A Universal Voltage-Enhancement Strategy Based on Multifunctional Ligand-Mediated Modulation for Na-Layered Oxide...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Sodium-ion batteries (SIBs) offer a low-cost, abundant alternative to lithium-ion batteries.
• Practical SIB application is limited by the low operating voltage of cathode materials.
• Enhancing cathode voltage is crucial for advancing SIB technology.

Purpose of the Study:

• To introduce a universal ligand-field engineering strategy to modulate electronic structure and enhance voltage in transition metal oxide cathodes.
• To investigate the effect of weak-field ligands on the electronic structure and electrochemical performance of Na_0.67Mg_0.2Mn_0.8O₂.
• To establish a correlation between electronic structure modification and operating voltage in SIB cathode materials.

Main Methods:

• Ligand-field engineering by introducing weak-field ligands to alter the coordination environment of MnO₆ octahedra.
• Experimental characterization and theoretical calculations (e.g., DFT) to analyze electronic structure changes.
• Electrochemical testing to evaluate operating voltage, discharge capacity, and cycling stability.

Main Results:

• Weak-field ligands reduced Mn octahedral splitting energy, downshifting the $e_g^{\ast }$ orbital energy.
• This shift elevated the Mn³⁺/Mn⁴⁺ redox potential, increasing the average operating voltage by 0.24 V.
• Discharge capacity increased by 35.7% (153.2 mA h g^-1), and capacity retention improved to 94.4% after 200 cycles, suppressing detrimental side reactions.

Conclusions:

• Ligand-field engineering is an effective strategy for enhancing the operating voltage of SIB cathodes.
• Modulating $e_g^{\ast }$ orbital energy provides foundational insights for designing high-voltage cathode materials.
• This approach is extendable to other transition metal oxide systems for advanced energy storage applications.