Effect of the air oxidation stabilization of pitch on the microstructure and sodium storage of hard carbons

Hard carbon anode materials for sodium ion batteries were prepared from petroleum pitch by air oxidation stabilization followed by carbonization. The effects of the oxidation stabilization temperature on the compositions and microstructures of the oxidized samples, as well as on the morphology, microstructure and sodium storage property of the carbonized samples were investigated. Results show that air oxidation introduces a large number of oxygen-containing functional groups, induces dehydrogenation condensation and oxidative crosslinking reactions, and transforms the petroleum asphalt from thermoplastic to thermosetting. The air oxidation stabilization treatment effectively hinders the inherent tendency of asphalt to graphitize during high temperature carbonization, resulting in carbons with randomly oriented carbon layers with more defects. Electrochemical tests show that o-PDC-350-1400 (oxidation stabilization at 350 °C, carbonization at 1400 °C) has a high charging specific capacity of 276.8 mAh g⁻¹ at 100 mA g⁻¹ and a high initial coulombic efficiency of 73.38%. Compared with sample PDC-1400 that was directly carbonized at 1400 °C, the charging specific capacity was increased by about 1.8 times and the initial coulombic efficiency was increased by 22%. The charging specific capacity of o-PDC-350-1400 after 200 cycles reached 170.2 mAh g⁻¹, indicating good cycling stability.