Application Of Complex Molybdenum-based Compound And Carbon Material In Lithium Sulfur Batteries

In response to the ecological and environmental problems caused by the excessive use of fossil fuels,countries around the world have increased their investment in the development of new energy technologies.Advanced energy storage systems play a vital role in the development of new energy technologies.Lithium-sulfur batteries have a high theoretical energy density(2600 Wh kg^-1),and they are one of the more promising energy storage systems than traditional lithium-ion batteries.However,due to the poor conductivity of monemental sulfur,the serious volume expansion of active substances and the shuttle effect of soluble lithium polysulfide,the cycle stability and Culomen efficiency of lithium-sulfur batteries cannot meet the needs of commercial applications.In order to solve the above problems and improve the electrochemical properties of lithium-sulfur batteries,the performance of lithium-sulfur batteries is studied from the two aspects of sulfur cathode material and separator modified coating material from the combination of molybdenum-based compound and carbon material in this paper.The main research contents are as follows:（1）Mo-based precursor was obtained by the solvent heat method using SCG as the carrier.Then,Mo₂C-SCG composites were prepared as sulfur carriers by high-temperature carbonization.SCG with pore-rich and large specific surface area was able to avoid the agglomeration of Mo₂C nanoparticles to expose more marginal active sites.Mo₂C nanoparticles uniformly loaded onto SCG surfaces can not only capture polysulfides,but also catalyze the redox reactions of Li PSs.In addition,SCG can also serve as a conductive medium to accelerate the charge transport of the positive electrode.Mo₂C-SCG composites play an important role in improving sulfur utilization,mitigating positive volume expansion and inhibiting shuttle effects.The results show that the lithium-sulfur batteries with Mo₂C-SCG/S show the initial discharge capacity of 1062 m Ah g^-1at 0.2 C,the discharge capacity is 828 m Ah g^-1at 1 C and remains 464 m Ah g^-1after 500 cycles with a capacity decay rate of 0.0879%per cycle.（2）Defective-rich 1T/2H-MoS₂nanosheets and N-doped graphene aerogel（MF-GA-MoS₂）composite materials were prepared as separator modified coatings by a simple one-step hydrothermal method using melamine sponge as template and MoS₂nanosheets with ammonium molybdate and thiourea as reactants.The melamine sponge reduces agglomeration during GO reduction,and its hydrolysis products promote the production of 1T-MoS₂.Defect-rich MF-GA-MoS₂composites not only enable fast charge transfer through a good conductive network,but also take advantage of a wealth of edge active sites to ensure its strong adsorption and catalytic conversion of Li PSs.The MF-GA-MoS₂coating can well limit polysulfide migration without affecting Li⁺transport.The results showed that lithium-sulfur batteries equipped with MF-GA-MoS₂coating separator have excellent electrochemical properties.Its initial discharge capacity at 0.2 C is up to 1323 m Ah g^-1.While the discharge capacity of 721 m Ah g^-1was provided at 3 C and 440 m Ah g^-1was retained after 800 cycles with a capacity decay rate of 0.0485%per cycle.