An electric vehicle battery (EVB) or traction battery is a rechargeable battery used for propulsion of battery electric vehicles (BEVs). Traction batteries are used in forklifts, electric Golf carts, riding floor scrubbers, electric motorcycles, full-size electric cars, trucks, and vans, and other electric vehicles.
Electric vehicle batteries differ from starting, lighting, and ignition (SLI) batteries because they are designed to give power over sustained periods of time. Deep cycle batteries are used instead of SLI batteries for these applications. Traction batteries must be designed with a high ampere-hour capacity. Batteries for electric vehicles are characterized by their relatively high power-to-weight ratio, energy to weight ratio and energy density; smaller, lighter batteries reduce the weight of the vehicle and improve its performance. Compared to liquid fuels, all current battery technologies have much lower specific energy; and this often impacts the maximum all-electric range of the vehicles.
Batteries are usually the most expensive component of BEVs. The cost of battery manufacture is substantial, but increasing returns to scale lower costs.[1] Since the late 1990s, advances in battery technologies have been driven by demand for laptop computers and mobile phones, with consumer demand for more features, larger, brighter displays, and longer battery time driving research and development in the field. The BEV marketplace has reaped the benefits of these advances.
Traction batteries are routinely used all day, and fast–charged all night. Forklifts, for instance, are usually discharged and recharged every 24 hours of the work week.
The predicted market for automobile traction batteries is over $37 billion in 2020.[2]
On an energy basis, the price of electricity to run an EV is a small fraction of the cost of liquid fuel needed to produce an equivalent amount of energy (energy efficiency). The cost of replacing the batteries dominates the operating costs.[3]
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Flooded lead-acid batteries are the cheapest and most common traction batteries available, usually discharged to roughly 80%. They will accept high charge rates for fast charges. Flooded batteries require inspection of electrolyte level and replacement of water.
Traditionally, most electric vehicles have used lead-acid batteries due to their mature technology, high availability, and low cost (exception: some early EVs, such as the Detroit Electric, used a nickel-iron battery.) Like all batteries, these have an environmental impact through their construction, use, disposal or recycling. On the upside, vehicle battery recycling rates top 95% in the United States. 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 energy density than petroleum fuels—in this case, 30–40 Wh/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 with 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%. Recent advances in battery efficiency, capacity, materials, safety, toxicity and durability are likely to allow these superior characteristics to be applied in car-sized EVs.
Charging and operation of batteries typically results in the emission of hydrogen, oxygen and sulfur, which are naturally occurring and normally harmless if properly vented. Early Citicar owners discovered that, if not vented properly, unpleasant sulfur smells would leak into the cabin immediately after charging.
Lead-acid batteries powered such early-modern EVs as the original versions of the EV1 and the RAV4EV.
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 boast an energy density of 30–80 Wh/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 surviving NiMH RAV4EVs that still operate well after 100,000 miles (160,000 km) and over a decade of service. Downsides include the poor efficiency, high self-discharge, very finicky charge cycles, and poor performance in cold weather.
GM Ovonic produced the NiMH battery used in the second generation EV-1, and Cobasys makes a nearly identical battery (ten 1.2 V 85 Ah NiMH cells in series in contrast with eleven cells for Ovonic battery). This worked very well in the EV-1. Patent encumbrance has limited the use of these batteries in recent years.
The sodium or "zebra" battery uses a molten chloroaluminate (NaAlCl4) sodium as the electrolyte. This chemistry is also occasionally referred to as "hot salt". A relatively mature technology, the Zebra battery boasts an energy density of 120Wh/kg and reasonable series resistance. Since the battery must be heated for use, cold weather doesn't strongly affect its operation except for in increasing heating costs. They have been used in several EVs. Zebras can last for a few thousand charge cycles and are nontoxic. The downsides to the Zebra battery include poor power density (<300 W/kg) and the requirement of having to heat the electrolyte to about 270 °C (520 °F), which wastes some energy and presents difficulties in long-term storage of charge.
Zebra batteries have been used in the Modec vehicle commercial vehicle since it entered production in 2006.
Lithium-ion (and similar lithium polymer) batteries, widely known through their use in laptops and consumer electronics, dominate the most recent group of EVs in development. The traditional lithium-ion chemistry involves a lithium cobalt oxide cathode and a graphite anode. This yields cells with an impressive 200+ Wh/kg energy density[4] and good power density, and 80 to 90% charge/discharge efficiency. The downsides of traditional lithium-ion batteries include short cycle lives (hundreds to a few thousand charge cycles) and significant degradation with age. The cathode is also somewhat toxic. Also, traditional lithium-ion batteries can pose a fire safety risk if punctured or charged improperly. These laptop cells don't accept or supply charge in cold conditions, and so expensive and energy inefficient systems are necessary to warm them up. The maturity of this technology is moderate. The Tesla Roadster uses "blades" of traditional lithium-ion "laptop battery" cells that can be replaced individually as needed.
Most other EVs are utilizing new variations on lithium-ion chemistry that sacrifice energy and power density to provide fire resistance, environmental friendliness, very rapid charges (as low as a few minutes), and very long lifespans. These variants (phosphates, titanates, spinels, etc.) have been shown to have a much longer lifetime, with A123 expecting their lithium iron phosphate batteries to last for at least 10+ years and 7000+ charge cycles,[5] and LG Chem expecting their lithium-manganese spinel batteries to last up to 40 years.[6]
Much work is being done on lithium ion batteries in the lab.[7] Lithium vanadium oxide has already made its way into the Subaru prototype G4e, doubling energy density. Silicon nanowires,[8][9] silicon nanoparticles,[10] and tin nanoparticles[11][12] promise several times the energy density in the anode, while composite[13][14] and superlattice[15] cathodes also promise significant density improvements.
The cost of the battery when distributed over the life cycle of the vehicle (compared with an up to 10 years life cycle of an internal combustion engine vehicle) can easily be more than the cost of the electricity. This is because of the high initial cost relative to the life of the batteries. Using the 7000 cycle or 10 year life given in the previous section, 365 cycles per year would take 19 years to reach the 7000 cycles. Using the lower estimate of a ten year life gives 3650 cycles over ten years giving 146000 total miles driven. At $500 per kWh an 8 kWh battery costs $4000 resulting in $4000/146000 miles or $0.027 per mile. In reality a larger pack would be used to avoid stressing the battery by avoiding complete discharge or 100% charge. Adding a 2 kWh in battery adds $1000 to the cost resulting in $5000/146000 miles or $0.034/mile.
Scientists at Technical University of Denmark paid $10,000USD for a certified EV battery with 25kWh capacity, with no rebates or overprice.[16] Two out of 15 battery producers could supply the necessary technical documents about quality and fire safety.[17] Estimated time is 10 years before battery price comes down to 1/3 of present.[16] Battery professor Poul Norby states that lithium batteries will need to double their energy density and bring down the price from $500 (2010) to $100 per kWh capacity in order to make an impact on petrol cars.[18]
A solution to the range problem is detailed in an article on Battery Exchange and explains how the total battery needs would be reduced by using a battery exchange or battery swap system http://www.members.cox.net/rdoctors/evs.html. This requires substantial investment in setting up exchange stations but would allow for the use of lighter batteries as they would not be required to provide many miles of use. Lighter batteries make the ecar system far more efficient and lower overall costs.
The LiFePO4 technology has yielded batteries that have a higher miles/$ over the life of the packs but they require a complex control system. The manufacture of the batteries is still being developed and is not a reliable source.
Some batteries can be leased or rented instead of bought (see Think Global).
Toyota Prius 2012 plug-in's official page [19] declare 21 kilometres (13 mi) of autonomy and a battery capacity of 5.2 kWh with a ratio of 4 kilometres (2.5 mi) /(kW·h).
One article indicates that 10 kW·h of battery energy provides a range of about 20 miles (32 km) in a Toyota Prius, but this is not a primary source, and does not fit with estimates elsewhere of about 5 miles (8.0 km) /(kW·h).[20] The Chevrolet Volt is expected to achieve 50 MPG when running on the auxiliary power unit (a small onboard generator) - at 33% thermodynamic efficiency that would mean 12 kW·h for 50 miles (80 km), or about 240 watt-hours per mile. For prices of 1 kW·h of charge with various different battery technologies, see the "Energy/Consumer Price" column in the "Table of rechargeable battery technologies" section in the rechargeable battery article.
Rechargeable batteries used in electric vehicles include lead-acid ("flooded", Deep cycle, and VRLA), NiCd, nickel metal hydride, lithium ion, Li-ion polymer, and, less commonly, zinc-air and molten salt 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 watt hours.
The parity means that an electric vehicle does not cost more in the showrooms than a similar vehicle with an internal combustion engine. According to Kammen et al., 2008, new PEVs would become cost efficient to consumers if battery prices would decrease from $1300/kWh to about $500/kWh (so that the battery may pay for itself).[21]
The Nissan Leaf battery pack will be sold at a price of $18,000.[22] Nissan's initial price tag is at $750 per kilowatt hour[22] which may exceed production costs in the first two years[22].
Driving range parity means than the electric vehicle has the same range than an average all-combustion vehicle (500 kilometres or 310 miles), with 1+ kWh/Kg batteries.[23]
Japanese and European Union officials are in talks to jointly develop advanced rechargeable batteries for electric cars to help nations reduce greenhouse-gas emissions. Developing a battery that can power an electric vehicle 500 kilometres (310 mi) on a single charging is feasible, said Japanese battery maker GS Yuasa Corp. Sharp Corp and GS Yuasa are among Japanese solar-power cell and battery makers that may benefit from cooperation.[24]
Battery pack designs for Electric Vehicles (EVs) are complex and vary widely by manufacturer and specific application. However, they all incorporate a combination of several simple mechanical and electrical component systems which perform the basic required functions of the pack.
The actual battery cells can have different chemistry, physical shapes, and sizes as preferred by various pack manufacturers. Battery pack will always incorporate many discrete cells connected in series and parallel to achieve the total voltage and current requirements of the pack. Battery packs for all electric drive EVs can contain several hundred individual cells.
To assist in manufacturing and assembly, the large stack of cells is typically grouped into smaller stacks called modules. Several of these modules will be placed into a single pack. Within each module the cells are welded together to complete the electrical path for current flow. Modules can also incorporate cooling mechanisms, temperature monitors, and other devices. In most cases, modules also allow for monitoring the voltage produced by each battery cell in the stack by the Battery Management System (BMS).[28]
The battery cell stack has a main fuse which limits the current of the pack under a short circuit condition. A “service plug” or “service disconnect” can be removed to split the battery stack into two electrically isolated halves. With the service plug removed, the exposed main terminals of the battery present no high potential electrical danger to service technicians.[28][29]
The battery pack also contains relays, or contactors, which control the distribution of the battery pack’s electrical power to the output terminals. In most cases there will be a minimum of two main relays which connect the battery cell stack to the main positive and negative output terminals of the pack, those supplying high current to the electrical drive motor. Some pack designs will include alternate current paths for pre-charging the drive system through a pre-charge resistor or for powering an auxiliary buss which will also have their own associated control relays. For obvious safety reasons these relays are all normally open.[28][29]
The battery pack also contains a variety of temperature, voltage, and current sensors. Collection of data from the pack sensors and activation of the pack relays are accomplished by the pack ’s Battery Monitoring Unit (BMU) or Battery Management System (BMS). The BMS is also responsible for communications with the world outside the battery pack.[28]
Batteries in BEVs must be periodically recharged. BEVs most commonly charge from the power grid (at home or using a street or shop recharging point), which is in turn generated from a variety of domestic resources, such as coal, hydroelectricity, nuclear and others. Home power such as roof top photovoltaic solar cell panels, microhydro or wind may also be used and are promoted because of concerns regarding global warming.
Charging time is limited primarily by the capacity of the grid connection. A normal household outlet is between 1.5 kilowatts (in the US, Canada, Japan, and other countries with 110 volt supply) to 3 kilowatts (in countries with 240 V supply). Many European countries feed domestic consumers with a 3 phase system fused at 16-25 amp allowing for a theoretical capacity around 20-30 kW. However, this capacity is also required to feed the rest of the location and hence cannot be used practically and will also not be supported "en masse" by the distribution network. At this higher power level charging even a small, 7 kilowatt-hour (14–28 mi) pack, would probably require one hour. This is small compared to the effective power delivery rate of an average petrol pump, about 5,000 kilowatts. Even if the supply power can be increased, most batteries do not accept charge at greater than their charge rate ("1C"), because high charge rate has adverse effect on the discharge capacities of batteries.[30]
In 1995, some charging stations charged BEVs in one hour. In November 1997, Ford purchased a fast-charge system produced by AeroVironment called "PosiCharge" for testing its fleets of Ranger EVs, which charged their lead-acid batteries in between six and fifteen minutes. In February 1998, General Motors announced a version of its "Magne Charge" system which could recharge NiMH batteries in about ten minutes, providing a range of sixty to one hundred miles.[31]
In 2005, handheld device battery designs by Toshiba were claimed to be able to accept an 80% charge in as little as 60 seconds.[32] Scaling this specific power characteristic up to the same 7 kilowatt-hour EV pack would result in the need for a peak of 340 kilowatts of power from some source for those 60 seconds. It is not clear that such batteries will work directly in BEVs as heat build-up may make them unsafe.
Most people do not always require fast recharging because they have enough time, six to eight hours, during the work day or overnight to recharge. As the charging does not require attention it takes a few seconds for an owner to plug in and unplug their vehicle. Many BEV drivers prefer refueling at home, avoiding the inconvenience of visiting a fuel station. Some workplaces provide special parking bays for electric vehicles with charging equipment provided.
The charging power can be connected to the car in two ways. The first is a direct electrical connection known as conductive coupling. This might be as simple as a mains lead into a weatherproof socket through special high capacity cables with connectors to protect the user from high voltages.The modern standard for plug-in vehicle charging is the SAE 1772 conductive connector (IEC 62196 Type 1) in the USA. The ACEA has chosen the VDE-AR-E 2623-2-2 (IEC 62196 Type 2) for deployment in Europe, which, without a latch, means unnecessary extra power requirements for the locking mechanism.
The second approach is known as inductive charging. A special 'paddle' is inserted into a slot on the car. The paddle is one winding of a transformer, while the other is built into the car. When the paddle is inserted it completes a magnetic circuit which provides power to the battery pack. In one inductive charging system,[33] one winding is attached to the underside of the car, and the other stays on the floor of the garage. The advantage of the inductive approach is that there is no possibility of electrocution as there are no exposed conductors, although interlocks, special connectors and ground fault detectors can make conductive coupling nearly as safe. Inductive charging can also reduce vehicle weight, by moving more charging componentry offboard.[34] An inductive charging proponent from Toyota contended in 1998 that overall cost differences were minimal, while a conductive charging proponent from Ford contended that conductive charging was more cost efficient.[34]
In France, Électricité de France (EDF) and Toyota are installing recharging points for PHEVs on roads, streets and parking lots.[35] EDF is also partnering with Elektromotive, Ltd.[36] to install 250 new charging points over six months from October 2007 in London and elsewhere in the UK.[37] Recharging points also can be installed for specific uses, as in taxi stands. Public charging has been described as costly, unmanageable, and resource-intensive.
The range of a BEV depends on the number and type of batteries used. The weight and type of vehicle as well as terrain, weather, and the performance of the driver also have an impact, just as they do on the mileage of traditional vehicles. Electric vehicle conversion performance depends on a number of factors including the battery chemistry:
Finding the economic balance of range versus performance, battery capacity versus weight, and battery type versus cost challenges every EV manufacturer.
With an AC system or Advanced DC systems regenerative braking can extend range by up to 50% under extreme traffic conditions without complete stopping. Otherwise, the range is extended by about 10 to 15% in city driving, and only negligibly in highway driving, depending upon terrain.
BEVs (including buses and trucks) can also use genset trailers and pusher trailers in order to extend their range when desired without the additional weight during normal short range use. Discharged baset trailers can be replaced by recharged ones in a route point. If rented then maintenance costs can be deferred to the agency.
Such BEVs can become Hybrid vehicles depending on the trailer and car types of energy and powertrain.
An alternative to recharging is to exchange drained or nearly drained batteries (or battery range extender modules) with fully charged batteries. This is called battery swapping and is done in exchange stations.[41]
On the other hand, MIRA has announced a retrofit hybrid conversion kit that provides removable battery packs that plug into a wall outlet for charging.[42] Also XP Vehicles uses extension-cord-free charging hot-swap battery [43] ( removable power pack to recharge at home without extension cord [44]).
Features of swap stations include:[45]
Concerns about swap stations include:
Zinc-bromine flow batteries can be re-filled using a liquid, instead of recharged by connectors, saving time.
Three companies are working on battery lease plans. Greenstop[49] has completed trials of their ENVI Grid Network which allows consumers to easily monitor and recharge electric vehicle batteries. Think Car USA plans to lease the batteries for its City electric car to go on sale next year. Better Place is creating a system for consumers to "subscribe" to a service that offers recharging stations and battery exchange.[50]
Electric utilities are considering plans which would include providing electric vehicles to users (at a low price) and get their profits from selling the energy.[51]
Smart grid allows BEVs to provide power to the grid at any time, especially:
Pacific Gas and Electric Company (PG&E) has suggested that utilities could purchase used batteries for backup and load levelling purposes. They state that while these used batteries may be no longer usable in vehicles, their residual capacity still has significant value.[52]
Individual batteries are usually arranged into large battery packs of various voltage and ampere-hour capacity products to give the required energy capacity. Battery service life should be considered when calculating the extended cost of ownership, as all batteries eventually wear out and must be replaced. The rate at which they expire depends on a number of factors.
The depth of discharge (DOD) is the recommended proportion of the total available energy storage for which that battery will achieve its rated cycles. Deep cycle lead-acid batteries generally should not be discharged to below 20% of total capacity. More modern formulations can survive deeper cycles.
In real world use, some fleet Toyota RAV4 EVs, using NiMH batteries, have exceeded 100,000 miles (160,000 km) with little degradation in their daily range.[53] Quoting that report's concluding assessment:
Lithium ion batteries are perishable to some degree; they lose some of their maximum storage capacity per year even if they are not used. Nickel metal hydride batteries lose much less capacity and are cheaper for the storage capacity they give, but have a lower total capacity initially for the same weight.
Jay Leno's 1909 Baker Electric (see Baker Motor Vehicle) still operates on its original Edison cells. Battery replacement costs of BEVs may be partially or fully offset by the lack of regular maintenance such as oil and filter changes required for ICEVs, and by the greater reliability of BEVs due to their fewer moving parts. They also do away with many other parts that normally require servicing and maintenance in a regular car, such as on the gearbox, cooling system, and engine tuning. And by the time batteries do finally need definitive replacement, they can be replaced with later generation ones which may offer better performance characteristics, in the same way as you might replace old batteries from a digital camera with improved ones.
The safety issues of battery electric vehicles are largely dealt with by the international standard ISO 6469. This document is divided in three parts dealing with specific issues:
Firefighters and rescue personnel receive special training to deal with the higher voltages and chemicals encountered in electric and hybrid electric vehicle accidents. While BEV accidents may present unusual problems, such as fires and fumes resulting from rapid battery discharge, there is apparently no available information regarding whether they are inherently more or less dangerous than gasoline or diesel internal combustion vehicles which carry flammable fuels.
Patents may be used to suppress development or deployment of this technology. For instance, patents relevant to the use of Nickel metal hydride cells in cars were held by an offshoot of Chevron Corporation, a petroleum company, who maintained veto power over any sale or licensing of NiMH technology.[54][55]
R&D Magazine's [56] prestigious R&D 100 Awards — also called the “Oscars of Invention”— for 2008:
Next-Alternative is developing a carbon nanotube lead acid battery pack that will, according to the company, deliver 380 miles (610 km) range and can be recharged in less than 10 minutes. They plan to extend current battery life times 4-fold with this technology.[59]
The future of battery electric vehicles depends primarily upon the cost and availability of batteries with high energy densities, power density, and long life, as all other aspects such as motors, motor controllers, and chargers are fairly mature and cost-competitive with internal combustion engine components. Li-ion, Li-poly and zinc-air batteries have demonstrated energy densities high enough to deliver range and recharge times comparable to conventional vehicles.
Battery-operated vehicles (like the Nissan Leaf) are projected to have annual sales in 2020 of 100,000 units in the U.S. and 1.3 million worldwide — 1.8 percent of the 71 million cars expected to be sold in 2020. Another 3.9 million plug-ins and hybrids will be sold worldwide, bringing the total electric and hybrid market to about 7 percent of all cars sold in 2020.[60]
Bolloré a French automotive parts group developed a concept car the "Bluecar" using Lithium metal polymer batteries developed by a subsidiary Batscap. It had a range of 250 km and top speed of 125 km/h.[61]
Electric double-layer capacitors (or "ultracapacitors") are used in some electric vehicles, such as AFS Trinity's concept prototype, to store rapidly available energy with their high power density, in order to keep batteries within safe resistive heating limits and extend battery life.[62][63]
Since commercially available ultracapacitors have a low energy density no production electric cars use ultracapacitors exclusively.
US President Barack Obama has announced 48 new advanced battery and electric drive projects that will receive $2.4 billion in funding under the American Recovery and Reinvestment Act. These projects will accelerate the development of U.S. manufacturing capacity for batteries and electric drive components as well as the deployment of electric drive vehicles, helping to establish American leadership in creating the next generation of advanced vehicles.[64]
The announcement marks the single largest investment in advanced battery technology for hybrid and electric-drive vehicles ever made. Industry officials expect that this $2.4 billion investment, coupled with another $2.4 billion in cost share from the award winners, will result directly in the creation tens of thousands of manufacturing jobs in the U.S. battery and auto industries.
The new awards cover $1.5 billion in grants to United States-based manufacturers to produce batteries and their components and to expand battery recycling capacity.
Vice President Biden announced in Detroit over $1 billion in grants to companies and universities based in Michigan. Reflecting the state's leadership in clean energy manufacturing, Michigan companies and institutions are receiving the largest share of grant funding of any state. Two companies, A123 and Johnson Controls, will receive a total of approximately $550 million to establish a manufacturing base in the state for advanced batteries, and two others, Compact Power and Dow Kokam,[65] will receive a total of over $300 million for manufacturing battery cells and materials. Large automakers based in Michigan, including GM, Chrysler, and Ford, will receive a total of more than $400 million to manufacture batteries and electric drive components. And three educational institutions in Michigan — the University of Michigan, Wayne State University in Detroit, and Michigan Technological University in Houghton, in the Upper Peninsula — will receive a total of more than $10 million for education and workforce training programs to train researchers, technicians, and service providers, and to conduct consumer research to accelerate the transition towards advanced vehicles and batteries.
Energy Secretary Steven Chu visited Celgard,[66] in Charlotte, North Carolina, to announce a $49 million grant for the company to expand its separator production capacity to serve the expected increased demand for lithium-ion batteries from manufacturing facilities in the United States. Celgard will be expanding its manufacturing capacity in Charlotte, North Carolina, and nearby Concord, NC,[67] and the company expects the new separator production to come online in 2010. Celgard expects that approximately hundreds of jobs could be created, with the first of those jobs beginning as early as fall 2009.
EPA Administrator Lisa Jackson was in St. Petersburg, Florida, to announce a $95.5 million grant for Saft America, Inc.[68] to construct a new plant in Jacksonville on the site of the former Cecil Field military base, to manufacture lithium-ion cells, modules and battery packs for military, industrial, and agricultural vehicles.
Deputy Secretary of the Department of Transportation John Porcari visited East Penn Manufacturing Co[69]., in Lyon Station, Pennsylvania, to award the company a $32.5 million grant to increase production capacity for their valve regulated lead-acid batteries and the UltraBattery, a lead-acid battery combined with a carbon supercapacitor, for micro and mild hybrid applications.