Preparation Method and Application of a Low-Shrinkage Ceramic Composite Separator

Abstract

The present invention discloses a preparation method and application of a low-shrinkage ceramic composite separator. The present invention belongs to the technical field of lithium battery separators. A resin slurry is used to coat the surface of a base separator to form a separator with slurry on the surface. The slurry does not contain ceramic particles or ceramic precursors. Instead, a ρ-Al2O3 powder binder is uniformly sprayed on the separator with slurry on the surface by means of spraying, avoiding the agglomeration caused by directly mixing the ρ-Al2O3 powder binder in the slurry. Electrostatic spraying can ensure that the particles sprayed onto the surface of the separator are uniform. The ρ-Al2O3 powder has a spontaneous hydration reaction at room temperature, and the gel formed by hydration has a cementing property. The resin slurry provides the reaction conditions for water. After steam curing, a hydration reaction will occur to form a gel, thus producing a binding effect. In addition, the separator with a gel ceramic coating can effectively avoid the shrinkage effect of the battery separator when heated, avoiding the occurrence of short circuits and dangers.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery separators, and particularly relates to a preparation method and application of a low-shrinkage ceramic composite separator. Background Art

[0002] The new nano-aluminum oxide ceramic-coated separator can improve the thermal stability of the separator, enhance the mechanical strength of the separator, and prevent the large-area contact between the positive and negative electrodes caused by the shrinkage of the separator. Currently, the most common method for the composite modification of polyolefin separators is to coat inorganic ceramic particles on the polyolefin base film. The composite modified separator coated with inorganic ceramic particles improves the thermal stability and wettability of the polyolefin separator to a certain extent, thereby improving the safety of lithium-ion batteries. However, due to the easy agglomeration of ceramic particles and the poor binding performance with the substrate, it is easy to cause the detachment of the ceramic coating, affecting the cycle performance of lithium batteries. For example, CN201410140154.0 discloses an aqueous ceramic-coated lithium-ion battery separator and its processing method, and the effect of solving the easy agglomeration and poor binding performance of ceramic particles is not good. Jia et al. designed and prepared a nanofiber separator with a ZrO2 ceramic coating. The ZrO2 ceramic coating endows the separator with excellent electrolyte wettability and thermal stability. Even at 300 °C, the separator does not undergo thermal shrinkage, and the entire preparation process is simple and environmentally friendly. Using a functional coating composite separator can make up for the problem of poor mechanical properties caused by the reduction of the separator thickness. Although the ceramic coating can improve the heat resistance, liquid absorption and retention properties, and the safety of the battery of the separator, it also brings some new problems, such as the increase in battery internal resistance and the increase in separator cost due to the increase in separator thickness, and the high requirements for the control of the ceramic particle coating process. For example, in the case of boehmite coating, due to the high surface activity of the particles, in a polar aqueous solution, due to Brownian motion, collisions occur, and small particles tend to aggregate into large particles, resulting in phenomena such as flocculation and stratification, making the coating performance of the separator poor. Those skilled in the art urgently need to develop a preparation method and application of a low-shrinkage ceramic composite separator to meet the existing application market and performance requirements. Summary of the Invention

[0003] In view of this, the present invention provides a preparation method and application of a low-shrinkage ceramic composite separator.

[0004] A preparation method of a low-shrinkage ceramic composite separator includes the following steps: First step, uniformly coat a resin slurry on one or both sides of a base separator, and the coating thickness is 2.5 - 4 μm; Second step, disperse ρ-Al2O3 powder binder into acetone to form a dispersion liquid with a mass fraction of 15% - 20%, electrostatically spray the dispersion liquid on the surface of the slurry in the previous step, and then dry it at 55 - 60 °C for 5 - 10 min to obtain a ρ-Al2O3 powder-bonded separator; Third step, spray-cure the coating: perform steam spray humidification and curing on the surface of the ρ-Al2O3 powder-bonded separator for 12 - 15 h to obtain the low-shrinkage ceramic composite separator.

[0005] ρ-Al2O3 has a spontaneous hydration reaction at room temperature and was previously used as a binder for high-purity amorphous refractories. It was not previously a raw material for diaphragm production and was not used in diaphragm production.

[0006] Curing was previously a technical term in the fields of plant protection or construction. For the spray curing coating disclosed in the present invention, curing provides environmental conditions suitable for the setting, hardening, and strength development of the ceramic coating, including appropriate temperature and humidity.

[0007] During static setting and steam curing, through hydrothermal reaction, the active components in the coating accelerate the hydration reaction and promote setting, hardening, and the generation of strength.

[0008] Previously, in the production of diaphragms and ceramic-coated diaphragms, there was no disclosed process method for a curing coating. Its steps are simple, the cost is low, and the application effect is efficient.

[0009] Further, the spray process in the second step is at a temperature of 23 - 25°C, a relative humidity of 60% - 80%, a working voltage of 10 - 15 kV, a receiving distance of 10 - 15 cm, and an injection speed of 1.5 - 2.0 mL / 10 min.

[0010] Electrostatic spraying can prepare a uniformly sprayed ρ-Al2O3 powder, and can ensure that the binder particles of the sprayed ρ-Al2O3 powder are uniform. Through the hydration reaction, it binds to the diaphragm.

[0011] Further, the resin slurry in the first step includes a dispersant, a water retainer, a binder, and a promoter in a mass ratio of 0.02 - 0.04∶0.04 - 0.05∶0.3 - 0.7∶0.02 - 0.03. The binder is one or more of PVDF slurry or polyacrylate slurry. The dispersant is one of sodium hexametaphosphate and sodium dodecylbenzenesulfonate. The promoter is citric acid or tartaric acid. The water retainer is carboxymethyl cellulose.

[0012] Further, the base diaphragm is one of a polyethylene film, a polypropylene film, or a polypropylene / polyethylene / polypropylene composite diaphragm with a thickness of 5 - 40 μm and a porosity of 30% - 40%.

[0013] Further, the particle size of the ρ-Al2O3 powder binder in the first step has a D50 particle size of 2 - 5.0 μm.

[0014] Further, the ρ-Al2O3 powder can preferably be ZF-1G or ZF-1, and Amersil Alphabond300 is also acceptable.

[0015] Further, the steam spray particle size for steam humidification in the third step is 3 - 5 μm, the temperature is 30 - 37°C, and the steam pressure is 0.1 - 0.2 MPa.

[0016] The low - shrinkage ceramic composite separator prepared by the above - mentioned preparation method of the low - shrinkage ceramic composite separator is applied to lithium batteries.

[0017] Advantages of the present invention:

[0018] The preparation method of the low - shrinkage ceramic composite separator disclosed by the present invention first uses a resin slurry to coat the surface of a base separator to form a separator with slurry on the surface. The slurry does not contain ceramic particles or ceramic precursors. Instead, a ρ - Al2O3 powder binder is uniformly sprayed on the separator with slurry on the surface by spraying. This avoids the agglomeration caused by directly mixing the ρ - Al2O3 powder binder in the slurry. Electrostatic spraying can ensure that the particles sprayed onto the separator surface are uniform. The ρ - Al2O3 powder has a spontaneous hydration reaction at room temperature, and the gel formed by hydration has cementing properties. The resin slurry provides the reaction conditions for water. After steam curing, a hydration reaction will occur to form a gel, thereby generating a binding effect. In addition, the separator with a gel ceramic coating can effectively avoid the shrinkage effect of the battery separator when heated, avoiding the occurrence of short - circuit and danger. In order to accelerate the curing speed and improve the strength, a dispersant, a water - retaining agent, and an accelerator are appropriately added. By applying the ρ - Al2O3 powder binder on one or both sides of the separator, the high - temperature dimensional stability of the polyolefin separator can be significantly improved. After hydration, the particles are embedded in the matrix resin, and porous network entanglement occurs, which is beneficial to improving the interfacial bonding force between the ceramic particles and the base separator. Specific embodiments

[0019] According to the following embodiments, the present invention can be better understood. However, those skilled in the art can easily understand that the content described in the embodiments is only used to illustrate the present invention and should not and will not limit the present invention described in detail in the claims. Example 1

[0020] Raw materials: A 35 - μm THPP / PE / PP three - layer co - extruded separator for lithium batteries has a longitudinal tensile strength of 139.5 MPa, a transverse tensile strength of 21.1 MPa, a longitudinal thermal shrinkage rate of 1.1% at 120°C for 2 h, a puncture strength of 413 gf, a porosity of 47%, and an air permeability of 275 sec / 100 mL. ρ - Al2O3 powder binder ZF - 1GD 50 2 μm, FCF - 301 PVDF slurry, Xingfa Industrial sodium hexametaphosphate, Siping Dongfang Chemical carboxymethyl cellulose; JQ - 15 Jiangsu Boming steam humidifier;

[0021] Preparation method of low-shrinkage ceramic composite separator, comprising the following steps: First step, uniformly coat a resin slurry on one or both sides of a base separator, with a coating thickness of 4 μm. The resin slurry comprises a dispersant, a water retainer, a binder, and a promoter with a mass ratio of 0.02∶0.04∶0.3∶0.02. The binder is a PVDF slurry, the dispersant is sodium hexametaphosphate, the promoter is citric acid, and the water retainer is carboxymethyl cellulose; Second step, disperse ρ-Al2O3 powder binder into acetone to form a dispersion with a mass fraction of 20%, electrostatically spray the dispersion on the surface of the slurry in the previous step, and then dry it at 60 °C for 10 min to obtain a ρ-Al2O3 powder-bonded separator. The spraying process is at a temperature of 25 °C, a relative humidity of 80%, a working voltage of 15 kV, a receiving distance of 15 cm, and an injection speed of 2.0 mL / 10 min; Third step, spray and cure the coating: perform steam spray humidification and curing on the surface of the ρ-Al2O3 powder-bonded separator for 15 h. The steam spray particle size of the steam humidification is 5 μm, the temperature is 37 °C, and the steam pressure is 0.2 MPa, thus obtaining the low-shrinkage ceramic composite separator.

[0022] Properties of the low-shrinkage ceramic composite separator: ceramic coating thickness 4 μm, longitudinal tensile strength 169.8 MPa, transverse 24.5 MPa, 2 h 120 °C MD heat shrinkage rate 0.8%, TD 0.1%; puncture strength 556 gf, air permeability 295 sec / 100 mL, 180° peel strength 3.6 N / cm. Example 2

[0023] Raw materials: 12 μm TH-II type PP-based lithium battery separator, longitudinal tensile strength 153.4 MPa, transverse 135.8 MPa, 1 h 105 °C MD heat shrinkage rate 2.5%, TD heat shrinkage rate 1.0%; puncture strength 415 gf, porosity 40%, air permeability 312 sec / 100 mL, ρ-Al2O3 powder binder ZF-1D 50 2 μm, dodecylbenzenesulfonic acid sodium of Chuzhou Sourcen Chemical Industry, polyacrylate slurry ECO3 of Shifang Xiangtai Chemical Industry; JQ-15 steam humidifier of Jiangsu Boming

[0024] Preparation method of low-shrinkage ceramic composite separator, comprising the following steps: First step, uniformly coat a resin slurry on one or both sides of a base separator, with a coating thickness of 2.5 μm. The resin slurry comprises a dispersant, a water retention agent, a binder, and a promoter in a mass ratio of 0.04∶0.05∶0.7∶0.03. The binder is one or more of PVDF slurry or polyacrylate slurry. The dispersant is sodium dodecyl benzene sulfonate, the promoter is tartaric acid, and the water retention agent is carboxymethyl cellulose. Second step, disperse ρ-Al2O3 powder binder into acetone to form a dispersion with a mass fraction of 15%, electrostatically spray the dispersion on the surface of the slurry in the previous step, and then dry it at 55 °C for 5 min to obtain a ρ-Al2O3 powder-bonded separator. The spraying process is at a temperature of 23 °C, a relative humidity of 60%, a working voltage of 10 kV, a receiving distance of 10 cm, and an injection speed of 1.5 mL / 10 min. Third step, spray and cure the coating: perform steam spray humidification and curing on the surface of the ρ-Al2O3 powder-bonded separator for 12 h. The steam spray particle size of the steam humidification is 3 μm, the temperature is 30 °C, and the steam pressure is 0.1 MPa, thus obtaining the low-shrinkage ceramic composite separator.

[0025] Properties of the obtained low-shrinkage ceramic composite separator: ceramic coating thickness 3 μm, air permeability 354 sec / 100 mL, puncture strength 502 gf, longitudinal tensile strength 172.4 MPa, transverse 143.5 MPa, thermal shrinkage at 100 °C for 1 h MD 0.9%, TD 0.2%, 180° peel strength 3.5 N / cm. Example 3

[0026] Raw materials: polyethylene lithium battery separator with TH 12 μm longitudinal tensile strength of 121.2 MPa, longitudinal thermal shrinkage rate of 3.5% at 120 °C for 1 h, transverse thermal shrinkage rate of 1.5%, puncture strength of 353 gf, porosity of 40%, and air permeability of 150 sec / 100 mL, ρ-Al2O3 powder binder Alphabond300, PVDF slurry LATEX932; JQ-15 Jiangsu Boming steam humidifier;

[0027] Preparation method of low-shrinkage ceramic composite separator, comprising the following steps: First step, uniformly coat a resin slurry on one or both sides of a base separator, with a coating thickness of 3.5 μm. The resin slurry comprises a dispersant, a water retention agent, a binder, and a promoter in a mass ratio of 0.03∶0.045∶0.5∶0.025. The binder is PVDF slurry. The dispersant is sodium hexametaphosphate, the promoter is citric acid, and the water retention agent is carboxymethyl cellulose. Second step, ρ-A lThe 2O3 powder binder is dispersed in acetone to form a dispersion with a mass fraction of 18%. The dispersion is electrostatically sprayed on the surface of the slurry in the previous step, and then dried at 58°C for 8 minutes to obtain a ρ-Al2O3 powder-bonded separator. The spraying process is at a temperature of 24°C, a relative humidity of 70%, a working voltage of 13 kV, a receiving distance of 12 cm, and an injection speed of 1.8 mL / 10 min. Thirdly, spray-cure the coating: Steam spray humidification and curing are carried out on the surface of the ρ-Al2O3 powder-bonded separator for 14 h. The steam spray particle size of the steam humidification is 4 μm, the temperature is 34°C, and the steam pressure is 0.15 MPa, thus obtaining the low-shrinkage ceramic composite separator.

[0028] Properties of the low-shrinkage ceramic composite separator: Coating thickness 4 μm, longitudinal tensile strength 139.8 MPa, longitudinal thermal shrinkage rate at 120°C for 1 h 1.5%, transverse thermal shrinkage rate 0.4%, puncture strength 393 gf, porosity 40%, air permeability 179 sec / 100 mL, 180° peel strength 3.4 N / cm.

[0029] Note: Refer to GB / T36363-2018 Polyolefin separators for lithium-ion batteries; among them, the air permeability is tested according to the requirements of JIS8117-2009; the tensile strength and elongation at break are tested according to the requirements of GB1040.3-2006. The specimens are prepared by the cutting method, and the specimen type is Type 2 specimen. The specimens are in the shape of a long strip with a length of 200 mm and a width of 25 mm, the distance between the clamps is 100 mm, and the test speed is 250 mm / min. The puncture strength is tested according to the requirements of ASTM D4833-00e1. The shape of the needle head is a hemisphere with Ф = 1.0 mm, and the running speed of the needle head is 1 mm / s. Among them, the peel strength: Test equipment tensile testing machine: Load cell resolution 0.01 N. Test speed: 300 mm / min. Clamp distance 100 mm. Double-sided tape: Width 20 mm, model 3M, 200P. Handheld pressure wheel: Weight 2.5 kg. Stainless steel plate: 170 mm × 50 mm. The specimens use a 100 mm × 300 mm sample cutting template and a 25 mm wide steel ruler, and the sample cutting specification is 25 mm × 250 mm. Test procedure: Stick the double-sided tape tightly on the steel plate, with a length of 100 mm. Tear off the surface layer of the tape, and paste the test surface of the sample face down flat on the double-sided tape. The sample needs to completely cover the double-sided tape surface. One end of the sample protrudes from the steel plate, and the other end is flush with the steel plate. Subsequently, use a 2.5 KG special pressure wheel, and roll it back and forth 3 times on the flat sample using the middle part of the pressure wheel. Lift and fold up the part without the tape, expose the side of the steel plate without the tape, and separate the coating film and the tape by 10 mm with force.

Claims

1. A preparation method of a low - shrinkage ceramic composite separator, characterized in that: It includes the following steps: First step: Uniformly coat the resin slurry on one or both sides of the base diaphragm, with the coating thickness being 2.5 - 4 μm; Second step: Disperse the ρ-Al2O3 powder binder into acetone to form a dispersion with a mass fraction of 15% - 20%. Electrostatically spray the dispersion on the surface of the slurry in the previous step, and then dry it at 55 - 60 °C for 5 - 10 min to obtain the ρ-Al2O3 powder-bonded diaphragm; Third step: Spray and cure the coating: Carry out steam spray humidification and curing on the surface of the ρ-Al2O3 powder-bonded diaphragm for 12 - 15 h to obtain the low-shrinkage ceramic composite diaphragm. The resin slurry provides moisture, and after steam spray humidification and curing, the ρ-Al2O3 powder undergoes a hydration reaction to form a gel.

2. The preparation method of the low-shrinkage ceramic composite separator according to claim 1, characterized in that, The spraying process in the second step is at a temperature of 23 - 25 °C, a relative humidity of 60% - 80%, a working voltage of 10 - 15 kV, a receiving distance of 10 - 15 cm, and an injection speed of 1.5 - 2.0 mL / 10 min.

3. The preparation method of the low-shrinkage ceramic composite separator according to claim 1, wherein, The resin slurry in the first step includes a dispersant, a water retention agent, a binder, and a promoter with a mass ratio of (0.02 - 0.04)∶(0.04 - 0.05)∶(0.3 - 0.7)∶(0.02 - 0.03). The binder is one or more of PVDF slurry or polyacrylate slurry. The dispersant is one of sodium hexametaphosphate and sodium dodecylbenzenesulfonate. The promoter is citric acid or tartaric acid, and the water retention agent is carboxymethyl cellulose.

4. The preparation method of the low-shrinkage ceramic composite separator according to claim 1, wherein The base diaphragm is one of a polyethylene film, a polypropylene film, or a polypropylene / polyethylene / polypropylene composite diaphragm with a thickness of 5 - 40 μm and a porosity of 30% - 40%.

5. The preparation method of the low-shrinkage ceramic composite separator according to claim 1, wherein The particle size D50 of the ρ-Al2O3 powder binder in the first step is 2 - 5.0 μm.

6. The preparation method of the low-shrinkage ceramic composite separator according to claim 1, wherein Among them, the steam spray particle size of the steam spray humidification and curing in the third step is 3 - 5 μm, the temperature is 30 - 37 °C, and the steam pressure is 0.1 - 0.2 MPa.

7. Application of the low-shrinkage ceramic composite diaphragm prepared by the preparation method of the low-shrinkage ceramic composite diaphragm according to any one of claims 1 - 6 in a lithium battery.