Self-charging stretchable fabric for wearables
The stretchable fabric incorporates both TENGs and MSCs fabricated through a resist-dyeing method in a planar configuration, with their Ni-coated electrodes shown to maintain conductivity at 600% and 200% tensile strain along course and wale directions, respectively.
Described in more detail in a paper titled “Stretchable Coplanar Self-Charging Power Textile with Resist-Dyeing Triboelectric Nanogenerators and Microsupercapacitors” published in the AC Nano journal, the self-charging fabric consists of a knitted fabric (90% polyester, 10% Spandex) onto which conductive nickel electrodes are selectively patterned through electroless Ni deposition.
Subsequently, to create the MSCs, reduced graphene oxide (rGO) films are deposited onto the conductive textiles by a hydrothermal reduction of graphene oxide with Ni. A gel-type electrolyte (PVALiCl) was applied to achieve the solid-state textile MSCs which the researchers demonstrated, could be designed into arbitrary-shaped logos or patterns for good aesthetics.
Such microsupercapacitors were reported to reach a voltage up to 3.2V and discharge capacitances of 5.0, 4.9, 4.2mF at a galvanostatic discharging current of 0.5, 1.0, 2.0mA, respectively. These textile-based planar MSCs were able to power a watch at a strain of 50% after being charged. As for the TENGs, they were formed as dual in-plane Ni-coated electrodes, with an elastomeric PDMS thin layer coated on top of only one of the electrodes. The stretchable fabric TENG then operates when a polyester textile comes in contact with the TENG textile.
Contact electrification occurs at the PDMS−polyester interfaces, generating net negative charges in the PDMS and positive charges in the polyester; similarly, the polyester fabrics will be negatively charged and the Ni-coated fabrics will be positively charged at the polyester−Ni interfaces. When the polyester fabric is gradually separating away from the TENG textile, under movement or stretching, the unbalanced positive charges in the Ni fabric flow through the external circuit to reach the other Ni-textile electrodes, so as to screen the static charges in the PDMS (see fig. 2 (ii)). The current flow stops when all of the static charges are screened and equilibrium is achieved (fig. 2 (iii)). If the counter polyester textile is approaching back to contact the TENG textile, a reversed current flow in the external circuit is generated until local charge equilibrium is achieved again (fig. 2 (iv)). The repeated touching separating motions are then converted into pulsed alternative current (AC).
The fabric in-plane MSC with reduced graphene oxides as active materials reached a maximum areal capacitance of 50.6mF cm−2 at 0.01V s−1 and showed no significant degradation at 50% of tensile strain. The stretchable fabric-based TENG was able to output a 49V open-circuit voltage and 94.5mW m−2 peak power density. Because both the MSCs and the TENGs in the stretchable self-charging power textile can be designed coplanar with a one-batch resist-dyeing fabrication process, this approach is compatible with conventional textile processing. The authors anticipate that such self-charging power textiles could be used to power small electronics intermittently, without extra recharging steps.
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