A team of researchers at MIT has developed a prototype liquid flow battery that doesn't require a pump system, making production and operation simpler and less costly. With an hourglass design, its angle can be adjusted in order to change the rate of flow, and therefore the rate of energy production.
Flow batteries typically rely on pumps and valves to feed liquid electrolytes stored in two external tanks into a central stack with two electrodes separated by a membrane. The MIT team's prototype battery was designed to operate without the complicated system of valves and pumps that conventional liquid batteries use, replacing them with a simple gravity-fed system that drives the liquid chemical compound through the chambers.
Liquid was only used in one side of the prototype, with the other half containing a solid sheet of lithium. This hybrid version, the team says, was designed to test the concept out in a simpler form before ultimately moving on to the goal of a battery where both sides contain a liquid electrode.
Getting the flow of the liquid right was a challenge, and took some tweaking of the mechanics of the battery and the mixture of the liquid, but the end result is a battery that is simpler, more compact and less expensive than other liquid flow battery designs. The team found that a close to horizontal angle was the best for achieving a steady but low flow rate for optimal efficiency.
Additionally, the researchers say this solid/liquid hybrid battery demonstrates it may be possible to create batteries that balance the advantages of all-solid and all-liquid batteries, depending on the desired application.
Although it is a just a proof of concept that the team doesn't expect to go into production, they say future batteries taking advantage of the design could be modular, allowing grid storage systems to expand as demand increases, which is particularly important for scaling up intermittent power sources like wind and solar.
"The authors have been able to build a bridge between the usually disparate fields of fluid mechanics and electrochemistry," says Venkat Viswanathan, an assistant professor of mechanical engineering at Carnegie Mellon University, who was not involved in this work. "Pumping represents a large part of the cost for flow batteries," he says, "and this new pumpless design could truly inspire a class of passively driven flow batteries."
The team's research appears in the journal Energy and Environmental Science.