Modeling of Space-Charge Layers in Solid-State Electrolytes: A Kinetic Monte Carlo Approach and Its Validation

The space-charge layer (SCL) phenomenon in Li+-ion-conducting solid-state electrolytes (SSEs) is gaining much interest in different fields of solid-state ionics. Not only do SCLs influence charge-transfer resistance in all-solid-state batteries but also are analogous to their electronic counterpart in semiconductors; they could be used for Li+-ionic devices. However, the rather "elusive"nature of these layers, which occur on the nanometer scale and with only small changes in concentrations, makes them hard to fully characterize experimentally. Theoretical considerations based on either electrochemical or thermodynamic models are limited due to missing physical, chemical, and electrochemical parameters. In this work, we use kinetic Monte Carlo (kMC) simulations with a small set of input parameters to model the spatial extent of the SCLs. The predictive power of the kMC model is demonstrated by finding a critical range for each parameter in which the space-charge layer growth is significant and must be considered in electrochemical and ionic devices. The time evolution of the charge redistribution is investigated, showing that the SCLs form within 500 ms after applying a bias potential.