Achieving Stable High‐Voltage All‐Solid‐State Lithium Batteries: Electrolytes, Interfaces, and Advanced Characterization

ABSTRACT Integrating the intrinsic safety of solid‐state electrolytes and the high energy density enabled by high‐voltage cathodes, high‐voltage all‐solid‐state lithium batteries (HV‐ASSLBs) have emerged as one of the most promising next‐generation energy storage technologies. However, their practical application is hindered by the limited electrochemical stability windows of solid electrolytes and the complex physicochemical degradation reactions at the electrode‐electrolyte interfaces. This review summarizes the fundamental theories of HV‐ASSLBs, outlining the core performance evaluation metrics for solid‐state electrolytes alongside the various intrinsic degradation mechanisms responsible for their failure. These critical challenges encompass the oxidative decomposition of electrolytes, interfacial side reactions, the formation of space charge layers, lithium dendrite growth, mechanical contact failure induced by volume deformation, and gas evolution. Based on a hierarchical design strategy, recent research advances in electrolyte modification are summarized across three primary directions: bulk electrolyte optimization, cathode–electrolyte interface regulation, and anode‐electrolyte interface stabilization. Furthermore, this review introduces emerging machine learning‐assisted characterization techniques, highlighting their effectiveness in elucidating the intrinsic mechanisms of the batteries. This review aims to provide design guidelines for developing stable, safe, and high‐energy‐density HV‐ASSLBs.