Toshiba Corp developed a Li-ion secondary battery "SCiB (Super Charge ion Battery)." The life cycle of the new battery is more than 10 years even if it is rapidly charged and discharged many times. And its safety is high.
Toshiba will begin commercial production of "TBP" series, standard modules that have 10 cells connected in series, in March 2008. The company plans to use the battery for industrial purposes such as emergency power sources, equalization power sources for wind power generators, unmanned transport vehicles and forklifts, in addition to motorized bicycles, electric motorcycles and hybrid cars.
The key feature of the Li-ion secondary battery is that lithium titanate (Li4Ti5O12) is used as a negative-electrode material with electrolyte with a high flash point and a separator with a high heat resistance. Because of this feature, a thermal runaway is less likely to occur in case of an internal short-circuit, so the risks of burst and combustion are reduced, Toshiba said.
For a positive-electrode material, lithium cobalt oxide (LiCoO2) was adopted as in the case of Li-ion secondary batteries for portable devices.
In the presentation, the movie of an external short-circuit test was shown. Even in the case of the external short circuit, the temperature of the cell did not go over 100°C, explode or catch fire.
The experiment of squashing the new Li-ion secondary battery (1:55)
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As for the charge-discharge behavior of the cell, the capacity of the cell decreases by less than 10% after about 3,000 times of rapid charges and discharges (25°C, 10C(42A) charge and 15A discharge), Toshiba said.
The company said that it is possible to charge and discharge the battery more than 5,000 times and that, if the battery is charged once a day, it can be used for more than 10 years.
Furthermore, the battery can be rapidly charged by high current of 50A. Both the cell and the standard module can be charged more than 90% in five minutes. And the battery retains more than 80% of its service capacity in the temperature of 30 degrees below zero, so it can be used in cold climates.
Its voltage is low, but DOD can be expanded to 80%
The current capacity and nominal voltage of the cell are 4.2Ah and 2.4V, respectively. Its dimension is approximately 62 × 95 × 13mm. And its weight is about 150g. Therefore, its energy density is about 67.2Wh/kg (131.6Wh/L).
On the other hand, the standard module with 10 cells connected in series is equipped with a "battery management system," which monitors power voltage and temperature and controls the balance of the cells.
The current capacity and nominal voltage of the standard module are 4.2Ah and 24V, respectively. Its size is approximately 100 × 300 × 45mm. And it weighs about 2,000g. Consequently, its energy density is about 50.4Wh/kg (74.7Wh/L).
Because the nominal voltage of the cell is as low as 2.4V, when it is used for the devices that require high voltage such as hybrid cars, the number of cells increases by about 50% compared with normal Li-ion secondary batteries, Toshiba said.
However, because it is possible to expand the cell's DOD (depth of discharge) to about 80% without greatly deteriorating the cell, the size of the system can be as small as that of conventional Li-ion secondary batteries developed by other companies for hybrid cars, the company said.