Study On Preparation And Performance Of Silicon-based Materials As Anode For Lithium Ion Batteries

Silicon is considered as one of the most promising anode materials for high-energy lithium ion batteries owing to the high theoretical specific capacity,low voltage plateau and abundance in earth.However,Si suffers from low intrinsic conductivity and extremely huge volumetric variation,which causes fracture and shedding of active materials,leading to poor cycle performance.In this work,carbon-coated Raney nickel/carbon nanotube/silicon(RN/CNT/Si@C),hard carbon-supported Si encapsulated in nitrogen-doped carbon(HC/Si@NC)and embedded Si/nitrogen-doped carbon(Si/NC)composites are synthesized to improve the electrochemical performance of Si anode.RN/Si@C composites are synthesized through ball-milling and magnesiothermic reaction,respectively with RN as host.The effects of synthesis route and addition of CNT on structure and electrochemical performance are estimated.Carboxylated CNT can for fiber-like carbon network on the surface of RN and the combination of the host and Si O₂ can be tighter as hydrogen bond can form between CNT and Si O₂.The network of CNT can further fix Si and enhance the electrical conductivity,which makes RN/CNT/Si@C composites exhibit better cycle and rate performance.The composite delivers a reversible capacity of 467 m Ah g^-1 after 100 cycles at a current density of 0.1A g^-1.Hierarchical HC/Si@NC composites are successfully synthesized via electrostatic self-assembly between an intrinsic negatively charged hard carbon precursor resorcinol formaldehyde resin sphere(RFS)and positively charged Si nanoparticles and consequent N-doped carbon coating.The hierarchical structure can effectively alleviate the expansion of Si.Porous carbon improves the infiltration of electrolyte and provides more channels for Li+transportation and the N doping enhances the conductivity.All these factors contribute to the excellent cycle and rate performance of the composites which deliver a reversible specific capacity of 541 m Ah g^-1 after 100 cycles at a current density of 0.2 A g^-1 and 350 m Ah g^-1 after 300 cycles at a higher current density of 1 A g^-1.Embedded Si/NC composites are synthesized through the polymerization of 3-aminophenol and formaldehyde via a one-step method.Si is embedded in porous carbon matrix,which can significantly address the volumetric effective of Si.The porous structure can provide amounts of channels for Li+transportation.Besides,N doping can enhance the conductivity and structural integrity.As a result,the optimal performance of Si/NC composites deliver a reversible capacity of 1169 m Ah g^-1 after100 cycles at a current density of 0.5 A g^-1.A capacity of 502 m Ah g^-1 is obtained at a higher current density of 2 A g^-1 according to the rate performance tests,which indicates excellent rate performance.