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Electrode lets lithium batteries charge in just two minutes

Batteries are an essential part of most modern gadgets, and their role is expected to expand as they’re incorporated into vehicles and the electric grid itself. But batteries can’t move charge as quickly as some competing devices like supercapacitors, and their performance tends to degrade significantly with time. That has sent lots of materials science types into the lab, trying to find ways to push back these limits, sometimes with notable success. Over the weekend, there was another report on a technology that enables fast battery charging. The good news is that it uses a completely different approach and technology than the previous effort, and can work with both lithium- and nickel-based batteries.

The previous work was lithium-specific, and focused on one limit to a battery’s recharge rate: how quickly the lithium ions could move within the battery material. By providing greater access to the electrodes, the authors allowed more ions to quickly exchange charge, resulting in a battery with a prodigious charging rate. The researchers increased lithium’s transport within the battery by changing the structure of the battery’s primary material, LiFePO4.

The new work also gets fast charges, but by a rather different route. The authors, from the University of Illinois, don’t focus on the speed of the lithium ions in the battery; instead, they attempt to reduce the distance the ions have to travel before reaching an electrode. As they point out, the time involved in lithium diffusion increases with the square of the distance travelled, so cutting that down can have a very dramatic effect. To reduce this distance, they focus on creating a carefully structured cathode.

The process by which they do this is fairly simple, and lends itself to mass production. They started with a collection of spherical polystyrene pellets. By adjusting the size of these pellets (they used 1.8µm and 466nm pellets), they could adjust the spacing of the electrode features. Once the spheres were packed in place, a layer of opal (a form of silica) was formed on top of them, locking the pattern in place with a more robust material. After that, a layer of nickel was electrodeposited on the opal, which was then etched away. The porosity of the nickel layer was then increased using electropolishing.

When the process was done, the porosity—a measure of the empty space in the structure—was about 94 percent, just below the theoretical limit of 96 percent. The authors were left with a nickel wire mesh that was mostly empty space.


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