Robust ion-rectifying polymer electrolyte membrane for high-rate solid-state lithium metal batteries

The uncontrolled dendrite growth and poor rate performance originating from crystallization-induced anisotropic ion transport and insufficient mechanical strength of solid polymer electrolytes (SPE) have significantly impeded the practical application of high-rate solid-state lithium metal batteries. Herein, we present a robust ion-rectifying PEO-based SPE membrane by incorporating titanium-oxo clusters (TOC) composed of a diameter of 2.69 nm and a height of 1.04 nm rigid backbone and hairy PEG chains into PEO-LiN(CF₃SO₂)₂ (LiTFSI) electrolyte, denoted as PEO-TOC membrane. This membrane realizes dendrite-free lithium metal deposition where TOC serves as a rhecology-tuning (by reducing crystallinity) and anion-trapping (through Lewis acid-base interactions) agent, thus achieving an ion-rectifying effect in the electrolyte membrane. Consequently, the rapid and homogeneous Li⁺ flux is achieved, resulting in a high ionic conductivity of 5.5 × 10⁻⁵ S cm⁻¹ at 30 °C and Li⁺ transference number of 0.51. Furthermore, the rigid backbone enables a robust compressive strength of 940 MPa for dendrite suppression. As a result, the robust ion-rectifying PEO-TOC membrane endows the Li-LFP cells with high-rate performance, achieving 111.9 mAh g⁻¹ at 3.5 C, and good cycling performance of 92.9% capacity retention over 250 cycles at 1 C, which routine SPE hardly fulfills with anisotropic Li⁺ flux and mechanical properties.