Biogenic birnessite is a stable form of manganese oxide found in nature that originates from microbial oxidation. Its unique structural properties provide potential for materials scientists to fabricate new functionalized materials. This study used a manganese-oxidizing fungus, Paraconiothyrium sp. WL-2, as a bio-oxidizer and biotemplate to prepare a lithium ion-sieve in the shape of a microtube through a solid-state transformation by calcination. The effect of calcination temperature was studied in terms of chemical composition, structure, and morphology. The results showed that the calcination temperature affects not only the weight fraction but also the crystallinity of the lithium manganese oxide spinel, which significantly influences the adsorption capacity of lithium ions.