Structural regulation and sodium storage mechanism of high-performance non-graphitic carbon derived from semi coke

Non-graphitic carbon (NGC) is considered as one of the most promising anodes for sodium-ion batteries (SIBs) because of its low cost and abundant reserves. Nevertheless, there is significant debate regarding the contribution mechanism of sloping and plateau capacity. Herein, a series of NGC with adjustable defect concentration, carbon phases and pore structure are synthesized with semi-coke as precursor to explore the sodium storage mechanism and an “adsorption-insertion-filling” model is proposed based on the in-depth analysis of microstructure and electrochemical behaviors. The very attraction about this work is that the entire discharge curve is divided into three regions for analysis, and the corresponding cause for each region is traced. To be specific, the defects and disordered structure contribute to the surface-controlled absorption behavior in the sloping region >0.1 V, the pseudo-graphitic structure shows diffusion-controlled insertion behavior in the plateau region between 0.1 and 0.05 V, and the closed pores formed by curved graphite-like structure provide plateau capacity (<0.05 V) through the filling of quasi-metallic sodium. This study provides theoretical education for the optimization of NGC anode structure and a novel approach for the excessive value-added utilization of semi coke.