VW's electric car battery evaluation includes laptop cylindrical cells

  • 29-Jul-2010 03:00 EDT
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The 18650 laptop cylindrical cell is one of the four lithium-ion configurations being evaluated by Volkswagen at the ERL.

Just a few years ago, European automakers were saying their fuel-economy future was based on the diesel. It's still true, but there's also a new emphasis on vehicle electrification. And the recent estimate that 3% of Volkswagen production by 2018 would be all-electric models was made emphatically by Dr. Martin Winterkorn, Chairman of the Board of Management of Volkswagen AG.

His pronouncement that "Volkswagen will be the automaker to mass-produce the electric car for everyone" didn't come from his German headquarters. It was made at the VW Electronics Research Laboratories (ERL) in Palo Alto, CA, in the heart of Silicon Valley. Adding emphasis was Martin Eberhard, a founder of Tesla who is now working at the ERL and making an effort to convince VW to take the Tesla approach to a battery pack.

That is based on the so-called 18650, the 18 x 65 mm (0.7 x 2.6 in) cylindrical lithium-ion cell used in laptops and the Tesla roadster. VW also is testing the other large Li-ion cell designs—the box-like prismatic, the pouch-type laminar, and even larger cylindrical types. But Eberhard made his case for the 18650.

He noted that over 2 billion of the 18650 type are produced every year, by a large number of suppliers, and production is based on decades of experience with small electronics, so high-quality cells can be sourced. He said the 18650 has the highest energy density and cited the following other advantages for the 18650 resulting from the size of the market and the number of suppliers:

• Available in every chemistry.

• Gets the newest engineering features first.

• Available at the lowest price per kilowatt hour (kW·h).

Further, Eberhard said, the small size is safer because less energy would be released in case of a thermal failure. The small size requires many cells, he agreed, but said a larger battery pack could be shaped to fit spaces in the vehicle that would pose packaging problems for individually larger cells. Because there would be so many more 18650 cells and with a history of good reliability, overall the battery pack would be more reliable and an individual cell failure would not be a significant event.

Eberhard pointed to two research projects at the laboratory, each with a first- and second-generation pack of 18650 cells.

One is the "ERL eTron," a performance car design with 8160 cells in a pack that weighs 550 kg (1213 lb). The first generation had a capacity of 63 kW·h and 319 kW power available at end of life (EOL). The second, at the same weight, had a capacity of 85 kW·h (35% improvement) and slightly more power (322 kWh) available at EOL.

The second is an eGolf, with a cell count of 4608 in a pack that weighs 320 kg (705 lb). The first generation had a capacity of 35 kW·h and 169 kW available at EOL. The second is rated at 48 kW·h (37% improvement) and slightly more power (172 kW) available at EOL.

The laboratory determination of EOL, he said, is equal to about 100,000 mi (160,000 km) of operation. Over 90% of the 18650 battery can be recycled, he said.

Eberhard admitted he hadn't actually "sold" VW on the 18650, but said he was satisfied with its growing acceptance at the ERL. Officially, VW continues to evaluate all battery chemistries and the four battery configurations, but Winterkorn laid out an aggressive introduction schedule for all-electrics, beyond the Touareg/Cayenne hybrid coming to market this year. He said an e-Golf and/or a production version of the e-Up concept (3.19-m/10.5-ft-long minicar that has been on the auto show circuit) would be available in 2013. The company's first all-electric to market, however, apparently will be an Audi-badged eTron, a low-volume model to be launched in late 2012.

Volkswagen has Li-ion battery development partnerships with Sanyo, Toshiba, Bosch, and BYD to lower costs. Winterkorn said that battery costs currently are €500-1000/kW·h.

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