Li1+xAlxTi2-x(PO4)3鋰離子固態電解質燒結程序最適化之研究

Optimization of Sintering Process on Li1+xAlxTi2-x(PO4)3 Solid Electrolytes for All-Solid-State Lithium-ion Batteries

嚴佩宜(Pei-Yi Yen)

指導教授 ： 劉偉仁

中原大學/工學院/化學工程研究所/碩士(2019年)

https://doi.org/10.6840/cycu201900421

摘要

鋰離子電池作為一種高效的儲能設備，被廣泛應用在手機，筆記型電腦，太陽能電站，甚至電動汽車等設備上，是現代社會能源鏈條上重要的一環。但目前鋰離子電池使用的電解質大部分為液態或者半液態的有機電解液，因此帶來了漏液、易燃易爆、不耐高溫等問題。使用固態電解質替換液態電解質製備全固態鋰離子電池有望克服以上的缺點，所以固態電解質是能源領域一個重要的研究方向。
本研究第一部份以具有NASICON結構之Li1.3Al0.3Ti1.7(PO4)3(LATP)為主題，實驗以透過簡單的溶劑熱法(水熱法)，配合異價離子摻雜，以Al3+部分取代Ti4+的位置合成出Al-doped LiTiOPO4前驅粉體，搭配TGA、EIS、SEM等分析找出LATP試片的最佳燒結程序，成功合成出Li1.3Al0.3Ti1.7(PO4)3固態電解質。
首先，以水熱法合成出之前驅粉體為具LiTiOPO4相的斜方晶結構(orthorhombic system)，從SEM元素分析可知Al元素分佈相當均勻，我們將此前驅粉體命名為Al-doped LiTiOPO4。接著探討了第一階段粉體之預燒結溫度以及第二階段LATP試片之燒結溫度，並以XRD與結構精算(Rietveld refinement)分析其結構，及討論其燒結後對孔隙率、微觀結構、導電性質等影響。
精算結果顯示成功合成出之Li1.3Al0.3Ti1.7(PO4)3晶體是具有R-3c(167)空間群的三方晶系(Trigonal system)結構。透過兩段燒結的探討，發現晶粒間良好的接觸與晶界間較低的第二相非晶含量，皆是獲得高鋰離子電導率的關鍵。實驗結果發現第一階段粉體之最佳預燒結溫度為900℃，透過結構精算後得知其Li1.3Al0.3Ti1.7(PO4)3相成分最高，為81%；第二階段LATP試片之最佳燒結溫度為1100℃，其晶粒電導率、晶界電導率及鋰離子總電導率分別為6.57*10-4、4.59*10-4、2.70*10-4 S cm-1，並有99.07%的最高緻密度，其活化能為0.17 eV。
本研究第二部分初步研究LATP應用於鋰離子電池，並成功組裝LATPS/NCM固態電池，在0.1C下充放電80圈後，放電電容量保留率為95.76%，說明LATPS/NCM固態電池有良好的循環穩定性，LATP為具有潛力、能應用於鋰離子電池之固態電解質材料。

關鍵字

鈉快離子導體 ； 磷酸鈦鋁鋰 ； 固態電解質 ； 離子電導率 ； 燒結程序 ； 鋰離子

並列摘要

Lithium-ion battery(LIB) plays an important role in the modern social energy chain. It is widely used in mobile phones, laptops, solar power plants, and even electric vehicles and other equipment. But these applications are mostly restricted by safety issues such as poor thermal stability, flammable reaction products, and leakage of electrolyte and internal short circuits for the use of liquid electrolytes in LIB. The use of solid electrolyte to replace liquid electrolyte preparation of all solid lithium-ion battery is expected to overcome the above shortcomings, which makes solid electrolyte an important research direction in the field of energy.
In the first part, our study focused on Li1.3Al0.3Ti1.7(PO4)3(LATP) with a NASICON structure. Al-doped LiTiOPO4 precursor powder was synthesized by a simple solvothermal method with heterovalent ion doping to partially replace Ti4+ by Al3+. According to the materials characterization, the optimal composition is Li1.3Al0.3Ti1.7(PO4)3.
In the first part, hydrothermal method was used to synthesize orthorhombic structure of LiTiOPO4 powder. The SEM elemental analysis shows that the distribution of Al element is fairly uniform. The second part discusses the different sintering processes involved in obtaining LATP which includes the pre-sintering temperature of the precursor powder and the sintering temperature of the LATP pellets. The structure was analyzed by XRD and Rietveld refinement, and the effects of sintering temperature on porosity, microstructure and electrical conductivity were discussed.
The Rietveld refinement results show that the synthesized Li1.3Al0.3Ti1.7(PO4)3 crystal is a trigonal structure with a R-3c(167) space group. Through the discussion of two-stage sintering, it is found that the good contact between the grains and the lower amorphous content of the second phase between the grain boundaries are the key in obtaining high lithium-ion conductivity. The experimental results show that the optimum pre-sintering temperature of the precursor powder is 900℃. Through the Rietveld refinement calculation, it can be seen that the precursor powder, Li1.3Al0.3Ti1.7(PO4)3 has the highest phase composition after sintering at 900℃. The optimal sintering temperature of LATP pellet is at 1100℃, which has the activation energy is 0.17 eV, and the highest density is 99.07%. Its grain conductivity, grain boundary conductivity and total lithium-ion conductivity are 6.57*10-4, 4.59*10-4, 2.70*10-4 S cm-1, respectively.
Lastly, LATP was applied to lithium-ion batteries, and LATPS/NCM solid-state batteries were successfully assembled. After charging and discharging at 0.1C for 80 cycles, the discharge capacity retention was 95.76%, indicating that the LATPS/NCM solid-state battery has good cyclic stability. Therefore, LATP is a potential candidate as a solid electrolyte for lithium-ion batteries.

並列關鍵字

NASICON ； LATP ； solid electrolyte ； ionic conductivity ； sintering process ； lithium-ion batteries

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