JP2005235426A - Battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery of low cost, not harmful to environment, and not limited for use for light-weight and compact electric products such as a lithium ion battery. <P>SOLUTION: Iron carbide and sulfur or sulfur compound are contained as an anode active material. The sulfur or the sulfur compound is preferred to be 0.1 to 20 weight parts to 100 weight parts of the iron carbide. Further, it is more preferable if a conductive agent such as a carbonaceous material of 0.1 to 20 weight parts is contained to 100 weight parts of iron carbide. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a battery, and more particularly, to a low-cost battery that is harmless to the environment and has a long life.

  A battery is a device that directly converts the chemical energy of a battery active material into electrical energy using an electrochemical oxidation-reduction reaction. The battery emits electrons to an external circuit by the electrochemical reaction and oxidizes itself. The negative electrode is composed of three main components: a positive electrode that receives electrons from an external circuit by an electrochemical reaction and is reduced by itself, and an electrolyte that serves as an ion transfer medium between the negative electrode and the positive electrode. In general, the materials for the negative electrode and the positive electrode are preferably a combination that provides light weight, high electromotive force, and large capacity.

  The practically used negative electrode material is selected in consideration of the reducing agent efficiency, discharge quantity (Ah / g), conductivity, cost, and the like. Although hydrogen is very attractive as a negative electrode material, a container for storing it in a gas state is required, and an electrochemical reaction must be efficiently generated in the container. Therefore, in practice, metals such as cadmium and hydrogen storage alloys are used for the negative electrode material.

  In addition, the positive electrode material is selected in consideration of high oxidant ability, stability when in contact with the electrolyte, effective operating voltage, and the like. Oxygen can be taken directly into the cell from the atmosphere and is a very attractive cathode material, but metal oxides such as manganese dioxide and silver oxide are used as the cathode material for the same reason as hydrogen. .

  However, manganese and cadmium are harmful to the human body, and silver oxide and hydrogen storage alloy are expensive.

  By the way, in order to select an optimum battery for a specific application, it is necessary to employ a battery having characteristics suitable for required performance. Recently, the demand for batteries is rapidly increasing in the fields of advanced electronic technology, portable electronic devices, electric vehicles, and the like, and various types of batteries have been proposed.

  For example, in Patent Document 1, as an alkaline storage battery excellent in the negative electrode oxidation suppression effect and charge / discharge cycle characteristics, a negative electrode made of a hydrogen storage alloy having yttrium or ytterbium powder and carbon powder on its surface, nickel hydroxide A nickel-hydrogen storage battery with a positive electrode is described.

  Patent Document 2 discloses that a nickel-metal hydride battery having excellent charging efficiency at high temperatures and a low self-discharge amount is obtained by physically mixing a negative electrode made of a hydrogen storage alloy containing misch metal and nickel hydroxide with a cobalt compound. In this case, a nickel electrode manufactured as described above is used as a positive electrode.

  Patent Document 3 includes a hydrogen storage alloy powder, nickel powder, a thickener, and a binder as a method for manufacturing a hydrogen storage alloy negative electrode for a nickel metal hydride battery capable of shortening the initial activation process. In the hydrogen storage alloy negative electrode, a method is described in which the hydrogen storage alloy powder and nickel powder are exposed to a hydrogen gas atmosphere at 150 to 300 ° C. before kneading with the thickener and the binder.

  Patent Document 4 discloses a slab having a hydrogen storage alloy composition containing rare earth elements as a 950 to 1100 as a method for producing a hydrogen storage alloy for nickel-metal hydride secondary batteries having excellent activity and corrosion resistance and having recyclability. A method of heat treatment at 30 ° C. for 30 minutes to 10 hours is described.

  Furthermore, Patent Document 5 discloses that a surface of a vanadium-based hydrogen storage alloy powder containing titanium is coated with a rare earth-based hydrogen storage alloy as a hydrogen storage alloy for electrodes having sufficient battery capacity and sufficient charge / discharge cycle characteristics. Is described.

  Patent Document 6 discloses a negative electrode current collector for nickel cadmium batteries that is easy to recycle, has high strength and excellent dimensional stability, has a Vickers hardness Hv of 350 to 450, and a carbon content of 0.01 to It is described that 0.1% nickel is formed into a thin plate shape having a large number of holes.

  Patent Document 7 describes a lithium ion battery positive electrode material capable of exhibiting rapid charge / discharge characteristics that contains a sulfur atom on the surface of the positive electrode material instead of an oxygen atom having a strong affinity for lithium ions. Yes.

  Patent Document 8 describes a non-aqueous electrolyte containing a sulfur compound in order to suppress decomposition of a non-aqueous electrolyte in which a lithium salt is dissolved and to improve electrical conductivity at a low temperature. ing.

  Further, Patent Document 9 describes a negative electrode for a non-aqueous electrolyte secondary battery that can occlude / release lithium ions, which includes a carbon material and carbon black.

Patent Document 10 uses LiMn ₂ O ₄ as a positive electrode active material and iron sulfide as a negative electrode active material for a positive electrode and a negative electrode of a nonaqueous electrolyte secondary battery capable of occluding and releasing lithium ions. Is described.
JP 2001-266860 A JP-A-6-283170 Japanese Patent Laid-Open No. 11-111281 JP 2002-294373 A JP 2003-13104 A JP 2002-184410 A JP 2002-170564 A JP 2001-185215 A JP 2002-324546 A JP 2000-243445 A

  However, the invention described in each of the above patent documents has the following drawbacks, or has a different basic configuration from the present invention.

  The hydrogen storage alloys made of rare earth metals described in Patent Documents 1 to 3 are very expensive.

  The method described in Patent Document 4 is a method in which an expensive hydrogen storage alloy slab is heat-treated at a high temperature of about 1000 ° C., which is very expensive.

  The vanadium-based hydrogen storage alloy described in Patent Document 5 is very expensive.

  The cadmium described in Patent Document 6 is harmful to the environment.

  The invention described in Patent Document 7 is limited to the positive electrode of a lithium ion battery.

  The invention described in Patent Document 8 is limited to improving the characteristics of the electrolyte solution of a lithium ion battery.

  The carbon material and carbon black described in Patent Document 9 are limited to the negative electrode active material of the lithium ion battery, and iron carbide and sulfur compounds are not described as the active material.

  The iron sulfide described in Patent Document 10 is limited to a negative electrode active material of a lithium ion battery, and iron carbide is not described as an active material.

  The present invention has been made in view of the shortcomings of each of the above-described batteries, and its purpose is low cost, is not harmful to the environment, and is limited to use in particularly lightweight and small electrical products such as lithium ion batteries. The object is to provide a battery that does not have a problem.

  In order to achieve the above object, the battery of the present invention is characterized by containing iron carbide and sulfur or a sulfur compound as a negative electrode active material.

  Iron carbide is a substance that can be easily manufactured by carbonizing a very abundant iron ore as a raw material with a carbon-containing gas such as methane gas, and sulfur and sulfur compounds are widely available. As described above, the battery of the present invention uses a low-cost and harmless material as the negative electrode active material, and its use is not limited.

As described above, the negative electrode material is selected in consideration of cost, electrical conductivity, electric discharge quantity, reducing agent efficiency, etc. Iron is one of the cheapest negative electrode materials. The present invention contains iron carbide (Fe ₃ C) and sulfur or a sulfur compound as a negative electrode active material. As shown in the following formula, iron carbide (Fe ₃ C) is obtained by carbonizing iron ore (Fe ₂ O ₃ ) with methane gas or the like, and can be manufactured at low cost and is harmless.

3Fe ₂ O ₃ + 5H ₂ + 2CH ₄ → 2Fe ₃ C + 9H ₂ O
Since carbon is a good electrical conductor, even if the metal (iron) of the negative electrode active material is chemically changed to an oxide or hydroxide, good electrical conductivity can be secured, and the discharge characteristics are deteriorated (the discharge voltage is reduced). Reduction) can be suppressed. In addition, as a specific method for obtaining iron carbide (Fe ₃ C), as disclosed in Japanese Patent Application Laid-Open No. 9-48604 filed by the present applicant, a reduction reaction of the iron-containing raw material using a reducing gas is performed. It is particularly preferable to carry out a part, and then to produce by the method of carrying out the remaining reduction reaction and carbonization reaction using reduction and carbonization gas, since iron carbide can be produced quickly and economically.

  By the way, the battery can be roughly divided into a primary battery and a secondary battery. The primary battery is not rechargeable and is discarded after one discharge, but the rechargeable secondary battery is It has a use for power storage that is charged by being connected to an energy source such as a generator and discharged when necessary, and a use for repeated use that is discharged in the same manner as a primary battery and recharged after discharge. ing. When the battery of the present invention is used as a secondary battery, it is necessary for the negative electrode active material to have characteristics suitable for the secondary battery, unlike a primary battery in which only discharge is performed.

  That is, an important feature of the secondary battery is that it can be charged and discharged, that is, the conversion of electric energy and chemical energy is performed almost reversibly. The degree of this reversibility is indicated by energy efficiency, and it is better that the change of the substance that reduces the cycle life is as small as possible. Moreover, it is preferable that a chemical reaction that causes deterioration of the battery material and the cycle life is not generated. Furthermore, it is preferable to have characteristics such as low cost and low pollution.

  Considering these points, it is preferable to contain sulfur or a sulfur compound in addition to iron carbide as the negative electrode active material of the secondary battery. This is because sulfur or a sulfur compound is a relatively stable substance and an inexpensive substance.

  As the sulfur compound, any of an inorganic substance and an organic substance can be used. For example, potassium sulfide, iron sulfide, carbon sulfide, hydrogen sulfide, boron sulfide, sulfamic acid, and the like can be used. Due to its effect and low cost, sulfur compounds that generate sulfide ions, such as potassium sulfide and iron sulfide, can be preferably used.

  The compounding amount of sulfur or sulfur compound with respect to iron carbide preferably contains 0.1 to 20 parts by weight of sulfur or sulfur compound with respect to 100 parts by weight of iron carbide. This is because the above action cannot be expected if the sulfur or sulfur compound is less than 0.1 parts by weight. On the other hand, if it contains more than 20 parts by weight of sulfur or a sulfur compound, it is not preferable because the disadvantage of insufficient active material ratio occurs.

  Moreover, it is preferable to add a conductive assistant since the conductive performance is further improved. As a conductive support agent, various metals, for example, powder and granular materials, such as nickel, cobalt, iron, aluminum, copper, zinc, titanium, tin, can be used. If a predetermined conductive performance can be obtained, it can be used as a conductive auxiliary agent in the state of not only a single metal but also a metal compound.

  Further, those that exhibit conductive performance by performing an appropriate treatment such as deoxidation, denitrification, deboronation, decarburization, defluorination, and dechlorination after addition can also be used as a conductive aid. That is, oxides, nitrides, borides, carbides, fluorides, chlorides, and the like of metals such as nickel, cobalt, iron, aluminum, copper, zinc, titanium, and tin can be used as the conductive aid.

  Other conductive aids include carbon-based materials such as natural carbon, artificial graphite, carbon black, acetylene black, ketjen black, PAN-based carbon fiber, pitch-based carbon fiber, activated carbon, and other amorphous carbon. Can be used.

  In addition, a gas or liquid carbon compound that can be fixed as a conductive auxiliary agent after addition can be used. That is, hydrides such as methane and ethane, and oxides such as carbon monoxide, carbon dioxide, and carbonyl compounds are electrically conductive with iron carbide and sulfur or sulfur compounds by reaction or adsorption under appropriate temperature, pressure and atmosphere. Mixtures with performance can be formed. Among the conductive aids, a carbon-based material is particularly preferable in consideration of cost and operability.

  The blending amount of the conductive assistant with respect to iron carbide preferably contains 0.1 to 20 parts by weight of the conductive assistant with respect to 100 parts by weight of iron carbide. This is because if the conductive assistant is less than 0.1 parts by weight, improvement in conductive performance cannot be expected. On the other hand, if it contains more than 20 parts by weight of the conductive assistant, the active material ratio is low and the battery capacity per weight is reduced, which is not preferable.

  The method for adding sulfur or a sulfur compound and a conductive additive to iron carbide is not particularly limited. As a machine for mixing iron carbide, sulfur or a sulfur compound, and a conductive additive, for example, a general mixer such as a roller mill, a hammer mill, a ball mill, a jet mill or the like can be used. The mixing temperature may be ordinary temperature, the pressure may be atmospheric pressure, and the atmosphere may be an air atmosphere. In particular, the effect of increasing the battery capacity can be expected if iron carbide and sulfur or a sulfur compound and a conductive additive compound are exposed to a high temperature and high pressure of 0.1 MPa or higher and a reducing atmosphere after mixing. ,preferable.

  In particular, when the sulfur compound is a liquid, it can be added by kneading, impregnating, etc. the liquid sulfur compound with iron carbide or a conductive additive. Moreover, after depositing a liquid sulfur compound as a precipitate in the presence of an appropriate compound, the sulfur compound that has become a precipitate can be added. Furthermore, a liquid sulfur compound can be directly added to the electrolytic solution.

  In particular, when the sulfur compound is a gas, the gaseous sulfur compound can be brought into contact with iron carbide or a conductive additive to be adsorbed, or can be added after being deposited as a solid under an appropriate compound and reaction conditions. Further, a gaseous sulfur compound can be directly blown into the electrolytic solution.

  In addition, the sulfur compound is not added separately, but in the iron carbide manufacturing process, for example, by adding hydrogen sulfide at a high temperature, the sulfur compound is added by sulfiding a part of the iron carbide. The same effect can be achieved. Also, instead of adding a conductive aid separately, in the iron carbide manufacturing process, a conductive aid is added by precipitating carbon on the surface of the iron carbide by adding an excessive amount of carbon-based material as a raw material. The same effect can be achieved.

  The battery of the present invention is characterized by containing iron carbide and sulfur or a sulfur compound as a negative electrode active material. The inventor considers the discharge capacity improvement mechanism as follows.

  That is, although deterioration due to repeated charge / discharge becomes remarkable with iron carbide alone, the deterioration can be suppressed and the discharge capacity can be improved because sulfur or sulfur compounds are present on the iron carbide surface by adsorption or the like.

  As described above, according to the battery of the present invention, sulfur acts as a barrier for suppressing oxidation of iron, which is a negative electrode, by oxygen in the air, which can greatly contribute to the extension of battery life. .

Examples of the present invention will be described below, but changes and modifications can be appropriately made without departing from the technical scope of the present invention.
(1) Manufacture of iron carbide powder When iron ore is heated to 550 to 750 ° C. in the presence of methane gas, the iron ore is reduced to metallic iron, and when the reaction continues, iron carbide (Fe ₃ C ) Was generated and the proportion increased. Although the electrical conductivity increases as the weight ratio of carbon increases, sufficient conductivity can be ensured if there is about 0.1% or more of carbon by weight ratio. In this example, iron carbide having been carbonized to about 5% was obtained by heat treatment for about 4 hours in a state controlled to the above temperature range. The degree of carbonization was confirmed by measuring the magnetic permeability.

The iron carbide obtained as described above was crushed with a vibration crusher (T1-100 type manufactured by CTM) for about 1 minute to obtain iron carbide powder.
(2) Mixing of iron carbide powder and sulfur or sulfur compound and conductive additive Iron carbide powder obtained as described above, sulfur (model number 195-04625 manufactured by Wako Pure Chemical Industries, Ltd.), potassium sulfide (Wako Pure) Model number 169-04505 manufactured by Yakuhin Co., Ltd., iron sulfide (model number 095-01115 manufactured by Wako Pure Chemical Industries, Ltd.), carbon black (trade name 3050B manufactured by Mitsubishi Chemical Corporation) or activated carbon (trade name G2X manufactured by Takeda Pharmaceutical Co., Ltd.) They were blended as described in Table 1 below and mixed by a ball mill.

  The ball mill used was a stainless steel cylindrical container with a volume of 2 liters, and the balls used were 400 g of alumina 20 mm diameter and 300 g of 5 mm diameter. As the turntable, model AN-5S manufactured by Nippon Ceramics Co., Ltd. was used, and the cylindrical container was placed on the turntable and rotated at 100 rpm for 24 hours.

Further, sulfamic acid as a liquid sulfur compound was directly added to the electrolytic solution.
(3) Discharge capacity The active material obtained as described above is formed into a negative electrode, nickel oxyhydroxide is used for the positive electrode, an aqueous potassium hydroxide solution is used as the electrolyte, and this nickel / iron carbide secondary An Ag / AgCl reference electrode was used as a reference electrode for measuring the electrode potential of the battery.

  Table 1 shows numerical values related to the discharge capacity obtained from the discharge curve. The specific discharge capacity in Table 1 is a numerical value with the discharge capacity of the comparative example as 100. Here, the discharge capacity (Ah / g) is a value when discharging from an initial potential (about 1.2 V) to a potential of 0.8 V in the 10th charge / discharge cycle with relatively stable battery performance.

表１に明らかなように、炭化鉄に硫黄または硫黄化合物を添加することで電池性能が向上し、導電助剤（カーボンブラックまたは活性炭）を添加すると、さらに電池性能が向上することが分かる。
（４）長期充放電サイクル試験
次ぎに、負極活物質として炭化鉄と硫化鉄の混合物を使用した表１の実施例３の場合と、負極活物質として炭化鉄のみを使用した比較例の場合について、初期電位（約１．２Ｖ）から０.８ Ｖの電位まで放電したときの長期充放電サイクル試験の結果として、比較例（白い丸の記号）の放電サイクル１回目における放電容量を１００とする相対的な数値により、比較例と実施例３（黒い丸の記号）の放電容量を図１に示す。

As is apparent from Table 1, it is understood that the battery performance is improved by adding sulfur or a sulfur compound to iron carbide, and the battery performance is further improved by adding a conductive additive (carbon black or activated carbon).
(4) Long-term charge / discharge cycle test Next, in the case of Example 3 in Table 1 using a mixture of iron carbide and iron sulfide as the negative electrode active material, and in the case of a comparative example using only iron carbide as the negative electrode active material. As a result of the long-term charge / discharge cycle test when discharging from the initial potential (about 1.2 V) to the potential of 0.8 V, the discharge capacity in the first discharge cycle of the comparative example (white circle symbol) is 100. The discharge capacities of the comparative example and Example 3 (black circle symbols) are shown in FIG.

  As is apparent from FIG. 1, it can be seen that the battery performance of Example 3 of the present invention does not deteriorate even after repeated charge and discharge for a long time.

  For reference, the results of a long-term charge / discharge cycle test of the battery when carbon black or iron sulfide is used as the negative electrode and the conditions of the positive electrode and the electrolyte solution are the same as those described in (3) above are shown in FIG. It is written together. In FIG. 1, carbon black is indicated by a symbol “Δ”, and iron sulfide is indicated by a symbol “x”.

  As can be seen from FIG. 1, the battery using carbon black or iron sulfide as the negative electrode active material is inferior to the battery of the comparative example (battery using iron carbide as the negative electrode active material). .

It is a figure which shows the result of the long-term charging / discharging cycle test of the battery using the negative electrode active material of this invention, and the battery of a comparative example and a reference example.

Claims (6)

  A battery comprising iron carbide and sulfur or a sulfur compound as a negative electrode active material.   The battery according to claim 1, wherein 0.1 to 20 parts by weight of sulfur or a sulfur compound is contained with respect to 100 parts by weight of iron carbide.   The battery according to claim 1 or 2, further comprising a conductive assistant.   4. The battery according to claim 3, wherein the conductive assistant is contained in an amount of 0.1 to 20 parts by weight with respect to 100 parts by weight of iron carbide.   The battery according to claim 1, 2, 3, or 4, wherein the sulfur compound generates sulfide ions.   6. The battery according to claim 3, 4 or 5, wherein the conductive assistant is a carbon-based material.

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