Traction battery

A traction battery (also known as electric vehicle battery, driving battery or cycles battery hereinafter) is an energy store, for the drive of electric vehicles is used and a plurality of interconnected elements (hence “battery”) is composed. It consists of a few to thousands of accumulator cells or cell blocks connected in parallel and serially. Also, supercapacitors or mechanical flywheel accumulators may be referred to as a traction battery when multiple ones are combined to power a vehicle.

The traction battery in electric cars often has a nominal voltage of 350 to 400 volts, corresponding to the usual three-phase alternating current. For pedelecs and electric scooters voltages of 24, 36 and 48 volts are common. In forklift trucks with electric drive are usually lead-acid batteries used with 80 V rated voltage. The traction battery is used here to equalize the weight.

For light, windshield wipers, radio, remote control, etc. use electric vehicles usually not directly their high-voltage traction battery, but a conventional 12- or 48-volt electrical system with small electrical energy storage similar to the starter battery in conventional vehicles.

After the electricity was used at the beginning of the 19th century for the transmission of information, around 1837/1838 were also the basics for an electric motor drive known and developed the electric motor operational. 1854 was developed by Wilhelm Josef Sinsteden and building on 1859 by Gaston Planté the lead-acid battery.

An arrangement of six of these cells with a rated voltage of 2 volts and spirally wound lead plates formed in 1881 in the Trouvé Tricycle by Gustave Trouvé the first traction battery (rated voltage 12 volts) for driving the self-sufficient electric vehicle without rails or cable tie. It was regulated only by closing or opening the circuit. However, the Trouvé tricycle still had the cranks of the tricycle serving as a base.

A few months later, in 1882, the Ayrton & Perry electric tricycle not only had no cranks and electric lights, but also an improved traction battery. The ten lead cells stored at a rated voltage of 20 volts 1.5 kWh and could be individually switched on and off, which allowed a power and speed regulation. Already with the first vehicles, the heavy traction battery was arranged as low as possible in order to improve stability and handling.

But while the battery cells were still placed openly in the first vehicles, built in the first electric cars (from 1888), the traction battery already in special housing or disguised it. The Accumulator Factory Tudorsche System Büsche & Müller OHG (now known as VARTA) was the first company in Germany to produce lead-acid batteries in 1888 industrially. In the railway sector was the Wittfeld accumulator railcaroperated with these batteries. Around 1900, successful attempts were made to electrically propel barges using accumulators. As a result, Watt-Akkumulatoren-Werke AG, the successor of a study company, founded Ziegel-Transport-Aktiengesellschaft (ZTG) in Zehdenick. The electric motors of more than 100 barges were powered by batteries and provided Berlin with bricks.

With the nickel-iron accumulator (Thomas Edison) developed around 1900 and the nickel-cadmium accumulator developed by the Swede Waldemar Jungner, alternative cell chemistries for traction batteries were available. The NiFe battery has been proven to be used in various automobiles and has a very long life. Jay Leno in the US owns a Baker Electric, where the nickel-iron batteries are still functional after almost 100 years. Henry Ford developed the Ford Model Talso as an electric vehicle. He had already ordered 150,000 nickel-iron batteries from Edison when his electric vehicle department went up in flames.

The invention of the electric starter, by means of a starter battery, the engine could be started without physical effort, initiated the decline of the first heyday of electric cars, as a result, the accumulator and battery development stagnated. Deep cycle lead-acid batteries were virtually the standard for traction applications by the end of the 20th century. These included, among others, submarines, battery power cars, industrial vehicles, such as forkliftsand wheelbarrows, but also electric wheelchairs. French manufacturers produced several thousand street legal vehicles with nickel-cadmium batteries in the 1990s. In 1990 by the CARB legislating in California, the car manufacturers should be forced to gradually zero-emission vehicles (US = Zero Emission Vehicle) offering that Akkumulatorforschung received strong impulses again.

For example, while the first traction batteries of the General Motors EV1 still used the available low-cost lead-acid batteries (26 blocks with a total capacity of 16.3 kWh and a nominal voltage of 312 volts), in the second embodiment those of Stanford R. Ovshinsky ready for series developed nickel-metal hydride batteries used. The traction battery was firmly installed in a center tunnel in the vehicle floor, which contributed to a high crash safety and very good handling characteristics.

While the sodium-sulfur battery for the BMW E1 or the zinc bromine battery announced for the Hotzenblitz never reached series production readiness, the sodium-nickel chloride cell (Zebra Battery) not only to a practical range of over 200 km, but also to applications in the military and space. Also interesting in this vehicle is the compact block arrangement, which made it possible to mount the entire traction battery in one piece from below and also contributed to the high level of safety for the automotive application.

The basics of cell chemistry for lithium-ion batteries were also laid during this time. However, after the easing of the CARB laws, the automotive industry stopped these activities, so that lithium-ion batteries only became important as traction batteries in the 21st century. Today, the various variants count as hope for significant improvements in power-to-weight ratio and load-bearing capacity.

Physical-technical properties
Compared to portable batteries or consumer cells, the cells of a traction battery have a much higher capacity. In addition, they are developed and manufactured by various manufacturers in various designs, partly on customer request. Standardized sizes do not exist. Common are both round cells, in which the electrodes are rod-shaped and cup-shaped, for example products of A123 Systems, as well as prismatic cells with plate-shaped electrode arrangement, for example, cells from Winston Battery.

High current resistant, deep-cycle battery systems are used which are capable of delivering or receiving electrical energy depending on the driving conditions and survive many charge-discharge cycles. Unlike starter batteries, lead-acid batteries, for example, can be discharged up to 80% deep by special design of the lead grid and separators without being damaged.

While blocks for lead car starter batteries for 12 V or 24 V capacities 36-80 ampere-hours (Ah), have to be connected together for forklifts cells with capacities from 100 to 1000 Ah to operating voltages of, for example 24 to 96 volts, for Electric cars can reach up to several hundred volts. The sizes are therefore considerably larger. Higher voltages reduce the currents flowing and thus, among other things, reduce the ohmic losses in the lines and the thermal losses during charging and discharging and reduce the weight (cable).

By serial interconnection of individual cells results in the driving voltage or traction voltage. By increasing the size of the cells or by connecting cells in parallel, the storage capacity and ampacity can be increased. The product of traction voltage (V) and electrical charge / galvanic capacity of the single cells / cells connected in parallel (Ah) gives the energy content of the traction battery.

Requirements for use in vehicles
The mobile application of traction batteries requires higher safety requirements compared to stationary use. Above all, the safety of mechanical actions has to be proven. This is achieved by using safe cell chemistries (for example, lithium iron phosphate accumulators) with often poorer electrical characteristics, the safe design of the accommodation in the vehicle (for example, crash-tested battery trays in the subsoil) or a combination of both methods. How strong the influence of the safety requirements of traction batteries is, can be exemplified by the delayed start of production of the Opel Amperabe traced. Reason was the (only several weeks) after a crash test on fire traction battery of the identical model Chevrolet Volt.

Different requirements for all-electric and hybrid vehicles
Because all-electric vehicles store all the electrical energy needed to travel, high-capacity battery cells are used to minimize space and weight for the amount of energy needed. Due to the necessary capacity of the battery (cell or module size), the current carrying capacity of the cells for the discharging and charging processes is usually given. The load is also more uniform and with lower currents relative to the battery capacity than in hybrid vehicles.

In hybrid electric vehicles, the main part of the drive energy is carried in the form of chemical energy (fuel). The traction battery has a much smaller capacity. It stores electrical energy for locomotion and absorbs recuperation energy of the regenerative brake. For this purpose, high-current cells are used which, despite their lower capacitance, can realize the necessary (often short-term) high current load with good efficiency and the required service life.

Nominal capacity, load capacity, manufacturer’s information
The nominal capacity is the amount of energy that can be withdrawn by the manufacturer under specified criteria. For capacity comparisons, it is important to comply with these criteria. Thus, an accumulator with the specifications 12 V / 60 Ah C3 has a higher capacity than a rechargeable battery of the same size with the designation C5 or C20. The specification Cx characterizes the discharge duration for the specified capacity in hours. In C3 60 Ah can be taken in three hours uniform discharge, ie higher currents are possible than with C5 or C20, which is important for use as a traction battery, because the currents often are in practice for this measurement currents (see also C- Rate and Peukert equation).

For heavy-duty lithium-ion batteries, the statement of the current carrying capacity in relation to the capacity has prevailed. In this case, for example, for a cell 3.2 V 100 Ah for standard discharge at 0.5 C (or even 0.5 CA), this means that the capacitance was determined with a discharge current of 50 A. Usual are capacitance specifications at 0.5 C or 1 C, the permissible continuous load capacity of 3 C or more (in the example at 3 C ie 300 A), the short-term load even more (here 20 CA, ie 2000 A) may be.

Increasingly, the capacity of a traction battery is no longer given in ampere-hours of single cells, but in watt-hours. Thus, different types are comparable with each other, since the voltage is included. Starter batteries have an energy content of 496.8-960 Wh, traction batteries for forklift trucks at 4,800-28,800 Wh and for the Toyota Prius II at 1,310 Wh.

Battery cost
In 2010, scientists at the Technical University of Denmark paid $10,000 for a certified EV battery with 25 kWh capacity (i.e. $400 per kilowatt hour), with no rebates or surcharges. Two out of 15 battery producers could supply the necessary technical documents about quality and fire safety. In 2010 it was estimated that at most 10 years would pass before the battery price would come down to 1/3.

According to a 2010 study, by the National Research Council, the cost of a lithium-ion battery pack was about US$1,700/kWh of usable energy, and considering that a PHEV-10 requires about 2.0 kWh and a PHEV-40 about 8 kWh, the manufacturer cost of the battery pack for a PHEV-10 is around US$3,000 and it goes up to US$14,000 for a PHEV-40. The MIT Technology Review estimated the cost of automotive battery packs to be between US$225 to US$500 per kilowatt-hour by 2020. A 2013 study by the American Council for an Energy-Efficient Economy reported that battery costs came down from US$1,300 per kWh in 2007 to US$500 per kWh in 2012. The U.S. Department of Energy has set cost targets for its sponsored battery research of US$300 per kWh in 2015 and US$125 per kWh by 2022. Cost reductions through advances in battery technology and higher production volumes will allow plug-in electric vehicles to be more competitive with conventional internal combustion engine vehicles. In 2016, the world had a Li-Ion production capacity of 41.57 GWh.

The actual costs for cells are subject to much debate and speculation as most EV manufacturers refuse to discuss this topic in detail. However, in October 2015, car maker GM revealed at their annual Global Business Conference that they expected a price of US$145 per-kilowatt-hour for Li-ion cells entering 2016, substantially lower than other analyst’s cost estimates. GM also expects a cost of US$100 per kwh by the end of 2021.

According to a study published in February 2016 by Bloomberg New Energy Finance (BNEF), battery prices fell 65% since 2010, and 35% just in 2015, reaching US$350 per kWh. The study concludes that battery costs are on a trajectory to make electric vehicles without government subsidies as affordable as internal combustion engine cars in most countries by 2022. BNEF projects that by 2040, long-range electric cars will cost less than US$22,000 expressed in 2016 dollars. BNEF expects electric car battery costs to be well below US$120 per kWh by 2030, and to fall further thereafter as new chemistries become available.

Battery cost estimate comparison

Battery Type Year Cost ($/kWh)
Li-Ion 2016 130-145
Li-Ion 2014 200–300
Li-Ion 2012 500–600
Li-Ion 2012 400
Li-Ion 2012 520-650
Li-Ion 2012 752
Li-Ion 2012 689
Li-Ion 2013 800–1000
Li-Ion 2010 750
Nickel Metal Hydride 2004 750
Nickel Metal Hydride 2013 500–550
Nickel Metal Hydride 350
Lead acid 256.68

Battery longevity estimate comparison

Battery Type Year of Estimate Cycles Miles Years
Li-Ion 2016 >4000 1,000,000 >10
Li-Ion 100,000 5
Li-Ion 60,000 5
Li-Ion 2002 2-4
Li-Ion 1997 >1,000
Nickel Metal Hydride 2001 100,000 4
Nickel Metal Hydride 1999 >90,000
Nickel Metal Hydride 200,000
Nickel Metal Hydride 1999 1000 93,205.7
Nickel Metal Hydride 1995 <2,000
Nickel Metal Hydride 2002 2000
Nickel Metal Hydride 1997 >1,000
Nickel Metal Hydride 1997 >1,000
Lead acid 1997 300–500

EV parity
In 2010, battery professor Poul Norby stated that he believed that lithium batteries will need to double their specific energy and bring down the price from $500 (2010) to $100 per kWh capacity in order to make an impact on petrol cars. Citigroup indicates $230/kWh.

Toyota Prius 2012 plug-in’s official page declare 21 kilometres (13 mi) of autonomy and a battery capacity of 5.2 kWh with a ratio of 4 kilometres (2.5 mi)/kWh, while the Addax (2015 model) utility vehicle already reaches 110 kilometres (68.5 mi) or a ratio of 7.5 kilometers (4.6 mi)/kWh.

Battery electric cars achieve about 5 miles (8.0 km)/kWh. The Chevrolet Volt is expected to achieve 50 MPGe when running on the auxiliary power unit (a small onboard generator) – at 33% thermodynamic efficiency that would mean 12 kWh for 50 miles (80 km), or about 240 watt-hours per mile. For prices of 1 kWh 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.

United States Secretary of Energy Steven Chu predicted costs for a 40-mile range battery will drop from a price in 2008 of $12K to $3,600 in 2015 and further to $1,500 by 2020. Li-ion, Li-poly, Aluminium-air batteries and zinc-air batteries have demonstrated specific energies high enough to deliver range and recharge times comparable to conventional fossil fuelled vehicles.

Cost parity
Different costs are important. One issue is purchase price, the other issue is total cost of ownership. As of 2015, electric cars are more expensive to initially purchase, but cheaper to run, and in at least some cases, total cost of ownership may be lower.

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).

In 2010, the Nissan Leaf battery pack was reportedly produced at a cost of $18,000. Nissan’s initial production costs at the launch of the Leaf were therefore about $750 per kilowatt hour (for the 24 kWh battery).

In 2012, McKinsey Quarterly linked battery prices to gasoline prices on a basis of 5-year total cost of ownership for a car, estimating that $3.50/gallon equate to $250/kWh. In 2017 McKinsey estimated that electric cars are competitive at a battery pack cost of $100/kWh (around 2030), and expects pack costs to be $190/kWh by 2020.

In October 2015, car maker GM revealed at their annual Global Business Conference that they expected a price of $145 per kilowatt hour for Li-ion cells entering 2016.

Range parity
Driving range parity means that the electric vehicle has the same range than an average all-combustion vehicle (500 kilometres or 310 miles), with 1+ kWh/kg batteries. Higher range means that the electric vehicles would run more kilometers without recharge.

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.

The lithium-ion battery in the AC Propulsion tzero provides 400 to 500 km (200 to 300 mi) of range per charge (single charge range). The list price of this vehicle when it was released in 2003 was $220,000.
Driving in a Daihatsu Mira equipped with 74 kWh lithium ion batteries, the Japan EV Club has achieved a world record for an electric car: 1,003 kilometres (623 mi) without recharging.
Zonda Bus, in Jiangsu, China offers the Zonda Bus New Energy with a 500-kilometre (310 mi) only-electric range.[clarification needed]
Tesla Model S with 85 kWh battery has a range of 510 km (320 miles). Tesla Model S has been built since 2012. It is priced around US$100,000.
The supercar Rimac Concept One with 82 kWh battery has a range of 500 km. The car is built since 2013.
The pure electric car BYD e6 with 60 kWh battery has a range of 300 km.

Influences on usable capacity
In traction operation, the total rated capacity can not be used. On the one hand, the usable capacity is reduced until it drops to the set final voltage at high currents removed (see Peukert effect), on the other hand determined in serial interconnections, the cell / cell block with the least capacity, the usable capacity without damaging deep discharge.

The cells of a traction battery have production-related as well as use effects always differences in capacity and current output (internal resistance). As a result, during operation, the cells are charged differently, there is a drift apart, which reduces the usable capacity of the entire battery. While the capacity of the best cells can never be fully exploited, the weak cells are regularly overloaded, over-discharged or overcharged. Also, to reduce or avoid these effects, modern traction batteries include balancers and battery management systemsused. Lower temperatures also reduce the ability of the traction battery to discharge high currents and enhance the Peukert effect, as the mobility of the electrons generally decreases. To counteract this effect and as various battery technologies become unusable at lower temperatures, traction batteries are often also equipped with additional heating. This takes over either during the connection to the power grid, the temperature control or heats up from its energy content itself. This and additional consumers such as electric interior heating or air conditioning reduces the winter range, although the usable energy content of the traction battery is available even in winter.

The discharge depth of the battery cells is often limited by the battery management system (BMS), usually 60-80% of the rated capacity. Especially in consumption calculations and comparisons of different traction batteries, these circumstances must be taken into account. This “useful capacity” is rarely reported by the automaker, but described as a usable range of rated capacity. Thus, the Chevrolet Volt or Opel Ampera a usable battery window of 30-80% is given, which are (in favor of durability) only 50% of the nominal capacity of 16 kWh.

Lifetime and cycle stability
Plug in America carried out a survey of drivers of the Tesla Roadster regarding the lifetime of the installed batteries. It was found that after 160,000 km, the batteries still had a residual capacity of 80 to 85 percent. This was independent of the climate zone in which the vehicle was moved. The Tesla Roadster was built and sold between 2008 and 2012.

Lithium iron phosphate batteries, which are also used as traction batteries, reach more than 5000 cycles with a discharge depth of 70% according to the manufacturer.

The best-selling electric car is the Nissan Leaf, which has been in production since 2010. Nissan announced in 2015 that until then only 0.01% of the batteries had to be replaced due to defect or problems and that only because of externally inflicted damage. There are occasionally vehicles that have already driven more than 200 000 km. These would have no problems with the battery.

Loading times
Electric cars like Tesla Model S, Renault ZOE, BMW i3, etc. can recharge their batteries at fast charging stations by 80 percent within 30 minutes. In July 2013, Tesla CTO JB Straubel announced that the next generation of superchargers would only need 5 to 10 minutes, which he wanted to put into practice within the next few years. The superchargers as of 1 November 2016 have a maximum charging power of 120 kW in Europe and typically indicate 40 minutes for an 80% charge and 75 minutes for a full charge.

According to the manufacturer BYD, the lithium-iron-phosphate battery of the e6 electric car is 80% charged within 15 minutes at a fast charging station and 100% after 40 minutes.

Application examples
Traction batteries made of closed lead-acid batteries are used in electric forklifts and serve as counterweights to the stacked goods in order to be able to transport a certain (larger) physical mass with the help of the counterweights. They are still used in driverless transport systems for even applications. The high weight and the strong temperature dependence have an adverse effect on height differences or gradients and in winter operation. Therefore, they are less suitable for use in the electric bicycle, electric scooters and electric cars.

In modern electric bicycles / pedelecs almost exclusively rechargeable batteries based on lithium and lithium are used for space and weight reasons. Initially used lead-acid batteries have not been proven.

When electric scooters are as traction batteries various battery systems in use. Again, the lead acid battery is considered outdated, NiCd as proven and lithium-based batteries as powerful.

When used in hybrid vehicles such as the Toyota Prius or the Honda Civic IMA currently (2012) traction batteries type nickel metal hydride battery with voltages of several 100 volts and less than 10 ampere hours are used. The limitation of capacity results from patent regulations which severely restrict production and further developments. New developments are usually equipped with lithium-based traction batteries.

In solar vehicles, for weight and volume reasons, only modern high-performance lithium-based batteries are used. The world’s largest solar vehicle, the Tûranor PlanetSolar catamaran, currently has the world’s largest lithium traction battery, at 1.13 MWh. The cells come from the Thuringian cell producer Gaia Akkumulatorenwerk GmbH.

In electric cars today (1/2016) almost only lithium-ion batteries are used (see Tesla Model S, BMW i3, Renault ZOE, Nissan Leaf, VW e-up !, etc.). In the vehicles Blue Car and Bluebus of the French group Bolloré comes as a further technique of the lithium polymer accumulator used. The company Batscap, which produces these batteries in France and Québec, also belongs to the Bolloré group.

In submarines, traction batteries have been and are being used for underwater cruising, as this often prohibits the use of internal combustion engines generating exhaust gases.

Environmental aspects
Traction batteries consist of single cells, which lie in both the size (capacity) and in the number of single cells (voltage) significantly above the device batteries. Therefore, they contain larger amounts of individual raw materials, so that after use a return to the material cycle (recycling) economically and ecologically sensible and necessary. For starter batteries and traction batteries as lead acid battery therefore a battery deposit of 7.50 Euro / piece was introduced in Germany with the battery regulation. The return rate is over 90%.

For modern lithium-ion batteries such a deposit solution does not yet exist.

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 specific power, in order to keep batteries within safe resistive heating limits and extend battery life.

Since commercially available ultracapacitors have a low specific energy no production electric cars use ultracapacitors exclusively. But using an Electric car with both Battery and ultracapacitor can reduce the limitations of both.

As U.S. President Barack Obama announced 48 new advanced battery and electric drive projects that would 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.

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.

U.S. Vice President Joe 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 Systems 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, 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, 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, North Carolina, 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. 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, 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.

Source from Wikipedia