Electrolyte and interface engineering in solid-state lithium batteries: coordination-chemistry insights into ion transport, interfacial stability, and practical performance

Solid-state batteries are widely regarded as a promising route toward safer and higher-energy electrochemical storage. Yet, their practical development remains limited by coupled challenges in electrolyte transport, interfacial instability, mechanical degradation, and scalable manufacturing. This review presents a mechanism-centered analysis of recent original research, focusing on how electrolyte design governs interfacial chemistry, how interfacial chemistry regulates ion-transport continuity, and how these factors collectively determine electrochemical performance, safety, and device-level feasibility. Polymer, inorganic, composite, and advanced electrolyte systems are examined from the perspectives of transport pathways, defect chemistry, solvation structure, and chemo-mechanical compatibility. Particular emphasis is placed on the evolution of the solid electrolyte interphase and the cathode electrolyte interphase, Li + transfer across solid-solid interfaces, nucleation and growth behavior, charge-transfer kinetics, and the influence of processing history on cell reliability. The review further integrates advances in operando characterization, dry processing, multilayer architectures, adaptive interphases, multifunctional materials, and data-driven design. By linking materials chemistry with transport physics, interfacial evolution, and manufacturing constraints, this work establishes a unified framework for understanding why promising solid-state systems succeed or fail under realistic conditions and outlines key directions for developing high-performance solid-state batteries. The primary scope is solid-state lithium batteries; sodium, magnesium, zinc, and fluoride-ion systems are retained only as explicitly identified comparative cases when they isolate transferable coordination, interfacial, transport, safety, or manufacturing principles. Quantitative performance is interpreted within the reported temperature, stack pressure, electrolyte thickness, areal loading, voltage window, and cell-format conditions rather than as an unconditional cross-study ranking.