The Preparation And Treatment Of Tin-based Composites And The Research Of Its Performance About Sodium/lithium Storage

With the rise of portable electronic equipment and electric vehicles, people propose higher energy storage requirements for storage equipment. Lithium-ion battery has draw great attention because of its advantage of large capacity, high operating voltage, low pollution and other characteristics. However, the theoretical capacity of anode materials which have been put into commercial use is still difficult to meet the requirements of electrical appliances, although the carbon materials could deliver relatively high specific capacity 372 mA h/g. Hence silicon-based compounds (including Si, SiC),Tin-based compounds (including SnS2/SnSb), transition metal oxides (including FexOy,CoOx) etc have draw a lot of attention for their high specific capacities. But the novel anode materials will suffer pulverization because of the huge volume change during the lithium intercalation/deintercalation process, which directly result in poor cycling stability. The carbon materials have raised lots of concerns because it could effectively alleviate volume expansion during the lithium intercalation process. With the rise of wearable devices, the mechanical properties of battery have been put forward higher requirement. Electrode is a key component of the flexible battery. Carbon fibers and graphene with excellent electrical conductivity and mechanical properties have been concerned by expert as the electrode materials.The present thesis will investigate the Tin-based polymer fibers from many aspects such as synthesis mechanism, structural control, electrochemical properties regulation and so on.(1) Tin-based anode materials have draw much attention because of its excellent specific capacity and conductivity, but suffered from volume expansion. In this chapter, we designed a structure called Sn_xSb-graphene-carbon porous multichannel nanofiber mats with excellent lithium storage properties and mechanical properties for Tin-based anode materials. The outstanding performance of lithium storage was shown as followed:(1) it showed remarkable discharge specific capacity and good cycle performance, it could provide a discharge capacity of 729 mA h/g at 100 mA/g current densities after 500 cycles. (2) Sn_xSb-graphene-carbon porous multichannel nanofiber mats with excellent lithium intercalation/deintercalation performance showed good rate capacity, it could keep reversible capacities of 639,567,475,427, and 381 mA h/g at current densities of 0.1,0.2,0.5,1,2 A/g, respectively. The initial coulombic efficiency is 60%. (3) Sn_xSb-graphene-carbon porous multichannel nanofiber mats showed an excellent mechanical property, it smoothly passed the bending test without any damage.(2) Lithium-ion batteries have been widely used in electronics, transportation and other industries because of its advantages of high energy density, high output voltage and good cycle performance, But the shortage and the uneven distribution of lithium resource limited the development of lithium-ion battery. Because of the advantages of cost, the sodium-ion battery has the potential to replace the lithium-ion battery for large scale application. We have prepared Sn_xSb-graphene carbon multi-channel nanofiber mats as the negative electrode of sodium ion battery. The composite could deliver 630 mA h/g specific capacity at the current density of 100 mA/g within the first cycle. The reversible capacity is 300 mA h/g after 70th cycle. It could remain 150 mA h/g at the current density of 2 A/g. The excellent cycle performance could be attributed to the carbon fiber network could provide good conductivity, the structure of porous carbon fiber could furnish a suitable space for expansion, and the existence of graphene could strengthen the mechanical properties and electrical conductivity of carbon fibers.(3) Graphene is a two dimensional carbon material, has recently been considered as a kind of advanced lithium-ion battery electrode materials because of its superior conductivity, specific surface area, very thin thickness, flexibility and chemical stability. Graphene can improve the mechanical properties of carbon fibers and enhance the conductivity of carbon fiber. In this chapter we prepared Sn_xSb-graphene carbon multi-channel nanofiber mats containing various content of graphene. We found when the content of graphene is 0.019%, the electrochemical properties is the best. The initial coulombic efficiency is 73%. The reversible capacity is 617 mA h/g at the current density of 100 mA h/g after 300th cycles. It could keep reversible capacities of 609,550,480,420, and 369 mA h/g at current densities of 0.1,0.2,0.5, 1,2 A/g, respectively, showing remarkable rate performance. Excessive graphene is bad for cycle performance because graphene oxide could accelerate the graphitization of amorphous carbon but the compatibility between graphitic carbon and metal particle is so poor, which would cause the precipitation of particles and break the structure. This phenomenon provides a reliable reference for the future application of graphene to modify the electrode materials.