Configurational entropy-tailored NASICON cathode redox chemistry for capacity-dense and ultralong cyclability

Abstract

Sodium-ion batteries (SIBs) are a promising solution for large-scale energy storage, but their development is hindered by the limited performance of cathode materials. NASICON (Na superionic conductor)-type compounds offer fast Na⁺ diffusion and structural robustness, yet still suffer from low specific capacities (<120 mA h g⁻¹), poor cycling stability, and large volume changes – even after conventional doping. High-entropy (HE) engineering, a strategy that enhances structural and functional stability via multiple equimolar dopants, has shown great promise in layered oxides, but its application in NASICONs has been fundamentally challenging due to rigid polyanionic frameworks, dopant incompatibility, and redox mismatch. Here we report an entropy-stabilized NASICON cathode, Na_3.2V_1.5Cr_0.1Mn_0.1Fe_0.1Al_0.1Mg_0.1(PO₄)₃ (HE-V), synthesized by compositionally complex doping at the 12c Wyckoff site. The HE strategy enables the development of a single-phase material with enhanced redox flexibility and suppressed lattice strain. HE-V delivers a high reversible capacity of 170 mA h g⁻¹, enabled by multi-electron V⁵⁺/V⁴⁺/V³⁺/V²⁺ redox reactions, and demonstrates exceptional rate performance and cycling stability—maintaining performance over 10 000 cycles at 50C. Operando and ex situ characterization reveals a nearly zero-strain structure, low defect formation, and enhanced local bonding. Theoretical calculations further confirm bandgap narrowing and improved charge transport. This work establishes a new class of high-entropy polyanionic cathodes, overcoming long-standing limitations in NASICON chemistry and offering a viable path toward durable, high-energy SIBs.