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Fe3O4/MnO2 core–shell structured nanocomposites have been synthesized by a one-pot approach at ambient temperature and pressure.

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The synthesis of magnetite (Fe 3 O 4 )@C nanocapsules with Fe 3 O 4 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 Fe 3 O 4 @C-paraffin composite is À45.9 dB at 16.6 GHz at a thickness of 2.4 mm and the absorption bandwidth of 7.2 GHz (RL exceeding À10 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 Fe 3 O 4 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 Fe 3 O 4 @C nanocapsules display an attractive cycling performance up to 300 cycles (918 mA h g À1 retained at 0.1 A g À1 ) and a high initial coulomb efficiency of 85.6%. A capacity of 934 mA h g À1 is recoverable after the charge-discharge process at high rates. The present work presents Fe 3 O 4 @C nanocapsules as a new kind of EM absorptive anode material for LIBs.

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