Quercetin, an organic antioxidant, has been employed as an additive in lithium-ion cells to enhance the electrochemical performance to enhance the cycle life and the overcharging characteristics of LiPF6/EC + EMC + DMC (1 M) when used as an electrolyte. A LiCoO2/graphite full cell with 0.05% quercetin showed a significant improvement in safety associated with overcharging tolerance and thermal stability, without causing damage in C-rate capability, and even a small improvement in cycle life performance. The quercetin-containing lithium battery showed an improvement in its electrochemical properties with 92% capacity retention after 350 cycles from 2.8 to 4.3 V, at a rate of 1 C; compared to 85% capacity retention for a cell without quercetin operated under the same conditions. The electrochemical impedance spectroscopy (EIS) results for the LiCoO2 cathode show that the addition of 0.05% quercetin provides a significant suppression in the impedance of the cell after 60 cycles. The improvement might result from the formation of a passivation microstructure (from quercetin oxidation) on the electrode’s surface. The quercetin-containing batteries provided long term cycling and a high safety performance, making them a viable power source for applications involving electric devices with significant safety requirements.