Electrochemical Properties and Analysis of High Performance Nano-LiCoO2

Abstract

The long-term cycle behavior of nano-LiCoO2 cathodes over 500 cycles at high rates is investigated. The post-mortem analysis of the cycled nano-LiCoO2 cathodes using a combination of X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) shed light on the capacity decay mechanisms. It is found that crystalline nano-LiCoO2 after 500 charge/discharge cycles at 10C becomes amorphous, exhibits Co2+ species rather than the expected Co3+ at the fully lithiated condition, has longer Co-O bond length than pristine nano-LiCoO2 and micro-LiCoO2, and shows 53% specific capacity loss over 500 cycles at 10C. In addition, slow Li-ion intercalation and de-intercalation at the electrode/electrolyte interface are found to be the rate-limiting step for nano-LiCoO2 during discharge and charge, respectively. Thus, to achieve the high rate capability of LiCoO2, not only LiCoO2 particle sizes should be reduced to nanoscales, but also the Li-ion intercalation and de-intercalation rates at the electrode/electrolyte interface need to be enhanced.