Effect of oleic acid coating on electrochemical properties of Li ₄Ti₅O₁₂ nanofiber for anode materials

For preparing spinel Li₄Ti₅O₁₂ nanofiber, a hydrogen titanate nanofiber precursor was mixed with Li0H·H ₂0 and then the mixture was treated at 130°C in an autoclave for 24 hrs. The hydrogen titanate nanofiber precursor was made using a TiO ₂ and NaOH solution as the starting material. As a result, the diameter of the Li₄Ti₅O₁₂ nanofiber was 5-10nm and the length was over 100 nm longer fiber. The oleic acid (C ₁₇H₃₃COOH) coated Li₄Ti₅O ₁₂ nanofiber with different oleic acid contents (5, 7.5, and 10 wt%) was obtained by a simple mixing method and heat treatment at 450°C in a N₂ atmosphere. The results clearly revealed that the surface of the Li₄Ti₅O₁₂ nanofiber was coated with an amorphous carbon layer (1 nm). The crystallinity of the samples was also enhanced. The oleic acid coated Li₄Ti₅O₁₂ nanofiber (5 wt% and 7.5 wt%) displayed a much lower impedance than the Li ₄Ti₅O₁₂ nanofiber because of the decreased charge transfer resistance, therefore, it had an improved discharging/charging capacity, c-rate and cycle performance.