| With the continuous depletion of the earth’s resources,it is urgent to develop a new type of green and pollution-free chemical energy.Lithium-ion batteries have the characteristics of high voltage,high energy,long life,and low self-discharge.They play a vital role in energy storage and conversion,and can greatly affect the development of electronic products and new energy automobile industries.The choice of anode materials for lithium-ion batteries is a key factor in determining the performance of the battery.Currently,the most widely used negative electrode material commercially is graphite,but its limited specific capacity(372 m Ah g-1)is far from being able to meet the growing demand for energy storage.Although metal oxides and other negative electrodes have the advantage of large specific capacity,they all have some obvious shortcomings.For example,the voltage between charge and discharge is obviously lagging,and the energy efficiency is low.Magnesium hydride is regarded as one of the negative electrode materials with great development potential because of its theoretical specific capacity as high as 2038 m Ah g-1.However,its volume changes during the battery charge and discharge reaction.The continuous expansion and contraction of the volume will cause the instability of the SEI film on the active material and the fragmentation of the Mg H2 particles,which will continue to consume lithium,and eventually the battery will fail due to lithium consumption.Based on this,we combined the metal hydride Mg H2 with the two-dimensional conductive material MXene to prepare Mg H2@MXene composite material.The main contents and results of this paper are as follows:（1）A single layer of MXene material is obtained by selective solution etching of the"Al"layer atoms in the layered ternary MAX（Ti3Al C2）precursor.According to its self-assembly characteristics,Mg H2 nanoparticles were loaded in situ on the MXene layered surface by solvothermal method to prepare Mg H2@MXene composite materials.Adjust the ratio of reactants to prepare Mg H2@MXene composites with different loadings.In addition,physical property characterization（XRD,SEM,TEM）of the Mg H2@MXene composite material confirmed that the Mg H2 particles have been successfully loaded on the MXene matrix.When the loading is 20wt%,a large number of Mg H2 particles are in a monodisperse state and uniformly distributed on the MXene sheet.With the continuous increase of loading,Mg H2 particles began to pile up on the MXene matrix,the density of the particles on the surface of the material increased,and the porosity decreased.（2）Through the analysis of the electrochemical performance of the commercial bulk Mg H2 electrode,it can be obtained:After 20 cycles of the commercial Mg H2electrode,the discharge capacity is drastically reduced to below 400 m Ah g-1,the capacity is greatly attenuated,and the cycle stability is poor.In contrast,the 20wt%Mg H2@MXene electrode used as the negative electrode material showed a relatively stable discharge capacity after the first cycle,and the capacity did not decrease significantly after 50 cycles.This is mainly because Mg H2 nanoparticles act as active materials to provide high capacity for lithium-ion batteries.On the other hand,the unique structure of MXene not only ensures the uniform distribution of Mg H2 particles in the composite electrode,but also serves as a matrix to provide support for it,which can effectively alleviate the particle volume change and agglomeration phenomenon during the cycle.（3）MgH2@MXene composite materials with different masses are mixed with Li BH4 electrolyte and conductive agent Ketjen Black in a mass ratio of 4:3:3 to obtain electrode materials by ball milling,which are assembled with Li BH4 electrolyte and lithium sheets to form a half-cell for electrochemical performance test.The results show that when the loading is 20wt%,the Mg H2 particles in the Mg H2@MXene composite show excellent activity,and as the loading of Mg H2 continues to increase,Mg H2 begins to inactivate.Compared with 40wt%Mg H2@MXene,the half-cell assembled from 20wt%Mg H2@MXene composite material has low interface impedance and high cycle stability.After 50 charge-discharge cycles at a current density of 100 m A g-1,the specific discharge capacity of the Mg H2@MXene electrode reaches 532 m Ah g-1,and the coulombic efficiency is close to 99%.Compared with the tenth cycle,the capacity retention rate after 50 cycles reaches 88.5%.In addition,20wt%Mg H2@MXene has good cycle reversibility under different current densities.Based on the above data,the 20wt%Mg H2@MXene electrode has excellent electrochemical performance.In summary,in this paper,by loading MgH2 onto the MXene matrix,the volume change of Mg H2 particles during the reaction process is effectively alleviated.The prepared Mg H2@MXene composite electrode material exhibits excellent electrochemical performance,which is expected to provide technical ideas and theoretical references for the research on Mg H2 modification,and it is of positive significance to promote the performance of lithium-ion batteries. |
