Vine Shoots-Derived Hard Carbons as Anodes for Sodium-Ion Batteries: Role of Annealing Temperature in Regulating Their Structure and Morphology

Sodium-ion batteries (SIBs) are considered one of the most promising large-scale and low-cost energy storage systems due to the abundance and low price of sodium. Herein, hard carbons from a sustainable biomass feedstock (vine shoots) were synthesized via a simple two-step carbonization process at different highest temperatures to be used as anodes in SIBs. The hard carbon produced at 1200 & DEG;C delivered the highest reversible capacity (270 mAh g(-1) at 0.03 A g(-1), with an acceptable initial coulombic efficiency of 71 %) since a suitable balance between the pseudographitic domains growth and the retention of microporosity, defects, and functional groups was achieved. A prominent cycling stability with a capacity retention of 97 % over 315 cycles was also attained. Comprehensive characterization unraveled a three-stage sodium storage mechanism based on adsorption, intercalation, and filling of pores. A remarkable specific capacity underestimation of up to 38 % was also found when a two-electrode half-cell configuration was employed to measure the rate performance. To avoid this systematic error caused by the counter/reference electrode polarization, we strongly recommend the use of a three-electrode setup or a full-cell configuration to correctly evaluate the anode response at moderate and high current rates.