Decoupling 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 mechanical strength of gels. Herein, a mechanically stable gel electrolyte comprising 7 wt% methylcellulose (MC), 3 wt% 12-hydroxyoctadecanoic acid (12-HOA), and 90 wt% concentrated sulfone electrolyte (CSE) was developed. Because of its high electrolyte uptake, the MC/12-HOA gel electrolyte exhibits an ionic conductivity of 0.25 mS cm⁻¹, which is similar to that of the neat CSE, and a Li⁺ transference number of 0.57, which is even higher than that of the CSE. Abundant ether groups on MC and hydroxyl groups on 12-HOA can strongly immobilize TFSI⁻ via a hydrogen bond, endowing the MC/12-HOA gel with an elastic modulus of 10 MPa enough to form an 80 μm – thick self-supporting film and suppress 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 a result, the MC/12-HOA gel electrolyte displays reliable safety, practical flexibility, and suitable electrochemical performance in both the Li‖LiFePO₄ and Li‖LiNi_0.8Co_0.1Mn_0.1O₂ cells, suggesting the great promise of the MC/12-HOA scaffold in gel electrolytes with different solvents for a wide range of applications in flexible devices.