"Li-ion batteries used for hybrid, electric or plug-in hybrid vehicles should be much more reliable than those for IT devices"
28 Jul, 2009 05:48 pm
A japanese team succeeded in observing the interior of the lithium battery by using the MRI (Magneting Resonance Imaging) technique, which is widely used in medical fields. Professor Kawamura answers Scitizen's questions about this world first which should contribute to improve the safety of lithium batteries.
The high energy density of lithium battery is potentially accompanied by hazardous accidents as happened in 2006 on mobile phones and lap-top computers. The conventional lithium battery today contains organic liquid solution of a lithium salt which acts as electrolyte to allow the lithium ions pass though between the positive and the negative electrodes. Other batteries are using an aqueous electrolyte solution instead of the organic one. The organic electrolyte is a weak point of the lithium battery, since it may burn easily and might explode when the temperature of the battery is highly increased.
Safety issues are strongly relating to so called degradation problems, which are the phenomena observed as a capacity fading and a power fading when the battery are used for long time. Owing to this degradation, not only the battery life decreases but also the possibility of the over heating increases.
In order to avoid these problems, the modern conventional lithium batteries are equipped with small micro-chip to control the charge-discharge conditions and also some special additives are doped in the organic electrolyte to suppress the decomposition or over charging, over heating etc.
But, when the lithium ion batteries are used widely for hybrid vehicles (HV), electric vehicles (EV) or plug-in hybrid vehicles (PHEV), they should be much more reliable than those for IT devices, since the battery for a car is about 1000 times larger than that in a mobile phone and are used under much severe conditions.
How can the MRI images contribute to improve the safety of lithium batteries?
X-ray is a convenient tool to see the inside of the human body as well as industrial devices including lithium batteries. The conventional MRI is used to observe the nucleolus of hydrogen (proton) which most of the organic substances and water molecule contain. So, the organic electrolyte solution of the lithium battery is a good target of MRI. Another advantage of the MRI is to observe other nucleolus such as a lithium nucleolus, although which is less sensitive to the proton and difficult to observe.
In our experiments, we have successfully observed the proton and the lithium nucleus. By means of this technique we could observe the decomposition of the organic solvent in contact with the negative electrode, gel formation, gas generation etc. Also, we observed the lithium ion distribution in a battery cell as some section views. MRI technique will be also used as a mean for medical check of the lithium batteries in future.
What are the stakes for energy storage?
Energy storage device such as the lithium ion battery is a key for the green energy revolution in these days, which is used not only for HV, PHEV, EV but also as a load leveling mean for solar cells and wind farms. But, the large scale battery for energy storage has started only 20 years ago and little knowledge has been acquired on the detailed mechanism and possible problems. Safety and degradation problems are getting more and more important in future, since it determines the total cost of the green energy systems.
What are the commercial issues of lithium batteries?
I do not know so much about commercial issues. But, as far as I know, Mitsubishi and Fuji motor companies have just started to sell EVs in Japan, which are installed large scale lithium ion batteries. Other motor companies are focusing on PHEV, which can be charged at home in the night; the battery for PHEV should be the lithium battery. Anyway, the lithium battery market is growing tremendously now.
One market research says : ? 4.3 billion lithium batteries will be sold in 2013, which corresponds to over 1 trillion yens in Japan? [*]. Another research says, it will reach to 3.6 trillion yens for all over the world[**].
[*] http://www.spi-information.com/report/01036.html (in Japanese)
[**] http://response.jp/issue/2008/1126/article117026_1.html (in Japanese)
Interview by Clementine Fullias
Junichi Kawamura leads the Solid State Ion Physics Group at the Institute of Multidisciplinary Research for Advanced Materials (IMRAM) at Tohoku University.