Synergistic Solvation of Anion: An Effective Strategy toward Economical High‐Performance Dual‐Ion Battery

Abstract The solvation structure of anion plays a crucial role in determining the performance of dual‐ion batteries using graphite‐positive electrodes. In past research on dual‐ion batteries, the design criteria of electrolyte solutions were largely based on the traditional relationship between solvents and additives. Here, a distinctive synergistic solvation strategy is proposed for the design of electrolyte solutions. Despite some solvents performing poorly or even failing to operate when they are used alone for electrolyte solutions, an unexpected improved performance appears when they are combined based on their characteristic moieties. Based on the synergistic solvation strategy, an economical electrolyte solution system (LiPF6‐methyl acetate/diethyl carbonate) is successfully designed. The intercalation behavior of the solvated anion from this solution into the graphite electrode is investigated by conventional electrochemical tests, in situ electrochemical characterizations and theoretical calculations. A proof‐of‐concept dual‐ion battery based on this electrolyte solution delivers a discharge capacity of 100.08 mAh g−1 and ≈4.67 V medium discharge voltage at 10C (1 A g−1), along with 85.35% capacity retention after 1000 cycles at 5C. Moreover, this battery exhibits 93.8% of its room‐temperature capacity at −20 °C and can even work at −70 °C. Synergistic solvation offers a novel approach to design electrolyte solutions for dual‐ion batteries.