Elevating the Concentration of Na Ions to 1 in P2 Type Layered Oxide Cathodes

Abstract Layered oxide cathodes, particularly those with P2 and P3 type structures, have lower specific capacities limited by the Na‐ion content in their structure. In this study, the Na content is elevated to its uppermost limit with a cathode. The material is synthesized in a monophasic P3, monophasic P2 (with a minor O3 phase), and biphasic P3/P2 configuration. During electrochemical testing, the biphasic P3/P2 and the monophasic P2 type compounds exhibited excellent performance, with specific capacities reaching 102 and 87 mAh g −1 , respectively, at 6C. A full cell fabricated using the monophasic P2 type cathode demonstrated a specific capacity of 123 mAh g −1 at 0.1C and retained 90% of its initial specific capacity after 200 cycles at 0.2C. The structural integrity of both the biphasic P3/P2 and the monophasic P2 type cathode materials is supported by the operando synchrotron X‐ray diffraction data, which showed no phase transformations and P2 phase showing only a 0.78% variation in unit cell volume. These findings highlight the transformative potential of achieving high Na‐ion concentrations in P2‐type cathode materials, paving the way for developing high‐performance sodium‐ion batteries.