The development of LiFePO<sub>4</sub> as a cathode materials on lithium-ion battery was increased with the use of additional techniques such as atomic doping and coating. The material used in this report was LiFeSi<sub>0.06</sub>P<sub>0.94</sub>O<sub>4</sub>/C (LFP Si-6%), synthesized with doping silicon 6% and 11wt% carbon coating by a solid state method. X-ray Absorption Spectroscopy (XAS) characterization was used to investigate the effect on electronic and atomic structure of LFP Si-6%, especially in X-ray Absorption Near Edge Strucuture (XANES) region. XANES data measured on Fe K-edge and Si K-edge. Fe foil, FeO, Fe<sub>2</sub>O<sub>3</sub>, FePO<sub>4</sub>, Si powder, SiO, SiO<sub>2</sub> were used as a standard sample for comparison with the result of LFP Si-6%. XANES analysis showed that the energy absorption of Fe K-edge and Si K-edge in LFP Si-6% was 7124.94 eV and 1846.16 eV, respectively. The oxidation state of Fe was Fe<sup>2.576+</sup> between Fe<sup>2+</sup> and Fe<sup>3+</sup>, while Si was close to the estimation of Si<sup>4+</sup>. In addition, the linear combination fitting (LCF) in XANES Fe K-edge was performed to show the ratio of Fe<sup>2+</sup>/Fe<sup>3+</sup> (FeO/Fe<sub>2</sub>O<sub>3</sub>).
The oxidation state and local structure of LiFeSi0.01P0.99O4/C composites as a cathode on lithium-ion battery were investigated by Fe K-edge X-ray Absorption Near Edge Spectroscopy (XANES) and Extended X-ray Absorption Fine Structure (EXAFS). The LiFeSi0.01P0.99O4/C sample was prepared by solid-state reaction process. Based on the XANES analysis, the absorption of edge energy (E0) of the sample was 7124.92 eV. In addition, linear combination fitting (LCF) analysis of XANES confirmed the oxidation state of iron mixture of 2+ and 3+ as the effect of silicon doped in LiFePO4. The Fourier Transform (FT) of the Fe K-edge EXAFS fitting analysis showed that the nearest neighbors surrounding atom Fe were the main peak with high intensity that confirmed Fe-O bond; the second and third peak with lower intensity confirmed Fe-P and Fe-Fe bonds, respectively. In addition, the SQUID magnetometer result of LiFeSi0.01P0.99O4/C indicated the antiferromagnetic order temperature of LiFeSi0.01P0.99O4/C at ~51 K with the indication of the presence of impurity and structural distortion.
The synthesis of LiFeSi0.03P0.97O4/C (LFSP/C) composites have been done by solid state method. This study investigates the effects of carbon coating on the structure, microstructure and electrical conductivity of LFSP/C cathode materials. The carbon coating on Lithium Ferro Phosphate (LFP) plays a crucial role in determining its electrical conductivity. The variation of carbon content is 0wt.%; 6wt.%; 7wt.%; 8wt.% (LFP-0%, LFP-6%, LFP-7% and LFP-8%). The characterization was performed using X-Ray Diffraction (XRD), Scanning Electron Microscopy - Energy Dispersive X-ray (SEM-EDX), HighResolution-Transmission Electron Microscopy (HR-TEM) and LCR Meter tests. The XRD result have shown single-phase olivine (LiFePO4) in all samples. The analysis microstructure using SEM have shown increasing carbon content can reduce agglomeration. The particles size of LFSP is 845.570 nm, and after coating carbon the particles size decreased up to 457.191 nm. The EDX results showed that the amount of atomic percentage for carbon tends to increase as the amount of carbon content increased. HR-TEM images indicates that the formation of carbon layer have formed, but not perfectly coat the LFP particle. The average carbon layer size is 78,31 nm with the size of LFSP particle is 352.82 nm. The LCR Meter result showed that LFP-7% had the largest electronic conductivity (2,275x10-7 S/cm). The carbon coating led to significant enhancement in electronic conductivity from ~10-9-10-10 S/cm to ~10-7 S/cm.
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