A porous and flame-retardant rGO/PPTA modified PP composite separator suitable for high electrochemical performance and excellent security of lithium metal battery

Abstract

Thanks to their high energy density, small size, and light weight, lithium-metal batteries have been widely used over an extended period. However, lithium ions cannot be uniformly deposited, and their poor heat resistance hinders the practical application of lithium-metal batteries. Therefore, it is necessary to design a kind of separator with high electrolyte affinity and good heat resistance in order to improve the problem of a commercial separator. In this study, reduced graphene oxide (rGO) and polyphenylene terephthamide (PPTA) were combined in different ratios and coated onto one side of a commercial polypropylene (PP) separator using a feasible coating technique. A comparison of electrolyte absorptivity and flame retardancy revealed that the composite separator exhibited superior properties compared to those of a PP separator. The rGO₂/PPTA₃@PP separator with hierarchical porosity and flame-retardant properties, exhibited high ion conductivity (0.59 × 10⁻³ S cm⁻¹) and an improved lithium-ion transfer number (0.57) at room temperature. By using the composite separator in an LiFePO₄‖Li battery, the discharge specific capacity could still reach 125.6 mA h g⁻¹ even after 100 cycles under 1C. After undergoing a high–low temperature cycle, the average discharge specific capacity could remain 151 mA h g⁻¹ at 50 °C and 51 mA h g⁻¹ at −10 °C. In addition, after 1100 h cycles in the assembled Li‖Li symmetric battery, no obvious lithium dendrites appeared on the lithium metal surface, indicating that the composite separator could successfully inhibit the growth of lithium dendrites. This study presents a promising approach for the large-scale production of novel composite separators with high electrochemical performance and safety.