Flow cells show promise for Electroweb-scale storage because, like fuel cells, they decouple power output from energy storage when building cells: the reactor is the right size for the power output and the surrounding tanks are the right size for the energy capacity.
Given the low-cost working fluids and large tanks, they can store large amounts of energy.
In search of this low-cost fluid, MIT proposes to use a semisolid suspension of manganese dioxide particles and carbon black as an electrode and metallic zinc as a counter electrode.
The liquid does not choose to be sticky, it just has to keep manganese dioxide and carbon particles suspended.
It’s “like thick black paint or soft ice cream,” says Gareth McKinley, an engineer at the Massachusetts Institute of Technology. “these systems must be able to flow at a reasonable pressure, but the yield stress is also weak so that the active particles do not sink to the bottom of the trough and separate into oily transparent fluid phases and carbon particles and MnO 2 dense pastes when the system is not in use.”
Various combinations of components are possible, requiring 8% to 50% of the stored energy to run the pump, depending on the use case.
Is this cost-effective? The team has made some estimates.
“it is very difficult to assess the cost and performance of early technologies, which is an example of how to develop a standard method to help researchers at MIT and elsewhere,” said researcher Emre Gen ç er. “one message here is that when you include cost analysis during the development phase of your experimental work, you can understand the cost impact of the project as early as possible.”
MnO 2-Zn battery as compared with other technologies such as lithium-ion battery, vanadium redox flow battery, and hydrogen fuel cell, and the potential capital cost of energy storage for 8 hours, 24 hours, and 72 hours was evaluated.
According to the university, when the Discharge battery lasts more than one day, the semi-solid flow battery beats the lithium-ion battery and the vanadium redox flow battery because of its high pumping cost.
“I was skeptical that the battery would be competitive, but once I did the costing, it seemed reasonable,” Gen ç er said. “Lithium-ion batteries are very suitable for backup batteries of 8 hours or less, but materials that have been used for a long time are too expensive. Hydrogen is very expensive in a very short time, but good in a long time, and we will need all of this.
This work is covered by “low-cost manganese dioxide semisolid electrodes for flow batteries”, published in Joule magazine.
This is not the first time MIT has proposed mudflow batteries. More than a decade ago, a different team was studying lithium compounds mixed with liquid electrolytes.