Preparation And Electrochemical Properties Of Transition Metal Compound Anode Materials

In the past two decades,lithium-ion batteries?LIBs?have gained widespread focus due to their high energy and high power density and have been used in portable electronic devices.For anode materials in LIBs,commercial graphite2 with a relatively low theoretical specific capacity(372 mAh g^-1)and poor rate capability does not fully meet the energy density requirements of high performance batteries.Therefore,many efforts have been made to find new anode materials,which have high specific capacity and good cycle stability.Transition metal compounds?transition metal oxides and sulfides?have been found to be potential alternatives to anode materials in LIBs due to the very high specific capacity,high conductivity,and richer redox reaction,which 3d metal compounds possesses.However,in practical applications,it is still hindered by the low conductivity and structural collapse problems in the Li⁺ion intercalation-extraction process,which results in poor rate performance and rapid capacity decay during cycling.Therefore,it is a very effective strategy to prepare nanostructured materials with different morphologies or to mix and prepare them to prepare layered mixed materials.In this paper,the preparation and electrochemical properties of Ni@NiCo₂S₄ popcorns,Hierarchical CoMn₂O₄@NC?NC:Nitrogen doped carbon?microspheres,Hierarchical porous ZnMn₂O₄@MoS₂ Microflowers were studied.The main contents are as follows:?1?Foam nickel is used as the conductive substrate,CoCl₂?6H₂O and NiCl₂?6H₂O are used as the cobalt source and nickel source,Na₂S is used as the sulfur source,and urea is used as the precipitant.NiCo₂S₄ popcorns is synthesized on the foamed nickel substrate by two-step solvothermal method.Popcorn.NiCo₂S₄ popcorns is uniform in size,with an average particle size of about 2?m.At the same time,there is a certain gap between popcorns,which can effectively avoid the bonding and agglomeration of NiCo₂S₄ popcorns and increase the contact area with electrolyte.In addition,the popcorn structure is so stable as not easy to collapse,and adapts to the large volume change caused by the insertion-extraction of Li⁺ions during charge and discharge,and reduces the structural strain,thereby exhibiting high specific capacity,excellent cycle stability performance and rate performance.At a current density of100 mA g^-1,the reversible specific capacity is maintained at 973 mAh g^-11 after 60 cycles,and the coulombic efficiency of the whole process is always maintained at 99%;at a current density of up to 2000 mA g^-1,the ratio is The capacity was maintained at 663 mAh g^-1,and the specific capacity was as high as 959 mAh g^-11 when the current density returned to 100 mA g^-1again.?2?Using carbon sphere as template,The Co-Mn precursor was prepared by simple solvothermal method,calcined in air to obtain CoMn₂O₄ hollow spheres,then ZIF-67 was synthesized in situ,and the scoring Hierarchical hollow CoMn₂O₄@NC microspheres were calcined in a nitrogen atmosphere.The CoMn₂O₄@NC microspheres consist with CoMn₂O₄hollow spheres uniformly coated with NC microspheres,and the CoMn₂O₄ hollow spheres are porous.The coating of the NC enhances the electrical conductivity of the overall material.It's also the unique layered nanostructures,and the synergistic effect of the hollow CoMn₂O₄spheres and the NC layer which enhance the lithium storage performance.At a current density of 100 mA g^-1,the reversible specific capacity is maintained at 464 mAh g^-11 after 100 cycles,and the coulombic efficiency of the whole process is always maintained at 99%;at a current density of up to 2000 mA g^-1,the ratio is The capacity was maintained at 375 mAh g^-1,and when the current density returned to 100 mA g^-11 again,the specific capacity increased to 484mAh g^-1.?3?Firstly,the Zn-Mn precursor was synthesized by solvothermal method using carbon sphere as template,and then calcined in air to obtain hollow ZnMn₂O₄ microspheres.Then molybdenum dihydrate and thiourea dihydrate,which were respectively used as molybdenum source and sulfur source,through solvothermal method and vacuum calcined,form the Hierarchical porous ZnMn₂O₄@MoS₂ Microflowers.It's ZnMn₂O₄@MoS₂ Microflowers,with a diameter of about 760 nm,that consist of hollow ZnMn₂O₄ microspheres coated with interconnected ultra-thin MoS₂ nanosheets.What's more,the interconnected nanosheet porous structure can not only shorten the diffusion of Li⁺ions,but also enhance charge transfer,ion diffusion and the penetration of electrolytes.At 100 mA g^-11 current density,the ZnMn₂O₄@MoS₂ composites has a specific capacity of 750 mAh g^-11 after 100 cycles,and the coulombic efficiency is maintained at 99%,indicating good cycle performance;At up to 2000mA g^-1,the reversible specific capacity is 464 mA g^-1,and when the current density is again setted to 100 mA g^-1,the reversible capacity is 731 mAh g^-1.It indicates that the ZnMn₂O₄@MoS₂ composites maintains relatively good structural integrity and exhibits excellent rate performance.