Modulating Phase Angle Variations of O3-Type High-Entropy Layered Sodium Oxide for Practical Sodium-Ion Cylindrical Battery

Abstract

High-entropy oxides, with their diverse compositions and entropy-stabilized structures, have emerged as promising candidates for sodium-ion battery cathodes. However, phase transitions in these materials are highly sensitive to the specific transition metal composition, and effective design strategies remain underdeveloped. Herein, a six-element high-entropy layered oxide cathode, O3-Na_0.9Ni_0.3Fe_0.1Zn_0.1Cu_0.05Mn_0.3Ti_0.15O₂, is reported in which the incorporation of Zn and Cu not only alters the electronic structure but also affects the formation angle of desired OP2 phase. By fine-tuning Zn/Cu ratio, we optimize the phase transition behavior of high-entropy layered oxides, significantly enhancing structural stability and electrochemical performance. This material delivers a high specific capacity of 146.9 mAh g⁻¹ with superior cycling performance (80.4% capacity retention after 500 cycles). Furthermore, utilizing the as-prepared cathode and commercial hard carbon anode, 1.1 Ah cylindrical cells successfully demonstrated high initial Coulombic efficiency of 92% and rapid charge and discharge rates up to 5C, retaining 93.6% of the capacity. Notably, these cylindrical cells exhibit excellent cycling stability with capacity retention of 86% after 300 cycles.