Surface Analysis of Electrodes from Cells Containing Electrolytes with Stabilizing Additives Exposed to High Temperature

We have conducted a detailed investigation of the effect of thermal stabilizing additives, including dimethyl acetamide (DMAc), N -methyl pyrrolidone, vinylene carbonate (VC), and vinylethylene carbonate (VEC), on the reactions of the electrolyte with the surface of the electrodes in lithium-ion cells. Cells were constructed with mesocarbon microbead anodes, LiNi 0.8 Co 0.2 O 2 cathodes, and 1.0 M LiPF 6 in 1:1:1 ethylene carbonate/diethyl carbonate/dimethyl carbonate electrolyte with and without electrolyte additives. The cells were stored sequentially at 55, 60, and 65°C for 10 days at each temperature. The cells were then dismantled, and the surfaces of the electrodes were analyzed via a combination of infrared spectroscopy with attenuated total reflection, X-ray photoelectron spectroscopy, and scanning electron microscope–energy dispersive spectroscopy. The surface of the electrodes extracted from cells containing the baseline electrolyte contained thick surface films composed of electrolyte decomposition products. The addition of 1% DMAc inhibits the reaction of the electrolyte with surface of the electrodes, especially on the anode. The addition of 1.5% VC results in the formation of poly(vinylene carbonate) on both electrodes and inhibits the reaction of electrolyte with the electrodes, especially the cathode. The addition of 1.5% VEC or 10% DMAc did not significantly impede the reaction of the electrolyte with the electrodes.