CN104157819A - Ceramic-gel polymer multilayer composite lithium battery diaphragm and preparation method thereof - Google Patents

Abstract

The invention discloses a preparation method of a ceramic and gel polymer multilayer composite lithium battery diaphragm, which comprises the following steps: step 1: configuring water-based PVDF slurry and water-based ceramic slurry; step 2: polypropylene diaphragm and polyethylene Diaphragm compounding, thermally compound a layer of polypropylene diaphragm and a layer of polyethylene diaphragm at 50-100°C to obtain a PP/PE composite diaphragm; step 3: coating, use the PP/PE composite diaphragm obtained in step 2 as the coating Substrate, the water-based slurry prepared in step 1 is coated on the PE surface of the substrate, the water-based ceramic slurry is first coated to form a ceramic layer, and then the water-based PVDF slurry is coated to form a gel polymer layer. The coating rate is 5-100m/min, after drying in an oven at 30-100°C, the final four-layer composite diaphragm is obtained. The invention also discloses the separator prepared by the method. The invention has the advantages that the processed diaphragm has high thermal safety and strong ability to retain electrolyte.

Description

Ceramic and gel polymer multilayer composite lithium battery separator and preparation method thereof

technical field

The invention relates to a lithium ion battery separator, in particular to a ceramic and gel polymer multilayer composite lithium battery separator with high thermal safety and strong electrolyte retention capacity and a preparation method thereof.

Background technique

As one of the four major materials of lithium batteries, the separator is a key inner layer component in lithium batteries, although it does not participate in the electrochemical reactions in the battery. Key properties such as battery capacity, cycle performance, and charge-discharge current density are directly related to the diaphragm, and the improvement of the performance of the diaphragm plays an important role in improving the overall performance of the lithium battery. In a lithium battery, the separator absorbs the electrolyte and isolates the positive and negative electrodes to prevent short circuits, but at the same time allows the conduction of lithium ions. When overcharging or temperature rises, the diaphragm must also have high-temperature self-closing properties to block current conduction and prevent explosions. Not only that, the lithium battery separator also has the characteristics of high strength, fire prevention, chemical resistance, acid and alkali corrosion resistance, good biocompatibility, and non-toxicity.

The safety of lithium-ion batteries has always been the focus of attention in the industry, and the safety of separators is the top priority. This requires the separator to have excellent mechanical properties, low cell closure temperature and the ability to maintain shape at higher temperatures. Now large-scale commercial lithium battery separators are mainly made of polypropylene and polyethylene. As people have higher and higher performance requirements for lithium batteries, it is difficult to meet the thermal safety and electrolyte retention ability of these two separators alone. Research on the preparation of high-performance composite diaphragms of other materials and polyolefins has become the most important direction of diaphragm modification.

Contents of the invention

In order to overcome the above-mentioned shortcomings, the present invention provides a method for preparing a ceramic and gel polymer multilayer composite lithium battery diaphragm with high thermal safety and strong ability to retain electrolyte

The object of the present invention is achieved by the following technical measures, a preparation method of a ceramic and gel polymer multilayer composite lithium battery separator, comprising the steps of:

Step 1: Configure water-based PVDF slurry and water-based ceramic slurry;

Step 2: Polypropylene diaphragm and polyethylene diaphragm are compounded, and a layer of polypropylene diaphragm and a layer of polyethylene diaphragm are thermally compounded at 50-100 ° C to obtain a PP/PE composite diaphragm;

Step 3: Coating, use the PP/PE composite diaphragm obtained in step 2 as the coating substrate, apply the water-based slurry prepared in step 1 on the PE surface of the substrate, and first coat the water-based ceramic slurry to form a ceramic layer Afterwards, the water-based PVDF slurry is coated to form a gel polymer layer at a coating rate of 5-100 m/min, and dried in an oven at 30-100° C. to obtain the final four-layer composite diaphragm. Among them, the coating on the PE surface is because the PE layer is easy to deform at high temperature, and it mainly plays a role of thermal shutdown in the composite diaphragm. This helps to improve the phenomenon of powder falling off the coating separator when making batteries. (1) Stir the polyolefin resin, lubricant and other additives evenly through a mixing mixer to obtain a mixture;

As a preferred method, the water-based PVDF slurry preparation method in the step 1 is:

Using deionized water as a solvent, add water-soluble adhesives, surfactants, dispersants, and thickeners to deionized water at room temperature and stir to dissolve to make a solution; then add polymer powder particles, stir evenly, and make a water-based solution. Slurry; the slurry contains 0.1%-2% water-soluble polymer thickener, 0.01%-2% water-based dispersant, 0.01%-1% surfactant, 0.1%-5% water-based adhesive agent, 5% to 25% of polymer powder particles, 67% to 83% of deionized water, all of which are mass fractions; the weight average molecular weight of the polymer powder particles is 120,000-160,000, and the particle diameter is 100-300nm.

As a preferred mode, the preparation method of water-based ceramic slurry in the step 1 is:

Using deionized water as a solvent, add water-soluble adhesive and thickener to deionized water at room temperature and stir to dissolve to form a solution; then add surfactant, water-based dispersant and ceramic powder to the above solution in sequence, and stir Uniform, made into water-based slurry; the slurry contains 0.1%-2% thickener, 0.01%-2% water-based dispersant, 0.01%-1% surfactant, 0.1%-5% water-based glue Adhesive, 5% to 25% of ceramic powder particles, 67% to 83% of deionized water, all of which are mass fractions.

As a preferred manner, the thickness of the polypropylene porous film ranges from 8 μm to 100 μm, the porosity ranges from 30% to 80%, and the average pore diameter ranges from 0.01 μm to 10 μm.

As a preferred method, the polymer powder particles are one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylonitrile, and aramid resin or multiple types; the particle size of the polymer powder particles ranges from 0.01 μm to 10 μm.

As a preferred mode, the ceramic powder particles are any one or more of SiO ₂ , Al ₂ O ₃ , CaO, TiO ₂ , MgO, ZnO, SnO ₂ , and ZrO ₂ ; the particle size ranges from 0.01 μm to 10 μm.

The invention also discloses a ceramic and gel polymer multilayer composite lithium battery diaphragm prepared by the above method, which comprises a polypropylene support layer, a polyethylene partition layer, a ceramic coating layer and a polymer coating layer stacked in sequence.

As a preferred manner, the polypropylene supporting layer has a thickness ranging from 8 μm to 100 μm, a porosity ranging from 30% to 80%, and an average pore diameter ranging from 0.01 μm to 10 μm.

As a preferred manner, the polyethylene blocking layer has a thickness of 7 μm-30 μm and a porosity of 30%-60%; when the temperature is higher than 125° C., the pores of the PE layer are closed.

As a preferred manner, the total thickness of the ceramic coating layer and the polymer coating layer is 1 μm-10 μm.

The present invention has the following advantages:

1) The inorganic particle coating improves the thermal safety of the diaphragm, and the composite diaphragm is placed at a high temperature of 135° C. for 1 hour, and the heat shrinkage rate is less than 3%.

2) The inorganic particle coating improves the wettability of the electrolyte to the separator, which is convenient for the absorption of the electrolyte; the organic particle is PVDF-HFP powder, which can swell in the electrolyte, has a good ability to absorb and maintain the electrolyte, and has a high conductivity, so that the lithium battery has a good cycle life. At the same time, the positive and negative electrodes of the battery are well bonded and bonded, and the hardness and shape retention ability of the battery core are improved.

3) The PE layer in the composite separator has a lower melting temperature, so that the composite separator has a lower closed cell temperature, which can effectively prevent the thermal runaway of the lithium battery under abnormal conditions and provide high lithium battery safety.

4) The solvent used for coating the slurry is water, which does not contain organic solvents such as acetone, DMF, NMP, etc., which will not pollute the environment and will not endanger the health of workers. As an industrially produced product, using water as a solvent greatly reduces production costs and makes the product more competitive.

Description of drawings

Fig. 1 is the appearance topography figure of the polymer coating of embodiment 1 of the present invention;

2 is a cross-sectional view of a battery separator according to an embodiment of the present invention;

Fig. 3 is a graph showing the closed-cell rupture temperature curves of the embodiment of the present invention and the comparative example.

Detailed ways

The present invention will be described in further detail below.

A ceramic and gel polymer multilayer composite lithium battery separator, referring to FIG. 2 , includes a polypropylene support layer 1 , a polyethylene partition layer 2 , a ceramic coating layer 3 and a polymer coating layer 4 stacked in sequence. Its preparation method comprises the following steps:

Step 1: Configure water-based PVDF slurry and water-based ceramic slurry;

Step 2: Polypropylene diaphragm and polyethylene diaphragm are compounded, and a layer of polypropylene diaphragm and a layer of polyethylene diaphragm are thermally compounded at 50-100 ° C to obtain a PP/PE composite diaphragm;

Step 3: Coating, use the PP/PE composite diaphragm obtained in step 2 as the coating substrate, apply the water-based slurry prepared in step 1 on the PE surface of the substrate, and first coat the water-based ceramic slurry to form a ceramic layer Afterwards, the water-based PVDF slurry is coated to form a gel polymer layer at a coating rate of 5-100 m/min, and dried in an oven at 30-100° C. to obtain the final four-layer composite diaphragm. Among them, the coating on the PE surface is because the PE layer is easy to deform at high temperature, and it mainly plays a role of thermal shutdown in the composite diaphragm. This helps to improve the phenomenon of powder falling off the coating separator when making batteries. (1) Stir the polyolefin resin, lubricant and other additives evenly through a mixing mixer to obtain a mixture;

The preparation method of the ceramic and gel polymer multilayer composite lithium battery diaphragm of the present invention, on the basis of the previous technical scheme, the preparation method of the water-based PVDF slurry in step 1 is:

Using deionized water as a solvent, add water-soluble adhesives, surfactants, dispersants, and thickeners to deionized water at room temperature and stir to dissolve to make a solution; then add polymer powder particles, stir evenly, and make a water-based solution. Slurry; the slurry contains 0.1%-2% water-soluble polymer thickener, 0.01%-2% water-based dispersant, 0.01%-1% surfactant, 0.1%-5% water-based adhesive agent, 5% to 25% of polymer powder particles, 67% to 83% of deionized water, all of which are mass fractions; the weight average molecular weight of the polymer powder particles is 120,000-160,000, and the particle diameter is 100-300nm.

The preparation method of the ceramic and gel polymer multilayer composite lithium battery diaphragm of the present invention, on the basis of the previous technical scheme, the preparation method of the water-based ceramic slurry in step 1 is:

Using deionized water as a solvent, add water-soluble adhesive and thickener to deionized water at room temperature and stir to dissolve to form a solution; then add surfactant, water-based dispersant and ceramic powder to the above solution in sequence, and stir Uniform, made into water-based slurry; the slurry contains 0.1%-2% thickener, 0.01%-2% water-based dispersant, 0.01%-1% surfactant, 0.1%-5% water-based glue Adhesive, 5% to 25% of ceramic powder particles, 67% to 83% of deionized water, all of which are mass fractions.

The preparation method of the ceramic and gel polymer multilayer composite lithium battery separator of the present invention, on the basis of the previous technical scheme, the thickness of the polypropylene porous film ranges from 8 μm to 100 μm, and the porosity ranges from 30% to 80%. The average pore size is 0.01μm-10μm.

The preparation method of the ceramic and gel polymer multilayer composite lithium battery diaphragm of the present invention, on the basis of the previous technical scheme, the polymer powder particles are polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoro One or more of propylene copolymer, polyimide, polyacrylonitrile, and aramid resin, preferably polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene copolymer; the particles of the polymer powder particles The diameter range is 0.01 μm-10 μm, preferably 0.1 μm-2 μm.

The preparation method of the ceramic and gel polymer multilayer composite lithium battery diaphragm of the present invention, on the basis of the previous technical scheme, the ceramic powder particles are SiO ₂ , Al ₂ O ₃ , CaO, TiO ₂ , MgO, ZnO, SnO _2. Any one or more of ZrO ₂ , preferably SiO ₂ and Al ₂ O ₃ ; the particle size ranges from 0.01 μm to 10 μm, preferably from 0.1 μm to 3 μm.

The preparation method of the ceramic and gel polymer multilayer composite lithium battery diaphragm of the present invention, on the basis of the previous technical scheme, the thickness range of the propylene porous film is 8 μm-100 μm, the porosity range is 30%-80%, and the average The pore size is 0.01μm-10μm. This layer is the support layer in the composite diaphragm, and its heat resistance is better than that of the PE layer.

The preparation method of the ceramic and gel polymer multilayer composite lithium battery diaphragm of the present invention is based on the previous technical scheme, the thickness of the polyethylene microporous membrane is 7 μm to 30 μm, and the porosity is 30% to 60%. When the temperature is high (greater than 125°C), the pores of the PE layer are slowly closed. This layer mainly plays a role of thermal shutdown in the composite film, preventing thermal runaway and improving the safety of lithium batteries.

The preparation method of the ceramic and gel polymer multilayer composite lithium battery diaphragm of the present invention, on the basis of the previous technical scheme, the thickness of the ceramic coating layer and the polymer coating layer is 1 μm-10 μm, preferably 1 μm-4 μm .

In the following examples and comparative examples, the above solutions will be further described. In the following examples and comparative examples, the polypropylene separator is a dry-process uniaxially stretched film from S Company, with a thickness of 16μ and a porosity of 42%. The polyethylene diaphragm adopts the wet-process diaphragm of S Company, with a thickness of 12μ and a porosity of 44%. The two separators were thermally composited at 80°C to obtain a PE/PP composite separator, which was used as a base material for preparing a coating film. Micro-gravure coating is used in Examples and Comparative Examples, but not limited to this coating method, slot extrusion coating, dip coating, spray coating and other methods are all possible.

Example 1

Waterborne PVDF slurry preparation

The weight ratio of PVDF-HFP in the slurry: deionized water=100:500. First, add acrylic adhesive and tackifier CMC into deionized water, and stir at 300r/min for 20min at room temperature until completely dissolved, wherein the weight ratio of acrylic adhesive and CMC is adhesive: PVDF- HFP=5:100, CMC:PVDF-HFP=1:100. Then add fluorocarbon surfactant, dispersant polyvinylpyrrolidone (PVP) and PVDF-HFP powder to the above solution in sequence, continue to stir at 300r/min for 10min, and finally stir at 5000r/min for 5min, the slurry configuration is completed. Wherein fluorocarbon surfactant:PVDF-HFP=0.1:100, PVP:PVDF-HFP=0.3:100. The weight average molecular weight of PVDF-HFP is about 140,000, and the particle size is 100-300nm.

2) Ceramic slurry preparation

The weight proportion in the slurry is Al2O3: deionized water=100:150.

First, add PVA adhesive and tackifier CMC into deionized water, stir at 300r/min for 20min at room temperature until completely dissolved, wherein the weight ratio of PVA adhesive and CMC is adhesive: PVDF- HFP=4:100, CMC:PVDF-HFP=1:100. Then add sodium polyacrylate dispersant, continue to stir at 300r/min for 10min, finally add Al2O3 powder, stir at 7000r/min for 5min, and the slurry configuration is completed. Wherein sodium polyacrylate: Al2O3=0.5:100, Al2O3 powder D50=1.0 μm.

3) Implement coating

First, water-based ceramic slurry coating is carried out, and the coating rate is 20m/min with a micro-gravure roller; three-stage ovens are used for drying, and the temperatures of the ovens at each level are 50-57 ° C, 55-63 ° C, 63-63 ° C, respectively. 70℃, wait until PP/PE/ceramic layer three-layer composite separator, in which the thickness of the ceramic coating is 4μ. Then, using the above-mentioned three-layer composite diaphragm as the base material, coat a layer of water-based PVDF coating on the ceramic layer, the coating thickness is 2μ, the coating speed is 20m/min, the baking process is the same as above, and finally PP/PE/ Ceramic layer/PVDF layer four-layer composite diaphragm. Fig. 1 is the surface morphology diagram of the polymer coating of the present embodiment.

Example 2

1) Preparation of water-based PVDF slurry

The polymer coating layer is coated by water-based slurry, and the weight ratio of PVDF-HFP: deionized water in the water-based slurry is 100:500. First, add the adhesive PVA and tackifier CMC into deionized water, and stir at 300r/min for 20min at room temperature until completely dissolved, wherein the weight ratio of PVA and CMC is PVA:PVDF-HFP=5:100, CMC :PVDF-HFP=1:100. Then add fluorocarbon surfactant, dispersant polyoxyethylene dioleate and PVDF-HFP powder to the above solution in sequence, continue to stir at 300r/min for 10min, and finally stir at 5000r/min for 5min at high speed, the slurry configuration is completed . Among them, fluorocarbon surfactant: PVDF-HFP=0.1:100, polyoxyethylene dioleate: PVDF-HFP=0.3:100. The weight average molecular weight of PVDF-HFP is about 140,000, and the particle size is 100-300nm.

Others are the same as embodiment 1.

Comparative example 1

The base film is a 16 μ dry-process polypropylene microporous film from S Company, with a porosity of 42%. Other coating process conditions are the same as in Example 1, and a three-layer composite diaphragm of PP/ceramic layer/PVDF layer is finally obtained.

Comparative example 2

The base film is selected from S company 16μ dry-process polypropylene microporous membrane, and the porosity is 42%. Double layer composite diaphragm.

Comparative example 3

The base film is selected from S company 16μ dry-process polypropylene microporous membrane, the porosity is 42%, the slurry is selected from the water-based PVDF slurry in Example 1, and the water-based PVDF coating process in Example 1 is adopted to prepare a single-sided PVDF coating. Two-layer composite diaphragm.

Table 1

Diaphragm thermal shrinkage test method: Cut 3 samples of 100mm×100mm for each diaphragm, measure the length in MD direction and record it as L0, put the sample in a blast oven at a specified temperature, take it out after the specified time, measure the length in MD direction and record it as L , the calculation formula of thermal shrinkage rate is as follows:

ΔL=(L-L0)/L0×100%

Measure the heat shrinkage rate of three samples, and then take the average value to be the heat shrinkage rate of this kind of separator.

Where MD is the stretching direction of the dry-process uniaxially stretched membrane.

The test method of the liquid absorption rate: cut off the size of the diaphragm to be 100mm×100mm, soak it in the electrolyte for 1 hour; take out and dry the surface electrolyte, weigh the amount of the absorbed electrolyte; then calculate the weight of the electrolyte absorbed by the diaphragm per square meter, that is is the liquid absorption rate, and the unit is g/m ² .

Diaphragms prepared according to Examples and Comparative Examples, Table 1 shows the relevant test results of the diaphragms. As can be seen from Table 1, Examples 1 and 2 of the present invention have good heat resistance, high liquid absorption rate and excellent adhesion to the pole piece after being made into a battery, and a combination of ceramic coated diaphragm and polymer The advantages of both coated separators can be very effective in improving the safety of batteries.

Table 2 shows the closed cell membrane rupture temperature of some samples.

Diaphragm obturator rupture temperature test method: use a self-made mold to prepare a simple lithium battery, the two poles are connected to an internal resistance meter, and there is a temperature measuring probe inside. Put this simple battery into a 250°C incubator, and record the relationship between the internal resistance of the battery and the internal temperature. The first temperature inflection point is the closure temperature of the diaphragm, and the second temperature inflection point is the membrane rupture temperature of the diaphragm, see Figure 3 for details.

Combining Table 2 and Figure 3, it can be seen that the sample of Example 1 with a PE layer has a lower closed cell temperature than the comparative example, which can effectively prevent the thermal runaway of the lithium battery under abnormal conditions, and provide a high-quality lithium battery. security.

The above is a description of the ceramic and gel polymer multilayer composite lithium battery separator and its preparation method of the present invention, which is used to help understand the present invention, but the implementation of the present invention is not limited by the above examples, and any Changes, modifications, substitutions, combinations, and simplifications made under the principles of the present invention should all be equivalent replacements, and are all included within the protection scope of the present invention.

Claims (10)

1. a preparation method for the lithium battery diaphragm of pottery and gelatin polymer MULTILAYER COMPOSITE, is characterized in that comprising the steps:

Step 1: configuration water-based PVDF slurry and water-based ceramic size;

Step 2: polypropylene diaphragm and polyethylene barrier film are compound, by compound to one deck polypropylene diaphragm and layer of polyethylene barrier film heat at 50～100 DEG C, obtains PP/PE composite diaphragm;

Step 3: coating, in step 2, obtain PP/PE composite diaphragm as coated substrate, be coated on the PE face of base material preparing water paste in step 1, first be coated with after fabric aqueous ceramic size forms ceramic layer and be coated with again fabric aqueous PVDF slurry formation gel polymer layer, application rate is 5～100m/min, through 30～100 DEG C of oven for drying, obtain final four layers of composite diaphragm.

2. the preparation method of the lithium battery diaphragm of pottery according to claim 1 and gelatin polymer MULTILAYER COMPOSITE, is characterized in that: in described step 1, water-based PVDF slurry preparation method is:

Using deionized water as solvent, add deionized water for stirring to dissolve at normal temperature water-soluble gluing agent, surfactant, dispersant, thickener, wiring solution-forming; Add again polymer powder particle, stir, be made into water paste; In slurry, contain 0.1%～2% water soluble polymer thickener, 0.01%～2% aqueous dispersion, 0.01%～1% surfactant, 0.1%～5% Aqueous Adhesives, 5%～25% polymer powder particle, 67%～83% deionized water, above-mentioned is all mass fraction; The weight average molecular weight of polymer powder particle is 12-16 ten thousand, and particle diameter is 100-300nm.

3. the preparation method of the lithium battery diaphragm of pottery according to claim 1 and gelatin polymer MULTILAYER COMPOSITE, is characterized in that: in described step 1, water-based ceramic size compound method is:

Using deionized water as solvent, add at normal temperatures deionized water for stirring to dissolve water-soluble gluing agent, thickener, wiring solution-forming; Then in above-mentioned solution, add successively surfactant, aqueous dispersion and ceramic powders, stir, be made into water paste; In slurry, contain 0.1%～2% thickener, 0.01%～2% aqueous dispersion, 0.01%～1% surfactant, 0.1%～5% Aqueous Adhesives, 5%～25% ceramic powders particle, 67%～83% deionized water, above-mentioned is all mass fraction.

4. the preparation method of the lithium battery diaphragm of pottery according to claim 1 and gelatin polymer MULTILAYER COMPOSITE, it is characterized in that: the thickness range of described polypropylene porous membrane is at 8 μ m-100 μ m, porosity ranges is 30%-80%, and average pore size is at 0.01 μ m-10 μ m.

5. the preparation method of the lithium battery diaphragm of pottery according to claim 2 and gelatin polymer MULTILAYER COMPOSITE, is characterized in that: described polymer powder particle is that polytetrafluoroethylene, Kynoar, Kynoar-hexafluoropropylene copolymer, polyimides, polypropylene are fine, one or more in aramid fiber resin; The particle size range of poly-described polymer powder particle is 0.01 μ m-10 μ m.

6. the preparation method of the lithium battery diaphragm of pottery according to claim 3 and gelatin polymer MULTILAYER COMPOSITE, is characterized in that: described ceramic powders particle is SiO ₂, Al ₂o ₃, CaO, TiO ₂, MgO, ZnO, SnO ₂, ZrO ₂in any one or multiple; Particle size range is 0.01 μ m～10 μ m.

7. a lithium battery diaphragm for pottery and gelatin polymer MULTILAYER COMPOSITE, is characterized in that: comprise the polypropylene supporting layer, polyethylene insulating course, ceramic coating layer and the polymer-coated layer that stack gradually.

8. the lithium battery diaphragm of pottery according to claim 7 and gelatin polymer MULTILAYER COMPOSITE, is characterized in that: the thickness range of described polypropylene supporting layer is at 8 μ m-100 μ m, and porosity ranges is 30%-80%, and average pore size is at 0.01 μ m-10 μ m.

9. the lithium battery diaphragm of pottery according to claim 7 and gelatin polymer MULTILAYER COMPOSITE, is characterized in that: the thickness of described polyethylene insulating course is 7 μ m～30 μ m, and porosity is 30%～60%; In the time that temperature is greater than 125 DEG C, the bore closure of PE layer.

10. the lithium battery diaphragm of pottery according to claim 7 and gelatin polymer MULTILAYER COMPOSITE, is characterized in that: the thickness of described ceramic coating layer and polymer-coated layer is 1 μ m-10 μ m altogether.