Tennessee Valley Authority
Electric Vehicle Batteries
Battery technology is very important to the feasibility of electric cars and has progressed over time. Plug-in cars manufactured in 2010 or later will typically use lithium-ion batteries. Vehicles built before 2010 may have used lead-acid, nickel-metal-hydride or nickel-cadmium batteries.
Key characteristics of batteries affecting their performance and use include energy density (the amount of useful energy stored by the battery per unit of weight); power density (the rate at which energy is converted into work, per unit of weight) and energy efficiency. Battery cost and expected life are also key considerations, as are safety and environmental impacts.
Learn more about the different types of batteries below.
Nickel-Metal-Hydride Batteries
Lead-Acid Batteries
Lead-acid batteries are commonly used to provide start-up or backup power in gasoline- and diesel-powered vehicles. In addition, lead-acid batteries have often been used in many special-purpose vehicles, including fork-lifts, low-speed utility vehicles and golf carts. Some do-it-yourself conversion kits for electric vehicles also use lead-acid batteries.
Lead-acid batteries are well understood, highly recycled and relatively inexpensive, but are comparatively heavy. They contain lead, which is toxic, and sulfuric acid, which is a hazardous material. Lead-acid batteries also emit hydrogen gas while being charged, which creates a fire and explosion hazard unless adequate ventilation is provided.
Economic incentives and regulatory constraints ensure that most (99 percent of the total) lead acid batteries are recycled.
Nickel-Metal-Hydride Batteries
Nickel-metal-hydride batteries are currently used in many hybrid electric vehicles, such as the Toyota Prius, Honda Insight and Ford Escape. In addition, nickel-metal-hydride batteries have been used for many consumer electronics and power tools. These batteries are characterized by power density. However, they have lower energy density and lower efficiency compared to lithium-ion batteries.
Nickel-Cadmium Batteries
Nickel-cadmium batteries were commonly used to power consumer electronics and power tools. They have largely been supplanted by nickel-metal-hydride and lithium-ion batteries. Some homemade electric vehicles may use nickel-cadmium batteries.
Cadmium is toxic, and proper disposal or recycling of these batteries is important. However, the economic incentives and regulatory constraints are not as effective in ensuring recycling for these batteries as they are for lead-acid batteries.
Lithium-Ion Batteries
Lithium-ion batteries have supplanted nickel-cadmium and nickel-metal-hydride batteries in most consumer electronics products that use rechargeable batteries. They are also the battery of choice for many of the plug-in vehicles planned by major automakers.
They are characterized by higher energy density, higher power density and better energy efficiency than earlier battery systems. Within the lithium ion family there are a number of different varieties, depending on how they are packaged and which chemical compounds they use.
Packaging formats include cylindrical, prismatic, button and pouch. Generally the prismatic format is thought to be ideal for vehicles, while the other formats are used in many consumer electronics.
Chemistries include lithium cobalt oxide, lithium nickel cobalt aluminum, lithium iron phosphate, lithium nickel cobalt manganese, lithium manganese spinel and lithium titanate.
For hybrid and electric vehicles, use of the lithium-manganese-spinel, lithium-iron-phosphate and lithium-titanate chemistries are leading candidates. Because they are mass-produced for consumer electronics, the costs of lithium-ion batteries are now lower than its competitors, especially for the cylindrical format with lithium-cobalt-oxide chemistry.
Taking advantage of this, the Tesla company uses thousands of lithium-cobalt-oxide cylindrical batteries in their battery-electric sports car. This approach requires a greater investment in the battery management system to ensure safety and battery life.
Recycling of lithium-ion batteries is starting to develop in the United States. Automotive manufacturers and utilities, including TVA, are working to find ways to re-use batteries after they are no longer ideal for use in vehicles. These batteries may have ample life left in them and could provide support to the power system
As additional distributed generation, such as solar panels, contributes more to the power grid, these batteries will help even out the unpredictability of these new technologies and help decrease the cost of the vehicle batteries.