Lithium Stable Flexible Polyethylene Oxide-Based Composite Electrolyte with High Lithium-Ion Conducting NASICON-Type Solid Electrolyte for Lithium Batteries

Solid lithium-ion conducting polymer electrolytes are attractive candidates for battery applications because they are flexible and less flammable, and can be easily prepared as large-sized thin films. However, the room temperature conductivity of conventional polymer electrolytes is relatively low, and detrimental lithium dendrite formation is observed at high current density. In this study, a composite polymer electrolyte of polyethylene oxide (PEO) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and a high lithium-ion conducting NASICON-type solid electrolyte of Li1.4Al0.4Ge0.2Ti1.4(PO₄)₃-0.75 wt.% LiCl·H₂O (LAGTP-LiCl·H₂O) was developed. The electrical conductivity of PEO₁₈LiTFSI-5 wt.% LAGTP-LiCl·H₂O was 1.2 × 10⁻⁵ S cm⁻¹ at 25°C. The cell resistance of 10000 Ω for the Li/PEO₁₈LiTFSI-5 wt.% LAGTP-LiCl·H₂O/Li cell was decreased to 1700 Ω by the addition of a small amount of liquid plasticizer, tetraethylene glycol dimethyl ether (G4), and 1,2-dimethoxyethane (DME). The Li/(PEO₁₈LiTFSI-2G4)-5 wt.% LAGTP-LiCl·H₂O -10 wt.% DME/LiFePO₄ cell was successfully cycled at room temperature and 0.2 mA cm⁻².