Spin Effect to Promote Reaction Kinetics and Overall Performance of Lithium-Sulfur Batteries under External Magnetic Field.

Lithium-sulfur batteries (LSBs) are still limited by the shuttle of lithium polysulfides (LiPS) and the slow Li-S reaction. Herein, we demonstrate that when using cobalt sulfide as a catalytic additive, an external magnetic field generated by a permanent magnet can significantly improve the LiPS adsorption ability and the Li-S reaction kinetics. More specifically, the results show both experimentally and theoretically how an electron spin polarization of Co ions reduces electron repulsion and enhances the degree of orbital hybridization, thus resulting in LSBs with unprecedented performance and stability. Under an external magnetic field, LSBs with 0.0084 % per cycle decay rate at 2 C during 8150 cycles are produced. Overall, this work not only demonstrates an effective strategy to promote LiPS adsorption and electrochemical conversion in LSBs at no additional energy cost but also enriches the application of the spin effect in the electrocatalysis fields.

Metal Ion Cutting-Assisted Synthesis of Defect-Rich MoS2 Nanosheets for High-Rate and Ultrastable Li2S Catalytic Deposition.

Active metal ions often show a strong cutting effect on the chemical bonds during high-temperature thermal processes. Herein, a one-pot metal ion cutting-assisted method was adopted to design defect-rich MoS2-x nanosheet (NS)/ZnS nanoparticle (NP) heterojunction composites on carbon nanofiber skeletons (CNF@MoS2-x/ZnS) via a simple Ar-ambience annealing. Results show that Zn2+ ions capture S2- ions from MoS2 and form into ZnS NPs, and the MoS2 NSs lose S2- ions and become MoS2-x ones. As sulfur hosts for lithium-sulfur batteries (LSBs), the CNF@MoS2-x/ZnS-S cathodes deliver a high reversible capacity of 1233 mA h g-1 at 0.1 C and keep 944 mA h g-1 at 3 C. Moreover, the cathodes also show an extremely low decay rate of 0.012% for 900 cycles at 2 C. Series of analysis indicate that the MoS2-x NSs significantly improve the chemisorption and catalyze the kinetic process of redox reactions of lithium polysulfides, and the heterojunctions between MoS2-x NSs and ZnS NPs further accelerate the transport of electrons and the diffusion of Li+ ions. Besides, the CNF@MoS2-x/ZnS-S LSBs also show an ultralow self-discharge rate of 1.1% in voltage. This research would give some new insights for the design of defect-rich electrode materials for high-performance energy storage devices.

Construction of all-carbon micro/nanoscale interconnected sulfur host for high-rate and ultra-stable lithium-sulfur batteries: Role of oxygen-containing functional groups.

Carbon nanotubes (CNTs) are often used to settle down the sluggish reaction kinetics in lithium-sulfur batteries (LSBs). However, the self-aggregation of CNTs often makes them fail to effectively inhibit the shuttling effect of soluble lithium polysulfide (LiPS) intermediates. Herein, a type of ultra-stable carbon micro/nano-scale interconnected "carbon cages" has been designed by incorporating polar acid-treated carbon fibers (ACF) into three-dimensional (3D) CNT frameworks during vacuum filtration processes. Results show that the ACF-CNT composite frameworks possess a reinforced-concrete-like structure, in which the ACFs can well work as the main mechanical supporting frames for the composite electrodes, and the oxygen-containing functional groups (OFGs) formed on them as cross linker between ACFs and CNTs. Benefitted from this design, the ACF-CNT/S cathodes deliver an excellent rate capability (retain 72.6% at 4C). More impressively, the ACF-CNT/S cathodes also show an ultrahigh cycling stability (capacity decay rate of 0.001% per cycle over 350 cycles at 2C). And further optimization suggests that the suitable treatment on CFs could balance the chemical adsorption (OFGs) and physical confinement (carbon cages), leading to fast and durable electrochemical reaction dynamics. In addition, the assembled soft-pack LSBs further show a high dynamic bending stability.

Dissymmetric interface design of SnO2/TiO2 side-by-side bi-component nanofibers as photoanodes for dye sensitized solar cells: Facilitated electron transport and enhanced carrier separation.

SnO2/TiO2 type II heterojunctions are often introduced to enhance the separation efficiency of photogenerated carriers in photoelectrochemical electrodes, while most of these heterojunctions are of core-shell structure, which often limits the synergistic effect from the two components. In this work, dissymmetric SnO2/TiO2 side-by-side bi-component nanofibers (SBNFs) with tunable composition ratios have been prepared by a novel needleless electrospinning technique with two V-shape connected conductive channels (V-channel electrospinning). Results show that this V-channel electrospinning technique is more stable, controllable and tunable for the large-scale preparation of SBNF materials compared to the traditional electrospinning using two side-by-side metal needles. And these SnO2/TiO2 SBNFs are dissymmetric and comprised of a tiny SnO2 NF (tunable diameter within 20-80 nm) and a Sn-doped TiO2 NF (diameter of ~ 250 nm) with a side-by-side structure. Moreover, the dye-sensitized solar cells (DSSCs) based these dissymmetric SnO2/TiO2 SBNFs show the maximum power conversion efficiency (PCE) of 8.3%, which is 2.59 times that of the ones based on the TiO2 NFs. Series of analyses indicate that the enhancements in PCE could mainly be due to the improved electron transport via SnO2 NFs and the enhanced carrier separation via dissymmetric SnO2/TiO2 heterojunction interface. This research will give some new insight in the preparation of SBNFs for high-performance photoelectrochemical devices.