Poly(Ionic Liquid)s-in-Salt Electrolytes with Co-coordination-Assisted Lithium-Ion Transport for Safe Batteries

Polymer electrolytes are seen as key components for safe, high-energy-density all-solid-state lithium (Li) batteries, given their appropriate mechanical properties along with the absence of volatile and flammable solvents. Here, we report a class of solvent-free polymer electrolytes by using poly(diallyldimethylammonium) bis(fluorosulfonyl)imide (PDADMA FSI) and a high content of Li bis(fluorosulfonyl)imide (LiFSI) salt. A homogeneous mixture, with a Li+ ion transference number of 0.56, is found at a 1:1.5 mole ratio of PDADMA FSI:LiFSI, whereas crystalline phases are observed at higher LiFSI contents. Molecular dynamics (MD) simulations indicate a co-coordination of the FSI anion with both the Li+ and the polymer backbone, and this co-coordination is maximized at 1:1.5 mole ratio, which facilitates Li+ transport. The optimized electrolyte has been demonstrated to support long-term stable Li-metal symmetrical cycling as well as Li-metal battery cycling (Li | LiFePO4 and Li | Li1/3Ni1/3Mn1/3CoO2) at elevated temperature, with areal capacity higher than 1.1 mAh cm−2.