Lithium ion batteries, which provide much greater power density than the nickel metal hydride batteries used in today's gas-electric hybrids, are being moved out of the lab and readied for the production line.

Valence Technology says its lithium ion phosphate batteries were tested by independent engineering firm Exponent, Inc. as not likely to overheat or explode when crushed. In a heat intensity test the peak temperature was "100°C below the temperature required to initiate thermal runaway," according to a report by Exponent.

The first generation of lithium ion batteries used in consumer electronics and computers feature metal oxide in the terminals and have prompted safety recalls from overheating and catching fire. Valence substitutes phosphate in the terminals and are aimed at the automotive market.

Tesla Motors' new Roadster will be the first car from the company with lithium ion batteries. According to the company, the car will include 6,831 lithium ion cells that have passed UN and UL 1642 safety testing.