Surface chemistry on LiCoPO4 electrodes in lithium cells: SEI formation and self-discharge

In this manuscript we investigate the surface chemistry of positive electrodes for Li-ion cell applications constituted by LiCoPO4 (LCP). This high potential material reversibly de-intercalates/intercalates lithium ions at 4-7-4.8 V vs. Li. However it suffers the occurrence of large irreversible capacity loss in the first galvanostatic cycle, capacity fading upon repeated cycling and self-discharge once fully charged up to 5 V vs. Li. These detrimental phenomena roots in the parasitic chemistry that occurs on the surface of the LCP electrodes upon cycling or in open circuit conditions after charge. Here we illustrate our recent findings about the evolution of LCP electrodes upon charge and self-discharge. The self-discharge in LCP electrodes is a self-feeding process that occurs with the spontaneous transfer of electrons from the electrolyte to the Co3+ ions in the de-lithiated electrode, mediated by a porous and partially reactive SEI film that is unable to fully passivate the electrode surface.