| As the anode material of lithium ion battery,silicon anode material has many advantages such as high theoretical specific capacity(4200 m Ah g-1),low electrode potential（<0.5 V）and abundant storage.However,during the silicon lithium alloying process,silicon with highly lithium inserting state could produce a violent volume expansion effect（up to 300%）,which would be easily lead to structural damage and powder falling off from the active material during the cycle process,thus seriously decreasing the cycling performance,coulomb efficiency and other electrochemical properties.In order to address these problems,in this thesis,the nano-silicon materials with reducing of silicon oxide materials was prepared with the low temperature molten salt method,and the spherical nano-porous hollow silicon（NPH-Si）materials was fabricated with sol-gel method.Besides,the spherical carbon coated hollow silicon（H-Si@C）composites was prepared with dopamine by in-situ polymerization to achieve controllable structure.In addition,the shell structure was designed by using the material’s own composition characteristics to realize the preparation and performance analysis of"honeycomb"hollow silicon/carbon double continuous carbon layer silicon carbon（CPH-Si/C）composite anode material.The specific research contents are as follows:1)Hollow silicon was reduced by low temperature molten salt method,which were prepared under 220℃conditions.Combined with sol-gel method,hollow silicon material with nano-porous structure was prepared,the XRD,SEM and other characterization methods was revealed the composite anode with good crystallinity and complete spherical morphology.The electrochemical performances were carried out revealed that it had a better electrochemical performance than commercial silicon.After 300 cycles of charge and discharge process at 1A g-1 current density,the reversible specific capacity is 1225 m Ah g-1 and coulomb efficiency is 81.3.After 500 cycles of constant current charge and discharge at a high current density of3 A g-1,the reversible specific capacity remains 884 m Ah g-1.When the current density is 0.1,1,2,3,and 5 A g-1,the reversible specific capacity is still up to 2132 m Ah g-1 when the current density ranged from 5A g-1 to 0.1 A g-1,which indicates that it has a good rate performance.2)The hollow silicon@carbon shell（H-Si@C）composite anode material with core-shell structure is designed.The surface of the hollow silicon material is coated with dopamine through in-situ polymerization,and finally H-Si@C composite material is obtained after high temperature carbonization.The test shows that H-Si@C has uniform core-shell structure,which is compared with H-Si/G anode material.H-Si@C electrode material has more excellent electrochemical performance:when the current density is 0.1 A g-1,the specific capacity of initial discharge is up to 2786.5 m Ah g-1,corresponding to the first coulomb efficiency of82.3%;Under the current density of 1 A g-1,the discharge specific capacity of 1840 m Ah g-1still remains after 500 cycles.The rate performance test shows that H-Si@C electrode material has excellent rate performance and stability.3)A preparation method of hollow silicon/carbon（CPH-Si/C）double continuous layer composite anode material was proposed based on polystyrene nanospheres were fused and crosslinked with oxysilane,using the material composition characteristics of oxysilane.Related characterization shows that CPH-Si/C materials have many hollow holes on the surface,showing a unique"honeycomb"structure morphology.When the current density is0.1 A g-1,the reversible specific capacity is up to 2621 m Ah g-1,and the initial coulomb efficiency is up to 83.2%.Under the current density 2 A g-1,after 500 cycles of charge and discharge,the reversible specific capacity is still 1625 m Ah g-1.The excellent electrochemical performance of CPH-Si/C materials is attributed to the carefully designed double continuous carbon layer and the contribution of pseudocapacitance to capacity. |
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