Effect of Coordination Behavior in Polymer Electrolytes for Sodium-Ion Conduction: A Molecular Dynamics Study of Poly(ethylene oxide) and Poly(tetrahydrofuran)

Alternatives to lithium-ion batteries are extensively studied due to concerns about lithium availability considering the constant increase in demand for rechargeable batteries. While several studies have investigated different liquid electrolytes, the transport of those ions in their polymer counterparts remains understudied. In this work, we used molecular dynamics simulations to characterize the main factors that affect sodium-ion transport in two polymer hosts: poly(ethylene oxide) (PEO) and poly(tetrahydrofuran) (PTHF). We analyzed the influence of oxygen density in each chain and its effect on diffusivity, conductivity, and cation-anion interactions. It is inferred that the weaker coordination in PTHF resulted in differences in the Na+-transport mechanism, with interchain hopping being more prominent in PTHF than in PEO. The faster diffusion observed in PTHF was, however, hindered by the significantly larger formation of ion clusters in the PTHF electrolyte, which could lead to smaller transference numbers in battery settings. These findings elucidate the fundamental influences and correlations of varied polymer ether content to ion coordination and transport, which can inform on novel syntheses that improve polymer electrolyte properties.