Exposed {010} Crystal Surfaces Drive High Rate Performance and Cyclability in Air Stable P2‐Type Cathode for Na‐Ion Batteries

ABSTRACT

Particle morphology and synthesis conditions play a major role in determining the electrochemical behavior of layered oxide cathodes. Herein, various structures (P2, O3, and P2/O3 biphasic) are achieved for dual pillar‐ion doped Na _x Mn _0.47 Ni _0.33 Ti _0.1 Al _0.1 O ₂ by varying sodium content and calcination temperature. P2‐type sample with 0.77Na exhibits excellent electrochemical properties, with a reversible specific capacity of 141.5 mAh g ⁻¹ at 0.1C (1.5‐4.1 V) and capacity retention of 93% after 100 cycles. Owing to the larger Na ⁺ conducting lateral {010} surfaces, this cathode achieves the best rate‐performance among all compositions, with about 84% capacity at 2C relative to 0.1C, as confirmed by galvanostatic intermittent titration technique and in situ electrochemical impedance spectroscopy (EIS) data. The distribution of relaxation times (DRT) analysis of temperature‐dependent EIS confirmed a much lower charge‐transfer activation energy (≈0.54 eV) in the P2‐Na _0.77 Mn _0.47 Ni _0.33 Ti _0.1 Al _0.1 O ₂ cell as compared to the O3‐analogous cell (≈0.97 eV). Ex situ XRD measurements showed that while O3‐Na _1.00 Mn _0.47 Ni _0.33 Ti _0.1 Al _0.1 O ₂ undergoes a determinantal O3↔P3 phase transformation, Na0.77‐850 cathode maintained a P2 dominant framework during charge‐discharge cycling in the 2.0–4.0 V range with low lattice strain. A Na0.77‐850||hard‐carbon full cell showed 85% capacity retention after 100 cycles, highlighting its potential for practical applications.