<p>Lithium-aluminum layered double hydroxide (Li/Al-LDH) has been widely used in lithium extraction from salt-lake brines due to its high selectivity, easy recyclability, and environmental friendliness. This study involved the calcination of boehmite to form activated alumina, which was then used as an aluminum source to prepare high-specific-surface-area Li/Al-LDH via a hydrothermal method. The structure and adsorption performance of the adsorbents were systematically examined. The results indicate that the Li/Al-LDH synthesized from activated alumina exhibits a high specific surface area, abundant hydroxyl groups, and a porous morphology. This structure effectively increases the volume of mesopores and macropores, provides more active sites, facilitates the diffusion of Li⁺ within the adsorbent, and ultimately enhances the lithium-ion adsorption capacity. The effects of adsorption time, initial Li⁺ concentration, and solution pH on the Li⁺ adsorption performance were systematically investigated. Kinetic and isotherm modeling revealed that the adsorption process followed the pseudo-second-order kinetic model and the Langmuir isotherm, suggesting a chemisorption-dominated monolayer adsorption mechanism. The adsorbent prepared by this approach exhibited high selectivity for Li⁺ in a mixed solution containing Li⁺, Ca²⁺, Na⁺, Mg²⁺, and K⁺, and maintained a high Li⁺ adsorption capacity even after five consecutive adsorption cycles. This work provides a promising strategy for enhancing the Li⁺ adsorption capacity of aluminum-based lithium adsorbents.</p>