Cobalt is a controversial raw material. There are both technical and ethical reasons for this. Researchers are therefore looking for alternatives for the cathode material.
NMC batteries are currently the most common type of battery for electric vehicles. They consist of various proportions of nickel, manganese and cobalt. These elements are the basis for the cathode material. The cathode, in turn, is considered to be the part of a lithium-ion battery (LIB) with the greatest potential for optimizing performance and energy density through the use of new materials.
Cobalt is an important component as it helps to increase the energy density of the batteries. "It also increases the stability of the cathodes and extends the service life of the batteries," explain researchers at the Swiss Paul Scherrer Institute (PSI). However, cobalt is extremely rare. According to the scientists, only 0.004% of the earth's crust consists of this rare metal. The Democratic Republic of Congo has the largest cobalt deposits in the world - around 70% of the world's annual demand comes from the Central African country.
Cobalt from Central Africa Under Criticism
The problem: cobalt mining in the Congo takes place under socially and ecologically questionable conditions. Most of it is carried out industrially; according to PSI estimates, between 15 and 30 % is accounted for by small-scale mining. "These are independent miners, often including women and children, who dig for the coveted metal by hand, sometimes with inadequate equipment, in tunnels at risk of collapse," it says. The supply chains are often opaque, the mining conditions are problematic and the exact origin of the raw material remains unknown despite the mining companies' declarations. Industrial mining can also lead to dust and sulphur dioxide emissions as well as pollution of drinking water, soil, fields and air.
Car Manufacturers Reduce Cobalt Content
So how do we deal with this problematic metal in batteries? Scientists have been researching solutions for some time. One approach is to simply reduce the use of cobalt. In recent years, the proportion of cobalt has already fallen - from a third (NMC-111) to a fifth (NMC-622) to a tenth (NMC-811).
Some car manufacturers are pursuing the strategy of merely reducing the proportion of the controversial raw material. The US automotive group General Motors, for example, presented its new battery series in 2022, which is said to contain 70% less cobalt than the previous generation. In the BMW iX3, the proportion of cobalt in the battery has been reduced by two thirds. The proportion of nickel and cobalt in Tesla batteries is also set to decrease. In addition, the solid-state battery that some companies such as Toyota have announced is based on a low-cobalt method. Finally, there is also the option of using a higher proportion of recycled cobalt, as Audi does, for example.
Nickel and Iron as Alternatives
Researchers in the laboratory for battery electrodes and cells at PSI are also looking for a cobalt substitute. The various alternatives for cobalt all have advantages and disadvantages in terms of energy density, service life, charging time, safety and availability of raw materials. According to the PSI, it is important to develop a broad spectrum of technologies so that they can be used to solve various problems in different areas of application. This would make it possible to reduce cobalt and avoid dependence on individual raw materials.
On the one hand, the proportion of nickel could be increased at the expense of cobalt. Nickel even has a higher energy density than cobalt, which means that batteries with a higher nickel content could potentially store more energy, according to the PSI researchers. Active materials for lithium-nickel-iron-manganese batteries are another option being researched at PSI. Here, the iron replaces the cobalt in the cathode material. The material has a very high capacity and a high working potential, which means that a much higher energy density can be achieved than with conventional batteries.
Sodium-ion Batteries and LFP Batteries
Relying on a completely cobalt-free battery is also an option. The Chinese battery manufacturer CATL is pursuing this strategy. On the one hand, CATL relies on sodium-ion batteries that do without lithium and cobalt, and on the other hand on cobalt-free lithium iron phosphate cells. Another example: the blade battery from Chinese car manufacturer BYD, also a lithium iron phosphate (LFP) composition, does not require cobalt, nickel or cadmium. The Chinese battery manufacturer Svolt has started producing cobalt-free cathode material. They are used in nickel-manganese battery cells (NMX).
Europe is also active. The German Aerospace Center (DLR) is researching cobalt-free lithium-ion batteries together with eleven European partners in the EU joint project Hydra. The electrodes of the new cells are to be free of cobalt and contain 85% less environmentally harmful raw materials. Instead, the cells will use iron, manganese and silicon. The Hydra project is scheduled to run until the end of August 2024.
Cobalt-free Cathode and Silicon Oxide Anode
The latest example of a battery alternative without cobalt comes from a Japanese research team at the University of Tokyo. As the researchers write in the journal "Nature Sustainability", they have combined a cobalt-free cathode with a silicon suboxide (SiOx) anode. The battery consists of a novel combination of the elements lithium, nickel, manganese, silicon and oxygen. The electrode combination is in turn based on a promising electrolyte formulation based on 3.4 M LiFSI/FEMC. In addition to lithium, nitrogen, sulphur, oxygen and fluorine, the new electrolyte also contains a special carbonate compound.
The battery developed is said to have a 60% higher energy density than conventional lithium-ion batteries. It can also provide a higher cell voltage of 4.4 V. In addition, the battery has long-term stability and still has 85% of its maximum storage capacity after 300 charging and discharging processes.