Carbon dioxide solid-phase embedding reaction of silicon-carbon nanoporous composites for lithium-ion batteries

•Using CO2 as the carbon source, the Si/carbon solid-phase doping is realized by introducing the active agent Mg.•The actual particle size of Si in the prepared Si-based anode material is less than 50 nm.•The three-dimensional network structure of carbon provides the most critical buffer layer for Si volume change. SiO2 is one of the critical raw materials for preparing Si anode. The direct use of porous Si made from SiO2 in LIBs is challenging. Although carbon cladding can improve the cycling performance of Si anode materials made from SiO2, the surface coating cannot address the comminution inside the material during repeated volume deformation. For the first time, we prepared an in-situ doped Si/carbon anode material that uses SiO2 and CO2 as Si and carbon sources and Mg as the reduction medium (Mg2Si + CO2 → MgO + Si + C). The in situ embedded carbon completes the nanosizing of Si (less than50 nm) and forms a three-dimensional (3-D) carbon network that enhances electrical conductivity and acts as a buffer layer. After 500 cycles at 0.5 A g−1, the discharge specific capacity is 912 mAh g−1, and the capacity still has 1487 mAh g−1 even at 4 A g−1. The simple method of preparing Si/carbon composite material in situ provides a new idea for modifying Si-based anode material and provides a valuable reference for carbon doping.