Dispersing agent for lithium ion battery as well as preparation method and application of dispersing agent

Abstract

The invention discloses a dispersing agent for a lithium ion battery as well as a preparation method and application of the dispersing agent. The dispersing agent for the lithium ion battery has a molecular structural formula as shown in a formula (1). According to the dispersing agent, particle aggregation is prevented through double electric layer repulsion and steric hindrance effects, so that the viscosity of slurry is reduced, and meanwhile, the high-solid-content slurry still has good flowability and slurry stability. When the dispersing agent is applied to the lithium ion battery, the side reaction of active particles and electrolyte can be reduced, the resistance of a pole piece is reduced, and the migration efficiency of lithium ions is improved. Meanwhile, the dispersing agent prolongs the cycle life by inhibiting electrode polarization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, and relates to a dispersant for lithium ion batteries and a preparation method and application thereof. BACKGROUND

[0002] Since the 1990s, the research and production of lithium ion batteries have made great progress, and the application in various fields is also more and more extensive, especially in the field of new energy vehicles, the market demand for lithium batteries grows rapidly. However, compared with other devices, new energy vehicles have higher requirements for the energy density and cycle life of lithium batteries.

[0003] When the lithium ion battery positive electrode is formed, the positive electrode slurry (such as lithium manganese iron phosphate slurry) needs to be coated on the current collector (such as aluminum foil), so the properties of the positive electrode slurry are directly related to the coating effect of the positive electrode.

[0004] At present, most lithium ion battery positive electrode slurries are mainly composed of positive electrode powder, conductive agent, binder and solvent, but there are still some problems in the production process. For example, the lithium ion battery positive active material lithium manganese iron phosphate and the conductive agent are not well dispersed in NMP, the positive electrode slurry has too high viscosity and is easy to form a gel, and the slurry stability is poor and is easy to agglomerate and precipitate. This causes the problem of surface cracking and powder falling of the pole piece after the positive electrode slurry is coated on the current collector. Therefore, in order to reduce the viscosity of the slurry, the solid content of the slurry is reduced, which corresponds to an increase in the amount of solvent (NMP) used in the production process of the slurry, and NMP as a valuable solvent leads to an increase in production cost and subsequent use and recovery cost, and at the same time, the reduction of the solid content of the electrode active material also affects the performance of the positive electrode.

[0005] Therefore, it is a technical problem to be solved at present to develop a dispersant for lithium ion batteries, so that the positive electrode slurry has good dispersibility and appropriate viscosity at a high solid content, thereby improving the coating effect of the pole piece. SUMMARY

[0006] In view of the above technical problems in the prior art, the present application aims to provide a dispersant for lithium ion batteries and a preparation method and application thereof.

[0007] To achieve the above purpose, the present application adopts the following technical solutions:

[0008] In a first aspect, the present application provides a dispersant for lithium ion batteries, which has a molecular structure formula shown in formula (1),

[0009] Formula (1);

[0010] Wherein, 20≤x≤30, 30≤y≤50, 5≤z≤15, 5≤n≤15, and 10≤m≤20.

[0011] In a second aspect, the present invention provides a method for preparing a dispersant for lithium-ion batteries as described in the first aspect, the method comprising the following steps:

[0012] 1) Acrylic acid monomer, acrylamide monomer, and maleic anhydride monomer undergo a first reaction under the action of a first initiator to generate a prepolymer;

[0013] 2) Add styrene monomer and sodium styrene sulfonate monomer to the prepolymer, and after a second reaction under the action of a second initiator, a dispersant for lithium-ion batteries is obtained.

[0014] Preferably, in step 1), by weight, the acrylic monomer is 20 to 30 parts, the acrylamide monomer is 30 to 50 parts, and the maleic anhydride monomer is 5 to 15 parts.

[0015] Preferably, the mass fraction of the first initiator is 0.8% to 1.2% based on the total mass of acrylic acid monomer, acrylamide monomer and maleic anhydride monomer.

[0016] Preferably, in step 2), the amount of styrene monomer is 5 to 15 parts by weight, and the amount of sodium styrene sulfonate monomer is 10 to 20 parts by weight.

[0017] Preferably, the mass fraction of the second initiator is 0.4% to 0.6% based on the total mass of styrene monomer and sodium styrene sulfonate monomer.

[0018] Preferably, the preparation method further includes adjusting the pH to 7-9 after the second reaction.

[0019] Thirdly, the present invention provides a method for preparing an electrode slurry, the method comprising the following steps: mixing electrode material, binder, conductive agent, additive and solvent to obtain an electrode slurry;

[0020] The additive is a dispersant prepared by the method described in the first aspect or the method described in the second aspect.

[0021] Preferably, the content of the additive is 0.1% to 0.3% based on the total mass of the electrode material, binder and conductive agent.

[0022] Fourthly, the present invention provides an electrode paste, which is prepared by the method of the third aspect.

[0023] Fifthly, the present invention provides an electrode obtained by coating the electrode slurry of the fourth aspect onto the surface of a current collector and drying it.

[0024] In a sixth aspect, the present invention provides a lithium-ion battery, which includes the electrodes of the fifth aspect.

[0025] Compared with existing technologies, the present invention has the following beneficial effects:

[0026] (1) Active particles and conductive agents in electrode slurry are prone to agglomeration, which leads to an increase in the viscosity of the electrode slurry. The dispersant of the present invention prevents particle agglomeration through double-layer repulsion and steric hindrance, thereby reducing the viscosity of the slurry and ensuring that the high solids content slurry still has good fluidity and stability.

[0027] (2) The dispersant of the present invention can promote the uniform distribution of the binder in the slurry, thereby improving the adhesion and interfacial stability of the electrode. Under fast charging conditions, the dispersant can prevent lithium plating on the negative electrode and maintain the integrity of the interface.

[0028] (3) When the dispersant of the present invention is applied to lithium-ion batteries, it can reduce the side reactions between active particles and electrolyte, reduce electrode resistance, and improve lithium-ion migration efficiency. At the same time, the dispersant improves cycle life by suppressing electrode polarization. Detailed Implementation

[0029] Reference will now be made to detailed embodiments of this application, one or more of which are described below. Each example is provided for explanation and not for limitation of this application. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to this application without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0030] Therefore, this application is intended to cover such modifications and variations falling within the scope of the appended claims and their equivalents. Other objects, features, and aspects of this application are disclosed in or will be apparent from the following detailed description. It will be understood by those skilled in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of this application.

[0031] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0032] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0033] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0034] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0035] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0036] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0037] In a first aspect, the present invention provides a dispersant for lithium-ion batteries, the dispersant having the molecular structure shown in formula (1).

[0038] Equation (1);

[0039] Wherein, 20≤x≤30, 30≤y≤50, 5≤z≤15, 5≤n≤15, and 10≤m≤20.

[0040] In some implementations, x can be, for example, but not limited to, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30; y can be, for example, but not limited to, 32, 34, 36, 38, 40, 42, 45, 47, 48, 50; z can be, for example, but not limited to, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15; n can be, for example, but not limited to, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15; m can be, for example, but not limited to, 10, 12, 13, 14, 15, 16, 18, 20.

[0041] Active particles and conductive agents in electrode slurries are prone to agglomeration, leading to increased viscosity. The dispersant of this invention effectively solves this problem. Its technical principle is as follows: The dispersant of this invention is an acrylic-based multi-component copolymer with a unique polymer backbone and nanoscale size. When used in electrode slurries, it tightly adsorbs onto the surface of active particles (e.g., the carbon layer on the outside of lithium manganese iron phosphate) through anchoring groups, generating a sufficiently thick adsorption layer. Hydrophilic groups form solvation chains and extend into the solvent phase, thereby forming a protective barrier around the particles. Electrostatic repulsion occurs between the particles, ensuring effective dispersion, and the active particles are stabilized by the steric hindrance of the macromolecules. Therefore, the dispersant prevents particle aggregation through double-layer repulsion and steric hindrance effects, reducing slurry viscosity while maintaining good flowability and stability even in high-solids-content slurries.

[0042] The dispersant of the present invention can solve the problems of poor solid dispersion, low solid content, and high viscosity of existing lithium-ion battery electrode slurries, which easily lead to gelation.

[0043] The dispersant of this invention can improve the dispersion performance of positive or negative electrode slurries, obtain suitable solid content and slurry viscosity, and ensure good coating effect. Furthermore, this dispersant has a better improving effect on positive electrode slurries, especially lithium manganese iron phosphate positive electrode slurries.

[0044] In a second aspect, the present invention provides a method for preparing a dispersant for lithium-ion batteries as described in the first aspect, the method comprising the following steps:

[0045] 1) Acrylic acid monomer, acrylamide monomer, and maleic anhydride monomer undergo a first reaction under the action of a first initiator to generate a prepolymer;

[0046] 2) Add styrene monomer and sodium styrene sulfonate monomer to the prepolymer, and after a second reaction under the action of a second initiator, a dispersant for lithium-ion batteries is obtained.

[0047] In the preparation method of this invention, the SO3 in the sodium styrene sulfonate monomer ⁻The ionization of the functional groups provides strong electrostatic repulsion, enhancing the stability of the dispersant, while the hydrophobic monomers of styrene provide steric hindrance.

[0048] In the preparation method of the present invention, a second initiator (e.g., ammonium persulfate) is added in step 2) to maintain the free radical concentration.

[0049] The preparation method of this invention is simple, easy to operate, and suitable for industrial production.

[0050] In some embodiments, by weight, in step 1), the acrylic monomer is 20 to 30 parts, for example, but not limited to 20, 22, 24, 25, 26, 28, or 30 parts; the acrylamide monomer is 30 to 50 parts, for example, but not limited to 30, 32, 33, 35, 36, 38, 39, 40, 42, 44, 46, 48, or 50 parts; and the maleic anhydride monomer is 5 to 15 parts, for example, but not limited to 5, 6, 8, 10, 12, 13, or 15 parts.

[0051] In some embodiments, the present invention does not specifically limit the type of the first initiator, including but not limited to at least one of ammonium persulfate, sodium bisulfite (NaHSO3) and azobisisobutyronitrile (AIBN), with ammonium persulfate being preferred because it is low in cost and has few side reactions.

[0052] Taking ammonium persulfate as an example, the reaction process is explained as follows: Ammonium persulfate decomposes upon heating to generate sulfate free radicals, which attack the double bonds of acrylic acid, acrylamide, and maleic anhydride, initiating chain growth. At a certain temperature (e.g., 60℃~80℃), the anhydride group of maleic anhydride partially hydrolyzes into a carboxyl group, which condenses with the amino group of acrylamide to form an amide bond, constituting a mildly cross-linked network. The carboxyl group of acrylic acid undergoes an esterification reaction with the hydrolysis products of maleic anhydride, increasing the density of cross-linking points.

[0053] In some embodiments, the mass fraction of the first initiator is 0.8% to 1.2% based on the total mass of acrylic acid monomer, acrylamide monomer and maleic anhydride monomer, for example, but not limited to 0.8%, 0.85%, 0.9%, 0.95%, 1%, 1.05%, 1.1%, 1.15% and 1.2%.

[0054] In some embodiments, the temperature of the first reaction is 60°C to 80°C, for example, but not limited to 60°C, 65°C, 70°C, 75°C, and 80°C; the time of the first reaction is 1h to 2h, for example, but not limited to 1h, 1.2h, 1.3h, 1.5h, 1.8h, and 2h.

[0055] In some embodiments, in step 2), by weight, the styrene monomer is 5 to 15 parts (e.g., but not limited to 5, 6, 8, 10, 12, 13, or 15 parts); the sodium styrene sulfonate monomer is 10 to 20 parts (e.g., but not limited to 10, 12, 14, 15, 16, 18, or 20 parts).

[0056] In some embodiments, the present invention does not specifically limit the type of the second initiator, including but not limited to at least one of ammonium persulfate, sodium bisulfite and azobisisobutyronitrile, with ammonium persulfate preferred because it is low in cost and has few side reactions.

[0057] In some embodiments, the mass fraction of the second initiator is 0.4% to 0.6% based on the total mass of styrene monomer and sodium styrene sulfonate monomer, for example, but not limited to 0.4%, 0.45%, 0.5%, 0.55%, and 0.6%.

[0058] In some embodiments, the temperature of the second reaction is 60°C to 80°C, for example, but not limited to 60°C, 65°C, 70°C, 75°C, and 80°C; the time of the first reaction is 2h to 4h, for example, but not limited to 2h, 2.2h, 2.3h, 2.5h, 2.8h, 3h, 3.3h, 3.6h, 3.8h, and 4h.

[0059] In some embodiments, the preparation method further includes adjusting the pH to 7-9 after the second reaction, for example, but not limited to 7, 7.2, 7.4, 7.6, 7.8, 8, 8.3, 8.5, 8.7, 8.8, and 9. If the pH is too low, the reaction may be incomplete, resulting in more byproducts, such as unreacted sulfonating agent (i.e., sodium styrene sulfonate monomer) residue, affecting product purity. If the pH is too high, it may cause hydrolysis of sulfonic acid groups, generating other byproducts, which will reduce sulfonation efficiency.

[0060] Thirdly, the present invention provides a method for preparing an electrode slurry, the method comprising the following steps: mixing electrode material, binder, conductive agent, additive and solvent to obtain an electrode slurry;

[0061] The additive is a dispersant prepared by the method described in the first aspect or the method described in the second aspect.

[0062] In some embodiments, the electrode material is a positive electrode active material, which includes compounds that can reversibly insert and deintercalate lithium ions.

[0063] In some embodiments, the positive electrode active material comprises one or more transition metal cations, such as manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof.

[0064] In some embodiments, the positive electrode active material is one of layered oxides, spinel, and polyanionic materials. For example, layered oxides (e.g., rock salt layered oxides) comprise one or more lithium-based positive electrode active materials selected from: LiCoO2 (LCO), LiNi x Mn y Co 1-x-y O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi 1-x-y Co x Al y O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi x Mn 1-x O2 (where 0 ≤ x ≤ 1), and Li 1+x MO2 (where M is one of Mn, Ni, Co, and Al and 0 ≤ x ≤ 1). Spinel contains one or more lithium-based cathode active materials selected from the following: LiMn2O4 (LMO) and LiNi. x Mn 1.5 O4. The olivine type comprises one or more lithium-based cathode active materials, LiMPO4 (where M is at least one of Fe, Ni, Co, and Mn). The polyanionic cation comprises, for example, phosphates such as LiV2(PO4). 24 And / or silicates such as LiFeSiO4.

[0065] In some embodiments, the binder enhances the bonding between the positive electrode active material particles.

[0066] In some embodiments, non-limiting examples of adhesives include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0067] In some embodiments, the conductive agent may include any conductive material, as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powders, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0068] In some embodiments, the content of the additive is 0.1% to 0.3% based on the total mass of the electrode material, binder and conductive agent, for example, but not limited to 0.1%, 0.15%, 0.2%, 0.25% and 0.3%.

[0069] Fourthly, the present invention provides an electrode paste, which is prepared by the method of the third aspect.

[0070] Fifthly, the present invention provides an electrode obtained by coating the electrode slurry of the fourth aspect onto the surface of a current collector and drying it.

[0071] In some embodiments, the electrode is a positive electrode sheet, including a positive current collector. Exemplarily, the positive current collector may be aluminum (Al), but is not limited thereto.

[0072] The dispersant of this invention promotes the uniform distribution of the binder in the slurry, thereby improving the electrode adhesion and interfacial stability. Under fast charging conditions, the dispersant can prevent lithium plating on the negative electrode and maintain interfacial integrity.

[0073] In a sixth aspect, the present invention provides a lithium-ion battery, which includes the electrodes of the fifth aspect.

[0074] The lithium-ion battery of the present invention employs an electrode of the fifth aspect. Because the electrode slurry used to prepare this electrode contains the dispersant of the first aspect, side reactions between the active particles and the electrolyte can be reduced, electrode resistance can be lowered, and lithium-ion migration efficiency can be improved. Simultaneously, the dispersant improves cycle life by suppressing electrode polarization.

[0075] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0076] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0077] In the following examples, "parts" refers to parts by mass.

[0078] Example 1

[0079] I. Preparation of Dispersants for Lithium-ion Batteries

[0080] The preparation method of the dispersant for lithium-ion batteries in this embodiment includes the following steps:

[0081] 1) Mix 25 parts of acrylic acid monomer, 40 parts of acrylamide monomer, 10 parts of maleic anhydride monomer with ammonium persulfate (the amount of initiator is 0.85% of the total mass of monomers used in step 1) and react at 70°C for 1.5 hours to generate a prepolymer (abbreviated as AA-AM-MAH).

[0082] 2) Add 10 parts of hydrophobic styrene monomer, 15 parts of sodium styrene sulfonate monomer, and 0.5% of the total mass of monomers used in step 2 as initiator to the above prepolymer and keep it at the temperature for 3 hours. Finally, adjust the pH to 8 with 40% NaOH solution to obtain the dispersant (abbreviated as AA-AM-MAH-St-SSS).

[0083] This embodiment provides a dispersant for lithium-ion batteries, which has the molecular structure shown in formula (1).

[0084] Equation (1);

[0085] Where x=25, y=40, z=10, n=10, m=15.

[0086] II. Preparation of Lithium-ion Batteries

[0087] The method for preparing lithium-ion batteries includes the following steps:

[0088] (1) Preparation of positive electrode slurry: Lithium manganese iron phosphate (LMFP), binder PVDF, conductive agent SP and dispersant are dispersed in solvent NMP and mixed evenly to obtain positive electrode slurry. Among them, based on the total mass of LMFP, PVDF and SP as 100%, the percentage contents of LMFP, PVDF and SP are 96.5%, 2% and 1.5% respectively, and the percentage contents of dispersant in the total mass of LMFP, PVDF and SP are 0.2%.

[0089] (2) Preparation of positive electrode sheet: The above positive electrode slurry is coated onto the surface of aluminum foil with a coating thickness of 150 μm and a roller compaction density of 2.3 g / cm³.

[0090] (3) Preparation of negative electrode sheet: Graphite, binder (SBR) and conductive agent SP are mixed evenly in solvent water to obtain negative electrode slurry. The negative electrode slurry is coated onto the surface of copper foil with a coating thickness of 93 μm and a roller compaction density of 1.6 g / cm³.

[0091] The prepared positive and negative electrode sheets are stacked with a polyethylene (PE) separator to form a stacked body. The separator is located between the positive and negative electrode sheets to isolate them. There are 29 positive electrode sheets. The stacked body is placed in an aluminum-plastic film for encapsulation. Finally, an electrolyte (1 mol / L LiPF6 dissolved in a mixed solvent of EC, DEC and EMC to form an electrolyte, EC:DEC:EMC = 1:1:1 (volume ratio)) is added to form a soft-pack battery.

[0092] Example 2

[0093] This embodiment provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Example 1 is that the amount of acrylic acid monomer is 20 parts, the amount of acrylamide monomer is 40 parts, the amount of maleic anhydride monomer is 10 parts, the amount of styrene monomer is 10 parts, and the amount of sodium styrene sulfonate monomer is 15 parts.

[0094] The dispersant in this embodiment has the molecular structure shown in formula (1).

[0095] Equation (1);

[0096] Where x=20, y=40, z=10, n=10, m=15.

[0097] Example 3

[0098] This embodiment provides a dispersant for lithium-ion batteries. The preparation method of the lithium-ion battery differs from that of Example 1 in that the amount of acrylic acid monomer is 30 parts, the amount of acrylamide monomer is 40 parts, the amount of maleic anhydride monomer is 10 parts, the amount of styrene monomer is 10 parts, and the amount of sodium styrene sulfonate monomer is 15 parts.

[0099] The dispersant in this embodiment has the molecular structure shown in formula (1).

[0100] Equation (1);

[0101] Where x=30, y=40, z=10, n=10, m=15.

[0102] Example 4

[0103] This embodiment provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Example 1 is that the amount of acrylic acid monomer is 25 parts, the amount of acrylamide monomer is 40 parts, the amount of maleic anhydride monomer is 5 parts, the amount of styrene monomer is 10 parts, and the amount of sodium styrene sulfonate monomer is 15 parts.

[0104] The dispersant in this embodiment has the molecular structure shown in formula (1).

[0105] Equation (1);

[0106] Where x=25, y=40, z=5, n=10, m=15.

[0107] Example 5

[0108] This embodiment provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Example 1 is that the amount of acrylic acid monomer is 25 parts, the amount of acrylamide monomer is 40 parts, the amount of maleic anhydride monomer is 15 parts, the amount of styrene monomer is 10 parts, and the amount of sodium styrene sulfonate monomer is 15 parts.

[0109] The dispersant in this embodiment has the molecular structure shown in formula (1).

[0110] Equation (1);

[0111] Where x=25, y=40, z=15, n=10, m=15.

[0112] Example 6

[0113] This embodiment provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Example 1 is that the amount of acrylic acid monomer is 25 parts, the amount of acrylamide monomer is 40 parts, the amount of maleic anhydride monomer is 10 parts, the amount of styrene monomer is 5 parts, and the amount of sodium styrene sulfonate monomer is 15 parts.

[0114] The dispersant in this embodiment has the molecular structure shown in formula (1).

[0115] Equation (1);

[0116] Where x=25, y=40, z=10, n=5, m=15.

[0117] Example 7

[0118] This embodiment provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Example 1 is that the amount of acrylic acid monomer is 25 parts, the amount of acrylamide monomer is 40 parts, the amount of maleic anhydride monomer is 10 parts, the amount of styrene monomer is 15 parts, and the amount of sodium styrene sulfonate monomer is 15 parts.

[0119] The dispersant in this embodiment has the molecular structure shown in formula (1).

[0120] Equation (1);

[0121] Where x=25, y=40, z=10, n=15, m=15.

[0122] Example 8

[0123] This embodiment provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Example 1 is that the pH value is adjusted to 7.

[0124] Example 9

[0125] This embodiment provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Embodiment 1 is that in step 2), the pH value is adjusted to 6.

[0126] Example 10

[0127] This embodiment provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Embodiment 1 is that in step 2), the pH value is adjusted to 10.

[0128] Example 11

[0129] This embodiment provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between the preparation method and that of Embodiment 1 is that when the dispersant is applied to the lithium-ion battery, the percentage content of the dispersant in the total mass of LMFP, PVDF and SP is 0.1%.

[0130] Example 12

[0131] This embodiment provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between the preparation method and that of Embodiment 1 is that when the dispersant is applied to the lithium-ion battery, the percentage content of the dispersant in the total mass of LMFP, PVDF and SP is 0.3%.

[0132] Example 13

[0133] This embodiment provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between the preparation method and that of Embodiment 1 is that when the dispersant is applied to the lithium-ion battery, the percentage content of the dispersant in the total mass of LMFP, PVDF and SP is 0.05%.

[0134] Example 14

[0135] This embodiment provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between the preparation method and that of Embodiment 1 is that when the dispersant is applied to the lithium-ion battery, the percentage content of the dispersant in the total mass of LMFP, PVDF and SP is 0.4%.

[0136] Comparative Example 1

[0137] This comparative example provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Example 1 is that the amount of acrylic acid monomer is 15 parts, the amount of acrylamide monomer is 40 parts, the amount of maleic anhydride monomer is 10 parts, the amount of styrene monomer is 10 parts, and the amount of sodium styrene sulfonate monomer is 15 parts.

[0138] The dispersant in this comparative example has the molecular structure shown in formula (1).

[0139] Equation (1);

[0140] Where x=15, y=40, z=10, n=10, m=15.

[0141] Comparative Example 2

[0142] This comparative example provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Example 1 is that the amount of acrylic acid monomer is 35 parts, the amount of acrylamide monomer is 40 parts, the amount of maleic anhydride monomer is 10 parts, the amount of styrene monomer is 10 parts, and the amount of sodium styrene sulfonate monomer is 15 parts.

[0143] The dispersant in this comparative example has the molecular structure shown in formula (1).

[0144] Equation (1);

[0145] Where x=35, y=40, z=10, n=10, m=15.

[0146] Comparative Example 3

[0147] This comparative example provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Example 1 is that the amount of acrylic acid monomer is 25 parts, the amount of acrylamide monomer is 40 parts, the amount of maleic anhydride monomer is 0 parts, the amount of styrene monomer is 10 parts, and the amount of sodium styrene sulfonate monomer is 15 parts.

[0148] The dispersant in this comparative example has the molecular structure shown in formula (1).

[0149] Equation (1);

[0150] Where x=25, y=40, z=0, n=10, m=15.

[0151] Comparative Example 4

[0152] This comparative example provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Example 1 is that the amount of acrylic acid monomer is 25 parts, the amount of acrylamide monomer is 40 parts, the amount of maleic anhydride monomer is 20 parts, the amount of styrene monomer is 10 parts, and the amount of sodium styrene sulfonate monomer is 15 parts.

[0153] The dispersant in this comparative example has the molecular structure shown in formula (1).

[0154] Equation (1);

[0155] Where x=25, y=40, z=20, n=10, m=15.

[0156] Comparative Example 5

[0157] This comparative example provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Example 1 is that the amount of acrylic acid monomer is 25 parts, the amount of acrylamide monomer is 40 parts, the amount of maleic anhydride monomer is 10 parts, the amount of styrene monomer is 0 parts, and the amount of sodium styrene sulfonate monomer is 15 parts.

[0158] The dispersant in this comparative example has the molecular structure shown in formula (1).

[0159] Equation (1);

[0160] Where x=25, y=40, z=10, n=0, m=15.

[0161] Comparative Example 6

[0162] This comparative example provides a dispersant for lithium-ion batteries and a lithium-ion battery. The difference between its preparation method and that of Example 1 is that the amount of acrylic acid monomer is 25 parts, the amount of acrylamide monomer is 40 parts, the amount of maleic anhydride monomer is 10 parts, the amount of styrene monomer is 20 parts, and the amount of sodium styrene sulfonate monomer is 15 parts.

[0163] The dispersant in this comparative example has the molecular structure shown in formula (1).

[0164] Equation (1);

[0165] Where x=25, y=40, z=10, n=20, m=15.

[0166] Comparative Example 7

[0167] This comparative example provides a lithium-ion battery whose preparation method differs from that of Example 1 in that no dispersant is added.

[0168] The following table shows the calculation method for the solid content of the positive electrode slurry:

[0169] Solid content = (Total mass of all solid substances / Total mass of slurry) × 100%;

[0170] The total mass of all solid substances consists of the mass of the positive electrode active material, binder, conductive agent and dispersant, and the total mass of the slurry is the sum of the mass of all solid substances and the mass of the solvent.

[0171] Viscosity tests were conducted on the positive electrode slurries used in the preparation of lithium-ion batteries in Examples 1-14 and Comparative Examples 1-7. The test method was as follows: a rotational viscometer was used, a sample volume (20 mL) was taken, and the viscosity change over 120 seconds was recorded, with the average value taken. The initial viscosity and the viscosity after 24 hours of storage were obtained, and the viscosity change rate was calculated based on these two data. The calculation formula was: Viscosity change rate = (Viscosity after 24 hours of storage - Initial viscosity) / Initial viscosity × 100%. The smaller the viscosity change rate, the better the stability of the slurry. The results are shown in Table 1.

[0172] The lithium-ion batteries prepared in Examples 1-14 and Comparative Examples 1-7 were subjected to cycle performance tests. The test method was as follows: under an ambient temperature of 25±2℃, the batteries were charged at a constant current and constant voltage of 0.33C to the upper limit voltage of 4.4V, and the cutoff current was set to 0.05C; the batteries were then allowed to stand for 30 minutes; followed by a constant current discharge of 1C to 2.5V; and then allowed to stand for 30 minutes. The charge-discharge cycle was repeated 500 times, and the discharge capacity of each cycle was recorded. The 500-cycle capacity retention rate was calculated based on the initial discharge capacity and the discharge capacity of the first 500 cycles. The calculation formula was: 500-cycle capacity retention rate = 500-cycle discharge capacity / initial discharge capacity × 100%. The results are shown in Table 1.

[0173]

[0174] As shown in Table 1, the dispersant of the present invention can reduce the viscosity of the slurry while maintaining good flowability and stability in slurries with high solid content (49%~65%). The application of the dispersant of the present invention in lithium-ion batteries can improve the cycle performance of lithium-ion batteries.

[0175] The dispersants in Comparative Examples 1 to 6 do not satisfy the molecular structure shown in Formula (1), resulting in the inability to achieve both low viscosity and good slurry stability. Furthermore, their cycle performance after application in lithium-ion batteries is poor.

[0176] Equation (1);

[0177] Wherein, 20≤x≤30, 30≤y≤50, 5≤z≤15, 5≤n≤15, and 10≤m≤20.

[0178] Meanwhile, comparing Example 1 with Examples 9-10, after heat preservation in step 2), a pH less than 7 will lead to poor dispersant stability; a pH greater than 9 will lead to poor storage stability of the dispersant and insensitivity to high-valence metal ions.

[0179] Comparing Example 1 with Examples 11-14, the percentage content of dispersant in the positive electrode slurry is preferably in the range of 0.1% to 0.3%. If the dispersant addition ratio is too small, it will lead to an increase in slurry viscosity and particle agglomeration after storage, which will cause uneven coating and discontinuity of the conductive network, resulting in a decrease in the cycle performance of the battery. If the dispersant addition ratio is too large, it will lead to excessive dissociation of the conductive network and an increase in interfacial impedance. At the same time, it will also exacerbate the risk of slurry gelation, resulting in an increase in slurry viscosity after storage and a decrease in the cycle performance of the battery.

[0180] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A dispersant for lithium-ion batteries, characterized in that, The dispersant for lithium-ion batteries has the molecular structure shown in formula (1). Equation (1); Wherein, 20≤x≤30, 30≤y≤50, 5≤z≤15, 5≤n≤15, and 10≤m≤20.

2. A method for preparing a dispersant for lithium-ion batteries as described in claim 1, characterized in that, The preparation method includes the following steps: 1) Acrylic acid monomer, acrylamide monomer, and maleic anhydride monomer undergo a first reaction under the action of a first initiator to generate a prepolymer; 2) Styrene monomer and sodium styrene sulfonate monomer are added to the prepolymer, and a second reaction is carried out under the action of a second initiator to obtain the dispersant for lithium-ion batteries.

3. The method for preparing a dispersant for lithium-ion batteries according to claim 2, characterized in that, In step 1), by weight, the acrylic monomer is 20 to 30 parts, the acrylamide monomer is 30 to 50 parts, and the maleic anhydride monomer is 5 to 15 parts. Preferably, the mass fraction of the first initiator is 0.8% to 1.2% based on the total mass of the acrylic acid monomer, the acrylamide monomer, and the maleic anhydride monomer.

4. The method for preparing a dispersant for lithium-ion batteries according to any one of claims 1-3, characterized in that, In step 2), by weight, the styrene monomer is 5 to 15 parts and the sodium styrene sulfonate monomer is 10 to 20 parts; Preferably, the mass fraction of the second initiator is 0.4% to 0.6% based on the total mass of the styrene monomer and the sodium styrene sulfonate monomer.

5. The method for preparing a dispersant for lithium-ion batteries according to any one of claims 1-4, characterized in that, The preparation method further includes adjusting the pH to 7-9 after the second reaction.

6. A method for preparing an electrode paste, characterized in that, The preparation method includes the following steps: mixing electrode material, binder, conductive agent, additive and solvent to obtain electrode slurry; The additive is a dispersant prepared by the method described in claim 1 or any one of claims 2-5.

7. The preparation method according to claim 6, characterized in that, Based on the total mass of the electrode material, binder, and conductive agent, the content of the additive is 0.1% to 0.3%.

8. An electrode paste, characterized in that, The electrode paste is prepared by the method described in claim 6 or 7.

9. An electrode, characterized in that, The electrode is obtained by coating the current collector surface with the electrode slurry as described in claim 8 and then drying it.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrode as described in claim 9.

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