Carbon-Based Composites For Cathode And Separator Coating Of Lithium Sulfur Battery

Elemental sulfur has high theoretical specific capacity(1672 mAh g^-1),high energy density(2567 Wh kg^-1),high natural abundance,low cost,and environmental friendliness,So lithium sulfur battery is considered to be one of the most promising next generation electrochemical energy storage device.However,the main drawbacks hindering Li-S battery practical application are followed:?1?Poor conductivity of sulfur and lithium polysulfide deteriorates batteries'rate performance;?2?The difference in the density of sulfur and lithium sulfide will lead to the expansion and contraction of the electrode volume during the charge-discharge process,resulting in the destruction and fall-off of the electrode material,which will seriously affect the cycling stability of the lithium-sulfur battery;?3?The lithium polysulfide is easily dissolved in the electrolyte during the charge-discharge process,thereby forming shuttle effect,which greatly reduces the utilization of active materials and the coulomb efficiency of the lithium-sulfur battery.In view of the above problems,this paper proposes the use of growing metal sulfides such as MoS₂ and MOF on graphene to prepare sulfur cathode composites and improve the electrochemical performance of lithium-sulfur batteries.On the other hand,a carbonization MOF modified membrane was prepared,and its mechanism of action is studied.The specific work is as follows:1.MoS₂ nanoflowers are successfully introduced into nitrogen-doped reduced graphene oxide by hydrothermal method to prepare three-dimensional composites with good conductivity and sulfur-fixing effect.Then the sulfur is loaded by melting method.The interior of the composite material is used for cathode of lithium-sulfur battery and exhibits excellent electrochemical performance.To explore the role of MoS₂ in composites,A series of composites with different MoS₂ content are prepared.2.NH₂-MIL-101?Al?crystals are grown on the surface of graphite oxide by hydrothermal method.There are abundant carboxyl groups on the surface of graphite oxide which can be combined with aluminum ions through coordination bonds.And GO@NH₂-MIL-101?Al?is obtained.Then the conductivity of the composite is enhanced by carbonization and Al₂O₃ is evenly distributed on the surface of graphite oxide.Thereby GO@NH₂-MIL-101?Al?-600 composite material is obtained.And the relationship between the structure and electrochemical properties of the composite is explored.3.NH₂-MIL-101?Al?metal organic framework material is successfully prepared by hydrothermal method,and the carbonized NH₂-MIL-101?Al?material is coated on the surface of the separator.The carbonized NH₂-MIL-101?Al?not only has rich pore structure which is conducive to the rapid transfer of lithium ions;but also has high electrical conductivity which can effectively reduce the battery's transmission impedance and improve the battery's rate performance.In addition,the uniform distribution of polar Al₂O₃ and nitrogen atoms in the composite material have a strong adsorption effect on LiPSs,which can effectively inhibit the side reaction caused by polysulfide shuttling.