Graphene-based Fe-coordinated framework porphyrin as an interlayer for lithium–sulfur batteries

Abstract

Lithium–sulfur (Li–S) batteries are deemed to be one of the most promising energy storage systems because of their high energy density, low cost, and environmental benignancy. However, existing drawbacks including the shuttling of intermediate lithium polysulfides (LiPSs), the insulating nature of sulfur and lithium sulfides, and the considerable volume change of the sulfur cathode result in low sulfur utilization and rapid capacity fading. Herein, graphene-based iron-coordinated framework porphyrin (G@POF-Fe) is proposed to fabricate multi-functional separators to retard these obstacles. Benefiting from the superior electrical conductivity of graphene and favorable chemisorption of iron-coordinated porphyrin, the as-obtained G@POF-Fe interlayer can simultaneously facilitate the charge transport, suppress the LiPS shuttling, and buffer the volume expansion. With these advantages, Li–S batteries with the G@POF-Fe interlayers deliver an outstanding rate capability (957 and 830 mA h g⁻¹ at 1 and 2C, respectively), impressive cycling stability (a high initial capacity of 1065 mA h g⁻¹, retaining 671 mA h g⁻¹ after 500 cycles at 0.5C), and excellent high-sulfur-loading performance (5.2 mA h cm⁻² with a sulfur loading of 6.54 mg cm⁻² for 250 cycles) even at high current densities. The framework porphyrin serves as a versatile material to precisely regulate electrical conductivity and polysulfide affinity at a molecular lever, which enriches the interface design strategies for high-performance Li–S batteries.