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

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 μL_E mg^–1_S) 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.