All-solid-state Li-ion batteries (ASSBs), considered to be potential next-generation energy storage devices, require solid electrolytes (SEs). Thiophosphate-based materials are popular, but these ...sulfides exhibit poor anodic stability and require specialty coatings on lithium metal oxide cathodes. Moreover, electrode designs aimed at high energy density are limited by their narrow electrochemical stability window. Here, we report new mixed-metal halide Li3–x M1–x Zr x Cl6 (M = Y, Er) SEs with high ionic conductivityup to 1.4 mS cm–1 at 25 °Cthat are stable to high voltage. Substitution of M (M = Y, Er) by Zr is accompanied by a trigonal-to-orthorhombic phase transition, and structure solution using combined neutron and single-crystal X-ray diffraction methods reveal a new framework. The employment of >4 V-class cathode materials without any protective coating is enabled by the high electrochemical oxidation stability of these halides. An ASSB showcasing their electrolyte properties exhibits very promising cycling stability up to 4.5 V at room temperature.
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 Li6PS5Cl family, Li6−xPS5−xCl1+x, and combine electrochemical impedance spectroscopy, neutron diffraction, and 7Li 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, Li5.5PS4.5Cl1.5, 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 Li6PS5Cl under identical processing conditions and comparable to metastable superionic Li7P3S11. 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.
At the limit of the solid solution regime: Li5.5PS4.5Cl1.5 exhibits a high Li+ ion conductivity of 9.4 mS cm−1 at 298 K with an activation energy of 0.29 eV, and a high Li+ diffusion coefficient of 1.01×10−11 m2 s−1 determined by NMR transport measurements, suggesting its excellent prospect as a solid Li‐ion electrolyte.
Owing to the ever‐increasing safety concerns about conventional lithium‐ion batteries, whose applications have expanded to include electric vehicles and grid‐scale energy storage, batteries with ...solidified electrolytes that utilize nonflammable inorganic materials are attracting considerable attention. In particular, owing to their superionic conductivities (as high as ≈10−2 S cm−1) and deformability, sulfide materials as the solid electrolytes (SEs) are considered the enabling material for high‐energy bulk‐type all‐solid‐state batteries. Herein the authors provide a brief review on recent progress in sulfide Li‐ and Na‐ion SEs for all‐solid‐state batteries. After the basic principles in designing SEs are considered, the experimental exploration of multicomponent systems and ab initio calculations that accelerate the search for stronger candidates are discussed. Next, other issues and challenges that are critical for practical applications, such as instability in air, electrochemical stability, and compatibility with active materials, are discussed. Then, an emerging progress in liquid‐phase synthesis and solution process of SEs and its relevant prospects in ensuring intimate ionic contacts and fabricating sheet‐type electrodes is highlighted. Finally, an outlook on the future research directions for all‐solid‐state batteries employing sulfide superionic conductors is provided.
Sulfide Li+ and Na+ superionic conductors are considered to be enabling materials in safe and high‐energy all‐solid‐state batteries. This progress report provides a brief review on superionic conductor solid electrolytes through both experimental and theoretical approaches on ionic conductivity, electrochemical stability, interface compatibility, and air‐stability. Further, design strategies, practical considerations, and emerging solution processes of solid electrolytes are discussed.
Development of new sulfide Li+ superionic conductors with mechanical sinterability is the key to the success of all-solid-state lithium batteries. While phosphorus-containing sulfide superionic ...conductor materials have been widely investigated, phosphorus-free materials showing good air-stability have been overlooked. Herein, the Li+ dynamics in Sb-substituted Li4SnS4 showing a high Li+ conductivity of max. 0.85 mS cm−1 at 30 °C and excellent dry-air stability as well as negligible H2S evolution is described. Structural analysis with X-ray and neutron diffraction reveals that Sb-substitution renders an expansion of the lattice volume and formation of Li vacancies. Additionally, 1D-preferable 3D Li+ diffusion channels in Li4-xSn1-xSbxS4 are disclosed. The fast Li+ diffusion in Li4-xSn1-xSbxS4 is rationalized by complementary analysis using AC impedance measurements, bond valence energy landscape calculation, and 7Li nuclear magnetic resonance spectroscopy. Excellent electrochemical performances of TiS2 electrodes employing Li3.85Sn0.85Sb0.15S4 in all-solid-state batteries are demonstrated.
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•Sb-substituted Li4SnS4 shows a maximum Li+ conductivity of 0.85 mS cm−1 at 30 °C.•Excellent dry-air stability and negligible H2S evolution are confirmed.•1D-preferable 3D Li+ diffusion channels disclosed by neutron diffraction analysis.•Performance of all-solid-state Li-ion batteries using Li3.85Sn0.85Sb0.15S4.
The wet‐chemical processability of sulfide solid electrolytes (SEs) provides intriguing opportunities for all‐solid‐state batteries. Thus far, sulfide SEs are wet‐prepared either from solid ...precursors suspended in solvents (suspension synthesis) or from homogeneous solutions using SEs (solution process) with restricted composition spaces. Here, a universal solution synthesis method for preparing sulfide SEs from precursors, not only Li2S, P2S5, LiCl, and Na2S, but also metal sulfides (e.g., GeS2 and SnS2), fully dissolved in an alkahest: a mixture solvent of 1,2‐ethylenediamine (EDA) and 1,2‐ethanedithiol (EDT) (or ethanethiol). Raman spectroscopy and theoretical calculations reveal that the exceptional dissolving power of EDA–EDT toward GeS2 is due to the nucleophilicity of the thiolate anions that is strong enough to dissociate the GeS bonds. Solution‐synthesized Li10GeP2S12, Li6PS5Cl, and Na11Sn2PS12 exhibit high ionic conductivities (0.74, 1.3, and 0.10 mS cm−1 at 30 °C, respectively), and their application for all‐solid‐state batteries is successfully demonstrated.
The universal solution synthesis of sulfide solid electrolytes is first demonstrated. The alkahest solvent, 1,2‐ethylenediamine–1,2‐ethanedithiol, fully dissolves not only Li2S (or Na2S), P2S5, and LiCl, but also metal sulfides (e.g., GeS2 and SnS2), forming homogeneous solid electrolyte solutions. Solution‐synthesized Li10GeP2S12, Li6PS5Cl, and Na11Sn2PS12 exhibit high ionic conductivities, and their applicability to all‐solid‐state batteries is successfully demonstrated.
For mass production of all‐solid‐state lithium‐ion batteries (ASLBs) employing highly Li+ conductive and mechanically sinterable sulfide solid electrolytes (SEs), the wet‐slurry process is ...imperative. Unfortunately, the poor chemical stability of sulfide SEs severely restrict available candidates for solvents and in turn polymeric binders. Moreover, the binders interrupt Li+‐ionic contacts at interfaces, resulting in the below par electrochemical performance. In this work, a new scalable slurry fabrication protocol for sheet‐type ASLB electrodes made of Li+‐conductive polymeric binders is reported. The use of intermediate‐polarity solvent (e.g., dibromomethane) for the slurry allows for accommodating Li6PS5Cl and solvate‐ionic‐liquid‐based polymeric binders (NBR‐Li(G3)TFSI, NBR: nitrile−butadiene rubber, G3: triethylene glycol dimethyl ether, LiTFSI: lithium bis(trifluoromethanesulfonyl)imide) together without suffering from undesirable side reactions or phase separation. The LiNi0.6Co0.2Mn0.2O2 and Li4Ti5O12 electrodes employing NBR‐Li(G3)TFSI show high capacities of 174 and 160 mA h g−1 at 30 °C, respectively, which are far superior to those using conventional NBR (144 and 76 mA h g−1). Moreover, high areal capacity of 7.4 mA h cm−2 is highlighted for the LiNi0.7Co0.15Mn0.15O2 electrodes with ultrahigh mass loading of 45 mg cm−2. The facilitated Li+‐ionic contacts at interfaces paved by NBR‐Li(G3)TFSI are evidenced by the complementary analysis from electrochemical and 7Li nuclear magnetic resonance measurements.
A new slurry‐fabricable solvate ionic liquid (SIL)‐based Li+‐conductive polymeric binder for all‐solid‐state lithium‐ion batteries is developed. Sheet‐type electrodes are tailored from a slurry using solvent with intermediate polarity (e.g., dibromomethane) which enables the accommodation of sulfide solid electrolytes and SIL together without suffering from any side reactions or phase separation. The resulting electrodes significantly outperform those made of conventional insulating binders.
All‐solid‐state sodium‐ion batteries that operate at room temperature are attractive candidates for use in large‐scale energy storage systems. However, materials innovation in solid electrolytes is ...imperative to fulfill multiple requirements, including high conductivity, functional synthesis protocols for achieving intimate ionic contact with active materials, and air stability. A new, highly conductive (1.1 mS cm−1 at 25 °C, Ea=0.20 eV) and dry air stable sodium superionic conductor, tetragonal Na3SbS4, is described. Importantly, Na3SbS4 can be prepared by scalable solution processes using methanol or water, and it exhibits high conductivities of 0.1–0.3 mS cm−1. The solution‐processed, highly conductive solidified Na3SbS4 electrolyte coated on an active material (NaCrO2) demonstrates dramatically improved electrochemical performance in all‐solid‐state batteries.
Dissolve and solidify: A new and highly conductive (1.1 mS cm−1), dry air‐stable sodium superionic conductor, tetragonal Na3SbS4, was developed. Importantly, its solution processability using methanol or water allows direct coating onto active materials. The solution‐processed highly conductive (0.1–0.3 mS cm−1) solidified Na3SbS4 coating on NaCrO2 solves the poor ionic contact problem in all‐solid‐state sodium‐ion batteries.
A new, highly conductive (4.1 × 10−4 S cm−1 at 30 °C), highly deformable, and dry‐air‐stable glass 0.4LiI‐0.6Li4SnS4 is prepared using a homogeneous methanol solution. The solution process enables ...the wetting of any exposed surface of the active materials with highly conductive solidified electrolytes (0.4LiI‐0.6Li4SnS4), resulting in considerable improvements in the electrochemical performance of these electrodes over conventional mixture electrodes.
The liquid‐phase synthesis (LS) of sulfide solid electrolytes (SEs) has promising potential for mass production of practical all‐solid‐state Li batteries (ASLBs). However, their accessible SE ...compositions are mostly metal‐free. Moreover, liquid‐phase‐synthesized‐SEs (LS‐SEs) suffer from high electronic conductivity due to carbon impurities, resulting in below‐par electrochemical performance of ASLBs. Here, the LS of highly deformable and air‐stable Li3+xP1‐xSnxS4 (0.19 mS cm−1) using 1,2‐ethylene diamine‐1,2‐ethanedithiol with tetrahydrofuran is reported. A low heat‐treatment temperature (260 °C) prevents the carbonization of organic residues. Importantly, a remarkable enhancement in the deformability of LS‐SEs compared to that of conventional solid‐state‐synthesized SEs (SS‐SEs) is identified for the first time. LiNi0.7Co0.15Mn0.15O2 electrodes employing LS‐SEs in ASLBs significantly outperform those using SS‐SEs, notably when assembled under a low fabricating pressure (148 vs 370 MPa, e.g., capacity loss: 2 vs 41 mA h g−1) or tested under a low operating pressure (12 or 3 MPa), which is attributed to reduced electrochemo‐mechanical effects. Finally, when employing SEs that are exposed to air (dew point of −20 °C), LiNi0.7Co0.15Mn0.15O2 electrodes employing SEs with Sn‐substituted composition or prepared by LS exhibit significantly better capacity retention than conventional SEs with Sn‐free composition or prepared by SS (e.g., 92.2% for LS‐Li3.2P0.8Sn0.2S4 vs 32.5% for SS‐Li3PS4).
Liquid‐phase‐derived highly deformable and air‐stable Sn‐substituted Li3PS4 for all‐solid‐state batteries is reported. Marginal organic residues at the nanoscale for liquid‐phase‐synthesized solid electrolytes remarkably enhance deformability, resulting in significantly improved performance of LiNi0.7Co0.15Mn0.15O2 electrodes compared to conventional solid‐state‐synthesized solid electrolytes, particularly when tailored at low fabricating pressure or tested under low operating pressure.
Sulfide Na‐ion solid electrolytes (SEs) are key to enable room‐temperature operable all‐solid‐state Na‐ion batteries that are attractive for large‐scale energy storage applications. To date, few ...sulfide Na‐ion SEs have been developed and most of the SEs developed contain P and suffer from poor chemical stability. Herein, discovery of a new structural class of tetragonal Na4−xSn1−xSbxS4 (0.02 ≤ x ≤ 0.33) with space group I41/acd is described. The evolution of a new phase, distinctly different from Na4SnS4 or Na3SbS4, allows fast ionic conduction in 3D pathways (0.2–0.5 mS cm−1 at 30 °C). Moreover, their excellent air stability and reversible dissolution in water and precipitation are highlighted. Specifically, TiS2/Na–Sn all‐solid‐state Na‐ion batteries using Na3.75Sn0.75Sb0.25S4 demonstrates high capacity (201 mA h (g of TiS2)−1) with excellent reversibility.
A new structural class of Na‐ion solid electrolytes Na4−xSn1−xSbxS4 (0.02 ≤ x ≤ 0.33), distinctly different from Na4SnS4 or Na3SbS4, is discovered. The new structure is fully identified by ab initio X‐ray structural analysis, revealing fast 3D ionic conduction (0.2–0.5 mS cm−1). With excellent air‐stability and aqueous‐solution processability for Na4−xSn1−xSbxS4, a promising electrochemical performance of TiS2/Na–Sn all‐solid‐state batteries is demonstrated.
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