Slurry that in-situ compounds aromatic polyamide, and preparation method therefor and use thereof

Abstract

The present invention relates to the technical field of lithium battery materials. Provided are slurry that in-situ compounds an aromatic polyamide, and a preparation method therefor and the use thereof. The slurry that in-situ compounds an aromatic polyamide achieves the compounding of two materials of nano ceramic particles and an aromatic polyamide, thereby effectively avoiding the problem in the prior art of nano ceramic particles being prone to falling off due to the fact that a binder needs to be added to bond the nano ceramic particles on a separator. A lithium battery separator prepared from the slurry that in-situ compounds an aromatic polyamide further improves the performance, such as peel strength, membrane rupture temperature and electrolyte contact angle, of the lithium battery separator in the prior art. Compared with batteries in the prior art, a battery prepared from the lithium battery separator has an improved capacity retention ratio, and improved normal-temperature capacity, high-temperature capacity (55ºC) and low-temperature capacity (-20ºC).

Description

In-situ composite aromatic polyamide slurry and its preparation method and use Technical Field

[0001] The present invention relates to the technical field of lithium battery materials, and in particular to an in-situ composite aromatic polyamide slurry, a preparation method and application thereof. Background Art

[0002] In the structure of lithium batteries, the diaphragm is one of the key internal components. The diaphragm is located between the positive and negative electrodes. Its main function is to separate the positive and negative active materials, preventing short circuits between the two electrodes due to contact, while allowing for the rapid transport of charged ions. To improve the heat resistance of the diaphragm, a layer of slurry needs to be applied to the diaphragm. The slurry can improve the heat resistance of the diaphragm and help protect the positive and negative electrodes of the lithium battery. However, the compatibility between the slurry and the diaphragm in the relevant existing technology is currently poor, resulting in the slurry easily falling off the diaphragm, resulting in a decrease in the heat resistance of the diaphragm product, which in turn affects the service life of the lithium battery.

[0003] Currently, commercial lithium battery separators are primarily polyolefin separators based on polyethylene and polypropylene, including single-layer PP separators, single-layer PE separators, and multi-layer PP / PE / PP composite separators. Polyolefin materials offer advantages such as high strength, good acid and alkali resistance, and excellent solvent resistance. However, they have a low melting point, generally below 180°C. When the internal or external temperature of a lithium battery rises close to its melting point, the separator can deform and shrink, or melt and rupture, causing a short circuit between the positive and negative electrodes and accelerating thermal runaway. Furthermore, when a lithium battery is discharged at high power, the internal temperature rise is correlated with impedance, which requires the separator to have improved impedance performance.

[0004] To improve the thermal performance of polyolefin separators, ceramic coating modification is currently widely used. However, ceramics are inorganic particles, and a binder needs to be added to improve the adhesion between ceramic particles and between ceramic and polyolefin base film to avoid powder loss. For example, CN 109411679 A discloses a ceramic slurry, a ceramic separator, and a lithium-ion battery. The ceramic slurry includes: ceramic powder; a binder, wherein the binder contains a polar binder and a non-polar binder; a dispersant; and a surfactant. The binder of the ceramic slurry of the ceramic separator contains too many polar functional groups. Although the adhesion of the slurry is improved, the polar groups formed by the polar functional groups are easily heated to cause thermochemical reactions between the components in the lithium-ion battery, resulting in thermal runaway of the lithium-ion battery and even explosion, posing a major safety hazard. Moreover, when using a ceramic-coated separator alone, although the separator has good heat shrinkage performance, it still has the disadvantage of a low membrane rupture temperature.

[0005] Currently, the most reported method for preparing aramid lithium-ion battery separators is the composite method, which is to coat the aramid solution on the surface of the polyolefin separator and then remove the solvent to obtain the aramid / polyolefin separator. However, the composite membrane prepared by this method has shortcomings such as large thickness and uneven pore size distribution. In addition, the processing process has strict requirements on the molecular weight of aramid. At the same time, aramid itself has poor solubility and requires a suitable solvent to dissolve, which increases the cost to a certain extent. For example, CN112531285A and CN112694610A proposed coating lithium-ion diaphragms with modified para-aramid, and introducing other monomers into traditional para-aramid to improve the comprehensive physical properties of the composite coating film. However, this method is complicated, and the prepared diaphragm is thick, has low porosity, and poor heat resistance, which leads to a decrease in battery performance; CN113140867A and CN113136121B disclose bio-based aramid polymers containing furan structures and their applications in lithium-ion diaphragms. The polymers are first synthesized and then separated, and finally a variety of additives are added to the coating liquid to improve the physical properties of the coating film. The preparation method is cumbersome and involves many raw materials. At the same time, the coating film does not have a three-dimensional network structure in three dimensions, and the electrolyte mobility is low.

[0006] CN115663394A discloses a para-aramid dissolution system and its application, an aramid diaphragm and its preparation method, and an aramid-ceramic composite diaphragm and its preparation method. In the examples of the specification, a method for preparing an aramid-ceramic composite diaphragm is provided, comprising: mixing a ceramic slurry with a dissolved para-aramid slurry formed by the application of the above examples to obtain an aramid-ceramic composite slurry; and coating the aramid-ceramic composite slurry on at least one side of a base membrane. However, directly coating the aramid and inorganic ceramic particles together results in poor adhesion between the coating and the base layer. Adding a conventional binder can affect the permeability and thermal performance of the diaphragm, leading to safety concerns.

[0007] Based on the above-mentioned existing technologies, how to combine aromatic polyamide with ceramic particles without affecting the performance of the diaphragm has become a technical problem that needs to be solved urgently.

[0008] Summary of the Invention

[0009] To solve the above technical problems, the present invention provides a slurry for in-situ composite aromatic polyamide. Nano-ceramic particles are first composited with isocyanate in situ for modification, wherein the modification is a reaction of hydroxyl groups on the surface of the nano-ceramic particles with isocyanate groups in the isocyanate to obtain modified nano-ceramic particles. The modified nano-ceramic particles are then composited with aromatic polyamide in situ through a grafting reaction. During the composite process, the isocyanate groups in the modified nano-ceramic particles undergo a grafting reaction with the amide bonds in the aromatic polyamide, thereby composited between the nano-ceramic particles and the aromatic polyamide to obtain the in-situ composite aromatic polyamide slurry. The viscosity of the slurry is 50-20,000 cp, wherein the isocyanate contains at least two isocyanate groups.

[0010] Furthermore, the nano-ceramic particles are one of aluminum oxide, silicon oxide and titanium oxide.

[0011] Furthermore, the particle size of the nano-ceramic particles is 10-1000 nm.

[0012] Furthermore, the aromatic polyamide is one of meta-aromatic polyamide, para-aromatic polyamide, heterocyclic aramid, and polyamide-imide.

[0013] Furthermore, the structural formula of the isocyanate is O=C=N-R1-N=C=O, wherein the structural formula of R1 is

[0014] When R1 is When the isocyanate is 4,4'-diphenylmethane diisocyanate (MDI);

[0015] When R1 is When the isocyanate is methyl-2,4-diisocyanate (2,4-TDI);

[0016] When R1 is When the isocyanate is methyl-2,6-diisocyanate (2,6-TDI).

[0017] The present invention also provides a method for preparing an in-situ composite aromatic polyamide slurry, comprising the following steps:

[0018] (1) drying the nano-ceramic particles at a temperature of 100-150° C. for 2-10 hours;

[0019] (2) adding the nano-ceramic particles dried in step (1) into a reactor, adding a toluene solution containing isocyanate, stirring and dispersing, introducing an inert gas into the reactor, heating to a fixed temperature under the protection of the inert gas, and reacting to obtain crude modified nano-ceramic particles after the reaction is completed, washing the crude modified nano-ceramic particles with an organic solvent, and drying again after washing to obtain modified nano-ceramic particles;

[0020] (3) The modified nano-ceramic particles obtained in step (2) are mixed with aromatic polyamide polymer solution and then subjected to grafting reaction to obtain an in-situ composite aromatic polyamide slurry having a viscosity of 50-20000 cp.

[0021] Furthermore, the concentration of isocyanate in the toluene solution in step (2) is 0.1-0.5 mol / L, and the mass of the nano-ceramic particles accounts for 1-20% of the mass of the toluene solution.

[0022] Furthermore, the stirring and dispersing in step (2) is carried out at a temperature of 20-30° C. and for a time of 20-60 min.

[0023] Furthermore, the inert gas in step (2) is nitrogen, the fixed temperature of heating after the nitrogen is introduced is 30-60°C, and the reaction time is 30-120min.

[0024] Furthermore, in the step (2), the organic solvent is acetone, and the modified nano-ceramic particles are washed with acetone 3-5 times.

[0025] Furthermore, the re-drying temperature in step (2) is 30-60° C., and the re-drying time is 10-30 minutes.

[0026] Furthermore, in step (2), the nano-ceramic particles are modified by in-situ compounding with isocyanate, and the reaction principle involved is as follows: oxygen atoms on the surface of the nano-ceramic particles adsorb water in the air to form hydroxyl groups on the surface, and the hydroxyl groups (-OH) react with the isocyanate groups (-N=C=O) in the isocyanate at the fixed temperature in step (2) to generate polymer A, i.e., modified nano-ceramic particles, wherein the surface of the nano-ceramic particles has one or more hydroxyl groups (-OH), and the isocyanate contains at least two isocyanate groups (-N=C=O).

[0027] Furthermore, the aromatic polyamide polymer solution in step (3) contains aromatic polyamide, and the mass ratio of the aromatic polyamide to the modified nano-ceramic particles is (2-10):(0.5-20).

[0028] Furthermore, the mass percentage of aromatic polyamide in the aromatic polyamide polymerization liquid is 2-10%.

[0029] Furthermore, the aromatic polyamide in the aromatic polyamide polymerization liquid is in a liquid state.

[0030] Furthermore, the reason for using the aromatic polyamide polymer liquid is that solid aromatic polyamide has low solubility, and different aromatic polyamides require different solvents and different dissolution conditions to be dissolved again into liquid aromatic polyamide. Directly using the aromatic polyamide polymer liquid in the process of preparing aromatic polyamide in step (2) can effectively avoid this problem, that is, the aromatic polyamide is utilized in the liquid state before becoming solid.

[0031] Furthermore, in the step (3), the isocyanate (-N=C=O) in the polymer A and the amide bond (-CO-NH-) in the aromatic polyamide undergo a grafting reaction when mixed, and the aromatic polyamide is in situ composited on the surface of the polymer A to generate polymer B, thereby obtaining a slurry of in-situ composite aromatic polyamide, thereby achieving the composite of the two materials without using a binder between the nano-ceramic particles and the aromatic polyamide, and preventing the nano-ceramic particles from falling off.

[0032] Furthermore, the temperature of the grafting reaction in step (3) is 20-90° C., and the reaction time is 20-120 min.

[0033] The present invention also provides a lithium battery separator, which comprises a substrate layer and a coating layer, wherein the coating layer is prepared from the slurry of the in-situ composite aromatic polyamide, and the separator peel strength of the lithium battery separator is ≥120Nm -1 , air permeability ≤300s / 100cc, transverse heat shrinkage value ≤2.0% at 150℃ for 1h, longitudinal heat shrinkage value ≤2.0% at 150℃ for 1h, membrane breaking temperature ≥200℃, electrolyte contact angle ≤25℃.

[0034] Furthermore, the steps of preparing the lithium battery separator include:

[0035] (1) uniformly mixing the slurry of the in-situ composite aromatic polyamide with a pore-forming agent and a polar solvent to obtain a mixture;

[0036] (2) After the degassed mixture is coated on one or both sides of the substrate layer, it is immersed in a coagulation tank for coagulation, that is, a coating layer is formed on one or both sides of the substrate layer. After coagulation, it is immersed in a water tank for water washing, and then dried and heat-set after water washing to obtain the lithium battery separator.

[0037] Furthermore, in the step (1), the mass ratio of the slurry of the in-situ composite aromatic polyamide: the pore-forming agent: the polar solvent is (2.5-30): (0.5-10): (60-97).

[0038] Furthermore, the pore-forming agent is one or more of polyethylene glycol, tripropylene glycol, polyvinyl pyrrolidone, anhydrous calcium chloride, anhydrous lithium chloride, methanol, ethanol, and propanol. The pore-forming agent plays a role in adjusting the porosity of the lithium battery separator, thereby increasing the porosity of the lithium battery separator from 25-35% in the prior art to 35-45%.

[0039] Furthermore, the polar solvent is one of N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, N-methylformamide, and N-ethylpyrrolidone.

[0040] Furthermore, the thickness of the coating layer in step (2) is 0.5-8 μm.

[0041] Furthermore, in step (2), the thickness of the substrate layer is 4-30 μm.

[0042] Furthermore, the material of the substrate layer is selected from one of dry-process PE (polyethylene), dry-process PP (polypropylene), PP / PE / PP three-layer composite diaphragm, wet-process PE, and non-woven fabric.

[0043] Furthermore, the coating method in step (2) is one of slit extrusion, roller coating, blade coating, and wire rod coating, and the coating temperature is room temperature.

[0044] Furthermore, the degassing time in step (2) is 5-30 min, the degassing method is static degassing or vacuum degassing, the vacuum degree of the vacuum degassing is 10-90 mmHg, the coagulation liquid in the coagulation tank includes an organic solvent and water, the volume fraction of the organic solvent in the coagulation liquid is 0-60%, the coagulation time is 10-300 s, the coagulation temperature is 0-60°C, the water washing time is 10-300 s, the water washing temperature is 0-60°C, the drying time is 5-300 s, the drying temperature is 40-100°C, the heat setting time is 0.15-30 min, and the temperature is 40-200°C.

[0045] Furthermore, the organic solvent is one of N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, N-methylformamide, and N-ethylpyrrolidone.

[0046] The present invention also provides a battery in which the aforementioned lithium battery separator is installed. The capacity retention rate of the battery after 100 cycles is 85-95%. The high-temperature capacity of the battery at 55°C is 3.6112-3.7171Ah, and the low-temperature capacity at -20°C is 1.9309-1.9726Ah.

[0047] Furthermore, the normal temperature capacity of the battery is 3.8362-3.8467 Ah.

[0048] The beneficial effects of the present invention are:

[0049] 1. The present invention first modifies nano-ceramic particles by in-situ compounding with isocyanate to obtain modified nano-ceramic particles, and then in-situ compounding the modified nano-ceramic particles with aromatic polyamide through a grafting reaction, thereby achieving compounding between the inorganic nano-ceramic particles and the organic aromatic polyamide to obtain the in-situ compounded aromatic polyamide slurry, effectively avoiding the problem in the prior art of adding a binder to bond the nano-ceramic particles to the diaphragm, which causes the nano-ceramic particles to fall off easily.

[0050] 2. The present invention uses the prepared in-situ composite aromatic polyamide slurry to prepare lithium battery separators, thereby improving the performance of lithium battery separators in the prior art, such as peel strength, membrane rupture temperature, electrolyte contact angle, etc., and in the process of preparing the lithium battery separator, the in-situ composite aromatic polyamide slurry is directly coated on the substrate layer without adding a binder, thereby solving the problem of poor adhesion between the coating layer and the substrate layer in the lithium battery separator. That is, in the prior art, conventional binders are added to solve the adhesion problem, and nano-ceramic particles are bonded to aromatic polyamide and then bonded to the substrate layer, thereby affecting a series of problems such as the air permeability and thermal performance of the separator. However, the present invention can achieve the improvement of the separator performance and the improvement of the bonding strength between the coating layer and the substrate layer without adding the binder used in the prior art, that is, the separator peel strength of the lithium battery separator is increased from 90Nm in the prior art. -1 Increase to 120Nm or more -1 The membrane rupture temperature is increased from 135-156°C in the existing technology to greater than or equal to 200°C, and the electrolyte contact angle is reduced from 31-46.7°C in the existing technology to less than or equal to 25°C. The excellent performance of air permeability value ≤300s / 100cc, transverse heat shrinkage value ≤2.0% at 150°C for 1h, and longitudinal heat shrinkage value ≤2.0% at 150°C for 1h is maintained.

[0051] 3. The battery prepared by the present invention adopts the lithium battery separator prepared as described above. After 100 cycles, the capacity retention rate of the battery is improved from 63.5-65.2% in the prior art to 85-95%, the room temperature capacity of the battery is improved from 3.8260-3.8359Ah in the prior art to 3.8362-3.8467A, the high temperature capacity (55°C) is improved from 3.2618-3.2825Ah in the prior art to 3.6112-3.7171Ah, and the low temperature capacity (-20°C) is improved from 1.6985-1.7510Ah in the prior art to 1.9309-1.9726Ah. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] FIG1 is a SEM image of the surface of the lithium battery separator in Example 7 of the present invention. DETAILED DESCRIPTION

[0053] In the following examples, Examples 1-4 are examples of preparing in-situ composite aromatic polyamide slurries, Examples 5-8 are examples of preparing lithium battery separators using the in-situ composite aromatic polyamide slurries prepared in Examples 1-4, Examples 9-12 are examples of preparing batteries using the lithium battery separators prepared in Examples 5-8, and Comparative Examples 1-2 are comparative examples of batteries prepared using lithium battery separators in the prior art.

[0054] Example 1 Sample 1

[0055] This embodiment provides a method for preparing an in-situ composite aromatic polyamide slurry, comprising the following steps:

[0056] (1) drying the nano-ceramic particles at a drying temperature of 100° C. for 2 h;

[0057] (2) adding 2 g of the nano-ceramic particles with a particle size of 10 nm after drying in step (1) into a reactor, and then adding 200 g of a toluene solution containing 0.1 mol / L isocyanate, stirring and dispersing at 20° C. for 20 min, introducing nitrogen into the reactor, heating to a fixed temperature of 30° C. under the protection of the nitrogen, and reacting for 30 min. After the reaction is completed, crude modified nano-ceramic particles are obtained, and the crude modified nano-ceramic particles are washed with acetone for 3 times, and dried at 30° C. for 10 min after washing to obtain modified nano-ceramic particles;

[0058] The nano-ceramic particles are aluminum oxide, the isocyanate is 4,4'-diphenylmethane diisocyanate (MDI), and the reaction principle involved is: oxygen atoms on the surface of the nano-ceramic particles adsorb water in the air to form hydroxyl groups on the surface, and the hydroxyl groups (-OH) react with the isocyanate groups (-N=C=O) in the isocyanate at the fixed temperature in step (2) to generate polymer A, i.e., modified nano-ceramic particles, wherein the surface of the nano-ceramic particles has one or more hydroxyl groups (-OH), and the isocyanate contains two isocyanate groups (-N=C=O);

[0059] (3) The modified nano-ceramic particles obtained in step (2) are mixed with an aromatic polyamide polymer solution and then subjected to a grafting reaction, wherein the mass ratio of the aromatic polyamide to the modified nano-ceramic particles is 2:0.5, the grafting reaction temperature is 20° C., and the reaction time is 20 min, thereby obtaining an in-situ composite aromatic polyamide slurry, wherein the viscosity of the in-situ composite aromatic polyamide slurry is 50 cp; the reaction principle involved is that the isocyanate (-N=C=O) in the polymer A and the amide bond (-CO-NH-) in the aromatic polyamide in the step (3) undergo a grafting reaction when mixed, and the aromatic polyamide is in-situ composited on the surface of the polymer A to generate polymer B, thereby obtaining an in-situ composite aromatic polyamide slurry, i.e., sample 1, thereby achieving the composite of the two materials between the nano-ceramic particles and the aromatic polyamide without using a binder, and the nano-ceramic particles will not fall off;

[0060] In this embodiment, the aromatic polyamide is meta-aromatic polyamide. The preparation process of the aromatic polyamide polymer solution is as follows: 4.3256 g of m-phenylenediamine is fully dissolved in 500 g of DMAC (N,N-dimethylacetamide) to obtain a mixed solution, the temperature of the mixed solution is maintained at room temperature, and then 8.1208 g of isophthaloyl chloride is added. After a reaction time of 40 minutes, calcium hydroxide is added to neutralize to a pH of 7.5. After neutralization, a meta-aromatic polyamide slurry is obtained, i.e., the aromatic polyamide polymer solution in this embodiment, wherein the mass percentage of the meta-aromatic polyamide in the aromatic polyamide polymer solution is 2%.

[0061] The reason for using the aromatic polyamide polymer liquid is that solid aromatic polyamide has low solubility. Different aromatic polyamides require different solvents and different dissolution conditions to be dissolved into liquid aromatic polyamide again. Directly using the aromatic polyamide polymer liquid in the process of preparing aromatic polyamide in step (2) can effectively avoid this problem, that is, the aromatic polyamide is utilized in the liquid state before becoming solid.

[0062] Example 2 Sample 2

[0063] This embodiment provides a method for preparing an in-situ composite aromatic polyamide slurry, comprising the following steps:

[0064] (1) drying the nano-ceramic particles at a drying temperature of 100° C. for 2 h;

[0065] (2) adding 40 g of the nano-ceramic particles with a particle size of 1000 nm after drying in step (1) into a reactor, and then adding 200 g of a toluene solution containing 0.5 mol / L isocyanate, stirring and dispersing at 30° C. for 60 min, introducing nitrogen into the reactor, heating to a fixed temperature of 30° C. under the protection of the nitrogen, and reacting for 30 min. After the reaction is completed, crude modified nano-ceramic particles are obtained, and the crude modified nano-ceramic particles are washed with acetone for 3 times, and dried at 30° C. for 10 min after washing to obtain modified nano-ceramic particles;

[0066] The nano-ceramic particles are silicon oxide, the isocyanate is methyl-2,4-diisocyanate (2,4-TDI), and the reaction principle involved is: oxygen atoms on the surface of the nano-ceramic particles adsorb water in the air to form hydroxyl groups on the surface, and the hydroxyl groups (-OH) react with the isocyanate groups (-N=C=O) in the isocyanate at the fixed temperature in step (2) to generate polymer A, that is, to generate modified nano-ceramic particles, wherein the surface of the nano-ceramic particles has more than one hydroxyl group (-OH), and the isocyanate contains two isocyanate groups (-N=C=O);

[0067] (3) The modified nano-ceramic particles obtained in step (2) are mixed with an aromatic polyamide polymer solution and then subjected to a grafting reaction, wherein the mass ratio of the aromatic polyamide to the modified nano-ceramic particles is 1:2, the grafting reaction temperature is 90° C., and the reaction time is 120 min, thereby obtaining an in-situ composite aromatic polyamide slurry, wherein the viscosity of the in-situ composite aromatic polyamide slurry is 20,000 cp; the reaction principle involved is that the isocyanate (-N=C=O) in the polymer A and the amide bond (-CO-NH-) in the aromatic polyamide in the step (3) undergo a grafting reaction when mixed, and the aromatic polyamide is in situ composited on the surface of the polymer A to generate polymer B, thereby obtaining an in-situ composite aromatic polyamide slurry, i.e., Sample 2, thereby achieving the composite of the two materials between the nano-ceramic particles and the aromatic polyamide without using a binder, and without the phenomenon of the nano-ceramic particles falling off;

[0068] In this embodiment, the aromatic polyamide is para-aromatic polyamide, and the preparation process of the aromatic polyamide polymer solution is as follows: 21.628 g of p-phenylenediamine is fully dissolved in 500 g of NMP (N-methylpyrrolidone) / CaCl2 (CaCl2 mass fraction is 7%) to obtain a mixed solution, the temperature of the mixed solution is reduced to 0°C, and then 42.192 g of terephthaloyl chloride is added. After the reaction time is 40 minutes, calcium hydroxide is added to neutralize to a pH of 6.5. After neutralization, a para-aromatic polyamide slurry is obtained, i.e., the aromatic polyamide polymer solution in this embodiment, wherein the mass percentage of para-aromatic polyamide in the aromatic polyamide polymer solution is 10%.

[0069] The reason for using the aromatic polyamide polymer liquid is that solid aromatic polyamide has low solubility. Different aromatic polyamides require different solvents and different dissolution conditions to be dissolved into liquid aromatic polyamide again. Directly using the aromatic polyamide polymer liquid in the process of preparing aromatic polyamide in step (2) can effectively avoid this problem, that is, the aromatic polyamide is utilized in the liquid state before becoming solid.

[0070] Example 3 Sample 3

[0071] This embodiment provides a method for preparing an in-situ composite aromatic polyamide slurry, comprising the following steps:

[0072] (1) drying the nano-ceramic particles at a drying temperature of 150° C. for 10 h;

[0073] (2) adding 20 g of the nano-ceramic particles with a particle size of 100 nm after drying in step (1) into a reactor, and then adding 200 g of a toluene solution containing 0.3 mol / L isocyanate, stirring and dispersing at 20° C. for 20 min, introducing nitrogen into the reactor, heating to a fixed temperature of 30° C. under the protection of the nitrogen, and reacting for 30 min. After the reaction is completed, crude modified nano-ceramic particles are obtained, and the crude modified nano-ceramic particles are washed with acetone for 3 times, and then dried at 60° C. for 30 min to obtain modified nano-ceramic particles;

[0074] The nano-ceramic particles are titanium oxide, and the isocyanate is methyl-2,6-diisocyanate (2,6-TDI). The reaction principle involved is: oxygen atoms on the surface of the nano-ceramic particles adsorb water in the air to form hydroxyl groups on the surface, and the hydroxyl groups (-OH) react with the isocyanate groups (-N=C=O) in the isocyanate at the fixed temperature in step (2) to generate polymer A, that is, to generate modified nano-ceramic particles, wherein the surface of the nano-ceramic particles has more than one hydroxyl group (-OH), and the isocyanate contains two isocyanate groups (-N=C=O);

[0075] (3) The modified nano-ceramic particles obtained in step (2) are mixed with an aromatic polyamide polymer solution and then subjected to a grafting reaction, wherein the mass ratio of the aromatic polyamide to the modified nano-ceramic particles is 1:2, the grafting reaction temperature is 40°C, and the reaction time is 80 min, thereby obtaining an in-situ composite aromatic polyamide slurry, and the viscosity of the in-situ composite aromatic polyamide slurry is 8000 cp; the reaction principle involved is that in the step (3), the isocyanate group (-N=C=O) in the polymer A and the amide bond (-CO-NH-) in the aromatic polyamide undergo a grafting reaction when mixed, and the aromatic polyamide is in situ composited on the surface of the polymer A to generate polymer B, thereby obtaining an in-situ composite aromatic polyamide slurry, i.e., sample three, thereby achieving the composite of the two materials between the nano-ceramic particles and the aromatic polyamide without using a binder, and the nano-ceramic particles will not fall off;

[0076] In this embodiment, the aromatic polyamide is heterocyclic aramid, and the preparation process of the aromatic polyamide polymer solution is as follows:

[0077] p-phenylenediamine and 2-(4-aminophenyl)-5-aminobenzimidazole were added to 500 g of NMP / CaCl2 (CaCl2 mass fraction of 7%) and fully dissolved to obtain a mixed solution, wherein the molar ratio of p-phenylenediamine to 2-(4-aminophenyl)-5-aminobenzimidazole was 1:2, and the total molar amount was 0.1 mol. The temperature of the mixed solution was lowered to 0°C, and then 21.096 g of terephthaloyl chloride was added. After a reaction time of 40 minutes, calcium hydroxide was added to neutralize the mixture to a pH of 6.5. After neutralization, a heterocyclic aramid slurry was obtained, i.e., the aromatic polyamide polymer solution in this embodiment, wherein the heterocyclic aramid accounted for 5% by mass of the aromatic polyamide polymer solution.

[0078] The reason for using the aromatic polyamide polymer liquid is that solid aromatic polyamide has low solubility. Different aromatic polyamides require different solvents and different dissolution conditions to be dissolved into liquid aromatic polyamide again. Directly using the aromatic polyamide polymer liquid in the process of preparing aromatic polyamide in step (2) can effectively avoid this problem, that is, the aromatic polyamide is utilized in the liquid state before becoming solid.

[0079] Example 4 Sample 4

[0080] This embodiment provides a method for preparing an in-situ composite aromatic polyamide slurry, comprising the following steps:

[0081] (1) drying the nano-ceramic particles at a drying temperature of 100° C. for 2 h;

[0082] (2) adding 10 g of the nano-ceramic particles with a particle size of 500 nm after drying in step (1) into a reactor, and then adding 200 g of a toluene solution containing 0.1 mol / L isocyanate, stirring and dispersing at 20° C. for 20 min, introducing nitrogen into the reactor, heating to a fixed temperature of 60° C. under the protection of the nitrogen, and reacting for 120 min. After the reaction is completed, crude modified nano-ceramic particles are obtained, and the crude modified nano-ceramic particles are washed with acetone for 5 times, and dried at 30° C. for 10 min after washing to obtain modified nano-ceramic particles;

[0083] The nano-ceramic particles are aluminum oxide, and the isocyanate is methyl-2,6-diisocyanate (2,6-TDI). The reaction principle involved is: oxygen atoms on the surface of the nano-ceramic particles adsorb water in the air to form hydroxyl groups on the surface, and the hydroxyl groups (-OH) react with the isocyanate groups (-N=C=O) in the isocyanate at the fixed temperature in step (2) to generate polymer A, that is, to generate modified nano-ceramic particles, wherein the surface of the nano-ceramic particles has more than one hydroxyl group (-OH), and the isocyanate contains two isocyanate groups (-N=C=O);

[0084] (3) The modified nano-ceramic particles obtained in step (2) are mixed with an aromatic polyamide polymer solution and then subjected to a grafting reaction, wherein the mass ratio of the aromatic polyamide to the modified nano-ceramic particles is 7:5, the grafting reaction temperature is 60° C., and the reaction time is 100 min, thereby obtaining an in-situ composite aromatic polyamide slurry, and the viscosity of the in-situ composite aromatic polyamide slurry is 10,000 cp; the reaction principle involved is that in the step (3), the isocyanate group (-N=C=O) in the polymer A and the amide bond (-CO-NH-) in the aromatic polyamide undergo a grafting reaction when mixed, and the aromatic polyamide is in situ composited on the surface of the polymer A to generate polymer B, thereby obtaining an in-situ composite aromatic polyamide slurry, i.e., sample 4, thereby achieving the composite of the two materials between the nano-ceramic particles and the aromatic polyamide without using a binder, and the nano-ceramic particles will not fall off;

[0085] In this embodiment, the aromatic polyamide is polyamide-imide, and the aromatic polyamide polymer solution is prepared as follows: in a nitrogen environment, trimellitic anhydride and toluene diisocyanate are added to a reactor in a molar ratio of 1:1, followed by the addition of N,N-dimethylformamide and stirring. After complete dissolution, the reaction solution is heated to 80-120°C and allowed to react for 2 hours. The precipitate is then washed thoroughly with water to obtain a precipitate, which is then dried to obtain a polyamide-imide solid. The molar ratio of N,N-dimethylformamide to trimellitic anhydride is 15:1. 7g of the above-mentioned polyamide-imide solid is added to 100g of N,N-dimethylformamide and stirred to dissolve to prepare a polyamide-imide mixed solution, which is equivalent to the aromatic polyamide polymer solution described in Examples 1-3.

[0086] In this embodiment, after the reaction is completed, a precipitate, i.e., solid aromatic polyamide, can be obtained. The polyamide-imide used in this embodiment is an easily soluble aromatic polyamide. If it is to be grafted with polymer A, it needs to be dissolved into a liquid again.

[0087] The viscosity properties of the in-situ composite aromatic polyamide slurries in Examples 1-4 are compared in Table 1:

[0088] Table 1 Viscosity of the slurry of in-situ compounded aromatic polyamide of Examples 1-4

[0089] The viscosity test is carried out using a rotational viscometer.

[0090] Example 5 Sample 5

[0091] In this embodiment, the slurry of the in-situ composite aromatic polyamide prepared in Example 1 is used to prepare a lithium battery separator. The steps of preparing the lithium battery separator include:

[0092] (1) uniformly mixing the slurry of the in-situ composite aromatic polyamide with a pore-forming agent and a polar solvent to obtain a mixture, wherein the mass ratio of the slurry of the in-situ composite aromatic polyamide: the pore-forming agent: the polar solvent is 2.5:0.5:97;

[0093] (2) Degassing the mixture by standing it for 5 minutes;

[0094] (3) After the deaerated mixture is coated on both sides of the substrate layer, it is immersed in a coagulation tank containing an organic solvent and water for coagulation, wherein the volume fraction of the organic solvent in the coagulation liquid is 60%, the coagulation time is 10 seconds, and the coagulation temperature is 60°C. A coating layer is formed on both sides of the substrate layer, and the thickness of the coating layer is 4 μm. After coagulation, it is immersed in a water tank for water washing, the water washing time is 10 seconds, and the water washing temperature is 60°C. After water washing, it is dried and heat-set, the drying time is 5 seconds, the drying temperature is 40°C, the heat setting time is 0.15 minutes, and the temperature is 40°C, to obtain the lithium battery separator;

[0095] wherein the polar solvent and the organic solvent are both N,N-dimethylacetamide;

[0096] The material of the substrate layer is wet PE (polyethylene), and the thickness of the substrate layer is 4 μm;

[0097] The slurry of the in-situ composite aromatic polyamide contains a pore-forming agent, polyethylene glycol, which plays a role in adjusting the porosity of the lithium battery separator. The porosity of the lithium battery separator is 35%.

[0098] The peel strength of the lithium battery separator (sample 5) obtained in this embodiment is 130Nm -1 , air permeability is 175s / 100cc, transverse heat shrinkage value is 2.0% at 150℃1h, longitudinal heat shrinkage value is 2.0% at 150℃1h, membrane breaking temperature is 230℃, and electrolyte contact angle is 25℃.

[0099] Example 6 Sample 6

[0100] In this embodiment, the slurry of the in-situ composite aromatic polyamide prepared in Example 2 is used to prepare a lithium battery separator. The steps of preparing the lithium battery separator include:

[0101] (1) uniformly mixing the slurry of the in-situ composite aromatic polyamide with a pore-forming agent and a polar solvent to obtain a mixture, wherein the mass ratio of the slurry of the in-situ composite aromatic polyamide: the pore-forming agent: the polar solvent is 3:1:6;

[0102] (2) Degassing the mixture by standing it for 10 minutes;

[0103] (3) After the deaerated mixture is coated on one side of the substrate layer, it is immersed in a coagulation tank comprising an organic solvent and water for coagulation, wherein the volume fraction of the organic solvent in the coagulation liquid is 60%, the coagulation time is 300 seconds, and the coagulation temperature is 60°C. A coating layer is formed on one side of the substrate layer, and the thickness of the coating layer is 8 μm. After coagulation, it is immersed in a water tank for water washing, the water washing time is 300 seconds, and the water washing temperature is 60°C. After water washing, it is dried and heat-set, the drying time is 300 seconds, the drying temperature is 100°C, the heat setting time is 30 minutes, and the temperature is 200°C, to obtain the lithium battery separator;

[0104] Wherein the polar solvent and the organic solvent are both N-methylpyrrolidone;

[0105] The material of the substrate layer is dry-process PP (polypropylene), and the thickness of the substrate layer is 12 μm;

[0106] The slurry of the in-situ composite aromatic polyamide contains tripropylene glycol, a pore-forming agent, which plays a role in adjusting the porosity of the lithium battery separator. The porosity of the lithium battery separator is 45%.

[0107] The peel strength of the lithium battery separator (sample 6) obtained in this embodiment is 120Nm -1 , the air permeability is 300s / 100cc, the transverse heat shrinkage value at 150℃ for 1h is 1.0%, the longitudinal heat shrinkage value at 150℃ for 1h is 1.0%, the membrane breaking temperature is 270℃, and the electrolyte contact angle is 21℃.

[0108] Example 7 Sample 7

[0109] In this embodiment, the in-situ composite aromatic polyamide slurry prepared in Example 3 is used to prepare a lithium battery separator. The scanning electron microscope image (SEM image) thereof is shown in FIG1 . The steps of preparing the lithium battery separator include:

[0110] (1) uniformly mixing the slurry of the in-situ composite aromatic polyamide with a pore-forming agent and a polar solvent to obtain a mixture, wherein the mass ratio of the slurry of the in-situ composite aromatic polyamide: the pore-forming agent: the polar solvent is 3:2:15;

[0111] (2) Degassing the mixture by standing it for 5 minutes;

[0112] (3) After the deaerated mixture is coated on both sides of the substrate layer, it is immersed in a coagulation tank comprising an organic solvent and water for coagulation, wherein the volume fraction of the organic solvent in the coagulation liquid is 60%, the coagulation time is 10 seconds, and the coagulation temperature is 60°C. A coating layer is formed on both sides of the substrate layer, and the thickness of the coating layer is 6 μm. After coagulation, it is immersed in a water tank for water washing, the water washing time is 10 seconds, and the water washing temperature is 60°C. After water washing, it is dried and heat-set, the drying time is 5 seconds, the drying temperature is 40°C, the heat setting time is 30 minutes, and the temperature is 200°C, to obtain the lithium battery separator;

[0113] wherein the polar solvent and the organic solvent are both N,N-dimethylformamide;

[0114] The material of the substrate layer is a PP / PE / PP three-layer composite membrane, and the thickness of the substrate layer is 30 μm;

[0115] The slurry of the in-situ composite aromatic polyamide contains a pore-forming agent, polyvinyl pyrrolidone, which plays a role in adjusting the porosity of the lithium battery separator. The porosity of the lithium battery separator is 40%.

[0116] The peel strength of the lithium battery separator (sample 7) obtained in this embodiment is 125Nm -1 The air permeability is 245s / 100cc, the transverse heat shrinkage value at 150℃ for 1h is 1.5%, the longitudinal heat shrinkage value at 150℃ for 1h is 1.5%, the membrane breaking temperature is 250℃, and the electrolyte contact angle is 23℃.

[0117] Example 8 Sample 8

[0118] This embodiment uses the in-situ composite aromatic polyamide slurry prepared in Example 4 to prepare a lithium battery separator. The steps of preparing the lithium battery separator include:

[0119] (1) uniformly mixing the slurry of the in-situ composite aromatic polyamide with a pore-forming agent and a polar solvent to obtain a mixture, wherein the mass ratio of the slurry of the in-situ composite aromatic polyamide: the pore-forming agent: the polar solvent is 12:5:83;

[0120] (2) Degassing the mixture by standing it for 5 minutes;

[0121] (3) After the degassed mixture is coated on both sides of the substrate layer, it is immersed in a coagulation tank containing an organic solvent and water for coagulation, wherein the volume fraction of the organic solvent in the coagulation liquid is 60%, the coagulation time is 10s, and the coagulation temperature is 60°C. A coating layer is formed on both sides of the substrate layer, and the thickness of the coating layer is 0.5 μm. After coagulation, it is immersed in a water tank for water washing, the water washing time is 10s, and the water washing temperature is 0°C. After water washing, it is dried and heat-set, the drying time is 5s, the drying temperature is 100°C, the heat setting time is 0.15min, and the temperature is 40°C, to obtain the lithium battery separator;

[0122] Wherein the polar solvent and the organic solvent are both N-methylformamide;

[0123] The material of the substrate layer is wet-process PE, and the thickness of the substrate layer is 4 μm;

[0124] The slurry of the in-situ composite aromatic polyamide contains anhydrous calcium chloride as a pore-forming agent. The pore-forming agent is used to adjust the porosity of the lithium battery separator, thereby increasing the porosity of the lithium battery separator to 42%.

[0125] The peel strength of the lithium battery separator (sample eight) obtained in this embodiment is 128Nm -1 , air permeability is 160s / 100cc, transverse heat shrinkage value is 2.0% at 150℃ for 1h, longitudinal heat shrinkage value is 2.0% at 150℃ for 1h, membrane breaking temperature is 200℃, and electrolyte contact angle is 22℃.

[0126] The performance comparison of the lithium battery separators in Examples 5-8 is shown in Table 2:

[0127] Table 2 Performance parameters of lithium battery separators in Examples 5-8

[0128] The above performance test method is carried out in accordance with the test specifications in GB / T 36363-2018.

[0129] Example 9 Sample 9

[0130] In this embodiment, the lithium battery separator prepared in Example 5 is used to prepare a battery, that is, a 4Ah 811 system ternary lithium battery (sample nine) is assembled. The test results are shown in Table 3.

[0131] Example 10 Sample 10

[0132] In this embodiment, the lithium battery separator prepared in Example 6 is used to prepare a battery, that is, a 4Ah 811 system ternary lithium battery (sample 10) is assembled. The test results are shown in Table 3.

[0133] Example 11 Sample 11

[0134] In this embodiment, the lithium battery separator prepared in Example 7 is used to prepare a battery, that is, a 4Ah 811 system ternary lithium battery (sample 11) is assembled. The test results are shown in Table 3.

[0135] Example 12 Sample 12

[0136] In this embodiment, the lithium battery separator prepared in Example 8 is used to prepare a battery, that is, a 4Ah 811 system ternary lithium battery (sample 12) is assembled. The test results are shown in Table 3.

[0137] Comparative Example 1 Sample 13

[0138] This comparative example uses a commercially available 7μm PE-based film as a lithium battery separator, wherein the lithium battery separator has an air permeability of 145s / 100cc, a film melting temperature of 150°C, a film rupture temperature of 135°C, and an electrolyte contact angle of 46.7°C.

[0139] The above-mentioned lithium battery separator was assembled into a 4Ah 811 system ternary lithium battery (sample 13). The test results are shown in Table 3.

[0140] Comparative Example 2 Sample 14

[0141] This comparative example uses a commercially available 9+2+2 μm PE / ceramic coating film as a lithium battery separator, wherein the separator peel strength of the lithium battery separator is 90 Nm -1 , air permeability 175s / 100cc, transverse heat shrinkage value 2.0% at 150℃1h, longitudinal heat shrinkage value 2.0% at 150℃1h, membrane rupture temperature 156℃, electrolyte contact angle 31℃.

[0142] The above-mentioned lithium battery separator was assembled into a 4Ah 811 system ternary lithium battery (sample 14). The test results are shown in Table 3.

[0143] Table 3 Battery performance test results

[0144] The above performance test method is carried out in accordance with the test specifications in GB / T 31241-2014.

[0145] In summary, compared with the commercially available lithium battery separators of Comparative Examples 1-2, the lithium battery separators prepared by the in-situ composite aromatic polyamide slurries prepared in Examples 1-4 have significantly improved performance, that is, the separator peel strength of the lithium battery separator prepared by the in-situ composite aromatic polyamide slurry of the present invention is ≥120Nm -1, air permeability ≤300s / 100cc, transverse heat shrinkage value ≤2.0% at 150℃ for 1h, longitudinal heat shrinkage value ≤2.0% at 150℃ for 1h, membrane breaking temperature ≥200℃, electrolyte contact angle ≤25℃; after the lithium battery separator prepared by the present invention is used to prepare a battery, the performance of the battery is significantly improved, that is, the lithium battery separator containing the slurry of the in-situ composite aromatic polyamide is further used to prepare a battery, and the capacity retention rate of the battery after 100 cycles is increased from 63.5 in the prior art to 100. -65.2% is increased to 85-95%, the room temperature capacity of the battery is increased from 3.8260-3.8359Ah in the prior art to 3.8362-3.8467A, the high temperature capacity (55°C) is increased from 3.2618-3.2825Ah in the prior art to 3.6112-3.7171Ah, and the low temperature capacity (-20°C) is increased from 1.6985-1.7510Ah in the prior art to 1.9309-1.9726Ah.

[0146] It should be understood that the present invention is not limited to the contents and structures described above and shown in the drawings, and various modifications and changes can be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A slurry for in-situ composite aromatic polyamide, characterized in that: First, nano-ceramic particles are in-situ composited with isocyanate for modification, wherein the modification is that the hydroxyl groups on the surface of the nano-ceramic particles react with the isocyanate groups in the isocyanate to obtain modified nano-ceramic particles, and then the modified nano-ceramic particles are in-situ composited with aromatic polyamide through a grafting reaction, during which the isocyanate groups in the modified nano-ceramic particles are grafted with the amide bonds in the aromatic polyamide to composite the nano-ceramic particles and the aromatic polyamide to obtain the in-situ composite aromatic polyamide slurry, wherein the viscosity of the slurry is 50-20000cp, wherein the isocyanate contains at least 2 isocyanate groups.

2. The slurry for in-situ composite aromatic polyamide according to claim 1, characterized in that: The nano ceramic particles are one of aluminum oxide, silicon oxide and titanium oxide; or the particle size of the nano ceramic particles is 10-1000 nm.

3. The slurry for in-situ composite aromatic polyamide according to claim 2, characterized in that: The aromatic polyamide is one of meta-aromatic polyamide, para-aromatic polyamide, heterocyclic aramid, and polyamide-imide.

4. The slurry for in-situ composite aromatic polyamide according to claim 3, characterized in that: The structural formula of the isocyanate is O=C=N-R1-N=C=O, wherein the structural formula of R1 is When R1 is When the isocyanate is 4,4'-diphenylmethane diisocyanate; When R1 is When the isocyanate is methyl-2,4-diisocyanate; When R1 is When the isocyanate is methyl-2,6-diisocyanate.

5. A method for preparing a slurry of in-situ composite aromatic polyamide according to any one of claims 1 to 4, characterized in that: The steps include: (1) drying the nano-ceramic particles at a drying temperature of 100-150° C. for a drying time of 2-10 h; (2) adding the nano-ceramic particles dried in step (1) into a reaction kettle, adding a toluene solution containing isocyanate, stirring and dispersing, introducing an inert gas into the reaction kettle, heating to a fixed temperature under the protection of the inert gas, and reacting to obtain a crude modified nano-ceramic particle after the reaction is completed, washing the crude modified nano-ceramic particle with an organic solvent, and drying again after washing to obtain a modified nano-ceramic particle; (3) The modified nano-ceramic particles obtained in step (2) are mixed with aromatic polyamide polymer solution and then subjected to grafting reaction to obtain an in-situ composite aromatic polyamide slurry having a viscosity of 50-20000cp.

6. The method for preparing the slurry of in-situ composite aromatic polyamide according to claim 5, characterized in that: The concentration of isocyanate in the toluene solution in step (2) is 0.1-0.5 mol / L, and the mass of the nano-ceramic particles accounts for 1-20% of the mass of the toluene solution.

7. The method for preparing the slurry of in-situ composite aromatic polyamide according to claim 5, characterized in that: The stirring and dispersing process in step (2) is performed at a temperature of 20-30° C. and for a time of 20-60 min.

8. The method for preparing the slurry of in-situ composite aromatic polyamide according to claim 5, characterized in that: The inert gas in step (2) is nitrogen. The fixed heating temperature after the nitrogen is introduced is 30-60° C., and the reaction time is 30-120 min.

9. The method for preparing the slurry of in-situ composite aromatic polyamide according to claim 5, characterized in that: In the step (2), the organic solvent is acetone, and the modified nano-ceramic particle crude product is washed with acetone 3-5 times.

10. The method for preparing the slurry of in-situ composite aromatic polyamide according to claim 5, characterized in that: The re-drying temperature in step (2) is 30-60° C., and the re-drying time is 10-30 min.

11. The method for preparing the slurry of in-situ composite aromatic polyamide according to claim 5, characterized in that: The aromatic polyamide polymerization liquid in the step (3) contains aromatic polyamide, and the mass ratio of the aromatic polyamide to the modified nano-ceramic particles is (2-10):(0.5-20); the mass percentage of aromatic polyamide in the aromatic polyamide polymerization liquid is 2-10%.

12. The method for preparing the slurry of in-situ composite aromatic polyamide according to claim 5, characterized in that: The temperature of the grafting reaction in step (3) is 20-90° C., and the reaction time is 20-120 min.

13. A lithium battery separator, characterized in that: The lithium battery separator comprises a substrate layer and a coating layer, wherein the coating layer is prepared from the slurry of the in-situ composite aromatic polyamide according to any one of claims 1 to 4, and the separator peel strength of the lithium battery separator is ≥120Nm -1 , air permeability ≤300s / 100cc, transverse heat shrinkage value ≤2.0% at 150℃ for 1h, longitudinal heat shrinkage value ≤2.0% at 150℃ for 1h, membrane breaking temperature ≥200℃, electrolyte contact angle ≤25℃.

14. A battery, characterized in that: The battery is installed with the lithium battery separator according to claim 13, and the capacity retention rate of the battery after 100 cycles is 85-95%. The high temperature capacity of the battery at 55°C is 3.6112-3.7171Ah, and the low temperature capacity at -20°C is 1.9309-1.9726Ah.

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