Rational Design of Mid-Ni Layered Oxides via Precursor-Encoded Spatial Distribution of Redox-Active Li2MnO3 Domains

초록

Li-rich layered oxides (LLOs) promise exceptional energy density via anionic redox but are plagued by instability stemming from irreversible oxygen release. Implementing this strategy in cost-effective, Co-free mid-Ni cathodes is attractive, yet requires precise control over the Li2MnO3 domains. Here, we demonstrate that a previously overlooked parameter-the precursor's Mn oxidation state, precisely modulated by the drying atmosphere (oxygen-rich vs. oxygen-free)-dictates the final spatial distribution of Li2MnO3 domains. An oxidized precursor (oxygen-rich) triggers the preferential formation of Li2MnO3 domains segregated at the particle surface (OR-LNR). In contrast, an oxygen-free atmosphere ensures a uniform Mn oxidation state, resulting in a homogeneous domain distribution throughout the bulk (OF-LNR). This homogeneous architecture is proven crucial for enhancing oxygen redox reversibility. Consequently, OF-LNR exhibits superior full-cell cycling stability compared to the surface-segregated OR-LNR. Mechanistic analysis reveals that the surface-segregated domains initiate a catastrophic degradation cascade, including internal void formation, impedance growth, and severe cathode-anode crosstalk. This work establishes a new precursor engineering principle, identifying Mn oxidation state control as a critical strategy for the rational design of high-energy, durable LLO cathodes.

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