Flux Synthesis of Robust Polyimide Covalent Organic Frameworks with High‐Density Redox Sites for Efficient Proton Batteries

Abstract Aqueous proton batteries are attracting increasing attention in the large‐scale next‐generation energy storage field. However, the electrode materials for proton batteries often suffer from low specific capacity and unsatisfactory cycle durability. Herein, we synthesize two highly crystalline and robust polyimide covalent organic frameworks (COFs) through a solvent‐free flux synthesis approach with benzoic acid as a flux and catalyst. The as‐synthesized COFs possess enriched redox‐active sites for proton storage and intrinsic Grotthuss proton conduction, rendering them ideal candidates for proton electrode materials. The optimal COF electrodes achieve a high specific capacity of 180 mAh/g at 0.1 A/g, among the highest COF‐based proton batteries, and exhibit an outstanding rate capability of up to 100 A/g and long‐term cycling stability with capacity retention of 99 % after 5000 cycles at 5 A/g. The assembled full cells deliver a specific capacity of 150 mAh/g at 0.2 A/g with a maximum energy density of 72 Wh/kg and a maximum supercapacitor‐level power density of 64 kW/kg, surpassing all reported COF‐based systems. This work paves a new avenue for the design of electrode materials for aqueous proton batteries with high energy density, power density, rate capability and long‐term cycling stability.