| 摘要: | 現今普遍的儲能裝置為鋰離子電池具備高功率、電流穩定、壽命長等優點，但現今鋰離子電池的液態電解質具有可燃特性安全性上存在疑慮，因此全固態鋰離子電池是很好的選擇，由於其使用固態電解質具有良好的耐熱性，在安全程度上比現今鋰離子電池還要來的安全，且同樣具有高功率以及電流穩定等特性。本實驗使用固態反應法來合成 Li7La3Zr2-xYxO12(LLZYO)粉體，並製備LLZYO固態電解質進行燒結與電性之研究，其中使用純ZrO2、3YSZ(含3mol%Y2O3)、8YSZ(含8mol%Y2O3) 三種粉體作為LLZYO中鋯與釔成分的來源。首先DSC/TGA分析結果顯示三種粉體，會產生吸熱峰值在80~120度、290~340度、400~500度，其原因可能與LiOH·H2O或La (OH)3脫水反應有關，630~900度有吸熱峰其原因應為此溫度下開始形成LLZYO固溶的石榴子石相，並且發現摻雜釔(Y)元素的LLZO可以有效降低粉體的合成溫度。透過XRD分析得到煅燒900度持溫12小時的3Y-LLZO粉體可以最快生成單一立方相結構，其平均晶粒大小為37.1±10.1 (nm)。接著將3Y-LLZO粉體進行壓錠燒結，結果顯示第一從XRD的分析得知經過燒結900、950、1000度持溫1、12、24小時後，LLZYO樣品的結晶相主要為立方相的鈣鈦礦結構，但會含有少量得正方相鈣鈦礦結構以及微量的La2Zr2O7二次相，而產生La2Zr2O7相原因與燒結錠內部的鋰元素在燒結過程中流失所導致，第二從密度分析顯示，LLZYO燒結錠的燒結密度隨著溫度和持溫時間的提高而降低，且通過SEM分析發現燒結錠存在許多孔洞導致晶粒之間無法緻密而密度下降。因此為了提高燒結錠密度以及穩定LLZO相，在粉體中添加1 wt%、2 wt%、4wt%氧化鋁(Al2O3)做為助燒劑，結果顯示添加4wt%助燒劑的燒結錠密度為最高，密度最高可以達到4.93 g/cm3，但是從XRD分析可以發現添加2wt%助燒劑的助燒錠可以有效穩定LLZO相，而添加4wt%助燒劑會產生少量的La2Zr2O7相。最後透過EIS電性分析得到添加2wt% 助燒劑的LLZYO燒結錠經過1000度持溫24小時的燒結後，可以得到最佳的導電度9.8×10-6 S/cm，並且在不同溫度下測量導電率，實驗結果為2wt%助燒劑燒結1000度持溫24小時在各種溫度下導電率皆為最佳，在95度時可以得到最高的導電率為1.1×10-4 S/cm。最後利用阿瑞尼士公式來計算25度~95度的活化能，數據顯示添加4wt%燒結1000度持溫24小時燒結錠具有最低的活化能0.314 eV
Currently, lithium-ion batteries are widely used as energy storage devices due to their high power, stable current, and long lifespan. However, the flammable nature of the liquid electrolyte in lithium-ion batteries raises safety concerns. As a result, solid-state lithium-ion batteries are considered a better choice. These batteries use a solid electrolyte, which provides excellent thermal stability and improved safety compared to current lithium-ion batteries, while still offering high power and stable current characteristics. The purpose of this experiment is to use the solid state reaction method to synthesize Li7La3Zr(2-x)YxO12 (LLZYO) powder, and fabricate the LLZYO solid electrolytes to understand the sintering behaviors and electrical properties. Three types of powders, namely pure ZrO2, 3YSZ (containing 3 mol% Y2O3), and 8YSZ (containing 8 mol% Y2O3), were used as sources of zirconium (Zr) and yttrium (Y) components in LLZYO. DSC/TGA analysis revealed exothermic peaks at 80~120°C, 290~340°C and 400~500°C for the three powders. These peaks corresponded to the dehydration of LiOH·H2O or La(OH)3. The endothermic peak at 630 ° C ~ 900 ° C revealed the formation of the garnet phase of LLZYO solid solution. It was found that LLZO doped with yttrium (Y) could effectively reduce the synthesis temperature of the powder. The XRD analysis showed that the 3Y-LLZO powder sintered at 900°C for 12 hours achieved the fastest formation of a single cubic phase structure, with an average grain size of 37.1±10.1 nm. Subsequently, the 3Y-LLZO powder was pressed and sintered. XRD analysis revealed that after sintering at 900°C 950°C, and 1000°C for 1, 12, and 24 hours, the crystalline phase of the LLZYO samples was primarily the cubic perovskite structure. However, a small amount of tetragonal perovskite structure and a trace amount of La2Zr2O7 secondary phase were also present. The formation of the La2Zr2O7 phase was attributed to the loss of lithium (Li) during the sintering process. Density analysis indicated that the sintered density of LLZYO pellets decreased with increasing temperature and holding time. SEM analysis revealed the presence of numerous pores in the sintered pellets, which resulted in reduced density and inadequate densification between grains. In order to increase the density of sintered ingots and stabilize LLZYO, 1 wt%, 2 wt%, and 4 wt% aluminum oxide (Al2O3) were added to the powder as sintering aids. The results showed that the addition of 4 wt% sintering aid achieved the highest sintered pellet density, reaching up to 4.93 g/cm3. However, The XRD analysis indicated that adding 2 wt% sintering aid effectively stabilized the LLZO phase, while the addition of 4 wt% sintering aid resulted in a small amount of La2Zr2O7 phase. Finally, electrical impedance spectroscopy (EIS) analysis was conducted to evaluate the electrical properties. The LLZYO sintered pellet with 2 wt% sintering aid, sintered at 1000°C for 24 hours, exhibited the optimal conductivity of 9.8×10-6 S/cm. The conductivity measurements at various temperatures showed that the LLZYO sintered pellet with 2 wt% sintering aid, sintered at 1000°C for 24 hours, consistently demonstrated the highest conductivity. At 95°C, the highest measured conductivity reached 1.1×10-4 S/cm. Using the Arrhenius equation, the activation energy for the temperature range of 25°C to 95°C can be calculated. The data shows that the addition of 4wt% sintering aid and sintering the pellet at 1000°C for 24 hours results in the lowest activation energy 0.314 eV. |
