Synthesis And Electrochemical Properties Of Titanates As Anode Materials For Lithium Ion Batteries

In the present commercial lithium-ion batteries, the low coulomb efficient and the safety issue of the carbonaceous anode have made electrochemical researchers to find alternative anode materials to graphite and carbonaceous materials. Being inherently safe and chemically compatible with the electrolyte, the spinel lithium titanate, various TiO2 polymorphs and other titanates have attracted more and more interests. Recent progress of titanates is reviewed in the dissertation, the conventional synthesis methods, doping and coating modifications are introduced. For the first time, spinel Li4Ti5O12 has been successfully synthesized by a green and environmental rheological phase method, which owned ultrafine particles and narrow size distribution and exhibited excellent high rate performance. Electrochemical lithium ions insertion into Na2Li2Ti6O14 for lithium-ion battery has been investigated for the first time. The results indicate the discharge and charge potential plateaus are about 1.3 V in the voltage window 1-3V. Facile combustion method and green molten salt reaction have been employed to synthesize sodium lithium titanium oxides. Additionally, other titanates as anode materials for lithium ion batteries have been studied. The concrete research contents are summarized as following:1. Owing to the low conductibility of spinel lithium titanate Li4Ti5O12, the high current is restricted during discharge and charge processes. It is a very efficient way to solve this problem by means of decreasing the particle size of product. Using different lithium salts and TiO2 as raw materials, the lithium titanate products have been synthesized by a conventional solid-state reaction. TG/DSC and X-ray diffraction results indicate that the pure phase lithium titanate could be easily obtained using lithium acetate dehydrate and TiO2 as raw materials compared to other lithium salts under the same condition. On this basis, using lithium acetate dihydrate and tetra-n-butyl titanate as the raw materials, spinel Li4Ti5O12 was successfully synthesized by a modified rheological phase method. Laser granulometer and scanning electron microscope (SEM) have been employed to estimate the particle size distribution, morphology and microstructure of the products. It reveals the prepared Li4Ti5O12 powder obtained from the precursor that had been experienced heat treatment at 110℃had a small particle size (about 140nm) and narrow size distribution. Galvanostatic charge and discharge tests indicate that the Li4Ti5O12 electrode material exhibited excellent high rate performance, due to the pure and well crystallized Li4Ti5O12 with ultrafine particles and narrow size distribution.2. Using lithium acetate dehydrate, sodium acetate, tetra-n-butyl titanate, citric acid and alcohol as the raw materials, the sodium lithium titanate with composition Na2Li2Ti6O14 has been synthesized by a sol-gel method. Electrochemical lithium ions insertion into Na2Li2Ti6O14 for lithium-ion battery has been investigated for the first time. The results indicate the discharge and charge potential plateaus are about 1.3 V in the voltage window 1-3V, and about 80mAh/g reversible capacity retained during cycling. X-ray diffraction (XRD) data and SEM results indicate the crystallization of lithium sodium titanate has occurred at about 600℃, and the crystal degree and the particle size of the samples increased with the increasing of calcination temperature. The sample prepared at low temperatures exhibits higher discharge specific capacity and the excellent retention of capacity on cycling due to the small particle size and the fine size distribution.3. The combustion method is an efficient and rapid synthesis method that preparing the inorganic powders. This synthesis technique makes use of the heat energy liberated by the redox exothermic reaction at relative low igniting temperature between metal nitrates and urea or other fuels, which produce a homogenous product in a short time without the use of expensive high-temperature furnaces. In this chapter, for the first time the combustion method has been applied to synthesize Na2Li2Ti6O14 by using the urea as a fuel. Pure phase and well crystallinity Na2Li2Ti6O14 was prepared at the ignition temperature of 600℃. We have studied the effect of the various discharge cut-off voltages for half cell on the specific capacity and capacity retention of Na2Li2Ti6O14 electrode materials.4. Using NaCl, KCl, LiCl and other salts as molten medium, sodium lithium titanate Na2Li2Ti6O14 with orthorhombic structure, spinel lithium titanate Li4Ti5O12 and sodium titanate Na2Ti6O13 with monoclinic structure have been prepared by a molten salt method. We have studied the influence of the different kind of salts, the amount of slats and the preparation temperature and time on the crystallinity and the morphologies and microstructures of the samples. Additionally, one dimensional nanomaterial sodium titanate with monoclinic structure as precursor, one dimensional nanomaterial lithium titanate has been obtained by a molten salt ion-exchange technique. The electrochemical properties of the samples were investigated, which demonstrates the reversible capacity and cycle retention of the one dimensional nanomaterial lithium titanate is superior to sodium titanate.5. Sodium lithium titanate Na0.66Li0.22Ti0.78O2 with hexagonal crystal structure has been synthesized by a sol-gel method, which was optimized by the changing of the synthesis temperatures and time. Discharge and charge tests indicated that the working potential of the electrode material locates in the range of 1.3V and 1.7V, and the electrode material shows high discharge specific capacity and the excellent retention on cycling.