Diaphragm, secondary battery and electric equipment

Abstract

The invention provides a diaphragm, a secondary battery and electric equipment. The ionic conductivity of the diaphragm under the pressure of 400 kgf is lambda 1 mS / cm, and the ionic conductivity of the diaphragm under the pressure of 600 kgf is lambda 2 mS / cm and lambda 2 gt; lambda 1 and lambda 2gt; 2.8, the loss factor of the diaphragm is tan delta, and tan delta is greater than or equal to 0.15. The ionic conductivity of the diaphragm under the pressure of 400kgf and 600kgf and the loss factor of the diaphragm are controlled to be within a certain range, so that the cycle performance and the safety of the secondary battery assembled by using the diaphragm are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of diaphragms, and in particular to a diaphragm, a secondary battery, and an electric device. BACKGROUND

[0002] Secondary batteries (such as lithium ion batteries) are widely used in electric vehicles, energy storage systems, and consumer electronics due to their high energy density, long cycle life, and low self-discharge rate. However, with the application of high-capacity electrode materials (such as silicon-based anodes and high-nickel cathodes), the battery will undergo significant volume expansion during charging and discharging, leading to internal stress accumulation and affecting the cycle stability and safety of the battery. SUMMARY

[0003] The present application aims to provide a diaphragm, a secondary battery, and an electric device to improve the cycle performance and safety of the secondary battery.

[0004] To achieve the above-mentioned purpose, the first aspect of the present application provides a diaphragm, the ion conductivity of which under a pressure of 400 kgf is λ1 mS / cm, the ion conductivity of which under a pressure of 600 kgf is λ2 mS / cm, λ2>λ1 and λ2>2.8, and the loss factor of which is tanδ, tanδ≥0.15.

[0005] As an embodiment of the present application, the ion conductivity of the diaphragm under a pressure of 400 kgf is λ1 mS / cm, satisfying: 2.6<λ1<2.95.

[0006] As an embodiment of the present application, the ion conductivity of the diaphragm under a pressure of 600 kgf is λ2 mS / cm, satisfying: 2.8<λ2≤3.1.

[0007] As an embodiment of the present application, the ion conductivity of the diaphragm under a pressure of 200 kgf is λ0 mS / cm, satisfying: 2.45<λ0≤2.55.

[0008] As an embodiment of the present application, the loss factor of the diaphragm is tanδ, satisfying: 0.15≤tanδ≤0.25.

[0009] As an embodiment of the present application, the diaphragm comprises a substrate and a ceramic layer provided on at least one side of the substrate, and the ceramic layer contains piezoelectric ceramic particles and conductive ceramic particles.

[0010] As an embodiment of the present application, the piezoelectric constant D33 of the piezoelectric ceramic particles is greater than or equal to 200 pC / N.

[0011] As an embodiment of the present application, the piezoelectric ceramic particles include one or more of lead zirconate titanate, potassium sodium niobate, bismuth sodium titanate, ZnO nanowires, bismuth zinc titanate-barium titanate, lead magnesium niobate-lead titanate, BaTiO3.

[0012] As an embodiment of the present application, the conductive ceramic particles include Li 3x La 2 / 3-x TiO3, Li 1+y Al y Ti 2-y (PO4)3, Li7La3Zr2O 12 , Li 10 GeP2S 12 , zinc oxide, wherein 0 < x < 2 / 3, 0 < y < 2.

[0013] As an embodiment of the present application, the separator further includes a binding polymer coating layer disposed on a side of the ceramic layer distal from the substrate.

[0014] As an embodiment of the present application, the binding polymer coating layer includes binding polymer particles.

[0015] As an embodiment of the present application, the binding polymer coating layer includes an auxiliary agent, the auxiliary agent including a functional group, the functional group including at least one of an epoxy group, an amino group, a carboxyl group, a siloxyl group.

[0016] As an embodiment of the present application, the binding polymer coating layer includes an auxiliary agent, the auxiliary agent including at least one of polyethylene oxide, polydopamine, polyacrylic acid, dimethylsiloxane, methylvinylsiloxane.

[0017] As an embodiment of the present application, a mass ratio of the binding polymer particles and the auxiliary agent is 1:1 to 9:1.

[0018] As an embodiment of the present application, the binding polymer particles have a core and a shell layer disposed on a surface of the core.

[0019] As an embodiment of the present application, the core includes 40 to 80 parts of a hard monomer, 5 to 10 parts of a crosslinking monomer, and the shell layer includes 10 to 30 parts of a soft monomer, 5 to 15 parts of a borate-modified monomer.

[0020] As an embodiment of the present application, the hard monomer includes at least one of methyl methacrylate, acrylonitrile, styrene.

[0021] As an embodiment of the present application, the crosslinking monomer includes at least one of glycidyl methacrylate, N-methylol acrylamide, acetylacetoxyethyl methacrylate, and vinyltrimethoxysilane.

[0022] As an embodiment of the present application, the soft monomer includes at least one of n-butyl acrylate, ethylhexyl acrylate, lauryl acrylate, and vinyl acetate.

[0023] As an embodiment of the present application, the borate group modified monomer includes at least one of 3-acrylamidophenylboronic acid, 4-vinylphenylboronic acid, bis(acryloyloxymethyl)borate, and 2-(acrylamido)ethylboronic acid.

[0024] In a second aspect of the present application, a secondary battery is provided, which includes the separator of the first aspect of the present application.

[0025] In a third aspect of the present application, an electrical device is provided, which includes the secondary battery of the second aspect of the present application.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] The separator of the present application has a pressure response characteristic and a large loss factor, and can solve the problem of the decrease of the adhesion between the electrode and the separator caused by the volume change of the high-capacity electrode during the charging and discharging process, and improve the cycle performance and safety performance of the secondary battery. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme of the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0029] In the present application, the technical features described in an open manner include both the closed technical scheme consisting of the listed features and the open technical scheme containing the listed features.

[0030] In the present application, when referring to a numerical interval, unless otherwise specified, the numerical interval is considered to be continuous and includes the minimum and maximum values of the range and every value between the minimum and maximum values. Further, when the range refers to integers, every integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be understood as including any and all sub-ranges subsumed therein.

[0031] The reagents or instruments used in the present application are all commercially available conventional products unless otherwise specified.

[0032] The embodiments of the present application provide a separator, the ion conductivity of the separator under a pressure of 400 kgf is λ1 mS / cm, the ion conductivity of the separator under a pressure of 600 kgf is λ2 mS / cm, λ2>λ1 and λ2>2.8, and the loss factor of the separator is tanδ, tanδ≥0.15.

[0033] The inventors of the present application have found that the application of high-capacity electrode materials (such as silicon-based negative electrodes and high-nickel positive electrodes) can cause significant volume expansion of the electrodes, affecting the cycle stability and safety of the secondary battery. By controlling the ion conductivity of the separator under a pressure of 600 kgf to be greater than 2.8 and greater than the ion conductivity of the separator under a pressure of 400 kgf and controlling the loss factor of the separator within a certain range, the long cycle performance and safety of the secondary battery can be significantly improved.

[0034] In some embodiments, the ion conductivity of the separator under a pressure of 400 kgf is λ1 mS / cm, satisfying 2.6<λ1<2.95. Exemplarily, the ion conductivity of the separator under a pressure of 400 kgf λ1 mS / cm can be any one of 2.61 mS / cm, 2.7 mS / cm, 2.75 mS / cm, 2.8 mS / cm, 2.9 mS / cm, 2.94 mS / cm or a range value between any two of them. The ion conductivity of the separator under a pressure of 400 kgf within the above range can improve the long cycle performance of the secondary battery.

[0035] In some embodiments, the ion conductivity of the separator under a pressure of 600 kgf is λ2 mS / cm, satisfying 2.8 < λ2 ≤ 3.1. Illustratively, the ion conductivity of the separator under a pressure of 600 kgf λ2 mS / cm can be any one of 2.81 mS / cm, 2.85 mS / cm, 2.9 mS / cm, 2.95 mS / cm, 3.0 mS / cm, 3.1 mS / cm or a range value between any two of them. The ion conductivity of the separator under a pressure of 600 kgf within the above range can improve the long cycle performance of the secondary battery.

[0036] In some embodiments, the ion conductivity of the separator under a pressure of 200 kgf is λ0 mS / cm, satisfying 2.45 < λ0 ≤ 2.55. Illustratively, the ion conductivity of the separator under a pressure of 200 kgf λ0 mS / cm can be any one of 2.46 mS / cm, 2.47 mS / cm, 2.48 mS / cm, 2.5 mS / cm, 2.52 mS / cm, 2.55 mS / cm or a range value between any two of them. The ion conductivity of the separator under a pressure of 200 kgf within the above range can improve the long cycle performance of the secondary battery.

[0037] In some embodiments, the loss factor of the separator is tan δ, satisfying 0.15 ≤ tan δ ≤ 0.25. Illustratively, the loss factor of the separator tan δ can be any one of 0.15, 0.17, 0.19, 0.21, 0.23, 0.25 or a range value between any two of them. The loss factor of the separator within the above range can provide the separator with excellent impact resistance, and the secondary battery prepared using the separator can thus have further enhanced safety.

[0038] In some embodiments, the separator comprises a substrate and a ceramic layer provided on at least one side of the substrate, the ceramic layer containing piezoelectric ceramic particles and conductive ceramic particles. The ceramic layer containing piezoelectric ceramic particles and conductive ceramic particles is provided on the surface of the substrate, and the combination of piezoelectric ceramic and conductive ceramic is used to meet the heat resistance requirement of the separator on the one hand, and the piezoelectric ceramic has a pressure response effect to generate a strong polarization electric field under stress. This piezoelectric electric field can reduce the ion migration energy barrier, promote the diffusion of active ions, homogenize the transmission of active ions, promote the uniform deposition of active ions on the negative electrode, avoid local aggregation, and can reduce the generation of dendrites, thereby reducing the risk of dendrites piercing the separator, while the high conductivity of the conductive ceramic material can assist the transmission of active ions, and the combination of the two can improve the kinetic performance, cycle performance and safety of the secondary battery.

[0039] In some embodiments, the ceramic layer has a thickness of 1-4 pm. Illustratively, the ceramic layer can have a thickness of any one of 1 pm, 2 pm, 3 pm, 4 pm, or a range between any two of them.

[0040] In some embodiments, the ceramic layer has a mass ratio of piezoelectric ceramic particles to conductive ceramic particles of 1:1-9:1. Illustratively, the ceramic layer can have a mass ratio of piezoelectric ceramic particles to conductive ceramic particles of any one of 1:1, 3:1, 5:1, 7:1, 9:1, or a range between any two of them.

[0041] In some embodiments, the piezoelectric ceramic particles have a piezoelectric constant D33 greater than or equal to 200 pC / N. Illustratively, the piezoelectric ceramic particles can have a piezoelectric constant D33 of any one of 200 pC / N, 220 pC / N, 250 pC / N, 280 pC / N, 300 pC / N, 320 pC / N, 340 pC / N, 360 pC / N, or a range between any two of them. With the piezoelectric constant D33 of the piezoelectric ceramic particles within the above range, the piezoelectric ceramic particles have a more sensitive piezoelectric response effect, which can enhance the piezoelectric response of the overall material. In some embodiments, the piezoelectric ceramic particles have a piezoelectric constant D33 greater than or equal to 200 pC / N and less than or equal to 360 pC / N. The piezoelectric constant D33 (or d 33 ) represents the charge density generated in the first direction (e.g., the electrode surface direction) when the material is subjected to mechanical stress in the third direction (e.g., the thickness direction), which can be tested according to international standards (e.g., ASTM D2915 or IEC 60384-10). During the test, the piezoelectric material is fixed in a clamp, a known alternating force (e.g., ultrasonic vibration) is applied, the amount of charge generated is measured by a charge amplifier, and the piezoelectric constant D33 is calculated.

[0042] In some embodiments, the piezoelectric ceramic particles include one or more of lead zirconate titanate, potassium sodium niobate, bismuth sodium titanate, ZnO nanowires, BZT-BC, lead magnesium niobate-lead titanate, BaTiO3.

[0043] In some embodiments, the conductive ceramic particles include one or more of Li 3x La 2 / 3-x TiO3, Li 1+y Al y Ti 2-y (PO4)3, Li7La3Zr2O 12 , Li 10 GeP2S 12 , zinc oxide, where 0 < x < 2 / 3 and 0 < y < 2.

[0044] In some embodiments, the substrate refers to a substrate having pores or voids inside. Examples of such substrates include microporous membranes, porous sheets made of fibrous materials such as nonwoven fabrics and paper-like sheets, or composite porous sheets obtained by laminating one or more other porous layers on microporous membranes or porous sheets. It should be noted that a microporous membrane refers to a structure having multiple interconnected micropores inside, allowing gas or liquid to flow from one side to the other.

[0045] In some embodiments, the material constituting the substrate can be either an organic or inorganic material with electrical insulating properties. From the viewpoint of imparting a shut-off function to the substrate, thermoplastic resin is particularly preferred as the constituent material of the substrate. Here, the shut-off function refers to the function that, when the battery temperature rises, the thermoplastic resin melts and blocks the pores of the porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery. As a thermoplastic resin, a thermoplastic resin with a melting point below 200°C is preferred, and polyolefins are particularly preferred.

[0046] In some embodiments, a polyolefin microporous membrane is preferred as the substrate used. As the polyolefin microporous membrane, a polyolefin microporous membrane suitable for conventional non-aqueous secondary battery separators, possessing sufficient mechanical properties and ion permeability, can be used. Furthermore, from the viewpoint of having the aforementioned shut-off function, the polyolefin microporous membrane preferably contains polyethylene, and the polyethylene content is preferably 95% by weight or more.

[0047] In some embodiments, as a porous sheet composed of fibrous materials, a porous sheet composed of fibrous materials, including polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, heat-resistant polymers such as aromatic polyamides, polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides, or a mixture of these fibrous materials, can be used.

[0048] In some embodiments, the composite porous sheet can be constructed by laminating a functional layer onto a porous sheet made of a microporous membrane or a fibrous material. Such a composite porous sheet is preferred from the perspective of adding further functionality using the functional layer. As the functional layer, for example from the viewpoint of imparting heat resistance, a porous layer made of a heat-resistant resin or a porous layer made of a heat-resistant resin and an inorganic filler can be used. Examples of heat-resistant resins include one or more heat-resistant polymers selected from aromatic polyamides, polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides. Examples of inorganic fillers include metal oxides such as alumina and metal hydroxides such as magnesium hydroxide. Methods of composite construction include coating the porous sheet with a functional layer, bonding it with an adhesive, and hot-pressing.

[0049] In some embodiments, the separator further includes an adhesive polymer coating disposed on the side of the ceramic layer away from the substrate, the adhesive polymer coating exhibiting pressure responsiveness at pressures ≥2 MPa. For example, it exhibits pressure responsiveness in pressure ranges of 2–3 MPa, 3–4 MPa, 4–5 MPa, 5–6 MPa, 6–7 MPa, 7–8 MPa, 8–9 MPa, and 9–10 MPa. The pressure responsiveness of the adhesive polymer coating means that the coating can reorganize its adhesive force after a certain pressure is applied, thereby improving the problem of weakened adhesion between the separator and the electrode caused by significant volume changes during the charging and discharging process of the secondary battery.

[0050] In some embodiments, the thickness of the adhesive polymer coating is 1–8 μm. Exemplarily, the thickness of the adhesive polymer coating can be any one or a range between any two of the following values: 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, and 8 μm.

[0051] In some embodiments, the adhesive polymer coating comprises adhesive polymer particles.

[0052] In some embodiments, the adhesive polymer coating comprises an auxiliary agent, the auxiliary agent comprising a functional group, the functional group comprising at least one of an epoxy group, an amino group, a carboxyl group, and a siloxy group.

[0053] In some embodiments, the auxiliary agent includes at least one selected from polyethylene oxide, polydopamine, polyacrylic acid, dimethylsiloxane, and methylvinylsiloxane. These substances have functional groups, such as epoxy groups, hydroxyl and amino groups, carboxyl groups, and siloxy groups, which enable them to undergo reversible recombination with the compressed adhesive polymer particles, thereby improving the weakened adhesion between the separator and the electrode and enhancing the long-cycle performance of the secondary battery.

[0054] In some embodiments, the mass ratio of the adhesive polymer particles to the auxiliary agent is 1:1 to 9:1. Exemplarily, the mass ratio of the adhesive polymer particles to the auxiliary agent can be any one of 1:1, 3:1, 5:1, 7:1, or 9:1, or a range between any two values. A mass ratio of adhesive polymer particles to the auxiliary agent within the above range is beneficial for improving the adhesion between the adhesive polymer coating and the electrode, thereby improving the long-cycle performance of the secondary battery.

[0055] In some embodiments, the adhesive polymer particles have a core and a shell disposed on the surface of the core.

[0056] In some embodiments, the core monomer comprises 40-80 parts hard monomer and 5-10 parts crosslinked monomer; the shell monomer comprises 10-30 parts soft monomer and 5-15 parts borate-modified monomer. The adhesive polymer particles prepared using hard monomer and crosslinked monomer as the core raw material, and soft monomer and borate-modified monomer as the shell raw material, possess the characteristics of a hard core and soft shell. On the one hand, the hard core provides polymer rigidity and resistance to polymer swelling; on the other hand, the soft shell provides adhesion and polymer flexibility, thereby improving the kinetic and cycle performance of the secondary battery.

[0057] In some embodiments, the method for preparing the adhesive polymer particles includes the following steps:

[0058] Step 1: Synthesis of kernel seed emulsion: Mix 3% to 10% of kernel monomer, reactive emulsifier and deionized water, stir, and simultaneously purge with nitrogen gas. Add a certain amount of initiator and heat to 70℃ to 80℃ for 0.5h to 1h to obtain kernel seed emulsion.

[0059] Step 2, Synthesis of core layer emulsion: The remaining kernel monomers and initiator are mixed and added to the kernel seed emulsion, heated to 80℃~90℃, and reacted for 1.5h~2h to obtain the kernel emulsion;

[0060] Step 3: Preparation of polymer particle emulsion: Take the core emulsion, add the shell monomer and deionized water, keep warm at 80℃~90℃, add a certain amount of initiator, and react for 1.5h~2h to obtain polymer particle emulsion.

[0061] In some embodiments, the hard monomer includes at least one of methyl methacrylate, acrylonitrile, and styrene.

[0062] In some embodiments, the crosslinking monomer includes at least one selected from glycidyl methacrylate, N-hydroxymethylacrylamide, acetylacetoxyethyl acrylate, and vinyltrimethoxysilane.

[0063] In some embodiments, the soft monomer includes at least one of n-butyl acrylate, ethylhexyl acrylate, lauryl acrylate, and vinyl acetate.

[0064] In some embodiments, the borate-modified monomer includes at least one of 3-acrylamidophenylboronic acid, 4-vinylphenylboronic acid, bis(acryloyloxymethyl)boronic acid, and 2-(acrylamido)ethylboronic acid.

[0065] In some embodiments, the reactive emulsifier includes one or more of polyoxyethylene acrylate (PEG-AA), allyl polyoxyethylene ether (APEG), epoxy polyoxyethylene ether (EPEG), sodium allyl sulfonate (ALS), and sodium styrene sulfonate (SSS). Using these substances as reactive emulsifiers can, on the one hand, stabilize the emulsion through emulsification; on the other hand, the reactive groups can react with the monomers to become part of the polymer, thereby significantly improving the performance and stability of the emulsion polymer and avoiding the excessive increase in permeability that free emulsifiers might cause to the membrane. The amount of the reactive emulsifier is 0.5% to 2% of the core monomer.

[0066] In some embodiments, the initiator includes at least one selected from tert-butyl hydroperoxide, sodium bisulfite, vitamin C, sodium persulfate, ammonium persulfate, potassium persulfate, benzoyl peroxide, and azobisisobutyronitrile, and the amount of the initiator is 2% to 8% of the monomer amount.

[0067] A second aspect of this application provides a secondary battery, the secondary battery including the separator described in the first aspect of this application. The secondary battery also includes a positive electrode, a negative electrode, and an electrolyte.

[0068] In some embodiments, the hardness of the secondary battery after 1500 cycles at 25°C is 7300–14100 gf.

[0069] In some embodiments, after the secondary battery is cycled 1500 times at 25°C, the peel force between the separator and the positive electrode is greater than or equal to 2N / m.

[0070] In some embodiments, the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer contains a positive active material.

[0071] In some embodiments, the positive electrode active material includes, but is not limited to, at least one of lithium iron phosphate, lithium manganese iron phosphate, and lithium nickel cobalt manganese oxide. The positive electrode active material may further preferably be LiNiO2, LiCoO2, LiMnO2, or LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.5 Co 0.2 Al 0.3 One or more of O2.

[0072] In some embodiments, the positive electrode active material layer further includes a positive electrode conductive agent and a positive electrode binder. This application does not limit the types of positive electrode conductive agents and positive electrode binders. The positive electrode conductive agent includes, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene-reduced graphene oxide, and carbon nanofibers. The positive electrode binder includes, but is not limited to, at least one of polyvinylidene fluoride, copolymers of polyvinylidene fluoride, polytetrafluoroethylene, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0073] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative active material layer contains a negative active material.

[0074] In some embodiments, the negative electrode active material includes, but is not limited to, at least one of silicon material, carbon material, and silicon-carbon composite material; the silicon material includes at least one of elemental silicon, silicon oxide, and silicon carbide; and the carbon material includes graphite.

[0075] In some embodiments, the negative electrode active material layer further includes a negative electrode conductive agent, a thickener, and a negative electrode binder. This application does not limit the types of negative electrode conductive agents, dispersants, and binders in the negative electrode active material layer. The negative electrode conductive agent includes, but is not limited to, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene-reduced graphene oxide, and carbon nanofibers. The dispersant includes, but is not limited to, carboxymethyl cellulose. The negative electrode binder includes, but is not limited to, styrene-butadiene rubber and polyacrylic acid.

[0076] Commonly used positive and negative current collectors in this art can be used to prepare the secondary battery described in this application. The negative current collector is preferably made of copper foil or carbon-coated copper foil. The positive current collector can be made of metal materials such as aluminum, stainless steel, nickel plating, titanium, or tantalum; carbon materials such as carbon cloth or carbon paper; or composite materials formed by polymers and metal layers. In some embodiments, the positive current collector is preferably made of aluminum foil or carbon-coated aluminum foil.

[0077] In some embodiments, the electrolyte includes a lithium salt and an organic solvent, and may also contain additives. The types and compositions of the lithium salt and organic solvent are not particularly limited and can be selected according to actual needs. The lithium salt may include lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, etc.; the solvent may include ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and propyl propionate, etc.; and the additives may include lithium difluorophosphate, lithium bis(oxalato)borate, tris(trimethylsilyl)borate, 1,3-propanesulfonyl lactone, and vinyl sulfate, etc.

[0078] A third aspect of this application provides an electrical device, which includes the secondary battery described in the second aspect of this application. The electrical device can be an application device such as a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, and power tool. Vehicles can be new energy vehicles, including pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles; spacecraft include airplanes, rockets, space shuttles, and spacecraft; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys; power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers. This application does not impose special limitations on the above-described device.

[0079] The following are specific embodiments of this application, and the technical solutions of this application are further described in conjunction with the embodiments. However, this application is not limited to these embodiments. Unless otherwise specified, the reagents, methods, and equipment used in this application are all conventional reagents, methods, and equipment in this technical field.

[0080] Example 1

[0081] This embodiment provides a diaphragm, the preparation method of which includes the following steps:

[0082] S1. Preparation of pressure-responsive ceramic coatings:

[0083] S11. Mix 0.3 parts sodium polyacrylate, 30 parts ceramic particles (25 parts lead zirconate titanate (PZT) and 5 parts Li... 1.5 Al 0.5 Ti 1.5 (PO4)3(LATP)), 3 parts polyacrylate and 66.7 parts deionized water are mixed evenly and stirred thoroughly using a high-speed disperser to obtain an aqueous slurry;

[0084] S12. The prepared water-based slurry is coated onto one side of a polyethylene substrate by roller coating, and after drying, a ceramic coating is obtained with a single-sided thickness of 2μm.

[0085] S13. Apply a DC electric field of 20kV / mm at 80℃ for 1h to activate the piezoelectricity of the ceramic coating. After polarization is complete, maintain the electric field to room temperature to obtain a pressure-responsive ceramic coating.

[0086] S2. Preparation of adhesive polymer coating:

[0087] S21. Mix 3 parts methyl methacrylate, 0.4 parts glycidyl methacrylate, 0.6 parts allyl polyoxyethylene ether and 5 parts deionized water and stir for 30 min while purging with nitrogen. Add 0.3 parts sodium persulfate and heat to 75°C for 0.5 h to obtain a kernel seed emulsion for later use.

[0088] S22. The remaining 57 parts of methyl methacrylate, 9.6 parts of glycidyl methacrylate, 0.7 parts of sodium persulfate and 35 parts of deionized water were mixed and added to the kernel layer seed emulsion. The mixture was heated to 80°C and reacted for 2 hours to obtain the kernel layer emulsion.

[0089] S23. Take the core layer emulsion, add 20 parts of n-butyl acrylate, 10 parts of 3-acrylamidophenylboronic acid and 20 parts of deionized water, keep warm at 85℃, add 0.3 parts of sodium persulfate, react for 2 hours to obtain an adhesive polymer particle emulsion.

[0090] S24. The above-mentioned adhesive polymer particle emulsion and polyethylene oxide auxiliary agent are mixed and stirred evenly. The ratio of adhesive polymer particles to polyethylene oxide is 9:1. The mixture is then coated onto the surface of a pressure-responsive ceramic coating by spraying. The coating thickness is 5 μm, thus obtaining the diaphragm.

[0091] Example 2

[0092] This embodiment provides a diaphragm, the preparation method of which includes the following steps:

[0093] S1. Preparation of pressure-responsive ceramic coatings:

[0094] S11. Mix 0.3 parts ammonium polyacrylate, 30 parts ceramic particles (25 parts sodium bismuth titanate (BNT) and 5 parts Li7La3Zr2O) 12 (LLZO)), 5 parts polyvinyl alcohol and 67.7 parts deionized water are mixed evenly and thoroughly stirred using a high-speed disperser to obtain an aqueous slurry;

[0095] S12. The prepared water-based slurry is coated onto one side of a polyethylene substrate by roller coating, and after drying, a ceramic coating with a thickness of 3 μm is obtained.

[0096] S13. Apply a DC electric field of 20kV / mm at 80℃ for 1h to activate the piezoelectricity of the coating. After polarization is complete, maintain the electric field to room temperature to obtain a pressure-responsive ceramic coating.

[0097] S2. Preparation of adhesive polymer coating:

[0098] S21. Mix 2.5 parts styrene, 0.5 parts vinyltrimethoxysilane, 0.6 parts sodium styrene sulfonate, and 5 parts deionized water and stir for 30 min while purging with nitrogen. Add 0.3 parts benzoyl peroxide and heat to 75°C for 0.5 h to obtain a kernel layer seed emulsion for later use.

[0099] S22. The remaining 47.5 parts of styrene, 9.5 parts of vinyltrimethoxysilane, 0.7 parts of benzoyl peroxide and 35 parts of deionized water were mixed and added to the core layer seed emulsion. The mixture was heated to 80°C and reacted for 2 hours to obtain the core layer emulsion.

[0100] S23. Take the core layer emulsion, add 30 parts of vinyl acetate, 12 parts of 2-(acrylamido)ethylboric acid and 20 parts of deionized water, keep warm at 85°C, add 0.3 parts of benzoyl peroxide, react for 2 hours to obtain an adhesive polymer particle emulsion.

[0101] S24. The above-mentioned adhesive polymer particles and polydopamine auxiliary agent are mixed and stirred evenly. The ratio of adhesive polymer particles to auxiliary agent is 9:1. The mixture is then coated onto the surface of a pressure-responsive ceramic coating by spraying. The coating thickness is 3 μm, thus obtaining the diaphragm.

[0102] Example 3

[0103] This embodiment provides a diaphragm, the preparation method of which differs from that of Example 1 in that the amount of 3-acrylamidophenylboronic acid is changed to 5 parts.

[0104] Example 4

[0105] This embodiment provides a diaphragm, the preparation method of which differs from that of Example 1 in that the amount of 3-acrylamidophenylboronic acid is changed to 15 parts.

[0106] Example 5

[0107] This embodiment provides a diaphragm whose preparation method differs from that of Example 1 in that 25 parts of lead zirconate titanate (PZT) and 5 parts of LATP are replaced with 15 parts of lead zirconate titanate (PZT) and 15 parts of LATP.

[0108] Example 6

[0109] This embodiment provides a diaphragm, the preparation method of which differs from that of Example 1 in that 25 parts of lead zirconate titanate (PZT) and 5 parts of LATP are changed to 27 parts of lead zirconate titanate (PZT) and 3 parts of LATP.

[0110] Example 7

[0111] This embodiment provides a diaphragm, the preparation method of which differs from that of Example 1 in that the ratio of adhesive polymer particles to polyethylene oxide auxiliaries is changed to 5:1.

[0112] Example 8

[0113] This embodiment provides a diaphragm, the preparation method of which differs from that of Example 1 in that the ratio of adhesive polymer particles to polyethylene oxide auxiliaries is changed to 1:1.

[0114] Comparative Example 1

[0115] This comparative example provides a diaphragm whose preparation method differs from that of Example 1 in that the amount of 3-acrylamidophenylboronic acid (AAPBA) is changed to 0 parts.

[0116] Comparative Example 2

[0117] This comparative example provides a diaphragm whose preparation method differs from that of Example 1 in that 25 parts of lead zirconate titanate (PZT) and 5 parts of LATP are replaced with 30 parts of lead zirconate titanate (PZT).

[0118] Comparative Example 3

[0119] This comparative example provides a diaphragm whose preparation method differs from that of Example 1 in that 25 parts of lead zirconate titanate (PZT) and 5 parts of LATP are replaced with 30 parts of LATP.

[0120] Comparative Example 4

[0121] This comparative example provides a diaphragm whose preparation method differs from that of Example 1 in that it does not use polyethylene oxide as an auxiliary agent.

[0122] The ionic conductivity and loss factor of the membranes prepared in each embodiment and comparative example were tested using the following methods, and the test results are shown in Table 1:

[0123] 1. Ionic conductivity:

[0124] The ionic conductivity of the coated separator was tested by assembling a symmetrical cell. Specifically, a symmetrical cell structure (copper foil + separator + copper foil) was assembled. By changing the number of separator layers, the impedance of the cell with different separator layer numbers was measured using EIS (electrochemical impedance spectroscopy), and a linear fit was performed. The slope was then taken as the separator impedance Rs. The separator ionic conductivity was calculated using the following formula: λ = d / Rs·S, where d is the separator thickness and S is the effective separator area. The separator impedance was tested under different pressures, and the ionic conductivity at these pressures, including 200 kgf, 400 kgf, and 600 kgf, was obtained.

[0125] 2. Loss factor:

[0126] (1) Sample preparation: The diaphragm was stacked in 32 layers, and the sample size was 10mm×10mm;

[0127] (2) Setting parameters: Prestress: 0.15N; Stress rate: 60MPa / min;

[0128] (3) Sample testing: Using a mechanical thermal analyzer, the storage modulus E′, loss modulus E″ and phase angle δ were measured at room temperature;

[0129] (4) Calculate the loss factor: tanδ=E″ / E′ to obtain the loss factor.

[0130] Table 1

[0131]

[0132] The separators prepared in Examples 1-8 and Comparative Examples 1-4 were assembled into lithium-ion batteries. The assembly method included the following steps:

[0133] (1) Preparation of the positive electrode sheet:

[0134] The positive electrode active material nickel-cobalt-manganese ternary material, conductive agent (SP), and binder PVDF are mixed and stirred in NMP at a mass ratio of 92:5:3 to form a positive electrode slurry. The slurry is evenly coated on both sides of aluminum foil, baked and dried, and the coated electrode sheet is cold-pressed, slit, and cut to obtain the positive electrode sheet.

[0135] (2) Preparation of negative electrode sheet:

[0136] The negative electrode active material graphite, conductive agent (SP), dispersant (CMC) and binder (SBR) are mixed in deionized water in a ratio of 91:3:3:3 to form a negative electrode slurry. The negative electrode slurry is coated on both sides of copper foil, baked and dried, and the coated electrode sheet is cold-pressed, slit and cut to obtain the negative electrode sheet.

[0137] (3) Preparation of electrolyte:

[0138] The electrolyte lithium hexafluorophosphate was dissolved in a mixed solvent in a mass ratio of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate of 1:2:1 to obtain a lithium-ion battery electrolyte.

[0139] (4) Lithium-ion battery assembly:

[0140] After the prepared positive electrode sheet, the separator and negative electrode sheet of the examples and comparative examples are stacked, they are wound, hot-pressed and shaped (3MPa&95℃&15s), and the tabs are welded to obtain a bare cell. The bare cell is placed in an aluminum shell, the prepared electrolyte is injected, and the lithium-ion battery is made through processes such as encapsulation, formation and capacity testing.

[0141] The performance of the prepared lithium-ion batteries was tested using the following methods, and the results are shown in Table 2:

[0142] (a) DCR: Under 25℃ conditions, the battery is fully charged to 4.2V at a rate of 1C, then charged to 0.05C at a constant voltage, then discharged at a rate of 1C for 40min (20% SOC), and then discharged at the required rate (0.1~1C) for 10s (sampling at 0.1s). The voltage drop ΔU and the current difference ΔI are recorded. Then DCR=ΔU / ΔI.

[0143] (ii) Cyclic test: Charge and discharge at 2C / 1C rates at 25℃ and 45℃ respectively, cycle the battery from 0 to 100% SOC to 1500 cycles, and record the discharge capacity retention rate at this time.

[0144] (III) Battery hardness test: Take a battery that has been cycled at 25℃, discharge the battery voltage to 0V at a rate of 0.1C, and perform a puncture test on the battery at 50mm / min with a needle diameter of 1mm.

[0145] (iv) Peeling force test: Take the battery that has been discharged to 0V after cycling at 25℃, disassemble it, place it in a dry room for 8 hours, cut the sample to 100*50mm in length and width, and perform a 180° peel test at a peeling speed of 80mm / min to obtain the positive electrode peeling force.

[0146] Table 2

[0147]

[0148]

[0149] As can be seen from the above examples and comparative examples, the secondary battery prepared by the separator provided in this application has excellent electrochemical performance and excellent cycle performance. In Examples 1 to 8, after 1500 cls of cycling, the discharge capacity retention rate at 25°C and 45°C is >80%.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A diaphragm, characterized in that, The ionic conductivity of the diaphragm at 400 kgf pressure is λ1 mS / cm, and the ionic conductivity of the diaphragm at 600 kgf pressure is λ2 mS / cm, where λ2 > λ1 and λ2 > 2.

8. The loss factor of the diaphragm is tanδ, where tanδ ≥ 0.

15.

2. The diaphragm according to claim 1, characterized in that, Satisfying at least one of the following characteristics: (1) 2.6 < λ1 < 2.95; (2) 2.8 < λ² ≤ 3.1; (3) 0.15≤tanδ≤0.

25.

3. The diaphragm according to claim 1, characterized in that, The ionic conductivity of the diaphragm at a pressure of 200 kgf is λ0 mS / cm, which satisfies the condition: 2.45 < λ0 ≤ 2.

55.

4. The diaphragm according to any one of claims 1 to 3, characterized in that, The diaphragm includes a substrate and a ceramic layer disposed on at least one side of the substrate, the ceramic layer containing piezoelectric ceramic particles and conductive ceramic particles.

5. The diaphragm according to claim 4, characterized in that, The piezoelectric constant D33 of the piezoelectric ceramic particles is greater than or equal to 200 pC / N.

6. The diaphragm according to claim 4, characterized in that, The piezoelectric ceramic particles include one or more of lead zirconate titanate, potassium sodium niobate, sodium bismuth titanate, ZnO nanowires, bismuth zinc titanate-barium titanate, lead magnesium niobate-lead titanate, and BaTiO3. And / or, the conductive ceramic particles include Li 3x La 2 / 3-x TiO3, Li 1+y Al y Ti 2-y (PO4)3, Li7La3Zr2O 12 Li 10 GeP2S 12 One or more of zinc oxide, wherein 0 <x<2 / 3,0<y<2。 7. The diaphragm according to claim 4, characterized in that, The diaphragm also includes an adhesive polymer coating disposed on the side of the ceramic layer away from the substrate.

8. The diaphragm according to claim 7, characterized in that, The adhesive polymer coating comprises adhesive polymer particles.

9. The diaphragm according to claim 8, characterized in that, The adhesive polymer coating includes an auxiliary agent, which contains a functional group, and the functional group includes at least one of epoxy group, amino group, carboxyl group, and siloxy group.

10. The diaphragm according to claim 9, characterized in that, The auxiliary agent includes at least one of polyethylene oxide, polydopamine, polyacrylic acid, dimethylsiloxane, and methylvinylsiloxane.

11. The diaphragm according to claim 9, characterized in that, The mass ratio of the adhesive polymer particles to the auxiliary agent is 1:1 to 9:

1.

12. The diaphragm according to claim 8, characterized in that, The adhesive polymer particles have a core and a shell disposed on the surface of the core.

13. The diaphragm according to claim 12, characterized in that, The polymer monomers of the core include 40-80 parts of hard monomers and 5-10 parts of crosslinking monomers; the polymer monomers of the shell include 10-30 parts of soft monomers and 5-15 parts of borate-modified monomers.

14. The diaphragm according to claim 13, characterized in that, The hard monomer includes at least one of methyl methacrylate, acrylonitrile, and styrene; And / or, the crosslinking monomer includes at least one of glycidyl methacrylate, N-hydroxymethylacrylamide, acetylacetoxyethyl methacrylate, and vinyltrimethoxysilane; And / or, the soft monomer includes at least one of n-butyl acrylate, ethylhexyl acrylate, lauryl acrylate, and vinyl acetate; And / or, the borate-modified monomer includes at least one of 3-acrylamidophenylboronic acid, 4-vinylphenylboronic acid, bis(acryloyloxymethyl)boronic acid, and 2-(acrylamido)ethylboronic acid.

15. A secondary battery, characterized in that, The secondary battery includes the separator as described in any one of claims 1 to 14.

16. An electrical appliance, characterized in that, The electrical equipment includes the secondary battery as described in claim 15.

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