Bifunctional LiI additive for poly(ethylene oxide) electrolyte with high ionic conductivity and stable interfacial chemistry

The development of polymer-based solid-state batteries is severely limited by the low ionic conductivity of solid polymer electrolyte and the instable interface between polymer electrolyte and Li-metal anode. In this work, lithium iodide (LiI) as a bifunctional additive was introduced into the poly(ethylene oxide) (PEO)-based electrolyte to improve the ionic conductivity and to construct a stable interphase at the Li/PEO interface. I anions offer a strong electrostatic interaction with hydrogen atoms on PEO chains (H-PEO) and forming massive I-H bonds that cross-link PEO chains, decrease crystallinity of PEO, and thus improve Li+ interchain transport. In addition, LiI participates in the formation of an inorganic-rich interphase layer, which decreases the energy barrier of Li+ transport across the interface and thus inhibits the growth of lithium dendrites. As a result, the composite PEO electrolyte with 2 wt% LiI (PEO-2LiI) presents a very high ionic conductivity of 2.1 x 10(-4) S cm(-1) and a critical current density of 2.0 mA cm(-2) at 45 degrees C. Li symmetric cell with this PEO-2LiI electrolyte exhibits a long-term cyclability over 600 h at 0.2 mA cm(-2). Furthermore, solid-state LiFePO4 and LiNi(0.8)Mn(0.4)Co(0)(.1)o(2) batteries with the PEO-2LiI electrolyte show an impressive electrochemical performance with outstanding cycling stability and rate capability at 45 degrees C. (C) 2022 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

This study successfully improves the ionic conductivity and interface stability between the polymer electrolyte and Li-metal anode in polymer-based solid-state batteries by introducing lithium iodide (LiI) as an additive.