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

• Surface modification of Li4Ti5O12 using oleylamine, oleic acid, and hexylamine.
• Subsequent calcination produces Li4Ti5O12/C nanocomposite.
• Carboxylic acid exhibits less ability to modify Li4Ti5O12 surface than amine group.
• Smaller particle size and larger Ti3+/carbon content resulted using oleylamine.
• Better discharge capacity with Li4Ti5O12/C using oleylamine.

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.

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