RESUMEN
Lithium-sulfur batteries have emerged as a promising energy storage device due to ultra-high theoretical capacity, but the slow kinetics of sulfur and polysulfide shuttle hinder the batteries' further development. Here, the 10% cobalt-doped pyrite iron disulfide electrocatalyst deposited on acetylene black as a separator coating in lithium-sulfur batteries is reported. The adsorption rate to the intermediate Li2S6 is significantly improved while surface oxidation of FeS2 is inhibited: iron oxide and sulfate, thus avoiding FeS2 electrocatalyst deactivation. The electrocatalytic activity has been evaluated in terms of electronic resistivity, lithium-ion diffusion, liquid-liquid, and liquid-solid conversion kinetics. The coin batteries exhibit ultra-long cycle life at 1 C with an initial capacity of 854.7 mAh g-1 and maintained at 440.8 mAh g-1 after 920 cycles. Furthermore, the separator is applied to a laminated pouch battery with a sulfur mass of 326 mg (3.7 mg cm-2) and retained the capacity of 590 mAh g-1 at 0.1 C after 50 cycles. This work demonstrates that FeS2 electrocatalytic activity can be improved when Co-doped FeS2 suppresses surface oxidation and provides a reference for low-cost separator coating design in pouch batteries.
RESUMEN
Lithium-sulfur batteries (LSBs) have been sought after by researchers owing to their high energy density; however, the inevitable capacity decay and slow reaction kinetics have hindered their advancement. Here, we prepare a Prussian blue analog, Co3[Co(CN)6]2 and synthesize carbon nanofibers/S vacancy CoS2-x (CNFs/CoS2-x) as electrocatalysts for separator coating via electrospinning, carbonization, sulfurization, and hydrogen reduction. CNFs/CoS2-x exhibits excellent electrocatalytic activity, wherein S vacancies induce the partial oxidation of Co2+ to Co3+ in CoS2 and CNFs provide long-range electron transport pathways. Various electrochemical tests, such as Tafel, ion diffusion coefficient, Li2S precipitation, and Li2S6 symmetric cells, further confirm the enhanced electrocatalytic activity. The LSBs with CNFs/CoS2-x modified separator delivers an initial discharge capacity of 1056.7 mAh g-1 at 0.2C, maintaining 840.8 mAh g-1 after 100 cycles at 0.2C. When S loading is increased to 4.42 mg cm-2, the battery retains a discharge capacity of 687.9 mAh g-1 (3.04 mAh cm-2) after 70 cycles at 0.1C. Our work can provide a reference for synthesizing anion-vacancy materials and designing anion-vacancy electrocatalytic composites for LSBs.
RESUMEN
The commercial application of lithium-sulfur batteries (LSBs) has been seriously hindered by the shuttle effect of lithium polysulfides (LiPSs) and their slow redox kinetics. In this work, g-C3N4/MoO3 composed of graphite carbon nitride (g-C3N4) nanoflake and MoO3 nanosheet is designed and applied to modify the separator. The polar MoO3 can form chemical bond with LiPSs, effectively slowing down the dissolution of LiPSs. And based on the principle of "Goldilocks", LiPSs will be oxidized by MoO3 to thiosulfate, which will promote the rapid conversion from long-chain LiPSs to Li2S. Moreover, g-C3N4 can promote the electron transportation, and its high specific surface area can facilitate the deposition and decomposition of Li2S. What's more, the g-C3N4 promotes the preferential orientation on the MoO3(021) and MoO3(040) crystal planes, which optimizes the adsorption capacity of g-C3N4/MoO3 for LiPSs. As a result, the LSBs with g-C3N4/MoO3 modified separator with a synergistic adsorption-catalysis, can achieve an initial capacity of 542 mAh g-1 at 4C with capacity decay rate of 0.0053% per cycle for 700 cycles. This work achieves the synergy of adsorption and catalysis of LiPSs through the combination of two materials, providing a material design strategy for advanced LSBs.