In Situ-Polymerized Separator-Free Ionogel Electrolyte with Enhanced Interfacial Compatibility for Integrated Solid-State Lithium Batteries

The gel polymer electrolyte (GPE) applied in solid lithium metal batteries (LMBs) is often prepared by an ex situ method and subsequently sandwiched between electrodes during battery assembly. However, despite the enhanced ionic conductivity and safety of GPEs, this assembly technique leads to inferior contact between the electrode layer and the electrolyte layer, causing a series of interfacial problems. To address this issue, an innovative in situ polymerization strategy is proposed in this work. First, a solvate ionic liquid ([Li(G4)][TFSI]) containing PEGDA and PETEA is used to wet a LiFePO4 cathode. Next, the cathode is irradiated by UV radiation to form an in situ ionogel electrolyte layer. The rapidly obtained in situ-integrated cathodes prepared without additional separators exhibit great mechanical properties and a favorable cathode–electrolyte interface. Thus, a significantly reduced resistance and enhanced tolerance to charge–discharge cycles are achieved. The as-prepared in situ Li|IC-1:3 batteries demonstrate stable long-term cycle stability (capacity retention of 94.32% at 0.5C and 91.08% at 1C, 300 cycles). This integrated electrode design with an optimized cathode–electrolyte interface prepared with an in situ process provides a feasible strategy for achieving long-life, safe, and practical solid-state LMBs.