AIST Develops New-type 'Li-air Battery'

Feb 26, 2009
Motohiko Hamada, Nikkei Automotive Technology

A large-capacity Li-air battery with a novel structure was developed by Zhou Haoshen, leader of the Energy Interface Technology Group, Energy Technology Research Institute at Japan's National Institute of Advanced Industrial Science and Technology (AIST), and Wang Yonggang, foreign research fellow at the Japan Society for the Promotion of Science (JSPS).

Though Li-ion batteries are widely used in mobile phones and notebook PCs, they are too low in energy density for use in electric cars. Because of this reason, the "Li-air battery," which can be enhanced in capacity in theory, is attracting attention as the next-generation large-capacity battery.

However, existing Li-air batteries have problems such as accumulation of solid reaction products on the cathode, which blocks the contact between electrolyte and air and stops discharging.

The newly developed battery uses organic electrolyte for the negative electrode (metallic lithium) side and water-based electrolyte for the positive electrode (air) side. And the two electrodes are separated by a solid electrolyte to prevent mixing of the electrolytes.

The battery reacts without any problem because the solid electrolyte allows only Li-ion to pass through. The reaction product on the positive electrode is soluble, generating no solid materials.

Also, a continuous discharge of 50,000mAh/g (discharge per unit mass of the air electrode) was confirmed in the experiment.

This technology is very promising for automotive batteries. If aqueous cathode electrolytes can be replaced at automobile service stations and anode metallic lithium is supplied in the form of a cassette, cars can be driven continuously without the need to wait for them to be charged.

Metallic lithium can be electrically regenerated easily from used aqueous electrolyte for repeated use. So, in a sense, this battery is a new type of fuel cell that uses metallic lithium as its fuel.

Electric vehicles have already been commercialized to a certain extent, and performance improvements and cost reductions are expected for the Li-ion batteries for uninterrupted long distance driving. However, existing Li-ion batteries have limitations in battery capacity, limiting long distance driving. And, to improve the range, a great number of batteries have to be mounted on the vehicle, significantly increasing the vehicle cost.

In order to promote the wider use of electric cars, the current energy density needs to be enhanced by as much as six or seven times. Therefore, the focus is placed on Li-air batteries, which theoretically has much higher energy density than Li-ion batteries. In a Li-air battery, the positive electrode uses oxygen in the air as active material, which means theoretically infinite cathode capacity, realizing a large capacity.