Self-activation strategy-synthesized hierarchical micro–mesoporous hard carbon with superior sodium ions storage

Porous hard carbon with good cycling durability attracts much attention in the application of sodium ions batteries as anode material, but the commonly used alkali metal ion-activation strategy with complex processes still renders its development. Herein, a simple and scalable method is proposed to synthesize hierarchical porous hard carbon. Benefitting from the efficient self-activation strategy, the hierarchical micro–mesoporous hard carbon (MMHC) with large interlayer distance possesses high specific surface area of 704.1 m² g⁻¹, which can provide shorter ionic diffusion path and much more accessible electrochemical active sites in the carbonaceous structure and then lead to fast sodium ion diffusivity kinetics (3.5 × 10^–9 cm² s⁻¹). In consequence, MMHC electrode delivers high specific capacity of 214.3 mAh g⁻¹ at 50 mA g⁻¹, 118.3 mAh g⁻¹ at 500 mA g⁻¹ after 1000 cycles and 47.4 mAh g⁻¹ even at 4000 mA g⁻¹. Notably, the capacity contribution ratio from low-voltage range is enhanced with engineering micro–mesoporous structure (from 28.5% for HC to 37.7% for MMHC). Promisingly, the hierarchical micro–mesoporous hard carbon holds great potential in commercial sodium ions batteries.