Zn and Cu Co-Doped Li4Ti5O12 Anode Material for Lithium Ion Batteries

Abstract

Lithium-ion batteries have been advanced the battery technology because of their prevalent power sources for electric vehicles and portable electronics devices. Spinel structure of lithium titanium oxide Li4Ti5O12 (LTO) has commended significant interest as an anode material for lithium-ion batteries because of several advantages such as high energy density, high safety, good chemical stability, long-life time, a flat operating voltage about 1.55 V and low cost. Modification of the surface structure of LTO based anode material by Cu and Zn has been significantly enhanced the conductivity of the electrode material by suppressing the decomposition of the electrode material and influencing their phase structure in some cases. Advanced spectroscopic techniques, such as Fourier-Transform Infrared Spectroscopy (FTIR), scanning electron microscopy (SEM), (EDX) and X-ray diffraction (XRD) are applied for the characterization of morphology, particle size and crystal structure of the prepared LTO based anode materials. In the finger print region sharp low frequency characteristic IR bands observed below 800 cm-1 which can be attributed to the symmetric stretching vibrations of Ti-O bonds of TiO6 octahedron in pure Li4Ti5O12, Li4Ti4.9Cu0.05Zn0.05O12, Li3.9Ti5Cu0.05Zn0.05O12 and Li3.9Ti4.9Cu0.1Zn0.1O12. At the same time strong stretching bands at around 2360.87, 2341.58 and 2331.94 cm-1 can be assigned to the Ti-O-Ti bonds in the prepared LTO and LTO based anode materials and corresponds to the published results. Li4Ti5O12 possess a face-centered cubic spinel structure grounded on space group symmetry of Fd3m. In the Li4Ti5O12 spinel structure, tetrahedral 8a sites are completely taken up by Li and the octahedral 16d sites are arbitrarily occupied by Li and Ti with an atomic ratio of 1:5 in a cubic close-packed oxygen array. The characteristic X-ray diffraction peaks of the prepared samples are found at 2θ of 18.3, 35.58, 43.2449, 43.1, 57.2065, 62.8447, and 66.1006 which correspond to the planes (111). (311), (400), (333), (440) and (531), respectively. The lattice parameter values were calculated for Li4Ti5O12, Li4Ti4.9Cu0.05Zn0.05O12, Li3.9Ti5Cu0.05Zn0.05O12 and Li3.9Ti4.9Cu0.1Zn0.1O12 and the values are 8.3692 Å, 8.3742 Å, 8.3834 Å and 8.3709 Å, respectively. XRD spectra that both pure Li4Ti5O12 and Cu & Zn co-doped LTOs showed peaks representing single phase of spinel lithium titanium oxide (cubic phase, space group Fd-3m) which are in good agreement with Joint Committee on Powder Diffraction Standards, JCPDS (No. 26- 1198) data. SEM photographs of prepared pure LTO (Li4Ti5O12), Li4Ti4.9Cu0.05Zn0.05O12, Li3.9Ti5Cu0.05Zn0.05O12 and Li3.9Ti4.9Cu0.1Zn0.1O12 possess chips like shape. No significant change happened in the morphologies due to the co-doping of different ratio of Cu & Zn into Li4Ti5O12. The morphologies of all prepared LTOs are almost same that correspond the X-ray diffraction result.