An Electrochemical Etching Process for Flow Battery Structures to Improve Performance and Reduce Manufacturing Cost

Redox flow batteries are among the most promising electrical storage technologies for distributed energy storage and load leveling applications. Traditional redox flow batteries have the structure shown in Figure 1a, using the example of the iron redox couple. The bipolar plate is separated from the membrane using a felt electrode (on the Fe^2+/Fe³⁺ redox side) and a plastic separator (on the Fe²⁺/Fe⁰ side). These electrodes have the following disadvantages:

• Lower battery performance by
  • Creating undesirable pressure drops, and
  • Decreasing reactant mass transfer
• Increased manufacturing costs due to
  • Difficulty in alignment during manufacturing,
  • Additional material (felt) cost.

To overcome these challenges, a pulse through mask electroetching process is being developed for fabrication of bipolar plates with novel engineered structures for redox flow batteries (RFBs). These engineered electrode/bipolar plate structures, which utilize arrays of posts, pyramids and/or pillars as well as flow fields and other structures on the bipolar plate surface to create uniform standoff between the plate and the membrane, may replace conventional bipolar plate components and eliminate the separate non-uniform carbon felt electrodes, as shown in Figure 1b. These engineered structures can be optimized with regard to gap, size and distribution, so as to obtain the desired electrolyte velocity while minimizing pressure loss and maximizing mass transfer. Furthermore, the surface textures of the structures can be engineered (roughened) to provide high surface area, for uniform iron deposition and for enhancing redox electron transfer kinetics. These modifications are being investigated with the intentions of promoting:

• Improved battery performance by increased reactant mass transfer while maintaining acceptable pressure drop,
• Reduced electrode cost (currently ~39% of total cell stack cost) by using thin metal substrates with engineered surfaces,
• Simplified cell manufacturing costs (currently ~10% of total cell stack cost) by reducing the parts count and integrating the electrode and bipolar plate components, and
• Enhancement in stack reproducibility by eliminating non-uniform felt type electrodes and maintaining a fixed membrane-plate separation.