高工作電壓鋰鎳錳氧正極材料之合成與其電化學行為的改善

Synthesis of High Voltage Cathode Material LiNi0.5Mn1.5O4 and Improvement of its Electrochemical Performance

江峻諺(Chun-Yen Chiang)

指導教授 ： 杜正恭

國立清華大學/工學院/材料科學工程學系/碩士(2008年)

摘要

尖晶石相鋰錳氧的延伸生化合物，鋰鎳錳氧正極材料擁有了高安全性與長時間循環壽命的優點。近幾年來，鋰鎳錳氧材料由於其具備了4。7V的高工作電壓，因而被廣泛的研究。
而鋰鎳錳氧電池經高溫充放電時，電容量損失的情形嚴重而降低其循環壽命。在本研究中，藉由添加3wt%奈米級的氧化鋁粉體於鋰鎳錳氧極片中，可以明顯地提升其在高溫環境下的循環壽命。在電化學的行為上，添加氧化鋁粉比未添加的極片好，結果顯示，在55oC下經過100次的充放電循環後，添加過氧化鋁粉的極片仍保有83%的電容量，反而未添加的極片只有66%的電容量。其之所以表現出較佳的電化學性能，從FE-EPMA與XPS的分析結果，可以知道最主要的原因，在於所添加的氧化鋁粉，會抑制高電阻值的氟化鋰沉積在鋰鎳錳氧的活物表面，因此減緩了電池內阻抗隨著高溫測試時上升的情形。
除此之外，為了提升鋰電池的效能，使其能夠達到在下個世代的油電混合車或電動車所需的高功率輸出。鋰鎳錳氧正極材料必須要具備有快速充放電的能力。在本研究中，藉由一新穎的粉體合成製程，可成功地生產出具有快速充放電能力的純相鋰鎳錳氧粉體。在較為低的600oC煆燒溫度下，所得之產物是具有奈米結構且結晶性良好的鋰鎳錳氧粉體。而此粉體展現出了相當優異的電化學性能，於慢速充放電之下，電容量為133mAh/g。更重要的是，其以10C的高速放電測試時，仍可得到122mAh/g的高電容量。

關鍵字

鋰電池 ； 鋰鎳錳氧 ； 電動車 ； 溶膠凝膠法

並列摘要

LiNi0.5Mn1.5O4 (LNMO), an extended compound of spinel LiMn2O4, possesses the advantages of safety and long cycle life. In recent years, LiNi0.5Mn1.5O4 has been extensively studied due to its high operation voltage around 4.7V (versus Li/Li+), which is higher that of the commonly used cathode material LiCoO2.
Bare LNMO suffered severe capacity fading during charge/discharge at elevated temperature. In this study, the cyclability of LNMO cells at 55oC can be significantly improved by adding 3 wt% nano-Al2O3 powders into LNMO electrodes. In comparing nano-Al2O3 contained with bare-LNMO cells, the former exhibite better electrochemical performance. After 100 cycles at 55oC, nano-Al2O3 contained LNMO cells preserve 83% of initial capacity whereas the capacity retention of bare LNMO cells is 66%. The main reason for better electrochemical performance of nano-Al2O3 contained LNMO cells is owing to the alleviation of increasing in cell impedance during 55oC cycling. It can be reasonably correlated to the suppression of formation of high resistive LiF on the surface of active masses, which is identified by FE-EPMA and XPS analysis.
Furthermore, to increase the power capability and to meet the requirement of new generation LIBs for EV/HEV, LiNi0.5Mn1.5O4 is expected to be capable of fast charge/discharge. In this study, high current rate capability and single phase LiNi0.5Mn1.5O4 powders were successfully produced via a novel synthesis procedure combining sol-gel route with combustion method. Through this approach, well-crystallized LiNi0.5Mn1.5O4 powders with nano-structure were obtained at a low temperature of 600oC. Nano-structured LiNi0.5Mn1.5O4 half-cells have exhibited superior electrochemical performances. At a slower discharge rate, a capacity of 133mAh/g could be delivered. Moreover, the nano-structured LiNi0.5Mn1.5O4 delivered a capacity of 122mAh/g at a discharge rate as high as 10C. Thus, a superior power capability was achieved.

並列關鍵字

Li ion battery ； LiNi0.5Mn1.5O4 ； sol-gel

參考文獻

75. J. C. Arrebola, A. Caballero, L. Hernán, and J. Morales, “Improving the Performance of Lithium-Ion Batteries by Using Spinel Nanoparticles”, J. Nanomater., 2008 (2008) Article ID 6593971

1. J.M. Tarascon and M. Armand, “Issue and challengs facing rechargeable lithium batteries”, Nature, 414 (2001) 359-367.

2. B. Scrosati, “Power Sources for Portable Electronics an Hybird Cars: Lithium Batteries and Fuel Cells”, Chem. Rec., 5 (2005) 286-297

3. J.B. Goodenough, “Cathode materials: A personal perspective”, J. Power Sources, 174 (2007) 996-1000.

4. Y. Gao, K. Myrtle, M. Zhang, J. N. Reimers and J. R. Dahn, “Valence band of LiNixMn2-xO4 and its effects an the voltage profiles of LiNixMn2-xO4/Li electrochemical cells“, Physical Review B, 54(23) (1996) 16670