本實驗第一部分，使用旋轉塗佈法製備固態電解質，此方法的優點為控制其薄膜的厚度、增加Li+ 的擴散通道，使Li+ 更加地容易傳送。固態電解質是由PEO、LiTFSI、Ga-doped LLZO混合而成的，而我們嘗試尋找旋轉塗佈法的最佳參數: 轉速1000 rpm、時間60秒、每滴溶劑150 μL、層數15層。而隨著固態電解質的濃度增加，可以有效地抑制電壓的抖動，故電解質的最佳比例則是PEO: LiTFSI : LLZO = 1:1:2。 我們沿用第一部分的最佳參數，第二部分則是比較五種LLZO製備固態電解質應用於鋰離子電池，而與其它種類的LLZO相比，Li6.25Ga0.25La3Zr2O12有最好的電化學性質，其0.1C下電容值約有120 mAh/g，庫倫效率約有97%，且發現粒徑大小會部分影響電化學性質，因為在固態電解質Li+ 傾向於在 LLZO 相中傳遞，所以我們降低固態電解質中的粒徑大小，便能夠使Li+ 更加容易地穿透，進而造成電化學性質提高。我們選擇填充物Al2O3取代LLZO，但卻得到很差的電化學性質，這邊推測為高分子主鏈運動不易，導致導電度不佳，故結過顯示填充物無法取代LLZO，固態電解質是必要的存在。 實驗第三部分，我們加入離子液體在固態電解質和鋰金屬之間，藉此降低其界面阻抗，並選擇三種不同摻雜的LLZO比較其電化學性質，而Li6.25Ga0.25La3Zr2O12加入離子液體1M LiTFSI/PMPTFSI有最好的電化學性質，其0.1C下電容值約有148 mAh/g，庫倫效率約有97%。以0.5C下作200圈循環壽命測試，維持率高達96% (137.48/143.21 mAh/g, 200th/1st )。 ;A single-phase Li7La3Zr2O12 (LLZO) solid electrolyte is synthesized using a solid-state reaction method. The influences of doping elements (Ga, Ta, and Mg) on the properties of LLZO are investigated. In addition, a hybrid electrolyte, composed of Ga-doped (or Ta-doped) LLZO, LiTFSI, and poly(ethylene oxide) was prepared, using the spin coating method. The LLZO/LiTFSI/PEO ratio of slurry and number of layers were changed to compare their electrochemical properties. As compared to LLZO pellet electrolyte, the hybrid electrolyte shows a higher ionic conductivity and a better charge-discharge performance in Li/LiFePO4 cells. We compare different kinds of LLZO and find out that Li6.25Ga0.25La3Zr2O12 has the best electrochemical properties. The charge is about 120 mAh/g and coulombic efficiency is also 97%. It was found that the particle size will affect the electrochemical performance. The Li+ ion tends to pass through the LLZO phase in the solid electrolyte, by reducing the particle size Li+ ion can penetrate more easily. The huge interface impedance still possesses a great challenge toward a better performance. We add the ionic liquid between the solid electrolyte and lithium metal to decrease the interface impedance. Li6.25Ga0.25La3Zr2O12-1M LiTFSI/PMPTFSI demonstrates good charge and discharge performance.The charge reaches up to 148 mAh/g and coulombic efficiency is also 97 %. The cycle retention at 0.5C is about 96% during the 200 cycles.
