High-heat-resistance and high-safety composite coating diaphragm for battery and preparation method thereof

Abstract

The invention belongs to the technical field of lithium battery diaphragms, and provides a high-heat-resistance and high-safety composite coating diaphragm for a battery and a preparation method of the high-heat-resistance and high-safety composite coating diaphragm. According to the invention, a technical scheme of composite coating of a high-heat-resistance organic material and an oxide material is adopted. The preparation method comprises the following steps: adding a dispersant into an organic solvent to prepare a dispersion solution; adding a high-heat-resistance organic material and an oxide material into the dispersion solution to be mixed and dispersed; adding zirconium beads, grinding, filtering, and adding a binder, a thickening agent and a wetting agent to prepare coating slurry; coating the surface of a polyolefin base membrane with the slurry; and extracting and drying to obtain the composite coating diaphragm. The prepared composite coating diaphragm has excellent high-temperature stability and safety performance, the wettability is obviously improved, the ionic conductivity is obviously improved, and the composite coating diaphragm is suitable for high-safety lithium batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium battery separator technology, specifically to a high heat resistance and high safety composite coated separator for batteries and its preparation method. Background Technology

[0002] Lithium-ion batteries (LIBs) have been widely used as the primary energy storage device in electric vehicles (EVs), smartphones, and laptops due to their high energy density and affordable cost.

[0003] A lithium-ion battery consists of four core components: the cathode, anode, electrolyte, and separator. The separator's primary function is to prevent physical contact between the positive and negative electrodes to avoid internal short circuits and to provide a pathway for lithium-ion transport. Although the separator cannot directly participate in the electrochemical process, it has a significant impact on the battery's cycle performance, safety, reliability, energy, and power density.

[0004] However, existing polyolefin separator technology suffers from the following problems: mechanical and thermal abuse can cause a rapid rise in internal temperature of the lithium-ion battery, leading to separator failure and internal short circuits. These short circuits generate extremely high current flows, producing significant heat through ohmic heating in localized areas, causing thermal decomposition of the internal materials and ultimately reaching a catastrophic ignition point. Furthermore, the poor electrolyte affinity and low surface energy of polyolefin separators result in incomplete filling of the pores by the liquid electrolyte, increasing ionic resistance and affecting the battery's electrochemical performance.

[0005] Therefore, there is an urgent need to develop high-performance separators that exhibit good wettability and improved thermal stability in order to improve the safety and electrochemical performance of lithium-ion batteries. Summary of the Invention

[0006] Based on the problems existing in the background technology, the present invention provides a high heat resistance and high safety composite coated separator for batteries and its preparation method. The method involves mixing and stirring high heat resistance organic materials and oxide materials with solvents, binders, thickeners and wetting agents to form a slurry, and then coating the high heat resistance composite material slurry onto a polyolefin battery separator to improve the high temperature resistance of the polyolefin separator, prolong the time to reach the thermal runaway trigger temperature, and improve the safety level of the battery.

[0007] This invention is implemented through the following technical solutions: A method for preparing a high-heat-resistant and high-safety composite coated separator for batteries includes the following steps: Step 1: Add the dispersant to the organic solvent and stir to obtain a dispersion solution; Step 2: Add the high heat-resistant organic material and oxide material to the dispersion solution obtained in Step 1, stir, and obtain a uniform dispersion solution; Step 3: Add zirconium beads to the uniformly dispersed solution obtained in step 2, grind, demagnetize and filter, then add binder, thickener and wetting agent and stir to obtain coating slurry; Step 4: Apply the coating slurry to the surface of the porous polyolefin-based membrane; Step 5: After extraction and drying, the coated base film is used to obtain a composite coated diaphragm.

[0008] Further, the dispersant is one or more of the following: alkylammonium salt of polycarboxylic acid, copolymer of low molecular weight unsaturated polycarboxylic acid polymer and polysiloxane, polycarboxylic acid salt of polyamine amide, polyether polyester modified phosphate ester, and styrene-maleic acid copolymer. The organic solvent is one or a mixture of two of the following: ethanol, diethyl ether, acetone, N-methylpyrrolidone, dimethylformamide, and dimethylacetamide.

[0009] Furthermore, the high heat-resistant organic material is one or more of the following: polyamide polymers containing heterocyclic aromatics, olefin polymers containing cyano functional groups, ester polymers containing aromatic rings, polymers containing ketone bonds and ether bonds, and nanocellulose containing carboxyl, hydroxyl or sulfonyl functional groups. The oxide material is one or more of the following: alumina, silica, boehmite, LLZO, and LATP.

[0010] Furthermore, in step 1, the mass of the dispersant accounts for 0.2-15% of the mass of the high heat-resistant organic material; the stirring temperature is 50-90℃, the stirring speed is 600-2000 r / min, and the stirring time is 20-120 min.

[0011] Furthermore, in step 2, the particle size D50 of the high heat-resistant organic material and the oxide material is 0.2–1.2 μm; the mass ratio of the high heat-resistant organic material to the oxide material is 1:(0.5–3); the stirring temperature is room temperature, the stirring speed is 500–2000 r / min, and the stirring time is 0.5–8 h.

[0012] Further, the adhesive is one or more of polymethyl acrylate, polyvinylpyrrolidone, polyvinylidene fluoride, polyacrylic acid, polyvinyl alcohol, polyacrylamide, and carboxymethyl cellulose; the molecular weight of the adhesive is 100,000 to 1,500,000; and the total mass ratio of the adhesive to the high heat-resistant organic material and oxide material is 1:(1-100). The thickener is one or more of methylcellulose, sodium carboxymethylcellulose, and hydroxypropyl methylcellulose; the mass ratio of the thickener to the high heat-resistant organic material is 1:(20-500); The wetting agent is one or more of polyols and fatty alcohol ethers; the mass ratio of the wetting agent to the high heat-resistant organic material is 1:(20-5000); The solid content of the coating slurry is 7-23%; the viscosity is 30-230 cp.

[0013] Furthermore, in step 3, the zirconium beads have a particle size of 200–800 μm, the grinding time is 8–15 h, the stirring temperature is room temperature, the stirring speed is 500–2000 r / min, and the stirring time is 0.5–3 h.

[0014] Furthermore, in step 4, the thickness of the porous polyolefin-based membrane is 3–20 μm, and the thickness of the dry coating film is 1–8 μm; the coating method is roller coating or wire rod coating; the coating position is one side or both sides of the polyolefin-based membrane.

[0015] Further, in step 5, the extraction involves immersing the coated diaphragm in a mixture of water or ethanol and a slurry solvent for 1–30 min; the drying temperature is 60–120 °C, and the drying time is 3–80 min.

[0016] The present invention also provides a high heat-resistant and high safety composite coated separator for batteries, comprising a polyolefin base film and a composite coating coated on the surface of the base film, wherein the composite coating comprises a high heat-resistant organic material, an oxide material and a binder, and the composite coated separator is prepared by the above method.

[0017] The beneficial effects of this invention are: The high-heat-resistant coated separator for batteries prepared by the method of this invention not only improves the high-temperature resistance of the polyolefin separator and prolongs the time to reach the thermal runaway trigger temperature, thus improving the overall safety of the battery, but also increases the separator's affinity for the electrolyte, enhancing its electrolyte storage capacity and improving ionic conductivity. Therefore, the high-heat-resistant separator prepared by this method not only improves the thermal performance of the battery blockchain (LIB) but also enhances its electrochemical performance. Attached Figure Description

[0018] The accompanying drawings are provided to further explain the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the high heat resistance and high safety composite coated diaphragm of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0020] like Figure 1As shown, the high heat-resistant and high-safety composite coated separator for batteries provided by the present invention includes a polyolefin base film and a high heat-resistant composite coating coated on the surface of the base film. The composite coating can be coated on one or both sides of the base film to form a single-sided or double-sided coated structure.

[0021] Example 1: This example prepares a high heat resistance and high safety composite coated separator for batteries. The coated separator includes a polyethylene microporous separator and a high heat resistance composite coating.

[0022] The high heat-resistant composite material is a mixture of poly(p-phenylenebenzodioxazole) (PBO) and alumina; The solvent used in the coating slurry is dimethylacetamide (DMAC); The dispersant is a polyether polyester modified phosphate ester, used at 0.5% of the PBO weight; The adhesive is polyvinylidene fluoride (PVDF); The D50 of PBO is 0.4 μm; the D50 of alumina is 0.8 μm; the mass ratio of the mixture of PBO and alumina to PVDF is 5:5, and the mass ratio of PBO to alumina is 4:6. The mass ratio of thickener (methylcellulose) to PBO is 1:100, and the mass ratio of wetting agent (polyol) to PBO is 1:200. The solid content of the coating slurry is 14%.

[0023] The preparation method includes the following steps: Step 1, Dispersion preparation: In a stirred tank, the polyether polyester modified phosphate dispersant is added to dimethylacetamide, stirred at 800 r / min and 60℃ for 60 min to obtain a uniform dispersion.

[0024] Step 2, material dispersion: Add the dried high heat-resistant PBO powder to the dispersion solution obtained in Step 1, stir at 1500 r / min, and stir for 90 min at room temperature to obtain a uniformly mixed dispersion solution.

[0025] Step 3, grinding and homogenization: Zirconium beads (particle size 400μm) are added to the dispersion solution obtained in step 2, and ground thoroughly on a shaker for 12 hours. After demagnetization and filtration, binder, thickener and wetting agent are added and stirred thoroughly to obtain a uniform coating slurry.

[0026] Step 4, Coating application: The coating slurry is applied to the surface of a 9μm polyethylene film by roller coating, and the coating thickness is controlled so that the dry film thickness is 3μm.

[0027] Step 5, extraction and drying: Immerse the coated diaphragm in a mixed solvent of water and dimethylacetamide for 3 min, and then bake at 70℃ for 30 min to obtain a high heat-resistant composite coated diaphragm.

[0028] Example 2: This example provides a high heat resistance and high safety composite coated separator for batteries. The difference between this example and Example 1 is that the mass ratio of the mixture of PBO and alumina to PVDF is 6:4.

[0029] Example 3: This example provides a high heat resistance and high safety composite coated separator for batteries. The main difference between this example and Example 1 is that the molecular weight of the binder is higher, with a molecular weight of 1,200,000; the secondary difference is that the mass ratio of the mixture of PBO and alumina to PVDF is 6:4.

[0030] Example 4: This example provides a high heat resistance and high safety composite coated separator for batteries. The difference between this example and Example 1 is that the mass ratio of the mixture of PBO and alumina to PVDF is 7:3.

[0031] Example 5: This example provides a high heat resistance and high safety composite coated separator for batteries. The difference between this example and Example 1 is that the mass ratio of the mixture of PBO and alumina to PVDF is 8:2.

[0032] Example 6: This example provides a high heat resistance and high safety composite coated separator for batteries. The difference between this example and Example 1 is that the high heat resistance organic material used is a composite of polyether ether ketone (PEEK) and alumina, with a mass ratio of PEEK to alumina of 4:6.

[0033] Example 7: This example provides a high heat resistance and high safety composite coated separator for batteries. The difference between this example and Example 1 is that the high heat resistance organic material used is a composite of poly(p-phenylenebenzodioxazole) (PBO) and alumina, with a mass ratio of PBO to alumina of 5:5.

[0034] Example 8: This example provides a high heat resistance and high safety composite coated separator for batteries. The difference between this example and Example 1 is that the high heat resistance organic material used is a composite of poly(p-phenylenebenzodioxazole) (PBO) and alumina, with a mass ratio of PBO to alumina of 3:7.

[0035] Comparative Example 1: To compare the effect of high heat-resistant materials on improving the safety and wetting performance of the diaphragm, the difference between this comparative example and Example 1 is that the coating material of Comparative Example 1 is alumina.

[0036] Comparative Example 2: To compare the effect of high heat-resistant materials on improving the safety and wetting performance of the diaphragm, the difference between this comparative example and Example 1 is that the coating material of Comparative Example 2 is a single coating material PBO.

[0037] Comparative Example 3: To compare the effect of high heat-resistant materials on improving the safety and wetting performance of the diaphragm, the difference between this example and Example 1 is that the coating is a single component and the high heat-resistant organic material used is polyether ether ketone (PEEK).

[0038] The performance of the coated diaphragms prepared in Examples 1-8 and Comparative Examples 1-3 was tested.

[0039] 1. Heat shrinkage test.

[0040] Test method: Cut the diaphragm into 100mm*100mm pieces, mark two equidistant points in the MD and TD directions, calculate the distances M0 and T0 between the two points in the MD and TD directions, place it in an oven, set the required temperature, and bake for 1 hour. Then, take it out and test the distances M1 and T1 between the two points in the MD and TD directions. Calculate the shrinkage rate based on the difference before and after baking.

[0041] 2. Wettability test.

[0042] Test method: Use tape to stretch and stick a 60mm*40mm diaphragm to an H-shaped plate to ensure that the diaphragm surface is flat. After dropping 2μL of electrolyte on the diaphragm surface, take a picture immediately and use a machine to calibrate the diameter of the electrolyte in the MD and TD directions. After standing for 5 minutes, take a picture of the same droplet again and measure the diameter of the electrolyte in the MD and TD directions. Then calculate the wetting value.

[0043] 3. Ionic conductivity test.

[0044] Test method: Cut 5 50*50mm membrane pieces, soak them in electrolyte for 1 hour, and use an electrochemical workstation to test the ionic conductivity. The fit should reach 99.9%.

[0045] 4. Hot nail puncture test.

[0046] Test method: A 50mm diameter coated film was fixed to a hot nail puncture testing machine using a clamp, ensuring the surface of the test mold was flat. The diameter of the pointed, rounded-corner hot nails was 0.2mm, the test temperature was set to 250℃, and the distance was set to -0.1mm. After the test, the diameter of the black spots or holes on the diaphragm was recorded under a digital microscope.

[0047] The test results are shown in Table 1 below.

[0048] Table 1. Performance test results of the coated diaphragms prepared in Examples 1-8 and Comparative Examples 1-3.

[0049] As shown in Table 1, comparing Examples 1-8 and Comparative Examples 1-3, it can be found that the high-temperature resistant composite material can significantly improve the high-temperature safety and wettability of the separator. Compared with Comparative Example 1, the wettability of MD in Example 1 increased by 2.6 times, and the ionic conductivity increased by 55.5%, indicating that the composite coating can improve the safety and electrochemical performance of the battery cell. The ratio of PBO, alumina, and binder affects the high-temperature resistance and wettability of the separator. Comparative Examples 2 and 3 show that PBO has superior thermal stability and good wettability. Comparing Example 1 and Comparative Examples 1-2, it can be found that the alumina and PBO composite coating has the best electrochemical performance and high-temperature stability. PBO material can serve as a flexible skeleton, providing excellent mechanical strength and toughness, ensuring the integrity of the coating structure, while alumina provides a good thermal barrier and electrolyte affinity. The composite coating structure formed by PBO and alumina exhibits excellent high-temperature performance. The flexible PBO framework binds the alumina particles, preventing them from pulverizing or detaching due to brittleness, thus maintaining the integrity and mechanical strength of the coating structure. Since PBO is relatively expensive, by optimizing the formulation and using a low-cost alumina and PBO composite, high-temperature stability, wettability, and ionic conductivity can reach the level of single-component PBO coatings, significantly reducing costs by at least 60%, which is beneficial for large-scale production.

[0050] Finally, it should be noted that the above embodiments are merely illustrative of several implementations of the present invention and are not intended to limit the scope of the invention. For those skilled in the art, any modifications, equivalent substitutions, or improvements made without departing from the concept of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a high-heat-resistant and high-safety composite coated separator for batteries, characterized in that, Includes the following steps: Step 1: Add the dispersant to the organic solvent and stir to obtain a dispersion solution; Step 2: Add the high heat-resistant organic material and oxide material to the dispersion solution obtained in Step 1, stir, and obtain a uniform dispersion solution; Step 3: Add zirconium beads to the uniformly dispersed solution obtained in step 2, grind, demagnetize and filter, then add binder, thickener and wetting agent and stir to obtain coating slurry; Step 4: Apply the coating slurry to the surface of the porous polyolefin-based membrane; Step 5: After extraction and drying, the coated base film is used to obtain a composite coated diaphragm.

2. The preparation method according to claim 1, characterized in that, The dispersant is one or more of the following: alkyl ammonium salt of polycarboxylic acid, low molecular weight unsaturated polycarboxylic acid polymer and polysiloxane copolymer, polycarboxylic acid salt of polyamine amide, polyether polyester modified phosphate ester, and styrene-maleic acid copolymer. The organic solvent is one or a mixture of two of the following: ethanol, diethyl ether, acetone, N-methylpyrrolidone, dimethylformamide, and dimethylacetamide.

3. The preparation method according to claim 1, characterized in that, The high heat-resistant organic material is one or more of the following: polyamide polymers containing heterocyclic aromatic groups, olefin polymers containing cyano functional groups, ester polymers containing aromatic rings, polymers containing ketone and ether bonds, and nanocellulose containing carboxyl, hydroxyl, or sulfonyl functional groups. The oxide material is one or more of the following: alumina, silica, boehmite, LLZO, and LATP.

4. The preparation method according to claim 1, characterized in that, In step 1, the mass of the dispersant accounts for 0.2-15% of the mass of the high heat-resistant organic material; the stirring temperature is 50-90℃, the stirring speed is 600-2000 r / min, and the stirring time is 20-120 min.

5. The preparation method according to claim 1, characterized in that, In step 2, the particle size D50 of the high heat-resistant organic material and oxide material is 0.2-1.2 μm; the mass ratio of the high heat-resistant organic material to the oxide material is 1:(0.5-3); the stirring temperature is room temperature, the stirring speed is 500-2000 r / min, and the stirring time is 0.5-8 h.

6. The preparation method according to claim 1, characterized in that, The adhesive is one or more of the following: polymethyl acrylate, polyvinylpyrrolidone, polyvinylidene fluoride, polyacrylic acid, polyvinyl alcohol, polyacrylamide, and carboxymethyl cellulose; the molecular weight of the adhesive is 100,000 to 1,500,000; and the total mass ratio of the adhesive to the high heat-resistant organic material and oxide material is 1:(1-100). The thickener is one or more of methylcellulose, sodium carboxymethylcellulose, and hydroxypropyl methylcellulose; the mass ratio of the thickener to the high heat-resistant organic material is 1:(20-500); The wetting agent is one or more of polyols and fatty alcohol ethers; the mass ratio of the wetting agent to the high heat-resistant organic material is 1:(20-5000); The solid content of the coating slurry is 7-23%; the viscosity is 30-230 cp.

7. The preparation method according to claim 1, characterized in that, In step 3, the zirconium beads have a particle size of 200–800 μm, the grinding time is 8–15 h, the stirring temperature is room temperature, the stirring speed is 500–2000 r / min, and the stirring time is 0.5–3 h.

8. The preparation method according to claim 1, characterized in that, In step 4, the thickness of the porous polyolefin-based membrane is 3–20 μm, and the thickness of the dry coating film is 1–8 μm; the coating method is roller coating or wire rod coating; the coating position is one side or both sides of the polyolefin-based membrane.

9. The preparation method according to claim 1, characterized in that, In step 5, the extraction involves immersing the coated diaphragm in a mixture of water or ethanol and slurry solvent for 1–30 min; the drying temperature is 60–120 °C and the drying time is 3–80 min.

10. A high-heat-resistant and high-safety composite coated separator for batteries, characterized in that, The membrane comprises a polyolefin-based membrane and a composite coating applied to the surface of the membrane, the composite coating comprising a high heat-resistant organic material, an oxide material and a binder, and the composite coated membrane is prepared by the method described in any one of claims 1-9.

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