Manfang Chen

Honeycomb-like Nitrogen and Sulfur Dual-Doped Hierarchical Porous Biomass-Derived Carbon for Lithium–Sulfur Batteries

Honeycomb-like nitrogen and sulfur dual-doped hierarchical porous biomass-derived carbon/sulfur composites (NSHPC/S) are successfully fabricated for high energy density lithium-sulfur batteries. The effects of nitrogen, sulfur dual-doping on the structures and properties of the NSHPC/S composites are investigated in detail by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and charge/discharge tests. The results show that N, S dual-doping not only introduces strong chemical adsorption and provides more active sites but also significantly enhances the electronic conductivity and hydrophilic properties of hierarchical porous biomass-derived carbon, thereby significantly enhancing the utilization of sulfur and immobilizing the notorious polysulfide shuttle effect. Especially, the as-synthesized NSHPC-7/S exhibits high initial discharge capacity of 1204 mA h g-1 at 1.0 C and large reversible capacity of 952 mA h g-1 after 300 cycles at 0.5 C with an ultralow capacity fading rate of 0.08 % per cycle even at high sulfur content (85 wt %) and high active material areal mass loading (2.8 mg cm-2 ) for the application of high energy density Li-S batteries.

Enhancing the performance of lithium–sulfur batteries by anchoring polar polymers on the surface of sulfur host materials

Lithium–sulfur (Li–S) batteries are attracting intense interest due to their high theoretical energy density and relatively low cost, but their practical applications are still hindered by quick capacity decay owing to the polysulfide shuttle effect. Based on the first-principles calculations, it has been found that the oxygen-containing functional groups (hydroxyl and ether group) of Triton X-100 are able to carry out effective trapping of lithium polysulfides by strong Li–O interactions, demonstrating a feasible strategy to alleviate the shuttle effect. Therefore, herein we present a facile and scalable synthetic route to suppress the polysulfide shuttle effect and further improve the overall performance of Li–S batteries through anchoring inherently polar polymer Triton X-100 on the surface of carbon materials. The results show that the MAC/S composite delivers a high discharge capacity of 1432 mA h g−1 in the first cycle, a capacity retention of 76% after 50 cycles at a rate of 0.2C with an excellent coulombic efficiency of 95% and a reversible specific capacity of above 889 mA h g−1 after 100 cycles at a rate of 0.5C with a low capacity decay of 0.3% per cycle.

Synergetic Effects of Multifunctional Composites with More Efficient Polysulfide Immobilization and Ultrahigh Sulfur Content in Lithium–Sulfur Batteries

A high sulfur loading cathode is the most crucial component for lithium-sulfur batteries (LSBs) to obtain considerable energy density for commercialization applications. The major challenges associated with high sulfur loading electrodes are poor material utilization caused via the nonconductivity of the charged product (S) and the discharged product (Li2S), poor stability arisen from dissolution of lithium polysulfides (LiPSs) into most organic electrolytes and pulverization, and structural damage of the electrode caused by large volumetric expansion. A multifunctional synergistic composite enables ultrahigh sulfur content for advanced LSBs, which comprises the sulfur particle encapsulated with an ion-selective polymer with conductive carbon nanotubes and dispersed around Magnéli phase Ti4O7 (MS-3) by the bottom-up method. The ion-selective polymer provides a physical shield and electrostatic repulsion against the shuttling of polysulfides with negative charge, whereas it can permit the transmission of lithium ion (Li+) through the polymer membrane, and the carbon nanotubes twined around the sulfur promote electronic conductivity and sulfur utilization as well as strong chemical adsorption of LiPSs by means of Ti4O7. Because of this hierarchical construction, the cathode possesses a lofty final sulfur loading of 72% and large sulfur areal mass loading of 3.56 mg cm-2, which displays the large areal specific capacity of 4.22 mA h cm-2. In the same time, it can provide excellent cyclic performance with the corresponding capacity attenuation ratio of 0.08% per cycle at 0.5 C after 300 cycles. Especially, while sulfur areal mass loading is sharply enhanced to 5.11 mg cm-2, the MS-3 composite exhibits a large initial areal capacity of 5.04 mA h cm-2 and still keeps a high reversible capacity of 696 mA h g-1 at 300th cycle even at a 1.0 C. The design of high sulfur content cathodes is a viable approach for boosting practical commercialized application of LSBs.

Multifunctional Heterostructures for Polysulfide Suppression in High-Performance Lithium-Sulfur Cathode

The commercialization of lithium-sulfur (Li-S) batteries is greatly hindered due to serious capacity fading caused by the polysulfide shuttling effect. Optimizing the structural configuration, enhancing reaction kinetics of the sulfur cathode, and increasing areal sulfur loading are of great significance for promoting the commercial applications of Li-S batteries. Herein, the multifunctional polysulfide scavengers based on nitrogen, sulfur co-doped carbon cloth (DCC), which is supported by flower-like MoS2 (1T-2H) decorated with BaMn0.9 Mg0.1 O3 perovskite particle (PrNP) and carbon nanotubes (CNTs), namely, DCC@MoS2 /PrNP/CNTs, are delicately designed and synthesized. The physical confinement, chemical coupling, and catalysis conversion for active sulfur are achieved simultaneously in this polysulfide motif. Due to these merits, the as-fabricated self-supported DCC@MoS2 /PrNP/CNTs/S manifests an excellent reversible areal capacity of 4.75 mAh cm-2 with an ultrahigh sulfur loading of 5.2 mg cm-2 at the 50th cycle. The outstanding cycling stability is obtained upon 800 cycles with a large reversible capacity of 871 mAh g-1 and a negligible fading rate of 0.02% per cycle at a rate of 1.0 C, suggesting its promising prospects for the commercial success of high-performance Li-S batteries toward flexible electronic devices and energy storage equipment.