Adsorbing and salvaging extremely small quantities of lithium ion, high-performance ion-exchange type lithium ion adsorbent was prepared through the ion-sieve formation method. The method uses acid treatment after the synthesis of spinel-structured nano-Li1.33Mn1.67O4 precursor through the tartaric acid gel process. It has good selectivity and high efficiency in adsorbing lithium ion in seawater. The generated adsorbent showed a 28.2 mg/g lithium uptake from artificial seawater. This adsorbent further showed a difference reproducibility that was lower than 10% when subjected to five cycles of adsorption and desorption experiments.