- 學位論文
鋰離子電池陰極材料熱穩定性探討
Thermal stability of LiCoO2 and LiNi0.8Co0.2O2 cathode for lithium ion battery
摘要
本論文以探討鋰電池陰極材料熱安全性與崩解機制為主，主要內容是將複合金屬氧化物塗佈於鈷酸鋰及鎳鈷酸鋰陰極材料表面，以期能比較各種改質物在過充電壓下的電池性能、熱穩定性及交流阻抗變化。研究方法是利用La3Al5O12（LAG），Y3Al5O12（YAG）、Yttria Stabilized Zirconia （YSZ）和MgAl2O4（MAO）等四種複合金屬氧化物的最佳條件，塗佈於商用鈷酸鋰及鎳鈷酸鋰兩種陰極材料表面上，並與工研院提供之MgO塗佈改質之鎳鈷酸鋰分析比較。電池性能測試顯示，鈷酸鋰部份以LAG及MAO改質最佳，循環壽命為385次及223次；鎳鈷酸鋰部份以LAG及最佳，循環壽命152次，工研院的MgO則僅有37次。微分掃描熱卡分析儀測試顯示，鈷酸鋰以LAG及MAO改質較佳，鎳鈷酸鋰的LAG熱穩定性明顯優於工研院之MgO。交流阻抗分析顯示，金屬氧化物塗佈層可抑制晶格相轉變，但也可能會造成鋰離子釋出陰極材料電荷轉移阻力，使初始電容量較低，電池循環壽命減少。在338 K高溫下的電池性能顯示，LAG塗佈層沒有保護作用，電容量迅速衰退。在1.0 C-rate與4.4 V過充電壓的電池性能顯示，MAO塗佈於鈷酸鋰仍能有效防止電容量衰退，提高安全性。
並列摘要
LiCoO2 is the most widely used commercial cathode material for LIBs. However, it suffers from severe limitations in cell capacity and safety due to overcharge problems, which occur when the cut-off charge potential exceeds 4.3 volts and metallic lithium can be electrodeposited from the LiCoO2 layer structure. The formation and presence of metallic lithium may create a fire and explosion hazard during extreme use. LiNixCo1-xO2, with its higher capacity, also has safety concerns, although to a lesser extent. In this work, we plan to investigate the cell safety and decomposition mechanism of LiCoO2 and LiNixCo1-xO2 cathode materials, in order to improve related cell performance, by using various coating materials, and to correlate improved performance with cell safety. Our tasks include: (1) studying the thermal runaway mechanism and analyzing the safety of the cathode materials of interest under various charge/discharge conditions or different intercalation/deintercalation conditions; (2) the thermal analysis of the above layer-structure cathode materials when surface treated with mixed metal oxides：LAG coatings under high temperatures, high charge potential or high charge/discharge rate; (3) evaluating the effect of using different mixed metal oxides or coating materials on cell safety.