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

Abstract

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 ∼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 (i₀) and electron transfer number (n) (i₀ > 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.