In two new projects, VARTA is working with partners on new technologies with which regeneratively generated energy can be stored in simple, cost-effective and sustainable ways.
Renewable energy sources are becoming more and more important. However, solar and wind energy face a central challenge: Where to put the green electricity when it is not needed? Stationary energy storage systems therefore play a central role for the success of the energy transition. VARTA AG is currently involved in two research projects that address precisely this challenge.
One project is researching the use of iron for energy storage, in the form of a so-called iron slurry/air storage. A slurry is a viscous mass in which iron is dissolved in an electrolyte as a storage medium.
The sticking point so far has been the performance
During operation, this mass is pumped from an external container, the reservoir, through the actual battery cell and back again. In the cell, the mass reacts with air and releases stored energy. Charging also takes place in this way. The system offers many advantages: Iron is readily available, non-hazardous and can easily be recycled. And: The power of the cell can easily be changed by the size of the reservoir. The larger the container, the more energy can be stored.
Cornelia Wiedemann, Project Manager Product Development, is in charge of the technical side of the "FeEnCap" project at VARTA. The name "FeEnCap" is composed of the chemical name of the element iron "Fe", the abbreviation "En" for "energy" and "Cap" for "capsuled". "The iron accumulator is quite an old technology. As a solid-state cell in which iron is used as the electrode material, it is even obsolete. What is new is that iron is used as a slurry," says Wiedemann.
The research project now aims to make the technology more powerful. This is to be done by increasing the conductivity of the slurry. "In previous iron batteries, the components were pressed into a tablet, which resulted in very good contact between the particles and good conductivity. In the slurry, the particles are free, they don't bind directly to each other and therefore don't always touch, so the conductivity of the slurry is worse." In a previous project, the conductivity was improved with material such as graphite. "FeEnCap now aims to improve the conductivity by encapsulating the slurry components so that the system has good charging and discharging capability," says Wiedemann.
Interesting alternative to lithium-ion cells for certain applications
The technology is not a replacement for lithium-ion batteries, says Wiedemann: "It is an alternative for certain applications. Lithium-ions have many advantages, they can deliver higher voltages - 3.6 volts compared to 1.x volts for iron - and the space requirement is also smaller. But it's a very interesting technology for stationary electricity storage, precisely because of its low cost, good availability and good recyclability."
The aim of the project, which is funded by the German Federal Ministry for Education and Research (BMBF) and in which VARTA is collaborating with four other companies and two research institutes, is to develop commercial stationary storage systems using this technology over the next five years.
Zinc-ion cells as sustainable battery storage devices
At the same time, VARTA is working with other partners on the further development of zinc-ion batteries. Here too, the aim is to use non-critical, low-cost materials to develop new types of stationary energy storage.
So-called aqueous zinc-ion batteries (ZIB) are based on zinc - a material that is sufficiently available. These batteries are considered environmentally friendly, economical and safe. There is no risk of explosion or fire, as water is an essential component of the cell.
Nicolas Bucher, Head of Funded Projects at VARTA AG: "Although these are all ideal conditions for green battery technology and although ZIB systems have already reached a high level of technological maturity, the technology has not yet been able to establish itself across broad fields of application compared to the lithium-ion battery (LIB). The main problem with ZIB so far is its low efficiency and short service life." This is where the ZIB2 research project comes in, in which VARTA is collaborating with three companies and two research institutions.
The aim is to increase the service life
Bucher: "Modern zinc-ion concepts actually belong to the type of zinc-metal batteries, but on the positive electrode they consist of materials such as manganese oxides, vanadium oxides or Prussian blue analogues (PBA) such as copper hexacyanoferrate, which enable reversible ion intercalation. Added to this is the use of aqueous electrolyte, which increases the safety of the ZIB system immensely."
The PBA cathode materials addressed in ZIB2 are characterised by their low energy losses and their ability to charge and discharge quickly. This makes them particularly relevant for an application in the stationary energy storage sector, because here it is necessary to react quickly to any load peaks in the power grid in order to be able to avoid widespread power outages. Another advantage of PBA cathode materials is their simple, scalable and cost-effective synthesis. In the course of rapid commercialisation, correspondingly large quantities of electrodes can be produced and thus cells can be produced correspondingly quickly. The major disadvantage of PBA systems so far has been their short service life of only 300 cycles (charging and discharging). However, the ZIB2 project partners have already been able to increase the lifetime of PBA-based ZIBs to 800 cycles by modifying the respective PBA structure. In the current project, the aim is to increase the performance of the ZIB technology and thus enable rapid use of the developed cells in real application scenarios.
The project is to be completed by 31st January 2026. Corresponding batteries for the stationary storage of renewable energies could come onto the market from 2030.
Rainer Hald, Chief Technology Officer (CTO) of VARTA AG: "If the energy transition is to succeed in all areas, there is no way around decentralised energy storage systems. VARTA is working intensively to ensure that, in addition to the existing, very good systems, new technologies can also be used in the future that offer advantages such as good availability, low costs and good reusability. Our research and development ensures that VARTA will continue to hold a leading role in battery technology in the future."