In Situ Formation of Gel Polymer Electrolytes According to Battery Technology: A Review

Abstract

Gel polymer electrolytes (GPEs) bridge the gap between liquid and solid electrolytes, combining room-temperature ionic conductivities close to those of liquids with improved interfacial contact and safety. In recent years, in situ strategies, where a low-viscosity liquid precursor is injected into the battery cell and then polymerized or cross-linked after sealing, have gained momentum because they minimize interfacial resistance, enable conformal wetting of porous electrodes, and facilitate robust interphases for long-life operation. A key advantage is manufacturing compatibility: the liquid precursor can be dispensed using the same electrolyte-filling step and fixtures already used on lithium-ion battery lines, followed by thermal or radiation curing (e.g., electron-beam) inside the sealed cell, which requires little or no retooling. In this review, we map in situ GPE polymerization chemistries to the specific battery technologies in which they are deployed: lithium-ion, lithium metal, lithium–sulfur, sodium-ion, and sodium metal. The goal is to highlight how the specific cell chemistry constrains the formulation and the polymerization route. While free radical cross-linking of acrylates is dominant in ion-based batteries, the reactivity of metal anodes and polysulfide shuttling in next-generation systems necessitate alternative strategies, such as salt-initiated cationic ring-opening polymerization or thiol–ene/epoxy formulations. In situ-formed gel electrolytes can suppress dendrites, stabilize SEI/CEI layers, and deliver >10–3 S cm–1 at 25 °C, but challenges remain in low-temperature transport, initiator compatibility with Li metal, polysulfide management in Li–S, scalability, and test standardization. We conclude by summarizing current challenges and proposing design rules aimed at translating in situ GPEs from lab prototypes to manufacturable, high-energy quasi-solid-state batteries.