An aqueous binder, method of preparation and use

Abstract

This invention discloses an aqueous binder for lithium-ion batteries, its preparation method, and its application. The binder is obtained by polymerizing a raw material comprising the following components: a) 20wt%-45wt% of at least one of olefinically unsaturated carboxylic acids or olefinically unsaturated carboxylic anhydrides; b) 20wt%-45wt% of an olefinically unsaturated nitrile monomer; c) 5wt%-30wt% of a carboxyl-free olefinically unsaturated hydrophilic monomer; d) 10wt%-40wt% of an olefinically unsaturated hydrophobic monomer; e) 0.15wt%-1wt% of a crosslinking monomer. The binder provided by this invention, when applied in the field of lithium-ion batteries, can improve the processing performance of the negative electrode sheet and the cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to a lithium-ion battery material and its preparation method, particularly a lithium-ion secondary battery negative electrode binder, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are considered the most promising mobile energy storage technology due to their advantages such as high energy density, long cycle life, and environmental friendliness, and are widely used in electronic products, electric vehicles, energy storage equipment and other fields.

[0003] Lithium-ion batteries are mainly composed of electrodes (including positive and negative electrodes), electrolytes, and separators. Electrodes are generally composed of active materials, conductive agents, dispersants, binders, and current collectors. In the electrode preparation process, the electrode active materials, conductive agents, dispersants, and binder solutions are usually mixed and homogenized, then coated onto the current collector, and then dried and calendered to form a complete electrode. In this process, the binder mainly plays a bonding role to maintain the integrity of the electrode.

[0004] Currently, the most widely used negative electrode binder is styrene-butadiene rubber solution (SBR). During use, carboxymethyl cellulose (CMC) needs to be added as a thickener and dispersant. However, CMC has generally low viscosity, high brittleness, and poor flexibility, making the electrode prone to cracking during charge and discharge. Furthermore, when SBR is used as a binder based on a point-to-point bonding mechanism in graphite and silicon-based novel negative electrodes, the repeated expansion and contraction of the graphite and silicon-based negative electrodes during charge and discharge cycles easily causes the point bonding to lose its adhesiveness, leading to capacity loss, especially deterioration in high-temperature storage and high-temperature cycling performance. In addition, SBR has a large swelling degree in the electrolyte (50%–200%), resulting in increased spacing between the negative electrode active materials. Simultaneously, the large swelling of the electrolyte reduces the adhesion of the binder to the copper foil or active materials, further degrading battery performance.

[0005] Existing technologies use PAA as a binder, which offers high bonding strength, low electrolyte swelling, and excellent high-temperature cycling performance. However, this polymer has a high glass transition temperature, which can easily lead to hard and brittle electrodes after coating. Therefore, this binder is prone to cracking during coating, developing numerous streaks after cold pressing, edge decarburization during cutting, and powder shedding at electrode bending points during winding, resulting in poor processability and severely limiting its application in batteries.

[0006] CN111139002B discloses a water-soluble binder for lithium-ion batteries, which is a ternary copolymer of acrylonitrile, 2-acrylamide-2-phenylethanesulfonic acid, and methacrylic acid. The molecular chain characteristics of this water-soluble polymer endow it with a face-to-face bonding mechanism, forming a network bond inside the electrode, enhancing the adhesion between active materials and between active materials and the substrate. It also has good dispersion performance and slurry stability, as well as low electrolyte swelling characteristics. Compared with SBR latex, it can significantly improve the high-temperature storage and high-temperature cycling performance of lithium-ion batteries, but the processing performance of the electrode needs to be further improved.

[0007] CN115312779A designed the raw materials and contents of polymer solution A and polymer solution B to prepare an aqueous polymer binder with a three-dimensional cross-linked structure. The aqueous polymer binder has good flexibility and high adhesion, and can be used to prepare negative electrode sheets for lithium-ion batteries. However, the preparation efficiency of this binder needs to be improved.

[0008] Therefore, providing a binder product with better dispersibility, higher adhesion and better flexibility has become an urgent technical problem to be solved, addressing the current issues of SBR dispersion performance, high-temperature cycling performance and PAA electrode processing. Summary of the Invention

[0009] The purpose of this invention is to provide an aqueous binder, its preparation method, and its application. Compared to SBR, this binder exhibits superior bonding performance and lower dissolution, ensuring excellent cycle life for lithium-ion batteries. Simultaneously, compared to existing PAA products, it demonstrates better flexibility, ensuring excellent processing performance for lithium-ion battery electrodes.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] On one hand, the present invention provides an aqueous adhesive, said adhesive being obtained by polymerizing a raw material comprising the following components:

[0012] a) 20wt%-45wt% of at least one of olefinic unsaturated carboxylic acids or olefinic unsaturated carboxylic anhydrides;

[0013] b) 20wt%-45wt% of olefinic unsaturated nitrile monomers;

[0014] c) 5wt%-30wt% of carboxyl-free olefinic unsaturated hydrophilic monomers;

[0015] d) 10wt%-40wt% olefinic unsaturated hydrophobic monomers;

[0016] e) 0.15wt%-1wt% crosslinking monomer.

[0017] In this invention, the olefinic unsaturated carboxylic acid and olefinic unsaturated carboxylic anhydride are preferably olefinic unsaturated carboxylic acids, and more preferably at least one of acrylic acid and methacrylic acid.

[0018] In this invention, the olefinic unsaturated nitrile monomer is selected from at least one of acrylonitrile, α-haloacrylonitrile, and α-alkylacrylonitrile, preferably at least one of acrylonitrile, α-chloroacrylonitrile, α-bromoacrylonitrile, methacrylonitrile, and ethylacrylonitrile.

[0019] In this invention, the carboxyl-free olefinic unsaturated hydrophilic monomer is at least one of acrylamide, methacrylamide, hydroxyethyl acrylate, ethoxyethoxyethyl acrylate, hydroxyethyl methacrylate, sodium vinyl sulfonate, and sodium p-styrene sulfonate.

[0020] In this invention, the olefinically bonded unsaturated hydrophobic monomer is at least one selected from styrene, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, hexyl acrylate, hexyl methacrylate, isooctyl acrylate, isooctyl methacrylate, decyl acrylate, decyl methacrylate, glycidyl acrylate, and glycidyl methacrylate.

[0021] In this invention, the crosslinking monomer is at least one selected from diacetone acrylamide, acetylacetooxyethyl methacrylate, divinylbenzene, ethylene glycol diacrylate, 1,3-butanediol diacrylate, 1,6-hexanediol diacrylate, allyl methacrylate, and pentaerythritol triallyl ether.

[0022] On the other hand, the present invention also provides a method for preparing an aqueous adhesive, comprising the following steps:

[0023] Step 1: Place the aqueous solution of the protective adhesive in the reactor and heat it;

[0024] Step 2: Add the four monomers (a), (b), (c), and (e) and the initiator into the reactor to initiate the polymerization reaction;

[0025] Step 3: After the polymerization is completed and the temperature is maintained, a neutralizing agent is added to adjust the pH to obtain polymer solution A;

[0026] Step 4: Simultaneously add the emulsifier, (a), (d), (e) and the initiator into the reactor of Step 3 to further initiate the polymerization reaction;

[0027] Step 5: After the polymerization is completed and the temperature is maintained, add a neutralizing agent to adjust the pH to obtain an aqueous binder.

[0028] In this invention, the protective adhesive in step one is selected from polyvinyl alcohol and / or sodium carboxymethyl cellulose; and / or, the amount of the protective adhesive is 0.1-1 wt% of the total amount of the five monomers (a), (b), (c), (d), and (e), preferably 0.3-0.8 wt%.

[0029] In this invention, the temperature for heating in step one is 30-85℃, preferably 35-80℃.

[0030] In this invention, the initiator in step two includes an oxidant and a reducing agent, and the mass ratio of the oxidant to the reducing agent is 1:2-2:1, preferably 1:1-2:1.

[0031] In this invention, the oxidant is selected from at least one of ammonium persulfate, sodium persulfate, potassium persulfate, tert-butyl hydroperoxide, and hydrogen peroxide, preferably sodium persulfate; the reducing agent is selected from at least one of sodium hydrosulfite, isoascorbic acid, sodium metabisulfite, and sodium bisulfite, preferably sodium bisulfite; and / or, the amount of the oxidant is 0.1-1 wt% of the total amount of the five monomers (a), (b), (c), (d), and (e), preferably 0.2-0.8 wt%; the amount of the reducing agent is 0.1-1 wt% of the total amount of the five monomers (a), (b), (c), (d), and (e), preferably 0.2-0.8 wt%.

[0032] In this invention, the amounts of monomers (a) and (e) in step two account for 75%-98% and 3%-40% of the total amount, respectively.

[0033] In this invention, the polymerization temperature in step two is 30-85℃, preferably 35-80℃; the reaction time is 3-6h, preferably 4-5h.

[0034] In this invention, the heat preservation time in step three is 1-3 hours, preferably 1.5-2 hours.

[0035] In this invention, the neutralizing agent in step three is selected from one or more aqueous solutions of NaOH, Na2CO3, LiOH, and lithium carbonate, and the pH is adjusted to 5.5-7.5.

[0036] In this invention, the emulsifier in step four is selected from one or more of the following: sodium allyl succinate sulfonate, polyether methacrylate, allyl-containing alkyl alcohol ether sulfate, double-bonded alkyl alcohol ether sulfate, double-bonded dialkyl sulfosuccinate, alkylpropylene phenoxy polyether sulfate, double-bonded polyether ammonium phosphate, polyphenylene ring polyoxyethylene ether sulfate or sulfonate, and fatty alcohol polyoxyethylene ether sulfate; and / or, the amount of the emulsifier is 0.05-0.5 wt% of the total amount of the five monomers in (a), (b), (c), (d), and (e), preferably 0.1-0.3 wt%.

[0037] In this invention, the initiator in step four is selected from at least one of ammonium persulfate, sodium persulfate, potassium persulfate, tert-butyl hydrogen peroxide, and hydrogen peroxide. The amount of the initiator is 0.05-0.5 wt% of the total amount of the five monomers in (a), (b), (c), (d), and (e), preferably 0.1-0.3 wt%.

[0038] In this invention, the amounts of monomers in step four (a) and (e) account for 2%-25% and 60%-97% of the total amount, respectively.

[0039] In this invention, the reaction temperature in step four is 70-90℃, preferably 75-85℃; the reaction time is 3-6h, preferably 4-5h.

[0040] In this invention, the heat preservation time in step five is 1-3 hours, preferably 1.5-2 hours; and / or, the neutralizing agent in step five is selected from one or more aqueous solutions of NaOH, Na2CO3, LiOH, and lithium carbonate, and the adjusted pH is 6-8.

[0041] In this invention, the solid content of the water-based adhesive is 4-10 wt%, preferably 5-8 wt%.

[0042] Finally, the present invention provides the application of the aqueous binder in the application of a negative electrode active material binder, wherein the negative electrode material is selected from artificial graphite, natural graphite, hard carbon, and silicon carbide.

[0043] The present invention has the following beneficial effects:

[0044] (1) The water-based binder of the present invention first uses a precipitation polymerization process to prepare a polymer that not only has excellent dispersibility and adhesion, but also exhibits excellent low dissolution characteristics in the electrolyte DMC. Using this macromolecule as an emulsifier in the second polymerization step can provide excellent polymerization stability and control the dissolution performance of the entire polymer, thus giving the battery excellent cycle performance.

[0045] (2) The water-based binder prepared by the two-step polymerization process of this invention has good toughness and endows the electrode with excellent processing performance.

[0046] (3) The polymer molecular chain of the water-based binder of the present invention contains functional groups such as cyano, hydroxyl, amide, and ester groups, which promote the conduction of lithium ions, reduce the internal resistance of lithium batteries, and improve the low-temperature performance of lithium batteries. Detailed Implementation

[0047] The present invention will be further illustrated by specific embodiments below. These specific embodiments are merely detailed descriptions of the present invention and are not intended to limit the scope of the present invention.

[0048] Table 1 Raw Materials and Sources:

[0049]

[0050]

[0051] The main raw materials and formulations used in the examples and comparative examples are shown in Table 1:

[0052] Table 2 Main raw materials and proportions for preparing water-based adhesives

[0053]

[0054]

[0055] Example 1

[0056] (1) Add 1g PVA2488 and 500g deionized water to the reactor, turn on the stirring and heat to 50℃;

[0057] (2) Mix 20g acrylic acid, 20g acrylonitrile, 10g acrylamide and 0.05g 1,3-butanediol dimethacrylate;

[0058] (3) Dissolve 0.8g APS in 50g water and 0.8g NaHSO3 in 50g water to prepare an oxygen-reduction initiator solution;

[0059] (4) Simultaneously add the mixed monomers in step (2) and the initiator aqueous solution in step (3) to the reaction vessel in step (1). The reaction temperature is 35℃, the addition time is 3h, and after the addition is completed, the temperature is raised to 80℃ and kept for 2h. Add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 6.0.

[0060] (5) Add 0.5g (active ingredient) NRS-1230 emulsifier, 12.5g water, 5g acrylic acid, 14g styrene, 30g butyl acrylate and 0.95g 1,3-butanediol dimethacrylate to the pre-emulsification tank.

[0061] (6) Dissolve 0.25g of APS in 50g of water to prepare an initiator solution;

[0062] (7) Simultaneously add the mixed monomers from step (5) and the initiator aqueous solution from step (6) to the reaction vessel from step (1). The addition time is 3 hours, and the temperature is maintained for 2 hours. After the reaction is completed, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 7.5.

[0063] Example 2

[0064] (1) Add 0.5g PVA2488 and 500g deionized water into the reactor, turn on the stirring and heat to 50℃;

[0065] (2) Mix 20g acrylic acid, 40g acrylonitrile, 25g acrylamide and 0.17g 1,3-butanediol dimethacrylate;

[0066] (3) Dissolve 0.35g APS in 50g water and 0.35g NaHSO3 in 50g water to prepare an oxygen-reduction initiator solution;

[0067] (4) Simultaneously add the mixed monomers in step (2) and the initiator aqueous solution in step (3) to the reaction vessel in step (1). The reaction temperature is 50℃, the addition time is 3h, and after the addition is completed, the temperature is raised to 70℃ and kept for 2h. Add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 6.0.

[0068] (5) Add 0.075g (active ingredient) NRS-1230 emulsifier, 4g water, 1g acrylic acid, 3.5g styrene, 10g butyl acrylate and 0.33g 1,3-butanediol dimethacrylate to the pre-emulsification tank.

[0069] (6) Dissolve 0.075g of APS in 50g of water to prepare an initiator solution;

[0070] (7) Simultaneously add the mixed monomers from step (5) and the initiator aqueous solution from step (6) to the reaction vessel from step (1). The addition time is 3 hours, and the temperature is maintained for 2 hours. After the reaction is completed, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 7.5.

[0071] Example 3

[0072] (1) Add 0.1g PVA2488 and 500g deionized water into the reactor, turn on the stirring and heat to 50℃;

[0073] (2) Mix 25g acrylic acid, 30g acrylonitrile, 15g acrylamide and 0.14g 1,3-butanediol dimethacrylate;

[0074] (3) Dissolve 0.1g APS in 50g water and 0.1g NaHSO3 in 50g water to prepare an oxygen-reduction initiator solution;

[0075] (4) Simultaneously add the mixed monomers in step (2) and the initiator aqueous solution in step (3) to the reaction vessel in step (1). The reaction temperature is 80℃, the addition time is 3h, and after the addition is completed, the temperature is raised to 90℃ and kept for 2h. Add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 6.0.

[0076] (5) Add 0.15g (active ingredient) NRS-1230 emulsifier, 8g water, 5g acrylic acid, 6.5g styrene, 18g butyl acrylate and 0.36g 1,3-butanediol dimethacrylate to the pre-emulsification tank.

[0077] (6) Dissolve 0.15g of APS in 50g of water to prepare an initiator solution;

[0078] (7) Simultaneously add the mixed monomers from step (5) and the initiator aqueous solution from step (6) to the reaction vessel from step (1). The addition time is 3 hours, and the temperature is maintained for 2 hours. After the reaction is completed, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 7.5.

[0079] Example 4

[0080] (1) Add 0.5g PVA2488 and 500g deionized water into the reactor, turn on the stirring and heat to 50℃;

[0081] (2) Mix 40g acrylic acid, 35g acrylonitrile, 10g acrylamide and 0.17g allyl methacrylate;

[0082] (3) Dissolve 0.35g APS in 50g water and 0.35g NaHSO3 in 50g water to prepare an oxygen-reduction initiator solution;

[0083] (4) Simultaneously add the mixed monomers in step (2) and the initiator aqueous solution in step (3) to the reaction vessel in step (1), raise the temperature to 50°C, add for 3 hours, raise the temperature to 80°C and keep for 2 hours after the addition is complete, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 6.0.

[0084] (5) Add 0.15g (active ingredient) NRS-1230 emulsifier, 4g water, 1g acrylic acid, 3.5g styrene, 10g isooctyl acrylate and 0.33g allyl methacrylate to the pre-emulsification tank.

[0085] (6) Dissolve 0.075g of APS in 50g of water to prepare an initiator solution;

[0086] (7) Simultaneously add the mixed monomers from step (5) and the initiator aqueous solution from step (6) to the reaction vessel from step (1). The addition time is 3 hours, and the temperature is maintained for 2 hours. After the reaction is completed, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 7.5.

[0087] Example 5

[0088] (1) Add 0.5g PVA2488 and 500g deionized water into the reactor, turn on the stirring and heat to 50℃;

[0089] (2) Mix 25g acrylic acid, 30g acrylonitrile, 15g acrylamide and 0.14g pentaerythritol triallyl ether;

[0090] (3) Dissolve 0.35g APS in 50g water and 0.35g NaHSO3 in 50g water to prepare an oxygen-reduction initiator solution;

[0091] (4) Simultaneously add the mixed monomers in step (2) and the initiator aqueous solution in step (3) to the reaction vessel in step (1), raise the temperature to 50°C, add for 3 hours, raise the temperature to 80°C and keep for 2 hours after the addition is complete, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 6.0.

[0092] (5) Add 0.15g (active ingredient) NRS-1230 emulsifier, 4g water, 5g acrylic acid, 6.5g styrene, 18g isooctyl acrylate and 0.36g pentaerythritol triallyl ether to the pre-emulsification tank.

[0093] (6) Dissolve 0.15g of APS in 50g of water to prepare an initiator solution;

[0094] (7) Simultaneously add the mixed monomers from step (5) and the initiator aqueous solution from step (6) to the reaction vessel from step (1). The addition time is 3 hours, and the temperature is maintained for 2 hours. After the reaction is completed, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 7.5.

[0095] Example 6

[0096] (1) Add 0.5g CMC and 500g deionized water to the reactor, turn on the stirring and heat to 50℃;

[0097] (2) Mix 35g acrylic acid, 30g acrylonitrile, 5g acrylamide, and 0.05g pentaerythritol triallyl ether;

[0098] (3) Dissolve 0.35g APS in 50g water and 0.35g NaHSO3 in 50g water to prepare an oxygen-reduction initiator solution;

[0099] (4) Simultaneously add the mixed monomers in step (2) and the initiator aqueous solution in step (3) to the reaction vessel in step (1), raise the temperature to 50°C, add for 3 hours, raise the temperature to 80°C and keep for 2 hours after the addition is complete, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 6.0.

[0100] (5) Add 0.15g (active ingredient) NRS-1230 emulsifier, 4g water, 5g acrylic acid, 6.85g styrene, 18g isooctyl acrylate and 0.1g pentaerythritol triallyl ether to the pre-emulsification tank.

[0101] (6) Dissolve 0.15g of APS in 50g of water to prepare an initiator solution;

[0102] (7) Simultaneously add the mixed monomers from step (5) and the initiator aqueous solution from step (6) to the reaction vessel from step (1). The addition time is 3 hours, and the temperature is maintained for 2 hours. After the reaction is completed, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 7.5.

[0103] Comparative Example 1:

[0104] (1) Add 0.5g PVA2488 and 500g deionized water into the reactor, turn on the stirring and heat to 50℃;

[0105] (2) Mix 40g acrylic acid, 35g acrylonitrile and 10g acrylamide;

[0106] (3) Dissolve 0.35g APS in 50g water and 0.35g NaHSO3 in 50g water to prepare an oxygen-reduction initiator solution;

[0107] (4) Simultaneously add the mixed monomers in step (2) and the initiator aqueous solution in step (3) to the reaction vessel in step (1), raise the temperature to 50°C, add for 3 hours, raise the temperature to 80°C and keep for 2 hours after the addition is complete, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 6.0.

[0108] (5) Add 0.15g (active ingredient) NRS-1230 emulsifier, 4g water, 1g acrylic acid, 4g styrene and 10g isooctyl acrylate to the pre-emulsification tank.

[0109] (6) Dissolve 0.075g of APS in 50g of water to prepare an initiator solution;

[0110] (7) Simultaneously add the mixed monomers from step (5) and the initiator aqueous solution from step (6) to the reaction vessel from step (1). The addition time is 3 hours, and the temperature is maintained for 2 hours. After the reaction is completed, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 7.5.

[0111] Comparative Example 2: Precipitation Polymerization

[0112] (1) Add 0.5g PVA2488 and 500g deionized water into the reactor, turn on the stirring and heat to 50℃;

[0113] (2) Mix 24.83g of acrylic acid, 50g of acrylonitrile, 25g of acrylamide and 0.17g of 1,3-butanediol dimethacrylate;

[0114] (3) Dissolve 0.5g APS in 50g water and 0.5g NaHSO3 in 50g water to prepare an oxygen-reduction initiator solution;

[0115] (4) Simultaneously add the mixed monomers in step (2) and the initiator aqueous solution in step (3) to the reaction vessel in step (1) for 3 hours. After the addition is complete, raise the temperature to 80°C and keep it warm for 2 hours. Add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 7.0.

[0116] Comparative Example 3: Emulsion Polymerization

[0117] (1) Add 0.5g PVA2488, 0.5g (active ingredient) NRS-1230 emulsifier, and 30g deionized water to a pre-emulsification tank, and then add 14g styrene, 25g acrylic acid, 20g acrylonitrile, 10g acrylamide, and 1g 1,3-butanediol dimethacrylate in sequence.

[0118] 30g of butyl acrylate was added to a pre-emulsification tank to prepare a pre-emulsion.

[0119] (2) Dissolve 0.5g APS in 50g water to prepare an initiator solution.

[0120] (3) Add 300g of water to the reaction vessel and heat it to 80 degrees Celsius. At the same time, add the mixed monomers in step (1) and the initiator aqueous solution in step (2) to the reaction vessel in step (3) dropwise. The dropwise addition time is 3h, and the temperature is kept for 2h. After the reaction is completed, add 10% sodium hydroxide aqueous solution to adjust the pH of the solution to 7.5.

[0121] Comparative Example 4

[0122] Commercially available SBR3001A / BCQ15-2CMC adhesive system.

[0123] Comparative Example 5

[0124] Commercially available Indira LA136D PAA adhesive

[0125] The lithium-ion battery prepared using the water-soluble binder of Examples 1-5 of the present invention and the binder of Comparative Examples 1-4 are mixed and dispersed with graphite, conductive carbon black and CMC dispersant to prepare lithium-ion negative electrode sheets.

[0126] The specific preparation method is as follows:

[0127] Preparation of negative electrode slurry: Graphite negative electrode material, conductive carbon black, and water-soluble binder (based on solid content) from the lithium-ion batteries of the embodiments and comparative examples of this invention are mixed in a mass fraction of 96.5 wt%, 1.0 wt%, and 2.5 wt%, respectively. Deionized water is added at a total solid content of 45 wt% to prepare the negative electrode slurry. The uniformly dispersed slurry is passed through a 100-mesh sieve and coated onto a 10 μm thick copper foil as a current collector. It is then directly placed in a furnace to dry at 120°C for 5 minutes, followed by natural cooling to room temperature in a furnace. The mixture is then dried at 10 × 10⁻⁶ mm. 4 Electrode sheets are obtained by rolling under a unit length load of N / m, which serve as the negative electrode of a lithium-ion battery.

[0128] The following method was used to determine the dissolution of polymer films:

[0129] Place 30g of adhesive solution in a 15cm×10cm×2cm container and place it in a 50℃ oven for 48 hours. Cut the adhesive film into 2cm×2cm square films, weigh them and record the weight as M1. Place them in a sealed glass bottle containing dimethyl carbonate (DMC) electrolyte and keep them at 60℃ for 48 hours. After that, gently remove the electrolyte from the surface of the film in a drying room and weigh them again, recording the weight as M2. The dissolution of the adhesive film is as follows:

[0130] Dissolution = (M2-M1) / M1×100%, and the test results are shown in Table 3;

[0131] The peel strength of the negative electrode sheet was determined using the following method:

[0132] The electrode sheets of the examples and comparative examples were cut into strips of 20cm × 2.5cm. A 1mm thick steel plate was glued to the current collector side with double-sided adhesive tape, and transparent tape was pasted on the coating layer side. The electrodes were peeled in a 180° direction at a speed of 100mm / min using a tensile testing machine, and the peel stress was measured. The test results are shown in Table 3.

[0133] The following method is used to evaluate the flexibility of the negative electrode sheet:

[0134] A mandrel with a diameter of Φ = 2.0 mm was placed on the current collector side of the rolled electrode of the examples and comparative examples, and a bending test was carried out. The state of the electrode was observed through an optical microscope. An intact electrode was marked as ○, and a detached or cracked electrode was marked as ×. The test results are shown in Table 3.

[0135] A lithium-ion battery is fabricated using graphite anode material electrode sheets made with the water-soluble binder of this invention, along with conventional cathode sheets, electrolyte, and separator. The cathode material is LG Chem NCM811, the anode material is BTR SFC-R, the separator is Liyou New Energy P25 separator, and the electrolyte is Wanhua WT325.

[0136] Lithium-ion battery performance evaluation:

[0137] The lithium-ion battery was tested using the constant current method to measure its initial coulombic efficiency and capacity retention after 50 cycles of charge and discharge. After 50 charge and discharge cycles, the ratio of the increase in electrode thickness to the electrode thickness before charge and discharge was recorded as the electrode expansion rate (%) under the lithium intercalation state of the electrode sheet. The results are shown in Table 3.

[0138] Table 3 Application Performance Evaluation Results

[0139]

[0140]

[0141] As shown in Table 3, the binders prepared using Examples 1-6 of the present invention have the characteristics of low polymer dissolution, high peel strength, good electrode flexibility, excellent cycle performance, and low electrode expansion rate compared with the binders prepared using Comparative Examples 1-5.

Claims

1. A water-based adhesive, said adhesive being obtained by polymerizing a raw material comprising the following components: a) 20wt%-45wt% of at least one of olefinic unsaturated carboxylic acids or olefinic unsaturated carboxylic anhydrides; b) 20wt%-45wt% of olefinic unsaturated nitrile monomers; c) 5wt%-30wt% of carboxyl-free olefinic unsaturated hydrophilic monomers; d) 10wt%-40wt% olefinic unsaturated hydrophobic monomers; e) 0.15wt%-1wt% crosslinking monomer; The method for preparing the water-based adhesive includes the following steps: Step 1: Place the aqueous solution of the protective adhesive in the reactor and heat it; Step 2: Add the four monomers (a), (b), (c), and (e) and the initiator into the reactor to initiate the polymerization reaction; Step 3: After the polymerization is completed and the temperature is maintained, a neutralizing agent is added to adjust the pH to obtain polymer solution A; Step 4: Add the emulsifier, (a), (d), (e) and the initiator simultaneously into the reactor from Step 3 to further initiate the polymerization reaction; Step 5: After the polymerization is completed and the temperature is maintained, add a neutralizing agent to adjust the pH to obtain an aqueous binder.

2. The water-based adhesive as described in claim 1, characterized in that, The olefinic unsaturated carboxylic acid is selected from at least one of acrylic acid and methacrylic acid; and / or, the olefinic unsaturated nitrile monomer is selected from at least one of acrylonitrile, α-haloacrylonitrile, and α-alkylacrylonitrile; and / or, the carboxyl-free olefinic unsaturated hydrophilic monomer is at least one of acrylamide, methacrylamide, hydroxyethyl acrylate, ethoxyethoxyethyl acrylate, hydroxyethyl methacrylate, sodium vinyl sulfonate, and sodium p-styrene sulfonate.

3. The water-based adhesive as described in claim 1, characterized in that, The olefinic unsaturated nitrile monomer is selected from at least one of acrylonitrile, α-chloroacrylonitrile, α-bromoacrylonitrile, methacrylonitrile, and ethylacrylonitrile.

4. The water-based adhesive according to any one of claims 1-3, characterized in that, The olefinically bonded unsaturated hydrophobic monomer is at least one of styrene, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, hexyl acrylate, hexyl methacrylate, isooctyl acrylate, isooctyl methacrylate, decyl acrylate, decyl methacrylate, glycidyl acrylate, and glycidyl methacrylate; and / or, the crosslinking monomer is at least one of diacetone acrylamide, acetylacetoethyl methacrylate, divinylbenzene, ethylene glycol diacrylate, 1,3-butanediol diacrylate, 1,6-hexanediol diacrylate, allyl methacrylate, and pentaerythritol triallyl ether.

5. The water-based adhesive according to any one of claims 1-3, characterized in that, In step one, the protective adhesive is selected from polyvinyl alcohol and / or sodium carboxymethyl cellulose; and / or, the amount of the protective adhesive is 0.1-1 wt% of the total amount of the five monomers (a), (b), (c), (d), and (e); and / or, the temperature for heating in step one is 30-85°C.

6. The water-based adhesive as described in claim 5, characterized in that, The amount of protective adhesive used in step one accounts for 0.3-0.8 wt% of the total amount of the five monomers (a), (b), (c), (d), and (e); and / or, the temperature for heating in step one is 35-80℃.

7. The water-based adhesive according to any one of claims 1-3, characterized in that, In step two, the initiator includes an oxidant and a reductant, with the mass ratio of oxidant to reductant being 1:2-2:1; and / or, the amount of oxidant used is 0.1-1 wt% of the total amount of the five monomers (a), (b), (c), (d), and (e); the amount of reductant used is 0.1-1 wt% of the total amount of the five monomers (a), (b), (c), (d), and (e).

8. The water-based adhesive as described in claim 7, characterized in that, The oxidant is selected from at least one of ammonium persulfate, sodium persulfate, potassium persulfate, tert-butyl hydroperoxide, and hydrogen peroxide; the reducing agent is selected from at least one of sodium hydrosulfite, isoascorbic acid, sodium metabisulfite, and sodium bisulfite; and / or, the amount of the oxidant is 0.2-0.8 wt% of the total amount of the five monomers (a), (b), (c), (d), and (e); the amount of the reducing agent is 0.2-0.8 wt% of the total amount of the five monomers (a), (b), (c), (d), and (e).

9. The water-based adhesive according to any one of claims 1-3, characterized in that, The polymerization temperature in step two is 30-85℃; the reaction time is 3-6h; and / or, the heat preservation time in step three is 1-3h; and / or, the emulsifier in step four is selected from one or more of the following: sodium allyl succinate sulfonate, polyether methacrylate, allyl-containing alkyl alcohol ether sulfate, double-bonded alkyl alcohol ether sulfate, double-bonded dialkyl sulfosuccinate, alkylpropylene phenoxy polyether sulfate, double-bonded polyether ammonium phosphate, polyphenylene ring polyoxyethylene ether sulfate or sulfonate, and fatty alcohol polyoxyethylene ether sulfate; and / or, the amount of the emulsifier is 0.05-0.5wt% of the total amount of the five monomers in (a), (b), (c), (d), and (e).

10. The water-based adhesive as described in claim 9, characterized in that, The polymerization temperature in step two is 35-80℃; the reaction time is 4-5h; and / or the heat preservation time in step three is 1.5-2h; and / or the amount of emulsifier is 0.1-0.3wt% of the total amount of the five monomers (a), (b), (c), (d), and (e).

11. The water-based adhesive according to any one of claims 1-3, characterized in that, In step four, the initiator is selected from at least one of ammonium persulfate, sodium persulfate, potassium persulfate, tert-butyl hydroperoxide, and hydrogen peroxide. The amount of the initiator is 0.05-0.5 wt% of the total amount of the five monomers (a), (b), (c), (d), and (e); and / or, the amounts of monomers (a) and (e) in step four are 2%-25% and 60%-97% of the total amount, respectively.

12. The water-based adhesive as described in claim 11, characterized in that, In step four, the amount of initiator used is 0.1-0.3 wt% of the total amount of the five monomers (a), (b), (c), (d), and (e).

13. The water-based adhesive according to any one of claims 1-3, characterized in that, The reaction temperature in step four is 70-90℃; the reaction time is 3-6h; and / or, the heat preservation time in step five is 1-3h; and / or, the neutralizing agent in step five is selected from one or more aqueous solutions of NaOH, Na2CO3, LiOH, and lithium carbonate, and the adjusted pH is 6-8.

14. The water-based adhesive as described in claim 13, characterized in that, The reaction temperature in step four is 75-85℃; the reaction time is 4-5h; and / or, the heat preservation time in step five is 1.5-2h.

15. The application of the aqueous binder according to any one of claims 1-14 in the application of a negative electrode active material binder, wherein the negative electrode material is selected from artificial graphite, natural graphite, hard carbon, and silicon carbide.

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