本研究以熱解法製備源自生物質的硬碳負極應用於鈉離子電池為主軸，探討不同生物質前驅物(蘋果和甘蔗渣)、熱處理溫度對材料性質和電化學特性之關聯性。於750 oC ~ 1050 oC的熱處理溫度範圍內，顯示在950 oC下，由於碳材有適當的比表面積、含氧官能基以及微量的石墨帶，因此，表現出最佳化之電化學特性。源自生物質(蘋果和甘蔗渣)之硬碳電極在1 M NaClO4-EC/DEC電解液中測試分別可得249、234 mAh g -1之電容值(0.03 A g -1)，此外，首圈庫倫效率分別達56、52%。當電流密度提升至2 A g -1時，可分別得78、85 mAh g -1之電容值。 本研究第二部分將探討硬碳負極在不同電解液中之電化學特性。在高濃度下的電解液由於溶劑會與鈉離子作用配位，使得原先的自由離子(Free)轉變成具有作用力的離子(Solvating)，整體電解液可視為高交聯性高分子，能穩定電化學反應。在高濃度的NaFSI-EC/PC電解液中，於0.03、2 A g -1之電流密度下分別可得299、86 mAh g -1之電容值，此電性表現具有室溫應用價值之潛力，克服傳統刻板觀念之高濃度配方的高黏度不適合作為電解液之瓶頸。此外，高濃度電解液優良的電化學穩定性可提升硬碳電極之首圈庫倫效率(80%)。循環壽命方面，有別於低濃度NaFSI-EC/PC的低電容維持率(78%)，高濃度的NaFSI-EC/PC電解液於50圈充放電循環後能維持99%的電容維持率。;In this study, the hard carbon derived from biomass using the pyrolysis synthesis method was employed as anode for sodium-ion battery. The effect of different biomass precursors (apple and sugar cane bagasse) and the heat treatment temperature on the structure and electrochemical properties of hard carbon for sodium storage properties were discussed. In the heat treatment temperature range between 750 oC to 1050 oC, it is found that hard carbon obtained at 950 oC shows superior electrochemical performance due to the proper specific surface area, oxygen-containing functional groups and trace amounts of graphite. The sodiation/desodiation properties were tested in 1 M NaClO4-EC/DEC electrolyte and capacities of 249 and 234 mAh g -1 was obtained at a current density of 0.03 A g -1 for hard carbon derived from apple and sugar cane bagasse biomass, respectively. At a high current density of 2 A g -1, capacities of 78 and 85 mAh g -1 can be obtained, respectively. The biomass derived hard carbon offered the outstanding cyclic stability of ~ 92% after 200 cycles at 0.1 A g -1. This study also explores the electrochemical properties of commercial hard carbon in different electrolytes (NaFSI in EC/PC and NaPF6 in EC/PC) with different concentrations (1 M, 2 M and 3 M). In the case of high concentration electrolyte, the solvent will react with Na-ions, so that the free ion will solvating and the overall electrolyte can be regarded as a high cross-linked polymer that can stabilize the electrochemical reaction. In high concentration 3 M NaFSI in EC/PC electrolyte, a maximum capacity of 299 mAh g -1 was obtained at current density of 0.03 A g -1. A capacity of 86 mAh g -1 is achieved at a high current density of 2 A g -1. In addition, first cycle coulombic efficiency (80%) obtained using 3 M NaFSI in EC/PC is the maximum ever achieved for any kind of hard carbon. The exceptional cycle stability of (~ 99%) is achieved for 3 M as compared to 1 M NaFSI in EC/PC (~ 78%) after 50 cycles at 0.1 A g -1. This study shows the high concentration electrolytes can be an ideal choice of electrolytes for high-performance sodium-ion batteries.
