High-flexibility water-soluble high-viscosity CMC material and application thereof

Abstract

The invention relates to the technical field of lithium ion battery binder materials, and particularly discloses a high-flexibility water-soluble high-viscosity CMC material, the chemical general formula of which is [C6H7O2 (OH) (3-x-y) (OCH2COONa) x (OSO3Na y)] n, x is equal to 0.85-0.95, y is equal to 0.18-0.22, and more than or equal to 95% in a sulfonic acid group is bonded to a C6 site of a glucose ring. The preparation method comprises the following steps: (a) dispersing sodium carboxymethyl cellulose in ethanol, and adding sulfuric acid to obtain CMC-H; (b) dispersing CMC-H in ethanol to form a CMC-H suspension, and reacting the CMC-H suspension with a CO2 saturated sodium sulfamate solution; and (c) carrying out vacuum drying treatment after washing. According to the application of the high-flexibility water-soluble high-viscosity CMC material, the high-flexibility water-soluble high-viscosity CM material is adopted as a negative electrode active substance, a conductive agent is dispersed in a solvent to form slurry, and then a lithium battery negative electrode plate is prepared through coating, drying and rolling. According to the scheme, carboxymethyl cellulose is subjected to protonation and sulfonated with sodium sulfamate under specific process conditions, so that the CMC material has high elongation at break (high flexibility) and high viscosity.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery binder materials, and in particular to a highly flexible, water-soluble, high-viscosity CMC material and its application. Background Art

[0002] Lithium battery binders are polymer compounds that adhere the active material of lithium battery electrodes to the current collector. Their core functions include: (1) providing adhesion to ensure close contact between the active material, conductive agent, and current collector; (2) maintaining the stability of the electrode structure and buffering volume changes during charge and discharge; and (3) ensuring the integrity of the ion / electron transport channel. During the electrode manufacturing process, the binder usually exists in powder form and needs to be dissolved in a dispersant (such as water or an organic solvent). It is mixed with the active material and conductive agent to form a slurry, which is then coated, dried, and rolled to form an electrode sheet.

[0003] At present, water-soluble binders are commonly used in the manufacture of negative electrode sheets. Sodium carboxymethyl cellulose (CMC) is widely used as an aqueous binder for negative electrode materials, but it has significant defects: 1. Existing CMC materials are not flexible enough to adapt to the mechanical stress of high-speed coating (coating speed ≥ 60m / min), resulting in cracks in the produced electrodes. To solve the problem of cracks during high-speed coating, manufacturers often need to add plasticizers. However, plasticizers not only increase costs, but also reduce electrode conductivity and battery cycle stability.

[0004] 2. Although the CMC materials produced by Japanese companies through the sludge method can increase the viscosity to about 9000cps, their elongation at break is around 12%. For a coating speed of 60m / min, it can significantly reduce or even avoid electrode cracks. However, with the current continuous increase in coating speed (80m / min coating), the CMC materials currently produced by Japanese companies are difficult to meet the requirements, and Japanese CMC materials are expensive.

[0005] Although the industry has tried to improve performance through composite binders (such as CMC blended with styrene-butadiene rubber SBR) or structural modifications, for example, the patent application number CN119799200A applied for in 2024 and published in 2025 is "Flame retardant binder and electrode slurry, electrode, battery and electrical device". The technology points out that sodium carboxymethyl cellulose (CMC) is used as the binder base material, and the binder CMC@CR formed by physical blending with chloroprene rubber (CR) not only has good adhesion ability, but also has a certain flame retardant effect. Although it is pointed out that it can solve the defect of single binder CMC that is prone to cracks, the physical blending method improves flame retardancy and flexibility, but the interface compatibility is poor and the risk of delamination after long-term circulation is high.

[0006] Therefore, there is an urgent need to develop a water-soluble CMC material with both high elongation at break and high viscosity, which is the key to breaking through the bottleneck of lithium battery manufacturing. Summary of the Invention

[0007] The present invention aims to provide a highly flexible, water-soluble, high-viscosity CMC material and its application, aiming to achieve both high elongation at break (high flexibility) and high viscosity by protonating carboxymethyl cellulose and then sulfonating it with sodium aminosulfonate under specific process conditions.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: A highly flexible, water-soluble, high-viscosity CMC material, the general chemical formula of which is: [C6H7O2(OH) (3-x-y) (OCH2COONa) x (OSO3Na y )] n Among them: x=0.85∼0.95, y=0.18∼0.22, and ≥95% of the sulfonic acid groups are bonded to the C6 position of the glucose ring.

[0009] A highly flexible, water-soluble, high-viscosity CMC material, the preparation method of which comprises the following steps: (a) Dispersing sodium carboxymethyl cellulose in ethanol, then adding sulfuric acid to adjust the pH of the system to 1.8-2.2, reacting at 30-45°C for 1.5-2.5 hours, and solid-liquid separation to obtain protonated CMC-H; (b) dispersing CMC-H in ethanol to form a CMC-H suspension, adding a sodium sulfamate solution pretreated with CO2 saturation, mixing the CMC-H suspension and the sodium sulfamate solution saturated with CO2 in a reactor with a centrifugal force of ≥800G and a liquid film thickness of ≤20μm, and reacting at 50-60°C; (c) washing the product obtained in step (b) and then vacuum drying it.

[0010] Preferably, as an improvement, the reaction temperature of step (a) is 35-50°C.

[0011] Preferably, as an improvement, the pH of the sodium sulfamate solution is ≤5.5 after being saturated with CO2.

[0012] Preferably, as an improvement, the sodium sulfamate solution, pretreated with CO₂ saturation, is added dropwise or by spraying. In a centrifugal reactor, the reaction materials have a large contact area but a very short residence time. This dropwise or spraying method can instantly disperse the highly active reagent into extremely small droplets or mist, allowing it to quickly and evenly contact the CMC-H suspension. This effectively avoids problems such as transient exothermic heat, side reactions, or material agglomeration caused by localized excessive concentration, ensuring a more uniform sulfonation reaction at the molecular level, improving substitution uniformity and product performance consistency.

[0013] Preferably, as an improvement, the sodium sulfamate solution in step (b) is added dropwise using a gradient: in the early stage 0-30min, the drop rate is 0.3-0.5L / min; in the middle stage 30-90min, the drop rate is 0.8-1.0L / min; in the later stage>90min, it is added dropwise at 0.2-0.4L / min until the sulfonation transposition is completely completed. After the sodium sulfamate solution is added, the reaction of step (b) is to first form a salt and release heat before sulfonation transposition. The gradient addition strategy effectively solves the core problem of the intense heat release in the early stage of the reaction by accurately regulating the addition rate of activated sodium sulfamate at different stages of the sulfonation reaction. The early slow dropwise addition strictly limits the heat release rate to prevent the temperature from rising sharply beyond the range of 60°C, avoids hydrolysis, degradation and coking caused by high temperature, and ensures the stability of the product structure; the mid-term accelerated dropwise addition increases the reactant concentration when the temperature sensitivity decreases, significantly accelerates the sulfonation process, and improves efficiency; the late slow dropwise addition is conducive to accurately controlling the reaction endpoint, ensuring that the reaction is complete and avoiding excessive reagents, while protecting the sulfonated groups that have been formed.

[0014] Preferably, as an improvement, the amount of sodium sulfamate used is 22-28% of the dry basis mass of CMC-H.

[0015] Beneficial Effects: If the sodium sulfamate dosage is too low, the sulfonation reaction may be incomplete, resulting in insufficient sulfonic acid group substitution degree (DS) in the final product, affecting its water solubility, viscosity, thickening ability, and interactions with other substances (such as intermolecular forces related to flexibility). Excessive sodium sulfamate, on the other hand, not only wastes reagents and increases costs, but may also cause excessive sulfonation or side reactions. Excessive sulfonation may destroy the molecular chain structure or introduce excessive charges, increasing the rigidity of the molecular chain, which is detrimental to achieving the goal of "high flexibility." Excessive electrolytes (unreacted sodium sulfamate or its byproducts) may also affect the purity and solubility of the final product, increasing the difficulty of subsequent washing.

[0016] After optimization, the dosage of this solution can ensure that the target sulfonic acid substitution degree (DS) is achieved, thereby giving the product the required high viscosity, excellent water solubility and key high flexibility properties, while avoiding the negative effects and cost increases caused by excessive reagents.

[0017] Preferably, as an improvement, step (c) adopts graded washing, specifically as follows: (i) First wash: washing with 70-85% ethanol aqueous solution; (ii) Second wash: washing with deionized water at 10-30°C; (iii) a third washing step: washing with an ethanol buffer solution containing 1.5-5.0 wt % of NaHCO 3 ; (iv) Fourth wash: dehydration with 90-98% ethanol; (v) Fifth wash: clean with anhydrous ethanol.

[0018] Preferably, as an improvement, the reaction process of step (a) requires stirring and sulfuric acid is added dropwise or by spraying, and the temperature of the added sulfuric acid is not higher than 10° C., ensuring that the sulfuric acid is added in a low temperature form, which is equivalent to providing a thermal buffer margin for the reaction and preventing local carbonization when the high-temperature acid contacts the CMC.

[0019] The mixing of sulfuric acid and CMC-Na (especially if it contains trace amounts of water or alkaline impurities) is a highly exothermic reaction. Adding the sulfuric acid dropwise or by spraying minimizes the amount of heat introduced by the low-temperature sulfuric acid, thus avoiding the sudden addition of excess acid in a certain area, which could lead to a violent, uncontrolled exotherm. This effectively prevents CMC molecular chain degradation (such as glycosidic bond cleavage) caused by localized high temperatures, thereby protecting the CMC's molecular weight and ensuring high viscosity in the final product.

[0020] Preferably, as an improvement, the pH value is monitored in real time in step (a). After the pH value is lower than 1.8, the addition of sulfuric acid is stopped and the stirring speed is increased to avoid the high acid concentration zone caused by too rapid addition of sulfuric acid, prevent dehydration and curling of the CMC molecular chain, and help to accurately control the reaction, reduce or even avoid the occurrence of over-acidity, and improve process stability.

[0021] The present invention also provides an application of a highly flexible, water-soluble, high-viscosity CMC material. The highly flexible, water-soluble, high-viscosity CM material is used as a binder, dispersed with a negative electrode active material and a conductive agent in a solvent to form a uniform slurry, which is then coated, dried, and roller pressed to obtain a lithium battery negative electrode sheet.

[0022] The principles and advantages of this solution are: 1. The present invention selectively sulfonates and grafts the C6 hydroxyl group (-OH) of the glucose ring of carboxymethyl cellulose (CMC) to introduce a strong hydrophilic sulfonic acid group (-OSO3 - ). This group has the dual functions of strong hydration and charge repulsion effect. In strong hydration: each -OSO3 -The combination of ≥10 water molecules significantly increases the hydration radius of the molecular chain and expands the hydrodynamic volume, so that the viscosity of the 1% aqueous solution of the obtained CMC material can approach or even exceed 10,000 cps; and the high charge density enhances the electrostatic repulsion of the molecular chain, thereby expanding the distance between the molecular chains, weakening the hydrogen bond network, and significantly reducing the chain segment slip energy barrier, ultimately allowing the CMC material to break the relatively low elongation at break (12%) of existing materials of this type and achieve an elongation at break of even more than 20%.

[0023] 2. In the acidification stage of step (a), the pH is controlled at 1.8-2.2 to completely protonate the carboxyl groups (-COO - →-COOH), inhibiting its reactivity; at the same time, the steric hindrance of the C6 hydroxyl group is small, laying the foundation for achieving >95% selective sulfonation at the C6 position in step (b) (avoiding the increase in rigidity caused by C2 / C3 substitution).

[0024] 3. Using a rotating packed bed reactor (centrifugal force ≥ 800G), the liquid film thickness is compressed to ≤ 20μm, and the volume mass transfer coefficient is greatly improved, which not only reduces the reaction time, but also makes CMC-H form a micron-sized suspension in ethanol. The micron-sized suspension (D 50 ≤5μm) to fully expose the carboxyl groups of CMC-H, and the sodium sulfamate atomized liquid or droplets instantly wrap the particles, taking up the time difference of the hydrolysis side reaction, and relying on protonated aminosulfonic acid ( + H3N-SO3 - ) releases a strong electrophile -SO3 + It precisely attacks the C6 hydroxyl group, confining the reaction to a micro-domain, suppressing the intermolecular cross-linking side reaction to ≤0.5%, ensuring uniform substitution degree and chain flexibility.

[0025] 4. The sodium sulfamate solution is pretreated with CO2 saturation to achieve a pH change from about 8.5 to 5.0-5.5. The sodium sulfamate solution pretreated with CO2 saturation is added to generate H2CO3 / HCO3 - Buffer, with the NH3 released by the sulfonation reaction ( + H3N-SO3 - →H2N-SO3 - + H + , H + +NH3→NH4 + ) forms a double buffer, so that the pH is naturally maintained at 2.5-3.0, completely eliminating the introduction of exogenous ions and ensuring the compatibility of the electrolyte from the source.

[0026] 5. In addition, the present invention adopts a graded purification method in step (c) to reduce ionic impurities by 90%. DETAILED DESCRIPTION

[0027] The following is further described in detail through specific implementation methods: Example 1 A highly flexible, water-soluble, high-viscosity CMC material with the general chemical formula: [C6H7O2(OH) (3-x-y) (OCH2COONa) x (OSO3Na y )] n Wherein: x=0.85-0.95, y=0.18-0.22, and ≥95% of the sulfonic acid groups are bonded to the C6 position of the glucose ring.

[0028] The following method was used for preparation: Step (a) Acidification: 1. Weigh 100kg of sodium carboxymethyl cellulose (dry basis, DP ≥ 2000 ± 50, DS = 0.90 ± 0.05, moisture ≤ 8%).

[0029] 2. Disperse CMC-Na in 800 L of anhydrous ethanol (liquid-to-solid ratio 8:1), place in a stirred reactor, and precool to 5°C.

[0030] 3. Heat the reactor to the set temperature (the set temperature is a fixed value, the set temperature range is 30-50℃, which is the acidification temperature), and add concentrated sulfuric acid (98%) pre-cooled to below 10℃ by spraying or dropping at a rate of 1L / min. During the process, the reactor is stirred and dispersed at 300rpm. The addition rate is controlled during the addition process to keep the pH value in the reactor at 1.8-2.2 (monitored by an online pH meter, stop dropping when the pH is lower than 1.8, and add sulfuric acid when the pH is higher than 2.2. The total amount of concentrated sulfuric acid is about 27.2L). The end point pH = 2.0±0.1.

[0031] 4. React at an acidified temperature of 30-45°C for 2 hours.

[0032] 5. After the reaction is completed, cool the reaction solution to 25°C, filter it with suction, and wash the filter cake three times with pre-cooled (4°C) ethanol to obtain CMC-H wet cake (water content of about 40% ± 2%).

[0033] Step (b) Sulfonation: 1. Disperse the CMC-H wet cake in 500 L of ethanol and transfer it to a rotating packed bed reactor.

[0034] 2. Prepare sodium sulfamate solution: Weigh sodium sulfamate and dissolve it in 100L of deionized water to form a sodium sulfamate aqueous solution. Then, introduce CO2 into the sodium sulfamate aqueous solution until saturated (pH after saturation ≤ 5.5). Refrigerate at 4°C until used. The amount of sodium sulfamate weighed should be 22-28% of the dry weight of CMC-H.

[0035] 3. Add the sodium sulfamate solution dropwise to the rotating packed bed. Centrifugal mixing is performed at a centrifugal force of 800G, ensuring a liquid film thickness of ≤20μm. The addition process is controlled using a gradient: during the first 0-30 minutes, add at a rate of 0.3-0.5L / min; during the middle period (30-90 minutes), add at a rate of 0.8-1.0L / min; and during the final period (>90 minutes), add at a rate of 0.2-0.4L / min. Maintain the temperature at 50-60°C during the addition process.

[0036] 4. After the reaction is complete, transfer the product out and cool it to room temperature.

[0037] The reaction time of the sulfonation stage is 2-3 hours. The specific time is based on the completion of the reaction. The completion of the reaction requires the following four conditions to be met at the same time: NH3 release rate is ≤50ppm / min for 5min continuously; FTIR characteristic peak: 1040cm -1 (-OSO3 - ) Strength change ≤ 0.5% / min; Viscosity change rate: ≤1% / min (based on 8000cps); pH stability: Fluctuation range ≤±0.1 for more than 10 minutes.

[0038] Step (c) washing and drying: 1. Gradual washing: (i) Wash with 70% ethanol in water (volume concentration) until the filtrate is colorless (approximately 3 volumes); (ii) washing with 20°C deionized water (second wash) until the conductivity is ≤100 μS / cm; (iii) washing with ethanol buffer solution containing 2.5 wt% NaHCO3 (volume concentration 80%) to pH = 6.5-7.0; (iv) dehydration and washing with 95% ethanol (volume concentration); (v) Wash with absolute ethanol to final purification.

[0039] 2. Place the filter cake in a vacuum drying oven and dry it at 50°C until the moisture content is ≤5%. Grind it through a 100-mesh sieve and test the moisture content (≤5%).

[0040] An orthogonal experiment was designed to select key variables for the above method. Acidification temperature, sulfonation temperature, sodium sulfamate dosage ratio, and sulfonation addition method were selected as variable factors for the orthogonal experiment. The acidification temperatures were 40°C, 45°C, and 50°C; the sulfonation temperatures were 50°C, 55°C, and 60°C; and the sodium sulfamate dosage ratio (as a percentage of the dry weight of CMC-H) was 22%, 25%, and 28%.

[0041] The specific dropwise addition method during sulfonation is shown in Table 1 below: Table 1: Specific settings for different addition methods in the sulfonation stage

[0042] The variable parameters of the test example are shown in Table 2 below. Except for the different test variables, the other parameters are the same. The viscosity and elongation at break of the product obtained from the test are tested, and the test results are shown in Table 3.

[0043] For the 1% aqueous solution viscosity test, a 1% aqueous solution was prepared according to the requirements of GB / T 15357-2014 "Determination of viscosity of liquid products using a rotational viscometer for surfactants and detergents" and measured with a viscometer at 25°C ± 0.1%.

[0044] The elongation at break test is carried out in accordance with the provisions of GBT 1040.3-2006 "Determination of tensile properties of plastics Part 3: Test conditions for films and sheets".

[0045] Table 2: Orthogonal test group variable parameter table

[0046] Table 3: Orthogonal test group test results

[0047] From the above orthogonal results, it can be seen that in Tests 1-9, the viscosity of the 1% aqueous solution in Test 2 and Test 6 exceeded 10,000 cps, and the elongation at break exceeded 20%. It can be seen that the CMC material prepared in this embodiment can achieve high viscosity and high elongation at break.

[0048] In test 6, the sulfonation temperature reached 60°C, which accelerated the sulfonation and made up for the deficiency caused by the smaller amount of sodium aminosulfonate, achieving a double breakthrough in viscosity and elongation at break.

[0049] In Test 3, the viscosity was high, and the elongation at break was close to 20%. Test 7 showed poor results. In Test 9, at an acidification temperature of 50°C and a sulfonation temperature of 60°C, the viscosity was only 7900 cps, and the elongation at break was only 15.2%, likely due to main chain scission caused by hydrolysis of β-1,4 glycosidic bonds. This indicates that high-temperature acidification leads to irreversible main chain degradation, and high-temperature sulfonation can also cause main chain scission.

[0050] In terms of the choice of sulfonation dropwise addition method, the experimental groups with excellent viscosity and break extension rate all came from the dropwise addition method of level 2. Therefore, it can be seen that the most reasonable dropwise addition speed is 0.4 L / min→0.9 L / min→0.3 L / min.

[0051] The most suitable acidification temperature is around 45°C, the most suitable sulfonation temperature is around 55°C, and the most suitable sodium aminosulfonate dosage is around 25%. Therefore, we further verified and designed the appropriate areas and designed the optimization verification group shown in Table 4. The test results of the optimization verification group are shown in Table 5.

[0052] Table 4: Optimized validation group parameters

[0053] Table 5: Optimization and validation group test results

[0054] As can be seen from Tables 4 and 5 above, Tests 10, 12, 14, and 15 all have excellent viscosity and excellent elongation at break. The viscosity of the 1% aqueous solution exceeds 10,000 cps, and the elongation at break exceeds 22%.

[0055] The sulfonation temperature in Test 13 was relatively high, which may have triggered disulfonation and caused a decrease in the elongation at break.

[0056] From the above experiments, it can be seen that the CMC material prepared by the present invention can achieve a 1% aqueous solution viscosity of 10,000 cps and can ensure that the elongation at break far exceeds the existing technology of about 12% and reaches or even exceeds 20%.

[0057] Example 2 This embodiment provides an application of a highly flexible, water-soluble, high-viscosity CMC material. The highly flexible, water-soluble, high-viscosity CMC material prepared in Example 1 is used as a binder, dispersed in a solvent with a negative electrode active material and a conductive agent to form a uniform slurry, and then coated, dried, and roller pressed to obtain a lithium battery negative electrode sheet.

[0058] After high-speed coating, infrared-hot air coupled drying is adopted. Specifically, infrared-hot air coupled drying is as follows: first, infrared radiation at 80°C is used for 60 seconds (short-term high temperature (80°C) quickly evaporates surface moisture to avoid sagging (surface temperature ≤ 70°C)), and then low temperature at 60°C is used to slowly release internal moisture.

[0059] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A highly flexible, water-soluble, high-viscosity CMC material, characterized in that: The general chemical formula is: [C6H7O2(OH) (3-x-y) (OCH2COONa) x (OSO3Na y )] n Wherein: x=0.85-0.95, y=0.18-0.22, and ≥95% of the sulfonic acid groups are bonded to the C6 position of the glucose ring.

2. A highly flexible water-soluble high-viscosity CMC material according to claim 1, characterized in that: The preparation method comprises the following steps: (a) Dispersing sodium carboxymethyl cellulose in ethanol, then adding sulfuric acid to adjust the pH of the system to 1.8-2.2, reacting at 30-45°C for 1.5-2.5 hours, and solid-liquid separation to obtain protonated CMC-H; (b) dispersing CMC-H in ethanol to form a CMC-H suspension, adding a sodium sulfamate solution pretreated with CO2 saturation, mixing the CMC-H suspension and the sodium sulfamate solution saturated with CO2 in a reactor with a centrifugal force of ≥800G and a liquid film thickness of ≤20μm, and reacting at 50-60°C; (c) washing the product obtained in step (b) and then vacuum drying it.

3. The highly flexible, water-soluble, high-viscosity CMC material according to claim 2, characterized in that: The reaction temperature of step (a) is 35-50°C.

4. The highly flexible, water-soluble, high-viscosity CMC material according to claim 2, characterized in that: The pH of sodium sulfamate solution is ≤5.5 after saturation with CO2.

5. The highly flexible, water-soluble, high-viscosity CMC material according to claim 1, characterized in that: The sodium sulfamate solution in step (b) is added dropwise using a gradient: in the early stage (0-30 min), the dropwise addition rate is 0.3-0.5 L / min; in the middle stage (30-90 min), the dropwise addition rate is 0.8-1.0 L / min; in the late stage (>90 min), the dropwise addition rate is 0.2-0.4 L / min until the sulfonation translocation is completely completed.

6. The highly flexible, water-soluble, high-viscosity CMC material according to claim 1, characterized in that: The dosage of sodium sulfamate is 22-28% of the dry basis mass of CMC-H.

7. The highly flexible, water-soluble, high-viscosity CMC material according to claim 1, characterized in that: Step (c) adopts graded washing, which is as follows: (i) First wash: washing with 70-85% ethanol aqueous solution; (ii) Second wash: washing with deionized water at 10-30°C; (iii) a third washing step: washing with an ethanol buffer solution containing 1.5-5.0 wt % of NaHCO 3 ; (iv) Fourth wash: dehydration with 90-98% ethanol; (v) Fifth wash: clean with anhydrous ethanol.

8. The highly flexible, water-soluble, high-viscosity CMC material according to claim 1, characterized in that: The reaction process of step (a) requires stirring and sulfuric acid is added dropwise or by spraying, and the temperature of the added sulfuric acid is not higher than 10°C.

9. The highly flexible, water-soluble, high-viscosity CMC material according to claim 8, characterized in that: In step (a), the pH value is monitored in real time. When the pH value is lower than 1.8, the addition of sulfuric acid is stopped and the stirring speed is increased.

10. An application of a highly flexible, water-soluble, high-viscosity CMC material, characterized by: The highly flexible water-soluble high-viscosity CMC material is used as a binder, dispersed with a negative electrode active material and a conductive agent in a solvent to form a uniform slurry, and then coated, dried and roller pressed to obtain a lithium battery negative electrode sheet.

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