Alkali-resistant modified sodium carboxymethyl cellulose, and preparation method and application thereof

Abstract

The present application relates to the field of battery materials, and more particularly to an alkali-resistant modified sodium carboxymethyl cellulose, a preparation method and application thereof; the alkali-resistant modified sodium carboxymethyl cellulose comprises a main chain and a modified side chain containing 4-tert-butyl benzene sulfonyl. The present application uses 4-tert-butyl benzene sulfonyl as an alkali-resistant protecting group of the CMC main chain, effectively hinders OH- from approaching the beta-1,4-glucosidic bond through the steric shielding effect of the tert-butyl group, inhibits the alkali degradation reaction from the molecular level, and significantly improves the thickening stability of the CMC under the condition of pH>10. The aromatic ring in the benzene sulfonyl structure forms a pi-sigma conjugated system with the sulfonyl group, enhancing the chemical stability of the side chain itself, making it not easy to be attacked and shed by OH- under alkaline conditions, and ensuring the long-term effectiveness of the modification. The present application covalently connects the protecting group to the CMC main chain through a stable sulfonamide or ester bond through a multi-step synthesis route, which is more firmly combined than physical blending or weak interaction.

Description

Technical Field

[0001] This invention relates to the field of battery materials, and in particular to an alkali-resistant modified sodium carboxymethyl cellulose, its preparation method, and its application. Background Technology

[0002] The anode material for sodium-ion batteries is mainly hard carbon. Compared to the graphite anode used in lithium-ion batteries, hard carbon has a high specific surface area and abundant surface functional groups, but it exhibits high alkalinity (pH value is usually 10.0-11.0) during aqueous slurry preparation. Sodium carboxymethyl cellulose (CMC) is commonly used as a thickener in the preparation of aqueous anode slurries. Its thickening mechanism lies in the high-viscosity network structure formed by the unfolding of macromolecular chains and hydration.

[0003] However, CMC is highly susceptible to alkaline-catalyzed degradation under highly alkaline conditions (pH > 10). Excess hydroxide ions (OH-) can attack the β-1,4-glycosidic bonds between the glucose rings of cellulose, leading to macromolecular chain breakage and degradation, resulting in a sharp decrease or even complete loss of viscosity in the adhesive. At the same time, the high pH environment can also easily cause demulsification of the binder styrene-butadiene rubber (SBR), ultimately leading to slurry settling and scrapping, which seriously affects the production yield.

[0004] In existing technologies, solutions to this problem can be mainly divided into three categories:

[0005] (a) Physical modification of the slurry formulation. The viscosity of the slurry is increased by adding a "thermally stable polymer" (synthesized via reverse microemulsion polymerization using acrylamide, 2-acrylamido-2-methylpropionic acid, and stearyl methacrylate as raw materials), utilizing hydrophobic association to form a dynamic physical cross-linked network. This approach does not alter the structure of the CMC itself and is a "post-treatment" physical strategy; the alkali resistance of the thickener itself is not improved.

[0006] (ii) Replacement or compounding of thickeners. Nonionic polyether compounds are compounded with CMC to improve slurry performance; another approach uses polyacrylic acid resin as a substitute thickener. The compounding route avoids rather than addresses the alkali resistance problem of CMC, and the addition of nonionic surfactants may affect the electrochemical interface performance of the electrodes; PAA-type thickeners rely on alkali neutralization for thickening, and are also pH-sensitive systems.

[0007] (III) Chemical Modification of CMC. A method of grafting dopamine onto CMC chains via amidation results in modified CMC molecules containing catechol structures, enhancing adhesion to silicon particle surfaces. The primary purpose of this method is to improve adhesion performance, rather than addressing alkali resistance. There are also reports in the literature on the application of graft-modified CMC for temperature and salt resistance—using acrylamide (AM) and sodium p-styrene sulfonate (STS) as monomers to graft copolymerize CMC for use in oilfield applications to improve temperature and salt resistance. However, the protective effect of the sulfonic acid groups under alkaline conditions and the applicable scenarios are significantly different from those in sodium-ion battery slurry systems. Additionally, the application of cross-linked CMC as a negative electrode gelling agent in alkaline manganese batteries has been disclosed. The cross-linked structure through ester bonds improves gel strength and storage stability. However, this cross-linked CMC is essentially insoluble in water and is not suitable for thickening systems in aqueous coating processes.

[0008] In summary, there is currently a lack of technical solutions for targeted chemical structural modification of CMC to enable it to possess thickening stability in a highly alkaline hard carbon slurry environment. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing technologies by providing an alkali-resistant modified carboxymethyl cellulose sodium, its preparation method, and its applications.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A first aspect of the present invention is to provide an alkali-resistant modified sodium carboxymethyl cellulose, comprising: a main chain and a modified side chain containing 4-tert-butylbenzenesulfonyl groups, wherein the modified side chain containing 4-tert-butylbenzenesulfonyl groups is covalently connected to the main chain.

[0012] Preferably, the grafting rate of the modified side chain containing 4-tert-butylbenzenesulfonyl group is 5-30 mol, based on glucosinolate units.

[0013] Preferably, the covalent bond is a sulfonamide bond or an ester bond.

[0014] Preferably, the alkali-resistant modified sodium carboxymethyl cellulose has a molecular weight of 100,000-800,000 g / mol and a degree of carboxymethyl substitution of 0.6-1.2.

[0015] A second aspect of the present invention is to provide a method for preparing the above-mentioned alkali-resistant modified sodium carboxymethyl cellulose, comprising the steps of:

[0016] S1. CMC-Na is acidified and then selectively oxidized to introduce aldehyde groups to obtain CHO-CMC.

[0017] S2. The CHO-CMC is subjected to a reductive amination reaction with a primary amine-containing intermediate to introduce an active amino group, thereby obtaining NH2-CMC.

[0018] S3. The NH2-CMC and 4-tert-butylbenzenesulfonyl chloride are subjected to a sulfonamide reaction in the presence of an acid-binding agent to obtain the alkali-resistant modified carboxymethyl cellulose sodium.

[0019] Preferably, in step S1, the acidification treatment includes: dissolving the CMC-Na in deionized water to prepare a solution with a mass fraction of 1-5%, adding dilute hydrochloric acid dropwise under stirring to adjust the pH to 2-3, stirring for 30-60 minutes to fully convert the CMC-Na into CMC-H, washing the CMC-H alternately with deionized water and anhydrous ethanol until neutral, and vacuum drying to obtain CMC-H powder;

[0020] The selective oxidation includes: dispersing the CMC-H powder in anhydrous dimethylformamide, adding an oxidant, and stirring the mixture at 25-40°C for 2-6 hours under light-protected and nitrogen-protected conditions to selectively oxidize and open the C2-C3 vicinal diols of the CMC main chain glucose ring, introducing aldehyde sites for subsequent coupling reactions. The reaction is terminated by adding an appropriate amount of ethylene glycol, purified by dialysis with deionized water, and freeze-dried to obtain CHO-CMC.

[0021] Preferably, in step S2, the reductive amination reaction includes: dissolving the CHO-CMC in phosphate buffer, adding an intermediate containing a primary amine group, stirring the reaction at room temperature for 4-8 hours to allow the aldehyde group and amino group to undergo a Schiff base condensation reaction, then adding a reducing agent, and continuing the reaction at room temperature for 12-24 hours to carry out reductive amination, reducing the imine bond to a stable secondary amine bond, and obtaining the intermediate product NH2-CMC containing an active amino group.

[0022] Preferably, in step S2, the primary amine-containing intermediate includes at least one of ethylenediamine, 1,6-hexanediamine, and p-phenylenediamine.

[0023] Preferably, in step S3, the sulfonation reaction includes: dissolving the NH2-CMC in DMF containing triethylamine as an acid-binding agent, adding a DMF solution of 4-tert-butylbenzenesulfonyl chloride dropwise under ice-water bath cooling conditions of 0-5°C, and stirring the reaction under nitrogen protection for 10-24 hours to achieve grafting with the amino group on the CMC side chain through a sulfonation reaction. After the reaction is completed, the product is dialyzed through a dialysis bag to remove unreacted small molecules and byproducts. The resulting solution is concentrated by rotary evaporation and then freeze-dried to obtain the alkali-resistant modified carboxymethyl cellulose sodium.

[0024] Preferably, the molar amount of 4-tert-butylbenzenesulfonyl chloride is 1.0-2.0 equivalents of the molar amount of the amino group introduced; the reaction temperature of the sulfonation reaction is 0-5°C; and the acid-binding agent is triethylamine.

[0025] A third aspect of the present invention is to provide a method for preparing the above-mentioned alkali-resistant modified carboxymethyl cellulose sodium, the steps of which include: swelling CMC-H powder in anhydrous pyridine, and then adding 4-tert-butylbenzenesulfonyl chloride at 0-5°C to carry out an esterification reaction, so that the 4-tert-butylbenzenesulfonyl chloride is covalently linked to the C6 hydroxyl group of the CMC main chain, thereby obtaining the alkali-resistant modified carboxymethyl cellulose sodium.

[0026] A fourth aspect of the present invention is to provide a thickener comprising at least one of modified sodium carboxymethyl cellulose and conventional sodium carboxymethyl cellulose; wherein the modified sodium carboxymethyl cellulose is the above-mentioned alkali-resistant modified sodium carboxymethyl cellulose or the alkali-resistant modified sodium carboxymethyl cellulose prepared by the above-mentioned preparation method.

[0027] Preferably, in the thickener, the mass ratio of the modified sodium carboxymethyl cellulose to the conventional sodium carboxymethyl cellulose is 1:9-9:1.

[0028] A fifth aspect of the present invention is to provide a sodium-ion battery negative electrode slurry, comprising: a hard carbon negative electrode active material, a conductive agent, a binder, the aforementioned thickener, and a solvent.

[0029] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0030] (1) This invention uses 4-tert-butylbenzenesulfonyl group as the alkali-resistant protecting group of the CMC main chain. Through the large steric hindrance of the tert-butyl group, it effectively prevents OH⁻ from approaching the β-1,4-glycosidic bond, inhibiting the alkali degradation reaction at the molecular level and significantly improving the thickening stability of CMC under pH>10 conditions. At room temperature, the modified CMC retains more than 85% of its viscosity after standing in an alkaline solution at pH=11 for 24 hours, while the unmodified CMC retains less than 30% of its viscosity under the same conditions.

[0031] (2) The aromatic ring in the benzenesulfonyl group structure forms a π-σ conjugated system with the sulfonyl group, which enhances the chemical stability of the side group itself, making it less likely to be attacked and removed by OH⁻ under alkaline conditions, thus ensuring the long-term effect of the modification.

[0032] (3) The present invention uses a multi-step synthesis route to covalently link the protecting group to the CMC main chain with stable sulfonamide or ester bonds. Compared with physical blending or weak interactions (such as hydrogen bonding and electrostatic adsorption), the binding is stronger and has good electrochemical inertness and compatibility in the battery negative electrode slurry system.

[0033] (4) The modification route of the present invention is adjustable. The grafting rate can be flexibly controlled by the feeding ratio. In the range of 5-30 mol%, the alkali resistance is enhanced as the grafting rate increases. At the same time, the thickening performance and solubility can be balanced to meet the actual needs of different slurry formulations. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0036] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0037] Example 1

[0038] This embodiment provides a method for preparing alkali-resistant modified sodium carboxymethyl cellulose with a grafting rate of 15 mol%, the steps of which include:

[0039] S1. Dissolve 10g of CMC-Na (DS=0.8, MW=250,000g / mol) in 500mL of deionized water, add 0.1M HCl to adjust the pH to 2.5, stir for 45min, wash until neutral, and vacuum dry to obtain 9.2g of CMC-H; disperse CMC-H in 300mL of anhydrous DMF, add 1.2g of NaIO4 (protected from light), stir at 30℃ for 4h (under nitrogen protection), add 2mL of ethylene glycol, dialyze and freeze dry to obtain 7.8g of CHO-CMC.

[0040] S2. Dissolve CHO-CMC in 200 mL of phosphate buffer (pH=7.0), add 3 mL of ethylenediamine, stir at room temperature for 6 h, add 1.5 g of NaBH3CN and continue the reaction for 16 h, dialyze and freeze dry to obtain 7.2 g of NH2-CMC.

[0041] S3. Dissolve the NH2-CMC in 150 mL of DMF containing 2 mL of triethylamine, cool to 0°C in an ice-water bath, add 2.8 g of DMF solution containing TBSCl (30 mL), stir at 0-5°C for 18 h, and then freeze-dry to obtain 6.5 g of MAR-CMC after dialysis and concentration.

[0042] Example 2

[0043] This embodiment provides a method for preparing alkali-resistant modified sodium carboxymethyl cellulose with a grafting rate of 10 mol%, the steps of which include:

[0044] In step S3, the amount of TBSCl was adjusted to 1.8 g, the reaction time was 12 h, and the rest were the same as in Example 1. The yield of MAR-CMC was 6.1 g. The 4-tert-butylbenzenesulfonyl grafting rate was calculated to be 10.5 mol%.

[0045] Comparative Example 1

[0046] This comparative example provides an aqueous solution of unmodified sodium carboxymethyl cellulose with a concentration of 1.5 wt%.

[0047] Comparative Example 2

[0048] This comparative example provides modified CMC with only benzenesulfonyl groups introduced and no tert-butyl groups.

[0049] The procedure was followed as in Example 1, except that in step S3, benzenesulfonyl chloride (2.1 g, 12.0 mmol) was used instead of 4-tert-butylbenzenesulfonyl chloride (TBSCl). The resulting product was benzenesulfonyl-modified CMC (BS-CMC) with a grafting rate of 15.3 mol%.

[0050] Comparative Example 3

[0051] This comparative example provides a dopamine-grafted CMC.

[0052] 5.0 g of CMC-Na was dissolved in 250 mL of phosphate buffer (pH 5.5), and 2.0 g of dopamine hydrochloride, 1.5 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC·HCl) and 0.9 g of N-hydroxysuccinimide (NHS) were added. The mixture was stirred at room temperature for 24 h. The reaction solution was purified by dialysis and freeze-dried to obtain dopamine-grafted CMC (DA-CMC), with a dopamine grafting rate of 13.8 mol%.

[0053] Comparative Example 4

[0054] This comparative example provides MAR-CMC with an excessively low grafting rate (2 mol%).

[0055] The procedure was the same as in Example 1, except that the amount of TBSCl in step S3 was adjusted to 0.35 g (1.5 mmol). The grafting rate of the resulting MAR-CMC product was only 2.1 mol%.

[0056] Comparative Example 5

[0057] This comparative example provides MAR-CMC with an excessively high grafting rate (40 mol%).

[0058] The procedure was the same as in Example 1, except that in step S3, the amount of TBSCl was adjusted to 8.0 g (34.3 mmol), and excess NaBH3CN was used to extend the reaction time to 48 h. The grafting rate of the obtained MAR-CMC product was approximately 40 mol%.

[0059] Detection Examples

[0060] The pH was adjusted to 11 with NaOH solution, and the initial viscosity and viscosity after standing for 24 hours of CMC in Examples 1-2 and Comparative Examples 1-5 were measured at room temperature. The results are shown in Table 1.

[0061] Table 1

[0062]

[0063] Comparative Example 5's MAR-CMC exhibits extremely poor solubility in water, requiring prolonged heating and stirring for partial dissolution, resulting in a turbid suspension rather than a clear solution. At a concentration of 1.5 wt%, its viscosity is significantly lower than that of unmodified CMC and products with low grafting rates. Compared to conventional CMC, the modified CMC shows better viscosity retention after 24 hours in an alkaline solution at pH 11, with better performance within the grafting rate range of 10-20 mol%.

[0064] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. An alkali-resistant modified sodium carboxymethyl cellulose, characterized in that, include: The main chain and the modified side chain containing 4-tert-butylbenzenesulfonyl group, wherein the modified side chain containing 4-tert-butylbenzenesulfonyl group is covalently connected to the main chain.

2. The alkali-resistant modified carboxymethyl cellulose sodium according to claim 1, characterized in that, The grafting rate of the modified side chain containing 4-tert-butylbenzenesulfonyl group is 5-30 mol, based on glucosinolate units.

3. The alkali-resistant modified carboxymethyl cellulose sodium according to claim 1, characterized in that, The covalent bond is a sulfonamide bond or an ester bond.

4. The alkali-resistant modified carboxymethyl cellulose sodium according to claim 1, characterized in that, The alkali-resistant modified sodium carboxymethyl cellulose has a molecular weight of 100,000-800,000 g / mol and a degree of carboxymethyl substitution of 0.6-1.

2.

5. A method for preparing alkali-resistant modified carboxymethyl cellulose sodium as described in any one of claims 1-4, characterized in that, step include: S1. CMC-Na is acidified and then selectively oxidized to introduce aldehyde groups to obtain CHO-CMC. S2. The CHO-CMC is subjected to a reductive amination reaction with a primary amine-containing intermediate to introduce an active amino group, thereby obtaining NH2-CMC. S3. The NH2-CMC and 4-tert-butylbenzenesulfonyl chloride are subjected to a sulfonamide reaction in the presence of an acid-binding agent to obtain the alkali-resistant modified carboxymethyl cellulose sodium.

6. The preparation method according to claim 5, characterized in that, In step S2, the primary amine-containing intermediate includes at least one of ethylenediamine, 1,6-hexanediamine, and p-phenylenediamine.

7. The preparation method according to claim 5, characterized in that, The molar amount of 4-tert-butylbenzenesulfonyl chloride is 1.0-2.0 equivalents of the molar amount of the amino group introduced; the reaction temperature of the sulfonation reaction is 0-5℃; and the acid-binding agent is triethylamine.

8. A method for preparing alkali-resistant modified carboxymethyl cellulose sodium as described in any one of claims 1-4, characterized in that, step include: After CMC-H powder is swollen in anhydrous pyridine, 4-tert-butylbenzenesulfonyl chloride is added at 0-5°C to carry out an esterification reaction, so that the 4-tert-butylbenzenesulfonyl chloride is covalently linked to the C6 hydroxyl group of the CMC main chain, thus obtaining the alkali-resistant modified carboxymethyl cellulose sodium.

9. A thickener, characterized in that, include: At least one of modified carboxymethyl cellulose sodium and conventional carboxymethyl cellulose sodium; wherein the modified carboxymethyl cellulose sodium is the alkali-resistant modified carboxymethyl cellulose sodium as described in any one of claims 1-4, or the alkali-resistant modified carboxymethyl cellulose sodium prepared by the preparation method as described in any one of claims 5-7, or the alkali-resistant modified carboxymethyl cellulose sodium prepared by the preparation method as described in claim 8.

10. A sodium-ion battery negative electrode slurry, characterized in that, include: Hard carbon negative electrode active material, conductive agent, binder, thickener as described in claim 9, and solvent.

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