WO2016084909A1

WO2016084909A1 - Silica-coated carbon black, electrode composition in which same is used, electrode for secondary cell, and secondary cell

Info

Publication number: WO2016084909A1
Application number: PCT/JP2015/083267
Authority: WO
Inventors: 裕輝名古; みか西川; 哲哉伊藤; 横田　博; 崇人今井
Original assignee: デンカ株式会社
Priority date: 2014-11-26
Filing date: 2015-11-26
Publication date: 2016-06-02
Also published as: JP6604965B2; CN107207876B; CN107207876A; JPWO2016084909A1

Abstract

The ratio of DBP absorption to compressed DBP absorption of carbon black (DBP absorption/compressed DBP absorption) is 2.2 or less, and silica-coated carbon black in which the silica is a hydrolyzed condensate of a tetraalkoxysilane having a specific structure is used to obtain longer service life of a cell, as well as good electroconductive characteristics and dispersibility.

Description

Silica-coated carbon black, electrode composition using the same, secondary battery electrode and secondary battery

The present invention relates to silica-coated carbon black, an electrode composition using the same, a secondary battery electrode, and a secondary battery.

The lithium ion secondary battery in which the negative electrode is formed using a material capable of occluding and releasing lithium ions can suppress the deposition of dendride compared to the lithium battery in which the negative electrode is formed using metallic lithium. Therefore, there is an advantage that a battery having a high capacity and a high energy density can be provided while safety is improved by preventing a short circuit of the battery.

In recent years, further improvement in the output density of this lithium ion secondary battery has been demanded. As one means for realizing this, a method of obtaining a high output density even at a small current density by using a positive electrode active material having a higher discharge voltage than that of the prior art has been studied. For example, by using lithium nickel manganate (LiNi _0.5 Mn _1.5 O ₂ ) having a spinel crystal structure as a positive electrode active material, a high discharge voltage of about 4.5 V can be realized.

However, when a positive electrode active material having a high potential as described above is used, the positive electrode and the electrolyte solution in the vicinity thereof are placed in a strong oxidizing environment, so that gas generation due to oxidative decomposition of the electrolyte solution proceeds and the battery life is reduced. There are challenges.

In order to improve battery life, for example, Patent Document 1 discloses a positive electrode material for a lithium ion secondary battery in which a halide is coated on the surface of the positive electrode material. Patent Document 2 discloses a positive electrode mixture in which the surface of the positive electrode current collector is coated with a fluorine compound.

By the way, Patent Document 3 discloses a BET specific surface area, DBP absorption amount, electric resistivity, sulfur content, and volatile component content as carbon black for non-aqueous secondary batteries excellent in conductivity and dispersibility. Carbon blacks each in a predetermined range are disclosed. Patent Document 4 discloses a carbon black slurry having good slurry stability.

JP 2009-104815 A JP 2011-205095 A JP 2012-221684 A Japanese Patent Laid-Open No. 2003-157846

Carbon black has been conventionally used as a conductive agent for secondary batteries. However, when a positive electrode active material having a high potential is used as described above, the carbon black that is a conductive agent has a large contact area with the electrolytic solution, which is a factor that easily causes oxidative decomposition and gas generation of the electrolytic solution. ing.

None of the methods described in Patent Documents 1 and 2 has improved carbon black, and the effect of suppressing gas generation due to oxidative decomposition of the electrolyte is insufficient.

By the way, carbon black has a structure in which primary particles close to a spherical shape are connected on a bead as a common structure, and such a structure is called a structure. In general, the longer the structure is connected, the greater the distance that can be conducted without contact resistance, so that the electron conductivity is improved.

The length of the structure is indirectly evaluated using a DBP absorption amount generally measured in accordance with JIS K6217-4. The larger the DBP absorption amount, the longer the structure and the better the conductivity. On the other hand, carbon black having a long structure is excellent in conductivity, but has an aspect that the interaction between particles becomes large, so that it is difficult to disintegrate and easily aggregates. Therefore, in general, when an electrode is produced, a method of applying an electrode composition in which an active material, a conductive agent and a binder are dispersed in water or an organic solvent is applied to a metal foil, but when carbon black having a long structure is used as a conductive agent, The conductive solution aggregates remain in the coating solution, causing irregularities on the electrodes, and the coating solution is too viscous to make application impossible. In addition, in the slurrying described in, for example, Patent Document 4, there is a concern that the structure is cut by mechanical crushing, and there is a possibility that sufficient electronic conductivity cannot be ensured.

In view of the above problems and circumstances, the present invention is a silica-coated carbon black that suppresses decomposition and gas generation of an electrolyte in a high-potential secondary battery, particularly a lithium ion secondary battery, and has excellent conductivity and dispersibility. An object of the present invention is to provide a secondary battery electrode and a secondary battery having excellent durability using the same.

That is, the present invention employs the following means in order to solve the above problems.
(1) It includes carbon black and silica that covers the surface of the carbon black, and a ratio of DBP absorption to compression DBP absorption of the carbon black (DBP absorption / compression DBP absorption) is 2.2 or less. Silica-coated carbon black, wherein the silica contains a hydrolyzed condensate of tetraalkoxysilane represented by the formula (1).

(In the formula, n represents an integer of 1 or more and 5 or less.)
(2) The silica is obtained by hydrolysis and condensation of the tetraalkoxysilane having a mass ratio of 20 to 250 with respect to the ammonium salt in the presence of the ammonium salt represented by the formula (2). The silica-coated carbon black described in 1.

(In the formula, X represents Cl, Br or I, and m represents an integer of 3 to 30.)
(3) The silica-coated carbon black according to (2), wherein the ammonium salt is hexadecyltrimethylammonium chloride.
(4) The silica-coated carbon black according to any one of (1) to (3), wherein n is an integer of 1 to 3.
(5) The silica-coated carbon black according to any one of (1) to (4), wherein a coating amount of the silica is 10% by mass to 30% by mass with respect to a total amount of the silica and the carbon black.
(6) The silica-coated carbon black according to any one of (1) to (5), wherein the carbon black is acetylene black.
(7) The silica-coated carbon black according to any one of (1) to (6), wherein the volume resistivity is 1 × 10 ⁵ Ω · cm or less.
(8) The silica-coated carbon black according to any one of (1) to (7), wherein the carbon black has a DBP absorption of 280 mL / 100 g.
(9) The silica-coated carbon black according to any one of (1) to (8), wherein the volume resistivity is 1 × 10 ³ Ω · cm or less.
(10) The silica-coated carbon black according to any one of (1) to (9), a positive electrode active material capable of occluding and releasing cations, and a negative electrode active capable of occluding and releasing cations An electrode composition comprising at least one selected from the group consisting of substances and a binder.
(11) An electrode for a secondary battery comprising a metal foil and a coating film of the electrode composition according to claim 10 provided on the metal foil.
(12) A secondary battery comprising the secondary battery electrode according to (11) on at least one of a positive electrode and a negative electrode.
(13) In a dispersion containing carbon black, the tetraalkoxysilane represented by the formula (1) is hydrolyzed and condensed, and the surface of the carbon black is silica containing the hydrolyzed condensate of the tetraalkoxysilane. A method for producing silica-coated carbon black, comprising a step of coating, wherein a ratio of DBP absorption to compression DBP absorption of carbon black (DBP absorption / compression DBP absorption) is 2.2 or less.

(In the formula, n represents an integer of 1 to 5, inclusive.)
(14) The production method according to (13), wherein the dispersion further contains an ammonium salt represented by the formula (2), and a mass ratio of the tetraalkoxysilane to the ammonium salt is 20 to 250.

(In the formula, X represents Cl, Br or I, and m represents an integer of 3 to 30.)

As a result of intensive studies, the present inventors have found that the silica-coated carbon black of the present invention can suppress decomposition of the electrolyte and gas generation in the secondary battery. In addition, the silica-coated carbon black of the present invention has excellent dispersibility and good conductivity. Further, the secondary electrode and the secondary battery using the silica-coated carbon black of the present invention have a feature that they have a long life.

1 is a scanning electron micrograph of silica-coated carbon black of Example 1. FIG. FIG. 2 is a scanning electron micrograph of carbon black of Comparative Example 1.

Hereinafter, preferred embodiments of the present invention will be described in detail. The silica-coated carbon black of the present embodiment includes carbon black and silica that coats the surface of the carbon black, and the ratio of DBP absorption amount to the compressed DBP absorption amount of the carbon black (DBP absorption amount / compressed DBP absorption amount). 2.2 or less, and the silica contains a hydrolyzed condensate of tetraalkoxysilane represented by the formula (1). In addition, the coating in this specification means a state where silica is adsorbed or adhered to at least a part or all of the surface of the carbon black particles as shown in FIG.

(In the formula, n represents an integer of 1 or more and 5 or less.)

The silica-coated carbon black of the present embodiment is a silica-coated carbon black obtained by coating the surface of carbon black with silica, and the ratio of the DBP absorption amount to the compressed DBP absorption amount of the carbon black (DBP absorption amount / compressed DBP absorption amount). Is 2.2 or less, and it can be said that the silica-coated carbon black is a hydrolysis-condensation product of tetraalkoxysilane represented by the formula (1).

The carbon black in the present embodiment is selected from acetylene black, furnace black, channel black, and the like, like carbon black as a general battery conductive agent. Among these, acetylene black having excellent crystallinity and purity is more preferable.

The DBP absorption amount of carbon black in the present embodiment is a value measured according to JIS K6217-4. The compressed DBP absorption amount is a value measured by the same method as the DBP absorption amount for a compressed sample produced according to JIS K6217-4 Annex A.

In the present embodiment, the ratio of the DBP absorption amount to the compressed DBP absorption amount of carbon black in this embodiment is 2.2 or less, and more preferably 1.4 to 2.1. A large DBP absorption value compared to the compressed DBP absorption amount means that the amount of agglomerated particles that are destroyed when producing a compressed sample is large, and that more energy is required to break them up. . Therefore, by setting the ratio of the DBP absorption amount to the compressed DBP absorption amount to 2.2 or less, the energy necessary for crushing the agglomerated particles can be suppressed, and the dispersibility becomes good.

The DBP absorption amount of carbon black in the present embodiment is preferably 280 mL / 100 g or less, and more preferably 200 mL / 100 g or less. By setting the DBP absorption amount to 280 mL / 100 g or less, aggregation due to entanglement between structures is suppressed, and dispersibility is improved. The DBP absorption amount of carbon black in the present embodiment may be 90 mL / 100 g or more, or 150 mL / 100 g or more.

Silica in the present embodiment is a hydrolyzed condensate of tetraalkoxysilane. The hydrolysis reaction and the condensation reaction are preferably performed in the presence of an ammonium salt represented by the formula (2) (also referred to as a halogenated alkyltrimethylammonium salt). Since the hydrolysis reaction of tetraalkoxysilane goes through an anionic intermediate, in the presence of alkyltrimethylammonium halide, which is a cationic surfactant, on the carbon black surface where the alkyltrimethylammonium halide molecule is adsorbed. A hydrolysis reaction and a condensation reaction proceed selectively. Therefore, silica obtained as a hydrolysis condensate in the presence of alkyltrimethylammonium halide of tetraalkoxysilane is easy to take a shape that coats the surface of carbon black in a shell shape, so the effect of preventing oxidative decomposition of the electrolyte is even better. It becomes.

As the halogenated alkyltrimethylammonium halide, one having an arbitrary halogen atom and alkyl group can be selected within the range in which the above-described effects can be obtained. As the halogen atom represented by X, chlorine is preferable. Further, the alkyl group preferably has 3 to 30 carbon atoms (that is, m), more preferably 10 to 20 carbon atoms. Among these, hexadecyltrimethylammonium chloride and dodecyltrimethylammonium chloride are preferable.

The mass ratio of tetraalkoxysilane to alkyltrimethylammonium halide (mass of tetraalkoxysilane / mass of alkyltrimethylammonium halide) is preferably 20 to 250. By setting the mass ratio (the mass of tetraalkoxysilane / the mass of alkyltrimethylammonium halide) to 250 or less, the amount of the cation relative to the anionic intermediate is sufficiently large, so that the hydrolysis reaction and the condensation reaction are more carbon. It progresses selectively on the black surface, and the silica coverage increases. Further, by setting the mass ratio (mass of tetraalkoxysilane / mass of halogenated alkyltrimethylammonium) to 20 or more, silica that is generated free in the solvent is suppressed, and the coating amount of silica is also increased.

The carbon number of the alkyl group of tetraalkoxysilane is 5 or less, and preferably 3 or less. Since the hydrolysis reaction of tetraalkoxysilane proceeds faster as the carbon number of the alkyl group is smaller, the yield of silica is increased by setting the carbon number to 5 or less even if the reaction time is short.

The coating amount of silica is preferably 10% by mass to 30% by mass with respect to the total amount of silica and carbon black. By setting the coating amount to 10% by mass or more, the surface of the carbon black is sufficiently covered with silica, so that the effect of preventing the oxidative decomposition of the electrolytic solution is improved. On the other hand, when the coating amount exceeds 30% by mass, the effect of silica inhibiting the conductivity of the carbon black is increased. Therefore, the coating amount is preferably 30% by mass or less. When carbon black is coated with silica, trace amounts of single particles of silica (hereinafter abbreviated as free silica) that are not involved in the coating of carbon black are by-produced. Regarding the free silica, it is preferable in terms of conductivity to be removed from the produced silica-coated carbon black. Free silica can be filtered to the filtrate side after synthesis of silica-coated carbon black, for example, with a filter having a mesh diameter of 1 to 9 μm.

The volume resistivity of silica-coated carbon black is a value obtained by measuring a powder sample compressed in a disk shape at a pressure of 24 MPa in an environment of 25 ° C. and a relative humidity of 50% by a four-terminal four-probe method.

The volume resistivity of the silica-coated carbon black is preferably 1 × 10 ⁶ Ω · cm or less, and more preferably 1 × 10 ³ Ω · cm or less. By setting the volume resistivity of the silica-coated carbon black to 1 × 10 ⁶ Ω · cm or less, the conductivity inside the electrode is improved and the internal resistance of the battery is lowered.

The method for producing the silica-coated carbon black of the present embodiment is not particularly limited. For example, Langmuir 2012, 28, 7055-7062. A known method as described in 1) can be used. Specifically, prepare a dispersion in which the original carbon black is dispersed in ethanol and a solution in which tetraethoxysilane is dissolved in ethanol. After mixing both, add aqueous ammonia to make it alkaline. By doing so, a method of hydrolyzing tetraethoxysilane can be used.

When producing an electrode using the silica-coated carbon black of the present embodiment, the silica-coated carbon black can be dispersed in a medium together with a positive electrode active material or a negative electrode active material and a binder and used as an electrode composition. The positive electrode active material may be any positive electrode active material that can occlude and release cations. As the positive electrode active material, composite oxides having a layered rock salt structure such as lithium cobaltate, lithium nickelate, nickel cobalt lithium manganate, nickel cobalt lithium aluminum oxide, and spinel structures such as lithium manganate and lithium nickel manganate And composite oxides having an olivine structure such as lithium iron phosphate, lithium manganese phosphate, and lithium iron manganese phosphate. Among these, it is preferable to use lithium nickel manganate having a spinel structure from the viewpoint that the gas generation suppressing effect can be remarkably exhibited.

The negative electrode active material may be any negative electrode active material that can occlude and release cations. Examples of the negative electrode active material include carbon-based materials such as artificial graphite, natural graphite, soft carbon, and hard carbon, metal-based materials alloyed with alkali metals such as silicon and tin, and metal composite oxides such as lithium titanate. .

Examples of the binder include polymers such as polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene copolymer, polyvinyl alcohol, acrylonitrile-butadiene copolymer, and carboxylic acid-modified (meth) acrylic acid ester copolymer. It is done. Among these, polyvinylidene fluoride is preferable from the viewpoint of oxidation resistance when used for the positive electrode, and polyvinylidene fluoride or styrene-butadiene copolymer is preferable from the viewpoint of adhesion when used for the negative electrode.

Examples of the dispersion medium for the electrode composition include water, N-methyl-2-pyrrolidone, cyclohexane, methyl ethyl ketone, and methyl isobutyl ketone. When using polyvinylidene fluoride as a binder, N-methyl-2-pyrrolidone is preferable from the viewpoint of solubility, and when using a styrene-butadiene copolymer, water is preferable.

As a mixing apparatus for producing an electrode composition, a mixing machine such as a rachi machine, a universal mixer, a Henschel mixer or a ribbon blender, or a medium stirring type mixer such as a bead mill, a vibration mill or a ball mill is used. be able to. In addition, the manufactured electrode coating liquid is preferably subjected to vacuum defoaming at a stage before coating in order to ensure smoothness without causing defects in the coating film. If air bubbles are present in the coating solution, the coating film will be defective when applied to the electrode, which may impair smoothness.

The electrode composition can contain components other than silica-coated carbon black, a positive electrode active material, a negative electrode active material, and a binder as long as the above-described effects are obtained. For example, carbon nanotubes, carbon nanofibers, graphite, graphene, carbon fibers, elemental carbon, glassy carbon, metal particles, and the like may be included in addition to silica-coated carbon black for the purpose of further improving conductivity. Further, for the purpose of improving dispersibility, polyvinyl pyrrolidone, polyvinyl imidazole, polyethylene glycol, polyvinyl alcohol, polyvinyl butyral, carboxymethyl cellulose, acetyl cellulose, a carboxylic acid-modified (meth) acrylic acid ester copolymer and the like may be included.

The preferred embodiment of the silica-coated carbon black according to the present invention has been described above, but the present invention is not limited to this.

For example, the present invention may relate to an electrode composition containing the silica-coated carbon black described above. In one embodiment of the present invention, the electrode composition may include the silica-coated carbon black, at least one selected from the group consisting of a positive electrode active material and a negative electrode active material, and a binder.

The present invention may also relate to a secondary battery electrode comprising a metal foil and a coating film of the electrode composition provided on the metal foil.

The metal foil may be, for example, an aluminum foil when used as a positive electrode. Moreover, when using as a negative electrode, copper foil etc. may be sufficient, for example. The shape of the metal foil is not particularly limited. From the viewpoint of facilitating workability, the thickness of the metal foil is preferably 5 to 30 μm.

The coating film of the electrode composition is, for example, a slot die method, a lip method, a reverse roll method, a direct roll method, a blade method, a knife method, an extrusion method, a curtain method, a gravure method, a bar method, a dip method, and a squeeze. It may be formed by applying a composition for an electrode on a metal foil by a method such as a method. Of these, the slot die method, the lip method, and the reverse roll method are preferable. The coating method may be appropriately selected according to the solution physical properties, drying properties, etc. of the binder. The coating film of the electrode composition may be formed on one side of the metal foil or on both sides. When the coating film of the electrode composition is formed on both surfaces of the metal foil, the electrode composition may be sequentially applied to the metal foil one side at a time or may be simultaneously applied to both surfaces of the metal foil. The application mode of the electrode composition may be continuous, intermittent, or striped.

The thickness, length and width of the coating film of the electrode composition may be appropriately determined according to the size of the battery. For example, the thickness of the coating film may be in the range of 10 μm to 500 μm.

The coating film of the electrode composition may be formed by applying and drying the electrode composition. The electrode composition can be dried using, for example, means such as hot air, vacuum, infrared rays, far infrared rays, electron beams, and low-temperature air, alone or in combination.

The secondary battery electrode may be pressed as necessary. As the pressing method, a generally adopted method may be used, and for example, a die pressing method, a calendar pressing method (cold or hot roll) and the like are preferable. The pressing pressure in the calender pressing method is not limited, but is preferably 0.02 to 3 ton / cm, for example.

The present invention may also relate to a secondary battery provided with the secondary battery electrode on at least one of a positive electrode and a negative electrode.

The secondary battery may be, for example, a lithium ion secondary battery, a sodium ion secondary battery, a magnesium ion secondary battery, a nickel hydride secondary battery, or an electric double layer capacitor.

The present invention may also relate to a method for producing silica-coated carbon black. In one embodiment of the present invention, the method for producing a silica-coated carbon black comprises hydrolyzing and condensing the tetraalkoxysilane in a dispersion containing the carbon black, so that the surface of the carbon black is made of the tetraalkoxysilane. It may include a step of coating with silica containing a hydrolysis condensate. The dispersion may further contain the alkyltrimethylammonium halide. The mass ratio of the tetraalkoxysilane to the ammonium salt may be 20 to 250.

The present invention may also relate to a conductive agent for a secondary battery containing the silica-coated carbon black, and may relate to the use of the silica-coated carbon black as a conductive agent for a secondary battery. The present invention may also relate to the use of the silica-coated carbon black for the production of a secondary battery electrode, and may relate to the use of the silica-coated carbon black for the production of a secondary battery. .

Hereinafter, one embodiment of the silica-coated carbon black according to the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

<Example 1>
(Carbon black)
In this example, acetylene black (HS100, manufactured by Denki Kagaku Kogyo K.K.) having a DBP absorption of 171 mL / 100 g and a compressed DBP absorption of 83 mL / 100 g was used as carbon black. In addition, the DBP absorption amount and compression DBP absorption amount of carbon black were measured by the following methods.

[DBP absorption and compressed DBP absorption]
DBP absorption was measured by a method according to JIS K6217-4. Further, the compressed DBP absorption amount was measured by the same method as the DBP absorption amount for a compressed sample prepared by compressing four times at 165 MPa according to JIS K6217-4 Annex A.

(Manufacture of silica-coated carbon black)
Using 2.0g of acetylene black and 44mg of hexadecyltrimethylammonium chloride (manufactured by Kanto Chemical Co., Inc.) in 200g of water / ethanol = 1/1 (mass ratio) mixed solvent using a precision dispersion emulsifier (manufactured by M Technique Co., Ltd., Claremix). Then, 1N ammonia water (manufactured by Kanto Chemical Co., Inc.) was added to adjust the pH to 11. While stirring this dispersion with a magnetic stirrer, 4.0 g of tetraethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise at room temperature over 10 hours, and the mixture was further stirred for 2 hours to be reacted. Thereafter, the reaction solution was suction filtered, washed with pure water and dried to obtain 2.1 g of silica-coated carbon black as a black powder. At this time, the mass ratio of tetraethoxysilane to hexadecyltrimethylammonium chloride (mass of tetraethoxysilane / mass of hexadecyltrimethylammonium chloride) was 91. 1 is a scanning electron micrograph of silica-coated carbon black of Example 1. FIG.

(Evaluation of silica-coated carbon black)
The physical properties and the like of silica-coated carbon black were evaluated as follows. The results are shown in Table 1.

[Silica coverage]
Using a thermogravimetric analyzer (TG-DTA2000SA manufactured by Bruker), the silica-coated carbon black Ag was held at 1000 ° C. for 1 hour in the air. In this state, the carbon black burns and burns away from the sample, so the residue consists only of silica. Then, it cooled to room temperature and measured the mass Bg of the residue. The silica coverage was determined by the following formula.
Silica coverage = B / A × 100 (%)

[Volume resistivity]
Weigh 0.5 g of silica-coated carbon black and leave it in an environment of 25 ± 1 ° C and relative humidity of 50 ± 2% for 24 hours. Use a powder resistance measurement system (MCP-PD51, manufactured by Mitsubishi Chemical Analytech Co., Ltd.). The volume resistivity was measured in a state of being compressed into a disk shape having a diameter of 20 mm under a load of 24 MPa.

(Production of electrode composition and electrode)
90 parts by mass of spinel-type lithium nickel manganate (manufactured by Hosen Co., Ltd.) as an active material, 5 parts by mass of silica-coated carbon black, and a polyvinylidene fluoride solution (manufactured by Kureha Chemical Co., Ltd., “KF Polymer (registered trademark) 1120” as a binder In addition, 5 parts by mass of a solid content concentration of 12% by mass) and 30 parts by mass of N-methyl-2-pyrrolidone (manufactured by Kishida Chemical Co., Ltd.) as a dispersion medium, Mixing was performed using Tori Netaro ARV-310) to obtain an electrode composition. This electrode composition was applied to a 20 μm thick aluminum foil using a Baker-type applicator, dried, then pressed and cut to obtain a positive electrode for a lithium secondary battery.

(Evaluation of electrode composition and electrode)
The dispersibility of the electrode composition and secondary battery electrode prepared above was evaluated as follows. The results are shown in Table 1.

[Evaluation of dispersibility (electrode composition)]
The dispersibility of the silica-coated carbon black in the electrode composition was evaluated by a method using a crush gauge described in JIS K5600-2-5. Specifically, a scraper was used to apply the coating solution, and the graduations were measured at locations where three or more linear traces of 10 mm or more continuous on the sample surface were arranged in one groove. The lower the numerical value, the better the dispersibility.

[Evaluation of dispersibility (secondary battery electrode)]
The dispersibility of the silica-coated carbon black in the secondary battery electrode was judged by the appearance of the positive electrode for the lithium secondary battery. Specifically, five 100 mm square electrodes were prepared and evaluated according to the following scale.
A: No streak of coating marks and aggregates were observed on the electrode surfaces of all five sheets.
B: Streaky coating marks or aggregates less than 1 mm were observed on one or more electrode surfaces.
C: Agglomerates of 1 mm or more were observed on one or more electrode surfaces.

(Production of secondary battery)
Using the secondary battery electrode as a positive electrode, a secondary battery was produced as follows.

(Preparation of negative electrode)
Rotating by adding 98 parts by mass of graphite powder (MAG-D manufactured by Hitachi Chemical Co., Ltd.) as an active material, 2 parts by mass of a polyvinylidene fluoride solution as a binder, and 30 parts by mass of N-methyl-2-pyrrolidone as a dispersion medium It mixed using the revolution type mixer, and the composition for electrodes for negative electrodes was obtained. This was applied to a copper foil having a thickness of 15 μm using a Baker type applicator, dried, and then pressed and cut to obtain a negative electrode for a lithium secondary battery.

(Production of battery)
A positive electrode for a secondary battery produced using the electrode composition as a positive electrode was cut into 40 mm length and 40 mm width, and a negative electrode for the secondary battery cut into 44 mm length and 44 mm width was used as a negative electrode. Then, a non-woven fabric made of olefin fiber was used as a separator for electrically isolating them, and an aluminum laminate film was used as an exterior to make a laminated battery. As electrolyte, EC (ethylene carbonate, manufactured by Aldrich), DEC (diethyl carbonate, manufactured by Aldrich) was mixed in a volume ratio of 1: 2, lithium hexafluorophosphate (LiPF6, manufactured by Stella Chemifa) 1 mol / L dissolved was used.

(Evaluation of secondary battery)
The secondary battery produced above was evaluated as follows. The results are shown in Table 1. Unless otherwise specified, the evaluation value is an arithmetic average value of the evaluation values of the three batteries.

[Discharge capacity, Coulomb efficiency]
First, a positive electrode active material amount (g) present on the positive electrode was determined from the mass of the positive electrode, and a value (mA) obtained by dividing this by 140 was defined as a current value “1C”. A constant current / constant voltage charge is performed with a current of 1 C and an upper limit voltage of 5.0 V, and a constant current discharge is performed with a current of 1 C and a lower limit voltage of 3.0 V. The charge capacity per 1 g of the positive electrode active material ( The ratio (%) of the discharge capacity (mAh / g) per gram of the positive electrode active material to the mAh / g) was defined as the Coulomb efficiency. In addition, it means that the electrical conductivity of an electrode is excellent and the resistance of a battery is so low that discharge capacity is high. Moreover, it means that there are few side reactions which bring about lifetime reduction, such as an oxidation reaction of electrolyte solution, so that Coulomb efficiency is high.

[Cycle characteristics]
As an evaluation of the life, the cycle characteristics were measured as follows. A constant current / constant voltage charge was performed with a current of 1 C and an upper limit voltage of 5.0 V, and then a constant current was performed with a current of 1 C and a lower limit voltage of 3.0 V, which was repeated 200 times. The ratio (%) of the 200th discharge capacity to the first discharge capacity was defined as the cycle characteristic value. When the discharge capacity became zero after less than 200 cycles, the cycle characteristic value of the battery was assumed to be 0, and the arithmetic average value of the three batteries was calculated.

[Gas generation amount]
As an evaluation of the gas generation suppression effect, the volume change (mL) of the battery before and after the cycle characteristic test was measured as a gas generation amount. The volume of the battery was measured in a constant temperature room at 25 ± 1 ° C. using a specific gravity measuring device (AUW220D manufactured by Shimadzu Corporation). Moreover, about the battery in which the discharge capacity became 0 in less than 200 cycles, it measured after the cycle in which the discharge capacity became 0 for the first time.

<Examples 2 to 8>
A silica-coated carbon black and an electrode composition were prepared in the same manner as in Example 1 except that the addition amounts of hexadecyltrimethylammonium chloride and tetraethoxysilane in Example 1 were changed to the mass ratio shown in Table 1. A secondary battery electrode and a secondary battery were prepared and evaluated. The results are shown in Table 1.

<Example 9>
Except for changing the carbon black of Example 1 to furnace black (SuperPLi, manufactured by Timcal Graphite and Carbon, Inc.) having a DBP absorption of 234 mL / 100 g and a compressed DBP absorption of 115 mL / 100 g, the same as in Example 1 The silica-coated carbon black, the electrode composition, the secondary battery electrode and the secondary battery were prepared by various methods, and each evaluation was performed. The results are shown in Table 2.

<Example 10>
The same method as in Example 1 except that the carbon black in Example 1 was changed to acetylene black (AB powder, manufactured by Denki Kagaku Kogyo Co., Ltd.) having a DBP absorption of 228 mL / 100 g and a compressed DBP absorption of 125 mL / 100 g. The silica-coated carbon black, the electrode composition, the secondary battery electrode and the secondary battery were prepared and evaluated. The results are shown in Table 2.

<Example 11>
In the same manner as in Example 1, except that the carbon black of Example 1 was changed to acetylene black (SAB, manufactured by Denki Kagaku Kogyo Co., Ltd.) having a DBP absorption of 338 mL / 100 g and a compressed DBP absorption of 240 mL / 100 g. Coated carbon black, an electrode composition, an electrode for a secondary battery, and a secondary battery were prepared and evaluated. The results are shown in Table 2.

<Example 12>
The tetraethoxysilane of Example 1 was changed to tetrabutoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.), and the addition amounts of tetrabutoxysilane and hexadecyltrimethylammonium chloride were changed so that the mass ratio shown in Table 2 was obtained. Produced a silica-coated carbon black, an electrode composition, an electrode for a secondary battery, and a secondary battery in the same manner as in Example 1, and performed each evaluation. The results are shown in Table 2.

<Example 13>
The tetraethoxysilane in Example 1 was changed to tetrapropoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.), and the addition amount of tetrabutoxysilane and hexadecyltrimethylammonium chloride was changed to the mass ratio shown in Table 2. Produced a silica-coated carbon black, an electrode composition, an electrode for a secondary battery, and a secondary battery in the same manner as in Example 1, and performed each evaluation. The results are shown in Table 2.

<Example 14>
Except that hexadecyltrimethylammonium chloride of Example 1 was changed to dodecyltrimethylammonium chloride (manufactured by Tokyo Chemical Industry Co., Ltd.), silica-coated carbon black, electrode composition, secondary battery electrode were obtained in the same manner as in Example 1. And the secondary battery was produced and each evaluation was implemented. The results are shown in Table 2.

<Comparative Example 1>
Except that the amount of tetraethoxysilane added in Example 1 was changed to 0, silica-coated carbon black, an electrode composition, a secondary battery electrode, and a secondary battery were prepared in the same manner as in Example 1, Evaluation was performed. The results are shown in Table 3. In the secondary battery of Comparative Example 1, the discharge capacity was zero in less than 200 cycles in the measurement of cycle characteristics. FIG. 2 is a scanning electron micrograph of carbon black of Comparative Example 1.

<Comparative example 2>
The carbon black of Example 1 was changed to Furnace Black (SuperC65 manufactured by Timcal Graphite and Carbon) having a DBP absorption of 254 mL / 100 g and a compressed DBP absorption of 104 mL / 100 g. Silica-coated carbon black, an electrode composition, a secondary battery electrode, and a secondary battery were prepared by the method, and each evaluation was performed. The results are shown in Table 3. The secondary battery electrode of Comparative Example 2 was inferior in electrode appearance. Further, the secondary battery of Comparative Example 2 had a low cycle characteristic.

From the results of Tables 1, 2 and 3, it was found that the silica-coated carbon black of the examples was excellent in conductivity and dispersibility, and further, the batteries produced using these were excellent in life.

The above results were the same for the lithium ion secondary battery negative electrode produced in the same manner as the lithium ion secondary battery positive electrode used in the examples, and also for the electrode for the sodium ion secondary battery.

By using the silica-coated carbon black of the present invention, an electrode composition and a secondary battery electrode excellent in conductivity and dispersibility can be obtained. Thereby, a long-life secondary battery in which decomposition of the electrolyte and generation of gas can be suppressed can be obtained.

Claims

Carbon black,
Silica covering the surface of the carbon black;
Including
The ratio of the DBP absorption amount to the compressed DBP absorption amount of the carbon black (DBP absorption amount / compressed DBP absorption amount) is 2.2 or less,
Silica-coated carbon black, wherein the silica contains a hydrolytic condensate of tetraalkoxysilane represented by the formula (1).

(In the formula, n represents an integer of 1 or more and 5 or less.)
The silica according to claim 1, wherein the tetraalkoxysilane having a mass ratio of 20 to 250 with respect to the ammonium salt is hydrolyzed and condensed in the presence of the ammonium salt represented by the formula (2). Silica coated carbon black.

(In the formula, X represents Cl, Br or I, and m represents an integer of 3 to 30.)
The silica-coated carbon black according to claim 2, wherein the ammonium salt is hexadecyltrimethylammonium chloride.
The silica-coated carbon black according to any one of claims 1 to 3, wherein n is an integer of 1 to 3.
The silica-coated carbon black according to any one of claims 1 to 4, wherein a coating amount of the silica is 10% by mass to 30% by mass with respect to a total amount of the silica and the carbon black.
The silica-coated carbon black according to any one of claims 1 to 5, wherein the carbon black is acetylene black.
The silica-coated carbon black according to any one of claims 1 to 6, having a volume resistivity of 1 x 10 5 Ω · cm or less.
The silica-coated carbon black according to any one of claims 1 to 7, wherein the DBP absorption amount of the carbon black is 280 mL / 100 g.
The silica-coated carbon black according to any one of claims 1 to 8, having a volume resistivity of 1 × 10 3 Ω · cm or less.
Silica-coated carbon black according to any one of claims 1 to 9,
At least one selected from the group consisting of a positive electrode active material capable of occluding and releasing cations and a negative electrode active material capable of occluding and releasing cations;
A binder,
An electrode composition comprising:
Metal foil,
The coating film of the composition for electrodes according to claim 10 provided on the metal foil,
A secondary battery electrode.
A secondary battery comprising the secondary battery electrode according to claim 11 on at least one of a positive electrode and a negative electrode.
A step of hydrolyzing and condensing the tetraalkoxysilane represented by the formula (1) in a dispersion containing carbon black and coating the surface of the carbon black with silica containing the hydrolyzed condensate of the tetraalkoxysilane. Including
A method for producing silica-coated carbon black, wherein a ratio of DBP absorption amount to compressed DBP absorption amount of carbon black (DBP absorption amount / compression DBP absorption amount) is 2.2 or less.

(In the formula, n represents an integer of 1 or more and 5 or less.)
The dispersion further contains an ammonium salt represented by the formula (2),
The production method according to claim 13, wherein a mass ratio of the tetraalkoxysilane to the ammonium salt is 20 to 250.

(In the formula, X represents Cl, Br or I, and m represents an integer of 3 to 30.)