The nature of the phases obtained by acid digestion of LiMn2O4 phases prepared at 800°C from a mixture of Mn02 (EMD) and Li2CO3 was investigated. We found that the complete transformation toward a-Mn02 and then -y-Mn02 observed for LiMn2O, treated in 2.5 M H2S04 for 24 h at 05°C is highly dependent on the amount of water in the reaction medium. The ) -. u/-y transformation was found to be the result of a dissolution.-crystallization mechanism that can be completely avoided by adding a soluble Ri, Pb, or TI salt to the reaction medium. By coupling energy dispersive spectroscopy analysis, infrared spectroscopy, and potentiometric titration, we demonstrated the presence of Bi species adsorbed at the surface of the X-MnO, oxide thus modifying its reactivity. In addition, the kinetics of the X -°u/-y phase transformation was found to depend on the amount of added Bi salt, suggesting the complexing role of Bi toward Mn (Ri-Mn complexes), thereby affecting the crystallization step of the reaction. The same treatment was applied to LiMn,04 in the presence of a Bi salt in anhydrous electrolyte (LiPF6/ethylene carbonate/dimethyl carbonate). In this case, the spinel oxide dissolution slows down and Ru1 precipitates. With respect to recent findings about the mechanisms involved in the electrochemical capacity failure at elevated temperature in Li-ion LiMn2O4 cells, these results open new alternatives to solve this recurrent problem.