Water-resistant and temperature-resistant diaphragm, preparation method thereof and secondary battery

Abstract

The invention discloses a water-resistant and temperature-resistant diaphragm and a preparation method thereof and a secondary battery, the water-resistant and temperature-resistant diaphragm comprises a base membrane, a temperature-resistant coating arranged on at least one surface of the base membrane and a hydrophobic layer arranged on the outer surface of the temperature-resistant coating, slurry of the temperature-resistant coating contains hydrophobic particles, and during drying, the hydrophobic particles are uniformly dispersed in the temperature-resistant coating. And the hydrophobic particles float upwards to the surface of the temperature-resistant coating to form the hydrophobic layer. According to the water-resistant and temperature-resistant diaphragm provided by the invention, the hydrophobic particles are added into the slurry of the temperature-resistant coating, during drying, the hydrophobic particles float to the surface of the temperature-resistant coating to form the hydrophobic layer, and the hydrophobic layer can effectively improve the water resistance of the temperature-resistant coating, so that the phenomenon that the temperature-resistant coating leaks out of a base material after being subsequently coated with a water-based coating is avoided.

Description

Technical Field

[0001] The present invention relates to the field of secondary batteries, and particularly to a water and temperature resistant separator, a preparation method thereof, and a secondary battery. Background Art

[0002] Lithium-ion batteries have been widely used in modern electronic devices due to their excellent performance, such as high specific energy, high specific power, high voltage platform, low self-discharge rate, long cycle life, small environmental impact, and no memory effect. As one of the key components of lithium batteries, the separator plays a crucial role in the safety of lithium batteries. The emergence of ceramic-coated separators has significantly improved the high-temperature tolerance of lithium batteries and greatly reduced the risk of battery runaway.

[0003] However, in the ceramic separator system, the conventional high-temperature resistant separator has become the biggest shortcoming restricting the improvement of the safety of lithium batteries. Therefore, various solutions have emerged in the separator field. To improve the high-temperature tolerance of the separator binder, the heat resistance of some binder products has indeed been improved by adding them. However, the conventional high-temperature resistant coating includes a high-temperature water-soluble binder. Coating a water-based coating on top of this aqueous binder very easily dissolves the underlying coating, resulting in the leakage of the separator substrate.

[0004] Therefore, there is an urgent need to develop a water and temperature resistant separator that can effectively improve the water resistance of the temperature resistant separator. Summary of the Invention

[0005] The purpose of the present invention is to provide, in view of the deficiencies of the prior art, a water and temperature resistant separator that can effectively improve the water resistance of the temperature resistant separator.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A water and temperature resistant separator includes a base film, a temperature resistant coating provided on at least one surface of the base film, and a hydrophobic layer provided on the outer surface of the temperature resistant coating. The slurry of the temperature resistant coating contains hydrophobic particles, and when dried, the hydrophobic particles float to the surface of the temperature resistant coating to form the hydrophobic layer.

[0008] Preferably, the hydrophobic particles account for 0.1 - 30% of the total solid weight of the temperature resistant coating.

[0009] Preferably, the hydrophobic particles include at least one of polyolefin microspheres, polystyrene microspheres, polymethyl methacrylate microspheres, polylactic acid and its copolymer microspheres, organosilicon-acrylate copolymer microspheres, and superhydrophobic monodisperse polymer microspheres.

[0010] Preferably, the particle size D50 of the hydrophobic particles is 5 - 800 nm.

[0011] Preferably, the thickness of the temperature-resistant coating is 0.2 - 10 μm, and the thickness of the hydrophobic layer is 0.005 - 1 μm.

[0012] Preferably, the temperature-resistant coating further includes ceramic particles and a binder;

[0013] The ceramic particles include at least one of alumina, zirconia, silicon carbide, silicon nitride, boehmite, silica, titanium dioxide, magnesium dioxide, barium sulfate, zirconium oxide, and calcium oxide;

[0014] The binder includes at least one of carboxymethyl cellulose, lithium carboxymethyl cellulose, polyacrylic acid, sodium alginate, and polyvinyl alcohol.

[0015] Preferably, the base film is at least one of a PP film, a PE film, a PI film, an aramid film, a PET film, and a PAN film.

[0016] In addition, the present invention also provides a method for preparing a water- and temperature-resistant separator for a secondary battery, including the following steps:

[0017] Step S1: Mix ceramic particles, hydrophobic particles, and a binder to obtain a temperature-resistant coating slurry;

[0018] Step S2: Uniformly coat the temperature-resistant coating slurry on at least one surface of the base film, dry it, and cause the hydrophobic particles to float to the surface of the coating and solidify, thereby obtaining the water- and temperature-resistant separator.

[0019] Preferably, in step S2, the drying temperature is 30 - 80 °C, and the time is 0.1 - 10 min.

[0020] In addition, the present invention also provides a secondary battery, which includes a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, and the separator is the above-mentioned water- and temperature-resistant separator.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] By adding hydrophobic particles to the slurry of the temperature-resistant coating in the present invention, during drying, the hydrophobic particles float to the surface of the temperature-resistant coating to form the hydrophobic layer, and this hydrophobic layer can effectively improve the water resistance of the temperature-resistant coating and prevent leakage from the substrate after subsequent coating of the water-based coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic structural diagram of a water- and temperature-resistant separator according to an embodiment of the present invention.

[0024] Figure 2 It is a schematic structural diagram of the water- and temperature-resistant separator before drying according to an embodiment of the present invention.

[0025] Among them, 1 - base film; 2 - heat - resistant coating; 3 - hydrophobic layer; 4 - hydrophobic particles. Detailed implementation manners

[0026] To make the technical solutions and advantages of the present invention clearer, the following will, in combination with specific embodiments, clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are some, rather than all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts belong to the scope of protection of the present invention.

[0027] According to the first aspect of the present application, the present application aims to provide a water - and heat - resistant diaphragm, including a base film, a heat - resistant coating provided on at least one surface of the base film, and a hydrophobic layer provided on the outer surface of the heat - resistant coating. The slurry of the heat - resistant coating contains hydrophobic particles. During drying, the hydrophobic particles float to the surface of the heat - resistant coating to form the hydrophobic layer.

[0028] Among them, the hydrophobic layer can effectively improve the water resistance of the heat - resistant coating and prevent leakage of the substrate after subsequent coating of the water - based coating.

[0029] In some embodiments, the hydrophobic particles account for 0.1 - 30% of the total solid weight of the heat - resistant coating. For example, it can be 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25% or 30%. Controlling the proportion of the hydrophobic particles in the total solid weight of the heat - resistant coating within this range is beneficial for the floating of the hydrophobic particles during the drying process. When it is greater than this range, it will cause difficulty in the floating of the hydrophobic particles during the drying process.

[0030] In some embodiments, the hydrophobic particles include at least one of polyolefin microspheres, polystyrene microspheres, polymethylacrylate microspheres, polylactic acid and its copolymer microspheres, organosilicon - acrylate copolymer microspheres, and super - hydrophobic monodisperse polymer microspheres.

[0031] In some embodiments, the particle size D50 of the hydrophobic particles is 5 - 800 nm. For example, it can be 5 nm, 50 nm, 100 nm, 200 nm, 400 nm, 600 nm, 700 nm or 800 nm. Controlling the particle size D50 of the hydrophobic particles within this range is for the floating of the hydrophobic particles during the drying process. When it is greater than this range, it will cause difficulty in the floating of the hydrophobic particles during the drying process.

[0032] In some embodiments, the thickness of the heat-resistant coating is 0.2 - 10 μm, for example, it can be 0.2 μm, 0.5 μm, 1 μm, 2 μm, 5 μm, 8 μm or 10 μm, and the thickness of the hydrophobic layer is 0.005 - 1 μm, for example, it can be 0.005 μm, 0.01 μm, 0.1 μm, 0.5 μm, 0.8 μm or 1 μm. Controlling the thickness of the heat-resistant coating within the range is to maintain certain heat resistance and energy density. When it is less than this range, the heat resistance will be insufficient, and when it is greater than this range, the energy density will be insufficient. Controlling the thickness of the hydrophobic layer within the range is controlled according to the size of the hydrophobic particles.

[0033] In some embodiments, the heat-resistant coating further includes ceramic particles and a binder;

[0034] The ceramic particles include at least one of alumina, zirconia, silicon carbide, silicon nitride, boehmite, silica, titanium dioxide, magnesium dioxide, barium sulfate, zirconium oxide and calcium oxide;

[0035] The binder includes at least one of carboxymethyl cellulose, lithium carboxymethyl cellulose, polyacrylic acid, sodium alginate and polyvinyl alcohol.

[0036] In some embodiments, the base film is at least one of a PP film, a PE film, a PI film, an aramid film, a PET film and a PAN film.

[0037] According to the second aspect of the present application, the present application aims to provide a method for preparing a water-resistant and heat-resistant separator, including the following steps:

[0038] Step S1: Mix the ceramic particles, hydrophobic particles and the binder to obtain a heat-resistant coating slurry;

[0039] Step S2: Uniformly coat the heat-resistant coating slurry on at least one surface of the base film, dry it, so that the hydrophobic particles float to the surface of the coating and solidify, thus obtaining the water-resistant and heat-resistant separator.

[0040] In some embodiments, in step S2, the drying temperature is 30 - 80 °C, for example, it can be 30 °C, 40 °C, 50 °C, 60 °C, 70 °C or 80 °C, and the time is 0.1 - 10 min, for example, it can be 0.1 min, 1 min, 2 min, 4 min, 6 min, 8 min or 10 min. When the drying temperature is too low, it will be difficult to dry the slurry, and when the drying temperature is too high, the base film will shrink and be affected.

[0041] According to the third aspect of the present application, the present application provides a secondary battery, which includes a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, and the separator is the above-mentioned water-resistant and heat-resistant separator.

[0042] Among them, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material can be one or more combinations of compounds represented by, but not limited to, chemical formulas such as Li a Ni x Co y M z O 2-b N b (where 0.95 ≤ a ≤ 1.2, x > 0, y ≥ 0, z ≥ 0, and x + y + z = 1, 0 ≤ b ≤ 1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S). The positive electrode active material can also be one or more combinations of, but not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, TiS2, etc. The positive electrode active material can also be modified. The methods for modifying the positive electrode active material should be known to those skilled in the art. For example, methods such as coating and doping can be used to modify the positive electrode active material, and the materials used for the modification can be one or more combinations of, but not limited to, Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc. The positive electrode current collector is usually a structure or part for collecting current, and the positive electrode current collector can be various materials suitable for use as the positive electrode current collector of a lithium-ion battery in the art. For example, the positive electrode current collector can be, but not limited to, a metal foil, and more specifically, it can be, but not limited to, an aluminum foil, etc.

[0043] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode active material layer can be one or several of, but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate, or other metals that can form alloys with lithium.

[0044] Among them, the graphite can be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; the tin-based material can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector is usually a structure or part that collects current. The negative electrode current collector can be various materials in the art suitable for use as the negative electrode current collector of a lithium-ion battery. For example, the negative electrode current collector can include, but is not limited to, metal foils, etc., and more specifically can include, but is not limited to, copper foils, etc. This secondary battery also includes an electrolyte, and the electrolyte includes an organic solvent, an electrolyte lithium salt, and an additive. Among them, the electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-preventing electrolytes; it can also be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DFC, DMC, or EMC; it can also be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additive includes at least one of, but is not limited to, a film-forming additive, a conductive additive, a flame-retardant additive, an overcharge-preventing additive, an additive for controlling the content of H2O and HF in the electrolyte, an additive for improving low-temperature performance, and a multifunctional additive.

[0045] To make the technical solutions and advantages of the present invention clearer, the present invention and its beneficial effects will be further described in detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto.

[0046] Example 1

[0047] Preparation of a water- and temperature-resistant separator

[0048] Step S1: Mix ceramic particles (zirconia), hydrophobic particles (polyolefin microspheres), and a binder (carboxymethyl cellulose) to obtain a temperature-resistant coating slurry.

[0049] Step S2: Uniformly coat the temperature-resistant coating slurry on at least one surface of a 9u PE-based film, and dry it at 30°C for 5 minutes to make the hydrophobic particles float to the surface of the coating and solidify, thus obtaining the water- and temperature-resistant separator.

[0050] Among them, the hydrophobic particles account for 10% of the total solid weight of the temperature-resistant coating, the particle size D50 of the polyolefin microspheres is 500 nm, the thickness of the temperature-resistant coating is 5 um, and the thickness of the hydrophobic layer is 0.5 um.

[0051] Example 2

[0052] Different from Example 1, in this example, the hydrophobic particles account for 0.1% of the total solid weight of the temperature-resistant coating.

[0053] The rest is the same as in Example 1 and will not be elaborated here.

[0054] Example 3

[0055] Different from Example 1, in this example, the hydrophobic particles account for 30% of the total solid weight of the temperature-resistant coating.

[0056] The rest is the same as in Example 1 and will not be elaborated here.

[0057] Example 4

[0058] Different from Example 1, in this example, the particle size D50 of the hydrophobic particles is 5 nm.

[0059] The rest is the same as in Example 1 and will not be elaborated here.

[0060] Example 5

[0061] Different from Example 1, in this example, the particle size D50 of the hydrophobic particles is 800 nm.

[0062] The rest is the same as in Example 1 and will not be elaborated here.

[0063] Example 6

[0064] Different from Example 1, in this example, the thickness of the temperature-resistant coating is 0.2 μm, and the thickness of the hydrophobic layer is 0.005 μm.

[0065] The rest is the same as in Example 1 and will not be elaborated here.

[0066] Example 7

[0067] Different from Example 1, in this example, the thickness of the temperature-resistant coating is 10 μm, and the thickness of the hydrophobic layer is 1 μm.

[0068] The rest is the same as in Example 1 and will not be elaborated here.

[0069] Example 8

[0070] Different from Example 1, in this example, in step S2, the drying temperature is 30 °C and the time is 10 min.

[0071] The rest is the same as in Example 1 and will not be elaborated here.

[0072] Example 9

[0073] Different from Example 1, in this example, in step S2, the drying temperature is 80 °C and the time is 0.1 min.

[0074] The rest is the same as in Example 2 and will not be elaborated here.

[0075] Example 10

[0076] Different from Example 1, in this example, the hydrophobic particles are polymethacrylate microspheres.

[0077] The rest is the same as in Example 2 and will not be elaborated here.

[0078] Comparative Example 1

[0079] Different from Example 1, in this comparative example, no hydrophobic particles are included.

[0080] The rest is the same as in Example 1 and will not be elaborated here.

[0081] Comparative Example 2

[0082] Different from Example 1, in this comparative example, the hydrophobic particles account for 40% of the total solid weight of the temperature-resistant coating.

[0083] The rest is the same as in Example 1 and will not be elaborated here.

[0084] Comparative Example 3

[0085] Different from Example 1, in this comparative example, the particle size D50 of the hydrophobic particles is 900 nm.

[0086] The rest is the same as in Example 1 and will not be elaborated here.

[0087] Comparative Example 4

[0088] Different from Example 1, in this comparative example, the thickness of the temperature-resistant coating is 15 μm.

[0089] The rest is the same as in Example 1 and will not be elaborated here.

[0090] Comparative Example 5

[0091] Different from Example 1, in this comparative example, the thickness of the hydrophobic layer is 5 μm.

[0092] The rest is the same as in Example 1 and will not be elaborated here.

[0093] Comparative Example 6

[0094] Different from Example 1, in this comparative example, in step S2, the drying temperature is 120 °C and the time is 20 min.

[0095] The rest is the same as in Example 1 and will not be elaborated here.

[0096] The following performance tests were conducted on the temperature-resistant and water-resistant diaphragms prepared in the examples and comparative examples respectively:

[0097] (1) Hydrophobic effect test: Drop deionized water on the temperature-resistant and water-resistant diaphragm prepared above, and measure the diameter value of the water droplet on the diaphragm surface within 1 minute after standing for one minute.

[0098] (2) Heat shrinkage test: Cut the temperature-resistant and water-resistant diaphragm prepared above into a rectangular piece of 100 mm × 120 mm, measure the MD and TD dimensions, place it in the oven of the heat shrinkage rate detector, and ensure that the sample is flat. After heating to 120 °C for one hour, take it out and cool it to room temperature, then measure its shrunk dimensions, and calculate the MD and TD shrinkage rate values.

[0099] The results of the above performance tests are shown in Table 1 below.

[0100] Table 1

[0101]

[0102] From the data comparison between Examples 1-10 and Comparative Examples 1-6 in Table 1, it can be seen that in the present invention, by adding hydrophobic particles to the slurry of the temperature-resistant coating, during drying, the hydrophobic particles float to the surface of the temperature-resistant coating to form the hydrophobic layer, and this hydrophobic layer can effectively improve the water resistance of the temperature-resistant coating and avoid leakage from the substrate after subsequent coating of the water-based coating.

[0103] According to the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments, and any obvious improvements, substitutions or variations made by those skilled in the art on the basis of the present invention all fall within the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A water- and temperature-resistant diaphragm, characterized in that, It includes a base film, a heat-resistant coating provided on at least one surface of the base film, and a hydrophobic layer provided on the outer surface of the heat-resistant coating. The slurry of the heat-resistant coating contains hydrophobic particles, and when dried, the hydrophobic particles float to the surface of the heat-resistant coating to form the hydrophobic layer.

2. The water- and temperature-resistant separator according to claim 1, wherein The hydrophobic particles account for 0.1-30% of the total solid weight of the heat-resistant coating.

3. The water- and temperature-resistant separator according to claim 1, wherein The hydrophobic particles include at least one of polyolefin microspheres, polystyrene microspheres, polymethyl methacrylate microspheres, polylactic acid and its copolymer microspheres, silicone-acrylate copolymer microspheres, and superhydrophobic monodisperse polymer microspheres.

4. The water- and temperature-resistant diaphragm according to claim 1 or 3, characterized in that The particle size D50 of the hydrophobic particles is 5-800 nm.

5. The water- and temperature-resistant separator according to claim 1, characterized in that, The thickness of the heat-resistant coating is 0.2-10 μm, and the thickness of the hydrophobic layer is 0.005-1 μm.

6. The water- and temperature-resistant separator according to claim 1, wherein, The heat-resistant coating further includes ceramic particles and a binder; The ceramic particles include at least one of alumina, zirconia, silicon carbide, silicon nitride, boehmite, silica, titanium dioxide, magnesium dioxide, barium sulfate, zirconium oxide, and calcium oxide; The binder includes at least one of carboxymethyl cellulose, lithium carboxymethyl cellulose, polyacrylic acid, sodium alginate, and polyvinyl alcohol.

7. The water- and temperature-resistant separator according to claim 1, characterized in that, The base film is at least one of a PP film, a PE film, a PI film, an aramid film, a PET film, and a PAN film.

8. A method for preparing a water- and temperature-resistant separator according to any one of claims 1-7, characterized in that, It includes the following steps: Step S1: Mix the ceramic particles, hydrophobic particles, and binder to obtain a heat-resistant coating slurry; Step S2: Uniformly coat the heat-resistant coating slurry on at least one surface of the base film, dry it, and make the hydrophobic particles float to the surface of the coating and solidify, thus obtaining the water-resistant and heat-resistant separator.

9. The preparation method of the water- and temperature-resistant separator according to claim 8, characterized in that, In step S2, the drying temperature is 30-80 °C and the time is 0.1-10 min.

10. A secondary battery, characterized in that, It includes the water-resistant and heat-resistant separator according to any one of claims 1-7.

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