Cycle life evaluation of 3 Ah Li sub(x)Mn sub(2)O sub(4)-based lithium-ion secondary cells for low-earth-orbit satellites: II. Harvested electrode examination

Lithium-ion batteries are a candidate for the energy storage system onboard low-earth-orbit satellites. Terrestrial experiments are able to capture the performance degradation of cells in orbit, therefore providing the opportunity for lifetime investigations. The lifetime performance of 3 Ah commercial Li sub(x)Mn sub(2)O sub(4)-based pouch cells was evaluated in a matrix of different cycling depths-of-discharge (DODs: 0, 20, 40%) and temperatures (25, 45 [deg]C). Aged cells were disassembled and the electrochemical performance of harvested electrodes investigated with two- and three-electrode pouch cells. The positive electrode had a larger decrease in capacity than the negative electrode. Both the positive and negative electrode contributed to the increase of cell impedance measured at high states-of-charge (SOCs). The data at low SOCs indicated that the increase of cell impedance was associated with the positive electrode, which showed a significant increase in the magnitude of the high-frequency semi-circle. This SOC-dependence was observed for cells cycled for either extended periods of time or at higher temperatures with a 40% DOD swing. Low-current cycling of positive electrodes revealed a change in the second potential plateau, possibly reflecting a structural change of the Li sub(x)Mn sub(2)O sub(4). This could impact on the electrode kinetics and provide a possible explanation for the SOC-dependent change of the impedance.