Preparation And Electrochemical Properties Of Silicon-Based Anode Material For Lithium-Ion Batteries

Silicon is one of candidates replacing the graphite because of its high theoretical capacity of ~4200 mAh g-1 and low discharge potential(~0.4 V vs Li/Li+). In addition, silicon is one of the most popular element distribution in the crust which is a competitive environmental protection materials. However, the large volume change(up to 300%) of silicon during lithium alloying and lithium de-alloying and the low electronic conductivity result in pulverization, disconnection of electrical contacts, instability of the solid electrolyte interphase(SEI) and rapid capacity fade. In this paper, the optimization of electrode process and material preparation were investigated to study the influence on electrochemical performance of silicon-based anode materal for lithium-ion batteries.The conductive agent, binder and additive in the electrolyte of types and content of silicon anode electrodes were optimized to study the effect of morphology and addition amount additives on the electrochemical performance of silicon anode electrodes. The results shows the electrode with 15 wt% SuperP and 15 wt% CMC exhibits the initial reversible capacity of 2971.3 mAh/g and corresponding coulombic efficiency of 80.5%, maintains a reversible capacity of 1143.8 mAh/g after 50 cycles.on the basic of that optimization, the silicon electrode retains a stable capacity of 842.6 mAh g-1 at high current density of 1 A g-1 after 100 cycles. In addition, silicon thin electrode prepared by electron beam deposition method, the morphology and electrochemical behavior of deposited silicon film were studied. The deposition time was controlled to change the thickness of deposited silicon film, and the electrochemical performance of deposited silicon film electrode was investigated. The results indicate that the deposited silicon film has amphous structure, and the same electrochemical behavior as that of crystalline silicon. The deposited silicon film electrode exhibits the initial reversible capacity of 3215.0 mAh g-1, retains 905.0 mAh g-1 after 50 cycles at 1 C. The simulated batteries had been designed to research the photodynamics-electrochemistry of silicon electrodes, the deformation of the silicon electrodes during charge/discharge process had been obtained.In this work, first, the physicochemical and electrochemical properties of the doped polyaniline in lithium ion electrolyte were investigated. Second, the nano-silicon/polyaniline(Si/PANI) composites with a core/shell structure were successfully synthesized by dispersing the nano-silicon particles in polyaniline conductive matrix. Meanwhile, the impact of varying the PANI content on the electrochemical performance of Si/PANI composites was systematically investigated. It is demonstrated that PANI dealt with lithium ion electrolyte keeps a part of electrical conductivity because of the presence of the quinone diamide conjugate structure and the amorphous PANI has no influence on the mechanism of the battery. The good electrochemical properties can be attributed to the core/shell structure of the Si/PANI composite, which accommodates the volume change of silicon during the charge-discharge processes and impoves electrochemical performance of the Si/PANI composites.The Si/PANI composite with 12.3 wt% PANI exhibits the optimum electrochemical performance. The electrode still maintains better reversible capacity of 766.6 mAh g-1 and the capacity retention 72% is retained after 50 cycles at current density of 2 A g-1.In the synthesis of the Si/PANI composite material as the foundation, the polyaniline coated on the silicon was acted as carbon source to prepare the Si/C composite material. The results indicate that the polyaniline coated on the silicon is pyrolyzed to form the carbon coated on the silicon, the composite material keeps the original core/shell structure, and impoves the electrochemical performance. The reversible capacity retains 672.2 mAh g-1 at 1A g-1 after 50 cycles.