MoO2 nanoparticles embedded in N-doped hydrangea-like carbon as a sulfur host for high-performance lithium–sulfur batteries

Revealing Performance Enhancement Mechanism for Lithium-Sulfur Battery Using In Situ Electrochemical-Fluorescence Technology

Lithium-sulfur batteries (LSBs) as a next-generation promising energy storage device have a great potential commercial application due to their high specific capacity and energy density. However, it is still a challenge to real-time monitor the evolution process of polysulfides during the LSBs discharge process. Herein, an in situ electrochemical-fluorescence technology is developed to measure the fluorescence intensity change of cadmium sulfide quantum dots (CdS QDs) during the LSBs discharge process in real-time, which could monitor the evolution process of polysulfides. First, the real-time fluorescent spectrum and confocal fluorescence imaging of discharge processes for LSBs with CdS QDs are integrally illustrated. Furthermore, the fluorescence spectra and imaging results show that CdS QDs could immobilize polysulfides through bonding with polysulfides to improve the LSB device performance. This in situ electrochemical-fluorescence technology provides a new in situ and real-time-monitor method for better understanding the working mechanism of LSBs.

Balanced capture and catalytic ability toward polysulfides by designing MoO2-Co2Mo3O8 heterostructures for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries, as the next generation of energy storage systems, are currently limited by insufficient capture ability and sluggish catalytic reaction kinetics, thus leading to serve the shuttle effect of lithium polysulfides (LiPSs). Realizing the accelerated conversion of polysulfides in the cathode host of Li-S batteries is an effective way to improve its coulombic efficiency. The essence of fast conversion relies on enhanced oxidation reaction kinetics by virtue of the metal catalyst, but the generation of various intermediates exacerbate the complexity of the system and perplex the perfect operation of batteries relying on only one catalyst. In this work, the xMoO₂:yCo₂Mo₃O₈ heterostructures were designed, in which controlling the content of cobalt could balance the capture capability towards LiPSs by MoO₂ and catalytic ability of liquid-solid conversion by Co₂Mo₃O₈ catalytic sites. Therefore, utilizing synergy effect of MoO₂-Co₂Mo₃O₈ heterostructure enhances capture and catalytic ability toward polysulfides in Li-S batteries. As a result, the 9MoO₂:2Co₂Mo₃O₈-based cathode delivers excellent reversibility of 880 mA h g^-1 after 100 cycles at 0.2C and 509 mA h g^-1 after 1000 cycles at 1C with 0.056% capacity decay each cycle. This work provides a new method for synthesizing heterostructures by doping metals. Moreover, it promotes the understanding of balancing and promoting the capture capacity and catalytic conversion ability toward LiPSs.

Vertical 2-dimensional heterostructure SnS-SnS2 with built-in electric field on rGO to accelerate charge transfer and improve the shuttle effect of polysulfides

Traditional carbon materials as sulfur hosts of Li-sulfur(Li-S) cathodes have slightly physical constraint for polysulfides, due to their no-polar property. Therefore, it is necessary to further enhance the affinity between sulfur hosts and polysulfides, and relieve the shuttle effects in the Li- S batteries. Herein, we report a novel vertical 2-dimensional (2D) p-SnS/n-SnS₂ heterostructure sheets which grown on the surface of rGO. The excellent electrochemical properties of SnS-SnS₂@rGO as Li-S cathode are ascribed to the stronger absorption effect of metal sulphides for polysulfides and the smooth trapping-diffusion-conversion effect of p-SnS/n-SnS₂ heterostructure for polysulfides. As a conductive carrier for the growth of vertical 2D p-SnS/n-SnS₂ heterostructure nanosheets, rGO can protect the steadiness and enhance the cycle stability of electrode, compared with heterostructure without rGO. In addition, the built-in electric field in the 2D p-SnS/n-SnS₂ heterostructure during the discharge/charge processes can effectively accelerate charge transfer, and the charge transfer mechanism in SnS-SnS₂ heterostructure during cycling has been investigated. At a rate capability of 2C, the designed SnS-SnS₂@rGO as Li-S cathode delivers high specific capacities of 907 mAh g^-1 and 571 mAh g^-1 after the first cycle and 500 cycles, respectively, which shown excellent cycling ability.