Study On The Preparation Of Black Phosphorene/MXene Composite And Its Lithium Storage Performance

The conventional commercial lithium-ion battery（LIB）graphite anode material(theoretical specific capacity 372 mAh g^-1)has a low specific capacity,and it has been difficult to satisfy the market demand for high-performance LIBs.Therefore,it is particularly urgent to develop anode material with high specific capacity.Black phosphorene（BP）and titanium carbide（Ti₃C₂T_x）become an important driving forces for the development of high-performance LIBs due to their high theoretical specific capacity(2596 mAh g^-1)and excellent electrical conductivity,respectively.However,both BP and Ti₃C₂T_x（T=O,OH,F）are unstable,and they are easily reacted with water and oxygen when they are exposed to room temperature conditions,which cause their structures to be destroyed.Furthermore,when they are applied to lithium-ion batteries,the bare BP has the problems of poor conductivity and volume expansion,and the Ti₃C₂T_x also has a disadvantage of low energy density（mass-specific capacity）.Therefore,to address the existing problems in the application of BP and Ti₃C₂T_x for LIBs,this paper carries out the following research work,the details are as follows:（1）Two-dimensional layered Ti₃C₂T_x materials were prepared by using Ti₃AlC₂,lithium fluoride and hydrochloric acid as raw materials by stirring corrosion and ultrasonic stripping.The microstructure and morphology of the as-prepared Ti₃C₂T_x were characterized by XRD,SEM,TEM and Raman.The result showed that Ti₃C₂T_x was successfully prepared.（2）Two-dimensional（2D）BP/Ti₃C₂T_x heterostructure was prepared by ultrasonic dispersion and freeze-drying.The structure,morphology and composition of the as-prepared samples were characterized by XRD,TEM,XPS and Raman.The air and water stabilities of the BP,Ti₃C₂T_x and BP/Ti₃C₂T_x heterostructure were evaluated using color variation of aqueous dispersions,UV-Vis,optical images and XPS.The results showed that the stability of the 2D BP/Ti₃C₂T_x heterostructure was superior to that of the bare BP and Ti₃C₂T_x.The improved stability can be ascribed to the formation of P-O-Ti bonds between BP and Ti₃C₂T_x during sonication,which prevents the oxidation of bare BP and Ti₃C₂T_x.In addition,the BP and Ti₃C₂T_x sheets stacked on top of each other and formed the BP/Ti₃C₂T_x heterostructure during the drying process.（3）The use of a bare Ti₃C₂T_x and BP/Ti₃C₂T_x composite in LIBs has found that BP/Ti₃C₂T_x composite（volume ratio BP:Ti₃C₂T_x=6:1）had better cycle stability,rate performance and high reversible specific capacity compared to the bare material.During the first cycle,a reversible capacity of 1006 mAh g^-1 for BP/Ti₃C₂T_x composite was obtained at a current density of 100 mA g^-1.However,the reversible capacity of bare Ti₃C₂T_x was only 342 mAh g^-1.The composite shows a stable reversible specific capacity of 992 mAh/g after 50 cycles,and its capacity retention rate is 70.2%,indicating that the composite has good cycle performance.Especially at a high current density of 1000 mA g^-1,the BP/Ti₃C₂T_x composite still has a high reversible specific capacity of 679 mAh g^-1.In this composite material,the presence of Ti₃C₂T_x not only improves the conductivity,but also improves the problem of volume expansion and stability of BP during charge and discharge process.Meanwhile,the agglomeration of the bare BP is avoided to a certain extent,and the ionic and electronic conductivity of the composite material is improved.