Effective wrapping of graphene on individual Li4Ti5O12 grains for high-rate Li-ion batteries

Abstract

An effective way of synthesizing graphene-wrapped Li₄Ti₅O₁₂ particles was developed by solid-state reaction between graphene oxide-wrapped P25 (TiO₂) and Li₂CO₃. Compared to the previously reported graphene/Li₄Ti₅O₁₂ composites, prior wrapping of TiO₂ with subsequent chemical lithiation led to more effectively confined Li₄Ti₅O₁₂. The Li₄Ti₅O₁₂ tightly bound by graphene exhibited a remarkable specific capacity of 147 mA h g⁻¹ at a rate of 10 C (1 C = 175 mA g⁻¹) after 100 cycles. This rate capability is one of the highest values among reported Li₄Ti₅O₁₂ with 150 ± 50 nm grains. The improved rate capability was attributed to the enhanced electronic conductivity of each Li₄Ti₅O₁₂ grain via uniform graphene wrapping, with single-grain growth during annealing from the initial ∼25 nm TiO₂ nanoparticles enclosed by outer graphene sheets. Graphene-eliminated Li₄Ti₅O₁₂ by thermal decomposition was also directly compared to the graphene-coated sample, to clarify the role of graphene with nearly equivalent particle size/morphology distributions.