Synthesis of Li₄Ti₅O₁₂/carbon nanocomposites in supercritical methanol for anode in Li-ion batteries: Effect of surface modifiers

Abstract Li₄Ti₅O₁₂/carbon (LTO/C) nanocomposites are synthesized by preparing surface-modified LTO nanoparticles in supercritical methanol and subsequently calcinating the modified LTO under an Ar/H₂ condition. The effects of surface modifiers with different functional groups and chain lengths (oleylamine, oleic acid, hexylamine) on the particle morphology, particle size, crystallinity, carbon structure, and electrochemical properties are examined. During heat treatment at 750 C, the carbonization of the modifiers attached to the surface of LTO effectively inhibit the particle growth and reduce some of the Ti⁴⁺ in LTO to Ti³⁺. A higher degree of surface modification, in the order of oleylamine > hexylamine > oleic acid, results in a higher carbon content, smaller particle size, and higher Ti³⁺ content; these factors may result in better battery performance of the LTO/C synthesized using oleylamine. At a low rate of 0.1 C, the LTO/C samples synthesized using the different surface modifiers exhibit similar discharge capacities of 175 mA h/g (which approaches the theoretical capacity of LTO), while at a high rate of 10 C, the discharge capacities are in the order of oleylamine (147.1 mA h/g) > hexylamine (124.2 mA h/g) > oleic acid (101.5 mA h/g). The LTO/C nanocomposites prepared using the three different surface modifiers exhibit excellent cyclability up to 200 cycles at 1.0 C.