JP2010031214A - Carbon black composite and application thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon black composite having excellent electroconductivity-imparting ability. <P>SOLUTION: The carbon black composite is prepared by linking fibrous carbon with a carbon black, and has ≤1.0 mass% of the ash content defined by JIS K 1469. Preferably, the content of the fibrous carbon is 1-50 mass%, and the average diameter of the fibrous carbon is ≤100 nm. The carbon black is preferably acetylene black. An electrode for a battery and an active material for the battery containing the carbon black composite are also provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a carbon black composite and use thereof.

  There is a conductive agent for a non-aqueous secondary battery electrode as an application utilizing the conductivity imparting ability of carbon black. The positive electrode of the non-aqueous secondary battery electrode is composed of a positive electrode active material composed of a composite oxide such as lithium cobaltate and lithium manganate, a conductive agent, and a composition comprising a binder and a metal foil such as an aluminum foil. The negative electrode has a structure in which a negative electrode active material made of a carbonaceous material such as graphite, a conductive agent, and a binder are collected from a metal foil such as a copper foil. It has a structure that is attached to an electric body. These electrodes are manufactured by preparing a slurry containing a conductive agent, a positive electrode active material or a negative electrode active material, and a binder, and applying and drying the slurry on a current collector made of metal foil. Is done.

  As the conductive agent for the positive electrode or the negative electrode, ketjen black (for example, trade name “Ketjen EC300J” manufactured by Ketjenblack International Co., Ltd.), acetylene black (for example, trade name “Denka Black powdered product” manufactured by Denki Kagaku Kogyo Co., Ltd.) Etc. are used.

  However, in recent years, against the background of increasing safety performance requirements of lithium-ion secondary batteries and the knowledge of environmental resources, the conventional active materials such as lithium cobaltate have been studied as alternatives to lithium manganate and lithium nickelate, manganese, Studies are being made on adjusting the component ratio of nickel and cobalt, and conversion to lithium iron phosphate and the like. However, these have higher resistance than conventional lithium cobaltate, and a large amount of carbon black has to be added as a conductive agent, which necessitates a reduction in the amount of active material, resulting in reduced capacity. There was a problem.

For such problems, it has been proposed to use carbon nanotubes as a conductive agent (Patent Document 1). Here, the electrical conductivity of the carbon nanotube is utilized to reduce the resistance value and improve the rate characteristics. However, since carbon nanotubes have poor dispersibility, there is a problem in that the conductivity of the entire electrode varies and it is difficult to obtain stable charge / discharge characteristics. Moreover, since it does not have a structure structure like carbon black, it cannot play a role as a buffer material for expansion / contraction of the active material during charge / discharge, resulting in a problem that cycle characteristics deteriorate.
JP 2003-77476 A WO / 2007/013678

  An object of the present invention is to provide a carbon black composite having excellent conductivity imparting ability. The carbon black composite of the present invention can be suitably used for battery electrodes and battery active materials.

  The carbon black composite of the present invention is a carbon black composite characterized in that fibrous carbon and carbon black are linked, and an ash content defined by JIS K 1469 is 1.0% by mass or less. The content of fibrous carbon is preferably 1 to 50% by mass, and the average diameter of the fibrous carbon is preferably 100 nm or less. Further, the carbon black is preferably acetylene black.

  Further, it is an electrode for a battery containing a carbon black composite and an active material for a battery containing a carbon black composite.

  According to the present invention, it is possible to obtain a carbon black composite that is further excellent in conductivity imparting ability.

  The carbon black composite of the present invention is one in which fibrous carbon and carbon black are linked. Although the production method is not particularly limited, for example, a method of introducing and combining fibrous carbon during hydrocarbon pyrolysis, as described in WO / 2007/013678, during pyrolysis of acetylene gas And / or a method in which a hydrocarbon containing a fibrous carbonization catalyst is supplied and combined in a state where the acetylene gas is thermally decomposed. In addition, fibrous carbon and carbon black are dispersed in a carbonization raw material liquid such as hydrocarbon or alcohol, and carbonized by an operation such as heating in a liquid or gasified state of the carbonized raw material liquid. May be connected. This carbon black composite has an ash content defined by JIS K 1469 of 1.0% by mass or less. The ash is mainly composed of a catalyst at the time of fibrous carbon production, impurities metals (for example, Fe, Ni, etc.) and oxides thereof, and when the ash content exceeds 1.0% by mass, for example, a Li ion secondary battery, There is a risk that metal deposits on the negative electrode during charging and the charge / discharge capacity decreases, and there is a risk of ignition by breaking through the separator and short-circuiting.

  Coupling is not just contact, it means that it is physically fused with carbonaceous matter, and it is not easily separated by normal mechanical operations, but between the connected fibrous carbon and carbon black. Electrons can move freely without resistance. Therefore, even when mixed with an active material, the carbon black composite remains as it is, and good dispersibility can be obtained and at the same time high conductivity can be maintained. When fibrous carbon alone is mixed with an active material or other materials, it is difficult to obtain good dispersibility due to orientation and entanglement between fibers, resulting in variations in conductivity. When carbon black and fibrous carbon are simply mixed, the shape is different and the variation further increases. However, one feature of the carbon black composite of the present invention is that it has excellent conductivity stability. Here, the content of fibrous carbon is preferably 1 to 50% by mass. When the content of fibrous carbon is less than 1% by mass, sufficient conductivity cannot be obtained, and when it exceeds 50% by mass, the connection with carbon black is not sufficient, and at the same time, aggregation of fibrous carbon, etc. Dispersibility is significantly reduced.

  The fibrous carbon used in the carbon black composite of the present invention is carbon fiber (carbon fiber), vapor grown carbon fiber (VGCF), carbon nanotube, carbon nanofiber, or the like. In the present invention, fibrous carbon can be selected as appropriate. However, since fibrous carbon effectively exchanges electrons with the active material, it is preferable that the fibrous carbon is smaller than the particle size of the active material. For example, when the average particle diameter of the active material is less than 20 μm, the average diameter is preferably 100 nm or less. The average diameter of the fibrous carbon is preferably 5 nm or more in order to give a certain level of strength.

  The carbon black used in the carbon black composite of the present invention maintains the conductivity of the entire electrode and plays a role as a buffer for expansion / contraction of the active material. For example, thermal black, furnace black, lamp black, Examples thereof include channel black and acetylene black. Among these, acetylene black is preferable because it has a reaction in a reducing atmosphere called thermal decomposition of acetylene gas, and therefore, when fibrous carbon is introduced and combined, there is little combustion loss.

  The carbon black composite of the present invention can be used as an active material for a battery. The technique is not particularly limited, and known methods such as a method of mixing the carbon black composite of the present invention during the production of the active material, a carbothermal treatment, an electrophoretic electrodeposition treatment, and the like can be applied. For example, in the carbothermal treatment, the carbon black composite of the present invention is mechanically bonded to a known active material, which will be described later, using a planetary ball mill or the like, and further heat-treated at 300 to 600 ° C. in an inert atmosphere. it can.

  The carbon black composite of the present invention can be used as an electrode for a battery. For example, in a non-aqueous secondary battery electrode, the electrode is prepared by dispersing a positive electrode active material or a negative electrode active material and the above-described carbon black composite (conductive agent) in a liquid containing a binder to prepare a slurry, which is made from a metal foil. The current collector can be applied by coating and drying. As for the compounding quantity of a electrically conductive agent, 0.5-20 mass% is preferable as a ratio in solid content adhering to the electrical power collector. In addition, it can use similarly as a water-system secondary battery electrode.

When the non-aqueous secondary battery electrode is a positive electrode, the active material is, for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiFeO ₂ or this type of Li _x MO ₂ (where M is one or more transition metals) A lithium composite oxide mainly composed of 0.05 ≦ x ≦ 1.0), an olivine-type lithium phosphate represented by LiMPO ₄ (M = V, Fe, Ni, Mn), TiS ₂ , Known active materials such as metal sulfides and metal oxides that do not contain lithium, such as MoS ₂ , NbSe ₂ , and V ₂ O _5, can be used.

  When the nonaqueous secondary battery electrode is a negative electrode, various carbonaceous materials can be used as the active material. Examples thereof include known active materials such as natural graphite, artificial graphite, graphite, activated carbon, coke, needle coke, and mesocarbon microbeads.

  As the binder, known binders such as polyethylene, nitrile rubber, polybutadiene, butyl rubber, polystyrene, styrene butadiene rubber, polysulfide rubber, nitrocellulose, tetrafluoroethylene resin, polyvinylidene fluoride, and polychlorochloroprene are used. It is done.

  The current collector is not particularly limited, but is a metal foil of gold, silver, copper, platinum, aluminum, iron, nickel, chromium, manganese, lead, tungsten, titanium, or an alloy containing these as components. Is used. The thickness of the metal foil is preferably thinner. In view of ease of handling, aluminum is suitably used for the positive electrode and copper is suitably used for the negative electrode.

  Examples of the electrolyte include propylene carbonate, ethylene carbonate, γ-butyllactone, N-methylpyrrolidone, acetonitrile, N, N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, 1,3-dioxolane, methyl formate, sulfolane, oxozolidone, and thionyl chloride. 1,2-dimethoxyethane, diethylene carbonate and derivatives thereof are used. As electrolytes, lithium halide, lithium perchlorate, lithium thiocyanate, lithium borofluoride, lithium phosphorous fluoride, lithium arsenic fluoride, lithium aluminum fluoride, lithium Trifluoromethyl sulfate and the like are used. Components such as a separator, a terminal, and an insulating plate are attached as necessary.

  The non-aqueous secondary battery electrode is at least one of a positive electrode and a negative electrode. In order to produce a non-aqueous secondary battery, the electrode of the present invention may be used instead of the conventional positive electrode and negative electrode. do not need.

  Applications of the secondary battery using the carbon black composite of the present invention include a video camera, a personal computer, a word processor, a mobile phone, a radio control, other small electronic devices, an automobile, a power storage system, and the like.

  The fibrous carbon powder was produced by the following method. Mass ratio of benzene (reagent manufactured by Kanto Chemical Co., 99% or more) as a carbon source gas, ferrocene (reagent manufactured by Kanto Chemical Co., 98% or more) as a catalyst, and thiophene (reagent manufactured by Kanto Chemical Co., 98% or more) as a co-catalyst 90: 8: 2 gasified at 300 ° C., and sprayed with nitrogen gas from a nozzle installed above the vertical tube furnace, with a flow rate of 0.5 to 100 m / s and a temperature of 600 to 1200 ° C. Fibrous carbon having various diameters was produced and collected with a bag filter installed below. Furthermore, what was baked at 2000 ° C., removed the catalyst, and crystallized was used as fibrous carbon.

The positive electrode active material was produced by the following method. Li ₂ CO ₃ (reagent manufactured by Kanto Chemical Co., Ltd., 99% or more) and Co ₃ O ₄ (reagent manufactured by Kanto Chemical Co., Ltd., 99.95% or more) were mixed at a molar ratio of 1: 1 and mixed in the atmosphere in an electric furnace. And baked at 850 ° C. for 20 hours, and the obtained LiCoO ₂ was pulverized with a vibration mill until the average particle size became 10 μm, and 10 μm of LiCoO ₂ was obtained. In addition, LiCH ₃ COO · 2H ₂ O (reagent manufactured by Kanto Chemical Co., 99% or more), (NH ₄ ) ₂ HPO ₄ (reagent manufactured by Kanto Chemical Co., 99% or more) and FeC ₂ O ₄ (reagent manufactured by Kanto Chemical Co., Ltd.) , 98.5%) was mixed at a molar ratio of 1: 1: 1, and baked in an electric furnace under argon flow (100 ml / min) at 350 ° C. for 3 hours, and further baked at 570 ° C. for 5 hours. after an average particle size of pulverized until 200 nm, to obtain a 200 nm LiFePO ₄ of.

Examples 1-3 Comparative Example 1
Acetylene gas (purity 99% or more) is supplied from one of the two nozzles installed at the top of the reactor (total furnace length 6 m, furnace diameter 1 m), and fibrous carbon powder (average diameter 20 nm) from the other nozzle. And 400 nm in length), the acetylene gas was thermally decomposed at 2000 ° C. to form carbon black, and was combined with fibrous carbon. The carbon black composite was collected from a bag filter directly connected to the lower part of the furnace. The following evaluation was performed about them, and a result is shown in Table 1.
(1) About the average diameter of fibrous carbon, the diameter of 100 fibrous carbon was measured with the transmission electron microscope (TEM) by the magnification of 30,000 times, and the average value was made into the average diameter.
(1) BET specific surface area: measured according to JIS K 6217-2.
(2) Powder resistance: measured in accordance with JIS K 1469.

(3) Electrode evaluation of non-aqueous secondary battery 90% by mass of LiCoO ₂ having a particle size of 10 μm as a positive electrode active material and 10% by mass of the carbon black composite (conductive agent) obtained in Example 1 were mixed. After that, the slurry was prepared by dispersing it in an N-methylpyrrolidone solution (“KF polymer L # 1120” manufactured by Kureha) containing PVDF (polyvinylidene fluoride: binder) at a solid concentration of 45%. The positive electrode was coated and dried on an electric body.

Example 4
Acetylene black (“Denka black powder” manufactured by Denki Kagaku Kogyo Co., Ltd.) and fibrous carbon (average diameter 20 nm, length 400 nm) in a mass ratio of 1: 1 ethanol (Kanto Chemical Co., Ltd. reagent: purity 99.5%) The same evaluation as in Example 1 was performed except that a slurry mixed with 1% by mass was calcined at 1500 ° C. under a flow of nitrogen (10 L / min) in an electric furnace to obtain a carbon black composite.

In Example 5, 90% by mass of LiCoO ₂ having a particle size of 10 μm as a positive electrode active material and 10% by mass of the carbon black composite (conductive agent) obtained in Example 1 were mixed, and the mixture was carbothermal. The electrode evaluation similar to Example 1 was performed except having processed. The carbothermal treatment conditions were as follows: a 3 L alumina pot was filled with 2 kg of 10 mm alumina balls, 200 g of the mixture was treated and coalesced for 1 hour, and fired at 500 ° C. in a nitrogen atmosphere.

  Comparative Example 2 is an example except that 10% by mass of fibrous carbon powder (average diameter 20 nm, length 400 nm) and 90% by mass of carbon black produced in Comparative Example 1 were used as the conductive agent. A positive electrode was produced in the same manner as in 1. Comparative Example 3 is the same as Example 1 except that 60% by mass of fibrous carbon powder (average diameter 20 nm, length 400 nm) and 40% by mass of the carbon black produced in Comparative Example 1 were used as the conductive agent. A positive electrode was produced in the same manner as described above.

  The state of the coating film on the positive electrode was visually observed, and judged as ：: smooth and good, ○: normal, Δ: defective with peeling. The surface resistance of the positive electrode was measured according to JIS K 7194 using “Loresta GP” manufactured by Dia Instruments Co., Ltd. using a TFP probe. The surface resistance was measured at nine locations for one sample, and the average value was obtained, and at the same time, the variation ratio was calculated from the maximum value and the minimum value.

  Using lithium metal as a counter electrode, a coin-type battery was manufactured using a solution obtained by dissolving 1 molar concentration of lithium phosphofluoride in a solution in which ethylene carbonate / dimethyl carbonate was mixed at a volume ratio of 1/2.

  The coin-type battery manufactured as described above was charged in a low current mode of 0.2 C and then charged in a low voltage mode of 4.2 V. Next, discharge was performed at a current density of 0.2 C and 1 C, capacity was confirmed at a discharge voltage of 2.1 V, and the amount of 1 C discharge was calculated using the 0.2 C discharge amount as 100% as an index of rate characteristics. .

  A charge / discharge test with a cycle number of 100 was performed, and the discharge capacity after 100 times was divided by the initial capacity to obtain a capacity retention rate, which was used as an index of cycle characteristics. The test was performed with respect to metallic lithium at 4.7 to 3.0 V and a constant current of 0.8 mA. The discharge capacity is a capacity per weight of the active material. Moreover, the coin-type battery after the charge / discharge test was disassembled, and the rate of change in thickness with respect to the thickness of the positive electrode before the charge / discharge test was measured.

Examples 6 and 7 and Comparative Example 4
In Example 6, a coin-type battery was produced in the same manner as in Example 1 except that the carbon black composite of Example 1 was used and LiFePO ₄ having a particle size of 200 nm was used as the positive electrode active material. In Example 7, a coin-type battery was produced in the same manner as in Example 3 except that the carbon black composite of Example 3 was used and LiFePO ₄ having a particle size of 200 nm was used as the positive electrode active material. In Comparative Example 4, as in Comparative Example 3, a mixture of 60% by mass of fibrous carbon powder (average diameter 20 nm, length 400 nm) and 40% by mass of carbon black produced in Comparative Example 1 was used as a conductive agent. A coin-type battery was produced in the same manner as in Comparative Example 3 except that LiFePO ₄ having a particle size of 100 nm was used as the positive electrode active material.

Examples 8 and 9
In Example 8, a carbon black composite was prepared in the same manner as in Example 1 except that fibrous carbon having an average diameter of 90 nm and a length of 1500 nm was used, and then subjected to carbothermal treatment in the same manner as in Example 5. A coin-type battery was produced in the same manner as in Example 5. In Example 9, a carbon black composite was prepared in the same manner as in Example 1 except that fibrous carbon having an average diameter of 150 nm and a length of 3000 nm was used, and then a carbothermal treatment was performed in the same manner as in Example 5. A coin-type battery was produced in the same manner as in Example 5. The rate characteristics and cycle characteristics were evaluated in the same manner as described above.

Example 10 and Comparative Example 5
In Example 10, acetylene gas was supplied at 15 m ³ / h from a nozzle installed above a reaction furnace (furnace total length 6 m, furnace diameter 1 m), and acetylene gas was pyrolyzed at 2000 ° C. to produce carbon black. However, from the upper portion of 900 ° C., toluene (reagent manufactured by Kanto Chemical Co., 2 kg / h), ferrocene (reagent manufactured by Kanto Chemical Co., 0.2 kg / h), thiophene (reagent manufactured by Kanto Chemical Co., 0.025 kg) / H) was supplied to produce fibrous carbon. The carbon black composite was collected from a bag filter directly connected to the lower part of the furnace. In Comparative Example 5, a carbon black composite was produced in the same manner as in Example 10 except that a mixed gas of toluene (4 kg / h), ferrocene (0.35 kg / h), and thiophene (0.05 kg / h) was supplied. did. When the ash content defined in JIS K 1469 was measured for the carbon black composites of Examples 1 and 10 and Comparative Example 5, they were less than 0.01% by mass, 0.85% by mass, and 1.22% by mass, respectively. It was.

  From Tables 1 and 2, the carbon black composites obtained by the examples of the present invention have lower powder resistance than uncomposited carbon black or carbon black and fibrous carbon. The electrode produced using the carbon black composite of the present invention has a good coating state, low surface resistance, and reduced variation in surface resistance. Moreover, rate characteristics and cycle characteristics are good, and the expansion coefficient after the charge / discharge test is also suppressed.

  The carbon black composite of the present invention can be used as a conductive agent for batteries such as primary batteries, secondary batteries, fuel cells, capacitors, etc., in addition to non-aqueous secondary battery electrodes.

Claims (6)

A carbon black composite characterized in that fibrous carbon and carbon black are linked, and an ash content defined by JIS K 1469 is 1.0% by mass or less. The carbon black composite according to claim 1, wherein the content of fibrous carbon is 1 to 50% by mass. The carbon black composite according to claim 1 or 2, wherein the fibrous carbon has an average diameter of 100 nm or less. The carbon black composite according to any one of claims 1 to 3, wherein the carbon black is acetylene black. An electrode for a battery comprising the carbon black composite according to any one of claims 1 to 4. The active material for batteries formed by containing the carbon black composite as described in any one of Claims 1-4.