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

Silicon suboxide (SiOx, x approximate to 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 SiOx by solid-phase Mg doping reaction using low-cost Mg powder as a reducing agent. We show that Mg reduces SiO2 in SiOx to Si and forms MgSiO3 or Mg2SiO4. The MgSiO3 or Mg2SiO4 are mainly distributed on the surface of SiOx, which suppresses the irreversible lithium-ion loss and enhances the ICE of SiOx. However, the formation of MgSiO3 or Mg2SiO4 also sacrifices the capacity of SiOx. Therefore, by controlling the reaction process between Mg and SiOx, we can tune the phase composition, proportion, and morphology of the Mg-doped SiOx 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 SiOx without Mg doping. By the synergistical modification of both Mg doping and prelithiation, the capacity of SiOx is further increased to 1477 mAh g(-1) with a minimal compromise in the ICE (83.77%).