Cell design is largely the task of combining active and inactive cell components to make a complete cell usable in electric vehicle applications, something that requires an extensive optimisation process. Since there is no single combination suitable for all vehicle applications, usage behaviours, or performance requirements, different combinations of materials are possible. In this chapter, the cell design constraints will be discussed in terms of active materials, electrode design, and how to make the complete cell ready to be incorporated into a battery. Initially, focus will be on the design of the composite electrodes, which is essential for how the cell can be optimised towards energy or power. The electrode design and manufacturing are also the basis for durability and safety.
All-electric vehicles are, however, dependent on the power and energy performance of the cells but, as previously described (Section 1.6.4), these two performance characteristics cannot be combined without somehow oversizing the battery. A critical point in the cell development process is to match, or balance, the electrodes in order to obtain optimal cell performance during charge and discharge, exhibiting optimal capacity over a lifetime. Furthermore, size and format of the cell may be significant with regard to the performance of the cell, the battery, and subsequently the electric vehicle. Different cell formats will be discussed, as they also affect the thermal and packaging constraints of the final battery. Finally, a brief overview of the main production steps will also be given.
The active electrode material is mixed with an electron-conducting material and a binder to create a composite electrode. This is attached to a current collector, typically a thin metal foil. This basic set up of a composite electrode – negative or positive – is illustrated in Figure 4.1, displaying the electron conduction pathways, where the electrons are conducted from the active material, via the conductive material, to the current collectors. The ions are conducted via the electrolyte, which is incorporated in the voids between the particles, to the active electrode materials.