Regulating the 3d-orbital occupancy on Ni sites enables high-rate and durable Ni(OH)₂ cathode for alkaline Zn...

The capacity and cycling stability of β-Ni(OH)₂-based cathodes in aqueous alkaline Ni-Zn batteries are still unsatisfactory due to their undesirable OH^- adsorption/desorption dynamics during the electrochemical redox process. To settle this issue, we introduce a new atomic-level strategy to finely modulate the OH^- adsorption/desorption of β-Ni(OH)₂ through tailoring the 3d-orbital occupancy of Ni center by Co/Cu co-doping (denoted as Co-Cu-Ni(OH)₂). Both experimental outcomes and density functional theory calculations validate that the co-doping of Co and Cu endows the Ni species in Co-Cu-Ni(OH)₂ with appropriate proportion of the unoccupied 3d-orbital, leading to optimized adsorption/desorption strength of OH^-. As anticipated, the Co-Cu-Ni(OH)₂ electrode demonstrates superior performance, achieving an areal capacity of 0.83 mAh cm^-2 and a gravimetric capacity of 164.3 mAh g^-1 at ∼50 mA cm^-2 (10 A g^-1). Furthermore, it sustains an impressive capacity of 170.8 mAh g^-1 (2.3 mAh cm^-2) at a high mass loading of 13.5 mg cm^-2, alongside a long-term cycling performance over 1000 cycles. The assembled Co-Cu-Ni(OH)₂//Zn cell is able to provide a peak energy density of 0.98 mWh cm^-2 and excellent durability. This work highlights the potential of an orbital engineering strategy in the development of next-generation high-capacity and durable energy storage materials.