Fourier-transform infrared (FTIR) spectroscopy has been used to identify the solid electrolyte interphase (SEI) formed on Li-doped spinel Li1.05Mn1.96O4 cathode. The major components in the SEI have been assigned, and the formation and evolution of the SEI over the initial charge–discharge cycle are discussed. By Fourier-transform infrared spectroscopy, it has been found that during the charge–discharge process, the SEI can be directly formed on the Li1.05Mn1.96O4 cathode, and is mainly composed of R-CO3Li and Li2CO3. In terms of composition, it is very similar to those formed on a carbon anode. In the initial cycle, the formation of R-CO3Li begins at 4.10V during the charging process, and becomes more distinct with increasing charge voltage. The formation of Li2CO3 begins at 4.10V during the discharge process, and becomes more distinct with decreasing discharge voltage. The SEI becomes more evident over subsequent cycles.