Lithium-ion satellite cell development: past, present and future

High energy density, lithium secondary cells are very attractive for use on future spacecraft. However, a number of technical challenges remain. Specifically, the ability of lithium secondary cells to achieve the high cycle life and long calendar life required for use on high-reliability spacecraft, as well as the difficulties in scaling up the available small cell technology to larger sizes required for spacecraft power systems. The purpose of this paper is to summarize efforts being undertaken by Eagle-Picher Industries (EPI) to develop lithium-ion (Li-Ion) technology for spacecraft applications. The intent is to keep the satellite community abreast of recent developments at the cell level and to help direct sound decisions in power system design variations from the current nickel-hydrogen (NiH/sub 2/) and nickel-cadmium (NiCd) technologies. The focus of this paper is the summation of past, present and future work with direct emphasis upon the development of cycle life and related components. Other covered issues include: cell design, operational temperature variations, rate capability and energy density. Accelerated performance will be characterized both in GEO and LEO "on-orbit" profiles. To support findings and authenticity of the test data being presented, details of the test configuration and test parameters will be covered as applicable. In addition, future endeavors will be discussed, encompassing expected performance improvements and developmental planning. With a significant improvement over existing cell technology, the Li-Ion system will someday provide tremendous savings in launch cost as well as package flexibility. There are, of course, technological advances needed before this product will be available to the aerospace community. The EPI technology will meet most qualification loads with a C rate capability. The energy density at the C rate is better than 70 Wh/Kg and exceeds 100 Wh/Kg at lesser rates. The cycle life of the large cell Li-Ion technology has yet to prove itself. On-going high rate tests have a current cycle life of >620 cycles at 100% DOD, >1360 cycles at 25% and >8550 cycles at 10%.