Building a better battery
University of Nottingham
Many
electric vehicles (EV) are powered by rechargeable lithium-ion batteries, but
they can lose energy and power over time. Under certain conditions, such
batteries can also overheat while working or charging, which can also degrade
battery life and reduce miles per charge.
To
solve these issues, the University of Nottingham is collaborating with six
scientific research institutes across China to develop an innovative and
affordable energy store with the combined performance merits of a solid-oxide fuel
cell and a metal-air battery. The new battery could significantly extend the
range of electric vehicles, while being fully recyclable,
environmentally-friendly, low-cost and safe.
A solid-oxide fuel cell converts hydrogen and oxygen into electricity as a result of a chemical reaction. While they are highly-efficient at extracting energy from a fuel, durable, low-cost and greener to produce, they are not rechargeable.
Meanwhile, metal-air batteries are electrochemical cells that uses a cheap metal such as iron and the oxygen present in air to generate electricity. During charging, they emit only oxygen into the atmosphere.
Although not very durable, these high-energy dense batteries are rechargeable
and can store and discharge as much electricity as lithium-ion batteries, but
much more safely and cheaply.
In
the early research phases, the research team explored a high-temperature,
iron-air battery design that used molten salt as a type of electrolyte --
activated by heat -- for electrical conductivity. Cheap and inflammable, molten
salts help to give a battery impressive energy storage and power capability and
a lengthy lifecycle.
However,
molten salts also possess adverse characteristics. University of Nottingham
study lead, Professor George Chen 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 now successfully improved the technology by turning the molten salt into soft-solid salt, using solid oxide nano-powders.
Professor Jianqiang
Wang, from the Shanghai Institute of Applied Physics, Chinese Academy of
Sciences, who is leading this collaboration project has predicted that this
quasi-solid-state (QSS) electrolyte is suitable for metal-air batteries which
operate at 800 ºC; as it suppresses the evaporation and fluidity of the molten
salts that can occur at such high operating temperatures.
Project
collaborator, Dr Cheng Peng, also from the Shanghai Institute of Applied
Physics, Chinese Academy of Sciences, explains a unique and useful design
aspect of this experimental research. The quasi-solidification has been
achieved using nanotechnology to construct a flexibly-connected network of
solid oxide particles that act as a structural barrier locking in the molten
salt electrolytes, while still allowing them to safely conduct electricity in
extreme heat.
Professor
Chen, who is leading a molten salt electrolysis laboratory in Nottingham, hopes
the team's "encouraging results" will help to establish a simpler and
more efficient approach to designing low-cost and high-performance molten salt
metal-air batteries with high stability and safety.
He
adds, "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. 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."
