Electrochemical Performance of Cation Disordered Li Rich Li-Mn-O Material with NaCl Type Structure

摘要

A lithium rich manganese oxide (Li2Mn03) with a layered structure, is a potential candidate for next generation electrode material for Lithium ion battery due to its high theoretical capacity, 460 mAh/g. However, its low electric conductivity restricts especially initial electrochemical activity and subsequent electrochemical performance. Recently, other Li rich materials such as Li3Nb04 based materials et al, with NaCl type structure are reported to show good electrochemical properties. In this study, we found that the Li2Mn03 was improved by structural change from the layer-type to a NaCl-type in which Li and Mn are disordered. The NaCl-type Li2Mn03 was prepared by mechanically milling layer-type material. The NaCl-type material shows large reversible capacity of 320 mAh/g, respectively, while layer-type material, which is used as the precursor of the NaCl-type material, initially delivers reversible capacity of 50 mAh/g. However, its 15th discharge capacity showed about 50% of initial capacity. To improve the cycling performance, NaCl-type Li2MnO3 was combined with spinel type LiMn2O4. The composite was also prepared by mechanically milling the mixture of layer-type Li2MnO3 and LiMn2O4. The Li2MnO3-LiMn2O4 composite also adopts the NaCl type structure. The composite showed better electrochemical performance than that of NaCl-type Li2MnO3. The initial discharge capacity of the composite was 388 mAh/g, which is higher than that of NaCl-type Li2MnO3. The 15th discharge capacity of the composite showed more than 80% of initial capacity. Ex-situ XRD revealed that the lattice volume of NaCl-Li2Mn03 after 10 cycles expanded by about 25%, on the other hand, the composite expanded only 1 %, indicating that the spinel component restricted volume expansion during cycling and improved its cycling stability.