Battery Technology

History

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In 1990, the auto industry was forced into establishing an electric passenger car market when California’s Air Resources Board (CARB) implemented a Zero Emission Vehicle (ZEV) program: 2% of the vehicles produced for sale in California had to be ZEVs, increasing to 5% in 2001 and 10 percent in 2003. By 1996, CARB backed down on the 1998 deadline for the program, and in 2001, the program relaxed its standards to include “partial” zero emission vehicles (PZEV).

1993: The Clinton Administration announced a government initiative called the Partnership for a New Generation of Vehicles (PNGV). In the program, the government worked with the American auto industry to develop a clean car that could operate at up to 80 miles per gallon. Every prototype was a hybrid.

1997: The Toyota Prius was introduced to the Japanese market, two years before its original launch date, and first-year sales were nearly 18,000 units.

1997: Audi became the first manufacturer in Europe to take a hybrid vehicle into volume production: the Audi Duo, based on the A4 Avant. The vehicle was powered by a 90 horsepower 1.9-litre TDI in conjunction with a 29 horsepower electric motor.

1997 - 1999: A small selection of all-electric cars from the big automakers—including Honda’s EV Plus, GM’s EV1 and S-10 electric pickup, a Ford Ranger pickup, and Toyota’s RAV4 EV—were introduced in California. Despite the initial interest, these EVs failed to reach beyond a few hundred drivers for each model. Within a few years, the all-electric programs were dropped.

1999: Honda released the two-door Insight, the first hybrid car to hit the mass market in the United States. The Insight wins numerous awards, and received EPA mileage ratings of 61 mpg city and 70 mpg highway.

2000: Toyota released the Toyota Prius, the first hybrid four-door sedan available in the United States.

2002: Honda introduces the Honda Civic Hybrid, its second commercially available hybrid gasoline-electric car.

Introduction

Production of purely electric vehicles for commercial use has fallen by the wayside. General Motors, Ford, Honda and Toyota have all discontinued their electric vehicle (EV) programs - despite growing concern for the environment and over ever-increasing fuel costs, the market for EVs never really flourished. Today's hybrid vehicle uses a combination of a conventional gasoline engine and an evolved generation of the battery found in electric vehicles (EV). Because a hybrid also uses a gas engine, the size of the battery is not as large as a pure electric vehicle battery.

However, improvements in battery technology may one day resurrect EVs by extending their driving range. Electric vehicle advocates and engineers are now looking at gas-electric hybrids, which, unlike current hybrid offerings, could be plugged in to provide a greater capacity for running purely on electric power. A 'plug-in' hybrid electric vehicle (PHEV) is a hybrid which has additional battery capacity and the ability to be recharged from an external electrical outlet. The vehicle can be used for short trips of moderate speed without needing the internal combustion engine (ICE) component of the vehicle, thereby saving fuel costs.

Battery Types

Lead Acid

The lead acid battery in a conventional car contains enough energy to drive a small electric motor; these batteries are designed to deliver a burst of current for a short period of time only. Otherwise, the battery is only needed to support accessories such as the radio, lighting, power windows, etc. while the engine is not running. A hybrid vehicle uses a conventional lead acid battery for all the same reasons that a conventional car does; however, a hybrid also has a rechargeable deep cycle battery. The difference is that hybrid vehicles use electric motors to provide some portion of their driving force, and therefore need a great deal of stored electrical energy. And unlike gasoline engines, electric motors can be greater than 90 percent efficient at using that electrical energy.

Lead acid batteries were found to have too many limitations, making their continued use impractical. Because they are so heavy, it is unreasonable to add more or larger units in order to cope with the higher electrical demands of hybrid vehicles. They are also relatively slow charging, and do not lend themselves to deep cycling - a full discharge causes extra strain, and each cycle robs the battery of a small amount of capacity. They also pose more environmental concerns regarding proper disposal/recycling.

Lead-free alternatives, such as nickel metal hydride and lithium ion batteries, are already on the market in electric and electric-hybrid vehicles, and offer several advantages over conventional lead acid starter batteries. Performance and environmental benefits include:

• Higher energy (power) density
• Reduced weight/volume
• Longer battery life
• Improved fuel economy due to lighter weight and higher energy capacity
• Less material used, lower toxicity, and potentially recyclable

Nickel Metal Hydride

A nickel metal hydride battery (abbreviated NiMH) is a type of rechargeable battery similar to a nickel-cadmium (NiCd) battery, but has a hydride absorbing alloy for the anode instead of cadmium, which is an environmental hazard; therefore, it is less detrimental to the environment. Nickel metal hydride batteries are lightweight, have a longer shelf life, and produce more energy than lead acid batteries. For example: the first generation GM EV1s used lead-acid batteries in 1996, and a second generation batch with nickel metal hydride batteries in 1999. The "Gen I" cars got 55 to 95 miles (90 to 150 km) per charge with the lead acid batteries, while "Gen II" cars got an improved 75 to 150 miles (120 to 240 km) per charge with nickel metal hydride batteries.

Most - not all - current hybrids have a rechargeable NiMH battery as an integral part of their hybrid system, to assist in fuel savings and lower emissions. Applications of NiMH type batteries include hybrid vehicles such as the Honda Insight and Toyota Prius.

Lithium Ion

Lithium ion batteries (sometimes abbreviated Li-Ion) are a type of rechargeable battery commonly used in consumer electronics. They are currently one of the most popular types of battery, with one of the best energy-to-weight ratios, no memory effect and a slow loss of charge when not in use. Lithium ion battery applications have the potential of eclipsing the NiMH battery in hybrid vehicles [1]; compared to a lithium ion battery, the NiMH battery's volumetric energy density (amount of potential energy stored in the battery) is lower and self-discharge is higher. Lithium ion batteries are smaller, lighter, and have fewer volatile gases than NiMH batteries. However, they are not currently scaled for use in hybrid vehicle applications - while they have potential cost-saving attributes, they can be dangerous if mistreated, and, because they are less durable, may have a shorter lifespan compared to other battery types.

The Future

Based on further changes agreed upon in 2003, the ZEV program is scheduled to restart in 2005 with a set of complicated rules and tables which allow carmakers to use low-speed, low-range electric cars, hybrids, full function electric cars and ultimately fuel cells to pass prescribed standards and quantities up through 2017. These ZEV mandates could significantly increase the number of hybrids on the road.

External Links

http://www.hybridcars.com/battery-comparison.html

http://www.evworld.com/view.cfm?section=article&storyid=1042