Researchers at Nottingham University in the UK have designed a rechargeable molten salt metal air battery that could help accelerate the transition to electric transportation.
Molten salt metal air battery. Credit: Nottingham University
Molten salt metal air battery. Credit: Nottingham University
Rechargeable lithium-ion batteries lose energy over time and can overheat whilst charging or working under certain conditions, which ultimately leads to a degradation of battery life reduced mileage per charge.
Nottingham University has collaborated with six scientific institutes in China to develop an energy storage system that combined the performance attributes of a solid-oxide fuel cell and a metal-air battery. The researchers claim the new battery could extend the range of electric vehicles significantly, while also being fully recyclable, low-cost, and environmentally friendly.
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In solid-oxide fuel cells, a chemical reaction converts hydrogen and oxygen into electricity. While they are highly efficient at energy extraction from fuel, highly durable, cheap and better for the environment, they are not rechargeable.
Metal-air batteries are electrochemical cells that use a cheap, abundant metal such as iron, which reacts with the oxygen in air to generate energy. While charging, they emit oxygen into the atmosphere. These high-energy, dense batteries, while not very durable, are rechargeable and able to store and discharge as much energy as lithium-ion batteries, but more cheaply and much more safely.
In the project's early stages, the research team explored a high-temperature, iron-air battery design that used molten salt as a type of electrolyte – activated by heat – to conduct electricity. Cheap and inflammable, molten salts help to give a battery impressive energy storage and power capability and a favourable lifecycle. However, molten salts also possess adverse characteristics.
In a statement, Professor George Chen, Nottingham University study lead, said: “In extreme heat, molten salt can be aggressively corrosive, volatile and evaporate or leak, which is challenging to the safety and stability of battery design. There was an urgent need to fine-tune these electrolyte characteristics for better battery performance and to enable its future use in electric transport.”
The researchers have managed to significantly improve the technology by transforming the molten salt into soft-solid salt using solid oxide nano-powders. The nanotechnology constructs a flexible, connected network of solid oxide particles, which act as a structural barrier and locks in molten salt electrolytes while still allowing them to conduct electricity even in extreme heat.
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Professor Chen says he hopes the "encouraging results" will lead to the establishment of a simpler, more efficient approach to designing low-cost, high-performance molten salt metal air batteries.
“The modified molten salt iron-oxygen battery has great potential applications in new markets, including electric transport and renewable energy which require innovative storage solutions in our homes and at grid-level,” he said.
“The battery is also, in principle, capable of storing solar heat as well as electricity, which is highly desirable for both domestic and industrial energy needs. Molten salts are currently used at large scale in Spain and China to capture and store solar heat which is then converted to electricity – our molten salt metal air battery does the two jobs in one device.”
The findings have been published in a paper - ‘Quasi-solid-state electrolyte for rechargeable high-temperature molten salt iron-air battery’ in the scientific journal Energy Storage Materials.
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