鋰金屬因其高理論電容量（3,860 mAh/g）和低氧化還原電位（-3.04 V vs. SHE）而被公認為是可充電電池負極材料的“聖杯”，在過去的幾十年中已被廣泛的重新審視優化，以用於鋰金屬電池中的實際應用。然而，電池中部份鋰金屬會因為充放電過程中的不可逆反應導致其失去活性而形成非活性鋰，使電池壽命縮短，效率下降，影響其電化學表現。對於新型的無陽極鋰金屬電池，因沒有負極或是鋰金屬可提供過量的鋰源，所以針對鋰的重複使用變得更加重要。因此想要提升無陽極鋰金屬電池的電化學性能，當務之急就是要減少非活性鋰的生成。
本研究探討以I2作為無陽極電池的添加劑，透過離子態I3-/ I-的自身氧化還原反應來使非活性鋰活化，藉此達到電池回春與延長可循環壽命的目的。充電時，I3-會在電流收集器被還原成I-，驅使非活性鋰氧化轉變為鋰離子。而放電時，伴隨著鋰離子回到脫鋰態的正極，還原性添加劑I-也會變氧化成I3-，透過這些往復式的反應，能夠持續回收因循環所形成的非活性鋰。研究發現在1M LiPF6 EC/DEC中添加一定濃度的碘(0.1wt%)之後，NMC532║Cu的無陽極鋰金屬電池在第十圈循環充放電後的電容保持率可以提升至29.28%，相比商用電解液提升了將近10%。透過UV-vis、SEM及XPS分析，證實碘確實與非活性鋰反應。這項工作為提高無陽極鋰金屬電池的性能和延長電池壽命，提供了一種新的解決方案。
第二部分工作是建立了一個滴定量化平台，從多種滴定方式嘗試之後，選擇使用酸鹼指示劑中，變色範圍在中性，且顏色變化明顯的溴瑞香草酚藍來分析鋰銅電池中非活性鋰的死鋰部分，透過分離非活性鋰中固態電解質介質的鋰離子及死鋰的鋰金屬可以比較出不同電解液下這兩者的影響。在眾多電解液中，以1M LiPF6 EC/DEC (v/v : 5/5)添加5 wt% FEC有著最佳的庫倫效率，透過SEM也可看出其表面較為平整，並且從所有量化的數據可歸納出庫倫效率對於SEI與死鋰之間的比值有著一定程度的關係。此平台的建立，可不必透過貴重儀器的分析，利用較為簡單迅速的模式來篩選未來的新型電解液，成為其中一種分析工具。

Li metal, recognized as the “holy grail” of anode materials for rechargeable batteries due to its high theoretical capacities (3,860 mAh/g) and low redox potential (-3.04 V vs. SHE), has been extensively revisited over the past decades for the practical application in lithium-metal batteries (LMBs). However, the severe dendrite and inactive-Li formation upon charging/discharging cause potential safety hazards, poor coulombic efficiency, and cycle performance. For new cell configurations like anode-free lithium metal batteries, the conservation of lithium becomes more critical since there is no negative or lithium metal electrode that can provide excess lithium sources. Therefore, the priority is to reduce inactive lithium formation to enhance the electrochemical performance of an anode-free lithium metal battery.
Herein, we have developed a method to rejuvenate the inactive lithium using I2 as a redox shuttle additive. I3- ion will be reduced to I- at the current collector, converting inactive lithium back into lithium ions. In the discharge state, the reductive additive I- will oxidize to I3-, and replenish the lithium ions to the delithiated cathode. These reactions can continue to recover the inactive lithium formed in subsequent cycles. By adding the 0.1wt% I2 in 1M LiPF6 EC/DEC, the capacity retention of NMC532║Cu cell could enhance to 29.28%, 10% higher than commercial one. Analyzing by UV-vis, SEM and XPS, we proved that the iodide react with the inactive lithium. This work shows a new solution to improve the performances of the anode-free lithium metal batteries and prolong the cell lifespan.
In the second half of the thesis, we demonstrate a novel titration method to quantify the inactive Li within the LMBs. From trying the different titration technique, We have chosen the acid-base indicator, Bromothymol blue, which had the color change in neutral to separate the contribution of Li+ in SEI and the isolated Li in different liquid electrolytes through the developed quantification method. 1M LiPF6 EC/DEC (v/v : 5/5) with 5wt% FEC has the highest coulombic efficiency among all the electrolytes and observed the smooth morphology from the SEM measurement. From all the quantitative results, we could infer that the coulombic efficiency is closely related to the ratio between SEI and dead lithium. Due to the establishment of this platform, we didn’t use costly instruments(GC-MS, NMR), but just developed the simple and efficient tool to facilitate the screening of new electrolyte development in the future.

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