Interfacial stability analysis between Ca-doped Na₃PS₄ solid electrolyte and Na anode from first-principles calculations

In this work, the chemical and mechanical stability of the interfaces between the Ca²⁺ doped Na₃PS₄ solid electrolyte and Na anode and between the un-doped Na₃PS₄ solid electrolyte and Na anode are systematically studied by first-principles calculations. The crystal structure, electronic structure, and mechanical properties of the two interface structures were analyzed respectively. When Ca²⁺ was doped into the Na₃PS₄ solid electrolyte, the decomposition of the solid electrolyte after contact with the Na anode was reduced, and the chemical stability of the interface structure was enhanced. Moreover, Ca²⁺ doping may significantly improve the mechanical strength (ultimate tensile strain and ultimate tensile strength) of the interface structure. The improvement of interface stability alleviates battery performance and capacity degradation. Therefore, the improved stability of the Na-Ca_0.125Na_2.75PS₄ interface structure was the result of a mechanical-chemical coupling. This surface modification of Ca²⁺ doping enhanced the stability of the interface structure and provided direction for designing all-solid-state batteries (ASSB) with high capacity and long cycle life.