A method for analyzing and detecting the content of negative electrode material formula and its application

Abstract

The present application discloses a method and application for analyzing and detecting the content of a negative electrode material formula, wherein the analysis and detection method comprises: taking a portion of the negative electrode material and performing a first thermogravimetric analysis to obtain a first weight loss rate; removing the aqueous dispersant from the remaining negative electrode material to obtain a negative electrode material free of the aqueous dispersant; performing a second thermogravimetric analysis on the negative electrode material free of the aqueous dispersant to obtain a second weight loss rate; performing a third thermogravimetric analysis and a fourth thermogravimetric analysis on standard substances of the aqueous binder and the aqueous dispersant, respectively, to obtain a third weight loss rate and a fourth weight loss rate; and taking the product of the ratio of the second weight loss rate to the third weight loss rate and 100% as the mass content of the aqueous binder in the negative electrode material. The method for analyzing and detecting the content of the negative electrode material formula of the present application can verify the removal effect of the aqueous dispersant through the TG curve, and the analytical detection results of the content of the binder and the like are highly reliable and accurate.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a method for analyzing and detecting the content of a negative electrode material formula and its application. Background Art

[0002] The content of main materials, binders, dispersants, and conductive agents in the negative electrode formula of lithium-ion batteries is one of the core technologies of lithium-ion batteries. Different formula contents correspond to different performances and also correspond to different failure manifestations. Establishing a method for analyzing and detecting the content of lithium-ion battery negative electrode formula is of great significance to the failure analysis and performance characterization of lithium-ion batteries.

[0003] Currently, in the field of lithium-ion batteries, relevant technologies detect the uniformity of SBR distribution in electrodes through bromine water treatment and subsequent extraction, but there is no systematic method for analyzing and detecting the content of negative electrode formulas.

[0004] Therefore, there is an urgent need for a systematic method to analyze and detect the content of the negative electrode formula. Summary of the Invention

[0005] In view of this, one purpose of the present application is to provide a method for analyzing and detecting the content of the negative electrode material formula, by excluding the influence of the weight loss of the carbon material, first performing a TG test on the entire negative electrode material of the graphite negative electrode, and then removing the aqueous dispersant and performing the TG test again, combining the weight loss rate of each TG test and the weight loss rate obtained by the TG test of the aqueous binder and aqueous dispersant standard substance, the content of the aqueous binder and aqueous dispersant in the negative electrode material can be accurately calculated. This method can verify the removal effect of the aqueous dispersant through the TG curve, and the analytical detection results of the aqueous binder and aqueous dispersant content are highly reliable and accurate.

[0006] Another object of the present application is to provide an application of a method for analyzing and detecting the content of a negative electrode material formula.

[0007] To achieve the above objectives, the first aspect of the present application provides a method for analyzing and detecting the content of a negative electrode material formula, wherein the negative electrode material is composed of a carbon material, an aqueous binder, and an aqueous dispersant, and the carbon material is composed of graphite and a carbon-based conductive agent; the analysis and detection method comprises:

[0008] Taking a portion of the negative electrode material for a first thermogravimetric analysis to obtain a first weight loss rate;

[0009] removing the aqueous dispersant from the remaining negative electrode material to obtain a negative electrode material free of the aqueous dispersant;

[0010] performing a second thermogravimetric analysis on the negative electrode material without the aqueous dispersant to obtain a second weight loss rate;

[0011] performing a third thermogravimetric analysis and a fourth thermogravimetric analysis on respective standard substances of the aqueous binder and the aqueous dispersant within a first temperature range, respectively, to obtain a third weight loss rate and a fourth weight loss rate; within the first temperature range, the graphite does not undergo thermal weight loss, and the weight loss of the carbon-based conductive agent is negligible;

[0012] The mass content of the aqueous binder in the negative electrode material is calculated according to formula (1), and the mass content of the aqueous dispersant in the negative electrode material is calculated according to formula (2):

[0013] C1=D2 / D1*100% Formula (1)

[0014] C2=(D4-D2) / D3*100% Formula (2)

[0015] Among them, D1 is the third weight loss rate, D2 is the second weight loss rate, D3 is the fourth weight loss rate, D4 ​​is the first weight loss rate, C1 is the mass content of the aqueous binder in the negative electrode material, and C2 is the mass content of the aqueous dispersant in the negative electrode material.

[0016] In some embodiments, the method for analyzing and detecting the content of the negative electrode material formula further includes:

[0017] The mass content of the carbon material in the negative electrode material is calculated according to the following formula:

[0018] C3=(1-C1-C2)*100%

[0019] Wherein, C3 is the mass content of the carbon material in the negative electrode material.

[0020] In some embodiments, the first temperature range is 25-750°C.

[0021] In some embodiments, the third thermogravimetric analysis and the fourth thermogravimetric analysis are both performed in an inert gas atmosphere.

[0022] In some embodiments, the heating rates of the third thermogravimetric analysis and the fourth thermogravimetric analysis are both 1-3 k / min.

[0023] In some embodiments, the conditions for the first thermogravimetric analysis and the second thermogravimetric analysis are: inert gas atmosphere, heating rate of 1-3 k / min, and test temperature range of 25-750°C.

[0024] In some embodiments, removing the aqueous dispersant from the remaining negative electrode material to obtain a negative electrode material free of the aqueous dispersant comprises:

[0025] The remaining negative electrode material is subjected to a first reflux in a first solvent, followed by a first filtration and a first drying to obtain the negative electrode material free of the aqueous dispersant.

[0026] In some embodiments, the first solvent includes water and an organic solvent, and the organic solvent includes at least one of methanol, ethanol, ethylene glycol, and propanol.

[0027] In some embodiments, the temperature of the first reflux is 60-90°C.

[0028] In some embodiments, the first reflux time is 4-6 hours.

[0029] In some embodiments, the method for analyzing and detecting the content of the negative electrode material formula further includes a step of first grinding the negative electrode material before performing the first thermogravimetric analysis and the step of removing the aqueous dispersant.

[0030] In some embodiments, the method for analyzing and detecting the content of the negative electrode material formula further includes a step of performing a second grinding on the negative electrode material without the aqueous dispersant before performing the second thermogravimetric analysis.

[0031] In some embodiments, the negative electrode material is a fresh negative electrode material mixed with a carbon material, an aqueous binder, and an aqueous dispersant, or a negative electrode material obtained from a negative electrode sheet of a lithium-ion battery to be tested.

[0032] In some embodiments, when the negative electrode material is a negative electrode material obtained from a negative electrode sheet of a lithium-ion battery to be tested, the method for analyzing and detecting the negative electrode material formula content further includes:

[0033] The negative electrode plate is washed and dried for a second time, and then the negative electrode material layer of the negative electrode plate is scraped off. The negative electrode material is then subjected to a second reflow, a second filtration, and a third drying in a second solvent to obtain the negative electrode material.

[0034] In some embodiments, the washing solvent and the second solvent both include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methanol, ethanol, ethylene glycol, and propanol.

[0035] In some embodiments, the temperature of the second reflux is 60-90°C.

[0036] In some embodiments, the second reflux time is 4-6 hours.

[0037] In some embodiments, when the negative electrode material is a negative electrode material obtained from a negative electrode sheet of a lithium-ion battery to be tested, the method for analyzing and detecting the negative electrode material formula content further includes:

[0038] The lithium-ion battery to be tested is discharged to a cut-off voltage, and then disassembled in an environment with a humidity of less than 10% to obtain the negative electrode sheet.

[0039] In some embodiments, the discharge current of the lithium-ion battery to be tested is 0.01-0.05C.

[0040] In some embodiments, the graphite includes at least one of artificial graphite, natural graphite, and mesocarbon microbeads.

[0041] In some embodiments, the carbon-based conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, porous carbon, graphene, multi-walled carbon nanotubes, and single-walled carbon nanotubes.

[0042] In some embodiments, the water-based binder includes at least one of styrene butadiene and modified organic emulsions thereof, styrene acrylate and modified organic emulsions thereof, polyethylene emulsion, and polypropylene emulsion.

[0043] In some embodiments, the aqueous dispersant includes at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium carboxyethyl cellulose, and lithium carboxyethyl cellulose.

[0044] The second aspect of the present application relates to the application of the analysis and detection method of the negative electrode material formula content described in the present application in the field of secondary batteries.

[0045] The analysis and detection method of the negative electrode material formula content described in this application can at least bring the following beneficial effects:

[0046] By eliminating the influence of carbon material weight loss, the entire graphite anode material is first subjected to TG testing, followed by another TG test after removing the aqueous dispersant. Combining the weight loss rates from each TG test with the weight loss rates obtained from TG testing of standard aqueous binder and aqueous dispersant materials, the content of aqueous binder and aqueous dispersant in the anode material can be accurately calculated. This method can verify the effectiveness of aqueous dispersant removal through TG curves, and the analytical test results for aqueous binder and aqueous dispersant content are highly reliable and accurate.

[0047] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings.

[0049] in:

[0050] Figure 1 This is a flow chart of a method for analyzing and detecting the content of anode material formula according to an exemplary embodiment of the present application.

[0051] Figure 2 This is the weight loss curve (TG-DTG curve) of the negative electrode material (solid 1) in Example 1.

[0052] Figure 3 This is the weight loss curve (TG-DTG curve) of the negative electrode material from which CMC was removed in Example 1.

[0053] Figure 4 This is the weight loss curve (TG-DTG curve) of the artificial graphite and carbon-based conductive agent SP standard substance in Example 1.

[0054] Figure 5 This is the weight loss curve (TG-DTG curve) of the water-based binder SBR and the water-based dispersant CMC standard substances in Example 1. DETAILED DESCRIPTION

[0055] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present application, but should not be understood as limiting the present application.

[0056] Throughout this application, the disclosure of numerical ranges includes disclosure of all values ​​within the entire range and further subdivided ranges, including the endpoints and subranges given within those ranges.

[0057] In this application, the raw materials, equipment, etc. involved, unless otherwise specified, are all raw materials and equipment that can be obtained through commercial channels or known methods; the methods involved, unless otherwise specified, are all conventional methods.

[0058] The term "and / or," when used in conjunction with a list of two or more items, means that any of the listed items can be used alone or in combination with any one or more of the listed items. For example, the expression "A and / or B" is intended to mean A or B or A and B, that is, only A, only B, or a combination of A and B.

[0059] The inventors discovered that by selecting a suitable atmosphere and eliminating the weight loss effect of carbon materials (graphite and carbon-based conductive agents) within a specific temperature range, under an inert gas atmosphere such as N2, graphite and carbon-based conductive agents do not lose weight or lose weight so little as to be negligible at 25-750°C, and the weight loss peaks of aqueous binders such as SBR and aqueous dispersants such as CMC at 25-750°C are split more completely. Therefore, the aqueous dispersant or aqueous binder in the negative electrode material can be first removed (for example, by selecting a suitable solvent for dissolution and removal), and the removal effect of the aqueous dispersant can be verified by TG curve. Then, the content of aqueous binders such as SBR and aqueous dispersants such as CMC in the negative electrode material can be calculated by combining the thermal weight loss ratio of standard substances such as aqueous dispersants such as CMC and aqueous binders such as SBR. Then, based on the sum of the components in the negative electrode material being 100% (i.e., 1), the content of carbon material (graphite and carbon-based conductive agent) in the negative electrode material can be calculated.

[0060] Specifically, when the negative electrode material is obtained from the negative electrode sheet of the lithium ion battery to be tested, the negative electrode material mixed powder is washed to remove the influence of impurities on subsequent analysis, and the washed negative electrode material powder is subjected to a TG test to obtain the weight loss ratio (i.e., the first weight loss rate) of the aqueous binder, aqueous dispersant and carbon material (graphite and carbon-based conductive agent); then the aqueous dispersant is dissolved, and a TG test is performed on the mixture containing only the aqueous binder and the carbon material (graphite and carbon-based conductive agent). The content of aqueous binders such as SBR is calculated based on the weight loss ratio of pure aqueous binders such as SBR (i.e., the third weight loss rate) and the weight loss ratio of the negative electrode material after removing the aqueous dispersant (i.e., the second weight loss rate); then the proportion of aqueous binders such as SBR is substituted into the first weight loss rate, and the proportion of aqueous dispersants is calculated based on the weight loss ratio of pure aqueous dispersants (i.e., the fourth weight loss rate), and the content of carbon materials (graphite and carbon-based conductive agents) in the graphite negative electrode of the lithium ion battery is obtained by calculation. It has been verified that the analytical detection method for the negative electrode material formula content of the embodiment of the present application has high reliability and accuracy for detecting the content of the aqueous binder and the aqueous dispersant.

[0061] The following describes in detail a method for analyzing and detecting the content of a negative electrode material formula according to an embodiment of the present application with reference to the accompanying drawings.

[0062] Figure 1 This is a flow chart of a method for analyzing and detecting the content of anode material formula according to an exemplary embodiment of the present application.

[0063] like Figure 1 As shown, the analysis and detection method of the negative electrode material formula content includes the following steps:

[0064] S101. Taking a portion of the negative electrode material and performing a first thermogravimetric analysis to obtain a first weight loss rate.

[0065] In the embodiment of the present application, the first weight loss rate is also the weight loss rate of the negative electrode material.

[0066] In some embodiments, the negative electrode material consists of a carbon material, an aqueous binder, and an aqueous dispersant, and the carbon material consists of graphite and a carbon-based conductive agent.

[0067] In some embodiments, the graphite includes but is not limited to at least one of artificial graphite, natural graphite, mesocarbon microbeads and other carbon-based negative electrode active materials.

[0068] In some embodiments, the carbon-based conductive agent includes but is not limited to at least one of conductive carbon black, acetylene black, Ketjen black, porous carbon, graphene, multi-walled carbon nanotubes, single-walled carbon nanotubes and other chain-shaped, granular, porous or tubular conductive agents.

[0069] In some embodiments, the water-based binder includes but is not limited to at least one of styrene butadiene and its modified organic emulsion (SBR), styrene acrylate and its modified organic emulsion, polyethylene emulsion, and polypropylene emulsion.

[0070] In some embodiments, the aqueous dispersant includes at least one of carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium carboxyethyl cellulose, and lithium carboxyethyl cellulose.

[0071] In the embodiments of the present application, a small amount of the negative electrode material, for example, 5-10 mg, can be used for the first thermogravimetric analysis (TG test).

[0072] In some embodiments, the test conditions of the first thermogravimetric analysis are: inert gas atmosphere, heating rate of 1-3 k / min, and test temperature range of 25-750°C.

[0073] Exemplarily, the inert gas includes at least one of nitrogen (N2), helium or argon, and nitrogen can be selected.

[0074] For example, in the first thermogravimetric analysis, the heating rate includes but is not limited to 1 k / min, 2 k / min, or 3 k / min.

[0075] In some embodiments, the negative electrode material is a fresh negative electrode material mixed with a carbon material, an aqueous binder, and an aqueous dispersant.

[0076] In other embodiments, the negative electrode material is a negative electrode material obtained from a negative electrode sheet of a lithium-ion battery to be tested.

[0077] It should be understood that in the embodiments of this application, the lithium-ion batteries to be tested refer to lithium-ion batteries using graphite as the negative electrode active material (i.e., negative electrode active material), including lithium-ion batteries using lithium iron phosphate, lithium nickel cobalt manganese oxide, or lithium titanate as the positive electrode active material and graphite as the negative electrode active material. The negative electrode plate refers to a negative electrode plate using graphite as the negative electrode active material, and its negative electrode material is the negative electrode material described in this application.

[0078] In some embodiments, when the negative electrode material is a negative electrode material obtained from a negative electrode sheet of a lithium-ion battery to be tested, the method for analyzing and detecting the negative electrode material formula content further includes:

[0079] The negative electrode plate is washed and dried for a second time, and then the negative electrode material layer of the negative electrode plate is scraped off. The negative electrode material is then subjected to a second reflow, a second filtration, and a third drying in a second solvent to obtain the negative electrode material.

[0080] In some embodiments, the washing method comprises the following steps:

[0081] (1) placing the negative electrode sheet in a washing solvent, leaving it to stand for a period of time, and then using ultrasound to clean the negative electrode sheet;

[0082] (2) Rinse the front and back surfaces of the negative electrode sheet after ultrasonic cleaning with a spray bottle filled with a washing solvent.

[0083] In the embodiments of the present application, the purpose of washing the negative electrode sheet is to remove byproducts on the surface of the negative electrode sheet.

[0084] In some embodiments, the washing solvent and the second solvent include but are not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methanol, ethanol, ethylene glycol, propanol, etc.

[0085] In some embodiments, the second drying method includes but is not limited to at least one of drying (eg, drying in a forced air drying oven, etc.), vacuum drying, spray drying, etc.

[0086] In the embodiments of the present application, the purpose of the second reflux is to remove lithium salts and further remove byproducts on the surface of the negative electrode. Therefore, the second solvents are all solvents that can dissolve and remove lithium salts and other impurities not composed of the negative electrode material. Reflux is a more thorough method for removing lithium salts and impurities.

[0087] Therefore, the washing solvent and the second solvent are solvents that can dissolve the lithium salt and the by-products on the surface of the negative electrode plate, but cannot dissolve the negative electrode material composition.

[0088] In some embodiments, the temperature of the second reflux is 60-90°C, including but not limited to 65°C, 70°C, 75°C, 80°C or 85°C.

[0089] In some embodiments, the second reflux time is 4-6 hours, including but not limited to 4.5 hours, 5 hours or 6 hours.

[0090] In some embodiments, when the negative electrode material is a negative electrode material obtained from a negative electrode sheet of a lithium-ion battery to be tested, the method for analyzing and detecting the negative electrode material formula content further includes:

[0091] The lithium-ion battery to be tested is discharged to a cut-off voltage, and then disassembled in an environment with a humidity of less than 10% to obtain the negative electrode sheet.

[0092] In some embodiments, the discharge current of the lithium-ion battery to be tested is 0.01-0.05C.

[0093] S102 , removing the aqueous dispersant from the remaining negative electrode material to obtain a negative electrode material free of the aqueous dispersant.

[0094] In the embodiments of the present application, the method of removing the aqueous dispersant from the remaining negative electrode material includes but is not limited to at least one of reflux and the like.

[0095] As an optional example, removing the aqueous dispersant from the remaining negative electrode material to obtain a negative electrode material free of the aqueous dispersant comprises:

[0096] The remaining negative electrode material is subjected to a first reflux in a first solvent, followed by a first filtration and a first drying to obtain the negative electrode material free of the aqueous dispersant.

[0097] In the embodiment of the present application, the first solvent is a solvent that can dissolve the aqueous dispersant but does not dissolve the aqueous binder and the carbon material (graphite and carbon-based conductive agent). In other words, the first solvent is a solvent that only dissolves the aqueous dispersant in the negative electrode material.

[0098] In some embodiments, the first solvent includes water and an organic solvent.

[0099] Illustratively, the organic solvent includes but is not limited to at least one of methanol, ethanol, ethylene glycol, propanol, and the like.

[0100] Illustratively, the mass ratio of water to organic solvent in the first organic solvent is (30-70):(70-30), including but not limited to 30:70, 40:60, 50:50 or 60:40.

[0101] As an optional example, the first organic solvent is water and an organic solvent.

[0102] In some embodiments, the temperature of the first reflux is 60-90°C, including but not limited to 65°C, 70°C, 75°C, 80°C or 85°C.

[0103] In some embodiments, the first reflux time is 4-6 hours, including but not limited to 4.5 hours, 5 hours or 6 hours.

[0104] In some embodiments, the first drying method includes but is not limited to at least one of drying (eg, drying in a forced air drying oven, etc.), vacuum drying, spray drying, etc.

[0105] S103 , performing a second thermogravimetric analysis on the negative electrode material without the aqueous dispersant to obtain a second weight loss rate D2.

[0106] In some embodiments, the test conditions of the second thermogravimetric analysis (TG test) are: inert gas atmosphere, heating rate of 1-3 k / min, and test temperature range of 25-750°C.

[0107] Exemplarily, the inert gas includes at least one of nitrogen (N2), helium or argon, and nitrogen can be selected.

[0108] For example, in the second thermogravimetric analysis, the heating rate includes but is not limited to 1 k / min, 2 k / min, or 3 k / min.

[0109] In the embodiments of the present application, the second weight loss rate is also the weight loss rate of the negative electrode material without the aqueous dispersant.

[0110] S104. Perform a third thermogravimetric analysis and a fourth thermogravimetric analysis on the standard substances of the aqueous binder and the aqueous dispersant within the first temperature range, respectively, to obtain a third weight loss rate and a fourth weight loss rate; within the first temperature range, the graphite does not undergo thermal weight loss, and the weight loss of the carbon-based conductive agent is negligible.

[0111] In the embodiments of the present application, the third weight loss rate is also the weight loss rate of the water-based binder standard substance, and the fourth weight loss rate is also the weight loss rate of the water-based dispersant standard substance.

[0112] In some embodiments, the first temperature range is 25-750°C.

[0113] In some embodiments, the third thermogravimetric analysis (TG test) and the fourth thermogravimetric analysis (TG test) are both performed in an inert gas atmosphere.

[0114] Exemplarily, the inert gas includes at least one of nitrogen (N2), helium or argon, and nitrogen can be selected.

[0115] In some embodiments, the heating rates of the third thermogravimetric analysis and the fourth thermogravimetric analysis are both 1-3 k / min, including but not limited to 1 k / min, 2 k / min, or 3 k / min.

[0116] It should be noted that, in the embodiments of the present application, the TG test shows that graphite has no weight loss at 25-750°C under an inert atmosphere, and carbon-based conductive agents such as SP lose less than 0.4% of their weight at 25-750°C under an inert atmosphere. It is well known in the art that in the formulation of negative electrode materials with graphite as the negative electrode active material, the proportion of carbon-based conductive agents such as SP is generally less than 3wt%, and the weight loss of carbon-based conductive agents such as SP in the entire negative electrode material is less than 0.02%, which is negligible; the first solvent only dissolves aqueous dispersants such as CMC, and does not dissolve aqueous binders such as SBR, and therefore has no effect on the SBR content.

[0117] S105. Calculate the mass content of the aqueous binder in the negative electrode material according to formula (1), and calculate the mass content of the aqueous dispersant in the negative electrode material according to formula (2):

[0118] C1=D2 / D1*100% Formula (1)

[0119] C2=(D4-D2) / D3*100% Formula (2)

[0120] Among them, D1 is the third weight loss rate, D2 is the second weight loss rate, D3 is the fourth weight loss rate, D4 ​​is the first weight loss rate, C1 is the mass content of the aqueous binder in the negative electrode material, and C2 is the mass content of the aqueous dispersant in the negative electrode material.

[0121] It can be understood that step S105 can also be expressed as: the product of the ratio of the second weight loss rate to the third weight loss rate and 100% is used as the mass content of the aqueous binder in the negative electrode material, and the product of the ratio of the difference between the first weight loss rate and the second weight loss rate and the fourth weight loss rate and 100% is used as the mass content of the aqueous dispersant in the negative electrode material.

[0122] In some embodiments, the method for analyzing and detecting the content of the negative electrode material formula further includes:

[0123] The mass content of the carbon material in the negative electrode material is calculated according to the following formula (3):

[0124] C3=(1-C1-C2)*100% Formula (3)

[0125] Wherein, C3 is the mass content of the carbon material in the negative electrode material.

[0126] In some embodiments, the method for analyzing and detecting the content of the negative electrode material formula further includes a step of first grinding the negative electrode material before performing the first thermogravimetric analysis and the step of removing the aqueous dispersant.

[0127] In some embodiments, the method for analyzing and detecting the content of the negative electrode material formula further includes a step of performing a second grinding on the negative electrode material without the aqueous dispersant before performing the second thermogravimetric analysis.

[0128] The analytical detection method for the negative electrode material formula content of the embodiment of the present application, by excluding the influence of carbon material weight loss, first performs a TG test on the entire negative electrode material of the graphite negative electrode, and then removes the aqueous dispersant and performs a TG test again. Combining the weight loss rate of each TG test and the weight loss rate obtained by the TG test of the aqueous binder and aqueous dispersant standard substance, the content of the aqueous binder and aqueous dispersant in the negative electrode material can be accurately calculated. This method can verify the removal effect of the aqueous dispersant through the TG curve, and the analytical detection results of the aqueous binder and aqueous dispersant content are highly reliable and accurate.

[0129] The analysis and detection method for the negative electrode material formula content of the embodiment of the present application can be widely used in the field of secondary batteries.

[0130] Certain features of the present technology are further illustrated in the following non-limiting examples.

[0131] In the following embodiments, the mass content of the aqueous binder in the negative electrode material is recorded as C1, the mass content of the aqueous dispersant in the negative electrode material is recorded as C2, and the mass content of the carbon material (artificial graphite and carbon-based conductive agent) in the negative electrode material is recorded as C3; the weight loss rate of solid 1 (i.e., the negative electrode material), i.e., the first weight loss rate, is recorded as D4; the weight loss rate of solid 2 (i.e., the negative electrode material not containing the aqueous dispersant or the negative electrode material from which the aqueous dispersant is removed), i.e., the second weight loss rate, is recorded as D2; the weight loss rate of the aqueous binder standard substance, i.e., the third weight loss rate, is recorded as D1; ​​the weight loss rate of the aqueous dispersant standard substance, i.e., the fourth weight loss rate, is recorded as D3.

[0132] The mass content of the aqueous binder C1, the mass content of the aqueous dispersant C2, and the mass content of the carbon material (artificial graphite and carbon-based conductive agent) C3 in the negative electrode material are calculated according to formula (1), formula (2), and formula (3), respectively:

[0133] C1=D2 / D1*100% Formula (1)

[0134] C2=(D4-C1*D1) / D3*100%=(D4-D2) / D3*100% Formula (2)

[0135] C3=(1-C1-C2)*100% Formula (3)

[0136] Example 1

[0137] It is known that the formula of a lithium ion battery negative electrode material using graphite as the negative electrode active material is: artificial graphite: aqueous dispersant CMC: aqueous binder SBR: carbon-based conductive agent SP = 95.6wt%: 1.4wt%: 2wt%: 1wt%.

[0138] The inventors, knowing the material composition of the negative electrode material but not knowing the specific content of each material component, used the analysis and detection method of the negative electrode material formula content of this embodiment to analyze and detect the mass content of the aqueous binder SBR, aqueous dispersant CMC and carbon material (artificial graphite and carbon-based conductive agent SP) in the negative electrode material. The specific analysis and detection method includes the following steps:

[0139] S1. Take the lithium-ion battery to be tested that uses graphite as the negative electrode active material and discharge it at 0.02C to a cut-off voltage of 2.0V. Disassemble the battery in an environment with a humidity of less than 10% (for example, a humidity of 5%) to obtain 30g of the negative electrode sheet; completely immerse the obtained negative electrode sheet in dimethyl carbonate (DMC), let it stand for 3 hours, and then use ultrasonic cleaning for 3 minutes; after ultrasonic cleaning, immediately remove the negative electrode sheet from the DMC and rinse the front and back of the negative electrode sheet with a spray bottle filled with DMC; place the rinsed negative electrode sheet in a blast drying oven to dry.

[0140] S2. Take the baked negative electrode sheet and place it flat on a glass plate. Use a ceramic knife to scrape 5 g of negative electrode material layer powder. Put the scraped negative electrode material layer powder into a conical flask. Add 100 mL of anhydrous ethanol to a clean conical flask. Place the conical flask on a heating table, connect the reflux tube and condensed water, and reflux at 80°C for 5 hours.

[0141] S3, use filtration to separate the mixed solution in the conical flask that has completed the reflux in step S2, put the solid 1 (i.e., the negative electrode material) obtained by centrifugation into a surface dish with a cover, and place it in a blast drying oven to dry; take the dried solid 1 and put it into an agate mortar to grind it into powder, and take 10 mg of the ground solid 1 powder for TG testing. The TG test conditions are: N2 atmosphere, heating rate 2k / min, and test temperature range 25-750℃. The weight loss curve of solid 1 (i.e., negative electrode material) obtained by TG test is as follows Figure 2As shown, the weight loss rate of solid 1 (ie, negative electrode material) is obtained according to the weight loss curve, that is, the first weight loss rate, recorded as D4, and the value is shown in Table 1.

[0142] S4. Take about 3 g of the ground solid 1 and add it to a clean conical flask. Add 150 mL of a mixed solvent of pure water and ethanol (the mass ratio of pure water to ethanol is 50:50) to the conical flask. Place the conical flask on a heating table, connect the reflux tube and condensed water, and reflux at 80°C for 5 hours.

[0143] S5, use filtration to separate the mixed solution in the conical flask that has completed the reflux in step S4, put the filtered solid 2 (that is, the negative electrode material without CMC or the negative electrode material with CMC removed) into a surface dish with a cover, and place it in a blast drying oven to dry; take the dried solid 2 and put it into an agate mortar to grind it into powder, and take 10 mg of the ground solid 2 powder for TG testing. The TG test conditions are: N2 atmosphere, heating rate 2k / min, test temperature range 25-750℃. The TG test obtains the weight loss curve of solid 2 (that is, the negative electrode material without CMC or the negative electrode material with CMC removed) Figure 3 As shown, the weight loss rate of solid 2 (that is, the negative electrode material without CMC or the negative electrode material with CMC removed) is obtained according to the weight loss curve, that is, the second weight loss rate, recorded as D2, and the value is shown in Table 1.

[0144] S6, take 10 mg of each standard substance of pure SBR emulsion, pure CMC powder, artificial graphite, and SP respectively, and perform TG test. The TG test conditions are: N2 atmosphere, heating rate 2k / min, test temperature range 25-750℃, and obtain their respective weight loss curves, such as Figure 4 and Figure 5 As shown. Figure 5 The weight loss rates of the SBR and CMC standard substances were obtained from the weight loss curves. The weight loss rate of the SBR standard substance, also known as the third weight loss rate, is recorded as D1, and the weight loss rate of the CMC standard substance, also known as the fourth weight loss rate, is recorded as D3. The weight loss rates of the artificial graphite standard substance, the SP standard substance, the SBR standard substance, and the CMC standard substance are shown in Table 1.

[0145] S7, through TG testing, it can be found that artificial graphite has no weight loss at 25-750℃ under N2 atmosphere, and the carbon-based conductive agent SP loses less than 0.4% of its weight at 25-750℃ under N2 atmosphere. In the negative electrode material formula, the proportion of SP is generally less than 3wt%, and the weight loss of SP in the negative electrode material is less than 0.02%, which can be ignored. Based on the weight loss ratio of SBR standard substance and solid 2 at 25-750℃, the mass content of the water-based binder SBR in the negative electrode material formula is calculated according to formula (1). Based on the weight loss ratio of CMC standard substance, SBR standard substance and solid 1 at 25-750℃, the mass content of the water-based dispersant CMC in the negative electrode material formula is calculated according to formula (2). Then, the mass content of the carbon material (main material artificial graphite and carbon-based conductive agent SP) is calculated according to formula (3).

[0146] Table 1

[0147]

[0148] The mass content of aqueous binder SBR in the negative electrode material formula = (1.79% / 92.95%)*100% = 1.93%

[0149] The mass content of aqueous dispersant CMC in the negative electrode material formula = [(2.51%-1.93%*92.95%) / 52.76%]*100% = [(2.51%-1.79%) / 52.76%]*100% = 1.36%

[0150] The carbon material (artificial graphite + carbon-based conductive agent SP) in the negative electrode material formula = (1-1.93%-1.36%) * 100% = 96.71%.

[0151] Example 2

[0152] This embodiment is basically the same as embodiment 1, except that:

[0153] In step S4, the mixture was refluxed at 60° C. for 6 h.

[0154] In step S5, the TG test shows that the weight loss rate D2 of the solid 2 (ie, the negative electrode material without CMC or the negative electrode material with CMC removed) is 1.82%.

[0155] In step S7:

[0156] The mass content of aqueous binder SBR in the negative electrode material formula = (1.82% / 92.95%)*100% = 1.95%

[0157] The mass content of aqueous dispersant CMC in the negative electrode material formula = [(2.51%-1.95%*92.95%) / 52.76%]*100% = [(2.51%-1.82%) / 52.76%]*100% = 1.31%

[0158] The carbon material (artificial graphite + carbon-based conductive agent SP) in the negative electrode material formula = (1-1.95%-1.31%) * 100% = 96.74%.

[0159] Example 3

[0160] This embodiment is basically the same as embodiment 1, except that:

[0161] In step S4, the mixture was refluxed at 90° C. for 4 h.

[0162] In step S5, the TG test shows that the weight loss rate D2 of the solid 2 (ie, the negative electrode material without CMC or the negative electrode material with CMC removed) is 1.75%.

[0163] In step S7:

[0164] The mass content of aqueous binder SBR in the negative electrode material formula = (1.75% / 92.95%)*100% = 1.88%

[0165] The mass content of aqueous dispersant CMC in the negative electrode material formula = [(2.51%-1.88%*92.95%) / 52.76%]*100% = [(2.51%-1.75%) / 52.76%]*100% = 1.44%

[0166] The carbon material (artificial graphite + carbon-based conductive agent SP) in the negative electrode material formula = (1-1.88%-1.44%) * 100% = 96.68%.

[0167] Example 4

[0168] This embodiment is basically the same as embodiment 1, except that:

[0169] In step S4, 150 mL of a mixed solvent of pure water and ethylene glycol (the mass ratio of pure water to ethylene glycol is 70:30) is added to a conical flask.

[0170] In step S5, the TG test shows that the weight loss rate D2 of the solid 2 (ie, the negative electrode material without CMC or the negative electrode material with CMC removed) is 1.85%.

[0171] In step S7:

[0172] The mass content of aqueous binder SBR in the negative electrode material formula = (1.85% / 92.95%)*100% = 1.99%

[0173] The mass content of aqueous dispersant CMC in the negative electrode material formula = [(2.51%-1.99%*92.95%) / 52.76%]*100% = [(2.51%-1.85%) / 52.76%]*100% = 1.25%

[0174] The carbon material (artificial graphite + carbon-based conductive agent SP) in the negative electrode material formula = (1-1.99%-1.25%) * 100% = 96.76%.

[0175] Example 5

[0176] This embodiment is basically the same as embodiment 1, except that:

[0177] In step S2, 100 mL of ethyl methyl carbonate (EMC) was added to a clean conical flask.

[0178] In step S3, the TG test shows that the weight loss rate D4 of the solid 1 (ie, the negative electrode material) is 2.58%.

[0179] In step S5 , the TG test shows that the weight loss rate D2 of the solid 2 (ie, the negative electrode material without CMC or the negative electrode material with CMC removed) is 1.89%.

[0180] In step S7:

[0181] The mass content of aqueous binder SBR in the negative electrode material formula = (1.89% / 92.95%)*100% = 2.03%

[0182] The mass content of aqueous dispersant CMC in the negative electrode material formula = [(2.58%-2.03%*92.95%) / 52.76%]*100% = [(2.58%-1.89%) / 52.76%]*100% = 1.31%

[0183] The carbon material (artificial graphite + carbon-based conductive agent SP) in the negative electrode material formula = (1-2.03%-1.31%) * 100% = 96.66%.

[0184] Example 6

[0185] This embodiment is basically the same as embodiment 1, except that:

[0186] The known formula of a certain negative electrode material is: artificial graphite: aqueous dispersant CMC: aqueous binder SBR: carbon-based conductive agent SP = 95.6wt%: 1.4wt%: 2wt%: 1wt%.

[0187] The inventors, knowing the material composition of the negative electrode material but not knowing the specific content of each material component, used the analysis and detection method of the negative electrode material formula content of this embodiment to analyze and detect the mass content of the aqueous binder SBR, aqueous dispersant CMC and carbon material (artificial graphite and carbon-based conductive agent SP) in the negative electrode material. In the specific test analysis method:

[0188] Excluding step S1 and step S2;

[0189] Step S3 involves grinding the known negative electrode material (Solid 1) into a powder in an agate mortar. TG testing is then performed on 10 mg of the ground Solid 1 powder. The TG testing conditions are: N2 atmosphere, a heating rate of 2 kJ / min, and a test temperature range of 25-750°C. The TG testing results in a weight loss rate D4 of 2.55% for Solid 1 (i.e., the negative electrode material).

[0190] In step S5, the TG test shows that the weight loss rate D2 of the solid 2 (ie, the negative electrode material without CMC or the negative electrode material with CMC removed) is 1.85%.

[0191] In step S7:

[0192] The mass content of aqueous binder SBR in the negative electrode material formula = (1.85% / 92.95%)*100% = 1.90%

[0193] The mass content of aqueous dispersant CMC in the negative electrode material formula = [(2.55%-1.90%*92.95%) / 52.76%]*100% = [(2.55%-1.85%) / 52.76%]*100% = 1.33%

[0194] Carbon material in the negative electrode material formula (artificial graphite + carbon-based conductive agent SP) = (1-1.90%-1.33%) * 100% = 96.77% In this application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0195] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0196] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for analyzing and detecting the content of a negative electrode material formula, characterized in that: The negative electrode material is composed of a carbon material, an aqueous binder and an aqueous dispersant, wherein the carbon material is composed of graphite and a carbon-based conductive agent; the analysis and detection method includes: Taking a portion of the negative electrode material for a first thermogravimetric analysis to obtain a first weight loss rate; removing the aqueous dispersant from the remaining negative electrode material to obtain a negative electrode material free of the aqueous dispersant; performing a second thermogravimetric analysis on the negative electrode material without the aqueous dispersant to obtain a second weight loss rate; performing a third thermogravimetric analysis and a fourth thermogravimetric analysis on respective standard substances of the aqueous binder and the aqueous dispersant within a first temperature range, respectively, to obtain a third weight loss rate and a fourth weight loss rate; within the first temperature range, the graphite does not undergo thermal weight loss, and the weight loss of the carbon-based conductive agent is negligible; The mass content of the aqueous binder in the negative electrode material is calculated according to formula (1), and the mass content of the aqueous dispersant in the negative electrode material is calculated according to formula (2): C1=D2 / D1*100% Formula (1) C2=(D4-D2) / D3 *100% Formula (2) Wherein, D1 is the third weight loss rate, D2 is the second weight loss rate, D3 is the fourth weight loss rate, D4 ​​is the first weight loss rate, C1 is the mass content of the aqueous binder in the negative electrode material, and C2 is the mass content of the aqueous dispersant in the negative electrode material; The conditions of the first thermogravimetric analysis and the second thermogravimetric analysis both include: an inert gas atmosphere and a test temperature range of 25-750°C.

2. The analysis and detection method according to claim 1, characterized in that The method for analyzing and detecting the content of the negative electrode material formula also includes: The mass content of the carbon material in the negative electrode material is calculated according to the following formula: C3=(1-C1-C2)*100% Wherein, C3 is the mass content of the carbon material in the negative electrode material.

3. The analysis and detection method according to claim 1, characterized in that The first temperature range is 25-750° C.; and / or, The third thermogravimetric analysis and the fourth thermogravimetric analysis are both performed in an inert gas atmosphere; and / or, The heating rates of the third thermogravimetric analysis and the fourth thermogravimetric analysis are both 1-3 k / min; and / or, In the first thermogravimetric analysis and the second thermogravimetric analysis, the heating rate is 1-3 k / min.

4. The analysis and detection method according to claim 1, characterized in that: Removing the aqueous dispersant from the remaining negative electrode material to obtain a negative electrode material free of the aqueous dispersant, comprising: The remaining negative electrode material is subjected to a first reflux in a first solvent, followed by a first filtration and a first drying to obtain the negative electrode material free of the aqueous dispersant.

5. The analysis and detection method according to claim 4, characterized in that: The first solvent includes water and an organic solvent, and the organic solvent includes at least one of methanol, ethanol, ethylene glycol, and propanol; and / or, The temperature of the first reflux is 60-90° C.; and / or, The first reflux time is 4-6 hours.

6. The analysis and detection method according to claim 1, characterized in that: The method for analyzing and detecting the content of the negative electrode material formula further includes the step of first grinding the negative electrode material before performing the first thermogravimetric analysis and the step of removing the aqueous dispersant; and / or, The method for analyzing and detecting the content of the negative electrode material formula further includes a step of performing a second grinding on the negative electrode material without the aqueous dispersant before performing the second thermogravimetric analysis; and / or, The negative electrode material is a fresh negative electrode material mixed with a carbon material, an aqueous binder and an aqueous dispersant, or a negative electrode material obtained from a negative electrode sheet of a lithium-ion battery to be tested.

7. The analysis and detection method according to claim 6, characterized in that: When the negative electrode material is obtained from a negative electrode sheet of a lithium-ion battery to be tested, the method for analyzing and detecting the formula content of the negative electrode material further includes: Washing the negative electrode sheet, performing a second drying, and then scraping the negative electrode material layer of the negative electrode sheet, followed by a second reflow, a second filtration, and a third drying in a second solvent to obtain the negative electrode material; and / or, When the negative electrode material is obtained from a negative electrode sheet of a lithium-ion battery to be tested, the method for analyzing and detecting the formula content of the negative electrode material further includes: The lithium-ion battery to be tested is discharged to a cut-off voltage, and then disassembled in an environment with a humidity of less than 10% to obtain the negative electrode sheet.

8. The analysis and detection method according to claim 7, characterized in that: The washing solvent and the second solvent both include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methanol, ethanol, ethylene glycol, and propanol; and / or, The temperature of the second reflux is 60-90° C.; and / or, The second reflux time is 4-6 hours; and / or, The discharge current of the lithium-ion battery to be tested is 0.01-0.05C.

9. The analysis and detection method according to any one of claims 1 to 8, characterized in that: The graphite includes at least one of artificial graphite, natural graphite, and mesocarbon microbeads; and / or, The carbon-based conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, porous carbon, graphene, multi-walled carbon nanotubes, and single-walled carbon nanotubes; and / or, The water-based binder includes at least one of styrene butadiene and modified organic emulsions thereof, styrene acrylate and modified organic emulsions thereof, polyethylene emulsion, and polypropylene emulsion; and / or, The aqueous dispersant includes at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium carboxyethyl cellulose, and lithium carboxyethyl cellulose.

10. Application of the method for analyzing and detecting the content of negative electrode material formula according to any one of claims 1 to 9 in the field of secondary batteries.

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