Binder for secondary battery as well as preparation method and application of binder
By using a latex particle structure composed of a core polymer and a shell polymer, the problem of easy demulsification of emulsion-type binders during processing is solved, achieving improved adhesion, anti-expansion ability, and electrical performance, thereby improving the fast-charging performance and cycle life of secondary batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-04
- Publication Date
- 2026-03-27
AI Technical Summary
Existing emulsion-type binders are prone to demulsification during processing, resulting in decreased adhesion and an inability to simultaneously provide excellent adhesion, anti-swelling ability, and electrical properties, thus affecting the fast-charging performance and cycle life of secondary batteries.
A core-shell structure binder is formed by using a latex particle structure composed of a core polymer and a shell polymer. The core polymer contains a first hydrophilic monomer with double bonds and a hydrophobic monomer with double bonds, while the shell polymer contains a second hydrophilic monomer with double bonds. Through a specific ratio and preparation method, a core-shell structure binder is formed, which improves the stability and electrical properties of the binder.
It improves the adhesive strength and shear stability of the binder, enhances the dispersibility of the electrode active material, provides good anti-expansion ability and electrical properties, and improves the kinetic performance and cycle life of the secondary battery.
Smart Images
Figure CN121736675A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of binders, in particular to a binder for secondary batteries and a preparation method and application thereof. BACKGROUND
[0002] Lithium ion batteries are one of the most widely used secondary batteries at present, but inevitably, their applicable working conditions are still limited by parameters such as energy, power, charge-discharge rate, cost, cycle life, safety, and environmental impact. The above performance parameters are largely determined by the properties and characteristics of the component materials used in assembling the battery and the battery engineering and system integration involved. With the gradual development of the secondary battery market, fast charging technology has become the core direction of battery performance upgrading, which puts forward more stringent requirements for the negative electrode material. Silicon-based negative electrodes are widely considered to be the preferred alternative material to traditional graphite negative electrodes due to their high specific capacity (e.g., the specific capacity of silicon is 3592 mAh / g), which can support faster charging speeds. However, silicon expands by up to 300% when fully lithiated, which can cause electron transport obstruction and repeated formation of a solid electrolyte interface (SEI), shortening the battery's service life. Polyacrylic acid (PAA) binder is a common choice when facing volume expansion problems. The large number of carboxyl groups on the PAA molecular chain can form covalent bonds with the surface of silicon-based materials, effectively buffering volume expansion, and also promoting the formation of a stable SEI film, reducing the internal resistance of the battery, and improving the diffusion rate of lithium ions. Moreover, it uses water as a solvent, which is more environmentally friendly. On this basis, existing data also shows that emulsion-type binders can exhibit more excellent electrochemical performance during fast charging cycles. Therefore, the existing technology proposes to use PAA in combination with styrene-butadiene latex (SBR) as a binder to simultaneously improve the fast charging performance of the binder and alleviate volume expansion. However, this process is complicated, and during the homogenization and dispersion process, the latex particles are easily broken down and their morphology is damaged under the action of a large shear force, leading to a decrease in performance. At the same time, the addition of SBR can cause the peel strength of the entire system to decrease, which is not conducive to maintaining the cycle performance of the battery. SUMMARY
[0003] The present application provides a binder for secondary batteries and a preparation method and application thereof to solve the problem that emulsion-type binders cannot simultaneously provide excellent adhesion, anti-expansion ability, and good electrical performance for battery electrodes in the prior art.
[0004] In a first aspect, the present application provides a binder for secondary batteries, which includes latex particles, the latex particles including an inner core polymer and an outer shell polymer coated on at least part of the surface of the inner core polymer. The raw material monomers of the inner core polymer include a first double-bond-containing hydrophilic monomer, a double-bond-containing hydrophobic monomer, and a first functional monomer. The mass of the hydrophobic monomer with double bonds is 1% to 25% of the mass of the first hydrophilic monomer with double bonds. The first hydrophilic monomer with double bonds includes acrylonitrile and a hydrophilic monomer with double bonds other than acrylonitrile; the mass ratio of acrylonitrile to the hydrophilic monomer with double bonds other than acrylonitrile in the first hydrophilic monomer with double bonds is 55:45 to 95:5. The raw monomers of the shell polymer include the second hydrophilic monomer with double bonds.
[0005] In an optional embodiment, the raw monomers of the shell polymer further include a second functional monomer, and the mass of the second functional monomer is 0.01% to 0.38% of the mass of the second hydrophilic monomer with double bonds.
[0006] In an optional embodiment, the mass of the first functional monomer is 0.05% to 0.70% of the mass of the first hydrophilic monomer with double bonds.
[0007] In an optional embodiment, the mass ratio of the raw monomers of the core polymer to the raw monomers of the shell polymer is 10:90 to 67:33.
[0008] In an optional embodiment, the glass transition temperature Tg1 of the core polymer is 50℃ < Tg1 < 105℃.
[0009] In an optional embodiment, the glass transition temperature Tg2 of the shell polymer is 90℃ < Tg2 < 165℃.
[0010] In an optional embodiment, the particle size D of the latex particles is 120nm to 750nm; optionally, the particle size D of the latex particles is 250nm to 550nm. 50 50 In an optional embodiment, the particle size D of the latex particles is 120nm to 750nm; optionally, the particle size D of the latex particles is 250nm to 550nm.
[0011] In an optional embodiment, the weight average molecular weight of the latex particles is 200000 to 750000; optionally, the weight average molecular weight of the latex particles is 350000 to 550000.
[0012] In an optional embodiment, the pH of the binder for secondary batteries is 7 to 9.
[0013] In the binder for secondary batteries provided by the present application, the solid content of the binder for secondary batteries is typically and non-limitingly 1% to 15%; optionally, the solid content of the binder for secondary batteries is 3% to 8%; the solid content of the binder can be adjusted by a person skilled in the art according to actual use requirements.
[0014] In an alternative embodiment, the non-acrylonitrile, double bond-containing hydrophilic monomer includes at least one of acrylic acid, methacrylic acid, acrylamide, methacrylamide, itaconic acid.
[0015] In an alternative embodiment, the second double bond-containing hydrophilic monomer includes at least one of acrylic acid, methacrylic acid, acrylamide, methacrylamide, itaconic acid, acrylonitrile, methacrylonitrile; the second double bond-containing hydrophilic monomer preferably uses a combination of acrylonitrile and other monomers.
[0016] In an alternative embodiment, the double bond-containing hydrophobic monomer includes an acrylate monomer with a glass transition temperature ranging from -70 to 10°C; alternatively, the double bond-containing hydrophobic monomer includes at least one of methyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate.
[0017] In an alternative embodiment, the first functional monomer and the second functional monomer are each independently selected from at least one of divinylbenzene, diallyl phthalate, pentaerythritol triallyl ether, ethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, N,N-methylenebisacrylamide.
[0018] In a second aspect, the present application provides a preparation method of the above-mentioned secondary battery binder, comprising the following steps: S1: preparing a pre-emulsion A for synthesizing an inner core polymer; The pre-emulsion A includes raw material monomers of the inner core polymer, water, and an emulsifier; S2: preparing a pre-emulsion B for synthesizing an outer shell polymer; The pre-emulsion B includes raw material monomers of the outer shell polymer, water, and an emulsifier; S3: preparing a base water, which is an aqueous solution of the emulsifier and / or protective colloid; S4: preparing an initiator aqueous solution; S2: adding the pre-emulsion A and the initiator aqueous solution dropwise into the base water, and after the addition is completed, performing a first-stage heat preservation; S3: after the first-stage heat preservation is completed, adding the pre-emulsion B and the initiator aqueous solution dropwise, and after the addition is completed, performing a second-stage heat preservation; S4: after the second-stage heat preservation is completed, continuously adding the initiator aqueous solution to obtain the secondary battery binder.
[0019] In the preparation method of the secondary battery binder provided by the present application, typically and non-limitatively, the initiator aqueous solution can be prepared in one or more portions, for example, one portion of aqueous solution can be prepared, and the aqueous solution is used in S2, S3 and S4; or three portions of aqueous solutions with different initiator and mass concentration can be prepared, and different initiator aqueous solutions are used in S2, S3 and S4.
[0020] In an alternative embodiment, in the pre-emulsion A, the mass of water is 38% to 135% of the mass of the raw monomers of the inner core polymer.
[0021] In an alternative embodiment, in the pre-emulsion A, the mass of the emulsifier is 0.1% to 2.5% of the mass of the raw monomers of the inner core polymer.
[0022] In an alternative embodiment, in the pre-emulsion B, the mass of water is 45% to 140% of the mass of the raw monomers of the shell polymer.
[0023] In an alternative embodiment, in the pre-emulsion B, the mass of the emulsifier is 0.15% to 2.50% of the mass of the raw monomers of the shell polymer.
[0024] In an alternative embodiment, in the bottom water, the mass concentration of the emulsifier and / or protective colloid is 0.015% to 0.500%.
[0025] In an alternative embodiment, in S2, the mass of the initiator in the initiator aqueous solution is 0.1% to 1% of the mass of the raw monomers of the inner core polymer in the pre-emulsion A.
[0026] In an alternative embodiment, in S3, the mass of the initiator in the initiator aqueous solution is 0.1% to 1% of the mass of the raw monomers of the shell polymer in the pre-emulsion B.
[0027] In an alternative embodiment, in S4, the mass of the initiator in the initiator aqueous solution is 0.1% to 1% of the sum of the mass of the raw monomers of the inner core polymer in the pre-emulsion A and the mass of the raw monomers of the shell polymer in the pre-emulsion B.
[0028] In an alternative embodiment, in S2, the mass of the emulsifier and / or protective colloid in the bottom water is 0.1% to 1.0% of the mass of the raw monomers of the inner core polymer in the pre-emulsion A.
[0029] In an alternative embodiment, after S4, a step of adjusting the pH of the secondary battery binder to 7 to 9 by using an alkali solution is further included; in a further alternative embodiment, the alkali solution includes at least one of lithium hydroxide solution and sodium hydroxide solution.
[0030] In an alternative embodiment, in the S2, the temperature for dropping the pre-emulsion A and the initiator aqueous solution is 65-85 DEG C, and the time is 90-240 min.
[0031] In an alternative embodiment, in the S2, the temperature for the first-stage heat preservation is 65-85 DEG C, and the time is 30-120 min.
[0032] In an alternative embodiment, in the S3, the temperature for dropping the pre-emulsion B and the initiator aqueous solution is 35-85 DEG C, and the time is 90-240 min.
[0033] In an alternative embodiment, in the S3, the temperature for the second-stage heat preservation is 35-85 DEG C, and the time is 30-90 min.
[0034] In an alternative embodiment, in the S4, the temperature for dropping the initiator aqueous solution is 35-85 DEG C, and the time is 30-60 min.
[0035] In an alternative embodiment, the emulsifier comprises a reactive emulsifier containing propylene oxide and / or a reactive emulsifier containing sulfonic acid group; in a further alternative embodiment, the emulsifier comprises at least one of acrylamide isopropyl sulfonic acid sodium, vinyl sulfonic acid sodium, p-styrene sulfonic acid sodium, 2-acrylamide-2-methyl propane sulfonic acid sodium salt, 3-allyloxy-2-hydroxy-1-propane sulfonic acid sodium salt, and 2-acrylamide-2-methyl propane sulfonic acid.
[0036] In an alternative embodiment, the protective colloid comprises at least one of sodium carboxymethyl cellulose and fatty alcohol polyoxyethylene ether.
[0037] In an alternative embodiment, the initiator comprises at least one of ammonium sulfate, sodium persulfate, potassium persulfate, ammonium persulfate, erythorbic acid, and sodium bisulfite.
[0038] In an alternative embodiment, the mass concentration of the initiator aqueous solution is 0.1%-1.5%.
[0039] In a third aspect, the application further provides a negative electrode tab comprising the above-mentioned secondary battery binder or the secondary battery binder prepared by the above-mentioned preparation method.
[0040] The technical scheme of the application has the following advantages: 1.A secondary battery binder provided by the present application, comprising latex particles, the latex particles comprising an inner core polymer and a shell polymer coated on at least part of the surface of the inner core polymer; the inner core polymer is prepared from raw monomers, the raw monomers comprising a first double-bond-containing hydrophilic monomer, a double-bond-containing hydrophobic monomer and a first functional monomer; the mass of the double-bond-containing hydrophobic monomer is 1%-25% of the mass of the first double-bond-containing hydrophilic monomer; the first double-bond-containing hydrophilic monomer comprises acrylonitrile and a non-acrylonitrile double-bond-containing hydrophilic monomer; the mass ratio of acrylonitrile to the non-acrylonitrile double-bond-containing hydrophilic monomer in the first double-bond-containing hydrophilic monomer is 55:45-95:5; the shell polymer is prepared from raw monomers, the raw monomers comprising a second double-bond-containing hydrophilic monomer. The secondary battery binder has high adhesion, excellent shear stability, good dispersibility for electrode active materials, and can provide good anti-swelling ability and electrical properties for the secondary battery.
[0041] Specifically, the inner core polymer of the latex particles in the secondary battery binder provided by the present application is prepared from raw monomers, the raw monomers comprising a first double-bond-containing hydrophilic monomer and a double-bond-containing hydrophobic monomer, and the mass of the double-bond-containing hydrophobic monomer is 1%-25% of the mass of the first double-bond-containing hydrophilic monomer. The slightly cross-linked network structure formed by using a large amount of hydrophilic monomers and a small amount of hydrophobic monomers can improve the rigidity of the latex particles, so that the latex particles in the binder will not deform during subsequent processing, such as rolling, and will maintain a good spherical structure; this can improve the strength of the material itself, and also allows a certain gap to be left between the active materials of the electrode sheet, so as to ensure the infiltration of the electrolyte into the electrode sheet, facilitate the migration of ions, and thus improve the kinetic performance of the battery, and the gap left can also provide space for the expansion of the active materials during charging and discharging, relieving the rebound expansion of the electrode sheet during charging and discharging.
[0042] The addition of the double-bond-containing hydrophobic monomer in the raw monomers of the inner core polymer also increases the affinity of the secondary battery binder for the electrolyte, which is beneficial to the infiltration of the electrolyte in the electrode sheet. The hydrophilic groups on the first double-bond-containing hydrophilic monomer in the raw monomers of the inner core polymer can provide a channel for the transmission of ions inside the binder, reducing the influence of the binder on the conductivity of the battery. Since the amount of the double-bond-containing hydrophobic monomer in the inner core polymer is relatively low, and the amount of the first double-bond-containing hydrophilic monomer is relatively high, this will have a certain impact on the polymerization stability. Therefore, the acrylonitrile content is specified to improve the polymerization stability.
[0043] In the raw monomers of the shell polymer, the use of the second double-bond-containing hydrophilic monomer can improve the emulsion stability of the corresponding active material slurry during preparation, and also ensures the peeling ability of the electrode sheet using the binder, and is beneficial to the high-speed transmission of ions on the surface of the latex particles and between the latex particles.
[0044] 2. This invention provides a method for preparing the above-mentioned binder for secondary batteries, comprising the following steps: S1: preparing a pre-emulsion A for synthesizing the core polymer; the pre-emulsion A includes the raw material monomers of the core polymer, water, and an emulsifier; preparing a pre-emulsion B for synthesizing the shell polymer; the pre-emulsion B includes the raw material monomers of the shell polymer, water, and an emulsifier; preparing a base water, wherein the base water is an aqueous solution of an emulsifier and / or a protective colloid; preparing an initiator aqueous solution; S2: adding pre-emulsion A and the initiator aqueous solution dropwise to the base water, and performing a first stage of heat preservation after the dropwise addition is completed; S3: after the first stage of heat preservation is completed, adding pre-emulsion B and the initiator aqueous solution dropwise, and performing a second stage of heat preservation after the dropwise addition is completed; S4: after the second stage of heat preservation is completed, continuing to add the initiator aqueous solution dropwise to obtain the binder for secondary batteries. This method achieves stable preparation of the binder for secondary batteries, which is beneficial for the large-scale production of the binder. Attached Figure Description
[0045] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0046] Figure 1 This is a particle size distribution diagram of the binder for secondary batteries obtained in Example 1 of the present invention; Figure 2 This is a SEM image of the secondary battery adhesive obtained in Example 1 of the present invention after coating and baking; Figure 3 The image shows the cyclic voltammetry curve of a coin cell made using the binder for secondary batteries obtained in Example 1 of this invention. Figure 4 This is an image of the AC impedance curve of a coin cell made using the binder for secondary batteries obtained in Example 1 of the present invention. Detailed Implementation
[0047] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.
[0048] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagents or instruments, and all reagents are of analytical grade.
[0049] Experimental materials Sodium 3-allyloxy-2-hydroxy-1-propanesulfonate (HAPS): Produced by Inokai; Methacrylic acid (MAA): Produced by Wanhua Chemical; Acrylic acid (AA): Produced by Wanhua Chemical; Acrylonitrile (AN): Produced by Wanhua Chemical; Methyl acrylate (MA): Produced by Wanhua Chemical; Pentaerythritol triallyl ether (APE): Produced by Inokai; Acrylamide (AM): Produced by Wanhua Chemical; Sodium persulfate (SPS): Produced by Jinan Jinhao Chemical Co., Ltd. Sodium carboxymethyl cellulose (CMC): Produced by Sinopec Sichuan Chemical Industry Co., Ltd.
[0050] Example 1 This embodiment provides a binder for secondary batteries and its preparation method, including the following steps: (1) Take methacrylic acid and acrylonitrile at a mass ratio of 10:80 as the first hydrophilic monomer containing double bonds, take methyl acrylate at 11% of the mass of the first hydrophilic monomer containing double bonds as the hydrophobic monomer containing double bonds, and take pentaerythritol triallyl ether at 0.33% of the mass of the first hydrophilic monomer containing double bonds as the first functional monomer; take the mass of the first hydrophilic monomer containing double bonds, the hydrophobic monomer containing double bonds, the first functional monomer, and the mass of the raw material monomers of the core polymer; take 3-allyloxy-2-hydroxy-1-propanesulfonate sodium salt at 1.0% of the mass of the raw material monomers of the core polymer as the emulsifier, and take water at 100% of the mass of the raw material monomers of the core polymer. Mix the emulsifier, water, and raw material monomers of the core polymer to obtain pre-emulsion A.
[0051] Methacrylic acid, acrylamide, and acrylonitrile were used as the second hydrophilic monomer containing double bonds in a mass ratio of 20:5:25. In this embodiment, the mass of the second hydrophilic monomer containing double bonds is the same as the mass of the raw material monomer of the shell polymer. Sodium 3-allyloxy-2-hydroxy-1-propanesulfonate was taken at 1.0% of the mass of the raw material monomer of the shell polymer. Water was taken at 100% of the mass of the raw material monomer of the shell polymer. The emulsifier, water, and raw material monomer of the shell polymer were mixed to obtain pre-emulsion B.
[0052] Prepare an aqueous solution of the first initiator with a sodium persulfate mass concentration of 1.0%.
[0053] Prepare an aqueous solution of the second initiator with a sodium persulfate concentration of 0.8%.
[0054] A 0.100% (w / w) aqueous solution of sodium 3-allyloxy-2-hydroxy-1-propanesulfonate was prepared in the reactor as the bottom water.
[0055] (2) Heat the bottom water in the reactor to 80°C, and add preemulsion A and the first initiator aqueous solution dropwise over a period of 180 min. The mass of sodium 3-allyloxy-2-hydroxy-1-propanesulfonate in the bottom water is 1.0% of the total mass of the raw material monomers of the core polymer in preemulsion A (hereinafter referred to as monomers in preemulsion A), and the mass of sodium persulfate in the first initiator aqueous solution is 0.5% of the total mass of monomers in preemulsion A. After the dropwise addition is completed, continue to keep the temperature at 80°C for 30 min to obtain the polymer emulsion used as the core.
[0056] (3) Maintain 80°C and continue to add preemulsion B and the second initiator aqueous solution dropwise to the reactor for 180 min. The ratio of the total mass of monomers in preemulsion A to the total mass of raw material monomers of the shell polymer in preemulsion B (hereinafter referred to as monomers in preemulsion B) is 66.7:33.3. The mass of sodium persulfate in the second initiator aqueous solution is 0.4% of the total mass of monomers in preemulsion B. After the dropwise addition is completed, continue to keep the temperature at 80°C for 30 min.
[0057] (4) After the heat preservation is completed, the third initiator aqueous solution is added dropwise to the reactor at 80°C to eliminate residual monomers; the mass of sodium persulfate in the third initiator aqueous solution is 0.13% of the total mass of monomers in pre-emulsion A and pre-emulsion B. After the dropwise addition is completed, a polymer emulsion with a core-shell structure is obtained. The pH is adjusted to 8 with a 15% sodium hydroxide solution to obtain a binder for secondary batteries.
[0058] Example 2 This embodiment provides an adhesive for secondary batteries and its preparation method. Compared with Embodiment 1, the difference is that in step (1), methacrylic acid and acrylonitrile are used as the first hydrophilic monomer containing double bonds at a mass ratio of 10:85, methyl acrylate is used as the hydrophobic monomer containing double bonds at 5.3% of the mass of the first hydrophilic monomer containing double bonds, and pentaerythritol triallyl ether is used as the first functional monomer at 0.32% of the mass of the first hydrophilic monomer containing double bonds.
[0059] Example 3 This embodiment provides a binder for secondary batteries and its preparation method. Compared with Embodiment 2, the difference is that in step (1), in the preparation of preemulsion A, an equal mass of acrylic acid is used to replace methacrylic acid; in the preparation of preemulsion B, an equal mass of acrylic acid is used to replace methacrylic acid.
[0060] Example 4 This embodiment provides a binder for secondary batteries and its preparation method. Compared with embodiment 2, the difference is that in step (3), the ratio of the total mass of monomers in pre-emulsion A to the total mass of monomers in pre-emulsion B is 50:50.
[0061] Example 5 This embodiment provides a binder for secondary batteries and its preparation method. Compared with embodiment 3, the difference is that in step (1), methacrylic acid, acrylamide and acrylonitrile are used as the second hydrophilic monomer containing double bonds in a mass ratio of 15:5:30.
[0062] Example 6 This embodiment provides a binder for secondary batteries and its preparation method. Compared with Embodiment 1, the difference is that in step (1), a sodium carboxymethyl cellulose aqueous solution with a mass concentration of 0.2% is prepared in the reaction vessel as the bottom water; in steps (2) and (3), the temperature is 85°C.
[0063] Example 7 This embodiment provides a binder for secondary batteries and its preparation method, including the following steps: (1) Acrylonitrile and acrylamide are used as the first hydrophilic monomer containing double bonds in a mass ratio of 55:45. Butyl acrylate, which accounts for 25% of the mass of the first hydrophilic monomer containing double bonds, is used as the hydrophobic monomer containing double bonds. Ethylene glycol dimethacrylate, which accounts for 0.70% of the mass of the first hydrophilic monomer containing double bonds, is used as the first functional monomer. The mass of the first hydrophilic monomer containing double bonds, the hydrophobic monomer containing double bonds, the first functional monomer, and the raw material monomers of the core polymer are used as the raw material monomers. Sodium vinyl sulfonate, which accounts for 0.1% of the mass of the raw material monomers of the core polymer, is used as the emulsifier. Water, which accounts for 38% of the mass of the raw material monomers of the core polymer, is used as the emulsifier. The emulsifier, water, and raw material monomers of the core polymer are mixed to obtain pre-emulsion A.
[0064] Itaconic acid, acrylamide, and acrylonitrile were used as the second hydrophilic monomer containing double bonds in a mass ratio of 15:10:25. 0.01% of N,N-methylenebisacrylamide (by mass of the second hydrophilic monomer containing double bonds) was used as the second functional monomer. The mass of the second hydrophilic monomer containing double bonds, the second functional monomer, and the raw material monomers of the shell polymer were used. Sodium acrylamide isopropyl sulfonate (by mass of 2.5% of the raw material monomers of the shell polymer) was used as an emulsifier. Water (by mass of 140% of the raw material monomers of the shell polymer) was used. The emulsifier, water, and raw material monomers of the shell polymer were mixed to obtain pre-emulsion B.
[0065] Prepare an initiator aqueous solution with a potassium persulfate mass concentration of 0.5%.
[0066] A 0.015% (w / w) aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid was prepared in the reactor as the base water.
[0067] (2) Heat the bottom water in the reactor to 65°C, and add pre-emulsion A and initiator aqueous solution dropwise over a period of 240 min. The mass of 2-acrylamido-2-methylpropanesulfonic acid in the bottom water is 1.0% of the total mass of monomers in pre-emulsion A, and the mass of potassium persulfate in the initiator aqueous solution is 1% of the total mass of monomers in pre-emulsion A. After the addition is complete, continue to keep the temperature at 65°C for 120 min to obtain the polymer emulsion used as the core.
[0068] (3) Cool down to 35°C and continue to add preemulsion B and initiator aqueous solution dropwise to the reactor for 240 min. The ratio of the total mass of monomers in preemulsion A to the total mass of monomers in preemulsion B is 10:90, and the mass of potassium persulfate in the initiator aqueous solution is 1% of the total mass of monomers in preemulsion B. After the addition is completed, continue to keep warm at 35°C for 90 min.
[0069] (4) After the heat preservation is completed, an initiator aqueous solution is added dropwise to the reactor to eliminate residual monomers; the mass of potassium persulfate in the initiator aqueous solution is 0.1% of the total mass of monomers in pre-emulsion A and pre-emulsion B. After the dropwise addition is completed, a polymer emulsion with a core-shell structure is obtained. The pH is adjusted to 7 with a 15% sodium hydroxide solution to obtain a binder for secondary batteries.
[0070] Example 8 This embodiment provides a binder for secondary batteries and its preparation method, including the following steps: (1) Acrylonitrile and itaconic acid are used as the first hydrophilic monomer containing double bonds in a mass ratio of 95:5. Ethyl acrylate is used as the first hydrophobic monomer containing double bonds at 1% of the mass of the first hydrophilic monomer containing double bonds. Divinylbenzene is used as the first functional monomer at 0.05% of the mass of the first hydrophilic monomer containing double bonds. The mass of the first hydrophilic monomer containing double bonds, the hydrophobic monomer containing double bonds, the first functional monomer, and the raw material monomers of the core polymer are used as the mass. Sodium p-styrene sulfonate is used as the emulsifier at 2.5% of the mass of the raw material monomers of the core polymer. Water is used as the raw material monomers of the core polymer at 135% of the mass. The emulsifier, water, and raw material monomers of the core polymer are mixed to obtain pre-emulsion A.
[0071] Methacrylic acid, acrylamide, and acrylonitrile were used as the second hydrophilic monomer containing double bonds in a mass ratio of 5:15:30. 0.38% by mass of 1,4-butanediol diacrylate was used as the second functional monomer. The mass of the second hydrophilic monomer containing double bonds, the second functional monomer, and the raw material monomers of the shell polymer were used as the emulsifier. 0.15% by mass of sodium acrylamide isopropyl sulfonate was used as the emulsifier. 45% by mass of water was used as the raw material monomers of the shell polymer. The emulsifier, water, and raw material monomers of the shell polymer were mixed to obtain pre-emulsion B.
[0072] Prepare an initiator aqueous solution with a sodium bisulfite mass concentration of 1%.
[0073] A 0.5% sodium carboxymethyl cellulose aqueous solution was prepared in the reactor as the bottom water.
[0074] (2) Heat the bottom water in the reactor to 85°C, and add pre-emulsion A and initiator aqueous solution dropwise over a period of 90 min. The mass of sodium carboxymethyl cellulose in the bottom water is 0.1% of the total mass of monomers in pre-emulsion A, and the mass of sodium bisulfite in the initiator aqueous solution is 0.1% of the total mass of monomers in pre-emulsion A. After the dropwise addition is complete, continue to keep the temperature at 85°C for 30 min to obtain the polymer emulsion used as the core.
[0075] (3) Cool down to 85℃ and continue to add preemulsion B and initiator aqueous solution dropwise to the reactor for 90 min. The ratio of the total mass of monomers in preemulsion A to the total mass of monomers in preemulsion B is 65:35, and the mass of sodium bisulfite in the initiator aqueous solution is 0.1% of the total mass of monomers in preemulsion B. After the addition is completed, continue to keep warm at 85℃ for 30 min.
[0076] (4) After the heat preservation is completed, an initiator aqueous solution is added dropwise to the reactor to eliminate residual monomers; the mass of sodium bisulfite in the initiator aqueous solution is 1% of the total mass of monomers in pre-emulsion A and pre-emulsion B. After the dropwise addition is completed, a polymer emulsion with a core-shell structure is obtained. The pH is adjusted to 9 with a 15% sodium hydroxide solution to obtain a binder for secondary batteries.
[0077] Comparative Example 1 This comparative example provides a binder for secondary batteries and its preparation method. Compared with Example 1, the difference is that in step (1), methyl acrylate containing 28% by mass of the first hydrophilic monomer containing double bonds is used as the hydrophobic monomer containing double bonds.
[0078] Comparative Example 2 This comparative example provides a binder for secondary batteries and its preparation method. Compared with Example 1, the difference is that in step (1), methacrylic acid and acrylonitrile are used as the first hydrophilic monomer containing double bonds in a mass ratio of 60:30.
[0079] Comparative Example 3 Huitian New Materials 1205 (acrylic water-based adhesive) was used as the adhesive for secondary batteries in this comparative example.
[0080] Comparative Example 4 Showa LB300J (styrene-acrylic emulsion) was used as the binder for the secondary battery provided in this comparative example.
[0081] Comparative Example 5 This comparative example provides a binder for secondary batteries and its preparation method. Compared with Example 1, the difference is that in step (1), an equal mass of the first hydrophilic monomer containing double bonds is used to replace the first functional monomer.
[0082] Comparative Example 6 This comparative example provides a binder for secondary batteries and its preparation method. Compared with Example 1, the difference is that in step (1), methyl acrylate containing 0.5% by mass of the first hydrophilic monomer containing double bonds is taken as the hydrophobic monomer containing double bonds.
[0083] Comparative Example 7 This comparative example provides a binder for secondary batteries and its preparation method. Compared with Example 1, the difference is that in step (1), only acrylonitrile is used as the first hydrophilic monomer containing double bonds.
[0084] The binder for secondary batteries prepared in this comparative example has poor polymerization stability, making it impossible to obtain the final product and thus impossible to conduct subsequent testing.
[0085] Comparative Example 8 This comparative example provides a binder for secondary batteries and its preparation method. Compared with Example 1, the difference is that in step (1), pre-emulsion B is not prepared; and step (3) is not performed.
[0086] Experimental Example 1 The binders for secondary batteries prepared in the examples and comparative examples were tested for their latex particle size, weight-average molecular weight, glass transition temperature (Tg1) of the core polymer, glass transition temperature (Tg2) of the outer shell polymer, and solid content. The test methods are as follows, and the results are shown in Table 1.
[0087] (1) Testing the particle size (D50) of latex particles in the binder for secondary batteries: Weigh 5 g of the binder for secondary batteries, dilute it 10 times with deionized water, add it to the particle size analyzer, and take the test result D. 50 Data. The particle size distribution diagram of the binder for secondary batteries obtained in Example 1 is shown below. Figure 1 .
[0088] (2) Test the weight average molecular weight of latex particles in the binder for secondary batteries: refer to GB / T 36214.4-2018 for testing.
[0089] (3) Test Tg1 and Tg2: Refer to ISO 11357-1:2023 for testing.
[0090] Table 1
[0091] Experiment Example 2 The binder for secondary batteries prepared in the examples and comparative examples was used to prepare a negative electrode slurry, and then a negative electrode sheet was prepared, and the negative electrode sheet was assembled into a secondary battery.
[0092] The negative electrode slurry is prepared as follows: at room temperature, 0.5 parts by mass of sodium carboxymethyl cellulose are added to 100 parts of deionized water and stirred at high speed for 20 minutes at a speed of 1500 rpm. Then, 2.5 parts of conductive carbon black SP, 95.5 parts of negative electrode active material (graphite) and 1.5 parts of the above binder are added sequentially. After each material is added, the mixture is stirred at high speed for 15 minutes to ensure uniform mixing at a speed of 2000 rpm. The mixture is then filtered through a 100-mesh filter to obtain the negative electrode slurry.
[0093] The negative electrode sheet is prepared as follows: a 10 μm thick copper foil is used as the negative electrode current collector, and a 300 μm thick negative electrode slurry is coated onto one side of the current collector. Then, it is dried in a 90 ℃ oven for 5 min and naturally cooled to room temperature to obtain an unrolled negative electrode sheet. After rolling, the electrode sheet has a compacted density of 1.6 g / cm³. 3 Then, it is placed in a 135℃ oven and dried for 60 minutes to obtain the negative electrode sheet after rolling.
[0094] Assembly of the secondary battery: Lithium foil is used as the counter electrode, PP membrane (2500) is used, and 1.0M LiPF6 electrolyte is used. The electrolyte also includes 5.0wt% fluoroethylene carbonate (FEC). The solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 1:1:1. The counter electrode, membrane, electrolyte and the above-mentioned rolled negative electrode are assembled into a CR2025 coin cell.
[0095] The following performance tests were conducted, and the results are shown in Table 2.
[0096] (1) Test the dispersibility of the negative electrode slurry: Observe the number of pits n after baking the prepared negative electrode sheet that has not been rolled. o The fewer the number of pits, the better the dispersibility of the negative electrode slurry, and the lower the dispersibility grade. Specifically, n o When n = 0, the dispersion is recorded as level 0; 0 < n o When the dispersion is ≤10, it is recorded as level 1; when 10 < n o When the dispersion is ≤20, it is recorded as level 2; n o When the dispersion is greater than 20, it is recorded as level 3.
[0097] (2) Testing the shear resistance of latex particles in the binder for secondary batteries: Weigh 500 g of the binder for secondary batteries into a container and stir it for 1 h at 2000 r / min using a high-speed disperser. Use the high-speed, long-time stirred binder for secondary batteries obtained here to replace the untreated binder for secondary batteries, and prepare the electrode sheet according to the above preparation steps for negative electrode slurry and negative electrode sheet. Observe the morphology of latex particles on the electrode sheet by scanning electron microscopy (SEM). The corresponding SEM image of the binder for secondary batteries obtained in Example 1 is shown in [reference needed]. Figure 2 The diameter of latex particles was measured using SEM software to evaluate the shear resistance of the emulsion. Specifically, the maximum diameter of the latex particles was denoted as 'a', and the minimum diameter of the latex particles was denoted as 'b'. A shear resistance was considered good if a ≤ 5%a; moderate if 5%a < ab ≤ 15%a; and poor if ab > 15%a.
[0098] (3) Testing the polymerization stability of the binder for secondary batteries: Polymerization stability is reflected by residue content, which is the mass of non-volatile substances remaining after the sample is baked. When the polymerization stability is high, the binder is either completely cured or decomposed into volatile small molecules, resulting in a low residue content. When the polymerization stability is low, unreacted monomers or oligomers in the binder will remain, resulting in a high residue content. The binder was filtered using a 200-mesh filter. The filter residue was baked in an oven at 90°C for 30 minutes, and its mass was weighed to calculate the residue content. Specifically, a residue content ≤ 50 ppm indicates good polymerization stability; 50 ppm < residue content ≤ 200 ppm indicates moderate polymerization stability; and residue content > 200 ppm indicates poor polymerization stability.
[0099] (4) Testing the peel strength of the negative electrode sheet: The rolled negative electrode sheet was cut into sheets 200 mm long and 25 mm wide along the rolling direction. The sheet was flatly attached to a smooth steel plate with 3M double-sided tape. The stainless steel plate was then fixed on a tensile testing machine. The portion of the electrode sheet not attached to the tape was clamped in the opposite direction onto the probe of the tensile testing machine. The base of the tensile testing machine pulled the sheet at a speed of 10 cm / min. The sensor measured the peel force during the process. Five parallel samples were tested for each type of sample, and the average value was taken as the final peel strength, in N / m.
[0100] (5) Testing the oxidation peak of the secondary battery using CV (cyclic voltammetry): The prepared secondary batteries were connected to a CHI660e electrochemical workstation, and the CV peak was measured at a scan rate of 0.5 mV / s in the range of 0.01~3.0 V (vs Li / Li). + The potential range of the secondary battery was tested to obtain the corresponding CV curve, and the CV oxidation peak was obtained through CV curve analysis. The cyclic voltammogram of the corresponding coin half-cell for the binder used in Example 1 is shown below. Figure 3 .
[0101] (6) Testing the charge transfer resistance (Rct) of the secondary battery: The prepared secondary batteries were connected to a CHI660e electrochemical workstation, and the test frequency range was controlled from 10 mHz to 100 kHz to obtain their EIS (electrochemical impedance spectroscopy) curves. The Rct value was further analyzed. The AC impedance curve of the corresponding coin half-cell of the secondary battery obtained in Example 1 using the binder is shown in the figure. Figure 4 , Figure 4 In the diagram, the horizontal axis represents the real part of the impedance, and the vertical axis represents the imaginary part of the impedance.
[0102] (7) Testing the full-charge expansion of the secondary battery: The expansion test of the coin cell was carried out using the MCS1000 model battery coin cell in-situ expansion test system. The test parameters were: current density of 0.6 mA / cm². 2 The voltage is 0~3V.
[0103] Table 2
[0104] A comparison of the data from the examples and comparative examples in Tables 1 and 2 shows that the binder prepared using the binder preparation method for secondary batteries provided in this invention in the examples simultaneously meets the following requirements: the glass transition temperature of the core polymer is 50℃ < Tg1 < 105℃, the glass transition temperature of the outer shell polymer is 90℃ < Tg2 < 165℃, and the particle size D of the latex particles is [not specified]. 50 The latex particles, with a weight-average molecular weight of 200,000 to 750,000 and a range of 120–750 nm, exhibit excellent adhesion, shear resistance, and polymerization stability. They provide excellent dispersibility for electrode slurries and offer better electrical performance and lower electrode swelling at full charge. Regarding electrical performance, the binder for secondary batteries provided in the examples results in half-cells with smaller CV oxidation peaks, less battery polarization, and less negative impact on battery performance; the Rct value is also significantly lower, leading to smoother charge transfer during charging and discharging. While Comparative Examples 5 and 6 also meet the above requirements for glass transition temperature, particle size range, and weight-average molecular weight, Comparative Example 5 lacks a first functional monomer in its core polymer monomers, resulting in higher residue content, higher swelling at full charge, and poorer electrical performance. Comparative Example 6, on the other hand, has a lower amount of hydrophobic core monomers in its core polymer monomers, leading to higher residue content, poor dispersibility, lower peel strength, and poorer electrical performance.
[0105] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.
Claims
1. An adhesive for secondary batteries, characterized in that, It includes latex particles, the latex particles comprising a core polymer and a shell polymer covering at least a portion of the surface of the core polymer; The raw material monomers of the core polymer include a first hydrophilic monomer containing double bonds, a hydrophobic monomer containing double bonds, and a first functional monomer. The mass of the hydrophobic monomer containing double bonds is 1% to 25% of the mass of the hydrophilic monomer containing double bonds; The first hydrophilic monomer containing double bonds includes acrylonitrile and non-acrylonitrile hydrophilic monomers containing double bonds; in the first hydrophilic monomer containing double bonds, the mass ratio of acrylonitrile to non-acrylonitrile hydrophilic monomers containing double bonds is 55:45 to 95:
5. The raw material monomers of the shell polymer include a second hydrophilic monomer containing double bonds.
2. The adhesive for secondary batteries according to claim 1, characterized in that, The raw material monomers of the shell polymer also include a second functional monomer, the mass of which is 0.01% to 0.38% of the mass of the second hydrophilic monomer containing double bonds; And / or, the mass of the first functional monomer is 0.05% to 0.70% of the mass of the first hydrophilic monomer containing double bonds; And / or, the mass ratio of the raw material monomers of the core polymer to the raw material monomers of the shell polymer is 10:90 to 67:
33.
3. The adhesive for secondary batteries according to claim 1 or 2, characterized in that, The glass transition temperature Tg1 of the core polymer is 50℃ < Tg1 < 105℃; And / or, the glass transition temperature Tg2 of the outer shell polymer is 90℃ < Tg2 < 165℃; And / or, the particle size D of the latex particles 50 The range is 120~750nm; optionally, the particle size D of the latex particles is... 50 The range is 250~550nm; And / or, the weight-average molecular weight of the latex particles is 200,000 to 750,000; optionally, the weight-average molecular weight of the latex particles is 350,000 to 550,000. And / or, the pH of the binder for the secondary battery is 7-9.
4. The adhesive for secondary batteries according to claim 2, characterized in that, The non-acrylonitrile hydrophilic monomer containing double bonds includes at least one of acrylic acid, methacrylic acid, acrylamide, methacrylamide, and itaconic acid; And / or, the second hydrophilic monomer containing double bonds includes at least one of acrylic acid, methacrylic acid, acrylamide, methacrylamide, itaconic acid, acrylonitrile, and methacrylonitrile; And / or, the hydrophobic monomer containing double bonds includes acrylate monomers with a glass transition temperature range of -70 to 10°C; optionally, the hydrophobic monomer containing double bonds includes at least one of methyl acrylate, ethyl acrylate, butyl acrylate, and isooctyl acrylate. And / or, the first functional monomer and the second functional monomer are each independently selected from at least one of divinylbenzene, diallyl phthalate, pentaerythritol triallyl ether, ethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate, and N,N-methylenebisacrylamide.
5. A method for preparing a binder for secondary batteries as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1: Prepare pre-emulsion A for the synthesis of core polymers; The preemulsion A includes the raw material monomers of the core polymer, water, and emulsifier; Prepare a pre-emulsion B for synthesizing the shell polymer; The preemulsion B includes the raw material monomers of the shell polymer, water, and emulsifier; Prepare a base water, wherein the base water is an aqueous solution of emulsifier and / or protective colloid; Prepare an aqueous solution of the initiator; S2: Add pre-emulsion A and initiator aqueous solution dropwise to the bottom water. After the addition is completed, perform the first stage of heat preservation. S3: After the first stage of heat preservation is completed, add pre-emulsion B and initiator aqueous solution dropwise. After the addition is completed, proceed with the second stage of heat preservation. S4: After the second stage of heat preservation is completed, continue to add the initiator aqueous solution to obtain the binder for the secondary battery.
6. The preparation method according to claim 5, characterized in that, In the preemulsion A, the mass of water is 38% to 135% of the mass of the raw material monomers of the core polymer; And / or, in the preemulsion A, the mass of the emulsifier is 0.1% to 2.5% of the mass of the raw material monomers of the core polymer; And / or, in the preemulsion B, the mass of water is 45% to 140% of the mass of the raw material monomers of the shell polymer; And / or, in the preemulsion B, the mass of the emulsifier is 0.15% to 2.50% of the mass of the raw material monomers of the shell polymer; And / or, in the bottom water, the mass concentration of the emulsifier and / or protective colloid is 0.015% to 0.500%.
7. The preparation method according to claim 5, characterized in that, In step S2, the mass of the initiator in the initiator aqueous solution is 0.1% to 1% of the mass of the raw material monomers of the core polymer in preemulsion A; And / or, in S3, the mass of the initiator in the initiator aqueous solution is 0.1% to 1% of the mass of the raw material monomer of the shell polymer in preemulsion B; And / or, in S4, the mass of the initiator in the initiator aqueous solution is 0.1% to 1% of the sum of the raw material monomers of the core polymer in preemulsion A and the raw material monomers of the shell polymer in preemulsion B; And / or, in S2, the mass of the emulsifier and / or protective colloid in the bottom water is 0.1% to 1.0% of the mass of the raw material monomers of the core polymer in the pre-emulsion A; And / or, after S4, the method further includes a step of adjusting the pH of the binder for the secondary battery to 7-9 using an alkaline solution; optionally, the alkaline solution includes at least one of lithium hydroxide solution and sodium hydroxide solution.
8. The preparation method according to claim 5, characterized in that, In step S2, the temperature at which the preemulsion A and the initiator aqueous solution are added is 65~85℃, and the time is 90~240min; And / or, in S2, the temperature of the first stage of heat preservation is 65~85℃, and the time is 30~120min; And / or, in S3, the temperature at which the preemulsion B and the initiator aqueous solution are added is 35~85℃, and the time is 90~240min; And / or, in S3, the temperature of the second stage of heat preservation is 35~85℃, and the time is 30~90min; And / or, in S4, the temperature of the initiator aqueous solution added is 35~85℃, and the time is 30~60min.
9. The preparation method according to any one of claims 5 to 8, characterized in that, The emulsifier includes reactive emulsifiers containing an acryloxy group and / or reactive emulsifiers containing a sulfonic acid group; optionally, the emulsifier includes at least one of sodium acrylamide isopropyl sulfonate, sodium vinyl sulfonate, sodium p-styrene sulfonate, sodium 2-acrylamido-2-methylpropane sulfonate, sodium 3-allyloxy-2-hydroxy-1-propane sulfonate, and 2-acrylamido-2-methylpropane sulfonic acid. And / or, the protective adhesive includes at least one of sodium carboxymethyl cellulose and fatty alcohol polyoxyethylene ether; And / or, the initiator includes at least one of ammonium sulfate, sodium persulfate, potassium persulfate, ammonium persulfate, isoascorbic acid, and sodium bisulfite; And / or, the mass concentration of the initiator aqueous solution is 0.1% to 1.5%.
10. A negative electrode sheet, characterized in that, Includes the binder for secondary batteries as described in any one of claims 1 to 4, or the binder for secondary batteries prepared by the preparation method described in any one of claims 5 to 9.