3D Branched Burr Carbon Fiber Yarn Electrodes for High-Rate Flexible Supercapacitors

Abstract Conventional carbon fiber (CF) yarn current collectors suffer from severe localized Joule heating and scarce active sites, limiting the high-rate performance and safety of fiber-shaped supercapacitors. Herein, we construct 3D branched burr-structured CF yarns (CFY2, CFY3, and CFY4) via a scalable twist-fracture wrapping strategy. By tuning the twisting intensity, the burr density is systematically regulated from 29.33% to 62.02%. This multipath conduction skeleton promotes macroscopic current sharing, redistributes localized Joule heating, and enhances lateral heat spreading, as evidenced by a significant drop in saturation temperature from 70.1 to 50.2 °C and a broadening of the radial thermal profile full width at half maximum from 43 to 96 pixels. This electrothermal advantage persists after polyaniline (PANI) deposition. The abundant protruding burrs provide an enlarged exposed interface that favors more continuous PANI deposition. Benefiting from the enlarged electrochemically accessible interface, enhanced local ion accessibility to PANI redox sites, and favorable charge-transfer characteristics, the optimized PANI@CFY4 electrode delivers a specific capacitance of 410.0 F g–1 at 0.5 A g–1 with 96.4% retention at 5 A g–1, a charge-transfer resistance of 0.33 Ω·cm2. The assembled symmetric fiber supercapacitor achieves a 1 V voltage window, 26.8 Wh kg–1 at 236.9 W kg–1, and 70.4% capacitance retention after 10,000 cycles under an electrolyte-maintained protocol, while stably powering wearable electronics.