Preparation of micro-nano hierarchical Si/C composites by CO₂ oxidation of porous Mg₂Si and lithium storage properties

With the advantages of abundant reserves, stable working voltage and high energy density, silicon-based anode materials are regarded as a kind of promising anode for lithium-ion batteries. However, their high volume expansion of 300% and low ionic conductivity are very detrimental to battery cycling. In this paper, a micro-nano hierarchical three-dimensional MN-p-Si/C composite was successfully synthesized by using a one-step CO₂ oxidation process with porous Mg₂Si as raw material. During the oxidation process, the Mg was transformed into MgO and etched away by diluted hydrochloric acid solution, and nanoscaled voids were thus introduced in the micro porous Si system. The micro-nano hierarchical structured MN-p-Si/C not only alleviates the volume expansion of silicon during the delithiation process but also provides a three-dimensional effective channel for the transportation of ions/electrons. The carbon layer on MN-p-Si/C substantially improves the electrical conductivity of the composite. Owing to these structural advantages, the MN-p-Si/C composites demonstrated excellent electrochemical properties. Their first charge/discharge specific capacity was 2 869.2 mAh/g,2 364.5 mAh/g with an initial Coulomb efficiency of 82.41%, and the MN-p-Si/C reversible capacity could be maintained at 1 127.1 mAh/g after 200 cycles at a high current density of 1 A/g. The specific capacity retention rate was 70.9 with good application prospects.