Fabrication of porous SiOx/nanoSi@C composites with homogeneous silicon distribution for high-performance Li-ion battery anodes

The application of high-capacity silicon anodes in lithium batteries is restricted by the significant volume changes that occur during electrochemical alloying and long-term galvanic segregation cycles. In this work, we proposed a gas-phase magnesiothermic reduction strategy to fabricate highly porous SiOx/nanoSi@C (0 < x < 2) composites. This approach diffused the evaporated magnesium atoms into the interior of the SiO2, preventing the fast self-propagating magnesium thermal reduction reaction only on the surface of the silicon oxide particles and regulating the distribution and relative content of SiOx and nanoSi in the active material network. Thus, the proposed approach formed a porous structure of silicon nanocrystals that were diffusely distributed in the silicon oxide matrix. For the as-prepared SiOx/nanoSi@C composites, the nano-Si component increased the reversible capacity of the composite, the porous SiOx matrix suppressed the volume expansion of crystalline silicon by generating Li2O and lithium silicate protective layers, and the carbon coatings further accommodated volume expansion and increased surface contact between the active material and the electrolyte. As a result, the 0.75SiOx/0.25nanoSi@C anode exhibited excellent electrochemical performance with a reversible capacity of 1067.92 mAh/g after 400 cycles at a current density of 1 A/g.