Lithium insertion into manganese spinels

Lithium has been inserted chemically and electrochemically into Mn3O4 and Li[Mn2]O4 at room temperature. From X-ray diffraction, it is shown that the [Mn2]O4 subarray of the A[B2]X4 spinels remains unperturbed and that the electrons compensating for the Li+-ion charge reduce Mn3+ to Mn2+ in Mn3O4 and Mn4+ to Mn3+ in Li[Mn2]O4. In LixMn3O4, the tetragonal distortion due to a cooperative Jahn-Teller distortion by octahedral-site Mn3+ ions decreases with x from ca = 1.157 for x = 0 to ca = 1.054 for x = 1. The system Li1+x[Mn2]O4, is cubic at x = 0 and tetragonal (ca = 1.161) at x = 1.2. Electrochemical data reveal a two-phase region in the Li1+xMn2O4 system and a maximum xm = 1.25. X-ray diffraction confirms the coexistence of a cubic and a tetragonal phase in the compositional range 0.1 ≤ x ≤ 0.8. The X-ray data also show that the inserted Li+ ions occupy the interstitial octahedral positions of the spinel structure. However, in LixMn3O4 the tetrahedral-site Mn2+ions are displaced from the A positions to the interstitial octahedral positions, as in LixFe3O4, whereas the tetrahedral-site Li+ ions in Li[Mn2]O4 remain on the A sites.