• October 21, 2016 at 11:58 am

    LiPo cells follow the history of lithium-ion and lithium-metal cells which underwent significant research during the 1980s, reaching a significant milestone with Sony’s first commercial cylindrical Li-ion cell in 1991. After that, other packaging techniques evolved, including the pouch format now also called “LiPo”.

    Design origin and terminology of Lithium-ion battery

    The original kind of cell named ” lithium polymer ” has technologically evolved from lithium-metal and lithium-ion battery. The primary difference is that instead of using a lithium-salt electrolyte (such as LiPF6) held in an organic solvent (such as EC/DMC/DEC), the battery uses a solid polymer electrolyte (SPE) such as poly(ethylene oxide)(PEO) and so on.

    The solid electrolyte can be typically classified as one of three types: dry SPE, gelled SPE and porous SPE. The dry SPE was the first used in prototype batteries, around 1978 by Michel Armand, Domain University, and 1985 by ANVAR and Elf Aquitaine of France, and Hydro Quebec of Canada. From 1990 several organisations like Mead and Valence in the United States and GS Yuasa in Japan developed batteries using gelled SPEs.In 1996, Bellcore in the United States announced a rechargeable lithium polymer cell using porous SPE.

    In parallel to the development of these “polymer electrolyte” batteries, the term “lithium polymer” started being used for liquid electrolyte Li-ion cells in pouch format. These cells started appearing in consumer electronics around 1995, eventually becoming known as “LiPo” for some applications.

    The confusion in the names may stem from the construction of the basic lithium-ion battery. A typical cell has four main components: positive electrode, negative electrode, separator and electrolyte. The separator itself may be a polymer, such as a microporous film of polyethylene (PE) or polypropylene (PP); thus, even when the cell has a liquid electrolyte, it will still contain a “polymer” component. In addition to this, the positive electrode can be further decomposed in three parts: the lithium-transition-metal-oxide, a conductive additive, and a polymer binder of poly(vinylidene fluoride) (PVdF). The negative electrode material may have the same three parts, only with carbon replacing the lithium-metal-oxide.

    Therefore, even if a bare, unfinished cell lacks a polymer separator, or any liquid or solid electrolyte, it may still have a “polymer” component in the active materials of the electrodes. This polymer, however, is just a small fraction, typically less than 5% by weight, and does not participate in the electrochemical reactions, being only useful for binding the active particles together to maintain good conductivity, and help make the slurry mix adhere well to the copper and aluminium foils that compose the current collectors of the battery cell.