Ab Initio Thermodynamics of Space Charge Formation at Solid State Electrochemical Interfaces

We explore the ionic space charge at metal/Li oxide interfaces by extending the phenomenological model of semiconductor space charge to incorporate defect chemistry of Li-containing materials. Defect energetics from standard density functional theory (DFT) calculations are used to determine the charge concentration as a function of the Fermi level \(E_{{\text{F}}}\) and Li chemical potential \(\mu_{{{\text{Li}}}}\) . This is subsequently coupled with Poisson’s equation to calculate the ionic space charge profile. The results demonstrate how \(\mu_{{{\text{Li}}}}\) differences in the cathode and anode are converted to voltage difference across the battery stack via band bending due to formation of ionic space charge. Additionally, we discuss explicit atomistic modeling of interfaces via DFT calculations for addressing the effect of the many approximations in such phenomenological modeling. A bottleneck in this direction has been the combinatorial explosion in the number of defect configurations, and we introduce emerging machine learning and sampling methods to overcome this limitation.