Engineering Needle-like Nickel–Cobalt Layered Double Hydroxide Nanoarrays for Stable and Rapid Aqueous Magnesium-Ion Storage

Aqueous magnesium-ion batteries are attractive next-generation energy-storage systems because of their high safety, low cost, and environmental compatibility. However, the strong solvation and high charge density of Mg2+ lead to sluggish interfacial reaction kinetics and limited ion transport. Here, self-supported NiCo-LDH array electrodes were directly grown on nickel foam, and NH4F-assisted synthesis was employed to regulate the morphology and defect structure. Compared with nanosheet-based NiCo-LDH, needle-like N-NiCo-LDH/NF exhibits a more open three-dimensional architecture, a larger BET surface area, and a higher defect concentration, which together improve electrode–electrolyte accessibility and interfacial kinetics, as evidenced by a lower charge-transfer resistance. N-NiCo-LDH/NF delivers 87.1 mAh/g at 1 A/g, compared with 68.3 mAh/g for NS-NiCo-LDH/NF, and retains 89.7% capacity after 500 cycles and 69.7% after 2000 cycles at 5 A/g. Ex situ XPS and XRD reveal reversible Ni/Co valence evolution and Mg-related structural changes, supporting a coupled Mg2+/H+ charge-compensation process. Full cells assembled with activated carbon and PTCDI anodes retain 80.9% and 81.8% capacity, respectively, after 2000 cycles. These results establish correlations among growth-induced morphology/defect regulation, interfacial kinetics, structural stability, and multicarrier charge compensation in aqueous Mg-ion energy-storage systems, clarifying the benefits of integrated electrode design.