Carbon materials have aroused extensive interests for their remarkable electrical properties as electromagnetic wave (EMW) absorption. However, the synthesis of the wide-band electromagnetic wave absorbent is an insuperable challenge for attaining effective refection loss and electromagnetic matching. Herein, a facile method for large-scale synthesis of monodispersed Fe/Fe 3 O 4 /C composite microspheres is proposed. The carbon microspheres (1-2 μm in diameter) imbedded with nanosized Fe/Fe 3 O 4 2 particles (10-20 nm) are uniformly produced by polymerization and carbothermic reduction processes. The products exhibit the minimum refection loss-45.5 dB at 9.4 GHz and a broad bandwidth of 4.1 GHz below-10 dB from 7.8 GHz to 11.9 GHz with a thickness of 3.0 mm. The absorption mechanism indicates a unique deviated Debye dipolar relaxation effect in the absorbing bandwidth.
The solid-state method is extensively
applied to the synthesis
of electrode materials for its simplicity and low cost. However, particles
obtained using the traditional solid-state method exhibited a large,
uneven particle size and a severe aggregation phenomenon, leading
to an unsatisfactory electrochemical performance. Here, spinel LiNi0.5Mn1.5O4 (LNMO) with good dispersion
was synthesized using the solid-state method with the addition of N,N-dimethylpyrrolidone (NMP). During the
LNMO preparation process, NMP is effective in refining and optimizing
the particle size and suppressing the aggregation phenomenon. Meanwhile,
the N element migration phenomenon was also observed in the bulk of
LNMO, and it was beneficial for extending solid-solute reactions as
demonstrated by in situ X-ray diffraction. LNMO prepared with NMP
(LNMO-N-x) exhibited a higher discharge voltage and
capacity (115.3 mA h g–1 at 2 C) compared with LNMO
(105.8 mA h g–1). These results reveal the function
of NMP in the preparation of LNMO and the effect of the physical characteristic
changes on structure and phase transition in a working battery, and
it can be easily incorporated into other electrode materials; if well
engineered, it will contribute a lot to the further applications of
lithium ion batteries.
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