Use of battery storage
The electric traction battery, a high-voltage battery with a nominal voltage of 400-1,000 volts, is the central element of a BEV. Its characteristics determine range and charging times, which are key factors for practicality and comfort and thus for the market success of the vehicles. With a weight of several hundred kilograms and capacities of 20-100 kWh, it is also the most expensive component of electric cars.
In principle, the traction battery can be placed in different areas of the vehicle body. It is usually installed in the vehicle floor. It also serves as a storage location for the recuperation energy, which is recovered from the kinetic energy of the vehicle during braking. The on-board electronics are usually supplied from a separate (low-voltage) battery. In principle, alternating battery models are possible, but hardly pursued at present. Instead, the storage unit is usually permanently installed. It can be charged at the home charging station ("wall box") or at public charging stations.
The use of a traction battery is also common in electric vehicles with fuel cells: this can be charged both by the fuel cell and by recuperating braking energy. The battery is used in driving situations that require a lot of engine power. Depending on the context of use, BEVs or FCEVs may appear advantageous: For city cars, for example, the battery-electric drive is likely to be more attractive in terms of purchase costs, refuelling options and energy efficiency. For taxis, on the other hand, hydrogen may be the preferred option due to its greater range.6
Central motives for the promotion of electric cars are climate and resource protection concerns. It therefore goes without saying that the battery storage systems used must meet high environmental standards: Their production should require as little energy and (critical) raw materials as possible; their performance parameters (specific energy, performance over time, deep discharge capability) should enable "a lot of use with little battery" in operation; and their cycle stability should allow many years of use.
Furthermore, safety aspects play an important role. In normal operation and especially in accident situations, battery storage should not be a fire or explosion hazard. The same applies with regard to parking and charging times. Finally, a third performance factor is the fast-charging capability: it determines the duration of the individual charging processes and thus decisively the comfort for the vehicle user. However, fast charging can be a significant driver of battery ageing.
Up to now, traction batteries have usually been designed so large that fast charging without ageing damage and a long range are possible at the same time. In the future, the efficiency potential of electric cars will only be realised if fast-charging capability, low battery ageing and a long range can be achieved with batteries that are as small as possible.
6 Wrede, Insa (2019): Brennstoffzelle versus Batterie: Wer macht das Rennen? Deutsche Welle.
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