Diaphragm, preparation method and battery

Abstract

The invention relates to the technical field of batteries, and particularly discloses a diaphragm, a preparation method and a battery. The diaphragm disclosed by the invention comprises a base film and a coating layer arranged on at least one side surface of the base film in the thickness direction, the base film comprises polyolefin; the coating comprises a binder and inorganic particles; the inorganic particles at least comprise first ceramic particles, and the first ceramic particles comprise boron nitride; the binder comprises a polyacrylic acid polymer containing a metal ion group. According to the diaphragm disclosed by the invention, the high-temperature resistance, the heat-conducting property and the electrolyte infiltration property of the diaphragm can be effectively improved; meanwhile, the diaphragm has good ion migration performance at low temperature.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a separator, a preparation method thereof, and a battery. Background Technology

[0002] Polyolefin microporous membranes possess a uniform pore structure, good mechanical strength, and chemical stability, making them commonly used as battery separators. However, polyolefin microporous membranes typically have a low melting point, and during battery charging and discharging, the increased internal temperature causes severe shrinkage. Furthermore, their poor wettability with the electrolyte limits their application in high-energy-density batteries.

[0003] Currently, coating the surface of polyolefin microporous membranes with a ceramic layer can effectively improve their high-temperature resistance; however, the above method still has problems such as weak bonding between the polyolefin microporous membrane and the ceramic layer, low ionic conductivity, and poor thermal conductivity. Summary of the Invention

[0004] In view of the above-mentioned technical problems, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a separator, a preparation method, and a battery, which can effectively improve the high-temperature resistance, thermal conductivity, and electrolyte wetting performance of the separator; simultaneously, the separator exhibits good ion migration performance at low temperatures (around -20°C).

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0006] According to a first aspect of the present invention, a diaphragm is provided, comprising: a base film, and a coating disposed on at least one surface of the base film in the thickness direction;

[0007] The base film comprises a polyolefin; the coating comprises an adhesive and inorganic particles;

[0008] The inorganic particles include at least a first ceramic particle, which includes boron nitride; the binder includes a polyacrylic polymer containing metal ion groups.

[0009] In one alternative implementation, the surface energy of the base film is greater than 45 mN / m.

[0010] In one optional implementation, the surface arithmetic mean roughness Ra of the base film is 5 nm to 50 nm.

[0011] In one optional implementation, the thickness of the base film is 5 μm to 16 μm.

[0012] In one alternative embodiment, the porosity of the base membrane is 30% to 50%.

[0013] In one optional embodiment, the base film has a Gurley value of 50 s / 100 mL to 200 s / 100 mL.

[0014] In one alternative embodiment, the inorganic particles further include second ceramic particles, which include aluminum-containing ceramic particles, preferably at least one of alumina or boehmite.

[0015] In one optional embodiment, the polyacrylic polymer containing metal ion groups includes at least one of lithium polyacrylate, a copolymer of polyacrylic acid grafted with lithium sulfonic acid side chains, or a copolymer of polyacrylic acid grafted with lithium carboxylic acid side chains.

[0016] In one optional implementation, the median particle size D of the second ceramic particles 50 The range is 100nm to 800nm.

[0017] In one optional implementation, the median particle size D of the boron nitride 50 The wavelength range is 100nm to 1000nm, and a sheet-like structure is preferred.

[0018] In one alternative embodiment, the boron nitride accounts for 5% to 30% of the total weight of the inorganic particles.

[0019] In one optional implementation, the weight of the second ceramic particle accounts for 70% to 95% of the total weight of the inorganic particles.

[0020] In one optional implementation, the thickness of the coating is 1 μm to 3 μm.

[0021] In one alternative implementation, the peel strength between the base film and the coating is greater than 100 N / m.

[0022] In one alternative embodiment, the adhesive further includes an auxiliary agent, which includes at least one of a styrene-butadiene rubber (SBR) emulsion, an acrylate copolymer emulsion, or a polyurethane (PU) emulsion.

[0023] In one alternative embodiment, the auxiliary agent accounts for 5% to 40% of the total solid content of the adhesive.

[0024] In one alternative embodiment, the adhesive further includes a modifier, which includes at least one of a fluorinated surfactant, a fluorinated acrylate copolymer emulsion, or a fluorinated silane coupling agent.

[0025] In one alternative embodiment, the modifier accounts for 1% to 10% of the total amount of the binder.

[0026] In one alternative implementation, the diaphragm exhibits a heat shrinkage rate (MD) of less than 3% after being held at 150°C for 1 hour.

[0027] In one alternative embodiment, the diaphragm exhibits a heat shrinkage rate (TD) of less than 3% after being kept at 150°C for 1 hour.

[0028] In one optional embodiment, the diaphragm, after being impregnated with electrolyte, exhibits an ionic conductivity greater than 1.0 mS / cm at 20°C to 25°C.

[0029] According to a second aspect of the present invention, the present invention also provides a method for preparing a diaphragm, comprising the following steps:

[0030] The polyolefin membrane is pretreated to obtain the base membrane;

[0031] Inorganic particles and binder are mixed evenly to obtain a slurry;

[0032] The slurry is placed on at least one surface in the thickness direction of the base film and dried to obtain the diaphragm.

[0033] The inorganic particles include at least boron nitride; the binder includes a polyacrylic polymer containing metal ion groups.

[0034] In one alternative implementation, the pretreatment includes APGD plasma treatment, in which the discharge gas includes an inert gas.

[0035] In one alternative embodiment, the discharge gas further includes an active gas, which includes at least one of O2, H2, or NH3.

[0036] In one optional implementation, the discharge power density of the APGD plasma treatment is 0.5 W / cm². 2 ~10W / cm 2 The processing time is 0.1s to 5s.

[0037] In one optional implementation, the linear velocity of the APGD plasma treatment is 5 m / min to 60 m / min.

[0038] In one optional embodiment, the solid content in the slurry is 20wt% to 60wt%.

[0039] In one optional embodiment, the viscosity of the slurry is 100 mPa·s to 2000 mPa·s.

[0040] In one optional implementation, the drying temperature is less than or equal to 120°C, and the drying adopts stepped temperature drying, with the first stepped temperature range being 50°C to 80°C and the second stepped temperature range being 80°C to 115°C.

[0041] In one optional embodiment, the mass ratio of the inorganic particles to the binder is 1:(0.01 to 0.1).

[0042] According to a third aspect of the present invention, the present invention also provides a battery comprising: a separator as described in any embodiment of the first aspect of the present invention, and / or a separator prepared by any preparation method of the second aspect of the present invention.

[0043] The technical solution of this invention also has at least the following beneficial effects:

[0044] 1. The separator of the present invention, by forming a coating on any surface of the base membrane, wherein the coating comprises inorganic particles and a binder, wherein the inorganic particles contain at least boron nitride, and the binder comprises a polyacrylic polymer containing metal ion groups; thereby giving the separator good thermal stability and thermal conductivity, which can rapidly dissipate heat inside the battery and effectively avoid or delay the thermal runaway process of the battery; at the same time, the presence of a polyacrylic polymer in the binder gives the separator good electrolyte wetting properties, thereby improving the battery capacity and cycle performance.

[0045] 2. In a preferred embodiment of the present invention, by pretreating the base film to give the base film surface a certain roughness and / or surface energy, the interfacial bonding performance between the coating and the base film can be greatly enhanced, making the coating more firmly bonded and the base film and coating less prone to peeling.

[0046] 3. In a preferred embodiment of the present invention, the polyacrylic acid polymer contains metal ion groups, such as lithium sulfonate, which can construct a stable lithium ion conductive channel, reduce interfacial impedance, and improve the ionic conductivity of the separator; and effectively improve the wettability of the separator to the electrolyte. Through synergistic effect, the rate performance, low temperature performance and cycle stability of the battery are significantly improved.

[0047] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0048] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0049] Figure 1 The diagram shown is a schematic diagram of the diaphragm structure provided by the present invention.

[0050] Explanation of reference numerals in the attached figures:

[0051] 10—Base film; 20—Coating; 21—Inorganic particles; 22—Binder.

[0052] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0053] The technical solution of the present invention and how the technical solution of the present invention solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0054] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0055] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0056] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0057] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may 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.

[0058] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0059] The following are explanations of the terms used in this invention:

[0060] Gurley value: This is an indicator used to characterize the air permeability of a material. Specifically, it refers to the time required for a given volume of air to pass through a membrane of a specific area under a given pressure. For example, at a pressure of 5 cmHg, 10 mL of gas can pass through a membrane of 1 cm² area. 2 The time required for the diaphragm to be in place.

[0061] APGD: refers to atmospheric glow discharge, a type of low-temperature plasma generated under atmospheric pressure. It can alter the chemical composition and microstructure of material surfaces by generating high-energy particles such as electrons, ions, and free radicals.

[0062] Heat shrinkage rate: refers to the volume change of thermoplastic materials (such as ABS (a terpolymer of acrylonitrile (A), butadiene (B), and styrene (S) monomers), paraffin wax, etc.) due to their inherent thermal expansion rate. It is the primary cause of shrinkage. The shrinkage amount caused by heat shrinkage is: ΔL=δ×(L+Δ / 2)×Δt, where δ is the linear expansion coefficient of the material, / ℃; L is the X / Y dimension of the part, mm; Δt is the temperature difference, ℃; Δ is the tolerance of the part (compensated by taking the larger of the machining allowance). Heat shrinkage rate MD refers to the shrinkage of the material in the mold direction, and heat shrinkage rate TD refers to the shrinkage of the material in the transverse direction perpendicular to the mold direction.

[0063] Arithmetic mean roughness Ra: Represents the arithmetic mean of the absolute values ​​of the peaks and valleys of the surface profile over a reference length. Specifically, Ra is the average of the absolute values ​​of the height deviation of each point from the average height, usually expressed in micrometers (μm).

[0064] A composite membrane formed by depositing a ceramic layer on the surface of a polyolefin microporous membrane can withstand high temperatures to a certain extent when used as a battery separator. However, when a ceramic layer is deposited on the surface of a polyolefin microporous membrane, if the ceramic layer is loose and porous, the ion permeability and electrolyte retention capacity of the separator are improved, but the structural support is insufficient at high temperatures, and the improvement in the thermal stability of the separator is limited. If the ceramic layer is dense, the high-temperature dimensional stability and wettability of the separator are improved, but excessively high ceramic layer density will significantly reduce the effective pores, increase the separator impedance, and reduce the ionic conductivity. In addition to heat resistance and wettability, other properties of the separator need to be considered in high-rate charge-discharge and low-temperature environments. For example, at a low temperature of -20°C, conventional microporous separators experience a significant decrease in battery capacity due to increased electrolyte viscosity and slower ion diffusion. During high-current discharge (such as 2C to 5C rates), the ion transport resistance is high, which leads to increased polarization and a decrease in usable capacity. Under these circumstances, the aforementioned composite membrane can affect the migration performance of lithium ions. Therefore, how to ensure that the separator has good high-temperature resistance and electrolyte wetting performance, while also providing a favorable lithium ion conduction channel to facilitate smoother migration and thus improve the rate performance and low-temperature performance of the battery, has become an important research topic.

[0065] In view of the above-mentioned technical problems, the present invention provides a separator, a preparation method and a battery, which can effectively improve the high temperature resistance, thermal conductivity and electrolyte wetting performance of the separator; at the same time, the separator has good ion migration performance at low temperature (around -20°C).

[0066] The specific technical solution of the present invention is as follows:

[0067] [Septum]

[0068] In some embodiments of the present invention, a diaphragm is provided, comprising: a base membrane, and a coating disposed on at least one surface of the base membrane in the thickness direction; the base membrane comprises a polyolefin; the coating comprises an adhesive and inorganic particles; the inorganic particles comprise at least first ceramic particles, the first ceramic particles comprising boron nitride; the adhesive comprises a polyacrylic polymer containing metal ion groups.

[0069] The base film includes, but is not limited to, polyolefins, and can be any one of polyethylene (PE) film, polypropylene (PP) film, polyethylene / polypropylene (PP / PE) film, or polyvinylidene fluoride (PVDF) film. A coating is formed on any one side surface along the thickness direction of the base film, or on both sides of the base film. For example, if the coating is formed on one side surface of the base film, it forms... Figure 1 The structure shown; if the coatings are respectively placed on both sides of the base film, an "ABA sandwich structure" is formed, in which the base film is located between the two coatings.

[0070] Those skilled in the art will understand that the coating can be obtained by mixing a binder and inorganic particles, wherein the inorganic particles contain at least a first ceramic particle, which includes boron nitride. Since boron nitride has various crystal forms, such as cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN), in a preferred embodiment, the boron nitride can be selected from hexagonal boron nitride (h-BN). By including a portion of boron nitride in the inorganic particles, the high-temperature resistance of the separator can be improved, and the thermal conductivity of the coating can also be improved. When thermal runaway occurs inside the battery, it can assist in the rapid dissipation of heat inside the battery, delaying the thermal runaway process, thereby improving the battery's safety performance. Of course, in addition to boron nitride, the inorganic particles may also include, but are not limited to, one or more of diatomaceous earth, silicon dioxide, aluminum oxide, or boehmite (AlOOH), giving the separator excellent high-temperature resistance.

[0071] Polyacrylic acid polymers containing metal ion groups include, but are not limited to, organic functional groups containing metal ions, such as lithium sulfonate (-SO3Li), lithium carboxylic acid (-COOLi), or sodium sulfonate (-SO3Na), or metal ions such as lithium ions, potassium ions, sodium ions, or calcium ions. These polymers can have lithium sulfonate groups or lithium carboxylic acid groups grafted onto the side chains of polyacrylic acid, or lithium polyacrylate, or potassium polyacrylate, etc. By modifying polyacrylic acid, these metal ion-containing polymers can be used as part of a binder, enabling good adhesion between the binder and inorganic particles, as well as between inorganic particles. Furthermore, the metal ion groups in the binder, such as lithium sulfonate, can construct ion transport channels, improving the ionic conductivity of the battery and thus giving the battery excellent low-temperature performance. Simultaneously, the presence of hydrophilic groups such as carboxyl groups in these polymers enhances the wetting properties of the separator.

[0072] In some embodiments, the surface energy of the base film is greater than 45 mN / m.

[0073] Specifically, the surface energy of the base film can be any value of 45mN / m, 46mN / m, 47mN / m, 48mN / m, 49mN / m, or 50mN / m and above. By limiting the surface energy of the base film, a more reliable bond can be formed between the base film and the coating, preventing the base film and coating from peeling off due to the high temperature of the separator during battery charging and discharging, which would affect the battery's cycle performance. At the same time, the coating contains a hydrophilic binder, which, by limiting the surface energy of the base film, can enhance the chemical bonding force between the coating and the base film. This combination of physical and chemical effects results in a stronger interfacial bond between the base film and the coating. If the surface energy of the base film is less than the above range, it may affect the bonding force between the base film and the coating, thereby affecting the battery's capacity, cycle performance, and safety performance.

[0074] In some embodiments, the surface arithmetic mean roughness Ra of the base film is 5 nm to 50 nm.

[0075] Specifically, the arithmetic mean roughness Ra of the base film can be any one of 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, or 50nm, or any value between any two. By limiting the average roughness of the base film, it can be ensured that the coating can be firmly bonded to the surface of the base film, thereby improving the interfacial bonding force between the base film and the coating and making it less likely for the coating to peel off from the surface of the base film. If the roughness of the base film is less than the above range, the adhesion between the base film and the coating may become worse. If it is greater than the above range, the mechanical properties of the base film may decrease, and when coating the surface of the base film, the effective contact area between the base film and the coating may be reduced, which may reduce the adhesion between the base film and the coating.

[0076] In some embodiments, the thickness of the base film is 5 μm to 16 μm.

[0077] Specifically, the thickness of the base film can be any one of 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or 16μm, or any value between any two. By limiting the thickness of the base film, it can be ensured that the thickness of the separator is not too thick, so that the separator has good lithium-ion migration performance. If the base film is too thick, the lithium-ion migration performance may be reduced, and lithium ions may easily deposit on the separator to form lithium dendrites, increasing the risk of internal short circuit in the battery. If the base film is too thin, it may reduce the mechanical strength of the base film, making it easy to tear.

[0078] In some embodiments, the porosity of the base membrane is 30% to 50%.

[0079] Specifically, the porosity of the base membrane is any one of 30%, 31%, 32%, 35%, 40%, 45%, 48%, or 50%, or any value between any two. By limiting the porosity of the base membrane, good electrolyte wettability can be ensured, thereby enabling the battery to have excellent cycle performance and capacity. If the porosity of the base membrane is lower than the above range, the wettability of the separator may deteriorate, the ion transport channels of the separator may be reduced, and the impedance of the separator may be increased. If it is higher than the above range, the structural support performance of the separator may be insufficient, reducing the thermal stability of the separator.

[0080] In some embodiments, the Gurley value of the base membrane is 50 s / 100 mL to 200 s / 100 mL.

[0081] Specifically, the Gurley value of the base membrane can be any one of 50 s / 100 mL, 60 s / 100 mL, 70 s / 100 mL, 80 s / 100 mL, 90 s / 100 mL, 100 s / 100 mL, 120 s / 100 mL, 150 s / 100 mL, 180 s / 100 mL, or 200 s / 100 mL, or any value between any two. Similarly, by limiting the Gurley value of the base membrane, it can be ensured that the base membrane has good thermal stability while also having good electrolyte wetting properties, so as not to compromise between the wettability and thermal stability of the separator.

[0082] In some embodiments, the inorganic particles further include second ceramic particles, which include aluminum-containing ceramic particles, preferably at least one of alumina or boehmite.

[0083] The second ceramic particles include, but are not limited to, one or more of silicon dioxide, alumina, or boehmite. By adding these ceramic particles and mixing them with boron nitride to form a coating, the high-temperature resistance and thermal stability of the separator can be significantly improved, effectively suppressing thermal shrinkage of the separator at high temperatures. Simultaneously, it can also effectively improve the thermal conductivity of the separator, effectively preventing or delaying thermal runaway of the battery. Those skilled in the art will understand that the mixing ratio of boron nitride and inorganic particles can be adjusted by those skilled in the art using this invention; no specific limitations are made here, and all such adjustments are within the scope of protection of this invention.

[0084] In some embodiments, the polyacrylic polymer containing metal ion groups includes at least one of lithium polyacrylate, a copolymer of polyacrylic acid grafted with lithium sulfonic acid side chains, or a copolymer of polyacrylic acid grafted with lithium carboxylic acid side chains.

[0085] Polyacrylic acid polymers containing metal ion groups include, but are not limited to, one or more of lithium polyacrylate, copolymers of polyacrylic acid grafted with lithium sulfonic acid side chains, or copolymers of polyacrylic acid grafted with lithium carboxylic acid side chains. For example, lithium polyacrylate can be obtained by reacting polyacrylic acid with lithium hydroxide; copolymers of polyacrylic acid grafted with lithium sulfonic acid side chains can be obtained by reacting lithium sulfonate with polyacrylic acid under conditions initiated by benzoyl peroxide or similar initiators; of course, those skilled in the art can synthesize the above substances themselves, and no specific limitations are made here.

[0086] In some embodiments, the median particle size D of the second ceramic particles 50 The range is 100nm to 800nm.

[0087] Specifically, the median particle size D of the second ceramic particles 50 It can be any value between or within any one of 100nm, 110nm, 120nm, 200nm, 300nm, 500nm, 650nm, 700nm, or 800nm. The median particle size D of the second ceramic particles is used. 50 This ensures that the diaphragm has good porosity and mechanical properties. If the particle size of the ceramic particles is too large, it may increase the surface roughness of the diaphragm and affect its mechanical properties; if the particle size of the ceramic particles is too small, it may worsen the thermal stability of the diaphragm.

[0088] In some embodiments, the median particle size D of boron nitride 50 The wavelength range is 100nm to 1000nm, and a sheet-like structure is preferred.

[0089] Specifically, the median particle size D of boron nitride 50 It can be any value from 100nm, 150nm, 200nm, 300nm, 500nm, 600nm, 800nm, 900nm, or 1000nm, or any point between any two. Similarly, by limiting the median particle size D of boron nitride... 50 This ensures the diaphragm possesses excellent thermal stability, thermal conductivity, and mechanical properties. If the boron nitride particle size is too large, the mechanical properties of the diaphragm will deteriorate; if the boron nitride particle size is too small, the thermal conductivity of the diaphragm may deteriorate. In a preferred embodiment, using a plate-like boron nitride structure can better improve the thermal conductivity of the diaphragm.

[0090] In some embodiments, boron nitride accounts for 5% to 30% of the total weight of the particles.

[0091] Specifically, the weight of boron nitride can account for any one of 5%, 10%, 15%, 20%, 25%, or 30% of the total weight of the particles, or any value between any two. By limiting the weight percentage of boron nitride, the separator can be guaranteed to have good thermal stability while also having good thermal conductivity, thereby effectively avoiding or delaying thermal runaway of the battery.

[0092] In some embodiments, the weight of the second ceramic particles accounts for 70% to 95% of the total weight of the inorganic particles.

[0093] Specifically, the weight of the second ceramic particle can be any one of 70%, 75%, 80%, 85%, 90%, or 95% of the total weight of the inorganic particles, or any value between any two. Similarly, by limiting the weight percentage of the ceramic particles, the separator can be guaranteed to have good thermal stability while also having good thermal conductivity, thereby effectively avoiding or delaying thermal runaway of the battery.

[0094] In some embodiments, the coating thickness is 1 μm to 3 μm.

[0095] Specifically, the coating thickness can be any one of 1μm, 1.1μm, 1.2μm, 1.5μm, 2μm, 2.5 or 3μm, or any value between any two. By limiting the coating thickness, the membrane can be guaranteed to have good thermal stability and excellent adhesion between the base film and the coating. If the coating thickness is too thick, it may affect the ion transport performance of the membrane and its mechanical properties; if the coating thickness is too thin, it may degrade the thermal stability and thermal conductivity of the membrane.

[0096] In some embodiments, the peel strength between the base film and the coating is greater than 100 N / m.

[0097] The peel strength between the base film and the coating can be 100 N / m, 110 N / m, or 150 N / m and above. By limiting the peel strength between the base film and the coating, it can be ensured that the base film and the coating will not peel off from each other due to the high temperature of the battery, thereby affecting the cycle performance of the battery.

[0098] In some embodiments, the adhesive further includes an auxiliary agent, which includes at least one of a styrene-butadiene rubber (SBR) emulsion, an acrylate copolymer emulsion, or a polyurethane (PU) emulsion.

[0099] The additives include, but are not limited to, one or more of styrene-butadiene rubber (SBR) emulsions, acrylate copolymer emulsions, or polyurethane (PU) emulsions. By adding additives, the flexibility of the coating can be enhanced and its resistance to electrolyte swelling can be improved.

[0100] In some embodiments, the auxiliary agent comprises 5% to 40% of the total solid content of the adhesive. Specifically, the auxiliary agent may comprise any one or any value between 5%, 10%, 15%, 20%, 30%, or 40% of the total solid content of the adhesive.

[0101] In some embodiments, the binder further includes a modifier, which includes at least one of a fluorinated surfactant, a fluorinated acrylate copolymer emulsion, or a fluorinated silane coupling agent.

[0102] Modifiers include, but are not limited to, one or more of fluorinated surfactants, fluorinated acrylate copolymer emulsions, or fluorinated silane coupling agents. By adding modifiers, the wettability of the coating to the electrolyte can be improved.

[0103] In some embodiments, the modifier accounts for 1% to 10% of the total amount of the binder; specifically, the modifier accounts for any one or any value between any two of 1%, 1.01%, 1.1%, 1.5%, 2%, 5%, 8%, 9% or 10% of the total amount of the binder.

[0104] In some embodiments, the heat shrinkage rate MD of the diaphragm after holding at 150°C for 1 hour is less than 3%; and / or the heat shrinkage rate TD of the diaphragm after holding at 150°C for 1 hour is less than 3%.

[0105] Specifically, the thermal shrinkage rate (MD) and / or TD of the separator after being kept at 150°C for 1 hour can be 3%, 2.8%, or 2.5% or less. By limiting the thermal shrinkage rate of the separator after being kept at 150°C for 1 hour, the separator can be guaranteed to have excellent thermal stability. This ensures that the separator is not easily shrunk when high temperatures are generated during battery charging and discharging, and will not affect the battery's capacity, cycle performance, or safety performance.

[0106] In some embodiments, the ionic conductivity of the diaphragm after being wetted with electrolyte is greater than 1.0 mS / cm at 20°C to 25°C.

[0107] Specifically, the ionic conductivity of the separator after being wetted with electrolyte at room temperature can be 1.0 mS / cm, 2.2 mS / cm, or 2.3 mS / cm or higher. By limiting the ionic conductivity of the separator, it can be ensured that the separator still has good ion transport performance at low temperatures (around -20°C), thereby enabling the battery to have good low-temperature performance.

[0108] In some embodiments, the mass ratio of inorganic particles to binder is 1:0.01 to 0.1; specifically, the mass ratio of inorganic particles to binder can be any one of 1:0.01, 1:0.02, 1:0.05, 1:0.008, 1:0.009 or 1:0.1 or any ratio between any two.

[0109] [Membrane Preparation Method]

[0110] In other embodiments of the present invention, a method for preparing a diaphragm is also provided, comprising the following steps:

[0111] S101. Pre-treat the polyolefin membrane to obtain the base membrane.

[0112] Pretreatment includes, but is not limited to, APGD plasma treatment of polyolefin films. Pretreatment can ensure that the base film has a certain roughness and / or surface energy, thereby enabling a more robust bonding of the coating.

[0113] S102. Mix the inorganic particles and binder evenly to obtain a slurry.

[0114] When preparing the slurry, high-shear stirring, ball milling, or sand milling can be used to uniformly disperse inorganic particles in the binder.

[0115] S103. The slurry is placed on at least one surface in the thickness direction of the base film and dried to obtain the diaphragm; wherein the inorganic particles include at least boron nitride; and the binder includes a polyacrylic polymer containing metal ion groups.

[0116] In step S102, the obtained slurry is coated onto the surface of the base film obtained in step S101. The coating method can be microgravure coating or slot extrusion coating. After coating, drying is performed, which can be carried out by freeze drying or heat drying.

[0117] In some embodiments, the pretreatment includes APGD plasma treatment, in which the discharge gas includes an inert gas. In a preferred embodiment, the discharge gas further includes an active gas, which includes at least one of O2, H2, or NH3.

[0118] When APGD plasma is used to process polyolefin molds, the discharge gas includes inert or active gases such as helium, argon, or nitrogen. The active gases include, but are not limited to, one or more of O2, H2, or NH3.

[0119] In some embodiments, the discharge power density of the APGD plasma treatment is 0.5 W / cm². 2 ~10W / cm 2 The processing time is 0.1s to 5s.

[0120] The discharge power density of APGD plasma treatment can reach 0.5 W / cm². 2 1W / cm 2 2W / cm 2 5W / cm 2 8W / cm2 9W / cm 2 Or 10W / cm 2 The processing time can be any one of the following values, or any value between any two: 0.1s, 0.5s, 1s, 2s, 3s, 4s, or 5s. By limiting the discharge power density and processing time of the APGD plasma treatment, the roughness and surface energy of the base film can be ensured to reach a suitable range, thereby guaranteeing the overall performance of the membrane.

[0121] In some embodiments, the linear velocity of the APGD plasma treatment is 5 m / min to 60 m / min.

[0122] Specifically, the linear velocity of the APGD plasma treatment can be any one of 5 m / min, 10 m / min, 20 m / min, 30 m / min, 40 m / min, 50 m / min, or 60 m / min, or any value between any two. By limiting the linear velocity, the base film can have good roughness and surface energy, thereby achieving excellent adhesion to the coating after coating is applied.

[0123] In some embodiments, the solid content in the slurry is 20 wt% to 60 wt%.

[0124] Specifically, the solid content in the slurry can be any one of 20wt%, 30wt%, 40wt%, 50wt%, or 60wt%, or any value between any two. By limiting the solid content in the slurry, inorganic particles can be uniformly dispersed in the binder, thereby achieving a more uniform coating on the base film.

[0125] In some embodiments, the viscosity of the slurry is 100 mPa·s to 2000 mPa·s.

[0126] Specifically, the viscosity of the slurry can be any one of 100 mPa·s, 200 mPa·s, 300 mPa·s, 400 mPa·s, 500 mPa·s, 1000 mPa·s, 1500 mPa·s, 1800 mPa·s, or 2000 mPa·s, or any value between any two. By limiting the viscosity of the slurry, inorganic particles can be evenly dispersed, and the slurry can be coated more evenly. If the viscosity is too high, the inorganic particles may not be evenly dispersed, thus affecting the overall performance of the diaphragm, and the slurry may also be difficult to coat. If the viscosity is too low, the thermal stability of the diaphragm may be affected.

[0127] In some embodiments, the drying temperature is less than or equal to 120°C, and the drying is carried out using stepped temperature drying, with the first stepped temperature range being 50°C to 80°C and the second stepped temperature range being 80°C to 115°C.

[0128] The drying temperature can be 120℃, 115℃, or 110℃ or below, using a stepped temperature drying method. The first step temperature range is any value between 50℃, 60℃, 70℃, or 80℃, or any two of these values. The second step temperature range is any value between 80℃, 90℃, 100℃, or 115℃, or any two of these values. By limiting the drying temperature and method, it can be ensured that the separator will not crack during the drying process, and the coating will have good density and be crack-free. If the drying temperature is too high, the coating will crack, which will affect the performance of the battery.

[0129] [Battery]

[0130] In some embodiments of the present invention, a battery is also provided, comprising: the separator in any of the above embodiments.

[0131] In some embodiments, the battery includes a separator prepared by the method described in any of the above embodiments.

[0132] The battery also includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode active material included in the positive electrode can be lithium iron phosphate, ternary materials, etc.; the negative electrode active material included in the negative electrode can be graphite, silicon-based materials, etc.

[0133] Since the battery provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0134] The present application will be described in detail below with reference to the accompanying drawings and examples. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0135] Performance testing:

[0136] 1. Peel strength (180° peel test):

[0137] Cut a sample 15±0.5mm wide and 200mm long. Gradually attach the coated side of the diaphragm to the adhesive tape from one end, ensuring an adhesion length of approximately 75mm. Then, attach a 100mm long and 12.6mm wide strip of 3M transparent tape to the peeling surface of the diaphragm. Peel a 25mm section of the diaphragm from the folded end of the diaphragm onto the steel plate. Clamp one end of the steel plate in the jig of the tensile testing machine, and clamp the free end of the diaphragm in another jig. Peel continuously at a rate of 100mm / min. After the load jig has been operated, disregard the value obtained during the mechanical peeling of the first 25mm section of the diaphragm, and use the average peel force obtained for the next 50mm section as the peel force, which is then converted into peel strength.

[0138] 2. Heat shrinkage rate (150℃, 1h):

[0139] Cut 100mm × 100mm square diaphragm samples, marking the longitudinal and transverse directions. Place the cut diaphragms on an image analyzer and measure the longitudinal length as Lz0 and the transverse length as Lh0. Place the diaphragms between A4 paper and in the center of an oven, maintaining a temperature of 150℃ for 1 hour. After baking, measure the longitudinal length of the sample as Lz and the transverse length as Lh using the image analyzer. Calculate the longitudinal and transverse shrinkage rates of the diaphragm using the formula ΔLz=(Lz0-Lz) / Lz.

[0140] 3. Electrolyte (1M LiPF6 in EC / DEC / EMC = 1:1:1 vol%) contact angle:

[0141] First, pre-treat the substrate (clean and dry with acetone, deionized water, and ethanol). Under inert conditions (glove box or nitrogen protection), use a microsyringe to drop 5-10 μL of electrolyte onto the substrate. Calculate the static contact angle by fitting the droplet profile using a contact angle meter with the lying-drop method. For dynamic testing, different time points can be selected to analyze the spreading rate. Care must be taken to control water, oxygen, and temperature to prevent electrolyte evaporation. Each sample should be measured at least three times, and the average value should be taken.

[0142] 4. Room temperature ionic conductivity (AC impedance method):

[0143] Under a constant temperature environment of 25±1℃, immerse membrane samples with a diameter ≥15mm in 1M LiPF6 / EC-DMC electrolyte for 30 minutes to fully wet them. After draining, place them in a two-electrode test cell (stainless steel sheet or lithium sheet), ensuring close contact between the electrodes and the membrane. Apply an AC voltage of 5-10mV using an electrochemical workstation, and run the test for 10 minutes. 6 Impedance spectrum was obtained by scanning from Hz to 10-2Hz. The bulk resistance R of the diaphragm was extracted from the intersection of the semicircular arc and the real axis in the high-frequency region of the Nyquist plot. The conductivity was calculated according to σ=L / (R·S) (L is the diaphragm thickness and S is the electrode contact area).

[0144] 5. Battery performance:

[0145] The specific method involves using a mixture of LiFePO4, SP (conductive carbon black), and PVDF (weight ratio 96:2:2) as the positive electrode, and a mixture of artificial graphite, SP (conductive carbon black), CMC, and styrene-butadiene rubber (weight ratio 95:1.5:1.5:2) as the negative electrode. Tinci EL-01A electrolyte and the composite separator prepared above are selected. The lithium-ion battery is fabricated using a traditional stacking process, and its electrical performance is then tested.

[0146] Example 1

[0147] S11. A wet-process PE microporous membrane with a thickness of 7 μm, a porosity of 41%, and a Gurley value of 100 s / 100 mL (purchased from Hebei Jinli) was selected. The PE microporous membrane was subjected to APGD plasma treatment: the PE microporous membrane was fed into an atmospheric pressure glow discharge plasma treatment device, using an Ar / O2 (95:5 vol%) mixed gas as the discharge gas, a radio frequency power supply frequency of 13.56 MHz, and a power density set to 2 W / cm². 2 The processing linear velocity was 20 m / min. The surface energy after processing was measured to be 50 mN / m.

[0148] S12, Weigh 85 parts by weight of α-Al2O3 particles (D 50 =300nm, nearly spherical, purchased from Zhengzhou Zhonglv) and 10 parts by weight of h-BN particles (D 50 =400nm, flake-like); weigh 5 portions of lithium polyacrylate (M) grafted with lithium sulfonate groups. w ≈500kDa, sulfonic acid grafting rate of about 5mol%, laboratory-made) as binder; weigh 0.5 parts by weight of sodium polycarboxylate (purchased from Dow Chemical) as auxiliary binder; add the above solid components to an appropriate amount of deionized water so that the final slurry solid content is 40wt%, first perform high-speed stirring pre-dispersion for 30 minutes, then transfer to a zirconia bead mill for grinding for 2 hours until the slurry fineness is qualified; measure the slurry viscosity as approximately 500mPa·s.

[0149] S13. Using a microgravure coating machine, the above slurry is evenly coated on both sides of the APGD-treated PE microporous membrane, controlling the coating amount so that the dry film thickness on one side is approximately 2μm. The coated wet film is then dried sequentially through a three-stage hot air oven. The temperature of the first zone is set to 60℃, the temperature of the second zone is set to 90℃, and the temperature of the third zone is set to 110℃, with a total drying time of approximately 2 minutes. The membrane is then wound up to obtain the composite coated separator.

[0150] Example 2

[0151] Except for the following conditions, everything else is the same as in Example 1:

[0152] S12 and APGD plasma treatment: using a N2 / H2 (98:2 vol%) mixed gas, with a power density of 3 W / cm³. 2 The processing linear speed is 15 m / min, and the surface energy after processing is 48 mN / m.

[0153] S22, 75 parts by weight of boehmite (AlOOH, D 50 =500nm, sheet-like) and 20 parts by weight of h-BN particles (D 50 =600nm, flake-like); the binder is 3 parts by weight of lithium polyacrylate and the auxiliary agent is 2 parts by weight of SBR emulsion (solid content 50%); 0.3 parts by weight of perfluoroalkyl ether nonionic surfactant is added as a modifier; the slurry solid content is adjusted to 45wt% and the viscosity is about 800mPa·s.

[0154] S23, maximum drying temperature 115℃.

[0155] Example 3

[0156] Except for the following conditions, everything else is the same as in Example 1:

[0157] S31. A wet-process PE microporous membrane with a thickness of 7 μm, a porosity of 41%, and a Gurley value of 100 s / 100 mL (purchased from Hebei Jinli) was selected. The PE microporous membrane was subjected to APGD plasma treatment: the PE microporous membrane was fed into an atmospheric pressure glow discharge plasma treatment device, using an Ar / O2 (95:5 vol%) mixed gas as the discharge gas, a radio frequency power supply frequency of 13.56 MHz, and a power density set to 2 W / cm². 2 The processing linear velocity was 20 m / min. The surface energy after processing was measured to be 50 mN / m.

[0158] S32, 90 parts by weight of α-Al2O3 particles (D 50 =200nm, near spherical) and 5 parts by weight of h-BN particles (D50=300nm, flake-like); the main binder is 6 parts by weight of partially lithium polyacrylic acid salt (LiPAA, neutralization degree about 30%, Mw≈600kDa), without additional grafting modification; no additional modifiers were added; the slurry solid content is 35wt%, and the viscosity is about 400mPa·s.

[0159] S33. Using a microgravure coating machine, the above slurry is evenly coated on both sides of the APGD-treated PE microporous membrane, controlling the coating amount so that the dry film thickness on one side is approximately 2μm. The coated wet film is then dried sequentially through a three-stage hot air oven. The temperature of the first zone is set to 60℃, the temperature of the second zone is set to 90℃, and the temperature of the third zone is set to 110℃, with a total drying time of approximately 2 minutes. The membrane is then wound up to obtain the composite coated separator.

[0160] Comparative Example 1

[0161] The difference between Comparative Example 1 and Example 1 is that the wet-process PE microporous membrane in Comparative Example 1 is not pretreated and the coating thickness is 3 μm.

[0162] Comparative Example 2

[0163] The only difference between Comparative Example 2 and Example 1 is that the binder used is ordinary unmodified sodium polyacrylate (PAA-Na), and no h-BN particles are added (only 95 parts of Al2O3 are used).

[0164] Table 1. Test Data

[0165]

[0166]

[0167] As can be seen from the comparison between the examples and comparative examples, the present invention adopts an APGD plasma treatment combined with a specific water-based composite ceramic coating (containing BN and modified PAA-Li binder), which can significantly improve the adhesion between the coating and the base film, enhance the thermal stability, thermal conductivity, ionic conductivity and electrolyte wettability of the separator, and thus improve the overall electrochemical performance of the lithium-ion battery.

[0168] The reagents, instruments, and materials used in this invention are all commercially available. The parts of this invention not described in detail are techniques well-known to those skilled in the art.

[0169] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0170] It should be noted that the terms "and / or" or " / " used herein are merely descriptions of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The singular forms "a," "described," and "the" used in the embodiments of the invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0171] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0172] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A diaphragm, characterized in that, include: A base film, and a coating disposed on at least one surface of the base film in the thickness direction; The base film comprises a polyolefin; the coating comprises an adhesive and inorganic particles; The inorganic particles include at least a first ceramic particle, which includes boron nitride; the binder includes a polyacrylic polymer containing metal ion groups.

2. The diaphragm according to claim 1, characterized in that, Satisfying at least one of features (1) to (5): (1) The surface energy of the base film is greater than 45 mN / m; (2) The surface arithmetic mean roughness Ra of the base film is 5 nm to 50 nm; (3) The thickness of the base film is 5μm to 16μm; (4) The porosity of the base film is 30% to 50%; (5) The Gurley value of the base membrane is 50s / 100mL to 200s / 100mL.

3. The diaphragm according to claim 1, characterized in that, The inorganic particles also include second ceramic particles, which include aluminum-containing ceramic particles, preferably at least one of alumina or boehmite. And / or, the polyacrylic polymer containing metal ion groups includes at least one of lithium polyacrylate, a copolymer of polyacrylic acid grafted with lithium sulfonic acid side chains, or a copolymer of polyacrylic acid grafted with lithium carboxylic acid side chains.

4. The diaphragm according to claim 3, characterized in that, Satisfying at least one of features (1) to (4): (1) The median particle size D of the second ceramic particles 50 The range is 100nm to 800nm; (2) The median particle size D of the boron nitride 50 The wavelength range is 100nm to 1000nm, preferably a sheet-like structure; (3) The weight of the boron nitride accounts for 5% to 30% of the total weight of the inorganic particles; (4) The weight of the second ceramic particle accounts for 70% to 95% of the total weight of the inorganic particles.

5. The diaphragm according to claim 1, characterized in that, The thickness of the coating is 1μm to 3μm; And / or, the peel strength between the base film and the coating is greater than 100 N / m.

6. The diaphragm according to claim 1, characterized in that, Satisfying at least one of features (1) to (2): (1) The adhesive further includes an auxiliary agent, which includes at least one of styrene-butadiene rubber latex, acrylate copolymer latex or polyurethane latex; And / or, the auxiliary agent accounts for 5% to 40% of the total solid content of the adhesive; (2) The adhesive further includes a modifier, which includes at least one of a fluorinated surfactant, a fluorinated acrylate copolymer emulsion, or a fluorinated silane coupling agent; And / or, the modifier accounts for 1% to 10% of the total amount of the binder.

7. The diaphragm according to claim 1, characterized in that, Satisfying at least one of features (1) to (3): (1) The heat shrinkage rate (MD) of the diaphragm after being kept at 150°C for 1 hour is less than 3%; (2) The heat shrinkage rate TD of the diaphragm after being kept at 150°C for 1 hour is less than 3%; (3) The ionic conductivity of the diaphragm after being wetted with electrolyte is greater than 1.0 mS / cm at 20℃~25℃.

8. A method for preparing a diaphragm, characterized in that, Includes the following steps: The polyolefin membrane is pretreated to obtain the base membrane; Inorganic particles and binder are mixed evenly to obtain a slurry; The slurry is placed on at least one surface in the thickness direction of the base film and dried to obtain the diaphragm. The inorganic particles include at least boron nitride; the binder includes a polyacrylic polymer containing metal ion groups.

9. The method for preparing the diaphragm according to claim 8, characterized in that, Satisfying at least one of features (1) to (5): (1) The pretreatment includes APGD plasma treatment, in which the discharge gas includes an inert gas; The discharge gas also includes an active gas, which includes at least one of O2, H2 or NH3; And / or, the discharge power density of the APGD plasma treatment is 0.5 W / cm². 2 ~10W / cm 2 The processing time is 0.1s to 5s; And / or, the linear velocity of the APGD plasma treatment is 5 m / min to 60 m / min; (2) The solid content in the slurry is 20wt% to 60wt%; (3) The viscosity of the slurry is 100 mPa·s to 2000 mPa·s; (4) The drying temperature is less than or equal to 120°C, and the drying adopts stepped temperature drying, with the first stepped temperature range being 50°C to 80°C and the second stepped temperature range being 80°C to 115°C. (5) The mass ratio of the inorganic particles to the binder is 1:(0.01~0.1).

10. A battery, characterized in that, The membrane includes the membrane according to any one of claims 1 to 7; and / or the membrane prepared by the preparation method according to claim 8 or 9.

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