Research On The Graphene Based Cathode Materials Of Lithium Sulfur Batteries

Lithium sulfur battery enjoys a lot of advantages such as high energy density,low cost,environmental friendly and rich resource in the nature.However,the application of lithium sulfur battery are compromised by lots of problems which include the low utilization of sulfur,poor cycle stability and poor rate performance.Based on the existing research and the work of our laboratory,in order to improve the conductivity of the materials four kinds of porous carbon are used to prepared carbon-sulfur composite materials in this article.Moreover,In order to suppress the volume expansion of the S cathode during charge and discharge,the titanium dioxide and graphene were mixed coated on the surface of S.In addition,a new method for the preparation of lithium sulfur self-supporting electrode was studied.Finaly,the article also studied doping metal elements to S cathode so that it could reduce the polysulfide shuttle effect and analyze their electrochemical performances.In this paper,we first fabricated the composite material using porous carbon,CNT,carbonized polyaniline,Super P and activated carbon to coat S.CNT is a one-dimensional carbon with excellent sulfur-bearing properties.CNTS have the discharge capacity of 870.1 mAh/g under the first 0.1C discharge,the materials have the discharge capacity of 409.2 mAh/g after 100 cycles of 0.1C.The three-dimensional structure of activated carbon is stable and the pore size is large,thus it has excellent sulfur-bearing properties.ACS have the discharge capacity of 870.1 mAh/g under the first 0.1 C discharge,the materials have the discharge capacity of 248.8 mAh/g after 100 cycles of 0.1 C.In this paper,we prepared a new self-supporting graphene-based sulfur-containing material.The graphene-based sulfur-containing materials contains good mechanical properties.The results show that the reduction environment of strong acid and alkali is not favorable for graphene-coated sulfur.The results show that the graphene-based sulfur-containing materials in the reduction environment at strong acid and alkali is unuseful for graphene to coat sulfur.CNT doped in graphene can significantly increase the porosity of the graphene-based material.The use of hydrogen peroxide to make graphite oxide can increase the porosity of the material because the holes are beneficial for the contact of the active material with the electrolyte.The electrochemical performance of the self-supporting sulfur-containing thin film doped with CNT is the best,which was reduced in the pure water,the materials have the discharge capacity of 621 mAh/g under the first 0.1 C discharge,the materials have the discharge capacity of 381 mAh/g after 100 cycles of 0.1 C.In this work,the core-shell structure of titanium dioxide/graphene double-layer coated sulfur was studied.When the mass ratio of S to TiO2 is 8: 2,the electrochemical performance of TiO2/S is the best,the materials have the discharge capacity of 900.5 mAh/g under the first 0.1 C discharge,the materials have the discharge capacity of 248.8 mAh/g after 100 cycles of 0.1 C.When the mass ratio of S to TiO2 and rGO is 8: 2: 1,the electrochemical performance of r GO@TiO2@S is the best,the materials have the discharge capacity of 969.1 mAh/g under the first 0.1 C discharge,the materials have the discharge capacity of 558.6 mAh/g after 100 cycles of 0.1 C.TiO2 decrease the effect of anti-volume expansion is significantly,and limit polysulfide shuttle significantly.The coating of graphene can improve the electrochemical properties of the composites.Such as conductivity,and limiting polysulfide shuttle significantly,graphene and titanium dioxide coated coordination effect,making the electrochemical properties of the material is improved.In this paper,the effects of graphene oxide and its doping and pore modification was studied,which coat sulfur by hydrothermal process.The properties of the materials doped CNT,PVP and metal elements in hydrothermal process were studied.The performance of aerated grafted sulfuricides with porous graphene also were studied.The results show that CNT can increase the porosity of the material,and the doping of PVP can promote the stability of the electrode structure.After using hydrogen peroxide,the material has a better ion channel.The porous graphene coated sulfur have the discharge capacity of 898.3 mAh/g under the first 0.1 C discharge,the materials have the discharge capacity of 490.3 mAh/g after 100 cycles of 0.1 C,which was doped CNT.The Ni,Co and Fe metal elements are doped in graphene,the metal elements are chemically adsorbed with polysulfide,which can limit the shuttle effect of polysulfide and improve the electrochemical performance of the material.the materials doped Fe have the discharge capacity of 1160.5 mAh/g under the first 0.1 C discharge,the materials have the discharge capacity of 381 mAh/g after 394.8 cycles of 0.1 C.