Thermodynamics and kinetics of self-discharge in graphite-lithium electrodes

Li/EC-DMC-LiPF/sub 6//Li/sub x/C/sub 6/ half-cells were discharged to 0V vs. Li/sup +//Li then stored at temperatures ranging between 50 and 85/spl deg/C for times between 1 and 12 days. The remaining capacity was measured by galvanostatic delithiation. The time evolution of the open-circuit voltage (OCV) was also monitored during storage. The activation energy of the self-discharge reaction was determined independently from the temperature dependence of the reaction rate constant and from analysis of the OCV curves. It was found to be approximately 50 kJ.mol/sup -1/. Most of the capacity losses were recoverable after further charge/discharge cycling. The remarkable thermal stability of Li/sub x/C/sub 6/ electrode is related to the protective role of the solid electrolyte interphase (SEI). The SEI evolves to more stable composition during aging due to an increase of its insoluble inorganic part.