CN115732696A - Positive electrode slurry, positive electrode plate, preparation method and lithium ion battery - Google Patents
Positive electrode slurry, positive electrode plate, preparation method and lithium ion battery Download PDFInfo
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- CN115732696A CN115732696A CN202211684359.6A CN202211684359A CN115732696A CN 115732696 A CN115732696 A CN 115732696A CN 202211684359 A CN202211684359 A CN 202211684359A CN 115732696 A CN115732696 A CN 115732696A
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Abstract
The application provides a positive electrode slurry comprising an additive, which is a safety additive. The safety additive comprises a conjugated diene monomer and a dienophile monomer, or; including a cyclopentadiene based monomer, wherein the conjugated diene monomer and the dienophile monomer are capable of forming a thermoreversible structure, or the cyclopentadiene based monomer is capable of forming a thermoreversible structure. The coating and drying process has the advantages that the monomers are mixed and uniformly dispersed in the anode slurry, and a protective layer is formed inside the pole piece in the coating and drying process by using the active functional groups of the additives. The thermal reversible structure formed by the safety additive can be depolymerized and absorb heat when the battery is subjected to high temperature, and oxygen radicals are absorbed to prevent thermal runaway, so that the safety performance of the battery is improved; the additive can also comprise a structure-maintaining additive, and the structure-maintaining additive can be added to 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, the ion transmission can be improved, the decomposition of the electrolyte can be inhibited, and the cycle performance of the battery can be improved.
Description
Technical Field
The application relates to the field of batteries, in particular to positive electrode slurry, a positive electrode plate, a preparation method of the positive electrode plate, a lithium ion battery, and application of a safety additive and a structure retention additive in preparation of the positive electrode plate.
Background
The lithium ion battery is widely applied to the fields of electronic products, electric automobiles and large-scale energy storage due to high energy density and good cycle performance. Along with the expansion of the application range, the safety problem of the lithium ion battery is gradually exposed, especially in a large-scale module, a certain unit is out of control due to heat, chain reaction occurs to adjacent electric cores at high temperature, and large-scale explosion is further caused. At present, the key factor of thermal runaway of the lithium ion battery is that oxygen radicals are separated from a positive electrode material at high temperature, and the oxygen radicals, a negative electrode lithium intercalation material and electrolyte undergo a strong chemical reaction to release huge energy, so that a battery cell explodes.
The preparation method is characterized in that a special additive is doped into slurry in the preparation process of the positive pole piece, the slurry is dried and remains in the pole piece, and the additive improves the safety of the pole piece through certain special reactions when the battery is abused, which is a commonly applied technical route at present, for example: in patent document CN 109309208B, a thienyl compound is added into a positive electrode plate, and then the positive electrode plate is changed into polythiophene through an electrochemical polymerization manner, and the thermal safety performance of a battery can be obviously improved by utilizing the characteristic that the resistance of the polythiophene is obviously increased along with the increase of temperature; in patent document CN 109728245B, benzoxazine is dispersed in an anode plate, and after the temperature of a battery rises to a certain degree, the benzoxazine undergoes a polymerization reaction and is coated on the surface of an electrode material, so that the reactivity of the electrode material is reduced, and the safety of a battery cell is improved; in patent document CN 112952100B, a sulfone compound containing an unsaturated bond is doped into the positive electrode slurry, and the sulfone compound is polymerized in the coating process to form a protective layer on the surface of the positive electrode material, so that the side reaction of the electrode material and the electrolyte is reduced, and the thermal stability of the battery cell is improved.
The thermal runaway process of the battery is accompanied by violent chemical reaction and electrochemical reaction, the increase of the internal resistance of the pole piece can only reduce the influence caused by the electrochemical reaction to a certain extent, but the thermal runaway of the battery is often determined by the chemical reaction of the crosstalk of the positive pole and the negative pole, so the problem of the thermal runaway of the battery core cannot be fundamentally solved by the conventional method at present.
Disclosure of Invention
The application provides a method, which comprises the steps of adding a monomer containing a thermal reversible structure and a structure maintaining additive into anode slurry, coating and drying to generate a polymerization reaction, and forming a cross-linked polymer functional protective layer on the surface of an anode material in situ. The method comprises the following specific steps:
a positive electrode slurry comprising an additive including a safety additive,
the safety additive comprises a conjugated diene monomer and a dienophile monomer, or;
the safety additive comprises a cyclopentadiene-based monomer,
wherein the conjugated diene monomer and the dienophile monomer are capable of forming a thermoreversible structure, or the cyclopentadiene monomer is capable of forming a thermoreversible structure.
Further, the additive also includes a structure-retaining additive that undergoes a copolymerization reaction with the safety additive to form a crosslinked polymer.
Further, the dienophile 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- (1,3-phenylene) bismaleimide, N- (4,4-phenylene) bismaleimide, 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.
Further, the conjugated diene monomer is selected from the group consisting of glycidyl furfuryl ether, furfuryl alcohol, furfuryl amine, furfuryl methacrylate, 2,2' - (dithiodimethylene) difuran, 3- (2-furyl) propan-1-amine, 4-methylenepropenofuran, 6-furyl-1-hexene, 2-furylpropanol, 3- [5- (3-hydroxypropyl) -2-furan ] -propan-1-ol, trans-2-furanacrylic acid, 3- (5-acetyl-2-furyl) acrylic acid, 2-vinylfuran, (E) -3- (2-furan) acrylonitrile, 2-allylfuran, 4- (2-furyl) -1-buten-4-ol, 2-allyl furoate, N- (furan-2-methyl) -2-propen-1-amine.
Further, the cyclopentadiene monomer is one or more selected from cyclopentadiene and dicyclopentadiene.
Further, the structure-retaining additive is selected from one or more of the following: isocyanate monomers and dimers, trimers and multimers thereof; an epoxy monomer; a polyol monomer; polyamine monomers; unsaturated monomers.
Further, when the structure of the dienophile or the conjugated diene has a carbon-carbon double bond group other than the diene structure, the structure-retaining additive is selected from unsaturated monomers;
when the dienophile or conjugated diene contains active hydrogen, the structure-retaining additive is selected from the group consisting of isocyanate-based monomers and dimers, trimers and multimers thereof, epoxy-based monomers and optionally further added polyols and/or polyamines.
<xnotran> , , , , 9843 zxft 9843 ' - , , , , , , 3524 zxft 3524- , 3754 zxft 3754 ' - -4984 zxft 4984 ' - , 5272 zxft 5272- , -7945 zxft 7945- , , , , , 3272 zxft 3272- , , , , 3424 zxft 3424 ' - , , 3535 zxft 3535 ' - , , , 3584 zxft 3584 ' - -4284 zxft 4284 ' - , 5325 zxft 5325 ' - -5623 zxft 5623 ' - , 2- , 6262 zxft 6262 ' - ,4- -3256 zxft 3256- , 3456 zxft 3456 ' - , , 3838 zxft 3838 ' - , , -5749 zxft 5749 ',4"- , </xnotran> Tris (4-phenylisocyanate) thiophosphate, dimethyltriphenylmethane tetraisocyanate, p-toluenesulfonyl isocyanate (PTSI), pentafluorophenyl isocyanate (PFPI), and dimers, trimers, and multimers of the foregoing isocyanates.
Further, the polyalcohol monomers are selected from one or more than two of polyester diol, polycarbonate diol, polyether diol, polysiloxane polyol, polyethylene glycol adipate diol, 1,4-butanediol adipate diol, 1,6-hexanediol adipate diol, polycaprolactone diol, polydiol phthalate diol, polyethylene glycol, polypropylene glycol, polytetrahydrofuran ether diol, trihydroxy polyether and hydroxyl silicone oil; polyether diols and trihydroxy polyethers are preferred.
Further, the polyamine monomer is one or more selected from ethylenediamine, diethylenetriamine, triethylenetetramine, polyether diamine, diaminodiphenylmethane, and diethyltoluenediamine.
The epoxy monomer is one or more selected from 1,2,4,4-diepoxybutane, 1,4-butanediol diglycidyl ether, 1,7 octadiene epoxy compound, polyethylene glycol diglycidyl ether, polypentylglycol diglycidyl ether, bisphenol A diglycidyl ether, phenol diglycidyl ether, and glycerol triglycidyl ether.
Further, the unsaturated monomer is selected from one or more of vinyl ethylene carbonate, vinylene carbonate, hydroxypropyl acrylate, methyl methacrylate, butyl methacrylate, dodecyl acrylate, neopentyl glycol diacrylate, trifluoroethyl methacrylate, hexafluorobutyl methacrylate, heptafluorobutyl acrylate, pentafluorophenyl methacrylate, ethoxylated bisphenol a dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, tris (2-acryloyloxyethyl) isocyanurate, bis (acryloyloxyethyl) isocyanurate, N-methylene bisacrylamide, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate, pentaerythritol hexaacrylate, 2-acrylic acid- (2-hydroxy-1,3-methylene) bis [ oxy (2-hydroxy-3,1-propylene) ] ester, N-methylene bisacrylamide, 1,4-diacryloylpiperazine.
Further, the structure-retaining additive is selected from one or two or more of the following:
polyisocyanates containing benzene ring structure and dimers, trimers and polymers thereof;
polyether polyols;
multifunctional acrylates containing ether segments.
Preferably, the first and second electrodes are formed of a metal,
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;
the polyether polyol is one or more selected from polyethylene glycol, polypropylene glycol and trihydroxy polyether;
the multifunctional acrylate containing ether chain segments is selected from one or more than two of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate and pentaerythritol hexaacrylate.
Further, the molar ratio of the conjugated diene monomer to the dienophile monomer is 1: (0.25-4), preferably 1: (0.5-2).
Further, the mass ratio of the safety additive to the structure-maintaining additive is 1: (0.2-6), preferably 1: (0.25-2).
Further, the positive electrode slurry also comprises a positive electrode material, a conductive agent, a binder, a solvent and an initiator;
preferably, the additive is 0.001 to 10 parts by weight in mass with respect to 100 parts by weight of the positive electrode material.
Further, the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile, dibenzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, isopropylbenzene hydroperoxide, dimethyl azobisisobutyrate, stannous octoate, N, N-dimethylcyclohexylamine, bis (2-dimethylaminoethyl) ether, N, N, N ', N' -tetramethylalkylenediamine, triethylamine, N, N-dimethylbenzylamine and dibutyltin dilaurate.
The positive pole piece is formed by coating the positive pole slurry on a base material and carrying out in-situ polymerization,
wherein the conjugated diene monomer and the dienophile monomer in the positive electrode slurry form a thermoreversible structure through in-situ polymerization, or the cyclopentadiene monomer forms a thermoreversible structure through in-situ polymerization.
A preparation method of a positive pole piece comprises the following steps:
and coating the positive electrode slurry on a base material, and carrying out in-situ polymerization to obtain the positive electrode piece.
A lithium ion battery comprises the positive pole piece or the positive pole piece prepared by the method.
Compared with the prior art, the beneficial effects of this application do:
the polymer material is in a cross-linking state at room temperature and wraps the surface of the anode material, so that the contact between electrolyte and an anode is reduced, the circulation stability is improved, when the battery is subjected to external high temperature, the cross-linked polymer is depolymerized to generate a large number of unsaturated double-bond groups, and the process is an endothermic reaction and reduces the internal temperature of the battery; when the battery is continuously heated, the internal temperature is continuously increased to the oxygen evolution temperature of the positive electrode, the positive electrode can generate oxygen radicals, and at the moment, the depolymerization product of the thermal reversible crosslinked polymer and the oxygen radicals can generate an addition reaction to absorb the oxygen radicals, so that the situation that the oxygen radicals are diffused to the negative electrode to cause strong thermal runaway is avoided, and the safety of the battery core is improved. The preparation method is simple and easy to expand production.
Drawings
FIG. 1 is an SEM photograph of the positive electrode sheet in example 1;
FIG. 2 is an SEM photograph of the positive electrode sheet in comparative example 1;
FIG. 3 shows LSV test results of two electrode sheets of example 1 and comparative example 1;
fig. 4 is a graph of the hot box test of the 10Ah soft-packed cells of example 1 and comparative example 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application, and it is obvious that the described embodiments are some but not all of the embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The application provides a positive electrode slurry, including the additive, the additive includes can improve the safety additive of battery thermal stability, the safety additive includes conjugated diene monomer and dienophile monomer, or the safety additive includes cyclopentadiene class monomer, wherein, conjugated diene monomer with dienophile monomer can form the thermoreversible structure, perhaps, cyclopentadiene class monomer can form thermoreversible structure each other.
In some embodiments of the present application, the dienophile 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- (1,3-phenylene) bismaleimide, N- (4,4-phenylene) bismaleimide, 4-arm-PEG-maleimide, N-allylmaleimide; preferably one or more of N-allylmaleimide, bismaleimide-diethylene glycol, bismaleimide-triethylene glycol, bismaleimide-tetraethylene glycol, and bismaleimide-PEG.
In some embodiments of the present application, the conjugated diene monomer is selected from the group consisting of glycidyl furfuryl ether, furfuryl amine, furfuryl methacrylate, 2,2' - (dithiodimethylene) difuran, 3- (2-furyl) propan-1-amine, 4 methylenepropenofuran, 6-furyl-1-hexene, 2-furylpropanol, 3- [5- (3-hydroxypropyl) -2-furan ] -propan-1-ol, trans-2-furanacrylic acid, 3- (5-acetyl-2-furyl) acrylic acid, 2-vinylfuran, (E) -3- (2-furan) acrylonitrile, 2-allylfuran, 4- (2-furyl) -1-buten-4-ol, allyl 2-furoate, N- (furan-2-methyl) -2-propen-1-amine.
In some embodiments herein, the cyclopentadiene-based monomer is selected from one or more of cyclopentadiene and dicyclopentadiene.
In the present application, when the thermoreversible structure is subjected to external high heat, the internal temperature gradually rises, and after the internal temperature rises to a certain degree, the positive electrode material releases oxygen radicals, and the oxygen radicals further diffuse to the negative electrode to cause a severe thermal runaway reaction. The application discloses thermoreversible structure releases oxygen free radical at the positive pole and absorbs oxygen free radical before diffusing to the negative pole, controls at thermal runaway initial stage, avoids taking place the violent explosion in later stage.
The additives described herein also include structure-retaining additives. It is expressed as a class of compounds or polymers that can copolymerize with the security additive through active hydrogens and/or unsaturated double bonds to form polymers. The copolymerization reaction is the addition of unsaturated double bonds, the reaction of isocyanate and active hydrogen and the reaction of epoxy and active hydrogen.
In some embodiments of the present application, the structure-retaining additive is selected from one or more of the following: isocyanate monomers and dimers, trimers and multimers thereof; an epoxy monomer; a polyol monomer; polyamine monomers; unsaturated monomers.
In some embodiments of the present application, the isocyanate monomer is selected from toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, 4,4' -dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, biuret triisocyanate, lysine diisocyanate, xylylene diisocyanate, tetramethylxylene diisocyanate, 1,5-naphthalene diisocyanate, 3,3' -dimethyl-4,4 ' -biphenyl diisocyanate, 1,4-cyclohexyl diisocyanate, trimethyl-1,6-hexamethylene diisocyanate, tetramethyltoluene dimethylene diisocyanate, methylcyclohexyl diisocyanate, decamethylene diisocyanate, dodecyl diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, triphenylmethane triisocyanate, toluene triisocyanate, and mixtures thereof Triphenylisocyanate thiophosphate, cyclohexanedimethylene diisocyanate, 4,4' -dicyclohexylmethane diisocyanate, polymethylenepolyphenyl polyisocyanate, 4,4' -diphenyldiisocyanate, norbornane diisocyanate, p-phenylene diisocyanate, 3,3' -dimethyl-4,4 ' -diphenylmethane diisocyanate, 3,3' -dimethoxybiphenyl-4,4 ' -diisocyanate, 2-methylpentane diisocyanate, 4,4' -diphenylether diisocyanate, 4-methyldiphenylmethane-3,4-diisocyanate, 2,4' -diphenylsulfide diisocyanate, diethylbenzene 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 multimers of the above isocyanates.
In some embodiments of the present application, the polyol-based monomer is selected from one or more of polyester diol, polycarbonate diol, polyether diol, polysiloxane polyol, polyethylene adipate diol, polyethylene adipate 1,4-butanediol diol, polyethylene adipate 1,6-hexanediol diol, polycarbonate diol, polycaprolactone diol, polyphthalate diol, polyethylene glycol, polypropylene glycol, polytetrahydrofuran ether diol, trihydroxypolyether, hydroxyl silicone oil; polyether diols and trihydroxy polyethers are preferred.
In some embodiments of the present application, the polyamine-based monomer is selected from one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, polyetherdiamine, diaminodiphenylmethane, and diethyltoluenediamine.
In some embodiments of the present application, the epoxy-based 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, polypentylglycol diglycidyl ether, bisphenol a diglycidyl ether, phenol diglycidyl ether, and glycerol triglycidyl ether.
In some embodiments of the present application, the unsaturated monomer is selected from one or more of ethylene carbonate, hydroxypropyl acrylate, methyl methacrylate, butyl methacrylate, dodecyl acrylate, neopentyl glycol diacrylate, trifluoroethyl methacrylate, hexafluorobutyl methacrylate, heptafluorobutyl acrylate, pentafluorophenyl methacrylate, ethoxylated bisphenol a dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, tris (2-acryloyloxyethyl) isocyanurate, bis (acryloyloxyethyl) isocyanurate, N-methylene bisacrylamide, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate, pentaerythritol hexaacrylate, 2-acrylic acid- (2-hydroxy-1,3-methylene) bis [ oxy (2-hydroxy-3,1-propylene) ] ester, N-methylene bisacrylamide, 1,4-diacryloylpiperazine.
In the present application, "active hydrogen" denotes in this document a deprotonatable hydrogen atom attached to a nitrogen-, oxygen-or sulfur-atom. "active hydrogen" in this application denotes a hydrogen atom of a hydroxyl group, a mercapto group or an amino group. The source of active hydrogen in this application may be a conjugated diene, a dienophile monomer, a polyol, a polyamine.
The copolymerization of the safety additives and the structure-retaining additives can be divided into two categories: when the dienophile or conjugated diene has an additional C = C, such as N-allylmaleimide, then the structure-retaining additive is selected from unsaturated monomers in order to be reactive therewith; when the dienophile or conjugated diene has active hydrogen, such as furfuryl amine, the structure-maintaining additive selects isocyanate and epoxy monomers for reaction, and simultaneously adds active hydrogen-containing monomers such as polyol and polyamine for chain extension. The structure maintaining additive and the formed thermal reversible structure are subjected to copolymerization reaction; the copolymerization reaction comprises addition of unsaturated double bonds, reaction of isocyanate and active hydrogen and epoxy active hydrogen reaction, wherein the active hydrogen is derived from a dienophile monomer, a conjugated diene monomer, a polyalcohol monomer and a polyamine monomer.
In one class of embodiments of the present application, after the safety additive and the structure-maintaining additive are mixed, a Diels-Alder reaction occurs between a monomer containing a maleimide functional group and a monomer containing a furan functional group in the safety additive to form a thermoreversible structure with an active hydrogen group, and the structure-maintaining additive, because of containing isocyanate or epoxy group, undergoes a copolymerization reaction with the thermoreversible structure containing an active hydrogen group to form a polymer with a reversible cross-linked structure.
Therefore, when the dienophile or conjugated diene has active hydrogen, such as furfuryl amine, the structure-maintaining additive is selected from isocyanate monomers and epoxy monomers in order to react with the structure-maintaining additive, and polyol and polyamine structure-maintaining additive are optionally further added, so that the structure-maintaining additive can further participate in the chain extension reaction.
For a particular monomer combination, when the safety additive conjugated diene monomer is selected from active hydrogen containing furans, such as: from glycidyl furfuryl ether, furfuryl alcohol, furfuryl amine, 3- (2-furyl) propan-1-amine, 2-furylpropanol, 3- [5- (3-hydroxypropyl) -2-furan ] -propan-1-ol, 4- (2-furyl) -1-buten-4-ol, N- (furan-2-methyl) -2-propen-1-amine, in which case the dienophilic safener is selected from the group consisting of olefinic maleimides or non-olefinic polymaleimides, e.g.; bismaleimide ethane, bismaleimide-diethylene glycol, bismaleimide-triethylene glycol, bismaleimide-tetraethylene glycol, bismaleimide-PEG, BIS-MAL-DPEG (R) 3, N- (1,3-phenylene) bismaleimide, N- (4,4-phenylene) bismaleimide, 4-arm PEG-maleimide, N-allylmaleimide; in order to form a covalently bonded polymer with the safener and achieve the preferred results, the structure-retaining additive should be selected from the group consisting of polyether polyols and isocyanate compositions containing benzene rings, such as: toluene diisocyanate and polyethylene glycol compositions, toluene diisocyanate trimer and polyethylene glycol compositions, diphenylmethane diisocyanate trimer and polyethylene glycol compositions.
In another embodiment of the present application, after the safety additive and the structure-maintaining additive are mixed, the monomer containing maleimide functional group in the safety additive and the monomer containing furan functional group are subjected to Diels-Alder reaction to form a thermally reversible structure with unsaturated double bonds, and the structure-maintaining additive, because of the unsaturated double bond-containing group, is subjected to copolymerization reaction with the thermally reversible structure with double bonds, thereby forming a polymer with a reversibly crosslinked structure.
Thus, when the dienophile or conjugated diene contains a carbon-carbon double bond other than a diene bond, such as N-allylmaleimide, the structure-retaining additive is selected from the unsaturated monomers for the purpose of reacting therewith.
For a particular combination of monomers, when the safener conjugated diene monomer is selected from furan containing olefinic groups, such as: furfuryl methacrylate, 4-methylenepropylene furan, 6-furyl-1-hexene, 3- (5-acetyl-2-furyl) acrylic acid, 2-vinyl furan, (E) -3- (2-furan) acrylonitrile, 2-allyl furan, allyl 2-furoate, N- (furan-2-methyl) -2-propen-1-amine, in which case the dienophile safener is selected from the group consisting of olefinic maleimides or non-olefinic polymaleimides, e.g.; bismaleimide ethane, bismaleimide-diethylene glycol, bismaleimide-triethylene glycol, bismaleimide-tetraethylene glycol, bismaleimide-PEG, BIS-MAL-DPEG (R) 3, N- (1,3-phenylene) bismaleimide, N- (4,4-phenylene) bismaleimide, 4-arm PEG-maleimide, N-allylmaleimide; in order to form a covalently bonded polymer with the security additive and to achieve the preferred results, the structure-retaining additive should be selected from multifunctional acrylates containing ether segments, such as: ethoxylated bisphenol a dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, tris (2-acryloxyethyl) isocyanurate, bis (acryloxyethyl) isocyanurate, N-methylenebisacrylamide, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate, pentaerythritol hexaacrylate.
In some preferred embodiments of the present application, the structure-retaining additive may further preferably be selected from one or two or more of the following: polyisocyanates containing benzene ring structures and dimers, trimers and multimers thereof; polyether polyols; multifunctional acrylates containing ether segments.
In some preferred embodiments herein, the polyisocyanate containing a phenyl ring structure is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanate, 4,4' -diphenylether diisocyanate, pentafluorophenyl isocyanate; the polyether polyol is selected from one or more of polyethylene glycol, polypropylene glycol and trihydroxy polyether; the multifunctional acrylate containing ether chain segments is selected from one or more than two of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate and pentaerythritol hexaacrylate.
In some preferred embodiments herein, the molar ratio of the conjugated diene monomer to the dienophile monomer is 1: (0.25-4), preferably 1: (0.5-2);
for example, the molar ratio of the conjugated diene monomer and the dienophile monomer may 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 therebetween. When the proportion of the two is beyond the range, incomplete reaction of a certain monomer is caused to be excessive, and side reaction is caused in the charging and discharging process to cause obvious reduction of electrical property;
in some preferred embodiments of the present application, the weight ratio of the safety additive to the structure-maintaining additive is 1: (0.2-6), preferably 1: (0.25-2).
For example, the mass ratio of the safety additive to the structure-retaining additive is 1. When the proportion of the safety additive is too low, the quantity of the thermally reversible structural units is too small, and the quantity of the depolymerized groups is too small after thermal runaway, so that the quantity of absorbed heat and oxygen free radicals is too small, and the safety performance of the battery cannot be obviously improved; when the proportion of the safety additive is too high, the film-forming property of the polymerized product is poor, the reaction activity is not high, the formed products are often oligomers, the thermally reversible group is in a ring-shaped rigid structure, the flexibility of the polymer is reduced after the proportion is too high, the continuous jumping of lithium ions on a polymer chain segment is not facilitated, and the compatibility of the thermally reversible group and electrolyte is poor, so that the impregnation of the electrolyte is not facilitated.
In some preferred embodiments of the present application, the positive electrode slurry further includes a positive electrode material, a conductive agent, a binder, a solvent, and an initiator.
In some preferred embodiments of the present application, the additive is 0.001 to 10 parts by weight in mass per 100 parts by weight of the positive electrode material;
<xnotran> , 100 , 0.001 , 0.01 ,0.1 , 0.2 , 0.3 , 0.4 , 0.5 , 0.6 , 0.7 , 0.8 , 0.9 ,1 , 1.1 , 1.2 , 1.3 , 1.4 , 1.5 , 1.6 , 1.7 , 1.8 , 1.9 ,2 , 2.1 , 2.2 , 2.3 , 2.4 , 2.5 , 2.6 , 2.7 , 2.8 , 2.9 ,3 , 3.1 , 3.2 , 3.3 , 3.4 , 3.5 , 3.6 , 3.7 , 3.8 , 3.9 ,4 , 4.1 , 4.2 , 4.3 , 4.4 , 4.5 , 4.6 , 4.7 , 4.8 , 4.9 ,5 , 5.1 , 5.2 , 5.3 , 5.4 , 5.5 , 5.6 , 5.7 , 5.8 , 5.9 ,6 , 6.1 , 6.2 , 6.3 , 6.4 , 6.5 , 6.6 , 6.7 , 6.8 , 6.9 ,7 , 7.1 , 7.2 , 7.3 , 7.4 , 7.5 , 7.6 , 7.7 , 7.8 , 7.9 , 8 , 8.1 , 8.2 , 8.3 , 8.4 , 8.5 , 8.6 , 8.7 , 8.8 , 8.9 , 9 , 9.1 , 9.2 , 9.3 , 9.4 , 9.5 , 9.6 , </xnotran> 9.7 parts by weight, 9.8 parts by weight, 9.9 parts by weight, 10 parts by weight, or any range therebetween.
In some preferred embodiments herein, the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile, dibenzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, isopropylbenzene hydroperoxide, dimethyl azobisisobutyrate, stannous octoate, N-dimethylcyclohexylamine, bis (2-dimethylaminoethyl) ether, N' -tetramethylalkylenediamine, triethylamine, N-dimethylbenzylamine, dibutyltin dilaurate.
In the present application, the choice of initiator is adapted to the type of safety additive and to the type of structure-retaining additive.
In some embodiments of the present application, a positive electrode slurry, comprising additives including a safety additive and a structure-retaining additive, the safety additive including a conjugated diene monomer and a dienophile monomer, or; the safety additive includes a cyclopentadiene based monomer, wherein the conjugated diene monomer and the dienophile monomer are capable of forming a thermoreversible structure, or the cyclopentadiene based monomer is capable of forming a thermoreversible structure.
In some embodiments of the present application, the safety additive and the structure-maintaining additive are connected by covalent bonds, so that the safety additive and the structure-maintaining additive need to have functional groups capable of undergoing polymerization reaction, when the dienophile monomer and the conjugated diene monomer react with the unsaturated monomer, a D-a reaction occurs to form a thermally reversible structure with unsaturated double bonds at two ends, and at a high temperature in the coating stage, the radical initiator initiates the thermally reversible structure of the unsaturated monomer and the unsaturated double bonds to undergo a copolymerization reaction to form a polymer inside the pole piece, wherein the unsaturated monomer is a main framework structure of a polymer network, so that the polymer has good film-forming property, elasticity and high-temperature structural integrity; the safety additive is distributed in the polymer chain segment in the form of side chains and crosslinking points, and the thermal reversible structure can provide depolymerization and heat absorption when the temperature of the battery rises, absorb oxygen radicals and improve the safety performance of the battery.
In some embodiments of the present application, the safety additive and the structure-maintaining additive are linked by covalent bonds, so that the safety additive and the structure-maintaining additive need to have functional groups capable of undergoing polymerization, when the dienophile monomer and the conjugated diene monomer react with the isocyanate monomer, the furfuryl amine and the maleimide react D-A to generate a thermoreversible group with amine groups at two ends in a mixing stage, and the thermoreversible group with amine groups at two ends and the isocyanate monomer react with-NH at high temperature in a coating stage 2 The polymerization reaction of-OH generates a polymer which takes polyether chain segment polyurethane as a main chain and takes a thermoreversible structure as a crosslinking point or a side chain, and the polyether chain segment polyurethane ensures that the polymer has good film-forming property, elasticity and high-temperature structural integrity; the safety additive is distributed in the polymer chain segment in the form of side chains and crosslinking points, and the thermal reversible structure can provide depolymerization and heat absorption when the temperature of the battery rises, absorb oxygen radicals and improve the safety performance of the battery.
In some embodiments of the present application, the safety additive and the structure-retaining additive are covalently linked, so the safety additive and the structure-retaining additive need to have a functional group capable of undergoing a polymerization reaction, and the structure-retaining additive is an ether-containing segment unsaturated acrylate monomer also containing an unsaturated double bond in order to react therewith; cyclopentadiene is polymerized to generate a polymer with a thermoreversible structure in a material mixing stage, and the polymer and an unsaturated acrylate monomer containing an ether chain segment are subjected to polymerization reaction of unsaturated double bonds under the action of high temperature and an initiator in a coating stage to generate a polymer taking ether-containing acrylate as a main chain and taking the cyclopentadiene polymer as a side chain or a crosslinking point, wherein the ether-containing acrylate is a main frame structure of a polymer network, so that the polymer has good film-forming property, elasticity and high-temperature structural integrity; the safety additive is distributed in the polymer chain segment in the form of side chains and crosslinking points, and the thermal reversible structure can provide depolymerization and heat absorption when the temperature of the battery rises, absorb oxygen radicals and improve the safety performance of the battery.
In a specific embodiment of the application, a positive electrode material, a conductive agent, PVDF and an additive are put into a solvent NMP to obtain a positive electrode slurry, the positive electrode slurry is uniformly stirred and then coated on a current collector and dried to obtain a positive electrode plate; wherein, the additive comprises a safety additive and a structure maintaining additive, the safety additive comprises a conjugated diene monomer and a dienophile monomer, and the initiator is azodiisobutyronitrile.
In the present application, the cathode material is one of any cathode materials that can be known to those skilled in the art. For example, the positive electrode material is selected from one or more of lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium iron silicate, lithium cobaltate, a nickel-cobalt-manganese ternary material, a nickel-manganese/cobalt-manganese/nickel-cobalt binary material, lithium manganate and a lithium-rich manganese-based material.
In the present application, the conductive agent is one of any conductive agents 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 fibers.
In the present application, the binder is one of any binders known to those skilled in the art, for example, the binder is selected from any one or more of polyvinylidene fluoride, acrylic resin, polytetrafluoroethylene, styrene butadiene rubber.
In the present application, the solvent is one of any solvents 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, ethyl methyl carbonate, propyl propionate and acetate, N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide ethanol, acetonitrile, tetrahydrofuran.
The application provides a positive pole piece, which is formed by coating the positive pole slurry on a base material and carrying out in-situ polymerization, wherein the conjugated diene monomer and the dienophile monomer in the positive pole slurry form a thermally reversible structure through in-situ polymerization, or the cyclopentadiene monomer forms the thermally reversible structure through in-situ polymerization.
The application provides a preparation method of a positive pole piece, wherein the positive pole slurry is coated on a base material and subjected to in-situ polymerization to obtain the positive pole piece.
The application provides a lithium ion battery, which comprises the positive pole piece or the positive pole piece prepared by the method.
The safety additive and the structure maintaining additive provided by the application can obviously improve the thermal safety and the cycling stability of the battery after reaction, wherein the safety additive forms a polymer with a thermal reversible group after polymerization, the polymer is subjected to depolymerization reaction after the temperature of the battery exceeds a certain range, a large number of unsaturated bonds are generated, a part of heat is taken away, and oxygen radicals are absorbed to prevent the thermal runaway of the battery; the structure-maintaining additive is polymerized to form a polymer containing chain segments of polyether, polyester and the like, the polymer has good phase affinity with the electrolyte, the electrolyte infiltration is facilitated, the side reaction of the electrolyte on a positive electrode material is reduced, ether and ester groups can be coordinated with lithium ions, migration sites are provided in the transmission process, and more uniform ion current is provided; the preparation method is compatible with the existing production process and easy to expand production, and because small molecules are mixed before polymerization, the additive is more uniformly mixed with the positive electrode material, the conductive agent and other bonding agents, the bonding is tighter after polymerization, and the internal resistance of the battery is better due to the interface contact between the polymer and the electrode material.
Example 1
1) Adding 95g of NCM811 positive electrode material, 3g of conductive agent, 2g of PVDF and 5g of additive into 80g of NMP to obtain positive electrode slurry, uniformly stirring the positive electrode slurry, coating the positive electrode slurry on a current collector, and drying to obtain a positive electrode plate with the single-side surface density of 200g/m 2 (ii) a Wherein the additive comprises a safety additive and a structure-maintaining additive, the safety additive comprises a conjugated diene monomer and a dienophile monomer, and the conjugated diene monomer is N-allyl maleimide1.8g, 2.2g of furfuryl methacrylate as a dienophile monomer, 1:1 the molar ratio of a conjugated diene monomer to a dienophile monomer, 1g of ethoxylated trimethylolpropane triacrylate as a structure-retaining additive, 5g of the sum of the mass of the safety additive and the structure-retaining additive, 4:1 the mass ratio of the safety additive to the structure-retaining additive, and 0.05g of azobisisobutyronitrile as an initiator;
2) Dissolving 96g of graphite, 1.2g of CMC, 1.5g of SBR and 1.3g of conductive agent in 150g of pure water, stirring, coating the mixture on a current collector, and drying to obtain a negative pole piece with the single-side surface density of 114g/cm 2 ；
3) Preparing 10Ah soft package cells by using the pole pieces prepared in the steps 1) and 2) and a commercial diaphragm, injecting electrolyte (EC/EMC/DMC = 1/1/1% 6 ) And infiltrating for 24 hours, and then carrying out formation and grading to obtain the final soft-packaged battery cell.
The following tests were performed on the above-described soft-packed cell;
thermal runaway temperature: placing the battery in a special heating oven for the lithium ion battery, heating to 130 ℃ at a speed of 5 ℃/min, and then staying for 1h at 10 ℃ every time, wherein the highest temperature is 200 ℃; taking the ambient temperature of the battery close to an explosion point in the oven as the thermal runaway temperature of the lithium ion battery;
and (3) cycle testing: carrying out charge and discharge tests on the battery by adopting Wuhan blue electricity equipment, wherein the voltage range is 2.75-4.25V,0.1C/0.1C is used for charging and discharging, the first-circle discharge capacity is used as 0.1C capacity to play, and the number of cycle turns when the capacity is attenuated to 80% is counted;
LSV test: replacing the positive electrode material in the step 1) with conductive carbon black (SP) completely, coating the conductive carbon black (SP) on the positive electrode material to form an SP positive electrode sheet, coating the SP positive electrode sheet with the additive on the surface of the SP material to form an effect similar to that of coating the positive electrode material, and enabling the SP positive electrode sheet, the lithium sheet and the electrolyte (EC/EMC/DMC =1/1/1 3 to be equal to VC 1MLiPF 6 ) Assembling the button cell, and then carrying out linear volt-ampere scanning test, wherein the scanning speed is 1mV/s, and the voltage range is as follows: OCV-5V.
In example 1, the safety additive is N-allylmaleimide and furfuryl methacrylate containing unsaturated carbon-carbon double bonds, the structure retention additive is ethoxylated trimethylolpropane triacrylate, the initiator is azobisisobutyronitrile, after being mixed into the positive electrode slurry, the N, -allylmaleimide and furfuryl methacrylate are subjected to D-a reaction in the mixing stage to form a thermoreversible structure with unsaturated double bonds at two ends, and the radical initiator initiates the copolymerization reaction of the ethoxylated trimethylolpropane triacrylate and the thermoreversible structure with unsaturated double bonds at high temperature in the coating stage to form a polymer in the pole piece, wherein the ethoxylated trimethylolpropane triacrylate is the main frame structure of the polymer network, so that the polymer has good film-forming property, elasticity and high-temperature structural integrity; the safety additive is distributed in the polymer chain segment in the form of side chains and crosslinking points, and the thermal reversible structure can provide depolymerization and heat absorption when the temperature of the battery rises, absorb oxygen radicals and improve the safety performance of the battery.
Example 2
Example 2 differs from example 1 only in that the structure retention additive ethoxylated trimethylolpropane triacrylate in example 1 was replaced with the structure retention additive polyethylene glycol dimethacrylate; the rest conditions are the same.
Example 3
Example 3 differs from example 1 only in that the structure-retaining additive ethoxylated trimethylolpropane triacrylate in example 1 is replaced by the structure-retaining additive butyl methacrylate; the rest conditions are the same.
Example 4
Example 4 differs from example 1 only in that the additives include conjugated diene monomer and dienophile monomer and structure-preserving additive, the dienophile monomer is 2.12g bismaleimide ethane, the conjugated diene monomer is 1.88g furfuryl amine, the structure-preserving additive is 0.6g toluene diisocyanate trimer and 0.4g polyethylene glycol of molecular weight 2000, the initiator used is 0.05g stannous octoate; the rest conditions are the same.
The safety additive in the embodiment 4 is furfuryl amine, bismaleimide, in order to react with furfuryl amine, the structure keeping additive of the invention is toluene diisocyanate trimer and polyethylene glycol with molecular weight of 2000, and the catalyst is stannous octoate; furfuryl amine and maleimide in the compounding stageD-A reaction is carried out on amine to generate a thermoreversible group with amine groups at two ends, and isocyanate and-NH are generated among the thermoreversible group with amine groups at two ends, toluene diisocyanate tripolymer and polyethylene glycol with molecular weight of 2000 at high temperature in the coating stage 2 The polymerization reaction of-OH generates a polymer which takes polyether chain segment polyurethane as a main chain and takes a thermally reversible structure as a crosslinking point or a side chain, and the polyether chain segment polyurethane ensures that the polymer has good film-forming property, elasticity and high-temperature structural integrity; the safety additive is distributed in the polymer chain segment in the form of side chains and crosslinking points, and the thermal reversible structure can provide depolymerization and heat absorption when the temperature of the battery rises, absorb oxygen radicals and improve the safety performance of the battery.
Example 5
Example 5 differs from example 4 only in that the toluene diisocyanate trimer in example 4 was changed to toluene diisocyanate; the rest conditions are the same.
Example 6
Example 6 differs from example 4 only in that the toluene diisocyanate trimer in example 4 was replaced by hexamethylene diisocyanate; the rest conditions are the same.
Example 7
Example 7 differs from example 4 only in that the structure retention additive of example 4 was entirely changed to 1,4-butanediol diglycidyl ether 1g, without initiator, and the other conditions were the same.
Example 8
Example 8 differs from example 7 only in that 1,4-butanediol diglycidyl ether in example 7 is replaced with glycerol triglycidyl ether; the rest conditions are the same.
Example 9
Example 9 differs from example 1 only in that the additives include 4g of cyclopentadiene based monomer, 1g of ethoxylated trimethylolpropane triacrylate and 0.05g of dibenzoyl peroxide as initiator; the rest conditions are the same.
The safety additive in example 9 was cyclopentadiene, which was an ethoxylated trimethylolpropane triacrylate, likewise containing an unsaturated double bond, in order to be able to react with it; in the material mixing stage, cyclopentadiene is subjected to self-polymerization to generate a polymer with a thermoreversible structure, and the polymer and ethoxylated trimethylolpropane triacrylate are subjected to polymerization reaction of unsaturated double bonds under the action of high temperature and dibenzoyl peroxide as an initiator in the coating stage to generate a polymer taking the ethoxylated trimethylolpropane triacrylate as a main chain and the cyclopentadiene polymer as a side chain or a crosslinking point, wherein the ethoxylated trimethylolpropane triacrylate is a main framework structure of a polymer network, so that the polymer has good film-forming property, elasticity and high-temperature structural integrity; the safety additive is distributed in the polymer chain segment in the form of side chains and crosslinking points, and the thermal reversible structure can provide depolymerization and heat absorption when the temperature of the battery rises, absorb oxygen radicals and improve the safety performance of the battery.
Example 10
Example 10 differs from example 9 only in that the structure retention additive ethoxylated trimethylolpropane triacrylate of example 9 was replaced with the structure retention additive polyethylene glycol dimethacrylate; the rest conditions are the same.
Example 11
Example 11 differs from example 9 only in that the structure retention additive ethoxylated trimethylolpropane triacrylate of example 9 is replaced by the structure retention additive butyl methacrylate; the rest conditions are the same.
Example 12
Example 12 differs from example 1 only in that the additive in example 1 was reduced from 5g to 0.01g in an equal proportion; the rest conditions are the same.
Example 13
Example 13 differs from example 1 only in that the additive in example 1 was scaled up from 5g to 10g; the rest conditions are the same.
Example 14
Example 14 differs from example 1 only in that the additive in example 1 was scaled up from 5g to 15g; the rest conditions are the same.
Example 15
Example 15 differs from example 1 only in the molar ratio of conjugated diene monomer to dienophile monomer 1:2 and the sum of the masses is 4g, the other conditions being the same.
Example 16
Example 16 differs from example 1 only in the molar ratio of conjugated diene monomer to dienophile monomer 1:4 and the sum of the masses is 4g, with the remainder being identical.
Example 17
Example 17 differs from example 1 only in the molar ratio of conjugated diene monomer to dienophile monomer 2:1 and the sum of the masses is 4g, the other conditions being the same.
Example 18
Example 18 differs from example 1 only in the molar ratio of conjugated diene monomer to dienophile monomer 4:1 and the sum of the masses is 4g, the other conditions being the same.
Example 19
Example 19 differs from example 1 only in that the sum of the masses of the security additive and the structure-retaining additive is 5g and the ratio of the masses of the security additive and the structure-retaining additive is 6:1, the remaining conditions being the same.
Example 20
Example 20 differs from example 1 only in that the sum of the masses of the security additive and the structure-retaining additive is 5g and the ratio of the masses of the security additive and the structure-retaining additive is 3:1, the other conditions being the same.
Example 21
Example 21 differs from example 1 only in that the sum of the masses of the security additive and the structure-retaining additive is 5g and the ratio of the masses of the security additive and the structure-retaining additive is 2:1, the remaining conditions being the same.
Example 22
Example 22 differs from example 1 only in that the sum of the masses of the security additive and the structure-retaining additive is 5g and the ratio of the masses of the security additive and the structure-retaining additive is 1:1, the other conditions being the same.
Example 23
Example 23 differs from example 1 only in that the sum of the masses of the security additive and the structure-retaining additive is 5g and the ratio of the masses of the security additive and the structure-retaining additive is 1:2, the other conditions being identical.
Example 24
Example 24 differs from example 1 only in that the sum of the masses of the security additive and the structure-retaining additive is 5g and the ratio of the masses of the security additive and the structure-retaining additive is 1:4, the other conditions being the same.
Example 25
Example 25 differs from example 1 only in that the sum of the masses of the safety additives is 5g, no structure-retaining additive and the remaining conditions are identical.
Comparative example 1
Comparative example 1 differs from example 1 only in that comparative example 1 does not have any additives, and the rest of the conditions are the same.
Comparative example 2
Comparative example 2 differs from example 1 only in that comparative example 2 contains only 5g of the structure retention additive ethoxylated trimethylolpropane triacrylate, the other conditions being the same.
Although the present disclosure has been described with reference to particular embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure, and the scope of the present disclosure should be limited only by the terms of the appended claims.
TABLE 1 Effect of Structure Retention additive type on Performance
It can be seen from example 1 and comparative example 1 that the safety additive and/or the structure retention additive provided by the present solution can significantly improve the cycling stability and thermal safety of the battery after being added, and as can be seen from the comparison of two sets of experimental positive pole SEMs (fig. 1, fig. 2), the positive pole surface of the example 1 is polymerized in situ to form a protective layer after being dried, while the positive pole material of the comparative example 1 is exposed on the surface, and as can be seen from the LSV (fig. 3) test, the current density of the pole piece containing the protective layer in the scanning process is smaller and the electrochemical side reactions are less with the continuous increase of the applied potential, so that the protective layer can effectively inhibit the oxidative decomposition of the electrolyte on the electrode surface, greatly improve the stability thereof, and significantly improve the cycling of the battery. From the thermal safety test result (fig. 4), the thermal runaway occurs when the battery temperature suddenly rises sharply when the ordinary battery is heated to 150-160 ℃, while the thermal runaway occurs when the battery core adopting the scheme is heated to 180 ℃, because the in-situ polymerization protective layer is thermally depolymerized after receiving high temperature to take away part of the heat, and the thermally depolymerized product can react with oxygen radicals released by the anode to prevent the oxygen radicals from diffusing to the cathode to initiate more serious thermal runaway.
From the results of examples 1 to 3, it is clear that the crosslinked polyether structure is more advantageous for improving the cycle and thermal safety because the crosslinked material itself has better oxidation resistance, is more tightly coated on the surface of the electrode, and is more advantageous for preventing the decomposition of the electrolyte; in the heating process of the battery core, the polymer structure can still be kept complete after the thermally reversible structure of the cross-linking material is depolymerized, the adsorption capacity to the electrolyte cannot be obviously reduced, the amount of free electrolyte is less, and the vaporization and combustion of the electrolyte can be reduced.
From the results of example 1 and example 25, it is understood that the cycle stability of the battery is somewhat lowered when the structure-maintaining additive is not added, because the film forming property of the product after polymerization of the safety additive is poor, and the reactivity is not high, and the formed product is often an oligomer, and the stability in the high-voltage positive electrode is poor.
TABLE 2 Effect of Structure Retention additive type on Performance
As can be seen from Table 2, the addition of the structure-maintaining agent contributes to the improvement of the battery performance, wherein, in examples 7-8, the use of the epoxy compound also has the similar effect of improving the battery cycle performance as the isocyanate monomer, but the improvement capability is slightly inferior to that of the isocyanate, because some-OH groups remain after the reaction of the epoxy and the amine, which slightly affects the electrical properties to a certain extent; in addition, the examples 4 to 6 show that the isocyanate with benzene ring has more advantages in electrical property, the isocyanate with benzene ring has higher reaction activity, is less prone to residue after reaction, and the benzene ring structure is less prone to oxidation, so that the electrical and thermal stability of the material can be better improved.
TABLE 3 Effect of safety additives
As can be seen from table 3, when the safety additive is a cyclopentadiene monomer, it also exhibits the advantages of a crosslinked polyether structure, having good battery performance; from examples 1 and 9 and comparative example 2, it can be seen that the improvement of the thermal safety of the battery cell mainly comes from the introduction of the thermally reversible structure of the safety additive, and if only the conventional polymeric monomer is added, the improvement effect on the thermal safety of the battery is not obvious.
TABLE 4 Effect of addition amount on Properties
The results of examples 1, 12, 13 and 14 show that the thermal safety effect on the battery cannot be greatly reduced when the additive amount is too low, and excessive polymer is coated on the surface of the electrode after the additive amount is too high, so that lithium ion transmission is influenced, and the electrical property is greatly reduced.
TABLE 5 influence of the molar ratio of conjugated diene monomer and dienophile monomer on Properties
In examples 15 to 18 and example 1, when the molar ratio of the conjugated diene monomer to the dienophile monomer was 1: when the proportion is beyond the range, the cycling stability of the battery core is obviously reduced, because both monomers have unsaturated double bonds and are easy to oxidize at a high-voltage positive electrode, the two monomers are crosslinked according to 1:1 during reaction, excessive residue in a certain range has little influence on the electrical property, and when the proportion is beyond the range, the rapid attenuation of the battery capacity is obviously seen.
Table 6 safety additive occupancy ratio impact on performance
In examples 19 to 25, the optimal ratio range of the safety additive to the structure-maintaining additive exists, and when the ratio of the safety additive is increased, the content of the thermally depolymerized group is increased, so that the safety performance can be obviously improved, but the thermally reversible group is a ring-shaped rigid structure, the flexibility of the polymer is reduced after the ratio is too high, so that the continuous jumping of lithium ions on the polymer chain segment is not facilitated, and the compatibility of the thermally reversible group and the electrolyte is poor, so that the electrolyte is not facilitated to be infiltrated; the optimal proportion is (1-4): 1.
Claims (20)
1. a positive electrode slurry comprising an additive including a safety additive,
the safety additive comprises a conjugated diene monomer and a dienophile monomer, or;
the safety additive comprises a cyclopentadiene-based monomer,
wherein the conjugated diene monomer and the dienophile monomer are capable of forming a thermoreversible structure, or the cyclopentadiene monomer is capable of forming a thermoreversible structure.
2. The positive electrode slurry according to claim 1,
the additive also includes a structure-retaining additive that undergoes a copolymerization reaction with the safety additive to form a crosslinked polymer.
3. The positive electrode slurry according to claim 1 or 2,
the dienophile monomer is selected from one or more than two of bismaleimide ethane, bismaleimide-diethylene glycol, bismaleimide-triethylene glycol, bismaleimide-tetraethylene glycol, bismaleimide-PEG, BIS-MAL-DPEG (R) 3, N- (1,3-phenylene) bismaleimide, N- (4,4-phenylene) bismaleimide, 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.
4. The positive electrode slurry according to claim 1 or 2,
the conjugated diene monomer is selected from the group consisting of glycidyl furfuryl ether, furfuryl alcohol, furfuryl amine, furfuryl methacrylate, 2,2' - (dithiodimethylene) difuran, 3- (2-furyl) propan-1-amine, 4 methylenepropenofuran, 6-furyl-1-hexene, 2-furylpropanol, 3- [5- (3-hydroxypropyl) -2-furan ] -propan-1-ol, trans-2-furanacrylic acid, 3- (5-acetyl-2-furyl) acrylic acid, 2-vinylfuran, (E) -3- (2-furan) acrylonitrile, 2-allylfuran, 4- (2-furyl) -1-buten-4-ol, allyl 2-furoate, N- (furan-2-methyl) -2-propen-1-amine.
5. The positive electrode slurry according to claim 1 or 2,
the cyclopentadiene monomer is one or more than two of cyclopentadiene and dicyclopentadiene.
6. The positive electrode slurry according to claim 2,
the structure-retaining additive is selected from one or more than two of the following: isocyanate monomers and dimers, trimers and multimers thereof; an epoxy-based monomer; a polyol monomer; polyamine monomers; unsaturated monomers.
7. The positive electrode slurry according to claim 6,
when the structure of the dienophile or the conjugated diene has a carbon-carbon double bond group other than the diene structure, the structure-maintaining additive is selected from unsaturated monomers;
when the dienophile or conjugated diene contains active hydrogen, the structure-retaining additive is selected from the group consisting of isocyanate-based monomers and dimers, trimers and multimers thereof, epoxy-based monomers and optionally further added polyols and/or polyamines.
8. The positive electrode slurry according to claim 6,
the isocyanate monomer is selected from toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, 4,4 '-dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, biuret triisocyanate, lysine diisocyanate, xylylene diisocyanate, tetramethylxylene diisocyanate, 1,5-naphthalene diisocyanate, 3,3' -dimethyl-4,4 '-biphenyl diisocyanate, 1,4-cyclohexyl diisocyanate, trimethyl-1,6-hexamethylene diisocyanate, tetramethyltoluene dimethylene diisocyanate, methylcyclohexyl diisocyanate, decamethylene diisocyanate, dodecyl diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, triphenylmethane triisocyanate, toluene triisocyanate, and mixtures thereof Triphenylisocyanate thiophosphate, cyclohexanedimethylene diisocyanate, 4,4' -dicyclohexylmethane diisocyanate, polymethylenepolyphenyl polyisocyanate, 4,4 '-diphenyldiisocyanate, norbornane diisocyanate, p-phenylene diisocyanate, 3,3' -dimethyl-4,4 '-diphenylmethane diisocyanate, 3,3' -dimethoxybiphenyl-4,4 '-diisocyanate, 2-methylpentane diisocyanate, 4,4' -diphenylether diisocyanate, 4-methyldiphenylmethane-3,4-diisocyanate, 2,4 '-diphenylsulfide diisocyanate, diethylbenzene 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 multimers of the above isocyanates.
9. The positive electrode slurry according to claim 6,
the polyalcohol monomers are selected from one or more of polyester diol, polycarbonate diol, polyether diol, polysiloxane polyol, polyethylene glycol adipate diol, polyethylene 1,4-butanediol adipate diol, polyethylene 1,6-hexanediol adipate diol, polycaprolactone diol, poly (phthalic acid) diol, polyethylene glycol, polypropylene glycol, polytetrahydrofuran ether diol, trihydroxy polyether and hydroxy silicone oil;
polyether diols and trihydroxy polyethers are preferred.
10. The positive electrode slurry according to claim 6,
the polyamine monomer is one or more than two of ethylenediamine, diethylenetriamine, triethylene tetramine, polyether diamine, diaminodiphenylmethane and diethyl toluenediamine.
11. The positive electrode slurry according to claim 6,
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, polypentylene glycol diglycidyl ether, bisphenol A diglycidyl ether, phenol diglycidyl ether and glycerol triglycidyl ether.
12. The positive electrode slurry according to claim 6,
the unsaturated monomer is selected from one or more of ethylene carbonate, vinylene carbonate, hydroxypropyl acrylate, methyl methacrylate, butyl methacrylate, dodecyl acrylate, neopentyl glycol diacrylate, trifluoroethyl methacrylate, hexafluorobutyl methacrylate, heptafluorobutyl acrylate, pentafluorophenyl methacrylate, ethoxylated bisphenol A dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, tris (2-acryloyloxyethyl) isocyanurate, bis (acryloyloxyethyl) isocyanurate, N-methylene bisacrylamide, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate, pentaerythritol hexaacrylate, 2-acrylic acid- (2-hydroxy-1,3-methylene) bis [ oxy (2-hydroxy-3,1-propylene) ] ester, N-methylene bisacrylamide, 1,4-diacryloylpiperazine.
13. The positive electrode slurry according to claim 6,
the structure-retaining additive is selected from one or more than two of the following:
polyisocyanates containing benzene ring structures and dimers, trimers and multimers thereof;
polyether polyols;
a multifunctional acrylate containing an ether segment;
preferably, the first and second electrodes are formed of a metal,
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;
the polyether polyol is one or more selected from polyethylene glycol, polypropylene glycol and trihydroxy polyether;
the multifunctional acrylate containing ether chain segments is selected from one or more than two of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol pentaacrylate and pentaerythritol hexaacrylate.
14. The positive electrode slurry according to claim 1,
the molar ratio of the conjugated diene monomer to the dienophile monomer is 1: (0.25-4), preferably 1: (0.5-2).
15. The positive electrode slurry according to claim 2,
the mass ratio of the safety additive to the structure-retaining additive is 1: (0.2-6), preferably 1: (0.25-2).
16. The positive electrode slurry according to claim 1,
the positive electrode slurry also comprises a positive electrode material, a conductive agent, a binder, a solvent and an initiator;
preferably, the first and second electrodes are formed of a metal,
the additive is 0.001 to 10 parts by weight with respect to 100 parts by weight of the positive electrode material.
17. The positive electrode slurry according to claim 16,
the initiator is selected from one or more of azodiisobutyronitrile, azodiisoheptonitrile, dibenzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, isophenylhydroperoxide, dimethyl azodiisobutyrate, stannous octoate, N, N-dimethylcyclohexylamine, bis (2-dimethylaminoethyl) ether, N, N, N ', N' -tetramethylalkylenediamine, triethylamine, N, N-dimethylbenzylamine and dibutyltin dilaurate.
18. A positive electrode sheet, which is formed on a substrate by coating the positive electrode slurry according to any one of claims 1 to 17 on the substrate and carrying out in-situ polymerization,
wherein the conjugated diene monomer and the dienophile monomer in the positive electrode slurry form a thermoreversible structure through in-situ polymerization, or the cyclopentadiene monomer forms a thermoreversible structure through in-situ polymerization.
19. A preparation method of a positive pole piece comprises the following steps:
coating the positive electrode slurry of any one of claims 1 to 17 on a substrate, and carrying out in-situ polymerization to obtain the positive electrode plate.
20. A lithium ion battery comprising the positive electrode sheet of claim 18 or the positive electrode sheet prepared by the method of claim 19.
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| CN117659331A (en) * | 2024-01-31 | 2024-03-08 | 江苏一特新材料有限责任公司 | Preparation method of three-dimensional network anti-cracking dispersion material and preparation method of positive electrode plate |
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| CN117659331A (en) * | 2024-01-31 | 2024-03-08 | 江苏一特新材料有限责任公司 | Preparation method of three-dimensional network anti-cracking dispersion material and preparation method of positive electrode plate |
| CN117659331B (en) * | 2024-01-31 | 2024-04-05 | 江苏一特新材料有限责任公司 | Preparation method of three-dimensional network anti-cracking dispersion material and preparation method of positive electrode plate |
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