UC Berkeley

ABSTRACT Sol–gel synthesis is a wet‐chemical processing route for fabricating functional materials with control over composition and microstructure at relatively low temperatures compared to conventional solid‐state synthesis. While sol–gel process initiates with intermixed molecular precursors, the early‐stage nucleation pathways are insufficiently understood. Here, the chemical and structural transformation of disordered rocksalt (DRX) Li 1.2 Mn 0.4 Ti 0.4 O 2 (LMTO), a promising cathode material for lithium batteries, is studied by multiscale characterizations. In situ heating transmission electron microscopy (TEM) using a liquid cell visualizes and identifies crystallization pathways at the nanoscale. While some regions follow a classical multi‐step transition through thermodynamically stable intermediates, others exhibit a kinetic shortcut via a localized amorphous matrix to directly form the DRX structure. Macroscale Fourier transform infrared spectroscopy corroborates the findings and reveals that transition metal ions are more strongly incorporated into the acetate‐coordinated network than lithium. Although in situ heating TEM captures diverse local transformation pathways, in situ synchrotron X‐ray diffraction indicates that the macroscopic transformation proceeds predominantly through spinel LMTO and lithium titanates toward DRX‐LMTO. The findings uncover the spatiotemporal chemical and structural transformations in sol–gel derived DRX‐LMTO materials, and call for fine‐tuning of such sol–gel chemistries to manipulate the crystallization pathways and achieve target material homogeneity more efficiently.