08. April 2021, 10:29 Uhr | Ute Häußler
Ecological and inexpensive alternatives to cobalt are a must as the number of electric vehicles and mobile devices increases. In the EU project Cobra, 19 partners are researching a cobalt-free cathode for longer battery ranges as well as smart BMS sensors and environmentally friendly housings.
Cobra stands for »Cobalt-free Batteries for Future Automotive Applications«; the EU project has been running since the beginning of 2020 and covers virtually the entire value chain of the European battery industry via the partners involved. The cobalt-free alternative to Li-ion batteries is intended to overcome the existing shortcomings of batteries for electric vehicles - in other words, to deliver more range for less money and be ecologically harmless. The goals are quite ambitious: at the lowest possible cost, both the energy density and the number of charging cycles are to be increased - specifically, 750 Wh/l cell energy density, a service life of more than 2,000 cycles and a maximum cost of 90 euros/kWh for the mass production of the more environmentally friendly battery pack are targeted. The »good« batteries are to be fast-chargeable with 3C certification and extremely light, as well as naturally receiving automotive certification.
After four years of project duration, a Cobra prototype according to TRL6 status should be ready by the end of 2023. To achieve this, the interdisciplinary team from research institutions and companies is focusing on improving electrochemical performance with a cobalt-free cathode, an advanced silicon composite as anode, and electrolytes/separators. In addition, the partners are working on novel cell manufacturing and testing of electrical and electrochemical performance, the use of smart, networked sensors in system control, and a safe and »green« package.
The three largest Cobra partners among the 19 participating companies are semiconductor specialist Infineon, battery developer AVL and Liacon
as a manufacturing expert. John de Roche, founder and head of innovation at the smallest Cobra partner Aentron, sees other fields of application for the sustainable batteries besides their use in the automotive industry. »Digitalization and electrification are not limited to mobility. We see great potential also for autonomous and electric vehicles in industry - this can range from driverless transport systems (AGVs) to tractors - and equally enrich the maritime sector, i.e. environmentally friendly ships for passenger traffic and transport.« According to de Roche, both sectors are also currently in an »optimization phase« and have to comply with EU CO2 directives, plus are focusing on growth and efficiency through innovative technologies.
Fig. 1. The housing of the cobalt-free batteries is made of cellulose and comes from the 3D printer at Aentron in Gilchig.
Aentron is responsible for the housing and as system integrator in the Cobra project. The battery specialist from Gilching near Munich is creating a reference design that must use green materials to provide the same fire and short-circuit protection as conventional housings (Fig. 1). The choice for Cobra fell on cellulose, which comes directly from a 3D printer at Aentron's headquarters for the test series. The wood-like material is not only safe, but also lightweight and offers good conditions for very efficient integration of the battery cells and overall technology. »We're building the battery together,« says John de Roche. Five years ago, he was co-founder of Aentron; today, as head of innovation, he has a young team drawing up the specifications for Cobra battery integration. How can the individual battery components be accommodated in the safest, most space-saving and most effective way on the base plate and in the housing?
After the first year, and thus around a quarter of the scheduled project duration, the first samples will be tested and validated at Ingolstadt Technical University. The learning effects will flow back to Aentron and, as an interaction between all partners, form the basis for the final sample of the Cobra battery in 2023.
Infineon holds the highest share of the total project amount of 11.85 million euros funded under »Horizon 2020« with 1.25 million. In the Cobra project, the Neubiberg-based semiconductor specialist is focusing on smart sensor technology via electrochemical impedance spectroscopy (EIS). In this process, a small signal is sent into the battery via the already existing leads to the battery poles and the real and imaginary parts of the response are measured as a function of the signal frequency. This provides a »minimally invasive« view into the interior of the cell without introducing additional components or additionally penetrating the cell envelope. With EIS, a reliable determination of the average cell nucleus temperature and further insights into the state of the cell (SoX) become possible. If, for example, impurities occur during cell production, damaged cells can easily be identified with the method. The so-called thermal runaway, a thermal runaway of the battery cell, is also quickly detected.
Infineon is also contributing to the Cobra project by installing an extremely small, semiconductor-based pressure sensor that measures outgassing in the battery module. Other sensor types are being investigated within the participating partners, and Infineon says it is providing support there as needed to »make these sensors smart« as well.
Fraunhofer ISIT in Itzehoe is taking care of the basic material development for the environmentally friendly batteries in the Cobra project. A team led by Dr. Reinhard Mörtel faces the challenge of replacing cobalt with other material mixtures or at least minimizing its proportion to a large extent - with an energy storage density comparable to that of the controversial element. Nickel, manganese and cobalt have so far mostly been used for cathodes in a ratio of 8/1/1. »For Cobra, we are experimenting with the balance between base materials, electrolytes and separators and testing the electrochemical feasibility. It's sort of the art of mixing so we can get the highest cathode performance.« According to research to date, nickel-manganese-based overalloyed systems could be the solution for the cathode component. Layered materials with phase transformation doped with aluminum and boron for stabilization will be used.
The collaboration within the Cobra project is coordinated by IREC (Institut de Recerca en Energia de Catalunya) in Barcelona. According to Dr. Mörtel, the first year was »challenging due to Corona«; all partners had to get used to the virtual collaboration. Nevertheless, the »Series One« is to be completed and subsequently tested as early as this spring, or by fall at the latest. »The target is 20-ah cells. The second series, which will be released later, will have an alternative design. This will allow us to directly compare which scenario is best suited for the final sample of the 2023 EU project.«