Fabrications and electrochemical properties of fluorine-modified spinel LiMn₂O₄ for lithium ion batteries

Spinel LiMn₂O₄ was modified by an aqueous fluoride modification method (AFMM). It is found that tiny crystals of potassium manganese trifluoride (KMnF₃) grew on the surface of the spinel particles during the electrochemical process. The quantity and the integrality of the KMnF₃ crystals were controlled by varying current density and processing time. The mechanisms of the formation of KMnF₃ were discussed. The harmful two-phase reaction of LiMn₂O₄ upon cycling was suppressed after the cathode was processed by AFMM. The chemical diffusion coefficients (D_s) of Li⁺ were measured by a potential relaxation technique (PRT). The values of D_s obtained in this way are of the order of 10^-10-10^-9 cm²/s.