Toward State Estimation of Satellite-Borne Lithium-Ion Battery Based on Low Frequency Impedance Data

The satellite borne batteries should be composed by safe materials if we don’t want to have a risk of explosion caused by batteries. Therefore, we focused on two safe batteries. One is a lithium-ion battery with an ionic liquid electrolyte, and the other is a LiFePO4/C type lithium-ion battery. To check whether the batteries are suit for space applications or not, we demonstrate the ionic liquid type batteries and LiFePO4/C type battery in orbit by mounting on “Hodoyoshi-3” microsatellite, and test LiFePO4/C type cell on the ground at various conditions for a better understanding. On the ground tests, AC impedance and capacity of the cells were initially measured, and charge/discharge cycling was constantly repeated at 10, 23 and 45°C. The cells were discharged by constant current (CC) protocol to DOD 50% with 1.0 C for 30 minutes. They were then charged by a constant-current/constant voltage (CC-CV) protocol to 3.6 V for 65 minutes with 0.5 C. For capacity check, the cells were charged at 1.0 C in CC-CV mode until their charge current becomes 60 mA, and discharged at 1.0 C in CC mode to 2.0 V at 23°C. The AC impedance was measured by applying 100 mA of AC oscillation over the frequency range from 0.01 Hz to 10 kHz at SOC 50%. As a result, the decrease in the impedance for the charge transfer through the cycles was observed at each test condition. Furthermore, especially in over recommended charge condition at 10°C, cells that were charged and discharged at 1.1 A/1.1 A were led to internal short circuit. The results suggested that the negative electrode performed as a “lithium-ion excess” by cycles. We define “lithium-ion excess” that lithium-ion happens to stay inside the negative electrode without desorption after cells discharge