Understanding Volume Change in Lithium-Ion Cells during Charging and Discharging Using In Situ Measurements

Abstract

Because structural change in lithium cobalt oxide cathode is primarily responsible for the performance degradation of lithium-ion cells in simulated satellite operation, it is important to investigate the operating-condition effect on cell-volume change. In this work, we used in situ strain-gauge measurement to probe the total volume change during charging and discharging of five 50 Ah-class lithium-ion cells with graphite anodes and cathodes. Some interesting phenomena concerning the correlation of the taper voltage with the strain change at the end of the charge were found in the strain trend curve. To explain these phenomena, we examined the strain change of a commercial 0.65 Ah-class lithium-ion polymer cell with the same electrodes as a function of taper voltage by using in situ load-cell measurement and were able to deduce that the cell-volume change during charging correlated to the structure transition of the cathode from the initial hexagonal phase (H1) to a new hexagonal phase (H2) at a taper voltage near . We conclude that the taper voltage should be maintained below to maximize the cycle life of lithium-ion cells with graphite anodes and cathodes during practical satellite operation.