WO2020031595A1

WO2020031595A1 - Method for producing negative electrode

Info

Publication number: WO2020031595A1
Application number: PCT/JP2019/027251
Authority: WO
Inventors: 剛司近藤; 智之田崎; 圭吾小▲柳▼津
Original assignee: 株式会社豊田自動織機
Priority date: 2018-08-10
Filing date: 2019-07-10
Publication date: 2020-02-13
Also published as: JP2020027746A

Abstract

According to the present invention, a step for producing a negative electrode is shortened by using a compound obtained by condensation of poly(acrylic acid) and a polyfunctional amine. This method for producing a negative electrode containing a compound obtained by condensation of poly(acrylic acid) and a polyfunctional amine represented by general formula (1) is characterized by: including a) a step for causing a radical polymerization initiator to act in a solution obtained by dissolving acrylic acid in an organic solvent, thereby synthesizing poly(acrylic acid), b) a step for mixing the poly(acrylic acid) and the polyfunctional amine represented by general formula (1) in the organic solvent so as to produce a mixed solution, c) a step for mixing the mixed solution with a negative electrode active substance so as to produce a composition for forming a negative electrode active substance layer, d) a step for coating the composition for forming a negative electrode active substance layer on a current collector so as to produce a negative electrode precursor, and e) a step for heating the negative electrode precursor so as to promote a condensation reaction between the poly(acrylic acid) and the polyfunctional amine represented by general formula (1); and step a) and step b) being carried out in the same reaction vessel.

Description

Manufacturing method of negative electrode

The present invention relates to a method for manufacturing a negative electrode used for a power storage device such as a secondary battery.

Generally, a power storage device such as a secondary battery includes a positive electrode, a negative electrode, and an electrolyte as main components. The negative electrode includes a current collector and a negative electrode active material involved in charge and discharge. The industry has been demanding an increase in the capacity of a power storage device, and various technologies are being studied to meet the demand. As one of the specific techniques, there is known a technique in which a Si-containing negative electrode active material containing Si having a high ability to absorb a charge carrier such as lithium is used as a negative electrode active material of a power storage device.

It is known that the Si-containing negative electrode active material expands and contracts during charge and discharge. Therefore, in a negative electrode including the Si-containing negative electrode active material, it is necessary to employ a binder suitable for the Si-containing negative electrode active material. It is preferable.

Patent Document 1 describes that a compound obtained by condensation of polyacrylic acid and a polyfunctional amine is excellent as a binder for a negative electrode having a Si-containing negative electrode active material. In this document, a lithium ion secondary battery using a compound obtained by condensation of polyacrylic acid and 4,4′-diaminodiphenylmethane as a negative electrode binder uses polyamideimide as a negative electrode binder. It is described that the battery characteristics were better than the lithium ion secondary battery, together with specific test results.

Patent Document 1 specifically describes that a negative electrode containing a compound obtained by condensation of polyacrylic acid and a polyfunctional amine was obtained by the following production method (see Example 1). .).

Producing a polyacrylic acid solution in which polyacrylic acid is dissolved in N-methyl-2-pyrrolidone ↓
Producing a polyfunctional amine solution in which a polyfunctional amine is dissolved in N-methyl-2-pyrrolidone ↓
The polyacrylic acid solution and the polyfunctional amine solution are mixed to produce an N-methyl-2-pyrrolidone solution of the intermediate composition containing polyacrylic acid and the polyfunctional amine at 130 ° C. ↓
Using the N-methyl-2-pyrrolidone solution of the intermediate composition to produce a slurry-like negative electrode active material layer forming composition ↓
Apply the composition for forming a negative electrode active material layer to the negative electrode current collector and remove N-methyl-2-pyrrolidone ↓
By performing a heat treatment at 160 ° C. for 3 hours, the intermediate composition is subjected to a condensation reaction to form a polymer having a crosslinked structure, thereby producing a negative electrode.

ポリ In addition, polyacrylic acid is generally produced by radical polymerization of an acrylic acid monomer in an aqueous solution. In fact, Patent Documents 2 to 5 specifically describe a method for producing polyacrylic acid by radical polymerization of an acrylic acid monomer in an aqueous solvent.

International Publication No. WO 2016/063882 JP-A-64-38403 JP-A-5-86125 JP-A-11-315115 JP 2004-210878 A

とおり As described above, since polyacrylic acid is generally produced by radical polymerization of an acrylic acid monomer in an aqueous solvent, polyacrylic acid is produced as a solution in an aqueous solvent.

On the other hand, in the case of producing a compound obtained by condensing polyacrylic acid and a polyfunctional amine described in Patent Document 1, the polyfunctional amine is hardly soluble in water. N-methyl-2-pyrrolidone, which is an organic solvent, is employed as a dissolution solvent. Therefore, when producing a compound obtained by condensation of polyacrylic acid and a polyfunctional amine described in Patent Document 1, water is removed from an aqueous solution of polyacrylic acid using water as a solvent to dry the polyacrylic acid. Then, it was necessary to dissolve the polyacrylic acid in N-methyl-2-pyrrolidone.

て However, from the viewpoint of work efficiency and cost, it is preferable that the manufacturing process is short.

The present invention has been made in view of such circumstances, and has as its object to shorten the process of manufacturing a negative electrode using a compound obtained by condensation of polyacrylic acid and a polyfunctional amine.

The present inventor recalled that instead of producing polyacrylic acid by radical polymerization of an acrylic acid monomer in an aqueous solvent, polyacrylic acid was produced by radical polymerization of an acrylic acid monomer in an organic solvent. Furthermore, the present inventor has recalled that the step of producing polyacrylic acid and the step of mixing polyacrylic acid and polyfunctional amine are performed in One-Pot.
And, actually, when acrylic acid monomer was radically polymerized in an organic solvent to produce polyacrylic acid, the modification of the chemical structure was suppressed compared to the production method in which acrylic acid monomer was radically polymerized in an aqueous solvent. And so on.
Based on such knowledge, the present inventors have completed the present invention.

The method for producing a binder for a negative electrode of the present invention includes:
a) reacting a radical polymerization initiator in a solution of acrylic acid in an organic solvent to synthesize polyacrylic acid;
b) mixing the polyacrylic acid and a polyfunctional amine of the following general formula (1) in the organic solvent to produce a mixed solution,
The step a) and the step b) are performed in the same reaction vessel.

Y is a linear alkyl group having 1 to 4 carbon atoms, a phenylene group, or an oxygen atom, and R ¹ and R ² are each independently a single or plural hydrogen atoms, a methyl group, an ethyl group, a trifluoromethyl Or a methoxy group.

The method for producing a negative electrode of the present invention is a method for producing a negative electrode containing polyacrylic acid and a compound obtained by condensation of a polyfunctional amine of the following general formula (1),
a) reacting a radical polymerization initiator in a solution of acrylic acid in an organic solvent to synthesize polyacrylic acid;
b) mixing the polyacrylic acid and a polyfunctional amine of the following general formula (1) in the organic solvent to produce a mixed solution;
c) mixing the mixed solution and a negative electrode active material to produce a negative electrode active material layer forming composition;
d) a step of applying the composition for forming a negative electrode active material layer to a current collector to produce a negative electrode precursor;
e) heating the negative electrode precursor to advance a condensation reaction between the polyacrylic acid and the polyfunctional amine of the following general formula (1),
The step a) and the step b) are performed in the same reaction vessel.

Since the method for producing a binder for a negative electrode of the present invention and the method for producing a negative electrode of the present invention can synthesize polyacrylic acid in which the modification of the chemical structure is suppressed, the production process can be shortened, It is possible to provide a negative electrode binder and a negative electrode which are excellent in quality and cost.

1 is a ¹ H-NMR chart of polyacrylic acid produced in step a) of Example 1. 1 is a ¹ H-NMR chart of a commercially available polyacrylic acid used in Comparative Example 1. 14 is an infrared absorption spectrum at 30 ° C. in Reference Evaluation Example 6. 14 is an infrared absorption spectrum at 250 ° C. in Reference Evaluation Example 6.

Hereinafter, embodiments for carrying out the present invention will be described. Unless otherwise specified, the numerical range “ab” described in this specification includes the lower limit a and the upper limit b. A numerical range can be formed by arbitrarily combining these upper and lower limits and the numerical values listed in the examples. Further, numerical values arbitrarily selected from within these numerical ranges can be set as new upper and lower numerical values.

a) The step will be described.
The step a) is a step of synthesizing polyacrylic acid by allowing a radical polymerization initiator to act in a solution in which acrylic acid is dissolved in an organic solvent.

The organic solvent is not limited as long as acrylic acid, polyacrylic acid and the polyfunctional amine of the general formula (1) can be dissolved therein.

Specific organic solvents include dimethyl sulfoxide, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, dimethylcarbonate, diethylcarbonate, ethylmethylcarbonate, tetrahydrofuran, dichloromethane, methanol, ethanol, propanol, isopropanol, acetone, methylethylketone And methyl isobutyl ketone.

In the step c) of the method for producing a negative electrode of the present invention, since a composition for forming a negative electrode active material layer containing an organic solvent is produced, the organic solvent is widely used as a solvent for the composition for forming a negative electrode active material layer. It is preferable to employ N-methyl-2-pyrrolidone.

配合 The mixing ratio of the organic solvent to acrylic acid is preferably in the range of 1 to 20, more preferably in the range of 1.5 to 10, and even more preferably in the range of 2 to 5 by mass ratio.

The radical polymerization initiator is not limited as long as it is soluble in the organic solvent used in the step a).
Specific examples of the radical polymerization initiator include azobisisobutyronitrile, azobispaleronitrile, 4,4'-azobis (4-cyanovaleric acid), 2,2'-azobis [2-methyl-N- (2-hydroxyethyl) propionamide], 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobisiso Azo compounds such as butyronitrile, 2,2'-azobis (2-methylpropionate), benzoyl peroxide, lauroyl peroxide, methyl ethyl ketone peroxide, di-t-butyl peroxide, dicumyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxypivalate, di-isopropylperoxydi Peroxides such as carbonate, di-t-butylperoxyisophthalate, 1,1 ', 3,3'-tetramethylbutylperoxy-2-ethylhexanoate and t-butylperoxyisobutyrate. be able to.

The molar ratio of the radical polymerization initiator to acrylic acid is preferably in the range of 0.0001 to 0.1, more preferably 0.001 to 0.05, and more preferably 0.003 to 0.01. Within the range is more preferable.

The reaction temperature in step (a) may be a temperature at which the radical polymerization initiator decomposes. For example, ranges of 60 to 90 ° C. and 60 to 80 ° C. can be exemplified. The reaction time in the step a) may be a time when acrylic acid disappears from the reaction solution. For example, 0.5 to 5 hours and 1 to 3 hours can be exemplified.

Step (a) is preferably performed in an inert gas atmosphere. Examples of the inert gas include nitrogen, helium, and argon.

The molecular weight of the polyacrylic acid synthesized in step a) is controlled by appropriately adjusting the compounding ratio of the organic solvent to acrylic acid, the compounding ratio of the radical polymerization initiator to acrylic acid, and the reaction temperature in step a). it can.

The weight average molecular weight of polyacrylic acid is preferably in the range of 5,000 to 1,000,000, more preferably in the range of 10,000 to 500,000, still more preferably in the range of 20,000 to 300,000, and still more preferably in the range of 30,000 to 200,000. Particularly preferred is a range of from 40,000 to 100,000.
The higher the weight average molecular weight of polyacrylic acid, the higher the binding strength, but the higher the viscosity when dissolved in a solvent.

The number average molecular weight of the polyacrylic acid is preferably in the range of 5,000 to 500,000, more preferably in the range of 7,000 to 300,000, further preferably in the range of 9000 to 200,000, and still more preferably in the range of 10,000 to 100,000. It is particularly preferably in the range of 10,000 to 50,000.

Mw / Mn, which is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of polyacrylic acid, is preferably in the range of 1 to 5, more preferably 1 to 4, and more preferably 1 to 3. The range of 5 is more preferable, and the range of 1 to 3 is even more preferable.

Next, the step b) will be described. Step b) is a step of mixing the polyacrylic acid synthesized in step a) with the polyfunctional amine of the general formula (1) in an organic solvent to produce a mixed solution. Steps a) and b) are performed using the same reaction vessel. That is, the steps a and b) are the One-Pot synthesis method. By employing the One-Pot synthesis method, the manufacturing steps are shorter than in the conventional manufacturing method.

The amount of the polyfunctional amine of the general formula (1) to be added to the polyacrylic acid is preferably from 2: 1 to 50: 1, more preferably from 4: 1 as a molar ratio of the acrylic acid monomer and the polyfunctional amine of the general formula (1). ３０30: 1 is more preferable, 7: 1 to 25: 1 is further preferable, and 10: 1 to 20: 1 is particularly preferable.
If the molar ratio of the polyfunctional amine of the general formula (1) to the acrylic acid monomer is too small, it may be difficult to appropriately maintain the capacity of the power storage device. If the molar ratio of the polyfunctional amine of the general formula (1) to the acrylic acid monomer is too large, the binding property may decrease.

The polyfunctional amine represented by the general formula (1) is a polyfunctional amine described in Patent Literature 1, is poorly soluble in water, and soluble in an organic solvent such as N-methyl-2-pyrrolidone. .

In the general formula (1), Y is a linear alkyl group having 1 to 4 carbon atoms, a phenylene group, or an oxygen atom, and R ¹ and R ² are each independently a single or plural hydrogen atoms, a methyl group. , An ethyl group, a trifluoromethyl group, or a methoxy group.

When Y is a linear alkyl group or a phenylene group, a substituent may be bonded to carbon constituting the structure. For example, examples of the substituent bonded to carbon constituting the linear alkyl group include a methyl group, an ethyl group, a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a methoxy group, an ethoxy group, and an oxo group. One of these substituents may be bonded, or two or more of these substituents may be bonded. The number of substituents bonded to one carbon may be one or two. Further, the substituent bonded to the carbon atoms constituting the linear alkyl group and the phenylene group may be an amino group or a substituent containing an amino group.

Specific examples of the polyfunctional amine represented by the general formula (1) include 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, 3,4′-diaminodiphenylmethane, 4,4'-ethylenedianiline, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 2,2'-bis (4-aminophenyl) hexafluoropropane, 4,4'-diaminobenzophenone, 4'-methylenebis (2-ethyl-6-methylaniline), pararoseaniline, 1,3,5-tris (4-aminophenyl) benzene.

Step b) is preferably performed under heating conditions. Heating can promote the formation of a precursor of a compound formed by condensation of polyacrylic acid and the polyfunctional amine of the general formula (1). Examples of the range of the heating temperature include 50 to 150 ° C., 60 to 130 ° C., 70 to 100 ° C., and 80 to 90 ° C.
Here, the precursor of the compound obtained by condensing polyacrylic acid with the polyfunctional amine of the general formula (1) is defined as the carboxyl group of the polyacrylic acid and the amino group of the polyfunctional amine of the general formula (1) are ion-bonded. In this case, a part of the carboxyl group and the amino group may be bonded to form an amide bond.

多 The polyfunctional amine of the general formula (1) may be dissolved in an organic solvent and then added to the polyacrylic acid solution obtained in the step a). Further, the polyfunctional amine of the general formula (1) may be previously dissolved in the organic solvent in the step a) before the synthesis of polyacrylic acid.

好適 Examples of suitable steps a) and b) to which heating conditions are added include the following steps a-1) and b-1), or the following steps a-2) and b-2).

a-1) a step of reacting a radical polymerization initiator in a solution of acrylic acid in an organic solvent to synthesize polyacrylic acid; b-1) adding the polyfunctional amine to the reaction solution after the step a-1); And heating the mixture to produce a mixed solution containing a precursor of a compound obtained by condensing polyacrylic acid and the polyfunctional amine of the general formula (1).

a-2) a step of reacting a radical polymerization initiator in a solution in which acrylic acid and the polyfunctional amine are dissolved in an organic solvent to synthesize polyacrylic acid b-2) a reaction solution after the step a-2) To produce a mixed solution containing a precursor of a compound obtained by condensation of polyacrylic acid and a polyfunctional amine of the general formula (1)

The mixed solution obtained through the step b) is one embodiment of the negative electrode binder of the present invention.

Next, the step c) will be described. Step c) is a step of mixing the mixed solution obtained in step b) and the negative electrode active material to produce a negative electrode active material layer forming composition.

The composition for forming a negative electrode active material layer is produced by mixing constituent components. The composition for forming a negative electrode active material layer may include a conductive additive and other additives.
The amount of the organic solvent is preferably from 20 to 80% by mass, more preferably from 45 to 75% by mass, based on the whole composition for forming a negative electrode active material layer.

Next, the step d) will be described. Step d) is a step of applying the composition for forming a negative electrode active material layer to a current collector to produce a negative electrode precursor.

塗布 Examples of the coating method in the step d) 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.

After the application, a heat drying step or a pressing step of pressing the negative electrode to make the density of the negative electrode active material layer appropriate is performed to remove the organic solvent from the negative electrode active material layer forming composition. May be. The heating and drying step and the pressing step may be performed under normal pressure or may be performed under reduced pressure.

The heating and drying step is preferably performed in a temperature range of 50 to 150 ° C., more preferably performed in a temperature range of 70 to 140 ° C., and further preferably performed in a temperature range of 90 to 130 ° C. preferable. By sufficiently distilling off the organic solvent in the heating and drying step, the time required in the following step e) can be reduced. However, setting the temperature of the heating and drying step to a temperature exceeding 150 ° C. is not preferable. The reason is that the step d) is supposed to be performed in the atmosphere, and the current collector and the like are set to a temperature exceeding 150 ° C. in the heating and drying step performed as a part of the step d). This is because the strength may decrease due to oxidation.

e) The step will be described.
Step e) is a step of heating the negative electrode precursor to cause a condensation reaction between the polyacrylic acid and the polyfunctional amine of the general formula (1) to proceed. In step e), heating may be performed to such an extent that the above-described condensation reaction can proceed. Therefore, the mode of heating in the step e) is not particularly limited, but it is preferable to perform the step e) by irradiating the negative electrode precursor with light having a wavelength of 4 to 8 μm.

The light having a wavelength of 4 to 8 μm is light in a wavelength region where H ₂ O or a functional group having a carbon-oxygen double bond specifically absorbs. The wavelength range of light specifically absorbed by H ₂ O is approximately 5.5 to 7 μm, and the wavelength range of light specifically absorbed by the carbon-oxygen double bond of the carboxyl group is approximately 5.5. Considering that the wavelength is about 7 μm, it can be said that the wavelength of the light irradiated in the step e) is preferably 5.5 to 7 μm.

光 Light having a wavelength of 4 to 8 μm is considered to promote a nucleophilic dehydration reaction caused by an amino group of the polyfunctional amine of the general formula (1) with respect to a carboxyl group of polyacrylic acid. As a result, it is considered that the cross-linking of the polyacrylic acid chain by the polyfunctional amine of the general formula (1) is promoted.

光 Because light having a wavelength of 4 to 8 μm corresponds to infrared light, irradiating the negative electrode precursor with light having a wavelength of 4 to 8 μm necessarily results in a heated state. The degree of output of light having a wavelength of 4 to 8 μm can be determined by the temperature in the step e). It can be said that the higher the output of light having a wavelength of 4 to 8 μm, the higher the temperature in the step e), and that the desired nucleophilic dehydration reaction proceeds rapidly.

The temperature in step e) is preferably from 170 to 250 ° C, more preferably from 180 to 220 ° C, even more preferably from 190 to 210 ° C.
If the temperature in step e) is too low, the desired reaction may not proceed sufficiently. If the temperature in the step e) is too high, the dehydration reaction between carboxyl groups of the polyacrylic acid chain proceeds excessively, that is, the structure of the acid anhydride is excessively generated, so that polyacrylic acid and the general formula (1) The function of the compound obtained by condensation of the polyfunctional amine of (2) as a binder may be reduced. Further, if the temperature in the step e) is excessively high, a compound obtained by condensation of polyacrylic acid and the polyfunctional amine of the general formula (1) may be decomposed.

In a compound obtained by condensation of polyacrylic acid and a polyfunctional amine of the general formula (1), the intensity of the peak derived from the carbonyl of the amide group is determined by the carbonyl of the acid anhydride as measured by infrared spectroscopy. It can be said that those having a higher intensity than the peaks derived therefrom are preferable.
The polyacrylic acid and the polyfunctional amine of the general formula (1) are each soluble in an organic solvent, but the compound obtained by condensation of the polyacrylic acid and the polyfunctional amine of the general formula (1) is a basic compound. Thus, it becomes sparingly soluble in organic solvents.

In the step e), 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. Particularly preferred. For example, when the temperature in step e) is 200 ° C., about 3 minutes is sufficient for the light irradiation time in step e).
If the irradiation time in step e) is too short, the desired reaction may not proceed sufficiently. If the irradiation time in the step e) is too long, energy may be wasted and an undesired side reaction may occur.

In addition, light having a wavelength of 4 to 8 μm can be transmitted as long as the thickness is about the thickness of the negative electrode active material layer. Therefore, polyacrylic acid existing inside the negative electrode active material layer and the polyfunctional amine represented by the general formula (1) can be used. It is considered that light having a wavelength of 4 to 8 μm reaches a compound precursor obtained by condensation, or polyacrylic acid and a polyfunctional amine of the general formula (1). Then, it is considered that a desired reaction can be promoted not only on the surface of the negative electrode active material layer but also on the inside.

Step e) is preferably performed in an inert gas atmosphere to suppress undesired oxidation. Examples of the inert gas include nitrogen, helium, and argon. After the light irradiation, a pressing step of pressing the negative electrode to make the density of the negative electrode active material layer appropriate may be performed.

In the step e), a roll unwinding unit for unloading the roll-shaped negative electrode precursor, a roll winding unit for winding the rolled negative electrode, and a roll unwinding unit and the roll unwinding unit are disposed between the roll unwinding unit and the roll winding unit. It is convenient for mass production of the negative electrode to use a device having an irradiation unit for irradiating light having a wavelength of 4 to 8 μm.
By using the device, the negative electrode can be manufactured under the condition that the manufacturing variation hardly occurs because the flat negative electrode active material layer is present on the flat current collector, and thus the property of the negative electrode after the step e) is uniform. Is done. Further, light irradiation under uniform conditions is easy, and the setting of the light irradiation time is easy, so that the performance variation of the negative electrode hardly occurs. Further, it can be applied to increase of production capacity and labor saving.

Specifically, the negative electrode of the present invention contains a current collector, a compound obtained by condensing polyacrylic acid and a polyfunctional amine of the general formula (1), and a negative electrode active material on the surface of the current collector. A negative electrode active material layer is provided. In the negative electrode of the present invention, a compound obtained by condensation of polyacrylic acid and the polyfunctional amine of the general formula (1) functions as a binder.

(4) The current collector refers to a chemically inert electronic conductor for continuously supplying a current to the electrode during discharging or charging of a secondary battery such as a lithium ion secondary battery. The material of the current collector is not particularly limited as long as the metal can withstand a voltage suitable for the active material to be used. As the material of the current collector, 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 And other metal materials. The current collector may be covered with a known protective layer. A current collector whose surface is treated by a known method may be used as the current collector.

The current collector can be in the form of foil, sheet, film, wire, rod, mesh, and the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of a foil, a sheet or a film, the thickness is preferably in the range of 1 μm to 100 μm.

厚み Examples of the thickness of the negative electrode active material layer include 1 to 200 μm, 5 to 150 μm, and 10 to 100 μm.

The negative electrode active material layer includes a compound obtained by condensing polyacrylic acid and a polyfunctional amine represented by the general formula (1), a negative electrode active material capable of inserting and extracting a charge carrier such as lithium ion, and further, if necessary. And additives such as a conductive aid. The anode active material layer preferably contains the anode active material in an amount of 60 to 95% by mass, more preferably 70 to 90% by mass, based on the mass of the entire anode active material layer. Further, the negative electrode active material layer contains a compound obtained by condensation of polyacrylic acid and the polyfunctional amine of the general formula (1) in an amount of 1 to 20% by mass based on the total mass of the negative electrode active material layer. More preferably, it is contained at 5 to 15% by mass.

As the negative electrode active material, a material capable of inserting and extracting a charge carrier can be used. Therefore, there is no particular limitation as long as it is a simple substance, an alloy or a compound capable of inserting and extracting a charge carrier such as lithium ions. For example, as a negative electrode active material, Li, a group 14 element such as carbon, silicon, germanium and tin; a group 13 element such as aluminum and indium; a group 12 element such as zinc and cadmium; a group 15 element such as antimony and bismuth; And an alkaline earth metal such as calcium, and a group 11 element such as silver and gold may be used alone. Specific examples of alloys or compounds include tin-based materials such as Ag-Sn alloys, Cu-Sn alloys, Co-Sn alloys, carbon-based materials such as various graphites, and SiO _x (which is disproportionated to silicon alone and silicon dioxide). 0.3.ltoreq.x.ltoreq.1.6), a simple substance of silicon, or a composite of a combination of a silicon-based material and a carbon-based material. As the negative electrode active material, an oxide 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 materials can be used as the negative electrode active material.

好ましい In view of the possibility of increasing the capacity, preferable negative electrode active materials include graphite, Si-containing materials, and Sn-containing materials. Also, in view of the preferable properties of a compound obtained by condensation of polyacrylic acid and the polyfunctional amine of the general formula (1) as a binder, a Si-containing negative electrode active material having a large degree of expansion and contraction during charge and discharge is required. Particularly preferred.

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

具体 As a specific example of the Si-containing negative electrode active material, a silicon material (hereinafter, simply referred to as “silicon material”) disclosed in WO 2014/080608 and the like can be given.

The silicon material has a structure in which a plurality of plate-like silicon bodies are stacked 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.

An ideal reaction formula for a method of manufacturing a silicon material using hydrogen chloride as an acid is as follows.
3CaSi ₂ + 6HCl → Si ₆ H ₆ + 3CaCl ₂
Si ₆ H ₆ → 6Si + 3H ₂ ↑

However, in the upper reaction of synthesizing Si ₆ H ₆ as polysilane, water is usually used as a 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 upper reaction, the layered silicon compound is hardly produced as containing only Si ₆ H ₆ , The silicon compound is represented by Si ₆ H _s (OH) _t X _u (X is an element or group derived from an anion of an acid, s + t + u = 6, 0 <s <6, 0 <t <6, 0 <u <6). Manufactured as such. In the above chemical formula, inevitable impurities such as Ca that may remain are not considered. The silicon material obtained by heating the layered silicon compound also contains elements derived from oxygen and anions of acids.

As described above, the silicon material has a structure in which a plurality of plate-like silicon bodies are stacked in the thickness direction. In order to efficiently store and release charge carriers such as lithium ions, the plate-like silicon body preferably has a thickness in the range of 10 nm to 100 nm, more preferably 20 nm to 50 nm. The length in the longitudinal direction of the plate-like silicon body is preferably in the range of 0.1 μm to 50 μm. Further, the plate-like silicon body preferably has a ratio of (length in the longitudinal direction) / (thickness) in the range of 2 to 1,000. The laminated structure of the plate-like silicon body can be confirmed by observation with a scanning electron microscope or the like. This laminated structure is considered to be a remnant of the Si layer in the raw material CaSi ₂ .

The silicon material preferably includes amorphous silicon and / or silicon crystallite. In particular, in the plate-like 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, still more 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 Scherrer's formula using the half-value width of the diffraction peak of the Si (111) plane in the obtained X-ray diffraction chart by performing X-ray diffraction measurement on the silicon material. .

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

The Si-containing negative electrode active material is preferably 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 a powder, which is an aggregate of particles. The average particle diameter of the Si-containing negative electrode active material is preferably in the range of 1 to 30 μm, and more preferably in the range of 2 to 20 μm. The average particle diameter herein means a D ₅₀ in the case of measuring a sample in a conventional laser diffraction particle size distribution analyzer.

Other binders, polyvinylidene fluoride, polytetrafluoroethylene, fluorine-containing resins such as fluororubber, polypropylene, thermoplastic resins such as polyethylene, polyimides, imide-based resins such as polyamideimide, alkoxysilyl group-containing resins, Acrylic resins such as poly (meth) acrylic acid, styrene-butadiene rubber (SBR), and cellulose derivatives such as carboxymethyl cellulose can be exemplified.

The conductive additive is added to increase the conductivity of the negative electrode. Therefore, the conductive assistant 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 additive may be any chemically inert high electron conductor, and examples thereof include carbon black fine particles such as carbon black, graphite, vapor grown carbon fiber (VaporapGrown Carbon Fiber), and various metal particles. You. Examples of the carbon black include acetylene black, Ketjen Black (registered trademark), furnace black, and channel black. These conductive assistants can be added to the negative electrode active material layer alone or in combination of two or more.

配合 The compounding ratio of the conductive assistant in the negative electrode active material layer is preferably 1 to 20% by mass, more preferably 3 to 15% by mass, and still more preferably 5 to 13% by mass. The mass ratio between the negative electrode active material and the conductive additive is preferably from 99: 1 to 85:15, more preferably from 97: 3 to 90:10, even more preferably from 95: 5 to 92: 8, and preferably from 94: 6 to 93: 7 is particularly preferred.

The negative electrode of the present invention can be used as a negative electrode of a 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 a lithium ion secondary battery that is a typical example of the power storage device.

Hereinafter, a lithium ion secondary battery including the negative electrode of the present invention is referred to as a lithium ion secondary battery of the present invention.
One embodiment of the lithium ion secondary battery of the present invention includes the negative electrode, the positive electrode, the separator and the electrolytic solution, or the solid electrolyte of the present invention.
The positive electrode includes a current collector and a positive electrode active material layer formed on a surface of the current collector.

As the current collector of the positive electrode, those described for the negative electrode may be appropriately selected.

(4) When the potential of the positive electrode is set to 4 V or more based on lithium, it is preferable to employ aluminum as the positive electrode current collector.

Specifically, it is preferable to use a collector made of aluminum or an aluminum alloy as the current collector for the positive electrode. Here, aluminum refers to pure aluminum, and aluminum having a purity of 99.0% or more is referred to as pure aluminum. An alloy obtained by adding various elements to pure aluminum is referred to as 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.

Specific examples of aluminum or aluminum alloy include, for example, A1000 series alloys (pure aluminum series) such as JIS A1085 and A1N30, A3000 series alloys (Al-Mn series) such as JIS A3003 and A3004, and JIS A8079, A8021 and the like. A8000 series alloy (Al-Fe series).

The positive electrode active material layer contains a positive electrode active material capable of occluding and releasing charge carriers such as lithium ions, and, if necessary, a binder and a conductive assistant. The positive electrode active material layer preferably contains the positive electrode active material at 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, sc, Sn, in, Y, Bi, S, Si, Na, K, P, at least one element selected from 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 selected from the group consisting of 1.7 ≦ f ≦ 3). Examples thereof include a lithium composite metal oxide and Li ₂ MnO ₃ . 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 (wherein M is selected from at least one of Co, Ni, Mn, and Fe). 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 of the metal oxides used as the positive electrode active material may have the above composition formula as a basic composition, and those obtained by replacing a metal element contained in the basic composition with another metal element can also be used. Further, as the positive electrode active material, a material not containing a charge carrier (for example, lithium ions contributing to charge and discharge) may be used. For example, a simple substance of sulfur, a compound in which sulfur and carbon are combined, a metal sulfide such as TiS ₂ , an oxide such as V ₂ O ₅ and MnO ₂ , a compound containing polyaniline and anthraquinone, and an aromatic compound thereof in a chemical structure, a conjugated compound 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, nitronyl nitroxide, galvinoxyl, and phenoxyl may be employed as the positive electrode active material. When a positive electrode active material containing no 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 in a non-ionic state such as a metal. For example, when the charge carrier is lithium, the charge carrier may be integrated by attaching a lithium foil to the positive electrode and / or the negative electrode.

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 is 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 the group consisting of Rh, Fe, Ge, Zn, Ru, Sc, Sn, In, Y, Bi, S, Si, Na, K, P, and 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 It is preferable to employ a lithium composite metal oxide represented by the following formula: 1.7 ≦ f ≦ 3).

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 satisfying 0 <b <1, 0 <c <1, and 0 <d <1. In addition, at least one of b, c, and d is in the range of 30/100 <b <90/100, 10/100 <c <90/100, and 1/100 <d <50/100. More preferably, it is more preferably in the range of 40/100 <b <90/100, 10/100 <c <50/100, 2/100 <d <30/100, and more preferably 50/100 <b <90/100. More preferably, the ratio is in the range of 10/100 <c <30/100 and 2/100 <d <10/100.

a, e, and f may be numerical values within the range defined by the above general formula, and are preferably 0.5 ≦ a ≦ 1.5, 0 ≦ e <0.2, and 1.8 ≦ f ≦ 2. 0.5, more preferably 0.8 ≦ a ≦ 1.3, 0 ≦ e <0.1, and 1.9 ≦ f ≦ 2.1.

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

Specific positive electrode active material _can be exemplified by _{_{_{LiFePO 4, Li 2 FeSiO 4,}}} LiCoPO 4, Li 2 CoPO 4, Li 2 MnPO 4, Li 2 MnSiO 4, 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 polyvinylidene fluoride, polytetrafluoroethylene, fluorine-containing resins such as fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide-based resins such as polyimide and polyamideimide, resins containing an alkoxysilyl group, and carboxymethylcellulose. A known material such as styrene-butadiene rubber may be used.

As the conductive additive, those described for the negative electrode may be employed.
The amounts of the binder and the conductive additive in the positive electrode active material layer may be appropriately set as appropriate. In addition, in order to form the positive electrode active material layer on the surface of the current collector, a known method may be appropriately used.

(4) The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass therethrough while preventing a short circuit due to contact between the two electrodes. Known separators may be used as the separator, and synthetic resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic @ polyamide), polyester, and polyacrylonitrile; polysaccharides such as cellulose and amylose; and fibroin. , Nonwoven fabrics and woven fabrics using one or more of electrically insulating materials such as ceramics and natural polymers such as keratin, lignin and suberin. Further, the separator may have a multilayer structure.

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

環状 As the non-aqueous solvent, cyclic carbonate, cyclic ester, chain carbonate, chain ester, 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 alkyl propionate, dialkyl malonate, and alkyl acetate. 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 part or all of the hydrogen in the specific chemical structure of the solvent is substituted with fluorine may be used.

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 electrolyte, a lithium salt is added to a non-aqueous solvent such as fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate in an amount of about 0.5 mol / L to 3 mol / L, preferably 1.5 mol / L to 2 mol / L. An example is a solution dissolved at a concentration of 0.5 mol / L.

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

One embodiment of a specific method for manufacturing the lithium ion secondary battery of the present invention will be described.
For example, an electrode body is formed by sandwiching a separator between a positive electrode and a negative electrode. The electrode body may be any of a stacked type in which a positive electrode, a separator, and a negative electrode are stacked, or a wound type in which a stacked body of a positive electrode, a separator, and a negative electrode is wound. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collecting lead or the like, then adding an electrolytic solution to the electrode body to form a lithium ion secondary battery. Good.

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

リチウム 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 a part of its power source, such as 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. Examples of devices equipped with a lithium ion secondary battery include various home electric appliances, office equipment, industrial equipment, and the like, other than vehicles, such as personal computers and portable communication devices, which are driven by batteries. Further, the lithium ion secondary battery of the present invention is a power storage device and a power smoothing device for wind power generation, photovoltaic power generation, hydroelectric power generation and other power systems, power sources for ships and the like and / or power supply sources for auxiliary equipment, aircraft, Power supply for spacecraft and other power supplies and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, The present invention may be applied to a power storage device that temporarily stores electric power required for charging at 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. The present invention can be implemented in various forms with modifications, improvements, and the like 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 more specifically with reference to Examples and Comparative Examples. Note that the present invention is not limited by these examples.

(Example 1)
a) Step In a flask, 159.2 g (2.2 mol) of acrylic acid was dissolved in 486.2 g of N-methyl-2-pyrrolidone to prepare an acrylic acid solution. After replacing the gas in the flask with nitrogen gas, 1.80 g (0.01 mol) of azobisisobutyronitrile as a radical polymerization initiator was added to obtain a reaction solution. The reaction solution under stirring was heated to 60 ° C. and stirred for 3 hours, and then heated to 90 ° C. and stirred for 12 hours to allow a radical polymerization reaction to proceed to synthesize polyacrylic acid.
When the progress of the reaction was monitored, it was confirmed that the radical polymerization reaction was started under the heating condition of 60 ° C., and that acrylic acid was almost consumed within one hour under the heating condition of 60 ° C. Was done.

b) Step 27.4 g (0.14 mol) of 4,4'-diaminodiphenylmethane was dissolved in 190 g of N-methyl-2-pyrrolidone to obtain a polyfunctional amine solution.
a) A polyfunctional amine solution was added to the polyacrylic acid solution obtained in step a) to obtain a mixed solution. The solution of Example 1 containing a precursor of a compound obtained by condensation of polyacrylic acid and a polyfunctional amine was produced by stirring the mixed solution under a heating condition of 110 ° C. for 2 hours. In the solution of Example 1, the molar ratio of acrylic acid monomer to 4,4'-diaminodiphenylmethane corresponds to 16: 1.

c) Step The solution of Example 1 in an amount of 72.5 parts by mass of the carbon-coated silicon material as the Si-containing negative electrode active material, 13.5 parts by mass of acetylene black as the conductive additive, and 14 parts by mass of the solid content as the binder And an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry-like composition for forming a negative electrode active material layer.

d) Process A 30 μm thick electrolytic Cu foil wound into a roll was prepared as a negative electrode current collector.
A roll unwinding unit for unloading the current collector, a roll winding unit on which a rolled negative electrode precursor is wound, and a negative electrode active material layer formed between the roll unwinding unit and the roll winding unit; A coating section for applying the composition for film formation, a drying section disposed between the coating section and the roll winding section, and a press section disposed between the drying section and the roll winding section. An apparatus for producing a negative electrode precursor was prepared.
The current collector for a negative electrode and the composition for forming a negative electrode active material layer were supplied to the device, and a negative electrode precursor was produced in the atmosphere. Note that the drying temperature in the drying section was set to 80 ° C. The thickness of the negative electrode active material layer in the negative electrode precursor was 20 μm.

e) Step: a roll unwinding section for unloading the rolled negative electrode precursor, a roll winding section for winding the rolled negative electrode, and a roll unwinding section and a roll winding section. An irradiation unit for irradiating light having a wavelength of 6 μm was prepared. In this apparatus, the process of irradiating the negative electrode precursor with light was performed under a nitrogen gas atmosphere.
The output of the light having a wavelength of 6 μm was set so that the temperature of the irradiation part was 200 ° C. 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 manufactured by placing the negative electrode precursor obtained in step d) in the above device and operating the above device under the above conditions.

<Manufacture 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 serve as a counter electrode. As a separator, a glass filter (Hoechst Celanese) and celgard 2400 (Polypore), which is a single-layer polypropylene, were prepared. In addition, an electrolyte was prepared by dissolving LiPF ₆ at 1 mol / L in a mixed solvent of ethylene carbonate and diethyl carbonate 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, celgard 2400, and the evaluation electrode to form an electrode body. This electrode body was accommodated 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 designated as a lithium ion secondary battery of Example 1.

(Comparative Example 1)
A commercially available aqueous solution of polyacrylic acid (Toagosei Co., Ltd.) was prepared. The polyacrylic acid is produced in water.
The aqueous solution of polyacrylic acid was dried to remove water. The dried polyacrylic acid was dissolved in N-methyl-2-pyrrolidone to obtain a polyacrylic acid solution.

溶液 A solution, a negative electrode, and a lithium ion secondary battery of Comparative Example 1 were produced in the same manner as in Example 1, except that step b) was performed using the above-mentioned polyacrylic acid solution.

(Evaluation Example 1)
The polyacrylic acid synthesized in the step a) of Example 1 and the commercially available polyacrylic acid used in Comparative Example 1 were respectively analyzed by gel permeation chromatography, and the number average molecular weight (Mn) and the weight average molecular weight were analyzed. (Mw) was measured. Table 1 shows the results.

From the results of Mw / Mn, it can be said that the polyacrylic acid produced in the step a) of Example 1 has a molecular weight distribution closer to monodispersion.

(Evaluation example 2)
Example 1 which is a polyacrylic acid synthesized in the step a) of Example 1, the commercially available polyacrylic acid used in Comparative Example 1, and a mixed solution of polyacrylic acid and 4,4′-diaminodiphenylmethane And the solution of Comparative Example 1 were analyzed by ¹ H-NMR. As a result, it was confirmed that each of the substances had the desired chemical structure.

A ^{1 H-NMR} chart of polyacrylic acid produced in the step a) of Example 1 shown in FIG. 1, a ^{1 H-NMR} chart of a commercially available polyacrylic acid used in Comparative Example 1 in FIG.
1 and 2, it can be seen that the peak intensities detected at 2 to 2.2 ppm and 4 ppm are smaller in FIG. 1 and larger in FIG. Peaks detected at 2 to 2.2 ppm and 4 ppm are peaks derived from polyacrylic acid modification such as crosslinking. Therefore, it can be said that the polyacrylic acid produced in step a) of Example 1 has little modification.

(Evaluation example 3)
For the lithium ion secondary batteries of Example 1 and Comparative Example 1, initial charging / discharging was performed by charging to 0.01 V at 0.05 C and then discharging to 1 V.
After the initial charge / discharge, the charge / discharge cycle of charging to 0.1 V at 0.01 V and discharging to 1 V was repeated 49 times.

As a result, the lithium ion secondary batteries of Example 1 and Comparative Example 1 showed the same charge / discharge curve and the same capacity retention ratio.

(Reference Example 1)
Polyacrylic acid having a weight average molecular weight of 100,000 was dissolved in N-methyl-2-pyrrolidone to prepare a polyacrylic acid solution containing 19% by mass of polyacrylic acid. Also, 4,4'-diaminodiphenylmethane was dissolved in N-methyl-2-pyrrolidone to prepare a 4,4'-diaminodiphenylmethane solution. Under stirring conditions, a 4,4′-diaminodiphenylmethane solution was added dropwise to the polyacrylic acid solution, and the resulting mixture was stirred at room temperature for 30 minutes. Thereafter, using a Dean-Stark apparatus, the mixture was stirred at 130 ° C. for 3 hours to produce a solution of Reference Example 1.
In the solution of Reference Example 1, the molar ratio of acrylic acid monomer to 4,4′-diaminodiphenylmethane corresponds to 16: 1.

c) Step 72.5 parts by mass of the carbon-coated silicon material as the Si-containing negative electrode active material, 13.5 parts by mass of acetylene black as the conductive agent, and the solution of Reference Example 1 having a solid content of 14 parts by mass as the binder And an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry-like composition for forming a negative electrode active material layer.

e) Step: a roll unwinding section for unloading the rolled negative electrode precursor, a roll winding section for winding the rolled negative electrode, and a roll unwinding section and a roll winding section. An irradiation unit for irradiating light having a wavelength of 6 μm was prepared. In this apparatus, the process of irradiating the negative electrode precursor with light was performed under a nitrogen gas atmosphere.
The output of the light having a wavelength of 6 μm was set so that the temperature of the irradiation part was 200 ° C. 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.
d) The negative electrode precursor obtained in the step was placed in the above-mentioned device, and the above-mentioned device was operated under the above conditions, thereby producing the negative electrode of Reference Example 1.

<Manufacture of lithium ion secondary batteries>
The negative electrode of Reference 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 serve as a counter electrode. As a separator, a glass filter (Hoechst Celanese) and celgard 2400 (Polypore), which is a single-layer polypropylene, were prepared. In addition, an electrolyte was prepared by dissolving LiPF ₆ at 1 mol / L in a mixed solvent of ethylene carbonate and diethyl carbonate 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, celgard 2400, and the evaluation electrode to form an electrode body. This electrode body was accommodated 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 designated as a lithium ion secondary battery of Reference Example 1.

(Reference Example 2)
In the step e), the negative electrode and the lithium-ion secondary battery of Reference Example 2 were manufactured in the same manner as in Reference Example 1, except that the output of light having a wavelength of 6 μm was set so that the temperature of the irradiated portion was 180 ° C. did.

(Reference Comparative Example 1)
e) A negative electrode and a lithium ion secondary battery of Reference Comparative Example 1 were manufactured in the same manner as in Reference Example 1, except that the following heating step was performed without performing the step.
Heating process:
The negative electrode precursor wound in a roll was placed in a vacuum heating furnace and heated at 200 ° C. for 2 hours under a reduced pressure atmosphere to produce a negative electrode of Reference Comparative Example 1. Some wrinkles were observed in the negative electrode of Reference Comparative Example 1.

(Reference evaluation example 1)
The negative electrode precursor of Reference Example 1, the negative electrode of Reference Example 1, the negative electrode of Reference Example 2, and the negative electrode of Reference Comparative Example 1 were immersed in chloroform to extract 4,4′-diaminodiphenylmethane. The obtained chloroform solution of 4,4′-diaminodiphenylmethane was analyzed by GC-MS. Table 2 shows the results.

From the results in Table 2, it can be seen that under the heating conditions of Reference Example 1 and Reference Comparative Example 1, the reaction between polyacrylic acid and 4,4′-diaminodiphenylmethane was completed.
From the results of Reference Example 2, it can be said that under the heating conditions of Reference Example 2, a part of the reaction between polyacrylic acid and 4,4′-diaminodiphenylmethane was not completed. If the heating condition is 3 minutes, it can be said that heating at about 200 ° C. is necessary, and if the heating temperature is 180 ° C., the heating time needs to be longer than 3 minutes. I can say.

(Reference evaluation example 2)
The surfaces of the negative electrode precursor in Reference Example 1, the negative electrode in Reference Example 1, and the negative electrode in Reference Comparative Example 1 were analyzed for Si by X-ray photoelectron spectroscopy (XPS).

As a result, in the negative electrode of Reference Example 1, there was almost no change in the intensity of the Si peak on the negative electrode surface as compared with the negative electrode precursor of Reference Example 1. However, in the negative electrode of Reference Comparative Example 1, the intensity of the Si peak on the negative electrode surface was significantly increased as compared with the negative electrode precursor of Reference Example 1.

From the above results, the precursor of the compound obtained by condensation of polyacrylic acid and the polyfunctional amine of the general formula (1) is changed to a compound obtained by condensation of polyacrylic acid and the polyfunctional amine of the general formula (1). At that time, in the negative electrode of Reference Example 1, it can be said that the degree of the Si-containing negative electrode active material being coated with the precursor or the compound hardly changed.
However, in the negative electrode of Reference Comparative Example 1, the degree of coating of the Si-containing negative electrode active material with the compound was significantly reduced, and it can be said that the Si-containing negative electrode active material was exposed. This phenomenon occurs in a compound formed by condensation between polyacrylic acid and a polyfunctional amine represented by the general formula (1). The cross-linking between polyacrylic acid chains due to the progress of a dehydration reaction between carboxyl groups of polyacrylic acid. It is considered that the reaction proceeded excessively and the volume of the compound formed by condensation of polyacrylic acid and the polyfunctional amine of the general formula (1) shrank.

(Reference evaluation example 3)
From the solution of Reference Example 1, N-methyl-2-pyrrolidone was distilled off to produce a film. Using a thermomechanical analyzer (Rigaku TMA8310), the shrinkage of the film under the following

temperature conditions

1 and 2 under a tensile load of 49 mN and a nitrogen gas atmosphere was measured.
Temperature condition 1: The temperature is raised from room temperature to 200 ° C., kept at 200 ° C. for 5 minutes, and cooled to room temperature.
Temperature condition 2: The temperature is raised from room temperature to 200 ° C., kept at 200 ° C. for 1 hour, and cooled to room temperature.

フィルム The shrinkage of the film under temperature condition 1 was about 1%, and the shrinkage of the film under temperature condition 2 was about 2%. From this result, the longer the retention time at high temperature, the more the cross-linking reaction between the polyacrylic acid chains in the compound obtained by condensation between polyacrylic acid and the polyfunctional amine of the general formula (1) progresses, It is suggested that the volume shrinks.

(Reference evaluation example 4)
The temperature of the negative electrode precursor in Reference Example 1 was increased from room temperature to 200 ° C. by EGA-MS in which a temperature raising heater and a mass spectrometer were combined, and the temperature was kept at 200 ° C. for 2 hours to analyze generated gas.

As a result, water that was presumed to be attached water, N-methyl-2-pyrrolidone, and water that was presumed to be derived from the dehydration reaction were detected in this order. Water presumed to be derived from the dehydration reaction was detected by 7 minutes after reaching 200 ° C. When the heating temperature in the step c) is 200 ° C., it can be said that the heating time is 7 minutes or less.

(Reference Evaluation Example 5)
The peel strength of the negative electrode precursor of Reference Example 1, the negative electrode of Reference Example 1, the negative electrode of Reference Example 2, and the negative electrode of Reference Comparative Example 1 was measured using a tensile tester. The test method was based on JIS Z 0237. The test method was described in detail. The negative electrode active material layer side was downwardly attached to the pedestal with an adhesive tape, and the peeling strength was measured by pulling the negative electrode upward in the direction of 90 degrees. Table 3 shows the results of the peel strength together with the heating temperature of each negative electrode.

From Table 3, in the negative electrode of Reference Comparative Example 1 in which heating at a high temperature was performed for a long time, the compound obtained by condensing polyacrylic acid and the polyfunctional amine of the general formula (1) has a capacity as a binder. Can be said to have decreased.
On the other hand, from the results of the negative electrode precursor of Reference Example 1, the negative electrode of Reference Example 1, and the negative electrode of Reference Example 2, polyacrylic acid and the polyfunctional compound of the general formula (1) were obtained regardless of the presence or absence of heating in the step e). A compound obtained by condensation of an amine or a precursor thereof can be said to exhibit a suitable binding force.

(Reference Evaluation Example 6)
CaF ₂ was crushed and pressed to produce CaF ₂ tablets. After the solution of Reference Example 1 was dropped on a CaF ₂ tablet, N-methyl-2-pyrrolidone was distilled off and dried to obtain a sample for measurement. The measurement sample was subjected to a thermal scanning-infrared spectrometer to analyze a change in IR spectrum under heating conditions. The heating conditions were as follows.
30 ° C → Heat up to 180 ° C → Hold at 180 ° C for 2 hours → Heat up to 250 ° C

FIG. 3 shows an infrared absorption spectrum at 30 ° C. In FIG. 3, no peak derived from the carbonyl of the amide group was observed.
FIG. 4 shows an infrared absorption spectrum at 250 ° C. In FIG. 4, a peak derived from the carbonyl of the amide group was strongly observed. Further, although the peak intensity was small, a peak derived from the carbonyl of the acid anhydride was also observed.

推移 The transition of the peak behavior of the infrared absorption spectrum with the transition of the heating conditions is shown below.

The intensity of the peak derived from the amino group decreased with increasing temperature, and after holding at 180 ° C. for 2 hours, the peak derived from the amino group disappeared. In conjunction with the peak behavior derived from the amino group, the intensity of the peak derived from the amide group increased with increasing temperature. Further, the intensity of the peak derived from the imide group also increased with increasing temperature. It can be said that after the amino group and the carboxyl group react to form an amide group, part of the amide group reacts with a nearby carboxyl group to form an imide group.

During holding at 180 ° C for 2 hours, a peak derived from an acid anhydride in which carboxyl groups were dehydrated and condensed began to be observed. The intensity of the peak derived from the acid anhydride increased with increasing temperature up to 250 ° C. Although the intensity of the peak derived from the carboxyl group decreased with increasing temperature, the peak derived from the carboxyl group was observed even at 250 ° C.

Considering the results of Reference Evaluation Example 1 to Reference Evaluation Example 6 in total, in the negative electrode of Reference Comparative Example 1 subjected to heat treatment at 200 ° C. for 2 hours, the carboxyl groups of the polyacrylic acid chain are dehydrated and condensed. It can be said that the peel strength was lowered because a relatively large amount of acid anhydride was produced.
On the other hand, a polyacrylic acid and a compound obtained by condensation of the polyfunctional amine of the general formula (1) or a precursor thereof are treated under light irradiation at 200 ° C. for 4 minutes to 8 μm for about 3 minutes to obtain polyacrylic acid. While the dehydration-condensation reaction between the acid and the polyfunctional amine of the general formula (1) is accelerated, the dehydration-condensation reaction between the carboxyl groups of the polyacrylic acid chain is suppressed, and a binder exhibiting a suitable binding force is obtained. It can be said that.

(Reference Evaluation Example 7)
For the lithium ion secondary batteries of Reference Example 1 and Reference Comparative Example 1, initial charging and discharging were performed by charging to 0.01 V at 0.05 C and then discharging to 1 V.
Further, following the initial charge and discharge, a charge and discharge cycle of charging to 0.1 V at 0.15 C and then discharging to 1 V was repeated 499 times.

The capacity retention was calculated according to the following equation. Table 4 shows the results.
Capacity maintenance rate (%) = 100 × (discharge capacity at last cycle) / (initial discharge capacity)

結果 From the results in Table 4, it can be seen that Reference Example 1, in which the heating time was 3 minutes, exhibited a capacity retention ratio equal to or higher than Reference Comparative Example 1, which was heated in a heating furnace for 2 hours.

Claims

A method for producing a negative electrode comprising a compound obtained by condensation of polyacrylic acid and a polyfunctional amine of the following general formula (1),
a) reacting a radical polymerization initiator in a solution of acrylic acid in an organic solvent to synthesize polyacrylic acid;
b) mixing the polyacrylic acid and the polyfunctional amine of the following general formula (1) in the organic solvent to produce a mixed solution;
c) mixing the mixed solution and a negative electrode active material to produce a negative electrode active material layer forming composition;
d) a step of applying the composition for forming a negative electrode active material layer to a current collector to produce a negative electrode precursor;
e) heating the negative electrode precursor to advance a condensation reaction between the polyacrylic acid and the polyfunctional amine of the following general formula (1),
A method for producing a negative electrode, wherein the steps a) and b) are performed in the same reaction vessel.

Y is a linear alkyl group having 1 to 4 carbon atoms, a phenylene group, or an oxygen atom, and R 1 and R 2 are each independently a single or plural hydrogen atoms, a methyl group, an ethyl group, a trifluoromethyl Or a methoxy group.
2. The production of a negative electrode according to claim 1, wherein the steps a) and b) are the following steps a-1) and b-1) or the following steps a-2) and b-2). Method.
a-1) a step of reacting a radical polymerization initiator in a solution of acrylic acid in an organic solvent to synthesize polyacrylic acid; b-1) adding the polyfunctional amine to the reaction solution after the step a-1); Is added and heated to produce a mixed solution containing the precursor of the compound. A-2) A radical polymerization initiator is allowed to act in a solution in which acrylic acid and the polyfunctional amine are dissolved in an organic solvent, Step b-2) of heating the reaction solution after the step a-2) to produce a mixed solution containing a precursor of the compound
(3) The method for producing a negative electrode according to (1) or (2), wherein the step e) is a step of irradiating the negative electrode precursor with light having a wavelength of 4 to 8 μm.
The step e) includes disposing a roll unwinding unit that unwinds the roll-shaped negative electrode precursor, a roll winding unit that winds the roll-shaped negative electrode, and the roll unwinding unit and the roll winding unit. 4. The method for producing a negative electrode according to claim 3, wherein the method comprises using an apparatus having an irradiation unit for irradiating light having a wavelength of 4 to 8 μm.
a) reacting a radical polymerization initiator in a solution of acrylic acid in an organic solvent to synthesize polyacrylic acid;
b) mixing the polyacrylic acid and a polyfunctional amine of the following general formula (1) in the organic solvent to produce a mixed solution,
A method for producing a negative electrode binder, wherein the steps a) and b) are performed in the same reaction vessel.

Y is a linear alkyl group having 1 to 4 carbon atoms, a phenylene group, or an oxygen atom, and R 1 and R 2 are each independently a single or plural hydrogen atoms, a methyl group, an ethyl group, a trifluoromethyl Or a methoxy group.