Entropy Engineering Accelerating the Phase Transformation Dynamics of Phosphate Cathode for Ultra-High Rate...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sodium-ion batteries (SIBs) are a cost-effective alternative to lithium-ion batteries.
• NASICON-type Na3.5V1.5Mn0.5(PO4)3 (NVMP) is a promising SIB cathode material.
• NVMP suffers from sluggish kinetics and poor structural stability, limiting its practical application.

Purpose of the Study:

• To develop a high-performance cathode material for SIBs.
• To enhance the electrochemical performance of NASICON-type materials.
• To investigate the effect of multi-cation doping on the reaction mechanism and stability of NVMP.

Main Methods:

• Synergistic doping of Al, Ni, and Zr into the transition metal sites of NVMP.
• Synthesis of Na3.5V1.35Mn0.5Al0.05Ni0.05Zr0.05(PO4)3/C (NVMANZP).
• Electrochemical characterization, including rate capability and cycling stability tests.

Main Results:

• NVMANZP exhibits a solid-solution-like reaction mechanism, unlike the biphasic reaction in pristine NVMP.
• The entropy-stabilized mechanism reduces Na+ migration barriers and minimizes Jahn-Teller strain.
• NVMANZP delivers a high reversible capacity of 118.3 mAh g-1 at 0.2C and retains 77.3 mAh g-1 at 100C.
• The material shows excellent cycling stability, maintaining 80.76% capacity retention after 4,000 cycles at 10C.
• A full cell using NVMANZP achieves an energy density of 378 Wh kg-1 at 0.2C.

Conclusions:

• Multi-cation doping effectively transforms the reaction mechanism of NVMP towards a solid-solution-like process.
• NVMANZP demonstrates superior rate capability and long-term cycling stability compared to pristine NVMP.
• Entropy-driven mechanisms are crucial for tailoring NASICON cathode performance for high-rate, long-life SIBs.