The pervasive issue with renewable energy sources such as solar and wind is that their abundant availability trips on intermittency. Storing the excess energy from solar and wind requires large storage capacities at cost competitive levels. It is safe to state that there is currently no fully commercial battery technology capable of meeting the demanding performance requirements of the grid, namely the high power, long serving lifetime and low cost, despite the compelling need for such technology. This means that grid level storage if solved could revolutionize the energy transition of our generation.
In a 2012 TED talk, Prof. Donald Sadoway of MIT revealed how could the grid level battery look like in the future. He reckoned that his battery story “is more than an account of inventing technology, it is a blueprint of inventing inventors” as the development process tracked un-conventional wisdom full spectrum. The inovative technology made of a three-layered battery using liquid metal is claimed to empirically suited to shut-up the clamor around the solar and wind intermittency.
The humble beginnings of battery technology are attributed to A. Volta who pioneered the field of electro-chemistry and brought about a new technology – electroplating. The first battery was made of a stack of zinc and silver coins separated by cardboard soaked in brine. This was the starting point for designing a battery. Two electrodes – in this case metals of different compositions – and electrolyte – in this case salt dissolved in water. The science is that simple!
Prof. Sadoway found inspiration for the liquid metal battery in a modern aluminum smelter. In the cell house of an aluminum smelter shelters roll after roll of cells are aligned inside a long room. The inside of these rolls resemble Volta’s battery with some important differences. Volta’s battery works at room temperature, is fitted with solid electrodes and an electrolyte that is a solution of salt and water. The aluminum smelter operates at high temperature (a temperature high enough that the aluminum product is liquid). The electrolyte is not a solution of salt and water, but molten salt. This combination of liquid metal, molten salt and high temperature allows us to send high current through this thing.
In economic terms currently virgin metal from ores can be produced at a cost of less than €1/kg. This economic miracle of modern electro-metallurgy compelled the inventor’s motivation to take advantage and encapsulate the technology driven economy of scale for the liquid metal battery.
Prof. Sadoway succeeded in doing so by making both metals liquid and using molten salt for the electrolyte. He put low density liquid metal at the top, a high density liquid metal at the bottom and molten salt in between. The choice of metals was carried out to meet:
(i) the constraints of Earth abundance,
(ii) different opposite densities,
(iii) high mutual reactivity.
He felt the thrill of realization when coming upon the answer. Magnesium (Mg) for the top layer and Antimony (Sb) for the bottom layer.
To produce current Mg looses 2e to become Mg ion which migrates to the electrolyte where it accepts 2e from Sb and mixes with it to form an alloy. The electrons go to work in the real world powering devices. To charge the battery, the technology needs to be connected to an energy source which reverses the current and thus forces Mg to de-alloy and return to the upper electrode restoring the initial constitution of the battery. The current passing between the electrodes generates enough heat to keep it at temperature.
The theoretical model of this battery proved rather lengthy to implement and test in lab conditions. The technology initially set at 1Wh cell was perfected by operating more than 400 of them, refining their performance with the “plurality of chemistry” (currently is not just Mg-Sb). The model proved expandable at 20Wh cells and 200Wh with very encouraging results. The technology was proving itself to be robust and scalable.
Having a piloted idea seemed to be for Prof. Sadoway and his team insufficient to advance and commercialize the liquid battery technology. This prompted them to open a company (LMBC) and attract venture capital. The unit battery produced today at LMBC is .4m in diameter at a storage capacity of 1000 Wh (=1kWh). The next project on the horizon is a .9m diameter battery with a storage capacity of 4kWh.
Further down the road, the company envisions that the 4kWh modules can be stacked in modules and aggregated in 40 foot shipping containers that can store up to 2MWh of energy. This represents the current average consumption of 200 American households.
This silent and emission free (when operational) technology can prove to be the support renewable energy technologies need to become competitive with fossil fuels. Besides the various environmental benefits that it offers, this technology addresses in a simple manner one of the most sensitive issues in the energy transition cost: this technology was designed to the market price without subsidy.
This ought to look sunny for the future of remote renewable power installations!