Improved electrochemical performance of onion-like carbon coated magnetite nanocapsules as electromagnetic absorptive anode materials for lithium-ion batteries

Abstract

The synthesis of magnetite (Fe₃O₄)@C nanocapsules with Fe₃O₄ nanoparticles as the core and onion-like carbon as the shell has been reported. The electromagnetic (EM) characteristics and electrochemical performance are studied. The onion-like carbon shell improves dielectric loss and EM matching degree, leading to enhanced EM properties. The optimal reflection loss (RL) value of the Fe₃O₄@C–paraffin composite is −45.9 dB at 16.6 GHz at a thickness of 2.4 mm and the absorption bandwidth of 7.2 GHz (RL exceeding −10 dB) covers 9.8–17.0 GHz at 3.0 mm. The EM absorption mechanism may be explained by the combination of the EM loss model and the quarter-wavelength cancellation condition. The onion-like defective carbon shell not only can accommodate the volume change of Fe₃O₄ nanoparticles but also can prevent the formation of solid electrolyte interface films on the surface of nanoparticles, resulting in the remarkable electrochemical performance for lithium ion batteries (LIBs). The Fe₃O₄@C nanocapsules display an attractive cycling performance up to 300 cycles (918 mA h g⁻¹ retained at 0.1 A g⁻¹) and a high initial coulomb efficiency of 85.6%. A capacity of 934 mA h g⁻¹ is recoverable after the charge–discharge process at high rates. The present work presents Fe₃O₄@C nanocapsules as a new kind of EM absorptive anode material for LIBs.