In this study, triphenylphosphine boron trifluoride (BF3 · PPh3) was synthesized to be used as an electrolyte additive in Li/LiCoO2 half-cells. Fourier-transform infrared spectroscopy, X-ray diffraction, nuclear magnetic resonance, and X-ray photoelectron spectroscopy analysis techniques were used to determine the structure and composition of the synthesized substance. The battery performance was investigated by adding certain amounts of BF3 · PPh3 in 1 M LiPF6-ethylene carbonate/dimethyl carbonate/diethyl carbonate (1:1:1 by volume) electrolyte. CR2032 coin cells were assembled with the electrodes and electrolytes prepared in the laboratory. The electrochemical behaviors of the battery were investigated via cyclic voltammetry and charge–discharge tests. The addition of 0.5 wt% and 1 wt% BF3 · PPh3 in the electrolyte improved the lithium-ion battery’s ionic conductivity and capacity retention. The results show that BF3 · PPh3 has potential applications in lithium-ion batteries.