鋰離子電池在 90 年代首次被商用化後，持續被視為有效率的儲能系統之一。相較於傳統的鋰鈷氧層狀正極材料，富鋰正極材料 Li1.2Ni0.2Mn0.6O2 可以提供更高的電容量(~250 mAh/g)、更大的能量密度(~1000 mAh/g)。然而，距離商用化仍須克服該材料的問題如結構穩定性、充放電電壓平台衰退、高充放電速率下的衰退。藉由密度泛函理論計算，首先確立 Li1.2Ni0.2Mn0.6O2 原子級結構。為解決結構不穩定之問題，我們提出透過參雜過度金屬鎘於層狀材料當中，不但可以抑制材料體積變化且減緩楊¬-泰勒效應(Jahn-Teller Distortion)發生。透過能態密度(Density of States)分析發現，當鎘參雜在鎳金屬位置時，參雜後的層狀材料因為鎘無法隨著充放電改變價數，使數量較少的鎳離子更快地價數轉移從 +2到 +4，減緩了會在 +3 發生的楊¬-泰勒效應。我們後續比較鉀、鈣、鋁等非過度金屬微量參雜，比較晶格參數、體積變化、生成能、電位、能態密度後，我們發現鎘參雜於富鋰材料中仍是最佳的選擇。於提升富鋰電極效能上，此研究結果透過理論計算提供給實驗學者一個新的參雜想法與策略。

Li-ion batteries have been viewed as an efficient energy storage system since they firstly commercialized in the 1990s. Compared with convention lithium cobalt oxide, Li1.2Ni0.2Mn0.6O2 layered material can deliver higher specific capacity (~250 mAh/g) and high energy density (~1000 Wh/kg). Nevertheless, these materials still face some critical problems such as structural instability, voltage fading, and low rate performance. By the aid of DFT calculations, we demonstrated Li1.2Ni0.2Mn0.6O2 structure in atomic level. To solve the structural instability problem, in this study we have proposed doping of different metal atoms such as Cd, Ca, K and Al in different sites of Li1.2Ni0.2Mn0.6O2 and investigated their structural and electronic properties. The PDOS results show that the Ni ions in the pristine Li1.2Ni0.2Mn0.6O2 structure maintained the 3+ oxidation state for a longer time and resulted in the structural deformation during the long cycling process. Whereas, the Ni ions in the Cd, K and Ca-doped Li1.2Ni0.2Mn0.6O2 structure are in the 3+ oxidation state for a very short time compared to pristine. Our DFT results show that the doping of Cd ion in Ni site of Li1.2Ni0.2Mn0.6O2 is the most suitable one because it inhibits the structural change, lowers the formation energy, suppresses the Jahn-Teller compared with pristine and other dopant atoms. This theoretical study gives new insight about doping strategy, and will help in improving the electrochemical performance of Li-rich cathode materials

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