A positive electrode tab glue, a positive electrode tab glue slurry, a positive electrode plate and a secondary battery

Abstract

The positive electrode tab glue provided by the present invention comprises an acrylate polymer, an organic salt and an organic solvent. The molecular weight Mw of the acrylate polymer is 100,000 - 350,000, and the weight percentage of the organic salt in the acrylate polymer is 0.1% - 0.8%. The acrylate polymer comprises a hard segment resin and a soft segment resin, the glass transition temperature Tg of the hard segment resin is ≥20°C, and the glass transition temperature Tg of the soft segment resin is ≤0°C. After mixing the positive electrode tab glue with ceramic particles in proportion, a positive electrode tab glue slurry is obtained, which is coated simultaneously with the positive electrode slurry on the aluminum foil at the edge of the positive electrode tab. After drying, a positive electrode tab with a functional coating is obtained. The positive electrode tab is applied to a lithium-ion secondary battery, which can improve the bonding strength with the aluminum foil and the separator, improve the processing performance and safety performance of the battery, and improve the cycle performance of the battery cell.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and particularly relates to a positive pole ear glue, a positive pole ear glue slurry, a positive pole piece and a secondary battery. Background Art

[0002] Lithium-ion secondary batteries generally mainly consist of a positive electrode, a negative electrode, a separator, an electrolyte and a battery case. Among them, the separator is one of the key inner components, and its main function is to separate the positive and negative electrodes of the battery to prevent the positive and negative electrodes from coming into contact and short-circuiting.

[0003] During the processing of lithium-ion secondary batteries, there are many processing problems, and the battery performance will also be affected accordingly. Since the positive electrode sheet is generally smaller than the negative electrode sheet, burrs are likely to appear at the edges of the wide sides of the electrode sheets during cutting. Once the separator is pierced and contacts the negative electrode, it will cause a battery short circuit. Because the surface of boehmite is smooth, after using boehmite to coat the positive electrode edge, the positive electrode edge can be filled, and the cut surface is smooth and free of burrs.

[0004] There are many factors affecting the safety of lithium-ion secondary batteries. Among them, the ear cracking of the composite separator is likely to cause problems such as burrs, abnormal protrusions and fractures during the subsequent electrode assembly process, resulting in battery safety problems, which have attracted much attention in recent years. Since the ear is a key component for conducting current connection in a lithium-ion battery, the ear is usually formed by cutting from the edge of the electrode sheet. In the battery core structure, there is a partial area at the root of the positive pole ear that overlaps with the negative active material area.

[0005] During the preparation process of the battery core, the problem of ear misalignment will occur. The electrode sheet and the separator can be bonded to improve the ear misalignment. To improve the safety of lithium-ion batteries, a ceramic layer is coated in the overlapping area of the positive pole ear.

[0006] To solve the above problems, there is an urgent need for a positive pole ear glue, which coats ceramic particles on the surface of a positive aluminum foil substrate to form a ceramic / polymer composite coating, and uses a thermal composite process to bond the positive aluminum foil and the separator, thereby improving situations such as short circuits and ear misalignment caused by edge burrs.

[0007] The positive pole ear glue has a relatively high demand for peel strength. After coating, it is bonded to the positive aluminum foil substrate and bonded to the PP / PE / ceramic separator through thermal composite. At the same time, because the positive pole ear glue slurry and the positive electrode slurry are coated simultaneously, it is required that there is no cross-material between the positive pole ear glue slurry and the positive electrode slurry, and there are specific requirements for the physical properties of the positive pole ear glue slurry.

[0008] The current positive electrode tab glue selected in the market mainly adopts the PVDF (polyvinylidene fluoride) system. However, the most obvious disadvantage of PVDF is its poor peel strength and poor wet adhesion effect. After long-term immersion in the electrolyte, peeling will occur, posing certain safety hazards. It will also cause obvious deformation of the battery cell in the later stage of cycling, resulting in a decrease in capacity.

[0009] The adhesion between the separator and the interface of the electrode sheet safety coating has a great impact on safety. There is an urgent need for a material that can improve the adhesion between the composite ceramic aluminum foil and the separator, thereby improving the processing performance and safety performance of the battery and improving the cycling performance of the battery cell. Summary of the Invention

[0010] In order to solve the problems existing in the existing positive electrode tab glue materials, the purpose of the present invention is to provide a positive electrode tab glue, a positive electrode tab glue slurry, a positive electrode sheet and a secondary battery.

[0011] The present invention realizes the above technical effects through the following technical solutions:

[0012] In a first aspect, the positive electrode tab glue provided by the present invention comprises an acrylate polymer, an organic salt and an organic solvent. The molecular weight Mw of the acrylate polymer is 100,000 - 350,000, and the weight percentage of the organic salt in the acrylate polymer is 0.1% - 0.8%. The acrylate polymer comprises a hard segment resin and a soft segment resin. The glass transition temperature Tg of the hard segment resin is ≥ 20°C, and the glass transition temperature Tg of the soft segment resin is ≤ 0°C.

[0013] Preferably, the weight percentage of the organic salt in the acrylate polymer is 0.4% - 0.8%.

[0014] Preferably, the glass transition temperature Tg of the hard segment resin is 20 - 90°C, and the glass transition temperature Tg of the soft segment resin is -60 - 0°C.

[0015] Preferably, the mass ratio of the hard segment resin to the soft segment resin is (20 - 35):(65 - 80).

[0016] Preferably, the hard segment resin comprises a first main structural unit and a first polar structural unit; the soft segment resin comprises a second main structural unit and a second polar structural unit; both the first main structural unit and the second main structural unit comprise acrylate structural units and each independently and selectively contains aromatic vinyl structural units; the first polar structural unit and the second polar structural unit are independently selected from structural units containing polar groups; the polar groups include one or more of carboxyl, cyano, hydroxyl, epoxy group, amino group, amide group, acetoxy group.

[0017] Preferably, the mass ratio of the first main structural unit to the first polar structural unit is (80 - 97):(3 - 20); the mass ratio of the second main structural unit to the second polar structural unit is (75 - 97):(3 - 25).

[0018] Preferably, the content of the structural unit containing a carboxyl group in the acrylate polymer is 2 - 15 wt%.

[0019] Preferably, the acrylate structural unit is selected from one or more of a methyl methacrylate structural unit, a methyl acrylate structural unit, an ethyl acrylate structural unit, a butyl acrylate structural unit, a sine octyl acrylate structural unit, an isooctyl acrylate structural unit, a hexyl acrylate structural unit, a cyclohexyl methacrylate structural unit, an isobornyl acrylate structural unit, and a methacrylic acid isobornyl ester structural unit. The aromatic vinyl structural unit is selected from one or a combination of two of a styrene structural unit and a methyl styrene structural unit.

[0020] Preferably, the first polar structural unit and the second polar structural unit can each independently be selected from one or a combination of two of a methacrylic acid structural unit, an acrylic acid structural unit, an acrylonitrile structural unit, a 2-hydroxyethyl acrylate structural unit, a 2-hydroxyethyl methacrylate structural unit, a 2-hydroxypropyl methacrylate structural unit, a glycidyl methacrylate structural unit, an allyl glycidyl ether structural unit, a 2-(dimethylamino)ethyl acrylate structural unit, a 2-(dimethylamino)ethyl methacrylate structural unit, a 2-(tert-butylamino)ethyl methacrylate structural unit, an acrylamide structural unit, a diacetone acrylamide structural unit, a hydroxymethyl acrylamide structural unit, a 2-(acetoacetoxy)ethyl methacrylate structural unit, a butyl itaconate structural unit, and a β-acryloyloxypropionic acid structural unit.

[0021] Preferably, the structural unit containing a carboxyl group in the acrylate polymer is selected from one or a combination of two of a methacrylic acid structural unit and an acrylic acid structural unit.

[0022] The acrylate structural unit, aromatic vinyl structural unit, polar structural unit, etc. selected for the hard segment resin and the soft segment resin can be the same or different, and must meet the requirements of the corresponding glass transition temperature Tg.

[0023] Preferably, the hard segment resin further includes a first post-reaction structural unit containing a post-reaction group, the soft segment resin further includes a second post-reaction structural unit containing a post-reaction group, and the first post-reaction structural unit and the second post-reaction structural unit are connected to each other by a chemical bond. It can be understood that the above structure can be obtained by reacting a first post-reaction monomer containing a post-reaction group with a second post-reaction monomer containing a post-reaction group.

[0024] Preferably, the first post-reaction structural unit accounts for 3-10% of the weight of the hard segment resin, and the second post-reaction structural unit accounts for 3-10% of the weight of the soft segment resin.

[0025] Preferably, the post-reaction groups are selected from one or more of carboxyl, amino, epoxy, and acetoxy groups; it can be understood that the post-reaction groups on the first post-reaction monomer must be able to react with the post-reaction groups on the second post-reaction monomer. For example, the post-reaction groups in the first post-reaction monomer are carboxyl and / or amino, and the corresponding post-reaction groups in the second post-reaction monomer are epoxy and / or acetoxy groups respectively. That is, when the post-reaction group in the first post-reaction monomer is carboxyl, the post-reaction group in the second post-reaction monomer is epoxy; when the post-reaction group in the first post-reaction monomer is amino, the post-reaction group in the second post-reaction monomer is epoxy and / or acetoxy groups.

[0026] Preferably, the first post-reaction monomer is selected from one or more of β-acryloyloxypropionic acid, methacrylic acid, acrylic acid, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, glycidyl methacrylate, allyl glycidyl ether, and acetylacetoxyethyl methacrylate; the second post-reaction monomer is selected from one or more of β-acryloyloxypropionic acid, methacrylic acid, acrylic acid, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, glycidyl methacrylate, allyl glycidyl ether, and acetylacetoxyethyl methacrylate.

[0027] In the hard segment resin, the monomers forming the first polar structural unit include the first post-reaction monomer and the monomers of other polar structural units; the monomers forming the first polar structural unit can be the same as the first post-reaction monomer. When the monomers forming the first polar structural unit are the same as the first post-reaction monomer, it is only necessary that the dosage of the monomers of the first polar structural unit satisfies the range of the mass ratio of the first main structural unit to the first polar structural unit, and the structural unit of the first post-reaction group accounts for 3-10% of the weight of the hard segment resin.

[0028] Similarly, in the soft segment resin, the monomers forming the second polar structural unit include the second post-reaction monomer and the monomers of other polar structural units; the monomers forming the second polar structural unit can be the same as the second post-reaction monomer. When the monomers forming the second polar structural unit are the same as the second post-reaction monomer, it is only necessary that the dosage of the monomers of the second polar structural unit satisfies the range of the mass ratio of the second main structural unit to the second polar structural unit, and the structural unit of the second post-reaction group accounts for 3-10% of the weight of the soft segment resin.

[0029] Preferably, the molar ratio of the post-reaction groups on the first post-reaction monomer to the post-reaction groups on the second post-reaction monomer is (0.9 - 1.1):1. In the present invention, when the molar ratio of the two is not within the above preferred range, the presence of the excess post-reaction groups will not have a significant impact on the performance of the positive electrode tab glue.

[0030] When the monomers forming the first polar structural unit, the monomers forming the second polar structural unit, and the first post-reaction monomer all contain carboxyl groups, the mass ratio of the total amount of the carboxyl group-containing monomers in the monomers forming the first polar structural unit and the monomers forming the second polar structural unit to the total monomer amount for preparing the acrylate polymer is used as the content of the structural unit containing carboxyl groups in the acrylate polymer.

[0031] Preferably, the solid content of the positive electrode tab glue is 18 - 22%, the organic salt includes at least one of alkyl sulfonates, alkyl sulfates, and alkyl benzene sulfonates, and the organic solvent includes NMP (N-methylpyrrolidone).

[0032] Preferably, when the positive electrode tab glue is used for a ternary positive electrode and is coated simultaneously with the ternary positive electrode slurry, the molecular weight Mw of the acrylate polymer is 100,000 - 350,000; or when the positive electrode tab glue is used for a lithium iron phosphate positive electrode, the molecular weight Mw of the acrylate polymer is 200,000 - 350,000.

[0033] In the second aspect, the present invention provides a positive electrode tab glue slurry, which includes ceramic particles and the aforementioned positive electrode tab glue, and the mass ratio of the ceramic particles to the positive electrode tab glue is (80 - 95):(5 - 20). The positive electrode tab glue slurry is obtained by mixing the positive electrode tab glue and the ceramic particles in proportion. Preferably, the mass ratio of the ceramic particles to the positive electrode tab glue is (80 - 85):(15 - 20).

[0034] In the third aspect, the present invention provides a positive electrode tab, which includes a functional coating obtained by drying the aforementioned positive electrode tab glue slurry. The positive electrode tab glue slurry and the positive electrode slurry are coated simultaneously and coated on the aluminum foil at the edge of the positive electrode tab, and after drying, a positive electrode tab with a functional coating is obtained.

[0035] In the fourth aspect, the present invention provides a secondary battery, which includes a negative electrode tab, a separator, an electrolyte, and the aforementioned positive electrode tab.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] This application uses an acrylate polymer system to replace the traditional PVDF system as the positive electrode tab glue, solving the limitations of low wet adhesion strength and aluminum foil curling in existing products. The positive electrode tab glue of the acrylate polymer in this application can not only improve the wet adhesion strength, but also effectively improve the aluminum foil curling due to the good flexibility of the acrylate polymer. Moreover, due to its high wet adhesion strength, it can improve the battery cycle performance. The positive electrode tab glue is mixed with ceramic particles to form a ceramic / polymer composite coating slurry, which is coated on the aluminum foil at the edge of the electrode together with the positive electrode slurry, and bonded to the PP / PE / ceramic separator through hot pressing to realize the bonding between the electrode and the separator, which can improve the bonding between the composite ceramic aluminum foil and the separator, thereby improving the processing performance and safety of the battery and other performances, and improving the cycle performance of the battery core.

[0038] The acrylate polymer in this application has a soft segment resin and a hard segment resin. When in use, the two resins are first mixed, then mixed with ceramic particles, and then coated on the aluminum foil at the edge of the positive electrode tab to form a functional coating, and then hot pressed with the PP / PE / ceramic separator. The soft segment resin can realize the bonding with the PP / PE / ceramic separator, and the hard segment resin can realize the bonding with the aluminum foil. At the same time, when hot pressing, the resin will flow to the pores of the separator and form a riveting structure with higher strength after post-curing. Through the above design, the bonding between the separator and the aluminum foil can be realized, the production process can be optimized, the production efficiency can be improved, and the production cost can be reduced. At the same time, the electrolyte wettability can be improved, and the high-rate cycle performance of the battery core can be improved. Description of the Drawings

[0039] Figure 1 It is the stringing test diagram in Embodiment 1 of the present invention;

[0040] Figure 2 It is the stringing test diagram in Comparative Example 1 of the present invention;

[0041] In the figure: 1 - positive electrode tab glue slurry, 2 - positive electrode slurry. Detailed Embodiments

[0042] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the following further details the present invention in conjunction with specific embodiments. It should be understood that the embodiments described herein are some embodiments of the present invention, rather than all embodiments, and are only used to explain the present invention, not to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work belong to the protection scope of the present invention.

[0043] It should be noted that:

[0044] In the present invention, the acrylate polymer is a general term for acrylate resins copolymerized from acrylate monomers containing ester bonds (such as methyl acrylate, isooctyl acrylate, etc.) or monomers copolymerizable with unsaturated olefin monomers (such as styrene, etc.).

[0045] In the present invention, the content of relevant structural units in the acrylate polymer is calculated as the weight percentage of the monomers of the relevant structural units in the total amount of monomers. For example, the content of the structural unit containing a carboxyl group in the acrylate polymer is the weight percentage of the monomer of the structural unit containing a carboxyl group in the total amount of monomers used in the preparation of the positive electrode tab glue.

[0046] In the present invention, the structural unit in the polymer or resin refers to the structure corresponding to the raw material monomer used in the preparation of the polymer or resin after polymerization and present in the polymer or resin.

[0047] In the first aspect, the positive electrode tab glue provided by the present invention comprises an acrylate polymer, an organic salt, and an organic solvent. The molecular weight Mw of the acrylate polymer is 100,000 - 350,000, and the weight percentage of the organic salt in the acrylate polymer is 0.1% - 0.8%. The acrylate polymer comprises a hard segment resin and a soft segment resin. The glass transition temperature Tg of the hard segment resin is ≥ 20 °C, and the glass transition temperature Tg of the soft segment resin is ≤ 0 °C.

[0048] In the positive electrode tab glue, if the weight percentage of the organic salt in the acrylate polymer > 0.8%, the positive electrode tab slurry and the positive electrode slurry will show a phenomenon of mutual penetration; if the weight percentage of the organic salt in the acrylate polymer < 0.1%, the wettability of the slurry will decrease, and there will be missed coating during coating.

[0049] In the positive electrode tab glue, if the molecular weight Mw of the acrylate polymer < 100,000, the viscosity of the slurry will decrease, and the positive electrode tab slurry and the positive electrode slurry will show a phenomenon of mutual penetration; if the molecular weight Mw of the acrylate polymer > 350,000, due to the too large molecular weight, the chain segment movement is difficult during hot pressing, and the bonding strength with the separator decreases.

[0050] The methods for controlling the molecular weight of the acrylate polymer are well known to those skilled in the art. For example, adjusting the initiator concentration, using a chain transfer agent, controlling the reaction conditions (time, temperature, stirring speed, etc.). In the present invention, it is preferred to use a chain transfer agent to control the molecular weight of the acrylate polymer. Various chain transfer agents commonly used in the prior art can be adopted in the present invention, such as thiol-based and mercapto-based compounds, specifically dodecyl mercaptan. The addition amount of the chain transfer agent is adjusted according to the molecular weight of the acrylate polymer to be obtained, and the adjustment method of the addition amount is well known to those skilled in the art.

[0051] Preferably, the content of the structural unit containing a carboxyl group in the acrylate polymer is 2-15%. If the content of the structural unit containing a carboxyl group in the acrylate polymer <2 wt%, the ceramic cannot be effectively dispersed; if the content of the structural unit containing a carboxyl group in the acrylate polymer >15 wt%, the system is unstable.

[0052] Therefore, in order to meet the requirements of the present application for the safety, strong dry adhesion strength and wet adhesion strength of the positive pole tab glue, the molecular weight Mw of the acrylate polymer in the present application is limited to 100,000-350,000, specifically it can be 100,000, 120,000, 140,000, 180,000, 220,000, 240,000, 260,000, 280,000, 300,000 or 350,000, etc.; the content of the structural unit containing a carboxyl group in the acrylate polymer is limited to 2-15 wt%, specifically it can be 2 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt% or 15 wt%, etc.; the weight percentage of the organic salt in the acrylate polymer is limited to 0.1%-0.8%, specifically it can be 0.1%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7% or 0.8%, etc., preferably 0.4%-0.8%.

[0053] In some specific embodiments, the acrylate polymer includes a hard segment resin and a soft segment resin. The larger the Tg of the hard segment resin, the weaker the dry adhesion strength and the smaller the influence on the wet adhesion strength; the lower the Tg of the soft segment resin, the higher the dry adhesion strength and the lower the wet adhesion strength. Therefore, in order to make the dry adhesion strength and wet adhesion strength of the positive pole tab glue relatively high, the present application limits the glass transition temperature Tg of the hard segment resin ≥ 20 °C, specifically it can be 20 °C, 30 °C, 45 °C, 67 °C, 82 °C or 90 °C, etc., and the glass transition temperature Tg of the hard segment resin is preferably 20-90 °C; the glass transition temperature Tg of the soft segment resin ≤ 0 °C, specifically it can be 0 °C, -10 °C, -20 °C, -30 °C, -40 °C, -50 °C or -60 °C, etc., and the glass transition temperature Tg of the soft segment resin is preferably -60-0 °C.

[0054] When the proportion of the soft segment is relatively large, the wet adhesion strength decreases and the dry adhesion strength increases. In order to make the dry adhesion strength and wet adhesion strength of the positive pole tab glue relatively high, the mass ratio of the hard segment resin to the soft segment resin is (20-35):(65-80). Specifically, the mass ratio of the hard segment resin to the soft segment resin can be 20:80, 24:76, 28:72, 32:68 or 35:65, etc.

[0055] In some specific embodiments, the hard segment resin includes a first main structural unit and a first polar structural unit; the soft segment resin includes a second main structural unit and a second polar structural unit; both the first main structural unit and the second main structural unit include acrylate structural units, and each independently and selectively contains aromatic vinyl structural units, and the first polar structural unit and the second polar structural unit are independently selected from structural units containing polar groups; the polar groups include one or more of carboxyl, cyano, hydroxyl, epoxy, amino, amide, and acetoxy groups.

[0056] In some specific embodiments, the mass ratio of the first main structural unit to the first polar structural unit is (80 - 97):(3 - 20); the mass ratio of the second main structural unit to the second polar structural unit is (75 - 97):(3 - 25).

[0057] In some specific embodiments, the acrylate structural units are selected from one or more of methyl methacrylate structural units, methyl acrylate structural units, ethyl acrylate structural units, butyl acrylate structural units, sine octyl acrylate structural units, isooctyl acrylate structural units, hexyl acrylate structural units, cyclohexyl methacrylate structural units, isobornyl acrylate structural units, and isobornyl methacrylate structural units. The aromatic vinyl structural units are selected from one or a combination of two of styrene structural units and methyl styrene structural units.

[0058] In some specific embodiments, the first polar structural unit and the second polar structural unit can each independently be selected from one or a combination of two of methacrylic acid structural units, acrylic acid structural units, acrylonitrile structural units, 2 - hydroxyethyl acrylate structural units, 2 - hydroxyethyl methacrylate structural units, 2 - hydroxypropyl methacrylate structural units, glycidyl methacrylate structural units, allyl glycidyl ether structural units, 2 - (dimethylamino)ethyl acrylate structural units, 2 - (dimethylamino)ethyl methacrylate structural units, 2 - (tert - butylamino)ethyl methacrylate structural units, acrylamide structural units, diacetone acrylamide structural units, hydroxymethyl acrylamide structural units, 2 - (acetoacetoxy)ethyl methacrylate structural units, dibutyl itaconate structural units, and β - acryloyloxypropionic acid structural units.

[0059] In some specific embodiments, the structural units containing carboxyl groups in the acrylate polymer are selected from one or a combination of two of methacrylic acid structural units and acrylic acid structural units.

[0060] The acrylate structural units, aromatic vinyl structural units, polar structural units, etc. selected for the hard segment resin and the soft segment resin can be the same or different, and must meet the requirements of the corresponding glass transition temperature Tg.

[0061] In some specific embodiments, the hard segment resin further includes a first post-reaction structural unit containing a post-reaction group, the soft segment resin further includes a second post-reaction structural unit containing a post-reaction group, and the first post-reaction structural unit and the second post-reaction structural unit are connected to each other by a chemical bond. It can be understood that the above structure can be obtained by reacting a first post-reaction monomer containing a post-reaction group with a second post-reaction monomer containing a post-reaction group. At this time, the hard segment resin and the soft segment resin are polymerized into one body, which is very beneficial to improving the adhesion.

[0062] The higher the proportion of the post-reaction group, the greater the dry adhesion and wet adhesion peel strength. When it exceeds a certain range, the peel strength decreases, and when the proportion is greater than 10%, the system is unstable. Based on this, in this application, it is further defined that the first post-reaction structural unit accounts for 3-10% of the weight of the hard segment resin, specifically it can be 3%, 5%, 6.3%, 8%, 9.1% or 10%, etc.; the structural unit of the second post-reaction group accounts for 3-10% of the weight of the soft segment resin, specifically it can be 3%, 4%, 6%, 7.5%, 8.4% or 10%, etc.

[0063] In some specific embodiments, the post-reaction group is selected from one or more of a carboxyl group, an amino group, an epoxy group, and an acetoxy group; it can be understood that the post-reaction group on the first post-reaction monomer must be able to react with the post-reaction group on the second post-reaction monomer. For example, the post-reaction group in the first post-reaction monomer is a carboxyl group and / or an amino group, and the corresponding post-reaction groups in the second post-reaction monomer are an epoxy group and / or an acetoxy group respectively. That is, when the post-reaction group in the first post-reaction monomer is a carboxyl group, the post-reaction group in the second post-reaction monomer is an epoxy group; when the post-reaction group in the first post-reaction monomer is an amino group, the post-reaction groups in the second post-reaction monomer are an epoxy group and / or an acetoxy group. In this way, when the hard segment resin and the soft segment resin are mixed, they will post-cure at ≥80°C.

[0064] In some specific embodiments, the first post-reaction monomer is selected from one or more of β-acryloyloxypropionic acid, methacrylic acid, acrylic acid, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, glycidyl methacrylate, allyl glycidyl ether, and acetylacetoxyethyl methacrylate; the second post-reaction monomer is selected from one or more of β-acryloyloxypropionic acid, methacrylic acid, acrylic acid, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, glycidyl methacrylate, allyl glycidyl ether, and acetylacetoxyethyl methacrylate.

[0065] Specifically, when the first post-reaction monomer in the hard segment resin is one or more of butyl itaconate, β-acryloyloxypropionic acid, methacrylic acid, acrylic acid, etc., the second post-reaction monomer in the soft segment resin is one or more of glycidyl methacrylate, allyl glycidyl ether, etc.

[0066] Specifically, when the first post-reaction monomer in the hard segment resin is one or more of dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, tert-butylaminoethyl methacrylate, etc., the second post-reaction monomer in the soft segment resin is one or more of glycidyl methacrylate, allyl glycidyl ether, acetylacetoxyethyl methacrylate, etc.

[0067] In the hard segment resin, the monomers forming the first polar structural unit include the first post-reaction monomer and the monomers of other polar structural units; the monomers forming the first polar structural unit may be the same as the first post-reaction monomer. When the monomers forming the first polar structural unit are the same as the first post-reaction monomer, it is only necessary that the amount of the monomers of the first polar structural unit satisfies the range of the mass ratio of the first main structural unit to the first polar structural unit, and the structural unit of the first post-reaction group accounts for 3-10% of the weight of the hard segment resin.

[0068] Similarly, in the soft segment resin, the monomers forming the second polar structural unit include the second post-reaction monomer and the monomers of other polar structural units; the monomers forming the second polar structural unit may be the same as the second post-reaction monomer. When the monomers forming the second polar structural unit are the same as the second post-reaction monomer, it is only necessary that the amount of the monomers of the second polar structural unit satisfies the range of the mass ratio of the second main structural unit to the second polar structural unit, and the structural unit of the second post-reaction group accounts for 3-10% of the weight of the soft segment resin.

[0069] Preferably, the molar ratio of the post-reaction group on the first post-reaction monomer to the post-reaction group on the second post-reaction monomer is (0.9-1.1):1. In the present invention, when the molar ratio of the two is not within the above preferred range, the presence of the excess post-reaction group will not significantly affect the performance of the positive pole ear glue.

[0070] When the monomers forming the first polar structural unit, the monomers forming the second polar structural unit and the first post-reaction monomer all contain carboxyl groups at the same time, the mass ratio of the total amount of the carboxyl group-containing monomers in the monomers forming the first polar structural unit and the monomers forming the second polar structural unit to the total monomer amount for preparing the acrylate polymer is used as the content of the carboxyl group-containing structural unit in the acrylate polymer.

[0071] In some specific embodiments, the solid content of the positive electrode tab glue is 18% - 22%, specifically it can be 18%, 19%, 20%, 21% or 22%, etc. The organic salt includes at least one of alkyl sulfonate, alkyl sulfate, alkyl benzene sulfonate, specifically it can be sodium dioctyl sulfosuccinate, sodium dihexyl sulfosuccinate, sodium dodecyl sulfate, sodium hexadecyl sulfate, sodium octadecyl sulfate or sodium dodecyl benzene sulfonate, etc. Considering the simultaneous coating of the positive electrode tab glue slurry and the positive electrode slurry, the commonly used solvent for the positive electrode slurry is NMP (N-methylpyrrolidone), so the organic solvent in the positive electrode tab glue is preferably NMP.

[0072] In some specific embodiments, when the positive electrode tab glue is used for the ternary positive electrode and is coated simultaneously with the ternary positive electrode slurry, the molecular weight Mw of the acrylate polymer is 100,000 - 350,000, specifically it can be 100,000, 136,000, 152,000, 178,000, 203,000, 250,000, 277,000, 300,000, 320,000 or 350,000, etc. Or, when the positive electrode tab glue is used for the lithium iron phosphate positive electrode and is coated simultaneously with the lithium iron phosphate slurry, the molecular weight Mw of the acrylate polymer is 200,000 - 350,000, specifically it can be 200,000, 220,000, 240,000, 256,000, 278,000, 300,000, 320,000 or 350,000, etc. In this way, the positive electrode tab glue slurry and the positive electrode slurry can be coated simultaneously without cross-material.

[0073] In the second aspect, the present invention provides a positive electrode tab glue slurry, which includes ceramic particles and the aforementioned positive electrode tab glue. The mass ratio of the ceramic particles to the positive electrode tab glue is (80 - 95):(5 - 20), specifically it can be 80:20, 85:15, 88:12, 92:8 or 95:5, etc. The positive electrode tab glue slurry is obtained by mixing the positive electrode tab glue binder and the ceramic particles in proportion. Preferably, the mass ratio of the ceramic particles to the positive electrode tab glue is (80 - 85):(15 - 20).

[0074] In the third aspect, the present invention provides a positive electrode plate, which includes a functional coating obtained by drying the aforementioned positive electrode tab glue slurry. The positive electrode tab glue slurry and the positive electrode slurry are coated simultaneously and applied on the aluminum foil at the edge of the positive electrode plate. After drying, a positive electrode plate with a functional coating is obtained.

[0075] In the fourth aspect, the present invention provides a secondary battery, which includes a negative electrode plate, a separator, an electrolyte and the aforementioned positive electrode plate.

[0076] The preparation method of the positive electrode tab glue of the present application:

[0077] First, select monomers that meet the requirements of hard / soft segment resins. According to the molecular weight requirements, add a chain transfer agent, preferably dodecyl mercaptan, and the addition amount accounts for 0.02 - 0.05% of the total weight of the monomers. Add 0.1 - 0.8% of organic salts and an appropriate amount of organic solvents based on the total weight of the monomers, mix them, and then add an initiator. The initiator is azobisisobutyronitrile or azobisisoheptonitrile, and the initiator accounts for 1 - 2% of the total weight of the monomers. React at a temperature of 70 - 90 °C for 12 - 20 hours to obtain solutions of hard segment resin and soft segment resin respectively. Mix the solution of hard segment resin and the solution of soft segment resin according to the mass ratio of hard segment resin (total mass of monomers) to soft segment resin (total mass of monomers) of (20 - 35):(65 - 80), react at 90 - 100 °C, and then adjust the amount of NMP solvent to make the solid content 18 - 22% to obtain an acrylate polymer solution, that is, the positive electrode tab glue.

[0078] As mentioned above, the positive electrode tab glue provided by the present invention is applicable to various positive electrode slurries commonly used at present. Among them, the composition and types of positive electrode slurries can adopt various ones commonly used in the prior art.

[0079] For example, the positive electrode slurry includes the following weight components: 90 - 98 parts of positive electrode active material, 0.5 - 3 parts of binder, 1 - 5 parts of conductive agent, and optionally 0 - 0.5 parts of secondary battery additives.

[0080] Use N-methylpyrrolidone solvent to disperse ternary positive electrode active particles lithium nickel cobalt manganese oxide NCM523, conductive carbon black Super P, and binder polyvinylidene fluoride to form a ternary NCM positive electrode slurry. Among them, the mass ratio of positive electrode active particles, conductive agent, and binder is 97.5:1.0:1.5.

[0081] Alternatively, dissolve 3 parts of binder PVDF in 400 parts of N-methylpyrrolidone solvent to prepare a solution, and sequentially add 94 parts of positive electrode active material lithium iron phosphate, 2.6 parts of conductive carbon black, and 0.4 parts of dispersant, with a rotation speed of 120 r / min and stir for 30 min to make the powder materials fully and evenly mixed in the solvent to obtain a lithium iron phosphate positive electrode slurry.

[0082] The following will further explain the specific embodiments of the present invention through examples and comparative examples.

[0083] The reagents, materials, and instruments used in the following description are all conventional reagents, conventional materials, and conventional instruments if not otherwise specified, and can be obtained commercially. The reagents involved can also be synthesized by conventional synthesis methods. The methods in the examples are all conventional methods in the art if not otherwise specified.

[0084] The monomers conforming to this application are commercially available. The glass transition temperature can be selected at the time of purchase or tested independently. For example, it can be detected using a differential scanning calorimeter (DSC). The molecular weight Mw of the acrylate polymer can be determined using gel permeation chromatography (GPC).

[0085] Example 1

[0086] (1) Preparation of the positive terminal lug adhesive:

[0087] Monomer composition of the hard segment resin: 58 parts of styrene, 27 parts of isooctyl acrylate, 15 parts of methacrylic acid (86 g / mol, the monomer forming the first polar structural unit, of which 9.89 parts are used as the first post-reaction monomer), 0.05 part of dodecyl mercaptan;

[0088] Monomer composition of the soft segment resin: 75 parts of isooctyl acrylate, 15 parts of styrene, 3 parts of acrylonitrile (the monomer forming the second polar structural unit), 7 parts of glycidyl methacrylate (142 g / mol, the monomer forming the second polar structural unit and also the second post-reaction monomer), 0.05 part of dodecyl mercaptan;

[0089] In the monomer composition of the hard segment resin, 0.4 part of sodium dodecyl sulfate is added. After mixing with an appropriate amount of NMP solvent, 1 part of azobisisobutyronitrile is added, and the reaction is carried out at 75 °C for 12 hours to obtain a solution of the hard segment resin, whose glass transition temperature Tg is 45.5 °C.

[0090] In the monomer composition of the soft segment resin, 0.4 part of sodium dodecyl sulfate is added. After mixing with an appropriate amount of NMP solvent, 1 part of azobisisobutyronitrile is added, and the reaction is carried out at 75 °C for 12 hours to obtain a solution of the soft segment resin, whose glass transition temperature Tg is -40.3 °C.

[0091] The solution of the hard segment resin and the solution of the soft segment resin are mixed according to the mass ratio of the hard segment resin (total monomer mass) to the soft segment resin (total monomer mass) of 30:70, and then the reaction is carried out at 90 °C. Then, the amount of NMP solvent is adjusted to make the solid content 20% to obtain an acrylate polymer solution, that is, the positive terminal lug adhesive. The molecular weight Mw of the acrylate polymer is 180,000, and the content of the structural unit containing a carboxyl group is 4.52%.

[0092] (2) Positive terminal lug adhesive slurry: The ceramic particles and the prepared positive terminal lug adhesive are mixed according to a mass ratio of 85:15 to obtain the positive terminal lug adhesive slurry.

[0093] (3) Positive electrode slurry: N-methylpyrrolidone solvent is used to disperse ternary positive electrode active particles lithium nickel cobalt manganese oxide NCM523, conductive carbon black Super P, and binder polyvinylidene fluoride to form ternary NCM positive electrode slurry. Among them, the mass ratio of positive electrode active particles, conductive agent, and binder is 97.5:1.0:1.5.

[0094] Take one drop of each of the above positive electrode tab glue slurry and positive electrode slurry, drop them into a container, and make the two slurries contact. If the boundaries of the two drops of slurry are clear and there is no mutual penetration phenomenon, it is determined that there is no cross-mixing; if the boundary is blurred and there is a mutual penetration phenomenon, it is determined that cross-mixing has occurred.

[0095] As Figure 1 shown, the boundary between the positive electrode tab glue slurry 1 and the positive electrode slurry 2 is clear, and no cross-mixing phenomenon has occurred.

[0096] (4) Positive electrode tab: The positive electrode tab glue slurry and ternary positive electrode slurry are simultaneously coated on aluminum foil to prepare a positive electrode tab. The positive electrode tab glue slurry is coated on the aluminum foil at the edge of the positive electrode tab, and after drying, a positive electrode tab with a functional coating is obtained.

[0097] (5) Preparation of lithium-ion secondary battery:

[0098] The negative electrode tab, separator, and electrolyte of the lithium-ion battery prepared by the conventional method in the art, and the positive electrode tab prepared by this application are assembled into a lithium-ion secondary battery according to the general process of preparing a lithium-ion battery.

[0099] Example 2

[0100] The positive electrode tab glue, positive electrode tab glue slurry, positive electrode tab, and lithium-ion secondary battery are prepared according to the method of Example 1. The main difference between Example 2 and Example 1 is that

[0101] In the preparation of the positive electrode tab glue, the types and dosages of organic salts added in the monomer composition of the hard / soft segment resin and the dosage of the chain transfer agent are different. It is 0.1 part of sodium lauryl sulfate and 0.045 part of dodecyl mercaptan, specifically as follows:

[0102] Monomer composition of the hard segment resin: 58 parts of styrene, 27 parts of isooctyl acrylate, 15 parts of methacrylic acid (86 g / mol, the monomer forming the first polar structural unit, and 9.89 parts of which are used as the first post-reaction monomer), 0.045 part of dodecyl mercaptan;

[0103] Monomer composition of the soft segment resin: 75 parts of isooctyl acrylate, 15 parts of styrene, 3 parts of acrylonitrile (the monomer forming the second polar structural unit), 7 parts of glycidyl methacrylate (142 g / mol, the monomer forming the second polar structural unit and also the second post-reaction monomer), 0.045 part of dodecyl mercaptan;

[0104] In the monomer composition of the hard segment resin, 0.1 part of sodium hexadecyl sulfate was added. After mixing with an appropriate amount of NMP solvent, 1 part of azobisisobutyronitrile was added, and the reaction was carried out at 75 °C for 12 hours to obtain a solution of the hard segment resin, and its glass transition temperature Tg was 45.5 °C.

[0105] In the monomer composition of the soft segment resin, 0.1 part of sodium hexadecyl sulfate was added. After mixing with an appropriate amount of NMP solvent, 1 part of azobisisobutyronitrile was added, and the reaction was carried out at 75 °C for 12 hours to obtain a solution of the soft segment resin, and its glass transition temperature Tg was -40.3 °C.

[0106] The positive electrode tab glue was prepared, and the molecular weight Mw of the acrylate polymer was 200,000.

[0107] Example 3

[0108] The positive electrode tab glue, the positive electrode tab glue slurry, the positive electrode sheet and the lithium ion secondary battery were prepared according to the method of Example 1. The main difference between Example 3 and Example 1 was that:

[0109] For the preparation of the positive electrode tab glue, the types and dosages of the organic salts added in the monomer compositions of the hard / soft segment resins and the dosage of the chain transfer agent were different, which were 0.8 part of sodium dodecylbenzenesulfonate and 0.045 part of dodecyl mercaptan, specifically as follows:

[0110] Monomer composition of the hard segment resin: 58 parts of styrene, 27 parts of isooctyl acrylate, 15 parts of methacrylic acid (86 g / mol, the monomer forming the first polar structural unit, and 9.89 parts of which were used as the first post-reaction monomer), 0.045 part of dodecyl mercaptan;

[0111] Monomer composition of the soft segment resin: 75 parts of isooctyl acrylate, 15 parts of styrene, 3 parts of acrylonitrile (the monomer forming the second polar structural unit), 7 parts of glycidyl methacrylate (142 g / mol, the monomer forming the second polar structural unit and also the second post-reaction monomer), 0.045 part of dodecyl mercaptan;

[0112] In the monomer composition of the hard segment resin, 0.8 part of sodium dodecylbenzenesulfonate was added. After mixing with an appropriate amount of NMP solvent, 1 part of azobisisobutyronitrile was added, and the reaction was carried out at 75 °C for 12 hours to obtain a solution of the hard segment resin, and its glass transition temperature Tg was 45.5 °C.

[0113] In the monomer composition of the soft segment resin, 0.8 part of sodium dodecylbenzenesulfonate was added. After mixing with an appropriate amount of NMP solvent, 1 part of azobisisobutyronitrile was added, and the reaction was carried out at 75 °C for 12 hours to obtain a solution of the soft segment resin, and its glass transition temperature Tg was -40.3 °C.

[0114] The positive electrode tab glue was prepared, and the molecular weight Mw of the acrylate polymer was 200,000.

[0115] Example 4

[0116] The positive electrode tab glue, the positive electrode tab glue slurry, the positive electrode sheet and the lithium ion secondary battery were prepared according to the method of Example 1. The main difference between Example 4 and Example 1 is as follows:

[0117] For the preparation of the positive electrode tab glue, the dosage of the chain transfer agent added in the monomer composition of the hard / soft segment resin was different. It was 0.025 parts of dodecyl mercaptan, and the mass ratio of the hard segment resin to the soft segment resin was 20:80. Specifically as follows:

[0118] Monomer composition of the hard segment resin: 58 parts of styrene, 27 parts of isooctyl acrylate, 15 parts of methacrylic acid (86 g / mol, the monomer forming the first polar structural unit, and all of them were used as the first post-reaction monomer), 0.025 parts of dodecyl mercaptan;

[0119] Monomer composition of the soft segment resin: 75 parts of isooctyl acrylate, 15 parts of styrene, 3 parts of acrylonitrile (the monomer forming the second polar structural unit), 7 parts of glycidyl methacrylate (142 g / mol, the monomer forming the second polar structural unit and also the second post-reaction monomer), 0.025 parts of dodecyl mercaptan;

[0120] In the monomer composition of the hard segment resin, 0.4 parts of sodium dodecyl sulfate was added. After mixing with an appropriate amount of NMP solvent, 1 part of azobisisobutyronitrile was added, and the reaction was carried out at 75 °C for 12 hours to obtain a solution of the hard segment resin, and its glass transition temperature Tg was 45.5 °C.

[0121] In the monomer composition of the soft segment resin, 0.4 parts of sodium dodecyl sulfate was added. After mixing with an appropriate amount of NMP solvent, 1 part of azobisisobutyronitrile was added, and the reaction was carried out at 75 °C for 12 hours to obtain a solution of the soft segment resin, and its glass transition temperature Tg was -40.3 °C.

[0122] The solution of the hard segment resin and the solution of the soft segment resin were mixed according to the mass ratio of the hard segment resin (total monomer mass) to the soft segment resin (total monomer mass) of 20:80, and the reaction was carried out at 90 °C. Then, the amount of the NMP solvent was adjusted to make the solid content 20% to obtain an acrylate polymer solution, that is, the positive electrode tab glue.

[0123] The positive electrode tab glue was prepared, and the molecular weight Mw of the acrylate polymer was 350,000, and the content of the structural unit containing a carboxyl group was 3%.

[0124] Example 5

[0125] The positive electrode tab glue, positive electrode tab glue slurry, positive electrode sheet and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between Example 5 and Example 1 is as follows:

[0126] For the preparation of the positive electrode tab glue, the dosage of the chain transfer agent added in the monomer composition of the hard / soft segment resin is different. It is 0.025 parts of dodecyl mercaptan, and the mass ratio of the hard segment resin to the soft segment resin is 35:65. Specifically as follows:

[0127] Monomer composition of the hard segment resin: 58 parts of styrene, 27 parts of isooctyl acrylate, 15 parts of methacrylic acid (86 g / mol, the monomer forming the first polar structural unit, of which 7.87 parts is used as the first post-reaction monomer), 0.025 parts of dodecyl mercaptan;

[0128] Monomer composition of the soft segment resin: 75 parts of isooctyl acrylate, 15 parts of styrene, 3 parts of acrylonitrile (the monomer forming the second polar structural unit), 7 parts of glycidyl methacrylate (142 g / mol, the monomer forming the second polar structural unit and also the second post-reaction monomer), 0.025 parts of dodecyl mercaptan;

[0129] In the monomer composition of the hard segment resin, 0.4 parts of sodium dodecyl sulfate was added. After mixing with an appropriate amount of NMP solvent, 1 part of azobisisobutyronitrile was added, and the reaction was carried out at 75 °C for 12 hours to obtain a solution of the hard segment resin, and its glass transition temperature Tg was 45.5 °C.

[0130] In the monomer composition of the soft segment resin, 0.4 parts of sodium dodecyl sulfate was added. After mixing with an appropriate amount of NMP solvent, 1 part of azobisisobutyronitrile was added, and the reaction was carried out at 75 °C for 12 hours to obtain a solution of the soft segment resin, and its glass transition temperature Tg was -40.3 °C.

[0131] The solution of the hard segment resin and the solution of the soft segment resin were mixed according to the mass ratio of the hard segment resin (total monomer mass) to the soft segment resin (total monomer mass) of 35:65, and the reaction was carried out at 90 °C. Then, the amount of NMP solvent was adjusted to make the solid content 20% to obtain an acrylate polymer solution, that is, the positive electrode tab glue.

[0132] The positive electrode tab glue was prepared, and the molecular weight Mw of the acrylate polymer was 350,000, and the content of the structural unit containing a carboxyl group was 5.25%.

[0133] Example 6

[0134] The positive electrode tab glue, positive electrode tab glue slurry, positive electrode sheet and lithium-ion secondary battery were prepared according to the method of Example 1. The main difference between Example 6 and Example 1 is as follows:

[0135] Preparation of the positive tab glue slurry: The mass ratio of ceramic particles to the positive tab glue is 80:20.

[0136] Example 7

[0137] Prepare the positive tab glue, positive tab glue slurry, positive electrode sheet and lithium-ion secondary battery according to the method of Example 1. The main difference between Example 7 and Example 1 is that:

[0138] Preparation of the positive tab glue slurry: The mass ratio of ceramic particles to the positive tab glue is 95:5.

[0139] Comparative Example 1

[0140] The difference between Comparative Example 1 and Example 1 is that: A positive tab glue of the PVDF system is selected.

[0141] Test whether the positive tab glue and the positive electrode slurry of this comparative example are mixed according to the method of Example 1. As Figure 2 shown, the boundary between the positive tab glue slurry 1 and the positive electrode slurry 2 is blurred, and mutual penetration occurs, resulting in mixing.

[0142] Comparative Example 2

[0143] Prepare the positive tab glue, positive tab glue slurry, positive electrode sheet and lithium-ion secondary battery according to the method of Example 1. The difference between Comparative Example 2 and Example 1 is that: There is no organic salt in the positive tab glue.

[0144] Comparative Example 3

[0145] Prepare the positive tab glue, positive tab glue slurry, positive electrode sheet and lithium-ion secondary battery according to the method of Example 1. The difference between Comparative Example 3 and Example 1 is that: The weight percentage of the organic salt in the acrylate polymer is 1%, specifically as follows:

[0146] In the monomer composition of the hard segment resin, add 1 part of sodium dodecyl sulfate, mix with an appropriate amount of NMP solvent, then add 1 part of azobisisobutyronitrile, and react at 75 °C for 12 hours to obtain a solution of the hard segment resin, and its glass transition temperature Tg is 45.5 °C.

[0147] In the monomer composition of the soft segment resin, add 1 part of sodium dodecyl sulfate, mix with an appropriate amount of NMP solvent, then add 1 part of azobisisobutyronitrile, and react at 75 °C for 12 hours to obtain a solution of the soft segment resin, and its glass transition temperature Tg is -40.3 °C.

[0148] Comparative Example 4

[0149] Prepare the positive electrode tab glue, positive electrode tab glue slurry, positive electrode sheet and lithium-ion secondary battery according to the method of Example 1. The difference between Comparative Example 4 and Example 1 is as follows: In the preparation of the positive electrode tab glue, the dosage of the chain transfer agent added to the monomer composition of the hard / soft segment resin is different, which is 0.1 part of dodecyl mercaptan, and the molecular weight Mw of the acrylate polymer is 50,000. The monomer compositions of the hard segment and soft segment resins are specifically as follows:

[0150] Monomer composition of the hard segment resin: 58 parts of styrene, 27 parts of isooctyl acrylate, 15 parts of methacrylic acid (86 g / mol, the monomer forming the first polar structural unit, of which 9.89 parts are used as the first post-reaction monomer), 0.1 part of dodecyl mercaptan;

[0151] Monomer composition of the soft segment resin: 75 parts of isooctyl acrylate, 15 parts of styrene, 3 parts of acrylonitrile (the monomer forming the second polar structural unit), 7 parts of glycidyl methacrylate (142 g / mol, the monomer forming the second polar structural unit and also the second post-reaction monomer), 0.1 part of dodecyl mercaptan.

[0152] Comparative Example 5

[0153] Prepare the positive electrode tab glue, positive electrode tab glue slurry, positive electrode sheet and lithium-ion secondary battery according to the method of Example 1. The difference between Comparative Example 5 and Example 1 is as follows: In the preparation of the positive electrode tab glue, the dosage of the chain transfer agent added to the monomer composition of the hard / soft segment resin is different, which is 0.01 part of dodecyl mercaptan, and the molecular weight Mw of the acrylate polymer is 400,000. The monomer compositions of the hard segment and soft segment resins are specifically as follows:

[0154] Monomer composition of the hard segment resin: 58 parts of styrene, 27 parts of isooctyl acrylate, 15 parts of methacrylic acid (86 g / mol, the monomer forming the first polar structural unit, of which 9.89 parts are used as the first post-reaction monomer), 0.01 part of dodecyl mercaptan;

[0155] Monomer composition of the soft segment resin: 75 parts of isooctyl acrylate, 15 parts of styrene, 3 parts of acrylonitrile (the monomer forming the second polar structural unit), 7 parts of glycidyl methacrylate (142 g / mol, the monomer forming the second polar structural unit and also the second post-reaction monomer), 0.01 part of dodecyl mercaptan.

[0156] Comparative Example 6

[0157] Prepare the positive electrode tab glue, positive electrode tab glue slurry, positive electrode sheet and lithium-ion secondary battery according to the method of Example 1. The difference between Comparative Example 6 and Example 1 is as follows: The mass ratio of the hard segment resin to the soft segment resin in the acrylate polymer is 60:40.

[0158] Performance test:

[0159] Perform performance tests on the positive electrode tab glue slurry, positive electrode sheet, and secondary battery prepared in the above examples and comparative examples.

[0160]

Strand mixing

[0161]

Dry adhesion peel strength with foil

[0162] Cut the positive electrode sheet prepared in this application into strips of 20 * 100 mm, press them for 60 s under the conditions of 100 °C and 8 Mwa, and use an electronic tensile machine (Dazhong Instruments Co., Ltd., Dongguan City, model DZ-101) to test the coating peel strength.

[0163]

Wet adhesion peel strength with foil

[0164]

Dry adhesion peel strength with separator

[0165]

Wet adhesion peel strength with separator

[0166]

Internal resistance of the battery cell

[0167]

High-temperature storage capacity retention rate

[0168]

High-rate cycling capacity retention rate

[0169] For the batteries prepared in the above examples and comparative examples, at a temperature of 25°C ± 2°C, discharge the battery at a constant current of 0.5C until the voltage reaches 2.75V, then charge it at a constant current of 1C until the voltage reaches 4.3V, and then charge it at a constant voltage until the cut-off current is 0.05C to obtain a fully charged battery. Subsequently, discharge it at a current of 1C until the voltage reaches 2.75V, and record the discharge capacity C2 of the battery; then, charge it at a constant current of 2C until the voltage reaches 4.3V, and then charge it at a constant voltage until the cut-off current is 0.05C to obtain a fully charged battery. Subsequently, discharge it at a constant current of 2C until the voltage reaches 2.75V. Cycle it 500 times at 2C in this way, and record the discharge capacity of the battery after cycling as C3. Then, the high-rate cycling capacity retention rate (%) = C3 / C2 × 100%.

[0170] The performance test results are shown in Table 1.

[0171] Table 1:

[0172] It can be seen from the test results of Examples 1 to 7 and Comparative Example 1 that in this application, an acrylate polymer system is used to replace the traditional PVDF system as the positive electrode tab adhesive, which can improve the adhesion between the aluminum foil and the separator, especially the wet adhesion peel strength, thereby improving the processing performance and safety of the battery, and improving the cycle performance of the battery core.

[0173] It can be seen from the test results of Examples 1 to 3 and Comparative Examples 2 to 3 that in the positive electrode tab adhesive, when the weight percentage of the organic salt in the acrylate polymer > 0.8%, the positive electrode tab slurry and the positive electrode slurry penetrate each other (stringing), which affects the specific capacity of the main material, and the capacity decreases during high-temperature storage and high-rate cycling. When no organic salt is added to the positive electrode tab adhesive, the wettability of the slurry decreases, resulting in missed coating during coating, and the test battery core shows a short circuit. After analysis, it is found that the burrs during die-cutting pierce the separator. When the weight percentage of the organic salt in the acrylate polymer is 0.4% - 0.8%, the performance is better.

[0174] As can be seen from the test results of Examples 1 to 5 and Comparative Examples 4 to 5, when the molecular weight Mw of the acrylate polymer is less than 1 million, mutual penetration (material mixing) occurs between the positive electrode tab paste and the positive electrode paste, which affects the specific capacity of the main material, and the capacity decreases during high-temperature storage and high-rate cycling; when the molecular weight Mw of the acrylate polymer is greater than 3.5 million, due to the too large molecular weight, the chain segment movement is difficult during hot pressing, resulting in a decrease in the wet adhesion peeling strength with the separator, and the capacity also decreases during high-temperature storage and high-rate cycling.

[0175] As can be seen from the test results of Example 1, Examples 4 to 5 and Comparative Example 6, when the proportion of the soft segment resin is relatively large, the wet adhesion peeling strengths with the foil and the separator are both significantly reduced, the dry adhesion peeling strength with the separator increases, and the capacity also decreases during high-temperature storage and high-rate cycling. When the mass ratio of the hard segment resin to the soft segment resin is (20 - 35):(65 - 80), the performance is better.

[0176] As can be seen from the test results of Example 1 and Examples 6 to 7, when the mass ratio of the ceramic particles to the positive electrode tab glue in the positive electrode tab glue paste is (80 - 85):(15 - 20), the performance in all aspects is better.

[0177] Thus, it can be seen that the positive electrode tab glue of the acrylate polymer solution provided by the present invention can improve the wet adhesion strength. At the same time, the acrylate polymer solution has good flexibility, can effectively improve the curling of the aluminum foil. At the same time, due to its high wet adhesion strength, the processing performance and safety of the battery are improved, and the cycle performance of the battery cell is improved.

[0178] The above further describes the present invention with the aid of specific embodiments. However, it should be understood that the specific descriptions herein should not be construed as limiting the essence and scope of the present invention. Various modifications made by those of ordinary skill in the art to the above embodiments after reading this specification all fall within the scope protected by the present invention.

Claims

1. A positive electrode tab glue, characterized in that, The positive electrode tab glue comprises an acrylate polymer, an organic salt, and an organic solvent. The organic salt includes at least one of alkyl sulfonate, alkyl sulfate, and alkyl benzene sulfonate. The organic solvent includes NMP. The molecular weight Mw of the acrylate polymer is 100,000 to 350,000, and the weight percentage of the organic salt in the acrylate polymer is 0.1% to 0.8%. The acrylate polymer includes a hard segment resin and a soft segment resin. The glass transition temperature Tg of the hard segment resin is ≥ 20°C, and the glass transition temperature Tg of the soft segment resin is ≤ 0°C. The mass ratio of the hard segment resin to the soft segment resin is (20 to 35):(65 to 80). The hard segment resin includes a first main structural unit and a first polar structural unit. The soft segment resin further includes a second main structural unit and a second polar structural unit. The first main structural unit and the second main structural unit both include acrylate structural units and aromatic vinyl structural units. The first polar structural unit and the second polar structural unit are independently selected from structural units containing polar groups. The polar groups include one or more of carboxyl, cyano, hydroxyl, and epoxy groups. The mass ratio of the first main structural unit to the first polar structural unit is (80 to 97):(3 to 20). The mass ratio of the second main structural unit to the second polar structural unit is (75 to 97):(3 to 25). The content of the structural unit containing carboxyl in the acrylate polymer is 2 to 15 wt%. The first polar structural unit in the hard segment resin includes a first post-reaction structural unit and other polar structural units. The second polar structural unit in the soft segment resin includes a second reaction structural unit and other polar structural units. When the post-reaction group in the first post-reaction structural unit is carboxyl, the post-reaction group in the second post-reaction structural unit is epoxy.

2. The positive electrode tab glue according to claim 1, wherein The glass transition temperature Tg of the hard segment resin is 20 to 90°C, and the glass transition temperature Tg of the soft segment resin is -60 to 0°C.

3. The positive electrode tab glue according to claim 1, wherein The first post-reaction structural unit and the second post-reaction structural unit are connected to each other by chemical bonds.

4. The positive electrode tab glue according to claim 1, wherein The first polar structural unit in the hard segment resin is the same as the first post-reaction structural unit, and the second polar structural unit in the soft segment resin is the same as the second reaction structural unit.

5. The positive electrode tab glue according to claim 1, wherein The solid content of the positive electrode tab glue is 18 to 22%.

6. A positive electrode tab glue paste, characterized in that, It includes ceramic particles and the positive electrode tab glue according to any one of claims 1 to 5. The mass ratio of the ceramic particles to the positive electrode tab glue is (80 to 95):(5 to 20).

7. A positive electrode sheet, characterized in that, It includes a functional coating obtained by drying the positive electrode tab glue slurry according to claim 6.

8. A secondary battery, characterized in that, It includes a negative electrode sheet, a separator, an electrolyte, and the positive electrode sheet according to claim 7.

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