Fabrication And Electrochemical Performances Of Tin-Based/Carbon Composite Materials

Tin-based materials, such as tin oxide and tin anode material, have attracted much attention and intensive study because of their high specific capacity, varied morphology and abundant source. However, the cycle and rate performance of Tin-based anode materials are poor which caused by the huge volume changes and poor electroconductivity, respectively, which prevent their widespread use. To solve the problem of large volume changes, many researches were focused on introducing void space for Tin-based materials to buffer the volume expansion, such as hollow sphere, nanobox, and nanotube. N-doped carbon can effectively improve the electroconductivity of metal and metallic oxide due to its high ionic conductivity, better chemical stability and high mechanical strength. The combination of N-doped carbon materials is considered to be an effective strategy to enhance the electrical conductivity, which can not only improve the electroconductivity but also accommodate the volume changes of Tin-based materials during cycles. By integrating the both design principles mentioned above, we designed tin and N-doped carbon composite material, and tin dioxide and N-doped carbon composite material, respectively. The specific research works are as follows:1. A yolk-shell N-doped carbon coated SnO2sphere composite with well-designed void space between the SnO2shell and the N-doped carbon shell was fabricated by template synthesis. The void space of SnO2@void@NC between the yolk and the shell can serve as a buffer phase to overcome the large volume changes of the core material during Li+insertion/extraction, and the shell can act as a buffer layer. Meanwhile, the core of the yolk-shell structured powders will improve the energy density by increasing the weight fraction of the electrochemically active component. SnO2@void@NC composite showed better cycling performance and high specific capacity when acted as anode of lithium-ion battery. It exhibited a reversible lithium storage capacity of973mAh·g-1after100cycles at a current density of200mA·g-1between0.01-3V and an enhanced cyclability. This material also showed excellent rate performance, capacity retention ratio were kept at81.27%and58.31%when increased the current density to500mA·g-1and1A·g-1.2. We introduce Sn into the N-doped mesoporous hollow carbon sphere (NMHCS) by using confined synthesis method and the obtained material is named Sn@NMHCS. The method of this experiment is novel and the condition is controllable. The N-doped carbon in Sn@NMHCS composite can reserve room for Sn and keep a good contact with current collector, and eventually improve material cycle and rate performance. The results showed that Sn@T-NMHCS exhibited a reversible lithium storage capacity of565mAh·g-1at a current density of200mA·g-1after100cycles.