Preparation And Supercapacitive Properties Of Nickel-cobalt Based Electrode Materials

Ni-Co based oxide electrode materials have been widely investigated for the application of supercapacitor because they have features like low cost, high conductivity and rich redox chemistry. In this work, we adopt an ion-exchange method to prepare NiCo2S4 flaky structure and a hydrothermal mathod to prepare NiCo2O4/V2O5 hierarchical structure. The structure, formation mechanism and electrochemical performance of these products are investigated and the main contents are as follows:1. Synthesis of NiCo2S4 flaky structure samples:We adopt an ion-exchange coupled with a hydrothermal method. At first, nickel cobalt hydroxide carbonate precursor was precipitated directly on the nickel foam and followed by annealing to achieve nickel cobaltite. Nickel cobalt sulfide was then obtained through exhanging oxygen ion with sulphur ion in Na2S aqueous solution. This modified approach has proven the following advantages. Firstly, the electrode material was grown directly on the surface of the current collector getting rid of the conductive agent and binder used in conventional process so as to improve the electrochemical perfomance. Secondly, the unique structure combined the merits of one dimensional and two dimensional materials. Surface area and ion condutivity was augmented due to the existence of the innumerable flakes. Also, electron condutivity was enhanced because the one dimensional array structure bridged a straight path between electrolyte and current collector. The electrochemical measurements revealed that when the concentration of S2- was 0.05 M, the NiCo2S4 flaky structure with the largest specific surface area (40.98 m2 g-1) have a high specific capacitance of 2044 F g-1. Furthermore, NiCo2S4 flaky structure also exhibit a good capacitance retention of 77% after 2000 charge-discharge cycles.2. Synthesis of NiCo2O4/V2O5 hierarchical structure samples:Firstly, nickel cobalt hydroxide carbonate precursor was grown on the surface of nickel foam by a hydrothermal method. Then, the nickel foam carried with precursor was immersed in NH4VO3 solution and subsequently heated in electric oven at 160℃ for 30 mins. After the last procedure of calcination in air, the NiCo2O4/V2Os product was obtained. The formation mechanism of products was investigated and the supercapacitive performance was measured. The results indicated that when using 0.02 M NH4VO3 solution, the NiCo2O4/V2O5 samples with larger specific surface area (59.68 m2 g-1) exhibit highest specific capacitance of (2396 F g-1). Furthermore, the sample also delivered good capacitance retention of 78.5% after 1000 charge-discharge cycles.