In-situ arc discharge-derived FeSn₂/onion-like carbon nanocapsules as improved stannide-based electrocatalytic anode materials for lithium-ion batteries

Core/shell-structured FeSn₂/onion-like carbon (FeSn₂/OLC) nanocapsules of confined size range of sub-50 nm are synthesized via an in-situ arc-discharge process, and are evaluated in comparison with FeSn₂ nanoparticles as an improved stannide-based electrocatalytic anode material for Li-ion batteries (LIBs). The in-situ arc-discharge process allows a facile one-pot procedure for forming crystalline FeSn₂ stannide alloy nanoparticle cores coated by defective OLC thin shells in addition to a confined crystal growth of the FeSn₂ nanoparticle cores. The LIB cells assembled using the FeSn₂/OLC nanocapsules as the electrocatalytic anodes exhibit superior full specific discharge capacity of 519 mAh·g⁻¹ and specific discharge capacity retention of ~62.1% after 100 charge-discharge cycles at 50 mA·g⁻¹ specific current. The electrochemical stability of FeSn₂/OLC nanocapsules is demonstrated from the good cycle stability of the LIBs with a high specific discharge capacity retention of 67.5% on a drastic change in specific current from 4000 to 50 mA·g⁻¹. A formation mechanism is proposed to describe the confined crystal growth of the FeSn₂ nanoparticle cores and the formation of the FeSn₂/OLC core/shell structure. The observed electrochemical performance enhancement is ascribed to the synergetic effects of the enabling of a reversible lithiation process during charge-discharge of the LIB cells by the FeSn₂ nanoparticle cores as well as the protection of the FeSn₂ nanoparticle cores from volume change-induced pulverization and solid electrolyte interphase-induced passivation by the OLC shells.