An adhesive, a negative electrode sheet, and a battery

Abstract

The present invention provides an adhesive, a negative electrode sheet and a battery. The adhesive comprises a polyimide-based adhesive material, and the polyimide-based adhesive material includes: a first structural unit derived from an amino sulfonic acid monomer, a second structural unit derived from an amine monomer, and a third structural unit derived from an acid anhydride monomer; the mass percentage content of sulfonate groups in the polyimide-based adhesive material is 15-35 wt%. The adhesive provided by the present invention has good adhesion effect, which is beneficial to improving the battery stability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium - ion batteries, and particularly to a binder, a negative electrode sheet and a battery. Background Art

[0002] Lithium batteries are widely used in various fields due to their high energy density and long life. At present, the negative electrode material of lithium - ion batteries is mainly graphite, which is widely used as the negative electrode of lithium - ion batteries because of its stable structure, small volume expansion, high conductivity and good cycle stability. However, its low theoretical capacity (372 mAh / g) limits its application in high - capacity battery systems. Compared with graphite materials, silicon - based materials have a higher mass - specific capacity (4200 mAh / g) and are one of the most promising next - generation negative electrode materials for lithium - ion batteries. However, silicon - based negative electrode materials have serious volume expansion (>300%) during charge and discharge processes. Therefore, there are problems such as the fragmentation and pulverization of electrode material particles during the charging process, resulting in the separation between the silicon material and the substrate, rapid attenuation of battery capacity and poor cycle performance.

[0003] Due to the poor mechanical properties of traditional binders, it is difficult to adapt to the significant volume expansion of high - silicon negative electrodes during charge and discharge. Although polyimide - based binders have good mechanical properties, they usually need to be dissolved in polar solvents such as N - methylpyrrolidone. Considering environmental protection and slurry processability, the existing negative electrode slurries are usually aqueous. Therefore, polyimide - based binders dissolved in polar solvents are difficult to be fully mixed with aqueous negative electrode slurries, greatly affecting their binding effect. Water - soluble polyimide - type binders can well solve the above problems. Common water - soluble polyimide - type binders are usually stored in the form of their precursor polyamic acid salts, and high - temperature imidization treatment of polyamic acid salts is required during use, increasing equipment costs. In addition, due to the short duration of the high - temperature imidization process to match the coating line speed, the degree of imidization of polyamic acid salts is limited, resulting in poor binding performance when used as a binder.

[0004] Therefore, there is an urgent need for a binder that is water - soluble, has a high degree of imidization and good binding performance. Summary of the Invention

[0005] The present invention provides a binder that is water - soluble, can be fully mixed with the components of the negative electrode slurry during battery preparation, has a good binding effect, and is beneficial to improving battery stability.

[0006] The present invention provides a negative electrode sheet prepared by using the above - mentioned binder. The binder tightly binds the active material particles, conductive agent and current collector in the negative electrode sheet together, and can also maintain the integrity of the electrode material during repeated charge and discharge processes, reducing the risk of active material shedding.

[0007] The present invention provides a battery, including the above-mentioned negative electrode sheet. This battery can maintain its battery efficiency during repeated charge and discharge processes and can provide a stable power output.

[0008] In the first aspect of the present invention, a binder is provided, which includes a polyimide-based binder material. The polyimide-based binder material includes: a first structural unit derived from an amino sulfonic acid monomer, a second structural unit derived from an amine monomer, and a third structural unit derived from an acid anhydride monomer.

[0009] The mass percentage content of sulfonate groups in the polyimide-based binder material is 15 - 35 wt%.

[0010] For the binder as described above, the molar ratio of the first structural unit to the second structural unit is (4 - 9) : (6 - 1); and / or,

[0011] The molar ratio of the sum of the first structural unit and the second structural unit to the third structural unit is (0.95 - 1.10) : 1.

[0012] For the binder as described above, the weight average molecular weight of the polyimide-based binder material is 30000 - 400000 g / mol.

[0013] For the binder as described above, the binder further includes an alkali solution of a monovalent cation that dissolves the polyimide-based binder material;

[0014] and / or, the molar ratio of the monovalent cation from the alkali to the sulfonate groups in the polyimide-based binder material is (0.8 - 1.05) : 1.

[0015] For the binder as described above, the amino sulfonic acid monomer includes a diamine compound containing a sulfonic acid group; and / or,

[0016] The amine monomer includes at least one of an aromatic diamine compound, an amino silane compound, a dimer amine compound, and a polyether amine compound.

[0017] For the binder as described above, the amino sulfonic acid monomer includes at least one of 2,5-diaminobenzenesulfonic acid, 2,4-diaminobenzenesulfonic acid, 2,2'-biphenyldiamine disulfonic acid, 2,5-diaminobenzene-1,4-disulfonic acid, and 4,4'-diaminostilbene-2,2'-disulfonic acid.

[0018] For the binder as described above, the amine monomer includes at least one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, ethylene glycol bis(2-aminophenyl) ether, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, dimer amine, and polyether amine.

[0019] The binder as described above, wherein the anhydride monomer includes at least one of pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride), butanetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride.

[0020] The second aspect of the present invention provides a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode active layer, and the negative electrode active layer includes the binder as described above.

[0021] The third aspect of the present invention provides a battery, wherein the battery includes the negative electrode sheet as described above.

[0022] The binder provided by the present invention can be fully mixed with the components of the negative electrode slurry during the battery preparation process by using a water-soluble polyimide-based binder material, and tightly bond each component into one body, which is beneficial to maintaining the integrity of the battery negative electrode and improving the stability of the battery. Detailed embodiments

[0023] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] During the preparation of lithium batteries, in order to improve the theoretical capacity of the battery, silicon-based materials are often used as the active materials of the negative electrode battery. However, compared with conventional graphite negative electrode materials, the silicon-based negative electrode active materials are more likely to undergo volume expansion during charge and discharge, resulting in the failure of the binder, the multi-directional shedding of silicon particles, accelerating the collapse of the electrode structure, and ultimately causing a rapid decline in battery performance.

[0025] The reason for the limited binding effect of the above binder may be that most binders are often dissolved in organic solvents during use, and the organic solvents are difficult to fully contact with the components of the negative electrode material dissolved in water, thus resulting in a limited binding effect.

[0026] Therefore, a water-soluble binder is needed, which can fully contact with the components of the negative electrode material dissolved in water, improve the binding effect between the components, and improve the stability of the battery.

[0027] Based on this, in the first aspect of the present invention, an adhesive is provided, which includes a polyimide-based adhesive material. The polyimide-based adhesive material includes: a first structural unit derived from an amino sulfonic acid monomer, a second structural unit derived from an amine monomer, and a third structural unit derived from an acid anhydride monomer;

[0028] The mass percentage content of sulfonate groups in the polyimide-based adhesive material is 10-35 wt%.

[0029] Specifically, in the present invention, a polyimide-based adhesive material is obtained by introducing sulfonate salts onto polyimide, making the adhesive have good water solubility and ion conduction ability. The inventor speculates that the reason may be that the sulfonic acid group has a high polarity, making it show good solubility in water or other polar solvents. In addition, as a strong polar group, the sulfonate structure can interact with lithium ions in the lithium-ion battery environment, providing a channel for ion transport and facilitating the transport of lithium ions during the operation of the lithium battery.

[0030] The polyimide-based adhesive material of the present invention is composed of a first structural unit derived from an amino sulfonic acid monomer, a second structural unit derived from an amine monomer, and a third structural unit derived from an acid anhydride monomer. Among them, the second structural unit derived from the amine monomer provides a soft segment structure for the polyimide-based adhesive material, and the first structural unit derived from the amino sulfonic acid monomer and the third structural unit derived from the acid anhydride monomer provide a hard segment structure. The structure combining the hard and soft segments makes the polyimide-based adhesive material have a higher elastic modulus and elongation at break. Further, the adhesive including the polyimide-based adhesive material can better maintain its shape and reduce deformation when subjected to external forces, thereby improving the mechanical strength of the overall structure of the battery. In addition, the structure combining the hard and soft segments also makes the polyimide-based adhesive material have a high elongation at break, enabling the polyimide-based adhesive material to undergo reversible deformation within a large range without rupture, showing excellent toughness. This helps the adhesive including the polyimide-based adhesive material to absorb and disperse stress when the electrode material undergoes volume changes (such as expansion and contraction during charge and discharge cycles), prevent crack propagation, ensure the stable performance of the electrode during long-term use, maintain the integrity of the internal structure of the electrode, reduce the risk of active material shedding, and thus extend the service life of the battery.

[0031] In addition, in order to balance the dissolution performance, adhesion performance, and ion conduction performance of the adhesive, the present invention further defines that the mass percentage content of sulfonate groups in the polyimide-based adhesive material is 15-35 wt%. For example, the mass percentage content of sulfonate groups in the polyimide-based adhesive material includes, but is not limited to, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt% or the range composed of any two of them.

[0032] Specifically, the mass percentage of sulfonate groups in the above polyimide-based binder material can be measured and calculated by nuclear magnetic resonance hydrogen spectroscopy.

[0033] In the present invention, a polyimide-based binder material is composed of a first structural unit derived from an amino sulfonic acid monomer, a second structural unit derived from an amine monomer, and a third structural unit derived from an acid anhydride monomer. Further, by controlling the mass percentage of sulfonate groups in the polyimide-based binder material to be 10-35 wt%, the binder has good binding and ion transport effects in a lithium-ion battery, and endows the binder with a relatively high elastic modulus and elongation at break.

[0034] In the above polyimide-based binder material, the molar ratio of the first structural unit to the second structural unit is (4-9):(6:1). For example, the molar ratio of the first structural unit to the second structural unit includes, but is not limited to, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, or a range composed of any two of them.

[0035] In another specific embodiment, the molar sum of the first structural unit and the second structural unit to the molar ratio of the second structural unit is (0.95-1.05):1. For example, the molar ratio of the first structural unit and the second structural unit includes, but is not limited to, 0.95:1, 0.97:1, 1:1, 1.03:1, 1.05:1, or a range composed of any two of them.

[0036] The molar ratio of the first structural unit and the second structural unit and the molar ratio of the third structural unit to the second structural unit in the above polyimide-based binder material can be analyzed by nuclear magnetic resonance spectroscopy. Specifically, the polyimide-based binder material is fully dissolved in deuterium water to prepare an aqueous polymer solution with a concentration of 30-60 mg / mL, and the polyimide-based binder material is subjected to 1H NMR measurement using a nuclear magnetic resonance spectrometer. The composition of each unit structure in the polyimide-based binder material is calculated based on the chemical shift value and the integral area.

[0037] By controlling the molar ratio of the first structural unit and the second structural unit and the molar ratio of the third structural unit to the second structural unit, the present invention can control the molar ratio of the soft segment and the hard segment in the polyimide-based binder material, which is beneficial to further improving the elastic modulus and elongation at break of the polyimide-based binder material.

[0038] In addition, the inventors found that the weight-average molecular weight of the polyimide-based binder material also affects its bonding performance. Therefore, the present invention further defines that the weight-average molecular weight of the polyimide-based binder material is 30,000 to 400,000 g / mol. For example, the weight-average molecular weight of the polyimide-based binder material includes, but is not limited to, 30,000 g / mol, 100,000 g / mol, 200,000 g / mol, 400,000 g / mol, or the range composed of any two of them. When the weight-average molecular weight of the polyimide-based binder material is within the above range, the polyimide-based binder material has good hardness, which can make the binder have high mechanical strength.

[0039] As described above, the polyimide-based binder material is a condensate formed by the condensation of an amino sulfonic acid monomer, an amino monomer, and an acid anhydride monomer. Specifically, the amino sulfonic acid monomer and the amino monomer provide amino groups to undergo condensation with the acid anhydride monomer. Among them, the condensate formed after the amino monomer participates in the condensation provides a soft segment structure, and the condensates formed after the amino sulfonic acid monomer and the acid anhydride monomer participate in the condensation provide a hard segment structure. The structure of the combination of the soft and hard segments makes the polyimide-based binder material have a higher elastic modulus and elongation at break, enabling the polyimide-based binder material to have good mechanical properties and toughness, which is conducive to maintaining good stability and bonding performance of the binder including the polyimide-based binder material in lithium batteries.

[0040] It should be clear that the polyimide-based binder material can be stored in a solid form or a liquid form. When the polyimide-based binder material is stored in a solid form, the solid is a pure polyimide-based binder material. At this time, the sulfonic acid group structure in the polyimide-based binder material is in the form of sulfonic acid; when the polyimide-based binder material is stored in a liquid form, it can be stored by dissolving the solid of the polyimide-based binder material in an alkali solution. At this time, the sulfonic acid groups in the polyimide-based binder material exist in the form of sulfonates. The present invention does not make special limitations on the type of alkali in the alkali solution, as long as it can dissolve the polyimide-based binder material. For example, the alkali is selected from at least one of potassium hydroxide, sodium hydroxide, and triethylamine.

[0041] The binder provided by the present invention is in a liquid form during use, that is, the binder of the present invention also includes an alkali solution of a monovalent cation that dissolves the polyimide-based binder material. At this time, the sulfonic acid groups in the polyimide-based binder material exist in the form of sulfonates. Through the action of the alkali solution, the sulfonic acid in the polyimide-based binder material forms a sulfonate with the alkali in the alkali solution, enabling the polyimide-based binder material to be completely dissolved in water, greatly improving the water solubility of the binder.

[0042] In another specific embodiment, in order to further improve the water solubility of the binder, the present invention further controls the molar ratio of the monovalent cations derived from the base in the alkali solution to the sulfonate groups in the polyimide-based binder material to be (0.80 to 1.10):1. For example, the molar ratio of the monovalent cations derived from the base in the alkali solution to the sulfonate groups in the polyimide-based binder material includes, but is not limited to, 0.80:1, 0.90:1, 1.00:1, 1.10:1, or the range composed of any two of them.

[0043] In the binder as described above, the amino sulfonic acid monomer includes a diamine compound containing a sulfonic acid group.

[0044] In another specific embodiment, the amino monomer includes at least one of an aromatic diamine compound, an amino silane compound, a dimer amine compound, and a polyether amine compound.

[0045] The above-mentioned types of amino sulfonic acid monomers and amino monomers can undergo an efficient condensation reaction with the acid anhydride monomers, providing a hard segment structure and a soft segment structure for the polyimide-based binder material generated after the condensation reaction, which is beneficial to improving the elastic modulus and elongation at break of the polyimide-based binder material, and further beneficial to improving the bonding performance of the binder.

[0046] Furthermore, the amino sulfonic acid monomer includes at least one of 2,5-diaminobenzenesulfonic acid, 2,4-diaminobenzenesulfonic acid, 2,2'-biphenyldiamine disulfonic acid, 2,5-diaminobenzene-1,4-disulfonic acid, and 4,4'-diaminostilbene-2,2'-disulfonic acid. The above-mentioned amino sulfonic acid monomers can provide a hard segment structure for the polyimide-based binder material, which is beneficial to improving the mechanical strength of the polyimide-based binder material.

[0047] As described above, the amino monomer includes at least one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, ethylene glycol bis(2-aminophenyl) ether, 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, dimer amine, and polyether amine. For example, the dimer amine includes at least one of ethylenediamine, hexamethylenediamine, phenylenediamine, isophoronediamine, diethylenetriamine, and triethylenetetramine, and the polyether amine includes at least one of aminoethylaminopropyl-terminated polyethylene glycol (PEG) and bis[3-(aminomethyl)oxypropyl]amine. The above compounds have good flexibility and can provide a soft segment structure for the polyimide-based binder material in the present invention, which is beneficial to improving the elongation at break of the binder.

[0048] In addition, the anhydride monomers include at least one of pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride), butanetetracarboxylic dianhydride, and 3,3’,4,4’-diphenylsulfone tetracarboxylic dianhydride. The above anhydride monomers can also provide a hard segment structure for the polyimide-based binder material, which is conducive to improving the mechanical strength of the polyimide-based binder material.

[0049] The binder of the present invention is obtained through the following preparation method, which includes the following steps:

[0050] Carry out a condensation reaction on the sulfamic acid amino monomer, amino monomer, and anhydride monomer to obtain a polyimide-based binder material;

[0051] Dissolve the above polyimide-based binder material in an alkali solution to obtain the above binder.

[0052] By using the above method, the present invention can prepare a water-soluble binder. It should be clear that in the above preparation method, the polyimide binder material prepared after the condensation reaction can be stored as a solid, and when in use, it can be dissolved in an alkali solution; or the polyimide-based binder material can be dissolved in an alkali solution to obtain the finished binder for storage.

[0053] Furthermore, in the preparation method of the above binder, the preparation process of the polyimide-based binder material includes:

[0054] 1) Dissolve the sulfamic acid monomer and amino monomer in a solvent to obtain a mixed solution;

[0055] 2) Add the anhydride monomer to the mixed solution for a condensation reaction to obtain a mixed system containing the condensation product;

[0056] 3) After adding a water-carrying agent to the mixed system, carry out water treatment under reflux to obtain the condensation product;

[0057] Mix the condensation product with a poor solvent and carry out precipitation treatment to obtain the polyimide-based binder material.

[0058] In step 1), the present invention does not impose special limitations on the type of solvent, as long as it can dissolve the sulfamic acid monomer and the amine monomer. For example, the solvent includes at least one of dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and m-cresol. The present invention also does not impose special limitations on the dissolution method, as long as the sulfamic acid monomer and the amine monomer can be completely dissolved in the solvent. For example, the sulfamic acid monomer and the amine monomer can be added to the solvent and then stirred to make the above two solutes evenly distributed in the solvent.

[0059] In step 2), the present invention adds an acid anhydride monomer to the above mixed solution for a condensation reaction. In the condensation reaction, the sulfamic acid monomer and the amine monomer each provide an amino group to react with the acid anhydride monomer to form a condensate, obtaining a mixed system containing the condensation product.

[0060] In the above condensation reaction, water will be generated in the mixed system containing the condensate. In step 3), the present invention can remove the condensation product in the mixed system by adding a water-carrying agent to the above mixed system. The present invention does not impose special limitations on the usage amount of the water-carrying agent, which can be determined according to the actual situation. It should be clear that the water-carrying agent can timely bring out the by-product water generated in the thermal imidization process of the condensation product, promoting the right shift of the reaction. The imidization degree of the obtained condensation product is relatively high. Therefore, the step of thermally imidizing the polyimide binder in the conventional industry is also omitted, which is beneficial to saving industrial costs and improving industrial economy.

[0061] Then, the above condensation product is mixed with a poor solvent and subjected to precipitation treatment to obtain a polyimide binder material. The present invention does not impose special limitations on the type of the poor solvent, as long as it does not react with the condensation product and can cause the condensation product to precipitate. For example, the poor solvent includes at least one of ethanol, isopropanol, n-hexane, cyclohexane, dichloromethane, acetone, and tetrahydrofuran.

[0062] The present invention also does not limit the usage amount of the poor solvent, which can be selected according to the actual situation. It can be understood that before the above precipitation treatment, it also includes cooling the condensation product to avoid the influence of temperature on the poor solvent; after the above precipitation treatment, it also includes washing and drying the precipitate obtained by the precipitation treatment to obtain a dry polyimide binder material.

[0063] The present invention does not specifically limit the reagents for washing treatment, the treatment temperature, the treatment time for drying treatment, and the treatment temperature, as long as a dry polyimide-based binder material can be obtained. For example, the above-cooled condensation product can be precipitated and washed in an ethanol solution at room temperature, and then dried in a vacuum drying oven at 60-120 °C for 6-24 h to obtain a dry polyimide-based binder material.

[0064] Specifically, in the above mixed solution, the molar ratio of the aminosulfonic acid monomer to the amine monomer is (4-9):(6-1). For example, the molar ratio of the aminosulfonic acid monomer to the amine monomer includes but is not limited to 4:6, 5:5, 7:3, 8:2, 9:1, or the range composed of any two of them. By further limiting the molar ratio of the aminosulfonic acid monomer to the amine monomer, a polyimide-based binder material with a suitable soft segment and hard segment composition can be obtained.

[0065] In another specific embodiment, the molar ratio of the total molar amount of the aminosulfonic acid monomer and the amine monomer to the molar amount of the anhydride monomer in step 2) is 1:(0.95-1.05). For example, the molar ratio of the total molar amount of the aminosulfonic acid monomer and the amine monomer to the molar amount of the anhydride monomer includes but is not limited to 1:0.95, 1:1, 1:1.05, or the range composed of any two of them. By limiting the molar ratio of the total molar amount of the aminosulfonic acid monomer and the amine monomer to the molar amount of the anhydride monomer, the present invention can effectively control the occurrence of the condensation reaction and prepare a polyimide-based binder material with a weight average molecular weight of 30,000-400,000 g / mol and a suitable soft segment and hard segment composition.

[0066] In another specific embodiment, the reaction temperature of the condensation reaction is 0-60 °C, and the reaction time is 6-24 h. For example, the reaction temperature of the condensation reaction includes but is not limited to 0 °C, 10 °C, 20 °C, 30 °C, 40 °C, 50 °C, 60 °C, or the range composed of any two of them; the reaction time of the condensation reaction includes but is not limited to 6 h, 10 h, 14 h, 18 h, 20 h, 24 h, or the range composed of any two of them. By controlling the reaction temperature and reaction time of the condensation reaction, the present invention is beneficial to generating a polyimide-based binder material with a suitable molecular weight size and improving the bonding performance of the binder.

[0067] Considering the effectiveness of the thermal imidization treatment, in another specific embodiment, the thermal imidization treatment temperature is 140 - 200 °C, and the treatment time is 2 - 8 h. For example, the treatment temperature of the thermal imidization treatment includes but is not limited to 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, 190 °C, 200 °C or the range composed of any two of them; the reaction time of the condensation reaction includes but is not limited to 2 h, 4 h, 6 h, 8 h or the range composed of any two of them. The present invention controls the treatment temperature and treatment time of the thermal imidization treatment within the above ranges, which is beneficial to effectively perform the thermal imidization treatment on the condensation product, obtain a polyimide-based binder with a higher imidization degree, and is beneficial to improving the bonding performance of the binder.

[0068] In another specific embodiment, the water-carrying agent in the above preparation method includes at least one of toluene, xylene, and cyclohexane. By using the above water-carrying agent, it can effectively form an azeotropic mixture with the by-product water in the thermal imidization process, thereby reducing the boiling point of water in the system, making it easier for the condensation by-product water to be distilled out of the reaction system, and promoting the forward progress of the thermal imidization reaction.

[0069] The second aspect of the present invention provides a negative electrode plate, which includes a negative electrode active layer, and the negative electrode active layer includes the above binder or a binder prepared by the preparation method of the above binder. In the negative electrode active layer, each component is tightly adhered together by the binder and can still maintain its integrity during the charge and discharge process of the battery, which is beneficial to improving the cycle stability and life of the battery.

[0070] The third aspect of the present invention provides a battery, including the negative electrode plate provided by the third aspect of the present invention. This battery can maintain its high performance during repeated charge and discharge processes, ensuring a stable and reliable power output.

[0071] Hereinafter, the technical solution of the present invention will be further described in conjunction with specific embodiments.

[0072] Example 1

[0073] The preparation method of the binder in this example includes the following steps:

[0074] 1) Add 2,5-diaminobenzene-1,4-disulfonic acid (134.1 g, 0.5 mol) and ethylene glycol bis(2-aminophenyl) ether (122.2 g, 0.5 mol) to NMP (4071.6 g), and stir until dissolved to obtain a mixed solution.

[0075] 2) Add pyromellitic dianhydride (196.1 g, 1.0 mol) in three portions, with an interval of 2 h each time, and react at 25 °C for 24 hours to obtain a mixed system containing the condensation product.

[0076] 3) After adding 407 g of toluene as a water-carrying agent to the above mixed system, stir evenly and heat up to 180 °C, reflux to remove water for 8 h; after cooling, precipitate the product in ethanol, wash it, and dry it under vacuum at 100 °C for 6 h to obtain a dried polyimide-based binder material;

[0077] Among them, the mass percentage content of sulfonate groups in the polyimide-based binder material is 19 wt%;

[0078] In the polyimide-based binder material, the molar ratio of the first structural unit from the amino sulfonic acid monomer to the second structural unit from the amino monomer is 1:1;

[0079] The total molar ratio of the first structural unit from the amino sulfonic acid monomer and the second structural unit from the amino monomer to the third structural unit from the anhydride monomer is 5:5;

[0080] The molar ratio of the monovalent cation from the base to the sulfonate groups in the polyimide-based binder material is 1:1;

[0081] The weight-average molecular weight of the polyimide-based binder material is 286,000 g / mol.

[0082] 4) Dissolve potassium hydroxide (112.2 g, 2 mol; the molar ratio of lithium ions to sulfonate groups is 1:1) in 4248 g of water to prepare an alkaline solution, and add the above dried polyimide-based binder material to the alkaline solution, and continuously stir until it dissolves to obtain a binder.

[0083] Example 2

[0084] This example is basically the same as Example 1, the difference is that,

[0085] In step 1), add 2,5-diaminobenzene-1,4-disulfonic acid (187.7 g, 0.7 mol) and ethylene glycol bis(2-aminophenyl) ether (73.3 g, 0.3 mol) to NMP (4071.6 g), and stir until dissolved to obtain a mixed solution.

[0086] In step 2), add cyclobutane tetracarboxylic dianhydride (196.1 g, 1.0 mol) in three portions, with an interval of 2 h each time, and carry out a condensation reaction at 25 °C for 24 h to obtain a mixed system containing the condensation product.

[0087] The mass percentage content of sulfonate groups in the polyimide-based binder material of this example is 27 wt%;

[0088] In the polyimide-based binder material, the molar ratio of the first structural unit from the amino sulfonic acid monomer to the second structural unit from the amino monomer is 7:3;

[0089] The molar ratio of the total of the first structural unit derived from the sulfamic acid monomer and the second structural unit derived from the amine monomer to the third structural unit derived from the acid anhydride monomer is 1:1;

[0090] The weight-average molecular weight of the polyimide-based binder material is 227,000 g / mol.

[0091] Example 3

[0092] This example is basically the same as Example 1, except that

[0093] In step 1), 2,5-diaminobenzene-1,4-disulfonic acid (241.4 g, 0.8 mol) and ethylene glycol bis(2-aminophenyl) ether (24.4 g, 0.2 mol) were added to NMP (4071.6 g), and stirred until dissolved to obtain a mixed solution.

[0094] In step 2), cyclobutane tetracarboxylic dianhydride (196.1 g, 1 mol) was added in three portions at intervals of 2 h, and the condensation reaction was carried out at 25 °C for 24 h to obtain a mixed system containing the condensation product.

[0095] In the polyimide-based binder material prepared in this example, the molar ratio of the first structural unit to the second structural unit is 8:2;

[0096] The molar ratio of the total of the first structural unit derived from the sulfamic acid monomer and the second structural unit derived from the amine monomer to the third structural unit derived from the acid anhydride monomer is 1:1;

[0097] The mass percentage content of sulfonate groups in the polyimide-based binder material of this example is 30.4 wt%;

[0098] The weight-average molecular weight of the polyimide-based binder material is 185,000 g / mol.

[0099] Example 4

[0100] This example is basically the same as Example 1, except that

[0101] In step 1), 2,5-diaminobenzene-1,4-disulfonic acid (160.9 g, 0.6 mol) and ethylene glycol bis(2-aminophenyl) ether (97.7 g, 0.4 mol) were added to NMP (4071.6 g), and stirred until dissolved to obtain a mixed solution.

[0102] In step 2), cyclobutane tetracarboxylic dianhydride (196.1 g, 1 mol) was added in three portions at intervals of 2 h, and the condensation reaction was carried out at 25 °C for 24 h to obtain a mixed system containing the condensation product.

[0103] In the polyimide-based adhesive material prepared in this example, the molar ratio of the first structural unit to the second structural unit is 6:4;

[0104] The molar sum of the first structural unit from the amino sulfonic acid monomer and the second structural unit from the amine monomer to the molar ratio of the third structural unit from the acid anhydride monomer is 1:1;

[0105] The mass percentage content of sulfonate groups in the polyimide-based adhesive material of this example is 23.4 wt%;

[0106] The weight-average molecular weight of the polyimide-based adhesive material is 248,000 g / mol.

[0107] Example 5

[0108] This example is basically the same as Example 1, except that in this example, the molar ratio of the monovalent cation from the base to the sulfonate groups in the polyimide-based adhesive material is 1.2:1.

[0109] Example 6

[0110] This example is basically the same as Example 1, except that in this example, the molar sum of the first structural unit from the amino sulfonic acid monomer and the second structural unit from the amine monomer to the molar ratio of the third structural unit from the acid anhydride monomer is 0.95:1; the weight-average molecular weight of the polyimide-based adhesive material is 35,000 g / mol; the molar ratio of the monovalent cation from the base to the sulfonate groups in the polyimide-based adhesive material is 1:1.

[0111] Example 7

[0112] This example is basically the same as Example 1, except that in this example, the amino sulfonic acid monomer used is 2,2'-biphenylenedisulfonic acid and the amine monomer used is 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, and the acid anhydride monomer used is 4,4'-oxydiphthalic anhydride;

[0113] In the polyimide-based adhesive material, the molar ratio of the first structural unit from the amino sulfonic acid monomer to the second structural unit from the amine monomer is 7:3;

[0114] The molar sum of the first structural unit from the amino sulfonic acid monomer and the second structural unit from the amine monomer to the molar ratio of the third structural unit from the acid anhydride monomer is 1:1;

[0115] The mass percentage content of sulfonate groups in the polyimide-based adhesive material prepared in this example is 19.2 wt%;

[0116] The molar ratio of the monovalent cation from the base to the sulfonate group in the polyimide-based binder material is 1:1;

[0117] The weight-average molecular weight of the polyimide-based binder material is 364,000 g / mol.

[0118] Comparative Example 1

[0119] This comparative example is basically the same as Example 1, except that

[0120] In step 1), 2,5-diaminobenzene-1,4-disulfonic acid (40.2 g, 0.15 mol) and ethylene glycol bis(2-aminophenyl) ether (207.7 g, 0.85 mol) were added to NMP (4071.6 g), and stirred until dissolved to obtain a mixed solution.

[0121] In step 2), cyclobutane tetracarboxylic dianhydride (196.1 g, 1 mol) was added in three portions at intervals of 2 h, and the condensation reaction was carried out at 25 °C for 24 h to obtain a mixed system containing the condensation product.

[0122] In the polyimide-based binder material prepared in this comparative example, the molar ratio of the first structural unit from the sulfamic acid monomer to the second structural unit from the amine monomer is 1.5:8.5;

[0123] The molar ratio of the total molar amount of the first structural unit from the sulfamic acid monomer and the second structural unit from the amine monomer to the third structural unit from the acid anhydride monomer is 1:1;

[0124] The weight-average molecular weight of the polyimide-based binder material is 248,000 g / mol.

[0125] The mass percentage content of the sulfonate group in the polyimide-based binder material in this comparative example is 5.9%.

[0126] The molar ratio of the monovalent cation from the base to the sulfonate group in the polyimide-based binder material is 1:1;

[0127] This polymer cannot be dissolved in an aqueous solution of the base.

[0128] Comparative Example 2

[0129] This comparative example is basically the same as Example 1, except that in the polyimide-based binder material, the molar ratio of the first structural unit from the sulfamic acid monomer to the second structural unit from the amine monomer is 10:0;

[0130] The molar ratio of the total molar amount of the first structural unit from the sulfamic acid monomer and the second structural unit from the amine monomer to the third structural unit from the acid anhydride monomer is 1:1;

[0131] The mass percentage content of sulfonic acid groups in the polyimide-based binder material prepared in this example is 37.8 wt%;

[0132] The number average molecular weight of the polyimide-based binder material is 293000 g / mol.

[0133] Test example:

[0134] Preparation of the positive electrode sheet: Mix 96.80 wt% of lithium nickel cobalt manganese oxide ternary material, 1.5 wt% of conductive agent Super. P, 0.5 wt% of conductive graphite KS-6, 1.20 wt% of binder polyvinylidene fluoride and N-methylpyrrolidone to prepare a positive electrode slurry, and then coat the positive electrode slurry on the surface of aluminum foil. After drying and rolling, the positive electrode sheet is obtained;

[0135] Preparation of the negative electrode sheet: Mix 1.5 wt% of the binder provided above, 0.5 wt% of thickener sodium carboxymethyl cellulose, 1 wt% of conductive agent Super. P, 1 wt% of styrene-butadiene rubber, 5.0 wt% of silicon-carbon active negative electrode, 92.0 wt% of graphite and deionized water to prepare a negative electrode slurry, and then coat the negative electrode slurry on the surface of copper foil. After drying and rolling, the negative electrode sheet is obtained;

[0136] Preparation of the electrolyte: In a glove box filled with argon, mix ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a mass ratio of 3:2:5, add lithium hexafluorophosphate, and stir evenly to obtain the electrolyte for the lithium-ion battery.

[0137] Preparation of the lithium-ion battery: Assemble the above positive electrode sheet, negative electrode sheet, electrolyte and separator to obtain the lithium-ion battery.

[0138] Mechanical property test of the binder:

[0139] Pour the binders in Examples 1-7 and Comparative Example 2 into a dumbbell-shaped mold with a length of 100 mm, a width of 10 mm and a thickness of 0.5 mm. After standing at room temperature for 48 h, demold and trim the edges, and then bake in an oven at 85 °C for 4 h to obtain a binder film. Use an electronic universal testing machine to conduct a mechanical property test. At room temperature, keep the lower fixture stationary and the upper fixture stretch upward at a stretching rate of 5 mm / min. Record the elastic modulus and elongation at break measured in the elastic deformation section. The test results are shown in Table 1.

[0140] Capacity retention rate test:

[0141] Test the capacity retention rate of each obtained battery. The specific test method is as follows: At 25°C, charge at a constant current of 1C until 4.50V, then charge at a constant voltage of 0.05C until 4.50V, and then discharge at a discharge rate of 1C until 3.0V. Repeat this charge-discharge cycle 500 times, and measure the discharge capacity in the first cycle and the discharge capacity in the 500th cycle. Calculate the capacity retention rate Q after 500 cycles according to the following formula:

[0142] Capacity retention rate Q = Q 200 / Q1 * 100%, and the specific test results are shown in Table 1.

[0143] Table 1

[0144]

[0145] "-" indicates that measurement is not required.

[0146] As can be seen from the table, when the binders prepared in Examples 1-7 are used in the battery compared with those in Comparative Examples 1-2, the negative electrode sheet can have higher electrical conductivity, elastic modulus, cycle stability, and elongation at break, making the battery have better stability and longer life.

[0147] Finally, it should be noted that: The above embodiments are only used to illustrate the technical solutions of the present invention, not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: They can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A binder, characterized in that: The polyimide adhesive material includes: a first structural unit derived from an aminosulfonic acid monomer, a second structural unit derived from an amino monomer, and a third structural unit derived from an anhydride monomer; The mass percentage of sulfonate in the polyimide adhesive material is 15-35 wt%; The adhesive further comprises an alkaline solution that dissolves the monovalent cations of the polyimide-based adhesive material; The aminosulfonic acid monomer includes at least one of 2,5-diaminobenzenesulfonic acid, 2,4-diaminobenzenesulfonic acid, 2,2'-benzidine disulfonic acid, 2,5-diaminobenzene-1,4-disulfonic acid, and 4,4'-diaminostilbene-2,2'-disulfonic acid; The amino monomer includes at least one of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, ethylene glycol bis(2-aminophenyl) ether, and 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane; The anhydride monomer includes at least one of pyromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-biphenyl ether dianhydride, 4,4'-(4,4'-isopropylidene diphenoxy)bis(phthalic anhydride), and 3,3',4,4'-diphenyl sulfonetetracarboxylic dianhydride.

2. The adhesive according to claim 1, characterized in that The molar ratio of the monovalent cation from the base in the binder to the sulfonate group in the polyimide-based binder material is (0.8-1.05):

1.

3. The adhesive according to claim 1 or 2, characterized in that: The molar ratio of the first structural unit to the second structural unit is (4-9): (6-1); and / or, The molar ratio of the sum of the first structural unit and the second structural unit to the third structural unit is (0.95-1.10):

1.

4. The adhesive according to claim 1 or 2, characterized in that: The weight average molecular weight of the polyimide adhesive material is 30,000-400,000 g / mol.

5. A negative electrode plate, characterized in that: The negative electrode sheet comprises a negative electrode active layer, and the negative electrode active layer comprises the binder according to any one of claims 1 to 4.

6. A battery, characterized in that: The battery comprises the negative electrode sheet according to claim 5.

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