鋰離子電池具有電容量高、能量密度高、重量輕等優點，經常被組裝成電池模組，做為電動車的動力來源使用，以提升電動車的續航力。鋰離子電池正極材料的選用，主導了電池的工作電壓與電容值的表現，而層狀結構的LiCoO2與LiNixCoyMn1-x-yO2，由於具有相當優異的理論電容量，已經普遍被商業化使用，然而，在過度充放電的情況下，層狀正極材料會有結構變化與過渡金屬原子溶出的現象產生，導致電池電容量的衰退，限制了電池能夠穩定運作的電壓、電容量範圍。
電極與電解液間介面扮演著鋰離子進出正極材料重要門戶的角色，不僅是正極材料中鋰含量變化最大的區塊，同時也是過渡金屬原子溶出現象所發生的區域，故介面間所發生的反應同時也深深地影響著鋰離子電池的表現。
為探討目前鋰離子電池正極材料與電解液介面間所發生的反應，本研究利用第一原理理論計算的方式，建立出穩定的LiNi1/3Co1/3Mn1/3O2層狀正極表面模型，與EC、DMC、ADM等不同電解液系統模型，將兩者結合成電極與電解液介面模型，透過第一原理分子動力學模擬的方式，觀察介面模型在333K溫度條件下所發生的介面反應，並分析當介面模型持溫平衡後，模型中電解液分子、過渡金屬原子的電荷變化與結構變化，試圖找出有助於改善層狀正極材料結構穩定性的方法。
電荷分析的結果顯示，當鋰離子電池充電時，LiNi1/3Co1/3Mn1/3O2正極內部(塊材模型)主要發生電荷改變的元素為鎳跟鈷，錳原子基本維持在帶有高電荷數的狀態不受影響；反觀在LiNi1/3Co1/3Mn1/3O2材料最表面的區域，鎳、鈷原子所帶的電荷數基本與塊材模型中的狀態相同，錳原子則明顯出現了電荷數下降的情形，若與實驗上的結論相連結，價數下降的現象代表著錳原子溶入電解液的機率相對提高，對於層狀材料的結構穩定性有著不好的影響。本研究發現當LiNi1/3Co1/3Mn1/3O2正極表面有電解液分子的出現與吸附，最表層錳原子所帶的電荷數會有回升至接近塊材模型狀態之趨勢，電解液分子有穩定模型表面結構的現象。
若從過渡金屬與鄰近氧原子所形成的MO6八面體(M=Ni, Co, Mn)結構中，鎳氧、鈷氧、錳氧鍵長改變的角度進行分析，表面模型內層的MO6八面體基本維持與塊材模型狀態相同的鍵結長度，但模型最表層的鎳氧平均鍵長卻有明顯縮短的現象，有機會導致模型表面因為出現局部結構扭曲的現象，而在交界區域有應力的產生；電解液系統的出現與吸附，則有緩解表面模型內外層MO6鍵長差異的效果，有機會助於層狀材料表面結構穩定性之維持。

LiNi1/3Co1/3Mn1/3O2 (NMC) is a popular cathode material with high theoretical capacity and working voltage in Li-ion batteries. However, after extensive cycling, Li-ion batteries usually suffer from capacity fading issue, which might be related to irreversible reactions such as phase transformation and dissolution of transition metal ions in the electrode/electrolyte interface region of cathode materials.
In the present study, first-principles molecular dynamics simulation was applied to investigate the electrode/electrolyte interface between the (012) and (104) surface of NMC cathode and different electrolyte systems, e.g. EC, DMC and ADM with 1M LiPF6. NMC bulk and surface models with different Li concentration were also introduced to mimic the charging process of cathode materials. All the models were kept at 333K for several picoseconds until they reached equilibrium state.
With the results of charge analysis, the presence and adsorption of electrolyte molecules on NMC surface could stabilize the charge number of surface Mn ions and prevent the leaching of transition metal ions. By calculating the average bond length between the center metal ion and neighboring O atoms in MO6 octahedron (M=Ni, Co, Mn) in each model, the results revealed that the electrolytes could decrease the M-O bond length difference between outermost layers and the middle region of NMC surface model. Such circumstance might have the effect on stabilizing the surface structure of NMC. The results showed that the existence of electrolytes in the electrode/electrolyte interface could help to stabilize NMC surface.

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