April 20, 2009 Chrysler this week announced it will use batteries from A123 Systems in its range of Electric Vehicles, the first of which should be a Tesla Roadster competitor - the Dodge Circuit. A123 and Chrysler have been working together over the last three years to develop a modular battery system based on prismatic cells using the same lithium iron nano-phosphate chemistry that has already gained a huge reputation following the world records set by Killacycle.

The companies have developed battery modules that could be easily adapted to fit different vehicles in order to cater for the automaker's plans to start selling several electric vehicles at around the same time. Each module is made up of what is known as a prismatic cell - one with a flat shape as opposed to cylindrical - which are bundled together with the battery management system electronics housed at either end. Interestingly, one of the reason given by General Motors for not awarding the Volt battery contract to A123 was that they could not supply the prismatic cells they required.

The cells use a lithium iron nano-phosphate electrode that is chemically much more stable than the lithium cobalt oxide used in most laptops and in some electric vehicles. To keep the larger cobalt oxide battery packs found in electric vehicles stable, companies such as Tesla Motors have designed elaborate cooling systems that carry coolant past each of the thousands of cells in the pack. Because iron nano-phosphate cells are less prone to overheating, the coolant system can be far simpler - the battery modules sit on a heat sink (a flat metal sheet) which is cooled by a coolant loop.

A123's battery chemistry has gained a huge reputation as the first on the market of a new generation of batteries with charge and discharge rates that can accept an 80% charge in as little as 5 minutes. In an electric vehicle application this should eliminate the last perceived hurdle to wide spread acceptance of electric cars, slow charge times. On the other hand there is a disadvantage compared with some other types of lithium ion batteries, including cobalt oxide, in that they store slightly less energy, which could limit the range of a car.

Where a Cobalt oxide Li-ion battery deteriorates quickly if it is completely discharged A123 cells can be discharged almost completely without degrading. All rechargeable Li-ion battery systems use a battery management system (BMS) to prevent over charging or full discharging and as is the case with the Chevy Volt, they're typically electronically limited to using only half of their energy capacity. With A123 batteries the battery pack can be discharged to as low as 10% charge to provide a range of up to 200 miles - comparable to the range in similarly sized batteries with chemistries that store more energy.

A123 has had a good month so far. On top of the announcement of a production deal with Chrysler the company also raised $69 Million in a new round of private financing and was awarded $100 Million in Refundable Tax Credits from Michigan Economic Development Corporation to go towards the planned $2.3 Billion Lithium Ion Battery Mass Production Facility to be constructed in Michigan which will be used to supply multiple Automotive customers in the Electric and Hybrid Electric vehicle markets.

Paul Evans

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