Novel carbon-free niobium silicide/oxide nanocomposites for lithium-ion battery anodes

Abstract

Carbon-free niobium silicide (NbSi2)-based composites, starting from silicon monoxide and niobium metal elements, are synthesized by a simple top-down approach with a high-energy mechanical milling process facilitating the manufacture of nanosized materials, and are employed as anode materials for lithium-ion batteries. The final product has three phases comprising Nb, NbSi2, and Nb2O5, whose structures and morphologies are thoroughly examined using advanced characterization techniques. Although the as-prepared Nb/NbSi2@Nb2O5 composites do not contain carbon, the volume expansion is mitigated during the (de)alloying process with Li ions and the composites possess good electrical conductivity. The carbon-free Nb/NbSi2@Nb2O5 composites, specifically the Nb/NbSi2@Nb2O5 (2:8 & 3:7) electrodes, exhibit stable electrochemical performance (430 & 400 mAh g−1 after 300 cycles) as well as remarkable rate performance with discharge capacities of 699 & 491 mAh g−1 at a high current density of 10 A g−1 with 86 & 80% of normalized capacity retentions. This noticeable improvement can be due to the presence of Nb in the NbSi2 phase and the amorphous Nb2O5 matrix in the composites, which provide high electrical conductivity (for Nb) in addition to forming stable structural stability (for Nb and Nb2O5). Therefore, the novel Nb/NbSi2@Nb2O5 composites presented here provide potential for viable application in high-performance anodes for lithium-ion cells.