Diaphragm and electrochemical device

Abstract

The invention provides a diaphragm and an electrochemical device, and particularly relates to the technical field of batteries. The diaphragm comprises a porous base membrane and a heat-resistant layer, wherein the heat-resistant layer is arranged on at least one surface of the porous base membrane; wherein the heat-resistant layer comprises a ceramic material and a first adhesive, and D50 / (BET of the ceramic material / D50 of the ceramic material) of the first adhesive is less than or equal to 0.5%. The surface of the heat-resistant layer of the diaphragm is smooth and compact, so that the effective contact area of the heat-resistant layer and the porous base membrane can be increased, the bonding force between the heat-resistant layer and the porous base membrane is further improved, and the problem of insufficient bonding force between the diaphragm and a pole piece is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a diaphragm and an electrochemical device. Background Art

[0002] Lithium-ion batteries have the advantages of high operating voltage, high energy density, long cycle life, low self-discharge, and no memory effect, so they are widely used in digital products, electric vehicles, energy storage and other fields. As an important component of lithium-ion batteries, the separator not only isolates the positive and negative electrodes to avoid short circuits, but also provides a channel for lithium ion migration and transmission due to its porous structure.

[0003] At present, the commercialized diaphragm is mainly a polyolefin microporous membrane. Although the polyolefin diaphragm can provide sufficient mechanical strength and chemical stability at room temperature, it shows a large thermal shrinkage under high temperature conditions, which causes the positive and negative electrodes to contact and quickly accumulate a large amount of heat, causing the battery to catch fire or explode due to a short circuit. In terms of improving the performance of the diaphragm, the main method is to apply ceramic coating to the diaphragm to improve the heat resistance and safety of the diaphragm, as well as to improve the mechanical strength of the diaphragm, thereby extending the service life of the diaphragm. However, this type of diaphragm often encounters the problem of insufficient adhesion, resulting in wrinkles on the fully charged interface, which affects the cycle performance of the battery. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention provides a diaphragm and an electrochemical device to improve the problem of cell interface wrinkles caused by insufficient adhesion between the diaphragm and the electrode.

[0005] To achieve the above-mentioned purpose and other related purposes, the first aspect of the present invention provides a diaphragm, which includes: a porous base film and a heat-resistant layer, wherein the heat-resistant layer is arranged on at least one surface of the porous base film; wherein the heat-resistant layer includes a ceramic material and a first adhesive, and the D50 / (BET of the ceramic material / D50 of the ceramic material) of the first adhesive is ≤0.5%.

[0006] In one embodiment of the present invention, the ratio of the BET of the ceramic material to the D50 of the ceramic material is in a range of 40 to 80.

[0007] In one embodiment of the present invention, the microstructure of the ceramic material is flaky particles.

[0008] In one embodiment of the present invention, the diaphragm also includes an adhesive layer, which is arranged on the porous base film and / or the heat-resistant layer. The adhesive layer includes a polymer and a second adhesive, and the polymer includes at least one of polyvinylidene fluoride, polymethyl methacrylate, and acrylate.

[0009] In one embodiment of the present invention, the ratio of D50 of the second adhesive to D50 of the ceramic material is in a range of 0.1 to 0.2.

[0010] In one embodiment of the present invention, the effective adhesion R of the diaphragm is 50% to 80%, wherein the effective adhesion refers to the ratio of the effective bonding area to the theoretical bonding area per unit area of ​​the diaphragm.

[0011] In one embodiment of the present invention, the bulk density of the heat-resistant layer is 1.2 to 2.0 g / cm 3 .

[0012] In one embodiment of the present invention, the coating amount of the adhesive layer is 0.5 to 1.25 g / m 2 .

[0013] In one embodiment of the present invention, the first adhesive and the second adhesive are independently selected from at least one of acrylate, acrylonitrile, and acrylic polymer.

[0014] A second aspect of the present invention provides an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the separator is any of the separators described above in the present invention.

[0015] The diaphragm provided by the present invention adjusts the relationship between the ceramic material particles and the adhesive particles in the heat-resistant layer so that the flat and small ceramic particles and the adhesive with a large size difference from the ceramic particles are tightly bonded to form a heat-resistant layer with a smooth surface and a dense surface. Compared with the uneven heat-resistant layer, the effective contact area between the heat-resistant layer and the porous base film of the present invention is increased, and the effective contact area between the adhesive in the heat-resistant layer and the porous base film is increased, and then the bonding force between the heat-resistant layer and the porous base film is improved, which can effectively improve the problem of insufficient bonding force between the diaphragm and the pole piece.

[0016] Furthermore, an adhesive layer is provided on the heat-resistant layer or the porous base film. After hot pressing, an adhesive force is formed between the adhesive layer and the pole piece, which has the effect of battery shaping. At the same time, it can also inhibit the wrinkling and deformation of the battery cell caused by the expansion of the pole piece after the cycle, thereby improving the cycle life of the battery. In addition, the flat and dense surface of the heat-resistant layer also increases the effective contact area between the adhesive layer and the heat-resistant layer, further improving the adhesion between the diaphragm and the pole piece.

[0017] Furthermore, the particle size ratio of the adhesive in the bonding layer and the ceramic material in the heat-resistant layer is adjusted so that the adhesive particles in the bonding layer are stuck in the dense stacking gaps of the heat-resistant layer, and the bottom of the adhesive is fixed and the top protrudes from the stacking gaps of the heat-resistant layer, thereby improving the connection force between the bonding layer and the heat-resistant layer and effectively increasing the number of effective bonding points of the bonding layer.

[0018] Furthermore, the effective bonding degree of the diaphragm is controlled to be 50-80%, so that the density of effective bonding points is sufficient, thereby improving the bonding force between the diaphragm and the pole piece. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying creative work.

[0020] Figure 1 It is a schematic structural diagram of a diaphragm of the present invention in one embodiment;

[0021] Figure 2 is a schematic structural diagram of a diaphragm of the present invention in another embodiment;

[0022] Figure 3 A schematic diagram of the internal particle arrangement of the diaphragm of the present invention in one embodiment;

[0023] Figure 4 FIG. 4 is a schematic structural diagram of an electrochemical device according to an embodiment of the present invention.

[0024] Component number description:

[0025] 100, separator; 110, porous base film; 120, heat-resistant layer; 130, adhesive layer; 200, lithium-ion battery. DETAILED DESCRIPTION

[0026] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0027] It should be noted that, in the absence of conflict, the features in the following examples and embodiments can be combined with each other. It should also be understood that the terms used in the examples of the present invention are intended to describe specific embodiments rather than to limit the scope of the present invention. The test methods in the following examples that do not specify specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturers.

[0028] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" etc. used in this specification are only for the convenience of description and are not intended to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships, without substantially changing the technical content, should also be regarded as the scope of implementation of the present invention.

[0029] Herein, when it comes to numerical ranges, unless otherwise specified, the distribution of optional values ​​within the numerical range is considered continuous and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical range, as well as each value between the two numerical endpoints. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be combined. Unless otherwise defined, all technical and scientific terms used in the present invention are familiar to those skilled in the art and the description of the present invention, and any methods, devices and materials of the prior art similar or equivalent to the methods, devices, and materials in the embodiments of the present invention can also be used to implement the present invention.

[0030] In this document, "multiple", "multiple", "multiple times", etc., unless otherwise specified, refer to a number greater than 2 or equal to 2. For example, "one or more" means one or greater than or equal to two. "Further", "further", "particularly", etc. are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of the present invention.

[0031] D50 is a parameter commonly used in particle size testing, which indicates the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%. Specifically, the physical meaning of D50 is that particles with a particle size greater than D50 account for 50%, and particles with a particle size less than D50 also account for 50%. Therefore, D50 is also called the median diameter or median particle size, and is often used to indicate the average particle size of powders. In this article, D50 is tested by Malvern 3000 particle size analyzer.

[0032] BET (Brunauer-Emmett-Teller) is a test method for measuring the specific surface area of ​​a material. The BET in this article is measured by a NOVA-4200e specific surface area analyzer.

[0033] When the diaphragm forms a battery cell with the positive and negative electrodes, it is necessary to maintain a certain connection force with the electrodes to prevent the battery cell from wrinkling and deforming due to the expansion of the electrodes during the cycle. However, at present, the diaphragm and the electrodes always fall off. The reason is the insufficient adhesion between the diaphragm and the electrodes. The inventors of this application found in their research that the insufficient adhesion between the diaphragm and the electrodes is closely related to the heat-resistant layer. The contact area between the heat-resistant layer and the porous base film is the sum of the top areas of each bump. If the surface of the heat-resistant layer is uneven, the effective bonding area between the heat-resistant layer and the porous base film is insufficient, which will cause the heat-resistant layer and the porous base film to fall off due to insufficient adhesion.

[0034] Based on this, the present invention provides a diaphragm and an electrochemical device. By adjusting the relationship between the ceramic material particles and the adhesive particles in the heat-resistant layer, the flat and small ceramic particles and the adhesive with a large size difference from the ceramic particles are tightly bonded to form a heat-resistant layer with a smooth surface and a dense surface, thereby increasing the effective contact area between the heat-resistant layer and the porous base membrane, and increasing the effective contact area between the adhesive in the heat-resistant layer and the porous base membrane, thereby improving the adhesion between the heat-resistant layer and the porous base membrane, and improving the problem of insufficient adhesion between the diaphragm and the electrode.

[0035] See also Figure 1 The present invention provides a diaphragm 100, which includes: a porous base film 110 and a heat-resistant layer 120, wherein the porous base film 110 serves as a substrate of the diaphragm 100, and any porous material having an insulating isolation function and providing a channel for lithium ion transmission in the art can be selected, and the heat-resistant layer 120 is arranged on at least one side surface of the porous base film 110 to improve the heat resistance of the diaphragm 100.

[0036] In one embodiment, the porous base membrane 110 can be a composite of one or more polymer microporous membranes and non-woven membranes. For example, a single-layer or multi-layer composite polymer microporous membrane, a single-layer or multi-layer composite non-woven membrane, or a composite membrane of a polymer microporous membrane and a non-woven membrane can be used. The polymer microporous membrane is selected from polyethylene microporous membrane, polypropylene microporous membrane, polypropylene / polyethylene / polypropylene three-layer composite microporous membrane, polyvinylidene fluoride microporous membrane, polyvinylidene fluoride-hexafluoropropylene microporous membrane, polyimide microporous membrane, etc. The non-woven membrane is selected from polyethylene non-woven membrane, polypropylene non-woven membrane, polyester non-woven membrane, polyimide non-woven membrane, aramid non-woven membrane, spandex non-woven membrane, etc. The thickness of the porous base membrane 110 is generally 3 to 30 mm, the porosity is 20% to 80%, and the air permeability is 50 to 300s / 100cc. The thickness of the porous base membrane 110 can be, for example, 5 mm, 10 mm, 20 mm or 25 mm; the porosity of the porous base membrane 110 can be, for example, 30%, 50% or 70%; the air permeability of the porous base membrane 110 can be, for example, 100s / 100cc, 200s / 100cc or 300s / 100cc. The specific materials and parameters of the porous base membrane 110 can be selected according to actual production and are not limited here.

[0037] Since the porous base film 110 material has a low melting point, it is easy to shrink greatly at high temperature, thereby affecting the safety performance of the battery. The separator 100 of the present invention is provided with a heat-resistant layer 120 on at least one side surface of the porous base film 110, that is, the porous base film 110 has a first surface and a second surface arranged opposite to each other along its thickness direction. The heat-resistant layer 120 can be arranged on the first surface of the porous base film 110, can also be arranged on the second surface of the porous base film 110, and can also be arranged on the first surface and the second surface at the same time ( Figure 1 Only the case where the heat-resistant layer is provided on one side is exemplified. Preferably, the heat-resistant layer 120 is provided on both the first surface and the second surface of the porous base film 110. The provision of the heat-resistant layer 120 can improve the heat resistance of the separator 100.

[0038] See also Figure 1 and Figure 3, the heat-resistant layer 120 includes a ceramic material and a first adhesive, wherein the ceramic material is selected from a high-temperature resistant material, including but not limited to aluminum oxide, hydrated aluminum oxide (boehmite), aluminum hydroxide, silicon dioxide, titanium dioxide, barium sulfate, barium titanate, magnesium hydroxide or magnesium oxide. That is, the ceramic material can be selected from any one of the listed materials, such as aluminum oxide, or titanium dioxide, or magnesium oxide, etc. The ceramic material can also be selected from any combination of two or more of the listed materials, such as a composition of barium sulfate and barium titanate, or a composition of aluminum oxide, hydrated aluminum oxide and aluminum hydroxide, and so on. It should be noted that when the ceramic material is a composition of two or more, there is no restriction on the ratio between the components in the composition, and they can be mixed in any proportion. The first adhesive is filled between the ceramic material particles and is used to bond the ceramic material particles to form the heat-resistant layer 120. The first adhesive is selected from at least one of acrylate, acrylonitrile, and acrylic polymer. That is, the first adhesive can be selected from any one of the materials listed above, such as acrylonitrile, or acrylic polymer, or acrylate, etc. The first adhesive can also be selected from any combination of two or more of the materials listed above, such as a combination of acrylonitrile and acrylic polymer, etc. In order to ensure that the heat resistance of the diaphragm 100 meets the use requirements, the volume proportion of the ceramic material in the heat-resistant layer 120 of the present invention is 80% or more. The content of ceramic material in the heat-resistant layer 120 is too little to meet the heat resistance of the diaphragm 100. At the same time, the low content of ceramic material means that the content of the first adhesive is high. If the content of the first adhesive is too high, the swelling of the adhesive during the cycle will easily cause the heat-resistant layer 120 to close the pores, thereby affecting the cycle performance of the battery. Further, the volume proportion of the ceramic material in the heat-resistant layer 120 is 90% to 99%, and further, the volume proportion of the ceramic material in the heat-resistant layer 120 is 95%.

[0039] In the present invention, the D50 of the first adhesive particles and the D50 and specific surface area BET of the ceramic material particles satisfy the relationship: D50 of the first adhesive / (BET of the ceramic material / D50 of the ceramic material) ≤ 0.5%. Under this condition, it is possible to achieve tight adhesion between the flat and small ceramic particles and the first adhesive having a large size difference with the ceramic particles, and form a heat-resistant layer 120 with a smooth and dense surface after accumulation. The effective contact area between the dense and smooth heat-resistant layer 120 and the porous base film 110 is increased, and the effective contact area between the first adhesive in the heat-resistant layer 120 and the porous base film 110 is increased, thereby improving the bonding force between the heat-resistant layer 120 and the porous base film 110.

[0040] Further, D50 of the first adhesive / (BET of the ceramic material / D50 of the ceramic material) ≤ 0.3%, and further, D50 of the first adhesive / (BET of the ceramic material / D50 of the ceramic material) ≤ 0.1%, and so on.

[0041] In one embodiment, the microstructure of the ceramic material is flaky particles, and the steady-state shape of the flaky ceramic particles is parallel to the contact surface thereof. Under the action of gravity, the flaky ceramic particles tend to be parallel to the plane of the base film, thereby improving the flatness of the surface of the heat-resistant layer 120 formed by them. Further, the ratio of the BET of the ceramic material to the D50 of the ceramic material ranges from 40 to 80, for example, the ratio of the BET of the ceramic material to the D50 of the ceramic material can be 40, 60 or 80, etc. Under this condition, a more densely stacked layer and a smoother surface can be formed, further improving the adhesion between the heat-resistant layer 120 and the porous base film 110.

[0042] The thickness of the heat-resistant layer 120 affects the overall thickness of the separator 100. In one embodiment, the thickness of the heat-resistant layer 120 is 0.5-3.0 μm, and the surface density of the heat-resistant layer per 1 μm is 1.2-2.0 g / m 2 , that is, the bulk density of the heat-resistant layer 120 is 1.2 to 2.0 g / cm 3 As an example, the thickness of the heat-resistant layer 120 may be 0.5 μm, 1 μm, 2 μm or 3 μm, etc.; the bulk density of the heat-resistant layer 120 may be 1.2 g / cm 3 , 1.5g / cm 3 , 1.8g / cm 3 or 2.0g / cm 3 wait.

[0043] The preparation process of the heat-resistant layer 120 is as follows: first, the ceramic material, the first adhesive and the solvent are mixed and stirred in proportion to obtain a ceramic slurry, and then the ceramic slurry is coated on the surface of the porous base film 110 by gravure, micro-gravure, wire rod or spray, and the heat-resistant layer 120 is obtained after curing and drying. Since the solvent is mainly used to disperse inorganic heat-resistant particles and adhesives, and the heat-resistant layer 120 needs to be dried, the amount of solvent does not need to be particularly limited and can be selected according to actual production needs, based on the ability to evenly disperse the ceramic material and the first adhesive. As an example, the amount of solvent added to the ceramic slurry is added based on a solid content of 40wt% in the slurry (ceramic material + first adhesive + additive), and the solvent is, for example, deionized water.

[0044] In one embodiment, the heat-resistant layer 120 further includes a dispersing wetting agent. Adding the dispersing wetting agent to the ceramic slurry can reduce the interfacial tension, so that the ceramic slurry can be better spread on the surface of the porous substrate 110, and can also improve the uniformity of the coating and the engineering capacity of the coating process. The dispersing wetting agent can be selected from polyvinylidene fluoride (PVDF), polyetheretherketone (PEEK), polyethylene terephthalate (PET) or polyimide (PI), etc. These materials have good heat resistance and chemical stability.

[0045] See also Figure 2 and Figure 3 In one embodiment, the diaphragm 100 further includes an adhesive layer 130, which can be disposed on the heat-resistant layer 120, or on the porous base film 110, or on both the heat-resistant layer 130 and the porous base film 110. That is, when the heat-resistant layer 120 is disposed on both sides of the porous base film 110, the adhesive layer 130 is disposed on the heat-resistant layer 120; when the heat-resistant layer 120 is disposed on only one side of the porous base film 110, the adhesive layer 130 can be disposed on the heat-resistant layer 120 or on both the heat-resistant layer 120 and the porous base film 110. After the battery is hot-pressed, the diaphragm 100 is bonded to the pole piece through the adhesive layer 130. The adhesive layer 130 adheres to the surface of the heat-resistant layer 120 and / or the porous base film 110, which can improve the bonding force between the diaphragm 100 as a whole and the pole piece.

[0046] In one embodiment, the adhesive layer 130 includes a polymer and a second adhesive, and the polymer includes at least one of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), and acrylate, that is, the polymer can be selected from any one of the materials listed above or a combination of two or more, such as polyvinylidene fluoride, or polyvinylidene fluoride and polymethyl methacrylate. The second adhesive is selected from at least one of acrylate, acrylonitrile, and acrylic polymer. For example, acrylonitrile, or acrylic polymer, or acrylate, or a combination of acrylonitrile and acrylic polymer. The ratio of the polymer to the second adhesive is, for example, 9:1. When preparing the adhesive layer 130, the second adhesive, deionized water, and polymer are first configured into a slurry in proportion, and then coated on the surface of the heat-resistant layer 120 or the porous base film 110 by spin spraying or the like. Since the surface of the heat-resistant layer 120 is dense and smooth, the adhesive layer 130 coated on the heat-resistant layer 120 can increase the effective contact area between the second adhesive in the adhesive layer 130 and the heat-resistant layer 120 , thereby improving the adhesion between the adhesive layer 130 and the heat-resistant layer 120 .

[0047] In one embodiment, the ratio of D50 of the second adhesive particles to D50 of the ceramic material particles is 0.1 to 0.2, for example, it can be 0.1, 0.15 or 0.2, etc. Under this condition, when the second adhesive particles encounter the stacking gap of the heat-resistant layer 120, they can be stuck in the stacking gap of the heat-resistant layer 120, and the second adhesive will not be directly embedded in the stacking gap of the heat-resistant layer 120, but the bottom is embedded in the stacking gap of the heat-resistant layer 120 to be fixed, and the top protrudes from the stacking gap of the heat-resistant layer 120, thereby increasing the connection force between the heat-resistant layer 120 and the bonding layer 130, and can also effectively increase the number of effective bonding points per unit area of ​​the bonding layer 130.

[0048] In one embodiment, the effective adhesion R of the diaphragm is 50% to 80%, wherein the effective adhesion refers to the ratio of the effective bonding area per unit area of ​​the diaphragm to the theoretical bonding area. Furthermore, the effective adhesion R of the diaphragm is 60% to 80%, for example, the effective adhesion R of the diaphragm can be 60%, 70% or 80%, etc. When the effective adhesion R meets the above range, it can ensure that the bonding density of the pole piece is sufficient. The effective adhesion of the diaphragm can be adjusted by controlling the viscosity of the bonding layer slurry, the rotation speed of the spraying process, the flow rate and other conditions.

[0049] In addition, in principle, the greater the coating amount of the adhesive layer 130, the greater the adhesion between the pole piece and the diaphragm, and the less the interface wrinkle problem of the battery cell. However, the inventors found that in actual production, blindly increasing the coating amount of the adhesive layer 130 did not improve the problem of interface wrinkles due to the increase in the coating amount of the adhesive layer 130. On the contrary, due to the increase in the amount of glue, the coverage rate of the glue on the surface of the diaphragm 100 increased, and the problem of pore plugging easily occurred, thereby increasing the overall impedance of the diaphragm 100 and affecting the dynamic performance of the battery cell. The coating amount of the adhesive layer 130 of the present invention is 0.5g / m 2 Up to 1.25g / m 2 Specifically, the coating amount of the adhesive layer 130 can be 0.5 g / m 2 , 1.0g / m 2 or 1.25g / m 2 Because the surface of the heat-resistant layer 120 is flat and smooth, and the effective contact area with the adhesive layer 130 is large, the adhesive layer 130 of the present invention can achieve a better bonding effect by coating a small amount, and will not affect the impedance of the diaphragm and the dynamic performance of the battery cell.

[0050] The diaphragm of the present invention adjusts the relationship between the particle size and specific surface area of ​​the ceramic material particles and the adhesive particles in the heat-resistant layer to obtain a heat-resistant layer with dense stacking and a flat and smooth surface, which not only increases the effective contact area between the heat-resistant layer and the porous base film, but also improves the bonding force between the heat-resistant layer and the porous base film; when an adhesive layer is provided on the heat-resistant layer, the effective contact area between the adhesive in the adhesive layer and the heat-resistant layer is also increased, so that the bonding force between the adhesive layer and the heat-resistant layer is improved. The improvement of the bonding force on both sides of the heat-resistant layer improves the bonding force between the diaphragm as a whole and the pole piece, which can effectively improve the problem of insufficient bonding force of the diaphragm.

[0051] The present invention further provides an electrochemical device, which comprises the above-mentioned separator 100 of the present invention. The electrochemical device can be a supercapacitor, a lithium ion battery, a sodium ion battery, etc. The following is a detailed description of the electrochemical device being a lithium ion battery as an example, but it is not limited thereto.

[0052] See also Figure 4The lithium-ion battery 200 includes a positive electrode sheet, a negative electrode sheet and a separator 100, wherein the separator 100 is arranged between the positive electrode sheet and the negative electrode sheet to play an insulating isolation role; the positive electrode sheet, the separator and the negative electrode sheet are formed into a bare battery cell by stacking or winding.

[0053] Specifically, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector. The positive electrode current collector may be a metal foil, such as an aluminum foil, or a composite current collector, that is, a polymer resin material is used as an intermediate layer, and aluminum is deposited on the upper and lower surfaces thereof. The polymer resin material may be polyethylene terephthalate PET, polypropylene PP, polyimide PI, polystyrene PS, polyamide PA, etc. The positive electrode current collector has a first surface and a second surface that are disposed oppositely along its thickness direction, and the positive electrode active material layer may be disposed on one of the first surface and the second surface, or may be disposed on both surfaces at the same time. The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder, wherein the positive electrode active material is the main substance involved in the electrochemical reaction, including but not limited to lithium iron phosphate, a ternary positive electrode material, lithium cobalt oxide, or lithium manganese oxide, and other traditional materials that can be used as positive electrode active materials may also be used. These materials may be used alone or in combination. Conductive agents include but are not limited to at least one of conductive carbon black (SP), conductive graphite, carbon fiber, carbon nanotubes, and graphene. Optionally, the conductive agent is conductive carbon black; or, a combination of carbon fiber and conductive carbon black; or, a combination of carbon nanotubes and graphene, and the like. The binder is used to bond the positive electrode active material and the conductive agent, and to provide a certain bonding force for the positive electrode active material layer so that it is bonded to the positive electrode current collector. As an example, the binder is selected from any one or more of polyvinylidene fluoride, polyvinylidene fluoride, polyhexafluoropropylene copolymer poly(vinylidene fluoride-hexafluoropropylene) and poly(acrylonitrile-sodium acrylate), for example, the binder is polyvinylidene fluoride, or a combination of polyvinylidene fluoride and polyvinylidene fluoride, and the like. The ratio of the positive electrode active material, the conductive agent and the binder can be set according to actual production requirements. As an example, the positive electrode active material layer includes a positive electrode active material with a mass percentage of 92 to 98%, a conductive agent with a mass percentage of 1 to 4%, and a binder with a mass percentage of 1 to 4%. The positive electrode active material layer is formed by mixing the positive electrode active material, the conductive agent and the binder in a certain ratio in a solvent and stirring them evenly to form a positive electrode slurry, which is then coated on the positive electrode collector and dried.

[0054] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode current collector can be selected from a metal foil, such as a copper foil, or a composite current collector, that is, a polymer resin material is used as an intermediate layer, and copper is deposited on the upper and lower surfaces thereof, and the polymer resin material can be selected from polyethylene terephthalate PET, polypropylene PP, polyimide PI, polystyrene PS, polyamide PA, etc. The negative electrode current collector has a first surface and a second surface arranged oppositely along its thickness direction, and the negative electrode active material layer can be arranged on one of the first surface and the second surface, or on both surfaces at the same time. The negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder and a thickener, wherein the negative electrode active material can be selected from carbon materials such as artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, and silicon single substance, silicon oxide, silicon carbon material and lithium titanate, etc. However, the present application is not limited to the materials listed above, and other traditional materials that can be used as negative electrode active materials can also be used. These negative electrode active materials can be used alone or in combination of two or more. Conductive agents include but are not limited to at least one of conductive carbon black (SP), conductive graphite, carbon fiber, carbon nanotubes, and graphene. Optionally, the conductive agent is conductive carbon black; or, a composition of carbon fiber and conductive carbon black; or, a composition of carbon nanotubes and graphene, and the like. The binder is used to bond the negative electrode active material and the conductive agent, and to provide a certain bonding force for the negative electrode active material layer so that it is bonded to the negative electrode current collector. As an example, the binder is selected from at least one of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), styrene-acrylate, and acrylic copolymers. For example, the binder is polyvinylidene fluoride, or a composition of styrene-butadiene rubber and carboxymethyl cellulose, and the like. The ratio of the negative electrode active material, the conductive agent, and the binder can be set according to actual production requirements. As an example, the negative electrode active material layer includes 94-97% by mass of negative electrode active material, 1-2% by mass of conductive agent and 2-4% by mass of binder. The negative electrode active material layer is formed by mixing and stirring the negative electrode active material, conductive agent and binder in a solvent in a certain ratio to form a negative electrode slurry, and then coating the negative electrode slurry on the negative electrode current collector and drying it.

[0055] The lithium-ion battery 200 also includes an electrolyte, which can be a solid electrolyte or a liquid electrolyte. In this embodiment, the electrolyte is a liquid electrolyte (i.e., an electrolyte), and the liquid electrolyte includes a lithium salt and an organic solvent. The present application does not limit the specific types of the lithium salt and the organic solvent, and lithium salts and organic solvents known in the art can be selected. As an example, the lithium salt is selected from LiPF 6 , LiBF 4 、LiN(SO 2 F)2 (abbreviated as LiFSI), LiN(CF 3 SO 2 ) 2 (abbreviated as LiTFSI), LiClO 4 、LiAsF 6 、LiB(C 2 O 4 ) 2 (abbreviated as LiBOB), LiBF 2 C 2 O 4 (abbreviated as LiDFOB). The organic solvent is selected from a non-aqueous organic solvent, and the non-aqueous organic solvent may include any type of carbonate and / or carboxylate. The carbonate may include a cyclic carbonate or a chain carbonate. The non-aqueous organic solvent may also include a halogenated compound of a carbonate. Specifically, the organic solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, pentylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), γ-butyrolactone, methyl formate, ethyl formate, ethyl propionate, propyl propionate, and tetrahydrofuran. Normally, the content of lithium salt in the electrolyte is 12% to 17%.

[0056] Furthermore, some functional additives may be added to the liquid electrolyte (electrolyte) according to actual needs, such as vinyl sulfate (DTD), 1,3-propane sultone (PS), vinyl carbonate (VC) or vinyl ethylene carbonate (VEC).

[0057] The lithium-ion battery 200 also includes a shell 210. The shape and material of the shell 210 are related to the type of lithium-ion battery. For example, if the lithium-ion battery 200 is a soft-pack battery, its shell 210 can be packaged with an aluminum-plastic film; if the lithium-ion battery 200 is a square-shell battery or a cylindrical battery, the shell 210 can be a square shell or a cylindrical shell that matches the shape of the bare battery cell, and the material can be stainless steel or other materials.

[0058] It should be noted that the structures not described in detail in the above lithium-ion battery can be configured with reference to the prior art and will not be described in detail here.

[0059] The lithium-ion battery 200 of the present invention can be used in the form of a single cell, a battery module or a battery pack for any electronic device that needs to provide power support. The electronic device includes but is not limited to mobile phones, tablets, laptops, electric toys, battery cars, new energy vehicles, ships, spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, for example, game consoles, electric car toys, electric ship toys and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles and spacecrafts, etc. New energy vehicles can be pure electric vehicles, hybrid vehicles or extended-range vehicles, etc.

[0060] The technical scheme of the present invention is described in detail below through several specific examples and comparative examples. Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the examples are all commercially available.

[0061] Example 1

[0062] See also Figure 1 This embodiment provides a diaphragm 100, which includes a porous base film 110 and a heat-resistant layer 120, wherein the porous base film 110 is a porous polyethylene film with a thickness of 7 μm, and the heat-resistant layer 120 is arranged on both side surfaces of the porous base film 110, and the heat-resistant layer 120 includes a ceramic material and a first adhesive. The parameters of the heat-resistant layer 120 refer to the preparation method and Table 1.

[0063] Diaphragm preparation:

[0064] 1) After 2 parts by weight of an adhesive (acrylate) and 60 parts by weight of water are stirred evenly, 36 parts of ceramic (boehmite) are added, and 2% of a dispersing wetting agent is added and stirred evenly to form a 40%wt ceramic slurry;

[0065] 2) The ceramic slurry is coated on a porous polyethylene film with a thickness of 7 μm by micro-gravure coating or wire rod coating, and an ultra-thin heat-resistant layer is formed after drying to obtain a diaphragm with heat-resistant layers on both sides. The thickness of the heat-resistant layer on one side after drying is 2 μm.

[0066] The present invention also provides Examples 2 to 8 and Comparative Example 1. The changed parameters of each Example and Comparative Example are shown in Table 1, and the remaining steps remain unchanged.

[0067] See also Figure 2 and Figure 3 The present invention further provides embodiments 9 to 28. The difference between embodiments 9 to 28 and embodiment 1 is that an adhesive layer 130 is added, and the membrane parameters of each embodiment are shown in Table 2.

[0068] The preparation methods of the diaphragms of Examples 9 to 28 are as follows:

[0069] 1) After 2 parts by weight of adhesive (acrylate) and 60 parts by weight of water are stirred evenly, 36 parts of ceramic (boehmite) are added, and 2% of dispersing wetting agent is added, and stirred evenly to form a 40%wt ceramic slurry; 90 parts by weight of water are added, 1 part of adhesive (acrylonitrile) and 9 parts of polymer powder (polyvinylidene fluoride, PVDF) are added, and stirred evenly to form a 10%wt coating slurry;

[0070] 2) The ceramic slurry is coated on a porous polyethylene film with a thickness of 7 μm by micro-gravure coating or wire rod coating, and an ultra-thin heat-resistant layer is formed after drying. Among them, the single-sided thickness of the heat-resistant layer after drying is 2 μm. The above slurry is coated on a substrate by micro-gravure coating or wire rod coating, and an ultra-thin heat-resistant layer is formed after drying, and the thickness of the heat-resistant layer is 2 μm; then the glue-coated slurry is sprayed on the surface of the heat-resistant layer (thickness see Table 2), and a diaphragm with an adhesive layer and a heat-resistant layer on both sides is obtained.

[0071] See also Figure 4 The present invention also assembles the diaphragms prepared in Examples 1 to 28 and Comparative Example 1 into lithium ion batteries respectively. The preparation process of the lithium ion battery is as follows:

[0072] (1) Preparation of positive electrode sheet

[0073] The positive electrode active material NCM622 (Ni, Co, Mn molar ratio 6:2:2), the conductive agent acetylene black, and the adhesive polyvinylidene fluoride (PVDF) are fully stirred and mixed in N-methylpyrrolidone at a weight ratio of 96:2:2, coated on the positive electrode current collector aluminum foil, and then dried and cold pressed to obtain the positive electrode sheet.

[0074] (2) Negative electrode sheet preparation

[0075] The negative electrode active material artificial graphite, the conductive agent acetylene black, the adhesive styrene-butadiene rubber (SBR), and the sodium carboxymethyl cellulose (CMC-Na) are fully stirred and mixed in deionized water at a weight ratio of 97:1:1:1, coated on the negative electrode current collector copper foil, and then dried and cold pressed to obtain the negative electrode sheet.

[0076] (3) Preparation of electrolyte

[0077] In an argon atmosphere glove box with a water content of <10 ppm, EC, PC, and DEC were mixed at a volume ratio of EC:PC:DEC=1:1:1, and then the fully dried lithium salt LiPF 6 Dissolve in a mixed organic solvent and mix well to obtain an electrolyte (LiPF 6 The mass content is 12%).

[0078] (4) Assembly

[0079] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to play an isolating role, and then they are wound to obtain a bare battery cell; the bare battery cell is placed in an outer packaging aluminum foil, and the prepared electrolyte is injected into the dried bare battery cell. After vacuum packaging, standing, forming, shaping and other processes, a lithium-ion battery is obtained.

[0080] The performance tests were carried out on the separators and assembled batteries of various embodiments. The test methods are as follows. The test results are shown in Tables 1 and 2.

[0081] (1) Test of effective adhesion R of diaphragm:

[0082] Take 1m 2 For diaphragms of different sizes, the KEYENCE VHX-7000 scans the surface of the diaphragm to output the initial unit area S1 of the bonding layer; after stacking with a pole piece of the same area, hot pressing is performed, and the hot pressing parameters are: hot pressing temperature of 95°C, hot pressing pressure of 3Mpa, and hot pressing time of 60s; after hot pressing, the diaphragm is peeled off from the pole piece, and the KEYENCE VHX-7000 scans the surface of the pole piece to output the unit bonding layer area S2, and the effective bonding degree of the diaphragm is R=S2 / S1.

[0083] (2) Adhesion test:

[0084] The diaphragm and the positive electrode piece were hot pressed in a hot press at 95°C and 3 MPa for 60 s. The hot-pressed composite was cut into 200 mm*15 mm strips. Three strips were tested separately: the lower end of the strip was opened, the electrode piece was clamped in the lower clamp of the tensile testing machine, the diaphragm was pulled open in the opposite direction and clamped to the upper clamp, the tensile testing machine was turned on, the stretching rate was 50 mm / min, and the average adhesion strength of the three strips was read after the sample was peeled off.

[0085] (3) Cycle test:

[0086] At 25°C, place for 30 minutes, 0.5C CC (constant current charge) to 4.35V, place for 10 minutes, 1C DC (constant current discharge) to 3.2V, place for 10 minutes. Repeat the above process until the capacity retention rate is below 80%.

[0087] (4) Interface improvement degree:

[0088] After the battery cell is fully charged, it is disassembled to observe the wrinkles on the negative electrode plate and compared with the fully charged interface of the battery cell prepared in comparative example 1. The number of wrinkles on the electrode plate to be tested is counted, and the reduction ratio of the number of wrinkles on the electrode plate to be tested compared with the number of wrinkles on the electrode plate of the battery cell prepared with the diaphragm in comparative example 1 is calculated.

[0089]

[0090]

[0091]

[0092] Referring to Table 1, comparing Examples 1 to 3 with Comparative Example 1, under the premise of keeping other conditions the same, changing the ratio of D50 / (BET of ceramic material / D50 of ceramic material) of the first adhesive, the cycle performance of the battery and the degree of improvement of the interface of the battery cell will change. When the ratio is less than or equal to 0.5%, the surface of the heat-resistant layer tends to be smooth, the effective contact area between the heat-resistant layer and the porous base film increases, and the adhesion between the heat-resistant layer and the porous base film increases, thereby increasing the adhesion between the entire diaphragm and the pole piece, and the cycle performance of the battery and the degree of improvement of the interface of the battery cell are better; when the ratio exceeds 0.5%, the interface appears seriously wrinkled, and the cycle performance of the battery drops sharply. This is because the ceramic material and the first adhesive cannot form a heat-resistant layer with a flat surface, resulting in insufficient adhesion between the heat-resistant layer and the porous base film. As the battery cycles, the pole piece and the diaphragm fall off, thereby affecting the cycle performance of the battery.

[0093] Comparative Examples 4 to 8, on the basis of the ratio of D50 / (BET of ceramic material / D50 of ceramic material) of the first adhesive being ≤5%, the BET / D50 ratio of the ceramic material is further adjusted. From the test results, it can be concluded that when the BET / D50 ratio of the ceramic material is in the range of 40-80, the cycle performance and interface improvement of the battery are better than those not in this range. This is because when the BET / D50 ratio of the ceramic material is in the range of 40-80, a denser stacking layer and a smoother surface can be formed, while when the ratio is lower than 40, the particles of the ceramic material are relatively large and the stacking is not dense enough; and when the ratio is greater than 80, the particles of the ceramic material are relatively small and the stacking is too dense, resulting in closed pores in the diaphragm, thereby affecting lithium ion transmission and causing the cycle performance of the battery to deteriorate.

[0094] Compared with the diaphragm in Table 1, the diaphragm in Table 2 has an additional adhesive layer, and the bonding strength between the diaphragm and the electrode is further improved.

[0095] Among them, in comparison with Examples 9 to 13, on the basis of Example 5, an adhesive layer is added, and the ratio of the second adhesive D50 / ceramic material D50 in the adhesive layer is adjusted. When the ratio of the second adhesive D50 / ceramic material D50 is within the range of 0.1-0.2, the interface improvement degree of the battery cell reaches more than 70%, and the cycle performance of the battery is significantly improved. When the ratio of the second adhesive D50 / ceramic material D50 is less than 0.1, the particles of the second adhesive are relatively small, stuck in the accumulation gap of the heat-resistant layer, unable to be exposed, and unable to effectively play its bonding role; when the ratio of the second adhesive D50 / ceramic material D50 is greater than 0.2, the particles of the second adhesive are relatively large, unable to be embedded in the accumulation gap of the heat-resistant layer, and the bonding effect between the adhesive layer and the heat-resistant layer is not good.

[0096] Comparative Examples 14 to 18, on the basis of Example 10, the effective adhesion R of the diaphragm is further adjusted. When the R value is between 50% and 80%, the cycle performance of the battery is optimal; when R < 50%, the bonding density between the diaphragm and the electrode is relatively low, which affects the adhesion between the electrode and the diaphragm, thereby affecting the cycle performance of the battery; when R > 80%, the bonding points between the diaphragm and the electrode are dense, resulting in too little space remaining between the diaphragm and the electrode, which greatly reduces the amount of electrolyte retained. In the later stage of the cycle, the electrolyte is insufficient, and purple spots are likely to occur, thereby affecting the cycle performance of the battery.

[0097] Comparative Examples 19 to 23, based on Example 15, the bulk density of the heat-resistant layer is further adjusted. When the bulk density of the heat-resistant layer is between 1.2 and 2.0 g / m 3 When the stacking density is less than 1.2 g / m 3 When the stacking density is greater than 2.0 g / m, the heat-resistant layer is not dense enough and the surface is not smooth enough, which affects the adhesion between the heat-resistant layer and the base film or adhesive layer, and thus the adhesion between the diaphragm as a whole and the pole piece, and the battery cycle performance is relatively poor; when the stacking density is greater than 2.0 g / m 3 When the heat-resistant layer is stacked too densely, the porosity in the heat-resistant layer decreases, affecting the transmission of lithium ions and thus affecting the cycle performance of the battery.

[0098] Comparative Examples 24 to 28, based on Example 20, the coating amount of the adhesive layer is further adjusted. When the coating amount of the adhesive layer is 0.5-1.25 g / cm 2 When the coating amount of the adhesive layer is less than 0.5 g / cm 2When the coating amount of the adhesive layer is higher than 1.25g / cm 2 When the amount of adhesive layer increases, the bonding force between the diaphragm and the electrode does not increase. On the contrary, the transmission channel of lithium ions is blocked due to excessive bonding layer, thus affecting the cycle performance of the battery.

[0099] The diaphragm provided by the present invention adjusts the relationship between the ceramic material particles and the adhesive particles in the heat-resistant layer so that the flat and small ceramic particles and the adhesive with a large size difference with the ceramic particles are tightly bonded to form a heat-resistant layer with a smooth surface and a dense surface, thereby increasing the effective contact area between the heat-resistant layer and the porous base film, and then improving the bonding force between the heat-resistant layer and the porous base film, and improving the problem of insufficient bonding force between the diaphragm and the pole piece. An adhesive layer is further arranged on the heat-resistant layer. After hot pressing, an adhesive force is formed between the adhesive layer and the pole piece, which has the effect of battery shaping, and can also inhibit the wrinkle deformation of the battery cell caused by the expansion of the pole piece after the cycle, thereby improving the cycle life of the battery. In addition, the heat-resistant layer with a smooth and dense surface also increases the effective contact area between the adhesive layer and the heat-resistant layer, and further increases the bonding force between the diaphragm and the pole piece. Therefore, the present invention effectively overcomes some practical problems in the prior art and has a high utilization value and use significance.

[0100] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A diaphragm, characterized in that: include: Porous base membrane; A heat-resistant layer is disposed on at least one side of the porous base film; The heat-resistant layer includes a ceramic material and a first adhesive, and D50 of the first adhesive / (BET of the ceramic material / D50 of the ceramic material) is ≤0.5%.

2. The diaphragm according to claim 1, characterized in that The ratio of the BET of the ceramic material to the D50 of the ceramic material ranges from 40 to 80.

3. The diaphragm according to claim 1, characterized in that The microstructure of the ceramic material is flake-like particles.

4. The diaphragm according to claim 1, characterized in that It also includes an adhesive layer, which is arranged on the porous base film and / or the heat-resistant layer. The adhesive layer includes a polymer and a second adhesive. The polymer includes at least one of polyvinylidene fluoride, polymethyl methacrylate, and acrylate.

5. The diaphragm according to claim 4, characterized in that The ratio of D50 of the second adhesive to D50 of the ceramic material is in the range of 0.1 to 0.

2.

6. The diaphragm according to claim 4, characterized in that The effective adhesion R of the diaphragm is 50% to 80%, wherein the effective adhesion refers to the ratio of the effective bonding area to the theoretical bonding area per unit area of ​​the diaphragm.

7. The diaphragm according to any one of claims 1 to 6, characterized in that: The bulk density of the heat-resistant layer is 1.2 to 2.0 g / cm 3 .

8. The diaphragm according to claim 4, characterized in that The coating amount of the adhesive layer is 0.5 to 1.25 g / m 2 .

9. The diaphragm according to claim 4, characterized in that The first adhesive and the second adhesive are independently selected from at least one of acrylate, acrylonitrile and acrylic polymer.

10. An electrochemical device, characterized in that: include: A positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, wherein the separator is the separator according to any one of claims 1 to 9.

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