Strategically tailored polyethylene separator parameters enable cost-effective, facile, and scalable development of ultra-stable liquid and all-solid-state lithium batteries

Abstract

All-solid-state lithium batteries hold tremendous potential for next-generation batteries due to their exceptional theoretical energy density and intrinsic safety advantages. The forthcoming solid-state batteries employing solid electrolytes are widely expected to adopt a separator-free design strategy. However, porous separators, distinguished by their mechanical robustness, economic viability, and manufacturing scalability, present a feasible solution to address the industrialization challenges faced by solid electrolytes. Herein, a multifunctional polyethylene separator (denoted as S7540) was rationally designed through systematic optimization of structural parameters and anisotropic characteristics. Notably, the developed S7540 separator achieves an optimal balance between ultra-high porosity and broad pore size spectrum while maintaining superior mechanical integrity, enabling seamless compatibility across both liquid and solid state battery production lines. When implemented in Li/LiCoO₂ configurations, the S7540 separator shows long-term cycling stability under high rate (10C) and high areal capacity (∼6.2 mAh cm⁻²), significantly outperforming the traditional commercial separator. Additionally, the S7540 architecture boosts mechanical properties of polymer-oxide solid electrolytes by approximately 50 times, demonstrating excellent tensile strength (42.1 MPa) and great cyclability (>6000 h) in Li/Li symmetric cells. All-solid-state Li/LiFePO₄ cells exhibit outstanding capacity retention rates of 90.7 % and 81.3 % after 500 and 700 cycles at 0.5C, respectively. Importantly, the solvent-free S7540-based electrolyte demonstrates exceptional thermal stability with negligible mass loss (<0.3 %) during prolonged 120°C exposure (6 h) and minimal decomposition below 250°C. This work emphasizes the crucial relationship between separator structure optimization and battery performance metrics, while establishing a cost-effective and scalable manufacturing pathway for practical solid electrolyte implementation across various battery systems.