Boosting Sodium Storage in Hard Carbon: A Low-Temperature Ball Milling Approach for Superior Anode Performance

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Hard carbon (HC) is a promising anode material for sodium-ion batteries (SIBs) due to its excellent sodium storage capabilities.
• The high cost of traditional HC precursors limits widespread adoption.
• Coal, a low-cost precursor, often results in suboptimal performance due to graphitization during high-temperature carbonization.

Purpose of the Study:

• To develop a cost-effective method for synthesizing high-performance hard carbon anodes from coal for SIBs.
• To investigate the impact of defect engineering on the electrochemical performance of coal-derived HC.
• To optimize the hard carbon structure for enhanced sodium storage.

Main Methods:

• A low-temperature assisted ball milling (LT-ABM) strategy was employed using dry ice (solid CO2) as a grinding medium.
• Carbonized bituminous coal was modified to enhance defect concentration and control particle size.
• Physicochemical synergistic effects were leveraged to improve surface etching and suppress agglomeration.

Main Results:

• The synthesized hard carbon nanoparticles exhibited a high reversible specific capacity of 308.14 mAh g-1 at 30 mA g-1.
• The material maintained 78% of its initial capacity after 500 cycles at 300 mA g-1, demonstrating good cycle stability.
• Kinetic analysis indicated a strong correlation between surface defect concentration and sodium storage capacity, supporting an "adsorption-insertion-filling" model.

Conclusions:

• Controlled defect engineering via LT-ABM significantly enhances the reversible capacity of coal-derived hard carbon anodes.
• The proposed method offers a viable pathway for producing cost-effective, high-performance HC anodes from abundant coal resources.
• A trade-off exists between defect density and Na+ diffusion kinetics, impacting high-rate performance, suggesting further optimization is needed.