Questions and answers on lithium-ion batteries

The lithium-ion battery that powers the Dreamliner has emerged as the focus of a probe into why an All Nippon Airways plane was forced into an emergency landing.

Electrolyte leaks and burn marks have been found on the metal casing of the battery in the ANA operated plane, the airline has said.

Here are some basic questions and answers on lithium-ion batteries.

Q. What is a lithium-ion battery and what are they used for?

A. A lithium-ion battery is a family of rechargeable battery types in which lithium-ions move from the negative electrode to the positive electrode during discharge, and back when charging. Lithium is a highly-reactive alkaline metal.

Because it is generally lighter than other types of rechargeable batteries of the same size, it has been widely used for electronic gadgets such as laptop computers and mobile phones.

Carmakers have recently started using lithium-ion batteries for their electric cars because they are lighter and more powerful than nickel-metal hybrid batteries that have been used in hybrid cars.

Q. What are the advantages of a lithium-ion battery?

A. Lithium-ion batteries have a high power density with a long life. They are also relatively light. The battery is able to take repeated charges because it has no so-called "memory effect", a process in which other types of rechargeable batteries lose their powers of retention if they do not run down completely.

Q. And the disadvantages?

A. The batteries are currently more expensive than conventional nickel-cadmium and nickel-metal hybrid packs. Overcharging of the packs creates heat, which in some cases can cause combustion.

Q. What could have gone wrong with the Dreamliner battery?

A. Tatsuo Nishina, a battery technology expert at Yamagata University in Japan said he did not know the specifics of the case, but that overheating, either caused by a defect in the battery itself or in the electrical system to which it is connected, was a possible cause.

"If people who don't know the mechanism of lithium-ion batteries design the electrical system, it could cause trouble," he said.