Analysis of the self-discharge process in LiCoPO 4 electrodes: bulks

LiCoPO4 (LCP) is a promising high voltage cathode for next-generation high energy Li-ion batteries. However, once electrochemically de-lithiated, it suffers from a spontaneous self-discharge process in open circuit conditions. Here we present our systematic study about the phase composition and structural changes of LCP electrodes upon charging and self-discharging processes by ex situ synchrotron X-ray diffraction and Fast-Fourier Transform Infrared Spectroscopy (FT-IR) analyses. Various initial charging states and different current rates have been studied. Our investigation highlights large structural alterations of the de-lithiated CoPO4 phase upon self-discharge. However, after 160 hours with open circuit the pristine LCP structure is recovered. The electrochemically de-lithiated phase reincorporates lithium by a spontaneous reduction reaction releasing gaseous CO2 and likely degrading the electrolyte molecules.