Phase transition of lithiated-spinel Li2Mn2O4 at high temperature
(1. School of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China
2. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China)
2. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China)
Abstract: The phase transition of Li2Mn2O4 spinel at high temperature was investigated by XRD, TG/DTA, average oxidation state of Mn and cyclic voltammeric techniques. The results reveal that the Li2Mn2O4 spinel is unstable. At high temperature, it is easy to transform into [Li2-2x]tet[Mn2-xLix]octO4, which accompanies the formation of Li2MnO3 impurities. The phase transition is associated with the transfer of Li+ from tetrahedral 8a sites to octahedral 16d sites. With the increasing sintering temperature from 450 ℃ to 850 ℃, the phase structure varies from lithiated-spinel Li2Mn2O4 to Li4Mn5O12-like to LiMn2O4-like and finally to rock-salt LiMnO2-like. In addition, a way of determining x with average oxidation state of Mn and the content of Li2MnO3 was also demonstrated.
Key words: lithium manganese oxide; Li2Mn2O4; phase transition; lithium-ion batteries