Preparation Of Nickel Cobalt Oxide Nano-materials And Their Applications In Supercapacitors

Under the background of less social resources and more energy consumption, in order to protect the environment, also save energy and resource, the new green energy storage devices have been developed gradually. As a new energy storage device, the supercapacitor has been widely attracted a lot of attentions of researchers due to its numerous advantages. In this paper,we focused on the researches of a positive electrode material for supercapacitors, did a series of experiments to explore the effects of different preparation methods, different nickel, cobalt source, different reaction temperatures and reactant ion concentration ratio on NiCo2O4.Meanwhile, we compared the comprehensive performances of NiCo2O4/nickel foam composites, which were prepared by surface coating method and situ growth method, the main work and conclusions are as follows:At the same reaction temperature and reactant ion concentration, compared to traditional hydrothermal method, NiCo2O4 nanopowders prepared by microwave hydrothermal method had better dispersibility and more prominent micro-nano structures, it is the better way to prepare NiCo2O4 nanopowders with micro-nano structures.The black spinel structure Ni Co2O4 nanopowders were prepared by microwave hydrothermal method using chloride, nitrate and sulfate of nickel and cobalt as source, urea as precipitant, at different temperatures(90, 100, 110, 120 ?) and reactant ion concentration ratio(n(Ni2++ Co2+): n(CO(NH2)2) = 5, 10, 15, 20), and being calcined finally. The NiCo2O4 nanopowders presented morphologies of microspheres constituted by nanothorn, nanowool and nanoflakes, their specific surface areas were 142.5, 125.5, 147.8 m2/g; mesopore distributions were concentrated in the ranges of 3-8, 2-9, 2-6 nm, respectively. The NiCo2O4 nanopowders with uniform morphologies and prominent micro-nano structures were prepared at lower temperature and larger reactant ion concentration ratio for all kinds of source.According to the above-mentioned strategy, the Ni Co2O4/foam nickel composites were prepared by situ growth method and subsequently calcination treatment, presented the morphologies of mutually articulated chain-like, uniform grass-like and cross-cutting spreading needle-like. For the preparation of nickel and cobalt nitrate, as the temperature rises,the loading amount of Ni Co2O4 showed a decreasing trend after the first increase, but therewas no regularity for the effects of reactant ion concentration ratio on loading amount, the specific capacitance was decreasing with the increasing of loading amount of Ni Co2O4. The charge storage was pseudocapacitance mechanism with good reproducibility and reversibility.The electrochemical test results presented NiCo2O4/nickel foam composites prepared at reaction temperature of 90 ?, reactant ion concentration ratio of 1:15, had the best compositive performance. The specific capacitance was 902.77 F/g at the scan rate of 5 mV/s,when the scan rate increased 10 times, the value was down to 548.62F/g, capacity loss was39.23 %. Solution resistance was 0.71 ?, charge transfer resistance was 2.21 ?. At the power density of 1.93 kW/kg, the energy density was 80.58 Wh/kg. For nickel, cobalt chloride and sulfate, there was no obvious regularity for the effects of temperature and reactant ion concentration ratio on loading amount of Ni Co2O4. The specific capacitance was still decreasing with the increasing of loading amount of NiCo2O4 and the charge storage was still pseudocapacitance mechanism with good reproducibility and reversibility. The electrochemical test results presented that NiCo2O4/nickel foam composites prepared at reaction temperature of 100 ?, reactant ion concentration ratio of 1:20, had the best compositive performance. For nickel, cobalt chloride, the specific capacitance was 1031.46F/g at the scan rate of 5 mV/s, when the scan rate increased 10 times, the value was down to829.38 F/g, capacity loss was 19.59 %. Solution resistance was 0.58 ?, which presented rapid charge transfer rate, good reversibility and impedance characteristics. At the power density of2.32 kW/kg, the energy density was 135.39 Wh/kg. For nickel and cobalt sulphate, the specific capacitance was 884.16 F/g at the scan rate of 5 mV/s, when the scan rate increased10 times, the value was down to 640.69 F/g, capacity loss was 27.54 %. Solution resistance was 0.78 ?, charge transfer resistance was 3.12 ?. At the power density of 2.32 kW/kg, the energy density was 135.39 Wh/kg.Compared to surface coating method, NiCo2O4 /nickel foam composites prepared in situ growth method had better compositive performance. At the same loading amount of NiCo2O4,the NiCo2O4/nickel foam composites which were prepared in nickel and cobalt chloride presented much better compositive electrochemical performance than the others.