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...

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).

No abstract