High-entropy engineering unlocks high-voltage redox chemistry in NASICON-type Na3.25V1.44Fe0.25Mn0.25Mg0.02Nb0.02Zr0.02(PO4)3 cathodes for advanced sodium-ion batteries

High-voltage vanadium-based NASICON cathodes for sodium-ion batteries (SIBs) are fundamentally constrained by limited electronic conductivity, insufficient capacity arising from incomplete redox utilization, and structural instability during cycling. Herein, we propose a synergistic engineering strategy integrated with conductive carbon coating to address these challenges. A multi-component NASICON cathode, Na3.25V1.44Fe0.25Mn0.25Mg0.02Nb0.02Zr0.02(PO4)3 (HE-NVP), is rationally designed, in which Fe³⁺ and Mn²⁺ substitution activates the reversible high-voltage V⁴⁺/V⁵⁺ redox couple, while Mg²⁺, Nb⁵⁺, and Zr⁴⁺ server as structural stabilizers to reinforce lattice integrity. The resulting configurational entropy and multi-element simultaneously regulate electronic structure, accelerate Na⁺ diffusion kinetics, and suppress structural degradation. Benefiting from these cooperative effects, HE-NVP delivers a high reversible specific capacity of 120.9 mAh g-1 at 1 C with an average voltage of 3.43 V. Remarkably, it maintains 82.4 mAh g-1 after 1100 cycles at 20 C, demonstrating excellent rate capability and long-term durability. In-situ X-ray diffraction reveals that Na⁺ storage proceeds via a highly reversible hybrid mechanism involving both solid-solution and two-phase reactions, underscoring the structural resilience of the entropy-stabilized framework. This study elucidates the mechanistic role of high-entropy design in unlocking high-voltage redox activity while mitigating phase instability, offering a viable materials engineering paradigm for advanced NASICON-type sodium-ion battery cathodes.