Diaphragm and preparation method thereof, secondary battery and electric device

Abstract

The present application relates to a separator, comprising: a substrate; a ceramic coating on at least one surface of the substrate; and a polymer coating on the ceramic coating, wherein the polymer coating comprises a material having a thermal conductivity of less than or equal to 0.12 W / (m·K). The present application also relates to a method for preparing the separator, a secondary battery, and an electrical device.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a diaphragm and a preparation method thereof, a secondary battery and an electrical device. Background Art

[0002] In recent years, as the application scope of secondary batteries becomes wider and wider, secondary batteries are widely used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. As secondary batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and safety performance. However, the cycle performance and safety performance of existing secondary batteries need to be further improved. Summary of the invention

[0003] The present application is made in view of the above-mentioned problems, and its object is to provide a separator so that a secondary battery including the separator has good cycle performance and safety performance.

[0004] In order to achieve the above-mentioned objectives, the present application provides a diaphragm and a preparation method thereof, a secondary battery and an electrical device.

[0005] A first aspect of the present application provides a diaphragm, comprising:

[0006] Base material;

[0007] a ceramic coating on at least one surface of the substrate; and

[0008] a polymer coating on the ceramic coating,

[0009] Wherein, the polymer coating comprises a material having a thermal conductivity less than or equal to 0.12 W / (m·K).

[0010] Therefore, the present application includes a material with a thermal conductivity of less than or equal to 0.12W / (m·K) in the polymer coating of the diaphragm, so that when the electrode assembly is cooled after passing through the tunnel furnace, the temperature of the polymer coating drops slowly, and good adhesion with the positive and negative electrode sheets can be maintained during cold pressing, thereby improving the cycle performance and safety performance of the secondary battery using the diaphragm.

[0011] In any embodiment, the material having a thermal conductivity less than or equal to 0.12 W / (m·K) includes at least one of tungsten diselenide and aluminum silicate, and may be tungsten diselenide.

[0012] In any embodiment, the coating density of the material having a thermal conductivity less than or equal to 0.12 W / (m·K) is 0.0000649-0.000195 mg / mm 2(0.1-0.3mg / 1540.25mm 2 ), optionally 0.0000649-0.000130 mg / mm 2 (0.1-0.2mg / 1540.25mm 2 ). When the coating density of the material is within the range, the cycle performance and safety performance of the secondary battery can be further improved.

[0013] In any embodiment, the coating density of the polymer coating is 0.00039-0.00422 mg / mm 2 (0.6-6.5mg / 1540.25mm 2 ). When the coating density of the polymer coating is within the given range, good bonding between the separator and the positive and negative electrode sheets can be ensured.

[0014] In any embodiment, the weight percentage of the material having a thermal conductivity less than or equal to 0.12 W / (m·K) in the polymer coating is 1.5%-30%. When the weight percentage of the material in the polymer coating is within the given range, the effect of slowing down the temperature drop of the polymer coating when the electrode assembly is cooled after passing through the tunnel furnace can be achieved without affecting the function of the polymer coating.

[0015] A second aspect of the present application provides a method for preparing a diaphragm, which comprises the following steps:

[0016] (1) providing a substrate;

[0017] (2) providing a ceramic slurry, coating the ceramic slurry on at least one surface of the substrate and drying the ceramic slurry to form a ceramic coating; and

[0018] (3) providing a polymer slurry containing a material having a thermal conductivity of less than or equal to 0.12 W / (m·K), applying the polymer slurry on the ceramic coating and drying the polymer coating to form the polymer coating, thereby obtaining the separator,

[0019] Wherein, the diaphragm comprises:

[0020] Base material;

[0021] a ceramic coating on at least one surface of the substrate; and

[0022] a polymer coating on the ceramic coating,

[0023] The polymer coating comprises a material having a thermal conductivity less than or equal to 0.12 W / (m·K).

[0024] Therefore, the method of the present application includes a material with a thermal conductivity less than or equal to 0.12 W / (m·K) in the polymer coating of the diaphragm in a simple manner, and the polymer coating can be kept warm when the electrode assembly is cooled after passing through a tunnel furnace, thereby improving the cycle performance and safety performance of the secondary battery containing the diaphragm.

[0025] A third aspect of the present application provides a secondary battery, which includes the separator according to the first aspect of the present application or the separator prepared by the method according to the second aspect of the present application.

[0026] A fourth aspect of the present application provides an electrical device, comprising the secondary battery of the third aspect of the present application.

[0027] The electric device of the present application includes the secondary battery of the present application, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a temperature-time curve diagram of the electrode assembly (ie, battery cell JR) in the prior art when cold pressed on a cold pressing plate.

[0029] Figure 2 It is a schematic diagram of an electrode assembly according to one embodiment of the present application.

[0030] Figure 3 It is a schematic diagram of a battery cell according to an embodiment of the present application.

[0031] Figure 4 yes Figure 3 An exploded view of a battery cell according to an embodiment of the present application is shown.

[0032] Figure 5 is a schematic diagram of a battery module according to an embodiment of the present application.

[0033] Figure 6 It is a schematic diagram of a battery pack according to one embodiment of the present application.

[0034] Figure 7 yes Figure 6 An exploded view of a battery pack according to an embodiment of the present application is shown.

[0035] Figure 8 FIG. 1 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

[0036] Description of reference numerals:

[0037] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell; 51 shell; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION

[0038] Hereinafter, the embodiments of the diaphragm and its preparation method, secondary battery and electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0039] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0041] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0042] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, it is mentioned that the method may also include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0043] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0044] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0045] In the preparation process of secondary batteries, the electrode assembly (i.e., battery cell JR) consisting of the positive electrode sheet, separator and negative electrode sheet will be heated in a tunnel furnace after winding to soften the polymer coating of the separator, and then transferred to a cold press plate for cold pressing to bond the separator and the positive and negative electrode sheets together. However, in some secondary batteries, the battery cell JR is relatively thin, and the heat dissipation is fast when it is cooled after passing through the tunnel furnace, and the temperature of the polymer coating on the separator drops quickly (such as Figure 1 As shown in the figure, the bonding with the positive and negative pole pieces becomes worse, and fluffy cells are likely to appear during cold pressing, thus affecting the cycle performance and safety performance of the secondary battery.

[0046] The present application uses a material with a thermal conductivity of less than or equal to 0.12 W / (m·K) to insulate the diaphragm, thereby ensuring the adhesion of the diaphragm to the positive and negative electrode sheets during cold pressing, thereby improving the cycle performance and safety performance of the secondary battery.

[0047] [Diaphragm]

[0048] In one embodiment of the present application, the present application proposes a diaphragm, which comprises:

[0049] Base material;

[0050] a ceramic coating on at least one surface of the substrate; and

[0051] Polymer coatings on ceramic coatings,

[0052] The polymer coating comprises a material having a thermal conductivity less than or equal to 0.12 W / (m·K).

[0053] Although the mechanism is not yet clear, the applicant unexpectedly discovered that: the present application insulates the diaphragm by including a material with a thermal conductivity less than or equal to 0.12W / (m·K) in the polymer coating of the diaphragm, so that when the electrode assembly is cooled after passing through the tunnel furnace, the temperature of the polymer coating drops slowly, and good adhesion with the positive and negative electrode sheets can be maintained during cold pressing, thereby improving the cycle performance of the secondary battery using the diaphragm.

[0054] In addition, the lithium deposition of the secondary battery is also improved. This is because when the bonding between the diaphragm and the positive and negative pole pieces is good, the gap between the positive and negative pole pieces is small, and the lithium ion transmission distance is uniform and small; when the bonding is poor, the distance between the positive and negative pole pieces is uneven, the local distance is too large, the lithium ion transmission path is long, and lithium deposition is easy. Therefore, the present application includes a material with a thermal conductivity of less than or equal to 0.12W / (m·K) in the polymer coating of the diaphragm, which can maintain good bonding between the diaphragm and the positive and negative pole pieces during cold pressing, thereby improving lithium deposition, that is, improving the safety performance of the secondary battery.

[0055] In the embodiment of the present application, the material with a thermal conductivity less than or equal to 0.12 W / (m·K) is also referred to as a thermal insulation material.

[0056] In some embodiments, the thermal conductivity of the material having a thermal conductivity less than or equal to 0.12 W / (m·K) is greater than 0 and less than or equal to 0.12 W / (m·K), and may be 0.01-0.12 W / (m·K).

[0057] In some embodiments, the material having a thermal conductivity less than or equal to 0.12 W / (m·K) includes at least one of tungsten diselenide and aluminum silicate, and may be tungsten diselenide.

[0058] In some embodiments, the thermal conductivity of tungsten diselenide is 0.02-0.026 W / (m·K), and the thermal conductivity of aluminum silicate is 0.04-0.1 W / (m·K).

[0059] In some embodiments, the coating density of the material with a thermal conductivity less than or equal to 0.12 W / (m·K) is 0.1-0.3 mg / 1540.25 mm 2 , optionally 0.1-0.2mg / 1540.25mm 2 , further optionally 0.2mg / 1540.25mm 2 .

[0060] When the coating density of the material with a thermal conductivity of less than or equal to 0.12W / (m·K) is too high, it will affect the heat dissipation of the diaphragm during later use; when the coating density of the material with a thermal conductivity of less than or equal to 0.12W / (m·K) is too low, it cannot achieve the above-mentioned heat preservation effect. Therefore, when the coating density of the material with a thermal conductivity of less than or equal to 0.12W / (m·K) is within the above range, the cycle performance and safety performance of the secondary battery can be further improved.

[0061] Although the unit of coating density is sometimes expressed as "mg / 1540.25mm 2 ” is used for expression, but this expression is not intended to express or imply any specific requirement for the area.

[0062] In some embodiments, the coating density of the polymer coating is 0.6-6.5 mg / 1540.25 mm 2 When the coating density of the polymer coating is within the given range, good bonding between the separator and the positive and negative electrode sheets can be ensured.

[0063] In some embodiments, the weight percentage of the material having a thermal conductivity of less than or equal to 0.12 W / (m·K) in the polymer coating is 1.5%-30%. When the weight percentage of the material having a thermal conductivity of less than or equal to 0.12 W / (m·K) in the polymer coating is within the given range, the effect of slow temperature drop of the polymer coating can be achieved when the electrode assembly is cooled after passing through the tunnel furnace without affecting the function of the polymer coating.

[0064] In some embodiments, the thickness of the ceramic coating is 0.5-4 μm

[0065] In some embodiments, the ceramic coating comprises ceramic particles and a binder, and the weight ratio of the ceramic particles to the binder is 4:1-9:1.

[0066] In some embodiments, the ceramic particles are selected from at least one of boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), zirconium titanate (SrTiO3), barium titanate (BaTiO3), and magnesium fluoride (MgF2).

[0067] In some embodiments, the binder is selected from at least one of polyvinylidene fluoride, polyacrylate, polymethyl methacrylate, polyacrylonitrile, polyimide, polyethylene oxide, polyvinyl alcohol, and the like.

[0068] In some embodiments, the polymer coating has a thickness of 1-20 μm.

[0069] In some embodiments, the polymer is selected from at least one of polyvinylidene fluoride (PVDF) and polyacrylate.

[0070] In some embodiments, the substrate is selected from at least one of glass fiber, non-woven fabric, polyethylene and polypropylene.

[0071] In some embodiments, the thickness of the substrate is 5-30 μm.

[0072] In one embodiment of the present application, the present application proposes a method for preparing a diaphragm, which comprises the following steps:

[0073] (1) providing a substrate;

[0074] (2) providing a ceramic slurry, coating the ceramic slurry on at least one surface of a substrate and drying the ceramic slurry to form a ceramic coating; and

[0075] (3) providing a polymer slurry containing a material having a thermal conductivity of less than or equal to 0.12 W / (m·K), applying the polymer slurry on the ceramic coating and drying the polymer coating to form a polymer coating, thereby obtaining a separator,

[0076] The diaphragm includes:

[0077] Base material;

[0078] a ceramic coating on at least one surface of the substrate; and

[0079] Polymer coatings on ceramic coatings,

[0080] The polymer coating comprises a material having a thermal conductivity less than or equal to 0.12 W / (m·K).

[0081] Therefore, the method of the present application includes a material with a thermal conductivity less than or equal to 0.12 W / (m·K) in the polymer coating of the diaphragm in a simple manner, and the polymer coating can be kept warm when the electrode assembly is cooled after passing through a tunnel furnace, thereby improving the cycle performance and safety performance of the secondary battery containing the diaphragm.

[0082] In some embodiments, in step (2), coating may be gravure coating, wherein the gravure coating uses a coater, wherein the coater comprises a gravure roller, wherein the line number of the gravure roller is 50-400 LPI, and the speed of the gravure coating is 5-50 m / min.

[0083] In some embodiments, in step (2), the solid content of the ceramic slurry is 40-80%.

[0084] In some embodiments, in step (2), the drying temperature is 30-80°C.

[0085] In some embodiments, in step (3), the coating is sprayed at a rate of 0.01-0.1 mL / min / mm 2 .

[0086] In some embodiments, in step (3), the drying temperature is 30-80°C.

[0087] In some embodiments, the polymer coating is in the form of islands.

[0088] In addition, the secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0089] In one embodiment of the present application, a secondary battery is provided. The secondary battery may be in the form of a battery cell, a battery module, or a battery pack. The battery module and the battery pack may include a battery cell, and the battery pack may also include a battery module.

[0090] Typically, a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery charge and discharge process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through. The positive electrode sheet, the negative electrode sheet, and the electrolyte can use existing products for metal ion batteries.

[0091] [Positive electrode]

[0092] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0093] As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0094] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0095] In some embodiments, the positive electrode active material may adopt a positive electrode active material for a battery that is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0096] In some embodiments, the content of the positive electrode active material in the positive electrode film layer is 70-98 wt %, based on the total weight of the positive electrode film layer.

[0097] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0098] In some embodiments, the binder accounts for 0.1% to 15% by mass of the positive electrode film layer.

[0099] In some embodiments, the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0100] In some embodiments, the conductive agent accounts for 0.1% to 15% by mass of the positive electrode film layer.

[0101] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0102] [Negative electrode]

[0103] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.

[0104] As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0105] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0106] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0107] In some embodiments, the mass percentage of the negative electrode active material in the negative electrode film layer is 75% to 99%, and optionally 80% to 98%.

[0108] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0109] In some embodiments, the binder accounts for 0.1% to 3.5% by mass of the negative electrode film layer, and optionally 0.5% to 2.5% by mass.

[0110] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0111] In some embodiments, the conductive agent accounts for 0.1% to 5% by mass of the negative electrode film layer, and can be optionally 0.3% to 3% by mass.

[0112] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0113] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0114] [Electrolytes]

[0115] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0116] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0117] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0118] In some embodiments, the concentration of the electrolyte salt in the non-aqueous electrolyte is 0.5-2 mol / L (mole / liter), and can be optionally 0.7-1.3 mol / L.

[0119] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0120] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0121] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly (ie, a battery cell JR) by a winding process or a lamination process.

[0122] like Figure 2 As shown, the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator. The separator includes a substrate, a ceramic coating and a polymer coating, and the polymer coating contains a heat-insulating material.

[0123] In some embodiments, the thickness of the electrode assembly (ie, the battery cell JR) is 5-60 mm.

[0124] In some embodiments, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0125] In some embodiments, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0126] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 3 The battery cell 5 is a square structure as an example.

[0127] In some embodiments, reference Figure 4 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0128] In some embodiments, battery cells may be assembled into a battery module. The number of battery cells contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0129] Figure 5 4 is an example of a battery module. Figure 5 In the battery module 4, the plurality of battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells 5 may be fixed by fasteners.

[0130] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0131] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0132] Figure 6 and Figure 7 1 is a battery pack 1 as an example. Figure 6 and Figure 7The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0133] In addition, the present application also provides an electric device, which includes a secondary battery provided in the present application. The secondary battery can be used as a power source for the electric device, or as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, 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, etc., but are not limited thereto.

[0134] As the electrical device, a secondary battery can be selected according to its usage requirements.

[0135] Figure 8 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0136] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a battery cell may be used as a power source.

[0137] Example

[0138] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0139] 1. Preparation of diaphragm

[0140] Diaphragm 1:

[0141] (1) providing a polyethylene (PE) film with a thickness of 7 μm as a substrate;

[0142] (2) Ceramic particles Al2O3 and binder PVDF were mixed uniformly in an appropriate amount of solvent deionized water at a weight ratio of 7:1 to obtain a ceramic slurry with a solid content of 60%, and the ceramic slurry was coated on both surfaces of the substrate by a coating machine, and dried to form a ceramic coating with a single-side thickness of 2 μm. The line number of the gravure roller of the coating machine was 150 LPI, the coating speed was 10 m / min, the drying temperature was 40°C, and the drying time was 2 hours;

[0143] (3) The polymer PVDF and tungsten diselenide (thermal conductivity of 0.022 W / (m·K)) are mixed uniformly in a weight ratio of 6:1 to obtain a polymer slurry, and the polymer slurry is sprayed onto the ceramic coating and dried to form an island-shaped polymer coating, thereby obtaining a diaphragm. The spraying speed is 0.03 mL / min / mm 2 The weight and thickness of the polymer coating on both sides are consistent, and the coating density of the polymer coating is 1.4mg / 1540mm 2 The coating density of tungsten diselenide is 0.2mg / 1540mm 2 ; The drying temperature is 40°C and the drying time is 5 hours.

[0144] The preparation method of diaphragm 2-8 is similar to that of diaphragm 1, except that the coating density of the thermal insulation material, the material type of the thermal insulation material (the thermal conductivity of aluminum silicate used in diaphragm 5 is 0.044W / (m·K)), the coating density of the polymer coating and the weight content of the thermal insulation material in the polymer coating are adjusted. See Table 1 for details.

[0145] 2. Preparation of secondary batteries

[0146] Example 1

[0147] 1. Preparation of positive electrode sheet

[0148] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black (Super P), binder polyvinylidene fluoride (PVDF) are mixed evenly in a proper amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.2:2.7:1.1 to obtain positive electrode slurry, which is then coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, slit, and cut to obtain positive electrode sheets. The positive electrode surface density is 0.207 mg / mm 2 , compacted density is 3.5g / cm 3 .

[0149] 2. Negative electrode preparation

[0150] The negative electrode active material artificial graphite, conductive agent carbon black (Super P), binder styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC-Na) are mixed evenly in a proper amount of solvent deionized water at a mass ratio of 96.4:0.7:1.8:1.1 to obtain a negative electrode slurry, which is then coated on the negative electrode current collector copper foil, and then dried, cold pressed, slit, and cut to obtain a negative electrode sheet. The negative electrode surface density is 0.126 mg / mm 2 , compacted density is 1.7g / cm 3 .

[0151] 3. Diaphragm

[0152] The separator used was the separator 1 prepared as described above.

[0153] 4. Preparation of electrolyte

[0154] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a mass ratio of 30:70 to obtain an organic solvent, and fully dried electrolyte salt LiPF6 is dissolved in the mixed solvent, the concentration of the electrolyte salt is 1.0 mol / L, and the mixture is evenly mixed to obtain an electrolyte solution.

[0155] 5. Preparation of secondary batteries

[0156] The positive electrode sheet, separator and 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 wound to obtain an electrode assembly (whose thickness is 18 mm); the electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried secondary battery. After vacuum packaging, standing, formation and shaping processes, a secondary battery with a capacity of 71Ah is obtained.

[0157] The preparation methods of the secondary batteries of Examples 2-7 and Comparative Example 1 are similar to the preparation methods of the secondary battery of Example 1, except that different separators are used. See Table 1 for details.

[0158] 3. Performance Test

[0159] 1. Test method for the inner ring temperature of the electrode assembly after cooling for 4 minutes

[0160] A temperature sensing line TT-K-40-SLE-15 was arranged in the inner circle of the electrode assembly to detect the temperature of the innermost circle of the electrode assembly after cooling for 4 minutes.

[0161] 2. Capacity retention rate test method

[0162] In an environment of 25°C, the first charge and discharge are performed, and constant current and constant voltage charging is performed at an equivalent charging current of 2.2C until the upper limit voltage is 4.3V. Then, constant current discharge is performed at a discharge current of 1C until the final voltage is 3.0V, and the first discharge capacity value Cn is recorded. Subsequently, 2.2Cn / 1Cn, 3.0-4.30V continuous charging and discharging cycles are performed, the discharge capacity value during the cycle is recorded, and the cycle capacity retention rate is calculated. The capacity retention rate of the Nth cycle = (discharge capacity of the Nth cycle / discharge capacity of the first cycle) × 100%.

[0163] 3. Test method for lithium precipitation degree

[0164] The secondary battery was subjected to a cyclic charge and discharge procedure, with the charge and discharge currents being 2.2C and 1C respectively, and the number of cycles being 2000. After the cyclic charge and discharge procedure was completed, the secondary battery was disassembled to evaluate the degree of lithium deposition of the negative electrode sheet.

[0165] The evaluation method of lithium precipitation degree is as follows:

[0166] No lithium deposition: No lithium deposition area in a single electrode assembly

[0167] Primary lithium deposition: The maximum area of ​​a single lithium deposition area is ≤5×5mm 2 , the number of lithium deposition areas of a single electrode assembly is ≤1;

[0168] Secondary lithium deposition: 5×5mm 2 <The maximum area of ​​a single lithium deposition area ≤ 10×10mm 2 , the number of lithium deposition areas of a single electrode assembly is ≤1;

[0169] Level 3 lithium plating: does not meet the judgment conditions of the first two levels.

[0170] The above embodiments and comparative examples were tested according to the above process, and the specific values ​​are shown in Table 1.

[0171]

[0172] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A diaphragm, comprising: Base material; a ceramic coating on at least one surface of the substrate; and a polymer coating on the ceramic coating, in, The polymer coating comprises a material having a thermal conductivity less than or equal to 0.12 W / (m·K).

2. The diaphragm according to claim 1, wherein The material with a thermal conductivity less than or equal to 0.12 W / (m·K) includes at least one of tungsten diselenide and aluminum silicate, and can be tungsten diselenide.

3. The diaphragm according to claim 1 or 2, wherein: The coating density of the material with a thermal conductivity less than or equal to 0.12 W / (m·K) is 0.1-0.3 mg / 1540.25 mm 2 , optionally 0.1-0.2mg / 1540.25mm 2 .

4. The diaphragm according to claim 1 or 2, wherein: The coating density of the polymer coating is 0.6-6.5 mg / 1540.25 mm 2 .

5. The diaphragm according to claim 1 or 2, wherein: The weight percentage of the material with a thermal conductivity coefficient less than or equal to 0.12 W / (m·K) in the polymer coating is 1.5%-30%.

6. A method for preparing a diaphragm, comprising the following steps: (1) providing a substrate; (2) providing a ceramic slurry, coating the ceramic slurry on at least one surface of the substrate and drying the ceramic slurry to form a ceramic coating; as well as (3) providing a polymer slurry containing a material having a thermal conductivity of less than or equal to 0.12 W / (m·K), applying the polymer slurry on the ceramic coating and drying the polymer coating to form the polymer coating, thereby obtaining the separator, Wherein, the diaphragm comprises: Base material; a ceramic coating on at least one surface of the substrate; and a polymer coating on the ceramic coating, The polymer coating comprises a material having a thermal conductivity less than or equal to 0.12 W / (m·K).

7. A secondary battery, wherein: A separator comprising the separator according to any one of claims 1 to 5 or a separator prepared by the method according to claim 6.

8. An electrical device, wherein: A secondary battery comprising the secondary battery according to claim 7.

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