Lithium Argyrodite as Solid Electrolyte and Cathode Precursor for Solid-State Batteries with Long Cycle Life

All-solid-state batteries with conversion-type cathodes promise to exceed the performance of lithium-ion batteries due to their high theoretical specific energy and potential safety. However, the reported performance of solid-state batteries is still unsatisfactory due to poor electronic and ionic conduction in the composite cathodes. Here, in situ formation of active material as well as highly effective ion- and electron-conducting paths via electrochemical decomposition of Li₆PS₅Cl_0.5Br_0.5 (LPSCB)/multiwalled carbon nanotube mixtures during cycling is reported. Effectively, the LPSCB electrolyte forms a multiphase conversion-type cathode by partial decomposition during the first discharge. Comprehensive characterization, especially operando pressure monitoring, reveals a co-redox process of two redox-active elements during cycling. The monolithic LPSCB-based cell shows stable cycling over 1000 cycles with a very high capacity retention of 94% at high current density (0.885 mA cm⁻², ≈0.7 C) at room temperature and a high areal capacity of 12.56 mAh cm⁻² is achieved.