以原位聚合法製備鋰金屬電池膠態電解質及其在零下溫度的應用

Abstract

商用鋰離子電池經常使用有機溶劑液態電解質，但其存在電解質洩漏、高可燃性及低溫性能不佳等問題。以聚合物為基材吸附電解液的膠態聚合物電解質(GPEs)能夠捕捉有機溶劑，防止洩漏和快速蒸發，被認為是提高安全性的有效策略。此外，GPEs能夠在寬溫度範圍內保持恆定的流變行為，提高低溫適應性。 1,3-二氧戊環(1, 3-dioxolane, DOL)是一種經常使用於液態電解質的溶劑，能夠在電池內部進行陽離子開環聚合反應進行原位成膠，將液態DOL轉化為聚合物的polyDOL電解質。透過此操作可以在電池內部原位生成GPE，從而使電解質與電極之間的良好界面接觸。並且由於製造工藝簡單且反應條件溫和，此方法適合大規模生產。 在本研究中，我們引入碳酸乙烯酯(Ethylene carbonate, EC)和氟代碳酸乙烯酯(Fluoroethylene carbonate, FEC)作為DOL的共溶劑來製備原位聚合GPE，並系統化研究鋰鹽組成和濃度對凝膠行為和GPE導電性的影響。我們進一步添加了三羥甲基丙烷三縮水甘油醚(Trimethylolpropane triglycidyl ether, TPTE)作為交聯劑，以抑制聚DOL的結晶性並提高凝膠的長期完整性。透過調整DOL前驅液的組成，調整熱、機械和電化學性質，使GPE具有高導電性、長期穩定性及與電極良好的界面接觸，並具備低溫適應性。最具潛力的GPE是由DOL/EC/FEC和TPTE組成的前驅液製備而成，在20°C下顯示出5.08 x 10-4 S cm-1的導電性，在-20°C下顯示出1.77 x 10-4 S cm-1的導電性。在電流密度為1.0 mA cm-2和充放電時間各2小時的條件下，鋰對稱電池在恆電流循環中表現出超過400小時的穩定循環，表明本研究中開發的GPE在鋰金屬電池的低溫運行中具有很高的潛力。

Commercial lithium-ion batteries employ organic solvent-based liquid electrolytes are the most common setup as far. However, the risk of electrolyte leakage, high flammability as well as unsatisfactory cell performance at sub-zero temperatures are issues to be resolved. Gel polymer electrolytes (GPEs) comprising a polymeric matrix and absorbed liquid electrolytes are considered to be an effective strategy to enhance the safety, as the GPEs could trap organic solvent to prevent leakage and rapid vaporization. Furthermore, the low-temperature applicability would be improved as GPEs could retain constant rheology behaviors through a wide range of temperature. 1,3-Dioxolane (DOL) is a commonly used solvent for liquid electrolytes, and which can undergo in-situ gelation within the battery via cationic ring opening polymerization to convent the liquid DOL into a polymeric poly(DOL) electrolyte. Through this operation, a GPE could be obtained in-situ to allow good interfacial contact between the electrolyte and the electrodes. With the advantages of simple fabrication process and mild reaction conditions, this method is suitable for large-scale manufacturing. In this study, we introduced ethylene carbonate (EC) and fluoroethylene carbonate (FEC) as co-solvents of DOL to prepare in-situ GPEs. The effect of the compositions and concentrations of lithium salts on the gelation behavior and the conductivity of the GPE are systematically investigated. We further added trimethylolpropane triglycidyl ether (TPTE) as crosslinking reagent to suppress the crystallinity of polyDOL and improve the long term integrity of the gel. By systematically tuning the composition of the precursor DOL liquid electrolytes, the thermal, mechanical, and electrochemical properties are tailored to enable the GPE exhibits high conductivity, long term stability and good interfacial contact with the electrodes, along with sub-zero temperature applicability. The most promising GPE is prepared from the precursor LE consisting of DOL/EC/FEC with TPTE , and which shows a viscoelastic gel behavior to enable a conductivity of 5.08 x 10-4 (S cm-1) at 20°C and 1.77 x 10-4 (S cm-1) at -20°C. The lithium symmetric cell upon galvanostatic cycling at a current density of 1.0 mA cm-2 and 2h/2h charging/discharging time demonstrates stable cycling over 400 hours, suggesting a high potential of the GPE developed in this work for lithium metal batteries with capability of low temperature operation.