Single- Versus Dual-Ion UV-Cross-Linked Gel Polymer Electrolytes for Li–O₂ Batteries

Lithium–O₂ batteries represent one of the most appealing candidates for battery electric vehicles because of their remarkable theoretical high energy density, similar to fossil fuels. Solid polymer electrolytes represent a plausible solution to tackle some of the challenges associated with conventional liquid-based Li–O₂ batteries, including safety concerns. Herein, cross-linked robust gel polymer electrolytes (GPEs) based on poly­(ethylene glycol) dimethacrylate and tetraethylene glycol dimethyl ether as a plasticizer are prepared by rapid UV-photopolymerization. Both types of robust GPEs presented high ionic conductivity at room temperature (1.6 × 10^–4 and 1.4 × 10^–3 S·cm^–1 for single ion or dual ion, respectively). Both types of GPEs, single-ion and dual-ion lithium conductors, have been compared for the first time on Li–O₂ cells. First, their performance was investigated in symmetrical Li|Li cells. In this case, the dual-ion GPE showed outstanding behavior where the overpotential was <0.2 V versus Li⁰/Li⁺ for more than 40 h at a current density as high as ±1 mA·cm^–2. On the other hand, in the full Li–O₂ configuration, the single-ion GPE cell showed superior discharge capacity, up to 2.38 mA·h·cm^–2. Here, a dynamic discharge characterization technique is proposed as a method for evaluating the polarization effect in electrolytes during discharge in an easy, quantifiable, and reproducible manner.