Diaphragm and electrochemical device and electronic device containing the same

Abstract

The present invention discloses a diaphragm and an electrochemical device and electronic device containing the same. The diaphragm includes a base film, and a ceramic layer and a glue layer sequentially arranged on one surface of the base film; the glue layer includes a strip-type glue area and a strip-type blank area; the strip-type blank area includes a transverse blank area and a plurality of longitudinal blank areas; the transverse blank area is located in the middle of the diaphragm and parallel to one side of the length of the diaphragm; wherein the width percentage of a single longitudinal blank area is 2%-10%; the width percentage of the transverse blank area is 2%-10%; the total area percentage of the strip-type blank area does not exceed 50%. The diaphragm can not only control the cost of using the glue layer, but also help to improve the electrolyte infiltration problem in the central area of ​​the diaphragm, avoid wrinkling of the negative electrode and purple spots on the negative electrode interface, and improve the cycle performance of the electrochemical device (especially lithium-ion battery).

Description

Technical Field

[0001] The invention relates to a diaphragm and an electrochemical device and an electronic device containing the diaphragm. Background Art

[0002] Lithium-ion batteries have achieved rapid development in the past 20 years, and have also brought about rapid breakthroughs in materials science, especially in the field of diaphragm materials. The main diaphragm material products in lithium-ion batteries are PP and PE diaphragms. Based on PP and PE diaphragms, PP+ceramic coating, PE / PP+ceramic coating+glue coating, etc. have been further developed. Among them, PE / PP+ceramic coating+glue coating has been widely used in the fields of power and energy storage batteries. However, the diaphragms containing glue layers are currently expensive, the electrolyte infiltration in the central area is difficult, and there are problems such as wrinkling of the negative electrode and purple spots on the negative electrode interface when used to prepare wound batteries. The battery cycle performance is poor. The existence of the above problems undoubtedly limits the further development of lithium-ion battery technology. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a diaphragm and an electrochemical device and electronic device containing the same. The diaphragm can not only control the use cost of the coating layer, but also help to improve the electrolyte infiltration problem in the center area of ​​the diaphragm, avoid wrinkling of the negative electrode and purple spots on the negative electrode interface, and ensure that the prepared electrochemical device (especially lithium-ion battery) has excellent cycle performance.

[0004] To achieve the above objectives, the present invention adopts the following technical solutions.

[0005] In a first aspect, the present invention provides a diaphragm, which comprises a base film, and a ceramic layer and a glue layer sequentially arranged on a surface of the base film; the glue layer comprises a strip-type glue coating area and a strip-type blank area; the strip-type blank area comprises a transverse blank area and a plurality of longitudinal blank areas; the transverse blank area is located in the middle of the diaphragm and parallel to one side of the length of the diaphragm; the longitudinal blank area is perpendicular to the transverse blank area, and the longitudinal blank area is spaced apart from the strip-type glue coating area; wherein,

[0006] The width percentage of a single longitudinal blank area is 2%-10%, where the percentage is the percentage of the width of a single longitudinal blank area to the width of the diaphragm;

[0007] The width percentage of the horizontal blank area is 2%-10%, where the percentage is the percentage of the width of the horizontal blank area to the width of the diaphragm;

[0008] The total area percentage of the strip-type blank area does not exceed 50%, where the percentage is the percentage of the total area of ​​the strip-type blank area to the total area of ​​the diaphragm;

[0009] The number of the longitudinal blank areas is 10-20 per meter;

[0010] Among the plurality of longitudinal blank areas, widths of the longitudinal blank areas are equal.

[0011] In a second aspect, the present invention provides an electrochemical device comprising the above-mentioned separator.

[0012] In a third aspect, the present invention provides an electronic device comprising the electrochemical device as described above.

[0013] The positive and progressive effects of the present invention are:

[0014] The present invention provides a diaphragm having a coating layer provided with a transverse blank area and a plurality of longitudinal blank areas. The diaphragm can not only control the use cost of the coating layer, but also help to improve the electrolyte infiltration problem in the central area of ​​the diaphragm, avoid wrinkling of the negative electrode and the appearance of purple spots on the negative electrode interface, and can also ensure that the obtained electrochemical device (especially lithium-ion battery) has excellent cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the structure of the diaphragm prepared in Example 1 of the present invention.

[0016] Figure 2 Schematic diagram of the wrinkling of the negative electrode in Example 1 of the present invention and Comparative Example 1.

[0017] Reference numerals:

[0018] Basement membrane 1

[0019] Ceramic layer 2

[0020] Glue coating 3 DETAILED DESCRIPTION

[0021] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0022] Diaphragm

[0023] In the diaphragm described in the first aspect of the present invention, it includes a base film, and a ceramic layer and a glue layer arranged in sequence on one surface of the base film; the glue layer includes a strip-type glue coating area and a strip-type blank area; the strip-type blank area includes a transverse blank area and a plurality of longitudinal blank areas; the transverse blank area is located in the middle of the diaphragm and parallel to one side of the length of the diaphragm; the longitudinal blank area is perpendicular to the transverse blank area, and the longitudinal blank area is spaced apart from the strip-type glue coating area; wherein,

[0024] The width percentage of a single longitudinal blank area is 2%-10%, where the percentage is the percentage of the width of a single longitudinal blank area to the width of the diaphragm;

[0025] The width percentage of the horizontal blank area is 2%-10%, where the percentage is the percentage of the width of the horizontal blank area to the width of the diaphragm;

[0026] The total area percentage of the strip-type blank area does not exceed 50%, where the percentage is the percentage of the total area of ​​the strip-type blank area to the total area of ​​the diaphragm;

[0027] The number of the longitudinal blank areas is 10-20 per meter;

[0028] Among the plurality of longitudinal blank areas, widths of the longitudinal blank areas are equal.

[0029] In some preferred embodiments, the width percentage of a single longitudinal blank area is 2%-5%, for example, 3%.

[0030] In some preferred embodiments, the width percentage of the transverse blank area is 2%-5%, for example, 3%.

[0031] In some preferred embodiments, the total area percentage of the striped blank area is 4%-15%, for example, 4.35%, 6.49%, 6.70%, 10.70%, 12.16% or 13.76%.

[0032] In some preferred embodiments, the number of the longitudinal blank areas is 10-20 per meter.

[0033] In some preferred embodiments, among the plurality of longitudinal blank areas, the widths of the longitudinal blank areas are equal.

[0034] In some preferred embodiments, when the width of the diaphragm is 120 mm, the width of the transverse blank area is 2.4-12 mm, for example, 3.6 mm or 6 mm.

[0035] In some preferred embodiments, when the width of the diaphragm is 120 mm, the width of a single longitudinal blank area is 2.4-12 mm, for example, 3.6 mm or 6 mm.

[0036] In a specific embodiment, in the diaphragm, the width percentage of a single longitudinal blank area is 2%; the width percentage of the transverse blank area is 2%; the total area percentage of the strip-type blank areas is 4.35%; and the number of the longitudinal blank areas is 10 / meter.

[0037] In a specific embodiment, in the diaphragm, the width percentage of a single longitudinal blank area is 3%; the width percentage of the transverse blank area is 3%; the total area percentage of the strip-type blank areas is 6.49%; and the number of the longitudinal blank areas is 10 / meter.

[0038] In a specific embodiment, in the diaphragm, the width percentage of a single longitudinal blank area is 5%; the width percentage of the transverse blank area is 5%; the total area percentage of the strip-type blank areas is 10.70%; and the number of the longitudinal blank areas is 10 / meter.

[0039] In a specific embodiment, in the diaphragm, the width percentage of a single longitudinal blank area is 10%; the width percentage of the transverse blank area is 2%; the total area percentage of the strip-type blank areas is 13.76%; and the number of the longitudinal blank areas is 10 / meter.

[0040] In a specific embodiment, in the diaphragm, the width percentage of a single longitudinal blank area is 2%; the width percentage of the transverse blank area is 2%; the total area percentage of the strip-type blank areas is 6.70%; and the number of the longitudinal blank areas is 20 per meter.

[0041] In a specific embodiment, in the diaphragm, the width percentage of a single longitudinal blank area is 2%; the width percentage of the transverse blank area is 10%; the total area percentage of the strip-type blank areas is 12.16%; and the number of the longitudinal blank areas is 10 / meter.

[0042] Basement membrane

[0043] In some preferred embodiments, the base film has a thickness of 3-25 μm, such as 7 μm or 9 μm.

[0044] In some preferred embodiments, the air permeability of the base film is 150-250 s / 100 cc, for example, 178±5 s / 100 cc or 185±5 s / 100 cc.

[0045] In some preferred embodiments, the base film is polyethylene (PE) and / or polypropylene (PP), for example polyethylene.

[0046] Ceramic layer

[0047] In some preferred embodiments, the thickness of the ceramic layer is 1-8 μm, for example, 3 μm.

[0048] In some preferred embodiments, the ceramic layer includes ceramic particles and a binder.

[0049] In a specific embodiment, the mass ratio of the ceramic particles to the binder is 13:7.

[0050] In some more preferred embodiments, the ceramic particles include alumina and / or boehmite.

[0051] In some more preferred embodiments, the binder includes one or more of polyvinylidene fluoride, vinylidene fluoride copolymer and polymethyl methacrylate.

[0052] In a specific embodiment, the ceramic layer includes boehmite and polyvinylidene fluoride.

[0053] In some embodiments, the method for preparing the ceramic layer comprises the following steps: adding the ceramic particles to a mixture of the binder and the solvent for dispersion to obtain a ceramic slurry; coating the ceramic slurry on a base film and drying the base film.

[0054] In some specific embodiments, the preparation method of the ceramic layer includes the following steps: first, adding the binder into a solvent to obtain a mixed solution, then adding the ceramic particles and stirring to pre-disperse them, and after pre-dispersion, vacuuming and stirring to obtain a ceramic slurry; then, coating the ceramic slurry on a base film by coating, and drying the mixture.

[0055] In a specific embodiment, the mass ratio of the binder, the solvent and the ceramic particles is 35:60:65.

[0056] In a specific embodiment, the solvent is N-methylpyrrolidone.

[0057] Glue coating

[0058] In some preferred embodiments, the thickness of the adhesive layer is 2-20 μm, for example, 5 μm or 7 μm.

[0059] In some preferred embodiments, the coating layer comprises a resin material.

[0060] In some more preferred embodiments, the resin material includes one or more of polyvinylidene fluoride, vinylidene fluoride copolymer, polyethylene oxide, polypropylene oxide, polyetherimide, polyacrylonitrile and polymethyl methacrylate.

[0061] In some preferred embodiments, the coating layer further comprises one or more of a dispersant, a wetting agent, a defoaming agent, an anti-settling agent and a binder.

[0062] In some more preferred embodiments, the coating layer further comprises a dispersant, a wetting agent, a defoaming agent, an anti-settling agent and a binder.

[0063] In a specific embodiment, in the coating layer, the mass ratio of the resin material, the dispersant, the wetting agent, the defoaming agent, the anti-settling agent and the binder is 20:10:0.2:2:0.5:10.

[0064] In some preferred embodiments, the dispersant includes one or more of silicates, alkali metal phosphates, sodium dodecyl sulfate and methyl amyl alcohol.

[0065] In some preferred embodiments, the wetting agent includes one or more of nonionic surfactants.

[0066] In some preferred embodiments, the defoaming agent includes one or more of polydimethylsiloxane, emulsified glycerin and glyceryl ether polymer.

[0067] In some preferred embodiments, the anti-settling agent includes one or more of solvent-based rheological additives, solvent-free rheological additives and novel rheological additives, for example, one or more of N-methylpyrrolidone (NMP), polyurea and polyamide wax.

[0068] In some preferred embodiments, the binder includes one or more of vinylidene fluoride, vinylidene fluoride copolymer and polymethyl methacrylate.

[0069] In some embodiments, the method for preparing the adhesive layer comprises the following steps: coating a mixture of the components of the adhesive layer and a solvent on the ceramic layer, performing a drying treatment and then performing a destaticizing treatment to obtain the adhesive layer.

[0070] In some preferred embodiments, the solvent includes water and an organic solvent; the organic solvent is, for example, one or both of acetone and toluene.

[0071] In some preferred embodiments, the coating is performed by gravure coating.

[0072] In some preferred embodiments, the gravure coating method uses a gravure roller designed based on a blank width for coating, wherein the gravure roller has a diameter of 200-260 mm, and the gravure roller is provided with grooves and depths designed according to the blank area and thickness of the adhesive layer.

[0073] In some specific embodiments, the preparation method of the coating layer includes the following steps: adding a dispersant to deionized water and stirring and dispersing; then adding a wetting agent and stirring and dispersing; then adding a defoaming agent and an anti-settling agent, heating and stirring to disperse a solution; dissolving a resin material in the solution and mechanically dispersing it until it is uniformly dispersed; then adding a binder and stirring and dispersing it to prepare a coating slurry; coating the coating slurry on the ceramic layer by gravure coating; drying it, and then subjecting it to a destaticizing treatment to obtain the product.

[0074] Electrochemical Devices

[0075] In the electrochemical device described in the second aspect of the present invention, it includes the separator as described above.

[0076] In the present invention, the electrochemical device may be a sodium ion battery or a lithium ion battery, preferably a lithium ion battery.

[0077] In some optional embodiments, the lithium-ion battery further includes a negative electrode sheet, a positive electrode sheet and an electrolyte.

[0078] Wherein, the electrolyte is the electrolyte conventionally used in the art.

[0079] Negative plate

[0080] In the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0081] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, and a thickener.

[0082] In some specific embodiments, the mass ratio of the negative electrode active material, the conductive agent, the binder and the thickener is 97:0.7:1.8:0.5.

[0083] The negative electrode active material may be a negative electrode active material conventionally used in the art for preparing negative electrode sheets, and may be one or more of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microbeads, silicon dioxide and silicon carbon.

[0084] In one specific embodiment, the negative electrode active material is artificial graphite.

[0085] The addition of the thickener can increase the system viscosity of each component in the negative electrode slurry, and can be a thickener conventionally used in the art for preparing negative electrode sheets, such as sodium carboxymethyl cellulose (CMC).

[0086] There are no particular restrictions on the conductive agent, as long as it has conductivity and does not cause chemical changes in the battery. For example, the conductive agent may be: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black (Super P), acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black or carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives.

[0087] The type of the binder is not particularly limited, and can be selected from polyvinylidene fluoride, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene terpolymer and its sulfonate, styrene-butadiene rubber (SBR), fluororubber and various copolymers.

[0088] In a specific embodiment, the binder is styrene-butadiene rubber.

[0089] For the negative electrode current collector, the negative electrode current collector may be a current collector conventionally used for the negative electrode in the art, and may be a common current collector or a composite current collector. The negative electrode current collector may use a material that does not cause chemical changes and has conductivity without restriction. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon or aluminum-cadmium alloy, or copper, stainless steel material or aluminum-cadmium alloy surface-treated with carbon, nickel, titanium or silver may be used. In addition, in order to enhance the adhesion of the negative electrode active material, micro-embossing may be formed on the surface of the negative electrode current collector. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh or porous body.

[0090] In some optional embodiments, the thickness of the negative electrode current collector is 5-10 μm.

[0091] In some specific embodiments, the negative electrode current collector is a copper foil with a thickness of 6 μm.

[0092] In some optional embodiments, the negative electrode sheet can be prepared by conventional methods in the art, for example, the following method can be used: after mixing the negative electrode active material, conductive agent, binder and thickener in a certain mass ratio, adding a solvent and mixing evenly to obtain a negative electrode slurry; then the negative electrode slurry is evenly coated on the negative electrode collector; and then drying, rolling, cutting and other processes are performed to prepare the negative electrode sheet.

[0093] In one embodiment, the solvent is water.

[0094] Positive electrode

[0095] In the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0096] In some embodiments, the positive active material layer includes a positive active material, a conductive agent, a binder, and a dispersant.

[0097] In some specific embodiments, the mass ratio of the positive electrode active material, the conductive agent, the binder and the dispersant is 97:1:1.9:0.1.

[0098] The positive electrode active material is a positive electrode active material conventionally used in the art for preparing positive electrode sheets, for example, one or more of lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium manganese iron phosphate and lithium-rich manganese-based.

[0099] In a specific embodiment, the positive electrode active material is LiFePO4.

[0100] There are no particular restrictions on the conductive agent, as long as it has conductivity and does not cause chemical changes in the battery. For example, the conductive agent may be: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black (Super P), acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black or carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives.

[0101] Among them, the binder plays a role in improving the bonding between the positive electrode active materials and the adhesion between the positive electrode active materials and the positive electrode current collector. The type of the binder is not particularly limited. Specific examples of the binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used.

[0102] The dispersant may be a dispersant commonly used in the art, such as a modified styrene maleic anhydride copolymer.

[0103] For the positive electrode current collector, materials that do not cause chemical changes and have high conductivity can be used without restriction. For example, stainless steel, aluminum, nickel, titanium or calcined carbon, or aluminum or stainless steel materials surface-treated with carbon, nickel, titanium, silver, etc. can be generally used. In order to enhance the adhesion of the positive electrode active material, micro-embossing can be formed on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms, such as a film, a sheet, a foil, a mesh or a porous body.

[0104] In some optional embodiments, the thickness of the positive electrode current collector is 8-16 μm.

[0105] In some specific embodiments, the positive electrode current collector is an aluminum foil with a thickness of 16 μm.

[0106] In some optional embodiments, the positive electrode sheet can be prepared by conventional methods in the art, for example, the following method can be used: after mixing the positive electrode active material, conductive agent, binder and dispersant in a certain mass ratio, adding a solvent and mixing evenly to obtain a positive electrode slurry; then the positive electrode slurry is evenly coated on the positive electrode collector; and then drying, cold pressing and slitting are performed to obtain the positive electrode sheet.

[0107] In a specific embodiment, the solvent is NMP.

[0108] In the present invention, the preparation method of the lithium-ion battery can be a conventional preparation method in the field, which can be a battery cell that is obtained by winding the positive electrode sheet, the separator and the negative electrode sheet, the adhesive layer of the separator and the positive electrode sheet are arranged relative to each other, the battery cell is hot-pressed to obtain a roll core, and then the roll core is packaged in a packaging shell and injected with the electrolyte; or it can be a battery cell that is obtained by stacking the negative electrode sheet, the separator, the positive electrode sheet and the separator in this order, the adhesive layer of the separator and the positive electrode sheet are arranged relative to each other, the battery cell is hot-pressed to obtain a roll core, and then the roll core is packaged in a packaging shell and injected with the electrolyte; wherein the temperature of the hot pressing is, for example, 95°C; the time of the hot pressing is, for example, 60s; the pressure of the hot pressing is, for example, 11000kgf.

[0109] Electronic devices

[0110] The electronic device described in the third aspect of the present invention comprises the electrochemical device described above.

[0111] Exemplarily, the electronic device described in the present invention may be, but is not limited to, mobile devices (such as mobile phones, tablet computers, laptop computers, video recorders, portable printers / copiers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems and backup power supplies, etc.

[0112] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0113] The reagents and raw materials used in the present invention are commercially available.

[0114] Example 1

[0115] The structure of the diaphragm in this embodiment is as follows Figure 1 As shown, a ceramic layer 2 is arranged on the base film 1, and a glue coating layer 3 is arranged on the ceramic layer 2.

[0116] A PE film with a thickness of 7 μm was selected as the base film 1, the width of the base film was 120 mm, and the air permeability of the base film was 178±5 s / 100cc.

[0117] Among them, the preparation method of the ceramic layer 2 includes the following steps: first, 35 parts of the binder PVDF are added to 60 parts of the N-methylpyrrolidone reagent to prepare a glue solution, and then 65 parts of boehmite are added and stirred for 5 hours for pre-dispersion, and after pre-dispersion, the ceramic slurry is prepared by vacuum stirring for 10 hours; then, the 3μm thick ceramic slurry is coated on the base film by coating, and the coated ceramic slurry is baked and dried at a temperature of 90°C to prepare a base film 1 with a ceramic layer 2 on one side (the thickness of the ceramic layer 2 is 3μm).

[0118] The preparation method of the adhesive layer 3 comprises the following steps:

[0119] Add 10 parts of dispersant sodium dodecyl sulfate to 50 parts of deionized water and stir and disperse for 30 minutes. Then add 0.2 parts of wetting agent alkylphenol polyoxyethylene ether, stir and disperse for 30 minutes; then add 2 parts of defoaming agent polydimethylsiloxane and 0.5 parts of anti-settling agent NMP, heat and stir and disperse for 30 minutes, the heating temperature is 45±5℃; take 20 parts of PVDF particles and dissolve them in the stirred solution, and mechanically disperse them until they are uniformly dispersed; add 10 parts of binder PVDF to the uniformly dispersed solution, stir and disperse for 60 minutes to make PVDF coating slurry. A 5μm thick PVDF coating slurry is coated on the ceramic layer by gravure coating (set a horizontal blank area and several vertical blank areas, the blank width of the horizontal blank area and the single vertical blank area is 2.4mm, the corresponding width percentage is 2%, and the number of vertical blanks is 10 / m). The coated base film was dried in an oven at 60°C and then subjected to a destaticizing treatment. An electrostatic rod was used to eliminate the static electricity of the base film, thereby obtaining a diaphragm including a base film 1, a ceramic layer 2 and a coating layer 3 (the thickness of the coating layer 3 is 5 μm).

[0120] The diaphragm is used to prepare a lithium ion battery, wherein the preparation method of the lithium ion battery comprises the following steps:

[0121] The positive electrode sheet, separator and negative electrode sheet are wound to obtain a battery cell (the rubber coating layer of the separator and the positive electrode sheet are arranged opposite to each other), and then hot-pressed (temperature is 95°C, time is 60s, pressure is 11000kgf) to obtain a coil core, so that the rubber coating layer on the surface of the separator is melted and bonded to the positive electrode sheet, and finally assembled, welded, paired, baked, injected with electrolyte, and formed into a lithium-ion battery; the high-temperature standing time of the lithium-ion battery after the first injection is 5 hours, and the infiltration temperature is 45°C.

[0122] Among them, the preparation of the positive electrode sheet includes the following steps: 97 parts of positive electrode active material (LiFePO4), 1 part of conductive agent carbon black (Super P), 1.9 parts of binder PVDF and 0.1 parts of dispersant modified styrene maleic anhydride copolymer are mixed, and 35 parts of NMP are added and mixed evenly to obtain positive electrode slurry; then the positive electrode slurry is evenly coated on the positive electrode collector (aluminum foil with a thickness of 16μm); and then the positive electrode sheet is obtained after drying, cold pressing and slitting.

[0123] Among them, the preparation of the negative electrode sheet includes the following steps: 97 parts of negative electrode active material (artificial graphite), 0.7 parts of conductive agent carbon black (Super P), 1.8 parts of binder SBR and 0.5 parts of thickener carboxymethyl cellulose (CMC) are mixed, and 55 parts of deionized water are added and mixed evenly to obtain a negative electrode slurry; then the negative electrode slurry is evenly coated on the negative electrode collector (copper foil with a thickness of 6 μm); and then after drying, rolling, cutting and other processes, a negative electrode sheet is prepared.

[0124] Among them, the electrolyte used is commercially available electrolyte (the manufacturer is Xinya Shanshan New Materials Technology (Quzhou) Co., Ltd., model E3).

[0125] Example 2

[0126] The only difference between this embodiment and embodiment 1 is that the thickness of the base film is 9 μm, and the air permeability of the base film is 185±5 s / 100cc. The other conditions are the same as those in embodiment 1.

[0127] Example 3

[0128] The difference between this embodiment and embodiment 2 is that when preparing the adhesive layer, the blank widths of the transverse blank area and the single longitudinal blank area are both 3.6 mm (the width percentage is both 3%). The other conditions are the same as those of embodiment 2.

[0129] Example 4

[0130] The difference between this embodiment and embodiment 2 is that when preparing the adhesive layer, the blank widths of the transverse blank area and the single longitudinal blank area are both 6 mm (the width percentage is both 5%). The other conditions are the same as those of embodiment 2.

[0131] Example 5

[0132] The difference between this embodiment and embodiment 2 is that the thickness of the coating layer is 7 μm. The other conditions are the same as those in embodiment 2.

[0133] Example 6

[0134] The difference between this embodiment and embodiment 5 is that when preparing the adhesive layer, the blank widths of the transverse blank area and the single longitudinal blank area are both 3.6 mm (the width percentage is both 3%). The other conditions are the same as those of embodiment 5.

[0135] Example 7

[0136] The difference between this embodiment and embodiment 5 is that when preparing the adhesive layer, the blank widths of the transverse blank area and the single longitudinal blank area are both 6 mm (the width percentage is both 5%). The other conditions are the same as those of embodiment 5.

[0137] Example 8

[0138] The difference between this embodiment and embodiment 1 is that when preparing the adhesive layer, the blank width of a single longitudinal blank area is 12 mm (the width percentage is 10%). The other conditions are the same as those in embodiment 1.

[0139] Example 9

[0140] The difference between this embodiment and embodiment 1 is that when preparing the adhesive layer, the number of longitudinal blanks is 20 per meter. The other conditions are the same as those in embodiment 1.

[0141] Example 10

[0142] The difference between this embodiment and embodiment 1 is that when preparing the adhesive layer, the width of the horizontal blank area is 12 mm (the width percentage is 10%). The other conditions are the same as those in embodiment 1.

[0143] Comparative Example 1

[0144] This comparative example uses a commercial diaphragm (manufacturer: Shenzhen Xingyuan Material Technology Co., Ltd., model specification 15+2+3). Among them, the base film is a PP film with a thickness of 15μm, the thickness of the ceramic layer is 2μm, and the thickness of the coating layer (PVDF) is 3μm.

[0145] Comparative Example 2

[0146] The difference between this comparative example and Example 1 is that when preparing the adhesive layer, the number of the transverse blank areas is 2 (each 40 mm away from the transverse edge of the separator). The other conditions are the same as those in Example 1.

[0147] Comparative Example 3

[0148] The difference between this comparative example and Example 1 is that no horizontal blank area is left when preparing the adhesive layer. The other conditions are the same as those in Example 1.

[0149] Comparative Example 4

[0150] The difference between this comparative example and Example 1 is that when preparing the adhesive layer, the blank width of a single longitudinal blank area is 1.2 mm (the width percentage is 1%). The other conditions are the same as those in Example 1.

[0151] Comparative Example 5

[0152] The difference between this comparative example and Example 1 is that when preparing the adhesive layer, the blank width of a single longitudinal blank area is 18 mm (the width percentage is 15%). The other conditions are the same as those in Example 1.

[0153] Comparative Example 6

[0154] The difference between this comparative example and Example 1 is that when preparing the adhesive layer, the blank width of the horizontal blank area is 1.2 mm (the width percentage is 1%). The other conditions are the same as those in Example 1.

[0155] Comparative Example 7

[0156] The difference between this comparative example and Example 1 is that when preparing the adhesive layer, the blank width of the horizontal blank area is 18 mm (the width percentage is 15%). The other conditions are the same as those in Example 1.

[0157] The specific parameters of the adhesive layer of the separator in the above-mentioned Examples 1-10 and Comparative Examples 1-7 are shown in Table 1. The number of longitudinal blanks is calculated based on the separator length of 1 meter; when calculating the total area percentage of the blank area, the calculation is based on the separator length of 1 meter.

[0158] Effect Example 1

[0159] The membranes in Examples 1-10 and Comparative Examples 1-7 were tested for membrane air permeability, membrane wettability, and residual adhesive content. The specific testing methods are as follows:

[0160] (1) Diaphragm air permeability

[0161] Select fresh membrane (membrane area larger than 10×10cm 2 ), place the diaphragm in the test position of the air permeability tester and read the test result.

[0162] (2) Membrane wettability

[0163] Select 10×10cm 2 1g of electrolyte (manufacturer: Xinya Shanshan New Materials Technology (Quzhou) Co., Ltd., model: E3) was dripped into the center of the separator, and the time required for the electrolyte to diffuse to the edge was observed, which is the wettability of the separator.

[0164] (3) Residual glue amount

[0165] The amount of residual adhesive after hot pressing of lithium-ion batteries (temperature is 95°C, pressure is 11000kgf) is calculated according to the average thickness of the positive and negative electrodes before hot pressing, the thickness of the diaphragm, the thickness of the winding core after hot pressing, and the number of layers of the electrode and diaphragm. The specific calculation method is as follows;

[0166] Residual glue amount = (core thickness - (positive electrode thickness × number of positive electrode layers) - (negative electrode thickness × number of negative electrode layers)) / number of diaphragm layers - base film thickness - ceramic layer thickness.

[0167] Effect Example 2

[0168] The lithium ion batteries prepared in Examples 1-10 and Comparative Examples 1-7 were tested and observed as follows:

[0169] (1) DC resistance (DCR)

[0170] In a 25℃ incubator, the battery was left for 1 hour, charged to 3.65V at a constant current rate of 1C, and then charged at a constant voltage until the current was less than or equal to 0.05C. At this time, the battery's state of charge (SOC) was 100%. After standing for 30 minutes, the battery was discharged at a constant current rate of 1C for 30 minutes to adjust the battery's state of charge (SOC) to 50%. Battery A with a 50% SOC was left standing for another 30 minutes, discharged at a constant current rate of 0.2C for 30 seconds, and then discharged at a constant current rate of 1C for 5 seconds. The voltage U1 at the last 1 second of the last 0.2C constant current discharge, the voltage U2 at the last 1 second of the 1C constant current discharge, the current I1 of the 0.2C constant current discharge, and the current I2 of the 1C constant current discharge were recorded. Calculate the DCR of the battery at 25℃, 50% SOC, and 1C constant current discharge for 30s = (U2-U1) / (I2-I1). The test results are shown in Table 2.

[0171] (2) Purple spots on the negative electrode interface

[0172] After the lithium-ion battery is fully charged and disassembled after formation, the interface wetting is observed, and purple spots will appear on the negative electrode interface with poor wetting. The results are shown in Table 2, where purple spots with a length greater than 10 cm and a number less than 10 are considered a small number of purple spots, and purple spots with a length greater than 10 cm and a number ≥ 10 are considered a large number of purple spots.

[0173] (3) Negative electrode wrinkling

[0174] After the lithium-ion battery was fully charged and disassembled, the wrinkling of the negative electrode was observed visually. The results are shown in Table 2 and Figure 2 shown.

[0175]

[0176]

[0177] The adhesive layer of the separator of the present invention includes a horizontal blank area and a plurality of vertical blank areas, which can reduce the adhesive coating cost while improving the diffusion and storage path of the electrolyte, thereby improving the battery infiltration effect. In addition, the reserved blank area reserves space for stress release, solves the problem of wrinkling of the negative electrode of the winding cell, improves the consistency of the battery, and helps to improve the cycle performance of the battery, with a capacity retention rate of more than 94.1%.

[0178] By comparing Examples 1-7 with Comparative Example 1, it can be seen that the problem of wrinkling of the negative electrode of the wound battery cell can be effectively solved by reserving blank space in the glue coating layer. This may be because the blank area leaves a certain space for the expansion of artificial graphite as the negative electrode active material, so that when the outer ring expands to contact the shell, the force of the shell on the electrode sheet can be released, which helps to solve the problem of wrinkling of the negative electrode. Figure 2 As shown, the outer ring of the negative electrode using the separator in Comparative Example 1 is slightly wrinkled, but the negative electrode using the separator in Example 1 has no wrinkles.

[0179] Compared with Example 1, the number of horizontal blanks in Comparative Example 2 is 2. Although the wrinkling situation can be improved, the problem of center wetting cannot be effectively solved. A large number of purple spots appear on the negative electrode interface, and the capacity retention rate of the lithium-ion battery is reduced. When no horizontal blank is set (Comparative Example 3), although there is no wrinkling, a large number of purple spots also appear on the negative electrode interface, and the capacity retention rate of the lithium-ion battery deteriorates. When the longitudinal blank width accounts for too high (Comparative Example 5) or too low (Comparative Example 4), although there are only a few purple spots or even no purple spots on the negative electrode interface, there is wrinkling on the outer circle of the negative electrode. When the horizontal blank width accounts for too low a proportion (Comparative Example 6), although there is no wrinkling, there are a large number of purple spots on the negative electrode interface, and the problem of center wetting cannot be effectively solved. When the horizontal blank width accounts for too high a proportion (Comparative Example 7), the problem of center wetting can be effectively improved, but wrinkles appear in the center of the interface, and the stress problem cannot be alleviated.

[0180] Comparison between Example 2 and Comparative Example 1 shows that the coating layer including a strip-type coating area and a strip-type blank area in the diaphragm of the present invention can improve the air permeability of the diaphragm and significantly shorten the diffusion time of the electrolyte, which is beneficial to the ion diffusion and electrochemical reaction kinetics inside the battery cell. The DCR test and interface disassembly also prove the advantages of the diaphragm of the present invention. The DCR is significantly reduced. At the same time, the purple spots on the negative electrode interface are also significantly reduced under a very short battery cell infiltration time (5h).

[0181] The comparison between Example 1 and Example 2 shows that the increase in the thickness of the base film has no significant effect on the wetting and electrochemical reaction kinetics of the lithium ion battery.

[0182] The comparison between Example 2, Example 3 and Example 4 shows that the width percentage of a single longitudinal blank area has a certain degree of influence on the air permeability and wettability of the diaphragm. The increase in the width percentage is conducive to improving the air permeability of the diaphragm and improving the wettability of the diaphragm. At the same time, the amount of residual glue after hot pressing is reduced, which also proves that the glue coating area extends to the blank area during hot pressing, indicating that the reasonable blank area design in the diaphragm of the present invention can also play the role of a conventional diaphragm. Compared with Comparative Example 1, the purple spots on the negative electrode interface of Examples 3 and 4 are significantly improved, indicating that the diaphragm of the present invention is conducive to improving the problems existing in the wettability of lithium-ion batteries.

[0183] Examples 5, 6, and 7 increase the thickness of the coating layer compared to Examples 2, 3, and 4, and have basically the same effect on improving the interface. Although the membrane permeability decreases and the DCR increases with the increase in the thickness of the coating layer, the capacity retention rate can still reach more than 94.1%.

[0184] Although the specific embodiments of the present invention are described above, it should be understood by those skilled in the art that this is only for illustration and the protection scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A diaphragm, characterized in that: It includes a base film, and a ceramic layer and a glue layer arranged in sequence on one surface of the base film; the glue layer includes a strip-type glue coating area and a strip-type blank area; the strip-type blank area consists of a transverse blank area and a plurality of longitudinal blank areas; the transverse blank area is located in the middle of the diaphragm and parallel to one side of the length of the diaphragm; the longitudinal blank area is perpendicular to the transverse blank area, and the longitudinal blank area is spaced apart from the strip-type glue coating area; wherein, The width percentage of a single longitudinal blank area is 2%-10%, where the percentage is the percentage of the width of a single longitudinal blank area to the width of the diaphragm; The width percentage of the transverse blank area is 2%-10%, where the percentage is the percentage of the width of the transverse blank area to the width of the diaphragm; The total area percentage of the strip-type blank area does not exceed 50%, where the percentage is the percentage of the total area of ​​the strip-type blank area to the total area of ​​the diaphragm; The number of the longitudinal blank areas is 10-20 per meter; Among the plurality of longitudinal blank areas, widths of the longitudinal blank areas are equal.

2. The diaphragm according to claim 1, characterized in that The width percentage of a single longitudinal blank area is 2%-5%.

3. The diaphragm according to claim 1, characterized in that The width percentage of the horizontal blank area is 2%-5%.

4. The diaphragm according to claim 1, characterized in that The total area percentage of the strip-type blank area is 4%-15%.

5. The diaphragm according to claim 1, characterized in that It meets one or more of the following conditions: a. The thickness of the coating layer is 2-20 μm; b. The thickness of the ceramic layer is 1-8 μm; c. The thickness of the base film is 3-25 μm; d. The air permeability of the base film is 150-250s / 100cc.

6. The diaphragm according to claim 1, characterized in that It satisfies one or more of the following conditions: e. The base film is polyethylene and / or polypropylene; f. The ceramic layer comprises ceramic particles and a binder; g. The coating layer includes resin material.

7. The diaphragm according to claim 6, characterized in that It satisfies one or more of the following conditions hj: h. The ceramic particles include alumina and / or boehmite; i. The binder comprises one or more of vinylidene fluoride, vinylidene fluoride copolymer and polymethyl methacrylate; j. The resin material includes one or more of polyvinylidene fluoride, vinylidene fluoride copolymer, polyethylene oxide, polypropylene oxide, polyetherimide, polyacrylonitrile and polymethyl methacrylate.

8. An electrochemical device, characterized in that: It comprises the diaphragm according to any one of claims 1 to 7.

9. An electronic device, characterized in that: It comprises the electrochemical device as claimed in claim 8.

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