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 (Formula presented.) 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. © 2025 Wiley-VCH GmbH.