There are a number of battery technologies available today that are available on a large industrial scale. However, not all of them are suitable for use in purely electrically powered vehicles. The purpose of this article is to summarize the currently available custom lithium battery packs technologies based on the requirements described in Chapter 3. The basis of the evaluation is a detailed examination of the various battery parameters and properties that were used to describe the individual requirements.
The evaluations explain why lithium-ion technology currently best meets all requirements and offers the greatest potential for further technical developments.
The following battery technologies are currently technically available and have already been used in electric vehicles in the past:
Lead-gel battery
Nickel-cadmium battery
Nickel-metal hydride battery
Sodium nickel chloride high temperature battery
Lithium Ion Battery
In recent years, double-layer capacitors have been increasingly discussed for use in electric vehicles due to significant advances in technical development, but due to their high self-discharge rate, they are not (yet) an option for purely electric drives. This technology should therefore not be considered further. A summary of the technology assessment can be found in Table 1. The fulfillment of the individual requirements has been assessed on a scale of poor, average and good. In addition to the requirements, the main advantages and disadvantages of the battery system are listed. In addition, it is indicated whether, based on the central disadvantages, the batteries are generally suitable for traction purposes or not.
Lead-gel battery
Lead acid batteries are a very old technology and have been widely used as starter batteries in vehicles for decades. The energy content of the lead batteries is very low compared to the other custom lithium battery packs. Gravimetric energy densities of 20-30 Wh / kg are possible. High gravimetric power densities of up to 430 W / kg can be achieved, but lead to very low cycle stability and therefore a very short lifespan. The lifespan of the lead acid batteries is very short compared to the technologies available.
With a discharge depth of 80%, a service life of around 350 cycles can be achieved. The achievable calendar life is 5-15 years depending on the mode of operation and storage. Lead-acid batteries are currently the cheapest of all available battery systems. The manufacturing costs for the same capacity are around one fifth of those of lithium-ion batteries (as of 2010). However, since the batteries are a mature technology with already large production quantities, no major cost reductions can be expected in the future.
Due to the robust design, the safety risks for lead batteries are relatively low. They are thermally stable, which means that even at elevated temperatures, the battery does not self-heat or even explode. Although lead is a toxic heavy metal and sulfuric acid can also cause environmental damage, the environmental impact of this technology can be rated as average. This is because the thickening of the electrolyte into gel pastes limits the uncontrolled leakage of the electrolyte liquid to a certain extent even when the battery housing is destroyed, and there is an extraordinarily good disposal infrastructure for lead batteries. Overall, it can therefore be stated that this technology is basically suitable for use in electric vehicles.
Nickel cadmium
The nickel-cadmium battery has been mass-produced for several decades and is used in many household and industrial areas. However, the energy density is poor compared to the other technologies. When discharged for two hours, the battery has gravimetric energy densities of 40-55 Wh / kg with a very low cycle efficiency of only a maximum of 80% and a fairly high self-discharge rate, which is around 20% per month at room temperature. The availability of services is rather average. Gravimetric power densities of up to 700 W / kg per battery are possible. The cycle stability is almost twice as high as with lead systems. Up to 2000 cycles can be run at a depth of discharge of 80%, a key advantage compared to the short-lived lead-acid batteries.
A complete system can cost between € 250 and € 500 / kWh, twice as much as for lead batteries. In addition, due to the decades of development and production, the technology is already very mature and major cost reductions are no longer to be expected. What speaks for use in electric vehicles is the thermal stability of the nickel-cadmium battery. However, nickel-cadmium batteries consist of 20% of the highly toxic and carcinogenic metal cadmium and can therefore be classified as very environmentally harmful if not properly disposed of. At a European level, a ban on the use of cadmium was already decided by directive in 2006 and then implemented in national law at the end of 2008. For this reason, this battery technology is not suitable for future use as a traction battery.
