Preparation And Electrochemical Performances Of MXene-based Composites

As a graphene-liked two-dimensional layered material,MXene exhibits the advantages of good electrical conductivity,abundant surface functional groups and excellent hydrophilicity.However,the phenomenon of self-stacking in the two-dimensional direction hinders its further development.In this paper,to develop MXene-based composites with excellent electrochemical properties,the etching method,surface modification and material composite of MXene were studied.The specific research contents as follows:(1)Ti₃AlC₂ MAX material was selected as the research object,and the effects of etching time,intercalation agent and intercalation time on Ti₃C₂ materials were explored.The research results showed that when HF was used as the etchant,appropriate etching time is helpful to synthesize smooth and accordion-liked Ti₃C₂material.MXene materials with uniform interlayer spacing and monolayer flakes were obtained by further employing TMAOH as intercalating agent.Meanwhile,the electrochemical performance of the etched MXene material was enhanced.The initial reversible specific capacity was increased to 242.2 mAh g^-1 from 30.7 mAh g^-1of the unetched.(2)In order to further improve the electrochemical performance of MXene,negatively charged MXene was combined with positively charged melamine through electrostatic interaction,followed by high temperature treatment to obtain modified m-MXene materials.The effects of different melamine addition amount,different calcination temperature and different calcination time on m-MXene material were also studied.Among them,when the addition amount of melamine was 5:1,the calcination temperature was 550?,and the calcination time was 4 h,the m-MXene material showed the excellent lithium storage performance.At 0.1 A g^-1,the initial reversible specific capacity was 411.5 mAh g^-1,and the reversible specific capacity was delivered of 292.9 mAh g^-1 after 100 cycles,with a capacity retention rate of71.2%.(3)LFP/MXene/C composites were successfully synthesized by solvothermal method,then MXene content,carbonization temperature and carbonization time were systematically investigated.The test results showed that when the MXene content was7%,the carbonization temperature was 700?,and the carbonization time was 6 h,LFP/MXene/C displayed more excellent rate performance and electrode process kinetics characteristics.its reversible specific capacity was 151.5 mAh g^-1 at 0.1 C,and 97.6%of the first coulombic efficiency,which was superior to other materials at carbonization temperature.It contributed the average reversible capacities of 143.2,130.2,117.8 and 107.2 mAh g^-1 at the rate of 0.2 C,0.5 C,1 C and 5 C,respectively.When the current density regain to 0.1 C,the reversible specific capacity could still be148.5 mAh g^-1,and the capacity recovers to 98.0%of the coulombic efficiency.The low temperature(-20?)performance test was carried out.The results show that the composite revealed good low temperature performance,and its initial discharge specific capacity could reach 86.4,72.1,60.4 mAh g^-1 and 52.5 mAh g^-1 at the current density of 0.1 C,0.2 C,0.5 C and 1 C,respectively.