Quantitative incorporation of dopants in medium-entropy cathodes for sodium-ion batteries: From design to validation

The diffusion kinetics of electrons and ions are enhanced by the beneficial medium-entropy effect in medium-entropy cathodes, which results in a significant improvement of sodium storage capacity. However, the design of medium-entropy materials is usually characterized by high randomness and uncertainty, primarily due to the absence of established quantitative design methodologies. In this paper, NaMn_4/12Fe_3/12Ni_4/12Ti_1/12O₂ (MFNT), a medium-entropy (1.286 R) cathode material for sodium-ion batteries, was rationally designed based on a quantitative doping threshold determined via theoretical screening. The distinct contributions of Ni, Fe, and Ti to enhancing redox potential, improving electrical conductivity, modulating redox activity of transition metals (TM), inhibiting phase transitions, and enabling oxygen charge compensation were investigated systematically. Featuring a medium-entropy crystalline state, MFNT delivered a specific capacity of 127 mAh·g^–1 at 0.1 C. After 100 cycles, 96 mAh·g^–1 was retained, and even at 5 C, 71 mAh·g^–1 was sustained. The entropy-stabilized structure, activated oxygen redox, and enhanced Na⁺ diffusion kinetics were confirmed experimentally. The reversibility of phase transitions during the electrochemical reaction of this medium-entropy cathode was verified by ex-situ X-ray diffraction. The combined computational–experimental strategy accelerates material development and promotes sustainable design principles for next-generation sodium-ion batteries.