Idemitsu Showcases A6-size Laminated All-solid Li-ion Battery

Mar 5, 2010 18:36 Tsunenori Tomioka, Nikkei Monozukuri

Idemitsu Kosan Co Ltd exhibited an A6-size laminated all-solid lithium-ion (Li-ion) battery at the 1st Int'l Rechargeable Battery Expo, which took place from March 3 to 5, 2010, in Tokyo.

The battery is made by using lithium sulfide (solid-state inorganic material) as an electrolyte and has higher safety, high-temperature properties, resistance to overdischarge and potential for large capacity than normal Li-ion batteries that use a liquid organic material as an electrolyte. Idemitsu Kosan prototyped a similar battery with a size of a business card one year ago.

The advantages of using lithium sulfide as an electrolyte are as follows. First, because lithium sulfide is an inorganic material, it is stable even at a high temperature. Second, because it is in a solid state, the inner pressure normally does not rise due to evaporation unlike a liquid. Third, it is not decomposed by an electric current until the voltage reaches 20V. Fourth, it enables to use a sulfurous material, which has an electrochemically high capacity, as a positive-electrode material.

The first and second advantages enhance safety and high-temperature properties. The third advantage improves the resistance to overdischarge. And the last one increases the potential for large capacity.

The positive and negative electrodes of the prototyped A6-size battery use the same materials as those of existing Li-ion batteries. But, by using a sulfurous material for the positive electrode and a lithium-containing material for the negative electrode, it is possible to increase the gravimetric energy density from the current 100-150Wh/kg to 500-700 Wh/kg in theory, Idemitsu Kosan said.

The company expanded the area of the battery to A6 size by developing a technology to firmly attach granular lithium sulfide to the electrodes and form a sheet. Though Idemitsu Kosan did not disclose the details, the company dispersed the granular lithium sulfide in a solvent, made it go into the electrodes, formed a sheet and dried it up. Also, the company formed a sheet by pressure. And it combined such methods to enlarge the area of the battery.

With cells connected in series (four lines), the A6-size battery has an output voltage of 14-16V and a solid electrolyte membrane with a thickness of about 100μm. Its output density and energy density have not been disclosed.

Idemitsu Kosan plans to reduce the thickness of the membrane to 10-20μm to lower the resistance and search for an electrode material that is compatible with the electrolyte. The company aims to commercialize its all-solid Li-ion battery in 2012.

24 Hours | 7 Days