Tuning Redox Potentials in NASICON Cathode via Covalent Lattice Modulation

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• NASICON-type Na3MnTi(PO4)3 cathodes show promise for sodium-ion batteries (SIBs).
• Limited energy density is due to incomplete activation of high-potential manganese redox couples.
• Tuning electronic structure is key to unlocking higher performance.

Purpose of the Study:

• To enhance the energy density of NASICON-type cathodes by modulating manganese redox potentials.
• To investigate the effect of chromium incorporation on the electronic structure and electrochemical performance.
• To develop a generalizable strategy for designing high-voltage polyanionic frameworks.

Main Methods:

• Synthesis of chromium-substituted Na3.5MnTi0.5Cr0.5(PO4)3 cathode material.
• Electrochemical characterization including discharge voltage, energy density, and cycling stability tests.
• Mechanistic studies to understand the reaction mechanism and volume expansion.

Main Results:

• The Na3.5MnTi0.5Cr0.5(PO4)3 cathode achieved a high average discharge voltage of 3.40 V.
• A competitive energy density of 586 Wh kg-1 was obtained, surpassing many reported NASICON cathodes.
• Exceptional cycling stability with 87.6% retention over 5000 cycles at 20 C and minimal volume expansion (2.5%).
• High cyclability in a full-cell configuration (88.6% retention after 1000 cycles at 2 C).

Conclusions:

• Strategic chromium incorporation effectively modulates Mn-O covalency, elevating Mn redox potentials.
• The developed material offers a promising pathway for high-voltage, high-energy-density sodium-ion batteries.
• Covalent modulation provides a generalizable strategy for designing advanced polyanionic frameworks for energy storage.