Understanding the Influence of Functional Groups on the PEO Composite Electrolytes through a Theoretical, Spectroscopic, and Conduction Behavior Study of Model Systems

Introducing functional groups via blending or copolymerization is a promising approach to improve Li+ transference number and ionic conductivity of poly(ethylene oxide) (PEO) electrolytes in solid-state lithium battery. Nevertheless, the laws governing the impact of functional groups on ion coordination and transport at the microscopic level remain unclear, mainly due to intricate competitive interactions among multiple components and the absence of controllable variables in experimental models. In this work, potential energy surface search methods based on density functional theory, combined with molecular dynamics simulation, spectroscopy, and experiments of standardized models, were employed to examine the binding and migration property of lithium ions and anions with four functional groups showing distinctly different electronic effect: −NH2, −OH, −CN, and −CH3. The results show that the binding trends for lithium ions were −NH2 > −OH > −CN > −CH3, and for anions, they were −NH2 > −CN > −OH > −CH3. These varying binding preferences led to differences in conductivity and transference numbers for the grafted silica particle-PEO composite electrolytes. It could be a guideline for designing solid polymer electrolyte with improved ionic conduction performance by modifying filler surface or optimizing polymer chain structure with different functional groups.