Preparation And Electrochemical Performance Of Stannic Oxide/graphene Composites

The advantages of high capacity and low operating potential made Sn O₂ very potential to be used as an anode material,but huge volume changes during cycling（>250%）and poor conductivity defects hindered its practical application.In this paper,stannic chloride was used as a source of tin;cobalt chloride and urea were used as cobalt source and nitrogen source,respectively;ethylene glycol was used to replace deionized water to successfully prepare Co,N co-doped amorphous tin dioxide through a pot of solvent hot method.On the basis of it,graphene was introduced to prepare Co,N co-doping amorphous tin dioxide/graphene composites.And a novel double-carbon structure was designed to reduce the amount of graphene in composites.The main research content and conclusions of this thesis are as follows:（1）Co,N co-doping reduced the band gap of Sn O₂ to improve its conductivity;increased the cell size,which was conductive to lithium ion inserting and releasing;when Sn O₂ was combined with graphene,made graphene was N-doped simultaneously to promote Sn O₂ was uniformly anchor on the graphene sheet.Amorphous Sn O₂ had abundant dangling bonds that could bond with Li⁺to significantly improve the specific capacities,and its isotropy,and long-range disorder also contributed to the insertion and release of lithium ions,and relieved the mechanical stress caused by volume expansion.Co,N co-doped amorphous Sn O₂ presented uniformly distributed nanoscale particles in morphology,which facilitated to full contact with the electrolyte to promote reaction,shorten the transmission path of lithium ions and electrons and could better released the stress caused by volume change.（2）The Sn O₂ was combined with graphene,which could greatly improve electrochemical properties of Sn O₂ with the synergistic effect of amorphous structure and Co and N co-doping.After 400 cycles at 0.5 A g^-1 current density,the prepared（Co,N）-a-Sn O₂/GR product still provided a discharge specific capacity of 1056.8 m Ah g^-1,and the reversible capacity retention rate was up to 89%.（3）Carbon microspheres were introduced into the Sn O₂/graphene composite,which greatly reduced the preparation cost of the composite material under the premise of ensuring good electrochemical proformance of the CMS@Sn O₂/GR composite.Using abundant free space in the carbon microspheres as a cushioning area for volume expansion of Sn O₂ particles,and to form a double-carbon protection structure with the outside graphene.45 figures,5 tables and 103 references...