Unlocking fast charging of supercapacitors: a job-sharing mechanism for ion transport and storage

Abstract

Mesopores are crucial for balancing fast-charge/high-rate capability with high electrode density in carbon-based supercapacitors. However, the mechanisms governing ion transport and storage within mesopores are often simplified to descriptions of ion buffer pools or diminished pore confinement effects. Herein, we present a comprehensive kinetic model of ion transport and charging dynamics within mesopores by integrating constant-potential molecular dynamics simulations of mesoporous electrodes with experimental electrochemical investigations. Quantitative simulations matching the results of experiments indicate that the charging dynamics and rate performance of mesopores significantly outperform those of micropores. Surpassing traditional understandings, we propose a novel job-sharing mechanism between the diffusion layer and the Stern layer that governs the superior ion dynamics of mesopores. Specifically, the diffusion layer ions facilitate rapid ion migration through preserved solvation structures and low energy barriers, while the Stern layer ions predominantly contribute to charge storage. This spatial separation of ion transport and charge storage provides a fundamental explanation for the enhanced dynamic performance of mesoporous structures, offering valuable guidance for the rational design of porous carbon materials with optimized fast-charge/rate and volumetric performance.