What Is a Lithium Polymer Battery

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A lithium polymer (abbreviated as LiPo) battery is a rechargeable lithium ion battery that uses a solid polymer electrolyte instead of a liquid electrolyte. It is technically a lithium-ion polymer battery. The electrochemistry of a LiPo battery is essentially the same as a Li-ion battery. Both systems use identical reactive materials for the electrodes and contain a similar amount of electrolyte. The difference between lithium-ion and lithium-polymer batteries is the form of electrolyte used. The electrolyte used in a LiPo battery has been "plasticized" or "gelled" through a polymer additive, whereas the electrolyte of a standard lithium-ion battery is made of liquid organic solvents with dissolved lithium salts.

Lithium polymer batteries are designed for applications requiring ultra-thin or flexible geometric shapes. Conventional lithium-ion batteries use a rigid framework. Thin layers of the positive electrode (cathode), the negative electrode (anode), and the separator which is typically a polymeric membrane saturated with a liquid electrolyte are inserted into a rigid stainless steel or aluminum cell housing or can. Lithium polymer batteries do not require a rigid metal casing to press the electrodes. Instead they come in a soft package or pouch format and the cell housing made of laminated flexible aluminum foils. By eliminating the rigid housing, LiPo batteries offer a flexibility in cell sizes and shape. These batteries can be more easily formed to the dimensions required for specific applications. This compelling advantage has prompted the widespread use of LiPo batteries in smartphones, laptop computers, digital cameras, GPS devices, wireless controllers for video game consoles, wireless PC peripherals, electronic cigarettes, radio-controlled aircraft, radio-controlled cars and large scale model trains.

The core innovation in lithium polymer batteries is the solid polymer electrolyte (SPE). SPEs not only provide superior processability and enhanced electrode/electrolyte interfacial compatibility, the absence or reduced use of organic solvents allows the hazard posed from this flammable component to be mitigated or completely eliminated. Polymer electrolytes can be directly on the electrodes and act as a glue to hold the battery components together. The SPE can be made from polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA) or polyvinylidene fluoride (PVdF). However, it still remains a challenge to solve the problems of low ionic conductivity and low lithium transference of polymer electrolytes. Poor salt dissociation of SPEs results in a low ionic conductivity. The low ionic conductivity of polymer electrolytes at room temperature is a practical concern. Stronger interaction of the polymer matrix with lithium cation as compared to the anion causes the SPE to have a low lithium transference.

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