Lithiated Nafion membrane as a single-ion conducting polymer electrolyte in lithium batteries

Single lithium-ion conducting polymer electrolytes are promising candidates for next generation safer lithium batteries. In this work, Li⁺-conducting Nafion membranes have been synthesized by using a novel single-step procedure. The Li-Nafion membranes were characterized by means of small-wide angle X-ray scattering, infrared spectroscopy and thermal analysis, for validating the proposed lithiation method. The obtained membranes were swollen in different organic aprotic solvent mixtures and characterized in terms of ionic conductivity, electrochemical stability window, lithium stripping-deposition ability and their interface properties versus lithium metal. The membrane swollen in ethylene carbonate:propylene carbonate (EC:PC, 1:1 w/w) displays good temperature-activated ionic conductivities (σ ≈ 5.5 × 10^–4 S cm⁻¹ at 60 °C) and a more stable Li-electrolyte interface with respect to the other samples. This Li-Nafion membrane was tested in a lithium-metal cell adopting LiFePO₄ as cathode material. A specific capacity of 140 mAhg⁻¹, after 50 cycles, was achieved at 30 °C, demonstrating the feasibility of the proposed Li-Nafion membrane.