Investigation Of Metal Hydroxide/Oxide Supercapacitor Electrode Materials

With the rapid advances of new energy driven equipments,it is urgent to develop the efficient energy storage system.Supercapacitors are called as a kind of new type energy storage components with high energy density and high power density,which has become an integral part of the development of new energy industry.The materials with high specific capacity are very considerable for devices,which is regarded as a kind of important substance.The performances of electrode materials depend not only on the chemical properties of the material itself,such as the electrical conductivity,etc.,but also on the physical characteristics,such as the microstructure and specific surface area.The transition metal oxides/hydroxides are recognized as a kind of energy storage materials with high electrochemical activity,as well as with the advantages of easy preparation and wide sources of raw materials.Therefore,the main work of this paper carries out the research on the design and regulation of transition metal materials.The main research works are as following:?1?The rare earth yttrium?Y?element can improve the inherent conductivity of Ni?OH?₂,which was used as a dopant.Y doped Ni?OH?₂ composites were fabricated via a hydrothermal process.The effect of Y doping amount on the structure and electrochemical performance of Ni?OH?₂ were investigated.It was found that the phase of Ni?OH?₂transformed from?to?after Y doping,which resulted into the increasing of lattice spacing.When the molar ratio of Y³⁺/Ni²⁺was 10%,the specific surface area of Y-doped Ni?OH?₂ was 119.3531 m²/g.The Y-doped Ni?OH?₂ electrode exhibited the optimal specific capacity of 735.46 C/g at 1.5 A/g,and good long-term electrochemical stability with 80.39%capacity retention after 3000 cycles.?2?A highly conductive Y-doped?-nickel hydroxide flower-like nanostructure was successfully prepared in solvothermal system,cetyltrimethylammonium bromide?CTAB?as organic surfactant,ethanol as solvent,via one-step solvothermal process?160^oC,15h?.The effect of the initial amount of Y on the crystal structure,morphology and electrochemical properties of Ni?OH?₂-based were studied.The increased of the introduced amount of Y,the crystallinity of Ni?OH?₂ gradually decreasesd,their specific surface area tended to increase first and then decrease.The reaction kinetics and the charge transfer efficiency were improved by introduced of Y.The Y-Ni?OH?₂ electrode had not only enhanced specific capacitance,but also shown good long-term electrochemical stability?retention of 72.39%,better than 48.7%of undoped Ni?OH?₂?.The assembled Y-Ni?OH?₂//AC aqueous asymmetric supercapacitor delivered an energy density of 68.3Wh/kg at a power density 1093.7 W/kg,and good cycling performance with 82.37%retention after 8000 cycles.?3?A new Y-Ni?OH?₂/graphene heterostructure?Y-Ni/GNS?was fabricated via a solvothermal method using the heteroelement Y as dopant,graphene and CTAB as raw materials.The incorporation of Y and graphene improved the conductivity of Ni?OH?₂,meanwhile the addition of graphene improved the wettability of the whole electrode system,whcih promoted the penetration of electrolyte ions.The Y-Ni/GNS heterostructure exhibited a remarkable specific capacity of 822.3 C/g at 1 A/g,and and ultra-long cycling life,with 76.24%retention after 6000 cycles.The as-fabricated device based on Y-Ni/GNS and AC shown an energy density of 81.6 Wh/kg.?4?Based on the high electrochemical activity of Al and Ni,An Al/Ni double-doped ternary oxide?AlNiCo-O?was synthesized by a hot-air oven-based method?90^oC/6h?.The strong synergistic electrochemical effects between different metals cations was ascribed to the coexistence of Ni and Co battery features and the combined contribution of electronic efficiency Al,Ni and Co,and their coexistence provided more metal centers for redox reactions.The AlNiCo-O electrode exhibited high-efficient charge storage,with outstanding specific capacity of 1008.5 C/g at 1 A/g.The supercapacitor based on the AlNiCo-O and AC obtained a high energy density of 63.3 Wh/kg at 881.4 W/kg.?5?3D network framework is composed of nanofilms and nanowires.We fabricated the network-like structure consisting of an amorphous Ni–Co layered double hydroxide nanofilm anchored to Co₃O₄ nanowires?Co₃O₄/NiCo-LDH?grown on NF,which involved hydrothermal reaction?120^oC/6h?with annealing?300^oC/2h?and electrochemical deposition.The thickness of NiCo-LDH nanofilms on the surface of Co₃O₄ were controlled by the deposition time,and their electrochemical performances of the overall electrode were explored.The loading mass of NiCo-LDH film increased as the deposition time increased,lead to the Co₃O₄/NiCo-LDH performance degradation.The specific capacities of the Co₃O₄/NiCo-LDH electrodes synthetized by deposition times of 120s was 1067 C/g at 1 A/g.The Co₃O₄/NiCo-LDH//AC device exhibited a maximum energy density of 74.4Wh/kg at 989 W/kg,and excellent cycling stability,with 91.57%retention after 7000cycles.?6?Core-shell structures which are composed of nanosheets/nanowires and nanosheets,were gradually recognized as high-performance materials.We designed the Core-branched NiCo₂S₄@CoNi-LDH heterostructure by hot-air oven-based and electrochemical deposition methods.The highly active NiCo₂S₄“branch”provided sufficient capacity during redox process of Ni²⁺/Ni³⁺and Co²⁺/Co³⁺/Co⁴⁺,which maked up the gap of inner CoNi-LDH.Based on the strong synergistic electrochemical effects,the CN-LDH@NCS NSs electrode displayed excellent charge storage,with a notable specific capacity of 1385.7of 1008.5 C/g at 1 A/g.The NiCo₂S₄@NiCo-LDH//AC device achieved a high energy density of 93.21 Wh/kg.