Spin-Polarized Surface Capacitance Effects Enable Fe₃ O₄ Anode Superior Wide Operation-Temperature Sodium Storage

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Iron oxide (Fe3O4) is a promising anode material for ambient sodium-ion batteries (SIBs).
• Limited research exists on the electrochemical performance of Fe3O4 anodes across a wide operating temperature range.
• Understanding temperature-dependent behavior is crucial for practical SIB applications.

Purpose of the Study:

• To investigate the electrochemical properties of a novel Fe3O4-based anode material for SIBs under wide operating temperatures (-40 to 60°C).
• To explore the role of graphene and carbon encapsulation in enhancing anode performance.
• To elucidate the mechanism behind improved sodium-ion storage at varying temperatures.

Main Methods:

• Synthesis of Fe3O4 nanoparticles encapsulated by carbon nanolayers and dispersed on graphene (Fe3O4/C@G).
• Electrochemical characterization of the Fe3O4/C@G anode in half and full SIB cells across a temperature range of -40 to 60°C.
• Analysis of material structure and nanoparticle size using advanced techniques.

Main Results:

• The Fe3O4/C@G anode exhibited high capacity and excellent fast-charging capability.
• The material demonstrated remarkable cycling stability across the wide operating temperature range.
• Ultra-small superparamagnetic Fe nanoparticles (≈2 nm) induced a spin-polarized surface capacitance effect, enhancing Na-ion transport and storage.

Conclusions:

• Fe3O4 is a viable anode material for sodium-ion batteries operating under wide temperature conditions.
• Graphene and carbon encapsulation significantly improve Fe3O4 nanoparticle size and electrode conductivity.
• The spin-polarized surface capacitance effect is key to achieving high performance in wide-temperature SIBs.