Lithium polymer battery

A lithium- polymer battery ( also lipoly or LiPo) is a rechargeable energy storage ( battery ) and an execution of Lithium -ion batteries.

As with most lithium -ion batteries, the negative electrode is 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. The components of the battery - power supply, negative electrode, electrolyte, positive electrode - can be produced inexpensively as films with a thickness of less than 100 microns. For lithium - polymer batteries many configurations are possible, including angled or curved shapes, but mostly round cells or flat cells are manufactured.

• 5.1 Solar Vehicle
• 5.2 Electric Car
• 5.3 Model
• 5.4 Mobile phones
• 5.5 MP3 Player
• 5.6 Fixed power station energy storage

Properties

Solid electrolyte film to reach a sufficiently high ionic conductivity only at a operating temperature of about 60 ° C. In modern lithium - polymer batteries, however, comes as a gel electrolyte is used, which has sufficient (ionic ) conductivity at room temperature.

Since lithium -filled carbon electrodes have a very deep potential in the electrochemical series, not very far away from the -3.04 volts of pure lithium, a high potential difference is guaranteed to almost any cathode material. The cell voltage is, depending on the material used for the positive electrode from 3.5 to 4.3 V; the rated voltage of such a battery is usually 3.7 V.

Since the electrolyte is bound in a lithium -polymer battery in a gel-like polymer ( plastic) and not liquid as in a conventional lithium -ion battery, the accumulator a fixed housing to the technical structures does not necessarily need (distances electrodes, electrolyte distribution) sure. Therefore, it can be produced in many forms. Instead of a solid housing can be used may be composite films, which also leads to a slightly higher energy density of the overall system. An example of such electrolyte is lithium [3,5-bis (trifluoromethyl) pyrazolide ]. Specifications:

• Gravimetric energy density: about 140 Wh / kg (up to 180 Wh / kg, as of April 2005)
• Gravimetric power density: about 300 W / kg ( up to 5000 W / kg, as of September 2011)

The initially high due to the small numbers prices have dropped significantly by mass production. Due to the excellent power to weight ratio and the steadily improving resilience they are also increasingly used in the model. For electrically -powered racing boat, car and airplane models are now standard. Since 2004, electric drive systems using lithium- polymer batteries can be used successfully even in the F3A World Championships.

Lithium polymer batteries are mechanically, electrically and thermally sensitive: damage, overcharging, deep discharge, excessive currents, operating at too high (over 60 ° C) or low temperatures (below 0 ° C) and long storage in a discharged state damage or destroying the cell in most cases.

Lithium- polymer batteries can be overcharged bloat (gas formation by decomposition ) and detonate and ignite - therefore a constructed for this battery or a special Li- Battery Charger ( I / U ) method is to charge must be used, see Article lithium - ion battery. Risk of ignition and mechanical strength could be significantly improved by heat-resistant ceramic separators.

Commercially available lithium -polymer battery packs for consumer devices already contain a developed for the specific battery protection circuit ( against undervoltage and overcurrent); the cell and load management (see Battery Management System) is generally integrated in the associated device, but often cell data is stored in the battery pack and via SMBus read (Smart Battery System).

Charging

New lithium -polymer batteries are shipped pre-loaded by the manufacturer to avoid a harmful discharge until use. Before the first use, the cells / batteries should be fully charged with a suitable charger and any voltage differences between the cells balanced ( balanced) are.

Lithium -polymer batteries react when overcharged significantly more sensitive than other battery types ( including the destruction by fire ) and are thus unusable. As maximum voltage 4.2 V is often stated as a minimum 3 V. Because of the dangers of overloading special chargers must be used.

Since generally reduced at low temperatures, the mobility of the electrons and many lithium polymer batteries are useless below the freezing point, a storage / use above 10 ° C is recommended. The losses occurring due to the internal resistance of the cells during charging lead to warming. Therefore, it is often when loading, especially when fast charging with high currents in a short time, a temperature monitoring / cooling.

The charging process is usually carried out by the I / V method, first with a constant current of typically 1 C (with appropriate cells up to 6 C). The abbreviation "C " stands for the ratio of charging current in amperes divided by the cell capacity in ampere-hours and is thus inversely proportional to the charging time. (Note: By " capacity " here is not the capacitance of a capacitor meant by the unit farad and "C " is not the unit of electric charge coulomb! ) A charging current of 0.5 C means that a cell whose capacity for B. indicated with 2 Ah, is charged with an initial charge current of 1 A in about two hours, 1 C: 2 a in one hour, C 2 that is characterized by a charging time of 0.5 hours.

Reaches the maximum cell voltage is further charged with constant voltage (not to exceed the maximum voltage ), whereby the charging current slowly decreases. Is he dropped to a specified minimum level (eg, 5 percent of the original charging current ), the charge to be finished and the cell is considered fully.

Compared to NiCd or NiMH batteries have LiPo batteries like most lithium -ion batteries only a low self-discharge and can be stored for several months without significant loss of charge. For long-term storage some manufacturers recommend the ( partial) unloading or loading on only 80-90 % and the storage in a cool place.

Currently, lithium polymer batteries with up to 45C discharge rate are available. Short-term (5-10 seconds ), these can also be unloaded with the double C - rate ( 90C ).

Voltage matching

Due to variations and tolerances to have a battery in series interconnected cells ( in model usually 2 to 6 pieces) never quite the same properties (capacity, self-discharge, current strength, aging, ... ). If the charger only measure the total voltage of all cells and then regulate the current, it would apply in the weaker cells repeatedly overcharge and thus further shortened performance and durability. Therefore, high-quality batteries contain individual cells in order to reduce these effects by internal resistance and cell capacitance selected ( " matched ").

For smaller batteries in the consumer sector the corresponding electronics is often integrated in the battery housing. LiPo battery packs for model feature next to the terminals of the cells connected in series via another connector on which each cell contact is brought out separately. A so-called Balancer ( English for " equalizer " ) measures in the loading operation on these lines, the individual cell voltages and controls on the charging current for each cell. To ensure that all cells are charged to full capacity, without overloading individual. In this case, because of the lower currents flowing, the cable can be designed for the balancer with a smaller cross -section. There are different types of plugs.

For larger cells as traction batteries the balancer is part of the battery management system. It is also possible during the discharge to equalize the cell voltages, in order to prevent premature discharge or different deep discharge of individual cells. In most applications will be omitted in this way for reasons of cost.

Life

In the life of lithium -polymer batteries, the cycle stability and the calendrical aging is to distinguish. As a general rule, an accumulator as worn, if it has less than 80% of the nominal capacity. General statements are difficult to make, because in addition to the technical design and quality of the practical working conditions have a major influence. While LiPo cells are often operated in model on the performance and specification limit and wear accordingly quickly, keep flat gezykelte traction batteries, for example, in electric cars for many years. The cycle stability is determined on the one constructive, the other improved frequent reloading without overloading the entire achievable energy conversion, ie, the cycle stability. Disadvantage in everyday devices usually cheap electronics and especially lack of cooling, which leads to faster calendrical aging. The battery capacity decreases even without use of the irreversible processes in the cell.

Recommendations:

• Frequent reloading (shallow discharge cycles )
• High quality battery management system
• Operating in the optimum temperature range, storage when not in use rather cool

Structure of a mobile phone - battery unit

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 mobile phone. After removing the plastic cover, top right, the protection circuit is exposed. In the lid of the aluminum block an electrical fuse against overload is integrated. The aluminum block protects the three films of lithium - polymer, which were pulled in the picture below.

The plastic film (polymer) takes up the electrolyte. A film coated with the electrode material for the positive contact and the other with graphite for the negative. The two-sided coating doubles the capacity at the wound together.

Unlike conventional batteries, the design of lithium - polymer batteries depends on the requirements of the manufacturer, not according to standards. In case of failure of the accumulator battery, the entire unit must be replaced. Even if you opened the battery pack, it is not ensured that the charging circuitry cooperates with spare batteries of unknown specification.

Applications

Solar vehicle

With a lithium - polymer battery of the Sky Ace TIGA is equipped with 165 km / h holder of the world speed record for solar vehicles. Likewise, the latest solar-powered aircraft Solar Impulse currently uses this accumulator.

Electric car

Since 2007, have been tested as a traction battery in an electric car type Hotzenblitz of 1996 at the company Kruspan Engineering in Switzerland lithium polymer batteries the company Kokam with high energy density. The vehicle tests undertaken ranges have been achieved over 350 km. This Hotzenblitz took 2011 as the " Team 9 Faraday USA" with Roger Miauton, Mark Fuller and Mike Collier at the Wave2011 (World Advanced Vehicle Expedition ), a tour of 3000 km, which led by eight countries participate.

The battery subsidiary of the French conglomerate Bolloré Group, the company BatScap, developed a lithium - polymer battery and its performance from 2005 an electric car called Bluecar, which was presented at the Geneva Motor Show 2009.

On 25 October 2010 a converted production model of the Audi A2 undertook a 605 km long record trip from Munich to Berlin. The managing director of the company founded in the summer of 2009, the Berlin company DBM Energy had worked according to own data since 2005 on battery for lithium - metal - polymer-based and organized the record attempt along with sponsors and the Federal Ministry of Economics as a media event. Later, this ride has been questioned, especially by ADAC and then by various other media. Criticisms was the cancellation of the notary and the dual disappearance of Lekker automobile out of sight of the press bus. In later articles about the record run more unresolved issues were raised. On 17 January 2011, announced that the record car was on 12 December 2010 Completely destroyed by a fire in a Berlin warehouse. The ADAC speculated that the battery was responsible for the fire, and called for an immediate investigation. After this message, the DBM Energy CEO took in business week in more detail about the incident. Accordingly, the record battery at the time of the fire should not have been in the car; it had already been working on a new test vehicle. With this new experimental vehicle a long distance test at the DEKRA was carried out in March 2011 and tested the battery by BAM. On 31 March 2011, the Tagesspiegel reported in an article about the failed tests at BAM and DEKRA and the arson at the Berlin warehouse. The hummingbird battery has passed the tests according to the UN inspection manual and the range check in accordance with ECE -R 101. The Audi rebuilt reached the range check, despite the smaller battery 455 km, the efficiency was 97 percent. When applied to the supposedly used in the world record battery capacity of 98.8 kWh this would correspond to a mileage of 714 km. So the Hummingbird battery would be the first lithium - metal - polymer battery without the otherwise associated with this technology risks and disadvantages.

Bolloré is also developing a lithium - polymer battery for the Microbus Gruau Electrique the French commercial vehicle manufacturer Gruau Group.

Model

Lithium -polymer batteries found in recent years the rapid spread in the model, since it caused a huge performance boost for radio controlled models here. Used as a drive, receiver and transmitter battery, it covers the whole division. See also RC model.

Mobile phones

Also in the mobile phones lithium polymer batteries use.

MP3 player

While earlier MP3 players were generally stocked for price reasons with conventional batteries, so are in this increasingly today, especially for models in the lower price segment, lithium polymer batteries. For cost reasons, they are often permanently installed or have a proprietary format. A defect can thus mean a total loss because the replacement outside the warranty period would no longer financially worthwhile.

Fixed power station energy storage

The company Hummingbird Power Systems AG ( holding company of DBM Energy GmbH) developed storage systems consisting of lithium - metal-polymer battery packs, for fixed power station energy storage applications from 20 kW to 5 MWh.