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The Tesla Roadster Battery System

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The Tesla Roadster Battery System
Tesla Motors
August 16, 2006
By Gene Berdichevsky, Kurt Kelty, JB Straubel and Erik Toomre

Summary
This paper provides details about the design of the Tesla Roadster’s lithium-ion (Li-ion) battery pack (otherwise known as the ESS, or Energy Storage System) with a particular focus on the multiple safety systems, both passive and active, that are incorporated into the pack. This battery pack has been under development and refinement for over three years and is the cornerstone of the Tesla Roadster. The high level of redundancy and multiple layers of protection in the Tesla
Roadster battery pack have culminated in the safest large Li-ion battery that we or many of the experts in the field, with …show more content…

The Tesla Roadster battery pack is comprised of about 6800 of these 18650 cells, and the entire pack has a mass of about 450kg.
The engineers at Tesla Motors selected cells from reputable Fortune 500 battery suppliers that have each produced billions of safe, reliable, Li-ion batteries. All the cell manufacturers that
Tesla Motors has considered invest a great deal of money and engineering resources to minimize manufacturing defects within their cells. Overall, the selection criteria used by Tesla Motors included multiple factors, confirmed by extensive internal and external testing, that directly relate to the cell’s overall safety in the Tesla Roadster.
Design Safety Features: Cell Level
Since the 18650 cell is the fundamental building block of the battery pack, it is important that it be fault tolerant. The cells used in the Tesla Roadster all have an internal positive temperature coefficient (PTC) current limiting device. The primary role of this PTC is to limit short circuit current on an individual cell level. It is important to note that this device is completely passive and functions without any inputs from the rest of the battery pack systems.
A second level of protection is provided by the Current Interrupt Device (CID). Each battery cell used in the Tesla Roadster has an internal CID. These devices serve to protect the cell from

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