Battery storage capacity is an increasingly critical factor for reliable and efficient energy transmission and storage—from small personal devices to systems as large as power grids.
This is especially true for aging power grids that are overworked and have problems meeting peak energy demands. Companies are scrambling to develop scalable battery solutions that can stabilize these grids by increasing energy efficiency and storage capacity.
The liquid metal battery is based on research conducted at the Massachusetts Institute of Technology.Tests with cells made of low-cost, Earth-abundant materials confirm that the liquid battery operates efficiently without losing significant capacity or mechanically degrading — common problems in today’s batteries with solid electrodes.
How does it work?
In most batteries, the electrodes — and sometimes the electrolyte — are solid. But in a liquid metal battery, all three are liquid.Two liquid electrodes (magnesium and antimony) are separated by a molten salt electrolyte; The negative electrode — the top layer in the battery — is a low-density liquid metal that readily donates electrons. The positive electrode — the bottom layer — is a high-density liquid metal that’s happy to accept those electrons. And the electrolyte — the middle layer — is a molten salt that transfers charged particles but won’t mix with the materials above or below. Because of the differences in density and the immiscibility of the three materials, they naturally settle into three distinct layers and remain separate as the battery operates.
When a liquid metal battery cell is at operating temperature, potential energy exists between the two electrodes, creating a cell voltage. When discharging the battery, the cell voltage drives electrons from the magnesium electrode and delivers power to the external load, after which the electrons return back into the antimony electrode. Internally, this causes magnesium ions to pass through the salt and attach to the antimony ions, forming a magnesium-antimony alloy. When recharging, power from an external source pushes electrons in the opposite direction, pulling magnesium from the alloy and redepositing it back onto the top layer.
How is it better than other batteries?
The liquid metal battery platform offers an unusual combination of features. In general, batteries are characterized by how much energy and how much power they can provide. (Energy is the total amount of work that can be done; power is how quickly work gets done.) In general, technologies do better on one measure than the other. For example, with capacitors, fast delivery is cheap, but abundant storage is expensive. With pumped hydropower, the opposite is true.
But for grid-scale storage, both capabilities are important — and the liquid metal battery can potentially do both. It can store a lot of energy (say, enough to last through a blackout) and deliver that energy quickly (for example, to meet demand instantly when a cloud passes in front of the sun). Unlike the lithium-ion battery, it should have a long lifetime; and unlike the lead-acid battery, it will not be degraded when being completely discharged. And while it now appears more expensive than pumped hydropower, the battery has no limitation on where it can be used. With pumped hydro, water is pumped uphill to a reservoir and then released through a turbine to generate power when it’s needed. Installations, therefore, require both a hillside and a source of water. The liquid metal battery can be installed essentially anywhere. No need for a hill or water.
Liquid electrodes offer a robust alternative to solid electrodes, avoiding common failure mechanisms of conventional batteries, such as electrode particle cracking.
Other advantages of liquid metal batteries include:
- Modular design that can be customized to meet specific customer needs
- Because the components are liquid, the transfer of electrical charges and chemical constituents within each component and from one to another is ultrafast, permitting the rapid flow of large currents into and out of the battery.
- Negligible cycle-to-cycle capacity fades over thousands of cycles and years of operation because the electrodes are reconstituted with each charge.
- Uses inexpensive, earth-abundant materials
- Can respond to grid signals in milliseconds
- Stores up to 12 hours of energy and discharges it slowly over time
- Operates silently with no moving parts, easy to install
What is its role in the future?
The novel rechargeable battery could one day play a critical role in the massive expansion of solar generation needed to mitigate climate change by mid-century.
The ability to store large amounts of electricity and deliver it later when it’s needed will be critical if intermittent renewable energy sources such as solar and wind are to be deployed at scales that help curtail climate change in the coming decades. Such large-scale storage would also make today’s power grid more resilient and efficient, allowing operators to deliver quick supplies during outages and to meet temporary demand peaks without maintaining extra generating capacity that’s expensive and rarely used.
However, there are some disadvantages to the liquid metal battery:
- High operating temperatures
- Extremely heavy, this makes its energy density(<200 Wh/kg) considerably less than lithium-ion batteries
- Since they are in liquid form, that they are not well suited to mobile applications
- There is a very high possibility of potential leak
Bringing it to market
Ambri (formerly Liquid Metal Battery Corporation) is developing an electricity storage solution that will change the way electric grids are operated worldwide.
Ambri has now designed and built a manufacturing plant for the liquid metal battery in Marlborough, Massachusetts. As expected, manufacturing is straightforward: Just add the electrode metals plus the electrolyte salt to a steel container and heat the can to the specified operating temperature. The materials melt into neat liquid layers to form the electrodes and electrolyte. The cell manufacturing process has been developed and implemented and will undergo continuous improvement. The next step will involve automating the processes to aggregate many cells into a large-format battery including the power electronics.
Ambri has not been public about which liquid metal battery chemistry it is commercializing, but it does say that it has been working on the same chemistry for the past four years.
Ambri researchers are now tackling one final engineering challenge: developing a low-cost, practical seal that will stop air from leaking into each individual cell, thus enabling years of high-temperature operation. Once the needed seals are developed and tested, battery production will begin.