Preparation And Performance Study Of Silicon Based Composite Electrode Materials

The low specific capacity of graphite anode materials cannot satisfy people’s longing for high specific capacity lithium-ion battery anode materials.High specific capacity and low source of silicon material are the advantages of being suitable for commercial lithium-ion batteries.However,as a semiconductor material,low conductivity of silicon will directly affect the rate performance of the battery,and the huge volume expansion（>300%）of silicon in the process of lithium embedding easily leads to the crushing of the material matrix on the anode side.The main factors that hinder its application in commercial lithium-ion batteries are the separation of active substance from collector fluid and the continuous electrolyte consumption caused by the repeated construction of SEI film on electrode material surface.In this paper,from the perspective of structural design of electric materials,the morphology,physicochemical composition and lithium storage performance of the prepared silicon carbon composite anode materials for lithium-ion batteries were studied by various testing and characterization methods,and the dynamic mechanism of lithium storage was also discussed.This paper aims to analyze and reveal the objective factors of improving the lithium storage performance of silicon carbon composite anode material compared with pure silicon material.In this paper,a silicon carbon composite anode material（Si@C@ZNC）was prepared by sol-gel method and self-template method.The specific discharge capacity of the material remains 790m Ah g^-1after 100 cycles at 0.2 A g^-1current density.The material in the rate performance test,after 3 A g^-1current density cycle,and then to 0.05 A g^-1current density cycle,discharge capacity still retained 1037 m Ah g^-1.Through the analysis of the characterization results,it was found that the good rate and cycling performance of the material was due to the fact that the carbon coating derived from phenolic resin material on the surface of the nano silicon effectively enhanced the electrical contact between the silicon nanoparticles.The carbon coating derived from ZIF-8 material with larger surface area provides more sites for the adsorption of lithium ions.The pore channels in the mesoporous carbon coating effectively shorten the transport path of lithium ions and increase the transport rate of lithium ions.This part of the work shows that the multicore yolk-shell structure can improve the cycle stability of electrode materials,and the silicon carbon composite anode material prepared through the experiment has good energy storage performance,and can overcome many adverse factors affecting the lithium storage performance of silicon based anode materials to a certain extent.A silicon carbon composite anode material with multicore yolk-shell structure and double buffered carbon coated layer was prepared by self-template method（Si@ZNC@CNC）.After 400 cycles at 0.5 A g^-1current density,the specific discharge capacity of the material can still retain 586 m Ah g^-1,and the capacity retention rate is 80.7%.In the rate performance test,after 3 A g^-1current density cycle,and then with 0.1 A g^-1current density cycle,discharge specific capacity still retained 682 m Ah g^-1,and after 50 cycles of discharge specific capacity retention rate is higher（90%）.Through the analysis of the test data,it is found that the good lithium storage performance of Si@ZNC@CNC material is due to the space reserved between the double buffered carbon cladding layers for the volume deformation of silicon material in the cycle.The existence of mesoporous carbon cladding layer with large specific surface area increases the transmission rate of lithium ions and improves the rate performance of the battery.This part of the work shows that the silicon carbon composite anode material with double buffer coated carbon layer and multicore yolk-shell structure has improved the cycle stability and electrical conductivity compared with pure silicon material,achieving the set goal of improving the lithium storage performance of silicon anode material.A silicon carbon composite anode material coated with HKUST nanoparticles was prepared by a simple one-step hydrothermal method（Si@Cu-NC）.In the long-term cycle performance test at 0.5 A g^-1current density,the discharge specific capacity of the material remains 748.9 m Ah g^-1after 680 cycles,and the capacity retention rate is 71.4%.In the rate performance test,the cycle can be stable at all current densities,and the cycle can still be stable after the high current charging and discharging test back to the low current charging and discharging test.Through the analysis of the experimental data,it is found that the good electrochemical performance of Si@Cu-NC material is due to the fact that the carbon coating derived from HKUST material can effectively buffer the volume expansion of silicon in the process of lithium intercalation.The presence of elemental Cu nanoparticles in the carbon layer further improves the overall deformation resistance of the electrode material.The graphitization degree of the carbon cladding layer increases due to the presence of metal catalyst.This part of work shows that HKUST material is suitable for silicon carbon composite electrode material system,and the prepared silicon carbon composite anode material（Si@Cu-NC）has overcome many adverse factors affecting the performance of silicon based anode materials for lithium storage to a certain extent.