Facilitation of lithium polysulfides adsorption by nitrogen doped carbon nanofibers with 3D interconnected pore structures for high-stable lithium-sulfur batteries

A Review of Electrospun Carbon-Based Nanofibers Materials used in Lithium-Sulfur Batteries

Commercial lithium-ion batteries are gradually approaching their theoretical specific energy, which cannot meet the fast-growing energy storage demands. Lithium-sulfur (Li-S) batteries are anticipated to supersede lithium-ion batteries as the next-generation energy storage system owing to their high atheoretical specific capacity (1675 mAh g-1) and energy density (2600 Wh kg-1). Nonetheless, Li-S batteries encounter several challenges, including the inadequate conductivity of sulfur and lithium sulfide, sulfur's volume expansion, and the shuttle effect of lithium polysulfides, all of which significantly impact the practical utilization of Li-S batteries. Electrospun carbon-based nanofibers can simultaneously resolve these issues with their economical preparation, distinctive nanostructure, and exceptional flexibility. This review presents the most recent research findings on electrospun carbon-based nanofibers materials serving as sulfur hosts and interlayer components in Li-S batteries. We analyzed the impact of the material's structural design on the performance of Li-S batteries and the relative underlying mechanism. Finally, the current challenges and issues faced by carbon-based nanofibers composites in the application of Li-S batteries are summarized, and the future development trajectory are outlined.

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.

A Full Li-S Battery with Ultralow Excessive Li Enabled via Lithiophilic and Sulfilic W2 C Modulation

The practical application of Li-S batteries demands low cell balance (Li_capacity /S_capacity ), which involves uniform Li growth, restrained shuttle effect, and fast redox reaction kinetics of S species simultaneously. Herein, with the aid of W₂ C nanocrystals, a freestanding 3D current collector is applied as both Li and S hosts owing to its lithiophilic and sulfilic property. On the one hand, the highly conductive W₂ C can reduce Li nucleation overpotentials, thus guiding uniform Li nucleation and deposition to suppress Li dendrite growth. On the other hand, the polar W₂ C with catalytic effect can enhance the chemisorption affinity to lithium polysulfides (LiPSs) and guarantee fast redox kinetics to restrain S species in cathode region and promote the utilization of S. Surprisingly, a full Li-S battery with ultralow cell balance of 1.5:1 and high sulfur loading of 6.06 mg cm^-2 shows obvious redox plateaus of S and maintains high reversible specific capacity of 1020 mAh g^-1 (6.2 mAh cm^-2 ) after 200 cycles. This work may shed new sights on the facile design of full Li-S battery with low excessive Li supply.

Lotus Root-Like Nitrogen-Doped Carbon Nanofiber Structure Assembled with VN Catalysts as a Multifunctional Host for Superior Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) are regarded as one of the most promising energy-recycling storage systems due to their high energy density (up to 2600 Wh kg^-1), high theoretical specific capacity (as much as 1672 mAh g^-1), environmental friendliness, and low cost. Originating from the complicated redox of lithium polysulfide intermediates, Li-S batteries suffer from several problems, restricting their application and commercialization. Such problems include the shuttle effect of polysulfides (Li₂S_x (2 < x ≤ 8)), low electronic conductivity of S/Li₂S/Li₂S₂, and large volumetric expansion of S upon lithiation. In this study, a lotus root-like nitrogen-doped carbon nanofiber (NCNF) structure, assembled with vanadium nitride (VN) catalysts, was fabricated as a 3D freestanding current collector for high performance LSBs. The lotus root-like NCNF structure, which had a multichannel porous nanostructure, was able to provide excellent (ionically/electronically) conductive networks, which promoted ion transport and physical confinement of lithium polysulfides. Further, the structure provided good electrolyte penetration, thereby enhancing the interface contact with active S. VN, with its narrow resolved band gap, showed high electrical conductivity, high catalytic effect and polar chemical adsorption of lithium polysulfides, which is ideal for accelerating the reversible redox kinetics of intermediate polysulfides to improve the utilization of S. Tests showed that the VN-decorated multichannel porous carbon nanofiber structure retained a high specific capacity of 1325 mAh g^-1 after 100 cycles at 0.1 C, with a low capacity decay of 0.05% per cycle, and demonstrated excellent rate capability.

A novel biomimetic dandelion structure-inspired carbon nanotube coating with sulfur as a lithium-sulfur battery cathode

Lithium-sulfur (Li-S) batteries have attracted considerable attention because of their high theoretical energy density. However, poor conductivity and a large volume change in S during cycling, together with a shuttle effect of polysulfides, severely restrict the battery performance, and remain a great challenge. Herein, inspired by a natural dandelion structure, we present a novel biomimetic S-coated carbon nanotube composite consisting of dandelion-like three-dimensional carbon nanotubes coated with S particles on the surface. Carbon nanotubes provide high-speed electron transfer pathways for S during cycling, while the special dandelion-like morphology provides a suitable environment for accommodating the volume change in S upon charge-discharge. The dandelion-like S-coated carbon nanotube-based Li-S batteries exhibit a stable capacity exceeding 760 mAh g^-1 after 500 cycles at 0.1 C, along with a Coulombic efficiency as high as 99.9%. Even under repeated rounds of rate-performance measurements, and cycling at different charge versus discharge rates, the batteries retain high capacities and good recovery capabilities. In addition, the proportion of capacitive contribution in the overall capacity is high, indicating a good reversible capacity provided by the composite.