An Effective Strategy to Enable Argyrodite Sulfides as Superb Solid-State Electrolytes: Safeguarding Remarkable Ionic Conductivity and Interfacial Stability with Electrodes

Abstract: The argyrodite sulfides are getting more and more attractive as highly promising solid-state electrolytes (SSEs) for high-performance all-solid-state batteries (ASSBs), owing to their high ionic conductivity, adequate plasticity, and decent mechanical strength. However, their poor incompatibility with Li metal anode and high voltage cathodes and as well as serious sensitivity to air significantly hinder their practical applications. Herein, we have devised an effective strategy to overcome these challenging shortcomings through modification of chalcogen chemistry under the guidance of theoretical modeling. The resultant Li6.25PS4O1.25Cl0.75 delivered excellent electrochemical compatibility with both pure Li anode and high-voltage LiCoO2 cathode, without detrimental impact upon the superb ionic conductivity of the pristine sulfide. Furthermore, the current SSE also exhibited highly improved stability to oxygen and moisture in air, with further advantage being more insulating to electrons. The remarkably enhanced compatibility with electrodes is attributed to in situ formation of solid anode electrolyte interphase (AEI) and cathode electrolyte interphase (CEI) layers. The formation of in situ AEI enabled ultra-stable Li plating/stripping at a record high current density up to 1 mAh cm-2 in Li|Li6.25PS4O1.25Cl0.75|Li symmetric cells over 1800 hours. The in situ CEI facilitated protection of the SSE from decomposition at elevated voltage. Consequently, the synergistic effect of AEI and CEI helped the LiCoO2|Li6.25PS4O1.25Cl0.75|Li battery cell to achieve markedly better cycling stability than that using the pristine Li6PS5Cl as SSE, at a high areal loading of the active cathode material (4 mg cm-2). This work adds a desirable SSE in the argyrodite sulfide family, so that high-performance solid battery cells could even be fabricated in ambient air.