| From the latest implementation of a number of national standards and documents closely related to lithium-ion batteries,we can know that focus on the key indicator of free acid content in electrolyte of lithium ion batteries,the lithium-ion battery industry,which directly serves the"Made in China 2025"and the main battlefield of the national economy,is still using acid-base titration and potentiometric titration that are completely unsuitable for the determination of trace components.So the technical bottleneck has not been effectively overcome in domestic and abroad for 30 years,which have to develop a new quantitative analysis methods and detection techniques.On the basis of overcoming the three influencing factors that limit the determination of free acid,this project proposes coulometric titration in non-aqueous media for the determination of free acid content in lithium-ion battery electrolytes.The proposed method is a simple,rapid,accurate and automatic and low detection limit quantitative analysis method for the lithium-ion battery industry,and has obtained satisfactory results.The specific research contents and research results are as follows:?1?To develop the coulometric titration for the determination of trace hydrofluoric acid in aqueous solution,so as to make up for the vacancy of coulometric titration for the determination of trace hydrofluoric acid so far.The electrolysis conditions of supporting electrolyte and its concentration,electrolysis current,titration end-point pH,etc.were investigated in detail.The results showed that the Er%of the determination results of different content of hydrofluoric acid was below 2.0,the RSD%was below 1.5,and the measured recoveries were between99.5%?101.1%,indicating that the proposed method was suitable for the determination of trace components.?2?To develop the coulometric titration for the determination of trace hydrofluoric acid in non-aqueous media,and lay a foundation for further study on the determination of free acid content in lithium hexafluorophosphate products.The organic solvent,supporting electrolyte and its concentration,electrolysis current,indicating electrode pair,titration end-point pH and other electrolysis conditions were discussed in detail.The best experimental conditions were as follows:the support electrolyte solution was 0.5 mol·L-1 LiCl ethanol solution,the working electrode pair was a platinum working electrode and a platinum wire auxiliary electrode,and the indicating electrode was a pH composite glass electrode,the constant current intensity was 0.200?3.000 mA,and the titration end-point was pH 5.50.When the hydrofluoric acid content was 10.0?g or more,the accuracy and precision of the measurement results were below 1.0%,and the accuracy and precision of the hydrofluoric acid content of 2.0?g and above were slightly poor,but it could be guaranteed below2.0%.In the recovery experiment,the recoveries were between 99.0%?102.0%,indicating that the proposed method was accurate and reliable.?3?In view of the three constraints of poor thermal stability of lithium hexafluorophosphate,reacting with water to produce hydrofluoric acid,and the difficulty of accurate determination of trace free acid,and based on the determination of trace hydrofluoric acid content in non-aqueous media,the study on the determination of free acid content in lithium hexafluorophosphate products by coulometric titration in non-aqueous media was carried out,which provides a simple,fast,accurate,automatic and low detection limit quantitative analysis method for fluorine chemical industry and lithium-ion battery industry.The measurement results showed that the relative standard deviation was below 2.0%as the content of free acid was 2.0?g and above.The lower limit of detection was 1.0?g and the recoveries were between 99.7%?102.3%.The determination results of the free acid content of the six products of lithium hexafluorophosphate were not significantly different from the national standard method,and the precision was below 1.0%.The effects of carbonate solvents,common additives,temperature changes and moisture content on the determination of free acid content were investigated,and the results show that the method was completely unaffected by the above factors.It not only provides a simple,fast,accurate,automatic and low detection limit quantitative analysis method for fluorine chemical industry and lithium-ion battery industry,but also provides technical support for the subsequent research on the effect of free acid on the performance of lithium-ion batteries. |
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