Iron decorated ultrathin cobaltous hydroxide nanoflakes with impressive electrochemical reactivity for aqueous Zn batteries

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

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.

Zinc-dual-halide complexes suppressing polyhalide formation for rechargeable aqueous zinc-halogen batteries

Aqueous zinc-halogen batteries suffer from poor coulombic efficiency and short cycle life owing to the formation and dissolution of polyhalides in electrolytes. Herein, we apply a zinc-dual-halide complex strategy to confine free halides and suppress polyhalide formation. The high stabilities of zinc-dual-halide complexes are identified to be essential for effective confinement. The resulting Zn-Br2 and Zn-I2 cells deliver excellent rate capability and cycling stability, as well as high coulombic efficiency and energy efficiency.