Preparation And Electrochemical Performance Of SiO_x/MXene Composite Anode Materials For Lithium-ion Batterie

Due to the advantages of high theoretical specific capacity,low lithium intercalation potential and high natural abundance,silicon-based anode materials have become one of the candidate materials for high energy density lithium-ion battery anodes.However,the volume effect and low intrinsic conductivity of silicon-based anode materials during charge and discharge greatly hinder their practical application.The use of silicon oxide(SiOx)materials can alleviate the volume expansion to a certain extent,because the formation of lithium oxide(Li20)and lithium silicate can act as a buffer matrix,but the coulombic efficiency of the first cycle of the electrode will be further reduced.In addition,the conductivity of silicon oxide is lower than that of pure silicon.Therefore,it is very important to obtain a material construction strategy to effectively overcome the above problems for the industrial application of silicon-based anodes.MXenes are an emerging class of two-dimensional materials,which not only possess ultrahigh metal conductivity and excellent mechanical flexibility,but also possess good hydrophilicity and surface-rich chemical properties.Introducing MXenes into silicon-based anode materials can take advantage of the high specific capacity of silicon-based anode materials and the high conductivity of MXenes.In addition,the mechanical flexibility of MXenes can also greatly improve the stability of the material,effectively alleviate the volume effect during the cycle of silicon-based anode materials,and is expected to greatly improve the electrochemical performance of the anode.However,due to problems such as hydrophilic incompatibility and electrostatic repulsion,the composite of silicon-based materials and MXenes is still challenging.In view of the above problems,a simple and scalable electrostatic self-assembly strategy was designed in this paper,and two SiOx/MXene(0≤x<2)composites were successfully prepared.The specific research contents are as follows:(1)Using the electrostatic self-assembly method,the silicon nanospheres(Si NPs)was surface-modified and then electrostatically self-assembled with Ti3C2 MXene in aqueous solution and Si NPs/MXene composites were obtained after annealing.Then the phase characterization and electrochemical performance test of the composite material were carried out.The results showed that Si NPs were successfully attached to MXene nanosheets through electrostatic self-assembly,which inhibited the self-stacking of MXene nanosheets and the agglomeration of Si NPs to some extent.In addition,MXene nanosheets provide fast electron and lithium ion transport channels for Si NPs,and their mechanical flexibility can alleviate the volume effect of Si NPs during cycling.Benefiting from the above advantages,the Si NPs/MXene electrode exhibits good cycle performance,maintaining a high reversible capacity of 1917.9 mAh/g after 300 cycles at a charge-discharge current density of 500 mA/g.(2)Combining the high-energy ball milling method and the electrostatic self-assembly method,the large-particle silicon oxide(SiO)is subjected to high-energy ball milling to reduce the particle size,and then the surface is modified to carry out electrostatic self-assembly with Ti3C2 MXene in aqueous solution,and finally annealed to obtain the ball-milled(BM)SiO/MXene composite.Material characterization tests and electrochemical tests were carried out on BM SiO/MXene composites.The results showed that the particle size of SiO was effectively reduced by high-energy ball milling,and SiO particles fully contacted with MXene nanosheets under electrostatic action to form a three-dimensional compact structure,which effectively shortened the transmission path of lithium ions and electrons.MXene nanosheets also provides a buffer for the volume expansion of SiO at the same time.Therefore,BM SiO/MXene exhibits excellent electrochemical performance,and can still retain a reversible capacity of 598 mAh/g after charging and discharging 300 times at a high current density of 800 mA/g,with a capacity retention rate of 75.5%.