Simple construction of molybdate anions-intercalated NiCo-based layered double hydroxides nanosheet arrays on carbon fibers for enhanced flexible fiber-shaped supercapacitors

As the energy supply devices for miniaturized, wearable, portable and intellectualized electronic products, flexible fiber-shaped supercapacitors (FSCs) have attracted great attention by virtue of their peculiar superiorities such as ultra-fast charge/discharge ability, ultra-high output power, ideal service life, outstanding mechanical flexibility, and superior compatibility with the human body. The performance enhancement of FSCs is highly dependent on the high-performance active electrode materials. In this work, a series of molybdate anionsintercalated Ni-Co based layered double hydroxides (NiCoMo-LDHs) have been synthesized on flexible carbon fiber (CF) by a simple electrodeposition strategy by regulating the Mo content and the growth time. It turns out that the intercalation of molybdate anions can significantly widen the interlayer spacing and reduce the crystallinity of the synthesized LDH materials. The morphological differences between the LDHs with different Ni/Co/Mo ratios are analyzed, and the morphological evolution process of the materials with the specific Ni/Co/ Mo ratio of 1:3:0.2 are systematically investigated. The well-developed NiCoMo-LDH nanosheets electrode with appropriate Ni/Co/Mo ratio (NCM2-500) delivers the best electrochemical performances among all the synthesized LDHs. In particular, the synthesized NCM2-500 fiber electrode exhibits excellent specific capacitance, superior electrical conductivity and favourable cycling stability. Additionally, the assembled parallel type NCM2-500//AC FSC device using NCM2-500 and activated carbon (AC) as the cathode and anode with the assistance of PVA/KOH gel electrolyte demonstrates a brilliant specific energy of 36 Wh cm- 1 at 845 W cm- 1 (nearly 17 Wh kg- 1 at about 400 W kg-1) and a high cycle lifespan of maintaining 103 % of the pristine capacity after 5000 cycles. This FSC device is an ideal candidate for next-generation applications due to its remarkable electrochemical properties.