Silicon nanoparticles encapsulated in Si3N4/carbon sheaths as an anode material for lithium-ion batteries

Abstract

Novel composite materials comprising of silicon nanoparticles (SiNPs) encapsulated with thin layers of silicon nitride and reduced graphene oxide shells (Si@Si3N4@rGO) are prepared using a simple and scalable method. The composite exhibits significantly improved cycling stability and rate capability compared to bare SiNPs. The presence of inactive α and β phases of Si3N4 increases the mechanical endurance of SiNPs. Amorphous SiN x , which is possibly present with Si3N4, also contributes to high capacity and Li-ion migration. The rGO sheath enhances the electronic conduction and improves the rate capability. 15-Si@Si3N4@rGO, which is prepared by sintering SiNPs for 15 min at 1300 °C, spontaneous-coating GO on Si@Si3N4, and reducing GO to rGO, delivers the highest specific capacity of 1396 mAh g−1 after 100 cycles at a current density of 0.5 A g−1. The improved electrochemical performance of 15-Si@Si3N4@rGO is attributed to the unique combination of positive effects by Si3N4 and rGO shells, in which Si3N4 mitigates the issue of large volume changes of Si during charge/discharge, and rGO provides efficient electron conduction pathways. Si@Si3N4@rGO composites are likely to have great potential for a high-performance anode in lithium-ion batteries.