Study On The Preparation And Electrochemical Properties Of MXene Based Composite Anode Materials

The growing energy needs of human science and industry require efficient and clean energy storage systems and conversion devices.Lithium-ion batteries are currently the dominant energy storage systems due to their high energy and power density,long cycle life and low self-discharge rate.However,current lithium-ion battery technology faces the challenge of achieving higher energy density and power output.MXene,a new two-dimensional material,has a band structure similar to that of metal and therefore has excellent electrical conductivity.However,the theoretical specific capacity of MXene is low,and the layer is easy to stack,which limits the performance.To solve the above problems,MXene was combined with coir carbon and Ni-MOF electrode materials in this study to improve the electrochemical performance of the composite materials.The main research contents are as follows:The growing energy needs of human science and industry require efficient and clean energy storage systems and conversion devices.Lithium-ion batteries are currently the dominant energy storage system due to their high energy/power density,long cycle life,and low self-discharge.However,with the development of society,the low theoretical specific capacity of traditional graphite materials is difficult to meet people’s requirements for high-performance batteries,so lithium-ion battery technology is facing the challenge of achieving higher energy density and power output.The new two-dimensional material MXene has a similar band structure to metal,with excellent conductivity,hydrophilicity and abundant surface tube energy groups.However,the theoretical specific capacity of MXene is low,and the layer is easy to stack,which limits the performance and affects the improvement of the electrochemical performance of lithium ion batteries.To solve the above problems,coconut shell carbon and Ni-MOF materials were introduced into MXene interlayer and on the surface of MXene lamella,and MXene/coconut shell carbon and MOF@MXene composite materials were constructed by solution agitation,co-precipitation,high-temperature pyrolysis and other methods.The microstructure and electrochemical properties of the composite materials were discussed.The main research contents were as follows:Firstly,coconut shell activated carbon anode material was prepared by high temperature pyrolysis and activation.The effects of activation on its structure,morphology and electrochemical properties were investigated.The results showed that the activated coconut shell carbon had high disordered degree and was rich in microporous and mesoporous porous structures.The initial discharge specific capacity reached 918.2 mAh·g^-1at 0.1 A·g^-1and 447 mAh·g^-1after 200 cycles at 1A·g^-1.By replacing HF with HCl and Li F,Ti₃Al C₂was etched and exfoliated to obtain layered Ti₃C₂T_x.The morphology,structure and electrochemical properties of the material at different reaction temperatures and reaction times were discussed.The results show that with the increase of etching temperature and reaction time,the material is over-etched by hydrofluoric acid,the particle refinement is serious,and the electrochemical performance is decreased obviously.The multilayer Ti₃C₂hasaccordion structure and the initial discharge capacity reaches 1230 mAh·g^-1at 0.1 A·g^-1current density after reaction at 30℃for 24 h.By mixing MXene with coir carbon in deionized water solution,the effects of different proportions on the structure,morphology and electrochemical properties of the composite materials were investigated.The results show that the coir carbon particles enter and adhere to the MXene lamella,interspersed with some coir carbon particles.This structure inhibits the stacking of MXene to a certain extent,enlarges the layer spacing of MXene,and is conducive to the transmission of lithium ions.According to the electrochemical performance test,the sample with recombination ratio of 1:2 has the best electrochemical performance.The initial discharge specific capacity is up to 1951.7 mAh·g^-1at 0.1A·g^-1,and 800.8 mAh·g-1 after 200 cycles at 1 A·g^-1.Finally,using two-dimensional MXene nanosheets as substrate,Ni-MOF was grown on the surface of MXene nanosheets by coprecipitate method,and then subjected to high temperature heat treatment in argon atmosphere,to investigate the effects of different temperatures on the structure,morphology and electrochemical properties of Ni-MOF@MXene composites.The results show that:on the one hand,the introduction of Ni-MOF improves the specific surface area and pore size distribution of two-dimensional MXene substrate.On the other hand,the conductivity of the composites is enhanced by high temperature heat treatment.Electrochemical test shows that Ni-MOF@MXene-500℃has the best electrochemical performance,at 0.1 A·g^-1,after 200 cycles,discharge capacity up to 591.6 mAh·g^-1,at 5 A·g^-1,after 500 cycles,The specific discharge capacity is still 497 mAh·g^-1.