Bio-derived hard carbon nanosheets with high rate sodium-ion storage characteristics

Biomass is a sustainable precursor of hard carbons destined for use in sodium-ion batteries. This study explores the synthesis of hard carbon nanosheets (HCNS) from oxidized cork and impact of synthesis temperature on the hard carbon characteristics. An increase in the carbonization temperature from 1000 to 1500 degrees C generally leads to lower BET specific surface areas (similar to 55 to 20 m(2) g(-1)) and d(002) interlayer spacing (similar to 4.0 to 3.7 angstrom). The effect of synthesis temperature is reflected in the initial coulombic efficiency (iCE) which increases from 72% at 1000 degrees C to 88% at 1500 degrees C, as a result of the decrease in surface area, and structural defects in the hard carbon as verified using Raman scattering. The impact of cycling temperature (similar to 25, 30 and 55 degrees C) on the rate capability and long-term cycling is investigated using high precision coulometry cycler. For a galvanostatic test at 20 mA g(-1) and similar to 25 degrees C, a reversible capacity of 276 mAh g(-1) is observed with an iCE of similar to 88%. Increasing cycling temperature enhances the rate performance, but slightly lowers the iCE (similar to 86% at 30 degrees C and similar to 81% at 55 degrees C). At 20 mA g(-1), the reversible capacities obtained at 30 degrees C and 55 degrees C are on average similar to 260 and similar to 270 mAh g(-1), respectively. For constant-current constant-voltage (CCCV) tests conducted at 30 degrees C, reversible capacities ranging from 252 to 268, 247-252, and 237-242 mAh g(-1) can be obtained at 10, 100, and 1000 mA g(-1), respectively. The respective capacities obtained at 55 degrees C are about 272-290, 260-279, and 234-265 mAh g(-1) at 10, 100 and 1000 mA g(-1). The applicability of the HCNS electrodes is eventually evaluated in full-cells with Prussian white cathodes, for which a discharge capacity of 152 mAh g(-1) is obtained with an iCE of similar to 90%.

Automated summary

This study investigates the synthesis of hard carbon nanosheets from oxidized cork and the impact of synthesis temperature on the characteristics of hard carbon. It is found that higher carbonization temperature leads to lower specific surface areas and interlayer spacing, as well as higher initial coulombic efficiency. The rate performance of hard carbon can be improved by increasing the cycling temperature, but it slightly decreases the initial coulombic efficiency. The applicability of hard carbon nanosheets in full-cells is also evaluated in this study.