The Preparation And Electrochemical Performances Of Binary Oxides/Carbon Composite Materials

With the rapid development of the global economy, the depletion of fossil fuels, and increasing environmental pollution, there is an urgent need for efficient, clean, and sustainable sources of energy, as well as new technologies associated with energy conversion and storage. Recently, electrochemical supercapacitors have attracted significant attention, mainly due to their high power density, long lifecycle and good safety performance. On this basis, the composite electrode materials of metal double hydroxides and carbon materials which combined with the double layer capacitance and redox capacitance storage mechanisms, can greatly improve the electrochemical performance of the material. The research works are as follows:1. A series of MnFe-LDH host containing co-intercalated dodecyl sulfonate and methyl methacrylate were synthesized by co-precipitation, followed by calcinated at a certain temperature. We investigated the effects of different MnFe molar ratio and calcination temperature on the structure and properties. When the molar ratio of MnFe is 3, calcination temperature is 500℃, the structure and electrochemical performance are excellent. With the increment of organic compounds intercalated, carbon content increases after being calcinated. The obtained Mn-Fe oxide/C composites have a good conductivity owing to the metal oxides and carbon materials have a composition in nano-scale. The composite materials have high specific capacities and cycle performance. With the increase of carbon content in a certain range, the capacity and cycle stability of the composites improve. When the carbon content is too high, double electric layer is dominant, somewhat making the capacity lower. When the carbon content is 13.32%, MnFe mole ratio is 3, the electrochemical performance of composite is optimal. A specific capacitance of 330 F·g-1 was obtained in 1 M KOH solution at a current density of 1 A·g-1, with a capacitance retention up to 80% after 1000 cycles.2. By preparation NiFe-LDH with different structure of carbon materials (such as carbon sphere, graphene, carbon nanotube), we have a research in its morphology and electrochemical performance. All of the carbon materials and hydrotalcite have a good composite. On the one hand, carbon materials are uniformly dispersed between the layers and hydrotalcite particles, strengthening the conductivity, and inhibiting the agglomeration of LDHs, while increasing the contact area with the electrolyte. On the other hand, the capacitance of electric double layer improves the capacity and cycle performance ratio. It is found that the specific capacitance as high as 840 F·g-1, 660 F·g-1,763 F·g-1 at a current density of 1 A·g-1 in 6 M KOH solution and capacitive retention rate is ca.90% for LDH-carbon sphere,82% for LDH-CNT and 86% for LDH-RGO, respectively. The electronic conductivity of carbon materials is beneficial to the electron transfer, improving the conductivity of the composite, and the composite capacity has greatly improved. The carbon spheres after calcination are inserted between the hydrotalcite layers, increasing the conductivity of the hydrotalcite layers, effectively inhibiting stacked layers of hydrotalcite, which lead to a high specific capacity and cycling stability.