Effects of 3-fluoroanisol as an Electrolyte Additive on Enhancing the Overcharge Endurance and Thermal Stability of Lithium-Ion Batteries

The overcharge issue still occupies a high safety risk for NCM cathode materials with less stable structure. In this work, an original overcharge protection electrolyte additive named as 3-fluoroanisol (3FA) is recommended for NCM 622. The anti-overcharge effect of 3FA was verified in detail by cycle voltammetry, constant-current overcharge and discharge, AC impendence and scanning electron microscopy measurement. The electrolyte conductivity and long-term cycle performance tests were conducted to evaluate the impact of 3FA on the cell system operated in conventional voltage range. The 3FA is electro-polymerized at about 4.4 V and the time from upper cut-off voltage to overcharge state is extended from 5.46 h to 11.82 h in CR2032 cell, no adverse effects are shown during normal use at the same time under the additive amount of no more than 5 wt.%. Moreover, C80 micro-calorimeter test shows that 3FA increases thermal stability of electrolyte and NCM 622 cathode system. The heat production during overcharge was measured further. With the increase of the amount of 3FA added, the heat production during overcharge increases and the peak heat release rate occurs near 4.4 V, which further proves the effect of overcharge protection of 3FA. Thus, 3FA enhances overcharge endurance and thermal stability of lithium-ion battery with NCM 622 cathode.