When LiNi_xMn_yCo_(1-x-y)O₂ (NMC)/graphite Li-ion cells are operated at elevated temperature or at a cutoff potential above 4.2 V, electrolyte oxidation becomes increasingly severe leading to gaseous products and other oxidized species. Lithiated graphite and delithiated NMC electrode materials taken from high voltage NMC/graphite full cells were studied individually using the pouch bag method. The results obtained from the pouch bag method show that charged NMC positive electrodes stored at elevated temperature in pouch bags create more gas than the same electrodes stored in pouch full cells at the same temperature. The charged NMC electrodes removed from pouch bags after storage at elevated temperature had larger impedance than those removed from pouch full cells. These two observations show that there are interactions between positive and negative electrodes that limit gas evolution and reduce impedance growth in Li-ion cells. X-ray photoelectron spectroscopy studies were used to eliminate some possible mechanisms responsible for these phenomena.