Seeker Blog

Tesla Motors’ battery system is the make-or-break of the car. This Tesla blog post gives some insight into the sophistication of the design:

The Tesla Roadster’s battery is extraordinary and in some respects is our company’s “secret sauce.” We call it the Energy Storage System (ESS). It is comprised of 6,831 individual lithium ion cells, each similar to the 6 to 12 cells (made by top-tier 18650 cell providers) found in many standard laptop computers. The cells, in turn, are housed in 11 modules. The ESS weighs about 900 pounds and contains about 53 kilowatt-hours of energy.

Our ESS contains multiple overlapping safety systems – some active and some passive. Each module has its own microprocessor circuitry that monitors a wide range of conditions as well as actively balancing the cell voltage to help mitigate the danger of overcharging (and potential damage from over-discharge). There are sensors inside the ESS that sniff for smoke, check for the existence of water immersions (if the car were driven into a lake, for example), and continually monitor the pack to ensure that it is thermally stable. Each cell is independently fused, not once, but twice. And the pack has been designed to passively contain any single cell entering thermal runaway (e.g. start burning) without propagating further. (For more information on the Tesla Roadster’s ESS, see our blog and white paper on the subject.)

Collectively all these features (plus some others) give us confidence that the ESS is among the safest Li-ion battery packs made. In this post, I’ll address some of the regulatory work and support testing that we have done to validate the safety of the ESS. Given the size of our Li-ion pack, our volume projections, and the automotive future that Tesla Motors represents, we are getting attention from regulators (and not just in the United States).

To begin with, let’s talk about some of the process steps in bringing a new large Li-ion battery to market. Almost anybody can start a company and assemble batteries. However, depending on the volumes and chemistry involved, you can’t sell and ship them to the general public or untrained users without going through a whole battery (get the pun? ) of tests to demonstrate safety.

It is very bad marketing mojo to have the batteries blow up. And in the end it all comes down to regulations — which means mountains of paperwork and killo-hours of testing.

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