Liquid-Phase Synthesis of Highly Deformable and Air-Stable Sn-Substituted Li3PS4 for All-Solid-State Batteries Fabricated and Operated under Low Pressures

Abstract

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 degrees 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 degrees 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).