(301a) First Principles Modeling of Interfacial Charge Transfer and Redox Chemistry in Solid State Batteries

Solid electrolytes in rechargeable lithium ion batteries provide enhanced thermal stability over more traditional liquid electrolytes. Solid electrolytes could also enable the safe application of lithium metal anodes and in turn, an expanded voltage window in comparison to conventional lithium ion systems.^[1] In spite of recent advancements in solid state battery technology with respect to Li⁺ ionic conductivity, there remain many issues broadly associated with resistivity at the interface between electrodes and the solid electrolyte. For example, the electrochemical stability window is often limited by the oxidation and/or reduction potentials of solid electrolytes against high voltage cathodes and lithium metal anodes, respectively.^[2] Under such oxidizing and reducing conditions solid-state superionic conductors are not thermodynamically stable, and various decomposition products are thermodynamically favored instead.^[3]

In this work, we probe the atomistic details of such interfacial decomposition reactions by analyzing the well-documented reactivity^[4] between lithium lanthanum titanate (LLTO) solid electrolytes and lithium metal anodes. First principles density functional theory (DFT) calculations are performed within a Li grand potential ensemble^[2,3,5] to describe bulk thermodynamic driving forces. These thermodynamic driving forces are then mapped onto a La-Ti-O convex hull, where we subsequently generate explicit solid-solid interfacial models that likely exist under operating conditions. A subset of these interfacial models is then used to initialize ab initio molecular dynamics (AIMD) simulations. These AIMD simulations directly suggest structure-sensitive reconstruction mechanisms and redox chemistry based on the particular LLTO surface termination that is interfaced with the lithium metal anode. The atomistic insights from these AIMD studies combined with interfacial band alignment analysis^[6] further unravels the physical origins of charge transfer^[7] and redox chemistry at Li/LLTO interfaces. We apply these insights to propose synthetic strategies to kinetically stabilize electrode-electrolyte interfaces in solid-state batteries. These theoretical predictions are further supported by operando X-ray scattering studies. This overall approach combines DFT based bulk and interfacial thermodynamic analyses, AIMD simulations of explicit solid-solid interfaces, and band alignment calculations to reveal new design principles to enhance interfacial stability in solid state batteries.

[1] G. Crabtree, Science 2019, 366, 422.

[2] W. D. Richards, L. J. Miara, Y. Wang, J. C. Kim, G. Ceder, Chem. Mater. 2016, 28, 266.

[3] Y. Zhu, X. He, Y. Mo, ACS Appl. Mater. Interfaces 2015, 7, 23685.

[4] S. Wenzel, T. Leichtweiss, D. Krüger, J. Sann, J. Janek, Solid State Ion. 2015, 278, 98.

[5] R. E. Warburton, H. Iddir, L. A. Curtiss, J. Greeley, ACS Appl. Mater. Interfaces 2016, 8, 11108.

[6] K. L. Bassett, R. E. Warburton, S. Deshpande, T. T. Fister, K. Ta, J. L. Esbenshade, A. Kinaci, M. K. Y. Chan, K. M. Wiaderek, K. W. Chapman, J. P. Greeley, A. A. Gewirth, Adv. Mater. Interfaces 2019, 6, 1801923.

[7] M. W. Swift, Y. Qi, Phys. Rev. Lett. 2019, 122, 167701.