The state-of-health (SoH) provides insights into the current state of the energy storage system. Various measured values are taken into account, such as battery capacity, temperatures and current flows. The SoH is expressed as a percentage and makes it possible to assess the condition of the battery in an electric vehicle and determine how healthy it still is.
The common battery type in electric cars is the lithium-ion battery. It has been on the market since 1991 and achieves a high energy density with a long service life and low weight. There are several types of lithium-ion battery, which differ among other things due to the different materials on the positively charged cathode. The most important are:
- Lithium-cobalt dioxide battery
- NMC batteries with lithium-nickel-manganese-cobalt oxides
- NCA batteries with lithium-nickel-cobalt-aluminium oxides
- LFP batteries with iron phosphate
The energy density varies depending on the battery type, so other properties such as length of service life can vary.
The battery consists of several battery cells, each of which has a cathode and an anode and is separated by a separator. There is a liquid, ion-conducting electrolyte between the cathode and the anode. The composition of electric car batteries for lithium-ion batteries usually includes lithium, graphite, nickel, iron phosphate or cobalt. Lithium is used mainly due to its excellent chemical properties.
The service life of an electric car battery is not measured in years, but by the number of charging cycles. A cycle consists of a charging process and a discharging process. Depending on usage and charging behaviour, lithium-ion batteries enable an average of 1,500 charging cycles. After this, the battery is not defective, but simply no longer has its full capacity. Old batteries can then be used for a second life (see also the question: What happens to old batteries?).
Second life: depending on their operating conditions, conventional batteries are too weak for continued use in electric cars after eight to ten years. But they still have enough power for a second life, e.g. as a stationary energy storage unit. These can be combined with other old batteries as stationary battery storage units to absorb wind or solar power and stabilise the electricity grid.
Recycling: including second use, electric car batteries have a service life of up to twenty years in total. When the end of the life cycle has been reached, electric car batteries can be recycled appropriately and professionally. The raw materials contained in the battery are professionally separated and reused, for example for the production of new batteries.