Ionic Liquid Functionalized Gel Polymer Electrolytes for Stable Lithium Metal Batteries

Metallic lithium (Li) is regarded as the ideal anode material in lithium-ion batteries due to its low electrochemical potential, highest theoretical energy density and low density. There are, however, still significant challenges to be addressed such as Li-dendrite growth and low interfacial stability, which impede the practical application of Li metal anodes. In order to circumvent these shortcomings, herein, we present a gel polymer electrolyte containing imidazolium ionic liquid end groups with a perfluorinated alkyl chain (F-IL) to achieve both high ionic conductivity and Li ion transference number by fundamentally altering the solubility of salt within the gel electrolyte through Lewis-acidic segments in the polymer backbone. Moreover, the presence of F-IL moieties decreased the binding affinity of Li cation towards the glycol chains, enabling a rapid transfer of Li cation within the gel network. These structural features enabled the immobilization of anions on the ionic liquid segments to alleviate the space-charge effect while promoting stronger anion coordination and weaker cation coordination in the Lewis-acidic polymers. Accordingly, we realized a high Li ion conductivity (9.16x10(-3) S cm(-1)) and high Li ion transference number of 0.69 simultaneously, along with a good electrochemical stability up to 4.55 V, while effectively suppressing Li dendrite growth. Moreover, the gel polymer electrolyte exhibited stable cycling performance of the Li|Li symmetric cell of 9 mAh cm(-2) for more than 1800 hours and retained 86.7 % of the original capacity after 250 cycles for lithium-sulfur (Li-S) full cell.

Automated summary

A gel polymer electrolyte was developed with imidazolium ionic liquid end groups and perfluorinated alkyl chain to address challenges such as Li-dendrite growth and low interfacial stability in Li metal anodes. The electrolyte demonstrated high Li ion conductivity, high Li ion transference number and good electrochemical stability, effectively suppressing Li dendrite growth and exhibiting stable cycling performance.