Unravelling the Nature of the Intrinsic Complex Structure of Binary‐Phase Na‐Layered Oxides
Anil Kumar Paidi, Woon Bae Park, P. Ramakrishnan, Seonghun Lee, Jin‐Woong Lee, Kug‐Seung Lee, Hyungju Ahn, Tongchao Liu, Jihyeon Gim, Maxim Avdeev, Myoungho Pyo, Jung Inn Sohn, Khalil Amine, Kee‐Sun Sohn, Tae Joo Shin, Docheon Ahn, Jun Lü
Abstract
Abstract The layered sodium transition metal oxide, NaTMO 2 (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 Na 1− x TMO 2 cathode materials, Na 0.76 Ni 0.20 Fe 0.40 Mn 0.40 O 2 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.