Preparation And Lithium Storage Properties Of Hemp Straw-based Oxide Composites

With the increasing demand of green and environmental protection technology for high-efficiency power,lithium-ion batteries with high energy density and long cycle life have become one of the key devices for high-efficiency energy storage and conversion.For lithium-ion batteries,it is critical to choose a new anode with high capacity to replace the traditional graphite(theoretical capacity is 372 m Ah g^-1).Transition metal oxides have attracted much attention because of their high theoretical capacity and large lithium ion(Li⁺)implantation coefficient.However,in the process of charge and discharge,the volume changes seriously and the conductivity is low,resulting in poor cycle stability and reduced rate capacity,which is not conducive to its practical application in LIBs.In order to overcome the shortcomings of transition metal oxide anode in LIBs,many attempts have been made.The results show that the nanostructure design can effectively alleviate the volume expansion and enhance its circulation capacity;Shorten the electron transfer path and improve the rate performance.In addition,carbon materials such as graphene,carbon nanotubes and porous carbon(PC)are combined with transition metal oxides to improve the charge discharge efficiency and conductivity of the hybrid anode.Therefore,in this paper,the porous carbon was prepared from hemp straw and hydrothermal compounded with transition metal oxides NiO and Zn O with different morphologies respectively.The prepared electrode materials were physically characterized and electrochemically tested.The specific study contents are as follows:(1)The porous carbon of hemp straw was prepared by pore forming of hemp straw by activation method.Nano spherical NiO particles were prepared by mixing nickel nitrate hexahydrate with ammonium bicarbonate.The porous carbon of hemp straw was hydrothermal compounded with NiO precursor,and the product was calcined in a tubular furnace to obtain the composite.The effects of different activation temperature and hydrothermal time on the properties of the composites were investigated.The electrochemical properties of hemp straw carbon,NiO and composites were compared and analyzed.After 700 cycles at 2 C rate,the reversible specific capacity of the electrode material can be maintained at 1086.4 m Ah g^-1.(2)Flake nano zinc oxide was prepared from zinc sulfate hexahydrate.The Zn O precursor was hydrothermal compounded with the prepared porous carbon of hemp straw,and the composite sample was obtained after drying.The effects of different hydrothermal time and temperature on the electrochemical properties and micromorphology of the composites were investigated.When the hydrothermal time is 15 h and the hydrothermal temperature is 240?,the structure of the sample is the most stable.After 400 cycles at 2 C rate,the reversible specific capacity can be maintained at 1157.1 m Ah g^-1.