Mg‐doped, carbon‐coated, and prelithiated SiO_x 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 SiO₂ in SiO_x to Si and forms MgSiO₃ or Mg₂SiO₄. The MgSiO₃ or Mg₂SiO₄ 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 MgSiO₃ or Mg₂SiO₄ 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%).