CN114400416B - Lithium battery diaphragm with thermal shutdown property and preparation method - Google Patents

Lithium battery diaphragm with thermal shutdown property and preparation method Download PDF

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CN114400416B
CN114400416B CN202111517526.3A CN202111517526A CN114400416B CN 114400416 B CN114400416 B CN 114400416B CN 202111517526 A CN202111517526 A CN 202111517526A CN 114400416 B CN114400416 B CN 114400416B
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diaphragm
layer
thermal shutdown
lithium battery
temperature
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CN114400416A (en
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杨锋
李守占
刘泓麟
吴桐
曹亚
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Sichuan University
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Sichuan University
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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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
    • 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

Abstract

The invention discloses a lithium battery diaphragm with thermal shutdown property and a preparation method thereof, wherein the lithium battery diaphragm is a three-layer composite diaphragm, and specifically comprises two support layers and a middle thermal shutdown layer, the thickness of the diaphragm is 15-19 mu m, the porosity is 35-40%, the support layers comprise 99.7wt% of polypropylene and 0.3wt% of beta crystal nucleating agent, and the middle thermal shutdown layer comprises 70.0-90.0wt% of polypropylene, 10.0-30.0wt% of low-deformation-temperature amorphous material and 0.1-1.0wt% of nucleating agent. When the thermal runaway of the battery occurs, the diaphragm provided by the invention can close the microporous structure on the premise of keeping the dimensional stability, so that the internal reaction of the battery is prevented, the porosity and the thickness of the diaphragm are not influenced, the preparation method is simple, the process steps are simple and environment-friendly, the process requirement is low, the temperature condition in the preparation process is only 220 ℃ at most, no toxic reagent is doped, the raw material cost is low, and the diaphragm is suitable for industrial application.

Description

Lithium battery diaphragm with thermal shutdown property and preparation method
Technical Field
The invention relates to the technical field of lithium battery diaphragms, in particular to a lithium battery diaphragm with thermal shutdown and a preparation method thereof.
Background
Lithium ion batteries stand out in the field of energy storage with the advantages of high specific energy, long service life, low self-discharge rate, environmental protection and the like, and are widely applied to the fields of power automobiles, portable electronic equipment, consumer electronic products, energy storage equipment and the like.
The lithium battery mainly comprises a positive electrode, a negative electrode and a diaphragm soaked by electrolyte, wherein the diaphragm is one of key components in the lithium battery. One of the main functions of the diaphragm is to isolate the positive electrode and the negative electrode, prevent the short circuit of the battery and provide guarantee for the safety of the lithium battery. Currently, the separator materials used in the commercial lithium batteries are mainly polyolefin materials such as polyethylene, polypropylene and mixtures thereof. Wherein, the polyethylene product is mainly prepared by a wet process, and the polypropylene product is mainly prepared by a dry process. The polyolefin diaphragm has the advantages of excellent mechanical property, good chemical and electrochemical stability, easy processing and the like. However, the polyolefin material has a low melting point, and the internal temperature may exceed the melting point of the polyolefin material during the operation of the lithium battery, so that the diaphragm shrinks, the positive electrode and the negative electrode are in contact with each other, and further, danger is generated.
In the prior art, one or two ceramic layers are coated on a polyolefin-based film, and the characteristic of higher high temperature resistance of the ceramic layers is utilized, so that micropores of the polyolefin layer are closed under the condition of overheating of the composite diaphragm, and the ceramic layers enable the diaphragm to keep dimensional stability, thereby obtaining the lithium battery diaphragm with thermal shutdown performance. In addition, the electrospinning technology is also used for preparing a multilayer composite diaphragm, the composite diaphragm comprises a supporting layer and a thermal shutdown layer, and the thermal shutdown performance of the multilayer composite diaphragm is realized by utilizing the difference of the closed pore temperatures of different layers.
The separator having the thermal shutdown property obtained through coating modification has good safety performance, but the method increases the thickness and mass of the separator so as to reduce the mass specific energy and the mass specific capacity of the battery. Meanwhile, the coating modification is easy to generate the side effect of hole blocking, so that the porosity of the diaphragm is reduced, and the liquid storage and retention capacity of the diaphragm is reduced. Although the electrostatic spinning technology can prepare the diaphragm with the thermal shutdown performance, the diaphragm has overlarge pore diameter and more uneven pore diameter distribution, and meanwhile, the electrostatic spinning technology is complex to operate, cannot be produced in a large scale and is difficult to realize commercialization. Therefore, a process which does not affect the porosity and the thickness of the separator and has a simpler preparation method is needed.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a lithium battery diaphragm with thermal shutdown and a preparation method thereof, when thermal runaway of a battery occurs, the diaphragm can close a microporous structure on the premise of keeping dimensional stability, so that internal reaction of the battery is prevented, porosity and diaphragm thickness are not influenced, the preparation method is simple, the process steps are simple and environment-friendly, the lithium battery diaphragm is suitable for industrial application, and the problems in the background art are solved.
In order to achieve the purpose, the invention provides the following technical scheme: the lithium battery diaphragm is a three-layer composite diaphragm, and specifically comprises two support layers and a middle thermal shutdown layer, wherein the thickness of the diaphragm is 15-19 mu m, and the porosity is 35-40%.
Preferably, the support layer comprises 99.0-99.9wt% of polypropylene and 0.1-1.0wt% of beta crystal nucleating agent.
Preferably, the intermediate thermal shutdown layer comprises 70.0 to 90.0wt% polypropylene, 10.0 to 30.0wt% low deformation temperature amorphous material, 0.1 to 1.0wt% nucleating agent.
Preferably, the low deformation temperature amorphous material is hydrogenated petroleum resin.
In order to achieve the purpose, the invention also provides a technical scheme that: a preparation method of a lithium battery separator with thermal shutdown performance comprises the following steps:
s1, feeding a supporting layer and an intermediate heat-closing layer according to raw materials in percentage by mass respectively, uniformly melting and mixing in three extrusion devices respectively, then carrying out tape casting extrusion from a die through a distributor, and carrying out constant temperature crystallization to obtain a three-layer composite tape casting sheet with high beta crystal content;
and S2, carrying out biaxial tension on the three-layer composite casting sheet obtained in the step S1 to obtain the three-layer composite diaphragm.
Preferably, in step S1, the extrusion temperature is 190-220 ℃; crystallization at constant temperature is 120 ℃.
Preferably, in step S2, the stretching conditions of the biaxial stretching are: preheated at 90 ℃ for 2min, then stretched to 3X 1 in the MD direction, and subsequently stretched to 3X 3 in the TD direction at 120 ℃.
The beneficial effects of the invention are: the lithium ion battery diaphragm provided by the invention is a three-layer composite system, and a microporous structure is formed in biaxial tension by blending low-deformation-temperature substances (amorphous materials) such as hydrogenated petroleum resin and cyclic olefin copolymer with different softening points in a polypropylene matrix of a thermal shutdown layer and utilizing a beta crystal pore forming mechanism (namely, beta crystals are loosely arranged and are separated from each other under the action of external force to cause pore formation). The thermal shutdown layer of the diaphragm contains a low deformation temperature substance-hydrogenated petroleum resin, can be softened at about 125 ℃ to block the microporous structure of the diaphragm, and has little influence on the porosity and the thickness of the diaphragm. The preparation method provided by the invention has the advantages of simple process and low process requirement, the temperature condition in the preparation process is only 220 ℃ at most, no toxic reagent is doped in the preferred scheme, the raw material cost is low, and the preparation method is suitable for industrial application.
Drawings
FIG. 1 is a schematic flow chart of the preparation process of the present invention;
FIG. 2 is an SEM image of the surface of a membrane prepared according to the present invention;
FIG. 3 is a side SEM image of a three-layer separator prepared according to the present invention;
fig. 4 is a graph of Gurley value versus temperature for a separator prepared according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
A three-layer lithium battery separator includes two support layers and an intermediate thermal shutdown layer. The support layer comprises 99.7% of isotactic polypropylene and 0.3% of beta-crystal nucleating agent. The thermal shutdown layer comprises 79.7% of isotactic polypropylene, 20% of hydrogenated petroleum resin and 0.3% of beta-crystal nucleating agent, wherein the percentages are mass percentages.
The preparation process flow is shown in figure 1 and specifically comprises the following steps: the support layer and the intermediate thermal shutdown layer are respectively fed according to the weight ratio of raw materials, and are uniformly melted and mixed in three extruders (the materials extruded by the extruder A and the extruder C are isotactic polypropylene containing 0.3 percent of beta nucleating agent and are used as the support layer, the material extruded by the extruder B is a mixed material containing a low deformation temperature amorphous material and is used as the intermediate thermal shutdown layer), the extrusion temperature is 220 ℃, and then the three-layer composite tape casting sheet with high beta crystal content is obtained by tape casting extrusion from a die through a distributor and constant temperature crystallization at 120 ℃. And then carrying out biaxial stretching on the cast sheet under the conditions that the cast sheet is preheated for 2min at the temperature of 90 ℃, then stretched to 3 multiplied by 1 along the MD direction, and then stretched to 3 multiplied by 3 along the TD direction at the temperature of 110 ℃ to obtain the three-layer composite membrane. And finally, carrying out traction trimming, shaping and winding on the diaphragm.
The SEM image of the surface of the membrane and the SEM image of the side of the three-layer membrane prepared in this example are respectively shown in fig. 2 and fig. 3, and it can be clearly seen from the SEM images of the surface and the side that the three-layer composite membrane was successfully prepared, and the physical property characterization of the membrane shows that the membrane has good porosity, liquid absorption rate, gurley value and tensile strength, which are specifically shown in table 1. Meanwhile, a Gurley value comparison test is performed on the three-layer membrane and the single-layer PP membrane, and as can be seen from fig. 4, the result shows that the three-layer membrane can generate closed pores after the temperature exceeds 120 ℃, that is, the air permeability of the membrane is rapidly reduced, and the Gurley value is rapidly increased according to data.
Example 2
A three-layer lithium battery separator includes two support layers and an intermediate thermal shutdown layer. The support layer comprises 99.7% of isotactic polypropylene and 0.3% of beta-crystal nucleating agent. The thermal shutdown layer comprises 94.7 percent of isotactic polypropylene, 5 percent of hydrogenated petroleum resin and 0.3 percent of beta-crystal nucleating agent, wherein the percentages are mass percentages.
The preparation method comprises the following steps: the support layer and the intermediate thermal shutdown layer are respectively fed according to the weight ratio of raw materials, and are uniformly melted and mixed in three extruders (the materials extruded by the extruder A and the extruder C are isotactic polypropylene containing 0.3 percent of beta nucleating agent and are used as the support layer, the materials extruded by the extruder B are mixed materials containing amorphous materials with low deformation temperature and are used as the intermediate thermal shutdown layer), the extrusion temperature is 220 ℃, then the three-layer composite tape casting cast sheet with high beta crystal content is obtained by tape casting extrusion from a die through a distributor and constant temperature crystallization at 120 ℃. And then carrying out biaxial stretching on the cast sheet under the conditions that the cast sheet is preheated for 2min at the temperature of 90 ℃, then stretched to 3 multiplied by 1 along the MD direction, and then stretched to 3 multiplied by 3 along the TD direction at the temperature of 110 ℃ to obtain the three-layer composite membrane. And finally, carrying out traction trimming, shaping and winding on the diaphragm.
Example 3
A three-layer lithium battery separator includes two support layers and an intermediate thermal shutdown layer. The support layer comprises 99.7% of isotactic polypropylene and 0.3% of beta-crystal nucleating agent. The thermal shutdown layer comprises 89.7% of isotactic polypropylene, 10% of hydrogenated petroleum resin and 0.3% of beta-crystal nucleating agent, wherein the percentages are mass percentages.
The preparation method comprises the following steps: the support layer and the intermediate thermal shutdown layer are respectively fed according to the weight ratio of raw materials, and are uniformly melted and mixed in three extruders (the materials extruded by the extruder A and the extruder C are isotactic polypropylene containing 0.3 percent of beta nucleating agent and are used as the support layer, the materials extruded by the extruder B are mixed materials containing amorphous materials with low deformation temperature and are used as the intermediate thermal shutdown layer), the extrusion temperature is 190 ℃, then the three-layer composite tape casting cast sheet with high beta crystal content is obtained by tape casting extrusion from a die through a distributor and constant temperature crystallization at 120 ℃. And then carrying out biaxial stretching on the cast sheet under the conditions that the cast sheet is preheated for 2min at the temperature of 90 ℃, then stretched to 3 x 1 along the MD direction, and then stretched to 3 x 3 along the TD direction at the temperature of 110 ℃ to obtain the three-layer composite membrane. And finally, carrying out traction trimming, shaping and winding on the diaphragm.
Example 4
A three-layer lithium battery separator includes two support layers and an intermediate thermal shutdown layer. The support layer comprises 99.0% of isotactic polypropylene and 1.0% of beta-crystal nucleating agent. The thermal shutdown layer comprises 69.7% of isotactic polypropylene, 30% of hydrogenated petroleum resin and 0.3% of beta-crystal nucleating agent, wherein the percentages are mass percentages.
The preparation method comprises the following steps: the support layer and the intermediate thermal shutdown layer are respectively fed according to the weight ratio of raw materials, and are uniformly melted and mixed in three extruders (the materials extruded by the extruder A and the extruder C are isotactic polypropylene containing 0.3 percent of beta nucleating agent and are used as the support layer, the materials extruded by the extruder B are mixed materials containing amorphous materials with low deformation temperature and are used as the intermediate thermal shutdown layer), the extrusion temperature is 220 ℃, then the three-layer composite tape casting cast sheet with high beta crystal content is obtained by tape casting extrusion from a die through a distributor and constant temperature crystallization at 120 ℃. And then carrying out biaxial stretching on the cast sheet under the conditions that the cast sheet is preheated for 2min at the temperature of 90 ℃, then stretched to 3 x 1 along the MD direction, and then stretched to 3 x 3 along the TD direction at the temperature of 110 ℃ to obtain the three-layer composite membrane. And finally, carrying out traction trimming, shaping and winding on the diaphragm.
Comparative example
A single-layer lithium battery diaphragm comprises 99.7% of isotactic polypropylene and 0.3% of beta-crystal nucleating agent, wherein the percentages are mass percentages.
The preparation method comprises the following steps: the raw materials are fed according to the weight ratio, are evenly melted and mixed in an extruder, the extrusion temperature is 220 ℃, then the materials are cast and extruded from a neck ring die, and the cast sheet with high beta crystal content is obtained by constant temperature crystallization at 120 ℃. And then carrying out biaxial stretching on the cast sheet under the conditions that the cast sheet is preheated for 2min at the temperature of 90 ℃, then stretched to 3 x 1 along the MD direction, and then stretched to 3 x 3 along the TD direction at the temperature of 110 ℃ to obtain the three-layer composite membrane. And finally, carrying out traction trimming, shaping and winding on the diaphragm.
Table 1 characterization of physical properties of separators in examples and comparative examples
Figure BDA0003399345750000061
From the above table, it can be seen that example 1 can obtain the maximum closed cell effect after high temperature treatment, i.e. the Gurley value after 140 ℃ treatment is rapidly increased, on the premise that the porosity, the initial Gurley value and the comparative example are not different.
The invention does not need non-woven fabrics or inorganic ceramic layers, has simple preparation method, adopts dry preparation for the supporting layer and the middle thermal shutdown layer, can directly prepare the three-layer composite diaphragm from granules, and has simple process flow. From the manufacturing material point of view, the invention does not choose to use substances with low melting temperature, such as polyester series, or natural or synthetic waxes. The patent gets rid of the limitation of melting point, selects non-crystalline material, that is the heat distortion temperature of polymer is irrelevant with the melting point, and the obturator temperature is controllable, for example the hydrogenated petroleum resin that this patent embodiment adopted, for non-crystalline oligomer material, the deformation temperature is the softening point temperature, can select the trade mark of different softening points wantonly to prepare the diaphragm of different obturator temperatures. In addition, amorphous materials with lower glass transition temperatures can be selected as blends to prepare thermal shutdown layers, such as cyclic olefin copolymers and the like.
The diaphragm is a three-layer composite diaphragm, the middle layer of the diaphragm is mixed with an amorphous material with low deformation temperature, and the multilayer composite diaphragm prepared by the method has a thermal shutdown function, namely, when the thermal runaway of the battery occurs, the diaphragm can close a micropore structure on the premise of keeping the dimensional stability, so that the reaction in the battery is prevented from proceeding. Meanwhile, the porosity and the diaphragm thickness cannot be influenced, and the preparation method is simple, simple in process steps and environment-friendly, and is suitable for industrial application.
Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that various changes in the embodiments and/or modifications of the invention can be made, and equivalents and modifications of some features of the invention can be made without departing from the spirit and scope of the invention.

Claims (4)

1. A lithium battery diaphragm with thermal shutdown is characterized in that the lithium battery diaphragm is a three-layer composite diaphragm and specifically comprises two support layers and a middle thermal shutdown layer, a microporous structure is formed in biaxial tension by blending a low-deformation-temperature amorphous material in a polypropylene matrix of the thermal shutdown layer and utilizing a beta crystal pore-forming mechanism; the thickness of the diaphragm is 15-19 μm, and the porosity is 35-40%; the support layer comprises 99.0 to 99.9 weight percent of polypropylene and 0.1 to 1.0 weight percent of beta-crystal nucleating agent; the middle thermal shutdown layer comprises 70.0 to 90.0 weight percent of polypropylene, 10.0 to 30.0 weight percent of amorphous material with low deformation temperature and 0.1 to 1.0 weight percent of beta-crystal nucleating agent; the low deformation temperature amorphous material is hydrogenated petroleum resin.
2. A method for preparing a lithium battery separator having a thermal shutdown property according to claim 1, comprising: the method comprises the following steps:
s1, feeding a supporting layer and an intermediate heat-closing layer according to raw materials in percentage by mass respectively, uniformly melting and mixing in three extrusion devices respectively, then carrying out tape casting extrusion from a die through a distributor, and carrying out constant temperature crystallization to obtain a three-layer composite tape casting sheet with high beta crystal content;
and S2, carrying out biaxial tension on the three-layer composite casting sheet obtained in the step S1 to obtain the three-layer composite diaphragm.
3. The method for producing a lithium battery separator having a thermal shutdown property according to claim 2, characterized in that: in the step S1, the extrusion temperature is 190-220 ℃; the constant temperature crystallization is 120-125 ℃.
4. The method for producing a lithium battery separator having a thermal shutdown property according to claim 2, characterized in that: in step S2, the stretching conditions of the biaxial stretching are: preheated at 90 ℃ for 2min, then stretched to 3X 1 in the MD direction, and subsequently stretched to 3X 3 in the TD direction at 120 ℃.
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JPH0651808B2 (en) * 1987-04-28 1994-07-06 宇部興産株式会社 High shrinkability and high adhesion polyolefin film
JP4229504B2 (en) * 1999-01-06 2009-02-25 旭化成株式会社 Fluid-permeable microporous film and method for producing the same
CN105355816B (en) * 2015-12-14 2018-02-23 苏州锂盾储能材料技术有限公司 A kind of preparation method of lithium ion battery separator material
CN106565961B (en) * 2016-11-10 2019-06-07 河南惠强新能源材料科技股份有限公司 Polypropylene lithium ion battery separator intensity strengthening agent and utilize battery diaphragm prepared by it
CN108039443B (en) * 2017-11-21 2020-06-19 新纶复合材料科技（常州）有限公司 Composite diaphragm for lithium battery and preparation method thereof
CN108346764A (en) * 2017-12-12 2018-07-31 北方华锦化学工业股份有限公司 A kind of preparation method of dry method biaxial tension lithium battery diaphragm
CN110277535B (en) * 2018-03-15 2023-11-03 株式会社理光 Porous insulator, electrode, and nonaqueous electricity storage element
CN109968777B (en) * 2019-03-08 2020-01-07 山东大学 Medical super-tough puncture-resistant high-barrier composite film and preparation method thereof

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