Lithium battery separator and method of making the same

Abstract

The application discloses a lithium battery diaphragm and a preparation method thereof. The lithium battery diaphragm comprises a base film and a coating layer coated on the base film, wherein the coating layer comprises nano microcapsules and ceramic. The nano microcapsules are capsules with perfluorohexanone as a core and a polymer as a shell. The polymer is a mixture of one or both of polyurethane and polymethyl methacrylate. The ceramic is one of aluminum oxide powder and titanium silicate powder. The lithium battery diaphragm has a self-extinguishing function by adding the nano microcapsules to the coating layer. On this basis, the synergistic effect of the nano microcapsules and the ceramic also improves the breakdown voltage of the diaphragm.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery separators, and particularly relates to a lithium battery separator and a preparation method thereof. BACKGROUND

[0002] With the progress of science and technology, lithium ion batteries are widely used in various electronic devices due to their high energy density and long cycle life. However, lithium ion batteries also have safety hazards such as fire and explosion. In order to improve the safety of lithium batteries, the existing technology mainly coats a layer of ceramic material on the separator to prevent internal short circuit of the battery. However, this method cannot effectively extinguish the fire when the battery overheats. Therefore, it is an urgent need to develop a lithium battery separator with fire extinguishing function. SUMMARY

[0003] In view of the deficiencies of the prior art, the purpose of the present application is to provide a slurry.

[0004] Another purpose of the present application is to provide a preparation method of the above-mentioned slurry.

[0005] Another purpose of the present application is to provide a lithium battery separator.

[0006] Another purpose of the present application is to provide a method for preparing the above-mentioned lithium battery separator.

[0007] The purpose of the present application is achieved by the following technical solutions.

[0008] A slurry, comprising: nano-microcapsules, ceramic and water, the ratio of the nano-microcapsules and the ceramic is (10-30):(70-90) by mass fraction, the nano-microcapsules are capsules with perfluorohexanone as the core and a polymer as the shell, and the polymer is a mixture of one or both of polyurethane (PU) and polymethyl methacrylate (PMMA).

[0009] In the above technical solution, the slurry further comprises: a binder and an additive, the ratio of the mass fraction of the nano-microcapsules, the volume fraction of the binder and the volume fraction of the additive is (10-30):(2-3):(0.01-1), the unit of the mass fraction is mg, and the unit of the volume fraction is mL.

[0010] In the above technical solution, the particle size of the nano-microcapsules is not more than microns.

[0011] In the above technical solution, the ceramic is one of alumina powder and titanium silicate powder.

[0012] In the above technical solution, the binder is a mixture of one or more of polyacrylate, acrylic resin and polyester resin.

[0013] In the technical solution, the additive is one or more of a leveling agent, a defoaming agent and a pore-forming agent, the leveling agent is polydimethylsiloxane, the defoaming agent is polymethylsiloxane, and the pore-forming agent is isopropyl alcohol.

[0014] In the technical solution, the ratio of the ceramic to the water is 1:(1.2-2.4) by mass fraction.

[0015] When the slurry comprises a binder and an additive, the preparation method of the slurry comprises the following steps:

[0016] S1, mixing the nano-microcapsules and a ceramic coating to be uniform to obtain a first solution, wherein the ceramic coating is a mixture of ceramic and water, and the ratio of the nano-microcapsules to the ceramic in the ceramic coating is (10-30):(70-90) by mass fraction;

[0017] In S1, the nano-microcapsules and the ceramic coating are mixed and stirred at a speed of 200-1500 rpm for 30-45 minutes to be uniform.

[0018] In S1, the ratio of the ceramic to the water is 1:(1.2-2.4) by mass fraction.

[0019] S2, mixing the first solution, a binder and an additive to be uniform to obtain the slurry, wherein the ratio of the mass fraction of the nano-microcapsules, the volume fraction of the binder and the volume fraction of the additive is (10-30):(2-3):(0.01-1), the unit of the mass fraction is mg, and the unit of the volume fraction is mL.

[0020] In the technical solution, the method for preparing the nano-microcapsules comprises the following steps:

[0021] Step 1, mixing perfluorohexanone, an emulsifier, a stabilizer and a polymer solution to obtain a first substance, wherein the ratio of perfluorohexanone, the emulsifier, the stabilizer and the polymer in the polymer solution is (10-15):(1-1.5):(0.5-1):(0.5-1.5) by mass fraction.

[0022] In step 1, the polymer solution is a mixture of a polymer and a solvent, and the mass fraction of the polymer in the polymer solution is 0.5-0.7 wt%.

[0023] In step 1, the emulsifier is a mixture of one or more of Tween 60, Tween 80 and Pluronic F127.

[0024] In step 1, the stabilizer is a mixture of one or both of polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP).

[0025] In step 1, the polymer is a mixture of one or both of polyurethane (PU) and polymethyl methacrylate (PMMA).

[0026] In the above technical solution, the solvent is a mixture of one or more of N,N-dimethylformamide (DMF), dimethylacetamide (DMAc) and ethyl cellosolve.

[0027] In step 1, the emulsification temperature is 30-40℃, and the emulsification pressure is 1atm.

[0028] In step 2, an initiator is added to the first substance to further polymerize the polymer, and after the polymerization is completed, centrifugation, washing, and drying are performed to obtain the nanocapsule, wherein the mass ratio of the perfluorohexanone to the initiator is (10-15):(0.1-0.2).

[0029] In step 2, the initiator is a mixture of one or more of potassium persulfate, ammonium persulfate and azobisisobutyronitrile.

[0030] In step 2, the centrifugation speed is 4000-4500rpm, and the centrifugation time is 15-30 minutes.

[0031] In step 2, the washing is performed using anhydrous ethanol or methanol. A lithium battery separator, comprising: a base film and a coating layer coated on the base film, the coating layer comprising: nanocapsules and ceramic, the mass ratio of the nanocapsules to the ceramic being (10-30):(70-90), the nanocapsules being capsules with perfluorohexanone as the core and a polymer as the shell, the polymer being a mixture of one or both of polyurethane (PU) and polymethyl methacrylate (PMMA), and the ceramic being one of alumina powder and titanium silicate powder.

[0032] A method for preparing the above lithium battery separator, comprising: coating the slurry on one side or both sides of the base film and drying to obtain the lithium battery separator.

[0033] In the above technical solution, the coating method is one of roll coating, spraying and dipping.

[0034] Compared with the prior art, the present application has the following advantages:

[0035] The present application realizes the self-extinguishing function of the lithium battery by adding the nano microcapsule into the coating of the lithium battery diaphragm. When the lithium battery is in thermal runaway or fire, the perfluorohexanone in the nano microcapsule is expanded by heat, and finally breaks through the microcapsule film and is automatically sprayed out, thereby achieving the effect of extinguishing fire by heat absorption and temperature reduction. This method not only improves the safety of the lithium battery, but also uses the green and environmentally friendly extinguishing agent perfluorohexanone, which is friendly to the environment. The present application has broad application prospect and market value. On this basis, the synergistic effect of the nano microcapsule and the ceramic also improves the breakdown voltage of the diaphragm. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 A schematic diagram of the distribution of the ceramic and the nano microcapsule in the coating of the present application. DETAILED DESCRIPTION

[0037] The technical solutions of the present application will be further described below in combination with specific examples.

[0038] The raw material information involved in the following examples is as follows:

[0039] Perfluorohexanone: molecular formula: C6F 12 O.

[0040] Polymethyl methacrylate (PMMA): weight average molecular weight 300-600 million.

[0041] Polymer is polyurethane (PU): weight average molecular weight 15-40 million.

[0042] The instrument information involved in the following examples is as follows:

[0043] The base film in the following examples is a PE film with a thickness of 9um.

[0044] The particle size of the nano microcapsule in the following examples is not more than microns.

[0045] Example 1

[0046] A preparation method of a slurry, comprising the following steps:

[0047] S1, mix the nano microcapsule and the ceramic coating, stir in a double planetary mixer at a speed of 300 rpm for 30 minutes until the nano microcapsule is uniformly dispersed, to obtain a first solution, wherein the ratio of the nano microcapsule to the ceramic in the ceramic coating is 10:90 by mass fraction, the nano microcapsule is a capsule with perfluorohexanone as the core and a polymer as the shell, the ceramic coating is a mixture of ceramic and water, the ceramic is aluminum oxide powder, and the ratio of the ceramic to water is 1:2 by mass fraction;

[0048] S2, mixing the first solution, the binder and the additive to be uniform to obtain a slurry, wherein the ratio of the mass fraction of the nanocapsule, the volume fraction of the binder and the volume fraction of the additive is 10:2:0.01, the unit of the mass fraction is mg, the unit of the volume fraction is mL, the binder is polyacrylate, the additive is a leveling agent, the leveling agent is polydimethylsiloxane, and the binder and the leveling agent are added to improve the adhesion and surface smoothness of the coating.

[0049] A method for preparing a nanocapsule, comprising the following steps:

[0050] Step 1, mixing perfluorohexanone, emulsifier, stabilizer and polymer solution, stirring at 15000 rpm for 15 minutes (emulsification) at 40℃, 1 atm using a high-speed homogenizer to obtain a first substance (a stable oil-water emulsion), wherein the ratio of perfluorohexanone, emulsifier, stabilizer and polymer in the polymer solution is 10:1:0.5:0.7 by mass fraction, the polymer solution is a mixture of polymer and solvent, the mass fraction of polymer in the polymer solution is 0.5wt%, the emulsifier is Tween 80, the stabilizer is polyvinyl alcohol (PVA), the polymer is polyurethane (PU), and the solvent is N,N-dimethylformamide (DMF);

[0051] Step 2, adding an initiator to the first substance (polymer is initiated by the initiator to undergo polymerization again), stirring at 15000 rpm for 180 minutes at 60℃, centrifuging at 4000 rpm for 30 minutes after the polymerization reaction is completed, washing with anhydrous ethanol for 3 times, and drying at 40℃ for 24 hours to obtain a nanocapsule, wherein the ratio of perfluorohexanone and initiator is 10:0.1 by mass fraction, and the initiator is potassium persulfate.

[0052] Example 2

[0053] A method for preparing a slurry, comprising the following steps:

[0054] S1, mixing the nanocapsule and the ceramic coating, stirring in a double planetary mixer at a speed of 200 rpm for 45 minutes to uniformly disperse the nanocapsule to obtain a first solution, wherein the ratio of the nanocapsule and the ceramic in the ceramic coating is 20:80 by mass fraction, the nanocapsule is a capsule with perfluorohexanone as the core and a polymer as the shell, the ceramic coating is a mixture of ceramic and water, the ceramic is titanium silicate powder, and the ratio of the ceramic and water is 1:2 by mass fraction;

[0055] S2, mixing the first solution, the binder and the additive to be uniform to obtain a slurry, wherein the ratio of the mass fraction of the nanocapsule, the volume fraction of the binder and the volume fraction of the additive is 20:3:1, the unit of the mass fraction is mg, the unit of the volume fraction is mL, the binder is acrylic resin, the additive is defoaming agent, the defoaming agent is polymethylsiloxane, and the binder and the defoaming agent are used to improve the adhesion of the coating and reduce bubbles in the coating process.

[0056] A method for preparing a nanocapsule, comprising the following steps:

[0057] Step 1, mixing perfluorohexanone, emulsifier, stabilizer and polymer solution, stirring at 12000 rpm for 20 minutes (emulsification) under the condition of 30℃ and 1atm using a high shear mixer to obtain a first substance (a stable oil-water mixture), wherein the ratio of perfluorohexanone, emulsifier, stabilizer and polymer in the polymer solution is 15:1.5:1.0:1.0 by mass fraction, the polymer solution is a mixture of polymer and solvent, the mass fraction of polymer in the polymer solution is 0.7wt%, the emulsifier is Pluronic F127, the stabilizer is polyvinyl alcohol (PVA), the polymer is polymethyl methacrylate (PMMA), and the solvent is dimethylacetamide (DMAc);

[0058] Step 2, adding an initiator to the first substance (polymer is initiated to occur polymerization reaction by the initiator), stirring at 12000 rpm for 60 minutes at 30℃, centrifuging at 4500 rpm for 20 minutes after the completion of the polymerization reaction, washing with anhydrous ethanol for 4 times, and drying at 45℃ for 18 hours to obtain a nanocapsule, wherein the ratio of perfluorohexanone and initiator is 15:0.2 by mass fraction, and the initiator is ammonium persulfate.

[0059] Example 3

[0060] A method for preparing a slurry, comprising the following steps:

[0061] S1, mixing the nanocapsule and the ceramic coating to obtain a first solution, wherein the ratio of the nanocapsule and the ceramic in the ceramic coating is 30:70 by mass fraction, the nanocapsule is a capsule with perfluorohexanone as the core and a polymer as the shell, the ceramic coating is a mixture of ceramic and water, the ceramic is alumina powder, and the ratio of the ceramic and water is 1:2 by mass fraction, and the nanocapsule is uniformly dispersed in the ceramic coating by stirring at 1500 rpm for 30 minutes in a double planetary mixer.

[0062] S2, mixing the first solution, the binder and the additive to be uniform to obtain a slurry, wherein the ratio of the mass fraction of the nanocapsule, the volume fraction of the binder and the volume fraction of the additive is 30:2:0.5, the unit of the mass fraction is mg, the unit of the volume fraction is mL, the binder is polyester resin, and the additive is a pore-forming agent, and the pore-forming agent is isopropyl alcohol, and the binder and the pore-forming agent are added to improve the mechanical properties of the coating.

[0063] A method for preparing nanocapsules, comprising the following steps:

[0064] Step 1, mixing perfluorohexanone, emulsifier, stabilizer and polymer solution, using an ultrasonic emulsifier at 1 kHz for 15 minutes (emulsification) under the condition of 40℃ and 1 atm to obtain a first substance (stable emulsion), wherein the ratio of perfluorohexanone, emulsifier, stabilizer and polymer in the polymer solution is 13:1.2:0.8:0.8 by mass fraction, the polymer solution is a mixture of polymer and solvent, the mass fraction of polymer in the polymer solution is 0.6wt%, the emulsifier is Tween60, the stabilizer is polyvinylpyrrolidone (PVP), the polymer is polymethyl methacrylate (PMMA), and the solvent is dimethylacetamide (DMAc);

[0065] Step 2, adding an initiator to the first substance (initiating polymerization again by the initiator), stirring at 500 rpm for 45 min at 40℃, centrifuging at 4000 rpm for 15 min after the completion of the polymerization reaction, washing with methanol for 3 times, and drying at 40℃ for 24 hours to obtain nanocapsules, wherein the ratio of perfluorohexanone and initiator is 13:0.15 by mass fraction, and the initiator is azobisisobutyronitrile.

[0066] Comparative Example 1

[0067] A method for preparing a lithium battery separator, comprising: transferring a conventional alumina slurry to a coating tank of a coating machine, adjusting the liquid level to ensure continuous coating, using a lithographic coating method to coat the conventional alumina slurry on one side of the base film (the coating speed is set to 60 m / min), drying in a hot air drying oven at 50℃ for 5 minutes, obtaining a coating layer on the base film (the coating thickness is 3um, and the coating thickness is controlled by adjusting the coating gap), and obtaining a lithium battery separator, wherein the method for obtaining the conventional alumina slurry is: dispersing alumina powder in deionized water, grinding with a sand mill until the D50 particle size reaches 0.9um to ensure good dispersibility, obtaining an alumina dispersion liquid, adding a dispersant (sodium polyacrylate) to the alumina dispersion liquid to prevent particle aggregation, and ultrasonic treatment until uniform dispersion to obtain the conventional alumina slurry, wherein the ratio of the alumina powder, deionized water and dispersant is 30:50:2 by mass fraction.

[0068] Examples 4-6

[0069] A method for preparing a lithium battery separator, comprising: transferring a slurry into a trough of a coating machine, adjusting the liquid level of the trough to ensure stable slurry supply during coating, coating the slurry on a base film by using a micro gravure roll, drying at A ℃ for 1 min to obtain a coating layer (coating thickness is 3 um, coating thickness is controlled by adjusting the coating gap) on the base film, to obtain a lithium battery separator, wherein the thread count of the micro gravure roll is 120 threads / inch (uniform coating is ensured by thread count), the coating speed is B m / min, and the slurry is one of the slurries prepared in Examples 1-3. The values of A and B are shown in Table 1.

[0070] Table 1

[0071]

[0072] The lithium battery separators prepared in Examples 4-6 and Comparative Example 1 were tested for performance, and the results are shown in Table 2. The "fire extinguishing effect" was obtained by a fire extinguishing experiment, in which a base film with a length of 10 cm and a width of 1 cm was cut, and the slurry was coated on the first 5 cm to obtain a coating film. The base film at the end not coated with the slurry was ignited, and the time when the flame was extinguished was recorded, starting from the point where the flame reached the boundary between the base film and the coating film. The time when the flame was extinguished is shown in Table 2, and the shorter the time, the better the fire extinguishing effect.

[0073] Table 2

[0074]

[0075] Experimental conclusion: As the content of nano-microcapsules increases, the breakdown voltage performance of the lithium battery separator becomes more and more excellent, and the fire extinguishing effect becomes better and better.

[0076] As shown in Figure 1 , the position distribution of the nano-microcapsules is below the ceramic coating. The multiple interfaces of different substances improve the overall breakdown voltage of the separator. Figure 1 In the present application, "ceramic" refers to alumina powder in the slurries of Example 1 and Example 3, and titanium silicate powder in the slurry of Example 2.

[0077] The above is an exemplary description of the present application, and it should be noted that any simple modification, modification or other equivalent replacement that does not deviate from the core of the present application and can be made by those skilled in the art without creative labor falls within the protection scope of the present application.

Claims

1. A lithium battery separator, characterized by, The application relates to a polyvinyl film and a coating layer coated on the polyvinyl film, wherein the coating layer comprises: nano microcapsules and ceramic, the ratio of the nano microcapsules and the ceramic is (10-30):(70-90) in mass fraction, the nano microcapsules are capsules with perfluorohexanone as the core and a polymer as the shell, the polymer is a mixture of one or both of polyurethane and polymethyl methacrylate, and the ceramic is one of alumina powder and titanium silicate powder; the nano microcapsules are distributed below the ceramic coating layer; the nano microcapsules and the ceramic cooperate to improve the safety of lithium batteries and the breakdown voltage of the separator; the coating layer is obtained by coating a slurry on the polyvinyl film and drying; and a method for preparing the nano microcapsules comprises the following steps. In step 1, perfluorohexanone, an emulsifier, a stabilizer and a polymer solution are mixed and emulsified to obtain a first substance, wherein the ratio of the perfluorohexanone, the emulsifier, the stabilizer and the polymer in the polymer solution is (10-15):(1-1.5):(0.5-1):(0.5-1.5) in mass fraction. In step 2, an initiator is added to the first substance for polymerization, and after the polymerization is completed, centrifugation, washing and drying are carried out to obtain the nano microcapsules, wherein the ratio of the perfluorohexanone and the initiator is (10-15):(0.1-0.2) in mass fraction. The slurry comprises:

2. The lithium battery separator of claim 1, wherein, The nano microcapsules, the ceramic and water, and the ratio of the nano microcapsules and the ceramic is (10-30):(70-90) in mass fraction. The slurry further comprises: a binder and an additive, and the ratio of the mass fraction of the nano microcapsules, the volume fraction of the binder and the volume fraction of the additive is (10-30):(2-3):(0.01-1), the unit of the mass fraction is mg, and the unit of the volume fraction is mL.

3. The lithium battery separator of claim 2, wherein, The binder is a mixture of one or more of polyacrylate, acrylic resin and polyester resin; and the additive is one or more of a leveling agent, a defoaming agent and a pore-forming agent.

4. The lithium battery separator of claim 3, wherein, The leveling agent is polydimethylsiloxane, the defoaming agent is polymethylsiloxane, and the pore-forming agent is isopropyl alcohol.

5. The lithium battery separator of claim 4, wherein, The ratio of the ceramic and water is 1:(1.2-2.4) in mass fraction.

6. The lithium battery separator of claim 2, wherein, In step 1, the emulsification temperature is 30-40 DEG C, and the emulsification pressure is 1 atm.

7. The lithium battery separator of claim 1, wherein, The preparation method of the slurry comprises the following steps:

8. The lithium battery separator of claim 2, wherein, S1, the nano microcapsules and ceramic paint are mixed to be uniform to obtain a first solution, wherein the ceramic paint is a mixture of ceramic and water, and the ratio of the nano microcapsules and the ceramic in the ceramic paint is (10-30):(70-90) in mass fraction; S2, the first solution, a binder and an additive are mixed to be uniform to obtain the slurry, wherein the ratio of the mass fraction of the nano microcapsules, the volume fraction of the binder and the volume fraction of the additive is (10-30):(2-3):(0.01-1), the unit of the mass fraction is mg, and the unit of the volume fraction is mL. ​

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