Achieving high initial Coulombic efficiency for competent Na storage by microstructure tailoring from chiral nematic nanocrystalline cellulose

Although it has been proven that porous, heteroatomic, and defective structures improve Na storage performance, they also severely affect the initial Coulombic efficiency (ICE) due to the huge irreversible capacity in the first cycle, which always limits the practical application of carbon anodes in commercial Na‐ion batteries (NIBs). Here, we show the successful synthesis of nanocrystalline cellulose and the derivative hard carbons. A series of treatments including acid hydrolysis, hydrothermal carbonization, and high‐temperature pyrolysis help tune the pores, heteroatoms, and defects to achieve an optimized balance between superior ICE and reversible capacity of up to 90.4% and 314 mAh g−1. This study highlights that tailoring the electrode microstructure could be an important strategy in the future design of carbonaceous anode materials for high‐performance Na‐ion batteries. Chiral nematic nanocrystalline cellulose was successfully prepared by acid hydrolysis, and the derivative hard carbons were synthesized by various hydrothermal carbonization and high‐temperature carbonization processes to tune the microstructures. The resulting hard carbon anodes could achieve competent Na storage performance and high initial Coulombic efficiency.