本實驗利用Sol-gel法對Li(Ni1/3Co1/3Mn1/3)O2晶粒進行表面改質,希望藉由表面改質來改善Li(Ni1/3Co1/3Mn1/3)O2的循環穩定性。對Li(Ni1/3Co1/3Mn1/3)O2包覆一層ZnO薄膜,避免電解液與正極材料直接接觸反應,並且產生一較穩定的固體電解質界面(Solid Electrolyte Interphase, SEI),可以防止電解液腐蝕正極材料。Sol-gel法擁有合成尺寸細小且均勻、純度高且均勻等優點。因此我們利用Sol-gel法合成ZnO,且均勻包覆住正極材料,改善Li(Ni1/3Co1/3Mn1/3)O2的電化學特性。利用X光繞射分析(XRD)鑑定其結構、場發射電子掃描顯微鏡(FE-SEM)與穿透式電子顯微鏡(TEM)分析粉末顆粒大小及型貌,並利用充放電儀、循環伏安法(CV)、交流阻抗分析(EIS)分析其Li+離子擴散係數。 用XRD分析,出現了ZnO的繞射面(1 0 0)與(0 0 2),而其繞射峰顯示包覆ZnO並不會改變Li(Ni1/3Co1/3Mn1/3)O2晶格結構。SEM則顯示了當包覆的ZnO濃度上升時,Li(Ni1/3Co1/3Mn1/3)O2的表面粗糙度下降;而雷射粒徑分析則顯示了有兩個粒徑分布,分布範圍分別為0.2~2.7μm與4.3~36.5μm,此與SEM觀察到的結果相符。在TEM圖中可以觀察到一層薄膜包覆在Li(Ni1/3Co1/3Mn1/3)O2晶粒外圍,經由EDS元素分析後可以發現此層薄膜應為ZnO薄膜。連續充放電在0.1C~5C的速率下,包覆0.5wt% ZnO的電容量均較其他高,在1C充放電50圈的循環穩定性測試中,亦是包覆0.5wt% ZnO的效能亦最佳,經50圈充放電後其電容量仍保有89%。利用EIS、CV與GITT法計算其Li+離子擴散係數,比較之後可得知Li+離子擴散係數會因鋰離子崁入數量而有所改變,亦會因不同的模型而有所不同。
In this study, ZnO is used to modify the surface of the Li(Ni1/3Co1/3Mn1/3)O2 by sol-gel method and improve the capacity of cycle stability. The Li(Ni1/3Co1/3Mn1/3)O2 powder is coated with ZnO films, to avoid direct contact reaction between the electrode and electrolyte. It also product a stable solid electrolyte interphase (SEI) layer which can helps to prevent corrosion by the electrolyte. The advantages of sol-gel method are small particle size, high purity and uniformity, etc. The electrochemical performance of Li(Ni1/3Co1/3Mn1/3)O2 can be improved by ZnO coating. The structure, morphology and electrochemical properties of Li(Ni1/3Co1/3Mn1/3)O2 were characterized by XRD, FE-SEM and charge-discharge analysis system and the Li+-ion diffusion coefficient was measured by EIS, CV and GITT method. The XRD patterns show the structure of Li(Ni1/3Co1/3Mn1/3)O2 didn’t change with ZnO coating and it also shows two peaks at (110) and (002) for ZnO. The SEM images show surface roughness if Li(Ni1/3Co1/3Mn1/3)O2 decreased with ZnO coating amount increased. The particle size analyzer shows that the particle size have two distribution range, one was 0.2~2.7 μm and the other one was 4.3~36.5 μm. The TEM images show the Li(Ni1/3Co1/3Mn1/3)O2 particle was coated with a film and the EDX analysis confirmed that the film was ZnO. The charge-discharge curves show that the coating with 0.5wt% ZnO had highest capacity in the charge-discharge rate of 0.1C~5.0C. The cycle stable also shows the sample coating with 0.5wt% ZnO was the best, the capacity preserve 89% after 50cycle. The Li+-ion diffusion coefficient was calculated by EIS, CV and GITT methods, shows the Li+-ion diffusion coefficient was strongly depend on different model and the concentration of Li+-ion inserted the Li(Ni1/3Co1/3Mn1/3)O2 structure.