Aqueous binder for lithium-ion batteries

Abstract

The application relates to the technical field of water-based adhesives, and particularly provides a lithium ion battery water-based adhesive. The lithium ion battery water-based adhesive is prepared by mixing a first water-based solution containing a first polymer, a second water-based solution containing a second polymer and a third water-based solution containing a third polymer, the different performance characteristics of the three kinds of polymers are comprehensively exerted, high dispersibility of negative electrode material active particles is realized, the obtained slurry has good stability, high adhesion to the pole piece, high cohesion, the pole piece is flexible, the final pole piece has low impedance, and thus low internal resistance is brought to the battery cell.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water-based adhesives, in particular to a lithium ion battery water-based adhesive. BACKGROUND

[0002] The water-based adhesive is one of the key raw material components of the lithium ion battery, which realizes the dispersion of the positive and / or negative materials, the adhesion to the pole piece, etc. Therefore, the performance of the water-based adhesive, such as the dispersibility of the positive and negative materials, the cohesive strength, the adhesion to the pole piece, the flexibility, etc. has an important influence on the electrical performance of the lithium ion battery.

[0003] The current water-based adhesive materials include polyacrylic acid PAA, styrene-butadiene latex SBR, sodium carboxymethyl cellulose CMC, etc. The PAA water-based adhesive has good performance in adhesion to the pole piece and the cohesion of the pole piece, but also has problems such as insufficient dispersibility and insufficient flexibility, which ultimately leads to poor electrical performance of the lithium ion battery, especially low initial efficiency. SUMMARY

[0004] Modifying the PAA water-based adhesive is the most important means to improve the performance of the PAA water-based adhesive, but a single modification cannot obtain a PAA water-based adhesive with good comprehensive performance, especially for today's lithium ion batteries, low impedance has become an increasingly important performance parameter, such as impedance affecting the initial efficiency of lithium ions, the lower the impedance, the higher the initial efficiency. In order to solve the above technical problems in the prior art, the present application provides a lithium ion battery water-based adhesive, the effective components in the water-based adhesive are composed of three different functional polyacrylate polymers.

[0005] The present application adopts the following technical scheme:

[0006] A lithium ion battery water-based adhesive, the lithium ion battery water-based adhesive is mixed by a first water-based solution containing a first polymer, a second water-based solution containing a second polymer, and a third water-based solution containing a third polymer;

[0007] The weight percentage content of the first polymer, the second polymer and the third polymer in the lithium ion battery water-based adhesive is in the ratio of 1:1.5-3:1-6;

[0008] The first water-based solution is prepared by the following method: a first monomer combination composed of a first hydrophilic monomer and a first hydrophobic monomer is subjected to a first polymerization in water, and then a second monomer combination composed of a second hydrophilic monomer and a second hydrophobic monomer is added to perform a second polymerization, and then the first water-based solution is obtained;

[0009] The general formula of the second polymer is shown in the following formula (1),

[0010]

[0011] wherein R 1 , R 2 and R 3 are independently selected from H or C1-C4 alkyl, R 4 is selected from at least one of H, Na + , Li + and K + , R 5 is selected from C2-C18 alkyl, C2-C18 substituted alkyl, amino or substituted amino, R 6 has the general formula -R 7 CN, R 7 is absent or selected from at least one of C1-C4 alkylene, a > 0, b ≥ 0, c > 0, a:b:c = 2-5:0-4:2-5;

[0012] The third aqueous solution is prepared by adding a surfactant and / or a protective colloid into water, then adding a mixed monomer composed of a third monomer, a fourth monomer and a fifth monomer, and performing a polymerization reaction.

[0013] The third monomer has the general formula CH2=CR 8 COOM, wherein R 8 is selected from H or C1-C4 alkyl, and M is selected from at least one of H, Na + , Li + and K + .

[0014] The fourth monomer contains at least a second soft monomer.

[0015] The fifth monomer is selected from R 9 CH=CHR 10 CN, wherein R 9 is selected from H or methyl, and R 10 is absent or selected from at least one of C1-C4 alkylene.

[0016] Preferably, the first hydrophilic monomer accounts for 60-100% by weight in the first monomer combination, and the second hydrophilic monomer accounts for 0-60% by weight in the second monomer combination.

[0017] Preferably, the first hydrophilic monomer and the second hydrophilic monomer are independently selected from monomers having the general formula CH2=CR 11 R 12 , wherein R 11 is selected from H or C1-C4 alkyl, and R 12selected from the group consisting of -CONH2, -CONHCH3, -CONHCH2CH3, -CON(CH3)2, -CON(CH2CH3)2, -CONHCH2OH, -CONHCH2CH2OH, -COOCH2CH2OH, -COOCH2CH2CH2OH, -COOCH2CHCH3OH, -COOCH2CH2CH2CH2OH, -COO(CH2CH2O) d H and -COO(CH2) e PO3H, and / or one or more of the organic structures containing -COOM, -(C6H5)COOM, -SO3M and -(C6H5)SO3M functional groups, d = 1-18, e = 1-12, M is selected from one or more of the group consisting of H, Li + , Na + and K + .

[0018] Preferably, the first hydrophobic monomer and the second hydrophobic monomer are independently selected from the group consisting of monomers of the general formula CH2=CR 13 R 14 , wherein R 13 is selected from H or C1-C4 alkyl, R 14 is selected from one or more of the group consisting of -COOC n H 2n+1 and -C m H 2m CN, n = 1-18, m = 0-6.

[0019] Preferably, the weight ratio of the first monomer combination and the second monomer combination is 1:9-9:1.

[0020] Preferably, the conversion rate of the first monomer combination after the first polymerization is not less than 70%.

[0021] Preferably, the second soft monomer is of the general formula CH2=CHCOOR 15 , wherein R 15 is selected from C2-C18 alkyl or C2-C18 substituted alkyl.

[0022] Preferably, the mixed monomers consist of 5-50% of the third monomer, 5-50% of the fourth monomer and 20-90% of the fifth monomer by 100% weight.

[0023] Preferably, the weight percentage of the surfactant or the protective colloid in the mixed monomers is 0-50%.

[0024] Preferably, the weight concentration of the aqueous binder for lithium ion batteries is 5-60%.

[0025] The principle of the aqueous binder of the present application is as follows: the first polymer is more inclined to be adsorbed on the surface of the active particles due to the uneven distribution of the hydrophilic and hydrophobic parts on the polymer chain, thereby playing a role in wrapping and dispersing the active particles, but the particle dispersion does not necessarily stably suspend in the slurry, and sufficient steric hindrance effect is also needed to ensure that the particles do not re-agglomerate; the polar groups such as carboxyl groups on the second polymer chain segment can more effectively interact with the hydrophilic segments of the first polymer adsorbed on the surface of the active particles stretched in the aqueous phase through van der Waals force, thereby ensuring sufficient steric hindrance between the active particles, and the active particles in the slurry have high dispersion and dispersion stability; the third polymer is a branched polymer, and the molecular chain is not completely stretched in the aqueous phase, but is dispersed in the slurry in a "agglomeration" or "swelling" state. Therefore, on the one hand, although the third polymer is a "soft" polymer containing more soft monomers, it is theoretically more inclined to be adsorbed on the surface of the active particles, but because of its special existence form (agglomeration or swelling), and because the particle surface has already adsorbed the first polymer, it is more inclined to exist between the active particles rather than on the surface of the active particles, which can effectively avoid the influence of too much polymer on the lithium ion conduction at the interface between the active particles and the electrolyte, and reduce the final cell resistance; on the other hand, the carboxyl groups in the third polymer can also interact with the carboxyl groups in the second polymer through hydrogen bonds, which can improve the cohesion of the pole piece, ensure the stability of the pole piece structure, participate in the film forming process of the whole pole piece, introduce "soft" agglomeration points in the pole piece, thereby reducing the hardness of the pole piece and improving the flexibility. In addition, because of the improvement of the stability of the slurry, the proportion of the first polymer adsorbed on the surface of the active particles in the slurry can be lower, thereby reducing the influence on the lithium ion conduction at the interface between the active particles and the electrolyte, and the finally formed cell has lower internal resistance. Therefore, the technical effect of the aqueous binder of the present application is not a simple superposition of the three aqueous solutions, and the synergistic effect of the three polymers is achieved.

[0026] In summary, the present application has the following beneficial effects:

[0027] 1、In this application, three kinds of acrylate polymers are used, the first polymer can provide good dispersion ability of positive material and / or negative material active particles and the stability of the final slurry, the second polymer can provide good adhesion between the positive material and / or negative material active particles and copper foil and the cohesion between the active particles, the third polymer can improve the flexibility of the electrode sheet without losing the adhesion and cohesion of the active particles to the electrode sheet, and at the same time, improve the compatibility with the electrolyte, further reduce the interface impedance, so as to finally obtain a low-impedance battery. Therefore, the water-based adhesive of the present application combines the characteristics of the three kinds of acrylate polymers, has high dispersion ability for active particles, especially negative material active particles, good stability of the obtained slurry, high adhesion and cohesion to the electrode sheet, flexible electrode sheet and low final electrode sheet impedance, thereby bringing low internal resistance to the battery.

[0028] 2、Through structural design and process optimization, three polymers with different properties are obtained, and the three polymers can synergistically play a role to obtain a water-based adhesive for lithium ion batteries with excellent comprehensive performance, and at the same time, improve the swelling degree of the electrolyte to the electrode film and the dispersibility of the negative material active particles, so as to effectively reduce the impedance of the lithium ion battery and improve the initial efficiency. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described in detail below.

[0030] Throughout this specification, unless otherwise specifically indicated, the terms used herein are understood to have the meanings as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as generally understood by those skilled in the art to which the present application belongs. If there is a conflict, the present specification takes precedence.

[0031] The present application provides a water-based adhesive for lithium ion batteries, which is mixed by a first aqueous solution containing a first polymer, a second aqueous solution containing a second polymer and a third aqueous solution containing a third polymer.

[0032] The weight percentage content ratio of the first polymer, the second polymer and the third polymer in the water-based adhesive for lithium ion batteries is 1:1.5-3:1-6.

[0033] The weight concentration of the water-based adhesive for lithium ion batteries is 3-60%. For example, the weight concentration can be 3%, 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% and the like. Further, the weight concentration of the water-based adhesive for lithium ion batteries is 5-50%.

[0034] first aqueous solution

[0035] The first aqueous solution is prepared by the following method: the first monomer combination composed of the first hydrophilic monomer and the first hydrophobic monomer is polymerized in water for the first time, and then the second monomer combination composed of the second hydrophilic monomer and the second hydrophobic monomer is added for the second polymerization.

[0036] The first aqueous solution is polymerized by the combination and sequence of the hydrophilic monomer and the hydrophobic monomer, and the first polymer has good dispersibility for the active particles of the positive electrode material and / or the negative electrode material.

[0037] The weight percentage of the first hydrophilic monomer in the first monomer combination is 60-100%, and the weight percentage of the second hydrophilic monomer in the second monomer combination is 0-60%. After the first polymerization, the hydrophilicity of the first polymer chain segment is high, and after the second polymerization, the hydrophobicity of the second polymer chain segment is high. The hydrophilic and hydrophobic characteristics inside the first and second polymer chain segments and between the first and second polymer chain segments give the first polymer good dispersibility. Further, the weight percentage of the first hydrophilic monomer in the first monomer combination is 65-95%, for example, the weight percentage can be 65%, 70%, 75%, 80%, 85%, 90%, 95%, etc.; further, the weight percentage of the second hydrophilic monomer in the second monomer combination is 10-50%, for example, the weight percentage can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.

[0038] In the present application, the above-mentioned first and second hydrophilic monomers are independently selected from monomers of the general formula CH2=CR 11 R 12 , wherein R 11 is selected from H or C1-C4 alkyl, and R 12 is selected from one or more of -CONH2, -CONHCH3, -CONHCH2CH3, -CON(CH3)2, -CON(CH2CH3)2, -CONHCH2OH, -CONHCH2CH2OH, -COOCH2CH2OH, -COOCH2CH2CH2OH, -COOCH2CHCH3OH, -COOCH2CH2CH2CH2OH, -COO(CH2CH2O) d H, and -COO(CH2) e PO3H, and / or one or more of organic structures containing -COOM, -(C6H5)COOM, -SO3M, and -(C6H5)SO3M functional groups, d=1-18, e=1-12, M is selected from H, Li + , Na + , and K+ One or more of these. For example, the first hydrophilic monomer and the second hydrophilic monomer can be acrylic acid, sodium acrylate, methacrylic acid, sodium methacrylate, acrylamide, N-methacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, polyether acrylate, etc.

[0039] In this application, the first hydrophobic monomer and the second hydrophobic monomer are individually selected from those with the general formula CH2=CR. 13 R 14 The monomer, of which R 13 Selected from H or C1-C4 alkyl, R 14 Selected from -COOC n H 2n+1 and -C m H 2m One or more of CN, n = 1-18, m = 0-6. For example, the first hydrophobic monomer and the second hydrophobic monomer can be acrylonitrile, methacrylonitrile, butyl acrylate, ethyl acrylate, isooctyl acrylate, lauryl acrylate, n-octyl acrylate, etc.

[0040] In this application, the weight ratio of the first monomer combination and the second monomer combination is 1:9-9:1. Further, the weight ratio can be 1:7-7:1. For example, it can be 1:7, 2:7, 3:7, 4:7, 5:7, 6:7, 1:1, 7:7, 7:5, 7:4, 7:3, 7:2, 7:1, etc., without any particular limitation.

[0041] In this application, after the first polymerization, the conversion rate of the first monomer combination is not less than 70%. The conversion rate of the first monomer combination within the above range has minimal impact on the proportions of various monomers in the second monomer combination. Further, the conversion rate of the first monomer combination is not less than 75%, or even further, not less than 80%.

[0042] second aqueous solution

[0043] The general formula of the second polymer in the second aqueous solution is shown in formula (1) below.

[0044]

[0045] Among them, R 1 R 2 and R 3 Individually selected from H or C1-C4 alkyl, R 4 Selected from H, Na + Li + and K + At least one of them; R 5 Unlike R4 and R 6 , R 5 may be selected from C2-C18 alkyl, C2-C18 substituted alkyl, amino or substituted amino, for example, the substituted amino can be N,N-dimethylamino, N-methylamino, N,N-diethylamino, N-ethylamino, N-hydroxymethylamino, N-hydroxyethylamino, etc.; R 6 of the general formula is -R 7 CN, R 7 is nothing or at least one selected from C1-C4 alkylene, a > 0, b ≥ 0, c > 0, a:b:c = 2-5:0-4:2-5.

[0046] For example, the monomer CH2=CR 1 COOR 4 may be sodium acrylate, acrylic acid, methacrylic acid, sodium methacrylate, etc.; the monomer CH2=CR 2 COOR 5 contains or does not contain a first soft monomer. In this application, the soft monomer refers to a homopolymer obtained by homopolymerization of the monomer, and the glass transition temperature Tg of the homopolymer is lower than 0℃, or further, Tg is not more than -10℃, for example, the first soft monomer can be ethyl acrylate, butyl acrylate, isooctyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, etc. The monomer CH2=CR 2 COOR 5 may be a combination of acrylate monomers and acrylamide monomers in a weight ratio of 1:1-10:1 or can also be a single acrylamide monomer, the acrylate monomer can be ethyl acrylate, butyl acrylate, isooctyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, etc., the acrylamide monomer can be acrylamide, N,N-dimethylacrylamide, N-methylacrylamide, N-ethylacrylamide, N-hydroxymethylacrylamide, N,N-diethylacrylamide, etc., without particular limitation. The monomer CH2=CR 3 COOR 6 may be acrylonitrile, methacrylonitrile, 3-butenenitrile, etc.

[0047] The second polymer can be prepared by free radical polymerization, which is well known to those skilled in the art. For example, one polymerization method is to heat water to the polymerization temperature, drop the monomer mixture composed of three monomers, and drop the water-soluble initiator solution at the same time. The monomer mixture and the water-soluble initiator solution are dropped synchronously within 1-6 hours. After dropping, the reaction is continued for 0-8 hours at a constant temperature to obtain the product. Alternatively, the polymerization method can be to add the monomer mixture composed of three monomers to water, heat to the polymerization temperature, drop the water-soluble initiator solution within 10 min-4 h, and continue the reaction for 0-8 hours at a constant temperature to obtain the product.

[0048] third aqueous solution

[0049] The third aqueous solution is prepared by adding a surfactant and / or a protective colloid to water, then adding a mixed monomer composed of a third monomer, a fourth monomer, and a fifth monomer, and then performing a polymerization reaction to obtain the product.

[0050] The general formula of the third monomer is CH2=CR 8 COOM, wherein R 8 is selected from H or C1-C4 alkyl, and M is selected from at least one of H, Na + , Li + , and K + ; for example, the third monomer can be acrylic acid, sodium acrylate, sodium methacrylate, sodium acrylate, etc.

[0051] The fourth monomer contains at least a second soft monomer, and the general formula of the second soft monomer is CH2=CHCOOR 15 , wherein R 15 is selected from C2-C18 alkyl or C2-C18 substituted alkyl; for example, the second soft monomer can be selected from butyl acrylate, isooctyl acrylate, octyl acrylate, hydroxypropyl acrylate, hydroxyethyl acrylate, lauryl acrylate, and stearyl acrylate. Alternatively, the fourth monomer is the above CH2=CHCOOR 15 monomer combined with an acrylamide monomer at a weight ratio of 1:1-10:1; for example, the acrylamide monomer can be acrylamide, N,N-dimethyl acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N-hydroxymethyl acrylamide, N,N-diethyl acrylamide, etc., without any particular limitation. Further, the weight ratio of the second soft monomer in the fourth monomer is not less than 50%.

[0052] The fifth monomer is selected from R 9 CH=CHR 10 CN, wherein R 9 is selected from H or methyl, and R 10R1is absent or at least one selected from C1-C4 alkylene. For example, the fifth monomer can be selected from acrylonitrile, 3-butene nitrile, and the like.

[0053] In the present application, the mixed monomers can consist of 5-50% of the third monomer, 5-50% of the fourth monomer, and 20-90% of the fifth monomer, by weight of 100%. Further, the mixed monomers can consist of 10-40% of the third monomer, 10-40% of the fourth monomer, and 40-80% of the fifth monomer, by weight of 100%. For example, the mixed monomers can consist of 20% of the third monomer, 20% of the fourth monomer, and 60% of the fifth monomer, or consist of 20% of the third monomer, 30% of the fourth monomer, and 50% of the fifth monomer, or consist of 15% of the third monomer, 15% of the fourth monomer, and 70% of the fifth monomer, or consist of 40% of the third monomer, 10% of the fourth monomer, and 50% of the fifth monomer, and the like.

[0054] In the present application, the weight percentage of the surfactant and / or protective colloid in the mixed monomers is 0-50%. The surfactant can be an anionic surfactant or a non-ionic surfactant, or a combination of two or more thereof. For example, the surfactant can be AEO-3, AEO-9, Tween 20, Tween 80, Span 20, Span 80, Span 60, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, and the like. Further, the weight percentage of the surfactant in the mixed monomers can be 0-5%, or further, 0.5-5%. For example, the weight percentage of the surfactant in the mixed monomers can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, and the like. The protective colloid can be polyvinyl alcohol PVA, polyethylene glycol PEG, polyvinyl pyrrolidone PVP, sodium carboxymethyl cellulose, sodium hydroxypropyl cellulose, and the like. Further, the weight percentage of the protective colloid in the mixed monomers can be 0-10%, or further, 0.5-10%. For example, the weight percentage of the protective colloid in the mixed monomers can be 0.5%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, and the like.

[0055] The technical solutions of the present application are described in detail below in combination with examples and comparative examples. Unless otherwise specified, the parts in the following examples and comparative examples are parts by weight.

[0056] Preparation of the first aqueous solution in Preparation Example 1-3

[0057] Preparation Example 1

[0058] In a reaction kettle, 400 parts of water were added, and under stirring at 180 rpm, a first monomer combination composed of 45 parts of methacrylic acid, 15 parts of acrylamide, 10 parts of hydroxypropyl acrylate, and 30 parts of acrylonitrile monomers, and 5 parts of sodium bicarbonate were added and mixed uniformly, and the temperature was raised to 75°C, and 10 parts of an aqueous solution containing 0.2 parts of ammonium persulfate were added dropwise within 30 min, and after the dropwise addition was completed, the reaction was maintained for 90 min; the stirring speed was adjusted to 250 rpm, and a second monomer combination composed of 5 parts of methacrylic acid and 30 parts of acrylonitrile, and 20 parts of water were continuously added to the reaction kettle, and mixed thoroughly, and 10 parts of an aqueous solution containing 0.3 parts of ammonium persulfate were added, and the reaction was maintained for 180 min, and the temperature was lowered to below 40°C, and a certain amount of sodium bicarbonate and water were added, and the pH was adjusted to 7.0-7.5, and the solid content was 8wt%, to obtain a first aqueous solution.

[0059] Preparation Example 2

[0060] Preparation Example 2 differs from Preparation Example 1 in that in the first monomer combination in Preparation Example 1, 45 parts of methacrylic acid is adjusted to 50 parts, 15 parts of acrylamide is adjusted to 25 parts, and 30 parts of acrylonitrile is adjusted to 15 parts. The remaining steps remain unchanged.

[0061] Preparation Example 3

[0062] Preparation Example 3 differs from Preparation Example 1 in that in the second monomer combination in Preparation Example 1, 5 parts of methacrylic acid and 30 parts of acrylonitrile are adjusted to 10 parts of methacrylic acid and 60 parts of acrylonitrile. The remaining steps remain unchanged.

[0063] Preparation of a second aqueous solution in Preparation Examples 4-6

[0064] Preparation Example 4

[0065] In a reaction vessel, 500 parts of water were added, and 36 parts of methacrylic acid, 10.7 parts of butyl acrylate, and 35.3 parts of acrylonitrile (molar ratio 3:0.5:4) were added, and then 4 parts of sodium bicarbonate were added, and mixed uniformly, and the temperature was raised to 73°C, and 10 parts of an aqueous solution containing 0.3 parts of ammonium persulfate were added dropwise within 30 min, and the reaction was continued for 180 min after the addition was completed, and the temperature was lowered to below 40°C, and a certain amount of sodium bicarbonate and water were added, and the pH was adjusted to 7.0-7.5, and the solid content was 10wt%, to obtain a second aqueous solution.

[0066] Preparation Example 5

[0067] Preparation Example 5 differs from Preparation Example 4 in that in Preparation Example 4, 10.7 parts of butyl acrylate is adjusted to 11.8 parts of acrylamide. The remaining steps remain unchanged.

[0068] Preparation Example 6

[0069] Preparation Example 6 is different from Preparation Example 4 in that the acrylonitrile is adjusted from 35.3 parts to 17.7 parts in Preparation Example 4. The remaining steps remain unchanged.

[0070] Preparation of the third aqueous solution in Preparation Examples 7-9

[0071] Preparation Example 7

[0072] Into a reactor, 10 parts of PVABP-17 and 350 parts of water were added, the temperature was raised to 90°C, and the BP-17 was completely dissolved. The temperature was lowered to below 50°C, and 20 parts of acrylic acid, 30 parts of isooctyl acrylate, 10 parts of methyl acrylate, and 40 parts of acrylonitrile were added in sequence. The temperature was raised to 75°C, and 50 parts of an aqueous solution containing 0.3 g of ammonium persulfate was added dropwise. The dropwise addition was completed in 120 min, and the reaction was continued for 100 min. The temperature was lowered to below 40°C, and sodium bicarbonate and water were added to adjust the pH to 7.0-7.5 and the solid content to 16 wt%, thereby obtaining a third aqueous solution.

[0073] Preparation Example 8

[0074] Preparation Example 8 is different from Preparation Example 7 in that the isooctyl acrylate is adjusted from 30 parts to 20 parts and the acrylonitrile is adjusted from 40 parts to 50 parts in Preparation Example 7. The remaining steps remain unchanged.

[0075] Preparation Example 9

[0076] Preparation Example 9 is different from Preparation Example 7 in that the BP-17 is adjusted from 10 parts to 2 parts in Preparation Example 7. The remaining steps remain unchanged.

[0077] Example 1

[0078] A lithium ion battery aqueous binder was prepared by mixing the first aqueous solution of Preparation Example 1, the second aqueous solution of Preparation Example 4, and the third aqueous solution of Preparation Example 7 in a weight ratio of 1:2:1.

[0079] Example 2

[0080] A lithium ion battery aqueous binder was prepared by mixing the first aqueous solution of Preparation Example 2, the second aqueous solution of Preparation Example 5, and the third aqueous solution of Preparation Example 7 in a weight ratio of 1:2:1.

[0081] Example 3

[0082] A lithium ion battery aqueous binder was prepared by mixing the first aqueous solution of Preparation Example 3, the second aqueous solution of Preparation Example 6, and the third aqueous solution of Preparation Example 7 in a weight ratio of 1:2:1.

[0083] Example 4

[0084] A lithium-ion battery aqueous binder was prepared by mixing the first aqueous solution of Preparation Example 1, the second aqueous solution of Preparation Example 4, and the third aqueous solution of Preparation Example 8 in a weight ratio of 1:2:1.

[0085] Example 5

[0086] A lithium-ion battery aqueous binder was prepared by mixing the first aqueous solution of Preparation Example 1, the second aqueous solution of Preparation Example 5, and the third aqueous solution of Preparation Example 9 in a weight ratio of 1:2:1.

[0087] Example 6

[0088] A lithium-ion battery aqueous binder was prepared by mixing the first aqueous solution of Preparation Example 2, the second aqueous solution of Preparation Example 4, and the third aqueous solution of Preparation Example 7 in a weight ratio of 2:2:1.

[0089] Example 7

[0090] A lithium-ion battery aqueous binder was prepared by mixing the first aqueous solution of Preparation Example 2, the second aqueous solution of Preparation Example 5, and the third aqueous solution of Preparation Example 8 in a weight ratio of 2:2:3.

[0091] Example 8

[0092] A lithium-ion battery aqueous binder was prepared by mixing the first aqueous solution of Preparation Example 3, the second aqueous solution of Preparation Example 6, and the third aqueous solution of Preparation Example 9 in a weight ratio of 1:1:2.

[0093] Example 9

[0094] A lithium-ion battery aqueous binder was prepared by mixing the first aqueous solution of Preparation Example 3, the second aqueous solution of Preparation Example 4, and the third aqueous solution of Preparation Example 8 in a weight ratio of 1:2:3.

[0095] Comparative Example 1

[0096] The first aqueous solution of Preparation Example 1.

[0097] Comparative Example 2

[0098] The second aqueous solution of Preparation Example 4.

[0099] Comparative Example 3

[0100] The third aqueous solution of Preparation Example 7.

[0101] Comparative Example 4

[0102] A lithium-ion battery aqueous binder was prepared by mixing the first aqueous solution of Preparation Example 1 and the second aqueous solution of Preparation Example 4 in a weight ratio of 1:2.

[0103] Comparative Example 5

[0104] A lithium-ion battery aqueous binder was prepared by mixing the first aqueous solution of Preparation Example 1 and the third aqueous solution of Preparation Example 7 at a weight ratio of 1:1.

[0105] Comparative Example 6

[0106] A lithium-ion battery aqueous binder was prepared by mixing the second aqueous solution of Preparation Example 4 and the third aqueous solution of Preparation Example 7 at a weight ratio of 2:1.

[0107] The preparation process of the graphite negative electrode sheet is as follows: the to-be-tested aqueous binder and 50% water are dispersed at 1000 rpm for 15 minutes, then the conductive agent SP conductive carbon black is added and wetted for 12 minutes, and then high-speed stirring is carried out at 1600 rpm for 120 minutes; then the negative electrode material S360-L2-H and the remaining 50% water are continuously added and high-speed stirring is carried out at 1600 rpm for 120 minutes. After dispersion is completed, the viscosity (23°C) is adjusted to be between 2500-2700 mPa·s, and the discharge is completed after filtration with a 150-mesh filter screen. The copper foil is placed on a coating machine, the doctor blade scale of the wet film preparation device is adjusted, the filtered slurry is uniformly poured, and the slurry is sent into a 100°C environment for air baking until dry, and a sheet with a specification of 12.5 cm x 5 cm and a single-side area density of 100-110 g / m 2 .

[0108] The electrode sheet peeling force test method is as follows: the cut electrode sheet is sent into a 35% RH constant temperature room for 30 minutes, the coating side faces outward, and the copper foil side faces inward to adhere two electrode sheets, and the electrode sheets are sent into an electric roller press to be rolled to 1.6 g / cm 3 . After rolling, it is placed for another 30 minutes, during which five 12.5 x 5 cm stainless steel plates are selected, double-sided adhesive tapes of the corresponding specifications are attached to the steel plates, the electrode sheets are attached to the double-sided adhesive tapes with the coating facing downward, a 2.5 cm wide masking tape is attached to the copper foil, and the electrode sheet steel plate is rolled back and forth for one round at a certain pressure by the electric roller, and then the adhesion of the electrode sheet is tested by an electronic peeling machine; in the same way as described above, only the electrode sheet is attached to the double-sided adhesive tape with the coating facing upward, and the cohesion of the electrode sheet can be tested.

[0109] The electrode sheet flexibility test method is as follows: a softness tester ITM-RRD01 is used for testing.

[0110] The test method of the electrolyte swelling rate of the adhesive film is as follows: the adhesive film without bubbles is first trimmed, and then cut into a size of 1*4 cm, and then placed into a 105°C air drying oven for drying for 4 hours, and then taken out and weighed and recorded as M1, and then placed into a small bottle containing electrolyte (1M LiPF6 in EC:DMC:EMC=1:1:1) for constant temperature immersion for 48 hours, and then taken out and wiped with filter paper to remove the surface electrolyte, and the wiping and weighing process is controlled within 1 min, and then weighed and recorded as M2, and the adhesive film swelling rate is (M2-M1) / M1*100%.

[0111] The assembly sequence of the button cell is as follows from bottom to top: negative shell-elastic sheet-gasket-lithium sheet-electrolyte-separator-electrolyte-pole piece-positive shell; the first coulombic efficiency and impedance test are as follows:

[0112] The first efficiency test is 0.1C, 0.005-1.5V charge-discharge; and the impedance scan is from 100 kHz to 0.1 Hz.

[0113] The results are shown in Table 1 below.

[0114] Table 1 Performance test results

[0115]

[0116] Therefore, from the data in the above table, it can be seen that the water-based adhesive of the application contains three polymers, and can realize the comprehensive characteristics of dispersibility, cohesion, flexibility, low impedance and good compatibility with the adhesive film.

[0117] The dispersion stability of the slurry obtained according to the preparation of the graphite negative electrode pole piece is tested as follows: 90g of the just prepared slurry is placed in a 100ml transparent PET bottle (specification: main body diameter 46mm, mouth diameter 28mm, height 94mm, wall thickness 1mm), the upper layer slurry is taken for testing the solid content, which is recorded as H0; the upper layer slurry is taken after the slurry is left standing for 48 hours for testing the solid content, which is recorded as H1, and the solid content change ΔH=H0-H1. Five samples are taken for each test, and the average value is calculated. The results are shown in Table 2 below. The smaller the solid content change, the more stable the prepared slurry and the better the dispersibility.

[0118] Table 2 Dispersion stability

[0119]

[0120]

[0121] From the data results in Table 2, it can be seen that the water-based adhesive of the application is used to prepare the negative material active particle slurry, and the dispersion stability is good.

[0122] Therefore, according to the above results, the water-based adhesive has good comprehensive performance, good dispersibility of the negative electrode particle active material, and can obtain an electric core with low impedance.

[0123] The embodiments are only used to explain the application, and are not used to limit the application, and any modification without creative contribution made by the person skilled in the art according to the embodiments after reading the specification is protected by the patent law as long as the modification is within the scope of the claims of the application.

Claims

1. A lithium-ion battery aqueous binder, characterized by, The lithium ion battery water-based adhesive is mixed by a first water-based solution containing a first polymer, a second water-based solution containing a second polymer, and a third water-based solution containing a third polymer; The weight percentage content of the first polymer, the second polymer and the third polymer in the lithium ion battery water-based adhesive is in a ratio of 1:1.5-3:1-6; The first water-based solution is prepared by first polymerizing a first monomer combination consisting of a first hydrophilic monomer and a first hydrophobic monomer in water, then adding a second monomer combination consisting of a second hydrophilic monomer and a second hydrophobic monomer, and then performing a second polymerization, wherein the weight percentage of the first hydrophilic monomer in the first monomer combination is 60-100%, and the weight percentage of the second hydrophilic monomer in the second monomer combination is 0-60%; said second polymer is formed by copolymerization of monomer a, monomer b and monomer c, wherein monomer a is selected from CH2=CR 1 COOR 4 , monomer b is selected from CH2=CR 2 COOR 5 , and monomer c is selected from acrylonitrile, methacrylonitrile or 3-butenenitrile; wherein R 1 , R 2 are individually selected from H or C1-C4 alkyl, R 4 is selected from at least one of H, Na + , Li + and K + , and R 5 is selected from C2-C18 alkyl, and the polymerization degree ratio of monomer a: monomer b: monomer c = 2-5: 0-4: 2-5; The third water-based solution is prepared by adding a surfactant and / or a protective colloid to water, then adding a mixed monomer consisting of a third monomer, a fourth monomer and a fifth monomer, and then performing a polymerization reaction; The third monomer has the general formula CH2=CR 8 COOM, wherein R 8 is selected from H or C1-C4 alkyl, and M is selected from at least one of H, Na + , Li + , and K + . The fourth monomer contains at least a second soft monomer having the general formula CH2=CHCOOR 15 wherein R 15 is selected from C2-C18 alkyl; said fifth monomer is selected from R 9 CH=CHR 10 CN, wherein R 9 is selected from H or methyl, R 10 is either absent or at least one selected from C1-C4 alkylene; said first hydrophilic monomer and said second hydrophilic monomer are individually selected from monomers of the general formula CH2=CR 11 R 12 wherein R 11 is selected from H or C1-C4 alkyl, and R 12 is selected from -CONH2, -CONHCH3, -CONHCH2CH3, -CON(CH3)2, -CON(CH2CH3)2, -CONHCH2OH, -CONHCH2CH2OH, -COOCH2CH2OH, -COOCH2CH2CH2OH, -COOCH2CHCH3OH, -COOCH2CH2CH2CH2OH, -COO(CH2CH2O) d H, and -COO(CH2) e PO3H, d = 1-18, e = 1-12; The first hydrophobic monomer and the second hydrophobic monomer are each selected from the general formula CH2=CR 13 R 14 The monomer, of which R 13 Selected from H or C1-C4 alkyl, R 14 Selected from and One or more of them, n = 1-18, m = 0-6.

2. The aqueous binder for lithium ion batteries according to claim 1, wherein The weight ratio of the first monomer combination and the second monomer combination is 1:9-9:

1.

3. The aqueous binder for lithium ion batteries according to claim 1, wherein After the first polymerization, the conversion rate of the first monomer combination is not less than 70%.

4. The aqueous binder for lithium ion batteries according to claim 1, wherein The mixed monomer consists of 5-50% of the third monomer, 5-50% of the fourth monomer and 20-90% of the fifth monomer by weight.

5. The aqueous binder for lithium ion batteries according to claim 1, wherein The weight percentage of the surfactant and / or the protective colloid in the mixed monomer is 0-50%.

6. The aqueous binder for lithium ion batteries according to claim 1, wherein The weight concentration of the lithium ion battery water-based adhesive is 5-60%.

Images