Phase Stability of Garnet Solid-Electrolyte Interfacing with Various Cathodes in All-Solid-State Batteries

Garnet-structured Li6.75La3Zr1.75Ta0.25O12 (LLZTO) is one of the most promising electrolyte materials for solid-state Li batteries (SS-LiB). The design and fabrication of a good cathode/electrolyte interface is an important criterion for the SS-LiB. In this work, we performed a systematic study on the impact of cathode crystal structure and chemical compositions on their chemical stabilities against the LLZTO at elevated temperatures, which are required for their adhesion during cell fabrication processes. X-ray Diffraction (XRD) and Rietveld refinement analyses revealed the chemical stabilities of various cathode materials in contact with the LLZTO. While layered LiCoO2 cathode showed good stability in contact with LLZTO to 900 C, LiNiO2 or Ni-rich LiNixMnyCo1?x?yO2 (NMC) cathodes suffered from the formation of La4NiLiO8 due to La-diffusion from LLZTO. Mn-rich LiMn2O4 spinel and layered LiNi1/3Mn1/3Co1/3O2 cathodes suffered from the formation of La2Zr2O7 due to Li-diffusion and production of Li2MnO3. As a result, LiNi0.6Mn0.2Co0.2O2, having an ideal balance of Ni/Mn/Co composition, or Li2MnO3 containing cathodes such as Li1.2Ni0.15Mn0.55Co0.1O2 were found to have excellent phase stability as the cathodes for LLZTObased SS-LiBs.