Abstract: During the lifetime of Deep space detectors and GEO satellites, the batteries work occasionally and are kept in storage most of the time. The battery capacity would continuously decrease as the result of side reaction during storage. Through dV/dQ curve、EIS and cell disassemble analysis, the active Li loss is the main reason for capacity degradation. When the cell is stored at 100%SoC, the electrolyte decomposition on the cathode would cause the R_SEI and R_CR of cathode increasing significantly. To prevent the battery over discharge and reduce the irreversible capacity lost, the battery should be kept around 20%SoC and be charged regularly.