Abstract: The spinel precursor Li_1.6Mn_1.6O₄ was synthesized via a solid-state reaction, followed by hydrochloric acid treatment to obtain the lithium-ion sieve MnO₂·0.5H₂O. Physical characterization revealed that both the polycrystalline precursor Li_1.6Mn_1.6O₄ and the MnO₂·0.5H₂O ion sieve maintained nearly pure spinel structures, exhibiting high structural stability during the adsorption-desorption process. Calcination at 425 ℃, with a Li/Mn molar ratio of 1.1, resulted in the lithium-ion sieve MnO₂·0.5H₂O, prepared by acid washing the precursor with 0.1 mol/L hydrochloric acid, achieving an adsorption capacity of up to 34.617 mg/g, with only a 1.49% manganese leaching loss. Its adsorption behavior conformed to the Langmuir isotherm model and pseudo-second-order kinetics model, indicating that the MnO₂·0.5H₂O ion sieve possessed uniform adsorption sites during the Li⁺ adsorption process, and that process was characterized as chemical adsorption. In separation experiments using simulated solutions, it was found that the MnO₂·0.5H₂O ion sieve exhibited a high selective adsorption capacity for Li⁺ in simulated solutions with high concentrations of Na⁺ and K⁺. Therefore, this adsorbent can be effectively applied for Li⁺ recovery from lithium precipitation mother liquor.