Preparation And Electrochemical Properties Of MXene-based Composites

With the rapid development of electronic devices industry,the demand for power density and energy density of energy storage devices is increasing.It is urgent to develop energy storage devices that are safe,efficient and suitable for large-scale use.Electrode material is the core part of energy storage devices,which determines its electrochemical performance.Therefore,it is crucial to develop high-performance electrode materials.In this paper,MXene(Ti₃C₂T_x)was used as the substrate to improve the electrochemical performance of energy storage devices by regulating the morphology,reactive sites and conductivity of electrode materials.Ti₃C₂T_x-based electrode materials were synthesized by vacuum filtration,hydrothermal method,natural deposition method,and freeze-drying method.The detailed studies are as follows:(1)An independent self-supporting film(Mo S₂/C@Ti₃C₂T_x)was synthesized by vacuum filtration and hydrothermal method.Under hydrothermal and high temperature conditions,the conversion of polyvinylpyrrolidone(PVP)into amorphous carbon was encapsulated in Mo S₂ interlayer,which expanded the interlayer spacing of Mo S₂ and facilitated the rapid diffusion of lithium ions and electrons between layers.The Mo S₂/C nanosheets were embedded into the interlayer of Ti₃C₂T_x to form an independent self-supporting film,which not only inhibits the self-stacking defect of Ti₃C₂T_x,but also buffers the volume change of Mo S₂ during the energy storage process.Therefore,at the anode of lithium-ion battery,the capacity retention rate of Mo S₂/C@Ti₃C₂T_x electrode was as high as 96.7%after 150 cycles at the current density of 2 A g^-1.(2)CoNi-DH@Ti₃C₂T_x composites consisting of hierarchical cobalt-nickel hydroxide nanoarrays and Ti₃C₂T_x films were prepared by natural deposition and in-situ etching deposition at room temperature.The Ti₃C₂T_x film prepared by natural deposition method as the support skeleton,which could inhibit the aggregation of Co Ni-DH nanoarrays and further improve the conductivity of electrode material.Hierarchically structured Co Ni-DH nanoarrays promotes the penetration of the electrolyte.Due to the excellent properties of these two materials,the Co Ni-DH@Ti₃C₂T_x electrode material exhibits good rate and cycle performance.Moreover,the theoretical results demonstrate that the chemical bonds between Ti₃C₂T_x and Co Ni-DH are crucial for charge transport,conductivity and structural stability.(3)Ti₃C₂T_x/VN composites were prepared by one-step high-temperature nitridation reduction with melamine as nitrogen source,and the high conductivity Ti₃C₂T_x and high specific capacity vanadium nitride nanoparticles(VN)were compounded.Ti₃C₂T_xnanosheets have high conductivity and large surface area as support skeleton,VN nanoparticles were uniformly embedded between Ti₃C₂T_x plates,which not only exposed more active sites of VN nanoparticles,but also effectively inhibited the aggregation of VN nanoparticles.As a supercapacitor electrode Ti₃C₂T_x/VN,its specific capacity is as high as 382.1 F g^-1 at 1 A g^-1,and its capacity retention is still 83%after 4000 cycles at15 A g^-1,showing good rate performance and cycle life.