Pliable
energy-storage devices have attracted great attention recently
due to their important roles in rapid-growing wearable/implantable
electronic systems among which yarn-shaped supercapacitors (YSCs)
are promising candidates since they exhibit great design versatility
with tunable sizes and shapes. However, existing challenges of YSCs
include an inferior power output and poor performance consistency
as compared to their planar counterparts, mainly due to their unique
linear geometry and curved interfaces. Here, a YSC comprising wet-spun
fibers of reduced graphene oxide and MXene sheets is demonstrated,
which exhibits prominent decreases in the equivalent series resistance
and thus increases in the power output upon increasing the length,
which is contradictory to the common expectations of a typical YSC,
showing revolutionary promises for practical applications. A much
higher power density (2502.6 μW cm–2) can
be achieved at an average energy density of 27.1 μWh cm–2 (linearly, 510.9 μW cm–1 at
5.5 μWh cm–1) via our unique dual-core design.
The YSCs also present good stability upon stretching and bending,
compatible with further textile processing. This work provides new
insights into the fabrication of textile-based energy-storage devices
for real-world applications.