Decoupling of Li+ Conductivity and Mechanical Stability in a Thermally Reversible Concentrated Sulfone-based Gel Electrolyte for Lithium Metal Batteries

Abstract

Increasing the liquid content has been recognized as an effective strategy to enhance the Li+ conductivity and electrode compatibility of gel electrolytes for lithium-metal batteries (LMBs). However, a low gelator content reduces the poor mechanical strength of the gel. Here, a mechanically stable gel electrolyte comprising 7 wt% methylcelluloses (MC), 3 wt% 12-hydroxyoctadecanoic acid (12-HOA), and 90 wt% concentrated sulfone electrolyte (CSE) has been developed. Because of its high electrolyte uptake, the MC/12-HOA gel electrolyte shows an ionic conductivity (0.25 mS cm–1) similar to neat CSE, and a Li+ transference number (0.57) even higher than CSE. Abundant ether groups on MC and hydroxyl groups on 12-HOA can strongly immobilize TFSI– by hydrogen bond, enabling the MC/12-HOA gel an elastic modulus of 10 MPa enough to form an 80 μm-thick self-supporting film and suppress the Li dendrite growth. Additionally, a reversible gel-sol transition occurs in the MC/12-HOA gel at 329-331 K, which can be utilized to promote electrode wetting and seal the damages of electrolytes. As the results, the MC/12-HOA gel electrolyte displays reliable safety, practical flexibility, and suitable electrochemical performance in both the Li||LiFePO4 and Li||LiNi0.8Co0.1Mn0.1O2 cell, suggesting the great promise of MC/12-HOA scaffold in gel electrolytes with different solvents for broad applications in flexible devices.