A series of LiFe1–x
V
x
PO4/C samples have been successfully prepared using a two-step solid-state reaction route. The effect of vanadium incorporation on the performance of LiFePO4 has systematically been investigated with X-ray diffraction, Raman spectroscopy, charge/discharge measurements, and cyclic voltammetry tests. It is found that V incorporation significantly enhances the electrochemical performance of LiFePO4. Particularly, the LiFePO4/C sample with 5 at. % vanadium doping exhibits the best performance with a specific discharge capacity of 129 mAh g–1 at 5.0 C after 50 cycles; the capacity retention ratio is higher than 97.5% at all C rates from 0.1 to 5.0 C. X-ray absorption spectroscopy results show that the valence of V in LiFe0.95V0.05PO4/C is between +3 and +4. It is confirmed that the samples with x ≤ 0.03 are in single phase, whereas the samples with 0.05 ≤ x < 1.00 contain two impurity phases: Li3V2(PO4)3 and LiVOPO4. A clear feature of vanadium incorporation in LiFePO4 has been specified.
A NO 2 gas sensor based on mesoporous WO 3 thin film with low operating temperatures and its sensing characteristics are reported. The mesoporous WO 3 thin film exhibits regular pores with an average pore size of 5 nm and specific surface area of 151 m 2 /g. Excellent sensing properties are found upon exposure to 3 ppm of NO 2 at 35-100°C for mesoporous WO 3 thin film. The sensor response is 180 for 3 ppm NO 2 at 100°C. The ability to sense NO 2 at such low temperatures is attributed to the large surface area ͑151 m 2 /g͒ that offers many active sites for reaction with NO 2 molecules.
We report an effective strategy to inhibit the phase transition of LiCoO2 from hexagonal layered to cubic spinel during delithiation. The small thermal vibration amplitude of the Sn dopant helps pin the lattice vibration, stabilizing CoO6 octahedra during charge/discharge.
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