Dual polarization in extended π-conjugated zwitterionic COF facilitates Li+ aligned transportation for high-performance solid-state lithium–metal batteries

Abstract

Rational design of covalent organic frameworks (COFs) with tailored topology and multipolar characteristics offers a promising avenue for developing advanced composite electrolytes in high-rate solid-state lithium–metal batteries (SLMBs). Herein, we report an extended π-conjugated zwitterionic COF (QZwiCOF) that innovatively modulates the microstructure of PVDF-HFP to enable aligned Li⁺ transport. The unique dual polarization induced by enhanced intramolecular charge transfer in QZwiCOF maximizes PVDF-HFP's dipole moment and structural regularity. Coupled with the amphiphilic nanochannel of QZwiCOF that provides Li⁺-selective conduction, the resulting QZwiCOF-based composite electrolyte (ZiCP CPE) with merely 3 wt% QZwiCOF achieves enhanced ionic conductivity (σ = 3.44 × 10⁻⁴ S cm⁻¹), a high Li⁺ transference number (t_Li⁺ = 0.56), improved mechanical and thermal stability. Consequently, a Li‖NCM811 cell with ZiCP CPE achieves excellent rate performance, delivering a specific capacity of 145 mAh g⁻¹ at 3.0C, much higher than that of a cell using PVDF-HFP SPE (51 mAh g⁻¹). Notably, even under 80 °C and 6.0C, it retains a capacity of 96 mAh g⁻¹ after 200 cycles while the cell with PVDF-HFP SPE experiences a short circuit within 50 cycles, highlighting its potential for thermally resilient high-rate SLMBs. This work provides a molecular-level design strategy for engineering high-performance CPEs through zwitterionic COF-mediated ion channel regulation.