Structure and Electrochemistry of SiOx Made By Reactive Gas Milling

Abstract

SiO x is a promising Li-ion battery negative electrode material because of its high capacity and unique microstructure that leads to good cycle life. However, SiO is typically made by high temperature methods that are expensive and difficult to realize, especially at lab scale. Here, SiO x negative electrode materials were synthesized by ball milling Si in air. This method allows efficient control of oxygen content, as shown in Figure 1a and results in a similar microstructure as a commercially purchased SiO. XRD and TEM results show that the SiOx prepared by ball milling in air are composed of nanocrystalline Si embedded in an amorphous silicon oxide matrix (Figure 1b). The very low initial coulombic efficiency (ICE) of conventionally made SiO (measured here to be ~55% for Aldrich SiO) is one of its major drawbacks. In contrast, reactive gas milled SiO x have much higher reversible capacities (>1500 mAh/g) and higher ICE values (>70%). Reactive gas milled SiO x has a number of attractive features: an inexpensive and simple synthesis process, high capacity, high ICE, high thermal stability (stable microstructure at 800 °C, Figure 1c), and a special microstructure that protects Si from reaction with electrolyte, resulting in excellent cycling performance (Figure 1d). Here a detailed study will be presented describing SiO x synthesis by reactive gas milling, thermal properties, and its electrochemical performance in relation to its composition and microstructure. Figure 1