探討NCM陰極材料在鋰離子電池之反應機制
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2020
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使用LiNixCoyMnzO2（NCM）陰極材料的鋰離子電池具有高電容量，也同時有很好的循環壽命，但是它們在（脫）鋰化時會受嚴重的結構變化，這不利地影響了循環穩定性，所以我們透過臨場X-ray繞射（XRD）、臨場X-ray 快速吸收光譜（q-hXAS）觀察其不穩定的原因，並將結果與鈕扣電池恆電流循環的數據相關聯，最後為了更加了解鋰離子嵌入嵌出的機制，使用先恆電流再恆電位的充放電模式，探討在特定電位下之反應過程和與熱力學或動力學之關係。
XRD顯示當x（Li）為0.65時，由於層間距的塌陷，單位晶格體積急速收縮；q-hXAS顯示過渡金屬-氧層的收縮主要為鎳的氧化，錳主要為維持結構的穩定性；然後使用了奈米探針實驗，看出每個粒子反應是不均勻的，且在高電位時，鎳會與電解液發生反應；最後ICP-MS顯示在充放電過後，會有部分的過渡金屬離子溶於電解液，綜合上述結論，表明NCM陰極材料在充放電循環不可避免地伴隨著電荷轉移引起的晶格塌陷和過渡金屬的溶解。
恆電流再恆電位的充放電模式中，XRD顯示鋰離子在嵌入嵌出過程主要是電位控制，所以為熱力學反應，而結構的崩壞主要是動力學反應；q-hXAS顯示NCM811再充至4.25V有三種不同的斜率，NCM523只有兩種，綜合上述結論，表明NCM811反應機制和NCM523是不同的。
關鍵詞：鋰離子電池、鎳鈷錳三元材料、臨場X-ray繞射、臨場快速X-ray吸收、奈米探針、奈米繞射
LiNixCoyMnzO2 (NCM) cathode materials have high capacity and also have long cycle life, but they are subjected to severe structural changes during (de)lithiation, which adversely affects cycle stability. To investigate the stability of NCM, we use in-situ X-ray diffraction (XRD) and in-situ X-ray quick- absorption spectroscopy (q-hXAS), and correlate the results with data from galvanostatic cycling in coin cell. Finally, to understand the mechanism of delithiation and lithiation, we use the constant current and constant potential for in-situ XRD and in-situ q-hXAS, and investigate the relationship with thermodynamics or kinetics. XRD result shows that when x(Li)<0.65, the unit cell volume shrinks rapidly due to the collapse of the interlayer spacing; q-hXAS result shows that the shrinkage of the transition metal-oxygen layer mainly originates from nickel oxidation. Finally, we use the X-ray nanoprobe, we can know each particle is non-uniform after cycling. Overall, the conclusions indicate that the NCM cathode material is inevitably accompanied by charge-transfer-induced lattice collapse during the charge and discharge process. In the constant currentand constant potential charging and discharging mode, XRD shows that the delithiation is mainly controlled by potential, so it is a thermodynamic reaction, and the collapse of the structure is mainly a kinetic reaction; q-hXAS shows that NCM811 charge to 4.25V has three different slopes, and NCM523 has only two. Overall, the conclusions indicate the reaction mechanism of NCM811 and NCM523 are different. Keywords: Lithium ion battery, NCM, In-situ XRD, In-situ q-XAS, Nanoprobe, Nanodiffraction
LiNixCoyMnzO2 (NCM) cathode materials have high capacity and also have long cycle life, but they are subjected to severe structural changes during (de)lithiation, which adversely affects cycle stability. To investigate the stability of NCM, we use in-situ X-ray diffraction (XRD) and in-situ X-ray quick- absorption spectroscopy (q-hXAS), and correlate the results with data from galvanostatic cycling in coin cell. Finally, to understand the mechanism of delithiation and lithiation, we use the constant current and constant potential for in-situ XRD and in-situ q-hXAS, and investigate the relationship with thermodynamics or kinetics. XRD result shows that when x(Li)<0.65, the unit cell volume shrinks rapidly due to the collapse of the interlayer spacing; q-hXAS result shows that the shrinkage of the transition metal-oxygen layer mainly originates from nickel oxidation. Finally, we use the X-ray nanoprobe, we can know each particle is non-uniform after cycling. Overall, the conclusions indicate that the NCM cathode material is inevitably accompanied by charge-transfer-induced lattice collapse during the charge and discharge process. In the constant currentand constant potential charging and discharging mode, XRD shows that the delithiation is mainly controlled by potential, so it is a thermodynamic reaction, and the collapse of the structure is mainly a kinetic reaction; q-hXAS shows that NCM811 charge to 4.25V has three different slopes, and NCM523 has only two. Overall, the conclusions indicate the reaction mechanism of NCM811 and NCM523 are different. Keywords: Lithium ion battery, NCM, In-situ XRD, In-situ q-XAS, Nanoprobe, Nanodiffraction
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鋰離子電池, 鎳鈷錳三元材料, 臨場X-ray繞射, 臨場快速X-ray吸收, 奈米探針, 奈米繞射, Lithium ion battery, NCM, In-situ XRD, In-situ q-XAS, Nanoprobe, Nanodiffraction