Almost-solid-state electrolyte with quadruple-hydrogen-bond-based semi-interpenetrating network for lithium metal batteries

Abstract

Owing to their high stability and leakage resistance, solid-state electrolytes are well suited for use in lithium metal batteries (LMBs). However, the well-established poly(ethylene oxide)-based solid polymer electrolytes (SPEs) have a limited application scope because of their low room-temperature ionic conductivity and Li⁺ transport number. Herein, 2-ureido-4[1H]pyrimidinone-capped poly(ethylene glycol) was used as a solid plasticiser that interacted with the polymer matrix to expand the amorphous regions therein and formed quadruple hydrogen bonds as dynamic physical cross-links to afford a SPE with a semi-interpenetrating polymer network. The synergistic transference of Li⁺ by the solid plasticizer and polymer backbone resulted in a high Li⁺ transport number (0.63) and ionic conductivity (6.21 × 10⁻⁵ S cm⁻¹ at 25 °C). The symmetric LMBs assembled using this SPE could be stably cycled for >1800 h, while the corresponding Li‖LiFePO₄ battery could be stably operated for >300 cycles at 0.2 C, exhibiting a high capacity retention of 78.1%. Thus, this study provides a new strategy for improving the performance of poly(ethylene oxide)-based solid-state electrolytes.