Researchers at the University of Cambridge have found that materials known as niobium tungsten oxides form microscopic structures that let lithium ions flow through them at much greater rates than current technology allows. The finding could be the key to building next-generation lithium-ion cells that charge in minutes rather than hours, and are not prone to dangerous overheating.
Lithium-ion batteries have been a wonderful innovation since their introduction in the early 1990s, but their energy density has only been improving by a modest 3 to 4 percent a year, far slower than EV and consumer electronics manufacturers would wish. What's more, these improvements usually come from optimizing the packaging materials rather than the electrodes themselves, in a strategy that does little to remedy another inherent drawback of battery technology – its slow charging rate.
To improve the charging rate, one must improve the rate at which the electrically charged lithium ions travel from the positive to the negative electrode. In the past, scientists have tried to achieve this by building peculiar nanostructures inside the electrodes, usually with the aim of reducing the distance that lithium ions have to travel. But nanoparticles are tricky and expensive to work with, and they also produce unwanted chemical reactions that shorten the battery's lifespan.
In this latest development, researchers at the University of Cambridge have gone a different route, opting for larger particles with rigid, open pillar-like structures that allow lithium ions to travel unobstructed and in large numbers, improving their flow by several orders of magnitude.
The new electrode material could be a safer alternative too. The negative electrodes in most lithium-ion batteries are made of graphite, which, especially when charged at high rates, can form dendrites, microscopic lithium fibers that can short-circuit a cell or even set it on fire. The new electrodes don't suffer from that issue.
"In high-rate applications, safety is a bigger concern than under any other operating circumstances," says Professor Clare Grey, senior author of the study. "These materials, and potentially others like them, would definitely be worth looking at for fast–charging applications where you need a safer alternative to graphite."
Nanostructures take multiple steps to make, and have low yields, posing issues of scalability. Niobium tungsten oxides, on the other hand, are reportedly simpler to make and don't require additional chemicals or solvents.
More work is certainly needed, but this finding could open up new avenues of investigation to create safe, fast-charging batteries for EVs and grid storage applications.
A study detailing the advance was published in the journal Nature.
Source:University of Cambridge