JP6645792B2 - Electrode, lithium ion secondary battery, method for manufacturing electrode, and method for manufacturing lithium ion secondary battery - Google Patents

Description

  The present invention relates to an electrode, a lithium ion secondary battery, a method for manufacturing an electrode, and a method for manufacturing a lithium ion secondary battery.

  Generally, a lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte. Hereinafter, the positive electrode and the negative electrode are simply referred to as “electrode”. The electrode is formed by forming an electrode active material layer on a current collector, and the electrode active material layer is made of an electrode material in which an active material, a conductive assistant, and a binder are mixed. Patent Literature 1 describes a negative electrode using a silicon compound. A negative electrode containing a silicon compound as an active material undergoes structural damage such as deterioration and separation of the electrode active material layer due to repeated expansion and contraction associated with charge and discharge. As a result, there is a problem that the charge / discharge characteristics such as the discharge capacity and the capacity retention rate deteriorate.

JP 2014-212977 A

  For a lithium ion secondary battery that is repeatedly charged and discharged, further improvement in the capacity retention rate (cycle characteristics) and improvement in the structural strength of the electrode are required.

  An object of the present invention is to provide an electrode having at least one of excellent capacity retention ratio and strength, a lithium ion secondary battery, a method for manufacturing an electrode, and a method for manufacturing a lithium ion secondary battery.

[1] A current collector, and an electrode active material layer formed on the current collector, wherein the electrode active material layer includes an active material and a binder, and the binder includes a first polymer compound and A second polymer compound having a smaller weight average molecular weight (Mw) than the first polymer compound, and [Mw of the first polymer compound / Mw of the second polymer compound]. An electrode wherein the expressed Mw ratio is between 1.5 and 10.
[2] The electrode according to [1], wherein the Mw ratio is 5 to 10.
[3] The electrode according to the above [1] or [2], wherein the second polymer compound has Mw of 10,000 to 4,000,000.
[4] The electrode according to the above [1] or [2], wherein the second polymer compound has a Mw of 100,000 to 1,000,000.
[5] The content ratio of the first polymer compound is 30 to 80% by mass relative to the total mass of the binder,
The electrode according to any one of the above [1] to [4], wherein the content ratio of the second polymer compound is 20 to 70% by mass.
[6] The electrode according to any one of [1] to [5], wherein the mass ratio of the active material and the binder (active material / binder) is 1 to 10.
[7] The electrode according to any one of [1] to [6], wherein at least one of the first polymer compound and the second polymer compound has a carboxyl group.
[8] The method according to any one of [1] to [7], wherein at least one of the first polymer compound and the second polymer compound is poly (meth) acrylic acid or a salt thereof. electrode.
[9] The electrode according to any one of [1] to [8], wherein the active material includes a carbon material or a metal oxide capable of storing lithium.
[10] The electrode according to the above [9], wherein the active material is silicon oxide.
[11] A lithium ion secondary battery including the electrode according to any one of [1] to [10], a counter electrode, and an electrolyte.
[12] A method for producing an electrode, comprising a step of forming an electrode active material layer by applying an electrode material containing an active material and a binder to a current collector or a base material and drying the applied material.
The binder includes a first polymer compound and a second polymer compound having a smaller weight average molecular weight (Mw) than the first polymer compound,
A method for producing an electrode, wherein an Mw ratio represented by [Mw of the first polymer compound / Mw of the second polymer compound] is 1.5 to 10.
[13] The method for producing an electrode according to the above [12], further comprising a step of obtaining the electrode material by dispersing the active material and the binder in a solvent.
[14] The method for producing an electrode according to the above [12] or [13], wherein the applied electrode material is dried at 30 to 140 ° C.
[15] The above-mentioned [12] to [12], wherein the applied electrode material is dried, and the amount of the solvent contained in the formed electrode active material layer is set to 100 ppm or less based on the total mass of the electrode active material layer. The method for producing an electrode according to any one of [14].
[16] The production of the electrode according to any one of [12] to [15], wherein a mass ratio (active material / binder) of the active material and the binder contained in the electrode material is 1 to 10. Method.
[17] The method for producing an electrode according to any one of [12] to [16], wherein at least one of the first polymer compound and the second polymer compound has a carboxyl group.
[18] The method for producing an electrode according to any one of [12] to [17], wherein the active material includes a carbon material or a metal oxide capable of storing lithium.
[19] The method for producing an electrode according to any one of [12] to [18], wherein the active material is silicon oxide.
[20] The method for producing an electrode according to the above [17], wherein the polymer compound having a carboxyl group has at least a part of the hydrogen atoms of the carboxyl group replaced by lithium ions.
[21] The method for producing an electrode according to the above [20], wherein the polymer compound having a carboxyl group has a substitution rate of the hydrogen atom by a lithium ion of 10 to 50 mol%.
[22] The method according to any one of the above [12] to [21], wherein at least one of the first polymer compound and the second polymer compound is poly (meth) acrylic acid or a salt thereof. Manufacturing method of electrode.
[23] A lithium ion secondary, comprising: a step of obtaining an electrode by the method for producing an electrode according to any one of [12] to [22]; and a step of installing an electrolyte between the electrode and a counter electrode. Battery manufacturing method.

  The present invention can provide an electrode having at least one of excellent capacity retention ratio and strength, and a lithium ion secondary battery including the electrode.

1 is a schematic cross-sectional view illustrating an example of an embodiment of a lithium ion secondary battery of the present invention.

"electrode"
The electrode of the present invention includes a current collector and an electrode active material layer formed on the current collector. The electrode active material layer includes an active material and a binder. The binder includes a first polymer compound and a second polymer compound having a smaller weight average molecular weight (Mw) than the first polymer compound, [Mw / The Mw ratio represented by [Mw of the second polymer compound] is 1.5 to 10.

  When the Mw ratio is 1.5 to 10, preferably 5 to 10, excellent capacity retention and strength can be obtained.

  When the Mw (second Mw) of the second polymer compound is preferably 10,000 to 4,000,000, more preferably 100,000 to 1,000,000, more excellent capacity retention and strength can be obtained.

  The Mw of the two types of polymer compounds contained in the manufactured electrode is measured by gel permeation chromatography (GPC) using a polystyrene standard substance.

  It is preferable that the content ratio of the first polymer compound is 30 to 80% by mass and the content ratio of the second polymer compound is 20 to 70% by mass based on the total mass of the binder constituting the electrode. . With the above configuration, more excellent capacity retention ratio and strength can be obtained.

The mass ratio between the first polymer compound and the second polymer compound constituting the electrode is preferably 9: 1 to 1: 9, more preferably 8: 2 to 2: 8, and 6: 4 to 4: 6 is more preferred.
With the above mass ratio, the capacity retention ratio and strength of the electrode can be further increased.

  When the mass ratio (active material / binder) of the active material and the binder constituting the electrode is 1 to 10, more excellent capacity retention and strength can be obtained.

  It is preferable that at least one of the first polymer compound and the second polymer compound has a carboxyl group. It is preferable that at least one of the first polymer compound and the second polymer compound is poly (meth) acrylic acid or a salt thereof. When the binder contains these high molecular compounds, more excellent capacity retention and strength can be obtained.

The active material preferably contains a carbon material or a metal oxide capable of storing lithium. When the active material is any of these materials, more excellent capacity retention and strength can be obtained.
The active material is preferably silicon oxide. When the active material is silicon oxide, more excellent capacity retention and strength can be obtained.

  Preferred materials for the electrode according to the present invention will be described below together with the method for producing an electrode according to the present invention.

≪Method of manufacturing electrodes≫
The method for manufacturing an electrode according to the present invention is a method for manufacturing an electrode including a step of forming an electrode active material layer by applying an electrode material containing an active material and a binder to a current collector or a base material and then drying the same.

  The electrode may be either a positive electrode or a negative electrode. The electrodes can be used for various electrochemical devices other than lithium ion secondary batteries.

  The active material may be any material that can occlude (absorb) and release the charge transporter contained in the electrolyte. For example, in a lithium ion secondary battery, the active material absorbs (absorbs) and releases lithium ions. Known negative electrode active materials and known positive electrode active materials can be used.

  The binder may be any polymer compound that binds the active materials to each other and can be bonded to a current collector or a base material. For example, the binder is used for a positive electrode or a negative electrode of a lithium ion secondary battery. Binders.

  The electrode material is prepared by dispersing the active material and the binder in a solvent. The type of the solvent is not particularly limited as long as the active material and the binder can be dispersed, and is appropriately selected from known solvents. Examples of the dispersing method include a method in which a known mixer such as a blender or a mixer is used and stirring is performed while the active material and the binder are charged into the solvent. At this time, the active material may be charged first, the binder may be charged first, or the active material and the binder may be charged simultaneously. Alternatively, a dispersion (electrode material) containing the active material and the binder may be obtained by dispersing each of the active material and the binder in a solvent in a separate container and mixing the respective dispersions later.

  In the present invention, a binder containing two types of polymer compounds having different weight average molecular weights (Mw), a first polymer compound and a second polymer compound is used as the binder. Here, the Mw of each polymer compound is a value measured by a known gel filtration chromatography method (GPC method) using a polystyrene standard substance.

  In the present invention, of the two types of polymer compounds, a compound having a relatively large first Mw is referred to as a first polymer compound, and a compound having a relatively small second Mw is referred to as a second polymer compound. It may be called a polymer compound. That is, first Mw> second Mw.

In the present invention, the ratio (first Mw / second Mw) of Mw (first Mw) of the first polymer compound to Mw (second Mw) of the second polymer compound is 1. 5-10, preferably 5-10.
When the ratio of Mw is in the above range, an electrode having an excellent capacity retention ratio and strength can be obtained. Further, when preparing the electrode material, by dispersing the first polymer compound and the second polymer compound in a solvent, an electrode material having a viscosity suitable for application can be obtained.

Mw of the first polymer compound is preferably 50,000 to 4,000,000, more preferably 150,000 to 2,000,000, and still more preferably 200,000 to 1.5,000,000.
Within the above range, the capacity retention ratio and strength of the electrode can be further increased.

Mw of the second polymer compound is preferably 10,000 to 2,000,000, more preferably 50,000 to 1,000,000, and still more preferably 70,000 to 600,000.
Within the above range, the capacity retention ratio and strength of the electrode can be further increased.

The average molecular weight A of the first polymer compound and the second polymer compound is preferably 220,000 to 500,000. More preferably, it is 250,000 to 450,000, and still more preferably, 300,000 to 350,000.
When the average molecular weight A is 220,000 to 500,000, the peel strength is excellent. Thus, it is considered that peeling of the active material is suppressed, and a decrease in the capacity retention ratio can be suppressed.
The average molecular weight A is a value calculated by “k × p + 1 × q”.
When the total mass of the first polymer compound and the second polymer compound is 1, the ratio of the first polymer compound is p, and the ratio of the second polymer compound is q.
Let Mw of the first polymer compound be k and Mw of the second polymer compound be 1.

As for the blending amount of each polymer compound when preparing the electrode material, the blending ratio of the first polymer compound is 30 to 80% by mass with respect to the total mass of the binder, The compounding ratio of the compound is preferably 20 to 70% by mass.
With the above mixing ratio, the viscosity of the electrode material becomes suitable for coating, and the capacity retention and strength of the electrode can be further increased.

The mass ratio of the mixture of the first polymer compound and the second polymer compound when preparing the electrode material is preferably 9: 1 to 1: 9, more preferably 8: 2 to 2: 8, 6: 4 to 4: 6 is more preferred.
With the mass ratio of the above composition, the capacity retention ratio and strength of the electrode can be further increased.

The mass ratio (active material / binder) of the active material and the binder when preparing the electrode material is preferably 1 to 10, more preferably 2 to 8, and still more preferably 3 to 6.
With the above mass ratio, the viscosity of the electrode material becomes suitable for coating, and the capacity retention rate and strength of the electrode can be further increased.

Preferably, at least one of the first polymer compound and the second polymer compound contained in the binder has a carboxyl group (—COOH), and more preferably both have a carboxyl group.
When the polymer compound has a carboxyl group, the bonding force between the active material and the polymer compound is improved, and an electrode having even higher strength can be obtained.

  Hydrogen atoms of a plurality of carboxyl groups of the polymer compound may be unsubstituted, or at least a part of the hydrogen atoms may be substituted. Further, the polymer compound is a mixture of a polymer compound in which hydrogen atoms of a plurality of carboxyl groups of the polymer compound are unsubstituted and a polymer compound in which at least a part of the hydrogen atoms is substituted. There may be. Examples of the substance that replaces the hydrogen atom include a cation having a valence of one or more. Specific examples include alkali metal ions and alkaline earth metal ions. A suitable ion for partially or entirely substituting the hydrogen atom is, for example, a lithium ion.

In the polymer compound having a carboxyl group, it is preferable that at least a part of the hydrogen atoms of the carboxyl group is substituted by a lithium ion, that is, the carboxyl group forms a lithium salt.
When at least some hydrogen atoms of a plurality of carboxyl groups of the polymer compound are substituted with lithium ions, the substitution rate of the hydrogen atoms is preferably 10 to 50 mol%, and preferably 20 to 40 mol%. Is more preferably 25 to 35 mol%. Here, the substitution rate of the hydrogen atom by the lithium ion is a numerical value determined by a known acid / base titration.

  When the substitution rate is 10 to 50 mol%, the capacity retention rate of the electrode can be further improved. This mechanism is considered to be because the substitution suppresses the interaction between carboxyl groups, thereby suppressing the aggregation between the polymers and improving the dispersibility.

  As a method of adjusting the substitution rate to 10 to 50 mol%, for example, it can be adjusted by mixing an appropriate amount of an unsubstituted polymer compound with a substituted polymer compound.

  It is preferable that at least one of the first polymer compound and the second polymer compound contained in the binder is poly (meth) acrylic acid or a salt thereof.

  Here, the term “poly (meth) acrylic acid” is used to mean “a polymer containing at least one of acrylic acid and methacrylic acid as a monomer”. The poly (meth) acrylic acid may contain at least one of an acrylic ester and a methacrylic ester as a monomer copolymerized with acrylic acid or methacrylic acid. The poly (meth) acrylic acid preferably contains at least one of acrylic acid and methacrylic acid in a monomer composition ratio of 50 mol% or more, preferably 80 mol% or more.

  Examples of the poly (meth) acrylic acid salt include those in which at least a part of the hydrogen atoms of the carboxyl group of poly (meth) acrylic acid is replaced by an alkali metal ion or an alkaline earth metal ion. Above all, lithium (poly) (meth) acrylate, which is a salt of lithium ion, is preferable from the viewpoint of improving charge / discharge characteristics.

Lithium polyacrylate is obtained, for example, by the following method.
In an aqueous solution, polyacrylic acid (manufactured by Aldrich, model number: 416002-500ML) and lithium hydroxide (manufactured by Wako Pure Chemical Industries, model number: 169-18591) are mixed and reacted at a molar ratio of 100: 20. This makes it possible to prepare lithium polyacrylate in which 20 mol% of all the acid groups have become a lithium salt. From the viewpoint of improving the charge / discharge characteristics, it is preferable that lithium polyacrylate has 10 to 50 mol% of lithium salts in all acid groups (all carboxyl groups).

  Examples of the polymer compound having no carboxyl group include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-propylene hexafluoride copolymer (PVDF-HFP), styrene butadiene rubber (SBR), polyvinyl alcohol (PVA), Examples thereof include polyethylene oxide (PEO), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyimide (PI).

  A conductive assistant may be added to the electrode material in addition to the active material. Examples of the conductive additive include carbon materials such as acetylene black, Ketjen black, graphite, fullerene, and nanotube.

  Examples of the current collector to which the electrode material is applied include a known positive electrode current collector and a known negative electrode current collector. In the application of the lithium ion secondary battery, for example, a positive electrode current collector made of aluminum foil and a negative electrode current collector made of copper foil are given. Instead of the current collector, another substrate may be used.

Examples of the method of applying the electrode material to a current collector or a substrate include various coating methods such as a bar coater, a gravure coater, a comma coater, and a lip coater; a doctor blade method; a dipping method. Is mentioned.
The thickness of the electrode material when applied is, for example, 1 μm to 500 μm.

By drying the applied electrode material and removing an unnecessary solvent, an electrode active material layer made of the electrode material can be formed on the current collector or the base material.
When the electrode active material layer is formed on the current collector, an electrode including the current collector and the electrode active material layer is obtained after drying.
When the electrode active material layer is formed on the base material, after drying, the electrode active material layer is peeled off from the base material, and the electrode active material layer is placed on a separately prepared current collector. And an electrode comprising the electrode active material layer.

The temperature for drying the electrode material depends on the type of the binder, but is preferably, for example, 30 to 140 ° C.
When the temperature is 30 ° C. or higher, the drying speed becomes sufficient, and the water and the solvent of the electrode material can be sufficiently removed.
When the temperature is 140 ° C. or lower, the deterioration of the polymer compound as the binder can be prevented, and the occurrence of cracks and peeling in the electrode active material layer can be prevented.

  As a degree to which the electrode material is dried, for example, the amount of the solvent contained in the electrode active material layer composed of the electrode material after drying is 100 ppm or less (that is, 0.01 mass) with respect to the total mass of the electrode active material layer. %) Is preferable. When the content is 100 ppm or less, the structural stability of the electrode active material layer is increased, and good conductivity is easily obtained. Here, the amount of the solvent is a value measured by the Karl Fischer method.

《Negative electrode manufacturing method》
Hereinafter, a method for manufacturing a negative electrode applicable to a lithium ion secondary battery will be described as one embodiment of a method for manufacturing an electrode according to the present invention.
Specifically, the method includes applying a negative electrode material containing a metal oxide capable of storing lithium and a binder having a carboxyl group as a functional group to a current collector, and then drying the negative electrode material at 30 to 140 ° C. The method will be described.

(Drying temperature of negative electrode material)
By performing the drying temperature of the negative electrode material (electrode material for the negative electrode) applied on the current collector at 30 to 140 ° C., the cycle characteristics of the secondary battery can be improved. The mechanism presumed here is that by setting the temperature to 30 ° C. or higher, moisture remaining in the negative electrode material can be removed, and by drying at 140 ° C. or lower, the dehydration reaction and dehydration of the carboxyl group of the binder in the negative electrode material can be performed. It is considered that since the condensation reaction is suppressed, the number of interaction points between the hydroxyl group and the carboxyl group on the surface of the metal oxide is increased, so that the binding property with the metal oxide surface is improved, so that the cycle characteristics are improved.

  In consideration of the above mechanism, the drying temperature of the negative electrode material is preferably 35 to 140 ° C, more preferably 50 to 120 ° C, and still more preferably 80 to 100 ° C.

(Drying time of negative electrode material)
The drying time of the negative electrode material applied on the current collector is preferably 4 hours to 30 hours, more preferably 5 hours to 20 hours, and still more preferably 6 hours to 12 hours in a temperature range of 30 to 140 ° C.
By performing the drying treatment for 4 to 6 hours or more, the negative electrode material applied with a thickness of, for example, about 18 to 35 μm can be sufficiently dried and fixed on the current collector.
By performing the drying treatment for 12 to 30 hours or less, the dehydration reaction and dehydration condensation reaction of the carboxyl group of the binder in the negative electrode material can be suppressed.

(Content of solvent in negative electrode)
One of the criteria for ending the drying treatment is that the content of the solvent in the negative electrode material is sufficiently reduced. That is, when a solvent is contained in the negative electrode material, the amount of the solvent contained in the negative electrode obtained after drying is preferably 100 ppm or less, more preferably 50 ppm or less, by removing the solvent in the drying treatment. More preferably, it is 10 ppm or less. By sufficiently removing the solvent contained in the negative electrode, adverse effects on the battery performance due to the solvent can be eliminated.

(binder)
The binder used in the production method of the present embodiment is, as described above, two types of polymer compounds having different Mw.
As a polymer compound having a carboxyl group as a functional group, for example, polyacrylic acid (PAA), polymethacrylic acid, lithium polyacrylate (PAALi), lithium polymethacrylate, carboxymethylcellulose (CMC), sodium carboxymethylcellulose (CMCNa) And other known binders used in the field of lithium ion secondary batteries.

  In order to improve both the structural strength of the negative electrode active material layer formed of the negative electrode material applied on the current collector and the cycle characteristics of a secondary battery including the negative electrode active material layer, poly (meth) acrylic acid is included. It is preferred to use a binder. The content of poly (meth) acrylic acid contained in the binder is preferably 50 to 100% by mass based on the total mass of the binder.

  In the manufacturing method of the present embodiment, the content of the binder having a carboxyl group is preferably from 10 to 95% by mass, more preferably from 30 to 85% by mass, and preferably from 50 to 50% by mass, based on the total mass of the binder constituting the negative electrode material. 80 mass% is more preferred. By using the binder having a carboxyl group at a content of 50% by mass or more, the affinity with the silicon-based active material is improved.

(Metal oxide capable of storing lithium ions)
In the manufacturing method of the present embodiment, the kind of the metal oxide is not particularly limited, and a metal oxide capable of storing lithium ions, which is used as a known electrode material of a lithium ion secondary battery, can be applied. A preferred example is silicon oxide.

(Silicon oxide)
_{Examples of the} silicon oxide used in the production method of the present embodiment include a silicon oxide represented by a general formula “SiO _z (where z is any number from 0.5 to 1.5)”. it can. Here, when silicon oxide is viewed in “SiO” units, this SiO is amorphous SiO or around the nanocluster Si so that the molar ratio of Si: SiO ₂ is about 1: 1. Is a composite of Si and SiO _{2 in} which SiO ₂ exists. It is assumed that SiO ₂ has a buffering effect on the expansion and contraction of Si during charge and discharge.

  The silicon oxide is preferably in the form of powder, more preferably in the form of particles, for example, the average particle diameter is preferably 30 μm or less, more preferably 20 μm or less, and more preferably 10 μm or less. Is particularly preferred, and most preferably 2.0 μm or less. Although it depends on the mixing ratio of silicon oxide and the binder, the average particle diameter tends to be most preferably 1.0 μm or less. By using such finely powdered silicon oxide, the effect of the combined use of the particulate conductive aid and the fibrous conductive aid described later can be more remarkably obtained.

The average particle diameter of the silicon oxide is determined, for example, by measuring the particle diameter of about 100 arbitrary silicon oxide particles using an electron microscope and calculating the average value.
The average particle diameter can be adjusted to a desired value by pulverizing silicon oxide by a known method using, for example, a ball mill.

(Mass ratio of metal oxide to binder in negative electrode material)
The mass ratio (metal oxide / binder) between the metal oxide and the binder in the negative electrode material used in the production method of the present embodiment is preferably 1 to 10, more preferably 2 to 10, and 3 -8 is more preferable.

  Among the above ranges of 1 to 10, the closer to the more preferable range of 3 to 8, the metal oxide and the other negative electrode active material can be sufficiently fixed on the current collector, and the content ratio of the metal oxide is increased. High energy density can be obtained. Further, the ratio of the surface of the metal oxide covered with the binder can be increased. By increasing the ratio, a binder such as polyacrylic acid functions as a surface protective film of the metal oxide, prevents an excessive reaction between the metal oxide and the electrolyte, and further improves the cycle characteristics of the lithium ion secondary battery. Can be done. As the coating ratio, for example, it is preferable that 50% or more of the surface is coated, and it is more preferable that 70% or more is coated.

(Conduction aid)
It is preferable that the negative electrode material used in the manufacturing method of the present embodiment contains a conductive auxiliary in order to increase the conductivity of the negative electrode. The type of the conductive additive is not particularly limited, and a known conductive additive used for a lithium ion secondary battery can be applied. Specific examples include a particulate conductive aid and a fibrous conductive aid.

  In the negative electrode material, the content of the metal oxide with respect to the total mass of the metal oxide, the particulate conductive aid, the fibrous conductive aid, and the binder is preferably 40 to 89% by mass, and 60 to 89% by mass. More preferably, it is 80% by mass. When the content of the metal oxide is 40% by mass or more, the discharge capacity of the lithium ion secondary battery is further improved. When the content of the metal oxide is 89% by mass or less, a more stable negative electrode structure. Is obtained.

(Particulate conductive assistant)
The particulate conductive assistant is not particularly limited as long as it is a particulate one that functions as a conductive assistant, but preferred are carbon black such as acetylene black and Ketjen black; graphite (graphite); Can be illustrated.

  The average particle diameter of the particulate conductive additive is preferably 10 nm to 100 nm, and more preferably 15 nm to 60 nm. In addition, it is preferable that the particulate conductive auxiliary agent has a structure in which the particles are connected to each other, such as a string of beads. When the particulate conductive aid having such an average particle diameter or structure is used, the effect of the combined use with the fibrous conductive aid is more remarkably obtained.

  The average particle size of the particulate conductive assistant is determined by the same method as in the case of the above-described average particle size of silicon oxide. In addition, as a method for adjusting the average particle diameter of the particulate conductive auxiliary agent, a method for adjusting the average particle diameter of general fine particles can be applied.

  The particulate conductive auxiliary has a structure in which particles are connected to each other in a negative electrode active material layer described later, and by increasing a contact area with at least one of the metal oxide and a fibrous conductive auxiliary described later, It is presumed that it has contributed to the improvement of the conductivity of.

  In the production method of the present embodiment, the particulate conductive auxiliary may be used alone or in combination of two or more, and when two or more are used in combination, the combination and ratio thereof May be appropriately adjusted according to the purpose.

  In the negative electrode material, the content of the particulate conductive auxiliary with respect to the total mass of the metal oxide, the particulate conductive auxiliary, a fibrous conductive auxiliary described later, and a binder is 3 to 30% by mass. More preferably, it is more preferably 5 to 20% by mass. When the content of the particulate conductive aid is 3% by mass or more, the effect of using the particulate conductive aid is more remarkably obtained, and the content of the particulate conductive aid is 30% by mass or less. In this case, the effect of the combined use with the fibrous conductive additive can be more remarkably obtained.

(Fibrous conductive assistant)
The fibrous conductive aid is not particularly limited as long as it is a fibrous one that functions as a conductive aid. Preferred examples include carbon nanotubes and carbon nanohorns.

  The average fiber diameter of the fibrous conductive assistant is preferably 5 nm to 300 nm, more preferably 10 nm to 150 nm. Moreover, the average fiber length of the fibrous conductive auxiliary agent is preferably 0.1 μm to 30 μm, and more preferably 0.5 μm to 20 μm. By using such a fibrous conductive aid, the effect of the combined use with the particulate conductive aid is more remarkably obtained.

  The average fiber diameter of the fibrous conductive aid can be determined, for example, by measuring the fiber diameter of about 100 arbitrary fibrous conductive aids using an electron microscope and calculating the average value. Similarly, the average fiber length of the fibrous conductive additive is determined by, for example, measuring the fiber length of about 100 arbitrary fibrous conductive aids using an electron microscope and calculating the average value.

  The fibrous conductive aid contributes to the stabilization of the structure of the negative electrode active material layer by forming a network structure in the negative electrode active material layer, which will be described later, preferably over the entire negative electrode active material layer. It is presumed that a conductive network is formed therein to contribute to the improvement of conductivity.

  In the production method of the present embodiment, the fibrous conductive auxiliary may be used alone or in combination of two or more, and when two or more are used in combination, the combination and ratio thereof May be appropriately adjusted according to the purpose.

  In the negative electrode material, the content of the fibrous conductive aid is preferably 1 to 25% by mass relative to the total mass of the metal oxide, the particulate conductive aid, the fibrous conductive aid, and the binder. It is more preferable that the content be 15 to 15% by mass. When the content of the fibrous conductive aid is 1% by mass or more, the effect of using the fibrous conductive aid is more remarkably obtained, and the content of the fibrous conductive aid is 25% by mass or less. In this case, the effect of the combined use with the particulate conductive additive is more remarkably obtained.

  In the negative electrode material used in the production method of the present embodiment, the mass ratio (mixing mass ratio) of the compounding amount of “particulate conductive auxiliary: fibrous conductive auxiliary” is 90:10 to 30:70. , And more preferably 80:20 to 40:60. When the compounding mass ratio of the particulate conductive aid and the fibrous conductive aid is in such a range, the effect of the combined use of the particulate conductive aid and the fibrous conductive aid is more remarkably obtained.

(Other components)
The negative electrode material may be a material in which other components other than these, in addition to the silicon oxide, the particulate conductive auxiliary, the fibrous conductive auxiliary, and the binder, are further compounded.
The other components are not particularly limited and can be arbitrarily selected according to the purpose. For example, as a preferred component, a solvent for dissolving or dispersing the above-mentioned components (silicon oxide, particulate conductive aid, fibrous conductive aid, binder) can be exemplified.
The negative electrode material containing the solvent is preferably a liquid composition having fluidity during use.

The solvent can be arbitrarily selected according to the type of the component. For example, preferable solvents include water and an organic solvent.
Preferred examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol and 2-propanol; linear or cyclic amides such as N-methylpyrrolidone (NMP) and N, N-dimethylformamide (DMF); And the like.
The solvents may be used alone or in combination of two or more. When two or more solvents are used in combination, the combination and ratio may be appropriately selected depending on the purpose.

  The amount of the solvent in the negative electrode material is not particularly limited, and may be appropriately adjusted depending on the purpose. For example, when a negative electrode material, which is a liquid composition in which a solvent is blended, is applied and dried to form a negative electrode active material layer described below, the liquid composition has a viscosity suitable for coating. The amount of the solvent may be adjusted. Specifically, in the negative electrode material, the mixing ratio of the solvent is adjusted so that the ratio of the total amount of the components other than the solvent to the total amount of the components is preferably 5 to 60% by mass, more preferably 10 to 35% by mass. Adjust the amount.

  When a component (other solid component) other than the solvent is blended as the other component, the ratio of the blended amount of the other solid component to the total amount of the blended component other than the solvent in the negative electrode material is 10% by mass. Or less, more preferably 5% by mass or less.

  The negative electrode material is particularly preferably a negative electrode material in which the particulate conductive aid is carbon black and the fibrous conductive aid is carbon nanotube.

The negative electrode material can be manufactured by blending the silicon oxide, the particulate conductive auxiliary, the fibrous conductive auxiliary, a binder, and other components as necessary.
At the time of compounding each component, it is preferable to add each component and sufficiently mix them by various means. The components may be mixed while sequentially adding them individually, or all the components may be added at once and then mixed, and it is preferable that the components are uniformly mixed.

  When blending the solvent as the other component, at least a portion of the solvent is selected from the group consisting of the silicon oxide, the particulate conductive aid, the fibrous conductive aid, a binder, and other solid components. One or more of them may be pre-mixed and formulated as a solution or dispersion of the selected component. The solvent used for preparing the solution or dispersion may be the total amount of the solvent to be blended.

The mixing method of each component is not particularly limited, and for example, a known method using a stirrer, a stirring blade, a ball mill, a stirrer, an ultrasonic disperser, an ultrasonic homogenizer, a self-revolving mixer, or the like can be applied. Further, a plurality of methods may be combined and mixed.
Mixing conditions such as mixing temperature and mixing time may be appropriately set according to various methods. Usually, the temperature at the time of mixing is preferably from 10 to 50C, more preferably from 15 to 35C. The mixing time is preferably about 3 to 40 minutes, more preferably about 5 to 20 minutes.

  The composition obtained by mixing the components may be used as a negative electrode material as it is, or any operation may be performed on the obtained composition, for example, by removing a part of the blended solvent by distillation or the like. A material obtained by additionally performing the above may be used as a negative electrode material.

[Negative electrode]
The negative electrode obtained by the manufacturing method of the present embodiment is obtained by applying the negative electrode material on a current collector and drying. The negative electrode preferably has a negative electrode active material layer formed of the negative electrode material on the current collector. In addition, from the viewpoint of increasing the capacity development rate of the battery, it is preferable that the negative electrode active material layer is pre-doped with lithium. Other configurations of the negative electrode can be the same as those of a known negative electrode.

As the current collector, a known current collector used in the field of a lithium ion secondary battery can be applied. Specific examples include metals such as copper, aluminum, titanium, nickel, and stainless steel.
The shape of the current collector is not particularly limited, but is preferably a sheet. Although the thickness of the sheet-like current collector is not particularly limited, a thickness of, for example, 5 to 20 μm is exemplified.

  The thickness of the negative electrode active material layer formed by drying the negative electrode material is not particularly limited, but is preferably 5 to 100 μm, and more preferably 10 to 60 μm.

  As a method of applying (coating) the negative electrode material constituting the negative electrode active material layer on the current collector, for example, a method using various coaters such as a bar coater, a gravure coater, a comma coater, and a lip coater; a doctor blade method; Various coating methods such as a dipping method can be exemplified.

  Drying of the negative electrode material applied on the current collector can be performed under a normal pressure or a reduced pressure by a known method. The drying temperature and the drying time are as described above.

  The negative electrode active material layer may be formed directly on the current collector, or may be formed on another base material, then moved onto the current collector, and pressed on the current collector. The negative electrode active material layer formed directly on the current collector may be pressed.

The method of pre-doping lithium into the negative electrode active material layer is not particularly limited, and includes, for example, a method in which the negative electrode active material layer is brought into contact with metallic lithium via an electrolytic solution. According to this pre-doping method, lithium can be pre-doped in a wide area of the negative electrode active material layer. The electrolyte is preferably the same as the electrolyte used when manufacturing a lithium ion secondary battery using this negative electrode. The metal lithium to be brought into contact is preferably in the form of a sheet (metal lithium foil). Note that pre-doping of lithium needs to be performed using lithium metal (Li) instead of lithium ion (Li ⁺ ).
As another method of pre-doping lithium, there is a method of pre-doping by mixing lithium metal or a lithium alloy into an active material slurry (a composition of a material for forming a negative electrode active material layer). Further, a known method of electrochemically pre-doping using an external power supply may be used.

The amount of lithium pre-doped in the negative electrode is preferably 1 to 4 times, more preferably 2 to 4 times the molar amount of silicon dioxide (SiO ₂ ) in the negative electrode active material layer. It is particularly preferred that the molar amount is 3 to 4 times.

It is presumed that lithium pre-doped in the negative electrode irreversibly reacts with silicon dioxide in the negative electrode active material layer to generate lithium silicate (Li ₄ SiO ₄ ). In the lithium ion secondary battery including the pre-doped negative electrode, when lithium is occluded in the negative electrode in the initial charging step, the above reaction with silicon oxide in the negative electrode active material layer is suppressed, The release of lithium at the time of discharge is not hindered, and a decrease in discharge capacity is suppressed.

<< Positive electrode manufacturing method >>
By the method for manufacturing an electrode according to the present invention, a positive electrode applicable to a lithium ion secondary battery can also be manufactured. The positive electrode can be manufactured by the same method as that for the negative electrode except that the positive electrode material is used instead of the negative electrode material. Specifically, for example, a positive electrode active material, a binder and a solvent, and, if necessary, a positive electrode material comprising a conductive additive is applied to the current collector, and then the positive electrode material is dried to collect current. A positive electrode having a positive electrode active material layer on the body is obtained. The positive electrode active material layer can be formed with a thickness of, for example, 20 to 60 μm.

  As the binder, solvent and current collector in the positive electrode, those similar to the binder, solvent and current collector in the negative electrode can be applied.

Suitable conductive assistants for the positive electrode include, for example, carbonaceous materials such as graphite and acetylene black.
The conductive auxiliary agent in the positive electrode may be used alone, or two or more kinds may be used in combination.When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose. I just need.

  Examples of the positive electrode active material include known metal lithium compounds. For example, lithium cobaltate, lithium nickelate, lithium manganate, olivine type lithium phosphate and the like can be exemplified. The positive electrode active material may be used singly, or two or more kinds may be used in combination.If two or more kinds are used in combination, the combination and ratio may be appropriately selected depending on the purpose. Good.

  For the total mass of each component blended in the positive electrode material, the content of each component of the positive electrode active material, the binder, the solvent, and the conductive auxiliary is based on the total mass of each component blended in the negative electrode material, The contents of the respective components of the negative electrode active material, the binder, the solvent, and the conductive auxiliary may be the same or different.

<< Production method of lithium ion secondary battery >>
The method for manufacturing a lithium ion secondary battery according to the present invention includes a step of obtaining an electrode by the above-described method of manufacturing an electrode, and a step of installing an electrolyte between a counter electrode (a counter electrode).
When the electrode is a negative electrode, the counter electrode is a positive electrode, and when the electrode is a positive electrode, the counter electrode is a negative electrode. The counter electrode may be a counter electrode obtained by the above-described method for manufacturing an electrode according to the present invention, or may be a counter electrode manufactured by another method.

  A lithium ion secondary battery obtained by the manufacturing method according to the present invention includes the electrode obtained by the electrode manufacturing method according to the present invention. Except for having this electrode, a configuration similar to that of a conventional lithium ion secondary battery can be applied. Examples of the configuration include a configuration including an anode and a cathode, and an electrolyte such as an electrolyte solution (electrolyte solution), a gel electrolyte, and a solid electrolyte. Further, a separator may be provided between the negative electrode and the positive electrode.

[Electrolyte]
As the electrolyte, an electrolyte used in a conventional lithium ion secondary battery can be used. For example, an electrolytic solution containing lithium carboxylate as an electrolyte is preferable.

Examples of the lithium carboxylate include lithium salts of monovalent carboxylic acids such as lithium formate and lithium acetate; lithium salts of divalent carboxylic acids such as lithium oxalate and lithium malonate; and salts having a hydroxyl group such as lithium lactate. Examples thereof include lithium salts of polyvalent carboxylic acids. Among these, lithium formate, lithium acetate, lithium oxalate, and lithium succinate are more preferable, and lithium oxalate is particularly preferable.
As the lithium carboxylate, one type may be used alone, or two or more types may be used in combination. When two or more kinds are used in combination, the combination and ratio may be appropriately selected according to the purpose.

  It is also possible to use boron trifluoride or a boron trifluoride complex capable of forming a complex with lithium carboxylate as an electrolyte together with lithium carboxylate.

Preferred boron trifluoride complexes include boron trifluoride dimethyl ether complex (BF ₃ .O (CH ₃ ) ₂ ), boron trifluoride diethyl ether complex, boron trifluoride di-n-butyl ether complex, and the like. Boron alkyl ether complex; boron trifluoride alcohol complex such as boron trifluoride methanol complex (BF ₃ .HOCH ₃ ), boron trifluoride propanol complex, boron trifluoride phenol complex and the like.

  The organic solvent constituting the electrolytic solution is not particularly limited, for example, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, vinylene carbonate, γ-butyrolactone, tetrahydrofuran, dimethoxyethane, methyl formate, It is preferably at least one selected from the group consisting of methyl acetate, methyl propionate, acetonitrile and sulfolane.

  The blending amount of the organic solvent in the electrolytic solution is not particularly limited, and may be appropriately adjusted according to, for example, the type of the electrolyte. Usually, the amount is adjusted so that the concentration of lithium atoms (Li) is preferably 0.2 to 3.0 mol / kg, more preferably 0.4 to 2.0 mol / kg. preferable.

  In addition, as the electrolyte, a known lithium salt such as lithium hexafluorophosphate, lithium boron tetrafluoride, lithium bisfluorosulfonylimide, and bis (trifluoromethanesulfonyl) imide lithium is dissolved in an organic solvent as an electrolyte. Can also be exemplified.

  A known gel electrolyte in which a known matrix polymer is contained in the electrolytic solution and the electrolytic solution is in a gel state may be used for manufacturing the lithium ion secondary battery of the present embodiment. In addition, a known solid electrolyte in which a solvent constituting the electrolytic solution or the gel electrolyte is dried and removed to be in a solid state may be used for manufacturing the lithium ion secondary battery of the present embodiment.

[Separator]
The material of the separator is not particularly limited, but a polymer film having micropores, an inorganic film having micropores, a nonwoven fabric, a glass fiber, and the like can be exemplified, and it is preferable that the separator be at least one selected from the group consisting of these materials. .

  FIG. 1 is a schematic sectional view showing an example of an embodiment of a lithium ion secondary battery obtained by the present invention. The lithium ion secondary battery 1 exemplified here has a configuration in which a sheet-like negative electrode 13 and a positive electrode 11 are stacked with a separator 12 interposed therebetween. The separator may be a single layer, or a plurality of layers in which two or more layers are stacked. In FIG. 1, the electrolyte is impregnated in the separator 12. The electrolyte may be in any form of an electrolyte, a gel electrolyte or a solid electrolyte. Here, a configuration in which the negative electrode 13 and the positive electrode 11 are stacked one by one is shown. However, as another configuration, for example, a stacked body in which the negative electrode 13, the separator 12, and the positive electrode 11 are stacked in this order is disposed. Further, a configuration in which a plurality of layers are repeatedly laminated via a separator 12 may be used.

The lithium ion secondary battery may be manufactured according to a known method, for example, in a glove box or in a dry air atmosphere, using the electrolytic solution, gel electrolyte or solid electrolyte, electrodes, and the like.
For example, in the case of a lithium ion secondary battery provided with a gel electrolyte, a heated gel electrolyte is applied to one or both of the negative electrode and the positive electrode, and then the gel electrolyte is applied. The provided negative electrode and positive electrode are laminated via a gel electrolyte so that these electrode surfaces face each other, and if necessary, a separator can be interposed between these electrode surfaces to facilitate manufacture. The liquid gel electrolyte can be applied on the electrode surface by a method using various coaters such as a bar coater.
Further, for example, in the case of a lithium ion secondary battery provided with an electrolyte solution, except that this electrolyte solution is disposed in contact with the electrode surfaces of the negative electrode and the positive electrode instead of the gel electrolyte, the above-described gel electrolyte is used. It can be easily manufactured by the same method as the provided lithium ion secondary battery.

  The shape of the lithium ion secondary battery is not particularly limited, and can be adjusted to various types such as a cylindrical type, a square type, a coin type, and a sheet type.

  When using a lithium carboxylate and boron trifluoride and / or a boron trifluoride complex, or a lithium carboxylate-boron trifluoride complex, the lithium ion secondary battery has a structure in which the fluorine is formed on the surface of the negative electrode during initial charging. An interfacial film containing lithium fluoride (LiF) (hereinafter, abbreviated as “SEI”) is formed. The SEI prevents solvent molecules solvated in lithium ions from entering the negative electrode during charge and discharge, suppresses the destruction of the negative electrode structure, and contributes to the improvement of cycle characteristics of the lithium ion secondary battery.

The lithium ion secondary battery manufactured according to the present invention has a negative electrode active material layer formed using a negative electrode material formed by mixing silicon oxide, particulate conductive aid, fibrous conductive aid and a binder, Further, it is preferable to provide a negative electrode pre-doped with lithium.
The lithium ion secondary battery uses a particulate conductive aid and a fibrous conductive aid in combination, and further uses a negative electrode that is pre-doped with lithium. Both the capacity retention rate is high and the charge / discharge characteristics are excellent.

  Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to the examples described below.

(1) Raw materials used The raw materials used in this example are shown below.
-Conductive aid Acetylene black ("HS-100" manufactured by Denki Kagaku Kogyo Co., Ltd., average particle diameter 48 nm)
Carbon nanotubes (“NT-7” manufactured by Hodogaya Chemical Co., Ltd., average fiber diameter 65 nm, average fiber length 6 μm or more)
・ Binder Styrene-butadiene resin (hereinafter abbreviated as “SBR”) (manufactured by JSR)
Polyacrylic acid (100,000) (weight average molecular weight Mw = 100,000, manufactured by Aldrich)
Polyacrylic acid (250,000) (weight average molecular weight Mw = 250,000, manufactured by Aldrich)
Polyacrylic acid (1,000,000) (weight average molecular weight Mw = 1,000,000, manufactured by Aldrich)
Lithium hydroxide (Wako Pure Chemical Industries, Ltd.)
-Lithium carboxylate Lithium oxalate (Alfa)
· Boron trifluoride complex of boron trifluoride diethyl etherate _{(BF 3 · O (C 2} H 5) 2) ( manufactured by Aldrich)
-Organic solvent Ethylene carbonate (hereinafter abbreviated as "EC") (manufactured by Kishida Chemical Co., Ltd.)
Propylene carbonate (hereinafter abbreviated as "PC") (manufactured by Kishida Chemical Co., Ltd.)
-Solvent dimethyl carbonate (hereinafter abbreviated as "DMC") (manufactured by Kishida Chemical Co., Ltd.)

<Synthesis of organic acid lithium salt-boron trifluoride complex>
[Synthesis Example 1] (Synthesis of lithium oxalate-boron trifluoride complex)
Lithium oxalate (22.3 g, 223 mmol) was weighed into a round bottom flask and suspended in 200 mL of DMC. After slowly dropping boron trifluoride diethyl ether complex (63.3 g, 446 mmol) at 23 ° C., the mixture was stirred at room temperature (23 ° C.) for 24 hours, and the reaction solution became transparent and no insoluble matter was observed. It was confirmed that a homogeneous solution was obtained. Next, the solvent and impurities were distilled off from the reaction solution using a rotary evaporator. Thereafter, the precipitated white solid was dried at 50 ° C. to obtain a white powder of lithium oxalate-boron trifluoride complex ((COOLi) _2. (BF ₃ ) ₂ ) (yield 96.5). %).

<Manufacture of lithium ion secondary batteries>
[Test Example 1]
(Manufacture of negative electrode material)
Silicon monoxide (SiO, average particle diameter 1.0 μm, 69 parts by mass), acetylene black (10 parts by mass), carbon nanotube (6 parts by mass), polyacrylic acid (100,000) ( hereinafter, “PAA (100,000) 10 parts by mass) and SBR (5 parts by mass) were placed in a reagent bottle, the concentration was adjusted by adding distilled water, and then mixed at 2,000 rpm for 3 minutes using a self-revolving mixer. Next, the obtained mixture was subjected to a dispersion treatment for 10 minutes by an ultrasonic homogenizer, and the obtained dispersion was mixed by a self-revolving mixer at 2,000 rpm for 3 minutes to obtain a negative electrode material. Or more of the operation was carried out in all 25 ℃.

(Manufacture of electrolyte)
As an organic solvent, a mixed solvent of EC and PC (EC: PC = 30: 70 (volume ratio)) was weighed into a sample bottle, and lithium oxalate-boron trifluoride complex (1.82 g) was added thereto. The concentration of lithium atoms in the lithium oxalate-boron trifluoride complex was adjusted to 1.0 mol / kg, and the mixture was mixed at 23 ° C. to obtain an electrolytic solution.

(Manufacture of negative electrode)
Using a bar coater, a negative electrode material was applied to both sides of a copper foil having a thickness of 18 μm, dried on a hot plate at 60 ° C., and then pressed at 1 kN using a roll press to obtain a current collector. A negative electrode active material layer having a thickness of 25 μm was formed on a certain copper foil to obtain a negative electrode precursor. Further, the electrodes were dried under vacuum at 50 ° C. for 6 hours before producing a lithium battery in order to sufficiently remove residual moisture.

An electrolytic solution was dropped at 50 μL / cm ² on the formed negative electrode active material layer, and a 200 μm-thick lithium metal foil was overlaid thereon. By allowing this state to stand for 24 hours, the negative electrode active material layer was pre-doped with lithium to obtain a negative electrode. The lithium metal foil remaining after the pre-doping was removed.

(Manufacture of positive electrode)
Nickel / cobalt / lithium manganate (Ni: Co: Mn = 1: 1: 1, LiNMC) (93 parts by mass), polyvinylidene fluoride (PVDF) (3 parts by mass), and carbon black as a conductive additive ( 4 parts by mass), and the resulting mixture was dispersed in N-methylpyrrolidone (NMP) to obtain a positive electrode material (slurry). Next, a positive electrode material was applied to both surfaces of a 15 μm-thick aluminum foil using a bar coater, dried under reduced pressure at 100 ° C., 0.1 MPa, and 10 hours, and then roll-pressed to obtain a current collector. A positive electrode in which a positive electrode active material layer having a thickness of 60 μm was formed on a certain aluminum foil was obtained.

(Manufacture of lithium ion secondary batteries)
The negative electrode and the positive electrode obtained above were punched into a disk having a diameter of 16 mm. Further, a separator made of glass fiber was punched into a disk shape having a diameter of 17 mm. The disc-shaped positive electrode, the separator and the negative electrode are laminated in this order in a SUS battery container (CR2032), and the electrolytic solution obtained above is impregnated into the separator, the negative electrode and the positive electrode. Was mounted (1.2 mm thick, 16 mm diameter), and a lid was produced, thereby manufacturing a coin-type lithium ion secondary battery.

[Test Example 2]
In the production of the negative electrode, 10 parts by mass of polyacrylic acid (250,000) ( hereinafter sometimes abbreviated as “PAA (250,000)”) was used instead of 10 parts by mass of PAA (100,000). A lithium ion secondary battery was manufactured in the same manner as in Test Example 1.

[Test Example 3]
In the production of the negative electrode, 10 parts by mass of polyacrylic acid (1 million) ( hereinafter sometimes abbreviated as “PAA (1 million)”) was used instead of 10 parts by mass of PAA (100,000). A lithium ion secondary battery was manufactured in the same manner as in Test Example 1.

[Test Example 4]
In the production of the negative electrode, Test Example 1 was repeated except that 9 parts by mass of PAA (250,000) and 1 part by mass of PAA (1 million) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

[Test Example 5]
In the production of the negative electrode, Test Example 1 was repeated except that 7 parts by mass of PAA (250,000) and 3 parts by mass of PAA (1 million) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

[Test Example 6]
In the production of the negative electrode, Test Example 1 was repeated except that 5 parts by mass of PAA (250,000) and 5 parts by mass of PAA (1 million) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

[Test Example 7]
In the production of the negative electrode, Test Example 1 was repeated except that 3 parts by mass of PAA (250,000) and 7 parts by mass of PAA (1 million) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

[Test Example 8]
In the production of the negative electrode, Test Example 1 was repeated except that 1 part by mass of PAA (250,000) and 9 parts by mass of PAA (1 million) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

[Test Example 9]
In the production of the negative electrode, in place of PA A (10 50,000) 10 parts by mass, and PAA (10 50,000) 9 parts by weight, except that it was used by mixing with PAA (100 50,000) 1 part by weight, the the Test Example 1 In the same manner as in the above, a lithium ion secondary battery was manufactured.

[Test Example 10]
In the production of the negative electrode, in place of PA A (10 50,000) 10 parts by mass, and PAA (10 50,000) 7 parts by weight, except that it was used by mixing with PAA (100 50,000) 3 parts by weight, the the Test Example 1 In the same manner as in the above, a lithium ion secondary battery was manufactured.

[Test Example 11]
In the production of the negative electrode, Test Example 1 was repeated except that 5 parts by mass of PAA (100,000) and 5 parts by mass of PAA (1 million) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

[Test Example 12]
In the production of the negative electrode, Test Example 1 was repeated except that 3 parts by mass of PAA (100,000) and 7 parts by mass of PAA (1 million) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

[Test Example 13]
In the production of the negative electrode, Test Example 1 was repeated except that 1 part by mass of PAA (100,000) and 9 parts by mass of PAA (1 million) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

[Test Example 14]
In the production of the negative electrode, Test Example 1 was repeated except that 9 parts by mass of PAA (100,000) and 1 part by mass of PAA (250,000) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

[Test Example 15]
In the production of the negative electrode, Test Example 1 was repeated except that 7 parts by mass of PAA (100,000) and 3 parts by mass of PAA (250,000) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

[Test Example 16]
In the production of the negative electrode, Test Example 1 was repeated except that 5 parts by mass of PAA (100,000) and 5 parts by mass of PAA (250,000) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

[Test Example 17]
In the production of the negative electrode, Test Example 1 was repeated except that 3 parts by mass of PAA (100,000) and 7 parts by mass of PAA (250,000) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

[Test Example 18]
In the production of the negative electrode, Test Example 1 was repeated except that 1 part by mass of PAA (100,000) and 9 parts by mass of PAA (250,000) were used in place of 10 parts by mass of PAA (100,000). Similarly, a lithium ion secondary battery was manufactured.

The lithium ion secondary batteries of Test Examples 1 to 3 are secondary batteries of Comparative Examples provided with a negative electrode containing one type of binder.
The lithium ion secondary batteries of Test Examples 4 to 18 are the secondary batteries of Examples provided with negative electrodes containing two types of binders having different weight average molecular weights.

<Evaluation of charge / discharge characteristics of lithium ion secondary batteries>
For the lithium ion secondary batteries produced in each of the test examples, constant-current constant-voltage charging of 0.2 C at 25 ° C. was performed at an upper limit voltage of 4.2 V until the current value converged to 0.1 C. Was discharged to 2.5 V. Next, the charge / discharge cycle was repeated three times in the same manner with the charge / discharge current set to 1 C to stabilize the state of the lithium ion secondary battery. Next, the charge / discharge cycle was repeated by the same method with the charge / discharge current set to 1 C, and the capacity retention rate at 100 cycles ({[discharge capacity at 100th cycle (mAh)] / [discharge capacity at 1st cycle (mAh) )]} × 100) (%) was calculated. The results are shown in Tables 2 to 4.

<Evaluation of peel strength of negative electrode>
The peel strength of the negative electrode produced in each test example was measured with a 90-degree peel tester (TE-3001: manufactured by Tester Sangyo Co., Ltd.).
A 19 mm wide double-sided tape (SPG-19: manufactured by 3M Japan KK) was attached to a base of an aluminum plate as a measuring unit of the testing machine, and a negative electrode was attached and crimped thereon. With reference to JIS Z 0237 (2000), pressure bonding was performed with a metal roller.
Subsequently, an operation of pulling the end portion of the attached negative electrode was performed once. The peeling speed was 30 mm / min, the peeling angle was 90 degrees, and the peeling strength at the time of peeling was measured. The larger the value of the peel strength, the better the resistance to external stress. The results are shown in Tables 2 to 4.

The following is clear from the above results.
-The capacity retention rates and peel strengths of Test Examples 4, 5, 10, and 18 are excellent.

DESCRIPTION OF SYMBOLS 1 ... Lithium ion secondary battery, 11 ... Positive electrode, 12 ... Separator and electrolyte, 13 ... Negative electrode, 14 ... Case (case), 15 ... Insulating gasket, 16 ... Cap

Claims (20)

A current collector and an electrode active material layer formed on the current collector, wherein the electrode active material layer includes an active material and a binder,
The binder includes a first polymer compound and a second polymer compound having a smaller weight average molecular weight (Mw) than the first polymer compound,
An electrode having an Mw ratio represented by [Mw of the first polymer compound / Mw of the second polymer compound] of 1.5 to 10 ,
The content ratio of the first polymer compound is 30 to 80% by mass, and the content ratio of the second polymer compound is 20 to 70% by mass, based on the total mass of the binder,
At least one of the first polymer compound and the second polymer compound has a carboxyl group,
An electrode, wherein the polymer compound having a carboxyl group has a part of hydrogen atoms of the carboxyl group replaced by lithium ions . 2. The electrode according to claim 1, wherein a substitution rate of the hydrogen atoms by lithium ions is 10 to 50 mol%. The Mw ratio is 5 to 10, the electrode according to claim 1 or 2. The electrode according to any one of claims 1 to 3, wherein Mw of the second polymer compound is 10,000 to 4,000,000. The electrode according to any one of claims 1 to 4, wherein Mw of the second polymer compound is 100,000 to 1,000,000.   The electrode according to any one of claims 1 to 5, wherein a mass ratio of the active material and the binder (active material / binder) is 1 to 10. The electrode according to any one of claims 1 to 6 , wherein at least one of the first polymer compound and the second polymer compound is poly (meth) acrylic acid or a salt thereof. The active material may include a storable carbon material or metal oxide of lithium, the electrode according to any one of claims 1-7. The electrode according to claim 8 , wherein the active material is silicon oxide. A lithium ion secondary battery comprising the electrode according to any one of claims 1 to 9 , a counter electrode, and an electrolyte. After applying an electrode material containing an active material and a binder to a current collector or a substrate, a method for producing an electrode having a step of forming an electrode active material layer by drying,
The binder includes a first polymer compound and a second polymer compound having a smaller weight average molecular weight (Mw) than the first polymer compound,
Mw ratio expressed by [Mw of Mw / the second polymer compound of the first polymer compound] is Ri 1.5-10 der,
The content ratio of the first polymer compound is 30 to 80% by mass, and the content ratio of the second polymer compound is 20 to 70% by mass, based on the total mass of the binder,
At least one of the first polymer compound and the second polymer compound has a carboxyl group,
The method for producing an electrode, wherein the polymer compound having a carboxyl group has a part of hydrogen atoms of the carboxyl group substituted by lithium ions . The method for producing an electrode according to claim 11, wherein a substitution rate of the hydrogen atoms by lithium ions is 10 to 50 mol%. The method for manufacturing an electrode according to claim 11 or 12, further comprising a step of obtaining the electrode material by dispersing the active material and the binder in a solvent. The method for producing an electrode according to any one of claims 11 to 13 , wherein the applied electrode material is dried at 30 to 140 ° C. Drying the coated electrode material, the amount of solvent contained in the electrode active material layer formed, to 100ppm or less based on the total weight of the electrode active material layer, any of claims 11 to 14 A method for producing an electrode according to claim 1. The method for producing an electrode according to any one of claims 11 to 15, wherein a mass ratio (active material / binder) of the active material and the binder contained in the electrode material is 1 to 10. The method for producing an electrode according to any one of claims 11 to 16 , wherein the active material includes a carbon material or a metal oxide capable of storing lithium. The method for manufacturing an electrode according to any one of claims 11 to 17 , wherein the active material is silicon oxide. The method for producing an electrode according to any one of claims 11 to 18 , wherein at least one of the first polymer compound and the second polymer compound is poly (meth) acrylic acid or a salt thereof. A method for manufacturing a lithium ion secondary battery, comprising: obtaining an electrode by the method for manufacturing an electrode according to any one of claims 11 to 19 ; and installing an electrolyte between the electrode and a counter electrode.

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