Li_4Ti_5O_(12) thin-film electrodes by sol-gel for lithium-ion microbatteries

摘要

Spinel Li_4Ti_5O_(12) has been considered as one of the most prospective anode materials for Li-ion micro-batteries. Homogeneous, transparent and crack-free Li_4Ti_5O_(12) coatings with thickness around 110 nm have been prepared by dipping gold-coated quartz substrates in sols prepared using titanium isoprop-oxide and lithium acetate. The influence of the thermal treatment on the phase composition, structure and electrochemical behavior was studied. Rutile TiO_2 (considered as an impurity in this study) is only detected in the coatings treated at 700 ℃. 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 ℃ presents a redox reaction around 1.55 V indicating that the film is simple phase of Li_4Ti_5O_(12). The shift to slightly lower voltage in samples treated at 700 ℃ is a consequence of Rutile impurities. Larger capacity and good reversibility in the sample heat-treated at 600 ℃ can be attributed to high crystallinity of Li_4Ti_5O_(12) and phase purity. RBS analysis specifies a composition close to Li_4Ti_5O_(12) in the case of the pristine and charged samples, and Li_7Ti_5O_12 for the discharged sample. Surface XPS study confirms the presence of an outermost layer containing LiF and Li_2CO_3.