Preparation And Lithium Storage Properties Of Transition Metal Mo And Mn-based Compound Electrode Materials

With the advancement of society,only using traditional fossil energy can no longer meet the current development requirements.Developing and researching new energy sources has become a world consensus.Lithium ion batteries have occupied the mainstream position in the current new energy market due to their advantages of environmental friendliness and high energy density.After more than 20 years of development and commercial use of lithium ion batteries,their existing capacity cannot meet the needs of the industry.How to achieve greater capacity and better cycle performance for lithium ion batteries is a key issue in current industry research.Transition metal compounds have become a research hotspot since they were first proposed due to their rich resources,high specific capacity,and ease of processing.Mo and Mn based materials are also one of them.MoS₂ is a traditional two-dimensional layered material with advantages such as adjustable interlayer spacing,high theoretical capacity,and simple preparation.Molybdenum disulfide has a weak van der Waals force between layers,and atoms within the layer are connected by strong covalent bonds,so it has excellent dynamic characteristics and energy storage potential.Manganese based compounds,as one of the transition metal compounds,have become a potential negative electrode material with the advantages of multivalent states,multiple compounds,low prices,and high theoretical specific capacity.Accordingly,this article has conducted relevant research on molybdenum sulfide and manganese based compound materials,as follows:（1）Pure MoS₂ was prepared by a one-step hydrothermal method,and used as a control group for the preparation and performance testing of lithium ion negative electrode materials.Subsequently,rGO was introduced to prepare MoS₂-rGO composite materials,which were characterized and tested as negative electrode materials for lithium ion batteries.Furthermore,the test results show that the reversible specific capacities of MoS₂-rGO composites are 1157.3m Ah g^-1 and 906 m Ah g^-1 after charging and discharging cycles at a current density of 100 m A g^-1（after 100 cycles）and 1000 m A g^-1（after 400 cycles）,respectively.Under the same test conditions,pure MoS₂ has reversible specific capacities of 249.6 m Ah g^-1 and 179.95 m Ah g^-1,respectively.The introduction of rGO improves the conductivity of pure MoS₂ and improves the volume change of MoS₂ during charging and discharging,which is an effective method to improve the lithium storage performance of materials.（2）MoS₂ materials with different proportions of Se doping prepared by annealing method.Doping Se into MoS₂ not only increases the interlayer spacing of MoS₂,exposing more active sites,but also reduces the volume expansion of MoS₂ caused by the insertion and desorption of lithium ions during battery cycling,improving its lithium storage capacity.The reversible specific capacities of MoS₂-Se-1:1 materials were found to be 368 m Ah g^-1（200 cycles）,400m Ah g^-1（2000 cycles）,and 134.7 m Ah g^-1（2000 cycles）at current densities of 100 m A g^-1,1000 m A g^-1,and 5000 m A g^-1,respectively,which were higher than those of pure MoS₂ and other proportions of Se doped samples under the same test conditions..（3）MnO was oxidized by H₂O₂ to form a Mn₃O₄/MnO mixed phase material.The oxidation of the oxidant causes Mn₃O₄/MnO to have rich oxygen-containing terminal functional groups on the surface,and then it is embedded in a conductive nitrogen-carbon（NC）shell to produce Mn₃O₄/MnO@NC compound material.The O terminal group improves the trapping ability of Li⁺in the material,while the NC shell layer reduces the volume change of Mn₃O₄/MnO.The electrode has been tested to have a stable high reversible specific capacity:at a current density of 100 m A g^-1,the reversible specific capacity after 120 cycles is 1209.1m Ah g^-1;At a current density of 1000 m A g^-1,the reversible specific capacity after 300 cycles is 1048 m Ah g^-1.