Preparation And Electrochemical Properties Research Of Silicon-Based Anode Materials For Lithium-Ion Batteries

With the increasing demand for energy density of lithium-ion battery by new energy storage equipment,the capacity development of commercial graphite anode has reached the bottleneck,and it is urgent to develop high capacity anode materials to replace graphite anode.Silicon-based anodes have the advantages of ultra high theoretical specific capacity,abundant reserves,low price and low toxicity,which is very attractive for future industrial application and is one of the most promising anode materials for the next generation of lithium-ion batteries.However,the severe volume fluctuation of silicon-based anode during the charge/discharge process will lead to the crushing of active materials,the unrestricted growth of solid electrolyte interface（SEI）,the loss of contact between active components and current collectors,and the high cost of silicon nanoparticles（SiNPs）,which seriously limits its practical application.Therefore,in view of the main problems faced by siliconbased anode,this paper improves the electrochemical performance of silicon-based anode materials from the aspects of material selection,structural design,preparation process,performance optimization and safety performance improvement,including the following aspects.（1）Melamine foam skeleton was used to replace metal copper as the current collector loaded with silicon,and MXene nanosheets were covered on the surface of SiNPs/NC Foam by self-assembly method to synthesize MXene/SiNPs/NC Foam cathode materials,which can effectively solve the problem of severe volume fluctuation of SiNPs.The results of half-cell test show that the first-cycle discharge specific capacity of MXene/SiNPs/NC Foam electrode is as high as 3216 mAh g^-1,and the initial coulombic efficiency is 80.3%.At a high current density of 0.5 C,its reversible specific capacity is 857 mAh g^-1 after 500 cycles.The electrochemical prelithiation strategy was adopted to compensate the anode electrode.The charge capacity and discharge specific capacity of the assembled battery are 159.6 mAh g1 and 148 mAh g^-1 respectively during the first cycle,and the initial cycle coulombic efficiency is as high as 92%.After 300 cycles,the battery still maintains a high reversible specific capacity,and its capacity retention rate is as high as 80.4%.（2）In order to solve the problems of complex preparation process and high cost of traditional silicon-based anode materials,the coated Si@C microsphere composite was obtained by using industrial photovoltaic cutting silicon waste as silicon source and combining high-energy ball milling and hydrothermal technology.The raw materials used were cheap and the synthesis process was simple.The results of half-cell test showed that the reversible specific capacity of Si@C microsphere electrode is 948 mAh g^-1 after 500 cycles.The lithium-ion battery assembled by prelithiation of anode electrode materials by electrochemical short circuit method still maintains a high reversible specific capacity after 300 cycles at a current density of 0.5 C,and its capacity retention rate is as high as 82%.（3）To improve the rate and cycle performance of silicon-based composites,the precursor of silicon-copper alloy（Si/Cu/SiCu₃）was obtained by introducing inactive copper elements and silicon in high-energy ball milling process.Subsequently,Si/Cu/SiCu₃@C anode material was obtained by coating Si/Cu/SiCu₃ alloy with sucrose as carbon source.Using Si/Cu/SiCu₃ alloy phase as precursor can effectively inhibit the volume fluctuation of pure silicon phase during lithium intercalation and improve its conductivity,and the electronic conductivity and lithium ion diffusion coefficient of anode materials are obviously improved.Halfcell test results show that the reversible specific capacity of Si/Cu/SiCu₃@C electrode is 984 mAh g^-1 after 500 cycles at a high current density of 0.5 C,and the Si/Cu/Cu₃Si@C anode electrode shows good cycle stability.After deep prelithiation of the anode material by chemical immersion,the lithium-ion battery can maintain a high reversible specific capacity after a long cycle at a current density of 0.5 C,and its capacity retention rate is as high as 83.2%（4）Micro-silicon anode has high tap density,but its cycle performance needs to be improved.In this regard,using solid electrolyte instead of traditional liquid electrolyte and carrying high-load micron silicon cathode can reduce the consumption of lithium ions by interfacial side reactions,improve the stability and effectively ensure the safety.The cycle performance of micron silicon//solid electrolyte//metal lithium half-cell is as high as 733.8 mAh g^-1 after 200 cycles.The NCM111 cathode material matched with the high-load micron silicon cathode was used to assemble the all solid state lithium-ion battery.After a long cycle,it still maintained a high reversible specific capacity at a current density of 0.1 C,which had good cycle stability.