Investigation of hazelnut shells driven hard carbons as anode for sodium-ion batteries produced by hydrothermal carbonization method.

To be used as Na-ion battery anodes, hard carbon electrodes are synthesized from biomass, explicitly hazelnut shell (HS): via hydrothermal carbonization (HTC) followed by further pyrolysis at different temperatures (500, 750, 1000 °C). Then, the resulting hazelnut shell-based hard carbons are investigated using various methods including Fourier-transform infrared spectroscopy, scanning electron microscope, X-ray diffraction, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The effects of binders (PVdF, Na-alginate, CMC, and PAA) on electrochemical performance are determined. The obtained composite electrodes with different binders are tested in sodium half-cell configurations. A strong correlation is recognized between carbonization temperature and electrochemical performances and structural characteristics. The better cycling performance is accomplished with the electrode carbonized at 1000 °C with Na-alginate binder. After 100 cycles, specific capacity of 232 mAh × g-1 at 0.1C current density is achieved. This work represents an economical and feasible process to convert hazelnut shells into hard carbon.