Rational Design and Control of Mixed Ionic-Electronic Conducting Metal Organic Frameworks for Li-S Batteries

Lithium-sulfur batteries (LSBs), with their high theoretical energy densities, are promising candidates for next-generation rechargeable batteries. However, improving the capacity, cycling performance, and commercial viability of LSBs remains a challenge, mainly due to lithium polysulfide (LiPS) shuttling and sluggish Li-S reaction kinetics. One promising strategy to mitigate these issues is the use of ionically and electronically conductive porous metal-organic frameworks (MOFs) as cathode host materials. These MOFs can capture LiPSs within their pores and promote reaction kinetics through electronic conduction and catalytic effects at metal sites. In this work, we computationally investigate the rational design of such mixed ionic-electronic conducting MOFs to optimize their inherent properties for enhancing the performance of LSBs. The first part of our study focuses on modulating MOF pore size to control ion transport and inhibit LiPS diffusion. Using the conductive 2D MOF Ni₃(HITP)₂ as the model MOF material, we establish relationships between pore size and LiPS shuttling by performing molecular dynamics (MD) simulations with tuned classical force fields, based on density functional theory (DFT) calculations. In the second part of our work, we conduct DFT calculations to investigate LiPS adsorption on the MOF surface for inhibited LiPS diffusion, evaluate catalytic effects by characterizing conversion kinetics at MOF metal sites, and examine the impact of surface chemistry on the electronic properties of the MOF. This work informs design principles for optimizing pore size to enable efficient Li ion transport while encapsulating LiPS, contributing to the accelerated commercialization of LSBs.