Fructose‐Derived Hollow Carbon Nanospheres with Ultrathin and Ordered Mesoporous Shells as Cathodes in Lithium–Sulfur Batteries for Fast Energy Storage

Abstract

capacity (1675 mAh g −1 ) and energy density (2600 W h kg −1 ) of the batteries, as well as its abundant and economical source of sulfur. [1,2] Li-S batteries are particularly useful in fields that require high energy densities, such as portable electronics and electric vehicles. Unfortunately, despite the numerous advantages, the widespread, practical implementation of Li-S batteries has not been realized, as state-of-the-art Li-S batteries still suffer from poor performance in reversible capacity, cycling stability, and rate capability, which are closely related to the low electrical conductivity of sulfur species (S 8 , intermediate polysulfides, and Li 2 S, leading to poor rate capability), the facile dissolution of polysulfides in liquid electrolyte (leading to poor capacity and cycling stability), and the severe volume variation (≈80%) of the electrode (leading to severe electrode pulverization and poor cycling stability) during the charge-discharge process. [3,4] To address the abovementioned issues, a host that can provide rapid electron transfer, good electrolyte accessibility, and facile Li + diffusion was proposed to construct an effective conductive framework for Li-S battery cathodes. [4,5] In addition, as an ideal host for sulfur, this framework should also help suppress the formation of soluble sulfur intermediate species.Until now, a wide range of functional carbon materials with high specific areas and high porosities, such as carbon particles, carbon nanotubes, graphene, and 3D carbon frameworks, have been developed as hosts for sulfur reserve. [6][7][8][9][10][11] Since the energy density is directly related to the amount of sulfur in the electrode, the sulfur content in the electrode should be maximized. However, carbon/sulfur composites developed in early studies usually demonstrated low sulfur ratios (<50 wt%). [7,12] Hollow carbon spheres (HCS), with a vacant yolk and porous shell, are highly attractive hosts for sulfur because they offer far more volume for sulfur deposition/storage. [13,14] On the other hand, a hierarchically porous host can improve the sulfur utilization efficiency. Recently, progress in enhancing the high-rate performance and cycling stability of Li-S battery cathodes was made by applying HCS hosts in which a carbon shell had a tailored pore structure. [14,15] Hollow carbon nanospheres with diameters of ≈300 nm and ultrathin, ordered mesoporous shells (OP-HCS) are synthesized via the facile dualtemplate-assisted hydrothermal carbonization of eco-friendly, sustainable, and inexpensive fructose, in which ordered concave nanopore arrays with an average distance of 10-12 nm and a pore diameter of 4.37 nm are integrated into the balloon-like OP-HCS particles. Lithium-sulfur batteries with S/OP-HCS cathodes exhibit high sulfur utilization, excellent rate capabilities, and decent cycling stabilities. The S/OP-HCS cathode with 71 wt% sulfur demonstrates an excellent discharge capacity of 483 mAh g −1 at the ultrahigh current of 5 C with an overpotential of ≈0.1 V. The cathode a...

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