Binder and preparation method thereof, electrode plate and secondary battery

Abstract

The present invention belongs to the field of secondary battery technology and specifically relates to a binder and a preparation method thereof, an electrode plate, and a secondary battery. The binder comprises an imide polymer, a first conductive fiber, a second conductive fiber, and conductive particles. The first conductive fiber has a reactive group that reacts chemically with the imide polymer to form a chemical bond. The second conductive fiber has an average diameter of not less than 0.3 μm and an average length of not less than 10 μm. The binder provided by the present invention can not only effectively reduce the resistance of the electrode plate, thereby improving its conductivity, but also improve the cracking problem of thick electrode plates, increase the plate coating surface density, and thus improve the energy density of the battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and in particular relates to a binder and a preparation method thereof, an electrode plate and a secondary battery. Background Art

[0002] Lithium-ion secondary batteries, as a clean energy source, are widely used in various electronic devices and electric vehicles. With the continuous development of the consumer market, people are placing higher demands on the energy density of lithium-ion batteries. The content of active materials in the battery cell determines the battery's capacity and energy density. By reducing the proportion of inactive materials such as separators and current collectors in the battery cell and preparing high-area-density electrode sheets to increase the proportion of active materials in the battery cell, the energy density of lithium-ion batteries can be effectively improved.

[0003] However, increasing the active material loading to produce high-area-density electrode sheets is prone to brittle cracking of the active coating, which causes the active material to fall off during the drying process, affecting the electrode yield. On the other hand, achieving high-area-density electrode sheets inevitably requires increasing the thickness of the active coating, which increases the transmission distance of lithium ions and electrons, leading to an increase in the battery's internal resistance and affecting the overall performance of the battery cell.

[0004] Therefore, how to improve the cracking problem of thick electrode sheets and reduce the resistance of the electrode sheets is a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a binder and a preparation method thereof, an electrode plate and a secondary battery. The binder provided by the present invention can not only effectively reduce the resistance of the electrode plate, thereby improving the conductivity of the electrode plate, but also improve the cracking problem of thick electrode plates, increase the coating surface density of the electrode plate, and thus improve the energy density of the battery.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a binder comprising an imide polymer, a first conductive fiber, a second conductive fiber, and conductive particles, wherein the first conductive fiber has a reactive group, and the reactive group chemically reacts with the imide polymer to form a chemical bond, the average diameter of the second conductive fiber is not less than 0.3 μm, and the average length of the second conductive fiber is not less than 10 μm.

[0008] Here, the imide polymer is a polymerizable monomer composed of a diamine (whose structure contains two amino groups) and a dianhydride (whose structure contains ) can be prepared by polymerizing monomers.

[0009] The first conductive fibers are connected to the imide polymer via chemical bonds.

[0010] The present invention helps to form a "point-line" conductive structure with the conductive fibers by adding conductive particles, thereby improving the conductive effect of the conductive network.

[0011] The adhesive provided by the present invention can not only effectively reduce the resistance of the electrode plate, thereby improving the conductivity of the electrode plate, but also improve the cracking problem of thick electrode plates, increase the coating surface density of the plate, and thus improve the energy density of the battery.

[0012] In the above binder, as a preferred embodiment, the structure of the imide polymer includes an imide group and an auxiliary polar group.

[0013] Here, the imide group is a nitrogen atom connected to two carbonyl groups, with the general formula -C(O)-N(R)-C(O)-.

[0014] The present invention can further improve the cracking problem of thick electrode sheets by limiting the structure of the imide polymer to include auxiliary polar groups, reduce the resistance of the electrode sheets, and significantly improve the peel strength of the electrode sheets.

[0015] In the above binder, as a preferred embodiment, the first conductive fibers, the second conductive fibers and the conductive particles are uniformly distributed in the imide polymer.

[0016] Among the above-mentioned binders, as a preferred embodiment, the binder includes:

[0017] 60 to 100 parts by mass of an imide polymer (for example, 60 parts by mass, 80 parts by mass, or 100 parts by mass);

[0018] 1 to 10 parts by mass of the first conductive fiber (for example, 1 part by mass, 3 parts by mass, 5 parts by mass, or 10 parts by mass);

[0019] 10 to 100 parts by mass of the second conductive fiber (for example, 10 parts by mass, 30 parts by mass, 50 parts by mass, 70 parts by mass, or 100 parts by mass);

[0020] The amount of the conductive particles is 1 to 10 parts by mass (for example, 1 part by mass, 3 parts by mass, 5 parts by mass, or 10 parts by mass).

[0021] Among the above-mentioned binders, as a preferred embodiment, the binder includes:

[0022] 60-100 parts by mass of imide polymer;

[0023] 1 to 10 parts by weight of first conductive fiber;

[0024] 10 to 50 parts by mass of the second conductive fiber;

[0025] 1 to 10 parts by mass of conductive particles.

[0026] In the above-mentioned binder, as a preferred embodiment, the raw materials for preparing the imide polymer include diamine polymerizable monomers and dianhydride polymerizable monomers, and the molar ratio of the diamine polymerizable monomers to the dianhydride polymerizable monomers is 1:(0.9-1.5).

[0027] In the aforementioned binders, as a preferred embodiment, the weight-average molecular weight of the imide polymer is greater than 200,000. This weight-average molecular weight can be adjusted by controlling the monomer ratio, selecting the monomer activity, and controlling the synthesis process conditions. The use of high-molecular-weight imide polymers helps improve the mechanical strength of high-areal-density active material coatings, ensuring the structural integrity of thick coatings. Furthermore, the use of high-molecular-weight imide polymers helps improve the adhesion of the active material coating to the current collector foil, preventing the thick coating from shedding during long-term service, which can lead to rapid degradation of battery performance.

[0028] In the aforementioned binder, as a preferred embodiment, the imide polymer is soluble in a polar solvent. There are no particular limitations on the polar solvent; any polar solvent capable of dissolving the imide polymer satisfies the technical features of the present invention. Such polar solvents include, but are not limited to, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropionamide, and 1,4-dioxane. To balance the binder's processability and electrolyte resistance, an imide polymer that dissolves only in N-methylpyrrolidone may be selected.

[0029] The imide polymers have a strong structural rigidity and are mostly difficult to dissolve in solvents. The imide polymers described in the present invention can be dissolved in polar solvents.

[0030] In the above binder, as a preferred embodiment, the auxiliary polar group includes at least one of an amide group, an ester group, a urethane group, a urea group, a carbonate group, and a siloxy group.

[0031] In the above-mentioned adhesive, as a preferred embodiment, the imide polymer includes at least one of polyamide-imide, polyester-imide, polyurethane-imide, polyurea-imide, polycarbonate-imide, polyurethane-amide-imide, and polysiloxane-imide.

[0032] Imide polymers can interact with metal foil through hydrogen bonding, resulting in high adhesion. Furthermore, amide, ester, urethane, urea, carbonate, and siloxy groups have strong polarity and a high ability to form hydrogen bonds. The resulting hydrogen bonds have high energy, promoting a strong bond between the binder and the foil. Furthermore, the strong interaction of these hydrogen bonds helps to increase the cohesion of the binder, thereby improving the mechanical strength of thick-coated electrodes and enhancing the flexibility of the electrode active material layer. Therefore, these polymers are preferred.

[0033] The imide polymer can be obtained by polymerizing a diamine and a dibasic anhydride in a solvent to form polyamic acid, followed by high-temperature dehydration cyclization or chemical dehydration cyclization; can be obtained by reacting a diisocyanate and a dibasic anhydride in a solvent at a high temperature; can be obtained by polymerizing a diamine and an acid anhydride chloride in a solvent to form polyamide-amic acid, followed by high-temperature dehydration reaction; or can be obtained by polymerizing an active monomer containing an imide bond.

[0034] In the aforementioned binder, as a preferred embodiment, the chemical bond comprises at least one of an amide bond, an imide bond, an ester bond, a urethane bond, an ether bond, and a carbon-carbon bond. The chemical bond has a high bond energy, ensuring a tight bond between the imide polymer and the first conductive fiber, and preventing the imide polymer from detaching during high-speed shearing during mechanical dispersion.

[0035] The chemical bond is formed by a chemical reaction between the imide-based polymer and the first conductive fiber during the synthesis process.

[0036] There is no limitation on the chemical reaction form for forming the chemical bond, and the chemical bond can be formed through condensation polymerization, stepwise addition polymerization, ring-opening polymerization, free radical polymerization, cationic polymerization, anionic polymerization or coordination polymerization.

[0037] In the above binder, as a preferred embodiment, the reactive group includes at least one of a carboxyl group, an amino group, and a hydroxyl group.

[0038] In the above-mentioned binder, as a preferred embodiment, the first conductive fiber is a functionalized carbon fiber; preferably, the functionalized carbon fiber includes at least one of carboxylated graphite carbon fiber, amino graphite carbon fiber, hydroxylated graphite carbon fiber, carboxylated carbon nanotube fiber, amino carbon nanotube fiber, hydroxylated carbon nanotube fiber, carboxylated graphene fiber, amino graphene fiber, hydroxylated graphene fiber, carboxylated carbon cloth fiber, amino carbon cloth fiber, and hydroxylated carbon cloth fiber.

[0039] In the above-mentioned binder, as a preferred embodiment, the average diameter of the first conductive fiber is 5 to 50 nm (for example, 5 nm, 10 nm, 20 nm, 30 nm or 50 nm, etc.), and the average length is 0.2 to 20 μm (for example, 0.2 μm, 1 μm, 5 μm, 10 μm, 15 μm or 20 μm, etc.). The first conductive fiber is relatively thin, which is conducive to filling the gaps, forming a tight "microscopic" conductive network, and improving the conductivity of the binder. If the first conductive fiber is too short, it will lead to the inability to form an effective support network, and the thick coating will easily crack. At the same time, the conductivity will decrease, affecting the performance of the battery core.

[0040] In the above-mentioned binder, as a preferred embodiment, the second conductive fiber includes at least one of carbon fiber and metal fiber, wherein the carbon fiber includes at least one of graphite carbon fiber, carbon nanotube fiber, graphene fiber, and carbon cloth fiber; the metal fiber includes at least one of iron fiber, cobalt fiber, nickel fiber, copper fiber, zinc fiber, aluminum fiber, manganese fiber, gold fiber, silver fiber, titanium fiber, palladium fiber, platinum fiber, and bismuth fiber.

[0041] When the second conductive fiber is a functionalized carbon fiber, the conductivity of the prepared electrode plate will be slightly reduced.

[0042] In the above binder, as a preferred embodiment, the second conductive fibers have an average diameter of 0.3 to 30 μm (e.g., 0.3 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, or 30 μm), and an average length of 10 to 1000 μm (e.g., 10 μm, 50 μm, 100 μm, 200 μm, 300 μm, 500 μm, 700 μm, or 1000 μm). The second conductive fibers are relatively coarse, which facilitates the formation of a strong network support in the active material layer, improves the mechanical strength of the high-area-density active material coating, and ensures the structural integrity of the thick coating. At the same time, they form a tight "macro" conductive network, improving the conductivity of the binder.

[0043] From the perspective of further improving the uniformity of distribution of the first conductive fibers, the second conductive fibers and the conductive particles, methods such as adding a dispersant, increasing the power of the dispersing equipment, and reducing the solid content of the binder can be adopted during the preparation of the binder.

[0044] In the above binder, as a preferred embodiment, the conductive particles include at least one of conductive carbon particles, conductive polymer nanoparticles, and metal nanoparticles, wherein the conductive carbon particles include at least one of Super P, Ketjen black, and acetylene black, the conductive polymer nanoparticles include at least one of conductive polyaniline particles and conductive poly-3,4-ethylenedioxythiophene-polystyrene sulfonic acid particles, and the metal nanoparticles include at least one of copper nanoparticles, silver nanoparticles, gold nanoparticles, iron nanoparticles, platinum nanoparticles, and mercury nanoparticles; preferably, the D50 particle size of the conductive particles is less than 2000 nm; preferably, the specific surface area of ​​the conductive particles is 10 m 2 / g~10000m 2 / g.

[0045] In a second aspect, the present invention provides a method for preparing the binder according to the first aspect, comprising the following steps:

[0046] S1, reacting an imide polymer precursor with the first conductive fiber to obtain a conductive composite of the imide polymer and the first conductive fiber;

[0047] S2. Adding the conductive particles to the conductive composite and dispersing them evenly to obtain a dispersion of the composite and the conductive particles;

[0048] S3. Add the second conductive fiber to the dispersion and disperse it evenly to obtain the binder.

[0049] The preparation method of the binder provided by the invention is simple to operate, suitable for industrial production, and easy to promote and apply.

[0050] In the above-mentioned method for preparing the binder, as a preferred embodiment, the method for preparing the imide polymer precursor includes: reacting a diamine and a dibasic anhydride in a reaction solvent to obtain the imide polymer precursor.

[0051] In the preparation method of the above-mentioned binder, as a preferred embodiment, in the preparation process of the imide polymer precursor, the reaction solvent includes one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropionamide, and 1,4-dioxane, and the reaction time is 10 to 16 hours (for example, it can be 10 hours, 12 hours, 14 hours or 16 hours, etc.).

[0052] In the above-mentioned method for preparing the adhesive, as a preferred embodiment, in step S1, the reaction temperature is 200-400°C, for example, 200°C, 250°C, 300°C, 350°C or 400°C.

[0053] In the above-mentioned method for preparing the binder, as a preferred embodiment, in step S1, the imide polymer precursor and the first conductive fiber are first dispersed and then reacted.

[0054] In the preparation method of the above-mentioned binder, as a preferred embodiment, in step S1, the dispersion includes first dispersing at 400-600r / min (for example, 400r / min, 450r / min, 500r / min, 550r / min or 600r / min, etc.) for 5-20min (for example, 5min, 10min, 15min or 20min, etc.), and then dispersing at 2000-4000r / min (for example, 2000r / min, 2500r / min, 3000r / min, 3500r / min or 4000r / min, etc.) for 20-50min (for example, 20min, 30min, 40min or 50min, etc.).

[0055] In the preparation method of the above-mentioned binder, as a preferred embodiment, in step S2, the dispersion includes dispersing at 400-700 r / min (for example, it can be 400 r / min, 500 r / min, 600 r / min or 700 r / min, etc.) for 5-20 min (for example, it can be 5 min, 10 min, 15 min or 20 min, etc.).

[0056] In the preparation method of the above-mentioned binder, as a preferred embodiment, in step S3, the dispersion includes dispersing at 400-700 r / min (for example, it can be 400 r / min, 500 r / min, 600 r / min or 700 r / min, etc.) for 5-20 min (for example, it can be 5 min, 10 min, 15 min or 20 min, etc.).

[0057] In a third aspect, the present invention provides an electrode plate, which includes a current collector and an electrode membrane coated on the surface of the current collector, and the electrode membrane contains the binder described in the first aspect or the binder prepared by the binder preparation method described in the second aspect.

[0058] Here, the electrode plate is an electrode plate for a secondary battery, and the electrode plate is a positive electrode plate or a negative electrode plate.

[0059] In the above-mentioned electrode plate, as a preferred embodiment, the electrode membrane also contains electrode active material, and the mass percentage of the binder in the electrode membrane is 1%-16% (for example, it can be 1%, 3%, 5%, 8%, 10%, 14% or 16%, etc.).

[0060] Here, the electrode active material is a positive electrode active material or a negative electrode active material.

[0061] In a fourth aspect, the present invention provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet and / or the negative electrode sheet is the electrode sheet described in the third aspect.

[0062] Here, the secondary battery may be a lithium ion secondary battery.

[0063] Compared with the prior art, the present invention has at least one of the following advantages:

[0064] (1) The adhesive provided by the present invention can not only effectively reduce the resistance of the electrode plate, thereby improving the conductivity of the electrode plate, but also improve the cracking problem of thick electrode plates, increase the coating surface density of the plate, and thus improve the energy density of the battery.

[0065] (2) The present invention provides a binder for improving electrode conductivity and energy density, which can form a stable three-dimensional conductive network through a composite of a high molecular weight imide polymer and a first conductive fiber with a certain length and diameter, and uniformly dispersed second conductive fibers and conductive particles with a certain length and diameter. The electrode plate prepared by the binder has a stable thick coating plate active material layer structure, thereby obtaining a battery cell with high plate coating surface density and high battery energy density; at the same time, the electrode plate prepared by the binder also has excellent conductivity, which solves the problem of poor conductivity of thick electrode plates and large internal resistance of batteries assembled with high surface density electrode plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 This is a schematic diagram of the distribution of the first conductive fibers, the second conductive fibers, and the conductive particles in the binder provided by the present invention.

[0067] Among them, 1. first conductive fiber; 2. second conductive fiber; 3. conductive particles. DETAILED DESCRIPTION

[0068] In order to make the purpose, 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. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0069] The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the scope of protection of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally based on conventional conditions.

[0070] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0071] Throughout this disclosure, unless otherwise specified and / or explained, all references to component amounts are in parts by weight. Process parameters in the following examples, where specific conditions are not specified, generally follow conventional conditions. The experimental reagents used in the following examples, unless otherwise noted, are conventional biochemical reagents; and the amounts of experimental reagents used, unless otherwise noted, are those used in routine experimental procedures.

[0072] In a first aspect, an embodiment of the present invention provides a binder, comprising an imide polymer (60 to 100 parts by mass), a first conductive fiber (1 to 10 parts by mass), a second conductive fiber (10 to 100 parts by mass) and conductive particles (1 to 10 parts by mass), wherein the structure of the imide polymer comprises an imide group and an auxiliary polar group, the first conductive fiber carries a reactive group, and the reactive group reacts chemically with the imide polymer to form a chemical bond, and the raw materials for preparing the imide polymer include a binary Amine polymerizable monomers and dibasic anhydride polymerizable monomers, the molar ratio of the diamine polymerizable monomers to the dibasic anhydride polymerizable monomers is 1: (0.9-1.5), the weight average molecular weight of the imide polymer is greater than 200,000, the auxiliary polar group includes at least one of an amide group, an ester group, a urethane group, a urea group, a carbonate group, and a siloxy group, and the imide polymer includes at least one of polyamide-imide, polyester-imide, polyurethane-imide, polyurea-imide, polycarbonate-imide, polyurethane-amide-imide, and polysiloxane-imide. One, the chemical bond includes at least one of an amide bond, an imide bond, an ester bond, a urethane bond, an ether bond, and a carbon-carbon bond, the reactive group includes at least one of a carboxyl group, an amino group, and a hydroxyl group, the first conductive fiber is a functionalized carbon fiber, and the functionalized carbon fiber includes carboxylated graphite carbon fiber, amino graphite carbon fiber, hydroxylated graphite carbon fiber, carboxylated carbon nanotube fiber, amino carbon nanotube fiber, hydroxylated carbon nanotube fiber, carboxylated graphene fiber, amino graphene fiber, hydroxylated graphene fiber, carboxylated carbon cloth fiber, amino carbon cloth fiber, hydroxylated At least one of carbon cloth fibers, the first conductive fibers have an average diameter of 5 to 50 nm and an average length of 0.2 to 20 μm, the second conductive fibers include at least one of carbon fibers and metal fibers, wherein the carbon fibers include at least one of graphite carbon fibers, carbon nanotube fibers, graphene fibers, and carbon cloth fibers; the metal fibers include at least one of iron fibers, cobalt fibers, nickel fibers, copper fibers, zinc fibers, aluminum fibers, manganese fibers, gold fibers, silver fibers, titanium fibers, palladium fibers, platinum fibers, and bismuth fibers, and the average diameter of the second conductive fibers is 0.The conductive particles are 3 to 30 μm in diameter and 10 to 1000 μm in average length. The conductive particles include at least one of conductive carbon particles, conductive polymer nanoparticles, and metal nanoparticles. The conductive carbon particles include at least one of Super P, Ketjen black, and acetylene black. The conductive polymer nanoparticles include at least one of conductive polyaniline particles and conductive poly-3,4-ethylenedioxythiophene-polystyrene sulfonic acid particles. The metal nanoparticles include at least one of copper nanoparticles, silver nanoparticles, gold nanoparticles, iron nanoparticles, platinum nanoparticles, and mercury nanoparticles. Preferably, the D50 particle size of the conductive particles is less than 2000 nm. Preferably, the specific surface area of ​​the conductive particles is 10 m2. 2 / g~10000m 2 / g.

[0073] An embodiment of the present invention provides a binder for improving electrode conductivity and energy density. The battery binder comprises an imide polymer, a first conductive fiber, a second conductive fiber, and conductive particles, wherein the first conductive fiber is interconnected with the imide polymer through a chemical bond, and the first conductive fiber, the second conductive fiber, and the conductive particles are evenly distributed in the imide polymer, forming a uniform and efficient conductive network.

[0074] Figure 1 Schematic diagram of the distribution of the first conductive fibers, the second conductive fibers and the conductive particles in the binder provided by the present invention, as shown in FIG. Figure 1 As shown, the first conductive fibers 1 and the second conductive fibers 2 intersect and overlap, and the conductive particles 3 are evenly distributed in the first conductive fibers 1 and the second conductive fibers 2, thereby forming an efficient conductive network and improving the conductivity of the binder.

[0075] In a second aspect, an embodiment of the present invention provides a method for preparing the adhesive according to the first aspect, comprising the following steps:

[0076] S1. The imide polymer precursor and the first conductive fiber are first dispersed at 400-600 r / min for 5-20 min, then dispersed at 2000-4000 r / min for 20-50 min, and then reacted at 200-400°C to obtain a conductive composite of the imide polymer and the first conductive fiber, wherein the preparation method of the imide polymer precursor includes: a diamine and a dibasic anhydride react in a reaction solvent to obtain the imide polymer precursor, the reaction solvent includes one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropionamide, and 1,4-dioxane, and the reaction time is 10-16 h.

[0077] S2. Add the conductive particles to the conductive composite, disperse at 400-700 r / min for 5-20 min, and disperse evenly to obtain a dispersion of the composite and the conductive particles.

[0078] S3. Add the second conductive fiber to the dispersion, disperse at 400-700 r / min for 5-20 min, and disperse evenly to obtain the binder.

[0079] In a third aspect, an embodiment of the present invention provides an electrode plate, which includes a current collector and an electrode membrane coated on the surface of the current collector, wherein the electrode membrane contains the binder described in the first aspect or the binder prepared by the binder preparation method described in the second aspect, and the electrode membrane also contains an electrode active substance, and the mass percentage of the binder in the electrode membrane is 1%-16%.

[0080] In a fourth aspect, an embodiment of the present invention provides a lithium-ion secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and the positive electrode sheet and / or the negative electrode sheet is the electrode sheet described in the third aspect.

[0081] In order to further understand the present invention, the binder and its preparation method, electrode plate and secondary battery provided by the present invention are described in detail below with reference to the embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0082] Example 1

[0083] The adhesive provided in this embodiment includes polyamide-imide (weight average molecular weight of 230,000) (74.3g), amino-treated carbon nanotube fiber (3g), aluminum fiber (30g) and Super P (5g), wherein the structure of the polyamide-imide includes an imide group and an amide group, the amino-treated carbon nanotube fiber has an amino group, and the amino group forms a chemical bond (imide bond) with the polyamide-imide.

[0084] The binder provided in this embodiment that can improve the conductivity and energy density of the electrode is prepared as follows:

[0085] (1) 33.0 g of 4,4'-diaminobenzanilide was dissolved in N-methylpyrrolidone, and 46.5 g of 4,4'-biphenyl ether dianhydride was gradually added in three batches under stirring, and the mixture was stirred at room temperature for 12 h to obtain a viscous polyamide acid glue solution (imide polymer precursor) with a solid content of 12%; 3 g of amino carbon nanotube fibers (average diameter of 30 nm, average length of 1 μm) were added to the obtained glue solution, and then dispersed in a dispersing disk stirrer at 500 r / min for 10 min and then at 3000 r / min for 30 min to obtain a uniform black glue solution; the glue solution was placed in a high-temperature vacuum oven, evacuated and heated to 100°C to remove the solvent, and then heated to 300°C for high-temperature thermal curing for 30 min, and then crushed to obtain a conductive composite of polyamide-imide and amino carbon nanotube fibers;

[0086] (2) The obtained conductive composite was dissolved and dispersed in N-methylpyrrolidone to form a uniform conductive composite suspension with a solid content of 8%, and then 5g of conductive carbon particles (Super P, D50 is 40nm, specific surface area is 62m 2 / g), and dispersed at 600 r / min for 10 min using a dispersing disk stirrer to obtain a dispersion of the composite and the conductive particles;

[0087] (3) Add 30 g of aluminum fiber (average diameter 20 μm, average length 500 μm) to the resulting dispersion and disperse it evenly using a dispersing disk stirrer at 600 rpm for 10 min to obtain the binder of this example. The binder prepared in this example is soluble in N-methylpyrrolidone.

[0088] Example 2

[0089] The adhesive provided in this embodiment includes polyamide-imide (weight-average molecular weight of 250,000) (about 60.6 g), carboxylated carbon nanotube fibers (10 g), silver fibers (10 g) and Ketjen black (1 g), wherein the structure of the polyamide-imide includes an imide group and an amide group, the carboxylated carbon nanotube fibers have carboxyl groups, and the carboxyl groups form a chemical bond (amide bond) with the polyamide-imide.

[0090] The binder provided in this embodiment that can improve the conductivity and energy density of the electrode is prepared as follows:

[0091] (1) 19.0 g of 4,4'-diaminodiphenyl ether and 11.9 g of m-phenylenediamine were dissolved in N-methylpyrrolidone, and 40.1 g of trimellitic anhydride chloride was gradually added in three batches under stirring, and the mixture was stirred at room temperature for 24 h to obtain a viscous polyamide-amic acid glue solution (imide polymer precursor) with a solid content of 12%; 10 g of carboxylated carbon nanotube fibers (average diameter of 10 nm, average length of 0.2 μm) were added to the obtained glue solution, and then dispersed in a dispersing disk stirrer at 500 r / min for 10 min and then at 3000 r / min for 30 min to obtain a uniform black glue solution; the glue solution was placed in a high-temperature vacuum oven, evacuated and heated to 100°C to remove the solvent, and then heated to 300°C for high-temperature thermal curing for 30 min, and then crushed to obtain a conductive composite of polyamide-imide and carboxylated carbon nanotube fibers;

[0092] (2) The obtained conductive composite was dissolved and dispersed in N-methylpyrrolidone to form a uniform conductive composite suspension with a solid content of 8%, and then 1g of conductive carbon particles (Ketjen black, D50 is 20nm, specific surface area is 1500m 2 / g), and dispersed at 600 r / min for 10 min using a dispersing disk stirrer to obtain a dispersion of the composite and the conductive particles;

[0093] (3) Add 10 g of silver fibers (average diameter 1 μm, average length 100 μm) to the resulting dispersion and disperse uniformly using a dispersing disk stirrer at 600 rpm for 10 min to obtain the adhesive of this embodiment. The adhesive prepared in this embodiment is soluble in N-methylpyrrolidone.

[0094] Example 3

[0095] The adhesive provided in this embodiment includes polyurea-imide (weight-average molecular weight of 230,000) (94.5 g), amino-treated carbon nanotube fibers (3 g), aluminum fibers (30 g) and Super P (5 g), wherein the structure of the polyurea-imide includes an imide group and a urea group, the amino-treated carbon nanotube fibers have an amino group, and the amino group forms a chemical bond (urea bond) with the polyurea-imide.

[0096] The binder provided in this embodiment that can improve the conductivity and energy density of the electrode is prepared as follows:

[0097] (1) Dissolve 40.0 g of 4,4'-diaminodiphenyl ether in N-methylpyrrolidone, add 31.0 g of 4,4'-biphenyl ether dianhydride under stirring, stir and react at room temperature for 3 h, then add 27.1 g of 4,4'-diphenylmethane diisocyanate was stirred and reacted at room temperature for 2 hours to obtain a viscous polyurea-amic acid glue solution (imide polymer precursor) with a solid content of 10%; 3g of amino-modified carbon nanotube fibers (average diameter of 30nm, average length of 1μm) were added to the obtained glue solution, and then dispersed in a dispersing disk stirrer at 500r / min for 10 minutes and then at 3000r / min for 30 minutes to obtain a uniform black glue solution; the glue solution was placed in a high-temperature vacuum oven, evacuated and heated to 100°C to remove the solvent, and then heated to 300°C for high-temperature thermal curing for 30 minutes, and then crushed to obtain a conductive composite of polyurea-imide and amino-modified carbon nanotube fibers;

[0098] The remaining steps (2) and (3) are the same as those in Example 1.

[0099] The binder prepared in this example can be dissolved in N-methylpyrrolidone.

[0100] Example 4

[0101] The preparation method of the adhesive provided in this embodiment is basically the same as that in Example 1, except that the average diameter of the amino-treated carbon nanotube fibers is 10 nm and the average length is 5 μm; the average diameter of the aluminum fibers is 10 μm and the average length is 300 μm.

[0102] The binder prepared in this example can be dissolved in N-methylpyrrolidone.

[0103] Comparative Example 1

[0104] The preparation process of the binder provided in this comparative example is as follows:

[0105] (1) 33.0 g of 4,4'-diaminobenzanilide was dissolved in N-methylpyrrolidone, and 46.5 g of 4,4'-biphenyl ether dianhydride was gradually added in three batches under stirring, and the mixture was stirred and reacted at room temperature for 12 h to obtain a viscous polyamide acid glue solution with a solid content of 12%; the glue solution was placed in a high-temperature vacuum oven, vacuumed and heated to 100°C to remove the solvent, and then heated to 300°C for high-temperature thermal curing for 30 min, crushed, and then mixed with 3 g of amino-modified carbon nanotube fibers (average diameter of 30 nm, average length of 1 μm) to obtain a conductive composite of polyamide-imide and amino-modified carbon nanotube fibers;

[0106] (2) The obtained conductive composite was dissolved and dispersed in N-methylpyrrolidone to form a uniform conductive composite suspension with a solid content of 8%, and then 5g of conductive carbon particles (Super P, D50 is 40nm, specific surface area is 62m 2 / g), and dispersed at 600 r / min for 10 min using a dispersing disk stirrer to obtain a dispersion of the composite and the conductive particles;

[0107] (3) Add 30 g of aluminum fiber (average diameter 20 μm, average length 500 μm) to the obtained dispersion, and use a dispersing disk stirrer to disperse it at 600 r / min for 10 minutes until it is evenly dispersed to obtain the adhesive of this comparative example.

[0108] Comparative Example 2

[0109] The preparation process of the binder provided in this comparative example was carried out according to Example 1, except that the second conductive fiber (aluminum fiber) was not added.

[0110] Comparative Example 3

[0111] The preparation process of the binder provided in this comparative example is as follows:

[0112] (1) 43.3 g of 2,2-bis[4-(4-aminophenoxy)phenyl]propane was dissolved in N-methylpyrrolidone, and 33.5 g of 4,4'-biphenyl ether dianhydride was gradually added in three batches under stirring, and the mixture was stirred at room temperature for 12 h to obtain a viscous polyamic acid glue solution with a solid content of 12%; 3 g of amino-modified carbon nanotube fibers (average diameter of 30 nm, average length of 1 μm) were added to the obtained glue solution, and then dispersed in a dispersing disk stirrer at 500 r / min for 10 min and then at 3000 r / min for 30 min to obtain a uniform black glue solution; the glue solution was placed in a high-temperature vacuum oven, evacuated and heated to 100°C to remove the solvent, and then heated to 300°C for high-temperature thermal curing for 30 min, and then crushed to obtain a conductive composite of the imide polymer and the first conductive fiber;

[0113] (2) The obtained conductive composite was dissolved and dispersed in N-methylpyrrolidone to form a uniform conductive composite suspension with a solid content of 8%, and then 5g of conductive carbon particles (Super P, D50 is 40nm, specific surface area is 62m 2 / g), and dispersed at 600 r / min for 10 min using a dispersing disk stirrer to obtain a dispersion of the composite and the conductive particles;

[0114] (3) Add 30 g of aluminum fiber (average diameter 20 μm, average length 500 μm) to the obtained dispersion, and use a dispersing disk stirrer to disperse it at 600 r / min for 10 minutes until it is evenly dispersed to obtain the adhesive of this comparative example.

[0115] Comparative Example 4

[0116] The binder provided in this comparative example is PVDF (polyvinylidene fluoride), a conventional binder in lithium-ion batteries.

[0117] Comparative Example 5

[0118] The preparation method of the adhesive provided in this comparative example is basically the same as that of Example 1, except that the average diameter of the aluminum fibers is 30 nm and the average length is 500 μm.

[0119] Performance Testing

[0120] The binders prepared in Examples 1 to 4 and Comparative Examples 1 to 3 and Comparative Example 5 were used as active material binders to make pole pieces in the following manner:

[0121] To 93% (mass percentage) of ternary nickel-cobalt-manganese (nickel-cobalt-manganese ratio of 8:1:1) and 7% (mass percentage) of the binder prepared in the embodiment or comparative example, an appropriate amount of N-methylpyrrolidone was added at a solid content of 56% by mass, and dissolved and mixed using a double planetary mixer to prepare a battery electrode slurry. After the uniformly dispersed slurry was passed through a 100-mesh sieve, it was coated on a 13μm thick aluminum foil as a current collector using an electric scraper with adjustable height. After drying at 120°C for 10 minutes, it was dried at room temperature with a 1×10 4 The unit length load was calendered at N / m, and the surface density was 18 mg / cm 2 (single-sided surface density) electrode plate.

[0122] The binder prepared in Comparative Example 4 was used as an active material binder to make an electrode, and the method was as follows:

[0123] The ternary nickel-cobalt-manganese (nickel-cobalt-manganese ratio is 8:1:1), PVDF and Super P are added in a mass ratio of 93:4.6:2.4, with a mass fraction of 56% based on solid content, and an appropriate amount of N-methylpyrrolidone is added. The mixture is dissolved and mixed using a double planetary mixer to prepare a battery electrode slurry. After the uniformly dispersed slurry is passed through a 100-mesh sieve, it is coated on a 13μm thick aluminum foil as a current collector using an electric scraper with adjustable height. After drying at 120°C for 10 minutes, the slurry is dried at room temperature with a 1×10 4 The unit length load was calendered at N / m, and the surface density was 18 mg / cm 2 The electrode plate.

[0124] The performance test method of the electrode sheets prepared with the binders obtained in the above examples and comparative examples is as follows:

[0125] (1) Flexibility test:

[0126] The electrode flexibility test is carried out with reference to G / BT 1731-1993 "Determination of paint film flexibility".

[0127] At room temperature, cut the electrode sheet into 250mm x 100mm pieces. Place the center of each long side horizontally on a 120mm long, 5mm diameter steel mandrel with a fixed base, with the film layer of the test electrode facing upward. Press the electrode firmly against the mandrel with your thumb and index finger for 3 seconds. After bending, position your thumb and index finger symmetrically along the centerline of the mandrel. Observe the surface condition of the bent electrode sheet, marking it as "○" if intact, "□" if slightly cracked, and "×" if severely cracked.

[0128] (2) Maximum coating surface density:

[0129] In the process of preparing electrode plates, electrode plates with different surface densities are obtained by adjusting the height of the electric scraper. The electrode plate with the maximum surface density (referring to the maximum surface density of the electrode plate obtained after coating, drying and rolling) with no cracking on the surface of the plate (observed under a microscope) is taken as the highest coating surface density.

[0130] (3) Pole peel strength test:

[0131] The electrode sheets were cut into 100 mm × 20 mm strips, fixed to a 1 mm thick steel plate on the current collector side with double-sided tape, and transparent tape was pasted on the coating layer side. At 25°C, a 180° pull-off test was performed using a universal electronic testing machine at a peeling speed of 100 mm / min, and the peeling stress was recorded.

[0132] (4) Conductivity test:

[0133] The electrode sheet was cut into 5cm×5cm pieces, and the overall resistivity of the electrode sheet was measured using the ACCFILM film resistance test system and the controlled voltage dual-probe resistance method.

[0134] Table 1 shows the test results of the electrode sheets prepared in the examples and comparative examples.

[0135] Table 1

[0136]

[0137]

[0138] As can be seen from Table 1, by using a binder comprising an imide polymer having the polar group, a first conductive fiber, a second conductive fiber and conductive particles, wherein the first conductive fiber is interconnected with the imide polymer by a chemical bond, the average diameter of the second conductive fiber is not less than 0.3 μm, and the average length of the second conductive fiber is not less than 10 μm, an electrode sheet with good flexibility, a high maximum coating surface density, a high coating layer peeling strength and excellent conductivity can be obtained.

[0139] In the binder provided in Comparative Example 1, the imide polymer is only physically mixed with the first conductive fiber, and the imide polymer does not form a chemical bond with the first conductive fiber, thereby affecting the dispersibility of the first conductive fiber and causing a significant increase in the resistivity of the electrode plate.

[0140] The binder provided in Comparative Example 2 does not contain the second conductive fiber, and the binder cannot form a strong support for the active material layer, resulting in poor flexibility of the electrode sheet. Moreover, the lack of the second conductive fiber makes it impossible to form an efficient three-dimensional conductive network, resulting in a significant increase in the resistivity of the electrode sheet.

[0141] The adhesive provided in Comparative Example 3 uses an imide polymer without auxiliary polar groups, which reduces the adhesion to the foil. Moreover, the imide polymer lacking auxiliary polar groups cannot form hydrogen bond interactions within the adhesive, and cannot improve the mechanical strength of the thick coating electrode, thus reducing the flexibility.

[0142] The binder provided in Comparative Example 5 uses aluminum fibers with an average diameter of 30 nm, which results in poor flexibility of the prepared electrode plate and a significant decrease in the maximum coating surface density.

[0143] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A binder, characterized in that: The binder includes an imide polymer, a first conductive fiber, a second conductive fiber and conductive particles, wherein the first conductive fiber has a reactive group, and the reactive group chemically reacts with the imide polymer to form a chemical bond, the average diameter of the second conductive fiber is not less than 0.3 μm, the average length of the second conductive fiber is not less than 10 μm, the average diameter of the first conductive fiber is 5 to 50 nm, and the structure of the imide polymer includes an imide group and an auxiliary polar group, wherein the auxiliary polar group includes at least one of an amide group, an ester group, a urethane group, a urea group, a carbonate group, and a siloxy group.

2. The adhesive according to claim 1, characterized in that The binder comprises: 60-100 parts by mass of imide polymer; 1 to 10 parts by weight of first conductive fiber; 10 to 100 parts by mass of the second conductive fiber; 1 to 10 parts by mass of conductive particles.

3. The adhesive according to claim 1, characterized in that The weight average molecular weight of the imide polymer is greater than 200,000; and / or, the imide polymer is soluble in a polar solvent; and / or, the imide polymer includes at least one of polyamide-imide, polyester-imide, polyurethane-imide, polyurea-imide, polycarbonate-imide, polyurethane-amide-imide, and polysiloxane-imide; And / or, the chemical bond includes at least one of an amide bond, an imide bond, an ester bond, a urethane bond, an ether bond, and a carbon-carbon bond; And / or, the reactive group includes at least one of a carboxyl group, an amino group, and a hydroxyl group; And / or, the first conductive fiber is a functionalized carbon fiber, and the functionalized carbon fiber includes at least one of carboxylated graphite carbon fiber, amino graphite carbon fiber, hydroxylated graphite carbon fiber, carboxylated carbon nanotube fiber, amino carbon nanotube fiber, hydroxylated carbon nanotube fiber, carboxylated graphene fiber, amino graphene fiber, hydroxylated graphene fiber, carboxylated carbon cloth fiber, amino carbon cloth fiber, and hydroxylated carbon cloth fiber; and / or, the average length of the first conductive fibers is 0.2 to 20 μm; And / or, the conductive particles include at least one of conductive carbon particles, conductive polymer nanoparticles, and metal nanoparticles; And / or, the D50 particle size of the conductive particles is less than 2000 nm, and the specific surface area of ​​the conductive particles is 10 m 2 / g~10000m 2 / g.

4. The adhesive according to claim 1, characterized in that The second conductive fiber includes at least one of carbon fiber and metal fiber; And / or, the second conductive fibers have an average diameter of 0.3 to 30 μm and an average length of 10 to 1000 μm.

5. A method for preparing the adhesive according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, reacting an imide polymer precursor with the first conductive fiber to obtain a conductive composite of the imide polymer and the first conductive fiber; S2. Adding the conductive particles to the conductive composite and dispersing them evenly to obtain a dispersion of the composite and the conductive particles; S3. Add the second conductive fiber to the dispersion and disperse it evenly to obtain the binder.

6. The method for preparing the adhesive according to claim 5, wherein: The preparation method of the imide polymer precursor includes: reacting a diamine and a dibasic anhydride in a reaction solvent to obtain the imide polymer precursor, wherein the reaction solvent includes one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropionamide, and 1,4-dioxane, and the reaction time is 10 to 16 hours.

7. The method for preparing the adhesive according to claim 5, wherein: In step S1, the reaction temperature is 200-400°C; And / or, in step S1, the imide polymer precursor and the first conductive fiber are first dispersed and then reacted, wherein the dispersion includes first dispersing at 400-600 r / min for 5-20 min and then dispersing at 2000-4000 r / min for 20-50 min; And / or, in step S2, the dispersing comprises dispersing at 400-700 r / min for 5-20 min; And / or, in step S3, the dispersing comprises dispersing at 400-700 r / min for 5-20 min.

8. An electrode plate, comprising a current collector and an electrode membrane coated on the surface of the current collector, characterized in that: The electrode membrane contains the binder according to any one of claims 1 to 4 or the binder prepared by the method for preparing the binder according to any one of claims 5 to 7.

9. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that: The positive electrode sheet and / or the negative electrode sheet is the electrode sheet according to claim 8.

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