Enhancing electrochemical performance in sodium-ion batteries: Strategic modification of oxygen-containing functional groups in hard carbon

Developing sodium-ion batteries (SIBs) as alternatives to lithium-ion battery systems presents significant challenges, particularly in creating efficient anode materials due to the larger ionic radius of sodium. A novel synthesis strategy utilizing pre-oxidation and high-temperature carbonization is developed to obtain pre-oxidized pitch-based hard carbon (OPHC), further enhancing SIB anode performance. This method increases the layer spacing and integrates oxygen-containing functional groups, significantly modifying the carbon structure of the pitch. These modifications enhance reversible Na⁺ adsorption and increase active site availability for Na⁺ storage, which is crucial for battery performance. OPHC derived from pre-oxidation at 300 ℃ and carbonization at 1200 ℃ (OPHC-300–1200) exhibits a reversible Na⁺ storage capacity of 333.7 mAh/g at 50 mA g⁻¹ and maintains 121.3 mAh/g after 500 cycles at 1 A g⁻¹, demonstrating superior rate capability and cycling stability. The assembled OPHC-300–1200//Na₃V₂(PO₄)₃ full cell also achieves high energy and power densities (159.6 Wh kg⁻¹ at 994 W kg⁻¹). CASTEP simulations further confirm enhanced material conductivity due to a reduced band gap. These findings improve understanding of structural effects on SIB performance and suggest a practical method for developing robust anode materials, marking a significant advance towards sustainable energy storage.