Flexible supercapacitor patch adds power to textile wearables

The development, by Drexel University’s College of Engineering, in partnership with a team at Accenture Labs, is detailed in Journal of Materials Chemistry A.

The flexible, wearable supercapacitor patch 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.

“This is a significant development for wearable technology,” said Yury Gogotsi, PhD, Distinguished University and Bach professor in Drexel’s College of Engineering, who co-authored the study. “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.”

The study is said to build 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 it can withstand the rigours of being a textile and can also store and deliver enough power to run programmable electronics collecting and transmitting environmental data for hours.

“While there are many materials out there 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 textiles can easily be coated with MXene without using chemical additives - and additional production steps - to get the MXene to adhere to the fabric,” said Tetiana Hryhorchuk, a doctoral researcher in the College, and co-author. “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.”

Drexel researchers have been exploring the possibility of adapting MXene, a conductive two-dimensional nanomaterial, as a coating that can imbue materials with the properties of conductivity, durability, impermeability to electromagnetic radiation, and energy storage.

Recently, the team has looked at ways of using conductive MXene yarn to create textiles that sense and respond to temperature, movement and pressure. To fully integrate these fabric devices as ‘wearables’ the researchers also needed to add a woven power source.  

According to the team, 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. Previous studies reported sufficient mechanical strength to withstand industrial knitting, but the demonstrated application only included simple devices.”

The team set out to design its 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 team dipped small swatches of woven cotton textile into a 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 the team stacked five cells to create a power pack capable of charging to six volts.

“We came to the optimised 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,” said Alex Inman, a doctoral researcher in the College of Engineering, and co-author of the paper. “We also vacuum-sealed the cells to prevent degradation in performance. This packaging approach could be applicable to commercial products.”

The best-performing textile supercapacitor powered an Arduino Pro Mini 3.3V microcontroller that was able to wirelessly transmit temperature every 30 seconds for 96 minutes. This level of performance was maintained consistently for over 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 in a statement.

The research team noted that this is one of the highest total power outputs on record for a textile energy device, but it can be improved. As they 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.