Determination of Free Acid in LiPF₆ Electrolyte by Coulometric Titration in Ice-Water System

A new method for rapid determination of the content of free acid in LiPF₆ electrolyte in an ice-water system was proposed. The optimized instrumental working conditions were found as follows:① 0-4℃ in the ice-water system as reaction temperature; ② 1.0 mol·L^-1 KCl solution as supporting electrolyte; ③ composite glass electrode as indicating electrode, platinum electrode and platinum wire auxiliary electrode as working electrode pairs; ④ constant current of 0.250-20.00 mA; ⑤ pH 7.40 as the titration end-point. The titrant OH^- generated by constant current electrolysis of water was reacted with free acid in the electrolyte, and the content of free acid obtained was determined by the Faraday's law of electrolysis. The results showed that the whole measurement process could be completed within 5 minutes. The linearity range of the standard curve was kept in the range of 5.0-200 μg, with lower limit of determination of 5.0 μg; the recoveries found by the spiked test were ranged from 99.7% to 102%. Four actual samples were analyzed by this method, giving RSDs (n=5) of the measured values less than 1.0%, consistent with the coulometric titration in non-aqueous systems and far superior to the potentiometric titration method.