Lithium-ion battery and preparation method therefor, positive electrode sheet and electric device

Abstract

Provided in the present application are a lithium-ion battery and a preparation method therefor, a positive electrode sheet and an electric device. The lithium-ion battery comprises a positive electrode sheet; the positive electrode sheet comprises a positive electrode active layer; and the components of the positive electrode active layer comprise a positive electrode active material, a dispersing agent and a softening agent. The dispersing agent comprises a hydrogenated butadiene-acrylonitrile rubber, and the softening agent comprises a compound containing a linear chain segment. The positive electrode sheet in the lithium-ion battery has relatively good flexibility and does not easily crack, and the resistance of a film of the battery is also low.

Description

Lithium-ion batteries and their preparation methods, positive electrode plates and electrical devices

[0001] Related applications

[0002] This application claims priority to Chinese patent application filed on August 29, 2024, application number 2024111960041, entitled "Lithium-ion battery and preparation method thereof, positive electrode sheet and power device thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of secondary battery technology, and in particular to a lithium-ion battery and its preparation method, positive electrode sheet and power device. Background Technology

[0004] In recent years, the application of secondary batteries such as lithium-ion batteries has become increasingly widespread, and they are now 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, and many other fields. However, traditional lithium-ion batteries suffer from problems such as cracking of the positive electrode active layer due to poor brittleness and high film resistance. Summary of the Invention

[0005] To achieve the above objectives, this application provides a lithium-ion battery and an electrical device comprising the lithium-ion battery, wherein the positive electrode sheet in the lithium-ion battery has good flexibility and is not easy to crack, and the film resistance is low.

[0006] A first aspect of this application provides a lithium-ion battery, including a positive electrode sheet, the positive electrode sheet including a positive electrode active layer, the positive electrode active layer comprising a positive electrode active material, a dispersant and a softener; the dispersant comprising hydrogenated nitrile rubber, and the softener comprising a compound containing linear segments.

[0007] In the aforementioned lithium-ion battery, hydrogenated nitrile rubber is introduced as a dispersant in the positive electrode active layer, while a compound containing linear segments is introduced as a flexible agent. The linear segments in the flexible agent can synergistically work with the butadiene structural units in the hydrogenated nitrile rubber to reduce the brittleness of the positive electrode sheet and improve its flexibility. At the same time, it can also effectively improve the dispersibility of the material in the slurry, reduce gelation, and thus reduce the film resistance of the lithium-ion battery.

[0008] In some embodiments, the linear segment includes one or more copolymer segments selected from C6-C18 alkyl, aryl-O-C6-C36 alkyl, polar group-substituted C2-C18 alkyl, polar group-substituted -O-C6-C24 alkyl carbon chains, polyether segments, polyamine segments, and polysiloxane segments.

[0009] In some embodiments, the polar groups each independently include one or more of ester, amide, carbamate, carboxyl, hydroxyl, and amino groups.

[0010] By employing flexible agents with appropriate structures, the flexibility of the positive electrode can be further improved, cracking reduced, film resistance lowered, and the initial coulombic efficiency and cycle capacity retention of lithium-ion batteries enhanced. Furthermore, by rationally controlling the lengths (n values) of the linear segments in the flexible agent, lower brittleness and film resistance of the positive electrode can be achieved, along with higher initial coulombic efficiency and cycle capacity retention.

[0011] In some embodiments, the flexible agent comprises polyether segments and has the following structural features:

[0012] Each of R1 independently comprises a C1-C18 alkyl group or a C6-C12 aryl group;

[0013] G1 and G2 each independently include C1-C18 alkyl, C6-C18 aryl, C1-C18 ester, C1-C18 amide, C1-C18 aminocarbamate or hydroxyl groups;

[0014] 10≤n1≤500.

[0015] In some embodiments, the flexible agent comprises polyamine segments and has the following structural features:

[0016] Each of R2 independently comprises a C1-C18 alkyl group or a C6-C12 aryl group;

[0017] R3 each independently includes H, C1-C18 alkyl or C6-C12 aryl;

[0018] G3 and G4 each independently include C1-C18 alkyl, C6-C18 aryl, C1-C18 ester, C1-C18 amide or amino groups;

[0019] 10≤n²≤500.

[0020] In some embodiments, the flexible agent comprises a copolymer segment of polyamine and polyether segments, and the flexible agent has the following structural features:

[0021] Each of R4 independently comprises a C1-C18 alkyl group or a C6-C12 aryl group;

[0022] R5 each independently includes H, C1-C18 alkyl or C6-C12 aryl;

[0023] Each R6 independently comprises a C1-C18 alkyl group or a C6-C12 aryl group;

[0024] G5 and G6 each independently include C1-C18 alkyl, C6-C18 aryl, C1-C18 ester, C1-C18 amide, C1-C18 aminocarbamate, hydroxyl or amino groups;

[0025] 10≤n3+n4≤500.

[0026] In some embodiments, the flexible agent comprises polysiloxane segments, and the flexible agent has the following structural features:

[0027] R7 and R8 each independently include C1-C18 alkyl, C6-C12 aryl, polyether segments or polyoxyethylene ether-polyoxypropylene ether copolymer segments;

[0028] G7 and G8 each independently include C1-C18 alkyl, C6-C12 aryl, hydroxyl or amino groups;

[0029] 10≤n5≤500.

[0030] In some embodiments, the compound contains heteroatoms, which include one or more of O, N, and P.

[0031] In some embodiments, the mass ratio of the flexible agent to the dispersant is 10:1 to 1:10. Properly controlling this mass ratio allows for a balance between low film resistance and good electrode flexibility. Further, the mass ratio of the flexible agent to the dispersant is 3:1 to 1:3.

[0032] Furthermore, by rationally controlling the weight-average molecular weight, hydrogenation ratio, and molar percentage of acrylonitrile structural units of the hydrogenated nitrile rubber, the dispersion stability of the slurry can be improved, the diaphragm resistance can be reduced, and the electrode can have better flexibility.

[0033] In some embodiments, the hydrogenated nitrile rubber has at least one of the following features (1) to (3):

[0034] (1) Weight-average molecular weight is 500 to 1,000,000;

[0035] (2) The hydrogenation ratio is 10% to 100%; the hydrogenation ratio refers to the following: the molar content of double bonds in the nitrile rubber is P1, and the molar content of double bonds in the hydrogenated nitrile rubber obtained after hydrogenation is P2, and the hydrogenation ratio is (P1-P2) / P1.

[0036] (3) The molar percentage of acrylonitrile structural units is 5% to 30%.

[0037] In some embodiments, the hydrogenated nitrile rubber has at least one of the following features (1) to (3):

[0038] (1) Weight-average molecular weight is 1,000 to 200,000;

[0039] (2) The hydrogenation ratio is 30% to 50%;

[0040] (3) The molar percentage of acrylonitrile structural units is 10% to 20%.

[0041] In some embodiments, the softening agent is present in the positive electrode active layer at a mass percentage of 0.05% to 0.5%.

[0042] In some embodiments, the coating amount of the positive electrode active layer in the positive electrode sheet is ≥300mg / 1540.25mm². 2 .

[0043] In some embodiments, the compaction density of the positive electrode sheet is 3.3 g / cm³. 3 ~3.6g / cm 3 .

[0044] In some embodiments, the compaction density of the positive electrode sheet is 3.3 g / cm³. 3 ~3.5g / cm 3 .

[0045] In some embodiments, the positive electrode active material includes one or more of lithium transition metal oxides and lithium-containing phosphates with an olivine structure.

[0046] In some embodiments, the lithium transition metal oxide includes one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds; and / or

[0047] The lithium phosphates with the olivine structure include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0048] In some embodiments, the components of the positive electrode active layer also include a binder.

[0049] In some embodiments, the adhesive has at least one of the following features (1) to (2):

[0050] (1) The adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorinated acrylate resin;

[0051] (2) In the positive electrode active layer, the mass percentage of the binder is 1% to 2.5%.

[0052] A second aspect of this application provides a method for preparing a lithium-ion battery, including the step of preparing a positive electrode active layer:

[0053] A positive electrode slurry is prepared by mixing the components of the positive electrode active layer with a solvent; the components of the positive electrode active layer include a positive electrode active material, a dispersant, and a softener; the dispersant includes hydrogenated nitrile rubber, and the softener includes a compound containing linear segments;

[0054] The positive electrode slurry is molded to prepare the positive electrode active layer.

[0055] In some embodiments, the step of mixing the components of the positive electrode active layer and the solvent includes:

[0056] First, the dispersant, softener, and part of the solvent are mixed, and then the resulting mixture is mixed with the remaining components; wherein the solid content of the mixture is 5% to 75%.

[0057] In some embodiments, the solid content of the mixture is 7% to 20%.

[0058] In some embodiments, the positive electrode active layer comprises a positive electrode active material, a dispersant, and a softener; the dispersant comprises hydrogenated nitrile rubber, and the softener comprises a compound containing linear segments.

[0059] In some embodiments, the positive electrode is the same as the positive electrode in a lithium-ion battery as described above.

[0060] This application provides an electrical device comprising at least one of the following: a lithium-ion battery as described above, a lithium-ion battery prepared by the preparation method as described above, and a positive electrode sheet as described above. Attached Figure Description

[0061] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0062] Figure 1 is a schematic diagram of a lithium-ion battery according to an embodiment of this application.

[0063] Figure 2 is an exploded view of a lithium-ion battery according to an embodiment of this application, as shown in Figure 1.

[0064] Figure 3 is a schematic diagram of an electrical device using a lithium-ion battery as a power source according to an embodiment of this application.

[0065] Explanation of reference numerals in the attached drawings: 10, lithium-ion battery; 11, casing; 12, electrode assembly; 13, cover plate; 20, electrical device. Detailed Implementation

[0066] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of this application.

[0067] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0068] The "range" disclosed in this application can be defined in the form of 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 the specific range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be included or excluded independently, and they can be combined arbitrarily; 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 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 also listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" 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" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0069] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0070] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0071] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0072] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can 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.

[0073] In this application, unless otherwise specified, A (e.g., B) means that B is a non-limiting example of A, and it is understood that A is not limited to B.

[0074] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0075] In this application, the term "alkyl" refers to a monovalent residue formed by the loss of a hydrogen atom from a saturated hydrocarbon containing a primary (normal) carbon atom, a secondary carbon atom, a tertiary carbon atom, a quaternary carbon atom, or a combination thereof. Phrases containing this term, such as "C1-C18 alkyl," refer to alkyl groups containing 1 to 18 carbon atoms, and each occurrence can independently be C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl, C7 alkyl, C8 alkyl, C9 alkyl, C10 alkyl, C11 alkyl, C12 alkyl, C13 alkyl, C14 alkyl, C15 alkyl, C16 alkyl, C17 alkyl, C18 alkyl (the meaning of other alkyl groups with different carbon chain lengths is similar). Suitable examples include, but are not limited to: methyl (Me, -CH3), ethyl (Et, -CH2CH3), 1-propyl (n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1-butyl (n-Bu, n-butyl, -CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH2CH(CH3)2), 2-butyl (s-Bu, s-butyl, -CH(C H3)CH2CH3), 2-methyl-2-propyl (t-Bu, t-butyl, -C(CH3)3), 1-pentyl (n-pentyl, -CH2CH2CH2CH2CH3), 2-pentyl (-CH(CH3)CH2CH2CH3), 3-pentyl (-CH(CH2CH3)2), 2-methyl-2-butyl (-C(CH3)2CH2CH3), 3-methyl-2-butyl (-CH(CH3)CH(CH3)2), 3-methyl-1-butyl (- CH2CH2CH(CH3)2), 2-methyl-1-butyl(-CH2CH(CH3)CH2CH3), 1-hexyl(-CH2CH2CH2CH2CH2CH3), 2-hexyl(-CH(CH3)CH2CH2CH2CH3), 3-hexyl(-CH(CH2CH3)(CH2CH2CH3)), 2-methyl-2-pentyl(-C(CH3)2CH2CH2CH3), 3-methyl-2-pentyl(-CH(CH3)CH( CH3)CH2CH3), 4-methyl-2-pentyl (-CH(CH3)CH2CH(CH3)2), 3-methyl-3-pentyl (-C(CH3)(CH2CH3)2), 2-methyl-3-pentyl (-CH(CH2CH3)CH(CH3)2), 2,3-dimethyl-2-butyl (-C(CH3)2CH(CH3)2), 3,3-dimethyl-2-butyl (-CH(CH3)C(CH3)3 and octyl (-(CH2)7CH3).

[0076] In this application, the term "aryl" refers to an aromatic hydrocarbon group derived from an aromatic ring compound by removing one hydrogen atom. It can be a monocyclic aryl, a fused-ring aryl, or a polycyclic aryl, and for polycyclic rings, at least one is an aromatic ring system. For example, "C6-C18 aryl" refers to an aryl group containing 6 to 18 carbon atoms, and each occurrence can be independently C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, or C18 aryl (the meaning of other aryl groups with different carbon numbers is similar). Suitable examples include, but are not limited to, benzene, biphenyl, naphthalene, anthracene, phenanthrene, dinaphthalene, triphenylene, and their derivatives.

[0077] In traditional methods, hydrogenated nitrile rubber is typically used as a dispersant in the positive electrode active layer of lithium-ion batteries to improve the dispersion of components in the slurry and reduce film resistance. However, the film resistance remains relatively high. Furthermore, the winding and pressing processes used in lithium-ion battery production can easily cause the positive electrode active layer to crack due to its poor brittleness. Therefore, improving the flexibility of the positive electrode active layer and reducing cracking is a pressing issue that needs to be addressed.

[0078] Some embodiments of this application provide a lithium-ion battery, including a positive electrode sheet, the positive electrode sheet including a positive active layer, the positive active layer comprising a positive active material, a dispersant and a softener; the dispersant comprising hydrogenated nitrile rubber, and the softener comprising a compound containing linear segments.

[0079] In the aforementioned lithium-ion battery, hydrogenated nitrile butadiene rubber is introduced as a dispersant in the positive electrode active layer, along with a compound containing linear segments as a flexible agent. The linear segments in the flexible agent synergistically work with the butadiene structural units in the hydrogenated nitrile butadiene rubber to reduce the brittleness of the positive electrode sheet, improve its flexibility, and effectively enhance the dispersibility of the material in the slurry, reducing gelation and thus lowering the film resistance of the lithium-ion battery. The possible reason for this is:

[0080] On the one hand, the linear segments in the softener and the butadiene structural units in the hydrogenated nitrile rubber are both flexible segments. Moreover, these flexible segments have less linear branching and lower rotational energy barriers, which can be embedded into other components, such as the segments of the binder, to increase the slippage ability of the material, improve the flexibility of the positive electrode sheet, and reduce the problem of cracking in the positive electrode active layer due to poor brittleness.

[0081] On the other hand, the butadiene structural unit in hydrogenated nitrile rubber is an alkyl segment with a relatively long chain length and a certain degree of branching. The linear segment in the softener is similar. Both can fully expand in the slurry solvent, generate steric hindrance, reduce the proximity between material particles, thereby improving the dispersion of the material in the slurry, reducing gelation, and lowering the membrane resistance of lithium-ion batteries.

[0082] In addition, the reduction in membrane resistance can improve the initial coulombic efficiency and cycle capacity retention of lithium-ion batteries.

[0083] Furthermore, the problem of poor brittleness in traditional positive electrode sheets is addressed in thick-coated positive electrode sheets (where the coating amount of the positive active layer per unit area is ≥300 mg / 1540.25 mm²). 2 This is particularly evident in the case of the thick-coated positive electrode sheet, where the use of the aforementioned flexible agent can significantly improve the brittleness and enhance the flexibility of the sheet.

[0084] Without limitation, the presence of hydrogenated nitrile butadiene rubber and compounds containing linear segments in the positive electrode active layer can be obtained by separating and purifying the material of the positive electrode active layer (such as by organic solvent extraction or thin-layer chromatography), and then confirming the presence of hydrogenated nitrile butadiene rubber and polymers containing linear segments by means of characteristic peaks in gas chromatography-mass spectrometry and infrared spectroscopy.

[0085] In some embodiments, the linear segment comprises one or more copolymer segments selected from C6-C18 alkyl, aryl-O-C6-C36 alkyl, polar group-substituted C2-C18 alkyl, polar group-substituted aryl-O-C6-C24 alkyl, polyether segment, polyamine segment, and polysiloxane segment. Further, each polar group independently comprises one or more selected from ester group, amide group, carboxyl group, hydroxyl group, and amino group. Introducing the above-mentioned polar groups with conjugated structures into the alkyl group can improve the conductivity of the softener, further reduce the film resistance of the lithium-ion battery, and improve the cycle performance of the lithium-ion battery. Without limitation, there can be one or more polar groups. In some embodiments, the number of polar groups is 1 to 2.

[0086] In some embodiments, the flexible agent comprises polyether segments and has the following structural features:

[0087] Each of R1 independently comprises a C1-C18 alkyl group or a C6-C12 aryl group;

[0088] G1 and G2 each independently include C1-C18 alkyl, C6-C18 aryl, C1-C18 ester, C1-C18 amide, C1-C18 aminocarbamate or hydroxyl groups;

[0089] 10 ≤ n1 ≤ 500. Further, 10 ≤ n1 ≤ 50. Specifically, the value of n1 includes, but is not limited to: 10, 15, 20, 25, 30, 35, 40, 45, 50, or any two of the aforementioned values.

[0090] In some embodiments, the flexible agent comprises polyamine segments and has the following structural features:

[0091] Each of R2 independently comprises a C1-C18 alkyl group or a C6-C12 aryl group;

[0092] R3 each independently includes H, C1-C18 alkyl or C6-C12 aryl;

[0093] G3 and G4 each independently include C1-C18 alkyl, C6-C18 aryl, C1-C18 ester, C1-C18 amide or amino groups;

[0094] 10 ≤ n² ≤ 500. Further, 10 ≤ n² ≤ 50. Specifically, the value of n² includes, but is not limited to: 10, 15, 20, 25, 30, 35, 40, 45, 50, or any two of the aforementioned values.

[0095] In some embodiments, the flexible agent comprises a copolymer segment of polyamine and polyether segments, and the flexible agent has the following structural features:

[0096] Each of R4 independently comprises a C1-C18 alkyl group or a C6-C12 aryl group;

[0097] R5 each independently includes H, C1-C18 alkyl or C6-C12 aryl;

[0098] Each R6 independently comprises a C1-C18 alkyl group or a C6-C12 aryl group;

[0099] G5 and G6 each independently include C1-C18 alkyl, C6-C18 aryl, C1-C18 ester, C1-C18 amide, C1-C18 aminocarbamate, hydroxyl or amino groups;

[0100] 10 ≤ n³ + n⁴ ≤ 500. Further, 10 ≤ n³ + n⁴ ≤ 50. Specifically, the values ​​of n³ + n⁴ include, but are not limited to: 10, 15, 20, 25, 30, 35, 40, 45, 50, or any two of the aforementioned values.

[0101] In some embodiments, the flexible agent comprises polysiloxane segments, and the flexible agent has the following structural features:

[0102] Wherein, R7 and R8 each independently include C1-C18 alkyl, C6-C12 aryl, polyether segment or polyoxyethylene ether / polyoxypropylene ether copolymer segment; G7 and G8 each independently include C1-C18 alkyl, C6-C12 aryl, hydroxyl or amino group; without limitation, in this structural feature, the polyether segment may have the following structure: 2≤n6≤10, 2≤n7≤100, G9 includes C1~C18 alkyl or C6~C12 aryl; the polyoxyethylene ether polyoxypropylene ether copolymer segment can have the following structure: 2≤n8≤50, 1≤n9≤50, G 10 Including C1-C18 alkyl or C6-C12 aryl;

[0103] 10 ≤ n5 ≤ 500. Further, 10 ≤ n5 ≤ 50. Specifically, the value of n5 includes, but is not limited to: 10, 15, 20, 25, 30, 35, 40, 45, 50, or any two of the aforementioned values.

[0104] By employing flexible agents with suitable structures, the flexibility of the positive electrode sheet can be further improved, cracking reduced, film resistance lowered, and the initial coulombic efficiency and cycle capacity retention of lithium-ion batteries enhanced. Furthermore, by rationally controlling the lengths (n values) of the linear segments in the flexible agent, lower brittleness and film resistance of the positive electrode sheet can be achieved, along with higher initial coulombic efficiency and cycle capacity retention. Understandably, in the structural characteristics of the aforementioned flexible agents, the substituents in each structural unit can be the same or different; when different, it constitutes a copolymer of different structural units. Understandably, the degree of polymerization (n, i.e., the aforementioned length) of one or more copolymer segments selected from polyether segments, polyamine segments, and polysiloxane segments is 10–500.

[0105] Without limitation, the structure of the flexible agent can be obtained by separating and purifying the material of the positive electrode active layer (such as by organic solvent extraction or thin-layer chromatography), and then confirming the structure by characteristic peaks and peak areas in gas chromatography-mass spectrometry, infrared spectroscopy, and nuclear magnetic resonance spectroscopy.

[0106] In some embodiments, the compound contains heteroatoms, including one or more of O, N, and P. Introducing heteroatoms into the compound can improve the overall flexibility of the positive electrode sheet and reduce cracking, possibly because the presence of heteroatoms can better disrupt the hydrogen bonding between other components, such as binder segments, reducing their crystallinity.

[0107] Without limitation, N and P can be tested using phosphorus and nitrogen spectra, while O atoms, mainly derived from ether bonds, can be identified using carbon and hydrogen spectra of the linked C atoms.

[0108] In some embodiments, the mass ratio of the flexible agent to the dispersant is 10:1 to 1:10. The flexible agent and dispersant have a certain competitive relationship in their effects; a higher number of linear segments results in better flexibility but also a greater tendency to aggregate, and vice versa. Reasonably controlling the mass ratio of the two can achieve both lower film resistance and better electrode flexibility. Specifically, the mass ratio of the flexible agent to the dispersant includes, but is not limited to: 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, or any range between the foregoing. Further, the mass ratio of the flexible agent to the dispersant is 3:1 to 1:3.

[0109] Without limitation, the mass ratio of the softening agent to the dispersant can be separated by gas chromatography or thin-layer chromatography to obtain their respective contents.

[0110] In some embodiments, the weight-average molecular weight of the hydrogenated nitrile butadiene rubber is 500–1,000,000. Reasonably controlling the weight-average molecular weight of the hydrogenated nitrile butadiene rubber can reduce its intermolecular forces and structural rigidity while maintaining a certain number of flexible segments and cyano-anchoring groups. This facilitates better dissolution and dispersion in the slurry, thereby improving the dispersion stability of the slurry, reducing diaphragm resistance, and simultaneously giving the electrode better flexibility. Specifically, the weight-average molecular weight of the hydrogenated nitrile rubber includes, but is not limited to, 500, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500, 100000, 200000, 250000, 300000, 350000, 400000, 450000, 500000, 600000, 1000000, or any two of the foregoing. Further, the weight-average molecular weight is 1000 to 200000.

[0111] Without restriction, a Waters 2695 Isocratic HPLC gel electrophoresis system (differential refractive index detector 2141) was used. A 3.0% polystyrene solution was used as a reference, and a matched column (oil-based: Styragel HT5DMF7.8 300mm + Styragel HT4) was selected. A 3.0% polymer solution was prepared using purified N-methylpyrrolidone (NMP) solvent and allowed to stand for one day. For testing, tetrahydrofuran was first used to flush the syringe, repeated several times. Then, 5 mL of the test solution was drawn, air was expelled from the syringe, and the needle tip was dried. Finally, the sample solution was slowly injected into the injection port. Data was acquired after the reading stabilized.

[0112] In some embodiments, the hydrogenation ratio of the hydrogenated nitrile rubber is 10% to 100%. Different hydrogenation ratios correspond to different proportions of double bonds. The proportion of double bonds affects the subsequent crosslinking of the polymer, which in turn affects the expansion of flexible segments in the slurry solvent and the magnitude of steric hindrance. Reasonably controlling the hydrogenation ratio can further improve the dispersion stability of the slurry, reduce the membrane resistance, and simultaneously give the electrode better flexibility. Specifically, the hydrogenation ratio of the hydrogenated nitrile rubber includes, but is not limited to: 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or any range between the foregoing. Further, the hydrogenation ratio is 30% to 50%.

[0113] Understandably, the "hydrogenation ratio" refers to the following: if the molar content of double bonds in nitrile rubber is P1, and the molar content of double bonds in the hydrogenated nitrile rubber obtained after hydrogenation is P2, then the hydrogenation ratio is (P1-P2) / P1. Here, nitrile rubber and its hydrogenated counterpart have similar structural units; for example, the molar proportions of butadiene structural units (including hydrogenated and unhydrogenated) and acrylonitrile are consistent. By detecting the molar proportions of butadiene structural units (including hydrogenated and unhydrogenated) and acrylonitrile in the hydrogenated nitrile rubber, the corresponding nitrile rubber raw material can be derived in reverse, thus obtaining the P1 value.

[0114] Without limitation, the molar content of double bonds can be determined by the iodine value method: Weigh a certain amount of the test sample, dissolve it in chloroform, then add a certain amount of Widmanstätten reagent (ICl), allowing the test sample to react fully with the Widmanstätten reagent. After the specified reaction time, add potassium iodide and water, and finally titrate with sodium thiosulfate until the yellow color almost disappears. Then add starch solution, continue titrating while shaking vigorously until the blue color just disappears. The content of double bonds in the test sample can be calculated by the amount of sodium thiosulfate used in the titration. Repeat the above test procedure twice for the same sample and take the average value.

[0115] In some embodiments, the molar percentage of acrylonitrile structural units in the hydrogenated nitrile butadiene rubber is 5% to 30%. The cyano groups in the acrylonitrile structural units act as anchoring groups, which can anchor to the positive electrode active material through coordination, thereby improving dispersion performance. Reasonably controlling this molar percentage can achieve good anchoring while maintaining good flexibility in the hydrogenated nitrile butadiene rubber, further improving the dispersion stability of the slurry, reducing diaphragm resistance, and simultaneously giving the electrode good flexibility. Specifically, the molar percentage of acrylonitrile structural units in the hydrogenated nitrile butadiene rubber includes, but is not limited to: 5%, 10%, 15%, 20%, 25%, 30%, or any range between the foregoing. Further, the molar percentage of acrylonitrile structural units is 10% to 20%.

[0116] Without limitation, the molar percentage of acrylonitrile structural units in the hydrogenated nitrile rubber can be converted into free cyano groups by ignition, and then the cyano groups can be titrated to determine the molar percentage.

[0117] In some embodiments, the flexible agent comprises 0.05% to 0.5% by mass in the positive electrode active layer. Reasonably controlling the mass percentage of the flexible agent in the positive electrode active layer can improve the flexibility of the electrode, enhance the dispersion stability of the slurry, reduce film resistance, and also minimize the impact on the electrical performance of the lithium-ion battery (such as cycle performance). Specifically, the mass percentage of the flexible agent in the positive electrode active layer includes, but is not limited to: 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or any range between the foregoing. Further, the mass percentage of the flexible agent in the positive electrode active layer is 0.2% to 0.4%.

[0118] Without limitation, the mass percentage of the flexible agent in the positive electrode active layer can be obtained by separating and purifying the material of the positive electrode active layer (e.g., by organic solvent extraction or thin-layer chromatography) to obtain the flexible agent and calculate its mass.

[0119] Furthermore, it is understandable that the aforementioned different types of softeners and hydrogenated nitrile butadiene rubber can be obtained commercially or synthesized using conventional methods by purchasing the corresponding monomers (both commercially available). For example, the synthesis method of hydrogenated nitrile butadiene rubber typically includes the following steps:

[0120] (1) Butadiene and acrylonitrile were copolymerized to prepare an intermediate;

[0121] (2) The intermediate is subjected to Pd / C catalytic hydrogenation to prepare hydrogenated nitrile rubber.

[0122] In this step, hydrogenated nitrile butadiene rubbers with different weight-average molecular weights, hydrogenation ratios, or molar percentages of acrylonitrile structural units can be prepared by controlling the ratio of butadiene to acrylonitrile, reaction temperature, reaction time, hydrogenation pressure, etc.

[0123] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As a non-limiting example, the positive electrode active material may include one or more of the following materials: lithium-containing 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, one or more of lithium cobalt oxides (such as LiCoO2), lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium manganese iron phosphate and carbon composites. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include 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 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.8 Co 0.15 Al0.05 O2. Furthermore, the positive electrode active material includes lithium iron phosphate. The cyano group readily coordinates with the Fe in lithium iron phosphate, thereby improving the stability and dispersibility of the slurry.

[0124] It is understood that the lithium iron phosphate described in this application may include lithium iron phosphate material itself, or lithium iron phosphate products obtained by doping and / or coating lithium iron phosphate material with trace elements.

[0125] In some embodiments, the particle size D50 of the positive electrode active material is 0.2 micrometers (μm) to 20 μm.

[0126] In some embodiments, the positive electrode active layer further includes a binder.

[0127] As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. Further, the binder includes polyvinylidene fluoride. Using polyvinylidene fluoride as a binder results in better flexibility, presumably because linear segments and butadiene structural units are more easily inserted into the polyvinylidene fluoride segments, enhancing its slippage ability and thus improving the flexibility of the electrode.

[0128] In some embodiments, the adhesive has a mass percentage of 1% to 2.5%.

[0129] Other embodiments of this application provide a method for preparing a lithium-ion battery as described above, including a step for preparing a positive electrode active layer:

[0130] A positive electrode slurry is prepared by mixing the components of the positive electrode active layer with a solvent; the components of the positive electrode active layer include a positive electrode active material, a dispersant, and a softener; the dispersant includes hydrogenated nitrile rubber, and the softener includes a compound containing linear segments;

[0131] The positive electrode slurry is molded to prepare the positive electrode active layer.

[0132] The preparation method is simple and easy to apply in industrial processes.

[0133] Without limitation, dispersants and softeners can be added to the remaining components after pre-mixing, or they can be added to the remaining components sequentially.

[0134] In some embodiments, the step of mixing the components of the positive electrode active layer and the solvent includes:

[0135] First, the dispersant, softener, and part of the solvent are mixed, and then the resulting mixture is mixed with the remaining components; wherein the solid content of the mixture is 5% to 75%.

[0136] Premixing the dispersant, softener, and a portion of the solvent, and appropriately controlling the solid content of the mixture, can improve the uniformity of their dispersion in the slurry, thus maximizing their effectiveness. Specifically, the solid content of the mixture includes, but is not limited to: 5%, 7%, 10%, 13%, 15%, 17%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or any range between the two aforementioned.

[0137] Without limitation, the solid content can be tested by the following method: Weigh the copper foil in a loss rate measuring instrument and record it as M0, then zero the instrument; take a small amount of the mixture and coat it on the copper foil, then weigh it in a moisture analyzer and record it as M1; close the instrument and start drying; after the drying is completed, record the weighing data as M2, and calculate the solid content, which is (M2-M0) / (M1-M0).

[0138] Another embodiment of this application provides a lithium-ion battery. This lithium-ion battery includes the aforementioned positive electrode.

[0139] Another embodiment of this application provides an electrical device. The electrical device includes at least one of the above-described positive electrode and the above-described lithium-ion battery.

[0140] The lithium-ion battery and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0141] Typically, a lithium-ion 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 extracting. 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.

[0142] The positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, as described above, and will not be repeated here.

[0143] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0144] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on a polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymer material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0145] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0146] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as positive electrode active material, polymer, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents described in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface or both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%, where "wt%" represents mass percentage. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s. When coating the positive electrode slurry, the coating areal density per unit area, based on dry weight (excluding solvent), can be 15 mg / cm². 2 )~35mg / cm 2 The compacted density of the positive electrode sheet can be 3.0 g / cm³. 3 ~3.6g / cm 3 3.3g / cm³ is an option. 3 ~3.5g / cm 3 .

[0147] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0148] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0149] 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 polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the negative electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0150] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, 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.

[0151] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more 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).

[0152] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0153] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0154] 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 (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing, and other processes. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s. When coating the negative electrode slurry, the coating unit areal density (dry weight, minus solvent) can be 75 g / m². 2 )~220g / m 2 The compaction density of the negative electrode sheet can be 1.0 g / cm³. 3 ~1.8g / cm 3 .

[0155] Electrolytes function to conduct ions between the positive and negative electrode plates. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0156] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent.

[0157] In some embodiments, the electrolyte salt may include 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 difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0158] In some embodiments, the solvent may include 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), butene carbonate Fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0159] 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 may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0160] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0161] In some embodiments, the lithium-ion battery also includes a separator. 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.

[0162] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0163] In some embodiments, the thickness of the isolation membrane is 6 μm to 40 μm, and optionally 12 μm to 20 μm.

[0164] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0165] In some embodiments, the lithium-ion battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0166] In some embodiments, the outer packaging of the lithium-ion battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the lithium-ion battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastics can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0167] A lithium-ion battery includes at least one battery cell. A lithium-ion battery may include one or more battery cells.

[0168] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and generally includes at least a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the battery, active ions move back and forth between the positive and negative electrode plates, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrode plates.

[0169] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square-structured lithium-ion battery 10 as an example.

[0170] In some embodiments, referring to FIG2, the outer packaging may include a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator can be formed into electrode assemblies 12 via a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The lithium-ion battery 10 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to actual needs.

[0171] Lithium-ion batteries can be battery modules or battery packs.

[0172] A battery module includes at least one battery cell. The number of battery cells in a battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0173] In a battery module, multiple battery cells can be arranged sequentially along the length of the module. Of course, they can also be arranged in any other manner. Furthermore, these battery cells can be secured using fasteners.

[0174] Optionally, the battery module may also include a housing with a receiving space in which multiple battery cells are housed.

[0175] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the battery pack may contain one or more battery modules. Those skilled in the art can select an appropriate number based on the application and capacity of the battery pack.

[0176] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0177] In addition, this application also provides an electrical device, which includes the lithium-ion battery provided in this application. The lithium-ion battery 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, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0178] As an electrical device, lithium-ion batteries can be selected based on its usage requirements.

[0179] Figure 3 shows an example of an electrical device 20. This electrical device 20 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the lithium-ion battery for this electrical device, a battery pack or battery module can be used.

[0180] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0181] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0182] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0183] The test methods involved in the embodiments are as follows:

[0184] (1) Brittleness test of positive electrode sheet:

[0185] Take a positive electrode sheet without obvious defects and cut it longitudinally into samples with a length × width of 20cm × 2.5cm. The number of samples should be ≥8. First, pre-fold the sample in half. Then, place the sheet on the testing platform and roll it once with a 2kg cylindrical roller. If light is transmitted, the brittle light transmission test is performed once. If light is not transmitted, repeat the reverse folding and rolling test. Observe the crease against the light to check for light transmission or breakage. Record the actual number of folds and take the average as the test result.

[0186] (2) Diaphragm resistance (DCR) test:

[0187] Cut the dried positive electrode slurry (film layer) into small round pieces with a diameter of 3mm from the left, center, and right sides of the positive electrode sheet. Turn on the power of the Yuaneng Technology electrode resistance meter, place the probe at the appropriate position on the meter, and click the "Start" button. Wait for the reading to stabilize and then take the reading. Test two positions for each small round piece, and finally calculate the average of the six measurements, which is the resistance of the electrode film layer.

[0188] (3) Initial Coulomb efficiency:

[0189] At 25°C, the batteries of the above embodiments and comparative examples were charged at a constant current rate of 0.1C to a voltage of 3.65V. The charging capacity at this time was recorded as the first charge capacity of the lithium-ion battery. After resting for 5 minutes, the batteries were discharged at a constant current rate of 0.1C to a voltage of 2.0V and then rested for 5 minutes. This is one charge-discharge cycle. The discharge capacity of this cycle was recorded as the first discharge capacity of the lithium-ion battery, which is the initial capacity of the lithium-ion battery.

[0190] The first-cycle coulombic efficiency (%) of a lithium-ion battery = first-cycle discharge capacity / first-cycle charge capacity × 100%.

[0191] (4) Cyclic capacity retention:

[0192] 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 C of the battery after the nth cycle was recorded. n Then, the battery capacity retention rate after each cycle is: Pn = C n / C0×100%

[0193] 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 1 is the data measured after 300 cycles under the above test conditions, i.e., the value of P300.

[0194] Example 1

[0195] 1) Preparation of positive electrode sheet

[0196] Lithium iron phosphate (particle size D50 = 1.5 μm), conductive carbon black SP, binder PVDF, hydrogenated nitrile rubber, and softener 1 were weighed in a weight ratio of 97%:1.5%:1%:0.25%:0.25%. Hydrogenated nitrile rubber (weight average molecular weight 200,000, hydrogenation ratio 50%, acrylonitrile structural unit molar percentage 15%), softener 1, and an appropriate amount of solvent NMP were mixed to achieve a solid content of 50%, thus preparing a mixture. This mixture was then further dispersed in NMP along with the lithium iron phosphate, conductive carbon black SP, and binder PVDF, and mixed thoroughly to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto both sides of a positive electrode current collector aluminum foil. After drying and cold pressing, a positive electrode sheet was obtained, with a coating weight per unit area of ​​0.33 g / 1540.25 mm² on both sides. 2 .

[0197] 2) Preparation of negative electrode sheet

[0198] Artificial graphite (negative electrode active material), carbon black (Super P) (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) were mixed in a mass ratio of 96.4%:0.7%:1.8%:1.1%. Deionized water was added, and the mixture was stirred under vacuum to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto both sides of a copper foil. After the copper foil was dried at room temperature, it was transferred to a 120°C oven and dried for 1 hour. Then, it was cold-pressed and slit to obtain a negative electrode sheet, with a coating amount of 0.17 g / 1540.25 mm² on both sides. 2 .

[0199] 3) Separating membrane

[0200] A 12μm thick polypropylene separator membrane was selected.

[0201] 4) Preparation of electrolyte

[0202] The organic solvent consisted of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed uniformly at a volume ratio of 3 / 7. The thoroughly dried lithium salt LiPF6 was dissolved in the organic solvent and mixed uniformly in an argon-atmosphere glove box with a water content of <10 ppm and O2 of <0.1 ppm to obtain the electrolyte. The lithium salt comprised 12.5% ​​by mass.

[0203] 5) Battery manufacturing

[0204] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. After being wound into a square bare cell, it is placed in an aluminum-plastic film, baked at 80°C to remove water, and then 10g of the corresponding non-aqueous electrolyte is injected and sealed. After processes such as standing, hot and cold pressing, formation, clamping, and capacity testing, the finished lithium-ion battery is obtained.

[0205] The softening agent 1 used in Example 1 has the following structural characteristics: Me-O-(EO) 20 -(PO) 15 -OH.

[0206] The lithium-ion battery preparation method in Example 2 is similar to that in Example 1, the main difference being that flexible agent 2 is used instead of flexible agent 1. Flexible agent 2 has the following structural characteristics: Me-(NH-CH2-CH2) 35 -NH2.

[0207] The softening agent 2-1 used in Example 2-1 has the following structural characteristics: Me-(NH-CH2-CH2) 10 -NH2.

[0208] The softening agent 2-2 used in Example 2-2 has the following structural characteristics: Me-(NH-CH2-CH2) 50 -NH2.

[0209] The softening agent 2-3 used in Examples 2-3 has the following structural characteristics: Me-(NH-CH2-CH2) 500 -NH2.

[0210] The lithium-ion battery preparation method in Example 3 is similar to that in Example 1, the main difference being that flexible agent 3 is used instead of flexible agent 1. Flexible agent 3 has the following structural characteristics: Me-(NH-CH2-CH2). 10 -(EO) 25 -OH.

[0211] Example 4 is similar to the lithium-ion battery preparation method in Example 1, the main difference being that: flexible agent 4 is used instead of flexible agent 1, and flexible agent 4 has the following structural features:

[0212] Example 5 is similar to the lithium-ion battery preparation method in Example 1, the main difference being that: flexible agent 5 is used instead of flexible agent 1, and flexible agent 5 has the following structural features:

[0213] Example 6 is similar to the lithium-ion battery preparation method in Example 1, the main difference being that: flexible agent 6 is used instead of flexible agent 1, and flexible agent 6 has the following structural features: C 16 H 34 .

[0214] Example 7 is similar to the lithium-ion battery preparation method in Example 1, the main difference being that: flexible agent 7 is used instead of flexible agent 1, and flexible agent 7 has the following structural characteristics: Ph-OC 10 H 21 .

[0215] The parameters for Examples 1-2, 2-1, 2-2, 2-3 and Examples 3-7 are summarized in Table 1 below:

[0216] Table 1

[0217] Examples 8-11 are similar to the lithium-ion battery preparation method in Example 1, the main difference being that different mass ratios of the flexible agent to the hydrogenated nitrile rubber are used, while the total weight percentage of the hydrogenated nitrile rubber and the flexible agent in the positive electrode active layer is kept constant at 0.5%.

[0218] The parameters for Examples 1, 8-11 are summarized in Table 2 below:

[0219] Table 2

[0220] Examples 12-17 are similar to the lithium-ion battery preparation methods in Example 1, the main difference being that different weight-average molecular weights of hydrogenated nitrile rubber are used.

[0221] The parameters for Examples 1, 12-17 are summarized in Table 3 below:

[0222] Table 3

[0223] Examples 18-20 are similar to the lithium-ion battery preparation method in Example 1, the main difference being that different hydrogenation ratios of hydrogenated nitrile rubber are used.

[0224] The parameters for Examples 1, 18-20 are summarized in Table 4 below:

[0225] Table 4

[0226] Examples 21-24 are similar to the lithium-ion battery preparation method in Example 1, the main difference being the different molar percentages of acrylonitrile structural units in hydrogenated nitrile rubber.

[0227] The parameters for Examples 1 and 21-24 are summarized in Table 5 below:

[0228] Table 5

[0229] Examples 25 and 26 are similar to the lithium-ion battery preparation method in Example 1, the main difference being that different solid contents of the mixture are used.

[0230] The parameters for Examples 1 and 25-26 are summarized in Table 6 below:

[0231] Table 6

[0232] Note: In Example 26, the solid content of the mixture is 100%, which means that in the step of "1) Preparation of positive electrode sheet", the hydrogenated nitrile rubber, softener 1, positive electrode active material lithium iron phosphate, conductive carbon black SP and binder PVDF are directly dispersed in the solvent NMP, without mixing with an appropriate amount of solvent NMP in advance.

[0233] Examples 27 and 28 are similar to the lithium-ion battery preparation method in Example 1, the main difference being that different mass percentages of flexible agents are used in the positive electrode active layer, and the mass percentage of positive electrode active material in the positive electrode active layer is adjusted accordingly to meet 100%.

[0234] The parameters for Examples 1 and 27-28 are summarized in Table 7 below:

[0235] Table 7

[0236] The lithium-ion battery preparation method of Comparative Example 1 is similar to that of Example 1, the main difference being that: flexible agent 1 was not used, and the mass percentage of positive electrode active material in the positive electrode active layer was adjusted accordingly to meet 100%.

[0237] Comparative Example 2 is similar to the lithium-ion battery preparation method in Example 1, the main difference being that hydrogenated nitrile rubber was not used, and the mass percentage of positive electrode active material in the positive electrode active layer was adjusted accordingly to meet 100%.

[0238] The parameters of Example 1 and Comparative Examples 1 and 2 are summarized in Table 8 below:

[0239] Table 8

[0240] As can be seen from Tables 1 to 8, compared with Comparative Examples 1 to 2, Examples 1 to 28 can all reduce the brittleness of the positive electrode, obtain lower film resistance, and improve the first coulombic efficiency and cycle capacity retention of the battery.

[0241] A comparison between Examples 1-7 shows that using a suitable flexible agent structure can achieve lower brittleness and film resistance in the positive electrode, as well as higher initial coulombic efficiency and cycle capacity retention. Furthermore, a comparison between Example 2 and Examples 2-1 to 2-3 shows that properly controlling the length (n value) of the linear segments in the flexible agent can achieve lower brittleness and film resistance in the positive electrode, as well as higher initial coulombic efficiency and cycle capacity retention.

[0242] A comparison between Examples 1 and Examples 8-11 shows that by properly controlling the mass ratio of the softener to the hydrogenated nitrile rubber, lower brittleness of the positive electrode and film resistance, as well as higher initial coulombic efficiency and cycle capacity retention can be obtained.

[0243] A comparison between Example 1 and Examples 12-17 shows that by properly controlling the weight-average molecular weight of hydrogenated nitrile rubber, lower brittleness of the positive electrode and film resistance, as well as higher initial coulombic efficiency and cycle capacity retention can be obtained.

[0244] A comparison between Example 1 and Examples 18-20 shows that by reasonably controlling the hydrogenation ratio of hydrogenated nitrile rubber, lower brittleness of the positive electrode and film resistance, as well as higher initial coulombic efficiency and cycle capacity retention can be obtained.

[0245] A comparison between Example 1 and Examples 21-24 shows that by reasonably controlling the molar ratio of acrylonitrile structural units in hydrogenated nitrile rubber, lower brittleness of the positive electrode and film resistance, as well as higher initial coulombic efficiency and cycle capacity retention can be obtained.

[0246] A comparison between Example 1 and Examples 25-26 shows that, compared with direct mixing, mixing the materials with the solvent and preparing a slurry with a suitable solid content can achieve lower brittleness of the positive electrode and film resistance, as well as higher initial coulombic efficiency and cycle capacity retention.

[0247] A comparison between Example 1 and Examples 27-28 shows that by reasonably controlling the proportion of the flexible agent in the positive electrode active layer, lower brittleness and film resistance of the positive electrode sheet can be obtained, as well as higher initial coulombic efficiency and cycle capacity retention.

[0248] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0249] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A lithium-ion battery, comprising a positive electrode sheet, the positive electrode sheet comprising a positive active layer, the positive active layer comprising a positive active material, a dispersant, and a softener; the dispersant comprising hydrogenated nitrile rubber, and the softener comprising a compound containing linear segments.

2. The lithium-ion battery according to claim 1, wherein, The linear segments include one or more copolymer segments selected from C6-C18 alkyl, aryl-O-C6-C36 alkyl, polar group-substituted C2-C18 alkyl, polar group-substituted -O-C6-C24 alkyl carbon chains, polyether segments, polyamine segments, and polysiloxane segments.

3. The lithium-ion battery according to claim 2, wherein, Each of the polar groups independently includes one or more of the following: ester group, amide group, carboxyl group, hydroxyl group, and amino group.

4. The lithium-ion battery according to any one of claims 1 to 3, wherein, The softener comprises polyether segments and has the following structural features: Each of R1 independently comprises a C1-C18 alkyl group or a C6-C12 aryl group; G1 and G2 each independently include C1-C18 alkyl, C6-C18 aryl, C1-C18 ester, C1-C18 amide, C1-C18 aminocarbamate or hydroxyl groups; 10≤n1≤500。 5. The lithium-ion battery according to any one of claims 1 to 3, wherein, The softener comprises polyamine segments and has the following structural features: Each of R2 independently comprises a C1-C18 alkyl group or a C6-C12 aryl group; R3 each independently includes H, C1-C18 alkyl or C6-C12 aryl; G3 and G4 each independently include C1-C18 alkyl, C6-C18 aryl, C1-C18 ester, C1-C18 amide or amino groups; 10≤n2≤500。 6. The lithium-ion battery according to any one of claims 1 to 3, wherein, The softening agent comprises copolymer segments of polyamine and polyether segments, and the softening agent has the following structural features: Each of R4 independently comprises a C1-C18 alkyl group or a C6-C12 aryl group; R5 each independently includes H, C1-C18 alkyl or C6-C12 aryl; Each R6 independently comprises a C1-C18 alkyl group or a C6-C12 aryl group; G5 and G6 each independently include C1-C18 alkyl, C6-C18 aryl, C1-C18 ester, C1-C18 amide, C1-C18 aminocarbamate, hydroxyl or amino groups; 10≤n3+n4≤500.

7. The lithium-ion battery according to any one of claims 1 to 3, wherein, The softener comprises polysiloxane segments and has the following structural features: R7 and R8 each independently include C1-C18 alkyl, C6-C12 aryl, polyether segments or polyoxyethylene ether-polyoxypropylene ether copolymer segments; G7 and G8 each independently include C1-C18 alkyl, C6-C12 aryl, hydroxyl or amino groups; 10≤n5≤500。 8. The lithium-ion battery according to any one of claims 1 to 7, wherein, The compound contains heteroatoms, which include one or more of O, N, and P.

9. The lithium-ion battery according to any one of claims 1 to 8, wherein, The mass ratio of the softening agent to the dispersant is 10:1 to 1:

10.

10. The lithium-ion battery according to claim 9, wherein, The mass ratio of the softening agent to the dispersant is 3:1 to 1:

3.

11. The lithium-ion battery according to any one of claims 1 to 10, wherein, The hydrogenated nitrile rubber has at least one of the following characteristics (1) to (3): (1) Weight-average molecular weight is 500 to 1,000,000; (2) The hydrogenation ratio is 10% to 100%; the hydrogenation ratio refers to the following: the molar content of double bonds in the nitrile rubber is P1, and the molar content of double bonds in the hydrogenated nitrile rubber obtained after hydrogenation is P2, and the hydrogenation ratio is (P1-P2) / P1. (3) The molar percentage of acrylonitrile structural units is 5% to 30%.

12. The lithium-ion battery according to claim 11, wherein, The hydrogenated nitrile rubber has at least one of the following characteristics (1) to (3): (1) Weight-average molecular weight is 1,000 to 200,000; (2) The hydrogenation ratio is 30% to 50%; (3) The molar percentage of acrylonitrile structural units is 10% to 20%.

13. The lithium-ion battery according to any one of claims 1 to 12, wherein, The softening agent has a mass percentage of 0.05% to 0.5% in the positive electrode active layer.

14. The lithium-ion battery according to any one of claims 1 to 13, wherein, The coating amount of the positive electrode active layer in the positive electrode sheet is ≥300mg / 1540.25mm. 2 .

15. The lithium-ion battery according to any one of claims 1 to 14, wherein, The compaction density of the positive electrode sheet is 3.3 g / cm³. 3 ~3.6g / cm 3 .

16. The lithium-ion battery according to claim 15, wherein, The compaction density of the positive electrode sheet is 3.3 g / cm³. 3 ~3.5g / cm 3 .

17. The lithium-ion battery according to any one of claims 1 to 16, wherein, The positive electrode active material includes one or more of lithium transition metal oxides and lithium phosphates with an olivine structure.

18. The lithium-ion battery according to claim 17, wherein, The lithium transition metal oxide includes one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds; and / or The lithium phosphates with the olivine structure include one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

19. The lithium-ion battery according to any one of claims 1 to 18, wherein, The positive electrode active layer also includes a binder.

20. The lithium-ion battery according to claim 19, wherein, The adhesive has at least one of the following characteristics (1) to (2): (1) The adhesive includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorinated acrylate resin; (2) In the positive electrode active layer, the mass percentage of the binder is 1% to 2.5%.

21. A method for preparing a lithium-ion battery, comprising the step of preparing a positive electrode active layer: A positive electrode slurry is prepared by mixing the components of the positive electrode active layer with a solvent; the components of the positive electrode active layer include a positive electrode active material, a dispersant, and a softener; the dispersant includes hydrogenated nitrile rubber, and the softener includes a compound containing linear segments; The positive electrode slurry is molded to prepare the positive electrode active layer.

22. The method for preparing a lithium-ion battery according to claim 21, wherein, The step of mixing the components and solvent of the positive electrode active layer includes: First, the dispersant, softener, and part of the solvent are mixed, and then the resulting mixture is mixed with the remaining components; wherein the solid content of the mixture is 5% to 75%.

23. The method for preparing a lithium-ion battery according to claim 22, wherein, The solid content of the mixture is 7% to 20%.

24. A positive electrode sheet, the positive electrode sheet comprising a positive active layer, the positive active layer comprising a positive active material, a dispersant and a softener; the dispersant comprising hydrogenated nitrile rubber, the softener comprising a compound containing linear segments.

25. The positive electrode sheet according to claim 21, wherein, The positive electrode sheet in the lithium-ion battery according to any one of claims 2 to 20.

26. An electrical device comprising at least one of the following: a lithium-ion battery according to any one of claims 1 to 20, a lithium-ion battery prepared by the preparation method according to any one of claims 21 to 23, and a positive electrode according to any one of claims 24 to 25.

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