Solid‐State Proton Battery With Record High Specific Capacity Enabled by Covalent‐Organic Framework Electrolyte

Abstract Proton batteries have emerged as promising candidates for next‐generation energy storage technologies due to the minimal size, light weight, ultrafast diffusion kinetics and low cost of protons as charge carriers. However, the use of conventional liquid acid electrolytes poses great challenges, including electrode dissolution, current collector corrosion, and a restricted operating voltage window. In this work, a solid protonic electrolyte based on a covalent‐organic framework (COF) is presented to address these limitations and enable the development of solid‐state proton batteries. Methanesulfonic acid (MeSA) molecules are incorporated into the pores of a sulfonated COF (sCOF), resulting in the protonic electrolyte MeSA@sCOF. Notably, MeSA@sCOF displays a high proton conductivity over 10⁻ ² S cm⁻¹, good long‐term stability, and a wide electrochemical stability window. More importantly, when MeSA@sCOF is employed as the electrolyte in solid‐state proton batteries, it enables the batteries to achieve exceptional rate capability, excellent cycling stability, and a record‐high specific capacity compare to previously reported solid‐state proton batteries.