Modeling the Electrical Double Layer at Solid-State Electrochemical Interfaces

Models of the electrical double-layer (EDL) at electrode/liquid-electrolyte interfaces no longer hold for all-solid-state electrochemistry.  In this work, a new model for the EDL at a solid-state electrochemical interface based on the ``Poisson-Fermi-Dirac equation'' is formulated.  By combining this model with density functional theory predictions, the interconnected electronic and ionic degrees of freedom in all-solid-state batteries, including the electronic band bending and defect concentration variation in the space-charge layer, are captured self-consistently.  Along with a general mathematical solution, the EDL structure is presented in various materials that are thermodynamically stable in contact with a lithium metal anode: the solid electrolyte LLZO and the solid interlayer materials LiF, Li2O, and Li2CO3.  The model further predicts the optimum interlayer thicknesses to minimize the electrostatic barrier for lithium transport at relevant solid-state battery interfaces.