Cu(FSI)₂-Triggered Interfacial In-Situ Polymerization of DOL for High-Performance Solid-State Lithium Metal Batteries

The limited ionic conductivity and unstable interfaces, primarily caused by poor solid–solid contact, pose significant challenges to the stable cycling of solid-state batteries. This study proposes an interfacial in-situ polymerization strategy to construct a poly(1,3-dioxolane) (PDOL) gel electrolyte layer between a poly(vinylidene fluoride) (PVDF)-based solid polymer electrolyte and the electrodes. This approach aims to address interfacial compatibility issues in solid-state lithium metal batteries. By precisely tuning the composition of the gel precursor and employing characterization techniques such as FTIR and NMR, the efficient ring-opening polymerization of DOL was confirmed, achieving a high conversion rate of 90%. The precursor was drop-cast onto the PVDF-based electrolyte/electrode interfaces before cell assembly. Electrochemical evaluations revealed that the in-situ formed solidified interlayer significantly enhanced interfacial compatibility and ion transport, yielding a high Li⁺ transference number (0.341), an exceptional critical current density (1.4 mA cm⁻²), and remarkable cycling stability exceeding 1600 hours in Li||Li symmetric cells. Furthermore, full cells incorporating LiFePO₄ cathodes demonstrated excellent rate capability and long-term cyclability, retaining 92.1% of their capacity after 1200 cycles. These results collectively underscore the effectiveness of this in-situ solidification strategy in optimizing the interface structure and improving the overall performance of PVDF-based solid-state batteries.