Composite sodium carboxymethyl cellulose adhesive and preparation method thereof

Abstract

The invention discloses a composite sodium carboxymethyl cellulose adhesive and a preparation method thereof, the adhesive comprises sodium carboxymethyl cellulose A, sodium carboxymethyl cellulose B and polyacrylamide, and the mass ratio of the sodium carboxymethyl cellulose A to the sodium carboxymethyl cellulose B to the polyacrylamide is (60-80%): (20-40%): (5-10%); the molecular weight of the sodium carboxymethyl cellulose A is between 300,000 and 500,000, the molecular weight of the sodium carboxymethyl cellulose B is between 600,000 and 800,000, and the molecular weight of the polyacrylamide is between 20,000 and 300,000. The composite adhesive disclosed by the invention has the beneficial effects that the composite adhesive can form an interlaced bonding network, so that the cycling stability of a negative pole piece in a long-time cycling process can be effectively ensured, and the lithium ion battery can obtain very long cycle life by using a small amount of negative adhesive under very high energy density of the lithium ion battery.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion battery adhesives, and in particular relates to a composite sodium carboxymethyl cellulose adhesive and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have outstanding advantages such as high energy density, environmental friendliness, no memory effect, long cycle life, low self-discharge, and environmental protection, and have been widely used in consumer electronic products and new energy vehicles. At present, in the production of lithium-ion batteries, the negative electrode slurry generally uses a water-based adhesive ingredient combined with sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR).

[0003] Sodium carboxymethyl cellulose is a linear polymer cellulose ether. As a negative electrode adhesive for lithium-ion batteries, CMC has good thermal stability, conductivity and electrochemical properties. The structural characteristics of CMC itself, such as molecular weight, degree of substitution, usage, etc., have a very important influence on the performance of electrodes using CMC, affecting its solubility in aqueous solution, viscosity and affinity for graphite particles. The degree of substitution of CMC for lithium-ion batteries is generally between 0.6 and 1.4. CMC with a large molecular weight and a high degree of substitution often has a higher viscosity and better solubility, which is more conducive to the stability of the negative electrode slurry.

[0004] At present, the lithium-ion battery industry often uses a single CMC as a negative electrode adhesive. When a single CMC is used in a small amount, it is difficult to meet the requirements of a long cycle life of a lithium-ion battery. It is often necessary to add more CMC to meet the requirements of a long cycle life of a lithium-ion battery, which reduces the energy density of the battery, so it needs to be improved. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to provide a composite sodium carboxymethyl cellulose adhesive and a preparation method thereof, aiming to ensure that a lithium ion battery can obtain a long cycle life by using a small amount of negative electrode adhesive at a high energy density of the lithium ion battery.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is: A composite sodium carboxymethylcellulose adhesive and a preparation method thereof. The adhesive comprises sodium carboxymethylcellulose A, sodium carboxymethylcellulose B and polyacrylamide, wherein the mass ratio of sodium carboxymethylcellulose A: sodium carboxymethylcellulose B: polyacrylamide is 60-80%: 20-40%: 5-10%; the molecular weight of the sodium carboxymethylcellulose A is between 300,000 and 500,000, the molecular weight of the sodium carboxymethylcellulose B is between 600,000 and 800,000, and the molecular weight of the polyacrylamide is between 20 and 30 million; the preparation method of the adhesive comprises the following steps: (1) adding an equivalent amount of polyacrylamide to solvent water, and stirring at a stirring speed of 50-100 rpm to prepare a glue solution a; (2) adding equivalent amounts of sodium carboxymethyl cellulose A and sodium carboxymethyl cellulose B into solvent water, and stirring at a stirring speed of 1000-2000 rpm to prepare glue solution B; (3) The adhesive solution a and the adhesive solution b are mixed at a stirring speed of 500-1000 rpm to prepare a composite sodium carboxymethyl cellulose adhesive.

[0007] The viscosity of a 1% aqueous solution (at 25°C) of the sodium carboxymethyl cellulose A is 1500-3000 mPa.s, and the degree of substitution is 0.8-0.9; the viscosity of a 1% aqueous solution (at 25°C) of the sodium carboxymethyl cellulose B is 3500-4500 mPa.s, and the degree of substitution is 0.9-1.0.

[0008] The sodium carboxymethyl cellulose A has a morphology of long strips, short rods and granules, wherein the length-to-length ratio of the long strips is between 4:1 and 6:1. Figure 1 .

[0009] The sodium carboxymethyl cellulose B is in the form of a single long strip, with a length-to-width ratio greater than 10:1. Figure 2 .

[0010] The beneficial effect of the present invention is that a composite sodium carboxymethyl cellulose adhesive is prepared by compounding sodium carboxymethyl cellulose A with medium viscosity, sodium carboxymethyl cellulose B with high viscosity and a small amount of polyacrylamide, wherein the sodium carboxymethyl cellulose A in the form of long strips, short rods and particles, the sodium carboxymethyl cellulose B in the form of longer strips, and the polyacrylamide in the form of ultra-long strips can form an interwoven bonding network, thereby effectively ensuring the cycle stability of the negative electrode plate during a long cycle, thereby ensuring that the lithium ion battery can obtain a very long cycle life by using a small amount of negative electrode adhesive under a very high energy density of the lithium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a scanning electron microscope photo of sodium carboxymethyl cellulose A.

[0012] Figure 2 This is a scanning electron microscope photo of sodium carboxymethyl cellulose B.

[0013] Figure 3 1C cycle curves of the lithium ion batteries prepared in Example 3 and Comparative Examples 1 and 2. Implementation

[0014] The present invention is described in detail below in conjunction with specific embodiments. The description in this section is only exemplary and explanatory and should not have any limiting effect on the scope of protection of the present invention. Example

[0015] A composite sodium carboxymethylcellulose adhesive and a preparation method thereof. The adhesive comprises sodium carboxymethylcellulose A, sodium carboxymethylcellulose B and polyacrylamide, wherein the mass ratio of sodium carboxymethylcellulose A: sodium carboxymethylcellulose B: polyacrylamide is 80%: 20%: 10%. The molecular weight of the sodium carboxymethylcellulose A is 300,000, the molecular weight of the sodium carboxymethylcellulose B is 800,000, and the molecular weight of the polyacrylamide is 30 million. The preparation method of the adhesive comprises the following steps: (1) Add an equivalent amount of polyacrylamide to solvent water, and stir at a stirring speed of 50 rpm to prepare a glue solution a; (2) adding equivalent amounts of sodium carboxymethyl cellulose A and sodium carboxymethyl cellulose B into solvent water, and stirring at a stirring speed of 2000 rpm to prepare a glue solution B; (3) Glue solution a and glue solution b were mixed at a stirring speed of 500 rpm to prepare a composite sodium carboxymethyl cellulose adhesive. Example

[0016] A composite sodium carboxymethylcellulose adhesive and a preparation method thereof. The adhesive comprises sodium carboxymethylcellulose A, sodium carboxymethylcellulose B and polyacrylamide, wherein the mass ratio of sodium carboxymethylcellulose A: sodium carboxymethylcellulose B: polyacrylamide is 60%: 40%: 5%. The molecular weight of the sodium carboxymethylcellulose A is 500,000, the molecular weight of the sodium carboxymethylcellulose B is 600,000, and the molecular weight of the polyacrylamide is 20 million. The preparation method of the adhesive comprises the following steps: (1) adding an equivalent amount of polyacrylamide to solvent water, and stirring at a stirring speed of 100 rpm to prepare a glue solution a; (2) adding equivalent amounts of sodium carboxymethyl cellulose A and sodium carboxymethyl cellulose B into solvent water, and stirring at a stirring speed of 1000 rpm to prepare a glue solution B; (3) The adhesive solution a and the adhesive solution b were mixed at a stirring speed of 1000 rpm to prepare a composite sodium carboxymethyl cellulose adhesive. Example

[0017] A composite sodium carboxymethylcellulose adhesive and a preparation method thereof. The adhesive comprises sodium carboxymethylcellulose A, sodium carboxymethylcellulose B and polyacrylamide, wherein the mass ratio of sodium carboxymethylcellulose A: sodium carboxymethylcellulose B: polyacrylamide is 70%:30%:8%. The molecular weight of the sodium carboxymethylcellulose A is 400,000, the molecular weight of the sodium carboxymethylcellulose B is 700,000, and the molecular weight of the polyacrylamide is 25 million. The preparation method of the adhesive comprises the following steps: (1) Add an equivalent amount of polyacrylamide to solvent water, and stir at a stirring speed of 80 rpm to prepare a glue solution a; (2) adding equivalent amounts of sodium carboxymethyl cellulose A and sodium carboxymethyl cellulose B into solvent water, and stirring at a stirring speed of 1500 rpm to prepare a glue solution B; (3) The adhesive solution a and the adhesive solution b were mixed at a stirring speed of 800 rpm to prepare a composite sodium carboxymethyl cellulose adhesive.

[0018] Comparative Example 1: A sodium carboxymethylcellulose adhesive and a preparation method thereof, wherein the preparation method of the adhesive comprises the following steps: An equivalent amount of sodium carboxymethyl cellulose A is added to solvent water, and the mixture is stirred at a stirring speed of 1500 rpm to prepare a sodium carboxymethyl cellulose adhesive.

[0019] Comparative Example 2: A sodium carboxymethylcellulose adhesive and a preparation method thereof, wherein the preparation method of the adhesive comprises the following steps: An equivalent amount of sodium carboxymethyl cellulose B is added to solvent water, and the mixture is stirred at a stirring speed of 2000 rpm to prepare a sodium carboxymethyl cellulose adhesive.

[0020] The composite sodium carboxymethyl cellulose adhesive prepared in Example 3, the sodium carboxymethyl cellulose adhesive prepared in Comparative Example 1, and the sodium carboxymethyl cellulose adhesive prepared in Comparative Example 2 were mixed with graphite, conductive carbon black, and styrene-butadiene rubber (SBR) to prepare negative electrode sheets. The mass proportions of the three adhesives in the negative electrode were 1.0% (Example 3), 1.5% (Comparative Example 1), and 1.5% (Comparative Example 2). The positive electrode sheet was made of LiNi 0.5 Co 0.2 Mn 0.3 O2 ternary material, conductive carbon black, PVDF preparation, and then with the isolation film winding, aluminum plastic film packaging, liquid injection, baking, chemical formation, etc. to prepare a 5000mAh soft package lithium ion battery, the prepared lithium ion battery for 1C cycle test, the test results are as follows Figure 3The capacity retention rate of the lithium ion batteries prepared in Comparative Examples 1 and 2 dropped to 90% after about 500 1C cycles, while the capacity retention rate of the lithium ion battery prepared in Example 3 dropped to 90% after about 1200 1C cycles, showing excellent cycle performance.

[0021] The beneficial effect of the present invention is that a composite sodium carboxymethyl cellulose adhesive is prepared by compounding sodium carboxymethyl cellulose A with medium viscosity, sodium carboxymethyl cellulose B with high viscosity and a small amount of polyacrylamide, wherein the sodium carboxymethyl cellulose A in the form of long strips, short rods and particles, the sodium carboxymethyl cellulose B in the form of longer strips, and the polyacrylamide in the form of ultra-long strips can form an interwoven bonding network, thereby effectively ensuring the cycle stability of the negative electrode plate during a long cycle, thereby ensuring that the lithium ion battery can obtain a very long cycle life by using a small amount of negative electrode adhesive under a very high energy density of the lithium ion battery.

[0022] The above description is only a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any slight modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A composite sodium carboxymethyl cellulose adhesive and a preparation method thereof, characterized in that: The adhesive comprises sodium carboxymethyl cellulose A, sodium carboxymethyl cellulose B and polyacrylamide, and the mass ratio of sodium carboxymethyl cellulose A: sodium carboxymethyl cellulose B: polyacrylamide is 60-80%: 20-40%: 5-10%; the molecular weight of the sodium carboxymethyl cellulose A is between 300,000 and 500,000, the molecular weight of the sodium carboxymethyl cellulose B is between 600,000 and 800,000, and the molecular weight of the polyacrylamide is between 20 and 30 million; the preparation method of the adhesive comprises the following steps: (1) adding an equivalent amount of polyacrylamide to solvent water, and stirring at a stirring speed of 50-100 rpm to prepare a glue solution a; (2) adding equivalent amounts of sodium carboxymethyl cellulose A and sodium carboxymethyl cellulose B into solvent water, and stirring at a stirring speed of 1000-2000 rpm to prepare a glue solution B; (3) The adhesive solution a and the adhesive solution b are mixed at a stirring speed of 500-1000 rpm to prepare a composite sodium carboxymethyl cellulose adhesive.

2. A composite sodium carboxymethyl cellulose adhesive and a preparation method thereof according to claim 1, characterized in that: The viscosity of a 1% aqueous solution (at 25°C) of the sodium carboxymethyl cellulose A is 1500-3000 mPa.s, and the degree of substitution is 0.8-0.9; the viscosity of a 1% aqueous solution (at 25°C) of the sodium carboxymethyl cellulose B is 3500-4500 mPa.s, and the degree of substitution is 0.9-1.

0.

3. A composite sodium carboxymethyl cellulose adhesive and a preparation method thereof according to claim 1, characterized in that: The sodium carboxymethyl cellulose A has a shape of long strips, short rods and granules, wherein the length-to-length ratio of the long strips is between 4:1 and 6:

1.

4. A composite sodium carboxymethyl cellulose adhesive and a preparation method thereof according to claim 1, characterized in that: The sodium carboxymethyl cellulose B is in the shape of a single long strip, and its length-to-width ratio is greater than 10:1.

Images