What is lipo battery pack construction
This entry was posted on April 19, 2017.
LiPo is a short way of saying Lithium Polymer batteries, Lipo batteries are packaged generally in prismatic pouch made of some plastic polymers. These batteries are known for their exceptional "boost discharge capabilities". Lithium polymer batteries are labeled nnC where nn is a number. For example a 1000mAH Lipo battery with 50C label is capable of supplying 50 Amperes of current for a fixed time. Lipo is lighter in weight and hence is more energy dense than Lithium Ion batteries. You will find these batteries in toys where weight is a constraint e.g. flying toys for kids, toy quad-copters, heli, airplanes etc. But what is the basic construction of a LiPo battery? The lipo battery construction is as follows:
Anode: aluminum foil current collector. Metal oxide active material (NMC, NCA, LCO, LFP). Binder (PVDF - Polyvinyladine Fluoride). Conductive carbon (Acetylene black, Vulcan , graphite )
Cathode: copper current collector. Graphite active material. Binder (PVDF, or CMC/SBR -- carboxymethyl cellulose and styrene butadiene rubber). Conductive carbon.
Separator: polypropylene film, ionically conductive but electrically insulating, e.g. Celgard
Electrolyte: carbonate solvents including ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC). Lithium salt, eg lithium hexafluorophosphate (LiPF6)
Pouch material: aluminum with polymer coating.
Tabs: aluminum cathode tab, nickel anode tab
Construction: double sided anode and cathode sheets are stacked and wrapped in separator, sometimes in Z-fold pattern. Anode and cathode Electrode stack tabs are ultrasonically welded together, placing them in series. Anode and cathode tabs are further welded to external tabs (Al or Ni, see above). Welded stack is packaged in 3-side sealed pouch, filled with electrolyte, then 4th side is sealed in vacuum pouch step.