Local Study of Lithiation and Degradation Paths in LiMn2O4 Battery Cathodes: Confocal Raman Microscopy Approach

Abstract

Lithium manganese-based cathodes are widely used in rechargeable batteries due to their low cost, safety, and ecological stability. On the other hand, fast capacity fade occurs in LiMn2O4 mainly because of the induced manganese dissolution and formation of additional phases. Confocal Raman microscopy provides many opportunities for sensitive and spatially resolved structural studies of micro- and nanoscale phenomena. Here, we demonstrate advantages of confocal Raman spectroscopy approach for uncovering the mechanisms of lithiation/delithiation and degradation in LiMn2O4 commercial cathodes. The analysis of Raman spectra for inspecting local lithiation state and phase composition is proposed and exploited for the visualization of the inhomogeneous distribution of lithium ions. The cycling of cathodes is shown to be followed by the formation and dissolution of the Mn3O4 phase and local disturbance of the lithiation state. These processes are believed to be responsible for the capacity fade in the commercial batteries.