Preparation And Electrochemical Performance Of Silicon-Based Composite Anode Materials For Lithium-Ion Batteries

In the new type of electrochemical energy storage systems,lithium-ion batteries with high energy density,environmental friendly,no memory effect and good cycle performance occupy the market of the power supplies for mobile phone,laptop and other high-end portable electronic terminals [1,2].However,the actual capacity of graphite carbon anode materials used in lithium-ion batteries has been very close to its theoretical capacity[3],and the room for improvement is very limited.Therefore,it is an important research direction to find the anode materials with higher specific capacity.Silicon is one of the most promising alternative anode materials,but its poor conductivity and the volume effect under the condition of repeated charge-discharge processes will cause the pulverization of silicon powder,resulting in the rapid decay of the capacity.Although many researchers have explored lots of methods to solve the problem of silicon materials,most of the synthesis methods are complex,which limits the possibility of mass production.In order to solve this problem,the author attempts to prepare silicon-based composite materials by simple and low cost ways and study its electrochemical properties.The main contents and conclusions are as follows:1.Core-shell Si/C composites(Si@C)anodes were prepared by coating resorcinol-formaldehyde resin onto commercial Si nanoparticles(Nano-Si)followed by a carbonization process.Afterwards,the effects of the carbonization temperature and the binder type on electrochemical performance of the electrode were investigated systematically.The transmission electron microscope(TEM)analyses indicated that the Si@C consisted of Nano-Si coated by uniform amorphous carbon shells(thickness: 5~15nm).Electrochemical tests revealed that the Si@C carbonized at 750 °C with the binder of sodium alginate showed an initial discharge capacity of 2025.5 mAh g-1(initial coulombic efficiency: 76.6 %),and they still delivered reversible capacity of 571.4 mAh g-1 after 100 cycles.2.Si/C composite materials with hierarchical structure were prepared by coating resorcinol-formaldehyde resin onto commercial Si nanoparticles(Nano-Si)via solvothermal method followed by a carbonization process with expandable microspheres together.Afterwards,the effects of the content of expandable microspheres on electrochemical performance of the electrode were investigated.The Scanning electron microscopy(SEM)analysis showed that the Si@C particles with core-shell structure were attached to the carbon skeletons,which were the carbonization products of expandable microspheres,to form the hierarchical structure.The electrochemical results showed that the electrochemical performance of hierarchical Si/C composite materials were better than the core-shell Si/C composites.They delivered the first discharge capacity of 1739.3 mAh g-1,and the capacity retention rate is about 60% after 100 cycles.3.Cu-Si/Ag/C composite materials were prepared by one-step carbonization of the mixture of Si nanoparticles(Nano-Si),expandable microspheres and epoxy resin conductive silver adhesives.The XRD tests indicated that the composites contained the major phases of Si,Ag,Cu,Cu3 Si and amorphous C.The electrochemical tests showed that the initial discharge capacity of Cu-Si/Ag/C composites was 1016.8 mAh g-1,and the capacity retention was 69.1 % after 50 cycles.