阅读说明：本技术 一种电解液添加物中微量游离酸的检测方法 (Method for detecting trace free acid in electrolyte additive ) 是由 顾红香 何立 袁云龙 于 2020-03-20 设计创作，主要内容包括：本发明提供一种电解液添加物中微量游离酸的检测方法,包括：将电解液添加物溶于非醇类有机溶剂,以三乙胺-乙腈溶液为滴定剂,采用电位滴定法测定电解液添加物中游离酸的含量。本发明提供的一种电解液添加物中微量游离酸的检测方法,可有效地防止电解液添加物的水解与醇解,提高样品检测的准确性,其用非水相pH电极来判断等当点,具有分析时间短,操作简单,灵敏度高,精密度高等特点,结果准确度高、重复性好,适用范围广。(The invention provides a method for detecting trace free acid in an electrolyte additive, which comprises the following steps: dissolving the electrolyte additive in a non-alcohol organic solvent, taking triethylamine-acetonitrile solution as a titrant, and measuring the content of free acid in the electrolyte additive by adopting a potentiometric titration method. The method for detecting the trace free acid in the electrolyte additive can effectively prevent hydrolysis and alcoholysis of the electrolyte additive and improve the accuracy of sample detection, uses a non-aqueous phase pH electrode to judge equivalence points, and has the characteristics of short analysis time, simplicity in operation, high sensitivity, high precision and the like, and has high result accuracy, good repeatability and wide application range.)

1. A method for detecting trace free acid in an electrolyte additive comprises the following steps: dissolving the electrolyte additive in a non-alcohol organic solvent, taking triethylamine-acetonitrile solution as a titrant, and measuring the content of free acid in the electrolyte additive by adopting a potentiometric titration method.

2. The method for detecting trace free acid in electrolyte additive according to claim 1, wherein the electrolyte additive is one or more selected from vinyl sulfate, lithium difluoro oxalato borate, and ethoxy (pentafluoro) cyclotriphosphazene.

3. The method for detecting trace free acid in an electrolyte additive according to claim 1, wherein the non-alcoholic organic solvent is one or more selected from dimethyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, ethyl formate, and tetrahydrofuran.

4. The method for detecting the trace free acid in the electrolyte additive as claimed in claim 1, wherein the ratio of the mass g of the electrolyte additive to the volume m L of the non-alcoholic organic solvent is 0.1-20: 50-100.

5. The method for detecting the trace free acid in the electrolyte additive as claimed in claim 1, wherein the water content of the non-alcoholic organic solvent is less than or equal to 2000 μ g/m L, and the water content of the triethylamine-acetonitrile solution is less than or equal to 2000 μ g/m L.

6. The method for detecting trace free acid in electrolyte additive according to claim 1, wherein the triethylamine-acetonitrile solution is calibrated, comprising the following steps:

1) after adding a non-alcohol organic solvent into the hydrochloric acid standard solution, titrating the solution to an equivalent point by adopting a triethylamine-acetonitrile solution according to a potentiometric titration method to obtain the volume of the triethylamine-acetonitrile solution consumed by titrating the hydrochloric acid standard solution;

2) calculating according to the formula (1) to obtain the accurate concentration of the triethylamine-acetonitrile solution,

the formula (1) is: c₁V₁＝C₂V₂，

Wherein, C₁The exact concentration of triethylamine-acetonitrile solution, mol/L;

V₁the volume consumed for titrating the hydrochloric acid standard solution for the triethylamine-acetonitrile solution, m L;

C₂known exact concentrations of hydrochloric acid standard solutions, mol/L;

V₂volume of hydrochloric acid standard solution, m L.

7. The method for detecting the trace free acid in the electrolyte additive according to claim 6, wherein the volume ratio of the hydrochloric acid standard solution to the non-alcoholic organic solvent is 5-15: 70-110.

8. The method for detecting the trace amount of free acid in the electrolyte additive according to claim 1, wherein the step of measuring the content of the free acid in the electrolyte additive by using a potentiometric titration method comprises the following steps:

A) determination of blank sample: titrating the non-alcohol organic solvent to an equivalent point by adopting a calibrated triethylamine-acetonitrile solution to obtain the volume V consumed by the triethylamine-acetonitrile solution₀；

B) Determination of the actual sample: adding the electrolyte additive into a non-alcohol organic solvent for dissolving, and titrating to an equivalent point by using a calibrated triethylamine-acetonitrile solution to obtain the volume V consumed by the triethylamine-acetonitrile solution_{Triethylamine-acetonitrile}；

C) Calculating the content of free acid in the electrolyte additive according to the formula (2),

the formula (2) is:

wherein X is the content of free acid, mu g/m L;

C_{triethylamine-acetonitrile}The concentration of the calibrated triethylamine-acetonitrile solution is mol/L;

V₀the volume of triethylamine-acetonitrile solution consumed for titration of the blank sample, m L;

V_{triethylamine-acetonitrile}The volume of triethylamine-acetonitrile solution consumed for titration of electrolyte additives, m L;

W_{sample (A)}Mass of electrolyte additive, g;

M_HFrelative molecular mass of HF, 20.01 g/mol;

1000 is a scaling factor.

9. The method for detecting the trace free acid in the electrolyte additive according to claim 1, wherein the stirring speed of the titration by the potentiometric titration method is 2-4m L/min, and the liquid adding speed is 4-6m L/min.

Technical Field

The invention belongs to the technical field of lithium battery electrolyte detection, and relates to a method for detecting trace free acid in an electrolyte additive.

Background

The lithium ion battery is a green high-energy environment-friendly battery appearing in 90 s of the 20 th century, and compared with the traditional secondary battery, the lithium ion battery has the unique properties of high working voltage, high specific energy, small self-discharge, long cycle life, no memory effect, rapid charge and discharge and the like. Based on these advantages, lithium ion batteries have been developed with great leap and leap.

The lithium ion battery mainly comprises a positive electrode material, a negative electrode material, a diaphragm, an electrolyte material and the like. Electrolyte as lithium ion batteryOne of the four major materials, which is the medium for lithium ion transport in the battery, connects the positive and negative electrodes of the battery, and is figuratively called "blood" of the battery. The electrolyte is important to the exertion of various performances (such as energy density, cycle performance, rate capability, storage performance and the like) of the lithium ion battery, and has great influence on the safety performance of the battery. At present, the indexes affecting the quality of the electrolyte comprise: free acid, moisture, impurity metal ions, and the like. Wherein the content of free acids has a particularly important influence on the application of lithium batteries, on the one hand H⁺Can corrode the electrode, cause the dissolution damage of the anode material and generate interference on the SEI film on the surface of the electrode and the stability of the electrolyte. On the other hand, H⁺During the first charge and discharge process of the battery, lithium oxide, lithium hydroxide, hydrogen and the like are generated by direct reduction on the surface of the carbon negative electrode, limited lithium ions in the battery are consumed, the irreversible capacity and the internal pressure of the battery are increased, and the improvement of the electrochemical performance is not favorable.

Therefore, the content of free acid in the electrolyte additive should be controlled within a small range, and it is important to establish a method for quickly and accurately detecting acidity.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, the present invention provides a method for detecting trace free acid in an electrolyte additive, which is used to solve the problem of lack of rapid and accurate determination of the content of trace free acid in the electrolyte additive in the prior art.

In order to achieve the above and other related objects, the present invention provides a method for detecting trace amount of free acid in electrolyte additive, comprising: dissolving the electrolyte additive in a non-alcohol organic solvent, taking triethylamine-acetonitrile solution as a titrant, and measuring the content of free acid in the electrolyte additive by adopting a potentiometric titration method.

Preferably, the electrolyte is lithium ion battery electrolyte

Preferably, the electrolyte additive is selected from one or more of vinyl sulfate, lithium difluoro (oxalato) borate and ethoxy (pentafluoro) cyclotriphosphazene.

The electrolyte additive isAn additive dissolved in an electrolyte solvent in the electrolyte. The electrolyte solvent is selected from one or more of cyclic carbonate, linear carbonate and sulfone compounds. Wherein the cyclic carbonate is selected from one or more of Ethylene Carbonate (EC), fluoroethylene carbonate (FEC) and Propylene Carbonate (PC). The linear carbonate is selected from one or more of diethyl carbonate (DEC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC). The sulfone compound is oligoether sulfone EMES (molecular formula: CH)₃OCH₂CH₂SO₂C₂H₅)。

Preferably, the non-alcoholic organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, ethyl formate, tetrahydrofuran.

Preferably, the water content of the non-alcoholic organic solvent is less than or equal to 2000 [ mu ] g/m L, water may be present in the non-alcoholic organic solvent, but the water may cause hydrolysis and alcoholysis of the electrolyte additive, so that the water content of the non-alcoholic organic solvent needs to be strictly controlled to improve the detection accuracy of trace free acid in the electrolyte additive.

Preferably, the ratio of the mass (g) of the electrolyte additive to the volume (m L) of the non-alcoholic organic solvent is 0.1-20:50-100, more preferably, the ratio of the mass (g) of the electrolyte additive to the volume (m L) of the non-alcoholic organic solvent is 5-15: 70-90.

In the case of small content of free acid in the electrolyte additive, the sample weighing amount of the electrolyte additive sample is increased properly; in the case of a large free acid content in the electrolyte additive, the sample weighing of the electrolyte additive sample should be reduced appropriately; therefore, a normal E-V curve and an accurate equivalence point are ensured to be provided by the instrument detection, and the accuracy of the detection result is ensured.

Preferably, the water content of the triethylamine-acetonitrile solution is less than or equal to 2000 mu g/m L, the water content of the triethylamine-acetonitrile solution is strictly controlled so as to effectively prevent hydrolysis and alcoholysis of the electrolyte additive and improve the detection accuracy of trace free acid in the electrolyte additive.

Preferably, the triethylamine-acetonitrile solution is to be calibrated, comprising the following steps:

1) after adding a non-alcohol organic solvent into the hydrochloric acid standard solution, titrating the solution to an equivalent point by adopting a triethylamine-acetonitrile solution according to a potentiometric titration method to obtain the volume of the triethylamine-acetonitrile solution consumed by titrating the hydrochloric acid standard solution;

2) calculating according to the formula (1) to obtain the accurate concentration of the triethylamine-acetonitrile solution,

the formula (1) is: c₁V₁＝C₂V₂，

Wherein, C₁The exact concentration of triethylamine-acetonitrile solution, mol/L;

V₁the volume consumed for titrating the hydrochloric acid standard solution for the triethylamine-acetonitrile solution, m L;

C₂known exact concentrations of hydrochloric acid standard solutions, mol/L;

V₂volume of hydrochloric acid standard solution, m L.

The triethylamine-acetonitrile solution is used as a titrant and needs to be calibrated to determine the accurate concentration of the triethylamine-acetonitrile solution.

Specifically, the concentration of the hydrochloric acid standard solution is 0.05-0.5 mol/L.

More preferably, the volume ratio of the hydrochloric acid standard solution to the non-alcoholic organic solvent is 5-15: 70-110.

More preferably, the concentration of triethylamine in the triethylamine-acetonitrile solution is in the range of 0.05-0.5 mol/L.

Preferably, the electrode used in the potentiometric titration method is a non-aqueous phase pH electrode. More preferably, the non-aqueous phase pH electrode is an 6.0229.100 non-aqueous phase pH electrode.

Preferably, the method for measuring the content of the free acid in the electrolyte additive by adopting a potentiometric titration method comprises the following steps:

A) determination of blank sample: titrating the non-alcohol organic solvent to an equivalent point by adopting a calibrated triethylamine-acetonitrile solution to obtain the volume V consumed by the triethylamine-acetonitrile solution₀；

B) Determination of the actual sample: adding the electrolyte additive into a non-alcohol organic solvent for dissolving, and titrating to an equivalent point by using a calibrated triethylamine-acetonitrile solution to obtain the volume V consumed by the triethylamine-acetonitrile solution_{Triethylamine-acetonitrile}；

C) Calculating the content of free acid in the electrolyte additive according to a formula (2), wherein the formula (2) is as follows:

wherein X is the content of free acid, mu g/m L;

C_{triethylamine-acetonitrile}The concentration of the calibrated triethylamine-acetonitrile solution is mol/L;

V₀the volume of triethylamine-acetonitrile solution consumed for titration of the blank sample, m L;

V_{triethylamine-acetonitrile}The volume of triethylamine-acetonitrile solution consumed for titration of electrolyte additives, m L;

W_{sample (A)}Mass of electrolyte additive, g;

M_HFrelative molecular mass of HF, 20.01 g/mol;

1000 is a conversion factor;

the electrolyte additive is mostly a fluorine-containing compound, and the generated acid is mainly HF.

More preferably, the non-alcoholic organic solvent is added in the same volume in steps a) and B).

Preferably, the titration parameters of the potentiometric titration method are shown in table 1.

TABLE 1

As described above, the method for detecting trace free acid in electrolyte additive provided by the invention has the following beneficial effects:

(1) according to the method for detecting the trace free acid in the electrolyte additive, provided by the invention, triethylamine-acetonitrile solution is used as a titrant, and because the traditional titrant such as sodium hydroxide, potassium hydroxide or other alkaline solid substances is easily dissolved in water or an alcohol solvent, and triethylamine is liquid and can react with hydrochloric acid in an equimolar manner, the influence of water and alcohol substances on the electrolyte additive can be avoided, the hydrolysis and alcoholysis of the electrolyte additive can be effectively prevented, and the accuracy of sample detection is improved.

(2) According to the method for detecting the trace free acid in the electrolyte additive, provided by the invention, the non-alcohol organic solvent is selected to dissolve the electrolyte additive, so that the toxicity and the detection cost can be effectively reduced. Meanwhile, the titrant and the solvent are selected, so that the hydrolysis and alcoholysis of the electrolyte additive in the measurement process can be effectively prevented, and a normal E-V curve and an accurate equivalence point are provided.

(3) According to the method for detecting the trace free acid in the electrolyte additive, the free acid in the electrolyte additive is measured by adopting a potentiometric titrator, and the equivalence point is judged by using a non-aqueous phase pH electrode, so that the method has the characteristics of short analysis time, simplicity in operation, high sensitivity, high precision and the like, and is high in result accuracy, good in repeatability and wide in application range. The method is simple and easy to implement, and can be used for real-time central control analysis in research and development or production.

Drawings

FIG. 1 shows the calibration E-V diagram of a triethylamine-acetonitrile standard solution, wherein EP1 is the equivalence point.

Figure 2 shows solvent blank E-V diagrams for ethyl acetate.

Fig. 3 shows an E-V diagram of a sample electrolyte additive, wherein EP1 is the equivalence point.

Detailed Description

The present invention is further illustrated below with reference to specific examples, which are intended to be illustrative only and not to limit the scope of the invention.

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

The materials, reagents and equipment used in the following examples are as follows:

1. materials, reagents

The electrolyte additive comprises vinyl sulfate, lithium difluoro oxalate borate, ethoxy (pentafluoro) cyclotriphosphazene (Jingzhou Corpeng company), an electrolyte solvent, triethylamine (HP L C pure, CNW company), acetonitrile (HP L C pure, Merk company), dimethyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, ethyl formate, tetrahydrofuran (analytically pure, Runjie chemical) and a hydrochloric acid standard solution (national drug group).

2. Instrument for measuring the position of a moving object

809Titrando potentiometric titrators (Vantone, Switzerland); 6.0229.100 non-aqueous phase pH electrode (Switzerland).

In the specific implementation process, the content of free acid in the electrolyte additive is detected according to the following scheme.

The method comprises the steps of taking triethylamine-acetonitrile solution as a titrant, enabling the concentration range of triethylamine in the triethylamine-acetonitrile solution to be 0.05-0.5 mol/L, enabling the water content of the triethylamine-acetonitrile solution to be less than or equal to 2000 mu g/m L, and needing to be calibrated to determine the accurate concentration of the triethylamine-acetonitrile solution, adding a certain volume of non-alcohol organic solvent into a certain volume of hydrochloric acid standard solution with known accurate concentration, wherein the volume ratio of the hydrochloric acid standard solution to the non-alcohol organic solvent is 5-15: 70-110, and the concentration of the hydrochloric acid standard solution is 0.05-0.5 mol/L.

According to the potentiometric titration method, the triethylamine-acetonitrile solution is adopted to titrate to an equivalent point, the volume of the triethylamine-acetonitrile solution consumed by titrating the hydrochloric acid standard solution is obtained, and an E-V diagram is calibrated, and is shown in figure 1. And then calculating according to a formula (1) to obtain the accurate concentration of the triethylamine-acetonitrile solution, wherein the formula (1) is as follows: c₁V₁＝C₂V₂Wherein, C₁Of triethylamine-acetonitrile solutionExact concentration, mol/L, V₁Volume consumed for titrating hydrochloric acid aqueous solution for triethylamine-acetonitrile solution, m L, C₂Is the known accurate concentration of hydrochloric acid standard solution, mol/L, V₂Volume of aqueous hydrochloric acid solution, m L.

Taking a certain volume of non-alcohol organic solvent, titrating the calibrated triethylamine-acetonitrile solution to an equivalent point to obtain the volume V consumed by the triethylamine-acetonitrile solution₀The volume of triethylamine-acetonitrile solution consumed for titrating the blank sample is obtained, and an E-V diagram is shown in figure 2.

Adding a certain amount of electrolyte additive into a certain volume of non-alcohol organic solvent for dissolving, and titrating the calibrated triethylamine-acetonitrile solution to an equivalent point to obtain the volume V consumed by the triethylamine-acetonitrile solution_{Triethylamine-acetonitrile}I.e. the volume of triethylamine-acetonitrile solution consumed for titration of the electrolyte additive, figure E-V, is obtained, see figure 3, wherein the electrolyte additive is selected from one or more of vinyl sulfate, lithium difluorooxalato borate, ethoxy (pentafluoro) cyclotriphosphazene, the ratio of the mass (g) of electrolyte additive added to the volume of non-alcoholic organic solvent added (m L) is 0.1-20:50-100, preferably 5-15: 70-90.

The non-alcohol organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl acetate, methyl acetate, ethyl formate and tetrahydrofuran, the water content of the non-alcohol organic solvent is less than or equal to 2000 mu g/m L, an electrode adopted in the potentiometric titration method is a non-aqueous phase pH electrode, and the volumes of the non-alcohol organic solvent added in the measurement of the blank sample and the actual sample are the same.

Then, calculating the content of free acid in the electrolyte additive according to a formula (2), wherein the formula (2) is as follows:

wherein the content of the first and second substances,

x is free acid content, μ g/m L;

C_{triethylamine-acetonitrile}The concentration of the calibrated triethylamine-acetonitrile solution is mol/L;

V₀the volume of triethylamine-acetonitrile solution consumed for titration of the blank sample, m L;

V_{triethylamine-acetonitrile}The volume of triethylamine-acetonitrile solution consumed for titration of electrolyte additives, m L;

W_{sample (A)}Mass of electrolyte additive, g;

M_HFrelative molecular mass of HF, 20.01 g/mol;

1000 is a scaling factor.

The titration parameters of the above potentiometric titration method are shown in Table 1.