The future is between anode and cathode
As energy storage systems for electric vehicles, traction batteries are increasingly attracting attention as a key technology for climate-friendly mobility. Kay Dohnke takes a look at the current state of development and technological prospects.
While originally two concepts were pitted against each other, the rechargeable traction battery as the source for the propulsion power in the passenger car segment has currently prevailed against the hydrogen fuel cell. That’s reflected by both the vehicles being offered and the supporting infrastructure.
A paradigm shift in terms of perception and evaluation has occurred in this regard too: while in the case of cars with internal combustion (IC) engines, attention used to be focused on engine size and power output, it’s directed almost exclusively at the traction battery. In the case of electric cars, range and charging time are key criteria for purchasing decisions. While the output of the electric motor installed in the vehicle is of secondary importance. This emphasises the fact that the traction battery is the most important component of an electric vehicle.
In fact, there’s a range of factors yet to be optimised before traction batteries will have reached their full technical potential. Around the world, battery developers, scientific research institutes, startups, automakers and battery producers, separately or in collaboration, are working at full stretch on optimising the relevant parameters by changing the components, using different materials and modifying the battery architecture.
Attention is focused on the following factors, not only in the case of lithium-ion batteries but also with other battery storage technologies:
Top spot for the li-ion battery
Hundreds of thousands of traction batteries are by now in use and the type of the large-sized lithium-ion battery has long won out. The use of lithium-ions as energy sources in various setups has been proven in practice and the related batteries can be produced in large numbers.
Capacity: the amount of electric energy that a traction battery can make available in relation to its weight is called gravimetric energy density. Range depends on the capacity of the battery, the vehicle characteristics and the operating conditions.
Charging speed: If a traction battery can be fully discharged or recharged within one hour it has a C-rate of 1. If it requires only half an hour, the rate is 2 C, in the case of a quarter of an hour it would be 4 C. The intensity of the charging current is important in this regard: a Tesla supercharger charges clearly faster than a wall box at home. Charging speed also depends on ambient temperatures and the battery.
Number of potential charging events: Currently, a battery is supposed to still have at least 70% of its original capacity after 10-year use and 1,000 full charging cycles. However, initial long term experiences with this still young technology indicate lower aging losses, as current tests by TÜV Munich have confirmed.
Size and weight of the traction battery are decisive for its possible uses: in large, higher-powered vehicles, a large and heavy battery can easily be accommodated. In the case of smaller mid-size or compact cars, there’s currently only very limited space potential. That’s one of the reasons why a reduction of the content of passive materials by means of design changes is being pursued.
Price: Since electric motors are relatively small, can be produced in simple and cost-efficient ways and a complex powertrain is not required, the traction battery is the most expensive component of an electric vehicle. If the costs of traction batteries can be cut significantly by using cheaper materials and optimised manufacturing methods their potential uses will automatically grow because lower-priced vehicles can be electrified as well.
It’s not clear in which direction traction batteries are headed because, on the one hand, new solutions can be expected in view of the high development intensity. On the other hand, it’s often external factors that help make a solution successful. Yet no matter what, the future lies between the anode and the cathode.