Illuminating the multi-stage sodium storage mechanisms in high-rate porous hard carbon: mechanistic insights from a pore architecture

Abstract

Elucidating the multi-stage sodium storage mechanisms in porous hard carbon is pivotal for advancing sodium-ion battery (SIB) technology. In this work, we systematically investigate the three-stage sodium storage mechanisms in porous hard carbon featuring a tailored pore architecture, which achieves exceptional rate performance (204.8 and 158.83 mA h g⁻¹ at 1 and 2 A g⁻¹) while maintaining a capacity retention of 75% over 1000 cycles at 1 A g⁻¹. By combining electrochemical analyses with multi-scale characterization, we reveal how hierarchical porosity coordinates the three-stage sodium storage mechanisms: macropores facilitate rapid ion transport, mesopores enhance adsorption kinetics, and micropores enable stable pore-filling. In situ EIS and GITT analyses quantitatively correlate the interconnected pore network with improved Na⁺ diffusion kinetics and reduced interfacial resistance. These findings establish design principles for hard carbons that simultaneously optimize multi-mechanistic storage and high-power operation in practical SIBs.