Battery separator and preparation method and application thereof

Abstract

The application belongs to the field of advanced inorganic non-metallic materials and electronic core industry technology, and relates to a battery assembly, in particular to a lithium ion battery assembly, and in particular to a battery diaphragm and a preparation method and application thereof. Wollastonite, bentonite, a silane coupling agent, a titanate and anhydrous ethanol are uniformly mixed, the pH is adjusted to be acidic, and a modified porcelain powder is obtained by modifying reaction at 80-120 DEG C; the modified porcelain powder is mixed with glass powder and polyolefin to obtain a mixed powder, and the mixed powder is melt-extruded, stretched, extracted and shaped to obtain the battery diaphragm. The battery diaphragm provided by the application can not only avoid lithium battery combustion and explosion caused by temperature rise, but also improve the tensile property and puncture resistance of the battery diaphragm, and significantly improve the safety of the lithium battery.

Description

Technical Field

[0001] This invention belongs to the field of advanced inorganic non-metallic materials and core electronic industry technology, and relates to battery components, especially lithium-ion battery components, specifically a battery separator and its preparation method and application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Currently, commercially available lithium-ion battery separators use microporous films primarily composed of polyolefin materials. The biggest problem with these materials is their relatively low melting point. When the internal temperature of the battery rises rapidly, the separator ruptures, leading to internal short circuits and thermal runaway, ultimately causing the lithium-ion battery to burn or explode. The low melting point of polyolefins is the fundamental reason affecting the safety of lithium-ion battery separators. Effectively overcoming the limitations of polyolefin materials is key to developing high-safety lithium-ion battery separators.

[0004] According to the inventors' research, the main ways to improve the safety of lithium-ion battery separators include structural composites, mixing materials, and / or adding coatings. However, further research revealed that these methods offer limited improvement in the safety of lithium-ion battery separators, failing to overcome the inherent limitations of polyolefin materials. Furthermore, while improving safety, they often sacrifice other separator properties, such as puncture resistance and reduced permeability. Therefore, improving the safety of lithium-ion battery separators while ensuring other performance characteristics is a pressing technical challenge. Summary of the Invention

[0005] To improve the safety performance of lithium battery separators and avoid impacting other aspects of performance while enhancing safety, the present invention aims to provide a battery separator, its preparation method, and its application. Under the same conditions of thickness, air permeability, and porosity, the battery separator provided by the present invention can not only prevent lithium battery combustion and explosion caused by temperature rise, but also improve the tensile properties and puncture resistance of the battery separator, thus significantly improving the safety of lithium batteries.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] On one hand, a method for preparing a battery separator involves uniformly mixing wollastonite, bentonite, silane coupling agent, titanate, and anhydrous ethanol, fluorine-free pure water, or isopropanol; adjusting the pH to acidic; and heating to 80–120°C to perform a modification reaction to obtain modified ceramic powder; mixing the modified ceramic powder with glass powder and polyolefin to obtain a mixed powder; and then melting, extruding, stretching, extracting, and shaping the mixed powder with paraffin oil to obtain the final product.

[0008] Polyolefins are preferably polyethylene or polypropylene;

[0009] The mass ratio of wollastonite to bentonite is 2-6:0.5-1.5, the mass ratio of silane coupling agent to titanate is 2-8:2-6, and the total mass ratio of wollastonite and bentonite to the total mass ratio of silane coupling agent to titanate is 5-10:0.5-1.

[0010] The mass ratio of modified ceramic powder, glass powder and polyolefin is 8-15:2-7:78-90.

[0011] This invention uses modified ceramic powder, glass powder, and polyolefin to form a uniformly dispersed membrane material through melt extrusion, stretching, extraction, and shaping. At low temperatures, the mechanical strength of the polyolefin itself supports the porous structure of the membrane, allowing it to function normally. As the temperature rises, the polyolefin softens, and the mechanical strength of the modified ceramic powder continues to provide support, ensuring the separation between the positive and negative electrodes. As the temperature continues to rise, the glass powder melts and encapsulates and bridges with the modified ceramic powder, filling the pores formed by the melting of the polyolefin and maintaining the isolation between the positive and negative electrodes. When the temperature rises further, the glass powder, which is completely thermally decomposed and melted into a liquid phase, continues to increase and bridges and bonds with the ceramic powder components. The two undergo a eutectic reaction to form a hard ceramic structure that continues to maintain the isolation between the positive and negative electrodes.

[0012] Meanwhile, research shows that modified ceramic powder modified by silane coupling agent and titanate can improve its bonding performance with polyolefins. With the addition of the above proportions, the tensile properties and puncture resistance of the prepared diaphragm material are significantly improved.

[0013] On the other hand, a battery separator is obtained by the above preparation method.

[0014] Thirdly, the application of the aforementioned battery separator in lithium-ion batteries.

[0015] The beneficial effects of this invention are as follows:

[0016] In the battery separator prepared by this invention, during the rapid rise in battery temperature, the inorganic component, including the glass powder, melts into a liquid phase after reaching a certain temperature range. This liquid phase fills the voids in the molten polyolefin material while simultaneously bridging and coating the ceramic powder material, promoting the ceramicization reaction. An inorganic ceramic layer is formed between the positive and negative electrodes to prevent short circuits and avoid lithium battery combustion and explosion due to continued heating, significantly improving lithium battery safety. Furthermore, the addition of modified ceramic powder increases the bonding performance between the ceramic powder and polyolefin, thereby further enhancing the tensile and puncture resistance of the battery separator. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] Figure 1 The diagram shows the ceramicization mechanism of the battery separator prepared in the embodiments of the present invention. 1. Polyethylene matrix, 2. Modified ceramic powder (wollastonite), 3. Modified ceramic powder (bentonite), 4. Glass powder, 5. Pore structure.

[0019] Figure 2 The images are scanning electron microscope (SEM) images of the battery separator prepared in Example 1 of the present invention before and after sintering. a is before sintering and b is after sintering.

[0020] Figure 3 Thermogravimetric analysis (TGA) curves of the battery separator prepared for embodiments of the present invention;

[0021] Figure 4 The puncture performance curve of the battery separator prepared in the embodiments of the present invention;

[0022] Figure 5 The tensile strength curve of the battery separator prepared in an embodiment of the present invention. Detailed Implementation

[0023] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] Given that existing lithium-ion battery separators cannot simultaneously guarantee safety and puncture resistance, this invention proposes a battery separator, its preparation method, and its application.

[0026] A typical embodiment of the present invention provides a method for preparing a battery separator, comprising: uniformly mixing wollastonite, bentonite, silane coupling agent, titanate, and anhydrous ethanol; adjusting the pH to acidic; and heating to 80-120°C to carry out a modification reaction to obtain modified ceramic powder; mixing the modified ceramic powder with glass powder and polyolefin to obtain a mixed powder; and performing melt extrusion, stretching, extraction, and shaping of the mixed powder with paraffin oil to obtain the final product.

[0027] The mass ratio of wollastonite to bentonite is 2-6:0.5-1.5, the mass ratio of silane coupling agent to titanate is 2-8:2-6, and the total mass ratio of wollastonite and bentonite to the total mass ratio of silane coupling agent to titanate is 5-10:0.5-1.

[0028] The mass ratio of modified ceramic powder, glass powder and polyolefin is 8-15:2-7:78-90.

[0029] In some embodiments, the D of wollastonite 50 The D of bentonite with a particle size of 100-150 μm 50 The particle size is 100–150 μm.

[0030] In some embodiments, the silane coupling agent is silane coupling agent KH560.

[0031] In some embodiments, wollastonite, bentonite, silane coupling agent, titanate, and anhydrous ethanol are mixed thoroughly and the pH is adjusted to 4–5. Using the modified ceramic powder obtained under these conditions as raw material, the battery separator prepared exhibits better performance. The pH is adjusted using hydrochloric acid.

[0032] In some embodiments, the reaction time in the modification reaction is 5–7 hours. During the reaction, the rotation speed is 200–500 r / min.

[0033] In some embodiments, the mass ratio of the total mass of wollastonite and bentonite to the mass of anhydrous ethanol is 5–10:1–3.

[0034] The polyolefin described in this invention is polyethylene, polypropylene, or a mixture thereof. In some embodiments, the polyolefin is polyethylene. The viscosity-average molecular weight of the polyethylene is preferably 80–150 W, i.e., (0.8–1.5) × 10⁻⁶. 6 .

[0035] In some embodiments, the glass powder is a low-temperature glass powder. It is prepared by melt copolymerization of inorganic materials such as SiO2, P2O5, B2O3, Li2O, ZnO, BaO, K2O, and Na2O. In this invention, the low-temperature glass powder is melted in the range of 200–280°C.

[0036] In some embodiments, the mass ratio of the mixed powder to the paraffin oil is 20-40:60-80.

[0037] In some embodiments, during the melt extrusion process, the extruder temperature range is 180–220°C, the rotation speed is 90–150 rpm / min, the molten material is cast into a sheet through a die exit with a gap of 1.5–2.5 mm, and the sheet is pulled through a cooling roller to cool into a sheet, the roller speed is 4–8 m / min, and the roller temperature is 15–20°C.

[0038] In some embodiments, the stretching is performed using asynchronous bidirectional stretching or synchronous bidirectional stretching.

[0039] In some embodiments, the stretching temperature is 90–130°C and the stretching ratio is 6–15 times.

[0040] In some embodiments, dichloromethane is used to extract paraffin oil.

[0041] In some embodiments, the material is stretched and shaped again after extraction. The stretching temperature and the shaping temperature are 90–130°C, and the stretching ratio is 1–5 times.

[0042] Specifically, the steps are as follows:

[0043] 1. Modification of the porcelain powder: Wollastonite with a particle size D50 of 100-150 μm was mixed with bentonite, anhydrous ethanol, silane coupling agent KH560, and titanate. The pH was adjusted to 4-5 with HCl solution, the temperature was controlled in the range of 80-120℃, the rotation speed was 200-500 r / min, and the mixture was heated and stirred for 5-7 h. After the mixture was dried under vacuum, the modified porcelain powder was obtained. The mass ratio of wollastonite to bentonite was (2-6):(0.5-1.5), the mass ratio of KH560 to titanate was (2-8):(2-6), and the mass ratio of wollastonite / bentonite, anhydrous ethanol, and KH560 / titanate was (5-10):(1-3):(0.5-1).

[0044] 2. The modified ceramic powder, low-temperature glass powder, and polyethylene with a viscosity-average molecular weight of 80-150W prepared in step 1 are mixed in a high-speed mixer and discharged after 1-2 hours; wherein the mass ratio of ceramic powder, glass powder, and polyethylene is (8-15):(2-7):(78-90);

[0045] 3. The mixture obtained in step 2 and paraffin oil are added to a twin-screw extruder for melting through a metering system. The ratio of the mixture to paraffin oil is (20-40):(60-80). The extruder temperature range is 180-220℃, and the speed is 90-150 rpm / min. The molten material is cast into sheets through a die with a gap of 1.5-2.5 mm. The sheets are then pulled through cooling rollers to cool into sheets. The roller speed is 4-8 m / min, and the roller temperature is 15-20℃.

[0046] 4. The sheet obtained in step 3 is drawn into an asynchronous biaxial stretching or synchronous biaxial stretching device, with a stretching temperature of 90-130℃ and a stretching ratio of 6-15 times.

[0047] 5. Immerse the material obtained in step 4 in a device containing dichloromethane to extract paraffin oil, and then dry it at a temperature of 35-45°C.

[0048] 6. The material obtained in step 5 is drawn into a transverse stretching device, stretched and shaped into a film with a thickness of 2 to 16 μm. The stretching temperature and the shaping temperature are 90 to 130°C, and the stretching ratio is 1 to 5 times.

[0049] 7. The material obtained in step 6 is pulled into the winding device for winding.

[0050] In another embodiment of the present invention, a battery separator is provided, which is obtained by the above preparation method.

[0051] Specifically, the thickness is 2–16 μm.

[0052] Thirdly, the application of the aforementioned battery separator in lithium-ion batteries.

[0053] Specifically, a lithium-ion battery consists of a positive electrode, an electrolyte, a battery separator (as described above), and a negative electrode. The positive electrode is a conventional lithium-ion battery positive electrode, and its material can be lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese phosphate, or nickel-manganese-cobalt ternary materials, etc. The electrolyte is a conventional lithium-ion battery electrolyte, and its electrolyte composition can be lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), etc. The negative electrode is a conventional lithium-ion battery negative electrode, and its material can be graphite, silicon, alloy materials, etc.

[0054] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0055] Example 1:

[0056] Take particle size D 502.4 kg of 100–150 μm wollastonite and 0.6 kg of bentonite were added to a reactor, along with 23.5 kg of anhydrous ethanol, 1.8 kg of silane coupling agent KH560, and 1.2 kg of titanate. The reactor was heated to 90 °C, and hydrochloric acid was added to adjust the pH to 4.5. After stirring for 6 hours, the mixture was removed and dried to obtain modified vitrified powder. 3 kg of the modified vitrified powder, 25.5 kg of polyethylene with a viscosity-average molecular weight of 100 W, and 1.5 kg of glass powder were added to a high-speed mixer at 350 rpm for 60 minutes. 30 kg of the uniformly mixed material and 70 kg of paraffin oil were added to a twin-screw extruder for melt co-extrusion at 195 °C and 100 rpm. The die lip gap was 2.0 mm. The cast sheet was cooled by cooling rollers to form a 1.7 mm cast sheet. The cast sheet was then simultaneously stretched bidirectionally (transversely and longitudinally) and shaped into thinner sheets with a stretch ratio of 9.5 times in each direction. After stretching, the membrane is immersed in a CH2Cl2 extraction bath for extraction and pore formation, and then dried. After drying, the membrane is stretched laterally again and shaped into a 10 μm film with a stretching ratio of 1.23.

[0057] The ceramicization mechanism of the battery separator prepared in this embodiment is as follows: Figure 1 As shown, when the temperature is below 140℃, the mechanical strength of the polyethylene matrix itself can support the porous structure of the diaphragm, and the diaphragm maintains normal operation. When the temperature rises to 140-180℃, the molecular orientation of the polyethylene matrix is ​​disrupted and it softens. The mechanical strength of the ceramic powder itself continues to provide support, keeping the positive and negative electrodes from contacting each other. When the temperature rises to about 180-200℃, the polyethylene matrix melts and the membrane breaks down. At this time, the glass powder melts and encapsulates and bridges with the ceramic powder, filling the pores formed by the melting of polyethylene and continuing to maintain the isolation between the positive and negative electrodes. As the temperature rises further, the polyolefin matrix completely decomposes thermally, and the glass powder that melts into a liquid phase continues to increase, bridging and bonding with the ceramic powder components. The two undergo a eutectic reaction to form a hard ceramic structure that continues to maintain the isolation between the positive and negative electrodes.

[0058] The battery separator was sintered at 500℃ for 1 hour under a nitrogen atmosphere. SEM images before and after sintering are shown below. Figure 2 As shown. Figure 2 The results show that the modified ceramic powder and glass powder (as indicated by the arrow) have good compatibility, and the interface between the particles and the matrix is ​​blurred, indicating that the modified ceramic powder and the polyethylene matrix have achieved good bonding. Figure 2 b indicates that after high-temperature sintering, the polyethylene matrix is ​​completely decomposed, and the remaining ceramic powder is bonded together with the melted glass powder to form a ceramic skeleton structure. This structure provides further separation between the positive and negative electrodes of the battery.

[0059] Example 2:

[0060] Take particle size D 503.6 kg of 100–150 μm wollastonite and 0.9 kg of bentonite were added to a reactor, along with 38.25 kg of anhydrous ethanol, 1.35 kg of silane coupling agent KH560, and 0.9 kg of titanate. The reactor was heated to 90 °C, and hydrochloric acid was added to adjust the pH to 4.5. After stirring for 6 hours, the mixture was removed and dried to obtain modified vitrified powder. 10 kg of the modified vitrified powder, 24 kg of polyethylene with a viscosity-average molecular weight of 100 W, and 5 kg of glass powder were added to a high-speed mixer at 350 rpm for 60 minutes. The mixture was then removed. 30 kg of the homogeneous mixture and 70 kg of paraffin oil were added to a twin-screw extruder for melt co-extrusion at 195 °C and 100 rpm. The die lip gap was 2.0 mm. The resulting cast sheet was cooled by cooling rollers to form a 1.7 mm cast sheet. The cast sheet was then simultaneously stretched bidirectionally (transversely and longitudinally) and shaped into thinner sheets with a stretch ratio of 9.5 times in each direction. After stretching, the membrane is immersed in a CH2Cl2 extraction bath for extraction and pore formation, and then dried. After drying, the membrane is stretched laterally again and shaped into a 10 μm film with a stretching ratio of 1.23.

[0061] Comparative example:

[0062] 30 kg of polyethylene with a viscosity-average molecular weight of 100w and 70 kg of paraffin oil were added to a twin-screw extruder for melt co-extrusion at an extrusion temperature of 195℃, a rotation speed of 100 r / min, and a die lip gap of 2.0 mm. The cast sheet was cooled by cooling rollers to form a 1.7 mm thick cast sheet. The cast sheet was then simultaneously stretched bidirectionally (transversely and longitudinally) and shaped into a thinner sheet with a stretch ratio of 9.5 times in each direction. After stretching, the sheet was immersed in a CH2Cl2 extraction tank for extraction and pore formation, and then dried. After drying, it was stretched transversely again and shaped into a 10 μm film with a stretch ratio of 1.23.

[0063] The performance comparisons of the embodiments and comparative examples are shown in Table 1.

[0064] Table 1. Performance Comparison of Examples and Comparative Examples

[0065]

[0066] Note: The tensile strength test method refers to GB / T 1040.3-2006, the needle penetration test method refers to GB / T6672-2001, and the heat shrinkage test method refers to GB / T 135l9-2016.

[0067] As can be seen from Table 1, under the condition that the thickness, air permeability and porosity are basically the same, the tensile strength and puncture strength of the diaphragm are improved after the addition of modified ceramic powder and glass powder. At the same time, the thermal shrinkage performance of the diaphragm is significantly improved due to the addition of inorganic materials.

[0068] The TGA curves of the examples and comparative examples are as follows: Figure 3As shown, the unceramized polyethylene separator begins to decompose at around 400℃, reaches its maximum decomposition rate at around 445℃, and is almost completely decomposed at 480℃. With the addition of modified ceramic powder, as in Examples 1 and 2, a small amount of decomposition occurs between 380℃ and 420℃. This is mainly due to the endothermic release of crystal water from wollastonite and bentonite. Polyethylene begins to thermally decompose at 420℃, reaches its maximum decomposition rate at around 465℃, and is completely decomposed at 500℃. The increase in the temperature at which polyethylene begins to decompose and the increase in the temperature at which it reaches its maximum decomposition rate indicate that the addition of modified ceramic powder can effectively improve the thermal stability of polyethylene materials and the safety performance of lithium battery separators.

[0069] The puncture performance curves of the examples and comparative examples are as follows: Figure 4 As shown, the puncture resistance of polyethylene increased significantly after the addition of modified ceramic powder. Comparing the diaphragms with two different proportions of modified ceramic powder, it can be seen that the puncture resistance of the diaphragm increased with the increase of the proportion of modified ceramic powder. This indicates that the bonding between modified ceramic powder and polyethylene was improved, and this improved bonding enhanced the puncture resistance of the polyethylene matrix.

[0070] The tensile strength curves of the examples and comparative examples are as follows: Figure 5 As shown, the tensile strength and elongation of polyethylene are improved after the addition of modified ceramic powder, indicating that the bonding between the surface groups of the modified ceramic powder and the polyethylene molecules is enhanced. This improved bonding strengthens the toughness of the polyethylene molecular chains. However, when the proportion of ceramic material exceeds a certain level, the tensile strength begins to decline. This may be because the addition of too much modified ceramic powder reduces the uniformity of the system, leading to a decrease in the overall tensile strength of the diaphragm.

[0071] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a battery separator, characterized in that, Wollastonite, bentonite, silane coupling agent, titanate, and anhydrous ethanol are mixed evenly, the pH is adjusted to acidic, and the mixture is heated to 80-120 °C to carry out a modification reaction to obtain modified porcelain powder; the modified porcelain powder is mixed with glass powder and polyolefin to obtain a mixed powder; the mixed powder is then melt-extruded, stretched, extracted, and shaped with paraffin oil to obtain the final product. The mass ratio of wollastonite to bentonite is 2~6:0.5~1.5, the mass ratio of silane coupling agent to titanate is 2~8:2~6, and the total mass ratio of wollastonite and bentonite to the total mass ratio of silane coupling agent to titanate is 5~10:0.5~1. The mass ratio of modified ceramic powder, glass powder and polyolefin is 8~15:2~7:78~90.

2. The method for preparing the battery separator as described in claim 1, characterized in that, Wollastonite D 50 The D of bentonite with a particle size of 100~150 μm 50 The particle size is 100~150 μm; Alternatively, the silane coupling agent is silane coupling agent KH560; Alternatively, the polyolefin may be polyethylene.

3. The method for preparing the battery separator as described in claim 1, characterized in that, After thoroughly mixing wollastonite, bentonite, silane coupling agent, titanate, and anhydrous ethanol, the pH is adjusted to 4-5.

4. The method for preparing the battery separator as described in claim 1, characterized in that, The mass ratio of the total mass of wollastonite and bentonite to the mass of anhydrous ethanol is 5~10:1~3.

5. The method for preparing the battery separator as described in claim 1, characterized in that, The mass ratio of the mixed powder to the paraffin oil is 20~40:60~80.

6. The method for preparing the battery separator as described in claim 1, characterized in that, During the melt extrusion process, the extruder temperature range is 180~220℃, the rotation speed is 90~150rpm / min, the molten material is cast into a sheet through the die outlet with a gap of 1.5~2.5mm, and the sheet is pulled through the cooling roller to cool into a sheet. The roller speed is 4~8m / min, and the roller temperature is 15~20℃.

7. The method for preparing the battery separator as described in claim 1, characterized in that, The stretching process can be either asynchronous bidirectional stretching or synchronous bidirectional stretching. Alternatively, the stretching temperature is 90~130℃, and the stretching ratio is 6~15 times.

8. The method for preparing the battery separator as described in claim 1, characterized in that, After extraction, it is stretched and shaped again.

9. A battery separator, characterized in that, Obtained by the preparation method described in any one of claims 1 to 8.

10. The application of the battery separator according to claim 9 in a lithium-ion battery.

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