Dual‐Function Presodiation with Sodium Diphenyl Ketone towards Ultra‐stable Hard Carbon Anodes for Sodium‐Ion Batteries

Hard carbon (HC) is a promising anode material for sodium‐ion batteries, yet still suffers from low initial Coulombic efficiency (ICE) and unstable solid electrolyte interphase (SEI). Herein, sodium diphenyl ketone (Na‐DK) is applied to realize dual‐function presodiation for HC anodes. It compensates the irreversible Na uptake at the oxygen‐containing functional groups and reacts with carbon defects of five/seven‐membered rings for quasi‐metallic sodium in HC. The as‐formed sodium induces robust NaF‐rich SEI on HC in 1.0 M NaPF6 in diglyme, favoring the interfacial reaction kinetics and stable Na+ insertion and extraction. This renders the presodiated HC (pHC) with high ICE of ≈100 % and capacity retention of 82.4 % after 6800 cycles. It is demonstrated to couple with Na3V2(PO4)3 cathodes in full cells to show high capacity retention of ≈100 % after 700 cycles. This work provides in‐depth understanding of chemical presodiation and a new strategy for highly stable sodium‐ion batteries. Sodium diphenyl ketone is applied as a reducing reagent to compensate irreversible Na uptake at oxygen‐containing functional groups and react with defective carbon for quasi‐metallic Na to initiate robust SEI. It leads to ICE of 99.2 % and capacity retention of ≈100 % for 700 cycles in the full cells of presodiated hard carbon//Na3V2(PO4)3.