Lithium-ion battery, positive electrode sheet, and electrical device

Abstract

The present application provides a lithium-ion battery, a positive electrode sheet, and an electrical device. The positive electrode sheet comprises a positive electrode active layer. Components of the positive electrode active layer comprise a positive electrode active material and an additive. The positive electrode active material comprises lithium iron phosphate. The additive comprises hydrogenated nitrile butadiene rubber. The degree of hydrogenation of the hydrogenated nitrile butadiene rubber is 30% to 85%. The degree of hydrogenation is defined as follows: the molar content of double bonds in nitrile butadiene rubber is P1, the molar content of double bonds in the hydrogenated nitrile butadiene rubber obtained after corresponding hydrogenation is P2, and the degree of hydrogenation is (P1-P2) / P1. The film resistance of the lithium-ion battery is low.

Description

Lithium-ion batteries, 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 2024111959538, entitled "Lithium-ion Battery, Positive Electrode Sheet and Electrical Device", 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, a positive electrode sheet, and an electrical device. Background Technology

[0004] In recent years, the application of secondary batteries, such as lithium-ion batteries, has become increasingly widespread. They are now widely used in energy storage power systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, and electric vehicles. Due to the significant advancements in lithium-ion batteries, higher requirements have been placed on their energy density, cycle performance, and safety performance.

[0005] For battery systems using lithium iron phosphate as the positive electrode active material, hydrogenated nitrile rubber is usually used as a dispersant to improve the dispersibility of the slurry and thus reduce the film resistance. However, the slurry dispersibility of such battery systems needs further improvement. Summary of the Invention

[0006] To achieve the above objectives, this application provides a lithium-ion battery with low film resistance, a positive electrode, and an electrical device including the lithium-ion battery and the positive electrode.

[0007] In a first aspect, 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 and an additive, the positive electrode active material including lithium iron phosphate, the additive including hydrogenated nitrile rubber, the hydrogenation ratio of the hydrogenated nitrile rubber being 30% to 85%.

[0008] The hydrogenation ratio means that if 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, then the hydrogenation ratio is (P1-P2) / P1.

[0009] By reasonably controlling the hydrogenation ratio of hydrogenated nitrile rubber to 30%–85% in the above-mentioned lithium-ion batteries, a lower membrane resistance can be obtained.

[0010] In some embodiments, the hydrogenation ratio of the hydrogenated nitrile rubber is 55% to 70%.

[0011] In some embodiments, the hydrogenated nitrile rubber has at least one of the following features (1) to (2):

[0012] (1) Weight-average molecular weight is 500 to 1,000,000;

[0013] (2) The molar percentage of acrylonitrile structural units is 5% to 30%.

[0014] In some embodiments, the hydrogenated nitrile rubber has at least one of the following features (1) to (2):

[0015] (1) Weight-average molecular weight is 1,000 to 100,000;

[0016] (2) The molar percentage of acrylonitrile structural units is 10% to 20%.

[0017] Furthermore, by rationally controlling the weight-average molecular weight of the hydrogenated nitrile rubber and the molar proportion of acrylonitrile structural units, the dispersion stability of the slurry can be further improved, the membrane resistance can be reduced, the first coulombic efficiency of the lithium-ion battery can be improved, and better high-temperature cycle capacity retention can also be obtained.

[0018] In some embodiments, the hydrogenated nitrile rubber in the positive electrode active layer is 0.1% to 1% by mass.

[0019] In some embodiments, the lithium iron phosphate has a carbon coating layer on its surface. This carbon coating layer typically contains residues such as -OH and -COOH, which can form hydrogen bonds with the cyano groups in the hydrogenated nitrile rubber, thus improving the dispersion of the slurry.

[0020] In some embodiments, the degree of graphitization of the carbon coating is 10% to 30%.

[0021] A second aspect of this application provides a positive electrode sheet, the positive electrode sheet comprising a positive electrode active layer, the components of the positive electrode active layer comprising a positive electrode active material and an additive, the additive comprising hydrogenated nitrile butadiene rubber, the hydrogenation ratio of the hydrogenated nitrile butadiene rubber being 30% to 85%;

[0022] The hydrogenation ratio means that if 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, then the hydrogenation ratio is (P1-P2) / P1.

[0023] In some embodiments, the positive electrode is the same as the positive electrode in a lithium-ion battery as described above.

[0024] A third aspect of this application provides an electrical device comprising at least one of the lithium-ion battery and the positive electrode sheet as described above. Attached Figure Description

[0025] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort. In the drawings:

[0026] Figure 1 is a schematic diagram of a lithium-ion battery according to an embodiment of this application.

[0027] Figure 2 is an exploded view of a lithium-ion battery according to an embodiment of this application, as shown in Figure 1.

[0028] Explanation of reference numerals in the attached drawings: 1. Lithium-ion battery; 11. Casing; 12. Electrode assembly; 13. Cover plate. Detailed Implementation

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] Some embodiments of this application provide 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 and an additive, the positive electrode active material including lithium iron phosphate, the additive including hydrogenated nitrile rubber, the hydrogenation ratio of the hydrogenated nitrile rubber being 30% to 85%.

[0038] The hydrogenation ratio of hydrogenated nitrile butadiene rubber (NBR) in the aforementioned lithium-ion batteries is reasonably controlled between 30% and 85%. When the hydrogenation ratio is greater than 85%, the double bond content in the NBR is too low, resulting in high molecular regularity, which is not conducive to cross-linking and forming a cross-linked structure with large steric hindrance. This reduces the dispersibility and stability of the slurry, leading to higher membrane resistance. Conversely, when the hydrogenation ratio is less than 30%, the double bond content in the NBR is too high, resulting in excessive self-cross-linking and decreased dispersibility of lithium iron phosphate, also reducing the dispersibility and stability of the slurry and leading to higher membrane resistance. Therefore, by reasonably controlling the hydrogenation ratio of NBR in the lithium iron phosphate battery system to 30%–85%, a lower membrane resistance can be obtained. Furthermore, the reduction in membrane resistance can also improve the initial coulombic efficiency of the lithium-ion battery.

[0039] Understandably, compared to other cathode active materials, lithium iron phosphate exhibits poor dispersibility. This may be because, compared to other cathode active materials such as ternary materials, lithium iron phosphate has a smaller particle size, typically at the micrometer or even nanometer level, making it prone to agglomeration in the slurry. In some embodiments, the Dv50 of lithium iron phosphate is ≤100 micrometers, further ≤50 micrometers, even further ≤30 micrometers, and even further ≤10 micrometers. In some embodiments, the Dv50 of lithium iron phosphate is 0.1 micrometers to 10 micrometers.

[0040] In other embodiments of this application, using a hydrogenation ratio of 30% to 85% for hydrogenated nitrile butadiene rubber can also enable lithium-ion batteries to achieve better thermal stability and better cycle capacity retention under high-temperature conditions. When the hydrogenation ratio is less than 30%, the double bond content in the hydrogenated nitrile butadiene rubber is too high, making it prone to thermal decomposition, which significantly reduces heat resistance and thus affects the cycle capacity retention of the lithium-ion battery. When the hydrogenation ratio is greater than 85%, the double bond content in the hydrogenated nitrile butadiene rubber is too low, resulting in a low crosslinking ratio and a significant decrease in intermaterial adhesion under high-temperature conditions, which also reduces the cycle capacity retention of the battery.

[0041] 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.

[0042] 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 and shake 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. Titrate the same sample twice according to the above test steps and take the average value.

[0043] Specifically, the hydrogenation ratio of the hydrogenated nitrile rubber includes, but is not limited to, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or any range between the foregoing. Further, the hydrogenation ratio of the hydrogenated nitrile rubber is 55% to 70%.

[0044] 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 intermolecular forces and structural rigidity while maintaining a certain number of double bonds and cyano anchoring groups. This facilitates better dissolution and dispersion in the slurry, thereby further improving the dispersion stability of the slurry, reducing membrane resistance, increasing the initial coulombic efficiency of the lithium-ion battery, and also achieving better high-temperature cycle capacity retention. 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, 500000, 600000, 1000000, or any two of the foregoing. Further, the weight-average molecular weight is 1000 to 100000.

[0045] Without limitation, the weight-average molecular weight of the hydrogenated nitrile rubber can be determined by the following method:

[0046] 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 HT5 DMF7.8*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 as the sample. For testing, tetrahydrofuran was first used to flush the sample, repeated several times. Then, 5 mL of the experimental 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. After the reading stabilized, the data was obtained, which yielded the weight-average molecular weight.

[0047] 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 the dispersion performance of the polymer. Reasonably controlling the molar percentage of acrylonitrile structural units in the hydrogenated nitrile butadiene rubber can achieve good anchoring while retaining a certain number of double bonds, further improving the dispersion stability of the slurry, reducing membrane resistance, increasing the initial coulombic efficiency of the lithium-ion battery, and also achieving better high-temperature cycle capacity retention. 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%.

[0048] 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.

[0049] Without limitation, the end groups of the hydrogenated nitrile rubber include one or more of hydroxyl, carboxyl, alkoxy, phenoxy, alkyl ester, and aromatic ester groups.

[0050] Understandably, the different types of hydrogenated nitrile butadiene rubber mentioned above 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:

[0051] (1) Butadiene and acrylonitrile were copolymerized to prepare an intermediate;

[0052] (2) The intermediate is subjected to Pd / C catalytic hydrogenation to prepare hydrogenated nitrile rubber.

[0053] 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.

[0054] In some embodiments, the hydrogenated nitrile butadiene rubber in the positive electrode active layer is 0.1% to 1% by mass. Specifically, the mass percentage of the hydrogenated nitrile butadiene rubber includes, but is not limited to: 0.1%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any range between the foregoing.

[0055] Without limitation, the positive electrode active layer can be dissolved with an organic solvent and the inorganic particles can be filtered out. Then, a thin-layer chromatography column can be used for separation to obtain the amount of hydrogenated nitrile rubber, and then its mass percentage in the positive electrode active layer can be calculated.

[0056] Understandably, the lithium iron phosphate may include lithium iron phosphate material itself, or it may include lithium iron phosphate products obtained by trace element doping and / or coating of lithium iron phosphate material. In some embodiments, the surface of the lithium iron phosphate has a carbon coating layer. The carbon coating layer on the surface of the lithium iron phosphate typically contains residues such as -OH and -COOH, which can form hydrogen bonds with the cyano groups in the hydrogenated nitrile rubber, thereby improving the dispersion effect of the slurry. Further, the graphitization degree of the carbon coating layer is 10% to 30%. Reasonably controlling the graphitization degree of the carbon coating layer can enhance the hydrogen bonding interaction with the cyano groups in the hydrogenated nitrile rubber, thereby improving the dispersion effect of the slurry.

[0057] Without limitation, the degree of graphitization of the carbon coating can be determined by the mass percentage of carbon remaining after high-temperature burning.

[0058] In some embodiments, the positive electrode active layer also includes a conductive agent.

[0059] In some embodiments, the conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0060] In some embodiments, the conductive agent in the positive electrode active layer has a mass percentage of 0.5% to 3%. Specifically, the mass percentage of the conductive agent includes, but is not limited to, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any range between the foregoing.

[0061] Some embodiments of this application provide a positive electrode sheet, the positive electrode sheet including a positive electrode active layer, the components of the positive electrode active layer including a positive electrode active material and additives, the additives including hydrogenated nitrile rubber, the hydrogenation ratio of the hydrogenated nitrile rubber being 30% to 85%.

[0062] In some embodiments, the positive electrode is the same as the positive electrode in a lithium-ion battery as described above. Similar solutions and advantages are not repeated here.

[0063] This application also provides an electrical device in some embodiments. The electrical device includes at least one of the above-described lithium-ion battery and the above-described positive electrode.

[0064] The lithium-ion battery and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0065] 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.

[0066] 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.

[0067] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0068] In some embodiments, the positive electrode active layer may optionally include a binder. 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.

[0069] 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 the 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).

[0070] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, additives including hydrogenated nitrile rubber, 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 .

[0071] The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector, the negative active layer including a negative active material.

[0072] 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 layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0073] 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).

[0074] 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.

[0075] In some embodiments, the negative electrode active 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).

[0076] In some embodiments, the negative electrode active 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.

[0077] In some embodiments, the negative electrode active layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0078] 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 a 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 .

[0079] 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.

[0080] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0081] 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).

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] In some embodiments, the thickness of the isolation membrane is 6 micrometers (μm) to 40 μm, and optionally 12 μm to 20 μm.

[0088] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0089] 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.

[0090] 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 plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0091] A lithium-ion battery includes at least one battery cell. A lithium-ion battery may include one or more battery cells.

[0092] 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.

[0093] 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 1 as an example.

[0094] 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 1 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to actual needs.

[0095] Lithium-ion batteries can be battery modules or battery packs.

[0096] 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.

[0097] 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.

[0098] Optionally, the battery module may also include a housing with a receiving space in which multiple battery cells are housed.

[0099] 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. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0100] 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.

[0101] 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.

[0102] As an electrical device, lithium-ion batteries can be selected based on its usage requirements.

[0103] As an example, the electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of lithium-ion batteries for this electrical device, battery packs or battery modules can be used.

[0104] Another example of an electrical 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.

[0105] 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.

[0106] 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.

[0107] Test methods involved in the embodiments:

[0108] (1) Positive electrode slurry dispersion stability test:

[0109] The slurry flowability was assessed visually, and the viscosity change curve of the slurry was measured over 72 hours (sampled every 8 hours). The stability of the cathode slurry was then determined based on the degree of flowability and viscosity. When the slurry was non-flowing and had extremely high viscosity, it was classified as heavily gelled. When the heavily gelled time exceeded 20 hours, the corresponding slurry dispersion stability met the production requirements of the battery.

[0110] (2) Diaphragm resistance (DCR) test:

[0111] 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.

[0112] (3) Initial Coulomb efficiency:

[0113] 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.

[0114] The first-cycle coulombic efficiency (%) of a lithium-ion battery = first-cycle discharge capacity / first-cycle charge capacity × 100%.

[0115] (4) Cyclic capacity retention:

[0116] 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%

[0117] 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.

[0118] Example 1

[0119] 1) Preparation of positive electrode sheet

[0120] A positive electrode slurry was prepared by uniformly dispersing carbon-coated lithium iron phosphate (20% graphitization of the carbon coating layer, particle size Dv50 of 2μm-3μm), conductive carbon black SP, binder PVDF, and hydrogenated nitrile rubber (1w molecular weight, 70% hydrogenation ratio, 15% molar proportion of acrylonitrile monomer structural units, and hydroxyl groups at both ends) in a weight ratio of 96.5:2:1:0.5 in NMP solvent. The positive electrode slurry was then 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 of 0.7g / 1540.25mm² on both sides. 2 .

[0121] 2) Preparation of negative electrode sheet

[0122] 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, wherein the coating amount per unit area on both sides was 0.17 g / 1540.25 mm². 2 .

[0123] 3) Separating membrane

[0124] A 12μm thick polypropylene separator membrane was selected.

[0125] 4) Preparation of electrolyte

[0126] The organic solvent was 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 accounted for 12.5% ​​of the electrolyte by mass.

[0127] 5) Battery manufacturing

[0128] 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, a lithium-ion battery is obtained.

[0129] The lithium-ion batteries provided in Examples 2-5 and Comparative Examples 1-2 are similar to those in Example 1, with the main difference being that different hydrogenation ratios of hydrogenated nitrile rubber are used, as shown in Table 1 below.

[0130] Table 1

[0131] The lithium-ion batteries provided in Examples 6-10 are similar to those in Example 1, with the main difference being that hydrogenated nitrile rubber with different weight-average molecular weights is used, as shown in Table 2 below.

[0132] Table 2

[0133] The lithium-ion batteries provided in Examples 11-14 are similar to those in Example 1, with the main difference being that hydrogenated nitrile rubber with different molar proportions of acrylonitrile structural units is used, as shown in Table 3 below.

[0134] Table 3

[0135] The solid content of the cathode slurry in each embodiment and comparative example is controlled at around 60%.

[0136] As shown in Tables 1-3, compared to Comparative Examples 1-2, Examples 1-17, by reasonably controlling the hydrogenation ratio of hydrogenated nitrile rubber to 30%-85%, all achieve better slurry dispersion stability, resulting in lower diaphragm resistance, higher initial coulombic efficiency, and higher cycle capacity retention. A comparison between Examples 1-5 shows that the hydrogenation ratio of hydrogenated nitrile rubber is further preferably 55%-70%.

[0137] A comparison between Examples 1 and Examples 6-10 shows that by reasonably controlling the weight-average molecular weight of hydrogenated nitrile rubber, better slurry dispersion stability can be achieved, resulting in lower diaphragm resistance, higher initial coulombic efficiency, and higher cycle capacity retention.

[0138] A comparison between Example 1 and Examples 11-14 shows that by reasonably controlling the molar ratio of acrylonitrile structural units in hydrogenated nitrile rubber, better slurry dispersion stability can be achieved, resulting in lower diaphragm resistance, higher initial coulombic efficiency, and higher cycle capacity retention.

[0139] 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.

[0140] 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 electrode active layer, the positive electrode active layer comprising a positive electrode active material and an additive, the positive electrode active material comprising lithium iron phosphate, the additive comprising hydrogenated nitrile butadiene rubber, wherein the hydrogenation ratio of the hydrogenated nitrile butadiene rubber is 30% to 85%. The hydrogenation ratio means that if 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, then the hydrogenation ratio is (P1-P2) / P1.

2. The lithium-ion battery according to claim 1, wherein, The hydrogenation ratio of the hydrogenated nitrile rubber is 55% to 70%.

3. The lithium-ion battery according to claim 1 or 2, wherein, The hydrogenated nitrile rubber has at least one of the following characteristics (1) to (2): (1) Weight-average molecular weight is 500 to 1,000,000; (2) The molar percentage of acrylonitrile structural units is 5% to 30%.

4. The lithium-ion battery according to claim 3, wherein, The hydrogenated nitrile rubber has at least one of the following characteristics (1) to (2): (1) Weight-average molecular weight is 1,000 to 100,000; (2) The molar percentage of acrylonitrile structural units is 10% to 20%.

5. The lithium-ion battery according to any one of claims 1 to 4, wherein, In the positive electrode active layer, the mass percentage of the hydrogenated nitrile rubber is 0.1% to 1%.

6. The lithium-ion battery according to any one of claims 1 to 5, wherein, The lithium iron phosphate has a carbon coating on its surface.

7. The lithium-ion battery according to claim 6, wherein, The degree of graphitization of the carbon coating is 10% to 30%.

8. A positive electrode sheet, the positive electrode sheet comprising a positive electrode active layer, the positive electrode active layer comprising a positive electrode active material and an additive, the additive comprising hydrogenated nitrile rubber, the hydrogenation ratio of the hydrogenated nitrile rubber being 30% to 85%; The hydrogenation ratio means that if 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, then the hydrogenation ratio is (P1-P2) / P1.

9. The positive electrode sheet according to claim 8, wherein, The positive electrode sheet in the lithium-ion battery according to any one of claims 2 to 7.

10. An electrical device comprising at least one of the lithium-ion battery according to any one of claims 1 to 7 and the positive electrode sheet according to any one of claims 8 to 9.

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