Dispersant and preparation method thereof, and secondary battery

Abstract

A dispersant and a preparation method thereof, and a secondary battery, wherein the dispersant comprises a repeating unit A and a repeating unit B, wherein the structural formula of the repeating unit A is: #imgabs0#, and the structural formula of the repeating unit B is: #imgabs1#; wherein R1 is a chain group, R2 is a cyclic group, and R3 is H or an alkane. The present invention introduces a substituent R1 with a strong polarity chain structure and a substituent R2 with a weak polarity cyclic structure into the dispersant of polyacrylate, thereby improving the affinity between the dispersant and the positive electrode material and the carbon material. The dispersant can form a huge steric hindrance between the positive electrode slurry particles, hindering the agglomeration and physical gelation of the slurry particles, and making the slurry particles have higher fluidity; thereby improving the slurry solid content, improving the coating efficiency, reducing the use of solvents in the slurry, and reducing energy consumption.

Description

Technical Field

[0001] The present application 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 in the production and sales of new energy vehicles, the demand for lithium-ion batteries has increased rapidly, leading to a further increase in the demand for positive electrode materials. In order to improve the performance and safety of lithium-ion batteries, the slurry dispersion of positive electrode materials is particularly important, especially the mixed slurry of positive electrode materials and conductive carbon materials. In order to improve the dispersibility of positive electrode slurry, dispersants are added to the positive electrode slurry.

[0003] At present, the traditional dispersant PVP (polyvinyl pyrrolidone) used in most of the market is difficult to achieve the expected effect. On the one hand, the large amount of PVP dispersant added has limitations on increasing solid content and improving processing performance; on the other hand, the high cost of PVP dispersant has brought great pressure to major battery manufacturers. Although the current new dispersants are relatively low in cost and the amount added is reduced compared to traditional dispersants, their effect on reducing the viscosity of the positive electrode slurry and increasing the solid content is still not enough to meet the requirements of battery manufacturers, and their compatibility with most positive electrode materials is poor, which cannot well meet the needs of battery manufacturers to increase battery capacity, improve productivity and reduce the burden of the production process on the environment. Summary of the invention

[0004] The purpose of the present application 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 dispersibility in positive electrode slurry.

[0005] To achieve the purpose of this application, this application provides the following technical solutions:

[0006] In a first aspect, the present invention provides a dispersant, the dispersant comprising a repeating unit A and a repeating unit B, wherein the structural formula of the repeating unit A is: , the structural formula of the repeating unit B is: ; Among them, R1 is a chain group, R2 is a cyclic group, and R3 is H or alkane.

[0007] In one embodiment, the repeating unit A includes a repeating unit A1 and a repeating unit A2, wherein the repeating unit A1 includes a chain group containing an amine group, and the repeating unit A2 includes a chain group containing an amide group.

[0008] In one embodiment, the amino-containing chain group includes: , where R 11 An alkane chain consisting of 1 to 12 C atoms; the chain group containing an amide group includes: , where R 12 and R13 It is an alkane chain composed of H or 1 to 3 C atoms.

[0009] In one embodiment, the structural formula of the dispersant is as shown in Formula I: Formula I; wherein R 31 and R 32 For H or alkane, m1:m2:n is 1:1:(0.5~2).

[0010] In one embodiment, the repeating unit B includes a repeating unit B1 and / or a repeating unit B2, the repeating unit B1 includes a cyclic group containing an amine group, and the repeating unit B2 includes a cyclic group containing an amide group.

[0011] In one embodiment, the amine-containing cyclic group includes: , where R 21 is H or alkane; the amide-containing cyclic group includes: or .

[0012] In one embodiment, the number average molecular weight of the dispersant is 4000-30000.

[0013] In one embodiment, the viscosity of the dispersant is 100 mPa·s to 1000 mPa·s.

[0014] In a second aspect, the present invention provides a method for preparing a dispersant, comprising: dissolving a monomer A, a monomer B and an initiator in a solvent, and causing the monomer A and the monomer B to undergo a polymerization reaction to generate the dispersant; the structural formula of the monomer A is , the structural formula of the monomer B is Among them, R1 is a chain group, R2 is a cyclic group, and R3 is H or an alkane.

[0015] In one embodiment, the monomer A includes monomer A1 and monomer A2, the monomer A1 includes a chain group containing an amine group, and the monomer A2 includes a chain group containing an amide group; the monomer A, the monomer B and the initiator are dissolved in a solvent to induce a polymerization reaction between the monomer A and the monomer B to generate the dispersant, including: dissolving the monomer A1, the monomer A2, the monomer B and the initiator in solvent A, removing the solvent A after sufficient reaction, and obtaining a polyacrylate solid; grinding the polyacrylate solid and dissolving it in solvent B to obtain the dispersant.

[0016] 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 electrolyte may be a liquid electrolyte or a solid electrolyte; the positive electrode material comprises the dispersant described in each embodiment of the first aspect.

[0017] The present invention introduces a substituent R1 with a strong polar chain structure into the polyacrylate dispersant, so that the dispersant can react with the less graphitized SP 3 Amorphous carbon with similar structure is soluble in water. In the positive electrode slurry using such carbon material, the dispersant can show strong affinity to the positive electrode material and the positive electrode material coated with the carbon material.

[0018] The present invention also introduces a cyclic substituent R2 into the dispersant, which can weaken the polarity of the dispersant to a certain extent, making the dispersant less effective for graphitized carbon and conductive carbon black SP 2 Carbon exhibits a strong affinity, and in a positive electrode slurry using such a carbon material, the dispersant can exhibit a strong affinity for the positive electrode material and the positive electrode material coated with the carbon material.

[0019] Therefore, the present invention will be able to regulate the proportion of repeating unit A and repeating unit B in the dispersant, so that the dispersant can be applied to most of the positive electrode slurries, and the dispersant can form a huge steric hindrance between the slurry particles, hindering the agglomeration and physical gelation of the slurry particles, so that the slurry particles have higher fluidity, and the positive electrode slurry exhibits an excellent viscosity reduction effect; thereby increasing the solid content of the slurry, improving the coating efficiency, reducing the use of solvents in the slurry, and reducing energy consumption.

[0020] In addition, the repeating unit A provided by the present invention can also be configured with an alkane R3 as a solvation chain, so that the dispersant can fully extend in the positive electrode slurry system, further preventing aggregation between slurry particles, preventing viscosity rebound, and further improving the quality stability of the slurry. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 is a flow chart of a method for preparing a dispersant in one embodiment;

[0023] Figure 2 is the hydrogen spectrum of the polyacrylate of Example 1;

[0024] Figure 3 is the infrared spectrum of the polyacrylate of Example 1;

[0025] Figure 4 It is the multiplication cycle diagram of Verification Example B1, Verification Example B3, Comparative Verification Example B1, and Comparative Verification Example B2. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0027] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used in this application and in the specification are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used in this application includes any and all combinations of one or more of the related listed items.

[0028] In conjunction with the accompanying drawings, some embodiments of the present application are described in detail below. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0029] The present application provides a dispersant, wherein the dispersant includes polyacrylate, and the polyacrylate is used as a main dispersant material. The polyacrylate includes a repeating unit A and a repeating unit B, and the structural formula of the repeating unit A is: , the structural formula of repeating unit B is: ; Among them, R1 is a chain group, R2 is a cyclic group, and R3 is H or alkane.

[0030] Specifically, the dispersant includes polyacrylate, which is a homopolymer or copolymer with acrylic ester as a monomer. Repeating unit A and repeating unit B are polymer repeating units obtained by polymerization of two different acrylic ester monomers (high molecular polymers are connected in a simple repeating unit and repeating manner). R1 ​​is a substituent, specifically a substituent with a chain group; R2 is another substituent, specifically a substituent with a cyclic group; R3 can be H or alkane (-(CH2) p1 CH3, p1 is an integer of 0 or greater) substituent.

[0031] Among them, a chain group refers to a structure in which multiple groups are connected in sequence in the substituent (main chain) of a polymer. A cyclic group refers to a structure in which multiple groups are connected in sequence in the substituent (main chain) of a polymer to form a closed ring.

[0032] Furthermore, the polyacrylate provided by the present invention is used to prepare a dispersant, and the dispersant is used in the positive electrode slurry. The polyacrylate is a high molecular polymer with a comb-shaped structure. It should be explained that the high molecular polymer with a comb-shaped structure includes a connecting body and a tooth comb line, wherein the connecting body is the carbon-carbon main chain of the polyacrylate, and the tooth comb line is the substituent branch on the carbon-carbon main chain; since each repeating unit (carbon-carbon main chain) is connected to at least one substituent branch (R1 and R2), the polyacrylate forms a comb-shaped structure.

[0033] The present invention introduces a substituent R1 with a strong polar chain structure into the polyacrylate dispersant, so that the dispersant can react with the less graphitized SP 3 Amorphous carbon with similar structure is soluble in water. In the positive electrode slurry using such carbon material, the dispersant can show strong affinity to the positive electrode material and the positive electrode material coated with the carbon material.

[0034] The present invention also introduces a cyclic substituent R2 into the dispersant, which can weaken the polarity of the dispersant to a certain extent, making the dispersant less effective for graphitized carbon and conductive carbon black SP 2 Carbon exhibits a strong affinity, and in a positive electrode slurry using such a carbon material, the dispersant can exhibit a strong affinity for the positive electrode material and the positive electrode material coated with the carbon material.

[0035] Therefore, the present invention will be able to regulate the proportion of repeating unit A and repeating unit B in the dispersant, so that the dispersant can be applied to most of the positive electrode slurries, and the dispersant can form a huge steric hindrance between the slurry particles, hindering the agglomeration and physical gelation of the slurry particles, so that the slurry particles have higher fluidity, and the positive electrode slurry exhibits an excellent viscosity reduction effect; thereby increasing the solid content of the slurry, improving the coating efficiency, reducing the use of solvents in the slurry, and reducing energy consumption.

[0036] In addition, the repeating unit A provided by the present invention can also be configured with an alkane R3 as a solvation chain, so that the dispersant can fully extend in the positive electrode slurry system, further preventing aggregation between slurry particles, preventing viscosity rebound, and further improving the quality stability of the slurry.

[0037] In one embodiment, the repeating unit A includes a repeating unit A1 and a repeating unit A2, the repeating unit A1 includes a chain group containing an amine group, and the repeating unit A2 includes a chain group containing an amide group.

[0038] In one embodiment, the repeating unit B includes a repeating unit B1 and / or a repeating unit B2, the repeating unit B1 includes a cyclic group containing an amine group, and the repeating unit B2 includes a cyclic group containing an amide group.

[0039] Specifically, an amino-containing chain group (or an amino-containing cyclic group) refers to a chemical structure in which one or more hydrogen atoms in an ammonia molecule are replaced by an alkyl group or an aryl group, thereby forming a primary amine (RNH2, where R is a substituent, i.e., an amino group), a secondary amine (R2NH, where R is a substituent), or a tertiary amine (R3N, where R is a substituent). An amide-containing chain group (or an amide-containing cyclic group) refers to a chemical structure containing both a carbonyl group and an amine group ( , R is H or a substituent).

[0040] In a specific embodiment, both the amine group and the amide group show a stronger affinity with the positive electrode material and the conductive carbon than other functional groups, so the polyacrylate containing the amine group and the amide group is more stably anchored to the positive electrode material and the conductive carbon. Therefore, the amine group and the amide group are arranged in the repeating unit of the polyacrylate.

[0041] Optionally, in the composition of polyacrylate, the polyacrylate may include two different repeating units, specifically including: 1) polyacrylate includes repeating unit A1 and repeating unit B1; 2) polyacrylate includes repeating unit A1 and repeating unit B2; 3) polyacrylate includes repeating unit A2 and repeating unit B1; 4) polyacrylate includes repeating unit A2 and repeating unit B2. It can be understood that in the composition of the polyacrylic acid, two different acrylate monomers are included.

[0042] Optionally, in the composition of polyacrylate, the polyacrylate may include three different repeating units, specifically including: 1) polyacrylate includes repeating unit A1, repeating unit A2 and repeating unit B1; 2) polyacrylate includes repeating unit A1, repeating unit A2 and repeating unit B2; 3) polyacrylate includes repeating unit A1, repeating unit B1 and repeating unit B2; 4) polyacrylate includes repeating unit A2, repeating unit B1 and repeating unit B2. It can be understood that in the composition of the polyacrylic acid, three different acrylate monomers are included.

[0043] Optionally, in the composition of polyacrylate, the polyacrylate may include four different repeating units, specifically including: 1) the polyacrylate includes repeating unit A1, repeating unit A2, repeating unit B1 and repeating unit B2. It can be understood that in the composition of the polyacrylic acid, four different acrylate monomers are included.

[0044] The polyacrylate provided by the present invention contains a chain structure containing an amine group (and / or an amide group) and a ring structure containing an amine group (and / or an amide group). The characteristics of the molecular structure are that the amine group and the amide group can not only provide a large number of hydrogen protons but also serve as hydrogen bond receptors, so that the polyacrylate and SP 3 Carbon has a stronger adsorption capacity.

[0045] In one embodiment, the amino-containing chain group includes: , where R 11 is an alkane chain consisting of 1 to 12 C atoms. Optionally, in a specific embodiment, the alkane chain includes -(CH2) q1 -、-(CH2) q2 C(CH3)2- and -(CH2) q3 At least one of CH(CH3)-; wherein q1 is an integer between 1 and 12, q2 is an integer between 0 and 9, and q3 is an integer between 0 and 10.

[0046] By adopting the above-mentioned chain groups containing primary amines (-NH2), the adsorption of polyacrylate can be greatly improved, because in terms of adsorption strength, -NH2>-NH(CH3)>-N(CH3)2, -NH2 can provide more hydrogen protons to form more hydrogen bonds, thereby forming an anchor with the positive electrode material and conductive carbon.

[0047] In one embodiment, the chain group containing an amide group includes: , where R 12 and R 13 It is an alkane chain composed of H or 1 to 3 C atoms.

[0048] By adopting the above-mentioned chain group containing tertiary amine (-NR2), the number of alkanes on the polyacrylate side chain can be increased. More alkanes make the polyacrylate more soluble in organic solvents, so that the polyacrylate can be fully extended in the positive electrode slurry system, further preventing aggregation between slurry particles and viscosity rebound, thereby further improving the quality stability of the slurry.

[0049] In one embodiment, the cyclic group containing an amine group includes: , where R 21 is H or an alkane. Optionally, in a specific embodiment, the cyclic group containing an amine group can be or .

[0050] By adopting the above-mentioned cyclic group containing tertiary amine (-NR2), on the one hand, the number of alkanes on the polyacrylate side chain can be increased, thereby improving the solvation and stretchability of the polyacrylate; on the other hand, the cyclic group has a larger molecular structure and can form a huge steric hindrance between the slurry particles, further hindering the agglomeration of the slurry particles and physical gelation.

[0051] In one embodiment, the amide-containing cyclic group includes: or .

[0052] By adopting the above-mentioned cyclic groups containing a large number of carbonyl and amide groups, the polarity of the amine functional group can be moderately reduced, and the dispersant and the higher graphitized carbon and conductive carbon black on the surface of the positive electrode material have better adsorption.

[0053] In one embodiment, the structural formula of the polyacrylate is as shown in Formula I: Formula I; wherein R 31 and R 32 For H or alkane, m1:m2:n is 1:1:(0.5~2).

[0054] Specifically, based on the above embodiment, the structural formula of the polyacrylate provided by the present invention is shown in the above formula I, and the polyacrylate includes a repeating unit A1 of a chain group containing an amine group, a repeating unit A2 of a chain group containing an amide group, and a repeating unit B containing a cyclic group; wherein the type of the repeating unit B containing a cyclic group is not specifically limited (it may include a repeating unit B1 and / or a repeating unit B2). Optionally, m1:m2:n can be 1:1:0.5, 1:1:1, 1:1:1.5, 1:1:2.

[0055] In one embodiment, when the polyacrylate includes an amino-containing chain group, an amide-containing chain group, and an amino-containing cyclic group, the structural formula of the polyacrylate is as shown in Formula II:

[0056] Formula II. Therefore, in Formula II, R2 is a cyclic group containing an amine group.

[0057] In one embodiment, when the polyacrylate includes an amino-containing chain group, an amide-containing chain group, and an amide-containing cyclic group, the structural formula of the polyacrylate is as shown in Formula III:

[0058] Formula III. Therefore, in Formula III, R2 is a cyclic group containing an amide group.

[0059] In one embodiment, when the polyacrylate includes an amino-containing chain group, an amide-containing chain group, and an amide-containing cyclic group, the structural formula of the polyacrylate is as shown in Formula IV:

[0060] Formula IV. Therefore, in Formula IV, R2 is another cyclic group containing an amide group.

[0061] In one embodiment, when the polyacrylate includes an amino-containing chain group, an amide-containing chain group, and an amide-containing cyclic group, the structural formula of the polyacrylate is as shown in Formula V:

[0062] Formula V. Wherein, n1+n2=n. Therefore, in Formula V, R2 is of two types, namely, a cyclic group containing an amine group and a cyclic group containing an amide group.

[0063] In one embodiment, the number average molecular weight (Mn) of the dispersant is 4000-30000. Optionally, the number average molecular weight of the polyacrylate may be 4000, 6000, 8000, 10000, 12000, 14000, 16000, 18000, 20000, 22000, 24000, 26000, 28000, 30000. Optionally, the number average molecular weight of the polyacrylate is 5000-15000.

[0064] In one embodiment, the dispersant further includes an organic solvent, and the organic solvent may include a combination of one or more of NMP (N-methylpyrrolidone), DMAC (dimethylacetamide), DMSO (dimethyl sulfoxide), tetrahydrofuran, acetone, ethyl acetate, and ethylene dichloride.

[0065] In one embodiment, the dispersant may further include a defoaming agent, and the defoaming agent may include polydimethylsiloxane, trialkyl melamine, melamine cyanurate chloride, a copolymer of ethylene oxide and propylene oxide, and the like.

[0066] In one embodiment, the viscosity of the dispersant is 100 mPa·s to 1000 mPa·s. Optionally, the viscosity of the dispersant may be 100 mPa·s, 200 mPa·s, 300 mPa·s, 400 mPa·s, 500 mPa·s, 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, or 1000 mPa·s.

[0067] It can be understood that the viscosity of the dispersant is related to the molecular weight of the polyacrylate and the mass proportion of the polyacrylate. At the same mass ratio, the higher the molecular weight of the polyacrylate, the greater the viscosity of the dispersant; at the same molecular weight, the higher the mass proportion, the greater the viscosity of the dispersant. Optionally, when the mass proportion of the polyacrylate in the dispersant is 30%, the viscosity of the dispersant is 100mPa·s~1000mPa·s.

[0068] In one embodiment, the present invention further provides a method for preparing a dispersant, comprising: dissolving monomer A, monomer B and an initiator in a solvent, and causing monomer A and monomer B to undergo a polymerization reaction to generate polyacrylate;

[0069] The structural formula of monomer A is , the structural formula of monomer B is ; Among them, R1 is a chain group, R2 is a cyclic group, and R3 is H or alkane.

[0070] Specifically, monomer A is an acrylate monomer, specifically an acrylate monomer whose side chain (substituent) is a chain; monomer B is an acrylate monomer, specifically an acrylate monomer whose side chain (substituent) is a ring.

[0071] Optionally, in a specific embodiment, the initiator includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisovaleronitrile, azobiscyclohexylcarbonitrile, and dimethyl azobisisobutyrate. The solvent includes tetrahydrofuran or N,N-dimethylformamide.

[0072] Optionally, in a specific embodiment, the initiator accounts for 1.5% to 2.0% of the total monomers (including monomer A and monomer B) by molar ratio, and can be specifically 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2.0%.

[0073] Optionally, in a specific embodiment, monomer A, monomer B and an initiator are dissolved in a solvent, including: dissolving a certain mass of monomer A, monomer B and an initiator in a solvent to obtain a mixture, maintaining the concentration of the monomers at 1 mol / L, and placing the mixture in a four-necked flask equipped with a reflux condenser, a thermometer, a magnetic stirrer and a nitrogen inlet.

[0074] Optionally, in a specific embodiment, the polymerization reaction of monomer A and monomer B to generate polyacrylate comprises: stirring and dispersing the mixture at a speed of 700 rpm to 800 rpm for 0.5 h under the protection of nitrogen. In a water bath, the stirring speed is adjusted to 400 rpm to 600 rpm, and the mixture is slowly heated to 80° C. and kept warm for 5 to 10 h; after the insulation period, a polymerization inhibitor is added and stirring is continued to obtain a polyacrylate solution. At 60° C., the solvent is removed by rotary evaporation to obtain a solid polyacrylate.

[0075] Optionally, the reaction time of the polyacrylate can be 6 h to 8 h.

[0076] Optionally, the role of the polymerization inhibitor is to prevent the polymer from continuing to polymerize so as to achieve the purpose of controlling the molecular weight. The polymerization inhibitor includes at least one of phenothiazine, hydroquinone, p-hydroxyanisole, etc. The addition amount of the polymerization inhibitor is 0.2% of the total monomer molar amount.

[0077] In one embodiment, monomer A includes monomer A1 and monomer A2, monomer A1 includes a chain group containing an amine group, and monomer A2 includes a chain group containing an amide group. Specifically, monomer A1 is a chain acrylate monomer whose branch chain (substituent) is an amine group; monomer A2 is a chain acrylate monomer whose branch chain (substituent) is an amide group.

[0078] Optionally, in a specific embodiment, the monomer A1 may include methacrylate aminoalkyl ester, the structural formula of methacrylate aminoalkyl ester is , where R 11 It is an alkane chain consisting of 1 to 12 C atoms.

[0079] Optionally, in a specific embodiment, monomer A2 may include methacrylic acid alkyl amide, the methacrylic acid alkyl amide having the structural formula , where R 12 and R 13 It is an alkane chain composed of H or 1 to 3 C atoms.

[0080] In one embodiment, monomer B includes monomer B1 and monomer B2, monomer B1 includes a cyclic group containing an amine group, and monomer B2 includes a cyclic group containing an amide group. Specifically, monomer B1 is a cyclic acrylate monomer whose side chain (substituent) is an amine group; monomer B2 is a cyclic acrylate monomer whose side chain (substituent) is an amide group.

[0081] Optionally, in a specific embodiment, the monomer B1 may include methacrylic acid-tetramethyl-piperidyl ester or methacrylic acid-pentamethyl-piperidyl ester, and the structural formula of methacrylic acid-tetramethyl-piperidyl ester is ; The structural formula of methacrylate-pentamethyl-piperidinyl ester is .

[0082] Optionally, in a specific embodiment, monomer B2 may include ethylene-4-amino-2-pyrrolidone or acrylate-N-succinimidyl ester, and the structural formula of ethylene-4-amino-2-pyrrolidone is ; The structural formula of acrylic acid-N-succinimidyl ester is .

[0083] In one embodiment, the molar ratio of monomer A1, monomer A2 and monomer B is 1:1:(0.5-2).

[0084] In one embodiment, the present invention also provides a method for preparing a dispersant, please refer to Figure 1 ,include:

[0085] Step S10, dissolving monomer A1, monomer A2, monomer B and initiator in solvent A, removing solvent A after sufficient reaction, and obtaining polyacrylate solid.

[0086] Step S20, grinding the polyacrylate solid and dissolving it in solvent B to obtain a dispersant.

[0087] Optionally, solvent A includes tetrahydrofuran or N,N-dimethylformamide. Solvent B includes one or more of NMP (N-methylpyrrolidone), DMAC (dimethylacetamide), DMSO (dimethyl sulfoxide), tetrahydrofuran, acetone, ethyl acetate, and ethylene dichloride.

[0088] Optionally, in a specific embodiment, before adding the polyacrylate to the organic solvent, the method further includes: grinding the polyacrylate into powder, wherein the particle size of the powder is 100-200 meshes.

[0089] Optionally, in a specific embodiment, polyacrylate is added to an organic solvent, and the mixture is fully stirred and dispersed to obtain a dispersant, including: dissolving ground polyacrylate powder and a defoaming agent in an organic solvent, and then dispersing the mixture at a rotation speed of 1000 rpm for 6 hours at room temperature and low humidity to obtain a dispersant.

[0090] In one embodiment, the present invention also provides a secondary battery, which can be a commonly used composition system 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, and the use of the separator can be adaptively selected when a solid electrolyte is selected; the positive electrode plate includes a current collector and a positive electrode material layer arranged on the current collector, and the positive electrode material layer includes the dispersant provided above. The secondary battery includes a positive electrode material and a dispersant as provided in the above embodiment. Specifically, the positive electrode material may include a positive electrode active material and a positive electrode lithium supplement material. Optionally, the positive electrode active material may be a phosphate positive electrode active material and a ternary positive electrode active material. In a specific embodiment, it includes one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, fluorolithium vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0091] In one embodiment, the outer surface of the positive electrode material is coated with a carbon coating layer. The carbon coating layer includes a carbon material, and the carbon material may include SP 2 Carbon, SP3 Carbon, etc.

[0092] The technical solution of the present invention is described in detail below through specific embodiments.

[0093] Example 1

[0094] This embodiment provides a dispersant, which includes polyacrylate and an organic solvent. The organic solvent is NMP. The structural formula of the polyacrylate is: , where R 11 For alkanes with 1 to 3 carbon atoms, please refer to Figure 2 The number average molecular weight of the polyacrylate was 10,000, and the viscosity of the dispersant was 126 mPa·s.

[0095] The preparation method of the dispersant provided in this embodiment is as follows:

[0096] 1) Preparation of polyacrylate: Dissolve methacrylate aminoalkyl ester, acrylic acid-N-succinimide ester and initiator in a solvent; wherein the molar ratio of methacrylate aminoalkyl ester to acrylic acid-N-succinimide ester is 1:1, and the initiator accounts for 2% of the total monomer molar ratio. The monomer concentration is maintained at 1 mol / L, and all compounds are placed in a four-necked flask equipped with a reflux condenser, a thermometer, a magnetic stirrer and a nitrogen inlet. The mixture is stirred and dispersed at 800 rpm for 0.5 h under the protection of nitrogen. Under water bath conditions, the stirring speed is adjusted to 600 rpm, slowly heated to 80 ° C, and kept warm for 6 h. After keeping warm, 0.2% (accounting for the molar amount of the total monomer) of hydroquinone is added to the solution, and stirring is continued for 30 min to obtain a polyacrylate solution. The solvent is removed by rotary evaporation at 60 ° C to obtain a polyacrylate solid.

[0097] 2) Preparation of dispersant: Grind the polyacrylate solid into 200-mesh powder, dissolve the polyacrylate powder and defoamer in a flask filled with NMP, the mass ratio of polyacrylate powder, defoamer and NMP is 30:0.1:69.9, disperse at 1000 rpm for 6 hours under room temperature and low humidity environment to obtain the dispersant.

[0098] The number average molecular weight of the dispersant was 10,000 as determined by gel permeation chromatography (GPC).

[0099] Figure 3 The infrared spectrum of the polyacrylate in Example 1, wherein a (wave number about 3450 cm -1 , 3350 cm -1The double peaks of the branched linear primary amine -NH2 containing amino groups are the vibration absorption peaks, while the N of the cyclic quaternary amine -N(CH2)2 has no connected hydrogen, so there is no peak in the a region; b (wave number is about 3000~2900 cm -1 ) is the -CH stretching vibration peak of aliphatic; c (wave number about 1650 cm -1 ) is the vibration absorption peak of the carbonyl group of the ester group and the carbonyl group -C=O of the ring structure; d (wave number about 1460 cm -1 , 1430 cm -1 )) is the bending vibration peak of -CH2; e (wave number is about 1300 cm -1 ) is the CO vibration absorption peak of the ester group COOR; f (1230~1030cm -1 ) is the stretching vibration peak of CN; g (wave number is about 1000 cm -1 ) is the OC vibration absorption peak of O-CH. -1 There is no obvious peak, which proves that the corresponding polymer has been synthesized.

[0100] Example 2

[0101] This embodiment provides a dispersant, which includes polyacrylate, defoamer and organic solvent. The difference between this embodiment and embodiment 1 is that the structural formula of the polyacrylate is: The number average molecular weight of the polyacrylate is 10,000, and the viscosity of the dispersant is 155 mPa·s.

[0102] The difference between the preparation method of the dispersant provided in this embodiment and that in embodiment 1 is that the monomers are methacrylic acid alkylamide and methacrylic acid-tetramethyl-piperidyl ester.

[0103] The number average molecular weight of the dispersant was 10,000 as determined by gel permeation chromatography (GPC).

[0104] Example 3

[0105] This embodiment provides a dispersant, which includes polyacrylate, defoamer and organic solvent. The difference between this embodiment and embodiment 1 is that the structural formula of the polyacrylate is: The number average molecular weight of the polyacrylate is 9200, and the viscosity of the dispersant is 148 mPa·s.

[0106] The preparation method of the dispersant provided in this embodiment is different from that in Embodiment 1 in that the monomers are methacrylic acid aminoalkyl ester, methacrylic acid alkyl amide and methacrylic acid-tetramethyl-piperidyl ester, and the molar ratio of the three is 1:1:1.

[0107] The number average molecular weight of the dispersant was 9200 as determined by gel permeation chromatography (GPC).

[0108] Example 4

[0109] This embodiment provides a dispersant, which includes polyacrylate, defoamer and organic solvent. The difference between this embodiment and embodiment 1 is that the structural formula of the polyacrylate is: The number average molecular weight of the polyacrylate is 12500, and the viscosity of the dispersant is 200 mPa·s.

[0110] The preparation method of the dispersant provided in this embodiment is different from that in Embodiment 1 in that the monomers are methacrylate aminoalkyl ester, methacrylate alkyl amide and acrylic acid-N-succinimide ester, and the molar ratio of the three is 1:1:1.

[0111] The number average molecular weight of the dispersant was 12500 as determined by gel permeation chromatography (GPC).

[0112] Example 5

[0113] This embodiment provides a dispersant, which includes polyacrylate, defoamer and organic solvent. The difference between this embodiment and embodiment 1 is that the structural formula of the polyacrylate is: The number average molecular weight of the polyacrylate is 14,000, and the viscosity of the dispersant is 230 mPa·s.

[0114] The preparation method of the dispersant provided in this embodiment is different from that in Embodiment 1 in that the monomers are methacrylate aminoalkyl ester, methacrylate alkyl amide, acrylic acid-N-succinimide ester and methacrylate-tetramethyl-piperidinyl ester, and the molar ratio of the four is 1:1:1:1.

[0115] The number average molecular weight of the dispersant was 14,000 as determined by gel permeation chromatography (GPC).

[0116] Comparative Example 1

[0117] The organic solvent provided in this comparative example is NMP (N-methylpyrrolidone).

[0118] Comparative Example 2

[0119] This comparative example provides a dispersant, which includes polyacrylate, defoamer and organic solvent. The polyacrylate is a commonly used polyacrylate on the market.

[0120] Comparative Example 3

[0121] This comparative example provides a dispersant, and the dispersant is PVP-K15 ((polyvinyl pyrrolidone K-15)).

[0122] The dispersant parameters provided in Examples 1 to 5 are shown in Table 1:

[0123] Table 1 Dispersant parameters provided in the examples

[0124]

[0125] The dispersants provided in the above-mentioned Examples 1 to 5 and the solvents and dispersants provided in Comparative Examples 1 to 3 were respectively prepared into positive electrode slurries according to the following methods:

[0126] The dispersant is added to the positive electrode slurry of the lithium iron phosphate battery and named as Verification Example B1-Verification Example B5, Comparative Verification Example B1-Comparative Verification Example B3. Among them, the positive electrode slurry of the lithium iron phosphate battery is mixed with solid dry material and N-methylpyrrolidone (wherein, the weight of N-methylpyrrolidone 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. Stir polyvinylidene fluoride and Super P in N-methylpyrrolidone at 400 rpm for 20 minutes, add lithium iron phosphate and stir at 200 rpm for 10 minutes, then add the dispersant and stir at 2000 rpm for 70 minutes to obtain the positive electrode slurry.

[0127] The above verification examples B1-B5 and comparative verification examples B1-B2 were tested as follows, and the test results in Table 2 were obtained:

[0128] Viscosity test: Verification Example B1-Verification Example B5, Comparative Verification Example B1-Comparative Verification Example B3, test the viscosity of the slurry at the time of discharge and 24h respectively. Select a suitable rotor, fix the viscometer rotor, place 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 is 1min, and read the data after the display is stable. The viscosity reference value of the original positive electrode slurry (without dispersant added) is (10000±2000) mPa·s.

[0129] Fluidity test: For the slurry fluidity test, take an appropriate amount of positive electrode slurry (verification example B1-verification example B5, comparison verification example B1-comparison verification example B3) with a medicine spoon and observe whether the positive electrode slurry flows smoothly. If the natural flow is smooth, it is judged as OK; if the fluidity is not good, the slurry appears jelly-like and lumpy, indicating the presence of gel, it is judged as NG. The specific data is shown in Table 2:

[0130] Table 2

[0131]

[0132] From the test results of the verification examples and comparative verification examples in Table 2, it can be seen that the slurry viscosity stability performance of verification examples B1 to B5 is much better than that of comparative verification examples B1 to B3, showing excellent viscosity stability effect and extending the service life of the slurry. Adding 0.05% dispersant to the positive electrode slurry can increase the solid content by 5% to 9% in the DY-12, DY-17, YN-7, and S20 systems, especially the improvement of verification examples B3 and B4 is more obvious; it should be noted that DY-12, DY-17, YN-7, and S20 in Table 2 are all commercially available lithium iron phosphate (LFP) models, and DY-12, YN-7, and S20 are from different positive electrode material companies. In addition, when the addition amount of verification example B3 is 0.10%, the solid content in DY-12 and YN-7 can be increased by 10% and 11%, respectively, showing excellent dispersion performance. In the common polyacrylate of comparative verification example B2, it has no obvious effect on the reduction of slurry viscosity in the liquid phase method and solid phase method iron-lithium system, and cannot well improve the solid content of the slurry. In the common dispersant of comparative verification example B3, it has certain dispersing and viscosity reduction performance, but its universality is poor; and at the same addition amount or even doubled addition amount, it is far inferior to the viscosity reduction and solid content improvement of verification examples B1 to B5 at low addition amounts.

[0133] The positive electrode slurry (DY-12) provided in the above Verification Examples B1-B5 and Comparative Verification Examples B1-B3 was coated on the current collector to make a positive electrode sheet, and the positive electrode sheet was assembled into a secondary battery, and the electrochemical performance of the secondary battery was tested. The test results are shown in Table 3. In addition, the cycle capacity measurement is recorded from the second cycle after the first charge and discharge, that is, Figure 4 The cycle starts from the second cycle after the first charge and discharge. The specific data are shown in Table 3:

[0134] Table 3

[0135]

[0136] From the test results of the verification examples and comparative verification examples in Table 3, it can be seen that the electrochemical performance of verification examples B1 to B5 did not show any degradation compared with comparative verification example B1, and some electrochemical performance was even improved; on the other hand, the electrochemical performance of comparative verification example B2 was significantly reduced, and its cycle performance was significantly worse; comparative verification examples B1 and B3 were at normal levels, and the retention rates of verification examples B1 to B5 were improved. Figure 4 It can also be seen from the rate cycle diagrams of Verification Example B1, Verification Example B3, Comparative Verification Example B1, and Comparative Verification Example B2 that, under the same number of cycles, the specific capacity of the verification examples is higher than that of the comparative verification examples, thus proving that the dispersant provided by the present invention has better performance than the existing dispersants.

[0137] In the description of the embodiments of the present application, 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 application and simplifying the description, and do not indicate or imply 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 application.

[0138] What is disclosed above is only a preferred embodiment of the present application, and it certainly cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of implementing the above embodiment and equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A dispersant, characterized in that: The dispersant comprises a repeating unit A and a repeating unit B, and the structural formula of the repeating unit A is: , the structural formula of the repeating unit B is: ; Wherein, R1 is a chain group, R2 is a cyclic group, and R3 is H or an alkyl group; The repeating unit A includes a repeating unit A1, and the repeating unit A1 includes an amino-containing chain group; the amino-containing chain group includes: , where R 11 It is an alkane chain consisting of 1 to 12 C atoms; The repeating unit B includes a repeating unit B1 and / or a repeating unit B2, wherein the repeating unit B1 includes an amine-containing cyclic group, and the repeating unit B2 includes an amide-containing cyclic group; the amine-containing cyclic group includes: , where R 21 is H or alkyl; the amide-containing cyclic group includes: or ; The number average molecular weight of the dispersant is 4000-30000.

2. The dispersant according to claim 1, characterized in that The repeating unit A includes a repeating unit A2, and the repeating unit A2 includes a chain group containing an amide group.

3. The dispersant according to claim 2, characterized in that The chain group containing an amide group includes: , where R 12 and R 13 It is an alkane chain composed of H or 1 to 3 C atoms.

4. The dispersant according to claim 3, characterized in that The structural formula of the dispersant is shown in Formula I: Formula I; wherein R 31 and R 32 It is H or alkyl, and m1:m2:n is 1:1:(0.5~2).

5. The dispersant according to any one of claims 1 to 4, characterized in that The viscosity of the dispersant is 100 mPa·s to 1000 mPa·s.

6. A method for preparing a dispersant, characterized in that: include: Dissolving monomer A, monomer B and an initiator in a solvent to promote polymerization of the monomer A and the monomer B to generate the dispersant; The structural formula of the monomer A is , the structural formula of the monomer B is Wherein, R1 is a chain group, R2 is a cyclic group, and R3 is H or an alkyl group; The dispersant comprises a repeating unit A and a repeating unit B, wherein the repeating unit A comprises a repeating unit A1, and the repeating unit A1 comprises an amino-containing chain group; the amino-containing chain group comprises: , where R 11 It is an alkane chain consisting of 1 to 12 C atoms; The repeating unit B includes a repeating unit B1 and / or a repeating unit B2, wherein the repeating unit B1 includes an amine-containing cyclic group, and the repeating unit B2 includes an amide-containing cyclic group. The amine-containing cyclic group includes: , where R 21 is H or alkyl; the amide-containing cyclic group includes: or ; The number average molecular weight of the dispersant is 4000-30000.

7. The preparation method according to claim 6, characterized in that: The monomer A includes a monomer A1 and a monomer A2, wherein the monomer A1 includes a chain group containing an amine group, and the monomer A2 includes a chain group containing an amide group; the monomer A, the monomer B and the initiator are dissolved in a solvent to induce a polymerization reaction between the monomer A and the monomer B to generate the dispersant, comprising: The monomer A1, the monomer A2, the monomer B and the initiator are dissolved in a solvent A, and after sufficient reaction, the solvent A is removed to obtain a polyacrylate solid; The polyacrylate solid is ground and then dissolved in solvent B to obtain the dispersant.

8. 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 5.

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