Solid-state lithium-ion batteries hold great promise for obtaining higher energy densities but the power density is currently limited by the electrode-electrolyte interfaces. [1] The high resistances at SLIB interfaces are hypothesized to be due to chemical mixing, space charge formation, or secondary phase formation. [2,3] Although several secondary phases have been proposal theoretically, there is no experimental work studying the secondary phase formation as a function of temperature and applied voltage. Extended x-ray absorption fine structure spectroscopy (EXAFS) is a unique capability that allows us to probe the fine structure around the atoms at the electrode-electrolyte interface. Previous interface studies using XRD were not able to identify the secondary phases, either because secondary phases are small in amount or not crystalline. [3] Depth-sensitive x-ray absorption spectroscopy allows us to probe the changes in structure at the interface even if the secondary phases are not crystalline. This work studies the interface between Li₇La₃Zr₂O₁₂ (LLZO) and LiCoO₂ (LCO).

[1] Cheng, L. et al. Phys. Chem. Chem. Phys. 16, 18294–18300 (2014).

[2] Miara, L. J., et al. Chem. Mater. 27, 4040–4047 (2015).

[3] Park, K. et al. Chem. Mater. 28, 8051–8059 (2016).