The Preparation And Research On Electrochemical Performance Of LiFePO₄-V₂O₅-graphene Cathode Material For Lithium Ion Battery

With increasing environmental pollution and consumption of fossil energy, it is urgent for the development of new clean energy and energy storage devices.Among all of these energy storage devices, quite a lot of attention has been paid to lithium-ion batteries, which are environmental friendly and highly efficient, and they have been successfully commercialized.Among them, LiFePO₄ batteries have a broad application prospect due to its excellent safety performance and low price. However, with the development of electric vehicles and portable electronic devices, various properties of LiFePO₄ electrode, such as low specific capacity and discharge capacity, poor dynamics and other performance issues, become a major factor limiting its development,cycle life and rate capability,which require a substantial increase.Based on this,the article needs to prepare LiFePO₄ nanoparticles in order to shorten the ion diffusion path embarking from reducing the size of the material. and through the self-assembly among LiFePO₄ nanoparticles,the graphene with high conductivity and V₂O₅ with high specific capacity,this system can realize hybridization of ternary heterogeneous nanostructures, and then improve the conductivity and specific capacity.During the preparation of LiFePO₄ nanoparticles through the systematic study on the key parameters of the experiment, morphology of synthesized samples was more uniform and dispersed in those experimental conditions,that is,three kinds of raw materials come in a molar ratio Fe:PO₄:Li=1:1:2.5,and the reaction temperature is200 ?,and then the reaction time is 10 h.By studying the electrochemical performance of CV,EIS and the charge-discharge.When the current density are 0.05 C and 0.1 C, the discharge specific capacity of after cycling for 100 times can reach 74.8 mAhg^-1 and30.2 mAhg^-1 respectively.During the assembly process between LiFePO₄ nanoparticles and graphene sheets,the experimental conditions for the best assembly effect are ultrasonic for 8 h under a power for 140 W,and the mass ratio of the raw materials is 9:1.Its structure was characterized by these testing means including SEM,TEM,EDS and so on,and its electrochemical properties were compared with the sample of pure LiFePO₄,it is clear that the rate and cycle performance of the former has been greatly improved.When the current density are 0.05 C and 0.1 C, the discharge specific capacity of after cycling for100 laps can reach 129.6 mAhg^-1 and 125.8 mAhg^-1 respectively.Simultaneously when the current density are 2 C and 5 C, the discharge specific capacity of after cycling for100 laps can still reach 119.9 mAhg^-1 and 97.8 mAhg^-1 respectively.Therefore stable electrochemical performance at a large current can be improved.In addition, when thesample is tested at a current density including 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 5 C, 10 C for rate performance and the test system cycles 16 times respectively in each cycle,the discharge specific capacity of after cycling at a current density for 10 C can reach 82.2mAhg^-1.In the end, it is the assembly process among LiFePO₄ nanoparticles, V₂O₅ nanowires and graphene sheet.It also can be concluded that the experimental condition for the best assembly effect is ultrasonic for 8 h under the power for 140 W, and then we studied three kinds of different mass ratio in that experiment condition. It can be seen that when the mass ratio of the samples is 6:3:1,we can get better performance by the contrast of phase and the electrochemical properties, and when the current density are 2 C and 5 C, the discharge specific capacity of after cycle for 100 laps is 139.9 mAhg^-1 and 133.3 mAhg^-1 respectively. When the sample is tested at a current density including 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C, 5 C, 10 C for rate performance and the test system cycles 16 times respectively in each cycle, the discharge specific capacity of after cycling at a current density for 10 C can reach 97.9 mAhg^-1.