Dispersing agent, preparation method thereof and secondary battery

Abstract

The invention relates to a dispersant and a preparation method thereof, and a secondary battery, the dispersant comprises a main chain and a first branch chain, the main chain contains a benzene ring, the first branch chain is grafted and copolymerized on the benzene ring, and the first branch chain comprises a first amino-containing chain segment and a first flexible chain segment which are copolymerized and connected. The dispersing agent provided by the invention is used for dispersing electrode slurry and improving the stability of the slurry so as to reduce the agglomeration phenomenon.

Description

Technical Field

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

[0002] With the explosive growth of new energy vehicle production and sales, the application of lithium-ion batteries has increased, and the performance requirements for them have become higher and higher, resulting in a further increase in the demand for positive electrode materials. In order to increase the energy density of electrode slurry (especially positive electrode slurry), it is necessary to add dispersants to the positive electrode slurry to increase the solid content of the positive electrode slurry. The dispersants commonly used in industry are PVP (polyvinyl pyrrolidone), polyvinylidene fluoride (PVDF), etc. Although these dispersants improve the dispersion performance of positive electrode materials in organic solvents, the particles in the slurry are easy to stratify, resulting in difficulties in the use of positive electrode slurry, which in turn affects the performance of the prepared lithium-ion battery. Therefore, how to provide a dispersant with good dispersion effect and high stability has become the key. Summary of the invention

[0003] The purpose of the present invention is to provide a dispersant and a preparation method thereof, and a secondary battery, so as to solve the problem that the existing dispersant has poor stability for electrode slurry.

[0004] To achieve the purpose of the present invention, the present invention provides the following technical solutions:

[0005] In a first aspect, the present invention provides a dispersant, comprising a main chain and a first branch chain, wherein the main chain contains a benzene ring, the first branch chain is grafted and copolymerized on the benzene ring, and the first branch chain comprises a first amino-containing segment and a first flexible segment connected by copolymerization.

[0006] In one embodiment, the first amine-containing segment is substituted to connect the benzene ring, the first flexible segment is connected to the amine group on the first amine-containing segment, and the chemical formula of the first branch chain contains C a1 H b1 N c1 R d1 , where C a1 H b1 N c1 is the chemical formula of the first amino-containing segment, R is the first flexible segment, 4≤a1≤12, 4≤b1≤22, 3≤c1≤7, 4≤d1≤8.

[0007] In one embodiment, the first flexible segment includes a first polyether segment and a second polyether segment connected to each other, the first polyether segment and the second polyether segment have different polymer monomers, and the chemical formula of the first polyether segment comprises (C a2 H b2 O) n, the chemical formula of the second polyether segment comprises (C a3 H b3 O) m , among which, 2≤a2≤6, 4≤b2≤12, 2≤a3≤6, 4≤b3≤12, 1≤n≤60, 1≤m≤60.

[0008] In one embodiment, the first amine-containing segment includes one or more of triethylenetetramine, diethylenetriamine, tetraethylenepentamine, and polyethylenepolyamine.

[0009] In one embodiment, the polymerizable monomer of the first polyether segment includes one or more of ethylene oxide, propylene oxide, butylene oxide, pentylene oxide, and hexylene oxide.

[0010] In one embodiment, the polymerizable monomer of the second polyether segment includes one or more of ethylene oxide, propylene oxide, butylene oxide, pentylene oxide, and hexylene oxide.

[0011] In one embodiment, the benzene ring is a phenol containing a hydroxyl group.

[0012] In one embodiment, the dispersant further comprises a second branch chain grafted onto the benzene ring, wherein the second branch chain comprises a second amino-containing segment and a second flexible segment, wherein the second flexible segment connects the second amino-containing segment, and the second branch chain is the same as or different from the first branch chain.

[0013] In one embodiment, the second branch chain is the same as the first branch chain, the second branch chain and the first branch chain are connected at the meta position of the benzene ring, and the second branch chain and the first branch chain are axially symmetrical about the benzene ring.

[0014] In one embodiment, the main chain includes an alkane segment and a third flexible segment, the alkane segment and the third flexible segment are both connected to the benzene ring, and the chemical formula of the alkane segment contains C a4 H b4 , wherein 1≤a4≤20, 1≤b4≤50; the third flexible segment is the same as or different from the first flexible segment.

[0015] In one embodiment, the weight average molecular weight of the dispersant is 2,000 to 10,000.

[0016] In one embodiment, the molecular weight dispersity index of the dispersant is 1 to 1.6.

[0017] In a second aspect, the present invention provides a method for preparing a dispersant, comprising: mixing a main chain precursor and a first amino-containing segment precursor in a mass ratio for reaction, wherein the main chain precursor contains a benzene ring, to obtain a mixed precursor containing a first amino-containing segment; mixing the mixed precursor and a first flexible segment precursor in a mass ratio for reaction, wherein the main chain precursor forms a main chain, and the first flexible segment precursor is graft copolymerized on the first amino-containing segment to form a first side chain, to obtain a dispersant.

[0018] 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, wherein the positive electrode plate comprises a current collector and a positive electrode material layer disposed on the current collector, and the positive electrode material layer comprises the dispersant as described in the first aspect.

[0019] The dispersant provided by the present invention includes a main chain and a first branch chain connected to the main chain, and the first branch chain also includes a first amino-containing chain segment and a first flexible chain segment connected to each other, so that the dispersant forms a multi-branched structure, and the dispersant has a large steric hindrance effect. When the dispersant is applied to the electrode slurry, the branch anchoring groups of the multi-branched polymer will be tightly adsorbed on the surface of the active particles (such as electrode active materials, carbon materials, etc.) to prevent the particles in the slurry from agglomerating, thereby improving the stability of the slurry; at the same time, the amine groups in the first amino-containing chain segment and the flexible groups in the first flexible chain segment (such as ether bonds, carbonyl groups, etc.) have a synergistic viscosity reduction effect, and the amine groups and the flexible groups can form hydrogen bonds and other interactions with solvent molecules to increase the fluidity of the solvent, thereby indirectly reducing the viscosity of the slurry. In addition, the amine groups in the first amino-containing chain segment can also bond with non-polar functional groups on the carbon material outside the electrode active material to further improve the dispersibility, and the flexible groups in the first flexible chain segment (such as ether bonds, carbonyl groups, etc.) can also provide wettability for the dispersant. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 is a schematic diagram of the molecular structure of a dispersant in one embodiment;

[0022] Figure 2 is a schematic diagram of the molecular structure of the first branch in one embodiment;

[0023] Figure 3 is a schematic diagram of the molecular structure of the first amine-containing segment in one embodiment;

[0024] Figure 4 is a schematic diagram of the molecular structure of the first amine-containing segment and the first flexible segment in one embodiment;

[0025] Figure 5 is a schematic diagram of the molecular structure of a main chain, a first branch chain, and a second branch chain in one embodiment;

[0026] Figure 6 is a molecular structure diagram of a dispersant in one embodiment;

[0027] Figure 7 is a flow chart of a method for preparing a dispersant in one embodiment;

[0028] Figure 8 This is a SEM image of the electrode after the slurry prepared in Comparative Example 2 is coated on the electrode;

[0029] Fig. 9 This is a SEM image of the electrode after the slurry prepared in Example 1 is coated on the electrode. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the specification of the present invention 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.

[0032] It should be noted that the "range" disclosed in the present invention is defined in the form of a lower limit and an upper limit, and 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 range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. 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 can all be expected: 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 specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] All steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may also include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b, etc.

[0034] Some embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0035] The present invention provides a dispersant, please refer to Figure 1-Figure 6 .

[0036] The dispersant is applied to the battery and can be added to the slurry of the electrode material. The types of batteries include but are not limited to lithium ion batteries, sodium ion batteries or potassium ion batteries. The slurry of the electrode material includes positive electrode active materials, positive electrode lithium supplement materials and conductive agents. Of course, in other embodiments, the dispersant can also be added to the negative electrode material.

[0037] In one implementation, please refer to Figure 1 , the dispersant includes a main chain ( Figure 1 The X part containing the benzene ring) and the first branch ( Figure 1 The main chain contains a benzene ring, the first branch chain is grafted and copolymerized on the benzene ring, and the first branch chain includes a first amino group-containing segment ( Figure 1 Z part) and the first flexible segment ( Figure 1 In R), the first flexible segment is connected to the first amine-containing segment.

[0038] Specifically, the main chain includes a benzene ring, wherein the benzene ring can be located in the middle or end of the main chain, wherein the benzene ring is located in the middle of the main chain, that is, the benzene ring is also connected to other polymer segments except the first branch chain, and the type of polymer segment is not limited; optionally, the benzene ring can be a hydroxyl-containing phenol. The first amine-containing segment is directly or indirectly connected to the benzene ring; optionally, the first amine-containing segment includes at least one amine group, and the amine group includes a primary amine (ANH2), a secondary amine (B2NH), and a tertiary amine (D3N). The first flexible segment is directly or indirectly connected to the first amine-containing segment; optionally, the first flexible segment can be connected to an amine group or other groups. In a specific embodiment, the first flexible segment is directly connected to the amine group and replaces the hydrogen atom on the amine group, thereby increasing the flexibility of the first branch chain through the first flexible segment. The first flexible segment is a flexible polymer segment, which may have an ether bond and / or a carbonyl group. It is understandable that the reason why the ether bond is flexible is that the oxygen atom in its molecular structure connects two hydrocarbon groups, allowing the molecular chain to rotate freely, thereby showing flexibility.

[0039] The dispersant provided by the present invention includes a main chain and a first branch chain connected to the main chain, and the first branch chain also includes a first amino-containing chain segment and a first flexible chain segment connected to each other, so that the dispersant forms a multi-branched structure, and the dispersant has a large steric hindrance effect. When the dispersant is applied to the electrode slurry, the branch anchoring groups of the multi-branched polymer will be tightly adsorbed on the surface of the active particles (such as electrode active materials, carbon materials, etc.) to prevent the particles in the slurry from agglomerating, thereby improving the stability of the slurry; at the same time, the amine groups in the first amino-containing chain segment and the flexible groups in the first flexible chain segment (such as ether bonds, carbonyl groups, etc.) have a synergistic viscosity reduction effect, and the amine groups and the flexible groups can form hydrogen bonds and other interactions with solvent molecules to increase the fluidity of the solvent, thereby indirectly reducing the viscosity of the slurry. In addition, the amine groups in the first amino-containing chain segment can also bond with non-polar functional groups on the carbon material outside the electrode active material to further improve the dispersibility, and the flexible groups in the first flexible chain segment (such as ether bonds, carbonyl groups, etc.) can also provide wettability for the dispersant.

[0040] In one implementation, please refer to Figure 2 and Figure 3 The first amino-containing segment replaces the connected benzene ring, the number of the first flexible segments is multiple, the multiple first flexible segments are connected to the amine group on the first amino-containing segment, and the chemical formula of the first branch chain contains C a1H b1 N c1 R d1 , where C a1 H b1 N c1 is the chemical formula of the first amino-containing segment, R is the first flexible segment, 4≤a1≤12, 4≤b1≤22, 3≤c1≤7, 4≤d1≤8.

[0041] Specifically, the first amino group segment may include multiple amino groups, and one amino group on the first amino group segment is connected to the benzene ring through a methylene group. The chemical formula of the first amino group segment includes C a1 H b1 N c1 Optionally, the first amine-containing segment comprises triethylenetetramine (C6H 18 N4), diethylenetriamine (C4H 13 N3), tetraethylenepentamine (C8H 23 N5), one or more of polyethylene polyamines; wherein polyethylene polyamine refers to the co-product of ethylenediamine, diethylenetriamine, triethylenetetramine and tetraethylenepentamine, or may refer to other ethyleneamines (e.g., pentaethylenehexamine and above). It should be noted that the above ethyleneamines may be monomers for synthesizing dispersants, and the number of hydrogen atoms in the first amine-containing segment of the dispersant product may be different from that of the above ethyleneamines.

[0042] Optionally, multiple first flexible segments are connected to at least one amine group, or multiple amine groups are connected to the first flexible segment. In a specific embodiment, the number of amine groups on the first amine segment can be four, each of which is connected to at least one first flexible segment, and two first flexible segments can be connected to the terminal amine group (amino group) of the first amine segment. Optionally, the number of first flexible segments (R) can be 1 more than the number of nitrogen atoms, that is, c1<d1; of course; in other embodiments, the number of first flexible segments (R) can be the same as or less than the number of nitrogen atoms.

[0043] It should be noted that the chemical formula of the first branch contains C a1 H b1 N c1 R d1 , means in C a1 H b1 N c1 R d1 It can be the complete chemical formula of the first branch chain, that is, the first branch chain consists of carbon atoms, hydrogen atoms, nitrogen atoms and the first flexible segment. Of course, in other embodiments, the complete chemical formula of the first branch chain includes carbon atoms, hydrogen atoms, nitrogen atoms and the first flexible segment. a1 H b1 N c1 R d1Segments or elements other than C a1 H b1 N c1 R d1 The partial structure and partial element composition of the first branch chain are only indicated for adaptability. The first branch chain may also include other branches or elements. For example, the chemical formula of the first branch chain may also include C a1 H b1 N c1 R d1 O e1 S f1 P g1 , where O is an oxygen atom, S is a sulfur atom, P is a phosphorus atom, and any one of e1, f1, and g1 can be 0 or a non-negative number.

[0044] The present invention connects multiple first flexible segments to the first amino-containing segment so that the two form a dendritic structure. The multiple first flexible segments further form branches and provide a greater steric hindrance effect. The multiple first flexible segments can form a molecular network structure and be tightly adsorbed on the surface of the active particles, preventing the particles in the slurry from agglomerating, thereby improving the stability of the slurry.

[0045] In one implementation, please refer to Figure 4 The first flexible segment includes a first polyether segment and a second polyether segment connected to each other, the first polyether segment and the second polyether segment have different polymer monomers, and the chemical formula of the first polyether segment includes (C a2 H b2 O) n The chemical formula of the second polyether segment comprises (C a3 H b3 O) m , among which, 2≤a2≤6, 4≤b2≤12, 2≤a3≤6, 4≤b3≤12, 1≤n≤60, 1≤m≤60.

[0046] Specifically, the first flexible segment is a copolymer segment, including a first polyether segment and a second polyether segment connected to each other, the first polyether segment includes a first repeating unit, the second polyether segment includes a second repeating unit, and the first repeating unit and the second repeating unit are different, that is, the first polyether segment and the second polyether segment have different polymerized monomers. In the chemical formula of the first polyether segment, C a2 H b2 O is the first repeating unit; in the chemical formula of the second polyether segment, C a3 H b3 O is the second repeating unit; wherein a2 may be the same as or different from a3, b2 may be the same as or different from b3, and n may be the same as or different from m.

[0047] Optionally, the polymerized monomer (first repeating unit) of the first polyether segment includes ethylene oxide (C2H4O), propylene oxide (C3H6O), butylene oxide (C4H8O), pentylene oxide (C5H 10 O), cyclohexane (C6H 12 The first polyether segment may be formed by the polymerization of ethylene oxide, and the second polyether segment may be formed by the polymerization of propylene oxide. In other embodiments, the first polyether segment may be formed by the copolymerization of ethylene oxide and propylene oxide, and the second polyether segment may be formed by the copolymerization of propylene oxide and butylene oxide.

[0048] It should be noted that the chemical formula of the polyether segment includes (C a2 H b2 O) n or (C a3 H b3 O) m , means in (C a2 H b2 O) n or (C a3 H b3 O) m It can be the complete chemical formula of the polyether segment, or it can be the complete chemical formula of the polyether segment including (C a2 H b2 O) n or (C a3 H b3 O) m For the chain segments or elements other than the above, the specific explanation can refer to the explanation of the first branch chain in the above embodiment. In a specific embodiment, the polyether chain segment may also include a polyether derivative chain segment, etc.

[0049] The present invention arranges the first flexible segment to include a first polyether segment and a second polyether segment connected to each other, and the first polyether segment and the second polyether segment are different, and utilizes the branched alkyl groups on the first polyether segment or the second polyether segment to further increase the dendritic structure in the dispersant; and the alkyl groups on the first polyether segment or the second polyether segment can also form more hydrogen bonds with solvent molecules to reduce the viscosity of the slurry.

[0050] In one embodiment, the first flexible segment only includes the first polyether segment, that is, the chemical formula of the first flexible segment comprises (C a2 H b2 O) n+m For example, the first flexible segment can be polymerized from ethylene oxide, or the first flexible segment can be polymerized from ethylene oxide and propylene oxide. Figure 5 The dispersant also includes a second branch chain grafted onto the benzene ring, the second branch chain includes a second amino-containing segment and a second flexible segment, the second flexible segment connects the second amino-containing segment, and the second branch chain is the same as or different from the first branch chain.

[0051] Specifically, the second amine-containing segment is directly or indirectly connected to the benzene ring; optionally, the second amine-containing segment includes at least one amine group. The second flexible segment is directly or indirectly connected to the second amine-containing segment; optionally, the second flexible segment can be connected to the amine group or other groups. The second flexible segment is a flexible polymer segment, and the second flexible segment can have an ether bond and / or a carbonyl group. In a specific embodiment, the position of the first branch and the second branch can be ortho (the first branch and the second are adjacent), meta (the first branch and the second branch are separated by one carbon atom) or para (the first branch and the second branch are separated by two carbon atoms).

[0052] In one embodiment, the second amine-containing segment is connected to the benzene ring, the number of the second flexible segment is multiple, and multiple second flexible segments are connected to the amine group on the second amine-containing segment. The second amine segment may include multiple amine groups, and an amine group on the second amine segment is connected to the benzene ring through a methylene group. Optionally, the first amine-containing segment includes one or more of triethylenetetramine, diethylenetriamine, tetraethylenepentamine, and polyethylenepolyamine. Multiple second flexible segments are connected to at least one amine group, or multiple amine groups are connected to second flexible segments.

[0053] It should be noted that the second branch chain is different from the first branch chain in that at least one of the molecular connection structure, element composition, and atomic number (carbon, hydrogen, oxygen, nitrogen, etc.) of the second branch chain and the first branch chain is different. For example, the first amine-containing segment may be triethylenetetramine, and the second amine-containing segment may be tetraethylenepentamine; or, the first flexible segment may be polymerized from ethylene oxide, and the second flexible segment may be polymerized from propylene oxide.

[0054] In one implementation, please refer to Figure 5 , the second branch is the same as the first branch, the second branch is connected to the first branch at the meta position of the benzene ring, and the second branch is axially symmetrical with the first branch about the benzene ring. Specifically, the second branch is the same as the first branch means that the second branch also conforms to the chemical formula C a1 H b1 N c1 R d1 The first branch chain and the second branch chain are located at the meta position of the benzene ring, and the two are axially symmetrical about the benzene ring.

[0055] The present invention sets a second branch chain, and the second branch chain is the same as the first branch chain, and the second branch chain and the first branch chain are axially symmetrical about the benzene ring, so that the first branch chain and the second branch chain can provide a greater steric hindrance together, and the dispersant can prevent the electrode material from agglomerating; and the symmetrical first branch chain and the second branch chain can also provide lubricity to improve the compaction density of the slurry after coating.

[0056] In one implementation, please refer to Figure 5 The main chain includes an alkane segment and a third flexible segment, both of which are connected to the benzene ring. The chemical formula of the alkane segment contains C a4 H b4 , wherein 1≤a4≤20, 1≤b4≤50; the third polyether segment and the first polyether segment are the same or different.

[0057] Specifically, the alkane segment and the third flexible segment can be located at the ortho position, meta position or para position connected to the benzene ring; Figure 5 As shown, the alkane segment and the third flexible segment are connected to the para position of the benzene ring, that is, the benzene ring is located between the alkane segment and the third flexible segment. Figure 5 C q H 2q+1 That is C a4 H b4 The third polyether segment is a flexible polymer segment, and the second flexible segment may have an ether bond and / or a carbonyl group. In a specific embodiment, the first polyether segment, the second polyether segment and the third polyether segment may be the same, or the three may not be completely the same.

[0058] In one embodiment, the first branch and the second branch are connected at the ortho position of the third flexible segment. Alternatively, in other embodiments, the first branch and the second branch are connected at the meta position of the third flexible segment.

[0059] In one implementation, please refer to Figure 6 The dispersant includes a main chain, a first branch chain and a second branch chain, wherein the main chain includes a benzene ring, a third flexible chain segment and an alkyl chain segment are respectively connected to the para position of the benzene ring, the first branch chain and the second branch chain are the same, and the first branch chain and the second branch chain are respectively connected to the ortho position of the third flexible chain segment, the first branch chain includes a first amino-containing chain segment and multiple first flexible chain segments, and the first flexible chain segment and the second flexible chain segment are the same.

[0060] In one embodiment, the weight average molecular weight of the dispersant is 2000 to 10000. Optionally, the weight average molecular weight of the dispersant may be 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, or 10000. When the weight average molecular weight of the dispersant is within the above range, the viscosity of the dispersant itself can be ensured to be appropriate, so as to provide a higher viscosity reduction effect.

[0061] In one embodiment, the molecular weight dispersity index of the dispersant is 1 to 1.6. Specifically, the molecular weight dispersity index D (molecular weight distribution index) of the dispersant is an index used to indicate the degree of dispersion of the molecular weight distribution, D = M (w) / M (n), wherein M (w) is the weight average molecular weight, M (n) is the number average molecular weight, and when D = 1, it is a polymer of uniform molecular weight. The greater the value of D is than 1, the wider the molecular weight distribution is, and the greater the degree of polydispersity is. Optionally, the molecular weight dispersity index of the dispersant can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6.

[0062] The present invention provides a method for preparing a dispersant. Figure 7 .

[0063] In one embodiment, the preparation method of the dispersant specifically comprises the following steps:

[0064] Step S10, mixing a main chain precursor and a first amino group-containing segment precursor according to a mass ratio for reaction, wherein the main chain precursor contains a benzene ring, to obtain a mixed precursor containing a first amino group-containing segment.

[0065] Step S20, mixing the mixed precursor and the first flexible segment precursor according to a mass ratio for reaction, the main chain precursor forms a main chain, and the first flexible segment precursor is graft copolymerized on the first amino-containing segment to form a first side chain, thereby obtaining a dispersant.

[0066] Specifically, in step S10, the main chain precursor may include a benzene ring and a partial segment of the main chain, such as an alkyl segment. The main chain precursor may include alkylphenol, which is a type of compound produced by alkylation of phenol.

[0067] In a specific embodiment, the alkylphenol may include one or more of propylphenol, butylphenol, pentylphenol, heptylphenol, octylphenol, nonylphenol, decylphenol, 3-n-propylphenol and related long-chain alkylphenols. In a specific embodiment, the alkyl segment and the phenolic hydroxyl group in the alkylphenol are located in the para position.

[0068] The first amine-containing segment precursor may contain at least one amine group, preferably ethyleneamine and its derivatives. In a specific embodiment, the ethyleneamine includes one or more of triethylenetetramine, diethylenetriamine, tetraethylenepentamine, and polyethylenepolyamine.

[0069] In a specific embodiment, step S10 includes: mixing alkylphenol and vinylamine according to a mass ratio, heating the mixture for reaction, adding a first compounding agent at the same time, and adding a second compounding agent after the alkylphenol is completely dissolved to obtain an alkylphenol derivative modified with vinylamine. The vinylamine in the alkylphenol derivative modified with vinylamine is the first amino-containing chain segment, and the alkylphenol is the main chain portion.

[0070] Optionally, in step S10, the mass ratio of alkylphenol to vinylamine is (0.1-0.9): 1. Optionally, the mass ratio of alkylphenol to vinylamine can be 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1.

[0071] Optionally, in step S10, the conditions for the heating reaction are: placing the mixture in an oil bath and stirring it at a rotation speed of 200 rpm to 500 rpm, the stirring time is 20 min to 30 min, and the reaction temperature is 50° C. to 70° C.

[0072] Optionally, in step S10, the first compounding agent includes xylene, the added mass of the first compounding agent is 200% of the mass of the alkylphenol, and the reaction temperature is increased to 70°C after the first compounding agent is added.

[0073] Optionally, in step S10, the second compounding agent includes formaldehyde solution, the mass ratio of the second compounding agent to the alkylphenol is 1:(1-2), and the second compounding agent is added after the alkylphenol is completely dissolved to 30°C.

[0074] Specifically, in step S20, the first flexible segment precursor contains an ether bond and is a polymerizable organic monomer, preferably an epoxy organic substance. In a specific embodiment, the epoxy organic substance includes one or more of ethylene oxide, propylene oxide, butylene oxide, pentyl oxide, and hexyl oxide.

[0075] In a specific embodiment, step S20 includes: mixing the vinylamine-modified alkylphenol derivative and the catalyst to obtain a mixture, and then adding epoxy organic matter to the mixture to obtain a dispersant after sufficient reaction.

[0076] Optionally, in step S20, the mass ratio of the vinylamine-modified alkylphenol derivative to the epoxy organic compound is 1:

[0077] (10~99); wherein the mass ratio of the ethyleneamine-modified alkylphenol derivative and the epoxy organic matter can be 1:10, 1:15, 1:20, 1:30, 1:50, 1:80, 1:99. Optionally, in step S20, the catalyst includes one or more of sodium hydroxide, potassium hydroxide, potassium methoxide and sodium methoxide. Wherein, sodium hydroxide, potassium hydroxide, etc. are aqueous hydroxide solutions with a mass fraction of 40%. The mass percentage of the catalyst to the ethyleneamine-modified alkylphenol derivative is 0.1wt%~0.5wt%; wherein the mass percentage of the catalyst to the ethyleneamine-modified alkylphenol derivative can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%.

[0078] Optionally, in step S20, the process of mixing the ethyleneamine-modified alkylphenol derivative and the catalyst includes, after the two are stirred and mixed, vacuum dehydration is performed for 2 hours to 3 hours, and then the temperature is raised to 100° C. to 150° C.

[0079] Optionally, in step S20, the heated mixture is polymerized with epoxy organic matter for 1 hour to 6 hours. After the polymerization reaction, it is cleaned with a cleaning agent and dried at low temperature for 12 hours to 24 hours.

[0080] Optionally, in step S20, at least two epoxy organic substances are used, and the two epoxy organic substances are added successively for polymerization to obtain the first polyether segment and the second polyether segment. Specifically, epoxy organic substance A and epoxy organic substance B may be included, and the mass ratio of the two is (1-3.7):1; wherein the mass ratio of epoxy organic substance A to epoxy organic substance B may be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.7:1.

[0081] Optionally, in step S20, the epoxy organic matter may include ethylene oxide and propylene oxide, wherein ethylene oxide is first added for polymerization to obtain a first polyether segment, and then propylene oxide is added for polymerization to obtain a second polyether segment.

[0082] Optionally, in step S20, the polymerization time of the first epoxy organic compound is 1 h to 3 h, and after the polymerization is completed, the temperature is lowered to 90° C. to 140° C.; then the second epoxy organic compound is added, and the polymerization reaction time is 1 h to 2 h.

[0083] Optionally, in step S20, the epoxy organic compound can react with the amine group in the vinylamine-modified alkylphenol derivative, mainly the amine group on the vinylamine. The epoxy organic compound can also react with the phenolic hydroxyl group in the vinylamine-modified alkylphenol derivative, mainly the phenolic hydroxyl group on the alkylphenol, to obtain a complete main chain.

[0084] The invention also provides a pole piece.

[0085] In one embodiment, the electrode sheet includes an electrode material and a dispersant provided in the above embodiment, and the electrode material is a positive electrode material or a negative electrode material. Among them, the positive electrode material can reversibly deintercalate active lithium ions, and the active lithium ions migrate between the positive electrode and the negative electrode of the battery to realize 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 cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium phosphate oxygen, fluorolithium vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. And a lithium supplement material can be added to the positive electrode material. Exemplarily, the lithium supplement material can be lithium iron-rich lithium, lithium cobalt-rich lithium, lithium nickel-rich lithium, etc.

[0086] The invention also provides a secondary battery.

[0087] In one embodiment, the secondary battery can be a composition system commonly used in the prior art, for example including a negative electrode plate, an electrolyte, a separator and a positive electrode plate. The electrolyte can be a solid electrolyte or a liquid electrolyte. When a solid electrolyte is selected, the use of a separator can be adaptively selected; both the positive electrode plate and the negative electrode plate can include the dispersant provided above.

[0088] The technical solution of the present invention is described in detail below through specific embodiments.

[0089] Example 1

[0090] This embodiment provides a dispersant, and the molecular structure of the dispersant can be referred to Figure 6 The dispersant includes a main chain and a branch chain, wherein the main chain contains a benzene ring, an alkane segment (nonane) connected to the benzene ring, and also includes a third flexible segment connected to the para position of the alkyl segment; the branch chain includes a first branch chain and a second branch chain, the first branch chain and the second branch chain are the same, and the first branch chain and the second branch chain are respectively connected to the ortho position of the third flexible segment. The first branch chain includes a first amino-containing segment (triethylenetetramine), a first polyether segment (polyethylene oxide) and a second polyether segment (polypropylene oxide).

[0091] The weight average molecular weight of the dispersant is about 5000, and the molecular weight dispersity index of the dispersant is 1.3.

[0092] The preparation method of the dispersant provided in this embodiment is as follows:

[0093] 1) Nonylphenol and triethylenetetramine are placed in a three-necked flask at a mass ratio of 0.5:1, and reacted in an oil bath under the following conditions: rotation speed of 200 rpm, stirring time of 20 min, and reaction temperature of 50° C.; then 200% of xylene is dripped into the three-necked flask (the mass of xylene added is 200% of the mass of nonylphenol), the temperature is raised to 70° C. to completely dissolve the nonylphenol, the mixture is cooled to 30° C., and formaldehyde solution is slowly dripped in (the mass ratio of formaldehyde solution to nonylphenol is 1:2) to obtain triethylenetetramine-modified nonylphenol (initiator).

[0094] 2) After stirring and mixing 30 g of triethylenetetramine-modified nonylphenol (initiator) and 0.03 g of 40% sodium hydroxide aqueous solution, vacuum dehydration is performed for 2 hours, and then the temperature is raised to 110° C. and polymerized with propylene oxide, wherein the mass ratio of initiator to propylene oxide (PO) is 1:30, and the polymerization time is 1 hour, and then the temperature is lowered to 100° C. and polymerized with ethylene oxide for 1 hour, and the mass ratio of propylene oxide to ethylene oxide is 2.7:1; after the reaction is completed, it is filtered and washed with methanol and deionized water, and dried at 50° C. for 24 hours to obtain a multi-branched polymer dispersant.

[0095] Example 2

[0096] This embodiment provides a dispersant, and the difference between this embodiment and embodiment 1 is that the weight average molecular weight of the dispersant is about 1000. The difference between the preparation method of this embodiment and embodiment 1 is that the mass ratio of nonylphenol to triethylenetetramine in step 1) is 0.09:1; the mass ratio of initiator to propylene oxide (PO) in step 2) is 1:8, and the mass ratio of propylene oxide to ethylene oxide is 1:1.

[0097] Example 3

[0098] This embodiment provides a dispersant, and the difference between this embodiment and embodiment 1 is that the weight average molecular weight of the dispersant is about 12000. The difference between the preparation method of this embodiment and embodiment 1 is that the mass ratio of nonylphenol to triethylenetetramine in step 1) is 1:1; the mass ratio of initiator to propylene oxide (PO) in step 2) is 1:100, and the mass ratio of propylene oxide to ethylene oxide is 3.7:1.

[0099] Example 4

[0100] This embodiment provides a dispersant, and the difference between this embodiment and embodiment 1 is that the molecular weight dispersibility index of the dispersant is 2. The difference between the preparation method of this embodiment and embodiment 1 is that the reaction temperature in step 1) is 65°C; in step 2), the temperature is raised to 130°C and then polymerized with propylene oxide, and then cooled to 120°C and then polymerized with ethylene oxide for 1 hour.

[0101] Example 5

[0102] This embodiment provides a dispersant, and the difference between this embodiment and embodiment 1 is that: the first branch chain includes a first amino group-containing segment (triethylenetetramine) and a first polyether segment (polypropylene oxide), and does not include a second polyether segment (polyethylene oxide). The difference between the preparation method of this embodiment and embodiment 1 is that: in step 2), no ethylene oxide needs to be added after the polymerization of propylene oxide.

[0103] Example 6

[0104] This embodiment provides a dispersant, and the difference between this embodiment and embodiment 1 is that the triethylenetetramine in the first amino-containing segment is replaced by tetraethylenepentamine. The difference between the preparation method of this embodiment and embodiment 1 is that in step 1), nonylphenol and diethylenetriamine are mixed in a mass ratio of 0.5:1.

[0105] Example 7

[0106] This embodiment provides a dispersant, and the difference between this embodiment and embodiment 1 is that: the third flexible segment is located at the meta position of the alkane segment, the first branch chain and the second branch chain are respectively connected to the ortho position of the third flexible segment, and the first branch chain and the second branch chain do not have symmetry about the main chain. The preparation method of this embodiment is different from that of embodiment 1 in that: in step 1), 3-n-propylphenol and diethylenetriamine are mixed in a mass ratio of 0.5:1.

[0107] Example 8

[0108] This embodiment provides a dispersant, and the difference between this embodiment and embodiment 1 is that the alkane chain segment connected to the benzene ring is propane. The difference between the preparation method of this embodiment and embodiment 1 is that in step 1), propylphenol and diethylenetriamine are mixed in a mass ratio of 0.5:1.

[0109] Comparative Example 1

[0110] This comparative example provides a commercially available polyvinyl pyrrolidone dispersant.

[0111] Comparative Example 2

[0112] This comparative example provides a dispersant, which only includes nonylphenol, triethylenetetramine, and a first polyether segment (polyethylene oxide and polypropylene oxide).

[0113] The preparation method of the dispersant provided in this comparative example is as follows:

[0114] 1) nonylphenol and triethylenetetramine are uniformly mixed at a mass ratio of 0.5:1 to obtain a mixture 1, and then the mixture 1 and polypropylene oxide are uniformly mixed at a mass ratio of 1:30, and finally mixed with ethylene oxide, wherein the mass ratio of propylene oxide to ethylene oxide is 2.7:1; after the mixing is completed, the mixture is dried at 50° C. for 24 hours to obtain a dispersant.

[0115] The dispersant parameters provided by Examples 1 to 8 and Comparative Examples 1 to 2 are shown in Table 1:

[0116] Table 1 Dispersant parameters provided in Examples and Comparative Examples

[0117]

[0118]

[0119] The dispersants provided in the above-mentioned Examples 1 to 8 and Comparative Examples 1 to 2 are added to the positive electrode slurry of the lithium iron phosphate battery to prepare the positive electrode slurry, and then the positive electrode slurry is coated on the collector to make the positive electrode sheet, and the positive electrode sheet is assembled into a secondary battery.

[0120] Among them, the preparation process of the positive electrode slurry includes: the positive electrode slurry of the lithium iron phosphate battery is mixed with solid dry material and N-methyl pyrrolidone (wherein, the weight of N-methyl pyrrolidone is 41.75wt% of the total weight of the positive electrode slurry). Taking the total weight as 100wt%: the solid dry material in the positive electrode slurry includes 96.5wt% of lithium iron phosphate, 1.3wt% of Super P and 2.2wt% 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 5nm to 10nm. Stir polyvinylidene fluoride and Super P in N-methyl pyrrolidone at 400 rpm for 20 minutes, add lithium iron phosphate and stir at 200 rpm for 10 minutes, then add dispersant and stir at 2000 rpm for 70 minutes to obtain a positive electrode slurry. The amount of dispersant added is 0.1%, that is, the amount of dispersant added is 0.1% of the mass of the positive electrode active material.

[0121] The positive electrode slurry, positive electrode sheet and secondary battery of the embodiment and comparative example were tested as follows, and the test results are shown in Table 2:

[0122] 1) Viscosity test of positive electrode slurry: The viscosity of the positive electrode slurry of the embodiment and the comparative example at the time of discharge and 24h slurry was tested respectively. The test process includes: selecting a suitable rotor, fixing the viscometer rotor, placing the glue under the viscometer rotor, and the glue just submerges the scale line of the rotor, instrument model: Shanghai Fangrui NDJ-5S, rotor: 64#, speed: 15-30r / min, test temperature: 25℃, test humidity: 20RH%~30RH%, test time: 1min, wait for the display to stabilize and read the data.

[0123] 2) Compacted density test of positive electrode sheet: The compacted density test formula is, compacted density = active material layer density / thickness of active material layer after compacted electrode sheet. Among them, active material layer density is the surface density of active material layer formed after positive electrode slurry is coated on current collector, and thickness of active material layer after compacted electrode sheet = total thickness of electrode sheet after compacted electrode sheet - thickness of current collector.

[0124] 3) Positive electrode flexibility test: The positive electrode is tested multiple times by the folding test method and the average value is taken. The test process includes: 18mg / cm 2After the positive electrode sheet with the highest surface density is folded in half, it is rolled back and forth three times with a 2kg roller, and then the positive electrode sheet is flattened and the above operation is repeated until light leaks from the folded part, and the number of folds is recorded. Each group is tested 5 times and the average value is taken. Calculation method = (the sum of the 5 test results) / 5.

[0125] 4) Secondary battery electrical performance test: charge at a rate of 0.1C with a cut-off voltage of 4.7V; perform constant voltage charging at a cut-off of 4.7V; after the charging process is completed, let it stand for 10 minutes and discharge at a rate of 0.1C with a cut-off voltage of 2.5V, and obtain the 0.1C first cycle charging capacity, 0.1C first cycle discharge capacity and efficiency respectively.

[0126] Table 2 Test results of embodiments and comparative examples

[0127]

[0128] From the test results of the embodiment and the comparative example in Table 2, it can be seen that when the dispersant provided by the present invention is added to the slurry, the viscosity of the slurry after discharge and after being left for 24 hours is lower than that of the comparative example, indicating that the slurry of the embodiment has good fluidity and coatability; and the pole piece and battery containing the dispersant prepared by the present invention have excellent performance, the pole piece resistivity of the embodiment is lower than that of the comparative example, and the charge and discharge capacity and efficiency of the battery are higher than those of the comparative example. Please also refer to Figure 8 ; Figure 8 The SEM scanning electron microscope image of the slurry coated electrode prepared in Comparative Example 2 clearly shows that there are certain agglomerated particles; Fig. 9 This is a SEM scanning electron microscope image of the slurry coated electrode prepared in Example 1. The slurry is evenly distributed, and particles of different particle sizes can also be well dispersed to form a uniformly distributed slurry state, thereby ensuring the electrochemical performance of the electrode.

[0129] From the test results of Example 1-Example 3 in Table 2, it can be seen that the difference between Example 1-Example 3 is that the weight average molecular weight of the dispersant is different. In Example 2 and Example 3, since the weight average molecular weight of the dispersant is too large or too small, its viscosity reduction and viscosity stabilization performance is reduced, and the viscosity increase of the slurry is greater than that of Example 1. During the coating process, the viscosity of the slurry in Example 2 and Example 3 increases too fast, and the conductive carbon in the slurry is unevenly distributed, which leads to a decrease in the compaction density and flexibility of the prepared positive electrode sheet, and the battery performance is slightly affected.

[0130] It can be seen from the test results of Example 1 and Example 4 in Table 2 that the dispersibility index will also affect the viscosity reduction and stabilization performance of the dispersant and the performance of the electrode. In Example 4, due to the large dispersibility index of the dispersant, the viscosity increase of the slurry is greater than that of Example 1, the compaction density and flexibility of the prepared positive electrode electrode are reduced, and the battery performance is slightly affected.

[0131] It can be seen from the test results of Example 1, Example 5 to Example 8 in Table 2 that the solution provided by the present invention can also be applied to a polyether segment, or to other vinylamines, and can also be applied to other alkylphenols. This shows that the solution provided by the present invention has a high application prospect, and different dispersants can be prepared according to the required battery performance.

[0132] In the description of the embodiments of the present invention, it should be noted that the orientation or positional relationship of terms such as "center", "up", "down", "left", "right", "vertical", "horizontal", "inside" and "outside" are based on the orientation or positional relationship described in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0133] What is disclosed above is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and 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 dispersant comprises a main chain and a first branch chain, wherein the main chain contains a benzene ring, the first branch chain is graft-copolymerized on the benzene ring, and the first branch chain comprises a first amino-containing segment and a first flexible segment connected by copolymerization.

2. The dispersant according to claim 1, characterized in that The first amino-containing segment is substituted to connect the benzene ring, the first flexible segment is connected to the amine group on the first amino-containing segment, and the chemical formula of the first branch chain contains C a1 H b1 N c1 R d1 , where C a1 H b1 N c1 is the chemical formula of the first amino-containing segment, R is the first flexible segment, 4≤a1≤12, 4≤b1≤22, 3≤c1≤7, 4≤d1≤8.

3. The dispersant according to claim 2, characterized in that The first flexible segment comprises a first polyether segment and a second polyether segment connected to each other, the first polyether segment and the second polyether segment have different polymerized monomers, and the chemical formula of the first polyether segment comprises (C a2 H b2 O) n , the chemical formula of the second polyether segment comprises (C a3 H b3 O) m , among which, 2≤a2≤6, 4≤b2≤12, 2≤a3≤6, 4≤b3≤12, 1≤n≤60, 1≤m≤60.

4. The dispersant according to claim 3, characterized in that The first amine-containing segment comprises one or more of triethylenetetramine, diethylenetriamine, tetraethylenepentamine, and polyethylenepolyamine; and / or The polymerizable monomer of the first polyether segment includes one or more of ethylene oxide, propylene oxide, butylene oxide, pentyl oxide, and hexyl oxide; and / or The polymerizable monomer of the second polyether segment includes one or more of ethylene oxide, propylene oxide, butylene oxide, pentyl oxide, and hexyl oxide; and / or The benzene ring is phenol containing a hydroxyl group.

5. The dispersant according to claim 1, characterized in that It also includes a second branch chain grafted copolymerized on the benzene ring, wherein the second branch chain includes a second amino-containing segment and a second flexible segment, the second flexible segment connects the second amino-containing segment, and the second branch chain is the same as or different from the first branch chain.

6. The dispersant according to claim 5, characterized in that The second branch chain is the same as the first branch chain, the second branch chain and the first branch chain are connected at the meta position of the benzene ring, and the second branch chain and the first branch chain are axially symmetrical about the benzene ring.

7. The dispersant according to claim 1, characterized in that The main chain includes an alkane segment and a third flexible segment, wherein the alkane segment and the third flexible segment are both connected to the benzene ring, and the chemical formula of the alkane segment contains C a4 H b4 , wherein 1≤a4≤20, 1≤b4≤50; the third flexible segment is the same as or different from the first flexible segment.

8. The dispersant according to claim 1, characterized in that The weight average molecular weight of the dispersant is 2000 to 10000; and / or the molecular weight dispersity index of the dispersant is 1 to 1.

6.

9. A method for preparing a dispersant, characterized in that: include: Mixing a main chain precursor and a first amino group-containing segment precursor according to a mass ratio for reaction, wherein the main chain precursor contains a benzene ring, to obtain a mixed precursor containing the first amino group-containing segment; The mixed precursor and the first flexible segment precursor are mixed and reacted according to a mass ratio, the main chain precursor forms a main chain, and the first flexible segment precursor is graft-copolymerized on the first amino-containing segment to form a first side chain to obtain a dispersant.

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 8.

Images