Interfacial side-reactions at a LiNi0.5Mn1.5O4 electrode in organic carbonate-based electrolytes

Interfacial side-reactions at a LiNi0.5Mn1.5O4 spinel electrode in LiPF6/organic carbonate-based electrolyte were investigated using FTIR and fluorescence spectroscopy. In situ measurements at a carbon- and binder-free LiNi0.5Mn1.5O4 electrode showed formation of fluorescent species that coincides with the oxidation of NiII + in LiNi0.5Mn1.5O4. The majority of these electrolyte oxidation products diffuse away into the electrolyte but fluorescence images of cycled LiNi0.5Mn1.5O4 composite electrodes also show fluorescent residues at the surface of the electrode. FTIR and Raman spectra of the surface layer indicate formation of metal-ion doped organic and inorganic compounds upon electrolyte oxidation at potentials above 4.2 V.