Binder-Free Lignite-Derived Carbon/NiFe2O4 Fiber Structures as a Potential Anode Material for Na-ion Batteries

Rational structural design is crucial for achieving superior sodium storage performance in anode materials for Na-ion batteries. Although cost-effective coal-based carbon materials are highly attractive, their diverse structures often lead to poor performance during the Na/Na+ process. In this study, lignite-based activated carbon/NiFe2O4 nanofiber composites were synthesized using a simple low-temperature co-precipitation method at 100 degrees C. ZnCl2 and KOH were selected as activating agents for fabricating activated carbons from raw lignite sources. By employing different structural models, the estimated crystallite size of the lignite-based activated carbon ranges from 41 to 47 nm, while the range for NiFe2O4 nanofiber incorporation is between 95 and 143 nm. The Raman spectrum of the samples confirms sharp D, G, and shallow 2D bands of activated carbon located at similar to 1340, 1580, and 2700 cm(-1), respectively. The presence of sulfur and silicon residues in the activated carbon structure hinders sodium ion transport. The reduction of silicon content and the elimination of sulfur, combined with the incorporation of NiFe2O4 fibers and the creation of additional active zones, enhances the electrochemical performance by providing more Na-storage sites. The results indicate that the lignite-based activated carbon/NiFe2O4 nanofiber composites exhibit improved rate performance compared to individual lignite-derived activated carbons.