Root-Nodule-Inspired Cobalt Selenide with Sulfur-Doping-Induced Phase Transition for High-Performance Lithium-Sulfur...

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Legume root-nodule symbiosis provides a model for hierarchical mass transport and efficient biological nitrogen fixation.
• Lithium-sulfur (Li-S) batteries offer high theoretical energy density but suffer from issues like polysulfide shuttling and poor cycling stability.
• Developing advanced catalysts is crucial for improving Li-S battery performance by facilitating polysulfide conversion and enhancing charge transport.

Purpose of the Study:

• To design and synthesize a biomimetic catalyst inspired by legume root nodules for enhanced lithium-sulfur battery performance.
• To investigate the phase transition and electronic structure modulation of cobalt selenide through sulfur doping.
• To elucidate the catalytic mechanism of the synthesized material for lithium polysulfide conversion and its impact on battery performance.

Main Methods:

• Synthesis of cobalt selenide supported on carbon nanofibers (CoSe@C) with a biomimetic hierarchical structure.
• Controlled sulfur doping to induce a phase transition from hexagonal (h-CoSe) to orthorhombic (o-CoSeS) cobalt selenide.
• Characterization of the catalyst's structure, phase, and electronic properties using techniques like X-ray diffraction and X-ray photoelectron spectroscopy.
• Density Functional Theory (DFT) calculations to understand the electronic structure and catalytic mechanism.
• Fabrication and electrochemical testing of Li-S batteries utilizing the modified separator with o-CoSeS@C.

Main Results:

• A novel biomimetic CoSe@C catalyst was successfully synthesized, mimicking the root-nodule architecture for hierarchical mass transport.
• Sulfur doping induced a phase transition to orthorhombic o-CoSeS with a high-spin state, enhancing catalytic activity.
• DFT calculations confirmed that the electronic configuration of o-CoSeS strengthens lithium polysulfide (LiPSs) adsorption and accelerates redox kinetics.
• Li-S batteries with o-CoSeS@C modified separators exhibited a high initial discharge capacity (1509 mAh g⁻¹ at 0.1 C) and remarkable cycling stability (0.057% decay per cycle over 1000 cycles at 1 C).

Conclusions:

• The biomimetic hierarchical structure and optimized electronic state of o-CoSeS synergistically enhance catalytic activity and mass/charge transport in Li-S batteries.
• The study demonstrates a novel strategy for designing high-performance catalysts by mimicking natural systems and tuning transition metal electronic structures.
• The findings provide valuable atomic-level insights into catalyst optimization for advanced energy storage applications, particularly Li-S batteries.