ZIF-8 Derivatives Promote Lithium Storage Performance Of MoS₂

Under the background of"carbon peak"and"carbon neutralization",it is inevitable to accelerate the electrification of power system for the development of new energy vehicles.As the key technology of the power system of new energy vehicles,the market demand for energy density and cycle life of lithium-ion batteries becomes larger and larger.As one of the crucial materials of lithium-ion battery,anode material determines the electrochemical performance of the battery to a great extent.Among many anode materials,MoS₂ is regarded as a foreground material for lithium-ion batteries due to its like-graphene 2D layered structure and high theoretical capacity.However,the sluggish reaction kinetics and the dissolution and shuttle of lithium polysulfide always exist in the charge and discharge process of MoS₂ anode materials based on the conversion mechanism,contributing to the poor reversibility of electrochemical reaction and loss of active materials and poor electrochemical performance eventually.To solve the above problems,this paper constructs a flexible independent heterostructure anode and introduces an electrocatalyst to promote the catalytic conversion of lithium polysulfide,so as to improve the lithium storage performance of metal sulfides.The main research results are as follows:（1）The mixed structure of ZIF-8 was synthesized by in-situ growth of MoS₂ nanoflowers on flexible carbon cloth.Then it was pyrolyzed at high temperature in inert atmosphere to construct MoS₂/ZnS-NC@CC heterostructure.At the same time,ZIF-8 is pyrolyzed into nitrogen doped carbon materials surrounded by heterostructures,which can effectively alleviate the volume changes of electrode materials in the charge and discharge process.At the same time,it can also have a good adsorption on polysulfides generated by conversion reaction and reduce the dissolution of lithium polysulfide.The highly conductive space network constructed by carbon cloth and derived carbon materials accelerates the efficiency of ion/electron transmission.The free-standing electrode kept a high specific capacity of 1427.2 mAh g^-1after 200 cycles at a current density of 0.1 A g^-1.Compared to MoS₂@CC and MoS₂/ZnS-NC,the electrodes have better rate performance,lower charge transfer impedance,higher lithium-ion diffusion coefficient and higher pseudocapacitance contribution ratio.（2）The metal precursor Fe（acac）₃ was encapsulated by ZIF-8 to construct the molecular cage,and the iron-nitrogen doped porous carbon material（Fe-NC）was derived by pyrolysis in inert atmosphere.The membrane half layer is coated with polypropylene to assemble the membrane.The visual adsorption experiment and symmetrical battery test verify that Fe-NC has good adsorption and catalytic properties.In addition,through various electrochemical performance tests,the cell shows better cycle stability,magnification performance,higher pseudo capacitance behavior and smaller diffusion impedance.After 200 cycles at a current density of 0.2 C,it still maintains a capacity of 958 mAh g^-1,while 200 cycles at a high current of 1 C can also hold a relatively high specific capacity of 485 mAh g^-1.The above shows that the Fe-NC modified separator interlayer improves the reaction kinetics of lithium ion diffusion and promotes the catalytic conversion process of LiPSs→Li₂S.