CN116445109A - Positive electrode binder and lithium ion battery positive electrode and lithium ion battery using same - Google Patents

Positive electrode binder and lithium ion battery positive electrode and lithium ion battery using same Download PDF

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Publication number
CN116445109A
CN116445109A CN202310140977.2A CN202310140977A CN116445109A CN 116445109 A CN116445109 A CN 116445109A CN 202310140977 A CN202310140977 A CN 202310140977A CN 116445109 A CN116445109 A CN 116445109A
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China
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positive electrode
fluorine
electrode binder
lithium ion
parts
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Inventor
黄志平
阳铮
段栋
陈瑶
何巍
刘金成
刘建华
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Huizhou Eve Power Battery Co ltd
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Huizhou Eve Power Battery Co ltd
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Priority to CN202310140977.2A priority Critical patent/CN116445109A/en
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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
    • C09J133/04—Homopolymers or copolymers of esters
    • C09J133/14—Homopolymers or copolymers of esters of esters containing halogen, nitrogen, sulfur or oxygen atoms in addition to the carboxy oxygen
    • C09J133/16—Homopolymers or copolymers of esters containing halogen atoms
    • 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
    • C08F220/10—Esters
    • C08F220/22—Esters containing halogen
    • C08F220/24—Esters containing halogen containing perhaloalkyl radicals
    • 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
    • C08F220/48—Acrylonitrile with nitrogen-containing monomers
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H01M4/623—Binders being polymers fluorinated 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

Abstract

The invention provides a positive electrode binder, a positive electrode of a lithium ion battery and a lithium ion battery using the positive electrode binder, wherein raw materials for preparing the positive electrode binder comprise fluoroacrylate monomers and non-fluoride monomers, the non-fluoride monomers comprise at least one of acrylonitrile, acrylic ester and acrylamide, and the mass ratio of the fluoroacrylate monomers is as follows: non-fluorine monomer=1 to 2:1 to 5; the positive electrode binder is prepared by emulsion polymerization of fluorine-containing acrylic ester monomers and non-fluorine-containing monomers, and the reaction temperature of the emulsion polymerization is 40-90 ℃. The invention realizes the chemical blending of the fluorine-containing monomer and the non-fluorine-containing monomer by utilizing the copolymerization reaction, can simultaneously exert the characteristics of low surface energy of the fluorine-containing acrylic ester polymer and the advantages of high cohesiveness of the olefin polymer, and synergistically improves the alkali resistance and the gel resistance of the positive electrode binder.

Description

Positive electrode binder and lithium ion battery positive electrode and lithium ion battery using same
Technical Field
The invention belongs to the field of lithium ion batteries, and particularly relates to a positive electrode binder, a lithium ion battery positive electrode using the positive electrode binder and a lithium ion battery.
Background
The lithium ion battery has high energy density and long cycle life, and has wide application in the fields of portable electronic equipment, electric automobiles, energy storage and the like. The lithium ion battery mainly comprises a positive electrode, a negative electrode, a diaphragm, electrolyte and a shell, and the working principle of the lithium ion battery is that electric energy is stored and released through oxidation-reduction reaction of reversible intercalation/deintercalation of lithium ions in an active material. The preparation method of the positive electrode and the negative electrode of the lithium ion battery comprises the steps of preparing positive electrode active materials or negative electrode active materials, electrode binders, conductive agents, dispersion media and the like into slurry, coating the slurry on corresponding current collectors, and carrying out processing technologies such as drying, cold pressing, die cutting and the like.
The lithium ion battery is used in a dynamic process of charge and discharge, lithium ions conduct electrochemical reaction of intercalation and deintercalation in active material particles, and the change of the volume and the bonding state of electrode materials can be caused; in the static process, the electrode materials are completely soaked in the electrolyte, and the electrolyte is soaked among the materials and swells the binder to affect the performance of the battery. Therefore, the electrode binder must provide sufficient adhesive strength to ensure that the active material does not fall off from the electrode sheet during the production and use of the battery, thereby maintaining the mechanical structure of the electrode sheet and the stability of the electrochemical performance of the battery during the production and use of the battery.
Among the binders for positive electrodes, polyvinylidene fluoride (PVDF) dominates the positive electrode binder due to its excellent properties. However, in a ternary battery system, the PVDF electrode binder prepared by using a homopolymerization method has poor alkali resistance and is easy to gel, and only other monomers with stronger alkali resistance can be used for preparing electrode slurry by using a product of copolymerization with vinylidene fluoride (VDF). However, in such a copolymerization product, since the reactivity ratio of VDF and an olefin monomer is greatly different, copolymerization of an olefin monomer and VDF can be achieved only in a small proportion (the copolymerization proportion of an olefin is generally not more than 5%). Since VDF is a fluorine-containing material, it is expensive and there is a risk of insufficient fluorite ore reserves. However, the existing copolymerization products of VDF and olefin monomers on the market are difficult to reduce the content of fluorine monomers in the electrode binder, so that the use cost of the electrode binder is difficult to reduce. Therefore, there is a strong need to develop a binder with a lower content of fluorine-based monomers and which maintains good stability in a ternary battery system.
Disclosure of Invention
In order to reduce the use cost of the positive electrode binder and maintain good binding performance, alkali resistance and gel resistance in the preparation process and the use process of the lithium ion battery, the invention provides the positive electrode binder, and a positive electrode and a lithium ion battery using the positive electrode binder.
According to one aspect of the present invention, there is provided a positive electrode binder, wherein the raw materials for preparing the positive electrode binder include a fluoroacrylate monomer and a non-fluorine monomer, the non-fluorine monomer includes at least one of acrylonitrile, acrylic acid ester and acrylamide, and the mass ratio of the fluoroacrylate monomer is as follows: non-fluorine monomer=1 to 2:1 to 5; the positive electrode binder is prepared by emulsion polymerization of fluorine-containing acrylic ester monomers and non-fluorine-containing monomers, and the reaction temperature of the emulsion polymerization is 40-90 ℃.
According to the invention, the fluorine-containing acrylic ester monomer is matched with the non-fluorine monomer, and the non-fluorine monomer in the raw materials occupies a relatively large area in an emulsion polymerization mode, so that the fluorine-containing acrylic ester monomer and the non-fluorine monomer are copolymerized to form the positive electrode adhesive with strong binding force, high stability, good processability and good electrical property. On the one hand, a certain amount of non-fluorine monomer is used for preparing the fluorine-containing binder, so that the dosage of the fluorine-containing monomer can be reduced, and the production cost of the fluorine-containing binder can be reduced. On the other hand, the fluorine-containing acrylic ester monomer is adopted as the fluorine-containing monomer in the preparation of the fluorine-containing binder, and the fluorine-containing acrylic ester monomer and the non-fluorine-containing monomer have good copolymerization effect, so that the remarkable adverse effect on the processability, stability and electrical property of the fluorine-containing binder caused by the large-proportion introduction of the non-fluorine-containing monomer is avoided, and meanwhile, the fluorine-containing acrylic ester monomer is adopted as the raw material of the positive electrode binder, so that the positive electrode binder has the low surface energy characteristic of the fluorine-containing polymer and the high adhesive property of the olefin polymer.
Preferably, the fluorine-containing acrylate monomer comprises at least one of trifluoroethyl acrylate, tetrafluoropropyl acrylate, hexafluorobutyl acrylate, octafluoropentyl acrylate, perfluorohexyl methacrylate, dodecafluoroheptyl methacrylate and tridecyl methacrylate.
Preferably, the acrylate comprises at least one of methyl acrylate, methyl methacrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl propionate, hydroxyethyl acrylate, isooctyl acrylate, methacrylic acid.
Preferably, the non-fluorine-based monomer includes acrylonitrile, and the non-fluorine-based monomer further includes at least one of acrylate and acrylamide.
Preferably, the fluorine-containing acrylic ester monomer comprises the following components in percentage by mass: acrylonitrile=3 to 5:5 to 7. Under proper proportion, the acrylonitrile can endow the adhesive with stronger rigidity and cohesion, thereby improving the mechanical strength of the adhesive.
Preferably, the non-fluorine monomer comprises acrylonitrile, acrylic ester and acrylamide, wherein the acrylonitrile is calculated according to the mass ratio: acrylic ester: acrylamide=1 to 7:1 to 3:1 to 3. Under proper proportion, the non-fluorine monomer can cooperate to enhance the flexibility and the adhesive property of the adhesive.
Preferably, the method of preparing the positive electrode binder includes the steps of: s1, respectively preparing a first reaction solution and a second reaction solution, wherein the first reaction solution comprises 40-80 parts of fluorine-containing acrylate monomers and 50-110 parts of non-fluorine-containing monomers according to parts by weight, and the second reaction solution comprises 20-40 parts of fluorine-containing acrylate monomers and 30-70 parts of non-fluorine-containing monomers; s2, adding 1-5 parts of an emulsifier into 750-1000 parts of an aqueous solvent according to parts by mass, and then adding a first reaction solution, 0.5-3 parts of a chain transfer agent and 4-8 parts of an initiator under an inert atmosphere; s3, adding the second reaction solution and 3-6 parts of initiator into the reaction system simultaneously to react for 2-4 hours to obtain a third reaction solution; s4, demulsification treatment and drying treatment are carried out on the third reaction liquid, and then the positive electrode binder is obtained. The preparation method can ensure that the molecular weight distribution of the prepared adhesive is narrower by supplementing the reaction monomer in the polymerization process and maintaining the monomer concentration in the reaction process.
Preferably, the emulsifier comprises at least one of an alkyl salt emulsifier and an ether emulsifier.
Preferably, the emulsifier comprises at least one of sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, sodium dodecyl alcohol polyoxyethylene ether sulfate and perfluoropolyether.
Preferably, the initiator comprises at least one of a persulfate initiator and a peroxydicarbonate initiator.
Preferably, the initiator comprises at least one of diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-tert-butane peroxide, ammonium persulfate, potassium persulfate, sodium persulfate.
Preferably, the chain transfer agent includes at least one of an alcohol chain transfer agent, an ester chain transfer agent, and a thiol chain transfer agent.
Preferably, the chain transfer agent comprises at least one of ethyl acetate, butyl acetate, acetone, diethyl carbonate, methyl tertiary butyl ether, isopropanol, ethanol, methanol and dodecyl mercaptan.
Preferably, the mass percentage of each material added in the second reaction liquid is consistent with the mass percentage of each material added in the first reaction liquid.
Preferably, in S3, the second reaction solution and the initiator are added dropwise.
Preferably, in S3, the dropping speed of the second reaction liquid is 0.2 to 1 part/min.
Preferably, in S3, the initiator has a dropping rate of 0.01 to 0.05 parts/min.
Preferably, the oxygen content is maintained less than 200ppm during the reaction to prepare the binder.
Preferably, the weight average molecular weight of the positive electrode binder is 50 to 150 ten thousand.
According to a second aspect of the present invention, there is provided a lithium ion battery positive electrode comprising a current collector and a positive electrode active coating disposed on a surface of the current collector, the positive electrode active coating comprising any of the positive electrode binders described above. The positive electrode binder provided by the invention is used for preparing the positive electrode active coating of the positive electrode of the lithium ion battery, and based on the advantages that the positive electrode binder has low surface energy and high binding force, the characteristic of the low surface energy of the positive electrode binder is favorable for promoting the positive electrode active coating to be fully wetted by electrolyte, so that the lithium ion transmission dynamic property of the positive electrode of the lithium ion battery is improved, and the characteristic of the high binding force of the positive electrode binder is favorable for improving the structural stability of the lithium ion positive electrode, so that the situation that the positive electrode active coating is dropped or stripped from a positive electrode current collector still can not occur after the positive electrode binder is subjected to repeated charge and discharge cycles, and the cycle property of the lithium ion positive electrode is further improved.
According to a third aspect of the present invention, there is provided a lithium ion battery comprising the above lithium ion positive electrode. Based on the fact that the positive electrode of the lithium ion battery has good lithium ion dynamic transmission characteristics and cycle characteristics, the lithium ion battery provided by the invention can show good electrical performance.
Detailed Description
In order to make the technical solution of the present invention better understood by those skilled in the art, the technical solution of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention, and it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
Example 1
Treatment group 1A
1. Preparation of positive electrode binder
S1, respectively preparing a first reaction solution and a second reaction solution, wherein the first reaction solution comprises 50 parts of trifluoroethyl acrylate, 10 parts of ethyl acrylate, 12 parts of acrylamide and 50 parts of acrylonitrile according to parts by weight, and the second reaction solution comprises 40 parts of trifluoroethyl acrylate, 9 parts of ethyl acrylate, 11 parts of acrylamide and 40 parts of acrylonitrile;
s2, adding 1000 parts of water into a polymerization kettle, starting stirring, introducing nitrogen to keep the oxygen value of the reaction environment less than 200ppm, adding 2 parts of sodium dodecyl sulfate, then adding the first reaction liquid and 1 part of ethyl acetate, heating to 65 ℃ in a nitrogen atmosphere, and then adding 6 parts of ammonium persulfate with the concentration of 15wt% for reaction for 30min;
s3, continuously and simultaneously dropwise adding a second reaction solution and 5 parts of ammonium persulfate with the concentration of 15wt% into a reaction system to react for 3.5 hours to obtain a third reaction solution, wherein the dropwise adding speed of the second reaction solution is 0.47 part/min, and the dropwise adding speed of the ammonium persulfate is 0.024 part/min;
s4, demulsification treatment and drying treatment are carried out on the third reaction liquid, and then the powdery positive electrode binder is obtained.
2. Preparation of the Positive electrode
Cathode material 0.25Li 2 MnO 3 ·0.75LiMn 0.375 Ni 0.375 Co 0.25 O 2 The conductive agent acetylene black and the positive electrode binder are prepared into slurry according to the mass ratio of 95:3.5:1.5, the slurry is coated on an aluminum foil current collector, and then the aluminum foil current collector is dried in vacuum to prepare the positive electrode plate.
3. Preparation of lithium ion batteries
Preparing slurry from a negative electrode material graphite, a conductive agent acetylene black, a binder CMC and SBR according to a mass ratio of 94:1:2:3, coating the slurry on a copper foil current collector, and then carrying out vacuum drying to obtain a negative electrode plate;
the positive electrode sheet, the negative electrode sheet, the Celgard2400 separator and the electrolyte prepared above were then assembled into a soft-pack battery. Wherein the electrolyte used is a solution in which 1mol/L LiPF is dissolved 6 The volume ratio of the ethylene carbonate to the dimethyl carbonate is calculated as: dimethyl carbonate=1:1.
Treatment groups 2A to 5A of example 1 were prepared with reference to the formulation and method provided for treatment group 1A to prepare a positive electrode binder, a positive electrode slurry, a positive electrode, and a lithium ion battery, differing from treatment group 1A of example 1 in that treatment groups 2A to 5A of example 1 were used to prepare the mass ratio of the fluorine-containing acrylate monomer to the non-fluorine-containing monomer used in positive electrode bonding as variables shown in table 1. Wherein, the treatment groups 2A to 5A of example 1 realize the adjustment of mass ratio by reducing or increasing the mass fraction of trifluoroethyl acrylate, and the mass percentages of the materials added in the second reaction liquid are kept consistent with the mass percentages of the materials added in the first reaction liquid. Except for the above differences, the procedure for preparing the positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery of treatment groups 2A to 5A of example 1 was strictly consistent with treatment group 1A.
TABLE 1 variable for each treatment group of EXAMPLE 1
Comparative example 1
This comparative example the positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery were prepared with reference to the formulation and method provided in treatment group 1A of example 1, differing from treatment group 1A of example 1 in that this comparative example was based on the mass ratio of the fluorine-containing acrylic ester monomer to the non-fluorine-containing monomer as a variable, specifically, the fluorine-containing acrylic ester monomer: non-fluorine based monomer=1:6. The mass ratio of the trifluoroethyl acrylate is reduced to adjust the mass ratio, and the mass percentage of each material added in the second reaction liquid is consistent with that of each material added in the first reaction liquid. Except for the above-mentioned differences, the procedure for preparing the positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery of this comparative example was strictly consistent with the treatment group 1A of example 1.
Comparative example 2
This comparative example the positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery were prepared with reference to the formulation and method provided in treatment group 1A of example 1, differing from treatment group 1A of example 1 in that this comparative example was based on the mass ratio of the fluorine-containing acrylic ester monomer to the non-fluorine-containing monomer as a variable, specifically, the fluorine-containing acrylic ester monomer: non-fluorine based monomer=3:1. The mass ratio of the trifluoroethyl acrylate is adjusted by increasing the mass part of the trifluoroethyl acrylate, and the mass percentage of each material added in the second reaction liquid is consistent with that of each material added in the first reaction liquid. Except for the above-mentioned differences, the procedure for preparing the positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery of this comparative example was strictly consistent with the treatment group 1A of example 1.
Test example 1
1. Test object
Treatment groups 1A to 5A and positive electrode slurries, positive electrodes and batteries prepared in comparative examples 1 to 2.
2. Test method
(1) Viscosity of the positive electrode slurry: testing was performed using a german HAAKE MARS rheometer;
(2) And (3) testing the stripping force of the positive electrode slurry to the positive electrode: according to GB 2792 2014 test method for adhesive tape peel strength, 180 DEG peel test method is adopted to test the peel force of slurry to the positive electrode;
(3) Flexibility test of positive electrode: a cylindrical shaft bending experiment instrument is used, and the specific method is that a pole piece is cut into rectangular sample strips with the width of 5cm, then the rectangular sample strips are wound on a metal cylinder with the diameter of 2mm, the metal cylinder is pulled at a constant speed of 180 degrees, and whether the pole piece has breakage and cracks is observed. The flexibility of the pole piece is good, general and good from poor to good.
(4) Testing the normal temperature cycle performance of the battery: at 25 ℃, the lithium ion battery is charged to a voltage of 4.7V at a constant current of 0.5C (nominal capacity), then is charged to a current of less than or equal to 0.05C at a constant voltage of 4.7V, and is discharged to a voltage of 2.5V at a constant current of 1C after being placed for 10min, wherein the charging and discharging cycle is one time. The lithium ion battery is subjected to 800 charge-discharge cycles at 25 ℃ according to the conditions. Wherein the capacity retention is calculated according to formula (1).
3. Test results and analysis
The test results of test example 1 are shown in table 2. The test example mainly explores the influence of the mass ratio of the fluorine-containing acrylate monomer to the non-fluorine monomer in the preparation of the positive electrode bonding on the slurry and the positive electrode of the prepared bonding agent, and specifically explores the influence on the anticoagulation property of the slurry, the adhesive force of the positive electrode and the flexibility. In general, the peel force and the battery cycle capacity retention ratio for each of the treatment groups 1A to 5A were better than those of comparative example 1. By comparing the test results corresponding to the treatment groups 1A to 5A provided in example 1, it was found that the peeling force of the slurry against the positive electrode and the cycle capacity retention rate of the battery tended to be increased and then decreased with the increase in the content of the fluorine-containing acrylic acid ester monomer in the raw material for preparing the binder, and the peeling force corresponding to the treatment group 1A was the highest and the cycle capacity retention rate of the battery was the highest among the treatment groups 1A to 5A. And the viscosity of the positive electrode slurry of the treatment group 1A of example 1 was not greatly changed at 0h, 24h and 48h, which indicates that the viscosity stability of the prepared slurry was higher, i.e., the anticoagulation property of the slurry was better. Therefore, in the method for preparing the positive electrode binder provided by the invention, the optimal mass ratio of the fluorine-containing acrylic ester monomer to the non-fluorine-containing monomer in the raw materials is that: non-fluorine based monomer=1:1.6. However, when the mass ratio of the fluorinated acrylate monomer to the non-fluorinated monomer is too large, as shown in comparative example 1, the corresponding positive electrode peeling force is significantly reduced, and at the same time, the cycle capacity retention rate of the corresponding battery is also significantly reduced. When the content of trifluoroethyl acrylate in the raw material for preparing the binder is too high, as shown in comparative example 2, the anticoagulation performance of the corresponding positive electrode gel is reduced, and the specific changes of 0h, 24h and 48h are large, and particularly the viscosity ratio of 0h to 24h is as high as 19.3. This is because when the mass ratio of the fluorinated acrylate monomer to the non-fluorinated monomer exceeds the proper range, the fluorinated acrylate monomer itself undergoes homopolymerization, but does not undergo copolymerization with other non-fluorinated monomers.
According to the test example, when the mass ratio of the fluorine-containing acrylic ester monomer to the non-fluorine monomer is 1-2:1-5, the prepared positive electrode slurry, positive electrode and battery have better performance. In addition, the test example proves that the scheme provided by the invention can realize the copolymerization reaction of a higher proportion of non-fluorine olefin monomers and fluorine-containing acrylic ester monomers with smaller reactivity ratio, and the prepared positive electrode binder can keep good performance in an overbased and high-nickel environment.
TABLE 2 test results for test example 1
Example 2
Treatment group 1B
Treatment group 1B positive electrode binders, positive electrode slurries, positive electrodes, and lithium ion batteries were prepared according to the formulation and method provided in treatment group 1A.
Treatment groups 2B to 5B of example 2 positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery were prepared with reference to the formulation and method provided for treatment group 1B of example 2, treatment groups 2B to 5B of example 2 being different from treatment group 1B of example 2 in that treatment groups 2B to 5B of example 2 were used to prepare non-fluorine-based monomers used in the positive electrode binder, namely acrylonitrile: acrylic ester: the mass ratio of acrylamide was used as a variable, which is shown in table 3. Wherein, the treatment groups 2B to 5B of example 2 achieve the adjustment of mass ratio by decreasing or increasing the mass fraction of acrylonitrile, and the mass percentages of the materials added in the second reaction liquid are kept consistent with the mass percentages of the materials added in the first reaction liquid. Except for the above differences, the procedure for preparing the positive electrode binder, positive electrode slurry, positive electrode, and lithium ion battery in the treatment groups 2B to 5B of example 2 was strictly consistent with the treatment group 1B of example 2.
TABLE 3 variation of the mass ratio between non-fluorine-based monomers for each treatment group of EXAMPLE 2
Treatment group 6B
The treatment set was distinguished from the treatment set 1B of example 2 in that the treatment set replaced ethyl acrylate with equal mass of acrylonitrile, and the operation steps of the treatment set for preparing the positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery were strictly consistent with the treatment set 1B of example 2, except for the above differences, with reference to the formulation and method provided for the treatment set 1B of example 2 for preparing the positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery.
Treatment group 7B
The treatment set was distinguished from the treatment set 1B of example 2 in that the treatment set replaced acrylamide with acrylonitrile of equal mass, and the operation steps of the treatment set for preparing the positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery were strictly consistent with the treatment set 1B of example 2, except for the above differences, with reference to the formulation and method provided for the treatment set 1B of example 2.
Treatment group 8B
The treatment set was distinguished from the treatment set 1B of example 2 in that the treatment set was prepared with the same mass of acrylonitrile instead of ethyl acrylate and acrylamide by referring to the formulation and method provided for the treatment set 1B of example 2, and the operation steps of the treatment set for preparing the positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery were strictly consistent with the treatment set 1B of example 2, except for the above differences.
Treatment group 9B
The treatment set was distinguished from the treatment set 1B of example 2 in that the treatment set was prepared with the same mass of ethyl acrylate instead of acrylonitrile, acrylamide, and the operation procedure of the treatment set for preparing the positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery was strictly consistent with the treatment set 1B of example 2, except for the above-mentioned differences.
Treatment group 10B
The treatment set was distinguished from the treatment set 1B of example 2 in that the treatment set was prepared with the same mass of acrylamide instead of acrylonitrile, ethyl acrylate, and the operation steps of the treatment set for preparing the positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery were strictly consistent with the treatment set 1B of example 2, except for the above-mentioned differences, with reference to the formulation and method provided for the treatment set 1B of example 2.
Comparative example 3
The procedure for preparing the positive electrode binder, positive electrode slurry, positive electrode, and lithium ion battery of this comparative example was strictly consistent with the procedure for preparing the positive electrode binder, positive electrode slurry, positive electrode, and lithium ion battery of example 2, except that the same mass of trifluoroethyl acrylate was used instead of acrylonitrile, ethyl acrylate, and acrylamide as in the treatment group 1B of example 2, with the exception of the above.
Test example 2
1. Test object
Positive electrode slurries, positive electrodes and batteries were prepared in treatment groups 1B to 10B of example 2 and comparative example 3.
2. Test method
The test method performed in reference to test example 1 was used to test viscosity, peel force, flexibility, and cycle volume retention.
3. Test results and analysis
The test results of this test example are shown in Table 4. The test example is mainly for exploring the influence of the proportion of non-fluorine monomers used in the preparation of the positive electrode binder on the slurry, positive electrode and battery of the prepared binder, and specifically exploring the influence on the anticoagulation property of the slurry, the adhesive force and flexibility of the positive electrode and the cycle capacity retention rate of the battery. From the test results, it can be seen that when the ratio of acrylonitrile between non-fluorine monomers is properly increased, the peel strength of the positive electrode is improved, i.e., the peel force of the slurry to the positive electrode can be enhanced by acrylonitrile. Specifically, in the treatment groups 1B to 3B of example 2, as the ratio of acrylonitrile to the non-fluorine-based monomer increases, the peel strength of the slurry to the positive electrode increases, the flexibility of the positive electrode also improves significantly, and the cycle capacity retention rate of the battery also increases. However, when the acrylonitrile content was too low or too high, as shown in the treatment groups 4B and 5B of example 2, the peel strength of the corresponding positive electrode slurry, the flexibility of the positive electrode, and the cycle capacity retention rate of the battery were significantly reduced. This is because acrylonitrile can impart a strong rigidity and cohesion to the positive electrode binder, but when the content of acrylonitrile is too low, acrylonitrile cannot provide sufficient cohesion to the binder, and in particular, when acrylonitrile is not added, the peel strength corresponding to the produced positive electrode is significantly reduced as shown in treatment groups 9B to 10B of example 2. When the acrylonitrile content is too high, as shown in the treatment group 8B of example 2, the rigidity of the positive electrode binder is too high, and the prepared positive electrode has high brittleness and poor flexibility, which can affect the normal use of the positive electrode and further reduce the cycle capacity retention rate of the battery.
From the test results, it was found that when the non-fluorine-based monomer contained acrylonitrile, ethyl acrylate and acrylamide in the proper proportions, the prepared positive electrode exhibited the most excellent flexibility, as shown in the treatment groups 1B to 3B of example 2; when acrylonitrile, ethyl acrylate, acrylonitrile, and acrylamide were contained alone, as shown in the treatment groups 6B to 7B of example 2, it was found that the adhesive properties of the corresponding positive electrode produced were lowered. This is because the carbon chain of the acrylate and the amino group of the acrylamide can synergistically provide toughness to the prepared positive electrode binder, impart better flexibility to the corresponding positive electrode and enhance the peel force strength of the positive electrode binder.
In addition, when the emulsion polymerization reaction of the fluorine-containing acrylate monomer and the non-fluorine-containing monomer was not used in the preparation of the positive electrode binder, as shown in comparative example 3. The anticoagulation property, the adhesion to the positive electrode, the flexibility and the cycle capacity retention rate of the battery of the slurry corresponding to the treatment group 1B of example 2 were improved to some extent as compared with those of comparative example 3. The result shows that the positive electrode binder provided by the invention can keep good binding performance, alkali resistance and gel resistance in the preparation process and the use process of the lithium ion battery, and non-fluorine monomers are introduced in a proper proportion, so that the use cost of the positive electrode binder is reduced.
From the test results in this test case, it can be concluded that: the fluorine-containing acrylic ester monomer needs to be synergistic with the non-fluorine monomer in proper proportion to jointly improve the mechanical property of the positive electrode adhesive, so that the prepared positive electrode slurry has good gel resistance, good stripping force and flexibility, good cycle capacity retention rate of a battery and reduced use cost of the positive electrode adhesive.
TABLE 4 test results for test example 2
Example 3
Treatment group 1C
Treatment group 1C positive electrode binders, positive electrode slurries, positive electrodes, and lithium ion batteries were prepared according to the formulation and method provided in treatment group 1A of example 1.
Treatment groups 2C to 3C of example 3 positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery were prepared with reference to the formulation and method provided for treatment group 1C of example 3, treatment groups 2C to 3C of example 3 were different from treatment group 1C of example 3 in that treatment groups 2C to 3C of example 3 had the reaction temperature in preparing positive electrode binder as a variable, which is shown in table 5, and the operation steps of treatment groups 2C to 3C of example 3 for preparing positive electrode binder, positive electrode slurry, positive electrode and lithium ion battery were strictly consistent with treatment group 1C of example 3 except for the above differences.
TABLE 5 variation of reaction temperatures for treatment groups 1C-3C of example 3
Group of Reaction temperature/. Degree.C
Treatment group 1C 65
Treatment group 2C 40
Treatment group 3C 90
Comparative example 4
The procedure for preparing the positive electrode binder, positive electrode slurry, positive electrode, and lithium ion battery of this comparative example was strictly consistent with the treatment group 1C of example 3, except that the reaction temperature was 35 deg.c, which was different from the treatment group 1C of example 3, in the preparation of the positive electrode binder, positive electrode slurry, positive electrode, and lithium ion battery of this comparative example, which was described above, with reference to the formulation and method provided by the treatment group 1C of example 3.
Comparative example 5
The procedure for preparing the positive electrode binder, positive electrode slurry, positive electrode, and lithium ion battery of this comparative example was strictly consistent with the treatment group 1C of example 3, except that the reaction temperature was 95 deg.c, which was different from the treatment group 1C of example 3, in the preparation of the positive electrode binder, positive electrode slurry, positive electrode, and lithium ion battery of this comparative example, which was described above, with reference to the formulation and method provided by the treatment group 1C of example 3.
Test example 3
1. Test object
Positive electrode slurries, positive electrodes and batteries prepared in treatment groups 1C to 3C and comparative examples 4 to 5 of example 3.
2. Test method
The test method performed in reference to test example 1 was used to test viscosity, peel force, flexibility, and cycle volume retention.
Method for testing molecular weight and molecular weight distribution of binder: the determination was performed using gel permeation chromatography.
3. Test results and analysis
The test results of test example 3 are shown in table 6. From the test results, it can be found that the emulsion polymerization temperature provided by the invention can affect the performances of the positive electrode binder, and the positive electrode slurry, the positive electrode and the battery using the positive electrode binder. When the emulsion polymerization temperature for preparing the positive electrode binder was changed, as shown in the treatment groups 1C to 3C of example 3, it was found that the molecular weight of the binder was decreasing and the molecular weight distribution of the binder was widening with an increase in temperature. In particular, when the temperature is too low, as shown in comparative example 4, the corresponding binder molecular weight is too high, thereby leading to a large change in viscosity of the positive electrode slurry at different times, indicating poor anticoagulation and alkali resistance of the positive electrode slurry, resulting in a significant decrease in capacity retention rate of the battery; when the temperature is too high, as shown in comparative example 5, the molecular weight distribution is too broad, resulting in a decrease in the binding power of the positive electrode binder, thereby decreasing the capacity retention rate of the battery. The experimental results of the test example show that when the positive electrode binder is prepared at a proper temperature, the prepared positive electrode slurry has higher viscosity stability at different times, and the prepared battery has better capacity retention rate.
TABLE 6 test results for test example 3
Example 4
Treatment group 1D
Treatment group 1D positive electrode binders, positive electrode slurries, positive electrodes, and lithium ion batteries were prepared according to the formulation and method provided in treatment group 1A of example 1.
Treatment group 2D
The treatment group was distinguished from the treatment group 1D of example 4 in that the treatment group was not provided with the first reaction liquid and the second reaction liquid when preparing the positive electrode binder, the positive electrode slurry, the positive electrode, and the lithium ion battery with reference to the formulation and the method provided in the treatment group 1D of example 4, and the treatment group was kept strictly consistent with the treatment group 1D of example 4 except for the above-mentioned differences. Specifically, the procedure for preparing the positive electrode binder is as follows:
s1, adding 2 parts of sodium dodecyl sulfonate into 1000 parts of water according to parts by weight, introducing nitrogen to keep the oxygen value of the reaction environment at 200pm, then adding 90 parts of trifluoroethyl acrylate, 19 parts of ethyl acrylate, 23 parts of acrylamide, 90 parts of acrylonitrile, 1 part of ethyl acetate and 11 parts of ammonium persulfate with the concentration of 15wt%, and then heating to 65 ℃ under the nitrogen atmosphere and preserving heat for reaction for 3.5 hours;
s2, demulsification treatment and drying treatment are carried out on the reactant, and then the powdery positive electrode binder is obtained.
Treatment group 3D
The treatment group was distinguished from the treatment group 1D of example 4 in that the drip acceleration of the second reaction liquid for preparing the positive electrode binder was 1.2 parts/min and the drip acceleration of ammonium persulfate was 0.1 parts/min, referring to the formulation and method provided in the treatment group 1D of example 4 to prepare the positive electrode binder, the positive electrode slurry, the positive electrode and the lithium ion battery, and the treatment group 1D of example 4 were kept strictly identical except for the above differences.
Comparative example 6
The formulation and method provided by the comparative example with reference to treatment group 1D of example 4 produced a positive electrode binder, a positive electrode slurry, a positive electrode, and a lithium ion battery, differing from treatment group 1D of example 4 in that the comparative example produced a positive electrode binder by a suspension polymerization method, and the treatment group produced a positive electrode slurry, a positive electrode, and a lithium ion battery kept strictly consistent with treatment group 1D of example 4, except for the above-described differences. Specifically, the procedure for preparing the positive electrode binder is as follows:
90 parts of trifluoroethyl acrylate, 19 parts of ethyl acrylate, 23 parts of acrylamide, 90 parts of acrylonitrile, 1 part of ethyl acetate, 11 parts of ammonium persulfate with the concentration of 15wt% and 2 parts of hydroxypropyl methyl cellulose ether (suspending agent) are added into a reaction vessel, 1000 parts of water are added after the mixture is uniformly dispersed, the reaction monomers are dispersed into small liquid beads through rapid stirring, then the temperature is raised to 65 ℃ under the nitrogen atmosphere, the reaction is kept for 3.5 hours, and after the reaction is finished, the reactant is washed and dried to obtain the powdery anode binder.
Test example 4
1. Test object
Treatment groups 1D to 3D of example 4 and positive electrode slurry, positive electrode, and battery prepared in comparative example 6.
2. Test method
The test was performed according to the test method of test example 3.
3. Test results and analysis
The test results of test example 4 are shown in table 7. From the test results, it can be found that the preparation method provided by the invention can affect the performances of the positive electrode binder, the positive electrode slurry, the positive electrode and the battery using the positive electrode binder. Specifically, from the test results of the treatment group 1D of example 4 in the present test example, the performance of the corresponding positive electrode slurry, positive electrode, and battery was optimal because the treatment group 1D of example 4 was continuously fed with the reaction monomer during polymerization, and the dispersion tendency of the molecular weight of the prepared binder was able to be reduced by controlling the dropping speed to maintain the monomer and initiator concentrations during the reaction, so that the molecular weight distribution was narrowed. For the treatment group 2D of example 4, all of the reaction monomers were added at once to react, which resulted in a widening of the molecular weight distribution, thereby reducing the peel strength of the positive electrode binder. This is because, during the polymerization of the copolymerization reaction, the concentration of the reactant is decreasing, so that the dispersion of the molecular weight of the copolymer is increased, and it is not ensured that a copolymer having a narrow molecular weight distribution is formed. Similarly, in the treatment group 3D of example 4, the second reaction was also added dropwise together with the dropping speed of the initiator when the positive electrode binder was prepared, and too fast dropping would occur when the reaction was not yet ended and the concentration of the reactant was decreasing, thereby leading to a widening of the binder molecular weight distribution.
The cathode binder prepared in comparative example 6, and the corresponding slurry, cathode, and battery using the same, had significantly reduced anticoagulation, flexibility, and capacity retention. This is because it is difficult for the suspension polymerization method to uniformly maintain the equivalent balance of the shearing force and the interfacial force in the reaction process, and thus the reaction monomer beads are difficult to stabilize at similar particle sizes, and further the performance of the positive electrode binder is affected, and the performances of the slurry, the positive electrode and the battery using the same are remarkably reduced.
TABLE 7 test results for test example 4
The above embodiments are only for illustrating the technical solution of the present invention and not for limiting the scope of the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present invention may be modified or substituted without departing from the spirit and scope of the technical solution of the present invention.

Claims (10)

1. The positive electrode binder is characterized in that raw materials for preparing the positive electrode binder comprise fluoroacrylate monomers and non-fluorine monomers, wherein the non-fluorine monomers comprise at least one of acrylonitrile, acrylic acid ester and acrylamide, and the fluoroacrylate monomers comprise the following components in percentage by mass: the non-fluorine monomer=1 to 2:1 to 5; the positive electrode binder is prepared by emulsion polymerization of the fluorine-containing acrylic ester monomer and the non-fluorine monomer, and the reaction temperature of the emulsion polymerization is 40-90 ℃.
2. The positive electrode binder of claim 1, wherein: the non-fluorine-based monomer comprises the acrylonitrile, and the non-fluorine-based monomer further comprises at least one of the acrylic ester and the acrylamide.
3. The positive electrode binder according to claim 2, wherein the fluorine-containing acrylic acid ester monomer: acrylonitrile=3 to 5:5 to 7.
4. The positive electrode binder of claim 3, wherein: the non-fluorine monomer comprises the acrylonitrile, the acrylic ester and the acrylamide, and the non-fluorine monomer comprises the acrylonitrile according to the mass ratio: the acrylate: acrylamide=1 to 7:1 to 3:1 to 3.
5. The positive electrode binder according to any one of claims 1 to 4, wherein the method for preparing the positive electrode binder comprises the steps of:
s1, respectively preparing a first reaction solution and a second reaction solution, wherein the first reaction solution comprises 40-80 parts of fluorine-containing acrylate monomers and 50-110 parts of non-fluorine-containing monomers according to parts by weight, and the second reaction solution comprises 20-40 parts of fluorine-containing acrylate monomers and 30-70 parts of non-fluorine-containing monomers;
s2, adding 1-5 parts of an emulsifier into 750-1000 parts of an aqueous solvent according to parts by mass, and then adding the first reaction solution, 0.5-3 parts of a chain transfer agent and 4-8 parts of an initiator under an inert atmosphere;
s3, adding the second reaction liquid and 3-6 parts of the initiator into a reaction system simultaneously to react for 2-4 hours to obtain a third reaction liquid;
s4, demulsification treatment and drying treatment are carried out on the third reaction liquid to obtain the positive electrode binder.
6. The positive electrode binder according to claim 5, wherein the emulsifier comprises at least one of an alkyl salt emulsifier and an ether emulsifier.
7. The positive electrode binder of claim 5, wherein the initiator comprises at least one of a persulfate initiator and a peroxydicarbonate initiator.
8. The positive electrode binder of claim 5, wherein the chain transfer agent comprises at least one of an alcohol chain transfer agent, an ester chain transfer agent, and a thiol chain transfer agent.
9. The positive electrode of the lithium ion battery is characterized in that: the positive electrode of the lithium ion battery comprises a current collector and a positive electrode active coating layer arranged on the surface of the current collector, wherein the positive electrode active coating layer comprises the positive electrode binder as claimed in any one of claims 1 to 8.
10. A lithium ion battery, characterized in that: the lithium ion battery comprises the lithium ion battery positive electrode as claimed in claim 9.
CN202310140977.2A 2023-02-21 2023-02-21 Positive electrode binder and lithium ion battery positive electrode and lithium ion battery using same Pending CN116445109A (en)

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