Structural Regulation And Magnesium Storage Performance Of Molybdenum Sulfide Cathode Materials

Since the 21st century,under the background of the rapid development of new energy industry and portable electronic products industry,the lithium-ion battery（LIBs）is difficult to meet the huge market demand due to the limitations of the shortage of lithium resource,and the safety problems and so on.Magnesium ion batteries（MIBs）have attracted the attention of researchers due to their physical and chemical properties similar to metal lithium,high reserves,high energy density,and high safety coefficient.However,Mg²⁺has a high charge density and strong electrostatic interaction with the positive host material,which makes it difficult for ions to insertion/extraction,resulting in a poor electrochemical performance of MIBs.Therefore,the research on cathode material is one of the keys to promote the development of magnesium batteries.In this work,molybdenum sulfide is used as the research object,through the ion doping modification,structure construction,expanding layer spacing and other strategies.More Mg²⁺absorption/desorption sites are introduced into the molecular structure,Mg²⁺transport channels are widened,and stable morphology and structure are constructed,so as to improve the magnesium storage performance of molybdenum sulfide based cathode materials.The main research contents are as follows:1.We have modified MoS₂material by the cationic doping method.The Cu²⁺/Co²⁺is introduced into MoS₂lattice by a hydrothermal method to prepare the Cu-MoS₂and Co-MoS₂.The introduction of Cu²⁺/Co²⁺promotes the phase transformation of 2H-MoS₂to 1T-MoS₂with high conductivity,which enhances the electrical conductivity of the electrode material.At the same time,the cation insertion weakens the Mo-S bond and enlarges the layer spacing of MoS₂.Using the two materials as MIBs cathodes,the battery was assembled to test its magnesium storage performance.The results show that the positive Cu-MoS₂electrode exhibits excellent rate performance.The material can maintain a discharge specific capacity of 251.3 m Ah g^-1at a current density of 0.5 A g^-1after 100cycles.At this current density,the capacity of Co-MoS₂cathode is stable at 159.7 m Ah g^-1,which is obviously better than that of pure MoS₂electrode material.2.a-MoS₃/HCS composites were prepared by loading amorphous MoS₃（a-MoS₃）uniformly inside and outside hollow carbon spheres（HCS）by an acid coprecipitation method.Hollow carbon spheres（HCS）loaded with ascorbic acid intercalated MoS₂（1T/2H-MoS₂/HCS）composites were prepared by a hydrothermal method.MoS₃has a higher theoretical specific capacity,and its amorphous characteristics and special one-dimensional chain structure can provide more active sites.The large layer spacing（0.98 nm）and good electrical conductivity of 1T/2H-MoS₂/HCS materials are conducive to the rapid transfer of Mg²⁺,and the uniformly dispersed three-dimensional（3D）structure avoids the material agglomeration and alleviates the large volume change during the electrochemical reaction.When a-MoS₃/HCS material is used as a MIBs cathode,the initial discharge specific capacity is as high as 489.2 m Ah g^-1at 0.05 A g^-1.And the reversible discharge specific capacity is 262.8 m Ah g^-1after 200 cycles at a high current density of 1 A g^-1.In contrast,1T/2H-MoS₂/HCS materials have poor performance.At the current density of 1 A g^-1,the capacity can remain at 148.1 m Ah g^-1after 200 cycles.Finally,the storage mechanism of a-MoS₃/HCS composite with excellent magnesium storage performance was proved by first principles calculation.