Nanoscale Confinement Effects on Ionic Conductivity of Solid Polymer Electrolytes: The Interplay between Diffusion and Dissociation

Abstract

Solid polymer electrolytes (SPEs) are attractive for next-generation lithium metal batteries but still suffer from low ionic conductivity. Nanostructured materials offer design concepts for SPEs with better performance. Using molecular dynamics simulation, we examine SPEs under nanoscale confinement, which has been demonstrated to accelerate the transport of neutral molecules such as water. Our results show that while ion diffusion indeed accelerates by more than 2 orders of magnitude as the channel diameter decreases from 15 to 2 nm, the ionic conductivity does not increase significantly in parallel. Instead, the ionic conductivity shows a nonmonotonic variation, with an optimal value above, but on the same order as, its bulk counterparts. This trend is due to enhanced ion association with decreasing channel size, which reduces the number of effective charge carriers. This effect competes with accelerated ion diffusion, leading to the nonmonotonicity in ion conductivity.

Three-Component Construction of Mesoporous Metal–Organic Frameworks and Their Incorporation into Solid Polymer Electrolytes for Li-Ion Conduction

“…It is worth noting that the moderate channel size is large enough for polymer insertion and guarantees high diffusion but still prevents possible chain entanglement. In addition, unlike micropores, which may inhibit ion dissociation, the mesopores in FDM-76 allow enhanced ion dissociation, which is essential for Li-ion conductivity.…”

Machine Learning‐Assisted Property Prediction of Solid‐State Electrolyte

“…MD simulations serve as valuable tools for the evaluation of solid polymer electrolytes possessing attributes suitable for utilization in Li‐ion batteries. [ 105–107 ] Nevertheless, given the extensive space of polymer designs, expediting the screening process becomes imperative, necessitating a reduction in computational time about ion transport properties in simulations. A unique set of descriptors, derived from a 0.5 ns observation window at the outset of MD simulations, was utilized and assessed by Khajeh et al for predicting ionic properties ( Figure 7 a).…”

The Interplay of Solvation and Polarization Effects on Ion Pairing in Nanoconfined Electrolytes

“…Previous works suggest that ion pairing in confined electrolytes can differ substantially from that in bulk solutions. − Classical molecular dynamics (MD) simulations of confined aqueous electrolytes by Robin et al, for example, predicted a much greater prevalence of ion pairs under confinement, including the formation of polyelectrolyte-type ionic clusters upon application of an electric field . The authors rationalized these results based on continuum electrostatics, wherein the dielectric mismatch between the electrolyte and channel walls enhances the electric field generated by a confined ion.…”