Lithium ion battery diaphragm, preparation method and lithium ion battery

Abstract

The invention relates to a lithium ion battery diaphragm, a preparation method and a lithium ion battery in the technical field of lithium battery production. The lithium ion battery diaphragm comprises a base membrane and a coating layer arranged on the base membrane, and the coating layer comprises polysilazane and polyurethane. The base membrane is coated with the coating containing the polysilazane and the polyurethane, hydrogen bonds are formed between the polysilazane and the polyurethane, synergy of the polyurethane and the polysilazane is achieved, and therefore the heat resistance, the mechanical performance and the safety performance of the diaphragm can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery production, and in particular to a lithium ion battery separator and a preparation method thereof, and a lithium ion battery. Background Art

[0002] As a key component of the "four major parts" of lithium-ion batteries, the diaphragm plays an indispensable role in the lithium-ion battery system. The core function of traditional lithium-ion battery diaphragm materials, such as polypropylene (PP) and polyethylene (PE), is to effectively prevent short circuits between the positive and negative electrodes. However, with the advancement of the research and development of high-energy-density lithium-ion batteries, the accompanying safety hazards have become increasingly prominent. In recent years, electric vehicle fires have attracted widespread social attention. In-depth exploration of the root cause is mainly due to the thermal runaway of lithium-ion batteries, and the thermal shrinkage characteristics of traditional diaphragms under high temperature environments have been confirmed to be one of the key factors inducing battery thermal runaway. Although the PP diaphragm has a melting point of up to 160°C, in actual application scenarios, traditional lithium-ion battery diaphragms have been difficult to meet the current stringent requirements for the safety and stability of lithium-ion batteries. Based on this, the development of new diaphragm materials with high thermal stability is of extremely critical practical significance for further enhancing the safety of lithium-ion batteries and promoting the sustainable development of lithium-ion battery technology. It has become one of the key research directions in the current lithium-ion battery field.

[0003] Using polysilazane as a diaphragm coating can effectively improve the heat resistance of the diaphragm. Moreover, compared with traditional ceramic coatings, it has better continuity and can better cover the surface of the base membrane. Therefore, it has obvious advantages in improving the thermal stability of the diaphragm.

[0004] However, the diaphragm coating prepared by polysilazane is brittle and prone to breakage, and the improvement effect is ineffective.

[0005] The market is in urgent need of a technical solution to solve the above problems. Summary of the invention

[0006] In order to solve the above problems, the present invention discloses a lithium ion battery separator and a preparation method thereof, and a lithium ion battery. The technical solution of the present invention is implemented as follows:

[0007] A first aspect of the present invention provides a lithium-ion battery separator, which includes a base film and a coating disposed on the base film, wherein the coating includes polysilazane and polyurethane, and hydrogen bonds are formed between the polysilazane and the polyurethane.

[0008] Preferably, the mass ratio of the polysilazane to the polyurethane is 1:(3-7).

[0009] Preferably, the coating has a thickness of 1 μm to 2 μm.

[0010] Preferably, the material of the base film is selected from at least one of polyethylene, polypropylene, polyester, cellulose, polyimide and aramid; and the thickness of the base film is 7 μm to 12 μm.

[0011] Preferably, the coating further comprises a plasticizer;

[0012] Based on the total mass of the polysilazane and the polyurethane being 100, the mass of the plasticizer is 1 to 2.

[0013] The second aspect of the present invention discloses a method for preparing a lithium ion battery separator, which is used to prepare the lithium ion battery separator disclosed in the first aspect of the present invention. The preparation method comprises the following steps:

[0014] S100, weighing polysilazane and polyurethane in a mass ratio of 1:(3-7), adding solvents respectively and mixing them to form a slurry;

[0015] S200, coating the prepared slurry on the base film to form a diaphragm.

[0016] Preferably, the method further comprises step S110: adding a plasticizer to the prepared slurry.

[0017] Preferably, the solid content of the slurry is 20% to 40%.

[0018] Preferably, step S200 includes:

[0019] Double-sided coating: coating is performed on the first side surface of the base film, and then drying is performed; after drying, coating is performed on the second side surface.

[0020] The third aspect of the present invention discloses a lithium-ion battery, which includes the lithium-ion battery separator disclosed in the first aspect of the present invention, and also includes a positive electrode and a negative electrode, and the lithium-ion battery separator is arranged between the positive electrode and the negative electrode.

[0021] Preferably, the positive electrode comprises a positive electrode active material, and the negative electrode comprises a negative electrode active material.

[0022] Preferably, the negative electrode active material includes at least one of graphite, a composite material of single crystal silicon and graphite, soft carbon, and hard carbon.

[0023] The advantages of the present invention are as follows:

[0024] The present invention applies a coating including polysilazane and polyurethane on the base film, hydrogen bonds are formed between the polysilazane and the polyurethane, and the synergy of the polyurethane and the polysilazane is achieved, which can effectively improve the heat resistance, mechanical properties and safety performance of the diaphragm. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by technicians in the technical field to which the present invention belongs; the terms used in the specific implementation methods are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" in the description and claims of the present invention and any variations thereof are intended to cover non-exclusive inclusions.

[0027] In the description of the specific implementation methods of the present invention, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present invention, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0028] Reference to "embodiments" in the present invention means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present invention may be combined with other embodiments.

[0029] In the description of the embodiments of the present invention, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects before and after are in an "or" relationship.

[0030] Throughout the present invention, numerical values ​​represent approximate measures or limits of ranges to cover minor deviations from given values ​​as well as embodiments with about the values ​​mentioned and embodiments with the exact values ​​mentioned. Except for the working examples provided at the end of the detailed description, all numerical values ​​of parameters (e.g., amounts or conditions) in this specification (including the appended claims) should be understood to be modified by the term "about" in all cases, regardless of whether "about" actually appears before the numerical value. "About" indicates that the stated numerical value allows some minor imprecision (close to the exact value of the value to some extent; approximately or reasonably close to the value; almost). If the imprecision provided by "about" is not otherwise understood in this ordinary sense in the art, "about" as used in the present invention at least indicates the variation that can be produced by the ordinary methods of measuring and using such parameters. For example, "about" may include a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in some aspects, optionally less than or equal to 0.1%.

[0031] Additionally, disclosure of ranges includes disclosure of all values ​​within the entire range and further divided ranges, including endpoints and sub-ranges given for such ranges.

[0032] Although the PP separator has a melting point of up to 160°C, in actual application scenarios, traditional lithium-ion battery separators are no longer able to meet the current stringent requirements for lithium-ion battery safety and stability. Based on this, the development of new separator materials with high thermal stability is of great practical significance for further enhancing the safety of lithium-ion batteries and promoting the sustainable development of lithium-ion battery technology. It has become one of the key research directions in the field of lithium-ion batteries.

[0033] Using polysilazane as a diaphragm coating can effectively improve the heat resistance of the diaphragm. Moreover, compared with traditional ceramic coatings, it has better continuity and can better cover the surface of the base film. Therefore, it has obvious advantages in improving the thermal stability of the diaphragm. However, the diaphragm coating prepared by polysilazane is brittle and prone to fracture, and the improvement effect is ineffective.

[0034] In order to solve the above problems, the present invention proposes a technical solution. The specific details are as follows:

[0035] A first aspect of the present invention provides a lithium ion battery separator, comprising a base film and a coating disposed on the base film, wherein the coating comprises polysilazane and polyurethane, and hydrogen bonds are formed between the polysilazane and the polyurethane.

[0036] Specifically, when polysilazane is compounded with polyurethane, the lone pair of electrons of the nitrogen atom in polysilazane forms a hydrogen bond with the hydrogen atom of the ~NH~ group in polyurethane. At the same time, the hydrogen atom in polysilazane forms a hydrogen bond with the carbonyl oxygen atom in polyurethane.

[0037] The present invention applies a coating including polysilazane and polyurethane on the base film. Polysilazane and polyurethane form hydrogen bonds during the blending process to achieve synergy between polyurethane and polysilazane, which can effectively improve the heat resistance, mechanical properties and safety performance of the diaphragm.

[0038] In some embodiments, the mass ratio of the polysilazane to the polyurethane is 1:(3-7).

[0039] In specific applications, the mass ratio of the polysilazane to the polyurethane can be selected to be 1:3, 1:4, 1:5, 1:6, 1:7, etc. The numerical ratios listed above are only examples and are not limiting. Without exceeding the scope of understanding of those skilled in the art, those skilled in the art can arbitrarily implement any numerical ratio within the range of 1: (3 to 7).

[0040] In some embodiments, the coating has a thickness of 1 μm to 2 μm.

[0041] In specific applications, the thickness of the coating can be selected to be 1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.8μm, 2.1μm, etc. The above-listed values ​​are only examples and are not limiting. Without exceeding the scope of understanding of those skilled in the art, those skilled in the art can arbitrarily implement any thickness within the range of 1μm to 2μm.

[0042] In some embodiments, the material of the base film is selected from at least one of polyethylene, polypropylene, polyester, cellulose, polyimide, and aramid; and the thickness of the base film is 7 μm to 12 μm.

[0043] The term "at least one" in the present invention refers to any one of the above materials, or a mixture of two, three or four of the above materials. It should be noted that the above materials do not react with each other, so the physical and chemical properties of each material will not be affected when they are mixed and added.

[0044] In specific applications, the thickness of the base film can be selected to be 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 11μm, 12μm, etc. The above-listed values ​​are only examples and are not limiting. Without exceeding the scope of understanding of those skilled in the art, those skilled in the art can arbitrarily implement any thickness within the range of 7μm to 12μm.

[0045] In some embodiments, the coating further comprises a plasticizer.

[0046] In the present invention, the role of the plasticizer is to soften the polysilazane / polyurethane composite material, improve the interface compatibility between the base film and the coating, and at the same time can adjust the distance between molecules in the polymer system, which is beneficial to ion transmission.

[0047] It should be noted that the plasticizer is one of the components of the diaphragm organic coating slurry, and the plasticizers generally used for the diaphragm organic coating slurry are all suitable for the technical solution of the present invention.

[0048] Based on the total mass of the polysilazane and the polyurethane being 100, the mass of the plasticizer is 1 to 2.

[0049] If the proportion of plasticizer in the coating is increased, the softening effect of the diaphragm can be effectively improved. However, too high a plasticizer content will reduce the mechanical properties of the diaphragm. Therefore, the proportion of plasticizer in the coating must be controlled within a certain range to meet the dual requirements of the diaphragm's softening performance and mechanical properties.

[0050] In the present invention, when the mass of the plasticizer is 1 to 2 (based on the total mass of the polysilazane and the polyurethane being 100), the overall performance of the diaphragm is optimal.

[0051] The second aspect of the present invention discloses a method for preparing a lithium ion battery separator, which is used to prepare the lithium ion battery separator disclosed in the first aspect of the present invention. The preparation method comprises the following steps:

[0052] S100, weighing polysilazane and polyurethane in a mass ratio of 1:(3-7), adding solvents respectively and mixing them to form a slurry;

[0053] S200, coating the prepared slurry on the base film to form a diaphragm.

[0054] In some preferred embodiments, step S100 uses mechanical stirring, and the stirring time is set to 1 hour, and the stirring speed is set to 600 rpm to 1000 rpm.

[0055] In specific applications, the stirring speed of step S100 can be selected as 600rpm, 700rpm, 800rpm, 900rpm, 1000rpm, etc. The above-listed values ​​are only examples and are not limiting. Without exceeding the scope of understanding of those skilled in the art, those skilled in the art can arbitrarily implement any stirring speed within the range of 600rpm to 1000rpm.

[0056] In some embodiments, the preparation method further includes step S110: adding a plasticizer to the prepared slurry.

[0057] In some preferred embodiments, in step S110, after adding the plasticizer, the stirring device is turned on again for stirring at a stirring speed of 400 rpm to 800 rpm for 30 minutes until a uniformly mixed material is obtained.

[0058] In specific applications, the stirring speed of step S110 can be selected as 400rpm, 500rpm, 600rpm, 700rpm, 800rpm, etc. The above-listed values ​​are only examples and are not limiting. Without exceeding the scope of understanding of those skilled in the art, those skilled in the art can arbitrarily implement any stirring speed within the range of 400rpm to 800rpm.

[0059] In some embodiments, the solid content of the slurry is 20% to 40%.

[0060] In specific applications, the solid content of the slurry can be specifically selected as 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc. The above-listed values ​​are only examples and are not limiting. Without exceeding the scope of understanding of those skilled in the art, those skilled in the art can arbitrarily implement any solid content within the range of 20% to 40.

[0061] In some implementations, step S200 includes:

[0062] Double-sided coating: coating on the first side surface of the base film, drying after coating; coating on the second side surface after drying;

[0063] The thickness difference of the coatings on both sides of the diaphragm is ≤0.2 μm.

[0064] In some embodiments,

[0065] The third aspect of the present invention discloses a lithium-ion battery, which includes the lithium-ion battery separator disclosed in the first aspect of the present invention, and also includes a positive electrode and a negative electrode, and the lithium-ion battery separator is arranged between the positive electrode and the negative electrode.

[0066] In some embodiments, the positive electrode includes a positive electrode active material, and the negative electrode includes a negative electrode active material.

[0067] In some embodiments, the positive electrode further includes a positive electrode binder, which can improve the bonding between the positive electrode active material particles and also improve the bonding between the positive electrode material layer and the positive electrode current collector.

[0068] In some embodiments, non-limiting examples of the positive electrode binder include poly(tetrafluoroethylene) (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), nitrile rubber (NBR), styrene ethylene butylene styrene copolymer (SEBS), styrene butadiene styrene copolymer (SBS), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, lithium alginate, and combinations thereof.

[0069] In some embodiments, the positive electrode further includes a positive electrode conductive agent to impart conductivity to the electrode. The conductive agent may include any conductive material as long as it does not cause chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives) and mixtures thereof.

[0070] In some embodiments, the negative electrode includes a negative electrode active material. In the present invention, the specific types of the negative electrode active material are not specifically limited and can be selected according to needs. Specifically, the negative electrode active material includes at least one of graphite, a composite material of single crystal silicon and graphite, soft carbon, and hard carbon.

[0071] In some embodiments, the negative electrode active material may include a negative electrode binder. The negative electrode binder improves the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector.

[0072] In specific applications, non-limiting examples of negative electrode binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin, nylon, etc.

[0073] The embodiments of the present invention will be described in detail below through examples and comparative examples. All examples and comparative examples are all solid-state battery sample groups prepared by the same process, and the number of samples in each group is 20.

[0074] It should be noted that the improvement of the present invention lies in the coating on the diaphragm, and is not limited to the diaphragm substrate. In practical applications, any known conventional diaphragm substrate such as polypropylene (PP) / polyethylene (PE) is applicable to the implementation scheme of the present invention. The diaphragm substrates used in the following examples and comparative examples are all polypropylene (PP), but the implementation scheme of the present invention is not limited to polypropylene (PP).

[0075] In addition, the embodiments of the present invention are not limited only to the following examples.

[0076] Embodiment 1:

[0077] 1. Preparation of diaphragm coating slurry:

[0078] Polysilazane and polyurethane are accurately weighed in a mass ratio of 1:5, and then slowly added to the ethyl acetate solvent system. To ensure that the materials are fully mixed and uniform, mechanical stirring is adopted, the stirring time is set to 1 hour, and the stirring speed is accurately controlled at 800rpm. After the initial stirring is completed, the plasticizer dibutyl phthalate is added to the mixed system, and the amount added is calculated based on the total mass of polysilazane and polyurethane, accounting for 1.5%. Finally, turn on the stirring device again and continue stirring at a stirring speed of 600rpm for 30 minutes until a well-mixed and well-dispersed slurry is obtained. The solid content of the slurry is 30%, providing a reliable slurry for subsequent tests or applications.

[0079] Second, the preparation of the coated diaphragm:

[0080] A base film made of polypropylene (PP) is selected as the basic support structure. The slurry prepared in the early stage through the established process steps is evenly coated on the surface of the diaphragm using micro-gravure coating technology. The thickness of the diaphragm is 9 microns. During the coating operation, the coating thickness is precisely controlled to be 1.5 microns to ensure the consistency and stability of the coating quality. After completing the single-sided coating, the diaphragm coated with the slurry is quickly transferred to an oven with precise temperature control function. By reasonably setting the oven temperature and ventilation parameters, the solvent contained in the slurry is effectively removed. After the moisture is dried, the same micro-gravure coating process is used to perform the same coating operation on the other side of the diaphragm to achieve a double-sided coating effect. After the above series of process treatments, a diaphragm with a surface modified with a polysilazane and polyurethane composite was successfully prepared.

[0081] The polyurethane and diaphragm coatings were tested respectively. Compared with the polyurethane, the peak position of the "-NH-" stretching vibration peak of the coating shifted to a lower wave number of 32 cm -1 . Hydrogen bonds are formed between polyurethane and polysilazane.

[0082] Embodiment 2:

[0083] 1. Preparation of diaphragm coating slurry:

[0084] Polysilazane and polyurethane are accurately weighed in a mass ratio of 1:3, and then slowly added to the ethyl acetate solvent system. To ensure that the materials are fully mixed and uniform, mechanical stirring is adopted, the stirring time is set to 1 hour, and the stirring speed is accurately controlled at 800rpm. After the initial stirring is completed, the plasticizer dibutyl phthalate is added to the mixed system, and the amount added is calculated based on the total mass of polysilazane and polyurethane, accounting for 1.5%. Finally, turn on the stirring device again and continue stirring at a stirring speed of 600rpm for 30 minutes until a uniformly mixed and well-dispersed slurry is obtained. The solid content of the slurry is 30%, providing a reliable slurry for subsequent tests or applications.

[0085] Second, the preparation of the coated diaphragm:

[0086] A base film made of polypropylene (PP) is selected as the basic support structure. The slurry prepared in the early stage through the established process steps is evenly coated on the surface of the diaphragm using micro-gravure coating technology. The thickness of the diaphragm is 9 microns. During the coating operation, the coating thickness is precisely controlled to be 1.5 microns to ensure the consistency and stability of the coating quality. After completing the single-sided coating, the diaphragm coated with the slurry is quickly transferred to an oven with precise temperature control function. By reasonably setting the oven temperature and ventilation parameters, the solvent contained in the slurry is effectively removed. After the moisture is dried, the same micro-gravure coating process is used to perform the same coating operation on the other side of the diaphragm to achieve a double-sided coating effect. After the above series of process treatments, a diaphragm with a surface modified with a polysilazane and polyurethane composite was successfully prepared.

[0087] The polyurethane and diaphragm coatings were tested separately. Compared with the polyurethane, the peak position of the "-NH-" stretching vibration peak of the coating shifted to a lower wave number of 25 cm -1 . Hydrogen bonds are formed between polyurethane and polysilazane.

[0088] Embodiment 3:

[0089] 1. Preparation of diaphragm coating slurry:

[0090] Polysilazane and polyurethane are accurately weighed in a mass ratio of 1:7, and then slowly added to the ethyl acetate solvent system. To ensure that the materials are fully mixed and uniform, mechanical stirring is adopted, the stirring time is set to 1 hour, and the stirring speed is accurately controlled at 800rpm. After the initial stirring is completed, the plasticizer dibutyl phthalate is added to the mixed system, and the amount added is calculated based on the total mass of polysilazane and polyurethane, accounting for 1.5%. Finally, turn on the stirring device again and continue stirring at a stirring speed of 600rpm for 30 minutes until a well-mixed and well-dispersed slurry is obtained. The solid content of the slurry is 30%, providing a reliable slurry for subsequent tests or applications.

[0091] Second, the preparation of the coated diaphragm:

[0092] A base film made of polypropylene (PP) is selected as the basic support structure. The slurry prepared in the early stage through the established process steps is evenly coated on the surface of the diaphragm using micro-gravure coating technology. The thickness of the diaphragm is 9 microns. During the coating operation, the coating thickness is precisely controlled to be 1.5 microns to ensure the consistency and stability of the coating quality. After completing the single-sided coating, the diaphragm coated with the slurry is quickly transferred to an oven with precise temperature control function. By reasonably setting the oven temperature and ventilation parameters, the solvent contained in the slurry is effectively removed. After the moisture is dried, the same micro-gravure coating process is used to perform the same coating operation on the other side of the diaphragm to achieve a double-sided coating effect. After the above series of process treatments, a diaphragm with a surface modified with a polysilazane and polyurethane composite was successfully prepared.

[0093] The polyurethane and diaphragm coatings were tested respectively. Compared with the polyurethane, the peak position of the "-NH-" stretching vibration peak of the coating shifted to a lower wave number of 36 cm -1 . Hydrogen bonds are formed between polyurethane and polysilazane.

[0094] Embodiment 4:

[0095] 1. Preparation of diaphragm coating slurry:

[0096] Polysilazane and polyurethane are accurately weighed in a mass ratio of 1:5, and then slowly added to the ethyl acetate solvent system. To ensure that the materials are fully mixed and uniform, mechanical stirring is adopted, the stirring time is set to 1 hour, and the stirring speed is accurately controlled at 800rpm. After the initial stirring is completed, the plasticizer dibutyl phthalate is added to the mixed system, and the amount added is calculated based on the total mass of polysilazane and polyurethane, accounting for 1.5%. Finally, turn on the stirring device again and continue stirring at a stirring speed of 600rpm for 30 minutes until a well-mixed and well-dispersed slurry is obtained. The solid content of the slurry is 30%, providing a reliable slurry for subsequent tests or applications.

[0097] Second, the preparation of the coated diaphragm:

[0098] A base film made of polypropylene (PP) is selected as the basic support structure. The slurry prepared in the early stage through the established process steps is evenly coated on the surface of the diaphragm using micro-gravure coating technology. The thickness of the diaphragm is 9 microns. During the coating operation, the coating thickness is precisely controlled to be 1 micron to ensure the consistency and stability of the coating quality. After completing the single-sided coating, the diaphragm coated with the slurry is quickly transferred to an oven with precise temperature control function. By reasonably setting the oven temperature and ventilation parameters, the solvent contained in the slurry is effectively removed. After the moisture is dried, the same micro-gravure coating process is used to perform the same coating operation on the other side of the diaphragm to achieve a double-sided coating effect. After the above series of process treatments, a diaphragm with a surface modified with a polysilazane and polyurethane composite was successfully prepared.

[0099] The polyurethane and diaphragm coatings were tested respectively. Compared with the polyurethane, the peak position of the "-NH-" stretching vibration peak of the coating shifted to a lower wave number of 31 cm -1 . Hydrogen bonds are formed between polyurethane and polysilazane.

[0100] Embodiment 5:

[0101] 1. Preparation of diaphragm coating slurry:

[0102] Polysilazane and polyurethane are accurately weighed in a mass ratio of 1:5, and then slowly added to the ethyl acetate solvent system. To ensure that the materials are fully mixed and uniform, mechanical stirring is adopted, the stirring time is set to 1 hour, and the stirring speed is accurately controlled at 800rpm. After the initial stirring is completed, the plasticizer dibutyl phthalate is added to the mixed system, and the amount added is calculated based on the total mass of polysilazane and polyurethane, accounting for 1.5%. Finally, turn on the stirring device again and continue stirring at a stirring speed of 600rpm for 30 minutes until a well-mixed and well-dispersed slurry is obtained. The solid content of the slurry is 30%, providing a reliable slurry for subsequent tests or applications.

[0103] Second, the preparation of the coated diaphragm:

[0104] A base film made of polypropylene (PP) is selected as the basic support structure. The slurry prepared in the early stage through the established process steps is evenly coated on the surface of the diaphragm using micro-gravure coating technology. The thickness of the diaphragm is 9 microns. During the coating operation, the coating thickness is precisely controlled to be 2 microns to ensure the consistency and stability of the coating quality. After completing the single-sided coating, the diaphragm coated with the slurry is quickly transferred to an oven with precise temperature control function. By reasonably setting the oven temperature and ventilation parameters, the solvent contained in the slurry is effectively removed. After the moisture is dried, the same micro-gravure coating process is used to perform the same coating operation on the other side of the diaphragm to achieve a double-sided coating effect. After the above series of process treatments, a diaphragm with a surface modified with a polysilazane and polyurethane composite was successfully prepared.

[0105] The polyurethane and diaphragm coatings were tested respectively. Compared with the polyurethane, the peak position of the "-NH-" stretching vibration peak of the coating shifted to a lower wave number of 33 cm -1 . Hydrogen bonds are formed between polyurethane and polysilazane.

[0106] Embodiment 6:

[0107] 1. Preparation of diaphragm coating slurry:

[0108] Polysilazane and polyurethane are accurately weighed in a mass ratio of 1:5, and then slowly added to the ethyl acetate solvent system. To ensure that the materials are fully mixed and uniform, mechanical stirring is adopted, the stirring time is set to 1 hour, and the stirring speed is accurately controlled at 800rpm. After the initial stirring is completed, the plasticizer dibutyl phthalate is added to the mixed system, and the amount added is calculated based on the total mass of polysilazane and polyurethane, accounting for 1.5%. Finally, turn on the stirring device again and continue stirring at a stirring speed of 600rpm for 30 minutes until a well-mixed and well-dispersed slurry is obtained. The solid content of the slurry is 20%, providing a reliable slurry for subsequent tests or applications.

[0109] Second, the preparation of the coated diaphragm:

[0110] A base film made of polypropylene (PP) is selected as the basic support structure. The slurry prepared in the early stage through the established process steps is evenly coated on the surface of the diaphragm using micro-gravure coating technology. The thickness of the diaphragm is 9 microns. During the coating operation, the coating thickness is precisely controlled to be 1.5 microns to ensure the consistency and stability of the coating quality. After completing the single-sided coating, the diaphragm coated with the slurry is quickly transferred to an oven with precise temperature control function. By reasonably setting the oven temperature and ventilation parameters, the solvent contained in the slurry is effectively removed. After the moisture is dried, the same micro-gravure coating process is used to perform the same coating operation on the other side of the diaphragm to achieve a double-sided coating effect. After the above series of process treatments, a diaphragm with a surface modified with a polysilazane and polyurethane composite was successfully prepared.

[0111] The polyurethane and diaphragm coatings were tested respectively. Compared with the polyurethane, the peak position of the "-NH-" stretching vibration peak of the coating shifted to a lower wave number of 33 cm -1 . Hydrogen bonds are formed between polyurethane and polysilazane.

[0112] Embodiment 7:

[0113] 1. Preparation of diaphragm coating slurry:

[0114] Accurately weigh polysilazane and polyurethane in a mass ratio of 1:5, and then slowly add them into the ethyl acetate solvent system. To ensure that the materials are fully mixed and uniform, mechanical stirring is adopted, the stirring time is set to 1 hour, and the stirring speed is accurately controlled at 800rpm. After the initial stirring is completed, the plasticizer dibutyl phthalate is added to the mixed system, and the amount added is calculated based on the total mass of polysilazane and polyurethane, accounting for 1.5%. Finally, turn on the stirring device again and continue stirring at a stirring speed of 600rpm for 30 minutes until a uniformly mixed and well-dispersed slurry is obtained. The solid content of the slurry is 40%, providing a reliable slurry for subsequent tests or applications.

[0115] Second, the preparation of the coated diaphragm:

[0116] A base film made of polypropylene (PP) is selected as the basic support structure. The slurry prepared in the early stage through the established process steps is evenly coated on the surface of the diaphragm using micro-gravure coating technology. The thickness of the diaphragm is 9 microns. During the coating operation, the coating thickness is precisely controlled to be 1.5 microns to ensure the consistency and stability of the coating quality. After completing the single-sided coating, the diaphragm coated with the slurry is quickly transferred to an oven with precise temperature control function. By reasonably setting the oven temperature and ventilation parameters, the solvent contained in the slurry is effectively removed. After the moisture is dried, the same micro-gravure coating process is used to perform the same coating operation on the other side of the diaphragm to achieve a double-sided coating effect. After the above series of process treatments, a diaphragm with a surface modified with a polysilazane and polyurethane composite was successfully prepared.

[0117] The polyurethane and diaphragm coatings were tested separately. Compared with the polyurethane, the peak position of the "-NH-" stretching vibration peak of the coating shifted to a lower wave number by 30 cm -1 . Hydrogen bonds are formed between polyurethane and polysilazane.

[0118] Comparative Example 1:

[0119] A base film made of polypropylene (PP) is selected as the diaphragm, and the thickness of the diaphragm is 9 microns.

[0120] Comparative Example 2:

[0121] 1. Preparation of diaphragm coating slurry:

[0122] Slowly add polysilazane into the ethyl acetate solvent system. To ensure that the materials are fully mixed and uniform, mechanical stirring is used, the stirring time is set to 1 hour, and the stirring speed is precisely controlled at 800rpm. After the initial stirring is completed, add plasticizer dibutyl phthalate to the mixed system. The amount added is calculated based on the total mass of polysilazane and polyurethane, accounting for 1.5%. Finally, turn on the stirring device again and continue stirring at a stirring speed of 600rpm for 30 minutes until a uniformly mixed and well-dispersed slurry is obtained. The solid content of the slurry is 30%, providing a reliable slurry for subsequent tests or applications.

[0123] Second, the preparation of the coated diaphragm:

[0124] A base film made of polypropylene (PP) is selected as the basic support structure. The slurry prepared in the early stage through the established process steps is evenly coated on the surface of the diaphragm using micro-gravure coating technology. The thickness of the diaphragm is 9 microns. During the coating operation, the coating thickness is precisely controlled to be 1.5 microns to ensure the consistency and stability of the coating quality. After completing the single-sided coating, the diaphragm coated with the slurry is quickly transferred to an oven with precise temperature control function. By reasonably setting the oven temperature and ventilation parameters, the solvent contained in the slurry can be effectively removed. After the water is dried, a diaphragm modified with a single-sided polysilazane and polyurethane composite is prepared.

[0125] Comparative Example 3:

[0126] 1. Preparation of diaphragm coating slurry:

[0127] Slowly add polysilazane to the ethyl acetate solvent system. To ensure that the materials are fully mixed and uniform, mechanical stirring is used, the stirring time is set to 1 hour, and the stirring speed is precisely controlled at 800rpm. After the initial stirring is completed, add plasticizer dibutyl phthalate to the mixed system. The amount added is calculated based on the total mass of polysilazane and polyurethane, accounting for 1.5%. Finally, turn on the stirring device again and continue stirring at a stirring speed of 600rpm for 30 minutes until a uniformly mixed and well-dispersed slurry is obtained. The solid content of the slurry is 30%, providing a reliable slurry for subsequent tests or applications.

[0128] Second, the preparation of coating:

[0129] The slurry is prepared into a coating with a thickness of 1.5 microns, which can be coated on a release film first, and then the release film is removed after drying.

[0130] Comparative Example 4:

[0131] 1. Preparation of diaphragm coating slurry:

[0132] Accurately weigh polysilazane and polyurethane in a mass ratio of 1:5 and slowly add them to the ethyl acetate solvent system. To ensure that the materials are fully mixed and uniform, mechanical stirring is adopted, the stirring time is set to 1 hour, and the stirring speed is accurately controlled at 800rpm. After the initial stirring is completed, the plasticizer dibutyl phthalate is added to the mixed system, and the amount added is calculated based on the total mass of the polyurethane, accounting for 1.5%. Finally, turn on the stirring device again and continue stirring at a stirring speed of 600rpm for 30 minutes until a well-mixed and well-dispersed slurry is obtained. The solid content of the slurry is 30%, providing a reliable slurry for subsequent tests or applications.

[0133] Second, the preparation of coating:

[0134] The slurry is prepared into a coating with a thickness of 1.5 microns, which can be coated on a release film first, and then the release film is removed after drying.

[0135] Comparative test: A total of 11 groups of samples from Examples 1 to 7 and Comparative Examples 1 to 4 were taken for the following test, and all test results were averaged.

[0136] Test 1: 120℃, 1h thermal shrinkage test.

[0137] Test 2: Tensile strength test

[0138] After the test, all samples were assembled into lithium-ion batteries, and the steps were as follows:

[0139] 1. Preparation of positive electrode:

[0140] The positive electrode active material lithium manganese oxide, the conductive agent superconducting carbon (Super~P), and the binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 90:7:3 to form a positive electrode slurry, the positive electrode slurry is coated on both surfaces of the current collector aluminum foil, and dried at 100°C to form a positive electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit into strips to form a lithium-ion battery positive electrode.

[0141] 2. Preparation of negative electrode:

[0142] The negative electrode slurry is made of negative electrode active material graphite, conductive agent superconducting carbon (Super~P), binder sodium carboxymethyl cellulose (CMC), and binder styrene butadiene rubber (SBR) in a mass ratio of 96.5:1.0:1.0:1.5, coated on the current collector copper foil and dried at 90°C to form a negative electrode active material layer, and then cold pressed, trimmed, cut into pieces, and slit into strips to make the negative electrode of the lithium ion battery.

[0143] 3. Lithium-ion battery assembly:

[0144] The positive electrode and negative electrode prepared above were stacked in order with the separators prepared in Examples 1 to 7 and Comparative Examples 1 to 4, so that the separator was between the positive and negative electrodes to obtain a bare battery cell. The bare battery cell was placed in an outer packaging shell, and an electrolyte was injected (the electrolyte composition was EC, DEC, EMC in a volume ratio of 1:1:1, 1M lithium hexafluorophosphate, 0.2% FEC). After vacuum packaging, standing, formation, shaping and other processes, a total of 11 groups of lithium-ion batteries were obtained.

[0145] Number the 11 groups of lithium-ion batteries respectively, and then conduct the following tests:

[0146] Test 3: First discharge capacity test (theoretical 13 Ah): At 45°C, the prepared battery was discharged at a constant current of 1 C to a cut-off voltage of 3.0 V. The first cycle discharge capacity was obtained.

[0147] Test 4: Acupuncture test.

[0148] Test 5: 140℃ hot box test: After the battery is fully charged at 1C, put it in the oven, start from room temperature, heat up to 120℃ at a rate of 5℃ / min, and keep it at 120℃ for 1h. If there is no fire or explosion, continue the test, heat up to 130℃ at a rate of 5℃ / min and keep it at 1h. If there is no fire or explosion, continue the test, heat up to 140℃ at a rate of 5℃ / min and keep it at 1h.

[0149] The comparative test results are shown in the following table:

[0150]

[0151]

[0152] From the data of Examples 1 to 3, it can be seen that when the mass ratio of polysilazane to polyurethane changes, the heat resistance and mechanical properties of the diaphragm will change. The higher the proportion of polyurethane, the higher the tensile strength, the greater the shrinkage rate, and the heat resistance increases and decreases (1C, 45℃ first discharge capacity is the heat resistance), and when the proportion of polyurethane is too high, the puncture pass rate will drop significantly. Therefore, maintaining the mass ratio of polysilazane to polyurethane within a certain range can obtain the best performance diaphragm.

[0153] From the data of Example 1, Example 4 and Example 5, it can be seen that the heat resistance and mechanical properties of the separator will change as the thickness of the double-sided coating changes. The thicker the coating, the higher the tensile strength of the separator, the lower the shrinkage rate, and the higher the puncture pass rate, but the first discharge capacity at 45°C under 1C conditions will decrease, which means that the thicker the coating is, the better it is. Only by maintaining the coating in a certain range can the best performance separator be obtained.

[0154] From the data of Example 1, Example 6 and Example 7, it can be seen that the heat resistance and mechanical properties of the diaphragm will change with the change of the solid content of the coating. The higher the solid content, the higher the tensile strength of the diaphragm, the lower the shrinkage rate, the puncture rate will first increase and then decrease, and the first discharge capacity at 45°C under 1C conditions will decrease, which shows that the higher the solid content of the coating, the better. Maintaining the solid content within a certain range can obtain the diaphragm with the best performance.

[0155] It can be seen from Comparative Examples 3 and 4 that, compared with the single polysilazane coating, the tensile strength of the composite coating of polysilazane and polyurethane is significantly improved.

[0156] It should be pointed out that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium ion battery separator, characterized in that: The invention comprises a base film and a coating layer arranged on the base film, wherein the coating layer comprises polysilazane and polyurethane, and hydrogen bonds are formed between the polysilazane and the polyurethane.

2. The lithium-ion battery separator according to claim 1, characterized in that The mass ratio of the polysilazane to the polyurethane is 1:(3-7).

3. The lithium ion battery separator according to claim 1, characterized in that: The coating has a thickness of 1 μm to 2 μm.

4. The lithium-ion battery separator according to claim 1, characterized in that The material of the base film is selected from at least one of polyethylene, polypropylene, polyester, cellulose, polyimide and aramid; the thickness of the base film is 7 μm to 12 μm.

5. The lithium ion battery separator according to claim 2, characterized in that: The coating also includes a plasticizer; Based on the total mass of the polysilazane and the polyurethane being 100, the mass of the plasticizer is 1 to 2.

6. A method for preparing a lithium ion battery separator, characterized in that: The steps include: S100, weighing polysilazane and polyurethane in a mass ratio of 1:(3-7), adding solvents respectively and mixing them to form a slurry; S200, coating the prepared slurry on the base film to form a diaphragm.

7. The method according to claim 6, characterized in that The method further includes step S110: adding a plasticizer to the prepared slurry.

8. The method according to claim 7, characterized in that The solid content of the slurry is 20% to 40%.

9. The method according to claim 8, characterized in that Step S200 includes: Double-sided coating: coating is performed on the first side surface of the base film, and then drying is performed; after drying, coating is performed on the second side surface.

10. A lithium ion battery, comprising the lithium ion battery separator according to any one of claims 1 to 5, characterized in that: It also includes a positive electrode and a negative electrode; the lithium-ion battery separator is arranged between the positive electrode and the negative electrode.

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