Achieving Fast Ion/Electron Transportation and Smooth Phase Transition in Polyanion Cathode by the High Entropy Strategy

The high entropy strategy is employed for the preparation of NASICON-type polyanion compound, Na_3.6VMn_0.4Fe_0.4Ti_0.1Zr_0.1(PO₄)₃ (HE-NVMFTZP), for the first time. Ex situ and in situ characterizations and theoretical calculations reveal that the high entropy effect facilitates ion/electron conduction and alleviates phase transition and volume changes during the charge/discharge process, resulting in boosted electrochemical performance in terms of a remarkable rate capability (78.5 mAh g⁻¹ at 20 C) and ultralong lifespan (80.6% after 10 000 cycles at 10 C). This work presents an innovative high entropy strategy for polyanion cathodes that effectively achieves both structural stability and enhanced sodium storage performance.

Abstract

Polyanion compounds arouse significant interest as cathode materials for sodium-ion batteries due to their large 3D lattice structures and stable frameworks. Nonetheless, it remains a great challenge for polyanion cathodes to achieve both considerable rate capability and long-term cycling lifespan. Herein, a high entropy NASICON-type cathode, Na_3.6VMn_0.4Fe_0.4Ti_0.1Zr_0.1(PO₄)₃ (HE-NVMFTZP), is successfully synthesized for the first time and exhibits superior sodium storage performance. Specifically, it delivers a reversible capacity of 110 mAh g⁻¹, remarkable rate capability (78.5 mAh g⁻¹ even at 20 C), and an ultralong lifespan (80.6% after 10 000 cycles at 10 C), which outperforms all the reported metal-substituted NASICON electrodes. Moreover, in an expanded voltage window of 1.5–4.3 V, the HE-NVMFTZP electrode delivers an impressive capacity of 177.4 mAh g⁻¹ (≈494 Wh kg⁻¹). Comprehensive experimental characterizations and first-principles calculations reveal that the high entropy effect facilitates ion/electron transportation and alleviates volume expansion and phase transition during the charge/discharge process. This work provides a facile high entropy strategy on the local structural engineering of polyanion cathodes to effectively boost the sodium storage performance and can shed light on the design of stable and high-capacity cathode materials.