|The KHI Gigacell bipolar NiMH stack. Source: KHI. Click to enlarge.|
Kawasaki Heavy Industries Ltd. (KHI) will begin manufacturing versions of the Gigacell bipolar NiMH industrial battery—originally targeted for grid applications such as output smoothing for wind and solar—for transportation applications, beginning with systems for rail applications, according to a report in the Nikkei.
KHI is also testing Gigacell-powered forklifts, and plans to expand the product line to include high-power models for industrial-use vehicles and high-energy models for use as emergency power sources. The company is also investigating a more compact version of the Gigacell for vehicle applications.
The Gigacell, which was developed with support from Japan’s New Energy and Industrial Technology Development Agency (NEDO), offers a large storage capacity enabled by its bipolar three-dimensional structure; high rate charge and discharge ability; and long cycle durability. Nickel hydroxide is used as the positive electrode and metal hydride is used as the negative electrode.
The air-cooled battery is easily recycled, KHI points out, because it has no welding connections at all. Adjacent cells are connected with a bipolar partition plate between them, as shown in the diagram above.
|Examples of two stationary Gigacell stacks|
|196Ah stack||440Ah stack|
|Rated capacity [Ah]||196||440|
|Energy capacity [kWh]||2.35||5.28|
|Dimensions LxWxH [mm]||1065 x 147 x 414||1080 x 258 x 411|
|Volumetric energy density [Wh/L]||36.3||46.1|
|Gravimetric energy density [Wh/kg]||19.6||26.4|
KHI is also developing a 208Ah stack with improved charge and discharge rates that it described at the 214th meeting of the Electrochemical Society in October 2008. The 208Ah stack offers 2.5 kWh of capacity with a volumetric density of 40 Wh/L and a gravimetric density of 21 Wh/kg.
Rail applications and testing. In December 2007, KHI announced that it had completed a verification test on railcar regenerative braking using a Gigacell pack.
The Gigacell-driven system was tested at substations of the Osaka subway, with the cooperation of the Osaka Municipal Transportation Bureau and Kotsu Service Co., Ltd.. Kawasaki verified that energy generated by a train’s braking could be stored and reused to compensate for the voltage fall-offs that occur during startup, operation and congested rush hours.
Kawasaki also conducted tests on emergency operations during power outages and confirmed that the battery system enabled trains to reach the nearest station at a lower speed without compromising on air conditioning or lighting.
Kawasaki is also developing a next-generation light rail vehicle (SWIMO, Smooth WIn MOver), powered by a 200 Ah Gigacell pack installed under the seats of the car.
The 15m long SWIMO can seat 28 (total passenger capacity of 62) and runs at speeds up to 40 km/h, the maximum tram speed allowed in Japan. It has a 10 km range without a recharge, which takes 5 minutes.
Commercialization. Kawasaki currently has a prototype unit plant with an annual capacity of 10,000 kWh. Once it has sufficient orders, KHI plans to invest several billion yen in a factory specifically for the Gigacell. The company is anticipating initial annual sales of between several hundred million yen and 1 billion yen (US$10.6 million).
KHI Gigacell website
Terada et al. Development of Advanced Nickel Metal Hydride Batteries for Large Scale Energy Storage (214th meeting of the Electrochemical Society, October 2008)