In situ interfacial reactions in hydride–oxide composite electrolytes for stable all-solid-state Li–metal batteries†

Developing composite solid electrolytes (CSEs) represents a promising avenue for advancing commercial viability of all-solid-state batteries because none of the single electrolytes can meet the application requirements. However, the correlation of interfacial reconstruction among more than two composite solid electrolytes with property enhancements still remains unclear. In this study, lithium-based hydride-oxide solid electrolytes are chosen as a model to explore in situ interfacial reactions between these composites, with the goal of innovating design of electrolytes for all-solid-state batteries. Our research reveals the formation of dual core–shell-structured electrolytes with LiBO₂ as the intermediate layer and LiBH₄ as the outer layer embedded with Li_xM intermediates, resulting in the in situ reactions of LiBH₄ and Li_xMO_y (M = N, P, S) composites. These composites exhibit continuous conductive networks and demonstrate a high Li⁺ conductivity of ∼1.9 × 10⁻⁴ S cm⁻¹ at 75 °C. This impressive conductivity enables stable cycling of Li–Li symmetric cells for 650 h. Moreover, the critical current density can reach about 2.3 mA cm⁻², and the electrochemical window extends from −0.5 to 6 V. Notably, the reversible specific capacity attains 225.1 mA h g⁻¹ for Li‖TiS₂ batteries with an initial coulombic efficiency of 95.4%. This work provides valuable insights into the design and performance of composite solid electrolytes, offering a promising approach for the development of high-performance all-solid-state batteries.