Solid Electrolyte Interphase Formation on Lithium-Ion Electrodes: A [sup 7]Li Nuclear Magnetic Resonance Study

Lithium-7 nuclear magnetic resonance (NMR) measurements on electrodes from aged and cycled lithium-ion batteries have been performed. The active cathode material was LiNi 0.8 Co 0.2 O 2 , and the anode consisted of a commercial graphite blend. Cells were aged by storage under 60% charge at elevated temperatures. One of the primary failure mechanisms believed to occur in these cells is the formation of a passivating layer on the positive electrode that eventually leads to loss of electrical contact between active cathode particles. The NMR spectra demonstrate buildup of a solid electrolyte interphase (SEI), characterized by a relatively featureless absorption centered at 0 ppm (aqueous LiCl reference). By comparing relative integrated spectral intensities of the SEI and the main cathode signal at 580 ppm, the SEI growth can be quantitatively monitored by NMR methods.