Boosting electrochemical performance of Li-S batteries by cerium-based MOFs coated with polypyrrole

Abstract

Lithium-sulfur (Li-S) batteries are a promising next-generation energy storage technology due to high theoretical energy density, low cost and abundant reserves. However, the poor electronic conductivity of sulfur and huge volume change hindered their commercial applications. In this paper, selected as a cathode host of Li-S batteries from two Ce-MOFs with dissimilar open metal sites for the first time, Ce-MOF-808 was synthesized and then coated with a Polypyrrole (PPy) layer (Ce-MOF-808@S/PPy). Material characterization and electrochemical performance tests were conducted. Results show that Ce-MOF-808@S/PPy has a high specific surface area of 437.491 m2 g−1, with special micro-mesoporous structures. Ce-MOF-808@S/PPy composite possesses the initial discharge specific capacity of 1612.5 mA h g−1 and discharge specific capacity of 771.9 mA h g−1 at 0.1 C after 100 cycles. Additionally, the battery still maintains a reversible specific capacity above 470 mAh g−1 with 40% capacity retention rate at a rate of 2 C after 200 cycles of charge and discharge. Improved electrochemical performances are mainly attributed to the Ce-MOFs with special micro-mesoporous structures and high specific surface area conducive to inhibiting the shuttle effect and volume expansion through physical adsorption and stable channel structures, the Ce sites with unique adsorption and catalytic effect, and the PPy coating layer adsorbing the polysulfide and acting as charge collectors to enhance conductivity.