Lignin‐derived hard carbon anode with a robust solid electrolyte interphase for boosted sodium storage performance

Hard carbon is regarded as a promising anode candidate for sodium‐ion batteries due to its low cost, relatively low working voltage, and satisfactory specific capacity. However, it still remains a challenge to obtain a high‐performance hard carbon anode from cost‐effective carbon sources. In addition, the solid electrolyte interphase (SEI) is subjected to continuous rupture during battery cycling, leading to fast capacity decay. Herein, a lignin‐based hard carbon with robust SEI is developed to address these issues, effectively killing two birds with one stone. An innovative gas‐phase removal‐assisted aqueous washing strategy is developed to remove excessive sodium in the precursor to upcycle industrial lignin into high‐value hard carbon, which demonstrated an ultrahigh sodium storage capacity of 359 mAh g−1. It is found that the residual sodium components from lignin on hard carbon act as active sites that controllably regulate the composition and morphology of SEI and guide homogeneous SEI growth by a near‐shore aggregation mechanism to form thin, dense, and organic‐rich SEI. Benefiting from these merits, the as‐developed SEI shows fast Na+ transfer at the interphases and enhanced structural stability, thus preventing SEI rupture and reformation, and ultimately leading to a comprehensive improvement in sodium storage performance.