Molecular Dynamics Simulations of Ion Transport in High Transference Number Polyelectrolytes for Li-Ion Batteries

Conventional liquid electrolytes for Li-ion batteries suffer from low Li⁺ transference numbers, which limit mass transport in porous electrodes and thus reduce the battery’s energy density and rate capability. It has been proposed that replacing traditional Li-ion battery salts with lithium-neutralized polyanions dissolved in solution could be a means to increase the Li⁺ transference number while only modestly sacrificing ionic conductivity. While initial experimental studies have demonstrated the promise of this approach, rational design of optimal polyelectrolytes requires more fundamental, atomistic-level understanding of the ion transport mechanisms in these systems. To this end, we use classical molecular dynamics simulations to investigate the behavior of poly(allyl glycidyl ether-lithium sulfonate); this polyion has been thoroughly characterized experimentally for this application, enabling validation of the computational model. By characterizing the Li⁺ diffusion mechanism as well as ion aggregation behavior in the system, we elucidate the atomistic phenomena that most strongly govern experimentally-measured conductivity and transference numbers.