Engineering Spin State of Ni Single-Atoms to Enhance Electrocatalytic Activity of Sulfur Conversion in Lithium–Sulfur Batteries

Abstract

Understanding the correlation between spin state and electrocatalytic activity of single-atom catalysts (SACs) may help us to address the sulfur redox kinetics problems in lithium–sulfur batteries (LSBs). Herein, systematic experiments were carried out to study the catalytic activities of Ni SACs with different spin states via modulating the pyrrolic N/pyridinic N ratio. Ni SACs with high-spin state show strong catalytic activity toward lithium polysulfides (LPSs), whereas the Ni SACs with low-spin state have strong adsorption capacity for LPSs. Therefore, the preparation of Ni SACs with an intermediate spin state by controlling pyridinic N and pyrrolic N enables an excellent balance between the adsorption and catalytic. Importantly, the introduction of S atoms can enhance the content of pyrrolic N while ensuring a high total content of pyridinic N and pyrrolic N. Consequently, the sulfur cathode based on Ni-N_pd-pr-SC shows a remarkable battery performance with a high initial capacity of 606 mAh g⁻¹ at 4.0 C and a capacity retention of 81.3% after 300 cycles. It is believed that this work provides a profound understanding of optimizing the spin state of Ni SACs for LSBs.

Keywords

lithium polysulfides / lithium–sulfur batteries / Ni single-atom catalyst / pyrrolic N/pyridinic N / spin state

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