Dual-Shielding Solvent Strategy of High Dipole-Moment Monomers for Stabilizing Gel Polymer-Based Lithium Metal Batteries

Abstract

Gel polymer electrolytes exhibit excellent interfacial compatibility and high ionic conductivity attributed to the incorporation of high dipole-moment solvents. However, these solvents preferentially adsorb onto the anode compared to the polymer, decomposing into an organic-rich layer with sluggish Li-ion transport kinetics. Furthermore, the solvents dominate the solvation structure, intensifying the formation of unstable interfacial layers. Herein, a dual-shielding solvent strategy involving higher dipole-moment monomers is proposed to mitigate the undesirable interfacial effects in in situ gelled polymer electrolytes. High dipole-moment monomers (allylthiourea and 1,1,1,3,3,3-hexafluoroisopropyl acrylate) exhibit enhanced electrostatic adsorption, displacing solvents adsorbed onto the lithium metal. Moreover, the robust dipole–dipole interactions between high dipole-moment monomers and solvents inhibit the coordination of solvents with Li-ions, resulting in anion-dominated solvation structures. This strategy enables the functional monomers and more anions to synergistically form a stable interfacial passivation layer rich in LiF and Li₂S. Consequently, the symmetric lithium battery can operate stably for 5000 h at a current density of 0.25 mA cm^–2, and the LiFePO₄||Li battery maintains a 97% capacity retention rate after 2000 cycles at 2 C. This work integrates dipole-moment properties into the design of gel electrolytes, offering a promising strategy for addressing interfacial challenges in lithium metal batteries.