Diaphragm, method for manufacturing the same, and electric device

Abstract

The present application relates to a kind of diaphragm and its preparation method and electric device.The diaphragm includes base film, and the base film includes opposite first surface and second surface along the thickness direction;The first surface is provided with first coating, and the first coating includes polycaprolactone, metal oxide catalyst and bismuth-tin eutectic alloy;The second surface is provided with second coating, and the second coating includes core-shell material, and the core-shell material includes inner core and polymer shell, and the inner core includes perfluoropolyether and azobisisobutyronitrile;The base film includes polyether ether ketone and polyphenylene sulfide.The diaphragm provided by the present application uses polyether ether ketone and polyphenylene sulfide as mixed base film, and the first coating and the second coating are differentially set, the diaphragm heat response is sensitive, effectively prevent the occurrence of thermal runaway, the safety performance of lithium ion battery is significantly improved, meanwhile, the energy density of battery has also been greatly improved, and the cycle performance of battery is good.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to separators, and more particularly to a separator, its preparation method, and an electrical device thereof. Background Technology

[0002] With the growing global demand for clean energy and sustainable development, lithium-ion batteries, with their advantages such as high energy density and good cycle stability, have been increasingly widely used in many fields such as mobile electronic devices, electric vehicles, and large-scale energy storage.

[0003] In the structure of a lithium battery, the separator is one of the key internal components. Its main function is to separate the positive and negative electrodes, preventing short circuits caused by contact between the two electrodes. It also allows electrolyte ions to pass through. The performance of the separator determines the battery's interface structure, internal resistance, and other properties, directly affecting the battery's specific capacity, cycle stability, and safety performance. A high-performance separator plays a crucial role in improving the overall performance of the battery.

[0004] However, existing lithium battery separators still have some defects. Traditional polyolefin separators (PE / PP) have a low melting point (<160℃), which makes them prone to melting and shrinkage at high temperatures, leading to short circuits. In addition, the separator's ability to wet the electrolyte is poor, resulting in uneven electrolyte distribution inside the battery and uneven temperature distribution, which affects battery performance and thus battery life. At the same time, the separator surface lacks active sites, making it impossible to form a self-repairing or ion-selective transport mechanism with the electrolyte.

[0005] CN119495906A discloses a separator for preventing internal short circuits in lithium-ion batteries and its preparation method. The separator comprises a foamed material and a polymer film, wherein the foamed material is dispersed on the polymer film. This separator ensures that once an internal short circuit occurs in a lithium-ion battery, the localized internal short circuit will cause the short-circuit area to heat up. When the temperature reaches a certain level, the foamed material on the polymer film expands rapidly due to the heat, separating the positive and negative electrodes of the short circuit, stopping the internal short circuit reaction, and thus preventing the internal short circuit from continuing and further deteriorating.

[0006] CN112086608A discloses a Janus separator for lithium-ion batteries. The Janus separator comprises a high-temperature resistant support layer and polar and non-polar functional layers loaded on both sides of the high-temperature resistant support layer. The polar functional layer exhibits good interfacial compatibility with graphite materials and strong electrolyte absorption and retention capabilities, which is more conducive to the formation of a stable and uniform SEI film on the negative electrode surface. The non-polar functional layer possesses excellent electrochemical stability and suitable positive electrode adhesion, which is more conducive to the electrochemical performance of the positive electrode material, enabling it to achieve higher capacity and rate performance. The design of the high-temperature resistant support layer can significantly improve the dimensional stability of the separator, significantly reducing the risk of battery failure due to separator thermal shrinkage in high-temperature environments, thus improving battery safety and high-temperature cycle performance.

[0007] CN103199210A discloses a lithium-ion battery separator, which is composed of polyolefin and inorganic particles and prepared through processes such as extrusion, stretching, extraction, transverse or biaxial stretching, and heat treatment. In the heat treatment process, the heating temperature is 100~(polyolefin melting point + 70)℃, and the treatment time is 0.5~6 min. This ultra-high temperature heat treatment melts the polymer on the separator surface, resulting in a separator with a surface porosity lower than the central porosity. This not only prevents lithium crystals from penetrating the separator and causing short circuits during battery use, but also ensures a sufficiently high electrolyte retention rate and high battery capacity. The separator prepared by this invention has an overall porosity of 50~80%, a surface porosity of 20~50%, and a central porosity of 50~90%. It exhibits excellent high-temperature resistance.

[0008] Therefore, it is of great significance to provide a membrane with fast ion transport rate and high safety performance. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a separator, its preparation method, and an electrical device thereof. The separator provided by the present invention includes a first coating comprising polycaprolactone and a metal oxide catalyst, respectively disposed on a first surface of a base membrane, and a second coating comprising a core-shell material, disposed on a second surface of the base membrane. The core of the core-shell material comprises perfluoropolyether and azobisisobutyronitrile (AIB). When thermal runaway occurs in the battery, the polycaprolactone in the first coating rapidly softens and flows under the catalytic action of the catalyst, causing blockage of the micropores in the first coating and the first surface of the base membrane. This results in a sharp decrease in porosity on the first surface of the base membrane, preventing ion transport. Simultaneously, in the second coating, the AIB in the core of the core-shell material decomposes upon heating, generating gas that causes the outer shell to rupture. This release of perfluoropolyether from the core completely blocks the micropores of the base membrane, effectively preventing further propagation of thermal runaway.

[0010] To achieve this objective, the present invention employs the following technical solution: In a first aspect, the present invention provides a diaphragm comprising a base membrane, the base membrane comprising opposing first and second surfaces along its thickness direction; the first surface having a first coating comprising polycaprolactone, a metal oxide catalyst, and a bismuth-tin eutectic alloy; the second surface having a second coating comprising a core-shell material comprising a core and a polymer shell, the core comprising perfluoropolyether and azobisisobutyronitrile; and the base membrane comprising polyetheretherketone and polyphenylene sulfide.

[0011] This invention uses polyetheretherketone and polyphenylene sulfide as the base membrane, which is beneficial to improve the ion transport rate of the membrane and has high heat resistance, with a trigger temperature of up to 170°C.

[0012] This invention provides a first coating comprising polycaprolactone and a metal oxide catalyst on the first surface of a base film, and a second coating comprising a core-shell material on the second surface of the base film. The core of the core-shell material comprises perfluoropolyether and azobisisobutyronitrile (AIBN). When the internal temperature of the battery exceeds 60°C, the metal oxide catalyst in the first coating accelerates the thermal degradation of polycaprolactone, reduces its viscous flow activation energy, and causes it to melt and flow rapidly, covering and blocking the microporous channels of the first coating itself and the base film surface on one side of the first coating. This results in a sharp decrease in the porosity of the base film surface, significantly reducing ion transport and lowering the battery reaction rate, providing the first layer of protection for battery safety. When the battery temperature exceeds 80°C, in the second coating, the polymer shell of the core-shell material softens due to heat, and its mechanical strength decreases significantly. Meanwhile, the azobisisobutyronitrile (AIBN) core rapidly decomposes above ~65°C, generating a large amount of nitrogen gas (N2). The sudden increase in internal gas pressure and decrease in mechanical strength of the shell material cause the microcapsules to rupture. The encapsulated perfluoropolyether (PFPE) liquid and the gas generated by the decomposition of AIBN are rapidly released. At high temperature, the PFPE expands in volume and mixes with the gas to form a high-viscosity gel / foam system, which instantly blocks the remaining pores of the base film. Furthermore, PFPE can react with LiPF6 in the electrolyte to generate LiF solid and PF5 gas. The gas pressure causes the separator to expand secondary, completely blocking the ion transport path and preventing further spread of thermal runaway. This provides a second layer of protection for the battery's safety performance and significantly improves the battery's high-temperature safety performance.

[0013] The first coating of the diaphragm provided by the present invention also includes a bismuth-tin eutectic alloy. As a dispersant, the bismuth-tin eutectic alloy can help the metal oxide catalyst achieve more uniform nanoscale dispersion in the polycaprolactone matrix and reduce particle agglomeration. Furthermore, the low melting point of the bismuth-tin eutectic alloy (approximately 138°C) means that after the polycaprolactone melts, when the temperature reaches above 138°C, the bismuth-tin eutectic alloy transforms into a liquid state, thereby significantly improving the fluidity and spreading uniformity of the first coating material melt, enhancing the barrier effect on lithium-ion transport particle size, and preventing further spread of thermal runaway.

[0014] Preferably, in the first coating, the mass ratio of polycaprolactone to metal oxide catalyst is (95~99):(1~5).

[0015] Preferably, the mass of the bismuth-tin eutectic alloy is 3wt% to 5wt% of the total mass of polycaprolactone and metal oxide catalyst.

[0016] Preferably, in the core of the core-shell material, the mass ratio of perfluoropolyether to azobisisobutyronitrile is (7.5~9.5):1.

[0017] Preferably, the mass ratio of the core to the shell of the core-shell material is (1~3):1.

[0018] Preferably, in the base film, the mass ratio of polyetheretherketone to polyphenylene sulfide is 7:(1~3).

[0019] Preferably, the outer shell comprises polymethyl methacrylate.

[0020] Preferably, in the first coating, the metal oxide catalyst includes any one or a combination of at least two of tungsten trioxide, titanium dioxide, zirconium dioxide, vanadium pentoxide, manganese dioxide, or cerium dioxide.

[0021] Preferably, the average particle size of the metal oxide catalyst is 30 nm to 50 nm.

[0022] Preferably, the thickness of the first coating is 2μm to 4μm.

[0023] Preferably, the thickness of the second coating is 1μm to 3μm.

[0024] Preferably, the thickness of the base film is 12μm to 20μm.

[0025] Preferably, the porosity of the base film is 40%~50%, and the average pore size is 0.2μm~0.3μm.

[0026] In a second aspect, the present invention provides a method for preparing a diaphragm as described in the first aspect, the method comprising: (1) Preparation of base film: A mixed solution of polyether ether ketone and polyphenylene sulfide is coated on the surface of a substrate to obtain a cast film; the cast film is placed in a coagulation bath to solidify, and then removed and dried to obtain the base film; (2) Preparation of the first coating: Polycaprolactone and metal oxide catalyst are dispersed in a first solvent, bismuth-tin eutectic alloy is added, ball milling is performed to obtain a first slurry, which is coated on the first surface of the base film, and then subjected to a first heat treatment and a second heat treatment to obtain the first coating. (3) Preparation of the second coating: The mixture of perfluoropolyether and azobisisobutyronitrile is placed in a monomer solution of methyl methacrylate and polymerized in situ by emulsion polymerization to obtain the core-shell material; the core-shell material is dispersed in a second solvent to obtain a second slurry; the second slurry is sprayed onto the second surface of the base film to form a second coating; the order of steps (2) and (3) is not important.

[0027] The present invention prepares a base film by casting and prepares a core-shell material with a perfluoropolyether and azobisisobutyronitrile core and a polymer shell by emulsion polymerization. The interfacial bonding strength between the perfluoropolyether and the polymer shell is increased and the stability is good.

[0028] In the preparation of the first coating, this invention introduces a bismuth-tin eutectic alloy. During ball milling, the bismuth-tin eutectic alloy acts as a dispersant, helping the nano-metal oxide catalyst achieve more uniform nanoscale dispersion in the polycaprolactone matrix, reducing particle agglomeration, which is conducive to forming a "rigid-plastic" synergistic dispersion effect. During heat treatment, the pre-dispersed bismuth-tin eutectic alloy melts, promoting the rearrangement and interfacial fusion of polycaprolactone molecular chains through capillary action, thus pre-constructing a highly uniform, dense composite coating microstructure with good thermal conductivity, thereby improving the safety performance of the diaphragm.

[0029] Preferably, the solvent of the mixed solution in step (1) includes N-methylpyrrolidone.

[0030] Preferably, the solid content of the mixed solution in step (1) is 15% to 20%.

[0031] Preferably, the mixed solution in step (1) further includes 0.5wt% to 1wt% polyethylene glycol.

[0032] Preferably, the coagulation bath in step (1) comprises water and ethanol in a volume ratio of 1:(1~2).

[0033] Preferably, the temperature of the coagulation bath in step (1) is 20℃~40℃.

[0034] Preferably, the solidification time in step (1) is 5 min to 20 min.

[0035] Preferably, the drying time in step (1) is 80℃~120℃.

[0036] Preferably, in step (2), the first solvent comprises acetone and / or tetrahydrofuran.

[0037] Preferably, the rotation speed of the ball mill in step (2) is 100 rpm to 200 rpm.

[0038] Preferably, the ball milling time in step (2) is 1h to 2h.

[0039] Preferably, the temperature of the first heat treatment in step (2) is 60℃~100℃.

[0040] Preferably, the time for the first heat treatment in step (2) is 0.5h to 2h.

[0041] Preferably, the temperature of the second heat treatment in step (2) is 140℃~160℃.

[0042] Preferably, the time for the second heat treatment in step (2) is 2 min to 8 min.

[0043] Preferably, the heat treatment in step (2) is carried out in an inert atmosphere.

[0044] Preferably, the in-situ polymerization temperature in step (3) is 50℃~100℃.

[0045] Preferably, the in-situ polymerization time in step (3) is 4h to 8h.

[0046] Preferably, the solid content of the second slurry in step (3) is 8% to 15%.

[0047] Thirdly, the present invention provides an electrical device, the electrical device comprising a diaphragm as described in the first aspect, or comprising a diaphragm prepared by the preparation method described in the second aspect; The electrical device further includes a positive electrode and a negative electrode, wherein the first coating of the diaphragm is adjacent to the positive electrode and the second coating is adjacent to the negative electrode; The electrical device also includes an electrolyte, the components of which include trimethyl borate and / or lithium perfluorohexylsulfonylimide.

[0048] In the electrical device provided by this invention, the electrolyte components include trimethyl borate and / or lithium perfluorohexylsulfonylimide. During the initial stage of thermal runaway in the electrical device, the inner core-shell material ruptures, releasing perfluoropolyether. Trimethyl borate (TMB) can undergo an ester exchange reaction with the perfluoropolyether to generate a cross-linked network structure, repairing cracks in the separator caused by high temperature or mechanical stress, and preventing electrolyte leakage or dendrite penetration. Simultaneously, lithium perfluorohexylsulfonylimide (LiFHSI) decomposes in the early stage of heating (>80°C), and its products can construct a composite SEI film with high ionic conductivity and high mechanical strength on the negative electrode surface. Under thermal abuse conditions, this SEI film can more effectively maintain interface stability and homogenize the lithium-ion flow, thereby mitigating the surge in local current density and accelerated thermal runaway caused by interface collapse, and providing crucial reaction time for the separator's thermal response shutdown mechanism.

[0049] Preferably, the electrolyte contains 0.2wt% to 0.6wt% of trimethyl borate by mass.

[0050] Preferably, the electrolyte contains lithium perfluorohexylsulfonylimide at a mass percentage of 0.5 wt% to 1 wt%.

[0051] Compared with the prior art, the present invention has the following beneficial effects: (1) The separator provided by the present invention includes a first coating comprising polycaprolactone and a metal oxide catalyst respectively disposed on a first surface of a base membrane, and a second coating comprising a core-shell material disposed on a second surface of the base membrane, wherein the core of the core-shell material comprises perfluoropolyether and azobisisobutyronitrile. When the battery experiences thermal runaway, the metal oxide catalyst in the first coating can accelerate the thermal degradation of polycaprolactone, reduce its viscous flow activation energy, and cause it to melt and flow rapidly, covering and blocking the microporous channels of the first coating itself and the base membrane surface on one side of the first coating. The porosity of the base membrane surface drops sharply, significantly reducing ion transport and lowering the battery reaction rate. At the same time, in the second coating, the azobisisobutyronitrile in the core of the core-shell material decomposes upon heating to produce gas, causing the shell to rupture, and accompanied by the release of perfluoropolyether from the core, completely blocking the microporous channels of the base membrane, thereby effectively preventing the further spread of thermal runaway.

[0052] (2) By introducing a bismuth-tin eutectic alloy into the first coating, the bismuth-tin eutectic alloy acts as a dispersant during ball milling, which helps the nano-metal oxide catalyst achieve more uniform nanoscale dispersion in the polycaprolactone matrix and reduces particle agglomeration, thus facilitating the formation of a "rigid-plastic" synergistic dispersion effect. During heat treatment, the pre-dispersed bismuth-tin eutectic alloy melts and promotes the rearrangement and interface fusion of polycaprolactone molecular chains through capillary action, thus pre-constructing a highly uniform, dense composite coating microstructure with good thermal conductivity, thereby improving the safety performance of the diaphragm.

[0053] (3) In the electrical device provided by the present invention, the electrolyte components include trimethyl borate and / or lithium perfluorohexyl sulfonyl imide. When the electrical device experiences thermal runaway and the inner core-shell material ruptures and releases perfluoropolyether, trimethyl borate (TMB) can undergo an ester exchange reaction with the perfluoropolyether to generate a cross-linked network structure, repairing cracks in the diaphragm caused by high temperature or mechanical stress, and preventing electrolyte leakage or dendrite penetration. Simultaneously, lithium perfluorohexyl sulfonyl imide (LiFHSI) decomposes into F at >80℃. - And SO2, F - With Li on the negative electrode surface + LiF is generated, and SO2 participates in the formation of a thiocarbonate composite SEI membrane. This composite SEI membrane has high ionic conductivity and mechanical strength, which can optimize the ion transport path and improve rate performance. Detailed Implementation

[0054] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0055] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0056] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0057] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0058] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0059] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0060] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0061] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0062] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0063] In one specific embodiment, the present invention provides a diaphragm comprising a base membrane, the base membrane comprising opposing first and second surfaces along its thickness direction; the first surface is provided with a first coating comprising polycaprolactone, a metal oxide catalyst, and a bismuth-tin eutectic alloy; the second surface is provided with a second coating comprising a core-shell material comprising a core and a polymer shell, the core comprising perfluoropolyether and azobisisobutyronitrile; the base membrane comprising polyetheretherketone and polyphenylene sulfide.

[0064] This invention uses a combination of polyetheretherketone (PEEK) and polyphenylene sulfide (PPS) as the base membrane, which is beneficial for improving the ion transport rate of the membrane and exhibits high heat resistance, with a trigger temperature for thermal shrinkage reaching up to 170°C. The inherent high melting point, high heat resistance, and high mechanical strength of PEEK and PPS enable the base membrane to maintain structural integrity and prevent thermal shrinkage during the early stages of thermal runaway (≤170°C). This provides a stable structure and the necessary temperature transfer window for triggering active safety mechanisms, preventing internal short circuits caused by early membrane shrinkage. Simultaneously, the strong polarity of PEEK combined with the weak polarity of PPS optimizes the wettability of the base membrane to the electrolyte and the lithium-ion transport environment. The microstructure formed during the blending process facilitates the construction of uniform, interconnected microporous channels, thereby reducing the ion transport impedance of the membrane while ensuring safety. In addition, the highly heat-resistant polyetheretherketone and polyphenylene sulfide base film provides a strong adhesion substrate for the first and second coatings, ensuring that the coatings do not fall off during normal battery cycling. In the event of thermal runaway, the stable base film ensures that the coatings precisely trigger the shutdown reaction at specific locations as designed.

[0065] This invention provides a first coating comprising polycaprolactone and a metal oxide catalyst on the first surface of a base membrane, and a second coating comprising a core-shell material on the second surface of the base membrane. The core of the core-shell material comprises perfluoropolyether and azobisisobutyronitrile (AISO). When the internal temperature of the battery exceeds 60°C, the metal oxide catalyst in the first coating accelerates the thermal degradation of polycaprolactone, reducing its viscous flow activation energy and causing it to melt and flow rapidly. This melts and blocks the microporous channels of the first coating itself and the base membrane surface on one side of the first coating, resulting in a sharp decrease in the porosity of the base membrane surface. This causes the separator to significantly reduce ion transport through pore shrinkage, lowering the battery reaction rate and providing the first layer of protection for battery safety. When the internal temperature of the battery exceeds 80°C, in the second coating, the polymer shell of the core-shell material softens due to heat, and its mechanical strength decreases significantly, while the azobisisobutyronitrile core... Isobutyronitrile (AIBN) decomposes rapidly at temperatures above ~65°C, producing a large amount of nitrogen gas (N2). This causes a sharp increase in internal gas pressure and a decrease in the mechanical strength of the outer shell, leading to the rupture of the microcapsules. The encapsulated perfluoropolyether (PFPE) liquid is then rapidly released along with the gas produced by the decomposition of AIBN. Furthermore, the PFPE expands in volume at high temperatures and mixes with the gas to form a high-viscosity gel / foam system. This system instantly blocks all remaining pores in the base film, thereby preventing further spread of thermal runaway and providing a second layer of protection for the battery's safety performance, significantly improving the battery's high-temperature safety performance.

[0066] This invention introduces a perfluoropolyether into the core of a core-shell material. The CF bond energy in its molecule is as high as 485 kJ / mol (CH bond energy is 414 kJ / mol), and with the support of flexible ether (COC) segments, it can withstand a wide temperature range from -70°C to 300°C. Its perfluorinated structure shields the chemical activity of the molecular chain, resisting the corrosion of electrolyte solvents (such as carbonates). The perfluoropolyether flows at high temperatures and can fill microcracks, and can react with the F-generated compounds from the decomposition of LiFHSI in the electrolyte. - A LiF-rich SEI film is synergistically constructed to achieve dynamic repair of the SEI film. Furthermore, the perfluoropolyether has a low surface tension of 15-20 mN / m (far lower than PDMS's 22 mN / m), which promotes uniform dispersion of the core-shell material in the second coating and reduces the surface energy of the second coating, inhibiting lithium dendrite growth. The fluorine segments of the perfluoropolyether can also react with the F-segments of LiFHSI in the electrolyte. - It forms strong interactions (FF bonds), enhances ion transport efficiency, and stabilizes the electrode / electrolyte interface.

[0067] The first coating of the diaphragm provided by the present invention also includes a bismuth-tin eutectic alloy. As a dispersant, the bismuth-tin eutectic alloy can help the metal oxide catalyst achieve more uniform nanoscale dispersion in the polycaprolactone matrix and reduce particle agglomeration. Furthermore, the eutectic properties of the bismuth-tin eutectic alloy (typically, the melting point of the bismuth-tin eutectic alloy is about 138°C) can lower the melting point of the polycaprolactone matrix, promote the melting and leveling of PCL, thereby optimizing the continuity and uniformity of the coating.

[0068] In the first coating provided by this invention, if the mass ratio of polycaprolactone to metal oxide catalyst is too high, i.e., the content of metal oxide catalyst is too low, it may result in insufficient catalytic active sites during thermal runaway, slowing down the overall melting rate and flow rate of polycaprolactone, prolonging the time window from temperature triggering to effective clogging of the micropores of the base film, and failing to reduce the battery reaction rate in time, leading to aggravated thermal runaway and uncontrollable chain reactions inside the battery. If the mass ratio of polycaprolactone to metal oxide catalyst is too low, the excessive addition of metal oxide catalyst will disrupt the continuity of the polycaprolactone matrix, resulting in increased coating brittleness and decreased flexibility. Under the mechanical stress of long-term battery cycling, the coating is more prone to cracking or even peeling off from the base film, affecting the long-term reliability of the separator. Furthermore, excessive metal oxide catalyst occupies too much volume in the first coating, which may hinder the normal transport path of lithium ions, leading to increased internal resistance of the battery and affecting rate performance and cycle life.

[0069] In some embodiments, the mass ratio of polycaprolactone to metal oxide catalyst in the first coating is (95~99):(1~5), for example, it can be 95:5, 96:4, 97:3, 98:2 or 99:1.

[0070] In some embodiments, the mass of the bismuth-tin eutectic alloy is 3wt% to 5wt% of the total mass of polycaprolactone and metal oxide catalyst, for example, it can be 3wt%, 3.5wt%, 4wt%, 4.5wt% or 5wt%.

[0071] In some embodiments, the mass ratio of perfluoropolyether to azobisisobutyronitrile in the core of the core-shell material is (7.5~9.5):1, for example, it can be 7.5:1, 8:1, 8.5:1, 9:1 or 9.5:1.

[0072] In the second coating provided by this invention, the mass ratio of the core to the shell material is too large, resulting in a relatively thin shell with low mechanical strength. Under the mechanical stress of normal battery cycling or long-term electrolyte immersion, there is a risk of premature breakage, leading to premature release of the perfluoropolyether and disrupting the normal function of the battery. Conversely, if the mass ratio of the core to the shell material is too small, the relatively thick shell has excessively high mechanical strength. The gas pressure generated by the decomposition of azobisisobutyronitrile is insufficient to cause it to rupture in a timely and complete manner, resulting in a delayed response or even failure of the second safety protection mechanism. It cannot form an effective seal during the critical window period of rapid thermal runaway evolution. Furthermore, an excessively thick shell also increases the overall thickness of the second coating and the ion transport impedance.

[0073] In some embodiments, the mass ratio of the core to the shell of the core-shell material is (1~3):1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1 or 3:1.

[0074] In the base film provided by this invention, the mass ratio of polyetheretherketone (PEEK) to polyphenylene sulfide (PPS) is too high: the high viscosity of PEEK melt and an excessively high proportion will lead to greater processing difficulty, potentially causing difficulties in film formation, and resulting in greater brittleness of the base film, resulting in insufficient toughness under battery winding or mechanical impact. Conversely, a mass ratio of PEEK to PPS that is too low is not conducive to improving the base film's resistance to heat shrinkage and dimensional retention.

[0075] In some embodiments, the mass ratio of polyetheretherketone (PEEK) to polyphenylene sulfide (PPS) in the base film is 7:(1~3), for example, it can be 7:1, 7:1.5, 7:2, 7:2.5 or 7:3.

[0076] In some embodiments, the outer shell comprises polymethyl methacrylate.

[0077] In some embodiments, the metal oxide catalyst in the first coating includes any one or a combination of at least two of tungsten trioxide, titanium dioxide, zirconium dioxide, vanadium pentoxide, manganese dioxide, or cerium dioxide.

[0078] In this invention, the metal oxide catalyst is made of nanoscale particles to ensure high surface activity and dynamic response.

[0079] In some embodiments, the average particle size of the metal oxide catalyst is 30 nm to 50 nm, for example, it can be 30 nm, 35 nm, 40 nm, 45 nm or 50 nm.

[0080] The thickness of the first and second coatings has a crucial impact on the effectiveness of the coatings. If the thickness of the first coating is too small, insufficient functional materials will result in insufficient absolute amounts of polycaprolactone and catalyst in the coating. During thermal runaway, it will be impossible to form a sufficiently continuous and dense melt to completely block all micropores on the first side of the base film, leading to incomplete shut-off and an inability to effectively reduce the battery's reaction rate. Furthermore, ultra-thin coatings are prone to localized defects and incomplete coverage during the coating process, creating performance bottlenecks. However, the thickness of the first coating should not be too large either. An excessively thick coating will significantly prolong the vertical transport path of lithium ions, leading to increased internal resistance in the battery and impairing rate performance and cycle life. In addition, a thicker coating will generate greater internal stress due to volume changes during battery cycling, increasing the risk of peeling or cracking from the base film. Moreover, excessive coating thickness will increase the total thickness of the separator, reducing the battery's energy density.

[0081] In some embodiments, the thickness of the first coating is 2μm to 4μm, for example, it can be 2μm, 2.5μm, 3μm, 3.5μm or 4μm.

[0082] Excessive thickness of the second coating will increase the lithium-ion impedance of the separator, increase the total thickness of the separator, reduce the volumetric energy density, and require higher internal pressure to rupture, leading to a delayed thermal shutdown response. Conversely, insufficient thickness of the second coating will result in insufficient core-shell material, limiting the loading of perfluoropolyether and azobisisobutyronitrile in the core. In the event of thermal runaway, the released nitrogen and perfluoropolyether content will be too low, and the resulting high-viscosity gel / foam system will be insufficient to completely wet and seal the pores of the entire base membrane, causing the second safety mechanism to fail.

[0083] In some embodiments, the thickness of the second coating is 1 μm to 3 μm, for example, it can be 1 μm, 1.5 μm, 2 μm, 2.5 μm or 3 μm.

[0084] Although polyetheretherketone (PEEK) and polyphenylene sulfide (PPS) have high strength, excessively thin base films exhibit reduced puncture and tear resistance during battery assembly, cycling, or thermal expansion, making them prone to internal short circuits. Conversely, excessively thick base films directly and significantly reduce the battery's volumetric and gravimetric energy density, and also lengthen the path for lithium ions to pass through the micropores of the base film in the electrolyte, increasing concentration polarization and negatively impacting high-rate performance.

[0085] In some embodiments, the thickness of the base film is 12μm to 20μm, for example, it can be 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm or 20μm.

[0086] In some embodiments, the porosity of the base film is 40% to 50%, for example, it can be 40%, 42%, 44%, 46%, 48% or 50%, and the average pore size is 0.2μm to 0.3μm, for example, it can be 0.2μm, 0.22μm, 0.24μm, 0.26μm, 0.28μm or 0.3μm.

[0087] In another specific embodiment, the present invention provides a method for preparing a diaphragm as described in one of the foregoing specific embodiments, the method comprising: (1) Preparation of base film: A mixed solution of polyether ether ketone and polyphenylene sulfide is coated on the surface of a substrate to obtain a cast film; the cast film is placed in a coagulation bath to solidify, and then removed and dried to obtain the base film; (2) Preparation of the first coating: Polycaprolactone and metal oxide catalyst are dispersed in a first solvent, bismuth-tin eutectic alloy is added, ball milling is performed to obtain a first slurry, which is coated on the first surface of the base film, and then subjected to a first heat treatment and a second heat treatment to obtain the first coating. (3) Preparation of the second coating: The mixture of perfluoropolyether and azobisisobutyronitrile is placed in a monomer solution of methyl methacrylate and polymerized in situ by emulsion polymerization to obtain the core-shell material; the core-shell material is dispersed in a second solvent to obtain a second slurry; the second slurry is sprayed onto the second surface of the base film to form a second coating; the order of steps (2) and (3) is not important.

[0088] This invention introduces a bismuth-tin eutectic alloy into the first coating. During ball milling, the bismuth-tin eutectic alloy acts as a dispersant, helping the nano-metal oxide catalyst achieve more uniform nanoscale dispersion in the polycaprolactone matrix, reducing particle agglomeration. Furthermore, the eutectic properties of the bismuth-tin eutectic alloy lower the melting point of the polycaprolactone matrix (typically, the melting point of the bismuth-tin eutectic alloy is about 138°C), promoting the melting and leveling of the polycaprolactone matrix during heat treatment, thereby optimizing the continuity and uniformity of the coating.

[0089] In some embodiments, the solvent of the mixed solution in step (1) includes N-methylpyrrolidone.

[0090] In some embodiments, the solid content of the mixed solution in step (1) is 15% to 20%, for example, it can be 15%, 16%, 17%, 18%, 19% or 20%.

[0091] In some embodiments, the mixed solution in step (1) further includes 0.5wt% to 1wt% polyethylene glycol, for example, the content of polyethylene glycol can be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, or 1wt%. This invention adds polyethylene glycol as a pore-forming agent to the mixed solution for preparing the base membrane, thereby controlling the porosity of the base membrane and improving its porosity.

[0092] In some embodiments, the coagulation bath in step (1) comprises water and ethanol in a volume ratio of 1:(1~2), for example, the volume ratio of water and ethanol may be 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8 or 1:2.

[0093] In some embodiments, the temperature of the coagulation bath in step (1) is 20°C to 40°C, for example, it can be 20°C, 25°C, 30°C, 35°C or 40°C.

[0094] In some embodiments, the solidification time in step (1) is 5 min to 20 min, for example, it can be 5 min, 7 min, 9 min, 10 min, 12 min, 14 min, 16 min, 18 min or 20 min.

[0095] In some embodiments, the drying time in step (1) is 80°C to 120°C, for example, it can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C.

[0096] In some implementations, the dispersion method described in step (2) includes ultrasonic treatment.

[0097] In some implementations, the dispersion time in step (2) is 30 min to 60 min, for example, it can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min.

[0098] In some embodiments, the first solvent in step (2) includes acetone and / or tetrahydrofuran. When the first solvent includes acetone and tetrahydrofuran, the volume ratio of acetone and tetrahydrofuran is (3~5):1, for example, it can be 3:1, 3.5:1, 4:1, 4.5:1 or 5:1.

[0099] In some embodiments, the rotational speed of the ball mill in step (2) is 100 rpm to 200 rpm, for example, it can be 100 rpm, 120 rpm, 140 rpm, 160 rpm, 180 rpm or 200 rpm.

[0100] In some implementations, the ball milling time in step (2) is 1h to 2h, for example, it can be 1h, 1.2h, 1.4h, 1.6h, 1.8h or 2h.

[0101] In some embodiments, the temperature of the first heat treatment in step (2) is 60°C to 100°C, for example, it can be 60°C, 70°C, 80°C, 90°C or 100°C.

[0102] In some implementations, the time for the first heat treatment in step (2) is 0.5h to 2h, for example, it can be 0.5h, 1h, 1.5h or 2h.

[0103] During the preparation of the first coating of the diaphragm provided by the present invention, the pre-dispersed bismuth-tin eutectic alloy undergoes a brief melting process through a second heat treatment. This process promotes the rearrangement and interfacial fusion of polycaprolactone molecular chains through capillary action, thereby pre-constructing a highly uniform, dense composite coating microstructure with good thermal conductivity, thus improving the safety performance of the diaphragm.

[0104] In some embodiments, the temperature of the second heat treatment in step (2) is 140°C to 160°C, for example, it can be 140°C, 145°C, 150°C, 155°C or 160°C.

[0105] In some embodiments, the time for the second heat treatment in step (2) is 2 min to 8 min, for example, it can be 2 min, 3 min, 4 min, 5 min, 6 min, 7 min or 8 min.

[0106] In some embodiments, the heat treatment in step (2) is carried out in an inert atmosphere, which includes nitrogen and / or an inert gas, including argon and / or helium.

[0107] In some embodiments, the in-situ polymerization temperature in step (3) is 10°C to 100°C, for example, it can be 50°C, 60°C, 70°C, 80°C, 90°C or 100°C.

[0108] In some embodiments, the second solvent in step (3) includes water.

[0109] In some implementations, the in-situ polymerization time in step (3) is 4h to 8h, for example, it can be 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h.

[0110] In some embodiments, the solid content of the second slurry in step (3) is 8% to 15%, for example, it can be 8%, 9%, 10%, 11%, 12%, 13%, 14% or 15%.

[0111] In some implementations, the spraying method in step (3) includes pressure spraying.

[0112] In some embodiments, the inlet temperature of the spray in step (3) is 150°C to 200°C, for example, it can be 150°C, 160°C, 170°C, 180°C, 190°C or 200°C.

[0113] In some embodiments, the outlet temperature of the spray in step (3) is 60°C to 100°C, for example, it can be 60°C, 70°C, 80°C, 90°C or 100°C.

[0114] In yet another embodiment, the present invention provides an electrical device comprising a diaphragm as described in one of the preceding embodiments, or comprising a diaphragm prepared by the preparation method described in another of the preceding embodiments. The electrical device further includes a positive electrode and a negative electrode, wherein the first coating of the diaphragm is adjacent to the positive electrode and the second coating is adjacent to the negative electrode; The electrical device also includes an electrolyte, the components of which include trimethyl borate and / or lithium perfluorohexylsulfonylimide.

[0115] In the electrical device provided by this invention, the electrolyte components include trimethyl borate and / or lithium perfluorohexyl sulfonyl imide. When the electrical device experiences thermal runaway and the inner core-shell material ruptures, releasing perfluoropolyether, trimethyl borate (TMB) can undergo an ester exchange reaction with the perfluoropolyether to generate a cross-linked network structure, repairing cracks in the diaphragm caused by high temperature or mechanical stress, and preventing electrolyte leakage or dendrite penetration. Simultaneously, lithium perfluorohexyl sulfonyl imide (LiFHSI) decomposes into F at temperatures above 80°C. - And SO2, F - With Li on the negative electrode surface + LiF is generated, and SO2 participates in the formation of a thiocarbonate composite SEI membrane. This composite SEI membrane has high ionic conductivity and mechanical strength, which can optimize the ion transport path and improve rate performance.

[0116] In the electrolyte, insufficient trimethyl borate content means that the limited number of trimethyl borate molecules cannot react with sufficient perfluoropolyether to form a continuous and effective three-dimensional cross-linked network. This results in incomplete crack repair, a slow repair speed, and an inability to effectively prevent electrolyte leakage and dendrite penetration during the critical window of rapid thermal runaway. Conversely, excessive trimethyl borate content, due to its high reactivity, may cause side reactions with other components in the electrolyte (such as LiPF6 and solvents) under normal battery cycling voltage and temperature. This could increase interfacial impedance, consume active lithium, and accelerate capacity decay.

[0117] In some embodiments, the electrolyte contains 0.2wt% to 0.6wt% by mass, for example, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, or 0.6wt%.

[0118] If the content of lithium perfluorohexylsulfonylimide in the electrolyte is too low, the F produced by its decomposition will be insufficient. - Insufficient total SO2 content limits the strengthening effect on the SEI film, making it impossible to form a continuous and tough "protective" composite SEI film on the large negative electrode surface. On the other hand, excessive lithium perfluorohexylsulfonylimide content may lead to excessive and rapid gas production under thermal abuse, exacerbating the rise in internal pressure. Furthermore, the SO2 produced by its decomposition is an acidic gas, which may increase the acidity of the electrolyte and accelerate side reactions such as the dissolution of transition metals.

[0119] In some embodiments, the electrolyte contains lithium perfluorohexylsulfonylimide at a mass percentage of 0.5 wt% to 1 wt%, for example, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, or 1 wt%.

[0120] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0121] To further clarify the technical solution of the present invention, the positive electrode used in the embodiments of the present invention includes a carbon-coated aluminum foil and a positive electrode active material layer disposed on the surface of the carbon-coated aluminum foil. The positive electrode active material layer includes lithium iron phosphate, conductive carbon black and polyvinylidene fluoride in a mass ratio of 93:5:2. The negative electrode includes a copper foil and a negative electrode active material layer disposed on the surface of the copper foil, including graphite, conductive carbon black and sodium carboxymethyl cellulose in a mass ratio of 75:2:23.

[0122] The above description is only for clearly illustrating the technical solution of the present invention and should not be regarded as a further limitation of the present invention.

[0123] Example 1 This embodiment provides a diaphragm, including a base membrane with a thickness of 16 μm. The base membrane comprises polyetheretherketone (PEEK) and polyphenylene sulfide (PPS) in a mass ratio of 7:2. The porosity of the base membrane is 45%, and the average pore size is 0.25 μm. The base membrane includes a first surface and a second surface opposite each other along its thickness direction. The first surface is provided with a first coating with a thickness of 3 μm, which comprises polycaprolactone (PVC), tungsten trioxide (TDC), and a bismuth-tin eutectic alloy. The average particle size of the TDC is 40 nm, the mass ratio of PVC to TDC is 97:3, and the mass of the bismuth-tin eutectic alloy is 4 wt% of the total mass of PVC and TDC. The second surface is provided with a second coating with a thickness of 2 μm, which comprises a core-shell material. The core-shell material comprises a core and a polymer shell. The core comprises perfluoropolyether (PFPO) and azobisisobutyronitrile (AIOBR) in a mass ratio of 9:1, and the shell comprises polymethyl methacrylate (PMMA). The mass ratio of the core to the shell is 2:1. The method for preparing the diaphragm includes: (1) Preparation of the base film: Polyether ether ketone and polyphenylene sulfide were mixed in N-methylpyrrolidone to obtain a mixed solution with a solid content of 18%. Then, 1 wt% of polyethylene glycol was added to the mixed solution. The mixed solution was coated evenly onto the surface of a stainless steel substrate using an extrusion coating machine to obtain a cast film. A coagulation bath was prepared by mixing the two materials at a volume ratio of 1:1. The temperature of the coagulation bath was adjusted to 30°C. The cast film was placed in the coagulation bath and coagulated for 15 min. After being removed, it was dried at 100°C to obtain the base film. (2) Preparation of the first coating: Polycaprolactone and tungsten trioxide were ultrasonically dispersed in a mixed solvent of acetone and tetrahydrofuran in a volume ratio of 4:1. Bismuth-tin eutectic alloy was added. The ball milling speed was set to 200 rpm and the mixture was ball milled for 1 h to obtain the first slurry. The first slurry was coated on the first surface of the base film. The mixture was heat-treated at 80°C for 1 h in an inert atmosphere and then heat-treated at 145°C for 3 min to obtain the first coating. (3) Preparation of the second coating: The mixture of perfluoropolyether and azobisisobutyronitrile is placed in a monomer solution of methyl methacrylate and polymerized in situ at 80°C for 6 hours by emulsion polymerization to obtain the core-shell material; the core-shell material is dispersed in water to obtain a second slurry with a solid content of 10%; the second slurry is sprayed onto the second surface of the base film by pressure spraying with the inlet temperature set at 180°C and the outlet temperature at 80°C to form the second coating.

[0124] This embodiment also provides a lithium-ion battery, including a separator, a positive electrode, a negative electrode, and an electrolyte provided in this embodiment. The electrolyte is a 1 mol / L LiPF6 solution, wherein the solvent is ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1. The LiPF6 solution also includes 0.4 wt% trimethyl borate and 1 wt% lithium perfluorohexylsulfonylimide.

[0125] Example 2 This embodiment provides a diaphragm, which is the same as that in Example 1 except that the mass ratio of polyether ether ketone to polyphenylene sulfide in the base membrane is 7:3.

[0126] The preparation method of the diaphragm is the same as that in Example 1, except that the mass ratio of polyether ether ketone and polyphenylene sulfide in step (1) is 7:3.

[0127] This embodiment also provides a lithium-ion battery, which is the same as that in Embodiment 1 except that it uses the separator provided in this embodiment.

[0128] Example 3 This embodiment provides a diaphragm, which is the same as that in Example 1 except that the mass ratio of polyether ether ketone to polyphenylene sulfide in the base membrane is 7:1.

[0129] The preparation method of the diaphragm is the same as that in Example 1, except that the mass ratio of polyether ether ketone and polyphenylene sulfide in step (1) is 7:1.

[0130] This embodiment also provides a lithium-ion battery, which is the same as that in Embodiment 1 except that it uses the separator provided in this embodiment.

[0131] Example 4 This embodiment provides a diaphragm, which is the same as in Example 1 except that the first coating includes polycaprolactone and titanium dioxide, and the mass ratio of polycaprolactone to titanium dioxide is 99:5.

[0132] The preparation method of the diaphragm is the same as in Example 1, except that in step (2) titanium dioxide is used instead of tungsten trioxide and the mass ratio of polycaprolactone to titanium dioxide is 99:5.

[0133] This embodiment also provides a lithium-ion battery, which is the same as that in Embodiment 1 except that it uses the separator provided in this embodiment.

[0134] Example 5 This embodiment provides a diaphragm, which is the same as in Example 1 except that the first coating includes polycaprolactone and zirconium dioxide, and the mass ratio of polycaprolactone to zirconium dioxide is 99:1.

[0135] The preparation method of the diaphragm is the same as in Example 1, except that zirconium dioxide is used instead of tungsten trioxide in step (2) and the mass ratio of polycaprolactone to zirconium dioxide is 99:1.

[0136] This embodiment also provides a lithium-ion battery, which is the same as that in Embodiment 1 except that it uses the separator provided in this embodiment.

[0137] Example 6 This embodiment provides a diaphragm, which is the same as in Embodiment 1 except that in the second coating, the mass ratio of the core to the shell material is 3:1.

[0138] The preparation method of the diaphragm is the same as in Example 1, except that in step (3), the mass ratio of the total mass of perfluoropolyether and azobisisobutyronitrile to the mass of methyl methacrylate is adjusted to 3:1.

[0139] This embodiment also provides a lithium-ion battery, which is the same as that in Embodiment 1 except that it uses the separator provided in this embodiment.

[0140] Example 7 This embodiment provides a diaphragm, which is the same as in Embodiment 1 except that in the second coating, the mass ratio of the core to the shell material is 1:1.

[0141] The preparation method of the diaphragm is the same as in Example 1, except that in step (3), the total mass ratio of perfluoropolyether and azobisisobutyronitrile to methyl methacrylate is adjusted to 1:1.

[0142] This embodiment also provides a lithium-ion battery, which is the same as that in Embodiment 1 except that it uses the separator provided in this embodiment.

[0143] Example 8 This embodiment provides a diaphragm, which is the same as that in Embodiment 1 except that the thickness of the base film is 12 μm.

[0144] The preparation method of the diaphragm is the same as in Example 1, except that in step (1) the coating thickness of the cast film is adjusted to obtain a base film of 12 μm.

[0145] This embodiment also provides a lithium-ion battery, which is the same as that in Embodiment 1 except that it uses the separator provided in this embodiment.

[0146] Example 9 This embodiment provides a diaphragm, which is the same as that in Embodiment 1 except that the thickness of the base film is 20 μm.

[0147] The preparation method of the diaphragm is the same as in Example 1, except that in step (1) the coating thickness of the cast film is adjusted to obtain a base film of 20 μm.

[0148] This embodiment also provides a lithium-ion battery, which is the same as that in Embodiment 1 except that it uses the separator provided in this embodiment.

[0149] Example 10 This embodiment provides a diaphragm, which is the same as that in Embodiment 1 except that the thickness of the first coating is 2 μm.

[0150] The preparation method of the diaphragm is the same as that in Example 1, except that the coating thickness of the first coating is adjusted to 2 μm in step (2).

[0151] This embodiment also provides a lithium-ion battery, which is the same as that in Embodiment 1 except that it uses the separator provided in this embodiment.

[0152] Example 11 This embodiment provides a diaphragm, which is the same as that in Embodiment 1 except that the thickness of the first coating is 4 μm.

[0153] The preparation method of the diaphragm is the same as that in Example 1, except that the coating thickness of the first coating is adjusted to 4 μm in step (2).

[0154] This embodiment also provides a lithium-ion battery, which is the same as that in Embodiment 1 except that it uses the separator provided in this embodiment.

[0155] Example 12 This embodiment provides a diaphragm, which is the same as that in Embodiment 1 except that the thickness of the second coating is 1 μm.

[0156] The preparation method of the diaphragm is the same as that in Example 1, except that the spraying thickness of the second coating is adjusted to 1 μm in step (3).

[0157] This embodiment also provides a lithium-ion battery, which is the same as that in Embodiment 1 except that it uses the separator provided in this embodiment.

[0158] Example 13 This embodiment provides a diaphragm, which is the same as that in Embodiment 1 except that the thickness of the second coating is 3 μm.

[0159] The preparation method of the diaphragm is the same as that in Example 1, except that the spraying thickness of the second coating is adjusted to 3 μm in step (3).

[0160] This embodiment also provides a lithium-ion battery, which is the same as that in Embodiment 1 except that it uses the separator provided in this embodiment.

[0161] Example 14 This embodiment provides a lithium-ion battery, which is the same as in Example 1 except that the electrolyte contains 0.2 wt% trimethyl borate and 0.5 wt% lithium perfluorohexylsulfonylimide.

[0162] Example 15 This embodiment provides a lithium-ion battery, which is the same as in Example 1 except that the electrolyte contains 0.6 wt% trimethyl borate and 1 wt% lithium perfluorohexylsulfonylimide.

[0163] Example 16 This embodiment provides a lithium-ion battery, which is the same as that in Example 1 except that trimethyl borate and lithium perfluorohexyl sulfonyl imide are not added to the electrolyte.

[0164] Comparative Example 1 This comparative example provides a lithium-ion battery that is identical to that of Example 1, except that it uses a polypropylene separator.

[0165] Comparative Example 2 This comparative example provides a lithium-ion battery that is identical to that of Example 1, except that it uses a polyethylene separator.

[0166] Comparative Example 3 This comparative example provides a diaphragm that is identical to that of Example 1 except that it does not have a second coating.

[0167] The preparation method of the diaphragm is the same as that in Example 1, except that step (3) is omitted.

[0168] This comparative example also provides a lithium-ion battery, which is the same as that in Example 1 except that it uses the separator provided in this comparative example.

[0169] Comparative Example 4 This comparative example provides a diaphragm that is identical to that of Example 1 except that it does not have a first coating.

[0170] The preparation method of the diaphragm is the same as that in Example 1, except that step (2) is omitted.

[0171] This comparative example also provides a lithium-ion battery, which is the same as that in Example 1 except that it uses the separator provided in this comparative example.

[0172] Comparative Example 5 This comparative example provides a diaphragm that is identical to that of Example 1, except that it only includes a base film and does not have a first coating or a second coating.

[0173] The preparation method of the diaphragm is the same as that in Example 1, except that only step (1) is performed and steps (2) and (3) are not performed.

[0174] This comparative example also provides a lithium-ion battery, which is the same as that in Example 1 except that it uses the separator provided in this comparative example.

[0175] Performance testing: The performance of the lithium-ion batteries provided in all the above embodiments and comparative examples was tested: (1) Internal resistance test: The internal resistance of the lithium-ion battery is tested by using a battery internal resistance meter.

[0176] (2) Cycle capacity retention rate: At 25℃, the battery is charged at a constant current of 0.33C to 3.65V, and then charged at a constant voltage of 3.65V until the current I≤0.05C. The battery charging capacity is recorded as C0. After resting for 5 minutes, it is discharged at a constant current of 0.33C to 2.0V. After resting for 30 minutes, the above process is repeated 500 times and the battery discharge capacity is recorded as C1. The capacity retention rate of the 500th cycle is calculated as C1 / C0×100%.

[0177] (3) Battery energy density test: First, weigh the battery and record the weight as m. Then, at 25°C, charge the battery at a constant current of 0.33C to 3.65V, and then charge it at a constant voltage of 3.65V until the current decreases to 0.05C. After standing for 5 minutes, discharge it at a constant current of 0.33C to 2.0V and obtain the discharge energy Q. The battery energy density is calculated as Q / m.

[0178] (4) Diaphragm thermal response test: First, test the initial porosity of the diaphragm, then keep the diaphragm in a 60℃ constant temperature chamber for 30 min, and test the porosity of the diaphragm after 60℃ treatment. Then continue to raise the temperature to 120℃, keep it for 1 h, and test the porosity of the diaphragm after 120℃ treatment.

[0179] The test results are shown in Table 1.

[0180] Table 1 In summary, based on the test results of Examples 1 to 16 and Comparative Examples 1 to 5, the separator provided by the present invention uses polyetheretherketone and polyphenylene sulfide as a mixed base film, and differentiates the first coating and the second coating. The separator has a sensitive thermal response, effectively preventing thermal runaway, significantly improving the safety performance of the lithium-ion battery. At the same time, the energy density of the battery is also greatly improved, and the battery has good cycle performance.

[0181] Based on the test results of Examples 1 and 16, the present invention further regulates the composition of the electrolyte by introducing trimethyl borate and lithium perfluorohexyl sulfonyl imide into the electrolyte, which react with the perfluoropolyether in the second coating of the separator to repair cracks in the separator caused by high temperature or mechanical stress, prevent electrolyte leakage or dendrite penetration, and form a composite SEI membrane with high ionic conductivity and mechanical strength, optimize the ion transport path, and further improve the rate performance of the battery.

[0182] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A diaphragm, characterized in that, The diaphragm includes a base membrane, which has opposing first and second surfaces along its thickness direction; The first surface is provided with a first coating, the first coating comprising polycaprolactone, a metal oxide catalyst and a bismuth-tin eutectic alloy; The second surface is provided with a second coating, the second coating comprising a core-shell material, the core-shell material comprising a core and a polymer shell, the core comprising perfluoropolyether and azobisisobutyronitrile; The base film includes polyetheretherketone and polyphenylene sulfide.

2. The diaphragm as described in claim 1, characterized in that, In the first coating, the mass ratio of polycaprolactone to metal oxide catalyst is (95~99):(1~5); And / or, the mass of the bismuth-tin eutectic alloy is 3wt%~5wt% of the total mass of polycaprolactone and metal oxide catalyst; And / or, in the core of the core-shell material, the mass ratio of perfluoropolyether to azobisisobutyronitrile is (7.5~9.5):1; And / or, the mass ratio of the core to the shell of the core-shell material is (1~3):1; And / or, in the base film, the mass ratio of polyetheretherketone to polyphenylene sulfide is 7:(1~3); And / or, the housing comprises polymethyl methacrylate.

3. The diaphragm as described in claim 1, characterized in that, In the first coating, the metal oxide catalyst includes any one or a combination of at least two of tungsten trioxide, titanium dioxide, zirconium dioxide, vanadium pentoxide, manganese dioxide, or cerium dioxide; And / or, the average particle size of the metal oxide catalyst is 30 nm to 50 nm.

4. The diaphragm as described in claim 1, characterized in that, The thickness of the first coating is 2μm~4μm; And / or, the thickness of the second coating is 1μm~3μm; And / or, the thickness of the base film is 12μm~20μm; And / or, the porosity of the base film is 40%~50%, and the average pore size is 0.2μm~0.3μm.

5. A method for preparing a diaphragm as described in any one of claims 1 to 4, characterized in that, The preparation method includes: (1) Preparation of base film: A mixed solution of polyether ether ketone and polyphenylene sulfide is coated on the surface of a substrate to obtain a cast film; the cast film is placed in a coagulation bath to solidify, and then removed and dried to obtain the base film; (2) Preparation of the first coating: Polycaprolactone and metal oxide catalyst are dispersed in a first solvent, bismuth-tin eutectic alloy is added, ball milling is performed to obtain a first slurry, which is coated on the first surface of the base film, and then subjected to a first heat treatment and a second heat treatment to obtain the first coating. (3) Preparation of the second coating: The mixture of perfluoropolyether and azobisisobutyronitrile is placed in a monomer solution of methyl methacrylate and polymerized in situ by emulsion polymerization to obtain the core-shell material; the core-shell material is dispersed in a second solvent to obtain a second slurry; the second slurry is sprayed onto the second surface of the base film to form the second coating. The order of steps (2) and (3) is not important.

6. The preparation method according to claim 5, characterized in that, The solvent of the mixed solution in step (1) includes N-methylpyrrolidone; And / or, the solid content of the mixed solution in step (1) is 15%~20%; And / or, the mixed solution in step (1) further includes polyethylene glycol, wherein the mass percentage of polyethylene glycol in the mixed solution is 0.5wt%~1wt%; And / or, the coagulation bath in step (1) comprises water and ethanol in a volume ratio of 1:(1~2); And / or, the temperature of the coagulation bath in step (1) is 20°C to 40°C; And / or, the solidification time in step (1) is 5 min to 20 min; And / or, the drying time in step (1) is 80°C to 120°C.

7. The preparation method according to claim 5, characterized in that, Step (2) The first solvent includes acetone and / or tetrahydrofuran; And / or, the rotation speed of the ball mill in step (2) is 100 rpm to 200 rpm; And / or, the ball milling time in step (2) is 1h~2h; And / or, in step (2), the temperature of the first heat treatment is 60°C to 100°C; And / or, the duration of the first heat treatment in step (2) is 0.5h to 2h; And / or, in step (2), the temperature of the second heat treatment is 140°C to 160°C; And / or, the time for the second heat treatment in step (2) is 2 min to 8 min; And / or, the heat treatment in step (2) is carried out in an inert atmosphere.

8. The preparation method according to claim 5, characterized in that, The in-situ polymerization temperature in step (3) is 50℃~100℃; And / or, the in-situ polymerization time in step (3) is 4h~8h; And / or, in step (3), the solid content of the second slurry is 8%~15%.

9. An electrical device, characterized in that, The electrical device includes a diaphragm as described in any one of claims 1 to 4, or includes a diaphragm prepared by the preparation method described in any one of claims 5 to 8; The electrical device further includes a positive electrode and a negative electrode, wherein the first coating of the diaphragm is adjacent to the positive electrode and the second coating is adjacent to the negative electrode; The electrical device also includes an electrolyte, the components of which include trimethyl borate and / or lithium perfluorohexylsulfonylimide.

10. The electrical appliance as described in claim 9, characterized in that, The electrolyte contains trimethyl borate at a mass percentage of 0.2 wt% to 0.6 wt%. And / or, the electrolyte contains lithium perfluorohexylsulfonylimide at a mass percentage of 0.5 wt% to 1 wt%.

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