JP7180595B2 - Electrodes and storage devices - Google Patents

Description

The present invention relates to primary batteries, secondary batteries such as lithium-ion secondary batteries and nickel-hydrogen secondary batteries, electricity storage devices such as electrochemical capacitors, and in particular, non-aqueous electrolyte-based electricity storage using a non-aqueous electrolyte such as an organic solvent as the electrolyte. The present invention relates to electrodes used in devices and electricity storage devices.

Electricity storage devices such as lithium ion secondary batteries and electrochemical capacitors are used in electronic devices such as mobile phones, laptop computers, and camcorders. Recently, due to the increasing awareness of environmental protection and the development of related laws, the application of batteries for in-vehicle applications such as electric vehicles and hybrid electric vehicles and as storage batteries for household power storage is also progressing.

In addition, as these applications progress, higher performance is required for electricity storage devices, and improvements in members such as electrodes are being promoted. Electrodes used in such electricity storage devices are generally obtained by applying an electrode material comprising an active material, a conductive aid, a binder, and a solvent onto a current collector and drying it.

Therefore, in recent years, attempts have been made to improve binders used in electrodes. By improving the binder, the binding properties between the active materials, the binding properties between the active material and the conductive aid, and the binding properties between the active material and the current collector are improved, and the electrical properties (e.g., cycle characteristics, low-temperature output characteristics, and low resistance) have been proposed.

Binders are required to have excellent binding properties when used in electrodes and to impart excellent electrical properties to electrical storage devices. For example, Patent Document 1 proposes a new binder.

However, in recent years, there has been a demand for an electrode having excellent binding properties of a binder while maintaining a low resistance in an electric storage device, and further investigation is required.

WO2013/180103

The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide an electrode having excellent binding properties with a binder while maintaining a low resistance in an electricity storage device.

As a result of repeated studies to achieve the above object, the present inventors have found an electrode comprising a current collector and an electrode material layer formed on the surface of the current collector, the electrode material layer comprising: At least three 1 μm×1 μm square fields where no active material particles are present in the image obtained by observing the cross section of the electrode material layer with a scanning electron microscope, which contains material particles and binder particles. In the electrode where 3 to 20 binder particles are observed and 3 or more binder particles are not continuously in contact with each other, the electrode maintains a low resistance in the electricity storage device and improves the binding property of the binder. found to be superior to The present invention is an invention that was completed through further studies based on these findings. That is, the present invention relates to the following.

Section 1. An electrode comprising a current collector and an electrode material layer formed on the surface of the current collector,
The electrode material layer contains active material particles and binder particles,
Among the images obtained by observing the cross section of the electrode material layer with a scanning electron microscope, in at least three 1 μm × 1 μm square fields of view where the active material particles are not present, the binder particles are 3 to 3. An electrode in which 20 particles are observed and 3 or more of the binder particles are not continuously in contact with each other.
Section 2. Item 2. The electrode according to Item 1, wherein the particle size of the binder particles observed in the field of view is 30 to 200 nm.
Item 3. Item 3. The electrode according to Item 1 or 2, wherein the content of the binder particles in the electrode material layer is 0.1 to 15% by mass.
Section 4. Item 4. An electricity storage device comprising the electrode according to any one of Items 1 to 3.

ADVANTAGE OF THE INVENTION According to this invention, the electrode which is excellent in the binding property of a binder can be provided, maintaining low resistance in an electrical storage device. Moreover, according to this invention, an electrical storage device provided with this electrode can also be provided.

INDUSTRIAL APPLICABILITY The electrode of the present invention has excellent binding properties of a binder, and can realize low resistance in electric storage devices such as lithium ion secondary batteries and electrochemical capacitors. In particular, when the electrodes of the present invention are used in large batteries that have a lower density than small batteries (e.g., batteries for vehicle applications such as electric vehicles and hybrid electric vehicles, and storage batteries for household power storage) The binder can exhibit excellent binding power. For this reason, the electric storage device provided with the electrode of the present invention is particularly useful for in-vehicle applications such as electric vehicles and hybrid electric vehicles, and storage batteries for household electric power storage.

FIG. 2 is an SEM image (20,000×) of a cross section of the electrode material layer of the electrode obtained in Example 1 of Electrode Working. FIG. FIG. 2 is an SEM image (20,000×) of a cross section of the electrode material layer of the electrode obtained in Example 1 of Electrode Working. FIG. FIG. 2 is an SEM image (20,000×) of a cross section of the electrode material layer of the electrode obtained in Example 1 of Electrode Working. FIG. 4 is a SEM image (10,000 times) of a cross section of the electrode material layer of the electrode obtained in Comparative Preparation Example 1 of the electrode. FIG. 10 is a SEM image (20,000×) of a cross section of the electrode material layer of the electrode obtained in Electrode Comparative Preparation Example 2. FIG.

As used herein, the power storage device includes primary batteries, secondary batteries (lithium-ion secondary batteries, nickel-hydrogen secondary batteries, etc.), and electrochemical capacitors. Further, in this specification, "(meth)acrylate" means "acrylate or methacrylate", and the same applies to expressions similar thereto.

<1. Electrode>
An electrode of the present invention comprises a current collector and an electrode material layer.

A known current collector can be used, and specifically, metals such as aluminum, nickel, stainless steel, gold, platinum, and titanium are used as the positive electrode. Moreover, metals, such as copper, nickel, stainless steel, gold, platinum, and titanium, are used as a negative electrode.

Although the thickness of the current collector is not particularly limited, it is, for example, about 5 to 50 μm, preferably about 10 to 20 μm.

The electrode material layer is formed on the surface of the current collector. The electrode material layer contains active material particles and binder particles. The electrode material layer can be formed by coating the surface of the current collector with a binder composition containing active material particles, a binder, and the like that constitute the electrode material layer.

Although the thickness of the electrode material layer is not particularly limited, it is, for example, about 5 to 300 μm, preferably about 15 to 200 μm.

In the present invention, in the image obtained by observing the cross section of the electrode material layer with a scanning electron microscope (SEM), within a square field of view of 1 μm × 1 μm at at least three locations where no active material particles are present, It is characterized in that 3 to 20 binder particles are observed and that 3 or more binder particles are not continuously in contact with each other. That is, an SEM image of the cross section of the electrode material layer is obtained, and from the SEM image, 3 to 20 binder particles are observed in at least 3 square fields of 1 μm × 1 μm where no active material particles are observed. be. Furthermore, in the field of view, no particles were observed in which three or more binder particles were continuously in contact with each other. As described above, the electrode of the present invention has a structure in which the binder particles in the electrode material layer are appropriately dispersed, so that the binder particles exhibit excellent binding properties and maintain low resistance in the electricity storage device. be able to. When a SEM image of the cross section of the electrode material layer is obtained, the conventional electrode has a structure in which three or more binder particles are aggregated, and is inferior in dispersibility compared to the electrode of the present invention.

Specific conditions for observing the cross section of the electrode material layer with a scanning electron microscope (SEM) are as follows.

<Method for Observing Cross Section of Electrode Material Layer>
As the processing of the electrode cross-section sample, an Ar ion beam processing is performed using an ion milling device. Observations are then made using a scanning electron microscope (SEM) at a magnification of 10,000-20,000.

From the viewpoint that the binder particles exhibit excellent binding properties and maintain low resistance in the electrical storage device, in the present invention, 3 to 20 binder particles are observed, and 3 or more binder particles are continuously in contact. The 1 μm×1 μm square field of view, which does not exist as a square, should be present in at least three places in the SEM image, and more preferably three to six places. The fields of view at three or more locations may partially overlap each other, but it is preferable that at least three locations do not overlap each other.

Further, in the 1 μm×1 μm square field of view, 3 to 20 binder particles may be observed, more preferably 3 to 15 particles, and still more preferably 4 to 8 particles.

From the viewpoint that the binder particles exhibit excellent binding properties and maintain low resistance in the electrical storage device, the particle diameter of the binder particles is preferably about 30 to 200 nm, more About 50 to 180 nm is preferable. When the particle size of the binder particles is within such a range, the electrode can have a structure in which the binder particles in the electrode material layer are more appropriately dispersed.

From the same point of view, the content of the binder particles in the electrode material layer is preferably about 0.1 to 15% by mass, more preferably about 0.2 to 10% by mass, still more preferably 0.3 to 7% by mass. %. By setting the content of the binder particles in such a range, the electrode can have a structure in which the binder particles in the electrode material layer are more appropriately dispersed.

Furthermore, from the same point of view, the density of the electrode material layer is preferably about 1.5 to 3.7 g/cc, more preferably about 1.8 to 3.5 g/cc. By setting the density of the electrode material layer within this range, the electrode can have a structure in which the binder particles in the electrode material layer are more appropriately dispersed.

The binder particles include a polymer (A) having 0.1% by mass or more and 5% by mass or less of structural units derived from a polyfunctional (meth)acrylate, and a structural unit derived from a polyfunctional (meth)acrylate exceeding 5% by mass. and the polymer (B) having a content of 30% by mass or less. When the binder particles have such a composition, an electrode having a structure in which the binder particles in the electrode material layer as described above are more appropriately dispersed can be obtained.

First, the polymer (A) will be explained. The polymer (A) is preferably a copolymer containing 0.1% by mass or more and 5% by mass or less of structural units derived from a polyfunctional (meth)acrylate.

In the polymer (A), the structural unit derived from polyfunctional (meth)acrylate is preferably a structural unit derived from general formula (1) below.

In general formula (1), R ¹¹ is the same or different and represents a hydrogen atom or a methyl group, R ¹² is a pentavalent or less organic group having 2 to 100 carbon atoms, and m is an integer of 5 or less. is.

In the general formula (1), m is preferably 2 to 5 (that is, a structural unit derived from a difunctional to pentafunctional (meth)acrylate), and is preferably 3 to 5 (that is, a trifunctional to a pentafunctional (meth) Structural units derived from acrylates) are more preferable, and 3 to 4 (ie, structural units derived from trifunctional to tetrafunctional (meth)acrylates) are particularly preferable.

Structural units derived from difunctional to pentafunctional (meth)acrylates have excellent physical properties (flexibility, binding properties) as binder particles. Structural units derived from polyfunctional (meth)acrylates are particularly preferably structural units derived from trifunctional or tetrafunctional (meth)acrylates.

In the polymer (A), the number of structural units derived from polyfunctional (meth)acrylates may be one, or two or more.

Specific examples of structural units derived from bifunctional (meth)acrylates in the polymer (A) include triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, Tripropylene glycol di(meth)acrylate, tetrapropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, dioxane glycol di(meth)acrylate, bis(meth)acryloyloxy Structural units derived from bifunctional (meth)acrylates such as ethyl phosphate are exemplified.

Specific examples of structural units derived from trifunctional (meth)acrylates in the polymer (A) include trimethylolpropane tri(meth)acrylate, trimethylolpropane EO-added tri(meth)acrylate, trimethylolpropane PO-added tri(meth)acrylate, (Meth)acrylates, pentaerythritol tri(meth)acrylate, 2,2,2-tris(meth)acryloyloxymethylethylsuccinic acid, ethoxylated isocyanuric acid tri(meth)acrylate, ε-caprolactone-modified tris-(2- Structural units derived from trifunctional (meth)acrylates such as (meth)acryloxyethyl)isocyanurate, glycerin EO-added tri(meth)acrylate, glycerin PO-added tri(meth)acrylate and tris(meth)acryloyloxyethyl phosphate is mentioned. Among these, structural units derived from trifunctional (meth)acrylates selected from trimethylolpropane tri(meth)acrylate, trimethylolpropane EO-added tri(meth)acrylate, and pentaerythritol tri(meth)acrylate are preferred.

Specific examples of structural units derived from tetrafunctional (meth)acrylates in the polymer (A) include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate and pentaerythritol EO-added tetra(meth)acrylate. Structural units derived from tetrafunctional (meth)acrylates such as

In the polymer (A), specific examples of structural units derived from pentafunctional (meth)acrylates include structural units derived from dipentaerythritol penta(meth)acrylate.

The lower limit of the ratio of structural units derived from polyfunctional (meth)acrylates in the polymer (A) is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and 0.5. % by mass or more is particularly preferred. Further, the upper limit of the ratio of structural units derived from polyfunctional (meth)acrylates in the polymer (A) is preferably 5% by mass or less, more preferably 4% by mass or less, and 2.5% by mass. % or less is particularly preferred.

Polymer (A), in addition to structural units derived from polyfunctional (meth) acrylate, structural units derived from (meth) acrylate having a hydroxyl group, structural units derived from (meth) acrylic acid ester, and (meth) acrylic It may further have at least one structural unit among structural units derived from an acid.

In the polymer (A), the structural unit derived from (meth)acrylate having a hydroxyl group is preferably a structural unit derived from alkylene glycol mono(meth)acrylate having a molecular weight of 100 to 1000, and the alkylene glycol of the following general formula (2). Structural units derived from mono(meth)acrylate are more preferred, and structural units derived from alkylene glycol mono(meth)acrylate of the following general formula (3) are particularly preferred.

In general formula (2), R ¹ is a hydrogen atom or a linear or branched alkyl group having 1-4 carbon atoms, x is an integer of 2-8, and n is an integer of 2-30.

In formula (2), R ¹ preferably includes a hydrogen atom, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group and the like. A hydrogen atom or a methyl group is preferred. That is, the monomer having a hydroxyl group in the structural unit is preferably a (meth)acrylate monomer (R ¹ is a hydrogen atom or a methyl group).

In general formula (2), (C _x H _2x O) is a linear or branched alkyl ether group, x is an integer of 2 to 8, preferably an integer of 2 to 7, more preferably is an integer from 2 to 6.

In general formula (2), n is an integer of 2-30, preferably an integer of 3-25, more preferably an integer of 4-20.

In the general formula (3), R ¹ is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, o is an integer of 0 to 30, p is an integer of 0 to 30, and o + p is 2-30. Here, o and p only represent the composition ratio of the structural unit, and from the (C ₂ H ₄ O) repeating unit block and the (C ₃ H ₆ O) repeating unit block (C ₂ H ₄ O) repeating units and (C ₃ H ₆ O) repeating units are alternately or randomly arranged, or random parts and block parts are mixed It may be a compound.

In general formula (3), R ¹ preferably includes a hydrogen atom, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group and the like. A hydrogen atom or a methyl group is preferred. That is, the monomer having a hydroxyl group in the structural unit is preferably a (meth)acrylate monomer (R ¹ is a hydrogen atom or a methyl group).

In general formula (3), o is an integer of 0 to 30, p is an integer of 0 to 30, o+p is 2 to 30, o is an integer of 0 to 25, p is 0 to 25 and o+p is preferably 3-25, o is an integer of 0-20, p is an integer of 0-20, and o+p is particularly preferably 4-20.

Specific examples of structural units derived from (meth)acrylates having a hydroxyl group include diethylene glycol mono(meth)acrylate, triethylene glycol mono(meth)acrylate, tetraethylene glycol mono(meth)acrylate, and polyethylene glycol mono(meth)acrylate. (meth) acrylate, dipropylene glycol mono (meth) acrylate, tripropylene glycol mono (meth) acrylate, tetrapropylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol-propylene glycol-mono (meth) Structural units derived from (meth)acrylates having a hydroxyl group such as acrylates and polyethylene glycol-tetramethylene glycol-mono(meth)acrylates can be mentioned. These can be used singly or in combination of two or more. Among these, tetraethylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, tetrapropylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate having a hydroxyl group derived from (meth) acrylate A building block is preferred. The (meth)acrylate-derived structural unit having a hydroxyl group, which the polymer (A) has, may be of one type, or may be of two or more types.

The lower limit of the ratio of structural units derived from (meth)acrylate having a hydroxyl group in the polymer (A) is preferably 0.5% by mass or more, more preferably 1% by mass or more, and 1.5% by mass. It is particularly preferable that it is above. Further, the upper limit of the ratio of structural units derived from (meth)acrylate having a hydroxyl group in the polymer (A) is preferably 15% by mass or less, more preferably 12% by mass or less, and 10% by mass. The following are particularly preferred.

In the polymer (A), structural units derived from (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, ( meth) n-butyl acrylate, isobutyl (meth) acrylate, n-pentyl (meth) acrylate, n-amyl (meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate, ( Structural units derived from (meth)acrylic acid alkyl esters such as n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate can be mentioned. Composition derived from (meth)acrylic acid alkyl ester selected from methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, and n-butyl (meth)acrylate It is preferably a unit, preferably a structural unit derived from a (meth)acrylic acid alkyl ester selected from methyl (meth)acrylate, ethyl (meth)acrylate, and n-butyl (meth)acrylate. The structural unit derived from the (meth)acrylic acid ester contained in the polymer (A) may be of one kind, or may be of two or more kinds.

The lower limit of the ratio of structural units derived from (meth)acrylic acid ester in the polymer (A) is preferably 60% by mass or more, more preferably 70% by mass or more, and 75% by mass or more. is particularly preferred. Further, the upper limit of the ratio of structural units derived from methacrylic acid ester in the polymer (A) is preferably 97% by mass or less, more preferably 95% by mass or less, and 93% by mass or less. is particularly preferred.

Examples of structural units derived from (meth)acrylic acid include structural units derived from compounds selected from acrylic acid and methacrylic acid. The structural unit derived from (meth)acrylic acid, which the polymer (A) has, may be of one type, or may be of two or more types.

The lower limit of the ratio of structural units derived from (meth)acrylic acid in the polymer (A) is preferably 0% by mass or more, more preferably 1% by mass or more, and 3% by mass or more. is particularly preferred. The upper limit of the ratio of structural units derived from (meth)acrylic acid in the polymer (A) is preferably 25% by mass or less, more preferably 15% by mass or less, and 10% by mass or less. is particularly preferred.

Polymers having structural units derived from (meth)acrylic acid esters and structural units derived from polyfunctional (meth)acrylates include, in addition to the above, structural units derived from other monomers such as fumaric acid, maleic acid, Structural units derived from monomers selected from itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, crotonitrile, α-ethylacrylonitrile, α-cyanoacrylate, vinylidene cyanide, and fumaronitrile can have

Next, the polymer (B) will be explained. The polymer (B) is preferably a copolymer having more than 5% by mass and 30% by mass or less of structural units derived from a polyfunctional (meth)acrylate.

In the polymer (B), the structural unit derived from polyfunctional (meth)acrylate is preferably a structural unit derived from general formula (1) below.

In general formula (1), R ¹¹ is the same or different and represents a hydrogen atom or a methyl group, R ¹² is a pentavalent or less organic group having 2 to 100 carbon atoms, and m is an integer of 5 or less. is.

In the general formula (1), m is preferably 2 to 5 (that is, a structural unit derived from a difunctional to pentafunctional (meth)acrylate), and is preferably 3 to 5 (that is, a trifunctional to a pentafunctional (meth) Structural units derived from acrylates) are more preferable, and 3 to 4 (ie, structural units derived from trifunctional to tetrafunctional (meth)acrylates) are particularly preferable. Structural units derived from difunctional to pentafunctional (meth)acrylates have excellent physical properties (flexibility, binding properties) as binder particles. Structural units derived from polyfunctional (meth)acrylates are particularly preferably structural units derived from trifunctional or tetrafunctional (meth)acrylates.

In the polymer (B), the number of structural units derived from polyfunctional (meth)acrylates may be one, or two or more.

Specific examples of structural units derived from bifunctional (meth)acrylates in the polymer (B) include triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, Tripropylene glycol di(meth)acrylate, tetrapropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, polytetramethylene glycol di(meth)acrylate, dioxane glycol di(meth)acrylate, bis(meth)acryloyloxy Structural units derived from bifunctional (meth)acrylates such as ethyl phosphate are exemplified.

In the polymer (B), specific examples of structural units derived from trifunctional (meth)acrylates include trimethylolpropane tri(meth)acrylate, trimethylolpropane EO-added tri(meth)acrylate, trimethylolpropane PO-added tri(meth)acrylate, (Meth)acrylates, pentaerythritol tri(meth)acrylate, 2,2,2-tris(meth)acryloyloxymethylethylsuccinic acid, ethoxylated isocyanuric acid tri(meth)acrylate, ε-caprolactone-modified tris-(2- Structural units derived from trifunctional (meth)acrylates such as (meth)acryloxyethyl)isocyanurate, glycerin EO-added tri(meth)acrylate, glycerin PO-added tri(meth)acrylate and tris(meth)acryloyloxyethyl phosphate is mentioned. Among these, structural units derived from trifunctional (meth)acrylates selected from trimethylolpropane tri(meth)acrylate, trimethylolpropane EO-added tri(meth)acrylate, and pentaerythritol tri(meth)acrylate are preferred.

Specific examples of structural units derived from tetrafunctional (meth)acrylates in the polymer (B) include ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate and pentaerythritol EO-added tetra(meth)acrylate. Structural units derived from tetrafunctional (meth)acrylates such as

In the polymer (B), specific examples of structural units derived from pentafunctional (meth)acrylates include structural units derived from dipentaerythritol penta(meth)acrylate.

The lower limit of the ratio of the structural units derived from the polyfunctional (meth)acrylate in the polymer (B) preferably exceeds 5% by mass, more preferably 8% by mass or more, and particularly 12% by mass or more. preferable. The upper limit of the ratio of structural units derived from polyfunctional (meth)acrylates in the polymer (B) is preferably 35% by mass or less, more preferably 30% by mass or less, and 25% by mass or less. is particularly preferred.

Polymer (B), in addition to structural units derived from polyfunctional (meth) acrylate, structural units derived from (meth) acrylate having a hydroxyl group, structural units derived from (meth) acrylic acid ester, and (meth) acrylic It may further have at least one structural unit among structural units derived from an acid.

In the polymer (B), the structural unit derived from (meth)acrylate having a hydroxyl group is preferably a structural unit derived from alkylene glycol mono (meth) acrylate having a molecular weight of 100 to 1000, and the alkylene glycol mono of general formula (2) A structural unit derived from (meth)acrylate is more preferable, and a structural unit derived from alkylene glycol mono(meth)acrylate of general formula (3) is particularly preferable.

In general formula (2), R ¹ is a hydrogen atom or a linear or branched alkyl group having 1-4 carbon atoms, x is an integer of 2-8, and n is an integer of 2-30.

In formula (2), R ¹ preferably includes a hydrogen atom, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group and the like. A hydrogen atom or a methyl group is preferred. That is, the monomer having a hydroxyl group in the structural unit is preferably a (meth)acrylate monomer (R ¹ is a hydrogen atom or a methyl group).

In general formula (2), (C _x H _2x O) is a linear or branched alkyl ether group, x is an integer of 2 to 8, preferably an integer of 2 to 7, more preferably is an integer from 2 to 6.

In general formula (2), n is an integer of 2-30, preferably an integer of 3-25, more preferably an integer of 4-20.

In the general formula (3), R ¹ is a hydrogen atom or a linear or branched alkyl group having 1 to 4 carbon atoms, o is an integer of 0 to 30, p is an integer of 0 to 30, and o + p is 2-30. Here, o and p only represent the composition ratio of the structural unit, and from the (C ₂ H ₄ O) repeating unit block and the (C ₃ H ₆ O) repeating unit block (C ₂ H ₄ O) repeating units and (C ₃ H ₆ O) repeating units are alternately or randomly arranged, or random parts and block parts are mixed It may be a compound.

In general formula (3), R ¹ preferably includes a hydrogen atom, methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group and the like. A hydrogen atom or a methyl group is preferred. That is, the monomer having a hydroxyl group in the structural unit is preferably a (meth)acrylate monomer (R ¹ is a hydrogen atom or a methyl group).

In general formula (3), o is an integer of 0 to 30, p is an integer of 0 to 30, o+p is 2 to 30, o is an integer of 0 to 25, p is 0 to 25 and o+p is preferably 3-25, o is an integer of 0-20, p is an integer of 0-20, and o+p is particularly preferably 4-20.

Specific examples of structural units derived from (meth)acrylates having a hydroxyl group include diethylene glycol mono (meth) acrylate, triethylene glycol mono (meth) acrylate, tetraethylene glycol mono (meth) acrylate, and polyethylene glycol mono (meth) acrylate, Dipropylene glycol mono(meth)acrylate, tripropylene glycol mono(meth)acrylate, tetrapropylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol-propylene glycol-mono(meth)acrylate, and polyethylene glycol Structural units derived from (meth)acrylates having a hydroxyl group, such as -tetramethylene glycol-mono(meth)acrylate. These can be used singly or in combination of two or more. Among these, tetraethylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, tetrapropylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate having a hydroxyl group derived from (meth) acrylate A building block is preferred. The (meth)acrylate-derived structural unit having a hydroxyl group, which the polymer (B) has, may be of one type, or may be of two or more types.

The lower limit of the ratio of structural units derived from (meth)acrylate having a hydroxyl group in the polymer (B) is preferably 0.5% by mass or more, more preferably 1% by mass or more, and 1.5% by mass. It is particularly preferable that it is above. Further, the upper limit of the ratio of structural units derived from (meth)acrylate having a hydroxyl group in the polymer (B) is preferably 15% by mass or less, more preferably 12% by mass or less, and 10% by mass. The following are particularly preferred.

In the polymer (B), structural units derived from (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, ( meth) n-butyl acrylate, isobutyl (meth) acrylate, n-pentyl (meth) acrylate, n-amyl (meth) acrylate, isoamyl (meth) acrylate, n-hexyl (meth) acrylate, ( Structural units derived from (meth)acrylic acid alkyl esters such as n-heptyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate can be mentioned. The structural unit derived from the (meth)acrylic acid ester contained in the polymer (B) may be of one kind, or may be of two or more kinds.

The polymer (B) preferably has structural units derived from methyl methacrylate, and the lower limit of the ratio of the structural units derived from methyl methacrylate in the polymer (B) is 45% by mass or more. It is preferably 50% by mass or more, more preferably 55% by mass or more, and particularly preferably 55% by mass or more. In addition, the upper limit of the ratio of structural units derived from methyl methacrylate in the polymer (B) is preferably 90% by mass or less, more preferably 85% by mass or less, and 80% by mass or less. is particularly preferred.

The lower limit of the ratio of structural units derived from the (meth)acrylic acid ester other than methyl methacrylate in the polymer (B) is preferably 0% by mass or more, more preferably 5% by mass or more. , 10% by mass or more. Further, the upper limit of the ratio of structural units derived from methyl methacrylate in the polymer (B) is preferably 25% by mass or less, more preferably 20% by mass or less, and 15% by mass or less. is particularly preferred.

In the polymer (B), examples of structural units derived from (meth)acrylic acid include structural units derived from compounds selected from acrylic acid and methacrylic acid. The structural unit derived from (meth)acrylic acid, which the polymer (B) has, may be of one type, or may be of two or more types.

The lower limit of the ratio of (meth)acrylic acid-derived structural units in the polymer (B) is preferably 0% by mass or more, more preferably 1% by mass or more, and particularly 3% by mass or more. preferable. Further, the upper limit of the ratio of structural units derived from (meth)acrylic acid in the polymer (B) is preferably 25% by mass or less, more preferably 15% by mass or less, and 10% by mass or less. It is particularly preferred to have

In the polymer (B), as a polymer having a structural unit derived from a (meth)acrylic acid ester and a structural unit derived from a polyfunctional (meth)acrylate, in addition to the above, structural units derived from other monomers , fumaric acid, maleic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, crotonitrile, α-ethylacrylonitrile, α-cyanoacrylate, vinylidene cyanide, fumaronitrile It can have a structural unit derived from a monomer to be used.

In the binder particles of the present invention, the mass ratio of polymer (A) and polymer (B) is not particularly limited, but is preferably 3:97 to 97:3, and 5:95 to 95:5. It is more preferable to have

As a method for obtaining the polymer (A) and the polymer (B), a general emulsion polymerization method, a soap-free emulsion polymerization method, or the like can be used, respectively. Specifically, a composition containing a monomer, an emulsifier, a polymerization initiator, water, and, if necessary, a dispersant, a chain transfer agent, a pH adjuster, etc., is placed in an airtight container equipped with a stirrer and a heating device at room temperature to make it inactive. The monomers and the like are emulsified in water by stirring in a gas atmosphere. As the emulsifying method, methods using stirring, shearing, ultrasonic waves, etc. can be applied, and stirring blades, homogenizers, etc. can be used. Subsequently, by raising the temperature while stirring to initiate polymerization, a spherical polymer latex in which the polymer is dispersed in water can be obtained. The method of adding the monomers during the polymerization may be, in addition to batch charging, monomer dropping, pre-emulsion dropping, or the like, and two or more of these methods may be used in combination. Note that the pre-emulsion dropping refers to an addition method in which the monomer, emulsifier, water, etc. are emulsified in advance and the emulsion is dropped.

The emulsifier used in the present invention is not particularly limited. Emulsifiers are surfactants, including reactive surfactants having reactive groups. Nonionic surfactants and anionic surfactants generally used in emulsion polymerization can be used.

Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alcohol ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, polyoxyethylene Examples include fatty acid esters and polyoxyethylene sorbitan fatty acid esters. Examples of reactive nonionic surfactants include Latemul PD-420, 430, and 450 (manufactured by Kao Corporation), Adekaria Soap ER (manufactured by Adeka Corporation), and Aqualon. RN (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), Antox LMA (manufactured by Nippon Nyukazai Co., Ltd.), Antox EMH (manufactured by Nippon Nyukazai Co., Ltd.), and the like.

Examples of anionic surfactants include sulfate type, carboxylic acid type, or sulfonic acid type metal salts, ammonium salts, triethanolammonium salts, and phosphate ester type surfactants. Sulfuric ester type, sulfonic acid type and phosphate ester type are preferred, and sulfate ester type is particularly preferred. Typical examples of sulfate type anionic surfactants include metal alkyl sulfates such as dodecyl sulfate, ammonium, triethanolamine alkyl sulfates, polyoxyethylene dodecyl ether sulfate, polyoxyethylene isodecyl ether sulfate, polyoxyethylene Metal salts of polyoxyethylene alkyl ether sulfates such as tridecyl ether sulfuric acid, ammonium salts, triethanolamine polyoxyethylene alkyl ether sulfates, and the like can be mentioned. Specific examples of the sulfate type reactive anionic surfactants include Latemul PD-104, 105 (manufactured by Kao Corporation), Adekaria Soap SR (manufactured by Adeka Corporation), Aqualon HS (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and Aqualon KH (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). Preferred are sodium dodecylsulfate, ammonium dodecylsulfate, triethanolamine dodecylsulfate, sodium dodecylbenzenesulfonate, latemul PD-104 and the like.

One or more of these nonionic surfactants and/or anionic surfactants may be used.

Reactivity of a reactive surfactant means that it contains a reactive double bond and undergoes a polymerization reaction with a monomer during polymerization. In other words, the reactive surfactant acts as an emulsifier for the monomers during the polymerization for producing the polymer, and is covalently bonded to a part of the polymer after the polymerization. Therefore, the emulsion polymerization and dispersion of the produced polymer are good, and the physical properties (flexibility, binding property) as binder particles are excellent.

The amount of the structural unit of the emulsifier may be the amount generally used in the emulsion polymerization method. Specifically, it is in the range of 0.01 to 25% by mass, preferably 0.05 to 20% by mass, more preferably 0.1 to 20% by mass, based on the amount of charged monomer (100% by mass). is.

The polymerization initiator used in the present invention is not particularly limited, and polymerization initiators commonly used in emulsion polymerization and suspension polymerization can be used. Emulsion polymerization is preferred. A water-soluble polymerization initiator is used in the emulsion polymerization method, and an oil-soluble polymerization initiator is used in the suspension polymerization method.

Specific examples of the water-soluble polymerization initiator include water-soluble polymerization initiators represented by persulfates such as potassium persulfate, sodium persulfate and ammonium persulfate, 2-2′-azobis[2-(2 -imidazolin-2-yl)propane], or its hydrochloride or sulfate, 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2′-azobis(2- methylpropaneamidine), or its hydrochloride or sulfate, 3,3′-[azobis[(2,2-dimethyl-1-iminoethane-2,1-diyl)imino]]bis(propanoic acid), 2,2 Polymerization initiators of water-soluble azo compounds such as '-[azobis(dimethylmethylene)]bis(2-imidazoline) are preferred.

Oil-soluble polymerization initiators include organic peroxides such as cumene hydroperoxide, benzoyl peroxide, acetyl peroxide, t-butyl hydroperoxide, azobisisobutyronitrile, 1,1'-azobis(cyclohexane Polymerization initiators of oil-soluble azo compounds such as carbonitrile) and redox initiators are preferred. These polymerization initiators may be used singly or in combination of two or more.

The amount of the polymerization initiator to be used may be the amount generally used in the emulsion polymerization method or the suspension polymerization method. Specifically, it is in the range of 0.01 to 10% by mass, preferably 0.01 to 5% by mass, more preferably 0.02 to 3% by mass, based on the amount of charged monomer (100% by mass). is.

A chain transfer agent can be used as needed. Specific examples of chain transfer agents include alkylmercaptans such as n-hexylmercaptan, n-octylmercaptan, t-octylmercaptan, n-dodecylmercaptan, t-dodecylmercaptan and n-stearylmercaptan, 2,4-diphenyl-4 -methyl-1-pentene, 2,4-diphenyl-4-methyl-2-pentene, xanthogen compounds such as dimethylxanthogen disulfide, diisopropylxanthogen disulfide, terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram mono Thiuram compounds such as sulfide, phenolic compounds such as 2,6-di-t-butyl-4-methylphenol, styrenated phenol, allyl compounds such as allyl alcohol, halogens such as dichloromethane, dibromomethane, and carbon tetrabromide Hydrocarbon compounds, vinyl ethers such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexylthio Glycolate and the like may be mentioned, and one or more of these may be used. Although the amount of these chain transfer agents is not particularly limited, they are usually used in an amount of 0 to 5 parts by weight per 100 parts by weight of the charged monomers.

Polymerization time and polymerization temperature of the polymer are not particularly limited. Although it can be appropriately selected depending on the type of polymerization initiator to be used, the polymerization temperature is generally 20 to 100° C. and the polymerization time is 0.5 to 100 hours.

Further, the pH of the polymer obtained by the above method can be adjusted by using a base as a pH adjuster, if necessary. Specific examples of bases include alkali metal (Li, Na, K, Rb, Cs) hydroxides, ammonia, inorganic ammonium compounds, organic amine compounds, and the like. The pH range is pH 2-11, preferably pH 3-10, more preferably pH 4-9.

The binder particles preferably contain polymer (A) and polymer (B), and water or other substances such as emulsifiers may be contained inside or attached to the outside of the polymer. The amount of the substance contained inside or adhered to the outside is preferably 7 parts by mass or less with respect to 100 parts by mass of the total of the polymer (A) and the polymer (B), and 5 parts by mass. It is more preferably 3 parts by mass or less, and particularly preferably 3 parts by mass or less.

The binder composition contains binder particles together with a solvent, and the binder particles may be dispersed in the solvent. Water or an organic solvent can be used as the solvent. Examples of organic solvents include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, amyl alcohol, acetone, methyl ethyl ketone, ketones such as cyclohexanone; esters such as ethyl acetate and butyl acetate; ethers such as diethyl ether, dioxane and tetrahydrofuran; Aromatic hydrocarbons such as solvents, toluene, xylene, chlorobenzene, ortho-dichlorobenzene, and para-dichlorobenzene can be exemplified.

The binder composition is preferably an aqueous binder composition in which binder particles are dispersed in water.

The binder composition may be an emulsion obtained by mixing the emulsion produced when obtaining the polymer (A) and the emulsion produced when obtaining the polymer (B).

The content of the binder particles in the binder composition is not particularly limited, but it is preferably contained so that the solid content concentration of the binder particles is 0.2 to 80% by mass, and 0.5 to 70% by mass. More preferably, it is contained in an amount of 0.5 to 60% by mass, particularly preferably. It should be noted that the solids content in the binder composition is generally considered to be the polymer and the emulsifier (only when the polymer is used in emulsion polymerization).

The electrode material constituting the electrode material layer contains at least active material particles and binder particles, and may further contain a conductive aid. A binder composition containing binder particles together with a solvent can also be used in the production of the electrode material. The positive electrode material used for the positive electrode contains a positive electrode active material and binder particles, and may further contain a conductive aid. The negative electrode material used for the negative electrode contains a negative electrode active material, binder particles, and a conductive aid. It may contain an agent.

The positive electrode active material is an alkali metal-containing composite oxide having _{a composition} of any one of _AMO2 , _AM2O4 , _A2MO3 , and _AMBO4 . A is an alkali metal, M is composed of a single or two or more transition metals, some of which may contain non-transition metals. B consists of P, Si or a mixture thereof. The positive electrode active material is preferably a powder, and the particle size is preferably 50 microns or less, more preferably 20 microns or less. These active materials have an electromotive force of 3 V (vs. Li/Li+) or more.

Preferred specific examples of the positive electrode active material include Li _x CoO ₂ , Li _x NiO _{2 , Li x MnO 2 , Li x CrO 2 , Li x FeO 2 , Li x Co a Mn 1 -a} O ₂ , Li _x Co _a Ni1 _{- aO2 , LixCoaCr1 - aO2 , LixCoaFe1 - aO2 , LixCoaTi1 - aO2 , LixMnaNi1 - aO2 , LixMnaCr1 - aO2 , LixMnaFe1 - aO2 , LixMnaTi1 - aO2 , LixNiaCr1 - aO2 , LixNiaFe 1 - aO2} , _{LixNiaTi1 - aO2 , LixCraFe1 - aO2 , LixCraTi1 - aO2 , LixFeaTi1 - aO2 , LixCobMncNi1 - bcO2 , LixNiaCobAlcO2 , LixCrbMncNi1 - bcO2 , LixFebMncNi1 - bcO2 , _ _ _ _ _ _ LixTibMncNi1 - bcO2 , LixMn2O4 , LixMndCo2 - dO4 , LixMndNi2 - dO4 , LixMndCr2 - d _ _ O4 , LixMndFe2 - dO4 , LixMndTi2 - dO4 , LiyMnO3 , LiyMneCo1 - eO3 , LiyMneNi1 - eO 3 , LiyMneFe1 - eO3 , LiyMneTi1 - eO3 , LixCoPO4 , LixMnPO4 , LixNiPO4 , LixFePO4 , LixCofMn1 _ -fPO4 , LixCofNi1 - fPO4 , LixCofFe1 - fPO4 , LixMnfNi1 - fPO4 ,} LixMnfFe1 _{- fPO4 , Li xNifFe1 - fP O4 , LiyCoSiO4 , LiyMnSiO4 , LiyNiSiO4 , LiyFeSiO4 , LiyCogMn1 - gSiO4 , LiyCogNi1 - gSiO4 , LiyCogFe 1- gSiO4 , LiyMngNi1 - gSiO4 , LiyMngFe1 - gSiO4 , LiyNigFe1 - gSiO4 , LiyCoPhSi1 - hO4} , _{LiyMnPhSi1 - hO4 , LiyNiPhSi1 - hO4 , LiyFePhSi1 - hO4 , LiyCogMn1 - gPhSi1 - hO4 , LiyCogNi1 - gPhSi1 - hO4 , LiyCogFe1 - gPhSi1 - hO4 , LiyMngNi1 - gPhSi1 - hO4 _ , LiyMngFe1 - gPhSi1 - hO4 , and} LiyNigFe1 _{- gPhSi1 - hO4} . (where x = 0.01 to 1.2, y = 0.01 to 2.2, a = 0.01 to 0.99, b = 0.01 to 0.98, c = 0.01 to 0.98 However, b + c = 0.02 to 0.99, d = 1.49 to 1.99, e = 0.01 to 0.99, f = 0.01 to 0.99, g = 0.01 ~ 0.99, h = 0.01 ~ 0.99.)

Among the preferred positive electrode active materials, more preferred positive electrode active materials include Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x CrO ₂ , and Li _x Co _a Ni _{1 . -aO2 , LixMnaNi1 - aO2 , LixCobMncNi1 - bcO2 , LixNiaCobAlcO2 , LixMn2O4 , LiyMnO _ _ _ _ _ 3 , LiyMneFe1 - eO3 , LiyMneTi1 - eO3 , LixCoPO4 , LixMnPO4 , LixNiPO4 , LixFePO4 , LixMnfFe1 _ Mention} may be made of _-fPO4 . (where x = 0.01 to 1.2, y = 0.01 to 2.2, a = 0.01 to 0.99, b = 0.01 to 0.98, c = 0.01 to 0.98 provided that b+c=0.02 to 0.99, d=1.49 to 1.99, e=0.01 to 0.99, and f=0.01 to 0.99. The x and y values of will increase or decrease due to charging and discharging.)

As a negative electrode active material, a carbon material (natural graphite, artificial graphite, amorphous carbon, etc.) having a structure (porous structure) capable of absorbing/releasing lithium ions, or a lithium or aluminum-based material capable of absorbing/releasing lithium ions. It is a powder made of a metal such as a compound, a tin-based compound, a silicon-based compound, a titanium-based compound, or the like. The particle diameter is preferably 10 nm or more and 100 μm or less, more preferably 20 nm or more and 20 μm or less. Alternatively, it may be used as a mixed active material of a metal and a carbon material. It is desirable to use a negative electrode active material having a porosity of about 70%.

The content of the active material particles in the electrode material is not particularly limited, and is, for example, about 99.9 to 50% by mass, more preferably about 99.5 to 70% by mass, and still more preferably about 99 to 85% by mass. mentioned. The active material particles may be used singly or in combination of two or more.

As the conductive aid, a known conductive aid can be used, and examples thereof include graphite, furnace black, acetylene black, conductive carbon black such as Ketjen black, carbon fiber such as carbon nanotube, or metal powder. , conductive carbon black such as furnace black, acetylene black, and ketjen black, and carbon fibers such as carbon nanotubes. One or two or more of these conductive aids may be used.

When a conductive additive is used, the content of the conductive additive is not particularly limited, but is preferably 20 parts by mass or less, more preferably 15 parts by mass or less with respect to 100 parts by mass of the active material particles. When the positive electrode material contains a conductive aid, the lower limit of the content of the conductive aid is usually 0.05 parts by mass or more, 0.1 parts by mass or more, 0.2 parts by mass or more, 0 .5 mass parts or more, 2 mass parts or more can be exemplified.

The electrode material may contain a thickening agent as necessary. The type of thickening agent is not particularly limited, but sodium salts, ammonium salts, polyvinyl alcohols, polyacrylic acids and salts thereof of cellulose compounds are preferable.

Examples of sodium salts or ammonium salts of cellulosic compounds include sodium salts or ammonium salts of alkylcelluloses in which cellulosic polymers are substituted with various derivative groups. Specific examples include sodium salts, ammonium salts, and triethanolammonium salts of methylcellulose, methylethylcellulose, ethylcellulose, and carboxymethylcellulose (CMC). Sodium or ammonium salts of carboxymethylcellulose are particularly preferred. One of these thickeners may be used alone, or two or more of them may be used in combination at an arbitrary ratio.

When a thickener is used, the content of the thickener is not particularly limited, but is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, relative to 100 parts by mass of the active material. When a thickener is included, the lower limit of the content of the thickener is usually 0.05 parts by mass or more, 0.1 parts by mass or more, 0.2 parts by mass or more, and 0.5 parts by mass. Above, 1 mass part or more can be illustrated.

The electrode material may contain water to make it slurry. Water is not particularly limited, and commonly used water can be used. Specific examples include tap water, distilled water, ion-exchanged water, and ultrapure water. Among them, distilled water, ion-exchanged water, and ultrapure water are preferred.

When the electrode material is used as a slurry, the solid content concentration of the slurry is preferably 10 to 90% by mass, more preferably 20 to 85% by mass, and 30 to 80% by mass. Especially preferred.

When the electrode material is used as a slurry, the proportion of the polymer in the solid content of the slurry is preferably 0.1 to 15% by mass, more preferably 0.2 to 10% by mass. , 0.3 to 7% by weight.

The method for preparing the electrode material is not particularly limited, and the positive electrode active material or negative electrode active material, binder particles, conductive aid, water, etc. are dispersed using a conventional stirrer, disperser, kneader, planetary ball mill, homogenizer, or the like. All you have to do is In order to increase the efficiency of dispersion, the material may be heated within a range that does not affect the material.

A method for producing the electrode is not particularly limited, and a general method is used. It is carried out by uniformly applying the battery material to a suitable thickness on the surface of the current collector (metal electrode substrate) by a doctor blade method, an applicator method, a silk screen method, or the like.

For example, in the doctor blade method, an electrode slurry is applied to a metal electrode substrate, and then uniformized to an appropriate thickness by a blade having a predetermined slit width. After applying the active material, the electrode is dried, for example, with hot air at 100° C. or in a vacuum at 80° C. in order to remove excess organic solvent and water. An electrode material is manufactured by press-molding the dried electrode with a press machine. After pressing, heat treatment may be performed again to remove water, solvent, emulsifier, and the like.

The electrode is preferably pressed so that the density of the electrode material layer of the electrode of the present invention is preferably 3.7 g/cc or less, more preferably 3.5 g/cc or less. As described above, the electrodes of the present invention are used in large batteries (e.g., batteries for vehicle applications such as electric vehicles and hybrid electric vehicles, and storage batteries for household power storage) that have a lower density than small batteries. In this case, excellent binding strength can be exhibited. Therefore, when the density of the electrode material layer has such a value, it is possible to exhibit a particularly excellent binding force while maintaining a low resistance in the electricity storage device. In addition, the preferable range of the density of the electrode material layer of the electrode of the present invention is as described above.

<2. Energy storage device>
A power storage device of the present invention is characterized by comprising a positive electrode, a negative electrode, and an electrolytic solution. The details of the electrode of the present invention are as described above. In the electricity storage device of the present invention, the electrode of the present invention may be used for at least one of the positive electrode and the negative electrode.

The electrolytic solution is not particularly limited, and known electrolytic solutions can be used. A specific example of the electrolytic solution is a solution containing an electrolyte and a solvent. Each of the electrolyte and the solvent may be used alone, or two or more of them may be used in combination.

Examples of electrolytes include lithium salt compounds, specifically _LiBF4 , _{LiPF6 , LiClO4} , _{LiCF3SO3 ,} LiN( _{CF3SO2 ) 2} , LiN( _{C2F5SO2 ).} ) ₂ , LiN[CF ₃ SC(C ₂ F ₅ SO ₂ ) ₃ ] ₂ and the like, but are not limited thereto.

Electrolytes other than lithium salt compounds include tetraethylammonium tetrafluoroborate, triethylmonomethylammonium tetrafluoroborate, tetraethylammonium hexafluorophosphate, and the like.

Examples of the solvent used for the electrolytic solution include organic solvents and ambient temperature molten salts.

Examples of organic solvents include aprotic organic solvents, specifically propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane. , γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, dipropyl carbonate, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propylnitrile, anisole, acetate, propionate, diethyl ether. , and two or more types may be mixed and used.

A room-temperature molten salt is also called an ionic liquid, and is a "salt" composed only of ions (anions and cations), and liquid compounds are particularly called ionic liquids.

The room-temperature molten salt in the present invention refers to a salt that is at least partially liquid at room temperature, and room temperature refers to the temperature range in which batteries are generally assumed to operate. The temperature range in which the battery is expected to operate normally has an upper limit of about 120°C, possibly about 80°C, and a lower limit of about -40°C, sometimes about -20°C.

Pyridine, aliphatic amine, and alicyclic amine quaternary ammonium organic cations are known as the cation species of the ambient temperature molten salt. Examples of quaternary ammonium organic cations include imidazolium ions such as dialkylimidazolium and trialkylimidazolium, tetraalkylammonium ions, alkylpyridinium ions, pyrazolium ions, pyrrolidinium ions and piperidinium ions. In particular, imidazolium ions are preferred.

The tetraalkylammonium ion includes, but is limited to, trimethylethylammonium ion, trimethylethylammonium ion, trimethylpropylammonium ion, trimethylhexylammonium ion, tetrapentylammonium ion, triethylmethylammonium ion, and the like. is not.

Examples of alkylpyridinium ions include N-methylpyridinium ion, N-ethylpyridinium ion, N-propylpyridinium ion, N-butylpyridinium ion, 1-ethyl-2methylpyridinium ion, and 1-butyl-4-methylpyridinium ion. ions, 1-butyl-2,4 dimethylpyridinium ions, and the like, but are not limited to these.

Examples of imidazolium ions include 1,3-dimethylimidazolium ion, 1-ethyl-3-methylimidazolium ion, 1-methyl-3-ethylimidazolium ion, 1-methyl-3-butylimidazolium ion, 1- Butyl-3-methylimidazolium ion, 1,2,3-trimethylimidazolium ion, 1,2-dimethyl-3-ethylimidazolium ion, 1,2-dimethyl-3-propylimidazolium ion, 1-butyl- Examples include, but are not limited to, 2,3-dimethylimidazolium ion.

Examples of the anion species of the ambient temperature molten salt include halide ions such as chloride ion, bromide ion and iodide ion, perchlorate ion, thiocyanate ion, tetrafluoroborate ion, nitrate ion, AsF ₆ ⁻ , PF ₆ ⁻ . Inorganic acid ions such as stearylsulfonate ion, octylsulfonate ion, dodecylbenzenesulfonate ion, naphthalenesulfonate ion, dodecylnaphthalenesulfonate ion, 7,7,8,8-tetracyano-p-quinodimethane ion, etc. is exemplified by the organic acid ions of

The ambient temperature molten salt may be used singly or in combination of two or more.

Various additives can be used in the electrolytic solution as required. Examples of additives include flame retardants, nonflammable agents, positive electrode surface treating agents, negative electrode surface treating agents, and overcharge inhibitors. Flame retardants and non-flammable agents include brominated epoxy compounds, phosphazene compounds, tetrabromobisphenol A, halides such as chlorinated paraffin, antimony trioxide, antimony pentoxide, aluminum hydroxide, magnesium hydroxide, phosphate esters, polyphosphorus Acid salts, zinc borate, and the like can be exemplified. Examples of positive electrode surface treatment agents include inorganic compounds such as carbon and metal oxides (MgO, ZrO _{2 ,} etc.) and organic compounds such as ortho-terphenyl. Vinylene carbonate, fluoroethylene carbonate, polyethylene glycol dimethyl ether and the like can be exemplified as the negative electrode surface treatment agent. Examples of overcharge inhibitors include biphenyl and 1-(p-tolyl)adamantane.

The method for producing the electricity storage device of the present invention is not particularly limited, and the device is produced by a known method using a positive electrode, a negative electrode, an electrolytic solution, and, if necessary, a separator and the like. For example, in the case of a coin type, a positive electrode, a separator if necessary, and a negative electrode are inserted into an outer can. Electrolyte solution is put into this and impregnated. After that, the electrical storage device is obtained by joining the sealing body and the sealing body by tab welding or the like, enclosing the sealing body, and crimping. The shape of the electricity storage device is not limited, but examples thereof include a coin shape, a cylindrical shape, and a sheet shape.

The separator prevents direct contact between the positive electrode and the negative electrode to cause a short circuit in the storage battery, and known materials can be used. Specific examples of the separator include porous polymer films such as polyolefin, paper, and the like. As the porous polymer film, a film of polyethylene, polypropylene, or the like is preferable because it is less affected by the electrolytic solution.

Specific modes for carrying out the present invention will be described below with reference to Examples. However, the present invention is not limited to the following examples as long as it does not deviate from the gist thereof.

In this example, an electrode and a coin battery were produced, and an electrode adhesion test was performed as an evaluation of the electrode, and an internal resistance measurement was performed as an evaluation of the coin battery in the following experiments.

[Evaluation of physical properties of the produced electrode]
As a physical property evaluation of the produced electrode, an adhesion test was performed. The evaluation results are summarized in Table 1.

<Binding test>
(measuring device)
Peel strength tester: Strograph E3-L (Toyo Seiki Co., Ltd.)

(Binding test method)
An adhesion test was performed by a 180° peel test. Specifically, the electrode was cut into a width of 2 cm × length of 5 cm, a tape (adhesive tape: manufactured by Nichiban, width 1.8 cm, length 5 cm) was attached, and one end of the electrode in the length direction was attached to the strograph E3-L. While fixed, the tape was peeled off in a 180° direction at a test speed of 50 mm/min and a load range of 5N. The test was performed 3 times and the weighted average value was obtained.

[Evaluation of characteristics of fabricated battery]
As a characteristic evaluation of the produced coin battery, the internal resistance was measured by charging and discharging. The evaluation results are summarized in Table 2.

<Measurement of internal resistance>
(measuring device)
Charge/discharge evaluation device: TOSCAT-3100 (Toyo System Co., Ltd.)

(Measuring method)
The prepared lithium ion battery was charged to 4.2 V by constant current-constant voltage charging. The termination current was equivalent to 1C. After charging, the battery was allowed to rest for 10 minutes. Then, a constant current discharge at 2 C is performed, and the internal resistance R (Ω )=ΔE/I was measured.

<Measurement of average particle size of polymer>
The average particle size of the polymer was measured under the following conditions.
(measuring device)
Particle size distribution analyzer using dynamic light scattering: Zetasizer Nano (Spectris Inc.) (measurement conditions)
1. 50 μL of the synthesized emulsion solution is sampled.
2. The sampled emulsion solution is diluted by adding 700 μL of ion-exchanged water three times.
3. Withdraw 2100 μL of the diluted solution.
4. 700 μL of deionized water is added and diluted to the remaining 50 μL of the sample for measurement.

<Method for Observing Cross Section of Electrode Material Layer>
As the treatment of the electrode cross-section sample, an Ar ion beam treatment was performed using an ion milling apparatus IM-4000 manufactured by Hitachi High-Technologies Corporation. Next, using a JEOL JSM-7100F as a scanning electron microscope (SEM), observation was performed at a magnification of 10,000 to 20,000.

1 to 3 show images obtained by observing the cross section of the electrode material layer of Example 1 of Electrode Working Example 1 by SEM in the above-described manner. FIGS. 2 and 3 show the positions of the binder particles when three square fields of 1 μm×1 μm are selected from the SEM image of FIG. 1, respectively.

Of the three fields of view (square) shown in FIG. 2, five binder particles a to e (particle diameter of about 100 to 150 nm) are observed in the left field of view 1, none of which are in contact with each other. . In addition, five binder particles a to e (with a particle diameter of about 100 to 150 nm) are observed in the field 2 in the upper right of FIG. not. In addition, five binder particles a to e (with a particle diameter of about 100 to 150 nm) are observed in the visual field 3 in the lower right of FIG. not in contact.

In addition, of the three fields of view (square) shown in FIG. 3, six binder particles a to f (particle diameter of about 100 to 150 nm) were observed in the upper field of view 4, and they were all in contact with each other. not In addition, six binder particles a to f (with a particle diameter of about 100 to 150 nm) are observed in the field of view 5 in the lower left of FIG. not. In addition, four binder particles a to d (with a particle diameter of about 100 to 150 nm) are observed in the field of view 6 in the lower right of FIG. not in contact.

FIG. 4 shows an image obtained by observing the cross section of the electrode material layer of Comparative Preparation Example 1 of the electrode with the SEM by the above method. FIG. 4 shows numerically the positions of the binder particles when two square fields of 1 μm×1 μm are selected. Of the two fields of view (square) shown in FIG. 4, four binder particles a to d (particle diameter of about 50 to 100 nm) are observed in the upper field of view 1, and b, c, and d are continuous. in contact. Two binder particles a and b (with a particle diameter of about 50 to 100 nm) are observed in the lower field of view 2 in FIG. 4 and are not in contact with each other.

FIG. 5 shows an image obtained by observing the cross section of the electrode material layer of Comparative Preparation Example 2 of the electrode with the SEM by the above method. FIG. 5 shows numerically the positions of the binder particles when two square fields of 1 μm×1 μm are selected. Of the two fields of view (square) shown in FIG. 5, six binder particles a to f (particle diameter of about 100 to 150 nm) are observed in the upper field of view 1, and c to f are in continuous contact. ing. In addition, six binder particles a to f (with a particle diameter of about 100 to 150 nm) are observed in the lower field of view 2 in FIG. 5, and a to f are in continuous contact.

[Synthesis Example 1]
In a beaker, 89.2 parts by mass of n-butyl acrylate, 1.55 parts by mass of acrylic acid, 4.40 parts by mass of methacrylic acid, 4.15 parts by mass of polyethylene glycol monomethacrylate (manufactured by NOF: Blemmer PE-90) parts, trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: A-TMPT) 0.70 parts by weight, 1 part by weight of sodium dodecyl sulfate as an emulsifier, 180.00 parts by weight of ion-exchanged water and 0.12 parts by weight of ammonium persulfate as a polymerization initiator The parts by weight were added, and the mixture was sufficiently stirred using an ultrasonic homogenizer to obtain a milky lotion. A reaction vessel equipped with a stirrer was heated to 55° C. under a nitrogen atmosphere, and the latex was added over 2 hours. After addition of the emulsion, polymerization was continued for an additional hour, followed by cooling. After cooling, the pH of the polymerization liquid was adjusted from 2.6 to 8.0 using a 28% aqueous ammonia solution, and a binder composition A (polymerization conversion rate of 97% or more, solid content concentration of 39% by mass), which is an emulsion solution, was prepared. got The average particle size of the obtained polymer was 0.273 μm.

[Synthesis Example 2]
In a beaker, 69.57 parts by mass of methyl methacrylate, 1.68 parts by mass of acrylic acid, 4.79 parts by mass of methacrylic acid, 4.52 parts by mass of polyethylene glycol monomethacrylate (manufactured by NOF: Blenmer PE-90) , Trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical: A-TMPT) 19.44 parts by weight, 1 part by weight of sodium dodecyl sulfate as an emulsifier, 50.00 parts by weight of ion-exchanged water and 0.12 parts by weight of ammonium persulfate as a polymerization initiator The mixture was thoroughly stirred using an ultrasonic homogenizer to obtain an emulsion. A reaction vessel equipped with a stirrer was heated to 55° C. under a nitrogen atmosphere, and the latex was added over 2 hours. After addition of the emulsion, polymerization was continued for an additional hour, followed by cooling. After cooling, the pH of the polymerization liquid was adjusted from 2.9 to 8.0 using a 28% aqueous ammonia solution, and a binder composition B (polymerization conversion rate of 98% or more, solid content concentration of 39% by mass), which is an emulsion solution, was prepared. got The average particle size of the obtained polymer was 0.242 μm.

[Synthesis Example 3]
In a beaker, 69.55 parts by mass of methyl methacrylate, 1.68 parts by mass of acrylic acid, 4.77 parts by mass of methacrylic acid, and 4.52 parts by mass of polyethylene glycol monomethacrylate (manufactured by NOF: Blemmer PE-90) , Trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: A-TMPT) 19.48 parts by weight, 2 parts by weight of sodium dodecyl sulfate as an emulsifier, 40.00 parts by weight of ion-exchanged water and 0.12 parts by weight of ammonium persulfate as a polymerization initiator The mixture was thoroughly stirred using an ultrasonic homogenizer to obtain an emulsion. A reaction vessel equipped with a stirrer was heated to 55° C. under a nitrogen atmosphere, and the latex was added over 1 hour and 30 minutes. Then, 2-ethylhexyl acrylate 91.10 parts by mass, acrylic acid 1.11 parts by mass, methacrylic acid 3.13 parts by mass, polyethylene glycol monomethacrylate (manufactured by NOF: BLEMMER PE-90) 2.97 parts by mass , and 1.69 parts by mass of trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.: A-TMPT) were added over 30 minutes, polymerized for an additional hour, and then cooled. After cooling, the pH of the polymerization liquid was adjusted from 2.6 to 8.0 using a 28% aqueous ammonia solution, and the binder composition C (polymerization conversion rate of 97% or more, solid content concentration of 29% by mass), which is an emulsion solution. got The average particle size of the obtained polymer was 0.170 μm.

<Example of electrode preparation>
[Example 1 of electrode production]
95 parts by mass of nickel-cobalt-manganese lithium as a positive electrode active material, 3 parts by mass of acetylene black and 1 part by mass of carboxymethyl cellulose as a conductive aid, and the solid content of the binder composition A obtained in Synthesis Example 1 of the binder composition. 0.1 parts by mass, 0.9 parts by mass as the solid content of the binder composition B obtained in Synthesis Example 2 of the binder composition, and water so that the solid content concentration of the slurry is 72% by mass. In addition, they were thoroughly mixed using a planetary mill to obtain a positive electrode slurry.

The resulting positive electrode slurry was applied to an aluminum current collector having a thickness of 20 μm using a Baker applicator with a gap of 100 μm, dried at 110 ° C. in a vacuum state for 12 hours or more, and then pressed with a roll press to obtain a thickness. A positive electrode having a thickness of 35 μm and a density of the electrode material layer of 3.4 g/cc was produced. The evaluation results of the adhesion test and the evaluation results of SEM observation are shown in Example 1 of Table 1.

[Electrode Comparative Preparation Example 1]
95 parts by mass of nickel-cobalt-manganese lithium as a positive electrode active material, 3 parts by mass of acetylene black and 1 part by mass of carboxymethyl cellulose as a conductive aid, and the solid content of the binder composition C obtained in Synthesis Example 3 of the binder composition. and water was added so that the solid content concentration of the slurry was 72% by mass, and the mixture was sufficiently mixed using a planetary mill to obtain a positive electrode slurry. A positive electrode was prepared in the same manner as above. The thickness of the obtained positive electrode was 34 μm, and the density of the electrode material layer was 2.9 g/cc. Comparative Example 1 in Table 1 shows the evaluation results of the adhesion test and the evaluation results of SEM observation.

[Electrode Comparative Production Example 2]
95 parts by mass of nickel-cobalt-manganese lithium as a positive electrode active material, 3 parts by mass of acetylene black and 1 part by mass of carboxymethyl cellulose as a conductive aid, and the solid content of the binder composition B obtained in Synthesis Example 2 of the binder composition. and water was added so that the solid content concentration of the slurry was 72% by mass, and the mixture was sufficiently mixed using a planetary mill to obtain a positive electrode slurry. A positive electrode was prepared in the same manner as above. The thickness of the obtained positive electrode was 34 μm, and the density of the electrode material layer was 3.1 g/cc. Comparative Example 2 in Table 1 shows the evaluation results of the adhesion test and the evaluation results of SEM observation.

Table 1 shows the physical property evaluation results of the electrodes of Examples and Comparative Examples.

<Battery manufacturing example>
[Practical Production Example 1 of Coin Battery]
In a glove box filled with argon gas, the positive electrode obtained in Preparation Example 1, two polypropylene/polyethylene/polypropylene porous membranes with a thickness of 18 μm as separators, and a metallic lithium foil with a thickness of 300 μm as a counter electrode were used. The bonded laminate was sufficiently impregnated with 1 mol/L of ethylene carbonate, ethylmethyl carbonate, and diethyl carbonate (volume ratio 3:5:2) of lithium hexafluorophosphate as an electrolytic solution and crimped. manufactured a coin battery. Evaluation results of internal resistance measurement are shown in Example 1 of Table 2.

[Comparative production example 1 of coin battery]
Example of Coin Battery A coin battery was produced in the same manner as in Production Example 1 except that the positive electrode obtained in Comparative Production Example 1 of Electrodes was used. Evaluation results of internal resistance measurement are shown in Comparative Example 1 in Table 2.

[Comparative production example 2 of coin battery]
Example of Coin Battery A coin battery was produced in the same manner as in Production Example 1 except that the positive electrode obtained in Electrode Comparative Production Example 2 was used. Comparative Example 2 in Table 2 shows the evaluation results of the internal resistance measurement.

Table 2 shows the evaluation results of the characteristics of the batteries of Examples and Comparative Examples.

Example 1, which is a lithium ion battery using the positive electrode of the present invention, has higher binding properties than Comparative Examples 1 and 2, and is also a coin battery as compared to Comparative Examples 1 and 2. Equivalent performance was obtained at 100% state (SOC 100%).

INDUSTRIAL APPLICABILITY The electrode binder of the present invention has excellent binding properties and is useful for use in vehicles such as electric vehicles and hybrid electric vehicles, and in power storage devices such as storage batteries for household power storage.

Claims (4)

An electrode comprising a current collector and an electrode material layer formed on the surface of the current collector,
The electrode material layer contains active material particles and binder particles,
The content of the binder particles in the electrode material layer is 0.1 to 15% by mass,
Among the images obtained by observing the cross section of the electrode material layer with a scanning electron microscope, in at least three 1 μm × 1 μm square fields of view where the active material particles are not present, the binder particles are 3 to 3. An electrode in which 20 particles are observed and 3 or more of the binder particles are not continuously in contact with each other. 2. The electrode according to claim 1, wherein the binder particles observed in the field of view have a particle size of 30 to 200 nm. 3. The electrode according to claim 1, wherein the content of said binder particles in said electrode material layer is 0.2 to 10 % by mass. An electricity storage device comprising the electrode according to any one of claims 1 to 3.

Images