Electronegativity-induced modulation of polysulfide adsorption in halogen-doped Ni2P to accelerate conversion kinetics for lithium-sulfur batteries

Abstract

Heteroatom doping has emerged as a powerful strategy to optimize the catalytic and adsorption abilities of electrocatalysts by regulating the electronic structure, thereby enabling the development of efficient electrocatalysts for lithium-sulfur (Li-S) batteries. However, the correlation between the properties of doped atoms and adsorption-catalytic ability, as well as the interconnection between adsorption strength and catalytic activity, remains underexplored. Herein, we employed halogen atoms (F, Cl, and Br) with different electronegativities to dope nickel phosphide (Ni₂P), aiming to modulate the adsorption properties toward lithium polysulfides (LiPSs). We systematically explored the relationship between the electronegativity of the doping atoms and the adsorption strength, followed by exploring the connection between adsorption and catalytic capabilities. Combined experimental and theoretical analyses reveal that doping halogen atoms effectively strengthens d-p orbital hybridization between Ni atoms and S atoms, thereby enhancing LiPSs anchoring and conversion. Specifically, the chemical adsorption capability is enhanced as the electronegativity of the doped atoms increases. Moreover, the catalytic activity presents a volcano-like trend with the enhancement of adsorption performance, wherein the activity initially increases and subsequently diminishes. Therefore, Cl-doped Ni₂P with moderate chemisorption ability exhibits optimal redox kinetics in bidirectional sulfur conversion. Consequently, the Li-S batteries with Cl-Ni₂P-separators deliver a high-rate capacity of 790 mAh g⁻¹ at 5 C and achieve a remarkable areal capacity of 7.36 mAh cm⁻² under practical conditions (sulfur loading: 7.10 mg cm⁻²; electrolyte/sulfur (E/S) ratio: 5 μL mg⁻¹). This work uncovers the significance of achieving a balance between adsorption and catalytic capabilities, offering insights into designing efficient electrocatalysts for lithium-sulfur batteries.