水熱法合成多孔鋰鈦氧負極材料於鋰離子電池之應用

Hydrothermal Synthesis of Porous Li4Ti5O12 as Anode Materials for Lithium Ion Batteries

徐偉豪(WEI-HAO HSU)

指導教授 ： 王朝弘

國立中正大學/工學院/化學工程學系/碩士(2016年)

摘要

鋰離子電池為一種極具發展潛力的電化學動力來源，因此，被廣泛地應用於電動車與能量存儲裝置等系統。近年來，由於鈦基材料具備高安全性與極佳循環穩定度，此兩項優勢已經讓它被深入研究而作為鋰離子電池之替代負極材料，其中，尤以Li4Ti5O12更為人所推崇。
Li4Ti5O12可以經由很多方式來合成，最常見的方式為固態合成法與溶膠凝膠法。本研究則以TBOT(tetrabutyl orthotitanate)作為起始劑，LiOHH2O作為鋰源經水熱法以及後續熱處理步驟合成Li4Ti5O12負極材料。由於Li4Ti5O12導電性能不佳，此因素限制其於鋰離子電池之應用，因此，藉由合成多孔Li4Ti5O12來彌補此一缺點。於製備流程中加入碳黑，經由TBOT水解後產物將之包覆，之後碳黑於熱處理過程中被移除而形成多孔結構。另外，使用碳球來取代碳黑作為模板則可形成中空Li4Ti5O12，此兩種Li4Ti5O12將進行電化學性能之比較。
經過電化學測試後，於充放電速率0.2C下，多孔與中空Li4Ti5O12的電容量分別為161.7與162.6mAh/g，兩者相差不大，隨著充放電速率逐漸提升，兩者的電容量開始出現區別，於20C下，多孔Li4Ti5O12的電容量為92.4mAh/g，而中空Li4Ti5O12只有75.6mAh/g，結果顯示前者之倍率性能較為優異，鋰離子於多孔Li4Ti5O12中的擴散速度較快。
本研究還有利用TiO2作為起始劑，於LiOH水溶液中進行水熱反應，接著經過熱處理而獲得另一多孔Li4Ti5O12，過程中並無添加任何模板，即可合成多孔結構。與TBOT作為起始劑之實驗相比，此製備流程更加簡單。經由TiO2合成之多孔Li4Ti5O12，於20C下，其電容量仍保有119.0mAh/g，相較於TBOT合成之多孔Li4Ti5O12，倍率性能更為提升。而於5C下，TiO2合成之多孔Li4Ti5O12的首圈可逆電容量為129.5mAh/g，首圈庫倫效率則為92.5%，經過300圈循環後，其電容量為126.0mAh/g，存留率高達97.3%，幾乎無衰退，表現出十分穩定的循環性能。
另外，根據電化學阻抗分析的結果，也發現多孔Li4Ti5O12之電荷轉移阻抗與鋰離子擴散阻抗較小，這都歸功於多孔結構能使Li4Ti5O12與電解液的接觸面積增加，同時還能形成導電迴路，進而加快電子與鋰離子的移動速度，因此，多孔Li4Ti5O12適合作為高動力鋰離子電池之負極材料，極具發展潛力。

關鍵字

鋰離子電池 ； 水熱法 ； 多孔鋰鈦氧

並列摘要

Lithium ion batteries are one of the promising electrochemical power sources to be widely used in electric vehicles and energy storage devices. In recent years, Ti-based materials have been intensively investigated as anodes for lithium ion batteries due to their high safey and excellent cycling stability, especially Li4Ti5O12.
Many methods can be used to fabricate Li4Ti5O12, such as solid state reaction and sol-gel. In this research, Li4Ti5O12 was synthesized from tetrabutyl orthotitanate and LiOH by using a simple hydrothermal method, followed by a calcination procedure. To prepare porous Li4Ti5O12 powder, acidized carbon black was introduced during synthesis and it was removed under high-temperature environment. Besides, in order to compare the electrochemical performance with different structure, hollow Li4Ti5O12 was also manufactured via the identical process by substituting carbon black for carbon sphere as template.
After assembling into the half cell, it was progressively charged–discharged in series stages with the charge–discharge rate from 0.2 to 20C. At a rate of 0.2C, the capacity of porous and hollow Li4Ti5O12 was identical, and it remained 161.7 and 162.6mAh/g repectively. Both capacitive difference began to appear with the charge-discharge rate gradually increasing. At the high rate of 20C, the capacity of porous Li4Ti5O12 was 92.4mAh/g, and it was reduced to 75.6mAh/g for hollow Li4Ti5O12. The former exhibited a remarkable rate capability due to its fast lithium ion diffusion.
Another porous Li4Ti5O12 was synthesized by a hydrothermal treatment of TiO2 powder in LiOH solution and a following calcination procedure without employing templates. The fabrication process was easier than the experiment with tetrabutyl orthotitanate as a starting agent. Its capacity still retained 119.0mAh/g at the high rate of 20 C and exhibited more excellent rate capability. The initial capacity of porous Li4Ti5O12 via the TiO2 synthesis was 129.5mAh/g at a rate of 5C and the first coulombic efficiency was 92.5%. In addition, the capacity still maintained 126.0mAh/g after 300 charge/discharge cycles, and its retention reached up to 97.3%. It exhibited very stable cycling performance.
Besides, according to the result of electrochemical impedance spectroscopy, porous Li4Ti5O12 showed small charge transfer resistance and fast solid state diffusion of lithium ion. The superior rate performance of porous Li4Ti5O12 was attributed to its large contact surface area with the electrolyte and the possibility of forming a conducting network in which pores allowed both lithium ion and electron to migrate rapidly. Therefore, porous Li4Ti5O12 was very suitable as a anode material for high power lithium ion batteries.

並列關鍵字

Lithium Ion Battery ； Hydrothermal ； Porous Li4Ti5O12

參考文獻

[5] P. Verma, P. Maire and P. Novak, “A review of the features and analyses of the solid electrolyte interphase in Li-ion batteries”, Electrochimica Acta, Vol. 55, pp. 6332-6341, (2010).

[7] K. Ariyoshi, R. Yamato and T. Ohzuku, “Zero-strain insertion mechanism of Li[Li1/3Ti5/3]O4 for advanced lithium-ion (shuttlecock) batteries”, Electrochimica Acta, Vol. 51, pp. 1125-1129, (2005).

[8] A. Mukhopadhyay and B. W. Sheldon, “Deformation and stress in electrode materials for Li-ion batteries”, Progress in Materials Science, Vol. 63, pp. 58-116, (2014).

[9] T.-F. Yi, L.-J. Jiang, J. Shu, C.-B. Yue, R.-S. Zhu and H.-B. Qiao, “Recent development and application of Li4Ti5O12 as anode material of lithium ion battery”, Journal of Physics and Chemistry of Solids, Vol. 71, pp. 1236-1242, (2010).

[10] Y.-B. He, M. Liu, Z.-D. Huang, B. Zhang, Y. Yu, B. Li, F. Kang and J.-K. Kim, “Effect of solid electrolyte interface (SEI) film on cyclic performance of Li4Ti5O12 anodes for Li ion batteries”, Journal of Power Sources, Vol. 239, pp. 269-276, (2013).