Color-changing battery tech gets storage capacity upgrade

This is the first-ever report of a π-bridge spacer incorporated into polymer anode, claim researchers.
Ameya Paleja
Representation of recharging batteries
Representation of recharging batteries


A collaborative effort from researchers at multiple institutes in Korea has led to the development of a smart zinc ion battery that can change colors to indicate its charging and discharging process, a press release said.

With an explosion in the number of wearable devices being used around the world, there is a demand for smarter energy storage solutions with color-changing properties. This allows for rapid identification of the charged state of the device, which could also pave the way for the removal of displays on each of these devices.

While such batteries have been developed before, the electronic conductivity in the devices has been low, leading to slowed ion mobility and storage capacity. The technology does not just have applications in wearable devices but can also be used in devices that aid in cutting down energy consumption for indoor cooling by controlling solar absorbance.

Making a high-efficiency battery

Researcher Il-Doo Kim, a professor in the Department of Materials Science and Engineering at Korea Advanced Institute of Science and Technology (KAIST), led the effort to develop a zinc ion battery with an electrochromic polymer anode built with a "π-bridge spacer." π-bonds improve the mobility of electrons inside a structure speeding up ion movement and adsorption efficiency. This helps in enhancing the storage capacity of the battery.

Color-changing battery tech gets storage capacity upgrade
Electrochromic zinc ion battery whose anode is made of a polymer that turns dark blue when charged and transparent when discharged.

In the batteries developed by the researchers, the π-bridge spacer allowed more room for ion movement and facilitated an improvement of 40 percent in charging time. The team recorded a zinc-ion discharging capacity of 110 mAh/g, a major improvement over previous attempts.

In its electrochromic function, the researchers found a 30 percent increase as the device switched from a dark blue to transparent as the battery discharged.

This is also the first report of a π-bridge spacer incorporated in polymer anode in the world.

Futuristic energy storage system

The research team's achievements are not limited to successfully building an electrochromic zinc ion battery but also one that can maintain its properties even after long-term exposure to the atmosphere and mechanical deformations that occur over time.

Additionally, the team has also developed a futuristic energy storage system that may one day not only power wearables but could also help reduce energy consumption. For instance, applying the material on smart windows will not only help in better absorption of solar energy but also block out ultraviolet radiation and even replace curtains.

"This technique goes beyond the existing concept of batteries that are used simply as energy storage devices, and we expect this technology to be used as a futuristic energy storage system that accelerates innovation in smart batteries and wearable technologies,” said Il-Doo Kim in the press release.

The research effort also involved Tae Gwang Yun, a professor at the Materials Science and Engineering Department at Myongji University, Jiyoung Lee, a post-doctoral associate at Northwestern University, and Professor Han Seul Kim at Chungbuk National University.

The research was published in the journal Advanced Materials last month.


Zinc–ion batteries (ZIBs) have drawn much attention for next-generation energy storage for smart and wearable electronics due to their high theoretical gravimetric/volumetric energy capacities, safety from explosive hazards, and cost-effectiveness. However, current state-of-the-art ZIBs lack the energy capacity necessary to facilitate smart functionalities for intelligent electronics. In this work, a “π-bridge spacer”-embedded electron donor–acceptor polymer cathode combined with a Zn2+–ion-conducting electrolyte is proposed for a smart and flexible ZIB to provide high electrochromic–electrochemical performances. The π-bridge spacer endows the polymeric skeleton with improved physical ion accessibility and sensitive charge transfer through the cycles, providing extremely stable cyclability with high specific capacity (110 mAh g−1) at very fast rates (8 A g−1) and large coloration efficiency (79.8 cm2 C−1) under severe mechanical deformation over a long period. These results are markedly outstanding compared to the topological analogue without the π-bridge spacer (80 mAh g−1 at current density of 8 A g−1, 63.0 cm2 C−1). The design to incorporate a π-bridge spacer realizes notable electrochromism behaviors and high electrochemical performance, which sheds light on the rational development of multifunctional flexible-ZIBs with color visualization properties for widespread usage in powering smart electronics.

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