Formation of Lithium Titanate Hydrate Nanosheets: Insight into a Two-Dimension Growth Mechanism by in Situ Raman

Orthorhombic lepidocrocite-type lithium titanate hydrates (LTH), as one important member among two-dimensional (2D) materials, have drawn much attention due to their potential applications in nanoelectronics, energy conversion, and energy storage devices. However, only a few efforts have focused on an anisotropic growth mechanism that determines the formation kinetics of LTH and/or even their derivatives. In this context, in situ Raman observation was employed to the isothermal crystallization of LTH nanosheet crystals from amorphous precursor precipitates. During isothermal crystallization, the formation of monolayered LTH nuclei is controlled by oxygen diffusion with an activation energy of 0.72 eV; anisotropic growth along (010) planes induces an interblocking effect among LTH nanosheet crystals, which limits their size up to 50 nm. The nucleation-growth crystallization kinetics of LTH nanosheets were accurately interpreted by the modified Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, which considered their anisotropic 2D growth. Beyond LTH, the present study that combines in situ spectroscopic monitoring with kinetic modeling paves the way toward deeper comprehension and ultimate control of the growth kinetics of 2D titanate materials.