Engineers have created a battery from cheap, plentiful elements that might provide low-cost backup storage for renewable energy sources.
The novel architecture, which is less costly than lithium-ion battery technology, employs aluminum and sulfur as electrode materials, with a molten salt electrolyte in between.
Low-cost battery
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As the globe expands its wind and solar power installations, there is an increasing demand for cost-effective, large-scale backup systems to provide electricity when the sun goes down and the air is calm, as per ScienceDaily.
Most such applications are still too expensive for today's lithium-ion batteries, and alternative possibilities, such as pumped hydro, need certain topography that isn't usually accessible.
Researchers at MIT and others have invented a new type of battery that is completely built of abundant and affordable materials, which might help to address that gap.
The novel battery architecture, which employs aluminum and sulfur as electrode materials with a molten salt electrolyte in between, is detailed in Nature by MIT Professor Donald Sadoway and 15 colleagues from MIT, China, Canada, Kentucky, and Tennessee.
Sadoway, the John F. Elliott Professor Emeritus of Materials Chemistry, adds, "I wanted to design something better, much better, than lithium-ion batteries for small-scale stationary storage and, eventually, for automotive uses," as per ScienceDaily.
Lithium-ion batteries are not only pricey, but they also contain a flammable electrolyte, making them unsuitable for shipment.
So Sadoway began examining the periodic table in search of affordable, Earth-abundant metals that could be able to replace lithium.
According to him, the economically dominating metal, iron, lacks the necessary electrochemical characteristics for an effective battery.
However, aluminum is the second most prevalent metal in the market and the most abundant metal on Earth. "So I said, well, let's simply create it a bookend out of metal," he continues.
The next step was determining what to match the aluminum with for the second electrode, as well as what sort of electrolyte to use in between to transport ions back and forth during charging and discharging.
Sulfur is the least expensive of the nonmetals, hence it was chosen as the second electrode material. Sadoway explains that for the electrolyte, "we were not going to employ the volatile, flammable organic liquids" that have occasionally caused dangerous fires in vehicles and other lithium-ion battery uses.
They looked at several molten salts with relatively low melting temperatures - close to the boiling point of water, as compared to roughly 1,000 degrees Fahrenheit for common salts.
The three elements they ended up with are inexpensive and generally available: aluminum, which is similar to foil from the supermarket; sulfur, which is frequently a waste product from industries such as petroleum refining; and salts. "The components are inexpensive, and the device is safe - it cannot burn," Sadoway explains.
The scientists demonstrated in their trials that the battery cells could withstand hundreds of cycles at extremely fast charging rates, with a predicted cost per cell of around one-sixth that of equivalent lithium-ion cells.
They discovered that the charging rate was strongly dependent on the operating temperature, with 110 degrees Celsius (230 degrees Fahrenheit) exhibiting 25 times quicker rates than 25 degrees Celsius (25 degrees Celsius).
Towards a better understanding of aluminum sulfur batteries using imidazolium-based electrolytes
Because of the availability of both aluminum and sulfur, aluminum sulfur batteries with ionic liquid electrolytes are viable next-generation energy storage systems, as per Sciencedirect.
However, there is now very little understanding of the discharge mechanism, which impedes their growth.
To characterize the discharge performance and reversibility of Al-S cells at different current densities, a mathematical model that takes into account the complicated electrochemical reduction of the sulfide species, as well as the synthesis of the various polysulfides, is constructed.
The cells revealed various discharge processes and Al2S3 precipitation paths at varied current densities.
The key problem limiting discharge performance at high current densities was the contact resistance between the composite electrode and the current collector.
The reversibility of Al-S cells based on Al2S3 precipitates is greatly dependent on the operating current density.
The model created will be used by other researchers to improve the electrochemical performance of aluminum sulfur batteries.
