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

A new atomic-level strategy is introduced to finely optimize the OH− adsorption/desorption capability of β-Ni(OH) 2 through tailoring the 3d-orbital occupancy of Ni center via Co and Cu co-doping. [Display omitted] • The 3d-orbital electron occupancy of Ni species in β-Ni(OH) 2 can be optimized. • The interaction mechanism between OH− and Ni(OH) 2 is fully studied. • Co-Cu-Ni(OH) 2 electrode delivers a good capacity of 170.8 mAh g−1 and 2.3 mAh cm−2. 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. [ABSTRACT FROM AUTHOR]