Study On Barrier Layer Materials And Anode Materials For Silicon-based Thin-film Lithium-ion Batteries

Direct integration of power supply module with electronic devices or sensors on the same Si substrate is a way to further minimize the size of microelectronic system.Silicon-based lithium-ion battery is a promising candidate for such power supply module because of its high energy/power density,good compatibility during the fabrication process and easy integration with electronic devices.Integrated lithium-ion battery consists of substrate,diffusion barrier layer,current collector,anode,electrolyte and cathode.In order to realize such integration structure,the electrochemical properties of some common materials?Si,SiO₂ and SiN?used in semiconductor industry are studied in this thesis.In the integration structure stated above,diffusion barrier layer against lithium ions plays an essential role in bloking lithium ions from diffusing in case of degrading the performance of electronic device on the same substrate.The ability of thermal SiO₂ film as the barrier layer is investigated.8-nm thermal SiO₂ is effective to protect substrate from alloying with lithium ions,but F-Si-Li is formed near the Si/SiO₂interface after cycling.30-nm thermal SiO₂ proves to be a qualified diffusion barrier layer without any chemical reaction in the bulk because of its poor electrochemical reaction kinetics.Anode materials influence the performance of lithium-ion battery.Si has a high specific capacity(4200 mAh g^-1),however,the volume of Si expands and shrinks severely upon insertion and extraction of lithium.This phenomenon will damage the structure of electrode,leading to capacity fading and even battery failure.In order to prolong the lifespan of Silicon-based lithium-ion battery,SiN and Si thin-film anodes are investigated in this thesis.SiN thin-film anodes are prepared by ICP-CVD and PE-CVD techniques.ICP-CVD SiN anode with a thickness of 500 nm shows a low capacity(39 mAh g^-1).PE-CVD SiN anode with a thickness of 500 nm exhibits an abrupt increase of capacity after several low-capacity cycles,and then maintains a capacity of881 mAh g^-1 for over 300 cycles at 0.6 C.The sudeden change of capacity is ascribed to hydrogen dissociation in the PE-CVD anode,increasing the conductivity and reaction kinetics.Moreover,10-?m free-standing Si thin-film anodes are mainly produced by MEMS silicon bulk etching technique.The capacity of Si thin-film anode is high in the beginning,but decays quickly in the following cycles.With a SiN layer covered around the Si thin-film anode surface,the capacity retention improves apparently,because the SiN layer can maintain the anode structure during cycling.