Reversibility of Planar Gliding and Enhanced Structural Stability in Single‐Crystalline Cathodes Benefiting from High‐Entropy P2/O3 Biphase for Sodium‐Ion Batteries

ABSTRACT The practical application of P2‐type layered oxides for sodium‐ion batteries is hindered by issues such as low initial Coulombic efficiency and irreversible P2→O2 phase transitions, the latter of which induce gliding of transition‐metal–oxygen slabs, structural collapse, and rapid capacity fading. In this work, based on P2‐Na _0.67 Ni _0.33 Mn _0.67 O ₂ , a series of cathodes, Na _x Ni _0.33 Mn _0.4 Ti _0.1 Fe _0.07 Co _0.1 O ₂ (x = 0.62, 0.67, 0.70, 0.73, 0.78), were designed through multi‐element transition‐metal substitution to achieve performance optimization. The rational coupling of high‐entropy engineering with a P2/O3 biphasic strategy enables precise tuning of phase ratios and uniform cation distribution, which effectively suppresses the detrimental P2→O2 transition and improves the reversibility of planar gliding while enhancing Na ⁺ diffusion kinetics. The combining interfacial interlocking with local chemical homogenization by high‐entropy P2/O3 biphasic architecture mitigates lattice strain and planar gliding, suppressing crack formation and maintaining the structural integrity of the cathode material during cycling. The optimized biphasic high‐entropy Na _0.7 Ni _0.33 Mn _0.4 Ti _0.1 Fe _0.07 Co _0.1 O ₂ (P2/O3‐N0.7) electrode delivers prominent rate capability and good cycling stability at high rates. Moreover, P2/O3‐N0.7 also demonstrates good air and moisture environment stability and full‐cell application potential. This high‐entropy biphasic strategy offers an effective route toward cathode materials with both high capacity and long cycle life for sodium‐ion batteries.