For batteries made from an electrically conductive mixture, the consistency of molasses could help solve a critical piece of the decarbonization puzzle. MIT researchers have developed a semisolid flow battery that might be able to outperform lithium-ion and vanadium redox flow batteries. The semisolid flow battery can be a cost-competitive form of energy storage and backup for variable renewable energy (VRE) sources such as wind and solar.
The new battery features a new kind of electrode made of a mixture containing dispersed manganese dioxide (MnO2) particles, shot through with an electrically conductive additive, carbon black. The latter was used to add the pigment and the electric punch to the semisolid compound. This compound reacts with a conductive zinc solution or zinc plate at the stack to efficiently convert chemical energy into electricity. The fluid properties of this battery are far removed from the watery solutions used by other flow batteries.
“These systems have to be able to flow under reasonable pressures, but also have a weak yield stress so that the active MnO2 particles don’t sink to the bottom of the flow tanks when the system isn’t being used, as well as not separate into a battery/oily clear fluid phase and a dense paste of carbon particles and MnO2,” says Gareth McKinley, a co-author of the research.
The series of experiments informed the techno-economic analysis. By connecting the dots between composition, performance, and cost, researchers were able to make system-level cost and efficiency calculations for the Zn-MnO2 battery. They compared the Zn-MnO2 battery to a set of equivalent electrochemical battery and hydrogen backup systems, looking at the capital costs of running them at durations of eight, 24, and 72 hours.
“We performed a comprehensive, bottom-up analysis to understand how the battery’s composition affects performance and cost, looking at all the trade-offs,” says Thaneer Malai Narayanan SM ’18, Ph.D. ’21. “We showed that our system can be cheaper than others and can be scaled up.”
The team plans to continue working on the Zn-MnO2 system to see where it might fit in. “The next step is to take our battery system and build it up,” says Narayanan, who is working now as a battery engineer. “Our research also points the way to other chemistries that could be developed under the semisolid flow battery platform, so we could be seeing this kind of technology used for energy storage in our lifetimes.”