| 摘要: | 為滿足高耗能3C隨身器材及電動汽機車(HEV、EV)的快速發展，鋰離子電池的能量密度和電容量也不斷的提升。因此解決鋰離子電池的循環壽命的不足、高溫下的性能及安全性問題益發急迫。鋰離子電池電解液，會因為在循環過程中，與活性材料發生反應，電解液中的鋰鹽會在高溫環境下受熱而分解，造成鋰離子電池電容損失，若此情形未得到控制，則會持續產生氣體(CO2, H2, CO 等)，使內部壓力升高，更嚴重的是產生放熱反應使內部溫度上升，造成燃燒或爆炸等安全問題。故本研究旨在研發一新型電解質添加劑，以1,3-二甲基巴比妥酸(1,3-DBTA)與N,N′-(1,3-亞苯基)二馬來醯亞胺(HVA)和N-苯基馬來醯亞胺(PMI)進行共聚反應而得。此添加劑是具有網狀結構、抗氧化及抗熱等多項功能的新型添加劑(HPKS)，可以抑制或延緩電解質的分解情形，以及可在電極上形成穩定的SEI層，來改善鋰離子電池的電性表現及安全性。我們將此電解液添加劑對Li(Ni1/3Mn1/3Co1/3)O2/Li半電池(正極)和Li/MCMB半電池(負極)進行充放電測試，並利用液態核磁共振分析儀(NMR)分析添加劑在高溫下對電解液的影響以及使用電子掃描顯微鏡(SEM)和X-射線光電子光譜(XPS)分析電極表面的型態及組成和電化學主抗頻譜(EIS)觀察其內電組的變化。
另外，也比較了兩款結構不同的添加劑HPKS以及BPMI的效應。HPKS可以生成結構較緻密的人工SEI層，BPMI則生成較蓬鬆的人工SEI層。實驗結果顯示，在室溫環境下，經過80圈充放電後，使用VC為添加劑(UBK)、HPKS添加劑以及BPMI添加劑的電容保持率分別為88.2%、94.5%和96.5%。在高溫(60oC)環境下，經過30圈充放電後，它們的電容保持率分別為93.0%、97.4%和95.1%。
;This study disclosed a novel approach to improve lithium battery life cycle which also eliminated thermal run-away. The formation of artificial solid electrolyte interface (SEI) coating (achieved by several effective approaches) was shown to improve lithium battery cyclic performance at elevated temperature, high rate charge/discharge performance, and mostly avoided thermal run-away. These artificial solid electrolyte modifications with different degree of pore densities are found to exhibit different effects on lithium-ion cell performances using EC: DMC: EMC+VC+ LiPF6-based electrolyte. The study shows the pre-formed solid electrolyte interface on both anode (MCMB) and cathode (NMC=1:1:1), changed the SEI compositions with improved electrochemical stability, that consumes less carbonates and hindered salt decomposition, generates much less HF. The interface composition and structure after pre-formation and after cycling in coin cell is investigated via scanning electron microscope (SEM), electrochemistry impedance spectroscopy (EIS) and cyclic voltammetry (CV) test using both Li(Ni1/3Mn1/3Co1/3)O2/Li half-cell and Li/graphite half-cell. The chemical stability under elevated temperature is characterized by nuclear magnetic resonance (NMR).
We found that this additive formed more stable solid electrolyte interface (SEI) on electrodes during charge and discharge operation, and has prevented electrolyte and lithium salts from decomposition under high temperature operation conditions. Two types of Artificial SEI modifications bearing denser and harder SEI modifications (HPKS) and softer and more elastic SEI modifications (BPMI) are compared. After 80th cycling at room temperature, the capacity retention is found to be 88.2% with VC (vinylene carbonate), 94.5% with HPKS Artificial SEI, and about 96.5% with BPMI Artificial SEI. After 30th cycling at 60oC, the capacity retention is found to be 93.0% with VC Artificial SEI, 97.4% with HPKS Artificial SEI, and about 95.1% with BPMI Artificial SEI. |
