Development of Ni-MH batteries for hybrid vehicle

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Development of Ni-MH batteries for hybrid vehicle

Aitaka, Kazuhiko

By reducing cell resistance 27% over the previous model, and by increasing the number of cells by 10%, it was possible to achieve a 40% power increase in the IMA (integrated motor assist) battery. To study methods of enhancing durability, which is a cause for concern when increasing battery input and output power, an electrode material deterioration analysis was performed. It was conjectured that a major cause of battery deterioration is the formation of La(OH)3 on the anode. By studying the relationship between MH alloy oxygen quantity and internal resistance, it was confirmed that there is a sudden rise in internal resistance when the quantity of oxygen reaches a certain level. In addition, it was learned that the greater the MH alloy's initial oxygen quantity, the more power is produced at low temperatures, although deterioration is speeded up. Figures show that battery output power at -10 deg C is increased from 7 to 15 kW when raising the MH initial oxygen content from 1.5 to 3.5 % while the output power at 25 deg C decreases from 15 to 5 kW after cycling tests. From these findings, it is possible to create a design that adjusts the balance between power and durability by controlling the quantity of oxygen in the MH alloy of the anode, and to develop a battery that achieves both power and durability.