Semiconductor Energy Laboratory (SEL) Co Ltd developed a lithium-ion (Li-ion) rechargeable battery that uses an ionic liquid as a solvent of its electrolyte.
The company exhibited a prototype of the battery cell at Display Innovation 2014, a trade show that runs from Oct 29 to 31, 2014, in Yokohama City, Japan.
By using the ionic liquid, the new battery can be safely used even in high-temperature environments, SEL said. The flash point of the ionic liquid is more than 100°C higher than that of a conventional solvent of electrolyte. Therefore, it hardly ignites even in high-temperature environments, the company said. When the company performed an ignition test, the flash point of the electrolyte using the ionic liquid was higher than 300°C.
Resistance to sterilization
At the show, SEL put the prototyped Li-ion rechargeable battery cell in boiling water and demonstrated that it functioned in the water. The cell was connected to an OLED panel, and the panel was continuously emitting light.
By using this opportunity, SEL plans to find a partner, especially a battery manufacturer, for joint development. It expects to apply the new battery to medical devices, etc because they are often sterilized at a temperature of 100-120°C.
"Currently, they cannot be sterilized, or their batteries have to be removed each time for sterilization," the company said. "With the new battery, they will become resistant to sterilization treatment."
In another demonstration that took place near the demonstration using the boiling water, SEL used ice water. When an ionic liquid is used for a battery, its capacity drastically lowers and deterioration progresses in low-temperature environments. But the new battery adequately functions at 0°C, the company said. In fact, it was functioning in the ice water.
The prototyped battery cell has a capacity of 300mAh and a voltage of 3.2V. Its positive and negative electrode materials are lithium iron phosphate (LiFePO4) and graphite, respectively. It measures 2.9 x 75 x 60mm and weighs 15g (mass).