Exploring the evolution behavior of Li+, Na+, and Br− during the continuous phase transition of lithium titanate

Abstract

This study examines the continuous phase transition of NaBr-doped Li₄Ti₅O₁₂ during calcination, focusing on the migration and evolution of Li⁺, Na⁺, and Br⁻ and their impact on the transition. Results from high-temperature in situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations indicate that NaBr incorporation increased the TiO₂–Li₂TiO₃ transition temperature and reduced the Li₂TiO₃–Li₄Ti₅O₁₂ transition temperature. An appropriate amount of Li⁺ was doped into TiO₂ at low temperatures. Notably, with increasing temperature, Na⁺ was doped into the TiO₂ cell through the gap, while Br⁻ was adsorbed on the surface of TiO₂ without entering the TiO₂ cell. With the continuous increase in the temperature and doping of Li⁺, TiO₂ transforms into Li₂TiO₃. Na⁺ and Br⁻ gain more energy, Na⁺ enters the Li₂TiO₃ unit cell for gap doping, and Br⁻ enters the Li₂TiO₃ unit cell to replace O²⁻, promoting the transformation of Li₂TiO₃ to Li₄Ti₅O_12. Overall, this research provides an intrinsic connection between the microscopic properties of anions and cations during NaBr-doped Li₄Ti₅O₁₂ phase transition, clarifies the states of Li⁺, Na⁺, and Br⁻ in this transition, and offers a theoretical basis for the states of anions and cations during continuous Li₄Ti₅O₁₂ phase transition.