Abstract
In this work, the effect of carbon on the electrochemical properties of multiwalled carbon nanotube (MWCNT) functionalized lithium iron manganese phosphate was studied. In an attempt to provide insight into the structural and electronic properties of optimized electrode materials, a systematic study based on a combination of structural and spectroscopic techniques was conducted. The phosphor-olivine LiFe0.5Mn0.5PO4 was synthesized via a simple microwave synthesis using LiFePO4 and LiMnPO4 as precursors. Cyclic voltammetry was used to evaluate the electrochemical parameters (electron transfer and ionic diffusivity) of the LiFe0.5Mn0.5PO4 redox couples. The redox potentials show two separate distinct redox peaks that correspond to Mn2+/Mn3+ (4.1 V vs Li/Li+) and Fe2+/Fe3+ (3.5 V vs Li/Li+) due to interaction arrangement of Fe-O-Mn in the olivine lattice. The electrochemical impedance spectroscopy (EIS) results showed LiFe0.5Mn0.5PO4-MWCNTs have high conductivity with reduced charge resistance. This result demonstrates that MWCNTs stimulate faster electron transfer and stability for the LiFe0.5Mn0.5PO4 framework, which demonstrates to be favorable as a host material for Li+ ions.
Highlights
Material Characterization. e surface morphology, particle size, and size distribution of the composite were examined through SEM, TEM images, and Small-angle X-ray scattering (SAXS) obtained from JOEL JSM-7500F Scanning Electron Microscope (US), Tecnai G2 F20X-Twin MAT 200 kV Field Emission Transmission Electron Microscope (FEI Eindhoven, Netherlands), and Small-Angle X-ray Scattering obtained from Anton Paar GmbH (Anton-Paar Str 20 A-8054 Graz)
Upon addition of carbon nanotubes, the particle size is reduced to 3.7 ± 0.957 nm due to high surface multiwalled carbon nanotube (MWCNT) and it is more crystalline. e crystalline structure of LiFe0.5Mn0.5PO4MWCNTs has 3 different diffraction patterns; this is evident by the appearance of the 002, 111, and 121, at 30°, 40°, and 50°, respectively, as shown in Figure 2(b). e hexagonal crystalline carbon was indexed to (JCPDS No 41-1487), which complement the preferential growth of MWCNTs
SAXS reflections appear in similar positions with those observed on X-ray diffraction (XRD) (Figure 2(a)) due to the stable structure of LiFe0.5Mn0.5PO4MWCNTs. e intensity peaks of the pure carbon nanotubes are more intense upon adding LiFe0.5Mn0.5PO4; the peaks shift from 26° and 44° to 34° and 50°, respectively. ese peaks are in correspondence with the one obtained from SAXS. is indicates that the multiwalled carbon nanotubes are covered by LiFe0.5Mn0.5PO4. e single peak for LiMn0.5Fe0.5PO4 illustrates completed solid-reaction between LiMnPO4 and LiFePO4 precursors even after carbon-coating
Summary
E SAXS reflection appears in different positions with those observed on XRD (Figure 2(c)); this is due to the oxidation of LiFe0.5Mn0.5PO4, and the material is porous and unstable. E hexagonal crystalline carbon was indexed to (JCPDS No 41-1487), which complement the preferential growth of MWCNTs. SAXS reflections appear in similar positions with those observed on XRD (Figure 2(a)) due to the stable structure of LiFe0.5Mn0.5PO4MWCNTs. e intensity peaks of the pure carbon nanotubes are more intense upon adding LiFe0.5Mn0.5PO4; the peaks shift from 26° and 44° to 34° and 50°, respectively. LiFe0.5Mn0.5PO4-MWCNTs. The mixed was sonicated, sealed, and placed in the microwave reaction system for 30 min. The mixed was sonicated, sealed, and placed in the microwave reaction system for 30 min. 107 ppm NMR
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