硫銀鍺礦Li6PS5Cl無機固態電解質應用於鋰離子固態電池之合成與電性研究

鋰離子電池目前被廣泛運用於能源儲存設備上，如筆記型電腦、手機，甚至是這幾年受到極大關注的電動汽車產業。傳統的液態鋰離子電池存在安全問題，例如液態電解液是易燃易爆的，不能承受高溫，因此開發具有高離子傳導性和高電化學窗口的固態電解質是現今重要的研究方向。本研究以硫銀鍺礦Li6PS5Cl(LPSCl)無機硫化物固態電解質為主題，透過簡單的機械球磨後高溫燒結的方法合成出高離導率純相的固態電解質，利用XRD圖譜分析找到最佳的球磨時間，再搭配SEM、EDS、EIS等分析找出最佳的燒結溫度，並且得到最適合的合成途徑，這樣合成出來的Li6PS5Cl無機固態電解質的室溫離導率為1.06x10-3 S/cm，經過退火處理可以提高至3.12x10-3 S/cm。從SEM和元素分析可以得知P、S、Cl等元素皆很均勻的分布於樣品顆粒表面，這說明我們球磨的過程是可以讓每個元素達到均勻混和的。在不同溫度下持溫並做EIS交流阻抗分析可以得到阿瑞尼士圖，利用圖中的斜線斜率計算出Li6PS5Cl固態電解質的活化能為0.306 eV。通過組裝鋰鋰對稱電池進行充放電測試確認固態電解質的Li+傳導能力，分別經過固定的電流密度0.1、0.2和0.3 mA/cm2各10圈，再藉由EIS交流阻抗測量其電解質和電解質與鋰金屬之間的介面阻抗，觀察到有良好的Li+傳導能力，於是以定電流密度0.1 mA/cm2進行50個循環的測試，在長時間的循環測試下仍然有良好的表現，說明Li6PS5Cl固態電解質為良好的Li+導體。接下來為了提高能量密度，在Li6PS5Cl固態電解質加入高分子鐵氟龍，就可以將電解質的部分作成厚度較薄且具有可撓性的薄膜，而且鐵氟龍可以填補粉體固態電解質壓成錠後的孔洞，微量添加可以提升整體離導率，即可變成可撓且有一定離導率的固態電解質薄膜。為了瞭解此薄膜的機械強度，我們做了應力與應變的拉伸測試，計算出其彈性係數，也可以看出樣品是脆性材料還是延展性材料，其中Li6PS5Cl：PTFE重量比為90：10的樣品表現出最好的延展性，我們也組成了鋰鋰對稱電池去探討對鋰金屬接觸的穩定性。由於Li6PS5Cl硫化物固態電解質其空氣穩定性差，且與鋰金屬接觸時會產生副反應，於是我們使用研缽研磨的方式將Li6.4La3Zr1.4Ta0.6O12氧化物固態電解質導入硫化物固態電解質中，不僅可以填補硫化物電解質間的孔隙，還可以提升空氣穩定性以及電性，由H2S感測器的數據可以發現微量加入氧化物電解質可以提升其空氣穩定性，組成鋰鋰對稱電池並做較長循環時間的測試，當添加適量的氧化物固態電解質至硫化物固態電解質中時可以抑制鋰枝晶的成長。

關鍵字

硫化物固態電解質；硫銀鍺礦；離導率；複合固態電解質

並列摘要

Lithium-ion batteries are now widely used in energy storage devices such as notebooks, cell phones, and even in the electric vehicle industry, which has received significant attention in recent years. Traditional liquid lithium-ion batteries have safety problems, such as liquid electrolytes are flammable and explosive and cannot afford high temperatures, so the development of solid-state electrolytes with high ionic conductivity and high electrochemical windows is an important research direction today. We focus on argyrodites-Li6PS5Cl(LPSCl) inorganic sulfide solid electrolytes in this study. The high ionic conductivity pure phase LPSCl were synthesized by a simple mechanical ball milling followed by high temperature sintering method, and the optimum ball milling time was found by XRD analysis, the optimum sintering temperature was found by SEM, EDS and EIS analysis, then we can obtain the most suitable synthesis way. The ionic conductivity of the solid electrolytes synthesized by this method is "1.06×" 〖"10" 〗^"-3" " S/cm" at room temperature, through annealing treatment can increase it up to "3.12×" 〖"10" 〗^"-3" " S/cm" . From the SEM and EDS element analysis, we can see that P, S, and Cl element are uniformly distributed on the surface of the sample particles, which indicates that ball milling process can achieve uniform mixing of each element. We can obtain Arrhenius plot by doing EIS test at different temperature, calculate the slope of the line and we can get the activation energy of Li6PS5Cl solid electrolyte was 0.306 eV. The Li+ conductivity of the solid electrolyte was confirmed by the stripping and platting process by a lithium symmetric battery. The stripping and platting test at step-increasing current density of 0.1, 0.2 and 0.3 mA/cm2 every 10 cycles, and calculate the resistance of solid electrolyte and the interface between solid electrolyte and lithium metal by EIS fitting. Then we fixed current density at 0.1 mA/cm2 for 50 cycles stripping and platting test, the good performance under long cycling test indicates that Li6PS5Cl solid electrolyte is a good Li+ conductor. Next, in order to increase the energy density, polymeric Teflon was added in the Li6PS5Cl solid electrolyte to make a thin and flexible electrolyte film. Teflon can fill the holes in the solid electrolyte pellet, and the addition of small amount can improve the ionic conductivity. To understand the mechanical strength of this solid electrolyte film, we did a stress and strain test to calculate the elasticity coefficient, the sample with a mass ratio of 90(LPSCl)：10(PTFE) showed the best flexibility. We also assembled a lithium-lithium symmetric coin cell to investigate the stability of the contact with lithium metal. Because of the poor air stability of Li6PS5Cl sulfide solid electrolyte and the contact with lithium metal will produce side reactions, we introduce Li6.4La3Zr1.4Ta0.6O12 oxide solid electrolyte into the sulfide solid electrolyte. Not only can fill the pores between the sulfide electrolyte particles, but also can improve the air stability and electrical properties. The lithium-lithium symmetric coin cell was assembled and tested for a longer cycle time, and the growth of lithium dendrites was inhibited when an appropriate amount of oxide solid electrolyte was added to the sulfide solid electrolyte.

並列關鍵字

Li6PS5Cl ； Li6.4La3Zr1.4Ta0.6O12 ； sulfide solid electrolyte ； Argyrodites ； ionic conductivity ； composite solid electrolyte

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