Biphasic P3/O3 driven excellent electrochemical behavior and structural stability in a dual pillar-ions sodium layered oxide cathode

Abstract

Layered oxides suffer from detrimental phase transformations during the charge-discharge process, limiting their long-term cyclability and causing poor rate performance as Na-ion battery cathodes. Herein, Ti/Al co-doped Na<inf>2/3</inf>Mn<inf>2/3</inf>Ni<inf>1/3</inf>O<inf>2</inf> cathode with an optimized P3/O3 biphasic structure is designed that effectively constrains these undesirable phase transformations and cooperative Jahn–Teller distortion. Ti/Al doping imparts excellent electrochemical properties with Na<inf>0.77</inf>Mn<inf>0.47</inf>Al<inf>0.10</inf>Ti<inf>0.10</inf>Ni<inf>0.33</inf>O<inf>2</inf> (NMAT-10) shows an excellent specific capacity of ∼175.5 mAh g−1 at 0.1C in 1.5–4.2 V range and capacity retention of 83 % after 300 cycles at 2C in 2.0–4.2 V. It also exhibits a much-improved rate capability with about 80 % capacity at 5C relative to the capacity observed at 0.1C. These improvements in electrochemical performance are attributed to the stronger Al-O bond, which suppresses the severity of P3↔P3′↔O3 phase transformation, as confirmed by the operando synchrotron x-ray diffraction studies. The practical viability of NMAT-10 cathode is verified in a full cell using a commercial hard-carbon anode, which showed a discharge capacity of ∼80 mAh g−1 at 0.2C and a remarkable capacity retention of 86 % after 100 cycles. This work highlights the P3/O3 biphasic structure as an effective approach to achieve an excellent rate performance and better cycling stability in layered oxides for sodium-ion batteries. © 2025 Elsevier B.V., All rights reserved.