Nano-SiO2 Composite Solid Polyelectrolyte Membranes Based on Bis-Imidazole Cationic-Functionalized Benzonorbornadiene Block Copolymers for Solid-State Lithium-Ion Batteries

Solid polyelectrolytes (SPEs) have garnered considerable attention and extensive research due to their exceptional flexibility, low cost, and ease of industrial production. This study synthesized bis-imidazole cationic functionalized benzonorbornadiene block copolymers rP(NB-MGE-b-BenzoNBD-BisIm⁺TFSI⁻) via ring-opening metathesis polymerization (ROMP). The block copolymers were blended with lithium trifluoromethanesulfonate (LiTFSI) and nano SiO₂ to prepare the composite solid polyelectrolytes membrane (CSPEMs) rP(NB-MGE-b-BenzoNBD-BisIm⁺TFSI⁻)/LiTFSI/SiO₂ by a solution casting method for applications in lithium-ion batteries (LIBs). This research investigates the effect of different nano-SiO₂ content on the ionic conductivity and electrochemical stability of the composite SPEs. The relationship between the intrinsic structure and properties of rP(NB-MGE-b-BenzoNBD-BisIm⁺TFSI⁻)/LiTFSI/z wt% SiO₂ (z = 0, 2.5, 5.0, 7.5) was studied. When the SiO₂ content is 5.0 wt%, the maximum ionic conductivity reaches 9.3 × 10⁻⁵ S cm⁻¹ at 30°C and 1.5 × 10⁻³ S cm⁻¹ at 80°C. The NCM811/CSPEM/Li battery exhibits an initial reversible discharge capacity of 149.7 mAh g⁻¹ at a current density of 0.2 C, with a coulombic efficiency maintained above 96%. After 50 cycles at a current density of 0.2 C, the capacity remains at 148.9 ± 8 mAh g⁻¹, with the coulombic efficiency continuing to exceed 96%, which demonstrating robust cycling stability.