JP7548010B2 - Binder composition for non-aqueous secondary battery, slurry composition for functional layer of non-aqueous secondary battery, functional layer for non-aqueous secondary battery, battery member for non-aqueous secondary battery, and non-aqueous secondary battery - Google Patents

Description

The present invention relates to a binder composition for non-aqueous secondary batteries, a slurry composition for functional layers of non-aqueous secondary batteries, functional layers for non-aqueous secondary batteries, battery components for non-aqueous secondary batteries, and non-aqueous secondary batteries.

Non-aqueous secondary batteries such as lithium ion secondary batteries (hereinafter sometimes simply referred to as "secondary batteries") are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Non-aqueous secondary batteries generally include electrodes (positive and negative electrodes) and battery components for non-aqueous secondary batteries (hereinafter sometimes simply referred to as "battery components") such as separators that isolate the positive and negative electrodes and prevent short circuits between the positive and negative electrodes.

Here, as the battery component, a component is used that includes a polymer as a binder and, optionally, has a functional layer that includes particles (hereinafter, referred to as "functional particles") that are blended in order to cause the battery component to exhibit a desired function.
Specifically, the separator for the secondary battery is provided with an adhesive layer containing a binder on a separator substrate, or a porous membrane layer containing a binder and non-conductive particles as functional particles. The electrode for the secondary battery is provided with an electrode mixture layer containing a binder and electrode active material particles as functional particles on a current collector, or an electrode substrate provided with an electrode mixture layer on a current collector, and further provided with the above-mentioned adhesive layer or porous membrane layer.

The functional layer described above can be formed, for example, by drying a slurry composition for a non-aqueous secondary battery functional layer, in which a polymer as a binder and optionally contained functional particles are dispersed and/or dissolved in a solvent. In order to achieve further performance improvement of secondary batteries, attempts have been made to improve the slurry composition. For example, a method for improving the performance of secondary batteries by controlling the number of bacteria in the solvent used to prepare the slurry composition has been considered (see Patent Documents 1 and 2).

In Patent Document 1, a positive electrode paste for lithium-ion secondary batteries containing a positive electrode active material, a conductive material, a thickener, a binder and a solvent is prepared using a solvent to which sulfate-reducing bacteria have been added so that the number of bacteria is within a predetermined range, thereby reducing sulfate radicals ( _SO4 ^2- ), which cause deterioration of the characteristics of lithium-ion secondary batteries.
In Patent Document 2, a slurry for the negative electrode of a lithium ion secondary battery containing a negative electrode active material and a solvent is prepared using a solvent that has been irradiated with ultraviolet light or the like so that the number of bacteria falls within a predetermined range, and whose pH and temperature are each within a predetermined range. This prevents the thickening agent, carboxymethyl cellulose salt, from being hydrolyzed by bacterial cellulase, thereby preventing a decrease in the viscosity of the negative electrode slurry.

JP 2013-134924 A JP 2013-114959 A

However, in the above conventional technology, when preparing the slurry composition, the obtained slurry composition may become excessively viscous, and it is difficult to sufficiently ensure the viscosity stability of the slurry composition. In addition, it is not possible to ensure the adhesion of the functional layer obtained using the slurry composition while allowing the secondary battery to exhibit excellent cycle characteristics. Therefore, the above conventional technology has room for improvement in terms of improving the viscosity stability of the slurry composition, as well as improving the adhesion of the functional layer and the cycle characteristics of the secondary battery.

Therefore, an object of the present invention is to provide a binder composition for a non-aqueous secondary battery, which can prepare a slurry composition for a non-aqueous secondary battery functional layer having excellent viscosity stability.
Another object of the present invention is to provide a slurry composition for a non-aqueous secondary battery functional layer, which has excellent viscosity stability.
Another object of the present invention is to provide a functional layer for a non-aqueous secondary battery that has excellent adhesiveness.
It is yet another object of the present invention to provide a battery member for a non-aqueous secondary battery that enables the non-aqueous secondary battery to exhibit excellent cycle characteristics.
Another object of the present invention is to provide a nonaqueous secondary battery having excellent cycle characteristics.

The present inventors have conducted extensive research to solve the above problems. First, the present inventors have focused on the fact that bacteria may be unintentionally mixed in during the preparation of a binder composition during the manufacturing process, and have found that among these bacteria, bacteria with a large size in particular significantly reduce the stability of the polymer in the binder composition. The present inventors have also found that a binder composition containing bacteria with an average size of a predetermined value or less can be used to prepare a slurry composition with excellent viscosity stability, and can also improve the adhesion of the functional layer and the cycle characteristics of the secondary battery, thereby completing the present invention.

That is, the present invention aims to advantageously solve the above problems, and the binder composition for non-aqueous secondary batteries of the present invention is characterized in that it contains a polymer, bacteria, and water, and the average size of the bacteria is 0.5 μm or less. In this way, in a binder composition containing a polymer and bacteria in water, if the average size of the bacteria is controlled to be the above-mentioned value or less, the viscosity stability of a slurry composition prepared using the binder composition can be improved, and the adhesiveness of a functional layer obtained using the slurry composition can be increased, while a secondary battery equipped with the functional layer can exhibit excellent cycle characteristics.
In the present invention, the "average size" of the bacteria contained in the binder composition can be calculated as the arithmetic mean value of the measurements obtained by culturing the bacteria contained in the binder composition, measuring the size of the live bacteria present in any 1 cm x 1 cm section of the medium. Here, in the present invention, the "size" of the bacteria contained in the binder composition means the smallest diameter measured when observing a single live bacterium with an electron microscope (for example, the diameter of the sphere in the case of cocci, and the short diameter in the case of bacilli).

Here, the binder composition for a non-aqueous secondary battery of the present invention preferably has a surface tension of 22 mN/m or more and 55 mN/m or less. By using a binder composition having a surface tension within the above-mentioned range, it is possible to sufficiently improve the viscosity stability of the slurry composition, the adhesion of the functional layer, and the cycle characteristics of the secondary battery.
In the present invention, the "surface tension" of the binder composition can be measured by the method described in the examples of this specification.

In the binder composition for non-aqueous secondary batteries of the present invention, the polymer preferably has a tetrahydrofuran insoluble content of 10% by mass or more and 95% by mass or less. A polymer having a tetrahydrofuran insoluble content (hereinafter sometimes referred to as "THF insoluble content") within the above-mentioned range can be easily prepared, and the use of a binder composition containing the polymer can further improve the cycle characteristics of a secondary battery.
In the present invention, the "tetrahydrofuran insoluble content" of the polymer can be measured by the method described in the Examples of this specification.

The present invention also aims to advantageously solve the above problems, and the slurry composition for a non-aqueous secondary battery functional layer of the present invention is characterized in that it is prepared using any of the binder compositions for non-aqueous secondary batteries described above. A slurry composition containing any of the binder compositions described above has excellent viscosity stability. Then, by forming a functional layer from the slurry composition, the adhesion of the functional layer can be increased, and the battery component including the functional layer can provide the secondary battery with excellent cycle characteristics.

Here, the slurry composition for a non-aqueous secondary battery functional layer of the present invention may further contain functional particles. When the above-mentioned slurry composition contains functional particles, i.e., electrode active material particles or non-conductive particles, the slurry composition can be used to form an electrode mixture layer or a porous membrane layer that has excellent adhesion and can provide excellent cycle characteristics to the secondary battery.

The present invention also aims to advantageously solve the above problems, and the functional layer for a non-aqueous secondary battery of the present invention is characterized in that it is formed using any of the above-mentioned slurry compositions for a non-aqueous secondary battery functional layer. The functional layer formed from any of the above-mentioned slurry compositions has excellent adhesiveness. Furthermore, by using a battery member including the functional layer, it is possible to cause the secondary battery to exhibit excellent cycle characteristics.

The present invention also aims to advantageously solve the above problems, and the battery member for a non-aqueous secondary battery of the present invention is characterized by having the above-mentioned functional layer for a non-aqueous secondary battery. The battery member having the above-mentioned functional layer can cause the secondary battery to exhibit excellent cycle characteristics.

The present invention also aims to advantageously solve the above problems, and the non-aqueous secondary battery of the present invention is characterized by comprising the above-mentioned battery component for a non-aqueous secondary battery. A secondary battery comprising the above-mentioned battery component has excellent cycle characteristics.

In this specification, a functional layer containing a binder and electrode active material particles is referred to as an "electrode mixture layer," a functional layer containing a binder and non-conductive particles is referred to as a "porous membrane layer," and a functional layer containing a binder but neither electrode active material particles nor non-conductive particles is referred to as an "adhesive layer."

According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery, which can prepare a slurry composition for a non-aqueous secondary battery functional layer having excellent viscosity stability.
Moreover, according to the present invention, it is possible to provide a non-aqueous secondary battery functional layer slurry composition having excellent viscosity stability.
According to the present invention, a functional layer for a non-aqueous secondary battery having excellent adhesiveness can be provided.
Furthermore, according to the present invention, it is possible to provide a battery member for a non-aqueous secondary battery that allows the non-aqueous secondary battery to exhibit excellent cycle characteristics.
In addition, according to the present invention, a nonaqueous secondary battery having excellent cycle characteristics can be provided.

Hereinafter, an embodiment of the present invention will be described in detail.
Here, the binder composition for non-aqueous secondary batteries of the present invention is used for the manufacture of non-aqueous secondary batteries, and can be used, for example, for the preparation of the slurry composition for non-aqueous secondary battery functional layers of the present invention. The slurry composition for non-aqueous secondary battery functional layers of the present invention can be used to form any functional layer (e.g., an electrode mixture layer, a porous membrane layer, an adhesive layer) that performs functions such as electron transfer, reinforcement, or adhesion in a non-aqueous secondary battery. Furthermore, the functional layer for non-aqueous secondary batteries of the present invention is formed from the slurry composition for non-aqueous secondary battery functional layers of the present invention. Furthermore, the battery member for non-aqueous secondary batteries of the present invention includes the functional layer for non-aqueous secondary batteries of the present invention. And the non-aqueous secondary battery of the present invention includes the battery member for non-aqueous secondary batteries of the present invention.

(Binder composition for non-aqueous secondary batteries)
The binder composition of the present invention includes a polymer, a fungus, and water, wherein the fungus in the binder composition of the present invention has an average size of 0.5 μm or less.
The binder composition of the present invention may contain components other than the polymer, the bacteria, and water (hereinafter, referred to as "other components").

The binder composition of the present invention contains bacteria with an average size of 0.5 μm or less, so that the spoilage of the polymer by bacteria can be effectively suppressed, and a slurry composition with excellent viscosity stability can be prepared using the binder composition. Furthermore, the slurry composition with excellent viscosity stability can provide a functional layer having a uniform structure in which uneven distribution of components such as polymers and functional particles is suppressed, and the functional layer can provide a secondary battery with excellent cycle characteristics while increasing the adhesion of the functional layer.

<Polymer>
The polymer in the binder composition is a component that can function as a binding material, and in a functional layer formed using a slurry composition containing the binder composition, it prevents components such as functional particles from detaching from the functional layer, and enables adhesion between battery components via the functional layer.

<<Type of polymer>>
Here, as the polymer, any polymer can be used as long as it can be used as a binder in a secondary battery.
For example, the polymer may be a water-soluble polymer that can be dissolved in the binder composition containing water, or a water-insoluble particulate polymer that can be dispersed in the binder composition containing water. The binder composition of the present invention may contain one type of polymer or two or more types of polymers.
In the present invention, the term "water-soluble" refers to the fact that when 0.5 g of the polymer is dissolved in 100 g of water at 25° C., the insoluble content is less than 0.5% by mass. In addition, in the present invention, the term "water-insoluble" refers to the fact that when 0.5 g of the polymer is dissolved in 100 g of water at 25° C., the insoluble content is 90% by mass or more.
Hereinafter, an example will be described in which the polymer is a particulate polymer, but the present invention is not limited thereto.

There are no particular limitations on the particulate polymer, but from the viewpoint of ensuring sufficient adhesion of the functional layer and cycle characteristics of the secondary battery, acrylic polymers and conjugated diene polymers can be preferably used.

[Acrylic polymer]
The acrylic polymer is a polymer containing a (meth)acrylic acid ester monomer unit. Here, the acrylic polymer may contain a repeating unit (another repeating unit) other than the (meth)acrylic acid ester monomer unit.
In the present invention, "(meth)acrylic" means acrylic and/or methacrylic. In addition, in the present invention, "containing a monomer unit" means that "a polymer obtained by using the monomer contains a repeating unit derived from the monomer."

--(Meth)acrylic acid ester monomer unit--
Examples of (meth)acrylic acid ester monomers that can form (meth)acrylic acid ester monomer units include acrylic acids such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate. Acid alkyl esters: methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate. These may be used alone or in combination of two or more.

The content of the (meth)acrylic acid ester monomer unit in the acrylic polymer is preferably more than 50% by mass, more preferably 65% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, preferably 99% by mass or less, and more preferably 98% by mass or less, when the amount of all repeating units contained in the acrylic polymer is taken as 100% by mass. If the content of the (meth)acrylic acid ester monomer unit in the acrylic polymer is within the above-mentioned range, the flexibility of the acrylic polymer can be sufficiently ensured, and the adhesion of the functional layer and the cycle characteristics of the secondary battery can be further improved.

-Other repeating units-
Other repeating units that the acrylic polymer may optionally contain are not particularly limited as long as they are repeating units derived from monomers that can be copolymerized with the above-mentioned (meth)acrylic acid ester monomers, and include, for example, hydrophilic group-containing monomer units (monomer units having a carboxylic acid group, monomer units having a phosphoric acid group, monomer units having a sulfonic acid group, monomer units having a hydroxyl group, etc.), nitrile group-containing monomer units, and crosslinkable monomer units. Note that the hydrophilic group-containing monomers that can form the hydrophilic group-containing monomer units (monomers having a carboxylic acid group, monomers having a phosphoric acid group, monomers having a sulfonic acid group, monomers having a hydroxyl group, etc.), nitrile group-containing monomers that can form the nitrile group-containing monomer units, and crosslinkable monomers that can form the crosslinkable monomer units are not particularly limited, and for example, those described in International Publication No. WO 2015/064099 can be used.

Here, the acrylic polymer may contain an "aliphatic conjugated diene monomer unit" or an "aromatic vinyl monomer unit" which will be described later in the section "conjugated diene polymer". Usually, however, in the acrylic polymer, the content of the (meth)acrylic acid ester monomer unit is at least higher than the content of the aliphatic conjugated diene monomer unit.
The acrylic polymer may contain only one type of other repeating unit, or may contain two or more types of other repeating units.

[Conjugated diene polymer]
The conjugated diene polymer is a polymer containing an aliphatic conjugated diene monomer unit. Specific examples of the conjugated diene polymer include aliphatic conjugated diene polymers such as polybutadiene and polyisoprene; aromatic vinyl/aliphatic conjugated diene copolymers such as styrene-butadiene polymers (SBR); vinyl cyanide/conjugated diene copolymers such as acrylonitrile-butadiene polymers (NBR); hydrogenated SBR, hydrogenated NBR, and the like. Among these, aromatic vinyl/aliphatic conjugated diene copolymers such as styrene-butadiene polymers (SBR) are preferred.
Here, the aromatic vinyl-aliphatic conjugated diene copolymer contains aromatic vinyl monomer units and aliphatic conjugated diene monomer units, and may optionally contain repeating units (other repeating units) other than the aromatic vinyl monomer units and the aliphatic conjugated diene monomer units.

- Aromatic vinyl monomer unit -
Examples of aromatic vinyl monomers capable of forming aromatic vinyl monomer units include styrene, α-methylstyrene, vinyltoluene, divinylbenzene, etc. These can be used alone or in combination of two or more. Among these, styrene is preferred.

The content of aromatic vinyl monomer units in the aromatic vinyl-aliphatic conjugated diene copolymer is preferably 35% by mass or more, more preferably 45% by mass or more, even more preferably 55% by mass or more, preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 65% by mass or less, when the amount of all repeating units contained in the aromatic vinyl-aliphatic conjugated diene copolymer is taken as 100% by mass. If the content of aromatic vinyl monomer units in the aromatic vinyl-aliphatic conjugated diene copolymer is within the above-mentioned range, the strength and adhesiveness of the functional layer can be sufficiently ensured, and the cycle characteristics of the secondary battery can be further improved.

- Aliphatic conjugated diene monomer unit -
Examples of the aliphatic conjugated diene monomer capable of forming the aliphatic conjugated diene monomer unit include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadiene, substituted and side chain conjugated hexadienes, etc. These can be used alone or in combination of two or more. Among these, 1,3-butadiene is preferred.

The content of the aliphatic conjugated diene monomer unit in the aromatic vinyl-aliphatic conjugated diene copolymer is preferably 20% by mass or more, more preferably 30% by mass or more, more preferably 70% by mass or less, more preferably 60% by mass or less, even more preferably 50% by mass or less, and particularly preferably 35% by mass or less, when the amount of all repeating units contained in the aromatic vinyl-aliphatic conjugated diene copolymer is taken as 100% by mass. If the content of the aliphatic conjugated diene monomer unit in the aromatic vinyl-aliphatic conjugated diene copolymer is within the above-mentioned range, the flexibility and adhesion of the functional layer can be sufficiently ensured, and the cycle characteristics of the secondary battery can be further improved.

-Other repeating units-
Other repeating units that may be optionally contained in the aromatic vinyl-aliphatic conjugated diene copolymer are not particularly limited as long as they are repeating units derived from monomers that can be copolymerized with the aromatic vinyl monomer and the aliphatic conjugated diene monomer described above, and examples thereof include hydrophilic group-containing monomer units (monomer units having a carboxylic acid group, monomer units having a phosphoric acid group, monomer units having a sulfonic acid group, monomer units having a hydroxyl group, etc.), nitrile group-containing monomer units, and crosslinkable monomer units. Note that the hydrophilic group-containing monomers that can form the hydrophilic group-containing monomer units (monomers having a carboxylic acid group, monomers having a phosphoric acid group, monomers having a sulfonic acid group, monomers having a hydroxyl group, etc.), nitrile group-containing monomers that can form the nitrile group-containing monomer units, and crosslinkable monomers that can form the crosslinkable monomer units are not particularly limited, and for example, those described in International Publication No. WO 2015/064099 can be used.

Conjugated diene polymers such as aromatic vinyl-aliphatic conjugated diene copolymers may contain the (meth)acrylic acid ester monomer units described above in the "acrylic polymers" section, but typically, in conjugated diene polymers, the content of aliphatic conjugated diene monomer units is greater than the content of (meth)acrylic acid ester monomer units.

<<Tetrahydrofuran insoluble content of polymer>>
Here, the THF insoluble content of the polymer is preferably 10% by mass or more, more preferably 50% by mass or more, even more preferably 80% by mass or more, particularly preferably 85% by mass or more, and preferably 95% by mass or less. If the THF insoluble content of the polymer is 10% by mass or more, the polymer in the functional layer inside the secondary battery can be suppressed from dissolving into the electrolyte, and the cycle characteristics of the secondary battery can be further improved. In addition, since a polymer having a THF insoluble content of 95% by mass or less can be easily prepared, it is possible to efficiently produce a binder composition containing the polymer.
The THF-insoluble content of the polymer can be adjusted by changing the monomer composition of the polymer (types and ratio of monomers used) and polymerization conditions of the polymer (amount of molecular weight regulator used, reaction temperature, reaction time, etc.).

<<Volume average particle size of polymer>>
When the polymer is a particulate polymer, the volume average particle diameter of the polymer used to prepare the binder composition is preferably 0.4 μm or less, more preferably 0.2 μm or less. If the volume average particle diameter of the polymer is 0.4 μm or less, the polymer can be prevented from excessively clogging the filter holes during the filtration process described below, and a binder composition having a bacteria size of a predetermined value or less can be efficiently obtained. The lower limit of the volume average particle diameter of the particulate polymer used to prepare the binder composition is not particularly limited, but is usually 0.05 μm or more.
The volume average particle size of the polymer in the binder composition is preferably 0.05 μm or more, and is preferably 0.4 μm or less, and more preferably 0.2 μm or less.
In the present invention, the "volume average particle size" can be measured by the method described in the Examples of this specification.

<Bacteria>
<<Average size>>
The average size of the bacteria contained in the binder composition of the present invention must be 0.5 μm or less, preferably 0.4 μm or less, and more preferably 0.3 μm or less. According to the study by the present inventors, it has been found that when the average size of the bacteria contained in the binder composition exceeds 0.5 μm, the putrefaction of the polymer contained as a binder in the binder composition for non-aqueous secondary batteries is particularly promoted. Therefore, by controlling the average size of the bacteria contained in the binder composition of the present invention to 0.5 μm or less, the putrefaction of the polymer can be suppressed, and the viscosity stability of the slurry composition, the adhesion of the functional layer, and the cycle characteristics of the secondary battery can be improved. The lower limit of the average size of the bacteria is not particularly limited, but is usually 0.05 μm or more.

<< Shape of bacteria >>
The shape of the bacteria contained in the binder composition of the present invention is not particularly limited, and examples thereof include cocci and bacilli. The shapes of the multiple bacteria contained in the binder composition of the present invention may all be the same or different.

<<Bacteria count>>
Here, the binder composition of the present invention preferably has a bacterial count of 1.0×10 ⁶ /ml or less, more preferably 1.0×10 ⁵ /ml or less. When the bacterial count of the binder composition is 1.0×10 ⁶ /ml or less, the polymer can be sufficiently suppressed from spoiling, and the viscosity stability of the slurry composition can be further improved. The adhesiveness of the functional layer obtained by using the slurry composition and the cycle characteristics of the secondary battery equipped with the functional layer can be further improved. The lower limit of the bacterial count is not particularly limited, but from the viewpoint of suppressing a reduction in manufacturing efficiency due to excessive sterilization operations such as washing, and a decrease in the performance (binding ability, etc.) of the polymer in the binder composition due to excessive sterilization operations, it is preferable that the bacterial count is 1 /ml or more.
In the present invention, the "number of bacteria" contained in the binder composition can be measured in accordance with JIS K 0350-10-10 (2002).

<<Bacteria species>>
The species of bacteria contained in the binder composition of the present invention is not particularly limited as long as the average size is equal to or less than the above-mentioned value, and may include any bacteria. Examples of genera to which the bacteria may belong that may be contained in the binder composition of the present invention include the genus Serratia, the genus Bacillus, the genus Burkholderia, the genus Achromobacter, the genus Alcaligenes, the genus Stenotrophomonas, and the genus Pseudomonas. Here, the binder composition of the present invention may contain one type of bacteria, or may contain two or more types of bacteria. And, when the binder composition of the present invention contains two or more types of bacteria, these bacteria may belong to one genus or different genera.
In the present invention, the bacterial species contained in the binder composition can be identified by using the method described in the Examples of this specification.

However, from the viewpoint of suppressing an increase in the average size of the bacteria and sufficiently improving the viscosity stability of the slurry composition, the adhesion of the functional layer, and the cycle characteristics of the secondary battery, it is preferable that the binder composition of the present invention is substantially free of bacteria belonging to the genus Burkholderia, bacteria belonging to the genus Achromobacter, bacteria belonging to the genus Alcaligenes, bacteria belonging to the genus Stenotrophomonas, and bacteria belonging to the genus Pseudomonas.
In the present invention, the binder composition being "substantially free" of bacteria belonging to a specific genus means that bacteria belonging to that genus are not detected when the bacterial species identification procedure described in the Examples of this specification is carried out.

<Other ingredients>
The binder composition of the present invention may optionally contain, as other components, known additives that can be added to functional layers such as an electrode mixture layer, a porous membrane layer, and an adhesive layer, such as a conductive material, a wetting agent, an electrolyte additive, etc. In addition, the binder composition may contain various preparations (such as an emulsifier) used in the preparation of a polymer.
The binder composition of the present invention may contain a known preservative and/or bactericide capable of suppressing corrosion of the polymer. However, from the viewpoint of preventing deterioration of battery characteristics (such as cycle characteristics) due to their incorporation into the secondary battery, the amount of the preservative and bactericide in the binder composition is preferably 1 part by mass or less, more preferably 0.1 parts by mass or less, even more preferably 0.01 parts by mass or less, and particularly preferably 0 part by mass (i.e., no preservative or bactericide is included) per 100 parts by mass of the polymer, respectively.

<Method of producing binder composition>
The method for producing the binder composition of the present invention is not particularly limited as long as it is possible to control the average size of the bacteria contained in the binder composition to 0.5 μm or less.
A step of polymerizing a monomer composition containing a monomer and water in a reactor to obtain a mixed liquid containing a polymer and water (polymerization step);
a step of filtering the mixed liquid containing the polymer and water to recover the binder composition (filtering step);
By using a binder composition from which large-sized bacteria have been removed by filtering a mixed liquid containing a polymer and water, it is possible to satisfactorily provide a slurry composition having excellent viscosity stability, a functional layer having excellent adhesiveness, and a secondary battery having excellent cycle characteristics.

<<Polymerization process>>
In the polymerization step, a monomer composition containing, for example, the monomers described above in the section "Polymer" and water is polymerized. The content ratio of each monomer in the monomer composition can be determined based on the content ratio of a desired monomer unit (repeating unit) in the polymer.
Here, the polymerization method is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. can be used. In addition, any reaction such as ionic polymerization, radical polymerization, living radical polymerization, various condensation polymerization, addition polymerization, etc. can be used as the polymerization reaction. In addition, in the polymerization, a known emulsifier or polymerization initiator can be used as necessary.
The polymerization temperature is not particularly limited, but from the viewpoint of smoothly progressing the polymerization reaction while reducing the number of bacteria in the resulting binder composition, the polymerization temperature is preferably 60° C. or higher, more preferably 70° C. or higher, even more preferably 80° C. or higher, and preferably 90° C. or lower.

<<Filtration process>>
In the filtration step, the mixed liquid containing the polymer and water obtained in the above-mentioned polymerization step (aqueous solution or aqueous dispersion of the polymer) is filtered, and the mixed liquid after filtration is recovered as a binder composition.

Here, the filtration method is not particularly limited and any filtration method can be used as long as it is capable of removing large-sized bacteria using a filter.

The pore size of the filter used for filtration is preferably 12 μm or less, more preferably 8 μm or less, and even more preferably 6 μm or less. By using a filter with a pore size of 12 μm or less, it is possible to efficiently produce a binder composition in which bacteria having an average size of 0.5 μm or less are contained by sufficiently removing large-sized bacteria. In addition, the lower limit of the pore size of the filter is preferably 0.3 μm or more, more preferably 0.4 μm or more, from the viewpoint of preventing clogging of the filter by the polymer, particularly when the polymer is a particulate polymer.
In the present invention, the "pore size" of a filter means the average size of the pores in the filter.

<<Other processes>>
The above-mentioned method for producing the binder composition may include steps (other steps) other than the polymerization step and the filtration step.
For example, the method for producing the binder composition described above may include a step of adding the above-mentioned other components that are optionally used to a mixed liquid containing the obtained polymer and water after the polymerization step (optional component addition step).
For example, the above-mentioned method for producing the binder composition may include a step of sterilizing the mixed liquid after the polymerization step and/or the filtration step by irradiating it with ultraviolet light or the like (sterilization step). However, the sterilization step by ultraviolet light or the like may deteriorate the performance of the polymer, and may impair the adhesion of the functional layer and the cycle characteristics of the secondary battery. Therefore, it is preferable that the method for producing the binder composition of the present invention does not include a sterilization step.

For example, the above-mentioned method for producing the binder composition may include a step (cleaning step) of cleaning the inner surface of a pipe (for example, a pipe equipped with a filter used in the filtration step) used to transport a mixed liquid containing a polymer and water with water at 70 ° C. or higher prior to the filtration step. Bacteria tend to grow and adhere to the inner surface of the pipe through which the polymer is transported. However, if the binder composition is produced through the above-mentioned cleaning step, the bacteria on the inner surface of the pipe can be removed by the cleaning step to reduce the number of bacteria in the binder composition, and there is no need to perform excessive sterilization treatment (such as ultraviolet irradiation) after the polymerization step and/or the filtration step, so that the obtained polymer can have sufficiently good performance (such as binding ability). Therefore, by using the binder composition obtained through the above-mentioned steps, it is possible to provide a slurry composition with excellent viscosity stability, a functional layer with excellent adhesion, and a secondary battery with excellent cycle characteristics.

In the above-mentioned cleaning step, the inner surface of the pipe is cleaned with water at 70° C. or higher. Specifically, cleaning of the inner surface of the pipe can be performed by passing water at 70° C. or higher through the inside of the pipe. In order to effectively disinfect the inner surface of the pipe, the temperature of the water used for cleaning needs to be 70° C. or higher, and is preferably 80° C. or higher.
In the washing step, equipment other than the piping may be washed with water at 70° C. or higher. For example, prior to the above-mentioned polymerization step, washing of the reactor to be used in the polymerization step may be performed together with washing of the piping.

<Surface tension of binder composition>
Here, the surface tension of the binder composition is preferably 22 mN/m or more and 55 mN/m or less, more preferably 25 mN/m or more and 55 mN/m or less. By using a binder composition having a surface tension within the above-mentioned range, the polymer can fully exhibit its performance as a binding material, and the viscosity stability of the slurry composition, the adhesion of the functional layer, and the cycle characteristics of the secondary battery can be sufficiently improved.
The surface tension of the binder composition can be adjusted by changing the types and/or properties of the components contained in the binder composition (for example, the type and/or properties of the polymer).

(Slurry composition for non-aqueous secondary battery functional layer)
The slurry composition of the present invention is a composition used for forming a functional layer, and is prepared using the above-mentioned binder composition. The slurry composition of the present invention is prepared using the binder composition of the present invention, in which the average size of the bacteria contained therein is equal to or less than a predetermined value, and therefore has excellent viscosity stability. Furthermore, by using the slurry composition of the present invention, a functional layer having excellent adhesion can be obtained. And, by using a battery member having the functional layer, it is possible to make the secondary battery exhibit excellent cycle characteristics.

<Binder Composition>
The binder composition of the present invention described above is used as the binder composition. The amount of the binder composition in the slurry composition is not particularly limited. For example, when the slurry composition is an electrode slurry composition, the amount of the binder composition can be an amount in which the amount of the polymer derived from the binder composition is 0.5 parts by mass or more and 15 parts by mass or less in terms of solid content per 100 parts by mass of electrode active material particles. Also, for example, when the slurry composition is a porous membrane layer slurry composition, the amount of the binder composition can be an amount in which the amount of the polymer derived from the binder composition is 0.5 parts by mass or more and 30 parts by mass or less in terms of solid content per 100 parts by mass of non-conductive particles.

<Functional particles>
Here, examples of functional particles for enabling the functional layer to exhibit the intended function include electrode active material particles when the functional layer is an electrode mixture layer, and non-conductive particles when the functional layer is a porous membrane layer.

<<Electrode active material particles>>
The electrode active material particles are not particularly limited, and may be particles made of a known electrode active material used in secondary batteries. The electrode active material particles that can be used in the electrode mixture layer of the lithium ion secondary battery are not particularly limited, and particles made of the following electrode active materials can be used.

[Positive electrode active material]
The positive electrode active material to be blended in the positive electrode composite layer of the positive electrode of the lithium ion secondary battery may be, for example, a compound containing a transition metal, such as a transition metal oxide, a transition metal sulfide, a composite metal oxide of lithium and a transition metal, etc. Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, etc.
Specifically, the positive electrode active material is not particularly limited, and examples thereof include lithium-containing cobalt oxide (LiCoO ₂ ), lithium manganese oxide (LiMn ₂ O ₄ ), lithium-containing nickel oxide (LiNiO ₂ ), lithium-containing composite oxides of Co—Ni—Mn, lithium-containing composite oxides of Ni—Mn—Al, lithium-containing composite oxides of Ni—Co—Al, olivine-type lithium iron phosphate (LiFePO ₄ ), olivine-type lithium manganese phosphate (LiMnPO ₄ ), lithium-excess spinel compounds represented by Li _1+x Mn _2-x O ₄ (0<x<2), Li[Ni _0.17 Li _0.2 Co _0.07 Mn _0.56 ]O ₂ , LiNi _0.5 Mn _1.5 O ₄ , and the like.
The above-mentioned positive electrode active materials may be used alone or in combination of two or more.

[Negative electrode active material]
Examples of the negative electrode active material to be blended in the negative electrode mixture layer of the negative electrode of the lithium ion secondary battery include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that are combinations of these.
Here, the carbon-based negative electrode active material refers to an active material having a carbon skeleton that can insert lithium (also called "doped"). Specific examples of the carbon-based negative electrode active material include carbonaceous materials such as coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber, pyrolytic vapor-grown carbon fiber, phenolic resin baked body, polyacrylonitrile-based carbon fiber, pseudoisotropic carbon, furfuryl alcohol resin baked body (PFA) and hard carbon, as well as graphitic materials such as natural graphite and artificial graphite.
In addition, the metal-based negative electrode active material is an active material containing a metal, and usually refers to an active material that contains an element capable of inserting lithium in its structure and has a theoretical electric capacity per unit mass of 500 mAh/g or more when lithium is inserted. Examples of the metal-based active material include lithium metal, elemental metals that can form lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.), and oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. thereof. Furthermore, oxides such as lithium titanate can be mentioned.
The above-mentioned negative electrode active materials may be used alone or in combination of two or more.

<<Non-conductive particles>>
The non-conductive particles to be blended in the porous membrane layer are not particularly limited, and may be any known non-conductive particles used in secondary batteries.
Specifically, both inorganic and organic fine particles can be used as the non-conductive particles, but inorganic fine particles are usually used. Among them, materials that are stable in the use environment of the secondary battery and are electrochemically stable are preferred as the material of the non-conductive particles. From this viewpoint, preferred examples of materials of the non-conductive particles include oxide particles such as aluminum oxide (alumina), hydrated aluminum oxide (boehmite), silicon oxide, magnesium oxide (magnesia), calcium oxide, titanium oxide (titania), BaTiO ₃ , ZrO, and alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystal particles such as silicon and diamond; sparingly soluble ion crystal particles such as barium sulfate, calcium fluoride, and barium fluoride; clay fine particles such as talc and montmorillonite; and the like. In addition, these particles may be subjected to element substitution, surface treatment, solid solution formation, and the like as necessary.
The non-conductive particles may be used alone or in combination of two or more kinds.

<Other ingredients>
In preparing the slurry composition, components other than the binder composition and functional particles (other components) can also be used. The other components that can be mixed into the slurry composition are not particularly limited, and include the same components as those that can be mixed into the binder composition of the present invention. The other components may be used alone or in combination of two or more in any ratio.

<Preparation of Slurry Composition>
The method for preparing the slurry composition is not particularly limited.
For example, when the slurry composition is a slurry composition for an electrode, the binder composition, electrode active material particles, and other components used as necessary can be mixed in the presence of a solvent containing water to prepare the slurry composition.
In addition, when the slurry composition is a slurry composition for a porous membrane layer, the binder composition, the non-conductive particles, and other components used as necessary can be mixed in the presence of a solvent containing water to prepare the slurry composition.
When the slurry composition is a slurry composition for an adhesive layer, the binder composition can be used as is or after diluting with a solvent such as water to form a slurry composition, or the binder composition and other components used as necessary can be mixed in the presence of a solvent containing water to prepare a slurry composition.
The mixing method used in preparing the slurry composition is not particularly limited, but mixing is carried out using a commonly used stirrer or disperser.

(Functional layer for non-aqueous secondary batteries)
The functional layer of the present invention is a layer that performs functions such as electron transfer, reinforcement, or adhesion in a non-aqueous secondary battery. Examples of the functional layer include an electrode composite that transfers electrons via an electrochemical reaction. Examples of the functional layer include a material layer, a porous membrane layer for improving heat resistance and strength, and an adhesive layer for improving adhesion. The functional layer of the present invention is formed from the above-mentioned slurry composition of the present invention. For example, the above-mentioned slurry composition can be applied to the surface of a suitable substrate to form a coating film, and the coating film thus formed can be dried to form the coating film.

The functional layer of the present invention is formed from the slurry composition of the present invention prepared using the binder composition of the present invention, and therefore has excellent adhesion and allows a secondary battery having a battery component equipped with the functional layer of the present invention to exhibit excellent cycle characteristics.

<<Substrate>>
Here, there is no limitation on the substrate to which the slurry composition is applied, and for example, a coating film of the slurry composition may be formed on the surface of a release substrate, the coating film may be dried to form a functional layer, and the release substrate may be peeled off from the functional layer. In this way, the functional layer peeled off from the release substrate may be used as a free-standing film to form a battery component of a secondary battery.
However, from the viewpoint of omitting the step of peeling off the functional layer and increasing the manufacturing efficiency of the battery component, it is preferable to use a current collector, a separator substrate, or an electrode substrate as the substrate. Specifically, when preparing the electrode mixture layer, it is preferable to apply the slurry composition onto the current collector as the substrate. Also, when preparing the porous membrane layer or the adhesive layer, it is preferable to apply the slurry composition onto the separator substrate or the electrode substrate.

[Current collector]
As the current collector, a material having electrical conductivity and electrochemical durability is used. Specifically, as the current collector, for example, a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. can be used. Among them, copper foil is particularly preferable as the current collector used for the negative electrode. Also, aluminum foil is particularly preferable as the current collector used for the positive electrode. Note that the above-mentioned materials may be used alone or in combination of two or more kinds in any ratio.

[Separator substrate]
The separator substrate is not particularly limited, but may be any of known separator substrates such as an organic separator substrate. The organic separator substrate is a porous member made of an organic material, and examples of the organic separator substrate include microporous membranes or nonwoven fabrics containing polyolefin resins such as polyethylene and polypropylene, aromatic polyamide resins, etc., and polyethylene microporous membranes and nonwoven fabrics are preferred because of their excellent strength.

[Electrode substrate]
The electrode substrate (positive electrode substrate and negative electrode substrate) is not particularly limited, but examples thereof include an electrode substrate in which an electrode mixture layer containing electrode active material particles and a binder is formed on the above-mentioned current collector.
The electrode active material particles and binder contained in the electrode mixture layer in the electrode substrate are not particularly limited, and the electrode active material particles described above in the section "Slurry composition for non-aqueous secondary battery functional layer" and the polymer described above in the section "Binder composition for non-aqueous secondary battery" can be used.

<<Method of forming functional layer>>
Examples of methods for forming a functional layer on a substrate such as the current collector, separator substrate, or electrode substrate include the following methods.
1) A method in which the slurry composition of the present invention is applied to the surface of a substrate (in the case of an electrode substrate, the surface on the electrode mixture layer side; the same applies hereinafter) and then dried;
2) a method of immersing a substrate in the slurry composition of the present invention and then drying it; and 3) a method of applying the slurry composition of the present invention onto a release substrate, drying it to produce a functional layer, and transferring the obtained functional layer to the surface of the substrate.
Among these, the method 1) is particularly preferred because it is easy to control the thickness of the functional layer. Specifically, the method 1) includes a step of applying the slurry composition onto a substrate (application step) and a step of drying the slurry composition applied onto the substrate to form a functional layer (drying step).

[Coating process]
In the coating step, the method for coating the slurry composition on the substrate is not particularly limited, and examples thereof include a doctor blade method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

[Drying process]
In the drying step, the method for drying the slurry composition on the substrate is not particularly limited and may be any known method. Examples of the drying method include drying with warm air, hot air, or low-humidity air, vacuum drying, and drying by irradiation with infrared rays or electron beams.

(Battery components for non-aqueous secondary batteries)
The battery member of the present invention (such as a separator and an electrode) has the functional layer of the present invention described above, and includes, for example, the functional layer and the substrate (current collector, separator substrate, electrode substrate). The battery member of the present invention may include components other than the functional layer of the present invention and the substrate, as long as the effects of the present invention are not significantly impaired. Such components include, but are not limited to, an electrode mixture layer, a porous membrane layer, and an adhesive layer that do not fall under the functional layer of the present invention.
The battery member of the present invention may also have a plurality of functional layers of the present invention. For example, the electrode may have an electrode mixture layer formed from the electrode slurry composition of the present invention on the current collector, and a porous membrane layer and/or adhesive layer formed from the porous membrane layer and/or adhesive layer slurry composition of the present invention on the electrode mixture layer. For example, the separator may have a porous membrane layer formed from the porous membrane layer slurry composition of the present invention on the separator substrate, and an adhesive layer formed from the adhesive layer slurry composition of the present invention on the porous membrane layer.
The battery component of the present invention can be well bonded to adjacent battery components and can provide the secondary battery with excellent cycle characteristics.

(Non-aqueous secondary battery)
The secondary battery of the present invention includes the above-mentioned battery component of the present invention. More specifically, the nonaqueous secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, and includes the battery component of the present invention as at least one of the positive electrode, the negative electrode, and the separator. The secondary battery of the present invention can exhibit excellent cycle characteristics.

<Positive electrode, negative electrode and separator>
At least one of the positive electrode, negative electrode, and separator used in the secondary battery of the present invention is the battery member of the present invention having the functional layer of the present invention described above. Note that the positive electrode, negative electrode, and separator not having the functional layer of the present invention are not particularly limited, and known positive electrodes, negative electrodes, and separators can be used.

<Electrolyte>
As the electrolyte, an organic electrolyte in which a supporting electrolyte is dissolved in an organic solvent is usually used. As the supporting electrolyte, for example, a lithium salt is used in a lithium ion secondary battery. As the lithium salt, for example, _LiPF6 , _LiAsF6 , LiBF4, _LiSbF6 , _LiAlCl4 , _LiClO4 , _CF3SO3Li , _C4F9SO3Li , _CF3COOLi , ( _CF3CO ) _{2NLi , ( CF3SO2} ) _2NLi , ( _C2F5SO2 )NLi _, etc. are listed. Among them, _LiPF6 , _LiClO4 , _{and CF3SO3Li} are preferred because _they are easily dissolved in _a solvent and show _a high degree _of dissociation. The electrolyte may be used alone or in combination of two or more. In general, the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. 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), ethyl methyl carbonate (EMC), vinylene carbonate (VC), etc.; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; and the like are preferably used. A mixture of these solvents may also be used. Among them, carbonates are preferred because they have a high dielectric constant and a wide stable potential region. Usually, the lower the viscosity of the solvent used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted by the type of solvent.
The concentration of the electrolyte in the electrolytic solution can be appropriately adjusted. Known additives may also be added to the electrolytic solution.

<Method of manufacturing non-aqueous secondary battery>
The secondary battery of the present invention described above can be manufactured, for example, by stacking a positive electrode and a negative electrode with a separator therebetween, wrapping or folding the stack as necessary, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the battery container. At least one of the positive electrode, negative electrode, and separator is the battery component of the present invention. In addition, the battery container may be filled with an expand metal, a fuse, an overcurrent prevention element such as a PTC element, a lead plate, or the like as necessary to prevent pressure rise inside the battery and overcharging and discharging. The shape of the battery may be any of a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, and the like.

The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" expressing amounts are based on mass unless otherwise specified.
In the examples and comparative examples, the THF insoluble content and volume average particle size of the polymer, the average size, number and species of bacteria contained in the binder composition, the surface tension of the binder composition, the viscosity stability of the slurry composition, the adhesion of the porous membrane layer, and the cycle characteristics of the secondary battery were measured and evaluated by the following methods.

<THF insoluble content>
The obtained aqueous dispersion of the polymer (binder composition) was dried under an environment of 50% humidity and 23°C to 25°C to prepare a film having a thickness of 3±0.3 mm. The prepared film was cut into 5 mm squares to prepare a plurality of film pieces, and these film pieces were precisely weighed to about 1 g. The weight of the precisely weighed film piece was designated as W0. Next, the precisely weighed film piece was immersed in 100 g of tetrahydrofuran (THF) at 25°C for 24 hours. Thereafter, the film piece was pulled out of the THF, and the pulled out film piece was vacuum dried at 105°C for 3 hours, and its weight (weight of the insoluble portion) W1 was measured. Then, the THF insoluble content (%) was calculated according to the following formula.
THF insoluble content (%) = W1/W0 x 100
<Volume average particle size>
For aqueous dispersions of the polymers adjusted to a solid content concentration of 0.1% by mass, particle size distribution (volume basis) was measured using a laser diffraction particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name "LS-230"). Then, the particle size at which the cumulative volume calculated from the small diameter side in the obtained particle size distribution became 50% was determined, and this was taken as the volume average particle size (D50) of each polymer.
<Average size of bacteria>
A part of the binder composition was sampled as a specimen, smeared on an SCD agar medium (manufactured by Nippon Pharmaceutical Co., Ltd., product name "Daigo (registered trademark)"), and the bacteria were cultured aerobically at 35 ° C for 3 days. When the number of bacteria contained in the binder composition was small, 10 mL of the binder composition was inoculated into 90 mL of an SCD agar medium (manufactured by Nippon Pharmaceutical Co., Ltd., product name "Daigo") and cultured aerobically at 35 ° C for 3 days, and the specimen was used. The SCD agar medium was then observed with an electron microscope to measure the size (minimum diameter) of live bacteria present in an arbitrarily selected 1 cm x 1 cm section. The arithmetic mean value of the obtained measurements was calculated and used as the average size (μm) of the bacteria contained in the binder composition.
<Bacteria count>
The number of bacteria (cells/ml) per 1 ml of the binder composition was measured according to JIS K 0350-10-10 (2002).
<Identification of bacterial species>
Bacteria from the binder composition were isolated by the agar plate method, and the bacteria that grew in the medium of the optimum concentration were cultured as pure cultures. Different bacterial strains were selected from the pure cultured bacteria based on colony morphology and Gram staining images, and the bacterial species contained in the binder composition were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI/TOFMS).
Specifically, the bacterial isolation and pure culture by the agar plate method were carried out as follows.
A 10-fold serial dilution of the specimen was prepared using SCD agar medium (manufactured by Nippon Pharmaceutical Co., Ltd., product name "Daigo"). Next, 100 μL of the binder composition and each dilution of each concentration were smeared on SCD agar medium (manufactured by Nippon Pharmaceutical Co., Ltd., product name "Daigo"). After aerobically culturing for 3 days at 35°C, strains grown on the SCD agar medium that had different colony shapes, sizes, colors, etc. were picked up and subcultured on new SCD agar medium (manufactured by Nippon Pharmaceutical Co., Ltd., product name "Daigo") for pure culture.
When the number of bacteria contained in the binder composition was small, 10 mL of the binder composition was inoculated into 90 mL of SCD agar medium (manufactured by Nippon Pharmaceutical Co., Ltd., product name "Daigo") and cultured aerobically at 35°C for 3 days, after which bacterial isolation and pure culture were performed according to the above procedure.
<Surface tension>
The binder composition was poured onto a glass petri dish, and the surface tension was measured by the plate method using a platinum plate. The surface tensiometer used was a "CBVP-Z" manufactured by Kyowa Interface Science Co., Ltd. The measurement was performed twice in total, and the average value of the two measurements was regarded as the surface tension of the binder composition.
<Viscosity stability>
The viscosity η0 of the obtained slurry composition was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., product name "TVB-10", rotation speed: 60 rpm). Next, the slurry composition whose viscosity was measured was stirred for 24 hours using a planetary mixer (rotation speed: 60 rpm), and the viscosity η1 of the slurry composition after stirring was measured using the same B-type viscometer (rotation speed: 60 rpm) as above. Then, the viscosity maintenance rate Δη of the slurry composition before and after stirring was calculated as Δη=η1/η0×100(%), and the viscosity stability of the slurry composition was evaluated according to the following criteria. The temperature during the viscosity measurement was 25° C. The closer the value of the viscosity maintenance rate Δη is to 100%, the better the viscosity stability of the slurry composition is.
A: Viscosity maintenance rate Δη is 90% or more and 110% or less. B: Viscosity maintenance rate Δη is 80% or more and less than 90%. C: Viscosity maintenance rate Δη is 70% or more and less than 80%. D: Viscosity maintenance rate Δη is less than 70%. <Adhesion>
The separator with the prepared porous membrane layer was cut into a rectangle of 100 mm in length and 10 mm in width to prepare a test piece, and the surface of the porous membrane layer of the test piece was attached to a test stand (SUS substrate) via cellophane tape (specified in JIS Z1522) with the surface having the porous membrane layer facing down. Then, the stress (N/m) when one end of the separator substrate was pulled vertically at a pulling speed of 50 mm/min and peeled off was measured (note that the cellophane tape was fixed to the test stand). The same measurement as above was performed three times, and the average value was calculated, which was taken as the peel strength and evaluated according to the following criteria. The larger the peel strength value, the stronger the adhesion between the porous membrane layer and the separator substrate, and the better the adhesion of the porous membrane layer.
A: Peel strength is 3.0 N/m or more. B: Peel strength is 2.5 N/m or more and less than 3.0 N/m. C: Peel strength is 1.5 N/m or more and less than 2.5 N/m. D: Peel strength is less than 1.5 N/m. <Cycle characteristics>
The manufactured lithium ion secondary battery was left to stand for 24 hours in an environment at 25° C., and then charged to 4.4 V at a charge rate of 0.1 C in an environment at 25° C., discharged to 2.75 V at a discharge rate of 0.1 C, and the initial capacity C0 was measured. Thereafter, the same charge and discharge operation was repeated in an environment at 60° C., and the capacity C1 after 1000 cycles was measured.
The capacity retention rate ΔC (=(C1/C0)×100%) before and after the cycle was calculated and evaluated according to the following criteria. A larger value of the capacity retention rate ΔC indicates that the secondary battery has better high-temperature cycle characteristics and a longer life.
A: Capacity maintenance rate ΔC is 85% or more. B: Capacity maintenance rate ΔC is 80% or more and less than 85%. C: Capacity maintenance rate ΔC is 75% or more and less than 80%. D: Capacity maintenance rate ΔC is less than 75%.

Example 1
<Preparation of Binder Composition>
<<Polymerization step (acrylic polymer)>>
To a reactor equipped with a stirrer, 70 parts of ion-exchanged water, 0.15 parts of sodium lauryl sulfate (manufactured by Kao Chemical Corporation, "EMAL (registered trademark) 2F") as an emulsifier, and 0.5 parts of ammonium persulfate were supplied, the gas phase was replaced with nitrogen gas, and the temperature was raised to 60°C.
On the other hand, in another container, 50 parts of ion-exchanged water, 0.5 parts of sodium dodecylbenzenesulfonate as a dispersant, 94 parts of n-butyl acrylate as a (meth)acrylic acid ester monomer, 2 parts of methacrylic acid as a hydrophilic group-containing monomer, 2 parts of acrylonitrile as a nitrile group-containing monomer, 1 part of allyl methacrylate and 1 part of allyl glycidyl ether as crosslinkable monomers were mixed to obtain a monomer composition. This monomer composition was continuously added to the reactor over 4 hours to carry out polymerization. During the addition, the reaction was carried out at 60°C. After the addition was completed, the mixture was stirred at 70°C for another 3 hours to terminate the reaction, and an aqueous dispersion of an acrylic polymer, which is a particulate polymer (a mixed liquid containing an acrylic polymer and water), was obtained. Using this aqueous dispersion, the volume average particle diameter of the acrylic polymer was measured. The results are shown in Table 1.
<<Filtration process>>
The aqueous dispersion of the acrylic polymer obtained in the above-mentioned polymerization process was filtered through a filter (manufactured by Nippon Pall Co., Ltd., product name "NXT0.5", pore size: 5 μm) and collected as a binder composition in a collection container. Using the collected binder composition, the average size and number of bacteria were measured, and the species of bacteria were identified. In addition, the surface tension of the binder composition and the THF-insoluble content of the acrylic polymer were measured. The results are all shown in Table 1.
<Preparation of slurry composition for porous membrane layer>
Alumina particles (manufactured by Sumitomo Chemical Co., Ltd., product name "AKP-3000", volume average particle diameter D50: 0.45 μm, tetrapod-shaped particles) were prepared as non-conductive particles.
In addition, carboxymethyl cellulose (manufactured by Daicel FineChem, product name "D1200", degree of etherification: 0.8 to 1.0, viscosity of 1% aqueous solution: 10 to 20 mPa·s) was prepared as a viscosity modifier.
100 parts of the non-conductive particles, 1.5 parts of the viscosity modifier, and ion-exchanged water were mixed and dispersed so that the solid content concentration was 40%. 4 parts (solid content equivalent) of the binder composition obtained above and 0.2 parts of a polyethylene glycol surfactant (San Nopco SN Wet 366) were further added to the obtained dispersion and mixed to obtain a slurry composition for a porous membrane layer. The viscosity stability of this slurry composition for a porous membrane layer was evaluated. The results are shown in Table 1.
<Preparation of separator with porous membrane layer>
The slurry composition for the porous membrane layer obtained above was applied onto a separator substrate (made of polypropylene, product name "Celgard 2500") so that the coating amount of the slurry composition for the porous membrane layer was 0.3 mg/ ^cm2 , and the mixture was dried for 3 minutes at 50°C. This operation was performed on both sides of the separator substrate to obtain a separator with a porous membrane layer in which a porous membrane layer was formed on both sides of the separator substrate.
<Preparation of Positive Electrode>
₁₀₀ parts of LiCoO2 (volume average particle diameter D50: 12 μm) as positive electrode active material particles, 2 parts of acetylene black (manufactured by Denka Co., Ltd., product name "HS-100") as a conductive material, and 2 parts of PVDF (polyvinylidene fluoride, manufactured by Kureha Co., Ltd., product name "#7208") as a binder for the positive electrode composite layer, equivalent to solid content, were mixed in NMP (N-methylpyrrolidone) to a total solid concentration of 70%, and these were further mixed using a planetary mixer to prepare a slurry composition for the positive electrode.
The obtained positive electrode slurry composition was applied to a 20 μm thick aluminum foil current collector using a comma coater so that the film thickness after drying was about 150 μm, and then dried. This drying was performed by conveying the aluminum foil at a speed of 0.5 m/min in an oven at 60 ° C for 2 minutes. Then, the aluminum foil was heated at 120 ° C for 2 minutes to obtain a positive electrode raw sheet before pressing. This positive electrode raw sheet before pressing was rolled with a roll press to obtain a positive electrode having a positive electrode composite layer thickness of 80 μm.
<Preparation of negative electrode>
In a 5 MPa pressure vessel equipped with a stirrer, 33.5 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 62 parts of styrene, 1 part of 2-hydroxyethyl acrylate, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium peroxodisulfate as a polymerization initiator were added, thoroughly stirred, and then heated to 50 ° C. to start polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a binder (SBR) for the negative electrode mixture layer. A 5% aqueous sodium hydroxide solution was added to the mixture containing the binder for the negative electrode mixture layer, and the pH was adjusted to 8. After removing unreacted monomers by heating and vacuum distillation, the mixture was cooled to 30 ° C. or less to obtain a water dispersion containing the desired binder for the negative electrode mixture layer.
A mixture of 100 parts of artificial graphite (volume average particle diameter D50 is 15.6 μm) and 1 part of a 2% aqueous solution of sodium salt of carboxymethylcellulose (manufactured by Nippon Paper Industries Co., Ltd., MAC350HC) as a thickener in terms of solid content was adjusted to a solid content concentration of 68% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. After further adjusting the solid content concentration to 62% with ion-exchanged water, it was mixed at 25 ° C. for 15 minutes. The above-mentioned binder for the negative electrode mixture layer (SBR) was added in terms of solid content equivalent to 1.5 parts, and ion-exchanged water was added to adjust the final solid content concentration to 52%, and further mixed for 10 minutes. This was defoamed under reduced pressure to prepare a slurry composition for a negative electrode with good fluidity.
The obtained negative electrode slurry composition was applied to a 20 μm thick copper foil current collector with a comma coater so that the film thickness after drying was about 150 μm, and then dried. This drying was performed by conveying the copper foil at a speed of 0.5 m/min in an oven at 60 ° C for 2 minutes. Then, the negative electrode raw material before pressing was obtained by heat treatment at 120 ° C for 2 minutes. This negative electrode raw material before pressing was rolled with a roll press to obtain a negative electrode with a negative electrode composite layer thickness of 80 μm.
<Manufacture of secondary batteries>
The positive electrode obtained above was cut to 49 x 5 cm. Then, the separator with the porous membrane layer obtained above was cut to 55 x 5.5 cm and placed on the composite layer of the cut positive electrode. Furthermore, the negative electrode obtained above was cut to 50 x 5.2 cm and placed on the separator with the porous membrane layer so that the surface of the negative electrode composite layer faces the separator to obtain a laminate. This laminate was wound by a winding machine to obtain a wound body. This wound body was pressed at 60 ° C. and 0.5 MPa to form a flat body. This flat body was wrapped in an aluminum packaging exterior as the exterior of the battery, and an electrolyte (solvent: ethylene carbonate (EC) / diethyl carbonate (DEC) / vinylene carbonate (VC) = 68.5 / 30 / 1.5 (volume ratio), electrolyte: LiPF ₆ with a concentration of 1 M) was injected so that no air remained. Furthermore, in order to hermetically close the opening of the aluminum packaging material, the aluminum exterior was closed by heat sealing at 150° C., thereby producing a wound type lithium ion secondary battery.
The cycle characteristics of the wound lithium ion secondary battery thus fabricated were evaluated. The results are shown in Table 1.

Example 2
Except for using the binder composition prepared as follows, the slurry composition for the porous membrane layer, the separator with the porous membrane layer, the negative electrode, the positive electrode, and the secondary battery were manufactured in the same manner as in Example 1, and various measurements and evaluations were performed. The results are shown in Table 1.
<Preparation of Binder Composition>
<<Polymerization process (styrene-butadiene polymer)>>
Into the reactor, 150 parts of ion-exchanged water, 25 parts of an aqueous solution of sodium dodecylbenzenesulfonate (concentration 10%) as an emulsifier, 63 parts of styrene as an aromatic vinyl monomer, 3.5 parts of itaconic acid and 1 part of 2-hydroxyethyl acrylate as hydrophilic group-containing monomers, and 0.5 parts of t-dodecyl mercaptan as a molecular weight regulator were charged in this order. Next, the gas inside the reactor was replaced with nitrogen three times, and then 32.5 parts of 1,3-butadiene as an aliphatic conjugated diene monomer were charged. 0.5 parts of potassium persulfate were charged as a polymerization initiator into the reactor kept at 60°C to start the polymerization reaction, and the polymerization reaction was continued while stirring. When the polymerization conversion rate reached 96%, the mixture was cooled, and 0.1 parts of an aqueous solution of hydroquinone (concentration 10%) was added as a polymerization terminator to terminate the polymerization reaction, and an aqueous dispersion of a styrene-butadiene polymer, which is a particulate polymer (a mixed liquid containing a styrene-butadiene polymer and water) was obtained.
<<Filtration process>>
The aqueous dispersion of the styrene-butadiene polymer obtained in the above-mentioned polymerization step was filtered through a filter (manufactured by Nippon Pall Corporation, product name "NXT0.5", pore size: 5 μm) and collected in a collection container as a binder composition.

Example 3
In preparing the binder composition, a product name "NXT1" (pore size: 10 μm) manufactured by Nippon Pole Corporation was used as the filter used in the filtration process, but in the same manner as in Example 1, a binder composition, a slurry composition for a porous membrane layer, a separator with a porous membrane layer, a negative electrode, a positive electrode, and a secondary battery were produced, and various measurements and evaluations were performed. The results are shown in Table 1.

(Comparative Example 1)
In preparing the binder composition, the filtration process was not performed, and the aqueous dispersion of the acrylic polymer obtained in the polymerization process was used as the binder composition, but in the same manner as in Example 1, the binder composition, the slurry composition for the porous membrane layer, the separator with the porous membrane layer, the negative electrode, the positive electrode, and the secondary battery were manufactured, and various measurements and evaluations were performed. The results are shown in Table 1.

(Comparative Example 2)
In preparing the binder composition, except that a production facility (such as a reactor used in the polymerization process and a piping used in the recovery process) different from that in Comparative Example 1 was used, the binder composition, the slurry composition for the porous membrane layer, the separator with the porous membrane layer, the negative electrode, the positive electrode, and the secondary battery were manufactured in the same manner as in Comparative Example 1, and various measurements and evaluations were performed. The results are shown in Table 1.

In addition, in Table 1 shown below,
"ACL" refers to an acrylic polymer;
"SBR" refers to a styrene-butadiene polymer.

From Table 1, it can be seen that in Examples 1 to 3 using a binder composition containing a polymer, bacteria, and water, and in which the average size of the bacteria is equal to or less than a predetermined value, a slurry composition for a porous membrane layer having excellent viscosity stability can be obtained, and the cycle characteristics of the secondary battery can be improved while the porous membrane layer exhibits excellent adhesion.
On the other hand, from Table 1, it can be seen that in Comparative Examples 1 and 2 using binder compositions containing polymers, bacteria, and water, and in which the average size of the bacteria exceeds a predetermined value, the viscosity stability of the slurry composition for the porous membrane layer, the adhesiveness of the porous membrane layer, and the cycle characteristics of the secondary battery are reduced.

According to the present invention, it is possible to provide a binder composition for a non-aqueous secondary battery, which can prepare a slurry composition for a non-aqueous secondary battery functional layer having excellent viscosity stability.
Moreover, according to the present invention, it is possible to provide a non-aqueous secondary battery functional layer slurry composition having excellent viscosity stability.
According to the present invention, a functional layer for a non-aqueous secondary battery having excellent adhesiveness can be provided.
Furthermore, according to the present invention, it is possible to provide a battery member for a non-aqueous secondary battery that allows the non-aqueous secondary battery to exhibit excellent cycle characteristics.
In addition, according to the present invention, a nonaqueous secondary battery having excellent cycle characteristics can be provided.

Claims (8)

A particulate polymer, a fungus, and water are included,
A binder composition for a non-aqueous secondary battery (excluding those containing alumina particles or magnesium oxide particles), wherein the bacteria have an average size of 0.5 μm or less. The binder composition for a non-aqueous secondary battery according to claim 1, having a surface tension of 22 mN/m or more and 55 mN/m or less. The binder composition for a non-aqueous secondary battery according to claim 1 or 2, wherein the amount of tetrahydrofuran insoluble matter in the particulate polymer is 10% by mass or more and 95% by mass or less. A slurry composition for a non-aqueous secondary battery functional layer, prepared using the binder composition for a non-aqueous secondary battery according to any one of claims 1 to 3. The slurry composition for a non-aqueous secondary battery functional layer according to claim 4, further comprising functional particles. A non-aqueous secondary battery functional layer formed using the slurry composition for non-aqueous secondary battery functional layer according to claim 4 or 5. A battery member for a non-aqueous secondary battery comprising the functional layer for a non-aqueous secondary battery according to claim 6. A non-aqueous secondary battery comprising the battery member for a non-aqueous secondary battery according to claim 7.