Researchers propose new aluminum–sulfur battery with molten-salt electrolyte; low-cost, rechargeable, fire-resistant, recyclable
An international team of researchers led by Quanguan Pang at Peking University and Donald Sadoway at MIT reports a bidirectional, rapidly charging aluminum–chalcogen battery operating with a molten-salt electrolyte composed of NaCl–KCl–AlCl3. This differs from other aluminum batteries in the choice of a positive elemental-chalcogen electrode as opposed to various low-capacity compound formulations and in the choice of a molten-salt electrolyte as opposed to room-temperature ionic liquids that induce high polarization.
The multi-step conversion pathway between aluminium and chalcogen allows rapid charging at up to 200C, and the battery endures hundreds of cycles at very high charging rates without aluminum dendrite formation. A paper on the work is published in Nature.
Importantly for scalability, the cell-level cost of the aluminum–sulfur battery is projected to be less than one-sixth that of current lithium-ion technologies. Composed of earth-abundant elements that can be ethically sourced and operated at moderately elevated temperatures just above the boiling point of water, this chemistry has all the requisites of a low-cost, rechargeable, fire-resistant, recyclable battery.—Pang et al.
I wanted to invent something that was better, much better, than lithium-ion batteries for small-scale stationary storage, and ultimately for automotive.—Donald Sadoway
The researchers showed that the charging rate was highly dependent on the working temperature, with 110 degrees Celsius (230 degrees Fahrenheit) showing 25 times faster rates than 25 C (77 F).
The molten salt the team chose as an electrolyte simply because of its low melting point turned out to have a fortuitous advantage. One of the biggest problems in battery reliability is the formation of dendrites, which are narrow spikes of metal that build up on one electrode and eventually grow across to contact the other electrode, causing a short-circuit and hampering efficiency. But this particular salt, it happens, is very good at preventing that malfunction.
The battery requires no external heat source to maintain its operating temperature. The heat is naturally produced electrochemically by the charging and discharging of the battery.
This new battery formulation, Sadoway says, would be ideal for installations of about the size needed to power a single home or small to medium business, producing on the order of a few tens of kilowatt-hours of storage capacity.
For larger installations, up to utility scale of tens to hundreds of megawatt hours, other technologies might be more effective, including the liquid metal batteries Sadoway and his students developed several years ago and which formed the basis for a spinoff company called Ambri, which hopes to deliver its first products within the next year.
The smaller scale of the aluminum-sulfur batteries would also make them practical for uses such as electric vehicle charging stations, Sadoway says. He points out that when electric vehicles become common enough on the roads that several cars want to charge up at once, as happens today with gasoline fuel pumps, “if you try to do that with batteries and you want rapid charging, the amperages are just so high that we don’t have that amount of amperage in the line that feeds the facility.” Having a battery system such as this to store power and then release it quickly when needed could eliminate the need for installing expensive new power lines to serve these chargers.
The new technology is already the basis for a new spinoff company called Avanti, which has licensed the patents to the system, co-founded by Sadoway and Luis Ortiz ’96 ScD ’00, who was also a co-founder of Ambri. Sadoway is formally the Chief Scientific Advisor.
The research team included members from Peking University, Yunnan University and the Wuhan University of Technology, in China; the University of Louisville, in Kentucky; the University of Waterloo, in Canada; Oak Ridge National Laboratory, in Tennessee; and MIT. The work was supported by the MIT Energy Initiative, the MIT Deshpande Center for Technological Innovation, and ENN Group.
Pang, Q., Meng, J., Gupta, S. et al. (2022) “Fast-charging aluminium–chalcogen batteries resistant to dendritic shorting.” Nature 608, 704–711 doi: 10.1038/s41586-022-04983-9