Pore network tortuosity controls fast charging in supercapacitors.

Abstract

Ionic transport within porous carbon electrodes is crucial for optimizing charge and discharge rates in supercapacitors, yet the material properties governing ion dynamics remain poorly understood. Unlike the traditional viewpoint, here we find that mesoporosity does not necessarily correlate with a high supercapacitor rate capability. We employed pulsed-field-gradient nuclear magnetic resonance to directly measure the anionic effective diffusivities in the carbon pores. This technique probes ionic transport in supercapacitors. Our findings reveal a major discrepancy between short-range and long-range diffusivities, which captures the tortuosity of the pore network. Short-range diffusivities lack correlation with supercapacitor rate capability, whereas long-range diffusivities correlate strongly. Low-tortuosity nanoporous carbon exhibited superior rate capability, which highlights the importance of well-interconnected pore networks for efficient ion transport. Our study reveals that the pore network tortuosity is a key factor governing charging rates in amorphous nanoporous carbon and that it can be used to guide the design of electrodes with optimized transport channels to enhance supercapacitor performance.