Unravelling the nature of the intrinsic complex structure of binary‐phase Na‐layered oxides

The layered sodium transition metal oxide, NaTMO2 (TM = transition metal), with a binary or ternary phases has displayed outstanding electrochemical performance as a new class of strategy cathode materials for sodium‐ion batteries (SIBs). Herein, an in‐depth phase analysis of developed Na1−xTMO2 cathode materials, Na0.76Ni0.20Fe0.40Mn0.40O2 with P2‐ and O3‐type phases (NFMO‐P2/O3) is offered. Structural visualization on an atomic scale is also provided and the following findings are unveiled: i) the existence of a mixed‐phase intergrowth layer distribution and unequal distribution of P2 and O3 phases along two different crystal plane indices and ii) a complete reversible charge/discharge process for the initial two cycles that displays a simple phase transformation, which is unprecedented. Moreover, first‐principles calculations support the evidence of the formation of a binary NFMO‐P2/O3 compound, over the proposed hypothetical monophasic structures (O3, P3, O′3, and P2 phases). As a result, the synergetic effect of the simultaneous existence of P‐ and O‐type phases with their unique structures allows an extraordinary level of capacity retention in a wide range of voltage (1.5–4.5 V). It is believed that the insightful understanding of the proposed materials can introduce new perspectives for the development of high‐voltage cathode materials for SIBs. © 1999-2024 John Wiley & Sons

Keywords

Oxides, Layers, Sodium ions, Electric batteries, Crystals, Phase transformations, Alloys, Cathodes, Materials

Citation

Paidi, A. K., Park, W. B., Ramakrishnan, P., Lee, S.-H., Lee, J.-W., Lee, K.-S., Ahn, H., Liu, T., Gim, J., Avdeev, M., Pyo, M., Sohn, J. I., Amine, K., Sohn, K.-S., Shin, T. J., Ahn, D., & Lu, J. (2022). Unravelling the Nature of the Intrinsic Complex Structure of Binary-Phase Na-Layered Oxides. Advanced Materials, 34(29), 2202137. doi:10.1002/adma.202202137