Structural and Surfacial Modification of Carbon Nanofoam as an Interlayer for Electrochemically Stable Lithium-Sulfur Cells

Porous Carbon Interlayer Derived from Traditional Korean Paper for Li-S Batteries

A carbonized interlayer effectively helps to improve the electrochemical performance of lithium-sulfur (Li-S) batteries. In this study, a simple and inexpensive carbon intermediate layer was fabricated using a traditional Korean paper called "hanji". This carbon interlayer has a fibrous porous structure, with a specific surface area of 91.82 m2 g-1 and a BJH adsorption average pore diameter of 26.63 nm. The prepared carbon interlayer was utilized as an intermediary layer in Li-S batteries to decrease the charge-transfer resistance and capture dissolved lithium polysulfides. The porous fiber-shaped carbon interlayer suppressed the migration of polysulfides produced during the electrochemical process. The carbon interlayer facilitates the adsorption of soluble lithium polysulfides, allowing for their re-utilization in subsequent cycles. Additionally, the carbon interlayer significantly reduces the polarization of the cell. This simple strategy results in a significant improvement in cycle performance. Consequently, the discharge capacity at 0.5 C after 150 cycles was confirmed to have improved by more than twofold, reaching 230 mAh g-1 for cells without the interlayer and 583 mAh g-1 for cells with the interlayer. This study demonstrates a simple method for improving the capacity of Li-S batteries by integrating a functional carbon interlayer.

Carbon nanotube-embedded hollow carbon nanofibers as efficient hosts for advanced lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have attracted great research attention because of their high energy density and low cost. However, shuttling effects of polysulfides and insulation from elemental sulfur hinder their practical application. Herein, we report hollow carbon nanofibers filled with carbon nanotubes (denoted as HCNF/CNT) as host materials for sulfur to mitigate the shuttling behavior and improve the kinetics of insulative sulfur. The as-prepared HCNF/CNT with nano-conductive domains in the hollow carbon nanofibers enables high loading and efficient utilization of sulfur. Owing to their unique structural superiority, the sulfur-encapsulated HCNF/CNT cathode materials for Li-S batteries deliver excellent electrochemical performance, including high specific capacity of 1156 mA h g^-1 at 0.2 C, good rate performance and cycling stability with a capacity retention of 77.2% after 200 cycles at 2 C. Such a unique structure can provide inspiration for the rational structural design of carbon materials as hosts for high performance Li-S batteries.

Electrochemically Stable Rechargeable Lithium–Sulfur Batteries Equipped with an Electrospun Polyacrylonitrile Nanofiber Film

The high theoretical charge-storage capacity and energy density of lithium–sulfur batteries make them a promising next-generation energy-storage system. However, liquid polysulfides are highly soluble in the electrolytes used in lithium–sulfur batteries, which results in irreversible loss of their active materials and rapid capacity degradation. In this study, we adopt the widely applied electrospinning method to fabricate an electrospun polyacrylonitrile film containing non-nanoporous fibers bearing continuous electrolyte tunnels and demonstrate that this serves as an effective separator in lithium–sulfur batteries. This polyacrylonitrile film exhibits high mechanical strength and supports a stable lithium stripping and plating reaction that persists for 1000 h, thereby protecting a lithium-metal electrode. The polyacrylonitrile film also enables a polysulfide cathode to attain high sulfur loadings (4–16 mg cm−2) and superior performance from C/20 to 1C with a long cycle life (200 cycles). The high reaction capability and stability of the polysulfide cathode result from the high polysulfide retention and smooth lithium-ion diffusion of the polyacrylonitrile film, which endows the lithium–sulfur cells with high areal capacities (7.0–8.6 mA·h cm−2) and energy densities (14.7–18.1 mW·h cm−2).

Sustainable Synthesis of Sulfur-Single Walled Carbon Nanohorns Composite for Long Cycle Life Lithium-Sulfur Battery

Lithium-sulfur batteries are considered one of the most appealing technologies for next-generation energy-storage devices. However, the main issues impeding market breakthrough are the insulating property of sulfur and the lithium-polysulfide shuttle effect, which cause premature cell failure. To face this challenge, we employed an easy and sustainable evaporation method enabling the encapsulation of elemental sulfur within carbon nanohorns as hosting material. This synthesis process resulted in a morphology capable of ameliorating the shuttle effect and improving the electrode conductivity. The electrochemical characterization of the sulfur-carbon nanohorns active material revealed a remarkable cycle life of 800 cycles with a stable capacity of 520 mA h/g for the first 400 cycles at C/4, while reaching a value around 300 mAh/g at the 750th cycle. These results suggest sulfur-carbon nanohorn active material as a potential candidate for next-generation battery technology.