An ear tab glue, a negative electrode sheet and a lithium-ion battery

Abstract

The present invention provides a tab glue, a negative electrode sheet and a lithium-ion battery. The tab glue is an emulsion, the surface tension of the emulsion is 45-60 mN / m, and the viscosity is 2000 mPa·s or more. This tab glue is beneficial to reducing the capacity loss of the lithium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, relates to a tab glue, and particularly relates to a tab glue, a negative electrode sheet and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric bicycles, electric vehicles, aerospace and other fields due to their advantages such as high energy density, long cycle life, low self-discharge rate, wide operating temperature range, and environmental friendliness.

[0003] During the processing of lithium-ion batteries, the negative electrode sheet therein often needs to be die-cut for welding tabs; however, during the die-cutting process, burrs may appear at the edges of the negative electrode current collector copper foil, and such metal burrs may cause short circuits during the operation of the battery, resulting in battery abnormalities. Currently, an insulating layer (usually including ceramic particles and tab glue) is generally coated on the edge area of the copper foil to effectively avoid the appearance of burrs and improve battery safety; moreover, in some special batteries, such as blade batteries, in order to prevent misalignment between the electrode sheet and the separator during shell insertion, the tab glue in the ceramic layer is also required to bond the separator and the electrode sheet.

[0004] Currently, the tab glue for the negative electrode is generally an aqueous emulsion binder. This emulsion binder uses water as the dispersion medium and has characteristics such as high environmental friendliness, safety, and adhesiveness; however, it often causes a decrease in the battery capacity. Summary of the Invention

[0005] Aiming at the defect that the existing emulsion-type aqueous tab glue causes a decrease in battery capacity, the present invention provides a tab glue, which is beneficial to suppressing battery capacity loss.

[0006] The present invention also provides a negative electrode sheet including the above-mentioned tab glue. Therefore, when this negative electrode sheet is applied to a lithium-ion battery, the capacity loss can be effectively reduced.

[0007] The present invention also provides a lithium-ion battery. This battery includes the above-mentioned tab glue or the above-mentioned negative electrode sheet. Therefore, this battery has high cycle performance.

[0008] In the first aspect of the present invention, a tab glue is provided. The tab glue is an emulsion, and the surface tension of the emulsion is 45-60 mN / m, and the viscosity is 2000 mPa·s or more.

[0009] Generally, when preparing the electrode sheet, it is necessary to first coat the electrode slurry on the surface of the current collector, and a part of the blank current collector is reserved at the edge of the coated area of the electrode slurry for forming the tab. Then, an insulating slurry containing tab glue is coated on this blank area to form an insulating layer, and there is an overlapping area between this insulating layer and the coated area of the electrode slurry. However, the applicant has found that emulsifiers are usually required in existing emulsion-type tab glues to stabilize the latex particle micelles, and the emulsifiers are usually difficult to remove and will cause cross-mixing between the insulating slurry and the electrode slurry, resulting in loss of electrode capacity. By controlling the surface tension and viscosity of the tab glue emulsion within the above ranges, the present invention can effectively inhibit the occurrence of cross-mixing, thereby inhibiting the loss of electrode capacity.

[0010] The tab glue as described above, wherein the solid content of the tab glue is 20-25%.

[0011] The tab glue as described above, wherein the tab glue comprises a polymer, the polymer comprises a first polymer segment and a second polymer segment, the glass transition temperature Tg of the first polymer segment is ≥50 °C, and the glass transition temperature Tg of the second polymer segment is ≤ -30 °C.

[0012] When the tab glue contains polymer segments with different glass transition temperatures as described above, it is very beneficial to improve the bonding strength.

[0013] The tab glue as described above, wherein the first polymer segment comprises a first main structural unit, the first main structural unit is an acrylic structural unit, the second polymer segment comprises a second main structural unit, and the second main structural unit is an acrylate structural unit;

[0014] The first polymer segment further comprises a strongly polar structural unit, and the strongly polar structural unit comprises at least one of structural units containing carboxyl, hydroxyl, cyano, and amide groups;

[0015] The second polymer segment further comprises a weakly polar structural unit, and the weakly polar structural unit comprises at least one of structural units containing aromatic groups and ester groups.

[0016] In the present invention, when the glass transition temperatures of the first polymer segment and the second polymer segment are respectively within the above ranges, and at the same time the first polymer segment and the second polymer segment each contain the aforementioned groups, when this tab glue is used for the negative electrode sheet, the polymer in the tab glue can not only form a strong bonding force with the negative electrode current collector and the separator to achieve a high peel strength, but also has good wettability with the electrolyte, which helps to reduce the internal resistance of the battery cell and improve its high-temperature storage performance and cycling performance.

[0017] The tab glue as described above, wherein, in the polymer, the mass ratio of the first polymer segment to the second polymer segment is (5 to 30):(70 to 95).

[0018] The tab glue as described above, wherein the first polymer segment includes a first reactive structural unit, the second polymer segment includes a second reactive structural unit, and the first reactive structural unit and the second reactive structural unit can undergo a polymerization reaction under heating conditions.

[0019] The tab glue as described above, wherein the first reactive structural unit and the second reactive structural unit are each independently selected from one or more of a hydroxyl group, an isocyanate group, an epoxy group, and a carboxyl group.

[0020] The tab glue as described above, wherein the mass content of the first reactive structural unit in the first polymer segment is 3 to 10%;

[0021] and / or, the mass content of the second reactive structural unit in the second polymer segment is 3 to 10%.

[0022] The second aspect of the present invention provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer provided on at least a part of the surface of the negative electrode current collector; an insulating layer is further provided on the surface of the negative electrode current collector, and the insulating layer is prepared from an insulating layer slurry including the tab glue of the first aspect.

[0023] The third aspect of the present invention provides a lithium-ion battery, which includes the negative electrode sheet of the second aspect. Specific Embodiments

[0024] To make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. 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 scope of protection of the present invention.

[0025] The first aspect of the present invention provides a tab glue, which is an emulsion, and the surface tension of the emulsion is 45 to 60 mN / m, and the viscosity is 2000 mPa·s or more.

[0026] By controlling the surface tension and viscosity of the tab glue emulsion within the above ranges, the present invention can effectively inhibit the occurrence of stringing, thereby inhibiting the loss of electrode capacity.

[0027] Preferably, the surface tension of the emulsion is 45 to 60 mN / m, more preferably 50 to 55 mN / m. Specifically, it can be 45 mN / m, 46 mN / m, 47 mN / m, 48 mN / m, 49 mN / m, 50 mN / m, 51 mN / m, 52 mN / m, 53 mN / m, 54 mN / m, 55 mN / m, 56 mN / m, 57 mN / m, 58 mN / m, 59 mN / m or 60 mN / m.

[0028] In the present invention, the "surface tension" of the tab glue emulsion can be measured by a surface tensiometer, and the "viscosity" of the tab glue emulsion can be measured by a viscometer.

[0029] In the present invention, the viscosity of the tab glue is 2000 mPa·s or more, more preferably 2000 to 8000 mPa·s. Specifically, the viscosity of the tab glue can be 2000 mPa·s, 2500 mPa·s, 3000 mPa·s, 3500 mPa·s, 4000 mPa·s, 4500 mPa·s, 5000 mPa·s, 5500 mPa·s, 6000 mPa·s, 6500 mPa·s, 7000 mPa·s, 7500 mPa·s or 8000 mPa·s.

[0030] In a specific embodiment, the solid content of the tab glue is 20 to 25%. Preferably, the solid content is 21 to 23%. Specifically, the solid content of the tab glue can be 20%, 21%, 22%, 23%, 24% or 25%.

[0031] To further improve the bonding strength of the tab glue, preferably, the tab glue includes a polymer, and the polymer includes a first polymer segment and a second polymer segment. The glass transition temperature Tg of the first polymer segment is ≥50 °C, and the glass transition temperature Tg of the second polymer segment is ≤ -30 °C.

[0032] When the tab glue contains polymer segments with different glass transition temperatures as described above, it is very beneficial to improve the bonding strength of the tab glue.

[0033] Specifically, the glass transition temperature Tg of the first polymer segment is 50 to 110 °C; the glass transition temperature Tg of the second polymer segment is -50 to -30 °C.

[0034] The "glass transition temperature Tg" in the present invention refers to the temperature corresponding to the transition from the glassy state to the high elastic state, and can be measured by differential scanning calorimetry (DSC).

[0035] Exemplarily, the glass transition temperature Tg of the first polymer segment is 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C or 110°C.

[0036] Exemplarily, the glass transition temperature Tg of the second polymer segment is -50°C, -48°C, -46°C, -44°C, -42°C, -40°C, -38°C, -36°C, -34°C, -32°C or -30°C.

[0037] In a specific embodiment, in the polymer, the mass ratio of the first polymer segment to the second polymer segment is (5 - 30):(70 - 95), and specifically can be 5:95, 10:90, 15:85, 20:80, 25:75 or 30:70.

[0038] In the present invention, when there is too much of the first polymer segment, it is not conducive to further improving the bonding strength between the polymer in the tab glue and the separator; while when there is too much of the second polymer segment, it is not conducive to further improving the bonding strength between the polymer in the tab glue and the negative current collector, especially it may increase the risk of falling off after being soaked in the electrolyte. When the mass ratio of the first polymer segment to the second polymer segment is within the aforementioned range, the tab glue can form a strong bonding strength with the separator and the negative current collector, and is not easy to fall off after being soaked in the electrolyte.

[0039] The specific material types of the above-mentioned first polymer segment and second polymer segment can be adjusted according to actual needs. In the present invention, preferably, the first polymer segment includes a first main structural unit, and the first main structural unit is an acrylic structural unit; the second polymer segment includes a second main structural unit, and the second main structural unit is an acrylate structural unit.

[0040] Specifically, the acrylic structural unit is selected from one or more of an acrylic acid structural unit, a methacrylic acid structural unit, an ethylacrylic acid structural unit, a propylacrylic acid structural unit, a fluoroacrylic acid structural unit, a cyanoacrylic acid structural unit, an aminoacrylic acid structural unit, and a hydroxypropylacrylic acid structural unit.

[0041] The acrylate structural unit is selected from at least one of a methyl acrylate structural unit, an ethyl acrylate structural unit, a n-propyl acrylate structural unit, an isopropyl acrylate structural unit, a n-butyl acrylate structural unit, an isobutyl acrylate structural unit, a tert-butyl acrylate structural unit, a n-pentyl acrylate structural unit, an isopentyl acrylate structural unit, a n-hexyl acrylate structural unit, a n-octyl acrylate structural unit, an isooctyl acrylate structural unit, an isobornyl acrylate structural unit, a phenoxyethyl acrylate structural unit, a dicyclopentenyl acrylate structural unit, a cyclohexyl acrylate structural unit, a benzyl acrylate structural unit, a methyl methacrylate structural unit, an ethyl methacrylate structural unit, a n-propyl methacrylate structural unit, an isopropyl methacrylate structural unit, a n-butyl methacrylate structural unit, an isobutyl methacrylate structural unit, a tert-butyl methacrylate structural unit, a n-pentyl methacrylate structural unit, an isopentyl methacrylate structural unit, a n-hexyl methacrylate structural unit, an isooctyl methacrylate structural unit, an isobornyl methacrylate structural unit, a phenoxyethyl methacrylate structural unit, a dicyclopentenyl methacrylate structural unit, a cyclohexyl methacrylate structural unit, a benzyl methacrylate structural unit, an ethylene glycol diacrylate structural unit, an ethylene glycol dimethacrylate structural unit, an ethoxylated ethylene glycol diacrylate structural unit, an ethoxylated ethylene glycol dimethacrylate structural unit, an allyl methacrylate structural unit, a diallyl phthalate structural unit, a diallyl adipate structural unit, a trimethylolpropane triacrylate structural unit, a trimethylolpropane trimethacrylate structural unit, a pentaerythritol diacrylate structural unit, a pentaerythritol dimethacrylate structural unit, a pentaerythritol triacrylate structural unit, and a pentaerythritol trimethacrylate structural unit.

[0042] Furthermore, the first polymer segment further includes a strongly polar structural unit, and the strongly polar structural unit includes at least one of a structural unit containing a carboxyl group, a hydroxyl group, a cyano group, and an amide group; the second polymer segment further includes a weakly polar structural unit, and the weakly polar structural unit includes at least one of a structural unit containing an aromatic group and an ester group.

[0043] In the present invention, the strongly polar structural unit in the first polymer segment can be obtained by adding a monomer containing a corresponding strongly polar group (i.e., at least one of a carboxyl group, a hydroxyl group, a cyano group, and an amide group) during the formation of the first polymer segment; the weakly polar structural unit in the second polymer segment can be obtained by adding a monomer containing a corresponding weakly polar group (i.e., at least one of an aromatic group and an ester group) during the formation of the second polymer segment.

[0044] For example, the carboxyl, hydroxyl, cyano, and amide groups in the first polymer segment can be introduced correspondingly through one or more of acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxybutyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, and hydroxymethyl acrylamide; the aromatic and ester groups in the second polymer segment can be introduced correspondingly through one or more of styrene, methylstyrene, ethyl acrylate, butyl acrylate, isooctyl acrylate, and lauryl acrylate.

[0045] The content of the strongly polar structural units in the first polymer segment can vary within a wide range. Preferably, the mass ratio of the first main structural unit to the strongly polar structural unit is (50~95):(2~40).

[0046] The content of the weakly polar structural units in the second polymer segment can vary within a wide range. Preferably, the mass ratio of the second main structural unit to the weakly polar structural unit is (50~95):(2~40).

[0047] The content of the strongly polar structural units in the first polymer segment mentioned above is the ratio of the weight of the strongly polar monomers corresponding to the formation of the strongly polar structural units to the weight of the monomers corresponding to the formation of the first main structural unit among the raw material monomers for preparing the first polymer segment. Similarly, the content of the weakly polar structural units in the second polymer segment mentioned above is the ratio of the weight of the weakly polar monomers corresponding to the formation of the weakly polar structural units to the weight of the monomers corresponding to the formation of the second main structural unit among the raw material monomers for preparing the second polymer segment.

[0048] It can be understood that when the strongly polar structural units in the first polymer segment are acrylic acid-based structural units and / or methacrylic acid-based structural units, at this time, the strongly polar groups are the same as the first main structural unit, and there is no need to distinguish between the strongly polar structural units and the first main structural unit; and in the first polymer segment, the total content of the acrylic acid-based structural units and / or methacrylic acid-based structural units is the sum of the contents of the strongly polar structural units and the first main structural unit defined in the present invention.

[0049] Similarly, when the weakly polar structural units in the second polymer segment are acrylate-based structural units and / or methacrylate-based structural units, at this time, the weakly polar groups are the same as the second main structural unit, and there is no need to distinguish between the weakly polar structural units and the second main structural unit; and in the second polymer segment, the total content of the acrylate-based structural units and / or methacrylate-based structural units is the sum of the contents of the weakly polar structural units and the second main structural unit defined in the present invention.

[0050] In the present invention, when the glass transition temperatures of the first polymer segment and the second polymer segment are respectively within the above ranges, and the first polymer segment and the second polymer segment each further contain the aforementioned groups, the polymer in the tab glue can not only form a strong adhesion force with the negative current collector and the separator, achieving a high peel strength, but also has good wettability with the electrolyte, which helps to reduce the internal resistance of the battery cell, improve its high-temperature storage performance and cycling performance.

[0051] According to the present invention, the first polymer segment further includes a first reactive structural unit, and the second polymer segment further includes a second reactive structural unit. The first reactive structural unit and the second reactive structural unit can undergo a polymerization reaction under heating conditions.

[0052] Specifically, the first reactive structural unit and the second reactive structural unit are each independently selected from one or more of a hydroxyl group, an isocyanate group, an epoxy group, and a carboxyl group.

[0053] It can be understood that among the above reactive structural units, the hydroxyl group and the hydroxyl group, the hydroxyl group and the isocyanate group, the hydroxyl group and the epoxy group, and the carboxyl group and the epoxy group are paired as a combination that reacts with each other. That is, when the first reactive structural unit or the second reactive structural unit is a hydroxyl group, the other reactive structural unit is selected from at least one of a hydroxyl group, an isocyanate group, and an epoxy group; when the first reactive structural unit or the second reactive structural unit is a carboxyl group, the other reactive structural unit is selected from an epoxy group, and vice versa.

[0054] As a specific example, the first reactive structural unit and the second reactive structural unit are each independently selected from at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxypropyl methacrylate, hydroxymethylacrylamide, blocked isocyanate curing agent, epoxy resin, acrylic acid, methacrylic acid, and β-acryloyloxypropionic acid.

[0055] In the present invention, the contents of the first reactive structural unit and the second reactive structural unit can vary within a relatively large range. Preferably, the mass content of the first reactive structural unit in the first polymer segment is 3-10%. Similarly, the mass content of the second reactive structural unit in the second polymer segment is 3-10%.

[0056] The present invention does not specifically limit the temperature at which the first reactive structural unit and the second reactive structural unit undergo a polymerization reaction, and a suitable reaction temperature can be selected according to the actual situation. For example, the temperature of the polymerization reaction is 100-110 °C.

[0057] In the present invention, if the contents of the above-mentioned first reactive structural unit and second reactive structural unit are too high, it is not conducive to the stable storage of the tab glue emulsion, and to a certain extent, it affects the bonding strength between the tab glue and the negative current collector and the separator. When the mass content of the first reactive structural unit in the first polymer segment is within the foregoing range, and the mass content of the second reactive structural unit in the second polymer segment is within the foregoing range, the bonding strength between the tab glue and the negative current collector and the separator can be further improved.

[0058] Exemplarily, the mass content of the above-mentioned first reactive structural unit in the first polymer segment is 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%; the mass content of the above-mentioned second reactive structural unit in the second polymer segment is 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0059] Similar to the foregoing polar structural unit, the content of the above-mentioned first reactive structural unit is the ratio of the weight of the first reactive monomer corresponding to the formation of the first reactive structural unit to the weight of the monomer corresponding to the formation of the first polymer segment among the raw material monomers for preparing the first polymer segment. Similarly, the content of the above-mentioned second reactive structural unit is the ratio of the weight of the second reactive monomer corresponding to the formation of the second reactive structural unit to the weight of the monomer corresponding to the formation of the second polymer segment among the raw material monomers for preparing the second polymer segment.

[0060] When the first polymer segment and the second polymer segment contain the above-mentioned reactive structural units, the bonding strength of the tab glue to the separator and the negative current collector can be further improved.

[0061] The present invention does not specifically limit the sources of the first polymer segment and the second polymer segment. Polymers conforming to the present invention can be obtained by purchasing, or can be prepared by oneself. In one embodiment, it can be obtained by soap-free emulsion polymerization.

[0062] In one embodiment, the preparation method of the first polymer segment includes the following steps:

[0063] Mix the raw materials including acrylic monomers, monomers containing strong polar groups, and the first reactive monomer in the required proportions to obtain a monomer mixture; mix the monomer mixture with water at a volume ratio of 1: (3-5) to obtain a mixed solution; heat the foregoing mixed solution to 70-95 °C, then add an initiator, the mass of the initiator is 5-10 wt% of the mass of the monomer mixture, keep the temperature for reaction for 7-9 h, and keep stirring during the reaction, the stirring speed is 100-450 r / min, to obtain the first polymer segment.

[0064] The preparation method of the second polymer segment can be as follows: Mix acrylate monomers, monomers containing weakly polar groups, and second reactive monomers in the required proportions to obtain a monomer mixture; mix the monomer mixture with water at a volume ratio of 1: (3 - 5) to obtain a mixed solution; then heat the aforementioned mixed solution to 70 - 95 °C, add an initiator, where the mass of the initiator is 5 - 10 wt% of the mass of the monomer mixture, and keep the reaction at a constant temperature for 7 - 9 h. Stir during the reaction process, and the stirring speed is 100 - 450 r / min to obtain the second polymer segment.

[0065] The present invention does not specifically limit the type of initiator, and conventional water-soluble initiators in the art can be used. For example, at least one of persulfate initiators and azo initiators can be selected; among them, the persulfate initiator can be potassium persulfate (K2S2O8) or sodium persulfate (Na2S2O8), and the azo initiator can be 4,4'-azobis(4-cyanovaleric acid).

[0066] The present invention does not specifically limit the heating method during the reaction of the first polymer segment and the second polymer segment, and conventional methods in the art can be used for heating. For example, heating can be carried out by means of water bath heating.

[0067] The second aspect of the present invention provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer provided on at least a part of the surface of the negative electrode current collector; an insulating layer is further provided on the surface of the negative electrode current collector, and the insulating layer is prepared from an insulating layer slurry including the tab glue of the first aspect.

[0068] As in the existing technology, the above negative electrode current collector is a copper foil.

[0069] The present invention does not specifically limit the preparation method of the negative electrode sheet. In one embodiment, it can be prepared by including the following method:

[0070] Uniformly mix the negative electrode active material, binder, conductive agent, and solvent according to a preset mass ratio to obtain a negative electrode active slurry; uniformly mix ceramic particles, the tab glue of the first aspect, and a dispersant to obtain an insulating layer slurry; coat the aforementioned negative electrode active slurry and insulating layer slurry on the negative electrode current collector, and obtain the negative electrode sheet after drying, rolling, and slitting.

[0071] The present invention does not specifically limit the types of the negative electrode active material, binder, conductive agent, and solvent, and appropriate materials can be selected according to actual situations.

[0072] For example, the negative electrode active material includes at least one of hard carbon, graphite, and silicon-carbon materials.

[0073] The binder includes at least one of styrene-butadiene rubber (SBR), acrylic acid (PAA), and styrene-acrylic emulsion.

[0074] The conductive agent includes at least one of carbon black, graphite, carbon nanotubes, and Ketjen black.

[0075] The solvent is mainly deionized water, or a small amount of plasticizer such as N-methylpyrrolidone (NMP) is added.

[0076] Generally, the surface tension of the negative electrode active paste is 55-60 mN / m, and the difference between the surface tension of the tab glue and the surface tension of the negative electrode active paste is within 10 mN / m.

[0077] In a specific embodiment, the insulating layer includes a binder, ceramic particles, and a dispersant; wherein, the binder is formed by the polymer in the tab glue of the first aspect; the mass ratio of the ceramic particles, the binder, and the dispersant is (60-90):(10-40):1. Exemplarily, the mass ratio of the ceramic particles, the tab glue (calculated based on the solid content in the tab glue), and the dispersant is 60:40:1, 65:35:1, 70:30:1, 75:25:1, 80:20:1, 85:15:1, or 90:10:1.

[0078] The present invention does not specifically limit the types of the ceramic particles and the dispersant. For example, the ceramic particles mainly include boehmite and / or alumina, and the dispersant mainly includes polyacrylate and / or sodium carboxymethyl cellulose (CMC).

[0079] The present invention does not specifically limit the sources of the ceramic particles and the dispersant, and commercially available products or products prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0080] When the insulating layer includes the ceramic particles, the tab glue, and the dispersant in the aforementioned mass ratio, an insulating layer paste with normal slurry fineness, no stringing during coating, no sticking to the roller during over-roller winding, and capable of bonding the electrode sheet and the separator during hot pressing can be prepared.

[0081] The third aspect of the present invention provides a lithium-ion battery, which includes the negative electrode sheet of the second aspect. This lithium-ion battery has a lower internal resistance, a higher capacity, and a better cycle performance.

[0082] It can be understood that the lithium-ion battery in the present invention further includes a positive electrode sheet, a separator, and an electrolyte.

[0083] The present invention does not specifically limit the positive electrode sheet. The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer provided on at least part of the surface of the positive electrode current collector. The positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder.

[0084] Among them, the positive electrode current collector can be selected from the commonly used current collectors in the art. For example, aluminum foil is selected.

[0085] The positive electrode active material includes at least one of lithium cobalt oxide (LCO), lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese cobalt oxide (NMC), lithium iron phosphate (LFP), and sulfurized polyarylamide (SPC).

[0086] The conductive agent includes at least one of graphite, acetylene black, conductive carbon black, conductive carbon fiber, metal oxide, conductive polymer, carbon nanotube, and graphene; wherein, the metal oxide includes at least one of titanium dioxide, manganese dioxide, and nickel oxide, and the conductive polymer includes polypyrrole (PPy) and / or polyaniline (PAn).

[0087] The binder includes at least one of polyvinylidene fluoride (PVDF) and polyacrylate.

[0088] The present invention does not specifically limit the mass contents of the positive electrode active material, binder, and conductive agent in the positive electrode active layer, and appropriate mass ratios can be selected according to actual needs.

[0089] The present invention does not specifically limit the type of the separator, and it can be a commonly used separator material in the art. For example, any one of a polypropylene separator (PP), a polyethylene separator (PE), a polypropylene / polyethylene double-layer composite film (PP / PE), a polypropylene / polyethylene / polypropylene three-layer composite film (PP / PE / PP), and a separator with a ceramic coating can be selected.

[0090] The present invention does not specifically limit the electrolyte, and it can include organic solvents and lithium salts commonly used in current lithium-ion battery electrolytes; for example, the organic solvent can include at least one of diethyl carbonate (DEC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), ethyl acetate, propyl acetate, ethyl propionate, and propyl propionate; the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(oxalato)borate (LiBOB), and lithium tetrafluoroborate (LiBF4).

[0091] Hereinafter, the tab end glue, negative electrode sheet, and lithium-ion battery provided by the present invention will be introduced in detail through specific examples.

[0092] Example 1

[0093] 1) Preparation of tab end glue:

[0094] First polymer segment: 70 parts of acrylic acid, 25 parts of acrylonitrile, 5 parts of hydroxymethylacrylamide were mixed evenly with water at a volume ratio of 1:4 to obtain a monomer mixture. Then, the monomer mixture was heated to 75 °C by water bath heating, and then potassium persulfate as the initiator was added. The mass of the initiator was 6 wt% of the mass of the monomer mixture, and the reaction was carried out under insulation for 8 h while stirring during the reaction at a stirring speed of 300 r / min to obtain a colloidal emulsion of the first polymer segment. The glass transition temperature was detected to be 105 °C;

[0095] Second polymer segment: 90 parts of butyl acrylate, 5 parts of styrene, 5 parts of hydroxymethylacrylamide were mixed evenly with water at a volume ratio of 1:4 to obtain a monomer mixture. Then, the monomer mixture was heated to 75 °C by water bath heating, and then potassium persulfate as the initiator was added. The mass of the initiator was 6 wt% of the mass of the monomer mixture, and the reaction was carried out under insulation for 8 h while stirring during the reaction at a stirring speed of 300 r / min to obtain a colloidal emulsion of the second polymer segment. The glass transition temperature was detected to be -44 °C;

[0096] The colloidal emulsion of the first polymer segment and the colloidal emulsion of the second polymer segment were mixed at a polymer mass ratio of 20:80, and the solid content was adjusted to 22%. Subsequently, the pH of the mixed system was adjusted to 7 with sodium hydroxide to obtain an ear pad glue emulsion with a surface tension of 51 mN / m, a viscosity of 4253 mPa·s, and a pH value of 7.

[0097] 2) Preparation of the battery:

[0098] 96.80 parts of lithium nickel cobalt manganese oxide ternary material, 1.5 parts of conductive agent Super P, 0.5 part of conductive graphite KS-6, 1.20 parts of binder polyvinylidene fluoride and N-methylpyrrolidone were mixed to prepare a positive electrode slurry. Then, the positive electrode slurry was coated on the surface of aluminum foil, and after drying and rolling, a positive electrode sheet with a single-sided areal density of 180 g / m 2 , and a tap density of 3.5 g / cm 3 was obtained.

[0099] Artificial graphite, conductive carbon black, sodium carboxymethylcellulose, styrene-butadiene rubber (SBR) were mixed in a mass ratio of 93:3:2:2, and deionized water was added and stirred evenly to prepare a negative electrode slurry;

[0100] The aforementioned ear pad glue emulsion (calculated based on its solid content) was mixed with boehmite and CMC in a mass ratio of 40:60:1 to obtain an insulating layer slurry;

[0101] The aforementioned negative electrode paste is coated on the surface of the negative electrode current collector copper foil, and the insulating layer paste is coated on both sides of the negative electrode paste layer, and the insulating layer paste is in contact with but does not overlap the negative electrode paste; at the same time, an empty foil area is reserved at the edge in the width direction of the copper foil for subsequent cutting of the negative electrode tab; then, drying, rolling, and slitting are carried out to obtain the negative electrode sheet of this embodiment, and the single-sided surface density of the negative electrode sheet is 94 g / m 2 , and the compaction density is 1.6 g / cm 3 ;

[0102] The positive electrode sheet, the separator (PP film), and the negative electrode sheet are alternately stacked to assemble a laminated cell;

[0103] The laminated cell is placed in an aluminum-plastic film, and a liquid injection port is reserved. Electrolyte is injected into it through the liquid injection port, and then the liquid injection port is sealed to obtain a battery precursor; aging, formation, and aging treatments are carried out, and after processes such as grading, a soft-pack battery is prepared. Among them, the lithium salt in the electrolyte is lithium hexafluorophosphate (LiPF6), the concentration of the lithium salt is 1 M, and the organic solvent is a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) with a mass ratio of 1:2:1.

[0104] Examples 2 - 8

[0105] The ear glue, negative electrode sheet, and battery are prepared according to the method of Example 1. The difference is that the composition of the ear glue is adjusted according to the content of Table 1 and Table 2, and the viscosity, surface tension, and solid content of the prepared ear glue are shown in Table 2.

[0106] Comparative Example 1

[0107] The ear glue, negative electrode sheet, and battery are prepared according to the method of Example 1. The difference is that in step 1), during the preparation of the first polymer segment, sodium dodecyl sulfate is added while adding the initiator, and the mass of sodium dodecyl sulfate is 1 wt% of the mass of the monomer mixture;

[0108] During the preparation of the second polymer segment, sodium dodecyl sulfate is added while adding the initiator, and the mass of sodium dodecyl sulfate is 1 wt% of the mass of the monomer mixture.

[0109] Comparative Example 2

[0110] The ear glue, negative electrode sheet, and battery are prepared according to the method of Example 1. The difference is that in step 1), the pH of the mixed system is adjusted to 5 by sodium hydroxide.

[0111] Comparative Example 3

[0112] Prepare the tab glue, negative electrode sheet and battery according to the method of Example 1, except that in step 1), during the preparation of the first polymer segment, sodium dodecyl sulfate is added while adding the initiator, and the mass of sodium dodecyl sulfate is 1 wt% of the mass of the monomer mixture;

[0113] During the preparation of the second polymer segment, sodium dodecyl sulfate is added while adding the initiator, and the mass of sodium dodecyl sulfate is 1 wt% of the mass of the monomer mixture;

[0114] Adjust the pH of the mixed system to 5 with sodium hydroxide.

[0115] Table 1

[0116]

[0117] Table 2

[0118]

[0119] Test Example

[0120] Perform the following tests on the lithium-ion batteries prepared in the above examples and comparative examples:

[0121] 1) Dry adhesion peel strength between tab glue and foil

[0122] Cut the negative electrode sheet prepared by the method of the present invention into strips of 20 100 mm in length, press for 60 s at 100 °C and 8 MPa, and test the coating peel strength with an electronic tensile machine (Dazhong Instruments Co., Ltd., Dongguan City, model DZ-101).

[0123] 2) Wet adhesion peel strength between tab glue and foil

[0124] Cut the negative electrode sheet prepared by the method of the present invention into strips of 20 100 mm in length, press for 60 s at 100 °C and 8 MPa, soak in the electrolyte at 60 °C for 3 days, take out and dry, and then test the coating peel strength with an electronic tensile machine (Dazhong Instruments Co., Ltd., Dongguan City, model DZ-101).

[0125] 3) Dry adhesion peel strength between tab glue and separator

[0126] Cut the negative electrode sheet and the separator prepared by the method of the present invention into strips of 20 100 mm in length, press for 60 s at 100 °C and 8 MPa, and test the bonding strength with an electronic tensile machine (Dazhong Instruments Co., Ltd., Dongguan City, model DZ-101).

[0127] 4) Wet adhesion peel strength between tab glue and separator

[0128] The negative electrode sheet and the separator prepared by the solution of the present invention are respectively cut into strips with a length of 20 100 mm, pressed for 60 s under the conditions of 100 °C and 8 MPa, soaked in the electrolyte at 60 °C for 3 days, taken out and dried, and then the bonding strength is tested with an electronic tensile machine (Dazhong Instruments Co., Ltd., Dongguan, model DZ-101).

[0129] 5) Internal resistance of the battery cell

[0130] Tested with an internal resistance tester.

[0131] 6) Capacity retention rate after storage at high temperature of 60 °C for 30 days

[0132] After the soft-pack batteries prepared in the above examples and comparative examples are discharged at a constant current of 0.5C to a voltage of 2.7V, they are charged at a constant current of 1C to a voltage of 4.3V, and then charged at a constant voltage until the cut-off current is 0.05C. After the charging is completed, they are discharged at a constant current of 1C to 2.75V, and the discharge capacity before storage is recorded as C0; then they are charged at a constant current of 1C to a voltage of 4.3V, and then charged at a constant voltage until the cut-off current is 0.05C. At this time, the battery is in a fully charged state; the fully charged battery is discharged after being stored at 60 °C for 30 days, and the discharge capacity after storage is recorded as C1. Then the high-temperature storage capacity retention rate (%) = C1 / C0 × 100%.

[0133] 7) Capacity retention rate of high-rate cycling (2C / 1C) at room temperature for 500 cycles

[0134] For the batteries prepared in the above examples and comparative examples, at a temperature of 25 °C ± 2 °C, the battery is discharged at a constant current of 0.5C to a voltage of 2.75V, then charged at a constant current of 1C to a voltage of 4.3V, and then charged at a constant voltage until the cut-off current is 0.05C to obtain a fully charged battery. Subsequently, it is discharged under the condition of 1C until the voltage reaches 2.75V, and the discharge capacity of the battery is recorded as C2; then, it is charged at a constant current of 2C to a voltage of 4.3V, and then charged at a constant voltage until the cut-off current is 0.05C to obtain a fully charged battery. Subsequently, it is discharged at a constant current of 2C until the voltage reaches 2.75V. It is cycled 500 times at 2C in this way, and the discharge capacity of the battery after cycling is recorded as C3. Then the high-rate cycling capacity retention rate (%) = C3 / C2 × 100%.

[0135] The test results are shown in Table 3.

[0136] Table 3

[0137]

[0138] As can be seen from Table 3:

[0139] The tab glue provided by the present invention can effectively avoid the occurrence of cross-material, which is very beneficial to reducing the internal resistance of the battery cell, improving the high-temperature capacity retention rate and high-rate cycle capacity retention rate of the battery.

[0140] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A tip glue, characterized in that: The ear glue is an emulsion obtained by soap-free emulsion polymerization; the ear glue comprises a polymer, the polymer comprises a first polymer segment and a second polymer segment; the first polymer segment comprises a first main structural unit, the first main structural unit is an acrylic structural unit; the second polymer segment comprises a second main structural unit, the second main structural unit is an acrylic structural unit; The glass transition temperature Tg of the first polymer segment is ≥50°C, and the glass transition temperature Tg of the second polymer segment is ≤-30°C; the mass ratio of the first polymer segment to the second polymer segment is (5-30):(70-95); The solid content of the ear glue is 20-25%; the surface tension of the emulsion is 45-60 mN / m, and the viscosity is 2000-8000 mPa·s; The first polymer segment further comprises a strong polar structural unit, wherein the strong polar structural unit comprises at least one of a structural unit containing a carboxyl group, a hydroxyl group, a cyano group, and an amide group; The second polymer segment further comprises a weak polar structural unit, and the weak polar structural unit comprises at least one of a structural unit containing an aromatic group and an ester group.

2. The ear glue according to claim 1, characterized in that: The first polymer segment includes a first reactive structural unit, and the second polymer segment includes a second reactive structural unit. The first reactive structural unit and the second reactive structural unit are each independently selected from one or more of a hydroxyl group, an isocyanate group, an epoxy group, and a carboxyl group.

3. The ear glue according to claim 2, characterized in that: The first reactive structural unit and the second reactive structural unit may react under heating conditions.

4. The ear glue according to claim 2, characterized in that: The mass content of the first reactive structural unit in the first polymer segment is 3-10%; And / or, the mass content of the second reactive structural unit in the second polymer segment is 3-10%.

5. A negative electrode sheet, characterized in that: The negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on at least a portion of the surface of the negative electrode current collector; an insulating layer is also disposed on the surface of the negative electrode current collector, and the insulating layer is prepared from an insulating layer slurry comprising the ear glue according to any one of claims 1-4.

6. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to claim 5.

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