CN115101887B - Lithium ion battery diaphragm and preparation method and application thereof - Google Patents

Lithium ion battery diaphragm and preparation method and application thereof Download PDF

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Publication number
CN115101887B
CN115101887B CN202210866701.8A CN202210866701A CN115101887B CN 115101887 B CN115101887 B CN 115101887B CN 202210866701 A CN202210866701 A CN 202210866701A CN 115101887 B CN115101887 B CN 115101887B
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polyvinylidene fluoride
film layer
lithium ion
ion battery
fluoride film
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CN115101887A (en
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崔巍巍
王旭
马俊锋
吴斌
程小荣
张超
周良
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Suzhou Taihu Electric Advanced Material Co ltd
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Suzhou Taihu Electric Advanced Material Co ltd
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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
    • 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
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/417—Polyolefins
    • 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
    • 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
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • 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
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/491—Porosity
    • 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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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Cell Separators (AREA)

Abstract

The invention discloses a lithium ion battery diaphragm, a preparation method and application thereof, wherein the battery diaphragm comprises a first polyvinylidene fluoride film layer, a polyethylene microsphere layer and a second polyvinylidene fluoride film layer which are sequentially arranged; the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer are respectively provided with a micropore structure, the polyethylene microsphere layer is obtained by taking polyethylene microsphere dispersion liquid as a raw material and adopting an electrostatic spraying mode to spray on the first polyvinylidene fluoride film layer or the second polyvinylidene fluoride film layer, and the polyethylene microsphere dispersion liquid comprises polyethylene microspheres, lithium halide and a dispersion solvent; when the diaphragm is prepared, firstly, preparing a polyvinylidene fluoride film layer by adopting an electrostatic spinning method, then, spraying a polyethylene microsphere layer on the polyvinylidene fluoride film layer by adopting an electrostatic spraying method, and then, preparing another polyvinylidene fluoride film layer on the polyethylene microsphere layer by adopting an electrostatic spinning method; the diaphragm has the performances of thermal shutdown, good electrolyte wettability, good thermal dimensional stability, high porosity, high liquid absorption and the like.

Description

Lithium ion battery diaphragm and preparation method and application thereof
Technical Field
The invention relates to the technical field of lithium battery diaphragms, in particular to a lithium ion battery diaphragm, a preparation method and application thereof.
Background
The battery diaphragm (battery separator), which is a layer of diaphragm material between the positive electrode and the negative electrode of the battery, is a very critical part in the battery, has direct influence on the safety and the cost of the battery, and has the main effects that: the positive electrode and the negative electrode are isolated, electrons in the battery can not pass through freely, and ions in the electrolyte can pass through freely between the positive electrode and the negative electrode.
At present, the commercialized diaphragm material is mainly a polyolefin diaphragm, has relatively excellent chemical stability, corrosion resistance and relatively good mechanical properties, but the practice finds that the following problems are still difficult to be considered, and obvious phenomena of failure exist: (1) poor wettability of the electrolyte; (2) When the battery meets special use conditions and the temperature rises, the heat shrinkage is serious, and the battery is possibly short-circuited; (3) Without the function of shutting down the battery reaction at high temperature, even if it is equipped with the function, it is difficult to effectively adjust the temperature of thermal shutdown, and the separator needs to be improved again, resulting in a great increase in the development cost.
Disclosure of Invention
The invention aims to overcome one or more defects of the prior art and provides a novel lithium ion battery diaphragm, which solves the problem of the phenomenon in the prior art.
The invention also provides a preparation method of the lithium ion battery diaphragm.
The invention also provides a lithium ion battery comprising the lithium ion battery diaphragm.
In order to achieve the above purpose, the invention adopts a technical scheme that:
the lithium ion battery diaphragm comprises a first polyvinylidene fluoride film layer, a polyethylene microsphere layer and a second polyvinylidene fluoride film layer which are sequentially arranged; the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer are respectively provided with a micropore structure, the polyethylene microsphere layer is obtained by taking polyethylene microsphere dispersion liquid as a raw material and adopting an electrostatic spraying mode to be sprayed on the first polyvinylidene fluoride film layer or the second polyvinylidene fluoride film layer, and the polyethylene microsphere dispersion liquid comprises polyethylene microspheres, lithium halide and a dispersing solvent.
According to some preferred aspects of the invention, the lithium halide is lithium chloride and/or lithium bromide.
According to the invention, the addition of lithium halide not only can make the polyethylene microsphere suitable for electrostatic spraying, but also basically does not introduce other cations for the later-stage lithium ion battery, thereby being beneficial to ensuring the product quality.
According to some preferred aspects of the invention, the dispersing solvent is absolute ethanol.
According to some preferred aspects of the present invention, the lithium halide is added in an amount of 0.05% to 0.3% by mass of the polyethylene microsphere dispersion.
According to some preferred aspects of the present invention, the polyethylene microspheres are added in an amount of 8% -12% of the polyethylene microsphere dispersion, in mass%.
According to some preferred and specific aspects of the invention, the polyethylene microspheres have a particle size of 1-5 μm.
In some preferred embodiments of the present invention, the method for preparing a polyethylene microsphere dispersion comprises: respectively adding the polyethylene microspheres, the dispersing solvent and the lithium halide into a mixing container, and then carrying out ultrasonic treatment under ice water for 10-30min to obtain a uniformly dispersed polyethylene microsphere dispersion liquid.
According to some preferred aspects of the present invention, the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer are respectively spun by using polyvinylidene fluoride spinning solution as raw material and adopting an electrostatic spinning method.
Further, the polyvinylidene fluoride spinning solution is prepared by dispersing polyvinylidene fluoride in a mixed solvent, wherein the mixed solvent is composed of N, N-dimethylformamide and tetrahydrofuran.
Further, in the mixed solvent, the feeding mass ratio of the N, N-dimethylformamide to the tetrahydrofuran is 8-10:1.
According to some preferred aspects of the invention, the polyvinylidene fluoride spinning solution has a mass concentration of 16% -20%.
In some preferred embodiments of the present invention, the method for preparing a polyvinylidene fluoride spinning solution comprises: and respectively adding the polyvinylidene fluoride and the mixed solvent into a mixing container, and then stirring at 50-65 ℃ for 2-8 hours to obtain the polyvinylidene fluoride spinning solution.
According to some preferred aspects of the invention, in the electrostatic spraying manner, the process parameters are as follows: the electrostatic spraying voltage is 8-12kV, the spraying propelling speed is 0.8-1.2mL/h, the ambient humidity is 10% -20%, and the rotating speed of the receiver roller is 250-350r/min.
According to some preferred aspects of the invention, the process parameters of the electrospinning method are as follows: the spinning voltage is 8-12kV, the spinning propulsion speed is 1.3-1.8mL/h, the ambient humidity is 10% -20%, and the rotating speed of the receiver roller is 250-350r/min. In some preferred embodiments of the present invention, in the preparation process of the lithium ion battery separator, the mass concentration of the polyvinylidene fluoride spinning solution is controlled to be 16% -20%, the addition amount of the polyethylene microspheres in the polyethylene microsphere dispersion solution is 8% -12%, when the spinning amount of the polyvinylidene fluoride spinning solution is 4-6mL, the spraying amount of the polyethylene microsphere dispersion solution is 2-4mL, and the spinning amount of the polyvinylidene fluoride spinning solution is larger than the spraying amount of the polyethylene microsphere dispersion solution.
According to the invention, the lithium ion battery diaphragm comprises a working state and a thermal shutdown state, when the lithium ion battery diaphragm is in the working state, the polyethylene microsphere layer is provided with a pore channel communicated with the micropore structure, and the lithium ion battery diaphragm can conduct lithium ions;
when the lithium ion battery diaphragm is in a thermal shutdown state, the polyethylene microsphere layer is softened or melted to form a compact structure, and part of the polyethylene microsphere layer is permeated and blocked in the microporous structure, namely, the polyvinylidene fluoride membrane layer is sealed, so that the lithium ion battery diaphragm can block lithium ions from passing through.
The invention provides another technical scheme that: the preparation method of the lithium ion battery diaphragm comprises the following steps: spinning one of a first polyvinylidene fluoride film layer and a second polyvinylidene fluoride film layer by using polyvinylidene fluoride spinning solution as a raw material through an electrostatic spinning method, then forming a polyethylene microsphere layer on the spun polyvinylidene fluoride film layer by using a polyethylene microsphere dispersion solution as a raw material through an electrostatic spraying method, and forming the other one of the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer on the polyethylene microsphere layer by using the polyvinylidene fluoride spinning solution as a raw material through an electrostatic spinning method.
The invention provides another technical scheme that: a lithium ion battery comprising a positive electrode, a negative electrode, and a separator, wherein: the diaphragm is the lithium ion battery diaphragm.
Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:
the novel lithium ion battery diaphragm provided by the invention is characterized in that the polyethylene microspheres are specially designed to form the polyethylene microsphere dispersion liquid, so that the polyethylene microspheres are suitable for electrostatic spraying, the polyethylene microspheres and the polyvinylidene fluoride film layer are mutually attached and assembled without layering, and particularly after the polyethylene microspheres are mutually assembled, the thermal shutdown function of the battery diaphragm is endowed, the effective regulation and control of the thermal shutdown temperature can be realized by adjusting different polyethylene materials adopted by the polyethylene microspheres, the materials of the polyethylene microspheres can be selected according to the need on the basis of the prior art without improving the diaphragm again, and the thermal shutdown temperature is further adjusted, so that the research and development cost is greatly saved; meanwhile, the inventor unexpectedly found that after the first polyvinylidene fluoride film layer, the polyethylene microsphere layer and the second polyvinylidene fluoride film layer which are sequentially arranged are assembled, good thermal dimensional stability can be kept at high temperature, so that the battery diaphragm can still effectively separate the anode and the cathode at high temperature and avoid the occurrence of short circuit condition (generally, the battery is required to be miniaturized and has smaller volume, so that the anode and the cathode have smaller distance and are adjacent to each other, if the diaphragm has a more obvious thermal shrinkage phenomenon, the anode and the cathode of the battery are easily contacted and short-circuited); moreover, the polyethylene microsphere layer is positioned in the middle, so that the polyethylene microsphere is not easy to fall off.
In addition, the battery diaphragm provided by the invention has high porosity and high liquid absorption, has good wettability to electrolyte, and can provide sufficient space for lithium ion transmission.
Drawings
Fig. 1 is a schematic diagram of a separator structure of a lithium ion battery prepared in example 1 according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a separator structure (after thermal shutdown) of a lithium ion battery prepared in example 1 according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a lithium ion battery separator, a commercial Ceglard2325 separator and a single PVDF nanofiber membrane prepared in example 1 of the present invention (the preparation method of the PVDF nanofiber membrane is the same as that of example 1) after heat treatment at 160℃for 20 min;
FIG. 4 is a cross-sectional scanning electron microscope image of a lithium ion battery separator prepared in example 1 of the present invention after heat treatment at 110 ℃;
fig. 5 is a schematic diagram showing the open circuit voltage variation of a battery assembled by using the lithium ion battery separator prepared in example 1 in the embodiment of the present invention during the heating process;
fig. 6 is a charge-discharge graph at room temperature of a battery assembled by using the lithium ion battery separator prepared in example 1 according to the embodiment of the present invention;
fig. 7 is a charge and discharge graph at 110 c of a battery assembled using the lithium ion battery separator prepared in example 1 according to an embodiment of the present invention.
Detailed Description
The above-described aspects are further described below in conjunction with specific embodiments; it should be understood that these embodiments are provided to illustrate the basic principles, main features and advantages of the present invention, and that the present invention is not limited by the scope of the following embodiments; the implementation conditions employed in the examples may be further adjusted according to specific requirements, and the implementation conditions not specified are generally those in routine experiments.
All starting materials are commercially available or prepared by methods conventional in the art, not specifically described in the examples below. In the following, polyvinylidene fluoride powder was purchased from the company Ackerma, france under the trade name Kynar 761; polyethylene microspheres were purchased from Qingdao Sauno New Material Co.
Example 1
The embodiment provides a lithium ion battery diaphragm, which comprises a first polyvinylidene fluoride film layer, a polyethylene microsphere layer and a second polyvinylidene fluoride film layer which are sequentially arranged; the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer respectively have micropore structures, the polyethylene microsphere layer is obtained by taking polyethylene microsphere dispersion liquid as a raw material and spraying the polyethylene microsphere dispersion liquid on the first polyvinylidene fluoride film layer in an electrostatic spraying mode, and the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer are respectively spun by taking polyvinylidene fluoride spinning liquid as a raw material and adopting an electrostatic spinning method.
Specifically, the polyethylene microsphere dispersion is prepared by the following method: 1g of polyethylene microspheres was weighed into a 50mL beaker, 9g of absolute ethanol was added thereto, and 0.02g of LiCl was added. And carrying out ultrasonic treatment under ice water for 20min to obtain a uniformly dispersed polyethylene microsphere dispersion liquid.
The polyvinylidene fluoride spinning solution is prepared by the following steps: 2.21g of the dried polyvinylidene fluoride powder was poured into a three-necked flask, and 9g of N, N-dimethylformamide and 1g of tetrahydrofuran were further added to the three-necked flask. And fully stirring the mixture at about 60 ℃ for 6 hours to fully dissolve the polyvinylidene fluoride powder in the mixed solvent, thereby obtaining the polyvinylidene fluoride spinning solution.
The preparation method of the battery diaphragm comprises the following steps:
preparing a PVDF nanofiber membrane (a first polyvinylidene fluoride membrane layer in the example) by adopting a polyvinylidene fluoride spinning solution through an electrostatic spinning method, wherein the propulsion speed is 0.15mL/h;
changing the polyethylene microsphere dispersion liquid after spinning 5mL of spinning solution, spraying the polyethylene microsphere dispersion liquid on the surface of the first polyvinylidene fluoride film layer by an electrostatic spraying method, and adjusting the propelling speed to be 1mL/h;
spraying 3mL of polyethylene microsphere dispersion liquid, replacing polyvinylidene fluoride spinning liquid, and finally spinning a PVDF nanofiber membrane (a second polyvinylidene fluoride membrane layer in the example) at a propulsion speed of 0.15mL/h, and stopping spinning after 5mL of spinning liquid is spun;
the voltage of the whole spinning process is about 10kV, the rotating speed of the roller is about 300r/min, and the humidity is controlled to be about 10%.
Example 2
The embodiment provides a lithium ion battery diaphragm, which comprises a first polyvinylidene fluoride film layer, a polyethylene microsphere layer and a second polyvinylidene fluoride film layer which are sequentially arranged; the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer respectively have micropore structures, the polyethylene microsphere layer is obtained by taking polyethylene microsphere dispersion liquid as a raw material and spraying the polyethylene microsphere dispersion liquid on the first polyvinylidene fluoride film layer in an electrostatic spraying mode, and the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer are respectively spun by taking polyvinylidene fluoride spinning liquid as a raw material and adopting an electrostatic spinning method.
Specifically, the polyethylene microsphere dispersion is prepared by the following method: 1.2g of polyethylene microspheres were weighed into a 50mL beaker, 9g of absolute ethanol was added to the beaker, and 0.02g of LiCl was added. And carrying out ultrasonic treatment under ice water for 20min to obtain a uniformly dispersed polyethylene microsphere dispersion liquid.
The polyvinylidene fluoride spinning solution is prepared by the following steps: 2.5g of the dried polyvinylidene fluoride powder was poured into a three-necked flask, and 9g of N, N-dimethylformamide and 1g of tetrahydrofuran were further added to the three-necked flask. And fully stirring the mixture at about 60 ℃ for 6 hours to fully dissolve the polyvinylidene fluoride powder in the mixed solvent, thereby obtaining the polyvinylidene fluoride spinning solution.
The preparation method of the battery diaphragm comprises the following steps:
preparing a PVDF nanofiber membrane (a first polyvinylidene fluoride membrane layer in the example) by adopting a polyvinylidene fluoride spinning solution through an electrostatic spinning method, wherein the propulsion speed is 0.15mL/h;
changing the polyethylene microsphere dispersion liquid after spinning 5mL of spinning solution, spraying the polyethylene microsphere dispersion liquid on the surface of the first polyvinylidene fluoride film layer by an electrostatic spraying method, and adjusting the propelling speed to be 1mL/h;
spraying 3mL of polyethylene microsphere dispersion liquid, replacing polyvinylidene fluoride spinning liquid, and finally spinning a PVDF nanofiber membrane (a second polyvinylidene fluoride membrane layer in the example) at a propulsion speed of 0.15mL/h, and stopping spinning after 5mL of spinning liquid is spun;
the voltage of the whole spinning process is about 10kV, the rotating speed of the roller is about 300r/min, and the humidity is controlled to be about 10%. The resulting fiber diameter of the fiber film was slightly thicker than in example 1, and the PE intermediate layer was thicker during the same time.
Example 3
The embodiment provides a lithium ion battery diaphragm, which comprises a first polyvinylidene fluoride film layer, a polyethylene microsphere layer and a second polyvinylidene fluoride film layer which are sequentially arranged; the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer respectively have micropore structures, the polyethylene microsphere layer is obtained by taking polyethylene microsphere dispersion liquid as a raw material and spraying the polyethylene microsphere dispersion liquid on the first polyvinylidene fluoride film layer in an electrostatic spraying mode, and the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer are respectively spun by taking polyvinylidene fluoride spinning liquid as a raw material and adopting an electrostatic spinning method.
Specifically, the polyethylene microsphere dispersion is prepared by the following method: 1.1g of polyethylene microspheres were weighed into a 50mL beaker, 9g of absolute ethanol was added thereto, and 0.02g of LiCl was added. And carrying out ultrasonic treatment under ice water for 20min to obtain a uniformly dispersed polyethylene microsphere dispersion liquid.
The polyvinylidene fluoride spinning solution is prepared by the following steps: 2.21g of the dried polyvinylidene fluoride powder was poured into a three-necked flask, and 9g of N, N-dimethylformamide and 1g of tetrahydrofuran were further added to the three-necked flask. And fully stirring the mixture at about 60 ℃ for 6 hours to fully dissolve the polyvinylidene fluoride powder in the mixed solvent, thereby obtaining the polyvinylidene fluoride spinning solution.
The preparation method of the battery diaphragm comprises the following steps:
preparing a PVDF nanofiber membrane (a first polyvinylidene fluoride membrane layer in the example) by adopting a polyvinylidene fluoride spinning solution through an electrostatic spinning method, wherein the propulsion speed is 0.16mL/h;
changing the polyethylene microsphere dispersion liquid after spinning 5mL of spinning solution, spraying the polyethylene microsphere dispersion liquid on the surface of the first polyvinylidene fluoride film layer by an electrostatic spraying method, and adjusting the propelling speed to be 1mL/h;
spraying 3mL of polyethylene microsphere dispersion liquid, replacing polyvinylidene fluoride spinning liquid, and finally spinning a PVDF nanofiber membrane (a second polyvinylidene fluoride membrane layer in the example) at a propulsion speed of 0.16mL/h, and stopping spinning after 5mL of spinning liquid is spun;
the voltage of the whole spinning process is about 10kV, the rotating speed of the roller is about 300r/min, and the humidity is controlled to be about 10%.
The resulting fiber film had a finer fiber diameter than example 1.
Performance testing
The lithium ion battery separator prepared in example 1, the commercial celgard2325 separator on the market, and the individual PVDF nanofiber membrane (the PVDF nanofiber membrane was prepared in the same manner as in example 1) were each subjected to performance testing.
The structure of the lithium ion battery separator prepared in the embodiment 1 is shown in fig. 1, and the lithium ion battery separator comprises a first polyvinylidene fluoride membrane layer 1, a polyethylene microsphere layer 2 and a second polyvinylidene fluoride membrane layer 3 which are sequentially arranged, wherein the polyethylene microsphere layer 2 is provided with pore channels which are respectively communicated with the microporous structures of the first polyvinylidene fluoride membrane layer 1 and the second polyvinylidene fluoride membrane layer 3, and the lithium ion battery separator can conduct lithium ions;
when the lithium ion battery diaphragm is in a thermal shutdown state, as shown in fig. 2, the polyethylene microsphere layer 2' is softened or melted to form a compact structure, and part of the polyethylene microsphere layer is permeated and blocked in the microporous structures of the first polyvinylidene fluoride membrane layer 1' and the second polyvinylidene fluoride membrane layer 3', namely the polyvinylidene fluoride membrane layer is closed, and the lithium ion battery diaphragm can block lithium ions from passing through, so that thermal shutdown is realized.
As a result of thermal dimensional stability test, as shown in fig. 3, the Celgard2325, PVDF nanofiber membrane, and lithium ion battery separator prepared in example 1 were heat-treated at 160 ℃ for 20min, respectively, and then the dimensional stability of the membrane was observed. The thermal dimensional shrinkage of Celgard2325 (corresponding to a in fig. 3) reaches 57.2%, the thermal dimensional shrinkage of PVDF nanofiber membrane (corresponding to b in fig. 3) is 8.3%, and the thermal dimensional shrinkage of lithium ion battery separator (corresponding to c in fig. 3) prepared in example 1 is 11.0%, which indicates that the lithium ion battery separator prepared in example 1 has better thermal dimensional stability, and especially has small influence on thermal dimensional shrinkage after adding polyethylene microspheres which are hot melted on the PVDF nanofiber membrane, and meets the use requirement.
Fig. 4 is a sectional scanning electron microscope image of the lithium ion battery separator prepared in example 1 after heat treatment at 110 ℃. The clear three-layer structure can be seen from the figure, a clearer boundary exists, and after the polyethylene microspheres in the middle layer are melted, the polyethylene in the middle layer can permeate into the polyvinylidene fluoride film layers on the upper layer and the lower layer, so that the microporous structure of the fiber film can be completely blocked.
And assembling the button full battery according to the sequence of the positive electrode shell, the positive electrode, the diaphragm, the negative electrode, the steel sheet, the elastic sheet and the negative electrode shell, wherein the positive electrode material is ternary nickel cobalt manganese (NCM 523), and the negative electrode material is a graphite negative electrode.
Fig. 5 shows the open circuit voltage change of the battery assembled by the lithium ion battery separator prepared in example 1 during the heating process, and it can be seen that the open circuit voltage of the battery is maintained at about 3.15V at room temperature, the battery is placed in a constant temperature heating device at 110 ℃, the battery voltage is reduced to a certain extent, and then suddenly drops to 0 in about 16s at a certain stage. This shows that the lithium ion battery separator prepared in example 1 can rapidly respond thermally during battery operation. When the temperature in the battery is suddenly increased to the melting temperature of the polyethylene microspheres, the polyethylene microsphere layer of the lithium ion battery separator prepared in the embodiment 1 can be rapidly melted to rapidly block the microporous structure of the fibrous membrane, so that the effect of preventing lithium ion transmission is achieved, and the voltage is rapidly reduced to 0.
The assembled battery is respectively charged and discharged at room temperature and 100 ℃, and the test results are shown in figures 6-7;
setting a holding time of 1min between the charging and discharging steps, after finishing the constant-current constant-voltage charging step, putting the battery into a constant-temperature heating device at 110 ℃ for discharging during the battery holding period, and testing the discharge capacity of the battery at 110 ℃;
the battery can be charged and discharged normally at room temperature, and shows good discharge capacity of 162.47mAh/g;
however, when the battery was discharged at 110 ℃, the discharge capacity of the battery was reduced to 0.03mAh/g, and normal discharge was not performed. This is because when the temperature inside the battery reaches 110 c, the polyethylene microspheres of the polyethylene microsphere layer rapidly melt and form a dense layer, rendering the original pores of the separator ineffective. This shows that the lithium ion battery separator of the present invention can effectively shut down the battery reaction at 110 ℃.
In addition, the invention also tests the porosity and the liquid absorption rate of the lithium ion battery separator prepared in the example 1, and the results show that: it has a high porosity of 68.8% and a high wicking of 484%.
Porosity test
The porosity of the separator was tested using an n-butanol imbibition method. The membrane was made into a 2X 2cm 2 Is a square of (c). And placing the diaphragm to be tested in n-butanol, wherein the diaphragm is required to be completely soaked in n-butanol liquid for 4 hours. Sandwiching the soaked membrane between two pieces of filter paper, pressing for 10s with 20g weight to absorb n-butanol on the membrane surface, weighing, and recording as m 1 . The porosity is calculated according to equation (1).
Porosity (%) = (m) 1 -m 0 )/ρ b V (1)；
Wherein: m is m 0 For the mass of the diaphragm, m 1 To the mass of the diaphragm after soaking n-butanol, ρ b Is the density of n-butanol and V is the membrane volume.
Liquid absorption test
The membranes were subjected to a wicking test using a weighing method. The dried membrane to be tested is used in a sufficient amountIs fully soaked in the electrolyte of the membrane, is taken out every 10min, and is sucked by filter paper to remove the electrolyte on the surface of the membrane, and is weighed and marked as m i . The mass measured to the diaphragm no longer changes and the liquid absorption is calculated according to formula (2-2).
Liquid absorption (%) = [ (m) i -m 0 )/m 0 ]×100％ (2-2)；
Wherein: m is m 0 M is the dry weight of the separator i Is the wet weight of the separator.
The above embodiments are provided to illustrate the technical concept and features of the present invention and are intended to enable those skilled in the art to understand the content of the present invention and implement the same, and are not intended to limit the scope of the present invention. All equivalent changes or modifications made in accordance with the spirit of the present invention should be construed to be included in the scope of the present invention.
The endpoints and any values of the ranges disclosed herein are not limited to the precise range or value, and are understood to encompass values approaching those ranges or values. For numerical ranges, one or more new numerical ranges may be found between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point value, in combination with each other, and are to be considered as specifically disclosed herein.

Claims (8)

1. A lithium ion battery separator, characterized in that: the battery diaphragm comprises a first polyvinylidene fluoride film layer, a polyethylene microsphere layer and a second polyvinylidene fluoride film layer which are sequentially arranged; the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer respectively have micropore structures, the polyethylene microsphere layer is obtained by taking polyethylene microsphere dispersion liquid as a raw material and adopting an electrostatic spraying mode to be sprayed on the first polyvinylidene fluoride film layer or the second polyvinylidene fluoride film layer, and the polyethylene microsphere dispersion liquid comprises polyethylene microspheres, lithium halide and a dispersing solvent;
the addition amount of the lithium halide accounts for 0.05 to 0.3 percent of the polyethylene microsphere dispersion liquid, and the addition amount of the polyethylene microsphere accounts for 8 to 12 percent of the polyethylene microsphere dispersion liquid;
the grain diameter of the polyethylene microsphere is 1-5 mu m.
2. The lithium ion battery separator according to claim 1, wherein: the lithium halide is lithium chloride and/or lithium bromide; and/or, the dispersion solvent is absolute ethyl alcohol.
3. The lithium ion battery separator according to claim 1, wherein: the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer are respectively spun by taking polyvinylidene fluoride spinning solution as a raw material and adopting an electrostatic spinning method; the polyvinylidene fluoride spinning solution is prepared by dispersing polyvinylidene fluoride in a mixed solvent, wherein the mixed solvent consists of N, N-dimethylformamide and tetrahydrofuran.
4. A lithium ion battery separator according to claim 3, wherein: in the mixed solvent, the feeding mass ratio of the N, N-dimethylformamide to the tetrahydrofuran is 8-10:1, and the mass concentration of the polyvinylidene fluoride spinning solution is 16% -20%.
5. The lithium ion battery separator according to claim 3 or 4, wherein: in the electrostatic spraying mode, the technological parameters are as follows: the electrostatic spraying voltage is 8-12kV, the spraying propelling speed is 0.8-1.2mL/h, the ambient humidity is 10% -20%, and the rotating speed of the receiver roller is 250-350r/min; in the electrostatic spinning method, the technological parameters are as follows: the spinning voltage is 8-12kV, the spinning propulsion speed is 1.3-1.8mL/h, the ambient humidity is 10% -20%, and the rotating speed of the receiver roller is 250-350r/min.
6. The lithium ion battery separator according to claim 1, wherein: the lithium ion battery diaphragm comprises a working state and a thermal shutdown state, when the lithium ion battery diaphragm is in the working state, the polyethylene microsphere layer is provided with a pore channel communicated with the micropore structure, and the lithium ion battery diaphragm can conduct lithium ions;
when the lithium ion battery diaphragm is in a thermal shutdown state, the polyethylene microsphere layer is in a compact structure, and part of the polyethylene microsphere layer permeates and is blocked in the micropore structure, so that the lithium ion battery diaphragm can block lithium ions from passing.
7. A method for preparing the lithium ion battery separator according to any one of claims 1 to 6, characterized in that: the preparation method comprises the following steps: spinning one of a first polyvinylidene fluoride film layer and a second polyvinylidene fluoride film layer by using polyvinylidene fluoride spinning solution as a raw material through an electrostatic spinning method, then forming a polyethylene microsphere layer on the spun polyvinylidene fluoride film layer by using a polyethylene microsphere dispersion solution as a raw material through an electrostatic spraying method, and forming the other one of the first polyvinylidene fluoride film layer and the second polyvinylidene fluoride film layer on the polyethylene microsphere layer by using the polyvinylidene fluoride spinning solution as a raw material through an electrostatic spinning method.
8. A lithium ion battery, includes positive pole, negative pole and diaphragm, its characterized in that: the separator is a lithium ion battery separator as defined in any one of claims 1 to 6.
CN202210866701.8A 2022-07-22 2022-07-22 Lithium ion battery diaphragm and preparation method and application thereof Active CN115101887B (en)

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