Interfacial Degradation Processes in Solid-State Batteries during High Temperature Processing and the Mitigation Strategies

Abstract

Garnet-type solid electrolytes have been extensively investigated in recent times as potential candidates for solid-state batteries. Among them, garnets with nominal composition Li7La3Zr2O12(LLZO) have received particular attention due to their high Li-ion conductivity (10-3 Scm-1) at room temperature and chemical stability against metallic lithium besides possessing a large electrochemical window >5V.[1] Despite of striking properties, LLZO suffers from several challenges such as interfacial instability with cathodes, e.g., LCO, during high temperature processing, resulting in a huge interface resistance, which is one of the fundamental reasons for the failure of solid-state batteries based on LLZO.[2-4] So far, the high interfacial impedance has been related to LLZO|LCO interface decomposition occurring due to diffusion of Co across the cathode-electrolyte interface. Herein, we investigated the hypothesis that interfacial degradation originate from the incorporation of Co into the LLZO lattice. The solubility limit of Co is determined to be 0.16 per formula unit, whilst the concentrations beyond promote phase transition (cubic LLZO-to-tetragonal LLZO). We investigated in detail the temperature-dependent Co diffusion into LLZO and concluded that detrimental cross diffusion could take place at any relevant process condition. Besides, the optimal protective Al2O3 coating thickness for relevant temperatures was studied, which allowed to create a process diagram to provide mitigation strategies towards enabling stable LCO|LLZO interface in all-solid-state batteries. Keywords: Solid-state batteries, Interfaces, cross diffusion, interfacial degradation AcknowledgementsD.R. acknowledges financial support by the Austrian Federal Ministry for Digital and Economic Affairs, the National Foundation for Research, Technology and Development and the Christian Doppler Research Association (Christian Doppler Laboratory for Solid-State Batteries). D.R. and J. F. acknowledges financial support by the Austrian Science Fund (FWF) in the frame of the project InterBatt (P 31437). D.K. acknowledges funding by the European Union’s Horizon 2020 Research and Innovation Programme (Grant No. 823717, project “ESTEEM3”) and by the Zukunftsfond Steiermark.Reference[1] Murugan, R., Thangadurai, V. and Weppner, W., 2007. Fast Lithium Ion Conduction in Garnet‐type Li7La3Zr2O12. Angew. Chemie. Int. Edt., 46(41), 7778-7781.[2] Chen, X., Xie, J., Zhao, X., & Zhu, T., 2021. Electrochemical Compatibility of Solid‐State Electrolytes with Cathodes and Anodes for All‐Solid‐State Lithium Batteries: A Review. Adv. Energy Sustain. Res., 2(5), 2000101.[3] Sakuda, A., Hayashi, A., Tatsumisago, M., 2010. Interfacial Observation Between LiCoO2 Electrode and Li2S-P2S5 Solid Electrolytes of All-Solid-State Lithium Secondary Batteries Using Transmission Electron Microscopy. Chem. Mater., 22(3), 949–956.[4] Ihrig, M., Kuo, L.Y., Lobe, S., Laptev, A.M., Lin, C.A., Tu, C.H., Ye, R., Kaghazchi, P., Cressa, L., Eswara, S. and Lin, S.K., 2023. Thermal Recovery of the Electrochemically Degraded LiCoO2/Li7La3Zr2O12: Al, Ta Interface in an All-Solid-State Lithium Battery. ACS Appl. Mater. Interfaces.