Structural Modulation of Hard Carbons via Composition Regulation toward Efficient Sodium Storage

Abstract Biomass‐derived hard carbon (HC) materials are being established as promising anode materials for sodium ion batteries (SIBs) thanks to their merits of cost‐effectiveness and wide availability. It is still an enormous challenge to create closed pores to boost the sodium‐storage capability of biomass‐based HC anodes. Advanced HCs with smaller graphitic domains, enlarged interlayer spacings, and especially abundant closed‐pore structure are controllably synthesized from biowaste of sugarbeet leaf residues through regulating the pyrolysis temperatures and the precursor composition by acid‐ and alkali‐treatment. Systematic physic‐chemical characterizations authenticate that high‐content crystalline cellulose tends to curl and entangle during pyrolysis, thus forming the closed‐pore structures. The optimized HC anode (i.e., HC‐8h‐1400) delivers a high reversible discharge capacity of 342.7/130 mAh g −1 at 0.02/2.0 A g −1 , and stable cycling performance. Moreover, the full SIBs fabricated with the Na 3 V 2 (PO 4 ) 3 cathode demonstrate a discharge capacity of 93 mAh g −1 and good stability with 83.6% retention after 1000 cycles at 1.0 A g −1 . More meaningfully, the work here realizes the secondary utilization of biomass wastes and lightens a promising avenue for the large‐scale preparation of advanced HCs anode with superior Na storage property for SIBs.