Stabilizing Storage Energy

University of Michigan and University of Utah researchers, participating in the U.S. Department of Energy’s Joint Centre for Energy Storage Research, predict a better future for a sort of battery for grid storage called redox flow batteries. Employing a predictive model of molecules and their properties, the group has introduced a charge-storing molecule around 1,000 times more stable than current compounds.

“Our foremost compound had a half—like of about eight to12 hours,” says U Chemist Matthew Sigman, referring to the time period in which half of the compound would decompose. “The compound that we predicted was stable on the order of months.”

For a usual residential solar panel customer, electricity must be either employed as it is generated, sold back to the electronic grid, or stored in batteries. Deep-cycle lead batteries or lithium ion batteries are already on the market, but each sort presents challenges for use on the grid.

All batteries comprise chemicals that release and store electrical charge. But, redox flow batteries are not like the batteries in cell phones or cars. Redox flow batteries instead use two tanks to store energy, separated by a central set of inert electrodes. The tanks hold the solutions comprising molecules or charged atoms, called catholytes and anolytes, that release and store charge as the solution ‘flows’ past the electrodes, relying on whether electricity is being provided to the battery or extracted from it.

“If you intend to increase the capacity, you just more substance in the tanks and it flows through the same cell,” says University of Michigan chemist Melanie Sanford. “If you want to increase the rate of charge or discharge, you boost the number of cells.”

Present redox flow batteries use solutions comprising vanadium, a costly material that needs extra safety in handling because of its potential toxicity. Formulating the batteries is a chemical balancing act, since molecules that can store more charge tend to be less stable, losing charge and rapidly decomposing.

Sigman, Sanford and Minteer are now working to identify a catholyte to pair with this and future molecules. Other engineering milestones lay ahead in the development of a novel redox flow battery technology, but determining a framework for enhancing battery components is a key first step.

“It is a multipart challenge, but you can’t do anything if you don’t have stable molecules with low redox potentials,” says Sanford. “You require to work from there.” The group attributes their success thus far to the application of this structure function relationship toolset, usually employed in the pharmaceutical industry, to battery design. “We bring the tools of chemists to a field that was conventionally the purview of engineers,” says Sanford.