Facile Synthesis of Sulfur-Polypyrrole as Cathodes for Lithium-Sulfur Batteries

Interfacial Engineering and Coupling of MXene/Reduced Graphene Oxide/C3 N4 Aerogel with Optimized d-Band Center as a Free-Standing Sulfur Carrier for High-Performance Li-S Batteries

To overcome the shuttle effect and improve the energy density of Li-S batteries, developing free-standing sulfur carriers with high capture and catalytic effect towards polysulfides is an effective strategy. Herein, a MXene/reduced graphene oxide/C3 N4 aerogel (MG/C3 N4 ) with three-dimensional architecture prepared through low-temperature hydrothermal approach followed by thermal treatment is used as sulfur carrier for free-standing cathode of Li-S batteries. In the MG/C3 N4 , MXene and rGO construct a highly conductive framework, and the MXene nanosheets offer chemical capture and catalytic activity towards lithium polysulfides, in favor of good cycling stability. The introduction of g-C3 N4 further enhances the reactivity of C-Ti-N at the hetero-interface by engineering the electronic state of Ti atoms, leading to the optimized metal d-band for expediting the multistep conversion of sulfur electrochemistry. Therefore, the free-standing sulfur cathode with MG/C3 N4 carrier achieves excellent performance with a capacity of 1315.6 mAh g-1 at 0.2 C and a capacity retention of 97.5% after 100 cycles as well as superior rate capability with 1167.4 mAh g-1 at 2 C. Even at a high sulfur loading of 4.92 mg cm-2 , the cathode remains 940.3 mAh g-1 (4.62 mAh cm-2 ) after 200 cycles, indicating its promising potential for achieving high-performance Li-S batteries.

Hierarchically Porous SnO2 Nanoparticle-Anchored Polypyrrole Nanotubes as a High-Efficient Sulfur/Polysulfide Trap for High-Performance Lithium-Sulfur Batteries

Conductive supports could improve the electrical conductivity of the electrode in lithium-sulfur (Li-S) batteries but suffer from the shuttle effect originated from the polysulfide dissolution, while the hydrophilic metal oxides could avoid the shuttle effect but with poor conductivity. Herein, a facile approach was developed to fabricate hierarchically porous tin oxide (SnO₂) nanoparticle-anchored tubular polypyrrole (T-PPy) as a sulfur host, in order to integrate the advantages of conductive supports and metal oxides but overcome their shortcomings. In the unique structure, the T-PPy nanotubes acted as a conductive network to not only improve the electrical conductivity of cathodes but also accommodate the volume expansion of the sulfur cathode during cycling as well as relatively confine the polysulfide diffusion, while the SnO₂ nanoparticles served as a high-efficient polysulfide trap to mitigate the shuttle effect due to the chemical bond between SnO₂ and polysulfides. Moreover, the hierarchically porous structure and therefore large surface area of the proposed S/(T-PPy)@SnO₂ cathode were favorable for the accommodation of sulfur and lithium sulfides. Consequently, S/(T-PPy)@SnO₂ with 64.7% sulfur mass content exhibited excellent cyclic stability with a decay rate of only 0.05% per cycle along with 500 cycles at 1 C, rate capability of 383.7 mA h/g at 5 C, and Coulombic efficiency above 90%, outstanding among most of the reported PPy-based sulfur cathodes and PPy-based ternary sulfur cathodes.

Application Progress of Polyaniline, Polypyrrole and Polythiophene in Lithium-Sulfur Batteries

With the urgent requirement for high-performance rechargeable Li-S batteries, besides various carbon materials and metal compounds, lots of conducting polymers have been developed and used as components in Li-S batteries. In this review, the synthesis of polyaniline (PANI), polypyrrole (PPy) and polythiophene (PTh) is introduced briefly. Then, the application progress of the three conducting polymers is summarized according to the function in Li-S batteries, including coating layers, conductive hosts, sulfur-containing compounds, separator modifier/functional interlayer, binder and current collector. Finally, according to the current problems of conducting polymers, some practical strategies and potential research directions are put forward. We expect that this review will provide novel design ideas to develop conducting polymer-containing high-performance Li-S batteries.

MOF-derived NiO–NiCo2O4@PPy hollow polyhedron as a sulfur immobilizer for lithium–sulfur batteries

A MOF-derived NiO–NiCo₂O₄@PPy hollow polyhedron is prepared as a sulfur host to effectively enhance cell performance. S/NiO–NiCo₂O₄@PPy displays a high initial discharge capacity of 963 mA h g⁻¹ with a high initial coulombic efficiency of 95.2% at 0.2C.

Advances in Cathode Materials for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) represent a promising energy storage technology, and they show potential for next-generation high-energy systems due to their high specific capacity, abundant constitutive resources, non-toxicity, low cost, and environment friendliness. Unlike their ubiquitous lithium-ion battery counterparts, the application of LSBs is challenged by several obstacles, including short cycling life, limited sulfur loading, and severe shuttling effect of polysulfides. To make LSBs a viable technology, it is very important to design and synthesize outstanding cathode materials with novel structures and properties. In this review, we summarize recent progress in designs, preparations, structures, and properties of cathode materials for LSBs, emphasizing binary, ternary, and quaternary sulfur-based composite materials. We especially highlight the utilization of carbons to construct sulfur-based composite materials in this exciting field. An extensive discussion of the emerging challenges and possible future research directions for cathode materials for LSBs is provided.

Facile one-pot synthesis of well-defined coaxial sulfur/polypyrrole tubular nanocomposites as cathodes for long-cycling lithium-sulfur batteries

Well-defined core-shell structured coaxial sulfur/polypyrrole tubular nanocomposites, polypyrrole nanotubes wrapped by uniform rough sulfur layers, were fabricated as Li-S battery cathodes via a facile one-pot method. In the designed structure, the polypyrrole backbone can facilitate the charge transport and also restrain the soluble polysulfide diffusion, while the active sulfur layer can efficiently react with Li+ assisted by the PPy nanotubes, and the lithium polysulfides can be massively trapped by the PPy nanotubes during charge-discharge processes. The as-prepared coaxial sulfur/polypyrrole tubular nanocomposites with a sulfur loading of 53.3% exhibited a high initial discharge specific capacity of 1117 mA h g-1 with a remarkable cycling stability, retaining 692 mA h g-1 and 525 mA h g-1 after 200 cycles at a current density of 0.2C and 1C, respectively. Moreover, they expressed an excellent rate capability performance, maintaining 470 mA h g-1 at a high current density of 2C.