Effect of oxidation on the performance of low-temperature petroleum cokes as anodes in lithium ion batteries

The effect of an oxidative treatment on the electrochemical performance of various low-temperature cokes as anodes in lithium ion batteries was examined in order to optimize their chemical composition and textural properties. Annealing in a stream of dry synthetic air over short time and temperature ranges was found to result in substantially increased cell capacity and improved capacity retention during cycling in coke oxidized at 350 °C for 1 h, which exhibited a capacity as high as 385 mAh g−1 after 20 cycles at C/50. However, raising the oxidation temperature to 500 °C resulted in undesirably increased irreversible capacity and polarization between the charge and discharge branches, the effect being confirmed by the high impedance values obtained after only a few cycles. 7Li MAS NMR spectroscopy was used to assess covalency in lithium bonds and its relationship to electrochemical performance in the studied batteries.