Impact of thermal treatment on the Li-ion transport, interfacial properties, and composite preparation of LLZO garnets for solid-state electrolytes

Solid state batteries are the next generation of safe energy storage devices offering high energy and power. Li 7 La 3 Zr 2 O 12 garnets are fast Li-ion conductors and promising electrolytes to be used in solid-state batteries. However, they react with humid air to form LiOH and Li 2 CO 3 , reducing the ionic conductivity. In this work, the effect of heat treatment on local Li mobility in LLZO and the chemical evolution and phase transitions during the heating are investigated by a combination of solid state NMR, Raman, and XRD diffraction techniques. The results show that the activation energy for Li jumps obtained by variable temperature solid state NMR decreases after heat treatment at 750 °C and the Li dynamics are comparable to those of sintered pellets. Additionally, we show that the pretreatment of powders is an effective approach for obtaining garnet-rich composite electrolytes with better flexibility and garnet-polymer interphases, improving the prospects of this material towards processing. Heat treatment of LLZO garnets can effectively remove lithium hydroxide and carbonate layers from its surface, increase the Li dynamics in the structure and improve the processing of composite polymer electrolytes for solid-state batteries.