Defect-Targeted Passivation Enabling Capacity Compensation of Hard Carbon Anodes for Sodium-Ion Batteries

Abstract Hard carbon is an anode material for sodium-ion batteries, yet its performance is hindered by rapid capacity decay and insufficient rate capability. The challenges arise from uncontrolled defects, pore distribution, and interlayer spacing within the carbon framework. Herein, a defect-targeted passivation strategy is originally proposed that compensates the capacity of hard carbon anodes through precise control of defect types and distribution. Specifically, selective passivation of reactive edge defects suppresses parasitic reactions and irreversible Na+ consumption, while topological and compound defects provide reversible Na+ storage to boost diffusion kinetics. Benefiting from this strategy, the optimized hard carbon anodes deliver an operational temperature range (–50 to 60 °C), a reversible capacity of 405.7 mAh g–1, an initial Coulombic efficiency of 90.50%, a stabilized rate capability (up to 10 A g–1), and cycling stability. This work establishes a directional defect-engineering for concurrently boosting the rate capability and stability of hard carbon anodes.