Enhancing Lithium Storage Properties of Two-dimensional SiOx by Forming Composites with Molybdenum Oxides

Abstract

Lithium ion batteries (LIBs) have been widely employed for portable electronic devices, electrical vehicles (EVs), drones, and energy storage systems (ESSs) and their uses have been expanded as industries developed because of their high energy density and stable cycling performance. Graphite has been commonly used as an anode material for LIBs because it has some merits for anode material, such as low reduction potential and high stability. However, further advancement in LIBs is needed to meet the demand for batteries with high energy density for EVs and ESSs. Silicon has been considered as a promising anode material due to its much higher theoretical capacity than that of graphite. However, it suffered severe volume expansion during electrochemical reactions and it resulted in poor cycling performance. Therefore, various attempts were conducted for commercial uses of silicon-based anode materials and silicon oxide (SiOx) has received much attention as a leading candidate, because SiOx matrix can alleviate volume expansion problem of silicon anode. Two-dimensional (2D) structured SiOx nanofoils, which are one of the unique structured SiOx materials, also showed some promising anodic performance for LIBs including highly stable cycling performance, excellent dimensional stability, and rate capability. However, their low energy density and initial coulombic efficiency, compared to other silicon based anode materials, should be improved. Herein, composites were synthesized by treating molybdenum oxides (MoO3 and MoO2) on the surface of 2D SiOx nanofoils through simple mixing in ethanol solvent, to enhance their lithium storage properties of 2D SiOx. Molybdenum oxides have been known as conversion-type transition metal oxides and they have good chemical stability and high charge storage capability. These features were conducive to enhancing lithium storage properties of 2D SiOx nanofoils and MoO2 was more effective than MoO3. The structural properties and electrochemical properties will be discussed in detail in this work.