Synthesis and thermal stability of chemical delithiated lithium manganes oxide spinels

Synthesis and thermal stability of chemically delithiated Li1-xMn2O4 (0<X<1), which were made of LiMn2O4 using the ammonium persulfate ((NH4)(2)S2O8) as the oxidizing agent, were investigated. The resulting products were identified as a cubic spinel phase, and the characters of products corresponded to that of electrochemically prepared samples. From these results, we considered that the chemically delithiation process using (NH4)(2)S2O8 was the same as electrochemically charge process. The storage stability of Li1-xMn2O4 was examined in 1M LiPF6 ethylene carbonate (EC)/dimethyl carbonate (DMC) (1:2 by volume) electrolyte solution at 85 degrees C. Mn dissolution was increased with increase in Mn valence (Mn3+ --> Mn4+). However, the dissolution of Mn from Li1-xMn2O4 did not increase linearly with increase in Mn valence. Mn dissolution reaction was accelerated at a composition range of 0.4 < X < 0.6 in Li1-xMn2O4 compared with other range. In this range, the crystal structure of these compounds were transformed from homogenious spinel structure to two-phase spinel. We considered that Mn dissolution was affected by not only Mn valence but also the crystal structure.