Helmholtz Plane Regulation Empowers PF6− Permselectivity towards High Coulombic Efficiency Dual Ion Battery of 5.5 V

High‐voltage dual ion battery (DIB) is promising for stationary energy storage applications owing to its cost‐effectiveness, which has been a hot topic of research in rechargeable battery fields. However, it still suffers from rapid battery failure caused by the severe solvent co‐intercalation and electrolyte oxidation. To address these bottlenecks, herein a functional electrolyte additive hexafluoroglutaric anhydride (HFGA) is presented based on a Helmholtz plane regulation strategy. It is demonstrated that the HFGA can precisely enter into the Helmholtz plane and positively regulate anion solvation behaviors near the graphite electrode surface owing to its considerable H‐F affinity with ethyl methyl carbonate (EMC), thus alleviating EMC‐related co‐intercalation and oxidation decomposition during DIB charging. Meanwhile, HFGA can copolymerize with the presence of PF5 at the Helmholtz plane to participate in forming a CF2‐rich CEI layer with excellent PF6− permselectivity, conducive to achieving PF6− de‐solvation and simultaneously suppressing electrolyte oxidation decomposition. By virtue of such beneficial effects, the graphite cathode enables a 5.5 V DIB with a prominent capacity retention of 92% and a high average Coulombic efficiency exceeding 99% within 2000 cycles, demonstrating significantly enhanced electrochemical reversibility. The Helmholtz plane regulation strategy marks a milestone in advancing DIB technologies.