Structural changes of manganese spinel at elevated temperatures

A chemical synthesis route to Cr-doped and undoped Mn spinel was developed for the purpose of detailed structural analysis for elucidating the relationship between storage performance and structural changes at elevated temperatures. We identified a two-phase segregation in the lithium compositional range of 0.6<x<1.0 for LixMn2O4, which is in the same region wherein severe degradation upon storage at elevated temperatures was observed for electrochemical cells. These two phases also coexist in Cr-doped spinel in the lithium compositional range of 0.4<x<0.9 for LixCr0.15Mn1.85O4. The investigation by X-ray diffraction (XRD) indicated that the crystallinity of the spinel decreased after storage at elevated temperatures. X-ray absorption fine structure (XAFS) analysis revealed that the Cr-doped samples showed less change in the local structure after storage than the undoped spinel samples. These results suggest that the Cr-doped spinel has higher structural stability at elevated temperatures than the undoped spinel.