Effects of a solid electrolyte coating on the discharge kinetics of a LiCoO2 electrode: mechanism and potential applications

Abstract

The application of a Li⁺-conductive amorphous Li₂B₄O₇ coating on a LiCoO₂ electrode enhanced its discharge kinetics by increasing the local concentration of Li⁺ at the surface of LiCoO₂ particles. The origin of internal resistance in Li⁺ intercalation steps was elucidated by electrochemical impedance spectroscopy (EIS)-based characterization of discharge kinetics for states of charges of 0, 50, and 100%, while the activation energies of intercalation steps were determined from EIS data collected at different temperatures (−10, 0, 20, and 40 °C). The activation energy of Li⁺ desolvation was smaller than that previously reported for bare LiCoO₂ particles, which suggested that the significant changes in kinetics associated with polarization mitigation were due to the Li⁺ exchange reaction (Li⁺ adsorption and diffusion processes) on the surface of LiCoO₂ particles. Finally, C-rate capability tests performed at −10 °C revealed that the capacity retention of the electrode comprising Li₂B₄O₇-coated LiCoO₂ particles exceeded that of the electrode comprising bare LiCoO₂ particles (45% vs. 18%, respectively).