| 摘要: | 鋰離子電池在安全性一直是受矚目的重要課題之一。由於高耗能3C隨身產品以及電動汽機車(HEV、EV)的快速發展，鋰離子電池能量密度和電容量的需求也不斷提升。為了應用在高耗能的電池上，容易發生活性材料碎裂造成循環壽命不佳，或是電解液在高溫下會分解以及容易燃燒，因此解決鋰離子電池的循環壽命不足以及安全性問題更為迫切。先前研究指出，鋰離子電池電解液會因為在充放電循環下，與活性物質發生反應，而造成電解液中鋰鹽分解，釋放大量的熱。在過度充電和過熱條件下時，正極材料容易產生氧氣，使電池內部壓力提高，而活性氧氣也會與電解液反應，產生熱量使溫度提升，可能造成電池的危害，伴隨著電解液的燃燒甚至是爆炸等安全問題。
在電解液中含有添加劑有助於改善安全性問題，故本研究為了提升鋰離子電池的性能，利用兩種新型電解液添加劑mPhMI和p-PhMI來延長電池的循環壽命以及增加安全性。mPhMI為由含磷的雙馬來醯亞胺(BMI)化合物，Bis(4-meleimido phenoxy)phenyl phosphine oxide (PhMI)，與自由基捕捉劑1,3-二甲基巴比妥酸(1,3-DBTA)進行共聚合反應；而p-PhMI為PhMI單體獨自進行聚合反應的高分子。在共聚物mPhMI此添加劑具有PhMI分子含有磷原子，可減少氧分子釋放和抑制或延緩電解液分解情況發生，而1,3-DBTA有額外的功能可捕捉自由基阻止燃燒反應。這兩種添加劑的優勢在電極上形成穩定的SEI層，來改善電池長圈數電性與增加安全性。以添加劑修飾NMC材料實驗中的循環壽命測試，添加mPhMI和p-PhMI的電池在第80圈充放電後電容量分別保持在96.04%與90.59%。從變速率充放電圖中，使用mPhMI添加劑具有最佳的可逆電容量，其高達96.29%。更進一步由XPS光譜分析添加劑對SEI層影響，證實添加劑有降低電解液鋰鹽的分解。以及利用SEM觀測極片表面的型態，在100圈充放電後SEI仍然維持孔隙並沒有太大變化。
;Safety is the primary issues in all aspects of lithium ion battery applications. This issue is becoming even more important with the increasing adaption for advanced electronic devices and in electric car applications where higher power and energy density are required. Longer cycle life, stable high temperature performance and safety in these advances lithium ion batteries become highly critical. It is known that electrolyte will react with the active material under the charge/discharge cycle, causing the lithium salt in the electrolyte to decompose which releases heat. In over-charging and over-heating conditions, the cathode material releases oxygen which increases internal pressure and further raised the cell temperature. This which eventually causes the breakdown (termination) of the battery, or even worse causes the cell to burst and explode, accompanying with burning of the released electrolytes.
In this study, we will exam the boosting of performance on lithium battery by two new types of electrolyte additives; mPhMI and p-PhMI in terms of lengthening cycle life stability and improving safety. While mPhMI is prepared by copolymerization of 1,3-dimethyl-barbituric acid (1,3-DBTA) with Bis(4-meleimido phenoxy)phenyl phosphine oxide (PhMI), p-PhMI is the homo-polymerization of PhMI monomers alone. In the copolymer mPhMI, phosphorus atoms in PhMI unit can reduce the release of oxygen and inhibit the electrolyte decomposition, and 1,3-DBTA is found to serve additional function to capture free radicals which hinders the combustion reaction. These additives have the advantage of forming a stable SEI layer over coating the electrode to improve the lithium battery long cycle performance and improve safety. The cycle life test shows that with the addition of mPhMI and p-PhMI in the electrode, the capacity retention are 86.93% and 90.59%, respectively after 80 cycles. The XPS spectrum provides the direct evidence to the reduction of lithium salt decomposition on the SEI layer in presence of the electrolyte additives. SEM study also suggested negligible change of the pore structure on surface of the SEI layer and the development of crack on cathode particles, after 100 repeated cycles in presence of these electrolyte additives. |
