Electronic/Ionic Co-Modulation by N/P Co-Doping toward High-Rate Sodium Storage in Coal-Derived Hard Carbon

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Hard carbon is a key anode material for sodium-ion batteries.
• Sluggish sodium storage kinetics limit the rate performance of hard carbon anodes.
• Developing strategies to enhance sodium-ion diffusion and electronic conductivity is crucial.

Purpose of the Study:

• To improve the rate performance of coal-derived hard carbon anodes for sodium-ion batteries.
• To investigate the effects of nitrogen (N) and phosphorus (P) codoping on hard carbon structure and sodium storage.
• To elucidate the mechanisms behind enhanced sodium storage kinetics via electronic/ionic comodulation.

Main Methods:

• Synthesis of N/P codoped hard carbon from coal.
• Characterization of structural and electronic properties.
• Electrochemical testing including rate capability and cycling stability.
• Kinetic analysis and theoretical calculations.

Main Results:

• N/P codoping creates a hierarchical structure with expanded interlayer spacing, defects, and tailored porosity.
• Nitrogen doping enhances electronic conductivity and Na+ adsorption.
• Phosphorus doping increases interlayer spacing and promotes Na+ diffusion.
• Optimized anode shows high reversible capacity (240 mAh g-1 at 30 mA g-1) and excellent rate performance (126 mAh g-1 at 1500 mA g-1 over 250 cycles).
• A full cell demonstrates stable performance with a layered cathode material.

Conclusions:

• N/P codoping is an effective strategy for electronic/ionic comodulation in hard carbon.
• This approach significantly enhances sodium storage kinetics and high-rate performance.
• Codoped hard carbon shows great potential as an anode material for next-generation sodium-ion batteries.