ELuStat: Iron-air battery as stationary energy storage

Compensate fluctuating power generation by photovoltaic or wind energy systems

© Fraunhofer UMSICHT

Air electrode

To increase the stability of the air electrode of the battery stack, the electrode should be as free of carbon as possible.

Project aims

A new type of iron-air battery is being developed as part of the project. It will have an energy density of 250 Wh/kg, an efficiency of at least 60 percent and be capable of 500 full charge/discharge cycles. To achieve this, the researchers are realizing the battery as a stack with bipolar plates. In addition, a novel galvanic manufacturing process for the iron electrode is intended to achieve a significantly higher specific capacity of the iron-air battery and thus a higher energy density.

CO2 reduction through the use of batteries?

In addition to the actual battery development, another focus of the UMSICHT scientists is the question of how much greenhouse gas minimization can be achieved by using iron-air batteries. They are looking at the use of the storage to increase the degree of self-sufficiency of photovoltaic systems.

Benefits

A characteristic feature of electricity generation from renewable sources such as wind or sun is its fluctuation. In order to compensate for these fluctuations and to ensure a stable energy supply, new cost-effective storage technologies are needed that store electrical energy in the gigawatt range and feed it back into the grid. One possibility is stationary battery storage systems that are easy to handle. In addition, they provide sufficient resources for large-scale use.

High development potential of iron-air batteries

This is where iron-air batteries come in. They offer a high development potential, since both iron and potassium - the basis for the alkaline electrolytes - are present in bulk quantities. At the same time, the iron electrodes are very robust and can survive more than 10,000 charge/discharge cycles. This corresponds to a service life of about 30 years. In addition, iron-air batteries are insensitive to overcharging, partial and deep discharge.

Challenges

A disadvantage of conventional iron-air batteries: they have an efficiency of less than 50 percent. This is partly due to hydrogen evolution at the iron electrode and partly to the high overvoltage at the air electrode. Due to flooding and catalyst poisoning, the stability of the air electrode is also not yet sufficient for use as a stationary storage device in the context of regeneratively generated energy.

Reduce battery weight, increase electrode capacity

The scientists at Fraunhofer UMSICHT want to change this. Their goal is an iron-air battery with improved energy density and higher efficiency. To achieve this, they are focusing, for example, on measures to reduce the weight of the battery. This is to be achieved through the development of a multi-cell bipolar stack using novel lightweight and cost-effective graphite bipolar plates.

Another measure taken by part of development of the researchers is to increase the electrode capacity. Their approach: They want to produce iron as a cost-effective active mass by electroplating and use potash lye or caustic soda lye, for example, as available alkaline electrolytes. This should result in better coupling to the current collector and more effective use of the material. In addition, the electrochemical deposition process can be used for targeted passivation of the electrode surface to prevent side reactions. In particular, the scientists hope that this will prevent the parasitic formation of hydrogen without impairing the actual function of the battery.

Project partner

  • Hochschule Ruhr West