Method for testing moisture content in organic electrolyte by colorimetric method

Abstract

The invention relates to the technical field of testing of water content in electrolyte, in particular to a method for testing the water content in organic electrolyte by a colorimetric method, which comprises the following steps: A, preparing a carbonic ester solvent standard solution; b, taking the carbonic ester standard solution and the electrolyte to be detected which have the same volume, and respectively adding aldehyde ketone reagents with the same volume method into the carbonic ester standard solution and the electrolyte to be detected; c, color comparison: the color difference between the water content in the electrolyte and the standard solution is visually compared, and the carbonic ester comprises one or more reagent mixtures of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and ethyl methyl carbonate which are used as electrolyte solvents. According to the method, the water content in the electrolyte containing various additives is tested, the test cost is low, the test stability is good, and the performance and safety of the lithium ion battery are further guaranteed through accurate preparation and application of a proper indicator and strict operation procedures and instrument maintenance.

Description

Technical Field

[0001] The invention relates to the technical field of water content in electrolyte, in particular to a method for testing the water content in an organic electrolyte by colorimetry. Background Art

[0002] In the lithium-ion battery industry, the presence of water will have a great impact on battery quality, such as causing battery gassing, capacity reduction, etc. It will also cause the decomposition of the electrolyte to produce acid, which will further corrode the materials inside the battery, resulting in a decrease in battery performance, and in severe cases, battery explosion. Therefore, the moisture content must be strictly controlled in the battery materials and battery manufacturing process;

[0003] With the development and maturity of lithium and sodium batteries, the types of additives in their electrolytes have gradually increased. The general Coulometric aldehyde and ketone reagents cannot meet the determination of the moisture content of electrolytes in all states. Therefore, Karl Fischer reagent manufacturers have prepared a variety of formulas to adapt to different electrolytes. At the same time, different electrodes and Karl Fischer reagents are required. In particular, the various additives in the electrolyte will slowly react with the Karl Fischer reagent, and finally consume the iodine in the Karl Fischer reagent, resulting in a large amount of ineffective consumption of the Karl Fischer reagent. At present, in order to solve this problem, most manufacturers use the moisture content of the intermediate product to measure the moisture content of the finished product for the electrolyte moisture test, so there is a certain risk in the quality control of the finished product.

[0004] In this regard, China has applied for patent number: CN109254110A, which discloses a Karl Fischer reagent for detecting the moisture content of lithium-ion battery electrolyte and its preparation method. Calculated by mass fraction, the Karl Fischer reagent for detecting the moisture content of lithium-ion battery electrolyte of the present invention contains 1-10% iodine, 1-20% sulfur dioxide, 5-25% guanidine salt, 40-80% methanol, and 5-30% organic base. The present invention adds guanidine salt to methanol, stirs and dissolves it thoroughly, then adds organic base, and then adds iodine, stirs and dissolves it thoroughly, places the solution in an ice bath, and adds sulfur dioxide while stirring until the weight increases to the required weight of sulfur dioxide. After standing in the dark, the reagent is loaded into the Karl Fischer titrator used to obtain the Karl Fischer reagent. The reagent is cost-effective, safe and environmentally friendly, has little harm to the human body, can realize the accurate detection of the moisture content of lithium-ion battery electrolyte, and promotes the development of the battery industry;

[0005] Chinese patent application number: CN113671110A, discloses a method for detecting the moisture content of vinyl sulfate. The detection method uses Karl Fischer volumetric titration to measure the moisture content of vinyl sulfate. The detection method is configured with a titrant and a solvent. During the detection: first, a moisture meter is used to calibrate the titer to obtain the titer T of the titrant. Secondly, the moisture content of the vinyl sulfate sample to be measured is measured to obtain the moisture content W of the vinyl sulfate sample. The technical solution of the present invention is to use Karl Fischer volumetric titration to measure the moisture content of vinyl sulfate. Neither the titrant nor the solvent contains methanol. The titrant is composed of iodine, sulfur dioxide, chlorohydrin, and imidazole. Halogenated alcohol and cosolvent are added to the reaction solvent, which can ensure the hydroxyl group required for the Karl Fischer reaction and allow the reaction to proceed normally. It can also slow down the reaction of vinyl sulfate and alcohol. Even if a slight acidic reactant is generated, it can be neutralized by a large amount of imidazole in the solvent to buffer the pH value of the titration solution, slow down the side reaction, and finally achieve the water drop of vinyl sulfate.

[0006] The volumetric Karl Fischer reagent is used to titrate the water content in the electrolyte, but the minimum titration degree of the volumetric Karl Fischer is 2 mg, while the water content in the electrolyte is generally required to be less than 20 ppm. The amount of reagent required for titration is extremely small, and the error is large. At the same time, the potentiometric titration method of the volumetric Karl Fischer titrator is required. The titration process is slightly slow, and some side reactions will affect the titration results. Therefore, it has become an urgent problem to be solved to improve and perfect the above problems. Summary of the invention

[0007] The purpose of the present invention is to provide a method for testing the water content in an organic electrolyte by a colorimetric method, so as to solve the problem that the volumetric Karl Fischer reagent proposed in the above-mentioned background technology is used to titrate the water content in the electrolyte, but the minimum titration degree of the volumetric Karl Fischer is 2 mg, while the water content in the electrolyte is generally required to be less than 20 ppm, the amount of reagent required for titration is extremely small, the error is large, and the potentiometric titration method equipped with a volumetric Karl Fischer titrator is required, the titration process is slightly slow, and some side reactions will affect the titration results, while the visual colorimetric method has a simple operation process and low cost.

[0008] To achieve the above object, the present invention provides the following technical solution: a method for testing the water content in an organic electrolyte by colorimetry, comprising:

[0009] A. Prepare carbonate solvent standard solution;

[0010] B. Take the same volume of carbonate standard solution and electrolyte to be tested, and add the same volume of aldehyde and ketone reagent respectively;

[0011] C. Colorimetry: When the color of the electrolyte to be tested is darker or lighter than the color of the carbonate standard solution, the water content of the electrolyte to be tested is small.

[0012] Preferably, the carbonates include one or more reagent mixtures of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and ethyl methyl carbonate as electrolyte solvents.

[0013] Preferably, the step of preparing the standard aqueous solution of carbonate solvent comprises:

[0014] A. Take a carbonate organic solvent with a water content of less than 3ppm and add a certain amount of deionized water;

[0015] B. Determine the water content of the standard solution prepared in step A using coulometric titration.

[0016] Preferably, the carbonate standard solution and aldehyde ketone volumetric Karl Fischer reagent are stored in a sealed environment with a water content of <1 ppm, and care is taken to prevent the concentration of the standard solution from changing during storage. The validity period of the standard solution does not exceed 15 days.

[0017] Preferably, steps B and C are performed in an environment with a water content of less than 1 ppm. The moisture in the environment significantly interferes with the test and will affect the test.

[0018] Preferably, the colorimetry of the carbonate standard solution and the electrolyte to be tested is carried out in a colorimetric tube or other white transparent container. If the precise value of the water content in the electrolyte is to be tested, a series of carbonate standard solutions can be prepared.

[0019] Preferably, the colorimetry of the carbonate standard solution and the electrolyte to be tested is carried out in a colorimetric tube or other white transparent container.

[0020] Preferably, the operation time of steps B and C is 1-3 minutes.

[0021] Preferably, the Karl Fischer reagent comprises iodine, sulfur dioxide, pyridine and methanol.

[0022] Preferably, the preparation ratio of iodine, sulfur dioxide, pyridine and methanol is 1:3:10:50, and the preparation of Karl Fischer reagent is carried out in a dry environment.

[0023] Compared with the prior art, the beneficial effects of the present invention are: the method of using the colorimetric method to test the moisture content in an organic electrolyte can realize the test of the moisture content in an electrolyte containing a variety of additives, and the test cost is low and the test stability is good. By using the visual colorimetric method, the operation process is relatively simple and the cost is low. DETAILED DESCRIPTION

[0024] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The first embodiment provided by the present invention:

[0026] Hereinafter, preferred embodiments of the present invention will be described in detail, but the present invention is not limited to the contents of the examples.

[0027] A method for testing the water content in an organic electrolyte by colorimetry. The preferred embodiments of the present invention are described in detail below, but the present invention is not limited to the contents of the embodiments.

[0028] Prepare 20ppm diethyl carbonate standard solution:

[0029] In a glove box with a moisture content of less than 1ppm, 5A molecular sieves were added to the diethyl carbonate solvent and placed for 48 hours. The solvent was taken out and titrated using a coulometric potentiometric titrator, and the moisture content was 0.5ppm. In an environment with a dew point better than -50°C, 1000g of diethyl carbonate was taken, 20ul of deionized water was added thereto, and the mixture was stirred evenly. The mixture was then titrated using a coulometric Karl Fischer titrator to obtain a standard solution of diethyl carbonate with a moisture content of 20ppm. The standard solution of diethyl carbonate was placed in a glove box with a moisture content of less than 1ppm.

[0030] Sample preparation:

[0031] In the glove box, add 50 ml of diethyl carbonate standard solution to colorimetric tube 1, and add 50 ml of electrolyte containing boron, VC, FEC, DTD, PS, anhydride, and nitrile additives to colorimetric tubes 2 and 3 respectively, then quickly transfer 0.5 ml of aldehyde and ketone Karl Fischer reagent (titer is 2 mg / ml), and then quickly shake the test sample.

[0032] Colorimetric:

[0033] Comparing the colors of colorimetric tubes 2 and 3 with colorimetric tube 1, the colors of colorimetric tubes 2 and 3 are obviously browner than colorimetric tube 1. The water content in the electrolyte is measured to be less than 20 ppm.

[0034] Comparison method:

[0035] The coulometric method was used to test the water content in the electrolyte. 1.2 g of the above lithium-ion electrolyte was taken for water content test. The test result was 15.7 ppm. After the test, the drift value of the Karl Fischer titrator was always too high and the test could not be continued. The Karl Fischer reagent needed to be replaced and the titration cup and electrode cleaned.

[0036] The second embodiment provided by the present invention:

[0037] Hereinafter, preferred embodiments of the present invention will be described in detail, but the present invention is not limited to the contents of the examples.

[0038] Prepare 20ppm standard solution of diethyl carbonate DEC, dimethyl carbonate DMC, propylene carbonate PC (1:1:1):

[0039] In a glove box with a moisture content of less than 1ppm, add 5A molecular sieves to the DEC+DMC+PC (1:1:1) mixed solvent and place it for 48h. Take it out and titrate it with a coulometric potentiometric titrator. The moisture content is 0.5ppm. In an environment with a dew point environment better than 50℃, take 1000g of DEC+DMC+PC (1:1:1) mixed solvent, add 20ul of deionized water, stir evenly, and then titrate the mixture with a coulometric Karl Fischer titrator to obtain a DEC+DMC+PC (1:1:1) mixed solvent content of 20ppm. The standard solution of DEC+DMC+PC (1:1:1) mixed solvent is placed in a glove box with a moisture content of less than 1ppm.

[0040] Sample preparation:

[0041] In the glove box, add 50 ml of DEC+DMC+PC (1:1:1) mixed solvent standard solution into colorimetric tube 1, add 50 ml of sodium electrolyte containing boron, VC, FEC, DTD, PS, acid anhydride and nitrile additives into colorimetric tubes 2 and 3 respectively, then quickly transfer 0.5 ml of aldehyde and ketone Karl Fischer reagent (titer is 2 mg / ml), and then quickly shake the test sample.

[0042] Colorimetric:

[0043] Comparing the colors of colorimetric tubes 2 and 3 with colorimetric tube 1, the colors of colorimetric tubes 2 and 3 are obviously browner than colorimetric tube 1, and the water content in the electrolyte is measured to be less than 20 ppm.

[0044] Comparison method:

[0045] The coulometric method was used to test the water content in the electrolyte. 1.0 g of the sodium ion electrolyte with various additives was taken for water content test. The test result was 10 ppm. After the test, the drift value of the Karl Fischer moisture meter was always too high and the test could not be continued. The Karl Fischer reagent needed to be replaced and the titration cup and electrode cleaned.

[0046] It can be seen from the above two embodiments that: this method can realize the test of the water content in the electrolyte containing various additives, and the test cost is low and the test stability is good;

[0047] Colorimetry is a simple and rapid method for determining the water content in organic electrolytes. Through the precise preparation and application of appropriate indicators, as well as strict operating procedures and instrument maintenance, the quality of the electrolyte can be effectively evaluated, thereby ensuring the performance and safety of lithium-ion batteries.

[0048] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for testing the water content in an organic electrolyte by colorimetry, characterized in that: include: A. Prepare carbonate solvent standard solution; B. Take the same volume of carbonate standard solution and electrolyte to be tested, and add the same volume of aldehyde and ketone reagent respectively; C. Colorimetry: When the color of the electrolyte to be tested is darker or lighter than the color of the carbonate standard solution, the water content of the electrolyte to be tested is small.

2. The method for measuring the water content in an organic electrolyte by a colorimetric method according to claim 1, characterized in that: The carbonates include one or more reagent mixtures of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and ethyl methyl carbonate as electrolyte solvents.

3. The method for measuring the water content in an organic electrolyte by a colorimetric method according to claim 1, characterized in that: The steps for preparing the standard aqueous solution of a carbonate solvent include: A. Take a carbonate organic solvent with a water content of less than 3ppm and add a certain amount of deionized water; B. Determine the water content of the standard solution prepared in step A using coulometric titration.

4. The method for measuring the water content in an organic electrolyte by a colorimetric method according to claim 3, characterized in that: The carbonate standard solution and aldehyde and ketone volumetric Karl Fischer reagent are stored in an airtight environment with a water content of less than 1 ppm.

5. The method for measuring the water content in an organic electrolyte by colorimetry according to claim 3, characterized in that: The steps B and C are carried out in an environment with a water content of less than 1 ppm.

6. The method for measuring the water content in an organic electrolyte by colorimetry according to claim 3, characterized in that: The colorimetry of the carbonate standard solution and the electrolyte to be tested is carried out in a colorimetric tube or other white transparent container.

7. The method for measuring the water content in an organic electrolyte by colorimetry according to claim 3, characterized in that: The operation time of steps B and C is 1-3 minutes.

8. The method for measuring the water content in an organic electrolyte by colorimetry according to claim 4, characterized in that: The Karl Fischer reagent comprises iodine, sulfur dioxide, pyridine and methanol.

9. The method for measuring the water content in an organic electrolyte by colorimetry according to claim 8, characterized in that: The preparation ratio of iodine, sulfur dioxide, pyridine and methanol is 1:3:10:50, and the preparation of Karl Fischer reagent is carried out in a dry environment.