Zwitterionic vinylene-linked covalent organic framework as a functional filler for ionic-liquid-activated PVDF-HFP-based composite polymer electrolytes in lithium metal batteries

Solid polymer electrolytes (SPEs) with high ionic conductivity, high lithium-ion transference number (tLi + ), and strong mechanical integrity are important for safer lithium-metal batteries. Herein, a zwitterionic vinylene-linked covalent organic framework (ZVCOF) was synthesized from 2,4,6-trimethylpyridinium-propylsulfonate and 2,4,6-tris(4-formylphenyl)-1,3,5-triazine and incorporated into a PVDF-HFP matrix. At 5 wt% loading, the resulting membrane exhibited a uniform morphology, tensile strength of 2.5 MPa, elongation at break of ∼275%, and improved ion transport. After [EMIM][TFSI] activation, 5-ZV-SPE-IL delivered a room-temperature ionic conductivity of 0.85 × 10 -3 S cm -1 and tLi + of 0.52, while DMC activation increased tLi + to 0.74. Linear sweep voltammetry showed an oxidation onset near 5.2 V vs. Li/Li + for 5-ZV-SPE-IL. In SPE-based quasi-solid-state cells containing 10 μL of liquid electrolyte on the cathode side, LiFePO 4 |5-ZV-SPE-IL|Li retained ∼130 mAh g -1 after 500 cycles at 0.5 C, and Li symmetric cells operated for over 1000 h. DSC and TGA/DTG measurements further reveal loading-dependent thermal behaviour and decomposition resistance, while complete KK-consistent analysis supports the internal consistency of the cycle-dependent EIS series. Post-mortem XPS indicates formation of a LiF-rich interphase. These results identify 5 wt% ZVCOF as the most balanced composition within the tested formulation and activation window.