Electrochemical Performance of an Ultrathin Surface Oxide-Modulated Nano-Si Anode Confined in a Graphite Matrix for Highly Reversible Lithium-Ion Batteries

Abstract

Si-based anode materials have attracted considerable attention for use in high-capacity lithium-ion batteries (LIBs), but their practical application is hindered by huge volume changes and structural instabilities that occur during lithiation/delithiation and low-conductivity. In this regard, we report a novel Si-nanocomposite by modulating the ultrathin surface oxide of nano-Si at a low temperature and highly conductive graphene-graphite matrix. The Si nanoparticles are synthesized by high-energy mechanical milling of micro-Si. The prepared Si/SiO_x@C nanocomposite electrode delivers a high-discharge capacity of 1355 mAh g^-1@300th cycle with an average Coulombic efficiency of 99.5% and a discharge capacity retention of ∼88% at 1C-rate (500 mA g^-1). Remarkably, the nanocomposite exhibits a high initial Coulombic efficiency of ∼87% and excellent charge/discharge rate performance in the range of 0.5-5C. Moreover, a comparative investigation of the three different electrodes nano-Si, Si/SiO_x, and Si/SiO_x@C are presented. The exceptional electrochemical performance of Si/SiO_x@C is owing to the nanosized silicon and ultrathin SiO_x followed by a high-conductivity graphene-graphite matrix, since such a nanostructure is beneficial to suppress the volume changes of silicon, maintain the structural integrity, and enhance the charge transfer during cycling. The proposed nanocomposite and the synthesis method are novel, facile, and cost-effective. Consequently, the Si/SiO_x@C nanocomposite can be a promising candidate for widespread application in next-generation LIB anodes.

Keywords: Si/SiOx@C nanocomposite; anode; graphene−graphite; lithium-ion batteries; low-temperature Si oxidation.