Mechanistic Insights into Moisture-Assisted Low-Temperature Synthesis of LiCoO2 Revealed by In Situ X-ray Absorption Spectroscopy

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Abstract Layered lithium cobalt oxide (LiCoO2) is a benchmark cathode material for Li-ion batteries; however, conventional solid-state synthesis requires high temperatures (∼800 °C) and prolonged processing. Here, we demonstrate a low-temperature hydroflux method for LiCoO2 and elucidate its formation mechanism using in situ X-ray absorption spectroscopy (XAS), complemented by molecular dynamics (MD) simulations. Under alkali hydroflux conditions, moisture (H2O) induces a partial local structural transformation of Co(OH)2 toward an α-Co(OH)2-like coordination environment, locally expanding the interlayer region. The structural evolution creates pathways for lithium incorporation into the Co(OH)2 interlayers at temperatures as low as ∼150 °C, enabling the low-temperature nucleation and growth of layered LiCoO2. In contrast, syntheses under dry conditions proceed through CoO and Co3O4 intermediates and do not yield phase-pure LiCoO2 at these temperatures. Time-resolved in situ XAS reveals distinct reaction pathways in the presence and absence of moisture, identifying intermediate cobalt valence states and local structural changes consistent with the proposed mechanism. Supplementary MD simulations are consistent with this interpretation, suggesting that interlayer H2O/OH– species may assist Li+ incorporation into Co(OH)2. Collectively, these findings provide mechanistic insights into moisture-enabled low-temperature formation of LiCoO2 and suggest a viable strategy for energy-efficient production of layered oxide cathode materials.

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