Lithium polymer battery

Lore & Background

The dry solid polymer electrolyte was first used in prototype batteries around 1978 by Michel Armand, and in 1985 by ANVAR and Elf Aquitaine of France, and Hydro-Québec of Canada. Sony began research on lithium-ion cells with gelled polymer electrolytes in 1988, before the commercialisation of the liquid-electrolyte lithium-ion cell in 1991. This type of cell entered the market in 1998.

However, some argue that gelled membranes are not 'true' polymer electrolytes but rather hybrid systems where liquid phases are contained within the polymer matrix; these electrolytes may be dry to the touch yet still contain 30% to 50% liquid solvent. Since 1990, organisations such as Mead and Valence in the United States and GS Yuasa in Japan developed batteries using gelled solid polymer electrolytes. In 1996, Bellcore in the United States announced a rechargeable lithium polymer cell using a porous solid polymer electrolyte, called a plastic lithium-ion cell (PLiON), which was commercialised in 1999.

Like other lithium-ion cells, LiPo batteries operate via intercalation and de-intercalation of lithium ions between positive and negative electrodes, using a gelled or solid polymer-based electrolyte as the conductive medium. A microporous polymer separator prevents direct electrode contact while allowing lithium-ion transport.

The electrolyte types fall into two categories: dry solid polymer electrolytes (SPE) and gel polymer electrolytes (GPE). Dry SPEs initially had poor ion transfer and low conductivity at room temperature; to improve this, gelled electrolyte was added, forming GPEs. GPEs incorporate an organic liquid electrolyte in the polymer matrix, giving properties between those of liquid and solid electrolytes, with higher thermal stability and low volatility that contribute to safety.

Reader's Guide

Lithium polymer batteries have become significant due to their ability to be produced in almost any desired shape, meeting the space and weight requirements of mobile devices and notebook computers. Their low self-discharge rate of about 5% per month and high energy density outweigh cost considerations in many applications. They are now nearly ubiquitous in commercial and hobby drones, radio-controlled aircraft and cars, and large-scale model trains, where lower weight and increased capacity and power delivery justify the price. LiPo packs also see widespread use in airsoft for higher discharge currents and better energy density than traditional NiMH batteries.

In mobile devices, power banks, very thin laptops, portable media players, wireless controllers, and electronic cigarettes, their small form factors are sought. Hyundai Motor Company and Kia Motors use LiPo batteries in some battery-electric and hybrid vehicles, and the Bolloré Bluecar in car-sharing schemes also uses this type. LiPo batteries are increasingly used in uninterruptible power supply systems, offering benefits over traditional VRLA batteries in power-to-size and -weight ratios, longer cycle life, usable energy, and thermal runaway characteristics, particularly in data centers where space is at a premium. Portable jump starters for vehicles use three or six LiPo cells in series to start internal combustion engines, replacing larger and heavier lead-acid jump starters.