Ni-containing Layered Double Hydroxides/Carbon Composites Electrode Materials:Synthesis And Properties

Ni-containing layered double hydroxides(LDHs)are a kind of important electrode materials with high specific capacitances,abundant reserves and low cost.However,LDHs themselves are poorly conductive,making the energy storage performance gravely degenerating.In this thesis,three kinds of Ni-containing LDHs(including Ni-Al,Ni-Co and Ni-Mn LDHs)were selected as research objects.They were combined with nano-carbon materials to construct a hierarchical structure in order to improve the energy storage capabilities.The main work of this thesis is as follows:Ni-Al LDHs/graphene oxide(GO)composites were prepared by a microwave-assisted method.In the composites,Ni-Al LDHs nanosheets grew on the surfaces of GO to form a two-dimensional core-shell structure.The effects of Ni/Al ratio on the morphology,microstructure and electrochemical performances were investigated.Subsequently,the reduction of GO to reduced graphene oxide(rGO)by microwave irratiation and thermal reduction was carried out to study the capacitive properties of the two Ni-Al LDHs/rGO composites.The results indicate that Ni-Al LDHs/rGO composites have better rate stability and cycling performance than Ni-Al LDHs/GO.Furthermore,Ni-Al LDHs were in situ grown on the surfaces of CNTs by using γ-Al2O3 as the source of Al.Then,the morphology,structure and electrochemical properties of Ni-Al LDHs/CNTs composite were systematically studied.Ni-Co LDHs and Ni-Co oxyhydroxides/oxides were deposited on the surfaces of CNTs to form a core-shell structure by a coprecipitation method.Their high specific capacitances,good rate performances and excellent cycling stability were studied and analyzed by investigating their morphology,nanostructure and porosity.The results show that the good rate and cycling performances of the composites are due to the excellent electrical conductivity and structural stability of the composites with core-shell structures.Ni-Mn LDHs,Co-Mn LDHs and NiCoMn LDHs were synthesized by a coprecipitation method.They were then combined with rGO to obtain two-dimensional hierarchical structures,respectively.The effects of rGO on the morphology,porosity and electrochemical behavior of the composites were investigated.On one hand,rGO is directly linked to LDHs nanosheets by chemical bonds,which is favorable for electrochemical reaction.On the other hand,rGO acts as internal buffer layer to prevent the structure from collapse during the cycling.LDHs/rGO porous network structure could increase the specific surface area to provide a large number of reactive sites for faster electrochemical reaction,promoting ion migration and redox reaction.Then,Ni-Mn LDHs were grown on zero-dimensional carbon black particles,one-dimensional CNTs and two-dimensional rGO.The electrochemical performances of ternary Ni-Mn LDHs/rGO/CNTs composites are better than those of binary LDHs/carbon composites owing to their special spatial structures.The effects of electrolyte concentration and ion species on the electrochemical behavior of ternary Ni-Mn LDHs/rGO/CNTs were also studied.