Organic-Inorganic Dual-Network Composite Separators for Lithium Metal Batteries.

Abstract

The suboptimal ionic conductivity of commercial polyolefin separators exacerbates uncontrolled lithium dendrite formation, deteriorating lithium metal battery performance and posing safety hazards. To address this challenge, a novel organic-inorganic composite separator designed is prepared to enhance ion transport and effectively suppress dendrite growth. This separator features a thermally stable, highly porous poly(m-phenylene isophthalamide) (PMIA) electrospun membrane, coated with ultralong hydroxyapatite (HAP) nanowires that promote "ion flow redistribution." The synergistic effects of the nitrogen atoms in PMIA and the hydroxyl groups in HAP hinder anion transport while facilitating efficient Li⁺ conduction. Meanwhile, the optimized unilateral pore structure ensures uniform ion transport. These results show that the 19 µm-thick HAP/PMIA composite separator achieves remarkable ionic conductivity (0.68 mS cm^-1) and a high lithium-ion transference number (0.51). Lithium symmetric cells using HAP/PMIA separators exhibit a lifespan exceeding 1000 h with low polarization, significantly outperforming commercial polypropylene separators. Furthermore, this separator enables LiFePO₄||Li cells to achieve an enhanced retention of 97.3% after 200 cycles at 1 C and demonstrates impressive rate capability with a discharge capacity of 72.7 mAh g^-1 at 15 C.