Now it is time to take the next step towards a battery for an electric vehicle. The fundamental electrochemical processes in the previous chapter will now be dressed in ‘chemistry’ and materials. Due to the combinations available for electrodes and electrolytes, a wide range of battery technologies can be obtained, all having specific cell properties. The limitations and possibilities of the different combinations will affect cell performance considerably, but not all of them are of interest for electric vehicles. In the following chapter, only those concerning vehicle applications will be discussed and only for rechargeable battery technologies having acceptable energy and power capabilities for the demanding vehicle requirements. These technologies will be described in general and schematic terms, which may also be of interest for other types of applications, such as stationary and smart grid applications.
By combining a positive and a negative electrode in different ways, and then immersing them in a suitable electrolyte, a palette of cell potentials, charge/discharge characteristics, capacity, power and energy densities, cycle life, for example, can be obtained. Depending on the intended usage, some technologies and material combinations are more suitable than others. Indeed, the performance of a cell can vary significantly during actual operational conditions compared to ideal laboratory tests, and therefore the performance conditions should be evaluated. Many of the factors influencing cell performance under different operation conditions are linked together. The same battery technology may differ significantly between manufacturers and manufacturing processes due to specific cell constraints, e.g. material specifications and cell design. The cells may also vary from batch to batch from the same manufacturer. Moreover, storage and the age of the cells influence performance, which can change drastically; the performance obtained at beginning of life (BOL) is rarely the same as at end of life (EOL).
The following battery technologies will be described:
• lead-acid (Pb-acid)
• nickel metal-hydride (NiMH)
• high-temperature molten-salt
• nickel-zinc (NiZn)
• zinc-air (Zn-air)
• metal-ion (Me-ion)
• redox flow
In addition, high-energy density capacitors will also be described. They are not batteries in the classical sense, but still an electrical energy storage technology of considerable interest for electric vehicles. Another suitable technology for electric vehicles is fuel cells.