Inverted-phase suspension polymeric aqueous binder for lithium battery and preparation method of reversed-phase suspension polymeric aqueous binder

Abstract

The invention belongs to the field of binders, and particularly relates to a reversed-phase suspension polymerization aqueous binder for a lithium battery and a preparation method of the reversed-phase suspension polymerization aqueous binder. The reversed-phase suspension polymerization aqueous binder for the lithium battery provided by the invention is prepared from the following raw materials: polysaccharide, an acrylic monomer, a dispersing agent, an initiator, a cross-linking agent, neutralizing alkali, an oil-phase solvent and deionized water, and the product is prepared by adopting reversed-phase suspension polymerization. The reversed-phase suspension polymerization aqueous binder for the lithium battery has excellent binding performance, the 180-degree peel strength is larger than 8 N / m, and compared with the prior art, the reversed-phase suspension polymerization aqueous binder for the lithium battery has remarkable progress.

Description

Technical Field

[0001] The present invention belongs to the field of binders, and particularly relates to an inverse suspension polymerization lithium battery aqueous binder and a preparation method thereof. Background Art

[0002] Binders are important components in lithium-ion batteries (LIBs). Besides the basic binding function, they are crucial for ensuring the efficient and stable operation of the batteries. In the complex structure of LIBs, the binder mainly binds active materials such as lithium cobalt oxide, lithium nickel manganese cobalt oxide, or graphite, conductive agents, and current collectors tightly together to form an electrode structure that is both conductive and mechanically stable. The binder can effectively prevent the active materials from falling off or decomposing due to volume changes and mechanical stress during the repeated charge and discharge cycles of the battery, thus maintaining the long-term performance of the battery. Additionally, the binder also plays a key role in reducing the internal resistance of the battery by optimizing the microstructure inside the electrode. It can promote the smooth conduction of electrons and ions inside the electrode, reduce energy losses during the energy transfer process, and thereby improve the energy density and power output of the battery. Moreover, the selection and design of the binder directly affect the cycle life of LIBs. A suitable binder can effectively resist stress accumulation during charge and discharge, slow down the aging rate of the electrode, and extend the service life of the battery.

[0003] From the perspective of environmental protection, aqueous binders have currently become the mainstream choice for lithium-ion battery anode materials. Especially compared with oil-based binders, the production and use processes of aqueous binders are more environmentally friendly, have less impact on the environment, and have higher cost performance. In the market, the system composed of styrene-butadiene (SBR) latex and sodium carboxymethyl cellulose (CMC) has become the mainstream formula choice for common aqueous binders due to its good binding performance and electrical properties. However, actual research shows that there is still significant room for improvement in the binding performance of the SBR / CMC composite system binder. Chinese Patent CN112142917B discloses a modified chitosan aqueous binder and a preparation method thereof. Its preparation raw materials include chitosan, acrylic acid, trifluoroethyl acrylate, ammonium persulfate, etc., and are obtained through conventional preparation processes in the art. However, its peel strength mainly depends on the chemical modification of chitosan by fluorine elements, and the raw material cost is relatively high.

[0004] The inverse suspension system binder is a polymer material prepared based on inverse suspension polymerization technology. In traditional suspension polymerization, water is usually used as the continuous phase, while inverse suspension polymerization uses the oil phase as the continuous medium to disperse water-soluble monomers into tiny droplets for polymerization. The inverse suspension combination process is particularly suitable for preparing microspheres or particulate polymer materials with controllable particle sizes and uniform structures. However, there are relatively few relevant reports in China on the preparation of aqueous binders by the inverse suspension polymerization mechanism. Summary of the Invention

[0005] To solve the above technical problems, a first aspect of the present invention provides a method for preparing an aqueous binder for lithium battery by inverse suspension polymerization, which is characterized by comprising: S1. Add polysaccharide into a reaction kettle, then add water, heat up to 45 - 65 °C, stir for 1 - 1.5 h, and then cool to obtain an aqueous polysaccharide solution; Add acrylic acid monomer into another reaction kettle, cool down to 0 - 5 °C, dropwise add neutralizing base, then sequentially add crosslinking agent and initiator, mix evenly and then add it into the aqueous polysaccharide solution, mix evenly to obtain a dispersed phase; S2. Mix and stir the oil - phase solvent and dispersant to obtain a continuous phase; S3. Add the dispersed phase into the continuous phase, stir for 45 - 50 min to form an inverse suspension system, then heat up to 65 - 75 °C for polymerization reaction. After the reaction is completed, cool, filter and collect the solid. After washing the solid, add it into water, then add neutralizing base to adjust the pH of the system to 7 - 9, and dilute to obtain the aqueous binder.

[0006] Further, the mass ratio of the oil - phase solvent to water is 1:(3 - 10).

[0007] Further, the water is deionized water.

[0008] Further, the method for preparing the aqueous binder for lithium battery by inverse suspension polymerization comprises: S1. Add polysaccharide into a reaction kettle, then add deionized water. Under a nitrogen atmosphere, heat up to 45 - 65 °C, stir at a speed of 100 - 150 rpm for 1 - 1.5 h, and then cool to 20 - 30 °C to obtain an aqueous polysaccharide solution; Add acrylic acid monomer into another reaction kettle, cool down to 0 - 5 °C, dropwise add neutralizing base, then sequentially add crosslinking agent and initiator, mix evenly and then add it into the aqueous polysaccharide solution, mix evenly to obtain a dispersed phase; S2. Mix the oil - phase solvent and dispersant, then introduce nitrogen, and stir at a speed of 250 - 350 rpm to obtain a continuous phase; S3. Add the dispersed phase into the continuous phase, then introduce nitrogen, stir for 45 - 50 min to form an inverse suspension system, then heat up to 65 - 75 °C for polymerization reaction. After the reaction is completed, cool to 20 - 30 °C, filter and collect the solid. After washing the solid, add it into deionized water, then add neutralizing base to adjust the pH of the system to 7 - 9, and then dilute to obtain the aqueous binder.

[0009] As an implementable case, the mass ratio of the polysaccharide to the acrylic acid monomer is (3 - 30):(30 - 60).

[0010] As an implementable case, the polysaccharide includes one of gelatin, alginic acid, chitosan or mannan.

[0011] Furthermore, the polysaccharide includes chitosan.

[0012] Furthermore, the degree of deacetylation of the chitosan is greater than 90%, and it is purchased from Zhejiang Jinqiao Pharmaceutical Co., Ltd.

[0013] Chitosan is a natural polymer material with a wide range of sources, abundance and renewability. However, chitosan is prone to moisture absorption and is easily affected by moisture and deteriorated, which will affect its mechanical properties and use 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, enabling it to withstand greater loads and showing better adaptability. At the same time, through modification, the hydrophilicity and hydrophobicity of chitosan can be optimized, thereby better regulating the interaction between it and the material to be bonded, and further improving the bonding effect. In addition, based on maintaining the original biocompatibility and biodegradability, the electrical properties of the modified chitosan binder also have a certain improvement.

[0014] As an implementable case, the acrylic monomer includes at least one of acrylic acid and methacrylic acid.

[0015] As an implementable case, the initiator includes one or more of benzoyl peroxide, ammonium persulfate, potassium persulfate, sodium persulfate, and cumene hydroperoxide.

[0016] Furthermore, the initiator includes one of ammonium persulfate, potassium persulfate, and sodium persulfate.

[0017] As an implementable case, the dispersant includes at least one of Span dispersants and Tween dispersants.

[0018] Furthermore, the Span dispersant includes Span 60 or Span 80.

[0019] Furthermore, the Tween dispersant includes Tween 60 or Tween 80.

[0020] As an implementable case, the crosslinking agent includes N,N'-methylenebisacrylamide.

[0021] Furthermore, the mass ratio of the acrylic monomer, crosslinking agent and initiator is (30 - 60):(0.5 - 1.5):(0.2 - 1.0).

[0022] As an implementable case, the neutralizing base includes one of an aqueous sodium hydroxide solution, an aqueous sodium carbonate solution, or an aqueous sodium bicarbonate solution.

[0023] Further, the aqueous sodium hydroxide solution is an aqueous sodium hydroxide solution with a mass concentration of 10 - 30 wt%.

[0024] As an implementable case, the oil - phase solvent includes one of tetrahydrofuran, acetone, cyclohexane, dimethyl sulfoxide, and N - methylpyrrolidone.

[0025] Further, the oil - phase solvent is cyclohexane.

[0026] Further, the mass ratio of the oil - phase solvent to deionized water is 1:(3 - 10).

[0027] In the above - mentioned mass ratio of the oil - phase solvent to deionized water, the mass fraction of deionized water is the weight of deionized water used in the S1 step and the S3 step.

[0028] Inverse suspension polymerization is a polymerization method in which the dispersed phase (aqueous phase) is dispersed in the continuous phase (oil phase). The aqueous binder prepared by the inverse suspension polymerization method has a higher peel strength. The inventor speculates that mainly in the inverse suspension system, the aqueous - phase monomer droplets are tightly wrapped by the oil phase and form uniform - sized microspheres through stirring. The uniform particle structure can significantly improve the dispersibility of the binder in the electrode slurry, effectively reduce the agglomeration phenomenon, and the uniform particle surface can better wet the current collector, increasing the effective contact area and enhancing the physical anchoring effect between the binder and the substrate. At the same time, in the inverse suspension system, the cross - linker is confined within the aqueous - phase droplets, and the cross - link points are more evenly distributed during the reaction, forming a dense three - dimensional network structure. The three - dimensional network structure with a high cross - link density can significantly improve the cohesive strength of the aqueous binder, making it not easy to break during the peeling process, thus improving the peel strength.

[0029] In addition, the amino and hydroxyl groups in the chitosan molecular chain can form hydrogen bonds with the carboxyl groups of acrylic acid monomers, thereby enhancing the rigidity of the polymer network. The flexible chain segments formed by the polymerization of acrylic acid can absorb the mechanical stress during charge and discharge, effectively preventing the expansion of electrode cracks. After adding the neutralizing base, the system pH is adjusted to 7 - 9, ionizing the carboxyl groups of acrylic acid, 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 the interfacial chemical bonding. In the confined space of the inverse suspension system, the chitosan reacts with the monomer droplets of acrylic acid, making the entanglement and chemical bonding of the molecular chains more compact, so the bonding performance of the aqueous binder is further improved.

[0030] The second aspect of the present invention provides a reverse suspension polymerization lithium battery aqueous binder prepared by the preparation method of the reverse suspension polymerization lithium battery aqueous binder.

[0031] Beneficial effects (1) The binder plays a crucial role in lithium-ion batteries, affecting not only the initial performance of the battery but also its cycle life. The aqueous binder provided by the present invention improves the dispersion of raw material components, reduces agglomeration, thereby increasing the peel strength, and helps to improve the overall performance of lithium-ion batteries, especially their cycle life.

[0032] (2) The aqueous binder 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.

[0033] (3) In the preparation process of the aqueous binder of the present invention, a reverse suspension process is mainly carried out. By dispersing the dispersed phase in the continuous phase, the agglomeration phenomenon is effectively reduced, thereby increasing the effective contact area between the aqueous binder and the substrate and improving the bonding effect.

[0034] (4) The aqueous binder prepared by the reverse suspension polymerization method of the present invention has a higher peel strength compared with the binder of the commonly used aqueous SBR / CMC compound system on the market (the 180° peel strength is less than 4 N / m). Under the same addition amount, the aqueous binder provided by the present invention has a higher peel strength, so it can more effectively bond the active material, conductive agent and current collector, and prevent the decomposition of the active material during continuous charging and discharging.

[0035] (5) Compared with the oily binder, the aqueous binder is more environmentally friendly and has a higher cost performance. The aqueous binder synthesized based on the reverse suspension polymerization system of the present invention not only has advantages in bonding performance, but also meets the current market's pursuit of environmental protection and cost performance. Therefore, the product has broad market application prospects.

[0036] (6) By limiting the mass ratio of chitosan to acrylic acid monomer to (3 - 30):(30 - 60) in the present invention, the bonding performance of the aqueous binder can be further improved. If the amount of chitosan used is less, the bonding performance of the product will be significantly reduced. Specific embodiments

[0037] Example 1 The first aspect of this example provides a preparation method of a reverse suspension polymerization lithium battery aqueous binder, specifically as follows: S1. Add chitosan into a reaction kettle, then add 60 g of deionized water, introduce nitrogen at 0.01 MPa for 25 min. Under the nitrogen environment, heat up to 50 °C, stir at a speed of 110 rpm for 1.0 h, and then cool to 25 °C to obtain an aqueous chitosan solution; Add acrylic acid into another reaction kettle, cool down to 5 °C, dropwise add 80 g of 20 wt% sodium hydroxide aqueous solution, then sequentially add N,N'-methylenebisacrylamide and ammonium persulfate. After mixing evenly, add it into the aqueous chitosan solution and mix evenly to obtain a dispersed phase; S2. Mix cyclohexane and Span 60, introduce nitrogen at 0.01 MPa for 25 min, and stir at a speed of 300 rpm to obtain a continuous phase; S3. Add the dispersed phase into the continuous phase, then introduce nitrogen at 0.01 MPa for 30 min, stir for 50 min to form an inverse suspension system, then heat up to 65 °C and carry out a 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 into 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 thus obtain an aqueous binder with a solid content of 5 wt%.

[0038] The raw materials for preparing the inverse suspension polymerization lithium battery aqueous binder are specifically as follows by mass: 3.6 g of chitosan, 36 g of acrylic acid, 0.60 g of Span 60, 0.28 g of ammonium persulfate, 0.56 g of N,N'-methylenebisacrylamide, 80 g of 20 wt% sodium hydroxide aqueous solution, 28 g of 14 wt% sodium hydroxide aqueous solution, 350 g of cyclohexane, and 1190 g of deionized water.

[0039] The deacetylation degree of the chitosan is greater than 90%, and it is purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.

[0040] In the second aspect of this example, an inverse suspension polymerization lithium battery aqueous binder prepared by the preparation method of the inverse suspension polymerization lithium battery aqueous binder is provided.

[0041] Example 2 In the first aspect of this example, a preparation method of an inverse suspension polymerization lithium battery aqueous binder is provided, specifically as follows: S1. Add chitosan into a reaction kettle, then add 90 g of deionized water, introduce nitrogen at 0.01 MPa for 25 min. Under the nitrogen environment, heat up to 55 °C, stir at a speed of 150 rpm for 1.0 h, and then cool to 25 °C to obtain an aqueous chitosan solution; Add acrylic acid to another reaction kettle, cool down to 2 °C, dropwise add 80 g of 25 wt% sodium hydroxide aqueous solution, then successively add N,N'-methylenebisacrylamide and ammonium persulfate. After mixing evenly, add it to the chitosan aqueous solution and mix evenly to obtain the dispersed phase; S2. Mix cyclohexane and Span 80, introduce nitrogen at 0.01 MPa for 30 min, and stir at a speed of 300 rpm to obtain the continuous phase; S3. Add the dispersed phase to the continuous phase, then introduce nitrogen at 0.01 MPa for 25 min, stir for 50 min to form an inverse suspension system, then heat up to 70 °C and carry out the polymerization reaction for 6 h. After the reaction is completed, cool down to 25 °C, filter and collect the solid. Wash the solid and add it to 1500 g of deionized water, then add 20 g of 25 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 7, and obtain the aqueous binder with a solid content of 5 wt%.

[0042] The raw materials for preparing the inverse suspension polymerization lithium battery aqueous binder are specifically as follows by mass: 10 g of chitosan, 45 g of acrylic acid, 1.5 g of Span 80, 1.0 g of ammonium persulfate, 1.5 g of N,N'-methylenebisacrylamide, 100 g of 25 wt% sodium hydroxide aqueous solution, 450 g of cyclohexane, and 1590 g of deionized water.

[0043] The deacetylation degree of the chitosan is greater than 90%, and it is purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.

[0044] In the second aspect of this example, an inverse suspension polymerization lithium battery aqueous binder prepared by the preparation method of the inverse suspension polymerization lithium battery aqueous binder is provided.

[0045] Example 3 In the first aspect of this example, a preparation method of an inverse suspension polymerization lithium battery aqueous binder is provided, specifically as follows: S1. Add chitosan to the reaction kettle, then add 150 g of deionized water, introduce nitrogen at 0.01 MPa for 25 min. Under the nitrogen environment, heat up to 60 °C and stir at a speed of 150 rpm for 1.5 h, then cool down to 25 °C to obtain the chitosan aqueous solution; Add methacrylic acid to another reaction kettle, cool down to 3 °C, dropwise add 54 g of 25 wt% sodium hydroxide aqueous solution, then successively add N,N'-methylenebisacrylamide and potassium persulfate. After mixing evenly, add it to the chitosan aqueous solution and mix evenly to obtain the dispersed phase; S2. Mix cyclohexane and Tween 60, introduce nitrogen at 0.01 MPa for 30 min, and stir at a speed of 300 rpm to obtain a continuous phase; S3. Add the dispersed phase to the continuous phase, then introduce nitrogen at 0.01 MPa for 25 min, stir for 50 min to form an inverse suspension system, then heat up to 70 °C and carry out a polymerization reaction for 7 h. After the reaction is completed, cool to 25 °C, filter to collect the solid, wash the solid and add it to 1380 g of deionized water, and then add 18 g of 25 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 7, thus obtaining an aqueous binder with a solid content of 5 wt%.

[0046] The raw materials for preparing the inverse suspension polymerization lithium battery aqueous binder are specifically as follows by mass: 20 g of chitosan, 32.4 g of methacrylic acid, 1.5 g of Tween 60, 0.9 g of potassium persulfate, 1.1 g of N,N'-methylenebisacrylamide, 72 g of 25 wt% sodium hydroxide aqueous solution, 250 g of cyclohexane, and 1530 g of deionized water.

[0047] The deacetylation degree of the chitosan is greater than 90%, and it is purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.

[0048] In the second aspect of this example, an inverse suspension polymerization lithium battery aqueous binder prepared by the preparation method of the inverse suspension polymerization lithium battery aqueous binder is provided.

[0049] Example 4 In the first aspect of this example, a preparation method of an inverse suspension polymerization lithium battery aqueous binder is provided, specifically as follows: S1. Add chitosan to a reaction kettle, then add 180 g of deionized water, introduce nitrogen at 0.01 MPa for 25 min, under a nitrogen environment, heat up to 60 °C, stir at a speed of 180 rpm for 1.5 h, and then cool to 25 °C to obtain a chitosan aqueous solution; Add methacrylic acid to another reaction kettle, cool down to 5 °C, dropwise add 74.4 g of 20 wt% sodium hydroxide aqueous solution, then sequentially add N,N'-methylenebisacrylamide and potassium persulfate, mix evenly and then add it to the chitosan aqueous solution, mix evenly to obtain a dispersed phase; S2. Mix cyclohexane and Tween 80, introduce nitrogen at 0.01 MPa for 30 min, and stir at a speed of 300 rpm to obtain a continuous phase; S3. Add the dispersed phase to the continuous phase, then introduce nitrogen at 0.01 MPa for 25 min, stir for 60 min to form an inverse suspension system, then heat up to 75 °C and carry out the polymerization reaction for 6 h. After the reaction is completed, cool to 25 °C, filter to collect the solid, wash the solid and add it to 1630 g of deionized water, and then add 18.6 g of 20 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 7, thus obtaining an aqueous binder with a solid content of 5 wt%.

[0050] The raw materials for preparing the inverse suspension polymerization lithium battery aqueous binder are specifically as follows by mass: 25 g of chitosan, 40 g of methacrylic acid, 1.6 g of Tween 80, 0.9 g of potassium persulfate, 1.0 g of N,N'-methylenebisacrylamide, 93 g of 20 wt% sodium hydroxide aqueous solution, 600 g of cyclohexane, and 1810 g of deionized water.

[0051] The deacetylation degree of the chitosan is greater than 90%, and it is purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.

[0052] In the second aspect of this example, an inverse suspension polymerization lithium battery aqueous binder prepared according to the preparation method of the inverse suspension polymerization lithium battery aqueous binder is provided.

[0053] Comparative Example 1 This example provides an aqueous binder. By weight, the raw materials for preparation include: 28 g of SBR (50 wt% solid content), 6 g of CMC, and 420 g of deionized water.

[0054] The preparation method of the aqueous binder is: Mix and stir SBR, CMC, and deionized water at room temperature of 25 °C, and then it is obtained.

[0055] Both the SBR and CMC are purchased from Guangzhou Songbai Chemical Industry Co., Ltd., and the model of CMC is CMC-203.

[0056] Comparative Example 2 In the first aspect of this example, a preparation method of a non-inverse suspension polymerization lithium battery aqueous binder is provided, specifically as follows: S1. Add chitosan to the reaction kettle, then add 410 g of deionized water, introduce nitrogen at 0.01 MPa for 25 min. Under a nitrogen atmosphere, heat up to 50 °C and stir at a speed of 110 rpm for 1.0 h, and then cool to 25 °C to obtain an aqueous chitosan solution; Add acrylic acid into another reaction kettle, cool down the temperature to 5 °C, dropwise add 80 g of 20 wt% sodium hydroxide aqueous solution, then successively add N,N'-methylenebisacrylamide and ammonium persulfate. After mixing evenly, add it into the chitosan aqueous solution and mix evenly to obtain the dispersed phase. S2. Pass the dispersed phase into nitrogen gas at 0.01 MPa for 30 min, stir for 50 min, then raise the temperature to 65 °C, carry out the polymerization reaction for 8 h. After the reaction ends, cool down to 25 °C, filter and collect the solid. Wash the solid and add it into 1148 g of deionized water, then add 20 g of 20 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 7, thus obtaining the aqueous binder with a solid content of 5 wt%.

[0057] The raw materials for preparing the non-inverse phase suspension polymerization lithium battery aqueous binder are specifically as follows by mass: 3.6 g of chitosan, 36 g of acrylic acid, 0.28 g of ammonium persulfate, 0.56 g of N,N'-methylenebisacrylamide, 100 g of 20 wt% sodium hydroxide aqueous solution, 1558 g of deionized water.

[0058] The deacetylation degree of the chitosan is greater than 90%, and it is purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.

[0059] The second aspect of this example provides a non-inverse phase suspension polymerization lithium battery aqueous binder prepared by the preparation method of the non-inverse phase suspension polymerization lithium battery aqueous binder.

[0060] Comparative Example 3 The first aspect of this example provides a preparation method of an inverse phase suspension polymerization lithium battery aqueous binder, specifically as follows: S1. Add chitosan into the reaction kettle, then add 50 g of deionized water, pass nitrogen gas at 0.01 MPa for 25 min. Under the nitrogen environment, raise the temperature to 50 °C, stir at a speed of 110 rpm for 1.0 h, then cool down to 25 °C to obtain the chitosan aqueous solution. Add acrylic acid into another reaction kettle, cool down the temperature to 5 °C, dropwise add 80 g of 20 wt% sodium hydroxide aqueous solution, then successively add N,N'-methylenebisacrylamide and ammonium persulfate. After mixing evenly, add it into the chitosan aqueous solution and mix evenly to obtain the dispersed phase. S2. Mix cyclohexane and Span 60, pass nitrogen gas at 0.01 MPa for 25 min, and stir at a speed of 300 rpm to obtain the continuous phase. S3. Add the dispersed phase to the continuous phase, then introduce nitrogen at 0.01 MPa for 30 min, stir for 50 min to form an inverse suspension system, then heat up to 65 °C and carry out the polymerization reaction for 8 h. After the reaction is completed, cool to 25 °C, filter to collect the solid, wash the solid and add it to 1100 g of deionized water, and then add 28 g of 14 wt% sodium hydroxide aqueous solution to adjust the pH of the system to 7, thus obtaining an aqueous binder with a solid content of 5 wt%.

[0061] The raw materials for preparing the inverse suspension polymerization lithium battery aqueous binder are specifically as follows by mass: 1.0 g of chitosan, 36 g of acrylic acid, 0.60 g of Span 60, 0.28 g of ammonium persulfate, 0.56 g of N,N'-methylenebisacrylamide, 80 g of 20 wt% sodium hydroxide aqueous solution, 28 g of 14 wt% sodium hydroxide aqueous solution, 350 g of cyclohexane, and 1150 g of deionized water.

[0062] The deacetylation degree of the chitosan is greater than 90%, and it is purchased from Zhejiang Jinke Pharmaceutical Co., Ltd.

[0063] In the second aspect of this example, an inverse suspension polymerization lithium battery aqueous binder prepared according to the preparation method of the inverse suspension polymerization lithium battery aqueous binder is provided.

[0064] In the above Examples 1-4 and Comparative Examples 1-3, unless otherwise specified, all raw materials are ordinary commercially available products.

[0065] Performance Evaluation 1. Peel Strength Dilute 300 g of the aqueous binders of Examples 1-4 and Comparative Examples 2-3 with 150 g of deionized water, add 5 g of conductive agent and 480 g of graphite material. After the raw materials are completely wetted, disperse them at high speed for 4 h (rotation speed: linear speed 10 m / min), then add 65 g of deionized water to adjust the viscosity. Coat the prepared slurry on the copper foil through a single-sided intermittent coater and bake it, then coat again. Place the coated electrode sheet in an oven at 120 °C and dry it for 12 h. Roll press and cut the dried electrode sheet, and measure it according to the 180° peel strength test method for adhesives in GB / T 2790-1995. The test results are shown in Table 1 in detail.

[0066] Regarding the specific test method for Comparative Example 1: Add 5 g of conductive agent and 480 g of graphite material to 454 g of the binder of Comparative Example 1. After the raw materials are completely wetted, disperse them at high speed for 4 h, then add 76 g of deionized water to adjust the viscosity to 2500 mPa·s. Coat the prepared slurry on the copper foil through a single-sided intermittent coater and bake it, then coat again (single-sided coating, surface density is 0.95 g / dm2 ) The coated electrode sheets were placed in an oven at 120 °C for drying for 12 h. After drying, the electrode sheets were rolled, cut, and measured according to the adhesive 180° peel strength test method in GB / T 2790-1995. The test results are shown in Table 1.

[0067] The above conductive agent is of the type Super P and is purchased from Shanghai Huiping New Energy Co., Ltd.; the graphite material is of the type GHMG1420 and is purchased from Huzhou Chuangya Power Battery Materials Co., Ltd.

[0068] Table 1

[0069] It can be seen from the experimental results in Table 1 that the reverse suspension polymerization lithium battery aqueous binder prepared in Examples 1-4 of the present invention has a relatively high peel strength, and the 180° peel strength is greater than 8 N / m, which has more excellent adhesive properties compared with the SBR / CMC composite system binder (the 180° peel strength is 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 using the non-reverse suspension polymerization method, the 180° peel strength of the aqueous binder is only 2.32 N / m under the same addition amount, which cannot meet the normal use requirements (the normal use range is 180° peel strength ≥ 4 N / m); in addition, it can be seen from Comparative Example 3 that when the addition amount of chitosan is too low, the peel performance of the obtained product will be negatively affected, and the practicability is general.

Claims

1. A method for preparing an aqueous binder for an inverse phase suspension polymer lithium battery, characterized in that: include: S1, adding polysaccharide to a reaction kettle, then adding water, heating to 45-65°C, stirring, and then cooling to obtain a polysaccharide aqueous solution; Add acrylic acid monomer to another reaction kettle, cool to 0-5°C, drop neutralizing alkali, 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, stir to form a reverse suspension system, then heat to 65-75 °C to carry out polymerization reaction. After the reaction is completed, cool 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 adhesive.

2. 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 polysaccharide to the acrylic acid monomer is (3-30): (30-60).

3. The method for preparing an aqueous binder for reverse phase suspension polymer lithium battery according to claim 2, characterized in that: The polysaccharide comprises one of gelatin, alginate, chitosan or mannan.

4. The method for preparing an aqueous binder for reverse phase suspension polymer lithium battery according to claim 3, characterized in that: The deacetylation degree of the chitosan is greater than 90%.

5. The method for preparing an aqueous binder for reverse phase suspension polymer lithium battery according to claim 2, characterized in that: The acrylic acid monomer includes at least one of acrylic acid and methacrylic acid.

6. The method for preparing the aqueous binder for reverse phase suspension polymer lithium battery according to any one of claims 1 to 5, characterized in that: The initiator includes one or more of benzoyl peroxide, ammonium persulfate, potassium persulfate, sodium persulfate or cumene hydroperoxide.

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

8. 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 acrylic acid monomer, the initiator and the crosslinking agent is (30-60): (0.5-1.5): (0.2-1.0).

9. 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).

10. An aqueous binder for reverse phase suspension polymer lithium battery, characterized in that: The invention is prepared by the method for preparing an aqueous binder for reverse phase suspended polymer lithium battery according to any one of claims 1 to 9.

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