The importance of nonlinear fluid response in joint density-functional theory studies of battery systems

TL;DR

This paper introduces a nonlinear joint density-functional theory to accurately model electrolyte effects at electrochemical interfaces, capturing saturation effects crucial for realistic battery system simulations.

Contribution

The paper develops a nonlinear dielectric and ionic response model within joint density-functional theory, extending continuum solvation models to better handle strong electric fields at interfaces.

Findings

Nonlinear response agrees with linear models under typical conditions.

Saturation effects are essential for accurate interface modeling.

Improves understanding of electrolyte behavior at electrode surfaces.

Abstract

Delivering the full benefits of first principles calculations to battery materials demands the development of accurate and computationally-efficient electronic structure methods that incorporate the effects of the electrolyte environment and electrode potential. Realistic electrochemical interfaces containing polar surfaces are beyond the regime of validity of existing continuum solvation theories developed for molecules, due to the presence of significantly stronger electric fields. We present an ab initio theory of the nonlinear dielectric and ionic response of solvent environments within the framework of joint density-functional theory, with precisely the same optimizable parameters as conventional polarizable continuum models. We demonstrate that the resulting nonlinear theory agrees with the standard linear models for organic molecules and metallic surfaces under typical operating conditions. However, we find that the saturation effects in the rotational response of polar solvent molecules, inherent to our nonlinear theory, are crucial for a qualitatively correct description of the ionic surfaces typical of the solid electrolyte interface.