CN112635918A - Diaphragm, preparation method thereof and battery - Google Patents
Diaphragm, preparation method thereof and battery Download PDFInfo
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- CN112635918A CN112635918A CN202011569725.4A CN202011569725A CN112635918A CN 112635918 A CN112635918 A CN 112635918A CN 202011569725 A CN202011569725 A CN 202011569725A CN 112635918 A CN112635918 A CN 112635918A
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- 239000003795 chemical substances by application Substances 0.000 claims description 20
- 238000001035 drying Methods 0.000 claims description 19
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- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
-
- 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
Landscapes
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Cell Separators (AREA)
Abstract
The application discloses a diaphragm preparation method and a battery, and relates to the technical field of secondary batteries. The diaphragm described herein includes: a substrate; the coating is arranged on the surface of at least one side of the substrate and is provided with a top layer and at least one inner layer, the top layer and the inner layer are both of porous structures, and holes in the top layer and holes in the inner layer are of a nested structure. The coating has a multi-layer hole nesting structure, so that the bonding force between the coating and the diaphragm and between the diaphragm and the pole piece is improved; simultaneously, multilayer hole pile cover structure in this application can avoid appearing sclausura polymer "blind spot", and the porosity is big, ventilative loss is little, greatly improves to coat and pole piece high bonding, and unique network coating structure has increased the lithium storage space simultaneously, does benefit to lithium electricity process circulation, prevents that dendritic crystal from producing, phenomenon such as separating lithium, improves lithium cell cycle life.
Description
Technical Field
The application relates to the technical field of secondary batteries, in particular to a diaphragm, a preparation method thereof and a battery.
Background
The production process of the polymer-coated separator is mainly classified into two major categories, namely water-based coating and oil-based coating, wherein the water-based coating is taken as a market main body. The water-based coating process adopts water as a solvent, has the advantages of low production cost, small environmental pollution and the like, but has weak cohesiveness and is easy to generate phenomena of poor hot pressing with a pole piece and the like. The adhesion between the oily process coating and the pole piece is higher than that of the water-based coating, but the requirement on the coating process is extremely high, the phenomena of hole blocking, poor ventilation, coating falling, uneven pore forming and the like are easy to occur, particularly the problem of lithium black spot precipitation at the battery end caused by poor and uneven pore forming is solved, and a good evading method is still not provided at present.
Disclosure of Invention
The application aims to provide a diaphragm, a preparation method thereof and a battery, which solve the problems of poor cohesiveness of a water-based coating diaphragm and poor air permeability of an oil-based coating diaphragm in the prior art and take both adhesiveness and air permeability into consideration.
In order to achieve the above purpose, the embodiments of the present application adopt the following technical solutions: a septum, comprising: a substrate; the coating is arranged on the surface of at least one side of the substrate and is provided with a top layer and at least one inner layer, the top layer and the inner layer are both of porous structures, and holes in the top layer and holes in the inner layer are of a nested structure.
In the above technical solution, the coating layer in the embodiment of the present application has a multi-layer hole nesting structure, and the nesting includes a "skeleton network" on the top layer and a "sub-network" on the inner layer, so as to form a structure in which holes are nested in the inner layer of the hole nesting on the top layer. The top layer ' skeleton network ' has no air permeability loss, the skeleton network ' increases the attachment of the diaphragm and the pole piece, and the branched chain surface gel enhances the adhesive force, thereby improving the adhesive force between the coating and the diaphragm and between the diaphragm and the pole piece; the inner "subnetwork" results in less loss of gas permeability and improved adhesion. Simultaneously, multilayer hole pile cover structure in this application can avoid appearing sclausura polymer "blind spot", and the porosity is big, ventilative loss is little, greatly improves to coat and pole piece high bonding, and unique network coating structure has increased the lithium storage space simultaneously, does benefit to lithium electricity process circulation, prevents that dendritic crystal from producing, phenomenon such as separating lithium, improves lithium cell cycle life.
Further in accordance with an embodiment of the present application, wherein the pore size of the top layer is equal to the pore size of the inner layer.
Further in accordance with an embodiment of the present application, wherein the pore size of the top layer is larger than the pore size of the inner layer.
Further, according to the embodiment of the application, the inner layer is a multi-layer structure, the inner layers of the plurality of layers have different apertures, and the apertures with different sizes are alternately nested.
Further, according to the embodiment of the present application, wherein the pore size of the top layer is 1-10 μm.
Further, according to the embodiment of the present application, wherein the pore size of the inner layer is 0.01-10 μm.
Further, according to the embodiment of the present application, wherein the coating layer is formed by mixing a hydrophobic binder polymer and an amphiphilic binder polymer.
Further, according to the embodiment of the present application, wherein the hydrophobic binder polymer is one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyacrylonitrile, PMMA, PAI, PI, aramid, and the like.
Further, according to the embodiment of the present application, the amphiphilic binder polymer simultaneously contains one or more of hydrophilic and hydrophobic groups, modified polyethylene glycol such as polyethylene glycol methacrylate, polystyrene-polyethylene glycol, methoxypolyethylene glycol polylactic acid, polyisobutylene-l-poly (N, N-dimethylacrylamide), cyanohydroxyethylcellulose ether, polyvinyl alcohol, acrylamide, and cellulose.
Further in accordance with embodiments herein, wherein the porous structure of the coating is formed by any one of the following methods selected from:
a method comprises the steps of sequentially dissolving a hydrophobic adhesive polymer and an amphiphilic adhesive polymer into a solvent, then adding a pore-forming agent, and mixing and stirring to obtain a mixed glue solution; and
a method comprising the steps of coating a polymer mixed solution on a substrate, and drying the substrate.
Further, according to the embodiment of the application, the pore-forming agent is a compound with a boiling point of 50-400 ℃.
Further, according to the embodiment of the present application, wherein the pore-forming agent is one or more of ethyl acetate, ethylene glycol dimethyl ether, acrylic acid, butyl acetate, polyvinylpyrrolidone, and sorbitan monooleate.
Further in accordance with an embodiment of the present application, wherein the porogen comprises at least one group selected from the group consisting of carboxyl, hydroxyl, acrylate, ether, maleic anhydride.
Further, according to the embodiment of the present application, wherein the solvent is one of acetone, DMAC, NMP, tetrahydrofuran, dichloromethane, chloroform, and cyclohexane.
Further, according to the embodiment of the application, in the mixed glue solution, the total amount of the adhesive polymer accounts for 0.5-15 wt%, the pore-forming agent accounts for 1-50 wt%, and the solvent accounts for 40-98 wt%.
Further, according to an embodiment of the present application, wherein, in the binder polymer, the amphiphilic binder polymer accounts for 0.1 wt% to 50 wt% of the total amount of the binder polymer.
In order to achieve the above object, the embodiment of the present application further discloses a preparation method of a separator, including the following steps:
preparing slurry: dissolving a hydrophobic adhesive polymer into a solvent, then adding an amphiphilic adhesive polymer, and mixing and stirring to obtain a mixed glue solution; adding a pore-forming agent into the mixed glue solution, and uniformly dispersing to obtain coating slurry;
coating slurry: coating the coating slurry on at least one surface of the base material to form a coating on the surface of the base material, and then drying the base material to obtain a diaphragm;
the coating is provided with a top layer and at least one inner layer, the top layer and the inner layer are both of porous structures, and holes of the top layer and holes of the inner layer are of a nested structure.
Further, according to the embodiment of the application, the coating manner is one of micro-concave plate, spin coating and extrusion coating.
In order to achieve the above object, an embodiment of the present application further discloses a battery, including: a positive electrode plate; a negative pole piece; a separator as described above or a separator prepared by a preparation method as described above; and (3) an electrolyte.
In order to achieve the purpose, the embodiment of the application also discloses an object, and the object comprises the battery.
Further, according to the embodiment of the application, the object is an electronic product or an electric vehicle.
Compared with the prior art, the method has the following beneficial effects: the coating is made to be in a multi-layer hole nesting structure, and the nesting comprises a skeleton network of a top layer and a sub-network of an inner layer, so that the structure of holes in the inner layer of the hole nesting of the top layer is formed. The top layer ' skeleton network ' has no air permeability loss, the skeleton network ' increases the attachment of the diaphragm and the pole piece, and the branched chain surface gel enhances the adhesive force, thereby improving the adhesive force between the coating and the diaphragm and between the diaphragm and the pole piece; the inner "subnetwork" results in less loss of gas permeability and improved adhesion. Simultaneously, multilayer hole pile cover structure in this application can avoid appearing sclausura polymer "blind spot", and the porosity is big, ventilative loss is little, greatly improves to coat and pole piece high bonding, and unique network coating structure has increased the lithium storage space simultaneously, does benefit to lithium electricity process circulation, prevents that dendritic crystal from producing, phenomenon such as separating lithium, improves lithium cell cycle life.
Drawings
The present application is further described below with reference to the drawings and examples.
FIG. 1 is a photomicrograph of a surface of a separator of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clear and fully described, embodiments of the present invention are further described in detail below with reference to the accompanying drawings. It is to be understood that the specific embodiments described herein are merely illustrative of some embodiments of the invention and are not limiting of the invention, and that all other embodiments obtained by those of ordinary skill in the art without the exercise of inventive faculty are within the scope of the 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 those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention. Furthermore, the terms "a," "an," "first," "second," "third," "fourth," "fifth," and "sixth" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
For the purposes of simplicity and explanation, the principles of the embodiments are described by referring mainly 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 skilled in the art that the embodiments may be practiced without 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 diaphragm, including the substrate and coating at the coating on substrate surface, wherein, this coating has top layer and at least one deck inlayer, and top layer and inlayer are porous structure, and the hole of top layer and the hole of inlayer are the nested structure, specifically as shown in figure 1.
In the above technical solution, in the embodiment of the present application, the coating layer has a multi-layer hole nesting structure, and the nesting includes a "skeleton network" on the top layer and a "sub-network" on the inner layer, so as to form a structure in which holes are nested in the inner layer of the top layer. The top layer ' skeleton network ' has no air permeability loss, the skeleton network ' increases the attachment of the diaphragm and the pole piece, and the branched chain surface gel enhances the adhesive force, thereby improving the adhesive force between the coating and the diaphragm and between the diaphragm and the pole piece; the inner "subnetwork" results in less loss of gas permeability and improved adhesion. Simultaneously, multilayer hole pile cover structure in this application can avoid appearing sclausura polymer "blind spot", and the porosity is big, ventilative loss is little, greatly improves to coat and pole piece high bonding, and unique network coating structure has increased the lithium storage space simultaneously, does benefit to lithium electricity process circulation, prevents that dendritic crystal from producing, phenomenon such as separating lithium, improves lithium cell cycle life.
In contrast, the coating layer is formed by mixing a hydrophobic binder polymer and an amphiphilic binder polymer, and the porous structure of the coating layer is formed by adopting the following steps:
(a) sequentially dissolving a hydrophobic adhesive polymer and an amphiphilic adhesive polymer into a solvent, then adding a pore-forming agent, and mixing and stirring to obtain a mixed glue solution;
(b) the polymer mixed solution is coated on a substrate, and the substrate is dried.
In the technical scheme, the multi-layer pore structure is formed on the surface of the substrate through the pore-forming agent and the amphiphilic adhesive polymer. Specifically, on the one hand, when the pore-forming agent is separated from the coating, the coating is enabled to form holes; on the other hand, due to the hydrophilic property of the amphiphilic binder polymer, water or water vapor rapidly penetrates the inside of the coating layer, accelerating the formation of pores in the inner layer.
The top layer holes and the inner layer holes thus formed may have the following characteristics: the pore size of the top layer can be larger than or equal to that of the inner layer, the pore size of the top layer is preferably 1-10 μm, and the pore size of the inner layer is preferably 0.01-10 μm. Further, the inner layer can be a multilayer structure, and the inner layers of the plurality of layers have different apertures and different sizes and are overlapped in a crossed mode.
The hydrophobic binder polymer provides high viscosity for the coating, and specifically, one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyacrylonitrile, PMMA, PAI, PI, aramid fiber and the like can be used, without limiting the application.
The amphiphilic binder polymer simultaneously contains hydrophilic and hydrophobic groups, when the amphiphilic binder polymer is mixed with the hydrophobic polymer, part of the amphiphilic binder polymer is wrapped on the surface of the hydrophobic polymer branched chain, and the hydrophilic end is exposed outwards to form gel. The hydrophilic characteristic of the amphiphilic adhesive polymer is utilized, so that water or water vapor can quickly penetrate into the coating, and the profile with internal holes is accelerated. Specifically, the amphiphilic binder polymer may be one or more of modified polyethylene glycol such as polyethylene glycol methacrylate, polystyrene-polyethylene glycol, methoxypolyethylene glycol polylactic acid, polyisobutylene-l-poly (N, N-dimethylacrylamide), cyanohydrin ether, polyvinyl alcohol, acrylamide, and cellulose, without limiting the present application.
The pore-forming agent is a compound with a boiling point of 50-400 ℃, and at least comprises one group selected from carboxyl, hydroxyl, acrylate, ether and maleic anhydride, and specifically can adopt one or more of ethyl acetate, ethylene glycol dimethyl ether, acrylic acid, butyl acetate, polyvinylpyrrolidone and sorbitan monooleate, and is not limited in application. The pore-forming agent is separated from the coating in the drying process of the diaphragm, so that pores are formed in the coating.
The solvent is one of acetone, DMAC, NMP, tetrahydrofuran, dichloromethane, chloroform, and cyclohexane, and the application is not limited.
Furthermore, in the mixed glue solution, the total weight of the adhesive polymer accounts for 0.5-15 wt%, the pore-forming agent accounts for 1-50 wt%, and the solvent accounts for 40-98 wt%. Wherein, if the total amount of the binder polymer exceeds 15 wt%, pores of the coating layer are poorly formed, increasing the internal resistance of the battery. If the content of the pore-forming agent is less than 1 wt%, pore-forming of the coating is affected, the porosity is reduced, the nested structure is damaged, and if the content of the pore-forming agent is more than 50 wt%, pore-forming is too fast, so that the peeling phenomenon of the coating layer occurs.
Further, in the binder polymer, the amphiphilic binder polymer accounts for 0.1 wt% to 50 wt% of the total amount of the binder polymer. When the proportion of the amphiphilic binder polymer is less than 0.1 wt%, the pore-forming effect is poor, the formation of a nesting network is influenced, and the binding power is weakened; above 50 wt%, the coating is liable to come off.
In addition, the application also discloses a preparation method of the diaphragm, which comprises the following steps:
preparing slurry: dissolving a hydrophobic adhesive polymer into a solvent, then adding an amphiphilic adhesive polymer, and mixing and stirring to obtain a mixed glue solution; adding a pore-forming agent into the mixed glue solution, and uniformly dispersing to obtain coating slurry;
coating slurry: coating the coating slurry on at least one surface of the base material to form a coating on the surface of the base material, and then drying the base material to obtain a diaphragm;
the coating is provided with a top layer and at least one inner layer, the top layer and the inner layer are both of porous structures, and holes of the top layer and holes of the inner layer are of a nested structure.
Wherein, the coating mode adopts one of micro-concave plate, rotary spraying and extrusion coating.
For the technical scheme, the coating is in a multi-layer hole nesting structure, and the nesting comprises a skeleton network at the top layer and a sub-network at the inner layer, so that the structure of holes in the inner layer of the hole nesting at the top layer is formed. Compared with the water-based coating diaphragm in the prior art, the top layer 'skeleton network' in the application has no ventilation loss, the 'skeleton network' increases the adhesiveness of the diaphragm and the pole piece, and the branched chain surface gel enhances the adhesive force, so that the adhesive force between the coating and the diaphragm and between the diaphragm and the pole piece is improved; the inner "subnetwork" results in less loss of gas permeability and improved adhesion. The conventional oily diaphragm only has a porous layer, when the using amount is increased, the porosity of the coating is reduced by double, the service life of the lithium battery is rapidly shortened, and the air permeability loss can be reduced to a certain degree by reducing the using amount, but the adhesive force can be weakened greatly. The multilayer hole nested structure in this application avoids appearing sclausura polymer "blind spot", and the porosity is big, the air loss is little, greatly improves and films and pole piece high bonding, and unique network coating structure has increased the storage lithium space simultaneously, does benefit to lithium electricity process circulation, prevents that dendritic crystal from producing, phenomenons such as appearance lithium, improves lithium cell cycle life.
In order to further illustrate the above technical effects, the present application will refer to the following examples and comparative examples for comparison, but the present application is not limited to these examples.
[ example 1 ]
(1) Adding 5.5% (wt%, the same below) of polyvinylidene fluoride into 88% of DMAC, stirring for 2h, then adding 3.5% of methoxy polyethylene glycol polylactic acid, and stirring for 2h to obtain a mixed glue solution;
(2) adding 3% of sorbitan monooleate, and stirring for 1h to obtain coating slurry;
(3) coating the coating slurry on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating film; the coating film forms a nested structure, the large aperture of the top layer is about 3-5 μm, and the small aperture of the inner layer is 0.2-0.5 μm.
[ example 2 ]
(1) Adding 8.5% (wt%, the same below) polyvinylidene fluoride into 88% DMAC, stirring for 2h, then adding 0.5% methoxy polyethylene glycol polylactic acid, and stirring for 2h to obtain a mixed glue solution;
(2) adding 3% of sorbitan monooleate, and stirring for 1h to obtain coating slurry;
(3) coating the coating slurry on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating film; the coating film forms a nested structure, the large aperture of the top layer is about 1-4 μm, and the small aperture of the inner layer is 0.1-0.4 μm.
[ example 3 ]
(1) Adding 5.5% (wt%, the same below) of polyvinylidene fluoride into 71% of DMAC, stirring for 2h, then adding 3.5% of methoxy polyethylene glycol polylactic acid, and stirring for 2h to obtain a mixed glue solution;
(2) adding 20% of sorbitan monooleate, and stirring for 1h to obtain coating slurry;
(3) coating the coating slurry on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating film; the coating film forms a nested structure, the large aperture of the top layer is about 3-6 μm, and the small aperture of the inner layer is 0.3-0.7 μm.
[ example 4 ]
(1) Adding 8.5% (wt%, the same below) polyvinylidene fluoride into 71% DMAC, stirring for 2h, then adding 0.5% methoxy polyethylene glycol polylactic acid, and stirring for 2h to obtain a mixed glue solution;
(2) adding 20% of sorbitan monooleate, and stirring for 1h to obtain coating slurry;
(3) coating the coating slurry on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating film; the coating film forms a nested structure, the large aperture of the top layer is about 2-5 μm, and the small aperture of the inner layer is 0.2-0.4 μm.
[ example 5 ]
(1) Adding 8% (wt%, the same below) of polyvinylidene fluoride into 71% of DMAC, stirring for 2h, then adding 1% of methoxypolyethylene glycol polylactic acid, and stirring for 2h to obtain a mixed glue solution;
(2) adding 20% of sorbitan monooleate, and stirring for 1h to obtain coating slurry;
(3) coating the coating slurry on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating film; the coating film forms a nested structure, the large aperture of the top layer is about 3-5 μm, and the small aperture of the inner layer is 0.05-0.4 μm.
[ example 6 ]
(1) Adding 7% (wt%, the same below) of polyvinylidene fluoride into 71% of DMAC, stirring for 2h, then adding 2% of methoxypolyethylene glycol polylactic acid, and stirring for 2h to obtain a mixed glue solution;
(2) adding 20% of sorbitan monooleate, and stirring for 1h to obtain coating slurry;
(3) coating the coating slurry on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating film; the coating film forms a nested structure, the large aperture of the top layer is about 3-5 μm, and the small aperture of the inner layer is 0.3-0.6 μm.
[ example 7 ]
(1) Adding 5% (wt%, the same below) of polyvinylidene fluoride into 71% of DMAC, stirring for 2h, then adding 4% of methoxypolyethylene glycol polylactic acid, and stirring for 2h to obtain a mixed glue solution;
(2) adding 3% of sorbitan monooleate, and stirring for 1h to obtain coating slurry;
(3) coating the coating slurry on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating film; the coating film forms a nested structure, the large aperture of the top layer is about 3-5 μm, and the small aperture of the inner layer is 0.2-0.5 μm.
[ example 8 ]
(1) Adding 5.5% (wt%, the same below) polyvinylidene fluoride into 81% DMAC, stirring for 2h, then adding 3.5% methoxy polyethylene glycol polylactic acid, and stirring for 2h to obtain a mixed glue solution;
(2) adding 10% sorbitan monooleate, and stirring for 1h to obtain coating slurry;
(3) coating the coating slurry on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating film; the coating film forms a nested structure, the large aperture is about 2-5 μm, and the small aperture is 0.2-0.6 μm.
[ example 9 ]
(1) Adding 5.5% (wt%, the same below) of polyvinylidene fluoride into 56% of DMAC, stirring for 2h, then adding 3.5% of methoxy polyethylene glycol polylactic acid, and stirring for 2h to obtain a mixed glue solution;
(2) adding 35% of sorbitan monooleate, and stirring for 1h to obtain coating slurry;
(3) coating the coating slurry on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating film; the coating film forms a nested structure, the large aperture of the top layer is about 4-7 μm, and the small aperture of the inner layer is 0.3-0.7 μm.
[ example 10 ]
(1) Adding 5.5% (wt%, the same below) of polyvinylidene fluoride into 46% of DMAC, stirring for 2h, then adding 3.5% of methoxy polyethylene glycol polylactic acid, and stirring for 2h to obtain a mixed glue solution;
(2) adding 3% of sorbitan monooleate, and stirring for 1h to obtain coating slurry;
(3) coating the coating slurry on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating film; the coating film forms a nested structure, the large aperture of the top layer is about 4-9 μm, and the small aperture of the inner layer is 0.2-0.6 μm.
Comparative example 1
(1) Adding 9% (wt%, the same below) polyvinylidene fluoride into 88% DMAC, and stirring for 2h to obtain a mixed glue solution;
(2) adding 3% of sorbitan monooleate, and stirring for 1h to obtain coating slurry;
(3) coating the coating slurry on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating film; the coating film does not form a nested structure, and only has one layer of holes with the aperture of about 0.1-1 μm.
Comparative example 2
(1) Adding 3.5% (wt%, the same below) of polyvinylidene fluoride into 88% of DMAC, stirring for 2h, then adding 5.5% of methoxy polyethylene glycol polylactic acid, and stirring for 2h to obtain a mixed glue solution;
(2) adding 3% of sorbitan monooleate, and stirring for 1h to obtain coating slurry;
(3) coating the coating slurry on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating film; the pore diameter of the coating film is larger than 10 μm, and the adhesion of the coating film is insufficient.
Comparative example 3
(1) Adding 5.5% (wt%, the same below) of polyvinylidene fluoride into 91% of DMAC, stirring for 2h, then adding 3.5% of methoxy polyethylene glycol polylactic acid, and stirring for 2h to obtain a mixed glue solution;
(3) coating the mixed glue solution on one surface of a 9-micron polyethylene substrate, and drying to obtain a polymer coating; the coating film forms a nested structure, the large aperture of the top layer is about 1-5 μm, and the small aperture of the inner layer is 0.1-0.5 μm.
The examples and comparative examples were then tested for air permeability values, according to the GB/T458 specification.
The measuring method comprises the following steps: the composite separators of experimental examples 1 to 10 and comparative examples 1 to 3 were tested for air permeability value (unit: sec/100cc) using an asahi jowar air permeability tester and the air permeability increase value was calculated, and the results are shown in table 1.
The air permeability value, which reflects the permeability of the membrane, is the time (seconds) it takes 100ml of air to penetrate a certain area of the membrane under a certain pressure in an air permeameter.
TABLE 1 air permeability values (units: sec/100cc) and air permeability increase values
| Air permeability value of base film | Air permeability value of the diaphragm | Air permeability increase | |
| Example 1 | 146 | 157 | 11 |
| Example 2 | 148 | 163 | 15 |
| Example 3 | 150 | 159 | 9 |
| Example 4 | 145 | 158 | 13 |
| Example 5 | 147 | 159 | 12 |
| Example 6 | 145 | 159 | 14 |
| Example 7 | 148 | 155 | 7 |
| Example 8 | 149 | 163 | 14 |
| Example 9 | 152 | 165 | 13 |
| Example 10 | 151 | 162 | 11 |
| Comparative example 1 | 152 | 210 | 58 |
| Comparative example 2 | 148 | Coating detachment anomaly | / |
| Comparative example 3 | 155 | 197 | 42 |
As is clear from Table 1, the gas permeability of the separators of examples 1 to 10 was small and was 20 or less. Comparative example 1 shows that the increase in air permeability is greater without the addition of the amphiphilic binder polymer; in comparative example 2, however, the coating layer was peeled off when the amphiphilic binder polymer was present in an amount exceeding 50%; comparative example 3 shows that the gas permeability increase is higher when sorbitan monooleate, a pore-forming agent, is eliminated.
Next, examples 1 to 10 and comparative examples 1 to 3 were subjected to adhesion test, and the adhesion was expressed by the peel force between the coating film and the substrate, and between the separator and the electrode sheet.
First, the peel force between the coating film and the substrate was tested as follows: pasting a layer of double-sided adhesive tape on a steel plate, flatly and lightly pressing a diaphragm on the double-sided adhesive tape, then pasting a layer of test adhesive tape on the coating film, and holding a press roller (2000g) to roll on the test adhesive tape back and forth for three times;
tearing one end of the adhesive tape to the middle position of the sample, peeling off the adhesive tape by 180 degrees by using an experimental tensile machine, and peeling speed: 50mm/min, and the stripping test time is 1 min;
the test tensile value was divided by the width of the corresponding tape to obtain the final peel force N/m.
Second, the peel force between the separator and the pole piece was tested. Preparing a positive plate: 50 parts of lithium manganate, 10 parts of polyvinylidene fluoride, 5 parts of acetylene black and 80 parts of NMP are mixed, stirred, pulped, coated on two sides of an aluminum foil and dried to obtain a positive plate, and the thickness of the coating is 25 microns.
Test samples were prepared using the composite separators of experimental examples 1 to 10 and comparative examples 1 to 3 and the above-described positive electrode sheets as follows: and sequentially laminating the positive plate, the diaphragm, the positive plate and the diaphragm … … to 4 layers, hot-pressing for 10min at 90 ℃ and under the pressure of 4MPa, and cooling to test the stripping force of the diaphragm and the pole piece.
The peel force measurements were the same as for the film coating test method.
The test results are summarized in Table 2.
Table 2 adhesion test
As shown in table 2, the polymer composite coating containing the amphiphilic binder polymer greatly improved the adhesion of the coating to the separator, and also improved the adhesion between the separator and the pole piece. Specifically, the adhesive force is improved in the embodiments 1 to 10, and the adhesive force between the diaphragm and the pole piece is larger than 10N/m. As can be seen from comparative example 1, the polymer composite coating containing methoxy polyethylene glycol polylactic acid is beneficial to the adhesion of the pole piece; as can be seen from comparative example 3, the elimination of the pore former had no significant effect on the adhesion.
Then, testing the adhesive force between the diaphragm and the pole piece after being soaked by the electrolyte, wherein the testing method comprises the following steps:
1. compounding the diaphragm and the pole piece by hot pressing according to the method;
2. the compounded membrane is completely soaked in an electrolyte for 24 hours (the electrolyte is an organic electrolyte containing 1mol/L LiPF6, wherein the solvent is ethylene carbonate, diethyl carbonate, dimethyl carbonate and ethylene carbonate, and the ratio of the ethylene carbonate to the ethylene carbonate is 3:2:1: 1);
3. absorbing electrolyte on the surface and the periphery of the soaked membrane by using filter paper, and peeling off at 180 degrees by using a test tensile machine, wherein the peeling speed is as follows: 50mm/min, the stripping test duration is 1 min.
And observing whether the positive coating falls off along with the diaphragm after stripping. The test and observation results are shown in table 3.
TABLE 3 adhesion between separator and electrode plate after soaking in electrolyte
| Positive electrode coatingWhether or not a layer is peeled off | |
| Example 1 | Falling off |
| Example 2 | Falling off |
| Example 3 | Falling off |
| Example 4 | Falling off |
| Example 5 | Falling off |
| Example 6 | Falling off |
| Example 7 | Falling off |
| Example 8 | Falling off |
| Example 9 | Falling off |
| Example 10 | Falling off |
| Comparative example 1 | Is not fallen off |
| Comparative example 2 | / |
| Comparative example 3 | Falling off |
As shown in table 3, "peeling" means that the positive electrode coating material was peeled off from the separator due to the high adhesion of the separator coating polymer, and "non-peeling" means that the positive electrode material was intact and the separator could be peeled off more completely. Table 3 shows that the polymer composite coating containing the amphiphilic binder can improve the binding force between the separator and the pole piece after being soaked in the electrolyte.
Finally, the polymer diaphragms of the examples 1 to 10 and the comparative examples 1 to 3, the ternary positive pole piece and the graphite negative pole piece are manufactured into the flexible package lithium ion battery by adopting a winding process, and the discharge rate test is carried out.
And (3) testing discharge rate: and (3) charging the lithium ion battery to 4.2V at a constant current and a constant voltage of 0.5C respectively, then charging at a constant voltage until the current is reduced to 0.05C, stopping the charging, then discharging to 3.0V at currents of 0.2C and 2.0C respectively, and recording the discharge capacity under different discharge rates. The corresponding battery capacity retention was calculated with the discharge capacity at 0.2C as 100%, and the results are shown in table 4.
Here, the capacity retention rate at a certain rate of discharge is (discharge capacity at that rate of discharge/discharge capacity at 0.2C rate of discharge) × 100%.
TABLE 4 Battery capacity retention at different discharge rates
| 0.2C | 2C | |
| Example 1 | 100％ | 94.37％ |
| Example 2 | 100％ | 92.55％ |
| Example 3 | 100％ | 94.68％ |
| Example 4 | 100％ | 93.16％ |
| Example 5 | 100％ | 92.86％ |
| Example 6 | 100％ | 93.48％ |
| Example 7 | 100％ | 94.92％ |
| Example 8 | 100％ | 94.57％ |
| Example 9 | 100％ | 94.21％ |
| Example 10 | 100％ | 93.45％ |
| Comparative example 1 | 100％ | 80.28％ |
| Comparative example 2 | 100％ | / |
| Comparative example 3 | 100％ | 85.89％ |
As shown in table 4, in the nested polymer separators of examples 1 to 10, which were prepared by the method according to the present invention, the capacity retention rate was increased.
Although the illustrative embodiments of the present application have been described above to enable those skilled in the art to understand the present application, the present application is not limited to the scope of the embodiments, and various modifications within the spirit and scope of the present application defined and determined by the appended claims will be apparent to those skilled in the art from this disclosure.
Claims (21)
1. A septum, comprising:
a substrate;
the coating, the coating sets up the surface of at least one side of substrate, the coating has top layer and at least one deck inlayer, the top layer with the inlayer is porous structure, the hole of top layer with the hole of inlayer is the nested structure.
2. A membrane according to claim 1, wherein the pore size of the top layer is equal to the pore size of the inner layer.
3. A membrane according to claim 1, wherein the pore size of the top layer is larger than the pore size of the inner layer.
4. A separator as claimed in claim 1, wherein said inner layer is a multilayer structure, said inner layers of the multilayer having different pore sizes, and said pore sizes are alternately nested.
5. A separator as claimed in claim 1, wherein said top layer has a pore size of 1-10 μm.
6. A separator as claimed in claim 1, wherein the inner layer has a pore size of 0.01 to 10 μm.
7. The separator of claim 1, wherein said coating layer is formed by blending a hydrophobic binder polymer and an amphiphilic binder polymer.
8. The separator of claim 7, wherein said hydrophobic binder polymer is one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyacrylonitrile, PMMA, PAI, PI, aramid, etc.
9. The separator of claim 7, wherein the amphiphilic binder polymer comprises hydrophilic and hydrophobic groups, and the amphiphilic binder polymer is one or more selected from polyethylene glycol methacrylate, polystyrene-polyethylene glycol, methoxypolyethylene glycol polylactic acid, polyisobutylene-l-poly (N, N-dimethylacrylamide), modified polyethylene glycol such as cyanohydroxyethylcellulose ether, polyvinyl alcohol, acrylamide, and cellulose.
10. A separator as claimed in claim 7, wherein the porous structure of the coating is formed by any method selected from the group consisting of:
the method comprises the steps of sequentially dissolving the hydrophobic adhesive polymer and the amphiphilic adhesive polymer into a solvent, adding a pore-forming agent, and mixing and stirring to obtain a mixed glue solution; and
a method comprising the steps of coating a polymer mixed solution on the substrate, and drying the substrate.
11. A separator as claimed in claim 7, wherein said pore former is a compound having a boiling point in the range of 50 ℃ to 400 ℃.
12. The separator of claim 7, wherein said pore-forming agent is one or more of ethyl acetate, ethylene glycol dimethyl ether, acrylic acid, butyl acetate, polyvinylpyrrolidone, and sorbitan monooleate.
13. A separator as claimed in claim 7, wherein said pore forming agent comprises at least one group selected from carboxyl, hydroxyl, acrylate, ether and maleic anhydride.
14. A membrane according to claim 7, wherein the solvent is one of acetone, DMAC, NMP, tetrahydrofuran, dichloromethane, chloroform and cyclohexane.
15. The diaphragm of claim 7, wherein in the mixed glue solution, the total amount of the binder polymer accounts for 0.5-15 wt%, the pore-forming agent accounts for 1-50 wt%, and the solvent accounts for 40-98 wt%.
16. The separator as claimed in claim 15, wherein said amphiphilic binder polymer is present in said binder polymer in an amount of 0.1 to 50 wt% based on the total amount of said binder polymer.
17. A method for preparing a separator, comprising the steps of:
preparing slurry: dissolving a hydrophobic adhesive polymer into a solvent, then adding an amphiphilic adhesive polymer, and mixing and stirring to obtain a mixed glue solution; adding a pore-forming agent into the mixed glue solution, and uniformly dispersing to obtain coating slurry;
coating slurry: coating the coating slurry on at least one surface of the base material to form a coating on the surface of the base material, and then drying the base material to obtain a diaphragm;
the coating is provided with a top layer and at least one inner layer, the top layer and the inner layer are both of porous structures, and holes of the top layer and holes of the inner layer are of a nested structure.
18. The method of claim 17, wherein the coating is selected from the group consisting of micro-gravure, spin coating, and extrusion coating.
19. A battery, comprising:
a positive electrode plate;
a negative pole piece;
a separator as defined in any one of claims 1 to 16 or a separator produced by the production method as defined in any one of claims 17 to 18;
and (3) an electrolyte.
20. An object, characterized in that the object comprises a battery according to claim 19.
21. An object according to claim 20, wherein the object is an electronic product or an electric vehicle.
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