JP5764804B2 - Compound paste for positive electrode of lithium ion secondary battery - Google Patents

Description

  The present invention relates to a composite paste for a positive electrode of a lithium ion secondary battery in which the precipitation of a positive electrode active material is suppressed. The present invention also relates to a positive electrode for a lithium ion secondary battery in which a composite material layer is formed using the composite paste, and a lithium ion secondary battery having the positive electrode as a constituent element.

  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. Also, in large-sized secondary batteries for automobiles and the like, it is desired to realize a large non-aqueous electrolyte secondary battery instead of a conventional lead-acid battery.

  In order to meet such demands, lithium ion secondary batteries are being actively developed. As an electrode of a lithium ion secondary battery, a positive electrode in which an electrode mixture composed of a positive electrode active material containing lithium ions, a conductive additive, an organic binder, and the like is fixed to the surface of a current collector of metal foil, and a lithium ion A negative electrode is used in which an electrode mixture made of a removable negative electrode active material, a conductive additive, an organic binder, and the like is fixed to the surface of a current collector of a metal foil.

  In general, lithium transition metal composite oxides such as lithium cobaltate and lithium manganate are used as the positive electrode active material, and these are powder materials having a large specific gravity. Therefore, when the positive electrode mixture paste is prepared and then allowed to stand, the active material gradually settles with time, and it is difficult to maintain a uniform state. The mixture paste with significant settling has a constant composition and thickness of the formed mixture layer due to the risk of blockage due to settling and accumulation during piping, and the composition of the mixture paste changing with settling. There was a problem that it was difficult to obtain a uniform electrode.

  Here, as one method for preventing the positive electrode active material from settling, it is conceivable to increase the viscosity of the composite paste. For example, by increasing the amount of binder added, the paste can be thickened and the effect of preventing the positive electrode active material from settling can be obtained. However, according to this method, there is a concern that the discharge capacity per battery weight is reduced by reducing the ratio of the active material in the composite layer, and the conductivity of the composite layer is reduced by increasing the binder ratio. . Therefore, there is a limit to the amount of binder added, and it is difficult to obtain a battery with excellent charge / discharge capacity.

  Therefore, it has been proposed to use various anti-settling agents that impart thixotropy to the composite paste to prevent the active material from settling. For example, Patent Document 1 discloses the use of polyethylene oxide, fatty acid amide, and fatty acid glyceride as an anti-settling agent. However, in this case as well, if the amount added is increased, there is a concern about the effect on the battery characteristics. Therefore, the amount added is limited, and it is difficult to obtain a battery with excellent charge / discharge capacity.

  On the other hand, as disclosed in Patent Document 2 and Patent Document 3, a carbon material that is a conductive auxiliary agent is dispersed using a dispersant, thereby forming a uniform conductive network and reducing the internal resistance of the electrode. Has been made. However, in general, a paste using only a dispersant tends to have a reduced viscosity and a loss of thixotropy. For this reason, the composite paste simply containing a dispersing agent has a problem that the active material tends to settle, and it is difficult to maintain a uniform dispersed state. As described above, it is more difficult to produce a mixture paste having a higher viscosity or impart thixotropy than a mixture paste containing no dispersant.

JP 2001-266855 A Japanese Patent Laid-Open No. 2003-157846 Japanese Patent No. 4240157

  In view of the above problems, the present invention is a lithium ion secondary battery positive electrode having a viscosity excellent in coatability and excellent in aging stability (storage stability) in which precipitation of the positive electrode active material is suppressed. It is an object to provide a composite paste for use. In addition, by using the lithium ion secondary battery positive electrode mixture paste of the present invention, the discharge capacity retention rate is less likely to be reduced even if the charge / discharge cycle is repeated, and the positive electrode for a lithium ion secondary battery excellent in charge / discharge characteristics, And it aims at providing a lithium ion secondary battery.

  As a result of intensive investigations, the present inventors have found that the positive electrode active material, the binder, the carbon material that is a conductive auxiliary agent, the solvent, the dispersant, the general formula (1) and / or the general formula (2) and / or Alternatively, the present inventors have found that a mixture paste for a positive electrode of a lithium ion secondary battery in which precipitation of the positive electrode active material is suppressed can be prepared by including the salt represented by the general formula (3).

（一般式（４）中、
Ｔ ¹⁰¹ は、−ＮＨ−であり、
Ｔ ¹⁰² は、−ＮＨ−であり、
Ｙ ¹⁰¹ は、炭素数１〜２０で構成された、置換基を有してもよいアリーレン基であり、
Ｚ ¹⁰¹ は、−ＣＯＯＭ ¹⁰¹ であり、
Ｍ ¹⁰¹ は、１〜３価のカチオンの一当量であり、
Ｑ ¹⁰¹ は、−Ｏ−Ｒ ¹⁰² 、または−Ｔ ¹⁰¹ −Ｒ ¹⁰¹ であり、
Ｒ ¹⁰² は、水素原子であり、
ｎ ¹⁰¹ は、１〜４の整数であり、
Ｒ ¹⁰¹ は、置換基を有していてもよい複素環残基であって、複素環残基はベンズイミダゾロンまたはカルバゾールの残基である。）

一般式（７）

（一般式（７）中、
Ｔ ⁴⁰¹ は、直接結合であり、
Ｚ ⁴⁰¹ は、−ＳＯ ₃ Ｍ ⁴⁰¹ であり、
Ｍ ⁴⁰¹ は、１〜３価のカチオンの一当量であり、
Ｒ ⁴⁰¹ は、有機色素残基であって、有機色素残基はアゾ系色素またはキナクリドン系色素の残基であり、
ｎ ⁴⁰¹ は、１〜４の整数である。）
That is, the present invention includes a positive electrode active material, a binder, a carbon material that is a conductive auxiliary agent, a solvent, a dispersant, a general formula (1) and / or a general formula (2) and / or a general formula (3). A lithium ion secondary battery positive electrode composite paste comprising a salt represented by formula (7), wherein the dispersant is a triazine derivative having an acidic functional group represented by formula (4) and formula (7): The present invention relates to a composite paste for a lithium ion secondary battery positive electrode, which is one or more dispersants selected from organic dye derivatives having an acidic functional group .
General formula (1) AX _a
(In the formula, A is an a-valent element selected from Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, and Ba. X is halogen. A is the valence of A and 1 Or an integer of 2.)
General formula (2) NH ₄ X
(In the formula, N is nitrogen, H is hydrogen, and X is halogen.)
General formula (3) D (HX) _d
(In the formula, D is an amine having d amino groups in the molecule. H is hydrogen and X is halogen. D is the number of amino groups in the molecule of D and is an integer of 1 or more.)
General formula (4)

(In general formula (4),
T ¹⁰¹ is —NH—;
T ¹⁰² is a -NH-,
Y ¹⁰¹ is an arylene group which has 1 to 20 carbon atoms and may have a substituent,
Z ¹⁰¹ is —COOM ¹⁰¹ ;
M ¹⁰¹ is one equivalent of a monovalent to trivalent cation,
Q ¹⁰¹ is —O—R ¹⁰² or —T ¹⁰¹ —R ¹⁰¹ ,
R ¹⁰² is a hydrogen atom,
n ¹⁰¹ is an integer of 1 to 4,
R ¹⁰¹ is a heterocyclic residue which may have a substituent, and the heterocyclic residue is a benzimidazolone or carbazole residue. )

General formula (7)

(In general formula (7),
T ⁴⁰¹ is a direct bond,
Z ⁴⁰¹ is —SO ₃ M ⁴⁰¹ ,
M ⁴⁰¹ is one equivalent of a monovalent to trivalent cation,
R ⁴⁰¹ is an organic dye residue, and the organic dye residue is a residue of an azo dye or a quinacridone dye;
n ⁴⁰¹ is an integer of 1 to 4. )

General formula (1) AX _a
(In the formula, A is an a-valent element selected from Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, and Ba. X is halogen. A is the valence of A and 1 Or an integer of 2.)
General formula (2) NH ₄ X
(In the formula, N is nitrogen, H is hydrogen, and X is halogen.)
General formula (3) D (HX) _d
(In the formula, D is an amine having d amino groups in the molecule. H is hydrogen and X is halogen. D is the number of amino groups in the molecule of D and is an integer of 1 or more.)
The present invention also relates to the lithium ion secondary battery positive electrode composite paste, wherein the proportion of the salt in the total solid content of the composite paste is less than 0.2% by weight.

  Moreover, this invention relates to the positive electrode for lithium ion secondary batteries by which a composite material layer is formed using the said composite paste for lithium ion secondary battery positive electrodes.

  The present invention is a lithium ion secondary battery comprising a positive electrode having a positive electrode mixture layer on a current collector, a negative electrode having a negative electrode mixture layer on the current collector, and an electrolyte containing lithium, The present invention relates to a lithium ion secondary battery in which a positive electrode is the positive electrode for a lithium ion secondary battery.

  According to the present invention, a lithium ion secondary battery positive electrode mixture paste having a viscosity excellent in coating property and excellent in aging stability (storage stability), which suppresses the precipitation of the positive electrode active material, and By using it, a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery excellent in charge / discharge characteristics, in which the discharge capacity retention rate is not easily lowered even when the charge / discharge cycle is repeated, are obtained.

The lithium ion secondary battery positive electrode mixture paste according to the present invention includes a positive electrode active material, a binder, a carbon material as a conductive additive, a solvent, a dispersant, a general formula (1) and / or a general formula ( 2) and / or a salt represented by the general formula (3), which will be described in detail below.
<Positive electrode active material>
The positive electrode active material used in the present invention is not particularly limited, and metal oxides that can be doped or intercalated with lithium ions, metal compounds such as metal sulfides, and conductive polymers can be used. .

For example, lithium manganese composite oxide (for example, Li _x Mn ₂ O ₄ or Li _x MnO ₂ ), lithium nickel composite oxide (for example, Li _x NiO ₂ ), lithium cobalt composite oxide (Li _x Co ₂ ), lithium nickel cobalt composite oxides (e.g., _{Li x Ni 1-y Co y} O 2), lithium manganese cobalt composite oxides (e.g., _{Li x Mn y Co 1-y} O 2), lithium nickel manganese cobalt composite oxide (e.g., Li _x Ni _{1 / 3} Co _1/3 Mn _1/3 O ₂ ), spinel-type lithium manganese nickel composite oxide (eg Li _x Mn _{2 -y} Ni _y O ₄ ), etc., composite oxide powder of lithium and transition metal, olivine structure lithium phosphorus oxide powder having a (for example, _{Li x FePO 4, Li x Fe} 1-y Mn y PO 4, Li x CoPO 4), manganese oxide, iron oxide, , Nickel oxide, vanadium oxide (e.g. _{V 2 O 5, V 6 O} 13), a transition metal oxide powder such as titanium oxide, iron sulfate _{(Fe 2 (SO 4) 3} ), the transition of such TiS _2, and FeS Examples thereof include metal sulfide powder.

These positive electrode active materials can be used alone or in combination.
<Binder>
The binder used in the present invention is not particularly limited, but ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic ester, methacrylic acid, methacrylic ester, acrylonitrile, styrene, vinyl butyral. Polymers or copolymers containing vinyl acetal, vinyl pyrrolidone, etc. as structural units; polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicon Resins, fluororesins; cellulose resins such as carboxymethylcellulose; rubbers such as styrene-butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene That. Moreover, the modified body and mixture of these resin, and a copolymer may be sufficient. In particular, it is preferable to use a polymer compound containing a fluorine atom in the molecule, for example, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, etc. from the viewpoint of resistance.

Moreover, as for the weight average molecular weight of these resin as a binder, 10,000-1,000,000 are preferable. A low molecular weight is not preferable because the resistance of the binder may decrease. When the molecular weight is increased, the resistance of the binder is improved, but the viscosity of the binder itself is increased, the workability is lowered, the workability is decreased, and the mixture component may be significantly aggregated, which is not preferable.
<Conductive auxiliary agent (carbon material)>
As the conductive aid in the present invention, a carbon material is most preferable. The carbon material is not particularly limited as long as it is a conductive carbon material, but graphite, carbon black, carbon nanotube, carbon nanofiber, carbon fiber, fullerene, etc. alone or in combination of two or more. Can be used. 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.

As the specific surface area of the carbon black used increases, the contact point between the carbon black particles increases, which is advantageous for lowering the internal resistance of the electrode. Specifically, the specific surface area (BET) determined from the amount of nitrogen adsorbed is 20 m ² / g or more and 1500 m ² / g or less, preferably 50 m ² / g or more and 1500 m ² / g or less, more preferably 100 m ^2. / G or more and 1500 m ² / g or less are desirable. If carbon black having a specific surface area of less than 20 m ² / g is used, it may be difficult to obtain sufficient conductivity, and carbon black of more than 1500 m ² / g may be difficult to obtain from commercially available materials. is there.

  Further, the particle size of the carbon black to be used is preferably 0.005 to 1 μm, particularly preferably 0.01 to 0.2 μm in terms of primary particle size. However, the primary particle diameter here is an average of the particle diameters measured with an electron microscope or the like.

  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. (Columbian manufactured by Furnace Black), # 2350, # 2400B, # 30050B, # 3030B, # 3230B, # 3350B, # 3400B, # 5400B, etc. (Manufactured by Chemical Co., Furnace Black), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, etc. Furnace Black), Ensaco250G, Ensaco260G, Ensaco350G, SuperP-Li (manufactured by TIMCAL), Ketjen Black EC-300J, EC-600JD (manufactured by Akzo), Denka Black, Denka Black HS-100, FX-35 (Electrochemical Industry) However, it is not limited to these.

The carbon nanotube is a carbon material having a shape in which graphite is wound in a cylindrical shape, and has a diameter of several nm to 100 nm and a length of several nm to 1 mm. There are single-walled carbon nanotubes and multi-walled carbon nanotubes, but any structure may be used. In addition, fibers having a fiber diameter of about 100 nm to 1 μm, which are classified as carbon nanofibers, can be used.
<Solvent>
Examples of the solvent used in the present invention include alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, and phosphoric acid. Examples include esters, ethers, nitriles, water and the like.

  Among these, it is preferable to use a polar solvent having a relative dielectric constant of 15 or more. The relative dielectric constant is one of the indices indicating the strength of the polarity of the solvent, and is described in Asahara et al., “Solvent Handbook” (Kodansha Scientific Co., Ltd., 1990). For example, methyl alcohol (dielectric constant: 33.1), ethyl alcohol (23.8), 2-propanol (18.3), 1,2-ethanediol (38.66), 1,2-propanediol ( 32.0), diethylene glycol (31.69), 2-aminoethanol (37.7), acetone (20.7), methyl ethyl ketone (18.51), formamide (111.0), N-methylformamide (182. 4), N, N-dimethylformamide (36.71), N-methylacetamide (191.3), N, N-dimethylacetamide (37.78), N-methylpyrrolidone (32.0), hexamethylphosphoric triamide (29.6), dimethyl sulfoxide (48.9), sulfolane (43.3), acetonitrile (37.5), water ( 0.1) and the like, but not limited thereto.

  In particular, the use of a polar solvent having a relative dielectric constant of 15 or more and 200 or less, preferably 20 or more and 100 or less, and more preferably 25 or more and 100 or less, provides good solubility of the salts described later. preferable. A solvent having a relative dielectric constant of less than 15 is not preferable because the solubility of salts is remarkably lowered and it may not be dissolved to a practical concentration. Further, it is not preferable to use a solvent having a relative dielectric constant exceeding 200 because a remarkable effect of improving the solubility is often not obtained.

  In addition, the selection of the solvent in the present invention is performed in view of reactivity with the positive electrode active material, solubility of the binder, dispersion stability of the carbon material, solubility of the dispersant, and the like. It is preferable to select a solvent having low reactivity with the active material, high binder solubility, high carbon material dispersion stability, and high dispersant solubility.

  Furthermore, from the viewpoint of reducing environmental burdens and economic advantages, when recovering and reusing the solvent discharged in the electrode manufacturing process, it is preferable to use a single solvent instead of a mixed solvent.

As mentioned above, as a solvent having versatility in a single use, satisfying the solubility of salts described later, the reactivity with the positive electrode active material, the solubility of the binder, the dispersion stability of the carbon material, the solubility of the dispersant, Amide solvents are preferred, and in particular, amide aprotic such as N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methylpyrrolidone and hexamethylphosphoric triamide. The use of a reactive solvent is preferred.
<Dispersant>
Although it does not specifically limit as a dispersing agent used for this invention, The dispersing agent which contributes to the dispersion stabilization of a carbon material and / or a positive electrode active material, and has the effect of reducing the viscosity of the compound paste prepared is used. be able to. For example, surfactants such as anionic surfactants; mentioned triazine derivative having an acidic functional group, an organic dye derived having an acidic functional group, triazine derived material or the like having a basic functional group; resin having dispersibility It is done. These can be used alone or in combination of two or more.

  In particular, it is preferable to use at least one selected from triazine derivatives having an acidic functional group or organic dye derivatives having an acidic functional group. Although a detailed reason is unknown, it discovered that the precipitation inhibitory effect of a positive electrode active material appeared more notably when using together said derivative | guide_body and the salt mentioned later.

  As the triazine derivative having an acidic functional group or the organic dye derivative having an acidic functional group, use of a triazine derivative represented by the following general formula (4) or an organic dye derivative represented by the general formula (7) is preferable.

  General formula (4)

In general formula (4),
T ¹⁰¹ is —NH 2 —
T ¹⁰² is, -NH - a and,
Y ¹⁰¹ is composed of 1 to 20 carbon atoms, an arylene group which may have a substituent,
Z ¹⁰¹ is a -COO M ^101,
M ¹⁰¹ is one equivalent of a monovalent to trivalent cation,
Q ¹⁰¹ is —O—R ¹⁰² or —T ¹⁰¹ —R ¹⁰¹ ,
R ¹⁰² is hydrogen atom,
n ¹⁰¹ is an integer of 1 to 4,
R ¹⁰¹ is a heterocyclic residue may have a substituent.

The heterocyclic residue represented by R ¹⁰¹ in formula (4), for example, benzimidazolone include residues such Karubazo Le. In particular, the use of a heterocyclic residue containing at least one of S, N, and O heteroatoms is preferable because of excellent dispersibility.

Y ¹⁰¹ of the general formula (4) represents an arylene group but it may also have a substituent group having 20 or less carbon atoms, preferably an optionally substituted phenylene group, biphenylene group, naphthylene group or carbon, An alkylene group which may have a side chain having a number of 10 or less is mentioned.

Formula (4) substituent alkyl group which may have a represented by R ¹⁰² contained in Q ^101, the alkenyl group is preferably of 20 or less carbon atoms, more preferably carbon atoms The alkyl group which may have 10 or less side chains is mentioned. An alkyl group or alkenyl group having a substituent is a group in which a hydrogen atom of an alkyl group or an alkenyl group is substituted with a halogen group such as a fluorine atom, a chlorine atom, or a bromine atom, a hydroxyl group, or a mercapto group It is.

M ^{101 in the} general formula (4) represents one equivalent of a valence of 1 to 3, and represents, for example, any of a hydrogen atom (proton), a metal cation, or a quaternary ammonium cation. Moreover, when it has two or more M in a dispersing agent structure, M may be only any one of a proton, a metal cation, or a quaternary ammonium cation, and these may be combined. Examples of the metal include lithium, sodium, potassium, calcium, barium, magnesium, aluminum, nickel, and cobalt. The quaternary ammonium cation is a quaternary ammonium cation having a structure represented by the general formula (6), or a mixture thereof.

  General formula (6)

In General Formula (6), R ³⁰¹ , R ³⁰² , R ³⁰³ , and R ³⁰⁴ have hydrogen, an alkyl group that may have a substituent, an alkenyl group that may have a substituent, or a substituent. Any of the aryl groups that may be present.

R ³⁰¹ , R ³⁰² , R ³⁰³ , and R ³⁰⁴ in general formula (6) may be the same or different. In addition, when R ³⁰¹ , R ³⁰² , R ³⁰³ , and R ³⁰⁴ have a carbon atom, the carbon number is 1 to 40, preferably 1 to 30, and more preferably 1 to 20. If the carbon number exceeds 40, the conductivity of the electrode may be reduced.

  Specific examples of the quaternary ammonium cation include dimethylammonium, trimethylammonium, diethylammonium, triethylammonium, hydroxyethylammonium, dihydroxyethylammonium, 2-ethylhexylammonium, dimethylaminopropylammonium, laurylammonium, and stearylammonium. However, it is not limited to these.

  General formula (7)

In general formula (7),
T ⁴⁰¹ is a direct binding,
Z ⁴⁰¹ is —SO ₃ M ⁴⁰¹ ,
M ⁴⁰¹ is one equivalent of a monovalent to trivalent cation,
R ⁴⁰¹ is an organic dye residue,
n ⁴⁰¹ is an integer of 1 to 4.

The organic dye residue represented by R ⁴⁰¹ in formula (7), azo For example, disazo, azo dyes such as polyazo include residues such quinacridone color element. Of these azo dyes, the use of residues of quinacridone color element is preferable because of its excellent dispersibility.

M ^{401 in} the formula of the general formula (7) represents one equivalent of a monovalent to trivalent cation, for example, a hydrogen atom (proton), a metal cation, or a quaternary ammonium cation. In the case where the dispersant structure has two or more M, M ⁴⁰¹ may be only one of a proton, a metal cation or a quaternary ammonium cation, or a combination thereof. Examples of the metal include lithium, sodium, potassium, calcium, barium, magnesium, aluminum, nickel, and cobalt. The quaternary ammonium cation is a quaternary ammonium cation having a structure represented by the general formula (6), or a mixture thereof.

  The method for synthesizing the above derivatives is not particularly limited. For example, Japanese Patent Publication No. 39-28884, Japanese Patent Publication No. 45-11026, Japanese Patent Publication No. 45-29755, Japanese Patent Publication No. 64-5070. It can synthesize | combine by the method described in gazette or Unexamined-Japanese-Patent No. 2004-217842.

Among the above dispersants, for example, those having sulfonic acid or a salt thereof as an acidic functional group are generally sulfonated using a sulfonating agent such as fuming sulfuric acid, concentrated sulfuric acid, and chlorosulfonic acid. . In this case, the number of acidic functional groups has a distribution and can be, for example, a mixture of unsubstituted, monosubstituted, disubstituted, and the like. Not only sulfonic acid and its salts, but also carboxylic acid and phosphoric acid may be a mixture of those having different numbers of acidic functional groups depending on the synthesis method. As the dispersant of the present invention, it is also possible to use a mixture of those having different numbers of acidic functional groups.
<Salt>
The present invention is characterized by containing a salt. Although the detailed reason is unknown, it discovered that the mixture paste for lithium ion secondary battery positive electrodes which suppressed the precipitation of a positive electrode active material could be prepared by using salt. By adding a small amount of salt, it was confirmed that the viscosity of the lithium ion secondary battery positive electrode mixture paste increased and thixotropic properties were imparted. Thixotropic property is a property in which the sol-gel conversion, which is gel-like in a stationary state but softens and becomes a fluid sol when externally stressed, occurs reversibly depending on the presence or absence of stress. Also say.

  As a salt used at this time, the salt represented by General formula (1) and / or General formula (2) and / or General formula (3) can be used.

General formula (1) AX _a
(In the formula, A is an a-valent element selected from Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, and Ba. X is halogen. A is the valence of A and 1 Or an integer of 2.)
General formula (2) NH ₄ X
(In the formula, N is nitrogen, H is hydrogen, and X is halogen.)
General formula (3) D (HX) _d
(In the formula, D is an amine having d amino groups in the molecule. H is hydrogen and X is halogen. D is the number of amino groups in the molecule of D and is an integer of 1 or more.)
The above salt is preferably easily soluble in a solvent. If undissolved salt remains in the composite paste, it is not preferable because the conductivity of the composite layer formed on the current collector may be hindered or the deterioration of the battery may be accelerated by the resistance distribution. . Further, when the salt is hardly soluble in the solvent and long time stirring or heating is required for dissolution, it is not preferable because it may cause a problem in productivity and cost. A salt having a solubility of 0.1 part by weight or more with respect to 100 parts by weight of the solvent is preferable, and a salt having a solubility of 1 part by weight or more with respect to 100 parts by weight of the solvent is more preferable. If the solubility is less than 0.1 part by weight with respect to 100 parts by weight of the solvent, it may not be dissolved to a practical concentration, which is not preferable.

  Moreover, although the detailed reason is unknown, the effect of the above-mentioned salt was found to correlate with the amount of the halogen component. Therefore, the smaller the salt molecular weight, the smaller the atomic weight of the halogen, or the larger the ratio of the halogen atomic weight to the salt molecular weight, the more effective the effect can be achieved with a small amount of salt.

  By the way, in the lithium ion secondary battery, there are problems relating to safety such as reduction of battery performance due to reduction and deposition of metal components on the negative electrode and excessive heat generation and ignition due to occurrence of short circuit. For this reason, it was considered preferable not to contain a transition metal element such as Fe or Cu as a constituent component of the salt. Li, which is inevitably contained in a lithium ion secondary battery, or Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, or a salt containing ammonia or amine as constituent elements is used. can do. In particular, lithium halides that are necessarily contained in lithium ion secondary batteries and that have a large ratio of halogen atom weight to salt molecular weight due to small atomic weight are preferred.

From the viewpoints mentioned above, LiF, LiCl, LiBr and the like are selected as the optimum salts, but are not limited to these. Moreover, said salt can be used individually or in combination of 2 or more types.
<Method for Producing Compound Paste for Lithium Ion Secondary Battery Positive Electrode>
The lithium ion secondary battery positive electrode paste of the present invention can be produced by mixing a positive electrode active material, a binder, a carbon material as a conductive additive, a solvent, a dispersant, and a salt. it can. The order of addition of each component is not limited. For example, a method in which all components are mixed together; a method in which a carbon material is dispersed in a solvent in advance using a dispersant, and the remaining components are added thereto and mixed. A method in which after dispersing the dispersant in a solvent, the carbon material and the binder are added, the carbon material is dispersed and the binder is dissolved simultaneously, and the remaining components are added and mixed.

  The concentration of each component in the composite paste can be arbitrarily determined from the material to be used, the viscosity of the composite paste, the desired performance of the lithium ion secondary battery, and the like. The proper viscosity of the composite paste depends on the coating method, but generally it is preferably 100 mPa · s or more and 30,000 mPa · s or less.

  As a preferable composition ratio, the ratio of the positive electrode active material to the total solid content in the composite paste is 80% by weight or more and 98.5% by weight or less, the ratio of the binder is 0.5% by weight or more and 10% by weight or less. The proportion of the carbon material as the agent is 0.5 to 10% by weight, the proportion of the dispersant is 0.01 to 1% by weight, and the ratio of the salt is 0.001 to 0.2% by weight. Hereinafter, the ratio of the solvent in the composite paste is 20% by weight or more and 60% by weight or less.

  When the proportion of the positive electrode active material in the total solid content in the composite paste is less than 80% by weight, a battery having a sufficient capacity may not be obtained. Since the ratio of a component falls, there exists a possibility that the electroconductivity of the formed composite material layer may be inadequate, or the adhesiveness to a collector may not be obtained.

  When the ratio of the binder to the total solid content in the composite paste is less than 0.5% by weight, there is a possibility that sufficient adhesion to the current collector cannot be obtained because the binding property is lowered. If the ratio exceeds 50%, the ratio of other components decreases, and a battery with sufficient performance may not be obtained.

  If the proportion of the carbon material, which is a conductive additive, in the total solid content in the composite paste is less than 0.5% by weight, the formed composite layer may have insufficient conductivity, and may be 10% by weight. If the ratio exceeds 1, the ratio of other components decreases, and a battery with sufficient performance may not be obtained.

  If the ratio of the dispersing agent to the total solid content in the composite paste is less than 0.01% by weight, the carbon material and / or the positive electrode active material that is a conductive auxiliary agent may not be sufficiently dispersed and stabilized. Even if the content exceeds 1% by weight, there is a possibility that a significant improvement in dispersion stability cannot be expected.

  If the proportion of the salt in the total solid content in the composite paste is less than 0.001% by weight, the effect of suppressing the precipitation of the positive electrode active material may not be sufficiently obtained, and the content exceeds 0.2% by weight. In addition, the composite paste may have a very high viscosity, making it difficult to apply, and the metal component may adversely affect battery performance.

  If the proportion of the solvent in the composite paste is less than 20% by weight, the composite paste may have a very high viscosity and may be difficult to apply. If it exceeds 60% by weight, the effect of the salt in the present invention is achieved. Even so, there is a possibility that the precipitation of the positive electrode active material cannot be suppressed.

Moreover, as a device for producing the composite paste, a disperser usually used for pigment dispersion or the like can be used. For example, mixers such as dispersers, homomixers, planetary mixers, homogenizers ("Clearmix" manufactured by M Technique, PRIMIX "Fillmix", etc.), paint conditioners (manufactured by Red Devil), ball mills, sand mills ( Media type dispersers such as “Dynomill” manufactured by Shinmaru Enterprises, Inc.), Attritor, Pearl Mill (“DCP Mill” manufactured by Eirich), Coball Mill, etc., Wet Jet Mill (“Genus PY” manufactured by Genus, Sugino Machine Co., Ltd.) Media-less dispersers such as “Starburst” manufactured by Nanomizer, “Nanomizer” manufactured by Nanomizer, etc., “Claire SS-5” manufactured by M Technique, and “MICROS” manufactured by Nara Machinery Co., other roll mills, etc. It is not limited to.
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, the metal agitator and vessel use a ceramic or resin disperser, or the metal agitator and the vessel surface are coated with tungsten carbide spray or resin coating. It is preferable to use a disperser that has been treated as described above. As the media, glass beads, ceramic beads such as zirconia beads or alumina beads are preferably used. Moreover, also when using a roll mill, it is preferable to use a ceramic roll.

Only one type of disperser may be used, or a plurality of types of devices may be used in combination.
<Lithium ion secondary battery>
The lithium ion secondary battery includes a positive electrode having a positive electrode mixture layer on a current collector, a negative electrode having a negative electrode mixture layer on the current collector, and an electrolyte containing lithium.

  Regarding the electrode, the material and shape of the current collector to be used are not particularly limited, and as the material, metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel are used. In particular, as the positive electrode material, aluminum is used as the negative electrode. The material is preferably copper. As the shape, a flat plate foil is generally used, but a roughened surface, a perforated foil shape, and a mesh shape can also be used.

  The positive electrode composite material layer can be formed by applying and drying the composite material paste of the present invention.

The negative electrode mixture layer is composed of a negative electrode active material, a conductive aid, a binder, and the like. There are no particular limitations as an anode active material, lithium ion doping or capable of intercalating Li metal or its alloy, tin alloy, silicon alloy negative _{electrode, Li X Fe 2 O 3,} Li X Fe 3 O 4, Li _X WO ₂ or the like of the metal oxide-based, polyacetylene conductive polymers poly -p- phenylene, such as soft carbon or hard carbon, and amorphous-based carbon material, artificial graphite such as highly graphitized carbon material or naturally occurring, Carbonaceous materials such as carbonaceous powder such as graphite, carbon black, mesophase carbon black, resin-fired carbon material, gas-grown carbon fiber, and carbon fiber are used. Although it does not specifically limit as a conductive support agent and a binder, What was mentioned above as what can be used for the composite paste for positive electrodes is used.

  The thickness of the electrode mixture layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less. There is no restriction | limiting in particular about the coating method, A well-known method can be used. Specific examples include a die coating method, a dip coating method, a roll coating method, a doctor coating method, a spray coating method, a gravure coating method, a screen printing method, and an electrostatic coating method. Moreover, you may perform the rolling process by a lithographic press, a calender roll, etc. after application | coating.

As the electrolytic solution constituting the lithium secondary battery of the present invention, an electrolyte containing lithium is dissolved in a non-aqueous solvent. 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, LiBPh _{4 and the} like, but are not limited thereto.

  The non-aqueous solvent is not particularly limited, but carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone. Lactones such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, 1,2-dibutoxyethane, etc. Glymes, esters such as methyl formate, methyl acetate and methyl propionate, sulfoxides such as dimethyl sulfoxide and sulfolane, and nitriles such as acetonitrile. These solvents may be used alone or in combination of two or more.

  Furthermore, the electrolyte solution may be a gelled polymer electrolyte held in a polymer matrix. 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, a polysiloxane having a polyalkylene oxide segment, and the like.

  The structure of the lithium ion secondary battery using the composite paste of the present invention is not particularly limited, but is usually composed of a positive electrode and a negative electrode, and a separator provided as necessary, and is a paper type, cylindrical type, button type Various shapes can be formed according to the purpose of use, such as a laminated type.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to a following example, unless the summary is exceeded. In this example, “part” represents “part by weight” and “%” represents “% by weight”.

The positive electrode active materials, binders, carbon materials, solvents, dispersants, salts, and anti-settling agents used in the examples and comparative examples are shown below.
<Positive electrode active material>
Lithium cobaltate (LiCoO ₂ ): Average particle diameter 7.1 μm, specific surface area 0.38 m ² / g, hereinafter abbreviated as LCO.

Lithium manganate (LiMn ₂ O ₄ ): Average particle size 11.9 μm, specific surface area 0.63 m ² / g, hereinafter abbreviated as LMO.

Lithium nickel manganese cobalt composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ): average particle size 9.2 μm, specific surface area 0.36 m ² / g, hereinafter abbreviated as NMC.

Lithium iron phosphate (LiFePO ₄ ): Average particle size 3.6 μm, specific surface area 12.6 m ² / g, hereinafter abbreviated as LFP.
<Binder>
Polyvinylidene fluoride: KF polymer W # 7200 (manufactured by Kureha), hereinafter abbreviated as PVDF.

  Styrene-butadiene rubber: TRD2001 (manufactured by JSR), hereinafter abbreviated as SBR.

Carboxymethylcellulose: Sunrose F100MC (manufactured by Nippon Paper Chemicals), hereinafter abbreviated as CMC.
<Carbon material>
Acetylene black: Denka black granular product (manufactured by Denki Kagaku Kogyo), primary particle size 35 nm, specific surface area 68 m ² / g, hereinafter abbreviated as AB.

Carbon nanofiber: VGCF (manufactured by Showa Denko), fiber diameter 150 nm, fiber length 10-20 μm.
<Solvent>
N-methylpyrrolidone: relative dielectric constant 32.0, hereinafter abbreviated as NMP.

Purified water: relative dielectric constant 80.1.
<Dispersant>
Triazine derivatives having an acidic functional group: TA-a, TA-b.

  Organic dye derivatives having acidic functional groups: PA-a, PA-b.

  Triazine derivative having a basic functional group: TB.

  Anionic surfactant: Demol N (manufactured by Kao Corporation), sodium salt of β-naphthalenesulfonic acid-formalin condensate, hereinafter abbreviated as DemN.

  Resin having dispersibility: Rubytech K30 (manufactured by BASF), vinylpyrrolidone homopolymer, hereinafter abbreviated as PVP.

  Table 1 shows the structures of various derivatives that are dispersants.

<Salt>
Lithium chloride (LiCl): The amount of chlorine per gram is 23.6 mmol.

  Lithium bromide (LiBr): The amount of bromine per gram is 11.5 mmol.

Calcium chloride (CaCl ₂ ): The amount of chlorine per gram is 18.0 mmol.

Ammonium chloride (NH ₄ Cl): The amount of chlorine per gram is 18.7 mmol.

Triethylammonium chloride ((C ₂ H ₅ ) ₃ NHCl): The amount of chlorine per gram is 7.3 mmol.

  Sodium chloride (NaCl): The amount of chlorine per gram is 17.1 mmol.

Iron (III) chloride (FeCl ₃ ): The amount of chlorine per gram is 18.5 mmol.

Lithium acetate (CH ₃ COOLi)
<Anti-settling agent>
Polyethylene oxide: Disparon 4200-20 (manufactured by Kashiwagi Chemical Co., Ltd.), hereinafter abbreviated as DisP.
<Preparation of carbon material dispersion>
Dispersant TA-b (1 part) was dissolved in NMP (349 parts), then carbon material AB (25 parts) and PVDF (25 parts) were added, and dispersion / dissolution treatment was performed for 1 hour with a homogenizer to obtain carbon material dispersion liquid A.
<Preparation of composite paste for positive electrode of lithium ion secondary battery>
The evaluation of the composite pastes obtained in Examples and Comparative Examples was performed by measuring the viscosity (initial evaluation) and the presence or absence of sediment (evaluation with time). The viscosity was measured using a B-type viscometer (“BL” manufactured by Toki Sangyo Co., Ltd.) at 25 ° C., 6 rpm, and 60 rpm. Presence / absence of the precipitate was determined by standing at 25 ° C. and storing it, and after 1 day and 7 days, it was scooped up from the storage container with a spatula and whether or not a gel-like precipitate was observed.
[Example 1]
7 parts of PVDF was dissolved in 93 parts of NMP to prepare a binder solution. 1 part of lithium chloride was dissolved in 99 parts of NMP to prepare a salt solution. Next, according to the composition shown in Table 2, the active material LCO, the carbon material AB, the dispersant TA-a, the binder solution, and the salt solution were put into a planetary mixer and mixed for 1 hour. Further, NMP was added until the composition of Example 1 listed in Table 2 was reached, followed by a mixing treatment for 30 minutes with a planetary mixer to prepare a composite paste.
[Example 2]
According to the composition shown in Table 2, an active material was LMO, a carbon material was VGCF, a dispersant was PA-a, and a mixture paste was prepared in the same manner as in Example 1 except that the contents of these materials were changed. .
[Example 3]
According to the composition shown in Table 2, a composite paste was prepared in the same manner as in Example 1 except that the active material was NMC and the dispersant was TA-b.
[Example 4]
According to the composition shown in Table 2, a mixture paste was prepared in the same manner as in Example 1 except that the active material was LFP, the dispersant was PA-b, and the contents of these materials were changed.
[Example 5]
1 part of lithium chloride was dissolved in 99 parts of NMP to prepare a salt solution. Next, according to the composition shown in Table 2, the active material NMC, the carbon material dispersion A, and the salt solution were put into a planetary mixer and mixed for 1 hour. Furthermore, after adding NMP until it became the composition of Example 5 hung up in Table 2, it mixed by the planetary mixer for 30 minutes continuously, and prepared the composite paste.
[Example 6]
According to the composition shown in Table 2, a composite paste was prepared in the same manner as in Example 1 except that the active material was NMC, the dispersant was TA-b, and 2 parts of lithium bromide was used instead of 1 part of lithium chloride. . [Example 7]
According to the composition shown in Table 2, a composite paste was prepared in the same manner as in Example 1 except that the active material was NMC, the dispersant was TA-b, and calcium chloride was used instead of lithium chloride.
[Example 8]
8 parts of PVDF was dissolved in 92 parts of NMP to prepare a binder solution. 1 part of ammonium chloride was dissolved in 799 parts of NMP to prepare a salt solution. Next, according to the composition shown in Table 2, the active material NMC, the carbon material AB, the dispersant TA-b, and the binder solution were put into a planetary mixer and mixed for 1 hour. Further, a salt solution and NMP were added until the composition of Example 8 listed in Table 2 was added, and then a mixing treatment was performed for 30 minutes with a planetary mixer to prepare a composite paste.
[Example 9]
According to the composition shown in Table 2, a mixture paste was prepared in the same manner as in Example 1 except that the active material was NMC, the dispersant was TA-b, and 3 parts of triethylammonium chloride was used instead of 1 part of lithium chloride. .
[Example 10]
According to the composition shown in Table 2, a composite paste was prepared in the same manner as in Example 1 except that the dispersant was TB . Example 10 is a reference example.
[Example 12]
According to the composition shown in Table 2, a mixture paste was prepared in the same manner as in Example 1 except that the active material was LMO, the dispersant was PVP, and the contents of these materials were changed. Example 12 is a reference example.
[Example 13]
4 parts of SBR and 1 part of CMC were dissolved in 95 parts of purified water to prepare a binder solution. 1 part of sodium chloride was dissolved in 99 parts of purified water to prepare a salt solution. Next, according to the composition shown in Table 2, the active material LFP, the carbon material AB, the dispersant DemN, the binder solution, and the salt solution were put into a planetary mixer and mixed for 1 hour. Further, purified water was added until the composition of Example 13 listed in Table 2 was reached, and then mixed with a planetary mixer for 30 minutes to prepare a composite paste. Example 13 is a reference example.
[Comparative Example 1]
According to the composition shown in Table 2, a composite paste was prepared in the same manner as in Example 1 except that lithium chloride was not used.
[Comparative Example 2]
According to the composition shown in Table 2, a composite paste was prepared in the same manner as in Example 2 except that lithium chloride was not used.
[Comparative Example 3]
According to the composition shown in Table 2, a composite paste was prepared in the same manner as in Example 3 except that lithium chloride was not used.
[Comparative Example 4]
According to the composition shown in Table 2, a composite paste was prepared in the same manner as in Example 4 except that lithium chloride was not used.
[Comparative Example 5]
According to the composition shown in Table 2, a composite paste was prepared in the same manner as in Example 1 except that the active material was NMC, the contents of these materials were changed, and the dispersant and lithium chloride were not used.
[Comparative Example 6]
35 parts of PVDF and 7 parts of antisettling agent DisP were dissolved in 465 parts of NMP to prepare a mixed solution. Next, according to the composition shown in Table 2, the active material NMC, the carbon material AB, the dispersant TA-b, and the above mixed solution were put into a planetary mixer and mixed for 1 hour. Furthermore, after adding NMP until it became a composition of the comparative example 6 hung up over Table 2, it mixed by the planetary mixer for 30 minutes, and prepared the compound paste.
[Comparative Example 7]
According to the composition shown in Table 2, a composite paste was prepared in the same manner as in Example 1 except that the active material was NMC, the dispersant was TA-b, and iron (III) chloride was used instead of lithium chloride.
[Comparative Example 8]
According to the composition shown in Table 2, a composite paste was prepared in the same manner as in Example 13 except that lithium acetate was used instead of sodium chloride.

  From Table 2, it was confirmed that no sediment was observed in the composite pastes of the examples even after 7 days of storage and the sedimentation of the positive electrode active material was suppressed. From comparison between Example 1 to Example 4 and Comparative Example 1 to Comparative Example 4, it can be seen that sedimentation was suppressed by the addition of salt.

  No sediment was observed in the composite paste of Comparative Example 5 to which no dispersant was added, but the solid content of the composite paste was lowered in order to adjust the viscosity to a viscosity suitable for coating. I had to.

In the composite paste to which the anti-settling agent was added in Comparative Example 6, no precipitate was observed after 1 day of standing, but was observed after 7 days. It was confirmed that the composite paste of Comparative Example 7 was able to suppress sedimentation of the positive electrode active material as in the example. In the composite paste to which lithium acetate of Comparative Example 8 was added, sediment was observed after 1 day of standing.


<Assembly of lithium ion secondary battery positive electrode evaluation cell>
The previously prepared composite paste for lithium secondary battery positive electrodes (Examples 1 to 13 and Comparative Examples 1 to 8) was applied onto a 20 μm thick aluminum foil serving as a current collector using a doctor blade. Here, the coating speed (moving speed of the current collector) was 100 mm / min. In addition, a sufficient amount of the mixture paste was initially introduced into the liquid reservoir of the coating apparatus so that it was not added during the process. After heat drying at 120 ° C. under reduced pressure, the mixture was rolled with a roller press to produce a positive electrode mixture layer having a thickness of 100 μm. When this is punched out to a diameter of 9 mm, it is punched out from the middle part of coating (part of 5 m from the coating start end) and the end part of coating (part of 20 cm from the coating end) to form a working electrode, and a metal lithium foil (thickness 0.15 mm) As a counter electrode, a separator (# 2400 manufactured by Celgard) made of a porous polypropylene film is inserted and laminated between the working electrode and the counter electrode, and LiPF ₆ is added to a mixed solvent in which ethylene carbonate and diethyl carbonate are mixed 1: 1. Was filled with a non-aqueous electrolyte solution having a concentration of 1 M), and a two-pole sealed metal cell (HS flat cell manufactured by Hosensha) was assembled. The cell was assembled in a glove box substituted with argon gas.
<Characteristic evaluation of lithium ion secondary battery positive electrode>
The prepared positive electrode evaluation cell was fully charged at a constant current and constant voltage charge (upper limit voltage 4.2 V) at a room temperature (25 ° C.) with a charge rate of 1.0 C, and a discharge lower limit voltage 3 at a constant current at the same rate as during charging. Charging / discharging for discharging to 0.0 V was performed as one cycle (charging / discharging interval rest time 30 minutes), and this cycle was performed for a total of 20 cycles, and charging / discharging cycle characteristics (evaluation apparatus: SM-8 manufactured by Hokuto Denko Co., Ltd.) were measured. 20th cycle discharge capacity maintenance ratio calculated from the first discharge capacity (initial discharge capacity), 20th cycle discharge capacity (20th cycle discharge capacity), 20th cycle discharge capacity / initial discharge capacity in the measured charge / discharge cycle characteristics ( %) Is shown in Table 3.

  From Table 3, when the positive mix layer was formed using the composite paste of the example, good results were obtained in the discharge capacity and the 20 cycle discharge capacity retention rate. Further, it is considered that the discharge capacity is constant regardless of the punched portion of the working electrode, and a uniform electrode was obtained.

  In Comparative Examples 1 to 4 and Comparative Example 8, the discharge capacity varied depending on the punched portion of the working electrode. As time passes, sedimentation of the active material occurs in the puddle paste, and the active material content in the mixture layer increases at the middle part of the coating, and conversely decreases at the end of the coating. This is probably because an electrode was not obtained.

  In Comparative Example 5, the discharge capacity and the 20 cycle discharge maintenance rate were inferior to those of the Examples. This is thought to be due to poor dispersion of the conductive assistant and active material.

  In Comparative Example 6, the discharge capacity and the 20-cycle discharge retention rate were slightly inferior to those of Example 3 and the like. Further, the difference in discharge capacity due to the punched-out portion of the working electrode is relatively large, and it is considered that the electrodes were slightly non-uniform.

  In Comparative Example 7, the 20-cycle discharge maintenance rate was inferior to that of the Example. Since this is a salt containing iron, it is considered that the battery performance was adversely affected.

Claims (4)

A positive electrode active material, a binder, a carbon material as a conductive additive, a solvent, a dispersant, and a salt represented by the general formula (1) and / or the general formula (2) and / or the general formula (3) A lithium ion secondary battery positive electrode composite paste , wherein the dispersant is a triazine derivative having an acidic functional group represented by the general formula (4) and an acidic functional group represented by the general formula (7) A composite paste for a positive electrode of a lithium ion secondary battery, which is one or more dispersants selected from organic dye derivatives having a group .
General formula (1) AX _a
(In the formula, A is an a-valent element selected from Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, and Ba. X is halogen. A is the valence of A and 1 Or an integer of 2.)
General formula (2) NH ₄ X
(In the formula, N is nitrogen, H is hydrogen, and X is halogen.)
General formula (3) D (HX) _d
(In the formula, D is an amine having d amino groups in the molecule. H is hydrogen and X is halogen. D is the number of amino groups in the molecule of D and is an integer of 1 or more.)
General formula (4)

(In general formula (4),
T ¹⁰¹ is —NH—;
T ¹⁰² is a -NH-,
Y ¹⁰¹ is an arylene group which has 1 to 20 carbon atoms and may have a substituent,
Z ¹⁰¹ is —COOM ¹⁰¹ ;
M ¹⁰¹ is one equivalent of a monovalent to trivalent cation,
Q ¹⁰¹ is —O—R ¹⁰² or —T ¹⁰¹ —R ¹⁰¹ ,
R ¹⁰² is a hydrogen atom,
n ¹⁰¹ is an integer of 1 to 4,
R ¹⁰¹ is a heterocyclic residue which may have a substituent, and the heterocyclic residue is a benzimidazolone or carbazole residue. )

General formula (7)

(In general formula (7),
T ⁴⁰¹ is a direct bond,
Z ⁴⁰¹ is —SO ₃ M ⁴⁰¹ ,
M ⁴⁰¹ is one equivalent of a monovalent to trivalent cation,
R ⁴⁰¹ is an organic dye residue, and the organic dye residue is a residue of an azo dye or a quinacridone dye;
n ⁴⁰¹ is an integer of 1 to 4. )
  The composite paste for a lithium ion secondary battery positive electrode according to claim 1, wherein the proportion of the salt in the total solid content in the composite paste is less than 0.2% by weight.   The positive electrode for lithium ion secondary batteries by which a composite material layer is formed using the mixed material paste for lithium ion secondary battery positive electrodes of Claim 1 or 2.   A lithium ion secondary battery comprising: a positive electrode having a positive electrode mixture layer on a current collector; a negative electrode having a negative electrode mixture layer on the current collector; and an electrolyte containing lithium. The lithium ion secondary battery which is a positive electrode for lithium ion secondary batteries as described.