JP2017224407A - Conductive composition, backing layer-attached current collector for nonaqueous electrolyte secondary battery, electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive composition for forming a nonaqueous electrolyte secondary battery having the function of increasing the internal resistance when the internal temperature of a battery rises, which is superior in conductivity during a normal operation.SOLUTION: The above problem is solved by a conductive composition for forming a backing layer of an electrode for a nonaqueous electrolyte secondary battery. The conductive composition comprises: a conductive carbon material (A); a water-soluble resin (B) having a hydroxyl group; water-dispersible resin fine particles (C); and an aqueous liquid medium (D). The water-dispersible resin fine particles include at least olefin-based resin fine particles. In a total solid content, the content of the conductive carbon material (A) is 10-50 mass%; the content of the water-soluble resin (B) having the hydroxyl group is 10-50 mass%; and the content of the water-dispersible resin fine particles (C) is 30-70 mass%. The olefin-based resin fine particles included in the water-dispersible resin fine particles (C) account for 50-100 mass%.SELECTED DRAWING: None

Description

  The present invention relates to a conductive composition, an electrode for a nonaqueous electrolyte secondary battery obtained using the composition, and a nonaqueous electrolyte secondary battery obtained using the electrode. Specifically, the conductive composition is used for forming a base layer of an electrode for a non-aqueous electrolyte secondary battery, and has a function of increasing the internal resistance of the battery when the temperature of the battery rises, the non-aqueous electrolyte secondary The present invention relates to a battery electrode and a non-aqueous electrolyte secondary battery.

  In recent years, small portable electronic devices such as digital cameras and mobile phones have been widely used. These electronic devices have always been required to minimize the volume and reduce the weight, and the batteries to be mounted are also required to be small, light, and have a large capacity. In particular, lithium-ion secondary batteries have a higher energy density than water-based secondary batteries such as lead-acid batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. In addition, it is expected to be preferably used as a high-output power source mounted on a vehicle.

  Lithium ion secondary batteries, while having the advantage of high energy density, use a non-aqueous electrolyte, so a sufficient countermeasure for safety is required. In recent years, ensuring the safety has become a major issue as the size and capacity of batteries increase. For example, if the battery temperature rises abnormally and suddenly due to overcharging or a short circuit inside the battery, it is difficult to control the heat generation with only the safety mechanism provided outside the battery, and it ignites. There is a risk.

  Patent Document 1 describes a method of joining an electron conductive material having a function of a positive temperature coefficient resistor (hereinafter referred to as PTC) to a current collector. However, since the thickness of the electron conductive material is as thick as 50 μm, there is a problem that the energy density of the entire battery is lowered.

  Patent Document 2 discloses that any of a positive electrode, a negative electrode, and a non-aqueous electrolyte has PTC characteristics. However, in order to impart PTC characteristics to these, it is necessary to add a large amount of additives that do not contribute to battery capacity, resulting in a decrease in energy density.

  Patent Document 3 describes a method of providing a conductive layer made of a crystalline thermoplastic resin, a conductive agent, and a binder on the surface of a current collector. In this conductive layer, when the temperature in the battery exceeds the melting point of the crystalline thermoplastic resin, the resistance of the conductive layer increases and the current between the current collector and the active material is interrupted. However, there is a problem in that the internal resistance during normal operation of the battery increases and the output characteristics of the battery deteriorate.

  Patent Document 4 describes a method in which a conductive layer made of polyvinylidene fluoride and a conductive agent is provided on the current collector surface, and the current collector provided with the conductive layer is heated at a temperature exceeding 120 ° C. However, in addition to an additional heat treatment step, there is a problem that the resistance rise is not sufficient when the temperature in the battery rises.

  Patent Document 5 describes a method of providing a current collector provided with a conductive layer made of conductive particles, carboxymethyl cellulose, a water-dispersed olefin resin, and a dispersant. However, carboxymethylcellulose is used as a thickener for the dispersion, and its addition amount is as small as 5% by mass or less in the total 100% by mass of the solid content of the dispersion.

  Patent Document 6 describes a method of providing a conductive layer made of a composition in which the volume average particle diameter of particles that are heat-fusible is larger than the volume average particle diameter of conductive inorganic particles. However, there is a problem that the resistance rise is not sufficient when the temperature in the battery rises.

JP-A-10-241665 JP 11-329503 A JP 2001-357854 A JP 2012-104422 A International Publication No. 2015/046469 JP 2009-176599 A

  An object of the present invention is a non-aqueous electrolyte secondary battery having a function of increasing the internal resistance when the internal temperature of the battery is increased because of excellent electrical conductivity during normal operation, excellent battery output characteristics, etc. An object of the present invention is to provide a conductive composition for forming a lithium ion secondary battery (for example, a lithium ion secondary battery), which is excellent in the conductivity and safety function of a nonaqueous electrolyte secondary battery.

  The present invention relates to a nonaqueous electrolyte secondary battery electrode comprising a conductive carbon material (A), a water-soluble resin (B) having a hydroxyl group, and water-dispersed resin fine particles (C) containing at least olefin resin fine particles. In this conductive composition for forming an underlayer, the resistance of the current collector increases when the battery generates heat, and the current is interrupted to avoid ignition of the battery. In addition, since the resin that increases internal resistance during heat generation is water-dispersed resin fine particles, the electrical resistance of the carbon material (A) is not impaired, internal resistance during normal operation can be reduced, and output characteristics are improved. Can do.

Furthermore, as a result of intensive studies, the present inventor has a function that the water-soluble resin (B) having a hydroxyl group contained in the conductive composition continues to increase the internal resistance when the internal temperature of the battery increases. This has been found and the present invention has been made.
For example, when the internal temperature of the battery rises due to an internal short circuit or the like, the olefin-based resin fine particles contained in the conductive composition expand in volume, thereby cutting the contact between the conductive carbon materials. Thereby, since the resistance of the electrode itself is increased, it is considered that the current flowing through the short-circuited portion is reduced, the Joule heat generation is suppressed, and the battery safety is maintained. However, the resin fine particles were melted simultaneously with the volume expansion of the polyolefin resin fine particles, the carbon materials were brought into contact with each other again, the internal resistance of the battery was not sufficiently increased, and the safety could not be maintained.
On the other hand, even when the olefin resin fine particles are melted by including a predetermined amount of the water-soluble resin (B) having a hydroxyl group in the conductive composition, the water-soluble resin (B) having a hydroxyl group is re-contacted between carbons. As a result, it has been confirmed that the battery safety is drastically improved.
Furthermore, since the water-soluble resin (B) having a hydroxyl group is chemically stable in the conductive composition (slurry), there is little change with time and excellent coating properties when forming the underlayer.
Furthermore, it was found that by appropriately controlling the secondary agglomerated particle size of the conductive carbon material, the above resistance increase can be performed more effectively, and the safety of the battery can be dramatically improved. .

  Furthermore, by modifying the water-dispersed resin fine particles (C), it is possible to impart melting resistance of the resin fine particles, maintain the volume expansion of the polyolefin resin fine particles, and continue to maintain the cutting effect of the connection between the carbon materials. it can.

  It has been found that the above-described effects dramatically improve the safety of the battery.

That is, the present invention comprises a conductive carbon material (A), a water-soluble resin (B) having a hydroxyl group (however, excluding polyvinyl alcohol (PVA) and carboxymethyl cellulose having a saponification degree of 87 to 89 mol%), water, A conductive composition for forming an underlayer of an electrode for a non-aqueous electrolyte secondary battery, comprising dispersed resin fine particles (C) and an aqueous liquid medium (D), wherein the water-dispersed resin fine particles are at least olefin resin fine particles Of carbon material (A), water-soluble resin (B) having a hydroxyl group, and water-dispersed resin fine particles (C) in a total of 100% by mass of conductive carbon material (A) However, the content of the water-soluble resin (B) having a hydroxyl group is 10 to 50% by mass, and the content of the water-dispersed resin fine particles (C) is 30 to 70% by mass. Yes, water-dispersed resin fine particles C) The ratio of the olefin resin fine particles contained in the electrode is 50 to 100% by mass with respect to the entire water-dispersed resin fine particles (C). It relates to a sex composition.
The water-soluble resin (B) containing a hydroxyl group is polyvinyl alcohol (excluding polyvinyl alcohol (PVA) having a saponification degree of 87 to 89 mol%), polyvinyl alcohol derivative, guar gum, guar gum derivative, xanthan gum, xanthan gum derivative, chitosan, It is at least one selected from the group consisting of chitosan derivatives, cellulose, cellulose derivatives (excluding carboxymethylcellulose), alginic acid and alginic acid derivatives, for forming an underlayer of the electrode for a non-aqueous electrolyte secondary battery The present invention relates to a conductive composition.
The olefin resin fine particles contained in the water-dispersed resin fine particles (C) are olefin resin fine particles having a carbonyl group, and the maximum peak height (maximum absorbance) of 2800 to 3000 cm ⁻¹ in the infrared absorption spectrum of the olefin resin fine particles. ) (X) and the ratio (Y) / (X) of the maximum peak height (maximum absorbance) (Y) of 1690 to 1740 cm ⁻¹ is 0.05 to 1.0. The present invention relates to a conductive composition for forming a base layer of an electrode for a water electrolyte secondary battery.
The present invention relates to a current collector with a base layer for a nonaqueous electrolyte secondary battery, comprising a current collector and a base layer formed from the conductive composition for forming the base layer of the electrode for a nonaqueous electrolyte secondary battery.
A current collector, a base layer formed from the base layer-forming electric composition for the electrode for a conductive nonaqueous electrolyte secondary battery, and a composite formed from an electrode-forming composition containing an electrode active material and a binder. The present invention relates to a non-aqueous electrolyte secondary battery electrode having a material layer.
The present invention relates to a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an electrolyte solution, wherein at least one of the positive electrode and the negative electrode is the electrode for the non-aqueous electrolyte secondary battery.

  By including the conductive carbon material (A), the water-soluble resin (B) having a hydroxyl group, and the water-dispersed resin fine particles (C) containing at least olefin resin fine particles, the conductivity of the carbon material is not impaired. A nonaqueous electrolyte secondary battery having a function of increasing the internal resistance when the internal temperature of the battery rises can be provided.

<Conductive composition>
As described above, the conductive composition of the present invention can be used for forming a base layer of a nonaqueous electrolyte secondary battery. The conductive composition comprises a conductive carbon material (A), a water-soluble resin (B) having a hydroxyl group, water-dispersed resin fine particles (C) containing at least olefin resin fine particles, and an aqueous liquid medium (D). contains.
Content of conductive carbon material (A) in total 100 mass% of conductive carbon material (A), water-soluble resin (B) having a hydroxyl group, and solid content of water-dispersed resin fine particles (C) Is from 10 to 50% by mass, preferably from 15 to 50% by mass, and more preferably from 20 to 40% by mass, from the viewpoints of conductivity and internal resistance.
Content of water-soluble resin (B) having a hydroxyl group in a total of 100% by mass of the conductive carbon material (A), the water-soluble resin (B) having a hydroxyl group, and the solid content of the water-dispersed resin fine particles (C) The amount is from 10 to 50% by mass, preferably from 10 to 40% by mass, more preferably from 15 to 35% by mass, from the viewpoints of electrode adhesion and conductivity and increase in internal resistance of the battery during heat generation. .
The content of the water-dispersed resin fine particles (C) is 100% by mass in total of the conductive carbon material (A), the water-soluble resin (B) having a hydroxyl group, and the solid content of the water-dispersed resin fine particles (C). From the viewpoint of internal resistance and conductivity, and increase in internal resistance of the battery during heat generation, it is 30 to 70% by mass, preferably 30 to 60% by mass, more preferably 35 to 60% by mass.
The total solid content of the conductive carbon material (A), the water-soluble resin (B) having a hydroxyl group, and the water-dispersed resin fine particles (C) is 70% by mass or more of the entire conductive composition, preferably It is 80 mass% or more among electroconductive compositions, More preferably, it is 90 mass% or more among electroconductive compositions.
Moreover, although the appropriate viscosity of an electroconductive composition is based on the coating method of an electroconductive composition, generally it is preferable to set it as 10 mPa * s or more and 30,000 mPa * s or less.

First, the conductive carbon material (A) will be described.
The conductive carbon material (A) in the present invention is not particularly limited as long as it is a conductive carbon material, but graphite, carbon black, conductive carbon fiber (carbon nanotube, carbon nanofiber, carbon Fiber), fullerene, etc. can be used alone or in combination of two or more. From the viewpoint of conductivity, availability, and cost, it is preferable to use carbon black.

  Carbon black is a furnace black produced by continuously pyrolyzing a gas or liquid raw material in a reactor, especially ketjen black using ethylene heavy oil as a raw material. Channel black that has been rapidly cooled and precipitated, thermal black obtained by periodically repeating combustion and thermal decomposition using gas as a raw material, and particularly various types such as acetylene black using acetylene gas as a raw material, or 2 More than one type can be used in combination. Ordinarily oxidized carbon black, hollow carbon and the like can also be used.

  The oxidation treatment of carbon is performed by treating carbon at a high temperature in the air or by secondary treatment with nitric acid, nitrogen dioxide, ozone, etc., for example, such as phenol group, quinone group, carboxyl group, carbonyl group. This is a treatment for directly introducing (covalently bonding) an oxygen-containing polar functional group to the carbon surface, and is generally performed to improve the dispersibility of carbon. However, since it is common for the conductivity of carbon to fall, so that the introduction amount of a functional group increases, it is preferable to use the carbon which has not been oxidized.

  In addition, the carbon black used in the present invention is advantageous in decreasing the internal resistance of the electrode because the number of particles contained per unit mass increases as the primary particle diameter decreases, and the number of contact points between the carbon black particles increases. Specifically, from the viewpoint of conductivity and availability, it is preferably 1 to 100 nm, more preferably 10 to 80 nm, and even more preferably 20 to 70 nm. However, the primary particle diameter here is a spherical particle forming an aggregate (primary aggregate), and is an average of particle diameters measured with an electron microscope or the like.

The carbon black used in the present invention forms an agglomerate (secondary aggregate) formed by aggregating aggregates (primary aggregates). When the size of the secondary aggregate is larger than a predetermined size, it becomes easy to form a conductive network, which is advantageous in reducing the internal resistance of the electrode. Further, in the present invention, as a result of intensive studies, it was found that the internal resistance of the battery increases when the internal temperature of the battery rises due to the carbon black forming a predetermined secondary aggregate. . In the present invention, the secondary aggregate is represented by a volume average particle diameter. Specifically, the volume average particle diameter (D50) is preferably 0.3 to 5 μm, more preferably 0.3 to 3 μm.
The volume average particle size referred to here is the particle size (D50) at which the volume fraction becomes 50% when the volume ratio of the particles is integrated from the fine particles in the volume particle size distribution. For example, a laser scattering type particle size distribution meter ("Microtrack MT3300EXII" manufactured by Nikkiso Co., Ltd.). The volume average particle diameter can be measured by the laser scattering method as follows. A slurry obtained by mechanically dispersing a conductive carbon material (A) and a water-soluble resin (B) having a hydroxyl group is diluted with water 100 to 1000 times depending on the solid content. Measurement device [Nikkiso Co., Ltd. Microtrac MT3300EXII] cell was poured into the cell until the appropriate concentration was obtained in sampling loading, and the refractive index condition of the solvent (water in the present invention) corresponding to the sample was input and measured. I do.

  The volume average particle size of the carbon black used in the present invention is preferably larger than the volume average particle size of the water-dispersed resin fine particles (C). If the volume average particle size of the water-dispersed resin fine particles (C) is larger than the volume average particle size of the carbon black, when the internal temperature of the battery rises, the resistance of the battery does not increase efficiently, and the internal during normal operation Resistance may increase and battery performance may deteriorate. A method for measuring the volume average particle diameter of the water-dispersed resin fine particles (C) will be described separately.

The specific surface area of the carbon black used in the present invention is generally more advantageous as the value of the carbon black becomes smaller as the primary particle diameter of the carbon black decreases, increasing the contact point between the particles and lowering the internal resistance of the electrode. . Specifically, from the viewpoints of conductivity, coating suitability, electrode adhesion, and availability, the specific surface area (BET) determined from the amount of nitrogen adsorption, preferably 20-1500 m ² / g, more preferably Is preferably 40 to 1500 m ² / g.

Examples of commercially available carbon black include Toka Black # 4300, # 4400, # 4500, # 5500 (Tokai Carbon Co., Furnace Black), Printex L and the like (Degussa Co., Furnace Black), Raven 7000, 5750, 5250, 5000 ULTRA III, 5000 ULTRA, etc., Conductex SC ULTRA, Conductex 975 ULTRA, etc., PUER BLACK 100, 115, 205, etc. (manufactured by Colombian, Furnace Black), # 2350, # 2400B, # 2600B, # 3050B, # 30B, # 3030B # 3350B, # 3400B, # 5400B etc. (Mitsubishi Chemical Co., Furnace Black), MONARCH1400, 1300, 900, VulcanXC-7 R, BlackPearls2000, etc. (Cabot, Furnace Black), Ensaco250G, Ensaco260G, Ensaco350G, SuperP-Li (manufactured by TIMCAL), Ketjen Black EC-300J, EC-600JD (manufactured by Akzo), Denka Black, Denka Black HS Examples of graphite such as -100, FX-35 (manufactured by Denka Co., acetylene black) include natural graphite such as artificial graphite, flake graphite, massive graphite, and earth graphite, but are not limited thereto. Instead, two or more types may be used in combination.
As the conductive carbon fibers, those obtained by firing from petroleum-derived raw materials are preferable, but those obtained by firing from plant-derived raw materials can also be used. For example, VGCF manufactured by Showa Denko Co., Ltd. manufactured with petroleum-derived raw materials can be mentioned.

  The water-soluble resin (B) having a hydroxyl group used in the present invention is a mixture of 1 g of the water-soluble resin (B) having a hydroxyl group in 99 g of water at 70 ° C., stirred, left at 25 ° C. for 24 hours, separated, The resin can be dissolved in water without precipitation.

The water-soluble resin (B) having a hydroxyl group is not particularly limited as long as it is a water-soluble resin as described above. For example, acrylic resin, polyurethane resin, polyester resin, phenol resin, epoxy resin, polyvinyl Examples include alcohol, polyvinyl alcohol derivative, xanthan gum, xanthan gum derivative, guar gum, guar gum derivative, chitosan, chitosan derivative, cellulose, cellulose derivative, alginic acid, alginic acid derivative, starch, corn starch, corn starch derivative and the like. Moreover, if it is water-soluble, the modified substance, mixture, or copolymer of these resin may be sufficient. These water-soluble resins can be used alone or in combination.
The molecular weight of the water-soluble resin (B) having a hydroxyl group is not particularly limited, but the mass average molecular weight is preferably 5,000 to 5,000,000. The mass average molecular weight (Mw) indicates the molecular weight in terms of polyethylene oxide in gel permeation chromatography (GPC).

  In the present invention, the water-soluble resin (B) having a hydroxyl group is polyvinyl alcohol (excluding polyvinyl alcohol (PVA) having a saponification degree of 87 to 89 mol%) and / or polyvinyl alcohol derivative, xanthan gum and / or xanthan gum derivative. It is preferable to use at least one of guar gum and / or guar gum derivatives, chitosan and / or chitosan derivatives, cellulose and / or cellulose derivatives (excluding carboxymethylcellulose), alginic acid and / or alginic acid derivatives.

  Examples of the water-soluble resin having a hydroxyl group as described above include polyvinyl alcohol (excluding polyvinyl alcohol (PVA) having a saponification degree of 87 to 89 mol%), polyvinyl alcohol derivatives (such as anion-modified polyvinyl alcohol), xanthan gum, and xanthan gum derivatives. (Carboxymethyl xanthan gum etc.), chitosan, chitosan derivatives (hydroxyethyl chitosan, hydroxypropyl chitosan, carboxymethyl chitosan, glycerylated chitosan etc.), guar gum, guar gum derivatives (hydroxypropyl guar gum, cationized guar gum etc.), cellulose, cellulose derivatives ( Hydroxymethylcellulose, hydroxyethylcellulose, cellulose acetate, etc.), starch and starch derivatives (hydroxyethylated corn starch, etc.), Alginic acid, alginic acid derivatives (propylene glycol alginate, etc.) are exemplified, but the invention is not limited thereto. In addition, these water-soluble resins having hydroxyl groups are formed into salts using hydroxyalkyl etherification modification, carboxylic acid modification or base (amine compounds, alkali metal compounds, etc.) as necessary to improve water solubility. Can be used after forming a derivative.

Next, the water-dispersed resin fine particles (C) will be described.
The water-dispersed resin fine particles (C) used in the present invention are those in which a resin that does not dissolve in water is present in the form of fine particles in water, and the water dispersion is generally called an aqueous resin emulsion. And can be used in the present invention.
The water-dispersed resin fine particles include at least olefin-based resin fine particles, and the ratio of the olefin-based resin fine particles contained in the water-dispersed resin fine particles is 50 to 100% by mass, and if necessary, two or more kinds other than the olefin-based resin fine particles Water-dispersed resin fine particles may be combined. Water-dispersed resin fine particles other than olefin resin fine particles are not particularly limited, but (meth) acrylic emulsions, nitrile emulsions, urethane emulsions, diene emulsions (SBR (styrene butadiene rubber), etc.), fluorine emulsions (PVDF) (Polyvinylidene fluoride), PTFE (polytetrafluoroethylene) and the like).

  The water-dispersed resin fine particles may be resins that can expand the volume of the olefin-based resin fine particles within the range of 80 to 250 ° C. and peel off the contact between the conductive carbon materials dispersed in the conductive layer. There is no particular limitation. Examples of the olefin component constituting the olefin resin fine particles include ethylene, propylene, isobutylene, isobutene, 1-butene, 2-butene, 1-pentene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-hexene, 1-octene, norbonene and the like can be mentioned. The olefin resin fine particles may be a single polymer of these olefin components or a copolymer of two or more components. Further, from the effect of maintaining the volume expansion of the olefin resin fine particles when the internal temperature of the battery is increased, modification or copolymerization with a compound having a carboxylic acid or a carboxylic acid ester may be performed.

  In the present invention, the olefin resin fine particles contained in the water-dispersed resin fine particles (C) are preferably olefin resin fine particles having a carbonyl group modified with a compound having at least a carboxylic acid or a carboxylic acid ester. Since modification can provide melting resistance of resin fine particles, volume expansion of olefin resin fine particles can be maintained when the internal temperature of the battery rises due to internal short circuit, etc., and the cutting effect between carbon materials can be maintained. It is considered possible.

  Although it does not specifically limit as a component of carboxylic acid or carboxylic acid ester, Acrylic acid, methacrylic acid, maleic anhydride, maleic acid, itaconic anhydride, itaconic acid, fumaric acid, crotonic acid, methyl acrylate, (meth) acrylic acid Methyl, ethyl (meth) acrylate, propyl (meth) acrylate, butyl acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, lauryl (meth) acrylate, (meth ) Dodecyl acrylate, stearyl (meth) acrylate, vinyl formate, vinyl acetate, vinyl propionate, vinyl piperate.

The amount of modification of the carbonyl group-containing polyolefin resin fine particle carboxylic acid or carboxylic acid ester-containing compound is a total reflection measurement method (ATR) using a Fourier transform infrared spectrometer (FT-IR: Spectrum One / 100 manufactured by PerkinElmer). ) From 2800 to 3000 cm ⁻¹ olefin-derived maximum peak height (maximum absorbance) (X) and 1690 to 1740 cm ⁻¹ carbonyl-derived maximum peak height (maximum absorbance) (Y) The ratio (Y) / (X) is preferably 0.05 to 1.0. In the resin fine particles made of polyethylene, the above (Y) / (X) is 0.3 to 0.8, and in the resin fine particles made of polypropylene, the above (Y) / (X) is 0.05 to 0.8. More preferably, it is 0.5.
The peak height referred to here is a value obtained by measuring a solid obtained by removing the dispersion medium from the water-dispersed resin fine particles (C) and finally drying at 120 ° C. by FT-IR. The amount of modification of the polyolefin resin fine particles was determined by using a spectrum in which the absorbance was plotted against the wave number, and a line connecting the two points of the absorbance at 2700 m ^{−1 and} the absorbance at 3000 cm ⁻¹ was defined as the baseline BX. Among the two or four derived from olefins observed at 2800 to 3000 cm ⁻¹ , the height (maximum absorbance) (X) from the maximum peak to the baseline BX, and the point indicating the absorbance at 1650 m ⁻¹ Height from the maximum peak derived from the carbonyl of 1690 to 1740 cm ^-1 to the baseline BY (maximum absorbance) when the straight line connecting the two points with the point indicating the absorbance at 1850 cm ^-1 is defined as the baseline BY (Y) And the ratio (Y) / (X). In general, two polyethylene resins and four polypropylene resins are observed, and the maximum peak is observed in the vicinity of 2915 cm ^{-1 in} both cases.

  Commercially available products can be used as the water-dispersed resin fine particles as described above, and commercially available products such as Arrow Base SB-1200, SD-1200, SE-1200, TC-4010, TD-4010, and Toyo made by Unitika. Aqua Petro DP-2401, DP-2502 manufactured by Adre, Seixen AC, A, AC-HW-10, L, NC, N manufactured by Sumitomo Seika Co., Ltd., Chemipearl A100, A400, M200 manufactured by Mitsui Chemicals, S100, S200, S300V100, V200, V300, W100, W200, W300, W400, W4005, WP100, Hardren NZ-1004, NZ-1015 manufactured by Toyobo, Hitech E-6500, P-9018, S-manufactured by Toho Chemical Co., Ltd. 3121 etc. are mentioned, but it is not limited to these. It may be used in conjunction seen.

  As the dispersion medium of the water-dispersed resin fine particles (C) of the present invention, water is preferably used, but a liquid medium compatible with water may be used for stabilizing the resin fine particles. The dispersion medium may be separated from the water-dispersed resin fine particles (C) to constitute the conductive composition of the present invention, or may be used as it is as the aqueous liquid medium (D). Liquid media compatible with water include alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, and phosphoric acid esters , Ethers, nitriles and the like, and may be used as long as they are compatible with water.

  The average particle diameter of the water-dispersed resin fine particles (C) of the present invention is preferably 0.01 to 5 μm, more preferably 0.05 to 1 μm. If the particle size is too small, it will be difficult to produce stably, while if the particle size is too large, it will be difficult to keep the conductivity of the conductive layer uniform, the internal resistance during normal operation will increase, and the battery will Performance deteriorates.

  In addition, the average particle diameter in this invention represents a volume average particle diameter (D50), and can be measured by the dynamic light scattering method. The average particle diameter can be measured by the dynamic light scattering method as follows. The water-dispersed resin fine particle dispersion is diluted with water 200 to 1000 times depending on the solid content. About 5 ml of the diluted solution is injected into a cell of a measuring device [Nanotrack manufactured by Nikkiso Co., Ltd.], and after inputting the refractive index conditions of the solvent (water in the present invention) and the resin according to the sample, the measurement is performed.

Next, the aqueous liquid medium (D) will be described.
As the aqueous liquid medium (D) used in the present invention, it is preferable to use water, but if necessary, for example, a liquid medium compatible with water in order to improve the coating property to the current collector. May be used.

  Liquid media compatible with water include alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, and phosphoric acid esters , Ethers, nitriles and the like, and may be used as long as they are compatible with water.

  Furthermore, a film-forming auxiliary, an antifoaming agent, a leveling agent, a preservative, a pH adjusting agent, a viscosity adjusting agent and the like can be blended with the conductive composition as necessary.

(Disperser / Mixer)
As an apparatus used when obtaining the conductive composition of the present invention or a composite ink described later, a disperser or a mixer that is usually used for pigment dispersion or the like can be used.
For example, mixers such as dispersers, homomixers, or planetary mixers; homogenizers such as “Clairemix” manufactured by M Technique, or “Fillmix” manufactured by PRIMIX; paint conditioner (manufactured by Red Devil), ball mill, sand mill (Shinmaru Enterprises "Dynomill", etc.), Attritor, Pearl Mill (Eirich "DCP Mill", etc.), or Coball Mill, etc .; Media type dispersers; Wet Jet Mill (Genus, "Genus PY", Sugino Media-less dispersers such as “Starburst” manufactured by Machine, “Nanomizer” manufactured by Nanomizer, etc., “Claire SS-5” manufactured by M Technique, or “MICROS” manufactured by Nara Machinery; or other roll mills, etc. Although The present invention is not limited to these. Moreover, as the disperser, it is preferable to use a disperser that has been subjected to a metal contamination prevention treatment from the disperser.
For example, when using a media-type disperser, a disperser in which the agitator and vessel are made of a ceramic or resin disperser, or the surface of the metal agitator and vessel is treated with tungsten carbide spraying or resin coating. Is preferably used. As the media, it is preferable to use glass beads, ceramic beads such as zirconia beads or alumina beads. Moreover, also when using a roll mill, it is preferable to use a ceramic roll. Only one type of dispersion device may be used, or a plurality of types of devices may be used in combination. Further, in the case of a positive or negative electrode active material in which particles are easily broken or crushed by a strong impact, a medialess disperser such as a roll mill or a homogenizer is preferable to a media type disperser.

  The conductive composition of the present invention can be produced by applying appropriate shear and impact using the above-described disperser. If excessive shear or impact is applied, the secondary aggregates of the conductive carbon material may be crushed, and the internal resistance of the battery during normal operation or the internal resistance when the battery internal temperature rises may not be sufficiently increased.

The size of the secondary aggregate of carbon black in the conductive composition can be evaluated by the gloss of the coating film, and the gloss value of the coating film increases as the secondary aggregate decreases. The coating film obtained by applying and drying the conductive composition on a PET (polyethylene terephthalate) film can be measured with a gloss meter (60 °). Specifically, the gloss value of the coating film of the conductive composition is 0.1 to 40, preferably 0.1 to 30. When the gloss value is high, the secondary aggregate of carbon black becomes small, and thus the internal resistance of the battery during normal operation and the internal resistance when the battery internal temperature rises may not be sufficiently increased.
In the present invention, the gloss value of the coating film of the conductive composition can be measured as follows. The prepared conductive composition is applied to a PET (polyethylene terephthalate) film so as to have a thickness of about 1 to 5 μm, and then placed in an oven at 150 ° C. for 2 to 5 minutes to prepare a coating film. This coating film is placed on a black flat plate and measured with a gloss meter (micro-TRI-gloss manufactured by BYK). In the present invention, a value of 60 ° is read as a gloss value.
In measuring the gloss of the coating film, it is preferable to measure what is coated on a PET film, but what is coated on an Al foil or the like may be measured.

(Current collector with base layer for non-aqueous electrolyte secondary battery, electrode for non-aqueous electrolyte secondary battery)
The current collector with a base layer for a non-aqueous electrolyte secondary battery of the present invention has a base layer formed from the conductive composition of the present invention on the current collector.
Moreover, the electrode for nonaqueous electrolyte secondary batteries of the present invention is a composition for forming an electrode comprising an underlayer formed from the conductive composition of the present invention on a current collector, an electrode active material, and a binder. And a composite layer formed from a material (composite ink).

(Current collector)
The material and shape of the current collector used for the electrode are not particularly limited, and those suitable for various nonaqueous electrolyte secondary batteries can be appropriately selected.
For example, examples of the material for the current collector include metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel. In the case of a lithium ion battery, aluminum is particularly preferable as the positive electrode material, and copper is preferable as the negative electrode material. In general, a flat foil is used as the shape, but a roughened surface, a perforated foil, or a mesh current collector can also be used.

<Underlayer>
The base layer forming conductive composition for forming the base layer of the electrode for a non-aqueous electrolyte secondary battery of the present invention can be coated on the current collector and dried to form the base layer.
There is no restriction | limiting in particular as a method of apply | coating a conductive composition and the mixture ink mentioned later on a collector, A well-known method can be used. Specific examples include die coating method, dip coating method, roll coating method, doctor coating method, knife coating method, spray coating method, gravure coating method, screen printing method or electrostatic coating method, and the like. Examples of methods that can be used include standing drying, blow dryers, hot air dryers, infrared heaters, and far infrared heaters, but are not limited to these, and rolling treatment with a lithographic press or calender roll after application. May be performed.

  The thickness of the underlayer is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm, and still more preferably 0.5 to 3 μm. If the thickness of the underlayer is too thin, a bypass portion where the current collector and the active material are in direct contact is locally formed, and when the battery generates heat, the current blocking effect due to the increase in resistance of the underlayer portion becomes insufficient. . On the other hand, if the thickness of the underlayer is too thick, the proportion of the underlayer in the electrode increases, the content ratio of the active material decreases, and the battery capacity decreases.

  The underlayer can be provided on one side or both sides of the current collector, but it is preferably provided on both sides of the current collector from the viewpoint of increasing resistance due to heat and reducing the internal resistance of the battery.

<Composite ink>
The composite ink refers to an active material that is a component of electrodes used in primary and secondary batteries, a binder, a solvent, and the like in a liquid or paste form. The non-aqueous electrolyte of the present invention Also in the electrode for secondary batteries, an active material and a solvent are essential, and a conductive additive and a binder are contained as necessary.
The active material is preferably contained as much as possible. For example, the proportion of the active material in the solid material ink solid content is preferably 80 to 99% by mass or less. When the conductive assistant is included, the proportion of the conductive assistant in the solid ink solid content is preferably 0.1 to 15% by mass. When the binder is included, the ratio of the binder to the solid material ink solid content is preferably 0.1 to 15% by mass.

  Although it depends on the coating method, the viscosity of the composite ink is preferably 100 mPa · s or more and 30,000 mPa · s or less in the range of 30 to 90% by mass of the solid content.

(Active material)
The active material used in the composite ink will be described below.
The positive electrode active material for the lithium ion secondary battery is not particularly limited, but metal oxides capable of doping or intercalating lithium ions, metal compounds such as metal sulfides, and conductive polymers are used. be able to.

Examples thereof include transition metal oxides such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, transition metal oxide powders such as MnO, V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , layered structure lithium nickelate, lithium cobaltate, lithium manganate, spinel structure lithium manganate, etc. Examples thereof include composite oxide powders of lithium and transition metals, lithium iron phosphate materials that are phosphate compounds having an olivine structure, and transition metal sulfide powders such as TiS ₂ and FeS.

  In addition, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Moreover, you may mix and use said inorganic compound and conductive polymer.

The negative electrode active material for the lithium ion secondary battery is not particularly limited as long as it can be doped or intercalated with lithium ions. For example, metal Li, alloys thereof such as tin alloy, silicon alloy, lead alloy, Li _x Fe ₂ O ₃ , Li _x Fe ₃ O ₄ , Li _x WO ₂ (where x is an integer of 1 to 3) Amorphous carbonaceous materials such as metal oxides such as lithium titanate, lithium vanadate and lithium siliconate, conductive polymer such as polyacetylene and poly-p-phenylene, soft carbon and hard carbon And carbon-based materials such as artificial graphite such as highly graphitized carbon material, carbonaceous powder such as natural graphite, carbon black, mesophase carbon black, resin-fired carbon material, gas-grown carbon fiber, and carbon fiber. These negative electrode active materials can be used alone or in combination.

  The conductive assistant in the composite ink is not particularly limited as long as it is a carbon material having conductivity, and the same conductive carbon material (A) as described above can be used.

  The binder in the composite ink is used for binding particles such as an active material or a conductive carbon material, or a conductive carbon material and a current collector.

Examples of binders used in the composite ink include acrylic resin, polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, formaldehyde resin, silicon resin, fluorine resin, Cellulose resins such as carboxymethyl cellulose, synthetic rubbers such as styrene-butadiene rubber and fluororubber, conductive resins such as polyaniline and polyacetylene, and polymer compounds containing fluorine atoms such as polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene Is mentioned. Further, a modified product, a mixture, or a copolymer of these resins may be used. These binders can be used alone or in combination.
The binder suitably used in the water-based composite ink is preferably an aqueous medium, and examples of the aqueous medium binder include water-soluble type, emulsion type, hydrosol type, and the like. be able to.

  Furthermore, a film forming aid, an antifoaming agent, a leveling agent, a preservative, a pH adjuster, a viscosity adjuster, and the like can be blended in the composite ink as necessary.

<Method for producing electrode>
The conductive composition of the present invention can be applied and dried on a current collector to form a base layer, whereby a base layer electrode for a nonaqueous electrolyte secondary battery can be obtained.
Alternatively, the conductive composition of the present invention is coated and dried on a current collector to form a base layer, and a composite layer is provided on the base layer to obtain an electrode for a nonaqueous electrolyte secondary battery. You can also The composite material layer provided on the base layer can be formed using the above-described composite ink.

(Electrolytic solution of non-aqueous electrolyte)
A case of a lithium ion secondary battery will be described as an example. As the electrolytic solution, an electrolyte containing lithium dissolved in a non-aqueous solvent is used.
As electrolytes, LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₃ C , LiI, LiBr, LiCl, LiAlCl, LiHF ₂ , LiSCN, or LiBPh ₄ (where Ph represents a phenyl group), but is not limited thereto.

Although it does not specifically limit as a non-aqueous solvent, For example, carbonates, such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate;
Lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone;
Glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane;
Esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and
Nitriles such as acetonitrile are exemplified. These solvents may be used alone or in combination of two or more.
Furthermore, the electrolyte solution may be a polymer electrolyte that is held in a polymer matrix and made into a gel. Examples of the polymer matrix include, but are not limited to, an acrylate resin having a polyalkylene oxide segment, a polyphosphazene resin having a polyalkylene oxide segment, and a polysiloxane having a polyalkylene oxide segment.

(separator)
Examples of the separator include, but are not limited to, a polyethylene nonwoven fabric, a polypropylene nonwoven fabric, a polyamide nonwoven fabric and those obtained by subjecting them to a hydrophilic treatment.

Example 1
<Conductive composition>
25 parts by mass of acetylene black (A-1: Denka Black HS-100, manufactured by Denka) as an electrically conductive carbon material, an anion-modified polyvinyl alcohol (AT-17, Nippon Vinegar Poval) which is a water-soluble resin having a hydroxyl group (Product) 1000 parts by mass of a 2.5% aqueous solution (25 parts by mass as a solid content) was mixed in a mixer, and further dispersed in a sand mill. Next, 125 mass parts (50 mass parts as solid content) of polyolefin resin fine particles (Chemical Pearl W4005, solid content 40% aqueous dispersion, average particle size 0.57 μm, manufactured by Mitsui Chemicals, Inc.), which is water-dispersed resin fine particles, It mixed with the mixer and the electroconductive composition (1) was obtained.

The materials and coating films used in the examples and comparative examples were evaluated as follows.
(Modification amount of olefin resin fine particles (Y) / (X))
The water-dispersed resin fine particles (C) were placed in an oven at 80 ° C. to remove the dispersion medium, and then dried at 120 ° C. for 30 minutes to obtain a solid. This was measured by a total reflection measurement method (ATR) using a Fourier transform infrared spectrometer (FT-IR: Spectrum One / 100 manufactured by PerkinElmer).
Modification amount using spectral plotting absorbance against wave numbers, when used as a baseline BX a straight line connecting two points of the point indicating the absorbance at a point and 3000 cm ^-1 indicating the absorbance at 2700 cm ^-1, 2800 The height (maximum absorbance) (X) from the maximum peak derived from the olefin of ˜3000 cm ⁻¹ to the baseline BX is connected to the point indicating the absorbance at 1650 m ⁻¹ and the point indicating the absorbance at 1850 cm ⁻¹ . The ratio (Y) / (X) to the height (maximum absorbance) (Y) from the maximum peak derived from the carbonyl of 1690 to 1740 cm ⁻¹ to the baseline BY when the straight line was taken as the baseline BY was determined.

(Examples 2 to 18, Comparative Examples 1 to 3)
The conductive compositions shown in Table 1 are the same as those of the conductive composition (1) except that the conductive carbon material, the water-soluble resin having a hydroxyl group, the water-dispersed resin fine particles, and the composition ratio are changed. Products (2) to (21) were obtained.

The materials used in Examples and Comparative Examples are shown below.
(Conductive carbon material (A))
A-1: Denka Black HS-100 (Denka)
A-2: Mitsubishi Carbon # 3050B (Mitsubishi Chemical Corporation)
(Water-soluble resin having a hydroxyl group (B))
B-1: Anion-modified polyvinyl alcohol: AT-17 (Nippon Vinegar-Poval)
B-2: hydroxyethyl cellulose: SANHEC (manufactured by Sansho)
B-3: Sodium alginate: Kimika Argin I-1 (manufactured by KIMICA)
・ B-4: Guar gum: SUPERGEL40 (manufactured by Sansho)
-B-5: Chitosan: LL-80 (manufactured by KIMICA)
B-6: Xanthan gum: KELTROL CG-SFT (manufactured by Sansho)
B-7: Hydroxyethylated corn starch: COATMASTER K92F (manufactured by Sansho)
-B-8: Polyvinyl alcohol: P-610 (degree of saponification 95.0-97.0 mol%, manufactured by Nippon Synthetic Chemical Co., Ltd.)
B-9: Carboxymethylated guar gum: MEYPROID 8700 (manufactured by Sansho)
B-10: Glycol chitosan (manufactured by Wako Pure Chemical Industries, Ltd.)
B-11: Alginic acid: Kimika Argin G (manufactured by KIMICA)
(Water-dispersed resin fine particles (C))
C-1: Chemipearl W4005 (polyethylene resin fine particles, solid content 40% aqueous dispersion, average particle size 0.57 μm, manufactured by Mitsui Chemicals)
C-2: Arrow base TC-4010 (polypropylene resin fine particles, solid content 25% aqueous dispersion, average particle size 0.20 μm, manufactured by Unitika)
C-3: Syxen AC (polyethylene resin fine particles, 30% solid content aqueous dispersion, average particle size 0.04 μm, manufactured by Sumitomo Seika Co., Ltd.)
C-4: Hardene NZ-1004 (polypropylene resin fine particles, solid content 30% aqueous dispersion, average particle size 0.12 μm, manufactured by Toyobo Co., Ltd.)
C-5: polytetrafluoroethylene 30-J (fluorine resin fine particles, solid content 60% aqueous dispersion, average particle size 0.2 μm, manufactured by Mitsui DuPont Fluorochemicals)
C-6: TRD2001 (styrene butadiene resin fine particle, solid content 48% aqueous dispersion, manufactured by JSR)

(Comparative Example 6)
30 parts by mass of acetylene black (A-1: Denka Black HS-100, Denka Kogyo Co., Ltd.) as a conductive carbon material, 35 parts by mass of polyvinylidene fluoride (KF polymer # 9100 :: Kureha Co.) which is a water-insoluble resin; After mixing 900 parts by mass of N-methylpyrrolidone in a mixer and mixing, 35 parts by mass of solid polyolefin resin having a melting point of 130 ° C. and a density of 0.98 g / ml is placed in an oven at 160 ° C. to dissolve the polyolefin resin. After that, the mixture was dispersed in a sand mill to obtain a conductive composition (22).

(Comparative Example 7)
As a conductive carbon material, 28 parts by mass of acetylene black (A-1: Denka Black HS-100, Denka), 72 parts by mass of polyvinylidene fluoride (KF polymer # 9100: Kureha) as a water-insoluble resin, and N— 900 parts by mass of methylpyrrolidone was mixed in a mixer, and further dispersed in a sand mill to obtain a conductive composition (23).

<Current Collector with Underlayer> (Examples 1 to 12, Comparative Examples 1 and 2)
The conductive compositions (1) to (12), (19), and (20) were coated on a 20 μm thick aluminum foil serving as a current collector using a bar coater, and then heated and dried at 80 ° C. The current collectors (1) to (12), (19), and (20) with a base layer for a nonaqueous electrolyte secondary battery were obtained so that the thickness of the coating film was 2 μm.

<Current collector with underlayer> (Comparative Examples 6 and 7)
The conductive compositions (22) and (23) were applied on a 20 μm thick aluminum foil serving as a current collector to a thickness of 2 μm using a bar coater, and then heated and dried at 80 ° C. It was. Subsequently, it heat-processed for 5 hours in 145 degreeC oven, and obtained the collectors (22) and (23) with the base layer for nonaqueous electrolyte secondary batteries.

<Current Collector with Underlayer> (Examples 13 and 14, Comparative Example 3)
The conductive compositions (13), (14), and (21) were applied on a copper foil having a thickness of 20 μm serving as a current collector using a bar coater, and then heated and dried at 80 ° C. to obtain a thickness of 2 μm. Thus, current collectors (13), (14) and (21) with a base layer for a nonaqueous electrolyte secondary battery were obtained.

<Composite ink for lithium ion secondary battery positive electrode>
93 parts by mass of LiNi _0.5 Mn _0.3 Co _0.2 O ₂ as a positive electrode active material, 4 parts by mass of acetylene black as a conductive agent, 3 parts by mass of polyvinylidene fluoride (W # 7200, manufactured by Kureha), 45 parts by mass of N-methylpyrrolidone Were mixed to prepare a positive electrode mixture ink.

<Composite ink for negative electrode of lithium ion secondary battery>
As a negative electrode active material, 98 parts by mass of artificial graphite and 66.7 parts by mass of a carboxymethyl cellulose 1.5% aqueous solution (1 part by mass as a solid content) were put in a planetary mixer and kneaded, and 33 parts by mass of water, a styrene butadiene emulsion (TRD2001). , Manufactured by JSR Co., Ltd.) 48 mass% aqueous dispersion 2.08 parts by mass (1 part by mass as solid content) was mixed to obtain a mixture ink for negative electrode secondary battery electrode.

<Positive electrode for lithium ion secondary battery with underlayer> (Examples 1 to 12, Comparative Examples 1, 2, 6, and 7)
The lithium-ion secondary battery positive electrode composite ink described above is applied to the secondary battery undercoat current collector (1) to (12), (19), (20), (22), (23) on the doctor. After coating using a blade, the coating was adjusted by heating and drying at 80 ° C. so that the basis weight per unit area of the electrode was 20 mg / cm ² . Furthermore, the rolling process by roll press was performed and the positive electrode (1)-(12), (19), (20), (24), (25) from which the density of a compound-material layer became 3.1 g / cm < ³ > was produced. .

<Positive Electrode for Lithium Ion Secondary Battery Without Underlayer> (Positive electrodes for Examples 13 to 18, Comparative Examples 3, 4, and 5)
After applying the above-mentioned ink mixture for lithium ion secondary battery positive electrode on a 20 μm-thick aluminum foil serving as a current collector using a doctor blade, it is dried by heating at 80 ° C., and the basis weight per unit area of the electrode The amount was adjusted to 20 mg / cm ² . Furthermore, the rolling process by roll press was performed and the positive electrode (13)-(18), (21), (22), (23) from which the density of a compound-material layer became 3.1 g / cm < ³ > was produced.

<Negative Electrode for Lithium Ion Secondary Battery without Base Layer> (Negative Electrodes for Examples 1-12, Comparative Examples 1, 2, 4-7)
After applying the above-mentioned ink mixture for lithium ion secondary battery negative electrode on a copper foil having a thickness of 20 μm as a current collector using a doctor blade, it is dried by heating at 80 ° C. per unit area of the electrode The amount was adjusted to 12 mg / cm ² . Furthermore, the rolling process by roll press was performed and the negative electrode (1)-(12), (19), (20), (22)-(25) from which the density of a compound-material layer was set to 1.5 g / cm < ³ > was produced. .

<Negative Electrode for Lithium Ion Secondary Battery with Underlayer> (Examples 13 to 18, Comparative Example 3)
The above mixture ink for lithium ion secondary battery negative electrode was applied on the current collectors (13) to (18) and (21) with a base layer using a doctor blade, and then dried by heating at 80 ° C. The basis weight per unit area was adjusted to 12 mg / cm ² . Furthermore, the rolling process by a roll press was performed and the negative electrode (13)-(18), (21) from which the density of a compound material layer will be 1.5 g / cm < ³ > was produced.

<Laminated Lithium Ion Secondary Battery> (Examples 1 to 18, Comparative Examples 1 to 7)
The positive electrode and negative electrode shown in Table 2 are punched into 45 mm × 40 mm and 50 mm × 45 mm, respectively, and a separator (porous polypropylene film) inserted between them is inserted into an aluminum laminated bag, and after vacuum drying, an electrolytic solution ( After injecting LiPF ₆ at a concentration of 1M) into a mixed solvent in which ethylene carbonate and diethyl carbonate are mixed at a ratio of 1: 1 (volume ratio), the aluminum laminate is sealed and laminated. Type lithium ion battery was produced. Laminate type lithium ion batteries are manufactured in a glove box substituted with argon gas, and after making laminated type lithium ion batteries, the battery characteristics are evaluated for initial resistance, resistance increase, rate characteristics and cycle characteristics shown below. It was.

(Resistance measurement)
A laminate type battery that was discharged at a constant discharge current of 3.0 V at a discharge current of 12 mA (0.2 C) was subjected to resistance measurement at 500 kHz with an impedance analyzer (SP-50 manufactured by biologic).
The laminate type battery described above was heated from 25 ° C. to 180 ° C., and resistance measurement was performed at each temperature. The resistance measured at 25 ° C. was taken as the initial resistance, and the quotient of the resistance value measured at 180 ° C. and the resistance value measured at 25 ° C. was taken as the resistance increase. That is, the increase in resistance is expressed by the following (formula 1).
(Equation 1) Resistance increase = resistance value at 180 ° C./resistance value at 25 ° C. The results of evaluating the initial resistance and the resistance increase according to the following criteria are shown in Table 2.
Initial resistance ○: “The initial resistance is smaller than the initial resistance of Comparative Example 1 without an underlayer. Excellent.”
Δ: “The initial resistance is equivalent to the initial resistance of Comparative Example 1 without the underlayer”
X: “The initial resistance is larger than the initial resistance of Comparative Example 1 without the underlayer. Inferior”
・ Increased resistance ○: “Increased resistance is more than 5 times the initial resistance. Excellent”
Δ: “Increase in resistance is 3 times or more and less than 5 times the initial low ability. Insufficient current blocking effect”
X: “Increased resistance is less than 3 times the initial resistance. Current blocking effect is low. Inferior”

(Rate characteristics)
About the laminated battery mentioned above, charging / discharging measurement was performed using the charging / discharging apparatus (SM-8 by Hokuto Denko).
Constant current and constant voltage charge with a charge current of 12 mA (0.2 C) and a charge end voltage of 4.2 V (after a cut-off current of 0.6 mA, the discharge was terminated at a discharge current of 12 mA (0.2 C) and 120 mA (2 C). The constant current discharge was performed until the voltage reached 3.0 V, and the discharge capacity was obtained, respectively, and the rate characteristic is expressed by the ratio of 0.2 C discharge capacity to 2 C discharge capacity, that is, the following (Equation 2).
(Equation 2) Rate characteristics = 2C discharge capacity / 0.2C discharge capacity × 100 (%)
Table 2 shows the results of evaluation based on the following criteria.
・ Rate characteristic ○: “Rate characteristic is 80% or more. Particularly excellent.”
○ △: “Rate characteristic is 75% or more and less than 80%. Excellent”
Δ: “The rate characteristic is 70 or more and less than 75%. Equivalent to the rate characteristic of Comparative Example 1 without a base layer.”
X: “Rate characteristic is less than 70%. Inferior”

(Cycle characteristics)
After performing constant current and constant voltage charging (cutoff current 0.6 mA) at a charge current of 60 mA and a charge end voltage of 4.2 V in a 50 ° C. constant temperature bath, the discharge current reaches 60 V at a discharge current of 60 mA. The initial discharge capacity was obtained by performing constant current discharge until. This charge / discharge cycle was performed 200 times, and the discharge capacity maintenance ratio (percentage of the 200th discharge capacity with respect to the initial discharge capacity) was calculated. Table 2 shows the results of evaluation based on the following criteria.
Cycle characteristics ○: “Discharge capacity maintenance rate is 90% or more. Particularly excellent.”
○ △: “Discharge capacity maintenance ratio is 85% or more and less than 90%. Excellent”
Δ: “Discharge capacity maintenance ratio is 80% or more and less than 85%. Equivalent to the discharge capacity maintenance ratio of Comparative Example 1 without a base layer.”
×: “Discharge capacity maintenance rate is less than 80%. Inferior”

As shown in Table 2, it was confirmed that the internal resistance of the battery increased when the internal temperature of the battery increased by using the base layer formed from the conductive composition of the present invention. From this, for example, when the battery abnormally heats up due to an internal short circuit or the like, it is considered that the resistance of the current collector increases and the current is cut off to avoid ignition of the battery.
On the other hand, in Comparative Examples 4 and 5 in which the base layer is not formed and Comparative Examples 1, 2, 6, and 7 other than the present invention, even if the internal temperature of the battery is increased, the remarkable increase in the internal resistance of the battery is I couldn't see it. Since Comparative Examples 4 and 5 do not have a base layer formed, there is no effect of increasing resistance during heat generation. In Comparative Examples 1, 2, 6, and 7, the volume expansion of the resin during heat generation is insufficient, so This is probably because the conductive carbon materials dispersed in the layers could not be peeled off. Further, in Comparative Example 6, it is considered that the dispersibility of the polyolefin resin in the underlayer was non-uniform, so that the contact between the conductive carbon materials could not be efficiently peeled off. It is considered that the dispersibility of the functional carbon material and the polyolefin resin is not uniform, the conductivity of the underlayer is deteriorated, and the rate characteristics and the cycle characteristics are deteriorated.
As shown in Comparative Examples 2 and 3, when the content of the water-soluble resin (B) having a hydroxyl group was too small, the resistance increase due to heating was not so high. In Comparative Examples 2 and 3, the content of the water-soluble resin (B) having a hydroxyl group is small, and it is not possible to suppress the melting of the resin fine particles, which seems to occur simultaneously with the volume expansion of the polyolefin resin fine particles due to heating. This is thought to be due to the inability to cut each other.
On the other hand, as shown in Examples 3, 5, 6, 9 to 13, 15 to 18, even when the olefin-based water-dispersed resin fine particles (C) are used, those having a large amount of modification of carboxylic acid or carboxylic acid ester are As a result, a high resistance increase due to heating was obtained. This is considered to be because the polyolefin resin fine particles were able to suppress the melting of the resin fine particles during heating due to the modification of a certain amount or more, thereby effectively cutting the carbon materials. Further, as shown in Examples 3, 8, and 13, even when the same carbon material (A) and water-dispersed resin fine particles (C) are used, the degree of increase in resistance during heat generation is different, so details are unknown. However, it has become clear that the effect varies depending on the difference in the water-soluble resin (B) having a hydroxyl group.
From the above results, according to the present invention, the battery has excellent output characteristics and the like, and when the internal temperature of the battery rises due to overcharge, internal short circuit, etc., the current flowing is suppressed by increasing the internal resistance. It is possible to provide a conductive composition for forming a non-aqueous electrolyte secondary battery having a function of improving the safety of the battery.

Claims (6)

Conductive carbon material (A), water-soluble resin (B) having a hydroxyl group (however, excluding polyvinyl alcohol (PVA) and carboxymethylcellulose having a saponification degree of 87 to 89 mol%), and water-dispersed resin fine particles (C) And an aqueous liquid medium (D), a conductive composition for forming an underlayer of an electrode for a nonaqueous electrolyte secondary battery, wherein the water-dispersed resin fine particles include at least olefin resin fine particles, and a carbon material The total content of the solid content of (A), the water-soluble resin (B) having a hydroxyl group, and the water-dispersed resin fine particles (C) is 100% by mass, and the content of the conductive carbon material (A) is 10 to 50%. The content of the water-soluble resin (B) having a hydroxyl group is 10 to 50% by mass, the content of the water-dispersed resin fine particles (C) is 30 to 70% by mass, and the water-dispersed resin. Included in fine particles (C) The proportion of the olefin resin particles, the whole water-dispersible resin fine particles (C) with respect to the underlying layer forming the conductive composition of the nonaqueous electrolyte secondary battery, characterized in that 50 to 100 wt%. The water-soluble resin (B) containing a hydroxyl group is polyvinyl alcohol (excluding polyvinyl alcohol (PVA) having a saponification degree of 87 to 89 mol%), polyvinyl alcohol derivative, guar gum, guar gum derivative, xanthan gum, xanthan gum derivative, chitosan, 2. The electrode for a nonaqueous electrolyte secondary battery according to claim 1, which is at least one selected from the group consisting of chitosan derivatives, cellulose, cellulose derivatives (excluding carboxymethylcellulose), alginic acid and alginic acid derivatives. A conductive composition for forming an underlayer. The olefin resin fine particles contained in the water-dispersed resin fine particles (C) are olefin resin fine particles having a carbonyl group, and the maximum peak height (maximum absorbance) of 2800 to 3000 cm ⁻¹ in the infrared absorption spectrum of the olefin resin fine particles. The ratio (Y) / (X) of (X) to the maximum peak height (maximum absorbance) (Y) of 1690 to 1740 cm ⁻¹ is 0.05 to 1.0. 3. A conductive composition for forming a base layer of a nonaqueous electrolyte secondary battery electrode according to 1 or 2. A base layer for a non-aqueous electrolyte secondary battery, comprising: a current collector; and a base layer formed from the conductive composition for forming a base layer for a non-aqueous electrolyte secondary battery electrode according to any one of claims 1 to 3. Current collector with. A current collector, an underlayer formed from the conductive composition for forming the underlayer of the electrode for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, and an electrode formation containing an electrode active material and a binder An electrode for a nonaqueous electrolyte secondary battery comprising a composite layer formed from the composition for use. A nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an electrolyte solution, wherein at least one of the positive electrode or the negative electrode is an electrode for a nonaqueous electrolyte secondary battery according to claim 5. Secondary battery.