Coating, secondary battery and electronic device

Abstract

Disclosed in the present application are a coating, a secondary battery and an electronic device. The coating comprises diazine and a derivative thereof and / or triazine and a derivative thereof, wherein the structures of the diazine and the derivative thereof, and the triazine and the derivative thereof comprise nitrogen-containing six-membered heterocycles. The coating provided by the present application can improve the cycle performance and high-temperature stability of a secondary battery.

Description

Coatings, secondary batteries and electronic devices

[0001] This application claims priority to Chinese Patent Application No. 202411867014.3, filed on December 18, 2024, entitled "Coating, Secondary Battery and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical energy storage, and more particularly to a coating, a secondary battery, and an electronic device. Background Technology

[0003] To stabilize the structure of the positive electrode material, cyanide-containing additives are usually introduced into the electrolyte. However, when cyanide-containing additives are introduced into the electrolyte, the cyanide groups migrate to the negative electrode and become incompatible with graphite or metallic lithium on the negative electrode, causing a reduction reaction at the negative electrode. This leads to a deterioration in the battery's cycle performance, an increase in battery impedance, and accelerated battery degradation. Summary of the Invention

[0004] In view of this, this application provides a coating, a secondary battery, and an electronic device.

[0005] The first aspect of this application provides a coating comprising diazine and its derivatives and / or triazine and its derivatives, wherein the structure of the diazine and its derivatives comprises a nitrogen-containing six-membered heterocycle as shown in structural formula (I):

[0006] The structures of triazine and its derivatives include nitrogen-containing six-membered heterocycles as shown in structural formula (II):

[0007] The nitrogen-containing six-membered heterocycles shown in structural formulas (I) and (II) also include at least one functional group selected from amino, carbonyl, chlorine, pyridyl, bromophenoxy, methoxy, cyano, carboxyl, bromophenyl, or amide.

[0008] In this application, diazine and its derivatives and / or triazine and its derivatives with specific molecular structures are selected as coatings. Due to the electron-withdrawing ability of nitrogen atoms, the molecular structures of diazine and its derivatives and triazine and their derivatives exhibit delocalized aromaticity. When this coating is applied to the surface of the positive electrode or separator, it can provide electrons to the positive electrode material, thereby stabilizing the structure of the positive electrode material. On the other hand, free water molecules in the electrolyte can cause the electrolyte to react, leading to heat generation in the battery and negatively impacting its high-temperature stability. Diazine and its derivatives and triazine and their derivatives can adsorb free water in the electrolyte, improving the high-temperature stability and cycle performance of the secondary battery, and reducing its impedance.

[0009] Based on the first aspect, in some embodiments, diazine and its derivatives include at least one of 2-aminopyrazine, pyrazinamide, 5,6-diamino-2,3-dicyanopyrazine, 2-amino-6-methoxypyrazine, or 2,3-dicyanopyrazine.

[0010] Based on the first aspect, in some embodiments, the diazine and its derivatives are 2,3-dicyanopyrazine. 2,3-dicyanopyrazine exhibits better thermal stability and more stable chemical properties, which helps improve the high-temperature stability and cycle performance of the secondary battery and reduce its impedance.

[0011] Based on the first aspect, in some embodiments, triazine and its derivatives include at least one selected from symmetrical triaminotriazine, 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine, melamine cyanurate, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazin-2-yl)guanidine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, cyanuric chloride, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, tris(tribromophenoxy)triazine, or 2-amino-4,6-methoxy-1,3,5-triazine.

[0012] Based on the first aspect, in some embodiments, the triazine and its derivatives are symmetrical triaminotriazines. Symmetrical triaminotriazines have excellent ability to improve the high-temperature stability and cycle performance of secondary batteries and reduce the impedance of secondary batteries.

[0013] Based on the first aspect, in some embodiments, the mass percentage 'a' of diazine and its derivatives and / or triazine and its derivatives in the coating is 50 wt% to 95 wt%. Controlling the mass percentage of diazine and its derivatives and / or triazine and its derivatives in the coating within the above range helps to improve the compressive strength, i.e., mechanical properties, of the secondary battery. On the other hand, it has a good effect on stabilizing the structure of the positive electrode material, which helps to improve the cycle performance of the secondary battery and reduce the impedance of the secondary battery.

[0014] Based on the first aspect, in some embodiments, the Dv50 particle size of diazine and its derivatives and triazine and its derivatives is 300 nm to 1000 nm. The Dv50 particle size of diazine and its derivatives and triazine and its derivatives being within the above range is beneficial for their uniform dispersion in the coating, thereby improving the cycle performance of the secondary battery.

[0015] Based on the first aspect, in some embodiments, the morphology of diazine and its derivatives and triazine and its derivatives includes at least one of rod-shaped, sheet-shaped or stacked sheet-shaped.

[0016] Based on the first aspect, in some embodiments, diazine and its derivatives and / or triazine and its derivatives satisfy at least one of the following conditions:

[0017] (1) The length of rod-shaped diazine and its derivatives and triazine and its derivatives is 3 to 20 mm;

[0018] (2) The flatness of the sheet-like diazine and its derivatives and triazine and its derivatives is 3 to 50;

[0019] (3) The number of stacked layers of diazine and its derivatives and triazine and its derivatives is 3 to 20.

[0020] In diazine and its derivatives, and triazine and its derivatives, rod-shaped particles with a length of 3–20 mm can improve their dispersion uniformity in the coating and enhance the compressive strength of the secondary battery. They can also reduce the impedance of the secondary battery and improve its cycle performance. Flaky particles with a flatness of 3–50 mm are beneficial for reducing the impedance of the secondary battery and improving its compressive strength and cycle performance, without negatively impacting the impedance and compressive strength due to increased interparticle space obstruction. Stacked flaky particles with a stacking number of 3–20 layers are beneficial for improving the compressive strength, reducing the impedance, and enhancing the cycle performance of the secondary battery.

[0021] Based on the first aspect, in some embodiments, the melting points of diazine and its derivatives and / or triazine and its derivatives are 115°C to 360°C. When the melting points of diazine and its derivatives and / or triazine and its derivatives are within the above range, the secondary battery exhibits high compressive strength, low impedance, good cycle performance, and good high-temperature stability.

[0022] Based on the first aspect, in some embodiments, the coating further includes an adhesive, which includes at least one of melamine resin, isocyanate-based crosslinking agent, styrene-butadiene rubber, polyacrylate, carboxymethyl cellulose, or polyvinylidene fluoride.

[0023] A second aspect of this application provides a secondary battery, which includes a positive electrode, a negative electrode, a separator, and a coating. The separator is disposed between the positive electrode and the negative electrode. The positive electrode includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. The coating is disposed between the positive current collector and the positive active layer, and / or the coating is disposed between the positive active layer and the separator.

[0024] Based on the second aspect, in some embodiments, the coating is located between the positive electrode active layer and the separator, and the coating thickness is 1 μm to 4 μm. When the coating is located between the positive electrode active layer and the separator, controlling the coating thickness within the above range helps to improve the high-temperature stability and cycle performance of the secondary battery.

[0025] Based on the second aspect, in some embodiments, the coating is located between the positive electrode active layer and the positive electrode current collector, and the coating thickness is 0.5 μm to 2 μm. When the coating is located between the positive electrode active layer and the positive electrode current collector, controlling the coating thickness within the above range can reduce the impedance of the secondary battery and help improve the high-temperature stability and cycle performance of the secondary battery.

[0026] A third aspect of this application provides an electronic device including the aforementioned secondary battery. The secondary battery powers the electronic device and, after high-temperature stability testing and cycle performance testing, exhibits good high-temperature storage performance and cycle performance, as well as low impedance and high compressive strength. Detailed Implementation

[0027] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. The reagents and materials described in the following embodiments are all commercially available.

[0028] As used in this application, the terms “comprising,” “containing,” and “including” are used in their open, non-restrictive sense.

[0029] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0030] In the detailed description and claims, a list of items connected by the terms "one or more of," "one or more of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A or B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, or C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0031] This application provides a coating comprising diazine and its derivatives and / or triazine and its derivatives, wherein the structure of the diazine and its derivatives comprises a nitrogen-containing six-membered heterocycle as shown in structural formula (I):

[0032] The structures of triazine and its derivatives include nitrogen-containing six-membered heterocycles as shown in structural formula (II):

[0033] The nitrogen-containing six-membered heterocycles shown in structural formulas (I) and (II) further include at least one functional group selected from amino, carbonyl, chlorine, pyridyl, bromophenoxy, methoxy, cyano, carboxyl, bromophenyl, or amide.

[0034] In this application, diazine and its derivatives and / or triazine and its derivatives with specific molecular structures are selected as coatings. Due to the electron-withdrawing ability of nitrogen atoms, the molecular structures of diazine and its derivatives and triazine and their derivatives exhibit delocalized aromaticity. When this coating is applied to the surface of the positive electrode or separator, it can provide electrons to the positive electrode material, thereby stabilizing the structure of the positive electrode material. On the other hand, free water molecules in the electrolyte can cause the electrolyte to react, leading to heat generation in the battery and negatively impacting its high-temperature stability. Diazine and its derivatives and triazine and their derivatives can adsorb free water in the electrolyte, improving the high-temperature stability and cycle performance of the secondary battery, and reducing its impedance.

[0035] In some embodiments, diazine and its derivatives include at least one of 2-aminopyrazine, pyrazinamide, 5,6-diamino-2,3-dicyanopyrazine, 2-amino-6-methoxypyrazine, or 2,3-dicyanopyrazine.

[0036] In some embodiments, the diazine and its derivatives are 2,3-dicyanopyrazine. 2,3-dicyanopyrazine exhibits better thermal stability and more stable chemical properties, contributing to improved high-temperature stability and cycle performance of secondary batteries, as well as reduced battery impedance.

[0037] In some embodiments, triazine and its derivatives include at least one of symmetrical triaminotriazine, 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine, melamine cyanurate, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazin-2-yl)guanidine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, cyanuric chloride, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, tris(tribromophenoxy)triazine, or 2-amino-4,6-methoxy-1,3,5-triazine.

[0038] In some embodiments, the triazine and its derivatives are symmetrical triaminotriazines. Symmetrical triaminotriazines have excellent ability to improve the high-temperature stability and cycle performance of secondary batteries and reduce the impedance of secondary batteries.

[0039] In some embodiments, the mass percentage 'a' of diazine and its derivatives and / or triazine and its derivatives in the coating is 50 wt% to 95 wt%, for example, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, or any value within the range of any two of the above values. Controlling the mass percentage of diazine and its derivatives and / or triazine and its derivatives in the coating within the above range helps to improve the compressive strength, i.e., mechanical properties, of the secondary battery. Furthermore, it effectively stabilizes the structure of the positive electrode material, thus improving the cycle performance and reducing the impedance of the secondary battery.

[0040] In some embodiments, the Dv50 particle size of diazine and its derivatives and triazine and its derivatives is 300 nm to 1000 nm, for example, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, or any value within the range of any two of the above values. The Dv50 particle size of diazine and its derivatives and triazine and its derivatives being within the above range is beneficial for their uniform dispersion in the coating, thereby improving the cycle performance of the secondary battery.

[0041] In some embodiments, the morphology of diazine and its derivatives and triazine and its derivatives includes at least one of rod-shaped, sheet-shaped, or stacked sheet-shaped forms.

[0042] In some embodiments, diazine and its derivatives and triazine and its derivatives satisfy at least one of the following conditions:

[0043] (1) The length of rod-shaped diazine and its derivatives and triazine and its derivatives is 3 to 20 mm;

[0044] (2) The flatness of the sheet-like diazine and its derivatives and triazine and its derivatives is 3 to 50;

[0045] (3) The number of stacked layers of diazine and its derivatives and triazine and its derivatives is 3 to 20.

[0046] For example, the length of rod-shaped diazine and its derivatives and triazine and its derivatives can be 3, 5, 8, 10, 13, 15, 18, 20 or any value within the range of any two of the above values; the flatness of sheet-like diazine and its derivatives and triazine and its derivatives can be 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or any value within the range of any two of the above values; the number of stacked layers of stacked sheet-like diazine and its derivatives and triazine and its derivatives can be 3, 5, 8, 10, 13, 15, 18, 20 or any value within the range of any two of the above values. In diazine and its derivatives, and triazine and its derivatives, rod-shaped particles with an aspect ratio of 3–20 mm can improve their dispersion uniformity in the coating and enhance the compressive strength of the secondary battery. They can also reduce the impedance of the secondary battery and improve its cycle performance. Flaky particles with an aspect ratio of 3–50 mm are beneficial for reducing the impedance of the secondary battery and improving its compressive strength and cycle performance, without negatively impacting the impedance and compressive strength due to increased interparticle space obstruction. Stacked flaky particles with 3–20 stacked layers are beneficial for improving the compressive strength, reducing the impedance, and enhancing the cycle performance of the secondary battery.

[0047] In this application, "length" refers to the ratio of the major diameter to the minor diameter of the particle; "flatness" refers to the ratio of the minor diameter to the thickness of the particle.

[0048] In some embodiments, the melting point of diazine and its derivatives and / or triazine and its derivatives is 115°C to 350°C, for example, 115°C, 120°C, 140°C, 160°C, 180°C, 200°C, 220°C, 240°C, 260°C, 280°C, 300°C, 320°C, 340°C, 350°C, or any value within the range of any two of the above values. When the melting point of diazine and its derivatives and / or triazine and its derivatives is within the above range, the secondary battery exhibits high compressive strength, low impedance, good cycle performance, and good high-temperature stability.

[0049] In some embodiments, the coating further includes an adhesive, which includes at least one selected from melamine resin, isocyanate-based crosslinking agent, styrene-butadiene rubber, polyacrylate, carboxymethyl cellulose, or polyvinylidene fluoride. In some embodiments, the mass percentage b of the adhesive in the coating can be 2 wt% to 10 wt%, for example, 2 wt%, 4 wt%, 6 wt%, 8 wt%, 10 wt%, or any value within the range of any two of the above values. Appropriate amounts of adhesive help ensure the adhesion of the coating and improve the high-temperature storage performance of the secondary battery. In some embodiments, the remainder of the coating may include substances such as alumina, boehmite, or solid electrolyte.

[0050] This application also provides a secondary battery, which includes a positive electrode, a negative electrode, a separator, and a coating. The separator is disposed between the positive and negative electrode. The positive electrode includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector. In some embodiments, the coating is disposed between the positive current collector and the positive active layer. In other embodiments, the coating is disposed between the positive active layer and the separator. In still other embodiments, the coating is disposed between the positive current collector and the positive active layer, and between the positive active layer and the separator.

[0051] In some embodiments, the positive current collector can be aluminum foil, or other positive current collectors commonly used in the art can be used. In some embodiments, the thickness of the positive current collector can be from 1 μm to 200 μm.

[0052] In some embodiments, the positive electrode active layer may be coated only on a portion of the positive electrode current collector. In some embodiments, the thickness of the positive electrode active layer may be from 10 μm to 500 μm. It should be understood that these are merely exemplary, and other suitable thicknesses may be used.

[0053] In some embodiments, the positive electrode active layer includes a positive electrode active material (positive electrode material), which may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium nickel manganese oxide. The positive electrode active material may be doped and / or coated.

[0054] In some embodiments, the positive electrode active layer further includes a positive electrode binder and a positive electrode conductive agent. In some embodiments, the positive electrode binder may include at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene. In some embodiments, the positive electrode conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, or carbon fibers.

[0055] In some embodiments, the coating is located between the positive electrode active layer and the positive electrode current collector, and the coating thickness is 0.5 μm to 2 μm. For example, the coating thickness can be 0.5 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 2 μm, or any value within the range of any two of the above values. When the coating is located between the positive electrode active layer and the positive electrode current collector, controlling the coating thickness within the above range can reduce the impedance of the secondary battery and help improve the high-temperature stability and cycle performance of the secondary battery.

[0056] In some embodiments, the coating can be applied to the positive electrode current collector or to the positive electrode active layer, such that the coating is located between the positive electrode active layer and the positive electrode current collector. If the coating is applied to the positive electrode current collector, the coating can be applied to the surface of the positive electrode current collector facing the positive electrode active layer. If the coating is applied to the positive electrode active layer, the coating can be applied to the surface of the positive electrode active layer facing the positive electrode current collector.

[0057] In some embodiments, the coating is located between the positive electrode active layer and the separator, and the coating thickness is 1 μm to 4 μm. For example, the coating thickness can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, or any value within the range of any two of the above values. When the coating is located between the positive electrode active layer and the separator, controlling the coating thickness within the above range helps to improve the high-temperature stability and cycle performance of the secondary battery.

[0058] In some embodiments, a coating slurry may be applied to the surface of the separator, such that the coating is located between the positive electrode active layer and the separator.

[0059] The material and shape of the separator used in the secondary battery of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0060] In some embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0061] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0062] In some embodiments, the electrolyte of the secondary battery includes a lithium salt and a non-aqueous solvent. This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt is 5% to 23%. For example, the concentration of the lithium salt in the electrolyte may be 5%, 8%, 12%, 16%, 20%, 23%, or any value within the range of any two of the above values.

[0063] This application does not impose any particular limitation on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, etc. The non-aqueous solvent may contain at least one of the following: butyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the mass percentage of the non-aqueous solvent, as long as it achieves the purpose of this application. Exemplarily, based on the mass of the electrolyte, the mass percentage of the non-aqueous solvent is from 2% to 70%, for example, 2%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or any value within the range of any two of the above values.

[0064] In some embodiments, the secondary battery further includes a negative electrode sheet, which includes a negative current collector and a negative electrode material layer disposed on the negative current collector. The negative electrode material layer includes at least one of natural graphite, artificial graphite, or a silicon-based material. In some embodiments, the silicon-based material includes at least one of silicon, silicon oxide, silicon carbide, or silicon alloy.

[0065] The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil or carbon-based current collector, or any composite current collector disclosed in the prior art, or a current collector formed by combining the aforementioned conductive foil and polymer substrate in some optional embodiments, but not limited to.

[0066] The negative electrode material layer also includes a binder to bond the negative electrode active material particles, thereby facilitating the formation of the film layer and improving the bonding force between the negative electrode material layer and the negative electrode current collector. In some embodiments, the binder may include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0067] The negative electrode material layer may further include a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powder or metal fibers, and in some optional embodiments, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0068] The negative electrode material layer may also include a dispersant, which may include at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, carboxymethyl cellulose, lithium hydroxypropyl carboxymethyl cellulose, sodium hydroxypropyl carboxymethyl cellulose, lithium hydroxyethyl carboxymethyl cellulose, sodium hydroxyethyl carboxymethyl cellulose, or hydroxyethyl carboxymethyl cellulose.

[0069] In some embodiments, the secondary battery is a lithium-ion battery, but this application is not limited thereto.

[0070] In some embodiments of this application, taking a lithium-ion battery as an example, the positive electrode sheet, the separator, and the negative electrode sheet are wound or stacked in sequence to form an electrode assembly, which is then encapsulated in a housing such as an aluminum-plastic film, injected with electrolyte, formed, and encapsulated to produce a lithium-ion battery.

[0071] Embodiments of this application also provide electronic devices including the aforementioned secondary batteries. The secondary batteries power the electronic devices and exhibit good high-temperature stability and cycle performance after cycle performance testing and hot-box testing. These electronic devices may include, but are not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0072] The present application will be described below through specific embodiments and comparative examples. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0073] Coating feature testing

[0074] (1) Melting point

[0075] The coating was separated from the isolation membrane using N-methylpyrrolidone, the solution was filtered and dried to obtain the compound, and the position of the endothermic peak that appeared in the coating as the temperature increased was measured using differential scanning calorimetry (DSC).

[0076] If the melting points of diazine and its derivatives and triazine and its derivatives are too low, they are prone to decomposition and other reactions during the production process of lithium-ion batteries, leading to phenomena such as gas production and fire in lithium-ion batteries.

[0077] (2)Dv50

[0078] Take 0.5g of the sample powder to be tested and add it to water, then ultrasonically disperse it evenly. Add the sample dispersion to the circulation cell of a laser particle size analyzer for testing to obtain the volume average particle size Dv50 of diazine and its derivatives and triazine and its derivatives.

[0079] (3) The mass percentage of diazine and its derivatives and triazine and its derivatives in the coating, a

[0080] Separate the coating from the battery cell to obtain the coating composition, and weigh the coating composition as M1. Wash the coating composition with N-methylpyrrolidone or ethanol to obtain a mixture. Centrifuge the mixture and remove the supernatant. Repeat this operation 2-3 times. Dry the precipitate and weigh it as M2. The mass ratio a = M2 / M1.

[0081] Secondary battery performance test

[0082] (1) Impedance

[0083] The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 10 minutes. It was then charged at a constant current rate of 1C to 4.5V, and charged at a constant voltage of 4.5V to 0.05C. After standing for 10 minutes, the DC impedance of the lithium-ion battery under full charge was measured.

[0084] (2) Capacity retention rate during 45℃ cycling

[0085] First, in an environment of 45℃, the initial charge and discharge were performed. First, a constant current charge of 1C was used to charge to 4.5V, followed by a constant voltage charge to 0.05C. Then, a constant current discharge was performed at 0.5C to 3.0V. This charge-discharge cycle was repeated, and the discharge capacity of the 3rd cycle and the 200th cycle were recorded.

[0086] 45℃ cycle capacity retention rate = (discharge capacity of the 200th cycle / discharge capacity of the 3rd cycle) × 100%.

[0087] A higher 45℃ cycle capacity retention rate indicates better cycle performance of the battery.

[0088] (3) Hot box pass rate test

[0089] The lithium-ion batteries in each embodiment and comparative example were charged at room temperature with a constant current at a 1C rate to a full charge voltage of 4.5V. They were then charged further at a constant voltage of 4.5V until a cutoff current of 0.05C was reached, ensuring they were fully charged. The appearance was inspected to ensure the lithium-ion batteries were in normal working order. The fully charged lithium-ion batteries were then placed in an oven and heated at a rate of 5°C / min until the designated oven test temperature was reached. This temperature was maintained for one hour, during which time the state of the lithium-ion batteries was observed.

[0090] Judgment criteria: The battery does not catch fire or explode, meaning the battery passes the test temperature.

[0091] Increase the temperature by 1°C from the initial test temperature, obtain a new lithium-ion battery, and repeat the above test until the lithium-ion battery can no longer pass the test temperature. This gives the highest passable thermal chamber test temperature for the battery in a fully charged state. The higher the passable thermal chamber test temperature, the better the high-temperature stability of the battery.

[0092] (4) Cell compressive strength

[0093] The lithium-ion battery was placed in a 20℃ constant temperature chamber and allowed to stand for 10 minutes. It was then charged at a constant current rate of 1C to 4.5V, followed by constant voltage charging at 4.5V to 0.05C, and allowed to stand for 10 minutes. In a 20±5℃ testing environment, the battery cell was placed on a test platform with the barcode side facing up. A blunt nail with a diameter of 6mm was used, applying a pressure of 2500N and a drop speed of 300N / min. The test was conducted from the nickel tab of the sample (starting from the head step, 10±1mm from the top edge of the main body) until the maximum pressure required for the battery cell to catch fire and explode. Measurement frequency: Voltage and internal resistance were measured using a 1kHz standard, after pretreatment and after testing; measurements were also taken 24 hours after pretreatment.

[0094] Preparation of coating slurry for coating on separator membrane or positive electrode current collector

[0095] Add 15 kg of deionized water solution to a 35 L planetary mixing tank, add diazine and its derivatives and / or triazine and its derivatives, mix thoroughly, disperse and stir, then add binder and alumina, so that the weight ratio of diazine and its derivatives and / or triazine and its derivatives, binder and alumina is 90:5:5, and stir evenly to form a coating slurry.

[0096] Preparation of coating slurry for coating the positive electrode active layer

[0097] Add 15 kg of N-methylpyrrolidone solution to a 35 L planetary mixing tank, add diazine and its derivatives and / or triazine and its derivatives, mix thoroughly, disperse and stir, then add binder and alumina, so that the weight ratio of diazine and its derivatives and / or triazine and its derivatives, binder and alumina is 90:5:5, and stir evenly to form a coating slurry.

[0098] Preparation of lithium-ion batteries

[0099] (1) Preparation of positive electrode sheet

[0100] Lithium cobalt oxide (positive electrode active material), conductive carbon black (conductive agent), polyvinylidene fluoride (binder), and hydrogenated butadiene rubber (dispersant) were added to N-methylpyrrolidone in a weight ratio of 95:0.8:3.2:0.2 and stirred evenly to form a positive electrode slurry. The positive electrode slurry was uniformly coated on one side of the positive electrode current collector aluminum foil and dried to obtain a positive electrode sheet with a positive electrode active layer on one side. After cold pressing and cutting, the positive electrode sheet was obtained.

[0101] The coating slurry for coating the positive electrode sheet is applied to the surface of the positive active layer away from the positive current collector (aluminum foil) and dried to obtain a positive electrode sheet with a coating on the surface of the positive active layer.

[0102] (2) Preparation of negative electrode sheet

[0103] Artificial graphite (anode active material), sodium carboxymethyl cellulose (dispersant), and styrene-butadiene rubber (binder) are added to deionized water in a weight ratio of 96:1:3 and stirred evenly to form a cathode slurry. The cathode slurry is then uniformly coated onto one side of a copper foil current collector and dried. The above steps are repeated on the other side of the copper foil to obtain a cathode sheet with a cathode active layer on both sides. After cold pressing and cutting, the cathode sheet is obtained.

[0104] (3) Separating membrane

[0105] A polyethylene porous membrane with a thickness of 5μm and a porosity of 55% was selected as the isolation membrane.

[0106] (4) Preparation of electrolyte

[0107] In an argon-filled glove box, 3.5% succinate and 85% chain carbonate (EP:EMC:DEC:PP mass ratio of 15:20:20:45) were added to the electrolyte, with the remainder being lithium salt LiPF6.

[0108] (5) Assembly

[0109] Method 1: The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator between the positive and negative electrode and the coating between the positive active layer and the separator, to obtain a stacked electrode assembly. After welding the tabs, the electrode assembly is placed in the aluminum-plastic film of the packaging bag, heat-sealed around the perimeter, leaving the electrolyte injection port, and the electrolyte is injected. After vacuum sealing, settling, formation, degassing and other processes, a lithium-ion battery is obtained.

[0110] Method 2: Stack the prepared positive electrode, separator, and negative electrode in sequence, with the separator between the positive and negative electrode and the coating between the positive current collector and the positive active layer, to obtain a stacked electrode assembly. After welding the tabs, place the electrode assembly in the aluminum-plastic film of the packaging bag, heat seal the four sides, leaving the liquid injection port, inject the above-mentioned electrolyte, and after vacuum sealing, standing, formation, degassing and other processes, obtain a lithium-ion battery.

[0111] Example 1-1

[0112] The positive electrode, negative electrode, separator and electrolyte are obtained according to the aforementioned method. The coating is prepared according to the following method and assembled in mode 1 to obtain a lithium-ion battery.

[0113] Coating preparation: 15 kg of deionized water solution was added to a 35 L planetary mixing tank, followed by 2-aminopyrazine material with a Dv50 particle size of 500 nm. The mixture was thoroughly mixed and dispersed. Then, melamine resin and alumina were added as binders, ensuring a weight ratio of 90:5:5 for 2-aminopyrazine, melamine resin, and alumina. The mixture was stirred until homogeneous to form a coating slurry. This slurry was then applied to one surface of the separator membrane, with a coating thickness of 2 μm, positioned between the positive electrode active layer and the separator membrane. The 2-aminopyrazine consisted of plate-like particles with a length dimension of 1, a flatness of 10, and a stacking layer count of 0.

[0114] Examples 1-2 to Examples 1-17

[0115] Adjust the types of diazine and its derivatives or triazine and its derivatives to obtain the relevant parameters in Tables 1 to 4. The rest are the same as in Examples 1-1.

[0116] Comparative Examples 1-1 to 1-5

[0117] Adjust the type of diazine and its derivatives or triazine and its derivatives to obtain the relevant parameters in Tables 2 and 4. The rest are the same as in Examples 1-1.

[0118] Comparative Examples 1-6

[0119] The difference between Comparative Examples 1-6 and Examples 1-2 is that Comparative Examples 1-6 have no coating.

[0120] Comparative Examples 1-7

[0121] The difference between Comparative Examples 1-7 and Examples 1-2 is that the coatings of Comparative Examples 1-7 do not contain diazine or its derivatives or triazine or its derivatives, and the coating filler is boehmite particles.

[0122] Examples 1-18 to Examples 1-25

[0123] The mass percentage 'a' of diazine and its derivatives or triazine and its derivatives in the coating was adjusted. The mass percentage of the binder in Examples 1-18 and 1-20 to 1-25 remained unchanged, with the balance being alumina. The relevant parameters in Table 5 were obtained, and the rest was the same as in Examples 1-2. It should be noted that in Examples 1-19, the mass percentage of diazine and its derivatives or triazine and its derivatives in the coating reached 97 wt%, and the mass percentage of the binder in the coating was adjusted to 3 wt%. Therefore, no substances other than 2,3-dicyanopyrazine and the binder were added in the corresponding coating preparation methods.

[0124] Examples 1-26 to Examples 1-30

[0125] Adjust the Dv50 particle size of diazine and its derivatives or triazine and its derivatives to obtain the relevant parameters in Table 6. The rest are the same as in Examples 1-2.

[0126] Examples 1-31 to Examples 1-46

[0127] Adjust the particle morphology, length, flatness, and number of stacked layers of diazine and its derivatives or triazine and its derivatives to obtain the relevant parameters in Tables 7 and 8. The rest are the same as in Examples 1-2.

[0128] Examples 2-1 to 2-5

[0129] Adjust the coating thickness to obtain the relevant parameters in Table 9, and the rest are the same as in Examples 1-2.

[0130] Example 3-1

[0131] The difference between Example 3-1 and Example 1-2 is that in the preparation method of the coating slurry in Example 3-1, an N-methylpyrrolidone solution is used to replace an equal amount of deionized water solution, and the prepared coating slurry is coated on the surface of the positive electrode active layer, so that the coating is located between the positive electrode active layer and the positive electrode current collector. The rest is the same as in Example 1-2.

[0132] Examples 3-2 to 3-5

[0133] Adjust the coating thickness to obtain the relevant parameters in Table 10; the rest are the same as in Example 3-1.

[0134] Table 1

[0135] Table 2

[0136] Table 3

[0137] Table 4 In Table 4, “ / ” indicates that the comparative ratio could not be used to prepare lithium-ion batteries and there is no relevant performance test data.

[0138] In Tables 1 to 4 above, a comparison of Comparative Examples 1-6 and Examples 1-1 to 1-17 reveals that the coating between the positive electrode active layer and the separator helps reduce the impedance of the lithium-ion battery, improve its compressive strength, hot box test pass temperature, and 45°C cycle capacity retention. A comparison of Comparative Examples 1-7 and Examples 1-1 to 1-17 shows that when the coating contains diazine or triazine, the impedance of the lithium-ion battery is further reduced, its compressive strength, 45°C cycle capacity retention, and hot box test pass temperature are further improved. Compared to Comparative Examples 1-1 to 1-5, in Examples 1-1 to 1-17, when diazine and its derivatives, triazine and its derivatives contain structural formula (I) or structural formula (II) and have specific functional groups, and the melting point is within a suitable range, the compressive strength (i.e., mechanical properties) of the lithium-ion battery is improved, the impedance of the lithium-ion battery is reduced, and thus the 45°C cycle capacity retention rate and hot box test pass temperature of the lithium-ion battery are improved. Therefore, the cycle performance and high-temperature stability of the lithium-ion battery are improved. In particular, when the melting point is between 115°C and 360°C, the impedance of the lithium-ion battery is further reduced, the compressive strength of the lithium-ion battery is improved, and thus the high-temperature stability and cycle performance of the lithium-ion battery are further improved.

[0139] Table 5

[0140] In Table 5 above, in Examples 1-2 and Examples 1-18 to Examples 1-25, when the mass percentage 'a' of diazine and its derivatives or triazine and its derivatives in the coating is within a suitable range, it is beneficial to reduce the impedance of the lithium-ion battery, improve the compressive strength of the lithium-ion battery, and enhance the 45°C cycle capacity retention rate of the lithium-ion battery.

[0141] Table 6

[0142] In Table 6 above, in Examples 1-2 and Examples 1-26 to 1-30, when the Dv50 particle size of diazine and its derivatives or triazine and its derivatives is within a suitable range, it is beneficial to improve the 45°C cycle capacity retention rate of lithium-ion batteries.

[0143] Table 7

[0144] Table 8

[0145] In Tables 7 and 8 above, in Examples 1-2 and Examples 1-31 to 1-46, when the length of the rod-shaped particles, the flatness of the sheet-shaped particles, and the number of stacked layers of the sheet-shaped particles are within a suitable range, it is beneficial to reduce the impedance of the lithium-ion battery, improve the compressive strength of the lithium-ion battery, and improve the 45°C cycle capacity retention rate of the lithium-ion battery.

[0146] Table 9

[0147] In Table 9 above, compared to Examples 1-2, Examples 2-2 to 2-5, by placing the coating between the positive electrode active layer and the positive electrode current collector, can also improve the cycle performance and high-temperature stability of the lithium-ion battery. In particular, when the coating thickness is between 1 μm and 4 μm, the thermal test pass temperature and 45°C cycle capacity retention rate of the lithium-ion battery are further improved, thereby further enhancing the cycle performance and high-temperature stability of the lithium-ion battery.

[0148] Table 10

[0149] In Table 10 above, in Examples 3-2 to 3-5, the coating is disposed between the positive electrode active layer and the positive electrode current collector. When the thickness of the coating is in the range of 0.5μm to 2μm, it is beneficial to further reduce the impedance of the lithium-ion battery, improve the hot box test pass temperature and the 45℃ cycle capacity retention rate, that is, the cycle performance and high temperature stability of the lithium-ion battery are further improved.

[0150] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A coating characterized in that, The coating comprises diazine and / or its derivatives and / or triazine and / or its derivatives, wherein the structure of the diazine and / or its derivatives comprises a nitrogen-containing six-membered heterocyclic ring shown in structural formula (I): The structure of the triazine and its derivatives comprises a nitrogen-containing six-membered heterocyclic ring as shown in structural formula (II): The nitrogen-containing six-membered heterocycles shown in structural formulas (I) and (II) further include at least one functional group selected from amino, chlorine, pyridyl, bromophenoxy, methoxy, cyano, carboxyl, bromophenyl, or amide.

2. The coating of claim 1, wherein, The diazine and its derivatives include at least one of 2-aminopyrazine, pyrazinamide, 5,6-diamino-2,3-dicyanopyrazine, or 2,3-dicyanopyrazine.

3. The coating according to claim 1 or 2, characterized in that The diazine and its derivatives are 2,3-dicyanopyrazine.

4. The coating according to any one of claims 1 to 3, wherein The triazine and its derivatives include at least one of symmetrical triaminotriazine, 2,4,6-tris(aminohexanoic acid)-1,3,5-triazine, melamine cyanurate, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazin-2-yl)guanidine, 2,4-diamino-6-dimethylamino-1,3,5-triazine, cyanuric chloride, 2,4,6-tris(2-pyridyl)triazine, 2,4,6-triphenyl-1,3,5-triazine, tris(tribromophenoxy)triazine, or 2-amino-4,6-methoxy-1,3,5-triazine.

5. The coating according to any one of claims 1 to 4, wherein The triazine and its derivatives are symmetrical triaminotriazines.

6. The coating according to any one of claims 1 to 5, wherein The mass percentage (a) of the diazine and its derivatives and / or the triazine and its derivatives in the coating is 50 wt% to 95 wt%.

7. The coating according to any one of claims 1 to 6, wherein The Dv 50 particle size of the diazine and its derivatives and the triazine and its derivatives is 300 nm to 1000 nm.

8. The coating of any one of claims 1-7, wherein, The morphology of the diazine and its derivatives and the triazine and its derivatives includes at least one of rod-shaped, sheet-shaped, or stacked sheet-shaped forms.

9. The coating of any of claims 1-8, wherein, The diazine and its derivatives and / or the triazine and its derivatives shall satisfy at least one of the following conditions: (1) The length of the rod-shaped diazine and its derivatives and the triazine and its derivatives is 3 to 20 mm; (2) The flatness of the diazine and its derivatives and the triazine and its derivatives in sheet form is 3 to 50; (3) The number of stacked layers of the diazine and its derivatives and the triazine and its derivatives is 3 to 20.

10. The coating of any of claims 1-9, wherein, The melting points of the diazine and its derivatives and / or the triazine and its derivatives are 115°C to 360°C.

11. The coating of any of claims 1-9, wherein, The coating also includes an adhesive, which includes at least one of melamine resin, isocyanate-based crosslinking agent, styrene-butadiene rubber, polyacrylate, carboxymethyl cellulose, or polyvinylidene fluoride.

12. A secondary battery characterized by comprising: The invention includes a positive electrode, a negative electrode, a separator, and a coating as described in any one of claims 1-11, wherein the separator is disposed between the positive electrode and the negative electrode, the positive electrode includes a positive current collector and a positive active layer disposed on at least one side of the positive current collector, the coating is disposed between the positive current collector and the positive active layer, and / or the coating is disposed between the positive active layer and the separator.

13. The secondary battery according to claim 12, wherein The coating is located between the positive electrode active layer and the separator, and the thickness of the coating is 1 μm to 4 μm.

14. The secondary battery according to claim 12 or 13, wherein The coating is located between the positive electrode active layer and the positive electrode current collector, and the thickness of the coating is 0.5 μm to 2 μm.

15. An electronic device, comprising: Includes the secondary battery as described in any one of claims 12-14.

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