Study on Electrochemical Characteristics of Crystal Structure Changes Effects of Silicon Anode Materials for Lithium Ion Batteries

Abstract

Graphite is widely used as a representative anode material in commercialized lithium-ion secondary batteries. However, with a theoretical capacity of 370 mAh/g, it is difficult to manufacture high-capacity/high-density lithium-ion secondary batteries. Therefore, research is actively underway to find high-capacity substances to replace graphite. Silicon anode materials are currently attracting attention as next-generation high-capacity cathode materials. Silicon forms Li4.4Si when fully charged through an alloying/dealloying process with lithium during the reaction. Graphite is intercalation/deintercalation in reaction with lithium and LiC6 is formed when fully charged. That's why silicon has a theoretical capacity of 3800 mAh/g, about 10 times that of graphite.However, silicon is a high-capacity electrode material that overcomes the theoretical capacity limit of graphite, and has the disadvantage of experiencing volume expansion of about 400% during repeated charge/discharge cycles. Problems such as material cracks due to volume expansion can affect the safety of the battery. Various studies are being conducted to solve silicon-related challenges to effectively utilize silicon materials. Previous studies have explored the use of binders or additives to mitigate volume expansion. In addition, various types of silicon materials such as Si alloy and SiOx are being developed to suppress volume expansion through matrix formation. Nevertheless, despite the development of silicon materials, structural changes in the charging and discharging process of silicon remain unclear.This study aims to analyze the structural changes that occur during the charging and discharging process of silicon. The experiment evaluates the electrochemical characteristics of crystalline silicon and amorphous silicon and compares the behavior and structural changes during charging/discharging. The volumetric expansion measurements are performed with electrochemical characterization, and ex-situ X-ray diffraction (XRD) and transmission electron microscope (TEM) analyses are performed for comparison with crystal structural changes.