Efficient detection of hydrofluoric acid in electrolytes

The lithium hexafluorophosphate used in the lithium battery electrolyte inevitably entrains hydrofluoric acid into the final product during its preparation. When the content of hydrofluoric acid in a lithium battery exceeds a certain concentration, it will start to consume a limited amount of lithium ions, so that the irreversible capacity of the battery is increased, and the generated lithium oxide and lithium fluoride are not conducive to the improvement of the electrochemical performance of the electrode, and the reaction The generated gas causes an increase in the pressure inside the battery. As the hydrofluoric acid content continues to increase, the performance of the lithium battery such as charge and discharge, cycle efficiency, etc. is significantly reduced, and even completely destroyed.

Determination of hydrofluoric acid using NaOH standard solution

For the above reasons, it is necessary to strictly control the HF content in the lithium battery electrolyte to be less than 0.005%. Lithium hexafluorophosphate is hydrolyzed to form HF in contact with water. The determination of hydrogen fluoride in non-aqueous systems is mainly based on tetrabutylammonium hydroxide (NBu4OH) as a titrant and bromothymol blue (BTB) as an indicator, in an anhydrous methanol solvent, hydrogen fluoride and hydrogen in the electrolyte. Tetrabutylammonium oxide reacts:

N+Bu4OH-+HF=N+Bu4F-+H2O

But the reaction is accompanied by a reaction:

N+Bu4OH-+CH3OH=N+Bu4OCH3-+H2O

This side reaction brings some error to the analysis results, and the price of tetrabutylammonium hydroxide is also very expensive. In order to solve this problem, it has been proposed to use sodium methoxide as a titrant with some improvement. The commonality of the two methods is that BTB is used as an indicator to judge the end point by visual inspection, which will cause certain systematic errors. Therefore, the non-aqueous phase of acid-base titration is generally carried out with NaOH ethanol solution, and manual titration is carried out by using an automatic titrator or using bromocresol green as an indicator.

METTLER TOLEDO automatic potentiometric titrator

METTLER TOLEDO automatic potentiometric titrator

Today, titrations are usually done using a fully automated potentiometric titrator. The METTLER TOLEDO automatic titrator accurately controls the titration rate with a minimum drop of 0.5 μL and a titration curve with a first derivative that is more accurate. The automatic calculation of the instrument is convenient and fast, and the multi-row sample position autosampler effectively shortens the workflow.

OneClickTitration with automatic titrators truly achieves one-click titration, with automated multi-user management and flexible output capabilities to make experimentation easier.

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