Preparation And Performance Studies Of Si-SiO_x-Sn/C Anode Material For Li-ion Batteries

Carbon materials are utilized as anode materials for the improvement of safety and cycle life in lithium batteries. Although carbon materials show good reversibility and stability for cycles, their specific capacities are limited to 372 mAh g-1.It can't satisfied the demands of high-energy-density lithium batteries in electronics and electrical vehicles.As anode materials for Li-on batteries, silicon has a highest theoretical specific capacity of 4200 mAh g-1, tin has aspecific capacity of 994 mAh g-1. But silicon and tin undergo large volumetric change during lithium insertion, it is regarded that the expansion and contraction of lithium silicide during the charge-discharge cycling leads to the pulverizing of Si and Sn powder is formed.It would cause the breakdown of the electrode materials, resulting in the loss of capacity within several cycles. Therefore, many research works were carried out on methods to study and improve its cycle life in recent years.This dissertation is a result of research work in the area of Li-ion batteries, and it is believed that the subject under study is a frontier of current research topics. The modified Si-SiOx-Sn/C has been synthesized by a carbon thermal reduction method and a high temperature solid-state method, the influence of various temperatures and modify were investigated in this work through a series of experiments, and following conclusions were drawn:1. Si-SiOx-Sn/C composites were prepared by a carbon thermal reduction method. The electrochemical performance of the composites as anode material for lithium-ion batteries was studied.The composites were prepared at different temperature in nitrogen flow, and colded to room-temperature naturally. The Si-SiOx-Sn/C (950℃) composites showed the best electrochemical performance. The composites can deliver a specific capacity of 1475 mAh g-1 at 150 mA g-1.They have a higher specific capacities after sixty cycles.2. Modified Si-SiOx-Sn/C composites were synthesized by polymerization of furfuryl alcohol and solid phase synthesis process. The characteristics of the composites as anode material for lithium-ion batteries were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods. The electrochemical performance of the anode material was studied. Si-SiOx-Sn/C composites have a discharge specific capacity of 1595 mAh g"'and a charge specific capacity of 575 mAh g-1 at 150 mA g-1. Modified Si-SiOx-Sn/C composites have a higher discharge specific capacity of 1475 mAh g-1 and a higher charge specific capacity of 712 mAh g"1 at 150mA g-1 than Si-SiOx-Sn/C composites. Modified Si-SiOx-Sn/C composites can display a specific capacity of 1628 mAh g-1 at 90 mA g-1,1595 mAh g-1 at 150 mA g-1 and 1184 mAh g-1 at 225 mA g"'.The specific capacities have decreased with the increasing of their current density. After 120 cycles, the specific capacities have retained at 60% comparing to the 20th. Obviously, Modified Si-SiOx-Sn/C composites exhibited high specific capacities, good cyclability and excellent electrochemical performance of the anode material for lithium-ion batteries.