Method for rapidly determining content of free acid in lithium hexafluorophosphate electrolyte by coulometric titration digital end-point method

Abstract

The invention relates to a method for rapidly determining the content of free acid in a lithium hexafluorophosphate electrolyte by a coulometric titration digital end-point method. According to the method, thermal decomposition of lithium hexafluorophosphate is inhibited by means of a low-temperature test environment, OH <-> generated by an electrolytic reaction and free acid in a sample to be tested are subjected to a neutralization reaction, a solution pH value collected by a pH indication system in real time is substituted into a mathematical model for repeated calculation, and then a reaction endpoint is judged, so that the aim of automatically controlling titration is fulfilled. The whole determination process can be completed within about 5 min, an obtained test result is good in accuracy, precision and repeatability; and the method has the advantages of being easy and convenient to operate, rapid, high in automation degree and the like; and the analysis and test method has good application prospects in industrial production.

Description

technical field [0001] The invention relates to the technical fields of analysis and detection and battery electrolyte, in particular to a method for rapidly measuring free acid content in lithium hexafluorophosphate electrolyte by a coulometric titration digital endpoint method. Background technique [0002] Lithium hexafluorophosphate (LiPF 6 ) not only has excellent oxidation stability and high energy density, but also is environmentally friendly and has a long cycle life. It is currently the most widely used and only commercialized lithium salt for electrolyte. However, the thermal stability of lithium hexafluorophosphate is poor, and it is easy to thermally decompose to form PF. 5 , and further react with trace water in the electrolyte to generate hydrofluoric acid. The existence of excess hydrofluoric acid will not only damage the structure of the SEI film, but also seriously affect the charge-discharge and cycle efficiency of lithium-ion batteries. Therefore, the c...

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Problems solved by technology

This method is suitable for in-situ determination, not only the measurement time is extremely long but also requires special instruments, so it cannot be popularized

[0006] In addition, the inventor team of the present application disclosed earlier a simple and rapid analysis and detection method for free acid content in lithium hexafluorophosphate products with automatic analysis capabilities (see Chinese patent CN110261464A). This method has the following problems: 1. In order to prevent the hydrofluoric acid produced by the hydrolysis of lithium hexafluorophosphate, the non-aqueous LiCl ethanol solution was selected as the supporting electrolyte solution. However, the maximum electrolysis current that can be kept constant is only 3.50mA, which is not suitable for electrolytes with high free acid content. Lithium salt and Determination of electrolyte samples; 2. During the test process, inert gas must be continuously replenished in order to eliminate the influence of dissolved oxygen in the non-aqueous supporting electrolyte solution. The relatively special equipment and operating skills make this method unfavorable for popularization; 3. The titration process is relatively complicated and needs to be carried out in steps. First, pre-titration and then formal titration, and this method directly relies on the pH value of the mixed solution measured by the pH composite glass electrode to determine the reaction end point. Once the measurement system or measurement temperature changes, the end point pH value will be changed. Change accordingly, at this time, if the original fixed pH value is used as the only and direct judgment standard for the end point, wrong measurement results will inevitably be obtained

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