共摻雜鐵、鈷、鎂來改善磷酸鋰錳作為鋰離子電池陰極材料的電化學表現

本研究嘗試在水熱法合成的磷酸鋰錳中共摻雜鐵-鈷-鎂，以改變Li-O鍵結能和創造鋰缺陷，來使鋰離子傳導性更好。實驗結果為共摻雜鐵-鈷-鎂在高速率充放電有最好的表現，甚至比共摻雜鐵-鈷或鐵-鎂還要更好。XPS結果也顯示共摻雜鐵-鈷-鎂有最強的Mn-O和P-O鍵，因此Li-O鍵會相對變弱，鋰離子就能更快的嵌入脫出。至於循環壽命則是依據摻雜的鎂和鈷之比例而有不同的表現，共摻雜鐵-鈷有最高的電容量，而隨著鎂的量越多，電容量逐漸下降，因此共摻雜鐵-鎂的電容量為最低。不過穩定性的趨勢卻是相反的，隨著鎂的量越多，電容量的衰退幅度越小。綜合來說，共摻雜鐵-鈷-鎂在高速率充放電的協同作用比摻雜鐵-鈷和鐵-鎂還要明顯，而在0.5 C的循環壽命表現則與鈷/鎂的比例有關。

關鍵字

鋰離子電池；磷酸鋰錳；共摻雜

並列摘要

In this study, we synthesize lithium manganese phosphate co-doped Fe-Co-Mg by solvothermal method. Co-doping Fe-Co-Mg can change the binding energy and create Li vacancy, so lithium ions insert and extract faster. We also discuss co-doping effect of three conditions: Fe-Co, Fe-Mg and Fe-Co-Mg. The result shows that the cases of co-doping Fe-Co-Mg have better rate capability than the case of co-doping Fe-Co and Fe-Mg. According to XPS results, the cases of co-doping Fe-Co-Mg have stronger Mn-O bonds and P-O bonds than that of co-doping Fe-Co and Fe-Mg. It causes Li-O bonds become weaker, so lithium ions can insert/extract faster. As for cycle life, the case of co-doping Fe-Co has the highest initial capacity. The initial capacity decreases depending on the amount of Mg. The decrease of the initial capacity depends on the amount of Mg. Doping more Mg and less Co decrease the initial capacity. However, the trend of stability of cycle life is opposite. The cycle life decays more slowly with increasing amount of Mg doped. To sum up, co-doping three elements shows more significant synergistic effect about rate capability than co-doping two elements does.