Preparation method of modified lithium carboxymethyl cellulose for lithium ion battery

Abstract

The present invention discloses a preparation method of modified lithium carboxymethyl cellulose for lithium-ion batteries, belonging to the technical field of chemical modification of natural polymer materials. In the present invention, decarboxylation and acidification are carried out simultaneously, and hydrolysis and lithiation are carried out simultaneously, and the preparation and purification are simple; a branched structure is grafted onto lithium carboxymethyl cellulose, and additional carboxyl and hydroxyl groups are introduced after grafting and hydrolysis. The lithium content of the obtained modified lithium carboxymethyl cellulose is higher than that of ordinary lithium carboxymethyl cellulose, and the grafted branched polymer contains a multi-hydrogen bond structure, and the adhesion performance is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical modification of natural polymer materials, and specifically relates to a preparation method of modified lithium carboxymethyl cellulose for lithium-ion batteries. Background Art

[0002] Lithium carboxymethyl cellulose is a carboxymethylated derivative of cellulose and is a water-soluble ionic cellulose ether obtained through chemical modification. Because lithium carboxymethyl cellulose has the properties of thickening, water retention, emulsification, and dispersion in water, it is applied in lithium batteries. As a novel auxiliary material for the negative electrode binder of lithium batteries, lithium carboxymethyl cellulose mainly plays two roles. One is to act as an adhesive to tightly bond the negative electrode active materials such as graphite and silicon-carbon in the negative electrode and the current collector, maintaining the stability of the battery during charge and discharge. The other is to act as an auxiliary lithium supplement material to provide a lithium ion reservoir, which can improve the charge-discharge specific capacity and rate performance of lithium batteries.

[0003] In the prior art, the main synthesis methods of CMC-Li are as follows: (1) Direct lithiation method: Starting from cellulose raw materials, alkalization is directly carried out and carboxymethyl is introduced, and then lithiation is completed with lithium compounds, avoiding sodium salt intermediates, but the substitution rate of CMC-Li is relatively low; (2) Acidification-lithium salt exchange method: First, sodium carboxymethyl cellulose (CMC-Na) is converted into acid-type carboxymethyl cellulose (H-CMC), and then it reacts with lithium salt to displace H + for Li + to generate CMC-Li. The purity is relatively high, but if the acidification is incomplete, Na + may remain; (3) Ion exchange method: Through cation exchange resin or solution exchange, Na + in CMC-Na is replaced with Li + . The exchange efficiency is high and the product purity is good, but the cost is relatively high and the time consumption is long. Patent CN 115636882 uses lithium diisopropylamide and uses butyllithium as an auxiliary reagent to activate and alkalize cellulose, and then carries out an etherification reaction to finally obtain lithium carboxymethyl cellulose, overcoming the defect that LiOH has insufficient contact with cellulose during the alkalization process and the alkalization degree is low. However, the lithium diisopropylamide and butyllithium used in it have high activity and need to react in an anhydrous solvent at low temperature, with high cost and great danger. Summary of the Invention

[0004] To overcome the deficiencies of the above-mentioned prior art, the present invention provides a method for preparing modified lithium carboxymethyl cellulose for lithium-ion batteries. In the present invention, decarboxylation and acidification are carried out simultaneously, and hydrolysis and lithiation are carried out simultaneously. The preparation and purification are simple. After grafting and hydrolysis, additional carboxyl groups and hydroxyl groups are introduced. The lithium content of the obtained modified lithium carboxymethyl cellulose is higher than that of ordinary lithium carboxymethyl cellulose. The grafted and branched polymer contains a multi-hydrogen bond structure, and the adhesion performance is enhanced.

[0005] The technical solution for achieving the purpose of the present invention is as follows: A method for preparing modified lithium carboxymethyl cellulose for lithium-ion batteries, comprising the following steps:

[0006] (1) Decarboxylation and acidification: Under an inert gas atmosphere, sodium carboxymethyl cellulose and a peroxide are dispersed in water, and silver nitrate is dispersed in a solvent. After mixing, stir at 40-50 °C for at least 5 min;

[0007] (2) Grafting: A carboxylic acid monomer, a hydroxyl monomer, and silver nitrate are dispersed in a solvent. After mixing, add them to step (1). After stirring at 50-70 °C for at least 1 h, perform vacuum filtration. After filtration, wash the solid with alcohol and deionized water successively at least 2 times to obtain a grafted polymer;

[0008] (3) Hydrolysis and lithiation: Add the grafted polymer obtained in step (2) to an aqueous lithium hydroxide solution and alcohol successively for hydrolysis and lithiation. After stirring until the solid dissolves, continue stirring to obtain a crude product of lithium carboxymethyl cellulose;

[0009] (4) Purification: Neutralize, filter, wash, dry, and pulverize the crude product of lithium carboxymethyl cellulose prepared in step (3) to obtain modified lithium carboxymethyl cellulose;

[0010] The carboxylic acid monomer has one or more of the molecular structures in Formula I as follows:

[0011] 、 、 and , in Formula I, R1 is one or more of methyl, ethyl, or hydrogen, and n is 1-10;

[0012] The hydroxyl monomer has one or more of the molecular structures in Formula II as follows:

[0013] 、 、 and , in Formula II, R1 is one or more of methyl, ethyl, or hydrogen, m is 1-10, and i is 0-5;

[0014] In the carboxylic acid monomer and the hydroxyl monomer, at least one monomer contains a maleimide structure.

[0015] In steps (1) and (2) of the present invention, silver-catalyzed decarboxylative radical polymerization is carried out. The carboxyl groups in sodium carboxymethyl cellulose are removed to form free radicals, which initiate the polymerization of carboxylic acid monomers and hydroxyl monomers. In step (2), a part of silver nitrate is added to remove the carboxyl groups of the carboxylic acid monomers to form free radicals, further initiating the polymerization to form a branched structure, forming a branched imide and hydroxyl structure. That is, in step (1), silver-catalyzed decarboxylation can remove some of the carboxyl groups in sodium carboxymethyl cellulose, and in an acidic solution, the remaining sodium carboxylate is converted into a carboxylic acid structure. The purpose of step (2) is to introduce imide, hydroxyl and a small amount of carboxyl structures. Finally, the obtained solid structure is further washed with deionized water to remove the contained Na + .

[0016] In the present invention, the degree of branching of the grafted product is adjusted by adjusting the content and ratio of silver nitrate in steps (1) and (2).

[0017] During the polymerization in step (2), by adjusting the size of the rigid imide ring, acrylamide or acrylate structure and m, n, and i in the molecular structures of the above formula I and formula II, the molecular weight of the grafted polymer and the viscosity after hydrolysis are adjusted. The specific mechanism is as follows: (i) When the proportion of the rigid imide ring increases, as the polymerization proceeds, the molecular weight gradually increases, and the rigid structure leads to a decrease in its solubility in the solvent, resulting in a decrease in water solubility and the precipitation of the product; (ii) When the proportion of acrylamide or acrylate structures increases, the rigidity of the polymer is reduced, and a higher molecular weight is required for the polymer to precipitate; (iii) When m and n in the molecular structures of formula I and formula II increase, although the flexibility of the polymer can be increased to a certain extent, when the hydrophobic structure is too large, the water solubility of the polymer will be reduced, and it will also cause it to precipitate prematurely; (iv) When i in the molecular structures of formula I and formula II increases, its structure can increase both its water solubility and flexibility, but too long a chain will lead to a decrease in viscosity. That is, the introduction of the imide ring and hydrophobic structure causes the polymer to have poor solubility and thus precipitate, and a relatively pure intermediate product can be obtained through simple treatment.

[0018] The second function of introducing the cyclic imide structure in the present invention is that the imide ring structure is an unstable structure under alkaline conditions and can be hydrolyzed by LiOH. After hydrolysis, the five-membered ring opens, losing its rigid structure, and a large number of lithium carboxylate structures are introduced, which greatly increases the flexibility and hydrophilicity of the polymer and has good solubility in water. The specific mechanism is as follows:

[0019]

[0020] It should be noted that the amide group is very stable and will not be easily hydrolyzed by ordinary strong bases below 80 °C. Hydrazine or hydroxylamine is mostly used to hydrolyze amides.

[0021] Based on the above mechanism summary, in the present invention, the structure and molecular weight of the grafted polymer are controlled by the monomer structure and ratio and the silver nitrate content, so as to obtain modified lithium carboxymethyl cellulose with different viscosities. By controlling the hydrolysis and ring-opening of cyclic imide to control its water solubility, a low-Na intermediate product is obtained through acidification, decarboxylation, grafting and purification in steps (1) and (2). + In step (3), hydrolysis with LiOH gives water-soluble modified lithium carboxymethyl cellulose with a very high Li content.

[0022] Preferably, in step (1), the content of sodium carboxymethyl cellulose in the aqueous solution is 1-2 wt.%, the content of the peroxide in the aqueous solution is 2.0-4.0 wt.%, the solvent is at least one of tetrahydrofuran and acetonitrile, and the content of silver nitrate in the solvent is 0.025-0.20 wt.%.

[0023] Preferably, in step (2), the content of the carboxylic acid monomer in the solvent is 0.1-2.0 wt.%, the content of the hydroxyl monomer in the solvent is 2.0-6.0 wt.%, and the content of silver nitrate in the solvent is 0.025-0.20 wt.%.

[0024] Preferably, the volume ratio of the water in step (1) to the solvent in step (1) is 1:(0.2-0.8), and the volume ratio of the water in step (1) to the solvent in step (2) is 1:(0.2-0.8).

[0025] Preferably, in step (3), the mass fraction of the lithium hydroxide aqueous solution is 5-12 wt.%; the volume ratio of the alcohol to the lithium hydroxide aqueous solution is (1:1)-(1:3), the alcohol is at least one of methanol and ethanol, and the temperature of the hydrolysis and lithiation reaction is 20-50 °C, and the reaction time is 5-60 min after stirring until all the solids are dissolved and then continuing to stir.

[0026] Preferably, in step (4), the neutralization treatment is to add glacial acetic acid to adjust the pH to 7-9, the washing is carried out with at least one of water and ethanol; the drying is at least one of drying at 60-70 °C under vacuum and drying at 90-110 °C under normal pressure; the particle size of the modified lithium carboxymethyl cellulose obtained after the crushing treatment is not less than 200 mesh.

[0027] Beneficial effects

[0028] The present invention has the following beneficial effects: The decarboxylation and acidification of the present invention are carried out simultaneously, and the hydrolysis and lithiation are carried out simultaneously. By utilizing the rigid structure of polyimide to reduce the solubility of the product and its characteristic of being easily hydrolyzed under alkaline conditions, the preparation and purification are very convenient, and the obtained product has a relatively high purity. During hydrolysis, the polyimide ring opens to lose its rigid structure, increasing the flexibility of the polymer, and the carboxylic acid lithium structure is formed to enhance water solubility. The lithium content of the obtained modified lithium carboxymethyl cellulose is higher than that of ordinary lithium carboxymethyl cellulose. The grafted and branched polymer contains more hydrogen bond structures, and the branched structure and the linear structure can form a semi-interpenetrating network structure and multiple hydrogen interactions to improve its adhesion performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the synthesis and structure of the modified lithium carboxymethyl cellulose of the present invention;

[0030] Figure 2 It is a partial infrared spectrum diagram of the modified lithium carboxymethyl cellulose of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] The technical solutions in the embodiments of 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 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 belong to the protection scope of the present invention.

[0032] In the embodiments, the experimental methods used are all conventional methods unless otherwise specified, and the materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified.

[0033] The raw materials and equipment used in the examples and comparative examples are described as follows:

[0034] Sodium carboxymethyl cellulose: self-made or commercially available, M.W. 250000 (DS = 0.9), 1500 - 3100 mPa·s;

[0035] Silver nitrate: purchased from Sinopharm Reagent;

[0036] Peroxide: potassium persulfate, purchased from Sinopharm Reagent;

[0037] Ethanolamine: purchased from Macklin;

[0038] Diethanolamine: purchased from Wengjiang Reagent;

[0039] 1-(2-Aminoethoxy)-2-methoxyethane: purchased from Shanghai Bide Pharmaceutical;

[0040] Amino poly(ethylene glycol) monomethyl ether: MW: 600, purchased from Wengjiang Reagent;

[0041] β-alanine: purchased from Energy Chemical;

[0042] Maleic anhydride: purchased from Macklin;

[0043] Acryloyl chloride: purchased from Macklin;

[0044] Lithium hydroxide: purchased from Macklin;

[0045] Polyvinylidene fluoride (PVDF): purchased from Macklin;

[0046] Carboxylic acid monomer 1: Acrylic acid, purchased from Macklin;

[0047] Carboxylic acid monomer 2: Obtained by acylating acryloyl chloride with β-alanine or commercially available;

[0048] Hydroxy monomer 1: Obtained by reacting maleic anhydride with ethanolamine or commercially available;

[0049] Hydroxy monomer 2: Obtained by reacting maleic anhydride with diethylene glycol amine or commercially available;

[0050] Hydroxy monomer 3: Obtained by reacting maleic anhydride with amino polyethylene glycol monomethyl ether or commercially available;

[0051] Hydroxy monomer 4: Obtained by acylating acryloyl chloride with ethanolamine or commercially available.

[0052] The following are the test methods for the performance parameters involved in the present invention:

[0053] Determination of molecular weight and polydispersity index (PDI) by gel permeation chromatography: The molecular weight was detected by GPC method on a high performance liquid chromatography (HPLC) (Agilent HPLC 1260 InfinityII, Agilent PL aquagel-OH 508um column). The Agilent 1260 Infinity II liquid chromatography system has the hardware basis of gel permeation chromatography (GPC), which can support multi-column switching, and the number average molecular weight was tested using a gel chromatography column.

[0054] Viscosity measurement: Weigh 5.0 g each of the modified lithium carboxymethylcellulose, sodium carboxymethylcellulose, and PVDF in the examples and comparative examples that have been dried at 105 °C for 2 h, accurate to 0.001 g for standby. Take multiple wide-mouth bottles, measure 495 ml of water into each wide-mouth bottle, place each wide-mouth bottle on a heating mantle, adjust the rotation speed to 200 - 400 r / min, add each sample to different wide-mouth bottles respectively, slowly adjust the stirring speed to 900 r / min, and stir for about 2 h until the sample is completely dissolved and homogenized. Then conduct the test using a DV2T viscometer.

[0055] Peel test: The evaluation of adhesion performance is usually carried out through peel strength testing. When conducting the peel strength test, first paste the pre-prepared electrode sheet onto the aluminum plate substrate, and then firmly paste it onto the surface of the electrode coating with 3M tape. The specific operation is to stick a 120×25 mm electrode sample on the 3M transparent tape, stick it on the coating, and pull it at a 180° angle. Record the force required to pull the tape at a fixed speed of 100 mm / min; The preparation method of the electrode sheet is as follows: Weigh graphite:acetylene black:SBR:modified lithium carboxymethylcellulose (or other binder) with a mass ratio of 95:1.5:1.5:2 respectively. Dissolve the modified lithium carboxymethylcellulose (binder) through a solvent, and appropriately add solvent according to the viscosity of the solution. Add the weighed graphite and acetylene black into an agate mortar for grinding. After mixing evenly, add the dissolved modified lithium carboxymethylcellulose (or other binder), and add an appropriate amount of solvent again according to the viscosity of the slurry. Seal the small beaker with plastic wrap and place it on a stirrer for stirring for 12 h. Coating the stirred electrode slurry on a copper foil that has been wiped with anhydrous ethanol and dried to obtain an electrode plate. Place the electrode plate in an oven at 50 °C for drying for 12 h to obtain the electrode sheet.

[0056] Example 1

[0057] A preparation method of modified lithium carboxymethylcellulose for lithium-ion batteries, comprising the following steps:

[0058] (1) Decarboxylation and acidification: Under an inert gas atmosphere, disperse 20 g of sodium carboxymethylcellulose and 40 g of peroxide in 1000 ml of water, disperse 0.4 g of silver nitrate in 500 ml of tetrahydrofuran, mix them, and stir at 50 °C for 10 min;

[0059] (2) Grafting: Disperse 5 g of carboxylic acid monomer 1, 25 g of hydroxyl monomer 1, and 0.2 g of silver nitrate in 500 ml of tetrahydrofuran, mix them, and add them to step (1). After stirring at 65 °C for 3 h, perform vacuum filtration, wash the solid with alcohol and deionized water twice in sequence. After filtration, obtain the grafted polymer;

[0060] (3) Hydrolysis and lithiation: The grafted polymer obtained in step (2) was successively added with an aqueous lithium hydroxide solution with a concentration of 12 wt.% and methanol, and the volume ratio of the aqueous lithium hydroxide solution to methanol was 1:1. Hydrolysis and lithiation were carried out at a temperature of 35 °C. After stirring until the solid was dissolved, stirring was continued for 20 min to obtain crude lithium carboxymethyl cellulose;

[0061] (4) Purification: Glacial acetic acid was added to the crude lithium carboxymethyl cellulose prepared in step (3) to adjust the pH to 8. The obtained solid after filtration was washed successively with water and ethanol 3 times, dried at 90 °C under normal pressure, and pulverized to no less than 200 mesh to obtain modified lithium carboxymethyl cellulose 1.

[0062] Example 2

[0063] Compared with the preparation method of Example 1, the difference lies in that 0.2 g of silver nitrate in step (2) was replaced by 0.4 g.

[0064] Example 3

[0065] Compared with the preparation method of Example 1, the difference lies in that 5 g of carboxylic acid monomer 1 and 25 g of hydroxyl monomer 1 in step (2) were replaced by 10 g of carboxylic acid monomer 1 and 20 g of hydroxyl monomer 1.

[0066] Example 4

[0067] Compared with the preparation method of Example 1, the difference lies in that 5 g of carboxylic acid monomer 1 in step (2) was replaced by 5 g of carboxylic acid monomer 2.

[0068] Example 5

[0069] Compared with the preparation method of Example 1, the difference lies in that 25 g of hydroxyl monomer 1 in step (2) was replaced by 25 g of hydroxyl monomer 2.

[0070] Comparative Example 1

[0071] Compared with the preparation method of Example 1, the difference lies in that 25 g of hydroxyl monomer 1 in step (2) was replaced by 25 g of hydroxyl monomer 3. During preparation, the solid could not precipitate in step (2), and after removing the solvent, a fractional precipitation method was required for purification, and the treatment was relatively complex.

[0072] Comparative Example 2

[0073] Compared with the preparation method of Example 1, the difference lies in that 25 g of hydroxyl monomer 1 in step (2) was replaced by 25 g of hydroxyl monomer 4.

[0074] Comparative Example 3

[0075] Sodium carboxymethyl cellulose was used.

[0076] Comparative Example 4

[0077] PVDF was used.

[0078] Molecular weight test example: In an inert gas atmosphere, carboxylic acid monomer 2 and peroxide were dispersed in water. After mixing, carboxylic acid monomer, hydroxyl monomer, and silver nitrate solution were added. Carboxymethyl cellulose sodium was replaced with carboxylic acid monomer 2, and the free radicals formed after decarboxylation were used as initiators. The subsequent added carboxylic acid monomer and hydroxyl monomer were monomers, and the molar ratio of initiator to monomer was 1:30. The structures or ratios of carboxylic acid monomer, hydroxyl monomer, peroxide, and silver nitrate were polymerized according to those in Examples 1 - 5 and Comparative Examples 1 - 2, and the molecular weight and degree of branching were measured.

[0079] Table 1 Molecular weight test of corresponding ratios in examples and comparative examples

[0080]

[0081] The data in Table 1 are the properties of the branched polymers initiated by small molecules. Based on this, the properties of modified lithium carboxymethyl cellulose were inferred. From the data in Table 1, it can be seen that the molecular weights of Examples 1 and 2 are close, but the PDI of Example 2 is larger. In the ratio of Example 2, the content of silver nitrate catalyst in step (2) increases, resulting in an increase in the degree of branching; the PDI of Example 3 is slightly larger than that of Example 1, and the molecular weight is also larger. Compared with Example 1, the proportion of carboxyl monomer 1 in Example 3 increases. Since carboxyl monomer 1 does not contain a rigid ring structure, while hydroxyl monomer 1 is a cyclic structure, the solubility of the polymer is better than that of Example 1, so its molecular weight is larger; compared with Example 1, the molecular weight and PDI of Example 4 both increase slightly. This is because the structure of carboxylic acid monomer 2 has less steric hindrance at the carboxyl group compared to carboxylic acid monomer 1 and is more easily initiated; compared with Example 1, the molecular weight of Example 5 increases slightly because the flexible group introduced by hydroxyl monomer 2 is longer. In Comparative Example 1, a long hydroxyl monomer was introduced, so the solubility is better and the molecular weight increases significantly; the molecular weight increase in Comparative Example 2 is even greater because no rigid monomer was used.

[0082] Table 2 Performance test of examples and comparative examples

[0083]

[0084] As can be seen from Table 2, the effect of Example 2 is better than that of Example 1 because the degree of branching in Example 2 is higher and the hydrogen bond interaction is more obvious. The performance of Example 3 is better than that of Example 1. The molecular weight of Example 3 is larger, indicating a higher degree of polymerization and slightly more hydrogen bonds than Example 1. Therefore, its hydrogen bonds and intermolecular forces are better than those of Example 1. The viscosity and peel strength of Example 4 are the largest. Compared with other examples, 5 g of carboxylic acid monomer 1 in Example 4 is replaced with 5 g of carboxylic acid monomer 2. As can be seen from Table 1, the polymer grafted on the surface of Example 4 has a larger degree of branching. In addition, carboxylic acid monomer 2 contains N-H bonds, further enhancing the intermolecular hydrogen bond interaction. The performance of Example 5 is also better than that of Example 1, with the same mechanism as Example 3. Comparative Example 1 is synthesized using hydroxy monomer 3, which is obtained from maleic anhydride and amino polyethylene glycol monomethyl ether. Compared with Example 1 and Example 5, it has a larger steric hindrance and no hydroxyl group at the end, reducing the interaction between cellulose and thus reducing the viscosity. Comparative Example 2 does not use a rigid structure and has a larger molecular weight. However, since there is no imide group, it cannot be hydrolyzed to obtain a lithium carboxylate structure. Therefore, the hydrogen bond interaction is greatly reduced, and the molecular structure has good water solubility and is difficult to purify. Comparative Examples 3 and 4 are comparative tests of sodium carboxymethyl cellulose and polyvinylidene fluoride, and their performance is also inferior to that of the modified lithium carboxymethyl cellulose prepared in the examples of the present invention.

[0085] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and utilize the present invention well. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for preparing modified carboxymethyl cellulose lithium for lithium ion batteries, characterized in that: The following steps are involved: (1) Decarboxylation and acidification: In an inert gas atmosphere, disperse sodium carboxymethyl cellulose and peroxide in water, disperse silver nitrate in a solvent, mix and stir at 40-50 °C for at least 5 min; (2) Grafting: disperse the carboxylic acid monomer, hydroxyl monomer and silver nitrate in a solvent, mix and add to the mixture of step (1), heat to 50-70°C and stir for at least 1 hour, vacuum filter, wash with alcohol and deionized water at least twice in sequence, filter to obtain a grafted polymer; (3) Hydrolysis and lithiation: The grafted polymer obtained in step (2) is sequentially added with a lithium hydroxide aqueous solution and an alcohol for hydrolysis and lithiation, and stirred until the solid is dissolved, and then continued to stir to obtain a crude product of lithium carboxymethyl cellulose; (4) Purification: neutralizing, washing, drying and pulverizing the crude lithium carboxymethyl cellulose obtained in step (3) to obtain modified lithium carboxymethyl cellulose; In step (1), the content of sodium carboxymethyl cellulose in the aqueous solution is 1-2 wt.%, the content of peroxide in the aqueous solution is 2.0-4.0 wt.%, and the content of silver nitrate in the solvent is 0.025-0.20 wt.%; In step (2), the content of the carboxylic acid monomer in the solvent is 0.1-2.0 wt.%, the content of the hydroxyl monomer in the solvent is 2.0-6.0 wt.%, and the content of the silver nitrate in the solvent is 0.025-0.20 wt.%; The carboxylic acid monomer has one or more of the following molecular structures: , , and , in Formula I, R1 is one or more of methyl, ethyl or hydrogen, and n is 1 to 10; The hydroxyl monomer has one or more of the following molecular structures: , , and , in formula II, R1 is one or more of methyl, ethyl or hydrogen, m is 1 to 10, and i is 0 to 5; At least one of the carboxylic acid monomer and the hydroxyl monomer contains a maleimide structure.

2. The method for preparing modified carboxymethyl cellulose lithium for lithium ion batteries according to claim 1, characterized in that: The solvent in step (1) is at least one of tetrahydrofuran and acetonitrile.

3. The method for preparing modified carboxymethyl cellulose lithium for lithium ion batteries according to claim 1, characterized in that: The volume ratio of the water in step (1) to the solvent in step (1) is 1:(0.2-0.8), and the volume ratio of the water in step (1) to the solvent in step (2) is 1:(0.2-0.8).

4. The method for preparing modified carboxymethyl cellulose lithium for lithium ion batteries according to claim 1, characterized in that: In step (3), the mass fraction of the lithium hydroxide aqueous solution is 5-12 wt.%; the volume ratio of the alcohol to the lithium hydroxide aqueous solution is (1:1)-(1:3), the alcohol is at least one of methanol and ethanol, the temperature of the hydrolysis and lithiation reaction is 20-50°C, and the reaction time is stirring until the solid is completely dissolved and then continuing to stir for 5-60 min.

5. The method for preparing modified carboxymethyl cellulose lithium for lithium ion batteries according to claim 1, characterized in that: The neutralization treatment in step (4) is to add glacial acetic acid to adjust the pH to 7-9, the washing is performed by at least one of water and ethanol; the drying is performed by at least one of vacuum drying at 60-70°C and normal pressure drying at 90-110°C; the particle size of the modified lithium carboxymethyl cellulose obtained after the pulverization treatment is not less than 200 mesh.

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