A water-based binder for reverse phase suspension polymer lithium battery and preparation method thereof

Abstract

The present invention belongs to the field of binders, specifically relating to an aqueous binder for reversed-phase suspension polymerization of lithium batteries and its preparation method. The raw materials for preparing the aqueous binder for reversed-phase suspension polymerization of lithium batteries provided by the present invention include: a polysaccharide, an acrylic acid monomer, a dispersant, an initiator, a crosslinker, a neutralizing base, an oil-phase solvent, and deionized water. The product is produced by reversed-phase suspension polymerization. The aqueous binder for reversed-phase suspension polymerization of lithium batteries provided by the present invention has excellent bonding properties and a 180° peel strength greater than 8 N / m, representing a significant improvement over existing technologies.

Description

Technical Field

[0001] The present invention belongs to the field of binders, and specifically relates to a water-based binder for reverse phase suspension polymer lithium batteries and a preparation method thereof. Background Art

[0002] Binders are crucial components in lithium-ion batteries (LIBs). Beyond their basic bonding function, they are crucial for ensuring efficient and stable battery operation. Within the complex LIB structure, binders primarily bind active materials (such as lithium cobalt oxide, lithium nickel manganese cobalt oxide, or graphite) to conductive agents and current collectors, forming a conductive and mechanically stable electrode structure. Binders effectively prevent the active materials from shedding or decomposing during repeated charge and discharge cycles due to volume changes and mechanical stresses caused by chemical reactions, thereby maintaining long-term battery performance. Binders also play a key role in reducing the battery's internal resistance by optimizing the internal microstructure of the electrode. They facilitate smooth conduction of electrons and ions within the electrode, reducing energy losses during transmission and ultimately improving the battery's energy density and power output. Furthermore, the selection and design of the binder directly impact the cycle life of the LIB. A suitable binder can effectively resist stress accumulation during charge and discharge, slowing electrode aging and extending the battery's service life.

[0003] For environmental reasons, water-based binders have become the mainstream choice for lithium-ion battery anode materials. Compared to oil-based binders, water-based binders are more environmentally friendly to produce and use, have less environmental impact, and offer a higher cost-performance ratio. In the market, a system consisting of styrene-butadiene rubber (SBR) latex and sodium carboxymethyl cellulose (CMC) has become the most common water-based binder formulation due to its excellent bonding and electrical properties. However, actual research has shown that the bonding performance of SBR / CMC blends still has significant room for improvement. Chinese patent CN112142917B discloses a modified chitosan water-based binder and its preparation method. The binder's raw materials include chitosan, acrylic acid, trifluoroethyl acrylate, and ammonium persulfate. The binder is obtained using conventional techniques. However, its peel strength depends primarily on the chemical modification of chitosan with fluorine, resulting in high raw material costs.

[0004] Reverse suspension system binders are polymer materials prepared using reverse suspension polymerization technology. While traditional suspension polymerization typically uses water as the continuous phase, reverse suspension polymerization utilizes an oil phase as the continuous medium, dispersing water-soluble monomers into tiny droplets for polymerization. This reverse suspension bonding process is particularly suitable for preparing microspheres or granular polymer materials with controllable particle size and uniform structure. However, there are currently few reports in China on the preparation of water-based binders using the reverse suspension polymerization mechanism. Summary of the Invention

[0005] In order to solve the above technical problems, the first aspect of the present invention provides a method for preparing an aqueous binder for an inverse phase suspension polymer lithium battery, characterized in that it comprises:

[0006] S1. Add polysaccharide to a reactor, then add water, raise the temperature to 45-65°C, stir for 1-1.5 hours, and then cool to obtain a polysaccharide aqueous solution;

[0007] Add acrylic acid monomer to another reaction kettle, cool to 0-5°C, add neutralizing base dropwise, then add crosslinking agent and initiator in sequence, mix well, then add to polysaccharide aqueous solution, mix well to obtain dispersed phase;

[0008] S2, mixing the oil phase solvent and the dispersant to obtain a continuous phase;

[0009] S3. Add the dispersed phase to the continuous phase and stir for 45-50 min to form a reverse suspension system. Then heat the mixture to 65-75°C to carry out polymerization. After the reaction is completed, cool the mixture and collect the solid by filtration. After washing the solid, add it to water and then add a neutralizing base to adjust the pH of the system to 7-9. Dilute the mixture to obtain a water-based binder.

[0010] Furthermore, the mass ratio of the oil phase solvent to water is 1:(3-10).

[0011] Furthermore, the water is deionized water.

[0012] Furthermore, the preparation method of the aqueous binder for reverse phase suspension polymer lithium battery comprises:

[0013] S1. Add polysaccharide to a reactor, then add deionized water, raise the temperature to 45-65°C under a nitrogen atmosphere, stir at 100-150 rpm for 1-1.5 h, and then cool to 20-30°C to obtain a polysaccharide aqueous solution;

[0014] Add acrylic acid monomer to another reaction kettle, cool to 0-5°C, add neutralizing base dropwise, then add crosslinking agent and initiator in sequence, mix well, then add to polysaccharide aqueous solution, mix well to obtain dispersed phase;

[0015] S2. Mix the oil phase solvent and the dispersant, then introduce nitrogen and stir at a speed of 250-350 rpm to obtain a continuous phase;

[0016] S3. Add the dispersed phase to the continuous phase, then introduce nitrogen and stir for 45-50 minutes to form a reverse suspension system. Then, heat the mixture to 65-75°C to carry out polymerization. After the reaction, cool the mixture to 20-30°C, filter and collect the solid. After washing the solid, add it to deionized water, then add a neutralizing base to adjust the pH of the system to 7-9, and then dilute it to obtain a water-based binder.

[0017] As an implementable case, the mass ratio of the polysaccharide to the acrylic acid monomer is (3-30): (30-60).

[0018] As an implementable example, the polysaccharide includes one of gelatin, alginate, chitosan or mannan.

[0019] Furthermore, the polysaccharide includes chitosan.

[0020] Furthermore, the chitosan has a deacetylation degree greater than 90% and is purchased from Zhejiang Golden Shell Pharmaceutical Co., Ltd.

[0021] Chitosan is a natural polymer material that is widely available, abundant, and renewable. However, chitosan is hygroscopic and easily deteriorates due to moisture, which affects its mechanical properties and stability as a binder. In addition, the solubility and degradation rate of chitosan do not fully meet the requirements of lithium battery bonding applications, so functional modification is required. When chitosan is modified with acrylic monomers, its mechanical strength and stability can be significantly improved, allowing it to withstand greater loads and exhibit better adaptability. At the same time, through modification, the hydrophilicity and hydrophobicity of chitosan can be optimized, thereby better regulating its interaction with the bonded material and thereby improving the bonding effect. In addition, the electrical properties of the modified chitosan binder are also improved while maintaining its original biocompatibility and degradability.

[0022] As an implementable case, the acrylic monomer includes at least one of acrylic acid and methacrylic acid.

[0023] As an implementable case, the initiator includes one or more of benzoyl peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, and cumene hydroperoxide.

[0024] Furthermore, the initiator includes one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0025] As an implementable case, the dispersant includes at least one of a Span dispersant and a Tween dispersant.

[0026] Furthermore, the Span dispersant includes Span 60 or Span 80.

[0027] Furthermore, the Tween dispersant includes Tween 60 or Tween 80.

[0028] As an implementable example, the cross-linking agent includes N,N'-methylenebisacrylamide.

[0029] Furthermore, the mass ratio of the acrylic acid monomer, the crosslinking agent and the initiator is (30-60): (0.5-1.5): (0.2-1.0).

[0030] As an implementable case, the neutralizing base includes one of a sodium hydroxide aqueous solution, a sodium carbonate aqueous solution or a sodium bicarbonate aqueous solution.

[0031] Furthermore, the sodium hydroxide aqueous solution is a sodium hydroxide aqueous solution with a mass concentration of 10-30 wt%.

[0032] As an implementable example, the oil phase solvent includes one of tetrahydrofuran, acetone, cyclohexane, dimethyl sulfoxide, and N-methylpyrrolidone.

[0033] Furthermore, the oil phase solvent is cyclohexane.

[0034] Furthermore, the mass ratio of the oil phase solvent to deionized water is 1:(3-10).

[0035] In the mass ratio of the oil phase solvent to deionized water, the mass fraction of deionized water is the weight of the deionized water used in step S1 and step S3.

[0036] Reverse suspension polymerization is a polymerization method in which a dispersed phase (aqueous phase) is dispersed in a continuous phase (oil phase). Water-based binders prepared by the reverse suspension polymerization method have higher peel strength. The inventors speculate that this is mainly because in the reverse suspension system, the aqueous phase monomer droplets are tightly wrapped by the oil phase and formed into uniformly sized microspheres through stirring. The uniform particle structure can significantly improve the dispersibility of the binder in the electrode slurry, effectively reducing agglomeration. The uniform particle surface can better wet the current collector, increase the effective contact area, and enhance the physical anchoring effect between the binder and the substrate. At the same time, in the reverse suspension system, the crosslinking agent is confined within the aqueous phase droplets, and the crosslinking points are more evenly distributed during the reaction, forming a dense three-dimensional network structure. The high crosslinking density of the three-dimensional network structure can significantly improve the cohesive strength of the water-based binder, making it less likely to break during the peeling process, thereby improving the peel strength.

[0037] In addition, the amino and hydroxyl groups in the chitosan molecular chain can form hydrogen bonds with the carboxyl groups of the acrylic acid monomers, thereby enhancing the rigidity of the polymer network. The flexible chain segments formed by acrylic acid polymerization can absorb the mechanical stress during the charge and discharge process, effectively preventing the expansion of electrode cracks. After adding a neutralizing base, the pH of the system is adjusted to 7-9, ionizing the acrylic acid carboxyl groups and enhancing the electrostatic adsorption force between the binder and the positively charged current collector. At the same time, chitosan is partially deacetylated under alkaline conditions, exposing more amino groups (-NH2), further enhancing interfacial chemical bonding. Within the confined space of the reverse suspension system, chitosan reacts with the monomer droplets of acrylic acid, making the entanglement and chemical bonding of the molecular chains tighter, thereby further improving the bonding properties of the water-based binder.

[0038] The second aspect of the present invention provides an aqueous binder for inverse phase suspension polymer lithium batteries prepared according to the method for preparing an aqueous binder for inverse phase suspension polymer lithium batteries.

[0039] Beneficial effects

[0040] (1) Binders play a crucial role in lithium-ion batteries, affecting not only the initial performance but also the cycle life. The aqueous binder provided by this invention improves the dispersibility of raw material components and reduces agglomeration, thereby increasing peel strength, thereby helping to enhance the overall performance of lithium-ion batteries, particularly their cycle life.

[0041] (2) The water-based adhesive provided by the present invention has a relatively high peel strength, with a 180° peel strength greater than 8 N / m. After use, it can improve the overall performance of lithium-ion batteries to a certain extent.

[0042] (3) The present invention mainly carries out a reverse suspension process in the preparation process of the water-based adhesive. By dispersing the dispersed phase in the continuous phase, the agglomeration phenomenon is effectively reduced, thereby increasing the effective contact area between the water-based adhesive and the substrate and improving the bonding effect.

[0043] (4) The aqueous binder prepared by the inverse suspension polymerization method of the present invention exhibits higher peel strength than commonly used aqueous SBR / CMC composite binders on the market (180° peel strength less than 4 N / m). The aqueous binder provided by the present invention exhibits higher peel strength at the same addition amount, thereby more effectively bonding the active material, conductive agent, and current collector, preventing decomposition of the active material during continuous charge and discharge.

[0044] (5) Compared with oil-based binders, water-based binders are more environmentally friendly and more cost-effective. The water-based binder synthesized by the present invention based on the inverse suspension polymerization system not only has advantages in bonding performance, but also meets the current market demand for environmental protection and cost-effectiveness. Therefore, the product has broad market application prospects.

[0045] (6) In the present invention, by limiting the mass ratio of chitosan to acrylic acid monomer to (3-30): (30-60), the bonding performance of the aqueous adhesive can be further improved. If the amount of chitosan used is small, the bonding performance of the product will be significantly reduced. DETAILED DESCRIPTION

[0046] Example 1

[0047] The first aspect of this example provides a method for preparing an aqueous binder for an inverse phase suspension polymer lithium battery, specifically:

[0048] S1. Add chitosan to a reactor, add 60 g of deionized water, and introduce 0.01 MPa nitrogen for 25 min. Under nitrogen, heat to 50 °C, stir at 110 rpm for 1.0 h, and then cool to 25 °C to obtain a chitosan aqueous solution.

[0049] Acrylic acid was added to another reaction kettle, cooled to 5°C, and 80 g of 20 wt% sodium hydroxide aqueous solution was added dropwise. Then, N,N'-methylenebisacrylamide and ammonium persulfate were added in sequence. After mixing evenly, the mixture was added to the chitosan aqueous solution and mixed evenly to obtain a dispersed phase.

[0050] S2. Cyclohexane and Span 60 were mixed, nitrogen gas at 0.01 MPa was introduced for 25 min, and the mixture was stirred at 300 rpm to obtain a continuous phase;

[0051] S3. Add the dispersed phase to the continuous phase, then introduce 0.01 MPa nitrogen for 30 min, stir for 50 min to form a reverse suspension system, then heat to 65 ° C, and carry out polymerization reaction for 8 h. After the reaction is completed, cool to 25 ° C, filter and collect the solid, wash the solid and add it to 1130 g of deionized water, then add 28 g of 14 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 7, and obtain an aqueous binder with a solid content of 5 wt%.

[0052] The raw materials for preparing the aqueous binder for reverse phase suspension polymerization lithium batteries are specifically as follows by mass: 3.6 g chitosan, 36 g acrylic acid, 0.60 g Span 60, 0.28 g ammonium persulfate, 0.56 g N,N'-methylenebisacrylamide, 80 g 20 wt% sodium hydroxide aqueous solution, 28 g 14 wt% sodium hydroxide aqueous solution, 350 g cyclohexane, and 1190 g deionized water.

[0053] The chitosan has a deacetylation degree greater than 90% and is purchased from Zhejiang Golden Shell Pharmaceutical Co., Ltd.

[0054] The second aspect of this example provides an aqueous binder for inverse phase suspension polymer lithium batteries prepared according to the method for preparing an aqueous binder for inverse phase suspension polymer lithium batteries.

[0055] Example 2

[0056] The first aspect of this example provides a method for preparing an aqueous binder for an inverse phase suspension polymer lithium battery, specifically:

[0057] S1. Add chitosan to a reactor, add 90 g of deionized water, and introduce 0.01 MPa nitrogen for 25 min. Under nitrogen atmosphere, heat to 55 °C, stir at 150 rpm for 1.0 h, and then cool to 25 °C to obtain a chitosan aqueous solution.

[0058] Acrylic acid was added to another reaction kettle, cooled to 2°C, and 80 g of 25 wt% sodium hydroxide aqueous solution was added dropwise. Then, N,N'-methylenebisacrylamide and ammonium persulfate were added in sequence. After mixing evenly, the mixture was added to the chitosan aqueous solution and mixed evenly to obtain a dispersed phase.

[0059] S2. Cyclohexane and Span 80 were mixed, nitrogen gas at 0.01 MPa was introduced for 30 min, and the mixture was stirred at 300 rpm to obtain a continuous phase;

[0060] S3. Add the dispersed phase to the continuous phase, then introduce 0.01 MPa nitrogen for 25 minutes, stir for 50 minutes to form a reverse suspension system, then heat to 70 ° C, and carry out polymerization reaction for 6 hours. After the reaction is completed, cool to 25 ° C, filter and collect the solid, wash the solid and add it to 1500 g of deionized water, and then add 20 g of 25 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 7, thereby obtaining an aqueous binder with a solid content of 5 wt%.

[0061] The raw materials for preparing the aqueous binder for the reverse phase suspension polymerization lithium battery are specifically as follows by mass: 10 g chitosan, 45 g acrylic acid, 1.5 g Span 80, 1.0 g ammonium persulfate, 1.5 g N,N'-methylenebisacrylamide, 100 g 25 wt% sodium hydroxide aqueous solution, 450 g cyclohexane, and 1590 g deionized water.

[0062] The chitosan has a deacetylation degree greater than 90% and is purchased from Zhejiang Golden Shell Pharmaceutical Co., Ltd.

[0063] The second aspect of this example provides an aqueous binder for inverse phase suspension polymer lithium batteries prepared according to the method for preparing an aqueous binder for inverse phase suspension polymer lithium batteries.

[0064] Example 3

[0065] The first aspect of this example provides a method for preparing an aqueous binder for an inverse phase suspension polymer lithium battery, specifically:

[0066] S1. Add chitosan to a reactor, add 150 g of deionized water, and introduce 0.01 MPa nitrogen for 25 min. Under nitrogen, heat to 60 °C, stir at 150 rpm for 1.5 h, and then cool to 25 °C to obtain a chitosan aqueous solution.

[0067] Add methacrylic acid to another reaction kettle, cool to 3°C, add 54 g of 25 wt% sodium hydroxide aqueous solution dropwise, then add N,N'-methylenebisacrylamide and potassium persulfate in sequence, mix well, and then add to the chitosan aqueous solution and mix well to obtain a dispersed phase;

[0068] S2. Cyclohexane and Tween 60 were mixed, nitrogen gas at 0.01 MPa was introduced for 30 min, and the mixture was stirred at 300 rpm to obtain a continuous phase;

[0069] S3. Add the dispersed phase to the continuous phase, then introduce 0.01 MPa nitrogen for 25 min, stir for 50 min to form a reverse suspension system, then heat to 70 ° C, and carry out polymerization reaction for 7 h. After the reaction is completed, cool to 25 ° C, filter and collect the solid, wash the solid and add it to 1380 g of deionized water, then add 18 g of 25 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 7, and obtain an aqueous binder with a solid content of 5 wt%.

[0070] The raw materials for preparing the aqueous binder for reverse phase suspension polymerization lithium battery are specifically as follows by mass: 20 g chitosan, 32.4 g methacrylic acid, 1.5 g Tween 60, 0.9 g potassium persulfate, 1.1 g N,N'-methylenebisacrylamide, 72 g 25 wt% sodium hydroxide aqueous solution, 250 g cyclohexane, and 1530 g deionized water.

[0071] The chitosan has a deacetylation degree greater than 90% and is purchased from Zhejiang Golden Shell Pharmaceutical Co., Ltd.

[0072] The second aspect of this example provides an aqueous binder for inverse phase suspension polymer lithium batteries prepared according to the method for preparing an aqueous binder for inverse phase suspension polymer lithium batteries.

[0073] Example 4

[0074] The first aspect of this example provides a method for preparing an aqueous binder for an inverse phase suspension polymer lithium battery, specifically:

[0075] S1. Add chitosan to a reactor, add 180 g of deionized water, and introduce 0.01 MPa nitrogen for 25 min. Under nitrogen, heat to 60 °C, stir at 180 rpm for 1.5 h, and then cool to 25 °C to obtain a chitosan aqueous solution.

[0076] Methacrylic acid was added to another reaction kettle, cooled to 5°C, and 74.4 g of a 20 wt% sodium hydroxide aqueous solution was added dropwise. Then, N,N'-methylenebisacrylamide and potassium persulfate were added in sequence and mixed well. The mixture was then added to the chitosan aqueous solution and mixed well to obtain a dispersed phase.

[0077] S2. Cyclohexane and Tween 80 were mixed, nitrogen gas at 0.01 MPa was introduced for 30 min, and the mixture was stirred at 300 rpm to obtain a continuous phase;

[0078] S3. Add the dispersed phase to the continuous phase, then introduce 0.01 MPa nitrogen for 25 minutes, stir for 60 minutes to form a reverse suspension system, then heat to 75 ° C, carry out polymerization reaction for 6 hours, after the reaction is completed, cool to 25 ° C, filter and collect the solid, wash the solid and add it to 1630 g of deionized water, then add 18.6 g of 20 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 7, and obtain an aqueous binder with a solid content of 5 wt%.

[0079] The raw materials for preparing the aqueous binder for reverse phase suspension polymerization lithium battery are specifically as follows by mass: 25 g chitosan, 40 g methacrylic acid, 1.6 g Tween 80, 0.9 g potassium persulfate, 1.0 g N,N'-methylenebisacrylamide, 93 g 20 wt% sodium hydroxide aqueous solution, 600 g cyclohexane, and 1810 g deionized water.

[0080] The chitosan has a deacetylation degree greater than 90% and is purchased from Zhejiang Golden Shell Pharmaceutical Co., Ltd.

[0081] The second aspect of this example provides an aqueous binder for inverse phase suspension polymer lithium batteries prepared according to the method for preparing an aqueous binder for inverse phase suspension polymer lithium batteries.

[0082] Comparative Example 1

[0083] This example provides a water-based binder. The raw materials for preparation include, by weight, 28 g of SBR (50 wt% solid content), 6 g of CMC, and 420 g of deionized water.

[0084] The preparation method of the water-based binder is as follows: SBR, CMC and deionized water are mixed and stirred at room temperature of 25° C.

[0085] The SBR and CMC were purchased from Guangzhou Songbai Chemical Co., Ltd., and the model of CMC was CMC-203.

[0086] Comparative Example 2

[0087] The first aspect of this example provides a method for preparing a water-based binder for a non-inverse suspension polymer lithium battery, specifically:

[0088] S1. Add chitosan to a reactor, add 410 g of deionized water, and introduce 0.01 MPa nitrogen for 25 min. Under nitrogen, heat to 50 °C, stir at 110 rpm for 1.0 h, and then cool to 25 °C to obtain a chitosan aqueous solution.

[0089] Acrylic acid was added to another reaction kettle, cooled to 5°C, and 80 g of a 20 wt% sodium hydroxide aqueous solution was added dropwise. Then, N,N'-methylenebisacrylamide and ammonium persulfate were added in sequence and mixed well. The mixture was then added to the chitosan aqueous solution and mixed well to obtain a dispersed phase.

[0090] S2. The dispersed phase was introduced into nitrogen at 0.01 MPa for 30 min, stirred for 50 min, then heated to 65 ° C and polymerized for 8 h. After the reaction was completed, it was cooled to 25 ° C, filtered to collect the solid, washed and added to 1148 g of deionized water, and then 20 g of 20 wt% sodium hydroxide aqueous solution was added to adjust the pH of the system to 7, thereby obtaining an aqueous binder with a solid content of 5 wt%.

[0091] The raw materials for preparing the aqueous binder for non-inverse suspension polymer lithium battery are specifically as follows by mass: 3.6 g chitosan, 36 g acrylic acid, 0.28 g ammonium persulfate, 0.56 g N,N'-methylenebisacrylamide, 100 g 20 wt% sodium hydroxide aqueous solution, and 1558 g deionized water.

[0092] The chitosan has a deacetylation degree greater than 90% and is purchased from Zhejiang Golden Shell Pharmaceutical Co., Ltd.

[0093] The second aspect of this example provides a non-inverse suspension polymer lithium battery aqueous binder prepared according to the preparation method of the non-inverse suspension polymer lithium battery aqueous binder.

[0094] Comparative Example 3

[0095] The first aspect of this example provides a method for preparing an aqueous binder for an inverse phase suspension polymer lithium battery, specifically:

[0096] S1. Add chitosan to a reactor, add 50 g of deionized water, and introduce 0.01 MPa nitrogen for 25 min. Under nitrogen, heat to 50 °C, stir at 110 rpm for 1.0 h, and then cool to 25 °C to obtain a chitosan aqueous solution.

[0097] Acrylic acid was added to another reaction kettle, cooled to 5°C, and 80 g of 20 wt% sodium hydroxide aqueous solution was added dropwise. Then, N,N'-methylenebisacrylamide and ammonium persulfate were added in sequence. After mixing evenly, the mixture was added to the chitosan aqueous solution and mixed evenly to obtain a dispersed phase.

[0098] S2. Cyclohexane and Span 60 were mixed, nitrogen gas at 0.01 MPa was introduced for 25 min, and the mixture was stirred at 300 rpm to obtain a continuous phase;

[0099] S3. Add the dispersed phase to the continuous phase, then introduce 0.01 MPa nitrogen for 30 min, stir for 50 min to form a reverse suspension system, then heat to 65 ° C, carry out polymerization reaction for 8 h, after the reaction is completed, cool to 25 ° C, filter and collect the solid, wash the solid and add it to 1100 g of deionized water, then add 28 g of 14 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 7, and obtain an aqueous binder with a solid content of 5 wt%.

[0100] The raw materials for preparing the aqueous binder for reverse phase suspension polymerization lithium batteries are specifically as follows by mass: 1.0 g chitosan, 36 g acrylic acid, 0.60 g Span 60, 0.28 g ammonium persulfate, 0.56 g N,N'-methylenebisacrylamide, 80 g 20 wt% sodium hydroxide aqueous solution, 28 g 14 wt% sodium hydroxide aqueous solution, 350 g cyclohexane, and 1150 g deionized water.

[0101] The chitosan has a deacetylation degree greater than 90% and was purchased from Zhejiang Golden Shell Pharmaceutical Co., Ltd.

[0102] The second aspect of this example provides an aqueous binder for inverse phase suspension polymer lithium batteries prepared according to the method for preparing an aqueous binder for inverse phase suspension polymer lithium batteries.

[0103] In the above Examples 1-4 and Comparative Examples 1-3, unless otherwise specified, all raw materials are common commercially available products.

[0104] Performance evaluation

[0105] 1. Peel strength

[0106] 300 g of the aqueous binder of Examples 1-4 and Comparative Examples 2-3 was diluted with 150 g of deionized water, 5 g of a conductive agent and 480 g of a graphite material were added, and after the raw materials were completely soaked, they were dispersed at high speed for 4 h (rotation speed: linear speed 10 m / min), and then 65 g of deionized water was added to adjust the viscosity. The prepared slurry was applied to a copper foil using a single-sided intermittent coater and baked, and then coated. The coated electrode was placed in a 120°C oven to dry for 12 h. The dried electrode was rolled and cut, and measured according to the 180° peel strength test method for adhesives in GB / T 2790-1995. The test results are shown in Table 1.

[0107] Specific test method for comparative example 1: 5 g of conductive agent and 480 g of graphite material were added to 454 g of the binder of comparative example 1. After the raw materials were completely soaked, they were dispersed at high speed for 4 h. Then 76 g of deionized water was added to adjust the viscosity to 2500 mPa·s. The prepared slurry was coated on copper foil through a single-sided intermittent coating machine and baked. Then, the coating was carried out (single-sided coating, surface density of 0.95 g / dm 2 ), the coated electrode was placed in a 120°C oven to dry for 12 h, the dried electrode was rolled and cut, and the adhesive 180° peel strength test method in GB / T 2790-1995 was used for testing. The test results are shown in Table 1.

[0108] The conductive agent is of the model Super P, purchased from Shanghai Huiping New Energy Co., Ltd.; the graphite material is of the model GHMG1420, purchased from Huzhou Chuangya Power Battery Materials Co., Ltd.

[0109] Table 1

[0110]

[0111] It can be seen from the experimental results in Table 1 that the aqueous binders for reversed-phase suspension polymerization lithium batteries prepared in Examples 1-4 of the present invention have high peel strength, with a 180° peel strength greater than 8 N / m, and have better bonding performance than the SBR / CMC composite system binder (180° peel strength of 3.87 N / m). It can be seen from the experimental results of Comparative Example 2 that although the product can also be obtained by the non-reverse suspension polymerization method, the 180° peel strength of the aqueous binder at the same addition amount is only 2.32 N / m, which cannot meet normal use (the normal use range is 180° peel strength ≥4 N / m); in addition, it can be seen from Comparative Example 3 that if the addition amount of chitosan is too low, the peeling performance of the obtained product will be negatively affected, and its practicality is general.

Claims

1. A method for preparing an aqueous binder for reverse phase suspension polymer lithium battery, characterized in that: include: S1. Add polysaccharide to a reactor, add water, heat to 45-65°C, stir, and then cool to obtain a polysaccharide aqueous solution; Add acrylic acid monomer to another reaction kettle, cool to 0-5°C, add neutralizing base dropwise, then add crosslinking agent and initiator in sequence, mix well, then add to polysaccharide aqueous solution, mix well to obtain dispersed phase; S2, mixing the oil phase solvent and the dispersant to obtain a continuous phase; S3. Add the dispersed phase to the continuous phase and stir to form a reverse suspension system. Then, heat the system to 65-75°C for polymerization. After the reaction is completed, cool the system and collect the solid. After washing the solid, add it to water and then add a neutralizing base to adjust the pH of the system to 7-9 to obtain a water-based binder. The polysaccharide is chitosan; The acrylic acid monomer is at least one of acrylic acid and methacrylic acid; The mass ratio of the polysaccharide to the acrylic acid monomer is (3-30): (30-60).

2. The method for preparing an aqueous binder for reverse phase suspension polymer lithium battery according to claim 1, wherein: The deacetylation degree of the chitosan is greater than 90%.

3. The method for preparing an aqueous binder for reverse phase suspension polymer lithium battery according to any one of claims 1 to 2, characterized in that: The initiator includes one or more of benzoyl peroxide, ammonium persulfate, potassium persulfate, sodium persulfate or cumene hydroperoxide.

4. The method for preparing an aqueous binder for reverse phase suspension polymer lithium battery according to claim 1, wherein: The dispersant includes at least one of a Span dispersant and a Tween dispersant.

5. The method for preparing an aqueous binder for reverse phase suspension polymer lithium battery according to claim 1, wherein: The mass ratio of the acrylic acid monomer, the initiator and the crosslinking agent is (30-60): (0.5-1.5): (0.2-1.0).

6. The method for preparing an aqueous binder for reverse phase suspension polymer lithium battery according to claim 1, characterized in that: The mass ratio of the oil phase solvent to water is 1:(3-10).

7. A water-based binder for reverse phase suspension polymer lithium battery, characterized in that: The invention discloses a water-based binder for reverse phase suspension polymer lithium battery prepared by the method for preparing the water-based binder for reverse phase suspension polymer lithium battery according to any one of claims 1 to 6.

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