An electric vehicle battery (EVB, also known as a traction battery) is a rechargeable battery used to power the electric motors of a battery electric vehicle (BEV) or hybrid electric vehicle (HEV). Typically lithium-ion batteries, are specifically designed for high electric charge (or energy) capacity.
Electric vehicle batteries differ from starting, lighting, and ignition (SLI) batteries as they are designed to give power over sustained periods of time and are deep-cycle batteries. Batteries for electric vehicles are characterized by their relatively high power-to-weight ratio, specific energy, and energy density; smaller, lighter batteries are desirable because they reduce the weight of the vehicle and therefore improve its performance. Compared to liquid fuels, most current battery technologies have much lower specific energy, and this often impacts the maximum all-electric range of the vehicles.
The most common battery type in modern electric vehicles is lithium-ion and lithium polymer, because of their high energy density compared to their weight. Other types of rechargeable batteries used in electric vehicles include lead–acid (“flooded”, deep-cycle, and valve-regulated lead acid), nickel-cadmium, nickel–metal hydride, and, less commonly, zinc-air, and sodium nickel chloride (“zebra”) batteries. The amount of electricity (i.e. electric charge) stored in batteries is measured in ampere-hours or in coulombs, with the total energy often measured in kilowatt-hours (kWh).
A lithium polymer battery, or more correctly lithium-ion polymer battery, is a rechargeable battery of lithium-ion technology using a polymer electrolyte instead of a liquid electrolyte. High-conductivity semisolid (gel) polymers form this electrolyte. These batteries provide higher specific energy than other lithium battery types and are used in applications where weight is a critical feature, such as mobile devices, radio-controlled aircraft, and some electric vehicles.
A battery electric vehicle, pure electric vehicle, only-electric vehicle, fully electric vehicle, or all-electric vehicle is a type of electric vehicle (EV) that exclusively uses chemical energy stored in rechargeable battery packs, with no secondary source of propulsion. BEVs use electric motors and motor controllers instead of internal combustion engines for propulsion. They derive all power from battery packs and thus have no internal combustion engine, fuel cell, or fuel tank. BEVs include – but are not limited to – motorcycles, bicycles, scooters, skateboards, railcars, watercraft, forklifts, buses, trucks, and cars.
Electric vehicle battery types
Flooded lead-acid batteries are the oldest, cheapest, and, in the past, most common vehicle batteries available. There are two main types of lead-acid batteries: automobile engine starter batteries, and deep-cycle batteries. Automobile engine starter batteries are designed to use a small percentage of their capacity to provide high charge rates to start the engine, while deep cycle batteries are used to provide continuous electricity to run electric vehicles like forklifts or golf carts. Deep cycle batteries are also used as auxiliary batteries in recreational vehicles, but they require different, multi-stage charging. No lead acid battery should be discharged below 50% of its capacity, as it shortens the battery’s life. Flooded batteries require inspection of electrolyte levels and occasional replacement of water, which gases away during the normal charging cycle.
Previously, most electric vehicles used lead-acid batteries due to their mature technology, high availability, and low cost, with the notable exception of some early BEVs, such as the Detroit Electric which used a nickel-iron battery. Deep-cycle lead batteries are expensive and have a shorter life than the vehicle itself, typically needing replacement every 3 years.
Lead-acid batteries in EV applications end up being a significant (25–50%) portion of the final vehicle mass. Like all batteries, they have significantly lower specific energy than petroleum fuels—in this case, 30–50 W⋅h/kg. While the difference isn’t as extreme as it first appears due to the lighter drive-train in an EV, even the best batteries tend to lead to higher masses when applied to vehicles within a normal range. The efficiency (70–75%) and storage capacity of the current generation of common deep cycle lead acid batteries decreases with lower temperatures, and diverting power to run a heating coil reduces efficiency and range by up to 40%.
Nickel-metal hydride batteries are now considered a relatively mature technology. While less efficient (60–70%) in charging and discharging than even lead-acid, they have a specific energy of 30–80 W⋅h/kg, far higher than lead-acid. When used properly, nickel-metal hydride batteries can have exceptionally long lives, as has been demonstrated in their use in hybrid cars and in the surviving first-generation NiMH Toyota RAV4 EVs that still operate well after 100,000 miles (160,000 km) and over a decade of service. Downsides include poor efficiency, high self-discharge, very finicky charge cycles, and poor performance in cold weather.
The sodium nickel chloride or “Zebra” battery uses a molten sodium chloroaluminate salt as the electrolyte. A relatively mature technology, the Zebra battery has a specific energy of 120 W⋅h/kg. Since the battery must be heated for use, cold weather does not strongly affect its operation except for increasing heating costs. They have been used in several EVs such as the Modec commercial vehicle. Zebra batteries can last for a few thousand charge cycles and are non-toxic. The downsides to the Zebra battery include poor specific power (<300 W/kg) and the requirement of having to heat the electrolyte to about 270 °C (518 °F), which wastes some energy, presents difficulties in long-term storage of charge, and is potentially a hazard.
lithium-ion (and the mechanistically similar lithium polymer) batteries, were initially developed and commercialized for use in laptops and consumer electronics. With their high energy density and long cycle life they have become the leading battery type for use in EVs. The first commercialized lithium-ion chemistry was a lithium cobalt oxide cathode and a graphite anode first demonstrated by N. Godshall in 1979, and by John Goodenough, and Akira Yoshino shortly thereafter. The downside of traditional lithium-ion batteries includes sensitivity to temperature, low-temperature power performance, and performance degradation with age. Due to the volatility of organic electrolytes, the presence of highly oxidized metal oxides, and the thermal instability of the anode SEI layer, traditional lithium-ion batteries pose a fire safety risk if punctured or charged improperly. These early cells did not accept or supply charge when extremely cold, so heaters can be necessary for some climates to warm them. The maturity of this technology is moderate. The Tesla Roadster (2008) and other cars produced by the company used a modified form of traditional lithium-ion “laptop battery” cells.
Non–plug-in hybrid cars have battery capacities between 0.65 kW⋅h (2012 Honda Civic Hybrid) and 1.8 kW⋅h (2001 Toyota Prius).
Plug-in hybrid cars have battery capacities between 4.4 kW⋅h (2012 Toyota Prius Plug-in Hybrid) and 34 kW⋅h (Polestar 1).
All-electric cars have battery capacities between 6.0 kW⋅h (2012 Renault Twizy) and 212.7 kW⋅h (2022 GMC Hummer EV).