Preparation And Electrochemical Performance Of Fluorinated Carbon/Manganese Dioxide Composites

Lithium-fluorine carbon batteries(Li-CFx)are widely used in aerospace,military equipment,health care,wearable devices and other fields due to their advantages of high theoretical specific capacity(865 mAh/g),excellent high-low temperature performance,and long shelf life.However,the CFx,material shows a very low electronic conductivity and it's prone to polarization because of the strong covalency between C-F bond,which results in a faster decay of the battery performance.In order to solve this problem,on the one hand,a-MnO2 nanowires are combined with fluorocarbon to improve the rate performance of lithium-fluorine carbon cathode materials;on the other hand,based on this,carbon nanotubes(CNTs)and fluorocarbon/manganese dioxide materials are selected to combine together to improve the battery electrochemical performances.Then,the microstructure and electrochemical performances of the resulting composites are characterized.The effects of different mass ratios of a-MnO2 and CNTs on the electrochemical performance of the composites are investigated further.The main conclusions are as follows:(1)The CFx/MnO2 composites with the mass ratios(CFx:a-MnO2)of 9:1,8:2 and 7:3 are prepared by hydrothermal method.The microstructure and electrochemical performances of the composites are characterized.Results show that:the discharge rate of three composites can reach 4 C,comparing with CEx material only with 1 C,the rate performance is greatly improved;Among them,the composite material with the mass ratio of CFx,to MnO2 of 8:2 has the best discharge performance,it has the highest specific capacity when discharged at the same rate.(2)The CFx,/CNTs composites with the mass ratios(CFx:CNTs)of 95:5,90:10 and 85:15 are prepared by grinding.The microstructure and electrochemical performances of the composites are characterized.Conclusions are the following:The composites with the mass ratio of CFx,to CNTs of 90:10 exhibits the best discharge performance,the maximum discharge rate can reach 4 C;at 0.1 C discharge rate,the discharge specific capacity reaches 814.6 mAh/g,which is 17.1%higher than CEx material.(3)Combining the advantages of better rate performance of CFx/MnO2 and higher specific capacity of CFx/CNTs,CFx/MnO2/CNTs composite is prepared by hydrothermal method,which mass ratio of CFx,a-MnO2 to CNTs is 7:2:1.The microstructure,electrochemical performances and high-low temperature performance of the composites are characterized.Conclusions are as follows:when CFX/MnO2/CNTs composite is discharged from 0.1 C to 4 C,the composite material exhibits greater advantages in terms of rate performance and specific capacity;at 0.1 C discharge rate,the specific capacity of the composite reaches 742.4 mAh/g;at 4 C discharge rate,the specific capacity of the composite is still 351.9 mAh/g.At-30 ?,100?,and 0.1 C discharge rate,the specific capacities of the composite are 489.0 mAh/g and 1090.4 mAh/g,showing excellent high and low temperature characteristics.