Negative electrode dispersant and preparation method thereof, secondary battery and electronic device

Abstract

The invention provides a negative electrode dispersant and a preparation method thereof, a secondary battery and an electronic device, the negative electrode dispersant comprises a polymer, deionized water is used as a solvent, and monomers forming the polymer comprise a hydrophobic monomer, a hydrophilic monomer and a functional monomer; wherein the hydrophobic monomer comprises a C4 to C21 long carbon chain monomer, the hydrophilic monomer comprises an acrylic acid monomer, and the functional monomer comprises at least one of acrylonitrile or acrylamide; the negative dispersant has a zeta potential of-45 mV to-60 mV at 25 DEG C and a solid content of 2 wt% to 10 wt%, and the zeta potential of the negative dispersant is-45 mV to-60 mV. Through the arrangement, the negative electrode dispersing agent has relatively high viscosity and good dispersity. When the composite material is applied to negative electrode slurry, the negative electrode slurry has good dispersity and stability.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a negative electrode dispersant and a preparation method thereof, a negative electrode plate, a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, offer high specific energy, high operating voltage, low self-discharge, compact size, and light weight, making them widely used in portable consumer electronics. With the rapid development of electric vehicles and mobile electronic devices in recent years, the performance requirements of lithium-ion batteries are becoming increasingly demanding.

[0003] The performance of electrode assemblies in the current battery industry depends largely on the manufacturing process, and a particularly critical part of this process is the mixing process. Existing negative electrode active materials are generally graphite or silicon, which are insoluble or dispersible in water and easily settle. They require the use of a dispersant for good dispersion and a thickener for thickening to effectively utilize the various properties of the active material during the subsequent charge and discharge processes. Therefore, there is an urgent need to develop dispersants with good dispersibility and high viscosity. Summary of the Invention

[0004] The purpose of the present application is to provide a negative electrode dispersant and a preparation method thereof, a secondary battery and an electronic device, so as to improve the dispersibility and stability of the negative electrode slurry during the preparation process of the secondary battery.

[0005] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides a negative electrode dispersant, comprising a polymer, using deionized water as a solvent, wherein monomers forming the polymer include a hydrophobic monomer, a hydrophilic monomer, and a functional monomer; wherein the hydrophobic monomer includes a long carbon chain monomer of C4 to C21, the hydrophilic monomer includes an acrylic monomer, and the functional monomer includes at least one of acrylonitrile or acrylamide. The negative electrode dispersant has a zeta potential (ZP, i.e., zeta potential) of -45 mV to -60 mV at 25°C and a solid content of 2 wt% to 10 wt%. By adding a hydrophobic segment, i.e., a long carbon chain monomer, to the negative electrode dispersant, and regulating the Zeta potential within the scope of the present application, the long carbon chain molecule opens the molecular segment of the hydrophilic monomer by alkali neutralization to form a hydrophobic association effect, which forms a physical cross-linked network through the interaction of intermolecular hydrophobic groups, thereby increasing the fluid mechanics volume of the solution, thereby increasing the solution viscosity, and due to the introduction of the long carbon chain monomer, the hydrophobic monomer and the hydrophilic monomer form another form of hydrogen bond, thereby increasing the viscosity, and at the same time, weakening the intramolecular and / or intermolecular hydrogen bonding of the hydrophilic monomer, and increasing the surface free negative charge, resulting in an increase in Zeta potential, a higher Zeta potential, and thus the dispersibility of the negative electrode dispersant is enhanced. Thus, the negative electrode dispersant of the present application has higher viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0007] In some embodiments of the present application, the molecular formula of the polymer is (C N1 H N2 O N3 ) n1 (C3H3N) n2 (RC3H3O2) n3 (C3H5NO) n4 , R is selected from a hydrogen atom, a methyl group, or an ethyl group, N1 is selected from a natural number within the range of 4 to 21, N2 is selected from a natural number within the range of 1 to 42, N3 is selected from a natural number within the range of 0 to 10, n1 is selected from a natural number within the range of 3000 to 20000, n3 is selected from a natural number within the range of 800 to 5000, n2 and n4 are each independently selected from a natural number within the range of 0 to 5000, and n2 and n4 are not both 0. By regulating the molecular formula of the polymer within the above range, the viscosity and dispersibility of the negative electrode dispersant are improved, and when applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0008] In some embodiments of the present application, the C4 to C21 long carbon chain monomer includes at least one of ethers, esters, or hydrocarbons containing an unsaturated double bond; and / or the acrylic monomer includes at least one of methacrylic acid, ethacrylic acid, or acrylic acid. By selecting the aforementioned hydrophobic monomers and / or hydrophilic monomers, the hydrophobic monomers and the hydrophilic monomers act synergistically, further enhancing the dispersibility and viscosity of the negative electrode dispersant. As a result, the negative electrode dispersant of the present application has high viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0009] In some embodiments of the present application, based on the mass of the hydrophobic monomer, the mass percentage of carbon in the hydrophobic monomer is m, where m is ≥ 75%, and the hydrophobic monomer includes at least one of an ether or a hydrocarbon containing an unsaturated double bond. When the carbon content of the hydrophobic monomer is 75% or greater, the negative electrode dispersant, when used with the above-mentioned hydrophobic monomer, has better dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has better dispersibility while maintaining stability.

[0010] In some embodiments of the present application, based on the mass of the polymer in the negative electrode dispersant, the mass percentage of the hydrophilic monomer unit in the repeating unit of the polymer is x, the mass percentage of the hydrophobic monomer unit in the repeating unit of the polymer is y, and the mass percentage of the functional monomer in the repeating unit of the polymer is z, 10%≤x≤50%, 20%≤y≤60%, and 20%≤z≤60%. By regulating the values of x, y, and z within the above ranges, the hydrophilic monomer, hydrophobic monomer, and functional monomer achieve a synergistic effect between viscosity, dispersibility, and stability, thereby improving the viscosity and dispersibility of the negative electrode dispersant. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0011] In some embodiments of the present application, 0.2≤x / y≤2.5. By regulating the value of x / y within the above range, it is helpful to regulate the molecular weight of the polymer within an appropriate range. When applied to the negative electrode slurry, the negative electrode slurry has better stability while taking into account the dispersibility.

[0012] In some embodiments of the present application, the negative electrode dispersant satisfies at least one of the following characteristics: (1) the pH of the negative electrode dispersant is 6.0 to 8.0; (2) the weight average molecular weight of the polymer is Mw g / mol, 3×10 5 ≤Mw≤1.5×10 6; (3) The viscosity of the negative electrode dispersant at 25°C and 12 rpm is ηmPa·s, 30000≤η≤100000; (4) The elastic modulus of the polymer film is E GPa, 5≤E≤20; (5) The swelling degree of the polymer in the electrolyte is c, 1%≤c≤10%. Through the above settings, the negative electrode dispersant has high viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability. When using the negative electrode slurry including the negative electrode dispersant of the present application to prepare the negative electrode sheet, it is beneficial to uniformly coat the negative electrode slurry on the negative electrode current collector, reduce polarization during the charge and discharge process of the secondary battery, and improve the cycle life of the secondary battery.

[0013] In some embodiments of the present application, a negative electrode dispersant is mixed with a negative electrode active material to obtain a first slurry with a solid content of 40 wt % to 50 wt %, the mass ratio of the polymer to the negative electrode active material in the first slurry is 1.5:98.5, the first slurry is allowed to stand for 5 to 14 days to obtain a second slurry, and the area from the surface of the second slurry to 1 / 4 of the total depth of the second slurry along the direction from the surface to the bottom of the second slurry is the upper slurry, and the area from 3 / 4 of the total depth of the second slurry to the bottom of the second slurry is the lower slurry, satisfying at least one of the following characteristics: (1) the difference in the electromotive potential between the upper slurry and the lower slurry is ≤±0.5 mV; (2) the difference in Dv50 between the particles of the upper slurry and the particles of the lower slurry is ≤0.5 μm. The above configuration demonstrates that the negative electrode dispersant, when applied to the first slurry, reduces the risk of sedimentation of the first slurry, and the negative electrode active particles are more evenly distributed in the slurry. The negative electrode dispersant of the present application has high viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0014] A second aspect of the present application provides a method for preparing a negative electrode dispersant, comprising the following steps:

[0015] (1) taking 900 to 4900 parts of deionized water as a solvent, adding a chain transfer agent and an initiator to the solvent to obtain a mixture; wherein the chain transfer agent includes at least one of n-dodecyl mercaptan, secondary dodecyl mercaptan, tert-dodecyl mercaptan, mercaptoethanol or thioglycolic acid, and the amount of the chain transfer agent added is 0.2 to 0.8 parts; the initiator includes at least one of potassium persulfate, sodium persulfate, ammonium persulfate, azobisisobutyronitrile or azobisisoheptonitrile, and the amount of the initiator added is 0.5 to 1 parts;

[0016] (2) adding a hydrophobic monomer, a hydrophilic monomer, and a functional monomer to the mixture, wherein the mass fraction of the hydrophilic monomer is 10 to 50 parts, the mass fraction of the hydrophobic monomer is 20 to 60 parts, the mass fraction of the functional monomer is 20 to 60 parts, and the mass fraction of the hydrophobic monomer, the hydrophilic monomer, and the functional monomer is 100 parts; continuing to heat to 60° C. to 80° C., and keeping the temperature for 2 to 10 hours; then performing reduced pressure distillation for 4 to 8 hours to obtain a polymer solution;

[0017] (3) adding a base to the polymer solution, wherein the base includes at least one of lithium hydroxide, sodium hydroxide, or potassium hydroxide, and the mass ratio of the base to the non-volatile solid in the polymer solution is a, 1 / 8≤a≤1 / 4, and mixing to obtain a negative electrode dispersant.

[0018] The negative electrode dispersant is prepared using the method provided in the second aspect of the present application, and the various parameters are controlled within the above ranges. The resulting negative electrode dispersant has high viscosity and good dispersibility. When applied to a negative electrode slurry, the negative electrode slurry has good dispersibility and stability. When a negative electrode sheet is prepared using a negative electrode slurry including the negative electrode dispersant of the present application, it is beneficial to uniformly coat the negative electrode slurry on the negative electrode current collector, reduce polarization during the charge and discharge process of the secondary battery, and improve the cycle life of the secondary battery.

[0019] The third aspect of the present application provides a secondary battery, which includes a positive electrode plate, a separator, an electrolyte, and a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, the negative electrode material layer includes a polymer, the monomers forming the polymer include a hydrophobic monomer, a hydrophilic monomer, and a functional monomer, the hydrophobic monomer includes a long carbon chain monomer from C4 to C21, the hydrophilic monomer includes an acrylic monomer, and the functional monomer includes at least one of acrylonitrile or acrylamide; or, a negative electrode dispersant prepared according to the preparation method provided in the second aspect of the present application. Through the above-mentioned arrangement, when preparing the negative electrode plate in the secondary battery, it is beneficial to uniformly coat the negative electrode slurry on the negative electrode current collector, reduce polarization during the charge and discharge process of the secondary battery, and improve the cycle life of the secondary battery, so that the secondary battery has good cycle performance.

[0020] In some embodiments of the present application, the molecular formula of the polymer in the secondary battery is (C N1 H N2 O N3 ) n1 (C3H3N) n2 (RC3H3O2) n3 (C3H5NO) n4, R is selected from a hydrogen atom, a methyl group, or an ethyl group, N1 is selected from a natural number within the range of 4 to 21, N2 is selected from a natural number within the range of 1 to 42, N3 is selected from a natural number within the range of 0 to 10, n1 is selected from a natural number within the range of 3,000 to 20,000, n3 is selected from a natural number within the range of 800 to 5,000, n2 and n4 are each independently selected from a natural number within the range of 0 to 5,000, and n2 and n4 are not both 0. When the molecular formula of the polymer in the secondary battery falls within the above range, it facilitates uniform coating of the negative electrode slurry on the negative electrode current collector during the preparation of the negative electrode sheet for the secondary battery, reduces polarization during the charge and discharge process of the secondary battery, and improves the cycle life of the secondary battery, resulting in the secondary battery having good cycle performance.

[0021] A fourth aspect of the present application provides an electronic device, which includes the secondary battery according to any one of the aforementioned embodiments. Therefore, the electronic device of the present application has good performance.

[0022] Beneficial effects of this application:

[0023] The present application provides a negative electrode dispersant and a preparation method thereof, a secondary battery and an electronic device. The negative electrode dispersant includes a polymer, deionized water is used as a solvent, and monomers forming the polymer include a hydrophobic monomer, a hydrophilic monomer and a functional monomer; wherein the hydrophobic monomer includes a long carbon chain monomer of C4 to C21, the hydrophilic monomer includes an acrylic monomer, and the functional monomer includes at least one of acrylonitrile or acrylamide; the negative electrode dispersant has an zeta potential of -45 mV to -60 mV at 25°C and a solid content of 2 wt% to 10 wt%. Through the above-mentioned setting, the long carbon chain molecules open the molecular segments of the hydrophilic monomers by alkali neutralization to form a hydrophobic association effect, which forms a physical cross-linking network through the interaction of the intermolecular hydrophobic groups, increases the volume of the solution's fluid mechanics, thereby increasing the solution viscosity, and due to the introduction of the long carbon chain monomers, the hydrophobic monomers and the hydrophilic monomers form another form of hydrogen bond, thereby increasing the viscosity, while weakening the intramolecular and / or intermolecular hydrogen bonding of the hydrophilic monomers, increasing the surface free negative charge, resulting in an increase in the Zeta potential, a higher Zeta potential, and thus enhancing the dispersibility of the negative electrode dispersant. Thus, the negative electrode dispersant of the present application has a higher viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability. When using the negative electrode slurry including the negative electrode dispersant of the present application to prepare the negative electrode sheet, it is beneficial to uniformly coat the negative electrode slurry on the negative electrode current collector, reduce polarization during the charge and discharge process of the secondary battery, and improve the cycle life of the secondary battery.

[0024] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in this application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0026] It should be noted that, in the specific embodiments of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries.

[0027] The manufacturing level of the previous process has a great influence on the performance of the electrode assembly, and in the process of preparing the pole piece, the stirring process is more important. The negative electrode active materials in the prior art, such as graphite materials or silicon materials, cannot be dissolved or dispersed in solvent water and are easy to settle, resulting in the particles of the negative electrode active material being easy to agglomerate. When the slurry is coated, it cannot be evenly distributed, which in turn affects the cycle performance of the secondary battery. Therefore, it is necessary to add a dispersant and a thickener to the negative electrode slurry to improve the uniformity of the slurry. In the prior art, sodium carboxymethyl cellulose (CMC) is generally used as a dispersant or thickener, but the dispersibility and viscosity are low when applied to the negative electrode slurry, and the improvement of the cycle performance of the secondary battery is limited. Based on this, the present application provides a negative electrode dispersant and a preparation method thereof, a secondary battery and an electronic device. The negative electrode dispersant has good dispersibility and high viscosity. When applied to the secondary battery, it is beneficial to improve the dispersibility and stability of the negative electrode slurry during the preparation of the secondary battery, thereby making the active material of the corresponding pole piece and other materials in the material layer more evenly distributed. The uniformity of each position of the material layer during the cycle is beneficial to reduce electrochemical polarization and improve the cycle life of the secondary battery. The specific technical solutions are as follows:

[0028] The first aspect of the present application provides a negative electrode dispersant, the negative electrode dispersant includes a polymer, deionized water is used as a solvent, and the monomers forming the polymer include a hydrophobic monomer, a hydrophilic monomer and a functional monomer; wherein the hydrophobic monomer includes a long carbon chain monomer of C4 to C21, preferably, the hydrophobic monomer includes a long carbon chain monomer of C7 to C15, for example, the carbon chain length of the long carbon chain monomer can be C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C20, C21 or a range consisting of any two values therein; the hydrophilic monomer includes an acrylic monomer, and the functional monomer includes at least one of acrylonitrile or acrylamide. The negative electrode dispersant has an electrokinetic potential (ZP, i.e., Zeta potential) of -45mV to -60mV at 25°C and a solid content of 2wt% to 10wt%. For example, the solid content can be 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt% or a range consisting of any two of the values; the ZP value can be -45, -46, -47, -48, -49, -50, -51, -52, -53, -54, -55, -56, -57, -58, -59, -60 or a range consisting of any two of the values.

[0029] The inventors have found that by adding a hydrophobic segment, i.e., a long carbon chain monomer, to the negative electrode dispersant and regulating the Zeta potential within the scope of this application, the long carbon chain molecule opens the molecular segment of the hydrophilic monomer, i.e., the acrylic acid (PAA) monomer, through alkali neutralization to form a hydrophobic association effect. This effect forms a physical cross-linked network through the interaction of the intermolecular hydrophobic groups, thereby increasing the hydrodynamic volume of the solution and thus increasing the solution viscosity; the use of functional monomers in combination with hydrophilic monomers is conducive to the formation of more hydrogen bonds, further increasing the viscosity of the dispersant; in addition, the acrylic acid monomer contains a functionalized carboxylic acid group and has good water solubility, which is conducive to improving the hydrophilicity of the polymer and is conducive to the formation of a uniform dispersion of the polymer in the aqueous system, thereby improving the uniformity and dispersibility of the negative electrode slurry; and due to the introduction of the long carbon chain monomer, the hydrophobic monomer and the hydrophilic monomer form another form of hydrogen bond, thereby increasing the viscosity. At the same time, the intramolecular and / or intermolecular hydrogen bonding of the hydrophilic monomer is weakened, the surface free negative charge increases, resulting in an increase in the Zeta potential, a higher Zeta potential, and thus the dispersibility of the negative electrode dispersant is enhanced. Therefore, the hydrophobic monomer, hydrophilic monomer and functional monomer in the polymer work synergistically, and the negative electrode dispersant of the present application has high viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability. When using the negative electrode slurry including the negative electrode dispersant of the present application to prepare the negative electrode sheet, it is beneficial to the uniform coating of the negative electrode slurry on the negative electrode current collector, so that the active material of the corresponding electrode sheet and other materials in the material layer are more evenly distributed. The uniformity of each position of the material layer during the cycle is beneficial to reduce the electrochemical polarization and improve the cycle life of the secondary battery. In the present application, it can be understood that the polymer is prepared by polymerization of hydrophobic monomers, hydrophilic monomers and functional monomers.

[0030] In some embodiments of the present application, the molecular formula of the polymer is (C N1 H N2 O N3 ) n1 (C3H3N) n2 (RC3H3O2) n3 (C3H5NO) n4, R is selected from a hydrogen atom, a methyl group or an ethyl group, N1 is selected from a natural number within the range of 4 to 21, N2 is selected from a natural number within the range of 1 to 42, N3 is selected from a natural number within the range of 0 to 10, n1 is selected from a natural number within the range of 3000 to 20000, n3 is selected from a natural number within the range of 800 to 5000, n2 and n4 are each independently selected from a natural number within the range of 0 to 5000, and n2 and n4 are not 0 at the same time. For example, the value of N1 can be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, or a range consisting of any two of them; the value of N2 can be 1, 3, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, or a range consisting of any two of them; the value of N3 can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 , 10 or a range consisting of any two of them; the value of n1 can be 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000 or a range consisting of any two of them; the value of n3 can be 800, 1000, 1200, 1500, 180 0, 2000, 2200, 2500, 2800, 3000, 3200, 3500, 3800, 4000, 4200, 4500, 4800, 5000 or a range consisting of any two of these values; the value of n2 can be 0, 1, 50, 100, 300, 500, 800, 1000, 1200, 1500, 1800, 2000, 2200, 2500, 2800, 3000, 3200, 3500, 3800 , 4000, 4200, 4500, 4800, 5000 or a range consisting of any two of the values; the value of n4 can be 0, 1, 50, 100, 300, 500, 800, 1000, 1200, 1500, 1800, 2000, 2200, 2500, 2800, 3000, 3200, 3500, 3800, 4000, 4200, 4500, 4800, 5000 or a range consisting of any two of the values.By regulating the molecular formula of the polymer within the above range, the long carbon chain monomer opens the molecular chain segment of the hydrophilic monomer, i.e., the acrylic monomer, through alkali neutralization to form a hydrophobic association, which can form a physical cross-linking network through the interaction of the hydrophobic groups between molecules, thereby increasing the hydrodynamic volume of the solution and thus increasing the solution viscosity. In addition, due to the introduction of the long carbon chain monomer, the hydrophobic monomer and the hydrophilic monomer form another form of hydrogen bond, thereby increasing the viscosity. At the same time, the hydrophilic monomer is weakened, so that the intramolecular and / or intermolecular hydrogen bonding of the hydrophilic monomer is weakened, and the free negative charge on the surface increases, resulting in an increase in the Zeta potential. The Zeta potential is high, and the dispersibility of the negative electrode dispersant is enhanced. Thus, the viscosity and dispersibility of the negative electrode dispersant are improved, and when it is applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0031] In some embodiments of the present application, the structural formula of the structural unit of the polymer is as shown in Formula I:

[0032]

[0033] Wherein, X is selected from a long carbon chain monomer of C4 to C21, preferably, X is selected from a long carbon chain monomer of C7 to C15. By selecting the polymer of the above structure, the long carbon chain monomer opens the molecular chain segment of the hydrophilic monomer, i.e., the acrylic monomer, by alkali neutralization to form a hydrophobic association, which can form a physical cross-linked network through the interaction of the intermolecular hydrophobic groups, thereby increasing the hydrodynamic volume of the solution and thus increasing the solution viscosity. In addition, due to the introduction of the long carbon chain monomer, the hydrophobic monomer and the hydrophilic monomer form another form of hydrogen bond, thereby increasing the viscosity. At the same time, the hydrophilic monomer is weakened, so that the hydrophilic monomer intramolecular and / or intermolecular hydrogen bonding effect increases the surface free negative charge, resulting in an increase in the Zeta potential, a higher Zeta potential, and thus the dispersibility of the negative electrode dispersant is enhanced. Thus, the viscosity and dispersibility of the negative electrode dispersant are improved, and it is applied to the negative electrode slurry, and the negative electrode slurry has good dispersibility and stability. It is understood that the number of monomers in the polymer meets the limitations of n1, n3, and n4 in the molecular formula, but the actual connection of the monomer units may be disordered. The structural formula in this application is drawn for schematic purposes.

[0034] In some embodiments of the present application, the structural formula of the structural unit of the polymer is as shown in Formula II:

[0035]

[0036] Wherein, X is selected from a long carbon chain monomer of C4 to C21, preferably, X is selected from a long carbon chain monomer of C7 to C15. By selecting the polymer of the above structure, the long carbon chain monomer opens the molecular chain segment of the hydrophilic monomer, i.e., the acrylic monomer, through alkali neutralization, forming a hydrophobic association. A physical cross-linked network can be formed through the interaction of the hydrophobic groups between the molecules, thereby increasing the hydrodynamic volume of the solution and thus increasing the solution viscosity. In addition, due to the introduction of the long carbon chain monomer, the hydrophobic monomer and the hydrophilic monomer form another form of hydrogen bond, thereby increasing the viscosity. At the same time, the hydrophilic monomer is weakened, resulting in the intramolecular and / or intermolecular hydrogen bonding of the hydrophilic monomer, increasing the free negative charge on the surface, resulting in an increase in the Zeta potential. The Zeta potential is high, and the dispersibility of the negative electrode dispersant is enhanced. Thus, the viscosity and dispersibility of the negative electrode dispersant are improved, and when applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability. It is understood that the number of monomers in the polymer meets the limitations of n1, n2, and n3 in the molecular formula, but the actual connection of the monomer units may be disordered. The structural formula in this application is drawn for schematic purposes.

[0037] In some embodiments of the present application, the long carbon chain monomers of C4 to C21 include at least one of ethers, esters or hydrocarbons containing unsaturated double bonds. By selecting the above-mentioned types of hydrophobic monomers, the long carbon chain monomers open the molecular segments of the hydrophilic monomers, i.e., acrylic acid (PAA) monomers, through alkali neutralization to form a hydrophobic association effect. This effect forms a physical cross-linked network through the interaction of intermolecular hydrophobic groups, thereby increasing the fluid dynamics volume of the solution, thereby further increasing the solution viscosity. In addition, due to the introduction of long carbon chain monomers, the hydrophobic monomers and the hydrophilic monomers form another form of hydrogen bond, thereby increasing the viscosity. At the same time, the hydrophilic monomers are weakened to allow intramolecular and / or intermolecular hydrogen bonding, and the surface free negative charge increases, resulting in an increase in Zeta potential. The Zeta potential is higher, and the dispersibility of the negative electrode dispersant is further enhanced. Therefore, the negative electrode dispersant of the present application has higher viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0038] In some embodiments of the present application, the acrylic monomer includes at least one of methacrylic acid, ethacrylic acid or acrylic acid. By selecting the above-mentioned types of hydrophilic monomers, the acrylic monomer contains a functionalized carboxylic acid group and has good water solubility, which is beneficial to improving the hydrophilicity of the polymer and is beneficial for the polymer to form a uniform dispersion in the aqueous system, thereby improving the uniformity and dispersibility of the negative electrode slurry. At the same time, it synergizes with the hydrophobic monomer in the polymer to form a physical cross-linked network through the interaction of intermolecular hydrophobic groups, thereby increasing the hydrodynamic volume of the solution and thus increasing the solution viscosity. Therefore, the negative electrode dispersant of the present application has high viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0039] In some embodiments of the present application, the C4 to C21 long carbon chain monomer includes at least one of ethers, esters or hydrocarbons containing unsaturated double bonds; and the acrylic monomer includes at least one of methacrylic acid, ethacrylic acid or acrylic acid. By selecting the above-mentioned types of hydrophobic monomers and hydrophilic monomers, the hydrophobic monomers and the hydrophilic monomers work synergistically, and the long carbon chain monomers open the molecular segments of the hydrophilic monomers, i.e., acrylic acid (PAA) monomers, by alkali neutralization to form hydrophobic association. This effect forms a physical cross-linked network through the interaction of intermolecular hydrophobic groups, which increases the hydrodynamic volume of the solution, thereby further increasing the solution viscosity. In addition, the acrylic monomers contain functionalized carboxylic acid groups and have good water solubility, which is beneficial to improving the hydrophilicity of the polymer and is beneficial for the polymer to form a uniform dispersion in the aqueous system, thereby improving the uniformity and dispersibility of the negative electrode slurry. Due to the introduction of long carbon chain monomers, the hydrophobic monomers and the hydrophilic monomers form another form of hydrogen bond, thereby increasing the viscosity. At the same time, the hydrophilic monomers are weakened so that the hydrophilic monomers are intramolecular and / or intermolecular hydrogen bonds, and the surface free negative charge increases, resulting in an increase in Zeta potential. The Zeta potential is high, and the dispersibility of the negative electrode dispersant is further enhanced. Thus, the negative electrode dispersant of the present application has a higher viscosity and good dispersibility. When applied to negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0040] In some embodiments of the present application, the C4 to C21 long carbon chain monomer includes at least one of butadiene, isoprene, styrene, vinyl acetate, butyl acrylate, n-octyl acrylate, isooctyl acrylate, lauryl acrylate, hexadecyl acrylate, octadecyl acrylate, hydroxybutyl vinyl ether, butyl vinyl ether, triethylene glycol divinyl ether, vinyl acetate, butyl acrylate or glyceryl acrylate. By selecting the above-mentioned types of long carbon chain monomers, the long carbon chain monomers open the molecular chain segments of the hydrophilic monomer, i.e., acrylic acid (PAA) monomer, through alkali neutralization to form a hydrophobic association. This effect forms a physical cross-linked network through the interaction of intermolecular hydrophobic groups, increases the hydrodynamic volume of the solution, thereby further increasing the solution viscosity. In addition, due to the introduction of long carbon chain monomers, the hydrophobic monomer and the hydrophilic monomer form another form of hydrogen bond, thereby increasing the viscosity. At the same time, the hydrophilic monomer is weakened, resulting in intramolecular and / or intermolecular hydrogen bonding, an increase in surface free negative charge, and an increase in Zeta potential. The Zeta potential is higher, and the dispersibility of the negative electrode dispersant is further enhanced. Therefore, the negative electrode dispersant of the present application has high viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0041] In some embodiments of the present application, based on the mass of the hydrophobic monomer, the mass percentage of carbon in the hydrophobic monomer is m, where m ≥ 75%, and the hydrophobic monomer includes at least one of an ether or a hydrocarbon containing an unsaturated double bond. When the carbon content in the hydrophobic monomer is greater than or equal to 75%, the negative electrode dispersant has better dispersibility when used with the above-mentioned hydrophobic monomer. When applied to the negative electrode slurry, the negative electrode dispersant has better affinity with the negative electrode active material, which is conducive to better exerting the dispersing effect of the negative electrode dispersant, while taking into account stability, and having better dispersibility of the negative electrode slurry.

[0042] In some embodiments of the present application, based on the mass of the polymer in the negative electrode dispersant, the mass percentage of the hydrophilic monomer unit in the repeating unit of the polymer is x, the mass percentage of the hydrophobic monomer unit in the repeating unit of the polymer is y, and the mass percentage of the functional monomer in the repeating unit of the polymer is z, 10%≤x≤50%, 20%≤y≤60%, and 20%≤z≤60%. For example, the value of x can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, or a range consisting of any two values therein; the value of y can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, or a range consisting of any two values therein; the value of z can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, or a range consisting of any two values therein. By regulating the values of x, y and z within the above range, the hydrophobic monomer opens the molecular chain segment of the hydrophilic monomer through alkali neutralization, forming a hydrophobic association effect. This effect forms a physical cross-linked network through the interaction of intermolecular hydrophobic groups, increases the fluid dynamics volume of the solution, and thus increases the solution viscosity. The use of functional monomers in combination with hydrophilic monomers is conducive to the formation of more hydrogen bonds, further increasing the viscosity of the dispersant; in addition, the hydrophilic monomer has good water solubility, which is conducive to improving the hydrophilicity of the polymer and facilitating the formation of a uniform dispersion of the polymer in the aqueous system, thereby improving the uniformity and dispersibility of the negative electrode slurry; and due to the introduction of the hydrophobic monomer, the hydrophobic monomer and the hydrophilic monomer form another form of hydrogen bond, thereby increasing the viscosity. At the same time, the intramolecular and / or intermolecular hydrogen bonding of the hydrophilic monomer is weakened, the free negative charge on the surface increases, resulting in an increase in the Zeta potential. The higher the Zeta potential, the enhanced dispersibility of the negative electrode dispersant. Thus, the hydrophilic monomer, hydrophobic monomer, and functional monomer achieve synergistic effects on viscosity, dispersibility, and stability, thereby improving the viscosity and dispersibility of the negative electrode dispersant. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0043] In some embodiments of the present application, 0.2≤x / y≤2.5. For example, the value of x / y can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5 or a range consisting of any two of the values. By regulating the value of x / y within the above range, it is beneficial to adjust the effects of the hydrophilic monomer and the hydrophobic monomer, maximize the hydrophobic association effect, improve the dispersibility, and make the polymer have better stability (high viscosity) and better dispersibility (the intramolecular hydrogen bonding of the hydrophilic monomer is suitable). When applied to the negative electrode slurry, while taking into account the dispersibility, the negative electrode slurry has better stability. When using the negative electrode slurry including the negative electrode dispersant of the present application to prepare the negative electrode sheet, it is beneficial to uniformly coat the negative electrode slurry on the negative electrode collector, reduce the polarization during the charging and discharging process of the secondary battery, and improve the cycle life of the secondary battery. The secondary battery prepared in this way has a good cycle life and cycle interface.

[0044] In some embodiments of the present application, the pH of the negative electrode dispersant is 6.0 to 8.0. For example, the pH of the negative electrode dispersant can be 6.0, 6.2, 6.5, 6.8, 7.0, 7.2, 7.5, 7.8, 8.0, or a range consisting of any two of these values. By regulating the pH of the negative electrode dispersant within the above range, it is beneficial for the hydrophilic monomer in the dispersant, i.e., the acrylic monomer, to further exert its dispersing effect, and it is beneficial for the carboxylic acid group in the acrylic monomer to dissociate and form a negative charge, thereby increasing the electrostatic repulsion between particles and reducing the possibility of particle agglomeration. While taking into account the viscosity, the dispersibility of the negative electrode dispersant is further improved.

[0045] In some embodiments of the present application, the weight average molecular weight of the polymer is Mw g / mol, 3×10 5 ≤Mw≤1.5×10 6 For example, the value of Mw can be 3×10 5 , 4×10 5 , 5×10 5 , 6×10 5 , 7×10 5 , 8×10 5 , 9×10 5 , 1×10 6 , 1.1×10 6 , 1.2×10 6 , 1.3×10 6 , 1.4×10 6 , 1.5×10 6Or a range consisting of any two of the values. By regulating the value of Mw within the above range, the polymer now has a longer molecular chain, which is conducive to better adsorption on the surface of the negative electrode active material, reducing the risk of agglomeration of the negative electrode active material particles, and improving the dispersibility of the negative electrode slurry. The high molecular weight polymer is conducive to forming a relatively stable three-dimensional network structure, which enhances the stability of the negative electrode slurry. Therefore, when the negative electrode dispersant of the present application is applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability. When using the negative electrode slurry including the negative electrode dispersant of the present application to prepare the negative electrode sheet, it is conducive to the uniform coating of the negative electrode slurry on the negative electrode current collector, further reducing the area of the thinning zone formed at the edge of the negative electrode material layer.

[0046] In some embodiments of the present application, the viscosity of the negative electrode dispersant at 25°C and 12 rpm is ηmPa·s, 30000≤η≤100000. For example, the value of η can be 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000 or a range consisting of any two values therein. By regulating the value of η within the above range, the negative electrode dispersant has a higher viscosity and good dispersibility. Applying it to the negative electrode slurry is beneficial for the negative electrode dispersant to be better adsorbed on the surface of the negative electrode active material, reducing the risk of agglomeration of the negative electrode active material particles, and improving the dispersibility of the negative electrode slurry. The high-viscosity negative electrode dispersant has a higher cohesive strength, reduces the fluidity of the negative electrode slurry during the coating process, is beneficial for the uniform coating of the negative electrode slurry on the negative electrode current collector, reduces polarization during the charge and discharge process of the secondary battery, and improves the cycle life of the secondary battery. Therefore, when the negative electrode dispersant of the present application is applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0047] In some embodiments of the present application, the elastic modulus of the polymer film (film size is 80mm×20mm×1mm) is E GPa, 5≤E≤20. For example, the value of E can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or a range consisting of any two values therein. By regulating the value of E within the above range, the viscosity of the negative electrode dispersant is relatively high. When applied to the negative electrode slurry to prepare the negative electrode sheet, the binding ability of the negative electrode active material particles is relatively strong. During the charge and discharge process of the secondary battery, it is beneficial to reduce the expansion of the negative electrode sheet, thereby improving the cycle performance and mechanical safety performance of the secondary battery.

[0048] In some embodiments of the present application, the degree of swelling of the polymer in the electrolyte is c, 1% ≤ c ≤ 10%. For example, the value of c can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two of these values. By regulating the value of c within the above range, the viscosity of the negative electrode dispersant is relatively high. When applied to the negative electrode slurry to prepare the negative electrode sheet, the binding ability of the negative electrode active material particles is relatively strong. During the charge and discharge process of the secondary battery, it is beneficial to reduce the expansion of the negative electrode sheet and reduce the risk of demolding of the negative electrode sheet interface due to bonding failure after the cycle, thereby improving the cycle performance and mechanical safety performance of the secondary battery; and the effect of the polymer and the electrolyte is relatively small, which can reduce the side reactions of the electrolyte. This is conducive to improving the electrochemical performance of the secondary battery and increasing the cycle life of the secondary battery.

[0049] The swelling degree refers to the ratio of the mass of the polymer molecules after swelling to the mass before swelling, when the polymer molecules adsorb solvent molecules and reach swelling equilibrium. This application does not specifically limit the electrolyte used to test the swelling degree, as long as it can achieve the objectives of this application. For example, a conventional electrolyte composition can be used. Specifically, the electrolyte composition can be the same as the electrolyte composition described in the Examples section of this application.

[0050] In some embodiments of the present application, the negative electrode dispersant satisfies the following characteristics: the pH of the negative electrode dispersant is 6.0 to 8.0, for example, the pH of the negative electrode dispersant can be 6.0, 6.2, 6.5, 6.8, 7.0, 7.2, 7.5, 7.8, 8.0 or a range consisting of any two values thereof; and / or the weight average molecular weight of the polymer is Mw, 3×10 5 ≤Mw≤1.5×10 6 , for example, the value of Mw can be 3×10 5 , 4×10 5 , 5×10 5 , 6×10 5 , 7×10 5 , 8×10 5 , 9×10 5 , 1×10 6 , 1.1×10 6 , 1.2×10 6 , 1.3×10 6 , 1.4×10 6 , 1.5×10 6or a range consisting of any two values thereof; and / or, the viscosity of the negative electrode dispersant at 25° C. and 12 rpm is η mPa·s, 30000≤η≤100000, for example, the value of η can be 30000, 40000, 50000, 60000, 70000, 80000, 90000, 100000 or a range consisting of any two values thereof; and / or, a polymer film (film size is 80 mm×20 mm×1 mm) The elastic modulus is EGPa, 5≤E≤20, for example, the value of E can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or a range consisting of any two of the values; and / or, the swelling degree of the polymer in the electrolyte is c, 1%≤c≤10%, for example, the value of c can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two of the values. Through the above settings, the negative electrode dispersant has high viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability. When using the negative electrode slurry including the negative electrode dispersant of the present application to prepare the negative electrode sheet, it is beneficial to uniformly coat the negative electrode slurry on the negative electrode current collector, reduce polarization during the charge and discharge process of the secondary battery, and improve the cycle life of the secondary battery.

[0051] In some embodiments of the present application, the negative electrode dispersant is mixed with the negative electrode active material to obtain a first slurry having a solid content of 40 wt% to 50 wt%. For example, the solid content of the first slurry can be 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt% or a range consisting of any two values thereof. The mass ratio of the polymer to the negative electrode active material in the first slurry is 1.5:98.5. The first slurry is allowed to stand for 5 to 14 days, for example, 5 days, 6 days, 7 days, 8 days, 9 days, 10 days, 11 days, 12 days, 13 days, 14 days, or a range consisting of any two values therein, to obtain a second slurry, wherein the area from the surface of the second slurry to 1 / 4 of the total depth of the second slurry is the upper slurry layer, and the area from 3 / 4 of the total depth of the second slurry to the bottom of the second slurry is the lower slurry layer, and the difference in zeta potential between the upper and lower slurries is Δ1 ≤ ± 0.5 mV. For example, the difference in zeta potential between the upper and lower slurries is Δ1, which can be -0.5 mV, -0.4 mV, -0.3 mV, -0.2 mV, -0.1 mV, 0 mV, 0.1 mV, 0.2 mV, 0.3 mV, 0.4 mV, 0.5 mV, or a range consisting of any two values therein. The above configuration shows that when the negative electrode dispersant is applied to the first slurry, it is beneficial to reduce the risk of sedimentation of the first slurry. The negative electrode dispersant of the present application has high viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0052] In some embodiments of the present application, the negative electrode dispersant is mixed with the negative electrode active material to obtain a first slurry with a solid content of 40 wt% to 50 wt%. For example, the solid content of the first slurry can be 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt% or a range consisting of any two values therein. The mass ratio of the polymer to the negative electrode active material in the first slurry is 1.5:98.5. The first slurry is The material is allowed to stand for 5 to 14 days, for example, 5 days, 6 days, 7 days, 8 days, 9 days, 10 days, 11 days, 12 days, 13 days, 14 days or a range consisting of any two values therein to obtain a second slurry, and along the direction from the surface to the bottom of the second slurry, the surface of the second slurry to 1 / 4 of the total depth of the second slurry is the upper slurry, and the total depth of the second slurry to 3 / 4 of the bottom of the second slurry is the lower slurry, and the difference Δ2 between the Dv50 of the particles of the upper slurry and the Dv50 of the particles of the lower slurry is ≤0.5μm. For example, the difference Δ2 between the Dv50 of the particles of the upper slurry and the Dv50 of the particles of the lower slurry can be 0μm, 0.05μm, 0.1μm, 0.15μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, 0.5μm or a range consisting of any two of these values. Through the above settings, it is shown that when the negative electrode dispersant is applied to the first slurry, it is beneficial to reduce the risk of sedimentation of the first slurry, and the negative electrode active particles are more evenly distributed in the slurry. The negative electrode dispersant of the present application has high viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0053] In some embodiments of the present application, a negative electrode dispersant is mixed with a negative electrode active material to obtain a first slurry having a solid content of 40 wt% to 50 wt%. For example, the solid content of the first slurry may be 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, 45 wt%, 46 wt%, 47 wt%, 48 wt%, 49 wt%, 50 wt%, or a range consisting of any two values thereof. The mass ratio of the polymer to the negative electrode active material in the first slurry is 1.5:98.5. The first slurry is allowed to stand for 5 to 14 days, for example, it can be allowed to stand for 5 days, 6 days, 7 days, 8 days, 9 days, 10 days, 11 days, 12 days, 13 days, 14 days, or a range consisting of any two values thereof to obtain a second slurry. Along the direction from the surface to the bottom of the second slurry, the surface of the second slurry to 1 / 4 of the total depth of the second slurry is the upper slurry, and 3 / 4 of the total depth of the second slurry is the upper slurry. The bottom surface of the second slurry is the lower slurry layer, and the difference between the zeta potential of the upper slurry layer and the lower slurry layer is ≤±0.5mV. For example, the difference Δ1 between the zeta potential of the upper slurry layer and the lower slurry layer can be -0.5mV, -0.4mV, -0.3mV, -0.2mV, -0.1mV, 0mV, 0.1mV, 0.2mV, 0.3mV, 0.4mV, 0.5mV or a range consisting of any two values therein; and / or, the upper The difference between the Dv50 of the particles of the upper slurry and the Dv50 of the particles of the lower slurry is ≤0.5μm. For example, the difference Δ2 between the Dv50 of the particles of the upper slurry and the Dv50 of the particles of the lower slurry can be 0μm, 0.05μm, 0.1μm, 0.15μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, 0.5μm or a range consisting of any two values therein. Through the above settings, it is shown that when the negative electrode dispersant is applied to the first slurry, it is beneficial to reduce the risk of sedimentation of the first slurry, and the negative electrode active particles are more evenly distributed in the slurry. The negative electrode dispersant of the present application has high viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability.

[0054] The present application has no particular limitation on the negative electrode active material used to prepare the first slurry as long as the purpose of the present application can be achieved. For example, a conventional negative electrode active material can be used, specifically, at least one of artificial graphite, natural graphite, silicon oxide, silicon carbon compound, hard carbon or amorphous carbon, wherein the silicon carbon compound is a silicon carbon composite material, and based on the mass of the silicon carbon composite material, the mass percentage of silicon element is 30% to 70%, and the mass percentage of carbon element is 30% to 70%, and the silicon oxide includes SiOx, wherein 0<x<2, and illustratively, the silicon oxide may include silicon monoxide (SiO, the molar ratio of silicon and oxygen is 1:1); or, the type of negative electrode active material may be the same as the type of negative electrode active material in the embodiment of the present application.

[0055] A second aspect of the present application provides a method for preparing a negative electrode dispersant, comprising the following steps:

[0056] (1) Deionized water with a W1 of 900 to 4900 parts is used as a solvent. For example, the W1 of deionized water can be 900, 1000, 1200, 1500, 1800, 2000, 2200, 2500, 2800, 3000, 3200, 3500, 3800, 4000, 4200, 4500, 4800, 4900, or a range consisting of any two of the values; a chain transfer agent and an initiator are added to the solvent to obtain a mixture; 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, or a range consisting of any two of the values; wherein the chain transfer agent includes n-dodecane The initiator comprises at least one of 2-hydroxy-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1,2-dimethyl-1

[0057] (2) adding a hydrophobic monomer, a hydrophilic monomer, and a functional monomer to the mixture, wherein the mass fraction W4 of the hydrophilic monomer is 10 to 50 parts, for example, the mass fraction W4 of the hydrophilic monomer can be 10 parts, 12 parts, 15 parts, 18 parts, 20 parts, 22 parts, 25 parts, 28 parts, 30 parts, 32 parts, 35 parts, 38 parts, 40 parts, 42 parts, 45 parts, 48 parts, 50 parts or a range consisting of any two of these values; the mass fraction W4 of the hydrophobic monomer is 10 to 50 parts. The mass fraction W5 of the hydrophilic monomer is 20 to 60 parts, for example, the mass fraction W5 of the hydrophilic monomer can be 20 parts, 22 parts, 25 parts, 28 parts, 30 parts, 32 parts, 35 parts, 38 parts, 40 parts, 42 parts, 45 parts, 48 parts, 50 parts, 52 parts, 55 parts, 58 parts, 60 parts or a range consisting of any two values therein; the mass fraction W6 of the functional monomer is 20 to 60 parts, for example, the mass fraction W6 of the functional monomer can be 20 parts, 22 parts, 25 parts, 28 parts, 30 parts, 32 parts, 35 parts, 38 parts, 40 parts, 42 parts, 45 parts, 48 parts, 50 parts, 52 parts, 55 parts, 58 parts, 60 parts or a range consisting of any two values therein; 0 parts, 32 parts, 35 parts, 38 parts, 40 parts, 42 parts, 45 parts, 48 parts, 50 parts, 52 parts, 55 parts, 58 parts, 60 parts or a range consisting of any two of the values; and the total mass of the hydrophobic monomer, the hydrophilic monomer and the functional monomer is 100 parts; continue to heat to T ° C, T is 60 ° C to 80 ° C, for example, T can be 60 ° C, 61 ° C, 62 ° C, 63 ° C, 64 ° C, 65 ° C, 66 ° C, 67 ° C, 68 ° C, 69 ° C, 70 ° C or wherein the range consists of any two values; the insulation time t is 2h to 10h, for example, the insulation time t can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h or a range consisting of any two values therein; and then the polymer solution is obtained after 4h to 8h of reduced pressure distillation, for example, the reduced pressure distillation time can be 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h or a range consisting of any two values therein.

[0058] The inventors have found that during the polymerization reaction, the hydrophobic monomer opens the molecular chain segments of the hydrophilic monomer through alkali neutralization, forming a hydrophobic association effect. This effect forms a physical cross-linked network through the interaction of intermolecular hydrophobic groups, increasing the hydrodynamic volume of the solution, thereby increasing the solution viscosity; the use of functional monomers in combination with hydrophilic monomers is conducive to the formation of more hydrogen bonds, further increasing the viscosity of the dispersant; in addition, acrylic monomers contain functionalized carboxylic acid groups and have good water solubility, which is conducive to improving the hydrophilicity of the polymer; and due to the introduction of hydrophobic monomers, the hydrophobic monomers and hydrophilic monomers form another form of hydrogen bonds, thereby increasing the viscosity. At the same time, the intramolecular and / or intermolecular hydrogen bonding of the hydrophilic monomer is weakened, the surface free negative charge increases, resulting in an increase in the Zeta potential. The higher the Zeta potential, the enhanced dispersibility of the negative electrode dispersant. At the same time, maintaining a high temperature and a long time during the reaction is conducive to promoting the reaction, so that the performance of the negative electrode dispersant is further enhanced. The negative electrode dispersant finally prepared by the above method only includes the alkalized polymer and solvent. A small amount of chain transfer agent and initiator added during the preparation process are removed by the desulfurization distillation after the polymerization reaction. After the desulfurization operation, the total residual amount of the remaining solid small molecules, except for the polymer, is at the level of one part per million, i.e., ppm, which can be ignored. The negative electrode dispersant is prepared by the method provided in the second aspect of the present application, and the various parameters are adjusted within the above range. The obtained negative electrode dispersant has high viscosity and good dispersibility. When applied to the negative electrode slurry, the negative electrode slurry has good dispersibility and stability. When using the negative electrode slurry including the negative electrode dispersant of the present application to prepare the negative electrode sheet, it is beneficial to uniformly coat the negative electrode slurry on the negative electrode current collector, reduce polarization during the charge and discharge process of the secondary battery, and improve the cycle life of the secondary battery.

[0059] The present application has no particular restrictions on the regulation of various parameters of the polymer and the negative electrode dispersant, as long as the purpose of the present application can be achieved. For example, the pH of the negative electrode dispersant can be adjusted by regulating the amount of hydrophilic monomers, i.e., acrylic monomers, added. For example, when other conditions remain unchanged, the amount of hydrophilic monomers added increases, and the amount of hydrophobic monomers and functional monomers added decreases accordingly. At this time, the pH of the negative electrode dispersant decreases accordingly, and vice versa. The weight average molecular weight Mw of the polymer can be adjusted by regulating the polymerization reaction temperature and time. For example, when other conditions remain unchanged, the higher the polymerization reaction temperature and the longer the time, the greater the weight average molecular weight, and vice versa. It can be understood that when the amount and / or type of each monomer in the polymer changes, the weight average molecular weight Mw of the polymer will also change accordingly. The viscosity η of the negative electrode dispersant at 25 ° C and 12 rpm can be adjusted by regulating the amount of hydrophobic monomer added, the polymerization reaction temperature and time. For example, when other conditions remain unchanged, the amount of hydrophobic monomer added increases, and the amount of hydrophilic monomer and functional monomer added decreases accordingly. The higher the polymerization temperature and the longer the time, the greater the viscosity of the alkalized hydrophobically modified polyacrylic acid at 25 ° C and 12 rpm, and vice versa. The elastic modulus E of the polymer film can be adjusted by regulating the addition ratio of the hydrophilic monomer and the hydrophobic monomer, the polymerization reaction temperature and time. For example, when other conditions remain unchanged, the greater the addition ratio of the hydrophilic monomer and the hydrophobic monomer, the higher the polymerization reaction temperature, the longer the time, the higher the elastic modulus, and vice versa. The swelling degree c of the polymer in the electrolyte can be adjusted by regulating the amount of hydrophilic monomer added, the polymerization reaction temperature and time. For example, when other conditions remain unchanged, the amount of hydrophilic monomer added increases, and the amount of hydrophobic monomer and functional monomer added decreases accordingly. The higher the polymerization reaction temperature and the longer the time, the smaller the swelling degree of the alkalized hydrophobically modified polyacrylic acid in the electrolyte, and vice versa. The mass percentage of the units of each monomer in the repeating unit of the polymer, i.e., the values of x, y and z, can be adjusted by regulating the mass fraction of the hydrophobic monomer, hydrophilic monomer and functional monomer added. The solid content of the negative electrode dispersant can be adjusted by regulating the number of deionized water added.

[0060] The third aspect of the present application provides a secondary battery, which includes a positive electrode plate, a separator, an electrolyte, and a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, the negative electrode material layer includes a polymer, the monomers forming the polymer include a hydrophobic monomer, a hydrophilic monomer, and a functional monomer, the hydrophobic monomer includes a long carbon chain monomer from C4 to C21, the hydrophilic monomer includes an acrylic monomer, and the functional monomer includes at least one of acrylonitrile or acrylamide; or, a negative electrode dispersant prepared according to the preparation method provided in the second aspect of the present application. Through the above-mentioned arrangement, when preparing the negative electrode plate in the secondary battery, it is beneficial to uniformly coat the negative electrode slurry on the negative electrode current collector, thereby reducing polarization during the charge and discharge process of the secondary battery, improving the cycle life of the secondary battery, and the secondary battery has good cycle performance, mechanical safety performance, and electrochemical performance.

[0061] In some embodiments of the present application, the molecular formula of the polymer in the secondary battery is (C N1 H N2 O N3 ) n1 (C3H3N) n2 (RC3H3O2) n3 (C3H5NO) n4 , R is selected from a hydrogen atom, a methyl group, or an ethyl group, N1 is selected from a natural number within the range of 4 to 21, N2 is selected from a natural number within the range of 1 to 42, N3 is selected from a natural number within the range of 0 to 10, n1 is selected from a natural number within the range of 3000 to 20000, n3 is selected from a natural number within the range of 800 to 5000, n2 and n4 are each independently selected from a natural number within the range of 0 to 5000, and n2 and n4 are not both 0. When the molecular formula of the polymer in the secondary battery meets the above range, when preparing the negative electrode sheet in the secondary battery, it is beneficial to uniformly coat the negative electrode slurry on the negative electrode current collector, thereby reducing polarization during the charge and discharge process of the secondary battery and improving the cycle life of the secondary battery. The secondary battery has good cycle performance, mechanical safety performance, and electrochemical performance.

[0062] It is understood that the negative electrode sheets in secondary batteries require a drying step during their preparation to remove the solvent used in the preparation process, thereby improving the safety and reliability of the secondary battery. The solvent included in the negative electrode dispersant of the present application is also removed during the drying process of the sheet. Therefore, when a negative electrode sheet is prepared using a negative electrode slurry including the negative electrode dispersant of the present application, the negative electrode material layer in the resulting negative electrode sheet only includes a polymer.

[0063] In the present application, the polymer includes the characteristics of the above-mentioned scheme: the molecular formula of the polymer, the specific type, the mass percentage range of each monomer in the polymer, the weight-average molecular weight, the elastic modulus, the swelling degree and other characteristics can be arbitrarily combined. When the secondary battery includes the polymer in the present application, the secondary battery has good cycle performance, mechanical safety performance and electrochemical performance.

[0064] The present application has no particular restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The positive electrode material layer of the present application includes a positive electrode active material. The present application has no particular restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05O2 (NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganate, lithium iron manganese phosphate or lithium titanate, etc. In the present application, the positive electrode active material may also contain non-metallic elements, for example, non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon or sulfur. In the present application, there is no particular restriction on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved. In the present application, the positive electrode material layer may also include a binder and a conductive agent. The present application has no particular restriction on the type of binder in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the binder may include but is not limited to at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The present application has no particular restrictions on the type of conductive agent in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metal materials or conductive polymers. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application has no particular restrictions on the mass ratio of the positive active material, conductive agent and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0065] In this application, the "negative electrode material layer located on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or can be disposed on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector or a partial area of the surface of the negative electrode current collector. There is no special limitation in this application, as long as the purpose of this application can be achieved. There is no special limitation on the negative electrode current collector in this application, as long as the purpose of this application can be achieved. For example, the negative electrode current collector can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector (such as lithium-copper composite current collector, carbon-copper composite current collector, nickel-copper composite current collector, titanium-copper composite current collector, etc.). The negative electrode material layer of this application contains negative electrode active material. There is no special limitation on the type of the negative electrode active material in this application, as long as the purpose of this application can be achieved. For example, the negative electrode active material can include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12 , Li-Al alloy or at least one of metallic lithium. In this application, there is no special limitation on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the purpose of this application can be achieved. Optionally, the negative electrode material layer can further include a conductive agent and a binder. There is no special limitation on the type of the conductive agent in the negative electrode material layer of this application, as long as the purpose of this application can be achieved. For example, the conductive agent can be of the same type as the conductive agent in the above-mentioned positive electrode material layer. There is no special limitation on the type of the binder in the negative electrode material layer of this application, as long as the purpose of this application can be achieved. For example, the negative electrode binder can be of the same type as the binder in the above-mentioned positive electrode material layer.

[0066] In the present application, the electrolyte includes a lithium salt and a non-aqueous solvent. The present application has no particular restrictions on the lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt may include but is not limited to at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB) or lithium difluoroborate. The present application has no particular restrictions on the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The present application has no particular restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The above-mentioned linear carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methylethyl carbonate (MEC). The above-mentioned cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinylethylene carbonate (VEC). The fluorocarbonate compound may include but is not limited to at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. The above-mentioned carboxylate compounds may include but are not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid, valerolactone or caprolactone. The above-mentioned ether compounds may include but are not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0067] The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include, but is not limited to, polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or at least one of aramid. The type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane. In some embodiments of the present application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven membrane or a composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The present application has no particular restrictions on inorganic particles. For example, inorganic particles can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application has no particular restrictions on the binder. For example, the binder can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene). In the present application, the thickness of the diaphragm is not particularly limited, as long as the purpose of the present application can be achieved, for example, the thickness of the diaphragm can be 3 μm to 30 μm.

[0068] The secondary battery also includes a shell for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the above-mentioned other components. This application does not particularly limit the shell, and it can be a shell known in the art, as long as it can achieve the purpose of this application. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal. This application does not limit the type of metal. A metal hard shell known in the art can be used, as long as it can achieve the purpose of this application. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0069] The secondary battery of the present application is not particularly limited and may include any device that generates an electrochemical reaction. In one or more embodiments, the secondary battery may include but is not limited to: a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0070] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, the preparation process of the secondary battery may include but is not limited to the following steps: stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and then fixing the four corners of the entire laminated structure with tape to obtain an electrode assembly with a laminated structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the shell to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0071] A fourth aspect of the present application provides an electronic device, which includes the secondary battery according to any one of the aforementioned embodiments. Therefore, the electronic device of the present application has good performance.

[0072] The present application does not particularly limit the type of electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0073] Example

[0074] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0075] Test methods and equipment:

[0076] Zeta potential test:

[0077] Turn on the Zeta potential analyzer (Zetasizer Nano ZS90, Malvern), calibrate the electrodes, select the Zeta potential test mode, set the sample cell temperature to 25°C, inject 0.75 mL of the anode dispersant sample into the sample cell, position the sample cell in the center of the instrument, start the measurement program, and obtain the reading. Test the anode dispersant sample three times for each group, and take the average value to determine the zeta potential of the anode dispersant.

[0078] Viscosity test:

[0079] At 25°C, place the sample horizontally and test the viscosity of the anode dispersant using a Brookfield DV1 viscometer. Estimate the viscosity of the anode dispersant and select an appropriate rotor. For example, if the estimated viscosity range is 0 to 2000 mPa·s, select rotor #61; if the estimated viscosity range is 50 to 10,000 mPa·s, select rotor #62; if the estimated viscosity range is 10,000 to 40,000 mPa·s, select rotor #63; and if the estimated viscosity range is 10,000 to 200,000 mPa·s, select rotor #64. Insert the rotor into the sample, set the rotor speed to 12 rpm, and start the test for 5 minutes. After the rotor viscosity value stabilizes for 2 minutes, the reading is the viscosity of the anode dispersant being tested (in mPa·s).

[0080] Elastic modulus test of polymer film:

[0081] Place the negative electrode dispersant in a rectangular template made of glass (specifications: 80mm×20mm×1mm), air-dry until there is no obvious moisture on the surface of the negative electrode dispersant, and then bake it in an 80°C oven until the weight no longer decreases to prepare a 1mm×80mm×20mm film. First, use a measuring tool with appropriate precision to measure the initial size of the sample, clamp the sample on the testing machine fixture, and ensure that the axis of the sample coincides with the direction of the tensile force. Set the test parameter tensile speed to 50mm / min. Start the testing machine to perform a tensile test, record the force-displacement data, calculate the stress-strain curve through data processing software, and calculate the elastic modulus of the polymer film from the linear part of the curve.

[0082] Swelling test of polymer in electrolyte:

[0083] The negative electrode dispersant was placed in a rectangular glass template (60 mm × 150 mm × 1 mm) and air-dried until no significant moisture was present on the surface. The film was then baked in an 80°C oven until its weight stopped decreasing. The film was weighed, recorded as m1, and then sealed and immersed in electrolyte. The film was then placed in an 85°C oven for 48 hours. The film was then removed and the electrolyte on the surface of the film was blotted dry with paper until no electrolyte remained. The weight was then weighed and recorded as m2. The polymer swelling ratio in the electrolyte, c, is then calculated as (m2 - m1) / m1 × 100%.

[0084] The composition and preparation steps of the electrolyte are the same as those of the electrolyte in Example 1-1.

[0085] Weight average molecular weight test:

[0086] The weight average molecular weight of the polymer was determined using an Agilent 1200 series liquid chromatograph. The negative electrode dispersant was filtered through a water filter membrane and then injected into an Agilent 1200 series liquid chromatograph for testing to obtain the weight average molecular weight of the measured polymer.

[0087] Slurry stability test:

[0088] The negative electrode dispersant and artificial graphite, the negative electrode active material, were mixed at 1000 rpm for 2 hours and then allowed to stand in a container to produce a first slurry with a solid content of 45 wt%. The mass ratio of polymer to negative electrode active material in the first slurry was 1.5:98.5. The slurry was scraped from the bottom of the container every 24 hours using a steel plate. Visual observation indicated that the slurry had settled when the negative electrode active material and liquid separated. The settling time was recorded to produce a second slurry.

[0089] (1) Electrokinetic potential test of upper and lower slurry layers:

[0090] Use a 5mL pipette to draw a tube of upper slurry (i.e., along the direction from the surface to the bottom of the second slurry, the surface value of the second slurry is 1 / 4 of the total depth of the second slurry). Turn on the Zeta potential meter (instrument model: Zetasizer Nano ZS90, manufacturer: Malvern), calibrate the electrode, select the Zeta potential test mode, set the sample cell temperature to 25°C, add 0.75mL of the above upper slurry into the sample cell, place the sample cell in the center of the instrument, start the measurement program, and obtain the reading. The negative electrode dispersant samples of the same group were tested three times, and the average value was taken as the Zeta potential of the upper slurry.

[0091] Use a 5mL pipette to draw a tube of lower slurry (i.e., along the direction from the surface to the bottom of the second slurry, from 3 / 4 of the total depth of the second slurry to the bottom of the second slurry). Turn on the Zeta potential meter (instrument model: Zetasizer Nano ZS90, manufacturer: Malvern), calibrate the electrode, select the Zeta potential test mode, set the sample cell temperature to 25°C, add 0.75mL of the above lower slurry into the sample cell, place the sample cell in the center of the instrument, start the measurement program, and obtain the reading. The negative electrode dispersant samples of the same group were tested three times, and the average value was taken as the Zeta potential of the lower slurry.

[0092] (2) Dv50 test of particles in upper and lower slurries:

[0093] Use a 5mL pipette to draw a tube of the upper slurry (i.e., from the surface to the bottom of the second slurry, the surface value of the second slurry is 1 / 4 of the total depth of the second slurry). Turn on the Malvern laser particle size analyzer, set the sample cell temperature to 25°C, add 1mL of the upper slurry to the sample cell, place the sample cell in the center of the instrument, start the program measurement, and obtain the reading Dv50. The negative electrode dispersant samples of the same group are tested three times, and the average value is taken, which is the Dv50 of the particles in the upper slurry.

[0094] Use a 5mL pipette to draw a tube of the lower layer slurry (i.e., from 3 / 4 of the total depth of the second slurry to the bottom of the second slurry along the direction from the surface to the bottom of the second slurry). Turn on the Malvern laser particle size analyzer and set the sample cell temperature to 25°C. Add 1mL of the above lower layer slurry to the sample cell. Place the sample cell in the center of the instrument, start the measurement program, and obtain the reading Dv50. The negative electrode dispersant samples of the same group are tested three times, and the average value is taken, which is the Dv50 of the particles in the lower layer slurry.

[0095] Adhesion test between negative electrode material layer and negative electrode current collector:

[0096] Stick the double-sided tape on the steel plate, cut the cold-pressed negative electrode sheet into strips with a width of 20 mm and a length of 100 mm and stick them on the double-sided tape, roll the strips back and forth on the strips with a pressure roller 4 times, clamp one end of the strips on the tensile testing machine fixture, start the tensile testing machine test, and pull the negative electrode sheet at a constant speed of 50 mm / min until the negative electrode material layer is peeled off from the current collector, that is, the peeling surface of the adhesion test should be between the negative electrode current collector and the negative electrode material layer, and the adhesion value between the negative electrode material layer and the negative electrode current collector is obtained by testing.

[0097] The test is considered complete when the current collector is visually exposed (to distinguish it from the case of the material layer cohesion test). The test angle is 180°.

[0098] 25℃ cycle capacity retention test:

[0099] A lithium-ion battery is charged at a constant current of 1.0C to 4.5V, then charged at a constant voltage of 4.5V to 0.025C, marking the end of charging; then discharged at a constant current of 0.2C to 3.0V, recording the capacity of one cycle (cl) as Q1; then the above charge and discharge process (1.0C constant current charging to 4.5V, then constant voltage charging to 0.025C, marking the end of charging; then 0.2C constant current discharging to 3.0V, recording the corresponding capacity as Qn) is repeated for 800 cls to obtain the corresponding capacity Qn. The capacity retention rate after 800 cls of cycling at 25°C is (Qn-Q1) / Q1×100%.

[0100] When the voltage range marked on the factory battery packaging is 3.0V to 4.5V, the charge cut-off voltage is 4.5V and the discharge cut-off voltage is 3.0V. Unless otherwise specified, the charge cut-off voltage of the lithium-ion battery used as an example is 4.5V and the discharge cut-off voltage is 3.0V.

[0101] Example 1

[0102] <Preparation of Negative Electrode Dispersant>

[0103] (1) 1566.7 parts of deionized water (W1) was used as a solvent, and a chain transfer agent, n-dodecyl mercaptan, and an initiator, sodium persulfate, were added to the solvent to obtain a mixture; wherein the amount of the chain transfer agent added, W2, was 0.5 parts, and the amount of the initiator added, W3, was 0.5 parts;

[0104] (2) adding a hydrophobic monomer isooctyl acrylate, a hydrophilic monomer acrylic acid, and a functional monomer acrylonitrile to the mixture, wherein the mass fraction W4 of the hydrophilic monomer is 40 parts; the mass fraction W5 of the hydrophobic monomer is 30 parts, the mass fraction W6 of the functional monomer is 30 parts, and the total mass fraction of the hydrophobic monomer, the hydrophilic monomer, and the functional monomer is 100 parts; continuing to heat to T, i.e., 70° C., holding time t is 4 hours, and then performing reduced pressure distillation for 4 hours to obtain a polymer solution;

[0105] (3) adding alkali lithium hydroxide to the polymer solution, wherein the mass ratio a of the alkali to the non-volatile solid in the polymer solution is 1 / 5, and mixing and stirring to obtain a negative electrode dispersant.

[0106] <Preparation of negative electrode sheet>

[0107] The negative electrode active material artificial graphite, the binder styrene-butadiene rubber, the conductive agent acetylene black, and the polymer in the negative electrode dispersant prepared above were mixed in a mass ratio of 97.3:1.2:0.5:1.0, and deionized water was added as a solvent to prepare a slurry with a solid content of 45 wt%. After stirring evenly in a vacuum mixer, a negative electrode slurry was obtained. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm and dried at 120°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side. The coating weight of the negative electrode material layer was 142 mg / 1540 mm 2 Repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode material layer. After drying at 120°C and cold pressing, the sheet is cut and the tabs are welded to obtain a negative electrode sheet measuring 78mm x 875mm for future use. The thickness of the negative electrode material layer on one side is 54.5μm.

[0108] <Preparation of positive electrode sheet>

[0109] The positive electrode active material lithium cobalt oxide (LiCoO2), the conductive agent Super P, and the binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.9:1.2, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the positive electrode slurry was obtained. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm and dried at 120℃ to obtain a positive electrode sheet with a single-sided positive electrode material layer. The coating weight of the positive electrode material layer was 267.8mg / 1540mm 2 Repeat the above steps on the other side of the aluminum foil to obtain a double-sided positive electrode sheet coated with a positive electrode material layer. After drying at 120°C and cold pressing, the sheet is cut and the tabs are welded to obtain a 74mm x 867mm positive electrode sheet ready for use. The thickness of the positive electrode material layer on one side is 42μm.

[0110] <Diaphragm>

[0111] A porous polyethylene film with a thickness of 7 μm (supplied by Celgard) was used as the separator.

[0112] <Preparation of Electrolyte>

[0113] In an environment with a water content of less than 10 ppm, dimethyl carbonate, diethyl carbonate, and ethylene carbonate are mixed in a mass ratio of 1:1:1 to obtain an organic solvent. A lithium salt, LiPF6, is then added to the organic solvent and mixed uniformly to obtain an electrolyte. The lithium salt comprises 12.5% by mass of the electrolyte, with the remainder being the organic solvent.

[0114] <Preparation of lithium-ion batteries>

[0115] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator positioned between the positive and negative electrode sheets to act as a separator, and then wound to form an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dehydrated at 80°C, and then injected with the electrolyte prepared above. The lithium-ion battery is produced through vacuum packaging, standing, forming, degassing, and trimming. The upper limit of the formation voltage is 4.15V, the formation temperature is 70°C, and the formation standing time is 2 hours.

[0116] Example 2 to Example 26

[0117] Except for adjusting the relevant preparation parameters according to Table 1, Table 2 and Table 3, the rest is the same as Example 1. In particular, the functional monomer in Example 23 is acrylamide, and the hydrophilic monomer in Example 24 is methacrylic acid.

[0118] Comparative Examples 1 to 7

[0119] Except for adjusting the relevant preparation parameters according to Table 1, Table 2 and Table 3, the rest is the same as Example 1.

[0120] Comparative Example 8

[0121] Except for preparing the negative electrode dispersant according to the following steps, the rest is the same as Example 1.

[0122] <Preparation of Negative Electrode Dispersant>

[0123] Plant cellulose, a 75% ethanol solution, and a sodium hydroxide solution are mixed in 3 parts, 8 parts, and 4.5 parts by mass, and allowed to react at room temperature and pressure for 60 minutes. Then, 4 parts of a 45% monochloroacetic acid-ethanol solution are added, and an etherification reaction is carried out at room temperature for 30 minutes. The reaction product is then washed with a 50% ethanol solution and purified twice by centrifugation to obtain sodium carboxymethyl cellulose (CMC). The mass percentage of sodium hydroxide based on the mass of the sodium hydroxide solution is 30%.

[0124] Comparative Example 9

[0125] Except for preparing the negative electrode dispersant according to the following steps, the rest is the same as Example 1.

[0126] <Preparation of Negative Electrode Dispersant>

[0127] 100 g of acrylic acid was added to 900 g of water and heated to 68° C. to obtain an acrylic acid aqueous solution with a mass fraction of 10% acrylic acid; then, 1 g of ammonium persulfate was added to the acrylic acid aqueous solution at 68° C. and a rotation speed of 100 rpm to cause the acrylic acid to undergo self-polymerization to obtain a solution containing polyacrylic acid; then, using a peristaltic pump, 170 g of a 30% mass fraction of sodium hydroxide aqueous solution was dropwise added to the polyacrylic acid solution over a period of 20 minutes at the same temperature and rotation speed, and stirring was continued for 0.5 hours to obtain a solution containing sodium polyacrylate as a negative electrode dispersant.

[0128] Comparative Example 10

[0129] Except for preparing the negative electrode dispersant according to the following steps, the rest is the same as Example 1.

[0130] <Preparation of Negative Electrode Dispersant>

[0131] 90 parts of vinyl acetate, 5 parts of methanol, and 5 parts of a 0.013 g / L isopropyl hydroperoxide-methanol solution (methanol as the solvent) (all previously deoxygenated using N2 bubbling) were added to a pressure reactor equipped with a stirrer, liquid and gas feed ports, cooling, and addition equipment. The air in the reactor was replaced with N2, and the internal temperature of the reactor was raised to 150°C to initiate polymerization. Maintaining the reactor temperature constant, after 8 hours of reaction, 90 parts of methanol was added to the reactor via a feed pump. The mixture was then cooled to 25°C to terminate polymerization, and the residual monomer was blown out to obtain a methanol solution of polyvinyl acetate. The mass fraction of the polyvinyl acetate was adjusted to 20%, and alcoholysis was carried out with a 40 g / L methanolic sodium hydroxide solution. The resulting polyvinyl alcohol powder was dried and pulverized to produce a negative electrode dispersant.

[0132] Comparative Example 11

[0133] Except for adjusting the relevant preparation parameters according to Table 1, Table 2 and Table 3, the rest is the same as Example 1. Wherein, the functional monomer is 2-hydroxyethyl methacrylate phosphate.

[0134] It can be understood that in the above embodiments and comparative examples, the mass ratio of the substances added to prepare the negative electrode slurry is the mass ratio of the solids contained in the substances.

[0135] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0136]

[0137]

[0138]

[0139] Table 2

[0140]

[0141]

[0142] Table 3

[0143]

[0144]

[0145] Note: “ / ” in Table 3 indicates no relevant preparation or result parameters.

[0146] It can be seen from Examples 1 to 26 and Comparative Examples 1 to 11 that by adding hydrophobic segments, i.e., long carbon chain monomers, to the negative electrode dispersant and regulating the Zeta potential within the scope of the present application, the sedimentation time of the slurry is longer, the bonding force between the negative electrode material layer and the negative electrode current collector is greater, and the capacity retention rate of the lithium-ion battery after 800cls of cycling at 25°C is higher, indicating that the negative electrode dispersant of the present application has good dispersibility and stability. At this time, the negative electrode active material in the negative electrode material layer corresponding to the negative electrode dispersant is more evenly distributed and stable. During the cycling of the lithium-ion battery, the risk of polarization problems such as excessive or insufficient local current is lower, which is beneficial to improving the cycling performance of the lithium-ion battery and increasing the cycle life.The zeta potential cannot be tested in Comparative Example 1. At this time, the amount of hydrophilic monomer is small, it is difficult to generate a polymer, and the negative electrode dispersant of the present application cannot be formed, so the zeta potential test and the corresponding performance test cannot be performed; the Zeta potential in Comparative Example 2 is not within the scope of the present application. At this time, the content of the hydrophilic monomer is high, resulting in a low pH value of the negative electrode dispersant and low stability of the negative electrode dispersant. At this time, the sedimentation time of the slurry is short, the bonding force between the negative electrode material layer and the negative electrode current collector is small, the capacity retention rate of the lithium ion battery after 800cls of cycling at 25°C is small, and the performance of the lithium ion battery is poor; the Zeta potential in Comparative Example 3 is not within the scope of the present application At this time, the content of hydrophobic monomer is low, the sedimentation time of slurry is short, the bonding force between negative electrode material layer and negative electrode current collector is small, the capacity retention rate of lithium ion battery after 800cls cycle at 25℃ is small, and the performance of lithium ion battery is poor; in comparative example 4, the zeta potential cannot be tested, at this time the content of hydrophilic monomer is less than the content of hydrophobic monomer, aqueous polymerization is difficult to occur, the negative electrode dispersant of the present application cannot be formed, and part of the monomer is precipitated, so the zeta potential test and the corresponding performance test cannot be performed; in comparative example 5, the Zeta potential is not within the scope of the present application, at this time the content of functional monomer is low, the bonding force between negative electrode material layer and negative electrode current collector is small, the capacity retention rate of lithium ion battery after 800cls cycle at 25℃ is small, and the performance of lithium ion battery is poor; in comparative example 4, the zeta potential cannot be tested, at this time the content of hydrophilic monomer is less than the content of hydrophobic monomer, aqueous polymerization is difficult to occur, the negative electrode dispersant of the present application cannot be formed, and part of the monomer is precipitated, so the zeta potential test and the corresponding performance test cannot be performed; in comparative example 5, the zeta potential is not within the scope of the present application, at this time the content of functional monomer is low, the bonding force between negative electrode material layer and negative electrode current collector is small, the capacity retention rate of lithium ion battery after 800cls cycle at 25℃ is small, and the performance of lithium ion battery is poor The bonding force is small, the capacity retention rate of the lithium-ion battery after 800cls of 25°C cycling is small, and the performance of the lithium-ion battery is poor; the Zeta potential in Comparative Example 6 is not within the scope of this application. At this time, the content of the functional monomer is high, the content of the hydrophilic monomer and the hydrophobic monomer is relatively low, the bonding force between the negative electrode material layer and the negative electrode current collector is small, the capacity retention rate of the lithium-ion battery after 800cls of 25°C cycling is small, and the performance of the lithium-ion battery is poor; the carbon chain length of the hydrophobic monomer in Comparative Example 7 is not within the scope of this application. At this time, the sedimentation time of the slurry is short, the bonding force between the negative electrode material layer and the negative electrode current collector is small, and the performance of the lithium-ion battery is poor. The capacity retention rate after 800 cls of cycling at 25°C is low, and the performance of the lithium-ion battery is poor. Comparative Examples 8 to 10 use conventional negative electrode dispersants, and the Zeta potential is outside the scope of this application. In these cases, the slurry sedimentation time is short, the bonding force between the negative electrode material layer and the negative electrode current collector is small, the capacity retention rate after 800 cls of cycling at 25°C of the lithium-ion battery is low, and the performance of the lithium-ion battery is poor. Comparative Example 11 has a Zeta potential outside the scope of this application, the bonding force between the negative electrode material layer and the negative electrode current collector is small, the capacity retention rate after 800 cls of cycling at 25°C of the lithium-ion battery is low, and the performance of the lithium-ion battery is poor. This indicates that the negative electrode dispersants produced in the comparative examples have poor dispersibility and / or stability, and the corresponding lithium-ion batteries have low cycling performance and a short cycle life.

[0147] The type of hydrophobic monomer typically affects the dispersibility and stability of the negative electrode dispersant, which in turn affects the cycling performance of the lithium-ion battery. As can be seen from Examples 1, 11, and 22, when the type of hydrophobic monomer is within the scope of this application, the slurry has a longer settling time, the bonding force between the negative electrode material layer and the negative electrode current collector is greater, and the lithium-ion battery has a higher capacity retention rate after 800 cls cycling at 25°C. This indicates that the negative electrode dispersant of this application has good dispersibility and stability, which is beneficial to improving the cycling performance and cycle life of the lithium-ion battery.

[0148] The type of hydrophilic monomer typically affects the dispersibility and stability of the negative electrode dispersant, which in turn affects the cycling performance of the lithium-ion battery. As can be seen from Examples 1 and 24, when the type of hydrophilic monomer is within the scope of this application, the slurry sedimentation time is longer, the bonding force between the negative electrode material layer and the negative electrode current collector is stronger, and the lithium-ion battery's capacity retention rate after 800 cls cycling at 25°C is higher. This demonstrates that the negative electrode dispersant of this application has good dispersibility and stability, which is beneficial for improving the cycling performance and cycle life of lithium-ion batteries.

[0149] The type of functional monomer typically affects the dispersibility and stability of the negative electrode dispersant, which in turn affects the cycling performance of the lithium-ion battery. As can be seen from Examples 1 and 23, when the type of functional monomer is within the scope of this application, the slurry sedimentation time is longer, the bonding force between the negative electrode material layer and the negative electrode current collector is stronger, and the lithium-ion battery's capacity retention rate after 800 cls at 25°C is higher. This indicates that the negative electrode dispersant of this application has good dispersibility and stability, which is beneficial to improving the cycling performance and cycle life of lithium-ion batteries.

[0150] The values of x, y, and z typically affect the dispersibility and stability of the negative electrode dispersant, and thus the cycling performance of the lithium-ion battery. As can be seen from Examples 1 to 10 and Comparative Examples 1 to 6, when the values of x, y, and z are within the ranges of this application, the slurry has a longer settling time, the bonding force between the negative electrode material layer and the negative electrode current collector is greater, and the lithium-ion battery has a higher capacity retention rate after 800 cls cycling at 25°C. This indicates that the negative electrode dispersant of this application has good dispersibility and stability, which is beneficial to improving the cycling performance and cycle life of the lithium-ion battery.

[0151] The value of x / y typically affects the dispersibility and stability of the negative electrode dispersant, which in turn affects the cycling performance of the lithium-ion battery. As can be seen from Examples 1 to 10, when the value of x / y is within the range of this application, the slurry has a longer settling time, the bonding force between the negative electrode material layer and the negative electrode current collector is greater, and the lithium-ion battery has a higher capacity retention rate after 800 cls cycling at 25°C. This indicates that the negative electrode dispersant of this application has good dispersibility and stability, which is beneficial to improving the cycling performance and cycle life of the lithium-ion battery.

[0152] The pH of the negative electrode dispersant typically affects the dispersibility and stability of the negative electrode dispersant, which in turn affects the cycling performance of the lithium-ion battery. As can be seen from Examples 1 to 26, when the pH of the negative electrode dispersant is within the range of this application, the slurry sedimentation time is longer, the bonding force between the negative electrode material layer and the negative electrode current collector is greater, and the lithium-ion battery's capacity retention rate after 800 cls cycling at 25°C is higher. This indicates that the negative electrode dispersant of this application has good dispersibility and stability, which is beneficial to improving the cycling performance of the lithium-ion battery and increasing the cycle life.

[0153] The weight-average molecular weight of the polymer typically affects the dispersibility and stability of the negative electrode dispersant, which in turn affects the cycling performance of the lithium-ion battery. As can be seen from Examples 1 to 24, when the weight-average molecular weight of the polymer is within the range of this application, the slurry sedimentation time is longer, the bonding force between the negative electrode material layer and the negative electrode current collector is greater, and the lithium-ion battery's capacity retention rate after 800 cls at 25°C is higher. This indicates that the negative electrode dispersant of this application has good dispersibility and stability, which is beneficial to improving the cycling performance and cycle life of the lithium-ion battery.

[0154] The viscosity of the negative electrode dispersant at 25°C and 12 rpm typically affects the dispersibility and stability of the negative electrode dispersant, and thus affects the cycling performance of the lithium-ion battery. As can be seen from Examples 1 to 26, when the viscosity of the negative electrode dispersant at 25°C and 12 rpm is within the range of this application, the slurry sedimentation time is longer, the bonding force between the negative electrode material layer and the negative electrode current collector is greater, and the lithium-ion battery's 25°C cycle capacity retention rate for 800 cls is higher, indicating that the negative electrode dispersant of this application has good dispersibility and stability, which is beneficial to improving the cycling performance of the lithium-ion battery and increasing the cycle life.

[0155] The elastic modulus of the polymer film typically affects the dispersibility and stability of the negative electrode dispersant, which in turn affects the cycling performance of the lithium-ion battery. As can be seen from Examples 1 to 26, when the elastic modulus of the polymer film is within the range of this application, the slurry sedimentation time is longer, the adhesion between the negative electrode material layer and the negative electrode current collector is greater, and the lithium-ion battery's capacity retention rate after 800 cls cycling at 25°C is higher. This indicates that the negative electrode dispersant of this application has good dispersibility and stability, which is beneficial for improving the cycling performance and cycle life of lithium-ion batteries.

[0156] The degree of polymer swelling in the electrolyte typically affects the dispersibility and stability of the negative electrode dispersant, which in turn affects the cycling performance of the lithium-ion battery. As can be seen from Examples 1 to 26, when the degree of polymer swelling in the electrolyte is within the range of this application, the slurry sedimentation time is longer, the bonding force between the negative electrode material layer and the negative electrode current collector is greater, and the lithium-ion battery's capacity retention rate after 800 cls at 25°C is higher. This indicates that the negative electrode dispersant of this application has good dispersibility and stability, which is beneficial to improving the cycling performance and cycle life of the lithium-ion battery.

[0157] The difference in the zeta potential between the upper and lower slurries typically affects the dispersibility and stability of the negative electrode dispersant, and thus the cycling performance of the lithium-ion battery. As can be seen from Examples 1 to 26, when the difference in the zeta potential between the upper and lower slurries is within the range of this application, the slurry sedimentation time is longer, the bonding force between the negative electrode material layer and the negative electrode current collector is greater, and the lithium-ion battery's 25°C cycle capacity retention rate for 800 cls is higher, indicating that the negative electrode dispersant of this application has good dispersibility and stability, which is beneficial to improving the cycling performance of the lithium-ion battery and increasing the cycle life.

[0158] The difference between the Dv50 of the particles in the upper slurry layer and the Dv50 of the particles in the lower slurry layer usually affects the dispersibility and stability of the negative electrode dispersant, and thus affects the cycle performance of the lithium-ion battery. From Examples 1 to 26, it can be seen that when the difference between the Dv50 of the particles in the upper slurry layer and the Dv50 of the particles in the lower slurry layer is within the range of this application, the slurry sedimentation time is longer, the bonding force between the negative electrode material layer and the negative electrode current collector is greater, and the lithium-ion battery has a high capacity retention rate for 800 cls cycle at 25°C, indicating that the negative electrode dispersant of this application has good dispersibility and stability, which is conducive to improving the cycle performance of the lithium-ion battery and increasing the cycle life.

[0159] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0160] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0161] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A negative electrode dispersant comprising a polymer, using deionized water as a solvent, wherein the monomers forming the polymer include a hydrophobic monomer, a hydrophilic monomer and a functional monomer; wherein: The hydrophobic monomer includes a long carbon chain monomer of C4 to C21, the hydrophilic monomer includes an acrylic monomer, and the functional monomer includes at least one of acrylonitrile or acrylamide; The negative electrode dispersant has a zeta potential of -45 mV to -60 mV at 25° C. and a solid content of 2 wt % to 10 wt %.

2. The negative electrode dispersant according to claim 1, wherein The molecular formula of the polymer is (C N1 H N2 O N3 ) n1 (C3H3N) n2 (RC3H3O2) n3 (C3H5NO) n4 , R is selected from a hydrogen atom, a methyl group or an ethyl group, N1 is selected from a natural number within the range of 4 to 21, N2 is selected from a natural number within the range of 1 to 42, N3 is selected from a natural number within the range of 0 to 10, n1 is selected from a natural number within the range of 3000 to 20000, n3 is selected from a natural number within the range of 800 to 5000, n2 and n4 are each independently selected from a natural number within the range of 0 to 5000, and n2 and n4 are not 0 at the same time.

3. The negative electrode dispersant according to claim 1, wherein The C4 to C21 long carbon chain monomer includes at least one of ethers, esters or hydrocarbons containing unsaturated double bonds; and / or the acrylic monomer includes at least one of methacrylic acid, ethacrylic acid or acrylic acid.

4. The negative electrode dispersant according to claim 3, wherein Based on the mass of the hydrophobic monomer, the mass percentage of carbon element in the hydrophobic monomer is m, where m≥75%, and the hydrophobic monomer includes at least one of ethers or hydrocarbons containing unsaturated double bonds.

5. The negative electrode dispersant according to claim 1, wherein Based on the mass of the polymer in the negative electrode dispersant, the mass percentage of the hydrophilic monomer unit in the repeating unit of the polymer is x, the mass percentage of the hydrophobic monomer unit in the repeating unit of the polymer is y, and the mass percentage of the functional monomer in the repeating unit of the polymer is z, 10%≤x≤50%, 20%≤y≤60%, and 20%≤z≤60%. The negative electrode dispersant according to claim 5 , wherein 0.2≤x / y≤2.

5.

7. The negative electrode dispersant according to claim 1, satisfying at least one of the following characteristics: (1) The pH of the negative electrode dispersant is 6.0 to 8.0; (2) The weight average molecular weight of the polymer is Mw g / mol, 3×10 5 ≤Mw≤1.5×10 6 ; (3) The viscosity of the negative electrode dispersant at 25° C. and 12 rpm is η mPa·s, 30,000 ≤ η ≤ 100,000; (4) The elastic modulus of the polymer film is E GPa, 5≤E≤20; (5) The degree of swelling of the polymer in the electrolyte is c, 1%≤c≤10%.

8. The negative electrode dispersant according to claim 1, wherein The negative electrode dispersant is mixed with a negative electrode active material to obtain a first slurry having a solid content of 40 wt % to 50 wt %, wherein the mass ratio of the polymer to the negative electrode active material in the first slurry is 1.5:98.

5. The first slurry is allowed to stand for 5 to 14 days to obtain a second slurry. In the direction from the surface to the bottom of the second slurry, the upper slurry layer is from the surface of the second slurry to 1 / 4 of the total depth of the second slurry, and the lower slurry layer is from 3 / 4 of the total depth of the second slurry to the bottom of the second slurry, and at least one of the following characteristics is met: (1) The difference between the zeta potential of the upper slurry layer and the lower slurry layer is ≤±0.5 mV; (2) The difference between the Dv50 of the particles of the upper slurry layer and the Dv50 of the particles of the lower slurry layer is ≤0.5 μm.

9. A method for preparing the negative electrode dispersant according to any one of claims 1 to 8, comprising the following steps: (1) taking 900 to 4900 parts of deionized water as a solvent, adding a chain transfer agent and an initiator to the solvent to obtain a mixture; wherein the chain transfer agent includes at least one of n-dodecyl mercaptan, secondary dodecyl mercaptan, tert-dodecyl mercaptan, mercaptoethanol or thioglycolic acid, and the amount of the chain transfer agent added is 0.2 to 0.8 parts; the initiator includes at least one of potassium persulfate, sodium persulfate, ammonium persulfate, azobisisobutyronitrile or azobisisoheptonitrile, and the amount of the initiator added is 0.5 to 1 parts; (2) adding the hydrophobic monomer, the hydrophilic monomer and the functional monomer to the mixture, wherein the mass fraction of the hydrophilic monomer is 10 to 50 parts, the mass fraction of the hydrophobic monomer is 20 to 60 parts, the mass fraction of the functional monomer is 20 to 60 parts, and the mass fraction of the hydrophobic monomer, the hydrophilic monomer and the functional monomer is 100 parts; continuing to heat to 60° C. to 80° C., keeping the temperature for 2 to 10 hours; then performing reduced pressure distillation for 4 to 8 hours to obtain a polymer solution; (3) adding a base to the polymer solution, wherein the base includes at least one of lithium hydroxide, sodium hydroxide or potassium hydroxide, and the mass ratio of the base to the non-volatile solid in the polymer solution is a, 1 / 8≤a≤1 / 4, and mixing to obtain the negative electrode dispersant.

10. A secondary battery comprising a positive electrode plate, a separator, an electrolyte and a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, wherein the negative electrode material layer comprises a polymer, and monomers forming the polymer comprise a hydrophobic monomer, a hydrophilic monomer and a functional monomer, wherein the hydrophobic monomer comprises a long carbon chain monomer of C4 to C21, the hydrophilic monomer comprises an acrylic monomer, and the functional monomer comprises at least one of acrylonitrile or acrylamide; or, a negative electrode dispersant prepared by the preparation method according to claim 9.

11. The secondary battery according to claim 10, wherein The molecular formula of the polymer is (C N1 H N2 O N3 ) n1 (C3H3N) n2 (RC3H3O2) n3 (C3H5NO) n4 , R is selected from a hydrogen atom, a methyl group or an ethyl group, N1 is selected from a natural number within the range of 4 to 21, N2 is selected from a natural number within the range of 1 to 42, N3 is selected from a natural number within the range of 0 to 10, n1 is selected from a natural number within the range of 3000 to 20000, n3 is selected from a natural number within the range of 800 to 5000, n2 and n4 are each independently selected from a natural number within the range of 0 to 5000, and n2 and n4 are not 0 at the same time. 12 . An electronic device comprising the secondary battery according to claim 10 .

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