In situ self-boosting catalytic synthesizing free-standing N, S rich transition metal sulfide/hierarchical CNF-CNT architectures enable high-performance lithium-sulfur batteries

Nickel and nickel oxide nanoparticle-embedded functional carbon nanofibers for lithium sulfur batteries

Lithium-sulfur (Li-S) batteries are attracting tremendous attention owing to their critical advantages, such as high theoretical capacity of sulfur, cost-effectiveness, and environment-friendliness. Nevertheless, the vast commercialisation of Li-S batteries is severely hindered by sharp capacity decay upon operation and shortened cycle life because of the insulating nature of sulfur along with the solubility of intermediate redox products, lithium polysulfides (LiPSs), in electrolytes. This work proposes the use of multifunctional Ni/NiO-embedded carbon nanofibers (Ni/NiO@CNFs) synthesized by an electrospinning technique with the corresponding heat treatment as promising free-standing current collectors to enhance the kinetics of LiPS redox reactions and to provide prolonged cyclability by utilizing more efficient active materials. The electrochemical performance of the Li-S batteries with Ni/NiO@CNFs with ∼2.0 mg cm-2 sulfur loading at 0.5 and 1.0C current densities delivered initial specific capacities of 1335.1 mA h g-1 and 1190.4 mA h g-1, retrieving high-capacity retention of 77% and 70% after 100 and 200 cycles, respectively. The outcomes of this work disclose the beneficial auxiliary effect of metal and metal oxide nanoparticle embedment onto carbon nanofiber mats as being attractively suited up to achieve high-performance Li-S batteries.

Cobalt-Carbon nanotubes supported on V2O3 nanorods as sulfur hosts for High-performance Lithium-Sulfur batteries

Exploring advanced sulfur cathode materials with high catalytic activity to accelerate the slow redox reactions of lithium polysulfides (LiPSs) is of great significance for lithium-sulfur batteries (LSBs). In this study, a coral-like hybrid composed of cobalt nanoparticle-embedded N-doped carbon nanotubes supported by Vanadium (III) oxide (V₂O₃) nanorods (Co-CNTs/C @V₂O₃) was designed as an efficient sulfur host using a simple annealing process. Characterization combined with electrochemical analysis confirmed that the V₂O₃ nanorods exhibited enhanced LiPSs adsorption capacity, and the in situ grown short-length Co-CNTs improved electron/mass transport and enhanced the catalytic activity for conversion to LiPSs. Owing to these merits, the S@Co-CNTs/C@V₂O₃ cathode exhibits effective capacity and cycle lifetime. Its initial capacity was 864 mAh g^-1 at 1.0C and remained at 594 mAh g^-1 after 800cycles with a decay rate of 0.039%. Furthermore, even at a high sulfur loading (4.5 mg cm^-2), S@Co-CNTs/C@V₂O₃ also shows acceptable initial capacity of 880 mAh g^-1 at 0.5C. This study provides new ideas for preparing long-cycle S-hosting cathodes for LSBs.

Designing High-Quality Electrocatalysts Based on CoO:MnO2@C Supported on Carbon Cloth Fibers as Bifunctional Air Cathodes for Application in Rechargeable Zn-Air Battery

To achieve the requirements of rechargeable Zn-air batteries (ZABs), designing efficient, bifunctional, stable, and cost-effective electrocatalysts is vital for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which still are struggling with unsolved challenges. The present research provides a concept based on the nanoscale composites which were engineered by using MnO₂@C, CoO@C, and CoO:MnO₂@C bifunctional electrocatalysts for fabrication of uniform carbon cloth (CC)-based electrodes. The CoO:MnO₂@C electrocatalyst represented more efficient electrochemical properties through ORR and OER processes with superior positive half-wave potential (E_1/2 = 0.78 V) and better limiting current density (i = 1.10 mA cm^-2) in comparison with MnO₂@C (E_1/2 = 0.71 V, i = 0.92 mA cm^-2) and CoO@C (E_1/2 = 0.69 V, i = 0.86 mA cm^-2) electrocatalysts. For the rechargeable ZABs fabricated by using CoO:MnO₂@C-CC as an O₂-breathing cathode, the specific capacity (SC), peak power density (P), open-circuit voltage (E_OCV), and gap of charge/discharge voltage resulted in values of 520 mAh g_Zn^-1, 210.0 mW cm^-2, and 1.45 and 0.45 V, respectively, that afforded greater electrochemical characters than what was obtained for ZABs based on MnO₂@C-CC (410 mAh g_Zn^-1, 195.0 mW cm^-2, 1.38 and 0.44 V) and CoO@C-CC (440 mAh g_Zn^-1, 165.0 mW cm^-2, 1.15 and 0.54 V). At the same time, lower E_i=10 (= 1.45 V) implied a more efficient OER in alkaline electrolyte solution for CoO:MnO₂@C than MnO₂@C (E_i=10 = 1.50 V) and CoO@C (E_i=10 = 1.39 V). Based on cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and X-ray photoelectron spectroscopy (XPS) results, it could be stated that the CoO:MnO₂@C catalytic surface could experience 30 and 32% lower charge transfer resistance (R_ct = 13.9 Ω) than MnO₂@C (R_ct = 20.1 Ω) and CoO@C (R_ct = 29.7 Ω), respectively, which empowers an enhancement in ORR/OER performance. Prominently, the design concept of proposed electrocatalysts could suggest clear horizon for the synthesis and development paradigms of bifunctional catalysts for energy storage materials and devices.

Nano-sulfur confined in a 3D carbon nanotube/graphene network as a free-standing cathode for high-performance Li-S batteries

A free-standing nano-sulfur-based carbon nanotube/graphene (S/CNT/G) film with a conductive interlinked three-dimensional (3D) nanoarchitecture is fabricated via a facile solution-based method. This 3D multidimensional carbon-sulfur network combines three different nanoarchitectures, as follows: zero-dimensional sulfur nanoparticles, one-dimensional carbon nanotubes, and two-dimensional graphene. The CNTs with a one-dimensional structure act as a conductive matrix, and graphene with two-dimensional sheets is intercalated into the CNT scaffold to build a 3D structure, extending in an additional dimension to provide improved restriction for sulfur/polysulfides. Zero-dimensional sulfur nanoparticles are anchored uniformly on the interpenetrative 3D carbon framework to form a free-standing cathode. Moreover, this well-designed S/CNT/G film is flexible, highly conductive, binder free and current collector free. When directly used as a flexible cathode electrode, the synthesized S/CNT/G film delivers both excellent long-term cycling and high-rate performances. A high initial capacity of 948 mA h g-1 is obtained, and subsequently, a reversible discharge capacity of 593 mA h g-1 over 200 cycles is achieved at 0.5C. Even at a high rate of 3C, the S/CNT/G film with a 50 wt% sulfur content still exhibits a discharge capacity of 598 mA h g-1. These results demonstrate the great potential of the S/CNT/G nanocomposite as a flexible and binder-free cathode for high performance Li-S batteries.