WO2024026791A1 - 粘结剂、制备方法、正极极片、二次电池及用电装置 - Google Patents

粘结剂、制备方法、正极极片、二次电池及用电装置 Download PDF

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WO2024026791A1
WO2024026791A1 PCT/CN2022/110373 CN2022110373W WO2024026791A1 WO 2024026791 A1 WO2024026791 A1 WO 2024026791A1 CN 2022110373 W CN2022110373 W CN 2022110373W WO 2024026791 A1 WO2024026791 A1 WO 2024026791A1
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monomer represented
formula
battery
binder
polymer
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PCT/CN2022/110373
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English (en)
French (fr)
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曾子鹏
李�诚
刘会会
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宁德时代新能源科技股份有限公司
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Priority to PCT/CN2022/110373 priority Critical patent/WO2024026791A1/zh
Publication of WO2024026791A1 publication Critical patent/WO2024026791A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers

Definitions

  • the present application relates to the technical field of secondary batteries, and in particular to an adhesive, a preparation method, a positive electrode sheet, a secondary battery, a battery module, a battery pack and an electrical device.
  • secondary ion batteries have been widely used in energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace.
  • Binders are commonly used materials in secondary ion batteries and are widely used in battery pole pieces, isolation films, packaging, etc.
  • traditional binders have high production costs, insufficient production capacity, are harmful to the environment, and are prone to gel during the preparation process, resulting in poor slurry stability and high processing costs.
  • the pole pieces prepared with them have poor conductivity, high resistance, and The yield rate is low and battery performance is unstable, making it difficult to meet market requirements for battery cost and performance. Therefore, existing adhesives still need to be improved.
  • This application was made in view of the above problems, and its purpose is to provide a binder that can slow down the gelation phenomenon of the slurry and improve the stability of the slurry and the conductivity of the pole piece.
  • a first aspect of the present application provides a binder.
  • the binder includes a polymer containing a structural unit derived from a monomer represented by Formula I, a structural unit derived from a monomer represented by Formula II, and a structural unit derived from a monomer represented by Formula II. From the structural unit of the monomer represented by formula III,
  • R 1 , R 2 and R 5 are each independently selected from hydrogen or substituted or unsubstituted C 1-5 alkyl, R 3 is selected from hydrogen or C 1-3 alkyl, and R 4 is selected from substituted or unsubstituted C 1-9 alkyl.
  • this polymer as a binder can significantly slow down the gelation phenomenon of the slurry, improve the stability of the slurry and reduce the diaphragm resistance of the pole piece.
  • the molar content of the structural units derived from the monomer represented by Formula I in the polymer is 70% to 90%, and the molar content of the structural units derived from the monomer represented by Formula II is 5% ⁇ 25%, the molar content of structural units derived from the monomer represented by formula III is 5% to 25%, based on the total moles of all structural units in the polymer.
  • the molar content of the structural units derived from the monomer represented by formula I in the polymer is within a suitable range, not only the stability of the slurry, the flexibility and conductivity of the pole pieces are improved, but also the battery has better cycle performance and safety performance.
  • the polymer has a weight average molecular weight of 5 ⁇ 10 5 to 12 ⁇ 10 5 .
  • the weight average molecular weight of the polymer is within this range, not only the stability of the slurry is improved, but also the pole piece has excellent adhesion and low diaphragm resistance, thereby improving the cycle performance of the battery.
  • the monomer represented by Formula I is selected from one or more of acrylonitrile and butenenitrile.
  • the monomer represented by Formula II is selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, isopentyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, acrylic acid One or more of hydroxyethyl ester and hydroxypropyl acrylate.
  • the monomer represented by Formula III is selected from one or two types of acrylic acid and methacrylic acid.
  • the above-mentioned raw materials are simple and easy to obtain, and can significantly reduce production costs and increase output compared with traditional binders.
  • the second aspect of the application also provides a method for preparing a binder, which includes the following steps: providing a monomer represented by formula I, a monomer represented by formula II, and a monomer represented by formula III,
  • R 1 , R 2 and R 5 are each independently selected from hydrogen or substituted or unsubstituted C 1-5 alkyl, R 3 is selected from hydrogen or C 1-3 alkyl, and R 4 is selected from substituted or unsubstituted C 1-9 alkyl;
  • the monomer represented by formula I, the monomer represented by formula II and the monomer represented by formula III are polymerized under polymerizable conditions to prepare a polymer.
  • the preparation method further includes the following steps: placing the monomer represented by Formula I, the monomer represented by Formula II, the monomer represented by Formula III and the initiator in a solution environment and a non-reactive gas atmosphere. Polymerize at 60°C to 70°C for 4-7 hours; add a chain transfer agent and polymerize at 70°C to 80°C for 3-5 hours to obtain the polymer.
  • the initiator is an organic peroxide, which can be selected from one or more of dibenzoyl peroxide, tert-amyl peroxypivalate, and 2-ethyl peroxycarbonate.
  • the chain transfer agent is selected from one or both of vinyl chloride and vinyl acetate.
  • the molar content of the monomer represented by Formula I is 70%-90%
  • the molar content of the monomer represented by Formula II is 5%-25%
  • the molar content of the monomer represented by Formula III is The molar content of monomers ranges from 5% to 25%, based on the total moles of the monomers.
  • the preparation method has low raw material cost, no pollution to the environment, and is conducive to increasing the output of the binder.
  • the adhesive prepared by this method can reduce the gelation phenomenon of the slurry, improve the stability of the slurry and reduce the resistance of the pole piece diaphragm.
  • a third aspect of the present application provides a positive electrode sheet, including a positive active material, a conductive agent, and a binder in any embodiment or a binder prepared by a preparation method in any embodiment.
  • the positive electrode piece has good flexibility, is easy to form and has low diaphragm resistance.
  • the positive active material is a lithium-containing transition metal oxide, which can be selected from lithium nickel cobalt manganese oxide, or its doped modified materials, or its conductive carbon coating modified materials, conductive metal coating The modified material or conductive polymer coats at least one of the modified materials.
  • the mass fraction of the binder is 0.01% to 3%, optionally 0.5% to 3%, based on the mass of the positive active material.
  • the mass fraction of the binder within this range can improve the stability of the slurry, allowing the pole piece to have both excellent resistance and bonding properties, and the battery to have better overall cycle performance.
  • the surface of the conductive agent includes silanol groups and/or hydroxyl groups, and the conductive agent is selected from one or more of conductive carbon black, conductive graphite, carbon nanotubes, graphene and carbon fiber.
  • the silanol groups and/or hydroxyl groups on the surface of the conductive agent can undergo an esterification reaction with the carboxyl groups contained in the binder to better build a conductive network on the surface of the active material, thereby reducing the membrane resistance.
  • a secondary battery including an electrode assembly and an electrolyte.
  • the electrode assembly includes the positive electrode sheet, the isolation film and the negative electrode sheet of the third aspect of the present application.
  • a battery module including the secondary battery of the fourth aspect of the present application.
  • a battery pack is provided, including the battery module of the fifth aspect of the present application.
  • an electrical device including at least one of the secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect, or the battery pack of the sixth aspect of the present application.
  • FIG. 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG. 2 is an exploded view of the secondary battery according to the embodiment of the present application shown in FIG. 1 .
  • FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.
  • Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5.
  • the numerical range “a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range “0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations.
  • a certain parameter is an integer ⁇ 2
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • step (c) means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.
  • condition "A or B” is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).
  • PVDF polyvinylidene fluoride
  • the electrode binder In the existing technology, polyvinylidene fluoride (PVDF) is often used as the electrode binder.
  • PVDF has many problems during use, such as being sensitive to water content during normal processes; during the battery recycling process, a large amount of HF pollutes the environment and cannot be recycled on a large scale due to environmental protection policies; in the process of preparing cathode slurry by mixing it with high-capacity cathode materials (such as high-nickel ternary materials), the strong polar groups on PVDF will activate the cathode The remaining hydroxyl groups on the material then react with the metal elements (such as nickel) in the cathode material to form chemical cross-links, which eventually leads to slurry gel, affecting the normal preparation of the slurry and subsequent electrode sheet processing.
  • metal elements such as nickel
  • PVDF is easy to crystallize, which is not conducive to the transmission of electrons in the pole piece, which leads to high resistance of the pole piece and poor electron transmission performance, which is not conducive to the performance of high-capacity cathode materials.
  • the binder includes a polymer.
  • the polymer contains structural units derived from the monomer represented by Formula I, structural units derived from the monomer represented by Formula II and derivatives. From the structural unit of the monomer represented by formula III,
  • R 1 , R 2 and R 5 are each independently selected from hydrogen or substituted or unsubstituted C 1-5 alkyl, R 3 is selected from hydrogen or C 1-3 alkyl, and R 4 is selected from substituted or unsubstituted C 1-9 alkyl.
  • binder refers to a chemical compound, polymer or mixture that forms a colloidal solution or colloidal dispersion in a dispersion medium.
  • polymer includes on the one hand an assembly of macromolecules that are chemically homogeneous but differ in degree of polymerization, molar mass and chain length, prepared by polymerization reactions.
  • the term on the other hand also includes derivatives of aggregates of macromolecules formed by polymerization reactions which are obtainable by reaction, for example addition or substitution, of functional groups in said macromolecules and which may be chemically homogeneous or chemically non-uniform compounds.
  • the dispersion medium of the binder is an aqueous solvent, such as water. That is, the binder is dissolved in an aqueous solvent.
  • the dispersion medium of the adhesive is an oily solvent.
  • the oily solvent include but are not limited to dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, acetone, dicarbonate Methyl ester, ethyl cellulose, polycarbonate. That is, the binder is dissolved in the oily solvent.
  • adhesives are used to hold electrode materials and/or conductive agents in place and adhere them to conductive metal components to form electrodes.
  • the binder serves as a positive electrode binder and is used to bind the positive electrode active material and/or conductive agent to form an electrode.
  • the binder serves as a negative electrode binder and is used to bind the negative electrode active material and/or conductive agent to form an electrode.
  • C 1-5 alkyl refers to a straight or branched hydrocarbon chain radical consisting exclusively of carbon and hydrogen atoms, with no unsaturation present in the radical, having from one to five carbon atoms, and Attached to the rest of the molecule by a single bond.
  • C 1-9 alkyl should be interpreted accordingly. Examples of C 1-5 alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, 1-methylethyl (isopropyl), butyl, pentyl.
  • substituted means that at least one hydrogen atom of the compound or chemical moiety is replaced by a substituent of another chemical moiety, where each substituent is independently selected from: hydroxyl, mercapto, amino, cyano , nitro group, aldehyde group, halogen atom, alkenyl group, alkynyl group, aryl group, heteroaryl group, C 1-6 alkyl group, C 1-6 alkoxy group.
  • methyl refers to the -CH 3 group.
  • cyano refers to the -CN group.
  • ester group refers to a -COOR 4 group, with R 4 selected from C 1-9 alkyl groups substituted or unsubstituted by substituents.
  • the polymer contains one or more structural units derived from monomers represented by Formula I. In some embodiments, the polymer includes one or more structural units derived from monomers represented by Formula II. In some embodiments, the polymer contains one or more structural units derived from monomers represented by Formula III.
  • polymers include, but are not limited to, acrylonitrile-methyl acrylate-acrylic acid polymer, acrylonitrile-ethyl methacrylate polymer-acrylic acid polymer, acrylonitrile-butyl acrylate-acrylic acid polymer, propylene Nitrile-isooctyl acrylate polymer, acrylonitrile-butyl acrylate-ethyl acrylate-acrylic acid polymer, acrylonitrile-isoamyl acrylate-acrylic acid polymer, crotonitrile-methyl acrylate-acrylic acid polymer, butene Nitrile-methyl acrylate-acrylic acid polymer, crotonitrile-butyl acrylate-acrylic acid polymer, crotonitrile-ethyl methacrylate-acrylic acid polymer, crotonitrile butyl acrylate-ethyl acrylate-acrylic acid polymer , Acrylonitrile-is
  • the binder does not contain fluorine, is environmentally friendly, and meets environmental protection requirements. At the same time, the binder is not highly sensitive to moisture and can improve the humidity resistance of the entire slurry system. Because it contains a highly polar cyano group, the binder has a strong viscosity, which can improve the dispersion of the binder to the substances in the slurry. Compared with traditional PVDF, the amount of binder added in the slurry can be reduced. . In addition, the strong polar cyano group can enhance the stability of the molecular structure, increase the glass transition temperature of the polymer, improve the rigidity and thermal stability of the polymer, and broaden the electrochemical window of the binder.
  • the polymer also has a highly polar cyano group, which has good affinity with the electrolyte and good electrochemical stability.
  • the ester functional group in the binder helps weaken the excessively strong dipole moment between the cyano groups and reduces the obstruction of the free movement of the binder chain segments caused by the excessive force between the cyano groups, causing the problem of pole piece brittleness.
  • the flexible segment of the ester functional group helps to improve the flexibility of the binder and pole piece, thereby improving the safety performance of the battery. Because it contains carboxyl functional groups, the binder has excellent wettability, dispersion and stability in the slurry, which helps to form a conductive network and can reduce the film resistance.
  • the carboxyl functional group contained in the binder can react with alkaline LiOH that is easily generated by high-nickel ternary materials in humid air, preventing the slurry from alkaline decomposition in humid air and further improving the stability of the slurry.
  • using this polymer as a binder can significantly slow down the gelation phenomenon of the slurry, improve the stability of the slurry and reduce the diaphragm resistance of the pole piece, which helps the battery improve the molding quality of the pole piece.
  • the molar content of the structural units derived from the monomer represented by Formula I in the polymer is 70% to 90%, and the molar content of the structural units derived from the monomer represented by Formula II is 5% ⁇ 25%, the molar content of structural units derived from the monomer represented by formula III is 5% to 25%, based on the total moles of all structural units in the polymer.
  • the polymer will have poor rigidity, a low glass transition temperature, and a low breaking strength; if the ratio of soft monomers shown in formula II and formula III is too low, Insufficient flexible segments in the polymer will result in greater brittleness of the polymer and excessive brittleness of the pole pieces during subsequent processing. During the bending process of the pole pieces, the current collector is easily exposed or even broken, leaving potential safety hazards.
  • the molar content of the structural units derived from the monomer shown in formula I is too high, and the content of the cyano functional group is too high, resulting in excessive viscosity of the slurry, which is not conducive to the processing of the slurry and the dispersion of the conductive agent, and affects the formation of the conductive network , thereby increasing the diaphragm resistance.
  • the molar content of the structural units derived from the monomer represented by formula I is too small, and the adhesive force of the binder is too low.
  • the bonding performance of the binder will be reduced, thereby affecting the cycle performance of the battery. If the molar content of the structural unit derived from the monomer represented by formula III is too small, the stability of the slurry will decrease and the internal resistance of the pole piece will increase.
  • the molar content of the structural units derived from the monomer represented by formula I in the polymer is within an appropriate range, not only the stability of the slurry is improved, but also the pole pieces have excellent adhesion and low diaphragm resistance, allowing the battery to simultaneously It has excellent cycle capacity retention and low internal resistance growth rate.
  • the polymer has a weight average molecular weight of 5 ⁇ 10 5 to 12 ⁇ 10 5 .
  • weight average molecular weight refers to the statistical average molecular weight averaged over molecular weights of different molecular weights in a polymer.
  • the molecular weight of the binder is too small, making it difficult to form a three-dimensional network bonding structure and unable to play an effective bonding role. If the molecular weight of the binder is too large, it will be difficult to dissolve the binder and easily agglomerate with the conductive agent. The viscosity of the slurry will be large, making it difficult to coat evenly, which is not conducive to subsequent processing and production.
  • the weight average molecular weight of the polymer is within this range, not only the stability of the slurry is improved, but also the pole pieces have excellent adhesion and low diaphragm resistance, which in turn enables the battery to have excellent cycle performance during cycling. capacity retention and lower internal resistance growth rate.
  • the monomer represented by Formula I is selected from one or more of acrylonitrile and crotonitrile.
  • the monomer represented by Formula II is selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, isopentyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, acrylic acid One or more of hydroxyethyl ester and hydroxypropyl acrylate.
  • the monomer represented by Formula III is selected from one or both of acrylic acid and methacrylic acid.
  • the above-mentioned raw materials are simple and easy to obtain, and can significantly reduce production costs and increase output compared with traditional binders.
  • a method for preparing an adhesive including the following steps:
  • R1, R2, and R5 are each independently selected from hydrogen or substituted or unsubstituted C1-5 alkyl, R3 is selected from hydrogen or C1-3 alkyl, and R4 is selected from substituted or unsubstituted C1- 9 alkyl;
  • the monomer represented by formula I, the monomer represented by formula II and the monomer represented by formula III are polymerized under polymerizable conditions to prepare a polymer.
  • polymerizable conditions refers to those conditions including temperature, pressure, reactant concentration, optional solvent/diluent, reactant mixing/addition parameters selected by one skilled in the art to facilitate a or other conditions for the reaction of multiple monomers in at least one polymerization reactor.
  • the monomer represented by Formula I, the monomer represented by Formula II, the monomer represented by Formula III and the initiator are polymerized in a solution environment and a non-reactive gas atmosphere at 60°C to 70°C. 4-7 hours; add a chain transfer agent and polymerize at 70°C to 80°C for 3-5 hours to obtain the polymer.
  • the degree of polymerization of the polymer can be increased, the bonding force of the binder can be further increased, and the bonding performance of the pole piece can be improved.
  • the initiator is an organic peroxide, which can be selected from one or more of dibenzoyl peroxide, tert-amyl peroxypivalate, and 2-ethyl peroxycarbonate. .
  • the chain transfer agent is selected from one or both of vinyl chloride and vinyl acetate.
  • the mass of the initiator is 0.5% to 1.5% of the total monomer mass, optionally 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%.
  • the mass of the chain transfer agent is 0.02% to 0.08% of the total monomer mass, optionally 0.03%, 0.04%, 0.05%, 0.06%, 0.07%.
  • the molar content of the monomer represented by the formula I is 70% to 90%
  • the molar content of the monomer represented by the formula II is 5% ⁇ 25%
  • the molar content of the monomer represented by the formula III The molar content of the monomers is 5% to 25%, based on the total moles of the monomers.
  • the binder preparation method can produce the binder of any embodiment of the present application.
  • the preparation method further includes the following steps: the molar content of the monomer represented by Formula I is 70% to 90%, and the molar content of the monomer represented by Formula II is 5% to 90%. 25%, the molar content of the monomer represented by Formula III is 5% to 25%, based on the total moles of the monomer.
  • This method has low raw material cost, no pollution to the environment, and is conducive to increasing binder production.
  • the adhesive prepared by this preparation method can reduce the gelling phenomenon of the slurry, improve the stability of the slurry and reduce the resistance of the pole piece diaphragm.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector.
  • the positive electrode film layer includes a positive electrode active material, a conductive agent and a binder in some embodiments or prepared by a preparation method in some embodiments. Binder.
  • the positive electrode plate has low diaphragm resistance.
  • the cathode active material may be a cathode active material known in the art for batteries.
  • the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds.
  • the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxides (such as LiNiO 2 ), lithium manganese oxides (such as LiMnO 2 , LiMn 2 O 4 ), lithium Nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1/3 Co 1/3 Mn 1/3 O 2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (can also be abbreviated to NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (can also be abbreviated to NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (can also be abbreviated to NCM 622 ), LiNi At least one of 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as Li Li
  • the olivine structure contains Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), composites of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), lithium manganese phosphate and carbon. At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • lithium iron phosphate such as LiFePO 4 (also referred to as LFP)
  • composites of lithium iron phosphate and carbon such as LiMnPO 4
  • LiMnPO 4 lithium manganese phosphate and carbon.
  • At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon At least one of composite materials, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.
  • the positive active material is a lithium-containing transition metal oxide, which may be lithium nickel cobalt manganese oxide, or its doped modified materials, or its conductive carbon coating modified materials, conductive metal coating
  • the modified material or conductive polymer coats at least one of the modified materials.
  • the mass fraction of the binder is 0.1% to 3%, optionally 0.5% to 3%, based on the mass of the positive active material. In some embodiments, the mass fraction of the binder can be selected from 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5% or 3%.
  • the binder When the binder content is too low, the binder cannot exert sufficient bonding effect. On the one hand, the binder cannot fully disperse the conductive agent and active material, causing the diaphragm resistance of the pole piece to increase; on the other hand, the binder cannot tightly bind to the surface of the active material, causing the surface of the pole piece to easily come off, causing the battery cycle Performance degrades.
  • the binder content is too high, the viscosity of the slurry will be too high, which will cause the binder coating layer covering the surface of the positive electrode active material to be too thick, affecting the transmission of electrons and ions during the battery cycle, causing the electrode to be damaged.
  • the capacity retention rate of the chip during the cycle decreases, and the internal resistance growth rate increases.
  • the mass fraction of the binder within this range can improve the stability of the slurry, allowing the pole piece to have both excellent resistance and bonding properties, and the battery to have better overall cycle performance.
  • the surface of the conductive agent includes silanol groups and/or hydroxyl groups, and the conductive agent is selected from one or more of conductive carbon black, conductive graphite, carbon nanotubes, graphene and carbon fibers.
  • silanol groups and hydroxyl groups are prepared by surface modification of conductive agents.
  • the silanol groups and/or hydroxyl groups on the surface of the conductive agent can undergo an esterification reaction with the carboxyl groups contained in the binder, which helps to build a conductive network on the surface of the active material, thereby reducing the membrane resistance.
  • the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • the metal foil aluminum foil can be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.
  • the composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.
  • a solvent such as N -methylpyrrolidone
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, where the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material.
  • the composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative active material may be a negative active material known in the art for batteries.
  • the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like.
  • the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys.
  • the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.
  • the negative electrode film layer optionally further includes a binder.
  • the binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polysodium acrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer optionally further includes a conductive agent.
  • the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative active materials, conductive agents, binders and any other components in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode piece can be obtained.
  • a solvent such as deionized water
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the type of electrolyte in this application can be selected according to needs.
  • the electrolyte can be liquid, gel, or completely solid.
  • the electrolyte is an electrolyte solution.
  • the electrolyte solution includes electrolyte salts and solvents.
  • the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.
  • the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.
  • the electrolyte optionally further includes additives.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.
  • the secondary battery further includes a separator film.
  • This application has no special restrictions on the type of isolation membrane, and any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.
  • a secondary battery including an electrode assembly and an electrolyte.
  • the electrode assembly includes a positive electrode piece, a separator film, and a negative electrode piece of any embodiment.
  • the positive electrode piece, the negative electrode piece, and the separator film can be made into an electrode assembly through a winding process or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
  • FIG. 1 shows a square-structured secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.
  • FIG. 3 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack.
  • the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • an electrical device including at least one of a secondary battery of any embodiment, a battery module of any embodiment, or a battery pack of any embodiment.
  • the electrical device includes at least one of the secondary battery, battery module, or battery pack provided by the present application.
  • the secondary battery, battery module, or battery pack may be used as a power source for the electrical device, or may be used as an energy storage unit for the electrical device.
  • the electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.
  • a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.
  • FIG. 6 is an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • a battery pack or battery module can be used.
  • the device may be a mobile phone, a tablet, a laptop, etc.
  • the device is usually required to be thin and light, and a secondary battery can be used as a power source.
  • the temperature is lowered to room temperature, filtered and washed several times with high-mesh gauze, vacuum dried overnight, and pulverized into powder to obtain a binder containing acrylonitrile-ethyl acrylate-acrylic acid copolymer.
  • NCM nickel cobalt manganese
  • conductive agent carbon black conductive agent carbon black
  • Example 1 binder conductive agent carbon black
  • NMP N-methylpyrrolidone
  • SBR binder styrene-butadiene rubber
  • CMC thickener sodium carboxymethylcellulose
  • Example 1 Stack the positive electrode piece, isolation film, and negative electrode piece in order in Example 1 so that the isolation film plays an isolation role between the positive and negative electrode pieces, then wind it to obtain a bare battery core, and weld the tabs to the bare battery core. , put the bare battery core into an aluminum case, bake it at 80°C to remove water, then inject electrolyte and seal it to obtain an uncharged battery. The uncharged battery then undergoes processes such as standing, hot and cold pressing, formation, shaping, and capacity testing to obtain the battery product of Example 1.
  • the batteries of Examples 2 to 10 were prepared in a similar manner to the battery of Example 1, but the molar ratios of acrylonitrile, ethyl acrylate, and acrylic acid monomers were adjusted. The specific parameters are as shown in Table 1.
  • the battery preparation methods of Examples 11 to 14 are similar to the batteries of Examples, but the molecular weight of the binder is adjusted.
  • the specific parameters are as shown in Table 1, and the preparation method is as follows:
  • the preparation method of the binder in Examples 11 and 12 compared with Example 1, increase the amount of initiator to increase the number of new chain segments, add a certain number of monomers, and judge the reaction termination time based on the spot plate results. A slightly lower molecular weight binder is obtained.
  • the preparation method of the binder in Examples 13 and 14 compared with Example 1, reduce the amount of initiator, increase the reflux reaction temperature to 85°C, add a certain number of monomers, and determine the reaction termination time based on the spot plate results, thus A slightly higher molecular weight binder is obtained.
  • Example 15 The battery of Example 15 is prepared in a similar manner to the battery of Example 1, but the acrylonitrile monomer is replaced by a crotonitrile monomer, and the molar ratio remains unchanged.
  • the specific parameters are as shown in Table 1.
  • the battery of Example 16 is prepared in a similar manner to the battery of Example 1, except that the ethyl acrylate monomer is replaced by isooctyl acrylate monomer, and the molar ratio remains unchanged.
  • the specific parameters are as shown in Table 1.
  • the battery of Example 17 is prepared in a similar manner to the battery of Example 1, but the acrylic acid monomer is replaced by a methacrylic acid monomer, and the molar ratio remains unchanged.
  • the specific parameters are as shown in Table 1.
  • the batteries of Examples 18 to 23 were prepared in a similar manner to the battery of Example 1, but the mass fraction of the binder was adjusted. The specific parameters are shown in Table 1.
  • the batteries of Examples 24 and 25 were prepared in a similar manner to the battery of Example 1, except that the conductive agent carbon black was replaced with carbon black surface-modified by silanol groups and carbon black surface-modified by hydroxyl groups, respectively.
  • the specific modification method is: pretreat the conductive agent in the original formula, add the conductive agent carbon black to trimethylsilanol or hydrogen peroxide, stir for a certain period of time, and graft silanol groups or hydroxyl groups on the surface.
  • the battery of Comparative Example 1 was prepared similarly to the battery of Example 1, but the binder was a PVDF binder purchased from Arkema Chemical Co., Ltd.
  • the battery of Comparative Example 2 was prepared in a similar manner to the battery of Example 1, but the binder was polymerized from acrylonitrile monomer. Compared with Example 1, the preparation method eliminated the addition of ethyl acrylate and acrylic acid monomers.
  • the battery of Comparative Example 3 was prepared in a similar manner to the battery of Example 1, but the binder was copolymerized from acrylonitrile and ethyl acrylate monomers.
  • the molar content of acrylonitrile was 80%, and the molar content of acrylate was 20%.
  • the preparation method eliminates the addition of acrylic acid monomer, and the ratio of acrylonitrile and ethyl acrylate monomer is 8:2.
  • the battery of Comparative Example 4 is prepared in a similar manner to the battery of Example 1, but the binder is copolymerized from acrylonitrile and acrylic acid monomers.
  • the molar content of acrylonitrile is 80% and the molar content of acrylic acid is 20%.
  • the preparation method is the same as that of Example 1. Compared with Example 1, the addition of ethyl acrylate monomer is eliminated, and the ratio of acrylonitrile and acrylic acid monomer is 8:2.
  • Coat the positive electrode slurry on the surface of the current collector such as a current collector
  • dry and cold-press it to form a pole piece (compacted density is 2.3g/cc)
  • Reserve first bend the pole piece in half and fix it, use a 2kg rolling roller to roll it once, and check whether there is light transmission and metal leakage at the folded part of the pole piece; if there is no light transmission and metal leakage, fold the pole piece in reverse and fix it.
  • the battery capacity retention rate test process is as follows: At 25°C, charge the prepared battery with a constant current of 1/3C to 4.3V, then charge with a constant voltage of 4.3V until the current is 0.05C, leave it for 5 minutes, and then charge it with a constant current of 1/3C Discharge to 2.8V, and the resulting capacity is recorded as the initial capacity C0. Repeat the above steps for the same battery, and at the same time record the discharge capacity Cn of the battery after the nth cycle.
  • Each point value is the ordinate, and the corresponding number of cycles is the abscissa, and a curve graph of battery capacity retention rate and number of cycles is obtained.
  • the battery capacity retention rate data corresponding to the examples or comparative examples in Table 1 is the data measured after 500 cycles under the above test conditions, that is, the value of P500.
  • the testing procedures of the comparative examples and other examples are the same as above.
  • the battery DC impedance test process is as follows: At 25°C, charge the prepared battery with a constant current of 1/3C to 4.3V, then charge with a constant voltage of 4.3V until the current is 0.05C. After leaving it aside for 5 minutes, record the voltage V1. Then discharge at 1/3C for 30 seconds and record the voltage V2, then (V2-V1)/1/3C, we get the internal resistance DCR1 of the battery after the first cycle.
  • the battery internal resistance increase ratio (DCRn-DCR1)/DCR1*100%.
  • the test process of the comparative example and other embodiments is the same as above.
  • the data in Table 1 are measured after 100 cycles under the above test conditions.
  • the binders in Examples 1 to 25 all include polymers, and the polymers all include structural units containing cyano groups (derived from acrylonitrile or crotonitrile), and structural units containing ester groups (derived from ethyl acrylate or isooctyl acrylate) and structural units containing carboxyl groups (derived from acrylic acid or methacrylic acid).
  • the adhesive can significantly slow down the gelation phenomenon of the slurry, improve the stability of the slurry and reduce the diaphragm resistance of the pole piece.
  • the molar content of structural units derived from acrylonitrile in the polymer is 70% to 90%, and the molar content of structural units derived from ethyl acrylate is 5%. ⁇ 25%, the molar content of structural units derived from acrylic acid is 5% ⁇ 25%, based on the total mole number of all structural units in the polymer, not only the stability of the slurry is improved, but also the pole piece has excellent adhesion
  • the junction force and low diaphragm resistance enable the battery to have both excellent cycle capacity retention and low internal resistance growth rate during cycling.
  • the mass fraction of the binder is 0.1% to 3%. Based on the mass of the positive active material, the slurry has good stability. When the mass fraction of the binder is 1% to 3%, the slurry has better stability and the pole pieces have improved resistance and bonding properties, which improves the overall cycle performance of the battery.
  • Example 1 From the comparison between Example 1 and Examples 24-25, it can be seen that after the surface of the conductive agent carbon black is modified by silanol groups or hydroxyl groups, the diaphragm resistance of the pole piece decreases.

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Abstract

本申请提供了一种粘结剂、制备方法、二次电池、电池模块、电池包及用电装置。粘结剂包含聚合物，所述聚合物含有衍生自式I所示的单体的结构单元、衍生自式II所示的单体的结构单元和衍生自式III所示的单体的结构单元，其中，R1、R2、R5各自独立地选自氢或取代或未取代的C1-5烷基，R3选自氢或C1-3烷基，R4选自取代或未取代的C1-9烷基。该粘结剂可以减轻浆料的凝胶现象，提高浆料的稳定性和加工性能。

Description

粘结剂、制备方法、正极极片、二次电池及用电装置 技术领域
本申请涉及二次电池技术领域，尤其涉及一种粘结剂、制备方法、正极极片、二次电池、电池模块、电池包及用电装置。
背景技术
近年来，二次离子电池广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。
粘结剂是二次离子电池中的常用材料，广泛应用于电池极片、隔离膜、封装处等。但是传统的粘结剂生产成本高、产能不足，对环境危害大，且在制备过程中容易出现凝胶，导致浆料稳定性差、加工成本高，以其制备的极片导电性差、电阻高、良品率低，电池性能不稳定，难以满足市场对于电池成本和性能的要求。因此，现有的粘结剂仍有待改进。
发明内容
本申请是鉴于上述课题而进行的，其目的在于，提供一种粘结剂，能够减缓浆料的凝胶现象，提高浆料的稳定性和极片的导电性。
本申请的第一方面提供一种粘结剂，粘结剂包含聚合物，聚合物含有衍生自式I所示的单体的结构单元、衍生自式II所示的单体的结构单元和衍生自式III所示的单体的结构单元，
Figure PCTCN2022110373-appb-000001
Figure PCTCN2022110373-appb-000002
其中，R 1、R 2、R 5各自独立地选自氢或取代或未取代的C 1-5烷基，R 3选自氢或C 1-3烷基，R 4选自取代或未取代的C 1-9烷基。
以该聚合物作为粘结剂可以显著减缓浆料的凝胶现象，提高浆料稳定性的同时降低极片的膜片电阻。
在任意实施方式中，聚合物中衍生自式I所示的单体的结构单元的摩尔含量为70％～90％，衍生自式II所示的单体的结构单元的摩尔含量为5％～25％，衍生自式III所示的单体的结构单元的摩尔含量为5％～25％，基于聚合物中所有结构单元的总摩尔数计。
衍生自式I所示的单体的结构单元在聚合物中的摩尔含量、衍生自式II所示的单体的结构单元在聚合物中的摩尔含量和衍生自式III所示的单体的结构单元在聚合物中的摩尔含量在合适范围内时，不但浆料的稳定性、极片的柔性和导电性均有所改善，而且电池具有更为优异的循环性能和安全性能。
在任意实施方式中，聚合物的重均分子量为5×10 5～12×10 5。聚合物的重均分子量在此范围内，不但浆料的稳定性得到改善，而且极片兼具优异的粘结力和较低的膜片电阻，进而使得电池的循环性能有所提升。
在任意实施方式中，式I所示的单体选自丙烯腈和丁烯腈中的一种或多种。
在任意实施方式中，式II所示的单体选自丙烯酸甲酯、丙烯酸乙酯、丙烯酸丁酯、丙烯酸异戊酯、丙烯酸异辛酯、甲基丙烯酸甲酯、甲基丙烯酸乙酯、丙烯酸羟乙酯、丙烯酸羟丙酯中的一种或多种。
在任意实施方式中，式III所示的单体选自丙烯酸、甲基丙烯酸中的一种或两种。
上述原材料简单易得，相比于传统粘结剂能够大幅度降低生产 成本，提高产量。
本申请的第二方面还提供一种粘结剂的制备方法，包括以下步骤：提供式I所示的单体、式II所示的单体和式III所示的单体，
Figure PCTCN2022110373-appb-000003
其中，R 1、R 2、R 5各自独立地选自氢或取代或未取代的C 1-5烷基，R 3选自氢或C 1-3烷基，R 4选自取代或未取代的C 1-9烷基；
在可聚合条件下将式I所示的单体、式II所示的单体和式III所示的单体聚合制备聚合物。
在任意实施方式中，制备方法还包括以下步骤：将式I所示的单体、式II所示的单体、式III所示的单体和引发剂在溶液环境，非反应性气体氛围中在60℃～70℃聚合4-7小时；加入链转移剂，在70℃～80℃聚合3-5小时，得到所述聚合物。
在任意实施方式中，引发剂为有机过氧化物，可选自过氧化二苯甲酰，过氧化新戊酸叔戊酯，2-乙基过氧化碳酸酯中的一种或多种。
在任意实施方式中，链转移剂选自氯乙烯，乙酸乙烯酯中的一种或两种。
在任意实施方式中，式I所示的单体的摩尔含量为70％～90％，所述式II所示的单体的摩尔含量为5％～25％，所述式III所示的单体的摩尔含量为5％～25％，基于所述单体的总摩尔数计。
该制备方法原材料成本低，对环境无污染，有利于粘结剂产量的提升。同时该方法制备的粘结剂，可以减轻浆料的凝胶现象，提高浆料稳定性的同时降低极片膜片的电阻。
本申请的第三方面提供一种正极极片，包括正极活性物质、导电剂和任意实施方式中的粘结剂或任意实施方式中的制备方法制备 的粘结剂。
该正极极片柔性好，易于成型且具有较低的膜片电阻。
在任意实施方式中，正极活性物质为含锂的过渡金属氧化物，可选为锂镍钴锰氧化物、或其掺杂改性材料、或其导电碳包覆改性材料、导电金属包覆改性材料或导电聚合物包覆改性材料中的至少一种。
在任意实施方式中，粘结剂的质量分数为0.01％～3％，可选为0.5％～3％，基于正极活性物质的质量计。
粘结剂的质量分数在此范围内，能够提高浆料的稳定性，使得极片兼具优异的电阻性能和粘结性能，电池具备更好的综合循环性能。
在任意实施方式中，导电剂的表面包括硅醇基团和/或羟基基团，导电剂选自导电炭黑、导电石墨、碳纳米管、石墨烯和碳纤维中的一种或多种。
导电剂表面的硅醇基团和/或羟基基团能与粘结剂中含有的羧基发生酯化反应，在活性物质表面更好地搭建导电网络，从而降低膜片电阻。
在本申请的第四方面，提供一种二次电池，包括电极组件和电解液，所述电极组件包括本申请第三方面的正极极片、隔离膜和负极极片。
在本申请的第五方面，提供一种电池模块，包括本申请第四方面的二次电池。
在本申请的第六方面，提供一种电池包，包括本申请第五方面的电池模块。
在本申请的第七方面，提供一种用电装置，包括本申请第四方面的二次电池、第五方面的电池模块或第六方面的电池包中的至少一种。
附图说明
图1是本申请一实施方式的二次电池的示意图。
图2是图1所示的本申请一实施方式的二次电池的分解图。
图3是本申请一实施方式的电池模块的示意图。
图4是本申请一实施方式的电池包的示意图。
图5是图4所示的本申请一实施方式的电池包的分解图。
图6是本申请一实施方式的二次电池用作电源的用电装置的示意图。
附图标记说明：
1电池包；2上箱体；3下箱体；4电池模块；5二次电池；51壳体；52电极组件；53盖板。
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的粘结剂、制备方法、电极、电池及用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组 合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
现有技术中常以聚偏二氟乙烯(PVDF)作为极片粘结剂，然而PVDF在使用过程中存在诸多问题，如生常过程中对水含量较为敏感；在电池回收过程中，会产生大量HF污染环境，受环保政策的限制无法大规模回收利用；在与高容量的正极材料(如高镍三元材料)混合制备正极浆料的过程中，PVDF上的强极性基团会活化正极材料上残留的羟基，进而与正极材料中的金属元素(如镍元素)发生键合反应，形成化学交联，最终导致浆料凝胶，影响浆料的正常制备以 及后续的极片加工。同时，PVDF容易结晶，不利于电子在极片中的传输，进而导致极片的电阻高、电子传输性能差，不利于高容量的正极材料性能的发挥。
[粘结剂]
基于此，本申请提出了一种粘结剂，粘结剂包含聚合物，聚合物含有衍生自式I所示的单体的结构单元、衍生自式II所示的单体的结构单元和衍生自式III所示的单体的结构单元，
Figure PCTCN2022110373-appb-000004
其中，R 1、R 2、R 5各自独立地选自氢或取代或未取代的C 1-5烷基，R 3选自氢或C 1-3烷基，R 4选自取代或未取代的C 1-9烷基。
在本文中，术语“粘结剂”是指在分散介质中形成胶体溶液或胶体分散液的化学化合物、聚合物或混合物。
在本文中，术语“聚合物”一方面包括通过聚合反应制备的化学上均一的、但在聚合度、摩尔质量和链长方面不同的大分子的集合体。
该术语另一方面也包括由聚合反应形成的这样的大分子集合体的衍生物，即可以通过上述大分子中的官能团的反应，例如加成或取代获得的并且可以是化学上均一的或化学上不均一的化合物。
在一些实施方式中，粘结剂的分散介质是水性溶剂，如水。即粘结剂溶解于水性溶剂中。
在一些实施方式中，粘接剂的分散介质是油性溶剂，油性溶剂的示例包括但不限于二甲基乙酰胺、N，N-二甲基甲酰胺、N-甲基吡咯烷酮、丙酮、碳酸二甲酯、乙基纤维素、聚碳酸酯。即，粘结剂溶解于油性溶剂中。
在一些实施方式中，粘结剂用于将电极材料及/或导电剂固定在合适位置并将它们粘附在导电金属部件以形成电极。
在一些实施方式中，粘结剂作为正极粘结剂，用于粘结正极活性材料及/或导电剂以形成电极。
在一些实施方式中，粘结剂作为负极粘结剂，用于粘结负极活性材料及/或导电剂以形成电极。
在本文中，术语“C 1-5烷基”是指仅由碳和氢原子组成的直链或支链烃链基团，基团中不存在不饱和，具有从一至五个碳原子，并且通过单键附接到分子的其余部分。术语“C 1-9烷基”应相应解释。C 1-5烷基的示例包括但不限于：甲基、乙基、正丙基、1-甲基乙基(异丙基)、丁基、戊基。
在本文中，术语“取代的”是指该化合物或化学部分的至少一个氢原子被另一种化学部分被取代基取代，其中的取代基各自独立地选自：羟基、巯基、氨基、氰基、硝基、醛基、卤素原子、烯基、炔基、芳基、杂芳基、C 1-6烷基、C 1-6烷氧基。
在本文中，术语“甲基”指的是-CH 3基团。
在本文中，术语“氰基”指的是-CN基团。
在本文中，术语“羧基”指的是-COOH基团
在本文中，术语“酯基”指的是-COOR 4基团，R 4选自被取代基取代或未取代的C 1-9烷基。
在一些实施方式中，聚合物包含一种或多种衍生自式I所示单体的结构单元。在一些实施方式中，聚合物包含一种或多种衍生自式II所示单体的结构单元。在一些实施方式中，聚合物包含一种或多种衍生自式III所示单体的结构单元。在一些实施方式中，聚合物包括但不限于丙烯腈-丙烯酸甲酯-丙烯酸聚合物、丙烯腈-甲基丙烯酸乙酯聚合物-丙烯酸聚合物、丙烯腈-丙烯酸丁酯-丙烯酸聚合物、丙烯腈-丙烯酸异辛酯聚合物、丙烯腈-丙烯酸丁酯-丙烯酸乙酯-丙烯酸聚合物、丙烯腈-丙烯酸异戊酯-丙烯酸聚合物、丁烯腈-丙烯酸甲酯-丙烯酸聚合物、丁烯腈-丙烯酸甲酯-丙烯酸聚合物、丁烯腈-丙烯 酸丁酯-丙烯酸聚合物、丁烯腈-甲基丙烯酸乙酯-丙烯酸聚合物、丁烯腈丙烯酸丁酯-丙烯酸乙酯-丙烯酸聚合物、丙烯腈-丙烯酸异戊酯-丙烯酸聚合物、丁烯腈-甲基丙烯酸乙酯-甲基丙烯酸聚合物、丁烯腈-丙烯酸甲酯-甲基丙烯酸聚合物。
该粘结剂中不包含氟元素，对环境友好，符合环保要求。同时，粘结剂对水分不会高度敏感，可以提高整个浆料体系的耐湿度。由于包含极性较强的氰基，粘结剂具有较强的粘度，能够提高粘结剂对于浆料中物质的分散性，相比于传统PVDF，可以减少浆料中粘结剂的添加量。另外强极性基团氰基可以增强分子结构的稳定性，可以提高聚合物的玻璃化转变温度，改善聚合物的刚性和的热稳定性，拓宽粘结剂的电化学窗口。同时具有强极性的氰基的聚合物，与电解液亲和性以及电化学稳定性好。粘结剂中的酯基官能团有助于削弱氰基之间过强的偶极矩，减少由于氰基之间作用力过强导致的粘结剂链段自由运动受阻，引发极片脆性问题。酯基官能团的柔性链段有助于改善粘结剂和极片的柔性，进而提高电池的安全性能。由于包含羧基官能团，该粘结剂在浆料中具有优异的润湿性，分散性和稳定性，有助于导电网络的形成，能够降低膜片电阻。同时，该粘结剂包含的羧基官能团可以与高镍三元材料在潮湿空气中容易生成的碱性的LiOH发生反应，避免浆料在潮湿空气中发生碱解，进一步提高浆料的稳定性。
综上，以该聚合物作为粘结剂可以显著减缓浆料的凝胶现象，提高浆料稳定性的同时降低极片的膜片电阻，有助于电池提高极片的成型质量。
在一些实施方式中，聚合物中衍生自式I所示的单体的结构单元的摩尔含量为70％～90％，衍生自式II所示的单体的结构单元的摩尔含量为5％～25％，衍生自式III所示的单体的结构单元的摩尔含量为5％～25％，基于聚合物中所有结构单元的总摩尔数计。
若式II和式III所示的软单体比例较高，则聚合物刚性较差，玻璃转化温度较低，断裂强度较低；若式II和式III所示的软单体比例 过低，聚合物中柔性链段不足，则会导致聚合物脆性较大，后续加工极片脆性过大，极片弯折过程中容易露出集流体，甚至断裂，留下安全隐患。
衍生自式I所示的单体的结构单元的摩尔含量过大，氰基官能团的含量过高导致浆料的粘度过大，不利于浆料的加工和导电剂的分散，影响导电网络的形成，进而增加膜片电阻。衍生自式I所示的单体的结构单元的摩尔含量过小，粘结剂的粘结力过低。
衍生自式II所示的单体的结构单元的摩尔含量过小，极片柔韧性不足，极片脆性大容易发生脆断，引发安全事故且加工难度大。
衍生自式III所示的单体的结构单元的摩尔含量过大，会降低粘结剂的粘结性能，进而影响电池的循环性能。衍生自式III所示的单体的结构单元的摩尔含量过少，浆料的稳定性下降，极片内阻增大。
衍生自式I所示的单体的结构单元在聚合物中的摩尔含量、衍生自式II所示的单体的结构单元在聚合物中的摩尔含量和衍生自式III所示的单体的结构单元在聚合物中的摩尔含量在合适范围内时，不但浆料的稳定性得到改善，而且极片兼具优异的粘结力和较低的膜片电阻，进而使得电池在循环过程中同时具有优异的循环容量保持率和较低的内阻增长率。
在一些实施方式中，聚合物的重均分子量为5×10 5～12×10 5。
在本文中，术语“重均分子量”是指聚合物中用不同分子量的分子重量平均的统计平均分子量。
粘结剂的分子量过小，较难形成三维网状粘结结构，无法起到有效的粘结作用。粘结剂的分子量过大，粘结剂溶解困难，易与导电剂团聚，浆料的粘度较大，难以涂布均匀，不利于后续加工生产。
聚合物的重均分子量在此范围内，不但浆料的稳定性得到改善，而且极片兼具优异的粘结力和较低的膜片电阻，进而使得电池在循环过程中同时具有优异的循环容量保持率和较低的内阻增长率。
在一些实施方式中，式I所示的单体选自丙烯腈和丁烯腈中的一种或多种。
在一些实施方式中，式II所示的单体选自丙烯酸甲酯、丙烯酸乙酯、丙烯酸丁酯、丙烯酸异戊酯、丙烯酸异辛酯、甲基丙烯酸甲酯、甲基丙烯酸乙酯、丙烯酸羟乙酯、丙烯酸羟丙酯中的一种或多种。
在一些实施方式中，式III所示的单体选自丙烯酸、甲基丙烯酸中的一种或两种。
上述原材料简单易得，相比于传统粘结剂能够大幅度降低生产成本，提高产量。
本申请的一个实施方式中，提供一种粘结剂的制备方法，包括以下步骤：
提供式I所示的单体、式II所示的单体和式III所示的单体，
Figure PCTCN2022110373-appb-000005
其中，R1、R2、R5各自独立地选自氢或取代或未取代的C1-5烷基，R 3选自氢或C 1-3烷基，R 4选自取代或未取代的C 1-9烷基；
在可聚合条件下将式I所示的单体、式II所示的单体和式III所示的单体聚合制备聚合物。
在本文中，术语“可聚合条件”是指包括本领域技术人员选择的温度、压力、反应物浓度、任选的溶剂/稀释剂、反应物混合/添加参数的那些条件，有助于一种或多种单体在至少一个聚合反应器内反应的其他条件。
在一些实施方式中，将式I所示的单体、式II所示的单体、式III所示的单体和引发剂在溶液环境，非反应性气体氛围中在60℃～70℃聚合4-7小时；加入链转移剂，在70℃～80℃聚合3-5小时，得到所述聚合物。
通过上述方法可以提高聚合物的聚合度，进一步增加粘结剂的粘结力，提高极片的粘结性能。
在一些实施方式中，所述引发剂为有机过氧化物，可选自过氧化二苯甲酰，过氧化新戊酸叔戊酯，2-乙基过氧化碳酸酯中的一种或多种。
在一些实施方式中，所述链转移剂选自氯乙烯，乙酸乙烯酯中的一种或两种。
在一些实施方式中，引发剂的质量是单体总质量的0.5％～1.5％，可选为0.7％，0.8％，0.9％，1.0％，1.1％，1.2％，1.3％，1.4％。
在一些实施方式中，链转移剂的质量是单体总质量的0.02％～0.08％，可选为0.03％，0.04％，0.05％，0.06％，0.07％。
在一些实施方式中，所述式I所示的单体的摩尔含量为70％～90％，所述式II所示的单体的摩尔含量为5％～25％，所述式III所示的单体的摩尔含量为5％～25％，基于所述单体的总摩尔数计。在一些实施方式中，粘结剂的制备方法能够生产本申请任意实施方式中的粘结剂。
在一些实施方式中，所述制备方法还包括以下步骤：所述式I所示的单体的摩尔含量为70％～90％，所述式II所示的单体的摩尔含量为5％～25％，所述式III所示的单体的摩尔含量为5％～25％，基于所述单体的总摩尔数计。
该方法原材料成本低，对环境无污染，有利于粘结剂产量的提升。该制备方法制备的粘结剂，可以减轻浆料的凝胶现象，提高浆料稳定性的同时降低极片膜片的电阻。
[正极极片]
正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，正极膜层包括正极活性材料、导电剂和一些实施方式中的粘结剂或一些实施方式中的制备方法制备的粘结剂。
该正极极片具有较低的膜片电阻。
在一些实施方式中，正极活性材料可采用本领域公知的用于电 池的正极活性材料。作为示例，正极活性材料可包括以下材料中的至少一种：橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。但本申请并不限定于这些材料，还可以使用其他可被用作电池正极活性材料的传统材料。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。其中，锂过渡金属氧化物的示例可包括但不限于锂钴氧化物(如LiCoO 2)、锂镍氧化物(如LiNiO 2)、锂锰氧化物(如LiMnO 2、LiMn 2O 4)、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物(如LiNi 1/3Co 1/3Mn 1/3O 2(也可以简称为NCM 333)、LiNi 0.5Co 0.2Mn 0.3O 2(也可以简称为NCM 523)、LiNi 0.5Co 0.25Mn 0.25O 2(也可以简称为NCM 211)、LiNi 0.6Co 0.2Mn 0.2O 2(也可以简称为NCM 622)、LiNi 0.8Co 0.1Mn 0.1O 2(也可以简称为NCM 811)、锂镍钴铝氧化物(如LiNi 0.85Co 0.15Al 0.05O 2)及其改性化合物等中的至少一种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂(如LiFePO 4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、磷酸锰锂(如LiMnPO 4)、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料中的至少一种。
在一些实施方式中，正极活性物质为含锂的过渡金属氧化物，可选为锂镍钴锰氧化物、或其掺杂改性材料、或其导电碳包覆改性材料、导电金属包覆改性材料或导电聚合物包覆改性材料中的至少一种。
在一些实施方式中，粘结剂的质量分数为0.1％～3％，可选为0.5％～3％，基于正极活性物质的质量计。在一些实施方式中，粘结剂的质量分数可选为0.1％、0.5％、1％、1.5％、2％、2.5％或3％。
当粘结剂含量过低时，粘结剂无法发挥足够的粘结效果。一方面粘结剂无法充分分散导电剂和活性物质，导致极片的膜片电阻升高；另一方面粘结剂无法紧密结合于活性物质表面，导致极片表面容易脱粉，造成电池的循环性能下降。
相反，粘结剂含量过高时，浆料的粘度过大，会导致包覆于正 极活性物质表面的粘结剂包覆层过厚，在电池循环过程中影响电子和离子的传输，造成极片在循环过程中的容量保持率下降，内阻增长率升高。
粘结剂的质量分数在此范围内，能够提高浆料的稳定性，使得极片兼具优异的电阻性能和粘结性能，电池具备更好的综合循环性能。
在一些实施方式中，导电剂的表面包括硅醇基团和/或羟基基团，导电剂选自导电炭黑、导电石墨、碳纳米管、石墨烯和碳纤维中的一种或多种。
在一些实施方式中，硅醇基团和羟基基团通过导电剂的表面改性制备。
导电剂表面的硅醇基团和/或羟基基团能与粘结剂中含有的羧基发生酯化反应，有助于在活性物质表面搭建导电网络，从而降低膜片电阻。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极膜层设置在正极集流体相对的两个表面的其中任意一者或两者上。
在一些实施方式中，所述正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如正极活性材料、导电剂、粘结剂和任意其他的组分分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。
[负极极片]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极膜层，所述负极膜层包括负极活性材料。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极膜层设置在负极集流体相对的两个表面中的任意一者或两者上。
在一些实施方式中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，负极活性材料可采用本领域公知的用于电池的负极活性材料。作为示例，负极活性材料可包括以下材料中的至少一种：人造石墨、天然石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂等。所述硅基材料可选自单质硅、硅氧化合物、硅碳复合物、硅氮复合物以及硅合金中的至少一种。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。但本申请并不限定于这些材料，还可以使用其他可被用作电池负极活性材料的传统材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
在一些实施方式中，负极膜层还可选地包括粘结剂。所述粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，负极膜层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
[电解质]
电解质在正极极片和负极极片之间起到传导离子的作用。本申请对电解质的种类没有具体的限制，可根据需求进行选择。例如，电解质可以是液态的、凝胶态的或全固态的。
在一些实施方式中，所述电解质采用电解液。所述电解液包括电解质盐和溶剂。
在一些实施方式中，电解质盐可选自六氟磷酸锂、四氟硼酸锂、高氯酸锂、六氟砷酸锂、双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂、三氟甲磺酸锂、二氟磷酸锂、二氟草酸硼酸锂、二草酸硼酸锂、二氟二草酸磷酸锂及四氟草酸磷酸锂中的至少一种。
在一些实施方式中，溶剂可选自碳酸亚乙酯、碳酸亚丙酯、碳酸甲乙酯、碳酸二乙酯、碳酸二甲酯、碳酸二丙酯、碳酸甲丙酯、碳酸乙丙酯、碳酸亚丁酯、氟代碳酸亚乙酯、甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、丁酸甲酯、丁酸乙酯、1,4-丁内酯、环丁砜、二甲砜、甲乙砜及二乙砜中的至少一种。
在一些实施方式中，所述电解液还可选地包括添加剂。例如添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
[隔离膜]
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离 膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
[二次电池]
本申请的一个实施方式中，提供一种二次电池，包括电极组件和电解液，所述电极组件包括任意实施方式的正极极片、隔离膜和负极极片。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯、聚对苯二甲酸丁二醇酯以及聚丁二酸丁二醇酯等。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图1是作为一个示例的方形结构的二次电池5。
在一些实施方式中，参照图2，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
[电池模块]
在一些实施方式中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块的应用和容量进行选择。
图3是作为一个示例的电池模块4。参照图3，在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
[电池包]
在一些实施方式中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以为一个或多个，具体数量本领域技术人员可根据电池包的应用和容量进行选择。
图4和图5是作为一个示例的电池包1。参照图4和图5，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
[用电装置]
本申请的一个实施方式中，提供一种用电装置，包括任意实施方式的二次电池、任意实施方式的电池模块或任意实施方式的电池包中的至少一种。
所述用电装置包括本申请提供的二次电池、电池模块、或电池包中的至少一种。所述二次电池、电池模块、或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电装置可以包括移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、 船舶及卫星、储能系统等，但不限于此。
作为所述用电装置，可以根据其使用需求来选择二次电池、电池模块或电池包。
图6是作为一个示例的用电装置。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
制备方法
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
实施例1
1)粘结剂的制备
以摩尔比例8:1:1分别称取丙烯腈、丙烯酸乙酯以及丙烯酸，量取一定体积的无水乙醇，加入四口烧瓶，通入大量氮气，并逐渐加大搅拌速度，至搅拌速度为1200rpm，升温至65℃。加入单体总质量1％的过氧化二苯甲酰，并逐渐加温升高至回流温度75℃，反应6h后补加单体质量0.05％的氯乙烯，回流反应4h。反应结束后，降低温度至室温，用高度目数的纱布过滤洗涤数遍，真空干燥过夜，粉碎成粉末，则得到包含丙烯腈-丙烯酸乙酯-丙烯酸共聚物的粘结剂。
2)正极极片的制备
将镍钴锰(NCM)材料、导电剂碳黑、实施例1粘结剂、N-甲基吡咯烷酮(NMP)按重量比为96.9：2：1：21搅拌混合均匀，得 到正极浆料；之后将正极浆料均匀涂覆于正极集流体上，之后经过烘干、冷压、分切，得到正极极片。极片的压实密度为3.4g/cm 3。
3)负极极片的制备
将活性物质人造石墨、导电剂碳黑、粘结剂丁苯橡胶(SBR)、增稠剂羟甲基纤维素钠(CMC)按照重量比为96.2：0.8：0.8：1.2溶于溶剂去离子水中，混合均匀后制备成负极浆料；将负极浆料一次或多次均匀涂覆在负极集流体铜箔上，经过烘干、冷压、分切得到负极极片。
4)电解液的制备
在氩气气氛手套箱中(H 2O<0.1ppm，O 2<0.1ppm)，将有机溶剂碳酸乙烯酯(EC)/碳酸甲乙酯(EMC)按照体积比3/7混合均匀，加入12.5％LiPF 6锂盐溶解于有机溶剂中，搅拌均匀，得到电解液。
5)隔离膜
以聚丙烯膜作为隔离膜。
6)电池的制备
将实施例1正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极片之间起到隔离的作用，然后卷绕得到裸电芯，给裸电芯焊接极耳，并将裸电芯装入铝壳中，并在80℃下烘烤除水，随即注入电解液并封口，得到不带电的电池。不带电的电池再依次经过静置、热冷压、化成、整形、容量测试等工序，获得实施例1的电池产品。
实施例2～10的电池与实施例1的电池制备方法相似，但是调整了丙烯腈、丙烯酸乙酯、丙烯酸单体的摩尔比，具体参数如表1所示。
实施例11～14的电池与实施例的电池制备方法相似，但是调整了粘结剂的分子量，具体参数如表1所示，制备方法如下：
实施例11、12中粘结剂的制备方法：与实施例1相比，增加引发剂用量，使得新增链段数目增加，加入单体数目一定，根据点板结果判断反应终止时间，由此获得分子量略低的粘结剂。
实施例13、14中粘结剂的制备方法：与实施例1相比，减少引发剂用量，提高回流反应温度至85℃，加入单体数目一定，根据点板结果确定反应终止时间，由此获得分子量略高的粘结剂。
实施例15的电池与实施例1的电池制备方法相似，但是将丙烯腈单体替换成丁烯腈单体，摩尔比例不变，具体参数如表1所示。
实施例16的电池与实施例1的电池制备方法相似，但是将丙烯酸乙酯单体替换成丙烯酸异辛酯单体，摩尔比例不变，具体参数如表1所示。
实施例17的电池与实施例1的电池制备方法相似，但是将丙烯酸单体替换成甲基丙烯酸单体，摩尔比例不变，具体参数如表1所示。
实施例18～23的电池与实施例1的电池制备方法相似，但是调整了粘结剂的质量分数，具体参数如表1所示。
实施例24、25的电池与实施例1的电池制备方法相似，但是分别将导电剂碳黑替换成硅醇基团表面改性后的碳黑、羟基基团表面改性后的碳黑。具体改性方法为：预处理原配方中的导电剂，将导电剂炭黑分别加入三甲基硅醇或双氧水中搅拌一定时间，在表面分别接枝硅醇基团或羟基基团。
对比例1的电池与实施例1的电池制备方法相似，但是粘结剂为PVDF粘结剂，PVDF粘结剂购自阿科玛化学有限公司。
对比例2的电池与实施例1的电池制备方法相似，但是粘结剂由丙烯腈单体聚合而成，制备方法与实施例1相比，取消丙烯酸乙酯以及丙烯酸单体添加。
对比例3的电池与实施例1的电池制备方法相似，但是粘结剂由丙烯腈、丙烯酸乙酯单体共聚而成，丙烯腈的摩尔含量为80％，丙烯酸酯的摩尔含量是20％，制备方法与实施例1相比，取消丙烯酸单体添加，且丙烯腈以及丙烯酸乙酯单体的比例为8:2。
对比例4的电池与实施例1的电池制备方法相似，但是粘结剂由丙烯腈、丙烯酸单体共聚而成，丙烯腈的摩尔含量为80％，丙烯酸 的摩尔含量是20％，制备方法与实施例1相比，取消丙烯酸乙酯单体添加，且丙烯腈以及丙烯酸单体的比例为8:2。
上述实施例1～25、对比例1～4的粘结剂的相关参数如下述表1所示。
另外，将上述实施例1～25和对比例1～4中得到的粘结剂、极片和电池进行性能测试。测试方法如下：
1、粘结剂的性质测试
1)重均分子量测试
采用Waters 2695 Isocratic HPLC型凝胶色谱仪(示差折光检测器2141)。质量分数为3.0％的聚苯乙烯溶液试样做参比，选择匹配的色谱柱(油性：Styragel HT5 DMF7.8*300mm+Styragel HT4)。用纯化后的N-甲基吡咯烷酮(NMP)溶剂配置3.0％的聚合物胶液，配置好的溶液静置一天，备用。测试时，先用注射器吸取四氢呋喃，进行冲洗，重复几次。然后吸取5ml实验溶液，排除注射器中的空气，将针尖擦干。最后将试样溶液缓缓注入进样口。待测试完后输出流出曲线图，分子量分布曲线图以及分子量统计结果。
2、浆料的性质测试
1)浆料的粘度测试
浆料出货后，取500ml浆料放置在烧杯中，利用旋转粘度计，选取转子，转速设置为12rpm，转动时间设置为5min，数值稳定后，读取并记录粘度数值。
2)浆料的稳定性测试
将浆料复搅30min后，取一定量的浆料倒入稳定性仪的样品瓶，放入样品瓶后，关闭测试塔盖，打开测试塔盖，测试界面开始出现扫描曲线，开始测试样品稳定性，持续测试48h以上完成测试。
3、极片的性能测试
1)正极极片的膜片电阻测试
将极片左、中、右处裁剪3*3mm小圆片。打开元能科技极片电阻仪指示灯，将置于膜片电阻仪“探头”合适位置，点击“开始” 按钮，待示数稳定，读取即可。每个小圆片测试两个位置，最后计算六次测量的平均值，即为该极片的膜片电阻。
2)正极极片的粘结力测试
将正极极片裁剪为20*100mm 2尺寸的测试试样，备用；试样用双面胶粘接需要测试的那一面，并用压辊压实，使双面胶与试样完全贴合；试样的双面胶的另外一面粘贴于不锈钢表面，将试样一端反向弯曲，弯曲角度为180°；采用高铁拉力机测试，将不锈钢一端固定于拉力机下方夹具，试样弯曲末端固定于上方夹具，调整试样角度，保证上下端位于垂直位置，然后以50mm/min的速度拉伸试样，直到试样全部从基板剥离，记录过程中的位移和作用力，一般认为受力平衡时的力为极片的粘结力。
3)极片脆性测试
将正极浆料涂覆于集流体(如)表面，经过干燥、冷压制成极片(压实密度为2.3g/cc)，将制备完成的极片裁剪为20*100mm尺寸的测试试样，备用；先将极片弯曲对折固定好，使用2kg重的碾压辊碾压一次，查看极片对折处是否透光漏金属；若无透光漏金属，再将极片反过来对折固定住，使用2kg的碾压辊碾压一次，查看极片对折处是否透光漏金属，重复以上步骤，直至极片对折处透光漏金属为止。取三个样品进行测试，取平均值。
4、电池的性能测试
1)电池容量保持率测试
电池容量保持率测试过程如下：在25℃下，将制备的电池，以1/3C恒流充电至4.3V，再以4.3V恒定电压充电至电流为0.05C，搁置5min，再以1/3C放电至2.8V，所得容量记为初始容量C0。对上述同一个电池重复以上步骤，并同时记录循环第n次后电池的放电容量Cn，则每次循环后电池容量保持率Pn＝Cn/C0*100％，以P1、P2……P100这100个点值为纵坐标，以对应的循环次数为横坐标，得到电池容量保持率与循环次数的曲线图。该测试过程中，第一次循环对应n＝1、第二次循环对应n＝2、……第100次循环对应n＝100。 表1中实施例或对比例对应的电池容量保持率数据是在上述测试条件下循环500次之后测得的数据，即P500的值。对比例以及其他实施例的测试过程同上。
2)、电池直流阻抗测试
电池直流阻抗测试过程如下：在25℃下，将制备的电池，以1/3C恒流充电至4.3V，再以4.3V恒定电压充电至电流为0.05C，搁置5min后，记录电压V1。然后再以1/3C放电30s，记录电压V2，则(V2-V1)/1/3C，得到第一次循环后电池的内阻DCR1。对上述同一个电池重复以上步骤，并同时记录循环第n次后电池的内阻DCRn(n＝1、2、3……100)，将上述DCR1、DCR2、DCR3……DCR100这100个点值为纵坐标，以对应的循环次数为横坐标，得到电池放电DCR与循环次数的曲线图。
该测试过程中，第一次循环对应n＝1、第二次循环对应n＝2、……第100次循环对应n＝100。表1中电池内阻增大比率＝(DCRn-DCR1)/DCR1*100％，对比例以及其他实施例的测试过程同上。表1中的数据是在上述测试条件下循环100次之后测得的数据。
测试结果
上述实施例1～25和对比例1～4中得到的粘结剂、浆料、极片和电池的性能测试结果如表1所示。
Figure PCTCN2022110373-appb-000006
Figure PCTCN2022110373-appb-000007
Figure PCTCN2022110373-appb-000008
Figure PCTCN2022110373-appb-000009
Figure PCTCN2022110373-appb-000010
根据上述结果可知，实施例1～25中的粘结剂均包含聚合物，聚合物均包含含有氰基的结构单元(衍生自丙烯腈或丁烯腈)、含有酯基的结构单元(衍生自丙烯酸乙酯或丙烯酸异辛酯)和含有羧基的结构单元(衍生自丙烯酸或甲基丙烯酸)。从实施例1～17和对比例1的对比可见，该粘结剂可以显著减缓浆料的凝胶现象，提高浆料稳定性的同时降低极片的膜片电阻。
从实施例1～3与对比例3的对比可见，聚合物中包含衍生自丙烯酸的结构单元可以进一步减缓浆料凝胶现象、降低电池内阻的同时，提高膜片粘结力，进而提高电池的循环容量保持率、减小电池的循环内阻增长率，优化电池循环过程中的综合性能。
从实施例1～3与对比例4的对比可见，聚合物中包含衍生自丙烯酸乙酯的结构单元不但可以提高极片的柔韧性，减小极片发生脆性断裂的概率，提高电池的安全性能，而且使得电池在循环过程中同时具有优异的循环容量保持率和较低的内阻增长率。
从实施例1～6和实施例7～10的对比可见，聚合物中衍生自丙烯腈的结构单元的摩尔含量为70％～90％，衍生自丙烯酸乙酯的结构单元的摩尔含量为5％～25％，衍生自丙烯酸的结构单元的摩尔含量为5％～25％，基于聚合物中所有结构单元的总摩尔数计时，不但浆料的稳定性得到改善，而且极片兼具优异的粘结力和较低的膜片电阻，进而使得电池在循环过程中同时具有优异的循环容量保持率和较低的内阻增长率。
从实施例1、11、13和实施例12、14的对比可见，丙烯腈-丙烯酸乙酯-丙烯酸聚合物的重均分子量为5×10 5～12×10 5时，不但浆料的稳定性得到改善，而且极片兼具优异的粘结力和较低的膜片电阻，进而使得电池在循环过程中同时具有优异的循环容量保持率和较低的内阻增长率。
从实施例1、18～23可见，粘结剂的质量分数为0.1％～3％，基于正极活性物质的质量计时，浆料具有较好的稳定性。当粘结剂的质量分数为1％～3％时，浆料具有更加优异的稳定性的同时，极片兼具 改善的电阻性能和粘结性能，使得电池的综合循环性能有所提高。
从实施例1与实施例24～25的对比可见，导电剂碳黑的表面经硅醇基团或羟基基团改性后，极片的膜片电阻下降。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (19)

  1. 一种粘结剂，其特征在于，所述粘结剂包含聚合物，所述聚合物含有衍生自式I所示的单体的结构单元、衍生自式II所示的单体的结构单元和衍生自式III所示的单体的结构单元，
    Figure PCTCN2022110373-appb-100001
    其中，R 1、R 2、R 5各自独立地选自氢或取代或未取代的C 1-5烷基，R 3选自氢或C 1-3烷基，R 4选自取代或未取代的C 1-9烷基。
  2. 根据权利要求1所述的粘结剂，其特征在于，在所述聚合物中所述衍生自式I所示的单体的结构单元的摩尔含量为70％～90％，所述衍生自式II所示的单体的结构单元的摩尔含量为5％～25％，所述衍生自式III所示的单体的结构单元的摩尔含量为5％～25％，基于所述聚合物中所有结构单元的总摩尔数计。
  3. 根据权利要求1或2所述的粘结剂，其特征在于，所述聚合物的重均分子量为5×10 5～12×10 5。
  4. 根据权利要求1至3中任一项所述的粘结剂，其特征在于，所述式I所示的单体选自丙烯腈和丁烯腈中的一种或多种。
  5. 根据权利要求1至4中任一项所述的粘结剂，其特征在于，所述式II所示的单体选自丙烯酸甲酯、丙烯酸乙酯、丙烯酸丁酯、丙烯酸异戊酯、丙烯酸异辛酯、甲基丙烯酸甲酯、甲基丙烯酸乙酯、 丙烯酸羟乙酯、丙烯酸羟丙酯中的一种或多种。
  6. 根据权利要求1至5中任一项所述的粘结剂，其特征在于，所述式III所示的单体选自丙烯酸、甲基丙烯酸中的一种或两种。
  7. 一种粘结剂的制备方法，其特征在于，包括以下步骤：
    提供式I所示的单体、式II所示的单体和式III所示的单体，
    Figure PCTCN2022110373-appb-100002
    其中，R 1、R 2、R 5各自独立地选自氢或取代或未取代的C 1-5烷基，R 3选自氢或C 1-3烷基，R 4选自取代或未取代的C 1-9烷基；
    在可聚合条件下将式I所示的单体、式II所示的单体和式III所示的单体聚合制备聚合物。
  8. 根据权利要求7所述的制备方法，其特征在于，还包括以下步骤：
    将式I所示的单体、式II所示的单体、式III所示的单体和引发剂在溶液环境，非反应性气体氛围中在60℃～70℃聚合4-7小时；
    加入链转移剂，在70℃～80℃聚合3-5小时，得到所述聚合物。
  9. 根据权利要求7或8所述的制备方法，其特征在于，所述引发剂为有机过氧化物，可选自过氧化二苯甲酰，过氧化新戊酸叔戊酯，2-乙基过氧化碳酸酯中的一种或多种。
  10. 根据权利要求7至9中任一项所述的制备方法，其特征在于， 所述链转移剂选自氯乙烯，乙酸乙烯酯中的一种或两种。
  11. 根据权利要求7至10中任一项所述的制备方法，其特征在于，
    所述式I所示的单体的摩尔含量为70％～90％，所述式II所示的单体的摩尔含量为5％～25％，所述式III所示的单体的摩尔含量为5％～25％，基于所述单体的总摩尔数计。
  12. 一种正极极片，包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，所述正极膜层包括正极活性物质、导电剂和权利要求1～6中任一项所述的粘结剂或如权利要求7～11中任一项所述的制备方法制备的粘结剂。
  13. 根据权利要求12所述的正极极片，其特征在于，所述正极活性物质为含锂的过渡金属氧化物，可选为锂镍钴锰氧化物、或其掺杂改性材料、或其导电碳包覆改性材料、导电金属包覆改性材料或导电聚合物包覆改性材料中的至少一种。
  14. 根据权利要求12或13所述的正极极片，其特征在于，所述粘结剂的质量分数为0.01％～3％，可选为0.5％～3％，基于正极活性物质的质量计。
  15. 根据权利要求12至14中任一项所述的正极极片，其特征在于，所述导电剂的表面包括硅醇基团和/或羟基基团，所述导电剂选自导电炭黑、导电石墨、碳纳米管、石墨烯和碳纤维中的一种或多种。
  16. 一种二次电池，其特征在于，包括电极组件和电解液，所述电极组件包括如权利要求12～15中任一项所述的正极极片、隔离 膜和负极极片。
  17. 一种电池模块，其特征在于，包括权利要求16所述的二次电池。
  18. 一种电池包，其特征在于，包括权利要求17所述的电池模块。
  19. 一种用电装置，其特征在于，包括选自权利要求16所述的二次电池、权利要求17所述的电池模块或权利要求18所述的电池包中的至少一种。
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