High-capacity Capacitor Stirring Up Automakers' Interest (2)

Jul 16, 2009 09:28 Masaru Yoshida, Nikkei Electronics

Continued from High-capacity Capacitor Stirring Up Automakers' Interest (1)

Battery costs could be reduced to 1/10

The solid polymer capacitor's output density per unit volume is 20,000W/L, which is much higher than that of existing electric double layer capacitors. When used in electric vehicles or hybrid cars, secondary batteries need a large output density to generate high output at startup and acceleration.

To enhance the output density, metallic colloids in the plated area were clustered together by adjusting plating conditions. Consequently, the inner resistance was lowered, increasing the output density. At the early stage of the development, a high inner resistance and a low energy density were major problems, but it is possible to say they are now practical enough.

Moreover, Eamex applied its proprietary methods to the pre-process of plating and the injection of electrolyte to enhance the energy density and output density, it said.

The prototype that achieved the energy density of 600Wh/L is as small as 0.2 x 0.5cm, but Eamex has already prototyped an A4-size model. Probably, it is not difficult to enlarge the capacitor without much affecting its performance.

To have the value of 600Wh/L, the conditions have to be optimized. So, it is not always possible to achieve that energy density. Nevertheless, the company has already realized an average energy density of 150Wh/L.

"This performance will be enough for a while," said Shingo Sewa, president of Eamex. "From now on, we will focus on developing stable cells."

Though the details were not disclosed, the company already prototyped a cell by stacking thin films. According to its estimates, if a battery with an energy density per unit mass of 100Wh/kg were mass-produced for use in electric vehicles by using the new method, its cost would be about ¥20,000 (approx US$214). That is about 1/10 the cost of existing Li-ion secondary batteries used in electric vehicles.

However, high levels of safety and reliability are required for automotive batteries. Sewa predicts that the solid polymer capacitor will be commercialized for small electronic devices such as notebook PCs and mobile phones in two or three years before they will be used for electric vehicles.

Meanwhile, he said, "We want to commercialize the capacitor for vehicles by about 2015 and start volume production by 2020," showing his enthusiasm for the large automotive market.

Currently, Eamex is checking the safety and other performances of the capacitor. So far, it has passed a nailing test and a withstand voltage test at 60V without showing any problems such as heat generation, according to the company. And the capacitor has temperature characteristics similar to those of Li-ion secondary batteries, it said.

Another challenge for commercialization is the costs of materials. Eamex is considering replacing Au, which is currently used for the electrodes, with a less expensive metal material. Also, it plans to use an inexpensive material as solid polymer instead of expensive fluorine resin while ensuring the same level of performance.

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