| Currently,Lithium graphite fluoride battery has the highest theoretical capacity in primary batteries.The theoretical capacity of Li-graphite fluoride battery is up to 865mAh/g.Lithium graphite fluoride battery also has excellent high and low temperature performance,the stable working voltage,no harm to the environment,high security,the low self-discharge and other obvious advantages,so its has important applications in aerospace,military,medical and everyday life.However,due to the strong covalent carbon-fluorine bond,which leads to poor conductivity of graphite fluoride materials.Hence,it's hard to achieve the desired discharge performance.In order to improve the electrical conductivity of CF_x materials and improve the electrochemical performance of the battery,such as discharge rate and discharge capacity,three kinds of organic carbon sources such as citric acid,sucrose and polyethylene glycol were selected in this paper.Each group of organic carbon sources selected four groups of different coating ratios for experiments.These organic carbon sources were prepared by hydrothermal method and coated on the surface of graphite fluoride materials,Twelve groups of CF_x@C cathode materials were obtained.Through the characterization of the obtained materials such as microstructure and electrochemical properties,we get the best carbon source and the corresponding coating ratio finally.The main contents and conclusions of this paper are as follows:(1)Citric acid was selected as the carbon source.CF_x@C materials were prepared by using four groups of fluorinated carbon materials with different mass ratios,marked as CF_x20:1,CF_x10:1,CF_x20:3,CF_x5:1.The morphology structure,composition of CF_x@C materials and the thickness of the carbon coating layer were characterized by scanning electron microscopy,X-ray diffraction and transmission electron microscopy.The electrochemical properties of the composites were measured by constant current discharge,rate discharge and AC impedance.The results show that the group CF_x20:1 has the better electrochemical performance in the four different coating ratios,and the corresponding carbon coating thickness is about 130 nm,the maximum discharge rate is up to 4C,discharge capacity is about 850 mAh/g under 0.1 C magnification;By means of transmission electron microscopy,the thickness of the coating layer is increased and the uniformity of the coating layer is deteriorated as the carbon content increases.(2)Select sucrose as carbon source,CF_x@C materials were prepared by using four groups of fluorinated carbon materials with different mass ratios,marked as CF_x20:1,CF_x10:1,CF_x20:3,CF_x5:1.Through the characterization of the obtained materials,such as microstructure and electrochemical properties,we get the following conclusions: in the four groups of different coating ratios,group CF_x20:1 has better electrochemical performance,and the corresponding carbon coating thickness is about 150 nm,the specific capacity of the discharge is about 841 m Ah/g under 0.1 C magnification.Through the transmission electron microscopy analysis,the coating thickness increased and the uniformity of the coating layer became worse with the increase of carbon in the coating ratio.(3)Polyethylene glycol was selected as the carbon source,CF_x@C materials were prepared by using four groups of fluorinated carbon materials with different mass ratios,marked as CF_x20:1,CF_x10:1,CF_x20:3,CF_x5:1.The results show that the group CF_x20:1has better electrochemical performance and the corresponding carbon coating thickness is about 170 nm in the four different coating ratios,the discharge capacity is 849 mAh/g under 0.1 C magnification;by transmission electron microscopy analysis,the coating uniformity of group CF_x5: 1 is poor.In summary,carbon materials were successfully coated on CF_x surface by hydrothermal method with different carbon sources,the electrochemical properties of CF_x materials were improved in this paper.Comparing magnification performance and discharge specific capacity of batteries,we found that the effect of CF_x@C material choosen citric acid as carbon source was the best,followed by sucrose,and finally polyethylene glycol.The above experimental study can provide relevant data for development and commercialization of lithium graphite fluoride battery industry in China. |
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