Redox Flow Batteries ...Then And Now (Part 1)
Posted by Lawrence H. Thaller, Ph.D. on Thu, Sep 04, 2008
Back in 1973, while I was a researcher at NASA, I invented the redox flow battery. This was in response to the need for bulk energy storage installations to be used in conjunction with base load power generation stations.
Following early publications of the concept initially developed within NASA under government sponsorship, other groups around the world began developing their own variations of the general theme of using two soluble oxidation/reduction couples, separating membranes, flow through electrodes, storage tanks, and pumps to circulate the solutions. By stacking multiple cells in series and using tanks of various sizes, a wide variety of electrochemical storage units having different voltage outputs and storage capacities could be assembled using common hardware components. By having the reactive materials as soluble liquids in both states of charge eliminated the basic shortcoming of traditional rechargeable batteries including shedding, slumping, grain growth, plate expansion and shape change were eliminated. More importantly, by having a common fluid being shared by all of the electrochemical cells, there was no build-up of cell to cell capacity imbalance. The basic redox battery concept included cells to monitor the overall state of charge of the redox fluids, make minor adjustments in system voltage as well as techniques to compensate for small amounts of capacity loss due to hydrogen generation during overcharge. While under development within NASA, fundamental design issues were examined to determine how cells should be designed and how pumping losses and shunt current losses could be minimized. The research and development team investigated the operational envelope and projected system costs as progress was made in developing selective ion exchange membranes used to separate the iron and chromium solutions.
And Now...
From its conception redox flow batteries were seen to be multi-billion dollar markets waiting to be tapped for several applications that are currently filled primarily by lead acid batteries. Float battery service, uninterruptable power supplies, daily cycle duty systems, distributed energy storage, remote energy storage coupled with solar or wind turbines, etc. are all candidate applications for redox flow battery systems. That being the case, research has continued in the areas that had been considered impediments to wide scale implementation of this technology.
Deeya Energy of Fremont, California has developed a unique unitized electrode/cell design with significant manufacturing and assembly advantages. Following the securing of capital resources, Deeya Energy proceeded to build and will soon field complete turnkey energy storage systems for a wide range of applications globally.
In upcoming blogs, I'll be writing about the secret sauce fueling Deeya's success, so stay tuned...