Separators and batteries

Abstract

The present invention relates to the field of batteries, and more specifically to a separator and a battery comprising the separator. The separator comprises a substrate layer and a coating applied to at least one surface of the substrate layer. The coating comprises inorganic particles and a functional binder. The functional binder comprises a sulfated polysaccharide material, wherein the sulfur content of the sulfated polysaccharide material accounts for 0.1% to 30% of the total weight of the sulfated polysaccharide material. The separator of the present invention has good adhesion, can effectively increase the hardness of the battery, and prevent battery deformation.

Description

Technical Field

[0001] The present invention relates to the field of batteries, in particular to a separator and a battery comprising the separator. Background Art

[0002] Lithium-ion batteries have been widely used as power sources in electronic products such as computers and mobile phones. In order to meet market demand, the energy density of lithium-ion batteries has gradually increased, and the expansion problem of the negative electrode of lithium-ion batteries has become more and more serious. The expansion of the negative electrode will cause the battery to deform, affecting the battery safety performance and the normal performance of the battery capacity. During the battery working cycle, lithium ions are repeatedly released and embedded between the positive and negative electrodes, and the diaphragm always plays the function of ion conduction and electronic insulation. In order to reduce the deformation problem of the battery during the cycle, one strategy is to coat the surface of the diaphragm with an adhesive layer, which can greatly enhance the adhesion between the diaphragm and the positive and negative electrodes, increase the hardness of the battery, and prevent deformation. At present, the adhesive material used for the diaphragm is mainly PVDF-HFP. However, after PVDF-HFP is swollen by the electrolyte, the internal resistance of the battery increases significantly, which will affect the performance of the battery rate performance.

[0003] Therefore, it is very important to find a separator with strong adhesion and little effect on battery electrical performance. Summary of the Invention

[0004] The present invention aims to overcome the above-mentioned problems existing in the prior art and provide a separator and a battery comprising the separator. The separator of the present invention has good adhesion, can effectively improve the hardness of the battery, and prevent the battery from deforming.

[0005] The inventors of the present invention discovered that polysaccharides contain active sites. After modification with a sulfating agent, the polysaccharide structure contains hydroxyl groups and sulfate groups, which can form hydrogen bonds with oxygen-containing groups on the surfaces of the positive and negative electrodes, thereby increasing the adhesion between the diaphragm and the positive and negative electrodes. When the sulfate content is low, the adhesion of the functional binder cannot be fully expressed. When the sulfate content is high, the electrolyte movement may be restricted due to strong hydrogen bonds, which has an adverse effect on the cycle performance of the battery. Therefore, an appropriate sulfate content can ensure the adhesion of the functional binder without adversely affecting the electrical performance of the battery.

[0006] The first aspect of the present invention provides a diaphragm, which includes a substrate layer and a coating coated on at least one side of the substrate layer, the coating including inorganic particles and a functional binder, the functional binder including a sulfated polysaccharide material, and the sulfur content in the sulfated polysaccharide material accounts for 0.1%-30% of the total weight of the sulfated polysaccharide material.

[0007] A second aspect of the present invention provides a battery, comprising a separator, wherein the separator is the separator described in the first aspect of the present invention.

[0008] Through the above technical solution, the present invention has at least the following advantages compared with the prior art: the diaphragm of the present invention adopts a functional binder including sulfated polysaccharide material, which has excellent adhesion to the inorganic particles, positive electrode sheets and negative electrode sheets in the coating, can effectively improve the hardness of the battery and prevent battery deformation.

[0009] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 FIG. 1 is a schematic cross-sectional view of the diaphragm along the width direction in an embodiment of the present invention. DETAILED DESCRIPTION

[0011] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0012] The first aspect of the present invention provides a diaphragm, which may include a substrate layer and a coating layer applied to at least one side of the substrate layer. Figure 1 The figure shows a cross-sectional view of the diaphragm along the width direction in one embodiment of the present invention, wherein Figure 1 (a) shows the case where the coating is applied on one side. Figure 1 (b) shows the coating on both sides. Figure 1 In (a), the diaphragm includes a substrate layer 1 and a coating layer 2 coated on one side of the substrate layer 1; Figure 1 In (b), the separator includes a substrate layer 1 and a coating layer 2 coated on both sides of the substrate layer 1 .

[0013] In the present invention, the coating may include inorganic particles and a functional binder, and the functional binder may include a sulfated polysaccharide material. The sulfur content in the sulfated polysaccharide material may account for 0.1%-30% of the total weight of the sulfated polysaccharide material, for example, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%.

[0014] In the present invention, the term "sulfated polysaccharide material" has the conventional meaning in the art. The term "sulfated polysaccharide material" refers to a type of active substance formed by partially replacing the active hydrogen at amino, hydroxyl, and other sites in the monosaccharide molecules on the polysaccharide macromolecular chain with sulfate groups.

[0015] Conventional commercially available polysaccharide materials can achieve the technical effects of the present invention. The polysaccharide materials may include, for example, chitosan, starch, cellulose, dextran and chitin.

[0016] The inventors of the present invention have discovered that the sulfated polysaccharide material has a specific sulfur content, which can ensure the bonding strength of the functional binder without adversely affecting the electrical performance of the battery.

[0017] In one example, the content of sulfur in the sulfated polysaccharide material accounts for 10%-20% of the total weight of the sulfated polysaccharide material.

[0018] In the present invention, based on the total weight of the coating, the content of the inorganic particles can be 0.1 wt%-30 wt% (for example, 0.1, 0.5, 1, 5, 10, 15, 20, 25 or 30 wt%), and the content of the functional binder can be 70 wt%-99.9 wt% (for example, 99.9, 99.5, 99, 95, 90, 85, 80, 75 or 70 wt%).

[0019] The inventors of the present invention have discovered that the inorganic particles and the functional binder in the coating have a specific ratio, so that the separator has both safety performance and excellent adhesion.

[0020] In one example, based on the total weight of the coating, the content of the inorganic particles is 1 wt % to 20 wt %, and the content of the functional binder is 80 wt % to 99 wt %.

[0021] In one example, based on the total weight of the coating, the content of the inorganic particles is 10 wt % to 15 wt %, and the content of the functional binder is 85 wt % to 90 wt %.

[0022] In the present invention, the inorganic particles are uniformly distributed in the coating. The inorganic particles are connected and fixed to each other by a binder, and are tightly connected to the substrate layer by the binder. At the same time, the gaps formed by the accumulation of inorganic particles form a porous structure.

[0023] In the present invention, the sulfated polysaccharide material may include at least one of sulfated astragalus polysaccharide, sulfated wolfberry polysaccharide, sulfated lentinan, sulfated angelica polysaccharide, sulfated chitosan, sulfated fucoidan, sulfated cellulose and sulfated chitin.

[0024] The inventors of the present invention have discovered that chitosan, cellulose and chitin are alkaline polysaccharides, which can form a gel structure after being sulfated (sulfation treatment), thereby further enhancing the bonding strength of the functional adhesive.

[0025] In one example, the sulfated polysaccharide material includes at least one of sulfated chitosan, sulfated cellulose, and sulfated chitin.

[0026] Furthermore, the inventors of the present invention discovered that chitosan has a structure in which "the adjacent position of the free amino group is a hydroxyl group". This structure has the function of chelating divalent metal ions. It can chelate the metal ions precipitated from the positive electrode and prevent the metal ions from being reduced to metal impurities on the surface of the negative electrode, thereby adversely affecting the battery.

[0027] In one embodiment, the sulfated polysaccharide material is sulfated chitosan.

[0028] In the present invention, the functional binder may further include component A, which may include at least one of polyvinylidene fluoride, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polytetrafluoroethylene and polyvinyl alcohol.

[0029] In one specific embodiment, the component A is a vinylidene fluoride-hexafluoropropylene copolymer.

[0030] In the present invention, the mass ratio of the sulfated polysaccharide material to the component A can be 1:(0.4-4), for example 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5 or 1:4.

[0031] In one example, the mass ratio of the sulfated polysaccharide material to the component A is 1:(0.8-1.5).

[0032] In the present invention, the inorganic particles satisfy a dielectric constant ≥ 5 (for example, a dielectric constant equal to 5, 6, 7, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 or 70).

[0033] The inorganic particles may be selected from at least one of alumina, magnesia, silica, zirconia, boehmite, magnesium hydroxide, and montmorillonite.

[0034] The inventors of the present invention have discovered that montmorillonite, a pure natural silicate material with a two-dimensional nano-layered structure similar to soil, can significantly reduce the effect of partially gelled sulfated polysaccharide materials on the air permeability of the diaphragm.

[0035] In one embodiment, the inorganic particles include at least montmorillonite, and the content of the montmorillonite can be 30 wt%-100 wt%, for example, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 wt%, based on the total weight of the inorganic particles.

[0036] In one embodiment, based on the total weight of the inorganic particles, the montmorillonite accounts for 50 wt% to 100 wt%.

[0037] In the present invention, the particle size of the inorganic particles may be 200 nm-800 nm, for example, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm or 800 nm.

[0038] The inventors of the present invention have found that the particle size of the inorganic particles is within a suitable range, so that the battery has better rate performance.

[0039] In one example, the particle size of the inorganic particles may be 300 nm to 500 nm.

[0040] In the present invention, the term "particle size" has the conventional meaning in the art. The term "particle size" is used to indicate the size of an inorganic particle. For example, the particle size of a spherical inorganic particle is the diameter of the spherical inorganic particle, the particle size of a cubic inorganic particle is the side length of the cubic inorganic particle, and the particle size of an irregular inorganic particle is the equivalent diameter of a sphere having the same technical effect as the irregular inorganic particle.

[0041] In the present invention, the thickness of the coating may be 0.5 μm-5 μm, for example, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm.

[0042] In one example, the coating has a thickness of 1 μm-2 μm.

[0043] In the present invention, the thickness of the coating layer refers to the thickness of the coating layer coated on one side of the current collector.

[0044] In the present invention, the substrate layer may be a conventional substrate layer in the art, such as a porous polyolefin substrate. The porous polyolefin substrate may be selected from at least one of polyethylene and polypropylene. The polyethylene may be selected from at least one of high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and ultra-high molecular weight polyethylene.

[0045] The present invention also provides a method for preparing the sulfated polysaccharide. The preparation method of the sulfated polysaccharide material is described below using sulfated chitosan as an example. The preparation method of the sulfated polysaccharide material comprises at least the following steps:

[0046] (1) Preparation of sulfation reagent: Add pyridine to a container, place in an ice bath, slowly add chlorosulfonic acid dropwise under stirring, and seal;

[0047] (2) Preparation of sulfated polysaccharide material: chitosan and formamide were added to a container, heated until completely dissolved, placed in an ice bath, and the sulfation reagent obtained in step (1) was added and reacted for 2-6 hours.

[0048] In the present invention, in step (1), the molar ratio of the pyridine to the chlorosulfonic acid may be 1:(0.01-1).

[0049] In one example, the molar ratio of the pyridine to the chlorosulfonic acid is 1:(0.1-0.5).

[0050] In the present invention, in step (2), the mass ratio of the formamide, the chitosan and the sulfating agent is 1:(0.1-1):(0.1-0.5).

[0051] The present invention also provides a method for preparing a diaphragm, comprising at least the following steps:

[0052] (1) preparing a functional binder solution: mixing the component A and the sulfated polysaccharide material, adding a solvent, and dissolving them;

[0053] (2) preparing a coating slurry by grinding inorganic particles and adding the ground inorganic particles to the functional binder solution obtained in step (1);

[0054] (3) Preparation of a diaphragm: applying the coating slurry obtained in step (2) to one or both sides of the substrate layer.

[0055] The specific selection and dosage of the materials used in the above preparation method are as described above and will not be repeated here.

[0056] In the present invention, in step (1), the solvent may include at least one of acetone, dimethylformamide and ethyl acetate.

[0057] In step (1), the mass ratio of the total mass of the component A and the sulfated polysaccharide material to the solvent can be (0.01-1):1.

[0058] In step (1), the dissolving may include dissolving at 40°C-60°C for 10h-14h.

[0059] In step (2), the grinding can be performed using conventional grinding processes in the art, such as ball milling for 10-15 hours. It is understood that the particle size of the inorganic particles can be controlled by the particle size and grinding time of the ball milling process.

[0060] The separator of the present invention includes a functional binder, wherein the functional binder includes a sulfated polysaccharide material, wherein the sulfated polysaccharide material contains sulfate groups and hydroxyl groups, wherein the sulfate groups are combined with oxygen-containing groups (for example, for the positive electrode, the oxygen-containing groups are from LiCoO2, Li(Ni x Co y Mn z )O2, LiMn2O4, LiFePO4 and other active materials and a trace amount of water on the surface of the aluminum foil; for another example, for the negative electrode sheet, the strength of the hydrogen bond formed between the oxygen-containing groups comes from sodium carboxymethyl cellulose, carboxymethyl cellulose, sodium alginate, polyacrylic acid and other binders is greater than the strength of the hydrogen bond formed between the hydroxyl group and the oxygen-containing group. The functional binder included in the diaphragm of the present invention has excellent adhesion, which can effectively improve the adhesion between the functional binder and the inorganic particles, the adhesion between the diaphragm and the positive electrode sheet, and the adhesion between the diaphragm and the negative electrode sheet, and will not adversely affect the electrical performance of the battery.

[0061] A second aspect of the present invention provides a battery, which may include a separator, and the separator may be the separator described in the first aspect of the present invention.

[0062] The components of the battery other than the separator (such as the positive electrode sheet, the negative electrode sheet and the electrolyte, etc.) can be selected from conventional options in the art.

[0063] The battery can be assembled in a conventional manner in the art.

[0064] The battery of the present invention has excellent rate performance and cycle performance.

[0065] The present invention will be described in detail below through examples. The examples described in the present invention are only some examples of the present invention, not all examples. All other examples obtained by persons of ordinary skill in the art based on the examples of the present invention without creative work are within the scope of protection of the present invention.

[0066] In the following examples, unless otherwise specified, all materials used were commercially available analytically pure; in the following examples, the dielectric constants of the inorganic particles used were all ≥5.

[0067] The following group I of examples is used to illustrate the separator of the present invention.

[0068] Example I1

[0069] Prepare the diaphragm as follows:

[0070] (1) Preparation of sulfation reagent: Add pyridine to a reaction flask, place in an ice bath to 0°C, slowly add chlorosulfonic acid dropwise while stirring, stir for 20 minutes until the reaction flask becomes a light yellow clear liquid, seal with a vacuum stopper, and prepare immediately before use, wherein the molar ratio of the pyridine to the chlorosulfonic acid is 80:20;

[0071] (2) Preparation of sulfated polysaccharide material: chitosan and formamide were added to a reaction flask, heated at 45°C until completely dissolved, cooled to room temperature, placed in an ice bath at 0°C, and the sulfation reagent obtained in step (1) was added, and the reaction was continued for 4 hours, wherein the mass ratio of the sulfation reagent to the formamide was 1:4, and the mass ratio of the chitosan to the formamide was 1:10;

[0072] (3) preparing a functional binder solution: mixing a vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and the sulfated chitosan obtained in step 2 (), adding acetone, and dissolving the mixture at 50° C. for 12 h, wherein the mass ratio of the sulfated chitosan to the vinylidene fluoride-hexafluoropropylene copolymer is 1:1, and the ratio of the total mass of the vinylidene fluoride-hexafluoropropylene copolymer and the sulfated chitosan to the mass of the acetone is 0.05:1;

[0073] (4) preparing a coating slurry: grinding montmorillonite by ball milling for 10 h until the particle size of the montmorillonite is 400 nm, adding the ground montmorillonite to the functional binder solution obtained in step (3), and stirring evenly, wherein the ratio of the mass of the montmorillonite to the total mass of the vinylidene fluoride-hexafluoropropylene copolymer and the sulfated chitosan is 12:88;

[0074] (5) Preparation of the diaphragm: The coating slurry obtained in step (4) was applied to both sides of a polyethylene separator (7 μm thick, 35% porosity) by a dip coating process.

[0075] A separator was obtained, wherein the thickness of the coating layer was adjusted to 1.5 μm.

[0076] Example 12

[0077] Prepare the diaphragm as follows:

[0078] (1) Preparation of sulfation reagent: Add pyridine to a reaction flask, place in an ice bath to 0°C, slowly add chlorosulfonic acid dropwise while stirring, stir for 20 minutes until the reaction flask becomes a light yellow clear liquid, seal with a vacuum stopper, and prepare immediately before use, wherein the molar ratio of the pyridine to the chlorosulfonic acid is 90:10;

[0079] (2) Preparation of sulfated polysaccharide material: chitosan and formamide were added to a reaction flask, heated at 45°C until completely dissolved, cooled to room temperature, placed in an ice bath at 0°C, and the sulfation reagent obtained in step (1) was added, and the reaction was continued for 4 hours, wherein the mass ratio of the sulfation reagent to the formamide was 1:4, and the mass ratio of the chitosan to the formamide was 1:10;

[0080] (3) preparing a functional binder solution: mixing a vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and the sulfated chitosan obtained in step 2 (), adding acetone, and dissolving the mixture at 50° C. for 12 h, wherein the mass ratio of the sulfated chitosan to the vinylidene fluoride-hexafluoropropylene copolymer is 1:0.8, and the ratio of the total mass of the vinylidene fluoride-hexafluoropropylene copolymer and the sulfated chitosan to the mass of the acetone is 0.05:1;

[0081] (4) preparing a coating slurry: grinding montmorillonite by ball milling for 12 h until the particle size of the montmorillonite is 300 nm, adding the ground montmorillonite to the functional binder solution obtained in step (3), and stirring evenly, wherein the ratio of the mass of the montmorillonite to the total mass of the vinylidene fluoride-hexafluoropropylene copolymer and the sulfated chitosan is 10:90;

[0082] (5) Preparation of diaphragm: The coating slurry obtained in step (4) was applied to both sides of a polyethylene separator (thickness 7 μm, porosity 35%) by a dip coating process and then dried.

[0083] A separator was obtained, wherein the coating layer had a thickness of 1 μm.

[0084] Example 13

[0085] Prepare the diaphragm as follows:

[0086] (1) Preparation of sulfation reagent: Add pyridine to a reaction flask, place in an ice bath to 0°C, slowly add chlorosulfonic acid dropwise while stirring, stir for 20 minutes until the reaction flask becomes a light yellow clear liquid, seal with a vacuum stopper, and prepare immediately before use, wherein the molar ratio of the pyridine to the chlorosulfonic acid is 70:30;

[0087] (2) Preparation of sulfated polysaccharide material: chitosan and formamide were added to a reaction flask, heated at 45°C until completely dissolved, cooled to room temperature, placed in an ice bath at 0°C, and the sulfation reagent obtained in step (1) was added, and the reaction was continued for 4 hours, wherein the mass ratio of the sulfation reagent to the formamide was 1:4, and the mass ratio of the chitosan to the formamide was 1:10;

[0088] (3) preparing a functional binder solution: mixing a vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and the sulfated chitosan obtained in step (2), adding acetone, and dissolving the mixture at 50° C. for 12 h, wherein the mass ratio of the sulfated chitosan to the vinylidene fluoride-hexafluoropropylene copolymer is 1:1.5, and the ratio of the total mass of the vinylidene fluoride-hexafluoropropylene copolymer and the sulfated chitosan to the mass of the acetone is 0.05:1;

[0089] (4) preparing a coating slurry: grinding montmorillonite by ball milling for 10 h until the particle size of the montmorillonite is 500 nm, adding the ground montmorillonite to the functional binder solution obtained in step (3), and stirring evenly, wherein the ratio of the mass of the montmorillonite to the total mass of the vinylidene fluoride-hexafluoropropylene copolymer and the sulfated chitosan is 15:85;

[0090] (5) Preparation of diaphragm: The coating slurry obtained in step (4) was applied to both sides of a polyethylene separator (thickness 7 μm, porosity 35%) by a dip coating process and then dried.

[0091] A separator was obtained, wherein the coating layer had a thickness of 2 μm.

[0092] Example 14

[0093] This set of examples is used to illustrate the effects of changes in sulfated polysaccharide materials.

[0094] This group of examples was carried out with reference to Example I1, except that the sulfated polysaccharide material was changed, specifically:

[0095] Example I4a, in step (2), chitosan is replaced with an equal mass of chitin;

[0096] In Example I4b, in step (2), chitosan is replaced with an equal mass of cellulose.

[0097] Example 15

[0098] This set of examples is used to illustrate the effects of changes in inorganic particles.

[0099] This group of examples was carried out with reference to Example I1, except that the inorganic particles were changed, specifically:

[0100] Example I5a, in step (4), the montmorillonite is replaced by a combination of boehmite and montmorillonite of equal weight, wherein the mass ratio of montmorillonite to boehmite is 1:1;

[0101] In Example I5b, in step (4), montmorillonite is replaced by a combination of boehmite and montmorillonite of equal mass, wherein the mass ratio of montmorillonite to boehmite is 2:3.

[0102] Example 16

[0103] This set of examples is used to illustrate the effects of changes in the sulfur content in sulfated polysaccharide materials.

[0104] This group of examples was carried out with reference to Example I1, except that the sulfur content in the sulfated chitosan was changed, specifically:

[0105] In Example I6a, in step (1), the molar ratio of pyridine to the chlorosulfonic acid is 20:1; in step (2), the mass ratio of the sulfating agent to the formamide is 1:20, and the mass ratio of the chitosan to the formamide is 1:4;

[0106] In Example I6b, in step (1), the molar ratio of pyridine to the chlorosulfonic acid is 50:50; in step (2), the mass ratio of the sulfating agent to the formamide is 1:4, and the mass ratio of the chitosan to the formamide is 1:10;

[0107] In Example I6c, in step (1), the molar ratio of pyridine to the chlorosulfonic acid is 50:50; in step (2), the mass ratio of the sulfating agent to the formamide is 3:20, and the mass ratio of the chitosan to the formamide is 1:10.

[0108] Example 17

[0109] This set of examples is used to illustrate the effects of changing the mass ratio of inorganic particles to functional binder.

[0110] This group of examples was carried out with reference to Example I1, except that the mass ratio of montmorillonite to functional binder was changed, specifically:

[0111] Embodiment 17a, wherein the ratio of the mass of the montmorillonite to the total mass of the vinylidene fluoride-hexafluoropropylene copolymer and the sulfated chitosan is 1:99;

[0112] Example I7b, wherein the ratio of the mass of the montmorillonite to the total mass of the vinylidene fluoride-hexafluoropropylene copolymer and the sulfated chitosan is 20:80.

[0113] Example 18

[0114] This set of examples is used to illustrate the effects of changing the mass ratio of sulfated polysaccharide material to component A.

[0115] This group of examples was carried out with reference to Example I1, except that the mass ratio of sulfated chitosan to vinylidene fluoride-hexafluoropropylene copolymer was changed, specifically:

[0116] In Example 18a, the mass ratio of the sulfated chitosan to the vinylidene fluoride-hexafluoropropylene copolymer is 1:0.5;

[0117] In Example I8b, the mass ratio of the sulfated chitosan to the vinylidene fluoride-hexafluoropropylene copolymer is 1:3.5.

[0118] Comparative Example D1

[0119] Refer to Example I1, except that the functional binder does not include sulfated chitosan.

[0120] Comparative Example D2

[0121] Refer to Example I1, except that sulfated chitosan is replaced with lithium dextran sulfate.

[0122] Test Case I

[0123] (1) Sulfur content test

[0124] The sulfated polysaccharide materials obtained in Group I of Examples and Comparative Examples were tested for sulfur content using an elemental analyzer, and the test results are recorded in Table 1.

[0125] (2) Peel strength test

[0126] The separators obtained from Group I of Examples and Comparative Examples were subjected to a peel strength test. The specific test method is as follows, and the test results are recorded in Table 1.

[0127] 1. Sampling: Cut the diaphragm into samples with a length of about 220mm and a width of about 23mm;

[0128] Apply double-sided tape to the steel plate, remove the release paper, and attach the cut diaphragm sample to the steel plate; apply Scotch tape parallel to the length of the diaphragm and evenly apply it to the middle of the diaphragm, and press back and forth once with a 2kg roller;

[0129] 2. Test: Use an electronic universal testing machine with the test speed set to 100 mm / min.

[0130] (3) Ionic conductivity test

[0131] The ion conductivity of the membranes obtained from Group I of Examples and Comparative Examples was tested. The specific testing method is as follows, and the test results are recorded in Table 1.

[0132] Use a punching machine to cut the diaphragm into four circular pieces with a diameter of 40 mm. Place the diaphragm in an electrolyte solution containing 1.0 mol / L lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. Keep it sealed and soak for 2 hours. Pour the electrolyte into the resistance test mold and place one layer of diaphragm in sequence. Test its AC impedance. Then place another layer and test its AC impedance resistance. Continue until four layers are placed. Measure the four AC impedance resistances, R1, R2, R3, and R4. During the test, ensure that the diaphragm is completely immersed in the electrolyte.

[0133] Draw a curve with the number of diaphragm layers as the horizontal coordinate and the resistances R1, R2, R3 and R4 as the vertical coordinate. Calculate the slope of the curve using the following formula:

[0134] R=K×1,

[0135] Where, R is the resistance value of the first diaphragm layer, in ohms (Ω); K is the slope of the curve;

[0136] σ=d / (R×S),

[0137] Wherein, σ is the ionic conductivity of the membrane, in Siemens per centimeter (S / cm); d is the thickness of one membrane layer, in micrometers (μm); R is the resistance of one membrane layer, in ohms (Ω); S is the area of ​​the membrane cut during the experiment, in square centimeters (cm 2 ).

[0138] (4) 130℃ thermal shrinkage test

[0139] The diaphragms obtained from Group I of Examples and Comparative Examples were subjected to a 130°C heat shrinkage test. The specific test method is as follows, and the test results are recorded in Table 1.

[0140] 1. Sampling: Use a membrane sample preparation mold to cut the membrane into three square membranes with a side length of 100 mm. Draw two parallel lines in the longitudinal (MD) and transverse (TD) directions of the membrane, and record the distance between the two lines in the MD and TD directions before baking.

[0141] 2. Place three A4 sheets of paper on each side of the diaphragm to secure it. Place the diaphragm and A4 sheets in the middle of the oven at 130°C. Close the oven door and wait for 1 hour until the temperature stabilizes.

[0142] 3. After heating, remove the diaphragm and wait for it to return to room temperature. Measure the longitudinal and transverse marking lengths again. The calculation formula is as follows:

[0143]

[0144] ΔL MD —Thermal shrinkage of the diaphragm in MD direction, %;

[0145] L MD前 —The distance between two parallel lines in the MD direction before the membrane is heated, unit: millimeter (mm);

[0146] L MD后 —The distance between two parallel lines in the MD direction after the membrane is heated, unit: mm

[0147] (mm);

[0148]

[0149] ΔL TD —Thermal shrinkage of the diaphragm in TD direction, %;

[0150] L TD前 —The distance between two parallel lines in the TD direction before the diaphragm is heated, unit: millimeter (mm);

[0151] L TD后 —The distance between two parallel lines in the TD direction after the diaphragm is heated, unit: millimeter (mm);

[0152] Calculate the transverse and longitudinal thermal shrinkage rates of the diaphragm, and take the average value of the three test results as the thermal shrinkage rate of the diaphragm.

[0153] (5) Air permeability test

[0154] Membrane air permeability reflects the membrane's permeability, i.e., the time required for a given volume of gas to pass through a membrane area of ​​1 square inch at a given pressure. Membranes obtained from Example 1 and Comparative Example 2 were subjected to air permeability testing. The specific testing instrument used was a Japanese Oken Densometer. The test results are recorded in Table 1.

[0155] Table 1

[0156]

[0157]

[0158] The following Group II Examples are used to illustrate the batteries of the present invention.

[0159] Prepare the battery as follows:

[0160] (1) Preparation of positive electrode sheet: lithium cobalt oxide, conductive carbon black (Super-P) and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97:1.5:1.5, dissolved in N-methylpyrrolidone (NMP), and stirred to obtain a positive electrode active slurry with a solid content of 42%. The positive electrode active slurry was evenly coated on both sides of an aluminum foil, dried, cold pressed, sliced, and the tabs were welded to obtain a positive electrode sheet;

[0161] (2) Preparation of negative electrode sheet:

[0162] Graphite, conductive carbon black (Super-P), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.5:1:1:1.5, dissolved in deionized water, and stirred to prepare a negative electrode active slurry with a solid content of 40%. The positive electrode active slurry was evenly coated on both sides of a copper foil, dried, cold-pressed, sliced, and the tabs were welded to obtain a negative electrode sheet.

[0163] (3) Preparation of electrolyte: lithium hexafluorophosphate (LiPF6) and solvent (ethylene carbonate, diethyl carbonate, methyl ethyl carbonate and vinylene carbonate in a mass ratio of 8:85:5:2) were mixed uniformly in a mass ratio of 8:92 to obtain an electrolyte;

[0164] (4) Preparation of a battery: The positive electrode sheet obtained in step (1), the negative electrode sheet obtained in step (2), and the separator obtained in Group I of the embodiment and the comparative example are wound and assembled into a battery cell, dried, injected with the electrolyte obtained in step (3), and then packaged to obtain a battery.

[0165] Test Case II

[0166] (1) Cyclic performance test

[0167] The batteries obtained from Group II of Examples and Comparative Examples were subjected to cycle performance tests. The specific test methods are as follows, and the test results are recorded in Table 2.

[0168] Charge and discharge system settings:

[0169] 1. Discharge at 0.2C to the lower limit voltage of 3.0V and let it stand for 10 minutes;

[0170] 2. Charge at 0.7C to the upper limit voltage, cut off 200mA, and let it stand for 10 minutes;

[0171] 3. Discharge at 0.2C to the upper limit voltage (for initial capacity test) and let it stand for 10 minutes;

[0172] 4. Charge at 5C to 4.15V and cut off at 3.7C, then charge at 3.7C to 4.25V and cut off at 3C, then charge at 3C to 4.45V and cut off at 2C, then charge at 2C to 4.5V and cut off at 200mA, then let it stand for 10 minutes;

[0173] 5. Discharge at 0.7C to 3.0V and let it stand for 10 minutes;

[0174] Repeat steps 4 to 5 above 500 times, and then repeat steps 2 to 3 500 times before performing a capacity test.

[0175] (2) Rate performance test

[0176] The batteries obtained from Group II of Examples and Comparative Examples were subjected to rate performance tests. The specific test methods are as follows:

[0177] 1. Discharge at 0.2C to the lower limit voltage of 3.0V and let it stand for 10 minutes;

[0178] 2. Discharge and charge at a certain rate (rate as follows), cut-off current 0.025C, and let it stand for 10 minutes;

[0179] Repeat the 1-2 cycle 5 times until all rate charge tests are completed.

[0180] Charging rate: 0.2C / 0.5C / 1.0C / 2.0C / 3.0C / 4.0C / 5.0C. The data of 0.2C, 1.0C and 5.0C are recorded in Table 2.

[0181] (3) K value test

[0182] The batteries obtained from Group II of Examples and Comparative Examples were subjected to K value tests. The specific test method is as follows, and the test results are recorded in Table 2.

[0183] Use OCV test equipment to measure the voltage of battery cells O1 and OB, and calculate the K value. The calculation formula is:

[0184] OCV1-first test voltage, unit: mV;

[0185] OCV2-second test voltage, unit: mV;

[0186] The time interval between the two tests is 24 hours.

[0187] Table 2

[0188]

[0189]

[0190] As shown in Table 1, the separators of the present invention offer a balanced combination of peel strength, ionic conductivity, thermal shrinkage, and air permeability compared to the comparative examples. The coating on the surface of the separators of the present invention contains a functional binder, which results in higher peel strength and ionic conductivity, as well as less swelling in the later stages of battery cycling. As shown in Table 2, batteries prepared using the separators of the present invention exhibit better capacity retention and rate performance than the comparative examples, and significantly improve self-discharge.

[0191] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A diaphragm, characterized in that: The diaphragm includes a substrate layer and a coating applied to at least one side of the substrate layer, wherein the substrate layer includes a porous polyolefin substrate, the coating is a porous structure, and the coating includes inorganic particles and a functional binder; based on the total weight of the coating, the content of the inorganic particles is 1% by weight to 30% by weight, and the content of the functional binder is 70% by weight to 99% by weight; the inorganic particles include at least montmorillonite, and the content of the montmorillonite is 30% by weight to 100% by weight based on the total weight of the inorganic particles. ; The functional binder includes a sulfated polysaccharide material, and the content of sulfur in the sulfated polysaccharide material accounts for 0.1%-30% of the total weight of the sulfated polysaccharide material; the functional binder also includes component A, and the component A includes at least one of polyvinylidene fluoride, vinylidene fluoride-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polytetrafluoroethylene and polyvinyl alcohol; the mass ratio of the sulfated polysaccharide material to the component A is 1:(0.4-4).

2. The diaphragm according to claim 1, wherein The content of sulfur in the sulfated polysaccharide material accounts for 10%-20% of the total weight of the sulfated polysaccharide material.

3. The diaphragm according to claim 1, wherein The sulfated polysaccharide material includes at least one of sulfated chitosan, sulfated cellulose and sulfated chitin. The diaphragm according to claim 3 , wherein: The sulfated polysaccharide material includes sulfated chitosan.

5. The diaphragm according to claim 1, wherein The mass ratio of the sulfated polysaccharide material to the component A is 1:(0.8-1.5). The diaphragm according to claim 1 , wherein: The inorganic particles are selected from inorganic particles with a dielectric constant of ≥5.

7. The diaphragm according to claim 6, wherein The inorganic particles further include at least one of aluminum oxide, magnesium oxide, silicon dioxide, zirconium oxide, boehmite and magnesium hydroxide.

8. The diaphragm according to claim 1, wherein The particle size of the inorganic particles is 300 nm to 500 nm; and / or the thickness of the coating is 1 μm to 2 μm.

9. A battery, characterized in that: The battery includes a separator, and the separator is the separator according to any one of claims 1 to 8.

Images