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Lithium-sulfur (Li-S) batteries, as one of the new energy storage batteries, show immense potential due to their high theoretical specific capacity and theoretical energy density. However, there are still some problems to be solved, among which the shuttle effect of lithium polysulfides is one extremely serious issue with respect to the industrial application of Li-S batteries. Rational design of electrode materials with effective catalytic conversion ability is an effective route to accelerate the conversion of lithium polysulfides (LiPSs). Herein, considering the adsorption and catalysis of LiPSs, CoO x nanoparticles (NPs) loaded on carbon sphere composites (CoO x /CS) were designed and constructed as cathode materials. The CoO x NPs obtained, with ultralow weight ratio and uniform distribution, consist of CoO, Co 3 O 4 , and metallic Co. The polar CoO and Co 3 O 4 enable chemical adsorption towards LiPSs through Co-S coordination, and the conductive metallic Co can improve electronic conductivity and reduce impedance, which is beneficial for ion diffusion at the cathode. Based on these synergistic effects, the CoO x /CS electrode exhibits accelerated redox kinetics and enhanced catalytic activity for conversion of LiPSs. Consequently, the CoO x /CS cathode delivers improved cycling performance, with an initial capacity of 980.8 mA h g -1 at 0.1C and a reversible specific capacity of 408.4 mA h g -1 after 200 cycles, along with enhanced rate performance. This work provides a facile route to construct cobalt-based catalytic electrodes for Li-S batteries, and promotes understanding of the LiPSs conversion mechanism.

Lithium-sulfur (Li-S) batteries generally suffer from a serious "shuttle effect" during the charging/discharging process, resulting in the loss of active components and sluggish redox reaction kinetics that hinder the cycle life and rate performance of the battery. To address this, CoSe/C hollow structures (CoSe/C HSs) were prepared via a simple hydrothermal strategy and used as a sulfur host for Li-S batteries. The battery with CoSe/C HSs exhibited a high initial specific discharge capacity of 1405 mA h g-1 with a coulombic efficiency of 99.8% at 0.1C. Additionally, S@CoSe/C HS cathodes with a high sulfur loading of 5.1 mg cm-2 delivered a considerable specific discharge capacity of 1256.1 mA h g-1 and maintained a high capacity of 1120 mA h g-1 after 100 cycles with a capacity decay rate of 0.11% per cycle at 0.1C. The unique raspberry-like structure of CoSe/C HSs prevents polysulfides from escaping the cathode host via both physical containment and the formation of Co-S and Se-Li chemical bonds, and it also enhances the polysulfide redox kinetics. Furthermore, the peculiar raspberry-like structure can withstand volume changes during charging/discharging to better protect the cathode.

A lithium-sulfur (Li-S) battery is considered a promising next-generation secondary battery owing to its high theoretical capacity and energy density. However, the volume change and poor conductivity of sulfur, and the shuttle effect, restrict its practical applications. Herein, we develop a yolk-shell Fe3O4@S@C nanochain as the Li-S battery cathode in which sulfur is encapsulated between the Fe3O4 core and the carbon shell. After cycling 500 times at 0.2C, the Fe3O4@S@C nanochains exhibit a stable capacity of 625 mA h g-1 and a coulombic efficiency exceeding 99.8%. When measuring at temperatures of -5 and 45 °C, the capacities remain stable, and a well-reversible rate performance under repeated testing for three rounds is also achieved. Furthermore, density functional theory (DFT) calculations show large adsorption energies of Fe3O4 towards polysulfides, indicating the capability of suppressing the shuttle effect during long-term charge and discharge.

The dissolution of polysulfides in an electrolyte is a thermodynamically favorable process, which in theory means that the shuttle effect in lithium-sulfur batteries (LSBs) cannot be completely suppressed. So, it is very important to modify the separator to prevent the migration of polysulfides to the lithium anode. The traditional coating modification process of the separator is cumbersome and uses a solvent that is harmful to the environment, and too many inactive components affect the overall energy density of the battery. It is thus imperative to find a simple and environmentally friendly modification process of the separator. In this study, a fast chemical film-forming method is proposed to modify the separator of a lithium-sulfur battery using tannic acid (TA) and cobalt ions (Co2+). This method requires only simple steps and environmentally friendly raw materials to obtain a thin coating (only 5.83 nm) that can effectively inhibit the shuttle effect. The lithium-sulfur battery with the TA-Co separator shows superior long cycle performance. After 500 cycles at 0.5 C, the capacity decay rate of each cycle is only 0.065%. On the other hand, the TA-Co separator can inhibit the growth of lithium dendrites and help to build a stable lithium anode, which can exhibit minimal polarization (56 mV) in a lithium-lithium symmetrical battery at the current density of 2 mA cm-2. The rapid and simple modification method proposed in this study has a certain reference value for the future large-scale application of lithium sulfur batteries.