Preparation Of Zinc-based Oxide Nanofibers And Their Electrochemical Properties

Supercapacitors has the advantages of fast charging-discharging ability, high power density and long cycle life and so on. It has become one of the most promising energy storage devices in easing the energy crisis and meeting the urgent requirements of the modern electronics industry. Electrode materials have been the most important factor of high performance supercapacitors. In this paper, the high performance electrode materials with core-shell heterostructure were prepared by using zinc-based oxide as the main material. The microstructure and electrochemical properties of the preparation electrode materials were also investigated, which showed the mechanism of the electrochemical energy storage and the synergistic effects. At the same time, we assembled asymmetric supercapacitors using the prepared the electrode, which prove that the synthesized materials show certain practical value. This paper provides the effective data for the study of the supercapacitor in the future.The detailed research contents are as follows:（1） A three-dimensional Zn O@Ni（OH）₂ core-shell heterostructure is controllably synthesized through an electrospinning method combined with a hydrothermal approach. The as-prepared Zn O@Ni（OH）₂ heterostructures are investigated as the electrodes for supercapacitors, which exhibit excellent electrochemical performances such as ultrahigh specific capacitance（2218 F g-1 at 2 m V s-1） and superior rate capability even at a high scan rate. Moreover, the assembled asymmetric supercapacitor with the as-obtained Zn O@Ni（OH）₂ hybrid as the positive electrode and the porous carbon nanofibers（PCF） as the negative electrode yields a high energy density of 57.6 Wh kg-1 with the power density of 129.7 W kg-1. Hence, the Zn O@Ni（OH）₂ hybrid holds great promise for high-performance energy storage applications.（2） Through a chemical bath deposition and electrospinning method that the Ni S₂ nanoparticles are directly grown on the surface of Zn O nanofibers. The obtained Zn O@Ni S₂ core-shell heterostructure has excellent energy storage performance, exhibiting a high capacitance of 2170 F g-1 at a scan rate of 2 m V s-1 and excellent cycle stability with 83 % of the initial specific capacitance retention after 5000 cycles（at a scan rate of 200 m V s-1）. Moreover, an asymmetric supercapacitor（ASC） with Zn O@Ni S₂ as positive electrode and the porous carbon nanofibers as the negative electrode yields an energy density of 49.7 Wh kg-1 and a maximum power density of 223.8 k W kg-1, implying that it has an outstanding potential for a promising future of practical applications.（3） Hierarchical Zn Co₂O₄ nanoneedle arrays are vertically grown on porous carbon nanofibers to form core-shell heterostructure through a facile hydrothermal method followed by thermal treatment. Such unique configuration makes full use of the synergistic effects from both excellent electrical conductivity of PCF and high specific capacitance of Zn Co₂O₄, endowing the hybrid to be an excellent electrode for flexible supercapacitors. Benefiting from their intriguing structural features, the PCF@Zn Co₂O₄ hybrid possesses fascinating electrochemical performance as integrated binder-free electrode for supercapacitors. Remarkably, this PCF@Zn Co₂O₄ electrode could achieve a high capacitance of 1384 F g-1 at a scan rate of 2 m V s-1. Besides, an all-solid-state asymmetric supercapacitor fabricated with the as-prepared PCF@Zn Co₂O₄ hybrid as positive electrode and PCF as negative electrode achieves a high energy density of 49.5 Wh kg-1 at a power density of 222.7 W kg-1. Furthermore, the all-solid-state asymmetric supercapacitor device exhibits remarkable cycling stability with 90 % specific capacitance retention after 3000 cycles.