Synergistic Ostwald Ripening Suppression and Organic Acid Ligand Engineering for Micrometer‐Scale β‐FeOOH Nanorod Arrays as Ultrahigh‐Capacity Lithium‐Ion Battery Anodes

Nanomaterials exhibit unique physicochemical properties that differ from their bulk counterparts, while controlled nanoparticle self-assembly enables collective properties beyond discrete nanostructures. Simultaneously achieving precise nanoscale control and macroscopic structural ordering remains a significant challenge. Herein, a synergistic approach combining Ostwald ripening suppression with organic ligand engineering is presented to achieve micrometer-scale β-FeOOH nanorod arrays. Adding ZnCl₂ and octanoic acid during FeCl₃ hydrothermal hydrolysis is key. ZnCl₂ both limits nanorod growth to sub-50 nm via competitive Zn²⁺/Fe³⁺ complexation, suppressing Ostwald ripening, and promotes oriented self-assembly via [ZnCl₄]^2- complex formation, compressing the electric double layer and enhancing interactions. Octanoic acid aids assembly via surface ligand engineering, enabling large-scale ordered domains. The resulting parallel-aligned nanorod architecture exhibits enhanced stability and promotes enhanced Li⁺ diffusion/charge transfer. As a lithium-ion battery anode, this hierarchical material delivers a high capacity of 2168.9 mAh g^-1 at 1 A g^-1 after 850 cycles, exceeding most reported anodes. This work establishes a generalizable approach for bridging nanoscale precision with macroscopic organization, offering opportunities for designing advanced energy storage materials via programmable assembly.