An in situ polymerizable deep eutectic solvent electrolyte based on TFEA-co-MBA for high-safety and high-voltage lithium metal batteries

Abstract

Solid-state electrolytes (SSEs) show considerable potential for improving the safety of lithium metal batteries by replacing flammable organic liquid electrolytes. However, the practical application of SSEs is constrained by low ionic conductivity (∼10⁻⁴ S cm⁻¹) and deficient electrochemical stability. Herein, superior non-flammable solid polymer electrolytes (SPEs) are elaborately designed using an in situ polymerizable deep eutectic solvent (PDES). The synthesized amorphous poly(PDES) electrolyte, composed of lithium bis(trifluoromethane sulfonyl)imide, 2,2,2-trifluoroethyl acrylate, N,N′-methylenebisacrylamide, and succinonitrile, shows excellent interfacial contact with the lithium metal and cathode electrodes, showing high ionic conductivity (1.46 × 10⁻³ S cm⁻¹ at room temperature), high lithium ion transfer number (0.57), and good oxidation potential (5.36 V vs. Li⁺/Li). As a result, the constructed 4.4 V Li‖LiCoO₂ full batteries using the poly(PDES) electrolyte achieve a high reversible capacity of 142.5 mA h g⁻¹ and a superior retention rate of 88.9% after 200 cycles at 1.0C and the 4.6 V Li‖LiCoO₂ full batteries exhibit a specific capacity of 147.8 mA h g⁻¹ at 1.0C with a capacity retention of 86.8% after 150 cycles. This work provides a new method for designing high-safety SPEs and facilitating the practical application of high-voltage lithium metal batteries.