Pore Network Tortuosity Controls Fast-Charging in Supercapacitors

Abstract

Ionic transport within porous carbon electrodes is crucial for optimizing charge/discharge rates in supercapacitors, yet the material properties governing ion dynamics remain poorly understood. Contrary to the traditional viewpoint, we find that mesoporosity does not necessarily correlate with high supercapacitor rate capability. Instead, we employed pulsed field gradient nuclear magnetic resonance to directly measure anionic effective diffusivities in the carbon pores, offering a probe of 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. Ultimately, low-tortuosity nanoporous carbons exhibited superior rate capability, highlighting the importance of well-interconnected pore networks for efficient ion transport. Our study reveals pore network tortuosity as a key factor that governs charging rates in amorphous nanoporous carbons and guides the design of electrodes with optimized transport channels to enhance supercapacitor performance.