Coatings, secondary batteries and electronic devices

Abstract

The present application discloses a coating, a secondary battery and an electronic device. The coating comprises diazine and its derivatives and / or triazine and its derivatives, wherein the structures of the diazine and its derivatives and the triazine and its derivatives comprise a nitrogen-containing six-membered heterocyclic ring. The coating provided by the present application can improve the cycle performance and high temperature stability of the secondary battery.

Description

Technical Field

[0001] The present application relates to the field of electrochemical energy storage, and in particular to a coating, a secondary battery and an electronic device. Background Art

[0002] In order 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 will migrate to the negative electrode and become incompatible with the graphite or metallic lithium on the negative electrode, causing a reduction reaction at the negative electrode, thereby deteriorating the battery's cycle performance, increasing the battery's impedance, and accelerating the attenuation. Summary of the invention

[0003] In view of this, the present application provides a coating, a secondary battery and an electronic device.

[0004] In a first aspect, the present application provides a coating, the coating comprising diazine and its derivatives and / or triazine and its derivatives, the structure of the diazine and its derivatives comprising a nitrogen-containing six-membered heterocyclic ring as shown in structural formula (I):

[0005] Structural formula (I);

[0006] The structure of triazine and its derivatives contains a nitrogen-containing six-membered heterocyclic ring as shown in structural formula (II):

[0007] Structural formula (II);

[0008] The nitrogen-containing six-membered heterocyclic ring represented by the structural formula (I) and the structural formula (II) further comprises at least one functional group selected from the group consisting of amino, carbonyl, chloro, pyridyl, bromophenoxy, methoxy, cyano, carboxyl, bromophenyl or amide.

[0009] In the present application, diazine and its derivatives and / or triazine and its derivatives of specific molecular structure are selected as coatings. In the molecular structure of diazine and its derivatives and triazine and its derivatives, due to the electron-withdrawing ability of N atoms, they have delocalized aromaticity. When the coating is applied to the surface of the positive electrode or the separator, it can provide electrons to the positive electrode material, playing a role in stabilizing the structure of the positive electrode material. On the other hand, free water molecules in the electrolyte will cause the electrolyte to react, causing the battery itself to heat up, which is not conducive to the high temperature stability of the battery, while diazine and its derivatives and triazine and its derivatives can absorb free water in the electrolyte, improve the high temperature stability and cycle performance of the secondary battery, and reduce the impedance of the secondary battery.

[0010] Based on the first aspect, in some embodiments, the 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.

[0011] Based on the first aspect, in some embodiments, diazine and its derivatives are 2,3-dicyanopyrazine. 2,3-dicyanopyrazine has better thermal stability and more stable chemical properties, which helps to improve the high temperature stability and cycle performance of the secondary battery and reduce the impedance of the secondary battery.

[0012] Based on the first aspect, 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-triazine-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.

[0013] Based on the first aspect, in some embodiments, the triazine and its derivatives are symmetrical triaminotriazines. Symmetric triaminotriazines have good ability to improve the high temperature stability and cycle performance of secondary batteries and reduce the impedance of secondary batteries.

[0014] Based on the first aspect, in some embodiments, the mass proportion a of diazine and its derivatives and / or triazine and its derivatives in the coating is 50 wt% to 95 wt%. Controlling the mass proportion of diazine and its derivatives and / or triazine and its derivatives in the coating within the above range helps to improve the compressive strength of the secondary battery, i.e., the mechanical properties, and on the other hand, stabilizes the structure of the positive electrode material, helps to improve the cycle performance of the secondary battery and reduce the impedance of the secondary battery.

[0015] Based on the first aspect, in some embodiments, the Dv50 particle size of diazines and their derivatives and triazines and their derivatives is 300 nm to 1000 nm. The Dv50 particle size of diazines and their derivatives and triazines and their derivatives within the above range is conducive to their uniform dispersion in the coating and improves the cycle performance of the secondary battery.

[0016] 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 a rod-like shape, a sheet-like shape, or a stacked sheet-like shape formed by stacking sheets.

[0017] 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:

[0018] (1) The length of the rod-shaped diazines and their derivatives and triazines and their derivatives is 3 to 20;

[0019] (2) The flatness of flaky diazines and their derivatives and triazines and their derivatives is 3 to 50;

[0020] (3) The number of stacking layers of the lamellar diazines and their derivatives and triazines and their derivatives is 3 to 20.

[0021] In diazines and their derivatives and triazines and their derivatives, the length of the rod-shaped particles is 3-20, which can improve their dispersion uniformity in the coating and improve the compressive strength of the secondary battery, and can reduce the impedance of the secondary battery and improve the cycle performance of the secondary battery; the flatness of the flaky particles is 3-50, which is conducive to reducing the impedance of the secondary battery and improving the compressive strength and cycle performance of the secondary battery, and will not have a negative impact on the impedance and compressive strength of the secondary battery due to the increase in space obstacles between particles. Laminated particles with a stacking number of 3-20 layers are conducive to improving the compressive strength of the secondary battery, reducing the impedance of the secondary battery and improving the cycle performance of the secondary battery.

[0022] Based on the first aspect, in some embodiments, the melting point of diazine and its derivatives and / or triazine and its derivatives is 115° C. to 360° C. When the melting point of diazine and its derivatives and / or triazine and its derivatives is within the above range, the secondary battery has high compressive strength, low impedance, good cycle performance and high temperature stability.

[0023] Based on the first aspect, in some embodiments, the coating further includes a binder, and the binder includes at least one of melamine resin, isocyanate-based crosslinking agent, styrene-butadiene rubber, polyacrylate, carboxymethyl cellulose or polyvinylidene fluoride.

[0024] A second aspect of the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate, a separator and a coating, wherein the separator is arranged between the positive electrode plate and the negative electrode plate, the positive electrode plate includes a positive electrode collector and a positive electrode active layer arranged on at least one side of the positive electrode collector, the coating is arranged between the positive electrode collector and the positive electrode active layer, and / or the coating is arranged between the positive electrode active layer and the separator.

[0025] Based on the second aspect, in some embodiments, 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. When the coating is located between the positive electrode active layer and the separator, controlling the thickness of the coating within the above range helps to improve the high temperature stability and cycle performance of the secondary battery.

[0026] 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 thickness of the coating 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 thickness of the coating 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.

[0027] The third aspect of the present application provides an electronic device, comprising the above-mentioned secondary battery. The secondary battery supplies power to the electronic device, and the secondary battery shows good high-temperature storage performance and cycle performance after high-temperature stability performance test and cycle performance test, and has the characteristics of low impedance and high compressive strength. DETAILED DESCRIPTION

[0028] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application. The reagents and materials described in the following embodiments can all be obtained from commercial sources.

[0029] As used in this application, the terms "including," "containing," and "comprising" are used in their open, non-limiting sense.

[0030] In addition, sometimes amounts, ratios and other numerical values ​​are presented in range format herein. It should be understood that such range format is for convenience and brevity, and should be flexibly understood to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or sub-ranges encompassed within the range, as if each numerical value and sub-range were explicitly specified.

[0031] 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, 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, 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 include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0032] The present application provides a coating, which comprises 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 heterocyclic ring represented by structural formula (I):

[0033] Structural formula (I);

[0034] The structure of triazine and its derivatives contains a nitrogen-containing six-membered heterocyclic ring as shown in structural formula (II):

[0035] Structural formula (II);

[0036] The nitrogen-containing six-membered heterocyclic ring represented by the structural formula (I) and the structural formula (II) further comprises at least one functional group selected from the group consisting of amino, carbonyl, chlorine, pyridyl, bromophenoxy, methoxy, cyano, carboxyl, bromophenyl or amide.

[0037] In the present application, diazines and their derivatives and / or triazines and their derivatives of specific molecular structures are selected as coatings. In the molecular structures of diazines and their derivatives and triazines and their derivatives, due to the electron-withdrawing ability of N atoms, they have delocalized aromaticity. When the coating is applied to the surface of the positive electrode or the 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 will cause the electrolyte to react, causing the battery itself to heat up, which is not conducive to the high temperature stability of the battery. However, diazines and their derivatives and triazines and their derivatives can absorb free water in the electrolyte, improve the high temperature stability and cycle performance of the secondary battery, and reduce the impedance of the secondary battery.

[0038] In some embodiments, the 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.

[0039] In some embodiments, diazine and its derivatives are 2,3-dicyanopyrazine. 2,3-dicyanopyrazine has better thermal stability and more stable chemical properties, which helps to improve the high temperature stability and cycle performance of the secondary battery and reduce the impedance of the secondary battery.

[0040] In some embodiments, triazine and its derivatives include at least one of symmetrical triaminotriazine, 2,4,6-tris(aminohexanoyl)-1,3,5-triazine, melamine cyanurate, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazine-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.

[0041] In some embodiments, triazine and its derivatives are symmetrical triaminotriazines. Symmetric triaminotriazines have good ability to improve the high temperature stability and cycle performance of secondary batteries and reduce the impedance of secondary batteries.

[0042] In some embodiments, the mass proportion a of diazines and their derivatives and / or triazines and their derivatives in the coating is 50 wt% to 95 wt%, such as 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 formed by any two of the above values. Controlling the mass proportion of diazines and their derivatives and / or the triazines and their derivatives in the coating within the above range helps to improve the compressive strength of the secondary battery, i.e., the mechanical properties, and on the other hand, stabilizes the structure of the positive electrode material, helps to improve the cycle performance of the secondary battery and reduce the impedance of the secondary battery.

[0043] In some embodiments, the Dv50 particle size of diazines and their derivatives and triazines and their 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 formed by any two of the above values. The Dv50 particle size of diazines and their derivatives and triazines and their derivatives within the above range is conducive to their uniform dispersion in the coating and improves the cycle performance of the secondary battery.

[0044] In some embodiments, the morphology of diazines and their derivatives and triazines and their derivatives includes at least one of a rod-like shape, a sheet-like shape, or a stacked sheet-like shape formed by stacking sheets.

[0045] In some embodiments, diazines and their derivatives and triazines and their derivatives satisfy at least one of the following conditions:

[0046] (1) The length of the rod-shaped diazines and their derivatives and triazines and their derivatives is 3 to 20;

[0047] (2) The flatness of flaky diazines and their derivatives and triazines and their derivatives is 3 to 50;

[0048] (3) The number of stacking layers of the lamellar diazines and their derivatives and triazines and their derivatives is 3 to 20.

[0049] For example, the length of diazines and their derivatives and triazines and their derivatives of rod-shaped particles can be 3, 5, 8, 10, 13, 15, 18, 20 or any value within the range formed by any two of the above values; the flatness of diazines and their derivatives and triazines and their derivatives of flaky particles can be 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or any value within the range formed by any two of the above values; the number of stacking layers of diazines and their derivatives and triazines and their derivatives of lamellar particles can be 3, 5, 8, 10, 13, 15, 18, 20 or any value within the range formed by any two of the above values. In diazines and their derivatives and triazines and their derivatives, the length of the rod-shaped particles is 3-20, which can improve their dispersion uniformity in the coating and improve the compressive strength of the secondary battery, and can reduce the impedance of the secondary battery and improve the cycle performance of the secondary battery; the flatness of the flaky particles is 3-50, which is conducive to reducing the impedance of the secondary battery and improving the compressive strength and cycle performance of the secondary battery, and will not have a negative impact on the impedance and compressive strength of the secondary battery due to the increase in space obstacles between particles. Laminated particles with a stacking number of 3-20 layers are conducive to improving the compressive strength of the secondary battery, reducing the impedance of the secondary battery and improving the cycle performance of the secondary battery.

[0050] In the present application, "length" refers to the ratio of the major diameter to the minor diameter of a particle; and "flatness" refers to the ratio of the minor diameter to the thickness of a particle.

[0051] 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 formed by 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 has high compressive strength, low impedance, good cycle performance and high temperature stability.

[0052] In some embodiments, the coating further comprises a binder, and the binder comprises at least one of a melamine resin, an isocyanate-based crosslinking agent, styrene-butadiene rubber, a polyacrylate, carboxymethyl cellulose or polyvinylidene fluoride. In some embodiments, the mass proportion b of the binder in the coating can be 2 wt%~10wt%, for example, 2 wt%, 4 wt%, 6 wt%, 8 wt%, 10wt% or any value within the range of any two of the above values. The amount of the binder is appropriate, which helps to 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 a solid electrolyte.

[0053] The present application also provides a secondary battery, the secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and a coating, the separator is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet comprises a positive current collector and a positive active layer arranged on at least one side of the positive current collector. In some embodiments, the coating is arranged between the positive current collector and the positive active layer. In other embodiments, the coating is arranged between the positive active layer and the separator. In other embodiments, the coating is arranged between the positive current collector and the positive active layer and between the positive active layer and the separator.

[0054] In some embodiments, the positive electrode current collector may be aluminum foil, and of course, other positive electrode current collectors commonly used in the art may also be used. In some embodiments, the thickness of the positive electrode current collector may be 1 μm to 200 μm.

[0055] In some embodiments, the positive electrode active layer may be coated only on a partial area of ​​the positive electrode current collector. In some embodiments, the thickness of the positive electrode active layer may be 10 μm to 500 μm. It should be understood that these are only exemplary and other suitable thicknesses may be used.

[0056] In some embodiments, the positive electrode active layer includes a positive electrode active material (positive electrode material), and the positive electrode active material 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, and the above positive electrode active material may be doped and / or coated.

[0057] In some embodiments, the positive electrode active layer further includes a positive electrode binder and a positive electrode conductor. In some embodiments, the positive electrode binder may include polyvinylidene fluoride, vinylidene 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 conductor may include at least one of conductive carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes or carbon fibers.

[0058] In some embodiments, 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. For example, the thickness of the coating can be 0.5 μm, 0.75 μm, 1 μm, 1.25 μm, 1.5 μm, 2 μm, or any value within the range formed by 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 thickness of the coating within the above range can reduce the impedance of the secondary battery, which helps to improve the high temperature stability and cycle performance of the secondary battery.

[0059] In some embodiments, the coating may be applied to the positive electrode current collector or to the positive electrode active layer, so 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 may 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 may be applied to the surface of the positive electrode active layer facing the positive electrode current collector.

[0060] In some embodiments, 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, for example, the thickness of the coating 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 formed by any two of the above values. When the coating is located between the positive electrode active layer and the separator, controlling the thickness of the coating within the above range helps to improve the high temperature stability and cycle performance of the secondary battery.

[0061] In some embodiments, the coating slurry may be coated on the surface of the separator so that the coating is located between the positive electrode active layer and the separator.

[0062] The material and shape of the separator used in the secondary battery of the present application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0063] In some embodiments, the isolation membrane may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film having 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 film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0064] A surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one of aluminum oxide, 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 vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride and poly (vinylidene fluoride-hexafluoropropylene).

[0065] In some embodiments, the electrolyte of the secondary battery includes a lithium salt and a non-aqueous solvent. The present application has no particular limitation on the lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt may include but is not limited to LiPF 6 , LiBF 4 、LiClO 4 、LiB(C 6 H 5 ) 4 、LiCH 3 SO 3 、LiCF 3 SO 3 、LiN(SO 2 CF 3 ) 2 、LiC(SO 2 CF 3 ) 3 , Li 2 SiF 6 , lithium bis(oxalatoborate) (LiBOB) or lithium difluoroborate. The present application has no particular limitation on the content of lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage of lithium salt is 5% to 23%. For example, the concentration of lithium salt in the electrolyte can be 5%, 8%, 12%, 16%, 20%, 23% or any value within the range of any two of the above values.

[0066] The present application has no particular restrictions on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is 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, difluoroethylene carbonate, 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, 1,1,2-trifluoro ... At least one of 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, cyclopentane, methyl cyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application has no particular restriction on the mass percentage of the non-aqueous solvent, as long as the purpose of the present application can be achieved. Exemplarily, based on the mass of the electrolyte, the mass percentage of the non-aqueous solvent is 2% to 70%, such as 2%, 10%, 20%, 30%, 40%, 50%, 60%, 70% or any value within the range composed of any two of the above values.

[0067] In some embodiments, the secondary battery further comprises a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector. The negative electrode material layer comprises at least one of natural graphite, artificial graphite or a silicon-based material. In some embodiments, the silicon-based material comprises at least one of silicon, a silicon-oxygen compound, a silicon-carbon compound or a silicon alloy.

[0068] The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil or a carbon-based current collector, or any composite current collector disclosed in the prior art. In some optional embodiments, but not limited to, the current collector is formed by combining the aforementioned conductive foil and a polymer substrate.

[0069] The negative electrode material layer also includes a binder to bind the negative electrode active material particles to facilitate the formation of a film layer, and at the same time, it can also improve the binding 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, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylic (ester) styrene butadiene rubber, epoxy resin or nylon, etc.

[0070] The negative electrode material layer may also include a conductive material, including but not limited to a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. In some embodiments, the carbon-based material may include but is not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material may include but is not limited to metal powder or metal fiber, in some optional embodiments copper, nickel, aluminum or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0071] The negative electrode material layer may further include a dispersant, the dispersant including at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, carboxymethyl cellulose, lithium hydroxypropyl carboxymethyl cellulose, sodium hydroxypropyl carboxymethyl cellulose, hydroxypropyl carboxymethyl cellulose, lithium hydroxyethyl carboxymethyl cellulose, sodium hydroxyethyl carboxymethyl cellulose or hydroxyethyl carboxymethyl cellulose.

[0072] In some embodiments, the secondary battery is a lithium-ion battery, but the present application is not limited thereto.

[0073] In some embodiments of the present application, taking lithium-ion batteries as an example, the positive electrode sheet, the isolation membrane, and the negative electrode sheet are wound or stacked in sequence to form an electrode assembly, and then placed in a shell such as an aluminum-plastic film for packaging, and the electrolyte is injected, formed, and packaged to make a lithium-ion battery.

[0074] The embodiment of the present application also provides an electronic device including the above-mentioned secondary battery. The secondary battery is powered by the electronic device, and the secondary battery shows good high temperature stability and cycle performance after cycle performance test and hot box test. Among them, the electronic device may include but is not limited to a laptop computer, a pen input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini CD, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium ion capacitor, etc.

[0075] The present application is described below by specific examples and comparative examples. Those skilled in the art should understand that the preparation methods described in the present application are only examples, and any other suitable preparation methods are within the scope of the present application.

[0076] Coating Characterization Test

[0077] (1) Melting point

[0078] The coating was separated from the isolation membrane using N-methylpyrrolidone, and the solution was filtered and dried to obtain a compound. The position of the endothermic peak of the coating as the temperature increased was measured using a differential scanning calorimeter (DSC).

[0079] If the melting points of diazines and their derivatives and triazines and their derivatives are too low, decomposition reactions and the like are likely to occur during the production of lithium-ion batteries, leading to gas production and fire in lithium-ion batteries.

[0080] (2) Dv50

[0081] 0.5 g of the sample powder to be tested was added to water and uniformly dispersed by ultrasonication. The sample dispersion was added to the circulation pool of the laser particle size tester for testing to obtain the volume average particle size Dv50 of the diazine and its derivatives and the triazine and its derivatives.

[0082] (3) Mass proportion of diazines and their derivatives and triazines and their derivatives in the coating

[0083] Separate the coating from the battery cell to obtain a coating composition, and weigh the coating composition as M1. Use N-methylpyrrolidone or ethanol to wash the coating composition to obtain a mixed solution, centrifuge the mixed solution, remove the supernatant, and repeat this operation 2-3 times. Dry the precipitate and weigh the mass M2. The mass ratio a=M2 / M1.

[0084] Secondary battery performance test

[0085] (1) Impedance

[0086] The lithium-ion battery was placed in a 25°C constant temperature box, left to stand for 10 minutes, charged at a constant current rate of 1C to 4.5V, charged at a constant voltage rate of 0.05C at 4.5V, left to stand for 10 minutes, and the DC impedance of the lithium-ion battery in the fully charged state was measured.

[0087] (2) 45℃ cycle capacity retention rate

[0088] First, in an environment of 45°C, the first charge and discharge were performed, first using a 1C current for constant current charging, charging to 4.5V, then constant voltage charging to a current of 0.05C, and then constant current discharge at a current of 0.5C to 3.0V. Repeat the above charge and discharge cycles, and record the discharge capacity of the 3rd cycle and the discharge capacity of the 200th cycle.

[0089] 45° C. cycle capacity retention rate=(discharge capacity at the 200th cycle / discharge capacity at the 3rd cycle)×100%.

[0090] The higher the 45°C cycle capacity retention rate is, the better the cycle performance of the battery is.

[0091] (3) Hot box pass rate test

[0092] The lithium-ion batteries in the embodiments and comparative examples were charged at room temperature at a constant current of 1C rate to a full charge voltage of 4.5V, and then continued to be charged at a constant voltage of 4.5V to a cut-off current of 0.05C to fully charge the batteries. The appearance was checked to ensure that the lithium-ion batteries were in a normal usable state. The fully charged lithium-ion batteries were placed in an oven and heated at a rate of 5°C / min until the specified hot box test temperature was reached. The temperature was kept constant for one hour, and the state of the lithium-ion batteries was observed during the process.

[0093] Judgment standard: The battery does not catch fire or explode, that is, the battery passes the test temperature.

[0094] The test temperature is raised by 1°C, and the lithium-ion battery is re-obtained and the above test is repeated until the lithium-ion battery fails to pass the test temperature. The highest passable hot box test temperature of the battery in a fully charged state is obtained. The higher the passable hot box test temperature, the better the high temperature stability of the battery.

[0095] (4) Compressive strength of battery cells

[0096] Place the lithium-ion battery in a 20℃ constant temperature box, let it stand for 10 minutes, charge it to 4.5V at a constant current rate of 1C, charge it to 0.05C at a constant voltage of 4.5V, and let it stand for 10 minutes. In a 20±5℃ test environment, place the battery cell on the test table with the barcode facing up, use a blunt nail with a diameter of 6mm, an extrusion force of 2500N, and a drop speed of 300N / Min, and test from the sample nickel Tab (starting from the head step, 10±1mm from the upper edge of the body) until the maximum extrusion force when the battery cell catches fire, explodes and burns; measurement frequency: voltage internal resistance measurement uses 1KHZ specifications, after pretreatment, and after testing; measurement is made 24h after pretreatment.

[0097] Preparation of coating slurry for coating on separator or positive electrode current collector

[0098] In a 35L planetary stirring tank, add 15kg of deionized water solution, 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.

[0099] Preparation of coating slurry applied to positive electrode active layer

[0100] In a 35L planetary stirring tank, add 15kg of N-methylpyrrolidone solution, 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.

[0101] Preparation of lithium-ion batteries

[0102] (1) Preparation of positive electrode

[0103] The positive electrode active material lithium cobalt oxide, the conductive agent conductive carbon black, the binder polyvinylidene fluoride, and the dispersant hydrogenated butadiene rubber are 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 is evenly coated on one side of the positive electrode collector aluminum foil and dried to obtain a positive electrode sheet coated with a positive electrode active layer on one side, and then cold pressed and cut to obtain a positive electrode sheet.

[0104] The coating slurry for coating the surface of the positive electrode plate is coated on the surface of the positive electrode active layer away from the positive electrode current collector (aluminum foil), and dried to obtain a positive electrode plate with a coating on the surface of the positive electrode active layer.

[0105] (2) Preparation of negative electrode

[0106] The negative electrode active material artificial graphite, the dispersant sodium carboxymethyl cellulose and the binder styrene-butadiene rubber are added to deionized water in a weight ratio of 96:1:3, and stirred evenly to form a negative electrode slurry. The negative electrode slurry is evenly coated on one side of the negative electrode collector copper foil, dried, and then the above steps are repeated on the other side of the copper foil to obtain a negative electrode sheet coated with a negative electrode active layer on both sides, which is then cold pressed and cut to obtain a negative electrode sheet.

[0107] (3) Isolation film

[0108] A polyethylene porous membrane with a thickness of 5 μm and a porosity of 55% was selected as the isolation membrane.

[0109] (4) Preparation of electrolyte

[0110] In a glove box filled with argon, 3.5% of the total mass of the electrolyte was succinonitrile and 85% of the chain carbonate (the mass ratio of EP:EMC:DEC:PP was 15:20:20:45), and the rest was lithium salt LiPF 6 .

[0111] (5) Assembly

[0112] Method 1: stack the prepared positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is between the positive electrode sheet and the negative electrode sheet, and the coating is between the positive electrode active layer and the separator, to obtain a stacked electrode assembly. After welding the pole ears, place the electrode assembly in an aluminum-plastic film packaging bag, heat-seal it all around, leaving a liquid injection port, inject the above-mentioned electrolyte, and undergo vacuum packaging, standing, formation, degassing and other processes to obtain a lithium-ion battery.

[0113] Method 2: Stack the prepared positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is between the positive electrode sheet and the negative electrode sheet, and the coating is between the positive current collector and the positive active layer, to obtain a stacked electrode assembly. After welding the pole ears, place the electrode assembly in an aluminum-plastic film packaging bag, heat-seal it all around, leaving a liquid injection port, inject the above-mentioned electrolyte, and undergo vacuum packaging, standing, formation, degassing and other processes to obtain a lithium-ion battery.

[0114] Example 1-1

[0115] The positive electrode sheet, the negative electrode sheet, the isolation membrane and the electrolyte are obtained according to the above method, the coating is prepared according to the following method, and the lithium-ion battery is assembled using method 1.

[0116] Preparation of coating: Add 15kg of deionized water solution to a 35L planetary stirring tank, add 2-aminopyrazine material with a Dv50 particle size of 500nm, mix thoroughly, disperse and stir, then add binder melamine resin and aluminum oxide, so that the weight ratio of 2-aminopyrazine, melamine resin and aluminum oxide is 90:5:5, and stir evenly to form a coating slurry. Then apply the coating slurry to one surface of the isolation membrane, the coating thickness is 2μm, so that the coating is located between the positive active layer and the isolation membrane. Among them, 2-aminopyrazine is a flaky particle with an length of 1, a flatness of 10, and a stacking layer of 0.

[0117] Example 1-2 to Example 1-17

[0118] The types of diazine and its derivatives or triazine and its derivatives were adjusted to obtain the relevant parameters in Tables 1 to 4, and the rest were the same as in Example 1-1.

[0119] Comparative Example 1-1 to Comparative Example 1-5

[0120] The types of diazine and its derivatives or triazine and its derivatives were adjusted to obtain the relevant parameters in Tables 2 and 4, and the rest were the same as in Example 1-1.

[0121] Comparative Examples 1-6

[0122] The difference between Comparative Example 1-6 and Example 1-2 is that Comparative Example 1-6 has no coating.

[0123] Comparative Examples 1-7

[0124] The difference between Comparative Example 1-7 and Example 1-2 is that the coating of Comparative Example 1-7 does not contain diazine and its derivatives or triazine and its derivatives, and the coating filler is boehmite particles.

[0125] Example 1-18 to Example 1-25

[0126] The mass proportion of diazine and its derivatives or triazine and its derivatives in the coating is adjusted to a, the mass proportion of the binder in Examples 1-18 and 1-20 to 1-25 remains unchanged, the balance is aluminum oxide, and the relevant parameters in Table 5 are obtained, and the rest are the same as in Example 1-2. It should be noted here that in Example 1-19, the mass proportion of diazine and its derivatives or triazine and its derivatives in the coating reaches 97 wt%, and the mass proportion of the binder in the coating is adjusted to 3 wt%, so no substances other than 2,3-dicyanopyrazine and the binder are added to the corresponding coating preparation method.

[0127] Example 1-26 to Example 1-30

[0128] The Dv50 particle size of diazine and its derivatives or triazine and its derivatives was adjusted to obtain the relevant parameters in Table 6, and the rest was the same as Example 1-2.

[0129] Example 1-31 to Example 1-46

[0130] The particle morphology, length, flatness and number of stacking layers of diazine and its derivatives or triazine and its derivatives were adjusted to obtain the relevant parameters in Table 7 and Table 8, and the rest were the same as in Example 1-2.

[0131] Example 2-1 to Example 2-5

[0132] The thickness of the coating was adjusted to obtain the relevant parameters in Table 9, and the rest was the same as in Example 1-2.

[0133] Example 3-1

[0134] The difference between Example 3-1 and Example 1-2 is that in the preparation method of the coating slurry in Example 3-1, N-methylpyrrolidone solution is used to replace an equal amount of deionized water solution, and the prepared coating slurry is applied to 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, and the rest is the same as Example 1-2.

[0135] Example 3-2 to Example 3-5

[0136] The thickness of the coating was adjusted to obtain the relevant parameters in Table 10, and the rest was the same as Example 3-1.

[0137] Table 1

[0138]

[0139] Table 2

[0140]

[0141] Table 3

[0142]

[0143] Table 4

[0144]

[0145] In Table 4, “ / ” indicates that the comparative example cannot produce a lithium-ion battery and has no relevant performance test data.

[0146] In the above Tables 1 to 4, when comparing Comparative Examples 1-6 with Examples 1-1 to 1-17, it can be found that the coating provided between the positive electrode active layer and the separator is beneficial to reducing the impedance of the lithium-ion battery, improving the compressive strength, hot box test passing temperature and 45°C cycle capacity retention rate of the lithium-ion battery. When comparing Comparative Examples 1-7 with Examples 1-1 to 1-17, it can be found that when the coating contains diazine or triazine, the impedance of the lithium-ion battery is reduced, and the compressive strength, 45°C cycle capacity retention rate and hot box test passing temperature of the lithium-ion battery are further improved. Compared with 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 the 45°C cycle capacity retention rate and the hot box test passing temperature of the lithium-ion battery are improved, so 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 the high temperature stability and cycle performance of the lithium-ion battery are further improved.

[0147] Table 5

[0148]

[0149] In the above Table 5, in Examples 1-2 and 1-18 to 1-25, when the mass proportion a of diazine and its derivatives or triazine and its derivatives in the coating is within an appropriate range, it is beneficial to reduce the impedance of the lithium-ion battery, improve the compressive strength of the lithium-ion battery and the 45°C cycle capacity retention rate of the lithium-ion battery.

[0150] Table 6

[0151]

[0152] In the above Table 6, in Examples 1-2 and 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 the lithium-ion battery.

[0153] Table 7

[0154]

[0155] Table 8

[0156]

[0157] In the above Tables 7 and 8, in Examples 1-2 and 1-31 to 1-46, when the length of the rod-like particles, the flatness of the flaky particles, and the number of stacking layers of the lamellar particles are within an appropriate range, it is beneficial to reduce the impedance of the lithium-ion battery, enhance the compressive strength of the lithium-ion battery, and improve the 45°C cycle capacity retention rate of the lithium-ion battery.

[0158] Table 9

[0159]

[0160] In the above Table 9, compared with Example 1-2, Example 2-2 to Example 2-5 set the coating between the positive electrode active layer and the positive electrode current collector, which can also improve the cycle performance and high temperature stability of the lithium-ion battery. In particular, when the thickness of the coating is 1μm ~ 4μm, the hot box test passing temperature and 45°C cycle capacity retention rate of the lithium-ion battery are further improved, thereby further improving the cycle performance and high temperature stability of the lithium-ion battery.

[0161] Table 10

[0162]

[0163] In the above Table 10, in Example 3-2 to Example 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 0.5 μm to 2 μm, it is beneficial to further reduce the impedance of the lithium-ion battery, improve the hot box test passing temperature and 45°C cycle capacity retention rate, that is, the cycle performance and high temperature stability of the lithium-ion battery are further improved.

[0164] The above implementation modes are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application is described in detail with reference to the above implementation modes, a person skilled in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present application.

Claims

1. A coating for a secondary battery, characterized in that: The coating comprises diazine and its derivatives and triazine and its derivatives, wherein the structure of the diazine and its derivatives comprises a nitrogen-containing six-membered heterocyclic ring represented by structural formula (I): Structural formula (I); The structure of the triazine and its derivatives comprises a nitrogen-containing six-membered heterocyclic ring represented by structural formula (II): Structural formula (II); The nitrogen-containing six-membered heterocyclic ring represented by the structural formula (I) and the structural formula (II) further comprises at least one functional group selected from the group consisting of amino, chlorine, pyridyl, bromophenoxy, methoxy, cyano, carboxyl, bromophenyl or amide; The morphology of the diazine and its derivatives and the triazine and its derivatives includes at least one of a rod-like shape, a sheet-like shape or a stacked sheet-like shape formed by stacking sheets; The diazines and their derivatives and the triazines and their derivatives 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; (2) The flatness of the flaky diazine and its derivatives and the triazine and its derivatives 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; Among them, the length refers to the ratio of the long diameter to the short diameter of the particle; the flatness refers to the ratio of the short diameter to the thickness of the particle.

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

4. The coating according to claim 1, characterized in that The triazine and its derivatives include at least one of symmetrical triaminotriazine, 2,4,6-tris(aminocaproic acid)-1,3,5-triazine, melamine cyanurate, 2-(4-bromophenyl)-4,6-dimethyl-1,3,5-triazine, 1-(4,6-diamino-1,3,5-triazine-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 claim 1, characterized in that The triazine and its derivatives are symmetrical triaminotriazines.

6. The coating according to claim 1, characterized in that The mass proportion a of the diazine and its derivatives and the triazine and its derivatives in the coating is 50 wt% to 95 wt%.

7. The coating according to claim 1, characterized in that The Dv50 particle size of the diazine and its derivatives and the triazine and its derivatives is 300nm~1000nm.

8. The coating according to any one of claims 1 to 7, characterized in that The melting points of the diazine and its derivatives and the triazine and its derivatives are 115° C. to 360° C.

9. The coating according to any one of claims 1 to 7, characterized in that The coating layer further includes a binder, and the binder includes at least one of melamine resin, isocyanate-based crosslinking agent, styrene-butadiene rubber, polyacrylate, carboxymethyl cellulose or polyvinylidene fluoride.

10. A secondary battery, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet, a separator and a coating as claimed in any one of claims 1 to 9, wherein the separator is arranged between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet comprises a positive electrode collector and a positive electrode active layer arranged on at least one side of the positive electrode collector, the coating is arranged between the positive electrode collector and the positive electrode active layer, and / or the coating is arranged between the positive electrode active layer and the separator.

11. The secondary battery according to claim 10, characterized in that The coating is located between the positive electrode active layer and the isolation film, and the thickness of the coating is 1 μm to 4 μm.

12. The secondary battery according to claim 10, characterized in that 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.

13. An electronic device, characterized in that: A secondary battery comprising any one of claims 10 to 12.

Images