Rotor blade grinding and re-annealing of LiCoO2: SEM, XPS, EIS and electrochemical study

The layered particles of lithium cobalt oxide (LiCoO2) have been modified using rotor blade grinding, re-annealing, and a combination of both treatments. SEM, XPS and EIS were used to study the effects of these treatments on the LiCoO2 particles, and changes in electrochemical behaviour in the 4-V region vs. Li+/Li were explored. After short grinding times (20 min), primary layered particles formed larger aggregates and poor electrochemical behaviour was observed. After 60 min grinding, LiCoO2 showed a net improvement in reversible specific capacity and capacity retention, which is due to the formation of ultrafine layered particles. Further grinding up to 180 min lead to surface carbonation, increased impedances and poor electrochemical performance. Re-annealing improved the electrochemical behaviour of both ground and unground LiCoO2. The best electrochemical behaviour was observed after grinding for 60 min and then re-annealing at 850 °C, which is linked with a low charge transfer resistance. XPS measurements revealed that the particles surface remained unchanged after heating to 500 °C, while heating to 850 °C eliminated surface carbonates, and prolonged grinding yielded extended surface carbonation.