Asymmetric Surface Charge Engineering Regulates Solvation Structure and Ionic Conductivity in Confined Polymer Electrolytes.

Solid polymer electrolytes (SPEs) have attracted considerable attention as promising alternatives to liquid electrolytes for high-energy-density lithium-metal batteries, offering enhanced safety and mechanical stability. However, their widespread adoption remains limited by low ionic conductivity and inadequate lithium-ion transference numbers at ambient conditions. Recent studies demonstrate that confining SPEs within nanoporous structures can markedly enhance ion transport, yet the molecular-level mechanisms underlying how surface electrostatic properties of nanopores influence lithium-ion dynamics remain unclear. Here, we employ comprehensive molecular dynamics simulations to systematically investigate the effects of surface charge distribution and electrostatic modification fractions of nanopore walls on ion transport properties in nanoconfined poly(ethylene oxide)/LiTFSI electrolytes. Our results show that introducing charged sites onto nanopore walls generally reduces ionic conductivity due to strong lithium-ion adsorption, hindering ion mobility. Critically, we find that asymmetric charge distributions selectively mitigate this adsorption effect, preferentially impeding anion mobility and thus enhancing lithium-ion transference numbers. Structural and dynamical analyses reveal that nanopore wall polarity disrupts lithium-polymer coordination, yet simultaneously introduces alternative lithium-ion solvation environments at charged sites. This competitive solvation landscape generates a critical trade-off, emphasizing the necessity of carefully balancing electrostatic modification fraction and charge asymmetry to optimize ionic conductivity. The molecular insights gained from this study provide actionable design principles for engineering nanopore-confined SPEs with superior ion transport properties. These findings pave the way for rational development of advanced polymer electrolyte architectures essential for next-generation lithium-metal battery technologies.