2003 Volume 71 Issue 12 Pages 1018-1024
Large capacity Li-ion cells with 100 Ah had been developed to meet the requirements of space applications. These cells are organic-electrolyte Li-ion cells of LiCoO2/Graphite systems. Calendar and cycle life characteristics of the 100 Ah Space Li-ion cells have been evaluated under various test conditions with wide range of temperature (0°C-60°C), depth of discharge (3%-80% DOD), and state of charge (0%-100% SOC). The test was started in June 1999, and the data have been accumulated for around four years. From these results, based on our capacity loss mechanism, we have confirmed that the calendar and cycle capacity loss of the Li-ion cells can be calculated by using simple formulas. To calculate the calendar capacity loss, multiply the rate constant (kf) by the square root of storage time. The rate constant kf is function of temperature and SOC, and we have confirmed that the kf is affected by electrical potential of a negative electrode. To calculate the cycle capacity loss, multiply the rate constant (kc) by the square root of cycle number. The rate constant kc is function of DOD, and we have confirmed that the kc is not affected by temperature in the range of 15°C to 60°C. Our life estimation results shows that our Space Li-ion cells have sufficient capability to achieve the mission life requirements for several kinds of artificial satellite such as geostationary orbit satellites (GEOs) and low earth orbit satellites (LEOs).