Is that their "unique safety technology"?
Tesla Motors, Inc., the US venture business developing electric cars, is fitting its "Tesla Roadster" model electric cars, which began commercial production in March 2008, with 18650-type Li-ion (lithium-ion) batteries, which are widely used in standard consumer electronic products. These are ordinary lithium-ion batteries, with dimensions of 18mm diameter and 65mm length. Tesla Motors has incorporated its own unique safety technology into these lithium-ion battery cells, and is now fitting its Tesla Roadster vehicles with the proprietary car battery pack containing 6,831 battery cells.
Usually, car battery packs might only contain around several dozen cells that have been developed for automotive-use. For example, the Mitsubishi Motors Corporation "iMiEV" (Mitsubishi innovative Electric Vehicle), scheduled for commercial production in 2009, is fitted with a lithium-ion battery pack containing just 88 rectangular-shaped lithium-ion battery cells, with each cell having dimensions of 113.5mm × 43.8mm × 171mm. In comparison to the iMiEV, the Tesla Roadster's car battery pack consists of smaller dimensions and a much higher number of cells.
The Tesla Roadster is a sports car developed with the affluent consumer in mind. It has great acceleration performance, going from zero to 100km/h(62mph) in just 4 seconds. Each battery charge delivers enough power to travel approximately 350km, which although seemingly short of travel distance of gasoline-powered vehicles, is still sufficiently practical. (it is worthwhile noting that the batteries themselves are heavy: with the battery pack occupying approximately 40% of the gross vehicle weight, or 450kg of the vehicle's gross 1125kg.)
The White Paper accessible from the Tesla Motors website reveals the reasons behind its decision to use standard 18650-type lithium-ion batteries, which are commonly used in consumer electronic products. Some of the reasons noted included being able to draw on advances in technology developed for lithium-ion batteries for consumer electronics over the past 15 years. This has led to success in keeping costs down whilst simultaneously improving energy density. Furthermore, the small cell size means that the amount of energy per cell is also small, and in the event that a single cell should suffer a defect, the overall impact will be much less than in the case of a defect occurring in a much larger battery cell. In addition, several billion 18650-type cells are manufactured each year, and these are also becoming safer year by year. In selecting battery manufacturers, Tesla Motors only considered reputable companies that had actively invested money and resources to minimize manufacturing defects within their cells.
In comparison to regular consumer electronic products, the usage conditions imposed on batteries for automotive-use are much stricter. For example, while regular batteries only need to be guaranteed to operate under temperatures between 0 and 70degrees C (32 to 158 degrees F), the corresponding range demanded for automotive-use battery is from -40 to +85 degrees C (-40 to 185 degrees F). It is interesting to note that although Tesla Motors has incorporated its own unique safety technology into its cells and battery packs it adopts the widely-used 18650-type commodity cells. We look forward to monitoring further developments in the future.
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