Regulating Electrolyte Solvation Structure via Trace LiPF₆ for High-Performance Sodium-Ion Batteries

Sodium-ion batteries have emerged as a promising alternative to lithium-ion batteries, offering distinct advantages that have garnered a significant amount of attention. However, challenges such as slow ion migration and unstable interfaces, stemming from the larger size and mass of sodium ions, severely impact the battery cycle life and fast-charging capabilities. To address these challenges, an effective solvation regulation strategy utilizing a trace amount of LiPF₆ additive is developed. The targeted introduction of LiPF₆ into the baseline NaPF₆ electrolyte induces the formation of unique Li⁺-Na⁺ composite solvation structures, including "dual-anion" centered on Li⁺ and ″Li⁺-Na⁺ dual-cation″ with anions acting as bridges.This strategy not only enhances ionic conductivity and interfacial stability but also optimizes the structure of the Na₃Fe₂(PO₄)P₂O₇ (NFPP) electrode materials. Consequently, the capacity retention rate of NFPP∥Na batteries using this electrolyte surpassed 98% after 3000 cycles at 10 C, and the capacity retention rate of hard carbon (HC)∥Na batteries achieved 86.83% after 400 cycles at a current density of 1.0 A/g. Furthermore, when implemented in NFPP||HC pouch cells, the electrolyte maintained exceptional electrochemical performance even under charge and discharge cycles at a current density of 3 C. More importantly, this study extensively investigated the correlation between the constructed composite solvation structure and the electrochemical performance of the battery, providing a promising design approach for enhancing the performance of sodium-ion battery electrolytes in terms of both high-rate capability and extended cycle life.