CN117410651A - Composite diaphragm, preparation method thereof, secondary battery and electric equipment - Google Patents

Composite diaphragm, preparation method thereof, secondary battery and electric equipment Download PDF

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Publication number
CN117410651A
CN117410651A CN202210798624.7A CN202210798624A CN117410651A CN 117410651 A CN117410651 A CN 117410651A CN 202210798624 A CN202210798624 A CN 202210798624A CN 117410651 A CN117410651 A CN 117410651A
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CN
China
Prior art keywords
heat
composite
inorganic particles
impedance
diaphragm
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Pending
Application number
CN202210798624.7A
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Chinese (zh)
Inventor
孙泽蒙
阳东方
谢封超
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Huawei Technologies Co Ltd
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Huawei Technologies Co Ltd
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Priority to CN202210798624.7A priority Critical patent/CN117410651A/en
Priority to PCT/CN2023/104146 priority patent/WO2024007964A1/en
Publication of CN117410651A publication Critical patent/CN117410651A/en
Pending legal-status Critical Current

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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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/451—Separators, membranes or diaphragms characterised by the material having a layered structure comprising layers of only organic material and layers containing inorganic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The application provides a composite diaphragm, a preparation method thereof, a secondary battery and electric equipment. The composite diaphragm comprises a base film and a heat-resistant coating bonded on at least one side surface of the base film, wherein the heat-resistant coating comprises heat-resistant resin and inorganic particles, the mass ratio of the heat-resistant resin to the inorganic particles is less than or equal to 6:4, the inorganic particles are of porous structures, and the specific surface area of the inorganic particles is 50-150m 2 And/g, the impedance of the composite diaphragm is less than or equal to 1 omega/cm 2 . Thus, the problem of the rising of the impedance of the diaphragm caused by the heat-resistant coating is solved to reduce the impedance of the diaphragm while ensuring the high thermal stability of the diaphragm.

Description

Composite diaphragm, preparation method thereof, secondary battery and electric equipment
Technical Field
The application relates to the field of batteries, in particular to a composite diaphragm, a preparation method thereof, a secondary battery and electric equipment.
Background
With the development of electric vehicles, smart terminals, and electronic mobile devices, secondary batteries, such as lithium ion batteries, have also been rapidly developed. The separator, which is one of the main materials of lithium ion batteries, plays an important role in battery safety. The most commonly used separator at present is a polyethylene separator, which typically has a heat shrinkage of MD > 10%; TD > 10% (150 ℃/1 h); and the rupture temperature of the membrane is generally less than 160 ℃. Therefore, when the temperature of the battery increases, the separator is heated to melt and shrink seriously, which results in direct contact between the positive electrode and the negative electrode of the battery, and thus, short circuit inside the battery is easily induced, and thermal runaway of the battery occurs. To improve the thermal stability of the separator, the surface of the separator is generally coated with a coating, such as an organic heat-resistant polymer coating or a ceramic coating, to improve the thermal stability of the separator. For example, after an organic heat-resistant polymer coating is added to a polyethylene separator, a pore-forming agent or particles are generally used to form pores in the separator so as to achieve the effect of ion permeation, wherein the pore-forming agent generally refers to an inorganic substance or an organic substance that can decompose to generate gas at a specific temperature, so that the organic heat-resistant polymer coating forms porous voids. This approach can improve the thermal stability of the separator, but the resistance of the separator may increase, resulting in a problem of reduced battery capacity.
Disclosure of Invention
The application provides a composite diaphragm, a preparation method thereof, a secondary battery and electric equipment, which can solve the problem of diaphragm impedance rising caused by a heat-resistant coating while ensuring high thermal stability of the diaphragm so as to reduce the impedance of the diaphragm.
In a first aspect, the present application provides a composite separator comprising a base film and a heat-resistant coating layer bonded to at least one side surface of the base film, the heat-resistant coating layer comprising a heat-resistant resin and inorganic particles, the mass ratio of the heat-resistant resin to the inorganic particles being 6:4 or less, the inorganic particles being of a porous structure, the specific surface area of the inorganic particles being 50 to 150m 2 And/g, the impedance of the composite diaphragm is less than or equal to 1 omega/cm 2 。
The heat-resistant resin in the heat-resistant coating of the composite membrane can raise the heat-resistant temperature of the composite membrane, and the heat-resistant resin in the heat-resistant coating can be used for preparing the composite membraneWhen the battery is abused by heat and machinery, the diaphragm can resist high temperature and not melt, can effectively isolate the positive electrode and the negative electrode of the battery, avoid short circuit caused by direct contact of the positive electrode and the negative electrode, and improve the safety of the battery. In addition, the inorganic particles in the heat-resistant coating can increase the thermal stability of the composite diaphragm, can effectively reduce shrinkage (shrinkage rate is less than or equal to 5 percent and 150 ℃ for 1 h) in heat abuse, reduce the probability of short circuit of the battery, and reduce the thermal runaway probability of the battery in a thermal runaway scene. The inorganic particles in the application are porous structures, and the specific surface area is 50-150 m 2 In the range of/g, the inorganic particles with specific surface area can have more through hole structures, improve the penetrability of active ions, simultaneously have better electrolyte adsorptivity and liquid retention property, and substantially reduce the impedance of the composite membrane to 1 omega/cm on the premise of ensuring heat resistance 2 And the impedance increase rate is less than or equal to 50%.
In one possible implementation, the heat resistant resin comprises an aramid. The heat-resistant resin can raise the rupture temperature of the composite diaphragm to 300 ℃ or above by selecting aramid fiber so as to further improve the heat resistance of the composite diaphragm. In one possible implementation, the rupture temperature of the composite membrane may be greater than or equal to 300 ℃.
In one possible implementation, the specific surface area of the inorganic particles is 60 to 150m 2 Preferably 60 to 140m 2 Preferably 60 to 110m 2 And/g. By optimizing the specific surface area of the inorganic particles, the impedance of the composite membrane can be further reduced while the heat resistance of the composite membrane is ensured.
In one possible implementation, the composite membrane has an impedance increase rate of 50% or less, preferably an impedance increase rate of 20% or less, and more preferably an impedance increase rate of 10% or less; wherein, the impedance increase rate of the composite membrane= (composite membrane impedance-base membrane impedance)/base membrane impedance×100%. Therefore, the composite diaphragm with smaller impedance can be obtained, so that the internal resistance of the battery core of the battery is reduced, and the quick charge performance of the battery is improved.
In an alternative implementation, the mass ratio of heat resistant resin to inorganic particles is less than or equal to 3:7. Illustratively, the mass ratio of the heat-resistant resin to the inorganic particles may be controlled to 1:9 or more. By optimizing the mass ratio of the heat-resistant resin and the inorganic particles, lower impedance can be obtained under the condition of ensuring that the composite diaphragm has higher rupture temperature.
In a second aspect, the present application provides a method of preparing a composite separator, the method comprising: the base film coated with the heat-resistant coating slurry is dried and thermally fixed to obtain a composite diaphragm; wherein the drying temperature is 50-120 ℃ and the drying time is less than or equal to 10min; the heat fixing temperature is 60-150 ℃, and the heat fixing time is less than or equal to 5min.
According to the preparation method, the solvent in the heat-resistant coating slurry can be fully evaporated by controlling the temperature and the time in the drying process, the intermolecular spacing in the heat-resistant resin cannot be influenced, and the proper molecular spacing between the molecules of the heat-resistant resin is kept, so that the passage of active ions is facilitated, and the composite diaphragm can obtain lower impedance. In the heat fixing stage, by controlling the heat fixing temperature and the heat fixing time, molecules in the heat-resistant coating are regularly arranged to fix the composite membrane, and meanwhile, the distance between the molecules in the heat-resistant coating is not excessively reduced, so that the composite membrane still has proper molecular distance, and further, the heat resistance of the composite membrane is improved, and meanwhile, the impedance of the composite membrane is prevented from being increased.
In an alternative implementation, the drying temperature is 50-100 ℃ and the drying time is less than or equal to 5min. In an alternative implementation, the heat fixing temperature is 60-110 ℃, and the heat fixing time is less than or equal to 2min. By optimizing the drying temperature and drying time and the heat fixing temperature and heat fixing time, the heat resistance of the composite diaphragm can be further improved and the impedance of the composite diaphragm can be further reduced.
The data in each possible implementation manner of the present application, such as the mass ratio of the heat-resistant resin and the inorganic particles, the specific surface area of the inorganic particles, the impedance of the composite membrane, the rupture temperature, the drying time, the heat fixing temperature, the heat fixing time and the like, are all understood to be within the scope defined by the present application in terms of engineering measurement error.
In a third aspect, the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and a composite separator as herein provided between the positive electrode sheet and the negative electrode sheet.
The secondary battery of the present application includes, but is not limited to, a lithium secondary battery, a potassium secondary battery, a sodium secondary battery, a zinc secondary battery, a magnesium secondary battery, or an aluminum secondary battery. On the basis that this application composite diaphragm possesses heat resistance well, impedance is low, the secondary cell of this application can have the security height and can realize quick charge's advantage.
In a fourth aspect, the present application provides an electrical consumer comprising a secondary battery of the present application.
The electric equipment comprises, but is not limited to, mobile terminal devices, such as computers, mobile phones, flat panels, wearable products, new energy automobiles and the like. The technical effects that the electric equipment can achieve can be described with reference to the corresponding effects in the third aspect, and the description is not repeated here.
Drawings
Fig. 1 is a schematic structural diagram of a composite membrane according to an embodiment of the present application.
Reference numerals: 11-composite separator; 12-base film; 13-heat resistant coating.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present application more apparent, the present application will be described in further detail with reference to the accompanying drawings.
The terminology used in the following embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the specification and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include, for example, "one or more" such forms of expression, unless the context clearly indicates to the contrary.
Reference in the specification to "one embodiment" or "some embodiments" or the like means that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the application. Thus, appearances of the phrases "in one embodiment," "in some embodiments," "in other embodiments," and the like in the specification are not necessarily all referring to the same embodiment, but mean "one or more but not all embodiments" unless expressly specified otherwise. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless expressly specified otherwise.
A separator, which is one of the main materials of a secondary battery, such as a lithium ion battery, plays an important role in battery safety. Under the conditions of mechanical abuse or thermal abuse, the diaphragm is easy to thermally shrink or break, and the battery is easy to short-circuit, so that the thermal runaway of the battery is caused. The heat-resistant high polymer is coated on the surface of the porous base film to form a heat-resistant coating, so that the heat shrinkage of the diaphragm is reduced, the rupture temperature of the diaphragm is improved, the heat resistance of the battery is improved, and the risks of short circuit and safety accidents caused by the heat shrinkage and the thermal rupture of the diaphragm under mechanical abuse or thermal abuse (such as high temperature) scenes of the battery are reduced. However, the heat-resistant high polymer is easy to shrink at high temperature, and the shrinkage rate of the separator can be reduced and the puncture strength of the separator can be improved by adding inorganic particles into the heat-resistant coating, so that the safety of the separator is ensured when the battery is used. However, the separator containing the heat-resistant coating with the structure has the problem of increased impedance relative to the base film while improving the safety of the separator, so that the separator cannot be applied to high-performance battery scenes such as quick charge.
In order to solve the technical problems, an embodiment of the application provides a composite diaphragm. FIG. 1 is a schematic structural view of a composite separator according to an embodiment of the present application, as shown in FIG. 1, in an embodiment, a composite separator 11 includes a base film 12 and a heat-resistant coating layer 13 bonded to at least one side surface of the base film 12, the heat-resistant coating layer 13 includes a heat-resistant resin and inorganic particles, the mass ratio of the heat-resistant resin to the inorganic particles is equal to or less than 6:4, the inorganic particles are porous, and the specific surface area of the inorganic particles is 50-150 m 2 And/g, the impedance of the composite diaphragm is less than or equal to 1 omega/cm 2 . It is understood that the heat-resistant coating 13 may be provided on one side surface of the base film 12, or may be provided on both side surfaces of the base film 12.
Referring to FIG. 1, the material of the base film 12 includes, but is not limited to, one or a combination of at least two of polyethylene, polypropylene, poly-1-butene, poly-1-pentene, poly-1-hexene, poly-4-methyl-1-pentene, poly-1-octene, polyvinyl acetate, polymethyl methacrylate, polystyrene, polyvinylidene fluoride, polytetrafluoroethylene, polymethyl methacrylate.
Referring to fig. 1, in the heat-resistant coating 13 of the embodiment of the present application, the heat-resistant resin includes, but is not limited to, one or a combination of at least two of polyamide, polysulfone, polyimide, polyamideimide, polyethersulfone, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polystyrene, polyacrylate or a modified product thereof, polyester, polyarylate, polyacrylonitrile, aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, polyetherimide, polybenzimidazole or a copolymer thereof. In a preferred embodiment of the present application, the heat-resistant resin is preferably polyamide, and further preferably aromatic polyamide including aramid. Wherein, the aromatic polyamide is selected as the heat-resistant resin, so that the rupture temperature of the composite diaphragm can be effectively improved.
With continued reference to fig. 1, in the heat-resistant coating 13 of the embodiment of the present application, the inorganic particles are inorganic particles of a porous structure. The porous structure of the inorganic particles can improve the liquid retention capacity of the composite diaphragm to the electrolyte, can store metal ions in the electrolyte in the porous structure of the inorganic particles, and can be used for reducing the overall impedance of the composite diaphragm. Among them, the inorganic particles of porous structure mentioned in the examples of the present application are inorganic particles having a porous structure or having a porous structure shape. The porous structure includes, but is not limited to, that the inorganic particles can be directly observed by SEM, TEM, or the like to obtain a porous structure. The porous structure properties include, but are not limited to, inorganic particles obtained in the following manner: through testing, the specific surface area is not less than 50m 2 Inorganic particles per gram; the aperture ratio of the inorganic particles is tested by a liquid soaking weighing method, a density method and the likeMore than 1%, and a relative density (relative to the density of the non-porous material) of less than 99%; the average gas pore diameter of the inorganic particles is not less than 0.005 μm as measured by mercury intrusion method or the like.
Wherein the inorganic particles are selected from the specific surface area of 50-150 m 2 The porous particles of/g are inorganic particles with specific surface area, so that the problem of impedance rise of the composite membrane caused by the heat-resistant coating can be solved while the thermal stability of the composite membrane is ensured, and therefore, the impedance of the composite membrane can be well reduced while the heat resistance of the composite membrane is effectively ensured, the safety of a battery is further realized, and the performance of quick charging is also met. As an exemplary illustration, the specific surface area of the inorganic particles may be, for example, 50m 2 /g、60m 2 /g、70m 2 /g、80m 2 /g、90m 2 /g、100m 2 /g、110m 2 /g、120m 2 /g、130m 2 /g、140m 2 /g, or 150m 2 /g。
In the heat-resistant coating, if the pores of the inorganic particles with porous structures are through holes, the inorganic particles directly serve as a transmission channel of metal ions in the charge and discharge processes of the battery, so that the impedance of the composite separator can be further reduced. In the composite separator of the present application, the inorganic particles preferably have a specific surface area of 60m or more, because the larger the specific surface area of the inorganic ions, the higher the possibility of forming the through-holes and the better the performance of reducing the impedance of the composite separator 2 Porous particles per gram. The specific surface area is 60-150 m 2 The porous particles of/g can increase the heat resistance of the composite membrane and the transmission channels of metal ions in the charge and discharge process, and the more the transmission channels of active ions are, the smaller the impedance of the composite membrane is. In an alternative embodiment of the present application, the impedance of the composite membrane is less than or equal to 0.9 Ω/cm 2 。
In the examples of the present application, the average particle diameter of the inorganic particles is not particularly limited, and particles having an average particle diameter of 2 μm or less may be preferable. It is understood that the shape and size of the holes of the inorganic particles, the through holes, and the like are not limited in the embodiments of the present application.
As an exemplary illustration, the inorganic particles of embodiments of the present application include, but are not limited to, one or a combination of at least two of metal oxides, metal nitrides, metal hydroxides, metal carbonates, metal sulfates, boehmite, apatite, boron nitride, silicon carbide, silicon nitride, cubic boron nitride, hexagonal boron nitride, graphite, graphene, and the like. The metal oxide may be, for example, at least one of aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, or magnesium oxide. The metal nitride may include, for example, at least one of aluminum nitride and titanium nitride. The metal hydroxide may include, for example, at least one of aluminum hydroxide and magnesium hydroxide. The metal carbonate may include, for example, at least one of aluminum carbonate, magnesium carbonate, and calcium carbonate. The metal carbonate may include, for example, at least one of aluminum phosphate, magnesium phosphate, and calcium phosphate. The metal sulfate may include, for example, at least one of aluminum sulfate, magnesium sulfate, barium sulfate, and the like.
In the composite separator of the embodiment of the application, the mass ratio of the heat-resistant resin in the heat-resistant coating to the inorganic particles satisfies the following condition that the mass ratio is less than or equal to 6:4, preferably the ratio of the two is less than or equal to 3:7. When the mass ratio of the heat-resistant resin and the inorganic particles satisfies the above range, the composite separator can be made to have a lower impedance while achieving a high rupture temperature. As an exemplary illustration, the mass ratio of the heat-resistant resin to the inorganic particles may be, for example, 6:4, 5:5, 4:6, 3:7, 2:8, or 1:9, etc.
The composition of the composite separator is explained above, and the method of preparing the composite separator will be further explained below.
The preparation method of the composite membrane can comprise the following steps: and drying and thermosetting the base film coated with the heat-resistant coating slurry in sequence to obtain the composite diaphragm. Wherein the drying temperature is 50-120 ℃, preferably 50-100 ℃, and the drying time is less than or equal to 10min, preferably less than or equal to 5min. The heat fixing temperature is 60-150 ℃, preferably 60-110 ℃, and the heat fixing time is less than or equal to 5min, preferably less than or equal to 2min.
The drying process can be performed in the drying boxes, the number of the drying boxes can be 1 or 2 or more, and when a plurality of drying boxes are arranged, the same or different temperatures can be set in each drying box, wherein the temperature in each drying box is consistent with the temperature range defined by the embodiment of the application. Likewise, the heat fixing process may be performed in heat fixing boxes, and the number of heat fixing boxes may be 1, 2, or more, and when a plurality of heat fixing boxes are provided, the same or different temperatures may be set in each heat fixing box, where the temperature in each heat fixing box should conform to the temperature range defined in the embodiment of the present application.
In the drying and heat-setting process, the heat-resistant resin in the heat-resistant coating layer has a heat-fixing effect, and the molecules in the heat-resistant coating layer have a regular arrangement to improve the mechanical strength and heat resistance of the heat-resistant coating layer, but in this process, the arrangement of the molecules is more regular, which easily results in a decrease in the inter-molecular spacing, thereby increasing the membrane resistance. The method can keep proper spacing between molecules of the heat-resistant coating on the basis of realizing regular arrangement of the molecules by controlling the drying temperature and the drying time in the preparation process of the composite membrane and controlling the heat fixing temperature and the heat fixing time, so that the impedance of the obtained composite membrane is less than or equal to 1 omega/cm while the mechanical strength and the heat resistance of the composite membrane are improved 2 。
As an exemplary illustration, the method of preparing the heat-resistant coating paste includes the steps of: 100 parts by weight of heat-resistant resin and 50 to 5000 parts by weight of inorganic particles are placed in a reactor, and then organic solvent is added for full dispersion, so that heat-resistant coating slurry is obtained. Wherein, the solid content in the obtained heat-resistant coating slurry is preferably 5% -50%; the solid content refers to the mass percentage of solid parts such as heat-resistant resin, inorganic particles and the like in the heat-resistant coating slurry.
Wherein, in the process of preparing the heat-resistant coating slurry, the organic solvent comprises one or more of N-methyl pyrrolidone, N-dimethylformamide, N-dimethylacetamide, acetone and ethanol.
In the preparation of the heat-resistant coating slurry, a cosolvent, a dispersant, an emulsifier, a polymer binder, and the like may be added as needed. Wherein, the cosolvent, the dispersing agent, the polymer binder and the like can be selected from commercial products, for example, the cosolvent can be one or a combination of a plurality of sodium benzoate, lithium chloride, calcium chloride, sodium hydroxide and acetamide; the dispersing agent can be one or more of polyethylene oxide, ethylene-acrylic acid copolymer and ethylene-vinyl acetate copolymer; the emulsifier can be one or more of cetyltrimethylammonium chloride, octadecyl trimethyl ammonium chloride, sodium polyacrylate, potassium polyacrylate, polyacrylamide, dodecyl trimethyl ammonium chloride, ethylene oxide-butylene oxide copolymer, and ethylene oxide-propylene oxide-butylene oxide copolymer; the polymeric binder may be one or a combination of more of polyvinylpyrrolidone, vinylpyrrolidone, ethylene acetate copolymer.
In an alternative embodiment of the present application, a specific preparation process of the composite separator may include the following steps:
step S11, preparing uniform heat-resistant coating slurry, and mixing by stirring, ultrasonic treatment and other modes to obtain heat-resistant coating slurry with uniform components;
step S12, coating heat-resistant coating slurry on one side or two sides of the base film;
step S13, washing the base film coated with the heat-resistant coating slurry with water, and removing the oil solvent; and then drying, thermosetting and rolling in sequence to obtain the rechecking diaphragm with the heat-resistant coating in the plane direction.
The performance of the composite separator of the present application will be described in further detail below in connection with specific examples and comparative examples.
Example 1
The embodiment is a composite membrane, the preparation process of which comprises the following steps:
step S11, selecting a 5.0 mu m polyethylene film as a base material, wherein the air permeability is 140S.
Step S12, preparation of heat-resistant coating slurry
100 parts by weight of meta-aramid having an average molecular weight of 100000, 400 parts by weight of a specific surface area of 74m 2 Per g of porous alumina particles, 4500 parts by weight of dimethylacetamide solvent (DMAC) was added thereto by stirring at a high speedA uniform heat-resistant coating slurry is obtained.
Step S13, preparation of composite diaphragm
Coating the heat-resistant coating slurry on one side of a polyethylene film through a metal rod, and then, passing water to remove an oil solvent; and then drying in a drying box, and thermally fixing in a thermal fixing box to obtain a composite diaphragm finished product. Wherein the temperature of the drying oven is 100 ℃, and the drying time is 2 minutes; the heat-fixing oven was set at 110℃for a heat-fixing time of 1 minute. The drying box and the hot setting box are arranged continuously and separately.
In the resulting composite separator, the thickness of the heat-resistant coating layer was 2 μm. The index of the composite separator is shown in table 1.
Example 2
This example is a composite separator, which differs from example 1 in that both sides of the base film are coated with a heat-resistant coating. Otherwise, the same as in example 1 was used. The index of the composite separator is shown in table 1.
Example 3
This example is a composite separator, and differs from example 1 in that the weight ratio of the heat-resistant resin to the inorganic particles in the heat-resistant coating layer of this example is different, and the other is the same as example 1. The index of the composite separator is shown in table 1.
Examples 4 to 6
Examples 4 to 6 are composite separators, respectively, and are different from example 1 in the specific surface area of the inorganic particles used in examples 4 to 6, and are otherwise identical to example 1. The indices of the composite separators of examples 4 to 6 are shown in Table 1.
Example 7
Example 7 is a composite separator, which is different from example 1 in that the drying process used in example 7 is different from the heat setting process, and otherwise is the same as example 1. In this example, the drying temperature was 60 ℃, the drying time was 2min, the heat fixing temperature was 80 ℃, and the heat fixing time was 1min.
Comparative example 1
The comparative example is a composite separator, which is different from example 1 in that the inorganic particles in the heat-resistant coating layer are inorganic particles of a non-porous structure, and specific surface area values are shown in table 1. Otherwise, the same as in example 1 was used. The indices of the composite separator are listed in table 2.
Comparative examples 2 to 3
Comparative examples 2 to 3 are composite separators, respectively, differing from example 1 in the specific surface area of the inorganic particles used in comparative examples 2 to 3, and otherwise identical to example 1. The indexes of the composite separators of comparative examples 2 to 3 are shown in table 2.
Comparative example 4
The comparative example was a composite separator, differing from example 2 in the drying conditions and the heat-set conditions, the oven temperature in the comparative example was 125 ℃ and the drying time was 15 minutes; the heat-fixing temperature is 135 ℃, and the heat-fixing time is 10 minutes. The remainder was the same as in example 2. The index of the composite separator of comparative example 4 is shown in table 2.
Comparative example 5
The comparative example is a composite separator, which is different from example 1 in that the inorganic particles in the heat-resistant coating layer are inorganic particles of a non-porous structure, and ammonium bicarbonate (pore-forming agent) having a mass ratio of 1% is added to the heat-resistant coating slurry during the preparation of the composite separator, and the drying process and the heat-fixing process are the same as those of example 1 of the present application.
Among them, the specific surface area of the inorganic particles in each of the above examples and comparative examples was measured as follows: the nitrogen adsorption method is adopted to test the NOVA2000e of the specific surface area tester of the United states Kang Da. The gas used is helium-nitrogen mixture, nitrogen is the adsorbed gas, helium is the carrier gas. When the sample injector is subjected to liquid nitrogen bath, the temperature in the injector is reduced to a certain degree, the energy of nitrogen molecules is reduced, and the nitrogen molecules are adsorbed by the solid surface under the action of Van der Waals force to achieve dynamic balance, so that a state similar to a monomolecular layer is formed. Since the specific surface area value of a substance is proportional to its adsorption amount. The specific surface area of the sample to be measured can be calculated by comparing the adsorption quantity of a known specific surface substance (standard sample) with the adsorption quantity of an unknown specific surface substance.
The composite separator in each of examples and comparative examples was tested for various performance parameters such as film thickness, shrinkage, rupture temperature, air permeability, base film resistance, separator resistance, and the like, and the test results are shown in tables 1 and 2. The specific test method of each performance parameter is as follows:
1) Film thickness measurement
Mode one: samples were taken from the membrane, and the number of test points was determined depending on the membrane (typically not less than 10 points); testing by a thickness measuring instrument at 23+/-2 ℃; the measured thickness values for each test point are measured and an arithmetic average is taken.
Mode two:
a. sampling: for products with a width < 200 mm: determining a point at intervals of 40mm plus or minus 5mm along the longitudinal (machine direction, MD) direction, wherein the number of test points is not less than 10, the number of test points can be determined according to the width of the diaphragm, and the distance between the measurement start point and the edge is not less than 20mm; for products with a width of more than or equal to 200 mm: and determining a point every 80mm plus or minus 5mm along the transverse direction (transverse direction, TD), wherein the number of test points is not less than 10, the number of test points can be determined according to the width of the diaphragm, and the distance between the measurement start point and the edge is not less than 20mm.
b. And (3) testing: each test point is tested by a thickness measuring instrument at the temperature of 23+/-2 ℃, the diameter of the measuring surface is between 2.5 and 10mm, and the load applied to the test sample by the measuring surface is between 0.5 and 1.0N.
c. And (3) data processing: the measured thickness values for each test point are measured and an arithmetic average is taken.
2) Heat shrinkage at 150 DEG C
a. Sampling: the full width randomly cuts out 6 samples, and the specific sampling of each sample can include: cutting 100mm along the MD direction of the diaphragm; when the TD direction of the separator is greater than 100mm, the length of the test sample in the TD direction may be 100mm; when the TD direction of the microporous membrane is less than 100mm, the length of the test sample in the TD direction may be practically equal.
b. And (3) testing: marking longitudinal and transverse marks of the samples, and measuring and recording the longitudinal and transverse dimensions of each sample; the sample is horizontally placed in a paper jacket layer, and the sample has no folding, wrinkling, adhesion and other conditions; placing the paper sleeve (the number of layers can be 10 for example) with the sample in the middle of the constant temperature oven flatly (the door opening time is not more than 3s for example); heating the sample to 150 ℃ by an electric heating constant temperature box for 1h; after taking out the sample, the sample was cooled to room temperature, and the longitudinal length and the transverse length were measured.
c. And (3) data processing: the heat shrinkage of each sample was calculated:
T＝(L 0 -L)/L 0 x 100%, where T may be the sample heat shrinkage (%), L 0 The length (mm) of the sample before heating may be used, and the length (mm) of the sample after heating may be used. The arithmetic average of the heat shrinkage in the MD and TD directions of the samples was calculated.
3) Rupture temperature (. Degree. C.)
And testing rupture temperature by adopting a baking method: placing the composite diaphragm in a clamp with the length of 8 multiplied by 8cm, placing the clamp in an oven, heating at a certain speed, monitoring whether the diaphragm in the clamp breaks the diaphragm or not, and recording the rupture temperature of the diaphragm when the diaphragm breaks the diaphragm along with the temperature change.
4) Air permeability (S)
The test was carried out in accordance with the method prescribed in JIS P8117-2009. The cylinder drives the pressure reducing valve to 0.25MPa and the test pressure to 0.05MPa. The measured point values were recorded and the average was taken 5 times.
5) Impedance (omega/cm) 2 )
Cutting the composite membrane to a size capable of covering the electrode for test, and soaking in 1M LiBF 4 After 24 hours of electrolyte, the impedance of the composite diaphragm is tested by an alternating current impedance method by using a stainless steel electrode, wherein the test condition is that the alternating current voltage is 10mV, the frequency is in the range of 1MHz-10mHz, and the impedance is converted according to the area of the electrode. The same diaphragm was measured 3 times and its average value was the diaphragm impedance.
TABLE 1
TABLE 2
As can be seen from the test data of examples 1 to 6 in Table 1, the rupture temperatures of the composite diaphragms of the examples of the present application can reach 300 ℃ and above, and the impedances of the composite diaphragms are also less than 1 Ω/cm 2 And the impedance increase rate is also less than 50%, wherein the impedance increase rate is substantially within 30%. This means that in the composite separator of the present application, the heat-resistant coating layer can have a low resistance, and the influence of the resistance of the whole composite separator is small, so that a low-resistance separator can be obtained. As is clear from the comparative data of examples 1 and 4 to 6, the specific surface area of the inorganic particles is 60 to 110m 2 In the range of/g, a composite separator having a lower shrinkage and a lower impedance can be obtained.
As can be seen from the comparison of tables 1 and 2, the composite separator of the examples of the present application has much smaller impedance than the comparative examples 1, 3, and 4. Comparative example 2 used a specific surface area of 300m 2 The porous particles per gram, although the obtained composite separator had a smaller resistance, the shrinkage was higher than that of the composite separator of each example of the present application, and the rupture temperature of comparative example 2 was lower than that of the composite separator of each example of the present application.
Among them, as can be seen from the related data of example 2 and comparative example 4, by changing the drying process and the heat-setting process in the preparation process of the composite separator, the resistance of the composite separator can be significantly reduced, thereby obtaining a composite separator with low shrinkage, high rupture temperature and low resistance. In addition, as is clear from the related test data of example 1 and example 7, when the drying process and the heat-setting process are optimized, the shrinkage of the resulting composite separator can be further reduced.
As can also be seen from the test data of example 1 and comparative example 5, in comparative example 5, when using the conventional process, for example, using non-porous inorganic particles in the heat-resistant coating, and increasing the pore size of the heat-resistant coating by adding a pore-forming agent to the heat-resistant coating slurry, the air permeability of the composite separator is reduced, wherein the lower the air permeability of the composite separator, the greater the spacing between the heat-resistant polymers of the composite separator is represented, the higher the penetrability of the active ions is, the method can achieve the purpose of reducing the impedance of the composite separator, but the heat resistance of the composite separator is significantly reduced, such as the rupture temperature is significantly reduced, and the heat shrinkage is significantly increased. The composite separator corresponding to this comparative example has failed to meet the requirements of the secondary battery for the thermal stability of the separator. In the composite separator of embodiment 1 of the present application, porous inorganic particles having a specific surface area are selected, so that a composite separator having low impedance can be obtained without changing the air permeability of the composite separator.
In summary, the composite membrane of the embodiment of the application not only can meet the requirement of thermal stability, but also can meet various effects of low impedance by adopting porous inorganic particles with specific surface areas.
The foregoing is merely specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily think about changes or substitutions within the technical scope of the present application, and the changes or substitutions are intended to be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims (10)

1. The composite diaphragm is characterized by comprising a base film and a heat-resistant coating bonded to at least one side surface of the base film, wherein the heat-resistant coating comprises heat-resistant resin and inorganic particles, the mass ratio of the heat-resistant resin to the inorganic particles is less than or equal to 6:4, the inorganic particles are of a porous structure, and the specific surface area of the inorganic particles is 50-150 m 2 And/g, wherein the impedance of the composite diaphragm is less than or equal to 1 omega/cm 2 。
2. The composite separator according to claim 1, wherein the specific surface area of the inorganic particles is 60 to 150m 2 /g。
3. The composite membrane according to claim 1 or 2, wherein the impedance increase rate of the composite membrane is equal to or less than 50%, wherein the impedance increase rate of the composite membrane= (composite membrane impedance-base membrane impedance)/base membrane impedance x 100%.
4. A composite membrane according to any one of claims 1-3, wherein the rupture temperature of the composite membrane is equal to or greater than 300 ℃.
5. The composite separator of any of claims 1-4 wherein the heat resistant resin comprises an aramid.
6. A method of making a composite separator according to any one of claims 1-5, comprising:
the base film coated with the heat-resistant coating slurry is dried and thermally fixed to obtain the composite diaphragm; wherein the drying temperature is 50-120 ℃ and the drying time is less than or equal to 10min; the heat fixing temperature is 60-150 ℃, and the heat fixing time is less than or equal to 5min.
7. The method according to claim 6, wherein the drying temperature is 50-100 ℃ and the drying time is less than or equal to 5min.
8. The method according to claim 6 or 7, wherein the hot setting temperature is 60 to 110 ℃, and the hot setting time is not more than 2 minutes.
9. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, and the composite separator according to any one of claims 1 to 5 disposed between the positive electrode sheet and the negative electrode sheet.
10. A powered device comprising the secondary battery according to claim 9.
CN202210798624.7A 2022-07-06 2022-07-06 Composite diaphragm, preparation method thereof, secondary battery and electric equipment Pending CN117410651A (en)

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