Long-Term Cycle Behavior of Nano-LiCoO2and Its Postmortem Analysis

Abstract

In this study, the long-term cycle behavior of nano-LiCoO2 cathodes over 500 cycles at high rates is investigated. Furthermore, the postmortem analysis of the cycled nano-LiCoO2 cathodes using a combination of X-ray absorption spectroscopy and X-ray diffraction is also conducted to 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 that of pristine nano-LiCoO2 and micro-LiCoO2, and exhibits 53% specific capacity loss over 500 cycles at 10C. In addition, slow Li-ion intercalation and deintercalation 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 deintercala...