Flame-retardant thin film and preparation method therefor, composite current collector and battery

Abstract

A flame-retardant thin film and a preparation method therefor, a composite current collector and a battery. The flame-retardant thin film comprises a base film and a first flame-retardant layer on at least one side surface of the base film. The base film comprises a high-molecular polymer and a flame retardant, wherein the flame retardant comprises a bio-based flame-retardant material. The flame-retardant thin film is made of a bio-based flame-retardant material, is environmentally friendly, has good flame-retardant effects and a high thermal stability, and can significantly improve the flame-retardant performance of a current collector and the safety performance of a battery.

Description

Flame-retardant film, preparation method thereof, and composite current collector and battery TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and relates to a flame-retardant film, a preparation method thereof, and a composite current collector and a battery. BACKGROUND

[0002] As a basic material in a lithium ion battery, the performance of a current collector directly affects the performance and service life of the lithium ion battery. Traditional negative electrode current collectors are usually mainly high-purity copper foils, but pure copper foils have serious shortcomings in the use of lithium ion batteries, i.e., insufficient safety. After an accident of a new energy electric vehicle, the vehicle catches fire because the copper foil is broken and punctures the separator, causing a short circuit between the positive electrode and the negative electrode. In order to improve the safety performance of the battery, a composite current collector emerges as the times require.

[0003] The composite current collector usually has a "metal-polymer film-metal" "sandwich" structure. Compared with traditional current collectors, the composite current collector applied in a battery can reduce the cost of the battery and improve the energy density and safety of the battery. For example, CN117352744A discloses a composite current collector for a lithium ion battery and a preparation method thereof. The disclosed composite current collector for a lithium ion battery is composed of an inner polymer layer, an intermediate double-layer protective agent layer, and an outer double-layer metal foil layer. The polymer layer is soaked in saturated calcium gluconate slurry and then dried to obtain a composite current collector inner layer loaded with calcium gluconate on the surface. Then, the metal foil layer is coated on the surface of the composite current collector inner layer through magnetron sputtering and electroplating (or evaporation), to form a sandwich-structured composite current collector. Although the traditional sandwich-structured composite current collector has higher safety performance than a copper foil, the flame-retardant performance of such a current collector is limited.

[0004] In the prior art, a flame-retardant substance is added to the current collector to improve the flame-retardant performance. For example, CN117117204A discloses a lithium ion battery current collector, a preparation method thereof, and a battery. The lithium ion battery current collector includes an active material coating area, a safety structure area, and a tab area. The safety structure area is located between the active material coating area and the tab area and is arranged in the width direction of the current collector. The safety structure area is uniformly distributed with micropores, and the micropores are filled with an electrically conductive flame-retardant coating. The basic unit of the electrically conductive flame-retardant coating includes a fluorine-containing acrylate flame-retardant polymer core layer and an electrically conductive polymer coating layer. However, the flame-retardant substance used in CN117117204A is not environmentally friendly, and the safety performance of the current collector still needs to be further improved.

[0005] Based on the above research, it is necessary to provide a flame-retardant film that is environmentally friendly and has excellent flame-retardant performance, and can improve the safety performance of the current collector.

[0006] SUMMARY

[0007] The following is a summary of the subject matter of the detailed description herein. This summary is not intended to limit the scope of the claims.

[0008] The present application aims to provide a flame-retardant film and a preparation method thereof and a composite current collector and a battery, in particular to an environmentally friendly flame-retardant film and a preparation method thereof and a composite current collector and a battery, the flame-retardant film uses a bio-based flame-retardant material, is environmentally friendly, has excellent flame-retardant effect and high thermal stability, and can significantly improve the safety performance of the current collector.

[0009] In a first aspect, the present application provides a flame-retardant film, the flame-retardant film comprising a base film and a first flame-retardant layer on at least one side surface of the base film, the base film comprising a high molecular polymer and a flame retardant, the flame retardant comprising a bio-based flame-retardant material.

[0010] In a second aspect, the present application provides a preparation method of the flame-retardant film according to the first aspect, the preparation method comprising the following steps:

[0011] (1) mixing the high molecular polymer and the flame retardant and film-forming to obtain a base film; and

[0012] (2) soaking the base film according to step (1) in a first flame-retardant layer solution and then drying to obtain the flame-retardant film.

[0013] In a third aspect, the present application provides a composite current collector, the composite current collector comprising the flame-retardant film according to the first aspect and a conductive layer arranged on both sides of the flame-retardant film.

[0014] In a fourth aspect, the present application provides a battery, the battery comprising the composite current collector according to the third aspect.

[0015] Compared with the prior art, the present application has the following beneficial effects:

[0016] The flame-retardant film according to the present application uses a bio-based flame-retardant material in the base film and sets a first flame-retardant layer on the surface of the base film, so that the flame-retardant film is not only environmentally friendly, but also has high flame-retardant performance; when the flame-retardant film according to the present application is applied to the current collector, the flame-retardant performance of the current collector is effectively improved, thereby significantly improving the safety performance of the battery.

[0017] Other aspects can be apparent after reading and understanding the detailed description. DETAILED DESCRIPTION

[0018] In the first aspect of the present application, a flame-retardant film is provided, the flame-retardant film comprising a base film and a first flame-retardant layer on at least one side surface of the base film, the base film comprising a high molecular polymer and a flame retardant, the flame retardant comprising a bio-based flame-retardant material.

[0019] The fire-retardant film of the present application is an environmentally friendly fire-retardant film, which comprises a base film and a first fire-retardant layer, and the base film further comprises a fire-retardant agent, so that the film of the present application has high fire-retardant performance; and the fire-retardant agent used in the present application is a bio-based fire-retardant material, which is not only environmentally friendly, but also has high thermal stability and can carbonize into a carbon layer at high temperatures, thereby playing a fire-retardant effect.

[0020] In some embodiments, the bio-based fire-retardant material comprises lignin and / or tea polyphenol, preferably lignin and tea polyphenol.

[0021] The bio-based fire-retardant material described in the present application is lignin and / or tea polyphenol, and the fire-retardant mechanism of lignin is as follows: ① carbonization: at high temperatures, lignin will carbonize to form a carbon layer, which can effectively block the transfer of heat and oxygen, protecting the underlying material from continuing to burn or slowing down the burning speed; ② thermal stability: lignin has good thermal stability, and when the temperature rises, it can release non-flammable gases such as water vapor and carbon dioxide, which can dilute the oxygen concentration around it and reduce the oxygen required for combustion; and ③ catalytic carbonization: certain components in lignin will change during pyrolysis, promoting more carbonization and thus increasing the formation of protective carbon layer.

[0022] The fire-retardant mechanism of tea polyphenol described in the present application is as follows: ① improved thermal stability: the addition of tea polyphenol to the polymer can improve the thermal stability of the material, allowing it to begin to decompose at a higher temperature, and the increase in decomposition temperature helps to slow down the spread of fire; and ② free radical scavenging: as a natural antioxidant, tea polyphenol can effectively scavenge free radicals, thereby interrupting the combustion chain reaction at the molecular level, and free radicals are the key active particles that maintain combustion, so scavenging free radicals can slow down or even stop the growth of flames.

[0023] In some embodiments, the content of the fire-retardant agent in the base film is 1-10 wt%, for example, it can be 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable, and preferably 3-7 wt%.

[0024] The addition amount of the fire-retardant agent of the present application will affect the performance of the battery, if the addition amount of the fire-retardant agent is too small, the fire-retardant performance will decrease; if the addition amount of the fire-retardant agent is too large, the film-forming performance of the film will be affected.

[0025] In addition, based on the fire-retardant mechanism of lignin and tea polyphenol, the fire-retardant agent of the present application preferably combines lignin and tea polyphenol, which can further improve the fire-retardant performance and other performance of the battery.

[0026] In some embodiments, the mass ratio of the lignin and tea polyphenol is (1-9):(1-9), for example, can be 1:6, 2:5, 1:3, 3:2, 4:2, 9:1 or 6:1, but is not limited to the listed values, other values not listed in the value range are also applicable, preferably (1-6):(1-6), further preferably (1-4):(1-4).

[0027] When the lignin and tea polyphenol are used together in the present application, the mass ratio of the two is within a certain range, which can exert the optimal effect of lignin and tea polyphenol respectively, thereby further improving the flame retardant performance and the like.

[0028] In some embodiments, the first flame retardant layer is a bio-based flame retardant layer.

[0029] The first flame retardant layer on the surface of the base film in the present application is a bio-based flame retardant layer, which further ensures that the flame retardant film is environmentally friendly.

[0030] In some embodiments, the thickness of the first flame retardant layer is 200-2000nm, for example, can be 200nm, 400nm, 600nm, 800nm, 1000nm, 1200nm, 1400nm, 1600nm, 1800nm or 2000nm, but is not limited to the listed values, other values not listed in the value range are also applicable, preferably 800-1200nm.

[0031] The thickness of the first flame retardant layer in the present application will affect the battery performance, if the first flame retardant layer is too thin, the flame retardant effect is poor, if the first flame retardant layer is too thick, the overall performance of the composite current collector is affected.

[0032] In some embodiments, the first flame retardant layer comprises an acid, a protein and a natural polysaccharide.

[0033] The first flame retardant layer described in the present application combines the protein-acid complex (a complex formed by an acid and a protein) and the natural polysaccharide by electrostatic adsorption, and constructs a biomass flame retardant coating on the surface of the cotton fabric in a layer-by-layer self-assembly manner, which can be uniformly adsorbed on the film.

[0034] In some embodiments, the mass concentration ratio of the natural polysaccharide, the acid and the protein is (1-3):(1-4):(1-4), for example, can be 1:2:1, 2:2:3 or 3:4:4, but is not limited to the listed values, other values not listed in the value range are also applicable, preferably 1:2:2.

[0035] In some embodiments, the acid comprises any one or a combination of at least two of boric acid, phosphoric acid, phytic acid, inositol acid, pyrophosphoric acid, diester phosphoric acid, triester phosphoric acid or glycerophosphoric acid, preferably phytic acid.

[0036] In some embodiments, the natural polysaccharide includes any one or a combination of at least two of cellulose, ammonium alginate, pectin, or mucopolysaccharide.

[0037] In some embodiments, the protein includes any one or a combination of at least two of whey protein, casein protein, acid protein, enzyme protein, globulin, or glutelin.

[0038] In some embodiments, the content of the high molecular polymer in the base film is 90.0-99.0 wt%, for example, can be 91 wt%, 92 wt%, 94 wt%, 96 wt%, 98 wt%, or 99.0 wt%, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0039] In some embodiments, the high molecular polymer includes any one or a combination of at least two of polypropylene, polyethylene terephthalate, polyimide, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenyl ether, polyester, polyethylene, polystyrene, and derivatives thereof.

[0040] In some embodiments, the thickness of the flame-retardant film is 2-20 μm, for example, can be 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, or 18 μm, but is not limited to the listed values, and other values not listed in the value range are also applicable, and is preferably 6-10 μm.

[0041] In the second aspect of the present application, a preparation method of the flame-retardant film according to the first aspect is provided, and the preparation method includes the following steps:

[0042] (1) mixing and film-forming the high molecular polymer and the flame retardant according to the formula amount to obtain a base film; and

[0043] (2) soaking the base film in the first flame-retardant layer solution, and then drying to obtain the flame-retardant film.

[0044] The base film according to the present application is prepared by mixing and extruding the high molecular polymer and the flame retardant, and using the melt-biaxial stretching method, and the first flame-retardant layer is prepared by soaking the base film in the first flame-retardant layer solution.

[0045] In some embodiments, the soaking time in the first flame-retardant layer solution in step (2) is 5-30 min, for example, can be 8 min, 12 min, 14 min, 16 min, 20 min, 23 min, 25 min, 28 min, or 30 min, but is not limited to the listed values, and other values not listed in the value range are also applicable, and is preferably 10-15 min.

[0046] In some embodiments, the first fire-retardant layer solution of step (2) comprises a solution of acid, natural polysaccharide and protein.

[0047] The soaking time of the above-mentioned application refers to the soaking time in the acid solution, the natural polysaccharide solution and the protein aqueous solution respectively; for example, the soaking time in the acid solution can be 5-30 min, for example, it can be 8 min, 12 min, 14 min, 16 min, 20 min, 23 min, 25 min, 28 min or 30 min, the soaking time in the natural polysaccharide solution can be 5-30 min, for example, it can be 8 min, 12 min, 14 min, 16 min, 20 min, 23 min, 25 min, 28 min or 30 min, and the soaking time in the protein can be 5-30 min, for example, it can be 8 min, 12 min, 14 min, 16 min, 20 min, 23 min, 25 min, 28 min or 30 min, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0048] In some embodiments, the soaking of step (2) comprises soaking in the natural polysaccharide solution, the acid solution and the protein aqueous solution in sequence; that is, soaking in the natural polysaccharide solution for 5-30 min, drying, then soaking in the acid solution for 5-30 min, drying again, and finally soaking in the protein aqueous solution for 5-30 min; after the soaking is completed, the soaking step of step (2) can be repeated, that is, soaking in the above-mentioned sequence and soaking time again.

[0049] In the third aspect of the application, a composite current collector is provided, which comprises the fire-retardant film according to the first aspect and a conductive layer arranged on both sides of the fire-retardant film.

[0050] The fire-retardant film according to the application can be used as the substrate of the current collector, which can improve the fire-retardant performance of the current collector and thus improve the safety of the battery.

[0051] In some embodiments, the surface of the conductive layer away from the fire-retardant film is further provided with a second fire-retardant layer.

[0052] The second fire-retardant layer is arranged on the surface of the conductive layer, which further improves the fire-retardant performance of the current collector.

[0053] In some embodiments, the second fire-retardant layer is an inorganic fire-retardant layer.

[0054] The material of the second fire-retardant layer is different from the material of the first fire-retardant layer. Since the first fire-retardant layer and the second fire-retardant layer are located at different positions, the second fire-retardant layer is set as an inorganic fire-retardant layer, so as to adopt a multi-layer and multi-stage fire-retardant mode as a whole, and further strengthen the fire-retardant effect.

[0055] In some embodiments, the second fire-retardant layer comprises any one or a combination of at least two of aluminum hydroxide, aluminum oxide, magnesium hydroxide, diantimony trioxide, zinc oxide, titanium oxide, or silicon carbide.

[0056] In some embodiments, the thickness of the second fire-retardant layer is 100-1000 nm, for example, can be 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, or 1000 nm, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0057] In some embodiments, the thickness of the conductive layer is 500-2000 nm, for example, can be 700 nm, 900 nm, 1100 nm, 1300 nm, 1500 nm, 1700 nm, or 1900 nm, but is not limited to the listed values, and other values not listed in the value range are also applicable.

[0058] In some embodiments, the conductive layer comprises any one or a combination of at least two of copper, copper alloy, titanium, titanium alloy, silver, silver alloy, aluminum, aluminum alloy, nickel alloy, nickel, or carbon material.

[0059] In the fourth aspect of the present application, a battery is provided, which comprises the composite current collector of the third aspect.

[0060] The technical solutions of the present application are further illustrated by specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application, and should not be regarded as specific limitations on the present application.

[0061] Example 1

[0062] The present embodiment provides a composite current collector, which comprises a second fire-retardant layer, a conductive layer, a fire-retardant film, a conductive layer, and a second fire-retardant layer which are sequentially stacked, and the fire-retardant film comprises a first fire-retardant layer, a base film, and a first fire-retardant layer which are sequentially stacked, wherein the thickness of the base film is 4.5 μm, the thickness of the first fire-retardant layer is 800 nm, the thickness of the conductive layer is 1 μm, and the thickness of the second fire-retardant layer is 200 nm.

[0063] The base film comprises 97.0 wt% of polypropylene and 3 wt% of lignin, the first flame-retardant layer comprises sodium alginate, phytic acid and protein, the protein is whey protein, the conductive layer comprises copper, and the second flame-retardant layer comprises aluminum oxide;

[0064] The preparation method of the composite current collector comprises the following steps:

[0065] (1) Base film preparation: 97.0 wt% of polypropylene and 3.0 wt% of lignin are mixed and extruded, and then a base film with a thickness of 4.5 μm is prepared by a melt-biaxial stretching method;

[0066] (2) Preparation of the first flame-retardant layer: sodium alginate, phytic acid and protein are respectively dissolved in pure water to prepare a 1% sodium alginate solution, a 2% phytic acid solution and a 2% protein aqueous solution;

[0067] The base film prepared in step (1) is first placed in the prepared sodium alginate solution and soaked for 10 min, then dried in an oven at 60°C for 30 min, then the base film treated by the sodium alginate solution is placed in the phytic acid solution and soaked for 10 min, then dried in an oven at 60°C for 30 min, then the base film treated by the sodium alginate and phytic acid aqueous solutions is placed in the protein aqueous solution and soaked for 10 min, then dried in an oven at 30°C for 30 min, and the above soaking step is repeated for 3 times to obtain the flame-retardant film;

[0068] (3) Preparation of the conductive layer:

[0069] The flame-retardant film prepared in step (2) is placed in a magnetron sputtering machine, a copper target (purity: 99.99%) is used as the target material, the power density is 5 W / cm 2 , the argon flow rate is 60 mL / min, and the film plating vacuum degree is 0.08 Pa, and the film is plated for 10 s;

[0070] Then the prepared magnetron film is placed in an acidic copper plating tank, and the copper layer on both sides of the magnetron film is thickened to about 1 μm by electroplating, wherein the main salt concentration in the copper plating tank is: the sulfuric acid content is 120 g / L, the copper sulfate content is 110 g / L, and the chloride ion concentration is 60 mg / L; and

[0071] (4) Preparation of the second flame-retardant layer: the film thickened by electroplating is placed in a vacuum sputtering chamber, and aluminum oxide is sputtered by a radio frequency sputtering method, an aluminum oxide target (purity: 99.99%) is used as the target material, the power density is 100 W, the argon flow rate is 50 mL / min, the frequency is 13.56 MHz, the film plating vacuum degree is 0.27 Pa, and the sputtering is stopped when the second flame-retardant layer is plated to a thickness of 200 nm, to obtain the composite copper current collector.

[0072] Example 2

[0073] This example provides a composite current collector, which is identical to Example 1 except that the base film comprises 95.0 wt% polypropylene and 5 wt% lignin;

[0074] The method of preparing the composite current collector is identical to Example 1 except that the raw materials used in preparing the base film are adaptively changed in formulation amount.

[0075] Example 3

[0076] This example provides a composite current collector, which is identical to Example 1 except that the base film comprises 93.0 wt% polypropylene and 7 wt% lignin;

[0077] The method of preparing the composite current collector is identical to Example 1 except that the raw materials used in preparing the base film are adaptively changed in formulation amount.

[0078] Example 4

[0079] This example provides a composite current collector, which is identical to Example 1 except that the base film comprises 90.0 wt% polypropylene and 10 wt% lignin;

[0080] The method of preparing the composite current collector is identical to Example 1 except that the raw materials used in preparing the base film are adaptively changed in formulation amount.

[0081] Example 5

[0082] This example provides a composite current collector, which is identical to Example 1 except that the base film comprises 99.0 wt% polypropylene and 1 wt% lignin;

[0083] The method of preparing the composite current collector is identical to Example 1 except that the raw materials used in preparing the base film are adaptively changed in formulation amount.

[0084] Example 6

[0085] This example provides a composite current collector, which is identical to Example 1 except that the base film comprises 80 wt% polypropylene and 20 wt% lignin;

[0086] The method of preparing the composite current collector is identical to Example 1 except that the raw materials used in preparing the base film are adaptively changed in formulation amount.

[0087] Example 7

[0088] The present example provides a composite current collector, which is the same as example 1 except that the base film comprises 93wt% polypropylene and 7wt% tea polyphenol;

[0089] The preparation method of the composite current collector is the same as example 1 except that the raw materials used in the preparation of the base film are adaptively changed in the formula amount.

[0090] Example 8

[0091] The present example provides a composite current collector, which is the same as example 1 except that the base film comprises 95wt% polypropylene, 1wt% lignin and 4wt% tea polyphenol;

[0092] The preparation method of the composite current collector is the same as example 1 except that the raw materials used in the preparation of the base film are adaptively changed in the formula amount.

[0093] Example 9

[0094] The present example provides a composite current collector, which is the same as example 1 except that the base film comprises 95wt% polypropylene, 2wt% lignin and 3wt% tea polyphenol;

[0095] The preparation method of the composite current collector is the same as example 1 except that the raw materials used in the preparation of the base film are adaptively changed in the formula amount.

[0096] Example 10

[0097] The present example provides a composite current collector, which is the same as example 8 except that the mass ratio of lignin and tea polyphenol is 4:1;

[0098] The preparation method of the composite current collector is the same as example 8 except that the raw materials used in the preparation of the base film are adaptively changed in the formula amount.

[0099] Example 11

[0100] The present example provides a composite current collector, which is the same as example 8 except that the mass ratio of lignin and tea polyphenol is 0.5:4.5;

[0101] The preparation method of the composite current collector is the same as example 8 except that the raw materials used in the preparation of the base film are adaptively changed in the formula amount.

[0102] Example 12

[0103] The present example provides a composite current collector, which is the same as that of Example 8 except that the mass ratio of lignin and tea polyphenol is 4.5:0.5.

[0104] The preparation method of the composite current collector is the same as that of Example 8 except that the raw materials used in the preparation of the base film are adaptively changed according to the formula amount.

[0105] Example 13

[0106] The present example provides a composite current collector, which is the same as that of Example 1 except that the thickness of the first flame-retardant layer is 400 nm.

[0107] The preparation method of the composite current collector is the same as that of Example 1 except that the soaking time in step (2) is 5 min.

[0108] Example 14

[0109] The present example provides a composite current collector, which is the same as that of Example 1 except that the thickness of the first flame-retardant layer is 1200 nm.

[0110] The preparation method of the composite current collector is the same as that of Example 1 except that the soaking time in step (2) is 15 min.

[0111] Example 15

[0112] The present example provides a composite current collector, which is the same as that of Example 1 except that the thickness of the first flame-retardant layer is 2400 nm.

[0113] The preparation method of the composite current collector is the same as that of Example 1 except that the soaking time in step (2) is 30 min.

[0114] Example 16

[0115] The present example provides a composite current collector, which is the same as that of Example 1 except that the thickness of the first flame-retardant layer is 3200 nm.

[0116] The preparation method of the composite current collector is the same as that of Example 1 except that the soaking time in step (2) is 40 min.

[0117] Example 17

[0118] The present example provides a composite current collector, which is the same as that of Example 1 except that the second flame-retardant layer is the same as the first flame-retardant layer.

[0119] The preparation method of the composite current collector is the same as that of Example 1, except that step (4) is the same as step (2).

[0120] Example 18

[0121] This example provides a composite current collector, which is the same as Example 1, except that the first flame-retardant layer does not contain protein.

[0122] The preparation method of the composite current collector is the same as that of Example 1, except that step (2) is not soaked in a protein aqueous solution.

[0123] Comparative Example 1

[0124] This comparative example provides a composite current collector, which is the same as Example 1, except that the base film does not contain the flame-retardant lignin.

[0125] The preparation method of the composite current collector is the same as that of Example 1, except that the raw materials used in the preparation of the base film are adaptively changed according to the formulation amount.

[0126] Comparative Example 2

[0127] This comparative example provides a composite current collector, which is the same as Example 1, except that it does not include the first flame-retardant layer.

[0128] The preparation method of the composite current collector is the same as that of Example 1, except that step (2) is not performed.

[0129] The composite current collectors obtained in the above examples and comparative examples are assembled into batteries, and the preparation method includes: a positive electrode sheet preparation step: adding a positive electrode active material LiNi 0.6 Mn 0.2 Co 0.2 O2(NCM622), conductive carbon black, and a binder into N-methylpyrrolidone, uniformly mixing, coating onto the surface of a conventional aluminum foil, drying, and cutting to obtain a positive electrode sheet; a negative electrode sheet preparation step: adding a negative electrode active material artificial graphite, conductive carbon black, a thickening agent, and a binder into N-methylpyrrolidone, uniformly mixing, coating onto the composite current collector obtained in the above examples and comparative examples, drying, and cutting to obtain a negative electrode sheet; a separator is a polypropylene film coated with zirconium oxide (thickness: 20 micrometers); an electrolyte is a 1 mol / L lithium hexafluorophosphate carbonate solution (EMC:EC:PC = 1:1:1); and the positive electrode sheet, the separator, and the negative electrode sheet are stacked in a Z shape, placed in a shell, injected with the electrolyte, sealed, and a stacked battery is obtained. The battery is placed for 24 h before testing to ensure that the electrode material is fully wetted by the electrolyte.

[0130] The test of the tensile strength of the composite current collector refers to the national standard GB / T 1040.3-2006, and the data are all MD direction data.

[0131] After the above battery is fully charged at room temperature at 0.5C and then stands for more than 3 hours, the needle-punch test is performed according to GB / T31485-2015, the flame extinguishing time during the experiment of each group of batteries is counted, the surface temperature rise is detected by using a real-time temperature tester, the thermocouple sensing probe of the temperature tester is placed on the surface of the battery, and the maximum surface temperature rise is calculated.

[0132] The test results are shown in Table 1:

[0133] Table 1

[0134] As can be seen from Table 1:

[0135] It can be seen from Examples 1-6 and Comparative Examples 1-2 that the addition of the flame retardant in the base film and the setting of the first flame-retardant layer can significantly improve the battery performance; it can be seen from Examples 1 and 2-7 that the addition amount of the flame retardant in the base film of the application will affect the battery performance; it can be seen from Examples 1-9 and Examples 10-12 that the flame retardant of the application is preferably a combination of lignin and tea polyphenol, and preferably in a suitable ratio range; it can be seen from Examples 1 and Examples 13-16 that the thickness of the first flame-retardant layer of the application will affect the battery performance; it can be seen from Examples 1 and Example 17 that the first flame-retardant layer and the second flame-retardant layer of the application are different in position on the current collector, and they play different roles, so they are different types of flame-retardant layers; it can be seen from Examples 1 and Example 18 that the first flame-retardant layer of the application preferably further contains protein.

[0136] In summary, the application provides a flame-retardant film, a preparation method thereof, a composite current collector and a battery. The flame-retardant film uses a bio-based flame-retardant material, is friendly to the environment, has excellent flame-retardant effect and high thermal stability, and can significantly improve the safety performance of the current collector.

[0137] The above merely provides a specific implementation of the application, but the protection scope of the application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed in the application can be easily conceived by those skilled in the art, and all fall within the protection scope and disclosure scope of the application.

Claims

1. A flame-retardant film, comprising a base film and a first flame-retardant layer on at least one side surface of the base film, wherein the base film comprises a high molecular polymer and a flame-retardant agent, and the flame-retardant agent comprises a bio-based flame-retardant material.

2. The flame-retardant film according to claim 1, wherein, The bio-based flame-retardant material comprises lignin and / or tea polyphenol, preferably lignin and tea polyphenol; Preferably, the content of the flame-retardant agent in the base film is 1-10 wt%, preferably 3-7 wt%; Preferably, the mass ratio of the lignin and tea polyphenol is (1-9) :(1-9), preferably (1-6) :(1-6), further preferably (1-4) :(1-4).

3. The flame-retardant film according to claim 1 or 2, wherein, The first flame-retardant layer is a bio-based flame-retardant layer; Preferably, the thickness of the first flame-retardant layer is 200-2000 nm, preferably 800-1200 nm; Preferably, the first flame-retardant layer comprises an acid, a protein and a natural polysaccharide; Preferably, the mass concentration ratio of the natural polysaccharide, the acid and the protein is (1-3) :(1-4) :(1-4), preferably 1:2:2; Preferably, the acid comprises any one or a combination of at least two of boric acid, phosphoric acid, phytic acid, inositol acid, pyrophosphoric acid, diester phosphoric acid, triester phosphoric acid or glycerophosphoric acid, preferably phytic acid; Preferably, the natural polysaccharide comprises any one or a combination of at least two of cellulose, ammonium alginate, pectin or mucopolysaccharide; Preferably, the protein comprises any one or a combination of at least two of whey protein, casein protein, acid protein, enzyme protein, globulin or glutelin.

4. The flame-retardant film according to any one of claims 1 to 3, wherein, The content of the high molecular polymer in the base film is 90.0-99.0 wt%; Preferably, the high molecular polymer comprises any one or a combination of at least two of polypropylene, polyethylene terephthalate, polyimide, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenyl ether, polyester, polyethylene, polystyrene and derivatives thereof; Preferably, the thickness of the flame-retardant film is 2-20 μm, preferably 6-10 μm. 5.A method for preparing the flame-retardant film according to any one of claims 1-4, comprising the following steps: (1) mixing and film-forming a high molecular polymer and a flame-retardant agent according to a formula to obtain a base film; and (2) immersing the base film in a first flame-retardant layer solution and then drying to obtain the flame-retardant film.

6. The production method according to claim 5, wherein The immersion time in the first flame-retardant layer solution in step (2) is 5-30 min, preferably 10-15 min; Preferably, the first flame-retardant layer solution in step (2) comprises a solution of an acid, a natural polysaccharide and a protein; Preferably, the immersion in step (2) comprises immersion in a natural polysaccharide solution, an acid solution and an aqueous protein solution in sequence. 7.A composite current collector, comprising the flame-retardant film according to any one of claims 1-4 and a conductive layer arranged on both sides of the flame-retardant film.

8. The composite current collector of claim 7, wherein, The surface of the conductive layer away from the flame-retardant film is further provided with a second flame-retardant layer; Preferably, the second flame-retardant layer is an inorganic flame-retardant layer. Preferably, the second flame retardant layer comprises any one or a combination of at least two of aluminum hydroxide, aluminum oxide, magnesium hydroxide, antimony trioxide, zinc oxide, titanium oxide or silicon carbide; Preferably, the second flame retardant layer has a thickness of 100-1000 nm.

9. The composite current collector of claim 7 or 8, wherein, The conductive layer has a thickness of 500-2000 nm; Preferably, the conductive layer comprises any one or a combination of at least two of copper, copper alloy, titanium, titanium alloy, silver, silver alloy, aluminum, aluminum alloy, nickel alloy, nickel or carbon material.

10. A battery comprising the composite current collector of any one of claims 7-9.

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