Binder, positive plate and battery

Abstract

The embodiment of the invention provides a binder, a positive plate and a battery, the binder comprises a nitrile structural unit, an ether structural unit, a nitrogen heterocyclic structural unit and a sulfonic acid structural unit, and the swelling degree of the binder is 20-40%. According to the present invention, the adhesion, the flexibility, the swelling resistance and other properties of the binder can be improved, the flexibility of the electrode plate using the binder can be improved, and the electrochemical properties such as the improvement of the first efficiency and the cycle life of the battery can be considered.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to a binder, a positive electrode sheet and a battery. Background Art

[0002] Batteries are common electrochemical energy storage devices with a wide range of applications. For example, lithium-ion batteries, with their high energy density and long cycle life, are widely used in various fields, including new energy vehicles and energy storage. Currently, PVDF is the primary binder for lithium-ion battery cathodes. However, due to factors such as the presence of fluorine, PVDF is environmentally unfriendly and its application is limited.

[0003] Currently, the main alternative to PVDF is the polyacrylonitrile modification route, which mainly uses acrylonitrile as the main body and obtains a multi-polymer through copolymerization with acrylic ester, and uses this multi-polymer to replace PVDF.

[0004] However, copolymers modified by copolymerization of acrylonitrile and acrylate generally have problems such as poor anti-swelling ability and poor flexibility of electrode sheets using such multi-polymers as binders, which affect the electrochemical properties of the battery such as the first effect and cycle life, and need to be solved urgently. Summary of the Invention

[0005] The present invention provides a binder, a positive electrode sheet and a battery, which at least solve the problems existing in the prior art, such as poor anti-swelling ability of the binder, poor flexibility of the electrode sheet, and poor initial efficiency and cycle life of the battery.

[0006] In one aspect of the present invention, a binder is provided, comprising a nitrile structural unit, an ether structural unit, a nitrogen heterocyclic structural unit and a sulfonic acid structural unit, wherein the swelling degree of the binder is 20% to 40%.

[0007] According to one embodiment of the present invention, the weight average molecular weight of the binder is 10 wg / mol to 40 wg / mol.

[0008] According to one embodiment of the present invention, the glass transition temperature of the binder is 0°C to 40°C.

[0009] According to one embodiment of the present invention, the particle size of the binder is 40 μm to 80 μm.

[0010] According to one embodiment of the present invention, the mass ratio of the nitrile structural unit, the ether structural unit, the nitrogen heterocyclic structural unit and the sulfonic acid structural unit is (30-50): (30-50): (20-30): (5-10).

[0011] According to one embodiment of the present invention, the nitrile structural unit includes one or more of an acrylonitrile structural unit and a methacrylonitrile structural unit; and / or the ether structural unit includes an allyl ether structural unit, and the allyl ether structural unit includes one or more of an allyl ethyl ether structural unit, an allyl propyl ether structural unit, an allyl butyl ether structural unit, an allyl hydroxyethyl ether structural unit, and an allyl propyl ether structural unit.

[0012] According to one embodiment of the present invention, the sulfonic acid structural unit includes an alkenyl sulfonic acid structural unit, and the alkenyl sulfonic acid structural unit includes a C2-C14 vinyl sulfonic acid structural unit.

[0013] According to one embodiment of the present invention, the nitrogen heterocyclic structural unit contains a nitrogen heterocycle, and the nitrogen heterocycle includes one or more of pyridyl, pyrazinyl, pyrimidinyl, quinolyl, isoquinolyl, and quinoxalinyl.

[0014] One aspect of the present invention provides a positive electrode sheet, comprising a positive electrode active layer, wherein the positive electrode active layer comprises the above-mentioned binder.

[0015] One aspect of the present invention provides a battery comprising the above-mentioned positive electrode sheet.

[0016] The present invention provides a binder, a positive electrode sheet and a battery. The binder includes a nitrile structural unit, an ether structural unit, a nitrogen heterocyclic structural unit and a sulfonic acid structural unit. The swelling degree of the binder is 20% to 40%. In the coexistence system of these structural units, the nitrile structural unit and the sulfonic acid structural unit can improve the adhesion of the binder, the ether structural unit can improve the flexibility of the electrode sheet, and the nitrogen heterocyclic structural unit can improve the anti-swelling property of the binder. The interaction between the alkaline nitrogen heterocyclic ring and the acidic sulfonic acid group to form an acid-base pair can synergistically play an anti-swelling role. Based on this, the present invention can take into account the improvement of the properties such as the adhesion, flexibility and anti-swelling property of the binder, improve the flexibility of the electrode sheet using the binder, reduce the brittleness of the electrode sheet, avoid the problem of powdering of the electrode sheet, and take into account the improvement of the electrochemical properties such as the first effect and cycle life of the battery. DETAILED DESCRIPTION

[0017] In order to enable those skilled in the art to better understand the solution of the present invention, the present application is further described in detail below. The specific embodiments listed below are only for describing the principles and features of the present invention. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts are within the scope of protection of the present invention.

[0018] In the related art, a copolymer of acrylonitrile and acrylate is used to replace PVDF. However, the copolymer of acrylonitrile and acrylate generally has problems such as poor anti-swelling ability and poor flexibility of the electrode sheet using the copolymer as a binder. Specifically, according to the long-term research of the inventors of this application, on the one hand, due to the high glass transition temperature of the copolymer of acrylonitrile and acrylate, the electrode sheet using the copolymer as a binder has poor toughness and a brittle texture. During the processing of the electrode sheet (for example, in the winding process of making a wound battery cell), powder loss and other phenomena are prone to occur, which cannot meet the battery manufacturing and processing requirements and is difficult to achieve direct replacement of PVDF. On the other hand, acrylate has a good affinity with the electrolyte. The introduction of acrylate will cause the copolymer of acrylonitrile and acrylate to swell too much, thereby causing a decrease in the electrochemical performance of the battery, such as the first effect and cycle life. Therefore, the development of a new fluorine-free binder with both good processing performance and electrochemical stability has become a key direction for breaking through technical bottlenecks.

[0019] In view of this, an embodiment of the present invention provides a binder comprising a nitrile structural unit, an ether structural unit, a nitrogen heterocyclic structural unit and a sulfonic acid structural unit, wherein the swelling degree of the binder is 20% to 40%.

[0020] According to the inventors' research, by simultaneously introducing nitrile structural units, ether structural units, nitrogen heterocyclic structural units, and sulfonic acid structural units into the binder, and controlling the swelling degree of the binder to 20% to 40%, the coexistence of these structural units can improve the adhesiveness, flexibility, and swelling resistance of the binder, improve the flexibility of the electrode sheet using the binder, reduce the brittleness of the electrode sheet, avoid problems such as powder loss in the electrode sheet, and improve the electrochemical performance of the battery, such as the first efficiency and cycle life. The reasons for this are as follows:

[0021] (1) In the above-mentioned binder composition system, the nitrile structural unit has a polar group (cyano group (-CN)), which can enhance the polarity of the binder, facilitate the interaction between the binder and the electrode active material, and between the binder and the electrode current collector, thereby improving the adhesion between the electrode coating on the electrode sheet and the electrode current collector, as well as the adhesion between the electrode active material and other materials in the electrode coating, thereby improving the structural stability of the electrode sheet;

[0022] (2) In the composition system of the above-mentioned binder, the ether structural unit contains an ether bond. The presence of the ether bond makes the polymer chain of the binder more flexible, thereby improving the flexibility of the binder, and further improving the flexibility of the electrode sheet using the binder, reducing the brittleness of the electrode sheet, and avoiding problems such as the electrode sheet falling off;

[0023] (3) In the above-mentioned binder composition system, the nitrogen heterocyclic structural unit has a stable ring structure, which can increase the steric hindrance of the binder, limit the penetration of electrolyte solvent molecules, and improve the stability of the binder, thereby improving the anti-swelling performance of the binder, so that the battery using the binder can have stable electrochemical performance; and the interaction between the alkaline nitrogen heterocyclic ring and the acidic sulfonic acid group to form an acid-base pair can synergistically play an anti-swelling role, which can further improve the anti-swelling performance of the binder.

[0024] (4) Under the above-mentioned binder composition system, the sulfonic acid group (-SO3H) in the sulfonic acid structural unit can form a strong intermolecular force with the electrode active material and the electrode current collector, thereby improving the adhesion between the electrode coating on the electrode sheet and the electrode current collector, as well as the adhesion between the electrode active material in the electrode coating and other materials. In addition, the sulfonic acid structural unit can also enhance the lithium ion transmission capacity of the binder.

[0025] Therefore, in the coexistence system of these structural units, based on the synergistic effect of these structural units, it is possible to improve the anti-swelling ability and adhesion of the binder, improve the structural stability of the electrode sheet, and reduce the glass transition temperature of the binder, improve the flexibility of the binder, and then improve the flexibility of the electrode sheet using the binder, avoid problems such as electrode sheet falling off, thereby improving the electrochemical properties of the battery such as the first effect and cycle life.

[0026] Furthermore, the adhesive of the present invention is a fluorine-free adhesive, which does not contain fluorine and has other environmental advantages. Furthermore, the adhesive of the present invention does not introduce acrylate structural units, thus avoiding the problem of poor anti-swelling properties of the adhesive caused by the high affinity of acrylate with the electrolyte.

[0027] In an embodiment of the present invention, the binder has good anti-swelling properties, which can prevent the binder from excessively swelling in the electrolyte, thereby improving the cycle life and other performance of the battery. The solubility A of the binder in the non-aqueous electrolyte is between 20% and 40%, for example, 20%, 25%, 30%, 35%, 40%, or a range consisting of any two thereof. The binder has an appropriate swelling degree, which can maintain the electrolyte's infiltration into the electrode sheet, shorten the lithium ion diffusion path, reduce the interfacial impedance, and improve the electrochemical performance of the battery. At the same time, it can avoid excessive swelling of the binder and the resulting collapse of the binder network due to excessive insertion of electrolyte solvent molecules, which in turn leads to separation of the electrode active material and the electrode current collector.

[0028] In embodiments of the present invention, the swelling degree of the binder is A = (W2 - W1) / W1, where W1 is the mass of the binder before being placed in the electrolyte, and W2 is the mass of the binder after immersion in the electrolyte at 55°C for 48 hours. Specifically, the binder can be formed into a film sample (e.g., a disc) and then its swelling degree in a non-aqueous electrolyte can be tested. The non-aqueous electrolyte used may comprise the following solvents: EC, DEC, and EMC, with a volume ratio of EC, DEC, and EMC of 2:3:1, and the lithium salt is LiPF6, with a LiPF6 concentration of 1 mol / L.

[0029] In an embodiment of the present invention, the weight-average molecular weight of the binder is 10wg / mol~40wg / mol (w represents the unit of ten thousand, that is, the molecular weight of the binder can be 100,000~400,000), for example, 10wg / mol, 15wg / mol, 20wg / mol, 25wg / mol, 30wg / mol, 35wg / mol, 40wg / mol or a range consisting of any two of them. In this way, the molecular weight of the binder is not less than 10wg / mol, which helps to improve the stability and swelling resistance of the binder. At the same time, the molecular weight of the binder is not higher than 40wg / mol, which helps to improve the flexibility of the binder. By controlling the molecular weight of the binder within the range of 10wg / mol~40wg / mol, it is beneficial to better balance the flexibility and swelling resistance of the binder, while taking into account improving the adhesion, flexibility and swelling resistance of the binder, and improving the structural stability and flexibility of the electrode sheet.

[0030] In an embodiment of the present invention, the binder is a multi-component copolymer system containing nitrile structural units, ether structural units, nitrogen heterocyclic structural units and sulfonic acid structural units. Specifically, it can be a quaternary copolymer system composed of nitrile structural units, ether structural units, nitrogen heterocyclic structural units and sulfonic acid structural units. While taking into account improving the adhesion and anti-swelling properties of the binder, it can also reduce the glass transition temperature of the binder and improve the flexibility of the binder. The reason for this is that the introduction of flexible ether structural units can reduce the glass transition temperature of the binder, reduce the glass transition temperature of the binder, enhance the mobility of the binder molecular chain, and improve the flexibility.

[0031] In some embodiments, the glass transition temperature of the binder can be 0~40°C, for example, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C or a range composed of any two of them, which is beneficial to further improve the adhesiveness, flexibility and anti-swelling properties of the binder, and enhance the structural stability and flexibility of the electrode sheet.

[0032] In the embodiment of the present invention, the glass transition temperature of the binder can be measured by a conventional test method for the glass transition temperature of a polymer.

[0033] In the related art, polyacrylonitrile binders are usually copolymers formed by the copolymerization of acrylonitrile and acrylic esters. Their adhesion and flexibility need to be further improved. At the same time, due to factors such as the good affinity between the acrylic ester structure and the electrolyte, the binder has poor anti-swelling ability, which seriously affects the battery's cycle life and other performance. In the embodiment of the present invention, the binder is a copolymer of a non-acrylic ester monomer and an unsaturated nitrile monomer such as acrylonitrile. By simultaneously introducing nitrile structural units, ether structural units, nitrogen heterocyclic structural units, and sulfonic acid structural units into the binder, not only can the adhesion and flexibility of the binder be improved, but the introduction of the acrylic ester structure can also be avoided, thereby avoiding problems such as the poor anti-swelling ability of the binder caused by factors such as the good affinity between the acrylic ester structure and the electrolyte.

[0034] In the embodiment of the present invention, the binder is in granular form, that is, the binder is polymer particles.

[0035] In an embodiment of the present invention, the particle size of the binder can be 40μm~80μm, that is, the particle size of the binder polymer particles is 40μm~80μm, for example, it can be 40μm, 50μm, 60μm, 70μm, 80μm or a range composed of any two of them, which is conducive to further improving the adhesiveness, flexibility and anti-swelling properties of the binder, and enhancing the structural stability and flexibility of the electrode sheet.

[0036] In the embodiment of the present invention, the mass ratio of the nitrile structural unit, the ether structural unit, the nitrogen heterocyclic structural unit and the sulfonic acid structural unit is (30-50): (30-50): (20-30): (5-10).

[0037] Specifically, the above-mentioned binder is a polymer binder, which can be a copolymer formed by copolymerizing monomer raw materials including unsaturated nitrile monomers, unsaturated ether monomers, unsaturated nitrogen heterocyclic monomers and unsaturated sulfonic acid monomers. These monomers are polymerized through their respective unsaturated bonds, and after copolymerization, form various structural units in the copolymer, that is, the binder includes unsaturated nitrile monomers forming nitrile structural units in the copolymer after copolymerization, unsaturated ether monomers forming ether structural units in the copolymer after copolymerization, unsaturated nitrogen heterocyclic monomers forming nitrogen heterocyclic structural units in the copolymer after copolymerization, and unsaturated sulfonic acid monomers forming sulfonic acid structural units in the copolymer after copolymerization.

[0038] In an embodiment of the present invention, the nitrile structural unit may include one or more of an acrylonitrile structural unit and a methacrylonitrile structural unit, which can improve the structural stability of the electrode sheet. The reason for this is that the nitrile structural unit has a polar group (cyano group (-CN)), which can enhance the polarity of the binder, facilitate the interaction between the binder and the electrode active material, and between the binder and the electrode current collector, thereby improving the adhesion between the electrode coating on the electrode sheet and the electrode current collector, as well as the adhesion between materials such as the electrode active material in the electrode coating.

[0039] Specifically, the nitrile structural unit is a structural unit formed by polymerizing a nitrile monomer containing an unsaturated bond (i.e., an unsaturated nitrile monomer) through an unsaturated bond. The nitrile monomer containing an unsaturated bond may include a nitrile monomer containing a double bond. For example, the unsaturated nitrile monomer may include acrylonitrile and / or methacrylonitrile.

[0040] For example, acrylonitrile monomer (CH2=CH-CN) contains a carbon-carbon double bond. After copolymerization, the acrylonitrile structural unit formed by acrylonitrile has the structure shown in the following formula 1-1:

[0041] -CH2-CH(CN)- Formula 1-1,

[0042] For example, the binder may contain a repeating unit formed by an acrylonitrile structural unit, and the repeating unit structure has a structure shown in the following formula 1-2:

[0043] -[-CH2-CH(CN)-] n - Formula 1-2,

[0044] wherein n represents the number of repeating units (—CH 2 —CH(CN)—) in Formula 1-2.

[0045] In an embodiment of the present invention, the ether structural unit may include an allyl ether structural unit, and the allyl ether structural unit includes one or more of an allyl ethyl ether structural unit, an allyl propyl ether structural unit, an allyl butyl ether structural unit, an allyl hydroxyethyl ether structural unit, and an allyl propyl ether structural unit, which can improve the flexibility of the binder, thereby improving the flexibility of the electrode sheet using the binder, reducing the brittleness of the electrode sheet, and avoiding problems such as the electrode sheet falling off. The reason for this is that the ether structural unit contains an ether bond, and the presence of the ether bond makes the polymer chain of the binder more flexible.

[0046] Specifically, the ether structural unit is a structural unit formed by polymerizing an ether monomer containing an unsaturated bond (i.e., an unsaturated ether monomer) through an unsaturated bond. The ether monomer containing an unsaturated bond may include an ether monomer containing a double bond. For example, the unsaturated ether monomer may include one or more of allyl ethyl ether, allyl hydroxyethyl ether, and allyl propyl ether.

[0047] For example, the allyl ether monomer (CH2=CH-CH2-O-CH2CH5) contains a carbon-carbon double bond. After copolymerization, the allyl ether structural unit formed by the allyl ether monomer has the structure shown in the following formula 1-3:

[0048] -CH2-CH(CH2-O-C2H5)- Formula 1-3,

[0049] For example, the binder may contain a repeating unit formed by an allyl ether structural unit, and the repeating unit structure has a structure shown in the following formula 1-4:

[0050] -[-CH2-CH(CH2-O-C2H5)-] n - Formula 1-4,

[0051] wherein n represents the number of repeating units of formula 1-4 (-CH2-CH(CH2-O-C2H5)-).

[0052] In an embodiment of the present invention, the nitrogen heterocyclic structural unit includes a nitrogen heterocyclic ring, which may include one or more of a pyridyl group, a pyrazinyl group, a pyrimidine group, a quinoline group, an isoquinoline group, and a quinoxaline group, which can improve the anti-swelling performance of the binder, so that the battery using the binder can have stable electrochemical performance. The reason for this is that the nitrogen heterocyclic structural unit has a stable ring structure, which can increase the steric hindrance of the binder, limit the penetration of electrolyte solvent molecules, and improve the stability of the binder.

[0053] In some preferred embodiments, the nitrogen heterocyclic structural unit containing a pyridyl group may include one or more of a 2-vinylpyridine structural unit, a 3-vinylpyridine structural unit, and a 4-vinylpyridine structural unit.

[0054] In some preferred embodiments, the nitrogen heterocyclic structural unit containing a pyrazinyl group may include a 2-vinylpyrazine structural unit.

[0055] In some preferred embodiments, the nitrogen heterocyclic structural unit containing a pyrimidine group may include a 2-vinylpyrimidine structural unit.

[0056] In some preferred embodiments, the nitrogen heterocyclic structural unit containing a quinoline group may include one or more of a 2-vinylquinoline structural unit, a 3-vinylquinoline structural unit, and a 4-vinylquinoline structural unit.

[0057] In some preferred embodiments, the nitrogen heterocyclic structural unit containing an isoquinolyl group may include a 1-vinylisoquinoline structural unit.

[0058] In some preferred embodiments, the nitrogen heterocyclic structural unit containing a quinoxaline group may include a 2-vinylquinoxaline structural unit.

[0059] Specifically, the nitrogen heterocyclic structural unit is a structural unit formed by polymerizing an nitrogen heterocyclic monomer containing an unsaturated bond (i.e., an unsaturated nitrogen heterocyclic monomer) through an unsaturated bond. The nitrogen heterocyclic monomer containing an unsaturated bond may include a nitrogen heterocyclic monomer containing a double bond. For example, the unsaturated nitrogen heterocyclic monomer may include 2-vinylpyridine and / or 2-vinylquinoxaline.

[0060] For example, the 2-vinylpyridine monomer (CH2=CH-C5H4N) contains a carbon-carbon double bond. After copolymerization, the 2-vinylpyridine monomer forms a 2-vinylpyridine structural unit having the structure shown in Formula 1-5 below:

[0061] -CH2-CH(C5H4N)- Formula 1-5,

[0062] For example, the binder may contain a repeating unit formed by a 2-vinylpyridine structural unit, and the repeating unit structure has a structure shown in the following formula 1-6:

[0063] -[-CH2-CH(C5H4N)-] n - Formula 1-6,

[0064] Wherein, n represents the number of repeating units (-CH2-CH(C5H4N)-) in Formula 1-6.

[0065] In an embodiment of the present invention, the sulfonic acid structural unit may include an alkenylsulfonic acid structural unit, and the alkenylsulfonic acid structural unit includes a C2~C14 vinylsulfonic acid structural unit (that is, the number of carbon atoms of the vinylsulfonic acid structural unit is 2~14), and the number of carbon atoms of the vinylsulfonic acid structural unit is, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 or 14, which can improve the adhesion between the electrode coating on the electrode sheet and the electrode current collector, as well as the adhesion between materials such as the electrode active substance in the electrode coating. The reason for this is that the sulfonic acid group (-SO3H) in the sulfonic acid structural unit can form a strong intermolecular force with the electrode active substance and the electrode current collector.

[0066] Specifically, the sulfonic acid structural unit is a structural unit formed by polymerizing a sulfonic acid monomer containing an unsaturated bond (i.e., an unsaturated sulfonic acid monomer) through an unsaturated bond. The sulfonic acid monomer containing an unsaturated bond may include a sulfonic acid monomer containing a double bond. For example, the unsaturated sulfonic acid monomer may include C2 vinyl sulfonic acid and / or C14 vinyl sulfonic acid.

[0067] For example, the C2 vinyl sulfonic acid monomer (CH2=CH-SO3H) contains a carbon-carbon double bond. After copolymerization, the C2 vinyl sulfonic acid monomer forms a C2 vinyl sulfonic acid structural unit having the structure shown in the following formula 1-7:

[0068] -CH2-CH(SO3H)- Formula 1-7,

[0069] For example, the binder may contain a repeating unit formed by a C2 vinyl sulfonic acid structural unit, and the repeating unit structure has a structure shown in the following formula 1-8:

[0070] -[-CH2-CH(SO3H)-] n - Formula 1-8,

[0071] wherein represents the number of repeating units (-CH2-CH(SO3H)-) in formula 1-8.

[0072] In an embodiment of the present invention, the mass proportion of the nitrile structural unit in the binder is 30 parts to 50 parts, for example, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts or a range consisting of any two of them, which is beneficial to further improve the adhesiveness, flexibility and anti-swelling properties of the binder, and enhance the structural stability and flexibility of the electrode sheet.

[0073] In an embodiment of the present invention, the mass proportion of the ether structural unit in the binder is 30 parts to 50 parts, for example, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts or a range of any two thereof, which is beneficial to further improve the adhesiveness, flexibility and anti-swelling properties of the binder, and enhance the structural stability and flexibility of the electrode sheet.

[0074] In an embodiment of the present invention, the mass proportion of the nitrogen heterocyclic structural unit in the binder is 20 parts to 30 parts, for example, 20 parts, 23 parts, 25 parts, 28 parts, 30 parts or a range of any two of them, which is beneficial to further improve the adhesiveness, flexibility and anti-swelling properties of the binder, and enhance the structural stability and flexibility of the electrode sheet.

[0075] In an embodiment of the present invention, the mass proportion of the sulfonic acid structural units in the binder is 5 parts to 10 parts, for example, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts or a range of any two of them, which is beneficial to further improve the adhesiveness, flexibility and anti-swelling properties of the binder, and enhance the structural stability and flexibility of the electrode sheet.

[0076] In general, the mass parts of each structural unit in the binder are substantially equal to the mass parts of the monomers used to form the structural unit when preparing the binder. For example, if the binder is a copolymer of an unsaturated nitrile monomer, an unsaturated ether monomer, an unsaturated nitrogen heterocyclic monomer and an unsaturated sulfonic acid monomer, then the mass parts of the nitrile structural unit in the binder are substantially equal to the mass parts of the unsaturated nitrile monomer.

[0077] In an embodiment of the present invention, a method for preparing a binder is provided, comprising the following steps: subjecting monomer raw materials including an unsaturated nitrile monomer, an unsaturated ether monomer, an unsaturated nitrogen heterocyclic monomer, and an unsaturated sulfonic acid monomer to a polymerization reaction (copolymerization reaction) to obtain the above-mentioned binder.

[0078] Specifically, the above-mentioned polymerization reaction can be emulsion polymerization. Emulsion polymerization is a process in which monomer raw materials form an emulsion in a dispersion medium (solvent) under the action of an emulsifier, and the polymerization is initiated by an initiator. That is, the above-mentioned monomer raw materials undergo a polymerization reaction under the action of an emulsifier and an initiator to produce a binder.

[0079] Specifically, the monomer raw materials may include unsaturated nitrile monomers, unsaturated ether monomers, unsaturated nitrogen heterocyclic monomers, and unsaturated sulfonic acid monomers, wherein the mass parts of the unsaturated nitrile monomers can be 30-50 parts, for example, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts or a range consisting of any two thereof, the mass parts of the unsaturated ether monomers can be 30-50 parts, for example, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts or a range consisting of any two thereof, the mass parts of the unsaturated nitrogen heterocyclic monomers can be 20-30 parts, for example, 20 parts, 23 parts, 25 parts, 28 parts, 30 parts or a range consisting of any two thereof, and the mass parts of the unsaturated sulfonic acid monomers can be 5-10 parts, for example, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts or a range consisting of any two thereof.

[0080] Specifically, the emulsifier may include one or more of sodium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium lauryl sulfonate, sodium octadecyl sulfate, sodium dioctyl succinate sulfonate, sodium fatty alcohol ether sulfate, sulfonate of ethoxylated fatty acid methyl ester, sodium α-olefin sulfonate, sodium secondary alkyl sulfonate, alcohol ether carboxylates, alcohol ether phosphates, lauryl alcohol ether phosphate, and isooctyl alcohol ether phosphate.

[0081] Specifically, the dispersion medium (solvent) includes water, and deionized water can be used in specific implementations.

[0082] Specifically, the initiator may include one or more of sodium persulfate, ammonium persulfate, and potassium persulfate.

[0083] In some embodiments, the process of polymerizing monomer raw materials including unsaturated nitrile monomers, unsaturated ether monomers, unsaturated nitrogen heterocyclic monomers, and unsaturated sulfonic acid monomers may include: mixing the monomer raw materials, an emulsifier, and water to obtain a pre-emulsion; then mixing the pre-emulsion with an initiator, and then performing a polymerization reaction to obtain a binder.

[0084] In a specific implementation, the pre-emulsifier can be added dropwise to a solution containing an initiator and a dispersion medium (solvent). Specifically, the pre-emulsifier can be added dropwise to a solution containing an initiator and a dispersion medium. During the addition of the pre-emulsifier, the temperature of the solution containing the initiator and the dispersion medium can be controlled to be between 60°C and 80°C, for example, 60°C, 65°C, 70°C, 75°C, 80°C, or any two thereof. The pre-emulsifier can be added dropwise for 2 hours to 4 hours, for example, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or any two thereof.

[0085] In the embodiment of the present invention, the pre-emulsifier can be added dropwise to the above solution by a conventional method for adding liquid reagents, and there is no particular limitation on this.

[0086] In some embodiments, the temperature for the polymerization reaction of monomer raw materials including unsaturated nitrile monomers, unsaturated ether monomers, unsaturated nitrogen heterocyclic monomers and unsaturated sulfonic acid monomers is 60°C to 80°C, for example, it can be 60°C, 65°C, 70°C, 75°C, or 80°C; the reaction time is 4-8h, for example, it can be 4h, 5h, 6h, 7h, 8h or a range consisting of any two of them.

[0087] Specifically, the preparation process of the above-mentioned binder may further include: drying the obtained liquid (generally an emulsion) after the polymerization reaction is completed, and specifically, the binder may be prepared by drying and powdering.

[0088] In specific implementation, after the polymerization reaction is completed, the obtained polymerization reaction system can be cooled to room temperature and then filtered to obtain an emulsion; and then the emulsion is dried to obtain the binder.

[0089] Specifically, the emulsion can be dried using a conventional drying process, for example, the drying process used can include any one of demulsification drying, spray drying, fluidized bed drying, flash drying, and microwave drying.

[0090] In an embodiment of the present invention, a positive electrode sheet is provided, comprising a positive electrode active layer, wherein the positive electrode active layer comprises the above-mentioned binder or the binder prepared by the above-mentioned binder preparation method.

[0091] In an embodiment of the present invention, the positive electrode sheet may mainly include a positive electrode collector and a positive electrode active layer, wherein the positive electrode active layer may mainly include a conductive agent, a binder, an electrode active material, etc. The positive electrode active layer may be arranged on one side of the positive electrode collector, or the positive electrode active layer may be respectively arranged on two opposite sides in the thickness direction of the positive electrode collector.

[0092] In other words, the binder of the embodiments of the present invention can be used to prepare positive electrode sheets. When applied to positive electrode sheets, the binder is more compatible with the positive electrode system and the preparation process of the positive electrode sheet, has good processing performance, and can improve the adhesion between materials such as the positive electrode active material in the positive electrode active layer, as well as the adhesion between the positive electrode active layer and the positive electrode current collector, thereby improving the structural stability of the positive electrode sheet. At the same time, the binder has good anti-swelling ability and can also improve the flexibility of the positive electrode sheet, avoiding problems such as material shedding of the positive electrode sheet.

[0093] An embodiment of the present invention further provides a battery, comprising the above-mentioned positive electrode sheet. The battery has advantages corresponding to the above-mentioned positive electrode sheet, which will not be described in detail.

[0094] Specifically, the battery may be a lithium-ion battery, and more specifically a nickel-cobalt-manganese ternary battery.

[0095] Generally speaking, a battery consists of a cell and a casing that encapsulates the cell. An electrolyte is injected into the cell within the casing. The cell includes a positive electrode sheet, a negative electrode sheet, and a separator located between the positive and negative electrodes. The cell can be a laminated cell, where the positive electrode sheet, separator, and negative electrode sheet are stacked alternately; or a wound cell, where the positive electrode sheet, separator, and negative electrode sheet are stacked in sequence and then wound.

[0096] In an embodiment of the present invention, the positive electrode sheet may include a positive electrode current collector and a positive electrode active layer located on at least one side surface of the positive electrode current collector. Specifically, the positive electrode active layer may be provided on one side surface of the positive electrode current collector, or the positive electrode active layer may be provided on two opposite surfaces in the thickness direction of the positive electrode current collector (i.e., the front and back surfaces of the positive electrode current collector), and the above-mentioned positive electrode active material is present in the positive electrode active layer.

[0097] Generally, the positive electrode active layer may include a positive electrode active material (positive electrode active substance), a conductive agent and the above-mentioned binder. The positive electrode active material and the conductive agent may be conventional materials in the field. For example, the positive electrode active material may include one or more of lithium nickelate, lithium iron phosphate, lithium cobaltate, lithium manganate, and positive electrode ternary materials. The positive electrode ternary material may include nickel cobalt manganese ternary material (NCM) and / or nickel cobalt aluminum ternary material (NCA). NCM may specifically include NCM811. The conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fiber.

[0098] In general, in the positive electrode active layer, the mass percentage of the positive electrode active material (i.e., the ratio of the mass of the positive electrode active material to the total mass of the positive electrode active layer) may be 70% to 99%, for example, 70%, 75%, 80%, 85%, 90%, 93%, 95%, 97%, 99% or a range consisting of any two thereof; the mass percentage of the conductive agent may be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two thereof; and the mass percentage of the binder may be 0.5% to 15%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 8%, 10%, 13%, 15% or a range consisting of any two thereof.

[0099] The embodiment of the present invention may adopt a conventional positive electrode current collector in the art, for example, the positive electrode current collector includes aluminum foil.

[0100] In embodiments of the present invention, the positive electrode sheet can be prepared by conventional methods in the art, such as a coating method. Specifically, the components used to form the positive electrode active layer, such as the positive electrode active material, conductive agent, and binder, can be dispersed in a first solvent, such as N-methylpyrrolidone (NMP), to prepare a positive electrode slurry, which is then coated on the surface of the positive electrode current collector. After drying and roller pressing, the positive electrode sheet is prepared. The coating, drying, and roller pressing steps involved are conventional operations for preparing positive electrode sheets using the coating method and are not particularly limited thereto.

[0101] In the embodiments of the present invention, conventional negative electrode sheets in the art may be used without particular limitation. For example, the negative electrode sheet may include a negative electrode current collector and a negative electrode active layer located on at least one side of the negative electrode current collector. Specifically, the negative electrode active layer may be located on one side of the negative electrode current collector, or on two opposite sides of the negative electrode current collector in the thickness direction.

[0102] Specifically, the negative electrode active layer may include a negative electrode active material (negative electrode active material), a conductive agent and a binder, all of which may be conventional materials in the art. For example, the negative electrode active material may include graphite, and the graphite may include artificial graphite and / or natural graphite. The conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNTs), acetylene black, graphene, Ketjen black, and carbon fibers; the binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0103] The embodiment of the present invention may adopt a conventional negative electrode current collector in the art, for example, the negative electrode current collector includes copper foil.

[0104] In the embodiments of the present invention, the negative electrode sheet can be prepared by conventional methods in the art, such as a coating method. Specifically, the components used to form the negative electrode active layer, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a solvent, such as water, to prepare a negative electrode slurry. The slurry is then coated on the surface of the negative electrode current collector. After drying and roller pressing, the negative electrode sheet is prepared. The coating, drying, and roller pressing steps involved are conventional operations for preparing negative electrode sheets using the coating method and are not particularly limited thereto.

[0105] In the embodiment of the present invention, conventional shell materials in the art may be used to encapsulate the battery cell. The shell may include, for example, a soft packaging material such as an aluminum-plastic film, but is not limited thereto.

[0106] The electrolyte of the embodiment of the present invention can be a conventional electrolyte in the field. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include an organic solvent, an additive and an electrolyte salt. The organic solvent includes, for example, one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and propylene carbonate (PC). The additive includes, for example, fluoroethylene carbonate (FEC) and / or vinylene carbonate (VC). The electrolyte salt may include a lithium salt, and the lithium salt includes, for example, lithium hexafluorophosphate (LiPF6), etc., but is not limited thereto.

[0107] In the embodiment of the present invention, the separator is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from short-circuiting. The embodiment of the present invention can adopt conventional separators in the art without special limitation.

[0108] In the embodiment of the present invention, components such as positive electrode sheets, separators and negative electrode sheets can be assembled into a battery by conventional methods in the field. For example, the positive electrode sheets, separators and negative electrode sheets can be stacked in an alternating manner to produce a laminated battery cell, or the positive electrode sheets, separators and negative electrode sheets can be stacked in sequence and then wound to form a wound battery cell; the battery cell is then placed in a casing, and after conventional processes such as liquid injection (i.e., injecting electrolyte) and formation, the battery is produced.

[0109] The present invention is further described below through specific examples.

[0110] In the following examples and comparative examples, the flexibility test method of the positive electrode sheet is as follows: after winding the positive electrode sheet with winding needles of different particle sizes, the corresponding winding needle diameter when cracks and powder loss occur on the surface of the positive electrode sheet is observed. The larger the winding needle diameter, the worse the flexibility of the positive electrode sheet. The unit of the winding needle diameter is mm. The results are shown in Table 3.

[0111] In the following Examples and Comparative Examples, the swelling degree A of the positive electrode binder was measured as follows: 20g of the binder was dissolved in 380g of N-methylpyrrolidone (NMP) solution to prepare a solution with a 5% solids content. The prepared solution was poured into a Teflon petri dish and dried in an 80°C forced air drying oven for 48 hours. After drying, the formed solid binder film (film) was removed and cut into discs with a diameter of 17mm. The mass of the disc was weighed and recorded as W1. The disc was placed in a sealed glass bottle filled with electrolyte and kept at 55°C for 48 hours. At this point, the disc was saturated with adsorption (i.e., further immersion would not increase the disc's mass). The disc was removed, the surface liquid wiped dry, and the disc's mass at this point was recorded as W2. The swelling degree of the positive electrode binder can be calculated by the following formula: A = (W2-W1) / W1×100%, where A is the swelling degree of the binder (%), W1 is the mass of the binder before absorbing the electrolyte (g), and W2 is the mass of the binder after absorbing the electrolyte (g). The results are shown in Table 3.

[0112] In the following examples and comparative examples, the first efficiency (first efficiency) test process of the prepared lithium-ion batteries is as follows: the battery is charged to 4.5V at 0.5C at 25°C, with a constant voltage of 4.5V and a cutoff current of 0.05C, and the charge capacity Q1 is recorded; the battery is then discharged to 3V at a constant current of 0.5C, and the discharge capacity Q2 is recorded. The first efficiency of the battery is calculated as the first discharge capacity Q2 / the first charge capacity Q1, that is, the first efficiency of the battery = Q2 / Q1×100%. The results are shown in Table 3.

[0113] In the following examples and comparative examples, the cycle performance (1C cycle (500 cycles) capacity retention rate) of the prepared lithium-ion batteries was tested as follows: the battery was charged to 4.5V at a constant current of 1C at 25°C, then charged at a constant voltage with a cut-off current value of 0.05mA, and then discharged to 3V at a constant current of 1C, which was considered one cycle; after repeating this cycle 500 times, the capacity retention rate of the battery after 500 cycles was calculated according to the following formula: Capacity retention rate of the battery after 500 cycles of 1C = (discharge capacity after 500 cycles / initial discharge capacity) × 100%. The results are shown in Table 3.

[0114] The present invention is further described below through specific examples.

[0115] Example 1

[0116] 1) Preparation of positive electrode binder (quaternary copolymer)

[0117] According to weight parts, 30 parts of acrylonitrile, 40 parts of allyl butyl ether, 25 parts of 2-vinyl pyridine, 5 parts of C2 vinyl sulfonic acid, 1 part of sodium lauryl sulfate, and 150 parts of deionized water were mixed and stirred to obtain a pre-emulsion;

[0118] 80 parts of deionized water and 1 part of ammonium persulfate were added to a reaction vessel, and the temperature of the solution in the reactor was controlled at 70°C. The pre-emulsion was then added dropwise to the solution in the reaction vessel at a uniform rate for 3 hours. The temperature was then raised to 75°C for polymerization for 6 hours. After the reaction was completed, the solution was cooled to room temperature, filtered to obtain an emulsion, and spray-dried to obtain a binder.

[0119] 2) Preparation of positive electrode sheet

[0120] According to weight parts, 95 parts of positive electrode active material NCM811, 3 parts of acetylene black, 2 parts of positive electrode binder (quaternary copolymer) and 100 parts of N-methylpyrrolidone were mixed evenly using a planetary mixer to obtain a positive electrode slurry; the above positive electrode slurry was coated on the surfaces of opposite sides of aluminum foil using a coating machine, and the positive electrode sheet was obtained after baking and rolling.

[0121] 3) Preparation of negative electrode sheet

[0122] According to weight, 95 parts of graphite, 3 parts of styrene-butadiene rubber binder, 2 parts of conductive carbon black and 100 parts of deionized water were stirred and mixed evenly using a planetary mixer to obtain a negative electrode slurry. The slurry was coated on the surfaces of opposite sides of the copper foil using a coater, and the negative electrode sheet was obtained after baking and rolling.

[0123] 4) Preparation of lithium-ion batteries

[0124] The negative electrode sheet, separator, positive electrode sheet, and separator are sequentially assembled into a lithium-ion button cell. After injection and formation, a lithium-ion battery is obtained. The electrolyte composition is as follows: the electrolyte solvents are EC, DEC, and EMC, the volume ratio of EC, DEC, and EMC is 2:3:1, and the lithium salt in the electrolyte is LiPF6, with a LiPF6 concentration of 1 mol / L.

[0125] Examples 2 to 11: The difference from Example 1 is that the formula of the prepared positive electrode binder is different. The remaining steps are consistent with Example 1. The specific differences are shown in Tables 1 and 2.

[0126] Example 12 to Example 15: The difference from Example 1 is that the amount of initiator added in the reaction is different. The remaining steps are consistent with Example 1. The specific differences are shown in Table 1 and Table 2.

[0127] Examples 16 to 20: The difference from Example 1 is that the formula of the prepared positive electrode binder is different. The remaining steps are consistent with Example 1. The specific differences are shown in Tables 1 and 2.

[0128] Comparative Example 1: The difference from Example 1 is that PVDF is used to replace the tetrapolymer in Example 1 as the positive electrode binder, and the remaining steps and conditions are the same as those in Example 1.

[0129] Comparative Example 2: A copolymer of acrylonitrile (55 parts), butyl acrylate (40 parts) and acrylic acid (5 parts) was used to replace the copolymer in Example 1 as the positive electrode binder. The remaining steps and conditions were the same as those in Example 1.

[0130] Comparative Example 3: The difference from Example 1 is that no ether monomer is added during the preparation of the positive electrode binder, as shown in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the remaining conditions, steps and conditions are the same as those in Example 1.

[0131] Comparative Example 4: The difference from Example 1 is that no nitrogen heterocyclic monomer is added during the preparation of the positive electrode binder, as shown in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the remaining conditions, steps and conditions are the same as those in Example 1.

[0132] Comparative Example 5: The difference from Example 1 is that no sulfonic acid monomer is added during the preparation of the positive electrode binder, as shown in Tables 1 and 2. Except for the differences shown in Tables 1 and 2, the remaining conditions, steps and conditions are the same as those in Example 1.

[0133] The weight average molecular weight, glass transition temperature, swelling degree of the positive electrode binder, flexibility of the positive electrode sheet, initial efficiency of the battery, and 1C cycle (500 cycles) capacity retention rate of the battery in each embodiment and comparative example obtained from the test are summarized in Table 3.

[0134] Table 1 Feeding data of Examples and Comparative Examples

[0135]

[0136] Table 2 Monomer types of Examples and Comparative Examples

[0137]

[0138] Table 3 Performance test data

[0139]

[0140] It can be seen from Tables 1 to 3 that, relative to Comparative Examples 1 to 5, the binders in Examples 1 to 20 include nitrile structural units, ether structural units, nitrogen heterocyclic structural units and sulfonic acid structural units, and the swelling degree of the binder is 20% to 40%, which can take into account the improvement of the adhesiveness, flexibility and anti-swelling properties of the binder, improve the flexibility of the electrode sheet using the binder, reduce the brittleness of the electrode sheet, and avoid problems such as powdering of the electrode sheet, thereby taking into account the improvement of the electrochemical properties of the battery, such as the first effect and cycle life.

[0141] The electrochemical properties such as the swelling degree of the positive electrode binder, the flexibility of the positive electrode sheet, the first effect and the cycle life of the battery are basically the same as those of Comparative Example 1 or can achieve better results than Comparative Example 1, indicating that the present invention can basically achieve the effect of replacing PVDF.

[0142] At the same time, compared with the PVDF in Comparative Example 1, the binders in Examples 1 to 20 do not contain fluorine, which is beneficial to environmental protection.

[0143] Compared with Example 12 and Example 15, the weight average molecular weight of the binder in Example 1 to Example 11, Example 13, Example 14 and Example 16 to Example 20 is 10wg / mol~40wg / mol. On the basis of improving the adhesion, flexibility and anti-swelling properties of the binder and improving the flexibility of the electrode sheet using the binder, it can further take into account the improvement of the electrochemical properties of the battery such as the first effect and cycle life.

[0144] Finally, it should be noted that those skilled in the art will readily identify other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. The present invention is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art not disclosed herein. The present invention is not limited to the foregoing description and may be modified and altered in various ways without departing from the scope thereof. The scope of the present invention is limited solely by the appended claims.

Claims

1. A binder, characterized in that: The binder comprises a nitrile structural unit, an ether structural unit, a nitrogen heterocyclic structural unit and a sulfonic acid structural unit, and the swelling degree of the binder is 20% to 40%.

2. The adhesive according to claim 1, characterized in that The weight average molecular weight of the binder is 10 wg / mol to 40 wg / mol.

3. The adhesive according to claim 1, characterized in that The glass transition temperature of the binder is 0°C to 40°C.

4. The adhesive according to claim 1, characterized in that The particle size of the binder is 40 μm to 80 μm.

5. The adhesive according to any one of claims 1 to 4, characterized in that The mass ratio of the nitrile structural unit, the ether structural unit, the nitrogen heterocyclic structural unit and the sulfonic acid structural unit is (30-50): (30-50): (20-30): (5-10).

6. The adhesive according to claim 5, characterized in that The nitrile structural unit includes one or more of an acrylonitrile structural unit and a methacrylonitrile structural unit; And / or, the ether structural unit includes an allyl ether structural unit, and the allyl ether structural unit includes one or more of an allyl ethyl ether structural unit, an allyl propyl ether structural unit, an allyl butyl ether structural unit, an allyl hydroxyethyl ether structural unit, and an allyl propyl ether structural unit.

7. The adhesive according to claim 5, characterized in that The sulfonic acid structural units include alkenyl sulfonic acid structural units, and the alkenyl sulfonic acid structural units include C2-C14 vinyl sulfonic acid structural units.

8. The adhesive according to claim 5, characterized in that The nitrogen heterocyclic structural unit contains a nitrogen heterocyclic ring, and the nitrogen heterocyclic ring includes one or more of pyridyl, pyrazinyl, pyrimidinyl, quinolyl, isoquinolyl, and quinoxalinyl.

9. A positive electrode sheet, characterized in that: The invention comprises a positive electrode active layer, wherein the positive electrode active layer comprises the binder according to any one of claims 1 to 8.

10. A battery, characterized in that: Including the positive electrode sheet according to claim 9.

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