Voltage dependent first-principles barriers to Li transport within Li-ion battery Solid-Electrolyte-Interphases

Charging a Li-ion battery requires Li ion transport between the cathode and the anode. This Li-ion transport is dependent upon (among other factors) the electrostatic environment the ion encounters within the Solid-Electrolyte-Interphase (SEI), which separates the anode from the surrounding electrolyte. Previous first principles work has illuminated the reaction barriers through likely atomistic SEI environments, but has had difficulty accurately reflecting the larger electrostatic potential landscape that an ion encounters moving through the SEI. In this work, we apply the recently developed Quantum Continuum Approximation (QCA) technique to provide an equilibrium electronic potentiostat for first-principles interface calculations. Using QCA, we calculate the potential barrier for Li-ion transport through LiF, Li$_2$O, and Li$_2$CO$_3$ SEIs along with LiF-LiF, and LiF-Li$_2$O grain boundaries, all paired with Li metal anodes. We demonstrate that the SEI potential barrier is dependent on the anode electrochemical potentials in each system. Furthermore, we find that the threshold potential at which the SEI potential barrier switches from encouraging Li ion transport toward the anode versus discouraging transport toward the anode is highly dependent on the exact SEI chemistry. Finally, we use these techniques to estimate the change in the diffusion barrier for a Li ion moving in a LiF SEI as a function of anode potential.