Titanium-modified Li 4 Ti 5 O 12 with a synergistic effect of surface modifying, bulk doping, and size reducing

Abstract

In this work, a one-step solid-phase sintering process via TiO₂ and Li₂CO₃ under an argon atmosphere, with ultra-fine titanium powder as the modifying agent, was used to prepare a nano-sized Li₄Ti₅O₁₂/Ti composite (denoted as LTO–Ti) at 800 °C. The introduction of ultra-fine metal titanium powder played an important role. First, X-ray photoelectron spectroscopy demonstrates that Ti⁴⁺ was partially changed into Ti³⁺, through the reduction of the ultra-fine metal titanium powder. Second, X-ray diffraction revealed that the ultra-fine metal titanium powder did not react with the bulk structure of Li₄Ti₅O₁₂, while some pure titanium peaks could be seen. Additionally, the size of LTO–Ti particles could be significantly reduced from micro-scale to nano-scale. The structure and morphology of LTO–Ti were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical tests showed a charge/discharge current of 0.5, 1, 5, and 10 C; the discharge capacity of the LTO–Ti electrode was 170, 161, 140, and 111 mAh g⁻¹. It is believed that the designed LTO–Ti composite makes full use of both components, thus offering a large contact area between the electrolyte and electrode, high electrical conductivity, and lithium-ion diffusion coefficient during electrochemical processes. Furthermore, ultra-fine titanium powder, as the modifying agent, is amenable to large-scale production.