Understanding the capacity of an electric car battery

Published by on 10.18.2019 - 5 min

The energy output of an electric car battery depends on the capacity and number of lithium-ion cells it contains, but also varies depending on the conditions under which it is used. The challenge is to find the right balance between capacity, ease of charging, bulk and components needed to boost its energy efficiency.

Why can’t our smartphones last longer than a day or two before needing to be recharged? Consumers want increasingly thinner devices, forcing manufacturers to equip them with smaller batteries.

The same problem affects electric vehicles, where the range of an electric car is in large part tied to the volume of its battery.

But the available space cannot be continually expanded! The challenge is to find ways to maximize capacity without compromising on the car’s spaciousness, comfort, bulk or responsive handling.

The battery of an electric car is an assembly of modules, which are themselves assemblies of individual cells. It is within these cells, veritable energy accumulators, that electro-chemical reactions take place allowing the battery to deliver or store electricity.

Improving the capacity of an electric car battery

ZE 50 Battery

To improve the capacity of an electric car battery without increasing its volume, a first step is to work at the chemical level within the cell’s electrodes in order to make them capable of storing a larger amount of energy. The other option involves working on the way the modules are arranged in the space inside the battery to maximize the volume given over to the cells.

This is what Renault’s engineers managed to do when they developed the Z.E. 50 battery that powers the New ZOE. While similar in size, the new unit provides a 20% increase in range compared to the previous generation!

Besides its stated capacity, the range of an electric car is also influenced by the conditions under which the battery operates . Cold, for example, increases the internal resistance of the cells within the lithium-ion battery, which slightly reduces the available energy and output.

From capacity to real-world range

To mitigate the effects of this inescapable characteristic of lithium-ion technology, it is possible to incorporate temperature control systems designed to bring the cells up to their optimal temperature range. These devices help to keep the performance level optimal, even in the middle of winter, especially where the electric motor’s output is high.

The reduced range observed in an electric vehicle at low temperatures is mainly due to the demands of keeping the temperature inside the car comfortable. While combustion engine cars meet this need with heat from the engine, electric vehicles have to use some of their battery capacity.

Capacity and life cycle

Gradual changes to the cells’ internal chemistry cause wear that, over time and after repeated charging cycles, eventually lowers the battery’s real capacity.

The amount of year depends on the degree of use, but it’s generally thought that a battery continues to meet the criteria of the automotive industry for at least 10 to 15 years. After that time, the battery can be reused for other less demanding applications – this is called a second life – such as stationary energy battery storage systems.

As for recycling, that will only happen several years after this point.


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