Universal Solution Synthesis of Sulfide Solid Electrolytes Using Alkahest for All‐Solid‐State Batteries

Abstract

integration to devices, sulfide superionic conductors hold great promise for practical ASSB technologies. [2a,c,j,3-5] Notably, several sulfide solid electrolyte (SE) materials can be synthesized or processed via soft chemistry using liquid solvents, which has become a popular topic in ASSB research. [6] The "wet" preparation for sulfide SEs is classified into three categories (Figure S1, Supporting Information): [6] i) suspension synthesis, ii) solution process, and iii) solution synthesis. In suspension synthesis, SE precursors are partly dissolved in organic solvents (e.g., tetrahydrofuran and acetonitrile) and the reaction proceeds via a suspension state, with organic solvents serving as a medium for soft chemistry. [7] Compared to conventional solid-state synthesis, the suspension synthesis of sulfide SEs has multiple advantages, such as a reduced reaction time and scalable production of SEs or electrodes. [6b,8] In the solution process, the sulfide SEs, not precursors, are dissolved in specific polar solvents, forming a homogeneous solution. Original SEs can be precipitated via the removal of solvents and subsequent heat treatment (HT). The liquefied sulfide SEs for the solution process can be utilized for coating on active materials [9] and the infiltration of porous composite electrodes or separators. [9a,10] In addition, in situ formation of nanocomposite electrodes via solution processing has been reported. [8b,11] All these methods have demonstrated exceptional advantages in forming intimate ionic contacts and alternative production capability of ASSBs.Solution synthesis, in which SE precursors are fully dissolved in solvents and SEs are formed via the removal of solvents, could be ideal because it combines the advantages of both the solution process (i.e., forming a homogeneous solution) and suspension synthesis (i.e., using SE precursors). However, solvents that are known to form homogeneous SE solutions (e.g., ethanol (EtOH) and water) are highly polar and protic, and they readily hydrolyze P 2 S 5 and/or Li 2 S precursors. [6a] This explains the limited types of solution-processable SEs, such as (LiI-) Li 4 SnS 4 using methanol (MeOH) or water, [9a] Li 6 PS 5 Cl (LPSCl) using EtOH, [9c,10] and Na 3 SbS 4 using MeOH or water. [9b] To date, only a few solution syntheses for sulfide SEs have been identified. [12] Notably, all suspension and solution syntheses of SEs thus far have covered only restricted compositions, those based on binary (Li 2 S-P 2 S 5 ) or ternary systems (Li 2 S-P 2 S 5 -LiX),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 Li 2 S, P 2 S 5 , LiCl, and Na 2 S, but also metal sulfides (e.g...

Emerging Halide Superionic Conductors for All-Solid-State Batteries: Design, Synthesis, and Practical Applications

“…Wet-chemical synthesis may be beneficial for the mass production of SEs, thanks to its reduced processing time and efforts for precursor mixing. ,− Solvent-mediated soft chemistry may also create novel metastable materials that would otherwise be inaccessible. ,− For cell fabrication, solution-processing enables direct SE coatings on electrode active materials and also allows the fabrication of sheet-type electrodes and SE membranes with intimate ionic contacts by infiltration. − ,,,− While these techniques have been widely investigated for sulfide SEs, the development of wet syntheses for halide SEs has been limited. Known examples are the synthesis of Li 3 InCl 6 using water, Li 3 YCl 6 using NH 4 Cl as a coordination agent, and Li 3 HoBr 6 using a vacuum-evaporation-assisted (VEA) method. ,− …”

Stabilizing Li4SnS4 Electrolyte from Interface to Bulk Phase with a Gradient Lithium Iodide/Polymer Layer in Lithium Metal Batteries

“…Subsequently, the effect of the PEO–LiI modification layer on the interface morphology and composition distribution between Li metal and LSS electrolyte was analyzed by cryo-TEM (Figure ). In Figure a, Li deposits under the LSS/PEO–LiI electrolyte were random blocks rather than Li spheres or Li dendrites frequently observed in liquid cells, which may be related to the relatively slow ion conduction in the solid state electrolyte. ,− On basis of the elemental mappings, the I, Sn, and S elements were found to be evenly distributed across the interface. Notably, the mass content of the I element was 18.7 wt % (Figures d and S15), indicating the great contributor of I-containing substances to SEI.…”

A Low-Cost Liquid-Phase Method of Synthesizing High-Performance Li6PS5Cl Solid-Electrolyte

“…Finally, we conducted a comprehensive comparison between our method and literature methods for making Li 6 PS 5 Cl solid electrolytes (Figure ). ,− ,− ,,,,− The ionic conductivity of Li 6 PS 5 Cl electrolytes made via solid-phase methods scattered in the range of 1–10 mS/cm, where the higher values seemed mainly from hot-pressing or fast-sintering treatments during the pellet fabrications. , The liquid-phase methods could also make Li 6 PS 5 Cl electrolytes with the ionic conductivity around 2 mS/cm, ,,, including ours herein (Figure a). Regarding the cyclability, our electrolyte presented the second best performance with 400 cycles at 1 C, leaving far behind the third best with 250 cycles at 1 / 10 C and all others below 100 cycles (Figure b).…”