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

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 Li1.35Ti1.75Al0.25P0.9Si0.1O12. 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.