Ultrathin bismuth nanosheets as an efficient polysulfide catalyst for high performance lithium-sulfur batteries

Although many materials have sprung up as catalysts to improve polysulfide conversion in lithium-sulfur batteries, the catalytic mechanism is vague and a universal and efficient catalyst is still absent. Herein, we developed ultrathin polycrystalline bismuth (2D-Bi) nanosheets (thickness of similar to 4 nm) as an electrocatalyst for polysulfide conversion. Such a 2D polycrystalline structure not only absorbs and immobilizes soluble polysulfides but also accelerates multistep polysulfide redox reactions, greatly inhibiting the polysulfide shuttling during charge-discharge cycles. Furthermore, we gained an in-depth understanding of the distinctive electrocatalysis mechanism of 2D-Bi nanosheets by steady-state and dynamic electrochemical testing methods. The results showed that with the 2D-Bi electrocatalyst, the exchange current density (i(0)) and electron transfer number (n) (i(0) > 3 mA cm(-2), n = 6.6 at 2.1 V) were significantly enhanced. As a consequence, a 2D-Bi modified Li-S battery exhibited good electrochemical performance with high reversible capacity, stable cycle life and superb rate performance (retaining a capacity of 408 mA h g(-1) after 500 cycles at 10C). Ultimately, a deep exploration and comprehension of the interior redox process as well as the conversion mechanism of sulfides provided a great avenue for accelerating the large-scale application of Li-S batteries in the near future.