Adsorption-Mediated Sodium Compensation for Hard Carbon Anodes Enabled by Soft-Contact Presodiation

Hard carbon (HC) anode in sodium-ion batteries suffer from low initial Coulombic efficiency and irreversible capacity loss, limiting practical energy density and cycle life of SIBs. While direct-contact presodiation of HC has been proposed to increase the initial Coulombic efficiency of SIBs, but its low utilization efficiency can cause residual Na on the HC surface, resulting in rapid degradation and even safety concerns. Herein, we proposed a soft-contact presodiation (SCP) method, which can remove and recycle Na source and therefore greatly improve the utilization of the Na source and safety of SIBs. The SCP-treated HC anode achieves a ≈30.0% increase in ICE when paired with a NaNi_1/3Fe_1/3Mn_1/3O₂ cathode, while maintaining minimal temperature rise (ΔT≈1.3°C) during treatment. The resulting SCP-HC exhibits exceptional thermal stability with negligible exothermic activity at 125.0°C and remains chemically stable for over 3.0 days. Through multimodal analysis, we reveal an adsorption-dominated compensation mechanism where replenished Na participates in solid electrolyte interphase formation while simultaneously occupying adsorption sites as metallic clusters. The pouch cell incorporating SCP-HC anode delivers 90.6% ICE and retains 80.0% capacity after 150 cycles. This work establishes a safe, efficient, and economically viable presodiation platform that paves the way for practical high-energy sodium-ion batteries.