High-Entropy and Na-Rich-Designed High-Energy-Density NaV(PO)/C Cathode.

The NaV(PO) (NVP) cathode holds the merit of a stable 3D NASICON structure for ultrafast Na diffusion, yet it is still confronted with poor electronic conductivity (10 S cm) and insufficient energy density (∼370 W h kg). Herein, a series of high-entropy-doped NaVZn(GaCrAlIn)(PO) ( = 0, 0.2, 0.35, and 0.5) cathodes are systematically prepared with an activated V⇌V high-voltage plateau (4.0 V) and elevated discharge capacity, which is derived from the charge compensation of divalent Zn substituting for trivalent V accompanied by extra Na input to create an Na-rich phase. A range of in situ/ex situ characterization studies and DFT calculations radically verify the charge conservation mechanism, enhanced bulk conductivity, and robust structural stability. Accordingly, in half-cells, the optimized cathode ( = 0.35) is capable of giving a much-improved discharge capacity (126.8 mA h g), reliable cycling stability (97.4%@5000 cycles@40 C), and a competitive energy density (426.1 W h kg) at 2.0-4.3 V. Upon reducing the discharge cutoff voltage to 1.4 V, the three-electron reaction (V⇌V) is entirely activated with superior stability, delivering an unparalleled capacity of 193.4 mA h g with higher energy density (544.3 W h kg). Besides, it displays high capacity (126.1 mA h g) and energy density (417.2 W h kg) in NVPZGCAI-35//hard carbon full-cells at 1.6-4.1 V. Hence, this pioneering high-entropy and Na-rich strategy is above rubies for developing high-energy-density and high-stability sodium-ion batteries.