Lithium-ion battery

A lithium -ion rechargeable battery (also lithium -ion battery, Li -Ion, Li- ion secondary battery, lithium battery or short Li-ion; fachsprachlich [li ː tiʊm ] pronounced, colloquially [li ː tsiʊm ] ( with s- sound) ) is the generic term for batteries based on lithium.

Lithium-ion batteries have, compared to other battery types in a high energy density, but require, in most applications of electronic protection circuits.

General

The lithium -ion batteries are characterized by high energy density. They are thermally stable and are subject to a very low memory effect. Depending on the structure and the electrode materials used in Li -ion batteries are further subdivided: the lithium - polymer battery, lithium Cobaltdioxid - accumulator ( LiCoO 2 ), lithium titanate battery, the lithium-air battery, the lithium - manganese accumulator, the lithium iron phosphate battery ( LiFePO4 ) and the tin - sulfur - lithium -ion battery. Characteristics, such as cell voltage, temperature sensitivity or the maximum allowable charge or discharge current, type of construction vary greatly and are much more on the used electrode material and electrolyte -dependent. The specification of the subtype (eg " lithium iron phosphate battery" ) is because of this informative than the words of the preamble "lithium ion battery ".

Depending on the type of about 80 g to 130 g of chemically pure lithium needed for the production of a rechargeable lithium battery with a storage capacity of a 1 kWh of energy.

History

Already in the 1970s, the basic operating principle of the reversible alkali metal ion intercalation into carbon anodes and oxide cathode and its application were at the Technical University of Munich in in lithium batteries and published, even if at that time the practical application as electrodes for lithium batteries was not detected.

The lithium Cobaltdioxid accumulator, also LiCoO2 battery even Lithiumcobaltdioxid accumulator, was the first available electrodes chemistry of a lithium -ion battery. The utility as electrode material was discovered in 1980 by a research group led by John B. Goodenough at the University of Oxford. The positive electrode consists of the eponymous substance lithium - cobalt ( III ) oxide.

A patent in Germany for a lithium - ion battery, a test pattern was registered in November 1989 and in the following manufactured and successfully tested. The German industry at that time was, however, no interest in the development.

The first commercially available Li -ion battery has been implicated as lithium Cobaltdioxid accumulator by Sony in 1991 on the market and used in the Hi8 video camera CCD TR 1. The battery has two series-connected cells, a cell voltage of 7.2 V and had a capacity of about 1200 mAh. To date (2012 ) accumulators of this design are available with capacities up to 6900 mAh and used in a variety of Sony devices.

Applications

Li -ion batteries provide portable devices with high energy requirements, for the conventional nickel -cadmium or nickel -metal hydride batteries would be too heavy or too large, such as mobile phones, digital cameras, camcorders, notebooks, handheld gaming consoles or flashlights. They are used in electric mobility as an energy store for Pedelecs, electric cars, electric wheelchairs and modern hybrid vehicles. In the RC model they have established themselves. Due to their light weight, they form, in conjunction with brushless DC motors and the corresponding controls, a drive unit used in model aircraft. Even lithium -ion batteries such as cordless screwdrivers and garden equipment used in power tools. In the 787 lithium cobalt oxide batteries come ( LiCoO2 ) for use, but have fired several times and therefore subsequently each received a steel casing. Other modern aircraft use the type with iron phosphate.

Large lithium -ion battery systems are also used in battery - storage power plants. 2011 was the most powerful lithium -ion battery - a battery - storage power plant in West Virginia - in operation. It can deliver 32 MW. Another example for the storage of wind energy is the 8 MW turbine at Tehachapi Pass, which can store an energy of 32 MWh. Based on the stored energy which is the largest battery in North America. The largest lithium -ion battery that will fit in a container can store an energy of 1.5 MWh. The Europe's largest commercial battery park is being built by WEMAG in Schwerin. He should go in August in 2014 and then can choose from 25000 lithium -ion batteries provide a total capacity of 5 megawatts.

Principle

In the lithium -ion battery, the electrical energy in the lithium atoms and is (mostly ) transition metal ions stored ( at the negative electrode ) ( the positive electrode) in a chemical process with fabric change. This distinguishes the Li- Ion battery from lithium -ion capacitor in which the storage of electrical energy takes place without material change. In Li -Ion Battery Lithium may in ionized form and back herwandern through the electrolyte between the two electrodes. Hence it is also the name of the lithium -ion batteries. In contrast to the lithium ions, the transition metal ions are fixed in place.

This lithium -ion flow is necessary to balance the external current flow during loading and unloading, so that the electrodes remain (largely) electrically neutral itself. When unloading give lithium atoms in the negative electrode of one electron from flowing through the external circuit to the positive electrode. At the same time the same number of lithium ions migrate through the electrolyte from the negative to the positive electrode. At the positive electrode but not the lithium ions occupy the electron back on, but the present there and strongly ionized in the charged state and therefore quite " electron hungry " transition metal ions. Depending on the battery type, the cobalt, nickel, manganese, iron ions can be etc.. The lithium is in a discharged state at the positive electrode therefore still present in ion form.

Because of the negative electrode, the lithium is not ionized, it would be optimal to construct a negative electrode of lithium metal. However, this is problematic in practice: Due to the fouling deposited lithium is not as compact metal, but dendritic. This finely divided lithium sponge is highly reactive. In addition, dendrites can perforate the separator, mixed to the positive electrode and thus short-circuit the cell.

Therefore, the ( relatively small ) lithium atoms are incorporated into another material, usually graphite, where they located between the graphite planes (nC ) store. One speaks of an intercalation compound ( LixnC ). Essential for the functioning of intercalation is the formation of a protective overcoat layer on the negative electrode, but is permeable to small, Li ions, for the solvent molecules impermeable. The top layer is formed is insufficient, there is the intercalation of Li ions together with the solvent molecules, so that the graphite electrode is irreversibly destroyed.

Construction

The active material of the negative electrode of a conventional Li -ion batteries (2010) is made from graphite. The positive electrode usually includes lithium metal oxides such as LiCoO2 ( Lithiumcobaltdioxid ), LiNiO2 or LiMn2O4.

The inside of a lithium -ion battery is completely free of water (content of H2O <20 ppm), to report any damage penetrating water reacts to excessive heat with fire and deflagration. The electrolyte consists of aprotic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate or 1,2-dimethoxyethane and lithium salts such as LiPF 6 dissolved.

On materials are used, among others the following:

  • Graphite ( lithium intercalation )
  • Nanocrystalline, amorphous silicon ( intercalation of lithium)
  • Li4Ti5O12 (lithium titanate battery)
  • Tin dioxide SnO2
  • Salts, such as LiPF6 ( lithium hexafluorophosphate ), LiBF.sub.4 (rarely ) in anhydrous aprotic solvents (eg, ethylene carbonate, diethyl carbonate, etc.) or LiBOB (rare)
  • Polymer of polyvinylidene fluoride (PVDF) or polyvinylidene fluoride - hexafluoropropene ( PVDF -HFP )
  • Li3PO4N Lithiumphosphatnitrid
  • LiCoO2
  • LiNiO2
  • LiNi 1 - xCoxO2
  • LiNi0, 85Co0, 1Al0, 05O2
  • LiNi0, 33Co0, 33Mn0, 33O2
  • LiMn2O4 spinel
  • LiFePO4 ( lithium iron phosphate in the lithium iron phosphate battery )

Reaction equations

A negative electrode (discharge):

Positive electrode (discharge):

Redox equation:

Metallic lithium is present in any reaction, but it is, with the exception of the lithium titanate battery, lithium atoms, non- ionic, which are intercalated to the negative electrode in the electrode material.

Production

Lithium- ion batteries have fallen into the focus of public attention especially because of the " National Development Plan for Electric Mobility " of the Federal Republic. Efforts are being made by universities and industry to great lengths to as quickly as possible to solve the many problems of future " car batteries ". As part of the exhibition " Productronica 2011" in Munich this was a special show " battery manufacturing " was shown, which was designed in close collaboration with the Association of Manufacturing Industry in the VDMA, the RWTH Aachen, the Fraunhofer Institute for Production Technology and leading companies. A film of this special exhibition, showing the production of lithium- ion batteries of the coating of the electrode material to the finished module was placed on the Internet by the magazine " Elektronik Praxis ".

Properties

Since lithium - ion battery the generic term for a variety of possible combinations of materials for the anode, cathode and separator is, it is difficult to make general statements. The properties differ in some cases significantly, depending on the combination of materials. Add to this the continuous improvement by the battery manufacturer, the particular could achieve significant improvements on the known problem areas such as durability and safety in recent years, while the power density was increased to a relatively small extent.

How to Handle with Li -ion batteries

Because of the variety of possible materials for the anode, cathode and separator, it is difficult to make general statements for Lithiumionakkus. The different types are optimized by the manufacturers for a variety of applications and differ in the handling, sometimes significantly.

  • The " Recommendations on the Transport of Dangerous Goods - Manual of Tests and Criteria (PDF, 4.9 MB) " (UN 38.3 - Transport test for lithium batteries Lithium-Akkumulatoren/-Batterien )
  • The Law on the Transport of Dangerous Goods ( GGBefG )
  • The " Dangerous Goods Ordinance Road, rail and inland waterway transport" ( GGVSEB )
  • The " European Agreement concerning the International Carriage of Dangerous Goods by Road " (ADR). The transitional provision gem. 1.6.1.20 ADR applies.
  • The presence of lithium-ion cells or batteries,
  • That the consignment is to be treated with special care,
  • That is at risk of damaging inflammation,
  • That when damage to the packaging to pack the package before further transport new, as well as to check the short circuit protection of the cells and make new is.

Hazards associated with lithium -ion batteries

In various lithium -ion batteries with liquid or polymer electrolyte may occur for thermal runaway without special protective measures. With the increasing use especially cheaper batteries have been reports of overheating increase. This leads to costly recalls by the manufacturers. In the automotive industry it is especially high security requirements due to the high installed power amounts partly to delays in service. So Opel postponed the delivery of the Ampera than three weeks after a crash test of an identical Chevrolet Volt overheated the experimental non -developed, fully-charged battery and caused the vehicle fire. Then, the safety concept of the traction battery has been revised. In working scientific investigations, it was found that the handling of high-performance energy storage, lithium-based, that is, their manufacture, installation, storage, disposal and certain operating conditions has little impact on the labor protection. The dangers of high voltages and additional hazardous materials (eg lithium) can be minimized by adapting and consistent implementation of existing security requirements.

The following risks are known:

Recent evidence in dealing with these batteries, the positive impact of the (clear ) water significantly on the negative aspects and predominate. The competent authority for the American fire departments as well as the relevant NFPA fire service literature in Europe has in recent editions to treat injured electric vehicles from the use of a large amount of water as the primary strategy. However, it is pointed out explicitly run the extinguishing tests in general, not directly to success. When the cell electrode materials and their decomposed thermally, the exothermic reaction of oxygen required for the further inside the cell is created. The exothermic decomposition can therefore not Stop (thermal runaway ). However, neighboring cells are sufficiently cooled by the use of large amounts of water that does not decompose this in the episode as well. In addition, large proportions of hazardous releases are bound by the water and / or diluted to an uncritical level solution.

In the cell itself, there are various safety devices that can make dealing with the cells very safe. For example, so-called "Shut -down separators " used that exploit the effect of melting targeted and to change from a porous plastic into an impermeable for further ion exchange film. More directly integrated in the cell protection by the electrical connection between the electrode material and the external cell terminal. The compound can be carried out so it acts like a fuse and is also torn when opening any bursting openings. These cell internal protection mechanisms are performed usually irreversible. In addition to the cell-internal protection devices are available in within modern batteries usually more electronic protection circuits. Their functions range from complex battery management systems ( BMS) with temperature sensors, electronic charging, battery status monitoring and external communication ports (smart batteries ) to simple mostly reversibly acting protection devices, which are only intended to prevent overcharging or overloading the battery.

Developments

In April 2006, wrote a group of scientists at the Massachusetts Institute of Technology, have developed a process that uses viruses for the production of nanometer-sized wires. This ultra-thin lithium -ion batteries can be produced with a higher energy density.

In June 2006, researchers from France set battery electrodes forth in nanometer size, which had several times the energy density compared to conventional electrodes.

In September 2006, researchers reported at the University of Waterloo in Canada in the journal Nature by a new cathode material in which the hydroxide group of the iron phosphate cathode was replaced by fluoride. This has a double advantage: first results during a charge cycle, a lower volume change in the cathode, thus leading to a longer life. Second, it allows the replacement of lithium by sodium or a sodium -lithium mixture, which is why it is also referred to as alkali - ion battery.

In December 2007, researchers at Stanford University reported a new anode material for lithium - ion batteries with ten times the energy density achieved so far. They used silicon nanowires on stainless steel. It is used the fact that silicon can store large quantities as carrier material of lithium than graphite; the small size of the wires will solve the problem of breaking the anode. However, the anode is only a part of the accumulator; with unchanged cathode, separator, and electrolyte is accordingly only a significantly lower total increase in the energy density to be expected. Similar approaches using nanoporous silicon pursuing the team of Jaephil Cho at Hanyang University in Ansan, South Korea.

On 12 March 2009 a further development of lithium -ion batteries by two MIT researchers Kang and Gerbrand Ceder Byoungwoo was published, which both reduces the charge and the discharge time to 10 seconds instead of 6 minutes for a small test battery.

Approximately in June 2011, researchers reported the Japanese company Sumitomo Electric Industries, that in the event that the arrester to the cathode, which is usually made of aluminum foil, would be replaced by the material aluminum Celmet, this is an increase in battery energy density by a factor allowing from 1.5 to 3.

Embodiments

Lithium- polymer battery

As with the lithium -ion battery with lithium Cobaltdioxid ( LiCoO2 ) as the electrode material is the negative electrode made ​​of graphite, the positive of lithium metal oxide. However, lithium polymer batteries contain no liquid electrolyte, but a polymer-based, which is present as a solid to gel-like sheet. Therefore, the lithium - polymer battery is to be regarded as a special design, not as an independent cell chemistry. The external form of lithium polymer batteries is subject to virtually no restrictions.

Lithium titanate battery

The lithium titanate battery is a further development of the lithium -ion battery, in which the conventional graphite anode by a nano-structured lithium titanate anode ( Li2TiO3 ) is replaced. Substantially stronger chemical bonding of the lithium titanate in the preventing the formation of a surface layer on the electrode, which is one of the main reasons for the rapid aging of many conventional Li-Ion battery. Characterized the number of possible cycles is increased drastically. Characterized in that the titanate is unable to react with oxides of the cathode, and the thermal runaway of the battery is prevented even when mechanical damage. In addition, the accumulator due to the lithium titanate anode can be operated in contrast to conventional lithium -ion batteries at low temperatures in a temperature range of -40 to 55 ° C.

The lithium titanate anode further has an effective specific surface area of 100 m2 per gram compared to 3 m2 per gram of a graphite electrode. This very short loading times and a very high power density of about 4 kW / kg can be achieved. The energy density is 70-90 Wh / kg, however, relatively low.

Under the trade name Super Charge Ion Battery ( SCiB ) is offered by Toshiba a lithium titanate battery for electric bikes like Schwinn Tailwind electric bike.

Lithium manganese battery

The lithium manganese battery is used as the lithium manganese oxide active material in the cathode. The anode is made of either conventional graphite ( high energy cells) or of an amorphous carbon structure ( amorphous carbon, in high-power cells ). Due to the larger anode surface resulting in improved resistance to high current. The cells are currently (2012 ) in both Pedelecs and E -bikes from different manufacturers (including the Swiss pedelec manufacturers Flyer), as well as in hybrid electric vehicles (eg: Nissan Fuga hybrid, Infinity Mh ) and electric cars (eg: Nissan Leaf ) employed. Large-format cells for traction batteries manufactures for example AESC for Nissan.

Lithium iron phosphate battery

The lithium iron phosphate secondary battery ( LiFePO4 accumulator) is a version of the lithium ion secondary battery in which the conventional lithium -cobalt oxide cathode was replaced by a lithium iron phosphate cathode. This battery is characterized by high charge and discharge, a very good temperature stability and long life. The nominal voltage is 3.2 V or 3.3 V, the energy density is 100 to 120 Wh / kg and power density of about 1.8 kW / kg.

Enhancements to improve the technical properties are doping with yttrium ( LiFeYPO4 ) and sulfur atoms.

Lithium-air accumulator

The lithium-air accumulator located in a research and development embodiment of a rechargeable lithium - ion secondary battery having a cell voltage of 2.91 V for the positive electrode of porous carbon executed oxygen for electrochemical reaction required. This accumulator has theoretically a very high specific energy density, but with technical difficulties with the implementation, so no batteries of this type available on the market with booth 2013.

Lithium- air batteries can also be performed with solid electrolyte and then among the group of solid state batteries.

Specific lithium ion secondary battery construction

There are numerous combinations of materials for the storage of lithium - ion is available. The chemical storage materials change the properties of the accumulator significantly so that it can be used to adjust to specific requirements. The figure shows a number of cathode and anode materials in a confrontation and identifies the potential difference of the materials.

The additional use of different, special separators (eg Keramikseparatoren ), electrolytes (eg ionic liquids ) and packaging materials can be set other properties of the battery, so that they also can meet extreme requirements.

As special demands on Lithium- ion batteries are:

  • High and low temperature resistance
  • Radiation tolerance (eg, gamma radiation in the aerospace industry )
  • High and low pressure resistance (up to rough vacuum )
  • Special form factors for film body or connecting poles
  • Shock resistance
  • Amagnetismus
  • Maximization of energy density or power density
  • Fast charging
  • Intrinsic Safety
  • Bending flexibility

Although these opportunities exist, the industrial mass production to the use of established storage materials such as lithium cobalt (III ) oxide and graphite supports. Only a few specialized manufacturers such as the German company Custom Cells Itzehoe GmbH and the American company Yardney Technical Products Inc. offer special solutions. The diagram opposite shows an accumulator, which in its energy density, pressure resistance and unusual shape ( hexagonal ) for use in an autonomous underwater vehicle ( AUV ) ) was optimized.

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