Application Of MXene-based Surface Modified Materials In Lithium-sulfur Batterie

The rapid development of new energy vehicles and the rapid popularization of portable electronic devices have greatly promoted the research on energy storage devices,which increases more demand for high energy density batteries.Compared to mature lithium ion batteries,lithium sulfur batteries have noticeable theoretical specific capacity and energy density advantages.However,while the ideal performance is outstanding,lithium sulfur batteries also face great challenges in practical applications.The poor conductivity of elemental sulfur and discharge products and large density difference between them lead to slow electron migration rates and poor electrochemical stability.The migration and reductive oxidation of reaction intermediates between positive and negative electrodes,known as the"shuttle effect",affects the long-term and efficient use of active substances,resulting in capacity degration,reduced Coulombic efficiency and poor rate performance of the battery.MXene,as a new two-dimensional material,has excellent electrical conductivity,rich surface polar functional groups（-OH,-O,-F,etc.）,and excellent mechanical flexibility,making it potentially an ideal sulfur carrier.Doping or oxidation treatment on the surface of materials can effectively improve the polar surface properties of materials.In this paper,urea was used as a nitrogen source to modify the surface of MXene material,which effectively enhancing the adsorption and catalytic conversion of lithium polysulfide,and achieving enhanced energy storage characteristics of lithium sulfur batteries.In addition,a Ti O₂/Ti₃C₂ heterojunction is created on the surface of the material through simple oxidation treatment,significantly improves the electrochemical performance of the battery through synergistic effects.The MAX phase titanium aluminum carbide precursor was etched into MXene nanosheets with high conductivity,strong polarity,and excellent mechanical properties by chemical etching.The surface of MXene nanosheets was doped with nitrogen using electrostatic adsorption self-assembly and thermal annealing methods.The adsorption and catalytic mechanisms of N-Doped Ti₃C₂ for lithium polysulfide were analyzed using lithium polysulfide adsorption experiments,material characterization,and performance testing.N-Doped Ti₃C₂ nanosheets can effectively anchor and promote the transformation of lithium polysulfide,alleviate the severe shuttle effect to some extent,and accelerate the transfer of interfacial charges.The S/N-Doped Ti₃C₂ composite material was prepared by melt diffusion method and used as a positive electrode to assemble the battery.The initial discharge specific capacity of the battery was 1160 m Ah g^-1 at a rate of 0.2 C.When the current rises to 2 C,it also had an initial capacity of 676.4m Ah g^-1.Using simple surface oxidation to produce anatase phase Ti O₂ crystals on the surface of MXene nanosheets,a Ti O₂/Ti₃C₂ heterojunction was constructed.The comprehensive effect of the rich functional groups on the surface of MXene material and the naturally generated Schottky barrier under the heterojunction enhances the transport of electrons in the material and enhances the utilization rate of active substances.The material after sulfur melting is used as the positive electrode and assembled into a battery.The battery has an initial capacity of 1158 m Ah g^-1 at a rate of0.2 C,and remains at 748.8 m Ah g^-1 after 300 cycles.The first discharge specific capacity of the battery at 1 C rate is 782.9 m Ah g^-1,with a capacity decay rate of 0.106%per cycle when undergoes 300 cycles.