Advanced hybrid supercapacitors assembled with CoNi LDH nanoflowers and nanosheets as high-performance cathode materials

In this work, CoNi layered double hydroxide with flower-like nanostructures (CoNi LDH NFs) and nanosheet-based shape (CoNi LDH NSs) were respectively prepared through a facile solvothermal approach, during which a mixed solvent of deionized water and ethylene glycol with different volume ratio was used. The NFs possessed a specific surface area of 101.28 m(2) g(-1) and was larger than the 38.54 m(2) g(-1) for NSs. The electrochemical performance of these CoNi LDHs was investigated in three-electrode & two-electrode systems, respectively, and they exhibited the battery-type electrochemical response. The CoNi LDH NFs delivered a specific capacity of 768.3C g(-1) at 1 A g(-1) and 643.1C g(-1) at 10 A g(-1), in contrast, the CoNi LDH NSs exhibited an inferior capacity of 669.3C g(-1). To evaluate the practical application potential in the field of supercapacitor, the hybrid supercapacitor (HSC) device was assembled with these CoNi LDHs as cathode and activated carbon (AC) as anode. The CoNi LDH NFs//AC HSC delivered an energy density (ED) of 37.1 W h kg(-1) at the power density (PD) of 748.0 W kg(-1), which was higher than the 31.0 W h kg(-1) for NSs-based HSC. The cycling performance and structural stability of such LDHs were investigated over 4000 cycles at a high current density of 10 A g(-1), and just a little capacity decay at the end of cycling was found. The CoNi LDH NFs & NSs may serve as battery-grade electrode materials with high performance and probably have great application potential in electrochemical energy storage. Besides, the present synthetic method is simple and can be extended to the preparation of other LDHs for the assembly of advanced HSC device with superior electrochemical performance.