Study On Lithium Storage Performance Of Nb₂CT_x MXene Electrode Material

In recent years,Nb₂CT_x,have received significant research interests as ideal matrices for active electrode materials in lithium-ion batteries,due to high theoretical specific capacity(542 m Ah g^-1),fast ion movement,very low diffusion barrier heights（<0.1 e V）and lower average intercalation potentials.But a simplified method to synthesize the structures with good cycling and rate performances is still a challenge for MXenes family,and due to the large number of surface functional groups on the surface of the Nb₂CT_xprepared by acid corrosion,its mass specific capacitance is impaired,and its lithium storage performance is greatly reduced,so it is difficult to meet the design requirements of high-performance lithium-ion battery electrodes.In response to these problems,the following researches are carried out in this paper:First,few-layer Nb₂CT_xMXene nanosheets were synthesized in one step by selectively etching Nb₂Al C powder with HF acid aqueous solution for the first time.Compared with the multilayer Nb₂CT_xelectrode material,the few-layer Nb₂CT_xnanosheets are more thoroughly delaminated and have a wider area of contact with the electrolyte.The few-layer Nb₂CT_xhas a larger specific surface area(38 m²g^-1),which is about 2.7 times that of the multilayer Nb₂CT_x,so the few-layer Nb₂CT_xnanosheets have a larger effective active area and more effective active sites,and fewer layers.The content of-F functional group of the Nb₂CT_xsurface is much smaller than that of the multilayer Nb₂CT_xsurface,which is more conducive to energy storage.The synthesized few-layer Nb₂CT_xelectrode material exhibits excellent rate and cycle performance,and it can provide a high discharge specific capacity of 354 m Ah g^-1at 0.05 A g^-1.At the same time,at a high current density of 1.0 A g^-1,the specific capacity can be stabilized at 225 m Ah g^-1after 800 cycles.The success of one-step synthesis of few-layer Nb₂CT_xis expected to promote its research and development in the field of lithium-ion batteries and related energy storage devices.Different kinds of functional groups have a great influence on the electrochemical performance of MXene.In order to solve this problem,we designed a simple and effective scheme to adjust the surface functional groups of Nb₂CT_x,and the electrochemical performance of Nb₂CT_xelectrode after Li⁺pre-intercalation and annealing treatment is better than that of the reported Nb₂CT_x,Ti₃C₂T_xand graphite electrode.The pre-intercalation of Li⁺and annealing can effectively regulate the functional groups on the surface of Nb₂CT_xMXene.Due to suitable surface functional groups,the Li-Nb₂CT_x-400 electrode can reach a high specific capacity of 448 m Ah g^-1at a current density of 0.05 A g^-1.In addition,at a high current density of 2 A g^-1,after2000 cycles of ultra-long cycles,the electrode material can maintain a high specific capacity of 342 m Ah g^-1.Compared with the previously reported Nb₂CT_xand Ti₃C₂T_xelectrodes,the Li-Nb₂CT_x-400 electrode has the highest specific capacity.The strategy of this work is of great significance for the development of Nb₂CT_xmaterials in lithium-ion batteries,and is expected to be applied to other MXene materials.