Lithium Polymer Battery (Li-Po)

LITHIUM POLYMER BATTERY

Lithium-ion polymer batteries, polymer lithium ion, or more commonly lithium polymer batteries (abbreviated Li-poly, Li-Pol, LiPo, LIP, PLI or LiP) are rechargeable batteries (secondary cell batteries). Normally batteries are composed of several identical secondary cells in parallel addition to increase the discharge current capability.

DESIGN ORIGIN

This type has technologically evolved from lithium-ion batteries. The primary difference is that the lithium-salt electrolyte is not held in an organic solvent but in a solid polymer composite such as polyethylene oxide or polyacrylonitrile. The advantages of Li-ion polymer over the lithium-ion design include potentially lower cost of manufacture, adaptability to a wide variety of packaging shapes, and ruggedness. Lithium-ion polymer batteries started appearing in consumer electronics around 1996.

TECHNOLOGY

Cells sold today as polymer batteries are pouch cells. Unlike lithium-ion cylindrical cells, which have a rigid metal case, pouch cells have a flexible, foil-type (polymer laminate) case. In cylindrical cells, the rigid case presses the electrodes and the separator onto each other; whereas in polymer cells this external pressure is not required because the electrode sheets and the separator sheets are laminated onto each other.

Since individual pouch cells have no strong metal casing, by themselves they are over 20% lighter than equivalent cylindrical cells. However, all Li-Ion cells expand at high levels of state of charge (SOC); if uncontained, this may result in delamination, and reduction of reliability and cycle life; the case of cylindrical cells provides that containment, while pouch cells, by themselves, are not contained. Therefore, to achieve the rated performance, a battery composed of pouch cells must include an overall, strong, external casing to retain its shape.Early in its development, lithium polymer technology had problems with internal resistance. Other challenges include longer charge times and slower maximum discharge rates compared to more mature technologies. Li-poly batteries typically require more than an hour for a full charge. Recent design improvements have increased maximum discharge currents from two times to 15 or even 30 times the cell capacity (discharge rate in amperes, cell capacity in ampere-hours). In December 2007 Toshiba announced a new design offering a much faster rate of charge (about 5 minutes to reach 90%). These cells were released onto the market in March 2008 and are expected to have a dramatic effect on the power tool and electric vehicle industries, and a major effect on consumer electronics.

APPLICATION OF LIPO BATTERY

A compelling advantage of Li-poly cells is that manufacturers can shape the battery almost however they please, which can be important to mobile phone manufacturers constantly working on smaller, thinner, and lighter phones.

Li-poly batteries are also gaining favor in the world of radio-controlled aircraft as well as radio-controlled cars, where the advantages of both lower weight and greatly increased run times can be sufficient justification for the price. Some airsoft gun owners have switched to LiPo batteries due to the above reasons and the increased rate of fire they provide. However, lithium polymer-specific chargers are required to avoid fire and explosion. Explosions can also occur if the battery is short-circuited, as tremendous current passes through the cell in an instant. Radio-control enthusiasts take special precautions to ensure their battery leads are properly connected and insulated. Furthermore fires can occur if the cell or pack is punctured. Radio-controlled car batteries are often protected by durable plastic cases to prevent puncture. Speciallydesigned electronic motor speed controls are used to prevent excessive discharge and subsequent battery damage. This is achieved using a low voltage cutoff (LVC) setting that is adjusted to maintain cell voltage greater than (typically) 3 V per cell.

Li-poly batteries are also gaining ground in PDAs and laptop computers, such as Apple's MacBook family, Amazon's Kindle, Lenovo's Think pad X300 and Ultra bay Batteries, the OQO series of palmtops, the HP Mini and Dell products featuring D-bay batteries. They can be found in small digital music devices such as iPods, Zunes, and other MP3 players and the Apple iPhone and iPad, as well as gaming equipment like Sony's PlayStation 3 wireless controllers. They are desirable in applications where small form factors and energy density outweigh cost considerations.

STORAGE

Unlike certain other types of batteries, lithium polymer batteries can be stored for one or two months without significantly losing charge. However, if storing for long periods, manufacturers recommend discharging the battery to 40% of full charge. In addition, other sources recommend refrigerating (but not freezing) the cell.

LITHIUM POLYMER CHARGER

LiPoly batteries must be charged carefully. The basic process is to charge at constant current until each cell reaches 4.2 V; the charger must then gradually reduce the charge current while holding the cell voltage at 4.2 V until the charge current has dropped to a small percentage of the initial charge rate, at which point the battery is considered 100% charged. Some manufacturers specify 2%, others 3%, but other values are also possible. The difference in achieved capacity is minute.

LIPO BATTERY CHARGER USED

Lipocharger is used for charging the 1 to 6 cells lipo battery with a dedicated slot for each type. The display shows the amount of charge left in the battery and allows selecting the current required to charge the battery. The maximum current depends on the power source used, which may vary from 0.1A to 5A.

There are two sets of wires provided with the charger. The battery can be charged in 3 modes that are,

·         Normal mode – in this mode the battery charging occurs using the specified current at a moderate rate. It maintains the partial balance.

·         Fast mode – here the battery is charged at a faster rate.

·          Balanced mode – maintains a perfect balance between all the three cells being charged.

Features:

·         Microprocessor controlled

·         Delta-peak sensitivity

·         Individual cell balancing

·         Li-ion, LiPo and LiFe capable

·         Ni-Cd and NiMH capable

·         Large range of charge currents

·         Store function, allows safe storage current

·         Time limit function

·         Input voltage monitoring. (Protects car batteries at the field)

·         Data storage (Store up to 5 packs in memory)

Specifications:

·         Input Voltage: 11~18v

·         Circuit power: Max Charge: 50W / Max Discharge: 5W

·         Charge Current Range: .1~5.0A

·         Discharge current range: .1~1.0A

·         Ni-MH/NiCd cells: 1~15

·         Li-ion/Poly cells: 1~6

·         Pb battery voltage: 2~20v

·         Weight: 277g

·         Dimensions: 133x87x33mm