Fast-charging aluminium-chalcogen batteries resistant to dendritic shorting.

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 technology1,2. Here we disclose a bidirectional, rapidly charging aluminium-chalcogen battery operating with a molten-salt electrolyte composed of NaCl-KCl-AlCl3. Formulated with high levels of AlCl3, these chloroaluminate melts contain catenated AlnCl3n+1- species, for example, Al2Cl7-, Al3Cl10- and Al4Cl13-, which with their Al-Cl-Al linkages confer facile Al3+ 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 formulations3-6, and in the choice of a molten-salt electrolyte as opposed to room-temperature ionic liquids that induce high polarization7-12. 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.

Critical Role of Framework Flexibility and Disorder in Driving High Ionic Conductivity in LiNbOCl4.

Understanding Li-ion transport is key for the rational design of superionic solid electrolytes with exceptional ionic conductivities. LiNbOCl4 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 [NbOCl4]- 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 cm2/s at room temperature (σicalc = 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 NbO2Cl4 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.

Energy storage emerging: A perspective from the Joint Center for Energy Storage Research.

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.

Impact of the Chlorination of Lithium Argyrodites on the Electrolyte/Cathode Interface in Solid-State Batteries.

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 Li6 PS5 Cl and Li5.5 PS4.5 Cl1.5 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 Li5.5 PS4.5 Cl1.5 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.

A New Sodium Thioborate Fast Ion Conductor: Na3 B5 S9.

We report a new sodium fast-ion conductor, Na3 B5 S9 , 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 B10 S20 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.

Innovative Approaches to Li-Argyrodite Solid Electrolytes for All-Solid-State Lithium Batteries.

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 Li6.6Si0.6Sb0.5S5I (24 mS·cm-1), Li6.6Ge0.6P0.4S5I (18 mS·cm-1), and Li5.5PS4.5Cl1.5 (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.

Lithium-Oxygen Batteries and Related Systems: Potential, Status, and Future.

The goal of limiting global warming to 1.5 °C requires a drastic reduction in CO2 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-O2 cells but include Na-O2, K-O2, and Mg-O2 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 O2 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-O2 cells.

Fast Ion-Conducting Thioboracite with a Perovskite Topology and Argyrodite-like Lithium Substructure.

We report a new fast ion-conducting lithium thioborate halide, Li6B7S13I, 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.

Elastic and Li-ion-percolating hybrid membrane stabilizes Li metal plating.

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.

Fast Li-Ion Conductivity in Superadamantanoid Lithium Thioborate Halides.

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.

The Role of Metal Substitution in Tuning Anion Redox in Sodium Metal Layered Oxides Revealed by X-Ray Spectroscopy and Theory.

We investigate high-valent oxygen redox in the positive Na-ion electrode P2-Na0.67-x [Fe0.5 Mn0.5 ]O2 (NMF) where Fe is partially substituted with Cu (P2-Na0.67-x [Mn0.66 Fe0.20 Cu0.14 ]O2 , NMFC) or Ni (P2-Na0.67-x [Mn0.65 Fe0.20 Ni0.15 ]O2 , 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 Fe4+ 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.

New Family of Argyrodite Thioantimonate Lithium Superionic Conductors.

We report on a new family of argyrodite lithium superionic conductors, as solid solutions Li6+xMxSb1-xS5I (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 S2-/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.

Coupled Cation-Anion Dynamics Enhances Cation Mobility in Room-Temperature Superionic Solid-State Electrolytes.

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, Na11Sn2PnX12 (Pn = P, Sb; X = S, Se). Facile [PX4]3- anion rotation exists in superionic Na11Sn2PS12 and Na11Sn2PSe12, but greatly hindered [SbS4]3- rotational dynamics are observed in their less conductive analogue, Na11Sn2SbS12. Along with introducing dynamic frustration in the energy landscape, the fluctuation caused by [PX4]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.

Boosting Solid-State Diffusivity and Conductivity in Lithium Superionic Argyrodites by Halide Substitution.

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 Li6 PS5 Cl family, Li6-x PS5-x Cl1+x , and combine electrochemical impedance spectroscopy, neutron diffraction, and 7 Li NMR MAS and PFG spectroscopy to show that increasing the Cl- /S2- ratio has a systematic, and remarkable impact on Li-ion diffusivity in the lattice. The phase at the limit of the solid solution regime, Li5.5 PS4.5 Cl1.5 , 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 Li6 PS5 Cl under identical processing conditions and comparable to metastable superionic Li7 P3 S11 . Weakened interactions between the mobile Li-ions and surrounding framework anions incurred by substitution of divalent S2- for monovalent Cl- play a major role in enhancing Li+ -ion diffusivity, along with increased site disorder and a higher lithium vacancy population.

Stabilizing Lithium Plating by a Biphasic Surface Layer Formed In†Situ.

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 Li4 Ti5 O12 (LTO)|Li cell over 1000 cycles is achieved.

Stabilization of Lithium Transition Metal Silicates in the Olivine Structure.

While olivine LiFePO4 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 [PO4]3- polyanion with a silicate [SiO4]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 LiInSiO4 and LiScSiO4 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 LixInyCo2-x-ySiO4. Stabilization of the structure was achieved by entropy provided by cation disorder.

Inhibiting Polysulfide Shuttle in Lithium-Sulfur Batteries through Low-Ion-Pairing Salts and a Triflamide Solvent.

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 LiNO3 additive.

Direct Evidence of Solution-Mediated Superoxide Transport and Organic Radical Formation in Sodium-Oxygen Batteries.

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.

The emerging chemistry of sodium ion batteries for electrochemical energy storage.

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.

Sulfur cathodes based on conductive MXene nanosheets for high-performance lithium-sulfur batteries.

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.