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Inside NiLar's Bi-Polar Battery
By EV World
Published: 14-Feb-2008

PHOTO CAPTION: Cutaway view of NiLar Bi-polar NiMH battery showing layers of cathode, anode and separator. The battery comes in both 12 and 24 volt models, both rated at 9 amp hours. Expected service life is 7-10 years and 2000 recharge cycles.



Neil Puester briefs EV World on the workings of his firm's new nickel metal hydride battery


The lead acid battery that powers your typical electric wheelchair can weigh 110 lbs. and needs to be replaced every year.

By contrast, a comparable bi-polar nickel metal hydride battery from Colorado-based NiLar would weigh between 25-35 lbs. and have a 7-10 year life cycle.

How it manages to accomplish this is the topic of a conversation I had with the company co-founder Neil Puester, whose background in battery development dates back to 1971 and the UTC battery that helped power the Apollo spacecraft, as well as underwater applications.

After working at Optima Battery between 1984 and 1996, he made the acquaintance of Lars Fredrickson in Norway while developing a battery for the Norwegian military. That friendship would eventually lead to the creation of NiLar in 2000 in order to commercialize a NiMH battery that wouldn't result in a patent fight with Energy Conversion Devices and Chevron Texaco, which owns the patents to certain key technologies found in most of the batteries that power today's hybrid cars.

Siting at a table off the side of the exhibition area at EVS 23, Puester generously took the time to explain the history and general workings of his bipolar cell, using the above cutaway model and a competing battery that uses conventional technologies.

What distinguishes the NiLar from a normal NiMH battery is how the internal components are arranged. Think of the traditional nickel metal battery as a jelly roll with three key layers: the cathode, the separator, the anode layers. These are rolled together with their respective positive and negative contact tabs at opposite ends of the roll. A lithium ion cobalt battery will generate between 3.3-3.6 volts. This compares to the typical lead acid cell at 2 volts.

In order to assemble the battery, all the individual cells have to have their respective tabs welded together, positive-to-negative-to-postive, etc. All these little "jelly rolls" are then wedged into the battery case, leaving open space between the round cells.

As Puester explained it, this type of construction means electrons have to follow an energy robbing, heat-producing circuitous path that his bipolar approach avoids.

Think of the NiLar cell as a lasagna, multiple alternating layers where the "tab" isn't a little slip of metal, but as an entire sheet that runs the length and breadth of the cell, as illustrated by the different colored layers in the cutaway. The advantage of this approach is it allows for more efficient flow of energy through the battery, as well as much easier and therefore less costly manufacturing. The biggest drawback, however, is that it generates just 1.2 volts per cell. This means it will take more cells to produce a workable voltage in most electric vehicle applications. A NiLar battery module like that above is rated at both 12 and 24 volts at 9 amp hours. The difference is there are more layers in the "lasagna". The operating temperature range of the battery is between 20-125 degrees F (-6 C to +52 C).

Nilar has been granted 13 patents and has an additional 3 applied for; interestingly all of them through its international headquarters in Sweden where Puester claims the patent filing process if faster and more thorough than elsewhere.

During 2007, the company was only able to turn out about 7,000 modules in low volume production, but it plans to ramp this up to more than 20,000 this year. In addition to the wheelchair application, Plug-in Conversions in San Diego is marketing the Nilar battery, mainly for use in Prius conversions. Puester has also identified another promising niche market, but he asked we not share it with our readers since he doesn't want his competitors learning of it. He would only say that the reason this particular niche likes it is because his battery "won't blow up."

The company web site also notes the following characteristics of the battery:

Offers more than 2,000 charge/discharge cycles
Maintenance-free operation
Fast charging
Fully recyclable