Modified Kirchhoff's Laws for Electric-Double-Layer Charging in Arbitrary Porous Networks

TL;DR

This paper introduces a theoretical framework using modified Kirchhoff's laws to efficiently model electric-double-layer charging in complex porous networks, significantly reducing computational costs while maintaining accuracy.

Contribution

The authors develop a novel circuit-based approach that extends Kirchhoff's laws to arbitrary pore networks, enabling fast and accurate predictions of EDL charging without geometric restrictions.

Findings

Framework matches direct numerical simulations with high accuracy.

Simulation speed is up to five orders of magnitude faster.

Pore connectivity and polydispersity significantly influence charging dynamics.

Abstract

Understanding the dynamics of electric-double-layer (EDL) charging in porous media is essential for advancements in next-generation energy storage devices. Due to the high computational demands of direct numerical simulations and a lack of interfacial boundary conditions for reduced-order models, the current understanding of EDL charging is limited to simple geometries. Here, we present a theoretical framework to predict EDL charging in arbitrary networks of long pores in the Debye-H\"uckel limit without restrictions on EDL thickness and pore radii. We demonstrate that electrolyte transport is described by Kirchhoff's laws in terms of the electrochemical potential of charge (the valence-weighted average of the ion electrochemical potentials) instead of the electric potential. By employing this equivalent circuit representation with modified Kirchhoff's laws, our methodology accurately captures the spatial and temporal dependencies of charge density and electric potential, matching results obtained from computationally intensive direct numerical simulations. Our framework provides results up to five orders of magnitude faster, enabling the efficient simulation of thousands of pores within a day. We employ the framework to study the impact of pore connectivity and polydispersity on electrode charging dynamics for pore networks and discuss how these factors affect the timescale, energy density, and power density of the capacitive charging. The scalability and versatility of our methodology make it a rational tool for designing 3D-printed electrodes and for interpreting geometric effects on electrode impedance spectroscopy measurements.