Understanding the Solid-State Electrode–Electrolyte Interface of a Model System Using First-Principles Statistical Mechanics and Thin-Film X-ray Characterization

Intermixing of atomic species at the electrode–electrolyte boundaries can impact the properties of the interfaces in solid-state batteries. Herein, this work uses first-principles statistical mechanics along with experimental characterization to understand intermixing at the electrode–electrolyte interface. For the model presented in this work, lithium manganese oxide (LiMn2O4, LMO) and lithium lanthanum titanate (Li3xLa2/3–xTiO3, LLTO) are employed as the cathode and electrolyte, respectively. The results of the computational work show that Ti–Mn intermixing at the interface is significant at synthesis temperatures. The experimental results in this work find that, at some critical temperatures between 600 and 700 °C for material preparation, the interface of LLTO–LMO becomes blurred. Calculations predict that the interface is unstable with regard to Ti–Mn intermixing starting at 0 K, suggesting that the critical temperature found in the experiment is related to kinetics. The work overall suggests that, in designing a solid-state battery, the fundamental reactions such as intermixing need to be considered.