Different vehicles have different needs and the corresponding requirements of the battery vary accordingly. No battery can be made that is able to fulfil all the functional and operational requirements of all types of electric vehicles. From a vehicle perspective, the battery should obviously deliver and accept power according to the usage conditions, but the battery should also be robust and reliable, possess long durability, and require minimal service and maintenance.
A battery is also more than just the cells contained. In order to be functional in a vehicle, the battery must include a thermal system, electronics, and a management unit. Vehicle performance will strongly affect the battery design and the selection of battery technology; design constraints that influence reliability and driveability. Consequently, exactly the right cell and battery can only be chosen with the electric vehicle in mind, to avoid oversized batteries – unnecessarily heavy and expensive. Examples will be given on how to select battery and cells in order to fulfil the vehicle requirements.
Vehicle types and requirements
The primary advantages of electric vehicles are environmental: reduced fossil fuel consumption, and hence CO2 emissions, and reduced pollution and noise levels in cities. Moreover, vehicle integration may be simplified since no mechanical connections are needed between the electric drive system and the battery. Another advantage is the ability to recuperate brake energy, which is free energy to be used in the overall energy management strategies of the vehicle.
The basis for all battery development for electric vehicles is the vehicle type and how the vehicle is to be used. Depending on how the electric vehicle is designed, different battery requirements are needed in terms of power and energy needs. These requirements will be discussed in the following sections, starting with the main types of electric vehicles.
5.1.1 Vehicle types
Electric vehicles can have different degrees of electrification, i.e. a certain amount of the energy consumption derives from electricity and the rest from the internal combustion engine (ICE), as illustrated in Figure 5.1. Several factors must be considered in order to select the optimal degree of electrification: required all-electric driving range, energy consumption per km, performance requirements (e.g. acceleration), geographical constraints such as ambient temperature and terrain.