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.
Highlights
The electrochemical studies of manganese oxides-based electrode materials based on LiMn2 O4(LMO) have been carried out since 1980 [1,2,3], providing an alternative to LiCoO2, which had been proposed three years earlier [4]
Raman spectroscopy for this studying intercalation/deintercalation the ion profile has to be changed approach smoothly, but approximation is valid in case of processes in lithium manganese spinel cathodes
Raman spectra acquired on a sharp profile, appearing due to specific kinetics of lithiation accompanied with the formation of large areas of active particles combined with spatially resolved ones the lower lithiation state in the center of particle and higher lithiation state near the particle edge could shed‘radial light on the main features inhomogeneous lithiation and delithiation
Summary
The electrochemical studies of manganese oxides-based electrode materials based on LiMn2 O4. In LiNi0.8 Co0.15 Al0.05 O2 , LiNi1/3 Co1/3 Mn1/3 O2 , Kostecki et al demonstrated significant non-uniformity depending on SOC within the electrode [26,27] They used intensity of some Raman bands to visualize state of charge of the material and to evaluate its correspondence to the distribution of carbon conductive filler [26,27]. F1g (1) peak is related to vibration of the lithium sublattice and, its intensity gradually decreases upon delithiation [31] This mode is absent in the λ-MnO2 state [31]. Kanoh et al analyzed in-situ Raman spectra of thin layered LMO electrode and correlated the ratio of ~600 cm−1 A1g mode intensities in lithiated and completely delithated state to the state of charge of the material [34]. The proposed approach of spatially resolved Raman spectroscopy was shown to be an attractive method for studying lithiation/delithiation processes and degradation of electrode material
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