| Supercapacitor is fabricate of positive and negative electrode materials as well as electrolyte,which possesses various merits like high power density,fast charging and discharging process and long cycle life.Among various electrode materials,layered double hydroxides are promising pseudocapacitance electrode materials for supercapacitor.As a layered double hydroxides,nickel-cobalt double hydroxides possesses higher theoretical capacitance for fast and reversible redox reaction.However,the erosion of the electrolyte during charge-discharge process lead to poor capacitance and cycling stability.Thus,in this paper a nickel-cobalt double hydroxide was used as the basis electrode and combined with carbon?C?and polypyrrole?PPy?,respectively,to study the electrochemical properties of binary nanocomposite nickel-based electrode materials,which is expected to break through the existing performance defects.?1?Nickel nitrate?Ni?NO3?2·6H2O?,cobalt nitrate?Co?NO3?2·6H2O?and hexamethylenetetramine?HMTA?were used as raw materials to prepare nano-flower-like nickel-cobalt double by hydrothermal method.The molar ratio of Ni?NO3?2·6H2O and Co?NO3?2·6H2O was controlled to prepare NiCo?OH?2 with different elemental ratios.The result analyse displays that all the NiCo?OH?2 show a nanoflower structure with a diameter of 4?m and thickness of 0.1 nm.Among them,the one with molar ratio of 7:3 have superior electrochemical properties of capacitance of 766.34 F g-11 at current density of 2 A g-11 and capacitance retention of80%after 10,000 cycles at a current density of 20 A g-1.?2?In order to improve the cycling life of NiCo?OH?2.A nanoflower-like C@Ni0.7Co0.3?OH?2is future designed and synthesized via a novel and facile step-by-step hydrothermal method using glucose as carbon source.The research results show that the cycling stability and specific capacitance of the composite increase first and then decrease with increasing of glucose content.Among them,the sample containing 1.5 g of glucose(C@Ni0.7Co0.3?OH?2-2)shows excellent cycling stability(about 98.9%retention of capacitance after 10,000 cycles at a current density of20 A g-1)and high specific capacitance of 806.37 F g-11 at a current of 2.0 A g-1.Obviously,carbon coating improves the cycle stability of Ni0.7Co0.3?OH?2 but without the capacitance,because it prevents sufficient contact between Ni0.7Co0.3?OH?2 and the electrolyte.?3?In order to further improve the capacitance and maintain excellent cycle stability of Ni0.7Co0.3?OH?2.PPy@Ni0.7Co0.3?OH?2 was prepared by chemical solvent method using hydrogen bond to connect two of them.Study results show that the as-prepared electrode material exhibits an outstanding electrochemical performance with capacitance of 1241.57 F g-11 at 2.0 A g-11 and capacity retention of 98%after 10,000 cycles a current density of 20 A g-1.To further demonstrate the electrochemical performance of PPy@Ni0.7Co0.3?OH?2,a PPy@Ni0.7Co0.3?OH?2//AC asymmetric supercapacitor was prepared using PPy@Ni0.7Co0.3?OH?2 and AC as positive and cathode electrode,respectively.The results show that the devise achieves an ultra-high specific capacitance of 153.17 F g-11 at current density of 1 A g-1,as well as outstanding cycling stability of capacity retention of 93%after 5000 cycles.The excellent electrochemical performance of PPy@Ni0.7Co0.3?OH?2 can mainly be attributed to the following points:?1?the nanoflower-like structures of Ni0.7Co0.3?OH?2 increased the contact area between Ni0.7Co0.3?OH?2 and PPy,which allows the intimate electrolyte penetration and fast ion/electronic transport.?2?The bonded PPy can not only efficiently improve the conductivity of Ni0.7Co0.3?OH?2 but also offer extra Faraday processes for the whole electrode.?3?The surface PPy prevents Ni0.7Co0.3?OH?2 form the erosion of electrolyte,which promote the stability of the electrode effectively. |
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