Synthesis And Li-Storage Performance Of Tin Dioxide And Carbon Composites

Current lithium ion batteries（LIBs）are superior to conventional rechargeable batteries owing to their high energy density,but they cannot meet the ever increasing demands of portable electronics and electric vehicles（EVs）.For the case of the anode,transition metal oxide-based conversion materials with high capacity have been investigated extensively in order to replace commercially available graphite anodes,which are limited by a low theoretical capacity of 372 mAh g^-1.Among them,tin dioxide（SnO₂）is considered a promising candidate because of its high theoretical capacity of 783 mAh g^-1,natural abundance,and environmental benignity.However,SnO₂ suffers from the typical bottlenecks of conversion-based materials such as poor rate and cyclic capabilities associated with the low electrical conductivity and large volume expansion（～300%）during the charging/discharging processes,respectively.The formation of the nanostructure is an attractive strategy to improve the electrochemical performances of high-capacity active materials owing to the large accessible area,shortened diffusion length and effective stress buffering.In particular,carbon nanotubes（CNTs）have been used to support or confine the high capacity active materials owing to their high conductivity,large surface area,and impressive electrochemical and mechanical stabilities for LIB applications.Therefore,this paper focuses on the composite modification of tin-based nanomaterials and conductive carbon nanomaterials,as well as the controllable construction of their structure and morphology,so as to explore the application of tin-based nanomaterials in the anode materials of lithium ion batteries and the electrochemical lithium storage properties,and further explore the modification mechanism.The main research work includes:1.SnO₂ fibers and SnO₂-C fibers with grid structure were prepared by electrostatic spinning technology through controlling precursor concentration and calcining conditions.Various physical and chemical properties show that the synthesized SnO₂ fibers and SnO₂-C fibers have a special three-dimensional grid structure.Many material gaps can effectively buffer the violent volume expansion of SnO₂ during charging and discharging.When the current density is 0.4,0.8,1.6,2.4and 4 A g^-1,10 times of constant current charge and discharge,the capacity is 1 372,832,685,642 and 599 mAh g^-1,respectively.When the current density drops to 0.4 A g^-1,the discharge capacity can rise back to 1 113 mAh g^-1.at the current density of 1.6A g^-1,the discharge capacity of the fibers after 200 times of constant current charging-discharging was retained at 613 mAh g^-1,and the coulombic efficiency was nearly 100%,with good multiplier performance,cycling stability and capacity restoring force.2.The electrostatic spinning and electrostatic spray technology be use to preparation of the three kinds of composite fiber film electrodes.at the current density of 0.4,0.8,1.6,2.4 and 4 A g^-1,the discharge capacity of electrode after 10 cycles was 797,659,626,534 and 468 mAh g^-1,respectively.When the current density dropped to 0.4 A g^-1,the discharge capacity can still reached 709 mAh g^-1.Even at high current density of 4 A g^-1,after 540 cycles the electrode capacity was still maintained at 457 mAh g^-1,and the coulomb efficiency was nearly 100%,showing a good capacity improvement and the growth of multiplier performance.3.Using CNTs as the container,SnO₂/CNTs lithium ion battery anode materials were prepared by filling the tin ions into the graphitized CNTs cavity by one-step wet method.Graphited treatment of CNTs at a high temperature（2400²800℃）,the higher the temperature,the less hydrophilic functional groups outside of CNTs,and control of the filling time,makeing the SnO₂ NPs filling into the CNTs cavity as possible.The filling time is the most important factor of the weight percentage of SnO₂ in composite materials.The longer of the react time,the higher levels of SnO₂of the composite.S-gCNTs-28t-100h show a good performance in electrochemical properties.When at a current density of 0.4 mA g^-1,the discharge capacity of 631mAh g^-1which is very high stable.Even at the high current density of 8 A g^-1,its discharge capacity can keep 308 mAh g^-1.In addition,S-gCNTs-28t-100h composite electrode also has a long cycle life.After 620 cycles,it can still maintain the reversible discharge capacity of 383 mAh g^-1under the current density is 4 A g^-1.