Cu-substitution-induced stabilization of P2-type Na0.67Mn-Ni-Fe layered cathodes for high-performance sodium-ion storage

초록

Nickel-containing P2-type layered-transition-metal oxide cathodes for sodium-ion batteries often suffer from irreversible phase transitions, cation mixing, and rapid capacity fading during high-voltage cycling. Herein, we report a series of Cu-substituted P2-type Na0.67Mn0.58Ni0.25-xFe0.17CuxO2 cathodes, where x = 0, 0.05, 0.10, and 0.15, prepared by a conventional solid-state method. The systematic variation of Cu content reveals a clear trade-off between reversible capacity, rate capability, and cycling stability. Na0.67Mn0.58Ni0.15Fe0.17Cu0.10O2 delivers the best overall electrochemical performance, achieving an initial discharge capacity of 191.3 mA h g−1, and decent rate capability up to 3 A g−1. In contrast, the higher-Cu composition Na0.67Mn0.58Ni0.10Fe0.17Cu0.15O2 exhibits improved long-term capacity retention but reduced high-rate performance. Ex situ Fe, Ni, and Mn K-edge X-ray absorption spectroscopy combined with DFT calculation reveals that charge compensation is primarily governed by Mn and Ni-centered redox, with additional contributions from Fe, while Cu substitution provides structural and electronic buffering by stabilizing Cu–O coordination and accommodating charge redistribution, thereby mitigating perturbation of the Ni–O environment. In situ synchrotron X-ray diffraction further confirms that optimized Cu substitution suppresses irreversible lattice distortion during cycling. These findings establish controlled Cu substitution as an effective strategy for stabilizing Ni-containing P2-type cathodes. © 2026 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

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