Reversibility of Planar Gliding and Enhanced Structural Stability in Single-Crystalline Cathodes Benefiting from...

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_0.67Ni_0.33Mn_0.67O₂, a series of cathodes, Na_xNi_0.33Mn_0.4Ti_0.1Fe_0.07Co_0.1O₂(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_0.7Ni_0.33Mn_0.4Ti_0.1Fe_0.07Co_0.1O₂ (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.