Synthesis and preparation method of high-purity lithium battery grade sodium carboxymethyl cellulose

Abstract

The invention relates to the technical field of synthesis of a lithium battery material sodium carboxymethyl cellulose, in particular to a synthesis and preparation method of high-purity lithium battery grade sodium carboxymethyl cellulose, which comprises the following preparation steps: S1, preparing modified montmorillonite; s2, preparing alkali cellulose; s3, etherifying the alkali cellulose; s4, carrying out acidification reaction; s5, carrying out secondary alkalization reaction; s6, carrying out neutralization reaction; and S7, post-processing. Through the application design of the preparation method, the sodium carboxymethyl cellulose raw fiber residues can be improved, and the problems that the uniformity and stability of produced cellulose are poor due to non-uniform heat and mass transfer in the process of a traditional kneading machine method, a filter element is easily blocked due to high content of insoluble substances, and the model switching is frequent due to non-uniform viscosity are solved; the method has the advantages of high product yield, few side reactions, few raw fiber residues, high product stability and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of the synthesis of sodium carboxymethyl cellulose for lithium battery materials, and specifically to a method for synthesizing and preparing high-purity sodium carboxymethyl cellulose for lithium batteries. Background Art

[0002] At present, the binders in the aqueous slurry of lithium-ion batteries are mainly used in combination with sodium carboxymethyl cellulose and styrene-butadiene rubber emulsion. Among them, sodium carboxymethyl cellulose, as an aqueous thickener, plays an auxiliary binding role for the styrene-butadiene rubber emulsion, is used to disperse the anode active material and the conductive agent, assists in binding the anode active material and the current collector, and plays a thickening role to prevent the anode slurry from settling, so that the anode coating has better fluidity.

[0003] Referring to "A Sodium Carboxymethyl Cellulose and Its Preparation Method and a Battery Anode Slurry and Its Preparation Method" with the publication number "CN114276461A", the technical effect of this application is that the prepared sodium carboxymethyl cellulose has advantages such as rapid dispersion and rapid viscosity release, and at the same time has a small insoluble matter content. During the preparation process of the anode slurry, the anode pulping time can be shortened by at least 50%, the production cost can be saved, and there will be no situation of blocked filter elements during the production process, no scratches will appear during the coating process, and the coating areal density is relatively stable.

[0004] Referring to "A Preparation Method of Lithium Carboxymethyl Cellulose for Lithium Batteries" with the publication number "CN12724266A", the technical effect of this application is that carboxymethyl cellulose hydrogen is obtained by a one-step method, the reaction between strong acid and sodium carboxymethyl cellulose is reduced, lithium carbonate is used to replace lithium hydroxide, the use efficiency of lithium salt is maximized, waste is reduced, and pollution is lowered.

[0005] Referring to "A Sodium Carboxymethyl Cellulose and Its Preparation Method and Application" with the publication number "CN114685688A", the technical effect of this application is that the sodium carboxymethyl cellulose material prepared by alkalization and etherification under specific methods and conditions has advantages such as high degree of substitution (0.9 - 1.1), fast dissolution rate (completely dissolved in 0.5 - 1.5 h at 1% concentration), high viscosity, and high purity.

[0006] The main production process of sodium carboxymethyl cellulose in the above patent is the kneader method. A pair of rotating blades that cooperate with each other in the kneader quickly mix the viscous materials evenly through strong shearing, extrusion, kneading, and stirring. However, due to the short solid reaction time and low heat and mass transfer efficiency of the kneader method, the reaction is uneven, the product stability is poor, there are more raw fiber residues and gel particles, and mechanical grinding must be used to obtain the powder. Therefore, it is easy to cause the product to turn yellow due to high-temperature aging, and even due to the high content of insoluble substances, it is easy to block the filter element during the preparation of the negative electrode slurry, and scratches appear during the lithium-ion battery coating process, and the coating surface density is unstable. These problems ultimately affect the performance of the battery cell and even the battery safety, making it difficult to meet the quality requirements of the lithium battery industry with high requirements for raw materials. Therefore, a new solution to the above problems is needed. Summary of the Invention

[0007] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a synthesis preparation method of high-purity lithium battery-grade sodium carboxymethyl cellulose.

[0008] To achieve the above purpose, the present invention provides the following technical solutions:

[0009] A synthesis preparation method of high-purity lithium battery-grade sodium carboxymethyl cellulose, comprising the following steps:

[0010] S1. Preparation of modified montmorillonite:

[0011] S11. Immerse 7-12 parts of montmorillonite by mass in a hydrochloric acid solution with a concentration of 0.5-1 mol / L for 0.5-1 h, then take it out and perform a drying treatment;

[0012] S12. Mix the montmorillonite treated in step S11 with 23-30 parts of the modification liquid, and stir for 1.5-2 h to obtain modified montmorillonite;

[0013] S2. Preparation of alkali cellulose: Take 12-15 parts of modified montmorillonite and mix it with 5-8 parts of wood cellulose. After stirring for 10-15 min, add 1-3 parts of solid sodium hydroxide and 40-50 parts of 95% ethanol solution for a primary alkalization reaction treatment to obtain alkali cellulose;

[0014] S3. Etherification of alkali cellulose: Dissolve 7-15 parts of chloroacetic acid solution in 95% ethanol solution to make an etherifying agent, and mix the alkali cellulose obtained in step S2 with the etherifying agent to obtain etherified alkali cellulose;

[0015] S4. Acidification reaction: Using 95% ethanol solution as the dispersion medium, disperse the etherified alkali cellulose therein, add 7-15 parts of 98% sulfuric acid under stirring, react for 1.5-4 h, and control the temperature at 30-45 °C to obtain the intermediate CMC-H;

[0016] S5. Secondary alkalization reaction: Disperse CMC-H in a 95% ethanol solution under atmospheric pressure, add 18 - 20 parts of an aqueous sodium hydroxide solution with a mass concentration of 40% to obtain CMC-H after secondary alkalization. The reaction temperature range is 30 - 45°C, and the reaction time is 1.5 - 4 h;

[0017] S6. Neutralization reaction: Use glacial acetic acid as a neutralizing agent and add it to the CMC-H after secondary alkalization to obtain a crude product solution containing sodium carboxymethyl cellulose;

[0018] S7. Post-treatment: Filter and wash the crude product solution containing sodium carboxymethyl cellulose, and after drying, crush the block by air flow pulverization, and sieve it with a 300-mesh sieve to obtain high-purity lithium battery-grade sodium carboxymethyl cellulose.

[0019] Preferably, the modification liquid in step S12 is a mixture of ammonium dihydrogen phosphate and cetyltrimethylammonium bromide with a mass ratio of 3:4.

[0020] Preferably, the temperature control range of the primary alkalization reaction in step S2 is 30 - 45°C.

[0021] Preferably, in step S3, the first etherification reaction is carried out for 1 - 2.5 h after the alkali cellulose obtained in step S2 is mixed with the etherifying agent, and the temperature is controlled at 40 - 60°C; the second etherification reaction is carried out for 2.5 - 3 h, and the temperature is controlled at 60 - 85°C; the reaction formula of the first etherification reaction is:

[0022] ClCH2COOH + NaOH → ClCH2COONa + H2O; the reaction formula of the second etherification reaction is:

[0023] Cell-(OH) 3-x (O - Na + ) x + nCCH2COONa → Cell-(OH) 3-x (ONa) x-n (OCH2COO - Na + ) n + nNaCl.

[0024] Preferably, the reaction formula of the acidification reaction in step S4 is:

[0025] Cell-CH2COONa (CMC-Na) + HX → Cell-CH2COOH (CMC-H) + NaX.

[0026] Preferably, the reaction formula of the secondary alkalization reaction in step S5 is:

[0027] Cell-CH2COOH(CMC-H) + NaOH → Cell-CH2COONa(CMC-Na) + H2O。

[0028] Preferably, the reaction formula of the neutralization reaction in step S6 is:

[0029] Cell-(OH) 3-x (ONa) x-n (OCH2COO-Na + ) n +(x - n)CH3COOG → Cell-(OH) 3-n (OCH2COO-Na + ) n +(x - n)CH3COONa,

[0030] wherein, x is a number less than or equal to 3, and n is the number of carboxymethyl groups substituted on each cellulose glucose ring group.

[0031] Preferably, in step S2, the control temperature range of the first alkalization reaction is 30 - 45°C, and the reaction time is 1.5 - 2 h.

[0032] Preferably, in step S5, the control temperature range of the second alkalization reaction is 30 - 45°C, and the reaction time is 1.5 - 4 h.

[0033] Preferably, in step S6, the pH at the neutralization end point is 5 - 8, and the neutralization reaction temperature is 20 - 35°C.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. Through the application design of the preparation method, the present invention can improve the residual raw fibers of sodium carboxymethyl cellulose, overcome the problems of poor uniformity, stability, and high insoluble matter content of the produced cellulose due to uneven heat and mass transfer in the traditional kneader method, which easily blocks the filter element and has uneven viscosity, resulting in frequent model switching. It can deeply process and repurify raw materials and low-end sodium carboxymethyl cellulose raw materials to obtain battery-grade carboxymethyl cellulose products with uniform molecular weight distribution, good degree of substitution, stability, good flexibility, few raw fibers, low impurities, and high consistency of viscosity and purity.

[0036] 2. The present invention provides better reaction conditions and precise process control. In combination with a unique formulation process, it effectively inhibits the activity of short-chain C2 and C3 and reduces the number of group substitutions, increases the activity of long-chain C6 and improves the substitution ratio of long-chain groups, significantly improves the flexibility performance of existing CMC-Na, the product has a stronger elongation at break, relatively higher flexibility, helps to improve the cracking and curling phenomena during the coating process, and enables the product to have less impurity content and better physical processing performance. This process has the advantages of high product yield, few side reactions, little residual raw fiber, and high product stability.

[0037] 3. In the preparation process of the modified montmorillonite in the present invention, it is acid-treated and mixed and stirred with a modification solution to make it have better activity and dispersibility. In the subsequent preparation step of alkali cellulose, after the modified montmorillonite is mixed with lignocellulose, it can be more evenly dispersed in the reaction system, thereby promoting the uniformity of heat and mass transfer and avoiding the problem of uneven reaction caused by uneven heat and mass transfer in the traditional kneader method. The addition of modified montmorillonite provides a more active reaction environment for the preparation of alkali cellulose, helps to improve the efficiency and uniformity of the alkalization reaction, makes the structure of alkali cellulose more uniform, and lays a good foundation for subsequent steps such as etherification reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is the process flow chart for the preparation of high-purity lithium battery-grade carboxymethyl cellulose sodium of the present invention;

[0039] Figure 2 is the schematic diagram of the comparison of light transmittance before and after the secondary alkalization of the intermediate CMC-H obtained in Example 1 of the present invention;

[0040] Figure 3 is the schematic diagram of the comparison of samples before and after the secondary alkalization of the intermediate CMC-H obtained in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] Please refer to Figures 1-3 , the present invention provides a technical solution:

[0043] Example 1

[0044] A synthesis and preparation method of high-purity lithium battery-grade carboxymethyl cellulose sodium:

[0045] S1. Preparation of modified montmorillonite:

[0046] Immerse 7 g of montmorillonite in a hydrochloric acid solution with a concentration of 0.5 mol / L for 0.5 h, then take it out and perform a drying treatment;

[0047]

[0046] Mix the montmorillonite treated in step S11 with 23 g of the modification solution and stir for 1.5 h to obtain modified montmorillonite, where the modification solution is a mixture of ammonium dihydrogen phosphate and cetyltrimethylammonium bromide with a mass ratio of 3:4;

[0048] Preparation of alkali cellulose: Take 12 g of modified montmorillonite and mix it with 5 g of wood cellulose. After stirring for 10 min, add 1 g of solid sodium hydroxide and 40 ml of a 95% ethanol solution for a primary alkalization reaction treatment to obtain alkali cellulose. The control temperature range for the primary alkalization reaction is 30°C, and the reaction time is 1.5 h;

[0049]

[0047] Dissolve 7 ml of chloroacetic acid solution in a 95% ethanol solution to prepare an etherifying agent. Mix the alkali cellulose obtained in step S2 with the etherifying agent, control the temperature at 40°C in 1 h, and control the temperature at 60°C in 2.5 h to finally obtain the etherified alkali cellulose;

[0050] Acidification reaction: Use a 95% ethanol solution as the dispersion medium, disperse the etherified alkali cellulose therein, add 7 ml of 98% sulfuric acid under stirring, react for 1.5 h, and control the temperature at 30°C to obtain the intermediate CMC-H;

[0051]

[0048] Secondary alkalization reaction: Disperse CMC-H in a 95% ethanol solution under normal pressure, add 18 ml of a 40% sodium hydroxide aqueous solution to obtain the secondary alkalized CMC-H. The reaction temperature range is 30°C, and the reaction time is 1.5 h;

[0052] Neutralization reaction: Use glacial acetic acid as the neutralizing agent to neutralize the secondary alkalized CMC-H. The pH at the neutralization end point is 5, and the neutralization reaction temperature is 20°C to obtain a crude product solution containing sodium carboxymethylcellulose;

[0053]

[0049] Post-treatment: Filter and wash the crude product solution containing sodium carboxymethylcellulose, dry it, and then pulverize the block by air flow pulverization and sieve it with a 300-mesh sieve to obtain high-purity lithium battery grade sodium carboxymethylcellulose.

[0054] Example 2

[0055] A method for synthesizing and preparing high-purity lithium battery grade sodium carboxymethylcellulose:

[0056] Preparation of modified montmorillonite:

[0057] S11. Immerse 12 g of montmorillonite in a hydrochloric acid solution with a concentration of 1 mol / L for 1 h, then take it out and perform a drying treatment;

[0058] S12. Mix the montmorillonite treated in step S11 with 30 g of a modification solution and stir for 2 h to obtain modified montmorillonite, where the modification solution is a mixture of ammonium dihydrogen phosphate and cetyltrimethylammonium bromide with a mass ratio of 3:4;

[0059] S2. Preparation of alkali cellulose: Take 15 g of modified montmorillonite and mix it with 8 g of wood cellulose. After stirring for 15 min, add 3 g of solid sodium hydroxide and 50 ml of 95% ethanol solution for a primary alkalization reaction treatment to obtain alkali cellulose. The control temperature range for the primary alkalization reaction is 45 °C, and the reaction time is 2 h;

[0060] S3. Etherification of alkali cellulose: Dissolve 15 ml of chloroacetic acid solution in 95% ethanol solution to prepare an etherifying agent. Mix the alkali cellulose obtained in step S2 with the etherifying agent, control the temperature at 60 °C for 2.5 h, and control the temperature at 85 °C for 3 h to finally obtain etherified alkali cellulose;

[0061] S4. Acidification reaction: Use 95% ethanol solution as a dispersion medium, disperse the etherified alkali cellulose in it, add 15 ml of 98% sulfuric acid under stirring, react for 4 h, and control the temperature at 45 °C to obtain intermediate CMC-H;

[0062] S5. Secondary alkalization reaction: Disperse CMC-H in 95% ethanol solution under normal pressure, add 20 ml of sodium hydroxide aqueous solution with a mass concentration of 40% to obtain secondary alkalized CMC-H. The reaction temperature range is 45 °C, and the reaction time is 4 h;

[0063] S6. Neutralization reaction: Use glacial acetic acid as a neutralizing agent to neutralize the secondary alkalized CMC-H. The pH at the neutralization end point is 8, and the neutralization reaction temperature is 35 °C to obtain a crude product solution containing sodium carboxymethylcellulose;

[0064] S7. Post-treatment: Filter and wash the crude product solution containing sodium carboxymethylcellulose, dry it, and then pulverize the block by air flow pulverization, and sieve it with a 300-mesh sieve to obtain high-purity lithium battery-grade sodium carboxymethylcellulose.

[0065] Example 3

[0066] A synthesis preparation method of high-purity lithium battery-grade sodium carboxymethylcellulose:

[0067] S1. Preparation of modified montmorillonite:

[0068] S11 Immerse 9 g of montmorillonite in a hydrochloric acid solution with a concentration of 0.7 mol / L for 0.7 h, then take it out and perform a drying treatment;

[0069] S12. Mix the montmorillonite treated in step S11 with 25 g of a modification solution and stir for 1.5 h to obtain modified montmorillonite, where the modification solution is a mixture of ammonium dihydrogen phosphate and cetyltrimethylammonium bromide with a mass ratio of 3:4;

[0070] S2. Preparation of alkali cellulose: Take 13 g of modified montmorillonite and mix it with 6 g of wood cellulose. After stirring for 12 min, add 2 g of solid sodium hydroxide and 43 ml of 95% ethanol solution for a primary alkalization reaction treatment to obtain alkali cellulose. The control temperature range for the primary alkalization reaction is 35 °C, and the reaction time is 1.5 h;

[0071] S3. Etherification of alkali cellulose: Dissolve 10 ml of chloroacetic acid solution in 95% ethanol solution to make an etherifying agent. Mix the alkali cellulose obtained in step S2 with the etherifying agent, control the temperature at 50 °C for 1.5 h, and control the temperature at 65 °C for 2.5 h to finally obtain the etherified alkali cellulose;

[0072] S4. Acidification reaction: Use 95% ethanol solution as a dispersion medium, disperse the etherified alkali cellulose in it, add 10 ml of 98% sulfuric acid under stirring, react for 2 h, and control the temperature at 35 °C to obtain the intermediate CMC-H;

[0073] S5. Secondary alkalization reaction: Disperse CMC-H in 95% ethanol solution under normal pressure, add 19 ml of a sodium hydroxide aqueous solution with a mass concentration of 40% to obtain the secondary alkalized CMC-H. The reaction temperature range is 35 °C, and the reaction time is 2 h;

[0074] S6. Neutralization reaction: Use glacial acetic acid as a neutralizing agent to neutralize the secondary alkalized CMC-H. The pH at the neutralization end point is 6, and the neutralization reaction temperature is 25 °C to obtain a crude product solution containing sodium carboxymethylcellulose;

[0075] S7. Post-treatment: Filter and wash the crude product solution containing sodium carboxymethylcellulose, dry it, and then pulverize the block by air flow pulverization, and sieve it with a 300-mesh sieve to obtain high-purity lithium battery-grade sodium carboxymethylcellulose.

[0076] Example 4

[0077] A method for synthesizing and preparing high-purity lithium battery-grade sodium carboxymethylcellulose:

[0078] S1. Preparation of modified montmorillonite:

[0079] S11 Immerse 11 g of montmorillonite in a hydrochloric acid solution with a concentration of 0.9 mol / L for 1 h by mass fraction, then take it out and perform a drying treatment;

[0080] S12. Mix the montmorillonite treated in step S11 with 28 g of a modification solution and stir for 2 h to obtain modified montmorillonite, where the modification solution is a mixture of ammonium dihydrogen phosphate and cetyltrimethylammonium bromide with a mass ratio of 3:4;

[0081] S2. Preparation of alkali cellulose: Take 14 g of modified montmorillonite and mix it with 7 g of wood cellulose, stir for 14 min, then add 2 g of solid sodium hydroxide and 48 ml of 95% ethanol solution for a primary alkalization reaction treatment to obtain alkali cellulose. The control temperature range for the primary alkalization reaction is 40 °C, and the reaction time is 2 h;

[0082] S3. Etherification of alkali cellulose: Dissolve 14 ml of chloroacetic acid solution in 95% ethanol solution to prepare an etherifying agent. Mix the alkali cellulose obtained in step S2 with the etherifying agent, control the temperature at 55 °C for 2 h, and then control the temperature at 80 °C for 3 h to finally obtain etherified alkali cellulose;

[0083] S4. Acidification reaction: Use 95% ethanol solution as a dispersion medium, disperse the etherified alkali cellulose in it, add 14 ml of 98% sulfuric acid under stirring, react for 3 h, and control the temperature at 40 °C to obtain an intermediate CMC-H;

[0084] S5. Secondary alkalization reaction: Disperse CMC-H in 95% ethanol solution under normal pressure, add 19 ml of a sodium hydroxide aqueous solution with a mass concentration of 40% to obtain secondary alkalized CMC-H. The reaction temperature range is 40 °C, and the reaction time is 3 h;

[0085] S6. Neutralization reaction: Use glacial acetic acid as a neutralizing agent to neutralize the secondary alkalized CMC-H. The pH at the neutralization end point is 7, and the neutralization reaction temperature is 30 °C to obtain a crude product solution containing sodium carboxymethyl cellulose;

[0086] S7. Post-treatment: Filter and wash the crude product solution containing sodium carboxymethyl cellulose, dry it, and then crush the block by air flow pulverization, and sieve it with a 300-mesh sieve to obtain high-purity lithium battery grade sodium carboxymethyl cellulose.

[0087] Performance test:

[0088] Prepare 1% CMC-Na aqueous solution of the high-purity lithium battery grade sodium carboxymethyl cellulose obtained in Examples 1-4 according to the national standard GB 1904-2005, test the viscosity at 25 °C, and finally determine the degree of substitution (DS) and purity by titration method and ash content determination method. The final obtained data is shown in Table 1 below:

[0089] Table 1

[0090] Viscosity (mPa·s) Degree of substitution Purity (%) Example 1 1200 0.85 99.5 Example 2 1235 0.92 99.7 Example 3 1214 0.86 99.5 Example 4 1204 0.88 99.6

[0091] Viscosity is an important performance index of sodium carboxymethyl cellulose for battery grade, which directly affects its thickening and dispersing effects in lithium battery slurry. From the data in Table 1, it can be seen that the high-purity sodium carboxymethyl cellulose for lithium battery obtained in the present invention has a relatively high viscosity, which can effectively prevent the sedimentation of the negative electrode slurry and improve the fluidity and uniformity during the coating process. The corresponding degree of substitution is within the ideal range, indicating that the high-purity sodium carboxymethyl cellulose for lithium battery obtained in the present invention has good solubility and stability. From the data in Table 1, it can be seen that the high-purity sodium carboxymethyl cellulose for lithium battery obtained in the present invention has a relatively high purity and extremely low impurity content, meeting the high-purity requirements of sodium carboxymethyl cellulose for lithium battery grade, and contributing to improving the electrochemical performance and safety of lithium batteries.

[0092] Reference appendix Figure 2 It can be known that in the present invention, the light transmittance of the intermediate CMC-H obtained in Example 1 before and after secondary alkalization is compared. Through the appendix Figure 2 It can be found that the clarified light transmittance of the intermediate CMC-H after the secondary alkalization reaction is higher, and the uniformity and stability are better. Through the appendix Figure 3 From the sample schematic diagrams of the intermediate CMC-H before and after secondary alkalization in the appendix, it can be found that the intermediate CMC-H after the secondary alkalization reaction is easily soluble, clarified, has less insoluble matter, and no raw fiber residue.

[0093] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for synthesizing high-purity lithium battery grade sodium carboxymethyl cellulose, characterized in that: The following steps are involved: S1. Preparation of modified montmorillonite: S11 immerse 7-12 parts of montmorillonite by mass in a 0.5-1 mol / L hydrochloric acid solution for 0.5-1 h, take it out and dry it; S12. The montmorillonite treated in step S11 is mixed with 23-30 parts of the modified solution and stirred for 1.5-2h to obtain a modified montmorillonite; S2. Preparation of alkali cellulose: 12-15 parts of modified montmorillonite and 5-8 parts of lignocellulose were mixed, stirred for 10-15 min, and then 1-3 parts of solid sodium hydroxide and 40-50 parts of 95% ethanol solution were added for an alkalization reaction to obtain alkali cellulose; S3 etherification of alkali cellulose: 7-15 parts of chloroacetic acid solution was dissolved in 95% ethanol solution to prepare an etherifying agent, the alkali cellulose obtained in step S2 and the etherifying agent were mixed to obtain etherified alkali cellulose; S4. Acidification reaction: using 95% ethanol solution as a dispersion medium, dispersing the etherified alkali cellulose therein, adding 7-15 parts of 98% sulfuric acid under stirring, reacting for 1.5-4h, and controlling the temperature at 30-45°C to obtain the intermediate CMC-H; S5. Secondary alkalization reaction: CMC-H is dispersed in 95% ethanol solution under normal pressure, 18-20 parts by mass of 40% aqueous sodium hydroxide solution is added to obtain secondary alkalized CMC-H, the reaction temperature range is 30-45 ° C, and the reaction time is 1.5-4h; S6. Neutralization reaction: glacial acetic acid is added as a neutralizing agent to the CMC-H after secondary alkalization to obtain a crude solution containing sodium carboxymethyl cellulose; S7. Post-processing: Filter and wash the crude solution containing sodium carboxymethyl cellulose, and crush the blocks by air flow milling after drying, and sieve with a 300-mesh sieve to obtain high-purity lithium battery grade sodium carboxymethyl cellulose.

2. The method for synthesizing high-purity lithium battery-grade sodium carboxymethyl cellulose according to claim 1, characterized in that: The modified liquid in step S12 is a mixture of diammonium phosphate and hexadecyltrimethylammonium bromide in a mass ratio of 3:

4.

3. The method for synthesizing high-purity lithium battery-grade sodium carboxymethyl cellulose according to claim 1, characterized in that: The controlled temperature range of the primary alkalization reaction in step S2 is 30-45°C.

4. The method for synthesizing high-purity lithium battery-grade sodium carboxymethyl cellulose according to claim 1, characterized in that: In step S3, the alkali cellulose obtained in step S2 and the etherifying agent are mixed for 1-2.5 hours for the first etherification reaction, and the temperature is controlled at 40-60°C; and for 2.5-3 hours for the second etherification reaction, and the temperature is controlled at 60-85°C.

5. The method for synthesizing high-purity lithium battery-grade sodium carboxymethyl cellulose according to claim 1, characterized in that: In step S2, the controlled temperature range of the primary alkalization reaction is 30-45° C., and the reaction time is 1.5-2 h.

6. The method for synthesizing high-purity lithium battery-grade sodium carboxymethyl cellulose according to claim 1, characterized in that: In step S5, the control temperature range of the secondary alkalization reaction is 30-45° C., and the reaction time is 1.5-4 h.

7. The method for synthesizing high-purity lithium battery-grade sodium carboxymethyl cellulose according to claim 1, characterized in that: In step S6, the pH at the neutralization endpoint is 5-8, and the neutralization reaction temperature is 20-35°C.

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