Preparation And Lithium/Sodium Storage Properties Of Nickel-Based MOF Derivatives

Metal-organic frameworks（MOFs）have a wide range of applications in the field of secondary batteries due to their unique advantages（high specific surface area,etc.）.In order to further improve the conductivity,MOFs are usually used as precursors and converted into metal compounds（MX,M=Fe,Co,Ni,etc.,X=O,S,P,Se,etc.）.In this study,Ni-Co Prussian blue analog（Ni-Co PBA）was used as a precursor to synthesize Ni-Co bimetallic oxides/sulfides/selenides.By adjusting the microstructure and compounding with reduced graphene oxide,superior electrochemical properties were achieved.Specific studies are as follows.（1）Firstly,cubic Ni-Co PBA with uniform particle size was prepared by a simple coprecipitation method.Subsequently,hollow structure Ni O-Co₃O₄nanoparticles were obtained by controlling oxidation temperature and oxidation time in the air.Finally,hollow Ni O-Co₃O₄@r GO composite material was prepared by hydrothermal reduction method by the composite of hollow Ni O-Co₃O₄ nanoparticles with GO.When used as anode materials for lithium-ion batteries,the hollow Ni O-Co₃O₄@r GO composites have good cycling performance and can maintain a reversible capacity of 804.5 mAh g^-1 for 100cycles.The reversible capacity of the hollow Ni O-Co₃O₄@r GO electrode can be maintained at 434.1 mAh g^-1 after 500 cycles at a large current(1 A g^-1).When used as anode material for sodium-ion batteries,the hollow Ni O-Co₃O₄@r GO composite material can maintain a reversible capacity of 269.2mAh g^-1 for 100 cycles at a current density of 0.1 A g^-1.The synergistic effect of the hollow structure and GO results in good electrochemical properties of the hollow Ni O-Co₃O₄@r GO composites.（2）The cage-like Ni-Co PBA with optimal morphology was obtained by adjusting the time of ammonia etching.The cage-like Ni-Co PBA@PDA@GO was obtained by the combination of the cage-like Ni-Co PBA with dopamine hydrochloride and GO.The cage-like Ni S₂-Co₃S₄@r GO composites were prepared by high-temperature annealing and high-temperature vulcanization of cage-like Ni-Co PBA@PDA@GO.The cage structure can increase the specific surface area of the material and provide more attachment sites for ions.In addition,the pores inside the cage structure can also provide channels for ions migration.When used as anode material for lithium-ion batteries,the cage-like Ni S₂-Co₃S₄@r GO composites can maintain the reversible capacity of 1392mAh g^-1 after 100 cycles.At a large current of 1 A g^-1,the reversible capacity of Ni S₂-Co₃S₄@r GO electrode is able to maintain 1511.1mAh g^-1 after 500 cycles.When used as the anode material for sodium-ion batteries,the reversible capacity of the cage Ni S₂-Co₃S₄@r GO composite is 711.2 mAh g^-1 and the capacity retention rate is 68.2%at the current density of 0.1 A g^-1 for 100 cycles.（3）Ni-Co PBA was prepared by the co-precipitation method and was etched with ammonia water.By adjusting the etching time,cage-like Ni-Co PBA with the best morphology was obtained.The cage-like Ni-Co PBA was compounded with dopamine hydrochloride and GO,and then annealed in an Ar atmosphere and selenized in H₂/Ar atmosphere to obtain cage-like（Ni,Co）Se₂@r GO composites.Combining graphene with cage-like（Ni,Co）Se₂nanoparticles can not only maintain the high capacity of cage-like（Ni,Co）Se₂nanoparticles but also enhance the overall electrical conductivity of the composites.When used as anode material for lithium-ion batteries,the cage-like（Ni,Co）Se₂@r GO composite maintains a reversible capacity of 1334.5mAh g^-1 after 100 cycles at a current density of 0.1 A g^-1.When the current density is 1 A g^-1,the cage-like（Ni,Co）Se₂@r GO composite can maintain a reversible capacity of 1658.3 mAh g^-1 after 300 cycles.When used as anode material for sodium-ion batteries,the cage-like（Ni,Co）Se₂@r GO composite can maintain a reversible capacity of 545.2 mAh g^-1 after 100 cycles at 0.1 A g^-1 current density.