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Researchers from the University of Cambridge identified a group of materials that could be used to make fast-charging batteries charge even faster. They found that lithium ions move faster through niobium tungsten oxides than through any other electrode material.
These materials do not have higher energy densities. However, they give the researchers an idea of how to produce safe, super-fast charging batteries. Additionally, the materials suggest that next-generation batteries may use unconventional materials. The results are reported in the journal Nature.
“We’re always looking for materials with high-rate battery performance which would result in a much faster charge and could also deliver high power output,” said Dr. Kent Griffith, a postdoctoral researcher in Cambridge’s Department of Chemistry.
The simplest explanation of the battery is that it is made of three components: a positive electrode, a negative electrode, and an electrolyte. While charging, lithium ions move from the positive electrode through the crystal structure and electrolyte to the negative electrode. The speed of the process dictates the charging speed of the battery.
Researchers have tried to increase the charging speed of batteries by making the particles smaller. By doing that, they decreased the distance between the electrodes so lithium ions have to travel less time. However, this method is hard to be implemented in the mass-produced fast-charging batteries. It makes the battery more expensive and the battery’s life significantly reduced.
The niobium tungsten oxides have a rigid, open structure that does not reap the inserted lithium and have larger particle sizes than many other electrode materials. Additionally, they have complex atomic arrangements that are most probably responsible for the fast transfer rates and were the reason they remained undiscovered for a longer time.
The fast-charging batteries made with these materials are much safer than conventional fast-charging batteries using graphite, because the latter form metal fibers at high rates inside the battery, causing an explosions and fire.
Additionally, the niobium tungsten oxides are cheap and easy to make, since they do not require additional chemicals and solvents.
They are not perfect: they do lead to a lower cell voltage than some electrode materials. However, when cycling fast, the practical energy density of these materials remains high.
The niobium tungsten oxides are useful for some specific applications, but we need more progress in the field. Therefore, the research of new chemistries and new materials is vital. “Fields stagnate if you don’t keep looking for new compounds,” says Professor Clare Grey, also from the Department of Chemistry and the paper’s senior author. “These interesting materials give us a good insight into how we might design higher rate electrode materials.”
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