Iron oxides nanobelt arrays rooted in nanoporous surface of carbon tube textile as stretchable and robust electrodes for flexible supercapacitors with ultrahigh areal energy density and remarkable cycling-stability.

We report a significant advance toward the rational design and fabrication of stretchable and robust flexible electrodes with favorable hierarchical architectures constructed by homogeneously distributed α-Fe2O3 nanobelt arrays rooted in the surface layer of nanoporous carbon tube textile (NPCTT). New insight into alkali activation assisted surface etching of carbon and in-situ catalytic anisotropic growth is proposed, and is experimentally demonstrated by the synthesis of the Fe2O3 nanobelt arrays/NPCTT. The Fe2O3/NPCTT electrode shows excellent flexibility and great stretchability, especially has a high specific areal capacitance of 1846 mF cm-2 at 1 mA cm-2 and cycling stability with only 4.8% capacitance loss over 10,000 cycles at a high current density of 20 mA cm-2. A symmetric solid-state supercapacitor with the Fe2O3/NPCTT achieves an operating voltage of 1.75 V and a ultrahigh areal energy density of 176 µWh cm-2 (at power density of 748 µW cm-2), remarkable cycling stability, and outstanding reliability with no capacity degradation under repeated large-angle twisting. Such unique architecture improves both mechanical robustness and electrical conductivity, and allows a strong synergistic attribution of Fe2O3 and NPCTT. The synthetic method can be extended to other composites such as MnO nanosheet arrays/NPCTT and Co3O4 nanowire arrays/NPCTT. This work opens up a new pathway to the design of high-performance devices for wearable electronics.

Achieving Rich Mixed-Valence Polysulfide/Carbon Nanotube Films toward Ultrahigh Volume Energy Density and Largely Deformable Pseudocapacitors.

In this work, new insights into dependence of electrochemical performance enhancement on transition metals' rich mixed valence and their atomic ratio as well as redox active polysulfides are proposed. Especially, the influence of atomic ratio is further demonstrated by both experiments and density functional theoretical calculation where increasing Co/S leads to the enlargement of both interatom distance and hole diameter in a MnxCoySz cell. We rationally designed and prepared novel flexible electrodes of a rich mixed-valence polysulfide MnxCoySz/carbon nanotube film (CNTF) through acid activation of a dense CNTF into a hydrogel-like conductive matrix, growth of the MnxCoy(CO3)0.5OH precursor on each CNT, and controlled sulfidation. Nanostructure control allows us to obtain fast electron/ion transfer and increased availability of active sites/interfaces. The optimal MnCo9S10/CNTF shows a specific capacitance reaching 450 F cm-3 at 10 mA cm-2, much higher than reported values for CNT-based electrodes. Also, it exhibits remarkable cycling stability with only 1.6% capacity loss after 10 000 cycles at a high current density of 80 mA cm-2. An all-solid-state asymmetric supercapacitor (ASC) applying MnCo9S10/CNTF delivers an exceptionally high volumetric energy density of 67 mW h cm-3 (at 10 W cm-3). Particularly, integrated electric sources with adjustable output voltages can be obtained by connecting several ASCs in series, and there are no structural failure and capacity loss during repeated large-angle twisting and vigorous hammering. This work provides a general route to energy storage devices with ultrahigh volumetric energy density and outstanding reliability for wearable electronics.