High Performance Co-Mn Micro/Nano Supercapacitor Electrode Materials

With the limited storage of fossil fuels and the greenhouse effect, people have begun to seek a sustainable, clean and renewable energy conversion and storage devices. Supercapacitors represent a new type of energy storage device that have the advantages of high power density, long cycle life, and the short charging time although its low energy density, and they show tremendous flexibility in complementing lithium-ion batteries. The mixed transition metal oxide and composite material, which have high conductivity and capacitance, are widely used in the electrode of supercapacitor. In this thesis, we prepared a series of Co-Mn composite oxide micro/nano materials, and studied their pseudocapacitance behavior and advanced activated method of the electrode to improve the performance of the slurry-coating electrode.Firstly, a facile CV activation method was presented for Ni foam electrode, and the effects of activation parameters for the nickel foam electrode and CoMn2O4/Ni electrodes were studied. At the scan rate of 100 mV·s-1 in the 0-0.8V voltage window, the electrodes achieved the best performance after continuous cyclic voltammetry activating 4000-5000 cycles. The specific capacitance of the activated nickel electrode improved greatly was raised from 0.52 F·cm-3 (10.4 mF·cm-2) to 12.4 F·cm-3 (248.0 mF-cm-2) at 1 mA·cm-2. However, the rate performance of such activated nickel electrode was poor. To solve this situation, MnCo2O4 microspheres were loaded to form MnCo2O4Ni composite electrode. After 5000 CV cycles, the specific capacitance was raised from initial 2.12 F·cm-3(42.5 mF·cm-2) to 15.4 F·cm-3 (308.8 mF·cm-2) at 1 mA·cm-2, and rate performance has improved significantly. The increasing capacity of Ni-based electrode was mainly due to the formation of anodic Ni (OH) 2 layer on the surface, and the topographical variations of MnCo2O4.Secondly, we prepared the Co-Mn carbonate precursor grown directly on the foamed nickel mesh by hydrothermal co-precipitation method.In order to obtain the CoMn2O4 nanosheet electrode, the as-grown precursor with nickel foam were annealed in air at 350℃. The effects of reaction time and the amount of NH4F for precursor had also been studied. Due to the direct growth of active materials on the current collector, the porous internal structure and open space, the CoMn2O4/Ni electrode had a specific capacitance of 1529 F·g-1 at a current density of 2 A-g-1, which is closing to the theoretical capacitance of 1507 F·g-1, showing good capacitive performance. The capacity retention was 102% after 3000 cycles.Finally, the effect of cation ratio on the Co-Mn carbonate arrays on the metal substrate was discussed. When increased the content of Co in the raw materials, the conversion time for the product from amorphous nanosheets to highly crystalline polyhedral particles was shortened, and the products has different morphologies depending on the cation ratio, suggesting that metal carbonate array on the rough substrate surface has its own growth habits. The areal capacitance of the as-prepared MnCo2O4.5/Ni electrode was 934.5 mF·cm-2 at 1 mA·cm-2 current density, and the capacity retention of 80.9% after 3000 successive charge and discharge cycles was achieved.