Positive electrode slurry, positive electrode tab, and secondary battery including the same

Abstract

Provided is a positive electrode slurry including a polyether phosphate ester, the polyether phosphate ester including at least structural units: and structural unit (IV) phosphate ester groups, A is hydrogen, halogen, or a halogenated alkyl group; B is a hydroxyl group, R, OR, or ROR', where R, R' are each independently a straight chain or branched alkyl group containing 1-8 carbons; and E is a phenyl group, an alkyl-substituted phenyl group, an ether-substituted phenyl group, or a halogenated phenyl group. The addition of the polyether phosphate ester described herein can increase the coating weight of the positive electrode plate, thereby increasing the energy density of the battery.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and more particularly to a positive electrode sheet comprising polyether phosphate. Furthermore, this application also relates to a secondary battery including the aforementioned positive electrode sheet, as well as a battery pack, battery module, and power-consuming device including the aforementioned secondary battery. Background Technology

[0002] In recent years, with the increasingly widespread application of lithium-ion batteries, they have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant advancements in lithium-ion battery technology, higher demands have been placed on improving their energy density and reducing their cost.

[0003] Currently, one effective way to improve the energy density of lithium-ion batteries is to increase the coating weight of the positive electrode. However, increasing the coating weight of the positive electrode can lead to serious risks during electrode manufacturing. Since the characteristics of the positive electrode slurry and the electrode directly affect the cell manufacturing process, increasing the coating weight of the positive electrode can also make it difficult to manufacture the cell.

[0004] Therefore, the positive electrode sheet still needs improvement. Summary of the Invention

[0005] This application is made in view of the above-mentioned issues, and its object is to provide a positive electrode slurry comprising a specific polyether phosphate and a positive electrode sheet prepared using said positive electrode slurry or a positive electrode sheet comprising said positive electrode slurry.

[0006] Therefore, a first aspect of this application provides a positive electrode slurry comprising a positive electrode active material and a polyether phosphate, wherein the polyether phosphate comprises at least the following structural units:

[0007]

[0008] And the structural unit (IV) phosphate ester group,

[0009] in,

[0010] A is hydrogen, halogen, or haloalkyl, wherein the halogen may be fluorine, chlorine, or bromine, and A may be hydrogen or fluoromethyl;

[0011] B is hydroxyl, R, OR, or ROR', wherein R and R' are independently straight-chain or branched alkyl groups containing 1 to 8 carbons; optionally, B is methyl, ethyl, or ethoxymethyl.

[0012] E is a phenyl, an alkyl-substituted phenyl, an etherified phenyl, or a halophenyl, wherein E may be a phenyl or a fluorophenyl.

[0013] In any embodiment of this application, the energy density of the resulting lithium-ion battery is significantly improved after adding the polyether phosphate to the positive electrode slurry. Furthermore, the improvement in the positive electrode sheet reduces the amount of battery cell material used, thereby lowering the total material cost of the battery cell.

[0014] In some embodiments, the number-average molecular weight of the polyether phosphate is in the range of 10,000 to 80,000, optionally in the range of 10,000 to 60,000, and more preferably in the range of 30,000 to 50,000.

[0015] If the molecular weight is too small, the stability of the positive electrode slurry is poor, and physical gelation is prone to occur. This also degrades the resistance of the positive electrode film, adversely affecting battery performance. If the molecular weight is too large, it is not conducive to the dispersion of polyether phosphate in the positive electrode slurry. Therefore, the number-average molecular weight of the polyether phosphate must be controlled within the above-mentioned range.

[0016] Based on the total molar amount of structural units (I) to (IV), the molar percentage of structural unit (I) is 0-75 mol%, the molar percentage of structural unit (II) is 0-65 mol%, the molar percentage of structural unit (III) is 5-65 mol%, and the molar percentage of structural unit (IV) is 4-15 mol%, wherein the molar percentages of structural unit (I) and structural unit (II) are not both zero.

[0017] The molar ratio of the above structural units (I)-(IV) ensures that the obtained polyether phosphate forms sufficient hydrogen bonds and an appropriate amount of covalent bonds with the positive electrode active material, current collector, etc., thereby ensuring the stability of the positive electrode preparation process and ensuring the flexibility of the positive electrode and the dispersibility of various positive electrode materials, thus improving the energy density of the battery.

[0018] In some embodiments, the weight ratio of the polyether phosphate to the positive electrode active material is 0.0005 to 0.030, with a preferred range of 0.001 to 0.02, a more preferred range of 0.001 to 0.01, and a most preferred range of 0.001 to 0.007.

[0019] When this ratio is too small, the positive electrode sheet will crack under high coating weight; when this ratio is too large, it will have an adverse effect on battery performance.

[0020] In some embodiments, the positive electrode active material is selected from at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel oxide, or mixtures thereof.

[0021] When the positive electrode active material is at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel oxide, or a mixture thereof, adding the polyether phosphate ester can better achieve the effects of improving electrode flexibility and increasing the maximum coating weight of the electrode.

[0022] In some embodiments, the gelation factor G of the positive electrode slurry ranges from 0 to 1, and optionally from 0 to 0.3.

[0023] Where G = (m1-m2) / m1, when G = 0 to 0.3, the slurry is judged not to gel, and when G > 0.3, it is judged to gel.

[0024] m1 is the mass of the positive electrode slurry obtained after filtering 2 kg of initial positive electrode slurry through a 100-mesh filter for 10 minutes.

[0025] m2 represents the mass of the positive electrode slurry obtained after filtering 2 kg of slurry that has been left to stand for 48 hours through a 100-mesh filter for 10 minutes.

[0026] The positive electrode slurry used in measuring m1 and the positive electrode slurry used in measuring m2 are from the same batch.

[0027] The closer the mass of the positive electrode slurry obtained after filtration following 48 hours of settling is to the initial mass, and the smaller the G value, the less prone the slurry is to gelation, and the better the slurry state. The positive electrode slurry described in this application has excellent gelation properties.

[0028] A second aspect of this application provides a positive electrode sheet, comprising:

[0029] Positive current collector; and

[0030] A positive electrode film layer is located on at least one surface of the positive current collector, the positive electrode film layer comprising the positive electrode slurry described in the first aspect of this application. As described above, by adding the polyether phosphate, this application allows for an increase in the maximum coating weight on the positive electrode sheet. This is also reflected in the increase in the maximum weight of the positive electrode film layer. In some embodiments, the mass of the positive electrode film layer on a unit area electrode sheet ranges from 13-43 mg / cm². 2 The selectable range is 22-31 mg / cm³. 2 The selectable range is 22-29 mg / cm³. 2 The mass referred to here is the mass of the positive electrode film layer on a single surface of the electrode. If the positive electrode has a positive electrode film layer on both surfaces, then the mass of the positive electrode film layer per unit area of ​​the electrode is twice the aforementioned range, i.e., the range is 26–86 mg / cm³. 2 The selectable range is 44–62 mg / cm³. 2The selectable range is 44–58 mg / cm³. 2 The mass refers to the mass of the positive electrode film layer on both surfaces of the electrode.

[0031] When the weight of the positive electrode film layer on a unit area positive electrode sheet is too small, the electrode uniformity is poor; when the weight of the positive electrode film layer on a unit area positive electrode sheet is too large, the electrode coating process suffers severe cracking, making production impossible. This application limits the weight of the positive electrode film layer on a unit area positive electrode sheet to the above range, ensuring that the best results can be achieved within this range.

[0032] The positive electrode sheet described in this application exhibits excellent flexibility, and the coating weight is significantly improved. Applying this positive electrode sheet to secondary batteries, for example, by directly adding it to the positive electrode slurry during preparation, can significantly increase the battery's energy density.

[0033] In some embodiments, the positive electrode film layer includes two sublayers parallel to and stacked on top of each other, wherein the weight content of polyether phosphate in the sublayer closest to the positive electrode current collector is in the range of 0 to 60, and optionally in the range of 0.1 to 30.

[0034] When the coating weight is 23 mg / cm³ 2 In the above cases, compared with a single thick coating, two coatings can reduce the material cost of flexible additives, while the polyether phosphate ester described in this application can perform better without affecting electrical properties.

[0035] In some embodiments, when measuring the flexibility of the positive electrode sheet using the winding needle described in this application,

[0036] When the diameter of the coiled needle R ≤ 3.0 mm, the positive electrode sheet does not develop cracks, or,

[0037] When the diameter of the coiling needle R = 3.0 mm, the positive electrode sheet develops cracks, but when the diameter of the coiling needle R = 4.0 mm, no cracks appear.

[0038] The addition of the polyether phosphate ester described in this application can reduce cold pressing pressure, thereby reducing cracks, reducing the risk of strip breakage, and thus improving the flexibility of the electrode sheet.

[0039] In some embodiments, the wettability improvement rate I of the positive electrode sheet ranges from 2% to 20%, with an optional range of 6% to 15%.

[0040] Where I = (I2 - I1) / I1 × 100%,

[0041] I2 is the wetting rate of the positive electrode in the electrolyte.

[0042] I1 represents the wetting rate of the positive electrode sheet excluding the polyether phosphate in the electrolyte.

[0043] The positive electrode used in measuring I1 is the same as the positive electrode used in measuring I2, the only difference being that the positive electrode used in measuring I1 does not contain the polyether phosphate, while the positive electrode used in measuring I2 contains the polyether phosphate.

[0044] The electrode sheet exhibits good wettability, enabling excellent wetting and retention of the electrolyte. This ensures effective wetting of the cell electrode sheet, preventing insufficient wetting, improving cell electrolyte injection efficiency and electrode wettability during cycling, thereby effectively enhancing battery product performance. The positive electrode sheet described in this application demonstrates excellent wetting performance in the electrolyte.

[0045] A third aspect of this application provides a secondary battery, wherein the negative electrode sheet described in the first aspect of this application is included.

[0046] A fourth aspect of this application provides a battery module comprising the secondary battery described in the second aspect of this application.

[0047] The fifth aspect of this application provides a battery pack that includes the battery module described in the third aspect of this application.

[0048] A sixth aspect of this application provides an electrical device comprising at least one of the secondary battery described in the third aspect of this application, the battery module described in the fourth aspect of this application, or the battery pack described in the fifth aspect of this application. Attached Figure Description

[0049] Figure 1 This is a schematic diagram illustrating the interaction between the polyether phosphate in the positive electrode and other substances in the positive electrode of this application, wherein the polyether phosphate is the polyether phosphate described in this application.

[0050] Figure 2 This is a schematic diagram illustrating the coating cracking process of a positive electrode sheet in the prior art due to capillary tension during the coating process. The active material is the positive electrode active material, and the force is the force exerted during the coating process. The polyether phosphate ester described in this application is not used.

[0051] Figure 3 This is a schematic diagram showing that the positive electrode sheet described in this application does not crack during the coating process, wherein the active material is the positive electrode active material, the force is the force during the coating process, and the polyether phosphate ester described in this application is used.

[0052] Figure 4This diagram illustrates the increase in maximum coating weight per unit area in the positive electrode sheet after using the polyether phosphate ester of this application. In the diagram, positive electrode material represents the positive electrode active material, SP represents the conductive agent used in the positive electrode sheet, and PVDF represents the binder used in the positive electrode sheet. X represents the maximum coating thickness of the positive electrode slurry without polyether phosphate ester, and Y represents the maximum coating thickness of the positive electrode slurry containing polyether phosphate ester under the same conditions. Obviously, Y is greater than X.

[0053] Figure 5 This is a schematic diagram of the coiling needle used in the flexibility test of the positive electrode sheet in this application. Detailed Implementation

[0054] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode sheet and its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0055] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-6. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0056] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0057] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0058] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, optionally sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0059] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0060] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0061] Inventive concept

[0062] For lithium-ion batteries, increasing energy density is a growing trend, and one way to do this is by increasing the coating weight of the positive electrode. However, the inventors of this application have discovered that, as... Figure 2 As shown, in the conventional coating process of positive electrode slurry, the positive electrode sheet cracks due to capillary tension during or after solvent evaporation, and this cracking propagates further, causing large-area cracking. Furthermore, edge curling of the electrode sheet also occurs during this process. Additionally, because the positive electrode sheet is hard and brittle, it may break during cold pressing, and the inner ring may suffer severe breakage during winding. Based on this, the inventors of this application designed and synthesized a flexible polymer material, polyether phosphate. By adding this flexible material, the coating weight is increased, the coating quality is improved, and the risks associated with cold pressing and winding are eliminated, while simultaneously reducing the overall cost of materials used in battery manufacturing.

[0063] Therefore, a first aspect of this application provides a positive electrode slurry comprising a positive electrode active material and a polyether phosphate ester, wherein the polyether phosphate ester comprises at least the following structural units:

[0064]

[0065] And the structural unit (IV) phosphate ester group,

[0066] in,

[0067] A is hydrogen, halogen, or haloalkyl, wherein the halogen may be fluorine, chlorine, or bromine, and A may be hydrogen or fluoromethyl;

[0068] B is hydroxyl, R, OR, or ROR', wherein R and R' are independently straight-chain or branched alkyl groups containing 1 to 8 carbons; optionally, B is methyl, ethyl, or ethoxymethyl.

[0069] E is a phenyl, an alkyl-substituted phenyl, an etherified phenyl, or a halophenyl, wherein E may be a phenyl or a fluorophenyl.

[0070] In the polyether phosphate ester described in this application, the structural unit (IV) exists as an end group.

[0071] Optionally, in some embodiments, the polyether phosphate is polymerized from the following components:

[0072] (a) Unsubstituted or halogenated C 1-8 Alkyl-substituted ethylene oxide;

[0073] (b) Ethylene oxide substituted with hydroxyl, hydroxyalkyl, R, OR, or ROR', wherein R and R' are each independently C 1-8 Alkyl groups, wherein the alkyl group in the hydroxyalkyl group is C1. 1-8 alkyl;

[0074] (c) Ethylene oxide substituted with halophenyl, haloalkylphenyl or phenyl;

[0075] (d) Phosphating agent, which is phosphorus pentoxide;

[0076] Based on the total molar amount of components (a)-(d), the molar percentage of component (a) is 0-75 mol%; the molar percentage of component (b) is 0-65 mol%; the molar percentage of component (c) is 5-65 mol%; and the molar percentage of component (d) is 4-15 mol%.

[0077] Components (a) and (b) are not both zero.

[0078] In some embodiments, component (a) may optionally be selected from ethylene oxide, epifluoropropane, epichlorohydrin, and epibromopropane.

[0079] In some embodiments, component (b) may optionally be selected from propylene oxide, ethyl glycidyl ether, isopropyl glycidyl ether, butyl glycidyl ether, isopropyl glycidyl ether, butane oxide, 1,2-butane oxide, 1,2-pentane oxide, 1,2-heptane oxide, octane oxide, decane oxide, 3-methylbutane oxide, and glycidyl.

[0080] In some embodiments, component (c) may optionally be selected from styrene oxide and phenyl.

[0081] In this application, C 1-8 The alkyl group is a straight-chain or branched alkyl group containing 1-8 carbon atoms, and the straight-chain or branched alkyl group containing 1-8 carbon atoms may be selected from, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, isopropyl, isobutyl, tert-butyl, isopentyl, tert-pentyl, neopentyl, 2-methylpentyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 2-methylhexyl, 3-methylhexyl, 2,2-dimethylpentyl, 3,3-dimethylpentyl, 2,3-dimethylpentyl, 2,4-dimethylpentyl, 3-ethylpentyl, 2 2,3-Trimethylbutyl, 2-Methylheptyl, 3-Methylheptyl, 4-Methylheptyl, 2,2-Dimethylhexane, 3,3-Dimethylhexane, 2,3-Dimethylhexane, 2,4-Dimethylhexane, 2,5-Dimethylhexane, 3,4-Dimethylhexane, 3-Ethylhexane, 2,2,3-Trimethylpentane, 2,2,4-Trimethylpentane, 2,3,3-Trimethylpentane, 2,3,4-Trimethylpentane, 2-Methyl-3-Ethylpentane, 3-Methyl-3-Ethylpentane, 2,2,3,3-Tetramethylbutane.

[0082] In this application, C 1-8 The alkenyl group is a straight-chain or branched alkenyl group containing 1-8 carbons, which may include, but is not limited to, vinyl, propenyl, allyl, 1-methylprop-2-en-1-yl, 2-methylprop-2-en-1-yl, but-2-en-1-yl, but-3-en-1-yl, 1-methylbut-3-en-1-yl and 1-methylbut-2-en-1-yl, etc.

[0083] In this application, the alkyl substituent may be a straight-chain or branched alkyl group containing 1-8 carbons, optionally selected from methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, and tert-butyl. Optionally, the alkyl substitution is monosubstituted or disubstituted. In some embodiments, the alkyl-substituted phenyl group may be selected from, for example, 3,4-dimethylphenyl, 2-methylphenyl, 3,5-dimethylphenyl, and 4-(2-methylpropyl)phenyl.

[0084] In this application, the alkyl group in the haloalkyl group may be a straight-chain or branched alkyl group containing 1-8 carbon atoms. For example, the alkyl group in the haloalkyl group may be selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, isopropyl, isobutyl, tert-butyl, isopentyl, tert-pentyl, neopentyl, 2-methylpentyl, 3-methylpentyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 2-methylhexyl, 3-methylhexyl, 2,2-dimethylpentyl, 3,3-dimethylpentyl, 2,3-dimethylpentyl, 2,4-dimethylpentyl, 3-ethyl The alkyl halide comprises pentyl, 2,2,3-trimethylbutyl, 2-methylheptyl, 3-methylheptyl, 4-methylheptyl, 2,2-dimethylhexane, 3,3-dimethylhexane, 2,3-dimethylhexane, 2,4-dimethylhexane, 2,5-dimethylhexane, 3,4-dimethylhexane, 3-ethylhexane, 2,2,3-trimethylpentane, 2,2,4-trimethylpentane, 2,3,3-trimethylpentane, 2,3,4-trimethylpentane, 2-methyl-3-ethylpentane, 3-methyl-3-ethylpentane, and 2,2,3,3-tetramethylbutane. The halogen in the alkyl halide may be selected from fluorine, chlorine, bromine, or iodine.

[0085] In this application, the ether substituent may be a straight-chain or branched alkoxy group containing 1-8 carbons, optionally selected from methoxy, ethoxy, propoxy, or butoxy. In some embodiments, the etherified phenyl group may be selected from, for example, 4-methoxyphenyl, 3-methoxyphenyl, etc.

[0086] In this application, haloalkylphenyl refers to a phenyl group substituted with a haloalkyl group, wherein the haloalkyl group refers to an alkyl group substituted with a halogen, and the alkyl group is C1. 1-8 alkyl.

[0087] In this application, halophenyl represents a phenyl group substituted with a halogen. The halogen may be selected from fluorine, chlorine, bromine, or iodine. In some embodiments, the halophenyl group may be selected from, for example, 4-fluorophenyl, 2-fluorophenyl, 2,6-difluorophenyl, 4-(trifluoromethyl)phenyl, 4-chlorophenyl, 3-chlorophenyl, 4-bromophenyl, 3-bromophenyl, or 2-bromophenyl.

[0088] In the polyether phosphate ester described in this application, structural unit (I) (or the structural unit formed by component (a)) can improve the ability of the polymer to form hydrogen bonds with the surface of the positive electrode particles, conductive carbon, and aluminum foil; structural unit (II) (or the structural unit formed by component (b)) can extend the molecular branches, ensuring that the polyether phosphate ester forms covalent bonds with the surface of the positive electrode particles, conductive carbon, and aluminum foil, ensuring that the positive electrode particles do not migrate during the coating process; structural unit (III) (or the structural unit formed by component (c)) can improve the rigidity of the polyether phosphate ester, giving it certain strength and hardness, thereby improving the oxidation resistance and electrolyte resistance of the polyether phosphate ester. At the same time, the benzene ring interacts with the surface of the positive electrode particles, ensuring the dispersibility of the polyether phosphate ester. The phosphate ester end group plays an anchoring role and can act as a wetting and dispersing agent to uniformly and stably disperse the positive electrode active component particles in the NMP medium.

[0089] like Figure 1 As shown, the polyether phosphate ester of this application is a long, flexible chain. It can form hydrogen bonds with the positive electrode active material and the positive electrode current collector through structural unit (I) (or the structural unit formed by component (a)), and covalent bonds with the positive electrode active material and the positive electrode current collector through structural unit (II) (or the structural unit formed by component (b)). Furthermore, it can interact with the surface of the positive electrode active material particles through the benzene ring in structural unit (III) (or the structural unit formed by component (c)). Additionally, covalent bonds can also form between the polyether phosphate esters of this application. Therefore, by adding a flexible additive, namely the polyether phosphate ester described in this application, to the positive electrode slurry, the stability of the positive electrode slurry can be improved, the flexibility of the positive electrode sheet can be increased, and the dispersibility of the various substances in the positive electrode sheet can be ensured, thereby increasing the coating weight of the positive electrode sheet. Figure 3 As shown, after adding the polyether phosphate ester, the cathode slurry of this application did not crack during the entire coating process. Figure 4 As shown, the maximum coating thickness (by weight) in the positive electrode sheet is significantly increased after the addition of the polyether phosphate of this application.

[0090] The polyether phosphate described in this application can be obtained using conventional techniques in the art, or it can be prepared using the following steps:

[0091] Step 1: The epoxy alkane monomer is reacted under alkaline conditions to form a polyether. Optionally, the solvent used is one or more of dimethyl sulfoxide, acetone, and diethyl ether. Optionally, the alkaline substance that may be added during the preparation is, for example, NaOH, KOH, or dicyclohexylcarbodiimide. Optionally, the reaction temperature range is 80–160°C, and the reaction time range is 3–7 h. Optionally, the stirring speed during the reaction ranges from 1000–2000 rpm. Optionally, after the reaction is completed, a vacuum distillation purification step is performed.

[0092] Step 2: React the polyether from step (1) with the phosphating agent to generate polyether phosphate ester. Optionally, the reaction is carried out in a reaction vessel. Optionally, the temperature range of the reaction is 60-130℃. Optionally, the reaction time range is 2-15h. Optionally, the reaction is stirred during the reaction. The stirring time range is 1-10h, and the stirring speed range is 1000-2000r / min. Optionally, after the reaction is completed, a vacuum distillation purification step is performed.

[0093] In some embodiments, the positive electrode slurry described in this application has a pH range of approximately 6 to 9 at 20–60°C. The pH value is tested using conventional methods in the art.

[0094] In any embodiment of this application, the energy density of the resulting lithium-ion battery is significantly improved after adding the polyether phosphate to the positive electrode slurry. Furthermore, the improvement in the positive electrode sheet reduces the amount of battery cell material used, thereby lowering the total material cost of the battery cell.

[0095] In some embodiments, the number-average molecular weight of the polyether phosphate is in the range of 10,000 to 80,000, optionally in the range of 10,000 to 60,000, and more preferably in the range of 30,000 to 50,000.

[0096] Molecular weight affects the processing performance of the positive electrode sheet. At lower molecular weights, the flexibility of the positive electrode sheet is not significantly improved, and cracking during coating may still occur, along with potential issues like cold-pressing breakage and winding fracture. If the molecular weight is too low, the stability of the positive electrode slurry is poor, making it prone to physical gelation and degrading the resistance of the positive electrode film, negatively impacting battery performance. Conversely, if the molecular weight is too high, it hinders the dispersion of polyether phosphate in the positive electrode slurry. Therefore, the number-average molecular weight of the polyether phosphate must be controlled within the aforementioned range.

[0097] In some embodiments, in the polyether phosphate ester described in this application, based on the total molar amount of structural units (I) to (IV), the molar percentage of structural unit (I) is 0-75 mol%, the molar percentage of structural unit (II) is 0-65 mol%, the molar percentage of structural unit (III) is 5-65 mol%, and the molar percentage of structural unit (IV) is 4-15 mol%, wherein the molar percentages of structural unit (I) and structural unit (II) are not simultaneously zero.

[0098] Optionally, based on the total molar amount of structural units (I) to structural units (IV), the molar percentage of structural unit (I) (or the molar percentage of component (a) based on the total molar amount of components (a) to (d)) can be approximately 0 mol%, approximately 5 mol%, approximately 10 mol%, approximately 14 mol%, approximately 15 mol%, approximately 17 mol%, approximately 20 mol%, approximately 25 mol%, approximately 26 mol%, approximately 27 mol%, approximately 28 mol%, approximately 29 mol%, approximately 30 mol%, approximately 31 mol%, approximately 32 mol%, approximately 33 mol%, approximately 35 mol%, approximately 40 mol%, approximately 42 mol%, approximately 45 mol%, approximately 50 mol%, approximately 55 mol%, approximately 60 mol%, approximately 62 mol%, approximately 65 mol%, approximately 68 mol%, approximately 70 mol%, approximately 72 mol%, or approximately 75 mol%. Alternatively, the molar percentage of structural unit (I) can be within any range of the above-mentioned values.

[0099] Optionally, based on the total molar amount of structural units (I) to (IV), the molar percentage of structural unit (II) (or the molar percentage of component (b) based on the total molar amount of components (a) to (d)) can be approximately 0 mol%, approximately 5 mol%, approximately 10 mol%, approximately 14 mol%, approximately 15 mol%, approximately 17 mol%, approximately 20 mol%, approximately 22 mol%, approximately 25 mol%, approximately 30 mol%, approximately 31 mol%, approximately 35 mol%, approximately 40 mol%, approximately 42 mol%, approximately 43 mol%, approximately 45 mol%, approximately 50 mol%, approximately 52 mol%, approximately 53 mol%, approximately 54 mol%, approximately 55 mol%, approximately 56 mol%, approximately 58 mol%, approximately 60 mol%, approximately 63 mol%, or approximately 65 mol%. Alternatively, the molar percentage of structural unit (II) can be within any range of the above-mentioned values.

[0100] Optionally, based on the total molar amount of structural units (I) to (IV), the molar percentage of structural unit (III) (or based on the total molar amount of components (a) to (d), the molar percentage of component (c)) is approximately 5 mol%, approximately 6 mol%, approximately 7 mol%, approximately 9 mol%, approximately 10 mol%, approximately 11 mol%, approximately 15 mol%, approximately 20 mol%, approximately 23 mol%, approximately 24 mol%, approximately 25 mol%, approximately 26 mol%, approximately 30 mol%, approximately 31 mol%, approximately 33 mol%, approximately 35 mol%, approximately 40 mol%, approximately 45 mol%, approximately 50 mol%, approximately 55 mol%, approximately 59 mol%, approximately 60 mol%, approximately 61 mol%, or approximately 65 mol%. Alternatively, the molar percentage of structural unit (III) may fall within any range of the aforementioned values.

[0101] Optionally, based on the total molar amount of structural units (I) to (IV), the molar percentage of structural unit (IV) (or based on the total molar amount of components (a) to (d), the molar percentage of component (d)) is approximately 4 mol%, approximately 5 mol%, approximately 6 mol%, approximately 7 mol%, approximately 8 mol%, approximately 9 mol%, approximately 10 mol%, approximately 11 mol%, approximately 12 mol%, approximately 13 mol%, approximately 14 mol%, or approximately 15 mol%. Alternatively, the molar percentage of structural unit (IV) may fall within any range of the aforementioned values.

[0102] In this application, “about” a certain value means a range, namely, the range of ±3% of that value.

[0103] The molar proportions of the above structural units (I)-(IV) (or components (a)-(d)) ensure that the obtained polyether phosphate forms sufficient hydrogen bonds and an appropriate amount of covalent bonds with the positive electrode active material, current collector, etc., thereby ensuring the stability of the positive electrode preparation process and ensuring the flexibility of the positive electrode and the dispersibility of various positive electrode materials, thus improving the energy density of the battery.

[0104] In some embodiments, the weight ratio of the polyether phosphate to the positive electrode active material is 0.0005 to 0.030, with a preferred range of 0.001 to 0.02, a more preferred range of 0.001 to 0.01, and a most preferred range of 0.001 to 0.007.

[0105] The weight ratio of the polyether phosphate to the positive electrode active material is 0.0005 to 0.030. When this ratio is too small, the positive electrode sheet will crack under high coating weight; when this ratio is too large, it will have an adverse effect on battery performance.

[0106] In some embodiments, the positive electrode active material is selected from at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel oxide, or mixtures thereof.

[0107] In theory, for the positive electrode of a secondary battery, this application can employ any positive electrode active material known in the art for batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0108] However, the inventors of this application have discovered that when the positive electrode active material is at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel oxide, or a mixture thereof, adding the polyether phosphate ester can better achieve the effects of improving the flexibility of the electrode sheet and increasing the maximum coating weight of the electrode sheet.

[0109] In some embodiments, the gelation factor G of the positive electrode slurry ranges from 0 to 1, and optionally from 0 to 0.3.

[0110] Where G = (m1-m2) / m1, when G = 0 to 0.3, the slurry is judged not to gel, and when G > 0.3, it is judged to gel.

[0111] m1 is the mass of the positive electrode slurry obtained after filtering 2 kg of initial positive electrode slurry through a 100-mesh filter for 10 minutes.

[0112] m2 represents the mass of the positive electrode slurry obtained after filtering 2 kg of slurry that has been left to stand for 48 hours through a 100-mesh filter for 10 minutes.

[0113] The positive electrode slurry used in measuring m1 and the positive electrode slurry used in measuring m2 are from the same batch.

[0114] The closer the mass of the positive electrode slurry obtained after filtration following 48 hours of settling is to the initial mass, and the smaller the G value, the less prone the slurry is to gelation, and the better the slurry state. The positive electrode slurry described in this application has excellent gelation properties.

[0115] A second aspect of this application provides a positive electrode sheet, comprising:

[0116] Positive current collector; and

[0117] A positive electrode film layer is located on at least one surface of the positive current collector, the positive electrode film layer comprising the positive electrode slurry described in the first aspect of this application. As described above, by adding the polyether phosphate, this application allows for an increase in the maximum coating weight on the positive electrode sheet. This is also reflected in the increase in the maximum weight of the positive electrode film layer. In some embodiments, the mass of the positive electrode film layer on a unit area electrode sheet ranges from 13-43 mg / cm². 2 The selectable range is 22-31 mg / cm³. 2 The selectable range is 22-29 mg / cm³. 2 The mass referred to here is the mass of the positive electrode film layer on a single surface of the electrode. If the positive electrode has a positive electrode film layer on both surfaces, then the mass of the positive electrode film layer per unit area of ​​the electrode is twice the aforementioned range, i.e., the range is 26–86 mg / cm³. 2 The selectable range is 44–62 mg / cm³. 2 The selectable range is 44–58 mg / cm³. 2 The mass refers to the mass of the positive electrode film layer on both surfaces of the electrode.

[0118] In some embodiments, after adding the polyether phosphate ester described in this application, the coating weight per unit area on the positive electrode sheet can reach up to 41 mg / cm². 2Optionally, the coating weight per unit area on the positive electrode can be up to 23-41 mg / cm³. 2 Within the range.

[0119] When the weight of the positive electrode film layer on a unit area positive electrode sheet is too small, the electrode uniformity is poor; when the weight of the positive electrode film layer on a unit area positive electrode sheet is too large, the electrode coating process suffers severe cracking, making production impossible. This application limits the weight of the positive electrode film layer on a unit area positive electrode sheet to the above range, ensuring that the best results can be achieved within this range.

[0120] The positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0121] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0122] In the positive electrode sheet, the mass content of the positive electrode active material in the positive electrode film layer is 90-97%, based on the positive electrode film layer. This content can be measured using EDS. If this mass content is too low, the energy density of the prepared battery will be low, failing to meet the battery capacity requirements; if this mass content is too high, there will be insufficient binder and conductive agent, resulting in poor battery performance.

[0123] In the positive electrode sheet, the binder content in the positive electrode film layer is 2-5% by mass, based on the total mass of the positive electrode film layer. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. Existing conventional positive electrode sheets use binders with a specific or similar degree of crystallinity, which are brittle after coating and drying, and the electrode sheet is prone to cracking under stress. However, the positive electrode sheet of this application uses a binder with the same degree of crystallinity, and the electrode sheet does not crack.

[0124] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0125] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0126] The positive electrode sheet described in this application exhibits excellent flexibility, and the coating weight is significantly reduced. Applying this positive electrode sheet to secondary batteries, for example, by directly adding it to the positive electrode slurry during preparation, can significantly improve the battery's energy density.

[0127] In some embodiments, the positive electrode film layer includes two sublayers parallel to and stacked on top of each other, wherein the weight content of polyether phosphate in the sublayer closest to the positive electrode current collector (i.e., the sublayer closest to the current collector) is in the range of 0 to 60 relative to the weight content of polyether phosphate in the sublayer furthest from the positive electrode current collector (i.e., the sublayer furthest from the current collector), with an optional range of 0.1 to 30.

[0128] In some embodiments, the weight ratio of the polyether phosphate in the sublayer closest to the positive current collector to the weight ratio of the polyether phosphate in the sublayer furthest from the positive current collector may be about 0.1, about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, about 13, about 14, about 15, about 16, or about 17. Approximately 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, or 60. Alternatively, the weight ratio of the polyether phosphate ester in the sublayer closest to the positive current collector to the weight content of the polyether phosphate ester in the sublayer furthest from the positive current collector is within any range of any of the above values.

[0129] In some alternative embodiments, in the sublayer closer to the current collector, the weight ratio of the polyether phosphate to the positive electrode active material is 0 to 0.043; in the sublayer farther from the current collector, the weight ratio of the polyether phosphate to the positive electrode active material is 0.0006 to 0.004.

[0130] When the coating weight is 23 mg / cm³ 2 In the above cases, compared with single-coat thick coating, multiple coatings can reduce the material cost of flexible additives, while the polyether phosphate ester described in this application can perform better without affecting electrical properties.

[0131] Optionally, when preparing a positive electrode film with two sublayers, two positive electrode slurries containing different amounts of polyether phosphate are first prepared, then one slurry is coated onto the current collector and dried, then the other slurry is coated and dried again.

[0132] In some embodiments, when measuring the flexibility of the positive electrode sheet using a needle coil,

[0133] When the diameter of the coiled needle R ≤ 3.0 mm, the positive electrode sheet does not develop cracks, or,

[0134] When the diameter of the coiling needle R = 3.0 mm, the positive electrode sheet develops cracks, but when the diameter of the coiling needle R = 4.0 mm, no cracks appear.

[0135] In any embodiment, when measuring the flexibility of the positive electrode sheet according to this application using a winding needle, an electrode sample with dimensions of 50 mm x 100 mm is prepared, wound on a specially designed winding needle, and the electrode sheet crack condition is observed using a combination of visual inspection and microscopy. The flexibility level is determined according to the following method:

[0136] The diameter of the coiling needle is R.

[0137] When R≤3.0mm, the electrode does not crack and is classified as Grade 1 in flexibility;

[0138] A crack is present when R=3.0mm, and no crack is present when R=4.0mm; this indicates a level 2 flexibility rating.

[0139] Cracks are present when R=4.0mm and when R=5.0mm, indicating a flexibility level of three.

[0140] R=5.0mm without cracks, R=6.0mm with cracks, classified as flexibility level four;

[0141] R=6.0mm without cracks, R=7.0mm with cracks, which is grade 5 for flexibility.

[0142] The preparation method of the rolled needle is as follows:

[0143] Cut a 60mm section from a standard 304 stainless steel bar with diameters of 3.0mm, 4.0mm, 5.0mm, 6.0mm, and 7.0mm, and weld it to a 150mm×300mm steel plate for fixation to obtain the coiled needle.

[0144] The smaller the diameter of the coiling needle used and the electrode does not crack, the better the flexibility of the electrode. Conversely, the larger the diameter of the coiling needle used and the electrode cracks, the worse the flexibility of the electrode.

[0145] During cold pressing, the formed hydrogen bonds are broken, and the flexible main chain extends. However, the addition of the polyether phosphate ester described in this application can reduce the cold pressing pressure, thereby reducing cracks and the risk of chain breakage.

[0146] In some embodiments, the wettability improvement rate I of the positive electrode sheet ranges from 2% to 20%, with an optional range of 6% to 15%.

[0147] Where I = (I2 - I1) / I1 × 100%,

[0148] I2 is the wetting rate of the positive electrode in the electrolyte.

[0149] I1 represents the wetting rate of the positive electrode sheet excluding the polyether phosphate in the electrolyte.

[0150] The positive electrode used in measuring I1 is the same as the positive electrode used in measuring I2, the only difference being that the positive electrode used in measuring I1 does not contain the polyether phosphate, while the positive electrode used in measuring I2 contains the polyether phosphate.

[0151] The electrode sheet exhibits good wettability, enabling excellent wetting and retention of the electrolyte. This ensures effective wetting of the cell electrode sheet, preventing insufficient wetting, improving cell electrolyte injection efficiency and electrode wettability during cycling, thereby effectively enhancing battery product performance. The positive electrode sheet described in this application demonstrates excellent wetting performance in the electrolyte.

[0152] A third aspect of this application provides a secondary battery, comprising a positive electrode sheet as described in the second aspect of this application, or prepared using a positive electrode slurry as described in the first aspect of this application. The energy density of the secondary battery described in this application is significantly improved. Furthermore, the total material cost is reduced during the preparation of the battery.

[0153] The secondary battery, battery module, battery pack, and power-consuming device of this application are described below.

[0154] Secondary batteries

[0155] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0156] [Positive electrode plate]

[0157] The positive electrode is prepared using the positive electrode sheet described in the second aspect of this application or using the positive electrode slurry described in the first aspect of this application.

[0158] [Negative electrode plate]

[0159] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0160] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0161] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0162] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, phosphorus-based materials, tin-based materials, and lithium titanate, etc. The phosphorus-based material may be selected from at least one of elemental phosphorus, phosphorus oxides, phosphorus-carbon complexes, phosphorus-nitrogen complexes, and phosphorus alloys. The tin-based material may be selected from at least one of elemental tin, tin oxides, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0163] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0164] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0165] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0166] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0167] [Electrolytes]

[0168] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0169] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0170] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0171] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0172] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature performance, etc.

[0173] [Isolation membrane]

[0174] In some embodiments, the secondary battery also includes a separator. The separator is disposed between the positive electrode and the negative electrode to provide isolation. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0175] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0176] [Outer Packaging]

[0177] In some embodiments, the secondary battery may include an outer packaging for encapsulating the positive electrode, negative electrode, and electrolyte. As an example, the positive electrode, negative electrode, and separator may be stacked or wound to form a stacked or wound battery cell, with the cell encapsulated within the outer packaging; the electrolyte may be a liquid electrolyte that wets the cell. The number of cells in the secondary battery may be one or more, adjustable as needed.

[0178] In one embodiment, this application provides an electrode assembly. In some embodiments, the positive electrode, negative electrode, and separator are fabricated into the electrode assembly using a winding process or a stacking process. The outer packaging can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0179] In some embodiments, the outer packaging of the secondary battery can be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS). In some embodiments, the outer packaging of the secondary battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell.

[0180] Methods for preparing secondary batteries

[0181] In one embodiment, this application provides a method for preparing a secondary battery, wherein the negative electrode sheet described in this application or the negative electrode sheet prepared according to the method described in this application is used.

[0182] The preparation of a secondary battery may further include the step of assembling the negative electrode, positive electrode, and electrolyte of this application to form a secondary battery. In some embodiments, the positive electrode, separator, and negative electrode can be wound or stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, thus obtaining a battery cell. The battery cell is then placed in an outer package, filled with electrolyte, and sealed to obtain a secondary battery.

[0183] In some embodiments, the preparation of a secondary battery may also include the step of preparing a positive electrode sheet. As an example, the positive electrode active material, conductive agent, and binder can be dispersed in a solvent (e.g., N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode slurry; the positive electrode slurry is coated on a positive electrode current collector, and after processes such as drying and cold pressing, a positive electrode sheet is obtained.

[0184] In some embodiments, the preparation of a secondary battery includes the step of preparing a negative electrode sheet according to the method described in this application.

[0185] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0186] In some embodiments, this application provides an electrical device, battery module, or battery pack, wherein the electrical device, battery module, or battery pack includes a secondary battery as described in this application or a secondary battery prepared according to the method described in this application.

[0187] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0188] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0189] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc. Another example device could be a mobile phone, tablet computer, laptop computer, etc. These devices typically require a thin and light design and can use a secondary battery as a power source. The secondary battery, battery module, or battery pack can be selected according to the usage requirements of the electrical device.

[0190] Therefore, this application provides a battery module that includes the secondary battery described in this application.

[0191] In addition, this application also provides a battery pack that includes the aforementioned battery module.

[0192] This application further provides an electrical device, which includes at least one of the secondary battery described in this application, the battery module described above, or the battery pack described above.

[0193] Example

[0194] The present application will be described in detail below through examples, which are not limiting.

[0195] 1. Preparation of polyether phosphate

[0196] Step 1: Precursor 1, Precursor 2, and Precursor 3 (see Table 1 for specific types and amounts) are reacted under alkaline conditions to generate polyether. The reaction is stopped when the number average molecular weight of the polyether reaches 2w (i.e., 20,000).

[0197] Step 2: React the polyether prepared in step (1) with a phosphating agent (phosphorus pentoxide) (see Table 1 for specific dosage) to generate polyether phosphate. After the reaction is complete, filter and dialyze to obtain polyether phosphate with a number average molecular weight of 2w-3w (i.e. 20000-30000).

[0198] 2. Preparation of positive electrode slurry

[0199] The positive electrode active material (lithium iron phosphate), conductive agent (conductive carbon black Super P), and binder PVDF (see Table 2 for specific dosages) were mixed for 30 min. The resulting mixture was then added to NMP and stirred for 180 min to ensure uniform dispersion. Finally, the polyether phosphate ester prepared in step 1 was added, and the mixture was stirred thoroughly for another 60 min to form a uniform positive electrode slurry.

[0200] 3. Preparation of the positive electrode sheet

[0201] The positive electrode slurry was coated onto the surface of the positive electrode current collector aluminum foil. After drying and cold pressing, the positive electrode sheet was obtained. A series of positive electrode sheet performance tests were conducted (mainly (1) testing whether the electrode sheet cracked during coating, (2) whether it broke after cold pressing, and (3) using the flexibility test method described herein; the maximum coating weight that is below flexibility level 2 and does not crack during coating or break after cold pressing is the maximum coating weight per unit area). The maximum coating weight per unit area was 41 mg / cm². 2 .

[0202] 4. Preparation of negative electrode sheet

[0203] The negative electrode active material (graphite), conductive agent (Super P), binder (SBR), and thickener (CMC) are thoroughly mixed in an appropriate amount of deionized water at a mass ratio of 96.2:0.8:1.8:1.2 to form a uniform negative electrode slurry. This negative electrode slurry is then coated onto both surfaces of the negative electrode current collector copper foil. After drying and cold pressing, the negative electrode sheet is obtained.

[0204] 5. Preparation of electrolyte

[0205] Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte with a concentration of 1 mol / L.

[0206] 6. Separating membrane

[0207] Polyethylene (PE) film is used.

[0208] 7. Preparation of secondary batteries

[0209] The positive electrode, separator, and negative electrode are stacked in sequence and wound to obtain an electrode assembly. The electrode assembly is then placed in an outer packaging, and the electrolyte is added. After encapsulation, settling, formation, and aging processes, the secondary battery of Example 1 is obtained. The outer packaging is a hard-shell casing with dimensions of 148mm × 28.5mm × 97.5mm.

[0210] Examples 2-19 and Comparative Example 1

[0211] Similar to Example 1, except that the raw materials and amounts shown in Tables 1 and 2 are used, and the number-average molecular weights of the polyether phosphates shown in Tables 5-6 are extracted during the preparation, except that polyether phosphates are not used in Comparative Example 1.

[0212] Example 21

[0213] The preparation processes for steps 1 and 4-7 are the same as in Example 1. The cutoff range for the number-average molecular weight of polyether phosphate is shown in Table 8. The preparation processes for steps 2-3 are modified as follows:

[0214] Step 2: Preparation of positive electrode slurry

[0215] 3124.9 g of positive electrode active material (lithium iron phosphate), 32.5 g of conductive agent (Super P), and 81.25 g of binder PVDF were mixed for 30 min. The resulting mixture was then added to 1750 g of NMP solvent and stirred for 180 min to ensure uniform dispersion. Finally, 11.38 g of polyether phosphate prepared in step 1 was added, and the mixture was stirred thoroughly for another 60 min to form a uniform positive electrode slurry 1.

[0216] 3134.6 g of positive electrode active material (lithium iron phosphate), 32.5 g of conductive agent (Super P), and 81.25 g of binder PVDF were mixed for 30 min. The resulting mixture was then added to 1750 g of NMP solvent and stirred for 180 min to ensure uniform dispersion. Finally, 1.63 g of the polyether phosphate ester prepared in step 1 was added, and the mixture was stirred thoroughly for another 60 min to form a uniform positive electrode slurry 2.

[0217] Step 3: Preparation of the positive electrode sheet

[0218] The positive electrode slurry 1 from step 2 is coated onto the surface of the positive electrode current collector aluminum foil. After drying, positive electrode slurry 2 is then coated onto the dried surface of slurry 1, with the coating thickness of positive electrode slurry 1 and positive electrode slurry 2 being consistent. After a series of positive electrode performance tests (mainly testing whether the electrode sheet cracks during coating and whether it breaks after cold pressing; refer to the positive electrode sheet flexibility test method described in this document; the maximum coating weight per unit area that has a flexibility level of 2 or below and does not crack during coating or break after cold pressing is the maximum coating weight per unit area), the total coating weight per unit area is 41 mg / cm². 2 .

[0219] Example 20

[0220] The difference from Example 21 is that the positive electrode slurry 1 does not contain polyether phosphate. The other preparation process is similar to that of Example 21. For specific method parameters, please refer to Tables 1 and 3. The cut-off number average molecular weight range is shown in Table 7.

[0221] Examples 22-26

[0222] The preparation process is similar to that of Example 21, except that the raw materials and amounts shown in Tables 1 and 3 are used, and the number-average molecular weight is cut off as shown in Table 8.

[0223] In this application, the positive electrode slurry in all embodiments and comparative examples is coated on both surfaces of the positive current collector, i.e., double-sided coating.

[0224] Table 1: Raw materials and dosages used in the preparation of polyether phosphate esters

[0225]

[0226] The precursors 1-3 and phosphating agents used in Examples 13-26 are the same as those in Example 1.

[0227] Table 2: Substances and Amounts Used in the Preparation of Positive Electrode Slurry

[0228] Example 1 Lithium iron phosphate 3123.25 13.00 Example 13 Lithium iron phosphate 3134.63 1.63 Example 14 Lithium iron phosphate 3038.75 97.50 Example 15 Lithium iron phosphate 3133.00 3.25 Example 16 Lithium iron phosphate 3071.25 65.00 Example 17 Lithium iron phosphate 3113.50 22.75 Example 18 Lithium iron phosphate 3135.60 0.65 Example 19 Lithium iron phosphate 2973.75 162.50

[0229] In Table 2, Examples 1 and 13-19 all used 1750g of solvent NMP, 32.5g of conductive carbon Super P, and 81.25g of binder PVDF. The amounts of each substance used to prepare the positive electrode slurry in Examples 2-12 were the same as in Example 1.

[0230] Table 3: Substances and amounts used in each sublayer of the positive electrode slurry, including those with a double-layer positive electrode film.

[0231]

[0232] IV. Performance Evaluation of the Positive Electrode Slurry and Positive Electrode Sheet of this Application

[0233] Testing of slurry parameters:

[0234] 1. Gel-state factor of positive electrode slurry

[0235] The gel state of the cathode slurry was evaluated using the following methods:

[0236] The gel state factor of the positive electrode slurry is denoted as G, where G = |(m2-m1) / m1|.

[0237] in

[0238] m1 is the mass of the positive electrode slurry obtained after filtering 2 kg of initial positive electrode slurry through a 200-mesh filter for 10 minutes.

[0239] m2 is the mass of the positive electrode slurry obtained after filtering 2 kg of positive electrode slurry that has been left to stand for 48 hours through a 200-mesh filter for 10 minutes.

[0240] The positive electrode slurry used in measuring m1 and the positive electrode slurry used in measuring m2 are from the same batch.

[0241] G is considered non-gelling when it is in the range of 0 to 0.3; G>0.3 is considered gelling.

[0242] Testing of positive electrode parameters

[0243] 1. Flexibility test of positive electrode sheet

[0244] The flexibility of the positive electrode sheet is evaluated by using a needle winding method, which is as follows:

[0245] Electrode samples with dimensions of 50 mm x 100 mm were prepared and wound on a specially designed winding needle. The cracks in the electrode were observed using a combination of visual inspection and microscopy.

[0246] Specially made coiling needles:

[0247] Cut 60mm sections from standard 304 stainless steel bars with diameters of 2.0mm, 3.0mm, 4.0mm, 5.0mm, 6.0mm, and 7.0mm, and weld them to a 150mm x 300mm steel plate for fixation. Figure 5 As shown.

[0248] The flexibility level can be determined using the following methods:

[0249] The diameter of the coiling needle is R.

[0250] When R≤3.0mm, the electrode does not crack and is classified as Grade 1 in flexibility;

[0251] A crack is present when R=3.0mm, and no crack is present when R=4.0mm; this indicates a level 2 flexibility rating.

[0252] Cracks are present when R=4.0mm and when R=5.0mm, indicating a flexibility level of three.

[0253] R=5.0mm without cracks, R=6.0mm with cracks, classified as flexibility level four;

[0254] R=6.0mm without cracks, R=7.0mm with cracks, which is grade 5 for flexibility.

[0255] 2. Improvement rate of wettability of positive electrode sheet

[0256] The increase in wettability of the positive electrode sheet is expressed as I, where I = (I2 - I1) / I1 × 100%.

[0257] in

[0258] I2 is the wetting rate of the positive electrode in the electrolyte.

[0259] I1 represents the wetting rate of the positive electrode sheet excluding the polyether phosphate in the electrolyte.

[0260] The positive electrode used in measuring I1 is the same as the positive electrode used in measuring I2, the only difference being that the positive electrode used in measuring I1 does not contain the polyether phosphate, while the positive electrode used in measuring I2 contains the polyether phosphate.

[0261] The determination process for I1 and I2 is as follows:

[0262] The capillary method was used to test the electrolyte absorption rate of the electrode. Electrodes with dimensions ≥50mm*50mm were prepared, with smooth, wrinkle-free surfaces and no peeling or powdering. A capillary tube with an inner diameter d=100um was selected and sanded until the end was neat. The capillary tube was used to draw electrolyte up to a height of h=5mm, maintaining the electrolyte level at 5mm. The capillary tube was placed under a microscope, ensuring it was in contact with the electrode. A stopwatch was used to record the time as the electrolyte level in the capillary tube decreased. Once the electrolyte level had completely decreased, the washing time was recorded as t. The electrolyte wetting rate was equal to...

[0263] π×(d / 2)^2×h×ρ / t,

[0264] Where π is 3.14 and ρ is the electrolyte density.

[0265] 3. Measurement of coating weight per unit area

[0266] Prepare blank aluminum foil and a positive electrode sheet that has been dried during the coating process (this positive electrode sheet has a coating on both sides of the positive current collector), and punch out the area of ​​each with a diameter of 1540.25 mm². 2 Fifteen small discs are used. The coating weight per unit area is obtained by subtracting the average mass of the empty aluminum foil discs from the average mass of the small discs, and then dividing by 2. "Single-sided" refers to coating only on one surface of the current collector, and is not the same concept as the number of "sublayers" mentioned in this application. The maximum coating weight per unit area in the table refers to the weight on one side.

[0267] The coating weight data in the tabular embodiments of this application all refer to the maximum coating weight per unit area on a single side. The electrode performance and battery performance are measured at the maximum coating weight.

[0268] The maximum coating weight per unit area refers to the maximum coating weight that is below the second level of flexibility and does not crack during coating or break after cold pressing, after (1) testing whether the coated electrode sheet cracks during the coating process, (2) testing whether it breaks during cold pressing, and (3) testing the flexibility of the positive electrode sheet described in this application.

[0269] Battery-related performance tests

[0270] 1. Energy density measurement

[0271] The batteries prepared in the examples and comparative examples were weighed to obtain the total mass of the battery. After capacity formation, the batteries were allowed to stand at 25°C for 10 minutes, then charged at 0.33C to 100% SOC. After depolarization with a small current, the batteries were allowed to stand for 10 minutes, and then discharged at 0.33C to 0% SOC. The resulting capacity is the 0.33C capacity of the battery. After the batteries were allowed to stand for 30 minutes, they were charged to 100% SOC, and after another 30 minutes of standing, they were discharged at a constant current of 0.01C for 30 minutes. The voltage reached a stable value, which is the charge / discharge plateau voltage. Finally, the gravimetric energy density of the battery was calculated, i.e., battery gravimetric energy density = battery capacity × discharge plateau voltage / total battery weight, with the basic unit being Wh / kg (watt-hours per kilogram).

[0272] 2. Measurement of Direct Current Resistance (DCR)

[0273] The battery capacity was tested at 25℃ using the method described above. Then, it was charged at a constant voltage of 0.05C, allowed to stand for 60 minutes, discharged at 0.33C to 50% SOC, allowed to stand for 60 minutes, discharged at 0.33C to 20% SOC, allowed to stand for 60 minutes, and discharged at 0.33C to 0% SOC. The open-circuit voltage at 0% SOC was measured, and the DCR data for 30 seconds was compiled.

[0274] The measurement results are shown in Tables 4 to 7, where “ / ” indicates that the item is not present, not added, or not detected.

[0275] In Table 4-7, “(I) / (II) / (III) / (IV)” represents the molar amount of structural unit (I) / molecular amount of structural unit (II) / molecular amount of structural unit (3) / molecular amount of structural unit (IV), where the molar amount of structural unit (I) corresponds to the molar amount of precursor 1 in each embodiment; the molar amount of structural unit (II) corresponds to the molar amount of precursor 2 in each embodiment; the molar amount of structural unit (3) corresponds to the molar amount of precursor 3 in each embodiment; and the molar amount of structural unit (IV) corresponds to the molar amount of phosphate ester group in each embodiment.

[0276]

[0277]

[0278]

[0279]

[0280]

[0281] As shown in Table 7, under the premise that the coating weight per unit area is basically the same in the examples, the battery with a positive electrode sheet having two sublayers has a higher energy density. Furthermore, the weight content of polyether phosphate in the sublayer closest to the positive current collector is in the range of 0 to 60 relative to the weight content of polyether phosphate in the sublayer farthest from the positive current collector. When this ratio is >60 (Example 26), it affects the stability of the slurry and the film resistance of the electrode sheet, and the DCR of the cell is larger.

[0282] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode slurry, characterized in that, Including positive electrode active material and polyether phosphate, The polyether phosphate ester includes at least the following structural units: （I）： 、 (II): 、 (III): 、 And the structural unit (IV) phosphate ester group, in, A is hydrogen, halogen, or haloalkyl; B is a hydroxyl group, R, OR, or ROR', where R and R' are independently straight-chain or branched alkyl groups containing 1 to 8 carbons; E is a phenyl, an alkyl-substituted phenyl, an ether-substituted phenyl, or a halophenyl; Based on the total molar amount of structural units (I) to (IV), the molar percentage of structural unit (I) is greater than 0 mol% and less than or equal to 75 mol%, the molar percentage of structural unit (II) is greater than 0 mol% and less than or equal to 65 mol%, the molar percentage of structural unit (III) is 5-65 mol%, and the molar percentage of structural unit (IV) is 4-15 mol.

2. The positive electrode slurry according to claim 1, characterized in that, The halogen is fluorine, chlorine, or bromine; B is methyl, ethyl, or ethoxymethyl; The E is a phenyl or fluorophenyl.

3. The positive electrode slurry according to claim 1, characterized in that, A is hydrogen or fluoromethyl.

4. The positive electrode slurry according to any one of claims 1-3, characterized in that, The number-average molecular weight of the polyether phosphate is in the range of 10,000 to 80,000.

5. The positive electrode slurry according to any one of claims 1-3, characterized in that, The number-average molecular weight of the polyether phosphate is in the range of 10,000 to 60,000.

6. The positive electrode slurry according to any one of claims 1-3, characterized in that, The number-average molecular weight of the polyether phosphate is in the range of 30,000 to 50,000.

7. The positive electrode slurry according to any one of claims 1-3, characterized in that, The weight ratio of the polyether phosphate to the positive electrode active material is 0.0005~0.

030.

8. The positive electrode slurry according to any one of claims 1-3, characterized in that, The weight ratio of the polyether phosphate to the positive electrode active material is 0.001 to 0.

02.

9. The positive electrode slurry according to any one of claims 1-3, characterized in that, The weight ratio of the polyether phosphate to the positive electrode active material is 0.001 to 0.

01.

10. The positive electrode slurry according to any one of claims 1-3, characterized in that, The weight ratio of the polyether phosphate to the positive electrode active material is 0.001 to 0.

007.

11. The positive electrode slurry according to any one of claims 1-3, characterized in that, The positive electrode active material is selected from at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel oxide, or mixtures thereof.

12. The positive electrode slurry according to any one of claims 1-3, characterized in that, The gel state factor G of the positive electrode slurry ranges from 0 to 1. Where G = (m1-m2) / m1, when G = 0~0.3, the slurry is judged not to gel, and when G > 0.3, it is judged to gel. m1 is the mass of the positive electrode slurry obtained after filtering 2 kg of initial positive electrode slurry through a 100-mesh filter for 10 minutes. m2 represents the mass of the positive electrode slurry obtained after filtering 2 kg of slurry that has been left to stand for 48 hours through a 100-mesh filter for 10 minutes. The positive electrode slurry used in measuring m1 and the positive electrode slurry used in measuring m2 are from the same batch.

13. The positive electrode slurry according to claim 12, characterized in that, The gelation factor G of the positive electrode slurry is in the range of 0~0.

3.

14. A positive electrode plate, comprising: Positive current collector; and A positive electrode film layer located on at least one surface of the positive current collector, the positive electrode film layer being prepared from the positive electrode slurry according to any one of claims 1-13, the positive electrode film layer having a mass range of 13~43 mg / cm² per unit area of ​​the positive electrode sheet. 2 The mass is the mass of the positive electrode film layer on a single surface of the electrode.

15. The positive electrode sheet according to claim 14, characterized in that, The mass of the positive electrode film on a unit area of ​​the positive electrode sheet ranges from 20 to 43 mg / cm². 2 .

16. The positive electrode sheet according to claim 14, characterized in that, The mass of the positive electrode film on a unit area of ​​the positive electrode sheet ranges from 22 to 33 mg / cm². 2 .

17. The positive electrode sheet according to claim 14, characterized in that, The mass of the positive electrode film on a unit area of ​​the positive electrode sheet ranges from 25 to 31 mg / cm². 2 .

18. The positive electrode sheet according to claim 14, characterized in that, The positive electrode film layer includes two sublayers, which are parallel to the positive electrode current collector and stacked on top of each other. The weight ratio of the polyether phosphate content in the sublayer closest to the positive electrode current collector to the weight content of the polyether phosphate in the sublayer furthest from the positive electrode current collector ranges from 0 to 60.

19. The positive electrode sheet according to claim 14, characterized in that, The positive electrode film layer includes two sublayers, which are parallel to the positive electrode current collector and stacked on top of each other. The weight ratio of the polyether phosphate in the sublayer closest to the positive electrode current collector to the weight content of the polyether phosphate in the sublayer furthest from the positive electrode current collector ranges from 0.1 to 30.

20. The positive electrode sheet according to claim 18 or 19, characterized in that, When measuring the flexibility of the positive electrode sheet using a needle coil, When the diameter of the coiled needle R ≤ 3.0 mm, the positive electrode sheet does not develop cracks, or, When the needle diameter R = 3.0 mm, the positive electrode sheet develops cracks, but when the needle diameter R = 4.0 mm, no cracks appear.

21. The positive electrode sheet according to claim 20, characterized in that, The wettability improvement rate I of the positive electrode sheet ranges from 2% to 20%. Where I = (I2-I1) / I1×100%, I2 is the wetting rate of the positive electrode in the electrolyte. I1 represents the wetting rate of the positive electrode sheet excluding the polyether phosphate in the electrolyte. The positive electrode used in measuring I1 is the same as the positive electrode used in measuring I2, the only difference being that the positive electrode used in measuring I1 does not contain the polyether phosphate, while the positive electrode used in measuring I2 contains the polyether phosphate.

22. The positive electrode sheet according to claim 21, characterized in that, The wettability improvement rate I of the positive electrode sheet ranges from 6% to 15%.

23. A secondary battery, characterized in that, It includes the positive electrode sheet according to any one of claims 14-22, or the positive electrode sheet obtained by the positive electrode slurry according to any one of claims 1-13.

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