Precursor-based surface modification of cathodes using Ta and W for sulfide-based all-solid-state batteries

Sulfide ionic conductors are promising candidates as solid electrolytes for all-solid-state batteries due to their high conductivity. However, interfacial instability between cathodes and sulfide electrolytes still remains a challenge because sulfides are highly reactive. To suppress undesirable side reactions at the cathode/sulfide electrolyte interface, the surface of the cathode has been modified using stable coating materials. Herein, a precursor based (PB) surface modification using Ta and W is introduced as an effective approach for the formation of a suitable cathode coating layer. Through heat-treatment of the PB surface modification, the source materials (Ta or W) coated on the precursors diffused into the cathode and acted as a dopant. Formation of the surface coating layer was confirmed by X-ray photoelectron spectroscopy (XPS) depth profiles and scanning transmission electron microscopy (STEM) images. The PB surface modified electrodes showed higher capacity, improved rate capability and enhanced cyclic performance compared to those of the pristine electrode. The impedance value of the cells dominantly decreased after cycling due to the modification effect. Moreover, considering the XPS analysis, undesirable reaction products that formed upon cycling were reduced by PB surface modification. These results indicate that PB surface modification using Ta and W effectively suppresses undesirable side reactions and stabilizes the cathode/sulfide electrolyte interface, which is a synergic effect of the doping and coating attributed to Ta and W.