Rational Design of a Ni3N0.85 Electrocatalyst to Accelerate Polysulfide Conversion in Lithium |
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Rational Design of a Ni3N0.85 Electrocatalyst to Accelerate Polysulfide Conversion in Lithium
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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 Ni3N (space group P6322) to tune its d-band center, leading to the strong interaction between polysulfides and Ni3N. Because of the greater electron population in the lowest occupied molecular orbital of Li2S4, the terminal S–S bonds were weakened for breaking. Temperature-dependent experiments confirm that Ni3N0.85 demonstrates a much low activation energy, thereby accelerating the conversion of polysulfides. A Li–S cell using Ni3N0.85 can deliver a high initial discharge capacity of 1445.9 mAh g–1 (at 0.02 C) and low decay per cycle (0.039%). The Ni3N0.85 cell can also demonstrate an initial capacity of 1200.4 mAh g–1 for up to 100 cycles at a high loading of 5.2 mg cm–2. The high efficiency of rationally designed Ni3N0.85 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.
中文翻译：
多硫化物转化反应的动力学慢会导致锂硫（Li–S）电池出现严重问题，例如，低倍率容量，多硫化物迁移和低库仑效率。这些挑战阻碍了Li-S电池的实际应用。在这项研究中，我们提出了一种合理的策略来调节催化剂的d波段，以加速多硫化物的转化。在六角形的Ni 3 N（空间群P 6 3 22）中设计了氮空位，以调节其d带中心，从而导致多硫化物与Ni 3 N之间的强相互作用。由于在电子的最低占据分子轨道中存在较大的电子种群李2 S 4，末端S-S键因断裂而被削弱。与温度有关的实验证实，Ni 3 N 0.85具有极低的活化能，从而加速了多硫化物的转化。使用Ni 3 N 0.85的Li–S电池可提供1445.9 mAh g –1的高初始放电容量（在0.02 C时）和每个循环的低衰减（0.039％）。Ni 3 N 0.85电池在5.2 mg cm -2的高负荷下，最多可进行100个循环，初始容量为1200.4 mAh g –1。合理设计的Ni 3 N 0.85的高效率 演示了d波段调谐策略对开发低活化能催化剂和促进对Li-S电池中多硫化物转化的原子理解的有效性。 |
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