Drive battery

from Wikipedia, the free encyclopedia
Drive battery of the Nissan Leaf electric car made up of cell blocks with several individual cells each

A traction battery (also known as high-voltage battery , traction battery or cycles battery hereinafter) is a mobile electrical energy storage device , preferably for drive of electric vehicles is used and supplies the electric motors of electric vehicles with energy. The term is used synonymously for the buffer battery in hydrogen fuel cell vehicles. It consists of several interconnected elements (hence “ battery ”) and from a few to thousands of accumulator cells or cell blocks interconnected in parallel and in series . Also, super-capacitors or mechanical flywheel storage means can be referred to as the traction battery, if a plurality thereof are combined to a vehicle to drive.

General

For electric cars , nominal voltages of several hundred volts direct voltage (hence the name high-voltage storage ), which can have a certain relation to the usual voltages in three-phase alternating current networks, are quite common. Higher nominal battery voltages (above 400 volts, going into the range of 1000 volts direct voltage) are not uncommon in battery-powered high-performance cars, as well as in battery buses. Voltages of 24, 36 and 48 volts are common for pedelecs and electric scooters . In forklifts and other industrial trucks with electric drive , lead batteries with a nominal voltage of 80 volts are often used, which also serve to balance the weight and are often referred to as traction batteries (batteries for traction applications ).

Consumers such as lights, windshield wipers, radio, remote control, etc. in electric vehicles are usually not supplied from the high-voltage drive battery , but from a standard 12- or 48-volt electrical system with a small electrical energy store similar to the starter battery in conventional vehicles. While starter batteries are connected to the body ("minus ground"), drive batteries with a higher voltage are installed in vehicles insulated from the body.

history

Drive battery in the Egger-Lohner electric vehicle , built in 1899

After electricity was used for communications at the beginning of the 19th century, the basics for an electric motor drive were known around 1837/1838 and the electric motor was developed ready for use. The lead accumulator was developed by Wilhelm Josef Sinsteden in 1854 and, based on this, by Gaston Planté in 1859 .

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

A few months later, in 1882, the Ayrton & Perry electric tricycle was not only on the road without cranks and with electric lighting, but also with an improved drive battery. The ten lead cells stored 1.5 kWh at a nominal voltage of 20 volts and could be switched on and off individually, which enabled power and speed to be regulated. Even in the first vehicles, the heavy drive battery was placed as deep as possible in order to improve stability and driving behavior.

While the battery cells were still open in the first vehicles, in the first electric cars (from 1888) the drive battery was built into special housings or covered. The accumulator factory Tudorschen Systems Büsche & Müller OHG (now known as Varta AG ) was the first company in Germany to manufacture lead-acid batteries on an industrial scale in 1888. In the railway sector , the Wittfeld accumulator railcar was operated with these batteries. Around 1900 there were successful attempts to drive inland waterway vessels electrically using accumulators. As a result, Watt-Akkumulatoren-Werke AG founded the Ziegel-Transport-Aktiengesellschaft (ZTG) in Zehdenick as the successor to a study company. The electric motors of over 100 barges were fed by accumulators and supplied 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 were available for drive batteries . The NiFe battery has been proven to be used in various automobiles and has a very long service life. Jay Leno in the USA owns a Baker Electric , in which the nickel-iron batteries are still functional after almost 100 years. Henry Ford also developed the Ford Model T 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 , through which the combustion engine could be started with the help of a starter battery without physical exertion, ushered in the decline of the first heyday of electric automobiles, as a result of which accumulator and battery development stagnated. Deep cycle lead-acid batteries were practically the standard for traction applications until the end of the 20th century. These included submarines , battery-powered rail vehicles, industrial vehicles such as forklifts and trucks , but also electric wheelchairs. French manufacturers produced several thousand street-legal vehicles with nickel-cadmium batteries in the 1990s. When, in 1990, the CARB legislation in California was supposed to force motor vehicle manufacturers to gradually offer zero -emission vehicles (US = Zero Emission Vehicle ), battery research received strong impetus again.

For example , while the available, inexpensive lead-acid batteries were still used in the first drive batteries of the General Motors EV1 (26 blocks with a total capacity of 16.3 kWh and a nominal voltage of 312 volts), the second version developed by Stanford Ovshinsky was ready for series production Nickel-metal hydride batteries are used. The drive battery was permanently installed in a center tunnel in the vehicle floor, which contributed to a high level of crash safety and very good driving characteristics.

While the sodium-sulfur battery for the BMW E1 or the zinc-bromine battery announced for the Hotzenblitz never reached series production, the sodium-nickel chloride cell ( zebra battery ) that was further developed for the "Mercedes-Benz A-Class electric" helped the vehicle not only for a practical range of over 200 km, but also for military and aerospace applications. Another interesting feature of this vehicle is the compact block arrangement, which made it possible to mount the entire drive battery in one piece from below and also contributed to the high level of safety for automotive applications.

The basics of cell chemistry for lithium-ion batteries were also laid during this time. However, after the relaxation of the CARB laws , the automotive industry stopped these activities, so that lithium-ion accumulators only became important as traction batteries in the 21st century. Today, the different variants are considered to be the beacons of hope for significant improvements in performance-weight and resilience.

Physical-technical properties

Cylindrical cell (18650) before assembly. A few thousand of them make up the battery of the Tesla Model S (see Gigafactory ).
Battery modules in the rear of a battery bus
Battery cells on the roof of a battery bus
Electric truck e-Force One

Compared to device batteries or consumer cells, the cells of a drive battery have a much higher capacity. In addition, they are developed and manufactured by various manufacturers in various designs, some at the request of the customer. There are no standardized sizes. Both round cells in which the electrodes are rod-shaped and cup-shaped, for example products from A123 Systems , and prismatic cells with a plate-shaped electrode arrangement, for example cells from Winston Battery, are common .

High-current-resistant, cycle-resistant accumulator systems are used, which are able to deliver or receive electrical energy depending on the driving condition and to withstand many charge-discharge cycles. In contrast to starter batteries , lead drive batteries , for example, can be discharged up to 80% deep without being damaged thanks to the special design of the lead grids and separators .

While blocks for lead car starter batteries at 12 V or 24 V have capacities of 36 to 80 ampere hours (Ah), cells with capacities of 100 to over 1000 Ah are interconnected for forklift trucks to generate operating voltages of, for example, 24 to 96  volts for Electric cars can reach several hundred volts. The sizes are accordingly sometimes considerably larger. Higher voltages reduce the flowing currents and should, among other things, reduce the ohmic losses in the lines and the thermal losses during charging and discharging processes, as well as reducing the weight (cables).

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

Requirements for use in vehicles

The mobile use of the drive batteries requires higher safety requirements compared to stationary use. Above all, the safety in the event of mechanical influences must be proven. This is achieved through the use of safe cell chemistries (e.g. lithium iron phosphate batteries ) with often poorer electrical characteristics, the safe structural design of the accommodation in the vehicle (e.g. crash-tested battery trays in the underbody) and a combination of both methods. How strong the influence of the safety requirements is on traction batteries can be seen using the example of the delayed start of production for the Opel Ampera . The reason was the drive battery of the identical Chevrolet Volt that caught fire after a crash test (only several weeks) .

Different requirements for fully electric and hybrid vehicles

Since fully electric vehicles store all of the electrical energy needed for locomotion, high-capacity battery cells are used to minimize space requirements and weight for the amount of energy required. Due to the necessary capacity of the battery (cell or module size), the current carrying capacity of the cells is usually given for the discharge and charge processes. The load is also more even and with lower currents in relation to the battery capacity than in hybrid vehicles.

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

Nominal capacity, load capacity, manufacturer information

The nominal capacity is the amount of energy that can be drawn off guaranteed by the manufacturer under specified criteria. It is important to consider these criteria when comparing capacities. An accumulator with the specifications 12 V / 60 Ah C3 has a higher capacity than an accumulator of the same size with the identification C5 or C20. The specification C x characterizes the discharge time for the specified capacity in hours. With C3, 60 Ah can be drawn evenly in three hours, so higher currents are possible than with C5 or C20, which is important for use as a drive battery, since in practice the currents are often above these measurement currents (see also C- Rate and Peukert equation ).

In the case of highly resilient lithium-ion batteries , the specification of the current carrying capacity in relation to the capacity has become established. For example, for a cell 3.2 V 100 Ah with a standard discharge at 0.5 C (or 0.5 CA), this means that the capacity was determined with a discharge current of 50 A. Capacities are usually stated at 0.5 C or 1 C, whereby the permissible continuous load can be 3 C or more (in the example at 3 C that is 300 A), the short-term load can be significantly more (here 20 CA, that is 2000 A).

More and more frequently, the capacity of a drive battery is no longer specified in ampere hours of the individual cells, but in watt hours . Different designs can also be compared with one another, since the voltage is also incorporated. Starter batteries have an energy content of 496.8–960 Wh, traction batteries for forklifts to 4,800–28,800 Wh and for the Toyota Prius II to 1,310 Wh.

Influences on the usable capacity

The entire nominal capacity cannot be used during operation. On the one hand, the usable capacity decreases until it drops to the specified final voltage with high currents drawn (see Peukert effect ), on the other hand, with serial connections, the cell / cell block with the lowest capacity determines the usable capacity without damaging deep discharge.

The cells of a drive battery always show differences in capacity and current output (internal resistance) due to production and usage influences. Since the cells are loaded differently during operation, this leads to a drift apart, which reduces the usable capacity of the entire battery. While the capacity of the best cells can never be fully used, the weak cells are regularly overloaded, deeply discharged or overcharged. In order to reduce or avoid these effects, balancers and battery management systems are used in modern drive accumulators . Lower temperatures also reduce the ability of the drive battery to deliver high currents and intensify the Peukert effect, as the mobility of the electrons is generally reduced. In order to counteract this effect and since various battery technologies become unusable at lower temperatures , drive batteries are often also equipped with an additional heater. This either takes over the temperature control during the connection to the power grid or heats itself from its energy content. This and additional consumers such as electrical interior heating or air conditioning reduce the winter range, although the usable energy content of the drive battery is also available in winter.

The depth of discharge of the battery cells is often limited by the battery management system (BMS) in favor of the service life , usually to 60–80% of the nominal capacity. These circumstances must be taken into account, especially when calculating consumption and comparing different drive batteries. This “usable capacity” is seldom shown by the car manufacturer, but rather as a usable range of the nominal capacity. In the case of the Chevrolet Volt or Opel Ampera , for example, a usable battery window of 30-80% is specified, which is (in favor of durability) only 50% of the nominal capacity of 16 kWh.

Service life and cycle stability

Plug in America conducted a survey among drivers of the Tesla Roadster regarding the service life of the installed batteries. It was found that after 160,000 km the batteries still had a remaining capacity of 80 to 85 percent. This was independent of the climatic zone in which the vehicle was driven. The Tesla Roadster was built and sold between 2008 and 2012.

Lithium iron phosphate batteries , which are used as drive batteries , achieve more than 5000 cycles at a discharge depth of 70% , according to the manufacturer .

The best-selling (before 2019) electric car is the Nissan Leaf , which has been in production since 2010. In 2015, Nissan stated that until then only 0.01% of the batteries had to be replaced due to defects or problems, and only because of externally inflicted damage. There are a few vehicles that have already driven more than 200,000 km. These would also have no problems with the battery.

loading time

BYD e6 taxi, recharge to 80 percent in 15 minutes

Electric cars such as Tesla Model S , Renault ZOE , BMW i3 etc. can charge their batteries to 80 percent within 30 minutes at fast charging stations. In July 2013, Tesla announced that the next generation of superchargers would only need 5 to 10 minutes, which it wants to make a reality within the next few years. The superchargers as of November 1, 2016 have a maximum charging power of 120 kW in Europe and typically specify 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 charged to 80% within 15 minutes at a fast charging station and 100% after 40 minutes.

Application examples

Drive
battery for a pedelec as a removable battery pack

Drive batteries from closed lead accumulators are used in electric forklifts and serve there at the same time as counterweights for the stacked goods in order to be able to transport a certain (larger) physical mass with the help of the counterweights . They are also still used in driverless transport systems for level applications. The high weight and the strong temperature dependency have a disadvantageous effect in the case of height differences or inclines and in winter operation. Therefore, they are less suitable for use in electric bicycles, electric scooters and electric cars .

In modern electric bicycles / pedelecs , lithium-based batteries are used almost exclusively for reasons of space and weight. Lead-acid batteries that were initially used have not proven their worth.

A wide variety of battery systems are used as drive batteries in electric scooters . Here, too, the lead-acid battery is considered outdated, NiCd is proven and lithium-based batteries are powerful.

When used in hybrid vehicles such as the Toyota Prius or the Honda Civic IMA , drive batteries of the nickel-metal hydride type with voltages of around 200 to 400 volts and less than 10 ampere hours are currently (2012) used. The capacity restriction resulted from patent law provisions that severely restricted production and further developments. New developments are increasingly equipped with lithium-based drive batteries.

For reasons of weight and volume, only modern high-performance lithium-based batteries are used in solar vehicles . The world's largest solar vehicle, the Tûranor PlanetSolar catamaran , currently has the world's largest lithium drive battery with 1.13 MWh. Their cells come from the Thuringian cell producer Gaia Akkumulatorenwerk GmbH .

Today (1/2016) almost only lithium-ion batteries are used in electric cars (see Tesla Model S , BMW i3 , Renault ZOE , Nissan Leaf , VW e-up! Etc.). Another technology used in the Bluecar and Bluebus vehicles from the French Bolloré group is the lithium polymer battery . The company Batscap, which produces these batteries in France and Québec, is also part of the Bolloré Group.

In submarines , drive batteries were and are used for underwater journeys, because here the use of combustion engines that produce exhaust gases and consume air and oxygen is prohibited.

In September 2019, Tesla, Inc. applied for a patent for VC lithium batteries with modified electrodes, which are to be installed in 2020 and have a service life of 20 years and 1.8 million km (more than 1 million miles ) (not range ) should hold up, compared to the previous technology with NMC electrodes, which lasted up to 500,000 miles.

Environmental aspects

Drive batteries consist of individual cells that are significantly higher than device batteries in terms of both size (capacity) and the number of individual cells (voltage) . Therefore, they contain larger amounts of individual raw materials, so that after use, a return to the material cycle ( recycling ) is economically and ecologically sensible and necessary. For starter batteries and drive batteries as lead accumulators , a battery deposit of 7.50 euros per unit was introduced in Germany with the battery ordinance. The return rate is over 90%.

Such a deposit solution does not yet exist for modern lithium-ion batteries .

safety

With regard to lithium traction batteries, it is known that vehicle fires involving the batteries can occur and are difficult to fight. At the beginning of the 2010s, these dangers were pointed out in several technical reports. In addition to the danger to the vehicle occupants, the problem of fire fighting by the fire brigade has been known since then.

Price development and manufacturer

Because of the available and inexpensive raw materials, the prices for traction batteries are only determined to a small extent by the raw materials. While prices for individual and small series production of lithium-ion batteries from 2008-2010 were sometimes well over € 500 / kWh nominal capacity, in 2012 they fell to € 280-350 / kWh for the first series-produced batteries. In 2013, Li-Tec put the price at € 200 / kWh and was looking for partners at the time to implement cost-effective mass production. According to General Motors, the price of a single cell in 2016 will be around $ 145 / kWh (approx. € 127 / kWh), and that of the battery $ 300 / kWh (approx. € 263 / kWh). Eric Feunteun, head of the electric vehicle division at Renault, announced in July 2017 that one kWh battery costs $ 80 for Renault. The cause of the drop in prices is the start of mass production, which significantly reduces unit costs through better technologies and economies of scale . However, the falling production costs are only passed on to customers with a delay, as there is little price pressure on this market, especially in Germany, due to the few offers .

The cells of the drive battery of the Mitsubishi i-MiEV with 16 kWh for a range of around 150 km cost around 3,200 euros to manufacture in 2013.

The most important manufacturers of traction batteries as of 2015/2016, Panasonic , Samsung SDI and LG Chem , are all also the most important manufacturers of lithium-ion batteries for electronic devices. The Japanese manufacturer Panasonic, which supplies Tesla Motors and is building the Gigafactory together with Tesla , has a market share in traction batteries that is estimated at 36% or 39%. For the South Korean company LG Chem, which z. B. supplies the batteries for the Chevrolet Volt and the Renault ZOE , a market share of 8% is stated, for Samsung SDI, which produce for BMW and Volkswagen , a market share of 5%. Other producers of traction batteries are AESC (Automotive Energy Supply Corporation), a joint venture between Nissan and NEC , the Chinese company BYD and the A123, which has been in Chinese ownership since 2013 .

Material-specific classification and practical information

Usually the drive batteries are differentiated according to the materials used for the galvanic cells . Due to the large number of different systems, only general recommendations for action can be given. The reference point should always be the respective manufacturer's recommendations, whereby the possibility of a different, more careful use should also be checked in order to counteract a possible planned obsolescence and to increase the economic efficiency (costs / kilometers over the service life).

Lead accumulators as drive batteries

Lead-acid battery systems have so far been the most frequently used drive battery types in Germany. Despite their external similarity, they differ in the structure and use of starter batteries , as they are optimized for higher energy density and longer cycle stability, while starter batteries, on the other hand, have a high power density (short-term high current output).

In order to maximize the service life, the load and depth of discharge should be kept low, which is often difficult to implement structurally (ratio of capacity to required output). In general, it is recommended that traction lead-acid batteries are charged with high currents promptly after each use and that they are not deeply discharged (flat cycles). A small depth of discharge of only 30% of the nominal capacity can multiply the service life. Battery management systems are hardly available, practical use is only known with the BADICHEQ system (Battery Diagnostic & Charge EQualizing) in the Hotzenblitz . Charge balancing can be achieved with PowerCheq balancers between cell blocks, but not between the individual cells. Operation in winter temperatures is hardly possible without heating. Even charging when the battery is cold can only be done with lower currents and higher internal losses. It should be stored in a fully charged state at low plus temperatures; timing and recharging are necessary because of the high self-discharge.

Nickel-cadmium accumulators as drive batteries

Nickel-cadmium battery systems are widely used because they are very robust and have a long service life. In Europe, they are primarily manufactured as wet cells by the company Saft and have also been used in various French electric cars. However, they contain the toxic cadmium. Although the Europe-wide ban on NiCd traction batteries is currently not in place, they are increasingly being replaced by newer technologies, particularly those based on lithium. NiCd batteries also suffer from the reversible memory effect , which requires a complete discharge and targeted equalization / overcharging at intervals to maintain capacity. In general, NiCd batteries are therefore cycled more deeply and are not recharged after each use. They are considered to be robust and can also be used at low temperatures.

Nickel-metal hydride accumulators as drive batteries

The nickel-metal hydride accumulator was successfully used as a traction accumulator due to its high energy density (e.g. General Motors EV1 ), but patent sanctions prevented the production of high-capacity cells (more than 10 Ah) and thus a wider spread and further development. Therefore, no BMS and chargers that are difficult to fit are available in the traction sector, whereas NiMH batteries are standard in the consumer sector. Avoid excessive overcharging when using it, as the heating accelerates aging and an exothermic reaction ( thermal runaway ) is possible, which can lead to fire. The charge shutdown according to DeltaPeak should at least be combined with a thermal shutdown. The best performance is achieved at around 25 ° C, the service life can be> 10 years with appropriate use (see Toyota Prius ).

Thermal batteries as drive batteries

Also Thermal batteries as the Zebra battery are used successfully as Antriebsakkumulator. It is particularly suitable for regular or continuous use, since the system-related energy losses are then negligible. The main advantage lies in the unrestricted winter suitability, since the ambient temperature has no influence due to the high operating temperatures, and the high level of operational safety. Failing cells become low-resistance and reduce the capacity, but do not prevent use.

Lithium-ion accumulators as drive batteries

Lithium-ion battery systems have been the preferred variant of drive batteries since 2012. In 2014, almost only lithium-ion batteries were used in electric cars, for example Tesla Model S , BMW i3 , Renault ZOE , Nissan Leaf , VW e-up! . "Lithium-ion accumulator" is a generic term for a large number of different variants of accumulators with different properties.

  • At both the lower and the upper cell voltage limit, processes begin which reduce the service life of the batteries or destroy them. Electronic controls ( balancers / BMS ) usually ensure compliance with the limit voltages during both charging and discharging.
  • With an average depth of discharge, the optimum operating range is the broad operating range in which the voltages fluctuate only slightly around the nominal voltage. Frequent reloading, shallow cycles are recommended. However, constant full charging, like deep discharging, is unfavorable for the service life. The drive battery should be used after a full charge. Longer storage when not in use should not be above about 95% charge level.
  • While lithium iron phosphate batteries (LiFePO 4 ) are rather insensitive to sub-zero temperatures, especially when discharging, other battery types (LiPo) are destroyed in frost. The best performance of LiFePO 4 batteries is obtained at 25–35 ° C, but higher temperatures increase the gradual loss of capacity due to aging.

literature

  • Jörg Becker , Daniel Beverungen, Martin Winter , Sebastian Menne: Re-dedication and further use of traction batteries . Springer-Verlag, 2019, ISBN 978-3-658-21021-2 .
  • Gianfranco Pistoia, Boryann Liaw (Ed.): Behavior of Lithium-Ion Batteries in Electric Vehicles: Battery Health, Performance, Safety and Cost . Springer, 2018, ISBN 978-3-319-69949-3
  • Chapter 5.2. Energy storage battery. In: Anton Karle: Electromobility: Basics and Practice. 2nd Edition. Hanser, 2017, ISBN 978-3-446-45099-8 , pp. 78-88
  • Chapter 29: Dennis A. Corrigan, Alvaro Masias: Batteries for Electric and Hybrid Vehicles. In: Thomas B. Reddy (Ed.): Linden's Handbook of Batteries. 4th edition. McGraw-Hill, New York 2011, ISBN 978-0-07-162421-3 .
  • Chapter 12.4. Electric vehicles. In: Dell, Rand: Understanding Batteries , Royal Society of Chemistry, 2001, ISBN 0-85404-605-4 , pp. 202-214
  • Chapter 6 Battery Technology. In: Robert Schoblick: Drives for electric cars in practice: Motors, battery technology, power electronics. Franzis, Haar near Munich 2013, ISBN 978-3-645-65166-0
  • Chapter 3. Storage of electrical energy. In: Helmut Tschöke (Ed.): The electrification of the drive train. Springer / Vieweg, Wiesbaden 2015, ISBN 978-3-658-04643-9 , p. 51ff.

Broadcast reports

Web links

Commons : Propulsion battery  - collection of pictures, videos and audio files

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