Iterative development of solid-state lithium-ion batteries: From hybrid solid-liquid to in-situ solidification

Solid-state lithium-ion batteries are increasingly pursued for grid-scale energy storage, where long cycle life, safety, and scalable manufacturing are critical. This review presents in-situ solidification as a systematic technological pathway that bridges hybrid solid-liquid systems and all-solid-state architectures, with a particular focus on the polymer-oxide composite electrolyte route, across four iterative battery configurations (Solid-state 1.0–4.0) with progressively reduced liquid content. By converting liquid electrolytes into conformal solid networks within electrodes and cells, in-situ solidification reconstructs solid-solid interfaces, enabling continuous ion transport and enhanced chemo-mechanical stability. This iterative framework integrates electrodes modification, polymer-oxide composite electrolyte design, ion-conducting separator development, and multi-level solidification strategies. Multiphysics simulation and advanced characterization elucidate the coupling between solidification kinetics, multiphase structural evolution, and electrochemical and thermal-safety performance. By unifying materials chemistry, structural integration, and process compatibility, in-situ solidification offers an evolution-compatible route toward safe, durable, and economically viable solid-state batteries for grid-scale energy storage.