Stable all-solid-state battery enabled with Li6.25PS5.25Cl0.75 as fast ion-conducting electrolyte

Abstract All-solid-state batteries (ASSB) with lithium anode have attracted ever-increasing attention towards developing safer batteries with high energy densities. While great advancement has been achieved in developing solid electrolytes (SE) with superb ionic conductivity rivalling that of the current liquid technology, it has yet been very difficult in their successful application to ASSBs with sustaining rate and cyclic performances. Here in this work, we have realized a stable ASSB using the Li6.25PS5.25Cl0.75 fast ion-conducting electrolyte together with LiNbO3 coated LiCoO2 as cathode and lithium foil as the anode. The effective diffusion coefficient of Li-ions in the battery is higher than 10−12 cm2 s−1, and the significantly enhanced electrochemical matching at the cathode-electrolyte interface was essential to enable long-term stability against high oxidation potential, with the LCO@LNO/Li6.25PS5.25Cl0.75/Li battery to retain 74.12% capacity after 430 cycles at 100 μA cm−2 and 59.7% of capacity after 800 cycles at 50 μA cm−2, at a high charging cut-off voltage of 4.2 V. This demonstrates that the Li6.25PS5.25Cl0.75 can be an excellent electrolyte for the realization of stable ASSBs with high-voltage cathodes and metallic lithium as anode, once the electrochemical compatibility between cathode and electrolyte can be addressed with a suitable buffer coating.