Lithium polymer accumulator
A lithium polymer battery (also known as LiPoly or LiPo ) is a rechargeable energy store ( battery ). It is a special type of lithium-ion battery , so it has the same cell chemistry. The specialty is the consistency of the electrolyte , which in lithium polymer batteries is a solid to gel-like film on a polymer basis . This enables the cell shape to be designed more freely, such as flat cells.
As with most lithium-ion batteries, the negative electrode is made of graphite . A lithium / metal oxide is used on the positive electrode . Lithium polymer batteries mainly use the inexpensive lithium cobalt (III) oxide on the positive electrode and are therefore lithium cobalt dioxide batteries in terms of cell chemistry .
In principle, lithium polymer batteries can also use other metal oxides on the positive electrode, such as lithium manganese oxide . In terms of cell chemistry, such accumulators are then lithium-manganese accumulators .
The components of the accumulator - power supply, negative electrode, electrolyte, positive electrode - can be manufactured inexpensively from foils with a thickness of less than 100 micrometers . A variety of designs are possible for lithium polymer batteries: cylindrical cells (18650 industrial batteries, 2170 from Panasonic for Tesla Motors ), prismatic cells (e.g. from Samsung SDI ) or cells in pocket format (e.g. from LG Chem ) for Electric cars and energy storage systems, in pentagonal form for wristwatches. There are also angled or curved shapes. Most often, however, round or flat cells are manufactured.
properties
Solid electrolyte foils only achieve a sufficiently high ionic conductivity from an operating temperature of around 60 ° C. In lithium polymer batteries, a gel is used as the electrolyte , which has sufficient (ion) conductivity at room temperature .
Since the electrolyte in a lithium polymer battery is bound in a gel-like polymer (plastic) and not liquid as in a conventional lithium-ion battery, the battery does not necessarily need a solid housing around the technical structures (spacing between electrodes, electrolyte distribution) to ensure. Hence it can be produced in many forms. Instead of a solid housing, composite foils can possibly be used, which also leads to a somewhat higher energy density of the overall system. An example of such an electrolyte is lithium [3,5-bis (trifluoromethyl) pyrazolide]. Technical specifications:
- Gravimetric energy density : approx. 140 Wh / kg (up to 180 Wh / kg, as of April 2005)
- Gravimetric power density : approx. 300 W / kg (up to 5000 W / kg, as of September 2011)
Lithium polymer batteries are mechanically, electrically and thermally sensitive: Damage, overcharging, deep discharging , excessively high currents, operation at temperatures that are too high (over 60 ° C) or too low (below 0 ° C) and long storage in a discharged state can damage or destroy the cell in most cases.
Lithium polymer batteries can swell up when overcharged (gas is formed by decomposition) and deflagrate and ignite. The risk of ignition and mechanical strength could be reduced or improved by using heat-resistant ceramic separators.
Commercially available lithium polymer battery packs for consumer devices contain a battery management system (BMS) developed for the respective battery , which is permanently connected to the battery pack and ensures that the individual cells are charged in a cell network.
construction
The picture on the right shows a lithium polymer battery with a nominal voltage of 3.6 V. The battery is integrated into the cover of a cell phone. After removing the plastic coating, the electrical circuit of the battery management system is on the right in the picture. An electrical protection against overload is integrated in the cover of the aluminum block . The aluminum block protects the three lithium polymer foils that were pulled out in the picture below.
The plastic film ( polymer ) absorbs the electrolyte. One foil is coated with the electrode material, usually lithium cobalt (III) oxide, for the positive contact, the other with graphite for the negative. The double-sided coating doubles the winding capacity.
Unlike conventional batteries, the design of lithium polymer batteries is based on the requirements of the manufacturer, not on standards. If the battery fails, the entire battery unit must be replaced. Even if you open the battery unit, there is no guarantee that the charging electronics will work with replacement batteries of unknown specifications.
Charge-discharge process
New lithium-polymer batteries are delivered precharged by the manufacturer in order to avoid harmful deep discharge until they are used. Before being used for the first time, the cells / batteries should be fully charged with a charger; any charge differences between the cells are compensated for using a balancer . The charging process usually takes place in accordance with the IU process, initially with a constant current of typically 1 C (with suitable cells up to 6 C).
Lithium polymer batteries react much more sensitively to overcharging than other types of batteries and are therefore unusable. It may also be appropriate to charge lithium polymer batteries only under supervision and not next to flammable materials.
Since the mobility of the ions is generally reduced at low temperatures and many lithium polymer accumulators become unusable below freezing point, storage / use above 10 ° C is recommended. The losses caused by the internal resistance of the cells during charging lead to heating. Therefore, temperature monitoring / cooling is often used when charging, especially when charging quickly with high currents in a short time.
Lithium polymer batteries are currently available with a discharge rate of up to 55 C. For a short time (5–10 seconds), these can also be discharged at twice the C rate (110 C).
The end-of- charge voltage must never be exceeded. Exceeding this limit can lead to irreversible damage to the cell due to the decomposition of the electrolyte. The end-of-charge voltage is 4.0-4.2 volts. If there are several cells connected in series, the balancer determines the maximum voltage across the cell.
When discharging, the accumulator is electrically loaded for a certain time until the end-of- discharge voltage is reached. The final discharge voltage is 3.3 volts.
lifespan
When it comes to the service life of lithium polymer batteries, a distinction must be made between cycle stability and calendar aging. In general, an accumulator is considered worn out if it has less than 80% of the nominal capacity . It is difficult to make general statements because, in addition to the technical design and quality, the practical application conditions have a major influence. While LiPo cells in model making are often operated at the performance and specification limit and accordingly wear out quickly, flat cycled traction batteries , for example in electric cars , last for many years. The cycle stability is determined on the one hand by the design, on the other hand frequent recharging without overcharging improves the total achievable energy conversion, i.e. the cycle stability. A lack of cooling usually has a disadvantage in everyday devices, which leads to rapid calendar aging. The battery capacity decreases due to irreversible processes in the cell, even without use.
Recommendations:
- frequent recharging (flat discharge cycles)
- Never exceed the end-of-charge voltage
- Battery management system adapted to the cell type
- Not deeply discharged
- Operation in the optimal temperature range
- Storage when not in use for a long time in a half-full state (approx. 3.85 V)
- Storage temperature, the cooler the less permanent capacity loss (not colder than indicated on the battery, usually −20 ° C to −25 ° C)
Applications
Solar vehicle
The Sky Ace TIGA is equipped with a lithium-polymer battery , and with a speed of 165 km / h it is the world record holder for solar vehicles . The latest solar aircraft, Solar Impulse , also uses this type of battery.
Electric car
Since 2007, the company Kruspan Engineering in Switzerland has been testing lithium-polymer accumulators from the company Kokam with high energy density as traction batteries in an electric car of the Hotzenblitz type from 1996. In the vehicle tests carried out, ranges of over 350 km were achieved. This Hotzenblitz took part in 2011 as “Team 9 Faraday USA” with Roger Miauton, Mark Fuller and Mike Collier in the Wave2011 (World Advanced Vehicle Expedition), a tour of 3000 km that led through eight countries.
Modelling
Lithium-polymer accumulators found a rapid spread in model making, as it brought about an enormous boost in performance for remote-controlled models. Used as a drive, receiver and transmitter battery, it covers the whole range. See also RC model making .
Mobile phones
Lithium polymer batteries are also being used more and more frequently in cell phones , in contrast to conventional lithium ion batteries.
MP3 player
Whereas in the past MP3 players were generally equipped with conventional batteries or rechargeable batteries for reasons of price, these now increasingly contain lithium polymer rechargeable batteries, especially in models in the lower price segment. For cost reasons, these are often permanently installed or have a proprietary format. A defect can therefore mean a total loss, because the exchange outside the guarantee period would no longer be financially worthwhile.
Web links
- Compendium: Li ‐ ion batteries (July 2015, PDF; 1.2 MB) BMWi ICT funding program for electric mobility II
- Script about various types of lithium batteries (as of Feb. 2005, PDF; 3.4 MB) Graz University of Technology, Institute for Chemical Technology of Inorganic Materials
- Battery forum Germany, information portal with links to the general battery compendium and lexicon
- Compendium: Lithium-ion batteries from the German Battery Forum
Individual evidence
- ↑ Grant M. Ehrlich: Handbook Of Batteries . Ed .: David Linden, Thomas B. Reddy. 3. Edition. McGraw-Hill, 2002, ISBN 0-07-135978-8 , Chapter 35.7: Polymer Li-Ion Batteries, pp. 35.71 - 35.85 .
- ↑ Blackhorselipo.de: Safety instructions ( Memento from February 22, 2014 in the Internet Archive )
- ↑ Markus Pflegerl: Conversion of a Hotzenblitz to Lithium Polymer from Kokam ( Memento of the original from December 24, 2013 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Watt gehtab Internet portal, November 20, 2007 (English)
- ^ Company MDW-Temperatursensorik GmbH: "Hotzenblitz" in use from 1996 to September 2010, subsection solar energy, accessed January 12, 2012
- ↑ Solar and electromobile news: Hotzen flash with lithium polymer batteries Article on the conversion project by Kruspan Engineering and MDW-Temperatursensorik GmbH
- ↑ : Company Kruspan Hotzenblitz with ~ 350km range in January called Website Company Kruspan, 7, 2012
- ↑ Organizer page : Teams ( Memento of the original from January 15, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed January 7, 2012
