The 3D & # 039; microbatteries & # 039; that could power ultra-low energy wearables

Image of 3d battery design

Main image: the future of wearables and IoT sensors depends on better batteries. Credit: CC0 Creative Commons

Fitness trackers, smartwatches, smart ears and other incredible wearables are the first wave in a new era in electronics. Most are paralyzed by the limited battery capacity, so the next wave – an army of small sensors that autonomously transfer data to other devices, better known as the Internet of Things (IoT) – will rely on a revolution in battery technology. Cue 3D micro batteries.

How do batteries work?

Batteries have a negative (cathode) and a positive (anode) electrode made of metal, with a non-conducting electrolyte in between that supports electrically charged atoms, mostly lithium ions, which travel between one and the other. When all those atoms are on the positive side, the battery has to be charged, after which the atoms (now with a supply of electrons) go the other way.

Given the limited size of the standard lithium-ion batteries in almost all portable electronics, from phones and cameras to Bluetooth earphones and wearables, scientists are constantly looking for smaller and more efficient designs.

What is a 3D battery?

A 3D battery is a complete redesign of how existing batteries are constructed to make them more powerful or smaller. Instead of a layer of anode, the electrolyte, then a layer of cathode, a 3D battery has a 3D-shaped anode and cathode that look more like puzzle pieces. Such a design increases the surface area of ​​the cathode and anode and may contain more lithium ions, and thus offer more power, or be many times smaller than a traditional battery. Effectively, 3D designs enhance the energy density of batteries.

What did UCLA do?

Researchers at the University of California, Los Angeles (UCLA) have created a powerful 3D lithium-ion battery that does not exceed 100 grains of salt. In their paper High Areal Energy Density 3D Lithium-Ion Microbatteries published in Joule in May of this year, they not only sketched a 3D battery, but a new way to construct it using the same techniques used to produce electronic circuits – That is the key, because although better in theory, 3D batteries have been difficult to construct so far.

The 3D batteries developed by UCLA. Credit: Hur et al / Joule

(Image: © Hur et al./Joule)

Instead of layers, the concentric tube design of the UCLA team uses 3D anode piles covered with a thin layer of a photopattern polymer electrolyte, with the area between the posts being filled by the cathode material. The end result had an energy density of 5.2 milliwatt hours per square centimeter, which is quite good for a 3D battery. Even more important for use in small appliances, however, was the small size: only 0.09 square centimeters. Wow.

How important is this?

Image of 3d battery design

3D batteries are a new type of battery architecture. Credit: Hur et al / Joule

(Image: © Hur et al./Joule)

More work is needed on components, assembly and packaging, but it could mean that 3D microbatteries for IoT applications are easier to produce. "For small sensors, you have to redesign the battery to be a skyscraper in New York instead of a California farm," says Bruce Dunn, professor of materials science and engineering at UCLA and senior author of the report, about using of cathode posts by the team.

"That's what a 3D battery does, and we can use semiconductor processing and a compliant electrolyte to create one that's compatible with the requirements of small Internet-connected devices."

The battery that is immediately charged

Image of a watch type battery

The IoT requires immediately rechargeable, flexible batteries. Credit: CC0 Creative Commons

The amount of power that a battery can store becomes less important if it can be charged very quickly. Think of Apple AirPods and other & # 39; true wireless & # 39; earphones; if it could be charged within a minute, would anyone care how long the battery really lasted? And what if those batteries can be charged in less than a second?

What did Cornell University do?

There are other ways to make 3D batteries that could mean wearables and IoT devices could be charged almost immediately, as proven by a Cornell University team that wanted to interweave the components in a battery. Instead of the standard cathode electrolyte anode design, they designed a 3D-gyroid structure with thousands of nano-sized pores filled with all the usual components of the battery.

"This is truly a revolutionary battery architecture," says Ulrich Wiesner, a professor of engineering at the Department of Materials Science and Engineering. "This three-dimensional architecture effectively eliminates all the losses of the dead volume in your device." He also pointed out that by shrinking everything to the nanoscale, you get an order with a higher power density. "So you have access to the energy in much shorter times than usual with conventional battery architectures."

So how soon will 3D battery be charged? "By the time you plug your cable into the socket, in seconds, maybe even faster, the battery would be charged," Wiesner said. The team block Copolymer derived from three-dimensional interpenetrating multifunctional gyroidal nanohybrids for electrical energy storage was published in Energy and Environmental Science in May 2018.

The flexible battery for wearables

Both 3D batteries are an attempt to breathe new life into the lithium-ion battery, but some think that a completely new type of battery is needed for flexible (and even stretchable) portable devices – think of smart clothes for fitness activities that constantly collect and steer data on all kinds of body figures.

Image of a golfer wearing a smartwatch

Wearables for the fitness market would eventually "mechanical flexibility & # 39; can have. Credit: Garmin

(Image: © Garmin)

Lithium-sulfur (Li-S) batteries are an option that has been investigated by a team of researchers in Korea, in a paper published in the Journal of Materials Chemistry. The team demonstrated a new class of batteries that uses a completely fibrous cathode separator and carbon nanotubes to create a metal foil form factor. As well as exceptional energy density improvements, that mechanical deformability means that the batteries can be crumbled without being affected.

Now that IoT is growing exponentially and the portable fitness tracker market is estimated to be worth $ 48.2 billion by 2023 alone, there will be a huge and growing demand for small batteries that have a higher capacity, can be recharged quickly and can even bend and bending – and giving more strength to those who can make them commercially viable first.

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