It
is well known that the electrochemical performance of spinel
LiMn2O4 can be improved by Al doping. Herein,
combining X-ray diffraction, Raman spectroscopy, X-ray photoelectron
spectroscopy, and spherical aberration-corrected scanning transmission
electron microscopy (Cs-STEM) with in situ electron-beam
(E-beam) irradiation techniques, the influence of Al doping on the
structural evolution and stability improvement of the LiMn2O4 cathode material is revealed. It is revealed that an
appropriate concentration of Al3+ ions could dope into
the spinel structure to form a more stable LiAl
x
Mn2–x
O4 phase
framework, which can effectively stabilize the surface and bulk structure
by inhibiting the dissolution of Mn ions during cycling. The optimized
LiAl0.05Mn1.95O4 sample exhibits
a superior capacity retention ratio of 80% after 1000 cycles at 10
C (1 C = 148 mA h g–1) in the voltage range of 3.0–4.5
V, which possesses an initial discharge capacity of 90.3 mA h g–1. Compared with the undoped LiMn2O4 sample, the Al-doped sample also shows superior rate performance,
especially the capacity recovery performance.
Aurivillius Bi5Ti3FeO15 (BTF) ceramics were synthesized using the conventional solid state reaction method by optimizing excess of Bi2O3 and sintering time. Their structures, magnetic, and optical properties were investigated in detail. The optimum process to sinter pure Aurivillius BTF ceramics was confirmed to be 3 wt. % excess Bi2O3 to compensate the Bi volatilization at 1050 °C for 240 min (BTF-240M). The microstructure and crystalline structure of the BTF ceramics had little dependence on the sintering time from the x-ray diffraction (XRD) and scanning electron microscopic data. Nevertheless, the magnetic and optical properties were closely related with the sintering time. The overall magnetic behavior of these BTF ceramics was superparamagnetic (SPM), whereas there were unambiguous clues for the existence of antiferromagnetic (AFM) interactions. However, whether the SPM behavior was intrinsic or arised from a tiny amount of spinel Fe3O4 impurity phase cannot be thoroughly ruled out in the XRD detection limit in the present stage. The AFM interactions were weakened upon extending the sintering time. The effective magnetic moment (μeff), however, demonstrated different dependency on the sintering time. It increased with the sintering time from 80 min to 240 min, and then dropped with further extending the sintering time. Compared with other BTF ceramics, the BTF-240M ceramic showed the highest values of the refractive index n and real part ε1, as well as the lowest ones of the extinction coefficient k and imagine part ε2 in whole photon energy range. Finally, a direct inter-band transition was confirmed for these BTF ceramics and optical energy band gaps were determined to be about 3.08, 3.18, and 3.39 eV for 80 min, 150 min, and 240 min sintered BTF ceramics, respectively, yet abnormal optical behavior was observed in BTF-360M ceramic.
A composite material (VS2@V2C) of vertically mosaic VS2 nanosheets was grown on a V2C substrate for electrolyzing water in the full pH range for hydrogen evolution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.