MXene supercapacitor patch proves suitable for wearable tech

Researchers at Drexel University, in partnership with a team at Accenture Labs, have reported the new design of a flexible wearable supercapacitor patch. It uses MXene to create a textile-based supercapacitor that can charge in minutes and power an Arduino microcontroller temperature sensor and radio communication of data for almost two hours.

Yury Gogotsi, PhD, who co-authored the study, said this is a significant development for wearable technology. “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,” he said.

Co-authored along with Gogotsi’s undergraduate and postdoctoral students; Genevieve Dion, professor and director of the Center for Functional Fabrics; and researchers from Accenture Labs in California, the study builds on previous research that looked at durability, electric conductivity and energy storage capacity of MXene-functionalised textiles that did not push to optimise the textile for powering electronics beyond passive devices such as LED lights. The latest work shows that not only can it withstand the rigors of being a textile; it can also store and deliver enough power to run programmable electronics collecting and transmitting environmental data for hours — progress that could position it for use in healthcare technology.

Co-author and doctoral researcher Tetiana Hryhorchuk noted that while there are many materials that can be integrated into textiles, MXene has a distinct advantage over other materials because of its natural conductivity and ability to disperse in water as a stable colloidal solution. This means that textiles can easily be coated with MXene without using chemical additives — and additional production steps — to get the MXene to adhere to the fabric. “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 researchers have been exploring the possibility of adapting MXene, a conductive two-dimensional nanomaterial, as a coating that can imbue a range of materials with exceptional properties of conductivity, durability, impermeability to electromagnetic radiation, and energy storage. The team has also looked at ways of using conductive MXene yarn to create textiles that sense and response to temperature, movement and pressure. To fully integrate these fabric devices as ‘wearables’, the researchers also needed to find a way to weave a power source into the mix.

The researchers found that flexible, stretchable and textile-grade energy storing platforms have so far remained missing from most e-textile systems due to the insufficient performance metrics of current available materials and technologies. The researchers designed an MXene textile supercapacitor patch with the goal of maximising energy storage capacity while using a minimal amount of active material and taking up the smallest amount of space — to reduce the overall cost of production and preserve flexibility and wearability of the garment. To create the supercapacitor, the researchers dipped small swatches of woven cotton textile into an MXene solution then layered on a lithium chloride electrolyte gel. Each supercapacitor cell consists of two layers of MXene-coated textile with an electrolyte separator also made of cotton textile. To make a patch with enough power to run some useful devices — such as Arduino programmable microcontrollers — the team stacked five cells to create a power pack capable of charging to six volts, the same amount as the larger rectangular batteries often used to power golf carts and electric lanterns, or for jump-starting vehicles.

The researchers came to the configuration of a dip-coated, five-cell stack with an area of 25 square centimetres to produce the electrical loading necessary to power programmable devices. The cells were also vacuum-sealed to prevent degradation in performance, an approach that could be applicable to commercial products. The best-performing textile supercapacitor powered an Arduino Pro Mini 3.3 V microcontroller that was able to wirelessly transmit temperature every 30 seconds for 96 minutes — it maintained this level of performance consistently for 20 days.

“The initial report of a MXene textile supercapacitor powering a practical peripheral electronics system demonstrates the potential of this family of two-dimensional materials to support a wide range of devices such as motion trackers and biomedical monitors in a flexible textile form,” Gogotsi said.

As the researchers continue to develop the technology, they will test different electrolytes and textile electrode configurations to boost voltage, as well as designing it in a variety of wearable forms. “Power for existing e-textile devices still largely relies on traditional form factors like Lithium-polymer and coin cell Lithium batteries. As such, most e-textile systems do not use a flexible e-textile architecture that includes flexible energy storage. The MXene supercapacitor developed in this study fills the void, providing a textile-based energy storage solution that can power flexible electronics,” the researchers said.

The researchers’ findings were published in the Royal Society of Chemistry’s Journal of Materials Chemistry A.

Image caption: 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. Image credit: Drexel University.