A method for determining the content of carboxymethyl cellulose in a lithium-ion battery negative electrode slurry

Abstract

This invention belongs to the field of lithium-ion battery technology, and particularly relates to a method for determining the carboxymethyl cellulose (CMC) content in a negative electrode slurry for lithium-ion batteries. The method includes the following steps: S1. Mixing a carboxymethyl cellulose (CMC) solution with a negative electrode active material at a certain mass ratio to obtain a mixture; S2. Performing an adsorption test on the mixture by shaking, and centrifuging to separate the supernatant; S3. Testing to determine the CMC concentration in the supernatant and calculating the adsorption amount of CMC by the negative electrode active material. q S4. Plot the isothermal adsorption curve. Use the Langmuir adsorption isotherm model for fitting to obtain the maximum adsorption capacity. q max S5. Based on the maximum adsorption capacity q max The optimal CMC addition mass ratio was then obtained by combining the isothermal adsorption curves. w opt This application can quickly and accurately determine the CMC content in the negative electrode slurry. While ensuring the stability of the slurry and the mechanical properties of the electrode, it minimizes the amount of CMC used in the negative electrode formulation, thereby reducing the surface resistivity of the electrode and the internal resistance of the whole cell, and improving the energy density, rate performance, low-temperature performance and cycle life of the whole cell.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry. Background Technology

[0002] Carboxymethyl cellulose (CMC) is a carboxymethylated derivative of cellulose. This chain-like ionic polymer is easily dispersed in water to form a transparent, viscous gel, and is widely used as a dispersant and binder in lithium-ion battery anode slurries. In the slurry, carboxymethyl cellulose (CMC) can improve the dispersibility of the anode active material, prevent particle agglomeration and sedimentation, and ensure the stability and uniformity of the slurry.

[0003] However, as a polymeric insulator, excessive addition of CMC significantly increases electrode impedance and overall cell internal resistance, leading to poor rate performance, low-temperature performance, and increased polarization during cycling. CMC is an inactive material; excessive addition reduces the proportion of active material in the negative electrode, lowering the battery's energy density. Excessive CMC addition can also cause abnormal slurry viscosity (too high or high thixotropy), affecting leveling and coating quality. Insufficient CMC, on the other hand, results in poor slurry dispersion, easy sedimentation, insufficient electrode adhesion, and easy powder shedding and demolding during cycling, accelerating battery cycle life degradation.

[0004] Currently, the industry relies heavily on experience to determine the CMC addition ratio in negative electrode slurries, typically controlling it between 0.5% and 5.0% or employing a trial-and-error method, such as gradient experiments. Another approach involves selecting CMCs with specific degrees of substitution or molecular weights; for example, Chinese invention patent CN101877393B discloses the use of sodium carboxymethyl cellulose with a weight-average molecular weight of 10 × 10⁻⁶. 5 ~12×10 5 When the degree of substitution is 0.65 to 0.9 and its mass percentage in the negative electrode material is 0.5 to 0.7 wt%, the dispersion of the negative electrode slurry is better, the uniformity of the prepared negative electrode sheet is better, thereby improving the low-temperature discharge performance of the battery.

[0005] The above methods still lack systematic and scientific theoretical guidance, and often involve excessive addition to ensure the stability of the slurry during coating. Therefore, there is an urgent need for a method to more accurately determine the minimum sufficient amount of CMC, maximizing the performance of the entire cell while ensuring electrode processing and full cell cycling. Summary of the Invention

[0006] In view of this, this application provides a method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry to overcome the deficiencies of the prior art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry includes the following steps: S1. Mix the carboxymethyl cellulose (CMC) solution with the negative electrode active material at a set mass ratio to obtain a mixture with different initial CMC concentrations; S2. The mixture obtained in step S1 is subjected to an adsorption test with shaking at a constant temperature. After reaching adsorption equilibrium, the supernatant is separated by centrifugation. S3. Determine the CMC concentration in the supernatant from step S2 to obtain the CMC equilibrium concentration. Based on the initial and equilibrium CMC concentrations, and after correction with a blank solution, calculate the adsorption capacity of the negative electrode active material for CMC. q Plotting with initial CMC concentration w The x-axis represents the adsorption amount. q The isothermal adsorption curve is represented by the vertical axis.

[0008] It should be noted that the blank solution is a suspension of negative electrode active material, without the addition of CMC.

[0009] S4. The Langmuir adsorption isotherm model was used to fit the data to obtain the fitting equation, and the theoretical maximum adsorption capacity q of the negative electrode active material for CMC was calculated. max .

[0010] S5. Based on the maximum adsorption amount q obtained in step S4 max The initial concentration w corresponds to the isothermal adsorption curve. max The optimal CMC addition ratio was obtained. w opt .

[0011] Preferably, in step S5, the optimal CMC addition mass ratio w opt The calculation formula is: w opt = C w max , In the formula: C is a constant.

[0012] Preferably, the constant C has a value range of 70%-95%, and more preferably 80%-90%.

[0013] Preferably, the fitting equation in step S4 is: c / q =a+b c In the formula: c The concentration of carboxymethyl cellulose (CMC) solution. qdenoted as the adsorption amount of CMC by the negative electrode active material, and a and b are fitting coefficients.

[0014] The Langmuir model calculation formula is as follows: In the formula: c The concentration of carboxymethyl cellulose (CMC) in aqueous solution is... q This represents the adsorption capacity of the negative electrode active material for CMC. q max This represents the theoretical maximum adsorption capacity of the negative electrode active material for CMC. K is the adsorption equilibrium constant.

[0015] Preferably, in step S3, the total organic carbon (TOC) concentration in the upper clear layer is determined using a total organic carbon (TOC) test; adsorption capacity... q The calculation formula is: q =( w e - w 空 ) (CMC molar mass / total molar mass of carbon atoms in CMC) v / M In the formula: w e This refers to the CMC equilibrium concentration, expressed in mg / mL. w 空 The TOC concentration is the blank solution, i.e., the suspension of negative electrode active material without CMC addition, in mg / mL. v The volume of the mixed solution is in mL; M represents the mass of the negative electrode active material in g. q The unit is mg / g.

[0016] Preferably, in step S1, the carboxymethyl cellulose (CMC) solution is added to the negative electrode active material in three separate additions for mixing, and the mass ratio of the three additions of CMC solution is (20%-40%):(20%-40%):(20%-60%), preferably 30%:30%:40%.

[0017] Preferably, in step S1, the mass ratio of carboxymethyl cellulose (CMC) solution to negative electrode active material is 0.2%-5.0%, more preferably 0.2%-3.0%, where 0.2% and 0.5% are mandatory points, and at least 4 points can be taken at fixed percentage intervals within the 0.5%-3.0% range, preferably 6-8 points.

[0018] Preferably, the time for the oscillation adsorption test to reach adsorption equilibrium in step S2 is at least 12 hours, and more preferably 18-36 hours.

[0019] Preferably, the negative electrode active material is at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, and silicon-carbon composite materials.

[0020] Preferably, the carboxymethyl cellulose (CMC) is at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; the concentration of the carboxymethyl cellulose (CMC) solution is in the range of 0.8-3.0%.

[0021] Compared with the prior art, the beneficial effects of the present invention are: This invention establishes a system with an initial CMC concentration. w The x-axis represents the adsorption amount. q The isothermal adsorption curve, with the ordinate as the vertical axis, was determined by fitting the Langmuir adsorption isotherm model. q max and with maximum adsorption capacity q max The initial concentration corresponding to the isothermal adsorption curve is denoted as . w max Set the optimal amount of CMC to add. w max The content ranges from 70% to 95%. On the one hand, this ensures that key active sites on the surface of the negative electrode active material particles are fully coated, meeting the basic requirements for slurry dispersion and stability. On the other hand, it minimizes or even eliminates the formation of free CMC, thereby fundamentally reducing electrode resistance and battery internal resistance, creating conditions for improving battery energy density, rate performance, low-temperature performance, and cycle life. Simultaneously, this ratio represents an optimal balance between ensuring battery performance and minimizing the amount used. Attached Figure Description

[0022] Figure 1 The isothermal adsorption curve of Example 1 of this application; Figure 2 This is the fitting result of the Langmuir isothermal adsorption model in Example 1 of this application; Figure 3 The isothermal adsorption curve of Comparative Example 3 of this application; Figure 4 The fitting results of the Langmuir isothermal adsorption model for Comparative Example 3 of this application; Figure 5 Cyclic capacity decay curves for Example 1 and Comparative Examples 1-3 of this application are shown. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and preferred embodiments.

[0024] Figure 1 In Example 1, the CMC-Na solution was added to the artificial graphite in three separate steps to obtain different initial CMC-Na concentrations. w The x-axis represents the adsorption amount. q The isothermal adsorption curve is represented by the vertical axis.

[0025] Figure 2 The isothermal adsorption curves for Example 1 are the results of fitting using the Langmuir adsorption isotherm model.

[0026] Figure 3 In Comparative Example 3, CMC-Na solution was added to artificial graphite in one step to obtain different initial CMC-Na concentrations. w The x-axis represents the adsorption amount. q The isothermal adsorption curve is represented by the vertical axis.

[0027] Figure 4 The isothermal adsorption curves for Comparative Example 3 are fitted using the Langmuir adsorption isotherm model.

[0028] Figure 5 Capacity decay curves for 800 cycles of implementation 1 and comparative examples 1-3.

[0029] Example 1: A method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry specifically includes the following steps: (1) Material preparation The negative electrode active material used in this embodiment is artificial graphite, wherein: BET=1.5m 2 / g, D50=19.5um, Carboxymethyl cellulose (CMC) is sodium carboxymethyl cellulose (CMC-Na), with a molecular weight (MW) of 400K, a degree of substitution (DS) of 0.65-0.75, and a concentration of 1.2% for the CMC-Na solution.

[0030] (2) Preparation of the mixture The mass ratios of CMC-Na to the negative electrode active material were set to 0.2%, 0.5%, 0.8%, 1.1%, 1.4%, 1.7%, 2.0%, 2.3%, and 2.6%. For each mixture, the CMC-Na solution was added to the artificial graphite in three portions, with each addition comprising 30%:30%:40% of the total CMC-Na mass. After each addition, the mixture was stirred at 2000 rpm for 3 minutes in a centrifugal mixer to ensure thorough mixing, thus obtaining different initial CMC-Na concentrations. w ; (3) Oscillating Adsorption Test Transfer each mixture from step (2) to a centrifuge tube and place it in a 25°C constant temperature water bath shaker. Shake at 150 rpm for 24 hours to ensure adsorption equilibrium is reached. (4) Concentration test After the adsorption process was completed by shaking, the sample was centrifuged at 25,000 rpm for 30 minutes, and the supernatant was collected. The concentration of CMC-Na in the supernatant was determined using a total organic carbon (TOC) analyzer and recorded as the CMC-Na equilibrium concentration. w e .

[0031] (5) Data calculation and fitting Based on CMC-Na equilibrium concentration w e Corrected with blank solution, adsorption capacity calculated. q =( w e - w 空 ) (CMC molar mass / total molar mass of carbon atoms in CMC) v / M In the formula: w e This refers to the CMC equilibrium concentration, expressed in mg / mL. w 空 The TOC concentration is the blank solution, i.e., the artificial graphite suspension without CMC, in mg / mL. v The volume of the mixed solution is in mL; M represents the mass of the negative electrode active material in g. q The unit is mg / g.

[0032] At initial concentration w The x-axis represents the adsorption amount. q Plot the isothermal adsorption curve with the vertical axis as the ordinate, as follows: Figure 1 As shown.

[0033] The Langmuir adsorption isotherm model was used for fitting, such as... Figure 2 As shown, the fitting equation is obtained: c / q = 0.0042 + 0.1786 c (R) 2 = 0.9996).

[0034] Calculation formula based on Langmuir model: In the formula: c The concentration of carboxymethyl cellulose (CMC) in aqueous solution is... q This represents the adsorption capacity of the negative electrode active material for CMC.q max This represents the theoretical maximum adsorption capacity of the negative electrode active material for CMC. K is the adsorption equilibrium constant.

[0035] Calculations yielded the theoretical maximum adsorption capacity. q max = 1 / 0.1786 ≈ 5.60 mg / g.

[0036] (6) Determine the optimal addition ratio of CMC-Na Find it in the isothermal adsorption curve q max =5.60 mg / g, corresponding to a CMC-Na concentration mass ratio w max =1.2%.

[0037] Taking a constant C = 80%, calculate the optimal CMC addition mass ratio. w opt = C w max = 80% 1.2% = 0.96%.

[0038] (7) Validity verification Slurry stability assessment: Using the optimal mass ratio of CMC-Na to graphite obtained by the above method, a slurry was prepared according to the formula graphite:CMC-Na:SBR= 97.56:0.94:1.50 (where graphite:CMC-Na = 99.04:0.96). The stability of the slurry was assessed by static settling test, and the test results are shown in Table 1.

[0039] Negative electrode performance evaluation: The above slurry was coated, rolled and sheared to prepare the negative electrode. The electrode resistance was tested by the four-probe method and the electrode adhesion was evaluated by the 180° peel strength test. The test results are shown in Table 1.

[0040] Full cell performance evaluation: The above-mentioned negative electrode, positive electrode, and separator are assembled into an electrode assembly by winding or stacking. The electrode assembly is then encapsulated with aluminum-plastic composite and subjected to processes such as drying, liquid injection, formation, degassing, hot pressing, and capacity testing to obtain a full cell.

[0041] Full battery performance testing methods: (1) Volumetric energy density test At 25±2℃, the battery was charged to 4.5V at 0.5C, then charged to 0.05C at a constant voltage. The thickness was measured using a platen thickness gauge (PPG), and the length and width were measured using an optical imaging meter (OMM) to obtain the volume (V). The battery was then discharged to 3V at 0.2C, and the discharge capacity (C) and discharge plateau voltage (U) were calculated. Its volumetric energy density (VED) can be calculated using the following formula: VED = C U / V is shown in Table 2.

[0042] (2) Rate discharge performance test At 25±2℃, the battery was discharged to 3.0V at 0.2C, allowed to stand for 5 minutes, charged to 4.5V at 1C, and then charged at a constant voltage to 0.05C. After standing for 5 minutes, the discharge rate was adjusted, and discharge tests were conducted at 0.2C, 0.5C, 1C, and 2C. The discharge capacity at each rate was obtained. The capacity obtained at 0.5C, 1C, and 2C was compared with the capacity obtained at 0.2C to obtain the ratio. The rate performance of the full battery was compared by comparing the ratio. The test results are shown in Table 2.

[0043] (3) Low-temperature discharge performance test At 25±2℃, the battery was charged to 4.5V at 1C, then charged to 0.05C at a constant voltage, and stored for 1 hour. At this temperature, it was discharged to 3V at 0.2C, and the discharge capacity was recorded. After being stored at 25±2℃ for 2 hours, the battery was charged to 4.5V at 1C, then charged to 0.05C at a constant voltage. After being stored at -20±2℃ for 2 hours, it was discharged to 3V at 0.2C at this temperature, and the discharge capacity was recorded. The low-temperature discharge performance of the full battery was compared by the percentage of the low-temperature discharge capacity to the 25℃ discharge capacity. The test results are shown in Table 2.

[0044] (4) Cyclic performance test The following steps were used to perform a cycle test on the full battery and calculate the discharge capacity retention rate. At 25±2℃, the battery was charged at a constant current of 1C to 4.5V, and then held at a constant voltage of 4.5V until the current dropped to 0.05C. After resting for 10 minutes, it was discharged at a constant current of 0.5C to 3V. The capacity obtained in this step was taken as the initial capacity. Following the aforementioned steps, a cycle test of 1C charge / 0.5C discharge was performed. The ratio of the capacity at each step to the initial capacity was used to obtain the cycle capacity decay curve, as shown below. Figure 5 As shown.

[0045] Comparative Example 1 The difference from Example 1 is that the constant C = 70%. w opt = 0.84%, the negative electrode formulation is graphite:CMC-Na:SBR=97.67:0.83:1.50 (where graphite:CMC-Na = 99.16:0.84), and the remaining items are the same as in Example 1.

[0046] Comparative Example 2 The difference from Example 1 is that the constant C = 95%. w opt = 1.14%, the negative electrode formulation is graphite: CMC-Na:SBR=97.38:1.12:1.50 (where graphite: CMC-Na = 98.86:1.14), and the remaining items are the same as in Example 1.

[0047] Comparative Example 3 The difference from Example 1 is that in step (1), the CMC-Na solution was added to the artificial graphite all at once during the preparation of the mixture. The initial concentration was obtained after oscillation adsorption testing and equilibrium concentration testing after adsorption centrifugation. w Isothermal adsorption curves with adsorption capacity q, such as Figure 3 As shown.

[0048] After data fitting, the fitting equation is obtained: c / q = 0.0021 + 0.2145 c (R) 2 = 0.9987), such as Figure 4 As shown. The maximum theoretical adsorption capacity was calculated. q max = 1 / 0.21 ≈ 4.76 mg / g, corresponding to the CMC-Na concentration mass ratio w max =1.5%, take constant C = 80%, calculate the optimal mass ratio of CMC-Na in the formula. w opt =C w max =80% 1.5% = 1.2%, the negative electrode slurry formulation is graphite: CMC-Na:SBR = 97.32:1.18:1.50, of which: graphite:CMC-Na = 98.8:1.2, the rest are the same as in Example 1.

[0049] Table 1 shows the test results of slurry stability and negative electrode performance in the examples and comparative examples.

[0050] Table 2 shows the full-cell performance test results for the examples and comparative examples.

[0051] The above test results show that, comparing Example 1 and Comparative Example 1, when C is 70%, the CMC-Na ratio in the formulation is low, resulting in poor slurry stability, with sedimentation occurring after 72 hours, low viscosity, and poor electrode adhesion. Comparing Example 1 and Comparative Example 2, when C is 95%, the CMC-Na ratio in the formulation is high, resulting in good slurry stability, but the slurry viscosity is high, resulting in slightly poor flowability and a tendency for tailing during coating. The electrode resistivity increases by 5%, adhesion increases by 5%, the full cell volumetric energy density decreases by approximately 0.4%, internal resistance increases by approximately 3%, 1C and 2C rate discharge performance decreases by 1-2%, and the -20℃ low-temperature discharge performance is slightly worse than in Example 1 and Comparative Example 1. The capacity retention rate after 800 cycles is also low.

[0052] By comparing Example 1 and Comparative Example 3, it was found that adding the mixture in one step (1) easily leads to the agglomeration of the negative electrode active material particles, resulting in an unbalanced adsorption and significantly affecting the optimal mass ratio. w opt The determination of the slurry in Comparative Example 3 shows high viscosity, high sheet resistance in the electrode, and decreased volumetric energy density, increased internal resistance, and worsened rate discharge and low-temperature discharge performance in the full cell, with a worse trend in cycle capacity retention.

[0053] In summary: In Example 1 of this application, a CMC-Na solution with a concentration of 1.2% was mixed with artificial graphite as the negative electrode active material at a set mass ratio. The CMC-Na solution was added to the negative electrode active material in three separate mixing steps. This resulted in a more uniformly dispersed negative electrode slurry, reducing the likelihood of particle agglomeration and adsorption imbalance, and thus not affecting the optimal mass ratio. w opt The optimal addition ratio C of CMC-Na was determined, and the optimal addition ratio C was set to [value missing]. q max The corresponding isothermal adsorption curve w max 80%-90% is optimal.

[0054] It is important to note that, through extensive experimentation, this invention has found that not all CMCs can effectively perform their dispersing and binding functions. The key lies in the "adsorbed CMCs" adsorbed by the negative electrode active material, while "free CMCs" dissolved in water are not only useless but also increase battery internal resistance and reduce energy density. Traditional empirical formulations typically add CMCs at a level higher than their maximum adsorption capacity. q max This inevitably leads to the generation of harmful free CMC. This invention establishes a system with the initial CMC concentration as the x-axis and the adsorption capacity... qThe isothermal adsorption curves are plotted on the ordinate, and the data are fitted using the Langmuir adsorption isotherm model to determine the... q max Set the optimal addition ratio C of CMC to 1. q max The corresponding isothermal adsorption curve w max The proportion of CMC in the formula is reduced to 70%-95% while ensuring the stability of the slurry. This increases the proportion of active material, improves the energy density of the whole cell, reduces the resistivity of the electrode surface and the internal resistance of the whole cell, improves the rate discharge capability and low temperature performance of the whole cell, reduces polarization during charge and discharge, and helps to extend cycle life.

[0055] The method provided by this invention does not distinguish between the type and physical properties of the negative electrode active material, and is applicable to artificial graphite, natural graphite, and silicon-graphite composite negative electrodes, thus possessing a certain degree of versatility. Furthermore, the carboxymethyl cellulose (CMC) solution concentration range in this invention is 0.8-3.0%, which is well compatible with actual production, demonstrating good process feasibility and operability.

[0056] The above description is merely an example of the embodiments of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for determining the carboxymethyl cellulose content in a lithium-ion battery negative electrode slurry, characterized in that, Includes the following steps: S1. Mix the carboxymethyl cellulose (CMC) solution with the negative electrode active material at a set mass ratio to obtain a mixture with different initial CMC concentrations; S2. The mixture obtained in step S1 is subjected to an adsorption test under constant temperature. After the adsorption of CMC on the negative electrode active material reaches equilibrium, the supernatant is separated by centrifugation. S3. Test to determine the CMC concentration in the supernatant from step S2, and obtain the CMC equilibrium concentration. w e The adsorption capacity of the negative electrode active material for CMC was calculated using blank solution correction. q Plotting with initial CMC concentration w The x-axis represents the adsorption amount. q The isothermal adsorption curve is represented by the vertical axis. S4. The data were fitted using the Langmuir adsorption isotherm model to obtain the fitting equation. Based on the Langmuir model calculation formula, the theoretical maximum adsorption capacity of the negative electrode active material for CMC was obtained. q max ; S5. The maximum adsorption amount obtained in step S4 q max The initial concentration corresponding to the isothermal adsorption curve is denoted as . w max The optimal CMC addition ratio was obtained. w opt .

2. The method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry according to claim 1, characterized in that, In step S5, the optimal CMC addition mass ratio w opt The calculation formula is: w opt = C w max In the formula: C is a constant.

3. The method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry according to claim 2, characterized in that, The constant C has a value range of 70%-95%, preferably 80%-90%.

4. The method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry according to claim 1, characterized in that, The fitting equation in step S4 is: c / q =a+b c In the formula: c The concentration of carboxymethyl cellulose (CMC) solution. q denoted as the adsorption amount of CMC by the negative electrode active material, and a and b are fitting coefficients; The Langmuir model calculation formula is as follows: In the formula: c The concentration of carboxymethyl cellulose (CMC) in aqueous solution is... q This represents the adsorption capacity of the negative electrode active material for CMC. q max This represents the theoretical maximum adsorption capacity of the negative electrode active material for CMC. K is the adsorption equilibrium constant.

5. The method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry according to claim 1, characterized in that, In step S3, the total organic carbon (TOC) concentration in the upper clear layer is determined using a total organic carbon (TOC) test; adsorption capacity... q The calculation formula is: q =( w e - w 空 ) (CMC molar mass / total molar mass of carbon atoms in CMC) v / M In the formula: w e This refers to the CMC equilibrium concentration, expressed in mg / mL. w 空 The TOC concentration is the blank solution, i.e., the negative electrode active material suspension without CMC addition, in mg / mL. v The volume of the mixed solution is in mL; M represents the mass of the negative electrode active material in g. q The unit is mg / g.

6. The method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry according to claim 1, characterized in that, In step S1, the carboxymethyl cellulose (CMC) solution is added to the negative electrode active material in three batches for mixing. The mass ratio of the three batches of CMC solution is (20%-40%):(20%-40%):(20%-60%), preferably 30%:30%:40%.

7. The method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry according to claim 1, characterized in that, In step S1, the mass ratio of CMC to negative electrode active material is 0.2%-5.0%, preferably 0.2%-3.0%. Among them, 0.2% and 0.5% are mandatory points. Within the range of 0.5%-3.0%, at least 4 points can be taken at fixed percentage intervals, preferably 6-8 points.

8. The method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry according to claim 1, characterized in that, In step S2, the time required for the oscillation adsorption test to reach adsorption equilibrium is at least 12 hours, preferably 18-36 hours.

9. The method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry according to claim 1, characterized in that, The negative electrode active material is at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, and silicon-carbon composite materials.

10. The method for determining the carboxymethyl cellulose content in lithium-ion battery negative electrode slurry according to claim 1, characterized in that, The carboxymethyl cellulose (CMC) is at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; the concentration range of the carboxymethyl cellulose (CMC) solution is 0.8-3.0%.

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