Microstructures and interface analysis of Y doped Li7La3Zr2O12 solid electrolyte coatings by colloidal coating process for the application of all solid-state lithium ion batteries

Abstract

The concept of all solid-state lithium ion battery (ASSLIB) compared with that of the current liquid electrolyte lithium ion batteries are more safety and with higher power densities. One of the key components of ASSLIB is the solid electrolyte. The study is attempt to investigate the microstructures of Y doped Li₇La₃Zr₂O₁₂ (Y-LLZO) solid electrolyte coatings and the interfaces between the solid electrolyte and LiCoO₂ (LCO) electrode of ASSLIB. The preparation of the Y-LLZO coatings are by a colloidal coating process via the spin coating method. And the Y-LLZO powders are synthesized by a solid-state reaction method. The as-prepared Y-LLZO powders after calcined at 900 °C for 12 h show the crystalline phase of cubic garnet. The dense Y-LLZO coating layers with the thickness around several microns deposited on the LCO substrate can be obtained after sintered at 1100 °C for 12 h. The EDS element mapping results show that three types of regions can be classified from the microstructures, including the (Co,O)-rich, (Co, La, O)-rich, and (La, Y, Zr, O)-rich regions near the interface of the Y-LLZO coatings and the LCO substrate. The (Co,O)-rich should be from the initial LCO grains, and the (La, Y, Zr, O)-rich regions should be from the initial Y-LLZO grains. And the (Co, La, O)-rich regions is possible due to the inter-diffusion of La and Co elements from Y-LLZO and LCO, respectively. The formation of the (Co, La, O)-rich regions is most possibly LaCoO₃ grains. Due to the over-diffusion and the formation of secondary phase between Y-LLZO solid-electrolyte coating layer and LCO cathode electrode substrate after sintered at 1100 °C for 12 h. It is suggested that the process temperature for the LLZO-based electrolyte should be <1100 °C.