Adhesive composition, positive electrode plate, secondary battery, and power consumption device

Abstract

The present application provides an adhesive composition, the adhesive composition comprising a first fluorine-containing polymer and a second fluorine-containing polymer, the first fluorine-containing polymer comprising polyvinylidene fluoride having a weight average molecular weight of 5 million to 9 million, and the weight average molecular weight of the second fluorine-containing polymer not exceeding 600,000.The adhesive composition has good processability, and can provide high adhesive strength to an electrode plate even with a small amount added, and can also improve the cycle performance of a battery.

Description

[Technical Field]

[0001] The present application relates to the field of secondary batteries, and in particular to fluorine-containing polymers, manufacturing methods, adhesive compositions, positive electrode plates, secondary batteries, and power consuming devices.

[0002] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application is based on PCT patent application No. PCT / CN2022 / 099187, filed on June 16, 2022, entitled "Adhesive, Manufacturing Method and Application Thereof," CN patent application No. 202211044631.4, filed on August 30, 2022, entitled "Fluorine-containing polymer, manufacturing method and application thereof, cathode slurry, secondary battery, battery module, battery pack, and power consumption device," and CN patent application No. 2022110520, filed on August 30, 2022, entitled "Fluorine-containing polymer, manufacturing method and application thereof, cathode slurry, secondary battery, battery module, battery pack, and power consumption device." See CN Patent Application No. 14.9, CN Patent Application No. 202211046282.X, filed on August 30, 2022, entitled "Adhesive, Manufacturing Method, Positive Electrode Plate, Secondary Battery, and Power Consumption Device," CN Patent Application No. 202211044756.7, filed on August 30, 2022, entitled "Adhesive, Manufacturing Method, Positive Electrode Plate, Secondary Battery, and Power Consumption Device," and CN Patent Application No. 202211043966.4, filed on August 30, 2022, entitled "Adhesive, Manufacturing Method, Positive Electrode Plate, Secondary Battery, and Power Consumption Device," all of which are incorporated herein by reference. [Background technology]

[0003] In recent years, secondary batteries have been widely applied in energy storage power systems such as hydroelectric, thermal, wind and solar power plants, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. As the application of secondary batteries becomes more widespread, higher requirements are being placed on their cycle performance, service life, etc.

[0004] Adhesives are commonly used materials in secondary batteries, and are in high demand for battery electrodes, separators, packaging, etc. However, conventional adhesives have poor adhesive properties and often require large amounts of additives to meet the adhesive strength requirements of electrodes, which limits the improvement of battery energy density. Therefore, conventional adhesives still need improvement. Summary of the Invention

[0005] The present application has been made in view of the above-mentioned problems, and has an object to provide an adhesive composition that can exhibit excellent adhesive strength even at a low addition amount and has good processability.

[0006] In order to achieve the above objectives, this application The first aspect of provides an adhesive composition, the adhesive composition comprising a first fluorine-containing polymer, a second fluorine-containing polymer, and a third fluorine-containing polymer, wherein the weight average molecular weight of the first fluorine-containing polymer is 3,000,000 to 10,000,000, the weight average molecular weight of the second fluorine-containing polymer is 600,000 to 1,100,000, and the weight average molecular weight of the third fluorine-containing polymer is 5,000 to 150,000.

[0007] This adhesive composition ensures that the electrode plates have sufficient adhesive strength even at low additive amounts, and can improve the cycle performance of the battery. Furthermore, this adhesive composition combines excellent flexibility and processability, and can further improve the safety and cycle performance of the battery.

[0008] In any embodiment, the mass content of the first fluorine-containing polymer is 10% to 86% based on the total mass of the adhesive composition.

[0009] By controlling the mass content of the first fluorine-containing polymer within an appropriate range, it is possible to ensure that the adhesive composition has sufficient adhesive strength to prevent the membrane layer from falling off during the battery cycling process. In addition, a certain content of the first fluorine-containing polymer can effectively reduce the amount of adhesive composition used and improve the loading amount of active material in the electrode plate.

[0010] In any embodiment, the mass content of the second fluorine-containing polymer is 10% to 86% based on the total mass of the adhesive composition.

[0011] The weight-average molecular weight of the second fluorine-containing polymer is relatively low, which can effectively improve the crystallinity of the first fluorine-containing polymer, improve the flexibility of the electrode plate, and reduce the cost of the battery.

[0012] In either embodiment, the adhesive composition has a crystallinity of no more than 40%, optionally between 5% and 40%.

[0013] Adding the second fluorine-containing polymer and the third fluorine-containing polymer to the first fluorine-containing polymer can effectively reduce the crystallinity of the adhesive, improve the flexibility of the electrode plate and the processability of the slurry, and enhance the cycle performance of the battery.

[0014] In either embodiment, the first fluorine-containing polymer comprises structural units derived from vinylidene fluoride.

[0015] In any embodiment, the first fluorine-containing polymer further comprises a structural unit according to Formula I: TIFF0007785176000001.tif32150 where R1 is a C group containing hydrogen, fluorine, chlorine, and at least one fluorine atom. 1-3 and alkyl groups.

[0016] In any embodiment, the first fluorine-containing polymer comprises one or more of polyvinylidene fluoride, vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene-hexafluoropropylene copolymer.

[0017] In any embodiment, the second fluorine-containing polymer comprises structural units shown in Formula II: TIFF0007785176000002.tif32150 where R2 and R3 each independently represent a hydrogen atom, a halogen atom, and a C group containing at least one fluorine atom. 1-3 and alkyl groups.

[0018] The second fluorine-containing polymer contains chlorine.

[0019] The second fluorine-containing polymer containing chlorine can further reduce the crystallinity of the adhesive composition, improve the flexibility of the electrode plate, and enhance the safety performance of the battery.

[0020] In either embodiment, the chlorine content in the second fluorine-containing polymer does not exceed 8%, based on the total weight of the second fluorine-containing polymer.

[0021] The second fluorine-containing polymer having a chlorine content not exceeding 8% has a low crystallinity and can significantly improve the flexibility of the electrode plate.

[0022] In either embodiment, the crystallinity of the second fluorine-containing polymer does not exceed 47%, and optionally does not exceed 30%.

[0023] In either embodiment, the weight average molecular weight of the second fluorine-containing polymer is 600,000 to 1,100,000.

[0024] In any embodiment, the second fluorine-containing polymer comprises at least one of polyvinylidene fluoride, chlorinated polyvinylidene fluoride, chlorinated poly(vinylidene fluoride-hexafluoropropylene), and poly(vinylidene fluoride-trifluorochloroethylene).

[0025] In either embodiment, the third fluorine-containing polymer comprises structural units shown in Formula III.

[0026] TIFF0007785176000003.tif32150 wherein R4 and R5 each independently contain at least one of hydrogen, fluorine, chlorine, or a trifluoromethyl group.

[0027] In any of the embodiments, the end group of the third fluorine-containing polymer contains a hydroxyl group or an ester group, and the third fluorine-containing polymer includes one of polytetrafluoroethylene, polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride-tetrafluoroethylene) copolymer, poly(vinylidene fluoride-trifluorochloroethylene) copolymer, and poly(vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene) copolymer.

[0028] A second aspect of the present application provides a fluorine-containing polymer, the fluorine-containing polymer comprising a structural unit derived from vinylidene fluoride and a structural unit represented by formula IV, TIFF0007785176000004.tif32150Here, R6 contains at least one of hydrogen, Cl, and F.

[0029] In any embodiment, the chlorine content in the fluorine-containing polymer does not exceed 8%, based on the total weight of the fluorine-containing polymer.

[0030] In any embodiment, the crystallinity of the fluorine-containing polymer does not exceed 30%. In any embodiment, the weight average molecular weight of the fluorine-containing polymer is 600,000 to 1,100,000.

[0031] In any embodiment, the fluorine-containing polymer comprises at least one of chlorinated polyvinylidene fluoride, chlorinated poly(vinylidene fluoride-hexafluoropropylene), and poly(vinylidene fluoride-trifluorochloroethylene).

[0032] A third aspect of the present application provides a method for producing a fluorine-containing polymer, the method comprising: employing a chlorinating agent to chlorinate polyvinylidene fluoride to produce a fluorine-containing polymer.

[0033] In one embodiment, the method specifically includes dispersing polyvinylidene fluoride in a solvent to prepare a polyvinylidene fluoride suspension, and adding an initiator and a chlorinating agent to chlorinate the polyvinylidene fluoride to prepare a fluorine-containing polymer.

[0034] In either embodiment, the chlorinating agent includes at least one of chlorine gas, hydrogen chloride, phosphorus pentachloride, phosphorus trichloride, sulfuryl chloride SO2Cl2, and phosgene COCl2.

[0035] In any embodiment, the initiator comprises at least one of dibenzoyl oxide, dilauroyl peroxide, azobisisobutyronitrile (AIBN), and azobisisoheptonitrile (ABVN).

[0036] In either embodiment, the solvent comprises at least one of carbon tetrachloride and water.

[0037] A fourth aspect of the present application provides a positive electrode plate, the positive electrode plate including a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material, a conductive agent, and the adhesive of any of the embodiments or the adhesive composition produced by the production method of any of the embodiments.

[0038] This positive electrode plate has excellent adhesive strength even with a low amount of adhesive added.

[0039] In any embodiment, the mass fraction of the adhesive composition does not exceed 1.5%, and optionally is 0.8%-1.2%, based on the total mass of the positive electrode membrane layer.

[0040] Controlling the mass fraction of the adhesive composition within an appropriate range can ensure that the electrode plate has sufficient adhesive strength while also maintaining the flexibility of the electrode plate, thereby improving the cycle performance and safety performance of the battery.

[0041] In either embodiment, the positive electrode active material is a lithium-containing transition metal oxide.

[0042] In any embodiment, the lithium-containing transition metal oxide is at least one of lithium iron phosphate or lithium nickel cobalt manganese oxide, or doped modifications thereof, or conductive carbon-coated, conductive metal-coated, or conductive polymer-coated modifications thereof.

[0043] A fifth aspect of the present application provides a secondary battery, the secondary battery including an electrode assembly and an electrolyte, the electrode assembly including a separator, a negative electrode plate, and the positive electrode plate of the fourth aspect of the present application.

[0044] A sixth aspect of the present application provides a power consuming device, the power consuming device including the secondary battery of the fifth aspect of the present application. [Brief explanation of the drawings]

[0045] [Figure 1] 1 is a schematic diagram of a secondary battery according to an embodiment of the present application; [Figure 2] FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. [Figure 3] 1 is a schematic diagram of a battery module according to an embodiment of the present application; [Figure 4] 1 is a schematic diagram of a battery pack according to an embodiment of the present application; [Figure 5] FIG. 5 is an exploded view of the battery pack according to the embodiment of the present application shown in FIG. 4. [Figure 6] 1 is a schematic diagram of a power consumption device in which a secondary battery according to an embodiment of the present application is used as a power source; DETAILED DESCRIPTION OF THE INVENTION

[0046] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing the present application's positive electrode active material and manufacturing method thereof, positive electrode plate, secondary battery, battery module, battery pack, and electric device will be described in detail. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and redundant descriptions of structures that are actually the same may be omitted. This is to avoid unnecessarily lengthening the following description and to facilitate understanding by those skilled in the art. Note that the drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0047] The "ranges" disclosed in this application are defined in the form of lower and upper limits. A given range is defined by selecting one lower limit and one upper limit, and the selected lower and upper limits define the boundaries of the particular range. Such defined ranges may be inclusive or exclusive of the end values ​​and may be arbitrarily combined, i.e., any lower limit may be combined with any upper limit to form a single range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if 1 and 2 are listed as minimum range values ​​and 3, 4, and 5 are listed as maximum range values, the ranges 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5 are all contemplated. In this application, unless otherwise specified, the numerical range "ab" represents a shorthand notation for any combination of real numbers from a to b, where a and b are both real numbers. For example, the numerical range "0-5" represents that the present specification has already listed all real numbers between "0-5," and "0-5" is merely a shorthand representation of combinations of these numbers. Also, expressing a parameter as an integer ≧2 is equivalent to disclosing that this parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0048] Unless otherwise stated, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0049] Unless otherwise stated, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0050] Unless otherwise specified, all steps in this application may be performed in order or randomly, and are preferably performed in order. For example, when the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed in order, or steps (b) and (a) performed in order. For example, when the method mentioned above may further include step (c), it means that step (c) may be added to the method in any order, and for example, the method may include steps (a), (b), and (c), or may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0051] Unless otherwise specified, the terms "comprise" and "include" used in this application may be open-ended or closed-ended. For example, the terms "comprise" and "include" may further include or include other components not listed, or may include or include only the listed components.

[0052] Unless otherwise stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, "A or B" is satisfied when A is true (or exists) and B is false (or does not exist), when A is false (or does not exist) but B is true (or exists), or when both A and B are true (or exist).

[0053] Fluorine-containing polymers are one of the most widely used adhesives in secondary batteries. However, due to the low viscosity of conventional fluorine-containing polymers, they often need to be added in large amounts to ensure effective adhesion of the active material, thereby achieving effective adhesion of the electrode plate. However, increasing the amount of conventional fluorine-containing polymers used reduces the load of the active material on the electrode plate, which affects the improvement of the battery energy density. However, adhesives with low content are also less likely to maintain sufficient adhesive strength during use, making it difficult to meet the market's requirements for battery cycle performance.

[0054] [Adhesive composition] The present application provides an adhesive composition, which includes a first fluorine-containing polymer, a second fluorine-containing polymer, and a third fluorine-containing polymer, wherein the weight-average molecular weight of the first fluorine-containing polymer is 3,000,000 to 10,000,000, the weight-average molecular weight of the second fluorine-containing polymer is 600,000 to 1,100,000, and the weight-average molecular weight of the third fluorine-containing polymer is 5,000 to 150,000.

[0055] As used herein, the term "adhesive composition" refers to a mixture that forms a colloidal solution or colloidal dispersion in a dispersing medium.

[0056] As used herein, the term "fluorine-containing polymer" refers to a polymer whose main synthetic monomer is a fluorine-containing monomer, and the polymer includes, on the one hand, an aggregate of large molecules produced by a polymerization reaction that are chemically uniform but differ in degree of polymerization, molar mass, and chain length. On the other hand, the term also includes derivatives of such large molecular aggregates formed by a polymerization reaction, i.e., compounds obtained by a reaction, for example, addition or substitution, of functional groups in the above-mentioned large molecules, and which may be chemically uniform or chemically heterogeneous. As used herein, the fluorine-containing polymer includes both homopolymers and copolymers.

[0057] As used herein, the term "weight average molecular weight" is the sum of the products of the weight fractions of molecules of different molecular weights in a polymer and the corresponding molecular weights.

[0058] In some embodiments, the dispersion medium of the adhesive composition is an oil-based solvent, examples of which include, but are not limited to, dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl carbonate, ethyl cellulose, and polycarbonate, i.e., the adhesive is dissolved in the oil-based solvent.

[0059] In some embodiments, the adhesive composition is used to hold the electrode active material and / or conductive agent in place and adhere them to the conductive metal member to form the electrode.

[0060] In some embodiments, the adhesive composition is used as a positive electrode adhesive to adhere a positive electrode active material and / or a conductive agent to form an electrode.

[0061] In some embodiments, the adhesive composition is used as a negative electrode adhesive to adhere a negative electrode active material and / or a conductive agent to form an electrode.

[0062] In some embodiments, the weight average molecular weight of the first fluorine-containing polymer is 3 million to 10 million, or 3 million, 3.5 million, 4 million, 4.5 million, 5 million, 5.5 million, 6 million, 6.5 million, 7 million, 7.5 million, 8 million, 8.5 million, 9 million, 9.5 million, 10 million, or any number therein.

[0063] In some embodiments, the weight average molecular weight of the second fluorine-containing polymer is 600,000 to 1,100,000. In some embodiments, the weight average molecular weight of the second fluorine-containing polymer is optionally 600,000, 650,000, 700,000, 750,000, 800,000, 850,000, 900,000, 950,000, 1,000,000, 1,050,000, 1,100,000, or any number therein.

[0064] In some embodiments, the weight average molecular weight of the third fluorine-containing polymer is 5,000 to 150,000. In some embodiments, the weight average molecular weight of the second fluorine-containing polymer is optionally 5,000, 10,000, 20,000, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, 110,000, 120,000, 130,000, 140,000, 150,000, or any number therein.

[0065] In this application, the weight-average molecular weight of the fluorine-containing polymer can be tested by any method known in the art, such as gel chromatography, using a Waters 2695 Isocratic HPLC-type gel chromatograph (differential refractive index detector 2141). In some embodiments, the test method uses a 3.0% mass fraction polystyrene solution sample as the standard and selects a matching chromatographic column (oil-based: Styragel HT5 DMF 7.8*300mm + Styragel HT4). A 3.0% adhesive glue solution is prepared using purified N-methylpyrrolidone (NMP) solvent, and the prepared solution is allowed to stand for one day before use. During testing, tetrahydrofuran is first drawn into a syringe, washed, and repeated several times. 5 ml of the test solution is then drawn into the syringe, the air in the syringe is removed, and the needle is wiped dry. Finally, the sample solution is slowly injected into the injection port. After the displayed value has stabilized, data is acquired and the weight average molecular weight is read.

[0066] The first fluorine-containing polymer, which has a weight-average molecular weight of 3 million to 10 million, can improve the adhesive strength of the electrode plate at a low addition level and improve the capacity retention rate during battery cycling. The addition of the low-molecular-weight second fluorine-containing polymer and the third fluorine-containing polymer can effectively improve the processing performance of the slurry, improve the quality of the electrode plate, alleviate the brittleness problem of the electrode plate, reduce processing and raw material costs, and the uniform adhesive composition can further improve the cycling performance of the battery.

[0067] In some embodiments, the mass content of the first fluorine-containing polymer is 10% to 86% based on the total mass of the adhesive composition.

[0068] In some embodiments, the mass content of the first fluorine-containing polymer, based on the total mass of the adhesive composition, is optionally 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 86%, or any number therein.

[0069] By controlling the mass content of the first fluorine-containing polymer within an appropriate range, it is possible to ensure that the adhesive composition has sufficient adhesive strength to prevent the membrane layer from falling off during the battery cycling process. In addition, a certain content of the first fluorine-containing polymer can effectively reduce the amount of adhesive composition used and improve the loading amount of active material in the electrode plate.

[0070] In some embodiments, the mass content of the second fluorine-containing polymer is 10% to 86% based on the total mass of the adhesive composition.

[0071] In some embodiments, the mass content of the second fluorine-containing polymer, based on the total mass of the adhesive composition, is optionally 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 86%, or any number therein.

[0072] The weight-average molecular weight of the second fluorine-containing polymer is relatively low, which can effectively improve the crystallinity of the first fluorine-containing polymer, improve the flexibility of the electrode plate, and reduce the cost of the battery.

[0073] In some embodiments, the adhesive composition has a crystallinity of no more than 40%, optionally between 5% and 40%.

[0074] In some embodiments, the adhesive composition has a crystallinity of optionally 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, or any value therein.

[0075] As used herein, the term "crystallinity" refers to the proportion of crystalline regions in a polymer, and in the microstructure, there are regions having some molecules that are stably and closely arranged, and the regions in which the molecules are closely and regularly arranged are called crystalline regions.

[0076] In the present application, the crystallinity test may be performed by selecting a method known in the art, for example, by using differential scanning calorimetry. In some embodiments, 0.5 g of the adhesive composition is placed in an aluminum crucible, flattened, and the crucible is covered with a lid. The test is performed using a US TA Instruments Model Discovery 250 differential scanning calorimeter (DSC) in a nitrogen gas atmosphere with a purge gas of 50 ml / min and a protective gas of 70 ml / min, with a heating rate of 10 ° C. / min, and a test temperature range of -100 ° C. to 400 ° C., to remove the thermal history.

[0077] In this test, the temperature change curve of the DSC / (Mw / mg) of the adhesive composition is obtained and integrated, and the peak area is the melting enthalpy ΔH (J / g) of the fluorine-containing polymer composition, and the adhesive crystallinity = ΔH / (ΔHm) × 100%, where ΔHm is the standard melting enthalpy (crystalline heat of fusion) of the fluorine-containing polymer, and ΔHm = 104.7 J / g.

[0078] By adding the second fluorine-containing polymer and the third fluorine-containing polymer to the first fluorine-containing polymer, the crystallinity of the adhesive can be effectively reduced, the flexibility of the electrode plate and the processability of the slurry can be improved, and the cycle performance of the battery can be improved.

[0079] In some embodiments, the first fluorine-containing polymer comprises structural units derived from vinylidene fluoride, in some embodiments, the first fluorine-containing polymer is a vinylidene fluoride homopolymer, in some embodiments, the first fluorine-containing polymer is a vinylidene fluoride copolymer.

[0080] In some embodiments, the first fluorine-containing polymer further comprises a structural unit according to Formula I: TIFF0007785176000005.tif32150 where R1 is a C group containing hydrogen, fluorine, chlorine, and at least one fluorine atom. 1-3 and alkyl groups.

[0081] In some embodiments, R1 includes one or more of hydrogen, fluorine, chlorine, and a trifluoromethyl group.

[0082] In some embodiments, the first fluorine-containing polymer comprises one or more of polyvinylidene fluoride, vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene-hexafluoropropylene copolymer.

[0083] In some embodiments, the second fluorine-containing polymer comprises structural units according to Formula II: TIFF0007785176000006.tif32150 where R2 and R3 each independently represent a C group containing hydrogen, a halogen, and at least one fluorine atom. 1-3 and alkyl groups.

[0084] In some embodiments, R2 and R3 each independently comprise hydrogen, fluorine, chlorine, or a trifluoromethyl group.

[0085] In some embodiments, the second fluorine-containing polymer comprises chlorine.

[0086] The second fluorine-containing polymer containing chlorine can further reduce the crystallinity of the adhesive composition, improve the flexibility of the electrode plate, and enhance the safety performance of the battery.

[0087] In some embodiments, the second fluorine-containing polymer is produced by chlorinating a fluorine-containing polymer.

[0088] In some embodiments, the second fluorine-containing polymer is prepared by copolymerizing polyvinylidene fluoride monomers with chlorine-containing monomers.

[0089] In some embodiments, the chlorine content of the second fluorine-containing polymer does not exceed 8%, based on the total weight of the second fluorine-containing polymer, In some embodiments, the chlorine content of the second fluorine-containing polymer is 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any value therein, based on the total weight of the second fluorine-containing polymer.

[0090] The second fluorine-containing polymer having a chlorine content not exceeding 8% has a low crystallinity and can significantly improve the flexibility of the electrode plate.

[0091] In some embodiments, the crystallinity of the second fluorine-containing polymer is not more than 47%, optionally not more than 30%. In some embodiments, the crystallinity of the second fluorine-containing polymer is 47%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, 4%, 3%, or any number therein. In some embodiments, the weight average molecular weight of the second fluorine-containing polymer is 600,000-1,100,000. In some embodiments, the weight average molecular weight of the second fluorine-containing polymer is 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,100,000, or any number therein.

[0092] In some embodiments, the second fluorine-containing polymer comprises at least one of polyvinylidene fluoride, chlorinated polyvinylidene fluoride, chlorinated poly(vinylidene fluoride-hexafluoropropylene), and poly(vinylidene fluoride-trifluorochloroethylene).

[0093] In some embodiments, the third fluorine-containing polymer comprises structural units shown in Formula III: TIFF0007785176000007.tif32150 wherein R4 and R5 each independently contain at least one of hydrogen, fluorine, chlorine, or a trifluoromethyl group.

[0094] In some embodiments, the end groups of the third fluorine-containing polymer contain hydroxyl or ester groups.

[0095] The third fluorine-containing polymer has a small weight-average molecular weight and a high mass content of end groups, so the end groups have a relatively large effect on the performance of the third fluorine-containing polymer. The end groups of the third fluorine-containing polymer contain hydroxyl groups or ester groups, which can effectively improve the adhesion of the third fluorine-containing polymer and reduce the reduction in plate adhesion performance caused by the addition of a low-molecular-weight third fluorine-containing polymer.

[0096] The end group structure of the polymer can be studied by nuclear magnetic resonance techniques. 19 F-NMR and 1 The end group structure of the polymer can be analyzed by H-NMR. For example, dimethyl sulfoxide is used as the solvent, CFCl3 is used as the fluorine spectrum standard, and TMS is used as the hydrogen spectrum standard.

[0097] In some embodiments, the third fluorine-containing polymer comprises one of polytetrafluoroethylene, polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride-tetrafluoroethylene) copolymer, poly(vinylidene fluoride-trifluorochloroethylene) copolymer, and poly(vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene) copolymer.

[0098] In one embodiment of the present application, there is provided a fluorine-containing polymer, the fluorine-containing polymer comprising a structural unit derived from vinylidene fluoride and a structural unit represented by formula IV, TIFF0007785176000008.tif32150Here, R6 contains at least one of hydrogen, Cl, and F.

[0099] The fluorine-containing polymer containing chlorine can further reduce the crystallinity of the adhesive composition, improve the flexibility of the electrode plate, and enhance the safety performance of the battery.

[0100] In some embodiments, the fluorine-containing polymer is obtained by producing a fluorine-containing polymer after chlorination.

[0101] In some embodiments, the fluorine-containing polymer is prepared by copolymerizing vinylidene fluoride with a chlorine-containing monomer.

[0102] In some embodiments, the chlorine content of the fluorine-containing polymer does not exceed 8%, based on the total weight of the fluorine-containing polymer, hi some embodiments, the chlorine content of the fluorine-containing polymer is 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any value therein, based on the total weight of the fluorine-containing polymer.

[0103] Fluorine-containing polymers with a chlorine content of not more than 8% have a low degree of crystallinity and can significantly improve the flexibility of the electrode plate.

[0104] In some embodiments, the crystallinity of the fluorine-containing polymer does not exceed 30%.

[0105] In some embodiments, the crystallinity of the fluorine-containing polymer is optionally 30%, 25%, 20%, 15%, 10%, 5%, or any number therein. In some embodiments, the weight average molecular weight of the fluorine-containing polymer is 600,000 to 1,100,000. In some embodiments, the weight average molecular weight of the fluorine-containing polymer is 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,100,000, or any number therein.

[0106] In some embodiments, the fluorine-containing polymer comprises at least one of polyvinylidene fluoride, chlorinated polyvinylidene fluoride, chlorinated poly(vinylidene fluoride-hexafluoropropylene), and poly(vinylidene fluoride-trifluorochloroethylene).

[0107] In one embodiment of the present application, there is provided a method for producing a fluorine-containing polymer, the method comprising the step of employing a chlorinating agent to chlorinate polyvinylidene fluoride to produce a fluorine-containing polymer.

[0108] In some embodiments, the method specifically includes dispersing polyvinylidene fluoride in a solvent to prepare a polyvinylidene fluoride suspension, and adding an initiator and a chlorinating agent to chlorinate the polyvinylidene fluoride to prepare a fluorine-containing polymer.

[0109] In some embodiments, the chlorinating agent comprises at least one of chlorine gas, phosphorus pentachloride (PCl5), hydrogen chloride (HCl), phosphorus trichloride (PCl3), sulfuryl chloride (SO2Cl2), and phosgene (COCl2).

[0110] In some embodiments, the initiator comprises at least one of dibenzoyl oxide, dilauroyl peroxide, azobisisobutyronitrile (AIBN), and azobisisoheptonitrile (ABVN).

[0111] In some embodiments, the solvent comprises at least one of carbon tetrachloride and water.

[0112] In one embodiment of the present application, there is provided a method for producing an adhesive composition, specifically comprising the following steps: Preparation of a first fluorine-containing polymer: A first polymerization reaction is carried out on a raw material containing a vinylidene fluoride monomer under polymerization conditions to prepare a first fluorine-containing polymer, and the weight-average molecular weight of the first fluorine-containing polymer is 3,000,000 to 10,000,000; Preparation of a third fluorine-containing polymer: carrying out a second polymerization reaction under polymerizable conditions to prepare a second fluorine-containing polymer, and the weight average molecular weight of the third fluorine-containing polymer is not more than 600,000; Blending: A first fluorine-containing polymer, a second fluorine-containing polymer having a weight-average molecular weight of 600,000 to 1,100,000, and a third fluorine-containing polymer are blended to produce an adhesive composition.

[0113] As used herein, the term "blending" refers to the process of producing two or more substances as a macroscopically homogeneous material under certain conditions such as temperature and / or shear stress.

[0114] This adhesive manufacturing method is simple, environmentally friendly, reduces costs, and is favorable for industrial production. At the same time, the adhesive composition manufactured by this method can achieve both flexibility of the electrode plate and cycle performance of the battery at a low additive amount, and can improve the capacity retention rate during the battery cycle process.

[0115] In some embodiments, the synthesis step of the first fluorine-containing polymer includes carrying out a polymerization reaction of a raw material including vinylidene fluoride monomer in a non-reactive gas atmosphere at a reaction pressure of 6 MPa to 8 MPa and a reaction temperature of 45°C to 60°C for 6 hours to 10 hours, and adding a chain transfer agent to reduce the pressure in the reaction system to 2 MPa to 2.5 MPa to terminate the reaction, perform solid-liquid separation, and leave a solid phase to produce the first fluorine-containing polymer.

[0116] In some embodiments, the step of synthesizing the first fluorine-containing polymer includes providing raw materials including vinylidene fluoride monomer and a reaction solvent, conducting a first-stage polymerization reaction to obtain a first product, conducting a second-stage polymerization reaction of the first product in a water-insoluble gas atmosphere, and adding a chain transfer agent and conducting a third-stage polymerization reaction to obtain the first fluorine-containing polymer.

[0117] The first product may refer to the reaction liquid obtained after the first-stage polymerization reaction, or may be a product obtained after the reaction liquid has been purified after the first-stage polymerization reaction.

[0118] In some embodiments, multiple first products are mixed and subjected to a second-stage polymerization reaction in a non-aqueous gas atmosphere. That is, the second-stage polymerization reaction is the self-polymerization of the first products. As can be appreciated, multiple first products may be produced simultaneously in multiple reactors, or multiple times in a single reactor. The multiple-stage synthesis method can improve the uniformity of the polyproduct.

[0119] Using the split polymerization method, ultra-high molecular weight polyvinylidene fluoride can be produced, allowing the adhesive to meet the adhesive strength requirements of electrode plates with a low additive amount, contributing to improved positive electrode active material loading and improving battery capacity retention during cycling. At the same time, the first polymerization step forms a first product, the second polymerization step forms molecular chain segments with a target molecular weight, and the third polymerization step adjusts and controls the molecular weight of the polymer, preventing the reduction in the uniformity of the weight-average molecular weight of polyvinylidene fluoride due to excessive molecular weight and improving the uniformity of the product. Split polymerization also increases reactor utilization, saves time, and reduces the residence time of polyvinylidene fluoride in the reactor during the polyvinylidene fluoride production process. The combination of the first, second, and third polymerization steps further improves polyvinylidene fluoride production efficiency.

[0120] In some embodiments, the reaction temperature of the first stage polymerization reaction is 45° C. to 60° C. In some embodiments, the reaction temperature of the first stage polymerization reaction is optionally 45° C. to 50° C., 50° C. to 55° C., 55° C. to 60° C., or 45° C. to 55° C.

[0121] In some embodiments, the reaction time of the first-stage polymerization reaction is 4 to 10 hours, or alternatively, 4 to 5 hours, 5 to 6 hours, 6 to 7 hours, 7 to 8 hours, 8 to 9 hours, 9 to 10 hours, 4 to 6 hours, 6 to 8 hours, 8 to 10 hours, or 5 to 10 hours.

[0122] In some embodiments, the initial polymerization pressure is 4 MPa to 6 MPa. In some embodiments, the initial polymerization pressure is optionally 4 MPa to 5 MPa, 5 MPa to 6 MPa. In some embodiments, the initial polymerization pressure is higher than the critical pressure of vinylidene fluoride.

[0123] In some embodiments, the reaction temperature of the second stage polymerization reaction is 60° C. to 80° C. In some embodiments, the reaction temperature of the second stage polymerization reaction is optionally 60° C. to 70° C., or 70° C. to 80° C.

[0124] In some embodiments, the reaction time of the second stage polymerization reaction is 2 hours to 4 hours. In some embodiments, the reaction time of the second stage polymerization reaction is optionally 2 hours to 3 hours, or 3 hours to 4 hours.

[0125] In some embodiments, the reaction pressure of the second stage polymerization reaction is 6 MPa to 8 MPa. In some embodiments, the reaction pressure of the second stage polymerization reaction is optionally 6 MPa to 7 MPa, or 7 MPa to 8 MPa.

[0126] In some embodiments, the reaction time for the third stage polymerization reaction is 1 hour to 2 hours.

[0127] By controlling the reaction pressure, reaction time, and reaction temperature of each polymerization reaction step within an appropriate range, the weight-average molecular weight of the polyvinylidene fluoride can be improved, while at the same time controlling the uniformity of the weight-average molecular weight of the polymerization product and ensuring that the product has a relatively low polydispersity coefficient, thereby improving the balance of the performance of the first polyvinylidene fluoride, thereby enabling the electrode plate to have excellent adhesion even with a low amount of adhesive added, and further improving the cycle capacity retention of the battery.

[0128] In some embodiments, the chain transfer agent comprises one or more of cyclohexane, isopropyl alcohol, methanol, and acetone.

[0129] A water-insoluble gas is a gas whose solubility is less than 0.1 L. Gas solubility is the pressure of a gas at 20°C that is 1.013 x 10 5 The volume of the gas is expressed in Pa when dissolved in 1 L of water and reaches saturation. In some embodiments, the water-insoluble gas is one or more selected from nitrogen gas, oxygen gas, hydrogen gas, and methane.

[0130] In some embodiments, the amount of chain transfer agent used is 1.5% to 3% of the total weight of vinylidene fluoride monomer. The amount of chain transfer agent used may even be, for example, 2% or 2.5%.

[0131] By controlling the amount of chain transfer agent used within an appropriate range, the chain length of the polymer can be controlled, thereby obtaining a polymer with an appropriate molecular weight range and uniform distribution.

[0132] In some embodiments, the first stage polymerization reaction comprises: Adding a water solvent and a dispersant to a vessel and removing oxygen gas from the reaction system; Adding a first initiator and a pH adjuster to the vessel, adjusting the pH value to 6.5-7, and adding vinylidene fluoride monomer, and setting the pressure in the vessel to 4 MPa-6 MPa; After stirring for 30 to 60 minutes, the mixture is heated to 45 to 60°C to carry out the first-stage polymerization reaction.

[0133] Before the temperature is raised to carry out the polymerization reaction, the materials are first mixed uniformly, which allows the reaction to proceed more thoroughly and the weight average molecular weight, crystallinity and particle size of the produced polymer to be more uniform.

[0134] In some embodiments, the amount of water solvent used in the process for producing the first fluorine-containing polymer is 2 to 8 times the total mass of the vinylidene fluoride monomers. The amount of solvent used may further be, for example, 3, 4, 5, 6, or 7 times the total mass of the vinylidene fluoride monomers. In some embodiments, the water solvent is deionized water.

[0135] In some embodiments, during the preparation of the first fluorine-containing polymer, the dispersing agent comprises one or more of a cellulose ether and a polyvinyl alcohol.

[0136] In some embodiments, during the preparation of the first fluorine-containing polymer, the dispersant comprises one or more of a methyl cellulose ether and a carboxyethyl cellulose ether.

[0137] In some embodiments, the amount of dispersant used in the process for producing the first fluorine-containing polymer is 0.1% to 0.3% of the total weight of vinylidene fluoride monomers, and may be, for example, 0.2% of the total weight of vinylidene fluoride monomers.

[0138] In some embodiments, the first initiator is an organic peroxide.

[0139] In some embodiments, the first initiator comprises one or more of tert-amyl peroxypivalate, peroxy tert-amyl pivalate, 2-ethyl peroxydicarbonate, diisopropyl peroxydicarbonate, and tert-butyl peroxypivalate.

[0140] In some embodiments, the amount of the first initiator used in the process for producing the first fluorine-containing polymer is 0.15% to 1% of the total weight of the vinylidene fluoride monomer, and may further be, for example, 0.2%, 0.4%, 0.6%, or 0.8% of the weight of the vinylidene fluoride monomer.

[0141] In some embodiments, the pH adjuster comprises one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, and aqueous ammonia.

[0142] In some embodiments, the amount of pH adjuster used is between 0.05% and 0.2% of the total weight of vinylidene fluoride monomer, and may even be, for example, 0.1% or 0.15% of the total weight of vinylidene fluoride monomer.

[0143] In some embodiments, the third method for producing a fluorine-containing polymer specifically comprises: carrying out a second polymerization reaction of at least one monomer represented by formula V in a non-reactive gas atmosphere at 0.1-5 MPa and a reaction temperature of 60°C to 90°C for 0.5 hours to 8 hours, terminating the reaction, and separating the solid phase from the liquid to obtain a third fluorine-containing polymer; TIFF0007785176000009.tif26150 where R4 and R5 are each independently hydrogen, halogen, or C containing at least one fluorine atom. 1-3 The alkyl group is selected from the group consisting of:

[0144] In some embodiments, the reaction pressure of the second polymerization reaction is 0.1 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, or any value therein.

[0145] In some embodiments, the reaction temperature of the second polymerization reaction is 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or any value therein.

[0146] By carrying out the polymerization reaction at high temperature and pressure, it is possible to improve the reaction efficiency, shorten the reaction time, increase the reaction conversion rate, and improve the uniformity and purity of the product.

[0147] In some embodiments, the second polymerization reaction comprises: adding a solvent and a dispersant to a vessel and filling the vessel with a non-reactive gas; The method further includes the steps of adding a monomer represented by formula III, raising the temperature to 60°C to 90°C, and then adding a second initiator and a chain transfer agent.

[0148] In some embodiments, the second initiator comprises an inorganic peroxide and may be selected from potassium persulfate or ammonium persulfate.

[0149] Nuclear magnetic resonance analysis showed that when inorganic peroxide was used as the initiator, the end groups of the second fluorine-containing polymer included -CF2-CH2OH or -CF2-CH2OOCCH3. The presence of hydroxyl and ester groups in the end groups effectively improved the adhesive properties of the second fluorine-containing polymer and reduced the deterioration of the adhesive performance of the adhesive composition due to its addition.

[0150] In some embodiments, the weight content of the initiator is 3%-12% based on the total weight of the monomers of Formula V.

[0151] High initiator content contributes to improving reaction efficiency, reducing reaction time and improving product uniformity.

[0152] In some embodiments, the chain transfer agent comprises one or more of cyclohexane, isopropyl alcohol, methanol, and acetone.

[0153] [Positive electrode plate] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material, a conductive agent, and in some embodiments, an adhesive composition.

[0154] This positive electrode plate has excellent adhesive strength even when the amount of the adhesive composition added is small.

[0155] In some embodiments, the mass fraction of the adhesive composition is no more than 1.5%, and optionally 0.8%-1.2%, based on the total mass of the positive electrode membrane layer. In some embodiments, the mass content of the adhesive composition is 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, or any value therein.

[0156] The adhesive composition can effectively improve the adhesive performance of the electrode plates even at a low addition amount, and the electrode plates have excellent flexibility and processability, providing the battery with high energy density and cycle performance.

[0157] In some embodiments, the positive electrode active material is a lithium-containing transition metal oxide.

[0158] In some embodiments, the positive electrode active material is at least one of lithium iron phosphate or lithium nickel cobalt manganese oxide, or doped modifications thereof, or conductive carbon-coated, conductive metal-coated, or conductive polymer-coated modifications thereof.

[0159] In some embodiments, the positive electrode current collector may be a metal foil sheet or a composite current collector. For example, aluminum foil may be used as the metal foil sheet. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0160] In some embodiments, the positive electrode active material may be a positive electrode active material known in the art and used in batteries. For example, the positive electrode active material may include at least one of a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and a modified compound of each. However, the present application is not limited to these materials, and other conventional materials usable as positive electrode active materials in batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Here, examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO), lithium nickel oxide (e.g., LiNiO), lithium manganese oxide (e.g., LiMnO, LiMnO), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (e.g., LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM 333 (may be abbreviated as "LiNi") 0.5 Co 0.2 Mn 0.3 O2(NCM 523 (may be abbreviated as "LiNi") 0.5 Co 0.25 Mn 0.25 O2(NCM 211 (may be abbreviated as "LiNi") 0.6 Co 0.2 Mn 0.2 O2(NCM 622 (may be abbreviated as "LiNi") 0.8 Co 0.1 Mn 0.1 O2(NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05Examples of the lithium-containing phosphate having an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4 (which may be abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0161] In some embodiments, the positive electrode film layer optionally further comprises a conductive agent, for example, the conductive agent may comprise at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0162] In some embodiments, a positive electrode plate can be manufactured as follows: Components for manufacturing the positive electrode plate, such as a positive electrode active material, a conductive agent, an adhesive, and any other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, which is then coated onto a positive electrode current collector, and the positive electrode plate is obtained after processes such as drying and cold pressing.

[0163] [Negative electrode plate] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0164] For example, the negative electrode current collector has two surfaces that face each other in the thickness direction thereof, and the negative electrode film layer is disposed on either one or both of the two facing surfaces of the negative electrode current collector.

[0165] In some embodiments, the negative electrode current collector may be a metal foil sheet or a composite current collector. For example, a copper foil may be used as the metal foil sheet. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, or silver alloy) on a polymer base material (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), or polyethylene (PE)).

[0166] In some embodiments, the negative electrode active material may be any negative electrode active material known in the art. For example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, a silicone-based material, a tin-based material, and lithium titanate. The silicone-based material may be selected from at least one of a silicone element, a silicone oxide, a silicone carbon composite, a silicone nitrogen composite, and a silicone alloy. The tin-based material may be selected from at least one of a tin element, a tin oxide, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials usable as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination.

[0167] In some embodiments, the negative electrode membrane layer optionally further comprises an adhesive, which may be selected from at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0168] In some embodiments, the negative electrode film layer optionally further comprises a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0169] In some embodiments, the negative electrode membrane layer optionally further comprises other additives, such as a thickener (eg, sodium carboxymethylcellulose (CMC-Na)).

[0170] In some embodiments, the negative electrode plate can be manufactured in the following manner: Components for manufacturing the negative electrode plate, such as a negative electrode active material, a conductive agent, an adhesive, and any other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, which is then coated onto a negative electrode current collector, and the negative electrode plate is obtained after processes such as drying and cold pressing.

[0171] [Electrolyte] The electrolyte serves to conduct ions between the positive and negative electrodes. The present application does not specifically limit the type of electrolyte, and it can be selected according to needs. For example, the electrolyte may be liquid, gel, or all solid.

[0172] In some embodiments, the electrolyte is an electrolytic solution, which includes an electrolyte salt and a solvent.

[0173] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0174] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, ethyl methyl sulfone, and diethyl sulfone.

[0175] In some embodiments, the electrolyte solution may further optionally contain additives, such as additives for forming a negative electrode film or a positive electrode film, and may further include additives that can improve some battery performance, such as additives for improving the overcharge performance of the battery or additives for improving the high-temperature or low-temperature performance of the battery.

[0176] [Separator] In some embodiments, the secondary battery further includes a separator. The present application does not particularly limit the type of separator, and any known porous separator with good chemical stability and mechanical stability may be selected.

[0177] In some embodiments, the separator may be made of at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and fluorine-containing polymers. The separator may be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without any particular limitation.

[0178] In some embodiments, the positive and negative electrodes and the separator can be fabricated into an electrode assembly by a winding or lamination process.

[0179] In some embodiments, the secondary battery may include an exterior body, which may be used to package the electrode assembly and electrolyte.

[0180] In some embodiments, the exterior of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The exterior of the secondary battery may be a pouch, such as a bag-shaped pouch. The pouch may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0181] The present application does not particularly limit the shape of the secondary battery, which may be cylindrical, rectangular, or any other shape. For example, Figure 1 shows an example of a rectangular secondary battery 5.

[0182] In some embodiments, referring to FIG. 2 , the exterior body may include a case 51 and a cover plate 53. Here, the case 51 may include a bottom plate and a side plate connected to the bottom plate, where the bottom plate and the side plate together form a surrounding accommodating cavity. The case 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to seal the accommodating cavity. The positive electrode plate, the negative electrode plate, and the separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is packaged within the accommodating cavity. An electrolyte is impregnated into the electrode assembly 52. ​​The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art can select the number according to actual needs.

[0183] In some embodiments, the secondary batteries may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, with the specific number being selectable by those skilled in the art depending on the application and capacity of the battery module.

[0184] Fig. 3 shows an example of a battery module 4. Referring to Fig. 3, in the battery module 4, a plurality of secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module 4. Of course, they may be arranged in any other manner. Furthermore, the plurality of secondary batteries 5 may be fixed by fasteners.

[0185] Optionally, the battery module 4 may further include a housing having an accommodating space, and the plurality of secondary batteries 5 are accommodated in this accommodating space.

[0186] In some embodiments, the battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, the specific number of which can be selected by those skilled in the art depending on the application and capacity of the battery pack.

[0187] 4 and 5 show an example of a battery pack 1. Referring to FIGS. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 installed in the battery box. The battery box includes an upper housing 2 and a lower housing 3, and the upper housing 2 covers the lower housing 3 to form a sealed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0188] The present application also provides a power consuming device, the power consuming device including at least one of a secondary battery, a battery module, or a battery pack according to the present application. The secondary battery, the battery module, or the battery pack may be used as a power source for the power consuming device or as an energy storage unit for the power consuming device. The power consuming device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0189] The power consumption device can be selected from a secondary battery, a battery module, or a battery pack depending on its usage needs.

[0190] 6 shows an example of a power consuming device, such as a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the demand for high power output and high energy density of the secondary battery of the power consuming device, a battery pack or battery module can be employed.

[0191] Other examples of devices include mobile phones, tablet computers, notebook computers, etc. These devices generally require a thin design and can use secondary batteries as their power source.

[0192] one, Example The following examples of the present application are described. The examples described below are illustrative and are used only to interpret the present application, and should not be understood as limitations on the present application. If specific techniques or conditions are not specified in the examples, they will be carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. If the manufacturer of the reagents or instruments used is not specified, they are all commercially available ordinary products.

[0193] Example 1 1) Production of adhesive composition Preparation of the first fluorine-containing polymer: First-stage polymerization reaction: Add 4 kg of deionized water and 2 g of methyl cellulose ether to No. 1 and No. 2 10 L autoclaves, evacuate, and replace O2 with N2 three times. Add 5 g of tert-butyl peroxypivalate and 2 g of sodium bicarbonate again, add 1 kg of vinylidene fluoride monomer, and pressurize to 5 MPa. Mix and stir for 30 minutes, heat to 45°C, and react for 4 hours. Second-stage polymerization reaction: The reaction liquid in reactors 1 and 2 was transferred to reactor 3, and nitrogen gas was filled up to a pressure of 7 MPa. The temperature was raised to 70°C, and the reaction was carried out with stirring for 3 hours. Third-stage polymerization reaction: After adding 40 g of cyclohexane, the reaction was continued for 1 hour and then stopped. After centrifuging the reaction system, the solid phase was collected, washed, and dried to obtain polyvinylidene fluoride adhesive.

[0194] Preparation of the second fluorine-containing polymer: A certain amount of PVDF powder (commercially available) with a weight average molecular weight of 1 million and a reaction medium (carbon tetrachloride) were prepared as a suspension and added to a 500mL three-neck flask. N2 was passed through while stirring, and the mixture was heated to 75°C and refluxed for 15 minutes (temperature controlled with a constant temperature water bath). After that, an initiator (5g / L BPO was used as an initiator) and a chlorinating agent (Cl2, with a flow rate of 170mL / min) were added. The HCl produced by the reaction was absorbed with water, and the degree of chlorination of the PVDF was controlled by weighing the amount of HCl absorbed. After the reaction was completed, nitrogen was passed through to remove residual chlorine. The product was washed with alcohol, filtered, and vacuum dried to a constant weight. Finally, PVDF with a chlorine content of approximately 8.0% was obtained.

[0195] Preparation of the third fluorine-containing polymer: A 0.5L autoclave was charged with 219g of deionized water and 0.1g of hydroxypropyl methylcellulose. The atmosphere was purged with nitrogen gas several times to remove oxygen, and then 120g of vinylidene fluoride monomer gas was added. After the monomer addition, the reaction temperature was controlled at 82°C, and 0.12g of water-soluble ammonium persulfate initiator and isopropyl alcohol chain transfer agent were added to initiate the reaction. The amount of initiator added was approximately 8% of the total amount of monomer added. The polymerization reaction time was 1.5h, and the pressure was maintained at 4.4MPa. The reaction product was washed with water and dried to obtain polyvinylidene fluoride polymer.

[0196] The first fluorine-containing polymer, the second fluorine-containing polymer and the third fluorine-containing polymer were blended so that the mass ratio of the first fluorine-containing polymer to the second fluorine-containing polymer to the third fluorine-containing polymer was 86:10:4, and an adhesive composition containing the first fluorine-containing polymer, the second vinylidene fluoride and the third vinylidene fluoride was obtained.

[0197] The production method in Examples 2-9 was the same as that in Example 1, except that the mass ratio of each fluorine-containing polymer in the adhesive composition was adjusted, as specifically shown in the table.

[0198] The production methods in Examples 10 to 13 were the same as those in Example 3, except that the degree of chlorination of PVDF was adjusted, as shown in the table.

[0199] The production method in Example 14 was the same as that in Example 3, except that the second fluorine-containing polymer was replaced with a (vinylidene fluoride-trifluorochloroethylene) copolymer.

[0200] The manufacturing method in Comparative Example 1 was the same as that in Example 1, except that the adhesive composition contained only polyvinylidene fluoride having a weight-average molecular weight of 5,000,000.

[0201] The adhesive compositions used in Examples 15-17 and 20 were the same as those used in Examples 10, 11, 3 and 12, and the batteries were manufactured using these adhesive compositions as adhesives, and the specific method was as follows.

[0202] 2) Manufacturing of positive electrode plates Lithium iron phosphate, an adhesive composition, and acetylene black were stirred in a planetary stirring tank at a revolution speed of 25 r / min for 30 minutes, wherein the mass fraction of the adhesive composition was 1% based on the total mass of the positive electrode film layer; 2.4 kg of N-methylpyrrolidone (NMP) solution was added to the stirring tank, and the mixture was stirred for 70 minutes at a revolution speed of 25 r / min and a rotation speed of 900 r / min. 12.3 g of polyvinylpyrrolidone dispersant was added to the stirring tank, and the mixture was stirred for 60 minutes at a revolution speed of 25 r / min and a rotation speed of 1300 r / min. After stirring was completed, the viscosity of the slurry was tested and controlled to be 8000-15000 mpa·s.

[0203] If the viscosity was high, an N-methylpyrrolidone (NMP) solution was added to reduce the viscosity to the above range. After adding the NMP solution, the mixture was stirred for 30 minutes at a revolution speed of 25 r / min and a rotation speed of 1200 to 1500 r / min to obtain a positive electrode slurry. The produced positive electrode slurry was applied to a carbon-coated aluminum foil, baked at 110°C for 15 minutes, cold-pressed, and then cut into a ring with a diameter of 15 mm to obtain a positive electrode plate.

[0204] 3) Negative electrode plate A piece of metallic lithium served as the negative electrode plate.

[0205] 4) Separator A polypropylene membrane was used as the separator.

[0206] 5) Electrolyte production In a glove box with an argon gas atmosphere (H2O<0.1 ppm, O2<0.1 ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed uniformly at a volume ratio of 3 / 7, LiPF6 lithium salt was added and dissolved in the organic solvent, and the mixture was stirred uniformly to prepare a 1M LiPF6EC / EMC solution, resulting in the electrolyte solution.

[0207] 6) Battery manufacturing The positive electrode plate, negative electrode plate, separator and electrolyte solution in Example 1 were assembled into a button cell box to form a button battery.

[0208] The manufacturing method of the batteries of Examples 18, 19, 21, and 22 was basically the same as that of Example 20, except that the amount of adhesive composition used in the electrode plates was changed, as shown in the table.

[0209] The manufacturing method of the batteries of Examples 23-26 was basically the same as that of Example 20, except that the ratio of each fluorine-containing polymer in the adhesive composition was changed, as shown in the table.

[0210] The manufacturing method of the batteries in Examples 27 to 29 was basically the same as that in Example 20, except that the weight average molecular weight of the third fluorine-containing polymer was changed.

[0211] In Example 27, the preparation method of polyvinylidene fluoride having a weight average molecular weight of 5,000 includes the following:

[0212] A 0.5 L autoclave was charged with 219 g of deionized water and 0.1 g of hydroxypropyl methylcellulose. The atmosphere was purged with nitrogen gas several times to remove oxygen, after which 120 g of vinylidene fluoride monomer gas was added. After the monomer addition, the reaction temperature was controlled at 87°C, and 0.15 g of water-soluble ammonium persulfate initiator and isopropyl alcohol chain transfer agent were added to initiate the reaction. The amount of initiator added was approximately 8% of the total amount of monomer added. The polymerization reaction time was 0.8 h, and the pressure was maintained at 4.4 MPa. The reaction product was washed with water and dried to obtain polyvinylidene fluoride polymer.

[0213] In Example 28, the preparation method of polyvinylidene fluoride with a weight average molecular weight of 20,000 includes the following:

[0214] A 0.5L autoclave was charged with 219g of deionized water and 0.1g of hydroxypropyl methylcellulose. The atmosphere was purged with nitrogen gas several times to remove oxygen, and then 120g of vinylidene fluoride monomer gas was added. After the monomer addition, the reaction temperature was controlled at 83°C, and the reaction was initiated by adding 0.14g of water-soluble ammonium persulfate initiator and isopropyl alcohol chain transfer agent. The amount of initiator added was approximately 8% of the total amount of monomer added. The polymerization reaction time was 1 hour, and the pressure was maintained at 4.4MPa. The reaction product was washed with water and dried to obtain polyvinylidene fluoride polymer.

[0215] In Example 29, the method for producing polyvinylidene fluoride with a weight average molecular weight of 150,000 includes the following:

[0216] A 0.5L autoclave was charged with 219g of deionized water and 0.1g of hydroxypropyl methylcellulose. The atmosphere was purged with nitrogen gas several times to remove oxygen, and then 120g of vinylidene fluoride monomer gas was added. After the monomer was added, the reaction temperature was controlled at 79°C, and 0.12g of water-soluble ammonium persulfate initiator and isopropyl alcohol chain transfer agent were added to initiate the reaction. The amount of initiator added was approximately 7.0% of the total amount of monomer added, and the polymerization reaction time was maintained at 4.4MPa for 1.5 hours. The reaction product was washed with water and dried to obtain polyvinylidene fluoride polymer.

[0217] The manufacturing method of the battery in Examples 30-31 was basically the same as that in Example 20, except that the weight average molecular weight of the second fluorine-containing polymer was changed, and both were commercially available.

[0218] The manufacturing method of the battery in Examples 32 and 33 was basically the same as that in Example 20, except that the weight average molecular weight of the first fluorine-containing polymer was changed.

[0219] The method for producing polyvinylidene fluoride having a weight average molecular weight of 3,000,000 in Example 32 is as follows.

[0220] Add 4kg of deionized water and 2g of methyl cellulose ether to a 10L autoclave, evacuate, and replace O2 with N2 three times. Add 5g of tert-butyl peroxypivalate and 2g of sodium bicarbonate, add 1kg of vinylidene fluoride monomer, and the pressure reaches 7MPa. Mix and stir for 30 minutes, then heat to 45℃ and carry out polymerization reaction. After 10 hours of polymerization, add 20g of cyclohexane to continue the reaction. When the pressure in the reactor drops to 2MPa, the reaction is stopped. The reaction system is centrifuged, and the solid phase is collected, washed, and dried to obtain polyvinylidene fluoride adhesive.

[0221] The method for producing polyvinylidene fluoride having a weight average molecular weight of 10,000,000 in Example 33 is as follows.

[0222] 4 kg of deionized water and 2 g of methylcellulose ether were added to a 10 L autoclave, and the inside of the autoclave was evacuated and replaced with N2.

[0223] First-stage polymerization reaction: Add 4 kg of deionized water and 2 g of methyl cellulose ether to No. 1 and No. 2 10 L autoclaves, evacuate, and replace O2 with N2 three times. Add 5 g of tert-butyl peroxypivalate and 2 g of sodium bicarbonate again, add 1 kg of vinylidene fluoride monomer, and pressurize to 5 MPa. Mix and stir for 30 minutes, heat to 45°C, and react for 9 hours. Second-stage polymerization reaction: The reaction liquid in reactors 1 and 2 was transferred to reactor 3, and nitrogen gas was filled up to a pressure of 7 MPa. The temperature was raised to 70°C, and the reaction was carried out with stirring for 3 hours. Third-stage polymerization reaction: After adding 20 g of cyclohexane, the reaction was continued for 1 hour and then stopped. After centrifuging the reaction system, the solid phase was collected, washed, and dried to obtain polyvinylidene fluoride adhesive.

[0224] The manufacturing method of the battery in Examples 34 and 35 was basically the same as that in Example 20, except that the type of the second fluorine-containing polymer was changed. The second fluorine-containing polymer in Example 34 was a vinylidene fluoride-trifluorochloroethylene copolymer, and the second fluorine-containing polymer in Example 35 was not subjected to chlorination treatment.

[0225] The vinylidene fluoride-trifluorochloroethylene copolymer in Example 34 was produced by the following method.

[0226] 0.8 g of benzoyl peroxide (BPO) was weighed and added to a 1 L autoclave containing 400 mL of 1,1,2-trifluorotrichloroethane. The reactor was sealed, cooled in a dry ice bath, and then evacuated. 25 g of trifluorochloroethylene was passed through, followed by 420 g of vinylidene fluoride. The temperature was raised to room temperature, and the mixture was heated to 45°C and reacted for 7.5 hours. The temperature was then lowered to room temperature, and the unreacted gas was released. The reactor was opened, and the colorless precipitate in the solution was removed and dried in a vacuum drying box at 55°C for 8 hours, finally yielding a P(VDF-TrFE) copolymer.

[0227] The manufacturing method of the battery in Example 36 was basically the same as that in Example 20, except that the type of the first fluorine-containing polymer in the adhesive composition was changed to a (vinylidene fluoride-hexafluoropropylene) copolymer, and the third fluorine-containing polymer was changed to a (vinylidene fluoride-hexafluoropropylene) copolymer.

[0228] The vinylidene fluoride-hexafluoropropylene copolymer having a weight-average molecular weight of 5,000,000 is produced by the following method.

[0229] First-stage polymerization reaction: Add 4 kg of deionized water and 2.5 g of methyl cellulose ether to No. 1 and No. 2 10 L autoclaves, evacuate, and replace O with N2 three times. Add 5 g of tert-butyl peroxypivalate and 2 g of sodium bicarbonate again, add 0.94 kg of vinylidene fluoride and 0.06 kg of hexafluoropropylene, and increase the pressure to 5 MPa. Mix and stir for 30 minutes, then heat to 45°C and react for 4 hours. Second-stage polymerization reaction: The reaction liquid in reactors 1 and 2 was transferred to reactor 3, and nitrogen gas was filled up to a pressure of 7 MPa. The temperature was raised to 70°C, and the reaction was carried out with stirring for 3 hours. Third-stage polymerization reaction: After adding 38 g of cyclohexane, the reaction was continued for 1 hour and then stopped. After centrifuging the reaction system, the solid phase was collected, washed, and dried to obtain a vinylidene fluoride-trifluorochloroethylene copolymer adhesive.

[0230] The method for producing a (vinylidene fluoride-hexafluoropropylene) copolymer having a weight-average molecular weight of 80,000 is as follows.

[0231] A 0.5 L autoclave was charged with 219 g of deionized water and 0.1 g of hydroxypropyl methylcellulose. After removing oxygen by adding nitrogen gas several times, 100 g of vinylidene fluoride monomer gas and 11.9 g of hexafluoropropylene were added. After the monomer addition, the reaction temperature was controlled at 85°C. After adding 0.12 g of water-soluble ammonium persulfate initiator and isopropyl alcohol chain transfer agent, the reaction was initiated. The amount of initiator added was approximately 8% of the total amount of monomer. The polymerization reaction time was 1 h, and the pressure was maintained at 4.6 MPa. The reaction product was washed with water and dried to obtain a second fluorine-containing polymer.

[0232] The adhesive compositions in Comparative Examples 1-3 have different compositions, see Tables 1 and 2 for details.

[0233] 2. Battery performance test 1. Polymer property test 1) Weight average molecular weight test A Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141) was used. A 3.0% mass fraction polystyrene solution sample was used as the standard, and a matching chromatographic column (oil-based: Styragel HT5 DMF 7.8*300mm + Styragel HT4) was selected. A 3.0% polymer glue solution was prepared in purified N-methylpyrrolidone (NMP) solvent and allowed to stand for one day before use. During the test, tetrahydrofuran was first drawn into the syringe and washed several times. Then, 5 ml of the test solution was drawn into the syringe, the air in the syringe was removed, and the needle was wiped dry. Finally, the sample solution was slowly injected into the injection port. After the displayed value stabilized, data was acquired and the weight-average molecular weight was read.

[0234] 2) Crystallinity test 0.5 g of fluorine-containing polymer was placed in an aluminum crucible, flattened, and the crucible was covered with a lid. The test was performed in a nitrogen gas atmosphere with a purge gas of 50 ml / min and a protective gas of 70 ml / min, with a heating rate of 10 °C / min and a test temperature range of -100 °C to 400 °C, using a TA Instruments Model Discovery 250 differential scanning calorimeter (DSC) from the United States to remove thermal history.

[0235] In this test, the temperature change curve of DSC / (Mw / mg) of the fluorine-containing polymer is obtained and integrated, and the peak area is the melting enthalpy ΔH (J / g) of the fluorine-containing polymer, and the adhesive crystallinity=ΔH / (ΔHm100%)*100%, where ΔHm100% is the standard melting enthalpy (crystallization heat of fusion) of the fluorine-containing polymer, and ΔHm100%=104.7 J / g.

[0236] 3) Chlorine content test The alkali fusion method was used to measure the chlorine content of chlorinated PVDF. The specific procedure is as follows: 0.6 grams (to the nearest 1 mg) of the previously ground second fluorine-containing polymer was accurately weighed and placed in a 40 ml porcelain crucible. A layer of a mixture of anhydrous sodium carbonate and potassium nitrate was placed at the bottom of the crucible. After the sample was added, another layer of a mixture of anhydrous sodium carbonate and potassium nitrate was placed on top. The mass ratio of anhydrous sodium carbonate to potassium nitrate was 3:2, both of which are chlorine-free reagents. Approximately 10 g of this mixture was used per sample. The crucible containing the sample was covered with a lid, but not sealed, allowing gas to escape. The crucible was placed in a muffle furnace and gradually heated to 600°C. After 4 hours of melting, heating was stopped when no noticeable gas was volatilized, the melt was uniform and consistent, and contained no black particles. The crucible was removed and allowed to cool slightly before adding boiling water to dissolve the solution. After cooling, the solution was transferred to a 250ml volumetric flask and filled to the mark with deionized water. 5ml of the solution was placed in an Erlenmeyer flask, and one drop of bromophenol blue indicator was added. Five drops of absolute ethanol were then added. The mixture was shaken to homogenize the solution. Concentrated nitric acid was then added to neutralize most of the alkali. 0.2ml / L of nitric acid was then added to turn the bromophenol blue yellow. A few more drops were added to bring the solution to a pH of 1.5-2. Five drops of diphenylcarbazone solution were then added, and the mixture was titrated with standard mercury nitrate solution. The color changed from yellow-red to reddish-purple at the end point. A blank experiment was performed under the same conditions. Three replicates were performed for each sample.

[0237] The mass fraction of chlorine, Cl%, was calculated using the following formula:

[0238] Cl%=[(Vl-V2)×C×35.46×2 / W]×100 where V1 and V2 are the volumes of the mercury nitrate standard solution consumed in the titration of the sample and blank, respectively, in mL; C is the concentration of the mercury nitrate standard solution, in mol / L; and W is the mass of the sample, in mg.

[0239] 2. Slurry performance test 1) Slurry fluidity test An appropriate amount of positive electrode slurry was taken with a chemical spoon, and the smooth gravity flow of the positive electrode slurry was observed. If the gravity flow was smooth, it was judged as OK, but if the fluidity was poor and the slurry became jelly-like and formed lumps, indicating the appearance of gel, it was judged as NG.

[0240] 2) Slurry filtration performance test A 500 ml beaker was placed on the bottom end of the 200 mesh filter bracket, and 500 ml of slurry was taken and placed on the filter to filter. The time when the volume of the slurry in the beaker reached 300 ml was recorded, and this time was used to judge the filtration performance of the slurry. If the filtration time was less than 120 seconds, it indicated that the filtration performance of the slurry was "OK", and if the slurry could not pass through the filter, it indicated that the filtration performance of the slurry was poor and was judged as "NG".

[0241] 3. Plate performance test 1) Adhesion test According to the national standard GB-T2790-1995 "Testing method for 180° peel strength of adhesives", the adhesive strength testing process for the examples and comparative examples of this application is as follows:

[0242] A sample 30 mm wide and 100-160 mm long was cut using a blade, and special double-sided tape was attached to a steel plate, making the tape 20 mm wide and 90-150 mm long. The positive electrode film layer surface of the electrode plate sample cut in the previous step was attached to the double-sided tape, and then rolled three times in the same direction using a 2 kg press roller.

[0243] A paper tape having the same width as the electrode plate and a length of 250 mm was fixed to the electrode plate current collector, and was also fixed with masking tape.

[0244] The Sansi tensioning device was turned on (sensitivity 1N) and the indicator light was lit. The stopper block was adjusted to the appropriate position, and the end of the steel plate not attached to the electrode plate was secured with the lower fixture. The paper tape was folded over and secured with the upper fixture. The position of the upper fixture was adjusted using the "up" and "down" buttons on the tensioning device's manual controller. The test was then performed and the numerical value was read. The force when the electrode plate was balanced under the force was divided by the tape width to determine the electrode plate adhesive strength per unit length, which characterized the adhesive strength between the positive electrode film layer and the current collector.

[0245] 2) Measurement of positive electrode film layer resistance: After drying, the positive electrode slurry (film layer) was cut into small rings with a diameter of 3 mm from the left, center, and right sides of the positive plate. Turn on the Yuan Neng Technology plate resistor, place it in the appropriate position on the plate resistor's "probe," click the "Start" button, and read the display value once it stabilizes. Each small ring was tested in two positions, and the average of the final six measurements was calculated to determine the film layer resistance of this plate.

[0246] 3) Plate brittleness test The positive electrode plate in the example was cut into a test sample of 20 x 100 mm in size and prepared for use. The electrode plate was bent in half, fixed, and pressed once with a 2 kg roller. A light-transmitting metal film was applied to the folded portion of the electrode plate. Cut Check for the presence of light-transmitting and metal Cut If there is no adhesive, fold the electrode plate in half again and fix it, then roll it once with a 2 kg roller to apply pressure to the folded part of the electrode plate. Cut Check for the presence of light-transmitting or metal particles at the folded part of the electrode plate. Cut The above steps were repeated until the positive electrode plate was folded in half and the number of times light was transmitted was recorded. Three sets were measured in parallel and the average value was calculated.

[0247] 4 , Battery performance test 1) Battery capacity retention test The battery capacity retention test process is as follows: At 25°C, a button battery is charged to 3.65V at a constant current of 1 / 3C, then further charged to 0.05C at a constant voltage of 3.65V, left for 5 minutes, and then discharged to 2.5V at a constant voltage of 1 / 3C. The resulting capacity is the initial capacity, C0. The same battery is repeated these steps, recording the discharge capacity, Cn, of the battery after the nth cycle. The battery capacity retention after each cycle is calculated as Pn = Cn / C0 * 100%. The values ​​of these 500 points, P1, P2...P500, are taken as the ordinate and the corresponding cycle number as the abscissa, to obtain a curve of battery capacity retention versus cycle number.

[0248] In this test process, the first cycle corresponds to n = 1, the second cycle corresponds to n = 2, ... the 500th cycle corresponds to n = 500. The battery capacity retention data in the table for the Examples and Comparative Examples is the data measured after 500 cycles under the above test conditions, i.e., the P500 value.

[0249] 3. Analysis of the test results of each example and comparative example According to the above method, the batteries of the examples and comparative examples were manufactured, and the performance parameters were measured. The results are shown in Tables 1 and 2 below.

[0250] [Table 1-1] [Table 1-2] [Table 1-3]

[0251] [Table 2-1] [Table 2-2] [Table 2-3] [Table 2-4] [Table 2-5] [Table 2-6] [Table 2-7] [Table 2-8] [Table 2-9] [Table 2-10] [Table 2-11] [Table 2-12] [Table 2-13]

[0252] As can be seen from a comparison between Examples 1-14 and Comparative Example 1, the inclusion of fluorine-containing polymers with different weight-average molecular weights in the adhesive composition can reduce the crystallinity of the polymer. As can be seen from Examples 1-9, the crystallinity of the adhesive composition decreased with an increase in the content of the second fluorine-containing polymer. As can be seen from Examples 10-13, when the chlorine content of the chlorinated polyvinylidene fluoride was 8%, the crystallinity was only 4.2%, and the adhesive composition was essentially amorphous.

[0253] As can be seen from Example 14, the vinylidene fluoride-trifluorochloroethylene copolymer, as the second fluorine-containing polymer, could also effectively reduce the crystallinity of the adhesive composition. However, when the chlorine content of the vinylidene fluoride-trifluorochloroethylene copolymer was 8%, its crystallinity was higher than that of chlorinated polyvinylidene fluoride.

[0254] As can be seen from the comparison between Examples 15-36 and Comparative Examples 1-2, the adhesive composition can significantly reduce the amount of fluorine-containing polymer used, and the inclusion of a third fluorine-containing polymer in the adhesive composition can effectively improve the processing performance of the slurry, improve the flexibility of the battery, and further optimize the cycle performance of the battery while maintaining high adhesive performance.

[0255] As can be seen from the comparison of Examples 15-17, 20 with Examples 35, 36, the addition of a second fluorine-containing polymer after chlorination further improved the flexibility of the polymer and reduced the possibility of embrittlement of the electrode plate.

[0256] As can be seen from Examples 18-22, with increasing dosage of adhesive composition, the adhesive strength of the electrode plates constantly increased, and flexibility and cycle capacity retention first increased and then decreased.

[0257] It should be noted that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any embodiment that has substantially the same configuration as the technical idea and achieves the same effects within the scope of the technical solution of the present application is included within the technical scope of the present application. In addition, various modifications that a person skilled in the art can make to the embodiments without departing from the spirit of the present application, and other methods configured by combining some of the components of the embodiments, are also included within the scope of the present application. [Explanation of symbols]

[0258] 1 battery pack, 2 upper housing, 3 lower housing, 4 battery module, 5 secondary battery, 51 case, 52 electrode assembly, 53 cover plate.

Claims

1. An adhesive composition comprising a first fluorine-containing polymer, a second fluorine-containing polymer, and a third fluorine-containing polymer, wherein the weight average molecular weight of the first fluorine-containing polymer is 3,000,000 to 10,000,000, the weight average molecular weight of the second fluorine-containing polymer is 600,000 to 1,100,000, and the weight average molecular weight of the third fluorine-containing polymer is 5,000 to 150,000, and the mass content of the first fluorine-containing polymer is 16% to 86% based on the total mass of the first fluorine-containing polymer, the second fluorine-containing polymer, and the third fluorine-containing polymer.

2. The adhesive composition according to claim 1, characterized in that the mass content of the second fluorine-containing polymer is 10% to 86% based on the total mass of the first fluorine-containing polymer, the second fluorine-containing polymer, and the third fluorine-containing polymer, and the mass content of the third fluorine-containing polymer is 4% or more based on the total mass of the first fluorine-containing polymer, the second fluorine-containing polymer, and the third fluorine-containing polymer.

3. 10. The adhesive composition of claim 1, wherein the adhesive composition has a crystallinity of no more than 40%.

4. The adhesive composition described in claim 3, characterized in that the crystallinity of the adhesive composition is 5% to 40%.

5. 2. The adhesive composition according to claim 1, wherein the first fluorine-containing polymer contains structural units derived from vinylidene fluoride.

6. The first fluorine-containing polymer further comprises a structural unit shown in Formula I: Here, R 1 is a C group containing fluorine, chlorine, and at least one fluorine atom 1-3 The adhesive composition of claim 1, further comprising one or more of:

7. 2. The adhesive composition according to claim 1, wherein the first fluorine-containing polymer comprises one or more of polyvinylidene fluoride, vinylidene fluoride-trifluorochloroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-trifluorochloroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride-trifluorochloroethylene-tetrafluoroethylene-hexafluoropropylene copolymer.

8. The second fluorine-containing polymer comprises structural units shown in Formula II: Here, R 2 , R 3 each independently represents a C group containing hydrogen, a halogen, and at least one fluorine atom; 1-3 The adhesive composition according to claim 1, characterized in that it contains at least one of an alkyl group and an alkyl group.

9. 2. The adhesive composition according to claim 1, wherein the second fluorine-containing polymer contains chlorine.

10. 2. The adhesive composition according to claim 1, wherein the chlorine content in the second fluorine-containing polymer does not exceed 8%, based on the total mass of the second fluorine-containing polymer.

11. 2. The adhesive composition of claim 1, wherein the crystallinity of the second fluorine-containing polymer does not exceed 47%.

12. The adhesive composition of claim 11, wherein the crystallinity of the second fluorine-containing polymer does not exceed 30%.

13. 2. The adhesive composition according to claim 1, wherein the weight average molecular weight of the second fluorine-containing polymer is 600,000 to 1,100,000.

14. 2. The adhesive composition according to claim 1, wherein the second fluorine-containing polymer comprises at least one of polyvinylidene fluoride, chlorinated polyvinylidene fluoride, chlorinated poly(vinylidene fluoride-hexafluoropropylene), and poly(vinylidene fluoride-trifluorochloroethylene).

15. The third fluorine-containing polymer comprises a structural unit shown in Formula III: Here, the R 4 , R 5 and each independently contain at least one of hydrogen, fluorine, chlorine, or a trifluoromethyl group.

16. 2. The adhesive composition according to claim 1, wherein the end group of the third fluorine-containing polymer contains a hydroxyl group or an ester group.

17. 2. The adhesive composition of claim 1, wherein the third fluorine-containing polymer comprises one of polytetrafluoroethylene, polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride-tetrafluoroethylene) copolymer, poly(vinylidene fluoride-trifluorochloroethylene) copolymer, and poly(vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene) copolymer.

18. 18. A positive electrode plate comprising: a positive electrode current collector; and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material, a conductive agent, and the adhesive composition according to claim 1.

19. The positive electrode plate according to claim 18 , wherein the mass fraction of the adhesive composition does not exceed 1.5% based on the total mass of the positive electrode film layer.

20. A positive electrode plate as described in Claim 19, characterized in that the mass fraction of the adhesive composition is 0.8% to 1.2% based on the total mass of the positive electrode film layer.

21. 19. The positive electrode plate according to claim 18, wherein the positive electrode active material is a lithium-containing transition metal oxide.

22. A positive electrode plate as described in claim 21, characterized in that the positive electrode active material is at least one of lithium iron phosphate or lithium nickel cobalt manganese oxide, or a doped modified material thereof, or a conductive carbon-coated modified material thereof, a conductive metal-coated modified material, or a conductive polymer-coated modified material thereof.

23. A secondary battery comprising an electrode assembly and an electrolyte, the electrode assembly comprising a separator, a negative electrode plate, and the positive electrode plate according to claim 18.

24. A power consuming device comprising the secondary battery of claim 23.

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