Modification And Application Of Fluorinated Carbon Cathode Materials For High-Performance Lithium Primary Battery

Lithium/fluorinated carbon（Li/CF_x）battery is widely used in electronic equipment,medical equipment,aerospace and other fields due to its advantages such as the high energy density（2180 Wh/kg）,stable discharge platform,wide working temperature range and high safety etc.The discharge specific capacity of Li/CF_x battery is positively associated with fluorine content of cathode CF_x materials.However,high fluorine content will lead to poor electronic and ionic conductivity of CF_x materials,resulting in serious electrode polarization and degradation in rate performance.Then the application of batteries is limited.In order to get Li/CF_x batteries with both high discharge specific capacity and high rate performance,CF_xmaterials was studied in this thesis from two aspects,namely,the plasma post-modification of CF_x materials and plasma enhanced fluorination method.In the aspect of CF_xmaterials plasma modification,high-density nitrogen and hydrogen plasma were used to modify commercial fluorinated carbon materials.The highly fluorinated layer of CF_x materials was chemically thinned by plasma,and the surface carbon content of material was increased.Furthermore,the amount of semi-ion carbon-fluorine bond with high electrochemical activity was increased,and the bond binding energy of carbon-fluorine bond was reduced.Therefore,the discharge voltage platform and rate performance of battery were simultaneously improved at 4 C current density.In the aspect of plasma enhanced fluorination method,plasma fluorinated graphite-like materials were prepared by plasma enhanced fluorination method using graphite,expanded graphite and graphene as carbon source,CF₄gas as fluorine source.The graphite material with small specific surface area and mostly lamellar structure had a lower fluoride content,smaller variation of specific surface area and higher C-F binding energy after fluorination.However,the expanded graphite and graphene with larger specific surface area and fewer lamellas had a higher fluoride content,larger variation of specific surface area,and lower C-F binding energy after fluorination.Acted as the cathode electrode of the primary battery,plasma fluorinated graphene shown 890.9 m Ah/g specific capacity（up to 1.5 V）at 0.1 A/g,and a 2.5 V discharge voltage platform.Moreover,a high specific capacity of 838.3 m Ah/g and 2.1 V voltage platform were obtained at 10 A/g,with a capacity attenuation just only 5.9%.In addition,inexpensive expanded graphite was fluorinated by plasma enhanced fluorination method,and the product displayed 877.7 m Ah/g specific capacity and 2.6 V voltage platform.What’s more,the fluorinated expanded graphite exhibited 771.4 m Ah/g specific capacity and 2.6 V voltage platform in a pouch-type battery.At last,the low temperature performance of fluorinated expanded graphite was evaluated,and its coin cell exhibited a specific capacity of 617.2 m Ah/g（0.1 A/g）at-20℃.In summary,on the basis of plasma technology,post-modification optimization and a new fluorination method for CF_x materials were studied in this thesis.CF_x cathode materials with both high energy density and rate performance were obtained,providing a new idea for the preparation of high performance CF_x cathode materials.