A novel grain restraint strategy to synthesize highly crystallized Li ₄Ti ₅O ₁₂ (∼20 nm) for lithium ion batteries with superior high-rate performance

In this paper, we develop a novel strategy to synthesize Li ₄Ti ₅O ₁₂ by employing a triblock copolymer (F127) as the chelating agent and particle-restraint reagent. X-ray diffraction, Raman spectrum, nitrogen adsorption-desorption, scanning electron microscopy and high resolution transmission electron microscopy measurements are performed to characterize the structures and morphologies of the as-derived samples. Highly crystallized and pure-phase Li ₄Ti ₅O ₁₂ is synthesized at a low calcination temperature of 750 °C, owing to the effective complexation of F127 with Ti ⁺ and Li ⁺ through coordination bonds. Moreover, the grain growth of Li ₄Ti ₅O ₁₂ is effectively restrained by the carbon generated from the carbonization of F127 in the calcination process, and a small particle size of Li ₄Ti ₅O ₁₂ (∼20 nm) is successfully obtained. The electrical conductivity is enhanced to 8.2 × 10 ^-3 S m ^-1 due to the formed carbon-network on the surface of the sample. The as-derived nanocrystalline Li ₄Ti ₅O ₁₂ is tested as the anode material for lithium ion batteries, exhibiting excellent reversible capacities of 166, 160, 155, 139 and 123 mA h g ^-1 at current densities of 1 C, 5 C, 10 C, 20 C and 40 C, respectively. The cell also demonstrates good capacity retentions and high coulombic efficiencies (∼100%) at all current rates. The excellent electrochemical performance makes our Li ₄Ti ₅O ₁₂ a promising anode material for high energy/power density lithium ion batteries.