Cathode slurry, cathode sheet, preparation method and lithium ion battery

Abstract

The application provides a positive electrode paste, which comprises an additive, and the additive is a safety additive. The safety additive comprises conjugated diene monomers and dienophile monomers, or comprises cyclopentadiene monomers. The conjugated diene monomers and the dienophile monomers can form a thermoreversible structure, or the cyclopentadiene monomers can form a thermoreversible structure. The application uniformly disperses the above monomers in the positive electrode paste, and uses the active functional groups of the additive itself to form a protective layer in the electrode piece during coating and drying. The thermoreversible structure formed by the safety additive can depolymerize and absorb heat when the battery is subjected to high temperature, absorb oxygen free radicals to prevent thermal runaway, and improve the safety performance of the battery. The additive can also comprise a structure maintaining additive. The addition of the structure maintaining additive can form a structure with the structure maintaining additive as a main chain and the safety additive as a side chain or a crosslinking point, so that the affinity of the safety additive and the electrolyte can be optimized, ion transmission can be improved, electrolyte decomposition can be inhibited, and the cycle performance of the battery can be improved.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to positive electrode slurry, positive electrode sheet and preparation method, lithium-ion battery, and the use of safety additives and structure retention additives in the preparation of positive electrode sheets. Background Technology

[0002] Lithium-ion batteries are widely used in electronic products, electric vehicles, and large-scale energy storage due to their high energy density and good cycle performance. However, with the expansion of their applications, safety issues related to lithium-ion batteries have gradually emerged, especially in large-scale modules. Thermal runaway in one cell can trigger a chain reaction in adjacent cells at high temperatures, leading to a large-scale explosion. Currently, it is generally believed that the key factor in lithium-ion battery thermal runaway is the decomposition of the positive electrode material at high temperatures, releasing oxygen free radicals. These oxygen free radicals then react violently with the negative electrode lithium intercalation material and the electrolyte, releasing enormous energy and causing the cell to explode.

[0003] In the preparation of the positive electrode sheet, special additives are incorporated into the slurry. After drying, these additives remain inside the electrode sheet. When the battery is abused, these additives improve the safety of the electrode sheet through certain special reactions. This is a commonly used technical approach. For example, patent document CN 109309208 B adds a thiophene compound to the positive electrode sheet and then converts it into polythiophene through electrochemical polymerization. The characteristic of polythiophene that its resistance increases significantly with temperature can significantly improve the thermal safety performance of the battery. Patent document CN 109728245B disperses benzoxazine in the positive electrode sheet. After the battery temperature rises to a certain level, the benzoxazine undergoes a polymerization reaction and coats the surface of the electrode material, reducing its reactivity and thus improving the safety of the cell. Patent document CN 112952100 B incorporates sulfone compounds containing unsaturated bonds into the positive electrode slurry. During the coating process, the sulfone compounds polymerize and form a protective layer on the surface of the positive electrode material, reducing side reactions between the electrode material and the electrolyte and improving the thermal stability of the cell.

[0004] The thermal runaway process of a battery is accompanied by violent chemical and electrochemical reactions. Increasing the internal resistance of the electrode can only reduce the impact of electrochemical reactions to some extent. However, battery thermal runaway is often determined by the chemical reactions of crosstalk between the positive and negative electrodes. Therefore, the commonly used methods cannot fundamentally solve the problem of cell thermal runaway. Summary of the Invention

[0005] This application provides a method for adding a monomer containing a thermally reversible structure and a structure-maintaining additive to a positive electrode slurry, coating and drying it to induce a polymerization reaction, thereby forming a cross-linked polymer functional protective layer in situ on the surface of the positive electrode material. Specifically:

[0006] A positive electrode slurry includes additives, said additives including safety additives.

[0007] The safety additives include conjugated diene monomers and dienophilic monomers, or;

[0008] The safety additives include cyclopentadiene monomers.

[0009] The conjugated diene monomer and the dienophile monomer can form a thermally reversible structure, or the cyclopentadiene monomer can form a thermally reversible structure.

[0010] Furthermore, the additive also includes a structure-maintaining additive, which undergoes a copolymerization reaction with the safety additive to form a crosslinked polymer.

[0011] Furthermore, the dienophilic monomer is selected from one or more of the following: bismaleimide ethane, bismaleimide-diethylene glycol, bismaleimide-triethylene glycol, bismaleimide-tetraethylene glycol, bismaleimide-PEG, BIS-MAL-DPEG(R)3, N,N-(1,3-phenylene)dimaleimide, N,N-(4,4-phenylene)dimaleimide, 4-arm-PEG-maleimide, and N-allylmaleimide.

[0012] Preferably, it is one or more of N-allyl maleimide, bismaleimide-diethylene glycol, bismaleimide-triethylene glycol, bismaleimide-tetraethylene glycol, and bismaleimide-PEG.

[0013] Furthermore, the conjugated diene monomer is selected from glycidyl furfuryl ether, furfuryl alcohol, furfurylamine, furfuryl methacrylate, 2,2′-(dithiodimethylene)difuran, 3-(2-furanyl)propane-1-amine, 4-methylenepropenyran, 6-furanyl-1-hexene, 2-furanpropanol, 3-[5-(3-hydroxypropyl)-2-furan]-propane-1-ol, trans-2-furanacrylic acid, 3-(5-acetyl-2-furanyl)acrylic acid, 2-vinylfuran, (E)-3-(2-furan)acrylonitrile, 2-allylfuran, 4-(2-furanyl)-1-buten-4-ol, allyl 2-furanate, and N-(furan-2-methyl)-2-propeny-1-amine.

[0014] Furthermore, the cyclopentadiene monomers are selected from one or more of cyclopentadiene and dicyclopentadiene.

[0015] Furthermore, the structure-maintaining additive is selected from one or more of the following: isocyanate monomers and their dimers, trimers and polymers; epoxy monomers; polyol monomers; polyamine monomers; and unsaturated monomers.

[0016] Furthermore, when the dienophile or conjugated diene structure has carbon-carbon double bond groups other than the diene structure, the structure-preserving additive is selected from unsaturated monomers;

[0017] When the dienophile or conjugated diene contains active hydrogen, the structure-preserving additive is selected from isocyanate monomers and their dimers, trimers and polymers, epoxy monomers and optionally further added polyols and / or polyamines.

[0018] Furthermore, the isocyanate monomers are selected from toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, biuret triisocyanate, lysine diisocyanate, phenylenediamine diisocyanate, tetramethylxylene diisocyanate, 1,5-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, 1,4-cyclohexyl diisocyanate, trimethyl-1,6-hexamethylene diisocyanate, tetramethyltoluene diisocyanate, methylcyclohexyl diisocyanate, decamethyl diisocyanate, dodecyl diisocyanate, 2,2,4-trimethylhexane diisocyanate, triphenylmethane triisocyanate, triphenyl thiophosphate diisocyanate, cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and poly(phenylene diisocyanate). Methyl polyphenyl polyisocyanate, 4,4'-diphenyl diisocyanate, norbornene diisocyanate, terephthalic diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, 2-methylpentane diisocyanate, 4,4'-diphenyl ether diisocyanate, 4-methyldiphenylmethane-3,4-diisocyanate, 2,4'-diphenyl sulfide diisocyanate Isocyanates, diethylphenyl diisocyanate, 4,4'-diphenylethane diisocyanate, dimethyldiphenylmethylene diisocyanate, triphenylmethane-4,4',4”-triisocyanate, tri(4-phenylisocyanate) thiophosphate, dimethyltriphenylmethane tetraisocyanate, p-toluenesulfonyl isocyanate (PTSI), pentafluorophenyl isocyanate (PFPI), and dimers, trimers, and polymers of the above isocyanates.

[0019] Furthermore, the polyol monomer is selected from one or more of the following: polyester diol, polycarbonate diol, polyether diol, polysiloxane polyol, polyethylene adipate diol, 1,4-butanediol adipate diol, 1,6-hexanediol adipate diol, polycaprolactone diol, polyphthalate diol, polyethylene glycol, polypropylene glycol, polytetrahydrofuran ether diol, trihydroxy polyether, and hydroxyl silicone oil; preferably polyether diol and trihydroxy polyether.

[0020] Furthermore, the polyamine monomer is selected from one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, polyetherdiamine, diaminodiphenylmethane, and diethyltoluenediamine.

[0021] Furthermore, the epoxy monomer is selected from one or more of 1,2,4,4-diepoxybutane, 1,4-butanediol diglycidyl ether, 1,7-octadiene epoxy compound, polyethylene glycol diglycidyl ether, polypentyl glycol diglycidyl ether, diglycidyl ether, bisphenol A diglycidyl ether, phenol diglycidyl ether, and glycerol triglycidyl ether.

[0022] Furthermore, the unsaturated monomers are selected from ethylene carbonate, vinylene carbonate, hydroxypropyl acrylate, methyl methacrylate, butyl methacrylate, dodecyl acrylate, neopentyl glycol diacrylate, trifluoroethyl methacrylate, hexafluorobutyl methacrylate, heptafluorobutyl acrylate, pentafluorophenyl methacrylate, bisphenol A dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and tri(2-acryloyl methacrylate) isocyanurate. Ethyl ester, bis(acryloyloxyethyl) isocyanurate, N,N-methylenebisacrylamide, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate, pentaerythritol hexaacrylate, 2-acrylate-(2-hydroxy-1,3-methylene)di[oxy(2-hydroxy-3,1-propylidene)] ester, N,N-methylenebisacrylamide, 1,4-disacryloylpiperazine, or one or more thereof.

[0023] Furthermore, the structure-maintaining additive is selected from one or more of the following:

[0024] Polyisocyanates containing benzene ring structures and their dimers, trimers and polymers;

[0025] Polyether polyols;

[0026] Polyfunctional acrylates containing ether segments.

[0027] Preferably,

[0028] The polyisocyanate containing a benzene ring structure is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and 4,4' diphenyl ether diisocyanate.

[0029] Polyether polyols are selected from one or more of polyethylene glycol, polypropylene glycol, and trihydroxy ether;

[0030] The ether-containing polyfunctional acrylate is selected from one or more of the following: ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate, and pentaerythritol hexaacrylate.

[0031] Furthermore, the molar ratio of the conjugated diene monomer to the dienophilic monomer is 1:(0.25-4), preferably 1:(0.5-2).

[0032] Furthermore, the mass ratio of the safety additive to the structure-maintaining additive is 1:(0.2-6), preferably 1:(0.25-2).

[0033] Furthermore, the positive electrode slurry also includes a positive electrode material, a conductive agent, a binder, a solvent, and an initiator;

[0034] Preferably, the additive is 0.001-10 parts by weight relative to 100 parts by weight of the cathode material.

[0035] Furthermore, the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dodecyl peroxide, diisopropyl peroxide dicarbonate, isophenylpropane hydroperoxide, dimethyl azobisisobutyrate, stannous octoate, N,N-dimethylcyclohexylamine, bis(2-dimethylaminoethyl) ether, N,N,N',N'-tetramethylalkylene diamine, triethylamine, N,N-dimethylbenzylamine, and dibutyltin dilaurate.

[0036] A positive electrode sheet is formed by coating the aforementioned positive electrode slurry onto a substrate and then polymerizing it in situ.

[0037] The conjugated diene monomers and dienophilic monomers in the positive electrode slurry form a thermally reversible structure through in-situ polymerization, or the cyclopentadiene monomers form a thermally reversible structure through in-situ polymerization.

[0038] A method for preparing a positive electrode sheet, wherein the method includes:

[0039] The above-mentioned positive electrode slurry is coated onto a substrate and then polymerized in situ to obtain a positive electrode sheet.

[0040] A lithium-ion battery includes the above-described positive electrode sheet or a positive electrode sheet prepared by the above method.

[0041] Compared with the prior art, the beneficial effects of this application are as follows:

[0042] The polymer material is cross-linked at room temperature, coating the surface of the positive electrode material. This reduces the contact between the electrolyte and the positive electrode, improving cycle stability. When the battery is subjected to high external temperatures, the cross-linked polymer depolymerizes, generating a large number of unsaturated double bond groups. This process is endothermic, lowering the internal temperature of the battery. When the battery is subjected to sustained high heat, and the internal temperature rises to the oxygen evolution temperature of the positive electrode, oxygen free radicals are generated. At this point, the depolymerization products of the thermally reversible cross-linked polymer undergo an addition reaction with the oxygen free radicals, absorbing them and preventing them from diffusing to the negative electrode and causing severe thermal runaway, thereby improving cell safety. Furthermore, the preparation method of this invention is simple and easy to scale up for production. Attached Figure Description

[0043] Figure 1 Here is a SEM image of the positive electrode sheet in Example 1;

[0044] Figure 2 Here is a SEM image of the positive electrode in Comparative Example 1;

[0045] Figure 3 The results of LSV testing for the two types of electrodes in Example 1 and Comparative Example 1 are shown.

[0046] Figure 4 The graphs show the thermal test curves of the 10Ah pouch cells in Example 1 and Comparative Example 1. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0048] This application provides a positive electrode slurry, including additives, the additives including safety additives that can improve the thermal stability of the battery, the safety additives including conjugated diene monomers and dienophilic monomers, or the safety additives including cyclopentadiene monomers, wherein the conjugated diene monomers and the dienophilic monomers can form a thermally reversible structure, or the cyclopentadiene monomers can form a thermally reversible structure with each other.

[0049] In some embodiments of this application, the dienophilic monomer is selected from one or more of bismaleimide ethane, bismaleimide-diethylene glycol, bismaleimide-triethylene glycol, bismaleimide-tetraethylene glycol, bismaleimide-PEG, BIS-MAL-DPEG(R)3, N,N-(1,3-phenylene)dimaleimide, N,N-(4,4-phenylene)dimaleimide, 4-arm-PEG-maleimide, and N-allylmaleimide; preferably one or more of N-allylmaleimide, bismaleimide-diethylene glycol, bismaleimide-triethylene glycol, bismaleimide-tetraethylene glycol, and bismaleimide-PEG.

[0050] In some embodiments of this application, the conjugated diene monomer is selected from glycidyl furfuryl ether, furfurylamine, furfuryl methacrylate, 2,2′-(dithiodimethylene)difuran, 3-(2-furanyl)propane-1-amine, 4-methylenepropenyran, 6-furanyl-1-hexene, 2-furanpropanol, 3-[5-(3-hydroxypropyl)-2-furan]-propane-1-ol, trans-2-furanacrylic acid, 3-(5-acetyl-2-furanyl)acrylic acid, 2-vinylfuran, (E)-3-(2-furan)acrylonitrile, 2-allylfuran, 4-(2-furanyl)-1-buten-4-ol, allyl 2-furanate, and N-(furan-2-methyl)-2-propeny-1-amine.

[0051] In some embodiments of this application, the cyclopentadiene monomer is selected from one or more of cyclopentadiene and dicyclopentadiene.

[0052] In this application, when the thermally reversible structure is subjected to external high heat, the internal temperature gradually increases. After reaching a certain level, the positive electrode material releases oxygen free radicals, which further diffuse to the negative electrode, causing a severe thermal runaway reaction. The thermally reversible structure of this application absorbs oxygen free radicals before they diffuse from the positive electrode to the negative electrode, controlling the thermal runaway in its initial stage and preventing a violent explosion in the later stages.

[0053] The additives described in this application also include structure-preserving additives. These are defined as compounds or polymers that can copolymerize with safety additives via active hydrogen and / or unsaturated double bonds to form polymers. The copolymerization reactions are addition reactions of unsaturated double bonds, reactions of isocyanates with active hydrogen, and reactions of epoxides with active hydrogen.

[0054] In some embodiments of this application, the structure-maintaining additive is selected from one or more of the following: isocyanate monomers and their dimers, trimers and polymers; epoxy monomers; polyol monomers; polyamine monomers; and unsaturated monomers.

[0055] In some embodiments of this application, the isocyanate monomers are selected from toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, biuret triisocyanate, lysine diisocyanate, phenylenediamine diisocyanate, tetramethylxylene diisocyanate, 1,5-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, 1,4-cyclohexyl diisocyanate, trimethyl-1,6-hexamethylene diisocyanate, tetramethyltoluene diisocyanate, methylcyclohexyl diisocyanate, decamethyl diisocyanate, dodecyl diisocyanate, 2,2,4-trimethylhexane diisocyanate, triphenylmethane triisocyanate, triphenyl thiophosphate diisocyanate, cyclohexane diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate. Ester, polymethylene polyphenyl polyisocyanate, 4,4'-diphenyl diisocyanate, norbornene diisocyanate, terephthalic diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, 2-methylpentane diisocyanate, 4,4'-diphenyl ether diisocyanate, 4-methyldiphenylmethane-3,4-diisocyanate, 2,4'-diphenylsulfuron Ether diisocyanates, diethylphenyl diisocyanates, 4,4'-diphenylethane diisocyanates, dimethyldiphenylmethylene diisocyanates, triphenylmethane-4,4',4”-triisocyanates, tri(4-phenylisocyanate) thiophosphate, dimethyltriphenylmethane tetraisocyanate, p-toluenesulfonyl isocyanate (PTSI), pentafluorophenyl isocyanate (PFPI), and dimers, trimers, and polymers of the above isocyanates.

[0056] In some embodiments of this application, the polyol monomer is selected from one or more of polyester diol, polycarbonate diol, polyether diol, polysiloxane polyol, polyethylene adipate diol, 1,4-butanediol adipate diol, 1,6-hexanediol adipate diol, polycarbonate diol, polycaprolactone diol, polyphthalate diol, polyethylene glycol, polypropylene glycol, polytetrahydrofuran ether diol, trihydroxy polyether, and hydroxyl silicone oil; preferably polyether diol and trihydroxy polyether.

[0057] In some embodiments of this application, the polyamine monomer is selected from one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, polyether diamine, diaminodiphenylmethane, and diethyltoluenediamine.

[0058] In some embodiments of this application, the epoxy monomer is selected from one or more of 1,2,4,4-diepoxybutane, 1,4-butanediol diglycidyl ether, 1,7-octadiene epoxy compound, polyethylene glycol diglycidyl ether, polypentyl glycol diglycidyl ether, diglycidyl ether, bisphenol A diglycidyl ether, phenol diglycidyl ether, and glycerol triglycidyl ether.

[0059] In some embodiments of this application, the unsaturated monomers are selected from ethylene carbonate, vinylene carbonate, hydroxypropyl acrylate, methyl methacrylate, butyl methacrylate, dodecyl acrylate, neopentyl glycol diacrylate, trifluoroethyl methacrylate, hexafluorobutyl methacrylate, heptafluorobutyl acrylate, pentafluorophenyl methacrylate, bisphenol A dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, tri(2) isocyanurate. One or more of the following: bis(acryloyloxyethyl) ester, bis(acryloyloxyethyl) isocyanurate, N,N-methylenebisacrylamide, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate, pentaerythritol hexaacrylate, 2-acrylate-(2-hydroxy-1,3-methylene)di[oxy(2-hydroxy-3,1-propylidene)] ester, N,N-methylenebisacrylamide, and 1,4-diacryloylpiperazine.

[0060] In this application, "active hydrogen" refers to a deprotonable hydrogen atom attached to a nitrogen-, oxygen-, or sulfur- atom. "Active hydrogen" also refers to a hydrogen atom in a hydroxyl, mercapto, or amino group. The source of active hydrogen in this application can be a conjugated diene, a dienophile monomer, a polyol, or a polyamine.

[0061] The copolymerization reactions of safety additives and structure-preserving additives can be divided into two categories: when the diephile or conjugated diene has an additional C=C, such as N-allylmaleimide, the structure-preserving additive uses unsaturated monomers to react with it; when the diephile or conjugated diene has active hydrogen, such as furfurylamine, the structure-preserving additive uses isocyanates or epoxy monomers to react with it, and simultaneously adds polyols, polyamines, and other monomers containing active hydrogen to extend the chain. The structure-preserving additive undergoes a copolymerization reaction with the aforementioned thermally reversible structure; the copolymerization reaction involves the addition of unsaturated double bonds, the reaction of isocyanates with active hydrogen, and the reaction of active hydrogen in epoxy. The active hydrogen originates from diephile monomers, conjugated diene monomers, polyol monomers, and polyamine monomers.

[0062] In one embodiment of this application, after the safety additive and the structure-retaining additive are mixed, the monomer containing maleimide functional group in the safety additive undergoes a Diels-Alder reaction with the monomer containing furan functional group to form a thermally reversible structure with active hydrogen groups. The structure-retaining additive, because it contains isocyanate or epoxy groups, will undergo a copolymerization reaction with the thermally reversible structure containing active hydrogen, thereby forming a polymer with a reversible crosslinked structure.

[0063] Therefore, when a dienophile or conjugated diene has an active hydrogen, such as furfurylamine, the structure-maintaining additive can be selected from isocyanate monomers or epoxy monomers to react with it. Optionally, polyols or polyamines can be added to further participate in the chain extension reaction.

[0064] Regarding specific monomer combinations, when the safety additive conjugated diene monomer is selected from furans containing active hydrogen, such as: autoglycidyl furfuryl ether, furfuryl alcohol, furfurylamine, 3-(2-furanyl)propane-1-amine, 2-furanpropanol, 3-[5-(3-hydroxypropyl)-2-furan]-propane-1-ol, 4-(2-furanyl)-1-buten-4-ol, N-(furan-2-methyl)-2-propen-1-amine, the diephilic safety additive is selected from olefinic maleimides or non-olefinic polymaleimides, such as: bismaleimide ethane, bismaleimide-diethylene glycol, bismaleimide-triethylene glycol, bismaleimide-tetraethylene glycol, bismaleimide-diethylene glycol, etc. -PEG, BIS-MAL-DPEG(R)3, N,N-(1,3-phenylene)dimaleimide, N,N-(4,4-phenylene)dimaleimide, 4-arm-PEG-maleimide, N-allylmaleimide; In order to form a covalently bonded polymer with the safety additive and achieve the preferred effect, the structure-maintaining additive should be a combination of polyether polyol and isocyanate containing benzene ring, such as: toluene diisocyanate and polyethylene glycol combination, toluene diisocyanate trimer and polyethylene glycol combination, diphenylmethane diisocyanate and polyethylene glycol combination, diphenylmethane diisocyanate trimer and polyethylene glycol combination.

[0065] In another embodiment of this application, after the safety additive and the structure-maintaining additive are mixed, the monomer containing maleimide functional group in the safety additive undergoes a Diels-Alder reaction with the monomer containing furan functional group to form a thermally reversible structure with unsaturated double bonds. Because the structure-maintaining additive contains unsaturated double bond groups, it will undergo a copolymerization reaction with the thermally reversible structure containing double bonds to form a polymer with a reversible cross-linked structure.

[0066] Therefore, when a diephile or conjugated diene contains a carbon-carbon double bond other than the diene bond, such as N-allylic maleimide, the structure-preserving additive should be an unsaturated monomer in order to react with it.

[0067] Regarding specific monomer combinations, when the safety additive conjugated diene monomer is selected from furans containing olefin groups, such as: furfuryl methacrylate, 4-methylenepropenyfuran, 6-furanyl-1-hexene, 3-(5-acetyl-2-furanyl)acrylic acid, 2-vinylfuran, (E)-3-(2-furan)acrylonitrile, 2-allylfuran, allyl 2-furanate, N-(furan-2-methyl)-2-propen-1-amine, the diephilic safety additive is selected from olefinic maleimides or non-olefinic polymaleimides, such as: bismaleimide ethane, bismaleimide-diethylene glycol, bismaleimide-triethylene glycol, bismaleimide-tetraethylene glycol, bismaleimide-PEG, BIS-MAL-DPEG(R)3, N,N-(1,3-phenylene)dimaleimide, N,N-(4 ... 4-Phenylidene dimaleimide, 4-arm-PEG-maleimide, N-allyl maleimide; In order to form a covalently bonded polymer with the safety additive and achieve the preferred effect, the structure-maintaining additive should be a multifunctional acrylate containing an ether segment, such as: bisphenol A dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, tri(2-acryloyloxyethyl) isocyanurate, bis(acryloyloxyethyl) isocyanurate, N,N-methylenebisacrylamide, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate, pentaerythritol hexaacrylate.

[0068] In some preferred embodiments of this application, the structure-maintaining additive may be further preferably selected from one or more of the following: polyisocyanates containing benzene ring structures and their dimers, trimers and polymers; polyether polyols; and polyfunctional acrylates containing ether segments.

[0069] In some preferred embodiments of this application, the polyisocyanate containing a benzene ring structure is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, 4,4'-diphenyl ether diisocyanate, and pentafluorophenyl isocyanate; the polyether polyol is selected from one or more of polyethylene glycol, polypropylene glycol, and trihydroxy polyether; and the ether-segment-containing polyfunctional acrylate is selected from one or more of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate, and pentaerythritol hexaacrylate.

[0070] In some preferred embodiments of this application, the molar ratio of the conjugated diene monomer to the dienophilic monomer is 1:(0.25-4), preferably 1:(0.5-2);

[0071] For example, the molar ratio of the conjugated diene monomer to the dienophilic monomer can be 1:0.25, 1:0.5, 1:0.75, 1:1, 1:1.25, 1:1.5, 1:1.75, 1:2, 1:2.25, 1:2.5, 1:2.75, 1:3, 1:3.25, 1:3.5, 1:3.75, 1:4, or any range thereof. When the ratio exceeds this range, it will lead to incomplete reaction of one monomer and excessive residue, resulting in side reactions during charge and discharge processes and a significant decrease in electrical performance.

[0072] In some preferred embodiments of this application, the mass ratio of the safety additive to the structure-maintaining additive is 1:(0.2-6), preferably 1:(0.25-2).

[0073] For example, the mass ratio of the safety additive to the structure-maintaining additive is 1:0.2, 1:0.25, 1:0.5, 1:0.75, 1:1, 1:1.25, 1:1.5, 1:1.75, 1:2, 1:2.25, 1:2.5, 1:2.75, 1:3, 1:3.25, 1:3.5, 1:3.75, 1:4, 1:4.25, 1:4.5, 1:4.75, 1:5, 1:5.25, 1:5.5, 1:5.75, 1:6, or any range thereof. When the proportion of safety additives is too low, the amount of thermally reversible structural units is too small. After thermal runaway, the number of depolymerization groups is too small, resulting in insufficient heat absorption and oxygen free radicals, which cannot significantly improve battery safety performance. When the proportion of safety additives is too high, the polymerized product has poor film-forming properties and low reactivity. It often forms oligomers. Furthermore, the thermally reversible groups are cyclic rigid structures. When their proportion is too high, the polymer flexibility decreases, which is not conducive to the continuous jumping of lithium ions on the polymer chain segments. In addition, the thermally reversible groups have poor affinity with the electrolyte, which is not conducive to electrolyte wetting.

[0074] In some preferred embodiments of this application, the positive electrode slurry further includes a positive electrode material, a conductive agent, a binder, a solvent, and an initiator.

[0075] In some preferred embodiments of this application, the mass of the additive is 0.001-10 parts by weight relative to 100 parts by weight of the cathode material;

[0076] For example, relative to 100 parts by weight of the cathode material, the mass of the additive can be 0.001 parts by weight, 0.01 parts by weight, 0.1 parts by weight, 0.2 parts by weight, 0.3 parts by weight, 0.4 parts by weight, 0.5 parts by weight, 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight, 0.9 parts by weight, 1 part by weight, 1.1 parts by weight, 1.2 parts by weight, 1.3 parts by weight, 1.4 parts by weight, 1.5 parts by weight, 1.6 parts by weight, 1.7 parts by weight, 1.8 parts by weight, 1.9 parts by weight, 2 parts by weight, 2. 1 part by weight, 2.2 parts by weight, 2.3 parts by weight, 2.4 parts by weight, 2.5 parts by weight, 2.6 parts by weight, 2.7 parts by weight, 2.8 parts by weight, 2.9 parts by weight, 3 parts by weight, 3.1 parts by weight, 3.2 parts by weight, 3.3 parts by weight, 3.4 parts by weight, 3.5 parts by weight, 3.6 parts by weight, 3.7 parts by weight, 3.8 parts by weight, 3.9 parts by weight, 4 parts by weight, 4.1 parts by weight, 4.2 parts by weight, 4.3 parts by weight, 4.4 parts by weight, 4.5 parts by weight, 4.6 parts by weight, 4.7 parts by weight, 4 0.8 parts by weight, 4.9 parts by weight, 5 parts by weight, 5.1 parts by weight, 5.2 parts by weight, 5.3 parts by weight, 5.4 parts by weight, 5.5 parts by weight, 5.6 parts by weight, 5.7 parts by weight, 5.8 parts by weight, 5.9 parts by weight, 6 parts by weight, 6.1 parts by weight, 6.2 parts by weight, 6.3 parts by weight, 6.4 parts by weight, 6.5 parts by weight, 6.6 parts by weight, 6.7 parts by weight, 6.8 parts by weight, 6.9 parts by weight, 7 parts by weight, 7.1 parts by weight, 7.2 parts by weight, 7.3 parts by weight, 7.4 parts by weight, 7. 5 parts by weight, 7.6 parts by weight, 7.7 parts by weight, 7.8 parts by weight, 7.9 parts by weight, 8 parts by weight, 8.1 parts by weight, 8.2 parts by weight, 8.3 parts by weight, 8.4 parts by weight, 8.5 parts by weight, 8.6 parts by weight, 8.7 parts by weight, 8.8 parts by weight, 8.9 parts by weight, 9 parts by weight, 9.1 parts by weight, 9.2 parts by weight, 9.3 parts by weight, 9.4 parts by weight, 9.5 parts by weight, 9.6 parts by weight, 9.7 parts by weight, 9.8 parts by weight, 9.9 parts by weight, 10 parts by weight, or any range thereof.

[0077] In some preferred embodiments of this application, the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dodecyl peroxide, diisopropyl peroxide dicarbonate, isophenylpropane hydroperoxide, dimethyl azobisisobutyrate, stannous octoate, N,N-dimethylcyclohexylamine, bis(2-dimethylaminoethyl) ether, N,N,N',N'-tetramethylalkylene diamine, triethylamine, N,N-dimethylbenzylamine, and dibutyltin dilaurate.

[0078] In this application, the selection of the initiator is adapted to the type and structure of the safety additives.

[0079] In some embodiments of this application, the positive electrode slurry includes additives, which include safety additives and structure-retaining additives. The safety additives include conjugated diene monomers and dienophilic monomers, or the safety additives include cyclopentadiene monomers, wherein the conjugated diene monomers and the dienophilic monomers are capable of forming a thermally reversible structure, or the cyclopentadiene monomers are capable of forming a thermally reversible structure.

[0080] In some embodiments of this application, the safety additive and the structure-maintaining additive are linked by covalent bonds. Therefore, the safety additive and the structure-maintaining additive need to have functional groups capable of polymerization. When the dienophilic monomer and the conjugated dien monomer react with the unsaturated monomer, a DA reaction occurs to form a thermally reversible structure with unsaturated double bonds at both ends. During the coating stage, at high temperatures, the free radical initiator initiates a copolymerization reaction between the unsaturated monomer and the thermally reversible structure with unsaturated double bonds to form a polymer inside the electrode. The unsaturated monomer is the main framework structure of the polymer network, giving the polymer good film-forming properties, elasticity, and high-temperature structural integrity. The safety additive is distributed in the polymer chain segments in the form of side chains and crosslinking points. The thermally reversible structure can provide endothermic depolymerization when the battery temperature rises and absorb oxygen free radicals to improve battery safety performance.

[0081] In some embodiments of this application, the safety additive and the structure-maintaining additive are linked by covalent bonds. Therefore, the safety additive and the structure-maintaining additive need to have functional groups capable of undergoing polymerization reactions. When the dienophilic monomer and the conjugated dien monomer react with the isocyanate monomer, furfurylamine and maleimide undergo a DA reaction during the mixing stage to generate thermally reversible groups with amino groups at both ends. During the coating stage, at high temperatures, the thermally reversible groups with amino groups at both ends and the isocyanate monomer undergo a polymerization reaction of isocyanate with -NH2 and -OH to generate a polymer with polyether segment polyurethane as the main chain and thermally reversible structures as crosslinking points or side chains. The polyether segment polyurethane gives the polymer good film-forming properties, elasticity, and high-temperature structural integrity. The safety additive is distributed in the polymer chain segments in the form of side chains and crosslinking points. The thermally reversible structure can provide endothermic depolymerization when the battery temperature rises and absorb oxygen free radicals to improve battery safety performance.

[0082] In some embodiments of this application, the safety additive and the structure-maintaining additive are linked by covalent bonds. Therefore, both the safety additive and the structure-maintaining additive need to have functional groups capable of undergoing polymerization. In order to react with it, the structure-maintaining additive is an ether-containing segmental unsaturated acrylate monomer containing unsaturated double bonds. During the mixing stage, cyclopentadiene undergoes self-polymerization to generate a polymer with a thermally reversible structure. During the coating stage, under the high temperature and the action of the initiator, it undergoes a polymerization reaction with the ether-containing segmental unsaturated acrylate monomer to generate a polymer with ether-containing acrylate as the main chain and cyclopentadiene polymer as side chains or crosslinking points. The ether-containing acrylate is the main framework structure of the polymer network, giving the polymer good film-forming properties, elasticity, and high-temperature structural integrity. The safety additive is distributed in the polymer chain segments in the form of side chains and crosslinking points. The thermally reversible structure can provide endothermic depolymerization when the battery temperature rises and absorb oxygen free radicals to improve battery safety performance.

[0083] In one specific embodiment of this application, a positive electrode material, a conductive agent, PVDF, and additives are added to a solvent NMP to obtain a positive electrode slurry. The positive electrode slurry is stirred evenly, coated onto a current collector, and then dried to obtain a positive electrode sheet. The additives include safety additives and structure-preserving additives. The safety additives include conjugated diene monomers and dienophilic monomers. The initiator used is azobisisobutyronitrile.

[0084] In this application, the cathode material is any cathode material known to those skilled in the art. For example, the cathode material is selected from one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium iron silicate, lithium cobalt oxide, nickel-cobalt-manganese ternary materials, nickel-manganese / cobalt-manganese / nickel-cobalt binary materials, lithium manganese oxide, and lithium-rich manganese-based materials.

[0085] In this application, the conductive agent is any conductive agent known to those skilled in the art. For example, the conductive agent is selected from any one or more of conductive graphite, conductive carbon black, acetylene black, carbon nanotubes, graphene, and carbon fiber.

[0086] In this application, the adhesive is any adhesive known to those skilled in the art, for example, the adhesive is selected from any one or more of polyvinylidene fluoride, acrylic resin, polytetrafluoroethylene, and styrene-butadiene rubber.

[0087] In this application, the solvent is any solvent known to those skilled in the art, for example, the solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propyl propionate and propyl acetate, N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide ethanol, acetonitrile, and tetrahydrofuran.

[0088] This application provides a positive electrode sheet, which is formed by coating the above-mentioned positive electrode slurry onto a substrate and then polymerizing it in situ. The conjugated diene monomer and dienophilic monomer in the positive electrode slurry form a thermally reversible structure through in-situ polymerization, or the cyclopentadiene monomer forms a thermally reversible structure through in-situ polymerization.

[0089] This application provides a method for preparing a positive electrode sheet, wherein the above-mentioned positive electrode slurry is coated onto a substrate and then polymerized in situ to obtain a positive electrode sheet.

[0090] This application provides a lithium-ion battery, including the above-described positive electrode sheet or the positive electrode sheet prepared by the above method.

[0091] The safety additive and structure-maintaining additive provided in this application can significantly improve battery thermal safety and cycle stability after reaction. The safety additive, after polymerization, forms a polymer with thermally reversible groups. When the battery temperature exceeds a certain range, it undergoes a depolymerization reaction, generating a large number of unsaturated bonds, carrying away some heat and absorbing oxygen free radicals to prevent battery thermal runaway. The structure-maintaining additive, after polymerization, forms a polymer containing polyether, polyester, and other chain segments. It has good affinity with the electrolyte, which is beneficial for electrolyte wetting and reduces side reactions of the electrolyte in the positive electrode material. Furthermore, the ether and ester groups can coordinate with lithium ions, providing migration sites during transport. This provides a more uniform ion flow. In this application, the above monomers are mixed and dispersed evenly inside the positive electrode slurry. Utilizing the active functional groups of the additives themselves, the safety additives and structure-maintaining additives undergo a copolymerization reaction during the coating and drying process, forming an in-situ polymer protective layer inside the electrode with the structure-maintaining additives as the main chain and the safety additives as side chains or cross-linking points. The preparation method is compatible with existing production processes and is easy to scale up. Furthermore, because the additives are mixed with small molecules before polymerization, the bonding and mixing of the additives with the positive electrode material, conductive agent, etc. are more uniform, and the bonding is tighter after polymerization. The interface contact between the polymer and the electrode material is better, and the battery internal resistance is lower.

[0092] Example 1

[0093] 1) Add 95g of NCM811 positive electrode material, 3g of conductive agent, 2g of PVDF, and 5g of additive to 80g of NMP to obtain a positive electrode slurry. After stirring the positive electrode slurry evenly, coat it onto a current collector and dry it to obtain a positive electrode sheet with a single-sided areal density of 200g / m². 2The additives include safety additives and structure-preserving additives. The safety additives include conjugated diene monomers and dienophilic monomers. The conjugated diene monomer is 1.8g of N-allyl maleimide, and the dienophilic monomer is 2.2g of furfuryl methacrylate. The molar ratio of the conjugated diene monomer to the dienophilic monomer is 1:1. The structure-preserving additive is 1g of ethoxylated trimethylolpropane triacrylate. The total mass of the safety additive and the structure-preserving additive is 5g, and the mass ratio of the safety additive to the structure-preserving additive is 4:1. The initiator used is 0.05g of azobisisobutyronitrile.

[0094] 2) Dissolve 96g graphite, 1.2g CMC, 1.5g SBR, and 1.3g conductive agent in 150g pure water, stir, coat the mixture with a current collector, and then dry to obtain a negative electrode sheet with a single-sided areal density of 114g / cm³. 2 ;

[0095] 3) Using the electrodes prepared in steps 1) and 2) and commercially available separators, a 10Ah soft-pack battery cell was prepared. After being injected with electrolyte (EC / EMC / DMC = 1 / 1 / 1 3% VC 1M LiPF6) and soaked for 24 hours, it was formed and capacity tested to obtain the final soft-pack battery cell.

[0096] The following tests were performed on the above-mentioned pouch cells;

[0097] Thermal runaway temperature: The battery is placed in a special heating oven for lithium-ion batteries and heated to 130°C at a rate of 5°C / min. Then, the temperature is increased by 10°C and held for 1 hour, with the maximum temperature reaching 200°C. The ambient temperature of the battery near the explosion point in the oven is the thermal runaway temperature of the lithium-ion battery.

[0098] Cyclic testing: The battery was charged and discharged using Wuhan Landian Equipment, with a voltage range of 2.75-4.25V and 0.1C / 0.1C charge and discharge. The capacity of the first discharge cycle was taken as the capacity at 0.1C, and the number of cycles when the capacity decayed to 80% was counted.

[0099] LSV test: Replace all the positive electrode material in step 1) with conductive carbon black (SP), leaving the rest unchanged, and coat it to form an SP positive electrode sheet. At this time, the additive is coated on the surface of the SP material, forming an effect similar to coating the positive electrode material. Assemble the SP positive electrode sheet, lithium sheet, and electrolyte (EC / EMC / DMC = 1 / 1 / 1 3% VC 1MLiPF6) into a button cell, and then perform a linear voltammetry scan test with a scan rate of 1mV / s and a voltage range of OCV-5V.

[0100] In Example 1, the safety additives are N-allylmaleimide and furfuryl methacrylate containing unsaturated carbon-carbon double bonds, the structure-maintaining additive is ethoxylated trimethylolpropane triacrylate, and the initiator is azobisisobutyronitrile. After being mixed into the positive electrode slurry, N-allylmaleimide and furfuryl methacrylate undergo a DA reaction during the mixing stage to form a thermally reversible structure with unsaturated double bonds at both ends. During the coating stage, at high temperatures, the free radical initiator initiates a copolymerization reaction between ethoxylated trimethylolpropane triacrylate and the thermally reversible structure with unsaturated double bonds to form a polymer inside the electrode. Ethoxylated trimethylolpropane triacrylate is the main framework structure of the polymer network, giving the polymer good film-forming properties, elasticity, and high-temperature structural integrity. The safety additives are distributed in the polymer chain segments in the form of side chains and crosslinking points. The thermally reversible structure can provide endothermic depolymerization when the battery temperature rises and absorb oxygen free radicals to improve battery safety performance.

[0101] Example 2

[0102] The only difference between Example 2 and Example 1 is that the structure-retaining additive ethoxylated trimethylolpropane triacrylate in Example 1 is replaced with the structure-retaining additive polyethylene glycol dimethacrylate; all other conditions are the same.

[0103] Example 3

[0104] The only difference between Example 3 and Example 1 is that the structure-preserving additive ethoxylated trimethylolpropane triacrylate in Example 1 is replaced with the structure-preserving additive butyl methacrylate; all other conditions are the same.

[0105] Example 4

[0106] The only difference between Example 4 and Example 1 is that the additives include conjugated diene monomers, dienophilic monomers, and structure-preserving additives. The dienophilic monomer is 2.12 g of bismaleimide ethane, the conjugated diene monomer is 1.88 g of furfurylamine, the structure-preserving additives are 0.6 g of toluene diisocyanate trimer and 0.4 g of polyethylene glycol with a molecular weight of 2000, and the initiator used is 0.05 g of stannous octoate; all other conditions are the same.

[0107] In Example 4, the safety additives are furfurylamine and bismaleimide. To maintain the structure of the invention, the additives are toluene diisocyanate trimer and polyethylene glycol with a molecular weight of 2000, and the catalyst is stannous octoate. During the mixing stage, furfurylamine and maleimide undergo a DA reaction to generate thermally reversible groups with amine groups at both ends. During the coating stage, at high temperature, the thermally reversible groups with amine groups at both ends, the toluene diisocyanate trimer, and the polyethylene glycol with a molecular weight of 2000 undergo a polymerization reaction of isocyanate with -NH2 and -OH, generating a polymer with polyether segment polyurethane as the main chain and thermally reversible structures as crosslinking points or side chains. The polyether segment polyurethane gives the polymer good film-forming properties, elasticity, and high-temperature structural integrity. The safety additives are distributed in the polymer chain segments in the form of side chains and crosslinking points. The thermally reversible structure can provide depolymerization endothermic reaction when the battery temperature rises and absorb oxygen free radicals to improve battery safety performance.

[0108] Example 5

[0109] The only difference between Example 5 and Example 4 is that the toluene diisocyanate trimer in Example 4 is replaced with toluene diisocyanate; all other conditions are the same.

[0110] Example 6

[0111] The only difference between Example 6 and Example 4 is that the toluene diisocyanate trimer in Example 4 is replaced with hexamethylene diisocyanate; all other conditions are the same.

[0112] Example 7

[0113] The only difference between Example 7 and Example 4 is that all the structure-preserving additives in Example 4 were replaced with 1g of 1,4-butanediol diglycidyl ether, and no initiator was used; all other conditions were the same.

[0114] Example 8

[0115] The only difference between Example 8 and Example 7 is that 1,4-butanediol diglycidyl ether in Example 7 is replaced with glycerol triglycidyl ether; all other conditions are the same.

[0116] Example 9

[0117] The only difference between Example 9 and Example 1 is that the additives include cyclopentadiene monomers and structure-preserving additives, wherein the cyclopentadiene monomers are 4g of cyclopentadiene, the structure-preserving additives are 1g of ethoxylated trimethylolpropane triacrylate, and the initiator used is 0.05g of benzoyl peroxide; the other conditions are the same.

[0118] In Example 9, the safety additive is cyclopentadiene. To maintain its reaction structure, the additive is ethoxylated trimethylolpropane triacrylate, which also contains unsaturated double bonds. During the mixing stage, cyclopentadiene undergoes self-polymerization to generate a polymer with a thermally reversible structure. During the coating stage, under high temperature and the action of the initiator benzoyl peroxide, it undergoes a polymerization reaction with the unsaturated double bonds of ethoxylated trimethylolpropane triacrylate, generating a polymer with ethoxylated trimethylolpropane triacrylate as the main chain and cyclopentadiene polymer as side chains or crosslinking points. Ethoxylated trimethylolpropane triacrylate is the main framework structure of the polymer network, giving the polymer good film-forming properties, elasticity, and high-temperature structural integrity. The safety additive is distributed in the polymer chain segments in the form of side chains and crosslinking points. The thermally reversible structure can provide endothermic depolymerization when the battery temperature rises and absorb oxygen free radicals to improve battery safety performance.

[0119] Example 10

[0120] The only difference between Example 10 and Example 9 is that the structure-retaining additive ethoxylated trimethylolpropane triacrylate in Example 9 is replaced with the structure-retaining additive polyethylene glycol dimethacrylate; all other conditions are the same.

[0121] Example 11

[0122] The only difference between Example 11 and Example 9 is that the structure-preserving additive ethoxylated trimethylolpropane triacrylate in Example 9 is replaced with the structure-preserving additive butyl methacrylate; all other conditions are the same.

[0123] Example 12

[0124] The only difference between Example 12 and Example 1 is that the additive in Example 1 is reduced proportionally from 5g to 0.01g; all other conditions are the same.

[0125] Example 13

[0126] The only difference between Example 13 and Example 1 is that the additive in Example 1 is increased from 5g to 10g in proportion; all other conditions are the same.

[0127] Example 14

[0128] The only difference between Example 14 and Example 1 is that the additive in Example 1 is increased from 5g to 15g in proportion; all other conditions are the same.

[0129] Example 15

[0130] The only difference between Example 15 and Example 1 is that the molar ratio of the conjugated diene monomer and the dienophilic monomer is 1:2 and the sum of their masses is 4g, while the other conditions are the same.

[0131] Example 16

[0132] The only difference between Example 16 and Example 1 is that the molar ratio of the conjugated diene monomer and the dienophilic monomer is 1:4 and the sum of their masses is 4g, while the other conditions are the same.

[0133] Example 17

[0134] The only difference between Example 17 and Example 1 is that the molar ratio of the conjugated diene monomer to the dienophilic monomer is 2:1 and the sum of their masses is 4g, while the other conditions are the same.

[0135] Example 18

[0136] The only difference between Example 18 and Example 1 is that the molar ratio of the conjugated diene monomer to the dienophile monomer is 4:1 and the sum of their masses is 4g, while the other conditions are the same.

[0137] Example 19

[0138] The only difference between Example 19 and Example 1 is that the total mass of the safety additive and the structure-preserving additive is 5g, and the mass ratio of the safety additive to the structure-preserving additive is 6:1. All other conditions are the same.

[0139] Example 20

[0140] The only difference between Example 20 and Example 1 is that the total mass of the safety additive and the structure-preserving additive is 5g, and the mass ratio of the safety additive to the structure-preserving additive is 3:1. All other conditions are the same.

[0141] Example 21

[0142] The only difference between Example 21 and Example 1 is that the total mass of the safety additive and the structure-preserving additive is 5g, and the mass ratio of the safety additive and the structure-preserving additive is 2:1. All other conditions are the same.

[0143] Example 22

[0144] The only difference between Example 22 and Example 1 is that the total mass of the safety additive and the structure-preserving additive is 5g, and the mass ratio of the safety additive and the structure-preserving additive is 1:1. All other conditions are the same.

[0145] Example 23

[0146] The only difference between Example 23 and Example 1 is that the total mass of the safety additive and the structure-preserving additive is 5g, and the mass ratio of the safety additive and the structure-preserving additive is 1:2. All other conditions are the same.

[0147] Example 24

[0148] The only difference between Example 24 and Example 1 is that the total mass of the safety additive and the structure-preserving additive is 5g, and the mass ratio of the safety additive to the structure-preserving additive is 1:4. All other conditions are the same.

[0149] Example 25

[0150] The only difference between Example 25 and Example 1 is that the total mass of the safety additives is 5g, and there are no structure-preserving additives; all other conditions are the same.

[0151] Comparative Example 1

[0152] The only difference between Comparative Example 1 and Example 1 is that Comparative Example 1 contains no additives, while the other conditions are the same.

[0153] Comparative Example 2

[0154] The only difference between Comparative Example 2 and Example 1 is that Comparative Example 2 contains only 5g of the structure-preserving additive ethoxylated trimethylolpropane triacrylate, while the other conditions are the same.

[0155] Although the present invention has been disclosed above with reference to embodiments, it is not intended to limit the present invention. Anyone skilled in the art may make some modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the scope of the appended patent application.

[0156] Table 1. Effect of Structure-Maintaining Additive Type on Performance

[0157]

[0158] As can be seen from Example 1 and Comparative Example 1, the safety additives and / or structure-maintaining additives provided in this scheme can significantly improve the cycle stability and thermal safety of the battery after addition. This is evident from the SEM images of the positive electrodes in both sets of experiments. Figure 1 , Figure 2 The comparison shows that in Example 1, the cathode material undergoes in-situ polymerization to form a protective layer after drying, while in Comparative Example 1, the cathode material is exposed on the surface. From the LSV ( Figure 3 The tests show that as the applied potential increases, the current density of the electrode with the protective layer is lower and there are fewer electrochemical side reactions during the scanning process. Therefore, this protective layer can effectively inhibit the oxidation and decomposition of the electrolyte on the electrode surface, greatly improving its stability and significantly enhancing the battery's cycle life. From the thermal safety test results... Figure 4From this perspective, ordinary batteries experience thermal runaway when heated to 150-160℃, while the cells using this solution only experience thermal runaway when heated to 180℃. This is because the in-situ polymerized protective layer undergoes thermal depolymerization after being subjected to high temperatures, which takes away some of the heat. Furthermore, the thermal depolymerization products react with the oxygen free radicals released from the positive electrode, preventing them from diffusing to the negative electrode and causing more severe thermal runaway.

[0159] The results of Examples 1-3 show that the cross-linked polyether structure is more conducive to improving cycle and thermal safety. This is because the cross-linked material itself has better oxidation resistance and is more tightly coated on the electrode surface, which is more conducive to preventing electrolyte decomposition. During the heating process of the battery cell, the polymer structure can still remain intact after the thermally reversible structure of the cross-linked material depolymerizes, and its adsorption capacity for electrolyte will not decrease significantly. There is less free electrolyte, which can reduce electrolyte vaporization and combustion.

[0160] The results of Examples 1 and 25 show that the battery cycle stability is reduced to a certain extent when no structure-maintaining additive is added. This is because the product of the safety additive polymerization has poor film-forming properties and low reactivity, and the resulting products are often oligomers, which have poor stability in the high-voltage positive electrode.

[0161] Table 2. Effect of Structure-Maintaining Additive Type on Performance

[0162]

[0163]

[0164] As shown in Table 2, adding structure retainers helps improve battery performance. Examples 7-8 show that epoxy compounds can also improve battery cycle performance similarly to isocyanate monomers, but their improvement ability is slightly weaker than that of isocyanates. This is because some -OH groups remain after the reaction of epoxy with amines, which will have a slight impact on electrical performance to some extent. In addition, Examples 4-6 show that isocyanates with benzene rings have better electrical performance. Isocyanates with benzene rings have higher reactivity, are less likely to leave residues after the reaction, and the benzene ring structure is less prone to oxidation, which can better improve the electrical and thermal stability of the material.

[0165] Table 3. Functions of Safety Additives

[0166]

[0167] As can be seen from Table 3, when the safety additive is a cyclopentadiene monomer, it also exhibits the advantages of the cross-linked polyether structure and has good battery performance. As can be seen from Examples 1 and 9 and Comparative Example 2, the improvement of cell thermal safety mainly comes from the introduction of the thermally reversible structure of the safety additive. However, if only conventional polymer monomers are added, the effect on improving battery thermal safety is not obvious.

[0168] Table 4. Effect of Addition Amount on Performance

[0169]

[0170] The results of Examples 1, 12, 13, and 14 show that when the amount of additive added is too low, its effect on battery thermal safety is greatly reduced. When the amount of additive added is too high, too much polymer coats the electrode surface, affecting lithium-ion transport and causing a significant decrease in electrical performance.

[0171] Table 5. Effect of molar ratio of conjugated diene monomer and dienophilic monomer on performance.

[0172]

[0173] In Examples 15-18 and Example 1, when the molar ratio of conjugated diene monomer to dienophilic monomer is in the range of 1:(0.5-2), the battery's electrical performance and safety performance are both taken into account. However, when the ratio exceeds this range, the cycle stability of the cell decreases significantly. This is because both monomers have unsaturated double bonds, which are easily oxidized at high-voltage positive electrodes. The two monomers crosslink in a 1:1 ratio during the reaction. Excessive residue within a certain range has little impact on electrical performance, but when the ratio exceeds this range, the battery capacity decays rapidly.

[0174] Table 6. Effect of the Proportion of Safety Additives on Performance

[0175]

[0176]

[0177] In Examples 19-25, the safety additive and the structure-maintaining additive are in an optimal ratio range. When the proportion of the safety additive is increased, the content of the pyrolytic poly groups increases, which can significantly improve the safety performance. However, the thermally reversible groups are cyclic rigid structures. If their proportion is too high, the flexibility of the polymer decreases, which is not conducive to the continuous jumping of lithium ions on the polymer chain segments. In addition, the thermally reversible groups have poor affinity with the electrolyte, which is not conducive to electrolyte wetting. The optimal ratio is (1-4):1.

Claims

1. A positive electrode slurry, characterized in that, Includes additives, including safe additives. The safety additives include conjugated diene monomers and dienophilic monomers, or; The safety additives include cyclopentadiene monomers. Wherein, the conjugated diene monomer and the dienophilic monomer can form a thermally reversible structure, or the cyclopentadiene monomer can form a thermally reversible structure; The dienophilic monomer is selected from olefinic maleimides or non-olefinic polymaleimides; The conjugated diene monomer is selected from glycidyl furfuryl ether, furfuryl alcohol, furfurylamine, furfuryl methacrylate, 2,2′-(dithiodimethylene)difuran, 3-(2-furanyl)propane-1-amine, 4-methylenepropenyran, 6-furanyl-1-hexene, 2-furanpropanol, 3-[5-(3-hydroxypropyl)-2-furan]-propane-1-ol, trans-2-furanacrylic acid, 3-(5-acetyl-2-furanyl)acrylic acid, 2-vinylfuran, (E)-3-(2-furan)acrylonitrile, 2-allylfuran, 4-(2-furanyl)-1-buten-4-ol, allyl 2-furanate, and N-(furan-2-methyl)-2-propeny-1-amine.

2. The positive electrode slurry according to claim 1, characterized in that, The additive also includes a structure-maintaining additive, which copolymerizes with the safety additive to form a cross-linked polymer.

3. The positive electrode slurry according to claim 1 or 2, characterized in that, The dienophilic monomer is selected from one or more of the following: bismaleimide ethane, bismaleimide-diethylene glycol, bismaleimide-triethylene glycol, bismaleimide-tetraethylene glycol, bismaleimide-PEG, BIS-MAL-DPEG(R)3, N,N-(1,3-phenylene)dimaleimide, N,N-(4,4-phenylene)dimaleimide, 4-arm-PEG-maleimide, and N-allylmaleimide.

4. The positive electrode slurry according to claim 1 or 2, characterized in that, The dienophilic monomer is selected from one or more of N-allylmaleimide, bismaleimide-diethylene glycol, bismaleimide-triethylene glycol, bismaleimide-tetraethylene glycol, and bismaleimide-PEG.

5. The positive electrode slurry according to claim 1 or 2, characterized in that, The cyclopentadiene monomers are selected from one or more of cyclopentadiene and dicyclopentadiene.

6. The positive electrode slurry according to claim 2, characterized in that, The structure-maintaining additive is selected from one or more of the following: isocyanate monomers and their dimers, trimers and polymers; epoxy monomers; polyol monomers; polyamine monomers; unsaturated monomers.

7. The positive electrode slurry according to claim 6, characterized in that, When the dienophile or conjugated diene structure has carbon-carbon double bond groups other than diene structure, the structure-preserving additive is selected from unsaturated monomers. When the dienophile or conjugated diene contains active hydrogen, the structure-preserving additive is selected from isocyanate monomers and their dimers, trimers and polymers, epoxy monomers and optionally further added polyols and / or polyamines.

8. The positive electrode slurry according to claim 6, characterized in that, The isocyanate monomers are selected from toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, biuret triisocyanate, lysine diisocyanate, phenylenediamine diisocyanate, tetramethylxylene diisocyanate, 1,5-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, 1,4-cyclohexyl diisocyanate, trimethyl-1,6-hexamethylene diisocyanate, tetramethyltoluene diisocyanate, methylcyclohexyl diisocyanate, decamethyl diisocyanate, dodecyl diisocyanate, 2,2,4-trimethylhexane diisocyanate, triphenylmethane triisocyanate, triphenyl thiophosphate triphenyl isocyanate, cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, polymethylene diisocyanate, etc. Polyphenyl polyisocyanate, 4,4'-diphenyl diisocyanate, norbornene diisocyanate, terephthalic diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate, 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, 2-methylpentane diisocyanate, 4,4'-diphenyl ether diisocyanate, 4-methyldiphenylmethane-3,4-diisocyanate, 2,4'-diphenyl sulfide diisocyanate Acetic acid esters, diethylphenyl diisocyanate, 4,4'-diphenylethane diisocyanate, dimethyldiphenylmethylene diisocyanate, triphenylmethane-4,4',4''-triisocyanate, tris(4-phenylisocyanate) thiophosphate, dimethyltriphenylmethane tetraisocyanate, p-toluenesulfonyl isocyanate (PTSI), pentafluorophenyl isocyanate (PFPI), and dimers, trimers, and polymers of the above isocyanates.

9. The positive electrode slurry according to claim 6, characterized in that, The polyol monomers are selected from one or more of the following: polyester diol, polycarbonate diol, polyether diol, polysiloxane polyol, polyethylene adipate diol, 1,4-butanediol adipate diol, 1,6-hexanediol adipate diol, polycaprolactone diol, polyphthalate diol, polyethylene glycol, polypropylene glycol, polytetrahydrofuran ether diol, trihydroxy polyether, and hydroxyl silicone oil.

10. The positive electrode slurry according to claim 6, characterized in that, The polyol monomers are polyether diols and / or trihydroxy polyethers.

11. The positive electrode slurry according to claim 6, characterized in that, The polyamine monomers are selected from one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, polyether diamine, diaminodiphenylmethane, and diethyltoluenediamine.

12. The positive electrode slurry according to claim 6, characterized in that, The epoxy monomers are selected from one or more of 1,2,4,4-diepoxybutane, 1,4-butanediol diglycidyl ether, 1,7-octadiene epoxy compound, polyethylene glycol diglycidyl ether, polypentyl glycol diglycidyl ether, diglycidyl ether, bisphenol A diglycidyl ether, phenol diglycidyl ether, and glycerol triglycidyl ether.

13. The positive electrode slurry according to claim 6, characterized in that, The unsaturated monomers are selected from ethylene carbonate, vinylene carbonate, hydroxypropyl acrylate, methyl methacrylate, butyl methacrylate, dodecyl acrylate, neopentyl glycol diacrylate, trifluoroethyl methacrylate, hexafluorobutyl methacrylate, heptafluorobutyl acrylate, pentafluorophenyl methacrylate, bisphenol A dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and tri(2-acryloyloxyethyl) isocyanurate. The following are one or more of the following: ester, bis(acryloyloxyethyl) isocyanurate, N,N-methylenebisacrylamide, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate, pentaerythritol hexaacrylate, 2-acrylate-(2-hydroxy-1,3-methylene)di[oxy(2-hydroxy-3,1-propylidene)] ester, N,N-methylenebisacrylamide, and 1,4-disacryloylpiperazine.

14. The positive electrode slurry according to claim 6, characterized in that, The structure-retaining additive is selected from one or more of the following: Polyisocyanates containing benzene ring structures and their dimers, trimers and polymers; Polyether polyols; Polyfunctional acrylates containing ether segments.

15. The positive electrode slurry according to claim 6, characterized in that, The polyisocyanate containing a benzene ring structure is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, and 4,4' diphenyl ether diisocyanate. Polyether polyols are selected from one or more of polyethylene glycol, polypropylene glycol, and trihydroxy ether; The ether-containing polyfunctional acrylate is selected from one or more of the following: ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate, and pentaerythritol hexaacrylate.

16. The positive electrode slurry according to claim 1, characterized in that, The molar ratio of the conjugated diene monomer to the dienophilic monomer is 1:(0.25-4).

17. The positive electrode slurry according to claim 1, characterized in that, The molar ratio of the conjugated diene monomer to the dienophilic monomer is 1:(0.5-2).

18. The positive electrode slurry according to claim 2, characterized in that, The mass ratio of the safety additive to the structure-maintaining additive is 1:(0.2-6).

19. The positive electrode slurry according to claim 18, characterized in that, The mass ratio of the safety additive to the structure-maintaining additive is 1:(0.25-2).

20. The positive electrode slurry according to claim 1, characterized in that, The positive electrode slurry also includes positive electrode material, conductive agent, binder, solvent and initiator.

21. The positive electrode slurry according to claim 20, characterized in that, The additive has a mass of 0.001-10 parts by weight relative to 100 parts by weight of the cathode material.

22. The positive electrode slurry according to claim 20, characterized in that, The initiator is selected from one or more of the following: azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, dodecyl peroxide, diisopropyl peroxide dicarbonate, isophenylpropane hydroperoxide, dimethyl azobisisobutyrate, stannous octoate, N,N-dimethylcyclohexylamine, bis(2-dimethylaminoethyl) ether, N,N,N',N'-tetramethylalkylene diamine, triethylamine, N,N-dimethylbenzylamine, and dibutyltin dilaurate.

23. A positive electrode plate, characterized in that, It is formed by coating the positive electrode slurry of any one of claims 1-22 onto a substrate and then polymerizing it in situ. The conjugated diene monomers and dienophilic monomers in the positive electrode slurry form a thermally reversible structure through in-situ polymerization, or the cyclopentadiene monomers form a thermally reversible structure through in-situ polymerization.

24. A method for preparing a positive electrode sheet, wherein, It includes: The positive electrode slurry according to any one of claims 1-22 is coated onto a substrate and then polymerized in situ to obtain a positive electrode sheet.

25. A lithium-ion battery comprising the positive electrode sheet of claim 23 or the positive electrode sheet prepared by the method of claim 24.

Images