P2-type layered oxides with the general Na-deficient composition NaxTMO₂ (x < 1, TM: transition metal) are a promising class of cathode materials for sodium-ion batteries. The open Na+ transport pathways present in the structure lead to low diffusion barriers and enable high charge/discharge rates. However, a phase transition from P2 to O2 structure occurring above 4.2 V and metal dissolution at low potentials upon discharge results in rapid capacity degradation. In this work, we demonstrate the positive effect of configurational entropy on the stability of the crystal structure during battery operation. Three different compositions of layered P2-type oxides were synthesized by solid-state chemistry, Na₀.₆₇(Mn₀.₅₅Ni₀.₂₁Co₀.₂₄)O₂, Na₀.₆₇(Mn₀.₄₅Ni₀.₁₈Co₀.₂₄Ti₀.₁Mg₀.₀₃)O₂ and Na₀.₆₇(Mn₀.₄₅Ni₀.₁₈Co₀.₁₈Ti₀.₁Mg₀.₀₃Al₀.₀₄Fe₀.₀₂)O₂ with low, medium and high configurational entropy, respectively. The high-entropy cathode material shows lower structural transformation and Mn dissolution upon cycling in a wide voltage range from 1.5 to 4.6 V. Advanced operando techniques and post-mortem analysis were used to probe the underlying reaction mechanism thoroughly. Overall, the high-entropy strategy is a promising route for improving the electrochemical performance of P2 layered oxide cathodes for advanced sodium-ion battery applications.
