SYNTHESIS AND CHARACTERIZATION OF LITHIUM TITANATE (LTO) NANOCOMPOSITES VIA SOLUTION GROWTH ROUTE FOR Li-ION BATTERIES

The novel bimetal oxide composite of Li4Ti5O12 was successfully synthesized by solution growth technique. The structural and microstructural properties of synthesized powders were characterized by powder X-ray diffraction (XRD), fourrier transform infrared spectroscopy (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray-spectroscopy (EDX). The electrochemical performance of the Li4Ti5O12 anode was investigated using galvanostatic charge-discharge techniques. The electrochemical property of the Lithium titanate anode was investigated. The good electrochemical performance is ascribed to the stable lithium storage host structure, decreased electrochemical resistance and enhanced lithium-ion diffusion coefficient. Therefore, Li4Ti5O12 may be a promising alternative anode material for Li-ion batteries.


INTRODUCTION
There is a remarkable interest in developing alternative and sustainable energy storage systems to meet modern society needs due to fossil fuel depletion. Compared with other existing energy storage systems, batteries are promising and lots of efforts have been taken by researchers to develop efficient device with affordable price. The development of Lithium-ion batteries with enhanced safety and a long cycle life is vital for mainly energy storage devices used in specific some fields such as electric vehicles (EVs) or hybride electrical vehicles (HEVs), cameras, laptops and mobile phones. Recently, researchers are attempting to develop the advanced nanomaterials for energy storage devices especially for batteries. Among the Nanostructured materials such as lithium cobalt oxide (LiCoO2) (1), lithium iron phosphate (LiFePO4) (2,3), lithium manganese oxide (LiMn2O4) (4) or oxides of vanadium (V2O5) (5-7), manganese (MnO2) (8,9) have been used as the cathode in Lithium ion batteries. Similarly, anode (TiO2 and graphite) materials have been developed for Lithium ion batteries (10-15). Ti-based materials have been intensively investigated and observed as good potential negative electrode materials for lithium-ion batteries owing to their safety, excellent rate capability and superior cyclic stability. These materials have shown several advantages for example easy and swift charging within ten minutes. Spinel lithium titanate has a high lithium intercalation voltage of 1.55 V against a lithium electrode with a theoretical capacity of 170 mAhg -1 and an actual discharge capacity of over 160 mAhg -1 . Now a day's new kind of anode materials being developed in order to reduce the cost as well as to make highly efficient devices. Among the new anode materials, Li4Ti5O12 is one of the right choices for anode materials due to its superior performance (16)(17)(18). Li4Ti5O12 nanomaterials have been prepared using several methods for instance hydrothermal methods (19), sol-gel process (20,21), solid sate reaction (22), spray pyrolysis, hydrothermal-microwave synthesis, gel-emulsion, and gel combustion (23)(24)(25). In this work, the preparation and characterization of nanostructured novel bimetal oxide Li4Ti5O12 by solution growth technique.

Materials preparation
Lithium titanate was prepared by solution growth technique. In a typical experimental procedure, titanium oxysulfate (TiOSO4) and lithium hydroxide (LiOH.H2O) were dissolved in double distilled water under strong stirring and consequently a precipitate was obtained. The precipitate was dried at 80 o C in hot air oven for 10 hr. Finally, colorless powder was obtained which was then heat treated at 850 o C in a muffle furnace for 3 h. The structural property of synthesized powder was studied using various advanced characterization techniques.

Materials Characterization
The X-ray diffraction (XRD) patterns of all the samples were measured on a (XPERT-PRO) diffractometer with monochromatic CuKαradiation (λ = 1.5406Å). FT-IR spectra of the samples were recorded on a (Thermo Nicolet 380, USA) spectrometer using a KBr pellet technique in the range of 4000-400 cm -1 . The SEM -EDX were recorded on a (JEOL JSM-6360LV) using an accelerating voltage of 30.0 kV

Fabrication of electrodes
1.3504 g of lithium titanate and 0.9079 g of carboxymethylcellulose (CMC) were taken in the porcelain dish and mixed well by adding few drops of distilled water. Then, 0.0966 g of binder was also added into the above mixer and then the mixture was homogeneously mixed manually with the aid of spatula. The paste is coated on the electrode using the Dr. Blade method. Then the electrode was dried in oven at 75 o C for 1 hour. Lithium was used as counter electrode and polypropylene was used as the separator. 1 M LiPF6 was dissolved in ethylene carbonate (EC) / dimethyl carbonate (DMC) /1, 2diethyl carbonate (DEC) and used as the electrolyte. The cell was assembled inside the glove box under the argon atmosphere. Galvanostatic charge/discharge cycle test was carried out for all the assembled cells at ambient temperature with constant current mode (0.1 mA) up to 1.5 V for charging and up to 2 V for discharging. D= kλ / β cosθ Where D is the average crystallite size, λ is the X-ray wavelength, β is the full width at half maximum, K is a constant related to crystallite shape, and β in 2θ axis of diffraction outline must be in radians. The θ can be in degrees, since the cos θ corresponds to the equal number.

X-ray Diffraction Analysis
The crystallite size of 50 nm was achieved for synthesized materials. Fig. 2 shows the SEM image of lithium titanate. The SEM image clearly reveals that the formation of homogeneous cubic morphological features. EDX spectrum of mixture of lithium titanate and titanium oxide nanopowders was measured (Fig.  3). It was found from the EDX spectrum that the presence of appropriate percentage of Ti and O in the synthesized sample. It should be indicated that the Li does not present in EDX spectrum because the Li is light weight element.

Raman studies
Raman spectroscopy is an effective technique to characterize the functional groups present in the synthesized samples.

Electrochemical Analysis
The investigations on the electrochemical property of the prepared Li4Ti5O12 materials were also carried out. The charge/discharge curve of lithium titanate anode is shown in Fig. 6. The lithium titanate anode shows discharge capacity of 83mAhg -1 at first cycle. The better lithium ion storage performance of the synthesized Lithium titanate anode may be due to the good electronic conductivity.