Research On Si-Based Anode Materials For Lithium Ion Batteries

As an important component of lithium ion batteries,anode materials are very significant for improving the capacity density and energy density of batteries.The traditional graphite anode material is difficult to meet the market demand,because its theoretical specific capacity and energy density is only 372 m A h g^-1.Therefore,silicon is considered to be a promising anode material due to its high theoretical specific capacity(3580 m A h g^-1 corresponding to Li₁₅Si₄),low discharge voltage,low cost,natural abundance and environmental friendliness.However,the practical application of silicon material is limited by the low intrinsic conductivity and the huge volume change during lithiation/delithiation process.In order to solve the above problems,core-shell-shell Si@C@Ti O₂ nanospheres and void-buffered Si@Ti O₂/C microspheres were prepared to improve the electrochemical performance of silicon-based anode materials.Core-shell-shell Si@C@Ti O₂ nanospheres were prepared by polymerization-evaporation hydrolysis method,in which titanium tetrachloride was used as the inorganic titanium source and phenolic resin synthesized by the polymerization of formaldehyde and resorcinol as the carbon source.The effects of the amount of Ti Cl₄ solution and the pyrolysis temperature were investigated.It can be observed by SEM and TEM that when the amount of Ti Cl₄ solution is 0.075 m L and the pyrolysis temperature is 700℃,Si@C@Ti O₂ nanospheres are constructed from amorphous carbon layer dotted with 4 nm titanium dioxide nanoparticles coated silicon nanoparticles.This structure can improve the electrochemical performance of the composite due to the dual functions of good electrical conductivity of amorphous carbon and strong mechanical properties of titanium dioxide particles.The optimized core-shell-shell Si@C@Ti O₂ electrode delivers a reversible specific capacity of 770m A h g^-1 after 100 cycles at a current density of 500 m A g^-1.Void-buffered Si@Ti O₂/C microspheres were prepared by electrostatic adsorption method,in which titanium tetrachloride was used as the inorganic titanium source and Si/C microspheres synthesized by the hydrothermal treatment of glucose and silicon nanoparticles as the hard template.The effects of template size and calcination temperature were investigated.It can be observed by SEM and TEM that when the template size is about 3.0～5.0μm and the calcination temperature is500℃,Si@Ti O₂/C microspheres are constructed from titanium dioxide anchored with minor amorphous carbon encapsulated dispersed silicon nanoparticles.This structure can provide buffer space for the volume change of silicon during charge/discharge to maintain the stability of the electrode structure,and lithiated mesoporous titanium dioxide shell can improve electrical conductivity of the composite.The optimized Si@Ti O₂/C microspheres delivers a reversible specific capacity of 1384 m A h g^-1 after 100 cycles at a current density of 200 m A g^-1 and a reversible capacity of 1038 m A h g^-1 can still be retained after 400 cycles at a current density of 500 m A g^-1.