Authors

Abstract

Poly(ethylene oxide) (PEO) was the first lithium-ion conducting polymer developed 50 years ago and is still the most popular electrolyte matrix for solid-state lithium metal batteries. While many studies focus on increasing PEO ionic conductivity through doping with Li salts, little work has addressed using PEO and Li to generate Li + -conducting species in-situ. Here, reaction between PEO thin films and Li leads to ionic conductivity largely from Li + , in contrast to the case of added salts where the anion contribution dominates. Electrochemical impedance spectroscopy shows the ionic conductivity increases up to three orders of magnitude (from 10 -7 to 10 -4 S cm -1 ) when contacted with Li at elevated temperature due to the reduction of ether bonds, which produces lithium alkoxides that are responsible for Li + transport. Density functional theory analysis confirms this mechanism as thermodynamically favorable. X-ray photoelectron spectroscopy shows the presence of organolithium species and Li2O, which are responsible for propagating reactions with PEO and forming an electronically insulating layer at the PEO-Li interface that halts further reaction, respectively. This work clarifies the underlying mechanisms of Li-polymer electrolyte reactions and presents new pathways for in-situ Li + -doping of polymer electrolytes.