Magnesiated Si‐Rich SiO _<i>x</i> Materials for High‐Performance Lithium‐Ion Batteries

Silicon monoxide (SiO)‐based materials have significant potential as high‐capacity anode materials for lithium‐ion batteries (LIBs). However, the low initial Coulombic efficiency (ICE) associated with the irreversible electrochemical reaction of the amorphous SiO 2 phase (a‐SiO 2 ) in SiO hinders its application in commercial LIBs. The preemptive phase transition of a‐SiO 2 to an inactive silicate phase using a metal hydride is a promising strategy for improving the ICE. However, this process inevitably leads to reversible capacity loss. In this study, a high‐capacity Si‐rich SiO x composite prepared by high‐energy mechanical milling is premagnesiated using MgH 2 , resulting in a significantly improved capacity and ICE compared to those of pristine SiO and Si‐rich SiO x composites. The resulting Si/Mg 2 SiO 4 composite electrode exhibited a high initial discharge capacity of 1961 mAh g −1 with a high ICE of 87.0% and maintained highly stable capacity retention after 200 cycles compared to the Si‐rich SiO x . These improved electrochemical properties are attributed to the preemptively synthesized Mg 2 SiO 4 , which not only prevents irreversible reactions between lithium and a‐SiO 2 during the initial lithiation but also acts as a buffer phase that effectively reduces volume expansion during cycling.