system. A positive shift in the oxidation peak indicates that the presence of lithium influences the reversibility of oxygen reduction. As shown by previous authors, this peak can be related to the oxidation of solvent decomposition products[14]. SEIRA analysis has been carried out to understand the In situ superoxide induced changes to the interface relating to the difference in reversibility observed in the CVs. Figure 4. Cyclic voltammograms for the reduction of oxygen (red) and the argon background (black) in 0.1 M LiClO4/PC, at 0.1 V/s scan rate. Corresponding SEIRA spectra in Figure 5b show strong positive as well as negative bands as the electrode is negatively polarized (the same spectra over a broader range are provided in the supporting information (Figure S2)). Upward going bands indicate the loss of PC at the interface, while strong downward bands indicate the formation of ring-opened carbonate species, ROCO2Li. All the downward going bands appearing at the less positive potentials remain stable, even at the most anodic polarizations, indicating that the surface layer formed is relatively stable. SEIRAS bands for PC-LiClO4 oxygenated as well as deoxygenated systems in the reduction as well as oxidations regions (2.12 V and 3.7 V respectively) are also summarized in Table 1 (please also see supplementary table S1). The PC opened species observed here is in line with the surface film observed on Li-O2 cathodes cycled in PC electrolyte[14], [34]. Superoxide species generated during the reduction of oxygen at the cathode are believed to be responsible for this degradation reaction[7], [14], [34]. We have left a moderate downward going peak seen around 1094 cm-1 unassigned; this band may be related to a coordinated superoxide species[36], but a detailed investigation is required before assigning this to superoxide because other species such as perchlorate also have infrared absorbance in this region.
system. A positive shift in the oxidation peak indicates that the presence of lithium influences the reversibility of oxygen reduction. As shown by previous authors, this peak can be related to the oxidation of solvent decomposition products[14]. In situ SEIRA analysis has been carried out to understand the superoxide induced changes to the interface relating to the difference in reversibility observed in the CVs. Figure 4. Cyclic voltammograms for the reduction of oxygen (red) and the argon background (black) in 0.1 M LiClO4/PC, at 0.1 V/s scan rate. Corresponding SEIRA spectra in Figure 5b show strong positive as well as negative bands as the electrode is negatively polarized (the same spectra over a broader range are provided in the supporting information (Figure S2)). Upward going bands indicate the loss of PC at the interface, while strong downward bands indicate the formation of ring-opened carbonate species, ROCO2Li. All the downward going bands appearing at the less positive potentials remain stable, even at the most anodic polarizations, indicating that the surface layer formed is relatively stable. SEIRAS bands for PC-LiClO4 oxygenated as well as deoxygenated systems in the reduction as well as oxidations regions (2.12 V and 3.7 V respectively) are also summarized in Table 1 (please also see supplementary table S1). The PC species observed here is in line with the surface film observed on Li-O2 cathodes cycled in PC electrolyte[14], [34]. Superoxide species generated during the reduction of oxygen at the cathode are believed to be responsible for this degradation reaction[7], [14], [34]. We have left a moderate downward going peak seen around 1094 cm-1 unassigned; this band may be related to a coordinated superoxide species[36], but a detailed investigation is required before assigning this to superoxide because other species such as perchlorate also have infrared absorbance in this region. opened