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Journal Article

Enabling Anionic Redox Stability of P2-Na5/6Li1/4Mn3/4O2 by Mg Substitution

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Hu,  Zhiwei
Zhiwei Hu, Physics of Correlated Matter, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;

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Citation

Huang, Y., Zhu, Y., Nie, A., Fu, H., Hu, Z., Sun, X., et al. (2022). Enabling Anionic Redox Stability of P2-Na5/6Li1/4Mn3/4O2 by Mg Substitution. Advanced Materials, 2105404, pp. 1-9. doi:10.1002/adma.202105404.


Cite as: https://hdl.handle.net/21.11116/0000-0009-F403-0
Abstract
Oxygen-based anionic redox reactions have recently emerged as a lever to increase the capacity of Mn-rich layered oxide cathodes in addition to the charge compensation based on cationic redox reactions for sodium-ion batteries. Unfortunately, the irreversibility of anionic redox often aggravates irreversible structure change and poor cycling performance. Here, a stable anionic redox is achieved through substituting Na ions by Mg ions in P2-type Na0.83Li0.25Mn0.75O2. Density functional theory (DFT) calculations reveal that Mg substitution effectively decreases the oxygen chemical potential, causing an improvement in lattice oxygen stability. Moreover, at a highly desodiated state, Mg ions that remain in the lattice and interact with O 2p orbitals can decrease the undercoordinated oxygen and the nonbonded, electron-deficient O 2p states, facilitating the reversibility of oxygen redox. When cycled in the voltage range of 2.6-4.5 V where only anionic redox occurs for charge compensation, Na0.773Mg0.03Li0.25Mn0.75O2 presents a much better reversibility, giving a 4 times better cycle stability than that of Na0.83Li0.25Mn0.75O2. Experimentally, Na0.773Mg0.03Li0.25Mn0.75O2 exhibits a approximate to 1.1% volume expansion during sodium insertion/extraction, suggestive of a "zero-strain" cathode. Overall, the work opens a new avenue for enhancing anionic reversibility of oxygen-related Mn-rich cathodes.