The acceptance of hybrid vehicles by American consumers, even with a price premium over gasoline autos, has surprised many industry watchers. According to one market analyst, the market for hybrid gas-electric vehicles has grown more than 960% since their institution in 2000. Although hybrid sales are only about 1% of the car market today, as gas prices continue to increase, so will the demand for hybrid vehicles.
When auto manufacturers first began developing hybrid vehicles, the most viable battery technology was nickel-metal-hydride (NiMH). These batteries have proven to be suitably safe for automotive applications, as overheating issues have been addressed through proper thermal management and limited spectrum of use. However, safe Li-ion battery technology is available as an alternative to NiMH. Phosphate Li-ion batteries are already being adopted by developers of commercial electric and hybrid fleet vehicles. To reach a level of acceptance in the consumer auto market, however, several key areas must be addressed: safety, cost efficiency, reliability and greater energy storage for flexibility in powering systems.
Those familiar with traditional Li-ion batteries realize the benefits they offer over other battery chemistries, such as higher energy density (lighter weight and smaller size), better cycle life, charge efficiency, ease of charge (charging quickly or when hot), minimal self-discharge during storage and better performance in extreme environmental temperatures. But, oxide-based Li-ion batteries are also known to exhibit thermal runaway in abuse conditions. This has limited the application of Li-ion to small portable devices, such as cellular phones and laptop computers.
Alternate designs of Li-ion batteries using safer cathode materials are now available in large formats and can provide the safety needed for automotive applications. Using a phosphate cathode material, today's most advanced Li-ion batteries greatly reduce the potential of thermal runaway that are present in traditional oxide-based Li-ion batteries. And, the elements in the phosphate-based cathode material are readily available, whereas with NiMH and some oxide-based Li-ion batteries, the abundance of cathode materials could be a limiting factor in high-volume production.
Using a lower-cost cathode material, phosphate Li-ion batteries can be less expensive than their cobalt-based counterparts. In non-automotive markets, cobalt Li-ion batteries command a price premium for the benefits they provide. These same benefits will apply to automotive applications, but with a premium. However, with the volume production, that premium will reduce significantly.
Choice of cell construction used within the battery pack can impact scale, price and reliability. The 18650 cell is currently the industry standard for Li-ion and is now the most cost-effective format. For future generations of automotive Li-ion battery packs, battery manufacturers are investigating the use of larger cells that could offer reliability and cost benefits.
A key reliability benefit of phosphate Li-ion batteries is the number of discharge/charge cycles they offer over NiMH batteries. In order to meet the requirement in some states that batteries in hybrid vehicles last at least 100,000 miles or 10 years, auto designers have limited the draw from NiMH packs to just 10% to 20% of the available energy. Li-ion batteries can be discharged more fully yet still provide the required longevity. This gives automotive system designers more flexibility in more fully using the battery to handle more and different loads from onboard systems.
Today's phosphate-based Li-ion batteries offer the safety, performance and reliability needed for the automotive industry. With continued near-term adoption by commercial fleet vehicle manufacturers, these batteries will come down in price. And, this may just be the catalyst to spur the ubiquitous adoption of hybrid vehicles in the consumer sector, helping America to reduce dependence on foreign oil as well as reduce greenhouse gas emissions.
ABOUT THE AUTHOR
Dean Bogues is president of the Americas and Europe, Valence Technology. He is responsible for all business functions in America and Europe, as well as for worldwide sales and marketing.