Rational Design of a Ni<sub>3</sub>N<sub>0.85</sub> Electrocatalyst to Accelerate Polysulfide Conversion in Lithium-Sulfur Batteries.
basic_science · Level V
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- Record sourced from PubMed, PMID 32463691.
- Also identified by DOI 10.1021/acsnano.9b09371.
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Abstract
Slow kinetics of polysulfide conversion reactions lead to severe issues for lithium-sulfur (Li-S) batteries, for example, low rate capability, polysulfide migration, and low Coulombic efficiencies. These challenges hinder the practical applications of Li-S batteries. In this study, we proposed a rational strategy of tuning the d-band of catalysts to accelerate the conversion of polysulfides. Nitrogen vacancies were engineered in hexagonal Ni<sub>3</sub>N (space group <i>P</i>6<sub>3</sub>22) to tune its d-band center, leading to the strong interaction between polysulfides and Ni<sub>3</sub>N. Because of the greater electron population in the lowest occupied molecular orbital of Li<sub>2</sub>S<sub>4</sub>, the terminal S-S bonds were weakened for breaking. Temperature-dependent experiments confirm that Ni<sub>3</sub>N<sub>0.85</sub> demonstrates a much low activation energy, thereby accelerating the conversion of polysulfides. A Li-S cell using Ni<sub>3</sub>N<sub>0.85</sub> can deliver a high initial discharge capacity of 1445.9 mAh g<sup>-1</sup> (at 0.02 C) and low decay per cycle (0.039%). The Ni<sub>3</sub>N<sub>0.85</sub> cell can also demonstrate an initial capacity of 1200.4 mAh g<sup>-1</sup> for up to 100 cycles at a high loading of 5.2 mg cm<sup>-2</sup>. The high efficiency of rationally designed Ni<sub>3</sub>N<sub>0.85</sub> demonstrates the effectiveness of the d-band tuning strategy to develop low-activation-energy catalysts and to promote the atomic understanding of polysulfide conversion in Li-S batteries.