固態鋰金屬電池之石榴石型電解質

Abstract

隨著高性能鋰金屬電池(lithium metal batteries; LMBs)需求日益增加，開發兼具優異離子導電性與電化學穩定性之固態電解質(solid-state electrolytes; SSEs)已成為研究焦點。其中，以石榴石結構為主之電解質，尤其為Li6.75La3Zr1.75Ta0.25O12 (LLZTO)，因其具備極佳之鋰離子導電性、寬廣之電化學穩定窗口及與鋰金屬負極之化學相容性，受到廣泛關注。本研究首先以燒結LLZTO錠片為電解質，並藉由添加改質材料進行界面優化，形成複合式負極，針對兩項關鍵問題進行改善：其一為高界面阻抗，其二為耐高電流密度能力不足。經界面改質後，可顯著降低阻抗並提高臨界電流密度(critical current density; CCD)，從而提升整體電池性能。 然而，儘管LLZTO電解質於電化學特性上具備優勢，其製備成本及規模化應用經濟性有限。為解決此問題，本研究進一步轉向複合高分子電解質(composite polymer electrolyte; CPE)系統，將LLZTO作為無機填料均勻地分散於聚合物基材中，兼顧其優異導電性與電解質系統之可撓性與可製程性。此複合電解質展現更佳之離子導電性與結構穩定性，更適合實際應用需求。此外，本研究亦針對LLZTO奈米顆粒進行表面改質，以進一步提升其於高分子基材中之分散性與電解質整體性能。由控制表面污染物(如碳酸鋰)與官能化處理，有效優化其表面化學性質，進而促進LLZTO於基材中之均勻分布並提高整體離子導電率。 綜合以上成果，將所開發之石榴石型複合電解質應用於無陽極鋰電池(anode-less lithium battery)系統顯示極大應用前景。於此類架構中，鋰金屬會於初次充電時原位沉積於裸露之集流體上，因此更須仰賴高效之鋰離子傳輸與穩定之界面以實現高可逆性與均勻鋰沉積。本研究所開發之複合電解質於柔性、導電性及界面相容性方面皆能滿足無陽極設計所須條件，提供一條有效途徑以進一步提升固態鋰電池之能量密度，達到去除過量鋰金屬與降低非活性材料使用量之目的。本論文強調LLZTO於石榴石型固態電解質發展中之關鍵角色，並探討其於提升界面穩定性、導電性、規模化製程性等方面之潛力，對次世代鋰金屬電池之發展具重要意義。

The growing demand for high-performance lithium metal batteries (LMBs) has spurred significant interest in developing solid-state electrolytes (SSEs) with superior ionic conductivity and electrochemical stability. Among them, garnet-type SSEs, particularly Li6.75La3Zr1.75Ta0.25O12 (LLZTO), have garnered attention due to their excellent lithium-ion conductivity, wide electrochemical stability window, and chemical compatibility with lithium metal anodes. In this research, LLZTO in pellet form was initially employed, with interface modifications using additive materials to create a composite anode that addresses two critical issues: high interfacial impedance and the need for improved tolerance to high current densities, which enhances the critical current density (CCD). This interface optimization showed promising results by significantly reducing impedance and increasing current tolerance, subsequently improving the battery’s overall performance. However, despite its appealing electrochemical properties, the pellet form of LLZTO proved economically unfeasible for large-scale applications. My research transitioned to composite polymer electrolyte (CPE) systems to address this limitation, incorporating LLZTO as an active inorganic filler within a polymer matrix. This approach leverages the advantageous properties of LLZTO while enhancing the flexibility and scalability of the electrolyte system. The composite electrolyte systems demonstrated improved ionic conductivity and structural integrity, making them more practical for real-world applications. Additionally, the surface modification of LLZTO nanoparticles was investigated to enhance the electrolyte's performance further. By regulating surface contaminants, such as Li2CO3, and implementing functionalization techniques, the surface chemistry was optimized to improve the dispersion of LLZTO nanoparticles within the polymer matrix, leading to a notable enhancement in the ionic conductivity of the composite system. Building upon these advances, the developed garnet-based composite electrolytes show significant promise for application in anode-less lithium battery systems, where lithium is plated in situ onto a bare current collector during the initial charge. In such configurations, the need for efficient lithium-ion transport and stable interfaces becomes even more critical to enable high reversibility and uniform lithium deposition. The flexibility, ionic conductivity, and interfacial compatibility demonstrated in this work align well with the stringent requirements of anode-less designs, offering a pathway to further increase the energy density of solid-state lithium batteries by eliminating excess lithium and reducing inactive components. This thesis highlights the potential of LLZTO as a key material in advancing garnet-based solid-state electrolytes and its critical role in addressing challenges associated with interfacial stability, conductivity, and scalability in next-generation lithium metal batteries.