A Ni/Co-Free High-Entropy Layered Cathode with Suppressed Phase Transion and Near-Zero Strain for High-Voltage Sodium-Ion Batteries

High-entropy layered oxides have emerged as a new class of cathode materials for sodium-ion batteries by providing infinite possibilities to tailor energy storage capabilities. However, owing to the lack of advanced high-entropy layered material, the influence of configurational entropy/compositional disorder on the high-voltage electrochemical performance of sodium-based layered cathode has seldom been explored. In this work, a Ni/Co-free high-entropy layered oxide P2-Na0.65Mn0.65Cu0.2Li0.06Mg0.015Ti0.015Al0.015Zr0.015Y0.015La0.015O2 (Mn-Cu-HEO) was prepared by stirring hydrothermal method, and investigated as a new cathode material for sodium-ion batteries. It is found that high configurational entropy and strong M-O configurations (M=Ti, Al, Zr, Y, and La) greatly stabilize the layered framework structure and MnO6 octahedral local structure, restraining the deleterious phase transition and large volume change during high-voltage cycling, thus resulting in high reversible cationic/anionic redox. In the meantime, disordered atomic arrangement in transition metal layer efficaciously mitigates Na+/vacancy ordering during de-/sodiation, enhancing the Na+ transport kinetics. Benefiting from the high-entropy stabilization effect, complex atomic arrangement, and multielemental composition, Mn-Cu-HEO displays splendid cyclic stability (87.2% capacity retention after 500 cycles, very small change in cell volume (0.53 %) after 100 cycles), excellent rate capability (55.5 mAh g-1 at 10 C), and a usable reversible capacity of 85.1 mAh g-1 at 1 C in high-voltage range of 2.0-4.5 V. This work expands the horizons of high-entropy layered materials, providing new insight in the design and construction of highly stable and high-voltage sodium ion host.