Expediting sulfur redox kinetics by redistributing d-orbital states in Ni2P via cation doping for high-performance lithium–sulfur battery

Abstract

Doping engineering is considered as a key approach to develop catalysts for Li-S batteries that can mediate redox reaction and chemisorption immobilization of polysulfides. However, the rationalization of doping elements selection and the intrinsic regulatory essences remain elusive. Herein, we propose a sensible strategy of modulating the electron-filled state of d-orbital of the Ni elements to accelerate redox dynamics of polysulfides. Concretely, we introduce dopants (V3+ or Mn2+) that feature empty or half-filled vacant 3d orbitals to substitute partial cations of Ni2P. The analysis confirms that the electrons of Ni 3d orbitals can be transferred to the doped atoms with unoccupied orbitals, resulting in a reduced electron-filling number of the Ni 3d orbitals. Notably, the electrons are more inclined to transfer to V with empty orbitals compared to Mn with partially occupied orbitals. More importantly, we delineate the relationship between electron-filled state of the Ni 3d orbitals and polysulfides adsorption-catalytic activity as well as corresponding intrinsic mechanism. Benefiting from the above advantages, the cell with V-Ni2P separator can achieve a discharge capacity of 1052 mAh g–1 at high sulfur loading (5.4 mg cm–2) and lean electrolyte (E/S = 6 μLE mg–1S) condition. This work illustrates essential link between d-electron filling state of metal atoms and adsorption-catalytic activity of polysulfides, which provides a pointer for rational selection of doping elements.