A lithium battery anode binder of modified lithium carboxymethyl cellulose

Abstract

The present invention discloses a lithium battery anode binder of modified lithium carboxymethylcellulose, belonging to the technical field of lithium ion batteries. The modified lithium carboxymethylcellulose of the present invention is prepared by grafting acrylic acid monomers and sulfonic acid monomers onto carboxymethylcellulose, followed by acidification, lithiation, crosslinking with cystine, and surface modification with 2-(3,4-dihydroxyphenyl)ethylamine. By grafting copolymer long chains of acrylic acid monomers and sulfonic acid monomers onto the main chain of carboxymethylcellulose, additional carboxyl groups and sulfonic acid groups are introduced, and cystine with disulfide bonds is introduced as a crosslinking agent, and 2-(3,4-dihydroxyphenyl)ethylamine with catechol groups is used as a tackifier to prepare modified lithium carboxymethylcellulose. The obtained modified lithium carboxymethylcellulose not only has a higher lithium content than ordinary lithium carboxymethylcellulose, but also has enhanced binding performance, improved toughness, and enhanced cycling performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a lithium battery anode binder of modified lithium carboxymethyl cellulose. Background Art

[0002] Commercial lithium-ion batteries generally use graphite as the anode material, but its theoretical capacity is only , and when applied to electric vehicles, it can only provide energy density, which cannot meet the current electrification requirements. Silicon has an extremely high theoretical capacity ( ), the voltage for the lithium-ion insertion / extraction reaction is only 0.4V, and it has abundant natural reserves, mature mining and processing technologies, is non-toxic and environmentally friendly, and is expected to replace graphite as the next-generation lithium-ion battery anode material. However, the commercial application of silicon-based anode materials still needs to solve the problem of 300% volume expansion during the cycle (Li 15 Si4 is generated during the lithiation process).

[0003] The binder is a crucial auxiliary functional material in lithium-ion batteries, and its main function is to bond the active material, conductive agent, and current collector together. This bonding ensures the cohesive connection between materials and prevents the active material from decomposing due to chemical and mechanical stresses during continuous charging and discharging. In addition, the binder plays a key role in forming a continuous electronic network, helps to form effective electronic and ionic pathways, reduces the internal resistance of the battery, and promotes good electronic and ionic conductivity within the battery. Therefore, the binder plays a crucial role in improving the overall performance of lithium-ion batteries.

[0004] At present, oil-based binders represented by polyvinylidene fluoride (PVDF) and water-based binders represented by styrene-butadiene rubber (SBR) emulsion / carboxymethyl cellulose (CMC) are the two most widely used types of binders in commercial applications. Biomass-derived CMC binders contain polar functional groups such as hydroxyl and carboxylic acid groups, which can form strong interactions with active materials or current foils through dipole-dipole interactions or secondary valence forces. From a mechanical perspective, CMC chains are relatively hard and brittle. However, early studies have shown that CMC is a very suitable binder for silicon-based anodes. When CMC is used alone as a binder for silicon-based anodes, the battery cycling performance is better than that of tough CMC / SBR and PVDF binders. However, CMC has high rigidity and a low elongation at break (5-8%), and cannot completely eliminate the stress caused by the volume expansion of silicon-based anode materials during cycling. Therefore, cracks often occur during repeated cycling, resulting in a significant attenuation of battery capacity; while SBR has certain elasticity, but its binding ability is weak, and the carbon-carbon double bonds will degrade during the charge and discharge process of the battery, causing the binder to fail; in addition, during the insertion and extraction of lithium ions in the battery, charges are likely to activate the ionization of CMC-Na, and the released sodium ions may exchange with lithium ions in the cathode material or electrolyte, leading to the problem of lithium deposition. Summary of the Invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a lithium-modified carboxymethyl cellulose lithium battery anode binder. By grafting acrylic acid monomers and sulfonic acid group monomers copolymer long chains on the main chain of carboxymethyl cellulose, introducing additional carboxyl groups and sulfonic acid groups, and introducing cystine with disulfide bonds as a cross-linking agent and 2-(3,4-dihydroxyphenyl)ethylamine with catechol groups as a tackifier, lithium-modified carboxymethyl cellulose is prepared. The obtained lithium-modified carboxymethyl cellulose not only has a higher lithium content than ordinary lithium carboxymethyl cellulose, but also has enhanced binding performance, improved toughness and enhanced cycling performance.

[0006] The technical solutions for achieving the object of the present invention are as follows:

[0007] A lithium battery anode binder of modified carboxymethyl cellulose lithium, and the preparation method of the modified carboxymethyl cellulose lithium includes the following steps:

[0008] S1. Grafting: Dissolve carboxymethyl cellulose in water, add acrylic acid monomers, sulfonic acid group monomers, and initiator, and stir and react at 40-60°C for 2-4 hours under anaerobic conditions. Add NaOH for neutralization and purify to obtain a CMC-Na graft copolymer;

[0009] S2. Acidification: Disperse the CMC-Na graft copolymer in an ethanol solution, add hydrochloric acid and stir and react for 2-4 hours, then wash with an ethanol solution and dry to obtain a CMC-H graft copolymer;

[0010] S3. Lithiation: Disperse the CMC-H copolymer in an aqueous solution of ethanol, add a LiOH solution at 40 - 60 °C to adjust the pH to 9 - 10, stir for 2 - 10 hours, then add acetic acid to adjust the pH to 7 - 8, filter, wash with an ethanol solution, and dry to obtain the CMC-Li graft copolymer;

[0011] S4. Crosslinking: Disperse the CMC-Li graft copolymer in an MES buffer solution, add EDC and NHS to activate the carboxyl groups, add cystine and stir for 4 - 8 h, then add 2-(3,4-dihydroxyphenyl)ethylamine and continue to react for 4 - 8 h, wash with an ethanol solution, and dry to obtain the modified lithium carboxymethylcellulose.

[0012] Preferably, in step S1, the mass ratio of the acrylic acid monomer, the sulfonic acid group monomer to the carboxymethylcellulose is (2 - 5):(0.5 - 1):1.

[0013] Preferably, the acrylic acid monomer is selected from at least one of acrylic acid and methacrylic acid; the sulfonic acid group monomer is selected from at least one of 2-acrylamido-2-methylpropanesulfonic acid and sodium p-styrenesulfonate.

[0014] Preferably, the initiator is ammonium persulfate and sodium bisulfite, and the addition amount of the initiator is 0.5 - 1 wt% of the total mass of the monomers.

[0015] Preferably, the carboxymethyl substitution degree of the carboxymethylcellulose is 0.7 - 1.4.

[0016] Preferably, the molar amount of cystine is 5 - 10 mol% of the total molar amount of the carboxyl groups and sulfonic acid groups of the CMC-Li graft copolymer, and the molar amount of 2-(3,4-dihydroxyphenyl)ethylamine is 1 - 5 mol% of the total molar amount of the carboxyl groups and sulfonic acid groups of the CMC-Li graft copolymer.

[0017] Preferably, the hydrochloric acid in step S2 is a hydrochloric acid solution with a mass concentration of 10 - 20 wt%, and the added molar amount of hydrochloric acid is 2 - 4 times the total molar content of the carboxyl groups and sulfonic acid groups of the CMC-Na graft copolymer.

[0018] Preferably, the LiOH solution in step S3 is a LiOH solution with a mass concentration of 5 - 10 wt%, and the added molar amount of LiOH is 1.5 - 3 times the total molar amount of the carboxyl groups and sulfonic acid groups of the CMC-Na graft copolymer.

[0019] Preferably, the ethanol solution is an ethanol aqueous solution with a volume concentration of 85 - 95%.

[0020] Beneficial effects

[0021] The present invention provides a lithium battery anode binder of modified carboxymethyl cellulose lithium, which has the following beneficial effects: (1) Long carbon chains with carboxyl groups and sulfonic acid groups are grafted onto the linear segments of carboxymethyl cellulose, increasing the content of anionic groups such as carboxyl groups and sulfonic acid groups in carboxymethyl cellulose, thereby increasing the binding sites on the surface of silicon and improving the bonding ability with the silicon anode; (2) Cystine with dynamic disulfide bonds is introduced as a crosslinking agent in the carboxymethyl cellulose and acrylic acid-sulfonic acid copolymer segments, transforming from the original linear brush-like structure into a crosslinked network structure, improving the toughness and elongation at break of carboxymethyl cellulose, and the dynamic disulfide bonds have a self-healing effect. When the silicon anode expands, the disulfide bonds break to release stress, reducing the embrittlement effect of the volume expansion of the silicon anode on the binder. When the volume shrinks, the disulfide bonds reconnect to achieve dynamic self-healing, improving the cycle stability of the lithium battery; (3) 2-(3,4-dihydroxyphenyl)ethylamine with catechol groups is introduced as a tackifier on the surface of carboxymethyl cellulose, further improving the tackifying performance of carboxymethyl cellulose, and the use requirements of the lithium battery binder can be met without additional addition of styrene-butadiene rubber; (4) Lithium ions are used to replace traditional sodium ions. CMC-Li not only inherits the excellent binding performance of CMC-Na but also has the ability to bind and release lithium ions. Compared with CMC-Na, it not only increases the number of lithium ions intercalating and deintercalating between the positive and negative electrodes, improves the specific capacity of the battery, but also improves the cycle efficiency and shortens the diffusion path of lithium between the electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the synthesis and structure of the modified carboxymethyl cellulose lithium of the present invention;

[0023] Figure 2 It is the infrared spectrum of carboxymethyl cellulose, CMC-Na graft copolymer and the modified carboxymethyl cellulose lithium of Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described 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. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0025] 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.

[0026] Now, the raw materials and equipment used in the examples and comparative examples are described as follows:

[0027] Carboxymethyl cellulose: M.W. 250000 (DS = 0.9), 1500 - 3100 mPa·s, Changshu Weiyi Technology Co., Ltd.;

[0028] Acrylic acid: 95%, Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0029] Sulfonic acid group monomer 1: 2 - acrylamido - 2 - methylpropanesulfonic acid, 98%, purchased from Macklin;

[0030] Sulfonic acid group monomer 2: Sodium p - styrenesulfonate, 90%, purchased from Macklin;

[0031] Cystine: L - cystine, 99%, purchased from Macklin;

[0032] 2 - (3,4 - Dihydroxyphenyl)ethylamine: 98%, purchased from Macklin;

[0033] LiOH: purchased from Macklin;

[0034] MES buffer solution: pH 5.0, 0.5 M, purchased from Macklin;

[0035] Unless otherwise specified, the component raw materials used in each example and comparative example of the present invention are all commercially available raw materials, and the component raw materials used in each parallel experiment are of the same kind.

[0036] Example 1

[0037] A lithium - ion battery anode binder of modified lithium carboxymethyl cellulose: self - made, and the preparation method is as follows:

[0038] S1. Grafting: Weigh 1 g of carboxymethyl cellulose powder and dissolve it in 500 ml of distilled water, stir to form a transparent viscous solution, pass nitrogen for 6 hours to remove oxygen. Dissolve 0.5 g of sodium p - styrenesulfonate in 10 ml of distilled water, and add it together with 2.5 g of acrylic acid, 0.3 g of ammonium persulfate and 0.3 g of sodium bisulfite into the carboxymethyl cellulose solution. Continuously stir for 3 h under a nitrogen atmosphere at 55 °C, add 3% NaOH solution to adjust the pH value to 6. After the reaction is completed, the product is precipitated and washed with absolute ethanol, and then soaked in distilled water for 24 hours to remove the homopolymer, and vacuum - dried to obtain the CMC - Na graft copolymer; The molar contents of carboxyl and sulfonic acid groups in the CMC - Na graft copolymer are detected by the ash - alkali method. The method is to remove the soluble salts in the CMC - Na graft copolymer with an ethanol aqueous solution of a certain concentration, dry it, and then burn it at high temperature in a muffle furnace. The residue is the alkali metal oxide Na2O. After adding water to dissolve it, add an excessive amount of sulfuric acid standard titration solution, and titrate the excessive sulfuric acid with a NaOH standard titration solution using methyl red as an indicator;

[0039] S2. Acidification: Disperse the CMC-Na graft copolymer in an ethanol solution, add HCl with a mass concentration of 20% at 35°C, stir and react for 2 h. After filtration, continue to wash with the ethanol solution three times and dry at 105°C to obtain the CMC-H graft copolymer; the molar amount of HCl added is 3 times the total molar content of the carboxyl and sulfonic acid groups of the CMC-Na graft copolymer.

[0040] S3. Lithiation: Disperse the CMC-H graft copolymer in an ethanol solution of LiOH with a mass concentration of 7%, react at 50°C for 2 h. The molar amount of LiOH added is 2 times the total molar content of the carboxyl and sulfonic acid groups of the CMC-H graft copolymer; after the reaction, add acetic acid to adjust the pH to 7, filter, continue to wash with the ethanol aqueous solution three times, and dry at 105°C to obtain the CMC-Li graft copolymer.

[0041] S4. Crosslinking: Dissolve the CMC-Li graft copolymer in MES buffer, add EDC and NHS to activate for 30 min. The addition amounts of EDC and NHS are 0.01 wt% of the CMC-Li graft copolymer; add L-cysteine, and the molar amount of L-cysteine is 5 mol% of the total molar content of the carboxyl and sulfonic acid groups of the CMC-H graft copolymer. Stir and react for 6 h under the conditions of light avoidance and nitrogen protection, then add 2-(3,4-dihydroxyphenyl)ethylamine solution, and the molar amount of 2-(3,4-dihydroxyphenyl)ethylamine is 1 mol% of the total molar content of the carboxyl and sulfonic acid groups of the CMC-Li graft copolymer. Continue to stir and react for 6 h, filter, continue to wash with the ethanol aqueous solution three times, and dry at 105°C to obtain modified lithium carboxymethylcellulose. Use a pulverizing machine to pulverize the modified lithium carboxymethylcellulose until it is in powder form, and pass through a 100-mesh sieve. The synthesis and structural schematic diagram of the modified lithium carboxymethylcellulose are as Figure 1 shown.

[0042] The ethanol solutions used in the above steps are all ethanol aqueous solutions with a volume concentration of 90%.

[0043] Use an infrared spectrometer with the model IR / Nicolet 6700 to perform infrared spectroscopy tests on carboxymethylcellulose, CMC-Na graft copolymer, and modified lithium carboxymethylcellulose. When preparing the sample, mix a small amount of sample powder with KBr and grind it. The ground sample should be transparent to ensure that light can pass through the sample. In the experiment, set the wavelength range of the spectral analyzer to 4000 cm -1 ~500 cm -1 ; The results are as Figure 2 shown.

[0044] Example 2

[0045] Compared with the preparation method of Example 1, the difference is that the molar amount of L-cysteine in step S4 is 8 mol% of the total molar content of carboxyl groups and sulfonic acid groups in the CMC-Li graft copolymer.

[0046] Example 3

[0047] Compared with the preparation method of Example 1, the difference is that the molar amount of L-cysteine in step S4 is 10 mol% of the total molar content of carboxyl groups and sulfonic acid groups in the CMC-Li graft copolymer.

[0048] Example 4

[0049] Compared with the preparation method of Example 1, the difference is that the molar amount of 2-(3,4-dihydroxyphenyl)ethylamine in step S4 is 3 mol% of the total molar content of carboxyl groups and sulfonic acid groups in the CMC-Li graft copolymer.

[0050] Example 5

[0051] Compared with the preparation method of Example 1, the difference is that the molar amount of 2-(3,4-dihydroxyphenyl)ethylamine in step S4 is 5 mol% of the total molar content of carboxyl groups and sulfonic acid groups in the CMC-Li graft copolymer.

[0052] Example 6

[0053] Compared with the preparation method of Example 1, the difference is that sodium p-styrenesulfonate in step S1 is replaced by 2-acrylamido-2-methylpropanesulfonic acid.

[0054] Comparative Example 1

[0055] Compared with the preparation method of Example 1, the difference is that L-cysteine is not added in step S4.

[0056] Comparative Example 2

[0057] Compared with the preparation method of Example 1, the difference is that 2-(3,4-dihydroxyphenyl)ethylamine is not added in step S4.

[0058] Comparative Example 3

[0059] Compared with the preparation method of Example 1, the difference is that the sulfonic acid group monomer is not added in step S1.

[0060] The modified lithium carboxymethylcellulose prepared in the examples and comparative examples was subjected to the following tests, and the results are shown in Table 1:

[0061] (1)Viscosity test: Weigh 5 g of the modified lithium carboxymethyl cellulose sample dried at 105 °C for 2 h, accurate to 0.001 g, and prepare a 1% solution for use; measure 495 mL of water to prepare a 1% CMC-Na solution) into a wide-mouth bottle; place the wide-mouth bottle under a stirrer, turn on the stirrer power supply, very slowly adjust the rotation speed to 300 revolutions, slowly add the sample, pay attention to adding all the sample to the solution, after the sample is completely added, slowly adjust the stirring speed to 900 revolutions per minute, and stir for about 2 h (stir high-viscosity products for 3 - 4 h) until the sample is completely dissolved and uniform; place the wide-mouth bottle containing the prepared sample solution in a constant temperature water bath at 25 °C, after keeping the temperature constant for at least 1 h, check the temperature of the sample solution, the value of which is within the range of 25 ± 0.2 °C, and conduct the test using a DV2T viscometer.

[0062] (2)Peel test: The evaluation of adhesion performance is usually carried out through peel strength test. 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 paste a 120×25 mm electrode sample onto the 3M transparent tape, paste it onto 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 silicon oxygen negative electrode, conductive carbon black, single-walled carbon nanotubes and modified lithium carboxymethyl cellulose binder with a mass ratio of 95:1:0.05:3.95 respectively. Dissolve the modified lithium carboxymethyl cellulose with a solvent, and appropriately add solvent according to the viscosity of the solution. Add the weighed silicon oxygen negative electrode, conductive carbon black and single-walled carbon nanotubes into an agate mortar and grind them. After mixing evenly, add the dissolved modified lithium carboxymethyl cellulose, 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 to stir for 12 h. Coating the stirred electrode slurry on the copper foil wiped with anhydrous ethanol and dried to obtain the electrode plate. Place the electrode plate in an oven at 50 °C and dry it for 12 h to obtain the electrode sheet.

[0063] (3)Cycle capacity retention rate: Stir, coat, roll press and die cut the positive electrode material (the active substance is NCM811) and the negative electrode material (silicon oxygen negative electrode, conductive carbon black, single-walled carbon nanotubes and modified lithium carboxymethyl cellulose binder with a mass ratio of 95:1:0.05:3.95) respectively to obtain the positive electrode sheet and the negative electrode sheet; Stack, spot weld, package and bake the obtained positive electrode sheet, negative electrode sheet and separator (12 + 4 ceramic-coated separator), inject the electrolyte (the solute is LiPF6, and the solvent is EC and DMC with a mass ratio of 4:1), and then carry out liquid injection, standing, formation, aging and grading capacity respectively to prepare a lithium-ion battery; Charge and discharge the obtained lithium-ion battery between 2.75 - 4.2 V at 1C / 1C for 500 cycles to test its capacity retention rate.

[0064] Table 1 Performance Tests of Examples and Comparative Examples

[0065]

[0066] It can be seen from Examples 1 to 3 that as the addition amount of cystine increases, the crosslinking density of lithium carboxymethyl cellulose increases, the viscosity increases, and the cycle capacity retention rate increases to some extent. However, the peel strength shows a trend of first increasing and then decreasing. This is because when the crosslinking density is too high, it will instead lead to an increase in the rigidity of the material and a decrease in flexibility, and stress concentration is more likely to occur during the peeling process, resulting in local damage to the material, thereby reducing the peel strength.

[0067] It can be seen from Examples 1 to 3 that as the addition amount of 2-(3,4-dihydroxyphenyl)ethylamine increases, the viscosity and peel strength of lithium carboxymethyl cellulose increase, and the cycle capacity retention rate also increases to some extent.

[0068] It can be seen from Example 1, Example 6 and Comparative Example 3 that grafting an acrylic acid-sulfonic acid copolymer onto the side chain of carboxymethyl cellulose to introduce sulfonic acid groups can improve the bonding ability and cycle capacity retention rate of the modified carboxymethyl cellulose. This may be because the high ionic conductivity and anti-swelling ability of sulfonic acid groups can significantly improve the cycle life of the silicon negative electrode.

[0069] 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 limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principle and practical application 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 modified carboxymethyl cellulose lithium negative electrode binder for lithium batteries, characterized in that: The preparation method of the modified lithium carboxymethyl cellulose comprises the following steps: S1. Grafting: dissolve carboxymethyl cellulose in water, add acrylic acid monomer, sulfonic acid monomer and initiator, stir and react at 40-60℃ for 2-4h under anaerobic conditions, add NaOH for neutralization, purify and obtain CMC-Na graft copolymer, the mass ratio of acrylic acid monomer, sulfonic acid monomer and carboxymethyl cellulose is (2-5): (0.5-1): 1; S2. Acidification: The CMC-Na graft copolymer was dispersed in an ethanol solution, hydrochloric acid was added, stirred and reacted for 2 to 4 hours, then washed with an ethanol solution, and dried to obtain a CMC-H graft copolymer, wherein the molar amount of hydrochloric acid added was 2 to 4 times the total molar amount of carboxyl and sulfonic acid groups in the CMC-Na graft copolymer; S3. Lithiation: Disperse the CMC-H copolymer in an aqueous solution of ethanol, add LiOH solution at 40-60°C to adjust the pH to 9-10 and stir for 2-10 hours, then add acetic acid to adjust the pH to 7-8, filter, wash with ethanol solution, and dry to obtain a CMC-Li graft copolymer, wherein the molar amount of the added LiOH is 1.5-3 times the total molar amount of the carboxyl and sulfonic acid groups of the CMC-Na graft copolymer; S4. Cross-linking: Disperse the CMC-Li graft copolymer in MES buffer, add EDC and NHS to activate the carboxyl group, add cystine and stir to react for 4-8 hours, then add 2-(3,4-dihydroxyphenyl)ethylamine and continue to react for 4-8 hours, wash with ethanol solution, and dry to obtain modified lithium carboxymethyl cellulose, wherein the molar amount of cystine is 5-10 mol% of the total molar amount of the carboxyl group and sulfonic acid group of the CMC-Li graft copolymer, and the molar amount of 2-(3,4-dihydroxyphenyl)ethylamine is 1-5 mol% of the total molar amount of the carboxyl group and sulfonic acid group of the CMC-Li graft copolymer.

2. The modified carboxymethyl cellulose lithium negative electrode binder for lithium batteries according to claim 1, characterized in that: The acrylic acid monomer is selected from at least one of acrylic acid and methacrylic acid; the sulfonic acid monomer is selected from at least one of 2-acrylamide-2-methylpropanesulfonic acid and sodium p-styrenesulfonate.

3. The negative electrode binder for lithium battery of modified carboxymethyl cellulose lithium according to claim 1, characterized in that: The initiators are ammonium persulfate and sodium bisulfite, and the added amount of the initiators is 0.5-1 wt % of the total weight of the monomers.

4. The negative electrode binder for lithium battery of modified carboxymethyl cellulose lithium according to claim 1, characterized in that: The carboxymethyl substitution degree of the carboxymethyl cellulose is 0.7-1.

4.

5. The modified carboxymethyl cellulose lithium negative electrode binder for lithium batteries according to claim 1, characterized in that: The hydrochloric acid in step S2 is a hydrochloric acid solution with a mass concentration of 10-20wt%.

6. The modified carboxymethyl cellulose lithium negative electrode binder for lithium batteries according to claim 1, characterized in that: The LiOH solution in step S3 is a LiOH solution with a mass concentration of 5-10wt%.

7. The negative electrode binder for lithium battery of modified carboxymethyl cellulose lithium according to claim 1, characterized in that: The ethanol solution is an ethanol aqueous solution with a volume concentration of 85-95%.

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