Study On Alloying Process Modification Of Silicon Anode Material For Lithium Ion Batteries

With the rapid development of new energy vehicle industry and intelligent electronic device industry,a new generation of high energy density lithium ion battery has become the focus of new energy academia and industry.In terms of anode materials for lithium ion batteries,the theoretical specific capacity of graphite with the highest commercialization is only 372 m Ah g^-1,which seriously limits the development of new energy industry and cannot meet the demand of people for the development of high capacity lithium ion batteries.Looking for a higher energy density anode material to replace graphite has gradually become the key of current research.At present,the theoretical specific capacity of silicon（Si）is 4200 m Ah g^-1,which is the highest capacity material among the anode materials for lithium ion batteries.Si anode materials are widely considered as the next generation of the most potential high energy density anode materials for lithium ion batteries due to their low lithium deintercalation platform,extensive sources and high safety performance.However,there are two urgent problems to be solved in Si materials.Firstly,the huge volume change of Si particles during the charging and discharging will lead to the crushing of Si particles,and the pulverization of electrode materials will fall off from the collector,which will lead to the rapid decline of cycling performance.Secondly,the low conductivity of Si materials will affect its rate performance,which cannot meet the high requirements of fast charging and discharging of batteries.These shortcomings undoubtedly greatly limit the large-scale promotion of Si anode materials.In order to solve the above two problems,this paper proposes two modification ideas.First,based on the deposition of silver（Ag）particles on the surface of Si particles by metal-assisted chemical deposition method,this paper focuses on enhancing the contact between Ag and Si interface（Ag-Si）by rapid thermal process（RTP）to form a stable Si/Ag alloy（Ag₂Si）.Finally,a Si anode material with high cycling performance and high rate performance was obtained.Second,copper（Cu）nanoparticles were deposited on the surface of Si particles by metal-assisted chemical deposition method to modify them,and then the Si modified with Cu particles（Si/Cu）was mixed and coated,and then RTP was carried out to prepare Si anode material with Cu-Si interface alloying and uniform carbon coating on the surface（Si/Cu₃Si/Cu@C）by one-step method.The main research contents are as follows:In this paper,Ag nanoparticles were deposited on the surface of Si particles for surface modification.Si particles with high conductivity could be obtained,and the volume expansion effect of Si could be inhibited to a certain extent.Ag-Si interface was alloyed to form Ag₂Si by RTP,which enhanced the interface contact between Si particles and Ag nanoparticles.Finally,Si/Ag₂Si/Ag anode material with high rate performance after long cycle was obtained.The reversible capacity of Si/Ag₂Si/Ag still remains 1138 m Ah g^-1over 100 cycles at 0.5 C(1 C=4.2 A g^-1),which is 465m Ah g^-1higher than of Si.Besides,Si/Ag₂Si/Ag holds the reversible capacity of 849m Ah g^-1at 2 C.All this is attributed to the fact that Ag is on the surface of Si,which improves the conductivity of Si.In order to further improve the stability of the electrochemical performance of the prepared materials,the RTP of the anode electrode was proposed in this paper.First,the sample of modified Cu particles on the surface of Si obtained by metal-assisted chemical deposition was mixed with conductive agent and sodium alginate colloid and evenly coated on the Cu foil.Then,the obtained electrode was processed by RTP,and the Si anode material（Si/Cu₃Si/Cu@C）with uniform carbon coating and Cu-Si interface alloying was prepared by one-step method.The composite anode electrode after the above treatment showed excellent electrochemical performance.The reversible capacity remains 1362 m Ah g^-1after 100cycles at 0.2 C current density,which is 997 m Ah g^-1higher than that of Si electrode.The capacity remained at 604 m Ah g^-1at 2 C.