Coordination polymer-reinforced composite polymer electrolyte for all-solid-state Li-metal batteries

Composite polymer electrolytes (CPEs) have garnered significant interest due to their lightweight, flexible, and suitability for large-scale processing. However, current CPEs still face challenges such as unsatisfactory ionic conductivity (σ), low Li+ transference number (t+), and poor interfacial stability. This study presents the synthesis of a coordination polymer by coordinating Co2+ with terpyridine-end-capped polyethylene glycol (Co(tpy)-PEG). The resulting Co(tpy)-PEG-reinforced PEO-based CPE exhibits exceptional properties, including a high σ of 0.22 mS cm−1, large t+ of 0.75, and superior durability in both Li|Li (1400 h at 0.2 mA cm−2) and Li|LiFePO4 cells (70% capacity retention after 1000 cycles at 1C) at 60 °C, comparable to the best available CPEs. The incorporation of Co(tpy)-PEG filler plays a vital role in enhancing the σ by disrupting the PEO crystallinity and creating additional Li+ conducting pathways. Additionally, it can free Li+ to increase t+ through Lewis acid-base interactions between Co2+ and TFSI−/O atoms, as well as NO3− and Li+. Furthermore, Co(tpy)-PEG facilitates the formation of a stable multicomponent solid electrolyte interphase containing beneficial Li2Sx, LiF, and Li3N. This work introduces a promising strategy for designing and preparing multifunctional fillers capable of simultaneously reinforcing the σ, t+, and interfacial stability of CPEs.