A Composite Polymer Electrolyte Protect Layer between Lithium and Water Stable Ceramics for Aqueous Lithium-Air Batteries

Abstract

The electrochemical properties of a composite polymer electrolyte consisting of polyethylene oxide (PEO)-lithium trifluoromethanesulfonylimide (LiTFSI) and poly(ethylene glycol) dimethyl ether (PEGDME) were examined as a protective layer between a lithium metal electrode and water-stable lithium ion-conducting glass ceramic of Li_1.35Ti_1.75Al_0.25P_0.9Si_0.1O₁₂. The lithium ion transport number was doubled and the lithium ion conductivity was enhanced from 1.3 × 10⁻⁴ for PEO₁₈LiTFSI to 3.8 × 10⁻⁴ S cm⁻¹ at 60°C by the addition of 18 wt% PEGDME. The lithium stripping and plating over-potentials for the Li/PEO₁₈LiTFSI-18 wt% PEGDME/LTAP/1M LiCl aqueous solution/Pt, air cell were 0.3 and 0.25 V at 1.5 mA cm⁻² and 60°C, respectively. Steady charge and discharge potentials for the Li/PEO₁₈LiTFSI-18 wt% PEGDME/LTAP/10 M LiCl-4 mM LiOH/Pt air cell were observed for 12 h at 1.0 mA cm⁻² and 60°C without short circuiting of the cell. Lithium dendrite formation at the lithium/PEO₁₈LiTFSI interface was suppressed by the addition of PEGDME.