Improving The Anode Performance Of SnO₂and Its Mechanistic Study

The commercialization of lithium-ion battery anode materials are carbon materials, such as graphite, mesophase microspheres carbon, etc. Their specific capacity is low, and the structure is not stable, can’t afford to large current charge and discharge. So although lithium ion battery materials nowadays has basically meet the need of portable facility, but high power lithium ion battery materials for electric vehicle still need us to improve and development.Tin oxide (SnO2) as part of the metal oxide, compared to graphite (372mAh/g) has more than twice the specific capacity (782mAh/g), is one of a promised power lithium ion battery cathode material, but metal oxide as lithium ion battery anode materials have a common defect:poor cycling performance, the short cycle life of metal oxide materials is caused by volume change in the process of charging and discharging (300%inflation), the repeated volume change will cause the active material pulverization and become insulate with the conductive substrate. In the state of large current charge, the crash will happen faster. To overcome this problem is currently the main focus of scientific researchers. The electrical conductivity of metal oxide is insufficient, which affecting its high rate charge and discharge performance. People tried many ways to overcome these drawbacks, such as produce hollow SnO2nanoparticles, coating amorphous carbon buffer layer on the nanoscale SnO2sufface, SnO2quantum dots, these methods increase the porosity of SnO2to accommodate the volume expansion effect, and improved the traditional SnO2specific surface area, shortened the lithium ion diffusion path, improve the electrical conductivity. But these methods have not perfect to solve this problem, SnO2cycle life still within50laps.In this paper the first chapter describes the current status of lithium ion battery and the technical challenges we face, and then briefly introduces the working principle of lithium ion batteries and common materials used in lithium ion batteries.The second part of the chapter briefly described a buckle type lithium battery, introduced the production methods of work electrode, assemble buckle type lithium ion battery, and at last, we produced graphite as the anode material and assemble buckle type lithium ion battery, discuss the anode performance of graphite.The third chapter first use a one step hydrothermal method synthesized nano SnO2@C composite, SnO2@C has characterized by the SEM、TEM and Raman spectra, thermogravimetric analysis(TGA), etc. TGA shows SnO2@C is composed of33%(quality content) amorphous carbon and67%SnO2. SnO2h nano particles can be clearly seen after SnO2@C annealing in450℃for4hours. SnO2@C as active material made into electrode of lithium ion button battery to test anode performance, constant current charge and discharge profile, cyclic voltammetry, ac impedance spectra has been performed on SnO2@C electrode, we can see the anode performance of SnO2@C is similar to other literature use hydrothermal method to prepare SnO2@C. However when use sodium alginate as electrode binder, SnO2@C showed exciting performance improvement, not only the first discharge capacity reached700mAh/g, capacity retention after50laps still has600mAh/g specific capacity. From the ac impedance spectrum we can see the main reason of the improvement is ascribed to sodium alginate electrodes has much faster li-ion conductivity compared to traditional PVDF binder electrode. In conclusion, high lithium ion diffusion coefficient, lower charge transfer resistance, And the sodium alginate film itself has high porosity, which can overcome the volume expansion of SnO2, these points resulting in the anode performance improve.