Method for detecting distribution of binder in pole piece and application

Abstract

The application provides a detection method for adhesive distribution in an electrode sheet and application. The detection method for adhesive distribution in the electrode sheet comprises the following steps: in the presence of a solvent, a mercapto compound containing a labeling element, a to-be-detected sample and an initiator are reacted to obtain the to-be-detected sample containing the labeling element; the labeling element comprises an S element; the to-be-detected sample is an electrode sheet containing adhesive; the adhesive comprises a compound containing a double bond; the distribution of the labeling element in the to-be-detected sample containing the labeling element is detected by using an X-ray energy spectrum analysis method to obtain the distribution of the adhesive in the to-be-detected sample. Compared with the existing detection method, the above detection method avoids the reaction of liquid bromine and copper foil to generate CuBr2, thereby reducing the interference of other components on the detection result, and is beneficial to improving the accuracy of the detection result; meanwhile, the harm to the human body can be reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery detection, in particular to a detection method for distribution of a binder in a pole piece and application. BACKGROUND

[0002] With the gradual development of battery technology, the types of binders are also increasingly diversified. Commonly used binders include polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), nitrile rubber (NBR), carboxymethyl cellulose (CMC), and polyacrylic acid (PAA), etc. Among them, SBR is a widely used battery binder, and its main structure is styrene butadiene rubber (a copolymer of butadiene and styrene). The SBR used in the battery manufacturing process is usually in the form of an emulsion. During the coating and baking process, the particulate SBR loses water to form a film and adheres to the surface of the material particles, thereby playing a binding role. At the same time, as the water evaporates, the SBR floats towards the surface of the pole piece, thereby reducing the adhesion between the active material and the foil. During the later cycle of the battery, the active material expands and contracts frequently. If the adhesion is too low, the active material will fall off the surface of the pole piece, which not only reduces the capacity of the battery, but also poses a significant safety hazard. In terms of elemental composition, most unmodified SBRs are composed of only C, H, and O, which are similar to the elemental composition of the negative active material, making it difficult to distinguish between them.

[0003] Therefore, how to characterize the distribution of SBR in the pole piece has been a technical difficulty in the field. The existing detection method for the distribution of the binder is complex and has poor accuracy. SUMMARY

[0004] The main purpose of the present application is to provide a detection method for the distribution of a binder in a pole piece and application, so as to solve the problem of poor accuracy of the detection results when the existing detection method is applied to detect the distribution of the binder in the pole piece.

[0005] In order to achieve the above-mentioned purpose, the present application provides a detection method for the distribution of a binder in a pole piece, which comprises: reacting a mercapto compound containing a labeling element, a sample to be tested, and an initiator in the presence of a solvent to obtain a sample to be tested containing a labeling element; the labeling element includes S element; the sample to be tested is a pole piece containing a binder; the binder includes a compound containing a double bond; and the distribution of the labeling element in the sample to be tested containing the labeling element is detected by X-ray energy spectrum analysis to obtain the distribution of the binder in the sample to be tested.

[0006] As an embodiment, the binder is selected from a copolymer of butadiene and styrene and / or a copolymer of acrylonitrile and butadiene.

[0007] As an implementation form, the molar ratio of the thiol compound containing the marking element, the initiator and the double bond in the adhesive is (0.5-5.0):(0.5-2.0):1.0; or the molar ratio of the thiol compound containing the marking element, the initiator and the double bond in the adhesive is (1.0-5.0):(1.0-2.0):1.0; or the molar ratio of the thiol compound containing the marking element, the initiator and the double bond in the adhesive is (1.5-3.0):(1.1-1.5):1.0.

[0008] As an implementation form, the marking element further includes one or more of the group consisting of N element, Si element and P element.

[0009] As an implementation form, the marking element further includes N element and / or Si element.

[0010] As an implementation form, the thiol compound containing the marking element has a general formula of R-SH; wherein the R group can be any group.

[0011] As an implementation form, the R group is one or more of the group consisting of hydroxyl-substituted C1-C6 alkyl, carboxyl-substituted C1-C6 alkyl, amino-substituted C1-C6 alkyl, and siloxyl with a main chain of 1-6 atoms.

[0012] As an implementation form, the thiol compound containing the marking element is selected from one or more of the group consisting of mercaptoethanol, mercaptoacetic acid, ethyl mercaptoacetate, mercaptoethylamine and mercaptopropyltrimethoxysilane.

[0013] As an implementation form, the initiator is a photoinitiator.

[0014] As an implementation form, the wavelength range of the light in the photoinitiation reaction system is 10-760 nm; or the wavelength range of the light is 200-400 nm. The wavelength of the light refers to the wavelength of the irradiated light, which is also the absorption wavelength of the initiator.

[0015] As an implementation form, the photoinitiator is selected from benzophenone compounds and / or benzoin compounds.

[0016] As an implementation form, the photoinitiator is selected from benzophenone and / or benzoin.

[0017] As an implementation form, the initiator is a thermal initiator.

[0018] As an implementation form, the reaction temperature of the thermal initiator is 25-150℃; or the reaction temperature of the thermal initiator is 50-80℃.

[0019] As an embodiment, the thermal initiator is selected from azo compounds and / or peroxide compounds.

[0020] As an embodiment, the thermal initiator is selected from azobisisobutyronitrile and / or benzoyl peroxide.

[0021] As an embodiment, the initiator is a redox initiator.

[0022] As an embodiment, the molar ratio of the oxidant to the reducing agent in the redox reaction system is (1.1-3.0):1.0; or the molar ratio of the oxidant to the reducing agent is (1.5-2.0):1.0.

[0023] As an embodiment, the redox initiator is selected from hydrogen peroxide / sodium bisulfite.

[0024] As an embodiment, the reaction time of the reaction is 0.5-120h; 1-120h; or 5-72h.

[0025] As an embodiment, the solvent is selected from one or more of water, alcohol, ether, ketone, alkane and ester.

[0026] As an embodiment, the solvent is selected from one or more of ethanol, diethyl ether, acetone, n-hexane and ethyl acetate.

[0027] As an embodiment, the electrode sheet containing the binder further comprises: a negative electrode active material or a positive electrode active material.

[0028] As an embodiment, when the electrode sheet containing the binder comprises the negative electrode active material, the negative electrode active material is selected from one or more of artificial graphite, natural graphite, micron-sized carbon spheres, silicon monoxide, lithium titanate and silicon; when the electrode sheet containing the binder comprises the positive electrode active material, the positive electrode active material is selected from one or more of lithium nickel cobalt manganese, lithium nickel cobalt aluminum, lithium nickel manganese, lithium iron phosphate, lithium manganate, lithium cobaltate and lithium manganese iron phosphate.

[0029] As an embodiment, the electrode sheet containing the binder further comprises a conductive agent; the conductive agent is selected from one or more of conductive carbon black, carbon fiber, carbon nanotube and conductive graphite.

[0030] As an embodiment, the application provides the application of the above-mentioned detection method of the distribution of the binder in the electrode sheet in the field of batteries.

[0031] In order to achieve the above-mentioned purpose, another aspect of the application also provides the application of the above-mentioned detection method of the distribution of the binder in the electrode sheet in the field of batteries.

[0032] The technical scheme of the present application makes the thiol compound containing the labeling element react with the compound containing the double bond, and the high selectivity of the reaction is used to add the thiol compound containing the labeling element to the double bond in the compound, so that the specific kind of labeling element is introduced into the structure of the compound containing the double bond. The X-ray energy spectrum analysis method is used to locate and track the labeling element, that is, the distribution of the labeling element in the compound containing the double bond is detected, and the distribution of the compound containing the double bond in the pole piece can be obtained. Compared with the existing detection method, the detection method provided by the present application avoids the reaction of liquid bromine and copper foil to generate CuBr2 on the one hand, thereby reducing the interference of other components on the detection result, and is beneficial to improve the accuracy of the detection result; on the other hand, the detection method can reduce the requirement of the experimental device, and reduce the harm to the human body. In addition, the above detection method is simple, efficient and convenient. BRIEF DESCRIPTION OF DRAWINGS

[0033] The drawings constituting a part of the specification of the present application are used to provide further understanding of the present application, the illustrative embodiments of the present application and the description thereof are used to explain the present application, and do not constitute improper limitation on the present application. In the drawings:

[0034] Figure 1a The S element distribution diagram of the negative electrode slurry layer surface in the sample to be tested in example 1 is shown;

[0035] Figure 1b The S element distribution diagram of the negative electrode slurry layer cross section in the sample to be tested in example 1 is shown;

[0036] Figure 2a The S element distribution diagram of the negative electrode slurry layer cross section in the sample to be tested in example 15 is shown;

[0037] Figure 2b The N element distribution diagram of the negative electrode slurry layer cross section in the sample to be tested in example 15 is shown. DETAILED DESCRIPTION

[0038] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments.

[0039] As described in the background, the existing detection method has the problem of poor accuracy when applied to detect the distribution of the binder in the pole piece. To solve the above technical problems, the present application provides a detection method for the distribution of the binder in the pole piece, which comprises: reacting a mercapto compound containing a labeled element, a sample to be tested and an initiator in the presence of a solvent to obtain a sample to be tested containing a labeled element; the labeled element comprises an S element; the sample to be tested is a pole piece containing a binder; the binder comprises a compound containing a double bond; and the distribution of the labeled element in the sample to be tested containing the labeled element is detected by X-ray energy spectrum analysis to obtain the distribution of the binder in the sample to be tested.

[0040] The mercapto compound containing a labeled element is reacted with the compound containing a double bond, and the high selectivity of the reaction is used to add the mercapto compound containing a labeled element to the double bond in the compound, so as to introduce a specific kind of labeled element into the structure of the compound containing a double bond. The above labeled element is located and tracked by X-ray energy spectrum analysis, i.e., the distribution of the labeled element in the compound containing a double bond is detected, so as to obtain the distribution of the compound containing a double bond in the pole piece. Compared with the existing detection method, the detection method provided by the present application avoids the reaction of liquid bromine and copper foil to generate CuBr2, thereby reducing the interference of other components on the detection result, and is beneficial to improve the accuracy of the detection result. On the other hand, the detection method can reduce the requirements of the detection method on the experimental device and reduce the harm to the human body. In addition, the above detection method is simple, efficient and convenient.

[0041] In an optional embodiment, the pole piece containing a binder has an active material layer coated on the surface of the current collector (such as copper foil or aluminum foil), and the active material layer can be coated on one side of the current collector or on both sides. The active material layer contains the binder.

[0042] In an alternative embodiment, in the process of locating and tracking the marker element on the adhesive by X-ray energy spectrum analysis, the content of the marker element in the cross section of the sample to be tested near the foil and far from the foil can be detected simultaneously, wherein near the foil refers to extending from the interface where the foil and the active substance layer contact each other outward (active substance layer) in the cross section of the sample to be tested, and the extending area accounts for 1-50% of the cross-sectional area of the active substance layer, or the extending area accounts for 5-30% of the cross-sectional area of the active substance layer, or the extending area accounts for 9-15% of the cross-sectional area of the active substance layer; far from the foil refers to extending from the interface where the active substance layer and the air contact each other inward (active substance layer) in the cross section of the sample to be tested, and the extending area accounts for 1-50% of the cross-sectional area of the active substance layer, or the extending area accounts for 5-30% of the cross-sectional area of the active substance layer, or the extending area accounts for 10% of the cross-sectional area of the active substance layer. The test method is conducive to further improving the accuracy of the test results.

[0043] In an alternative embodiment, the molar ratio of the thiol compound containing the marker element, the initiator and the double bond in the adhesive is (0.5-5.0):(0.5-2.0):1.0. Compared with other ranges, limiting the molar ratio of the thiol compound containing the marker element, the initiator and the double bond in the adhesive to the above range is conducive to improving the utilization rate of reaction raw materials, accurately positioning the marker element to the double bond site in the adhesive, and thus improving the positioning success rate of the adhesive, and further improving the accuracy of the distribution of the adhesive in the sample to be tested.

[0044] In order to further improve the utilization rate of reaction raw materials and thus improve the positioning success rate of the adhesive, as an embodiment, the molar ratio of the thiol compound containing the marker element, the initiator and the double bond in the adhesive is (1.0-5.0):(1.0-2.0):1.0; or (1.5-3.0):(1.1-1.5):1.0.

[0045] In an alternative embodiment, the thiol compound containing the marker element has the general formula R-SH. The R group is one or more of the following: a C 1～6 alkyl group substituted by a hydroxyl group, a C 1～6 alkyl group substituted by a carboxyl group, a C 1～6 alkyl group substituted by an amino group, and a siloxyl group with a main chain of 1-6 atoms. The types of thiol compounds containing the marker element include but are not limited to the above range, and limiting them to the above range is conducive to improving the solubility of the thiol compound containing the marker element in the solvent, and at the same time, improving its reactivity, making the reaction more thorough, and thus reducing the possibility of poor accuracy of the test results due to incomplete labeling.

[0046] In an alternative embodiment, the marking element further comprises at least one of N element, Si element and P element; or, the marking element further comprises N element and / or Si element. The at least one of N element, Si element and P element also comes from the mercapto compound, so that S and N (or Si and / or P) can simultaneously mark the sample to be tested, and their distribution positions are highly coincident, so that N (or Si and / or P) can form a synchronous control of S element, which is more conducive to improving the detection accuracy compared with using only S element for marking, and also conducive to greatly reducing the possibility of operation error.

[0047] In an alternative embodiment, the mercapto compound containing the marking element includes but is not limited to one or more of the group consisting of mercaptoethanol, mercaptoacetic acid, ethyl mercaptoacetate, mercaptoethylamine and mercaptopropyltrimethoxysilane. The types of mercapto compounds containing the marking element include but are not limited to the above range, which is limited in the above range, which is conducive to improving the solubility of the mercapto compound containing the marking element in the solvent, and also conducive to improving its reactivity, conducive to making the reaction more thorough, and further reducing the possibility of poor detection accuracy due to incomplete marking.

[0048] The above reaction can be carried out in a photoinitiating system, a thermal initiating system or a redox initiating system, and the reaction is widely adaptable and not limited by the initiating system.

[0049] In an alternative embodiment, the initiator used in the reaction is a photoinitiator. The photoinitiator is a kind of compound that can absorb certain energy in the ultraviolet or visible light region, thereby generating a mercapto radical; the mercapto radical attacks the carbon-carbon double bond, thereby initiating the reaction. In order to more efficiently initiate the reaction, as an embodiment, the wavelength of the irradiation light (also the absorption wavelength of the initiator) in the photoinitiating reaction system ranges from 10 to 760 nm. In order to further improve the efficiency of photoinitiation and further improve the reaction efficiency, the wavelength of the irradiation light (also the absorption wavelength of the initiator) ranges from 200 to 400 nm. It should be noted that the wavelength of the light refers to the wavelength of the irradiation light, and also the absorption wavelength of the initiator.

[0050] In an alternative embodiment, the photoinitiator includes but is not limited to benzophenone compounds and / or benzoin compounds. Compared with other types of photoinitiators, using the above types of photoinitiators is conducive to improving the reaction degree of the above reaction, thereby improving the generation rate of the sample to be tested containing the marking element, and further conducive to reducing the situation that the SBR detection result accuracy in the electrode sheet is reduced due to incomplete reaction.

[0051] As an embodiment, the photoinitiator includes but is not limited to benzophenone and / or benzoin.

[0052] In an alternative embodiment, the initiator used in the reaction is a thermal initiator. The thermal initiator is suitable for a thermal initiation system, the thermal initiator is cleaved to generate free radicals under the condition of heating, the free radicals take the hydrogen atom on the mercapto group to generate mercapto radicals; the mercapto radicals attack the carbon-carbon double bond to further initiate the reaction.

[0053] In order to provide more suitable reaction conditions and further more efficiently initiate the reaction, the reaction temperature of the thermal initiator is controlled to be 25-150°C. It should be noted that the reaction temperature of the thermal initiator also refers to the ambient temperature when the reaction occurs or the decomposition temperature of the thermal initiator.

[0054] In order to further improve the efficiency of the thermal initiation and further improve the reaction efficiency of the above reaction, preferably, the reaction temperature of the thermal initiator is controlled to be 50-80°C.

[0055] In an alternative embodiment, the thermal initiator includes but is not limited to azo compounds and / or peroxide compounds. Compared with other types of thermal initiators, the use of the above types of photo initiators is advantageous to improve the reaction degree of the above reaction, and further improve the generation rate of the sample to be tested containing the marker element, and further advantageously reduce the case that the accuracy of the SBR detection result in the pole piece is reduced due to incomplete reaction. Alternatively, the thermal initiator includes but is not limited to azobisisobutyronitrile and / or benzoyl peroxide.

[0056] In an alternative embodiment, the initiator is a redox initiator. In order to provide more suitable reaction conditions and improve the reaction efficiency, the molar ratio of the oxidizing agent to the reducing agent in the redox reaction system is (1.1-3.0):1.0. In order to further improve the efficiency of the redox initiation, the molar ratio of the oxidizing agent to the reducing agent is (1.5-2.0):1.0.

[0057] In an alternative embodiment, the redox initiator includes but is not limited to hydrogen peroxide / sodium bisulfite. Compared with other types of redox initiators, the use of the above types of redox initiators is advantageous to improve the reaction degree of the reaction, and further improve the generation rate of the sample to be tested containing the marker element, and further advantageously reduce the case that the accuracy of the SBR detection result in the pole piece is reduced due to incomplete reaction.

[0058] In an alternative embodiment, the reaction time of the above reaction is 0.5-120h or 1-120h. The reaction time includes but is not limited to the above range, which is limited in the above range is advantageous to make the reaction raw materials fully contact and react, and further improve the degree of reaction. In order to further improve the utilization rate of the reaction raw materials, the reaction time can be 5-72h.

[0059] A specific kind of solvent can provide a suitable chemical reaction environment for the above reaction. In an alternative embodiment, the solvent includes one or more of the group consisting of water, alcohol, ether, ketone, alkane and ester, but is not limited to. Alternatively, in order to improve the solubility of each raw material in the solvent and improve the uniformity of dispersion, the solvent includes one or more of the group consisting of ethanol, diethyl ether, acetone, n-hexane and ethyl acetate, but is not limited to.

[0060] In an alternative embodiment, the binder-containing electrode sheet further includes: a negative active material or a positive active material. In an alternative embodiment, when the binder-containing electrode sheet includes the negative active material, the negative active material is selected from one or more of the group consisting of artificial graphite, natural graphite, micron-sized carbon spheres, silicon monoxide, lithium titanate and silicon; when the binder-containing electrode sheet includes the positive active material, the positive active material is selected from one or more of the group consisting of lithium nickel cobalt manganese, lithium nickel cobalt aluminum, lithium nickel manganese, lithium iron phosphate, lithium manganate, lithium cobaltate and lithium manganese iron phosphate. Alternatively, in order to improve the adhesion performance of the electrode sheet and the overall performance, the binder-containing electrode sheet further includes sodium carboxymethyl cellulose (CMC).

[0061] When the binder includes a double-bond-containing compound, and the binder itself does not contain a marker element (an element other than C, H and O), the above detection method provided by the present application can also be used for detection.

[0062] However, when the negative active material or the positive active material contains P element, such as lithium iron phosphate or lithium manganese iron phosphate, the P element cannot be used as a marker element; when the negative active material or the positive active material contains Si element, such as nano-silicon or silicon monoxide, the Si element cannot be used as a marker element.

[0063] As an alternative embodiment, the binder-containing electrode sheet further includes a conductive agent. The conductive agent includes one or more of the group consisting of conductive carbon black, carbon fiber, carbon nanotube and conductive graphite, but is not limited to.

[0064] The second aspect of the present application also provides an application of the above detection method for detecting the distribution of the binder in the electrode sheet provided by the present application in the field of batteries.

[0065] The detection result of the above detection method for detecting the distribution of the binder in the electrode sheet provided by the present application has high accuracy, has low requirements for experimental devices, and can avoid harm to the human body. Moreover, the above detection method is simple, efficient and convenient to operate. The application of the above detection method in the field of batteries can effectively obtain the distribution of the binder in the electrode sheet, and provide an effective reference for solving the problem of binder floating caused by water evaporation during the drying process.

[0066] The application will be described in further detail below with reference to specific embodiments, which are not to be understood as limiting the scope of the application as claimed.

[0067] Example 1

[0068] A method for preparing a sample to be tested, comprising:

[0069] 92 parts by weight of artificial graphite, 2 parts by weight of conductive carbon black, 1.0 part by weight of conductive carbon fiber, 3.2 parts by weight of SBR (ZEON optical materials, 451B) and 1.8 parts by weight of CMC were uniformly stirred and slurried with water to prepare a negative electrode slurry.

[0070] The negative electrode slurry was coated on one side surface of a copper foil to obtain a copper foil containing a negative electrode slurry layer, the areal density of the negative electrode slurry layer being 160 g / m 2 After drying in an oven, the negative electrode sheet coated with the negative electrode slurry was rolled to obtain an electrode sheet containing a binder SBR, the compaction density being 1.4 g / cc. The electrode sheet was cut to obtain a square sheet with a side length of 10 mm to obtain a sample to be tested, which was ready for use.

[0071] A method for detecting the distribution of a binder in an electrode sheet, comprising:

[0072] In this embodiment, mercaptoethanol is used as a mercapto compound containing a labeled element S, which has the following chemical structural formula: Azo-bis-isobutyronitrile (AIBN) is used as a thermal initiator, which has the following chemical structural formula: Anhydrous ethanol is used as a solvent.

[0073] The prepared sample to be tested was mixed with 5 mL of anhydrous ethanol, 18 mg of AIBN and 10 mg of mercaptoethanol, and the reaction was started at 65°C (the decomposition temperature of AIBN is 65°C). The molar ratio of mercaptoethanol, AIBN and double bonds in SBR was 1.2:1.1:1. The reaction was allowed to proceed for 64 h under stirring. After the reaction was completed, the labeled sample to be tested was taken out, washed (to remove unreacted residual raw materials and initiators), and dried to obtain a sample to be tested.

[0074] The distribution of the binder SBR in the surface and cross section of the dried sample to be tested is detected by X-ray energy spectrum analysis method (EDS). Meanwhile, the content of the marker element near the copper foil position and the content of the marker element far from the copper foil position in the cross section of the sample to be tested are detected. The position near the copper foil refers to the interface between the copper foil and the negative electrode slurry layer in the cross section of the sample to be tested, extending outward (negative electrode slurry layer) to an area of 10% of the negative electrode slurry layer; the position far from the copper foil refers to the interface between the negative electrode slurry layer and the air in the cross section of the sample to be tested, extending inward (negative electrode slurry layer) to an area of 10% of the negative electrode slurry layer.

[0075] The test results of the distribution of S element are shown in Figure 1a and Figure 1b , wherein Figure 1a the S element in the surface of the negative electrode slurry layer in the sample to be tested is uniformly distributed, Figure 1b the S element in the cross section of the negative electrode slurry layer in the sample to be tested is also uniformly distributed. This shows that the binder SBR in the sample to be tested is uniformly distributed in the surface and cross section, and there is no obvious SBR floating.

[0076] Example 2

[0077] The preparation method of the sample to be tested and the detection method of the distribution of the binder in the pole piece are the same as those in Example 1.

[0078] The difference from Example 1 is that mercaptopropyl trimethoxysilane is used as the mercapto compound containing the marker elements S element and Si element in this example, which has the following chemical structural formula:

[0079] After EDS detection of the cross section of the sample to be tested, the S element content at the position near the copper foil is 0.60wt%, and the Si element content is 0.65wt%; the S element content at the position far from the copper foil is 0.71wt%, and the Si element content is 0.71wt%.

[0080] Example 3

[0081] The preparation method of the sample to be tested and the detection method of the distribution of the binder in the pole piece are the same as those in Example 1.

[0082] The difference from Example 1 is that the molar ratio of mercaptoethanol, AIBN and double bond in SBR is 1.0:1.0:1.0.

[0083] Example 4

[0084] The preparation method of the sample to be tested and the detection method of the distribution of the binder in the pole piece are the same as those in Example 1.

[0085] The difference from Example 1 is that the molar ratio of mercaptoethanol, AIBN and double bonds in SBR is 5.0:2.0:1.0.

[0086] Example 5

[0087] The preparation method of the sample to be tested and the detection method of the binder distribution in the pole piece are the same as those of Example 1.

[0088] The difference from Example 1 is that the molar ratio of mercaptoethanol, AIBN and double bonds in SBR is 1.5:1.1:1.0.

[0089] Example 6

[0090] The preparation method of the sample to be tested and the detection method of the binder distribution in the pole piece are the same as those of Example 1.

[0091] The difference from Example 1 is that the molar ratio of mercaptoethanol, AIBN and double bonds in SBR is 3.0:1.5:1.0.

[0092] Example 7

[0093] The preparation method of the sample to be tested and the detection method of the binder distribution in the pole piece are the same as those of Example 1.

[0094] The difference from Example 1 is that the molar ratio of mercaptoethanol, AIBN and double bonds in SBR is 0.5:0.5:1.0.

[0095] Example 8

[0096] The preparation method of the sample to be tested and the detection method of the binder distribution in the pole piece are the same as those of Example 1.

[0097] The difference from Example 1 is that the benzoyl peroxide (BPO) is used as a thermal initiator in this example, which has the following chemical structural formula:

[0098] Example 9

[0099] The preparation method of the sample to be tested and the detection method of the binder distribution in the pole piece are the same as those of Example 1.

[0100] The difference from Example 1 is that the tert-butyl peroxide (TBHP) is used as a thermal initiator in this example.

[0101] Example 10

[0102] The preparation method of the sample to be tested and the detection method of the binder distribution in the pole piece are the same as those of Example 1.

[0103] The difference from Example 1 is that the reaction time is 1 h.

[0104] Example 11

[0105] The preparation method of the sample to be tested and the detection method of the binder distribution in the pole piece are the same as those in Example 1.

[0106] The difference from Example 1 is that the reaction time is 120 h.

[0107] Example 12

[0108] The preparation method of the sample to be tested and the detection method of the binder distribution in the pole piece are the same as those in Example 1.

[0109] The difference from Example 1 is that the reaction time is 5 h.

[0110] Example 13

[0111] The preparation method of the sample to be tested and the detection method of the binder distribution in the pole piece are the same as those in Example 1.

[0112] The difference from Example 1 is that the reaction time is 72 h.

[0113] Example 14

[0114] The preparation method of the sample to be tested and the detection method of the binder distribution in the pole piece are the same as those in Example 1.

[0115] The difference from Example 1 is that the reaction time is 0.5 h.

[0116] Example 15

[0117] The preparation method of the sample to be tested and the detection method of the binder distribution in the pole piece are the same as those in Example 1.

[0118] The difference from Example 1 is that in this embodiment, mercaptoethylamine is used as a mercapto compound containing a labeled element N element, which has the following chemical structural formula: Benzophenone (BP) is used as a photoinitiator, which has the following chemical structural formula: Acetone is used as a solvent.

[0119] The above prepared sample to be tested is mixed with 5 mL of acetone, 1 mg of BP and 1.2 mg of mercaptoethylamine. Under the irradiation of ultraviolet light with a power of 80 W and a wavelength of 254 nm, the reaction is started, and the reaction is carried out under the condition of stirring at room temperature for 64 h. After the reaction is completed, the labeled sample to be tested is taken out, washed and dried to obtain the sample to be tested.

[0120] The distribution of the binder SBR in the surface and cross section of the dried sample to be tested is detected by X-ray energy spectrum analysis method (EDS), and the content of the marker element near the position of the pole piece and the content of the marker element far from the position of the pole piece in the cross section of the sample to be tested are detected.

[0121] It can be known from Figure 2a and Figure 2b that when the thiol ethylamine is used to add and modify the double bond in the SBR, the SBR can be located by the distribution of the S element and the N element, and it can be known from the detection results shown in Figure 2a and Figure 2b that the distribution of the binder SBR on the surface of the sample to be tested is relatively uniform. After the cross section of the sample to be tested is detected by EDS, the content of the S element in the negative electrode slurry layer near the position of the copper foil (same as in Example 1) is 0.56wt%, and the content of the N element is 0.60wt%; the content of the S element in the negative electrode slurry layer far from the position of the copper foil (same as in Example 1) is 0.65wt%, and the content of the N element is 0.68wt%.

[0122] Example 16

[0123] The preparation method of the sample to be tested and the detection method of the distribution of the binder in the pole piece are the same as those in Example 1.

[0124] The difference from Example 1 is that in this embodiment, mercaptoacetic acid is used as a mercapto compound containing a marker element S element, which has the following chemical structural formula: Hydrogen peroxide and sodium bisulfite are used as redox initiators.

[0125] The above prepared sample to be tested is mixed with 5mL ultrapure water, 1mg sodium bisulfite and 1.2mg mercaptoacetic acid and stirred, and then 1mg hydrogen peroxide is added to start the reaction, and the reaction is carried out under stirring at room temperature for 64h. After the reaction is completed, the labeled sample to be tested is taken out, washed and dried to obtain the sample to be tested.

[0126] Example 17

[0127] The preparation method of the sample to be tested and the detection method of the distribution of the binder in the pole piece are the same as those in Example 1.

[0128] The difference from Example 1 is that in this embodiment, mercaptoacetic acid is used as a mercapto compound containing a marker element S element, which has the following chemical structural formula:

[0129] Example 18

[0130] The detection method of the distribution of the binder in the pole piece is the same as that in Example 1.

[0131] The difference from Example 1 is that the composition of the negative electrode slurry includes 92 parts by weight of artificial graphite, 2 parts by weight of conductive carbon black, 1.0 part by weight of conductive carbon fiber, 3.2 parts by weight of NBR (Showa Denko, 6913), and 1.8 parts by weight of CMC and water. The difference from Example 1 is only that the kind of binder is different.

[0132] Comparative Example 1

[0133] The preparation method of the sample to be tested is the same as that of Example 1.

[0134] The difference from Example 1 is that the detection method of the binder distribution in the electrode sheet includes:

[0135] The sample to be tested is placed in bromine water (containing 4-6 wt% of bromine), so that the bromine water immerses the sample to be tested. After immersion treatment at room temperature for 1 min, the treated sample to be tested is taken out and dried for standby.

[0136] Comparative Example 2

[0137] The preparation method of the sample to be tested is the same as that of Example 18.

[0138] The difference from Example 18 is that the detection method of the binder distribution in the electrode sheet includes:

[0139] The sample to be tested is placed in bromine water (containing 4-6 wt% of bromine), so that the bromine water immerses the sample to be tested. After immersion treatment at room temperature for 1 min, the treated sample to be tested is taken out and dried for standby.

[0140] Tables 1 and 2 respectively show the S element content (or Br element content) at the position close to the copper foil and the S element content (or Br element content) at the position far from the copper foil after the cross section of the sample to be tested is detected by EDS using the detection method of the binder distribution in the electrode sheet of the above-mentioned examples and comparative examples of the present application. The above-mentioned element content represents the content of the binder at the corresponding position in the electrode sheet. It should be noted that in the above-mentioned examples and comparative examples, the position close to the copper foil refers to the position extending outward (the negative electrode slurry layer) from the interface where the copper foil and the negative electrode slurry layer contact each other, and the area of the extension accounts for 10% of the cross-sectional area of the negative electrode slurry layer; the position far from the copper foil refers to the position extending inward (the negative electrode slurry layer) from the interface where the negative electrode slurry layer and the air contact each other, and the area of the extension accounts for 10% of the cross-sectional area of the negative electrode slurry layer.

[0141] Table 1

[0142]

[0143] Table 2

[0144]

[0145] From the above description, it can be seen that the above-mentioned embodiments of the present application achieve the following technical effects:

[0146] Comparing Example 1 and Comparative Example 1, it can be seen that in Example 1, the content of S near the copper foil is 0.62wt%, i.e. the content of SBR near the copper foil is 0.62wt%, and the content of S far from the copper foil is 0.70wt%, i.e. the content of SBR far from the copper foil is 0.70wt%; while in Comparative Example 1, the content of Br near the copper foil is 0.68wt%, which is 9.7% higher than the detection result of Example 1, and the content of Br far from the copper foil is 0.78wt%, which is 11.4% higher than the detection result of Example 1. Similarly, comparing Example 18 and Comparative Example 2, it can be seen that in Comparative Example 2, the content of Br near the copper foil is 0.65wt%, i.e. the content of NBR near the copper foil is 0.65wt%, which is 3.2% higher than the detection result of Example 1, and the content of Br far from the copper foil is 0.73wt%, which is 4.3% higher than the detection result of Example 1.

[0147] Since both Comparative Example 1 and Comparative Example 2 use liquid bromine to track the double bond, according to the reaction principle, each double bond in SBR or NBR will undergo an addition reaction with two bromine atoms, which will cause the test result to be high; while in the examples, a thiol compound containing a marker element is used to track the double bond, and each double bond in SBR or NBR is connected to one sulfur atom after reaction, and the two are in a one-to-one correspondence. Therefore, under the premise that the sample to be tested is the same and the content of SBR is the same, the detection results of all examples in the present application are more accurate than those of Comparative Examples 1 and 2, and the detection results differ greatly. At the same time, because liquid bromine will also react with copper foil to generate CuBr2, this part of CuBr2 is also regarded as a marker of SBR or NBR, which causes the test result to be further high. Therefore, compared with the existing detection method, the above detection method provided by the present application can make the double bond in the adhesive correspond one-to-one with the marker element, which is convenient for tracking; at the same time, it also avoids the reaction of liquid bromine with copper foil to generate CuBr2, thereby reducing the interference with the detection result, and is conducive to improving the accuracy of the detection result.

[0148] It should be noted that the terms "first", "second", and the like in the specification and claims of the present application are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the terms thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those described herein.

[0149] The above merely illustrates some embodiments of the present application but is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for detecting the distribution of binder in an electrode sheet, characterized in that, The method for detecting the binder distribution in the electrode sheet includes: In the presence of a solvent, a thiol compound containing a labeled element, a test sample, and an initiator are reacted to obtain a test sample containing a labeled element; the labeled element includes sulfur (S); the test sample is an electrode containing a binder; the binder includes a compound containing carbon-carbon double bonds. The distribution of the labeled elements in the test sample containing the labeled elements was detected by X-ray energy dispersive spectroscopy, thereby obtaining the distribution of the binder in the test sample.

2. The method for detecting the distribution of binder in an electrode sheet according to claim 1, characterized in that, The adhesive is selected from copolymers of butadiene and styrene and / or copolymers of acrylonitrile and butadiene.

3. The method for detecting the distribution of binder in an electrode sheet according to claim 1, characterized in that, The molar ratio of the thiol compound containing the labeled element, the initiator, and the carbon-carbon double bond in the binder is (0.5-5.0):(0.5-2.0):1.

0.

4. The method for detecting the binder distribution in the electrode sheet according to any one of claims 1 to 3, characterized in that, The marking elements also include one or more elements from the group consisting of N, Si, and P.

5. The method for detecting the binder distribution in the electrode sheet according to any one of claims 1 to 3, characterized in that, The general formula of the mercapto compound containing the labeled element is R-SH; wherein R is one or more of the following groups: hydroxyl-substituted C1-C6 alkyl, carboxyl-substituted C1-C6 alkyl, amino-substituted C1-C6 alkyl, and silanoxy groups with a main chain consisting of 1 to 6 atoms.

6. The method for detecting the distribution of binder in an electrode according to any one of claims 1 to 3, characterized in that, The thiol compound containing the labeled element is selected from one or more of the group consisting of mercaptoethanol, mercaptoacetic acid, ethyl mercaptoacetate, mercaptoethylamine, and mercaptopropyltrimethoxysilane.

7. The method for detecting the distribution of binder in an electrode according to any one of claims 1 to 3, characterized in that, The initiator is a photoinitiator.

8. The method for detecting the distribution of binder in an electrode sheet according to claim 7, characterized in that, The wavelength range of light in the photoinitiated reaction system is 10–760 nm.

9. The method for detecting the distribution of binder in an electrode sheet according to claim 7, characterized in that, The photoinitiator is selected from benzophenone compounds and / or benzoin compounds.

10. The method for detecting the distribution of binder in an electrode sheet according to claim 7, characterized in that, The photoinitiator is selected from benzophenone and / or benzoin.

11. The method for detecting the binder distribution in an electrode according to any one of claims 1 to 3, characterized in that, The initiator is a thermal initiator.

12. The method for detecting the distribution of binder in an electrode sheet according to claim 11, characterized in that, The reaction temperature of the thermal initiator is 25–150 °C.

13. The method for detecting the distribution of binder in an electrode according to claim 11, characterized in that, The thermal initiator is selected from azo compounds and / or peroxide compounds.

14. The method for detecting the binder distribution in an electrode sheet according to claim 13, characterized in that, The thermal initiator is selected from azobisisobutyronitrile and / or benzoyl peroxide.

15. The method for detecting the binder distribution in an electrode according to any one of claims 1 to 3, characterized in that, The initiator is a redox initiator.

16. The method for detecting the distribution of binder in an electrode according to claim 15, characterized in that, The molar ratio of oxidant to reductant in the redox reaction system is (1.1 to 3.0): 1.

0.

17. The method for detecting the distribution of binder in an electrode according to claim 15, characterized in that, The redox initiator is selected from hydrogen peroxide and sodium bisulfite.

18. The method for detecting the distribution of binder in an electrode sheet according to claim 1, characterized in that, The reaction time is 0.5 to 120 hours.

19. The method for detecting the distribution of binder in an electrode sheet according to claim 1, characterized in that, The solvent is selected from one or more of the group consisting of water, alcohol, ether, ketone, alkanes and esters.

20. The method for detecting the distribution of binder in an electrode sheet according to claim 1, characterized in that, The solvent is selected from one or more of the group consisting of ethanol, diethyl ether, acetone, n-hexane, and ethyl acetate.

21. The method for detecting the distribution of binder in an electrode according to claim 1, characterized in that, The electrode containing the binder also includes: a negative electrode active material or a positive electrode active material.

22. The method for detecting the distribution of binder in an electrode according to claim 21, characterized in that, When the electrode containing the binder includes a negative electrode active material, the negative electrode active material is selected from one or more of the group consisting of artificial graphite, natural graphite, micron-sized carbon spheres, silicon suboxide, lithium titanate, and silicon. When the electrode containing the binder includes a positive electrode active material, the positive electrode active material is selected from one or more of the group consisting of lithium nickel cobalt manganese, lithium nickel cobalt aluminum, lithium nickel manganese, lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide, and lithium manganese iron phosphate.

23. The application of a method for detecting the distribution of binder in an electrode as described in any one of claims 1 to 22 in the field of batteries.

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