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

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 inactiveαandβphases of Si₃N₄increases the mechanical endurance of SiNPs. Amorphous SiN, 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^-1after 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 Si₃N₄and rGO shells, in which Si₃N₄mitigates 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.