JP2021015778A - Binder - Google Patents

Abstract

To provide a new technology and a binder for suppressing the occurrence of warpage of an electrode after removing water and suppressing excessive curing of an electrode active material layer when the electrode is manufactured using a composition for forming the electrode active material layer containing water.SOLUTION: A binder includes a compound formed by condensing polyacrylic acid with a polyol and/or amino alcohol.SELECTED DRAWING: None

Description

The present invention relates to a binder used for an electrode of a secondary battery or the like.

A power storage device such as a secondary battery includes a positive electrode and a negative electrode. The positive electrode is generally provided with a positive electrode active material layer containing a positive electrode active material and a binder, and the negative electrode is generally provided with a negative electrode active material layer containing a negative electrode active material and a binder.
Here, it is known that polyacrylic acid is used as a binder for the positive electrode and the negative electrode.

Patent Document 1 specifically describes a negative electrode containing a Si-containing negative electrode active material and polyacrylic acid as a binder, and specifically describes a lithium ion secondary battery including the negative electrode.
Patent Document 2 specifically describes a negative electrode containing a Si-containing negative electrode active material, graphite, and polyacrylic acid as a binder, and also specifically describes a lithium ion secondary battery including the negative electrode. ..

Patent Document 3 specifically describes a positive electrode having polyacrylic acid as a positive electrode active material and a binder, and a negative electrode having Si-containing negative electrode active material and graphite and polyacrylic acid as a binder. A positive electrode and a lithium ion secondary battery including the negative electrode are also specifically described.

JP-A-2017-152123 JP-A-2017-168376 JP-A-2017-224430

From the viewpoint of environmental consideration and cost, it is preferable to refrain from using an organic solvent during production, and it is preferable to use water as a substitute solvent for the organic solvent. In fact, in Patent Documents 1 and 2, water is used as a solvent for producing a negative electrode containing polyacrylic acid. That is, in these documents, a negative electrode is manufactured using a composition for forming a negative electrode active material layer containing polyacrylic acid, a negative electrode active material, and water.

At the time of industrialization, a large amount and rapid production of negative electrodes are required. Therefore, the present inventor recalls using a so-called roll-to-roll manufacturing apparatus in which a negative electrode precursor or a negative electrode is wound in a roll shape by using a current collector foil wound in a roll shape. did.
However, when a composition for forming a negative electrode active material layer containing polyacrylic acid, a negative electrode active material and water was applied to a current collector foil and dried to remove water, a dried negative electrode active material layer was formed. The present inventor has found that the electrode may be warped or the negative electrode active material layer after drying may be excessively hardened, making it difficult to wind the electrode into a roll.

The present invention has been made in view of such circumstances, and after removing water when producing an electrode using a composition for forming an electrode active material layer containing polyacrylic acid, an electrode active material and water. It is an object of the present invention to provide a new technique and a binder for suppressing the occurrence of warpage of the electrode and excessive curing of the electrode active material layer.

According to the present inventor, polyacrylic acid and hydrogen are the causes of electrode warpage and excessive curing of the electrode active material layer after water is removed when water is removed from the electrode active material layer forming composition. It was presumed that the volume of the electrode active material layer was excessively contracted as a result of the removal of the bound water.
Therefore, the present inventor recalled that a small amount of a water-soluble organic solvent having a boiling point higher than that of water was added to the composition for forming the electrode active material layer. The reason is that the water-soluble organic solvent can hydrogen bond with polyacrylic acid even after the water is removed, so that the defects of the electrode and the electrode active material layer are considered to be solved.

Then, N-methyl-2-pyrrolidone was adopted as a water-soluble organic solvent having a boiling point higher than that of water, and a study was conducted to add a small amount of this to the composition for forming an electrode active material layer. As a result, the above-mentioned electrodes and electrode activity were examined. It was found that the defect of the material layer was remarkably improved.
Furthermore, when a study was conducted in which a diol or aminoalcohol was used as a water-soluble organic solvent having a boiling point higher than that of water and a small amount of this was added to the composition for forming the electrode active material layer, the above-mentioned electrodes and the electrode active material layer were examined. In addition to finding that the defects were significantly improved, diols and aminoalcohols reacted with polyacrylic acid to form new binders, and lithium ion batteries equipped with such binders. It was found that the next battery has excellent battery performance.
Based on such findings, the present inventor has completed the present invention.

The binder of the present invention is characterized by containing a compound formed by condensing polyacrylic acid with a polyol and / or an amino alcohol.

A suitable electrode can be provided by the novel binder of the present invention. Further, by adopting the novel binder of the present invention, the occurrence of defects in the manufactured electrode and the electrode active material layer is suppressed.

3 is an infrared absorption spectrum of Sample 1 after heating at 50 ° C. in Evaluation Example 3. 3 is an infrared absorption spectrum of Sample 1 after heating at 230 ° C. in Evaluation Example 3. It is an overlay of the infrared absorption spectrum of the sample 1 after heating at 50 ° C. and 230 ° C. in Evaluation Example 3. 3 is an infrared absorption spectrum of Sample 2 after heating at 50 ° C. in Evaluation Example 3. 3 is an infrared absorption spectrum of Sample 2 after heating at 230 ° C. in Evaluation Example 3. It is an overlay of the infrared absorption spectrum of the sample 2 after heating at 50 ° C. and 230 ° C. in Evaluation Example 3. 3 is an infrared absorption spectrum of Sample 3 after heating at 80 ° C. in Evaluation Example 3. 3 is an infrared absorption spectrum of Sample 3 after heating at 230 ° C. in Evaluation Example 3. It is an overlay of the infrared absorption spectrum of the sample 3 after heating at 80 ° C. and 230 ° C. in Evaluation Example 3. This is the temperature raising program of Evaluation Example 4. It is an overlay of the infrared absorption spectrum in the evaluation example 4. It is a spectrum which expanded the infrared absorption spectrum of FIG.

Hereinafter, embodiments for carrying out the present invention will be described. Unless otherwise specified, the numerical range "a to b" described in the present specification includes the lower limit a and the upper limit b in the range. Then, a numerical range can be constructed by arbitrarily combining these upper and lower limit values and the numerical values listed in the examples. Further, a numerical value arbitrarily selected from these numerical values can be used as a new upper limit or lower limit numerical value.

The binder of the present invention is characterized by containing a compound formed by condensing polyacrylic acid with a polyol and / or an amino alcohol (hereinafter, may be referred to as a binder compound).

The above-mentioned polyacrylic acid, polyol, and amino alcohol are all assumed to be water-soluble. However, since the binder compound may be poorly soluble in water, it is rational to synthesize the binder compound in the process of manufacturing the electrode.

The method for producing an electrode containing the binder of the present invention is
a) The composition for forming an electrode active material layer containing the polyacrylic acid, water, a polyol and / or an amino alcohol and an electrode active material is applied to a current collector foil, and then water is removed to remove an electrode precursor. The process of manufacturing,
b) A step of heat-treating the electrode precursor,
It is characterized by having.

The binder of the present invention may be used as a binder for a positive electrode or as a binder for a negative electrode. From the viewpoint of the excellent properties of the binder of the present invention, it is preferable to use a binder for a negative electrode having a large degree of expansion and contraction during charging and discharging.
Hereinafter, the case where the binder of the present invention is used as the binder for the negative electrode will be described in detail along with the method for manufacturing the negative electrode, but the case where the binder of the present invention is used as the binder for the positive electrode will be described in detail. , The "negative electrode" in the following description may be read as "positive electrode".

The method for producing a negative electrode containing the binder of the present invention is
a) The composition for forming a negative electrode active material layer containing the polyacrylic acid, water, a polyol and / or an amino alcohol and a negative electrode active material is applied to a current collecting foil, and then water is removed to remove the negative electrode precursor. The process of manufacturing,
b) A step of heat-treating the negative electrode precursor,
It is characterized by having.

The negative electrode manufactured by the method for manufacturing a negative electrode containing the binder of the present invention is referred to as the negative electrode of the present invention.
The negative electrode of the present invention includes a current collector foil and a negative electrode active material layer containing the binder and the negative electrode active material of the present invention on the surface of the current collector foil.

a) The process will be described.
In the step a), a composition for forming a negative electrode active material layer containing polyacrylic acid, water, a polyol and / or amino alcohol and a negative electrode active material is applied to a current collecting foil, and then water is removed to remove the negative electrode precursor. This is the process of manufacturing the body.

The negative electrode precursor is composed of a current collector foil and a negative electrode active material layer formed on the current collector foil.
The presence of the polyol and / or the amino alcohol in the negative electrode precursor suppresses excessive shrinkage of the volume of the negative electrode active material layer, and the polyol and the amino alcohol can form a hydrogen bond with the polyacrylic acid. It is considered that the occurrence of warpage of the negative electrode precursor and excessive curing of the negative electrode active material layer are suppressed.

The polyacrylic acid and the polyol and / or amino alcohol undergo a dehydration condensation reaction in step b) to form a chemical structure in which the polyacrylic acid chain is crosslinked with the polyol and / or amino alcohol, and the binder is used. Functions as. b) In the step prior to the step, the polyacrylic acid and the polyol and / or the amino alcohol are present in the composition for forming the negative electrode active material layer or the negative electrode active material layer as the binder precursor.

Here, the binder precursor means that the cross-linking of the polyacrylic acid chain with a polyol and / or an amino alcohol is incomplete. In the binder precursor, the polyol and / or the amino alcohol may be ionically bonded to the carboxyl group of the polyacrylic acid, and some carboxyl groups may be bonded to the hydroxyl group or the amino group to form an ester bond or an amide bond. Alternatively, an imide bond may be formed.

The weight average molecular weight of the polyacrylic acid is preferably in the range of 5000 to 2500, more preferably in the range of 1000 to 2000000, further preferably in the range of 50,000 to 1800000, and even more preferably in the range of 100,000 to 1700000. The range of 400,000 to 1600000 is particularly preferable, and the range of 500,000 to 15000000 is most preferable.
The higher the weight average molecular weight of polyacrylic acid, the higher the binding force tends to be, but the higher the viscosity when dissolved in water.

The viscosity of the solution of polyacrylic acid dissolved in water and the viscosity of the solution of polyacrylic acid dissolved in N-methyl-2-pyrrolidone are lower in the former. Then, when water is used as the solvent of the composition for forming the negative electrode active material layer, it becomes possible to use polyacrylic acid having a larger average molecular weight and to dissolve polyacrylic acid at a higher concentration. Moreover, it can be said that the coating work can be easily carried out.

Water is a dissolving solvent for polyacrylic acid, polyol and / or amino alcohol, and is a medium for making the state of the composition for forming the negative electrode active material layer into a slurry.
The amount of water is preferably 20 to 70% by mass, more preferably 25 to 60% by mass, and even more preferably 30 to 50% by mass with respect to the entire composition for forming the negative electrode active material layer.

A polyol is a compound having a plurality of hydroxyl groups in one molecule, and an amino alcohol is a compound having an amino group and a hydroxyl group in one molecule. The amino group of the amino alcohol is preferably -NH _2, but a mono-substituted amino group in which one hydrogen is substituted with an alkyl group may be used.

As the polyol and amino alcohol, water-soluble ones are preferable. Here, the water-soluble polyol and amino alcohol mean a polyol and amino alcohol that can be dissolved in water at a concentration of 1 g / L or more.

Further, as the polyol and the amino alcohol, those having a boiling point higher than that of water are preferable. This is because if the polyol and amino alcohol have a boiling point lower than that of water, there is a high possibility that the polyol and amino alcohol will be removed before removing water in step a). The boiling point of the polyol and amino alcohol is preferably 130 ° C. or higher, and the boiling point range can be exemplified in the range of 130 ° C. to 300 ° C. and the range of 150 ° C. to 250 ° C.

Further, the polyol and amino alcohol are preferably liquid at 25 ° C. This is because a suitable action as a plasticizer can be expected inside the negative electrode precursor in the step a). The melting point of the polyol and the amino alcohol is preferably 20 ° C. or lower, and the melting point range can be exemplified in the range of −150 ° C. to 10 ° C. and the range of −130 ° C. to 0 ° C.

The following general formula (1) can be exemplified as a specific example of the polyol, and the following general formula (2) can be exemplified as a specific example of the amino alcohol.

General formula (1) H- (OR) _n- OH
General formula (2) H- (OR) _n- NH ₂

In the general formula (1) and the general formula (2), R is an independently divalent organic group, and n is an integer of 1 or more.
It is preferable that R is a saturated alkylene group having 2 or more carbon atoms independently. The saturated alkylene group may be linear, branched, or cyclic. The saturated alkylene group hydrogen may be substituted with a hydroxyl group or an alkoxy group. When R is a saturated alkylene group, the cross-linking site with the polyol and amino alcohol for polyacrylic acid is highly flexible.
Examples of the number of carbon atoms of the saturated alkylene group include 2 to 10, 2 to 8, 2 to 6, and 2 to 4.

Examples of the range of the integer n in the general formula (1) and the general formula (2) include 1 to 10, 1 to 6, 1 to 4, and 1 to 2.

As the polyol and the amino alcohol, one type may be adopted for each, or a plurality of types may be used in combination.

The total amount of the polyol and amino alcohol added to the polyacrylic acid is preferably in the range of 2: 1 to 100: 1 in the molar ratio of the acrylic acid monomer and the total of the polyol and amino alcohol to 3: 1. It is more preferably in the range of ~ 50: 1, further preferably in the range of 4: 1 to 20: 1, and particularly preferably in the range of 5: 1 to 10: 1.

As the negative electrode active material, a material capable of occluding and releasing charge carriers can be used. Therefore, there is no particular limitation as long as it is a simple substance, alloy or compound capable of occluding and releasing a charge carrier such as lithium ion. For example, as negative electrode active materials, Group 14 elements such as carbon, silicon, germanium and tin, Group 13 elements such as aluminum and indium, Group 12 elements such as zinc and cadmium, Group 15 elements such as antimony and bismuth, magnesium and calcium. Alkaline earth metals such as, silver, and group 11 elements such as gold may be used individually. Specific examples of alloys or compounds include tin-based materials such as Ag-Sn alloys, Cu-Sn alloys, and Co-Sn alloys, carbon-based materials such as various graphites, and SiO _{x that} disproportionates to elemental silicon and silicon dioxide. Examples thereof include a silicon-based material such as 0.3 ≦ x ≦ 1.6), a simple substance of silicon, or a composite of a silicon-based material and a carbon-based material. Further, as the negative electrode active material, oxides such as Nb ₂ O ₅ , TiO ₂ , Li ₄ Ti ₅ O ₁₂ , WO ₂ , MoO ₂ , Fe ₂ O ₃ or Li _3-x M _x N (M = Co). , Ni, Cu) may be used. One or more of these can be used as the negative electrode active material.

From the viewpoint of the possibility of increasing the capacity, graphite, Si-containing material, and Sn-containing material can be mentioned as preferable negative electrode active materials. Further, in view of the suitable properties of the binder compound as a binder, a Si-containing negative electrode active material having a large degree of expansion and contraction during charging and discharging is particularly preferable.

As a specific example of the Si-containing negative electrode active material, SiO _x (0.3 ≦ x ≦ 1.6) in which Si alone or two phases of Si phase and silicon oxide phase are disproportionated or unproportionated. ) Can be exemplified. The range of x is more preferably 0.5 ≦ x ≦ 1.5, and even more preferably 0.7 ≦ x ≦ 1.2.

Specific examples of the Si-containing negative electrode active material include a silicon material disclosed in International Publication No. 2014/08608 (hereinafter, simply referred to as “silicon material”).

The silicon material has a structure in which a plurality of plate-shaped silicon bodies are laminated in the thickness direction. The silicon material undergoes, for example, a step of reacting CaSi ₂ with an acid to synthesize a layered silicon compound containing polysilane as a main component, and a step of heating the layered silicon compound at 300 ° C. or higher to release hydrogen. It is manufactured.

The ideal reaction formula when hydrogen chloride is used as the acid shows the method for producing the silicon material as follows.
3CaSi ₂ + 6HCl → Si ₆ H ₆ + 3CaCl _{2
Si 6 H 6 → 6Si + 3H} 2 ↑

However, in the upper reaction for synthesizing Si ₆ H ₆ which is polysilane, water is usually used as the reaction solvent from the viewpoint of removing by-products and impurities. Since Si ₆ H ₆ can react with water, in the step of synthesizing the layered silicon compound including the reaction in the upper stage, the layered silicon compound is rarely produced as containing only Si ₆ H ₆ , and is layered. Silicon compounds are represented by Si ₆ H _s (OH) _t X _u (X is an element or group derived from an acid anion, s + t + u = 6, 0 <s <6, 0 <t <6, 0 <u <6). Manufactured as a compound. In the above chemical formula, unavoidable impurities such as Ca that may remain are not considered. The silicon material obtained by heating the layered silicon compound also contains an element derived from an anion of oxygen or acid.

As described above, the silicon material has a structure in which a plurality of plate-shaped silicon bodies are laminated in the thickness direction. In order to efficiently occlude and release a charge carrier such as lithium ion, the plate-shaped silicon body preferably has a thickness in the range of 10 nm to 100 nm, and more preferably in the range of 20 nm to 50 nm. The length of the plate-shaped silicon body in the longitudinal direction is preferably in the range of 0.1 μm to 50 μm. Further, the plate-shaped silicon body preferably has (length in the longitudinal direction) / (thickness) in the range of 2 to 1000. The laminated structure of the plate-shaped silicon body can be confirmed by observation with a scanning electron microscope or the like. Further, this laminated structure is considered to be a remnant of the Si layer in the raw material CaSi ₂ .

The silicon material preferably contains amorphous silicon and / or silicon crystallites. In particular, in the plate-shaped silicon body, it is preferable that amorphous silicon is used as a matrix and silicon crystallites are scattered in the matrix. The size of the silicon crystallite is preferably in the range of 0.5 nm to 300 nm, more preferably in the range of 1 nm to 100 nm, further preferably in the range of 1 nm to 50 nm, and particularly preferably in the range of 1 nm to 10 nm. The size of the silicon crystallite is calculated from Scheller's equation using the half width of the diffraction peak on the Si (111) plane of the obtained X-ray diffraction chart obtained by performing X-ray diffraction measurement on the silicon material. ..

The abundance and size of the plate-shaped silicon body, amorphous silicon, and silicon crystallites contained in the silicon material mainly depend on the heating temperature and heating time. The heating temperature is preferably in the range of 400 ° C. to 900 ° C., more preferably in the range of 500 ° C. to 800 ° C.

The Si-containing negative electrode active material is preferably one coated with carbon. The carbon coating improves the conductivity of the Si-containing negative electrode active material.

The Si-containing negative electrode active material is preferably in the form of powder, which is an aggregate of particles. The average particle size of the Si-containing negative electrode active material is preferably in the range of 1 to 30 μm, more preferably in the range of 2 to 20 μm. The average particle size in the present specification means D ₅₀ when the sample is measured by a general laser diffraction type particle size distribution measuring device.

A conductive auxiliary agent or other additives may be added to the composition for forming the negative electrode active material layer.

a) The composition for forming the negative electrode active material layer in the step can be prepared by mixing each component. Although the mixing order of each component is not limited, it is rational to mix the negative electrode active material after mixing the polyacrylic acid with the polyol and / or the amino alcohol with water to produce a composition for forming the negative electrode active material layer. Is.

Basically, the solid content other than water in the composition for forming the negative electrode active material layer is a constituent component of the negative electrode active material layer. Then, the compounding ratio of each component in the composition for forming the negative electrode active material layer becomes the compounding ratio in the negative electrode active material layer. The blending amount and blending ratio of the solid content in the composition for forming the negative electrode active material layer may be determined based on the suitable blending amount and blending ratio of each component in the negative electrode active material layer shown below.

The negative electrode active material layer preferably contains the binder compound in an amount of 1 to 20% by mass, more preferably 3 to 15% by mass, and 5 to 15% by mass, based on the total mass of the negative electrode active material layer. It is more preferably contained in an amount of 10% by mass.

The negative electrode active material layer preferably contains the negative electrode active material in an amount of 60 to 98% by mass, more preferably 70 to 97% by mass, and 80 to 96% by mass, based on the total mass of the negative electrode active material layer. It is more preferably contained in an amount of 90% by mass, and particularly preferably contained in an amount of 90 to 95% by mass.

The negative electrode active material layer may contain additives other than the binder compound, such as a binder and a conductive auxiliary agent.

Examples of other binders include fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. Examples thereof include acrylic resins such as poly (meth) acrylic acid, and cellulose derivatives such as styrene butadiene rubber and carboxymethyl cellulose.

The conductive auxiliary agent is added to increase the conductivity of the negative electrode. Therefore, the conductive auxiliary agent may be arbitrarily added when the conductivity of the negative electrode is insufficient, and may not be added when the conductivity of the negative electrode is sufficiently excellent. The conductive auxiliary agent may be a chemically inert electron high conductor, and examples thereof include carbon black, which are carbonaceous fine particles, graphite, Vapor Grown Carbon Fiber, and various metal particles. To. Examples of carbon black include acetylene black, Ketjen black (registered trademark), furnace black, and channel black. These conductive auxiliaries can be added to the negative electrode active material layer alone or in combination of two or more.

The blending ratio of the conductive auxiliary agent in the negative electrode active material layer is preferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, still more preferably 1 to 5% by mass. The mass ratio of the negative electrode active material and the conductive auxiliary agent is preferably 99: 1 to 85:15, more preferably 98: 2 to 90:10, and particularly preferably 97: 3 to 92: 8.

The current collector foil refers to a chemically inactive, foil-like electron conductor for keeping an electric current flowing through an electrode during discharge or charging of a secondary battery such as a lithium ion secondary battery. The material of the current collector foil is not particularly limited as long as it is a metal that can withstand the charge / discharge voltage of the negative electrode active material used. As the material of the current collector foil, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel. Metallic materials such as, can be exemplified. The current collector foil may be covered with a known protective layer. A current collector foil obtained by treating the surface of the current collector foil by a known method may be used as the current collector foil.

The thickness of the current collector foil can be exemplified in the range of 1 to 100 μm, 5 to 50 μm, and 7 to 30 μm.

Examples of the coating method include a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, and a curtain coating method.

In order to remove water from the composition for forming the negative electrode active material layer after being applied to the current collector foil, it is preferable to dry under ventilation and / or heating. Drying may be carried out under normal pressure or under reduced pressure.
By sufficiently removing water by drying, it is possible to suppress the occurrence of troubles in the b) step and shorten the time required in the b) step.
However, it is not preferable that the drying temperature exceeds 150 ° C. The reason is that drying is assumed to be carried out in the atmosphere, and if the temperature exceeds 150 ° C in the atmosphere, the current collector foil or the like may be oxidized and its strength may be reduced. Because there is. In addition, the dehydration condensation reaction that should originally proceed in step b) may proceed.
From the above items, the drying temperature is preferably carried out in the temperature range of 30 to 150 ° C, more preferably in the temperature range of 40 to 130 ° C, and within the temperature range of 50 to 110 ° C. It is more preferably done in.

The drying temperature is preferably carried out under a temperature rising condition in which the temperature is gradually increased from the beginning of drying to the end of drying. By drying under heating conditions, migration of polyacrylic acid, polyol and / or aminoalcohol, and binder precursor can be suppressed, and water bumping can also be suppressed.

a) In the step, it is arranged between the roll unwinding portion for carrying out the current collecting foil, the roll winding portion for winding the roll-shaped negative electrode precursor, and the roll unwinding portion and the roll winding portion. It is preferable to use an apparatus for producing a negative electrode precursor, which comprises a coating portion for applying the composition for forming a negative electrode active material layer in a film shape and a drying portion arranged between the coating portion and the roll winding portion. ..

A pressing step may be carried out on the negative electrode precursor after removing water so that the density of the negative electrode active material layer is appropriate. The pressing step may be carried out under normal pressure or under reduced pressure. Further, the pressing step may be carried out under heating conditions. However, the heating conditions are lower than the heat treatment temperature in step b).

Next, b) step will be described.
b) The step is a step of heat-treating the negative electrode precursor, and is a step of synthesizing a binder compound formed by condensing polyacrylic acid with a polyol and / or an amino alcohol due to the heating. That is, in step b), the dehydration condensation reaction of the binder precursor proceeds inside the negative electrode active material layer, and the binder having a chemical structure in which the polyacrylic acid chain is crosslinked with a polyol and / or an amino alcohol. It is believed that the compound is synthesized.

Among the presumed synthetic mechanisms of the binder compound, the portion where the polyol crosslinks the polyacrylic acid chain will be described in detail.
The carboxyl group of the first polyacrylic acid chain and the first hydroxyl group of the polyol undergo a dehydration condensation reaction to form an ester structure. Next, the other hydroxyl group of the above polyol bonded to the first polyacrylic acid chain undergoes a dehydration condensation reaction with the carboxyl group of the second polyacrylic acid chain to form an ester structure. It is considered that the chains of the second polyacrylic acid are crosslinked with each other.

Furthermore, among the presumed synthetic mechanisms of the binder compound, the portion where the amino alcohol crosslinks the polyacrylic acid chain will be described in detail.
The carboxyl group of the first polyacrylic acid chain and the amino group of the transamination reaction undergo a dehydration condensation reaction to form an amide structure. Alternatively, two carboxyl groups of adjacent acrylic acid monomer units in the first polyacrylic acid chain and an amino group of an amino alcohol undergo a dehydration condensation reaction to form a 6-membered ring-imide skeleton. Next, the hydroxyl group of the above amino alcohol bonded to the first polyacrylic acid chain undergoes a dehydration condensation reaction with the carboxyl group of the second polyacrylic acid chain to form an ester structure. It is considered that the chains of the second polyacrylic acid are crosslinked with each other.

It is impossible to crosslink a polyacrylic acid chain with an alcohol having only one hydroxyl group in one molecule. Further, although a diamine having two amino groups in one molecule can crosslink the polyacrylic acid chain, it is highly reactive, so it is considered that the reaction may proceed in step a), and as a result, the negative electrode precursor The negative electrode active material layer in the body may be excessively hardened.

b) The heating temperature in the step is preferably a temperature exceeding 180 ° C, more preferably 185 to 260 ° C, further preferably 190 to 250 ° C, particularly preferably 200 to 240 ° C, and most preferably 210 to 240 ° C.
b) If the temperature in the step is too low, the desired reaction may not proceed sufficiently. b) If the temperature in the step is too high, the dehydration reaction between the carboxyl groups of the polyacrylic acid chain proceeds excessively, that is, the structure of the acid anhydride is excessively generated, so that the binder compound is bound. There is a risk that the function as Further, if the temperature in the step b) is excessively high, the binder compound may be decomposed.

b) The heating in the step may be carried out by irradiating the negative electrode precursor with light having a wavelength of 4 to 8 μm. Since light having a wavelength of 4 to 8 μm corresponds to infrared rays, irradiating the negative electrode precursor with light having a wavelength of 4 to 8 μm inevitably brings about a heated state.

Light of wavelength 4~8μm is, H 2 _O or carbon - is a light in a wavelength region functional group having an oxygen double bond absorbs specific. The wavelength range of light H 2 _O absorbs specifically is generally 5.5～7Myuemu, and the carbon of the carboxyl group - wavelength range of light oxygen double bond absorbs specific is generally 5.5 Considering that it is ~ 7 μm, it can be said that the wavelength of the light irradiated in step b) is preferably 5.5 to 7 μm.

Light with a wavelength of 4-8 μm is believed to promote the nucleophilic dehydration reaction by polyols and / or aminoalcohols to the carboxyl group of polyacrylic acid. As a result, it is considered that the cross-linking formation of the polyacrylic acid chain by the polyol and / or the amino alcohol is promoted.

b) In the step, the time for irradiating an arbitrary portion of the negative electrode precursor with light having a wavelength of 4 to 8 μm is preferably 0.5 to 10 minutes, more preferably 1 to 5 minutes, and 1.5 to 4 minutes. Especially preferable. For example, when the temperature in the step b) is 230 ° C., the light irradiation time in the step b) is sufficient to be about 3 minutes.

Further, since light having a wavelength of 4 to 8 μm can be transmitted as long as it is about the thickness of the negative electrode active material layer, a binder precursor existing on the inner side of the negative electrode active material layer, or polyacrylic acid, polyol and / Or it is considered that light having a wavelength of 4 to 8 μm reaches the amino alcohol. Then, it is considered possible to promote the desired reaction not only on the surface of the negative electrode active material layer but also on the inside.

Examples of the thickness of the negative electrode active material layer include 1 to 500 μm, 5 to 300 μm, and 10 to 150 μm.

b) The step is preferably carried out in an inert gas atmosphere in order to suppress inconvenient oxidation. Examples of the inert gas include nitrogen, helium and argon.

b) In the step, the roll unwinding portion for carrying out the roll-shaped negative electrode precursor, the roll winding portion on which the roll-shaped negative electrode is wound, and the roll unwinding portion and the roll winding portion are arranged. It is convenient for mass production of the negative electrode to use a device including an irradiation unit for irradiating light having a wavelength of 4 to 8 μm.
By using this device, the negative electrode can be manufactured under the condition that the flat negative electrode active material layer exists on the flat current collector foil and the manufacturing variation is unlikely to occur. Therefore, b) The properties of the negative electrode after the step are made uniform. Will be done. Further, since it is easy to irradiate light under uniform conditions and it is easy to set the light irradiation time, it is difficult for the performance of the negative electrode to vary. Furthermore, it can be adapted to increase production capacity and labor saving.

The negative electrode of the present invention can be used as the negative electrode of the power storage device.
Examples of the power storage device include a primary battery, a secondary battery, and a capacitor. Hereinafter, the power storage device of the present invention including the negative electrode of the present invention will be described through the description of the lithium ion secondary battery which is a typical example of the power storage device.

Hereinafter, the lithium ion secondary battery provided with the negative electrode of the present invention will be referred to as the lithium ion secondary battery of the present invention. One aspect of the lithium ion secondary battery of the present invention includes the negative electrode and the positive electrode of the present invention, as well as a separator and an electrolytic solution, or a solid electrolyte.

The positive electrode includes a current collecting foil and a positive electrode active material layer formed on the surface of the current collecting foil.
As the current collecting foil for the positive electrode, the one described for the negative electrode may be appropriately selected.

When the potential of the positive electrode is 4 V or more based on lithium, it is preferable to use aluminum as the current collector foil for the positive electrode.

Specifically, it is preferable to use a current collector foil for the positive electrode made of aluminum or an aluminum alloy. Here, aluminum refers to pure aluminum, and aluminum having a purity of 99.0% or higher is referred to as pure aluminum. An alloy obtained by adding various elements to pure aluminum is called an aluminum alloy. Examples of the aluminum alloy include Al—Cu, Al—Mn, Al—Fe, Al—Si, Al—Mg, Al—Mg—Si, and Al—Zn—Mg.

Further, as aluminum or aluminum alloy, specifically, for example, A1000 series alloys such as JIS A1085 and A1N30 (pure aluminum series), A3000 series alloys such as JIS A3003 and A3004 (Al-Mn series), JIS A8079, A8021 and the like A8000 series alloy (Al—Fe series) can be mentioned.

The positive electrode active material layer contains a positive electrode active material that can occlude and release charge carriers such as lithium ions, and, if necessary, a binder and a conductive auxiliary agent. The positive electrode active material layer preferably contains the positive electrode active material in an amount of 60 to 99% by mass, more preferably 70 to 95% by mass, based on the total mass of the positive electrode active material layer.

As the positive electrode active material, the general formula of the layered rock salt _{structure: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D is W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, Rh, Fe, Ge, Zn, Ru, At least one element selected from Sc, Sn, In, Y, Bi, S, Si, Na, K, P, V, 1.7 ≦ f ≦ 3), or Li _a Ni _b Co _c Al _{d De O f (0.2 ≦ a ≦ 2} , b + c + d + e = 1,0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Zr, Ti, P , Ga, Ge, V, Mo, Nb, W, La, at least one element, 1.7 ≦ f ≦ 3), a lithium composite metal oxide represented by Li ₂ MnO _3. .. Further, as the positive electrode active material, a metal oxide having a spinel structure such as LiMn ₂ O ₄ , a solid solution composed of a mixture of a metal oxide having a spinel structure and a layered compound, LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (in the formula). M is selected from at least one of Co, Ni, Mn, and Fe) and the like. Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as the positive electrode active material may have the above composition formula as the basic composition, and those in which the metal element contained in the basic composition is replaced with another metal element can also be used. Further, as the positive electrode active material, a material that does not contain a charge carrier (for example, lithium ions that contribute to charging / discharging) may be used. For example, elemental sulfur, compounds complexed with sulfur and carbon, metal sulfides such as TiS _2, oxides such as V 2 _{O 5,} MnO _2, polyaniline and anthraquinone and compounds containing these aromatic in chemical structure, conjugated double Conjugated materials such as acetic acid-based organic substances and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronylnitroxide, galbinoxyl, and phenoxyl may be adopted as the positive electrode active material. When a positive electrode active material that does not contain a charge carrier such as lithium is used, it is necessary to add a charge carrier to the positive electrode and / or the negative electrode in advance by a known method. The charge carrier may be added in an ionic state or may be added in a nonionic state such as a metal. For example, when the charge carrier is lithium, a lithium foil may be attached to the positive electrode and / or the negative electrode to integrate them.

From the viewpoint of excellent and high capacity, and durability, as the positive electrode active material, the general formula of the layered rock salt _{structure: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D are W, Mo, Re, Pd, Ba, Cr, B, Sb, Sr, Pb, Ga, Al, Nb, Mg, Ta, Ti, La, Zr, Cu, Ca, Ir, Hf, At least one element selected from Rh, Fe, Ge, Zn, Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, V, 1.7 ≦ f ≦ 3), or _{Li a Ni b Co c Al d} D e O f (0.2 ≦ a ≦ 2, b + c + d + e = 1,0 ≦ e <1, D is Li, Fe, Cr, Cu, Zn, Ca, Mg, S, Si , Na, K, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, at least one element, a lithium composite metal oxide represented by 1.7 ≦ f ≦ 3). It is preferable to adopt it.

In the above general formula, the values of b, c, and d are not particularly limited as long as they satisfy the above conditions, but those having 0 <b <1, 0 <c <1, 0 <d <1 are used. It is good, and at least one of b, c, and d is in the range of 30/100 <b <90/100, 10/100 <c <90/100, 1/100 <d <50/100. More preferably, the range is 40/100 <b <90/100, 10/100 <c <50/100, 2/100 <d <30/100, 50/100 <b <90/100, It is more preferable that the range is 10/100 <c <30/100, 2/100 <d <10/100.

The values of a, e, and f may be values within the range specified by the above general formula, and preferably 0.5 ≦ a ≦ 1.5, 0 ≦ e <0.2, 1.8 ≦ f ≦ 2. 5.5, more preferably 0.8 ≦ a ≦ 1.3, 0 ≦ e <0.1, 1.9 ≦ f ≦ 2.1 can be exemplified, respectively.

As a positive electrode active material, Li _x Mn _{2-y Ay} O ₄ (A is Ca, Mg, S, Si, Na, K, Al, P, Ga) having a spinel structure, because of its high capacity and excellent durability. , At least one element selected from Ge, and at least one metal element selected from transition metal elements such as Ni. 0 <x ≦ 2.2, 0 ≦ y ≦ 1) can be exemplified. Examples of the range of the value of x include 0.5 ≦ x ≦ 1.8, 0.7 ≦ x ≦ 1.5, and 0.9 ≦ x ≦ 1.2, and the range of the value of y is 0. Examples thereof include ≦ y ≦ 0.8 and 0 ≦ y ≦ 0.6. Examples of specific spinel-structured compounds include LiMn ₂ O ₄ and Limn _1.5 Ni _0.5 O ₄ .

Specific examples of the positive electrode active material include LiFePO ₄ , Li ₂ FeSiO ₄ , LiCoPO ₄ , Li ₂ CoPO ₄ , Li ₂ MnPO ₄ , Li ₂ MnSiO ₄ , and Li ₂ CoPO ₄ F. As another specific positive electrode active material, Li ₂ MnO _3- LiCoO ₂ can be exemplified.

Examples of the binder include fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins and carboxymethyl cellulose. , A known material such as styrene-butadiene rubber may be used.

As the conductive auxiliary agent, the one described for the negative electrode may be adopted.
The blending amount of the binder and the conductive auxiliary agent in the positive electrode active material layer may be appropriately set to an appropriate amount. Further, in order to form the positive electrode active material layer on the surface of the current collector foil, a known method may be appropriately and appropriately adopted.

The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass through while preventing a short circuit due to contact between the two electrodes. As the separator, a known one may be adopted, and synthetic resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester and polyacrylonitrile, polysaccharides such as cellulose and amylose, and fibroin , Polyamides, non-woven fabrics and woven fabrics using one or more of natural polymers such as keratin, lignin and suberin and electrically insulating materials such as ceramics. Further, the separator may have a multi-layer structure.

The electrolytic solution contains a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent.

As the non-aqueous solvent, cyclic carbonates, cyclic esters, chain carbonates, chain esters, ethers and the like can be used. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and vinylene carbonate, and examples of the cyclic ester include gamma-butyrolactone, 2-methyl-gamma-butyrolactone, acetyl-gamma-butyrolactone, and gamma-valerolactone. .. Examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, and ethyl methyl carbonate, and examples of the chain ester include propionic acid alkyl ester, malonic acid dialkyl ester, and acetate alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. As the non-aqueous solvent, a compound in which some or all of the chemical structure of the specific solvent is replaced with fluorine may be adopted.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , and LiN (FSO ₂ ) ₂ .

As the electrolytic solution, a lithium salt is added to a non-aqueous solvent such as fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate in an amount of about 0.5 mol / L to 3 mol / L, preferably 1 mol / L to 2.5 mol. An example of a solution dissolved at a concentration of / L can be exemplified.

As the solid electrolyte, one that can be used as the solid electrolyte of the lithium ion secondary battery may be appropriately adopted.

A specific aspect of the method for manufacturing the lithium ion secondary battery of the present invention will be described.
For example, the separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. The electrode body may be of either a laminated type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a laminated body of a positive electrode, a separator and a negative electrode is wound. After connecting the positive electrode current collector foil and the negative electrode current collector foil to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collector lead or the like, an electrolytic solution is added to the electrode body to form a lithium ion secondary battery. Good.

The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical type, a square type, a coin type, and a laminated type can be adopted.

The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from a lithium ion secondary battery for all or part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. In addition to vehicles, devices equipped with lithium-ion secondary batteries include various battery-powered home appliances such as personal computers and mobile communication devices, office devices, and industrial devices. Further, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydraulic power generation and other power storage devices and power smoothing devices for electric power systems, power supply sources for power and / or auxiliary machinery such as ships, aircraft, and aircraft. Power supply sources for spacecraft and / or auxiliary equipment, auxiliary power sources for vehicles that do not use electricity as power sources, power sources for mobile household robots, power sources for system backup, power sources for non-disruptive power supply devices, It may be used as a power storage device that temporarily stores the electric power required for charging in a charging station for an electric vehicle or the like.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. It can be carried out in various forms with modifications, improvements, etc. that can be made by those skilled in the art, without departing from the gist of the present invention.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to these examples.

(Example 1)
17 parts by mass of carbon-coated silicon material as negative electrode active material, 77 parts by mass of graphite as negative electrode active material, polyacrylic acid, amino alcohol having a weight average molecular weight (Mw) of 1.5 million as analyzed by gel permeation chromatography 2- (2-Aminoethoxy) ethanol and an appropriate amount of water were mixed to prepare a slurry-like composition for forming a negative electrode active material layer of Example 1. The melting point of 2- (2-aminoethoxy) ethanol is −76 ° C., and the boiling point is 196 ° C.
In the composition for forming the negative electrode active material layer of Example 1, the mass ratio of polyacrylic acid, which is a raw material of the binder compound, to 2- (2-aminoethoxy) ethanol is 4.2: 1.8, and acrylic acid. The molar ratio of monomer to 2- (2-aminoethoxy) ethanol was 3.4: 1 and the water content was 36% by weight. Further, in the composition for forming the negative electrode active material layer of Example 1, the mass ratio of the negative electrode active material to the raw material of the binder compound was 94: 6.

a) Step As a current collector foil, an electrolytic Cu foil having a thickness of 10 μm was prepared by winding it into a roll.
Formation of a negative electrode active material layer arranged between a roll unwinding portion for carrying out a current collecting foil, a roll winding portion for winding a roll-shaped negative electrode precursor, and a roll unwinding portion and a roll winding portion. An apparatus for producing a negative electrode precursor was prepared, which provided a coating portion for applying the composition for film in a film shape and a drying portion arranged between the coating portion and the roll winding portion.

The current collector foil and the composition for forming the negative electrode active material layer of Example 1 were supplied to the apparatus, and the apparatus was operated to produce the negative electrode precursor of Example 1. Specifically, after applying the composition for forming the negative electrode active material layer of Example 1 to the current collector foil, water is removed to form the negative electrode active material layer on the surface of the current collector foil. Negative electrode precursor was produced. The drying temperature in the drying portion was set to 105 ° C. under the temperature rising condition that the temperature was gradually increased from the beginning of drying to the end of drying.
No warpage occurred in the negative electrode precursor of Example 1.
The negative electrode precursor of Example 1 was pressed to increase the density of the negative electrode active material layer and subjected to step b).

b) Step It is arranged between the roll unwinding portion for carrying out the roll-shaped negative electrode precursor, the roll winding portion for winding the roll-shaped negative electrode, and the roll unwinding portion and the roll winding portion. An apparatus including an irradiation unit for irradiating light having a wavelength of 6 μm was prepared. In the apparatus, the process of irradiating the negative electrode precursor with light was set to a nitrogen gas atmosphere.
The output of light having a wavelength of 6 μm was set so that the ambient temperature of the irradiated portion was 230 ° C. Further, the roll winding speed was set so that the time for irradiating an arbitrary portion of the negative electrode precursor with light was 3 minutes.
The negative electrode precursor of Example 1 was placed in the above-mentioned apparatus, and the above-mentioned apparatus was operated under the above conditions to manufacture the negative electrode of Example 1.
The thickness of the negative electrode active material layer formed on one surface of the current collecting foil in the negative electrode of Example 1 was 70 μm. The mass (hereinafter referred to as the basis weight) of the negative electrode active material layer formed in an area of 1 square centimeter on one surface of the current collecting foil in the negative electrode of Example 1 was 10 mg / cm ² .

<Manufacturing of lithium-ion secondary batteries>
The negative electrode of Example 1 was cut into a circle having a diameter of 11 mm and used as an evaluation electrode. A metal lithium foil having a thickness of 500 μm was cut into a circle having a diameter of 13 mm to form a counter electrode. As a separator, a glass filter (Hoechst Celanese) and a single-layer polypropylene celgard 2400 (Polypore Co., Ltd.) were prepared. Further, an electrolytic solution prepared by dissolving LiPF ₆ at 1 mol / L in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1. Two types of separators were sandwiched between the counter electrode and the evaluation electrode in the order of the counter electrode, the glass filter, the celgard 2400, and the evaluation electrode to form an electrode body. This electrode body was housed in a coin-type battery case CR2032 (Hosen Co., Ltd.), and an electrolytic solution was further injected to obtain a coin-type battery. This was used as the lithium ion secondary battery of Example 1.

(Example 2)
The negative electrode active material of Example 2 is carried out in the same manner as in Example 1 except that 1-amino-2-propanol is used as the amino alcohol instead of 2- (2-aminoethoxy) ethanol as the amino alcohol. A layer-forming composition, a negative electrode precursor, a negative electrode, and a lithium ion secondary battery were produced.
No warpage occurred in the negative electrode precursor of Example 2.
The melting point of 1-amino-2-propanol is -2 ° C, and the boiling point is 160 ° C.
In the composition for forming the negative electrode active material layer of Example 2, the mass ratio of polyacrylic acid to 1-amino-2-propanol, which is a raw material of the binder compound, is 4.2: 1.8, and the acrylic acid monomer and the acrylic acid monomer. The molar ratio of 1-amino-2-propanol was 2.4: 1. Further, in the composition for forming the negative electrode active material layer of Example 2, the mass ratio of the negative electrode active material to the raw material of the binder compound was 94: 6.

(Example 3)
The negative electrode active material layer of Example 3 is carried out in the same manner as in Example 1 except that 1,3-propanediol as a polyol is used instead of 2- (2-aminoethoxy) ethanol as an amino alcohol. A composition for forming, a negative electrode precursor, a negative electrode, and a lithium ion secondary battery were manufactured.
No warpage occurred in the negative electrode precursor of Example 3.
The melting point of 1,3-propanediol is −27 ° C. and the boiling point is 214 ° C.
In the composition for forming the negative electrode active material layer of Example 3, the mass ratio of polyacrylic acid, which is a raw material of the binder compound, and 1,3-propanediol is 4.2: 1.8, and the acrylic acid monomer and 1 , 3-Propanediol had a molar ratio of 2.5: 1. Further, in the composition for forming the negative electrode active material layer of Example 3, the mass ratio of the negative electrode active material to the raw material of the binder compound was 94: 6.

(Example 4)
Examples except that the mass ratio of polyacrylic acid to 1,3-propanediol was 4.6: 1.4 and the molar ratio of acrylic acid monomer to 1,3-propanediol was 3.5: 1. The composition for forming the negative electrode active material layer, the negative electrode precursor, the negative electrode, and the lithium ion secondary battery of Example 4 were produced in the same manner as in 3.
No warpage occurred in the negative electrode precursor of Example 4.

(Example 5)
Same as in Example 3 except that the mass ratio of polyacrylic acid to 1,3-propanediol was 5: 1 and the molar ratio of acrylic acid monomer to 1,3-propanediol was 5.3: 1. By the method, the composition for forming the negative electrode active material layer, the negative electrode precursor, the negative electrode, and the lithium ion secondary battery of Example 5 were produced.
No warpage occurred in the negative electrode precursor of Example 5.

(Example 6)
The negative electrode active material layer of Example 6 is carried out in the same manner as in Example 1 except that 1,2-butanediol as a polyol is used instead of 2- (2-aminoethoxy) ethanol as an amino alcohol. A composition for forming, a negative electrode precursor, a negative electrode, and a lithium ion secondary battery were manufactured.
No warpage occurred in the negative electrode precursor of Example 6.
The melting point of 1,2-butanediol is -114 ° C, and the boiling point is 193 ° C.
In the composition for forming the negative electrode active material layer of Example 6, the mass ratio of polyacrylic acid and 1,2-butanediol, which are the raw materials of the binder compound, is 4.2: 1.8, and the acrylic acid monomer and 1 , 2-Butanediol had a molar ratio of 2.9: 1. Further, in the composition for forming the negative electrode active material layer of Example 6, the mass ratio of the negative electrode active material to the raw material of the binder compound was 94: 6.

(Comparative Example 1)
The composition for forming a negative electrode active material layer of Comparative Example 1 in the same manner as in Example 1 except that 2- (2-aminoethoxy) ethanol was not used and polyacrylic acid was used in 6 parts by mass. Negative electrode precursors, negative electrodes and lithium ion secondary batteries were manufactured.
The negative electrode precursor of Comparative Example 1 had a warp in which the coated surface became concave.

(Comparative Example 2)
The negative electrode active material layer of Comparative Example 2 was formed in the same manner as in Comparative Example 1 except that N-methyl-2-pyrrolidone was added in an amount of 2% by mass with respect to the composition for forming the negative electrode active material layer. A composition for use, a negative electrode precursor, a negative electrode, and a lithium ion secondary battery were manufactured.
No warpage occurred in the negative electrode precursor of Comparative Example 2.
The melting point of N-methyl-2-pyrrolidone is −24 ° C., and the boiling point is 202 ° C.

(Comparative Example 3)
The negative electrode active material layer of Comparative Example 3 was used in the same manner as in Example 1 except that 1,5-diaminopentane, which is a diamine, was used instead of 2- (2-aminoethoxy) ethanol as the amino alcohol. A composition for forming, a negative electrode precursor, a negative electrode, and a lithium ion secondary battery were manufactured.
The negative electrode precursor of Comparative Example 3 was warped so that the coated surface became concave.
The melting point of 1,5-diaminopentane is 9 ° C., and the boiling point is 179 ° C.
In the composition for forming the negative electrode active material layer of Comparative Example 3, the mass ratio of polyacrylic acid and 1,5-diaminopentane, which are the raw materials of the binder compound, was 4.2: 1.8, and the acrylic acid monomer and 1 , 5-Diaminopentane had a molar ratio of 3.3: 1. Further, in the composition for forming the negative electrode active material layer of Comparative Example 3, the mass ratio of the negative electrode active material to the raw material of the binder compound was 94: 6.

An increase in viscosity with time was observed in the composition for forming the negative electrode active material layer of Comparative Example 3, and finally the composition for forming the negative electrode active material layer of Comparative Example 3 was gelled.

(Comparative Example 4)
The negative electrode of Comparative Example 4 was used in the same manner as in Example 1 except that the diamine diethylene glycol bis (3-aminopropyl) ether was used instead of 2- (2-aminoethoxy) ethanol as the amino alcohol. A composition for forming an active material layer, a negative electrode precursor, a negative electrode, and a lithium ion secondary battery were manufactured.
No warpage occurred in the negative electrode precursor of Comparative Example 4.
The melting point of diethylene glycol bis (3-aminopropyl) ether is −32 ° C., and the boiling point is 146 ° C.
In the composition for forming the negative electrode active material layer of Comparative Example 4, the mass ratio of polyacrylic acid, which is a raw material of the binder compound, to diethylene glycol bis (3-aminopropyl) ether is 4.2: 1.8, and acrylic acid. The molar ratio of monomer to diethylene glycol bis (3-aminopropyl) ether was 7.1: 1. Further, in the composition for forming the negative electrode active material layer of Comparative Example 4, the mass ratio of the negative electrode active material to the raw material of the binder compound was 94: 6.

An increase in viscosity with time was observed in the composition for forming the negative electrode active material layer of Comparative Example 4, and finally the composition for forming the negative electrode active material layer of Comparative Example 4 was gelled.

(Comparative Example 5)
The negative electrode of Comparative Example 5 was used in the same manner as in Example 1 except that isopropanol, which is a monoalcohol containing only one hydroxyl group, was used instead of 2- (2-aminoethoxy) ethanol as the amino alcohol. A composition for forming an active material layer, a negative electrode precursor, a negative electrode, and a lithium ion secondary battery were manufactured.
The negative electrode precursor of Comparative Example 5 was warped so that the coated surface became concave.
The melting point of isopropanol is −89 ° C., and the boiling point is 82 ° C.
In the composition for forming the negative electrode active material layer of Comparative Example 5, the mass ratio of polyacrylic acid to isopropanol was 4.2: 1.8, and the molar ratio of acrylic acid monomer to isopropanol was 1.9: 1. ..

(Comparative Example 6)
In the same manner as in Example 1, except that isobutylamine, which is a monoamine containing only one amino group and not containing a hydroxyl group, was used instead of 2- (2-aminoethoxy) ethanol as the amino alcohol. A composition for forming a negative electrode active material layer, a negative electrode precursor, a negative electrode, and a lithium ion secondary battery of Comparative Example 6 were produced.
The negative electrode precursor of Comparative Example 6 was warped so that the coated surface became concave.
The melting point of isobutylamine is −83 ° C., and the boiling point is 66 ° C.
In the composition for forming the negative electrode active material layer of Comparative Example 6, the mass ratio of polyacrylic acid to isobutylamine was 4.2: 1.8, and the molar ratio of acrylic acid monomer to isobutylamine was 2.4: 1. there were.

(Evaluation example 1)
For the negative electrode precursors of Examples 1 to 6 and the negative electrode precursors of Comparative Examples 1 to 6, a cylindrical mandrel bending tester defined by JIS-K5600-5-1 (mandrel diameter is 10 to 90 mm). Was used to evaluate the flexibility. As a specific procedure, the flexibility was evaluated in the order of mandrel diameter 90 mm → mandrel diameter 60 mm → mandrel diameter 32 mm → mandrel diameter 20 mm → mandrel diameter 10 mm, and the evaluation was completed when the negative electrode precursor cracked.

The above results are shown in Table 1.
The additives in Table 1 mean additives other than polyacrylic acid, the negative electrode active material, and water in the composition for forming the negative electrode active material layer. The molar ratio in Table 1 is the molar ratio of acrylic acid monomer to aminoalcohol, polyol, diamine, monoalcohol or monoamine. In the row of mandrel in Table 1, x indicates that cracks occurred in the evaluation of the mandrel diameter of 90 mm, and each numerical value is the minimum mandrel diameter in which cracks did not occur.

From Table 1, it can be said that the negative electrode precursors of Examples 1 to 6 using polyols or amino alcohols are excellent in flexibility.

On the other hand, it can be seen that the negative electrode precursors of Comparative Example 1, Comparative Example 3, Comparative Example 5 and Comparative Example 6 in which the polyol or amino alcohol was not used are inferior in flexibility.
Considering Comparative Example 3, both that the composition for forming the negative electrode active material layer of Comparative Example 3 was gelled and that the negative electrode precursor of Comparative Example 3 was warped so that the coated surface became concave. In view, it can be seen that the cross-linking reaction of the polyacrylic acid chain with 1,5-diaminopentane partially proceeded near the surface of the negative electrode precursor of Comparative Example 3. As a result, it is considered that the negative electrode precursor of Comparative Example 3 was inferior in flexibility.
In the negative electrode precursors of Comparative Examples 5 and 6, the added isopropanol and isobutylamine have a lower boiling point than water, so that isopropanol and isobutylamine were also removed when water was removed in step a). Conceivable.

It is considered that the reason why the negative electrode precursor of Comparative Example 2 was excellent in flexibility is that N-methyl-2-pyrrolidone remained inside the negative electrode precursor of Comparative Example 2.
Further, the negative electrode precursor of Comparative Example 4 showed a certain degree of flexibility in the (CH ₂ CH ₂ CH ₂ ) unit and (CH ₂ CH ₂ O) which are flexible to diethylene glycol bis (3-aminopropyl) ether. Since there are a plurality of units, it is presumed that the flexibility of the negative electrode precursor was maintained even if the cross-linking reaction of the polyacrylic acid chain with diethylene glycol bis (3-aminopropyl) ether proceeded partially.

(Evaluation example 2)
The lithium ion secondary batteries of Examples 1 to 6 and the lithium ion secondary batteries of Comparative Examples 1 to 6 are charged to 0.01 V at 0.05 C and then discharged to 1 V for the first charge and discharge. went.
Further, following the initial charge / discharge, the charge / discharge cycle of charging to 0.01 V at 0.15 C and then discharging to 1 V was repeated 19 times.

The initial efficiency and capacity retention rate were calculated according to the following formulas. The results are shown in Table 2.
Initial efficiency (%) = 100 x (initial discharge capacity) / (initial charge capacity)
Capacity retention rate (%) = 100 x (discharge capacity at the final cycle) / (initial discharge capacity)

From Table 2, it can be said that the lithium ion secondary battery provided with the binder of the present invention is excellent in both initial efficiency and capacity retention rate. From the results of Examples 3 to 5, it can be said that the molar ratio of the acrylic acid monomer to the aminoalcohol or polyol is preferably high to some extent.
From the results of Evaluation Example 1 and Evaluation Example 2, a negative electrode is manufactured by using a composition for forming a negative electrode active material layer containing polyacrylic acid, water, a polyol and / or an amino alcohol, and a negative electrode active material. It can be said that it is possible to manufacture a negative electrode having excellent performance while reducing the problems in the above.

(Evaluation example 3)
An aqueous solution of polyacrylic acid was added dropwise to a petri dish in an argon-substituted glove box and dried to obtain Sample 1. Similarly, an aqueous solution prepared by dissolving polyacrylic acid and 2- (2-aminoethoxy) ethanol at a mass ratio of 70:30 was added dropwise to a petri dish and dried to obtain Sample 2. Similarly, an aqueous solution prepared by dissolving polyacrylic acid and 1,3-propanediol at a mass ratio of 70:30 was added dropwise to a petri dish and dried to obtain Sample 3.
Samples 1 and 2 were analyzed with an infrared spectrophotometer after heating at 50 ° C. and after heating at 230 ° C. Sample 3 was analyzed with an infrared spectrophotometer after heating at 80 ° C. and after heating at 230 ° C.

The infrared absorption spectrum of Sample 1 after heating at 50 ° C. is shown in FIG. 1, the infrared absorption spectrum of Sample 1 after heating at 230 ° C. is shown in FIG. 2, and the overlay of both spectra is shown in FIG. ..
From the results for Sample 1, it can be seen that in polyacrylic acid, the carboxyl groups are dehydrated and condensed between 50 ° C. and 230 ° C. to form an acid anhydride structure.

The infrared absorption spectrum of the sample 2 after heating at 50 ° C. is shown in FIG. 4, the infrared absorption spectrum of the sample 2 after heating at 230 ° C. is shown in FIG. 5, and the overlay of both spectra is shown in FIG. ..
A peak derived from the carboxyl group can be clearly confirmed in the infrared absorption spectrum at 50 ° C. In the infrared absorption spectrum at 230 ° C., a peak derived from the ester structure and a peak derived from the amide structure and / or the imide structure can be clearly confirmed.
From the results for Sample 2, the condensation reaction between polyacrylic acid and 2- (2-aminoethoxy) ethanol did not proceed sufficiently at 50 ° C, and 2- (2-aminoethoxy) ethanol was used at 230 ° C. It can be seen that the cross-linking of the polyacrylic acid chain is completed.

The infrared absorption spectrum of Sample 3 after heating at 80 ° C. is shown in FIG. 7, the infrared absorption spectrum of Sample 3 after heating at 230 ° C. is shown in FIG. 8, and the overlay of both spectra is shown in FIG. ..
A peak derived from the carboxyl group can be clearly confirmed in the infrared absorption spectrum at 80 ° C. In the infrared absorption spectrum at 230 ° C., a peak derived from the ester structure can be clearly confirmed.
From the results for Sample 3, the condensation reaction between polyacrylic acid and 1,3-propanediol did not proceed sufficiently at 80 ° C., and the cross-linking of the polyacrylic acid chain with 1,3-propanediol at 230 ° C. You can see that is completed.

(Evaluation example 4)
An aqueous solution in which polyacrylic acid and 2- (2-aminoethoxy) ethanol were dissolved at a mass ratio of 70:30 was produced in an argon-substituted glove box.

CaF ₂ was pulverized in a mortar and pressure-molded to a diameter of 10 mm to obtain CaF ₂ pellets. The above aqueous solution was dropped onto CaF ₂ pellets in an argon-substituted glove box, dried in the glove box, and then subjected to analysis with a thermal scanning-infrared spectrophotometer.
The measurement conditions are as shown in the next paragraph.
The absorbance of the infrared absorption spectrum of the sample was calculated using the infrared absorption spectrum of the CaF ₂ pellet obtained in the same procedure as a control.

<Device used> Fourier transform infrared spectrophotometer Avatar360 (manufactured by Nicolet) Multimode cell (manufactured by ST Japan)
<Measurement conditions> Under helium circulation, resolution: 4 cm ^-1 , total number of times: 512, wave number range: 4000-400 cm ^-1 (detector: MCT), window material: KBr (infrared transmission lower limit: 450 cm ^-1) ), Measurement temperature: Room temperature (30 ° C), 100 ° C, 150 ° C, 180 ° C, 200 ° C, 200 ° C after 2 hours, 260 ° C
The heating program is as described in FIG.

After 2 hours at the measurement temperatures of 30 ° C., 100 ° C., 150 ° C., 180 ° C. and 180 ° C., the infrared absorption spectra at 230 ° C. and 260 ° C. are overwritten and shown in FIG. 11, and the enlarged spectrum thereof is shown in FIG. ..
From FIGS. 11 and 12, it can be seen that at 180 ° C., the intensity of the peaks derived from the amide structure and / or the imide structure and the ester structure near 1700 cm ^-1 is significantly increased. That is, it can be said that the cross-linking reaction of the polyacrylic acid chain with 2- (2-aminoethoxy) ethanol proceeds at 180 ° C. or higher.

Claims (11)

A binder characterized by containing a compound formed by condensing polyacrylic acid with a polyol and / or an amino alcohol. The binder according to claim 1, wherein the polyol and the amino alcohol are water-soluble and have a boiling point higher than that of water. The binder according to claim 1 or 2, wherein the polyol and the amino alcohol are liquid at 25 ° C. The binder according to any one of claims 1 to 3, wherein the polyol is represented by the following general formula (1).
General formula (1) H- (OR) _n- OH
In the general formula (1), R is an independently divalent organic group, and n is an integer of 1 or more. The binder according to any one of claims 1 to 4, wherein the amino alcohol is represented by the following general formula (2).
General formula (2) H- (OR) _n- NH ₂
In the general formula (2), R is an independently divalent organic group, and n is an integer of 1 or more. An electrode containing the binder according to any one of claims 1 to 5. A power storage device including the electrode according to claim 6. The method for manufacturing an electrode according to claim 6.
a) The composition for forming an electrode active material layer containing the polyacrylic acid, water, the polyol and / or amino alcohol, and the electrode active material is applied to the current collecting foil, and then the water is removed. , The process of manufacturing electrode precursors,
b) A step of heat-treating the electrode precursor,
A method for manufacturing an electrode, which comprises. In step a) above
The roll unwinding part for carrying out the current collector foil and
A roll winding portion on which the roll-shaped electrode precursor is wound, and a roll winding portion.
A coating portion for applying the electrode active material layer forming composition in a film form, which is arranged between the roll unwinding portion and the roll winding portion,
The method for manufacturing an electrode according to claim 8, wherein an electrode precursor manufacturing apparatus including a drying portion arranged between the coating portion and the roll winding portion is used. A step of manufacturing an electrode by the manufacturing method according to claim 8 or 9.
A method for manufacturing a power storage device having the above. A composition for forming an electrode active material layer containing polyacrylic acid, water, a polyol and / or an amino alcohol, and an electrode active material.