Coupling–Decoupling Transition between Li<sup>+</sup> Transport and Segmental Relaxation in Solid Polymer Electrolytes
Dengpan Dong, Aditya Choudhary, Dmitry Bedrov
Abstract
Solid polymer electrolytes (SPEs) provide a potential to enable lithium-ion and lithium-metal batteries to achieve high energy density, advanced manufacturing capabilities, and enhanced safety. However, the currently available SPEs do not yield the desired Li+ conductivity at ambient temperatures. The design strategies for polymer electrolytes often rely on the expectation of dynamical decoupling between ionic conductivity and polymer segmental relaxation, yet the underlying physics of assumed “decoupling” is unclear. In this Letter, atomistic molecular dynamics simulations are used to investigate the molecular origin of coupling–decoupling phenomena between Li+ mobility and polymer dynamics for a series of polymer architectures resulting in similar Li+ coordination environments. A transition from strong coupling between Li+ and the polymer segmental motion regime to a decoupling regime is clearly observed. In the latter regime, while anion motion shows a strong correlation with polymer segmental dynamics, the Li+ transport remains almost constant in systems where the polymer dynamics differs by orders of magnitude.