Siloxane-type single-ion conductors enable composite solid polymer electrolyte membranes with fast Li+ transporting networks for dendrite-proof lithium-metal batteries

Solid polymer electrolytes (SPEs) significantly improve the operational safety of lithium-metal batteries (LMBs) by replacing the flammable liquid electrolytes, but still suffer from key limitations including low ionic conductivities, inferior lithium-ion transference numbers (tLi+), and poor mechanical properties. Herein, a novel poly (ethylene oxide) (PEO)-based composite electrolyte, with a semi-interpenetrating polymer network, is fabricated via in-situ cross-linking siloxane-type single-ion conductors (SICs) in PEO SPEs by one-step sol–gel method, enabling they simultaneously achieve the enhanced electrochemical and physicochemical properties. Incorporating a thermodynamically compatible SIC network not only reduces the crystallization of PEO matrix while facilitating the segmental relaxation of polymer chains, but also contributes to dissociating Li-salt and forming a three-dimensional conducting network for fast Li-ion transport. Thus, the resulting composite SPEs exhibit higher ionic conductivities (1.10 × 10−5 S cm−1 at 25 °C and 1.41 × 10−4 S cm−1 at 60 °C), tLi+ (0.52), and electrochemical window stability (4. 59 V) than pure PEO SPEs. Furthermore, this stable SIC networks can also enhance the mechanical performance and thermal stability of the composite SPEs. Thanks to these merits, the composite SPEs show the significant feasibility to regulate Li deposition and suppress the growth of Li dendrites, affording excellent stability and compatibility with Li metal. As a result, the Li/Li symmetrical cells using the composite SPEs show excellent cycling performances without an evident polarization enlargement for more than 900 h. The LiFePO4/Li batteries also achieve a remarkable capacity of 132.8 mA g−1 at 1C and exhibit impressive cycling abilities with 91.9% retention over 250 cycles. This study provides a promising concept for developing advanced composite SPEs for potential application in solid-state dendrite-free LMBs.