Overcoming the Trade-Off between Initial Coulombic Efficiency and Rate Performance in Hard Carbon Anodes for...

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Hard carbon (HC) is a key anode material for sodium-ion batteries (SIBs) due to its low cost and voltage plateau.
• A major challenge for HC anodes is balancing initial Coulombic efficiency (ICE) with rate capability.

Purpose of the Study:

• To develop a scalable synthesis method for high-performance hard carbon anodes.
• To improve the structural characteristics of hard carbon for enhanced sodium storage.

Main Methods:

• Utilized a kilogram-scale melt-spinning technique combined with a hexamethylenetetramine (HMTA) cross-linking-oxidation strategy.
• Synthesized phenolic resin-derived hard carbon (CPF-1400) with controlled structural features, including enlarged interlayer spacing and optimized pore structure.
• Employed experimental studies and in situ characterizations to analyze electrochemical performance and storage mechanisms.

Main Results:

• The developed CPF-1400 exhibited a suppressed graphitization degree and an enlarged carbon interlayer spacing (0.381 nm).
• Achieved a low specific surface area (1.4 m² g⁻¹) and abundant closed pores (0.315 cm³ g⁻¹).
• Delivered a high reversible capacity (431 mAh g⁻¹), exceptional ICE (95%), and maintained good rate capability (308 mAh g⁻¹ at 1 A g⁻¹).
• Full cells demonstrated a high energy density of 293 Wh kg⁻¹.

Conclusions:

• The novel synthesis strategy effectively tailors hard carbon structure for superior sodium-ion battery anode performance.
• The study elucidated a three-stage sodium storage mechanism and the critical role of the solid-electrolyte interphase (SEI).
• This work offers a scalable pathway for producing high-performance hard carbon anodes for next-generation energy storage devices.