CN112500817B - Positive electrode adhesive and preparation method thereof, and battery positive electrode and lithium battery - Google Patents

Positive electrode adhesive and preparation method thereof, and battery positive electrode and lithium battery Download PDF

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CN112500817B
CN112500817B CN202011164308.1A CN202011164308A CN112500817B CN 112500817 B CN112500817 B CN 112500817B CN 202011164308 A CN202011164308 A CN 202011164308A CN 112500817 B CN112500817 B CN 112500817B
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methyl acrylate
acrylonitrile
positive electrode
adhesive
battery
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CN112500817A (en
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宋江选
靳谧涵
虎琳琳
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Xian Jiaotong University
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J133/00—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Adhesives based on derivatives of such polymers
    • C09J133/18—Homopolymers or copolymers of nitriles
    • C09J133/20—Homopolymers or copolymers of acrylonitrile
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
    • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F220/42—Nitriles
    • C08F220/44—Acrylonitrile
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

The invention discloses a positive adhesive and a preparation method thereof, and a battery positive electrode and a lithium battery, wherein the adhesive is a copolymer of acrylonitrile and methyl acrylate monomers, a large amount of cyano groups contained in the adhesive can generate coordination interaction with metal ions in a positive electrode material, so that the interface side reaction between the positive electrode material and electrolyte at high temperature is relieved, the interface impedance is reduced, the metal ion dissolution is inhibited, the surface structure of the positive electrode material is stabilized, the electrical property of the battery at high temperature is improved, the flexibility of the polymer can be improved by introducing the methyl acrylate monomers, the processability of an electrode plate is enhanced, and the failure possibility of the adhesive at high temperature is reduced.

Description

Positive electrode adhesive and preparation method thereof, and battery positive electrode and lithium battery
[ technical field ] A method for producing a semiconductor device
The invention belongs to the technical field of battery materials, and relates to a positive electrode adhesive, a preparation method thereof, a battery positive electrode and a lithium battery.
[ background of the invention ]
With the increasingly prominent energy problems and environmental problems, lithium ion batteries are widely applied to electric vehicles, 3C products, renewable energy sources and energy storage devices of smart grids due to a series of advantages of high energy density, high working voltage, large output power, small self-discharge effect, environmental protection and the like, and are gradually expanded to high-power systems and fields. However, the applicable temperature is narrow, and when the temperature is higher than 45 ℃, the capacity is attenuated quickly, and even combustion or explosion can occur, so that the application of the high-temperature environment is severely limited.
The capacity of the lithium ion battery is attenuated at high temperature mainly due to the damage of the positive electrode. On one hand, the interface reaction between the anode and the electrolyte in the battery is aggravated by high temperature, so that the interface impedance is increased, metal ions are dissolved out, and the structure of the anode material is finally damaged. On the other hand, at high temperature, the mechanical strength and adhesive force of the commercial positive electrode binder polyvinylidene fluoride (PVdF) are greatly reduced, and effective connection among the components of the electrode cannot be maintained, so that the integrity of a conductive network is ensured, and the performance of the battery is deteriorated; in addition, PVdF has a low melting point, and at high temperatures, exothermic reactions can occur and produce harmful products, increasing the risk of thermal runaway.
In order to solve the high-temperature problem of the battery, the most common strategy is the development of high-temperature electrolyte, interface reaction is reduced by using an electrolyte additive, the structure of the positive electrode is stabilized, and the cycling stability of the battery is improved. CN108511799A discloses a high-temperature electrolyte for lithium ion batteries, which passivates the surface of a positive electrode by forming a stable interfacial film on the surface of the positive electrode, thereby maintaining the structural stability of the positive electrode material, but currently, few studies are made on solving the problem of failure of the conventional positive electrode binder at high temperature.
[ summary of the invention ]
The invention aims to overcome the defects of the prior art and provides a positive adhesive, a preparation method thereof, a battery positive electrode and a lithium battery so as to solve the technical problems that the positive adhesive is easy to lose effectiveness at high temperature, the positive electrode/electrolyte interface reaction is easy to occur and the like in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
the positive electrode adhesive is an acrylonitrile-methyl acrylate copolymer, and the molecular structural formula is as follows:
Figure BDA0002745316010000021
wherein m is 210-270, n is 30-90, and m and n are natural numbers.
A preparation method of a positive electrode binder comprises the following steps:
step 1, dissolving an acrylonitrile monomer and a methyl acrylate monomer in N, N-dimethylformamide, wherein the molar ratio of the acrylonitrile monomer to the methyl acrylate monomer is (7-9): (1-3), uniformly stirring to form a reaction system A;
step 2, adding an initiator into the reaction system A, deoxidizing the reaction system A and introducing protective gas to form a reaction system B;
step 3, heating the reaction system B to 60-75 ℃, and keeping the temperature for 6-10 hours to perform a polymerization reaction to form a reaction system C;
and 4, dropping the reaction system C into a mixed solution of methanol and water to obtain a precipitate, washing the precipitate, and drying in vacuum to constant weight to obtain the acrylonitrile-methyl acrylate copolymer adhesive.
The invention is further improved in that:
preferably, in step 1, the total concentration of the acrylonitrile monomer and the methyl acrylate monomer in the N, N-dimethylformamide is 2 to 3 mol/L.
Preferably, in the step 2, the addition amount of the initiator is 0.6-1.2% of the sum of the mass of the acrylonitrile monomer and the mass of the methyl acrylate monomer.
Preferably, in step 2, the initiator is azobisisobutyronitrile, azobisisoheptonitrile or dimethyl azobisisobutyrate.
Preferably, in the step 4, the volume ratio of methanol to water in the mixed solution of methanol and water is (3-5): (5-7).
Preferably, in step 4, the drying temperature is 60 ℃.
The battery anode comprises a current collector and lithium ion battery anode slurry attached to the current collector, wherein the lithium ion battery anode slurry comprises the following components in percentage by mass (60-95): (4.5-25): (0.5-15) an active material, a conductive additive and a binder, wherein the binder is the positive electrode binder.
Preferably, the active material is a ternary material, lithium cobaltate, lithium manganate or lithium nickelate; the conductive additive is Super P, acetylene black or Ketjen black.
A lithium battery comprises the battery anode.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a positive electrode adhesive, which is a copolymer of acrylonitrile and methyl acrylate monomers, wherein a large amount of cyano groups contained in the positive electrode adhesive can generate coordination interaction with metal ions in a positive electrode material, so that the interface side reaction between the positive electrode material and electrolyte at high temperature is relieved, the interface impedance is reduced, the metal ions are inhibited from dissolving out, the surface structure of the positive electrode material is stabilized, the electrical property of a battery at high temperature is improved, the flexibility of the polymer can be improved by introducing the methyl acrylate monomers, the processability of an electrode plate is enhanced, and the possibility that the adhesive can fail at high temperature is reduced.
The invention also discloses a preparation method of the positive adhesive, which comprises the steps of firstly dissolving an acrylonitrile monomer and a methyl acrylate monomer in N, N-dimethylformamide, then initiating a polymerization reaction through an initiator, and finally generating a target product.
The invention also discloses a battery anode which comprises the prepared anode binder, and the anode prepared by the binder shows good cycling stability at 55 ℃.
The invention also discloses a lithium battery, and after the lithium battery adopting the adhesive is cycled for 100 weeks at the temperature of 55 ℃, the capacity retention rate is still above 81%.
[ description of the drawings ]
FIG. 1 is a chart of the infrared transmission spectrum of adhesive A3 in example 3.
Fig. 2 is a graph comparing the peel strength of positive electrode tabs of lithium ion batteries using the binder a3 of example 3 and the binder B1 of comparative example 1.
Fig. 3 is a graph comparing the cycle performance at 55 c of a lithium ion battery using binder a3 in example 3 and binder B1 in comparative example 1.
[ detailed description ] embodiments
The invention is described in further detail below with reference to the accompanying drawings:
in the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention; the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance; furthermore, unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly and encompass, for example, both fixed and removable connections; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
The invention aims to provide a positive adhesive, a preparation method thereof, a battery positive electrode and a lithium battery. The preparation method of the copolymer comprises the following steps:
(1) dissolving acrylonitrile monomer and methyl acrylate monomer in N, N-dimethylformamide, and uniformly stirring to form a reaction system A, wherein the molar ratio of the two monomers is acrylonitrile: methyl acrylate ═ 7-9: (1-3), the monomer concentration is 2-3 mol/L.
(2) Adding an initiator into the reaction system A, wherein the mass of the initiator is 0.6-1.2% of the total mass of the two monomers, the initiator is azobisisobutyronitrile, azobisisoheptonitrile or dimethyl azobisisobutyrate, and then blowing protective gas (nitrogen or argon) into the reaction system A for more than 40 minutes by using a bubbling method to remove oxygen so as to prevent the inhibition effect of oxygen on the polymerization reaction, thereby forming a reaction system B.
(3) And heating the reaction system B to 60-75 ℃ to initiate monomer polymerization, wherein the polymerization reaction time is 6-10 hours, and forming a reaction system C.
(4) And (3) precipitating the polymer in the reaction system C by using a mixed solution of methanol and water as a precipitating agent, wherein the molar ratio of methanol: water (3-5): (5-7), washing the precipitate with methanol for 2-3 times, and drying at 60 ℃ to constant weight to obtain the acrylonitrile-methyl acrylate copolymer adhesive.
The acrylonitrile-methyl acrylate copolymer adhesive can be used for a lithium ion battery anode, and the lithium ion battery anode comprises a current collector and lithium ion battery anode slurry attached to the current collector; the lithium ion battery anode slurry comprises an active material, a conductive additive and an adhesive, wherein the mass ratio of the active material to the conductive additive is as follows: conductive additive: (ii) a binder (60-95): (4.5-25): (0.5 to 15); the active material is a ternary material (LiNi)0.8Co0.1Al0.1O2、LiNi0.6Co0.2Al0.2O2、LiNi0.5Co0.2Al0.3O2Or LiNi0.8Co0.1Mn0.1O2、LiNi0.6Co0.2Mn0.2O2、LiNi0.5Co0.2Mn0.3O2) Lithium cobaltate (LiCoO)2) Lithium manganate (LiMn)2O4) Or lithium nickelate (LiNiO)2) (ii) a The conductive additive is Super P, acetylene black or Ketjen black.
The adhesive can be used for preparing the anode of the lithium ion battery and the corresponding lithium ion battery. For example, the preparation process of the ternary positive electrode of the lithium ion battery comprises the following steps:
(1) the preparation method comprises the following steps of (60-95): (4.5-25): (0.5-15), and uniformly dispersing the mixture in N-methyl pyrrolidone after ball milling to obtain uniformly mixed anode slurry.
(2) And (3) uniformly coating the slurry in the step (1) on an aluminum foil with the thickness of 9 microns by using an automatic coating machine, wherein the coating thickness is 150 microns, and then placing the aluminum foil in a vacuum drying oven to dry and remove the solvent. After drying, the part coated with the slurry was cut into a positive electrode sheet having a diameter of 12 mm by a manual sheet cutting machine.
(3) And (3) transferring the electrode plates prepared in the step (2) into a glove box filled with argon gas, and assembling into a 2032 button half cell. Using a pure lithium plate as the counter electrode, Celgard2325 Polypropylene-polyethylene-PolyA propylene (PP-PE-PP) film was used as the separator. The electrolyte solution used was lithium hexafluorophosphate (LiPF) containing 1M6) Ethylene Carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1: 1) the solution was mixed.
(3) And (3) standing the button cell assembled in the step (2) for 5 hours, and then cycling at a multiplying power of 0.1 ℃ for one week at a voltage range of 3-4.2V at 55 ℃ and then performing charge-discharge cycling at a multiplying power of 0.5 ℃. Wherein 1C is 180 mAh/g.
Comparative example
The method is characterized in that the PVdF is used as a binder B1, the PVdF is applied to the positive electrode and the lithium ion battery is assembled according to the method, and the preparation process of the positive electrode specifically comprises the following steps:
(1) reacting LiNi0.8Co0.1Al0.1O2And Super P and PVdF are mixed according to the mass ratio of 80:10:10, and are uniformly dispersed in N-methyl pyrrolidone after ball milling to obtain uniformly mixed anode slurry.
(2) And (3) uniformly coating the slurry in the step (1) on an aluminum foil with the thickness of 9 microns by using an automatic coating machine, wherein the coating thickness is 150 microns, and then placing the aluminum foil in a vacuum drying oven to dry and remove the solvent. After drying, the part coated with the slurry was cut into a positive electrode sheet having a diameter of 12 mm by a manual sheet cutting machine.
(3) And (3) transferring the electrode plates prepared in the step (2) into a glove box filled with argon gas, and assembling into a 2032 button half cell. A pure lithium sheet was used as the counter electrode and a Celgard2325 polypropylene-polyethylene-polypropylene (PP-PE-PP) membrane was used as the separator. The electrolyte solution used was lithium hexafluorophosphate (LiPF) containing 1M6) Ethylene Carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1: 1) the solution was mixed.
(3) And (3) standing the button cell assembled in the step (2) for 5 hours, and then cycling at a multiplying power of 0.1 ℃ for one week at a voltage range of 3-4.2V at 55 ℃ and then performing charge-discharge cycling at a multiplying power of 0.5 ℃. Wherein 1C is 180 mAh/g.
Example 1
(1) According to a molar ratio of 9: 2.0g (37.7mmol) of acrylonitrile and 0.361g (4.2mmol) of methyl acrylate are dissolved in 7.63mL of N, N-dimethylformamide solution, and the two monomers are sufficiently stirred at a concentration of 2mol/L in the solution.
(2) 0.014g of azobisisobutyronitrile (mass fraction: 0.6% of the mass of the two monomers) was added to the solution in (1), and nitrogen was passed through for 40 minutes to remove oxygen.
(3) The system was warmed to 70 ℃ and reacted for 8 hours.
(4) And (3) taking a mixed solution of methanol and water as a precipitating agent to precipitate and purify the copolymerization product, wherein the volume ratio of the methanol to the water is 3: and 7, washing the precipitate with methanol for 2 times, and transferring the precipitate to a vacuum oven to be dried to constant weight to obtain the pure acrylonitrile-methyl acrylate copolymer adhesive. The resulting adhesive is labeled a 1.
The prepared adhesive A1 is applied to a positive electrode and assembled into a lithium ion battery according to the method, and the preparation process of the positive electrode comprises the following steps:
(1) reacting LiNi0.8Co0.1Al0.1O2And (3) mixing the Super P and the acrylonitrile-methyl acrylate copolymer adhesive prepared in the step (4) according to the mass ratio of 80:10:10, and uniformly dispersing the mixture in N-methyl pyrrolidone after ball milling to obtain uniformly mixed anode slurry.
(2) And (3) uniformly coating the slurry in the step (1) on an aluminum foil with the thickness of 9 microns by using an automatic coating machine, wherein the coating thickness is 150 microns, and then placing the aluminum foil in a vacuum drying oven to dry and remove the solvent. After drying, the part coated with the slurry was cut into a positive electrode sheet having a diameter of 12 mm by a manual sheet cutting machine.
(3) And (3) transferring the electrode plates prepared in the step (2) into a glove box filled with argon gas, and assembling into a 2032 button half cell. A pure lithium sheet was used as the counter electrode and a Celgard2325 polypropylene-polyethylene-polypropylene (PP-PE-PP) membrane was used as the separator. The electrolyte solution used was lithium hexafluorophosphate (LiPF) containing 1M6) Ethylene Carbonate (EC) and diethyl carbonate (DEC) (volume ratio 1: 1) the solution was mixed.
(3) And (3) standing the button cell assembled in the step (2) for 5 hours, and then cycling at a multiplying power of 0.1 ℃ for one week at a voltage range of 3-4.2V at 55 ℃ and then performing charge-discharge cycling at a multiplying power of 0.5 ℃. Wherein 1C is 180 mAh/g.
Example 2
The preparation method, reaction conditions and purification method of acrylonitrile-methyl acrylate copolymer are the same as those of example 1, but the molar ratio of acrylonitrile to methyl acrylate is 8: 2. the resulting adhesive is labeled a 2.
The prepared adhesive A2 was applied to the positive electrode and assembled into a lithium ion battery according to the above method, and the high temperature electrical properties were tested.
Example 3
The preparation method, reaction conditions and purification method of acrylonitrile-methyl acrylate copolymer are the same as those of example 1, but the molar ratio of acrylonitrile to methyl acrylate is 7: 3. the resulting adhesive is labeled A3 and its IR spectrum is shown in FIG. 1. 2939cm can be seen in the figure-1，1453cm-1Corresponding to C-H stretching vibration absorption peak and bending vibration absorption peak on the main chain of the polymer, 2243cm-11733cm corresponding to the C ≡ N stretching vibration absorption peak in AN-1And 1236-1162 cm-1Corresponding to the C-O stretching vibration absorption peak and the C-O-C stretching vibration absorption peak in MA, the successful synthesis of P (AN-MA) is proved.
The prepared adhesive A3 was applied to the positive electrode and assembled into a lithium ion battery according to the above method, and the high temperature electrical properties were tested.
Fig. 2 shows the results of the peel performance test of the adhesive A3 prepared in example 3 and comparative example 1, and it can be seen that the average peel strength of the adhesive A3 of the present invention was 0.65N/cm, which is higher than that of the adhesive B1(0.37N/cm) in comparative example 1, demonstrating better adhesion to the components of the positive electrode.
Table 1 shows the test results of the lithium ion batteries manufactured by using the examples and comparative examples of the present invention for the positive electrode at 55 ℃:
numbering First week efficiency (%) Capacity after 100 weeks at 55 ℃Maintenance Rate (%)
Example 1 86.2 81.5
Example 2 87.1 80.8
Example 3 86.5 81.7
Comparative example 1 84.6 42.2
From the results in table 1, the first cycle efficiency of the lithium ion battery positive electrode binder provided by the invention reaches above 86% at 55 ℃, the change law is shown in fig. 3, the capacity retention rate after 100 cycles is above 80%, but the first cycle efficiency of the comparative example binder is about 84%, and the capacity retention rate after 100 cycles is only 42.2%. This is why. The adhesive provided by the invention obviously improves the cycle stability of the lithium ion battery at high temperature.
Example 4
(1) Acrylonitrile and methyl acrylate are taken according to the molar ratio of 7:2 and dissolved in 7.63mL of N, N-dimethylformamide solution, and the mixture is fully and uniformly stirred.
(2) Azodiisoheptanonitrile in a mass fraction of 1.2% of the mass of the two monomers was added to the solution in (1), and nitrogen gas was introduced for 40 minutes to remove oxygen.
(3) The system was warmed to 60 ℃ and reacted for 10 hours.
(4) And (3) precipitating and purifying the copolymerization product by taking a mixed solution of methanol and water as a precipitating agent, wherein the volume ratio of the methanol to the water is 5: and 5, washing the precipitate with methanol for 3 times, and transferring the precipitate to a vacuum oven to be dried to constant weight to obtain the pure acrylonitrile-methyl acrylate copolymer adhesive.
Preparing the prepared adhesive into a positive electrode, and preparing LiNi in the preparation process0.8Co0.1Mn0.1O2Mixing acetylene black and the acrylonitrile-methyl acrylate copolymer adhesive prepared in the step (4) according to the mass ratio of 60:25:15, and uniformly dispersing the mixture in N-methyl pyrrolidone after ball milling to obtain uniformly mixed anode slurry. The positive electrode slurry was used to prepare a battery according to the remaining procedures of example 1, and subjected to a high temperature test.
Example 5
(1) Acrylonitrile and methyl acrylate are taken according to the molar ratio of 8:1 and dissolved in 7.63mL of N, N-dimethylformamide solution, and the mixture is fully and uniformly stirred.
(2) Dimethyl azodiisobutyrate with the mass fraction of 1 percent of the mass of the two monomers is added into the solution in the step (1), and nitrogen is introduced for 40 minutes to remove oxygen.
(3) The system was warmed to 75 ℃ and reacted for 6 hours.
(4) And (3) taking a mixed solution of methanol and water as a precipitating agent to precipitate and purify the copolymerization product, wherein the volume ratio of the methanol to the water is 3: and 5, washing the precipitate with methanol for 3 times, and transferring the precipitate to a vacuum oven to be dried to constant weight to obtain the pure acrylonitrile-methyl acrylate copolymer adhesive.
And (3) preparing the prepared adhesive into a positive electrode, mixing lithium cobaltate, Ketjen black and the acrylonitrile-methyl acrylate copolymer adhesive prepared in the step (4) according to the mass ratio of 95:4.5:0.5, and uniformly dispersing the mixture in N-methyl pyrrolidone after ball milling to obtain uniformly mixed positive electrode slurry. The positive electrode slurry was used to prepare a battery according to the remaining procedures of example 1, and subjected to a high temperature test.
Example 6
(1) The acrylonitrile and the methyl acrylate are taken according to the molar ratio of 9:3 and dissolved in 7.63mL of N, N-dimethylformamide solution, and the mixture is fully and uniformly stirred.
(2) Dimethyl azodiisobutyrate in an amount of 0.8% by mass based on the mass of the two monomers was added to the solution in (1), and nitrogen gas was introduced for 40 minutes to remove oxygen.
(3) The system was warmed to 70 ℃ and reacted for 9 hours.
(4) And (3) taking a mixed solution of methanol and water as a precipitating agent to precipitate and purify the copolymerization product, wherein the volume ratio of the methanol to the water is 3: and 7, washing the precipitate with methanol for 3 times, and transferring the precipitate to a vacuum oven to be dried to constant weight to obtain the pure acrylonitrile-methyl acrylate copolymer adhesive.
And (3) preparing the prepared adhesive into a positive electrode, mixing lithium manganate, acetylene black and the acrylonitrile-methyl acrylate copolymer adhesive prepared in the step (4) according to the mass ratio of 70:20:10, and uniformly dispersing the mixture in N-methyl pyrrolidone after ball milling to obtain uniformly mixed positive electrode slurry. The positive electrode slurry was used to prepare a battery according to the remaining procedures of example 1, and subjected to a high temperature test.
Example 7
(1) Acrylonitrile and methyl acrylate are taken according to the molar ratio of 7:2 and dissolved in 7.63mL of N, N-dimethylformamide solution, and the mixture is fully and uniformly stirred.
(2) Azodiisoheptanonitrile in a mass fraction of 0.6% of the mass of the two monomers was added to the solution in (1), and nitrogen gas was introduced for 40 minutes to remove oxygen.
(3) The system was warmed to 65 ℃ and reacted for 7 hours.
(4) And (3) precipitating and purifying the copolymerization product by taking a mixed solution of methanol and water as a precipitating agent, wherein the volume ratio of the methanol to the water is 4: 6, washing the precipitate with methanol for 3 times, and transferring the precipitate to a vacuum oven to be dried to constant weight to obtain the pure acrylonitrile-methyl acrylate copolymer adhesive.
Preparing the prepared adhesive into a positive electrode, and preparing LiNi in the preparation process0.6Co0.2Mn0.2O2Mixing acetylene black and the acrylonitrile-methyl acrylate copolymer adhesive prepared in the step (4) according to the mass ratio of 85:10:5, and uniformly dispersing the mixture in N-methyl pyrrolidone after ball milling to obtain uniformly mixed anode slurry. Will be rightThe electrode slurry a battery was prepared and subjected to high temperature testing following the remaining steps of example 1.
Example 8
(1) Acrylonitrile and methyl acrylate are taken according to the molar ratio of 8:1 and dissolved in 7.63mL of N, N-dimethylformamide solution, and the mixture is fully and uniformly stirred.
(2) Azodiisoheptanonitrile in a mass fraction of 0.7% of the mass of the two monomers was added to the solution in (1), and nitrogen gas was introduced for 40 minutes to remove oxygen.
(3) The system was warmed to 75 ℃ and reacted for 8 hours.
(4) And (3) precipitating and purifying the copolymerization product by taking a mixed solution of methanol and water as a precipitating agent, wherein the volume ratio of the methanol to the water is 4: 6, washing the precipitate with methanol for 3 times, and transferring the precipitate to a vacuum oven to be dried to constant weight to obtain the pure acrylonitrile-methyl acrylate copolymer adhesive.
Preparing the prepared adhesive into a positive electrode, and preparing LiNi in the preparation process0.5Co0.2Mn0.3O2Mixing acetylene black and the acrylonitrile-methyl acrylate copolymer adhesive prepared in the step (4) according to the mass ratio of 90:5:5, and uniformly dispersing the mixture in N-methyl pyrrolidone after ball milling to obtain uniformly mixed anode slurry. The positive electrode slurry was used to prepare a battery according to the remaining procedures of example 1, and subjected to a high temperature test.
Example 9
(1) Acrylonitrile and methyl acrylate are taken according to the molar ratio of 9:2 and dissolved in 7.63mL of N, N-dimethylformamide solution, and the mixture is fully and uniformly stirred.
(2) Dimethyl azodiisobutyrate with a mass fraction of 1.1% of the mass of the two monomers was added to the solution in (1), and nitrogen gas was introduced for 40 minutes to remove oxygen.
(3) The system was warmed to 75 ℃ and reacted for 10 hours.
(4) And (3) precipitating and purifying the copolymerization product by taking a mixed solution of methanol and water as a precipitating agent, wherein the volume ratio of the methanol to the water is 4: and 7, washing the precipitate with methanol for 3 times, and transferring the precipitate to a vacuum oven to be dried to constant weight to obtain the pure acrylonitrile-methyl acrylate copolymer adhesive.
And (3) preparing the prepared adhesive into a positive electrode, mixing lithium cobaltate, acetylene black and the acrylonitrile-methyl acrylate copolymer adhesive prepared in the step (4) according to the mass ratio of 65:20:15, and uniformly dispersing the mixture in N-methyl pyrrolidone after ball milling to obtain uniformly mixed positive electrode slurry. The positive electrode slurry was used to prepare a battery according to the remaining procedures of example 1, and subjected to a high temperature test.
The invention provides an adhesive capable of improving the high-temperature cycle performance of a lithium ion battery, and a preparation method and application thereof. A series of acrylonitrile-methyl acrylate copolymers in varying proportions were prepared by free radical polymerization. Cyano in polyacrylonitrile can generate coordination interaction with metal ions in the anode material, so that the interface side reaction between the anode and electrolyte at high temperature is relieved, the metal ions are inhibited from dissolving out, the surface structure of the anode material is stabilized, the electrical property of the lithium ion battery at high temperature is improved, and the polymethyl acrylate can improve the flexibility of polymers and the processability of electrode plates. The lithium ion battery adopting the adhesive shows good cycling stability at 55 ℃. Meanwhile, the adhesive disclosed by the invention is simple in preparation method, good in high-temperature stability, strong in adhesive force and easy to regulate and control in structure, and can meet the requirements of different electrode materials in use at high temperature.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (8)

1. The use of an acrylonitrile-methyl acrylate copolymer adhesive for the positive electrode of a lithium ion battery is characterized in that the preparation method of the acrylonitrile-methyl acrylate copolymer adhesive comprises the following steps:
step 1, dissolving an acrylonitrile monomer and a methyl acrylate monomer in N, N-dimethylformamide, wherein the molar ratio of the acrylonitrile monomer to the methyl acrylate monomer is (7-9): (1-3), uniformly stirring to form a reaction system A;
in the step 1, the total concentration of acrylonitrile monomer and methyl acrylate monomer in N, N-dimethylformamide is 2-3 mol/L;
in the step 2, the addition amount of the initiator is 0.6-1.2% of the sum of the mass of the acrylonitrile monomer and the mass of the methyl acrylate monomer;
step 2, adding an initiator into the reaction system A, deoxidizing the reaction system A and introducing protective gas to form a reaction system B;
step 3, heating the reaction system B to 60-75 ℃, and keeping the temperature for 6-10 hours to perform a polymerization reaction to form a reaction system C;
and 4, dropping the reaction system C into a mixed solution of methanol and water to obtain a precipitate, washing the precipitate, and drying in vacuum to constant weight to obtain the acrylonitrile-methyl acrylate copolymer adhesive.
2. Use of the acrylonitrile-methyl acrylate copolymer binder according to claim 1 for a positive electrode of a lithium ion battery, wherein in step 2, the initiator is azobisisobutyronitrile, azobisisoheptonitrile or dimethyl azobisisobutyrate.
3. The use of the acrylonitrile-methyl acrylate copolymer binder as claimed in claim 1 for a positive electrode of a lithium ion battery, wherein in the step 4, the volume ratio of methanol to water in the mixed solution of methanol and water is (3-5): (5-7).
4. Use of the acrylonitrile-methyl acrylate copolymer binder according to claim 1 for positive electrodes of lithium ion batteries, characterized in that in step 4 the drying temperature is 60 ℃.
5. The use of the acrylonitrile-methyl acrylate copolymer binder of claim 1 for a positive electrode of a lithium ion battery, wherein the molecular structural formula of the acrylonitrile-methyl acrylate copolymer binder is:
Figure FDA0003392142040000011
wherein m is 210-270, n is 30-90; m and n are both natural numbers.
6. The battery anode is characterized by comprising a current collector and lithium ion battery anode slurry attached to the current collector, wherein the lithium ion battery anode slurry comprises the following components in percentage by mass (60-95): (4.5-25): (0.5 to 15) an active material, a conductive additive and a binder, wherein the binder is the acrylonitrile-methyl acrylate copolymer binder according to any one of claims 1 to 5.
7. The battery positive electrode according to claim 6, wherein the active material is a ternary material, lithium cobaltate, lithium manganate or lithium nickelate; the conductive additive is Super P, acetylene black or Ketjen black.
8. A lithium battery comprising the positive electrode for a battery according to claim 7.
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