Pyrrolidinium-PEG Ionic Copolyester: Li-Ion Accelerator in Polymer Network Solid-State Electrolytes

Nonflammable lithium-ion batteries (LIBs) are developed by adapting polymer solid electrolytes, but their insufficient electrochemical performance has not been fully addressed to date. Crosslinked polymer gel electrolytes with minimal organic solvents (hard gels) are proven to be nonflammable electrolytes, but their lithium metal battery performance is not comparable to those of conventional liquid electrolyte-based systems. Here, a semi-interpenetrating polymer network (semi-IPN) ion-transporting solid film that comprises a UV-curable crosslinked polymer and tailored linear pyrrolidinium-polyethylene glycol copolyester ion channels (named P_NPEG), is reported. P_NPEG can solvate Li⁺ effectively with the help of carbonate solvents. Molecular dynamics (MD) simulations confirm that Li⁺ transportation is accelerated due to the weaker interaction between P_NPEG and Li⁺ ions than between the solvents and ions. The semi-IPN electrolyte with P_NPEG exhibits a flexible, nonflammable nature with an ionic conductivity of 4.2 × 10⁻¹ mS cm⁻¹ and Li⁺ transference number of 0.51. The individual pyrrolidinium-Bis(trifluoromethanesulfonyl)imide (pyrrolidinium-Tf₂N) monomer and PEG chain ratios in P_NPEG strongly affect battery performance, and the optimized semi-IPN-based lithium metal half cells with LiCoO₂ cathodes show greatly improved discharge capacity retention at high c-rate conditions owing to effective Li⁺ transportation and excellent cycling performance (93.8% capacity retention after 200 cycles at 0.5 C).