A flame-retardant film, current collector, electrode, and battery

Abstract

The present invention relates to the technical field of flame-retardant batteries, and discloses a flame-retardant film, a current collector, an electrode and a battery. In the present invention, an inner layer film is prepared by blending polytetrafluoroethylene and potassium perfluorobutanesulfonate, an intermediate layer film is prepared by blending polybutylene terephthalate and ytterbium trifluoromethanesulfonate, and an outer layer film is prepared by blending polystyrene and triphenyl phosphate. The three-layer film is prepared into a flame-retardant film by hot pressing. Compared with the traditional single-layer flame-retardant film, the "sandwich" type multi-layer flame-retardant film prepared in the present invention has a synergistic effect and has more excellent flame retardancy and mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of flame-retardant batteries, and specifically to a flame-retardant film, a current collector, an electrode, and a battery. Background Art

[0002] All along, there has been a contradiction between high safety and high energy density. Whether the flame retardant is added to the electrolyte, the separator, or the positive and negative electrode materials, a new substance is introduced into the lithium ion transmission path, thereby affecting ion conduction, and further affecting the battery performance, and finally resulting in a decrease in energy density.

[0003] From the perspective of the internal structure, during the charging and discharging processes of the battery, lithium ions will pass through the electrolyte and the separator from one pole of the electrode material to reach the other pole. Therefore, in this process, as long as a new substance is added, it will affect the battery performance. For example, adding a flame retardant to the electrolyte will reduce the conductivity of the electrolyte. Then the current collector that does not participate in the lithium ion transport process is an ideal part for storing the flame retardant.

[0004] At present, traditional pure metal films use high-purity metals as raw materials, and it is difficult to add flame retardant substances to the dense metal layer. Therefore, it is of great significance to invent a flame-retardant battery. Summary of the Invention

[0005] The purpose of the present invention is to provide a flame-retardant film, a current collector, an electrode, and a battery to solve the problems raised in the above background art.

[0006] To solve the above technical problems, the present invention provides the following technical solutions:

[0007] A flame-retardant film, comprising raw materials with the following mass percentages: 85.0% - 99.0% polymer, 1.0% - 15.0% flame retardant.

[0008] Further, the flame-retardant film is prepared by the following method: after mixing the polymer and the flame retardant, a melt-biaxial stretching method is used to obtain the flame-retardant film.

[0009] Further, the polymer is one or more of polypropylene, polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyimide, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene sulfide, polyphenylene ether, polystyrene, and polyamide.

[0010] Further, the flame retardant is one or more of ytterbium trifluoromethanesulfonate, potassium perfluorobutanesulfonate, and triphenyl phosphate.

[0011] Further, the thickness of the flame-retardant film is 1 μm - 5 μm.

[0012] Further, the flame-retardant film is such that polybutylene terephthalate layers and polystyrene layers are symmetrically and sequentially arranged on both sides of the polytetrafluoroethylene layer, and the polybutylene terephthalate layer is arranged between the polytetrafluoroethylene layer and the polystyrene layer;

[0013] Further, the polytetrafluoroethylene layer comprises raw materials with the following mass percentages: 85.0% - 99.0% polytetrafluoroethylene, 1.0% - 15.0% potassium perfluorobutanesulfonate; the polybutylene terephthalate layer comprises raw materials with the following mass percentages: 85.0% - 99.0% polybutylene terephthalate, 1.0% - 15.0% ytterbium trifluoromethanesulfonate; the polystyrene layer comprises raw materials with the following mass percentages: 85.0% - 99.0% polystyrene, 1.0% - 15.0% triphenyl phosphate;

[0014] Further, in one side of the composite flame-retardant separator, the mass ratio of polytetrafluoroethylene in the flame-retardant separator, polybutylene terephthalate in the polybutylene terephthalate layer, and polystyrene in the polystyrene layer is 3:(2 - 3):4, and the other side of the composite flame-retardant separator is the same.

[0015] Further, the inner layer comprises raw materials with the following mass percentages: 85.0% - 99.0% polytetrafluoroethylene, 1.0% - 15.0% potassium perfluorobutanesulfonate; the middle layer comprises raw materials with the following mass percentages: 85.0% - 99.0% polybutylene terephthalate, 1.0% - 15.0% ytterbium trifluoromethanesulfonate; the outer layer comprises raw materials with the following mass percentages: 85.0% - 99.0% polystyrene, 1.0% - 15.0% triphenyl phosphate.

[0016] Further, the mass ratio of polytetrafluoroethylene:polybutylene terephthalate:polystyrene is 3:(2 - 3):4.

[0017] A flame-retardant current collector is prepared by the following method: In water, conductive carbon black is added and stirred for 100 min to obtain a uniform conductive carbon black slurry; after stirring evenly, alumina and silicon carbide are added to a solvent, and after stirring evenly, a first slurry is obtained. Then a binder is added, and after stirring evenly again, a second slurry is obtained. The obtained second slurry is coated on the surface of the metal layer through a coating system and then dried, and the final thickness of the protective layer is controlled by controlling the coating amount, and finally a flame-retardant current collector is obtained.

[0018] Further, the metal layer is prepared as follows: Place the prepared flame-retardant film in the chamber of vacuum evaporation. Melt and evaporate the high-purity copper wire (purity greater than 99.99%) in the metal evaporation chamber at a high temperature of 1500°C. The evaporated metal atoms pass through the cooling system in the vacuum coating chamber and are deposited on the two surfaces opposite to the modified layer to form a copper metal conductive layer with a thickness of 1 μm, thereby obtaining the metal layer.

[0019] Further, the thickness of the metal layer is 500 nm to 2000 nm.

[0020] Further, the material of the metal layer includes one or more of titanium, silver, aluminum alloy, aluminum, nickel alloy, nickel, copper alloy, and copper.

[0021] Further, a protective layer is provided on the surface of the metal layer.

[0022] Further, a protective layer is provided on the surface of the metal layer, and the thickness of the protective layer is 10 nm to 200 nm.

[0023] Further, a protective layer is provided on the surface of the metal layer, and the material of the protective layer includes one or two of aluminum oxide and silicon carbide.

[0024] A positive electrode is prepared as follows: Add active material, conductive agent, and binder to N-methylpyrrolidone (NMP), mix evenly to obtain the positive electrode slurry, and uniformly coat the positive electrode slurry on the surface of the flame-retardant current collector and dry it to obtain the positive electrode sheet.

[0025] Further, the active material is NMC811, the conductive agent is conductive carbon black, and the binder is polyvinylidene fluoride (PVDF).

[0026] A negative electrode sheet is prepared as follows: Add negative electrode active material, conductive agent, thickening agent, and binder to deionized water, mix evenly to obtain the negative electrode slurry, and uniformly coat the negative electrode slurry on the surface of the flame-retardant current collector and dry it to obtain the negative electrode sheet.

[0027] Further, the active material is graphite powder, the conductive agent is conductive carbon black, the thickening agent is sodium carboxymethyl cellulose (CMC), and the binder is styrene-butadiene rubber (SBR).

[0028] A flame-retardant battery is prepared as follows:

[0029] Stack the positive electrode sheet, negative electrode sheet, and separator to obtain a laminated body battery cell. Then, ultrasonically weld the tabs of all the positive electrode sheets and ultrasonically weld the tabs of all the negative electrode sheets, and then place them in a housing, inject electrolyte, and seal it to obtain the flame-retardant battery.

[0030] Further, the electrolyte is any one of dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and lithium hexafluorophosphate (LiPF6) with a concentration of 1M.

[0031] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The present invention prepares the inner layer film by blending polytetrafluoroethylene and potassium perfluorobutanesulfonate, prepares the intermediate layer film by blending polybutylene terephthalate and ytterbium trifluoromethanesulfonate, and prepares the outer layer film by blending polystyrene and triphenyl phosphate. The three-layer films are prepared into a flame-retardant film by hot pressing.

[0032] Compared with the traditional single-layer flame-retardant film, the "sandwich-like" multi-layer flame-retardant film prepared by the present invention has a synergistic effect, and synergistically exerts the gas-phase flame-retardant and solid-phase isolation effects, effectively improving the flame-retardant effect. In addition, while adding a flame retardant to the film, the mechanical properties of the film are also effectively improved;

[0033] When potassium perfluorobutanesulfonate in the inner layer is heated, the carbon-fluorine bond in its structure can be broken, releasing fluorine radicals and effectively capturing the free active radicals generated by the thermal degradation of polymer materials, which can effectively reduce the concentration of free radicals, thereby alleviating or terminating the free radical chain reaction of combustion and inhibiting flame propagation. Polytetrafluoroethylene, as the carrier of potassium perfluorobutanesulfonate, can help release fluorine radicals during the heating process;

[0034] Ytterbium trifluoromethanesulfonate in the intermediate layer has high thermodynamic stability and a high char residue amount below 600°C. It can form a carbonized layer on the surface after the current collector burns to play an isolation and heat insulation role, thereby gradually reducing the heat release rate; the free radicals generated during the thermal degradation of this substance have stronger capturing ability, which is the result of the combined action of cations and anions in rare earth compounds. Trifluoromethanesulfonate (anion) is very likely to generate free radicals under high-temperature conditions due to the strong electron-withdrawing ability of fluorine atoms, and then capture the free radicals generated by the base film. At the same time, Yb (cation) can capture free radicals through the reversible conversion of valence under high-temperature conditions due to its variable valence;

[0035] Triphenyl phosphate in the outer layer promotes the dehydration and carbonization of the base material, so that the polymer material cannot generate flammable gases. And because the non-volatile phosphorus compound acts as a coagulant, a protective carbon film is formed by the carbide to isolate the outside air and heat. Polystyrene, as the carrier of triphenyl phosphate, can help disperse and at the same time provide sufficient support for the carbon film formed after the carbonization of triphenyl phosphate by heating, making it not easy to collapse and greatly enhancing the stability of the carbon layer. Specific embodiments

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0037] In the following embodiments, the CAS registration number of polytetrafluoroethylene is 9002-84-0, the CAS registration number of polybutylene terephthalate is 26062-94-2, the CAS registration number of polystyrene is 9003-53-6, and the CAS registration number of polyethylene terephthalate is 25038-59-9.

[0038] Embodiment 1: Preparation of a flame-retardant film: S1: Mix 95.0 g of polyethylene terephthalate and 5.0 g of ytterbium trifluoromethanesulfonate, and then use the melt-biaxial stretching method to prepare the film, including the following steps: crystallization drying - melt extrusion - sheet casting - longitudinal stretching - transverse stretching - heat setting; the obtained film has a thickness of 5 μm.

[0039] S2: Place the prepared flame-retardant film in the chamber of vacuum evaporation. Melt and evaporate the high-purity copper wire (purity greater than 99.99%) in the metal evaporation chamber at a high temperature of 1500 °C. The evaporated metal atoms pass through the cooling system in the vacuum coating chamber and are deposited on the two surfaces opposite to the modified layer to form a copper metal layer with a thickness of 1 μm.

[0040] Embodiment 2: Preparation of a flame-retardant film: It is basically the same as Embodiment 1, and the main difference is that the flame retardant is 7.0% ytterbium trifluoromethanesulfonate.

[0041] Embodiment 3: Preparation of a flame-retardant film: It is basically the same as Embodiment 1, and the main difference is that the flame retardant is 10.0% ytterbium trifluoromethanesulfonate.

[0042] Embodiment 4: Preparation of a flame-retardant film: It is basically the same as Embodiment 1, and the main difference is that the flame retardant is 15.0% ytterbium trifluoromethanesulfonate.

[0043] Embodiment 5: Preparation of a flame-retardant film: It is basically the same as Embodiment 1, and the main difference is that the flame retardant is 3% ytterbium trifluoromethanesulfonate and 4% potassium perfluorobutanesulfonate.

[0044] Embodiment 6: Preparation of a flame-retardant film: It is basically the same as Embodiment 1, and the main difference is that the flame retardant is 3% ytterbium trifluoromethanesulfonate and 4% triphenyl phosphate.

[0045] Embodiment 7: Preparation of a flame-retardant film: It is basically the same as Embodiment 1, and the main difference is that the flame retardant is 7% triphenyl phosphate.

[0046] Example 8: Preparation of a flame-retardant film: It is basically the same as Example 1, with the main difference being that the flame retardant is 7% potassium perfluorobutanesulfonate.

[0047] Example 9: Preparation of a flame-retardant battery: S1: Mix 71.25 g of polytetrafluoroethylene, 3.75 g of potassium perfluorobutanesulfonate, 47.5 g of polybutylene terephthalate, 2.5 g of ytterbium trifluoromethanesulfonate, 95 g of polystyrene, and 5 g of triphenyl phosphate, and then use the melt-biaxial stretching method to prepare a film, including the following steps: crystallization drying - melt extrusion - sheet casting - longitudinal stretching - transverse stretching - heat setting, to obtain inner, middle, and outer layer films respectively. Place the middle layer on both sides of the inner layer, and the outer layer on the outer sides of the two middle layers, and then hot press to obtain a film with a thickness of 5 μm.

[0048] S2: Place the prepared flame-retardant film in the chamber of vacuum evaporation. Melt and evaporate the high-purity copper wire (purity greater than 99.99%) in the metal evaporation chamber at a high temperature of 1500 °C. The evaporated metal atoms pass through the cooling system in the vacuum coating chamber and are deposited on the two surfaces opposite to the modified layer to form a copper metal layer with a thickness of 1 μm.

[0049] S3: Add 2 kg of conductive carbon black to 20 kg of water and stir for 100 min to obtain a uniform conductive carbon black slurry. After stirring evenly, add 1 g of alumina and 1 g of silicon carbide to the solvent, stir evenly to obtain the first slurry, then add a binder, and then stir evenly to obtain the second slurry. Coat the second slurry on the surface of the metal layer through a coating system and then dry it. Control the final thickness of the protective layer by controlling the coating amount, and finally obtain a current collector with a protective layer thickness of 100 nm.

[0050] S4: The preparation method of the positive electrode sheet used includes the following steps: Add 96 g of active material NMC811, 2 g of conductive agent carbon black, and 2 g of binder PVDF to 80 g of NMP, mix evenly to obtain a ternary positive electrode slurry, and uniformly coat the ternary positive electrode slurry on the surface of the composite aluminum foil current collector obtained above, and then dry it to obtain the positive electrode sheet.

[0051] S5: The preparation method of the negative electrode sheet used includes the following steps: Add 95.4 g of negative electrode active material graphite powder, 2.6 g of conductive agent carbon black, 1 g of thickener CMC, and 1 g of binder SBR to 90 g of deionized water, mix evenly to obtain a negative electrode slurry, and uniformly coat the negative electrode slurry on the surface of the negative electrode sheet current collector copper foil with a thickness of 10 μm, and then dry it to obtain the negative electrode sheet.

[0052] S6: Stack the positive electrode sheet, negative electrode sheet and separator to obtain a laminated body battery cell. Then, ultrasonically weld the tabs of all the positive electrode sheets and ultrasonically weld the tabs of all the negative electrode sheets of the laminated body battery cell. Next, place it in a housing, inject dimethyl carbonate, and seal it to obtain the battery.

[0053] Comparative Example 1: Preparation of a flame-retardant film: It is basically the same as Example 1, with the main difference being that the flame retardant is 20% ytterbium trifluoromethanesulfonate.

[0054] Comparative Example 2: Preparation of a flame-retardant film: It is basically the same as Example 1, with the main difference being that no flame retardant is added.

[0055] Comparative Example 3: Preparation of a flame-retardant battery: It is basically the same as Example 9, with the main difference being that in S1: Mix 71.25 g of polytetrafluoroethylene, 3.75 g of potassium perfluorobutanesulfonate, 47.5 g of polybutylene terephthalate, 2.5 g of ytterbium trifluoromethanesulfonate, 125 g of polystyrene and 15 g of triphenyl phosphate respectively, and then use the melt-biaxial stretching method to prepare the film, including the following steps: crystallization drying - melt extrusion - casting - longitudinal stretching - transverse stretching - heat setting to obtain the inner layer, middle layer and outer layer films respectively. Place the middle layer on both sides of the inner layer, and place the outer layer on the outer side of the two middle layers, and then hot press to obtain a film with a thickness of 5 μm.

[0056] Comparative Example 4: Preparation of a flame-retardant battery: It is basically the same as Example 9, with the main difference being that the inner layer raw material and the outer layer raw material are exchanged.

[0057] Test:

[0058] Test the tensile strength and elongation at break of the metal layer-containing films prepared in Examples 1 - 9 and the metal layer-containing films prepared in Comparative Examples 1 - 4 with reference to the national standard GB / T 1040.3 - 2006, where the data are all longitudinal direction data.

[0059] Pinprick test:

[0060] Select 10 samples of each of the batteries prepared from the films of Examples 1 - 8 and Comparative Examples 1 - 2 and the batteries described in Example 9 and Comparative Examples 3 - 4 for testing. After fully charging at 0.7C at room temperature and standing for 3 hours, then conduct the pinprick test in accordance with GB / T31485 - 2015. Pass the test if there is no smoke and no fire. The passing rate of the pinprick experiment = the number of lithium-ion batteries passing the test / 10. The test results are shown in Table 1.

[0061] Surface temperature rise:

[0062] The batteries prepared from the thin films of Examples 1-8 and Comparative Examples 1-2, and the batteries described in Example 9 and Comparative Examples 3-4 were tested for the temperature rise on the battery surface. A real-time temperature tester was used for the test. The thermocouple induction probe of the temperature tester was placed on the surface of the batteries prepared in the examples and comparative examples, and the temperature was detected in real time, and the maximum surface temperature rise was calculated.

[0063]

[0064] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A flame-retardant film, characterized in that, The raw materials include the following mass percentages: 85.0% - 99.0% polymer, 1.0% - 15.0% flame retardant; The flame-retardant film has a polybutylene terephthalate layer and a polystyrene layer symmetrically and sequentially arranged on both sides of the polytetrafluoroethylene layer. The polybutylene terephthalate layer is arranged between the polytetrafluoroethylene layer and the polystyrene layer. The polytetrafluoroethylene layer includes the following mass percentages of raw materials: 85.0% - 99.0% polytetrafluoroethylene, 1.0% - 15.0% potassium perfluorobutanesulfonate; the polybutylene terephthalate layer includes the following mass percentages of raw materials: 85.0% - 99.0% polybutylene terephthalate, 1.0% - 15.0% ytterbium trifluoromethanesulfonate; the polystyrene layer includes the following mass percentages of raw materials: 85.0% - 99.0% polystyrene, 1.0% - 15.0% triphenyl phosphate; in one side of the flame-retardant film, the mass ratio of polytetrafluoroethylene in the polytetrafluoroethylene layer, polybutylene terephthalate in the polybutylene terephthalate layer, and polystyrene in the polystyrene layer is 3:(2 - 3):4, and the other side of the flame-retardant film is the same.

2. A flame-retardant film according to claim 1, wherein: The thickness of the flame-retardant film is 1μm - 5μm.

3. A flame-retardant current collector, characterized in that: It includes the flame-retardant film described in any one of claims 1 - 2 and a metal layer located on at least one side of the flame-retardant film.

4. A flame-retardant current collector according to claim 3, characterized in that: It includes at least one of the following features (1) - (5): (1) The thickness of the metal layer is 500nm - 2000nm; (2) The material of the metal layer includes one or more of titanium, silver, aluminum alloy, aluminum, nickel alloy, nickel, copper alloy, and copper; (3) A protective layer is provided on the surface of the metal layer; (4) A protective layer is provided on the surface of the metal layer, and the thickness of the protective layer is 10nm - 200nm; (5) A protective layer is provided on the surface of the metal layer, and the material of the protective layer includes one or two of alumina and silicon carbide.

5. A flame-retardant electrode, characterized in that: It includes the flame-retardant current collector described in claim 4, and an active material layer attached to at least one side of the flame-retardant current collector; The active material layer is a positive electrode paste or a negative electrode paste.

6. A flame-retardant battery, characterized in that: It includes the flame-retardant electrode described in claim 5.

7. A flame-retardant electrical device, characterized in that: It includes the flame-retardant battery described in claim 6.

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