Prefilled and Concerted Ion Transport Mechanism in Hierarchical Porous Carbons for Ultra-Fast Energy Storage

Abstract

Hierarchical porous structures have been extensively reported for their efficiency in achieving fast charging and high energy density in electrochemical capacitors. However, the microscopic dynamic mechanism through which hierarchical pores enhance ion transport and storage remains unclear. Here, we synthesize hierarchical mesopore-micropore carbons with varying mesopore contents of approximately 5 nm in size using a tunable “structure inheritance” strategy for comparative investigation. Advanced constant potential method molecular dynamics simulations and nuclear magnetic resonance spectroscopy are combined with electrochemical analyses to systematically investigate ion behaviors in the hierarchical- and microporous-dominant structures under the driving forces of both constant and cyclic voltages. The results indicate that a prefilled and concerted transport mode is responsible for the enhanced ion transport and storage in the hierarchical mesopore-micropore carbons. Notably, hierarchical pores exhibit a significant fast-charging enhancement, with at least a 50% reduction in response time, across various electrolytes, including aqueous, organic, water-in-salt, and ionic-liquid electrolytes. In all four tested electrolytes, the maximum power density of a typical hierarchical porous carbon is several times that of the microporous carbon. This work provides insights into how hierarchical structures improve ion transport and may promote the development of more efficient electrochemical energy storage materials and devices.