Preparation And Electrochemical Performance Study Of Zinc Stannate/Reduced Graphene Oxide Composites

With a specific surface area and great potential applications in the energy storage,carbon materials and carbon composites have aroused great interest of the researchers.As one of the thinnest and most powerful carbon materials,graphene is favored by more and more people due to its special electrical,mechanical,thermal and optical properties,and its unique two-dimensional（2D）structure,high conductivity,surface area,good hydrophilicity,the surfaceis modified easily and other advantages.Bimetallic oxide ZnSnO₃ is considered as a very promising Li-ion batteries anode material because of its high theoretical capacity,low cost,easy preparation,abundant resources and diverse shapes.The fabrication of ZnSnO₃ with different morphologies and sizes,then surface modification with graphene and other carbon materials monolayer or multilayer can effectively improve the electron transporting ability of the composites,buffer the change of the material volume in charging and discharging process and maintain the structural integrity of the electrode,greatly enhancing its applications potential in the energy storage devices.In this paper,the hollow ZnSnO₃@C/r GO microcube（ZS@C/r GO）composites and the small-sized mesoporous ZnSnO₃/r GO composites（ZSGC）were prepared by different methods respectively.The preparation process was as follows:（1）The amorphous hollow ZnSnO₃ microcubes were prepared by calcining the precursor hollow ZnSn（OH）6 microcube with the method of low temperature coprecipitation at 450 ?C for 2 h in N2 atmosphere.Followed,the material was carbon modified by using glucose as carbon source.The carbon-coated material modified by the poly（diallyldimethylammonium chloride）（PDDA）and graphene were compound by colloid-electrostatic self-assembly method.Finally,the ZS@C/r GO composites were obtained due to hydrothermal treatment of the composites at 180 ?C and vacuum freeze-drying treatment.（2）The ZnSn（OH）6 precursor was further synthesized by coprecipitation method with changing the temperature and concentration of alkali,the amorphous ZnSnO₃ materials were fabricated by calcining the precursor at 450 ?C for 2 h in N2 atmosphere.Followed,the prepared ZnSnO₃ was positively charged after modification by cationic surfactant PDDA,then the prepared positively charged ZnSnO₃ and the negatively charged graphene were compound by colloid electrostatic self-assembly method.Cylindrical gel ZSGC was obtained due to hydrothermal treatment of the composites at 180 ?C.Finally,the mesoporous ZSGC with a diameter of 10-20 nm was obtained by vacuum freeze-drying method.The ZnSnO₃,ZS@C,ZS@C/r GO and ZSGC samples were characterized by XRD,BET,SEM,TEM and other methods,and their electrochemical properties were investigated by electrochemical test.Electrochemical test results show ed that: the first discharge/charge capacity of the hollow ZS@C/r GO materials is as high as 1984/1283 mA h g-1 and reached 1040/1027 mA h g-1 after 45 cycles at the current density of 0.1 A g-1;The average discharge/charge capacity can be retained 828/813 mA h g-1 when testing rate performance at a relatively large current density of 1.0 A g-1 after 80 cycles.The Li storage performance of the ternary composites is better than ZS@C and pure ZnSnO₃,and the superior Li storage performance can be attributed to the synergistic effect among these characteristics,including unique hollow structure of the material,graphene coating and carbon coating twice carbon modification.The primary discharge/charge capacity of the small-sized mesoporous ZSGC is as high as 2013/1057 mA h g-1,and reached 718/696 mA h g-1 after 100 cycles at the current density of 0.1 A g-1;The average discharge/charge capacity can still be retained 333/341 mA h g-1 when testing rate performance at a relatively large current density of 1.0 A g-1 after 80 cycles.The electrochemical properties of the composites are better than ZnSnO₃ obviously,because the presence of graphene not only increases the conductivity of the material,but also buffers the volume expansion of the material during charging and discharging process.