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 1.5 million to 5 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] CROSS-REFERENCE TO RELATED APPLICATIONS This application references 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 Use Thereof, Positive Electrode Slurry, Secondary Battery, Battery Module, Battery Pack, and Power Consumption Device," CN patent application No. 202211052014.9, filed on August 30, 2022, entitled "Fluorine-Containing Polymer, Manufacturing Method and Use Thereof, Positive Electrode Slurry, Secondary Battery, Battery Module, Battery Pack, and Power Consumption Device," and CN patent application No. 202211046282.X, 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.

[0002] The present application relates to the field of secondary battery technology, and in particular to an adhesive, a manufacturing method, a positive electrode plate, a secondary battery, a battery module, a battery pack, and a power consuming device. [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 as its object to provide an adhesive that can exert excellent adhesive strength even at a low addition amount and has good processability.

[0006] To achieve the above object, a first aspect of the present application provides an adhesive, which comprises a first fluorine-containing polymer and a second fluorine-containing polymer, wherein the weight-average molecular weight of the first fluorine-containing polymer is 1.5 million to 5 million, and the weight-average molecular weight of the second fluorine-containing polymer does not exceed 600,000.

[0007] This adhesive can ensure that the plates have sufficient adhesive strength at low dosages, improving the cycling performance of the battery.

[0008] In any embodiment, the mass content of the second fluorine-containing polymer is 0.1% to 10% based on the total mass of the adhesive composition.

[0009] By controlling the mass ratio of the first fluorine-containing polymer to the second fluorine-containing polymer within an appropriate range, the adhesive can have excellent adhesive strength to the electrode plate even at a low addition amount, and can improve the capacity retention rate during battery cycling. Adding a small amount of the second fluorine-containing polymer to the first fluorine-containing polymer can effectively improve the crystallinity and processability of the adhesive, reduce production costs, and further improve the cycle performance of the battery.

[0010] In either embodiment, the adhesive composition has a crystallinity of 45% or less, optionally 15%-45%.

[0011] By adding the second fluorine-containing polymer to the first fluorine-containing polymer, the crystallinity of the adhesive can be effectively reduced and the flexibility of the electrode plate can be improved.

[0012] In either embodiment, the first fluorine-containing polymer comprises structural units derived from vinylidene fluoride.

[0013] In any embodiment, the first fluorine-containing polymer further comprises a structural unit according to Formula I: [ka] wherein R1 includes one or more of hydrogen, fluorine, chlorine, and trifluoromethyl groups.

[0014] In either embodiment, the polydispersity coefficient of the first fluorine-containing polymer is from 1.5 to 2.5, and optionally from 2 to 2.3.

[0015] By adjusting the polydispersity coefficient of the first fluorine-containing polymer within an appropriate range, it is possible to provide excellent adhesion to the electrode plate and improve the capacity retention rate during battery cycling, and also to effectively increase the solid content of the slurry and reduce production costs.

[0016] In either embodiment, the crystallinity of the first fluorine-containing polymer is 34%-48%, optionally 40%-48%.

[0017] In any embodiment, the viscosity of a glue solution containing 4% by mass of the first fluorine-containing polymer, which is produced by dissolving the first fluorine-containing polymer in N-methylpyrrolidone, is 2400 mPa·s to 5000 mPa·s, and optionally 3500 to 5000 mPa·s.

[0018] When preparing a positive electrode slurry, the adhesive must have a certain viscosity to prevent settling of the positive electrode active material and auxiliary agents such as conductive agents and to ensure the slurry is relatively stable. In conventional technologies, to achieve a glue solution viscosity of 2400 mPa·s to 5000 mPa·s, the glue solution must contain at least 7% by mass of adhesive. However, the first fluorine-containing polymer of the present application can achieve the expected viscosity of the glue solution with a usage amount of 4%, providing a basis for reducing the adhesive content in the positive electrode membrane layer.

[0019] 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.

[0020] In any embodiment, the second fluorine-containing polymer comprises structural units shown in Formula II: [ka] where R2 and R3 are each independently hydrogen, halogen, or C containing at least one fluorine atom. 1-3 It contains at least one alkyl group.

[0021] In any embodiment, R2 and R3 each independently comprise at least one of hydrogen, fluorine, chlorine, and a trifluoromethyl group.

[0022] In either embodiment, the end groups of the second fluorine-containing polymer contain hydroxyl groups or ester groups.

[0023] The second 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 second fluorine-containing polymer. The end groups of the second fluorine-containing polymer contain hydroxyl groups or ester groups, which can effectively improve the adhesion of the second fluorine-containing polymer and reduce the decrease in electrode plate adhesion performance caused by the addition of the second fluorine-containing polymer.

[0024] In any embodiment, the weight average molecular weight of the second fluorine-containing polymer is 5,000 to 600,000.

[0025] In any embodiment, the second fluorine-containing polymer comprises one or more of polytetrafluoroethylene, polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride-tetrafluoroethylene) copolymer, poly(vinylidene fluoride-chlorofluoroethylene) copolymer, and poly(vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene) copolymer.

[0026] A second aspect of the present application provides a method for producing an adhesive composition, comprising: producing a first fluorine-containing polymer by carrying out a first polymerization reaction on a raw material containing a vinylidene fluoride monomer under polymerizable conditions to produce a first fluorine-containing polymer, the weight-average molecular weight of the first fluorine-containing polymer being 1.5 million to 5 million; producing a second fluorine-containing polymer by carrying out a second polymerization reaction on a fluorine-containing monomer under polymerizable conditions to produce a second fluorine-containing polymer, the weight-average molecular weight of the second fluorine-containing polymer not exceeding 600,000; and blending: blending the first fluorine-containing polymer and the second fluorine-containing polymer to produce an adhesive composition.

[0027] In any embodiment, the first method for producing a fluorine-containing polymer specifically includes: carrying out a first polymerization reaction for 6 hours to 12 hours 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 a raw material containing vinylidene fluoride monomer; adding a chain transfer agent, lowering the pressure in the reaction system to 2 MPa to 2.5 MPa, stopping the reaction, and performing solid-liquid separation to leave a solid phase and obtain a first fluorine-containing polymer.

[0028] In any embodiment, the second method for producing a fluorine-containing polymer specifically includes: carrying out a second polymerization reaction of at least one monomer represented by formula III 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 into a liquid and a solid phase to obtain a second fluorine-containing polymer; [ka] where R4 and R5 are each independently hydrogen, halogen, or C 1-3 It contains at least one alkyl group.

[0029] In any embodiment, 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 adding a second initiator and a chain transfer agent to carry out a second polymerization reaction.

[0030] In either embodiment, the second initiator comprises an inorganic peroxide and may be selected from potassium persulfate or ammonium persulfate.

[0031] Nuclear magnetic testing 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.

[0032] In one embodiment, the weight content of the initiator is 3%-12% based on the total weight of the monomers of formula III.

[0033] In any embodiment, the chain transfer agent comprises one or more of cyclohexane, isopropyl alcohol, methanol, and acetone.

[0034] A third 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 according to any of the embodiments or the adhesive produced by the production method according to any of the embodiments.

[0035] This positive electrode plate has excellent adhesive strength even with a low amount of adhesive added.

[0036] In any embodiment, the mass fraction of the adhesive does not exceed 1.2%, based on the total mass of the positive electrode membrane layer.

[0037] By controlling the mass fraction of the adhesive within an appropriate range, it is possible to ensure that the electrode plates have sufficient adhesive strength while improving the loading amount of the active material in the battery electrode plates, thereby contributing to further improving the power performance of the battery.

[0038] In either embodiment, the positive electrode active material is a lithium-containing transition metal oxide.

[0039] 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.

[0040] A fourth 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 third aspect of the present application.

[0041] A fifth aspect of the present application provides a power consuming device, the power consuming device including the secondary battery of the fourth aspect of the present application. [Brief explanation of the drawings]

[0042] [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

[0043] Hereinafter, with appropriate reference to the drawings, embodiments specifically disclosing the adhesive composition and manufacturing method thereof, positive electrode plate, secondary battery, battery module, battery pack, and electric device of the present application 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.

[0044] 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.

[0045] Unless otherwise stated, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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).

[0050] Fluorine-containing polymers are currently 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 loading of the active material in the electrode plate, which affects the improvement of the battery's power performance and makes it difficult to meet the requirements for battery cycle performance.

[0051] [glue] The present application provides an adhesive composition, which includes a first fluorine-containing polymer and a second fluorine-containing polymer, wherein the weight-average molecular weight of the first fluorine-containing polymer is 1.5 million to 5 million, and the weight-average molecular weight of the second fluorine-containing polymer does not exceed 600,000.

[0052] As used herein, the term "adhesive composition" is a mixture that forms a colloidal solution or dispersion in a dispersing medium.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] In some embodiments, the weight average molecular weight of the first fluorine-containing polymer is 1.5 million to 5 million, or 1.5 million, 2 million, 2.5 million, 3 million, 3.2 million, 3.5 million, 4 million, 4.5 million, 5 million, or any number therein.

[0060] In some embodiments, the weight average molecular weight of the second fluorine-containing polymer does not exceed 600,000. 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, 200,000, 250,000, 300,000, 350,000, 400,000, 450,000, 500,000, 550,000, 600,000, or any number therein.

[0061] 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 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 * 300 mm + Styragel HT4). A 3.0% polymer 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. When the displayed value becomes stable, the data is acquired and the weight average molecular weight is read.

[0062] The fluorine contained in the first and second fluorine-containing polymers forms hydrogen bonds with hydroxyl and / or carboxyl groups on the active material and current collector surfaces, improving the adhesive strength of electrode plates. The first fluorine-containing polymer, with a weight-average molecular weight of 1.5 million to 5 million, can improve the adhesive strength of electrode plates at low addition levels and improve the capacity retention rate during battery cycling. Adding the second fluorine-containing polymer to the adhesive reduces the crystallinity of the adhesive, improving the flexibility of electrode plates and further improving the processability of the slurry. This prevents delamination during the drying process of electrode plate production, improves the uniformity of the active material dispersion in the electrode plates, reduces diaphragm resistance, and further optimizes the battery's cycling performance. The adhesive composition can ensure sufficient adhesive strength and flexibility of electrode plates at low addition levels, which is advantageous for improving the energy density and cycling performance of batteries.

[0063] In some embodiments, the mass content of the second fluorine-containing polymer is 0.1% to 10% based on the total mass of the adhesive composition.

[0064] In some embodiments, the mass content of the second fluorine-containing polymer, based on the total mass of the adhesive composition, is optionally 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any number therein.

[0065] If the mass ratio of the first fluorine-containing polymer to the second fluorine-containing polymer is too large, i.e., the mass of the first fluorine-containing polymer is too high, the purpose of reducing costs cannot be achieved. If the mass ratio of the first fluorine-containing polymer to the second fluorine-containing polymer is too small, i.e., the mass of the first fluorine-containing polymer is too low, the adhesion strength of the electrode plates will be reduced, which will affect the cycle performance of the battery.

[0066] By controlling the mass ratio of the first fluorine-containing polymer to the second fluorine-containing polymer within an appropriate range, the adhesive can have excellent adhesive strength to the electrode plate even at a low addition amount, and can improve the capacity retention rate during battery cycling. Adding a small amount of the second fluorine-containing polymer to the first fluorine-containing polymer can effectively improve the crystallinity and processability of the adhesive, reduce production costs, and further improve the cycle performance of the battery.

[0067] In some embodiments, the adhesive composition has a crystallinity of 45% or less, optionally 15%-45%.

[0068] 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.

[0069] In the present application, the crystallinity test can be carried out by selecting a method known in the art, for example, by adopting differential scanning calorimetry.In some embodiments, 0.5g of the fluorine-containing polymer composition is placed in an aluminum crucible, flattened, and the crucible is covered with a lid.The test is carried out in a nitrogen gas atmosphere with a purge gas of 50ml / min, a protective gas of 70ml / min, a temperature rise rate of 10°C / min, and a test temperature range of -100°C to 400°C using a differential scanning calorimeter (DSC) of TA Instruments, Model Discovery 250, USA, to remove thermal history.

[0070] In this test, the temperature change curve of DSC / (Mw / mg) of the fluorine-containing polymer 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 (crystallization heat of fusion) of the fluorine-containing polymer, and ΔHm=104.7 J / g.

[0071] By adding the second fluorine-containing polymer to the first fluorine-containing polymer, the crystallinity of the adhesive can be effectively reduced and the flexibility of the electrode plate can be improved.

[0072] 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.

[0073] In some embodiments, the first fluorine-containing polymer further comprises a structural unit according to Formula I: [ka] wherein R1 includes one or more of hydrogen, fluorine, chlorine, and trifluoromethyl groups.

[0074] 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.

[0075] In some embodiments, the polydispersity coefficient of the first fluorine-containing polymer is 1.5 to 2.5, optionally 2 to 2.3, or optionally 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, or any number therein.

[0076] As used herein, the term "polydispersity coefficient" is the ratio of the weight average molecular weight of a polymer to the number average molecular weight of the polymer.

[0077] As used herein, the term "number average molecular weight" is the sum of the products of the mole fractions occupied by molecules of different molecular weights in a polymer and the corresponding molecular weights.

[0078] If the polydispersity coefficient of the first fluorine-containing polymer is too large, the degree of polymerization of the first fluorine-containing polymer will be relatively dispersed, affecting the uniformity of the adhesive, and the adhesive will not be able to uniformly adhere the positive electrode active material to the current collector, affecting the cycle performance of the battery and reducing the solid content of the slurry, making it impossible to further improve the energy density of the battery. If the polydispersity coefficient of the first fluorine-containing polymer is too small, the manufacturing process will be more difficult, the yield will be relatively low, and the production cost will be relatively high.

[0079] By adjusting the polydispersity coefficient of the first fluorine-containing polymer within an appropriate range, it is possible to provide excellent adhesion to the electrode plate and improve the capacity retention rate during battery cycling, and also to effectively increase the solid content of the slurry and reduce production costs.

[0080] In this application, the polydispersity coefficient of the first fluorine-containing polymer can be tested by any method known in the art, such as gel chromatography, using a Waters 2695 Isocratic HPLC gel chromatograph (differential refractive index detector 2141). In some embodiments, a 3.0% mass fraction polystyrene solution sample is used as the reference, and a matching chromatographic column (oil-based: Styragel HT5 DMF 7.8*300mm + Styragel HT4) is selected. 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 and washed several times. 5 ml of the test solution is then drawn into the syringe, the air in the syringe is removed, and the needle tip is wiped dry. Finally, the sample solution is slowly injected into the injection port. Data is acquired when the displayed value stabilizes. The weight average molecular weight a and number average molecular weight b are read off, respectively. The polydispersity coefficient = a / b.

[0081] In some embodiments, the crystallinity of the first fluorine-containing polymer is 34% to 48%. In some embodiments, the crystallinity of the first fluorine-containing polymer is 40% to 48%. In some embodiments, the crystallinity of the first fluorine-containing polymer is 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, and any number therein.

[0082] In some embodiments, the viscosity of a glue solution containing the first fluorine-containing polymer at a mass content of 4% produced by dissolving the first fluorine-containing polymer in N-methylpyrrolidone is 2400 mPa·s to 5000 mPa·s. In some embodiments, the viscosity of the glue solution containing the first fluorine-containing polymer at a mass content of 4% prepared by dissolving the first fluorine-containing polymer in N-methylpyrrolidone is optionally 2500 mPa·s to 3000 mPa·s, 3000 mPa·s to 3300 mPa·s, 3300 mPa·s to 3500 mPa·s, 3500 mPa·s to 3800 mPa·s, 3800 mPa·s to 4000 mPa·s, 4000 mPa·s to 4200 mPa·s, 4200 mPa·s to 4600 mPa·s, 4600 mPa·s to 5000 mPa·s, 3100 mPa·s to 3400 mPa·s, 3400 mPa·s to 3800 mPa·s, 3800 mPa·s to 4600 mPa·s, 4600 mPa·s to 5000 mPa·s, The value is one of the following: mPa·s to 5000 mPa·s, 3600 mPa·s to 5000 mPa·s.

[0083] If the viscosity of the first fluorine-containing polymer is too high, the viscosity of the adhesive solution produced will be too high, making it difficult to stir and reducing the dispersibility of the adhesive, making it difficult for the adhesive to uniformly adhere the positive electrode active material to the current collector, which will affect the cycle performance of the battery and also reduce the viscosity of the adhesive solution, slowing down the speed of the slurry production process. If the viscosity of the first fluorine-containing polymer is too low, the viscosity of the adhesive solution produced will be too low, making it difficult for the electrode plate to have sufficient adhesive strength even at low addition amounts.

[0084] Furthermore, when preparing a positive electrode slurry, the adhesive must have a certain viscosity to prevent the positive electrode active material and auxiliary agents, such as conductive agents, from settling and to ensure the slurry remains relatively stable. In the prior art, achieving a glue solution viscosity of 2400 mPa·s to 5000 mPa·s required the adhesive to be present in an amount of at least 7% by mass, based on the mass of the glue solution. However, the first fluorine-containing polymer of the present application can achieve the desired viscosity of the glue solution with a usage amount of 4%, providing a basis for reducing the adhesive content in the positive electrode membrane layer.

[0085] By controlling the viscosity of the first fluorine-containing polymer solution within an appropriate range, the electrode plate can have excellent adhesive performance even with a low additive amount of adhesive, and the capacity retention rate during the cycle process of the battery can be improved.

[0086] In some embodiments, the second fluorine-containing polymer comprises structural units according to Formula II: [ka] where R2 and R3 are each independently selected from hydrogen, halogen, and C containing at least one fluorine atom. 1-3 and at least one alkyl group.

[0087] In some embodiments, R2 and R3 each independently comprise at least one of hydrogen, fluorine, chlorine, or a trifluoromethyl group.

[0088] In some embodiments, the second fluorine-containing polymer comprises one of polytetrafluoroethylene, polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride-tetrafluoroethylene) copolymer, poly(vinylidene fluoride-chlorofluoroethylene) copolymer, and poly(vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene) copolymer.

[0089] In some embodiments, the end groups of the second fluorine-containing polymer contain hydroxyl or ester groups.

[0090] The second 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 second fluorine-containing polymer. The end groups of the second fluorine-containing polymer contain hydroxyl groups or ester groups, which can effectively improve the adhesion of the second fluorine-containing polymer and reduce the decrease in electrode plate adhesion performance caused by the addition of the second fluorine-containing polymer.

[0091] 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.

[0092] In one embodiment of the present application, there is provided a method for producing an adhesive composition, the method comprising the steps of: 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 1.5 million to 5 million; Preparation of a second fluorine-containing polymer: carrying out a second polymerization reaction on a raw material containing vinylidene fluoride monomer under polymerizable conditions to prepare a second fluorine-containing polymer, and the weight-average molecular weight of the second fluorine-containing polymer is not more than 600,000; Blending: A first fluorine-containing polymer and a second fluorine-containing polymer are blended to produce an adhesive composition.

[0093] 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.

[0094] This adhesive manufacturing method is simple, environmentally friendly, reduces costs, and is favorable for industrial production. At the same time, the adhesive manufactured by this method provides excellent adhesion to the electrode plates and can improve the capacity retention rate during battery cycling at low additive amounts.

[0095] In some embodiments, in the blending step, the weight ratio of the first fluorine-containing polymer to the second fluorine-containing polymer is 999:1 to 9:1. In some embodiments, the weight ratio of the first fluorine-containing polymer to the second fluorine-containing polymer is optionally 9:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, 999:1, or any value therein.

[0096] By controlling the mass ratio of the first fluorine-containing polymer to the second fluorine-containing polymer within an appropriate range, the adhesive can have excellent adhesive strength to the electrode plate even with a small amount added, and can improve the processability of the battery.

[0097] In some embodiments, the step of synthesizing the first fluorine-containing polymer includes carrying out a first polymerization reaction for 6 hours to 12 hours using a raw material containing a 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; The reaction is stopped by adding a chain transfer agent and lowering the pressure in the reaction system to 2 MPa to 2.5 MPa, followed by solid-liquid separation to leave a solid phase.

[0098] As used herein, the term "non-reactive gas" refers to a gas that does not react with the reactants in the reaction system; common non-reactive gases are inert gases such as argon gas and nitrogen gas.

[0099] In some embodiments, the reaction pressure of the first polymerization reaction is one of 6 MPa to 6.5 MPa, 6.5 MPa to 7 MPa, 7 MPa to 7.5 MPa, 7.5 MPa to 8 MPa, 6 MPa to 7 MPa, and 7 MPa to 8 MPa.

[0100] In some embodiments, the reaction temperature of the first polymerization reaction is one of 45°C to 50°C, 50°C to 55°C, 55°C to 60°C, 45°C to 55°C, or 50°C to 60°C.

[0101] In some embodiments, the duration of the first polymerization reaction is one of 6 hours to 7 hours, 7 hours to 8 hours, 8 hours to 9 hours, 9 hours to 10 hours, 10 hours to 11 hours, 11 hours to 12 hours, 6 hours to 8 hours, and 6 hours to 10 hours.

[0102] When the polymerization reaction pressure is relatively high, the pressure at which the monomer enters the reaction solution is relatively high, and the monomer enters the reaction solution in large quantities, causing a large-scale polymerization reaction to occur, resulting in a large number of first fluorine-containing polymers being produced and a large polydispersity coefficient; with the decrease in monomer, the polymerization reaction will be short of monomer supply, and the weight-average molecular weight of the first fluorine-containing polymer being produced will be relatively small, which will affect the adhesion strength of the electrode plate and the cycle capacity retention rate of the battery.

[0103] If the polymerization reaction pressure is relatively low, the pressure at which the monomer enters the reaction solution is relatively low, and the reaction monomer cannot be continuously replenished, which is unfavorable to the continuous progress of the polymerization, and the weight-average molecular weight of the produced first fluorine-containing polymer is too low to meet the adhesive strength requirements, and the cycle performance of the battery is also somewhat reduced.

[0104] If the polymerization reaction temperature is low, the promotion force of copolymerization is relatively small, the polymerization reaction is insufficient, and the molecular weight of the first fluorine-containing polymer produced is small, the adhesive strength is greatly reduced, and the cycle performance is obviously reduced.

[0105] When the polymerization reaction temperature is high, a large-scale polymerization reaction occurs, resulting in a large number of first fluorine-containing polymers being produced, and as the monomer decreases, the polymerization reaction will be insufficient in monomer supply, resulting in a relatively small weight-average molecular weight of the first fluorine-containing polymer produced, which will affect the adhesive strength of the electrode plate and the cycle capacity retention rate of the battery.

[0106] If the polymerization reaction time is too short, the polymerization reaction cannot be continued, and the weight-average molecular weight of the produced first fluorine-containing polymer is small, which also leads to a decrease in adhesive strength and cycle performance.

[0107] If the polymerization reaction time is long, the polymerization conditions will no longer be achieved due to continuous consumption of monomer and reduction of pressure, and even if the reaction time is extended, the polymerization reaction cannot be continued, resulting in a decrease in production efficiency.

[0108] By controlling the reaction pressure, reaction temperature and reaction time of the polymerization reaction within appropriate ranges, the weight average molecular weight of the first fluorine-containing polymer can be controlled, and the electrode plate can have excellent adhesive strength, and the battery can have a relatively good cycle capacity retention rate during cycling.

[0109] In some embodiments, the first polymerization reaction comprises: adding a solvent and a dispersant to a container, evacuating the container, and then filling the container with a non-reactive gas; Adding a first initiator and a pH adjuster to the vessel, adjusting the pH value to 6.5-7, and adding raw materials including vinylidene fluoride monomer, and setting the pressure in the vessel to 6 MPa-8 MPa; After stirring for 30 to 60 minutes, the temperature is increased to 45 to 60°C, and a first polymerization reaction is carried out.

[0110] By first uniformly mixing the materials before raising the temperature to carry out the first polymerization reaction, the reaction can be more thorough, and the resulting polymer will have more appropriate polydispersity index, crystallinity, and particle size.

[0111] In some embodiments, the amount of solvent used in the first polymerization reaction is 2 to 8 times the mass of the vinylidene fluoride monomer. The amount of solvent used may further be, for example, 3, 4, 5, 6, or 7 times the mass of the vinylidene fluoride monomer. In some embodiments, the solvent is an aqueous solvent.

[0112] In some embodiments, the dispersing agent comprises one or more of a cellulose ether and a polyvinyl alcohol.

[0113] In some embodiments, the cellulose ether comprises one or more of a methyl cellulose ether and a carboxyethyl cellulose ether.

[0114] In some embodiments, the amount of dispersant used in the first polymerization reaction is 0.1% to 0.3% of the vinylidene fluoride monomer mass, and may even be, for example, 0.2% of the vinylidene fluoride monomer mass.

[0115] In some embodiments, the first initiator is an organic peroxide, including one or more of tert-amyl peroxypivalate, tert-amyl peroxypivalate, 2-ethyl peroxydicarbonate, diisopropyl peroxydicarbonate, and tert-butyl peroxypivalate.

[0116] In some embodiments, the amount of the first initiator used is 0.15% to 1% of the total monomer weight. The amount of the first initiator used may further be, for example, 0.2%, 0.4%, 0.6%, or 0.8% of the total monomer weight.

[0117] In some embodiments, the pH adjuster comprises one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, and aqueous ammonia.

[0118] In some embodiments, the amount of pH adjuster used is between 0.05% and 0.2% of the vinylidene fluoride monomer mass. The amount of pH adjuster used may also be, for example, 0.1% or 0.15% of the vinylidene fluoride monomer mass.

[0119] In some embodiments, the chain transfer agent comprises one or more of cyclohexane, isopropyl alcohol, methanol, and acetone.

[0120] In some embodiments, the amount of chain transfer agent used in the first polymerization reaction is 1.5% to 3% of the mass of vinylidene fluoride monomer, and the amount of chain transfer agent used may further be, for example, 2% or 2.5%. By controlling the amount of chain transfer agent used within an appropriate range, the chain length of the first fluorine-containing polymer can be controlled, thereby obtaining a first fluorine-containing polymer with an appropriate weight average molecular weight range.

[0121] In some embodiments, the method for producing the second fluorine-containing polymer specifically comprises: The method includes carrying out a polymerization reaction of at least one monomer represented by formula III 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 performing solid-liquid separation to leave a solid phase to obtain a second fluorine-containing polymer; [ka] Here, R4 and R5 each independently represent a C group containing hydrogen, halogen, and at least one fluorine atom. 1-3 and at least one alkyl group.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] In some embodiments, the second initiator comprises an inorganic peroxide and may be selected from potassium persulfate or ammonium persulfate.

[0127] 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.

[0128] In some embodiments, the weight content of the initiator is 3%-12% based on the total weight of the monomers of Formula III.

[0129] High initiator content contributes to improving reaction efficiency, reducing reaction time and improving product uniformity.

[0130] In some embodiments, the chain transfer agent comprises one or more of cyclohexane, isopropyl alcohol, methanol, and acetone.

[0131] [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, and the positive electrode film layer includes a positive electrode active material, a conductive agent, and an adhesive according to some embodiments or an adhesive manufactured by the manufacturing method according to some embodiments.

[0132] This positive electrode plate has excellent adhesive strength even with a low amount of adhesive added.

[0133] In some embodiments, the mass fraction of the adhesive composition does not exceed 1.2%, based on the total mass of the positive electrode membrane layer.

[0134] In some embodiments, the adhesive mass fraction is between 0.8% and 1.2%, hi some embodiments, the adhesive mass content is 0.8%, 0.9%, 1%, 1.1%, 1.2%, or any value therein.

[0135] 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.

[0136] In some embodiments, the positive electrode active material is a lithium-containing transition metal oxide.

[0137] 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.

[0138] In some embodiments, a method for manufacturing a positive electrode plate is provided, the method comprising the steps of:

[0139] First step: A positive electrode active material, a conductive agent, and the adhesive according to any one of the embodiments or the adhesive produced by the production method according to any one of the embodiments are mixed together, and a first stirring is performed.

[0140] Second step: A solvent is added and a second stirring is carried out.

[0141] Third step: Add a dispersant and perform a third stirring to obtain a slurry, and control the viscosity of the slurry to 8000 mpa·s to 15000 mpa·s.

[0142] Fourth step: The slurry is applied onto a positive electrode current collector to obtain a positive electrode plate.

[0143] This manufacturing method is simple and advantageous for industrial production. This manufacturing method is advantageous for reducing sedimentation in the slurry of the high-molecular-weight first fluorine-containing polymer, contributing to improving the quality of the slurry and the uniformity of the positive electrode plate.

[0144] In some embodiments, in the first stirring, the stirring revolution speed is 25 r / min and the stirring time is 30 min.

[0145] In some embodiments, in the second stirring, the revolution speed of the stirring is 25 r / min, the rotation speed of the stirring is 800 to 1000 r / min, and the stirring time is 50 to 80 min.

[0146] In some embodiments, in the third stirring, the rotation speed of the stirring is 1200 to 1500 r / min, and the stirring time is 50 to 70 min.

[0147] In some embodiments, the dispersing agent is at least one of polyethylene glycol octylphenyl ether, polyvinylpyrrolidone, polyvinyl alcohol, carboxymethyl cellulose, polyacrylamide, polyacrylic acid, sodium polyacrylate, and polyacetimide.

[0148] In some embodiments, the mass fraction of the dispersant is 0.2% to 0.5%, based on the total mass of the positive electrode membrane layer.

[0149] 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)).

[0150] 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 Mn0.2 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 0.05 Examples 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.

[0151] 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.

[0152] 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.

[0153] [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.

[0154] 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.

[0155] 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)).

[0156] 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.

[0157] 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).

[0158] 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.

[0159] In some embodiments, the negative electrode membrane layer optionally further comprises other additives, such as a thickener (eg, sodium carboxymethylcellulose (CMC-Na)).

[0160] 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.

[0161] [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.

[0162] In some embodiments, the electrolyte is an electrolytic solution, which includes an electrolyte salt and a solvent.

[0163] 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.

[0164] 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.

[0165] 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.

[0166] [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.

[0167] 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.

[0168] In some embodiments, the positive and negative electrodes and the separator can be fabricated into an electrode assembly by a winding or lamination process.

[0169] In some embodiments, the secondary battery may include an exterior body, which may be used to package the electrode assembly and electrolyte.

[0170] 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.

[0171] 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.

[0172] 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.

[0173] 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.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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.

[0179] The power consumption device can be selected from a secondary battery, a battery module, or a battery pack depending on its usage needs.

[0180] 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.

[0181] 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.

[0182] I. 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.

[0183] Example 1 1) Production of adhesive composition Preparation of first fluorine-containing polymer: 4kg of deionized water and 2g of methyl cellulose ether are added to a 10L autoclave, and the autoclave is evacuated and replaced with N2 three times. Then, 5g of tert-butyl peroxypivalate and 2g of sodium bicarbonate are added, and 1kg of vinylidene fluoride monomer is added, and the pressure reaches 7MPa. The mixture is mixed and stirred for 30 minutes, and the temperature is raised to 45℃, and polymerization is carried out. After polymerization for 10 hours, 20g of cyclohexane is added 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 a polyvinylidene fluoride adhesive with a weight average molecular weight of 3.2 million, that is, the first fluorine-containing polymer.

[0184] Polyvinylidene fluoride adhesive with a weight-average molecular weight of 3.2 million has a polydispersity coefficient of 2.2, a crystallinity of 45%, and a Dv50 particle size of 100 μm. It was dissolved in N-methylpyrrolidone solution to prepare a 4 wt% solution, and the measured viscosity of the solution was 4900 mPa·s.

[0185] Preparation of the second 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 was added, the reaction temperature was controlled at 85°C, and 0.14g 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, and the polymerization reaction time was 1 hour, with the pressure maintained at 4.4MPa. The reaction product was washed with water and dried to obtain polyvinylidene fluoride polymer.

[0186] The first fluorine-containing polymer and the second fluorine-containing polymer were blended so that the mass ratio of the first fluorine-containing polymer to the second fluorine-containing polymer was 99.9:0.1, and an adhesive composition containing the first fluorine-containing polymer and the second vinylidene fluoride was obtained.

[0187] 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, and the mass fraction of the adhesive composition was 1.2% 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.

[0188] 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.

[0189] 3) Negative electrode plate A piece of metallic lithium served as the negative electrode plate.

[0190] 4) Separator A polypropylene membrane was used as the separator.

[0191] 5) Electrolyte production In a glove box with an argon gas atmosphere (H2O<0.1ppm, O2<0.1ppm), 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 an electrolyte solution.

[0192] 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.

[0193] Examples 2-9 The mass ratio of the first fluorine-containing polymer to the second fluorine-containing polymer in the adhesive composition was adjusted, and the other manufacturing methods were the same as those in Example 1, with specific parameters as shown in Table 1-6.

[0194] Examples 10-15 The weight average molecular weight of the second fluorine-containing polymer in the adhesive composition was adjusted, and other methods were the same as in Example 3, and the specific parameters were as shown in Tables 1-6.

[0195] In Example 10, the weight average molecular weight of polyvinylidene fluoride is 5,000, and the production method is as follows.

[0196] 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.

[0197] In Example 11, the weight average molecular weight of polyvinylidene fluoride is 20,000, and the production method is as follows.

[0198] 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.

[0199] In Example 12, the weight average molecular weight of polyvinylidene fluoride is 80,000, and the production method is as follows.

[0200] 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.

[0201] In Example 13, the weight average molecular weight of polyvinylidene fluoride is 150,000, and the production method is as follows.

[0202] 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.

[0203] In Example 14, the weight-average molecular weight of the polyvinylidene fluoride was 400,000, and in Example 15, the weight-average molecular weight of the polyvinylidene fluoride was 600,000, both of which were commercially available.

[0204] Example 16 is basically the same as Example 3, except that the weight-average molecular weight of the first fluorine-containing polymer is 1.5 million. Example 17 is basically the same as Example 12, except that the weight-average molecular weight of the first fluorine-containing polymer is 1.5 million. Example 18 is basically the same as Example 14, except that the weight-average molecular weight of the first fluorine-containing polymer is 1.5 million. A method for producing polyvinylidene fluoride having a weight-average molecular weight of 1.5 million is as follows.

[0205] Add 4kg of deionized water and 2g of methylcellulose ether into a 10L autoclave, evacuate and replace O2 with N2 three times, add 5g of tert-butyl peroxypivalate and 2g of sodium bicarbonate again, add 1kg of vinylidene fluoride monomer and make the pressure reach 7MPa, mix and stir for 30min, heat to 45℃, carry out polymerization reaction, add 30g of cyclohexane after 5h of polymerization reaction, continue the reaction, when the pressure in the reactor drops to 2MPa, stop the reaction, centrifuge the reaction system, collect the solid phase, wash and dry to obtain.

[0206] This polyvinylidene fluoride has a polydispersity coefficient of 2.18, a crystallinity of 41.5%, and a Dv50 particle size of 45 μm. It was dissolved in N-methylpyrrolidone to prepare a 4 wt% solution, and the measured viscosity of the solution was 3000 mPa·s.

[0207] The manufacturing methods of Examples 19-21 are basically the same as those of Examples 16-18, except that the weight-average molecular weight of the first fluorine-containing polymer is 5,000,000. The specific manufacturing methods are as follows:

[0208] Add 4kg of deionized water and 2g of methylcellulose ether into a 10L autoclave, evacuate and replace O2 with N2 three times, add 5g of tert-butyl peroxypivalate and 2g of sodium bicarbonate again, add 1kg of vinylidene fluoride monomer and make the pressure reach 7MPa, mix and stir for 30min, heat to 45℃, carry out polymerization reaction, add 15g of cyclohexane after 12h of polymerization reaction, continue the reaction, when the pressure in the reactor drops to 2MPa, stop the reaction, centrifuge the reaction system, collect the solid phase, wash and dry to obtain.

[0209] This polyvinylidene fluoride has a polydispersity coefficient of 2.2, a crystallinity of 46%, and a Dv50 particle size of 150 μm. It was dissolved in N-methylpyrrolidone to prepare a 4 wt% solution, and the measured viscosity of the solution was 6500 mPa·s.

[0210] The manufacturing methods of Examples 22-26 are basically the same as those of Example 3, except that the type of the second fluorine-containing polymer is changed. In Example 22, the second fluorine-containing polymer is polytetrafluoroethylene having a weight-average molecular weight of 10,000, and the manufacturing methods are as follows:

[0211] 0.4 kg of deionized water and 0.2 g of carboxyethyl cellulose ether were added to a 1 L four-neck flask, and nitrogen gas was introduced to remove oxygen dissolved in the solution. 1.0 g of tert-amyl peroxypivalate and 0.1 g of potassium carbonate were added again, and 0.1 kg of tetrafluoroethylene was added. The mixture was mixed and stirred for 30 minutes, heated to 68°C, and polymerized for 3 hours. The polymerized solution was distilled, washed, separated, dried, and pulverized to obtain polytetrafluoroethylene.

[0212] In Example 23, the second fluorine-containing polymer is a vinylidene fluoride-hexafluoropropylene copolymer having a weight average molecular weight of 10,000, and the production method is as follows.

[0213] A 1-liter four-neck flask was charged with 0.4 kg of deionized water and 0.2 g of carboxyethyl cellulose ether, and nitrogen gas was introduced to remove dissolved oxygen in the solution. 1.0 g of tert-amyl peroxypivalate and 0.1 g of potassium carbonate were then added, and 0.8 kg of vinylidene fluoride and 0.2 kg of hexafluoropropylene were added. The mixture was mixed and stirred for 30 minutes, heated to 68°C, and polymerized for 4 hours. The polymerized solution was then distilled, washed, separated, dried, and pulverized to obtain polyvinylidene fluoride-hexafluoropropylene.

[0214] In Example 24, the second fluorine-containing polymer is polyvinylidene fluoride having a weight average molecular weight of 10,000, and the preparation method is as follows.

[0215] 0.4 kg of deionized water and 0.2 g of carboxyethyl cellulose ether were added to a 1 L four-neck flask, and nitrogen gas was introduced to remove oxygen dissolved in the solution. 1.0 g of 2-ethyl peroxydicarbonate and 0.1 g of sodium bicarbonate were then added, and 0.1 kg of vinylidene fluoride was added. The mixture was mixed and stirred for 30 minutes, heated to 68°C, and polymerized for 3 hours. The polymerized solution was distilled, washed, separated, dried, and pulverized to obtain polyvinylidene fluoride having a weight-average molecular weight of 10,000, i.e., a second fluorine-containing polymer.

[0216] In Example 25, the second fluorine-containing polymer is polytetrafluoroethylene having a weight average molecular weight of 10,000, and the production method is as follows.

[0217] 219g of deionized water and 0.1g of hydroxypropyl methylcellulose were added to a 0.5L autoclave, and nitrogen gas was added to replace the oxygen gas several times to remove oxygen. 120g of tetrafluoroethylene monomer gas was then added, the reaction temperature was controlled at 50°C, and ammonium persulfate initiator was added to start the reaction. The amount of initiator added was approximately 15% of the total amount of monomer. The reaction pressure was controlled at 0.7MPa, and the time was controlled at 1 hour. After the polymerization was completed, the polytetrafluoroethylene was discharged from the bottom of the autoclave and filtered, washed, dried, and polished to obtain a powder material.

[0218] In Example 26, the second fluorine-containing polymer is a vinylidene fluoride-hexafluoropropylene copolymer having a weight average molecular weight of 10,000, and the production method is as follows.

[0219] 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 0.14 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 4.4 MPa. The reaction product was washed with water and dried to obtain a second fluorine-containing polymer.

[0220] The types of the second fluorine-containing polymers in Examples 27-31 are the same as those in Examples 22-26, respectively, except that the weight-average molecular weight of the second fluorine-containing polymer is 80,000; In Example 27, the second fluorine-containing polymer is polytetrafluoroethylene having a weight average molecular weight of 80,000, and the production method is as follows.

[0221] 0.4 kg of deionized water and 0.2 g of carboxyethyl cellulose ether were added to a 1 L four-neck flask, and nitrogen gas was introduced to remove dissolved oxygen in the solution. 0.9 g of tert-amyl peroxypivalate and 0.1 g of potassium carbonate were added again, and 0.1 kg of tetrafluoroethylene was added. The mixture was mixed and stirred for 30 minutes, heated to 64°C, and polymerized for 6 hours. The mixture was then distilled, washed, separated, dried, and pulverized to obtain a polymerized solution.

[0222] In Example 28, the second fluorine-containing polymer is a vinylidene fluoride-hexafluoropropylene copolymer having a weight average molecular weight of 80,000, and the production method is as follows.

[0223] A 1-liter four-neck flask was charged with 0.4 kg of deionized water and 0.2 g of carboxyethyl cellulose ether, and nitrogen gas was introduced to remove dissolved oxygen in the solution. 0.9 g of tert-amyl peroxypivalate and 0.1 g of potassium carbonate were then added, and 0.8 kg of vinylidene fluoride and 0.2 kg of hexafluoropropylene were added. The mixture was mixed and stirred for 30 minutes, heated to 64°C, and polymerized for 7 hours. The polymerized solution was then distilled, washed, separated, dried, and pulverized to obtain polyvinylidene fluoride-hexafluoropropylene.

[0224] In Example 29, the second fluorine-containing polymer is polyvinylidene fluoride having a weight average molecular weight of 80,000, and the production method is as follows.

[0225] 0.4 kg of deionized water and 0.2 g of carboxyethyl cellulose ether were added to a 1 L four-neck flask, and nitrogen gas was introduced to remove the oxygen dissolved in the solution. 0.9 g of 2-ethyl peroxydicarbonate and 0.1 g of sodium hydrogen carbonate were added again, and 0.1 kg of vinylidene fluoride was added. The mixture was mixed and stirred for 30 minutes, heated to 64°C, and polymerized for 6 hours. The mixture was then distilled, washed, separated, dried, and pulverized to obtain a polymerized solution.

[0226] In Example 30, the second fluorine-containing polymer is polytetrafluoroethylene having a weight average molecular weight of 80,000, and the production method is as follows.

[0227] 219g of deionized water and 0.1g of hydroxypropyl methylcellulose were added to a 0.5L autoclave, and nitrogen gas was added to replace the oxygen gas several times to remove oxygen. 120g of tetrafluoroethylene monomer gas was then added, the reaction temperature was controlled at 50°C, and ammonium persulfate initiator was added to start the reaction. The amount of initiator added was approximately 15% of the total amount of monomer. The reaction pressure was controlled at 0.7MPa, and the time was controlled at 1 hour. After the polymerization was completed, the polytetrafluoroethylene was discharged from the bottom of the autoclave and filtered, washed, dried, and polished to obtain a powder material.

[0228] In Example 31, the second fluorine-containing polymer is a vinylidene fluoride-hexafluoropropylene copolymer having a weight average molecular weight of 80,000, and the production method is as follows.

[0229] 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.

[0230] In Example 32, the first fluorine-containing polymer is a vinylidene fluoride-trifluorochloroethylene copolymer having a weight-average molecular weight of 3.2 million, and the other properties are basically the same as those in Example 3. The preparation method of the first fluorine-containing polymer is as follows:

[0231] A 10L autoclave was charged with 4kg of deionized water and 2g of methylcellulose ether, evacuated, and purged with N2 three times. 5g of tert-butyl peroxypivalate and 2g of sodium bicarbonate were added, and 0.94kg of vinylidene fluoride and 0.06kg of trifluorochloroethylene were added. The system pressure was increased to 7MPa, and the mixture was stirred for 30 minutes. The temperature was raised to 45°C, and after 10 hours of reaction, 20g of cyclohexane was added and the reaction was continued. The reaction was stopped when the pressure in the reactor dropped to 2MPa. The reaction system was centrifuged, and the solid phase was collected, washed, and dried to obtain vinylidene fluoride-trifluorochloroethylene polymer.

[0232] Comparative Examples 1-4 and Examples 1, 16, 19, and 32 are basically the same, except that the adhesive does not contain the second fluorine-containing polymer, but contains only the first fluorine-containing polymer.

[0233] The adhesive in Comparative Example 5 is polyvinylidene fluoride with a weight average molecular weight of 800,000, which is brand 701A polyvinylidene fluoride produced by Dongyangguang Company.

[0234] 2. Battery performance test 1. Adhesive composition 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% adhesive glue solution was prepared using purified N-methylpyrrolidone (NMP) solvent. The solution was allowed to stand for one day before use. During the test, tetrahydrofuran was first drawn into the syringe, followed by washing, and this was repeated several times. 5 ml of the test solution was then 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. Once the reading stabilized, data was acquired and the weight-average molecular weight was read.

[0235] 2) Polydispersity coefficient 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% adhesive glue solution was prepared using purified N-methylpyrrolidone (NMP) solvent. The solution was allowed to stand for one day before use. During the test, tetrahydrofuran was first drawn into the syringe and washed several times. 5 ml of the test solution was then 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. Data was acquired once the displayed values ​​stabilized. The weight-average molecular weight (a) and number-average molecular weight (b) were read, respectively. The polydispersity coefficient (a / b) was used.

[0236] 3) Dv50 test Referring to GB / T 19077-2016, particle size distribution laser diffraction method, 0.1g-0.13g of first fluorine-containing polymer powder was weighed into a 50ml beaker, and 5g of anhydrous ethanol was added to the beaker containing the first fluorine-containing polymer powder. A 2.5mm stir bar was added and the beaker was sealed with plastic wrap. The sample was sonicated for 5 minutes in an ultrasonicator, then transferred to a magnetic mixer and stirred at 500 r / min for at least 20 minutes. Two samples per batch were extracted and tested, and the average value was calculated. Measurements were performed using a laser particle size analyzer, such as a Mastersizer 2000E laser particle size analyzer from Malvern Instruments, UK.

[0237] 4) Crystallinity test 0.5 g of the first 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, at a heating rate of 10°C / min, and in a test temperature range of -100°C to 400°C, using a US TA Instruments Model Discovery 250 differential scanning calorimeter (DSC), to remove thermal history.

[0238] In this test, the temperature change curve of DSC / (Mw / mg) of the first fluorine-containing polymer is obtained and integrated, and the peak area is the melting enthalpy ΔH (J / g) of the first 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.

[0239] 5) Viscosity test of glue solution 14g of the first fluorine-containing polymer and 336g of N-methylpyrrolidone (NMP) were weighed into a 500ml beaker to form a 4% mass fraction glue solution. The solution was stirred and dispersed using a Lichen high-speed grinder at a rotation speed of 800 r / min for 120 minutes, followed by 30 minutes of ultrasonic vibration to remove air bubbles. A test was then performed at room temperature using a Lichen Technology NDJ-5S rotational viscometer. A No. 3 rotor was selected and inserted into the glue solution, ensuring that the rotor's liquid level marker was flush with the glue solution's liquid level. The viscosity was tested at a rotor rotation speed of 12 r / min, and the viscosity data was read after 6 minutes.

[0240] 6) End group test The end group structure of the polymer was studied by nuclear magnetic resonance (NMR) method. The nuclear magnetic instrument was a Bruker AV400 instrument. 19 F-NMR and 1 The polymer end group structure was analyzed by H-NMR using dimethyl sulfoxide as the solvent, CFCl3 as the fluorine spectrum standard, and TMS as the hydrogen spectrum standard. 19 The F-NMR acquisition time was 0.33 s, the number of scans was 64, the pulse delay was 2 s, and the pulse width was 5 μs. 1 The acquisition time for H-NMR analysis is 2.2 s, the number of scans is 16, the pulse delay is 2 s, and the pulse width is 33 μs.

[0241] 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.

[0242] 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".

[0243] 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:

[0244] 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.

[0245] 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.

[0246] The power supply for the Sansi tensioning machine (sensitivity 1N) was turned on, and the indicator light was lit. The stopper block was adjusted to the appropriate position, and the end of the steel plate without the electrode plate attached was secured with the lower fixture. The paper tape was folded over and secured with the upper fixture, and the position of the upper fixture was adjusted using the "up" and "down" buttons on the manual controller attached to the tensioning machine. The test was then performed, and the numerical value was read. The force when the electrode plate was equilibrated under the force was divided by the width of the tape to determine the adhesive strength of the electrode plate per unit length, which characterized the adhesive strength between the positive electrode film layer and the current collector.

[0247] 2) Measurement of positive electrode film layer resistance: After drying, the positive electrode slurry (film layer) was cut from the left, center, and right sides of the positive plate and cut into small rings with a diameter of 3 mm. 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.

[0248] 3) Plate brittleness test The positive electrode plates in the examples were cut into test samples measuring 20 x 100 mm and prepared for use. The plates were bent in half, folded, and fixed, then pressed once with a 2 kg roller. The folded portions of the plates were checked for light transmission and metal breaks. If no light transmission or metal breaks were found, the plates were folded in half again, fixed, and pressed once with a 2 kg roller. The folded portions of the plates were checked for light transmission and metal breaks. These steps were repeated until light transmission and metal breaks were found at the folded portions of the plates. The number of light transmissions for the folded positive electrode plates was recorded. Three sets were measured in parallel, and the average value was calculated.

[0249] 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.

[0250] In this test process, the first cycle corresponded to n = 1, the second cycle corresponded to n = 2, ... the 500th cycle corresponded to n = 500. The battery capacity retention data in Table 1-6 corresponding to Examples 1 to 41 or Comparative Examples 1 to 3 are data measured after 500 cycles under the above test conditions, i.e., the P500 value.

[0251] 3. Analysis of the test results of each example and comparative example Batteries of each example and comparative example were manufactured according to the above method, and performance parameters were measured. The results are shown in Tables 1-6 below.

[0252] [Table 1] [Table 2] [Table 3] [Table 4] [Table 5] [Table 6]

[0253] [Table 7] [Table 8]

[0254] As can be seen from a comparison between Examples 1-32 and Comparative Example 5, the adhesive composition comprises a first fluorine-containing polymer and a second fluorine-containing polymer, the weight-average molecular weight of the first fluorine-containing polymer being 1.5 million to 5 million, and the weight-average molecular weight of the second fluorine-containing polymer not exceeding 600,000. Compared with the polyvinylidene fluoride adhesive used in the prior art, which has a weight-average molecular weight of 800,000, the adhesive composition of the present application effectively improves the adhesive performance of electrode plates and reduces the amount of adhesive used.

[0255] As can be seen from Examples 1-32, the first fluorine-containing polymer contained structural units derived from vinylidene fluoride and may be a homopolymer or a copolymer, and the second fluorine-containing polymer contained at least one of polytetrafluoroethylene, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene) copolymer.

[0256] As can be seen from a comparison between Examples 1-9 and Comparative Example 1, adhesive compositions containing 0.1% to 10% by mass of the second fluorine-containing polymer, based on the total mass of the adhesive composition, maintained high adhesive performance compared to the case where a large molecular weight polyvinylidene fluoride adhesive was used alone. This resulted in optimized adhesive processing, improved electrode uniformity, and improved battery cycle performance. As the content of the second fluorine-containing polymer in the adhesive composition increased, the adhesive strength of the adhesive composition gradually decreased, the crystallinity first decreased and then increased, and the flexibility of the electrode plate first increased and then decreased.

[0257] As can be seen from the comparison between Examples 10-21 and Comparative Example 1, when the weight-average molecular weight of the second fluorine-containing polymer is 5,000-600,000, the addition of the second fluorine-containing polymer can better optimize the overall performance of the battery, including adhesion performance, processability, flexibility, and cycle performance.

[0258] As can be seen from Examples 22-32, when the end group of the second fluorine-containing polymer contains a hydroxyl group or an ester group, the addition of the second fluorine-containing polymer improved the slurry processability and, at the same time, further improved the retention of electrode plate adhesiveness without significantly reducing the electrode plate adhesiveness.

[0259] 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]

[0260] 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 and a second fluorine-containing polymer, wherein the weight average molecular weight of the first fluorine-containing polymer is 1.5 million to 5 million, and the weight average molecular weight of the second fluorine-containing polymer does not exceed 600,000; An adhesive composition, characterized in that the mass content of the second fluorine-containing polymer is 0.1% to 10% based on the total mass of the adhesive composition.

2. 2. The adhesive composition according to claim 1, wherein the adhesive composition has a crystallinity of 45% or less.

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

4. The first fluorine-containing polymer further comprises a structural unit shown in Formula I: 【Chemistry 1】 Here, R １ The adhesive composition according to any one of claims 1 to 3, wherein contains one or more of hydrogen, fluorine, chlorine, and a trifluoromethyl group.

5. 4. The adhesive composition according to claim 1, wherein the first fluorine-containing polymer has a polydispersity coefficient of 1.5 to 2.

5.

6. 4. The adhesive composition according to claim 1, wherein the first fluorine-containing polymer has a crystallinity of 34% to 48%.

7. The adhesive composition according to any one of claims 1 to 3, wherein a glue solution containing the first fluorine-containing polymer at a mass content of 4% produced by dissolving the first fluorine-containing polymer in N-methylpyrrolidone has a viscosity of 2400 mPa·s to 5000 mPa·s.

8. 4. 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.

9. The second fluorine-containing polymer comprises structural units shown in Formula II: 【Chemistry 2】 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 any one of claims 1 to 3, characterized in that it contains at least one alkyl group.

10. R ２ , R ３ and each independently contain at least one of hydrogen, fluorine, chlorine, and a trifluoromethyl group.

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

12. 4. The adhesive composition according to claim 1, wherein the weight average molecular weight of the second fluorine-containing polymer is 5,000 to 600,000.

13. 4. The adhesive composition according to claim 1, wherein the second fluorine-containing polymer comprises one or more of polytetrafluoroethylene, polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride-tetrafluoroethylene) copolymer, poly(vinylidene fluoride-chlorofluoroethylene) copolymer, and poly(vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene) copolymer.

14. A method for producing an adhesive composition, comprising: Preparation of a first fluorine-containing polymer: carrying out a first polymerization reaction 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 1.5 million to 5 million; Preparation of a second fluorine-containing polymer: carrying out a second polymerization reaction on a raw material containing vinylidene fluoride monomer under polymerization conditions to prepare a second fluorine-containing polymer, and the weight average molecular weight of the second fluorine-containing polymer is not more than 600,000; Blending: Blending a first fluorine-containing polymer with a second fluorine-containing polymer to prepare an adhesive composition; a mass content of the second fluorine-containing polymer of 0.1% to 10% based on the total mass of the adhesive composition;

15. The first method for producing a fluorine-containing polymer specifically includes the steps of: carrying out a first polymerization reaction for 6 hours to 12 hours on a raw material containing 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; The method according to claim 14, further comprising adding a chain transfer agent, reducing the pressure in the reaction system to 2 MPa to 2.5 MPa, stopping the reaction, and performing solid-liquid separation to leave a solid phase and obtain the first fluorine-containing polymer.

16. The second method for producing a fluorine-containing polymer specifically includes the steps of: carrying out a second polymerization reaction of at least one monomer represented by formula III 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 performing solid-liquid separation to leave a solid phase to obtain a second fluorine-containing polymer; 【Transformation 3】 Here, R ４ , R ５ each independently represents a C group containing hydrogen, a halogen, and at least one fluorine atom; １－３ The method according to claim 14, characterized in that it comprises at least one alkyl group.

17. The second polymerization reaction is adding a solvent and a dispersant to a vessel and filling the vessel with a non-reactive gas; 15. The method of claim 14, further comprising the steps of adding the monomer of formula III, raising the temperature to 60°C to 90°C, and then adding a second initiator and a chain transfer agent to carry out a second polymerization reaction.

18. 18. The process of claim 17, wherein the second initiator comprises an inorganic peroxide and may be selected from potassium persulfate or ammonium persulfate.

19. 18. The method according to claim 17, wherein the mass content of the initiator is 3%-12% based on the total mass of the monomers of formula III.

20. 18. The process of claim 15 or 17, wherein the chain transfer agent comprises one or more of cyclohexane, isopropyl alcohol, methanol, and acetone.

21. 4. 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.

22. The positive electrode plate according to claim 21 , wherein the mass fraction of the adhesive composition does not exceed 1.2% based on the total mass of the positive electrode film layer.

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

24. 22. 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 21.

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

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