JP2013134884A - Positive electrode mixture, positive electrode, and nonaqueous electrolyte secondary battery including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an aqueous positive electrode mixture offering excellent dispersibility of a positive electrode active material, excellent storage stability, and an excellent coating property when applied to a collector, and allowing a positive electrode to offer excellent adhesion between the collector and the positive electrode active material after applied to the collector; a positive electrode; and a nonaqueous electrolyte secondary battery including the same.SOLUTION: The positive electrode mixture contains a positive electrode active material, a water-dispersible polymeric binder resin, a conductive assistant, and a surfactant. The water-dispersible polymeric binder resin includes at least a polyurethane resin, and the polyurethane resin contains at least a polyol and a polyisocyanate.

Description

  The present invention relates to a positive electrode mixture, a positive electrode, and a nonaqueous electrolyte secondary battery using the positive electrode mixture, and more specifically, to dispersibility of a positive electrode active material, storage stability, and coating property when applied to a current collector. A water-based positive electrode mixture, a positive electrode, and a non-aqueous electrolyte using the same, which can obtain a positive electrode excellent in adhesion to the current collector and the positive electrode active material after being applied to the current collector. Next battery.

  In recent years, electronic parts have become smaller and more multifunctional, and many portable electronic devices have appeared. These are desired to be reduced in size and weight, and a battery used as a power source is similarly required to be reduced in size and weight. In addition, against the background of environmental problems and resource problems, hybrid cars and electric cars have been developed, manufactured and sold. In such a so-called electric vehicle, it is indispensable to use a power supply device that can be charged and discharged in a small size and light weight and has a high energy density. As these power supply devices, secondary batteries such as lithium ion batteries and nickel metal hydride batteries, electric double layer capacitors, and the like are used. In particular, non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are attracting attention as power supply devices due to their high energy density and high durability that can withstand repeated charging and discharging. It has been.

  The electrode of the secondary battery is composed of an active material, a conductive additive, and a binder resin that binds these to a current collector. In the secondary battery, since the positive electrode or the negative electrode repeats volume expansion and contraction during charging and discharging, the active material and the conductive auxiliary agent may be dropped, thereby shortening the cycle life of charging and discharging. Therefore, the binder resin for secondary batteries is required to be flexible enough to withstand the swelling and shrinkage of the electrode. Conventionally, both the positive electrode and the negative electrode have many fluorine resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Has been used.

  However, since a general fluororesin has insufficient adhesion to the current collector, it has not been possible to meet the demand for further improvement of the charge / discharge cycle life. In particular, when polyvinylidene fluoride is used as a binder resin, the current collector and electrode are used during battery manufacture and during battery use because the binding force with the current collector or filler (positive electrode active material and conductive additive) is weak. Separation of the mixture occurred and the internal resistance of the battery increased.

  For such a problem, for example, Patent Document 1 proposes a copolymer of vinylidene fluoride and a polar monomer such as a monoester of an unsaturated dibasic acid as a fluororesin that is a binder resin. According to this, it is possible to improve the binding property between the fluororesin and the current collector. Patent Documents 2 and 3 disclose, as binder resins for negative electrode active materials, water-dispersed emulsions of styrene-butadiene copolymer (SBR) particles, sodium salts or ammonium salts of SBR particles and carboxymethyl cellulose (CMC). A composition consisting of As in Patent Documents 2 and 3, by using SBR particles as a binder resin, it is possible to prevent the negative electrode active material from falling off when the secondary battery is used.

  Furthermore, in Patent Document 4, a cross-linking agent is added to an acrylic resin as a binder resin dissolved in a solvent, and the acrylic resin and the cross-linking agent are reacted in the heating and pressure-bonding steps during electrode preparation to produce a three-dimensional cross-linked structure. Thus, there has been proposed a technique for preventing the active material and the conductive agent from falling off during charging and discharging of the secondary battery.

Japanese Patent No. 3121943 Japanese Patent No. 3101775 Japanese Patent No. 3260972 Japanese Patent No. 3066682

  However, the fluorine-based resin proposed in Patent Document 1 still has sufficient solvent resistance and chemical resistance in consideration of use under severe conditions such as when used as a binder resin for non-aqueous secondary battery electrodes. It is hard to say that you have sex. Further, in the use of the binder resin described in Patent Documents 2 and 3, although the SBR particles have the advantage that the negative electrode active material is not easily dropped even after repeated charge and discharge, a battery having a large capacity is obtained. There was a problem that could not. Further, the SBR particles tend to be adsorbed on the carbon material that is the negative electrode active material, and tend to cover the surface of the carbon material. Therefore, the electrolytic solution containing lithium ions is difficult to permeate and sufficient electrical characteristics may not be obtained. Furthermore, when the solvent-soluble binder resin proposed in Patent Document 4 is used, if the organic solvent is removed after applying the resin solution to the electrode substrate, the surface of the electrode active material is covered with the resin without any gaps. . Therefore, there has been a problem that sufficient electrical characteristics cannot be obtained. In Patent Documents 1 and 4, a fluororesin is used as the binder resin. However, since the fluororesin swells and dissolves only in a specific solvent such as N-methylpyrrolidone, the human body and environment such as a strange odor at the time of electrode preparation The adverse effect on was a problem.

  Accordingly, an object of the present invention is to provide excellent dispersion properties, storage stability, and coating properties when applied to a current collector, and after application to the current collector, the current collector and the positive electrode. An object of the present invention is to provide a water-based positive electrode mixture, a positive electrode, and a nonaqueous electrolyte secondary battery using the same, which can obtain a positive electrode having excellent adhesion to an active material.

  As a result of intensive studies to solve the above problems, the present inventor has added a surfactant to the positive electrode mixture and used a specific polymer material as the water-dispersible polymer binder resin, so that the positive electrode active The substance is easily and uniformly dispersed in a solvent, and the obtained positive electrode mixture is excellent in coating property when applied to a current collector, and the positive electrode obtained by drying this is a positive electrode mixture It has been found that the adhesion between the layer and the current collector plate is excellent, and the present invention has been completed.

  That is, the positive electrode mixture of the present invention contains a positive electrode active material, a water-dispersible polymer binder resin, a conductive additive, and a surfactant, and at least polyurethane as the water-dispersible polymer binder resin. And a polyurethane resin comprising at least a polyol and a polyisocyanate.

  In the positive electrode mixture of the present invention, the HLB value of the surfactant is preferably 13.0 to 20.0, and the surfactant is preferably a nonionic surfactant. Furthermore, the nonionic surfactant is preferably a fatty acid ester of polyethylene glycol. Furthermore, the weight average molecular weight of the polyurethane resin is preferably 8,000 to 1,500,000, and as the polyurethane resin, a polyurethane resin polymerized using a chain extender is suitable.

  The positive electrode of the present invention is characterized in that the positive electrode mixture of the present invention is applied to a current collector.

  Furthermore, the nonaqueous electrolyte secondary battery of the present invention is characterized by using the positive electrode of the present invention.

  According to the present invention, the positive electrode active material is excellent in dispersibility, storage stability, and coating property when applied to the current collector, and after being applied to the current collector, the current collector and the positive electrode active material. An aqueous positive electrode mixture, a positive electrode, and a nonaqueous electrolyte secondary battery using the same can be provided.

Hereinafter, embodiments of the present invention will be described in detail.
<Positive electrode mixture>
The positive electrode mixture of the present invention contains a positive electrode active material, a water-dispersible polymer binder resin, a conductive additive, and a surfactant, and includes at least a polyurethane resin as the water-dispersible polymer binder resin. . In the positive electrode mixture of the present invention, the polyurethane resin comprises at least a polyol and a polyisocyanate. By adding a surfactant to the positive electrode mixture, the positive electrode active material and the water-dispersible polymer binder resin can be uniformly dispersed in an aqueous solvent in a short time. In addition, since the positive electrode active material and the water-dispersible polymer binder resin are less likely to agglomerate and settle, the applicability to the current collector is also improved. Furthermore, since the positive electrode mixture of the present invention uses a polyurethane resin as the water-dispersible polymer binder resin, the positive electrode mixture is applied to the current collector as compared with the positive electrode mixture using a conventional fluororesin. The positive electrode produced by drying is excellent in adhesion and flexibility between the positive electrode active materials or between the positive electrode active material and the current collector foil. Furthermore, the non-aqueous electrolyte secondary battery using the obtained positive electrode can suppress a decrease in discharge capacity in a charge / discharge cycle even under a high temperature environment due to repeated charging and discharging and heat generation, and has a long life. A secondary battery can be obtained. Hereinafter, each component of the positive electrode mixture of the present invention and the production method thereof will be described in detail.

<Positive electrode active material>
In the positive electrode mixture of the present invention, for example, transition metal oxides, transition metal sulfides, lithium-containing composite metal oxides, and the like can be used as the positive electrode active material. Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo. Examples of the transition metal oxide include MnO, MnO ₂ , V ₂ O ₅ , _{V 6 O 13, TiO 2,} Cu 2 V 2 O 3, amorphous _{V 2 O-P 2 O 5} , MoO 3, V 2 O 5, V 6 O 13 and the like can be suitably used. In particular, MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ are preferable from the viewpoint of cycle stability and capacity. As the transition metal sulfide, TiS ₂ , TiS ₃ , amorphous MoS ₂ , FeS, or the like can be suitably used. The structure of the lithium-containing composite metal oxide is not particularly limited, but a layered structure, a spinel structure, an olivine structure, or the like can be preferably used.

The lithium-containing composite metal oxide having a layered structure includes a lithium-containing composite having a lithium-containing cobalt oxide (LiCoO ₂ ), a lithium-containing nickel oxide (LiNiO ₂ ), and a Co—Ni—Mn composite oxide as a main structure. Examples thereof include metal oxides, lithium-containing composite metal oxides having Ni-Mn-Al composite oxide as a main structure, and lithium-containing composite metal oxides having Ni-Co-Al composite oxide as a main structure. .

Examples of the lithium-containing composite metal oxide having a spinel structure include lithium manganate (LiMn ₂ O ₄ ) and Li [Mn _3/2 M _1/2 ] O _{4 in} which a part of Mn is substituted with another transition metal (wherein M may include Cr, Fe, Co, Ni, Cu and the like.

Li _X MPO ₄ (wherein, M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, lithium-containing composite metal oxide having an olivine structure) An olivine type lithium phosphate compound represented by at least one selected from Si, B and Mo, 0 ≦ X ≦ 2) can be given. Among lithium-containing composite metal oxides, LiFePO ₄ and LiCoPO ₄ are often used by being atomized because of their low conductivity, and since these have many pores, they have a large surface area and are compatible with a resin that serves as a binder. Is bad. However, since the positive electrode mixture of the present invention contains a surfactant, LiFePO ₄ and LiCoPO ₄ can be preferably used.

  In the positive electrode mixture of the present invention, as the positive electrode active material, those having an average particle diameter of 0.01 μm or more and less than 50 μm can be suitably used, and more preferably 0.1 μm to 30 μm. If the particle size is within the above range, the amount of the water-dispersible polymer binder resin can be reduced, the decrease in battery capacity can be suppressed, the aggregation of the positive electrode active material can be prevented, and the positive electrode mixture can be dispersed. A uniform electrode can be obtained with good properties. Here, the particle diameter is the maximum distance L among any two points on the particle outline, and the average particle diameter is a scanning electron microscope (SEM) or a transmission electron microscope. It is a value calculated as an average value of particle diameters of particles observed in several to several tens of fields using an observation means such as (TEM).

  When an iron-based oxide having poor electrical conductivity is used as the positive electrode active material, it can be used as a positive electrode active material covered with a carbon material by allowing a carbon source material to be present during reduction firing. These carbon source materials may be partially element-substituted. The positive electrode active material for a non-aqueous electrolyte secondary battery may be a mixture of the above inorganic compound and an organic compound that is a conductive polymer such as polyacetylene or poly-p-phenylene.

<Water-dispersible polymer binder resin>
In the positive electrode mixture of the present invention, the water-dispersible polymer binder resin is a polymer binder resin that can be dispersed in an aqueous solvent described later. In the positive electrode mixture of the present invention, at least a polyurethane resin is contained as a polymer binder resin, and the polyurethane resin is composed of at least a polyol and a polyisocyanate. In the positive electrode mixture of the present invention, since the polyurethane resin is used as the water-dispersible polymer binder resin, the adhesion to the current collector is excellent as compared with the positive electrode mixture that has conventionally used a fluorine resin. Yes. In the positive electrode mixture of the present invention, the polyol and polyisocyanate used for the synthesis of the polyurethane resin are not particularly limited, and known ones can be used. In the positive electrode mixture of the present invention, the polyurethane resin may be used in the form of an aqueous emulsion or an aqueous dispersion.

  As the polyol used for the synthesis of the polyurethane resin according to the positive electrode mixture of the present invention, polyester polyols can be suitably used. Examples of the polyester polyols include polyester polyol, polyester polycarbonate polyol, and polycarbonate polyol. Among these polyols, polyester polyols are preferable when a polyurethane resin is used as a binder resin because good durability and strength are provided.

  The polyester polyol is a direct esterification reaction between a low-molecular polyhydric alcohol and a polycarboxylic acid having an amount less than the stoichiometric amount of the low-molecular polyhydric alcohol or an ester-forming derivative such as an ester, an anhydride or a halide thereof. And / or what can be obtained by transesterification can be mentioned.

  Examples of the low molecular weight polyhydric alcohol include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3- Propanediol, 1,4-butanediol, neopentyl glycol, 3-methyl-2,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 3,5-heptanediol, 1,8-octane Diol, 2-methyl-1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, diethyleneglycol , Aliphatic diols such as triethylene glycol, alicyclic diols such as cyclohexanedimethanol and cyclohexanediol, trimethylolethane, trimethylolpropane, hexitols, pentitols, glycerin, pentaerythritol, tetramethylolpropane, etc. Mention may be made of alcohols having a higher value. These may be used singly or in combination of two or more.

  Examples of the polyvalent carboxylic acid or its ester-forming derivative include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2-methylsuccinic acid 2-methyladipic acid, 3-methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioic acid, 3,8-dimethyldecanedioic acid, 3,7-dimethyldecanedioic acid, hydrogenated dimer acid, Aliphatic dicarboxylic acids such as dimer acid, aromatic dicarboxylic acids such as phthalic acid, terephthalic acid, isophthalic acid and naphthalenedicarboxylic acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, trimellitic acid, trimesic acid, and castor oil fatty acid. Polycarboxylic acids such as tricarboxylic acids such as trimers, acid anhydrides of these polycarboxylic acids, Halides such as chlorides and bromides of polyvalent carboxylic acids, lower esters such as methyl esters, ethyl esters, propyl esters, isopropyl esters, butyl esters, isobutyl esters and amyl esters of the above polyvalent carboxylic acids, γ-caprolactone, δ- Examples include lactones such as caprolactone, ε-caprolactone, dimethyl-ε-caprolactone, δ-valerolactone, γ-valerolactone, and γ-butyrolactone. These may be used singly or in combination of two or more.

  Moreover, there is no restriction | limiting in particular as polyisocyanate used for the synthesis | combination of the polyurethane resin which concerns on the positive mix of this invention, A well-known polyisocyanate can be used. As the polyisocyanate, a mixture of diisocyanate and triisocyanate is preferable because the resulting polyurethane resin has good dispersibility and is inexpensive.

  Examples of the diisocyanate include 2,4- and / or 2,6-tolylene diisocyanate, diphenylmethane-4,4′-diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate, 3,3. Aromatic diisocyanates such as' -dimethyldiphenyl-4,4'-diisocyanate, dianisidine diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, trans-1,4-cyclohexyl diisocyanate, Cycloaliphatic diisocyanates such as norbornene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4 (2,4,4) -trimethylhexamethylene Isocyanates, and aliphatic diisocyanates such as lysine diisocyanate. In particular, alicyclic diisocyanates are preferred because they are excellent in hydrolysis resistance. These may be used singly or in combination of two or more.

  Examples of the triisocyanate include triphenylmethane triisocyanate, 1-methylbenzole-2,4,6-triisocyanate, isocyanurate trimerization, burette trimerization, and trimethylolpropane adduct of the above diisocyanate. it can. In particular, isocyanurate trimers are preferred because they give a stable dispersion to the polyurethane resin. These may be used singly or in combination of two or more.

  In the positive electrode mixture of the present invention, the weight average molecular weight of the polyurethane resin is preferably 8,000 to 1,500,000, and more preferably 10,000 to 1,000,000. If the weight average molecular weight of the polyurethane resin is less than 10,000, the durability as a binder resin may be reduced. On the other hand, when the weight average molecular weight of the polyurethane resin exceeds 1,500,000, the durability as a binder resin is improved, but the polyurethane resin itself aggregates and the dispersibility and coatability are significantly reduced. There is.

  In the positive electrode mixture of the present invention, a polyurethane resin polymerized using a chain extender may be used as the polyurethane resin. That is, when a high molecular weight polyurethane resin is required, it can be polymerized using a known chain extender used in a water-dispersed polyurethane composition. As the chain extender, a polyvalent amine compound, a polyvalent primary alcohol compound and the like are preferable, and a polyvalent amine compound is more preferable.

  Examples of the polyvalent amine compound include low molecular weight polyamines in which the alcoholic hydroxyl group of the above exemplified low molecular polyol such as ethylenediamine and propylenediamine is substituted with an amino group, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyoxypropylenediamine , Polyether polyamines such as polyoxypropylene triamine, mensendiamine, isophoronediamine, norbornenediamine, bis (4-amino-3-methyldicyclohexyl) methane, diaminodicyclohexylmethane, bis (aminomethyl) cyclohexane, N-aminomethyl Piperazine, alicyclic polyamines such as 3,9-bis (3-aminopropyl) 2,4,8,10-tetraoxaspiro (5,5) undecane, m-xylenediamine, α- m / p aminophenyl) ethylamine, m-phenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, diaminodiethyldimethyldiphenylmethane, diaminodiethyldiphenylmethane, dimethylthiotoluenediamine, diethyltoluenediamine, α, α'-bis (4-aminophenyl) -Aromatic polyamines such as p-diisopropylbenzene and dithiodianiline, hydrazine, ethylenediamine, propylenediamine, xylenediamine, adipic acid dihydrazide, isophoronediamine, piperazine and its derivatives, phenylenediamine, tolylenediamine, xylenediamine, isophthalic acid And dihydrazide. In the positive electrode material mixture of the present invention, these may be used singly or in combination of two or more.

  There is no restriction | limiting in particular about the manufacturing method of the polyurethane resin which concerns on the positive mix of this invention, A known manufacturing method can be used. For example, a prepolymer method is preferred in which a polyol, diisocyanate and triisocyanate are reacted together to prepare a urethane prepolymer in advance and the chain can be extended in water in the presence of a chain extender.

  The amount of the chain extender is not particularly limited, and any amount can be selected and used. For example, when the prepolymer method is selected as the synthesis of the polyurethane resin, the isocyanate group in the prepolymer The number of active hydrogens in the chain extender relative to the number 1 is preferably 0.1 to 1.5 because the resulting water-dispersible polyurethane composition has good dispersibility and no discoloration, and is preferably 0.5 to 1. 0 is more preferable.

  In the positive electrode mixture of the present invention, other polymer particles may be added to the water-dispersible polymer binder resin as necessary. Examples of polymer particles include non-fluorine polymers such as vinyl polymers, acrylic polymers, nitrile polymers, polyurethane polymers, and diene polymers; fluorine polymers such as PVDF and PTFE; In particular, a non-fluorine polymer is preferable from the viewpoint of adhesiveness. In the positive electrode mixture of the present invention, these polymer particles may be used alone or in combination of two or more.

  In the positive electrode mixture of the present invention, the content ratio of the polymer particles is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 in terms of solid content with respect to 100 parts by mass of the positive electrode active material. Part by mass. By making the content ratio of the polymer particles in the above range, the adhesion and flexibility of the positive electrode mixture layer obtained by applying and drying the positive electrode mixture of the present invention to the current collector are improved. be able to.

  In the positive electrode mixture of the present invention, the average particle size of the water-dispersible polymer binder resin is preferably 0.05 to 5 μm, more preferably 0.1 to 1 μm. If the particle size is too large, the binding property may decrease, and if the particle size is too small, the surface of the positive electrode active material may be covered and the internal resistance may be increased.

<Conductive aid>
In the positive electrode mixture of the present invention, as the conductive assistant, acetylene black, ketjen black, carbon black, graphite, vapor grown carbon fiber, and conductive carbon such as carbon nanotube, graphene, fullerene can be used. . By using a conductive additive, the electrical contact between the positive electrode active materials can be improved, and when used in a non-aqueous electrolyte secondary battery, the discharge rate characteristics can be improved. The blending amount of the conductive assistant is preferably 0.1 to 20 parts by mass, more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material.

<Surfactant>
In the positive electrode mixture of the present invention, the surfactant is particularly limited as long as it has high dispersibility in the electrolyte, low reactivity with lithium ions, etc., and does not hinder ion conduction in the electrolyte. is not. For example, examples of the surfactant include a cationic surfactant, an anionic surfactant, an amphoteric surfactant, and a nonionic surfactant, and it is particularly preferable to use a nonionic surfactant. . This is because the nonionic surfactant has low reactivity with surrounding ions (such as lithium ions) and does not hinder ion conduction in the electrolyte and on the active material surface. In the positive electrode mixture of the present invention, the surfactant may be used alone or in combination of two or more.

  Examples of the cationic surfactant include mono / di long chain alkyl type quaternary ammonium salts and alkylamine salts. Examples of the anionic surfactant include alkylbenzene sulfonate, alkyl sulfate, alkyl ether sulfate, alkenyl ether sulfate, alkenyl sulfate, α-olefin sulfonate, α-sulfo fatty acid or ester salt thereof. , Alkane sulfonate, saturated fatty acid salt, unsaturated fatty acid salt, alkyl ether carboxylate, alkenyl ether carboxylate, amino acid type surfactant, N-acyl amino acid type surfactant, alkyl phosphate ester or salt thereof, Examples thereof include alkenyl phosphate esters or salts thereof, and alkylsulfosuccinates. Examples of the amphoteric surfactant include a carboxyl type amphoteric surfactant and a sulfobetaine type amphoteric surfactant.

  Examples of the nonionic surfactant include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, and polyoxyethylene higher alkyl ether; Polyoxyethylene alkyl aryl ethers such as oxyethylene nonylphenyl ether; polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan Polystearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, etc. Oxyethylene sorbitan fatty acid ester; sucrose fatty acid ester; polyoxyethylene sorbitol fatty acid ester such as polyoxyethylene sorbitol tetraoleate; polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate Polyoxyethylene fatty acid ester such as polyoxyethylene alkylamine; polyoxyethylene hydrogenated castor oil; block copolymer of ethylene oxide and propylene oxide; sorbitan monolaurate, sorbitan monomyristate, sorbitan monopalmitate, sorbitan monostearate Rate, sorbitan tristearate, sorbitan monooleate, sorbitan trioleate Sorbitan fatty acid esters such as sorbitan sesquioleate and sorbitan distearate; glycerol fatty acid esters such as glycerol monostearate, glycerol monooleate, diglycerol monooleate and self-emulsifying glycerol monostearate; alkyl alkanolamides and the like It can be used suitably.

  In the positive electrode mixture of the present invention, when a nonionic surfactant is used as the surfactant, the nonionic surfactant is preferably a polymer material, and the weight average molecular weight of the nonionic surfactant is 500 or more. It is preferable that By setting the weight average molecular weight of the nonionic surfactant to 500 or more, the positive electrode active material is effectively dispersed by the surfactant. This is presumably because the high molecular surfactant increases the affinity between the solvent and the surfactant and makes it easier to hold the solvent in the vicinity of the particles, thereby suppressing aggregation between the particles. On the other hand, although there is no restriction | limiting in particular about the upper limit of a weight average molecular weight, It is preferable that it is 100,000 or less. The more preferable range of the weight average molecular weight of the nonionic surfactant in the positive electrode mixture of the present invention is 1,000 to 50,000. By setting the weight average molecular weight within this range, the dispersibility of the positive electrode active material becomes better, and ions can be moved smoothly.

  Among nonionic surfactants, polyethylene glycol surfactants that have high ion conductivity and can be used for electrolytes of lithium ion batteries are preferred, polyethylene glycol fatty acid ester surfactants are more preferred, and polyethylene is more preferred. Glycolic stearates. Polyethylene glycol stearates have a high thickening effect and an excellent effect of preventing sedimentation and aggregation of the active material. Moreover, the movement of lithium ions in the surfactant can be promoted by using a polyethylene glycol-based surfactant for coating the active material. In addition, in this invention, a polyethyleneglycol type surfactant refers to what contains an ethylene glycol chain in an activator compound.

The surfactant used in the positive electrode mixture of the present invention has an HLB of 13 to 20, preferably 15 to 20 by the Griffin method. In particular, when no organic solvent is used as the solvent, the HLB is more preferably 16-20. When HLB uses a surfactant in this range, the hydrophilic group and hydrophobic group of the surfactant are arranged in a well-balanced manner, so that uniform dispersion of the positive electrode active material and the binder resin having polarity in an aqueous solvent is promoted. The The Griffin method is based on the following formula based on the formula weight and molecular weight of the hydrophilic group of the surfactant:
HLB value = 20 × defined by the sum of formula weight of hydrophilic part / molecular weight.

  In the positive electrode mixture of the present invention, the blending amount of the surfactant is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material. is there. By making the compounding quantity of surfactant into the said range, the positive mix which was excellent in the dispersibility and coating property of the positive electrode active material in a positive mix can be obtained.

<Solvent>
The solvent used for the positive electrode mixture of the present invention is not particularly limited as long as it is compatible with a surfactant that uniformly disperses the water-dispersible polymer binder resin and the positive electrode active material and inhibits sedimentation and aggregation. For example, in the positive electrode mixture of the present invention, water can be suitably used as the solvent, but an organic solvent may be included as long as the above effects are not impaired. Examples of the organic solvent include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene and ethylbenzene; acetone, ethyl methyl ketone, disopropyl ketone, cyclohexanone, methylcyclohexane and ethyl. Ketones such as cyclohexane; chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; esters such as ethyl acetate, butyl acetate, γ-butyrolactone and ε-caprolactone; acylonitriles such as acetonitrile and propionitrile Ethers such as tetrahydrofuran and ethylene glycol diethyl ether: alcohols such as methanol, ethanol, isopropanol, ethylene glycol and ethylene glycol monomethyl ether; Examples include amides such as loridone and N, N-dimethylformamide.

<Other additives>
The positive electrode mixture of the present invention contains a positive electrode active material, a water-dispersible polymer binder resin, a conductive additive, and a surfactant, and includes a polyurethane resin as a water-dispersible polymer binder, and It is only important that this polyurethane resin is a polyurethane resin composed of at least a polyol and a polyisocyanate, and there is no particular limitation, and other than the above components, additives are included within a range that does not affect the battery reaction. Also good. For example, the positive electrode mixture of the present invention may contain components such as a reinforcing material, a thickener, a defoaming / leveling agent, and an electrolytic solution decomposition inhibitor in addition to the above components.

  As the reinforcing material, various inorganic and organic spherical, plate-like, rod-like, or fibrous fillers may be used. By using a reinforcing material, a tougher and more flexible electrode can be obtained, and excellent long-term cycle characteristics can be imparted. These may be used alone or in combination of two or more. The compounding quantity of a reinforcing material is 0.01-20 mass parts normally with respect to 100 mass parts of positive electrode active materials, Preferably it is 1-10 mass parts. By setting the blending amount of the reinforcing material within the above range, high capacity and high load characteristics can be imparted.

  The thickener is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used during electrode production and other materials used during battery use. For example, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and the like can be used. These may be used alone or in combination of two or more. The compounding quantity of a thickener is 0.01-20 mass parts normally with respect to 100 mass parts of positive electrode active materials, Preferably it is 1-10 mass parts. By setting the blending amount of the thickener within the above range, it is possible to satisfactorily prevent sedimentation and aggregation of the positive electrode active material having a high specific gravity.

  As the defoaming / leveling agent, surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants can be used. By mixing the surfactant, it is possible to prevent the repelling that occurs during coating and to improve the smoothness of the electrode. The blending amount of the defoaming / leveling agent is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material. By making the compounding quantity of a defoaming and leveling agent into the said range, the coating malfunction at the time of electrode coating can be prevented, and productivity can be improved.

  As the electrolytic solution decomposition inhibitor, vinylene carbonate or the like used in the electrolytic solution can be used. The amount of the electrolytic solution decomposition inhibitor in the electrode is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material. By setting the blending amount of the electrolytic solution decomposition inhibitor in the above range, the cycle characteristics and the high temperature characteristics can be further improved. Other examples include nanoparticles such as fumed silica and fumed alumina. By mixing the nanoparticles, the thixotropy of the electrode forming mixture can be controlled. The compounding amount of the nanoparticles in the positive electrode mixture of the present invention is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the positive electrode active material. By making the compounding quantity of a nano fine particle into the said range, mixture stability and productivity can further be improved and a higher battery characteristic can be provided.

<Method for producing positive electrode mixture>
The positive electrode mixture of the present invention can be obtained by mixing the positive electrode active material, a water-dispersible polymer binder, a conductive additive, a surfactant and a solvent, and other additives as necessary. it can. In producing the positive electrode mixture of the present invention, the mixing method is not particularly limited, and for example, a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type can be employed. Further, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, and a planetary kneader may be employed.

<Positive electrode>
Next, the positive electrode for nonaqueous electrolyte secondary batteries of this invention is demonstrated.
The positive electrode of the present invention is obtained by applying the positive electrode mixture of the present invention to a current collector. The positive electrode of the present invention is manufactured through an application step of applying the positive electrode mixture of the present invention on a current collector and a drying step of drying the obtained current collector to form a positive electrode mixture layer. be able to. In the positive electrode of the present invention, the positive electrode mixture layer may be formed on one side of the current collector, but is preferably formed on both sides. Hereinafter, the structure and manufacturing method of the positive electrode of the present invention will be described in detail.

<Current collector>
The current collector used for the positive electrode of the present invention is not particularly limited as long as it is an electrically conductive and electrochemically durable material, but a metal material having heat resistance is preferable. For example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. can be mentioned. In particular, aluminum or an aluminum alloy is preferable because of less oxidation deterioration during charging. The shape of the current collector is not particularly limited, but a sheet having a thickness of about 5 to 100 μm can be suitably used.

  In the positive electrode of the present invention, the current collector is preferably used after roughening in advance in order to increase the adhesive strength with the positive electrode mixture layer. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, it is possible to use abrasive cloth paper, abrasive wheels, emery buffs, wire brushes equipped with steel wires and the like to which abrasive particles are fixed. Further, an intermediate layer may be formed on the current collector surface in order to increase the adhesive strength and conductivity of the electrode layer.

<Application method>
There is no limitation in particular also about the method of apply | coating the positive mix of the said invention on a collector, A well-known method can be used. Examples of the coating method include a die coating method, a doctor coating method, a dip coating method, a roll coating method, a spray coating method, a gravure coating method, a screen printing method, and an electrostatic coating method.

<Drying method>
The method of drying the current collector obtained by the above coating method is not particularly limited. For example, drying with warm air, hot air, low-humidity air, vacuum drying, or drying by irradiation with (far) infrared rays or electron beams. Can be mentioned. The drying time is usually 5 to 30 minutes, and the drying temperature is usually 40 to 180 ° C.

<Rolling>
In the production method of the present invention, it is preferable to go through a rolling process in which the porosity of the positive electrode mixture layer is lowered by pressure treatment using a die press, a roll press or the like after passing through a coating process and a drying process. The preferable range of the porosity is 5% to 15%, and more preferably 7% to 13%. If the porosity exceeds 15%, the charging efficiency and the discharging efficiency are deteriorated, which is not preferable. On the other hand, when the porosity is less than 5%, it may be difficult to obtain a high volume capacity, or the positive electrode mixture layer may be easily peeled off from the current collector and may be defective. In addition, when using curable resin as binder resin, it is preferable to have the process of hardening this curable resin.

  The thickness of the positive electrode of the present invention is usually 5 to 400 μm, preferably 30 to 300 μm. By setting the thickness of the positive electrode within the above range, good flexibility and adhesion of the electrode plate can be obtained.

<Nonaqueous electrolyte secondary battery>
Next, the nonaqueous electrolyte secondary battery of the present invention will be described.
The nonaqueous electrolyte secondary battery of the present invention uses the positive electrode of the present invention, and has a positive electrode, a negative electrode, a separator, and an electrolytic solution. Hereinafter, the configuration of the nonaqueous electrolyte secondary battery of the present invention and the manufacturing method thereof will be described in detail.

<Negative electrode for non-aqueous electrolyte secondary battery>
The negative electrode for a non-aqueous electrolyte secondary battery according to the present invention is prepared by mixing a negative electrode active material, a conductive additive, a water-dispersible polymer binder resin, a solvent, and other additives as necessary to prepare a negative electrode mixture slurry. And it can manufacture by apply | coating to a collector, drying, and passing through rolling as needed.

  As the negative electrode active material, any known material that has been conventionally used can be used as long as it is an active material that can occlude and release lithium ions. Either a carbon-based active material or a non-carbon-based active material can be used. May be. Examples of the carbon-based active material include graphite, soft carbon, and hard carbon. As the non-carbon-based active material, for example, known materials such as lithium metal, lithium alloy, oxide, sulfide, lithium-containing metal composite oxide can be used.

  As a conductive support agent and a solvent, said conductive support agent and said solvent used for preparation of the positive electrode of this invention can be used. Moreover, as binder resin, what is generally used for nonaqueous electrolyte secondary batteries, such as SBR particle | grains and PVDF resin, can be used.

  The current collector used in the negative electrode for a non-aqueous electrolyte secondary battery according to the present invention is electrically conductive and electrochemically durable, like the positive electrode for a non-aqueous electrolyte secondary battery according to the present invention. If it is material, there will be no restriction | limiting in particular, The thing similar to the electrical power collector used for the positive electrode for nonaqueous electrolyte secondary batteries of the said invention can be used.

<Electrolyte>
Although there is no restriction | limiting in particular about the electrolyte solution used for this invention, For example, what melt | dissolved lithium salt as a supporting electrolyte in a non-aqueous solvent can be used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation can be suitably used. These may be used alone or in combination of two or more. The addition amount of the supporting electrolyte is usually 1% by mass or more, preferably 5% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less, with respect to the electrolytic solution. If the amount of the supporting electrolyte is too small or too large, the ionic conductivity decreases, and the charging characteristics and discharging characteristics of the battery decrease.

  The solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte, but dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate. (BC) and alkyl carbonates such as methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane; and tetrahydrofuran; including sulfolane and dimethyl sulfoxide. Sulfur compounds can be used. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable because high ion conductivity is easily obtained and the use temperature range is wide. These may be used alone or in combination of two or more.

  Other additives may be added to the electrolytic solution. Examples of the additive include carbonate compounds such as vinylene carbonate (VC), cyclohexylbenzene, diphenyl ether, and the like.

When an electrolyte other than the above is used for the nonaqueous electrolyte secondary battery of the present invention, for example, a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide or polyacrylonitrile with an electrolyte, lithium sulfide, LiI, Li ₃ An inorganic solid electrolyte such as N can be used.

<Separator>
The separator is a porous substrate having pores, (a) a porous separator having pores, (b) a porous separator having a polymer coating layer formed on one or both sides, or (c) inorganic A porous separator formed with a porous resin coating layer containing ceramic powder can be used, for example, polypropylene, polyethylene, polyolefin, aramid porous separator, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile , For solid polymer electrolyte such as polyvinylidene fluoride hexafluoropropylene copolymer, polymer film for gel polymer electrolyte, separator coated with gelled polymer coat layer, inorganic filler, dispersion for inorganic filler A porous membrane layer made of an agent It has been a separator, and the like can be given.

<Method for producing non-aqueous electrolyte secondary battery>
There is no restriction | limiting in particular about the manufacturing method of the nonaqueous electrolyte secondary battery of this invention. For example, the negative electrode and the positive electrode are overlapped via a separator, and this is wound or folded according to the shape of the battery and placed in the battery container, and the electrolytic solution is injected into the battery container and sealed. In the non-aqueous electrolyte secondary battery of the present invention, an expanded metal, an overcurrent prevention element such as a fuse and a PTC element, a lead plate, etc. are inserted as necessary to prevent an increase in pressure inside the battery and overcharge / discharge. You can also The shape of the battery may be any shape such as a laminate cell type, a coin type, a button type, a sheet type, a cylindrical type, a square shape, and a flat type.

Hereinafter, the present invention will be described in more detail with reference to examples.
<Example 1>
Cell seed NMC-111 (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) manufactured by Nippon Kagaku Kogyo Co., Ltd., which is a ternary active material, is used as the positive electrode active material. Adekabon titer HUX-822 (polyurethane emulsion resin: solid content 40% by mass) manufactured by ADEKA as a water-dispersible polymer binder resin with a solid content ratio of 2% by mass of VGCF-H (vapor-grown carbon fiber) manufactured by Denko Co., Ltd. Solid content ratio 1.5% by mass, Kao Co., Ltd. Emanon 3299RV (polyethylene glycol distearate) as a solid content ratio 1.5% by mass, and water as a solvent is 60% by mass It mix | blended so that it might become, and propeller stirring was performed for 10 minutes at 1700 rpm, and the positive mix was produced.

The produced positive electrode mixture was allowed to stand for 24 hours, and then applied to one side of an aluminum foil having a thickness of 20 μm using a 50 μm applicator. Then, it dried for 20 minutes at 150 degreeC with the hot-air circulation type box-type drying furnace, and removed the water which is a solvent. After cooling to room temperature, it is sandwiched between 1 mm stainless steel plates and rolled at room temperature for 1 minute at a pressure of 1.5 ton / cm ² using a flat plate press to have an active material mixture layer of 80 μm on one side. A positive electrode plate was prepared. The following items A to G were evaluated for the steps from preparation of the positive electrode mixture to preparation of the positive electrode plate. Details of the evaluation method are as follows. The obtained results are also shown in Table 1.

<Examples 2-6, Comparative Examples 1-4>
Stirring and mixing was carried out in the same manner as in Example 1 except that the composition of the water-dispersible polymer binder, surfactant, thickener, conductive assistant, and active material was changed as shown in Tables 1 to 3. A positive electrode mixture was prepared, and the dispersibility and the stability of sedimentation aggregation were evaluated. Using the produced positive electrode mixture, application, drying and rolling were performed in the same manner as in Example 1 to produce a positive electrode plate. The evaluation results are shown in Tables 1-3.

<A: Dispersibility>
When the prepared positive electrode mixture is applied to the positive electrode current collector of aluminum foil, a coarse active material particle lump or gel-like resin lump that has not been solved due to poor dispersion and has a streak-like mark on the coated surface. Visual evaluation was performed with “bad”, “good” for those with slight traces, and “good” for those with no streak-like traces.

<B: Precipitation aggregation stability>
If the produced positive electrode mixture is allowed to stand and sedimentation agglomerates occur on the bottom surface of the positive electrode mixture or water has separated on the liquid surface, it is regarded as “bad” and the one that has not changed is regarded as “good”. And evaluated.

<C: Appearance after drying>
After coating and drying the positive electrode mixture on the positive electrode current collector, the coating film surface with bubbles and repellency such as bubbles and repellency was defined as “bad”, and those with no abnormalities as “good”. Evaluation was performed.

<D: Adhesiveness after drying>
After coating and drying the positive electrode mixture on the positive electrode current collector, the coating film surface was cross-cut with a grid pattern of 25 squares with a cut interval of 2 mm according to JIS K-5600. The evaluation was made with “low” for those with little powder falling and “good” for those with no powder falling.

<E: Appearance of electrode layer>
Visual evaluation of the surface of the electrode was performed by assuming that the surface of the produced electrode plate had protrusions or cracks as “defective” and that there was no abnormality and was “good”.

<F: Adhesion of electrode layer>
Using the produced electrode plate, according to JIS K-5600, the adhesion between the current collector and the active material was evaluated by a cross-cut method test with a grid pattern of 25 squares at a cut interval of 2 mm. Evaluation is performed in 6 stages from 0 to 5, and the smaller the number, the better the adhesion.

<G: Resistance value of electrode layer>
The resistance value of the surface was measured using a tester (Mirium High Tester 3540, manufactured by Hioki Co., Ltd.) on the surface of the produced electrode plate.

1) Adekabon titer HUX-822 (polyurethane resin, molecular weight: 800,000 to 900,000) manufactured by ADEKA Corporation 2) HSV-900 (polyvinylidene fluoride resin) manufactured by Arkema Co., Ltd. 3) Emanon 3299RV (polyethylene) Glycol distearate nonionic surfactant HLB: 19.2 Molecular weight: about 11200) 4) Emanon 3199V (polyethylene glycol monostearate nonionic surfactant HLB: 19.4 Molecular weight: about 6800) Kao Corporation 5) Emanon 1112 (polyethylene glycol monolaurate nonionic surfactant HLB: 13.7 Molecular weight: about 730) Kao Corporation 6) Emanon CH-25 (Polyoxyethylene) Hardened castor oil-based nonionic surfactant H B: 10.7 Molecular weight: 1679) 7) Daicel CMC # 2200, Daicel Finechem Ltd. 8) VGCF-H (vapor-grown carbon fiber) 9) SP, Showa Denko KK -270 (graphite powder) manufactured by Nippon Graphite Industries Co., Ltd. 10) Cell seed NMC111 (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) manufactured by Nippon Chemical Industry Co., Ltd. 11) LFP (lithium iron phosphate) : LiFePO ₄ )

  From Tables 1-3, the positive electrode mixture of this invention is excellent in the dispersibility of a positive electrode active material, the storage stability, and the coating property with respect to a collector, and the positive electrode manufactured using this is a positive electrode mixture layer. It can be seen that it has excellent adhesion to the current collector. In Comparative Examples 1 and 2, the dispersibility and the sedimentation aggregation stability were good, but the surface of the coating film after drying became distorted, and even after pressing, it was not improved. Moreover, the adhesiveness was inferior and the electrode layer was cracked. Comparative Examples 3 and 4 seemed to be well dispersed in the slurry state, but rough particulate lumps and the like remained, dispersibility was poor, and coating film formation was difficult.

Claims (8)

  A positive electrode active material, a water-dispersible polymer binder resin, a conductive additive, and a surfactant; and the water-dispersible polymer binder resin includes at least a polyurethane resin, and the polyurethane resin A positive electrode mixture comprising at least a polyol and a polyisocyanate.   The positive electrode mixture according to claim 1, wherein the surfactant has an HLB value of 13.0 to 20.0.   The positive electrode mixture according to claim 1, wherein the surfactant is a nonionic surfactant.   The positive electrode mixture according to claim 3, wherein the nonionic surfactant is a fatty acid ester of polyethylene glycol.   The positive electrode mixture according to any one of claims 1 to 4, wherein the polyurethane resin has a weight average molecular weight of 8,000 to 1,500,000.   The positive electrode mixture according to claim 5, wherein the polyurethane resin is a polyurethane resin polymerized using a chain extender.   A positive electrode, wherein the positive electrode mixture according to any one of claims 1 to 6 is applied to a current collector.   A non-aqueous electrolyte secondary battery using the positive electrode according to claim 7.