Assembly And Electrochemical Performance Study Of The Two-dimensional MXene/LDH Electrode

As one of the most important energy storage devices,supercapacitors are widely used in energy storage systems and electric vehicles for their excellent power density and good cycling stability.Among them,electrode material is the core part of supercapacitor and plays a key role in the commercialization of supercapacitor.Among many electrode materials,two-dimensional materials have attracted much attention due to their unique layer-like structure and rich physicochemical properties.Based on this,this paper selected Ti₃C₂T_x MXene and NiCo-LDHs,the two-dimensional layer materials with matching structure and complementary performance,as the objects of study and constructed the composite electrode by interlayer assembly of these two-dimensional layer materials.Then,the interlayer assembly behavior and synergistic effect of the two materials in the composite electrode were studied.Meanwhile,the energy storage mechanism of the composite electrode in different electrolytes,the impedance relationship and the diffusion law of electrolyte ions in the interlayer of the composite electrode under different interlayer assembly methods were further investigated,as follows:（1）The Ti₃C₂T_x MXene/NiCo-LDHs composite electrode material was prepared by electrostatic assembly method.In the composite electrode,the high conductivity MXene and the high specific capacitance NiCo-LDHs complement each other,and the two two-dimensional materials play a synergistic role to improve the electrochemical performance of the electrode material.The results showed that the Ti₃C₂T_x MXene/NiCo-LDHs composite electrode demonstrated,at a current density of 0.5 g^-1,a higher specific capacitance of 639 F g^-1 and a capacitance retention capability of 93%after 6000 cycles by test calculations.In addition,it achieves an energy density of 31 Wh kg^-1 at a power density of 150 W kg^-1.（2）Based on the two-dimensional Ti₃C₂T_x MXene/NiCo-LDHs interlayer assembly composite electrode,the energy storage mechanism of the composite electrode in different electrolytes was further investigated.The charging and discharging processes of the Ti₃C₂T_xMXene/NiCo-LDHs electrode in electrolytes containing alkaline,acidic and neutral electrolytes were studied electrochemically by in-situ Raman spectroscopy,respectively.It was found that the hydration reactions of the two-dimensional electrodes were widely present in different electrolytes.Among them,OH^-in alkaline electrolytes promotes the electrochemical performance of NiCo-LDHs and also generates new electrochemical reactions with-F at the end of Ti₃C₂T_xMXene,thus greatly improving the overall electrochemical performance of Ti₃C₂T_xMXene/NiCo-LDHs.Therefore,the electrochemical performance of Ti₃C₂T_x MXene/NiCo-LDHs composite electrode is the most excellent in alkaline electrolytes.（3）Based on the two-dimensional Ti₃C₂T_x MXene/NiCo-LDHs interlayer-assembled composite electrode,the impedance mechanism model and the interfacial ion diffusion law of Ti₃C₂T_x MXene/NiCo-LDHs under different interlayer assembly methods were further investigated under alkaline electrolyte.We prepared interlayer assembled MXene/NiCo-LDHs composite electrodes in the ratios of 1:3,1:1 and 3:1,respectively,using 2D MXene and NiCo-LDHs as raw materials by direct spraying method on the substrate surface.The impedance analysis was performed by electrochemical impedance spectroscopy,and the diffusion coefficients of OH^-ions were calculated under the three models,respectively.It was found that for the two-dimensional interlayer assembled electrode,the interfacial impedance was the smallest(R_ct=56.5Ω)and the ion diffusion efficiency was the fastest(D_OH-(M₁L₃=7.5706×10^-15cm² s^-1)with the best electrochemical performance when the pseudocapacitance layer was closer to the electrolyte（at MXene:NiCo-LDHs=1:3）.