Modified binder and preparation method thereof, negative pole piece, battery and electric equipment

Abstract

The embodiment of the invention provides a modified binder and a preparation method thereof, a negative pole piece, a battery and electric equipment. Wherein the modified binder comprises a magnetic filler and a binder matrix. The modified binder can significantly improve the stripping force, reduce the possibility of material falling of a battery prepared from the modified binder, improve the overall conductivity of the material, optimize the electrochemical performance of the battery, make the adhesion force in the thickness direction of a pole piece uniformly distributed, improve the lithium ion diffusion rate, inhibit side reactions, and improve the battery performance. Therefore, the reaction between the electrolyte and the electrode interface is promoted.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a modified binder and a preparation method thereof, a negative electrode sheet, a battery, and an electrical device. Background Art

[0002] Lithium-ion batteries (LIBs) have been widely used in power batteries, consumer electronics, energy storage, and other fields due to their high energy density, long cycle life, and mature industrial manufacturability. As a critical component of the battery, the physical properties of the anode sheet after preparation directly affect the battery's performance.

[0003] The preparation of existing negative electrode sheets usually involves coating the negative electrode slurry on the negative electrode current collector. The negative electrode slurry mainly includes a binder, a thickener, an active material and a conductive agent. The binder can help other substances adhere closely to the negative electrode current collector to increase the conductive area. However, the binder is usually made of polymer materials, which are not conductive themselves. Adding too much will cause the conductivity to decrease. In addition, since the negative electrode sheet needs to be immersed in the electrolyte for a long time in the battery, if the addition amount is too low, the peeling force is low, which can easily lead to the problem of the binder floating, causing the negative electrode slurry to peel off from the negative electrode current collector and reduce the conductivity.

[0004] Therefore, the peeling force of existing adhesives does not meet the needs of users. Summary of the Invention

[0005] The embodiments of the present application provide a modified binder and a preparation method thereof, a negative electrode plate, a battery, and an electrical device to solve the problem that the peeling force of the existing binder does not meet the user's usage requirements.

[0006] In a first aspect, the present application provides a modified binder for use in a battery, the modified binder comprising:

[0007] A binder matrix containing a magnetic filler.

[0008] In a possible implementation manner, the mass ratio of the magnetic filler to the binder matrix is ​​1:(10-50).

[0009] In a possible implementation manner, the mass ratio of the magnetic filler to the binder matrix is ​​1:(10-40).

[0010] In one possible embodiment, the binder matrix includes one or more of styrene-butadiene rubber emulsion, carboxymethyl cellulose, and acrylic acid-modified styrene-butadiene rubber.

[0011] In a possible implementation, the magnetic filler includes one or more of ferroferric oxide, ferrite, and carbonyl iron powder.

[0012] In one possible embodiment, the magnetic filler includes magnetic filler nanoparticles, such as ferroferric oxide nanoparticles, ferrite nanoparticles, and carbonyl iron powder nanoparticles.

[0013] In a possible implementation, the modified binder further includes: a stabilizer, and / or a surfactant.

[0014] In one possible embodiment, the stabilizer includes one or more of sulfur, zinc oxide, and stearic acid.

[0015] In one possible embodiment, the surfactant includes one or more of γ-aminopropyltriethoxysilane, vinyltriethoxysilane, and vinyltrimethoxysilane.

[0016] In a second aspect, the present application provides a method for preparing a modified binder, comprising the following steps:

[0017] The magnetic filler solution is mixed with the binder to obtain a modified binder.

[0018] In a possible embodiment, before dispersing the magnetic filler into the first solvent, the method further includes: pre-treating the magnetic filler;

[0019] The pretreatment method comprises:

[0020] cleaning the magnetic filler;

[0021] mixing the cleaned magnetic filler, the surfactant, and the second solvent to obtain a first mixture;

[0022] The first mixture is separated into solid and liquid, and the solid is collected, washed and dried.

[0023] In a possible embodiment, before mixing the magnetic filler solution with the binder matrix, the preparation method further comprises:

[0024] A stabilizer is added to the magnetic filler solution and ultrasonic treatment is performed.

[0025] In a third aspect, the present application provides a negative electrode plate, comprising a negative electrode current collector, and a negative electrode active material layer present on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material and the above-mentioned modified binder or the modified binder prepared by the above-mentioned preparation method.

[0026] In one possible embodiment, the negative electrode active material includes one or more of natural graphite, artificial graphite, surface-modified natural graphite, soft carbon, hard carbon, and silicon-carbon composite materials.

[0027] In a possible embodiment, the negative electrode active material layer further includes a conductive agent, and the conductive agent includes one or more of acetylene black, Ketjen black, superconducting carbon black, carbon nanotubes, carbon fibers, and graphene.

[0028] In one possible implementation, the mass ratio of the negative electrode active material to the modified binder is 100:(2.5-3.75).

[0029] In a fourth aspect, the present application provides a battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises the above-mentioned negative electrode sheet.

[0030] In a fifth aspect, the present application provides an electrical device comprising the above-mentioned battery.

[0031] The modified binder and its preparation method, negative electrode plate, battery and electrical equipment provided by the present application modify the binder matrix by using magnetic fillers. Compared with the defects in the prior art, the modified binder prepared by the present application can significantly improve the peeling force and reduce the possibility of material shedding in the battery prepared with the modified binder. At the same time, it can also improve the conductive performance and utilize the good electronic conductivity of the magnetic filler itself to improve the overall conductivity of the material, thereby optimizing the electrochemical performance of the battery; and under the action of an external magnetic field, the pole piece is evenly distributed in the thickness direction, so that the bonding force is uniform; and the particle transport inside the electrode can be controlled by adjusting the orientation of graphite; and appropriate magnetic materials can affect the electric field distribution in the surrounding environment, which can increase the lithium ion diffusion rate, inhibit side reactions, etc., thereby promoting the reaction between the electrolyte and the electrode interface. DETAILED DESCRIPTION

[0032] To make the objectives, technical solutions, and advantages of the present invention more clear, 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 part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0033] Lithium-ion batteries are widely used in power batteries, consumer electronics, energy storage, and other fields. Existing negative electrode sheets are typically prepared by coating a negative electrode slurry onto a negative electrode current collector. The negative electrode slurry primarily consists of a binder, a thickener, an active material, and a conductive agent. The binder helps other materials adhere closely to the negative electrode current collector, thereby increasing the conductive surface area.

[0034] However, binders are usually made of polymer materials, such as styrene-butadiene rubber latex (SBR), which is not conductive in itself. Therefore, the amount added cannot be too high, otherwise the conductivity will be easily reduced. Also, since the negative electrode sheet needs to be immersed in the electrolyte for a long time in the battery, if the amount added is too low, it will easily lead to the problem of binder floating, causing the negative electrode slurry to peel off from the negative electrode current collector and reduce the conductivity.

[0035] The solution based on the prior art has the technical problem that the floating of the binder causes the peeling force and the decrease of electrical conductivity. The inventive concept of this application is that the binder will float with the solvent during the drying process of the negative electrode slurry, so that the bonding force between the negative electrode material and the current collector, and between the lower layer materials is reduced. However, after the binder is magnetically modified by magnetic fillers, sedimentation will occur under the action of the magnetic field. Under the action of the two phases, the modified binder is evenly distributed in the thickness direction of the pole piece, thereby enhancing the bonding force between the negative electrode main material and the current collector, and between the negative electrode materials. At the same time, the presence of the magnetic field can further adjust the orientation of the graphite, provide more lithium ion diffusion paths, enhance the rate performance and cycle life of the battery, and reduce the stress concentration caused by expansion during the lithiation / delithiation process, thereby improving the long-term stability and safety of the battery. It aims to solve the above technical problems of the prior art.

[0036] The following specific embodiments are used to describe in detail the technical solution of the present application and how the technical solution of the present application solves the above technical problems. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments.

[0037] First, a binder matrix containing magnetic fillers is prepared.

[0038] The binder matrix includes one or more of styrene-butadiene rubber emulsion, carboxymethyl cellulose, and acrylic acid-modified styrene-butadiene rubber.

[0039] This embodiment is described in detail by taking styrene-butadiene rubber emulsion as an example of the binder to be modified.

[0040] For example, a styrene-butadiene rubber latex containing a magnetic filler is prepared.

[0041] The magnetic filler includes one or more of ferroferric oxide, ferrite, and carbonyl iron powder.

[0042] Exemplarily, the ferrite may include cobalt ferrite, nickel zinc ferrite, nickel ferrite, manganese ferrite, and the like.

[0043] In a preferred embodiment, the magnetic filler is selected from magnetic nanoparticles having a higher specific surface area and better dispersibility, wherein the particle size of the magnetic nanoparticles is less than 100 nm, for example, magnetic nanoparticles such as ferroferric oxide nanoparticles, ferrite nanoparticles, and carbonyl iron powder nanoparticles.

[0044] The specific preparation method includes:

[0045] The magnetic filler solution is mixed with the styrene-butadiene rubber latex to obtain a modified binder.

[0046] The magnetic filler is dispersed in the first solvent to obtain a magnetic filler solution.

[0047] Exemplarily, the first solvent is water, and the magnetic filler is dispersed in the first solvent, for example, the magnetic filler is mixed with water to prepare an aqueous solution with a concentration of 1 wt %, and ultrasonic treatment is performed to prevent the magnetic filler from agglomerating.

[0048] The main function of water is to better disperse the magnetic filler, thereby facilitating the full mixing of the magnetic filler with the styrene-butadiene rubber emulsion.

[0049] In some embodiments, after preparing a magnetic filler solution with a concentration of 1 wt %, 0.01 wt % of a stabilizer, such as zinc oxide, may be added to the magnetic filler solution, and then ultrasonic treatment is performed to prevent the magnetic filler from agglomerating.

[0050] Wherein, the stabilizer includes one or more of sulfur, zinc oxide and stearic acid.

[0051] In some embodiments, the magnetic filler is magnetic nanoparticles, which can improve the mechanical strength and cycle stability of the electrode material and help reduce the problem of electrode material breakage caused by volume changes during the charge and discharge process.

[0052] For example, the magnetic filler solution is added to styrene-butadiene rubber latex with different mass fractions. For example, the magnetic filler solution is added to SBR at a mass ratio of 1: (10~50), and is fully mixed (for time > 24h) by heating (40-50°C) and ultrasonication to cause chemical cross-linking to obtain magnetic SBR.

[0053] This embodiment controls the mass ratio of the magnetic filler to the adhesive matrix to be 1:(10-50), thereby fully realizing the peeling force enhancement function of the magnetic filler while ensuring that the adhesive function of the modified adhesive is not affected, which is conducive to better application in the preparation of pole pieces.

[0054] Preferably, the mass ratio of the magnetic filler to the adhesive matrix is ​​adjusted to 1:(10-40), which can ensure that the peeling force is within a more appropriate range to meet the user's usage requirements.

[0055] Optionally, the magnetic filler may be surface pretreated before being dispersed in water, and the steps are as follows:

[0056] S21. Clean the magnetic filler.

[0057] Exemplarily, the magnetic filler, for example, ferrosoferric oxide, is ultrasonically cleaned using ethanol to ensure that the surface of the magnetic filler is clean and free of contamination.

[0058] S22, mixing the cleaned magnetic filler, surfactant, and second solvent to obtain a first mixture.

[0059] The second solvent may be a volatile organic solvent such as anhydrous ethanol, and the surfactant may include one or more of γ-aminopropyltriethoxysilane, vinyltriethoxysilane, and vinyltrimethoxysilane.

[0060] For example, a silane coupling agent is selected as the surfactant, and the silane coupling agent, for example, γ-aminopropyltriethoxysilane, is dissolved in anhydrous ethanol and the concentration is adjusted to 3%, thereby obtaining a silane coupling agent solution with a concentration of 3%.

[0061] 1 part by mass of the magnetic filler was dispersed into 5 parts by mass of a 3% silane coupling agent solution, and the mixture was stirred for 24 hours to allow the silane coupling agent to fully react with the functional groups on the surface of the magnetic filler.

[0062] S23, separating the first mixture into solid and liquid, collecting the solid, washing it, and drying it.

[0063] For example, the modified magnetic filler is separated from the solvent and washed with ethanol several times to remove unreacted silane coupling agent and other impurities, and then dried in a vacuum drying oven to constant weight to ensure that the filler is completely dry, thereby completing the surface activity pretreatment of the magnetic filler.

[0064] This embodiment also provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer present on at least one side of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, a conductive agent, and a binder;

[0065] The binder includes the modified binder or the modified binder prepared by the preparation method.

[0066] The method for preparing the negative electrode active material layer in the negative electrode sheet includes:

[0067] S31. Prepare negative electrode slurry.

[0068] The negative electrode slurry includes a binder, a conductive agent and a negative electrode active material.

[0069] In one possible embodiment, the negative electrode active material includes one or more of natural graphite, artificial graphite, surface-modified natural graphite, soft carbon, hard carbon, and silicon-carbon composite materials.

[0070] In a possible implementation, the conductive agent includes one or more of acetylene black, Ketjen black, superconducting carbon black, carbon nanotubes, carbon fibers, and graphene.

[0071] In a possible implementation, the binder includes the modified binder of the above embodiment, or a combination of the modified binder of the above embodiment and a non-modified binder.

[0072] For example, the mass ratio of the negative electrode active material to the modified binder is 100:(2.5-3.75).

[0073] This embodiment controls the ratio of the negative electrode active material and the modified binder, which is beneficial to adjusting the orientation of the graphite, affecting the electric field distribution in the surrounding environment, making the bonding force uniform, and improving the peeling force. At the same time, the magnetism of the modified binder can also be used to control the particle transport inside the electrode, thereby promoting the reaction between the electrolyte and the electrode interface and optimizing the electrochemical performance of the battery.

[0074] Among them, the non-modified binder can be selected from at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0075] In order to improve the performance of the binder, a mixture of carboxymethyl cellulose (CMC) and modified styrene-butadiene rubber latex can be used as the binder. While increasing the adhesion, it can also reduce the possibility of active substances falling into dust.

[0076] For example, a binder CMC is added to a deionized water solvent, stirred to obtain a uniformly dispersed binder slurry, and then a conductive agent, such as conductive carbon black, is added. The stirring speed is increased, and after uniform dispersion, the negative electrode active material is added twice. After high-speed stirring, the slurry viscosity is tested. The modified binder and N-methylpyrrolidone (NMP) are added, and after uniform dispersion, the mixture is stirred at a low speed for defoaming, and finally sieved through 200 mesh to obtain the negative electrode slurry.

[0077] S32, coating the negative electrode slurry on the negative electrode current collector.

[0078] Optionally, the material of the negative electrode current collector may be at least one of copper foil, nickel foam, and copper foam.

[0079] For example, copper foil is selected as the negative electrode current collector, and the negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet.

[0080] S33, rolling, drying and slitting.

[0081] The prepared negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium ion battery.

[0082] The present application provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises the negative electrode sheet prepared in the above embodiment.

[0083] The present invention is not strictly limited to the positive electrode active material in the positive electrode sheet, and can be any positive electrode active material commonly used in lithium-ion batteries, such as at least one composite oxide of lithium and a metal selected from the group consisting of cobalt, manganese, nickel, and combinations thereof. Specifically, it can be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate (LFP), lithium nickel manganese oxide, and lithium-rich manganese-based materials.

[0084] The present invention does not strictly limit the choice of electrolyte, and the electrolyte may include one or more solvents commonly used in lithium-ion battery electrolytes.

[0085] For example, the electrolyte lithium salts commonly used in lithium-ion electrolytes at present, the solvents may be ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, ethyl methyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; lithium salts may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0086] The present invention does not strictly limit the material selection of the diaphragm, and it can be a diaphragm material commonly used in lithium-ion batteries, such as polypropylene diaphragm (PP), polyethylene diaphragm (PE), polypropylene / polyethylene double-layer composite film (PP / PE), polyimide electrospun diaphragm (PI), polypropylene / polyethylene / polypropylene three-layer composite film (PP / PE / PP), cellulose non-woven fabric diaphragm, and one of the diaphragms with ceramic coating.

[0087] When preparing lithium-ion batteries, the positive electrode sheet, separator, and negative electrode sheet are wound or stacked to form a bare cell. The bare cell is then encapsulated in a pre-stamped aluminum-plastic film bag. After the encapsulated battery is dried at 85°C, the electrolyte is injected into the dried cell. The battery is then placed, formed, and sealed again to complete the lithium-ion battery production.

[0088] The battery of the present application can be a single cell, a battery pack, a battery pack or a cylindrical battery formed by connecting single cells, wherein these batteries can be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a mixture of these connection methods, etc., without special limitation.

[0089] The present application also provides an electrical device, including the battery prepared in the above embodiment. The electrical device of the present application can be conventional electrical devices in the art, such as power equipment (such as electric vehicles), electronic equipment (such as computers, mobile phones, digital cameras, printers, fax machines, etc.), wearable devices (such as watches, bracelets, VR glasses, etc.), household appliances (such as air conditioners, refrigerators, washing machines, microwave ovens, etc.), etc., without particular limitation.

[0090] The performance of the negative electrode sheet prepared in the embodiment of the present invention is further described in detail below using specific experiments as examples.

[0091] First, the magnetic filler and SBR were mixed in a mass ratio of 1:10, 1:30, 1:40, and 1:50, respectively, to obtain three magnetic SBRs with different ratios, which were marked as SBR-1, SBR-2, SBR-3, and SBR-4, respectively, and the one without magnetic filler was marked as SBR.

[0092] Then, negative electrode sheets with different negative electrode slurries were prepared using the mass fraction ratios shown in Table 1 below. The preparation method of the negative electrode sheets was as shown in the above-mentioned embodiment of the negative electrode sheets.

[0093] Table 1

[0094]

[0095] Specifically, the negative electrode sheet preparation methods of Examples 1-12 and Comparative Examples 1-3 of the control experiment are as follows:

[0096] Example 1

[0097] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR-1: CMC: H2O: NMP = 100:1:2.5:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0098] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0099] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0100] Example 2

[0101] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR-1: CMC: H2O: NMP = 100:1:3.375:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0102] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0103] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0104] Example 3

[0105] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR-1: CMC: H2O: NMP = 100:1:3.75:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0106] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0107] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0108] Example 4

[0109] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR-2: CMC: H2O: NMP = 100:1:2.5:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0110] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0111] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0112] Example 5

[0113] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR-2: CMC: H2O: NMP = 100:1:3.375:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0114] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0115] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0116] Example 6

[0117] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR-2: CMC: H2O: NMP = 100:1:3.75:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0118] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0119] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0120] Example 7

[0121] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR-3: CMC: H2O: NMP = 100:1:2.5:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0122] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0123] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0124] Example 8

[0125] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR-3: CMC: H2O: NMP = 100:1:3.375:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0126] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0127] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0128] Example 9

[0129] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR-3: CMC: H2O: NMP = 100:1:3.75:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0130] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0131] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0132] Example 10

[0133] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR-4: CMC: H2O: NMP = 100:1:2.5:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0134] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0135] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0136] Example 11

[0137] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR-4: CMC: H2O: NMP = 100:1:3.375:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0138] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0139] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0140] Example 12

[0141] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR-4: CMC: H2O: NMP = 100:1:3.75:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0142] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0143] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0144] Comparative Example 1

[0145] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR: CMC: H2O: NMP = 100:1:2.5:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed, and test the slurry viscosity; add the binder SBR and NMP, disperse them evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0146] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0147] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0148] Comparative Example 2

[0149] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR: CMC: H2O: NMP = 100:1:3.375:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed of stirring, and after uniform dispersion, add the negative electrode main material twice, stir at high speed to uniformly disperse, and test the slurry viscosity; add the binder SBR and NMP, disperse evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0150] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0151] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0152] Comparative Example 3

[0153] (1) The ratio of each component in the negative electrode slurry is graphite: carbon black: SBR: CMC: H2O: NMP = 100:1:3.75:1.6:110:3. The slurry preparation process is as follows: add the binder CMC to the deionized water solvent, stir to obtain a uniformly dispersed binder slurry, add the conductive agent, increase the speed and stir, and after uniform dispersion, add the negative electrode main material twice, stir at high speed and test the slurry viscosity; add the binder SBR and NMP, disperse them evenly, stir at low speed to defoam, and finally sieve through 200 mesh to obtain the negative electrode slurry;

[0154] (2) The negative electrode slurry is evenly coated on both sides of the copper foil at a speed of 2 m / min to obtain a negative electrode sheet;

[0155] (3) The negative electrode sheet is rolled, dried and cut to obtain the negative electrode sheet of the lithium-ion battery.

[0156] The negative electrode sheets produced from Examples 1-12 and Comparative Examples 1-3 were stacked.

[0157] The positive electrode slurry preparation process is as follows: the dispersant and binder are mixed and stirred to obtain a uniformly dispersed binder slurry. After adding the conductive agent, the stirring speed is increased. After uniform dispersion, the negative electrode main material is added in two batches. After high-speed stirring, the slurry viscosity is tested, and the slurry is stirred at a low speed to defoam. Finally, the slurry is sieved through 200 mesh to obtain the positive electrode slurry. The above slurry is coated on aluminum foil, baked, rolled, and cut to prepare the positive electrode sheets.

[0158] Among them, in the above-mentioned positive electrode slurry, the ratio of each component is lithium nickel cobalt manganese oxide (NCM): binder: dispersant: conductive agent = 100:1.1:8:2.

[0159] For example, the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polymers containing ethylene oxide, polyvinyl pyrrolidone, and polyurethane. The dispersant can be selected from one or more of polyacrylamide, polyacrylate, polyurethane, polyvinyl pyrrolidone, polyisobutylene succinimide, polyethylene oxide ether, hydroxyethyl cellulose, dodecyl polyethylene oxide ester, fatty acid polyethylene oxide ester, alkoxy polyalkylene oxide acrylate, polycaprolactone, polystyrene-vinyl pyrrolidone, and polystyrene-N,N-divinyl acrylamide. The conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber.

[0160] The positive electrode sheets and the corresponding negative electrode sheets of Examples 1-12 and Comparative Examples 1-3 were stacked to form a soft-pack battery. 4.8 g of electrolyte was injected, and the battery design capacity was 1.9 Ah.

[0161] The electrode layer test and the battery layer test were performed on Examples 1-12 and Comparative Examples 1-3, respectively, and a record was made of whether the negative electrode sheet fell off when the battery was disassembled after the test.

[0162] Among them, the methods of pole-level testing include:

[0163] The peeling force and electrical conductivity of the negative electrode sheets of Examples 1-12 and Comparative Examples 1-3 were tested, wherein the peeling force test was conducted in accordance with the standard GB / T 2792-2014 "Test method for peel strength of adhesive tapes".

[0164] Battery level testing methods include:

[0165] First effect test:

[0166] The soft-pack battery was subjected to a 0.33C constant current charge and discharge test at room temperature for three cycles to complete the capacity calibration of the soft-pack battery. The battery's initial charge and discharge efficiency was calculated based on the capacity of the first cycle test. The capacity when the battery was charged to 4.35V was recorded as the charge capacity, and the capacity when discharged to 2.5V at a 0.33C constant current was recorded as the battery's initial discharge capacity.

[0167] Calculate the first charge efficiency (%) = discharge capacity / charge capacity × 100%.

[0168] DCIR test:

[0169] At room temperature, charge at a constant current of 0.33C to 4.35V, hold for 30 minutes, discharge at a constant current of 0.33C for 90 minutes to adjust the charge to 50% SOC, hold for 2 hours, discharge at a constant current of 1.5C for 30 seconds, and record the shelf termination voltage E1 and the constant current discharge termination voltage E2.

[0170] Calculate DCIR (mΩ) = (E1-E2) / 1.5.

[0171] Rate discharge test:

[0172] At room temperature, charge the battery at a constant current and constant voltage of 0.33C to 4.35V, with a cutoff current of 0.05C. Wait for 10 minutes, discharge the battery at a constant current of 0.33C to 2.5V, and record the discharge capacity C0. Then charge the battery at a constant current and constant voltage of 0.33C to 4.35V, with a cutoff current of 0.05C. Wait for 10 minutes, discharge the battery at a constant current of 3C to 2.5V, and record the discharge capacity C1.

[0173] Rate discharge efficiency (%) = C1 / C0×100%=discharge capacity at 3C rate / discharge capacity at 0.33C×100%.

[0174] Cycle life test:

[0175] The battery was charged to 4.35V at 0.5C and discharged to 2.5V at 1C. After 1000 charge and discharge cycles, the discharge capacity at the first and 1000th cycles was recorded to calculate the cycle life.

[0176] Capacity retention (SOH, %) = discharge capacity after 1000 cycles / initial discharge capacity × 100%.

[0177] The above test results are summarized to obtain the following Table 2.

[0178] Table 2

[0179]

[0180] In order to improve the representativeness of the test results, another set of parallel examples was performed, and the following Table 3 was obtained.

[0181] Table 3

[0182]

[0183] Based on the above test results, it can be seen that the peeling force, conductivity, first efficiency and discharge capacity of Examples 1-12 are improved compared with those of Comparative Examples 1-3, indicating that the added magnetic filler is beneficial to the negative electrode plate.

[0184] Among them, based on Examples 1, 4, 7, and 10, it can be seen that as the amount of magnetic filler added decreases, the peeling force also gradually decreases, indicating that when the mass ratio of the magnetic filler to the adhesive matrix is ​​1: (10~50), it can meet the user's requirements for better peeling force and electrical performance.

[0185] Furthermore, by comparing Examples 1-9 with Examples 10-12, when the mass ratio of the magnetic filler to the binder matrix is ​​1:(10-40), the peeling force is better.

[0186] Based on Examples 1-3, Examples 4-6, Examples 7-9 and Examples 10-12, it can be seen that when the mass ratio of the negative electrode active material to the modified binder is 100:(2.5~3.75), the prepared negative electrode sheet has good electrical properties.

[0187] In summary, the modified binder of the present application can significantly improve the peeling force, reduce the possibility of material shedding in the battery prepared with the modified binder, and at the same time improve the electrical conductivity. The magnetic filler itself has good electronic conductivity. Adding it to SBR can improve the overall electrical conductivity of the material, thereby optimizing the electrochemical performance of the battery; the magnetic SBR material is evenly distributed in the thickness direction of the pole piece under the action of an external magnetic field, so that the bonding force is uniform; and the particle transport inside the electrode can be controlled by adjusting the orientation of the graphite; and appropriate magnetic materials can affect the electric field distribution in the surrounding environment, which can increase the lithium ion diffusion rate, inhibit side reactions, etc., thereby promoting the reaction between the electrolyte and the electrode interface.

[0188] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified binder, characterized in that: Applied to batteries, the modified binder includes: Magnetic filler and binder matrix.

2. The modified binder according to claim 1, characterized in that The mass ratio of the magnetic filler to the binder matrix is ​​1:(10-50).

3. The modified binder according to claim 2, characterized in that The mass ratio of the magnetic filler to the binder matrix is ​​1:(10-40).

4. The modified binder according to claim 1, characterized in that The binder matrix includes one or more of styrene-butadiene rubber emulsion, carboxymethyl cellulose, and acrylic acid-modified styrene-butadiene rubber.

5. The modified binder according to any one of claims 1 to 4, characterized in that: The magnetic filler includes one or more of ferroferric oxide, ferrite, and carbonyl iron powder.

6. The modified binder according to any one of claims 1 to 3, characterized in that: The modified binder further comprises: a stabilizer, and / or a surfactant.

7. The modified binder according to claim 6, characterized in that The stabilizer includes one or more of sulfur, zinc oxide, and stearic acid.

8. The modified binder according to claim 6, characterized in that The surfactant includes one or more of γ-aminopropyltriethoxysilane, vinyltriethoxysilane, and vinyltrimethoxysilane.

9. A method for preparing the modified binder according to any one of claims 1 to 8, characterized in that: The following steps are involved: The magnetic filler solution is mixed with the binder matrix to obtain a modified binder.

10. The method for preparing the modified binder according to claim 9, wherein: The method further comprises: pre-treating the magnetic filler; The pretreatment method comprises: cleaning the magnetic filler; mixing the cleaned magnetic filler, surfactant and ethanol to obtain a first mixture; The first mixture is separated into solid and liquid, and the solid is collected, washed and dried.

11. The method for preparing the modified binder according to claim 9 or 10, characterized in that: Before mixing the magnetic filler solution with the binder matrix, the preparation method further comprises: A stabilizer is added to the magnetic filler solution and ultrasonic treatment is performed.

12. A negative electrode plate, characterized in that: The invention comprises a negative electrode current collector and a negative electrode active material layer present on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material and the modified binder according to any one of claims 1 to 8 or the modified binder prepared by the preparation method according to any one of claims 9 to 11.

13. The negative electrode sheet according to claim 12, characterized in that: The mass ratio of the negative electrode active material to the modified binder is 100:(2.5-3.75).

14. A battery, characterized in that: Including the negative electrode sheet according to claim 12 or 13.

15. An electrical device, characterized in that: Including the battery according to claim 14.

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