Modulating Interfacial Potential Gradients in Metal-Carbon Catalysts via Phase-Engineering for Lithium-Sulfur Batteries

Abstract

Lithium-sulfur batteries (LSBs) suffer from sluggish sulfur redox kinetics and severe shuttling of lithium polysulfides (LiPSs). Although increasing the active surface area of metal-carbon electrocatalysts improves LiPSs redox kinetics, unlocking further improvements requires enhancing intrinsic catalytic activity of the expanded active sites. Herein, a fundamental investigation is conducted to enhance the catalytic capability of active sites by controlling the crystalline phase of the encapsulated cobalt. Theoretical calculations reveal that modulating the cobalt crystalline phase from HCP to FCC enhances the interfacial potential gradient, which serves as the driving force for electron transfer from cobalt to carbon shell at the metal-carbon interface. Guided by this insight, a deliberate temperature-controlled annealing is conducted to regulate the thermodynamically stable phase of cobalt, while alleviating the structural variations of carbon shells. Comprehensive spectroscopic analyses confirm that this approach modulates the electron band structure of the carbon shell, elevating the valence band maximum and enriching the electronic density near the Fermi level. As a result, F-Co@NC exhibits superior LiPSs redox kinetics and strong LiPSs adsorption capability, which in turn improves the electrochemical performance of LSBs. This work presents a broadly applicable design strategy for advancing metal-carbon electrocatalysts, capable of delivering synergistic effects with previous studies.