A mechano-integrated gradient electrolyte for long-cycling solid-state lithium metal batteries

Overcoming interfacial mechano-electrochemical failure remains a fundamental challenge in solid-state lithium metal batteries, where polymers offer conformal interfacial contact but suffer from low ionic conductivity, while oxides/sulfides provide high ionic conductivity but face severe interfacial issues. Here we show a mechano-integrated gradient electrolyte based on a hydrogen-bonded polyurethane matrix with dual chain extenders. The polyurethane matrix exhibits high viscoelasticity (>5000% fracture strain) and self-healing, allowing high filler loading and continuous triphasic lithium-ion percolation networks. A spatially graded Li_1.3Al_0.3Ti_1.7(PO₄)₃ architecture (10-100 wt%) decouples interfacial requirements: conformal contact with lithium metal negative electrode, high ionic conductivity (~10^-4 S cm^-1), and an electrochemical stability window up to 4.9 V. The homologous polymer framework eliminates chemo-mechanical degradation while providing mechanical strength (>80 MPa) and solution processability. This integrated design suppresses interfacial delamination and dendrite growth (>7500 h of stable lithium plating/stripping), and mitigates positive electrode degradation (74% capacity retention after 1000 cycles in Li | |LiFePO₄ cells at 0.5 C and stable operation in stack-pressure-free NCM811 pouch cells). This work provides a scalable platform for high-energy-density, long-lifespan solid-state lithium metal batteries.