Tesla Roadster – Click above for high-res image gallery
While the lithium ion battery technology that everyone expects to be at the heart of the upcoming generation of electric vehicles was initially used in consumer electronics devices, only one company so far has committed to using laptop-style cells. Tesla Motors builds a battery pack for the Roadster that consists of 6,831 cells of the type used in portable computers. Virtually every battery maker developing lithium ion for automotive applications is creating larger format cells that have what is referred to as a prismatic (flat rectangular) shape.
Interestingly, one company seems to be taking a different approach. Panasonic – which has a joint venture with Toyota to produce nickel metal hydride and lithium ion batteries for hybrid and plug-in vehicles – reportedly intends to produce automotive battery packs using laptop cells. The company claims to have developed a new method for connecting the cells which will bring the cost down by half compared to the larger format cells. The savings are claimed to come from using existing production facilities and tooling to produce cells.
However, critics suggest that while it may be true that producing cells on existing equipment will be cheaper than building new lines for prismatic ones, the quantity of cells required if EV sales approach projections over the next decade could quickly outpace this approach. Using larger format cells means far fewer interconnects are required and the complexity of building packs from the cells is greatly reduced. Because of the size of packs needed for car applications, the prismatic cells also provide greater density and improved thermal management.