Defect-Engineered Bulk Conversion Anodes for Fast and Temperature-Adaptive Na⁺ Storage

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Conversion-based metal sulfides/selenides are promising anodes for sodium-ion batteries (SIBs) due to high capacity and conductivity.
• However, large volume changes during cycling cause capacity decay, limiting commercial use.
• Developing cost-effective synthesis for enhanced sodium storage is crucial.

Purpose of the Study:

• To address capacity decay in SIB anodes by employing defect engineering in bulk Fe7Se8.
• To create a carbon-free, defect-rich anode material for improved sodium storage.
• To investigate the performance, mechanism, and potential applications of the engineered anode.

Main Methods:

• Fabrication of defect-rich bulk Fe7Se8-x through defect engineering.
• Electrochemical testing including cyclic stability, rate capability, and temperature adaptability.
• In/ex situ characterization, kinetics analysis, and DFT calculations to elucidate reaction mechanisms.
• Full cell assembly to demonstrate practical application potential.

Main Results:

• Optimized bulk Fe7Se8-x exhibited excellent cyclic stability (e.g., 384 mAh g-1 after 1300 cycles at 5 A g-1) and ultrahigh rate capability (up to 40 A g-1).
• The material demonstrated good performance at various temperatures (0°C and 40°C).
• The defect engineering strategy was successfully applied to other materials like bulk Fe7S8-x and bulk CoSe2-x.

Conclusions:

• Defect engineering in bulk Fe7Se8-x provides a viable strategy for high-performance, stable sodium-ion battery anodes.
• The carbon-free, defect-rich material overcomes limitations of traditional conversion anodes.
• This approach offers a universal method for enhancing other conversion-based anode materials for SIBs.