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.