Emerging Trends in Chemical Sciences by Ponnadurai Ramasami Minu Gupta Bhowon Sabina Jhaumeer Laulloo & Henri Li Kam Wah

Author:Ponnadurai Ramasami, Minu Gupta Bhowon, Sabina Jhaumeer Laulloo & Henri Li Kam Wah
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

Fig. 13.5AFM images of the LiPtAu0.02Mn1.98O4 in tapping mode (a) and three-dimensional views (b)

13.7.4 Crystal Structure and Phase Composition Analysis by X-ray Diffraction

The XRD patterns of PtAu coated-LiMn2O4 are shown in Fig. 13.6. Figure 13.6a shows that the lattice constant increases with temperature from 8.21 Å at 600 °C to 8.26 Å at 880 °C. This behavior suggests the gradual formation of stoichiometric spinel. The XRD peak positions of LiMn2O4 at room temperature shifted towards lower diffraction angles. The shift of diffraction peaks towards higher diffraction angles means that the crystal lattice is compressed and if the peaks are shifted towards lower diffraction angle that means the lattice is expanded. This is synonymous with enhanced stability of the spinel. Figure 13.6b shows that the LiPtAu0.02Mn1.98O4 composite crystallizes in a cubic spinel. Compared with that of pure LiMn2O4, the (1 1 1) peak of bimetallic nanoparticle modified material is intensified and shifted to a lower angle. The d spacing of (1 1 1) peak is 0.227 nm and 0.232 nm for LiMn2O4 and coated sample, respectively, which indicates that the LiPtAu0.02Mn1.98O4 composite was formed. The LiPtAu0.02Mn1.98O4 nanoparticles are highly crystalline and this could influence positively their electrochemical behavior in the lithium ion battery. The inset shows the PtAu alloy which exhibits a broad band at 38.35° (2θ) that matches with the (1 1 1) plane. The broad peak at 44.58° (2θ) is attributed to the (2 0 0) plane. Two additional bands are observed at 65° and 77.73° (2θ) corresponding to PtO2. The particle size calculated on the base of (1 1 1) peak is 7 nm which is in close proximity to the value obtained from TEM measurements. The peak of the PtAu nanoparticles is between those of monometallic gold and platinum nanoparticles. Hence, the PtAu nanoparticles used to coat are not the mixtures of individual nanoparticles but bimetallic nanostructures [28]. The lattice constant of LiPtAu0.02Mn1.98O4 increased slightly than that of LiMn2O4 from 8.2600 Å (7) to 8.2609 Å (5). This increase may be due to the lattice disparity between Pt and Au atoms [29] and the larger ionic radii compared to Mn3+.

Fig. 13.6XRD pattern of LiMn2O4 with peaks shifting towards higher diffraction angles after consecutive calcinations (a) and LiPtAu0.02Mn1.98O4 cathode powder (b)

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