Defect-Rich Single Atom Catalyst Enhanced Polysulfide Conversion Kinetics to Upgrade Performance of Li-S Batteries.

Lithium-sulfur (Li-S) batteries have attracted considerable attention owing to their extremely high energy densities. However, the application of Li-S batteries has been limited by low sulfur utilization, poor cycle stability, and low rate capability. Accelerating the rapid transformation of polysulfides is an effective approach for addressing these obstacles. In this study, a defect-rich single-atom catalytic material (Fe-N4/DCS) is designed. The abundantly defective environment is favorable for the uniform dispersion and stable existence of single-atom Fe, which not only improves the utilization of single-atom Fe but also efficiently adsorbs polysulfides and catalyzes the rapid transformation of polysulfides. To fully exploit the catalytic activity, catalytic materials are used to modify the routine separator (Fe-N4 /DCS/PP). Density functional theory and in situ Raman spectroscopy are used to demonstrate that Fe-N4 /DCS can effectively inhibit the shuttling of polysulfides and accelerate the redox reaction. Consequently, the Li-S battery with the modified separator achieves an ultralong cycle life (a capacity decay rate of only 0.03% per cycle at a current of 2 C after 800 cycles), and an excellent rate capability (894 mAh g-1 at 3 C). Even at a high sulfur loading of 5.51 mg cm-2 at 0.2 C, the reversible areal capacity still reaches 5.4 mAh cm-2 .

A Highly Efficient Sulfur Host Enabled by Nitrogen/Oxygen Dual-Doped Honeycomb-Like Carbon for Advanced Lithium-Sulfur Batteries.

High energy density and long cycle life of lithium-sulfur (Li-S) batteries suffer from the shuttle/expansion effect. Sufficient sulfur storage space, local fixation of polysulfides, and outstanding electrical conductivity are crucial for a robust cathode host. Herein, a modified template method is proposed to synthesize a highly regular and uniform nitrogen/oxygen dual-doped honeycomb-like carbon as sulfur host (N/O-HC-S). The unique structure not only offers physical entrapment for polysulfides (LiPSs) but also provides chemical adsorption and catalytic conversion sites of polysulfides. In addition, this structure offers enough space for loading sulfur, and a regular space of nanometer size can effectively prevent sulfur particles from accumulating. As expected, the as-prepared N/O-HC900-S with high areal sulfur loading (7.4 mg cm-2 ) shows a high areal specific capacity of 7.35 mAh cm-2 at 0.2 C. Theoretical calculations also reveal that the strong chemical immobilization and catalytic conversion of LiPSs attributed to the spin density and charge distribution of carbon atoms will be influenced by the neighbor nitrogen/oxygen dopants. This structure that provides cooperative chemical adsorption, high lithium ions flux, and catalytic conversion for LiPSs can offer a new strategy for constructing a polysulfide confinement structure to achieve robust Li-S batteries.

Tin disulfide embedded on porous carbon spheres for accelerating polysulfide conversion kinetics toward lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries are considered promising candidates for next-generation advanced energy storage systems due to their high theoretical capacity, low cost and environmental friendliness. However, the severe shuttle effect and weak redox reaction severely restrict the practical application of Li-S batteries. Herein, a functional catalytic material of tin disulfide on porous carbon spheres (SnS2@CS) is designed as a sulfur host and separator modifier for lithium-sulfur batteries. SnS2@CS with high electrical conductivity, high specific surface area and abundant active sites can not only effectively improve the electrochemical activity but also accelerate the capture/diffusion of polysulfides. Theoretical calculations and in situ Raman also demonstrate that SnS2@CS can efficiently adsorb and catalyse the rapid conversion of polysulfides. Based on these advantages, the SnS2@CS-based Li-S battery delivers an excellent reversible capacity of 868 mAh/g at 0.5C (capacity retention of 96 %), a high rate capability of 852 mAh/g at 2C, and a durable cycle life with an ultralow capacity decay rate of 0.029 % per cycle over 1000 cycles at 2C. This work combines the design of sulfur electrodes and the modification of separators, which provides an idea for practical applications of Li-S batteries in the future.

A calcium fluoride composite reduction graphene oxide functional separator for lithium-sulfur batteries to inhibit polysulfide shuttling and mitigate lithium dendrites.

Lithium-sulfur (Li-S) batteries have attracted tremendous attention as promising next-generation energy-storage systems due to their high specific capacity and high specific energy. However, the shuttle of polysulfides and the growth of Li dendrites severely obstruct the practical applications of these batteries. In this work, a functional separator is designed and fabricated in which nano-calcium fluoride (CaF2) particles are embedded in reduced graphene oxide (rGO) and bladed on a PP separator. The density functional theory (DFT) calculations of the adsorption energy and bond length reveal that CaF2 has a satisfying adsorption and catalytic effect on polysulfides (Li2Sn). The factional separator could accelerate homogenous Li+ flow and retard the growth of Li dendrites. In addition, an initial specific capacity of 1504 mAh g-1 at 0.05C is achieved, and it still retains a discharge capacity of 1050 mAh g-1 over 100 cycles at 0.2C. Moreover, the capacity decay rate is only 0.06% per cycle over 420 cycles at a high current density of 0.5 C. The excellent performance could be attributed to the CaF2@rGO modified separator not only accelerating the transmission of electrons but also effectively inhibiting the shuttling of polysulfides. This work provides a better method for attaining practical applications of high-performance lithium-sulfur batteries.

Stability-Enhanced α-Ni(OH)2 Pillared by Metaborate Anions for Pseudocapacitors.

α-Ni(OH)2 is an ideal candidate material for a supercapacitor except for its low conductivity and poor stability. In this work, BO2--intercalated α-NixCo(1-x)(OH)2 is synthesized by a hydrothermal method at a low cost. The Co dopant can decrease the charge-transfer resistance and enhance the cyclic stability. The special unsaturated electronic state of BO2- enhances the bonding with metal ions and attracts water molecules. Thus, the BO2- ions support the hydroxide layers as pillars and create efficient paths for proton transportation, optimizing the utilization of α-Ni(OH)2. The three-dimensional (3D) flowerlike morphology supplies an enormous number of active sites, and r-GO is added to improve the conductivity. As a result, the modified α-Ni(OH)2 exhibits the specific capacitance of 2179, 1592, and 1423 F·g-1 at 1, 20, and 40 A·g-1, respectively, showing improved rate performance. Matching with the commercial activated carbon (AC) as an anode, the asymmetric capacitor delivers an energy density of 40.66 W·h·kg-1 when its power density is 187.06 W·kg-1. Meanwhile, it retains 81.5% capacitance of the initial cycle at 5 A·g-1 after 3000 cycles. With conductivity enhanced and structure stabilized, the modified α-Ni(OH)2 confronts broader fields of application.