Preparation Of Graphene And Its Application In Cathode Material Of Li-ion Battery

With the advancement of social modernization,cars and ships have been an indispensable part of people's daily life as a means of transportation.While traditional transportation tools facilitate life,they also lead to serious energy crisis and environmental pollution yet.The emergence of new energy vehicles and ships is based on new energy sources.The energy consumption has been changed and the environmental pollution problem has been solved due to their appearance.Among them,lithium-ion batteries are the power supply equipment for new transportation vehicles,and also the development direction of electric vehicles and ships.Lithium-ion batteries,which are power systems for new energy vehicles,are expected to have higher energy density,longer battery life and longer service life.The current anode materials for lithium ion batteries usually use graphite-based carbon materials,but the theoretical capacity of conventional graphite materials is low which cannot meet the requirements for energy density of lithium ion batteries in various fields.Herein,graphene has been used instead of graphite as a battery anode material and the effect of residual oxygen content on the performance of the battery during the reduction of graphene oxide materials was investigated.Further,the graphene was doped with nitrogen to examine its properties.On this basis,the graphene/nano-silicon composite anode material was prepared in order to improve the actual capacity of the battery while maintaining the cycle stability of the lithium ion battery.Firstly,the reduced graphene oxide was prepared by a redox method and subjected to high temperature treatment at different temperatures.Also,The effects of the oxygen content in graphene on the electrochemical properties of the materials were investigated and the changes of oxygen content were characterized by SEM and XPS.The results showed that the LrGO sheet was thinner and the interlayer structure was more loose,which is more conducive to the transportation and movement of lithium ions.At the same time,the specific capacity of HrGO is 394 mAh/g,and the specific capacity of LrGO is 452 mAh/g,indicating that the reduction of oxygen content has a positive effect on improving electrochemical performance.Secondly,nitrogen-doped graphene was prepared by using urea as a nitrogen source,and was reduced at 600? and 1000? under argon gas as a shielding gas,respectively.At the same time,this paper has explored the effect of nitrogen doping content on the electrochemical performance of the prepared nitrogen-doped graphene.The results showed that the nitrogen source was decomposed,leading to the reduce of nitrogen content of materials.Also,the internal defects of graphene was reduced,and the electrochemical performance was poor.The nitrogen-doped graphene treated at 600? could be seen that the sheet space became larger,and the Raman results showed that it had more defects,which was more conducive to the deintercalation and movement of lithium ions.The discharge specific capacities of N-rGO-600 and N-rGO-1000 are 826 mAh/g and 636 mAh/g,respectively.Furthermore,nano-Si/rGO composite anode materials with different ratio of nano-silicon to graphene have been prepared by loading nano-silicon onto graphene.The results showed that the nano-silicon particles were uniformly distributed in the translucent graphene sheet structure.Corresponding to the reaction mass ratio of nano-silicon to graphene is 1:0.3,1:0.4,1:0.5,the specific discharge capacity of the test sample is 1475 mAh/g,2261 mAh/g,1936 mAh/g.It can be concluded that specific capacity contrast graphene have improved significantly,but the first coulombic efficiency was still low,pending further research and improvement.