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.
Highlights
Lithium sulfur batteries with high energy densities are promising next-generation energy storage systems
The as-obtained Black phosphorus (BP) products were designated as BP-4K, BP-8K according to their centrifugation rates of 4000 and 8000 rpm, respectively, and BP quantum dots (BPQDs)
We have demonstrated the catalytic effect of the BPQDs for efficient trapping and conversion of lithium polysulfides (LiPSs) via a suite of experimental and theoretical studies
Summary
Lithium sulfur batteries with high energy densities are promising next-generation energy storage systems. The edge-selective catalytic property of the BPQDs is further validated using density functional theoretical (DFT) calculations, where the zig-zag (ZZ) terminated BP flakes present stronger binding energies with Li2S at the edges than at terrace sites These results suggest that adsorptivity of LiPS in BP can be largely increased by downsizing BP flakes to QDs. As a proof of concept, we integrate a small amount of BPQDs (2 wt% of the cathode weight) with a sulfur/porous carbon fiber cathode, the LSBs exhibit no diffusion of polysulfides as well as excellent battery performance, including high-rate capability (784 mA h g−1 at 4 C) and exceptional cyclic stability (0.027% capacity fade per cycle for 1000 cycles). An impressive capacity retention of near 90% is observed for high sulfur loading cathodes (up to 8 mg cm−1) for 200 deep cycles under lean electrolyte conditions
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