A cation‐driven enhanced functionalization solid electrolyte interface for hard carbon anodes in sodium‐ion batteries

The formation of stable SEI with a hierarchical structure of functionalization is the key to improving the anode performance of secondary batteries. The effects of piperidine cation containing isobutyl as an additive in the SEI structure of hard carbon and corresponding Na+ transport functionality were comprehensively investigated. It is revealed that the large cationic groups of piperidine can promote the rapid migration of Na+ desolvation on the surface of HC anode, further promote the decomposition of anions, and induce the formation of double-layer SEI structure. As the result, the as-fabricated batteries achieved high cyclic stability, good reversible specific capacity and improved rate performance. The mixed electrolyte showed good reversible capacity and capacity retention rate (800 cycles @5C, 67.31%), which was significantly better than the initial electrolyte with a capacity retention rate( 42.01% for 500 cycles @5C). In particular, it is also observed some graphitized structural features on the surface of HC, which facilitate the migration of Na+. Meanwhile, the hierarchical structure of functionalization SEI in conjunction with "pseudo-SEI" contributed the improved performance of Na+ storage. This work provides the feasibility for the introduction of large cationic group additives in the electrolyte to enhance the cycle stability of the HC anode.