CN116845242A

CN116845242A - Binder composition for secondary battery electrode, electrode for secondary battery, and secondary battery

Info

Publication number: CN116845242A
Application number: CN202310841928.1A
Authority: CN
Inventors: 李怡霏; 张凌
Original assignee: Shanghai 100km New Material Technology Co ltd
Current assignee: Shanghai 100km New Material Technology Co ltd
Priority date: 2023-07-10
Filing date: 2023-07-10
Publication date: 2023-10-03

Abstract

The application aims to provide a binder composition for a secondary battery electrode, a secondary battery electrode and a secondary battery. The adhesive composition comprises a polymer M and N-methylpyrrolidone; wherein the polymer M satisfies at least the following conditions: comprising nitrile monomer units; the volume average particle diameter is 5-50 mu m; the temperature of more than 30wt% of the thermal weight loss is 150-400 ℃; the content of each element belonging to group 17 of the periodic table is less than 100 mass ppm. The binder composition enables the preparation of a slurry composition that is supplied to high-speed coating and high-speed pressing, and enables the formation of an electrode for a secondary battery that can give rise to excellent high-temperature storage and cycle characteristics to the secondary battery.

Description

Binder composition for secondary battery electrode, electrode for secondary battery, and secondary battery

Technical Field

The application belongs to the technical field of new energy, and relates to a binder composition for a secondary battery electrode, a slurry composition for the secondary battery electrode, an electrode for the secondary battery and a secondary battery.

Background

The binder is one of important constituent materials of the secondary battery pole piece, is a high molecular compound for adhering active substances and conductive agents in the electrode pole piece to the electrode current collector, has the functions of enhancing the contact among the active materials, the conductive agents and the current collector and stabilizing the pole piece structure, and is an additional material with higher technical content in the lithium ion battery material. Studies have shown that although the binder is used in a small amount in the electrode sheet, the merits of the binder properties directly affect the capacity, life and cycle characteristics of the battery.

The binder for lithium ion batteries that was first commercialized was polyvinylidene fluoride (PVDF). However, such binders have the following disadvantages: a: poor electronic and ionic conductivity; b: is easy to be swelled by electrolyte, so that the adhesiveness of active substances on a current collector is poor; c: the mechanical property and elasticity are not ideal; d: lithium carbide is easy to form with metal lithium, and the service life and the cycle performance of the battery are affected; e: the humidity requirement for the environment is high when in storage and use.

With the continuous development of the lithium ion battery industry, the performance requirements of the binder are also continuously improved. The lithium ion battery with the novel structure needs to have excellent mechanical properties by the binder. The power lithium ion battery needs to have good electric conductivity of electrons and ions while the binder has good adhesion due to high discharge power. High energy density lithium ion batteries use positive and negative active materials with high specific capacity, and these materials have large volume changes during the process of lithium intercalation, and in order to maintain the stability of the electrode structure, the binder needs to have good elasticity to buffer the volume effect.

Disclosure of Invention

Problems to be solved by the invention

In recent years, from the viewpoint of improving productivity of an electrode, it has been demanded to apply a slurry composition to a current collector at a high speed and press a slurry dried product formed on the current collector at a high speed, thereby improving the production speed of an electrode composite layer. In addition, the secondary battery is required to have not only good cycle characteristics at normal temperature but also excellent storage and cycle characteristics even in a high-temperature environment in the field of, for example, electric automobiles.

However, when the slurry composition obtained using the conventional binder composition is supplied to high-speed coating and high-speed pressing, there is a problem that the slurry dried product adheres to a pressing portion (pressing roller or the like) of the pressing device and peels off from the current collector at the time of high-speed pressing. In addition, even if an electrode composite layer is formed from a slurry composition obtained using the above-described conventional binder composition, an electrode having the electrode composite layer may have difficulty in sufficiently exhibiting excellent high-temperature storage and cycle characteristics of a secondary battery.

Therefore, in order to solve all or part of the technical problems described above, the present application provides the following technical solutions:

an object of the present application is to provide a binder composition for a secondary battery electrode, which enables the preparation of a slurry composition that can be supplied to high-speed coating and high-speed pressing, and enables the formation of a secondary battery electrode that can exhibit excellent high-temperature storage and cycle characteristics of a secondary battery.

Another object of the present application is to provide use of the binder composition for a secondary battery electrode in the preparation of a slurry composition for a secondary battery electrode, an electrode composite layer for a secondary battery, an electrode for a secondary battery, or a secondary battery.

A third object of the present application is to provide a slurry composition for a secondary battery electrode, which can be supplied to high-speed coating and high-speed pressing, and can form a secondary battery electrode that can exhibit excellent high-temperature storage and cycle characteristics of a secondary battery.

Further, a fourth object of the present application is to provide an electrode for a secondary battery which can give a secondary battery excellent in high-temperature storage and cycle characteristics.

Further, a fifth object of the present application is to provide a secondary battery excellent in high-temperature storage and cycle characteristics.

Solution for solving the problem

The present inventors have conducted intensive studies in order to solve the above-mentioned problems. Then, the present inventors found that a slurry composition capable of being supplied to high-speed coating and high-speed pressing and a secondary battery excellent in high-temperature storage and cycle characteristics can be formed if a binder composition comprising a polymer M and N-methylpyrrolidone, the above-mentioned polymer M satisfying specific conditions and having a volume average particle diameter within a prescribed range, is used, and completed the present application.

That is, the present application has an object to advantageously solve the above-mentioned problems, and a binder composition for a secondary battery electrode according to the present application is characterized by comprising a polymer M and N-methylpyrrolidone, wherein the polymer M satisfies the following: (1) having a nitrile monomer unit; (2) a volume average particle diameter of 5 μm or more and less than 50 μm; (3) A temperature at which a thermal weight loss of 30 mass% or more exceeds 150 ℃ and is less than 400 ℃; (4) The content of each element belonging to group 17 of the periodic table is less than 100 mass ppm.

As described above, according to the slurry composition obtained by using the binder composition containing the polymer M and N-methylpyrrolidone, an electrode can be produced well by high-speed coating and high-speed pressing, and the volume average particle diameter of the polymer M satisfies the specific conditions and falls within the predetermined range. In addition, according to the electrode thus fabricated, the secondary battery can exhibit excellent high-temperature storage and cycle characteristics.

In the present application, the term "monomer unit" of the polymer means "a repeating unit derived from a monomer contained in a polymer obtained by using the monomer".

In the present application, the term "volume average particle diameter" means "particle diameter (D50) in which the cumulative volume calculated from the small particle diameter side in the particle size distribution (volume basis) measured by the laser diffraction method is 50%.

In the present application, "a temperature of 30 mass% or more of thermal weight loss" and "a content of each element belonging to group 17 of the periodic table" can be measured by using the measurement method described in the examples of the present specification.

The insoluble content of the polymer M in N-methylpyrrolidone is 8 mass% or less. If the amount of the insoluble component of the polymer M in N-methylpyrrolidone is 8 mass% or less, the high-temperature storage and cycle characteristics of the secondary battery can be further improved.

In the present application, the "insoluble content of polymer M in N-methylpyrrolidone" can be measured by the method described in the examples of the present application.

Here, the polymer M contains a nitrile monomer unit in a proportion of 50 mass% or more. If the polymer M contains the nitrile monomer unit in a proportion of 50 mass% or more, the high-temperature storage and cycle characteristics of the secondary battery can be further improved.

The volume average particle diameter of the polymer M is preferably 10 μm or more and less than 40. Mu.m. If the volume average particle diameter of the polymer M is within the above range, the above effects of improving the high-temperature storage and cycle characteristics and/or electrolyte injection properties of the secondary battery can be further obtained.

Here, the binder composition for a secondary battery electrode of the present application preferably further comprises a phosphorus-containing additive containing at least one of an organic phosphate compound, an organic phosphite compound, an organic phosphonate compound, and a phosphazene compound; the content of the phosphorus-containing additive is 5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the polymer M. The binder composition contains a phosphorus-containing additive, which can inhibit the swelling of the polymer M in the electrolyte, so that the high-temperature storage and cycle characteristics of the secondary battery are further improved.

The present application also aims to advantageously solve the above-mentioned problems, and a secondary battery electrode slurry composition of the present application is characterized by comprising an electrode active material and any of the above-mentioned binder compositions for secondary battery electrodes. In this way, according to the slurry composition containing the electrode active material and any of the binder compositions described above, an electrode can be manufactured well by high-speed coating and high-speed pressing. In addition, according to the electrode thus fabricated, the secondary battery can exhibit excellent high-temperature storage and cycle characteristics.

Further, the present application has an object to advantageously solve the above-mentioned problems, and an electrode for a secondary battery of the present application is characterized in that the electrode comprises an electrode composite layer comprising an electrode composite layer formed of the above-mentioned paste composition for a secondary battery electrode. Thus, an electrode having an electrode composite layer obtained using a slurry composition containing an electrode active material and any one of the binder compositions described above can exhibit excellent high-temperature storage and cycle characteristics of a secondary battery.

The present application is also directed to a secondary battery that advantageously solves the above-described problems, and is characterized by comprising the above-described electrode for a secondary battery. In this way, if the above-described electrode for a secondary battery is used, a secondary battery excellent in high-temperature storage and cycle characteristics can be manufactured.

Effects of the application

According to the present application, it is possible to provide a binder composition for a secondary battery electrode, which can prepare a slurry composition that can be supplied to high-speed coating and high-speed pressing, and can form a secondary battery electrode that can give a secondary battery excellent in high-temperature storage and cycle characteristics.

Further, according to the present application, there can be provided the use of any of the binder compositions for secondary battery electrodes described above in the preparation of a slurry composition for secondary battery electrodes, an electrode composite layer for secondary batteries, an electrode for secondary batteries or a secondary battery.

Further, according to the present application, it is possible to provide a slurry composition for a secondary battery electrode that can be supplied to high-speed coating and high-speed pressing, and can form a secondary battery electrode that can give a secondary battery excellent in high-temperature storage and cycle characteristics.

Further, according to the present application, it is possible to provide an electrode for a secondary battery capable of exhibiting excellent high-temperature storage and cycle characteristics.

Further, according to the present application, a secondary battery excellent in high-temperature storage and cycle characteristics can be provided.

Detailed Description

Other advantages and effects of the present application will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present application with reference to specific examples. The application may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present application.

The binder composition for a secondary battery electrode of the present application can be used for preparing the slurry composition for a secondary battery electrode of the present application. The slurry composition for secondary battery electrodes of the present application can be used for forming an electrode (secondary battery electrode) of a secondary battery such as a lithium ion secondary battery. The secondary battery electrode of the present application is further characterized by comprising an electrode composite layer formed from the secondary battery electrode slurry composition of the present application. The secondary battery of the present application is characterized by having an electrode for a secondary battery produced using the slurry composition for a secondary battery electrode of the present application.

Binder composition for secondary battery electrode

The adhesive composition of the application comprises the polymer M and N-methylpyrrolidone, optionally together with further ingredients.

The adhesive composition of the present application is characterized in that the polymer M satisfies at least the following conditions: (1) having a nitrile monomer unit; (2) a volume average particle diameter of 5 μm or more and less than 50 μm; (3) A temperature at which a thermal weight loss of 30 mass% or more exceeds 150 ℃ and is less than 400 ℃; (4) The content of each element belonging to group 17 of the periodic table is less than 100 mass ppm.

Further, since the binder composition of the present application satisfies the above conditions and the volume average particle diameter of the polymer M is in the above range, if the binder composition is used, a slurry composition which can be applied at high speed and pressed at high speed can be produced, and an electrode which can give excellent high-temperature storage and cycle characteristics to a secondary battery can be produced. As described above, the reason why the above-described effects can be obtained by using the adhesive composition in which the polymer M is dispersed in N-methylpyrrolidone is not yet determined, and is presumed as follows: when the slurry composition obtained by using the binder composition of the present application is applied to a current collector at a high speed and dried, a slurry dried product in which the polymer from the polymer M and the electrode active material are firmly bonded can be formed by interaction of hydrogen bond and the like between the polymer M and the electrode active material in the slurry composition. Further, even if such a slurry dried product is pressed at a high speed, the polymer is strongly bonded to the electrode active material, and therefore, it is considered that the slurry dried product can be inhibited from peeling from the current collector.

Further, the polymer M in the slurry composition coated on the current collector at a high speed may be moved (migrated) in the surface direction of the slurry composition on the opposite side of the current collector due to thermal convection or the like at the time of drying the slurry composition. However, by using the polymer M having a small volume average particle diameter as described above, the adhesive strength between the polymer M and the electrode active material is improved, and migration of the polymer M can be suppressed. Thus, the polymer from the polymer M can be uniformly distributed in the resulting electrode composite layer. Further, if a polymer M having a small volume average particle diameter is used, the particle number of the polymer M can be relatively increased as compared with the case of using a polymer M having a large volume average particle diameter of the same mass. As described above, the polymer particles as the binder are distributed in the electrode composite layer in large amounts and uniformly, and thus it is considered that the phenomenon that the coordination of charge carriers (lithium ions and the like) is excessively concentrated on the surface of the electrode active material can be suppressed, and the high-temperature storage and cycle characteristics of the secondary battery can be improved.

Thus, if the binder composition of the present application is used, a slurry composition that can be supplied to high-speed coating and high-speed pressing can be obtained. In addition, if an electrode manufactured using the slurry composition including the binder composition of the present application is used, the secondary battery can exhibit excellent high-temperature storage and cycle characteristics.

Polymer M

The polymer M is a component that functions as a binder, and is held in the electrode composite layer formed on the current collector using the slurry composition containing the binder composition so that the component such as the electrode active material contained in the electrode composite layer does not separate from the electrode composite layer.

The polymer M comprises monomer units containing nitrile groups, optionally (meth) acrylate monomer units and/or alkylene structural units having 4 or more carbon atoms.

Monomer units containing nitrile groups

Examples of the nitrile group-containing monomer capable of forming a nitrile group-containing monomer unit include α, β -ethylenically unsaturated nitrile monomers. The α, β -ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α, β -ethylenically unsaturated compound having a nitrile group, and examples thereof include: acrylonitrile; alpha-halogenated acrylonitrile such as alpha-chloroacrylonitrile and alpha-bromoacrylonitrile; and α -alkylacrylonitriles such as methacrylonitrile and α -ethylacrylonitrile. Among them, from the viewpoints of improving the adhesion of the polymer M, improving the mechanical strength of the positive electrode, and improving the high-voltage cycle characteristics of the secondary battery, acrylonitrile and methacrylonitrile are preferable, and acrylonitrile is more preferable.

These may be used singly or in combination of two or more.

The content of the nitrile group-containing monomer units in the polymer M is preferably 60 mass% or more, and more preferably 70 mass% or more, based on 100 mass% of all the repeating units (the total of the monomer units and the structural units) in the polymer M. When the content ratio of the nitrile group-containing monomer units in the polymer M is within the above-described range, the conductive material in the positive electrode slurry of the present application is inhibited from agglomerating, and the dispersion stability of the slurry is improved. Further, the high-voltage cycle characteristics and cycle characteristics of the secondary battery can be improved.

(meth) acrylate monomer units

As the (meth) acrylate monomer capable of forming the (meth) acrylate monomer unit, there may be mentioned: alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, glycidyl methacrylate and other alkyl methacrylates. Among these, from the viewpoint of ensuring dispersion stability of the positive electrode slurry, the (meth) acrylic acid ester monomer is preferably an alkyl acrylate having 4 to 10 carbon atoms of an alkyl group bonded to a non-carbonyl oxygen atom, and specifically, n-butyl acrylate and 2-ethylhexyl acrylate are preferable, and n-butyl acrylate is more preferable. These may be used singly or in combination of two or more.

The content of the (meth) acrylate monomer unit in the polymer M is 10 mass% or more, preferably 20 mass% or more, more preferably 30 mass% or more, and preferably 40 mass% or less, based on 100 mass% of the total repeating units in the polymer M. By setting the content of the (meth) acrylate monomer unit in the polymer M to 40 mass% or less, the solubility of the polymer M in an organic solvent such as NMP can be improved, and the dispersion stability of the positive electrode slurry can be further improved. Further, by setting the content of the (meth) acrylate monomer unit in the polymer M to 10 mass% or more, the stability of the positive electrode composite material layer formed using the positive electrode slurry with respect to the electrolyte can be improved, and the high-voltage cycle characteristics of the secondary battery manufactured using the obtained positive electrode slurry can be improved.

Alkylene structural unit having 4 or more carbon atoms

The alkylene structural unit having 4 or more carbon atoms may be linear or branched, and is preferably linear, that is, a linear alkylene structural unit, from the viewpoint of improving the dispersion stability of the positive electrode slurry and the high-voltage cycle characteristics and cycle characteristics of the secondary battery.

The method of introducing the alkylene structural unit having 4 or more carbon atoms into the polymer M is not particularly limited, and examples thereof include the following methods (1) and (2):

(1) Method for converting conjugated diene monomer units into alkylene structural units by preparing a polymer from a monomer composition comprising the conjugated diene monomer, and hydrogenating the polymer

(2) A method for producing a polymer from a monomer composition containing a 1-olefin monomer having 4 or more carbon atoms. Among these, the method of (1) is preferable because it is easy to produce the polymer M.

Among them, examples of the conjugated diene monomer include conjugated diene compounds having 4 or more carbon atoms such as 1, 3-butadiene, isoprene, 2, 3-dimethyl-1, 3-butadiene, and 1, 3-pentadiene. Among them, 1, 3-butadiene is preferable. That is, the alkylene structural unit having 4 or more carbon atoms is preferably a structural unit (conjugated diene hydride unit) obtained by hydrogenating a conjugated diene monomer unit, more preferably a structural unit (1, 3-butadiene hydride unit) obtained by hydrogenating a 1, 3-butadiene monomer unit.

Examples of the 1-olefin monomer having 4 or more carbon atoms include 1-butene and 1-hexene.

These conjugated diene monomers and 1-olefin monomers having 4 or more carbon atoms may be used singly or in combination.

The content of the alkylene structural unit having 4 or more carbon atoms in the polymer M is preferably 20 mass% or less, more preferably 10 mass% or less, based on 100 mass% of the total repeating units (the total of the monomer units and the structural units) in the polymer M. When the content ratio of the alkylene structural unit having 4 or more carbon atoms in the polymer M is within the above range, the dispersion stability of the positive electrode slurry and the high-voltage cycle characteristics and cycle characteristics of the secondary battery can be improved.

Process for the preparation of polymers M

The method for producing the polymer M is not particularly limited, and may be produced, for example, by polymerizing a monomer composition containing the above-mentioned monomer to obtain a polymer, and optionally, hydrogenating the obtained polymer.

The content ratio of each monomer in the monomer composition of the present application can be determined based on the content ratio of each monomer unit and the structural unit (repeating unit) in the polymer M.

The polymerization method is not particularly limited, and any of solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, and the like may be used. In each polymerization method, a known emulsifier and a known polymerization initiator may be used as required.

The amount of the binder to be blended in the positive electrode slurry of the present application is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, based on 100 parts by mass of the positive electrode active material, in terms of solid matter conversion. By setting the amount of the binder to 0.1 part by mass or more with respect to 100 parts by mass of the positive electrode active material, the adhesion between the positive electrode active materials, the conductive material, and the current collector can be improved, and therefore, when a secondary battery is produced, good cycle characteristics can be obtained, and the battery life can be prolonged. In addition, when the positive electrode obtained by using the positive electrode slurry containing the binder is applied to a secondary battery, the dispersibility of the electrolyte solution can be ensured and good cycle characteristics can be obtained by making the amount of the binder 10 parts by mass or less.

Volume average particle diameter

Here, the polymer M used in the present application is required to have a volume average particle diameter of 5 μm or more and less than 50 μm, and the volume average particle diameter of the polymer M is preferably 10 μm or more, more preferably 15 μm or more, further preferably 20 μm or more, preferably 50 μm or less, more preferably 40 μm or less, further preferably 30 μm or less. When the volume average particle diameter of the polymer M is less than 5 μm, sufficient adhesive strength between the polymer M and the electrode active material cannot be ensured. Therefore, the adhesion of the slurry dried product to the pressing roller or the like at the time of high-speed coating and high-speed pressing cannot be suppressed, and the high-temperature storage characteristics of the secondary battery are degraded. On the other hand, when the volume average particle diameter of the polymer M is 50 μm or more, peeling of the slurry dried product from the current collector at the time of high-speed coating and high-speed pressing cannot be suppressed, and the high-temperature storage characteristics of the secondary battery are degraded.

The volume average particle diameter of the polymer M can be adjusted by changing the amount (concentration) of the polymer in the premix for phase inversion emulsification in an emulsification step described later, for example. Specifically, the volume average particle diameter of the polymer M obtained by phase inversion emulsification can be reduced by reducing the amount (concentration) of the polymer in the premix.

A temperature at which the thermal weight loss is 30 mass% or more

The temperature of the polymer M at which the thermal weight loss is 30 mass% or more is not particularly limited as long as it exceeds 150 ℃ and is less than 400 ℃ at atmospheric pressure, but is preferably 180 ℃ or more, more preferably 200 ℃ or more, preferably 397 ℃ or less, and more preferably 395 ℃ or less. If the temperature of the polymer M at which the thermal weight loss is 30 mass% or more is within the above-described range, the expansion of the storage thickness at high temperature of the secondary battery can be suppressed.

The content of each element belonging to group 17 of the periodic Table

The content of each element belonging to group 17 of the periodic table is not particularly limited as long as it is less than 100 mass ppm, preferably less than 50 mass ppm, more preferably less than 30 mass ppm, and most preferably all 1 mass ppm or less. If the content of each element belonging to group 17 of the periodic table is within the above-described range, the high-temperature storage and cycle characteristics of the secondary battery can be improved.

The "elements belonging to group 17 of the periodic table" means F, cl, br, I, at and Ts.

Insoluble component amount of Polymer M in N-methylpyrrolidone (NMP)

The amount of insoluble components in NMP is required to be 8 mass% or less, preferably 6 mass% or less, more preferably 5 mass% or less, even more preferably 4 mass% or less, and particularly preferably 3 mass% or less. It is presumed that the polymer M having an NMP insoluble content of 8 mass% or less is excellent in flexibility and thus has a property as a buffer material, and therefore is easily deformed without inhibiting displacement of an electrode active material or the like when the electrode composite layer is pressed before pressing. Therefore, if the binder composition containing the polymer M is used, an electrode having a highly densified electrode composite layer can be produced satisfactorily. The lower limit of the amount of insoluble components of the polymer M in NMP is 0 mass% or more, and is preferably 0.01 mass% or more from the viewpoint of suppressing excessive elution of the polymer M into the electrolyte solution and securing battery characteristics of the secondary battery.

The amount of insoluble components in NMP in the polymer M can be adjusted by changing the type and amount of the monomer used for preparing the polymer M, and the polymerization conditions such as the amount of the molecular weight regulator used, the reaction temperature, and the reaction time.

Other ingredients

The adhesive composition of the present application may contain components (other components) other than the above components. For example, a phosphorus-containing additive, which can inhibit swelling of the polymer M in the electrolyte, further improves the high-temperature storage and cycle characteristics of the secondary battery.

The phosphorus-containing additive comprises at least one of an organic phosphate compound, an organic phosphite compound, an organic phosphonate compound, or a phosphazene compound; the content of the phosphorus-containing additive is 5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the polymer M.

The phosphorus-containing additive comprises at least one of tri (2, 2-trifluoroethyl) phosphate, tri (2, 2-trifluoroethyl) phosphite, triphenyl phosphite, diethyl ethylphosphonate, diethyl phenylphosphonate, 2-ethoxy-2, 4, 6-pentafluoro-1,3,5,2,4,6-triphosphazene or pentafluoro (phenoxy) cyclotriphosphazene.

Preparation of binder composition for secondary battery electrode

The binder composition for a secondary battery electrode of the present application is not particularly limited. For example, a dispersion containing the polymer M obtained by the method described in the item "method for producing the polymer M" can be directly used as the binder composition. For example, the above-mentioned organic solvent and other components may be added to the dispersion liquid containing the polymer M and mixed by a known method to prepare a binder composition.

Slurry composition for secondary battery electrode

The slurry composition for a secondary battery electrode of the present application is a composition for forming an electrode composite layer, and comprises an electrode active material and the binder composition for a secondary battery electrode of the present application described above, and optionally further comprises other components. That is, the slurry composition for a secondary battery electrode of the present application generally contains an electrode active material, the polymer M described above, and a dispersion medium, and optionally further contains other components. Further, since the slurry composition of the present application contains the binder composition, it can be supplied to high-speed coating and high-speed pressing, and can provide a secondary battery exhibiting excellent high-temperature storage and cycle characteristics.

In the following, a case where the slurry composition for secondary battery electrode is a slurry composition for lithium ion secondary battery negative electrode will be described as an example, but the present application is not limited to the following example.

Electrode active material

Positive electrode active material

The positive electrode active material may include a compound capable of intercalating and deintercalating lithium, and in particular, may include one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof. As a specific example, a compound represented by one of the chemical formulas may be used. Li (Li) _a A _1-b X _b D ₂ (0.90≤a≤1.8，0≤b≤0.5)；Li _a A _1-b X _b O _2-c D _c (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05)；Li _a E _1-b X _b O _2-c D _c (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05)；Li _a E _2-b X _b O _4-c D _c (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05)；Li _a Ni _1-b-c Co _b X _c D _α (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.5，0＜α≤2)；Li _a Ni _1-b-c Co _b X _c O _2-α T _α (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0＜α＜2)；Li _a Ni _1-b-c Co _b X _c O _2-α T ₂ (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0＜α＜2)；Li _a Ni _1-b-c Mn _b X _c D _α (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0＜α≤2)；Li _a Ni _1-b- _c Mn _b X _c O _2-α T _α (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0＜α＜2)；Li _a Ni _1-b-c Mn _b X _c O _2-α T ₂ (0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0＜α＜2)；Li _a Ni _b E _c G _d O ₂ (0.90≤a≤1.8，0≤b≤0.9，0≤c≤0.5，0.001≤d≤0.1)；Li _a Ni _b Co _c Mn _d GeO ₂ (0.90≤a≤1.8，0≤b≤0.9，0≤c≤0.5，0≤d≤0.5，0.001≤e≤0.1)；Li _a NiG _b O ₂ (0.90≤a≤1.8，0.001≤b≤0.1)；Li _a CoG _b O ₂ (0.90≤a≤1.8，0.001≤b≤0.1)；Li _a Mn _1-b G _b O ₂ (0.90≤a≤1.8，0.001≤b≤0.1)；Li _a Mn ₂ G _b O ₄ (0.90≤a≤1.8，0.001≤b≤0.1)；Li _a Mn _1-g G _g PO ₄ (0.90≤a≤1.8，0≤g≤0.5)；QO ₂ ；QS ₂ ；LiQS ₂ ；V ₂ O ₅ ；LiV ₂ O ₅ ；LiZO ₂ ；LiNiVO ₄ ；Li _(3-f) J ₂ (PO ₄ ) ₃ (0≤f≤2)；Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0≤f≤2)；Li _a FePO ₄ (0.90≤a≤1.8)。

In the chemical formula, A is selected from Ni, co, mn and combinations thereof; x is selected from Al, ni, co, mn, cr, fe, nb, mg, sr, V, rare earth elements, and combinations thereof; d is selected from O, F, S, P and combinations thereof; e is selected from Co, mn, and combinations thereof; t is selected from F, S, P and combinations thereof; g is selected from Al, cr, mn, fe, nb, mg, la, ce, sr, V and combinations thereof; q is selected from Ti, mo, mn, and combinations thereof; z is selected from Cr, V, fe, sc, Y and combinations thereof; j is selected from V, cr, mn, co, ni, cu and combinations thereof.

The above-mentioned compound may have a coating layer on the surface, or may be mixed with another compound having a coating layer. The coating layer may include at least one coating element compound selected from the group consisting of an oxide of a coating element, a hydroxide of a coating element, a oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound used for the coating layer may be amorphous or crystalline. The coating elements included in the coating layer may include Mg, al, co, K, na, ca, si, ti, V, sn, ge, ga, B, as, nb, zr or a mixture thereof. The coating layer may be provided by a method of using these elements in the compound without adversely affecting the properties of the positive electrode active material, for example, the above-described method may include any coating method (e.g., spraying, dipping, etc.), but since it is well known to those skilled in the relevant art, it is not described in more detail.

Negative electrode active material

As the negative electrode active material, a material which can reversibly intercalate/deintercalate lithium ions, lithium metal, a lithium metal alloy, a material which can dope/dedope lithium, or a transition metal oxide can be used.

The material that reversibly intercalates/deintercalates lithium ions may include a carbon material, i.e., a carbon-based anode active material conventionally used in rechargeable lithium batteries. Examples of the carbon-based anode active material may include crystalline carbon, amorphous carbon, or a mixture thereof. The crystalline carbon may be amorphous (without a specific shape), plate-like, spherical or fibrous natural graphite or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonized product, sintered coke, or the like.

The lithium metal alloy includes an alloy of a metal selected from Na, K, rb, cs, fr, be, mg, ca, sr, si, sb, pb, in, zn, ba, ra, ge, al and Sn with lithium.

The material capable of doping/dedoping lithium may be Si, siO _x (0 < x < 2), si-Q alloy (wherein Q is an element selected from alkali metal, alkaline earth metal, group 13 element, group 14 element, group 15 element, group 16 element, transition metal, rare earth element and combinations thereof, but is not Si), si-carbon composite, sn, snO2, sn-R alloy (wherein R is an element selected from alkali metal, alkaline earth metal, group 13 element, group 14 element, group 15 element, group 16 element, transition metal, rare earth element and combinations thereof, but is not Sn), sn-carbon composite, etc., and at least one of these materials may be mixed with SiO ₂ Mixing. The elements Q and R may be selected from Mg, ca, sr, ba, ra, sc, Y, ti, zr, hf, rf, V, nb, ta, db, cr, mo, W, sg, tc, re, bh, fe, pb, ru, os, hs, rh, ir, pd, pt, cu, ag, au, zn, cd, B, al, ga, sn, in, ge, P, as, sb, bi, S, se, te, po and combinations thereof.

The transition metal oxide includes lithium titanium oxide.

Adhesive composition

As the adhesive composition, the adhesive composition of the present application containing the above-described predetermined polymer M and N-methylpyrrolidone, optionally containing the above-described other components, and the like can be used.

The content of the predetermined polymer M in the slurry composition may be, for example, 0.5 parts by mass or more and 15 parts by mass or less in terms of solid content conversion per 100 parts by mass of the electrode active material.

Other ingredients

The other components that can be blended in the slurry composition are not particularly limited, and the same components as those that can be blended in the binder composition of the present application can be mentioned.

Preparation of slurry composition for secondary battery electrode

The slurry composition described above can be prepared by mixing the above components by a known mixing method. Such mixing can be performed using, for example, a ball mill, a sand mill, a bead mill, a pigment dispersing machine, an attritor, an ultrasonic dispersing machine, a homogenizer, a planetary mixer, a Filmix, or the like.

Electrode for secondary battery

The electrode of the present application has an electrode composite layer formed using the above-described paste composition of the present application, and generally has a current collector and an electrode composite layer formed on the current collector. The electrode composite layer is usually a layer obtained by drying the slurry composition of the present application, and contains at least an electrode active material and the polymer M, and optionally other components. In the electrode composite layer, the polymer M may be in a particle shape (i.e., the polymer M is contained in the electrode composite layer as it is), or may be in any other shape.

Further, the electrode of the present application is produced by using the slurry composition of the present application, and therefore, the secondary battery can exhibit excellent high-temperature storage and cycle characteristics.

Electrode forming method

The electrode of the present application can be manufactured, for example, by the following steps: (1) a step of applying a slurry composition to a current collector (application step), (2) a step of drying the slurry composition applied to the current collector to form a dried product (drying step), and (3) a step of pressing the dried product on the current collector (pressing step).

Here, since the slurry composition of the present application is used for forming the electrode of the present application, even if the steps (1) to (3) (particularly the steps (1) and (3)) are performed at high speed, the slurry dried product can be prevented from adhering to a pressing roll or the like and being peeled off from the current collector.

Coating process

The method of applying the slurry composition to the current collector is not particularly limited, and a known method can be used. Specifically, as the coating method, a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like can be used. In the application, the slurry composition may be applied to only one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector before drying after coating may be appropriately set according to the thickness of the obtained electrode composite material layer.

Drying process

The method for drying the slurry composition on the current collector is not particularly limited, and known methods can be used, and examples thereof include: drying with warm air, hot air, and low humidity air; vacuum drying; drying method by irradiation with infrared ray, electron beam, etc. The slurry dried product is formed on the current collector by thus drying the slurry composition on the current collector.

Pressing process

The method for pressing the slurry dried product on the current collector is not particularly limited, and can be performed using a known pressing apparatus. Among them, pressing by pressing rolls (roll pressing) is preferable from the viewpoint of pressing the slurry dried product at high speed and high efficiency. Through the pressing process, the density of the electrode composite material layer can be increased, and the adhesion between the electrode composite material layer and the current collector can be improved, so that the high-temperature storage and cycle characteristics of the secondary battery can be further improved.

Secondary battery

The secondary battery of the present application has the electrode for a secondary battery of the present application. More specifically, the secondary battery of the present application has a positive electrode, a negative electrode, an electrolyte, and a separator, and the electrode for a secondary battery of the present application is used as at least one of the positive electrode and the negative electrode. Further, the secondary battery of the present application has the electrode for a secondary battery of the present application, and therefore, is excellent in high-temperature storage and cycle characteristics.

In the following, a case where the secondary battery is a lithium ion secondary battery will be described as an example, but the present application is not limited to the following example.

Electrode

As described above, the electrode for a secondary battery of the present application is used as at least one of the positive electrode and the negative electrode. That is, the positive electrode of the lithium ion secondary battery may be another known negative electrode, the negative electrode of the lithium ion secondary battery may be another known positive electrode, or both the positive electrode and the negative electrode of the lithium ion secondary battery may be an electrode of the present application.

As a known electrode other than the electrode for a secondary battery of the present application, an electrode in which an electrode composite layer is formed on a current collector by a known manufacturing method can be used.

Electrolyte solution

As the electrolyte solution, an organic electrolyte solution in which a supporting electrolyte is dissolved in an organic solvent can be generally used. As the supporting electrolyte, for example, a lithium salt can be used in a lithium ion secondary battery. Examples of the lithium salt include LiPF ₆ 、LiAsF ₆ 、LiBF ₄ 、LiSbF ₆ 、LiAlCl ₄ 、LiClO ₄ 、CF ₃ SO ₃ Li、C ₄ F ₉ SO ₃ Li、CF ₃ COOLi、(CF ₃ CO) ₂ NLi、(CF ₃ SO ₂ ) ₂ NLi、(C ₂ F ₅ SO ₂ ) NLi, etc. Wherein, liPF ₆ 、LiClO ₄ 、CF ₃ SO ₃ Li is preferable because it is easily dissolved in a solvent and exhibits a high dissociation degree. In addition, 1 kind of electrolyte may be used alone, or 2 or more kinds may be used in combination. Since the support electrolyte having a higher dissociation degree generally tends to have a higher lithium ion conductivity, the lithium ion conductivity can be adjusted according to the type of the support electrolyte.

As the organic solvent used in the electrolyte solution, there is no particular limitation as long as it can dissolve the supporting electrolyte, and for example, in a lithium ion secondary battery, carbonates such as dimethyl carbonate (DMC), ethylene Carbonate (EC), diethyl carbonate (DEC), propylene Carbonate (PC), butylene Carbonate (BC), and ethylmethyl carbonate (EMC) can be preferably used; esters such as gamma-butyrolactone, methyl formate, ethyl acetate, propyl propionate, and ethyl propionate; ethers such as 1, 2-dimethoxyethane and tetrahydrofuran; sulfolane, dimethyl sulfoxide and other sulfur-containing compounds. In addition, a mixture of these solvents may be used. Among them, carbonates are preferable because of their high dielectric constant and wide stable potential region. Since the lithium ion conductivity tends to be higher as the viscosity of the solvent used is lower, the lithium ion conductivity can be adjusted according to the kind of the solvent.

In addition, the concentration of the electrolyte in the electrolyte solution can be appropriately adjusted.

In addition, it is preferable to add a pentaerythritol diphosphite-based compound to the electrolyte. When the pentaerythritol diphosphite-based compound is added to the electrolyte, the decomposition reaction of the polymer M at high temperature along with the charge and discharge process can be suppressed, so that the high-temperature storage and cycle characteristics of the secondary battery are further improved.

Pentaerythritol diphosphite-based compounds may be represented by the following formula 1:

wherein in formula 1, R ₁ And R is ₂ Each independently selected from hydrogen, C ₁ To C ₁₀ Alkyl, -SiR ₃ R ₄ R ₅ 、-SO ₂ R ₆ 、-P(OR ₇ ) ₂ OR-P (O) (OR) ₈ ) ₂ ，R ₁ And R is ₂ At least one of them is-SiR ₃ R ₄ R ₅ 、-SO ₂ R ₆ 、-P(OR ₇ ) ₂ OR-P (O) (OR) ₈ ) ₂ And R is ₃ To R ₈ Each independently is a substituted or unsubstituted C ₁ To C ₁₀ Alkyl, substituted or unsubstituted C ₆ To C ₁₂ Aryl or substituted or unsubstituted 5 to 12 membered heteroaryl.

The pentaerythritol diphosphite-based compound is preferably at least one of the compounds of formula 2, formula 3 and formula 4:

in the compounds represented by formula 2, formula 3 and formula 4, R ₃ To R ₈ Each independently selected from substituted or unsubstituted C ₁ To C ₁₀ Alkyl, substituted or unsubstituted C ₆ To C ₁₂ Aryl or substituted or unsubstituted 5 to 12 membered heteroaryl, preferably R ₃ To R ₈ Are all methyl groups.

The content of the pentaerythritol diphosphite-based compound is preferably 7 parts by mass or more, more preferably 10 parts by mass or more, particularly preferably 15 parts by mass or more, preferably 30 parts by mass or less, more preferably 25 parts by mass or less, particularly preferably 20 parts by mass or less, per 100 parts by mass of lithium hexafluorophosphate. If the content of the pentaerythritol diphosphite compound is within the above range, the high-temperature storage and cycle characteristics of the secondary battery can be further improved.

Diaphragm

Among these, microporous films formed of polyolefin-based (polyethylene, polypropylene, polybutylene, polyvinyl chloride) resins are preferred, since the film thickness of the entire separator can be reduced, and thus the ratio of electrode active materials in the secondary battery can be increased, and the capacity per unit volume can be increased.

Method for manufacturing secondary battery

The secondary battery of the present application is manufactured, for example, by: the positive electrode and the negative electrode are stacked with a separator interposed therebetween, and the separator is wound, folded, or the like as needed in accordance with the shape of the battery, placed in a battery container, and an electrolyte is injected into the battery container to seal the battery container. At least one of the positive electrode and the negative electrode is made to be the electrode for a secondary battery of the present application. In order to prevent the pressure inside the secondary battery from rising and over-charge and discharge, an over-current preventing element such as a fuse or PTC element may be provided as needed; a metal mesh; guides, etc. The shape of the secondary battery may be any of coin type, button type, sheet type, cylinder type, square type, flat type, and the like, for example.

Examples

Hereinafter, the present application will be specifically described with reference to examples, but the present application is not limited to these examples. In the following description, unless otherwise specified, "%" and "parts" indicating amounts are based on mass.

In addition, in a polymer produced by polymerizing a plurality of monomers, unless otherwise specified, the proportion of monomer units formed by polymerizing a certain monomer in the above-mentioned polymer generally coincides with the proportion (addition ratio) of the certain monomer in all monomers used for polymerizing the polymer. Further, in examples and comparative examples, the volume average particle diameter, the volume expansion ratio, the element content, the amount of insoluble components of N-methylpyrrolidone (NMP), the high-speed coating and high-speed pressing suitability, the high-temperature storage and cycle characteristics of the secondary battery, and the electrolyte injection property at the time of manufacturing the secondary battery were evaluated by the following methods:

(1) Volume average particle diameter of Polymer M

The volume average particle diameter (D50) of the polymer M prepared in examples and comparative examples was measured using a laser diffraction type particle diameter distribution measuring apparatus (BECKMAN COULTER co., ltd. Product name "LS-230"). Specifically, an aqueous dispersion in which the solid content concentration of the polymer M was adjusted to 0.1 mass% was measured by the above-described apparatus, and the particle size (volume basis) of the obtained particle size distribution was determined as a volume average particle size (μm) by setting the cumulative volume calculated from the small particle size side to 50%.

(2) Measurement of temperature at which thermal weight loss is 30% by mass or more

The temperature at which the thermal weight loss was 30 mass% or more was measured by a TG-DSC synchronous thermal analyzer (Netzsch STA409 PC Luxx, germany). The measurement results are shown in Table 1.

(3) Determination of the content of elements of group 17 of the periodic Table

The content of each element belonging to group 17 of the periodic Table was measured in the polymer M by an ICP mass spectrometer (Agilent 8800, manufactured by Agilent Technologies). The measurement results are shown in Table 1.

(4) Insoluble component amount of Polymer M in N-methylpyrrolidone (NMP)

The NMP dispersion of the polymer M was dried at a humidity of 50% and at a temperature of 23℃to 25℃to prepare a film having a thickness of 1.+ -. 0.3 mm. The film produced was cut into 5mm squares and a plurality of film pieces were prepared, and about 1g of these film pieces were accurately weighed. The weight of the accurately weighed diaphragm is taken as W ₀ . Next, the accurately weighed film was put into an accurately weighed 80 mesh cage made of SUS (weight: W ₁ ). The netpen with the membrane placed in it was then immersed in 100g of NMP at 25℃for 24 hours. Thereafter, the cylinder mould was lifted from NMP, the lifted membrane and cylinder mould were vacuum-dried at 105℃for 3 hours, and the weight (sum of the weight of insoluble components and the weight of cylinder mould) W was measured ₂ . Then, the amount of NMP insoluble components was calculated according to the following formula (first decimal point rounded).

NMP insoluble component amount (%) = (W) ₂ -W ₁ )/W ₀ ×100％

(5) High speed coating and high speed compression adaptation

The mass per unit area after drying on an aluminum foil having a thickness of 9 μm as a current collector was 11mg/em at a coating rate of 60 m/min ² The slurry compositions for positive electrodes of secondary batteries prepared in examples and comparative examples were applied and dried. Thereafter, a roll press (press roll diameter: 500 mm) was used to set the density of the positive electrode composite material layer after pressing to 4.2g/cm at a press speed of 60 m/min ³ Is carried out by continuously pressing the slurry dried matter. In this continuous press, the deposit from the positive electrode composite material layer adhering to the surface of the press roll of the roll press was visually confirmed. The more difficult the adherent is to adhere to the surface of the pressing roller, the more suitable the slurry composition for forming the positive electrode composite material layer is for high-speed coating and high-speed pressing. Specifically, the evaluation was performed according to the following criteria. A, B, C in the high speed coating column in table 3 represents:

a: after the continuous pressing for 1000m, no deposit was observed on the roll surface.

B: the adhering substance was confirmed on the roll surface at the stage of continuously pressing at 800m or more and less than 1000 m.

C: the attached matter was confirmed on the roll surface at a stage of continuously pressing more than 0m and less than 800 m.

(6) Electrolyte injection

The pressed positive electrode, negative electrode and separator fabricated in examples and comparative examples were cut into 6cm each. The positive electrode was placed with the surface of the positive electrode composite material layer side on the upper side, and a separator was placed on the positive electrode composite material layer. Further, the cut negative electrode was disposed on the separator so that the surface of the negative electrode composite material layer side faced the separator, and a laminate was produced. The laminate thus produced was placed in an aluminum plastic film bag, and 0.2ml of an electrolyte (solvent: ethylene carbonate/propylene carbonate/propyl propionate=20/20/60 (mass ratio), electrolyte: 12 mass% LiPF was put in the bag ₆ ). Thereafter, the resultant was sealed using a heat sealer. The impregnation rate of the electrolyte after 1 minute of sealing was measured by using an ultrasonic inspection apparatus (ultrasonic inspection system NAUT21, manufactured by Japan Probe Co, ltd.). Then, the evaluation was performed according to the following criteria. The higher the impregnation rate of the electrolyte solution, the more excellent the electrolyte solution injection property at the time of manufacturing the secondary battery. A, B, C in the column of liquid injection in table 3 represents:

a: the impregnation rate of the electrolyte is more than 80 percent

B: the electrolyte has an impregnation rate of 75% or more and less than 80%

C: the impregnation rate of the electrolyte is less than 75 percent

(7) High temperature storage characteristics (cell expansion)

The secondary batteries fabricated in examples and comparative examples were left to stand in an environment of 25 ℃ for 24 hours. After confirming the initial capacity of the secondary battery thus produced, the secondary battery was charged at 25℃with a constant voltage and constant current (CC-CV) of 4.6V (Cut-off condition 0.02C). The thickness of the fully charged battery cell was measured at 10 using a thickness measuring machine, and the average thickness T was calculated by averaging the thicknesses ₀ . Then, after 300 cycles of charging and discharging in a constant voltage and constant current (CC-CV) mode of 4.6V and 1C and discharging in a Constant Current (CC) mode of 3.0V and 1C at 85 ℃, the average thickness T of the battery cell at the time of full charge is obtained ₂ And above-mentionedT (1) of (1) was measured in the same manner, and a thickness change rate (%) = (T) ₂ -T ₀ )/T ₀ X 100). The thickness change rate (%) was evaluated according to the following criteria. The smaller the thickness change rate means that the swelling of the battery cell (after 300 cycles) is suppressed. A, B, C, D in the column of high temperature storage characteristics in table 3 represents:

a: less than 5% after 500 cycles

B: more than 5% and less than 10% after 500 cycles

C: more than 10% and less than 15% after 500 cycles

D: after 500 cycles, 15% or more

(8) Cycle characteristics

The lithium ion secondary batteries fabricated in examples and comparative examples were left to stand in an environment of 25 ℃ for 24 hours. Then, the initial capacity C was measured by charging to 4.6V (Cut-off condition: 0.02C) at 25℃with a charge rate of 1C and constant current (CC-CV) and discharging to 3.0V with a discharge rate of 1C and Constant Current (CC), and performing the charge-discharge operation ₀ 。

Further, the same charge and discharge operations were repeated in an environment of 45℃to measure the capacity C after 500 cycles ₁ . Then, the capacity maintenance rate Δc= (C ₁ /C ₀ ) X 100 (%), was evaluated according to the following criteria. The higher the value of the capacity retention rate, the smaller the decrease in discharge capacity, and the more excellent the cycle characteristics. A, B, C, D in the column of the cycle characteristics in table 3 represents:

a: the capacity retention rate DeltaC is more than 90 percent

B: the capacity retention rate DeltaC is more than 85% and less than 90%

C: the capacity retention rate DeltaC is 80% or more and less than 85%

D: the capacity retention rate DeltaC is less than 80%

As B01, a commercially available polyacrylonitrile (North lake Michael 25014-41-9) can be used as the polymer M in the examples of the present application. And alkylene structural units (B02 to B04) having a nitrile group and optionally containing a (meth) acrylate monomer unit or having 4 or more carbon atoms are produced as follows. B05 to B06 are comparative examples, and B06 is commercially available PVDF (HSV 900). The polymers M (B02 to B05) in the examples of the present application were produced by the methods described in the following preparation of the polymer M in example 1.

Polymer M preparation 1:

in an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate as an emulsifier, 36.2 parts of acrylonitrile as a nitrile group-containing monomer, and 0.45 parts of t-dodecyl mercaptan as a chain transfer agent were successively added to replace the inside with nitrogen. Thereafter, 63.8 parts of 1, 3-butadiene as a conjugated diene monomer for introducing an alkylene structural unit into the polymer was introduced thereinto by pressing, 0.25 part of ammonium persulfate as a polymerization initiator was added thereto, and the polymerization reaction was carried out at a reaction temperature of 40 ℃. Then, a copolymer of acrylonitrile and 1, 3-butadiene was obtained. In addition, the polymerization conversion was 85%. The 1, 2-addition amount of 1, 3-butadiene in the copolymer before hydrogenation was determined by NMR measurement.

Ion-exchanged water was added to the obtained copolymer to obtain a solution in which the total solid content concentration was adjusted to 12 mass%. 400mL of the obtained solution (48 g in total solid content) was charged into an autoclave having a volume of 1L and equipped with a stirrer, dissolved oxygen in the solution was removed by introducing nitrogen gas for 10 minutes, and then 75mg of palladium acetate as a catalyst for hydrogenation reaction was dissolved in 180mL of ion-exchanged water to which 4-fold molar nitric acid was added relative to palladium (Pd), followed by addition. After the inside of the system was replaced with hydrogen for 2 times, the contents of the autoclave were heated to 50℃under pressure of 3MPa with hydrogen, and hydrogenation reaction (first-stage hydrogenation reaction) was carried out for 6 hours.

Then, the autoclave was returned to atmospheric pressure, and 25mg of palladium acetate as a catalyst for hydrogenation reaction was dissolved in 60mL of ion-exchanged water to which 4-fold mol of nitric acid was added to Pd, and the mixture was added. After 2 times of displacement with hydrogen, the contents of the autoclave were heated to 50℃under pressure of 3MPa with hydrogen, and hydrogenation reaction of the second stage of hydrogenation reaction i was carried out for 6 hours.

Then, the content was returned to room temperature to bring the inside of the system to a nitrogen atmosphere, and then concentrated to a solid content concentration of 40% by using an evaporator, whereby an aqueous polymer dispersion was obtained.

Further, after the aqueous dispersion of the polymer was coagulated by dropping it into methanol, the coagulated material was dried in vacuo at a temperature of 60℃for 12 hours to obtain a polymer B02 containing a nitrile group-containing monomer unit (acrylonitrile unit) and an alkylene structural unit (1, 3-butadiene hydride unit).

The content of nitrile groups, the weight average molecular weight, the iodine value and the intrinsic viscosity of the obtained polymer were measured. The ratio of the alkylene structural unit (1, 3-butadiene hydride unit) to the conjugated diene monomer unit (1, 3-butadiene unit) in the polymer is calculated from the iodine value of the polymer and the 1, 2-addition-bonding amount of 1, 3-butadiene in the copolymer before hydrogenation. The results are shown in Table 1.

Preparation of polymers M (B03 to B05) in the following examples was carried out in the same manner as in preparation example 1 except that the amounts and types of monomers to be fed were changed as shown in Table 1.

Specific constitution and related characterization of Polymer M represented by tables 1B 01-B06

The preparation method of the electrolyte in the embodiment of the application comprises the following steps:

a base electrolyte was prepared by mixing 4% fluoroethylene carbonate with a mixture of ethylene carbonate, propylene carbonate and propyl propionate in a weight ratio of 2:2:6, and dissolving lithium hexafluorophosphate to a concentration of 12 mass%. In some examples, a compound of formula 2, a compound of formula 3 or a compound of formula 4 (R ₃ To R ₈ All methyl) to form the example electrolyte. The compound of formula 2, the compound of formula 3 or the compound of formula 4 is contained in an amount of 5 to 30 parts by mass per 100 parts by mass of the lithium hexafluorophosphate. In the embodiment of the application, only the quaternary pentylter is added into the electrolyteThe types of the alcohol bisphosphite-based compounds are different (i.e., the compound of formula 2, the compound of formula 3 or the compound of formula 4 is added) and the addition amounts are different, and the others are the same. The electrolytes used in the following examples are shown in table 2.

Table 2 compositions of electrolytes represented by E01 to E05

Example 1

Slurry composition for positive electrode and positive electrode production

LiCoO as a positive electrode active material was stirred with a double planetary mixer ₂ 100 parts of an anode conductive material AB23+ HiPCO 2.0 parts, 2 parts of an anode binder polymer M (B01) and an appropriate amount of NMP.

As a current collector, an aluminum foil having a thickness of 9 μm was prepared. The coating weight of the aluminum foil on both sides after drying reaches 25mg/cm ² The above-mentioned slurry composition for positive electrode was applied and dried at 60℃for 20 minutes, and after drying at 120℃for 20 minutes, the resultant was heat-treated at 150℃for 2 hours to obtain a positive electrode film. The positive electrode raw film was rolled by a roll press to obtain a film having a density of 2.5g/cm ³ A sheet-like positive electrode comprising a positive electrode active material layer and an aluminum foil. The mixture was cut into a length of 50cm and a width of 4.8mm, and an aluminum wire was connected.

Slurry composition for negative electrode and production of negative electrode

A slurry composition for negative electrode was prepared by stirring 98 parts of styrene butadiene rubber (particle diameter: 180nm, glass transition temperature: 40 ℃ C.) as a binder, 1 part of carboxymethyl cellulose as a thickener, and a proper amount of water, using a double planetary mixer, as a negative electrode active material.

Copper foil having a thickness of 5 μm was prepared as a current collector. The coating weight of the copper foil after drying reaches 10mg/cm ² The above-mentioned slurry composition for negative electrode was applied, dried at 60℃for 20 minutes, dried at 120℃for 20 minutes, and then heat-treated at 150℃for 2 hours,obtaining the cathode raw film. The negative electrode raw film was rolled by a roll press to obtain a negative electrode raw film having a density of 1.8g/cm ³ A sheet-like negative electrode comprising a negative electrode active material layer and a copper foil. The mixture was cut into a length of 52cm with a width of 5.0mm, and a nickel lead was connected.

The sheet-like positive electrode and the sheet-like negative electrode thus obtained were wound with a core having a diameter of 20mm interposed between the separators, to obtain a wound body. As the separator, a microporous membrane made of polyethylene having a thickness of 7 μm was used. In the case of a roll, compression is carried out from one direction at a speed of 10 mm/sec until a thickness of 4.5mm is reached. The ratio of the major axis to the minor axis of the substantially elliptical shape was 7.7.

Electrolyte solution

The weight ratio of the ethylene carbonate, the propylene carbonate and the propyl propionate is 2:2:6, 3% fluoroethylene carbonate was mixed with the mixture, and lithium hexafluorophosphate was dissolved so as to reach a concentration of 12 mass%.

The electrode plate group was housed in a predetermined aluminum laminate case together with 3.2g of the electrolyte. Then, after the negative electrode lead and the positive electrode lead are connected to predetermined portions, the opening of the case is sealed by heat, thereby completing the secondary battery. The battery is in a soft package (pouch) shape with a width of 35mm, a height of 48mm and a thickness of 5mm, and the nominal capacity of the battery is 700mAh. The high temperature storage and cycle characteristics of the resulting battery are shown in table 3.

Examples 2 to 15

The positive electrode binder polymer M, other components (phosphorus-containing additives), and the electrolyte were changed as described in tables 1 and 2. Otherwise, the procedure was carried out in the same manner as in example 1.

The polymer M, other components and electrolyte used in examples 1 to 15 are shown in Table 3. Wherein the shorthand notation of the phosphorous-containing additives shown in table 3 represents: tris (2, 2-trifluoroethyl) phosphate (shorthand P01), tris (2, 2-trifluoroethyl) phosphite (shorthand P02), triphenyl phosphite (shorthand P03), 2-ethoxy-2, 4, 6-pentafluoro-1,3,5,2,4,6-triphosphazene (shorthand P04), pentafluoro (phenoxy) cyclotriphosphazene (shorthand P05).

Comparative examples 1 to 2

The same procedure as in example 1 was repeated except that the binder polymer M for positive electrode, other components (phosphorus-containing additive) and the electrolyte were changed as shown in tables 1 and 2 and described above. The polymer M, other components and electrolyte used in examples 1 and 2 are shown in Table 3.

TABLE 3 composition and Performance test of examples 1 to 15 and comparative examples 1 to 2

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From tables 1, 2 and 3, it is known that: in the examples satisfying the requirements of the present application, all the evaluation items gave good results in good balance.

(1) Comparative examples 1 to 4 and comparative examples 1 to 2 show that when the polymer M used is the polymer M satisfying the specific conditions according to the present application, the high-speed coating property of the slurry composition is more excellent, and the electrolyte injection property, the high-temperature storage property and the cycle characteristics of the prepared secondary battery are more excellent. When the polymer M is B05 or B06, B05, B06 contains no nitrile monomer unit, has a volume average particle diameter of 40 μm or more, has a temperature of 30 mass% or more of thermal weight loss, is too low or too high and has an insoluble content of 12wt% or more in NMP, resulting in poor high-speed coating properties of the resulting slurry composition, and thus the secondary battery produced has poor related properties.

(2) As is clear from comparative examples 1 and 5 to 9, when the phosphorus-containing additive is added to the binder composition, the high-temperature storage performance and cycle characteristics of the prepared secondary battery can be significantly improved because the phosphorus-containing additive can inhibit swelling of the polymer M in the electrolyte. In particular, when the phosphorus-containing additive is P02, P03, P04 or P05, the high-speed coating property of the slurry composition and/or the electrolyte injection property of the secondary battery can be further improved; and, the binder composition containing P04 or P05 exhibits more excellent overall properties.

(3) As is clear from comparative examples 9 and 10 to 12, the addition of a certain amount of pentaerythritol diphosphite based compound to the electrolyte can inhibit the decomposition reaction of the polymer M at high temperature along with the charge and discharge process, thereby further improving the high temperature storage and cycle characteristics of the secondary battery.

(4) The present application further discloses that the content of pentaerythritol diphosphite-based compound added is 5wt% to 30wt% of lithium hexafluorophosphate, and comparative examples 10 to 12 and example 13 show that when the content of pentaerythritol diphosphite-based compound exceeds the above range (for example, 35wt% of lithium hexafluorophosphate), the electrolyte liquid filling property, high-temperature storage property and cycle property of the secondary battery are degraded.

In summary, the present application can form an electrode for a secondary battery, which can be manufactured well by high-speed coating and high-speed pressing, and can provide excellent high-temperature storage and cycle characteristics for the secondary battery, by obtaining a slurry composition using a polymer M and N-methylpyrrolidone under specific conditions.

In particular, when the slurry composition contains a phosphorus-containing additive, the phosphorus-containing additive can inhibit the swelling of the polymer M in the electrolyte, so that the high-temperature storage and cycle characteristics of the secondary battery are further improved.

In particular, when the pentaerythritol diphosphite-based compound is added to the electrolyte, the decomposition reaction of the polymer M along with the charge and discharge process can be suppressed, so that the high-temperature storage and cycle characteristics of the secondary battery are further improved.

The above embodiments are merely illustrative of the principles of the present application and its effectiveness, and are not intended to limit the application. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the application. Accordingly, it is intended that all equivalent modifications and variations of the application be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.

Claims

1. A binder composition for secondary battery electrodes, characterized by: the adhesive composition includes a polymer M and N-methylpyrrolidone;

wherein the polymer M satisfies at least the following conditions: comprising nitrile monomer units; the volume average particle diameter is 5-50 mu m; the temperature of more than 30wt% of the thermal weight loss is 150-400 ℃; the content of each element belonging to group 17 of the periodic table is less than 100 mass ppm.

2. The binder composition for secondary battery electrodes according to claim 1, wherein: the content of the nitrile monomer units in the polymer M is 50wt% or more, preferably 60wt% or more, more preferably 70wt% or more of the total repeating units in the polymer M;

and/or the nitrile monomer units include monomer units formed from an α, β -ethylenically unsaturated nitrile compound; preferably, the α, β -ethylenically unsaturated nitrile compound comprises at least one of acrylonitrile, α -haloacrylonitrile, and α -alkylacrylonitrile; more preferably acrylonitrile and/or methacrylonitrile, and still more preferably acrylonitrile.

3. The binder composition for secondary battery electrodes according to claim 1 or 2, characterized in that: the polymer M also comprises (methyl) acrylic ester monomer units and/or alkylene structural units with more than 4 carbon atoms;

Preferably, the content of the (meth) acrylate monomer unit is 10wt% or more, more preferably 10wt% to 40wt%, of the total repeating units in the polymer M:

preferably, the content of the alkylene structural unit having 4 or more carbon atoms is 20wt% or less, more preferably 10wt% or less of the total repeating units in the polymer M.

4. The binder composition for secondary battery electrodes according to claim 1, wherein: the volume average particle diameter of the polymer M is 10 μm to 40. Mu.m, preferably 15 μm to 30. Mu.m; more preferably 20 μm to 30. Mu.m.

5. The binder composition for secondary battery electrodes according to claim 1, wherein: the insoluble content of the polymer M in N-methylpyrrolidone is 8% by weight or less, more preferably 0.01 to 8% by weight.

6. The binder composition for secondary battery electrodes according to claim 1, wherein: the binder composition further includes a phosphorus-containing additive including at least one of an organophosphate compound, an organophosphite compound, an organophosphonate compound, and a phosphazene compound;

preferably, the phosphorous-containing additive comprises at least one of tris (2, 2-trifluoroethyl) phosphate, tris (2, 2-trifluoroethyl) phosphite, triphenyl phosphite, diethyl ethylphosphonate, diethyl phenylphosphonate, 2-ethoxy-2, 4, 6-pentafluoro-1,3,5,2,4,6-triphosphazene and pentafluoro (phenoxy) cyclotriphosphazene;

Preferably, the content of the phosphorus-containing additive is 5 to 30wt% of the polymer M.

7. The use of the binder composition for secondary battery electrodes according to any one of claims 1 to 6 for preparing a slurry composition for secondary battery electrodes, an electrode composite layer for secondary batteries, an electrode for secondary batteries or a secondary battery.

8. A slurry composition for secondary battery electrodes, characterized by: the slurry composition comprising an electrode active material and the binder composition for a secondary battery electrode according to any one of claims 1 to 6;

preferably, the content of the polymer M is 0.5 to 15wt% of the electrode active material in terms of solid component conversion;

preferably, the electrode active material is a positive electrode active material, and the binder composition is contained in an amount of 0.1wt% to 10wt% of the positive electrode active material in terms of solid matter conversion.

9. An electrode for a secondary battery, characterized by: the electrode comprises an electrode composite layer comprising an electrode composite layer formed from the slurry composition for a secondary battery electrode according to claim 8.

10. A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that: the positive electrode and/or the negative electrode includes the electrode for a secondary battery according to claim 9.

11. The secondary battery according to claim 10, wherein: the electrolyte of the secondary electrode comprises a pentaerythritol diphosphite-based compound shown in a formula 1;

wherein R is ₁ And R is ₂ Each independently selected from hydrogen, C ₁ To C ₁₀ Alkyl, -SiR ₃ R ₄ R ₅ 、-SO ₂ R ₆ 、-P(OR ₇ ) ₂ OR-P (O) (OR) ₈ ) ₂ The method comprises the steps of carrying out a first treatment on the surface of the And R is ₁ And R is ₂ At least one of them is-SiR ₃ R ₄ R ₅ 、-SO ₂ R ₆ 、-P(OR ₇ ) ₂ OR-P (O) (OR) ₈ ) ₂ ，R ₃ ～R ₈ Each independently selected from substituted or unsubstituted C ₁ ～C ₁₀ Alkyl, substituted or unsubstituted C ₆ ～C ₁₂ Aryl or substituted or unsubstituted 5-to 12-membered heteroaryl.

12. The secondary battery according to claim 11, wherein: the pentaerythritol diphosphite-based compound includes at least one of the compounds of formulas 2, 3 and 4,

wherein R is ₃ ～R ₈ Each independently is a substituted or unsubstituted C ₁ ～C ₁₀ Alkyl, substituted or unsubstituted C ₆ ～C ₁₂ Aryl or substituted or unsubstituted 5-to 12-membered heteroaryl.

13. The secondary battery according to any one of claims 11 or 12, characterized in that: the electrolyte also comprises lithium hexafluorophosphate, and the content of the pentaerythritol diphosphite compound is 5-30wt% of the lithium hexafluorophosphate.