Cationic COF-based polymer electrolytes with synergistic hydrogen-bonding networks for enhanced Li+ desolvation and ionic conductivity in all-solid-state lithium metal batteries

Abstract

Polyethylene oxide (PEO)-based electrolytes for all-solid-state lithium metal batteries (ASSLMBs) struggle with rapid dendrite growth at the Li/electrolyte interface under high rates, driven by poor interfacial chemistry and slow Li⁺ transport. Here, we integrate a cationic covalent organic framework with hydrogen-bonding networks (HC-COF) into a PEO matrix to form a composite electrolyte (HC-COF@PEO). Featuring guanidinium units, this cationic COF immobilizes anions through hydrogen-bonding (H-bonding), thus weakening Li⁺ solvation and accelerating Li ion transport kinetics. Its C₃-symmetric π-conjugated structure ensures stability, ordered stacking, and enhanced mechanical strength. Synthesized via a facile one-step imine condensation at room temperature, HC-COF boosts Li⁺ conductivity up to 6.15 $\times$ 10⁻⁴ S cm⁻¹ at room temperature and enables uniform Li⁺ plating/stripping with a low overpotential of 90 mV over 450 h in symmetric cells. LiFePO₄-based ASSLMBs achieve remarkable cycling stability (1000 cycles at 1C) and superior rate performance. This work demonstrates a straightforward, effective approach to enhance PEO-based electrolytes using cationic COFs, paving the way for practical ASSLMBs.