Determination of Trace Free Acid Content in Lithium-ion Battery Electrolytes by Coulometric Titration in Non-aqueous Media
A new quantitative analysis method is proposed, aiming at the difficulty in accurately determining the trace content of free acid in lithium-ion battery electrolytes in the past 30 years. The presented method overcomes the three restrictive factors upon the lithium-ion battery electrolytes, such as poor thermal stability, formation of hydrofluoric acid with water and difficulty in accurate determination of trace free acid. Free acid in lithium-ion battery electrolytes is directly titrated with ethoxide ion, which is generated through the electrolyzation of 0.50 mol·L-1 LiCl ethanol solution. The content of free acid is obtained according to the Faraday’s law, and the whole determination process can be completed in 5 minutes. The relative standard deviation is below 2.0% as the content of free acid is 2.0 μg and above. The detection limit is 1.0 μg and the recovery rate is 99.5%‒102.5%. In this method, the free acid determination is not affected by temperature change and the existence of small amount of water. Thus, it provides a simple, fast and accurate analytical method with lower detection limit for the free acid in the lithium-ion battery industry, and comprehensively improves the quality of lithium-ion battery electrolytes and the performance of lithium-ion battery products.