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Iron Nanoparticle-Coated Graphite Flakes Could Vastly Improve Lithium Ion Batteries

ByJulia DavisNOVA NextNOVA Next

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Few objects define our lives today like the lithium ion battery. Without them, we probably wouldn’t have the smartphones, laptops, tablets, and other rechargeable electronics that have exploded in popularity in recent years.

But as our devices continue to get more powerful, batteries have fallen short. Plus, as electric vehicles have become commonplace, scientists have been searching for ways to increase battery performance and lifetime without sacrificing safety. And the answer may lie in magnets.

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Batteries function by allowing electrons to flow from the positively-charged cathode to the negatively-charged anode, producing an electric current.

A team of scientists, led by André Studart of ETH Zurich in Switzerland, built a lithium ion battery with a graphite anode, a fairly standard setup. (An anode is the part of the battery through which electrons flow into a device—the negative side.) But, in a twist, they used a magnetic field to align the graphite flakes inside the battery so that lithium ions can have a clear path as they move across the battery, leading in increased performance. The study was published in the journal Nature Energy .

Lithium-ion battery anodes are often composed of graphite flakes due to their safety, non-toxicity, and low-cost. However, graphite flakes have a significant drawback that can hamper a battery’s effectiveness. Here’s Shalini Saxena, writing for Ars Technica :

[Graphite] limits the movement of lithium ions, which is a fundamental part of charging and discharging. The lithium ions are only able to move within the planes between stacked graphene sheets and often have to navigate a highly tortuous path as they move around during charge and discharge. This slow movement through the electrodes remains a critical challenge in the development of batteries with improved performance.

Aligning the graphite flakes, the team thought, should give the lithium ions a clearer path, boosting the battery’s performance.

While the idea sounded good in theory, there was a slight problem: graphite isn’t magnetic, and therefore does not respond to magnetic fields. To work around this, scientists coated the graphite flakes with iron oxide nanoparticles and dunked the mixture in ethanol to make it easier for the graphite flakes to settle in a preferred orientation.

The graphite particles were then hit with a rotating magnetic field. Scientists found that after the graphite flakes were influenced by the magnetic field, they tilted at an angle of 60˚ above the plane of the current collector, forming channels for the lithium ions to escape. Flakes that had not been exposed to the magnetic field orientation fell almost parallel to the current collector, creating a maze-like path for the ions.

The magnetically oriented graphite offered the lithium ions a much straighter path through the electrode. In a trial scenario, the scientists found that the new, less twisted anode structures improved lithium storage capacity by 160–300%.

If this new fabrication technique can be implemented cheaply and at at scale, it could give ubiquitous lithium ion batteries a significant performance boost, enabling smaller devices with longer battery lives along with vastly more usable electric cars.