfur utilization, making them solvents of choice for lean electrolyte Li-S cells. However, their instability to reduction requires incorporation of an ion-conductive membrane that is stable with Li-such as garnet LLZO and also stable with sulfur/polysulfides. We report that even trace amounts of LiOH on a LLTZO surface trigger a complex reaction with sulfur dissolved in typical EPD solvents (i.e., N , N -dimethylacetamide, DMA) to produce a highly resistive impedance layer that quickly grows with time from 1000 to 10,000 Ω cm 2 over a few hours, thus impeding Li + transport across the interface. Decorating the LLZO with protective phosphate groups to produce a modified surface provides a very low charge-transfer resistance of 40 Ω cm 2 that is maintained over time and inhibits the reaction of LiOH and dissolved sulfur. Hybrid liquid-solid electrolyte cells constructed on this concept result in a high sulfur utilization of 1400 mAh g -1 which is 85% of theoretical and remains constant over cycling even with conventional, unoptimized carbon/sulfur cathodes.

We report a new sodium fast-ion conductor, Na 3 B 5 S 9 , that exhibits a high Na ion total conductivity of 0.80 mS cm -1 (sintered pellet; cold-pressed pellet=0.21 mS cm -1 ). The structure consists of corner-sharing B 10 S 20 supertetrahedral clusters, which create a framework that supports 3D Na ion diffusion channels. The Na ions are well-distributed in the channels and form a disordered sublattice spanning five Na crystallographic sites. The combination of structural elucidation via single crystal X-ray diffraction and powder synchrotron X-ray diffraction at variable temperatures, solid-state nuclear magnetic resonance spectra and ab initio molecular dynamics simulations reveal high Na-ion mobility (predicted conductivity: 0.96 mS cm -1 ) and the nature of the 3D diffusion pathways. Notably, the Na ion sublattice orders at low temperatures, resulting in isolated Na polyhedra and thus much lower ionic conductivity. This highlights the importance of a disordered Na ion sublattice-and existence of well-connected Na ion migration pathways formed via face-sharing polyhedra-in dictating Na ion diffusion., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Two major challenges hinder the advance of aqueous zinc metal batteries for sustainable stationary storage: (1) achieving predominant Zn-ion (de)intercalation at the oxide cathode by suppressing adventitious proton co-intercalation and dissolution, and (2) simultaneously overcoming Zn dendrite growth at the anode that triggers parasitic electrolyte reactions. Here, we reveal the competition between Zn 2+ vs proton intercalation chemistry of a typical oxide cathode using ex-situ/operando techniques, and alleviate side reactions by developing a cost-effective and non-flammable hybrid eutectic electrolyte. A fully hydrated Zn 2+ solvation structure facilitates fast charge transfer at the solid/electrolyte interface, enabling dendrite-free Zn plating/stripping with a remarkably high average coulombic efficiency of 99.8% at commercially relevant areal capacities of 4 mAh cm -2 and function up to 1600 h at 8 mAh cm -2 . By concurrently stabilizing Zn redox at both electrodes, we achieve a new benchmark in Zn-ion battery performance of 4 mAh cm -2 anode-free cells that retain 85% capacity over 100 cycles at 25 °C. Using this eutectic-design electrolyte, Zn | |Iodine full cells are further realized with 86% capacity retention over 2500 cycles. The approach represents a new avenue for long-duration energy storage., (© 2023. The Author(s).)

Lithium argyrodite-type electrolytes are regarded as promising electrolytes due to their high ionic conductivity and good processability. Chemical modifications to increase ionic conductivity have already been demonstrated, but the influence of these modifications on interfacial stability remains so far unknown. In this work, we study Li 6 PS 5 Cl and Li 5.5 PS 4.5 Cl 1.5 to investigate the influence of halogenation on the electrochemical decomposition of the solid electrolyte and the chemical degradation mechanism at the cathode interface in depth. Electrochemical measurements, gas analysis and time-of-flight secondary ion mass spectrometry indicate that the Li 5.5 PS 4.5 Cl 1.5 shows pronounced electrochemical decomposition at lower potentials. The chemical reaction at higher voltages leads to more gaseous degradation products, but a lower fraction of solid oxygenated phosphorous and sulfur species. This in turn leads to a decreased interfacial resistance and thus a higher cell performance., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The search for new solid electrolyte materials and an understanding of fast-ion conductivity are crucial for the development of safe and high-power all-solid-state battery technology. Herein, we present the synthesis, structure, and properties of a crystalline lithium-ion conductor, Li 3.3 Al 0.15 P 0.85 S 4 (i.e., Li 9.9 Al 0.45 P 2.55 S 12 ), found in the compositional range Li 3+2 x P 1- x Al x S 4 ( x = 0.15, 0.20, and 0.33). 31 P magic-angle spinning nuclear magnetic resonance (MAS-NMR) aided in identifying the successful introduction of Al into the lattice. At high values of x (>0.15), crystalline Li 5 AlS 4 and a glassy amorphous component exsolve to yield a multiphase mixture. The crystal structure of Li 3.3 Al 0.15 P 0.85 S 4 was elucidated by single-crystal X-ray diffraction and powder neutron diffraction, demonstrating that it belongs to the thio-LISICON family with the Pnma space group, a = 12.9572(13) Å, b = 8.0861(8) Å, c = 6.1466(6) Å, and V = 644.00(11) Å 3 . The Li + -ion conductivity and diffusivity in this bulk material (which contains about 10 wt % of an amorphous phase, as prepared) were studied by electrochemical impedance spectroscopy and 7 Li pulsed-field gradient nuclear magnetic resonance spectroscopy (PFG-NMR). The total ionic conductivity of Li 3.3 Al 0.15 P 0.85 S 4 is 0.22(2) mS·cm -1 at room temperature with an activation energy of 0.30(1) eV. A two-component analysis method based on the Kärger equations was developed to analyze the diffusive exchange between the bulk and amorphous phases of Li 3.3 Al 0.15 P 0.85 S 4 detected via the PFG-NMR signal attenuation curves. This approach was employed to quantitatively compare different sample morphologies (glass powder, crystalline powder, and crystalline pellets of Li 3.3 Al 0.15 P 0.85 S 4 ) and assess the influence of the macroscopic state on microscopic ion transport, as supported by NMR relaxation measurements.

Although batteries fitted with a metal negative electrode are attractive for their higher energy density and lower complexity, the latter making them more easily recyclable, the threat of cell shorting by dendrites has stalled deployment of the technology 1,2 . Here we disclose a bidirectional, rapidly charging aluminium-chalcogen battery operating with a molten-salt electrolyte composed of NaCl-KCl-AlCl 3 . Formulated with high levels of AlCl 3 , these chloroaluminate melts contain catenated Al n Cl 3n+1 - species, for example, Al 2 Cl 7 - , Al 3 Cl 10 - and Al 4 Cl 13 - , which with their Al-Cl-Al linkages confer facile Al 3+ desolvation kinetics resulting in high faradaic exchange currents, to form the foundation for high-rate charging of the battery. This chemistry is distinguished from other aluminium batteries in the choice of a positive elemental-chalcogen electrode as opposed to various low-capacity compound formulations 3-6 , and in the choice of a molten-salt electrolyte as opposed to room-temperature ionic liquids that induce high polarization 7-12 . We show that the multi-step conversion pathway between aluminium and chalcogen allows rapid charging at up to 200C, and the battery endures hundreds of cycles at very high charging rates without aluminium dendrite formation. Importantly for scalability, the cell-level cost of the aluminium-sulfur battery is projected to be less than one-sixth that of current lithium-ion technologies. Composed of earth-abundant elements that can be ethically sourced and operated at moderately elevated temperatures just above the boiling point of water, this chemistry has all the requisites of a low-cost, rechargeable, fire-resistant, recyclable battery., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

ConspectusAs the world transitions away from fossil energy to green and renewable energy, electrochemical energy storage increasingly becomes a vital component of the mix to conduct this transition. The central goal in developing next-generation batteries is to maximize the gravimetric and volumetric energy density and battery cycle life and improve safety. All solid-state batteries using a solid electrolyte and a lithium metal anode represent one of the most promising technologies that can achieve this goal. Highly conductive solid electrolytes (>10 mS·cm -1 ) are the key component to remove the safety concerns inherent with flammable organic liquid electrolytes and achieve high energy density by enabling high active material loading. Considering a range of inorganic solid electrolytes that have been developed to date, sulfide solid electrolytes exhibit the highest ionic conductivities, which even surpass those of conventional organic liquid electrolytes. Argyrodite-structured sulfide solid electrolytes are among the most promising materials in this class and are currently the dominantly used solid electrolytes for all-solid-state battery fabrication. Argyrodite solid electrolytes are particularly appealing because of their ultrahigh Li-ion conductivity, quasi-stable solid-electrolyte interphase (SEI) formed with Li metal, and ability to be prepared via scalable solution-assisted synthesis approaches. These factors are all vital for commercial applications.In this Account, we afford an overview of our recent development of several argyrodite superionic conductors, including Li 6.6 Si 0.6 Sb 0.5 S 5 I (24 mS·cm -1 ), Li 6.6 Ge 0.6 P 0.4 S 5 I (18 mS·cm -1 ), and Li 5.5 PS 4.5 Cl 1.5 (12 mS·cm -1 ), and a comprehensive understanding of the origin of the underlying high conductivity, namely, sulfide/halide anion site disorder and Li cation site disorder. A high degree of sulfide/halide anion site disorder (changes in anion distribution) modifies the anionic charge, which in turn strongly influences the lithium distribution. A more inhomogeneous charge distribution in anion-disordered systems generates a spatially diffuse and delocalized lithium density, resulting in faster ionic transport. Lithium cation site disorder generated by increasing Li carrier concentration through aliovalent substitution creates high-energy interstitial sites for Li ion diffusion, which activate concerted ion migration and flatten the energy landscape for Li ion diffusion. This enables high conductivity in Li-rich argyrodite superionic conductors. These concepts are also expected to promote the design of rational new solid electrolytes and fundamental understanding of the structure-ion transport relationships in inorganic ionic conductors.Collectively, a comprehensive and deep understanding of the interphase formation between argyrodite solid electrolytes and cathode active materials/Li metal and the failure mechanism of all-solid-state batteries with argyrodite solid electrolytes will lead to the bottom-up engineering of the cathode/anode-solid electrolyte interfaces, which will accelerate the development of safe, high-energy-density all-solid-state lithium batteries.

We report a new fast ion-conducting lithium thioborate halide, Li 6 B 7 S 13 I, that crystallizes in either a cubic or tetragonal thioboracite structure, which is unprecedented in boron-sulfur chemistry. The cubic phase exhibits a perovskite topology and an argyrodite-like lithium substructure that leads to superionic conduction with a theoretical Li-ion conductivity of 5.2 mS cm -1 calculated from ab initio molecular dynamics (AIMD). Combined single-crystal X-ray diffraction, neutron powder diffraction, and AIMD simulations elucidate the Li + -ion conduction pathways through 3D intra- and intercage connections and Li-ion site disorder, which are all essential for high lithium mobility. Furthermore, we demonstrate that Li + ordering in the tetragonal polymorph impedes lithium-ion conduction, thus highlighting the importance of the lithium substructure and lattice symmetry in dictating transport properties.

We investigate high-valent oxygen redox in the positive Na-ion electrode P2-Na 0.67-x [Fe 0.5 Mn 0.5 ]O 2 (NMF) where Fe is partially substituted with Cu (P2-Na 0.67-x [Mn 0.66 Fe 0.20 Cu 0.14 ]O 2 , NMFC) or Ni (P2-Na 0.67-x [Mn 0.65 Fe 0.20 Ni 0.15 ]O 2 , NMFN). From combined analysis of resonant inelastic X-ray scattering and X-ray near-edge structure with electrochemical voltage hysteresis and X-ray pair distribution function profiles, we correlate structural disorder with high-valent oxygen redox and its improvement by Ni or Cu substitution. Density of states calculations elaborate considerable anionic redox in NMF and NMFC without the widely accepted requirement of an A-O-A' local configuration in the pristine materials (where A=Na and A'=Li, Mg, vacancy, etc.). We also show that the Jahn-Teller nature of Fe 4+ and the stabilization mechanism of anionic redox could determine the extent of structural disorder in the materials. These findings shed light on the design principles in TM and anion redox for positive electrodes to improve the performance of Na-ion batteries., (© 2020 Wiley-VCH GmbH.)

Lithium thioborates are promising fast Li-ion conducting materials, with similar properties to their lithium thiophosphate counterparts that have enabled the development of solid-state Li-ion batteries. By comparison, thioborates have scarcely been developed, however, offering new space for materials discovery. Here we report a new class of lithium thioborate halides that adopt a so-called supertetrahedral adamantanoid structure that houses mobile lithium ions and halide anions within interconnected 3D structural channels. Investigation of the structure using single-crystal XRD, neutron powder diffraction, and neutron PDF reveals significant lithium and halide anion disorder. The phases are non-stoichiometric, adopting slightly varying halide contents within the materials. These new superadamantanoid materials exhibit high ionic conductivities up to 1.4 mS cm -1 , which can be effectively tuned by the polarizability of the halide anion within the channels., (© 2020 Wiley-VCH GmbH.)

Stabilizing high-valent redox couples and exotic electronic states necessitate an understanding of the stabilization mechanism. In oxides, whether they are being considered for energy storage or computing, highly oxidized oxide-anion species rehybridize to form short covalent bonds and are related to significant local structural distortions. In intercalation oxide electrodes for batteries, while such reorganization partially stabilizes oxygen redox, it also gives rise to substantial hysteresis. In this work, we investigate oxygen redox in layered Na 2-X Mn 3 O 7 , a positive electrode material with ordered Mn vacancies. We prove that coulombic interactions between oxidized oxideanions and the interlayer Na vacancies can disfavor rehybridization and stabilize hole polarons on oxygen (O - ) at 4.2 V vs. Na/Na + . These coulombic interactions provide thermodynamic energy saving as large as O-O covalent bonding and enable ~ 40 mV voltage hysteresis over multiple electrochemical cycles with negligible voltage fade. Our results establish a complete picture of redox energetics by highlighting the role of coulombic interactions across several atomic distances and suggest avenues to stabilize highly oxidized oxygen for applications in energy storage and beyond., Competing Interests: Conflicts of interest There are no conflicts of interest to declare.

The goal of limiting global warming to 1.5 °C requires a drastic reduction in CO 2 emissions across many sectors of the world economy. Batteries are vital to this endeavor, whether used in electric vehicles, to store renewable electricity, or in aviation. Present lithium-ion technologies are preparing the public for this inevitable change, but their maximum theoretical specific capacity presents a limitation. Their high cost is another concern for commercial viability. Metal-air batteries have the highest theoretical energy density of all possible secondary battery technologies and could yield step changes in energy storage, if their practical difficulties could be overcome. The scope of this review is to provide an objective, comprehensive, and authoritative assessment of the intensive work invested in nonaqueous rechargeable metal-air batteries over the past few years, which identified the key problems and guides directions to solve them. We focus primarily on the challenges and outlook for Li-O 2 cells but include Na-O 2 , K-O 2 , and Mg-O 2 cells for comparison. Our review highlights the interdisciplinary nature of this field that involves a combination of materials chemistry, electrochemistry, computation, microscopy, spectroscopy, and surface science. The mechanisms of O 2 reduction and evolution are considered in the light of recent findings, along with developments in positive and negative electrodes, electrolytes, electrocatalysis on surfaces and in solution, and the degradative effect of singlet oxygen, which is typically formed in Li-O 2 cells.

Energy storage is an integral part of modern society. A contemporary example is the lithium (Li)-ion battery, which enabled the launch of the personal electronics revolution in 1991 and the first commercial electric vehicles in 2010. Most recently, Li-ion batteries have expanded into the electricity grid to firm variable renewable generation, increasing the efficiency and effectiveness of transmission and distribution. Important applications continue to emerge including decarbonization of heavy-duty vehicles, rail, maritime shipping, and aviation and the growth of renewable electricity and storage on the grid. This perspective compares energy storage needs and priorities in 2010 with those now and those emerging over the next few decades. The diversity of demands for energy storage requires a diversity of purpose-built batteries designed to meet disparate applications. Advances in the frontier of battery research to achieve transformative performance spanning energy and power density, capacity, charge/discharge times, cost, lifetime, and safety are highlighted, along with strategic research refinements made by the Joint Center for Energy Storage Research (JCESR) and the broader community to accommodate the changing storage needs and priorities. Innovative experimental tools with higher spatial and temporal resolution, in situ and operando characterization, first-principles simulation, high throughput computation, machine learning, and artificial intelligence work collectively to reveal the origins of the electrochemical phenomena that enable new means of energy storage. This knowledge allows a constructionist approach to materials, chemistries, and architectures, where each atom or molecule plays a prescribed role in realizing batteries with unique performance profiles suitable for emergent demands., Competing Interests: The authors declare no competing interest.

Sodium batteries have emerged as a promising alternative for large-scale energy storage applications due to the low cost and high abundance of sodium. Sodium batteries require safe, high-voltage, and cost-effective electrolytes and cathode materials for their practical applications to be realized. In the present study, Na metal cells with a mixed-phase electrolyte comprising a high concentration of Na salt in an organic ionic plastic crystal (OIPC), namely, triisobutylmethylphosphonium bis(fluorosulfonyl)imide, are investigated-coupled with either a sodium vanadium phosphate-carbon composite (NVP/C) or a sodium iron pyrophosphate (NFpP) cathode. The performance of the Na/NVP/C and Na/NFpP cells are evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic cycling at 60 °C and room temperature. The results reported herein indicate the performance improvement in terms of cycling stability, with high Coulombic efficiency at 60 °C granted by the OIPC and ionic liquid mixtures, compared to a conventional organic solvent electrolyte.

Single-ion conducting solid electrolytes are gaining tremendous attention as essential materials for solid-state batteries, but a comprehensive understanding of the factors that dictate high ion mobility remains elusive. Here, for the first time, we use a combination of the Maximum Entropy Method analysis of room-temperature neutron powder diffraction data, ab initio molecular dynamics, and joint-time correlation analysis to demonstrate that the dynamic response of the anion framework plays a significant role in the new class of fast ion conductors, Na 11 Sn 2 PnX 12 (Pn = P, Sb; X = S, Se). Facile [PX 4 ] 3- anion rotation exists in superionic Na 11 Sn 2 PS 12 and Na 11 Sn 2 PSe 12 , but greatly hindered [SbS 4 ] 3- rotational dynamics are observed in their less conductive analogue, Na 11 Sn 2 SbS 12 . Along with introducing dynamic frustration in the energy landscape, the fluctuation caused by [PX 4 ] 3- anion rotation is firmly proved to couple to and facilitate long-range cation mobility, by transiently widening the bottlenecks for Na + -ion diffusion. The combined analysis described here resolves the role of the long-debated paddle-wheel mechanism, and is the first direct evidence that anion rotation significantly enhances cation migration in rotor phases. The joint-time correlation analysis developed in our work can be broadly applied to analyze coupled cation-anion interplay where traditional transition state theory does not apply. These findings deliver important insights into the fundamentals of ion transport in solid electrolytes. Invoking anion rotational dynamics provides a vital strategy to enhance cation conductivity and serves as an additional and universal design principle for fast ion conductors.

We report on a new family of argyrodite lithium superionic conductors, as solid solutions Li 6+ x M x Sb 1- x S 5 I (M = Si, Ge, Sn), that exhibit superionic conductivity. These represent the first antimony argyrodites to date. Exploration of the series using a combination of single crystal X-ray and synchrotron/neutron powder diffraction, combined with impedance spectroscopy, reveals that an optimal degree of substitution ( x ), and substituent induces slight S 2- /I - anion site disorder-but more importantly drives Li + cation site disorder. The additional, delocalized Li-ion density is located in new high energy lattice sites that provide intermediate interstitial positions (local minima) for Li + diffusion and activate concerted ion migration, leading to a low activation energy of 0.25 eV. Excellent room temperature ionic conductivity of 14.8 mS·cm -1 is exhibited for cold-pressed pellets-up to 24 mS·cm -1 for sintered pellets-among the highest values reported to date. This enables all-solid-state battery prototypes that exhibit promising properties. Furthermore, even at -78 °C, suitable bulk ionic conductivity of the electrolyte is retained (0.25 mS·cm -1 ). Selected thioantimonate iodides demonstrate good compatibility with Li metal, sustaining over 1000 h of Li stripping/plating at current densities up to 0.6 mA·cm -2 . The significantly enhanced Li ion conduction and lowered activation energy barrier with increasing site disorder reveals an important strategy toward the development of superionic conductors.

One of the very challenging aspects of Li-S battery development is the fabrication of a sulfur electrode with high areal loading using conventional Li-ion binders. Herein, we report a new multifunctional polymeric binder, synthesized by the free-radical cross-linking polymerization of [2-(acryloyloxy)ethyl]trimethylammonium chloride (AETMAC) and ethylene glycol diacrylate (EGDA) to form poly(AETMAC- co-EGDA), that not only helps to confine the soluble polysulfide species but also has the desired mechanical properties to allow stable cycling of high-sulfur loading cathodes. Through a combination of spectroscopic and electrochemical studies, we elucidate the chemical interactions that inhibit polysulfide shuttling. We also show that extensive cross-linkage enables this polymeric binder to exhibit a low degree of swelling as well as high tensile modulus and toughness. These attributes are essential to maintain the architectural integrity of the sulfur cathode during extended cycling. Using this material, Li-S cells with a high-sulfur loading (6.0 mg cm -2 ) and a low-intermediate electrolyte/sulfur ratio (7 μL:1 mg) achieve an areal capacity of 5.4 mA h cm -2 and can be (dis)charged for 300 cycles with stable reversible redox behavior after the initial cycles.

Developing high-performance all-solid-state batteries is contingent on finding solid electrolyte materials with high ionic conductivity and ductility. Here we report new halide-rich solid solution phases in the argyrodite Li 6 PS 5 Cl family, Li 6-x PS 5-x Cl 1+x , and combine electrochemical impedance spectroscopy, neutron diffraction, and 7 Li NMR MAS and PFG spectroscopy to show that increasing the Cl - /S 2- ratio has a systematic, and remarkable impact on Li-ion diffusivity in the lattice. The phase at the limit of the solid solution regime, Li 5.5 PS 4.5 Cl 1.5 , exhibits a cold-pressed conductivity of 9.4±0.1 mS cm -1 at 298 K (and 12.0±0.2 mS cm -1 on sintering)-almost four-fold greater than Li 6 PS 5 Cl under identical processing conditions and comparable to metastable superionic Li 7 P 3 S 11 . Weakened interactions between the mobile Li-ions and surrounding framework anions incurred by substitution of divalent S 2- for monovalent Cl - play a major role in enhancing Li + -ion diffusivity, along with increased site disorder and a higher lithium vacancy population., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Lithium metal batteries are capable of revolutionizing the battery marketplace for electrical vehicles, owing to the high capacity and low voltage offered by Li metal. Current exploitation of Li metal electrodes, however, is plagued by their exhaustive parasitic reactions with liquid electrolytes and dendritic growth, which pose concerns to both cell performance and safety. We demonstrate that a hybrid membrane, both elastic and Li + -ion percolating, can stabilize Li plating/stripping with high Coulombic efficiency. The compact packing of a Li + solid electrolyte phase offers percolated Li + -conducting channels and the consequent infiltration of an elastic polymer endows membrane flexibility to accommodate volume changes. The protected electrode allows Li plating with 95.8% efficiency for 200 cycles and stable operation of an LTO|Li cell for 2,000 cycles. This rationally structured membrane represents an interface engineering approach toward stabilized Li metal electrodes., Competing Interests: The authors declare no conflict of interest.

Lithium-oxygen (Li-O 2 ) batteries have attracted much attention owing to the high theoretical energy density afforded by the two-electron reduction of O 2 to lithium peroxide (Li 2 O 2 ). We report an inorganic-electrolyte Li-O 2 cell that cycles at an elevated temperature via highly reversible four-electron redox to form crystalline lithium oxide (Li 2 O). It relies on a bifunctional metal oxide host that catalyzes O-O bond cleavage on discharge, yielding a high capacity of 11 milliampere-hours per square centimeter, and O 2 evolution on charge with very low overpotential. Online mass spectrometry and chemical quantification confirm that oxidation of Li 2 O involves transfer of exactly 4 e - /O 2 This work shows that Li-O 2 electrochemistry is not intrinsically limited once problems of electrolyte, superoxide, and cathode host are overcome and that coulombic efficiency close to 100% can be achieved., (Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

The dendritic growth of Li metal leads to electrode degradation and safety concerns, impeding its application in building high energy density batteries. Forming a protective layer on the Li surface that is electron-insulating, ion-conducting, and maintains an intimate interface is critical. We herein demonstrate that Li plating is stabilized by a biphasic surface layer composed of a lithium-indium alloy and a lithium halide, formed in situ by the reaction of an electrolyte additive with Li metal. This stabilization is attributed to the fast lithium migration though the alloy bulk and lithium halide surface, which is enabled by the electric field across the layer that is established owing to the electron-insulating halide phase. A greatly stabilized Li-electrolyte interface and dendrite-free plating over 400 hours in Li|Li symmetric cells using an alkyl carbonate electrolyte is demonstrated. High energy efficiency operation of the Li 4 Ti 5 O 12 (LTO)|Li cell over 1000 cycles is achieved., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

While olivine LiFePO 4 shows amongst the best electrochemical properties of Li-ion positive electrodes with respect to rate behavior owing to facile Li + migration pathways in the framework, replacing the [PO 4 ] 3- polyanion with a silicate [SiO 4 ] 4- moiety in olivine is desirable. This could allow additional alkali content and hence electron transfer, and increase the capacity. Herein we explore the possibility of a strategy toward new cathode materials and demonstrate the first stabilization of a lithium transition metal silicate (as a pure silicate) in the olivine structure type. Using LiInSiO 4 and LiScSiO 4 as the parent materials, transition metal (Mn, Fe, Co) substitutions on the In/Sc site were investigated by computational modeling via atomic scale simulation. Transition metal substitution was found to be only favorable for Co, a finding confirmed by the successful solid state synthesis of olivine Li x In y Co 2-x-y SiO 4 . Stabilization of the structure was achieved by entropy provided by cation disorder.

The lithium-sulfur battery has long been seen as a potential next generation battery chemistry for electric vehicles owing to the high theoretical specific energy and low cost of sulfur. However, even state-of-the-art lithium-sulfur batteries suffer from short lifetimes due to the migration of highly soluble polysulfide intermediates and exhibit less than desired energy density due to the required excess electrolyte. The use of sparingly solvating electrolytes in lithium-sulfur batteries is a promising approach to decouple electrolyte quantity from reaction mechanism, thus creating a pathway toward high energy density that deviates from the current catholyte approach. Herein, we demonstrate that sparingly solvating electrolytes based on compact, polar molecules with a 2:1 ratio of a functional group to lithium salt can fundamentally redirect the lithium-sulfur reaction pathway by inhibiting the traditional mechanism that is based on fully solvated intermediates. In contrast to the standard catholyte sulfur electrochemistry, sparingly solvating electrolytes promote intermediate- and short-chain polysulfide formation during the first third of discharge, before disproportionation results in crystalline lithium sulfide and a restricted fraction of soluble polysulfides which are further reduced during the remaining discharge. Moreover, operation at intermediate temperatures ca. 50 °C allows for minimal overpotentials and high utilization of sulfur at practical rates. This discovery opens the door to a new wave of scientific inquiry based on modifying the electrolyte local structure to tune and control the reaction pathway of many precipitation-dissolution chemistries, lithium-sulfur and beyond.

The step-change in gravimetric energy density needed for electrochemical energy storage devices to power unmanned autonomous vehicles, electric vehicles, and enable low-cost clean grid storage is unlikely to be provided by conventional lithium ion batteries. Lithium-sulfur batteries comprising lightweight elements provide a promising alternative, but the associated polysulfide shuttle in typical ether-based electrolytes generates loss in capacity and low coulombic efficiency. The first new electrolyte based on a unique combination of a relatively hydrophobic sulfonamide solvent and a low ion-pairing salt, which inhibits the polysulfide shuttle, is presented. This system behaves as a sparingly solvating electrolyte at slightly elevated temperatures, where it sustains reversible capacities as high as 1200-1500 mAh g -1 over a wide range of current density (2C-C/5, respectively) when paired with a lithium metal anode, with a coulombic efficiency of >99.7 % in the absence of LiNO 3 additive., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Diffusion coefficients (D) for both Li + and Mg 2+ in Ti 2 S 4 were measured using the galvanic intermittent titration technique (GITT) as a function of both ion concentration (x) and temperature. During discharge at 60 °C, D Li descends gradually from 2 × 10 -8 cm 2 /s at x Li ≈ 0 to 2 × 10 -9 cm 2 /s at x Li ≈ 1.9. In contrast, D Mg decreases sharply from 2 × 10 -8 to 1 × 10 -12 cm 2 /s by x Mg ≈ 0.8. This kinetic factor limits the maximum practical discharge capacity of Mg x Ti 2 S 4 . The difference in behavior vis a vis Li + implies that either increasing Mg 2+ occupation of the tetrahedral site at x Mg > 0.6 and/or interactions between diffusing cations play a larger role in mediating the diffusion of divalent compared to monovalent cations. Diffusion activation energies (E a ) extracted from the temperature-dependent data revealed that E a,Mg (540 ± 80 meV) is about twice that of E a,Li (260 ± 50 meV), explaining the poorer electrochemical performance of Mg x Ti 2 S 4 at room temperature.

The complex surface chemistry that dictates the interaction between MXene and polysulfides - the formation of thiosulfate via consumption of -OH surface groups, followed by Lewis acid-base interaction between the exposed Ti atoms and polysulfides - is unravelled. Interweaving carbon nanotubes between the MXene layers creates a porous, conductive network with high polysulfide adsorptivity, enabling sulfur hosts with excellent performance even at high loading (5.5 mg cm -2 )., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The well-known all phenyl complex (APC) electrolyte for magnesium batteries is studied for the first time at high temperature using tetraglyme as a solvent. Combined with a molybdenum current collector, this enables the examination of positive electrode materials for Mg batteries at temperatures as high as 180 °C and up to 2 V vs. Mg, allowing discovery of the auspicious properties of CuS as a conversion cathode.

Advanced large-scale electrochemical energy storage requires cost-effective battery systems with high energy densities. Aprotic sodium-oxygen (Na-O2) batteries offer advantages, being comprised of low-cost elements and possessing much lower charge overpotential and higher reversibility compared to their lithium-oxygen battery cousins. Although such differences have been explained by solution-mediated superoxide transport, the underlying nature of this mechanism is not fully understood. Water has been suggested to solubilize superoxide via formation of hydroperoxyl (HO2), but direct evidence of these HO2 radical species in cells has proven elusive. Here, we use ESR spectroscopy at 210 K to identify and quantify soluble HO2 radicals in the electrolyte-cold-trapped in situ to prolong their lifetime-in a Na-O2 cell. These investigations are coupled to parallel SEM studies that image crystalline sodium superoxide (NaO2) on the carbon cathode. The superoxide radicals were spin-trapped via reaction with 5,5-dimethyl-pyrroline N-oxide at different electrochemical stages, allowing monitoring of their production and consumption during cycling. Our results conclusively demonstrate that transport of superoxide from cathode to electrolyte leads to the nucleation and growth of NaO2, which follows classical mechanisms based on the variation of superoxide content in the electrolyte and its correlation with the crystallization of cubic NaO2. The changes in superoxide content upon charge show that charge proceeds through the reverse solution process. Furthermore, we identify the carbon-centered/oxygen-centered alkyl radicals arising from attack of these solubilized HO2 species on the diglyme solvent. This is the first direct evidence of such species, which are likely responsible for electrolyte degradation.

Intense interest in the Li-O2 battery system over the past 5 years has led to a much better understanding of the various chemical processes involved in the functioning of this battery system. However, detailed decomposition of the nanostructured Li2O2 product, held at least partially responsible for the limited reversibility and poor rate performance, is hard to measure operando under realistic electrochemical conditions. Here, we report operando nanobeam X-ray diffraction experiments that enable monitoring of the decomposition of individual Li2O2 grains in a working Li-O2 battery. Platelet-shaped crystallites with aspect ratios between 2.2 and 5.5 decompose preferentially via the more reactive (001) facets. The slow and concurrent decomposition of individual Li2O2 crystallites indicates that the Li2O2 decomposition rate limits the charge time of these Li-O2 batteries, highlighting the importance of using redox mediators in solution to charge Li-O2 batteries.

A comprehensive experimental and theoretical analysis of the isothermal transport of species for the two model ternary-electrolytes with LiTFSI-Li2S4/dioxolane (DOL)-dimethoxyethane (DME) and LiTFSI-Li2S6/DOL-DME formulations is presented. An unambiguous picture of the polysulfide's mobility is set forth after a detailed investigation of the macroscopic transference number and diffusion coefficients. The new findings of incongruent diffusion for Li2S4 species and high significance of cross-term diffusion coefficients reformulate a fledgling view of the prevalent redox-shuttle phenomena. The practical implications of this complex mechanism are discussed in detail.

Although Na-O2 batteries have a low overpotential and good capacity retention, degradation reactions of glyme-based electrolytes are the primary reason for inefficiency in cell performance. The discharge capacity is accounted for through analysis of the side-products. Although sodium superoxide is the primary product (90 % theoretical), quantitative and qualitative evaluation of the side-products (using (1) H NMR, iodometric titration, and on-line mass spectrometry) shows the presence of sodium acetate (∼3.5 %), and three-fold less sodium formate, methoxy (oxo)acetic anhydride, and sodium carbonate. Our reaction mechanism proposes two paths for their formation. Because the side-products are not fully removed during oxidation, they accumulate on the cathode upon cycling. Resting the cell at open circuit potential during discharge results in consumption of the superoxide through the reaction with diglyme, which greatly increases the fraction of side products, as also confirmed by ex situ reaction studies. These findings have implications in the search for more stable electrolytes., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Lithium-sulfur batteries are attractive electrochemical energy storage systems due to their high theoretical energy density and very high natural abundance of sulfur. However, practically, Li-S batteries suffer from short cycling life and low sulfur utilization, particularly in the case of high-sulfur-loaded cathodes. Here, we report on a light-weight nanoporous graphitic carbon nitride (high-surface-area g-C3N4) that enables a sulfur electrode with an ultralow long-term capacity fade rate of 0.04% per cycle over 1500 cycles at a practical C/2 rate. More importantly, it exhibits good high-sulfur-loading areal capacity (up to 3.5 mAh cm(-2)) with stable cell performance. We demonstrate the strong chemical interaction of g-C3N4 with polysulfides using a combination of spectroscopic experimental studies and first-principles calculations. The 53.5% concentration of accessible pyridinic nitrogen polysulfide adsorption sites is shown to be key for the greatly improved cycling performance compared to that of N-doped carbons.

The lithium-sulfur battery is the subject of much recent attention, but the polysulfide shuttle remains problematic owing to dissolution of intermediate polysulfide species in the electrolyte. Despite much effort in limiting such dissolution via physical confinement or chemical binding to the sulfur host materials, the high cost and complicated preparation of the related materials present an impediment to their practical application. Here we demonstrate a simple methodology to fabricate an effective nanometric MnO2 shell on sulfur particles, which is realized by an in situ redox reaction between sulfur and KMnO4 under ambient conditions. The bifunctional MnO2 shell provides physical confinement and chemical interaction and shows excellent efficiency for trapping the polysulfides. MnO2 sheets crystallized onto nanosized sulfur particles result in cathodes with a very low fading rate of 0.039% per cycle over 1700 cycles in Li-S cells. Moreover, directly crystallizing nanometric shells of MnO2 on micrometer-sized sublimed sulfur delivers stable Li-S cycling performance over 800 cycles. Since both sulfur and KMnO4 are inexpensive and widely used, the production of MnO2-coated sulfur composites can be easily scaled-up for practical applications of Li-S batteries in light of the very simple reaction processes involved.

The major advantage of Mg batteries relies on their promise of employing an Mg metal negative electrode, which offers much higher energy density compared to graphitic carbon. However, the strong coulombic interaction of Mg 2+ ions with anions leads to their sluggish diffusion in the solid state, which along with a high desolvation energy, hinders the development of positive electrode materials. To circumvent this limitation, Mg metal negative electrodes can be used in hybrid systems by coupling an Li + insertion cathode through a dual salt electrolyte. Two "high voltage" Prussian blue analogues (average 2.3 V vs Mg/Mg 2+ ; 3.0 V vs Li/Li + ) are investigated as cathode materials and the influence of structural water is shown. Their electrochemical profiles, presenting two voltage plateaus, are explained based on the two unique Fe bonding environments. Structural water has a beneficial impact on the cell voltage. Capacities of 125 mAh g -1 are obtained at a current density of 10 mA g -1 (≈C/10), while stable performance up to 300 cycles is demonstrated at 200 mA g -1 (≈2C). The hybrid cell design is a step toward building a safe and high density energy storage system.

Owing to its high theoretical specific energy, the Li-oxygen battery is one of the fundamentally most promising energy storage systems, but also one of the most challenging. Poor rechargeability, involving the oxidation of insoluble and insulating lithium peroxide (Li2O2), has remained the "Achilles' heel" of this electrochemical energy storage system. We report here on a new redox mediator tris[4-(diethylamino)phenyl]amine (TDPA), that-at 3.1 V-exhibits the lowest and closest potential redox couple compared to the equilibrium voltage of the Li-oxygen cell of those reported to date, with a second couple also at a low potential of 3.5 V. We show it is a soluble "catalyst" capable of lowering the Li2O2 charging potential by >0.8 V without requiring direct electrical contact of the peroxide and that it also facilitates high discharge capacities. Its chemical and electrochemical stability, fast diffusion kinetics, and two dynamic redox potentials represent a significant advance in oxygen-evolution catalysis. It enables Li-O2 cells that can be recharged more than 100 cycles with average round-trip efficiencies >80%, opening a new avenue for practical Li-oxygen batteries.

A sulfur electrode exhibiting strong polysulfide chemisorption using a porous N, S dual-doped carbon is reported. The synergistic functionalization from the N and S heteroatoms dramatically modifies the electron density distribution and leads to much stronger polysulfide binding. X-ray photoelectron spectroscopy studies combined with ab initio calculations reveal strong Li(+) -N and Sn (2-) -S interactions. The sulfur electrodes exhibit an ultralow capacity fading of 0.052% per cycle over 1100 cycles., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report the fabrication of high-performance, self-standing composite sp(2)-carbon supercapacitor electrodes using single-walled carbon nanotubes (CNTs) as conductive binder. The 3-D mesoporous mesh architecture of CNT-based composite electrodes grants unimpaired ionic transport throughout relatively thick films and allows superior performance compared to graphene-based devices at an ac line frequency of 120 Hz. Metrics of 601 μF/cm(2) with a -81° phase angle and a rate capability (RC) time constant of 199 μs are obtained for thin carbon films. The free-standing carbon films were obtained from a chlorosulfonic acid dispersion and interfaced to stainless steel current collectors with various surface treatments. CNT electrodes were able to cycle at 200 V/s and beyond, still showing a characteristic parallelepipedic cyclic votammetry shape at 1 kV/s. Current densities are measured in excess of 6400 A/g, and the electrodes retain more than 98% capacity after 1 million cycles. These promising results are attributed to a reduction of series resistance in the film through the CNT conductive network and especially to the surface treatment of the stainless steel current collector.

The development of nonaqueous Li-oxygen batteries, which relies on the reversible reaction of Li + O2 to give lithium peroxide (Li2O2), is challenged by several factors, not the least being the high charging voltage that results when carbon is typically employed as the cathode host. We report here on the remarkably low 3.2 V potential for Li2O2 oxidation on a passivated nanostructured metallic carbide (Mo2C), carbon-free cathode host. Online mass spectrometry coupled with X-ray photoelectron spectroscopy unequivocally demonstrates that lithium peroxide is simultaneously oxidized together with the Li(x)MoO3-passivated conductive interface formed on the carbide, owing to their close redox potentials. The process rejuvenates the surface on each cycle upon electrochemical charge by releasing Li(x)MoO3 into the electrolyte, explaining the low charging potential.

In the search for improved energy storage, rechargeable metal-oxygen batteries are very attractive owing to their reliance on molecular oxygen, which forms oxides on discharge that decompose reversibly on charge. Much focus has been directed at aprotic Li-O2 cells, but the aprotic Na-O2 system is of equal interest because of its better reversibility. We report here on the critical role and mechanism of phase-transfer catalysis in Na-O2 batteries. We find that it is solely responsible for the growth and dissolution of micrometre-sized cubic NaO2 crystals and for the reversible cell capacity. In the absence of phase-transfer catalysis, quasi-amorphous NaO2 films are formed and cells exhibit negligible capacity. Electrochemical investigations provide a measure of the transportation of superoxide from the carbon electrode to the electrolyte phase by the phase transfer catalyst. This leads to a new understanding of the mechanism of Na-O2 batteries that, significantly, extends to Li-O2 cells and explains their different behaviour.

Lithium-sulfur batteries are amongst the most promising candidates to satisfy emerging energy-storage demands. Suppression of the polysulfide shuttle while maintaining high sulfur content is the main challenge that faces their practical development. Here, we report that 2D early-transition-metal carbide conductive MXene phases-reported to be impressive supercapacitor materials-also perform as excellent sulfur battery hosts owing to their inherently high underlying metallic conductivity and self-functionalized surfaces. We show that 70 wt % S/Ti2 C composites exhibit stable long-term cycling performance because of strong interaction of the polysulfide species with the surface Ti atoms, demonstrated by X-ray photoelectron spectroscopy studies. The cathodes show excellent cycling performance with specific capacity close to 1200 mA h g(-1) at a five-hour charge/discharge (C/5) current rate. Capacity retention of 80 % is achieved over 400 cycles at a two-hour charge/discharge (C/2) current rate., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Energy storage technology has received significant attention for portable electronic devices, electric vehicle propulsion, bulk electricity storage at power stations, and load leveling of renewable sources, such as solar energy and wind power. Lithium ion batteries have dominated most of the first two applications. For the last two cases, however, moving beyond lithium batteries to the element that lies below-sodium-is a sensible step that offers sustainability and cost-effectiveness. This requires an evaluation of the science underpinning these devices, including the discovery of new materials, their electrochemistry, and an increased understanding of ion mobility based on computational methods. The Review considers some of the current scientific issues underpinning sodium ion batteries., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)