Preparation of Li+:TiO2 nanowires, Li4Ti5O12 nanotubes, and a Li4Ti5O12 nanotube/graphene composite by single-spinneret electrospinning for application in a lithium-ion battery

Abstract

One-dimensional (1D) Li⁺:TiO₂ nanowires and Li₄Ti₅O₁₂ nanotubes and a Li₄Ti₅O₁₂ nanotube/graphene composite were prepared by using an electrospinning technique. The types and molecular weights of polymer templates and the annealing rate have important effects on the electrospun products. The Li₄Ti₅O₁₂ nanotubes and the Li₄Ti₅O₁₂ nanotube/graphene composite were obtained by heating at a rate of about 0.5 °C min⁻¹ from a polyvinylpyrrolidone (PVP) template, while the Li⁺:TiO₂ nanowires were obtained by heating at a rate of about 2 °C min⁻¹ from a polyethylene oxide (PEO) template. The Li₄Ti₅O₁₂ nanotubes have an outer diameter of approximately 120 to 200 nm and their wall thickness is in the range of 30 to 40 nm. The morphology and size of the Li₄Ti₅O₁₂ nanotube/graphene composite are similar to those of the Li₄Ti₅O₁₂ nanotubes. The Li⁺:TiO₂ nanowires have diameters in the range of 600–3000 nm. The crystal structure of the Li⁺:TiO₂ nanowires was changed from anatase TiO₂ to spinel Li₄Ti₅O₁₂ with increasing Li⁺ dopant concentration. The electrochemical performance of the Li₄Ti₅O₁₂ nanotubes and the Li₄Ti₅O₁₂ nanotube/graphene composite for intended use in a lithium-ion battery (LIB) was investigated and compared with that of the TiO₂:Li⁺ nanowires. The Li₄Ti₅O₁₂ nanotube/graphene composite specimen exhibits the highest discharge specific capacities and cycle stability, which can reach an initial capacity of 186.4 mA h g⁻¹, and remain at 175.0 mA h g⁻¹ after 100 cycles under a current density of 100 mA g⁻¹.