Exceptional catalytic effects of black phosphorus quantum dots in shuttling-free lithium sulfur batteries

Abstract

Lithium sulfur batteries with high energy densities are promising next-generation energy storage systems. However, shuttling and sluggish conversion of polysulfides to solid lithium sulfides limit the full utilization of active materials. Physical/chemical confinement is useful for anchoring polysulfides, but not effective for utilizing the blocked intermediates. Here, we employ black phosphorus quantum dots as electrocatalysts to overcome these issues. Both the experimental and theoretical results reveal that black phosphorus quantum dots effectively adsorb and catalyze polysulfide conversion. The activity is attributed to the numerous catalytically active sites on the edges of the quantum dots. In the presence of a small amount of black phosphorus quantum dots, the porous carbon/sulfur cathodes exhibit rapid reaction kinetics and no shuttling of polysulfides, enabling a low capacity fading rate (0.027% per cycle over 1000 cycles) and high areal capacities. Our findings demonstrate application of a metal-free quantum dot catalyst for high energy rechargeable batteries.

Polyethylenimine Expanded Graphite Oxide Enables High Sulfur Loading and Long‐Term Stability of Lithium–Sulfur Batteries

“…As is known, the LiPSs shuttle mainly happens during the transformation of S 8 to long‐chain LiPS (high discharge voltage) . The high Q H reservation indicates shuttle effect has been efficiently suppressed . Correspondingly, Q L decreases from 668 mAh g −1 to 575, 505, and 475 mAh g −1 , with a capacity retention of 86, 76, and 71%, respectively.…”

“…The rate capacity was further analyzed by separating the discharge/charge profiles of different C‐rates into two parts, including capacity contributed by the higher‐discharge plateau (>2.0 V, Q H ) and that of the lower‐discharge plateau (<2.0 V, Q L ). Q H value relates to the conversion of S 8 to long‐chain LiPS (solid‐to‐liquid), while Q L value corresponds to the conversion of soluble LiPS to solid lithium sulfide, Li 2 S 2 and/or Li 2 S (liquid‐to‐solid and/or solid‐to‐solid) . Theoretically, Q H equals to 419 mAh g −1 and Q L is 1256 mAh g −1 , corresponding to Q L / Q H = 3 .…”

“…The percentage of the real capacity to the theoretical capacity ( Q R / Q T %) and Q L / Q H ratios of different C‐rates are plotted in Figure f. Q R / Q T from both the high and low‐discharge plateau decrease along with the increase of C‐rates, indicating an increased polarization . Due to the poor conductivity of lithium sulfide (both ionic and electronic), the Q R / Q T of low‐discharge plateau is always lower than that of high‐discharge plateau, indicating the liquid‐to‐solid and/or solid‐to‐solid processes suffer from higher sluggish than that of solid‐to‐liquid process .…”

Adsorption‐Catalysis Design in the Lithium‐Sulfur Battery

“…They also reported that employing hierarchical N-doped carbon nanocages (hNCNC) to encapsulate sulfur as the cathode, the Li-S batteries showed excellent durability after 1000 cycles at 10 A g −1 with a capacity of 438 mAh g −1 . [31] Guo et al fabricated a highly uniform 3D hierarchical N-doped carbon nanoflower (NCNF) as shown in Figure 1b, which displays a high surface area (907 m 2 g −1 ) and large pore volume (1.85 cm 3 g −1 ), thereby acquiring high activities in oxygen reduction reaction and Li-S batteries.…”

“…b) The synthetic procedure schematic diagram and the reaction mechanism model of three dimensions hierarchical NCNF. Reproduced with permission [31] Copyright 2018, Springer Nature. [29] Copyright 2017, Royal Society of Chemistry.…”