Polymer, preparation method, dispersing agent, positive electrode slurry, positive electrode plate, secondary battery, and electrical apparatus

Abstract

The present application provides a polymer, a preparation method, a dispersing agent, a positive electrode slurry, a positive electrode plate, a secondary battery, and an electrical apparatus. The polymer comprises a structure as shown in a formula (I), X comprising at least one of a carboxyl group, an ester group, a sulfo group, a sulfonate group, a phosphate group and a phosphate ester group; X' comprising a non-polar group; L comprising a structural unit represented by formula (II), R1 comprising a C1-12 alkylene, a C6-12 arylene or formula (A), R2 containing a C1-12 alkylene, a C6-12 arylene or formula (B), and R3 containing hydrogen or a C1-3 alkyl, EO representing -CH2-CH2-O-, PO representing -CH(CH3)-CH2-O -, m1 and m2 each independently being an integer between 3 and 60, and n1 and n2 each independently being an integer between 0 and 60.

Description

Polymer, preparation method, dispersant, positive electrode slurry, positive electrode sheet, secondary battery and electrical device

[0001] Cross-references

[0002] This application refers to Chinese Patent Application No. 202310864261.7 filed on July 14, 2023, entitled “Polymer, Preparation Method, Dispersant, Positive Electrode Slurry, Positive Electrode Sheet, Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to a polymer, a preparation method, a dispersant, a positive electrode slurry, a positive electrode sheet, a secondary battery, and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0005] As the main component of the secondary battery, the positive electrode sheet directly affects the application performance of the secondary battery. The positive electrode sheet is generally composed of a current collector, a positive electrode active material, a conductive agent, and a binder. However, the positive electrode active material is generally a nano-scale material, which has a large specific surface area, resulting in a higher surface activity. During the homogenization of the positive electrode slurry, agglomeration is very likely to occur, forming larger agglomerates, which affects the coating effect of the electrode and makes the conductivity of the prepared electrode sheet low, which directly affects the electrochemical performance of the battery. In the prior art, a dispersant is generally added to improve the dispersibility of the slurry. However, the dispersant in the prior art cannot be applied to a slurry system containing positive electrode active materials with different degrees of graphitization produced by different processes. The dispersant in the prior art has poor versatility, which is not conducive to reducing manufacturing costs. Therefore, it is necessary to develop a new dispersant that is suitable for a slurry system containing positive electrode active materials produced by different processes.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned problems, and its purpose is to provide a polymer, which is used as a dispersant to adapt to positive electrode active materials with different degrees of graphitization, and can improve the dispersibility of the slurry system containing positive electrode active materials with different degrees of graphitization, effectively increase the solid content of the slurry, slow down the gelation phenomenon of the slurry, reduce the diaphragm resistance of the electrode, improve the flexibility of the electrode, and improve the first coulombic efficiency and high-temperature cycle performance of the battery.

[0008] The first aspect of the present application provides a polymer comprising a structure shown in Formula I, X′-LX Formula I

[0009] wherein X comprises at least one of a carboxyl group, an ester group, a sulfonic acid group, a sulfonate group, a phosphoric acid group, and a phosphate group,

[0010] X' comprises a nonpolar group;

[0011] L comprises a structural unit represented by formula II,

[0012] Where R1 contains C 1-12 Alkylene, C 6-12 Arylene or R2 contains C 1-12 Alkylene, C 6-12 Arylene or R3 contains hydrogen or C 1-3 Alkyl, wherein EO represents -CH2-CH2-O-, PO represents -CH(CH3)-CH2-O-, m1 and m2 are each independently an integer between 3 and 60, and n1 and n2 are each independently an integer between 0 and 60.

[0013] The terminal group of this polymer contains a non-polar group at one end, exhibiting lipophilicity, while the terminal group at the other end contains at least one of the following: carboxyl, ester, sulfonic acid, sulfonate, phosphate, or phosphate ester groups, exhibiting hydrophilicity. When this polymer is added to a slurry system, the carboxyl, ester, sulfonic acid, sulfonate, phosphate, or phosphate ester groups at one end act as anchor points and adsorb onto the surface of solid particles, while the non-polar group at the other end remains suspended in the slurry, forming a steric barrier. When the solid particles approach each other, this steric barrier generates a strong repulsive force, preventing particle agglomeration and forming a uniformly dispersed and stable slurry. Furthermore, the amide group contained in the structural unit represented by Formula II is a polar group, which can generate strong intermolecular inductive forces, further enhancing the dispersibility of the polymer. Furthermore, the L segments contain fewer side chains and relatively fixed bond angles, presenting a relatively linear structure in the slurry system. The segments are fully extended in the slurry system and are less likely to entangle with each other. The resulting steric hindrance effectively isolates the solid particles, further enhancing the dispersion effect.

[0014] In addition, the structural unit shown in Formula II in the L segment contains an amide group. Due to the p-π conjugation effect, the lone pair charges of the oxygen atom and the nitrogen atom on the amide group will be delocalized to the CN single bond. At the same time, the amide group, as a carboxylic acid derivative group, will produce enol interconversion under acidic or alkaline conditions, and its α-C and the C on the carbonyl group will produce a transient double bond. Therefore, the entire L segment contains partial double bond properties, and the L segment tends to be linear, which will reduce the sliding resistance between the positive active materials during the cold pressing process, thereby increasing the flexibility of the electrode and improving the flexibility of the electrode.

[0015] In summary, compared to existing dispersants, the polymer dispersant of the present application has a wide range of versatility and is suitable for slurry systems containing positive electrode active materials with different degrees of graphitization. Compared to existing dispersants, the present application improves the dispersibility of the polymer through the combined action of the terminal X group, amide group and L segment, improves the applicability of the polymer dispersant for positive electrode active materials with different degrees of graphitization, and helps to reduce preparation costs and improve production efficiency.

[0016] In any embodiment, the polymer comprises at least one of the structures represented by Formula I-1, Formula I-2, Formula I-3, and Formula I-4,

[0017] wherein a1 and a2 are each independently an integer between 2 and 12, and R4 and R5 are each independently hydrogen, C 1-12 Alkyl, C 1-12 At least one of an alkyl alcohol, *-NH-R9-OH, R6, R7, and R8 each independently contain hydrogen, C 1-12 Alkyl, C 1-12 Alkyl alcohol, *-NH-R 10 -OH At least one of which R9, R 10 Each independently contains C 1-12 Alkylene, R 11 Contains C 1-12 Alkyl or C 6-30 Aromatic group.

[0018] In any embodiment, the polymer comprises at least one of the structures represented by Formula I-1, Formula I-2, and Formula I-4,

[0019] wherein a1 and a2 are each independently an integer between 2 and 12, and R4 and R5 each independently contain C 1-12 At least one of an alkyl alcohol, *-NH-R9-OH, R8 contains hydrogen, C 1-12 Alkyl alcohol, *-NH-R 10 -OH, At least one of which R9, R 10 Each independently contains C 1-12 Alkylene, R 11 Contains C 1-12 Alkyl or C 6-30 Aromatic group.

[0020] In any embodiment, R3 in the structural unit represented by Formula II comprises hydrogen.

[0021] R3 in the structural unit shown in Formula II contains hydrogen, which can produce hydrogen bonds with oxygen atoms on the surface of the positive electrode active material, further increasing the dispersion effect of the polymer on the slurry, increasing the solid content of the slurry, slowing down the gelation phenomenon of the slurry, improving the flexibility of the electrode, reducing the membrane resistance of the electrode, and improving the first coulombic efficiency and high-temperature storage performance of the battery.

[0022] In any embodiment, R1 comprises R2 contains Wherein n1 or n2 is 0, and m1 and m2 are each independently an integer between 3 and 60.

[0023] The polymer contains polyethylene oxide chain segments or polyethylene oxide-propylene oxide chain segments, which can improve the flexibility of the polymer, reduce the sliding resistance between particles during the cold pressing process of the electrode, increase the flexibility of the electrode, and improve the first coulombic efficiency and high-temperature storage performance of the battery.

[0024] In any embodiment, R1 comprises R2 contains wherein n1 and n2 are each independently an integer between 1 and 60, and m1 and m2 are each independently an integer between 3 and 30.

[0025] The polymer contains polyethylene oxide-propylene oxide chain segments, which can further improve the flexibility of the polymer, reduce the sliding resistance between particles during the cold pressing process of the electrode, increase the flexibility of the electrode, reduce the diaphragm resistance of the electrode, and improve the battery's first coulombic efficiency and high-temperature storage performance.

[0026] In any embodiment, the number of repetitions of the structural unit represented by formula II in L is 3-100.

[0027] Controlling the number of repetitions of the structural units represented by Formula II within an appropriate range ensures that the polymer has a sufficient number of amide groups, which in turn ensures that the polymer generates sufficient intermolecular inductive forces, forming sufficient intermolecular forces with the solid particles in the slurry system, thereby improving the polymer's dispersibility. Furthermore, the appropriate number of structural units represented by Formula II provides the polymer with excellent solubility in the slurry system, allowing the polymer to fully extend within the slurry system, enabling the polymer to act as a dispersant.

[0028] In any embodiment, X' comprises C 3-30 Alkyl, C 6-30 At least one aromatic group.

[0029] In any embodiment, the weight average molecular weight of the polymer is from 1500 g / mol to 70000 g / mol.

[0030] In any embodiment, the polymer has a glass transition temperature of 50°C to 200°C.

[0031] In any embodiment, the polymer has a melting point of 70°C to 300°C at 1 standard atmosphere pressure.

[0032] In any embodiment, the polymer has a hydrophilic-lipophilic balance value of 6-16.

[0033] In any embodiment, the polymer has a hydrophilic-lipophilic balance value of 10-12.

[0034] The second aspect of the present application provides a method for preparing a polymer, the method comprising the following steps:

[0035] 1) Polycondensation reaction: at least one dibasic acid and at least one diamine are polymerized to prepare an intermediate polymer, the intermediate polymer comprising a structure shown in formula III, Y′-LY Formula III

[0036] wherein Y' and Y each independently comprise a carboxyl group or an amino group;

[0037] 2) End group reaction: The end groups of the intermediate polymer are reacted to obtain a polymer having a structure shown in Formula I, X′-LX Formula I

[0038] wherein X comprises at least one of a carboxyl group, an ester group, a sulfonic acid group, a sulfonate group, a phosphoric acid group, and a phosphate group;

[0039] X' comprises a nonpolar group;

[0040] L comprises a structural unit represented by formula II,

[0041] Where R1 contains C 1-12 Alkylene, C 6-12 Arylene or R2 contains C 1-12 Alkylene, C 6-12 Arylene or R3 contains hydrogen or C 1-3 Alkyl, wherein EO represents -CH2-CH2-O-, PO represents -CH(CH3)-CH2-O-, m1 and m2 are each independently an integer between 3 and 60, and n1 and n2 are each independently an integer between 0 and 60.

[0042] The preparation method of the present application can produce a polymer containing a carboxyl group, an ester group, a sulfonic acid group, a sulfonate group, a phosphoric acid group, or a phosphoric acid ester group at one end, a non-polar group at the other end, and an amide group in the main chain. Using this polymer as a dispersant can be applied to positive electrode active materials with varying degrees of graphitization, improve the dispersibility of slurry systems containing positive electrode active materials with varying degrees of graphitization, increase the solid content of the slurry, slow down the gelation of the slurry, reduce the sheet resistance of the electrode, improve the flexibility of the electrode, and enhance the initial coulombic efficiency and high-temperature cycling performance of the battery.

[0043] In any embodiment, the preparation method specifically comprises:

[0044] Stirring a catalyst, at least one dibasic acid, and at least one diamine at 20° C. to 300° C. for 2 h to 35 h to obtain an intermediate polymer, wherein both ends of the intermediate polymer have the same end group;

[0045] The terminal groups at both ends of the intermediate polymer are reacted to obtain a polymer.

[0046] The present invention adopts polycondensation reaction and terminalization reaction to prepare the polymer, which has a simple preparation method and improves production efficiency.

[0047] In a third aspect of the present application, a dispersant is provided, which includes the polymer of the first aspect or the polymer prepared by the preparation method of the second aspect.

[0048] The fourth aspect of the present application provides a use of the polymer of the first aspect in a secondary battery.

[0049] In a fifth aspect of the present application, a positive electrode slurry is provided, comprising a positive electrode active material, a conductive agent, a binder and a dispersant, wherein the dispersant comprises the polymer of the first aspect.

[0050] The positive electrode slurry has excellent dispersibility and high solid content, and can be used to prepare electrodes with excellent performance.

[0051] In any embodiment, the positive electrode active material includes lithium iron phosphate having a carbon coating layer on its surface.

[0052] In any embodiment, the degree of graphitization of the lithium iron phosphate having a carbon coating layer on the surface is 10%-30%.

[0053] The polymer dispersant of the present application can be applied to slurry systems using lithium iron phosphate with different degrees of graphitization as the positive electrode active material. It has universal applicability and helps to reduce preparation costs and improve production efficiency.

[0054] In any embodiment, the mass fraction of the dispersant is 0.01%-3%, based on the total mass of the solid matter in the positive electrode slurry.

[0055] When the mass fraction of the dispersant is within an appropriate range, the slurry has a high solid content, the electrode has excellent flexibility, and the battery has excellent first coulombic efficiency and high-temperature storage performance.

[0056] In any embodiment, the mass fraction of the dispersant is 0.03%-2%, based on the total mass of the solid matter in the positive electrode slurry.

[0057] When the mass fraction of the dispersant is within an appropriate range, the flexibility of the electrode can be further improved and the high-temperature storage performance of the battery can be enhanced.

[0058] In a sixth aspect of the present application, a positive electrode sheet is provided, comprising a positive electrode current collector and a positive electrode membrane arranged on at least one surface of the positive electrode current collector, wherein the positive electrode membrane is prepared from the positive electrode slurry of the fifth aspect.

[0059] The positive electrode plate of the present application has excellent flexibility and low membrane resistance, and the plate has excellent performance.

[0060] In a seventh aspect of the present application, a secondary battery is provided, comprising a separator, a negative electrode plate, an electrolyte, and the positive electrode plate of the sixth aspect.

[0061] In an eighth aspect of the present application, an electrical device is provided, comprising the secondary battery according to the seventh aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0063] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0064] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0065] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0066] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0067] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0068] Explanation of reference numerals: 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0069] Below, the embodiments of the polymer, preparation method, dispersant, positive electrode slurry, positive electrode sheet, secondary battery and electric device of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0070] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0071] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0072] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0073] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating 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.

[0074] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0075] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0076] The positive electrode slurry is mainly a solid-liquid phase mixed system formed by a positive electrode active material, a conductive agent, a binder and a solvent. In the prior art, a dispersant is often added to improve the dispersibility of the slurry. However, the dispersants in the prior art are usually only applicable to slurry systems with fixed components and have poor versatility. After the physical properties of the components in the slurry change, the dispersant often needs to be adjusted. For example, the lithium iron phosphate produced under different process conditions in the prior art has different degrees of carbon coating on its surface and different degrees of graphitization of the lithium iron phosphate. Often, a single dispersant cannot be applied to lithium iron phosphate with different degrees of graphitization. When the dispersants in the prior art are used in slurry systems with lithium iron phosphate with different degrees of graphitization as the positive electrode active material, the dispersibility of the slurry system is less than ideal, and it is difficult to meet the performance requirements of the electrode and the battery.

[0077] [Dispersant]

[0078] Based on this, the present application provides a polymer comprising a structure shown in Formula I, X′-LX Formula I

[0079] wherein X comprises at least one of a carboxyl group, an ester group, a sulfonic acid group, a sulfonate group, a phosphoric acid group, and a phosphate group, X' comprises a non-polar group, and L comprises a structural unit represented by formula II,

[0080] Where R1 contains C1-12 Alkylene, C 6-12 Arylene or R2 contains C 1-12 Alkylene, C 6-12 Arylene or R3 contains hydrogen or C 1-3 alkyl,

[0081] Wherein EO represents -CH2-CH2-O-, PO represents -CH(CH3)-CH2-O-, m1 and m2 are each independently an integer between 3 and 60, and n1 and n2 are each independently an integer between 0 and 60.

[0082] As used herein, the term "polymer" includes, on the one hand, a collection of chemically homogeneous macromolecules prepared by polymerization, but differing in degree of polymerization, molar mass, and chain length. The term also includes derivatives of such collections of macromolecules formed by polymerization, i.e., compounds that can be obtained by reaction, for example, addition or substitution, of functional groups in the aforementioned macromolecules and that can be chemically homogeneous or chemically heterogeneous.

[0083] As used herein, the term "carboxyl" refers to -COOH.

[0084] As used herein, the term "ester group" refers to R 12 A non-hydrogen group.

[0085] As used herein, the term "sulfonic acid" refers to -SO3H.

[0086] As used herein, the term "sulfonate group" refers to R 13 A non-hydrogen group.

[0087] As used herein, the term "phosphate group" refers to

[0088] As used herein, the term "phosphate group" refers to R 14 A non-hydrogen group.

[0089] As used herein, the term "amide group" refers to R 15 、R 16 are each independently hydrogen or a non-hydrogen group.

[0090] As used herein, the term "amino" refers to R 17 、R 18 are each independently hydrogen or a non-hydrogen group.

[0091] As used herein, the term "non-polar group" refers to a group in which the positive and negative charge centers coincide, including but not limited to alkyl groups and aromatic groups.

[0092] As used herein, the term "alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms with no unsaturation present in the radical.

[0093] As used herein, the term "aromatic" refers to an aromatic ring system in which at least one ring is aromatic.

[0094] In some embodiments, the non-polar group comprises C 3-30 Alkyl or C 6-30 Aromatic group.

[0095] In some embodiments, X' comprises C 3-30 Alkyl, C 6-30 At least one aromatic group.

[0096] In this article, the term “C 3-30 "Alkyl" refers to a straight or branched hydrocarbon chain radical consisting solely of carbon and hydrogen atoms, with no unsaturation present, having from 6 to 30 carbon atoms, and attached to the remainder of the molecule by a single bond. 1-3 Alkyl" and "C 1-12 "alkyl" should be interpreted accordingly.

[0097] In this article, the term “C 6‐30 An "aromatic group" refers to a monovalent functional group formed by removing a hydrogen atom from a ring of an aromatic hydrocarbon containing 6 to 30 carbon atoms, such as a phenyl group or a naphthyl group. An aromatic hydrocarbon refers to a hydrocarbon having an aromatic ring, and includes monocyclic and polycyclic hydrocarbons, wherein the additional rings of the polycyclic hydrocarbon may be aromatic or non-aromatic.

[0098] In this article, the term “C 1-12 "Alkylene" refers to branched and straight-chain saturated aliphatic divalent hydrocarbon radicals having the specified number of carbon atoms. There is no unsaturation in the radical, it has from 1 to 12 carbon atoms, and it is attached to the rest of the molecule by a single bond.

[0099] In this article, the term “C 6-12 The term "arylene group" refers to a divalent functional group formed by removing two hydrogen atoms from the ring of an aromatic hydrocarbon containing 6 to 12 carbon atoms, for example, phenylene or naphthalenediyl.

[0100] In this article, The EO units and PO units in the polymer may be arranged randomly or in blocks.

[0101] In this article, the term "dispersant" refers to a type of substance that prevents solid particles from aggregating with each other in a solid-liquid dispersion system and enables the solid particles to remain uniformly dispersed in the liquid phase for a longer period of time.

[0102] In some embodiments, the dispersion medium of the dispersant is an aqueous solvent, such as water, that is, the dispersant is dissolved in the aqueous solvent.

[0103] In some embodiments, the dispersant's dispersion medium is an oily solvent. Examples of such oily solvents include, but are not limited to, dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethyl cellulose, and polycarbonate. That is, the dispersant is dissolved in the oily solvent.

[0104] In some embodiments, the dispersant is used as a positive electrode slurry dispersant, and is used to disperse the positive electrode active material, the conductive agent, and the binder to form a positive electrode slurry.

[0105] In some embodiments, the dispersant is used as a negative electrode slurry dispersant, and is used to disperse the negative electrode active material, the conductive agent, and the binder to form the negative electrode slurry.

[0106] In some embodiments, the X group comprises a carboxyl group, a sulfonic acid group, or a phosphate group.

[0107] The carboxyl group, sulfonic acid group or phosphoric acid group can be ionized to generate negative ions, which are adsorbed on the surface of the positive electrode active material particles in the slurry system mainly through electrostatic interaction, anchoring one end of the polymer on the surface of the positive electrode active material particles.

[0108] In some embodiments, the X group comprises an ester group, a sulfonate group, or a phosphate group.

[0109] The ester group, sulfonate group or phosphate group is adsorbed on the surface of the positive electrode active material particles in the slurry system through intermolecular forces, anchoring one end of the polymer on the surface of the positive electrode active material particles.

[0110] The end group of one end of the polymer contains a non-polar group, exhibiting lipophilicity, while the end group of the other end contains at least one of the following: carboxyl, ester, sulfonic acid, sulfonate, phosphate, or phosphate ester groups, which are polar groups and exhibit hydrophilicity. When the polymer is added to the slurry system, the carboxyl, ester, sulfonic acid, sulfonate, phosphate, or phosphate ester group at one end acts as an anchor point and adsorbs on the surface of the positive electrode active material particles, while the other end is suspended in the slurry to form a steric barrier. When the particles approach each other, this steric barrier generates a strong repulsive force, preventing particle agglomeration and forming a uniformly dispersed and stable slurry. The amide group contained in the structural unit shown in Formula II is a polar group that can generate strong intermolecular inductive forces, forming strong intermolecular forces with the particles, further improving the dispersion ability of the polymer. In addition, the oxygen atoms and nitrogen atoms in the amide group can form hydrogen bonds with the hydroxyl and / or carboxyl groups on the surface of the positive electrode active material, and the nitrogen atoms and oxygen atoms can form coordination with the positive electrode active material, thereby jointly enhancing the dispersion of the particles in the slurry system by the polymer dispersant. The L segment contains fewer side chains, and the bond angle is relatively fixed. It presents a certain linear structure in the slurry system. The segment is fully stretched in the slurry system, and it is not easy to entangle between the segments. The steric hindrance it produces fully isolates each solid particle, and the full extension of the L segment also allows the amide group to fully interact with different particles, further improving the dispersion effect. The polymer dispersant of the present application can achieve multi-site adsorption on the surface of the positive electrode active material with different graphitization degrees, making the adsorption more significant and enhancing the dispersion effect of the polymer dispersant on the slurry.

[0111] In addition, the structural unit shown in Formula II in the L segment contains an amide group. Due to the p-π conjugation effect, the lone pair charge of the nitrogen atom on the amide group will be delocalized to the CN single bond. At the same time, the amide group, as a carboxylic acid derivative group, will produce enol interconversion under acidic or alkaline conditions, and its α-C and the C on the carbonyl group will produce a transient double bond. Therefore, the entire L segment contains partial double bond properties, and the L segment tends to be linear, which will reduce the sliding resistance between the positive active materials during the cold pressing process, thereby increasing the flexibility of the electrode and improving the flexibility of the electrode.

[0112] In summary, the polymer of this application, as a dispersant, can improve the dispersibility of slurries containing positive electrode active materials with different degrees of graphitization through multi-site adsorption, increase the solid content of the slurry, slow down the gelation of the slurry, reduce the sheet resistance of the electrode, and improve the initial coulombic efficiency and high-temperature cycling performance of the battery. It can also improve the flexibility of the electrode, providing a foundation for the subsequent preparation of thick-coated, high-voltage, dense electrode sheets.

[0113] The existing dispersants have poor compatibility and cannot adapt to the differences in positive electrode active materials under different process conditions in the slurry. The present application improves the dispersibility of the polymer through the combined action of the terminal X group, amide group and L segment, improves the applicability of the polymer dispersant for positive electrode active materials with different degrees of graphitization, and improves the universality of the polymer dispersant, which helps to reduce preparation costs and improve production efficiency.

[0114] In some embodiments, the polymer comprises at least one of the structures shown in Formula I-1, Formula I-2, Formula I-3, and Formula I-4.

[0115] wherein a1 and a2 are each independently an integer between 2 and 12, and R4 and R5 are each independently hydrogen, C 1-12 Alkyl, C 1-12 At least one of an alkyl alcohol, *-NH-R9-OH, R6, R7, and R8 each independently contain hydrogen, C 1-12 Alkyl, C 1-12 Alkyl alcohol, *-NH-R 10 -OH, At least one of which R9, R 10 Each independently contains C 1-12 Alkylene, R 11 Contains C 1-12 Alkyl or C 6-30 Aromatic group.

[0116] In this article, the term “C 1-12 "Alkyl alcohol" refers to a monovalent atomic group consisting of an alkylene group bonded to a hydroxyl group (-OH) and consisting of "-C n H 2n -OH" (wherein n is a natural number of 1 to 12).

[0117] In some embodiments, the polymer comprises at least one of the structures shown in Formula I-1, Formula I-2, and Formula I-4.

[0118] wherein a1 and a2 are each independently an integer between 2 and 12, and R4 and R5 each independently contain C 1-12 At least one of an alkyl alcohol, *-NH-R9-OH, R8 contains hydrogen, C 1-12 Alkyl alcohol, *-NH-R 10 -OH, At least one of which R9, R 10 Each independently contains C 1-12 Alkylene, R 11 Contains C 1-12 Alkyl or C 6-30Aromatic group.

[0119] In some embodiments, L further comprises *-NH-R2-HN-*, One or more of.

[0120] In some embodiments, R4 in the structure represented by Formula I-1 comprises hydrogen.

[0121] R4 contains hydrogen, and the polymer can ionize to produce negative ions, which can be adsorbed on the surface of the positive electrode active material particles in the slurry system through electrostatic action, thereby enhancing the dispersion effect of the polymer dispersant, increasing the solid content of the slurry, slowing down the gelation phenomenon of the slurry, improving the flexibility of the electrode, and improving the performance of the slurry and the electrode.

[0122] In some embodiments, R4 in the structure shown in Formula I-1 comprises C 1-12 Alkyl alcohol or *-NH-R9-OH.

[0123] R4 contains C 1-12 Alkyl alcohol or *-NH-R9-OH, wherein the amino group or hydroxyl group can generate adsorption force with the positive electrode active material particles in the slurry system, enhance the dispersing effect of the polymer dispersant, increase the solid content of the slurry, and improve the performance of the slurry.

[0124] In some embodiments, R5 in the structure represented by Formula I-2 comprises hydrogen.

[0125] R5 contains hydrogen, and the polymer can ionize to produce negative ions, which can be adsorbed on the surface of the positive electrode active material particles in the slurry system through electrostatic action, thereby enhancing the dispersion effect of the polymer dispersant, increasing the solid content of the slurry, slowing down the gelation phenomenon of the slurry, improving the flexibility of the electrode, reducing the diaphragm resistance of the electrode, and improving the first coulombic efficiency and high-temperature cycle performance of the battery.

[0126] In some embodiments, R5 in the structure shown in Formula I-2 comprises C 1-12 Alkyl alcohol or *-NH-R9-OH.

[0127] R5 contains C 1-12 Alkyl alcohol or *-NH-R9-OH, in which the amino or hydroxyl groups can generate adsorption force with the positive electrode active material particles in the slurry system, enhance the dispersion effect of the polymer dispersant, increase the solid content of the slurry, slow down the gelation phenomenon of the slurry, improve the flexibility of the electrode, reduce the diaphragm resistance of the electrode, and improve the first coulombic efficiency and high-temperature cycle performance of the battery.

[0128] In some embodiments, R6 or R7 in the structure represented by Formula I-3 comprises hydrogen.

[0129] R6 or R7 contains hydrogen, and the polymer can be ionized to produce negative ions, which can be adsorbed on the surface of the positive electrode active material particles in the slurry system through electrostatic action, thereby enhancing the dispersion effect of the polymer dispersant, increasing the solid content of the slurry, slowing down the gelation phenomenon of the slurry, improving the flexibility of the electrode, reducing the diaphragm resistance of the electrode, and improving the first coulombic efficiency and high-temperature cycle performance of the battery.

[0130] In some embodiments, R6 or R7 in the structure shown in Formula I-3 comprises C 1-12 Alkyl alcohol, *-NH-R 10 -OH or

[0131] R6 or R7 contains C 1-12 Alkyl alcohol, *-NH-R 10 -OH or The amino or hydroxyl groups can generate adsorption force with the positive electrode active material particles in the slurry system, enhance the dispersion effect of the polymer dispersant, increase the solid content of the slurry, slow down the gelation phenomenon of the slurry, improve the flexibility of the electrode, reduce the diaphragm resistance of the electrode, and improve the first coulombic efficiency and high-temperature cycle performance of the battery.

[0132] In some embodiments, R8 in the structure represented by Formula I-4 comprises hydrogen.

[0133] R8 contains hydrogen, and the polymer can ionize to produce negative ions, which can be adsorbed on the surface of the positive electrode active material particles in the slurry system through electrostatic action, thereby enhancing the dispersion effect of the polymer dispersant, reducing the diaphragm resistance of the electrode, and improving the battery's first coulombic efficiency and high-temperature storage performance.

[0134] In some embodiments, R8 in the structure shown in Formula I-4 comprises C 1-12 Alkyl alcohol, *-NH-R 10 -OH, At least one of .

[0135] R8 contains C 1-12 Alkyl alcohol, *-NH-R 10 -OH or *-CR 11 The amino, hydroxyl and ester groups can generate adsorption force with the positive electrode active material particles in the slurry system, enhance the dispersion effect of the polymer dispersant, improve the flexibility of the electrode, and improve the high-temperature storage performance of the battery.

[0136] In some embodiments, the polymer comprises the structure shown in Formula I-4.

[0137] Compared with the structure shown in Formula I-3 which contains one L segment, the structure shown in Formula I-4 contains two L segments, which can enhance the dispersing effect of the polymer dispersant, so that the slurry has a high solid content, improve the battery's first coulombic efficiency and high-temperature cycle performance, and improve the battery's electrochemical performance.

[0138] In some embodiments, R3 in the structural unit represented by Formula II comprises hydrogen.

[0139] R3 in the structural unit shown in Formula II contains hydrogen, which can produce hydrogen bonds with oxygen atoms on the surface of the positive electrode active material, further improving the dispersibility of the slurry, increasing the solid content of the slurry, slowing down the gelation phenomenon of the slurry, improving the flexibility of the electrode, reducing the diaphragm resistance of the electrode, and improving the first coulombic efficiency and high-temperature storage performance of the battery.

[0140] In some embodiments, R1 comprises C 1-12 Alkylene or R2 contains C 1-12 Alkylene or wherein m1 and m2 are each independently an integer between 3 and 60, and n1 and n2 are each independently an integer between 0 and 60.

[0141] Introducing a longer alkyl segment or a flexible polyether segment into the L segment can improve the flexibility of the electrode.

[0142] In some embodiments, R1 comprises R2 contains Wherein n1 or n2 is 0, and m1 and m2 are each independently an integer between 3 and 60.

[0143] As used herein, the term "polyoxyethylene segment" refers to a polymer segment comprising -CH2-CH2-O- structural units.

[0144] As used herein, the term "polyoxyethylene-oxypropylene segment" refers to a polymer segment comprising -CH2-CH2-O- and -CH(CH3)-CH2-O- structural units.

[0145] The polymer contains polyethylene oxide chain segments or polyethylene oxide-propylene oxide chain segments, which can improve the flexibility of the polymer, reduce the sliding resistance between particles during the cold pressing process of the pole piece, increase the flexibility of the pole piece, and improve the performance of the pole piece.

[0146] In some embodiments, R1 comprises R2 contains wherein n1 and n2 are each independently an integer between 1 and 60, and m1 and m2 are each independently an integer between 3 and 30.

[0147] The polymer contains polyethylene oxide-propylene oxide chain segments, which can further improve the flexibility of the polymer, reduce the sliding resistance between particles during the cold pressing process of the pole piece, increase the flexibility of the pole piece, improve the performance of the pole piece, and improve the high-temperature storage performance of the battery.

[0148] In some embodiments, the number of repetitions of the structural unit represented by formula II in L is 3-100.

[0149] In some embodiments, the number of repetitions of the structural unit represented by formula II in L can be selected from any value of 3, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a range consisting of any two values ​​therein.

[0150] In some embodiments, the number of repetitions of the structural unit represented by Formula II in L is 8-80.

[0151] In some embodiments, the number of repetitions of the structural unit represented by formula II in L can be selected from any value of 8, 10, 20, 30, 40, 50, 60, 70, 80, or a range consisting of any two values ​​thereof.

[0152] Controlling the number of repetitions of the structural units represented by Formula II within an appropriate range ensures that the polymer has a sufficient number of amide groups, which in turn ensures that the polymer generates sufficient intermolecular inductive forces, forming sufficient intermolecular forces with the solid particles in the slurry system, thereby improving the polymer's dispersibility. Furthermore, the appropriate number of structural units represented by Formula II provides the polymer with excellent solubility in the slurry system, allowing the polymer to fully extend within the slurry system, enabling the polymer to act as a dispersant.

[0153] In some embodiments, the mass percentage of X in the polymer is 0.5% to 20% based on the mass of the polymer.

[0154] In some embodiments, the total mass percentage of R1 and R2 in the polymer is 20% to 80% based on the mass of the polymer.

[0155] In some embodiments, based on the mass of the polymer, the The mass percentage is 0.5%-50%.

[0156] The mass percentages of the X group, R1, R2, and amide group are controlled within an appropriate range, so that the X anchoring group, L segment, and amide group can give full play to their respective advantages, and work together to give the polymer excellent dispersibility and improve the dispersibility of the slurry.

[0157] In some embodiments, the weight average molecular weight of the polymer is from 1500 g / mol to 70000 g / mol.

[0158] In some embodiments, the weight average molecular weight of the polymer can be 1500 g / mol, 2000 g / mol, 2500 g / mol, 3000 g / mol, 3500 g / mol, 4000 g / mol, 4500 g / mol, 5000 g / mol, 5500 g / mol, 6000 g / mol, 6500 g / mol, 7000 g / mol, 7500 g / mol, 8000 g / mol, 8500 g / mol, 9000 g / mol, 10000 g / mol, 11000 g / mol, 12000 g / mol, 13000 g / mol, 14000 g / mol, 15000 g / mol, 16000 g / mol, 17000 g / mol, 18000 g / mol, 19000 g / mol, 20000 g / mol, 21000 g / mol, 22000 g / mol, 23000 g / mol, 24000 g / mol, 25000 g / mol, 26000 g / mol, 27000 g / mol, 28000 g / mol, 29000 g / mol, 30000 g / mol, 35000 g / mol, 3500 g / mol, 9500 g / mol, 10000 g / mol, 15000 g / mol, 20000 g / mol, 25000 g / mol, 30000 g / mol, 35000 g / mol, 40000 g / mol, 45000 g / mol, 50000 g / mol, 55000 g / mol, 60000 g / mol, 65000 g / mol, and 70000 g / mol, or a range consisting of any two of the values.

[0159] As used herein, the term "weight average molecular weight" refers to the sum of the weight fractions of molecules of different molecular weights in a polymer multiplied by their corresponding molecular weights.

[0160] In the present application, the weight-average molecular weight of the polymer can be tested using methods known in the art, such as gel chromatography, such as using a Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141). In some embodiments, the testing method is to use a polystyrene solution sample with a mass fraction of 3.0% as a reference and select a matching chromatographic column (oily: Styragel HT5DMF7.8*300mm+Styragel HT4). A 3.0% fluoropolymer solution is prepared with purified N-methylpyrrolidone (NMP) solvent, and the prepared solution is allowed to stand for one day for use. During the test, tetrahydrofuran is first drawn into a syringe and rinsed, and repeated several times. Then 5 ml of the experimental solution is drawn, the air in the syringe is expelled, and the needle tip is wiped dry. Finally, the sample solution is slowly injected into the injection port. After the reading stabilizes, the data is acquired and the weight-average molecular weight is read.

[0161] If the weight-average molecular weight of the polymer is too large, the polymer will be difficult to dissolve and will not function as a dispersant. If the weight-average molecular weight of the polymer is too small, it will not function effectively as a dispersant, hindering the formation of a conductive network, resulting in an increase in the electrode sheet resistance and a decrease in the battery's initial coulombic efficiency and high-temperature storage performance.

[0162] In some embodiments, the polymer has a glass transition temperature of 50°C to 200°C.

[0163] In some embodiments, the glass transition temperature of the polymer is any value of 50°C, 60°C, 90°C, 100°C, 120°C, 140°C, 150°C, 170°C, 180°C, 190°C, 200°C, or a range consisting of any two of these values.

[0164] In this article, the term "glass transition temperature" refers to the transition temperature of an amorphous polymer (including the non-crystalline part of a crystalline polymer) from a glassy state to a highly elastic state or from a highly elastic state to a glassy state, which is the lowest temperature at which the macromolecular chains of an amorphous polymer can move freely.

[0165] In this article, the term "glassy state" refers to the state of an amorphous polymer in which deformation is minimal when subjected to an external force, with the deformation being proportional to the magnitude of the force and instantly recovering upon removal of the force. In the glassy state, the energy of molecular motion is too low to overcome the potential barrier to rotation within the main chain and stimulate segmental motion. The segments are thus frozen. For example, when subjected to an external force, the frozen segmental motion only causes minor changes in the bond lengths and angles of the main chain. Therefore, macroscopically, the deformation of the polymer after the force is applied is minimal.

[0166] In this article, the term "highly elastic" refers to the ability of amorphous polymers to undergo significant deformation under minimal external forces. In this highly elastic state, when subjected to external forces, the molecular chains adapt to the force through internal rotation of single bonds and conformational changes in chain segments. For example, when subjected to a tensile force, the molecular chains can shift from a curled state to an extended state, resulting in a significant macroscopic deformation. Once the force is removed, the molecular chains return to their original curled state through internal rotation of single bonds and segmental motion, manifesting as elastic retraction.

[0167] In this application, the glass transition temperature of a polymer can be measured using methods known in the art, such as a TA differential scanning calorimeter (Q1000). A 6-9g polymer sample is heated from room temperature to 200°C at a heating rate of 10°C / min. The resulting differential scanning calorimetry curve is analyzed to determine the polymer's glass transition temperature (in degrees Celsius).

[0168] In some embodiments, the polymer has a melting point of 70°C to 300°C at 1 atmosphere.

[0169] In some embodiments, the melting point of the polymer at 1 standard atmosphere is any value of 70°C, 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, or a range consisting of any two of these values.

[0170] As used herein, the term "1 standard atmosphere" refers to the air pressure at sea level under standard atmospheric conditions, which is 101.325 kPa and is the unit of pressure, recorded as atm.

[0171] In the present application, the melting point of a polymer at 1 standard atmosphere can be tested using methods known in the art, such as using a precision microscopic melting point tester (Model X-5) to test the melting point. Under a standard atmospheric pressure, take 0.01 mg of uniformly ground sample and place it on a glass slide. Cover it with another layer of glass slide and gently compact it, and place it in the center of the hot stage. After covering with a heat insulation board, adjust the focus of the microscope until the sample can be clearly observed. Then adjust the temperature knob, quickly raise the temperature until the polymer melts slightly, and then slowly adjust the heating rate until the sample is completely melted. Record the fully melted temperature as the melting point of the polymer in ° C.

[0172] In some embodiments, the polymer has a hydrophilic-lipophilic balance value of 6-16.

[0173] In some embodiments, the hydrophilic-lipophilic balance value of the polymer can be selected as any value among 6, 8, 10, 12, 14, 16, or a range consisting of any two values ​​therein.

[0174] In this article, the term "hydrophile-lipophile balance" is used to characterize the overall hydrophilic and lipophilic properties of a polymer. A larger hydrophile-lipophile balance indicates a more hydrophilic polymer. Conversely, a smaller hydrophile-lipophile balance indicates a less hydrophilic polymer and a more lipophilic polymer.

[0175] In this article, the hydrophilic-lipophilic balance (HLB) of a polymer can be measured using methods known in the art, such as the emulsification method. The principle is that when a polymer is emulsified into an oily medium, the resulting emulsion is most stable when its HLB value matches the HLB value required by the oily medium. The ideal HLB value can be achieved by mixing a standard sample with a known HLB value in a suitable proportion. This polymer is then emulsified into a prepared oily phase and allowed to stand for 24 hours. The HLB value required by the oily phase in the sample with the best stability is the HLB value of the polymer.

[0176] In some embodiments, the polymer has a hydrophilic-lipophilic balance value of 10-12.

[0177] In some embodiments, the hydrophilic-lipophilic balance value of the polymer can be selected as any value among 10, 11, 12, or a range consisting of any two values ​​therein.

[0178] One embodiment of the present application provides a method for preparing a polymer, the method comprising the following steps:

[0179] 1) Polycondensation reaction: at least one dibasic acid and at least one diamine are polymerized to prepare an intermediate polymer, the intermediate polymer comprising a structure shown in formula III, Y′-LY Formula III

[0180] wherein Y' and Y each independently comprise a carboxyl group or an amino group;

[0181] 2) End group reaction: The end groups of the intermediate polymer are reacted to obtain a polymer having a structure shown in Formula I, X′-LX Formula I

[0182] wherein X comprises at least one of a carboxyl group, an ester group, a sulfonic acid group, a sulfonate group, a phosphoric acid group, and a phosphate group;

[0183] X' comprises a nonpolar group;

[0184] L comprises a structural unit represented by formula II,

[0185] Where R1 contains C 1-12 Alkylene, C 6-12 Arylene or R2 contains C 1-12 Alkylene, C 6-12 Arylene or R3 contains hydrogen or C 1-3 Alkyl, wherein EO represents -CH2-CH2-O-, PO represents -CH(CH3)-CH2-O-, m1 and m2 are each independently an integer between 3 and 60, and n1 and n2 are each independently an integer between 0 and 60.

[0186] As used herein, the term "diamine" refers to an amine containing two amino groups.

[0187] As used herein, the term "diacid" refers to an acid containing two carboxyl groups.

[0188] In some embodiments, the diamine has the structure shown in Formula IV,

[0189] Where R2 contains C 1-12 Alkylene, C 6-12 aromatic groups, At least one of R3 hydrogen or C 1-3 Alkyl, m2 is any integer between 3-60, and n2 is any integer between 0-60.

[0190] In some embodiments, the diamine comprises

[0191] Any one of .

[0192] In some embodiments, the dibasic acid has the structure shown in Formula V,

[0193] Where R1 contains C 1-12 Alkylene, C 6-12 aromatic groups, At least one of, m1 is an integer between 3-60, and n1 is an integer between 0-60.

[0194] In some embodiments, the dibasic acid comprises

[0195] Any one of .

[0196] This preparation method uses inexpensive raw materials, which can reduce costs and environmental pollution, and is conducive to increasing the production of polymer dispersants. Furthermore, this preparation method can produce a polymer containing a polar group such as a carboxyl group, an ester group, a sulfonic acid group, a sulfonate group, a phosphoric acid group, or a phosphoric acid ester group at one end, a non-polar group at one end, and an amide group in the main chain. Using this polymer as a dispersant can be applied to positive electrode active materials with varying degrees of graphitization, improving the dispersibility of slurry systems containing positive electrode active materials with varying degrees of graphitization, increasing the solid content of the slurry, slowing the gelation of the slurry, reducing the diaphragm resistance of the electrode, improving the flexibility of the electrode, and enhancing the initial coulombic efficiency and high-temperature cycling performance of the battery.

[0197] In some embodiments, the preparation method specifically comprises:

[0198] Stirring a catalyst, at least one dibasic acid, and at least one diamine at 20° C. to 300° C. for 2 h to 35 h to obtain an intermediate polymer, wherein both ends of the intermediate polymer have the same end group;

[0199] The terminal groups at both ends of the intermediate polymer are reacted respectively to obtain the polymer.

[0200] In some embodiments, the terminal groups of the intermediate polymer are all carboxyl groups.

[0201] In some embodiments, the terminal groups of the intermediate polymer are all amino groups.

[0202] In some embodiments, the polymer synthesis route involves a polymerization reaction of at least one dibasic acid and at least one diamine under the action of a catalyst to produce an intermediate polymer. The dibasic acid or diamine is in excess, resulting in an amino or carboxyl end group at both ends. The amino or carboxyl end of one end undergoes a functional group reaction with a reactive monomer containing an X' group, and the amino or carboxyl end of the other end undergoes a functional group reaction with a reactive monomer containing an X group, thereby producing a polymer containing an X group at one end and an X' end at the other end. It will be understood that a reactive monomer containing an X' group refers to a monomer containing an X' group and a reactive functional group capable of reacting with an amino or carboxyl end of the intermediate polymer, and a reactive monomer containing an X group refers to a monomer containing an X group and a reactive functional group capable of reacting with a carboxyl or amino end of the intermediate polymer. The reactive functional group reactive with an amino group can be any of an epoxy group, a carboxyl group, an acid anhydride, an isocyanate group, a carbonyl chloride group, and a halogen atom, and the reactive functional group reactive with a carboxyl group can be a hydroxyl group or an amino group.

[0203] The present invention adopts polycondensation reaction and terminalization reaction to prepare the polymer, which has a simple preparation method and improves production efficiency.

[0204] In some embodiments, the terminal group of the intermediate polymer is an amino group, and the reactive monomer containing an X' group refers to a reactive monomer containing an X' group and a halogen atom.

[0205] In some embodiments, the terminal group of the intermediate polymer is an amino group, and the reactive monomer containing an X group refers to a reactive monomer containing an X group and a halogen atom.

[0206] In some embodiments, the terminal group of the intermediate polymer is an amino group, and the reactive monomer containing the X' group refers to X'-(CH2)mA, wherein m is an integer between 1 and 12, and A is F, Cl, Br or I.

[0207] In some embodiments, the terminal group of the intermediate polymer is an amino group, and the reactive monomer containing the X group refers to X-(CH2)nB, wherein n is an integer between 1 and 12, and B is F, Cl, Br or I.

[0208] In some embodiments, the polymer is prepared as shown below:

[0209] In some embodiments, the polymer is prepared as shown below:

[0210] In some embodiments, the catalyst comprises sodium hypophosphite.

[0211] In some embodiments, a dispersant is provided, comprising the polymer of any embodiment or the polymer prepared by the preparation method of any embodiment.

[0212] In some embodiments, use of the polymer according to any embodiment in a secondary battery is provided.

[0213] [Cathode slurry]

[0214] In some embodiments, a positive electrode slurry is provided, including a positive electrode active material, a conductive agent, a binder, and a dispersant, wherein the dispersant includes the polymer of any embodiment.

[0215] The positive electrode slurry has excellent dispersibility and high solid content, which is conducive to the preparation of pole pieces with excellent performance.

[0216] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0217] In some embodiments, the positive electrode slurry includes a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0218] In some embodiments, the positive electrode active material includes lithium iron phosphate having a carbon coating layer on its surface.

[0219] On the one hand, the structural unit represented by formula II in the L segment contains an amide group, and the oxygen and nitrogen atoms on the amide group can coordinate with the iron atom in the lithium iron phosphate. On the other hand, the oxygen and nitrogen atoms on the amide group can produce hydrogen bonds with the carboxyl or hydroxyl groups in the carbon coating layer. The two work together to improve the dispersion ability of the polymer in the slurry, so that the polymer dispersant has excellent dispersion ability for the slurry system with lithium iron phosphate having a carbon coating layer on the surface as the positive electrode active material.

[0220] In some embodiments, the degree of graphitization of the lithium iron phosphate having a carbon coating layer on its surface is 10%-30%.

[0221] In some embodiments, the graphitization degree of the lithium iron phosphate having a carbon coating layer on the surface can be any value selected from 10%, 15%, 20%, 25%, 30%, or a range consisting of any two values ​​therein.

[0222] In this application, the term "degree of graphitization" refers to the degree of graphitization of the carbon component, reflecting the integrity of the graphite crystal structure in the carbon-coated lithium iron phosphate, especially in the carbon coating layer, that is, the regularity of the arrangement of carbon atoms in the graphite structure.

[0223] In this article, the graphitization degree of lithium iron phosphate can be tested by methods known in the art, such as Raman spectroscopy. Specifically, the graphitization degree is characterized using a French HORIBA Jobin Yvon high-resolution Raman spectrometer, model LabRAM HR Evlution. After deducting the detection background, the following Gaussian function is used for fitting. Raman spectrum test conditions: wavelength 532nm, scanning range 200-4000cm ‐1 , accumulate twice, measure 10 points for each sample, and take the average value for fitting:

[0224] In the above formula, G is the degree of graphitization, Ai, Vi and wi are the peak intensity, peak position and peak width, respectively.

[0225] In order to improve the electronic and ionic conductivity of lithium iron phosphate in the prior art, carbon coating is performed on the surface of the positive electrode active material. However, there are many types of lithium iron phosphate coating processes on the existing market, and the degree of surface carbon coating varies. The degree of graphitization of lithium iron phosphate varies, and the existing dispersants are not applicable to slurries with lithium iron phosphate of different graphitization degrees as the positive electrode active material. The polymer dispersant of the present application has universality, which can improve the dispersibility of slurries with lithium iron phosphate of different graphitization degrees as the positive electrode active material, increase the solid content of the slurry, slow down the gelation phenomenon of the slurry, reduce the diaphragm resistance of the electrode, improve the flexibility of the electrode, and improve the first coulombic efficiency and high-temperature cycle performance of the battery. The polymer dispersant is universal for positive electrode slurries containing lithium iron phosphate of different graphitization degrees produced by different processes, which helps to reduce preparation costs and improve production efficiency.

[0226] In some embodiments, the mass fraction of the dispersant is 0.01%-3%, based on the total mass of the solid matter in the positive electrode slurry.

[0227] In some embodiments, based on the total mass of the solid matter in the positive electrode slurry, the mass fraction of the dispersant can be selected as any value of 0.01%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or a range consisting of any two values ​​therein.

[0228] When the mass fraction of the dispersant is within an appropriate range, the slurry has a high solid content, the electrode has excellent flexibility, and the battery has excellent first coulombic efficiency and high-temperature storage performance.

[0229] In some embodiments, the mass fraction of the dispersant is 0.03%-2%, based on the total mass of the solid matter in the positive electrode slurry.

[0230] In some embodiments, based on the total mass of the solid matter in the positive electrode slurry, the mass fraction of the dispersant can be selected as any value of 0.03%, 0.1%, 0.5%, 1%, 1.5%, 2% or a range consisting of any two values ​​therein.

[0231] When the mass fraction of the dispersant is within an appropriate range, the flexibility of the electrode can be further improved and the high-temperature storage performance of the battery can be enhanced.

[0232] [Positive electrode]

[0233] The positive electrode sheet includes a positive electrode current collector and a positive electrode membrane arranged on at least one surface of the positive electrode current collector, wherein the positive electrode membrane is prepared from the positive electrode slurry in any embodiment.

[0234] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode membrane is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0235] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0236] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, the dispersant and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0237] [Negative electrode]

[0238] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0239] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0240] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0241] In some embodiments, the negative electrode active material may be a negative electrode active material for a battery that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0242] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0243] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0244] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0245] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0246] [Electrolytes]

[0247] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0248] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0249] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0250] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0251] In some embodiments, the electrolyte may further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0252] [Isolation film]

[0253] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0254] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0255] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0256] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0257] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0258] [Secondary battery]

[0259] The present application does not particularly limit the shape of the secondary battery; it can be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 having a square structure as an example. The secondary battery can also be a sodium ion battery, a magnesium ion battery, or a potassium ion battery.

[0260] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0261] [Battery Module]

[0262] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0263] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0264] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0265] [Battery Pack]

[0266] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0267] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0268] [Electrical devices]

[0269] In one embodiment of the present application, an electric device is provided, comprising at least one of a secondary battery according to any embodiment, a battery module according to any embodiment, or a battery pack according to any embodiment.

[0270] The electrical device includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0271] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0272] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0273] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0274] Example

[0275] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0276] 1. Preparation method

[0277] Example 1

[0278] 1) Preparation of an intermediate polymer: Weigh a dibasic acid and a diamine at a molar ratio of 1:1.2 and add them to a three-necked flask. Add deionized water (8 times the weight of the monomers) and sodium hypophosphite (0.15% of the weight of the monomers). Seal the reactor, evacuate, and fill with nitrogen. Repeat this process three times. Then, raise the temperature to 180°C and react at this constant temperature for 1 hour. Then, raise the temperature to 230°C and react for 2 hours. Evacuate to 0.01 atm and raise the temperature to 270°C. After reacting for 4 hours, remove the heat source and maintain the vacuum. After the reactor cools, remove the product to obtain an intermediate polymer with amino groups at the end. The structural formulas of the dibasic acid and diamine are shown below.

[0279] 2 mol of an intermediate polymer with amino groups at both ends and 1 mol of 1-chlorododecane were dissolved in 1000 ml of dichloromethane and subjected to a halogenation reaction at room temperature. After 6 hours of reaction, 500 ml of deionized water was added to quench the reaction. The reaction mixture was extracted three times with dichloromethane, and the oil phase product was collected, dried over magnesium sulfate, and separated by rotary evaporation. Finally, the product was separated by column chromatography to obtain the first product.

[0280] 1 mol of the first product and 1.5 mol of Cl-C4H8-COOH were dissolved in 1000 ml of dichloromethane and subjected to a halogenation reaction at room temperature. After 6 hours, 500 ml of deionized water was added to quench the reaction. The reaction mixture was extracted three times with dichloromethane, and the oily product was collected, dried over magnesium sulfate, and separated by rotary evaporation. Finally, the product was separated by column chromatography to obtain polymer dispersant P-1.

[0281] The reaction process for preparing polymer dispersant P-1 is as follows:

[0282] Where R1 and R2 are

[0283] 2) Preparation of positive electrode slurry

[0284] The positive electrode slurry was prepared by adding carbon-coated lithium iron phosphate (LFP@C), a conductive agent acetylene black (SP), a binder polyvinylidene fluoride (PVDF), and a dispersant (P-1) to N-methylpyrrolidone (NMP) and stirring. The weight ratio of LFP@C, SP, and PVDF was 97:2:1, and the mass fraction of the dispersant was 1.5% of the total mass of the positive electrode active material, conductive agent, binder, and dispersant. The theoretical solid content of the positive electrode slurry was 60%. After stirring, the slurry viscosity was tested and controlled to be less than 20,000 mPa·s. If the viscosity was too high, NMP was added in the minimum amount to reduce the slurry viscosity to less than 20,000 mPa·s.

[0285] 3) Preparation of positive electrode sheet

[0286] The positive electrode slurry is evenly coated on both surfaces of the aluminum foil positive electrode current collector and then dried to obtain a film layer; thereafter, it is cold pressed and cut to obtain the positive electrode sheet.

[0287] 4) Preparation of negative electrode sheet

[0288] The negative electrode active material artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) are dissolved in solvent deionized water in a weight ratio of 96:2:1:1, mixed evenly and prepared into a negative electrode slurry; the negative electrode slurry is evenly coated on both surfaces of the negative electrode current collector copper foil multiple times, and the negative electrode sheets are obtained after drying, cold pressing and slitting.

[0289] 5) Isolation film

[0290] Polypropylene film is used as the isolation film.

[0291] 6) Preparation of electrolyte

[0292] In an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly in a volume ratio of 3 / 7, and LiPF6 lithium salt was dissolved in the organic solvent to prepare a 12.5% ​​solution to obtain an electrolyte.

[0293] 7) Preparation of secondary batteries

[0294] The positive electrode sheet, separator, and negative electrode sheet prepared in Example 1 were stacked in order, with the separator positioned between the positive and negative electrode sheets to provide isolation. The cells were then wound to obtain a bare cell. The tabs were welded to the bare cell and placed in an aluminum shell. The cells were then baked at 80°C to remove moisture. The electrolyte was then injected and sealed to obtain an uncharged battery. The uncharged battery then underwent a series of steps, including resting, hot and cold pressing, formation, shaping, and capacity testing, to obtain the lithium-ion battery product of Example 1.

[0295] Example 2-12

[0296] The preparation method of the battery of Example 2-12 is similar to that of the battery of Example 1, but the type of anchoring capping agent is adjusted, and the structural formula of the polymer is adjusted. The specific adjustment parameters are shown in Table 1.

[0297] Table 1

[0298] Wherein X' in the polymer structures of Examples 1 to 12 comprises -C 12 H 25 , the L segment contains

[0299] Examples 13-16

[0300] The preparation methods of the batteries of Examples 13-16 are similar to those of Example 1, but the types of dibasic acid and diamine are adjusted, and the structures of R1 and R2 in the polymer are adjusted. The specific adjustment parameters are shown in Table 2, and the corresponding R1 and R2 groups are shown in Table 3.

[0301] Table 2

[0302] Table 3

[0303] Examples 17-22

[0304] Compared with Example 1, the number of repeating units of the structural unit represented by Formula II is adjusted by adjusting the preparation parameters of the polymer. The specific preparation method is as follows:

[0305] Example 17

[0306] Compared with Example 1, the process for preparing the intermediate polymer was adjusted as follows:

[0307] A dibasic acid and a diamine were weighed at a molar ratio of 1:1.2 and added to a three-necked flask. Deionized water (8 times the weight of the monomers) and sodium hypophosphite (0.15% by weight of the monomers) were added. The reactor was sealed, evacuated, and filled with nitrogen three times. This process was repeated three times, then the temperature was raised to 100°C and the reaction was maintained at this temperature for 1 hour. The reaction was then evacuated to 0.01 atm and the temperature was raised to 120°C. After the reaction was completed for 2 hours, the heat source was removed, the vacuum was maintained, and the product was removed after the reactor cooled to obtain the intermediate polymer.

[0308] Example 18

[0309] Compared with Example 1, the process for preparing the intermediate polymer was adjusted as follows:

[0310] A dibasic acid and a diamine were weighed at a molar ratio of 1:1.2 and added to a three-necked flask. Deionized water (8 times the weight of the monomers) and sodium hypophosphite (0.15% by weight of the monomers) were added. The reactor was sealed, evacuated, and filled with nitrogen three times. This process was repeated three times, then the temperature was raised to 100°C and the reaction was maintained at this temperature for 1 hour. The reaction was then evacuated to 0.01 atm and the temperature was raised to 120°C. After the reaction was completed for 4 hours, the heat source was removed, the vacuum was maintained, and the product was removed after the reactor cooled to obtain the intermediate polymer.

[0311] Example 19

[0312] Compared with Example 1, the process for preparing the intermediate polymer was adjusted as follows:

[0313] A dibasic acid and a diamine were weighed at a molar ratio of 1:1.2 and added to a three-necked flask. Deionized water (8 times the weight of the monomers) and sodium hypophosphite (0.15% by weight of the monomers) were added. The reactor was sealed, evacuated, and filled with nitrogen three times. This process was repeated three times before the temperature was raised to 180°C and the reaction was maintained at this temperature for 2 hours. The temperature was then raised to 230°C and the reaction was continued for 5 hours. The reaction was then evacuated to 0.01 atm and the temperature was raised to 300°C. After the reaction was continued for 12 hours, the heat source was removed, the vacuum was maintained, and the product was removed after the reactor cooled to obtain the intermediate polymer.

[0314] Example 20

[0315] Compared with Example 1, the process for preparing the intermediate polymer was adjusted as follows:

[0316] A dibasic acid and a diamine were weighed at a molar ratio of 1:1.2 and added to a three-necked flask. Deionized water (8 times the weight of the monomers) and sodium hypophosphite (0.15% by weight of the monomers) were added. The reactor was sealed, evacuated, and filled with nitrogen three times. This process was repeated three times before the temperature was raised to 180°C and the reaction was maintained at this temperature for 2 hours. The temperature was then raised to 230°C and the reaction was continued for 5 hours. The reaction was then evacuated to 0.01 atm and the temperature was raised to 300°C. After the reaction was continued for 24 hours, the heat source was removed, the vacuum was maintained, and the product was removed after the reactor cooled to obtain the intermediate polymer.

[0317] Example 21

[0318] Compared with Example 1, the process for preparing the intermediate polymer was adjusted as follows:

[0319] A dibasic acid and a diamine were weighed at a molar ratio of 1:1.2 and added to a three-necked flask. Deionized water (8 times the weight of the monomers) and sodium hypophosphite (0.15% by weight of the monomers) were added. The reactor was sealed, evacuated, and filled with nitrogen three times. This process was repeated three times before the temperature was raised to 180°C and the reaction was allowed to continue at this constant temperature for 1 hour. The temperature was then raised to 230°C and the reaction continued for 2 hours. The reaction was then evacuated to 0.01 atm and the temperature was raised to 270°C. After the reaction continued for 3 hours, the heat source was removed, the vacuum was maintained, and the product was removed after the reactor cooled to obtain the intermediate polymer.

[0320] Example 22

[0321] Compared with Example 1, the process for preparing the intermediate polymer was adjusted as follows:

[0322] A dibasic acid and a diamine were weighed at a molar ratio of 1:1.2 and added to a three-necked flask. Deionized water (8 times the weight of the monomers) and sodium hypophosphite (0.15% by weight of the monomers) were added. The reactor was sealed, evacuated, and filled with nitrogen three times. This process was repeated three times before the temperature was raised to 180°C and the reaction was allowed to continue at this constant temperature for 1 hour. The temperature was then raised to 230°C and the reaction continued for 5 hours. The reaction was then evacuated to 0.01 atm and the temperature was raised to 300°C. After the reaction continued for 8 hours, the heat source was removed, the vacuum was maintained, and the product was removed after the reactor cooled to obtain the intermediate polymer.

[0323] Examples 23-27

[0324] Compared with Example 1, the mass fraction of the polymer dispersant was adjusted, see Table 5 of the Example for details.

[0325] Examples 28-31

[0326] Compared with Example 1, the graphitization degree of lithium iron phosphate was adjusted, as shown in Table 5 of the Example for details.

[0327] Example 32

[0328] Compared with Example 1, the positive electrode active material is adjusted to carbon-coated LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM@C).

[0329] Example 33

[0330] Compared with Example 1, the structural formula of the diamine was adjusted. The structural formula of the diamine is shown below:

[0331] Examples 34-36

[0332] The batteries of Examples 34-36 were prepared in a similar manner to that of Example 1, except that the types of dibasic acid and diamine were adjusted, thereby adjusting the structures of R1 and R2 in the polymer. The specific adjustment parameters are shown in Table 4, and the corresponding R1 and R2 groups are shown in Table 5. The diamine in Example 35 was p-phenylenediamine, and the dibasic acid in Example 36 was terephthalic acid.

[0333] Table 4

[0334] Table 5

[0335] Comparative Examples 1-4

[0336] Compared with Example 1, the dispersant was replaced with polyvinyl pyrrolidone (PVP) dispersant, and the graphitization degree of lithium iron phosphate was adjusted.

[0337] Comparative Example 5

[0338] Compared with Example 1, the dispersant was replaced with a polymer dispersant D-1, whose structural formula is C 12 H 25 -O-(EO) 80 -(PO) 40 -(CH2)4-COOH, the preparation process is as follows:

[0339] With 1 mol of C 12 H 25 -OH is an initiator, KOH with a mass percentage of 0.5% of the initiator is a catalyst, the system is evacuated and filled with nitrogen, the reaction apparatus is then heated to 130°C and evacuated, 85 mol of ethylene oxide gas is then introduced, the pressure in the reaction apparatus is maintained below 0.3 MPa, the reaction is carried out at this pressure and temperature for 1 hour, and the first product is obtained by cooling; thereafter, KOH with a mass percentage of 0.5% of the initiator is added, the system is evacuated and filled with nitrogen, the reaction apparatus is then heated to 130°C and evacuated, 45 mol of propylene oxide gas is then introduced, the reaction is carried out for 1 hour, the product is obtained by cooling, and the product is further neutralized by acid washing, extracted three times with dichloromethane, dried, filtered, and rotary evaporated to obtain the intermediate product.

[0340] Dissolve 1 mol of the intermediate product and 1.5 mol of the anchoring end-capping agent Cl-C4H8-COOH in 1000 ml of dichloromethane. Halogenation proceeds at room temperature for 6 hours, followed by quenching with 500 ml of deionized water. The reaction mixture is extracted three times with dichloromethane, and the oily product is collected, dried over magnesium sulfate, and separated by rotary evaporation. Finally, column chromatography is performed to yield polymer dispersant D-1.

[0341] Comparative Example 6

[0342] Compared with Example 1, the dispersant was replaced with polymer dispersant D-2. The preparation process was the same as that of Example 1, except that the anchoring capping agent was adjusted to Cl-C4H8-CH3.

[0343] 2. Performance Testing

[0344] 1. Characterization of polymers

[0345] 1) Weight average molecular weight

[0346] A Waters 2695 Isocratic HPLC gel chromatography instrument (2141 differential refractive index detector) was used. A 3.0% polystyrene solution was used as a reference, and a matching chromatographic column (oil-based: Styragel HT5 DMF 7.8*300mm + Styragel HT4) was selected. A 3.0% polymer solution was prepared using purified N-methylpyrrolidone (NMP) solvent. The prepared solution was allowed to stand for one day before use. During testing, tetrahydrofuran was first drawn into a syringe and rinsed several times. Then, 5 ml of the experimental solution was drawn into the syringe, air was expelled from the syringe, and the needle tip was wiped dry. Finally, the sample solution was slowly injected into the injection port. Data was acquired after the reading stabilized.

[0347] 2) Glass transition temperature

[0348] Glass transition temperature (Tg) measurements were performed using a TA Instruments differential scanning calorimeter (Q1000). A 6-9g polymer sample was heated from room temperature to 200°C at a heating rate of 10°C / min. The Tg of the polymer was determined by analyzing the resulting Tg curve (in °C).

[0349] 3) Melting point

[0350] Melting point tests were performed using a precision microscopic melting point tester (Model X-5). The test was conducted under standard atmospheric pressure. A 0.01 mg sample, evenly ground, was placed on a glass slide. This was covered with another glass slide, gently compacted, and then placed in the center of the hot plate. After covering with a heat shield, the microscope focus was adjusted until the sample could be clearly observed. The temperature knob was then adjusted to rapidly increase the temperature until the polymer slightly melted. The heating rate was then slowly adjusted until the sample was completely melted. The temperature at which the sample was completely melted was recorded as the melting point of the polymer in °C.

[0351] 4) Hydrophile-Lipophile Balance (HLB)

[0352] The emulsification method is used for determination. The principle is that when a polymer is emulsified into an oily medium, the resulting emulsion achieves optimal stability when its HLB value matches the HLB value required by the oil phase. The ideal HLB value can be achieved by mixing a standard sample with a known HLB value in a suitable proportion. This polymer is then emulsified into the prepared oil phase and allowed to stand for 24 hours. The HLB value required by the oil phase in the sample with the best stability is the HLB value of the polymer.

[0353] 2. Positive electrode active material

[0354] 1) Graphitization degree

[0355] The graphitization degree was characterized using a French HORIBA Jobin Yvon high-resolution Raman spectrometer, model LabRAM HR Evolution. After deducting the detection background, the following Gaussian function was used for fitting. Raman spectrum test conditions: wavelength 532nm, scanning range 200-4000cm ‐1 , accumulate twice, measure 10 points for each sample, and take the average value for fitting:

[0356] In the above formula, G is the degree of graphitization, Ai, Vi and wi are the peak intensity, peak position and peak width, respectively.

[0357] 3. Cathode slurry

[0358] 1) Solid content

[0359] Take the copper foil and weigh it in the weight loss rate measuring instrument, record it as M0, and reset it to zero;

[0360] Take a small amount of the positive electrode slurry and apply it on the copper foil, then put it into the moisture meter and weigh it, which is recorded as M1;

[0361] Close the device and start drying;

[0362] After completion, record the weighing data as M2, and calculate the solid content, which is (M2-M0) / (M1-M0).

[0363] 2) Slurry stability test

[0364] After re-stirring the slurry for 30 minutes, take a certain amount of slurry and pour it into the sample bottle of the stability instrument. After putting it into the sample bottle, close the test tower cover. Open the test tower cover, and a scanning curve will begin to appear on the test interface, and the sample stability test will begin. The test will continue for more than 72 hours to complete the test.

[0365] 4. Positive electrode

[0366] 1) Brittleness test

[0367] Take a defect-free positive electrode sheet and cut it longitudinally into samples measuring 20cm x 2.5cm in length and width. The sample should be ≥8 sheets. After pre-folding the sheet in half, place it on the test platform and roll it once with a 2kg cylindrical roller. If light is translucent, the number of times the brittleness is translucent is one. If not, repeat the folding and rolling in the opposite direction. Observe the crease against the light to see if it is translucent or broken. Record the actual number of folds and take the average as the test result.

[0368] 2) Diaphragm resistance

[0369] Cut the dried positive electrode slurry (film) into small discs with a diameter of 3mm at the left, center, and right sides of the positive electrode. Turn on the Yuanneng Technology electrode resistor meter, place the probe in the appropriate position, click the "Start" button, and wait for the reading to stabilize before reading. Test two locations on each disc. Calculate the average of the six measurements to obtain the resistance of the electrode film layer.

[0370] 5. Secondary batteries

[0371] 1) First Coulombic efficiency

[0372] At 25°C, the batteries of the above embodiments and comparative examples were charged at a constant current rate of 0.1C to a voltage of 4.3V. The charging capacity at this time was recorded as the first-cycle charging capacity of the secondary battery. After that, they were allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.1C to a voltage of 2.0V. The batteries were allowed to stand for 5 minutes. This is one charge and discharge cycle. The discharge capacity this time is recorded as the first-cycle discharge capacity of the secondary battery, that is, the initial capacity of the secondary battery.

[0373] The first cycle coulombic efficiency (%) of a secondary battery = first cycle discharge capacity / first cycle charge capacity×100%.

[0374] 2) 45℃ cycle capacity retention

[0375] At 45°C, the batteries in the examples and comparative examples were charged at a constant current of 1 / 3C to 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C, left for 10 minutes, and then discharged at 1 / 3C to 2.5V. The resulting capacity was recorded as the initial capacity C0. Repeat the above steps for the same battery and simultaneously record the discharge capacity Cn of the battery after the nth cycle. The battery capacity retention rate after each cycle is: Pn = C n / C0×100%

[0376] During the test, the first cycle corresponds to n = 1, the second cycle corresponds to n = 2, ..., and the 100th cycle corresponds to n = 100. The battery capacity retention rate data corresponding to Example 1 in Table 5 is the data measured after 300 cycles under the above test conditions, that is, the value of P300.

[0377] 3. Analysis of test results of various embodiments and comparative examples

[0378] Table 6 Example parameters and performance test results

[0379] Table 7 Example parameters and performance test results

[0380] According to the above results, the polymers in Examples 1-36 contain X'-LX, wherein X' contains -C 12 H 25 , X includes any one of a carboxyl group, an ester group, a sulfonic acid group, a sulfonate group, a phosphoric acid group, and a phosphate group,

[0381] L comprises a structural unit represented by formula II

[0382] Where R1 contains

[0383] R2 contains R3 comprises hydrogen or methyl.

[0384] As can be seen from the comparison of Examples 1-22, 33-36 with Comparative Example 3, the comparison of Example 28 with Comparative Example 1, the comparison of Example 29 with Comparative Example 2, and the comparison of Example 30 with Comparative Example 4, compared with the traditional PVP dispersant, the polymer dispersant of the present application has a wide range of versatility, can improve the dispersibility of the slurry with lithium iron phosphate of different degrees of graphitization as the positive electrode active material, increase the solid content of the slurry, slow down the gelation phenomenon of the slurry, reduce the diaphragm resistance of the pole piece, improve the flexibility of the pole piece, and improve the first coulombic efficiency and high temperature cycle performance of the battery. The polymer dispersant has universal applicability for the positive electrode slurry containing lithium iron phosphate of different degrees of graphitization produced by different processes, which helps to reduce the preparation cost and improve the production efficiency.

[0385] Comparison of Example 1 with Comparative Example 5 shows that the amide group in the structural unit represented by Formula II in the polymer dispersant of the present application can effectively increase the solid content of the slurry, slow down the gelation of the slurry, improve the flexibility of the electrode, reduce the membrane resistance of the electrode, and improve the initial coulombic efficiency and high-temperature cycling performance of the battery. Comparison of Examples 1-12 with Comparative Example 6 shows that the X group containing a carboxyl group, an ester group, a sulfonic acid group, a sulfonate group, a phosphoric acid group, or a phosphoric acid ester group in the polymer dispersant of the present application can effectively increase the solid content of the slurry, slow down the gelation of the slurry, improve the flexibility of the electrode, reduce the membrane resistance of the electrode, and improve the initial coulombic efficiency and high-temperature cycling performance of the battery.

[0386] From the comparison of Examples 1, 9-10 and Example 5, it can be seen that compared with the X group containing -C4H8-COO-C3H7, the X group containing -C4H8-COOH, -C4H8-COO-C3H6-OH or -C4H8-COO-NH-C3H6-OH in the polymer dispersant can further improve the dispersibility of the slurry, increase the solid content of the slurry, and improve the performance of the slurry. From the comparison between Example 1 and Examples 5, 9-10, it can be seen that, compared with the X group containing -C4H8-COO-C3H7, -C4H8-COO-C3H6-OH or -C4H8-COO-NH-C3H6-OH, the X group containing -C4H8-COOH in the polymer dispersant can further improve the dispersion effect of the slurry, increase the solid content of the slurry, slow down the gelation of the slurry, improve the flexibility of the electrode, reduce the diaphragm resistance of the electrode, improve the performance of the slurry and the electrode, and at the same time improve the first coulomb efficiency and high-temperature storage performance of the battery. From the comparison between Example 2 and Example 6, it can be seen that, compared with the X group containing -C4H8-SO3-C3H7, the X group containing -C4H8-SO3H in the polymer dispersant can further improve the dispersion effect of the slurry, increase the solid content of the slurry, slow down the gelation of the slurry, improve the flexibility of the electrode, reduce the diaphragm resistance of the electrode, and improve the first coulomb efficiency and high-temperature cycle performance of the battery.

[0387] Comparison of Examples 4, 11-12 with Example 8 shows that compared to the polymer dispersant containing Polymer dispersants contain It can further improve the flexibility of the electrode and improve the high temperature storage performance of the battery. Polymer dispersants contain The solid content of the slurry can be further increased, the gelation of the slurry can be slowed down, the flexibility of the electrode can be improved, the membrane resistance of the electrode can be reduced, and the initial coulombic efficiency and high-temperature storage performance of the battery can be improved. Polymer dispersants contain It can further slow down the gelation of the slurry, improve the flexibility of the pole piece, and improve the first coulombic efficiency and high temperature cycle performance of the battery. Polymer dispersants contain It can improve the first coulombic efficiency and high temperature cycle performance of the battery and improve the electrochemical performance of the battery. Polymer dispersants include The solid content of the slurry can be further increased, the flexibility of the electrode can be improved, and the first coulombic efficiency and high-temperature storage performance of the battery can be improved.

[0388] From the comparison between Example 1 and Example 33, it can be seen that compared with R3 containing methyl in the structural unit shown in Formula II, R3 containing hydrogen can further improve the dispersibility of the slurry, increase the solid content of the slurry, slow down the gelation phenomenon of the slurry, improve the flexibility of the electrode, reduce the diaphragm resistance of the electrode, and improve the first coulombic efficiency and high-temperature storage performance of the battery.

[0389] From the comparison of Examples 1 and 13 with Examples 14 and 36, it can be seen that R1 and R2 contain It can increase the solid content of the slurry, slow down the gelation of the slurry, improve the flexibility of the electrode, and improve the initial coulombic efficiency and high-temperature storage performance of the battery. The solid content of the slurry can be further increased, the gelation of the slurry can be slowed down, the flexibility of the electrode can be improved, the membrane resistance of the electrode can be reduced, and the first coulombic efficiency and high-temperature storage performance of the battery can be improved.

[0390] As can be seen from Examples 1 and 17-22, the repetition number of the structural unit shown in Formula II is 3-100, the slurry has a high solid content, the pole piece has excellent flexibility, and the battery has excellent first coulombic efficiency and high-temperature storage performance. As can be seen from the comparison of Examples 1, 18-19, 21-22 with Examples 17 and 20, the repetition number of the structural unit shown in Formula II is 8-80, which can further increase the solid content of the slurry, slow down the gelation of the slurry, improve the flexibility of the pole piece, and improve the performance of the slurry and the pole piece. As can be seen from the comparison of Examples 1, 21-22 with Examples 17-20, the repetition number of the structural unit shown in Formula II is 15-50, which can further increase the solid content of the slurry, slow down the gelation of the slurry, improve the flexibility of the pole piece, and improve the first coulombic efficiency and high-temperature storage performance of the battery.

[0391] The positive electrode slurry of Examples 1-36 contains a positive electrode active material, a conductive agent, a binder and a dispersant, wherein the dispersant is the polymer of the present application, and the positive electrode active material includes lithium iron phosphate without a carbon coating layer on the surface, lithium iron phosphate with a carbon coating layer on the surface, or lithium nickel cobalt manganese with a carbon coating layer on the surface.

[0392] From the comparison between Example 1 and Example 32, it can be seen that compared with lithium nickel cobalt manganese whose positive electrode active material is lithium iron phosphate with a carbon coating layer on the surface, the polymer dispersant of the present application is more suitable for lithium iron phosphate with a carbon coating layer on the surface, and can further increase the solid content of the slurry of lithium iron phosphate with a carbon coating layer on the surface, improve the flexibility of the electrode, reduce the membrane resistance, and improve the performance of the slurry and the electrode.

[0393] As can be seen from Examples 1, 29-31, the polymer dispersant of the present application has universal applicability and is suitable for slurry systems using lithium iron phosphate with a graphitization degree of 10%-30% as the positive electrode active material. A comparison of Examples 1, 29-31 with Example 28 shows that the use of lithium iron phosphate with a graphitization degree of 10%-30% can further improve the flexibility of the electrode, reduce the membrane resistance of the electrode, and improve the performance of the electrode.

[0394] As can be seen from Examples 1 and 23-27, based on the total mass of the solid matter in the positive electrode slurry, the mass fraction of the polymer dispersant is 0.01%-3%, the slurry has a high solid content, the electrode has excellent flexibility, and the battery has excellent first coulombic efficiency and high-temperature storage performance. As can be seen from the comparison of Examples 1 and 24-26 with Examples 23 and 27, based on the total mass of the solid matter in the positive electrode slurry, the mass fraction of the polymer dispersant is 0.03%-2%, which can improve the high-temperature storage performance of the battery and broaden the battery's operating temperature.

[0395] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A polymer, characterized in that The polymer comprises a structure shown in Formula I, X′-LX Formula I wherein X comprises at least one of a carboxyl group, an ester group, a sulfonic acid group, a sulfonate group, a phosphoric acid group, and a phosphoric acid ester group; X' comprises a nonpolar group; L comprises a structural unit represented by formula II, Where R1 contains C 1-12 Alkylene, C 6-12 Aromatic or R2 contains C 1-12 Alkylene, C 6-12 Aromatic or Wherein EO represents -CH2-CH2-O-, PO represents -CH(CH3)-CH2-O-, m1 and m2 are each independently an integer between 3 and 60, n1 and n2 are each independently an integer between 0 and 60, R3 contains hydrogen or C 1-3 of alkyl.

2. The polymer according to claim 1, characterized in that The polymer comprises at least one of the structures shown in Formula I-1, Formula I-2, Formula I-3, and Formula I-4, wherein a1 and a2 are each independently an integer between 2 and 12, and R4 and R5 are each independently hydrogen, C 1-12 Alkyl, C 1-12 At least one of an alkyl alcohol, *-NH-R9-OH, R6, R7, and R8 each independently contain hydrogen, C 1-12 Alkyl, C 1-12 Alkyl alcohol, *-NH-R 10 -OH, At least one of R9, R 10 Each independently contains C 1-12 Alkylene, R 11 Contains C 1-12 Alkyl or C 6-30 Aromatic group.

3. The polymer according to claim 1 or 2, characterized in that The polymer comprises at least one of the structures shown in Formula I-1, Formula I-2, and Formula I-4, wherein a1 and a2 are each independently an integer between 2 and 12, and R4 and R5 are each independently C 1-12 At least one of an alkyl alcohol, *-NH-R9-OH, R8 comprises hydrogen, C 1-12 Alkyl alcohol, *-NH-R 10 -OH, At least one of R9, R 10 Each independently contains C 1-12 Alkylene, R 11 Contains C 1-12 Alkyl or C 6-30 Aromatic group.

4. The polymer according to any one of claims 1 to 3, characterized in that R3 in the structural unit represented by formula II includes hydrogen.

5. The polymer according to any one of claims 1 to 4, characterized in that The R1 comprises The R2 comprises Wherein n1 or n2 is 0, and m1 and m2 are each independently an integer between 3 and 60.

6. The polymer according to any one of claims 1 to 4, characterized in that The R1 comprises The R2 comprises Wherein n1 and n2 are each independently an integer between 1 and 60, and m1 and m2 are each independently an integer between 3 and 30.

7. The polymer according to any one of claims 1 to 6, characterized in that The number of repetitions of the structural unit represented by formula II in L is 3-100.

8. The polymer according to any one of claims 1 to 7, characterized in that The X' comprises C 3-30 Alkyl, C 6-30 At least one of the aromatic groups.

9. The polymer according to any one of claims 1 to 8, characterized in that The weight average molecular weight of the polymer is 1500 g / mol-70000 g / mol.

10. The polymer according to any one of claims 1 to 9, characterized in that The glass transition temperature of the polymer is 50°C-200°C.

11. The polymer according to any one of claims 1 to 10, characterized in that The melting point of the polymer at 1 standard atmosphere is 70°C-300°C.

12. The polymer according to any one of claims 1 to 11, characterized in that The hydrophilic-lipophilic balance value of the polymer is 6-16.

13. A method for preparing a polymer, characterized in that: The preparation method comprises the following steps: 1) Polycondensation reaction: polymerizing at least one dibasic acid and at least one diamine to prepare an intermediate polymer, wherein the intermediate polymer comprises a structure shown in Formula III, Y′-LY Formula III wherein Y' and Y each independently comprise a carboxyl group or an amino group; 2) End group reaction: reacting the end groups of the intermediate polymer to obtain a polymer having a structure shown in formula I, X′-LX Formula I wherein X comprises at least one of a carboxyl group, an ester group, a sulfonic acid group, a sulfonate group, a phosphoric acid group, and a phosphoric acid ester group; X' comprises a nonpolar group; L comprises a structural unit represented by formula II, Where R1 contains C 1-12 Alkylene, C 6-12 Aromatic or R2 contains C 1-12 Alkylene, C 6-12 Aromatic or Wherein EO represents -CH2-CH2-O-, PO represents -CH(CH3)-CH2-O-, m1 and m2 are each independently an integer between 3 and 60, n1 and n2 are each independently an integer between 0 and 60, R3 contains hydrogen or C 1-3 of alkyl.

14. The preparation method according to claim 13, characterized in that: The preparation method specifically comprises: Stirring a catalyst, at least one dibasic acid and at least one diamine at 20° C.-300° C. for reaction for 2 h-35 h to obtain the intermediate polymer, wherein both ends of the intermediate polymer have the same end group; The terminal groups at both ends of the intermediate polymer are reacted respectively to obtain the polymer.

15. A dispersant, characterized in that the dispersant comprises the polymer according to any one of claims 1 to 12 or the polymer prepared by the preparation method according to claim 13 or 14.

16. Use of the polymer according to any one of claims 1 to 12 in a secondary battery.

17. A positive electrode slurry, characterized in that: The invention comprises a positive electrode active material, a conductive agent, a binder and a dispersant, wherein the dispersant comprises the polymer according to any one of claims 1 to 12.

18. The positive electrode slurry according to claim 17, characterized in that: The positive electrode active material includes lithium iron phosphate having a carbon coating layer on the surface.

19. The positive electrode slurry according to claim 18, characterized in that: The graphitization degree of the lithium iron phosphate with a carbon coating layer on the surface is 10%-30%.

20. The positive electrode slurry according to any one of claims 17 to 19, characterized in that: Based on the total mass of the solid matter in the positive electrode slurry, the mass fraction of the dispersant is 0.01%-3%, and can be optionally 0.03%-2%.

21. A positive electrode sheet, comprising a positive electrode current collector and a positive electrode membrane arranged on the positive electrode current collector, characterized in that: The positive electrode membrane is prepared from the positive electrode slurry according to any one of claims 17 to 20.

22. A secondary battery, characterized in that: It comprises a separator, a negative electrode plate, an electrolyte and the positive electrode plate as claimed in claim 21.

23. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 22.

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