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Miaofang Chi1 Xiaoming Liu1 Jeff Sakamoto2 Nancy Dudney1

1, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
2, University of Michigan, Ann Arbor, Michigan, United States

Advances in solid electrolytes and their interfaces represent major challenges for the development of future energy storage. An ideal solid electrolyte material must not only be highly ionically conductive but also exhibit desirable stability with metallic lithium and cathodes. While several new solid electrolyte materials have been developed that demonstrate high conductivity, little is known about their integration with electrodes. Unexpected high resistivity is often observed at solid electrolyte-electrode interfaces. Understanding how solid-solid interfaces are formed and how mass transport and charger transfer occur at these interfaces are crucial to the design of interfaces with high electrochemical performance. Many solid electrolytes are polycrystalline and contain significant amounts of grain boundaries that often exhibit completely different structure and chemistry from that of bulk grains. Particular attention has to be paid to the electrochemical stability of the grain boundaries that are exposed to the interfaces with electrodes. However, experimentally probing these embedded interfaces is challenging. Here, in situ and atomic-resolution scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) are used to study these interfaces. Al-Li7La3Zr2O12 (LLZO) and LLTO were used as model systems. In order to understand the crystalization mechanism of amorphous LCO on LLTO, phase evolution and chemical diffusion at the interface of LLTO with sputtered amorphous LiCoO2 were monitored in situ during thermal annealing. The competing elemental diffusion and crystallization were vividly revealed. At the interface of LLZO with Li metal, we focused on understanding how different types of grain boundaries response to the contact of Li metal both in a static state and upon an electrical bias. Our microscopy results provide valuable insights into the design and synthesis of solid electrolyte – electrode interfaces.

Acknowledgement
Research sponsored by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy. Microscopy performed as part of a user project at Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. DOE User Facility.

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