Polymer, method of preparation, dispersant, positive electrode slurry, positive electrode sheet, secondary battery, and power using device

Abstract

The application provides a polymer, a preparation method, a dispersant, a positive electrode slurry, a positive electrode sheet, a secondary battery and an electric device, the polymer comprising a structure shown in Formula I, 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, L comprises a structural unit shown in Formula II and Formula III, wherein R1 comprises at least one of C 1‑12 alkylene, C 6‑12 aralkylene and C 1‑12 alkylene, C 6‑12 aralkylene and C 1‑12 alkylene, C 6‑12 aralkylene and C 1‑12 alkylene, C 6‑12 aralkylene and C 1‑3 alkyl, wherein EO represents -CH2-CH2-O-, PO represents -CH(CH3)-CH2-O-, m1, m2, m3 and m4 are each independently an integer between 1 and 10, and n1, n2, n3 and n4 are each independently an integer between 0 and 10.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a polymer, a preparation method, a dispersant, a positive electrode slurry, a positive electrode sheet, a secondary battery and an electric device. BACKGROUND

[0002] In recent years, secondary batteries are widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0003] The positive electrode sheet directly affects the application performance of the secondary battery as the main component of the secondary battery. The positive electrode sheet is generally composed of a current collector, a positive active material, a conductive agent and a binder. However, the positive active material is generally a nanoscale material, which has a large specific surface area, resulting in a higher surface activity. During the uniform slurry process of the positive electrode slurry, agglomeration easily occurs, forming larger agglomerates, which affects the coating effect of the electrode, resulting in low conductivity of the electrode sheet prepared therefrom, and directly affecting 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 active materials produced by different processes and having different graphitization degrees. The dispersant in the prior art has poor universality and is not conducive to reducing the manufacturing cost. Therefore, it is necessary to develop a new dispersant to adapt to positive active materials produced by different processes and having different graphitization degrees. SUMMARY

[0004] The present application is carried out in view of the above-mentioned problems, and aims to provide a polymer, which is used as a dispersant to adapt to positive active materials having different graphitization degrees, can improve the dispersibility of a slurry system containing positive active materials having different graphitization degrees, can effectively increase the solid content of the slurry, slow down the gelation of the slurry, reduce the sheet resistance of the electrode sheet, improve the flexibility of the electrode sheet, and improve the first coulombic efficiency and high-temperature cycle performance of the battery.

[0005] A first aspect of the present application provides a polymer, which comprises a structure represented by Formula I,

[0006] X'-L-X Formula I

[0007] 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;

[0008] X' comprises a non-polar group;

[0009] L comprises structural units represented by Formula II and Formula III,

[0010]

[0011] R1 comprises C 1-12 alkylene, C 6-12 aromatic, at least one, R2 comprises C 1-12 alkylene, C 6-12 aromatic, at least one, R3 comprises C 1-12 alkylene, C 6-12 aromatic, at least one, R4 comprises C 1-12 alkylene, C 6-12 aromatic, at least one, R5 comprises hydrogen or C 1-3 alkyl,

[0012] wherein EO represents -CH2-CH2-O-, PO represents -CH(CH3)-CH2-O-, each of m1, m2, m3, m4 is independently an integer between 1 and 10, each of n1, n2, n3, n4 is independently an integer between 0 and 10.

[0013] The end group at one end of the polymer comprises a non-polar group, showing lipophilicity, and the end group at the other end comprises at least one of carboxyl, ester, sulfonic acid, sulfonate, phosphoric acid, and phosphate, being a polar group, showing hydrophilicity. The polymer is added into the slurry system, and the carboxyl, ester, sulfonic acid, sulfonate, phosphoric acid, or phosphate at one end is adsorbed on the surface of the solid particles as an anchoring site, and the non-polar group at the other end is suspended in the slurry to form steric hindrance, which generates strong repulsion when the solid particles approach each other, preventing the particles from agglomerating, and forming a uniformly dispersed and stable slurry. Meanwhile, the structural units represented by Formula II and Formula III contain ester and amide groups, both of which are polar groups, and can generate strong intermolecular induction, further improving the dispersion of the polymer. In addition, the L chain segment contains fewer branches, and the bond angle is relatively fixed, showing a certain linear structure in the slurry system, and the chain segment is fully stretched in the slurry system, and the chain segments are not easy to entangle, and the steric hindrance generated by them fully isolates the solid particles, further improving the dispersion effect.

[0014] In addition, the structural units shown as Formula II and Formula III in the L segment contain ester groups and amide groups. Due to the p-π conjugation effect, the lone pair charges of the oxygen atoms and the nitrogen atoms in the ester groups and the amide groups will delocalize to the C-O single bond and the C-N single bond. Meanwhile, the ester groups and the amide groups are carboxylic acid derivative groups, which will produce enol tautomerism under acidic or basic conditions, and the α-C and the C in 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 reduces the sliding resistance between the positive active materials in the cold pressing process, increases the flexibility of the pole piece, and improves the flexibility of the pole piece.

[0015] In summary, compared with the existing dispersants, the polymer dispersant has wide versatility and is suitable for slurry systems containing positive active materials with different graphitization degrees. Compared with the existing dispersants, the polymer dispersant improves the dispersing capacity of the polymer by the combined action of the terminal X group, the ester group, the amide group, and the L segment, improves the applicability of the polymer dispersant to positive active materials with different graphitization degrees, and helps to reduce the production cost and improve the production efficiency.

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

[0017]

[0018]

[0019] wherein a1, a2 are each independently an integer between 2 and 12, R6, R7 each independently comprise at least one of hydrogen, C 1-12 alkyl, C 1-12 alkyl alcohol, *-NH-R 11 -OH, 10 each independently comprise at least one of hydrogen, C 1-12 alkyl, C 1-12 alkyl alcohol, *-NH-R 12 -OH, wherein R 11 , R 12 each independently comprise C 1-12 alkylene, R 13 comprise C 1-12 alkyl or C 6-30 aromatic group.

[0020] In any embodiment, the polymer comprises at least one of the structures shown as Formula I-1, Formula I-2, Formula I-4,

[0021]

[0022]

[0023] wherein a1, a2 are each independently an integer between 2 and 12, R6, R7 each independently comprise at least one of hydrogen, C 1-12 alkyl alcohol, *-NH-R 11 -OH, R 10 comprise at least one of hydrogen, C 1-12 alkyl alcohol, *-NH-R 12 -OH, wherein R 11 , R 12 each independently comprise C 1-12 alkylene, R 13 comprise C 1-12 alkyl or C 6-30 aromatic group.

[0024] In any embodiment, R5 in the structural unit of Formula III comprises hydrogen.

[0025] R5 in the structural unit of Formula III comprises hydrogen, which can form hydrogen bond with oxygen atom on the surface of the positive active material, further increasing the dispersion of the polymer on the slurry, increasing the solid content of the slurry, slowing down the gelation of the slurry, improving the flexibility of the electrode sheet, and improving the performance of the electrode sheet.

[0026] In any embodiment, R1 comprises R2 comprises R3 comprises R4 comprises wherein at least one of n1, n2, n3, n4 is 0, and each of m1, m2, m3, m4 is an integer between 2 and 10.

[0027] The polymer containing polyethylene oxide segment or polyethylene oxide-propylene oxide segment can improve the flexibility of the polymer, reduce the sliding resistance between particles during the cold pressing of the electrode sheet, improve the flexibility of the electrode sheet, and improve the first coulomb efficiency and high-temperature storage performance of the battery.

[0028] In any embodiment, R1 comprises R2 comprises R3 comprises R4 comprises wherein each of n1, n2, n3, n4, m1, m2, m3, m4 is an integer between 1 and 10.

[0029] The polymer containing polyethylene oxide-propylene oxide segment can further improve the flexibility of the polymer, reduce the sliding resistance between particles during the cold pressing of the electrode sheet, improve the flexibility of the electrode sheet, and improve the high-temperature storage performance of the battery.

[0030] In any embodiment, the ratio of the number of repeating units of the structural unit represented by Formula II to the number of repeating units of the structural unit represented by Formula III in L is 1:7-7:1.

[0031] Controlling the ratio of the number of repeating units of the structural unit represented by Formula II to the number of repeating units of the structural unit represented by Formula III in L within a suitable range, the polymer can effectively disperse the slurry, 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.

[0032] In any embodiment, the ratio of the number of repeating units of the structural unit represented by Formula II to the number of repeating units of the structural unit represented by Formula III in L is 1:3-3:1.

[0033] Controlling the ratio of the number of repeating units of the structural unit represented by Formula II to the number of repeating units of the structural unit represented by Formula III in L within a suitable range, the flexibility of the pole piece can be improved, the first coulombic efficiency and high-temperature storage performance of the battery can be improved, and the electrochemical performance of the battery can be comprehensively improved.

[0034] In any embodiment, the number of repeating units of the structural unit represented by Formula II in L is 8-50, and the number of repeating units of the structural unit represented by Formula III in L is 8-50.

[0035] Controlling the number of repeating units of the structural unit represented by Formula II and the number of repeating units of the structural unit represented by Formula III within a suitable range can ensure that the polymer has a sufficient number of ester groups and amide groups, can enable the polymer to generate sufficient intermolecular induction force, and can form sufficient intermolecular force with solid particles in the slurry system, thereby improving the dispersion capacity of the polymer. At the same time, a suitable number of structural units represented by Formula II and structural units represented by Formula III enables the polymer to have excellent solubility in the slurry system, and the polymer can be fully stretched in the slurry system, so that the polymer can function as a dispersant.

[0036] In any embodiment, X' comprises at least one of C 3-30 alkyl, C 6-30 aromatic group.

[0037] In any embodiment, the weight average molecular weight of the polymer is 3000 g / mol-55000 g / mol.

[0038] In any embodiment, the glass transition temperature of the polymer is 30℃-150℃.

[0039] In any embodiment, the melting point of the polymer at 1 standard atmosphere is 60℃-210℃.

[0040] In any embodiment, the hydrophilic-lipophilic balance value of the polymer is 6-16.

[0041] A second aspect of the present application provides a method for preparing a polymer, the method comprising the steps of:

[0042] 1) a condensation reaction: polymerizing at least one diacid, at least one diol, and at least one diamine to prepare an intermediate polymer comprising a structure represented by Formula IV,

[0043] Y'-L-Y Formula IV

[0044] wherein Y' and Y each independently comprise at least one of a carboxyl group, a hydroxyl group, and an amino group;

[0045] 2) an end group reaction: reacting end groups of the intermediate polymer to obtain a polymer comprising a structure represented by Formula I,

[0046] X'-L-X Formula I

[0047] X comprises at least one of a carboxyl group, an ester group, a sulfonic acid group, a sulfonate ester group, a phosphoric acid group, and a phosphate ester group;

[0048] X' comprises a non-polar group;

[0049] L comprises structural units represented by Formula II and Formula III,

[0050]

[0051]

[0052] R1comprises at least one of a C 1-12 alkylene group, a C 6-12 aromatic group, R2comprises at least one of a C 1-12 alkylene group, a C 6-12 aromatic group, R3comprises at least one of a C 1-12 alkylene group, a C 6-12 aromatic group, R4comprises at least one of a C 1-12 alkylene group, a C 6-12 aromatic group, R5comprises hydrogen or a C 1-3 alkyl group, wherein EO represents -CH2-CH2-O-, PO represents -CH(CH3)-CH2-O-, each of m1, m2, m3, and m4 is independently an integer between 1 and 10, and each of n1, n2, n3, and n4 is independently an integer between 0 and 10.

[0053] The polymer obtained by the preparation method of the application has one end containing a carboxyl group, an ester group, a sulfonic acid group, a sulfonate group, a phosphoric acid group or a phosphate group, the other end containing a nonpolar group, and the main chain containing an ester group and an amide group. As a dispersant, the polymer can be applied to positive electrode active materials with different graphitization degrees, can improve the dispersibility of the slurry system containing positive electrode active materials with different graphitization degrees, effectively improve the solid content of the slurry, slow down the gelation of the slurry, reduce the film resistance of the pole piece, improve the flexibility of the pole piece, and improve the first coulomb efficiency and high-temperature cycle performance of the battery.

[0054] In any embodiment, the preparation method specifically comprises:

[0055] stirring and reacting the catalyst, the at least one dibasic acid, the at least one dibasic alcohol and the at least one dibasic amine at 20-250°C for 1-20h to obtain an intermediate polymer, wherein the two ends of the intermediate polymer have the same end groups;

[0056] reacting the end groups at the two ends of the intermediate polymer respectively to obtain the polymer.

[0057] The application adopts polycondensation reaction and end group reaction to prepare the polymer, and the preparation method is simple and improves production efficiency.

[0058] In a third aspect of the application, a dispersant is provided, which comprises the polymer of the first aspect or the polymer prepared by the preparation method of the second aspect.

[0059] In a fourth aspect of the application, the application of the polymer of the first aspect in a secondary battery is provided.

[0060] In a fifth aspect of the application, a positive electrode slurry is provided, which comprises a positive electrode active material, a conductive agent, a binder and a dispersant, and the dispersant comprises the polymer of the first aspect.

[0061] The positive electrode slurry has excellent dispersibility, high solid content, and can be prepared into a pole piece with excellent performance.

[0062] In any embodiment, the positive electrode active material comprises lithium iron phosphate with a carbon coating layer on the surface.

[0063] In any embodiment, the graphitization degree of the lithium iron phosphate with a carbon coating layer on the surface is 10%-30%.

[0064] The polymer dispersant of the application can be applied to a slurry system with lithium iron phosphate with different graphitization degrees as a positive electrode active material, has universality, and helps to reduce the production cost and improve the production efficiency.

[0065] In any embodiment, the mass fraction of the dispersant is 0.01%-3% based on the total mass of solid substances in the positive electrode slurry.

[0066] The mass fraction of the dispersant is in a suitable range, the slurry has a high solid content, the pole piece has excellent flexibility, and the battery has excellent first coulomb efficiency and high-temperature storage performance.

[0067] In any embodiment, the mass fraction of the dispersant is 0.03%-2% based on the total mass of solid substances in the positive electrode slurry.

[0068] The mass fraction of the dispersant is in a suitable range, which can further improve the flexibility of the pole piece and improve the use performance of the pole piece.

[0069] In a sixth aspect of the present application, a positive electrode pole piece is provided, comprising a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer is prepared from the positive electrode slurry of the fifth aspect.

[0070] The positive electrode pole piece of the present application has excellent flexibility and low membrane resistance, and the pole piece has excellent use performance.

[0071] In a seventh aspect of the present application, a secondary battery is provided, comprising a separator, a negative electrode pole piece, an electrolyte, and the positive electrode pole piece of the sixth aspect.

[0072] In an eighth aspect of the present application, an electric device is provided, comprising the secondary battery of the seventh aspect. BRIEF DESCRIPTION OF DRAWINGS

[0073] Figure 1 is a schematic diagram of a secondary battery of an embodiment of the present application;

[0074] Figure 2 is a schematic diagram of a secondary battery of an embodiment of the present application; Figure 1 is an exploded view of the secondary battery of an embodiment of the present application shown in FIG. 1;

[0075] Figure 3 is a schematic diagram of a battery module of an embodiment of the present application;

[0076] Figure 4 is a schematic diagram of a battery pack of an embodiment of the present application;

[0077] Figure 5 is a schematic diagram of a battery pack of an embodiment of the present application; Figure 4 is an exploded view of the battery pack of an embodiment of the present application shown in FIG. 5;

[0078] Figure 6 is a schematic diagram of an electric device using the secondary battery of an embodiment of the present application as a power source.

[0079] BRIEF DESCRIPTION OF DRAWINGS

[0080] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0081] Hereinafter, embodiments of the positive electrode active material and the method for manufacturing the same, the positive electrode sheet, the secondary battery, the battery module, the battery pack, and the electrical device according to the present application will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known well, repetitive description of substantially identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying drawings and the following description are provided to enable those skilled in the art to sufficiently understand the present application, and are not intended to limit the subject matter recited in the claims.

[0082] The ranges disclosed herein are defined by their lower and upper limits, and are inclusive of the recited ranges. Ranges are defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. Ranges defined by this approach can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if a range of 60-120 and a range of 80-110 are listed for a particular parameter, it is understood that a range of 60-110 and a range of 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 are listed, and if a maximum range value of 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing each and every intervening real number between the upper and lower limits of that range, wherein a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shorthand way of describing those numerical combinations. In addition, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0083] If not particularly stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0084] If not particularly stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0085] If not specified otherwise, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprising steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method further comprising step (c) means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0086] If not specified otherwise, the terms "comprising" and "including" as used in the present application are open-ended and also include the case where the other components are not present. For example, the terms "comprising" and "including" can mean that the other components can or can not be present.

[0087] If not specified otherwise, the term "or" in the present application is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following satisfy the condition "A or B": A is true (or present) and B is false (or not present); A is false (or not present) and B is true (or present); or both A and B are true (or present).

[0088] The positive electrode slurry is mainly a solid-liquid phase mixed system formed by the positive electrode active material, the conductive agent, the binder and the solvent. In the prior art, a dispersant is often added to improve the dispersibility of the slurry. However, the dispersant in the prior art is usually only suitable for the slurry system of fixed components, and has poor universality. When the physical properties of the components in the slurry change, the dispersant often needs to be adjusted. For example, the degree of carbon coating on the surface of lithium iron phosphate produced under different process conditions in the prior art is not the same, and the graphitization degree of lithium iron phosphate is not the same. A kind of dispersant cannot be used for lithium iron phosphate with different graphitization degrees. The dispersibility of the slurry system is not ideal when the dispersant in the prior art is used for the slurry system with lithium iron phosphate with different graphitization degrees as the positive electrode active material, and it is difficult to meet the performance requirements of the electrode sheet and the battery.

[0089] [dispersant]

[0090] Based on this, the present application provides a polymer, the polymer comprising a structure shown in formula I,

[0091] X'-L-Y Formula I

[0092] wherein X comprises at least one of carboxyl, ester, sulfonic acid, sulfonate, phosphoric acid, and phosphate;

[0093] X' comprises a non-polar group;

[0094] L comprises structural units of the formula II and the formula III,

[0095]

[0096] wherein R1comprises C 1-12 alkylene, C 6-12 aromatic, at least one, R2comprises C 1-12 alkylene, C 6-12 aromatic, at least one, R3comprises C 1-12 alkylene, C 6-12 aromatic, at least one, R4comprises C 1-12 alkylene, C 6-12 aromatic, at least one, R5comprises hydrogen or C 1-3 alkyl,

[0097] wherein EO denotes -CH2-CH2-O-, PO denotes -CH(CH3)-CH2-O-, m1, m2, m3, m4 are each independently an integer between 1 and 10, n1, n2, n3, n4 are each independently an integer between 0 and 10.

[0098] In the present context, the term "polymer" comprises on the one hand a collection of macromolecules which are chemically uniform, but which differ in the degree of polymerization, molar mass and chain length, prepared by a polymerization reaction. The term also comprises on the other hand derivatives of such a collection of macromolecules formed by a polymerization reaction, i.e. compounds which can be obtained by reaction, for example addition or substitution, of functional groups in the above macromolecules and which can be chemically uniform or chemically non-uniform.

[0099] In the present context, the term "carboxyl" means -COOH.

[0100] In the present context, the term "ester" means R 14 is a non-hydrogen group.

[0101] In the present context, the term "sulfonic acid" means -SO3H.

[0102] In the present context, the term "sulfonate" means R 15 is a non-hydrogen group.

[0103] In the present context, the term "phosphoric acid" means

[0104] In the present context, the term "phosphate" means R16 is a non-hydrogen group.

[0105] In the present text, the term "amide group" refers to R 17 , R 18 each independently is hydrogen or a non-hydrogen group.

[0106] In the present text, the term "non-polar group" refers to a group with coinciding centers of positive and negative charge, including but not limited to alkyl, aryl groups.

[0107] In the present text, the term "alkyl" refers to a straight-chain or branched hydrocarbon chain group consisting solely of carbon and hydrogen atoms, no unsaturation present in the group, having from 1 to 12 carbon atoms.

[0108] In the present text, the term "aryl" refers to an aromatic ring system with at least one ring being aromatic.

[0109] In some embodiments, the non-polar group comprises a C 3-30 alkyl or a C 6-30 aryl group.

[0110] In the present text, the term "C 3-30 alkyl" refers to a straight-chain or branched hydrocarbon chain group consisting solely of carbon and hydrogen atoms, no unsaturation present in the group, having from 6 to 30 carbon atoms, and attached to the rest of the molecule by a single bond. The terms "C 1-3 alkyl" and "C 1-12 alkyl" are to be interpreted accordingly.

[0111] In the present text, the term "C 6-30 aryl" refers to a monovalent functional group derived by removal of one hydrogen atom from a ring of an aromatic hydrocarbon containing from 6 to 30 carbon atoms, such as phenyl or naphthyl. Aromatic hydrocarbons refer to hydrocarbons having aromatic rings and include both monocyclic and polycyclic hydrocarbons, wherein the additional rings of the polycyclic hydrocarbons can be aromatic or non-aromatic.

[0112] In the present text, the term "C 1-12 alkylene" refers to a branched and straight-chain saturated aliphatic divalent hydrocarbon radical having the number of carbon atoms specified, no unsaturation present in the group, having from 1 to 12 carbon atoms, and attached to the rest of the molecule by single bonds.

[0113] In the present text, the term "C 6-12 arylene" refers to a divalent functional group derived by removal of two hydrogen atoms from a ring of an aromatic hydrocarbon containing from 6 to 12 carbon atoms, including but not limited to phenylene or naphthylene.

[0114] In the present text, The EO units and PO units in may be randomly arranged, or can be block arranged.

[0115] In some embodiments, R1 and R3 are the same.

[0116] In some embodiments, R1 and R3 are not the same.

[0117] In this context, the term "dispersant" refers to a class of substances that prevent solid particles from aggregating with each other in a solid-liquid dispersion system, allowing the solid particles to remain uniformly dispersed in the liquid phase for a long time.

[0118] 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.

[0119] In some embodiments, the dispersion medium of the dispersant is an oily solvent, examples of which include but are not limited to dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethyl cellulose, polycarbonate. That is, the dispersant is dissolved in the oily solvent.

[0120] In some embodiments, the dispersant functions as a positive electrode slurry dispersant. It is used to disperse the positive electrode active material, the conductive agent, and the binder to form a positive electrode slurry.

[0121] In some embodiments, the dispersant functions as a negative electrode slurry dispersant. It is used to disperse the negative electrode active material, the conductive agent, and the binder to form a negative electrode slurry.

[0122] In some embodiments, the X group contains a carboxyl group, a sulfonic acid group, or a phosphoric acid group.

[0123] The carboxyl group, the sulfonic acid group, or the phosphoric acid group can ionize to produce a negative ion, which is adsorbed to the surface of the positive electrode active material particles in the slurry system mainly through electrostatic interaction, anchoring one end of the polymer to the surface of the positive electrode active material particles.

[0124] In some embodiments, the X group contains an ester group, a sulfonate group, or a phosphate group.

[0125] The ester group, the sulfonate group, or the phosphate group is adsorbed to the surface of the positive electrode active material particles in the slurry system through intermolecular forces, anchoring one end of the polymer to the surface of the positive electrode active material particles.

[0126] The end group at one end of the polymer comprises a non-polar group, showing lipophilicity, and the end group at the other end 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, showing hydrophilicity. When the polymer is added to a slurry system, the carboxyl group, the ester group, the sulfonic acid group, the sulfonate group, the phosphoric acid group, or the phosphate group at one end is adsorbed on the surface of the positive electrode active material particles as an anchoring site, and the other end is suspended in the slurry to form steric hindrance, which generates a strong repulsive force when the particles approach each other, preventing particle agglomeration and forming a uniformly dispersed and stable slurry. The structural units represented by Formula II and Formula III contain an ester group and an amide group, both of which are polar groups, and can generate a strong intermolecular induction force, forming a strong intermolecular force with the particles, further improving the dispersing ability of the polymer. In addition, the oxygen and nitrogen atoms in the ester group and the amide group can form hydrogen bonding with the hydroxyl group and / or the carboxyl group on the surface of the positive electrode active material, and at the same time, the oxygen and nitrogen atoms can form coordination with the positive electrode active material, collectively enhancing the dispersion effect of the polymer dispersant on the particles in the slurry system. The L chain segment contains fewer branches, and the bond angle is relatively fixed, showing a certain linear structure in the slurry system. The L chain segment fully stretches in the slurry system, and the chain segments are not prone to entanglement, and the steric hindrance effect fully separates the solid particles. At the same time, the full stretching of the L chain segment also allows the ester group and 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 positive electrode active materials with different graphitization degrees, making the adsorption effect more significant and enhancing the dispersion effect of the polymer dispersant on the slurry.

[0127] In addition, the structural units represented by Formula II and Formula III in the L chain segment contain an ester group and an amide group. Due to the p-π conjugation effect, the lone pair charges of the oxygen atoms and the nitrogen atoms in the ester group and the amide group will delocalize to the C-O single bond and the C-N single bond. At the same time, the ester group and the amide group are carboxylic acid derivative groups, which will produce an enol tautomerism phenomenon under acidic or basic conditions, and the α-C and the C in the carbonyl group will form a transient double bond. Therefore, the entire L chain segment contains part of the double bond property, and the L chain segment tends to be linear, which can reduce the sliding resistance between the positive electrode active materials during cold pressing, increase the flexibility of the pole piece, and improve the flexibility of the pole piece.

[0128] In summary, the polymer of the present application as a dispersant can improve the dispersibility of the slurry containing positive electrode active materials with different graphitization degrees, effectively increase the solid content of the slurry, slow down the gelation of the slurry, reduce the sheet resistance of the pole piece, improve the first coulombic efficiency and high-temperature cycle performance of the battery. At the same time, it can also improve the flexibility of the pole piece, providing a basis for the subsequent preparation of thick-coated high-pressure dense pole pieces.

[0129] The dispersants in the prior art have poor compatibility and cannot adapt to the difference of the positive active material produced under different process conditions in the slurry. The polymer dispersing capacity is improved by the joint action of the terminal X group, the ester group, the amide group and the L chain segment, the applicability of the polymer dispersant to the positive active material with different graphitization degrees is improved, the universality of the polymer dispersant is improved, and the cost reduction and the production efficiency improvement are facilitated.

[0130] In some embodiments, the polymer comprises at least one of the structures represented by Formula I-1, Formula I-2, Formula I-3, Formula I-4,

[0131]

[0132] wherein a1, a2 are each independently an integer between 2 and 12, R6, R7 each independently comprise at least one of hydrogen, C 1-12 alkyl, C 1-12 alkyl alcohol, *-NH-R 11 -OH, R8, R9, R 10 each independently comprise at least one of hydrogen, C 1-12 alkyl, C 1-12 alkyl alcohol, *-NH-R 12 -OH, wherein R 11 , R 12 each independently comprise C 1-12 alkylene, R 13 comprise C 1-12 alkyl or C 6-30 aromatic group.

[0133] In this document, the term "C 1-12 alkyl alcohol" refers to a monovalent atomic group in which an alkylene group is bonded to one hydroxyl group (-OH), and is represented by "-C n H 2n -OH" (wherein n is a natural number of 1-12).

[0134] In some embodiments, the polymer comprises at least one of the structures represented by Formula I-1, Formula I-2, Formula I-4,

[0135]

[0136] wherein a1, a2 are each independently an integer between 2 and 12, R6, R7 each independently comprise at least one of hydrogen, C 1-12 alkyl alcohol, *-NH-R 11 -OH, R 10 comprise at least one of hydrogen, C 1-12 alkyl alcohol, *-NH-R 12-OH, at least one of R 11 , R 12 each independently comprises C 1-12 alkylene, R 13 comprises C 1-12 alkyl or C 6-30 aromatic group.

[0137] In some embodiments, R6 in the structure of Formula I-1 comprises hydrogen.

[0138] R6 comprises hydrogen, the polymer can ionize to generate negative ions, can produce adsorption with the surface of the positive active material particles in the slurry system through electrostatic action, enhance the dispersion effect of the polymer dispersant, increase the solid content of the slurry, slow down the gel phenomenon of the slurry, improve the flexibility of the electrode sheet, and improve the performance of the slurry and the electrode sheet.

[0139] In some embodiments, R6 in the structure of Formula I-1 comprises C 1-12 alkyl alcohol or *-NH-R 11 OH.

[0140] R6 comprises C 1-12 alkyl alcohol or *-NH-R 11 -OH, wherein the amino group or the hydroxyl group can produce adsorption with the positive active material particles in the slurry system, enhance the dispersion effect of the polymer dispersant, increase the solid content of the slurry, and improve the performance of the slurry.

[0141] In some embodiments, R7 in the structure of Formula I-2 comprises hydrogen.

[0142] R7 comprises hydrogen, the polymer can ionize to generate negative ions, can produce adsorption with the surface of the positive active material particles in the slurry system through electrostatic action, enhance the dispersion effect of the polymer dispersant, increase the solid content of the slurry, slow down the gel phenomenon of the slurry, improve the flexibility of the electrode sheet, reduce the sheet resistance of the electrode sheet, and improve the high-temperature cycle performance of the battery.

[0143] In some embodiments, R7 in the structure of Formula I-2 comprises C 1-12 alkyl alcohol or *-NH-R 11 -OH.

[0144] R7 comprises C 1-12 alkyl alcohol or *-NH-R 11 -OH, wherein the amino group or the hydroxyl group can produce adsorption with the positive 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 gel phenomenon of the slurry, improve the flexibility of the electrode sheet, reduce the sheet resistance of the electrode sheet, and improve the first coulomb efficiency and the high-temperature cycle performance of the battery.

[0145] In some embodiments, R8or R9in the structure of Formula I-3 comprises hydrogen.

[0146] R8or R9comprises hydrogen, the polymer can ionize to generate negative ions, can be adsorbed on the surface of the positive active material particles in the slurry system through electrostatic action, enhance the dispersion effect of the polymer dispersant, slow down the gel phenomenon of the slurry, improve the flexibility of the electrode sheet, and improve the first coulomb efficiency and high-temperature cycle performance of the battery.

[0147] In some embodiments, R8or R9in the structure of Formula I-3 comprises C 1-12 alkyl alcohol, *-NH-R 12 -OH, at least one of which.

[0148] R8or R9comprises C 1-12 alkyl alcohol, *-NH-R 12 -OH or The amino, hydroxyl, and ester groups therein can generate adsorption force with the positive active material particles in the slurry system, enhance the dispersion effect of the polymer dispersant, improve the solid content of the slurry, and improve the use performance of the slurry.

[0149] In some embodiments, R 10 comprises hydrogen.

[0150] R 10 comprises hydrogen, the polymer can ionize to generate negative ions, can be adsorbed on the surface of the positive active material particles in the slurry system through electrostatic action, enhance the dispersion effect of the polymer dispersant, improve the solid content of the slurry, and improve the use performance of the slurry.

[0151] In some embodiments, R 10 comprises C 1-12 alkyl alcohol, *-NH-R 12 -OH, at least one of which.

[0152] R 10 comprises C 1-12 alkyl alcohol, *-NH-R 12 -OH or The amino, hydroxyl, and ester groups therein can generate adsorption force with the positive active material particles in the slurry system, enhance the dispersion effect of the polymer dispersant, improve the solid content of the slurry, and improve the use performance of the slurry.

[0153] In some embodiments, the polymer comprises the structure of Formula I-4.

[0154] Compared with the structure shown in formula I-3 containing one L chain segment, the structure shown in formula I-4 contains two L chain segments, which can enhance the dispersion effect of the polymer dispersant, make the slurry have high solid content, improve the flexibility of the pole piece, improve the first coulomb efficiency of the battery, and improve the electrochemical performance of the battery.

[0155] In some embodiments, R5 in the structural unit shown in formula III comprises hydrogen.

[0156] R5 in the structural unit shown in formula III comprises hydrogen, which can form hydrogen bonds with oxygen atoms on the surface of the positive active material, further improve the dispersibility of the slurry, increase the solid content of the slurry, slow down the gelation of the slurry, improve the flexibility of the pole piece, and improve the use performance of the pole piece.

[0157] In some embodiments, R1 comprises C 1-12 alkylene or R2 comprises C 1-12 alkylene or R3 comprises C 1-12 alkylene or R4 comprises C 1-12 alkylene or

[0158] m1, m2, m3, m4 are each independently an integer between 1-10, and n1, n2, n3, n4 are each independently an integer between 0-10.

[0159] Introducing a longer alkyl chain segment or a flexible chain segment of polyether into the L chain segment can improve the flexibility of the pole piece.

[0160] In some embodiments, R1 comprises R2 comprises R3 comprises R4 comprises wherein at least one of n1, n2, n3, n4 is 0, and m1, m2, m3, m4 are each independently an integer between 2-10.

[0161] In this context, the term "polyoxyethylene chain segment" refers to a polymer chain segment comprising -CH2-CH2-O- structural units.

[0162] In this context, the term "polyoxyethylene-propylene oxide chain segment" refers to a polymer chain segment comprising -CH2-CH2-O- and -CH(CH3)-CH2-O- structural units.

[0163] The polymer containing a polyoxyethylene chain segment or a polyoxyethylene-propylene oxide chain segment can improve the flexibility of the polymer, reduce the inter-particle sliding resistance during cold pressing of the pole piece, improve the flexibility of the pole piece, and improve the use performance of the pole piece.

[0164] In some embodiments, R1 comprises R2 comprises R3 comprises R4 comprises wherein n1, n2, n3, n4, m1, m2, m3, m4 are each independently an integer between 1-10.

[0165] The polymer contains polyoxyethylene-propylene oxide segments, which can further improve the flexibility of the polymer, reduce the sliding resistance between particles during cold pressing of the pole piece, improve the flexibility of the pole piece, improve the performance of the pole piece, and improve the high-temperature storage performance of the battery.

[0166] In some embodiments, the ratio of the number of repeating units of the structural unit represented by Formula II to the number of repeating units of the structural unit represented by Formula III in L is 1:7-7:1.

[0167] In some embodiments, the ratio of the number of repeating units of the structural unit represented by Formula II to the number of repeating units of the structural unit represented by Formula III in L is selected from any value or a range consisting of any two values in the group consisting of 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1.

[0168] The ratio of the number of repeating units of the structural unit represented by Formula II to the number of repeating units of the structural unit represented by Formula III in a suitable range, the slurry has a high solid content, the pole piece has excellent flexibility, and the battery has excellent first coulomb efficiency and high-temperature storage performance.

[0169] In some embodiments, the ratio of the number of repeating units of the structural unit represented by Formula II to the number of repeating units of the structural unit represented by Formula III in L is 1:3-3:1.

[0170] In some embodiments, the ratio of the number of repeating units of the structural unit represented by Formula II to the number of repeating units of the structural unit represented by Formula III in L is selected from any value or a range consisting of any two values in the group consisting of 1:3, 1:2, 1:1, 2:1, 3:1.

[0171] Controlling the ratio of the number of repeating units of the structural unit represented by Formula II to the number of repeating units of the structural unit represented by Formula III in L in a suitable range can improve the flexibility of the pole piece, improve the first coulomb efficiency and high-temperature storage performance of the battery.

[0172] In some embodiments, the number of repeating units of the structural unit represented by Formula II in L is 8-50, and the number of repeating units of the structural unit represented by Formula III in L is 8-50.

[0173] In some embodiments, the repeating number of the structural unit of Formula II in L can be selected from any value among 8, 10, 20, 30, 40, 50 or a range between any two of the values.

[0174] In some embodiments, the repeating number of the structural unit of Formula III in L can be selected from any value among 8, 10, 20, 30, 40, 50 or a range between any two of the values.

[0175] Controlling the repeating number of the structural unit of Formula II and the repeating number of the structural unit of Formula III within a suitable range can ensure that the polymer has a sufficient number of ester groups and amide groups, and can ensure that the polymer generates sufficient intermolecular induction force and forms sufficient intermolecular force with the solid particles in the slurry system, thereby improving the dispersing ability of the polymer. Meanwhile, a suitable number of the structural unit of Formula II and the structural unit of Formula III can make the polymer have excellent solubility in the slurry system, and the polymer can be fully stretched in the slurry system, so that the polymer can play the role of a dispersant.

[0176] In some embodiments, the mass percentage of X in the polymer is 0.5%-5% based on the mass of the polymer.

[0177] In some embodiments, the total mass percentage of R1, R2, R3 and R4 in the polymer is 50%-80% based on the mass of the polymer.

[0178] In some embodiments, the mass percentage of in the polymer is 5%-20% based on the mass of the polymer.

[0179] Controlling the mass percentages of the X group, R1, R2, R3 and R4, the ester group and the amide group within a suitable range can make the X anchoring group, the L chain segment, the ester group and the amide group fully exert their respective advantages, and collectively make the polymer have excellent dispersing ability and improve the dispersibility of the slurry.

[0180] In some embodiments, the weight average molecular weight of the polymer is 3000 g / mol-55000 g / mol.

[0181] In some embodiments, the weight average molecular weight of the polymer can be selected from any of 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, 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, or a range defined by any two of them.

[0182] In some embodiments, the weight average molecular weight of the polymer is 6000 g / mol-30000 g / mol.

[0183] In some embodiments, the weight average molecular weight of the polymer can be selected from any of 6000 g / mol, 6500 g / mol, 7000 g / mol, 7500 g / mol, 8000 g / mol, 8500 g / mol, 9000 g / mol, 9500 g / mol, 10000 g / mol, 15000 g / mol, 20000 g / mol, 25000 g / mol, 30000 g / mol, or a range defined by any two of them.

[0184] In this context, the term "weight average molecular weight" refers to the sum of the products of the weight fraction of molecules of different molecular weights in a polymer and their corresponding molecular weights.

[0185] In this application, the weight average molecular weight of the polymer can be tested by methods known in the art, for example, by gel chromatography, such as by using Waters 2695 Isocratic HPLC type gel chromatograph (differential refractive 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 to select a matching chromatographic column (oil: Styragel HT5 DMF 7.8*300mm+Styragel HT4). A purified N-methyl pyrrolidone (NMP) solvent is used to prepare a 3.0% fluoropolymer solution, and the prepared solution is left to stand for one day for standby. During testing, the syringe is first used to suck up tetrahydrofuran for flushing, which is repeated several times. Then 5 ml of the experimental solution is sucked up, and the air in the syringe is excluded, and the needle tip is wiped dry. Finally, the sample solution is slowly injected into the sample port. After the reading is stable, the data is obtained, and the weight average molecular weight is read.

[0186] If the weight average molecular weight of the polymer is too large, the polymer is difficult to dissolve, and cannot play the role of dispersant. If the weight average molecular weight of the polymer is too small, it cannot play an effective dispersion role, is not conducive to the formation of the conductive network, leads to an increase in the sheet resistance of the pole piece, and a decrease in the first coulomb efficiency and high-temperature storage performance of the battery.

[0187] In some embodiments, the glass transition temperature of the polymer is 30-150℃.

[0188] In some embodiments, the glass transition temperature of the polymer is any of 30℃, 60℃, 90℃, 100℃, 120℃, 140℃, 150℃, or a range consisting of any two of them.

[0189] In this context, the term "glass transition temperature" refers to the transition temperature of a non-crystalline polymer (including non-crystalline parts in a crystalline polymer) from a glassy state to a high-elasticity state or from a high-elasticity state to a glassy state, which is the lowest temperature at which the amorphous polymer macromolecular chain segment is free to move.

[0190] In this context, the term "glassy state" refers to a state in which a non-crystalline polymer has very small deformation under the action of external force, and the deformation is proportional to the size of the force, and the deformation can immediately recover when the external force is removed. In the glassy state, the energy of molecular motion is very low, which is not enough to overcome the rotational barrier within the main chain, and is not enough to excite the movement of the chain segment, and the chain segment is in a frozen state. For example, when subjected to external force, the chain segment movement is frozen, only the bond length and bond angle of the main chain can be slightly changed, so from a macroscopic point of view, the deformation of the polymer after being subjected to force is very small.

[0191] In this context, the term "high-elasticity state" refers to a state in which a non-crystalline polymer produces a large deformation under the action of a small external force. In the high-elasticity state, when a non-crystalline polymer is subjected to an external force, the molecular chain changes its conformation through the internal rotation of single bonds and the movement of chain segments to adapt to the action of the external force. For example, when subjected to a tensile force, the molecular chain can change from a curled state to an extended state, thus a large deformation can occur in the macroscopic view. Once the external force is removed, the molecular chain will return to the original curled state through the internal rotation of single bonds and the movement of chain segments, which is manifested in the macroscopic view as an elastic shrinkage.

[0192] In this application, the glass transition temperature of the polymer can be tested by a method known in the art, for example, using a differential scanning calorimeter (Q1000 type) of TA Corporation to test the glass transition temperature. Take 6-9g of polymer sample, heat it from room temperature to 200℃ at a heating rate of 10℃ / min, analyze the obtained differential scanning calorimetry curve, and the glass transition temperature of the polymer can be obtained, which is in ℃.

[0193] In some embodiments, the polymer has a melting point at 1 atmosphere of 60°C to 210°C.

[0194] In some embodiments, the polymer has a melting point at 1 atmosphere of any of 60°C, 80°C, 100°C, 120°C, 140°C, 160°C, 180°C, 200°C, 210°C, or a range between any two of these values.

[0195] In this document, the term "1 atmosphere" refers to the pressure of the atmosphere at sea level under standard conditions, which has a value of 101.325 kPa, a unit of pressure, denoted atm.

[0196] In this application, the melting point of the polymer at 1 atmosphere can be tested using methods known in the art, for example, using a precision melting point apparatus (Model X-5) to test the melting point. At 1 atmosphere, 0.01 mg of uniformly ground sample is placed on a glass slide, covered with another glass slide and gently pressed, and placed in the center of the hot stage. After covering the heat shield, the microscope focus is adjusted until the sample can be clearly observed. Then the temperature knob is adjusted, and the temperature is quickly raised until the polymer shows a slight melting phenomenon, and then the temperature is slowly adjusted to the rate of sample melting, and the full melting temperature is recorded as the melting point of the polymer, in units of °C.

[0197] In some embodiments, the polymer has a hydrophilic-lipophilic balance of 6 to 16.

[0198] In some embodiments, the polymer has a hydrophilic-lipophilic balance of any of 6, 8, 10, 12, 14, 16, or a range between any two of these values.

[0199] In this document, the term "hydrophilic-lipophilic balance" is used to characterize the overall tendency of a polymer to be hydrophilic or lipophilic. The greater the hydrophilic-lipophilic balance, the better the hydrophilicity of the polymer, and vice versa, the smaller the hydrophilic-lipophilic balance, the better the lipophilicity.

[0200] In this document, the hydrophilic-lipophilic balance (HLB) of the polymer can be tested using methods known in the art, for example, using an emulsification method, which is based on the principle that when a polymer is emulsified in an oily medium, the emulsion stability is best when the HLB value of the polymer is the same as the required HLB value of the oil phase medium. By mixing standard samples with known HLB values in proportion, the desired HLB value can be obtained, and the oil phase prepared by emulsifying the polymer is allowed to stand for 24 h, and the HLB value required for the oil phase in the sample with the best stability is the HLB value of the polymer.

[0201] In some embodiments, the polymer has a hydrophilic-lipophilic balance of 10 to 12.

[0202] In some embodiments, the hydrophilic-lipophilic balance of the polymer can be selected from any of 10, 11, 12 or a range consisting of any two of them.

[0203] One embodiment of the present application provides a method for preparing a polymer, the method comprising the steps of:

[0204] 1) condensation reaction: polymerizing at least one diacid, at least one diol and at least one diamine to prepare an intermediate polymer, the intermediate polymer comprising a structure represented by Formula IV,

[0205] Y'-L-Y Formula IV

[0206] wherein Y' and Y each independently comprises at least one of a carboxyl group, a hydroxyl group, and an amino group;

[0207] 2) end group reaction: reacting an end group of the intermediate polymer to obtain a polymer comprising a structure represented by Formula I,

[0208] X'-L-X Formula I

[0209] X comprises at least one of a carboxyl group, an ester group, a sulfonic acid group, a sulfonate ester group, a phosphoric acid group, and a phosphate ester group;

[0210] X' comprises a non-polar group;

[0211] L comprises structural units represented by Formula II and Formula III,

[0212]

[0213] wherein R1 comprises at least one of a C 1-12 alkylene group, a C 6-12 aromatic group, R2 comprises at least one of a C 1-12 alkylene group, a C 6-12 aromatic group, R3 comprises at least one of a C 1-12 alkylene group, a C 6-12 aromatic group, R4 comprises at least one of a C 1-12 alkylene group, a C 6-12 aromatic group, R5 comprises hydrogen or a C 1-3 alkyl group, wherein EO represents -CH2-CH2-O-, PO represents -CH(CH3)-CH2-O-, each of ml, m2, m3, m4 is independently an integer between 1 and 10, and each of nl, n2, n3, n4 is independently an integer between 0 and 10.

[0214] In this context, the term "diamine" refers to an amine containing two amino groups.

[0215] As used herein, the term "diacid" refers to an acid containing two carboxyl groups.

[0216] As used herein, the term "diol" refers to an alcohol containing two hydroxyl groups.

[0217] In some embodiments, the diacid has a structure according to Formula VII,

[0218]

[0219] wherein R4 comprises at least one of a C 1-12 alkylene group, a C 6-12 aromatic group, R5 is hydrogen or a C 1-3 alkyl group, m4 is any integer between 1 and 10, and n4 is any integer between 0 and 10.

[0220] In some embodiments, the diol comprises

[0221]

[0222] any one of the foregoing.

[0223] In any embodiment, the diol has a structure according to Formula VI,

[0224] HO-R2-OH Formula VI

[0225] wherein R2 comprises at least one of a C 1-12 alkylene group, a C 6-12 aromatic group, m2 is any integer between 1 and 10, and n2 is any integer between 0 and 10.

[0226] In some embodiments, the diol comprises

[0227]

[0228] any one of the foregoing.

[0229] In some embodiments, the diacid has a structure according to Formula VII or Formula VIII,

[0230]

[0231] wherein R1 comprises at least one of a C 1-12 alkylene group, a C 6-12 aromatic group, R3 comprises at least one of a C 1-12 alkylene group, a C 6-12 aromatic group, At least one of them, m1 and m3 are each independent integers between 1 and 10, and n1 and n3 are each independent integers between 0 and 10.

[0232] In some embodiments, the dicarboxylic acid contains

[0233]

[0234] Any one of them.

[0235] This preparation method uses inexpensive raw materials, reducing costs and environmental pollution, and is beneficial for increasing the yield of polymer dispersants. Simultaneously, this method can obtain polymers with polar groups at one end (carboxyl, ester, sulfonic acid, sulfonate, phosphoric acid, or phosphate ester) and non-polar groups at the other end, with the main chain containing ester and amide groups. Using this polymer as a dispersant, it is suitable for positive electrode active materials with different degrees of graphitization, improving the dispersibility of slurry systems containing positive electrode active materials with varying degrees of graphitization. It can effectively increase the solid content of the slurry, mitigate gelation, reduce film resistance of the electrode, improve electrode flexibility, and enhance the initial coulombic efficiency and high-temperature cycle performance of the battery.

[0236] In some embodiments, the preparation method specifically includes:

[0237] A catalyst, at least one dicarboxylic acid, at least one diol, and at least one diamine are stirred and reacted at 20°C-250°C for 1-20 hours to obtain an intermediate polymer, wherein the intermediate polymer has the same end groups at both ends.

[0238] The end groups at both ends of the intermediate polymer are reacted to obtain the polymer.

[0239] In some embodiments, the terminal groups at both ends of the intermediate polymer are carboxyl groups.

[0240] In some embodiments, the terminal groups at both ends of the intermediate polymer are hydroxyl groups.

[0241] In some embodiments, the terminal groups at both ends of the intermediate polymer are amino groups.

[0242] In some embodiments, the synthesis route of the polymer is that at least one diacid, at least one diol and at least one diamine are subjected to polymerization under the action of a catalyst to generate an intermediate polymer, so that the diacid, the diamine or the diol is in excess, and both ends of the intermediate polymer are amino, carboxyl or hydroxyl groups, the amino, carboxyl or hydroxyl group at one end of the intermediate polymer is subjected to functional group reaction with an active monomer comprising an X' group, and the amino, carboxyl or hydroxyl group at the other end of the intermediate polymer is subjected to functional group reaction with an active monomer comprising an X group, to prepare a polymer comprising the X group at one end and the X' group at the other end. It can be understood that the active monomer comprising the X' group refers to a monomer comprising the X' group and comprising an active functional group capable of reacting with the amino, carboxyl or hydroxyl group at one end of the intermediate polymer. The active monomer comprising the X group refers to a monomer comprising the X group and comprising an active functional group capable of reacting with the amino, carboxyl or hydroxyl group at one end of the intermediate polymer. The active functional group capable of reacting with the amino group can be selected from any one of an epoxy group, a carboxyl group, an acid anhydride, an isocyanate group, a carbonyl chloride group and a halogen atom, the active functional group capable of reacting with the carboxyl group can be selected from a hydroxyl group or an amino group, and the active functional group capable of reacting with the hydroxyl group can be selected from any one of an epoxy group, a carboxyl group, an amino group, an isocyanate group, a halogen atom and an acid anhydride.

[0243] In some embodiments, the end group of the intermediate polymer is a hydroxyl group, and the active monomer comprising the X' group refers to an active monomer comprising the X' group and comprising a halogen atom.

[0244] In some embodiments, the end group of the intermediate polymer is a hydroxyl group, and the active monomer comprising the X group refers to an active monomer comprising the X group and comprising a halogen atom.

[0245] In some embodiments, the end group of the intermediate polymer is a hydroxyl group, and the active monomer comprising the X' group refers to X'-(CH2)m-A, wherein m is an integer between 1 and 12, and A is F, Cl, Br or I.

[0246] In some embodiments, the end group of the intermediate polymer is a hydroxyl group, and the active monomer comprising the X group refers to X-(CH2)n-B, wherein n is an integer between 1 and 12, and B is F, Cl, Br or I.

[0247] In some embodiments, the catalyst comprises n-butyl titanate.

[0248] The present application adopts polycondensation reaction and end group reaction to prepare the polymer, and the preparation method is simple, and the production efficiency is improved.

[0249] In some embodiments, a dispersant is provided, and the dispersant comprises the polymer in any of the embodiments or the polymer prepared by the preparation method in any of the embodiments.

[0250] In some embodiments, there is provided use of the polymer of any of the embodiments in a secondary battery.

[0251] [Positive electrode slurry]

[0252] In some embodiments, there is provided a positive electrode slurry comprising a positive electrode active material, a conductive agent, a binder, and a dispersant comprising the polymer of any of the embodiments.

[0253] The positive electrode slurry has excellent dispersibility, has a high solid content, and is advantageous in the production of an electrode sheet having excellent performance.

[0254] In some embodiments, the positive electrode active material can employ a positive electrode active material for a battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone only one or in combination of two or more. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to simply as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be referred to simply as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be referred to simply as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be referred to simply as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be referred to simply as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05O2) and modified compounds thereof, etc. Examples of the lithium-containing phosphate of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (which can also be referred to as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon.

[0255] In some embodiments, the cathode slurry includes a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0256] In some embodiments, the cathode active material includes lithium iron phosphate having a carbon coating layer on the surface.

[0257] On one hand, the oxygen atoms and nitrogen atoms in the ester groups and amide groups in the L segment can form coordination with the iron atoms in the lithium iron phosphate, and on the other hand, the oxygen atoms and nitrogen atoms in the ester groups and amide groups can form hydrogen bonds with the carboxyl groups or hydroxyl groups in the carbon coating layer, and the two work together to improve the dispersion capacity of the polymer on the slurry, so that the polymer dispersant has excellent dispersion capacity on the slurry system with lithium iron phosphate having a carbon coating layer on the surface as the cathode active material.

[0258] In some embodiments, the graphitization degree of the lithium iron phosphate having a carbon coating layer on the surface is 10%-30%.

[0259] In some embodiments, the graphitization degree of the lithium iron phosphate having a carbon coating layer on the surface can be selected as any value or a range formed by any two values in 10%, 15%, 20%, 25%, and 30%.

[0260] In this application, the term "graphitization degree" refers to the degree of graphitization of the carbon component, which reflects the degree of completeness of the graphite crystal structure in the carbon coating layer of the carbon-coated lithium iron phosphate, i.e., the degree of regularity of the arrangement of carbon atoms in the graphite structure.

[0261] In this application, the term "graphitization degree" refers to the degree of graphitization of the carbon component, which reflects the degree of completeness of the graphite crystal structure in the carbon coating layer of the carbon-coated lithium iron phosphate, i.e., the degree of regularity of the arrangement of carbon atoms in the graphite structure. -1 , and the following Gaussian function is used for fitting after deducting the detection background. Raman spectrum test conditions: wavelength 532 nm, scanning range 200-4000 cm

[0262]

[0263] In the above formula, G is the graphitization degree, Ai, Vi and wi are the peak intensity, peak position and peak width, respectively.

[0264] In the prior art, in order to improve the electronic and ionic conductivity of lithium iron phosphate, carbon coating is performed on the surface of lithium iron phosphate. However, there are various coating processes for lithium iron phosphate on the market, and the degree of surface carbon coating and the graphitization degree of lithium iron phosphate are different. The existing dispersants cannot be used for slurries with different graphitization degrees of lithium iron phosphate as the positive active material. The polymer dispersant of the present application has universality and can improve the dispersibility of the slurry with different graphitization degrees of lithium iron phosphate as the positive active material, increase the solid content of the slurry, slow down the gelation of the slurry, reduce the membrane resistance of the pole piece, improve the flexibility of the pole piece, and improve the first coulomb efficiency and high-temperature cycle performance of the battery. The polymer dispersant has universality for positive electrode slurries containing lithium iron phosphate with different graphitization degrees produced by different processes, which helps to reduce the preparation cost and improve the production efficiency.

[0265] In some embodiments, the mass fraction of the dispersant is 0.01%-3%, based on the total mass of the solid substances in the positive electrode slurry.

[0266] In some embodiments, the mass fraction of the dispersant can be selected as any value or a range consisting of any two values in 0.01%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, and 3%, based on the total mass of the solid substances in the positive electrode slurry.

[0267] The mass fraction of the dispersant is within a suitable range, the slurry has high solid content, the pole piece has excellent flexibility, and the battery has excellent first coulomb efficiency and high-temperature storage performance.

[0268] In some embodiments, the mass fraction of the dispersant is 0.03%-2%, based on the total mass of the solid substances in the positive electrode slurry.

[0269] In some embodiments, the mass fraction of the dispersant can be selected as any value or a range consisting of any two values in 0.03%, 0.1%, 0.5%, 1%, 1.5%, and 2%, based on the total mass of the solid substances in the positive electrode slurry.

[0270] The mass fraction of the dispersant is within a suitable range, which can further improve the flexibility of the pole piece and improve the performance of the pole piece.

[0271] [Positive electrode pole piece]

[0272] The positive electrode pole piece comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, and the positive electrode film layer is prepared from the positive electrode slurry in any of the embodiments.

[0273] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is provided on either one or both of the two surfaces of the positive electrode current collector.

[0274] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, etc.) on a polymer material base material such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0275] In some embodiments, the positive electrode tab can be prepared by dispersing the above-described components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, the dispersant, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector; and subjecting the same to a drying, cold-pressing, or the like process to obtain the positive electrode tab.

[0276] [Negative electrode tab]

[0277] The negative electrode tab includes a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0278] As an example, the negative electrode current collector has two surfaces opposite in the thickness direction thereof, and the negative electrode film layer is provided on either one or both of the two surfaces of the negative electrode current collector.

[0279] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be formed by forming a metal material (copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, etc.) on a polymer material base material such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0280] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0281] In some embodiments, the negative film layer can further optionally include a binder. The binder can 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).

[0282] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0283] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0284] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on a negative current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained.

[0285] [Electrolyte]

[0286] The electrolyte plays a role of conducting ions between the positive electrode sheet and the negative electrode sheet. The present application does not have a specific limitation on the type of electrolyte, which can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0287] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0288] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoroboric oxalate, lithium bisoxalate borate, lithium difluorobisoxalate phosphate, and lithium tetrafluorobisoxalate phosphate.

[0289] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl 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, cyclobutane sulfone, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0290] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain performance of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0291] [Separator]

[0292] In some embodiments, the secondary battery further includes a separator. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0293] 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, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0294] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator can be made into an electrode assembly through a winding process or a stacking process.

[0295] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the above-described electrode assembly and the electrolyte.

[0296] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0297] [Secondary battery]

[0298] The shape of the secondary battery is not particularly limited, and can be cylindrical, square, or any other shape. For example, Figure 1 is a square structure as an example of a secondary battery 5. The secondary battery can also be a sodium ion battery, a magnesium ion battery, or a potassium ion battery.

[0299] In some embodiments, with reference to Figure 2 , the outer package can include a housing 51 and a cover plate 53. The housing 51 can 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 housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and the skilled person in the art can select according to the specific actual needs.

[0300] [Battery module]

[0301] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by the skilled person in the art according to the application and capacity of the battery module.

[0302] Figure 3 is a battery module 4 as an example. With reference to Figure 3 , in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0303] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0304] [Battery pack]

[0305] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by the skilled person in the art according to the application and capacity of the battery pack.

[0306] Figure 4 and Figure 5 is a battery pack 1 as an example. With reference to Figure 4 and Figure 5In the battery pack 1, a battery case and a plurality of battery modules 4 disposed in the battery case can be included. The battery case includes an upper case 2 and a lower case 3, and the upper case 2 is capable of being provided on the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery case in any manner.

[0307] [Power consuming device]

[0308] In one embodiment of the present application, a power consuming device is provided, which includes at least one of the secondary battery of any embodiment, the battery module of any embodiment, or the battery pack of any embodiment.

[0309] The power consuming device includes at least one of the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0310] As the power consuming device, the secondary battery, the battery module, or the battery pack can be selected according to the use requirement thereof.

[0311] Figure 6 The power consuming device is an example. The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power consuming device, the battery pack or the battery module can be used.

[0312] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thin and light, and the secondary battery can be used as a power source.

[0313] Embodiment

[0314] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application. If the specific technology or condition is not mentioned in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument is not mentioned by the manufacturer, it is a conventional product that can be obtained by market purchase.

[0315] I. Preparation method

[0316] Example 1

[0317] 1) Preparation of intermediate polymer: Take the binary acid, binary alcohol and binary amine in a molar ratio of 2: 1.2: 1, respectively, into a three-necked flask, and melt the above monomers by water bath heating to 60℃, wherein the structural formula of the binary acid, binary alcohol and binary amine are as follows,

[0318] Binary acid

[0319] Binary alcohol

[0320] Binary amine

[0321] A large amount of nitrogen is introduced into the reaction system, and the system is heated to 140℃, and then heated to 195℃ at a rate of 30℃ / h. Then add 1% of the total mass of the monomers of glycerol and 0.25% of the total mass of the monomers of the catalyst n-butyl titanate, and stir for 20 min. Then gradually reduce the pressure of the reaction system to 60 Pa using a vacuum pump and a pressure regulating valve, and after reaching the maximum vacuum, heat the system to 225℃, and after 2.5h of reaction, cool the system to 200℃, and after the pressure inside and outside the reaction device is balanced, discharge the material, to obtain an intermediate polymer with hydroxyl groups at both ends.

[0322] 2) End group reaction: 2 mol of the intermediate polymer with hydroxyl groups at both ends, 1 mol of 1-chlorododecane is dissolved in 1000 ml of dichloromethane, and halogenation reaction is carried out at room temperature, after 6h of reaction, 500 ml of deionized water is added to quench the reaction. The reaction mixture is extracted three times in dichloromethane, the oil phase product is collected, then dried with magnesium sulfate, the product is separated by rotary evaporation, and finally chromatographic column separation is carried out to obtain the first product;

[0323] 1 mol of the first product, 1.5 mol of the anchoring capping agent Cl-C4H8-COOH is dissolved in 1000 ml of dichloromethane, and halogenation reaction is carried out at room temperature, after 6h of reaction, 500 ml of deionized water is added to quench the reaction. The reaction mixture is extracted three times in dichloromethane, the oil phase product is collected, then dried with magnesium sulfate, the product is separated by rotary evaporation, and finally chromatographic column separation is carried out to obtain the polymer dispersant P-1.

[0324] The reaction process for preparing the polymer dispersant P-1 is as follows,

[0325]

[0326] Wherein, R1, R2, R4 are

[0327] 2) Preparation of positive electrode slurry

[0328] The positive electrode active material lithium iron phosphate coated with carbon (LFP@C), conductive agent acetylene black (SP), binder polyvinylidene fluoride (PVDF), and dispersant (P-1) are added into N-methyl pyrrolidone (NMP) to stir to obtain a positive electrode slurry, wherein the weight ratio of LFP@C, SP, and PVDF is 97:2:1, the mass fraction of the dispersant is 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 is 60%, and the slurry viscosity is tested after stirring is completed, and the viscosity is controlled to be less than 20,000 mPa·s. If the viscosity is too high, the minimum amount of NMP is added to make the slurry viscosity less than 20,000 mPa·s.

[0329] 3) Preparation of positive electrode sheet

[0330] The positive electrode slurry is uniformly coated on both surfaces of the aluminum foil positive current collector, and then dried to obtain a film layer; and then cold-pressed and cut to obtain a positive electrode sheet.

[0331] 4) Preparation of negative electrode sheet

[0332] The negative electrode active material artificial graphite, conductive agent carbon black, binder styrene butadiene rubber (SBR), and thickening agent carboxymethyl cellulose sodium (CMC-Na) are dissolved in deionized water according to a weight ratio of 96:2:1:1, and uniformly mixed to prepare a negative electrode slurry; the negative electrode slurry is uniformly coated on both surfaces of the negative current collector copper foil for multiple times, and then dried, cold-pressed, and cut to obtain a negative electrode sheet.

[0333] 5) Separation film

[0334] A polypropylene film is used as the separation film.

[0335] 6) Preparation of electrolyte

[0336] In an argon atmosphere glove box (H2O<0.1 ppm, O2<0.1 ppm), organic solvents ethylene carbonate (EC) and methyl ethyl carbonate (EMC) are uniformly mixed according to a volume ratio of 3 / 7, and LiPF6 lithium salt is dissolved in the organic solvents to prepare a 12.5% solution to obtain an electrolyte.

[0337] 7) Preparation of secondary battery

[0338] The positive electrode sheet prepared in Example 1, the separation film, and the negative electrode sheet are sequentially stacked with the separation film between the positive and negative electrode sheets to play a separation role, and then wound to obtain a bare cell, the bare cell is welded with tabs, and the bare cell is loaded into an aluminum shell and baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain a non-charged battery. The non-charged battery is sequentially subjected to processes of standing, hot and cold pressing, formation, shaping, capacity testing, and the like to obtain a lithium ion battery product of Example 1.

[0339] Example 2-12

[0340] The battery of Example 2-12 was prepared in a similar manner as the battery of Example 1, but the type of anchoring end-capper was adjusted, thereby adjusting the structure of the polymer, see Table 1 for the specific adjustment parameters.

[0341] Table 1

[0342]

[0343]

[0344] wherein X' in the polymer structure in Examples 1-12 comprises -C 12 H 25 , the L segment comprises wherein R1, R2, R4 are

[0345] Examples 13-18

[0346] The battery of Examples 13-18 was prepared in a similar manner as the battery of Example 1, but the type of diamine, diacid and diol was adjusted, thereby adjusting the structure of R1, R2, R4 in the polymer, see Table 2 for the specific adjustment parameters, and the corresponding groups of R1, R2, R4 are shown in Table 3.

[0347] Table 2

[0348] Serial No. Diacid Dialcohol Diamine Example 13 HOOC-(EO)4-COOH HO-(EO)4-(PO)2-OH H2N-(EO)4-(PO)2 - NH2]]> Example 14 HOOC-(CH2)6-COOH HO-(EO)4-(PO)2-OH H2N-(EO)4-(PO)2-NH2 Example 15 HOOC-(EO)4-(PO)2-COOH HO-(CH2)6-OH H2N-(EO)4-(PO)2-NH2 Example 16 HOOC-(EO)4-(PO)2-COOH HO-(EO)4-OH H2N-(EO)4-(PO)2-NH2 Example 17 HOOC-(EO)4-(PO)2-COOH HO-(EO)4-(PO)2-OH H2N-(EO)4-NH2 Example 18 HOOC-(EO)4-(PO)2-COOH HO-(EO)4-(PO)2-OH H2N-(CH2)6-NH2

[0349] Table 3

[0350] Serial No. [R1] [R2] [R4] Example 13 -(EO)4- -(EO)4-(PO)2- -(EO)4-(PO)2- Example 14 -(CH2)6- -(EO)4-(PO)2- -(EO)4-(PO)2- Example 15 -(EO)4-(PO)2- -(CH2)6- -(EO)4-(PO)2- Example 16 -(EO)4-(PO)2- -(EO)4- -(EO)4-(PO)2- Example 17 -(EO)4-(PO)2- -(EO)4-(PO)2- -(EO)4- Example 18 -(EO)4-(PO)2- -(EO)4-(PO)2- -(CH2)6-

[0351] Examples 19-26

[0352] By adjusting the preparation parameters of the polymer, thereby adjusting the number of repeating units of the structural units shown in Formula II and III, compared to Example 1, the specific preparation method is as follows:

[0353] Example 19

[0354] Compared to Example 1, the molar ratio of diacid, diol and diamine was adjusted to 8.5:8:1.

[0355] Example 20

[0356] Compared to Example 1, the molar ratio of diacid, diol and diamine was adjusted to 8.5:1:8.

[0357] Example 21

[0358] Compared with Example 1, the process of preparing the intermediate polymer is adjusted as follows:

[0359] The dibasic acid, the dibasic alcohol and the dibasic amine are weighed in a molar ratio of 4:1:3.2 respectively and added into a three-necked flask. The above monomers are melted by water bath warming to 60°C. A large amount of nitrogen is introduced into the reaction system and the system is warmed to 140°C, and then warmed to 195°C at a rate of 30°C / h. Then 1% of the total mass of the above monomers of glycerol and 0.25% of the total mass of the above monomers of the catalyst n-butyl titanate are added, and stirred for 20 min. Then the pressure of the reaction system is gradually reduced to 60 Pa by using a vacuum pump and a pressure regulating valve. After reaching the maximum vacuum degree, the system is warmed to 200°C. After 1.5 h of reaction, the system is cooled, and the material is discharged after the pressure inside and outside the reaction device is leveled, to obtain an intermediate polymer with hydroxyl groups at both ends.

[0360] Example 22

[0361] Compared with Example 1, the process of preparing the intermediate polymer is adjusted as follows:

[0362] The dibasic acid, the dibasic alcohol and the dibasic amine are weighed in a molar ratio of 4:1:3.2 respectively and added into a three-necked flask. The above monomers are melted by water bath warming to 60°C. A large amount of nitrogen is introduced into the reaction system and the system is warmed to 140°C, and then warmed to 195°C at a rate of 30°C / h. Then 1% of the total mass of the above monomers of glycerol and 0.25% of the total mass of the above monomers of the catalyst n-butyl titanate are added, and stirred for 20 min. Then the pressure of the reaction system is gradually reduced to 60 Pa by using a vacuum pump and a pressure regulating valve. After reaching the maximum vacuum degree, the system is warmed to 200°C. After 1.5 h of reaction, the system is cooled, and the material is discharged after the pressure inside and outside the reaction device is leveled, to obtain an intermediate polymer with hydroxyl groups at both ends.

[0363] Example 23

[0364] Compared with Example 1, the process of preparing the intermediate polymer is adjusted as follows:

[0365] The binary acid, the binary alcohol and the binary amine are weighed in a molar ratio of 2: 1.2: 1 respectively and added into a three-necked flask. The above monomers are melted by water bath warming to 60°C. A large amount of nitrogen is introduced into the reaction system and the system is warmed to 70°C. Then the system is warmed to 110°C at a rate of 10°C / h. Subsequently, 1% of the total mass of the above monomers of glycerol and 0.25% of the total mass of the above monomers of the catalyst n-butyl titanate are added, and stirred for 20 min. Then the pressure of the reaction system is gradually reduced to 60 Pa using a vacuum pump and a pressure regulating valve. After reaching the maximum vacuum degree, the system is warmed to 140°C. After 1 h of reaction, the system is cooled. After the pressure inside and outside the reaction device is balanced, the product is discharged. The obtained intermediate polymer has hydroxyl groups at both ends.

[0366] Example 24

[0367] Compared with Example 1, the preparation method of the intermediate polymer is adjusted as follows:

[0368] The binary acid, the binary alcohol and the binary amine are weighed in a molar ratio of 2: 1.2: 1 respectively and added into a three-necked flask. The above monomers are melted by water bath warming to 60°C. A large amount of nitrogen is introduced into the reaction system and the system is warmed to 70°C. Then the system is warmed to 110°C at a rate of 10°C / h. Subsequently, 1% of the total mass of the above monomers of glycerol and 0.25% of the total mass of the above monomers of the catalyst n-butyl titanate are added, and stirred for 20 min. Then the pressure of the reaction system is gradually reduced to 60 Pa using a vacuum pump and a pressure regulating valve. After reaching the maximum vacuum degree, the system is warmed to 140°C. After 1 h of reaction, the system is cooled. After the pressure inside and outside the reaction device is balanced, the product is discharged. The obtained intermediate polymer has hydroxyl groups at both ends.

[0369] Example 25

[0370] Compared with Example 1, the preparation method of the intermediate polymer is adjusted as follows:

[0371] The binary acid, the binary alcohol and the binary amine are weighed in a molar ratio of 2: 1.2: 1 respectively and added into a three-necked flask. The above monomers are melted by water bath warming to 60°C. A large amount of nitrogen is introduced into the reaction system and the system is warmed to 70°C. Then the system is warmed to 110°C at a rate of 10°C / h. Subsequently, 1% of the total mass of the above monomers of glycerol and 0.25% of the total mass of the above monomers of the catalyst n-butyl titanate are added, and stirred for 20 min. Then the pressure of the reaction system is gradually reduced to 60 Pa using a vacuum pump and a pressure regulating valve. After reaching the maximum vacuum degree, the system is warmed to 140°C. After 1 h of reaction, the system is cooled. After the pressure inside and outside the reaction device is balanced, the product is discharged. The obtained intermediate polymer has hydroxyl groups at both ends.

[0372] Example 26

[0373] Compared with Example 1, the preparation method of the intermediate polymer is adjusted, which is as follows:

[0374] The diacid, diol and diamine are weighed in a molar ratio of 2:1.2:1, respectively, and added to a three-necked flask. The above monomers are melted by water bath warming to 60℃. A large amount of nitrogen is introduced into the reaction system, and the system is warmed to 70℃. Then the system is warmed to 110℃ at a rate of 10℃ / h. Then 1% of the total mass of the above monomers of glycerol and 0.25% of the total mass of the above monomers of n-butyl titanate catalyst are added, and stirred for 20 min. Then the pressure of the reaction system is gradually reduced to 60 Pa by using a vacuum pump and a pressure regulating valve. After reaching the maximum vacuum degree, the system is warmed to 250℃. After 12 h of reaction, the system is cooled, and the material is discharged after the pressure inside and outside the reaction device is balanced. The intermediate polymer with hydroxyl groups at both ends is obtained.

[0375] Examples 27-30

[0376] Compared with Example 1, the mass fraction of the polymer dispersant is adjusted, which can be seen from the example table.

[0377] Examples 31-34

[0378] Compared with Example 1, the graphitization degree of lithium iron phosphate is adjusted, which can be seen from the example table.

[0379] Example 35

[0380] Compared with Example 1, the positive active material is adjusted to carbon-coated LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM@C).

[0381] Example 36

[0382] Compared with Example 1, the type of diamine is adjusted, and the structural formula of the diamine is as follows,

[0383]

[0384] Comparative Examples 1-4

[0385] Compared with Example 1, the dispersant is replaced with polyvinylpyrrolidone (PVP) dispersant, and the graphitization degree of lithium iron phosphate is adjusted.

[0386] Comparative Example 5

[0387] Compared with Example 1, the dispersant is replaced with polymer dispersant D-1, and the structural formula is C 12 H 25 -O-(EO) 80 -(PO) 40-(CH2)4-COOH, which is prepared as follows:

[0388] 1 mol of C 12 H 25 -OH as initiator, 0.5% of KOH by mass of the initiator as catalyst, the system is vacuumed and filled with nitrogen, then the reaction device is heated to 130°C and vacuumed, then 85 mol of propylene oxide gas is introduced, the pressure in the reaction device is maintained below 0.3 MPa, and the reaction is carried out at this pressure and temperature for 1 h, and the first product is obtained after cooling; then 0.5% of KOH by mass of the initiator is added, the system is vacuumed and filled with nitrogen, then the reaction device is heated to 130°C and vacuumed, then 45 mol of propylene oxide gas is introduced, and the reaction is carried out for 1 h, and the product is obtained after cooling, which is further neutralized by acid washing, extracted with dichloromethane three times, dried and filtered, and rotary evaporated to obtain an intermediate product.

[0389] 1 mol of the intermediate product and 1.5 mol of the anchoring capping agent Cl-C4H8-COOH are dissolved in 1000 ml of dichloromethane, and a halogenation reaction is carried out at room temperature, after 6 h of reaction, 500 ml of deionized water is added to quench the reaction. The reaction mixture is extracted three times with dichloromethane, the oil phase product is collected, then dried with magnesium sulfate, the product is separated by rotary evaporation, and finally separated by column chromatography to obtain the polymeric dispersant D-1.

[0390] Comparative Example 6

[0391] Compared with Example 1, the dispersant is replaced with polymeric dispersant D-2, and the preparation process is the same as that of Example 1, except that the anchoring capping agent is adjusted to Cl-C4H8-CH3.

[0392] II. Performance Test

[0393] 1. Characterization of the polymer

[0394] 1) Weight average molecular weight

[0395] A Waters 2695 Isocratic HPLC gel chromatograph (differential refractive detector 2141) is used. A polystyrene solution sample with a mass fraction of 3.0% is used as a reference, and a matching chromatographic column (oil: Styragel HT5 DMF7.8*300mm+Styragel HT4) is selected. A 3.0% polymer solution is prepared using purified N-methyl pyrrolidone (NMP) solvent, and the prepared solution is left to stand for one day for standby. During testing, tetrahydrofuran is first sucked into a syringe for flushing, and the operation is repeated several times. Then 5 ml of the experimental solution is sucked, and the air in the syringe is excluded, and the needle tip is wiped dry. Finally, the sample solution is slowly injected into the sample port. After the reading is stable, the data is obtained.

[0396] 2) Glass transition temperature

[0397] The glass transition temperature was tested using a differential scanning calorimeter (Q1000 type of TA Instruments). A 6-9 g polymer sample was heated from room temperature to 200 °C at a heating rate of 10 °C / min. The glass transition temperature of the polymer was obtained from the differential scanning calorimetry curve obtained by analysis, in units of °C.

[0398] 3) Melting point

[0399] The melting point was tested using a precision micro melting point tester (X-5 type). The test was performed under a standard atmosphere, and 0.01 mg of a uniformly ground sample was placed on a glass slide, covered with another glass slide, and gently compacted in the center of the hot stage. After covering the heat insulation plate, the microscope focus was adjusted until the sample could be clearly observed. Then, the temperature knob was adjusted, and the temperature was rapidly increased until the polymer showed slight melting. The temperature was then slowly adjusted until the sample was completely melted. The full melting temperature was recorded as the melting point of the polymer, in units of °C.

[0400] 4) Hydrophilic-lipophilic balance (HLB)

[0401] The HLB was determined using an emulsification method. The principle is that when a polymer emulsifies an oily medium, the emulsion stability is best when the HLB value of the polymer is the same as the required HLB value of the oil phase medium. By mixing standard samples with known HLB values in proportion, the desired HLB value can be obtained. The oil phase was prepared by emulsifying the polymer, and the sample was allowed to stand for 24 h. The HLB value required by the oil phase in the sample with the best stability was the HLB value of the polymer.

[0402] 2) Positive electrode active material

[0403] 1) Graphitization degree

[0404] The graphitization degree was characterized using a high-resolution Raman spectrometer (LabRAM HR Evolution, HORIBA Jobin Yvon, France). After subtracting the background, the following Gaussian function was used for fitting. Raman spectrum test conditions: wavelength 532 nm, scanning range 200-4000 cm -1 , cumulative twice, 10 points per sample, average value fitting:

[0405]

[0406] In the above formula, G is the graphitization degree, Ai, Vi, and wi are the peak intensity, peak position, and peak width, respectively.

[0407] 3) Positive electrode slurry

[0408] 1) Solid content

[0409] Take the copper foil into the weightlessness rate measuring instrument, weigh, record as M0, and clear zero;

[0410] Take the positive electrode slurry, a small amount of which is coated on the copper foil, and then put into the water content measuring instrument, weigh, record as M1;

[0411] Close the device and start drying;

[0412] After completion, record the weighing data as M2, and calculate the solid content, which is (M2-M0) / (M1-M0).

[0413] 2) Slurry stability test

[0414] After stirring the slurry for 30 min, a certain amount of slurry is poured into the sample bottle of the stability instrument. After putting the sample bottle, the test tower cover is closed, the test tower cover is opened, and the scanning curve of the test interface starts to appear. The sample stability test is started, and the test is continued for more than 72 h to complete the test.

[0415] 4, Positive electrode tab

[0416] 1) Brittleness test

[0417] Take the defect-free positive electrode tab, cut it into a sample with a length of 20 cm and a width of 2.5 cm along the longitudinal direction, and the number of samples is ≥8. First, pre-fold the sample, place the film on the test platform, and roll it once with a 2kg cylindrical roller. If it is transparent, the transparent frequency of brittleness is 1. If it is not transparent, repeat the reverse folding and rolling. Observe whether it is transparent or broken by observing the fold mark, record the actual folding frequency, and take the average as the test result.

[0418] 2) Film resistance

[0419] Cut the dried positive electrode slurry (film layer) at the left, middle, and right of the positive electrode tab. Turn on the power of the Yuntianke tab resistance meter, place it in the appropriate position of the tab resistance meter "probe", click the "start" button, and read when the reading is stable. Test two positions for each small round piece, and finally calculate the average of six measurements, which is the resistance of the tab film layer.

[0420] 5, Secondary battery

[0421] 1) First coulombic efficiency

[0422] At 25°C, the battery of the above examples and comparative examples is charged at a rate of 0.1C to a voltage of 4.3V, and the charging capacity at this time is recorded as the first cycle charging capacity of the secondary battery. Then, after standing for 5 min, it is discharged at a rate of 0.1C to a voltage of 2.0V, and stands for 5 min. This is one charge-discharge cycle. The discharge capacity of this cycle is recorded as the first cycle discharge capacity of the secondary battery, which is the initial capacity of the secondary battery.

[0423] The first-cycle coulombic efficiency (%) of a secondary battery = first-cycle discharge capacity / first-cycle charge capacity × 100%.

[0424] 2) Capacity retention rate during 45℃ cycling

[0425] At 45°C, the batteries in the examples and comparative examples were charged to 3.65V at a constant current of 1 / 3C, then charged to a current of 0.05C at a constant voltage of 3.65V, left to rest for 10 minutes, and then discharged to 2.5V at 1 / 3C. The resulting capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle was recorded. The battery capacity retention rate after each cycle is then:

[0426] Pn = C n / C0×100%

[0427] During this test, the first cycle corresponds to n=1, the second cycle to n=2, ..., the 100th cycle 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, i.e., the value of P300.

[0428] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0429] Table 4. Parameters and Performance Test Results of the Examples

[0430]

[0431]

[0432]

[0433] Table 5. Parameters and Performance Test Results of the Examples

[0434]

[0435]

[0436]

[0437] Based on the above results, the polymers in Examples 1-36 contain X'-LX, wherein X' contains -C 12 H 25 X contains any one of the following groups: carboxyl group, ester group, sulfonic acid group, sulfonate group, phosphate group, and phosphate ester group.

[0438] L includes the structural unit shown in Formula II. The structural unit shown in Formula III

[0439]

[0440] wherein R1 and R3 are the same, R1 comprises

[0441]

[0442] R2 comprises R3 comprises

[0443] R4 comprises R5 comprises hydrogen or methyl.

[0444] As can be seen from the comparison of Examples 1-26, 31-34, 36 and Comparative Examples 1-4, compared with traditional PVP dispersants, the polymer dispersants of the present application have wide versatility, can improve the dispersibility of slurries of lithium iron phosphate with different graphitization degrees as positive active material, can effectively improve the solid content of the slurry, slow down the gel phenomenon of the slurry, reduce the film resistance of the pole piece, improve the flexibility of the pole piece, and improve the first coulomb efficiency and high-temperature cycle performance of the battery. The polymer dispersant is universal for positive electrode slurries containing lithium iron phosphate with different graphitization degrees produced by different processes, which helps to reduce the preparation cost and improve the production efficiency.

[0445] As can be seen from the comparison of Example 1 and Comparative Example 5, the ester group and amide group in the structural units represented by Formula II and Formula III in the polymer dispersant of the present application can effectively improve the solid content of the slurry, slow down the gel phenomenon of the slurry, improve the flexibility of the pole piece, reduce the film resistance of the pole piece, and improve the first coulomb efficiency and high-temperature cycle performance of the battery. As can be seen from the comparison of Examples 1-12 and Comparative Example 6, the X group comprising a carboxyl group, an ester group, a sulfonic acid group, a sulfonate group, a phosphoric acid group or a phosphate group in the polymer dispersant of the present application can effectively improve the solid content of the slurry, slow down the gel phenomenon of the slurry, improve the flexibility of the pole piece, reduce the film resistance of the pole piece, and improve the first coulomb efficiency and high-temperature cycle performance of the battery.

[0446] From the comparison of Example 1, 9-10 and Example 5, it can be seen that compared with the X group containing -C4H8-COO-C3H7, the dispersion of the slurry can be further improved, the solid content of the slurry can be increased, and the use performance of the slurry can be improved when the polymer contains X group of -C4H8-COOH, -C4H8-COO-C3H6-OH or -C4H8-COO-NH-C3H6-OH. From the comparison of Example 1 and Example 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 dispersion effect of the slurry can be further improved, the solid content of the slurry can be increased, the gel phenomenon of the slurry can be slowed down, the flexibility of the pole piece can be improved, and the use performance of the slurry and the pole piece can be improved when the polymer dispersant contains X group of -C4H8-COOH. From the comparison of Example 2 and Example 6, it can be seen that compared with the X group containing -C4H8-SO3-C3H7, the dispersion effect of the slurry can be further improved, the solid content of the slurry can be increased, the gel phenomenon of the slurry can be slowed down, the flexibility of the pole piece can be improved, and the high-temperature cycle performance of the battery can be improved when the polymer dispersant contains X group of -C4H8-SO3H. From the comparison of Example 4, 11-12 and Example 8, it can be seen that compared with the polymer dispersant containing

[0447] The polymer dispersant contains

[0448] The dispersion of the slurry can be further improved, the solid content of the slurry can be increased, and the use performance of the slurry can be improved. From the comparison of Example 4 and Example 8, 11-12, it can be seen that compared with the polymer dispersant containing

[0449]

[0450] The polymer dispersant contains The solid content of the slurry can be further increased, the gel phenomenon of the slurry can be slowed down, the flexibility of the pole piece can be improved, and the first coulomb efficiency of the battery can be improved. From the comparison of Example 3 and Example 7, it can be seen that compared with the polymer containing The polymer dispersant contains The gel phenomenon of the slurry can be further slowed down, the flexibility of the pole piece can be improved, and the first coulomb efficiency and high-temperature cycle performance of the battery can be improved. From the comparison of Example 8 and Example 7, it can be seen that compared with the polymer containing The polymer dispersant contains The first coulomb efficiency and high-temperature cycle performance of the battery can be improved, and the electrochemical performance of the battery can be improved. From the comparison of Example 4 and Example 3, it can be seen that compared with the polymer containing The polymer dispersant contains The solid content of the slurry can be further increased, the flexibility of the electrode sheet can be improved, and the first coulomb efficiency of the battery can be improved.

[0451] As can be seen from the comparison of Example 1 and Example 37, compared with the structure unit of Formula III containing methyl in R5, containing hydrogen in R5 can further improve the dispersibility of the slurry, increase the solid content of the slurry, slow down the gelation of the slurry, improve the flexibility of the electrode sheet, and improve the use performance of the electrode sheet.

[0452] As can be seen from the comparison of Example 1, 13 and Example 14, the comparison of Example 1, 16 and Example 15, and the comparison of Example 1, 17 and Example 18, R1, R2, R3, and R4 contain The solid content of the slurry can be increased, the flexibility of the electrode sheet can be improved, and the high-temperature storage performance of the battery can be improved. As can be seen from the comparison of Example 1 and Examples 13-18, R1, R2, R3, and R4 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 sheet can be improved, and the high-temperature storage performance of the battery can be improved.

[0453] As can be seen from Examples 1, 19-26, the ratio of the number of repeating units of the structure unit of Formula II to the number of repeating units of the structure unit of Formula III is 1:7-7:1, the slurry has a high solid content, the electrode sheet has excellent flexibility, and the battery has excellent first coulomb efficiency and high-temperature storage performance. As can be seen from the comparison of Examples 1, 21-26 and Examples 19-20, the ratio of the number of repeating units of the structure unit of Formula II to the number of repeating units of the structure unit of Formula III is 1:3-3:1, which can improve the flexibility of the electrode sheet, the first coulomb efficiency of the battery, and the high-temperature storage performance of the battery.

[0454] As can be seen from the comparison of Examples 1, 24-25 and Examples 23, 26, the number of repeating units of the structure unit of Formula II is 8-50, and the number of repeating units of the structure unit of Formula III is 8-50, which can further increase the solid content of the slurry, slow down the gelation of the slurry, improve the flexibility of the electrode sheet, and improve the use performance of the slurry and the electrode sheet.

[0455] 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.

[0456] As can be seen from the comparison between Example 1 and Example 35, compared with the positive electrode active material being lithium nickel cobalt manganese oxide with a carbon coating layer on the surface, the polymer dispersant of the application is more suitable for lithium iron phosphate with a carbon coating layer on the surface, can further increase the solid content of the slurry of lithium iron phosphate with a carbon coating layer on the surface, slow down the gel phenomenon of the slurry, improve the flexibility of the pole piece, reduce the membrane resistance, improve the first coulomb efficiency and high-temperature storage performance of the battery.

[0457] As can be seen from Examples 1, 32-34, the polymer dispersant of the application has universality and is suitable for the slurry system of lithium iron phosphate with a graphitization degree of 10%-30% as the positive electrode active material. As can be seen from the comparison between Examples 1, 32-34 and Example 31, using lithium iron phosphate with a graphitization degree of 10%-30% can further reduce the membrane resistance of the pole piece and improve the first coulomb efficiency of the battery.

[0458] As can be seen from Examples 1, 27-30, the mass fraction of the polymer dispersant is 0.01%-3% based on the total mass of the solid substances in the positive electrode slurry, the slurry has high solid content, the pole piece has excellent flexibility, and the battery has excellent first coulomb efficiency and high-temperature storage performance. As can be seen from the comparison between Examples 1, 28-29 and Examples 27, 30, the mass fraction of the polymer dispersant is 0.03%-2% based on the total mass of the solid substances in the positive electrode slurry, which can further improve the flexibility of the pole piece and improve the use performance of the pole piece.

[0459] It should be noted that the application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solution of the application are all included in the technical scope of the application. In addition, within the scope of the main idea of the application, various modifications of the embodiments that can be thought of by those skilled in the art, and other ways constructed by combining part of the constituent elements in the embodiments are also included in the scope of the application.

Claims

1. A polymer, characterized in that, The polymer comprises at least one of structures represented by Formula I-1, Formula I-2, Formula I-3, Formula I-4, Formula I-1 Formula I-2 Formula I-3 Formula I-4 wherein a1, a2 are each independently an integer between 2 and 12, R6, R7 each independently comprise hydrogen, C 1-12 alkyl, C 1-12 alkyl alcohol, at least one of R8, R9, R 10 each independently comprise hydrogen, C 1-12 alkyl, C 1-12 alkyl alcohol, , at least one of R 11 , R 12 each independently comprise C 1-12 alkylene, R 13 comprise C 1-12 alkyl or C 6-30 aromatic; X' comprises C 3-30 alkyl; L comprises structural units of formula II and formula III, Formula II Formula III wherein R1comprises , R2comprises , R3 , R4comprises , R5comprises hydrogen or C 1-3 alkyl, wherein EO represents -CH2-CH2-O-, and PO represents -CH(CH3)-CH2-O-, m1, m2, m3, m4 are each independently an integer between 1 and 10, and n1, n2, n3, n4 are each independently an integer between 0 and 10.

2. The polymer of claim 1, wherein The polymer comprises at least one of structures represented by Formula I-1, Formula I-2, Formula I-4, Formula I-1 Formula I-2 Formula I-4 wherein a1, a2 are each independently an integer between 2 and 12, R6, R7 each independently comprise hydrogen, C 1-12 alkyl alcohol, R 10 comprise hydrogen, C 1-12 alkyl alcohol, , at least one, wherein R 11 , R 12 each independently comprise C 1-12 alkylene, R 13 comprise C 1-12 alkyl or C 6-30 aromatic.

3. The polymer of claim 1, wherein R5 in the structure unit represented by Formula III comprises hydrogen.

4. The polymer according to any one of claims 1 to 3, characterized in that, said R1comprises said R2comprises said R3comprises said R4comprises wherein at least one of n1, n2, n3, n4 has the value 0 and each of m1, m2, m3, m4 independently is an integer between 2 and 10.

5. The polymer according to any one of claims 1 to 3, characterized in that, said R1 comprises , said R2 comprises , said R3 comprises , said R4 comprises , wherein n1, n2, n3, n4, m1, m2, m3, m4 are each independently an integer between 1 and 10.

6. The polymer according to any one of claims 1 to 3, characterized in that, The ratio of the number of repeating units of the structure unit represented by Formula II to the number of repeating units of the structure unit represented by Formula III in L is 1:7-7:

1.

7. The polymer according to any one of claims 1 to 3, characterized in that, The ratio of the number of repeating units of the structure unit represented by Formula II to the number of repeating units of the structure unit represented by Formula III in L is 1:3-3:

1.

8. The polymer according to any one of claims 1 to 3, characterized in that, The number of repeating units of the structure unit represented by Formula II in L is 8-50, and the number of repeating units of the structure unit represented by Formula III in L is 8-50.

9. The polymer according to any one of claims 1 to 3, characterized in that, The weight average molecular weight of the polymer is 3000 g / mol-55000 g / mol.

10. The polymer according to any one of claims 1 to 3, characterized in that, The glass transition temperature of the polymer is 30℃-150℃.

11. The polymer according to any one of claims 1 to 3, characterized in that, The melting point of the polymer at 1 standard atmosphere is 60℃-210℃.

12. The polymer according to any one of claims 1 to 3, characterized in that, The hydrophilic-lipophilic balance value of the polymer is 6-16.

13. A method of preparing a polymer, characterized by, The preparation method comprises the following steps: 1) condensation reaction: polymerizing at least one dibasic acid, at least one dibasic alcohol and at least one dibasic amine to prepare an intermediate polymer, the intermediate polymer comprising a structure represented by Formula IV, Formula IV wherein Y' and Y each independently comprise at least one of carboxyl, hydroxyl, and amino; 2) end group reaction: reacting the end groups of the intermediate polymer to obtain a polymer comprising at least one of structures represented by Formula I-1, Formula I-2, Formula I-3, Formula I-4, Formula I-1 Formula I-2 Formula I-3 Formula I-4 wherein a1, a2 are each independently an integer between 2 and 12, R6, R7 each independently comprise hydrogen, C 1-12 alkyl, C 1-12 alkyl alcohol, at least one of R8, R9, R 10 each independently comprise hydrogen, C 1-12 alkyl, C 1-12 alkyl alcohol, , at least one of R8, R9, R 11 , R 12 each independently comprise C 1-12 alkylene, R 13 comprise C 1-12 alkyl or C 6-30 aromatic; X' comprises C 3-30 alkyl; L comprises structure units represented by Formula II and Formula III, Formula II Formula III wherein R1comprises R2comprises R3comprises R4comprises R5comprises hydrogen or C 1-3 alkyl, wherein EO represents -CH2-CH2-O-, and PO represents -CH(CH3)-CH2-O-, m1, m2, m3, m4 are each independently an integer between 1 and 10, and n1, n2, n3, n4 are each independently an integer between 0 and 10.

14. The method of claim 13, wherein, The preparation method specifically comprises: stirring the catalyst, at least one dibasic acid, at least one dibasic alcohol and at least one dibasic amine at 20℃-250℃ for 1h-20h to obtain the intermediate polymer, wherein the two ends of the intermediate polymer have the same end groups; reacting the end groups of the two ends of the intermediate polymer respectively to obtain the polymer.

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

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

17. A positive electrode slurry, characterized by, A positive electrode active material, a conductive agent, a binder and a dispersant, the dispersant comprising the polymer of any one of claims 1 to 12.

18. The positive electrode slurry of claim 17, wherein, The positive electrode active material includes lithium iron phosphate having a carbon-coated layer on a surface thereof.

19. The positive electrode slurry of claim 18, wherein, The graphitization degree of the lithium iron phosphate having a carbon-coated layer on a surface thereof is 10% to 30%.

20. The positive electrode slurry of claim 17, wherein, The mass fraction of the dispersant is 0.01% to 3% based on the total mass of solid substances in the positive electrode slurry.

21. The positive electrode slurry of claim 17, wherein The mass fraction of the dispersant is 0.03% to 2% based on the total mass of solid substances in the positive electrode slurry.

22. A positive electrode sheet characterized by comprising: The positive electrode active material includes lithium iron phosphate having a carbon-coated layer on a surface thereof.

23. A secondary battery characterized by comprising: The positive electrode active material includes lithium iron phosphate having a carbon-coated layer on a surface thereof.

24. An electrical device, comprising: The positive electrode active material includes lithium iron phosphate having a carbon-coated layer on a surface thereof.

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