Li4Ti5O12 thin-film electrodes by sol-gel for lithium-ion microbatteries

Spinel Li4Ti5O12 has been considered as one of the most prospective anode materials for Li-ion microbatteries. Homogeneous, transparent and crack-free Li4Ti5O12 coatings with thickness around 110 nm have been prepared by dipping gold-coated quartz substrates in sols prepared using titanium isopropoxide and lithium acetate. The influence of the thermal treatment on the phase composition, structure and electrochemical behavior was studied. Rutile TiO2 (considered as an impurity in this study) is only detected in the coatings treated at 700 degrees C. XPS and TOF-SIMS depth profiles show a homogeneous distribution, with a Li increase and Ti reduction at the surface. Electrochemical characterization of samples treated at 600 degrees C presents a redox reaction around 1.55 V indicating that the film is simple phase of Li4Ti5O12. The shift to slightly lower voltage in samples treated at 700 degrees C is a consequence of Rutile impurities. Larger capacity and good reversibility in the sample heat-treated at 600 degrees C can be attributed to high crystallinity of Li4Ti5O12 and phase purity. RBS analysis specifies a composition close to Li4Ti5O12 in the case of the pristine and charged samples, and Li7Ti5O12 for the discharged sample. Surface XPS study confirms the presence of an outermost layer containing LiF and Li2CO3. (C) 2012 Elsevier B.V. All rights reserved.