EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

For high-energy-density lithium-based batteries, Li metal as anode material is considered to be a critical component. Due to its highly reductive nature when in contact with liquid electrolyte and its dimensional instability, tailored protection strategies are needed to facilitate its application. To solve these issues, nonflammable inorganic solid-state electrolytes (SSEs) have been widely investigated recently to protect lithium metal, mitigate dendrite formation, and to solve inherent safety issues of traditional lithium-ion batteries. Among all SSEs, Li₇La₃Zr₂O₁₂ (LLZO) with cubic garnet type structure is a promising candidate due to its high temperature stability, adequate ionic conductivity (10^-4 - 10^-3 S/cm) and good stability against both lithium and high oxidative potentials. However, poor physical contact between Li metal and the lithiophobic LLZO electrolyte leads to high interfacial resistance and inhomogeneous current distribution at the interface. As a result, dendrite formation induced by inhomogeneous Li deposition and dissolution was observed even at moderate current densities. Therefore, improving the interface contact to increase critical current densities and to suppress Li dendrite formation is paramount for cycling stability.

To improve the physical contact between LLZO und Li metal, different intermediate layers like gold, tin and tin oxide were introduced to the interface in this work via scalable thin-film deposition techniques. Detailed electrochemical analyses coupled with advanced correlative microscopic techniques (including Transmission Electron Microscopy and Secondary Ion Mass Spectrometry imaging) are implemented to provide a thorough understanding of the elemental composition, morphology and cycling stability of these interlayers. The impact of the developed interlayer composition, morphology and associated properties such as ionic- and electronic conductivities on electrochemical performance specifically dendrite growth suppression and critical current density are discussed elaborately.