CN113659285A - Polypropylene diaphragm for lithium ion battery and preparation method thereof - Google Patents
Polypropylene diaphragm for lithium ion battery and preparation method thereof Download PDFInfo
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- CN113659285A CN113659285A CN201810785717.XA CN201810785717A CN113659285A CN 113659285 A CN113659285 A CN 113659285A CN 201810785717 A CN201810785717 A CN 201810785717A CN 113659285 A CN113659285 A CN 113659285A
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- polypropylene
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
The invention relates to a polypropylene diaphragm for a lithium ion battery and a preparation method thereof. The polypropylene diaphragm for the lithium ion battery comprises polypropylene and nano inorganic oxide, wherein the nano inorganic oxide accounts for 0.5-2% of the total mass of the polypropylene and the nano inorganic oxide, and the particle size of the nano inorganic oxide is 1-10 nm. The polypropylene diaphragm for the lithium ion battery provided by the invention is mainly used for modifying polypropylene by controlling the particle size and the addition amount of the nano inorganic oxide, can be mixed into a molecular chain of the polypropylene in a dry film-making process, promotes the disentanglement and opening of the molecular chain, plays a role in toughening a resin matrix, and promotes uniform hole opening in a stretching film-making process. The performance detection result of the diaphragm shows that the polypropylene diaphragm can realize the consideration of high strength and high porosity under the level of 6-20 mu m, the air permeability is improved to a certain degree, and the comprehensive performance of the diaphragm is comprehensively improved.
Description
Technical Field
The invention belongs to the field of lithium ion battery diaphragms, and particularly relates to a polypropylene diaphragm for a lithium ion battery and a preparation method thereof.
Background
In a lithium battery structure system, a diaphragm is one of key inner layer components, the performance of the diaphragm determines parameters such as an interface structure, internal resistance and the like of a battery, so that the capacity, the circulation and the safety performance of the battery are influenced, and an excellent diaphragm product plays an important role in improving the comprehensive performance of the lithium ion battery. At present, each battery manufacturer strives to improve the energy density and the discharge power of the battery so as to meet the higher requirements of industries such as electric automobiles and the like on the battery.
The high-nickel battery is one of battery varieties with higher energy density, and is prepared by taking a high-nickel ternary material (NCM/NCA, the mole fraction of Ni is more than or equal to 0.6) as a positive electrode and matching with a silicon-carbon negative electrode material. In 811 high nickel battery, the conventional dry method PP separator often cannot meet the requirements of battery energy density and discharge power due to its low strength and low porosity.
The patent with publication number CN102376928B discloses a lithium ion battery diaphragm and a preparation method thereof, which is prepared by using polyolefin resin, an additive, an antioxidant and a flame retardant as raw materials and adopting a stretching-retracting-heat setting method. The diaphragm has higher strength and thermal stability under a certain thickness, and can meet the application requirements of common lithium ion batteries. On the basis of further reducing the thickness, the strength of the diaphragm is ensured, the porosity of the diaphragm is improved, and the method has important significance for improving the discharge power of high-energy-density batteries such as high-nickel batteries and the like.
Disclosure of Invention
The invention aims to provide a polypropylene diaphragm for a lithium ion battery, so as to solve the problems that the existing dry-method PP diaphragm has low strength and porosity at a lower thickness and cannot meet the use requirement of a high-energy-density battery. The invention also provides a preparation method of the polypropylene diaphragm.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
the polypropylene diaphragm for the lithium ion battery comprises polypropylene and a nano inorganic oxide, wherein the nano inorganic oxide accounts for 0.5-2% of the total mass of the polypropylene and the nano inorganic oxide, and the particle size of the nano inorganic oxide is 1-10 nm.
The polypropylene diaphragm for the lithium ion battery provided by the invention is mainly used for modifying polypropylene by controlling the particle size and the addition amount of the nano inorganic oxide, can be mixed into a molecular chain of the polypropylene in a dry film-making process, promotes the disentanglement and opening of the molecular chain, plays a role in toughening a resin matrix, and promotes uniform hole opening in a stretching film-making process. The performance detection result of the diaphragm shows that the polypropylene diaphragm can realize the consideration of high strength and high porosity under the level of 6-20 mu m, the air permeability is improved to a certain degree, and the comprehensive performance of the diaphragm is comprehensively improved.
In view of overall cost, strength of the separator, heat resistance, and the like, the nano inorganic oxide is preferably at least one of alumina, zirconia, and silica. In order to further optimize the effect of the nano inorganic oxide on the improvement of various performances of the separator, the particle size of the nano inorganic oxide is preferably 2-5 nm.
The polypropylene is a conventional raw material of the dry PP diaphragm, and preferably has a weight average molecular weight of 30-50 ten thousand from the viewpoint of optimizing the stability of the PP diaphragm.
Besides the main raw materials composed of polyolefin and nano inorganic oxide, the polypropylene separator product generally contains processing aids or additives to further optimize the processability or other properties of the separator. Preferably, the polypropylene separator further comprises an antioxidant. The mass percentage of the antioxidant in the polypropylene diaphragm is 0.001-1%. The antioxidant is dibutyl hydroxy toluene and/or butyl hydroxy anisol.
Preferably, the polypropylene separator further contains a flame retardant. The mass percentage of the flame retardant in the polypropylene diaphragm is 0.001-1%. The flame retardant is at least one of ammonium polyphosphate, octabromoether, triphenyl phosphate, hexabromocyclododecane and decabromodiphenylethane.
The preparation method of the polypropylene diaphragm for the lithium ion battery comprises the following steps: melting and mixing polypropylene, nano inorganic oxide and an auxiliary agent, extruding, casting, stretching and heat setting to obtain the polypropylene nano composite material.
The preparation method of the polypropylene diaphragm for the lithium ion battery provided by the invention has the advantages of simple process, low requirement on equipment, no pollution and suitability for industrial production.
In order to improve the dispersion uniformity of the nano inorganic oxide in the polymer matrix, preferably, the melt-mixing comprises the following steps: mixing the nano inorganic oxide, part of polypropylene and an auxiliary agent, mixing, extruding and granulating to obtain premixed granules; mixing the premixed granules with the balance of polypropylene, and carrying out extrusion granulation after mixing to obtain mixed granules; and mixing the mixed granules.
In order to better control the mixing effect of the nano inorganic oxide and ensure the consistency of the diaphragm product, the mass ratio of the nano inorganic oxide to the polypropylene in the pre-mixing granules is preferably (1-10) to (10-100). In the mixed pellet, the mass ratio of the premixed pellet to the polypropylene is 1 (1-20). The mixed granules with good mixing effect can be obtained by controlling the proportion of the nano inorganic oxide, the polypropylene and the premixed granules.
The mixed granules are mixed and extruded, and then the finished diaphragm product can be prepared by the technological processes of sheet casting, stretching, retraction, heat setting and the like. The above process can be adjusted by referring to the prior art, and preferably the treatment is carried out according to the process related to the patent with the publication number of CN102376928B, and the membrane is obtained after the base membrane is sequentially subjected to biaxial stretching, retraction, heat setting and corona treatment.
The preparation method of the polypropylene diaphragm for the lithium ion battery improves the dispersion effect of the nano inorganic oxide in the polymer base material, is beneficial to obtaining a diaphragm product with thin diaphragm thickness, high porosity and high strength, improves the quality stability of the dry PP diaphragm, and can effectively improve the discharge power of the battery when the obtained diaphragm is applied to the lithium ion battery.
Detailed Description
The following examples are provided to further illustrate the practice of the invention. In the following examples, the weight average molecular weight of the polypropylene resin is 30 to 50 ten thousand.
Example 1
The polypropylene diaphragm for the lithium ion battery in the embodiment is composed of polypropylene resin, nano-alumina, an antioxidant and a flame retardant, wherein the nano-alumina accounts for 1.515% of the total mass of the polypropylene resin and the nano-alumina, and the particle size of the nano-alumina is 2 nm. The antioxidant is butyl hydroxy anisole, and the mass content of the antioxidant in the polypropylene diaphragm is 0.01 percent; the flame retardant is ammonium polyphosphate, and the mass content of the flame retardant in the polypropylene diaphragm is 0.01 percent.
The preparation method of the polypropylene diaphragm for the lithium ion battery adopts the following steps:
1) uniformly mixing nano aluminum oxide, polypropylene resin, an antioxidant and a flame retardant, mixing by a double-screw extruder, and then extruding and granulating to obtain granules A; the mass ratio of the nano-alumina to the polypropylene resin in the granules A is 1: 5;
uniformly mixing the granules A and polypropylene resin, mixing by using a double-screw extruder, and then extruding and granulating to obtain granules B; the mass ratio of the pellets A to the polypropylene resin in the pellets B was 1: 10.
2) Filling the granules B into a single-screw extruder through a vacuum feeding machine, mixing the granules into a melt through the single-screw extruder, conveying the melt to a die head, extruding to obtain a base film, and performing longitudinal and transverse biaxial stretching on the base film at the stretching temperature of 110 ℃ and the stretching ratio of 1: 8; after the biaxial stretching, the film naturally retracts at 120 ℃, and the retraction time is 0.1 minute; after retraction treatment, heat setting is carried out for 0.1min at 115 ℃, and then corona treatment is carried out, wherein the voltage of the corona treatment is 10000V/m2The treatment time isAnd 0.1s, and then rolling to obtain the lithium ion battery diaphragm.
Example 2
The polypropylene diaphragm for the lithium ion battery in the embodiment is composed of polypropylene resin, nano inorganic oxide, an antioxidant and a flame retardant, wherein the nano inorganic oxide accounts for 0.826% of the total mass of the polypropylene resin and the nano inorganic oxide, the nano inorganic oxide is composed of nano aluminum oxide and nano silicon dioxide, the mass ratio of the nano aluminum oxide to the nano silicon dioxide is 1:1, and the particle size is 5 nm. The kinds of the antioxidant and the flame retardant and the content in the polypropylene separator were the same as in example 1.
The preparation method of the polypropylene diaphragm for the lithium ion battery adopts the following steps:
1) uniformly mixing the nano inorganic oxide, the polypropylene resin, the antioxidant and the flame retardant, and carrying out mixing by a double-screw extruder and then carrying out extrusion granulation to obtain granules A; the mass ratio of the nano inorganic oxide to the polypropylene resin in the granules A is 1: 10;
uniformly mixing the granules A and polypropylene resin, mixing by using a double-screw extruder, and then extruding and granulating to obtain granules B; the mass ratio of the pellets A to the polypropylene resin in the pellets B was 1: 10.
2) Filling the granules B into a single-screw extruder through a vacuum feeding machine, mixing the granules into a melt through the single-screw extruder, conveying the melt to a die head, extruding to obtain a base film, and performing longitudinal and transverse biaxial stretching on the base film at the stretching temperature of 130 ℃ in a stretching ratio of 1: 8; after the biaxial stretching, the film is naturally retracted at 110 ℃, and the retraction time is 5 minutes; after retraction treatment, heat setting is carried out for 5min at 120 ℃, and then corona treatment is carried out, wherein the voltage of the corona treatment is 10000V/m2And the treatment time is 1s, and then the lithium ion battery diaphragm is obtained by rolling.
Example 3
The composition and preparation method of the polypropylene diaphragm for the lithium ion battery are basically the same as those of the polypropylene diaphragm in the embodiment 1, and the difference is only that the nano alumina accounts for 1.8 percent of the total mass of the polypropylene resin and the nano alumina, and the particle size of the nano alumina is 3-4 nm; the antioxidant is dibutyl hydroxy toluene, and the flame retardant is octabromoether.
Comparative example 1
The polypropylene separator for lithium ion battery of this comparative example was prepared by the method of example 5 in patent publication No. CN102376928B, having a thickness of 16 μm, a pore diameter of 77nm, and a porosity of 47%.
Comparative example 2
The polypropylene separator for a lithium ion battery of the present comparative example had substantially the same composition and preparation method as those of example 1, and had a thickness of 16 μm, except that the nano-alumina had a particle size of 50 nm.
Test examples
In the test example, the polypropylene separators of example 1, example 2, comparative example 1 and comparative example 2 were used as examples, the preparation process conditions were controlled so that the thickness of the separator product of example was 16 μm and the average separator pore diameter was 75 to 80nm, and the properties of the final separator were measured as shown in table 1.
Table 1 test results of performance of polypropylene separators of examples and comparative examples
| Item | Example 1 | Example 2 | Comparative example 1 | Comparative example 2 |
| Thickness of | 16.1μm | 16.0μm | 16.2μm | 15.9μm |
| Porosity of the material | 74％ | 65％ | 47％ | 44％ |
| Pore diameter | 81nm | 72nm | 77nm | 74nm |
| Transverse tensile strength | 81MPa | 65MPa | 47MPa | 51MPa |
| Longitudinal tensile strength | 237MPa | 197MPa | 154MPa | 163MPa |
| Elongation at break in transverse direction | 70％ | 93％ | 132％ | 128％ |
| Elongation at break in the longitudinal direction | 42％ | 46％ | 57％ | 55％ |
| Puncture strength | 7N | 5N | 4N | 3.9N |
| Air permeability, s/100ml | 120 | 150 | 213 | 221 |
| Thermal shrinkage, longitudinal direction (90 ℃, 1h) | 2.1％ | 1.9％ | 1.5％ | 1.3％ |
| Heat shrinkage, transverse direction (90 ℃, 1h) | 0.9％ | 1.1％ | 0.7％ | 0.5％ |
From the test results of table 1, the polypropylene separators prepared in the examples have higher porosity and strength than the comparative examples at the same pore diameter, and at the same time, the air permeability is improved to a certain extent without much influence on the heat resistance. When the diaphragm is applied to a high-nickel battery, the internal resistance of the interface can be effectively reduced on the premise of ensuring the safety, and the energy density and the discharge power of the battery can be improved.
In other examples of the polypropylene separator for lithium ion batteries according to the present invention, nano-alumina was substituted with nano-zirconia of 1 to 6nm in an equivalent amount, which resulted in the test effect equivalent to that of example 1. When the nano oxide and the polypropylene resin are mixed, the specific ratio can be adjusted within the range defined by the invention. The auxiliary agents such as the antioxidant, the flame retardant and the like can be selected from conventional varieties in the field, the polypropylene diaphragm with the diaphragm porosity of 50-80%, the pore diameter of 30-90nm and the thickness of 6-20 mu m can be prepared according to the content of the nano inorganic oxide, the stretching process and other conditions, the obtained polypropylene diaphragm can improve the discharge power of a corresponding battery, and the polypropylene diaphragm is very suitable for being used in high nickel batteries or other lithium ion batteries.
Claims (8)
1. The polypropylene diaphragm for the lithium ion battery is characterized by comprising polypropylene and a nano inorganic oxide, wherein the nano inorganic oxide accounts for 0.5-2% of the total mass of the polypropylene and the nano inorganic oxide, and the particle size of the nano inorganic oxide is 1-10 nm.
2. The polypropylene separator for lithium ion batteries according to claim 1, wherein the nano inorganic oxide is at least one of alumina, zirconia, and silica.
3. The polypropylene separator for lithium ion batteries according to claim 1 or 2, wherein the nano inorganic oxide has a particle size of 2 to 5 nm.
4. The preparation method of the polypropylene separator for the lithium ion battery according to claim 1, comprising the following steps: melting and mixing polypropylene, nano inorganic oxide and an auxiliary agent, extruding, casting, stretching and heat setting to obtain the polypropylene nano composite material.
5. The method for preparing the polypropylene separator for lithium ion batteries according to claim 4, wherein the melt-kneading comprises the steps of: mixing the nano inorganic oxide, part of polypropylene and an auxiliary agent, mixing, extruding and granulating to obtain premixed granules; mixing the premixed granules with the balance of polypropylene, and carrying out extrusion granulation after mixing to obtain mixed granules; and mixing the mixed granules.
6. The method for preparing a polypropylene separator for a lithium ion battery according to claim 5, wherein the mass ratio of the nano inorganic oxide to the polypropylene in the pre-mixed pellets is (1-10) to (10-100).
7. The method for preparing a polypropylene separator for a lithium ion battery according to claim 6, wherein the mass ratio of the premixed pellet to the polypropylene in the mixed pellet is 1 (1-20).
8. The method for preparing a polypropylene separator for a lithium ion battery according to claim 4, wherein the weight average molecular weight of the polypropylene is 30 to 50 ten thousand.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
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| CN201810785717.XA CN113659285A (en) | 2018-07-17 | 2018-07-17 | Polypropylene diaphragm for lithium ion battery and preparation method thereof |
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| Application Number | Priority Date | Filing Date | Title |
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| CN201810785717.XA CN113659285A (en) | 2018-07-17 | 2018-07-17 | Polypropylene diaphragm for lithium ion battery and preparation method thereof |
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| CN113659285A true CN113659285A (en) | 2021-11-16 |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115425361A (en) * | 2022-08-15 | 2022-12-02 | 奎达高分子材料科技(宜兴)有限公司 | Low-adhesion PP isolation film and preparation method thereof |
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| CN102738427A (en) * | 2012-07-19 | 2012-10-17 | 河南义腾新能源科技有限公司 | Inorganic composite microporous membrane serving as lithium ion battery diaphragm and preparation method thereof |
| JP2018076474A (en) * | 2016-11-10 | 2018-05-17 | 有限会社ケー・イー・イー | High temperature low heat shrinkable polyolefin monolayer microporous film and method for producing the same |
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| CN1860627A (en) * | 2003-08-06 | 2006-11-08 | 三菱化学株式会社 | Nonaqueous electrolyte solution secondary battery separator and nonaqueous electrolyte solution secondary battery using the same |
| CN101051681A (en) * | 2006-04-06 | 2007-10-10 | 傅理平 | Polymer lithium cell diaphragm and processing method |
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| CN102738427A (en) * | 2012-07-19 | 2012-10-17 | 河南义腾新能源科技有限公司 | Inorganic composite microporous membrane serving as lithium ion battery diaphragm and preparation method thereof |
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| CN115425361A (en) * | 2022-08-15 | 2022-12-02 | 奎达高分子材料科技(宜兴)有限公司 | Low-adhesion PP isolation film and preparation method thereof |
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Application publication date: 20211116 |