An in-Operando XRD Study of TiO2 Based Anode Materials for Secondary Li Ion Batteries Application
Authors: Shen Yu-Min , Liao Guan-Bo , Wang Jyun-Siang , Huang Jow-Lay 
Published: February 2024

In recent years, lithium-ion batteries (LIB) have emerged as one of the most representative rechargeable energy-storage systems. Among the various anode materials used, titanium dioxide stands out for its excellent stability, superior safety, and high cycling performance. Moreover, its remarkable stability in high-capacity charge–discharge cycles is useful for developing fast-charging batteries. Therefore, this material has attracted significant attention from researchers. In this study, we investigate aluminum-doped and carbon-coated non-stoichiometric titanium dioxide for in operando X-ray diffraction (XRD) analysis using synchrotron radiation to explore the behavior of lithium ions intercalating into and deintercalating from the titanium dioxide lattice and draw insights from the variations in the characteristic lattice diffraction peaks.

In Al-TiOx part, the lithium-ion intercalation and deintercalation behaviors within the mixed-phase titanium dioxide used herein (anatase and rutile). During discharge, a new reversible intermediate phase, LiTiO2, as well as a partially irreversible intermediate phase, Li0.55TiO2, are generated in the anatase phase. This is the first reported experimental observation of the coexistence of these three phases. The irreversible reaction kinetics of these phases contribute to capacity decay. In the rutile phase, the diffraction peaks exhibit a trend of broadening and narrowing during charge–discharge, resembling an hourglass-like structure. This phenomenon implies non-uniform stress within the material due to lithium-ion diffusion through a relatively faster channel. By using in situ XRD, we propose an interaction mechanism between lithium ions and the lattice of mixed-phase (anatase, rutile) titanium dioxide. In C@TiOx part, the rutile TiO2 undergoes a non-uniform strain at a rate of 0.5 C, causing the peak to broaden and shift left after lithiation. The capacities of C@TiO
𝑥
batteries were lowered from 109.0 to only 79.2 mAh/g at 5 C. It is believed that the carbon coating protect the inner TiO
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core from phase transition so that nanosized rutile TiO2 was retained after lithiation at 0.5 C, which means lithiated rutile is not equivalent to lithium titanate. Instead, the lattice distortion occurs when Li ions are intercalated in the rutile TiO2 matrix. This means that the fast lithium-ion diffusion channel in the c axis of rutile is blocked by the carbon coating and phase transition was prohibited. Furthermore, high reversibility is observed in by the overlap of initial and final curves, which can be taken as an extra evidence for the high Coulombic efficiency.

In this study, we propose the concept of aluminum and carbon co-doped non-stoichiometric titanium dioxide for in operando XRD study. Our aim is to further enhance the conductivity of titanium dioxide and its battery performance in lithium-ion batteries through the synergistic effects of heteroatom doping and non-stoichiometric treatment. This includes improvements in the capacity, impedance, cycling lifespan, and high-rate performance of the titanium dioxide material within the battery system.

Keyword: Al-doped TiO2, C coated TiOx, in operando XRD, Anode materials, Li-ion batteries