Formation and Disappearance of Spinel Nanograins in Li[sub 1.2−x]Mn[sub 0.4]Fe[sub 0.4]O[sub 2] (0≤x≤0.99) during Extraction and Insertion of Li Ions

The authors investigated the changes in local structures and magnetic property of the positive electrode material for lithium-ion batteries during the first charge–discharge cycle. Although has a composite structure of the layered and disordered cubic rocksalt before the electrochemical testing, nanometer-sized grains with spinel structures are formed during the extraction of Li ions up to . The spinel nanograins have weak spontaneous magnetization (ca. ), which is associated with the movements of Fe ions from the octahedral to the tetrahedral sites in both the layered and disordered rocksalt structures. The fraction of spinel nanograins decreased after the subsequent insertion of Li ions.