3D Batteries Boost Output, Speed Recharge

By R. Colin Johnson

Whether it's your smartphone, your electric car or the backup batteries for a server farm, a new kind of 3D battery electrode is aiming to boost both their output and recharging speed by up to 100 times.

3D structures are adding the third dimension to a whole array of applications today, and now battery electrodes are following suit, increasing their ability to deliver lots of current quickly and speeding up their recharge time. 

Batteries have long been the weak link in the forward march of technological progress, mainly because the chemistry of their reactions is fixed by the laws of physics. However, by adding 3D patterning to the battery electrodes where these chemical reactions take place, recharging can be accelerated by as much as 100 times, according University of Illinois Professor Paul Braun, who performed the work with doctoral candidate Xindi Yu and postdoctoral researcher Huigang Zhang.

Many applications today are limited by the amount of instantaneous current that can be delivered, such as medical devices like defibrillators that deliver pulses. Today, such applications have to include a large capacitor that charges up from the battery. They then use this stored charge to deliver a big jolt. However, Braun's team claims its 3D battery electrodes not only allow faster recharging, but also can provide big jolts on demand. As a result, the researchers claim the new batteries will not only allow cell phones to recharge in seconds and vehicles to recharge in minutes, but will also allow instant-on defibrillators that work without a delay to power-up between pulses.

Current manufacturers of lithium-ion (Li-ion) or nickel metal hydride (NiMH) batteries offer quick-recharge modes, but the performance of the battery is degraded as a result. Thin-film batteries have been proposed that can recharge very quickly, but their lack of bulk material means their absolute capacity must be downsized too. Braun's approach combines the best of both worlds, by wrapping a quick-charge thin-film battery onto a three-dimensional electrode structure that combines high on-demand current-jolt capabilities as well as the high capacities of a bulk material.

Ion transport and electronic conduction is boosted 100 times in three-dimensional cathodes during battery discharge and charge. (Source: University of Illinois)

The electrodes are formed by using self-assembly techniques to tightly pack nanoscale spheres made of a sacrificial material onto a conventional battery electrode superstructure. A liquid metal is then poured between the spheres. After it cools, the spheres are dissolved, leaving behind a highly porous 3D scaffolding, like a metal sponge. Electropolishing then etches away surface structures, thereby enlarging the pores and creating an open framework with a vast surface area, which can then be coated with a thin film of the active battery material. 

In demonstrations, the researchers have shown 3D thin-film battery prototypes that can quickly charge and discharge large currents without degrading the performance or longevity of the battery. And even though these large capacity batteries can be replenished in under a minute with a special recharger, they can nevertheless be used in existing standard electronic devices, according to the researchers.

Funding was provided by the U.S. Army Research Laboratory and the Department of Energy.