It only takes a few minutes to fully charge!

Date:Apr 29, 2020

Lithium ion batteries are one of the most common types of rechargeable batteries in portable electronic devices. The power supply of the mobile phone used when you read this article is probably a lithium ion battery. Ordinary mobile phone batteries usually take several hours to fully charge, and a study from Cambridge University scientists can shorten this charging process to a few minutes in the future!

This study shows that niobium-tungsten oxide can be used as the positive electrode of lithium-ion batteries, making lithium-ion batteries have higher power and faster charging speed. The new battery can be adapted to more new equipment, such as electric vehicles, grid-level storage of renewable energy, etc.

The battery has three parts: the anode, the cathode and the electrolyte connecting the two poles. When the lithium ion battery is discharged, lithium ions move from the cathode to the anode, and when charged, lithium ions move from the anode to the cathode. The faster the lithium ions move in the battery, the faster the battery charges, and the higher the power in this process.

The most common way to increase the flow rate of lithium ions is to make electrode particles into nanoparticles to shorten the distance that lithium ions have to travel through. However, some challenges were encountered in this method. Nanoparticles are difficult to pack together, which limits the upper limit of the energy stored in each unit. At the same time, this may also lead to more side reactions, so the life of such batteries is generally not very long. In addition, the production of nanoparticles is also costly.

The senior author of this study, ClareGrey, a materials chemist at the University of Cambridge, and her colleagues studied niobium-tungsten oxide. They noticed that these substances have a rigid open crystal structure, which allows lithium ions to flow quickly, even among the relatively large micron-sized particles.

The researchers analyzed the properties of two different niobium-tungsten oxides: Nb16W5O55 and Nb18W16O93. They used pulsed field gradient nuclear magnetic resonance (similar to nuclear magnetic resonance imaging) to measure the movement of lithium ions in oxides.

"This research is largely new and there are very few studies in these areas." Said the study's important author Kent Griffith. Griffith is also a materials chemist at Cambridge University.

Scientists found that lithium ions move hundreds of times faster in niobium-tungsten oxide than in previous materials. This shows that niobium-tungsten oxide can help make higher power and faster charging batteries in the future.

"The most surprising thing about this material is that in these micron-sized particles, the rate of charge movement and diffusion reaches such a fast rate," Griffith said. "These materials can complete the charging process in a few minutes." He also mentioned that there is still a lot of work to be done to make commercial batteries.

The researchers also pointed out that niobium-tungsten oxide can not only help to make higher-power batteries, but also reduce the battery voltage. Although energy can enter and exit these niobium-tungsten oxides quickly, the new battery involves less energy per unit of time than traditional anode materials.

Low battery voltage can make the battery safer. For example, most lithium-ion batteries contain graphite anodes. The electrical properties of graphite lead to higher battery voltages, but also form elongated lithium metal fibers, dendrites, during high-speed charging. These dendrites cause a short circuit and further cause the battery to catch fire and explode. "Therefore, use a battery with a lower voltage, such as our battery, for high-speed rechargeable batteries." Griffith said.

A possible problem with the new material is that niobium and tungsten are relatively heavy atoms, resulting in heavy batteries. But Griffith believes that niobium-tungsten oxide can store twice as much electricity as conventional lithium-ion battery electrodes. In addition, the electrodes of niobium-tungsten oxide should not be made into nanoparticles, which also reduces the cost of new batteries.

Scientists are currently trying to find the best anode electrode material and make electrodes together with niobium tungsten oxide. They also believe that other materials may have similar properties to niobium-tungsten oxide. "We are optimistic about discovering other materials of similar nature in the future," Griffith said.

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