Li Plating/Stripping Reactions on Li6.6La3Ta0.4Zr1.6O12

Abstract

Li7La3Zr2O12 (LLZ) is an attractive candidate for oxide solid electrolyte for various Li-metal-based batteries such as all-solid-state-Li battery, Li-S battery, and Li-air battery. This is because LLZ has a high shear modulus and a wide electrochemical stability window and high Li+ conductivity (can be 10−3 S cm−1 depending on dopant element) at room temperature. However, LLZ still cannot perfectly suppress short-circuiting during Li plating/stripping cycles. Although several approaches to suppress the short-circuiting phenomenon have been reported1, why the short-circuiting occurs during Li plating/stripping cycles on LLZ has not essentially been understood. This study applies an in-situ scanning-electron microscope (SEM) observation technique2 to the investigation on the Li plating/stripping reactions on Li6.6La3Zr1.6Ta0.4O12 (LLZT). A LLZT plate (Toshima Manufacturing Co. Ltd.) with a thickness of 0.5 mm was used as the electrolyte1. A Cu current collector (CC) film was deposited on one side of a LLZT plate by pulsed laser deposition (PLD). A Li film with a thickness of 3 μm and a diameter of 9.0 mm was deposited on the other side of the LLZT plate as the counter electrode by vacuum evaporation. A fabricated Cu/LLZT/Li cell was sandwiched between Cu and brass plates. The Cu plate has a view port in the center. The cell was transferred into the SEM camber without exposure to the air. Li plating/stripping was conducted under galvanostatic conditions at room temperature during the SEM observation. Figure 1shows the voltage transient during Li plating at 100 uA cm−2 on Cu-coated LLZT. Li does not only nucleate at grain boundaries but also on grain cores. After 450 seconds, the voltage drops to 0 V indicating the occurrence of short-circuiting. This result indicates that only a small number of the nucleation sites exist on LLZT surfaces whereby the local current density is supposed to increase. We will also discuss the detail of short-circuiting mechanism of LLZT. Acknowledgement The authors gratefully acknowledge JSPS 17H04894 for the financial supports References [1] Motoyama et al., J. Electrochem. Soc., 162, A7067 (2015). [2] Yonemoto et al., J. Power Sources, 343, 207 (2017).