Stabilizing P2-phase in layered oxides via electronic modulation for high-performance sodium-ion batteries

Abstract

P2-type layered oxides are highly promising cathode candidates for sodium-ion batteries (SIBs) owing to their substantial theoretical capacity. Nevertheless, structural degradation caused by transition metal dissolution and irreversible phase transitions at high voltage severely compromises cycling stability. To address this limitation, we propose a Li/Ti co-doping strategy to design a Na_0.67Li_0.06Ni_0.27Mn_0.57Ti_0.1O₂ (NLMT) cathode for SIBs. In-situ X-ray diffraction (XRD) confirms that this deliberate strategy eliminates the adverse phase transition at high voltage and sustains the unitary P2 phase throughout cycling. In addition, strengthened transition metal–oxygen (TM–O) bonding via electronic modulation suppresses transition metal dissolution and reinforces the layered oxide framework, contributing to exceptional electrochemical performance. Consequently, the NLMT cathode exhibits an outstanding capacity of 92.8 mA h g⁻¹ within 2.5–4.3 V at 5 C (865 mA g⁻¹), with 87 % capacity retention over 200 cycles. Configured into a full cell, which achieves a competitive capacity of 107.7 mA h g⁻¹ at 0.1 C and retains 86.4 % capacity over 100 cycles at 0.5 C. This study validates co-doping as a potent strategy for significantly improving the long-term cyclability of layered oxide cathodes in SIBs.