Synthesis And Electrochemical Performance Of Silicon-based Composites

Lithium-ion batteries have been widely used in the fields such as electric vehicles and mobile devices due to their high energy/power density,long-term cycle life,and environmental safety.The development of the society triggers higher and higher requirements on the performance of both anode and cathode materials for lithium-ion batteries.For the anode materials of lithium ion batteries?LIBs?,compared to widely used graphite anode materials,silicon has become one of the most promising next-generation new materials due to its high theoretical capacity.However,silicon has the disadvantage of poor intrinsic conductivity and huge volume expansion during charge/discharge process.How to effectively improve the electrochemical performance of silicon anode materials has become an academic and industrial research frontier and hot topic.To adress such issues,this thesis proposes to modify the electrochemical performance of silicon anodes by combining with carbon nanomaterials.Firstly,we studied the modification of the electrochemical performance of silicon with carbon nanotubes?CNTs?;then,we fabricated three-dimensional silicon/reduced graphene oxide?Si/rGO?porous composite to improve the electrochemical performance;finally,N-doped graphene coated silicon anode was synthesized and investigated.The main content and results of this research are as follows.1.The synthesis and electrochemical performance of Si-CNTs anode material have been investigated.The results show that compared to the bare silicon powder,the Si-CNTs anode deliveres much better electrochemical performance due to the incorporation of CNTs.The capacity of the Si-CNTs remained 352 mAh g^-1 at 100 mA g^-1 with a capacity retention of 10%after 120 cycles,and 233 mAh g^-1 at 5000 mA g^-1,while the capacity of bare silicon powder decreases down to 113 mAh g^-1 from the initial 2250 mAh g^-1 after 30 cycles,with a capacity retention of 5%.The Si-CNTs exhibit enhanced electrochemical performance due to the introduction of CNTs which improves the conductivity,and facilitates the transfer of ions and electrons,resulting in significant increase in electrochemical performance.2.The synthesis and electrochemical performance of 3D Si-rGO have been investigated.The research reveals that 3D Si-rGO has excellent electrochemical performance:it delivers a capacity of 901 mAh g^-1 after 100 cycles with 24%capacity retention at 100 mA g^-1;it shows a capacity of 100 mAh g^-1 at 5000 mA g^-1.The three-dimensional porous structure not only enhances the conductivity of the anode,but also provides space for the volume change of silicon nanoparticles in the process of lithiation/delithiation,accommodates the volume expansion and keeps the structure,leading to improvement of the electrochemical performance.3.The synthesis and electrochemical performance of pomegranate-like silicon/nitrogen-doped graphene microspheres?PSNGM?have been investigated.The results show that with N-doped graphene,the PSNGM exhibited better electrochemical performance that the undoped PSGM.The PSNGM delivere a capacity of 1141 mAh g^-1 at 100 mA g^-1 with a capacity retention of 36.4%after 150 cycles,and a rate capacity of 273 mAh g^-1 at 5000mA g^-1.The excellent cyclic performance of the PSNGM anode can be attributed to the incorporation of the superior conductive N-doped graphene,which enhances the conductivity,offer abundant diffusion channels for Li ions,and accommodate the volume expansion of silicon,resulting in enhancement in the electrochemical performance.