Study On Two-dimensional MXene/LDH Interstratification Assembly Electrode And Electrochemical Energy Storage Performance

As the most crucial energy storage device,supercapacitors are widely used in electric vehicles,electronic devices,and energy harvesting systems due to their excellent power density,high specific capacitance,and good cycle stability.As the core component of supercapacitors,electrode materials play a crucial role in the commercial application of supercapacitors.Two-dimensional transition metal layered materials are considered the most potential electrode materials due to their high power density,high theoretical capacitance,and good rate capability.However,low energy density and cycle stability are the main bottlenecks restricting the commercial application of supercapacitors.According to the structural characteristics of two-dimensional layered materials,a series of preparation processes have been used by researchers to conduct a lot of research on two-dimensional layered materials.The electrochemical performance of the material has also been improved to a certain extent,but the effect achieved is still limited.In this paper,by taking the two-dimensional layered materials MXene and NiAl-layered double hydroxides（NiAl-LDHs）as the research objects,the two-dimensional layered materials with matching structures and complementary properties are interlayer assembled to study the interlayer assembly behavior and energy storage mechanism of these two materials.A new type of two-dimensional structural material has been developed further to improve the electrochemical performance of supercapacitor electrode materials.（1）Three-dimensional network structure electrode material MXene@PDDA/NiAl-LDHs was prepared by electrostatic self-assembly method.This structure takes full advantage of the high pseudocapacitive activity of NiAl-LDHs and the high electrical conductivity of MXene to accelerate the ion/electron transport during charging and discharging,thereby improving the overall electrochemical performance of the material.The MXene@PDDA/NiAl-LDHs electrode exhibits a high specific capacitance of 1825.8 F g^-1 at 1.0 A g^-1 and long-cycle stability after 5000 cycles at 1.0 A g^-1.The discharge cycle stability drops by only 0.9%.Furthermore,the 3D hybrid electrode exhibits a maximum energy density of 91.3 Wh kg^-1 at a power density of 300 W kg^-1.（2）To reveal the energy storage mechanism of the interlayer assembly of two-dimensional layered materials and improve the electrochemical performance of electrode materials.By adjusting the preparation process of two-dimensional layered MXene,the Ti₃C₂Cl₂ MXene with chloride ion functional groups on the surface was prepared by Lewis’s acid molten salt etching method,and quantum dot treatment was performed on it,so that MXene quantum dots were attached to the surface.Electrostatic self-assembly method to prepare QD-Ti₃C₂Cl₂@NiAl-LDHs electrode material.The study found that the surface functionalization and quantum dot modification of MXene can increase the specific surface area of the material,improve the surface activity,and then accelerate the transfer of electrons and the insertion of ions in the material.The QD-Ti₃C₂Cl₂@NiAl-LDHs electrode exhibits an excellent specific capacity of 2010.8 F g^-1 and the highest power density of 299.8 W kg^-1 at an energy density of 100.5 Wh kg^-1.Furthermore,it exhibits excellent cycling stability with only 5.9%degradation after 10,000 cycles at a current density of 1.0 A g^-1.（3）To explore the energy storage mechanism of the synergistic effect of the two-dimensional material structural units,and further improve the electrochemical performance of the electrode material.By optimizing the structure of two-dimensional layered NiAl-LDHs,a layered interwoven heterostructure CC/NiAl P/NiAl-LDHs@MXene electrode material was prepared by electrostatic self-assembly and applied to flexible capacitors,showing good electrochemical properties.The CC/NAPL@MXene hybrid electrode exhibits a high specific capacitance of 3.88 F g^-1 at 1.0 m A cm^-2 and excellent cycling stability（91.1%after 8000cycles）.The fabricated CC/NAPL@MXene//AC flexible asymmetric supercapacitor（FASC）exhibits a high power density of 1800 W kg^-1 and excellent cycling stability at an energy density of 81.1 Wh kg^-1.Analyzing the energy storage mechanism is mainly attributed to the following reasons.On the one hand,NiAl-LDH grown on the surface of CC/NiAl P by hydrothermal synthesis fully utilizes the electrical conductivity of NiAl P,but also provides a large number of layered channels for the rapid migration of electrons and ions.On the other hand,the synergistic effect of CC/NiAl P@NiAl-LDHs and Ti₃C₂Cl₂ MXene further enhances the electrical conductivity of the hybrid,resulting in more active sites and ion migration channels,which accelerates the rapid migration of electrons and ions during charge and discharge.