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Supercapacitor Patch Could Solve Power Problem for Wearables

Article-Supercapacitor Patch Could Solve Power Problem for Wearables

Image source Drexel University wearables-MXenesupercap.jpg
A flexible textile supercapacitor patch, created by Drexel University researchers, can power a microcontroller and wirelessly transmit temperature data for nearly two hours without a recharge.
A MXene-based solution can integrate with fabric to provide energy for health-monitoring wearable devices.

One of the key challenges that researchers have faced with making user-friendly and viable wearables technology is how to eliminate the need for wires or other bulky power sources. Now researchers at Drexel University may have found a way to do this once and for all with the design of a flexible wearable supercapacitor patch that can be integrated seamlessly into the fabric of the device, they said.

A team from Drexel's College of Engineering—working in collaboration with Accenture Labs—developed the patch using MXene, a carbon-based nano-material discovered by researchers at Drexel that is lightweight and highly conductive. The textile-based supercap can charge in mere minutes, and in tests demonstrated capability to power an Arduino microcontroller temperature sensor and use radio communication to transmit data for almost two hours, researchers said.

“This is a significant development for wearable technology,” said Yury Gogotsi, distinguished university and Bach professor in Drexel’s College of Engineering, who led the research, in a post on Drexel's news site. “To fully integrate technology into fabric, we must also be able to seamlessly integrate its power source—our invention shows the path forward for textile energy storage devices.”

Indeed, researchers have been trying to find power sources well-suited to the form factor of wearable sensors and other technology for fitness, health, and other applications so they can have enough energy to gather and transmit data without batteries or other technology that can hinder the necessity for efficiency and compactness in their design.

Graphene—which is similar to MXene—as a material already has factored into this equation with solutions such as a triboelectric generator that can harvest energy from the friction between two materials, and other nontraditional power sources scientists have devised to solve the problem.

Why MXene for Wearables?

The patch developed by the Drexel team study builds on previous research that the researchers conducted to examine durability, electric conductivity, and energy storage capacity of MXene-functionalized textiles. For that project, the team created technology that could power passive devices such as LED lights.

The latest research evolves that work further not only to demonstrate that the patch can withstand the demands of its role as a textile, but also store and deliver enough energy to power programmable electronics that collect and transmit environmental data for hours, researchers said.

One reason that MXene is well-suited to this application is that because of its ability to disperse in water as a stable colloidal solution, it can be applied as a coating to textiles without using chemical additives and thus additional production steps, noted Tetiana Hryhorchuk, a doctoral researcher in the college.

“As a result, our supercapacitor showed a high energy density and enabled functional applications such as powering programmable electronics, which is needed for implementing textile-based energy storage into the real-life applications," Hryhorchuk said.

The Wearable Patch's Design

The team set out to design its MXene textile supercapacitor patch as part of a larger goal to use conductive MXene yarn to create textiles that can act as sensors and respond to temperature, movement, and pressure.

Researchers wanted to create the patch to maximize energy-storage capacity while using a minimal amount of active material and in as small a form factor as possible. These design goals would serve to reduce the overall cost of production and preserve flexibility and wearability of the garment, they said.

To fabricate the supercap, researchers dipped small swatches of woven cotton textile into a MXene solution that they then layered on top of a lithium chloride electrolyte gel. Each supercapcell also included two layers of MXene-coated textile separated by an electrolyte that also was fabricated with a cotton textile, they said. Their goal was to create a patch that could power a device that might preview how to supercap could work with a healthcare-related wearable, such as one that could monitor vital signs or other health factors.

To achieve this, they made the patch powerful enough to provide energy for Arduino programmable microcontrollers by stacking five cells, creating a power pack capable of charging to 6 volts. This voltage is equal to that of the larger rectangular batteries often used to power golf carts, electric lanterns, or for jump-starting vehicles, researchers said.

Researchers also vacuum-sealed the cells to prevent degradation in performance, a step that also could be applied to commercial variations of products that use the patch, they said.

Results and Future Plans  

Researchers published a paper on their work in the Journal of Material's Chemistry A. In it they reported that the supercap could provide at least 20 days of power for an Arduino Pro Mini 3.3V microcontroller that wirelessly transmitted temperature every 30 seconds for 96 minutes. This result proves that MXene's use in a textile supercap has the potential "to support a wide range of devices such as motion trackers and biomedical monitors in a flexible textile form,” Gogotsi said.

 While this performance is one of the highest total power outputs on record for a textile energy device, researchers acknowledged that there is room for improvement.

To achieve better performance with their technology, they plan to continue their work by experimenting with different electrolytes and textile electrode configurations to boost voltage, as well as design the patch in a variety of wearable forms, they said.

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