CN116111286A - Modified PVDF (polyvinylidene fluoride) coated diaphragm and preparation method and application thereof - Google Patents
Modified PVDF (polyvinylidene fluoride) coated diaphragm and preparation method and application thereof Download PDFInfo
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- H—ELECTRICITY
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- 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
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- H—ELECTRICITY
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- 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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- 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
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- 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
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- 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
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Abstract
The application discloses a modified PVDF (polyvinylidene fluoride) coated diaphragm and a preparation method and application thereof, and relates to the technical field of secondary batteries. The modified PVDF coating diaphragm comprises a base film, a heat-resistant layer and an organic layer, wherein the organic layer is formed by dot-shaped organic layers and comprises a secondary particle size PVDF, the surface of the secondary particle size PVDF is coated with a surface oiliness layer, and the secondary particle size PVDF is connected with the surface oiliness layer. According to the method, the surface oiliness layer is formed on the surface of the PVDF with the secondary particle size, the surface is only modified, the core structure of the PVDF with the secondary particle size is still maintained, the swelling phenomenon is not easy to occur after the PVDF with the secondary particle size is coated to prepare the battery, and meanwhile, the liquid storage performance of the diaphragm and the pole piece after hot pressing is improved, so that the capacity retention rate of the battery is improved.
Description
Technical Field
The application relates to the technical field of secondary batteries, in particular to a modified PVDF (polyvinylidene fluoride) coated diaphragm and a preparation method and application thereof.
Background
The diaphragm is used as an important component of the lithium battery, and can block electrons from passing through and allow ions to freely shuttle due to the insulativity of the diaphragm, so that the short circuit caused by contact between the anode and the cathode is avoided. However, the separator has poor heat resistance, and a heat-resistant ceramic layer is often coated on the surface of the separator. The heat-resistant ceramic layer has no bonding effect with the anode and the cathode of the battery, and the battery is a soft battery core, so that an organic bonding layer can be coated on the heat-resistant ceramic layer in the prior art.
The prior art coating of organic adhesive layers mainly includes aqueous coating and oily coating. The aqueous coating is mainly to mix organic adhesive powder with glue, then spray the prepared organic adhesive slurry on the surface of the coating diaphragm by adopting an air gun spraying or rotary spraying technology and the like, so as to increase the adhesiveness of the diaphragm and the pole piece. For example, in chinese patent application publication No. CN113363672a, an organic adhesive layer is sprayed on one or both sides of a ceramic coated diaphragm by using a spraying technique, so that the diaphragm and the pole piece have a certain adhesion.
However, in order to pursue a higher hardness battery, the adhesive strength of the aqueous organic adhesive layer and the electrode sheet is not satisfactory, and thus the prior art introduces oily coating. The oil coating is to mix an organic adhesive with an organic solvent, dissolve the organic adhesive in the organic solvent, coat the organic adhesive on the surface of a separator, and dry the separator to obtain an organic adhesive layer, and the adhesive property between the obtained organic adhesive layer and the pole piece is much stronger than the adhesive property between the aqueous organic adhesive layer and the pole piece. According to the Chinese patent application with publication number of CN112018311A, PVDF dissolved by acetone is sprayed on a coated membrane to obtain a discontinuous porous structure coated membrane with thickness of 0.2-0.5 mu m. Although the method improves the adhesion between the coated diaphragm and the pole piece, the diaphragm and the pole piece have insufficient effective space for swelling PVDF after the electrolyte is injected by hot pressing, and the swelling phenomenon of the battery is probably caused. Meanwhile, as the wettability of the organic solvent is very good, the dot-shaped coating obtained by spraying is very fast in diffusion and easy to form full-face coating, and the porosity of the obtained coated diaphragm is 30% -50%, the influence on the whole ventilation of the coated diaphragm can be increased by oil coating, so that the ion impedance is increased, and the cycle performance of a battery is weakened.
Disclosure of Invention
The purpose of the application is to provide a modified PVDF (polyvinylidene fluoride) coated diaphragm, and a preparation method and application thereof, which are used for solving the problems that the existing oily coated diaphragm is easy to bulge and has large influence on the air permeability of the diaphragm.
In order to achieve the above purpose, the embodiment of the present application adopts the following technical scheme: a modified PVDF-coated separator comprising: a base film, which is a porous film; a heat-resistant layer provided on at least one side surface of the base film; the organic layer is arranged on the surface of the heat-resistant layer, the organic layer is distributed in a dot shape, the organic layer comprises a secondary particle size PVDF, the surface of the secondary particle size PVDF is coated with a surface oiliness layer, and the secondary particle size PVDF is connected with the surface oiliness layer.
In the above technical scheme, in the embodiment of the application, the surface oiliness layer is formed on the surface of the secondary particle size PVDF, only the surface of the surface oiliness layer is modified, but the core structure of the secondary particle size PVDF is still maintained, when the surface oiliness secondary particle size PVDF is bonded with the pole piece, the surface oiliness secondary particle size PVDF has high bonding property of an oiliness system and the pole piece, and has spraying particles with a certain height, and when the surface oiliness secondary particle size PVDF is hot-pressed with the pole piece, enough mechanical muelled point positions can be provided, and bonding between the diaphragm and the pole piece is increased, so that the bonding performance between the diaphragm prepared by the coating diaphragm and the oil coating prepared by the method is almost the same as that between the diaphragm and the pole piece. In addition, the organic layer in the application is in punctiform distribution, the whole ventilation of the coating diaphragm is almost unaffected, after the discontinuous punctiform spraying diaphragm and the pole piece are hot pressed, a certain swelling space can be provided for swelling of PVDF absorbing electrolyte, after the coating diaphragm is prepared into a battery, swelling phenomenon is not easy to occur, and meanwhile, the liquid storage performance of the diaphragm and the pole piece after the hot pressing is improved, so that the capacity retention rate of the battery is improved.
Further, according to an embodiment of the present application, the base film is one of a PP film, a PE film, and a PP/PE composite film.
Further, according to an embodiment of the present application, wherein the heat resistant layer comprises a ceramic, a stabilizer, a binder, and a wetting agent.
Further, according to an embodiment of the present application, the stabilizer is added in an amount of 1-3wt% of the ceramic.
Further, according to an embodiment of the present application, the binder is added in an amount of 1-8wt% of the ceramic.
Further, according to an embodiment of the present application, the wetting agent is added in an amount of 0.1-1wt% of the ceramic.
Further, according to the embodiment of the application, the organic layer is formed by spraying an organic layer slurry, and the organic layer slurry is prepared by the following method:
preparing an organic solvent, wherein the organic solvent comprises acetone and deionized water, and the addition amount of the acetone is 1-3wt% of the deionized water;
adding the PVDF with the secondary particle size into the organic solvent, and uniformly dispersing the PVDF with the secondary particle size in the organic solvent;
adding glue and stirring to obtain the organic layer slurry.
Further, according to the embodiment of the application, the particle size of the secondary particle size PVDF is 6-9 μm, and the melting point is 140-150 ℃.
Further, according to the embodiment of the application, the glue is polyacrylic acid, and the Tg temperature is 80-100 ℃.
In order to achieve the above purpose, the embodiment of the application also discloses a preparation method of the modified PVDF coated membrane, which comprises the following steps:
preparing an organic layer slurry: preparing an organic solvent, wherein the organic solvent comprises acetone and deionized water, and the addition amount of the acetone is 1-3wt% of the deionized water; adding the PVDF with the secondary particle size into the organic solvent, and uniformly dispersing the PVDF with the secondary particle size in the organic solvent; adding glue and stirring to obtain the organic layer slurry;
preparing a heat-resistant layer slurry: mixing and stirring ceramics, a stabilizing agent, a binding agent, a wetting agent and deionized water;
coating a heat-resistant layer slurry on at least one side surface of a base film to form the heat-resistant layer;
and spraying the organic layer slurry on the heat-resistant layer, wherein the spraying coverage rate is 5-15%, and obtaining the modified PVDF coating diaphragm.
In order to achieve the above purpose, the embodiment of the application also discloses application of the modified PVDF coated separator to lithium batteries.
Compared with the prior art, the application has the following beneficial effects: according to the method, the surface oiliness layer is formed on the surface of the secondary particle size PVDF, only the surface of the surface oiliness layer is modified, but the core structure of the secondary particle size PVDF is still maintained, when the surface oiliness secondary particle size PVDF is adhered to the pole piece, the surface oiliness secondary particle size PVDF has high adhesion between an oiliness system and the pole piece, and spraying particles with a certain height are sprayed, when the surface oiliness secondary particle size PVDF is hot-pressed with the pole piece, enough mechanical break-in points can be provided, and adhesion between the diaphragm and the pole piece is increased. In addition, the organic layer in the application is in punctiform distribution, the whole ventilation of the coating diaphragm is almost unaffected, after the discontinuous punctiform spraying diaphragm and the pole piece are hot pressed, a certain swelling space can be provided for swelling of PVDF absorbing electrolyte, after the coating diaphragm is prepared into a battery, swelling phenomenon is not easy to occur, and meanwhile, the liquid storage performance of the diaphragm and the pole piece after the hot pressing is improved, so that the capacity retention rate of the battery is improved.
Drawings
The present application is further described below with reference to the drawings and examples.
Fig. 1 is a schematic structural diagram of a secondary particle size PVDF in the present application.
Fig. 2 is a schematic view of spray points in the present application.
Fig. 3 is a schematic cross-sectional view of the highest point of the spray granule.
Detailed Description
In order to make the objects, technical solutions, and advantages of the present invention more apparent, the embodiments of the present invention will be further described in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are some, but not all, embodiments of the present invention, are intended to be illustrative only and not limiting of the embodiments of the present invention, and that all other embodiments obtained by persons of ordinary skill in the art without making any inventive effort are within the scope of the present invention.
In the description of the present invention, it should be noted that the terms "center," "middle," "upper," "lower," "left," "right," "inner," "outer," "top," "bottom," "side," "vertical," "horizontal," and the like indicate orientations or positional relationships based on the orientation or positional relationships shown in the drawings, merely to facilitate description of the present invention and simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "a," an, "" the first, "" the second, "" the third, "" the fourth, "" the fifth, "and the sixth" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.
For purposes of brevity and description, the principles of the embodiments are described primarily by reference to examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments. It will be apparent, however, to one of ordinary skill in the art that the embodiments may be practiced without limitation to these specific details. In some instances, well-known methods and structures have not been described in detail so as not to unnecessarily obscure the embodiments. In addition, all embodiments may be used in combination with each other.
The application discloses a modified PVDF coating diaphragm, which comprises a base film and a heat-resistant layer arranged on at least one side surface of the base film, wherein organic layers distributed in a punctiform manner are arranged on the heat-resistant layer. The organic layer comprises a secondary particle size PVDF, the structure of which is shown in figure 1, and comprises agglomerated primary particle size PVDF particles 1 and a surface oiliness layer 2, wherein the surface oiliness layer 2 is wrapped on the outer side of the agglomerated primary particle size PVDF particles 1 (namely, the secondary particle size PVDF).
Further, the dot-shaped organic layer is formed by spraying, and the formed spray particle dots have a plurality of secondary particle size PVDF particles 3 bonded together as shown in FIG. 2, and the secondary particle size PVDF particles 3 are connected by the above-mentioned surface oiliness layer.
In the above-described technical means, by forming the surface oiliness layer on the surface of the secondary particle size PVDF, only the surface thereof is modified, but the core structure of the secondary particle size PVDF is maintained, and the surface oiliness layer has high adhesion between the oiliness system and the pole piece when the secondary particle size PVDF is adhered to the pole piece.
Meanwhile, as shown in FIG. 3, the spray particles are conical, the diameter d of the bottom is 50-80 μm, the height h is 25-65 μm, and the connecting line 4 between the highest point and the edge of the spray particles and the heat-resistant layer form an included angle alpha, and the included angle alpha is 45-60 degrees. The spray particles formed by the method have a certain height, and can provide enough mechanical mueller point positions when being hot pressed with the pole piece, so that the adhesion between the diaphragm and the pole piece is increased. Therefore, the adhesive properties of the coated diaphragm prepared by the method and the adhesive properties of the diaphragm prepared by the oil coating and the pole piece are almost the same.
In addition, the organic layer in the application is in punctiform distribution, the whole ventilation of the coating diaphragm is almost unaffected, after the discontinuous punctiform spraying diaphragm and the pole piece are hot pressed, a certain swelling space can be provided for swelling of PVDF absorbing electrolyte, after the coating diaphragm is prepared into a battery, swelling phenomenon is not easy to occur, and meanwhile, the liquid storage performance of the diaphragm and the pole piece after the hot pressing is improved, so that the capacity retention rate of the battery is improved. Further, compared with the technical scheme in CN112018311a in the prior art, the spray particles in the present application can maintain a more compact structure due to the surface oiliness layer, are not easy to diffuse, and do not increase the influence on the overall ventilation of the coated membrane.
For this, the sprayed organic layer slurry was prepared by the following method:
preparing an organic solvent, adding the PVDF with the secondary particle size into the organic solvent, and uniformly dispersing the PVDF with the secondary particle size in the organic solvent;
adding glue and stirring to obtain organic layer slurry.
Wherein the organic solvent comprises acetone and deionized water, and the addition amount of the acetone is 1-3wt% of the deionized water. The particle size of the PVDF with the secondary particle size is 6-9 mu m, the melting point is 140-150 ℃, and the addition amount is 12-18wt% of deionized water. The glue is polyacrylic acid, the Tg (glass transition temperature) is 80-100 ℃, and the addition amount is 0.6-1.0wt% of deionized water.
The organic solvent and deionized water are mixed and then mixed with the secondary particle size PVDF, and as the organic solvent occupies smaller area, the secondary particle size PVDF is an aggregate formed by the primary particle size PVDF, and a small amount of organic solvent is difficult to dissolve the structure of the secondary particle size PVDF, so that the organic solvent can only corrode and dissolve the surface of the secondary particle size PVDF, and then spray coating and drying are carried out, so that the surface of the secondary particle size PVDF is oiled to form a surface oiled layer, and the core structure of the secondary particle size PVDF is still maintained.
In addition, the base film in the application is a porous film, in particular one of a PP film, a PE film and a PP/PE composite film, and the thickness is 5-16 mu m. The thickness of the heat-resistant layer is 1-5 μm, and the heat-resistant layer comprises ceramics, a stabilizer, a binder and a wetting agent. The ceramic is one or more of aluminum oxide, boehmite, aluminum hydroxide and silicon oxide, and the grain diameter D50 is 0.5-1.0 μm. The stabilizer is one or more of methylcellulose, xanthan gum, polyacrylate and sodium alginate, and the addition amount is 1-3wt% of the ceramic. The binder is one or more of styrene-butadiene rubber, polystyrene and polyacrylate, and the addition amount is 1-8wt% of the ceramic. The wetting agent is one or more of butyl naphthalene sulfonate sodium salt, nonylphenol polyoxyethylene ether and ethanol, and the addition amount is 0.1-1wt% of the ceramic.
The application also discloses a preparation method of the modified PVDF coated diaphragm, which comprises the following steps:
preparing an organic layer slurry;
preparing a heat-resistant layer slurry, and coating the heat-resistant layer slurry on at least one side surface of a base film to form a heat-resistant layer;
and spraying the organic layer slurry on the heat-resistant layer, wherein the spraying coverage rate is 5-15%, and obtaining the modified PVDF coating diaphragm.
The present application will be further described below by way of examples and comparative examples, but the present application is not limited to these examples.
[ example 1 ]
Step 1: mixing 1000 parts of deionized water and 12 parts of acetone uniformly, adding 150 parts of PVDF with secondary particle size of 6.5 mu m, sealing, heating to 40 ℃, emulsifying at high speed, and stirring slowly to uniformly disperse PVDF particles with secondary particle size in the mixed solution of water and acetone;
step 2: adding 8.0 parts of styrene-butadiene rubber into the mixed solution, and stirring to obtain an organic layer slurry;
step 3: mixing 100 parts of alumina powder with the particle size of 0.5 mu m, 1.5 parts of polyacrylate, 6 parts of polyoxyethylene nonylphenol ether and 200 parts of deionized water, stirring to obtain a heat-resistant layer slurry, and coating the heat-resistant layer slurry on a base film with the thickness of 7 mu m by using a micro gravure technology to form a heat-resistant layer with the thickness of 2 mu m;
step 4: the organic layer slurry was sprayed on the heat-resistant layer and dried to obtain a modified PVDF coated membrane having a spray point particle diameter of 280 μm, a height of 8.5 μm and a coverage of 13%.
[ example 2 ]
28 parts of acetone and 175 parts of PVDF with a secondary particle size of 8.8 μm are taken in step 1 of example 1; 9.5 parts of styrene-butadiene rubber is taken in the step 2; and in the step 4, the spraying flow and the spraying rotating speed are regulated to obtain the modified PVDF coated diaphragm with the spraying point particle diameter of 120 mu m, the height of 10.5 mu m and the coverage rate of 24 percent, and the modified PVDF coated diaphragm is otherwise the same as in the example 1.
[ example 3 ]
In step 1 of example 1, 20 parts of acetone and 125 parts of PVDF having a secondary particle size of 7.5 μm were taken; step 2, 7 parts of styrene-butadiene rubber is taken; in step 4, the spray flow rate and the spray rotation speed were adjusted to obtain a modified PVDF coated membrane having a spray point particle diameter of 180. Mu.m, a height of 9.0. Mu.m, and a coverage of 18%, otherwise the same as in example 1.
Comparative example 1
In step 1 of example 1, 5 parts of acetone and 150 parts of PVDF having a secondary particle size of 7.0 μm were taken; step 2, 8 parts of styrene-butadiene rubber is taken; and in the step 4, the spraying flow and the spraying rotating speed are regulated to obtain the modified PVDF coated diaphragm with the spraying point particle diameter of 220 mu m, the height of 9.5 mu m and the coverage rate of 15 percent, and the modified PVDF coated diaphragm is otherwise the same as in the example 1.
Comparative example 2
40 parts of acetone and 125 parts of PVDF with a secondary particle size of 6.5 μm are taken in step 1 of example 1; step 2, 8 parts of styrene-butadiene rubber is taken; and in the step 4, the spraying flow and the spraying rotating speed are regulated to obtain the modified PVDF coated diaphragm with the spraying point particle diameter of 190 mu m, the height of 6.8 mu m and the coverage rate of 22 percent, and the modified PVDF coated diaphragm is otherwise the same as in the example 1.
[ comparative example 3 ]
In step 1 of example 1, 0 part of acetone and 150 parts of PVDF with a secondary particle size of 6.5 μm were taken; 9 parts of styrene-butadiene rubber is taken in the step 2; and in the step 4, the spraying flow and the spraying rotating speed are regulated to obtain the modified PVDF coated diaphragm with the spraying point particle diameter of 250 mu m, the height of 8.8 mu m and the coverage rate of 14 percent, and the modified PVDF coated diaphragm is otherwise the same as in the example 1.
[ comparative example 4 ]
1000 parts of acetone, 0 part of deionized water and 125 parts of PVDF with a secondary particle size of 8.0 μm were taken in step 1 of example 1; step 2, taking 0 part of styrene-butadiene rubber; in step 4, the spray flow rate and the spray rotation speed were adjusted to obtain a modified PVDF coated membrane having a spray point particle diameter of 500. Mu.m, a height of 0.8. Mu.m, and a coverage of 80%, otherwise the same as in example 1.
The coated separator of the above example and comparative example was tested for air permeability growth, adhesion to pole pieces, ionic conductivity, capacity retention, and expansion coefficient. The test method is as follows:
air permeability growth rate (%): ventilation refers to the time required for 100ml of gas to pass through a fixed area membrane, the rate of increase in ventilation = (membrane ventilation-heat resistant layer coated ventilation)/heat resistant layer coated ventilation × 100%;
bonding force with pole piece: coating the adhesive force of the diaphragm and the positive plate at the conditions of 1MPa, 5min and 95 ℃, wherein the positive plate consists of 945 parts of lithium iron phosphate, 10 parts of conductive carbon black and 45 parts of PVDF with the melting point of 148 ℃, and the thickness of the positive plate is 140-150 mu m;
ion conductivity (S cm) -1 ): in an argon glove box, a 2016 button cell was fabricated from a separator, and an appropriate amount of electrolyte (EC: EMC: dec=3:5:2, liPF) was added 6 2 Mol/L), using an ac impedance test in an electrochemical workstation, σ=l/(rb×a), where σ is the ionic conductivity (S cm) -1 ) L is the thickness (cm) of the separator; rb is the intrinsic resistance (Ω) of the membrane; a is the effective area (cm) 2 ）；
Capacity retention (%): the battery was cycled 180 times at 0.25C charge and discharge, and the capacity before and after the cycle was tested, with capacity retention = post-cycle capacity/pre-cycle capacity;
coefficient of expansion: after hot-pressing winding and injecting electrolyte by the diaphragm and the pole piece, the temperature is 60 ℃, the sealing is kept for 15 days, and the thickness expansion coefficient of the battery is tested, wherein the expansion coefficient=the thickness after the sealing swells for 15 days/the thickness at the sealing.
The test results are shown in Table 1.
TABLE 1
| Air permeability growth rate (%) | Bonding force with pole piece (N/m) | Ion conductivity (S cm) -1 ） | Capacity retention (%) | Coefficient of expansion | |
| Example 1 | 2.0 | 8.2 | 0.743 | 97.3 | 1.00 |
| Example 2 | 2.8 | 8.8 | 0.724 | 97.5 | 1.00 |
| Example 3 | 2.5 | 8.5 | 0.751 | 97.2 | 1.00 |
| Comparative example 1 | 1.8 | 4.5 | 0.607 | 96.8 | 1.00 |
| Comparative example 2 | 3.5 | 3.3 | 0.648 | 95.6 | 1.05 |
| Comparative example 3 | 2.4 | 3.8 | 0.581 | 96.7 | 1.00 |
| Comparative example 4 | 10.2 | 8.8 | 0.527 | 94.3 | 1.14 |
As shown in table 1, the organic layers obtained in examples 1 to 3 and comparative examples 1 to 3 have less influence on the overall air permeability of the coated separator, mainly because a discontinuous dot-like organic adhesive layer with lower coverage is obtained by spraying; in comparative example 4, although the spraying method was used, after the secondary particle size PVDF was dissolved in the pure organic solvent, the overall surface tension of the slurry was low, and the secondary particle size PVDF had no core structure, so that the overall coverage was high and the overall air permeability of the coated separator was greatly affected at the same gram weight of the coating amount of the sprayed coating.
In the embodiments 1-3, the adhesive with higher Tg temperature and the PVDF with the surface oiliness secondary particle size are mixed and sprayed, so that the formed spraying point has a good point position rigid structure, when the spraying point is adhered to a pole piece, the point position with higher rigidity can be embedded into the coating of the positive pole piece to form an effective machine Mou Gedian, and meanwhile, the PVDF with the surface oiliness enhances the adhesion between the PVDF and the pole piece, so that the adhesive property between the coated diaphragm and the pole piece is better, and the overall adhesive force and the pure oiliness spraying difference are not great; the dot-shaped particles sprayed in the comparative example 1 have better heights, the included angle between the highest point and the edge of the particle point is larger, and the mechanical mixing is better, but the organic solvent is less, and the surface oiliness of the PVDF with the secondary particle size is weak, so the overall adhesiveness is relatively low; in comparative example 2, the surface oiliness of the PVDF with the secondary particle size is better due to excessive organic solvent, but the height of the sprayed particle points is lower, the included angle between the connecting line of the highest point and the edge of the particles and the heat-resistant layer is lower, so that the effect of embedding the particle points into the pole piece is poorer, the mechanical action of making a mu is weakened, and the overall adhesiveness is obviously reduced; the particle point sprayed in the comparative example 3 is higher, the mechanical action of the thermal pressing of the pole piece is better, but the oiliness of the surface of the PVDF with the secondary particle size is realized by no organic solvent, and the surface belongs to pure water-based PVDF spraying, so the overall adhesion is lower; comparative example 4 belongs to a pure oil coating, but the discontinuous point shape has no height, and the adhesive is bonded with the pole piece without mechanical break points, so the overall adhesive property is not greatly different from that of the embodiment.
The discontinuous point-like coated membrane prepared in the embodiment 1-3 has low overall coverage rate, and after the surface of the PVDF with the secondary particle size is oiled, the contact compatibility with the pole piece is better, so that the overall ion conductivity is higher; the PVDF with the secondary particle size in comparative example 1 has weak surface oiliness, reduces the compatibility of the diaphragm and the pole piece, so that the interface resistance is increased, and the overall ion conductivity of the coated diaphragm is lower; the PVDF with the secondary particle size in comparative example 2 has better surface oiliness, reduces the interface resistance of the diaphragm and the pole piece, but has lower thickness of the spraying point, and has smaller storage space and lower liquid storage property after the diaphragm and the pole piece are hot pressed, so the overall ionic conductivity is lower; in comparative example 3, the surface of the PVDF with the secondary particle size is oilless, so that the compatibility of the diaphragm and the pole piece is reduced, the interface resistance is increased, and the ionic conductivity is reduced; in comparative example 4, oil spraying is adopted, the coverage rate of the organic layer is large, the dot-shaped organic layer is basically free of thickness, and the liquid storage property is seriously reduced after hot pressing, so that the overall ionic conductivity is reduced.
The discontinuous dot-shaped organic coating diaphragms obtained in examples 1-3, comparative example 1 and comparative example 3 can provide a larger space for storing electrolyte after hot pressing with a pole piece, so that the overall capacity retention rate is high; in comparative example 2, the surface oiliness of the PVDF with the secondary particle size is high due to the high amount of the organic solvent, and the height of the spraying point is relatively low, so that the whole liquid storage space is reduced, and the capacity retention rate is relatively reduced; in comparative example 4, oily spraying is adopted, the obtained dot-shaped organic layer has no height basically, the overall liquid storage performance after hot pressing with the pole piece is lower, and the capacity retention rate is lower.
The discontinuous dot-shaped organic spray coating obtained in examples 1-3, comparative example 1 and comparative example 3 has higher dot-shaped organic layer height, and can provide larger space for swelling PVDF electrolyte after hot pressing, so that swelling phenomenon is not easy to occur after coating a diaphragm to prepare a battery; in the comparative example 2, the surface of PVDF with the secondary particle size is oiled too much, so that the thickness of a spraying point is low, and a coating diaphragm and a pole piece do not have enough space for swelling of PVDF electrolyte absorption after hot pressing, so that a certain swelling phenomenon can be caused after the battery is manufactured; comparative example 4 was prepared by spraying with pure oil, the spray point was almost free of height, and there was almost no space for swelling of PVDF electrolyte after hot pressing of the separator and the pole piece, so that the swelling of the battery was severe after the battery was fabricated.
While the foregoing has been described in terms of illustrative embodiments thereof, so that those skilled in the art may appreciate the present application, it is not intended to be limited to the precise embodiments so that others skilled in the art may readily utilize the present application to its various modifications and variations which are within the spirit and scope of the present application as defined and determined by the appended claims.
Claims (11)
1. A modified PVDF-coated membrane comprising:
a base film, which is a porous film;
a heat-resistant layer provided on at least one side surface of the base film;
the organic layer is arranged on the surface of the heat-resistant layer, the organic layer is distributed in a dot shape, the organic layer comprises a secondary particle size PVDF, the surface of the secondary particle size PVDF is coated with a surface oiliness layer, and the secondary particle size PVDF is connected with the surface oiliness layer.
2. The modified PVDF coated membrane of claim 1, wherein the base film is one of PP film, PE film, PP/PE composite film.
3. The modified PVDF-coated membrane of claim 1, wherein the heat resistant layer comprises ceramic, stabilizer, binder and wetting agent.
4. A modified PVDF-coated membrane according to claim 3, characterized in that the stabilizer is added in an amount of 1-3wt% of the ceramic.
5. A modified PVDF coated membrane according to claim 3, wherein the binder is added in an amount of 1 to 8wt% of the ceramic.
6. A modified PVDF coated membrane according to claim 3, wherein the wetting agent is added in an amount of 0.1 to 1wt% of the ceramic.
7. The modified PVDF-coated membrane of claim 1, wherein the organic layer is spray coated from an organic layer slurry prepared by:
preparing an organic solvent, wherein the organic solvent comprises acetone and deionized water, and the addition amount of the acetone is 1-3wt% of the deionized water;
adding the PVDF with the secondary particle size into the organic solvent, and uniformly dispersing the PVDF with the secondary particle size in the organic solvent;
adding glue and stirring to obtain the organic layer slurry.
8. The modified PVDF-coated membrane of claim 7, wherein the secondary particle size PVDF has a particle size of 6 to 9 μm and a melting point of 140 to 150 ℃.
9. The modified PVDF-coated membrane of claim 7 wherein the glue is polyacrylic acid and has a Tg of 80 to 100 ℃.
10. A method of preparing the modified PVDF-coated membrane of claim 1, comprising the steps of:
preparing an organic layer slurry: preparing an organic solvent, wherein the organic solvent comprises acetone and deionized water, and the addition amount of the acetone is 1-3wt% of the deionized water; adding the PVDF with the secondary particle size into the organic solvent, and uniformly dispersing the PVDF with the secondary particle size in the organic solvent; adding glue and stirring to obtain the organic layer slurry;
preparing a heat-resistant layer slurry: mixing and stirring ceramics, a stabilizing agent, a binding agent, a wetting agent and deionized water;
coating a heat-resistant layer slurry on at least one side surface of a base film to form the heat-resistant layer;
and spraying the organic layer slurry on the heat-resistant layer, wherein the spraying coverage rate is 5-15%, and obtaining the modified PVDF coating diaphragm.
11. Use of the modified PVDF-coated separator according to any of claims 1 to 9 or the modified PVDF-coated separator prepared by the method of preparing the modified PVDF-coated separator according to claim 10 in lithium batteries.
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