Nobutaka Imamura

Performance and Life Estimation of 175Ah Lithium-Ion Cell for Space Use

High energy density Li-ion battery is expected for the next generation satellite and the other space usage. Japan Storage Battery (JSB) and Mitsubishi Electric Corporation had developed 100Ah cell for space use that has completely sealed structure with hermetic seal and verified electrical and life performance of the cell. As the next development, we created and evaluated a 175 Ah cell model to replace existing large capacity Ni-H2 cells. The 175Ah cell showed the performance the same as the estimated. The relationship of electrical performance between 100Ah cell and 175Ah cell is proportional to capacity. No undesirable phenomenon due to enlargement was observed. Life of this cell at various conditions corresponding to LEO or GEO can be estimated by our formulas established by calendar and cycle life tests that use sixty nine 100Ah cells. The 175Ah cell can be applied to GEO and LEO satellites mission as well as the 100Ah cell.

SELF DISCHARGE CHARACTERISTICS OF LI-ION CELL FOR SPACE APPLICATION

Self discharge characteristics of Li-ion cell is one of the important factors in battery design. Storage tests of 100Ah Li-ion cells were performed. Self discharge rate of the cell at 15oC was about 0.25%/day at the Beginning of Life (BOL). Self discharge rate decreased with elapse of time and became almost constant at 0.015%/day. The test result shows that self discharge rate of JSB Li-ion cells is very small. Dispersion of self discharge rate was considered. JSB Li-ion cells are capable of being used for batteries without balancing circuit in short time and middle time applications. For long time applications longer than 10 years, equipment of balancing circuit is preferable.