Researchers at the University of Nottingham, working in collaboration with six scientific research institutions across China, have designed a new type of rechargeable battery using salt as a key ingredient, which they believe could revolutionise electric vehicles by extending range, being fully recyclable, environmentally friendly, low-cost, and safer.
The British and Chinese researchers set out to develop a new battery with the combined performance merits of a solid-oxide fuel cell and a metal-air battery, but without the potential hazards and challenges inherent in lithium-ion batteries – such as losing energy and power over time, as well as potential overheating.
While solid-oxide fuel cells are highly efficient at extracting energy from the chemical reaction achieved by the conversion of hydrogen and oxygen, as well as being durable, low-cost, and greener to produce, solid-oxide fuel cells are not rechargeable.
Metal-air batteries, on the other hand, are electrochemical cells that uses a cheap metal such as iron and the oxygen present in the air to generate electricity and emit only oxygen into the atmosphere. However, unlike solid-oxide fuel cells, they are not very durable, despite boasting high-energy density and being rechargeable, able to also store and discharge as much electricity as lithium-ion batteries but much more safely and cheaply.
In an effort to combine the merits of both solid-oxide fuel cells and metal-air batteries, the Chinese and British researchers explored a high-temperature, iron-air battery design that used molten salt as a type of electrolyte – activated by heat – for electrical conductivity. Unfortunately, while cheap and inflammable and providing impressive storage and power capability as well as a lengthy lifecycle, molten salts also possess their own drawbacks.
“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,” explained Professor George Chen, University of Nottingham study lead, from the Faculty of Engineering.
“There was an urgent need to fine-tune these electrolyte characteristics for better battery performance and to enable its future use in electric transport.”
Ploughing ahead, the researchers improved the technology by turning the molten salt into soft-solid salt by using solid oxide nano-powders. Their research published in the journal Energy Storage Materials.
According to Professor Jianqiang Wang, from the Shanghai Institute of Applied Physics, Chinese Academy of Sciences, who is leading this collaboration project, the resulting quasi-solid-state (QSS) electrolyte is suitable for metal-air batteries which operate at 800ºC – approximately the same temperature as that of the engine exhaust gas from a petrol or diesel engine – as it suppresses the evaporation and fluidity of the molten salts that can occur at such high operating temperatures.
The researchers expect that, in principle, maintaining an effective working temperature for their newly developed battery can be achieved by the currents for charging and discharging, good thermal insulation, and additional electric heating if necessary.
Dr Cheng Peng, also from the Shanghai Institute of Applied Physics, Chinese Academy of Sciences, but who is leading a molten salt electrolysis laboratory in Nottingham, hopes that the team’s “encouraging results” will be able to help establish a simpler and more efficient approach to designing low-cost and high-performance molten salt metal-air batteries with high stability and safety.
“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,” said Dr Peng.
“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 th