Method for identifying polyacrylic acid in lithium battery

Abstract

A method for identifying polyacrylic acid in a lithium battery comprises the following steps: pretreating the lithium battery to obtain a solution to be detected; adding an acidic reagent into the to-be-detected solution, observing whether a precipitate appears in the to-be-detected solution, and taking the solution with the precipitate as a first detection solution; adding an alkaline reagent into the first detection liquid; and if the precipitate in the first detection liquid is dissolved within a preset time, determining that the lithium battery contains polyacrylic acid. The method disclosed by the invention can be used for quickly identifying the existence of polyacrylic acid in the adhesive of the lithium battery.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of batteries, in particular to a method for identifying polyacrylic acid in a lithium battery. BACKGROUND

[0002] When performing comprehensive comparison and analysis on the battery cell in the industry, the cell tab design, structural part manufacturing, process and the like need to be analyzed, but the electrode analysis is particularly complex, especially the analysis of the composition of the binder in the tab. The main binder in the tab in the industry is generally CMC (sodium carboxymethyl cellulose) and PAA (polyacrylic acid), and the analysis of CMC in the industry is mature, but the analysis of PAA is insufficient. Most of the negative electrode is analyzed by EDS (energy dispersive X-ray spectroscopy), and the N element is analyzed to speculate that the negative electrode contains PAA. The analysis method has certain one-sidedness and subjectivity, and cannot well identify the existence of polyacrylic acid in the battery. SUMMARY

[0003] The purpose of the present application is to provide a method for identifying polyacrylic acid in a lithium battery, which solves the problem of how to identify whether polyacrylic acid exists in a lithium battery.

[0004] To achieve the purpose of the present application, the present application provides the following technical solution: The present application provides a method for identifying polyacrylic acid in a lithium battery, comprising: Pretreating the lithium battery to obtain a test solution; Adding an acidic reagent to the test solution and observing whether a precipitate appears in the test solution, and taking the solution with the precipitate as a first detection solution; Adding an alkaline reagent to the first detection solution; If the precipitate in the first detection solution dissolves within a preset time, it is determined that the lithium battery contains polyacrylic acid.

[0005] In one embodiment, the solution with the precipitate as the first detection solution further comprises: When the precipitate appears in the test solution, the precipitate in the test solution is extracted, and infrared testing is performed on the precipitate to obtain an infrared detection result; When the infrared detection result contains a -COOH peak, the solution with the -COOH peak precipitate is taken as the first detection solution.

[0006] In one embodiment, it further comprises: The first detection solution in which the precipitate is dissolved is taken as a second detection solution, and infrared testing is performed on the second detection solution to obtain an infrared detection result; When the infrared detection result contains a -CN peak, it is determined that the lithium battery contains modified polyacrylic acid.

[0007] In an embodiment, the acidic reagent has a pH of 0-2, and / or the basic reagent has a pH of 10-14.

[0008] In an embodiment, the acidic reagent comprises any one of hydrochloric acid, sulfuric acid, hydrobromic acid, and hydroiodic acid, and / or the basic reagent comprises any one of potassium hydroxide, sodium hydroxide, barium hydroxide, and calcium hydroxide.

[0009] In an embodiment, the volume ratio of the acidic reagent to the to-be-tested solution is 1: (1-3); and / or, the volume ratio of the basic reagent to the first detection solution is 1: (1-3).

[0010] In an embodiment, the lithium battery is pretreated to obtain a to-be-tested solution, comprising: washing the pole piece of the lithium battery to obtain a pretreated solution; stirring, centrifuging, and suction-filtering the pretreated solution to obtain the to-be-tested solution.

[0011] In an embodiment, the pole piece of the lithium battery is washed to obtain a pretreated solution, comprising: washing the pole piece with a first solvent; washing the pole piece with a second solvent to remove the current collector of the pole piece, to obtain the pretreated solution.

[0012] In an embodiment, the first solvent is a dimethyl carbonate solvent, and / or the second solvent is deionized water.

[0013] In an embodiment, the negative pole piece of the lithium battery is pretreated.

[0014] Polyacrylic acid is a flexible straight chain with high conformational freedom and low steric hindrance, and can form intermolecular and intramolecular hydrogen bonds. Polyacrylic acid is quickly protonated in an acidic environment, and the hydrogen bond interaction causes the molecular chain to aggregate and thus precipitate. By adding an acidic reagent to observe whether precipitation occurs, it can be preliminarily determined whether polyacrylic acid exists. If no turbidity and precipitation occur after the to-be-tested solution is added with the acidic reagent, it indicates that there is no polyacrylic acid in the to-be-tested solution. Then, a basic reagent is added to the first detection solution in which precipitation occurs. Since the content of carboxylate in polyacrylic acid is high in a basic environment, the intermolecular electrostatic repulsion causes the polyacrylic acid to stretch and dissolve in water. Therefore, if the precipitation in the first detection solution dissolves, and the precipitation occurs in the to-be-tested solution in an acidic environment and disappears in a basic environment, it can be determined that the to-be-tested solution contains polyacrylic acid. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to describe the technical solutions of the embodiments of the present application or the prior art more clearly, the accompanying drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced. Obviously, the accompanying drawings in the following description only represent some of the embodiments of the present application, and all of the other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0016] Figure 1 is a flow chart of a method for identifying polyacrylic acid in a lithium battery according to an embodiment; Figure 2 is a graph of experimental results of a method for identifying polyacrylic acid in a lithium battery according to an embodiment; Figure 3 is a flow chart of one step of a method for identifying polyacrylic acid in a lithium battery according to an embodiment; Figure 4 is a flow chart of another step of a method for identifying polyacrylic acid in a lithium battery according to an embodiment; Figure 5 is a graph of infrared test results of a second detection solution according to an embodiment; Figure 6 is a flow chart of still another step of a method for identifying polyacrylic acid in a lithium battery according to an embodiment; Figure 7 is a flow chart of yet another step of a method for identifying polyacrylic acid in a lithium battery according to an embodiment. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments only represent some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments of the present application, all the other embodiments obtained by those skilled in the art without any creative effort belong to the scope of protection of the present application.

[0018] It should be noted that when a component is referred to as being "fixed" to another component, it can be directly on the other component or there can be intervening components. When a component is referred to as being "connected" to another component, it can be directly connected to the other component or there can be intervening components.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The use of the terms "and / or" includes a combination of one or more of the associated listed items.

[0020] Some embodiments of the present application will be described in detail with reference to the drawings. The following examples and features in the examples can be combined with each other in the case of no conflict.

[0021] When performing a comprehensive comparative analysis of the battery cell in the industry, the cell tab design, structural part manufacturing, process, etc. need to be analyzed, but the electrode analysis is particularly complex, especially the analysis of the composition of the binder in the tab. The main binder in the tab in the industry is generally CMC (sodium carboxymethyl cellulose) and PAA (polyacrylic acid). At present, the analysis of CMC in the industry is mature, but there are deficiencies in the analysis of PAA. Most of the negative electrode tabs are analyzed by EDS (energy dispersive X-ray spectroscopy), and the negative electrode contains PAA by analyzing the N element. This analysis method has certain one-sidedness and subjectivity, and cannot well identify the existence of polyacrylic acid in the battery.

[0022] Please refer to Figure 1 and Figure 2 The present application provides a method for identifying polyacrylic acid in a lithium battery, comprising: Step S10, pretreating the lithium battery to obtain a test solution.

[0023] Step S20, adding an acidic reagent to the test solution and observing whether a precipitate appears in the test solution. The solution with the precipitate is used as a first detection solution.

[0024] Step S30, adding an alkaline reagent to the first detection solution.

[0025] Step S40, within a preset time, if the precipitate in the first detection solution dissolves, it is determined that the lithium battery contains polyacrylic acid.

[0026] In step S20, if no precipitate appears, it indicates that there is no polyacrylic acid in the test solution. In step S40, the preset time can be 1-30 minutes, and can be 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, etc. without limitation. Limiting the preset time helps to improve the experimental efficiency.

[0027] As can be seen from Figure 2 , in Figure 2 , (a) is the test solution provided in step S10, and the test solution is a light-colored clear solution, Figure 2 , (b) is the test solution after adding an acidic reagent in step S20, and the clear solution becomes turbid or even produces a precipitate, which can be considered as Figure 2 the (b) solution of Figure 2(c) in FIG. 4 is the first detection solution after adding the basic reagent in step S30, the precipitate of the turbid solution disappears, and the turbid solution becomes a clear solution.

[0028] Polyacrylic acid is a flexible straight chain with high conformational freedom and low steric hindrance, and can form intermolecular and intramolecular hydrogen bonds. Polyacrylic acid is quickly protonated in an acidic environment, and the hydrogen bond interaction causes the molecular chain to aggregate and thus precipitate. By adding an acidic reagent to observe whether a precipitate is formed, it can be preliminarily determined whether polyacrylic acid is present. If no turbidity and precipitate are generated after adding the acidic reagent to the solution to be tested, it indicates that there is no polyacrylic acid in the solution to be tested. Then, a basic reagent is added to the first detection solution in which a precipitate is present. Since the content of carboxylate in polyacrylic acid is high in a basic environment, the intermolecular electrostatic repulsion causes the polyacrylic acid to stretch and dissolve in water. Therefore, if the precipitate in the first detection solution dissolves, and the precipitate appears in the solution to be tested in an acidic environment and disappears in a basic environment, it can be determined that the solution to be tested contains polyacrylic acid.

[0029] Please refer to Figure 3 and Figure 5 In one embodiment, the solution with a precipitate in step S20 is also used as the first detection solution. Step S21: When a precipitate appears in the solution to be tested, the precipitate in the solution to be tested is extracted, and infrared testing is performed on the precipitate to obtain an infrared detection result.

[0030] Step S22: When there is a -COOH peak in the infrared detection result, the solution with the precipitate with the -COOH peak is used as the first detection solution.

[0031] Please refer to Figure 5 , Figure 5 FIG. 5 is an infrared spectrum of the precipitate in the solution to be tested in one embodiment. Polyacrylic acid contains characteristic groups of carboxyl (-COOH) and carboxylate (-COO-), and the infrared spectrum has significant absorption peaks at 1700-1750 cm - ¹ (carboxylic acid carbonyl stretching vibration) and 1550-1600 cm - ¹ (asymmetric stretching vibration of carboxylate). Figure 5 In FIG. 4, it can be concluded that the infrared spectrum of the precipitate in the solution to be tested has characteristic peaks of -COOH and -COO-, and in combination with the characteristic that the precipitate disappears after adding the basic reagent in step S30, it can be determined that the solution to be tested contains polyacrylic acid, i.e., the lithium battery contains polyacrylic acid.

[0032] Since the molecular chain flexibility of polyacrylic acid is limited, it is easy to break when the volume of materials such as silicon negative electrode expands / contracts, resulting in bonding failure. Therefore, the existing part of the adhesive will use modified polyacrylic acid. Alternatively, -CN (cyano) is a strong polar group, commonly found in polymers such as polyacrylonitrile (PAN), which can form hydrogen bonds and dipole forces with surrounding materials, improving electrode structure stability and electrolyte wettability. Polyacrylic acid can be blended with polymers containing -CN groups (such as PAN) to form a composite adhesive. At this time, the -CN bond comes from polyacrylonitrile, and the polyacrylic acid interacts with the polyacrylonitrile or other active substances through the carboxylic acid group to improve the bonding performance. Therefore, the present application also needs to determine whether the polyacrylic acid in the lithium battery is modified polyacrylic acid.

[0033] Please refer to Figure 4 and Figure 5 In one embodiment, further comprising: Step S41, the first detection solution of the precipitated dissolved is used as the second detection solution, the infrared test is carried out on the second detection solution, and the infrared detection result is obtained.

[0034] Step S42, when the -CN peak exists in the infrared detection result, it is determined that the lithium battery has modified polyacrylic acid.

[0035] Therefore, under the premise that the precipitate appears and disappears in steps S20-S40, and the -COOH peak is detected by infrared detection in step S42, if the -CN peak is also detected by infrared detection of the second detection solution, it can be concluded that the polyacrylic acid in the solution to be tested is modified polyacrylic acid.

[0036] In one embodiment, the present application can also use nuclear magnetic resonance technology (NMR) to detect the first detection solution and the second detection solution with precipitate, and compare the hydrogen bond difference between the first detection solution and the second detection solution, which can further indicate the presence of polyacrylic acid. Since polyacrylic acid is a flexible straight chain with high conformational freedom and low steric hindrance, it can form intermolecular and intramolecular hydrogen bonds. After adding an acidic reagent, polyacrylic acid can be quickly protonated, and hydrogen bonding causes molecular chain aggregation, resulting in the formation of a first detection solution with precipitate. After adding an alkaline reagent to the first detection solution, the number of hydrogen bonds decreases, and the electrostatic repulsion between molecules makes polyacrylic acid stretch and dissolve. By detecting the first detection solution and the second detection solution with nuclear magnetic resonance, and combining the hydrogen bond difference in the detection result, it can be determined that the solution to be tested has polyacrylic acid.

[0037] In one embodiment, the present application can also identify a plurality of pole pieces. Specifically, there are three kinds of pole pieces that need to be analyzed, the first pole piece contains only polyacrylic acid, the second pole piece contains only sodium carboxymethyl cellulose, and the third pole piece contains polyacrylic acid and sodium carboxymethyl cellulose.

[0038] The second electrode sheet among the three electrode sheets can be distinguished by adding an acidic reagent to the to-be-detected liquid provided in step S10. Since only part of the carboxymethyl cellulose sodium carboxyl group can be protonated, the residual carboxylate repels each other to make the chain of the carboxymethyl cellulose sodium relaxed, thus it is difficult to aggregate and precipitate. Therefore, if no precipitate appears in the to-be-detected solution after the addition of the acidic reagent, it indicates that there is no carboxymethyl cellulose sodium in the to-be-detected solution, and if a precipitate appears, it indicates that the corresponding electrode sheet is the second electrode sheet containing only carboxymethyl cellulose sodium.

[0039] If precipitates appear after the addition of the acidic reagent to the to-be-detected liquid provided in step S10, the to-be-detected liquid in which the precipitate appears is taken as the first detection liquid, an alkaline reagent is added to the first detection liquid, and it is observed whether the precipitate is dissolved. If the precipitates are all dissolved, the first detection liquid in which the precipitate is dissolved is taken as the second detection liquid, and the second detection liquid is subjected to infrared testing. The infrared testing result is analyzed. If the characteristic peak of carboxymethyl cellulose sodium appears in the infrared testing result, specifically, the characteristic peak of carboxymethyl cellulose sodium can be 1129 cm - -1, 1051-1069 cm - -1, the former is attributed to the stretching vibration of the cellulose ether bond (C-O-C), which is a sign of the formation of the ether bond after the substitution of the carboxymethyl group, and the latter is attributed to the absorption peak of the residual hydroxyl group, which can be accompanied by the vibration of the ether bond, reflecting part of the unsubstituted hydroxyl group. It indicates that the second test liquid contains carboxymethyl cellulose sodium, and the second test liquid corresponds to the third electrode sheet containing polyacrylic acid and carboxymethyl cellulose sodium. If there is no characteristic peak of carboxymethyl cellulose sodium in the infrared testing result, it indicates that the second test liquid corresponds to the first electrode sheet containing only polyacrylic acid.

[0040] Alternatively, the second detection liquid can also be subjected to scanning electron microscope testing and energy dispersive X-ray spectrum characteristic analysis. The scanning electron microscope result is analyzed to observe whether the scanning electron microscope pattern presents a strip-shaped structure, a smooth surface but a loose intermolecular distance, or whether the scanning electron microscope pattern shows a three-dimensional polymer network structure with many small pores. If the scanning electron microscope result does not have the foregoing characteristics, it indicates that the second test liquid corresponds to the first electrode sheet containing only polyacrylic acid. If the scanning electron microscope result contains the foregoing characteristics, it indicates that the second test liquid corresponds to the third electrode sheet containing polyacrylic acid and carboxymethyl cellulose sodium. The energy dispersive X-ray spectrum is analyzed to observe whether there is Na element. If the energy dispersive X-ray spectrum result shows that there is no Na element, it indicates that the second test liquid corresponds to the first electrode sheet containing only polyacrylic acid. If the energy dispersive X-ray spectrum result shows that there is Na element, it indicates that the second test liquid corresponds to the third electrode sheet containing polyacrylic acid and carboxymethyl cellulose sodium.

[0041] In summary, the application can not only analyze whether polyacrylic acid exists in the lithium battery, but also distinguish the lithium battery containing polyacrylic acid and / or sodium carboxymethyl cellulose, so that the application range of the identification method is widened.

[0042] In an embodiment, the pH of the acidic reagent is 0-2, and / or the pH of the basic reagent is 10-14.

[0043] Optionally, the pH of the acidic reagent can be 0, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, etc., without limitation.

[0044] Optionally, the pH of the basic reagent can be 10, 10.5, 10.8, 11, 11.5, 11.8, 12, 12.5, 12.8, 13, 13.5, 13.8, 14, etc., without limitation.

[0045] The reaction rate of polyacrylic acid with weak acid and weak base is usually slow, which requires a long reaction time or a high reaction temperature, and some reaction products may have poor stability and easily hydrolyze or degrade, which may cause incorrect judgment of the reaction result, therefore, the pH of the acidic reagent and the basic reagent is limited to improve the accuracy and reaction time of the reaction.

[0046] When the acidic reagent corresponding to the pH of the acidic reagent is a strong acid reagent, if the solution to be measured contains polyacrylic acid, the dissociation of the carboxyl group of the polyacrylic acid is completely inhibited, the degree of coiling of the molecular chain is significantly improved, the reaction phenomenon is obvious, and the time of precipitate appears is improved; when the basic reagent corresponding to the pH of the basic reagent is a strong base reagent, it is helpful to accelerate the neutralization reaction of the basic reagent with the acidic reagent in the first detection solution, and also accelerate the reaction of the basic reagent with the precipitate in the first detection solution. And the reaction conditions (such as concentration, temperature) of the solution to be measured and the first detection solution with the strong acid reagent and the strong base reagent are easy to control, and the reaction result is predictable.

[0047] In an embodiment, the acidic reagent includes any one of hydrochloric acid, sulfuric acid, hydrobromic acid, and hydroiodic acid, and / or the basic reagent includes any one of potassium hydroxide, sodium hydroxide, barium hydroxide, and calcium hydroxide.

[0048] Specifically, the acidic reagent is concentrated hydrochloric acid, and the basic reagent is saturated sodium hydroxide solution.

[0049] Since the acidic reagent has strong oxidizing property, it can destroy the structure of polyacrylic acid due to oxidation, which leads to an increase in side reactions, complex and difficult-to-control products, and even material degradation, therefore, the application selects an acidic reagent without strong oxidizing property for experiment. The acidic reagent is selected from the aforementioned strong acid reagent and strong base reagent without strong oxidizing property, which is helpful to accurately obtain the expected reaction result and improve the accuracy of the reaction.

[0050] In an embodiment, the volume ratio of the acidic reagent to the to-be-tested solution is 1:(1-3); and / or, the volume ratio of the basic reagent to the first detection solution is 1:(1-3).

[0051] Optionally, the volume ratio of the acidic reagent to the to-be-tested solution can be 1:1, 1:2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, etc., without limitation.

[0052] Optionally, the volume ratio of the basic reagent to the first detection solution can be 1:1, 1:2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, etc., without limitation.

[0053] If the volume ratio of the acidic reagent to the to-be-tested solution and the volume ratio of the basic reagent to the first detection solution are too small, the amount of the added acidic reagent and basic reagent will be too small, and the to-be-tested solution and the acidic reagent, the first detection solution and the basic reagent cannot fully react; if the volume ratio of the acidic reagent to the to-be-tested solution and the volume ratio of the basic reagent to the first detection solution are too large, the acidic reagent and the basic reagent will be wasted, and the experimental period will be prolonged; by limiting the amount of the added acidic reagent and basic reagent in steps S20 and S30, when the volume ratio of the acidic reagent to the to-be-tested solution and the volume ratio of the basic reagent to the first detection solution are moderate, the full reaction between the to-be-tested solution and the acidic reagent, the first detection solution and the basic reagent can be ensured, and the effective experiment can be ensured, and the waste of reagents can be avoided.

[0054] Please refer to Figure 1 and Figure 6 In an embodiment, step S10 comprises: Step S11, cleaning the pole piece of the lithium battery to obtain a pretreated solution.

[0055] Step S12, stirring, centrifuging and suction filtering the pretreated solution to obtain a to-be-tested solution.

[0056] The pole piece of the lithium battery in step S11 mainly includes a current collector and an active layer provided on the current collector, the active layer includes active material, conductive agent, binder and other components, the pretreatment solution needs to remove the current collector, active material and conductive agent and other components, and the application mainly analyzes the binder component in the pole piece. The conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotube, and the content of the conductive agent in the active layer is 3wt%-5wt%. When the pole piece is a negative pole piece, the active material of the negative electrode can be a carbon-based material, a silicon-based material and a titanium-based material, and in specific embodiments, includes one or more of graphite, carbon nanomaterial, silicon, silicon-based composite material, lithium titanate. When the pole piece is a positive pole piece, the active material of the positive electrode can be a phosphate positive active material and a ternary positive active material, and in specific embodiments, includes one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, fluorinated lithium vanadium phosphate, lithium titanate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum. When the pole piece is a negative pole piece, the corresponding current collector can be any one of copper foil, composite copper foil or carbon-coated copper foil, or any one of aluminum foil, composite aluminum foil or carbon-coated aluminum foil. When the pole piece is a positive pole piece, the corresponding current collector includes but is not limited to any one of aluminum foil, composite aluminum foil or carbon-coated aluminum foil.

[0057] Optionally, in step S12, the stirring speed can be 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, etc., without limitation, and the stirring time can be 5 min, 8 min, 10 min, 12 min, 15 min, 20 min, 22 min, 25 min, 28 min, 30 min, etc., without limitation.

[0058] Optionally, in step S12, the centrifugal speed can be 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, 3500 rpm, 4000 rpm, 5000 rpm, etc., without limitation, and the stirring time can be 5 min, 8 min, 10 min, 12 min, 15 min, 20 min, 22 min, 25 min, 28 min, 30 min, etc., without limitation.

[0059] Optionally, in step S12, the duration of suction filtration can be 10 min, 12 min, 15 min, 20 min, 22 min, 25 min, 28 min, 30 min, etc., without limitation. The pressure required for suction filtration is -20 kPa, -30 kPa, -40 kPa, -50 kPa, -60 kPa, -70 kPa, -80 kPa, etc., without limitation.

[0060] The solution to be tested obtained through the steps S11 and S12 can be considered to only contain the adhesive, and then the related tests are performed through the steps S20 and S30, and whether the polyacrylic acid is contained in the solution to be tested, i.e., whether the polyacrylic acid is contained in the adhesive of the lithium battery, is determined according to whether the precipitation appears in the solution to be tested and whether the precipitation disappears.

[0061] Please refer to Figure 6 and Figure 7 In one embodiment, the step S11 comprises: The step S111 comprises:

[0062] The step S112 comprises:

[0063] Optionally, the first solvent can be an organic solvent, and the first solvent is used to remove the active material and electrolyte and other components in the electrode tab.

[0064] Optionally, since the conductive agent is generally a carbon-based material, the carbon-based material is generally insoluble in water, and thus the second solvent can be deionized water, and the second solvent is used to remove part of the residual first solvent and to remove the conductive agent and carbon-based material in the electrode tab.

[0065] In one embodiment, the first solvent is a dimethyl carbonate solvent, and / or the second solvent is deionized water.

[0066] Optionally, the dimethyl carbonate solvent as the first solvent is a chain carbonate dimethyl carbonate solvent, which can effectively dissolve the residual electrolyte (containing lithium salt, organic solvent, etc.) on the surface of the negative electrode tab and the by-products (such as solid electrolyte interface film SEI, lithium deposit, etc.) generated in the charging and discharging process. Through immersion cleaning, the interference of these substances on the subsequent analysis or recycling process can be reduced.

[0067] Optionally, the deionized water as the second solvent can reduce the influence of the dimethyl carbonate solvent on the experimental results, and at the same time, the carbon-based material in the electrode tab is insoluble in the deionized water, so that the impurities in the solution to be tested can be further reduced, the solution to be tested only contains the adhesive, and the interference of the experiment is reduced.

[0068] In one embodiment, the negative electrode tab of the lithium battery is pretreated. The adhesive of the negative electrode tab is mainly a water-based system adhesive, which is generally carboxymethyl cellulose or polyacrylic acid. Therefore, the acid reagent and the alkaline reagent are used in the experiment to determine whether the main component in the adhesive of the negative electrode tab is carboxymethyl cellulose or polyacrylic acid.

[0069] The negative electrode tabs of the lithium batteries in Example 1 and Comparative Example 1 are subjected to the pretreatment steps S11 and S12 to obtain the solution to be tested of Example 1 and the solution to be tested of Comparative Example 1.

[0070] Example 1 The concentrated hydrochloric acid is added to the solution to be tested, and whether a precipitate appears in the solution to be tested is observed, and the solution with the precipitate is taken as the first detection solution.

[0071] The saturated sodium hydroxide solution is added to the first detection solution, and whether the precipitate in the first detection solution dissolves is observed, and when the precipitate in the first detection solution dissolves, it is determined that the lithium battery has polyacrylic acid.

[0072] Comparative Example 1 The concentrated hydrochloric acid is added to the solution to be tested, and whether a precipitate appears in the solution to be tested is observed, and the solution with the precipitate is taken as the first detection solution.

[0073] The precipitate appears in the solution to be tested after the addition of the acidic reagent in Example 1, forming the first detection solution, and the precipitate in the first detection solution disappears after the addition of the basic reagent, indicating that the adhesive of the negative plate of the lithium battery in Example 1 has polyacrylic acid. In Comparative Example 1, no precipitate appears in the solution to be tested after the addition of the acidic reagent, indicating that the adhesive of the negative plate of the lithium battery in Comparative Example 1 has no polyacrylic acid. The solution to be tested in Comparative Example 1 is analyzed by energy dispersive X-ray spectroscopy, and it is found that the adhesive of the negative plate of the lithium battery in Comparative Example 1 has sodium carboxymethyl cellulose.

[0074] In the description of the embodiments of the present application, it should be noted that the orientations or positional relationships of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", and the like are based on the orientations or positional relationships described in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0075] The above disclosure is only a preferred embodiment of the present application, and of course cannot limit the scope of the rights of the present application, and those of ordinary skill in the art can understand that all or part of the above-mentioned processes can be implemented, and equivalent changes made in accordance with the claims of the present application still fall within the scope of the present application.

Claims

1. A method for identifying polyacrylic acid in a lithium battery, characterized by, The application relates to a method for detecting polyacrylic acid in a lithium battery. The lithium battery is pretreated to obtain a to-be-tested solution; An acid reagent is added into the to-be-tested solution, and whether a precipitate appears in the to-be-tested solution is observed; the solution with the precipitate is taken as a first detection solution; An alkaline reagent is added into the first detection solution; If the precipitate in the first detection solution is dissolved within a preset time, it is determined that the lithium battery contains polyacrylic acid.

2. The method for identifying polyacrylic acid in a lithium battery according to claim 1, characterized by, The solution with the precipitate is taken as the first detection solution, and the method further comprises the following steps: When the precipitate appears in the to-be-tested solution, the precipitate in the to-be-tested solution is extracted, and infrared testing is performed on the precipitate to obtain an infrared detection result; When the infrared detection result contains a -COOH peak, the solution with the precipitate containing the -COOH peak is taken as the first detection solution.

3. The method for identifying polyacrylic acid in lithium batteries according to claim 1, characterized in that, The method further comprises the following steps: The first detection solution in which the precipitate is dissolved is taken as a second detection solution, infrared testing is performed on the second detection solution to obtain an infrared detection result; When the infrared detection result contains a -CN peak, it is determined that the lithium battery contains modified polyacrylic acid.

4. The method of claim 1, wherein the polyacrylic acid is identified in the lithium battery. The acid reagent has a pH of 0-2, and / or the alkaline reagent has a pH of 10-14.

5. The method of claim 4, wherein the polyacrylic acid is identified by the fact that the lithium battery is a lithium ion battery. The acid reagent comprises any one of hydrochloric acid, sulfuric acid, hydrobromic acid and hydroiodic acid, and / or the alkaline reagent comprises any one of potassium hydroxide, sodium hydroxide, barium hydroxide and calcium hydroxide.

6. The method of claim 1, wherein the polyacrylic acid is identified in the lithium battery by, The volume ratio of the acid reagent to the to-be-tested solution is 1: (1-3); and / or The volume ratio of the alkaline reagent to the first detection solution is 1: (1-3).

7. The method for identifying polyacrylic acid in lithium batteries according to claim 1, characterized in that, The lithium battery is pretreated to obtain a to-be-tested solution, and the method comprises the following steps: The pole piece of the lithium battery is cleaned to obtain a pretreated solution; The pretreated solution is stirred, centrifuged and suction-filtered to obtain the to-be-tested solution.

8. The method of claim 7, wherein the polyacrylic acid is identified by the fact that the lithium battery is a lithium ion battery. The pole piece of the lithium battery is cleaned to obtain a pretreated solution, and the method comprises the following steps: The pole piece is cleaned by using a first solvent; The pole piece is cleaned by using a second solvent, and the current collector of the pole piece is removed to obtain the pretreated solution.

9. The method of claim 8, wherein the polyacrylic acid is identified by the fact that the lithium battery is a lithium-ion battery. The first solvent is a dimethyl carbonate solvent, and / or the second solvent is deionized water.

10. The method of claim 1-9, wherein the polyacrylic acid is identified in the lithium battery by, The negative pole piece of the lithium battery is pretreated.

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