Hybrid cars are now attractive and battery powered cars and plug-in hybrids are becoming possible. This is directly attributable to the advances in battery technology in the past few years. Hybrid cars are both the beneficiary of this technology and are the driving force for improvements. Battery powered cars still are limited in range, perhaps between 30 and 100 miles before recharging. Plug-in hybrids do not suffer any mileage limitations and offer the greatest economy of any of these cars. However they require a larger battery pack than a hybrid to gain this advantage. For commutes or shopping trips of the same 30-100 miles they could be designed to run on battery power alone. When the battery gets low the gasoline engine takes over and powers the car while recharging the battery. Unfortunately plug-ins are only available as retrofits to regular hybrids such as offered by EDrive Systems for the Prius hybrids. They are quite expensive at the present time, but may be the preffered mode of travel in the future.
Lead acid batteries have been used in cars since the electric starter was invented. They are heavy and do not have the energy density required for hybrid or electric vehicles. Nickel Metal Hydride batteries are being used in current generation hybrids and Lithium-ion batteries are on the verge of being cost effective for hybrids.
Lead acid batteries are proven, having been used for over a 100 years. They are available as sealed, maintenance free products and are mass produced today. Their life cycle is shorter than more advanced batteries, making them more expensive over the life of a car. Although lead is a toxic substance, these batteries are recycled at the extraordinarily high rate of 97%. A recent Advanced Lead Acid Battery has been developed that is expected to operate at the life cycle rates required for hybrid vehicles and if it lives up to its expectations may challenge the more expensive Nickel Metal Hydride batteries.
Nickel Metal Hydride (NIMH) batteries They are reliable and light weight and are expected to have a long cycle life equivalent to 100,000 miles or more. They have twice the energy density and three times the life expectancy of lead acid batteries. While they are more expensive than lead acid batteries, their lighter weight and longer life makes them the battery of choice for hybrid vehicles. Nickel is a carcinogen and no significant recycling system has been established1 but vehicle manufacturers have said that they will assist in the development of a recycling infrastructure.
Lithium-Ion batteries have a even higher energy density than NIMH batteries. They offer a shorter recharge time than other batteries which could be an advantage in regenerative braking in hybrid vehicles. Lithium-ion batteries are less toxic than other batteries, but no recycling system has been established. They are potentially easier to dispose of than lead acid batteries. Their current expense prohibits their widespread use. According to Electric Power Research Institute (EPRI), p 2-8, the cost projected for mass produced lithium ion batteries is comperable or lower than NiMH batteries. 70% fewer cells are required and the cost of materials can be expected to be less than in NIMH batteries. The cathode material used in Valance's phosphate-based Lithium-ion battery "replaces toxic heavy metals with phosphates, creating batteries that are more chemically stable."
Valence's batteries are being used in the Prius plug-in hybrid cited above. Federal Express has recently selected lithium-ion batteries, made by Hitachi, for use in a new fleet of diesel electric hybrids. The Nissan's Altra all electric vehicle also used Hitachi lithium ion batteries. According to SAFT, "their batteries have been selected for the electric and hybrid demonstration vehicles of most European and American manufacturers."
A variation of the Lithium-ion battery is the Lithium polymer battery which is extremely compact and can be made in almost any shape making it easily fitted into a vehicle. The free electrolyte is immobilized in ion conductive polymers which makes possible an even higher energy density and the small size and variety of shapes.
The battery comparison data in the adjacent table was taken from references #1 and #2 who have much more data than I have shown. Cost factors are extremely variable because of the state of development and low production rates for the new technologies.
EPRI has prepared a comprehensive report on the status of battery technology for the hybrid and plug-in hybrid vehicle market which is good reading for those interested in a more in-depth analysis of batteries and their assesment of the state of the technology at the time the report was written. The state of the art of Lithium-ion batteries has improved significantly since this report was written as evidenced by the use of these batteries in their use in the the applications cited above.
Some of the battery suppliers for NiMH batteries are Cobasys, Panosonic EV Energy Co and Sanyo. Lithium-ion batteries are either supplied by or in late stages of development by Toshiba, Johnson Controls, LG Chem, and Valence Technology. SAFT manufactures both NiMH and lithium-ion batteries for vehicular use. BatScap, Avestor, and ABAT have supplied Lithium polymer batteries for protypes of next generation electric vehicles.
Green Car Congress has a large section on batteries and carries the latest news on the subject. Research for this post was made much easier by referencing posts in Green Car Congress.
1) This information from Toyota - Lab data for the hybrid battery shows the equivalent of 180,000 miles (289,681 km) with no deterioration and expect it to last the life of the vehicle. Battery technology continues to improve: the second-generation model battery is 15% smaller, 25% lighter, and has 35% more specific power than the first. This is true of price as well. Between the 2003 and 2004 models, service battery costs came down 36% and are expected to continue to drop so that by the time replacements may be needed it won't be a much of an issue. Since the Prius went on sale in 2000, Toyota has not replaced a single battery for wear and tear.
Toyota has a comprehensive battery recycling program in place and has been recycling nickel-metal hydride batteries since the RAV4 Electric Vehicle was introduced in 1998. Every part of the battery, from the precious metals to the plastic, plates, steel case and the wiring, is recycled. To ensure that batteries come back to Toyota, each battery has a phone number on it to call for recycling information and dealers are paid a $200 "bounty" for each battery.