Synergistic Oxygen Vacancy and Nanostructural Engineering of CoAl‐LDH on CNT‐Coated Yarn for Wearable Supercapacitors

ABSTRACT Yarn‐type supercapacitors (YSCs), combining high energy density and flexibility, are highly desired for wearable electronics. We studied oxygen vacancies (Ov) in CoAl‐LDH grown on CNT‐coated aramid yarn (CAY). NaBH 4 treatment not only created Ov but also thinned the nanosheets and expanded the interlayer spacing. The optimal Ov 0.6 ‑CoAl‑LDH@CAY (0.6 M NaBH 4 ) showed enhanced surface area, with XPS and EPR confirming Ov introduction. In a three‑electrode system, it delivered an areal capacitance of 3186.75 mF cm −2 at 3 mA cm −2 and a rate capability of 54.72% (at 25 mA cm −2 ), significantly outperforming the untreated sample (1146 mF cm −2 , 40.63%). This improvement is attributed to Ov‑induced redox sites and faster ion transport from thinner, expanded nanosheets. A quasi‑solid‑state symmetric YSC based on this electrode achieved an energy density of 35.01 µWh cm −2 at 77.78 µW cm −2 , retained 83.44% capacitance after 10,000 cycles, and performed stably under bending (0–135°). Integrated with a CAY strain sensor, the system enabled real‑time motion monitoring, verifying its potential for wearable energy storage and intelligent sensing.