Shape-conformable batteries based on 3D printing technology

Korean and US researchers have collaborated on a project to significantly enhance the variability of battery design, which is typically limited to spherical and/or rectangular structures and thus results in inefficient space use.

Most battery shapes today are optimised for coin cell and/or pouch cells — but since the battery as an energy storage device occupies most of the space in microelectronic devices with different designs, new technology to freely change its shape is required. Now, researchers from the Korea Advanced Institute of Science and Technology (KAIST) and Harvard University have successfully manufactured various kinds of battery shapes — such as ring-type, H-shape and U-shape — using 3D printing technology.

The research group adopted environmentally friendly aqueous Zn-ion batteries to make customised battery packs. This system, which uses Zn2+ instead of Li+ as charge carriers, is said to be much safer compared with the conventional lithium rechargeable batteries that use highly inflammable organic electrolytes. Moreover, the processing conditions of lithium-ion batteries are very complicated because organic solvents can ignite upon exposure to moisture and oxygen.

As the aqueous Zn-ion batteries adopted by the research team are stable upon contact with atmospheric moisture and oxygen, they can be fabricated in ambient air conditions. They also have advantages in packaging since packaged plastic does not dissolve in water, even when plastic packaging is applied using a 3D printer.

“Zn-ion batteries employing aqueous electrolytes have the advantage of fabrication under ambient conditions, so it is easy to fabricate the customised battery packs using 3D printing,” said Professor Il-Doo Kim, who led the KAIST team.

To fabricate a stable cathode that can be modulated in various forms and allows high charge-discharge, the research team fabricated a carbon fibre current collector using electrospinning process and uniformly coated electrochemically active polyaniline conductive polymer on the surface of carbon fibre for a current collector-active layer integrated cathode. The cathode, based on conductive polyaniline consisting of a 3D structure, exhibits very fast charging speeds (50% of the charge in two minutes) and can be fabricated without the detachment of active cathode materials, so various battery forms with high mechanical stability can be manufactured.

Collaborating with Dr Youngmin Choi at the Korea Research Institute of Chemical Technology (KRICT), the researchers applied their 3D-printed batteries to small-scale wearable electronic devices (wearable light sensor rings). As noted by Professor Jennifer A Lewis, leader of the Harvard team, “3D-printed batteries can be easily applied for niche applications such as wearable, personalised, miniaturised micro-robots, and implantable medical devices or microelectronic storage devices with unique designs.”

The research has been published in ACS Nano, a highly renowned journal in the field of nanoscience. Professor Kim was recently appointed as an associate editor of the journal.

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