固態電解質之電化學穩定性提升應用於全固態鋰電池之研究

Enhancement of Solid Electrolytes on Electrochemical Stability for All-Solid-State Lithium Batteries

李承峰(CHENG-FENG LI)

指導教授 ： 劉偉仁

中原大學/工學院/化學工程學系/碩士(2022年)

https://doi.org/10.6840/cycu202201208

摘要

本研究第一部份以具有NASICON結構之Li1.3Al0.3Ti1.7(PO4)3(LATP)為主題，實驗以透過簡單的固相法，搭配XRD、EIS、SEM、阿基米德法等分析找出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，其中燒結條件為1000℃ 的LATP試片擁有最高的離子電導率0.27 mS/cm。
由於LATP與鋰金屬之間的界面阻抗很大，因此本研究第二部份透過ZnO原子層沉積(Atomic layer deposition, ALD)對LATP試片進行表面改質，首先透過XRD、SEM、EDS、XPS、TEM來觀察ZnO是否有成功的沉積在LATP-1000℃試片上，接著將樣品組裝成全固態鋰對稱電極電池在0.01 mA/cm2電流密度下進行測試， 其中Li//LATP-ALD-50 cycle//Li表現出優越的電化學穩定性，在經過100 cycle鋰鋰對充測試後依然維持穩定循環且擁有較低的過電位(0.12 V)。
然而，Li//LATP-ALD-50 cycle//Li在高電流密度下之過電位變得相當大，因此本研究第三部分以Thio-LISICON結構硫化物固態電解質Li10GeP2S12 (LGPS)為主題，使用行星式球磨機通過機械研磨之後，搭配DSC、XRD、SEM分析找出最適化燒結程序，實驗結果得出燒結條件以400℃燒結8 h之LGPS擁有最高離子電導率3.1 mS/cm。
為了確認其電化學穩定性，我們以0.1 mA/cm2電流密度進行鋰鋰對充測試，發現在測試29圈後發生短路，且過電位高達0.21 V，因此本研究第四部份透過摻雜微量的Si離子以及O離子來合成Li10GeP2S12¬系統結構固態電解質Li10Ge1-xSixP2S12¬-2xOx (x= 0、0.2、0.4)並探討其晶體結構、離子電導率以及電化學穩定性，結果顯示Li10Ge0.8Si0.2P2S11.6O0.4在室溫下表現出高離子電導率(2.04 mS/cm)和極低的活化能(0.18 eV)且Li//Li10Ge0.8Si0.2P2S11.6O0.4//Li 對稱電池在0.1 mA/cm2下可以穩定循環充放電超過100 小時不發生短路，擁有較低的過電位(0.07 V) ，因此Li10Ge0.8Si0.2P2S11.6O0.4為具有潛力，能應用於全固態鋰電池之固態電解質材料。

關鍵字

鈉快離子導體 ； 磷酸鈦鋁鋰 ； 鋰快離子導體 ； 鋰鍺磷硫 ； 固態電解質 ； 離子電導率 ； 原子層沉積

並列摘要

In the first part, our study focused on Li1.3Al0.3Ti1.7(PO4)3(LATP) with a NASICON structure. The LATP powder was synthesized by a solid-state method. The as-synthesized LATP was characterized thorough wide angle powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and ionic conductivity was measured by an impedance analyzer. The optimal sintering temperature of LATP pellet is 1000℃, which exhibits the best total lithium-ion conductivity of 0.27 mS cm-1 at room temperature.
LATP has high interfacial resistance with electrode because of the poor contact between solid-state electrolytes and the electrode. Thus, we make a zinc oxide (ZnO) surface modification layer by atomic layer deposition (ALD) onto LATP pellets. First, we used XRD, SEM, EDS, XPS, TEM measurements to identify whether ZnO is successfully deposited on the LATP-1000℃. The stability of the SSE against Li metal was evaluated by Li/LATP/Li symmetrical cells, which were cycled at 0.01 mA/cm2, the Li// LATP-ALD-50 cycle //Li symmetric batteries can stably cycle for more than 100 h without short circuit at 0.01 mA/cm2 and have low overpotential (0.12 V).
However, the overpotential of the Li//LATP-ALD-50 cycle//Li started to grow and rise at high current density, therefore, we focused on Li10GeP2S12 with a Thio-LISICON structure. In the first part, the Li2S-GeS2-P2S5 precursor powder was prepared by mechanical milling using a planetary ball-milling apparatus. The as-synthesized Li10GeP2S12 was characterized thorough wide angle powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and ionic conductivity was measured by an impedance analyzer. The optimal sintering temperature of LGPS powder is at 400℃ for 8 h, where total lithium-ion conductivity is 3.18 mS cm-1.
The electrochemical stability of the SSE against Li metal was evaluated by Li/LGPS/Li symmetrical cells under a current density of 0.1 mA/cm2. The average overvoltage was 0.21 V during 29 cycles. A sudden drop indicated that an internal short-circuit was occurred. The lithium super-ionic conductor Li10Ge1-xSixP2S12¬2xOx (for concentrations x= 0, 0.2 and 0.4) examined the effects of the synthesis conditions, such as sintering temperatures, on the ionic conductivity and electrochemical stability. The as-synthesized Li10Ge0.8Si0.2P2S11.6O0.4 exhibited high total conductivity of 2.04 mS/cm at room temperature with an extremely low activation energy of 0.18 eV, the Li//Li10Ge0.8Si0.2P2S11.6O0.4//Li symmetric batteries can stabilize cycle life for more than 100 hours without short circuit at 0.1 mA/cm2 with a lower overpotential of 0.07 V.

並列關鍵字

NASICON ； LATP ； Thio-LISICON ； LGPS ； solid electrolyte ； ionic conductivity ； Atomic layer deposition

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