Dispersing agent, preparation method thereof and secondary battery

Abstract

The invention discloses a dispersing agent, a preparation method thereof and a secondary battery, the molecular structure of the dispersing agent is a three-dimensional network structure, the dispersing agent comprises a melamine unit and a functional unit, and the functional unit has amino and phenolic hydroxyl. The dispersing agent provided by the invention has a three-dimensional network structure and can form a more uniform dispersion system, agglomeration and sedimentation phenomena are avoided, the three-dimensional network structure can provide enough mechanical support, so that the dispersing agent can keep a stable dispersion state in electrode slurry, and amino and phenolic hydroxyl groups can be used as anchoring groups, so that the dispersing agent is more uniform in dispersion. And the anchoring group has adsorption sites and can be used for adsorbing an electrode material to improve the dispersity.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode materials, and particularly relates to a dispersant, a preparation method thereof, and a secondary battery. Background Art

[0002] With the rapid development of new energy industries such as electric vehicles and energy storage devices, the demand for high-performance lithium-ion batteries is increasing day by day. The dispersibility of the cathode slurry is one of the key factors affecting the battery performance. Good dispersibility can ensure the uniform distribution of the cathode active material in the slurry, thereby improving the consistency and efficiency of the battery. However, traditional cathode dispersants often have problems such as poor dispersion effect and poor stability, and it is difficult to meet the production requirements of high-performance lithium-ion batteries. At present, there are various types of cathode dispersants on the market, but most of them have deficiencies in terms of dispersion effect and stability. Therefore, it is particularly important to provide a cathode dispersant with good dispersibility and stability. Summary of the Invention

[0003] The purpose of the present invention is to provide a dispersant, a preparation method thereof, and a secondary battery, so as to solve the problems of poor dispersibility and stability of the existing dispersants.

[0004] To achieve the purpose of the present invention, the following technical solutions are provided by the present invention:

[0005] In the first aspect, the present invention provides a dispersant. The molecular structure of the dispersant is a three-dimensional network structure. The dispersant includes a melamine unit and a functional unit, and the functional unit has an amino group and a phenolic hydroxyl group.

[0006] In an embodiment, the dispersant further includes a linking unit. The melamine unit, the linking unit, and the functional unit together form a network polymer. The chemical formula of the network polymer includes: (C a H b -A-C a H b -B-C a H b ) n , where C a H b is the linking unit, A is the functional unit, B is the melamine unit, 1 ≤ a ≤ 7, 2 ≤ b ≤ 14, 0 < n < 50.

[0007] In an embodiment, the polymerization monomers of the functional unit include one or more of o-aminophenol, p-aminophenol, 3-amino-4-methoxyphenol, 2-amino-1,3-benzenediol, 2,4-diaminophenol, 2-amino-1,4-dihydroxybenzene, o-aminocresol, 5-amino-o-cresol.

[0008] In one embodiment, the polymerization monomers of the linking unit include one or more of formaldehyde, acetaldehyde, propionaldehyde, and aromatic aldehyde.

[0009] In one embodiment, the dispersant further includes a hydroxyl-containing segment, and the hydroxyl-containing segment is connected to the network polymer by a chemical bond. The chemical formulas of the hydroxyl-containing segment and the network polymer include: (R-O-C) m , where R is the network polymer, C is the hydroxyl-containing segment, and 0 < m < 50.

[0010] In one embodiment, the dispersant further includes a hydroxyl-containing segment, and the hydroxyl-containing segment is mixed and compounded with the network polymer.

[0011] In one embodiment, the hydroxyl-containing segment includes one or more of polyvinyl alcohol, polyethylene glycol, cellulose, hydroxyl-containing polyurethane, and polycaprolactone-coupled hydroxyl.

[0012] In one embodiment, the hydroxyl content in the hydroxyl-containing segment is greater than 5 mmol / g.

[0013] In one embodiment, the mass ratio of the network polymer to the hydroxyl-containing segment is 100:(30-100).

[0014] In one embodiment, the mass proportion of the functional unit in the dispersant is 20% - 100%.

[0015] In one embodiment, the mass proportion of the melamine unit in the dispersant is 20% - 100%.

[0016] In one embodiment, the molecular weight of the dispersant is 5000 Da - 50000 Da; and / or

[0017] In a second aspect, the present invention provides a preparation method of a dispersant. The preparation method is used to prepare the dispersant according to any one of the embodiments in the first aspect. The preparation method includes: mixing and reacting the polymerization monomers of the functional unit and the polymerization monomers of the melamine unit according to a mass ratio to obtain a polymerization product; removing the unreacted polymerization monomers, and freeze-drying the polymerization product to obtain the dispersant.

[0018] In one embodiment, the dispersant further includes a hydroxyl-containing segment, and the preparation method further includes: mixing and reacting the polymerization monomers of the functional unit and the polymerization monomers of the melamine unit according to a mass ratio to obtain a network polymer; adding the solution of the hydroxyl-containing segment to the solution of the network polymer, adding a catalyst, and reacting to obtain the polymerization product.

[0019] In a third aspect, the present invention provides a secondary battery, comprising a negative electrode plate, an electrolyte, a separator, and a positive electrode plate. The positive electrode plate includes a current collector and a positive electrode material layer disposed on the current collector, and the positive electrode material layer includes a dispersant as described in the first aspect.

[0020] The present invention provides a three-dimensional network structure dispersant composed of functional units and melamine units. The three-dimensional network structure dispersant has the following advantages: 1) The three-dimensional network structure enables the dispersant to form a more uniform dispersion system in the solution, avoiding the occurrence of agglomeration and sedimentation phenomena; 2) The three-dimensional network structure can provide sufficient mechanical support, enabling the dispersant to maintain a stable dispersion state in the electrode slurry; 3) Both amino groups and phenolic hydroxyl groups can serve as anchoring groups, and the anchoring groups have adsorption sites that can be used to adsorb electrode materials. Moreover, the anchoring groups also have a steric hindrance effect to prevent too many adsorption sites, resulting in weak anchoring adsorption force and thus reducing dispersibility; 4) Phenolic hydroxyl groups are strong polar groups that can form hydrogen bonds with polar solvent molecules in the slurry. The hydrogen bond interaction may help improve the dispersibility and stability of the slurry, prevent particle agglomeration, and thus play a role in reducing viscosity and stabilizing viscosity; 5) Compared with ordinary melamine, by adding functional units to melamine, the solubility of melamine in the electrode slurry, especially in organic solvents, can be improved by using the amino groups and phenolic hydroxyl groups in the functional units. The polymerized dispersant has higher solubility. Description of the Drawings

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0022] Figure 1 It is a schematic diagram of the reaction process of functional units and melamine units in an embodiment;

[0023] Figure 2 It is a molecular structural formula diagram of the dispersant in an embodiment;

[0024] Figure 3 It is a flowchart of the preparation method of the dispersant in an embodiment;

[0025] Figure 4 It is a reaction flowchart of functional units, polycyanamide units, and hydroxyl-containing segments in an embodiment;

[0026] Figure 5 It is a reaction flowchart of network polymers and hydroxyl-containing segments in an embodiment;

[0027] Figure 6 It is a schematic diagram of a secondary battery in an embodiment;

[0028] Figure 7 It is a scanning electron microscope image (SEM) of the positive electrode sheet prepared with the dispersant in Example 1;

[0029] Figure 8 It is a scanning electron microscope image (SEM) of the positive electrode sheet prepared with the dispersant in Comparative Example 3;

[0030] Figure 9 It is an infrared spectrum diagram of the dispersant in Example 2. Specific Embodiments

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0032] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the present invention in the specification are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The term "and / or" used in the present invention includes any and all combinations of one or more of the related listed items.

[0033] It should be noted that the "ranges" disclosed in the present invention are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In the present invention, unless otherwise stated, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" have been fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. In addition, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] All steps of the present invention can be carried out sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, if it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0035] The following will describe in detail some embodiments of the present invention with reference to the accompanying drawings. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0036] The following is a description of the instruments for testing the dispersant provided by the present invention:

[0037] 1) The hydroxyl content in the hydroxyl-containing chain segment can be detected by a gel permeation chromatograph (GPC) in combination with viscosity or light scattering method.

[0038] 2) The molecular weight of the dispersant can be detected by a gas chromatography-mass spectrometry (GC-MS).

[0039] The present invention provides a dispersant.

[0040] The dispersant is applied to a battery and can be added to the slurry of the electrode material. Among them, the types of batteries include, but are not limited to, lithium-ion batteries, sodium-ion batteries, potassium-ion batteries, etc. The slurry of the electrode material includes a positive electrode active material, a positive electrode lithium supplement material, a conductive agent, etc. Of course, in other embodiments, the dispersant can also be added to the negative electrode material.

[0041] In one embodiment, the molecular structure of the dispersant is a three-dimensional network structure. The dispersant includes a melamine unit and a functional unit, and the functional unit has an amino group and a phenolic hydroxyl group.

[0042] The present invention provides a three-dimensional network structure dispersant composed of a functional unit and a melamine unit. The three-dimensional network structure dispersant has the following advantages: 1) The three-dimensional network structure can enable the dispersant to form a more uniform dispersion system in the solution, avoiding the occurrence of agglomeration and sedimentation phenomena; 2) The three-dimensional network structure can provide sufficient mechanical support, enabling the dispersant to maintain a stable dispersion state in the electrode slurry; 3) Both the amino group and the phenolic hydroxyl group can serve as anchoring groups, and the anchoring group has an adsorption site, which can be used to adsorb the electrode material, and the anchoring group also has a steric hindrance effect to prevent too many adsorption sites, resulting in weak anchoring adsorption force and thus reducing the dispersibility; 4) The phenolic hydroxyl group is a strong polar group, which can form hydrogen bonds with polar molecules of the solvent in the slurry. The hydrogen bond interaction may help improve the dispersibility and stability of the slurry, prevent particle agglomeration, and thus play a role in reducing viscosity and stabilizing viscosity; 5) Compared with ordinary melamine, by adding a functional unit to melamine, the solubility of melamine in the electrode slurry, especially in organic solvents, can be improved by using the amino group and phenolic hydroxyl group in the functional unit. The polymerized dispersant has higher solubility.

[0043] In a specific embodiment, the dispersant is a three-dimensional network structure formed by polycondensation of a polymerization monomer (melamine and its derivatives) of the melamine unit and a polymerization monomer (aminophenol and its derivatives) of the functional unit. Among them, melamine and its derivatives include the structure of formula I-1 as shown in Figure 1 , and aminophenol and its derivatives include the structure of formula I-2 as shown in Figure 1 . The functional unit refers to an organic group that can be connected to the melamine unit and can provide a dispersing effect.

[0044] In one embodiment, the dispersant further includes a linking unit. The melamine unit, the linking unit, and the functional unit together form a network polymer. The chemical formula of the network polymer includes: (C a H b -A-C a H b -B-C a H b ) n , where Ca H b is a linking unit, A is a functional unit, B is a melamine unit, 1 ≤ a ≤ 7, 2 ≤ b ≤ 14, 0 < n < 50.

[0045] In a specific embodiment, the polymerization monomer of the linking unit can be an aldehyde group-containing organic compound. The aldehyde group-containing organic compound can first react with the polymerization monomer of melamine above, so that the aldehyde group-containing organic compound is connected to the amino group in melamine, and then the aldehyde group-containing organic compound reacts with the polymerization monomer of the functional unit. The carbon atom of the aldehyde group-containing organic compound can be connected to the vacant position in the polymerization monomer of the functional unit. The specific reaction is as Figure 1 shown.

[0046] In a specific embodiment, the polymerization monomer of the melamine unit is a nitrogen-containing heterocyclic compound, which has multiple amino groups. There are at least three amino groups on the melamine unit that can participate in the reaction. These amino groups may react with other molecules during the polymerization process to form a complex network structure. Therefore, the melamine unit and the functional unit can form a three-dimensional network structure. At the same time, after the polymerization monomer of the melamine unit reacts, it becomes the melamine unit, after the polymerization monomer of the functional unit reacts, it becomes the functional unit, and after the polymerization monomer of the linking unit reacts, it becomes the linking unit. The network polymer includes the structure of Formula I-3 as Figure 1 shown.

[0047] In one embodiment, the melamine unit and the functional unit are directly connected by a chemical bond, and the polymerization monomers of the melamine unit and the functional unit undergo a polycondensation reaction. Specifically, there are amino groups and phenolic hydroxyl groups on the functional unit, so the amino groups and phenolic hydroxyl groups on the functional unit can also directly undergo a polycondensation reaction with the amino groups on the melamine unit to form a polymer containing an imine bond (-NH-) or an amide bond (-CONH-).

[0048] In a specific embodiment, the dispersant can include a first network polymer and a second network polymer. Among them, the first network polymer includes a melamine unit, a linking unit, and a functional unit, and the second network polymer includes a melamine unit and a functional unit. That is, the dispersant provided by the present invention can obtain two network polymers with different molecular structures through at least two polycondensation reactions.

[0049] In one embodiment, the polymerization monomers of the functional unit include one or more of o-aminophenol, p-aminophenol, 3-amino-4-methoxyphenol, 2-amino-1,3-benzenediol, 2,4-diaminophenol, 2-amino-1,4-dihydroxybenzene, o-aminocresol, 5-amino-o-cresol. Specifically, the polymerization monomers of the functional unit provided by the present invention include a benzene ring and an amino group and a hydroxyl group connected to the benzene ring, and the connection positions of the amino group and the hydroxyl group are not specifically limited, nor are the numbers of the amino group and the hydroxyl group.

[0050] In a specific embodiment, the connecting positions of the amino group and the hydroxyl group can be ortho-position (the amino group and the hydroxyl group are adjacent), meta-position (there is one carbon atom between the amino group and the hydroxyl group), or para-position (there are two carbon atoms between the amino group and the hydroxyl group). The number of hydroxyl groups can be one, two or more than two. It can be understood that the number of phenolic hydroxyl groups can increase the proportion of hydrogen bond formation, thereby enhancing the viscosity reduction and viscosity stabilization effect.

[0051] In one embodiment, the polymerization monomers of the melamine unit include one or more of melamine, melamine-formaldehyde resin, melamine-lauryl alcohol, melamine-n-octyl alcohol, and melamine-polyethylene glycol monomethyl ether. Specifically, the polymerization monomers of the melamine unit provided by the present invention include a nitrogen-containing heterocycle and an amino group connected to the nitrogen-containing heterocycle. Of course, in other embodiments, other functional groups can be connected to the amino group.

[0052] It should be noted that in a specific embodiment, it is not necessary to add an aldehyde group-containing organic substance during the formation of the melamine unit and the functional unit. When the polymerization monomers of the melamine unit include an aldehyde group, it is not necessary to add an aldehyde group-containing organic substance, such as melamine-formaldehyde resin.

[0053] In one embodiment, the polymerization monomers of the linking unit include one or more of formaldehyde, acetaldehyde, propionaldehyde, and aromatic aldehyde.

[0054] In one embodiment, the dispersant further includes a hydroxyl-containing chain segment. The hydroxyl-containing chain segment is connected to the network polymer through a chemical bond. The chemical formulas of the hydroxyl-containing chain segment and the network polymer include: (R-O-C) m , where R is the network polymer, C is the hydroxyl-containing chain segment, and 0 < m < 50.

[0055] In a specific embodiment, the hydroxyl-containing chain segment is a chain structure, and at least one hydroxyl group is connected to the chain segment. O in the chemical formula is an oxygen atom. The network polymer and the hydroxyl-containing chain segment undergo an etherification reaction. Under acidic conditions, the phenolic hydroxyl group in the network polymer can react with the hydroxyl group in the hydroxyl-containing chain segment to form a product connected by an ether bond (-O-). For example, -Ar-OH (Ar represents an aromatic ring) in the polymer reacts with -OH of the hydroxyl-containing chain segment to dehydrate, forming a connecting structure of R-O-C.

[0056] In a specific embodiment, the structural formula of the dispersant is as Figure 2 shown. The dispersant includes a network polymer and a hydroxyl-containing chain segment. The network polymer includes a melamine unit, p-aminophenol as a functional unit, formaldehyde as a linking unit, and the hydroxyl-containing chain segment is polyvinyl alcohol. Among them, the degree of polymerization h of polyvinyl alcohol is 1 to 500.

[0057] It should be noted that in other embodiments, the hydroxyl-containing chain segment can also be other polymers, not limited to polyvinyl alcohol. That is, in the dispersant, for the chemical formula (R-O-C) of the hydroxyl-containing chain segment and the network polymer m in the case of, the type of C is not specifically limited, and any organic polymer containing hydroxyl groups can be used as the precursor of the hydroxyl-containing chain segment.

[0058] The advantage of further introducing the hydroxyl-containing chain segment in the present invention is that the hydroxyl group has good wettability and flexibility. By polymerizing the network polymer with the hydroxyl-containing chain segment, a dispersant with good flexibility, viscosity reduction and viscosity stabilization performance is obtained; the network polymer mainly relies on melamine units to form a network structure, and the network polymer has a good viscosity reduction and viscosity stabilization effect. This network polymer reacts with hydroxyl groups to obtain a polymer containing an ether bond structure, and the ether bond has the advantages of flexibility and wettability.

[0059] In one embodiment, the dispersant further includes a hydroxyl-containing chain segment, and the hydroxyl-containing chain segment is mixed and compounded with the network polymer. Specifically, no chemical bond (covalent bond or ionic bond) is formed between the hydroxyl-containing chain segment and the network polymer, and they can be combined only by hydrogen bonds.

[0060] In one embodiment, the hydroxyl-containing chain segment includes one or more of polyvinyl alcohol, polyethylene glycol, cellulose, hydroxyl-containing polyurethane, and polycaprolactone-coupled hydroxyl. Specifically, the hydroxyl-containing chain segment is a polymer chain segment obtained by polycondensation or copolymerization, and is preferably a straight-chain polymer chain segment with multiple hydroxyl groups connected to the main chain.

[0061] In one embodiment, the hydroxyl content in the hydroxyl-containing chain segment is greater than or equal to 5 mmol / g. Optionally, the hydroxyl content in the hydroxyl-containing chain segment can be 5 mmol / g to 10 mmol / g, 5 mmol / g to 15 mmol / g, 5 mmol / g to 20 mmol / g, 5 mmol / g to 30 mmol / g, 5 mmol / g to 50 mmol / g.

[0062] Satisfying that the hydroxyl content in the hydroxyl-containing chain segment is within the above range can ensure a relatively high hydroxyl content in the dispersant, thereby obtaining a high-performance dispersant. When the hydroxyl content in the hydroxyl-containing chain segment is too low, the hydroxyl content in the dispersant decreases, resulting in a poor viscosity reduction and viscosity stabilization effect.

[0063] In one embodiment, the mass ratio of the network polymer to the hydroxyl-containing chain segment is 100:(30 - 100). Optionally, the mass ratio of the network polymer to the hydroxyl-containing chain segment can be 100:30, 100:40, 100:50, 100:60, 100:70, 100:80, 100:90, 100:100.

[0064] Meeting the mass ratio of the network polymer to the hydroxyl-containing segment within the above range can ensure that the network polymer provides good viscosity reduction and viscosity stabilization effects, and the hydroxyl-containing segment provides good wettability and flexibility. When the proportion of the hydroxyl-containing segment is too small, the modification effect of the hydroxyl-containing segment on the network polymer becomes poor, and the wettability and flexibility of the dispersant decrease. When the proportion of the hydroxyl-containing segment is too large, the hydroxyl-containing segment crowds out the network polymer, making it difficult for the network polymer to play the role of viscosity reduction and viscosity stabilization.

[0065] In one embodiment, the mass proportion of the functional unit in the dispersant is 20% - 100%. Optionally, the mass proportion of the functional unit in the dispersant can be 20%, 25%, 30%, 35%, 40%, 50%, 60%, 70%, 80%, 90%, 100%.

[0066] Meeting the mass proportion of the functional unit in the dispersant within the above range is beneficial to improving the dispersibility and stability of the dispersant for the positive electrode active material. When the mass proportion of the functional unit in the dispersant is too small, the number of functional units connected to the melamine unit decreases, and the content of phenolic hydroxyl groups decreases, resulting in a decrease in the adsorption capacity for the electrode material. When the mass proportion of the functional unit in the dispersant is too large, some functional units exist in the form of monomers, affecting the concentration of the electrode slurry.

[0067] In one embodiment, the mass proportion of the melamine unit in the dispersant is 20% - 100%. Optionally, the mass proportion of the melamine unit in the dispersant can be 20%, 25%, 30%, 35%, 40%, 50%, 60%, 70%, 80%, 90%, 100%.

[0068] Meeting the mass proportion of the melamine unit in the dispersant within the above range is beneficial to improving the wettability and dispersion performance of the active material particles. When the mass proportion of the melamine unit in the dispersant is too small, as the central unit for connection, it will lead to a reduction in the connection sites of the functional units and an inability to form a rich three-dimensional network structure. When the mass proportion of the melamine unit in the dispersant is too large, it will affect the slurry stability and at the same time affect the solubility of the dispersant. Melamine is a nitrogen-containing heterocyclic compound with multiple amino groups. These amino groups may react with other molecules during the polymerization process to form a complex network structure. If the proportion of this network structure is too large, it is not conducive to improving the viscosity reduction and solid content increase performance of the slurry.

[0069] In one embodiment, the molecular weight of the dispersant is 5000Da - 50000Da. Optionally, the molecular weight of the dispersant can be 5000Da, 10000Da, 15000Da, 25000Da, 30000Da, 35000Da, 40000Da, 45000Da, 50000Da.

[0070] When the molecular weight of the dispersant meets the above range, it can ensure that the viscosity of the dispersant itself is appropriate to provide a high viscosity reduction and viscosity stabilization effect. When the molecular weight of the dispersant is too low, the dispersion effect provided by the dispersant becomes poor, and the viscosity of the slurry decreases. When the molecular weight of the dispersant is too high, the dispersant cannot fully disperse the electrode material, and it will increase the viscosity of the slurry, making it difficult to coat.

[0071] The present invention provides a preparation method of a dispersant, please refer to Figure 3 。

[0072] In one embodiment, the preparation method of the dispersant specifically includes the following steps:

[0073] Step S100, mixing and reacting the polymerization monomers of the functional unit and the polymerization monomers of the melamine unit according to a mass ratio to obtain a polymerization product.

[0074] Step S200, removing the unreacted polymerization monomers, and freeze-drying the polymerization product to obtain the dispersant.

[0075] Optionally, in step S100, the polymerization monomers of the functional unit include one or more of o-aminophenol, p-aminophenol, 3-amino-4-methoxyphenol, 2-amino-1,3-benzenediol, 2,4-diaminophenol, 2-amino-1,4-dihydroxybenzene, and o-aminop-cresol.

[0076] Optionally, in step S100, the polymerization monomers of the melamine unit include one or more of melamine, melamine-formaldehyde resin, melamine-lauryl alcohol, melamine-n-octanol, and melamine-polyethylene glycol monomethyl ether.

[0077] Optionally, in step S200, the unreacted polymerization monomers can be removed by dialysis, and then the solid dispersant can be obtained through freeze-drying technology. It can be understood that the dispersant provided by the present invention is solid, and when in use, it can be added to the electrode slurry, and the dispersant can dissolve in the organic solvent, thereby dispersing the electrode material.

[0078] In one embodiment, the dispersant further includes a linking unit, please refer to Figure 4 , step S100 includes:

[0079] Step S101, adding the polymerization monomers of the functional unit and the polymerization monomers of the melamine unit to an organic solvent according to a mass ratio.

[0080] Step S102, adjusting deionized water to be acidic or alkaline, adding the monomer of the linking unit to the deionized water, and obtaining a polymerization product through polycondensation reaction.

[0081] Optionally, in step S101, the organic solvent includes organic solvents such as N-methylpyrrolidone, acetonitrile, and dimethylformamide.

[0082] Optionally, in step S102, the acidic environment can be adjusted by hydrochloric acid, nitric acid, phosphoric acid, acetic acid, etc., and the alkaline environment can be adjusted by potassium hydroxide, sodium hydroxide, etc.

[0083] Optionally, in step S102, the polymerization monomer of the linking unit includes one or more of formaldehyde, acetaldehyde, propionaldehyde, and aromatic aldehyde.

[0084] Optionally, in step S102, the temperature of the polycondensation reaction is 80°C to 200°C, and the reaction time is 2 h to 6 h. The specific temperature of the polycondensation reaction can be 80°C, 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, and the reaction time can be 2 h, 3 h, 4 h, 5 h, 6 h.

[0085] In one embodiment, please refer to Figure 5 , the dispersant further includes a hydroxyl-containing segment, and step S100 includes:

[0086] Step S110, mixing and reacting the polymerization monomer of the functional unit and the polymerization monomer of the melamine unit according to a mass ratio to obtain a network polymer.

[0087] Step S120, adding a solution containing a hydroxyl-containing segment to the solution of the network polymer, adding a catalyst, and obtaining a polymerization product after reaction.

[0088] Optionally, in step S120, the hydroxyl-containing segment is one or more of polyvinyl alcohol, polyethylene glycol, cellulose, hydroxyl-containing polyurethane, and polycaprolactone-coupled hydroxyl.

[0089] Optionally, in step S120, the catalyst is an acid-type catalyst, including one or more of hydrochloric acid, sulfuric acid, and phosphoric acid. The dosage of the catalyst is 1% to 10% of the total monomer mass. The specific dosage of the catalyst is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% of the total monomer mass.

[0090] Optionally, in step S120, the temperature for the catalytic reaction using the catalyst is 50°C to 200°C, and the reaction time is 1 h to 4 h. The specific temperature of the catalytic reaction can be 50°C, 80°C, 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, and the reaction time can be 1 h, 2 h, 3 h, 4 h.

[0091] In the present invention, a copolymerization reaction occurs between the polymerization monomer of the functional unit and the polymerization monomer of the melamine unit to introduce a rigid aromatic ring and amino functional groups. This preparation method can obtain a dispersant with a three-dimensional network structure. The three-dimensional network structure enables the polymer to form a more uniform dispersion system in the solution, avoiding agglomeration and sedimentation. At the same time, the three-dimensional network structure can also provide sufficient mechanical support, enabling the polymer to maintain a stable dispersion state in the positive electrode slurry.

[0092] The present invention also provides a pole piece.

[0093] In one embodiment, the pole piece includes an electrode material and the dispersant provided in the above embodiment. The electrode material is a positive electrode material or a negative electrode material. Among them, the positive electrode material can reversibly deintercalate and intercalate active lithium ions, and the active lithium ions migrate between the positive electrode and the negative electrode of the battery to achieve battery charging and discharging. The positive electrode material can be a phosphate positive electrode material and a ternary positive electrode material. Exemplarily, the positive electrode material includes one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium fluorovanadate, lithium titanate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate. And a lithium supplement material can be added to the positive electrode material. Exemplarily, the lithium supplement material can be lithium-rich lithium ferrate, lithium-rich lithium cobaltate, lithium-rich lithium nickelate, etc.

[0094] The present invention also provides a secondary battery 1000, please refer to Figure 6 .

[0095] In one embodiment, the secondary battery can be a common composition system in the prior art. For example, it includes a negative electrode pole piece, an electrolyte, a separator, and a positive electrode pole piece. The electrolyte can be a solid electrolyte or a liquid electrolyte. When a solid electrolyte is selected, the use of the separator can be adaptively selected; both the positive electrode pole piece and the negative electrode pole piece can include the dispersant provided above.

[0096] The technical solution of the present invention will be described in detail below through specific examples.

[0097] Example 1

[0098] This example provides a dispersant. The dispersant includes a functional unit (p-aminophenol), a linking unit (formaldehyde), a melamine unit (melamine), and a hydroxyl-containing segment (polyvinyl alcohol). Among them, the functional unit and the melamine unit are connected through the linking unit to form a network polymer. The specific structural formula of the dispersant can be referred to Figure 2 .

[0099] The hydroxyl content in the hydroxyl-containing segment is 20 mmol / g; the mass ratio of the network polymer to the hydroxyl-containing segment is 100:60; the molecular weight of the dispersant is 30000 Da.

[0100] The preparation method of the dispersant provided by this embodiment is as follows:

[0101] 1) Dissolve p-aminophenol and melamine in deionized water, add hydrochloric acid to adjust the aqueous solution to be acidic, then add formaldehyde to N-methylpyrrolidone, raise the temperature to 100 °C and react for 2 hours, and then remove the unreacted monomers in the reaction product and obtain a network polymer by freeze-drying; wherein, the mass ratio of p-aminophenol, melamine and formaldehyde is 30%: 30%: 90%.

[0102] 2) Add a polyvinyl alcohol solution to the network polymer, raise the temperature to 100 °C, and dropwise add the corresponding hydrochloric acid as a catalyst, and obtain a polymer after reacting for 3 hours.

[0103] 3) Remove the unreacted monomers in the polymer by dialysis, and then obtain a solid dispersant by freeze-drying.

[0104] Example 2

[0105] This embodiment provides a dispersant. The difference between this embodiment and Example 1 is that the functional unit is replaced by 5-amino-o-cresol.

[0106] Example 3

[0107] This embodiment provides a dispersant. The difference between this embodiment and Example 1 is that the hydroxyl-containing chain segment is replaced by hydroxypropyl cellulose.

[0108] Example 4

[0109] This embodiment provides a dispersant. The difference between this embodiment and Example 1 is that the hydroxyl-containing chain segment and the network polymer are mixed and compounded, hydrochloric acid is not added as a catalyst in step 2) of the preparation method, and stirring is carried out at room temperature.

[0110] Example 5

[0111] This embodiment provides a dispersant. The difference between this embodiment and Example 1 is that the mass ratio of the network polymer to the hydroxyl-containing chain segment is 100:30.

[0112] Example 6

[0113] This embodiment provides a dispersant. The difference between this embodiment and Example 1 is that the mass ratio of the network polymer to the hydroxyl-containing chain segment is 100:90.

[0114] Example 7

[0115] This embodiment provides a dispersant. The difference between this embodiment and Example 1 is that the mass ratio of p-aminophenol, melamine and formaldehyde in the preparation method is 50%: 50%: 150%.

[0116] Example 8

[0117] This example provides a dispersant. The difference between this example and Example 1 is that in the preparation method, the mass ratio of p-aminophenol, melamine, and formaldehyde is 40%:40%:120%.

[0118] Example 9

[0119] This example provides a dispersant. The difference between this example and Example 1 is that the molecular weight of the dispersant is 3000 Da. The reaction time in step 1) of the preparation method is 1 hour, and the reaction time in step 2) is 1 hour.

[0120] Example 10

[0121] This example provides a dispersant. The difference between this example and Example 1 is that the molecular weight of the dispersant is 50000 Da. The reaction time in step 5) of the preparation method is 2 hours, and the reaction time in step 2) is 4 hours.

[0122] Example 11

[0123] This example provides a dispersant. The difference between this example and Example 1 is that it does not include a hydroxyl-containing segment (polyvinyl alcohol).

[0124] The preparation method of the dispersant provided in this example is as follows:

[0125] 1) Dissolve p-aminophenol and melamine in deionized water, add hydrochloric acid to adjust the aqueous solution to be acidic, then add formaldehyde to deionized water, raise the temperature to 120 °C and react for 1.5 hours, then remove the unreacted monomers in the reaction product and obtain a network polymer through freeze-drying.

[0126] Comparative Example 1

[0127] This comparative example provides a dispersant, and the dispersant includes polyvinylpyrrolidone (PVP).

[0128] Comparative Example 2

[0129] This comparative example provides a dispersant, and the dispersant includes melamine and polyvinylpyrrolidone (PVP).

[0130] Comparative Example 3

[0131] This comparative example provides a dispersant. The dispersant includes a main chain and side chains. Among them, the main chain includes a nonylphenyl chain segment and a flexible chain segment. The flexible chain segment is connected to the benzene ring and is located at the para position of the nonyl group. The flexible chain segment contains an ether bond. The number of side chains is two, and both side chains are connected to the benzene ring. The two side chains are respectively located at the ortho positions of the nonyl flexible chain segment. The side chains are obtained by polymerizing triethylenetetramine, polyethylene oxide, and polypropylene oxide. Among them, the weight-average molecular weight of the dispersant is about 5000, and the molecular weight dispersity index of the dispersant is 1.3.

[0132] The preparation method of the dispersant provided by this comparative example is as follows:

[0133] 1) Nonylphenol and triethylenetetramine were respectively put into a three-necked flask according to a mass ratio of 0.5:1 and reacted under an oil bath. The reaction conditions were: rotation speed 200 rpm, stirring time 20 min, reaction temperature 50 °C; then 200% of xylene was dropped into the three-necked flask (the added mass of xylene was 200% of the mass of nonylphenol), and the temperature was raised to 70 °C. After nonylphenol was completely dissolved, it was cooled to 30 °C, and a formaldehyde solution (the mass ratio of the formaldehyde solution to nonylphenol was 1:2) was slowly added dropwise to obtain nonylphenol modified with triethylenetetramine.

[0134] 2) After 30 g of nonylphenol modified with triethylenetetramine and 0.03 g of 40% aqueous sodium hydroxide solution were stirred and mixed, vacuum dehydration was carried out for 2 h. Then the temperature was raised to 110 °C and polymerized with propylene oxide. The mass ratio of the initiator to propylene oxide (PO) was 1:30, and the polymerization time was 1 h. Then the temperature was lowered to 100 °C and polymerized with ethylene oxide for 1 h. The mass ratio of propylene oxide to ethylene oxide was 2.7:1; after the reaction ended, it was filtered and washed with methanol and deionized water, and dried at 50 °C for 24 h to obtain a multi-branched polymer dispersant.

[0135] The dispersant parameters provided by Examples 1-11 and Comparative Examples 1-3 are shown in Table 1:

[0136] Table 1 Dispersant parameters provided by examples and comparative examples

[0137]

[0138]

[0139] It should be noted that the proportional relationship in the column of "monomer ratio of functional unit, melamine unit and linking unit in the preparation method" in Table 1 refers to the mass ratio of the raw materials used in step 1) of the preparation method of the dispersant, that is, the mass ratio of the polymerization monomers of the functional unit, the polymerization monomers of the melamine unit, and the polymerization monomers of the linking unit, rather than the mass ratio of the functional unit, the melamine unit and the linking unit in the finally obtained dispersant. In the examples, the mass ratio of the functional unit, the melamine unit and the linking unit should be less than the monomer ratio of the functional unit, the melamine unit and the linking unit in the preparation method.

[0140] The dispersants provided in the above Examples 1-11 and Comparative Examples 1-3 were added to the positive electrode slurry of the lithium iron phosphate battery to prepare a positive electrode slurry, and then the positive electrode slurry was coated on the current collector to make a positive electrode plate, and the positive electrode plate was assembled into a secondary battery.

[0141] Among them, the preparation process of the positive electrode slurry includes: the positive electrode slurry of the lithium iron phosphate battery is composed of solid dry materials and N-methylpyrrolidone (wherein the weight of N-methylpyrrolidone is 41.75 wt% of the total weight of the positive electrode slurry). Calculated based on the total weight of 100 wt%: the solid dry materials in the positive electrode slurry include 96.5 wt% of lithium iron phosphate, 1.3 wt% of Super P, and 2.2 wt% of polyvinylidene fluoride. Among them, the outer surface of the positive electrode active material (lithium iron phosphate) has a carbon coating layer, and the thickness of the carbon coating layer is 2 nm to 10 nm. Polyvinylidene fluoride and Super P were stirred in N-methylpyrrolidone at 400 revolutions per minute for 20 minutes, lithium iron phosphate was added and stirred at 200 revolutions per minute for 10 minutes, and then the dispersant was added and stirred at 2000 revolutions per minute for 70 minutes to obtain the positive electrode slurry. The addition amount of the dispersant is 0.1%, that is, the addition amount of the dispersant is 0.1% of the mass ratio of the positive electrode active substance.

[0142] The positive electrode slurries, positive electrode plates and secondary batteries of the examples and comparative examples were respectively tested as follows, and the test results are shown in Table 2:

[0143] 1) Positive electrode slurry viscosity test: The viscosity values of the positive electrode slurries of the examples and comparative examples at the time of discharging and after 24 hours of the slurry were respectively tested. The test process includes: selecting a suitable rotor, fixing the viscosity meter rotor, placing the glue solution under the viscosity meter rotor, and the glue solution just submerging the scale line of the rotor. Instrument model: Shanghai Fangrui NDJ-5S, rotor: 64#, rotation speed: 10-30 r / min, test temperature: 25 °C, test humidity: 20RH% - 70RH%, test time is 1 min, and wait for the reading to stabilize and read the data.

[0144] 2) Flexibility test of the positive electrode sheet: The positive electrode sheet was tested multiple times by the folding test method and the average value was taken. The test process included: folding the positive electrode sheet with a surface density of 18 mg / cm 2 and then using a pressure roller with a weight of 2 Kg to roll back and forth 3 times. After that, the positive electrode sheet was flattened, and the above operation was repeated until light leakage occurred at the folding point. The number of folds was recorded. Each group was tested 5 times and the average value was taken. The calculation method = (sum of the 5 test results) / 5.

[0145] 3) Electrical performance test of the secondary battery: The charge and discharge were carried out at a rate of 0.1C, and the potential range was 2.5 - 3.75V. The initial charge capacity at 0.1C, the initial discharge capacity at 0.1C, and the efficiency were obtained respectively.

[0146] Table 2 Test results of the examples and comparative examples

[0147]

[0148] It can be seen from the test results of Examples 1 - 11 and Comparative Examples 1 - 2 in Table 2 that the dispersant provided by the present invention is added to the slurry, and the viscosities of the slurry after discharging and after standing for 24 h are lower than those of the dispersants in the prior art, indicating that the slurry of the examples has good fluidity and coatability; moreover, the electrode sheets and battery performance containing the dispersant prepared by the present invention are excellent. The resistivity of the electrode sheets in the examples is lower than that of the comparative examples, and the charge and discharge capacity and efficiency of the batteries are higher than those of the comparative examples.

[0149] It can be seen from the test results of Example 1 and Comparative Example 3 in Table 2 that the dispersant provided by Example 1 has a better viscosity reduction and viscosity stabilization effect on the positive electrode slurry than Comparative Example 3, and does not affect the flexibility of the electrode sheet and the performance of the battery. This shows that the dispersant provided by Example 1 can form a more uniform dispersion system in the positive electrode slurry, avoid the agglomeration and sedimentation of the positive active material, and finally achieve the effect of viscosity reduction and viscosity stabilization.

[0150] It can be seen from the test results of Examples 1 - 3 in Table 2 that by replacing the functional unit or the hydroxyl-containing chain segment in Example 1 with other monomer raw materials, dispersants with similar effects can also be prepared. This shows that the raw materials for preparing the dispersant provided by the present invention have a wide selection range, the scheme has a high application prospect, and different dispersants can be formulated according to the required battery performance.

[0151] From the test results of Example 1 and Example 4 in Table 2, it can be seen that by replacing the network polymer and the hydroxyl-containing segment in Example 1 with a mixed formulation (Example 4), that is, without connecting the network polymer and the hydroxyl-containing segment by chemical bonds, the dispersant provided by the present invention can still be prepared. The positive electrode sheet of Example 4 has high flexibility and stable battery performance, indicating that the performance of the dispersant provided by Example 4 is superior to that of Comparative Example 1 and Comparative Example 2.

[0152] From the test results of Example 1 and Example 5 in Table 2, it can be seen that the performance of the dispersant can be affected by adjusting the proportion relationship between the network polymer and the hydroxyl-containing segment. Since the hydroxyl groups and ether bonds in the hydroxyl-containing segment have good wettability and flexibility, reducing the proportion of the hydroxyl-containing segment will lead to a decrease in the viscosity reduction and viscosity stabilization effect of the dispersant. However, the effect of the dispersant in Example 5 is still superior to that of Comparative Example 1 and Comparative Example 2.

[0153] From the test results of Example 1, Example 6 - Example 8 in Table 2, it can be seen that the performance of the dispersant can be regulated by adjusting the monomer proportion relationship of the functional unit, the melamine unit, and the linking unit. Since the melamine unit has three linking sites, the amount of the melamine unit used affects the complexity of the three-dimensional network structure. Similarly, as the linking unit and the functional unit are the effective components linked to the melamine unit, the proportion of the two will also affect the complexity of the three-dimensional network structure. Therefore, adjusting the proportion of the above three will affect the performance of the dispersant.

[0154] From the test results of Example 1, Example 9 and Example 10 in Table 2, it can be seen that if the weight-average molecular weight of the dispersant is too large or too small, the viscosity reduction and viscosity stabilization performance will decrease, and the viscosity increase of the slurry is greater than that of Example 1. During the coating process, the viscosity of the slurries in Example 9 and Example 10 increases too fast, and the conductive carbon in the slurry is unevenly distributed, resulting in a decrease in the compaction density and flexibility of the prepared positive electrode sheet, and the battery performance is slightly affected.

[0155] From the test results of Example 1 and Example 11 in Table 2, it can be seen that the scheme of using only the network polymer as the dispersant can also achieve the effect of viscosity reduction and viscosity stabilization, and the effect of viscosity reduction and viscosity stabilization is superior to that of Comparative Example 1 and Comparative Example 2. Therefore, the hydroxyl-containing segment can cooperate with the network polymer to enhance the viscosity reduction and viscosity stabilization effect of the dispersant, and the hydroxyl groups and ether bonds can provide better wettability and flexibility.

[0156] Figure 7 is the scanning electron microscope image of the positive electrode sheet prepared with the dispersant in Example 1, Figure 8 is the scanning electron microscope image of the positive electrode sheet prepared with the dispersant in Comparative Example 3. From Figure 7 and Figure 8It can be clearly seen that for the positive electrode sheet prepared using the dispersant provided in Example 1, the particles of the positive electrode material on the positive electrode sheet are evenly dispersed, and no obvious agglomeration occurs for small and large particles; for the positive electrode sheet prepared using the dispersant provided in Comparative Example 3, obvious agglomeration occurs for the particles of the positive electrode material on the positive electrode sheet, especially Figure 8 at positions A and B in

[0157] Figure 9 where small and large particles are significantly adhered together. Figure 9 is the infrared spectrogram of the dispersant in Example 2. It can be seen from -1 that vibration peaks (1550 cm -1 ) of the triazine ring on melamine appear on the polymer, indicating that the triazine ring in the obtained dispersant is not damaged. At 2850 cm -1 ~2950 cm -1 and 3250 cm -1 ~3500 cm -1 , the amino bonds on melamine and the amino bonds on aminophenol are retained; and at 2850 cm -1 ~2950 cm -1 , a methyl C-H peak appears, indicating that after the reaction of formaldehyde with the amino group on melamine, it is grafted onto the benzene ring of 5-aminocresol, and at the same time it also shows that the amino group on 5-aminocresol is not damaged. In addition, an ether bond peak also appears around 1070 cm -1 , indicating that polyvinyl alcohol reacts with the hydroxyl group on 5-aminocresol to form an ether. Therefore, it can be seen from the infrared spectrogram of the dispersant in Figure 9 that the dispersant including 5-aminocresol, melamine and polyvinyl alcohol is synthesized in Example 2.

[0158] In the description of the embodiments of the present invention, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship of the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0159] The above-disclosed is only a preferred embodiment of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A dispersant, characterized in that: The molecular structure of the dispersant is a three-dimensional network structure. The dispersant includes a melamine unit and a functional unit. The functional unit has an amino group and a phenolic hydroxyl group.

2. The dispersant according to claim 1, characterized in that The dispersant further comprises a connecting unit, and the melamine unit, the connecting unit and the functional unit together constitute a network polymer, and the chemical formula of the network polymer comprises: (C a H b -AC a H b -BC a H b ) n , where C a H b is the connecting unit, A is the functional unit, B is the melamine unit, 1≤a≤7, 2≤b≤14, 0<n<50.

3. The dispersant according to claim 2, characterized in that The polymerizable monomers of the functional units include one or more of o-aminophenol, p-aminophenol, 3-amino-4-methoxyphenol, 2-amino-1,3-benzenediol, 2,4-diaminophenol, 2-amino-1,4-dihydroxybenzene, o-amino-p-cresol, and 5-amino-o-cresol; and / or The polymerizable monomers of the linking units include one or more of formaldehyde, acetaldehyde, propionaldehyde, and aromatic aldehydes.

4. The dispersant according to claim 2, characterized in that The dispersant further comprises a hydroxyl-containing segment, wherein the hydroxyl-containing segment is connected to the network polymer via a chemical bond, and the chemical formula of the hydroxyl-containing segment and the network polymer comprises: (ROC) m , wherein R is the network polymer, C is the hydroxyl-containing segment, and 0<m<50.

5. The dispersant according to claim 2, characterized in that The dispersant further comprises a hydroxyl-containing segment, and the hydroxyl-containing segment is mixed and compounded with the network polymer.

6. The dispersant according to claim 4 or 5, characterized in that The hydroxyl-containing segment comprises one or more of polyvinyl alcohol, polyethylene glycol, cellulose, hydroxyl-containing polyurethane, and polycaprolactone coupled hydroxyl groups; and / or The hydroxyl content in the hydroxyl-containing segment is greater than 5 mmol / g; and / or The mass ratio of the network polymer to the hydroxyl-containing segment is 100:(30-100).

7. The dispersant according to any one of claims 1 to 6, characterized in that The mass percentage of the functional unit in the dispersant is 20% to 100%; and / or The mass percentage of the melamine unit in the dispersant is 20% to 100%; and / or The molecular weight of the dispersant is 5000Da to 50000Da.

8. A method for preparing a dispersant, characterized in that: The preparation method is used to prepare the dispersant according to any one of claims 1 to 7, and the preparation method comprises: The polymerized monomers of the functional units and the polymerized monomers of the melamine units are mixed and reacted according to a mass ratio to obtain a polymerized product; The polymerization monomers not involved in the reaction are removed, and the polymerization product is freeze-dried to obtain a dispersant.

9. The preparation method according to claim 8, characterized in that: The dispersant further comprises a hydroxyl-containing segment, and the preparation method further comprises: Mixing the polymerized monomer of the functional unit and the polymerized monomer of the melamine unit according to a mass ratio to obtain a network polymer; The solution of the hydroxyl chain segment is added to the solution of the network polymer, a catalyst is added, and the polymerization product is obtained after reaction.

10. A secondary battery, comprising a negative electrode plate, an electrolyte, a separator and a positive electrode plate, wherein the positive electrode plate comprises a current collector and a positive electrode material layer disposed on the current collector, characterized in that: The positive electrode material layer includes the dispersant according to any one of claims 1 to 7.

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