Development of integrated bipolar plate felt components for redox flow batteries
In order to continue with a cost-effective energy transition we will need storage systems in the megawatt range. High-efficiency long-life redox flow batteries are ideal as they barely discharge at all. Bipolar plates and graphite felts are core components of these batteries. The IBiFi research project aims to develop a less complex and more cost-effective manufacturing process in order to combine these components.
The more electricity that is produced by renewable sources in the future, the greater the need will be for powerful storage systems. Electrical power must be stored in large quantities over the long term in order to balance out fluctuations in wind and solar power. Durable redox flow batteries play a key role here as they can be used as large storage systems and feature performance and capacity levels that can be dimensioned independently of each other. The aim of the IBiFi project, which is funded by the Federal Ministry for Economic Affairs and Energy, is to develop a design that is less complex and thereby more cost-effective as compared with the procedures currently in use.
Redox flow batteries store energy in tanks with liquid-based electrolytes that circulate in two separate circuits. The dissolved salts are reduced when the battery is charged and oxidised when it is discharged. The charge exchange takes place in an electrochemical cell by ions passing through a membrane. This is accompanied by an anode and a cathode that in each case consist of a bipolar plate and porous carbon felts.
The morphological properties of the graphite material represent a particular challenge in developing a link between both elements that is stable over the long term. Graphite plates and felts have been compressed under high pressure up until now in order to provide an electrically conductive connection between them. The IBiFi project aims to glue or fuse them together with conductive plastic. This reduces the manufacturing effort required for compression without reducing porosity. At the same time, it decreases the number of individual components. Both lower material and manufacturing costs.
As part of the project, the Institute of Networked Energy Systems is examining which types of adhesion or fusion of the bipolar plates with the felt produce the optimum results. The combined material is being tested under real operating conditions at the institute's test benches. Here the batteries generally complete at least 500 charging and discharging cycles. Electrical conductivity, chemical and mechanical stability and adhesive power are among the features being evaluated. Suitable manufacturing processes also need to be developed. To this end, the expertise of the companies SGL Carbon and Polyprocess is being used.
October 2017 until September 2020
Federal Ministry for Economic Affairs and Energy (BMWi)
Institute of Networked Energy Systems
Project Manager at the Institute of Networked Energy Systems: