Effect of operation conditions on simulated low-earth orbit cycle-life testing of commercial lithium-ion polymer cells

Laminated lithium-ion polymer cells with gel electrolytes and laminate-film package are expected to replace the conventional alkaline batteries for space application due to their high energy density and high flexibility in configuration. To facilitate this, we assessed the effect of operation conditions, charge rate and taper voltage, on cycle-life testing of commercial lithium-ion polymer cells by simulating a satelliteʹs LEO operation with 40% DOD profile in this work. So far, 6000 cycles have been completed. A lower charge rate was found to be promising for long-term satellite operation. Impedance analysis disclosed a little change in cell internal impedance with charge rate. This encouraged us to attribute the poor cycling performance at high charge rate to excessive lithium-ion exhaust in electrode surface-film formation due to a longer holding duration at taper voltage. The taper voltage was also found to affect charge performance of lithium-ion polymer cells. Good cycling performance, such as the minimum current at the end of the charge and the maximum voltage at the end of the discharge were observed when using taper voltage range from 4.05 to 4.10 V. Theoretical analysis deduced that low current at the end of the charge correlated to (1) a low cell internal impedance and (2) a large slope in the capacity–voltage charge curve measured at a low rate. We further evaluated cell cycling behavior at a low rate and indeed observed the largest slope of capacity–voltage charge curve at voltages ranging from 4.05 to 4.10 V.