U.S. Department of Energy - Energy Efficiency and Renewable Energy
Vehicle Technologies Office
Batteries are important to our everyday lives and show up in various consumer electronics and appliances, from MP3 players to laptops to our vehicles. Batteries play an important role in our vehicles and are gradually becoming more and more important as they assume energy storage responsibilities from fuel in vehicle propulsion systems.
A battery is a device that stores chemical energy in its active materials and converts it, on demand, into electrical energy by means of an electrochemical reaction. An electrochemical reaction is a chemical reaction involving the transfer of electrons, and it is that reaction which creates electricity. There are three main parts of a battery: the anode, cathode, and electrolyte. The anode is the "fuel" electrode which gives up electrons to the external circuit to create the flow of electrons or electricity. The cathode is the oxidizing electrode which accepts electrons in the external circuit. Finally, the electrolyte carries the electric current, as ions, inside the cell, between the anode and cathode.
Batteries are made up of one or more basic electrochemical units called cells. Cells are usually connected in a series to increase the voltage. For example, two 1.5V AA cells connected in a series make a 3V battery. Batteries or cells are traditionally made from select chemistries that have high energy content.
Lead Acid Batteries
Lead acid batteries are the most prevalent battery chemistry used for vehicle starting and other ancillary power functions. They are also used in other applications such as backup power for utility companies, telecommunications, hospitals, and also, as power sources for golf carts, fork lifts, and other small motorized vehicles.
Nickel-Metal-Hydride Battery Pack
Nickel-Metal-Hydride batteries are used in a variety of applications from cell phones, to power tools, to hybrid vehicles. In fact, every hybrid vehicle on the market currently uses Nickel-Metal-Hydride high-voltage batteries in its battery system. Lithium ion batteries appear to be the future of battery chemistries, as they are not only rechargeable, but also relatively lightweight and have a high energy content.
Currently, lithium-ion batteries are used in cell phones, laptops, and, soon, their high-voltage counterparts are expected to be the battery chemistry of choice for hybrid and plug-in hybrid electric vehicles because of their performance in cold-weather applications, abuse tolerance, and ability to recharge at high rates.
The electrification of the vehicle is a growing trend. High-voltage batteries that store electric energy are used to help reduce the vehicle's fuel consumption. Traditionally, batteries were used for vehicle ignition, but are now progressing toward powering vehicle propulsion systems. The batteries that are used in vehicle propulsion are much larger, have a higher voltage and are more complex than the batteries that have been used in vehicle ignition.
Energy storage technologies, especially batteries, are essential for the development of advanced, fuel-efficient vehicles, which are critical components of the U.S. Department of Energy's (DOE) Energy Strategic Goal: "to protect our national and economic security by promoting a diverse supply and delivery of reliable, affordable, and environmentally sound energy."
The program's vision supports the development of durable and affordable advanced batteries that cover the full range of vehicle applications, from simple starting applications to full-power hybrid electric, all-electric, and fuel cell vehicles.
The Vehicle Technologies Office in Energy Efficiency and Renewable Energy Department at the DOE and the automotive industry identified several technical barriers associated with energy storage. These include cost, performance, life, and durability. These barriers are being addressed by the DOE's national research laboratories and battery manufacturers.
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