Mg‐doped, carbon‐coated, and prelithiated SiOx as anode materials with improved initial Coulombic efficiency for lithium‐ion batteries

Abstract Silicon suboxide (SiO x , x ≈ 1) is promising in serving as an anode material for lithium‐ion batteries with high capacity, but it has a low initial Coulombic efficiency (ICE) due to the irreversible formation of lithium silicates during the first cycle. In this work, we modify SiO x by solid‐phase Mg doping reaction using low‐cost Mg powder as a reducing agent. We show that Mg reduces SiO 2 in SiO x to Si and forms MgSiO 3 or Mg 2 SiO 4 . The MgSiO 3 or Mg 2 SiO 4 are mainly distributed on the surface of SiO x , which suppresses the irreversible lithium‐ion loss and enhances the ICE of SiO x . However, the formation of MgSiO 3 or Mg 2 SiO 4 also sacrifices the capacity of SiO x . Therefore, by controlling the reaction process between Mg and SiO x , we can tune the phase composition, proportion, and morphology of the Mg‐doped SiO x and manipulate the performance. We obtain samples with a capacity of 1226 mAh g –1 and an ICE of 84.12%, which show significant improvement over carbon‐coated SiO x without Mg doping. By the synergistical modification of both Mg doping and prelithiation, the capacity of SiO x is further increased to 1477 mAh g –1 with a minimal compromise in the ICE (83.77%).