In-Situ-Polymerized Higher-Performance Poly(Ionic Liquid) Solid Polymer Electrolyte Enabling a Stable Interface for Lithium Metal Batteries

Abstract A poly(ionic liquid)-based solid polymer electrolyte (PIL-SPE) was designed to achieve high ionic conductivity, reduced interfacial resistance, and improved compatibility with lithium metal through the suppression of dendritic growth. An electrolyte was synthesized from 1-vinyl-3-(2-benzoyl-ethyl) imidazolium bis(trifluoromethanesulfonyl)imide (VBEIm-TFSI), cross-linked with vinyl ethylene carbonate (VEC), and incorporated with LiTFSI as the lithium salt and lithium difluoro (oxalate)borate (LiDFOB) as an interfacial stabilizer, with polymerization initiated by azobisisobutyronitrile (AIBN) via in-situ thermal polymerization. The in-situ polymerization forms a conformal and stable electrolyte–electrode interface, enabling uniform salt distribution and low interfacial impedance. The resulting PIL-SPE exhibits ionic conductivities of 4.0 × 10–4 S cm–1 at 30 °C and 1.04 × 10–3 S cm–1 at 70 °C, a lithium-ion transference number of 0.52, and an electrochemical stability window of up to 4.8 V. Symmetric Li cells demonstrate stable plating/stripping over 1000 h at 0.1 mA cm–2. In LFP|PIL-SPE|Li cells, the electrolyte delivers 100 mAh g–1 at 1 C for 1000 h with an average Coulombic efficiency of 99.5%. These results demonstrate that the PIL-SPE is a promising candidate for next-generation solid-state lithium metal batteries (lithium-ion batteries, LIBs).