本實驗主要以PEG擬固態電解質作為主體並使用聚離子液體單體(VIm-Et-TFSI)組成與聚離子液體交聯劑(VIm-b-VIm-TFSI)試圖改善PEG擬固態電解質與鋰金屬的反應性以增加電池充放電長效循環穩定性。首先將高分子單體PEGMEMA(Mn=500)、塑化劑(PEGDME)、與鋰鹽(LiTFSI)進行混合，並加入合成之聚離子液體結構，將攪拌均勻的電解質前驅物(Precursor)直接於手套箱內滴至鋰金屬表面並加熱至55oC以進行原位聚合反應(In-situ polymerization)，形成與鋰金屬緊密接合之聚離子液體擬固態電解質(Poly(ionic liquid) Quasi-solid-state Electrolytes, PIL-QSEs)。由XRD與DSC分析可以發現各組成之電解質皆不具有結晶相的訊號，說明各電解質組成皆均勻分散且與鋰鹽擁有非常好的相容性；由DMA壓縮測試了解到PEG擬固態電解質薄膜本身具有良好的韌性與延展性，而當產生交聯高分子結構後會造成電解質薄膜變的脆硬；在TGA與LSV測試中可以發現聚離子液體的導入可以有效地增加電解質之熱穩定性與電化學穩定性；最後可以發現20%之聚離子液體導入可以使PEG擬固態電解質擁有最高的導離子度。在電池測試中，PEG擬固態電解質在效能測試上皆有不錯的表現，然而在室溫與60 oC下的長效測試穩定性上卻略有不足，經過實驗後發現僅使用PEG鏈段之擬固態電解質沒有辦法形成穩定且均勻之SEI層，這使得電池的庫倫效率在充放電的過程中不穩定而造成電容的衰退。在導入聚離子液體結構後明顯改善了庫倫效率不足等問題，這有可能是由於聚離子液體結構可減緩塑化劑與鋰金屬間反應所致。進一步導入的交聯高分子結構更使電池的充放電穩定性上升，其在室溫與60 oC以0.2C 充放電下可以維持初始電容值90%超過150圈。使用SEM觀察各組成電解質經過室溫0.2C充放電100圈的鋰金屬電極可以發現PEG擬固態電解質形成較為鬆散且較厚之SEI層，這使得其無法有效阻止鋰金屬與電解質間的反應性，造成電池庫倫效率不穩定。而在導入聚離子液體後可以發現SEI層變得較為緻密，而交聯結構能更進一步抑制鋰支晶(Lithium dendrites)的生成，產生較為均勻、平坦、緻密且厚度小的SEI層，使電池循環穩定性增加。

In order to manufacture high energy density batteries, lithium metal is considered to be the most suitable candidate to replace graphite anodes. However, uncontrolled growth of lithium dendrites during cycling has remained a potential risk of short circuit and explode for lithium metal batteries. The currently commercial liquid electrolytes can not effectively suppress the formation of lithium dendrites, leading to the shift of research focus to polymer electrolytes to improve the potential safety issues of lithium metal batteries. We report a quasi-solid-state polymer electrolytes comprising poly(ionic liquid-co-ethylene glycol), oligomer additives and lithium salts, which exhibited large operating temperature range and good cycling efficiency. These polymer electrolytes were formed in situ by coating the precursors directly onto the anode materials, followed by thermal polymerization. This approach not only combines the polymerization and membrane formation in a step, but also possibly facilitates the lithium transport by reducing the interface resistance between the electrolytes and electrodes. In this project, we also evinced the advantages of cationic and crosslinked polymer structure in PEG-based electrolytes. The experimental data showed that the polymer electrolyte with optimized weight percentages of imidazolium-containing crosslinking agent and poly(ethylene glycol) monomer exhibited ionic conductivity of 1.52*10-4 S/cm and electrochemical stability window of 5.4V at room temperature. Most importantly, the long-term cyclic performance is significantly improved by adding the imidazolium-based cationic crosslinker, and the discharge retained 90% initial capacity over 150 cycles both at 30 oC and 60 oC. After the cycling tests, the advantages of cationic and crosslinked polymer framework were evidenced by morphology observation of lithium metal anodes. As a consequence, we have successfully created a new type of polymer electrolytes representing a new design principle for quasi-solid-state electrolytes and offering opportunities for further commercialization.

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