Composite diaphragm as well as preparation method and application thereof

Abstract

The invention discloses a composite diaphragm and a preparation method and application thereof. The composite diaphragm comprises a diaphragm matrix; the functional layer is positioned on at least one side of the diaphragm base body, the functional layer comprises a fiber material, and the length-diameter ratio of the fiber material is (10: 1)-(5000: 1). By introducing the fiber material into the functional layer, the electrolyte infiltration rate of the composite diaphragm can be effectively improved, so that the cycle life of the battery is effectively prolonged.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of batteries, and particularly relates to a composite diaphragm and a preparation method and application thereof. BACKGROUND

[0002] The diaphragm is an indispensable part in a battery, which serves as an ion transmission channel and has good electronic insulation, so as to avoid the risk of thermal runaway caused by short circuit contact of the positive and negative electrodes. The characteristics of the diaphragm directly affect the power density, energy density, cycle stability and safety of the battery. The existing diaphragm (such as a commercial polyolefin diaphragm) has excellent mechanical and chemical stability, and has been widely used in lithium ion batteries. However, the existing diaphragm has poor wettability, resulting in poor cycle life of the battery, which needs to be further improved. SUMMARY

[0003] The present application aims to at least solve one of the technical problems in the related art. To this end, the present application aims to propose a composite diaphragm and a preparation method and application thereof. The present application can effectively improve the electrolyte wettability of the composite diaphragm by introducing a fiber material into the functional layer, thereby effectively improving the cycle life of the battery.

[0004] In one aspect of the present application, the present application proposes a composite diaphragm. According to embodiments of the present application, the composite diaphragm comprises:

[0005] a diaphragm substrate;

[0006] a functional layer located on at least one side of the diaphragm substrate, the functional layer comprising a fiber material;

[0007] The aspect ratio of the fiber material is 10:1-5000:1.

[0008] The composite diaphragm according to the embodiments of the present application can effectively enhance the capillary-adsorption effect of the functional layer on the electrolyte by introducing a fiber material into the functional layer, thereby enhancing the large-scale connectivity of the electrolyte in the transverse / longitudinal direction of the composite diaphragm, and further effectively improving the liquid retention capacity and electrolyte wettability of the composite diaphragm, thereby effectively improving the cycle life of the battery.

[0009] In addition, the composite diaphragm according to the above embodiments of the present application can also have the following additional technical features:

[0010] In some embodiments of the present application, the fiber material comprises at least one of aramid fiber, polyacrylonitrile fiber, metal organic framework compound-based composite fiber, carbon-based fiber, ceramic fiber and nanocellulose, preferably at least one of aramid fiber, polyacrylonitrile fiber, metal organic framework compound-based composite fiber, ceramic fiber and nanocellulose.

[0011] In some embodiments of this application, the fiber material accounts for 2 wt% to 50 wt% of the mass of the functional layer, preferably 5 wt% to 20 wt%.

[0012] In some embodiments of this application, the diameter of the fiber material is 0.02 μm to 1 μm; and / or, the aspect ratio of the fiber material is 100:1 to 500:1.

[0013] In some embodiments of this application, the functional layer further includes inorganic ceramic material, wherein the inorganic ceramic material accounts for 35wt% to 90wt% of the mass of the functional layer.

[0014] In some embodiments of this application, the inorganic ceramic material includes at least one of alumina, boehmite, silicon dioxide, magnesium hydroxide, titanium dioxide, and zirconium oxide.

[0015] In some embodiments of this application, the functional layer further includes an adhesive, wherein the adhesive accounts for 5 wt% to 15 wt% of the functional layer by mass.

[0016] In some embodiments of this application, the adhesive includes at least one of polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, polyacrylic acid, polyacrylonitrile, and styrene-butadiene rubber.

[0017] In some embodiments of this application, the membrane substrate includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, and nonwoven fabric.

[0018] In some embodiments of this application, the thickness of the functional layer on one side of the diaphragm substrate is 1.3 μm to 8 μm; and / or, the thickness of the diaphragm substrate is 3 μm to 30 μm.

[0019] In a second aspect, this application provides a method for preparing the aforementioned composite diaphragm. According to an embodiment of this application, the method includes:

[0020] The fiber material and solvent are mixed to obtain a mixed slurry.

[0021] The mixed slurry is coated on at least one side of the membrane substrate and dried to obtain a composite membrane.

[0022] The method for preparing the composite separator according to the embodiments of this application is simple to implement and easily industrialized. Furthermore, the composite separator prepared by this method exhibits excellent wetting ability with the electrolyte, thereby effectively improving the cycle life of the battery.

[0023] In addition, the method for preparing the composite separator according to the above-mentioned embodiments of the present application can further have the following additional technical features.

[0024] In some embodiments of the present application, the mixed slurry further comprises at least one of inorganic ceramic material, binder, dispersant.

[0025] In a third aspect of the present application, a battery is provided. According to embodiments of the present application, the battery comprises the electrode sheet and the composite separator according to the above-mentioned embodiments or prepared by the method according to the above-mentioned embodiments. Thus, the cycle performance of the battery can be effectively improved.

[0026] In a fourth aspect of the present application, a battery pack is provided. According to embodiments of the present application, the battery pack comprises the composite separator according to the above-mentioned embodiments or prepared by the method according to the above-mentioned embodiments or the battery according to the above-mentioned embodiments. Thus, the cycle performance of the battery pack can be effectively improved.

[0027] In a fifth aspect of the present application, an electric device is provided. According to embodiments of the present application, the electric device comprises the composite separator according to the above-mentioned embodiments or prepared by the method according to the above-mentioned embodiments or the battery according to the above-mentioned embodiments or the battery pack according to the above-mentioned embodiments. Thus, the electric device has the advantages of the battery, which are not repeated here.

[0028] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0029] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings, wherein:

[0030] Figure 1 Structure diagram of the composite separator according to some embodiments of the present application.

[0031] REFERENCE NUMERALS

[0032] 10 - composite separator, 11 - separator substrate, 12 - functional layer. DETAILED DESCRIPTION

[0033] Embodiments of the present application are described in detail below with reference to the attached drawings, wherein the same or similar components have the same or similar designations throughout the various figures and like reference numerals designate corresponding or like components. The embodiments described below are illustrative of the present application and are not intended to be limiting thereof.

[0034] The existing separators (such as commercial polyolefin separators, etc.) have excellent mechanical and chemical stability, and have been widely used in lithium ion batteries. Generally, a coating layer is provided on the surface of the separator to improve the thermal stability of the battery, etc., but the wettability of the existing separator is still poor and needs to be further improved. The wettability of the separator with different coating layers is different, and the electrolyte diffusion in the transverse / longitudinal direction of the entire separator is blocked by the local aggregation of the coating material, which exacerbates the poor electrolyte wettability problem, causing the internal part of the large-size battery to be short of liquid, thereby causing the performance of the battery to deteriorate.

[0035] Therefore, in one aspect of the present application, a composite separator 10 is provided. According to embodiments of the present application, referring to the accompanying drawings, Figure 1 The composite separator 10 includes: a separator substrate 11; a functional layer 12, the functional layer 12 is located on at least one side of the separator substrate 11, the functional layer 12 includes a fiber material, the fiber material has an aspect ratio of 10:1-5000:1 (for example, it can be 10:1, 50:1, 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, 1000:1, 1500:1, 2000:1, 2500:1, 3000:1, 3500:1, 4000:1, 4500:1, 5000:1 or any range between any two of them). Thus, by introducing the fiber material into the functional layer, the present application can effectively improve the electrolyte wettability rate of the composite separator, thereby effectively improving the cycle life of the battery.

[0036] The principle of the composite separator provided by the present application to achieve the above beneficial effects is described in detail as follows:

[0037] By introducing the fiber material into the functional layer, the present application can effectively enhance the capillary-adsorption effect of the functional layer on the electrolyte, thereby enhancing the large-scale connectivity of the electrolyte in the transverse / longitudinal direction of the composite separator, and further effectively improving the liquid retention capacity and electrolyte wettability rate of the composite separator, especially the holding and re-adsorption capacity of the electrolyte by the electrode core in the large battery.

[0038] In addition, by limiting the aspect ratio of the fiber material to a range of 10:1 to 5000:1, the application can construct an efficient capillary network. In particular, for large-capacity and large-size batteries, a continuous capillary network can be formed in the region, and electrolyte can quickly penetrate along the fiber axis by capillary action. This structure also reduces the curvature of the electrolyte penetration path and improves the ability of the electrolyte to penetrate deeply in the large-size direction. Through high wettability and a more unobstructed electrolyte return path, the electrolyte wettability rate of the composite separator is further improved, thereby further improving the cycle life of the battery. The inventors have found that if the aspect ratio of the fiber material is too large or too small, the electrolyte wettability rate of the composite separator cannot be effectively improved, thereby the cycle life of the battery cannot be effectively improved.

[0039] According to some embodiments of the application, the fiber material includes at least one of aramid fiber, polyacrylonitrile fiber, metal organic framework (MOFs) based composite fiber (e.g., ZIF-8 (Zn-2-methylimidazole) based composite fiber), carbon-based fiber, ceramic fiber, and nanocellulose. Thus, the above-mentioned types of fiber materials can further ensure the capillary-adsorption effect of the reinforcing functional layer on the electrolyte, thereby further ensuring the large-range connectivity of the electrolyte in the transverse / longitudinal direction of the reinforcing composite separator, and further ensuring the improvement of the liquid retention capacity and the electrolyte wettability rate of the composite separator. Preferably, at least one of aramid fiber, polyacrylonitrile fiber, metal organic framework based composite fiber, ceramic fiber, and nanocellulose. By introducing at least one of aramid fiber, polyacrylonitrile fiber, metal organic framework based composite fiber, ceramic fiber, and nanocellulose into the functional layer, the wettability of the composite separator to the electrolyte can be further improved, thereby further improving the cycle life of the battery.

[0040] In embodiments of the present application, Aramid Fiber is a high-performance synthetic fiber, the full name is aramid fiber, because its molecular chain contains benzene ring and amide bond (-CONH-). Polyacrylonitrile fiber (PAN fiber) is a synthetic fiber made of acrylonitrile (CH2=CH-CN) as the main monomer (mass content ≥ 85%), through free radical polymerization to obtain polyacrylonitrile resin, and then wet or dry spinning. Carbon-based fiber refers to a one-dimensional material with carbon element as the main skeleton, fiber form and micron-level diameter. Ceramic fiber is a kind of inorganic non-metallic oxide or nitride, carbide as the main component, through melt spinning, sol-gel spinning or precursor transformation process to make fiber-shaped light weight high temperature resistant material. Nanocellulose refers to a class of nanoscale fibers or crystals with size ≤100nm in at least one dimension, and composed of cellulose molecular chain (C6H 10 O5) n Metal-organic framework compound-based composite fiber is a material formed by effectively combining metal-organic framework compounds (MOFs) and fiber-forming substrates.

[0041] In embodiments of the present application, the preparation method of the above-mentioned metal-organic framework compound (MOFs) based composite fiber is not particularly limited, and as some specific embodiments, the above-mentioned method is as follows: mixing MOFs precursor solution and polymer solution (such as polyacrylonitrile-PAN solution, polyvinyl alcohol-PVA solution, etc.), and then preparing metal-organic framework compound (MOFs) based composite fiber through electrospinning process. As some other specific embodiments, the above-mentioned method is as follows: introducing groups as MOFs nucleation active sites on the formed fibers through chemical modification method (such as alkali treatment, chemical grafting, etc.), and then preparing metal-organic framework compound (MOFs) based composite fiber by coordination with metal ions.

[0042] According to still some specific embodiments of the present application, the mass percentage of the fiber material in the functional layer is 2wt%~50wt%, for example, it can be 2wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt% or any range between any two of them, thus, by limiting the mass percentage of the fiber material in the functional layer within the above range, the capillary-adsorption effect of the enhanced functional layer on the electrolyte can be further ensured, thereby further ensuring the large-scale communication ability of the electrolyte in the transverse / longitudinal direction of the composite diaphragm, and further ensuring the improvement of the liquid retention capacity and the electrolyte infiltration rate of the composite diaphragm. Preferably, the mass percentage of the fiber material in the functional layer is 5wt%~20wt%, thus, when the mass percentage of the fiber material in the functional layer is within the range of 5wt%~20wt%, the infiltration ability of the composite diaphragm on the electrolyte can be further improved, thereby further improving the cycle life of the battery.

[0043] According to still some specific embodiments of the present application, the tube diameter of the fiber material is 0.02μm~1μm, for example, it can be 0.02μm, 0.05μm, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm or any range between any two of them, by limiting the tube diameter of the fiber material within the above range, the capillary effect can be effectively utilized to form a retention layer on the diaphragm with good adsorption and retention capacity, thereby effectively improving the charge-discharge performance and cycle performance of the battery.

[0044] According to still some specific embodiments of the present application, the aspect ratio of the fiber material is 100:1~500:1, for example, it can be 100:1, 200:1, 300:1, 400:1, 500:1 or any range between any two of them, by limiting the aspect ratio of the fiber material within the above range, the fiber material has better mechanical strength and toughness, which helps the diaphragm to remain stable during the expansion and contraction of the battery during charging and discharging, reducing the damage and deformation of the diaphragm; at the same time, the fiber material within the above aspect ratio range can form longer capillary tubes, which helps the electrolyte to quickly infiltrate and distribute on a larger scale, thereby improving the charge-discharge performance and cycle performance of the battery. This rapid infiltration ability is particularly important for large-size batteries, as it can reduce the electrolyte from being squeezed out of the pole core during charging and returning to the pole core faster during discharging.

[0045] According to still some specific embodiments of the present application, the functional layer further comprises inorganic ceramic material, which can effectively improve the thermal stability of the composite separator. Further, the mass percentage of the inorganic ceramic material in the functional layer is 35wt% to 90wt%, for example, can be 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt% or any range between any two of them, by limiting the mass percentage of the inorganic ceramic material in the functional layer within the above range, the thermal stability of the composite separator can be further improved.

[0046] In the embodiments of the present application, the specific type of the inorganic ceramic material is not particularly limited, and those skilled in the art can select according to actual needs. As some preferred solutions, the inorganic ceramic material comprises at least one of alumina, boehmite, magnesium hydroxide, silicon dioxide, titanium dioxide, and zirconium oxide, which can further improve the thermal stability of the composite separator. More preferably, alumina, by introducing alumina into the functional layer, the thermal stability of the composite separator can be further improved.

[0047] According to still some specific embodiments of the present application, the functional layer further comprises a binder, which can improve the adhesion of the functional layer, so that the functional layer can be stably located on the surface of the separator substrate, and avoid the functional layer from falling off the separator substrate. Further, the mass percentage of the binder in the functional layer is 5wt% to 15wt%, for example, can be 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt% or any range between any two of them, thereby, by limiting the mass percentage of the binder in the functional layer within the above range, the adhesion of the functional layer can be further improved, so that the functional layer can be stably located on the surface of the separator substrate, and further avoid the functional layer from falling off the separator substrate.

[0048] In the embodiments of the present application, the specific type of the binder is not particularly limited, and those skilled in the art can select according to actual needs. As some preferred solutions, the binder comprises at least one of polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, polyacrylic acid, polyacrylonitrile and styrene butadiene rubber, which can effectively ensure the adhesion of the functional layer, so that the functional layer can be stably located on the surface of the separator substrate.

[0049] In the present application, the type of fiber material in the functional layer on the composite separator, the tube diameter and the aspect ratio of the fiber material, and the mass percentage of each component in the functional layer can be determined by using instruments and methods known in the art. Specifically, the composite separator of the finished product battery can be sampled, and whether there is a fibrous material in the functional layer on the surface of the separator can be observed by electron microscopy such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the tube diameter and length of the fibrous material can be measured. Randomly test several groups (for example, 20 groups) of data, and take the average value, that is, the tube diameter and the aspect ratio can be obtained.

[0050] For the type of each component in the functional layer, the functional layer on the surface of the separator can be sampled by scraping, combined with ultrasonic separation, and the corresponding components can be measured by using a thermogravimetric analyzer (TGA), an elemental analyzer, and other means. Generally, the binder is decomposed and lost at about 400°C, the aramid fiber is decomposed and lost at about 500°C-600°C, the polyacrylonitrile fiber is decomposed and lost at about 250°C-350°C, the decomposition temperature of the metal organic framework (MOFs) based composite fiber varies depending on the type (usually 300°C-500°C), and the decomposition temperature of the inorganic ceramic material is generally above 800°C. In addition, for the nitrogen (N) element in the aramid fiber and the polyacrylonitrile fiber, the nitrogen content can be determined by an elemental analyzer, and the special metal component of the metal organic framework (MOFs) based composite fiber can be calculated according to the corresponding weight. The specific description is as follows: ① The functional layer on the surface of the separator is sampled by scraping, and the corresponding fiber sample is obtained by ultrasonic separation in a solvent, and the type and elemental composition of the fiber are confirmed by TGA and elemental analyzer; ② The functional layer sample is taken again, dried, and then the mass percentage of each component is calculated by calculating the loss at each stage by TGA method, such as multiple components, combined with elemental analysis and the type in ①, and the weight and proportion of different fibers are calculated. In addition, the inorganic ceramic material is the residual mass in TGA, and the residual above 800°C is the inorganic ceramic material.

[0051] In the embodiments of the present application, the specific type of the above-mentioned separator substrate is not particularly limited, and those skilled in the art can select according to actual needs. As some preferred schemes, the separator substrate includes at least one of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), and non-woven fabric.

[0052] According to still another specific embodiment of the present application, the thickness of the functional layer on one side of the separator substrate is 1.3 μm-8 μm, for example, it can be 1.3 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm or any range between any two of them. By limiting the thickness of the functional layer on one side of the separator substrate within the above range, the performance of the above-mentioned functional layer can be further ensured.

[0053] According to some specific embodiments of the present application, the thickness of the diaphragm substrate is 3-30 μm, for example, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm or any range between any two of them. By limiting the thickness of the diaphragm substrate within the above range, the mechanical strength of the composite diaphragm can be ensured.

[0054] In the second aspect of the present application, a method for preparing the composite diaphragm is provided. According to embodiments of the present application, the method comprises:

[0055] S100: mixing the fiber material and the solvent to form a mixed slurry;

[0056] According to some specific embodiments of the present application, the mixed slurry further comprises at least one of inorganic ceramic material, binder and dispersant. The inorganic ceramic material can effectively improve the thermal stability of the composite diaphragm; the binder can improve the adhesion of the functional layer, so that the functional layer can be stably located on the surface of the diaphragm substrate, avoiding the functional layer from falling off the diaphragm substrate; and the dispersant can improve the dispersibility of the materials, so that the raw materials can be mixed more uniformly.

[0057] Specifically, the inorganic ceramic material and the fiber material can be mixed in a certain proportion, and then an appropriate amount of binder, dispersant and solvent can be added, and the mixture can be stirred and ultrasonicated to form a mixed slurry.

[0058] In embodiments of the present application, the specific type of the solvent is not particularly limited, and can be selected by those skilled in the art according to actual needs. As some preferred solutions, the solvent comprises at least one of water, N-methyl pyrrolidone (NMP), ethanol and acetone.

[0059] In embodiments of the present application, the specific type of the dispersant is not particularly limited, and can be selected by those skilled in the art according to actual needs. As some preferred solutions, the dispersant comprises at least one of sodium carboxymethyl cellulose, polyvinylpyrrolidone, sodium dodecyl sulfate and sodium dodecyl benzene sulfonate.

[0060] S200: coating the mixed slurry on at least one side of the diaphragm substrate, and drying to obtain the composite diaphragm.

[0061] In this step, the mixed slurry in step S100 can be coated on the diaphragm substrate by using a conventional film coating machine or a roll coating, spraying machine, and vacuum drying at a certain temperature to remove the solvent to obtain the composite diaphragm.

[0062] The method for preparing the composite separator according to the embodiments of the present application is simple and easy to implement, and can be easily industrialized. Meanwhile, the method can effectively enhance the capillary-adsorption effect of the functional layer on the electrolyte by adding the fiber material in the mixed slurry, thereby enhancing the large-range connectivity of the electrolyte in the transverse / longitudinal direction of the composite separator, and further effectively improving the liquid retention capacity and the electrolyte wetting rate of the composite separator, especially the holding and re-adsorption capacity of the electrolyte by the pole core in a large battery.

[0063] In a third aspect of the present application, a battery is provided. According to the embodiments of the present application, the battery includes the pole piece and the composite separator of the above embodiments or includes the composite separator prepared by the method of the above embodiments. Thus, the cycle performance of the battery can be effectively improved.

[0064] The battery includes a positive pole piece, a negative pole piece, and an electrolyte, and the composite separator is located between the positive pole piece and the negative pole piece. The specific type of the battery is not particularly limited, including but not limited to a lithium ion battery, a sodium ion battery, a potassium ion battery, etc.

[0065] In some embodiments of the present application, the positive pole piece includes a positive current collector and a positive active material layer located on at least one side surface of the positive current collector, and the positive active material layer includes a positive active material.

[0066] In some embodiments of the present application, the positive current collector can include a metal foil or a composite positive current collector. For example, the metal foil can be an aluminum foil. The composite positive current collector can include a polymer material base layer and a metal layer formed on at least one side surface of the polymer material base layer, for example, the composite negative current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material base material (such as a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0067] For example, the positive current collector has two opposite surfaces in the thickness direction of itself, and the positive active material layer is located on any one or both of the two opposite surfaces of the positive current collector.

[0068] In some embodiments of the present application, the positive active material layer can include a positive active material, and the positive active material includes lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate LiFe 1-x M xat least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, and B, 0 < x < 0.6, for example, x is 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.3, 0.4, 0.5, 0.6, or a range between any two of them.

[0069] In some embodiments of the present application, the positive active material layer can further optionally include a positive conductive agent. As an example, the positive conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] In some embodiments of the present application, the positive active material layer can further optionally include a positive binder. As an example, the positive binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0071] In some embodiments of the present application, the above-described negative electrode sheet can include a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, the negative active material layer including a negative active material.

[0072] In some embodiments of the present application, the negative active material can employ a negative active material for a battery known in the art. As an example, the negative active material can include at least one of graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, and lithium titanate, etc. The silicon-based material can include at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can include at least one of elemental tin, a tin oxide compound, and a tin alloy.

[0073] In some embodiments of the present application, the negative current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.

[0074] In some embodiments of the present application, the negative active material layer further optionally comprises a negative binder. The negative binder can comprise at least one of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0075] In some embodiments of the present application, the negative active material layer further optionally comprises a negative conductive agent. The negative conductive agent can comprise at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0076] In the embodiments of the present application, the above-mentioned battery further comprises an electrolyte, and the electrolyte comprises an electrolyte salt and a solvent, wherein the specific types and components of the electrolyte salt and the organic solvent are not particularly limited and can be selected according to actual needs.

[0077] In a fourth aspect of the present application, a battery pack is provided. According to the embodiments of the present application, the battery pack comprises the composite separator of the above embodiments or the composite separator prepared by the method of the above embodiments or the battery of the above embodiments. Thus, the cycle performance of the battery pack can be effectively improved.

[0078] In some embodiments, the battery pack can be a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0079] In some embodiments, the battery pack can be a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0080] In a fifth aspect of the present application, a power consuming device is provided. According to the embodiments of the present application, the power consuming device comprises the composite separator of the above embodiments or the composite separator prepared by the method of the above embodiments or the battery of the above embodiments or the battery pack of the above embodiments. Thus, the power consuming device has the above advantages of the battery, which will not be repeated here.

[0081] Specifically, the power consuming device can be, but is not limited to, a mobile phone, a tablet, a notebook computer, an electric toy, an electric tool, an electric car, an electric vehicle, a ship, a spacecraft, etc. The electric toy can include a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric plane toy, etc. The spacecraft can include an airplane, a rocket, a space shuttle, a spacecraft, etc.

[0082] The embodiments of the present application are described in detail below, it should be noted that the embodiments described below are exemplary, only for explaining the present application, and can not be understood as limiting the present application. In addition, if not specifically stated, all reagents used in the following examples are commercially available or can be synthesized according to the methods described herein or known methods, and the reaction conditions not listed are also readily available to those skilled in the art.

[0083] Example 1

[0084] 1) Preparation of composite separator

[0085] A separator substrate with a thickness of 9 μm (specifically, a PE-based film) is selected. The fiber material (specifically, aramid fiber with a tube diameter of 0.05 μm and an aspect ratio of 100:1) is mixed with inorganic ceramic material (specifically, aluminum oxide), binder (specifically, polyvinylidene fluoride PVDF) and solvent (specifically, N-methyl pyrrolidone NMP) to form a slurry, and then the slurry is coated on both sides of the above-mentioned PE-based film, and dried to remove the solvent, to form a composite separator. The weight of aramid fiber accounts for 10 wt% of the total mass of the coating (i.e. functional layer), the weight of aluminum oxide accounts for 80 wt% of the total mass of the coating, and the weight of the binder accounts for 10 wt% of the total mass of the coating. The thickness of the functional layer on one side of the above-mentioned composite separator is 3 μm.

[0086] 2) Preparation of positive electrode sheet

[0087] The positive electrode active material (specifically, LiFePO4), the positive electrode conductive agent (specifically, conductive carbon black), and the positive electrode binder (specifically, polyvinylidene fluoride PVDF) are added to N-methyl pyrrolidone (NMP) in a mass ratio of 96:2:2 to form a positive electrode slurry (the solid content in the positive electrode slurry is 56 wt%), and the positive electrode slurry is coated on the upper and lower surfaces of the aluminum foil and dried, then cold-pressed, and then edge-cut, cut into pieces, and divided into strips to form a positive electrode sheet.

[0088] 3) Preparation of negative electrode sheet

[0089] The negative electrode active material (specifically, graphite), the negative electrode conductive agent (specifically, conductive carbon black), the thickening agent (specifically, carboxymethyl cellulose CMC), and the negative electrode binder (specifically, butadiene rubber SBR) are added to deionized water in a mass ratio of 96.0:1.0:1.6:1.4 to form a negative electrode slurry (the solid content in the negative electrode slurry is 51 wt%), and the negative electrode slurry is coated on the upper and lower surfaces of the copper foil and dried, then cold-pressed, edge-cut, cut into pieces, and divided into strips to form a negative electrode sheet.

[0090] 4) Preparation of electrolyte

[0091] In the glove box filled with argon, LiPF6 was slowly added into the solvent (volume ratio of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate was 1:1:1), mixed uniformly, and the electrolyte with lithium salt concentration of 1 mol / L was obtained after the lithium salt was completely dissolved.

[0092] 5) Assembling the battery

[0093] The positive electrode sheet, the composite separator and the negative electrode sheet were stacked in sequence, the composite separator was between the positive and negative electrode sheets to play a role of isolating the positive and negative electrodes, the bare battery cell was obtained by winding, the tab was welded, the bare battery cell was placed in the outer package, the electrolyte prepared above was injected into the dried battery cell, and the lithium ion battery was prepared after packaging, standing, formation, shaping and the like.

[0094] Example 2

[0095] The preparation method of this example was basically the same as that of example 1, and the only difference was that:

[0096] 1) Preparation of composite separator

[0097] The inorganic ceramic material alumina was replaced by bormite.

[0098] Example 3

[0099] The preparation method of this example was basically the same as that of example 1, and the only difference was that:

[0100] 1) Preparation of composite separator

[0101] The tube diameter of aramid fiber was 0.7 μm, and the aspect ratio was 100:1.

[0102] Example 4

[0103] The preparation method of this example was basically the same as that of example 1, and the only difference was that:

[0104] 1) Preparation of composite separator

[0105] The tube diameter of aramid fiber was 1 μm, and the aspect ratio was 100:1.

[0106] Example 5

[0107] The preparation method of this example was basically the same as that of example 1, and the only difference was that:

[0108] 1) Preparation of composite separator

[0109] The tube diameter of aramid fiber was 0.02 μm, and the aspect ratio was 100:1.

[0110] Example 6

[0111] The preparation method of this example was basically the same as that of example 1, and the only difference was that:

[0112] 1) Preparation of composite separator

[0113] The fiber material aramid fiber is replaced by polyacrylonitrile fiber.

[0114] Example 7

[0115] The preparation method of this example is basically the same as that of Example 1, the difference is only that:

[0116] 1) Preparation of composite separator

[0117] The fiber material aramid fiber is replaced by metal organic framework compound-based composite fiber (specifically ZIF-8 (Zn-2-methylimidazole) based composite fiber).

[0118] Example 8

[0119] The preparation method of this example is basically the same as that of Example 1, the difference is only that:

[0120] 1) Preparation of composite separator

[0121] The fiber material aramid fiber is replaced by carbon-based fiber.

[0122] Example 9

[0123] The preparation method of this example is basically the same as that of Example 1, the difference is only that:

[0124] 1) Preparation of composite separator

[0125] The fiber material aramid fiber is replaced by ceramic fiber.

[0126] Example 10

[0127] The preparation method of this example is basically the same as that of Example 1, the difference is only that:

[0128] 1) Preparation of composite separator

[0129] The fiber material aramid fiber is replaced by nanocellulose.

[0130] Example 11

[0131] The preparation method of this example is basically the same as that of Example 1, the difference is only that:

[0132] 1) Preparation of composite separator

[0133] The weight of aramid fiber accounts for 2% of the total mass of the dried coating (i.e. functional layer), the weight of aluminum oxide accounts for 85wt% of the total mass of the dried coating, and the weight of the binder accounts for 13wt% of the total mass of the dried coating.

[0134] Example 12

[0135] The preparation method of this example is basically the same as that of Example 1, the only difference being that:

[0136] 1) Preparation of composite separator

[0137] The weight of aramid fiber accounts for 5% of the total mass of the dried coating (i.e. functional layer), the weight of aluminum oxide accounts for 90% of the total mass of the dried coating, and the weight of the binder accounts for 5% of the total mass of the dried coating.

[0138] Example 13

[0139] The preparation method of this example is basically the same as that of Example 1, the only difference being that:

[0140] 1) Preparation of composite separator

[0141] The weight of aramid fiber accounts for 20% of the total mass of the dried coating (i.e. functional layer), the weight of aluminum oxide accounts for 72% of the total mass of the dried coating, and the weight of the binder accounts for 8% of the total mass of the dried coating.

[0142] Example 14

[0143] The preparation method of this example is basically the same as that of Example 1, the only difference being that:

[0144] 1) Preparation of composite separator

[0145] The weight of aramid fiber accounts for 50% of the total mass of the dried coating (i.e. functional layer), the weight of aluminum oxide accounts for 35% of the total mass of the dried coating, and the weight of the binder accounts for 15% of the total mass of the dried coating.

[0146] Example 15

[0147] The preparation method of this example is basically the same as that of Example 1, the only difference being that:

[0148] 1) Preparation of composite separator

[0149] The diameter of the aramid fiber is 0.05 μm, and the aspect ratio is 10:1.

[0150] Example 16

[0151] The preparation method of this example is basically the same as that of Example 1, the only difference being that:

[0152] 1) Preparation of composite separator

[0153] The diameter of the aramid fiber is 0.05 μm, and the aspect ratio is 500:1.

[0154] Example 17

[0155] The preparation method of this example is basically the same as that of Example 1, the only difference being that:

[0156] 1 ) Preparation of composite separator

[0157] The aramid fibers have a tube diameter of 0.05 μm and an aspect ratio of 1000:1.

[0158] Example 18

[0159] The preparation method of this example is essentially the same as that of Example 1, with the exception that:

[0160] 1 ) Preparation of composite separator

[0161] The aramid fibers have a tube diameter of 0.05 μm and an aspect ratio of 3000:1.

[0162] Example 19

[0163] The preparation method of this example is essentially the same as that of Example 1, with the exception that:

[0164] 1 ) Preparation of composite separator

[0165] The aramid fibers have a tube diameter of 0.05 μm and an aspect ratio of 5000:1.

[0166] Comparative Example 1

[0167] The preparation method of this example is essentially the same as that of Example 1, with the exception that:

[0168] No fibrous material was added, and a conventional coating of alumina was used.

[0169] Comparative Example 2

[0170] The preparation method of this example is essentially the same as that of Example 2, with the exception that:

[0171] No fibrous material was added, and a conventional coating of bauxite was used.

[0172] Comparative Example 3

[0173] The preparation method of this example is essentially the same as that of Example 1, with the exception that:

[0174] 1 ) Preparation of composite separator

[0175] The aramid fibers have a tube diameter of 0.05 μm and an aspect ratio of 5:1.

[0176] Comparative Example 4

[0177] The preparation method of this example is essentially the same as that of Example 1, with the exception that:

[0178] 1 ) Preparation of composite separator

[0179] The aramid fibers have a tube diameter of 0.05 μm and an aspect ratio of 5500:1.

[0180] Test Example

[0181] (I) Physical property test

[0182] 1. Test of tube diameter and length-diameter ratio of fiber material

[0183] By taking the composite diaphragm of the battery cell, first, whether there is fibrous material in the functional layer on the diaphragm surface is observed by scanning electron microscope (SEM, model: Hitachi S-7800) and transmission electron microscope (TEM, model: JEOL JEM-2100), and the tube diameter and length of the fibrous material are measured. 20 groups of data are randomly tested, and the average value is taken, that is, the tube diameter and length-diameter ratio can be obtained.

[0184] 2. Test of types and mass percentages of components in the functional layer

[0185] ①The functional layer on the surface of the diaphragm is scraped to take a sample, which is separated by ultrasonic in dimethyl carbonate solvent to take the corresponding fiber sample. The types and element composition of the fiber are confirmed by thermogravimetric analyzer (TGA, model: METTLER TOLEDO TGA2) and element analyzer (model: Thermo ICAP 7000Series (ICP-OES)); ②The functional layer sample is taken again, dried, and then the mass percentage of each component is calculated by calculating the loss of each stage by TGA method. In addition, for aramid fiber and polyacrylonitrile fiber containing nitrogen (N) element, the nitrogen content can be determined by element analyzer, and metal organic framework compound (MOFs) based composite fiber has special metal components, so the corresponding weight can be calculated. Inorganic ceramic material belongs to residual mass in TGA, and the residual above 800℃ is inorganic ceramic material.

[0186] The parameters of Examples 1-19 and Comparative Examples 1-4 are shown in Table 1.

[0187] Table 1

[0188]

[0189]

[0190] (II) Performance test

[0191] 1. Test of simulated infiltration rate of pole core

[0192] The electrode sheet and the separator were cut into long strips with an area of about 90 mm*120 mm and dried, and the electrode sheet and the separator were combined and fixed into a sample; the sample was clamped on both sides by transparent plastic plates and fastening clamps, and the middle part of the electrode sheet and the separator combination clamped by the transparent plastic plate leaked out; by immersing the part with a height direction size of not more than 5% of the sample in an electrolyte tank with the same formula as that of Example 1, the changes of the electrolyte liquid level in the sample in the climbing H and time t were observed by an optical image instrument, and the infiltration rate K = H / (t^0.5) was calculated according to the Lucas-Washburn formula. The test results are shown in Table 2.

[0193] 2. Cycle life test of the battery

[0194] The battery was charged at 45°C at 1C to a voltage of 3.8V, rested for 30min, then discharged at a discharge rate of 1C to a voltage of 2.0V, and the cycle was repeated 500 times in turn, and the capacity retention rate was recorded. The capacity retention rate (%) after 500 cycles = the discharge specific capacity after 500 cycles / the discharge specific capacity after the 3rd cycle * 100%. The test results are shown in Table 2.

[0195] Table 2

[0196]

[0197]

[0198] As can be seen from Table 2, compared with Comparative Examples 1-4, the infiltration K value and the cycle life of Examples 1-19 are obviously improved, and it can be seen that by introducing the fiber material into the functional layer of the composite separator and limiting the aspect ratio of the fiber material to the range of 10:1-5000:1, the infiltration K value and the cycle life of the battery can be effectively improved.

[0199] As can be seen from Table 2, compared with Examples 11 and 14, the infiltration K value and the cycle life of Examples 1 and 12-13 are obviously improved, and it can be seen that by limiting the mass fraction of the fiber material in the functional layer to the range of 5wt%-20wt%, the infiltration K value and the cycle life of the battery are further improved.

[0200] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are contained in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0201] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and the person skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A composite separator, characterized by, The composite diaphragm comprises: a diaphragm substrate; a functional layer, the functional layer being located on at least one side of the diaphragm substrate, the functional layer comprising a fibrous material; the fibrous material has an aspect ratio of 10:1 to 5000:

1.

2. The composite separator of claim 1, wherein The fibrous material comprises at least one of aramid fiber, polyacrylonitrile fiber, metal organic framework-based composite fiber, carbon-based fiber, ceramic fiber, and nanocellulose, preferably at least one of aramid fiber, polyacrylonitrile fiber, metal organic framework-based composite fiber, ceramic fiber, and nanocellulose.

3. The composite separator of claim 1, wherein The mass fraction of the fibrous material in the functional layer is 2wt% to 50wt%, preferably 5wt% to 20wt%.

4. The composite separator of claim 1, wherein The fibrous material has a tube diameter of 0.02μm to 1μm; and / or, the fibrous material has an aspect ratio of 100:1 to 500:

1.

5. The composite separator according to any one of claims 1 to 4, characterized in that, The functional layer further comprises an inorganic ceramic material, the mass fraction of the inorganic ceramic material in the functional layer being 35wt% to 90wt%.

6. The composite separator of claim 5, wherein, The inorganic ceramic material comprises at least one of alumina, boehmite, silica, magnesium hydroxide, titanium dioxide, and zirconium oxide.

7. The composite separator according to any one of claims 1 to 4, wherein The functional layer further comprises a binder, the mass fraction of the binder in the functional layer being 5wt% to 15wt%.

8. The composite separator of claim 7, wherein, The binder comprises at least one of polyvinylidene fluoride, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, polyacrylic acid, polyacrylonitrile, and styrene butadiene rubber.

9. The composite separator according to any one of claims 1 to 4, wherein The diaphragm substrate comprises at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, and non-woven fabric.

10. The composite separator according to any one of claims 1 to 4, wherein The thickness of the functional layer on one side of the diaphragm substrate is 1.3μm to 8μm; and / or, the thickness of the diaphragm substrate is 3μm to 30μm.

11. A method for producing the composite separator according to any one of claims 1 to 10, characterized by, The method comprises: mixing a fibrous material and a solvent to obtain a mixed slurry, coating the mixed slurry on at least one side of a diaphragm substrate, and drying to obtain a composite diaphragm.

12. The method of claim 11, wherein, The mixed slurry further comprises at least one of an inorganic ceramic material, a binder, and a dispersant.

13. A battery, characterized by The battery comprises the composite diaphragm of any one of claims 1 to 10 or the composite diaphragm prepared by the method of any one of claims 11 or 12.

14. A battery pack, characterized by The battery comprises the composite diaphragm of any one of claims 1 to 10 or the composite diaphragm prepared by the method of any one of claims 11 or 12.

15. An electrical device, characterized by The battery comprises the composite diaphragm of any one of claims 1 to 10 or the composite diaphragm prepared by the method of any one of claims 11 or 12 or the battery of claim 13. The battery comprises the composite diaphragm of any one of claims 1 to 10 or the composite diaphragm prepared by the method of any one of claims 11 or 12 or the battery of claim 13 or the battery pack of claim 14.

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