Preparation And Electrochemical Properties Of Layered Double Hydroxides And Their Composites For Supercapacitors

Layered double hydroxides (LDHs) are a family of synthetic anionic clays. Considerable attention has been paid to the functional materials of this class because of the characteristic of tunable compositions and exchangeable anions. In the present study, electrodes of LDHs nanosheets have been achieved through coating or potentiostatic deposition. At present, synthesize LDHs with specific morphology and explore facile ways to fabricate LDHs electrodes are becoming intensive research topic because of their improved electrochemical properties for potential applications in spercapctitors. In this work, we reported a facile in situ method to prepare LDHs electrodes, developed an environmentally friendly hydrothermal/solvothermal approach to fabricate polymorphic LDHs and introduced Li, Co and carbon spheres into Ni/Al LDHs to improve the electrochemical performance of LDHs electrodes.Ni/Al LDHs nanosheets were successfully grown on the surface of nickel foam by a sample in situ method. Because of the developed three-dimensional network structures, the obtained electrode provided large contact areas with substrate and showed excellent electrochemical capacitive character.Ni/Al LDHs with high specific surface area and high porosity were developed via a facile hydrothermal/solvothermal approach. In the process of preparing Ni/Al LDHs, both the reaction time and the concentration of ethanol to have significant effect on the size and morphology of the final products. The obtained3D flowerlike hierarchical Ni/Al LDHs displayed better performance, suggesting the high potential as electrode materials in electrochemical capacitors.Li/Al layered double hydroxides (LDHs) were synthesized by a facile hydrothermal/solvothermal approach. A possible growth mechanism was proposed for the formation of these structures. In the sutdies, we explored the effect of metal ions, ethanol concentration, calconation temperature on the structure and morphology of the products. Electrochemical performances indicate that hexagonal Li/Al LDHs calcined at450℃exhibited the specific capacitance of887F·g-1at a current density of6.6A·g-1and good cycling stability.Ni/Al LDHs doped with Li or Co have been prepared through isomorphous substitution. The optimum doping amount to improve the capacitive of Ni/Al LDHs was decided through electrochemical tests. Compared with Li-doping sample, Co-doping (33%) LDHs exhibited higher specific capacitance.Ni-Al LDHs/C composites have been successfully fabricated via a facile in situ water/ethanol system. When urea was used as a precipitant, LDHs/C composites exhibited better degree of crystallinity, however, most LDHs particles tend to aggregate and are not uniformly dispersed on the surface of arbonaceous spheres. A phase separation always exists between the LDHs and carbonaceous spheres. When no urea was added, LDHs nanosheets prepared at50%ethanol system could highly disperse on the surface of colloidal carbonaceous spheres, making composite electrode exhibits better performances.