Polymorph Engineering for Boosted Volumetric Na-Ion and Li-Ion Storage

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Growing demand for high-performance rechargeable batteries necessitates improved electrode materials with higher volumetric capacity.
• Current electrode materials often require conductive additives, increasing complexity and reducing overall performance.
• Iron selenide (FeSe) exists in different polymorphs with varying electronic properties.

Purpose of the Study:

• To enhance the volumetric capacity of electrodes using polymorph engineering of FeSe.
• To develop conductive additive-free (CA-free) electrodes utilizing the properties of specific FeSe polymorphs.
• To investigate the potential of engineered FeSe for both sodium-ion and lithium-ion batteries.

Main Methods:

• Polymorph engineering of FeSe to create tetragonal and hexagonal phases.
• Fabrication of conductive additive-free (CA-free) electrodes using tetragonal FeSe.
• Electrochemical testing for sodium and lithium storage performance, including capacity, utilization, and efficiency.
• In situ X-ray diffraction (XRD) to study reaction mechanisms.

Main Results:

• Tetragonal FeSe, with its metallic conductivity, enabled a CA-free electrode with a sodium storage volumetric capacity of 1011 mAh cm^-3.
• The CA-free tetragonal FeSe electrode achieved 96.7 wt% active material utilization and 96% initial Coulombic efficiency for sodium storage.
• As a cathode for lithium-ion batteries, CA-free tetragonal FeSe delivered a volumetric energy density of 1373 Wh L^-1 and power density of 7200 W L^-1.
• Reversible conversion reactions were confirmed via in situ XRD for both sodium and lithium systems.

Conclusions:

• Polymorph engineering of FeSe is an effective strategy to significantly boost volumetric capacity in rechargeable batteries.
• Conductive additive-free electrodes based on tetragonal FeSe offer superior performance for both sodium-ion anodes and lithium-ion cathodes.
• The findings provide a new design approach for advanced electrode materials, inspiring future battery research.