Insight to defects regulation on sugarcane waste-derived hard carbon anode for sodium-ion batteries

Abstract

By controlling the interlayer spacing and the porosity through pyrolysis and microwave activation, sugarcane-derived hard carbon materials have been prepared to deepen the understanding of Na + storage mechanism in sodium-ion batteries. • High performance hard carbons are successfully synthesized from sugarcane. • Reversible Na-storage capacity of 323.6 mAh g −1 is obtained. • A capacity retention up to 96.7 % after 500 cycles at 50 mA g −1 is achieved. • Pyrolysis promotes graphitization, increasing plateau capacity. • Microwave activation provides enhanced porosity with larger sloping capacity. A great deal of attention has been paid on developing plant-derived hard carbon (HC) materials as anodes for sodium-ion batteries (SIBs). So far, the regulation of HC has been handicapped by the well-known ambiguity of Na + storage mechanism, which fails to differentiate the Na + adsorption and Na + insertion, and their relationship with the size of d -interlayer spacing and structural porosity. Herein, bagasse-derived HC materials have been synthesized through a combination of pyrolysis treatment and microwave activation. The combined protocol has enabled to synergistically control the d -interlayer spacing and porosity. Specifically, the microwave activation has created slit pores into HC and these pores allow for an enhanced Na + adsorption with an increased sloping capacity, establishing a strong correlation between the porosity and sloping capacity. Meanwhile, the pyrolysis treatment promotes the graphitization and it contributes to an intensified Na + insertion with an increased plateau capacity, proving that the plateau capacity is largely contributed by the Na + insertion between interlayers. Therefore, the structural regulation of bagasse-derived HC has provided a proof on positively explaining the Na + storage with HC materials. The structural changes in the pore size distribution, specific surface area, d -interlayer spacing, and the electrochemical properties have been comprehensively characterized, all supporting our understanding of Na + storage mechanism. As a result, the HC sample with an optimized d -interlayer spacing and porosity has delivered an improved reversible capacity of 323.6 mAh g −1 at 50 mA g −1 . This work provides an understanding of Na + storage mechanism and insights on enhancing the sloping/plateau capacity by rationally regulating the graphitization and porosity of HC materials for advanced SIBs.