本文主要是研究以乙二醇為基底之新型深共熔(Deep eutectic solvent, DES)電解液之電化學特性，並將其應用於鈉離子電池中。本研究首次提出以便宜且低黏度的乙二醇(Ethylene glycol, EG)作為氫鍵予體，搭配鈉鹽及 [C2mim][BF4]、醋酸膽鹼(ChOAc)，製備出高導電度、製程簡單且價格低廉之新型深共熔電解液。此新型深共熔電解液之電位視窗最大可達4.2 V；在26 ℃之下的離子導電度範圍落在2.3 mS/cm至11.3 mS/cm區間；在25 ℃之下的黏度範圍則落在16 cp至77 cp區間。 與傳統鈉離子電池所使用之有機電解液1 M NaClO4溶於EC-DEC(1:1 v/v) 相比，新型深共熔電解液具有較佳的熱穩定性(~100 ℃熱分解)及更寬廣的應用溫度範圍。且由燃燒測試可知ChOAc及[C2mim][BF4] 均為效果良好之阻燃劑。此外，進一步將此三元電解液系統之應用於鈉離子電池中，以Na0.44MnO2為正極材料、以NaTi2(PO4)3為負極材料，測試不同電解液之電池性能表現及循環穩定性，由實驗結果可知在100 mA/g的電流密度下經過100圈充放電循環後，新型深共熔電解液系統之電容維持率最高可達100 %，幾乎沒有任何電容量衰退; 與之相比，傳統有機電解液系統1 M NaClO4溶於EC-DEC(1:1 v/v) 之電容維持率為94 %，低於其它DES電解液系統。 基於以上實驗結果，可知新型深共熔溶劑可做為一新穎之鈉離子電池電解液，且比起傳統有機電解液系統(1 M NaClO4溶於EC-DEC(1:1 v/v)) 可提高其安全性能，是一項具有發展潛力之電解液選項。 ;In this research, we study the electrochemical properties of new Deep eutectic solvent (DES) from the view of their possible application as non-aqueous electrolytes in sodium-ion batteries. The new DES electrolytes are formulated by mixing ethylene glycol, sodium salts and additives (Choline acetate, ChOAc and 1-Ethyl-3-methylimidazolium tetrafluoroborate, [C2mim][BF4]) at room temperature. The potential window of different electrolytes is studied by linear sweep voltammetry (LSV) and cyclic voltammetry (CV) measurements. The new DES electrolytes containing ChOAc and [C2mim][BF4] are found to be electrochemically stable up to 4.1 V and 4.2 V (potential window). The ionic conductivity and viscosity of the new DES electrolytes are found exhibit ranging from 2.3 mS/cm to 11.3 mS/cm at 26 ℃and 16 cp to 77 cp at 25 ℃, respectively. Compared to conventional organic electrolyte (1 M NaClO4 in EC-DEC (1:1 v/v)), the new DES electrolytes show better thermal stability (~100 ℃) and non-flammability. In addition, different electrolytes used in Na-ion battery system (with Na0.44MnO2 and NaTi2(PO4)3 as a positive and negative electrode, respectively) are tested at room temperature. It was found that the new DES electrolytes show better capacity retention than traditional organic electrolyte (1 M NaClO4 in EC-DEC (1:1 v/v)) after 100 charge-discharge cycles. Based on its excellent electrochemical properties and cycling performances, the ethylene glycol based new DES can be considered as promising electrolytes for high-safety applications in sodium-ion battery.
