A\nSelf-Healing and Sweat-Chargeable Hydrogel Electrolyte\nfor All-in-One Flexible Supercapacitors

Flexible\nsolid-state supercapacitors (SCs) with hydrogel as an\nelectrolyte and separator combine the advantages of wearability and\nenergy storage and exhibit a broad application prospect in wearable\nenergy textiles. However, irreversible electrolyte damage and unstable\nelectrode–electrolyte interfaces during mechanical deformations\nremain bottlenecks in realizing truly wearable applications. Herein,\npoly(acrylic acid) (PAA)-Fe hydrogels were prepared through a simple\nthermal polymerization strategy. The dynamic reversible metal coordination\nbonds between Fe<sup>3+</sup> and carboxylic acids confers the hydrogels\nwith excellent self-healing properties. As expected, the prepared\nhydrogels exhibited superior mechanical strength (tensile stress of\n45.80 kPa), ionic conductivity (0.076 S cm<sup>–1</sup>), and\nself-healing properties. Subsequently, the SCs were constructed using\ncomposite hydrogel electrodes (MnO<sub>2</sub>@CC embedded in the\nPAA-Fe hydrogels) as symmetrical electrodes (marked as MSCs). The\nreversible metal coordination bonds between composite hydrogel electrodes\nformed an ultrastable electrode/electrolyte interface in the all-in-one\nMSCs, thus revealing excellent mechanical durability. The all-in-one\nMSCs delivered a remarkable specific capacitance (30.98 F g<sup>–1</sup> at 0.2 A g<sup>–1</sup>), excellent cyclic stability (87.24%\nafter 5000 cycles), outstanding mechanical deformation stability,\nand impressive electrochemical output stability after self-healing\n(capacitance retention of 85.34% after five cycles of cutting/self-healing).\nIt is noteworthy that the all-in-one MSCs employed NaCl as an electrolyte,\nwhich can be obtained from human sweat. As a proof of the self-charged\nconcept, the all-in-one MSCs can be reused in sweat, whose capacitance\nwas maintained at 90.05% of the initial state after three repetitions.\nThis work is expected to shine light into the design of all-in-one\nand fabric-based SCs and the development of wearable energy textiles.