Surface pyrolysis towards graphite heterojunctions for aqueous Zinc-ion capacitor

Abstract

Zinc-ion capacitors (ZICs) have attracted significant attention as energy storage devices. Significant efforts have been devoted over the past decades to develop ZICs with improved performance, enhanced safety, and lower cost for practical application. Herein, free-standing, binder-free and electrochemical active expanded graphite (AEG) based paper-like cathodes were designed via a simple and cost-effective pyrolysis and mechanical pressing approach. Density-functional theory (DFT) calculations evaluated the absorption capacity of Zn and SO₄ at graphite surface, suggesting that the capacitive behavior could be enhanced through these interactions. The AEG cathode exhibits an approximately 25-fold increase in surface area, abundant surface dopants, and a porous structure, demonstrating its potential for application in ZICs. The AEG-ZICs delivered an areal capacity of ∼ 4 mAh·cm⁻², an energy density ∼ 3.3 mWh·cm⁻², and excellent cycling stability for over 750 h. Our work provides a promising approach for developing robust, cost-effective, and eco-friendly cathodes, contributing to the fundamental understanding of the charge storage mechanism in highly loaded electrodes, and emphasizing the potential for the commercialization of AEG-derived ZICs.