Printed Li-ion batteries conform to any shape

Article By : Julien Happich

Using a simple stencil printing process followed by ultraviolet cross-linking, researchers have demonstrated a new type of Li-ion batteries.

Researchers in South Korea have developed a new technique that can print batteries on any surface. Today's Li-ion batteries can only be fabricated in fixed shapes and sizes, but these Li-ion batteries created at the Ulsan National Institute of Science and Technology (UNIST) can be printed in their entirety—including electrodes and electrolyte—almost anywhere.

Published in ACS Nano Letters in a paper titled “Printable Solid-State Lithium-Ion Batteries: A New Route toward Shape-Conformable Power Sources with Aesthetic Versatility for Flexible Electronics,” the printable solid state (PRISS) batteries consist of a solid-state composite electrolyte (SCE) layer and SCE matrix-embedded electrodes, which can be printed on just about any object of any shape, as it is possible with today's stencil process.

[EDNA battery 01]
__Figure 1:__ *Stencil printing of a conformable PRISS battery.*

The researchers were able to tune the rheological properties of the SCE paste and electrode slurry to give them thixotropic fluid characteristics suitable for complex deposition patterns on non-flat objects. They also had to design a high boiling point electrolyte to make the PRISS batteries compatible with heat curing.

The materials used allowed the researchers to circumvent solvent-drying and liquid-electrolyte injection process steps, while removing the need for conventional microporous separator membranes. This makes the printable batteries truly shape-conformable, opening new design opportunities for better battery integration.

Lead researcher and UNIST professor Sang-Young Lee expects the PRISS batteries to alleviate design constraints in wearable devices, removing the need for a pre-designated battery space with fixed dimension and shape.

One example being shown is the integration of the PRISS batteries directly onto smart glasses frames.

[EDNA battery 02]
__Figure 2:__ *Conventional battery integration (left) versus a conformal approach (right). A square-shaped Li-ion battery on a pair of paper glasses.*

What's more, after characterising the electrochemical behaviour of PRISS batteries, the researchers found that these batteries exhibited 90% capacity retention after 30 cycles, with no significant loss in charge or discharge capacities, a capacity retention which beats that of conventional Li-ion batteries.

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