Preparation Of Graphene/Phthalocyanine Composites And Their Applications As Cathodes For Lithium Sulfur Batteries

Lithium-sulfur batteries are considered to be the most promising new secondary batteries because of their high theoretical specific capacity,environmental friendliness and low cost.However,the development of lithium-sulfur batteries is greatly limited by the problems such as "shuttle effect",volume expansion and poor conductivity of sulfur and its products.In this paper,the cathode materials for lithium-sulfur batteries were designed,and the lithium-sulfur batteries with better electrochemical performance were obtained by adding catalysts.Graphene oxide was reduced into graphene by hydrothermal method,graphene and multi-walled carbon nanotubes were compounded by oil bath heating method.The results showed that the specific discharge capacity in the first cycle of rGO-S was 733 mAh·g-1.After 300 cycles,the capacity remained 437 mAh·g-1 and the capacity decay rate was 0.172%/cycle.The specific discharge capacity in first cycle of GS-MWCNTS was 756 mAh·g-1,which was not significantly improved compared with rGO-S,but the cycle performance was much better than that of lithium-sulfur batteries with rGOS as cathode material.After 100 cycles,the capacity was maintained at 517 mAh·g-1,and the capacity decay rate was only 0.126%/cycle.Using 4-nitrophthalic anhydride as precursor,three kinds of metal tetraaminophthalocyanine complexes were synthesized by template reaction method,namely manganese tetraaminophthalocyanine,ferrous tetraaminophthalocyanine and nickel tetraaminophthalocyanine.The reduction of graphene oxide and the addition of tetraaminophthalocyanine complexes were realized by hydrothermal method.The morphology and phase equivalence of the cathode materials were characterized and analyzed by SEM,TEM,FTIR,XRD and XPS and the effects of different kinds and contents of phthalocyanines on the electrochemical performance of lithium sulfur batteries were studied.The results showed that nickel tetraaminophthalocyanine had the best catalytic effect on the electrochemical reaction of lithium sulfur batteries.When the mass ratio of GO to TaPcNi was 2:1,the discharge capacity in first cycle can reach 1050 mAh·g-1 at 0.2C rate,and the discharge capacity remained 774 mAh·g-1 after 100 cycles at 0.5C rate.Ferrous tetraaminophthalocyanine and nickel tetraaminophthalocyanine were synthesized with graphene by high temperature sintering method.The materials were characterized and analyzed by SEM,TEM,FTIR,XRD and XPS.In order to explore the electrochemical properties of the materials,galvanostatic charge/discharge tests were carried out.The specific capacities in first cycle discharge of lithium-sulfur batteries with rGO/TaPcFe(?)/S-700 and rGO/TaPcNi/S-700 cathode were 1104 mAh·g-1 and 1123 mAh·g-1,respectively,which were 50.6%and 53.2%higher than that of rGO-S cathode,and they also showed good rate performance and cycle performance.