Li4Ti5O12 has been noticed about a negative electrode of a high powered and safe lithium ion secondary battery. These properties require single phase, high crystallization, larger specific surface area and fine nanoparticles. This study carried out the noble synthesis of Li4Ti5O12 using a solid phase synthesis by two steps sintering. These results showed Li4Ti5O12 of 6.1 m 2·g -1 and diameter of 110 nm with the single phase and high crystallization. Li 2TiO 3 will play an important role in this reaction, obtained by pre-sintering as a precursor.
Lithium ion secondary batteries have been noticed for many applications to high performances recently, and the developments have been performed [
Li4Ti5O12 has spinel structure and LiMn2O4 does likewise, which is applied to the positive electrode in the lithium ion secondary battery. The properties of Li4Ti5O12 are hardly expanded by the overcharge, and high stability in cycles of discharge and charge. The synthesis methods are known as solid phase synthesis, sol-gel process, hydrothermal synthesis, coprecipitation method and vapor phase deposition method. Especially, the solid phase synthesis is a good method for industrial processes, which is simple and easy to control composition of a chemical compound. However, it has some problems, such as a low reactivity, a control of fine particle size and a production of by-products. The synthesis developments have been performed to solve them [
Consequently, the synthesis method is needed to produce Li4Ti5O12 of a single phase, fine nano-size particles and a high crystalline in order to show high performance as the battery. A synthesis process has been performed by sintering with low temperatures by a two-step process of a pre-sintering at 400˚C - 500˚C and a sintering at 700˚C - 750˚C, because we have tried to synthesize a single phase and fine nano-size Li4Ti5O12.
Li4Ti5O12 synthesis was carried out by using CH3COOLi・2H2O (Wako Pure Chemical Industries, Ltd.) as a Li source that was melted with low temperature at about 300˚C, and anataseTiO2 (Toho Titanium Co., Ltd.) as a Ti source. The first synthesis process was mixed with the CH3COOLi・2H2O and TiO2 with Li:Ti = 4:5 by ball milling (Fritsch, Pulversitte 7) at 1 h, rotating speed at 320 rpm and orbital speed at 110 rpm in agate mortar and balls. The mixed powder was pre-sintering at 400˚C, 450˚C and 500˚C with 10˚C/min, 1 h in air, and a precursor was formed. Furthermore, the precursor was mixed by the ball milling at 1 h similarly, and was sintered at 700˚C and 750˚C with 10˚C/min at 1 h in air.
The obtained powder was identified by XRD (Rigaku Corp., Rint 2000) at scanning step 0.02 deg and scanning speed 5 deg/min by CuKα, and was also measured by BET specific surface area (Shimadzu Corp., FlowSorb III 2305) at 0.1 g sample, gas flow rate 80 cm3/min in N2 and current 50 mA, after degassing the sample with heating at 160˚C at 2 h. Particle size of the obtained sample was observed by FE-SEM (Hitachi, Ltd., S- 4200), and crystalline estimation tried with TEM (JEOL Ltd., JEM-2100).
Precursor was formed by pre-sintering the CH3COOLi・2H2O and TiO2 mixed powder at 400˚C, 450˚C and 500˚C in air, and showed in
SEM images were shown about the precursors in
BET specific surface area presented 27.7 m2∙g−1, 26.6 m2∙g−1 and 26.2 m2∙g−1 under 400˚C, 450˚C and 500˚C. The images of the grain observed two types as deference of contrast at 400˚C in
XRD peaks of samples ware showed at sintering temperature of 700˚C and 750˚C in
The value at 700˚C was 80%, 84% and 86% at the pre-sintering temperature of 400˚C, 450˚C and 500˚C, which were advantageous with the high pre-sintering temperature. Furthermore, the value at 750˚C was 92%, 99% and 100% similarly, and we could obtain the single phase Li4Ti5O12 at 750˚C. These results will show that the sub-phase Li2TiO3 give effects for the Li4Ti5O12 synthesis.
A surface separation of (002) face of Li2TiO3 at 4.80 Å is very close to that of (111) face of Li4Ti5O12 at 4.83 Å in the spinel structure, which Li4Ti5O12 would be able to form from Li2TiO3 with holding the structure [
SEM images of the samples showed in
TEM images of the samples showed in
Single phase Li4Ti5O12 was synthesized by the two-step sintering via Li2TiO3. The method especially obtained the fine nanoparticles at about 110 nm and 6.1 m2∙g−1 under sintering temperature of 750˚C. The process will bring about expectation for the mass production in the industry.