78 Chapter 7 Lithium-ion batteries have relatively few components in them, in fact there are really only about five major components and a typical bill of materials for a cell may have only between 10 and 20 line items ( Figure 4 ). Regardless of form factor, the major components of the cell are the cathode, an aluminum foil in many designs that is coated with the active cathode material. The second component is the anode, a copper foil that is coated with the active material of the anode. These two coated foils are kept separate through the use of a separator material most often made of some type of polypropylene (PP) or polyethylene (PE) plastic.
This forms the jellyroll, which is then inserted into the container or housing. This can be either a metal can, a plastic enclosure, or a metal foil-type pouch. Into this assembly is then injected the electro- lytic liquid. The entire assembly is then hermetically sealed and is ready to move into the next stage of cell manufacturing. Figure 5 shows a high level descriptor of the main components of a lithium-ion cell in relation to its cost. Figure 4 Prismatic lithium-ion cell components. Source: © Elsevier, Encyclopedia of Electrochemical Power Sources, P. Kurzweil, Lithium Rechargeable Systems, vol. 5.
Cathode Chemistries Lithium-ion is a very general term that refers to a wide variety of different chemistries, each of which has very different performance characteristics. The most common chemistry combi- nations used in lithium-ion cells include: LFP, NMC, LCO, NCA, and LMO. And of these five major chemistries, each cell manufacturer may use them in different combinations to achieve different performance results or in some cases the cell manufacturer may actually combine different chemistries in order to get the different benefits of each chemistry into one-cell design.