Multi-Functional Bilayer Carbon Structures with Micrometer-Level Physical Encapsulation as a Flexible Cathode Host for High-Performance Lithium-Sulfur Batteries

Abstract

With the exceptional merits of high energy density, low cost, and environmental friendliness, lithium-sulfur batteries are considered to be one of the most promising next-generation flexible rechargeable batteries. However, the notorious “shuttle effect” has seriously hindered their practical applications. Herein, a strategy for designing multi-functional bilayer carbon structures is proposed, specifically, by employing a micrometer-thick graphene nanoflowers (GF) layer to encapsulate a micrometer-scale hybrid network skeleton composed of metallic Co and carbon nanotubes (CNT) as a flexible sulfur cathode host (Co/CNT@GF). Beneficial from the merits of chemical adsorption and volume expansion mitigation from the internal skeleton as well as the micrometer-level physical domain confinement by the external GF layer, the developed host could effectively block, storage, and chemical trap the lithium polysulfides. Due to the synergistic effect of these functions, the Co/CNT@GF-S delivers a superior discharge capacity of 799 mAh g -1 with a decay rate as low as 0.08% per cycle after 400 cycles at 1 C. Even at a high sulfur loading of 8.16 mg cm -2 , the average discharge capacity is as high as 5.05 mAh cm -2 in 100 cycles. This work does not only contribute to the rational design of multi-functional bilayer structures but also offers a novel design method for the commercialization of flexible lithium-sulfur batteries with high-energy-density.

Keywords: metal-organic frameworks, graphene nanoflower, plasma-enhanced chemical vapor deposition, synergistic effects, lithium polysulfides, Li-S batteries