JP2012204177A - Cobalt-free alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline secondary battery in which both positive electrode and negative electrode are made cobalt free.SOLUTION: An alkaline secondary battery of the present invention includes: a positive electrode having a positive electrode material containing no cobalt; a negative electrode having a negative electrode material containing no cobalt; an electrolyte comprising an alkaline aqueous solution; and a separator. The positive electrode material is preferably a positive electrode active material having a surface coated with carbon, specifically, nickel hydroxide having a surface coated with carbon. The negative electrode active material is preferably a hydrogen storage alloy represented by chemical formula 1: REMgNiAl(RE represents an alkaline rare earth element, and 0.05≤x≤0.3, 2.9≤y≤4.4 and 0.1≤z≤0.3 are satisfied). The electrolyte is preferably an aqueous solution containing potassium hydroxide and lithium hydroxide.

Description

  The present invention relates to an alkaline secondary battery characterized in that the active material of the positive electrode and the negative electrode does not contain cobalt.

  In recent years, nickel-hydrogen batteries using nickel hydroxide for the positive electrode and a hydrogen storage alloy for the negative electrode have become the mainstream of alkaline secondary batteries. Examples of the alkaline secondary battery other than the nickel-hydrogen battery include a nickel-iron battery, a nickel-zinc battery, and a nickel-cadmium battery. These alkaline secondary batteries have problems such as low utilization, short cycle life, and low volumetric capacity density as compared to nickel-hydrogen batteries. Until the 1980s, nickel-cadmium batteries accounted for the share of secondary batteries as a typical rechargeable alkaline battery. However, it has been replaced with a nickel-hydrogen battery that has almost the same voltage, a large capacity, and a small environmental load.

Nickel-hydrogen batteries are being used in large-scale industrial equipment such as railway vehicles or ground storage facilities in addition to use in small equipment or hybrid vehicles. Conventionally, in a nickel-hydrogen battery, cobalt has been added to a positive electrode material as a conductive aid for improving the positive electrode utilization rate. In nickel-hydrogen batteries, cobalt has also been added to the negative electrode active material for the purpose of suppressing the pulverization of the alloy and extending the life of the electrode.

  Cobalt is a very expensive element and may occupy about half of the electrode raw material cost. For this reason, cost reduction is expected by realizing cobalt-free nickel-metal hydride batteries in which the positive electrode does not contain any cobalt as a conductive additive and the negative electrode active material contains no cobalt. Furthermore, cobalt is unevenly distributed, and there is a high possibility that supply shortages or price increases will occur due to political instability in the region. In particular, since large industrial batteries require a large number of electrodes, stable supply of cobalt as a material is essential, and development of cobalt-free nickel secondary batteries is expected.

  As a cobalt-free positive electrode composition for an alkaline secondary battery, Patent Document 1 discloses an active material, a conductive material, and a resin component, in which particles having a graphitization degree of 0.3 or more and 0.8 or less analyzed by Raman spectroscopy. A carbonaceous material is disclosed. An alkaline secondary battery including a positive electrode using the composition for an alkaline secondary battery disclosed in Patent Document 1 is said to have no impaired cycle life even when overcharged.

  Non-Patent Document 1 discloses a technique of using an oxidation-resistant carbon conductive material as a conductive material for a nickel positive electrode. Non-Patent Document 2 discloses a carbon-coated nickel hydroxide positive electrode in which a carbon material is uniformly coated with nickel hydroxide particles. The carbon-coated nickel hydroxide positive electrode of Non-Patent Document 2 exhibits cycle characteristics and output characteristics equivalent to those of a general-purpose cobalt-coated nickel positive electrode. Non-Patent Document 3 discloses the characteristics of conventional alloys that have been used as negative electrodes for nickel-hydrogen batteries.

JP 2006-54084 A

Nagashima, Tsutsumi, Higaki, Morimoto, Kakegawa; 72nd Electrochemical Society of Japan, II-27 (2005). Saito, Mukai, Sakai, Taka ▲ Saki ▼, Nishimura, Tsutsumi, Kinoshita, Kano, Nagato; 51st Battery Symposium, 2D-22 (2010). T. Sakai, T. Hazama, H. Miyamura, N. Kuriyama, A. Kato, H. Ishikawa, Journal of the Less-Common Metals, vol.172-174, (1991) pp.1175-1184.

  In the alkaline secondary battery, when cobalt is added to the positive electrode material or the negative electrode active material, the cobalt is eluted from the positive electrode or the negative electrode into the electrolytic solution. The eluted cobalt is oxidized during charging and re-deposited as cobalt oxyhydroxide (CoOOH) in the vicinity of the positive electrode. The reprecipitation of cobalt oxyhydroxide is an important reaction in order to form a conductive network that connects nickel hydroxide particles in the positive electrode. However, a part of cobalt oxyhydroxide is deposited not only on the positive electrode but also on the separator.

  Thereafter, when overdischarge occurs, cobalt oxyhydroxide is reduced to cobalt hydroxide, and cobalt that has contributed to the conductive network at the positive electrode is eluted into the electrolytic solution. Cobalt eluted in the electrolytic solution is oxidized and re-deposited at the time of charging, but does not necessarily re-deposit on the positive electrode to repair the conductive network, causing a significant decrease in utilization. Furthermore, cobalt is reprecipitated also in the separator to form a micro short circuit path between the positive electrode and the negative electrode, and the self-discharge amount is likely to increase.

  There is another type of cobalt added to the positive electrode. It is an internal addition to nickel hydroxide itself, which is a positive electrode active material. When cobalt is added internally, the generation of oxygen competing with the charging reaction is suppressed, and the charging efficiency can be improved. Thereby, the deterioration of the battery is suppressed, and the performance can be maintained for a long time. The same effect can be obtained by the internal addition of zinc. Therefore, cobalt may not be added when zinc is added. In the case of internal addition to nickel hydroxide, it is sufficient that zinc is added in an amount of 0.1 to 5 mol% and cobalt is 0.1 to 1 mol%. The internally added cobalt is incorporated in the crystal structure of nickel hydroxide, is difficult to dissolve, and is separated from cobalt hydroxide used as a conductive aid for the positive electrode or cobalt contained in the alloy that is the negative electrode active material. It is necessary to think.

On the other hand, as the negative electrode active material, Mm (Ni, Co, Mn, Al) _5- based hydrogen storage alloy is most commonly used. Mm is a misch metal, which is a mixture of light rare earth elements composed of La, Ce, Pr and Nd. Here, cobalt added to the negative electrode active material plays a role of preventing the pulverization of the hydrogen storage alloy and increasing the cycle life of the negative electrode. However, every time the charge / discharge cycle is repeated, the hydrogen storage alloy is gradually pulverized and cobalt and manganese are eluted from the new surface into the electrolyte. The eluted cobalt and manganese are re-deposited on the separator to form a micro short circuit path, which causes an increase in the amount of self-discharge.

  As described above, in an alkaline secondary battery such as a conventional nickel-hydrogen battery, the positive electrode is for the purpose of a conductive additive, and the negative electrode is for the purpose of preventing the hydrogen storage alloy from being pulverized and extending its life. In each case, it was essential to add cobalt to the active material. However, repeated charging / discharging of the alkaline secondary battery has also been a factor of deterioration of battery characteristics due to elution and reprecipitation of cobalt. As described above, if only one of the positive electrode and the negative electrode is made cobalt-free, elution of cobalt into the electrolytic solution cannot be prevented, and the fundamental cause of deterioration of the alkaline secondary battery cannot be solved.

  Large industrial batteries are assumed to be used in public infrastructure such as buses and trains. Such industrial large-sized batteries are expected to be used in harsh conditions as compared to the use of cylindrical batteries instead of dry batteries used for consumer use. Furthermore, large industrial batteries are required to be lower in cost than consumer products.

  From this point of view, while maintaining basic charge / discharge characteristics such as charge efficiency and discharge capacity at least equal to or higher than those of conventional nickel-hydrogen batteries, output, cycle life, overcharge resistance, overdischarge resistance, and self It can be said that improving battery performance such as a discharge suppressing function and further removing cobalt completely from the electrode material are essential conditions required for future alkaline secondary batteries. In particular, if cobalt is used for either the positive electrode or the negative electrode, the overdischarge resistance and the low self-discharge suppression function may be impaired due to the effects of elution and reprecipitation.

  An object of the present invention is to provide an alkaline secondary battery in which both the positive electrode and the negative electrode are cobalt-free.

  In order to make the positive electrode of the alkaline secondary battery cobalt-free, a conductive additive that substitutes for cobalt oxyhydroxide is necessary. When the surface of the positive electrode active material is coated with carbon, the present inventors have high conductivity and are not easily oxidized during charging. Therefore, the cycle life is long while maintaining a high discharge capacity (active material utilization rate). It was thought that an alkaline secondary battery could be obtained.

  The present inventors have found that the negative electrode of the alkaline secondary battery is also made cobalt-free, thereby eliminating the elution of cobalt into the electrolyte and solving the fundamental cause of deterioration of the alkaline secondary battery. The present invention has been completed.

Specifically, the present invention
A positive electrode having a positive electrode material containing no cobalt as a conductive additive;
A negative electrode having a negative electrode active material not containing cobalt;
An electrolyte solution comprising an alkaline aqueous solution;
A separator;
The present invention relates to an alkaline secondary battery.

  In the alkaline secondary battery of the present invention, cobalt is not eluted into the alkaline electrolyte by making both the positive electrode and the negative electrode cobalt-free, and an increase in the amount of self-discharge due to the formation of a micro short-circuit path can be prevented. .

  The positive electrode material is preferably a positive electrode active material whose surface is coated with carbon.

  By covering the surface of the positive electrode active material with carbon, sufficient conductivity can be imparted to the positive electrode active material even when cobalt free.

The positive electrode material
Core particles made of a positive electrode active material;
Conductive material particles made of carbon,
A structure in which a reaction part between the positive electrode active material and hydroxide ions and a conductive part covered with conductive material particles are formed on the surface of the core particle is preferable.

  It is preferable that two or more core particles are bonded via carbon.

  The conductive material particles preferably have a particle size smaller than the core particles, and a part of the surface of the core particles is preferably covered with the conductive material particles. In this case, the surface coverage of the core particles by the conductive material particles is preferably 10% or more and 95% or less.

  The conductive material particles are preferably formed of a carbon material having a graphitization degree (G value) of 0.3 or more and 0.8 or less.

  The core particles preferably contain an ethylene copolymer as a binder to which the conductive material particles are attached. In this case, the addition amount of the binder is preferably 50% by mass or more and 150% by mass or less by weight with respect to carbon, and is preferably 0.1% by mass or more and 10% by mass or less by weight with respect to the positive electrode active material.

  In the present invention, the positive electrode material is preferably nickel hydroxide having carbon coated on the surface.

In the present invention, the negative electrode active material is represented by the chemical formula 1: RE _1-x Mg _x Ni _y Al _z.
A hydrogen storage alloy represented by:
Where RE is a rare earth element;
0.05 ≦ x ≦ 0.3, 2.9 ≦ y ≦ 4.4, and 0.1 ≦ z ≦ 0.3.

The hydrogen storage alloy of Chemical Formula 1, which is a cobalt-free alloy, forms a stacked crystal in which lattices of RENi ₅ and MgNi ₂ are alternately stacked. Even if this laminated crystal does not contain cobalt, it is difficult to be pulverized and has a crystal structure suitable as a negative electrode active material for batteries.

  RE is (1) one or more simple rare earth elements selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Or (2) Mm (Misch metal) which is a mixed rare earth mainly composed of La, Ce, Pr and Nd; or (3) Di (didymium) which is a mixed rare earth composed of Pr and Nd: Contains.

  The coefficients x, y, and z are preferably 0.05 ≦ x ≦ 0.3, 2.9 ≦ y ≦ 4.4, and 0.1 ≦ z ≦ 0.3 (3.0 ≦ y + z ≦ 4.7), respectively. The hydrogen storage alloy of Chemical Formula 1 may be in this composition range, but if it is an alkaline secondary battery for industrial use, it is necessary to focus on high output characteristics and long cycle life characteristics. In this case, it is more preferable that 3.9 ≦ y + z ≦ 4.2.

  In the present invention, the electrolytic solution is preferably an aqueous solution containing potassium hydroxide and lithium hydroxide.

  The alkaline secondary battery of the present invention has a positive electrode and a negative electrode that are cobalt-free, and has a low discharge cost, high discharge voltage, long cycle life, Excellent chargeability. Furthermore, the self-discharge suppressing function and the overdischarge resistance are also improved.

The schematic diagram showing the structure of the positive electrode active material coated with carbon is shown. The schematic block diagram showing an example of the fluidized-bed coating apparatus used for manufacture of the carbon-coated positive electrode active material powder of FIG. 1 is shown. FIG. 3 shows a cross-sectional view of a nozzle used in the fluidized bed coating apparatus of FIG. 2. The SEM image of the nickel hydroxide powder which coat | covered carbon on the surface is shown. The graph regarding the test result of 1C and 10C discharge of the sealed battery of Examples 1-3 and the comparative example 1 is shown. The graph regarding the cycle characteristics (relationship between a utilization factor and the number of cycles) of the sealed batteries of Examples 1 to 3 and Comparative Example 1 is shown. The graph regarding the kind and quantity of the crystal phase which are obtained as a result of having performed the crystal structure analysis by the Rietveld method of the negative electrode alloy for sealed batteries of Examples 1-3 and the comparative example 1 is shown. About the sealed battery of Example 1 and Comparative Example 1, the discharge curve after standing at 45 ° C. for 1 week after charging is shown. The graph regarding the cycling durability characteristic of the sealed battery of Example 1 and Comparative Example 2 is shown. The graph regarding the high rate discharge characteristic of the sealed battery of Example 1 and Comparative Example 2 is shown. About the open type battery of Example 4 and Comparative Example 3, the graph which plotted the relationship between the short circuit days and the capacity | capacitance maintenance factor after 45 degreeC storage is shown. The charging / discharging curve of the open type battery of Example 4 and the comparative example 3 in the next charging / discharging cycle which performed discharge equivalent to 200% of battery capacity is shown.

  Embodiments of the present invention will be described with reference to the drawings as appropriate. The present invention is not limited to the following description.

<1. Positive electrode>
The alkaline secondary battery of the present invention is characterized in that the positive electrode material does not contain cobalt. Specifically, nickel hydroxide with carbon coated on the surface is used as the positive electrode material (positive electrode powder). Is preferred.

  The positive electrode material of the present invention is prepared, for example, by mixing nickel hydroxide, oxidation-resistant carbon and a binder uniformly with a solvent, filling this into a base material such as foamed nickel, and then drying and It can be manufactured by pressing.

  The positive electrode material (positive electrode powder) of the present invention can also be produced by a fluidized bed coating method. In the fluidized bed coating method, a conductive material uniformly made of carbon is formed on the surface of the positive electrode active material that becomes the core particle, rather than a method in which particles of the positive electrode active material (for example, nickel hydroxide), a carbon material, and a binder are mixed together with a solvent. Particles can be attached.

When the surface of the positive electrode active material particles is coated with carbon by a fluidized bed coating method, the carbon-coated positive electrode active material particles are:
Core particles made of a positive electrode active material;
Conductive material particles made of carbon,
It has a structure in which a reaction part of a positive electrode active material and a hydroxide ion and a conductive part covered with conductive material particles are formed on the surface of the core particle.

  FIG. 1 is a schematic view showing the structure of a carbon-coated positive electrode active material powder suitable as a positive electrode material (positive electrode powder) used in the present invention. In FIG. 1, the positive electrode active material is nickel hydroxide. In the positive electrode powder 21, conductive material particles 33 made of carbon adhere to the surfaces of the core particles 31 made of nickel hydroxide, which is a positive electrode active material. The conductive material particles 33 are attached to the surface of the core particles 31 in a uniform distribution. When the core particles 31 come into contact with each other through the conductive material particles 33, a conductive network is formed between the core particles 31. Yes.

  In the positive electrode powder 21, the conductive material particles 33 having a particle size smaller than the core particles 31 are firmly attached to the surface of the core particles 31 by the binder to cover a part of the surface of the core particles 31. ing. The portion covered with the conductive material particles 33 forms a conductive portion 35 having high conductivity, and the remaining portion forms a reaction portion 37 where the positive electrode active material and hydroxide ions react.

  The conductive material particles made of carbon uniformly adhere to the surface of the core particles made of the positive electrode active material, so that the electrons supplied from the current collector are distributed throughout the core particles, and the core particles in contact with the current collector Charge / discharge efficiency is improved. In addition, since a strong conductive network is formed between the positive electrode active materials, the core particles that do not come into direct contact with the current collector and indirectly receive the electron supply through the core particles in contact with the current collector are also uniform. It becomes easy to be charged. As a result, even if rapid charging / discharging is performed with a large current, the active material utilization rate is unlikely to decrease.

  Since the carbon material is cheaper than cobalt or a cobalt compound, an alkaline secondary battery having high output characteristics can be obtained by using a positive electrode active material (powder for positive electrode) coated with the carbon material as a conductive material as the positive electrode material. Can be manufactured at low cost.

  When a carbon-coated positive electrode active material (powder for positive electrode) produced by a fluidized bed coating method is used for a positive electrode as a positive electrode material, the positive electrode active material and carbon are mixed to produce a positive electrode mixture (slurry). Since the positive electrode mixture can be produced with an aqueous solvent without using an organic solvent required in some cases, process management becomes easy, and from this point, the manufacturing cost of the alkaline secondary battery can be reduced.

  As a general positive electrode for an alkaline secondary battery, a foamed nickel porous body having a pore size of about 100 μmφ is used as a current collector, and the current collector is filled with nickel hydroxide particles having a diameter of about 10 μmφ. Is used. For this reason, the filled nickel hydroxide particles include those that are in direct contact with the current collector and those that are not.

  In some cases, two or more active material particles are bound to the positive electrode powder produced by the fluidized bed coating method. If the size of this bonded body is up to about 100 μmφ, it is about the same as the pore size of the foamed nickel current collector, so there is no problem in filling and there is no major problem in battery characteristics.

  The conductive material particles preferably have a smaller particle size than the core particles, and a part of the surface of the core particles is preferably covered with the conductive material particles. According to this configuration, since the conductive material particles are present on the surface of the core particles, sufficient conductivity can be ensured, and only a part of the core particle surface is covered with the conductive material particles. By leaving the part where the conductive material particles do not exist, the reaction area of the positive electrode active material is secured, and the decrease in the utilization factor of the positive electrode active material is suppressed.

  The surface coverage of the core particles by the conductive material particles is preferably in the range of 10% to 95%, more preferably 30% to 95%. When the coverage is less than 10%, a conductive network that connects the core particles is not sufficiently formed, and there is a core particle that is not sufficiently charged, so a high utilization rate cannot be obtained. On the other hand, when the coverage is greater than 95%, the conductivity is sufficient, but due to the influence of the bulkiness of carbon, the packing density of the active material into the substrate is lowered, and the electrode capacity per volume is lowered. In order to obtain a coverage of 10% or more in nickel hydroxide particles having an average particle diameter of 10 mmφ, the carbon addition amount is preferably 2% by mass or more, and in order to keep the carbon addition amount to 95% or less, the carbon addition amount is 8%. It is preferable to make it mass% or less. The particle size ratio between the core particles and the conductive particles is preferably in the range of 5: 1 to 100: 1.

  In the positive electrode powder produced by the fluidized bed coating method, the conductive particles are preferably formed of a carbon material having a graphitization degree (G value) of 0.3 or more and 0.8 or less. According to this configuration, high conductivity is imparted to the positive electrode active material particles, and the oxidation resistance is improved.

  The positive electrode powder produced by the fluidized bed coating method preferably contains an ethylene copolymer as a binder for attaching the conductive material particles to the core particles. According to this configuration, the core particles and the conductive particles can be bound stably and uniformly.

The method for producing the carbon-coated positive electrode active material (positive electrode material) powder is as follows:
A fluidizing step of fluidizing the core particle powder by blowing an air flow from below to the core particle powder made of the positive electrode active material;
A coating liquid preparation step of preparing a coating liquid by dispersing conductive material particles made of carbon and a binder in a solvent;
A spraying process in which a coating liquid is sprayed toward the fluidized core particle powder to attach conductive material particles to the surface of the core particle;
Consists of

  According to such a configuration, the conductive material particles uniformly composed of carbon adhere to each surface of the core particle that is the positive electrode active material by the fluidized bed coating. As a result, a strong conductive network is formed between the active material particles and between the active material and the current collector, and an increase in the internal resistance of the battery is suppressed. As a result, it is possible to produce an alkaline secondary battery having high output characteristics at low cost by using the carbon-coated positive electrode active material powder.

The manufacturing method of the positive electrode active material (powder for positive electrode) whose surface is carbon-coated is:
In the fluidization process, nickel hydroxide is used as the positive electrode active material,
In the coating liquid preparation step, it is preferable to use an ethylene-based copolymer as a binder.

  According to such a configuration, since the carbon particles can be uniformly dispersed in the solvent, the surfaces of the positive electrode active material particles are coated with carbon evenly.

  It is preferable that the method for producing the positive electrode powder further includes a drying step of drying the core particles to which the conductive material particles are adhered, using an air flow in the fluidizing step.

  According to such a configuration, it is possible to efficiently dry the powder using an air flow for fluidizing the powder, and thus it is possible to manufacture the positive electrode powder at a lower cost. . In particular, when an organic solvent is used as the solvent of the coating solution, the residual amount of the organic solvent in the powder after drying can be reduced by using fluidized bed drying, which improves the storage stability of the powder after coating. However, it is possible to prevent exposure of the organic solvent to the human body in terms of handling.

  A suitable method for producing the positive electrode powder will be described in more detail.

  A positive electrode powder (positive electrode active material powder coated with carbon) 21 shown in FIG. 1 is manufactured by attaching conductive material particles 33 made of carbon to the surface of core particles 31 made of an active material by fluidized bed coating. Is done. FIG. 2 is a schematic configuration diagram showing an example of a fluidized bed coating apparatus used for manufacturing the positive electrode powder 21 of FIG.

  As shown in FIG. 2 (a), the fluidized bed coating apparatus 41 includes, as main components, a substantially cylindrical fluidized tank 43 that forms a space for fluidized bed coating, and a fluidized tank from below the fluidized tank 43. 43, an exhaust fan 45 for blowing an air flow A for fluidizing the particles to be coated, and a sprayer 49 for spraying the coating liquid CL containing the coating particles on the fluidized bed 47 made of the fluidized particles to be coated. It has.

  The fluidized bed coating uses the fluidized bed coating apparatus 41 to form the fluidized bed 47 by fluidizing the core particles 31, which are particles to be coated, by the air flow A from the exhaust fan 45 in the fluidized tank 43. In this method, the conductive material particles 33 are adhered to the surfaces of the core particles 31 by spraying the coating liquid CL containing the conductive material particles 33 that are the covering particles toward the fluidized bed 47 of the core particles 31.

  First, the air flow A is supplied from below to the powder of the core particles 31 introduced into the fluidized tank 43 by the exhaust fan 45. As a result, a fluidized bed 47 made of powder of the fluidized core particles 31 is formed in the fluidized tank 43 (fluidization step).

  As shown in FIG. 2B, the fluidized bed coating apparatus 41 is preferably a rolling type having a disk rotor 51 at the bottom. In this case, the coating liquid is formed in a state where the fluidized bed 47 forms a spiral circulating flow by the rolling by the disk rotor 51 at the bottom and the fluidized air flow A supplied from the clearance between the disk rotor 51 and the wall surface. CL is sprayed. By adjusting the rotational speed of the disc rotor 51 and the flow rate of the air forming the fluidized bed 47 in the fluidized tank 43, the fluidized state of the fluidized bed 47 can be controlled with high accuracy, so that a more desirable coating becomes possible.

  At the bottom of the fluid tank 43, an air dispersion plate 53 is disposed as a member for holding the powder made of the positive electrode active material in the apparatus 41 and rectifying the air flow A for forming the fluidized bed 47. . Specifically, as the air dispersion plate 53, a so-called punched plate can be used as a perforated plate, and meshes such as woven wire mesh (manufactured by Kansai Wire Mesh Co., Ltd.), Poremet (Fuji Filter Industry Co., Ltd.). Metal mesh such as Poiflow (manufactured by Nichidai Filter Co., Ltd.) can be used. An optimal mesh can be selected in consideration of the particle diameter of the positive electrode active material.

  As the flow rate of the air flow A, the superficial velocity (the value obtained by dividing the passing flow rate by the cross-sectional area) is 0.25 to 1.4 m on the basis of the cross-sectional area of the flow tank 43 located 5 cm above the position where the air dispersion plate 53 is installed / s, preferably 0.28 to 1.0 m / s, more preferably 0.30 to 0.7 m / s. If the superficial velocity is too low, fluidization will be insufficient. If the superficial velocity is too high, the air stream A blows through the fluidized bed 47, and a stable fluidized bed 47 cannot be formed, which is not preferable for coating.

  The speed of the outer peripheral portion of the disk rotor 51 (rotational peripheral speed) is preferably 1 to 20 m / s, and more preferably 2 to 15 m / s. When the rotational peripheral speed is too slow, the powder tends to accumulate on the disk rotor 51, and when the rotational peripheral speed is too fast, the frictional force applied to the surface of the core particle 31 becomes too large, and the core particle 31. There is a possibility that the conductive material particles 33 adhering to the surface may be peeled off. As a more preferable form of the fluidized bed coating apparatus 41, as shown in FIG. 2 (c), a crushing mechanism using an impeller 55 may be provided on the upper part of the disk rotor 51.

  While performing the fluidization process, the conductive material particles 33 made of carbon and the binder are dispersed in a solvent to prepare the coating liquid CL (coating liquid preparation process). The amount of the conductive material added to the active material in the positive electrode is preferably 2% by mass to 8% by mass of the conductive material, and 2.5% by mass to 6% by mass of the conductive material with respect to the positive electrode active material. Is more preferable. When the addition ratio of the conductive material is smaller than 2% by mass, a sufficient conductivity assist effect cannot be obtained, and the utilization factor of the active material is lowered. On the other hand, when the addition ratio of the conductive material is larger than 8% by mass, a sufficient battery energy density cannot be obtained.

  The carbon material is preferably a material that has conductivity and can withstand electrochemical oxidation. For example, a carbon material having a graphitization degree (G value) of 0.3 to 0.8 is preferably used.

The degree of graphitization (G value) can be calculated as follows. First, the particulate carbon material is analyzed by Raman spectroscopy, and the Raman spectrum obtained thereby is subjected to baseline correction and smoothing processing. Then, the Raman spectrum after these treatments is further curve-fitted, and in the Raman spectrum after curve fitting, the peak integrated intensity (Ja) due to the disorder of the graphite structure near 1360 cm ⁻¹ and the graphite structure near 1580 cm ⁻¹ The integrated intensity (Jb) of the peak to be obtained is obtained. The target degree of graphitization is obtained as a value (Ja / Jb) obtained by dividing the peak integrated intensity (Ja) by the peak integrated intensity (Jb). Incidentally, the above-mentioned Raman spectrum is obtained when a microscopic Raman spectrometer is used and a particulate carbon material is analyzed by Raman spectroscopy under the following conditions.

Excitation light: Ar ⁺ ion laser / 514.5nm
Excitation light output: 8mW
Objective mirror magnification: 50 times Integration count: 1 time Irradiation time: 120 seconds Measuring method: 180 ° backscattering Measurement range: 1100-1800cm ^-1
Wave number calibration: Silicon

  The graphitization degree (G value) indicates that the smaller the value, the higher the crystallinity as graphite (that is, the more graphitic). Therefore, the degree of graphitization (G value) of graphite is less than 0.3. More specifically, the degree of graphitization (G value) of artificial graphite obtained by graphitizing coke at 2800 ° C. is about 0.2.

  Such a particulate carbon material can be usually prepared by heat-treating an existing particulate carbon material (hereinafter referred to as a particulate carbon material raw material), such as carbon black. Incidentally, carbon black is a concept including furnace black, acetylene black, and ketjen black. The heat treatment temperature here is not generally stipulated by factors such as the type or properties of the particulate carbon material, but it is usually preferable to set the heat treatment temperature at 1800 ° C. or higher and 2600 ° C. or lower. The heat treatment time in the temperature range is preferably set to at least 2 hours, more preferably 3 hours or more, although it depends on the size of the container used during the heat treatment. When the heat treatment time is less than 2 hours, it may be difficult to uniformly heat the inside, and it may be difficult to obtain a particulate carbon material exhibiting electrolytic durability.

  The particulate carbon material raw material used here preferably satisfies the following condition A or condition B.

(Condition A)
Average particle size is 20 nm to 100 nm, preferably 30 nm to 70 nm. If the average particle size is less than 20 nm, the particles are likely to be damaged during the heat treatment, and the target particulate carbon material may be difficult to obtain. On the other hand, when it exceeds 100 nm, the resulting particulate carbon material may not easily lower its resistance value even if the same weight as that of other particulate carbon material is added to the active material. Here, the average particle diameter is a value measured based on a transmission electron micrograph.

(Condition B)
Absorption of dibutyl phthalate (DBP) is 100 cm ^3/100 g or more 250 cm ^3/100 g or less, preferably 120 cm ^3/100 g or more 200 cm ^3/100 g or less. In this case the absorption amount is less than 100 cm ^3/100 g is likely to be difficult to particulate carbon material of interest is obtained. Conversely, when it exceeds 250 cm ^3/100 g, there is a possibility that it becomes difficult to mix the particulate carbon material after the heat treatment uniformly and the active material. The absorption amount of DBP is a value measured according to the method specified in JIS K6217. Specifically, the DBP absorption amount per 100 g of the particulate carbon material when DBP is added to the particulate carbon material is a value measured using an absorber meter.

  The particulate carbon material raw material preferably has a higher bulk density in addition to the above-mentioned conditions A and B. The particulate carbon material raw material with a low bulk density is less charged into the container used during the heat treatment, which may increase the production cost of the target particulate carbon material. However, if the bulk density is too high, the target particulate carbon material obtained from the particulate carbon material raw material becomes difficult to uniformly mix with the active material, and thus needs to be pulverized. For this reason, it is preferable to use other carbon black having a higher bulk density than acetylene black and ketjen black, for example, granulated carbon black, as the particulate carbon material raw material.

  The particulate carbon material as described above is an ordinary carbon material, that is, a carbonaceous carbon material having a graphitization degree (G value) exceeding 0.8, and a graphitic carbon material having a graphitization degree (G value) of less than 0.3. It exhibits different specific oxidation resistance. Specifically, the carbonaceous carbon material is easily dry-oxidized by oxygen gas generated during overcharge of the alkaline secondary battery, and the graphitic carbon material is easily wet-oxidized by the alkaline electrolyte. On the other hand, since the above-mentioned particulate carbon material has a special property that cannot be distinguished from either a carbonaceous carbon material or a graphitic carbon material, it is difficult to receive both dry oxidation and wet oxidation in an alkaline secondary battery. High oxidation resistance (electrolytic durability).

  The solvent of the coating liquid CL of the conductive material containing the binder is not particularly limited as long as it is a liquid that does not react with the active material, has low viscosity, and easily volatilizes, and water, ethanol, xylene, or toluene can be used. And is selected in consideration of the solubility and dispersibility of the solute or dispersoid.

  As the binder, an ethylene copolymer resin such as ethylene vinyl acetate, a polyolefin resin such as polypropylene, or polytetrafluoroethylene can be used. The binder can be used in the form of any solution, suspension, dispersion or emulsion.

  The carbon material is added at a ratio of 0.01% by mass or more and 10% by mass or less with respect to the solvent, and is mixed with stirring. When the ratio of the carbon material to the solvent is less than 0.01% by mass, the time required for the spraying process to be described later becomes long and the amount of the necessary coating liquid also increases. On the other hand, when the ratio of the carbon material to the solvent exceeds 10% by mass, the viscosity increases, and it becomes difficult to spray the coating liquid and to disperse it uniformly.

  The amount of the binder added to the solvent is preferably about the same amount as that of the carbon material, specifically 50 mass% or more and 150 mass% or less with respect to the carbon material amount. When the amount of the binder is less than 50% by mass, the adhesion of the carbon material to the core particles is not sufficient, and the carbon material is easily peeled off from the core particles. On the other hand, when the amount of the binder is more than 150% by mass, the resistance of the carbon material is increased, which causes a decrease in charge / discharge efficiency and high rate charge / discharge performance.

  Even if the ratio of the carbon material to the solvent is as low as 0.01% by mass, the carbon material powder generally has a large bulk density and takes in air. It is difficult to disperse uniformly. Therefore, it is preferable to add a surfactant to the solvent to keep the surface tension low. The addition amount of the surfactant is preferably set within a range of 0.01% by mass to 3% by mass with respect to the carbon material. When the addition amount of the surfactant is less than 0.01% by mass, the surfactant effect is not sufficiently exhibited. When the addition amount is more than 3% by mass, the performance as a battery may be deteriorated.

  In order to enhance the dispersibility of the carbon material in the solvent, it is also preferable to add a dispersant to the coating liquid. As the dispersant, for example, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, sodium polyacrylate, acrylic acid copolymer resin, cellulose resin, or glue can be used. The addition amount of the dispersant is preferably set in the range of 0.01% by mass to 2% by mass with respect to the carbon material. When the addition amount of the dispersant is less than 0.01% by mass, the dispersion effect is not sufficiently exhibited, and when it is greater than 2% by mass, the performance as a battery may be deteriorated.

  The amount of conductive material added to the preferred positive electrode active material, the degree of graphitization (G value) of the carbon material, the type of solvent, the type and blending amount of the binder, the addition amount of the surfactant, the type and addition amount of the dispersant, The same applies to the case of producing a positive electrode active material (positive electrode powder) whose surface is coated with carbon by a method other than the fluidized bed coating method.

  When preparing a composite material in which nickel hydroxide, oxidation-resistant carbon and binder are uniformly mixed together with a solvent, and filling this into a base material such as foamed nickel, blending the solvent rather than the coating liquid used for fluidized bed coating It is better to reduce the amount significantly. By reducing the blending amount of the solvent, the effect of increasing the viscosity by the binder contained in the composite material is strengthened, and the materials having different specific gravities are uniformly dispersed. By filling this mixture into a foamed substrate and drying, a uniform carbon and binder coating layer is formed around the nickel hydroxide particles. 10-40 mass% is preferable and the compounding quantity of a solvent has more preferable 15-30 mass%. When the blending amount is less than 10% by mass, the viscosity of the composite material is too high, and unevenness is likely to occur in the filling amount into the base material. On the other hand, when it exceeds 40% by mass, the viscosity is lowered, the mixture itself becomes non-uniform due to the influence of the specific gravity of each material, and the filling density into the foamed substrate is lowered.

  Next, the produced coating liquid CL is sprayed toward the fluidized bed 47 in the fluidized tank 43 by the sprayer 49 of FIG. 2A (spraying process). As a result, the conductive material particles 33 made of carbon adhere to the surfaces of the core particles 31.

  The coating liquid CL is supplied into the fluid tank 43 from the nozzle 57 at the tip of the sprayer 49. The configuration of the nozzle 57 is not particularly limited as long as it is a nozzle that can be sprayed using the coating liquid CL as a mist, and an optimum nozzle can be selected in consideration of the particle diameter of the powder made of the positive electrode active material. . In order to prevent powder from adhering to and clogging the tip, a gas supply port 59 provided in the radial center of the nozzle 57 shown in FIG. 3 and a liquid supply provided in the outer peripheral portion of the gas supply port It is preferable to use a two-fluid nozzle 57 that includes a mouth 61 and mists the spray liquid by compressed air from the outer periphery.

  The liquid supply port 61 of the two-fluid nozzle 57 preferably protrudes within a range of 1 mm or more than the gas supply port 59, more preferably protrudes within a range of 0.1 mm to 1 mm, and 0.3 mm to 1 mm. Even more preferably, it protrudes in the range. This is because the battery active material is likely to be fixed at the tip of the two-particle nozzle, and therefore, if the liquid supply port 61 is configured to be concave from the gas supply port 59, the battery active material is likely to be fixed at the nozzle tip. If the protrusion is minute, sticking cannot be avoided, and if the protrusion amount is too large, atomization performance as a spray nozzle is lowered.

The spray of the coating liquid CL may be sprayed from the upper side to the lower side (top spray) or from the lower side to the upper side (bottom spray) in the fluidized tank 43 shown in FIG. Any method of spraying toward the tangential direction (tangential spray) may be used, and may be selected in consideration of the particle diameter of the core particle 31. In general, core particles 31 made of a positive electrode active material having a particle diameter of the order of a few tens of μm or less and a true specific gravity of 1 g / cm ³ or more are coated with droplets on the particle surface while imparting dispersion force to the powder. Preferred spray positions, i.e. tangential or bottom spray. Further, the coating liquid CL may be sprayed by combining these methods.

  The liquid feeding speed of the coating liquid CL to be sprayed is closely related to the temperature control in the fluidized tank 43 and affects the coating. The temperature of the exhausted air is set in consideration of the balance between the feeding speed of the coating liquid CL of the sprayer 49 and the flow rate and temperature of the air flow A, and is preferably about 30 ° C to 45 ° C. In the case of using an aqueous slurry, it is more desirable that the coating liquid CL is sprayed so as to be at least 2 ° C. or more, preferably 3 ° C. or more higher than the adiabatic saturation temperature. If the exhaust temperature is too high, before the coating liquid CL adheres to the powder, the solvent in the droplets of the coating liquid CL dries, and the conductive material particles 33 do not bind to the powder. The wearing efficiency is reduced. On the other hand, if the exhaust temperature is lower than the adiabatic saturation temperature, the core particles 31 in the fluidized tank 43 are too wet, the fluidity is lowered, and aggregation due to poor fluid flow may occur. Therefore, it is desirable to adjust the liquid feeding speed of the coating liquid CL to be sprayed so that the exhaust temperature is 3 to 12 ° C. higher than the adiabatic saturation temperature. For example, when the temperature of the fluidized air A is 80 ° C, the exhaust temperature is suitably about 30 ° C to 40 ° C.

  Next, the solvent is dried from the core particles 31 to which the conductive material particles 33 are attached (drying step). In this case, it is preferable to perform drying simultaneously using the air flow A in the fluidizing step. The air flow A supplied by the exhaust fan 45 is high temperature, specifically, preferably 40 ° C to 120 ° C, more preferably 60 ° C to 110 ° C, and 70 ° C to 100 ° C. Even more preferably. By adjusting the flow rate of the air flow A, the flow state can be adjusted.

  If the fluidized bed coating apparatus used in the method for producing the positive electrode powder forms the fluidized bed 47 of the powder made of the positive electrode active material and can spray the coating liquid CL containing the binder, the fluidized bed, the rolling fluidized bed, the jet flow Even in a composite fluidized bed equipped with a bed or a crushing mechanism, each apparatus can be used without any particular limitation. In consideration of the particle size of the target particles, an optimum apparatus can be selected. However, in the case of fine particles having a particle size of a positive electrode active material of 10 or less microns, a jet type or a rolling type A fluidized bed is more desirable.

  A filter 65 for separating the powder made of the positive electrode active material and the fluidized air stream A is installed in the upper part of the apparatus. The filter 65 may be a known filter such as a polyester woven fabric, a polyester nonwoven fabric, or a metal filter. Any material that satisfies the above functions can be used without being limited to the material or shape. The optimum filter 65 can be selected in consideration of the particle diameter of the powder made of the positive electrode active material. However, since the positive electrode active material generally contains many particles of less than 10 μm, it is preferable to use a metal filter.

  Further, a removal mechanism 67 for removing powder made of the positive electrode active material collected by the filter 65 from the filter 65 is provided. The powder removed from the filter 65 by the removal mechanism 67 is returned to the spray zone where the coating liquid CL is sprayed. By repeating such circulation, the conductive material particles 33 can be evenly attached to the core particles 31. At this time, the drop-off mechanism 67 can select an optimum one in consideration of the material or shape of the filter 65. For example, a shaking method or a pulse jet method by jetting instead of high-pressure air can be used. Particularly preferred in the handling of the positive electrode active material is a pulse jet system that can be used with a metal filter.

  As schematically shown in FIG. 1, the particles of the positive electrode powder 21 produced by fluidized bed coating are electrically conductive particles made of carbon on the surfaces of the core particles 31 that are the positive electrode active material by fluidized bed coating. 33 is attached with a uniform distribution. As a result, a strong conductive network is formed between the positive electrode active materials, so that a battery having high output characteristics can be manufactured at low cost using the positive electrode powder 21. When this positive electrode powder 21 is used, the positive electrode mixture slurry is prepared by an aqueous solvent without using an organic solvent that is required when a positive electrode active material and carbon are simply mixed to produce a positive electrode mixture slurry. Can be created.

<2. Negative electrode>
The alkaline secondary battery of the present invention is characterized in that the negative electrode active material does not contain cobalt. Specifically, a hydrogen storage alloy represented by chemical formula 1: RE _1-x Mg _x Ni _y Al _z ( RE is a rare earth element; preferably 0.05 ≦ x ≦ 0.3, 2.9 ≦ y ≦ 4.4, 0.1 ≦ z ≦ 0.3. As described above, for industrial applications, it is necessary to focus on high output characteristics and long cycle life characteristics. Therefore, 3.0 ≦ y + z ≦ 4.7 is preferable, and 3.9 ≦ y + z ≦ 4.2. It is more preferable.

The crystal structure of the hydrogen storage alloy of Formula 1 varies depending on the magnitude of “y + z”, which is the ratio of Ni and Al. Here, if MgNi ₂ = L, CaCu ₅ type lattice (crystal structure of hydrogen storage alloy Mm (Ni, Co, Mn, Al) ₅ used in the conventional negative electrode for nickel-hydrogen battery) = C, y + z = 3, the crystal phase of PuNi ₃ type or CeNi ₃ type laminated with the “LCLC” pattern becomes the main phase, but when y + z = 3.5, the Gd ₂ Co ₇ type or Ce laminated with the “LCCLCC” pattern. ₂ Ni ₇ type phase becomes the main phase.

When y + z> 3.5, a Ce ₅ Co ₁₉ type or a Pr ₅ Co ₁₉ type laminated with an “LCCCLCCC” pattern is also included, and a plurality of types of laminated crystal phases are mixed. Further, when y + z> 3.7, not only the laminated phase but also the CaCu ₅ type phase is mixed. When the Ni content in the hydrogen storage alloy is large, the hydrogen dissociation pressure is easily adjusted to a high value, and a high discharge voltage is easily obtained when a sealed battery is configured. The value of “y + z” that can obtain a high discharge voltage is preferably 3.9 or more and 4.7 or less. The CaCu ₅ type hydrogen storage alloy needs to contain Co to some extent in order to suppress pulverization at the time of charge and discharge and to prolong the life, but when a mixed phase with the laminated phase is formed, Even if it is not contained, it is possible to extend the life.

However, if the value of “y + z” increases too much, the proportion of the CaCu ₅ type crystal phase becomes too large, approaching the properties of a hydrogen storage alloy consisting only of the CaCu ₅ type crystal phase, and the cycle life also decreases. Considering both high voltage discharge and cycle life characteristics, the value of “y + z” is more preferably 3.9 or more and 4.2 or less.

By mixing a hydrogen storage alloy powder obtained by pulverizing an ingot-shaped hydrogen storage alloy, a binder, and a conductive powder added as necessary, a paste-like composite material is obtained. The mixture is applied or filled into a current collector, dried, and then rolled using a roller press, whereby a negative electrode made of a hydrogen storage alloy used in the present invention can be produced.
Specific examples of current collectors are punched metal, expanded metal, two-dimensional substrates such as wire mesh, foil-like substrates, plate-like substrates, foamed metal substrates, mesh-like sintered fiber substrates, woven fabrics or non-woven fabrics with tertiary plating Foam nickel used in the original substrate and the nickel positive electrode.

  Specific examples of the binder are sodium polyacrylate, polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), styrene butadiene rubber (SBR), and polyvinylidene fluoride (PVdF). Such a binder is preferably blended at a ratio of 0.1 to 5% by mass with respect to the mass of the hydrogen storage alloy.

  The conductive auxiliary agent may be a conductive powder. Specific examples of the conductive aid are a carbon material such as graphite powder or carbon black, or a metal powder such as nickel or copper. Such a conductive additive is preferably blended at a ratio of 0.1 to 5% by mass with respect to the mass of the hydrogen storage alloy.

In addition, since PTFE or carbon material exhibits hydrophobicity, it is added to the composite material of the hydrogen storage alloy negative electrode or applied to the negative electrode surface, so that solid phase-liquid phase-gas phase can be formed on the negative electrode surface. A phase interface is formed. This three-phase interface is suitable for the absorption reaction of oxygen gas generated from the positive electrode during overcharge (2MH + 1 / 2O ₂ → M + H ₂ O; M is a negative electrode active material, and MH is a negative electrode active material that occludes hydrogen). To promote.

<3. Electrolyte>
The alkaline secondary battery of the present invention uses an electrolytic solution made of an alkaline aqueous solution. As the electrolytic solution, an aqueous solution of KOH, NaOH, LiOH, or a mixed aqueous solution of two or more of these may be used. Among the three types, the aqueous solution of KOH has the highest ionic conductivity, and the 6-8N aqueous solution shows particularly high conductivity. In order to suppress the generation of oxygen generated in competition with the charging reaction and improve the charging efficiency, it is effective to appropriately add NaOH or LiOH. LiOH is highly effective in suppressing oxygen generation and improving charging efficiency, but the amount dissolved in an aqueous KOH solution is not so large. If the application requires an improvement in charging efficiency, it is necessary to supplement not only LiOH but also NaOH.

  A preferred example of the electrolytic solution is an aqueous solution containing KOH and LiOH. The concentration of KOH is preferably 6 to 8N, and the concentration of LiOH is preferably 0.05 to 2N. When LiOH is added to the KOH aqueous solution, the charging efficiency is improved and the electrode is hardly deteriorated, which is effective in improving the cycle life. However, since the conductivity is lower than that of KOH or NaOH, there is a possibility that the high output characteristics are deteriorated.

  When high output characteristics are important, the addition amount of LiOH may be reduced, or NaOH may be added instead of adding LiOH. In this case, the concentration of KOH is preferably 3 to 8N, the addition amount of NaOH is preferably 0.1 to 3N, and the concentration of lithium hydroxide is preferably 0 to 1N.

<4. Separator>
The separator material is not particularly limited as long as it is a material having electrical insulation properties, liquid replacement properties, and gas permeability, and also having alkali resistance and oxidation resistance. A polypropylene non-woven fabric whose hydrophilicity has been improved by sulfonation can be suitably used. About the polymer used as a material, in addition to polypropylene, for example, polyethylene, polyvinyl alcohol, ethylene vinyl alcohol, ethylene vinyl acetate, styrene-butylene-ethylene-styrene copolymer, polyvinylidene fluoride, polytetrafluoroethylene, polyethersulfone, or Polysulfone can also be used. As a form of the separator, in addition to the nonwoven fabric, a woven fabric, a microporous film, or a film can be used. A separator configured using a plurality of polymer materials can also be used.

<5. Battery configuration>
It is necessary to change the specifications of the positive electrode, the negative electrode, the electrolytic solution, or the separator depending on the application. For example, industrial batteries generally have to withstand long-term use of about 10 years while driving large vehicles. That is, it is necessary to improve both cycle life and high output characteristics.

  In order to improve the cycle life, it is preferable to use an aqueous KOH solution in which LiOH is dissolved to 1.5 mol / L as the electrolytic solution. However, in this case, the discharge voltage is lowered as compared with the case where KOH alone is used as the electrolytic solution, and the discharge voltage of 1C may be lower than 1.2V.

Therefore, it is preferable to adjust the alloy composition of the negative electrode in order to supplement high output characteristics. Specifically, Formula _1: if in the _{RE 1-x Mg x Ni y} Al z 3.9 ≦ y + z ≦ 4.2 in the hydrogen-absorbing alloy represented by while also maintaining battery life, shown in Figure 5 below As described above, high output characteristics can be improved.

  In addition, the battery performance can be adjusted by a method in which a part of nickel sites of nickel hydroxide, which is a positive electrode active material, is replaced with another element. Specifically, the other elements are (1) zinc or cobalt having an effect of improving charging efficiency; (2) aluminum or manganese having an effect of improving the theoretical capacity of nickel hydroxide by 1.2 to 1.5 times: .

  When zinc or cobalt is internally added to nickel hydroxide, the generation of oxygen competing with the charging reaction can be suppressed, and the charging efficiency can be improved. As a result, deterioration of the battery is suppressed, and long-term performance maintenance is possible. When the battery temperature does not rise so much and charging / discharging is repeated at around room temperature, the effect of suppressing deterioration and maintaining the performance can be sufficiently obtained by adding 0.1 to 5 mol% of zinc. In this case, cobalt does not need to be added, but when the battery temperature is 40 ° C. or higher, a small amount of cobalt is added together with zinc to obtain a deterioration suppressing effect and a performance maintaining effect. A cobalt addition amount of 0.1 to 1 mol% is sufficient.

  In this case, cobalt is incorporated in the crystal of nickel hydroxide and does not elute into the electrolytic solution like the cobalt compound which is a conductive additive coated on the surface of nickel hydroxide. Therefore, the alkaline secondary battery of the present invention can employ nickel hydroxide internally added with cobalt as the positive electrode active material.

  When aluminum or manganese is added, nickel hydroxide changes from a normal β-type crystal structure to an α-type crystal structure. The theoretical capacity of normal β-type nickel hydroxide is 289 mAh / g, but the theoretical capacity of α-type nickel hydroxide may increase to about 350 to 430 mAh / g. If this α-type nickel hydroxide is used, the capacity of the battery can be increased. If α-type nickel hydroxide is used, it is possible to reduce the amount of nickel hydroxide charged into the base material and produce a high output type thin electrode, while suppressing the decrease in electrode capacity.

  Conventionally, by adopting a thick separator, self-discharge caused by element elution from the electrode and formation of a short-circuit path due to reprecipitation of the eluted element has been prevented to some extent. However, in a cobalt-free battery, since there is no element that forms such a path, the separator can be made thin. In a conventional industrial battery, a separator having a thickness of 200 to 500 μm was used. However, in the alkaline secondary battery of the present invention, it is considered that the separator can be thinned to 150 μm or less. Since the number of electrodes that can be mounted increases as the separator becomes thinner, it is possible to increase the capacity of the battery (improve the volume energy density). As the distance between the positive electrode and the negative electrode is shortened, the charge / discharge reaction proceeds smoothly, which is considered to lead to an improvement in high output characteristics.

[Production example of positive electrode]
(1. Preparation of powder for cobalt-free positive electrode)
Carbon black with a graphitization degree (G value) analyzed by Raman spectroscopy of 0.33 is used as conductive material particles made of carbon, and this is mixed with an ethylene vinyl acetate binder to prepare a carbon black dispersion (coating liquid). did. This carbon black dispersion was sprayed onto nickel hydroxide particles in a rolling fluidized bed coating apparatus to perform carbon coating treatment. A specific manufacturing method will be described below.

5 parts by weight of a mixture of 50% by mass of ethylene vinyl acetate resin and 50% by mass of carbon is preliminarily ground in a mortar and dissolved in 95 parts by weight of xylene heated at 60 ° C. The coating liquid CL of the conductive material particles 33 containing was prepared. Next, using a fluidized bed coating device (MP-01, manufactured by Paulec Co., Ltd.), a wet laser diffraction / scattering method (manufactured by MICROTRAC, MT3000II) in advance, the refractive index of the average particle of all substances 1.81, the refraction of the dispersion solvent 1000 g of a positive electrode active material (nickel hydroxide, D50 = 12 μm) whose particle size distribution was measured at a rate of 1.333 was added. The core particles made of nickel hydroxide were rolled and fluidized by a fluidized air at 0.25 m ³ / min heated to 90 ° C. and a rotor at the bottom of the fluidized bed rotated at 300 min ⁻¹ .

  As the mesh of the fluidized bed coating apparatus, a metal mesh having a plain woven weave, 110 mesh and a filtration particle size of 150 μm was used. A cylindrical twilled weave 2 μm metal filter was used. Discharge was performed by jetting 0.5MPa of compressed air from the top of the filter in 0.2 second intervals at intervals of 3 seconds using the pulse jet method.

  Subsequently, while the prepared coating solution CL of the conductive auxiliary agent containing the binder was stirred using a magnetic Kustarr (manufactured by Yamato Kagaku Co., Ltd., MAG MIXER), 2 by a tubing pump (505S manufactured by Watson Marlo). The solution was fed at a rate of ~ 3 g / min, misted with a mist generator (manufactured by Schlick, 970-S23), and sprayed into the fluidized bed by tangential spray.

  At this time, the air flow rate (atomizing air) for misting the coating liquid CL was set to 45 L / min. The temperature of the air (exhaust) separated from the powder made of the positive electrode active material and exhausted outside the apparatus was 37 to 45 ° C. The prepared coating liquid CL was sprayed, and the coating was terminated when the weight ratio of carbon was 6 mass% with respect to the raw material powder charged.

  FIG. 4 shows an electron micrograph (SEM photograph) of the nickel hydroxide powder (carbon-coated nickel hydroxide) coated on the surface thus produced. As shown in FIG. 4, a part of the surface of the nickel hydroxide core particles was covered with conductive material particles having a particle size smaller than the core particles. The surface coverage of the core particles with the conductive material particles measured from the electron micrograph was about 30 to 50%.

(2. Preparation of cobalt-free positive electrode)
The obtained carbon-coated nickel hydroxide was dispersed in a CMC aqueous solution to prepare a slurry having a water content of 20% by mass. This slurry is filled in a foamed nickel current collector adjusted to a thickness of 0.65 mm, then dried, and pressed to a thickness of 0.35 mm using a roller press to obtain a cobalt-free positive electrode. It was. When the weight of the foamed substrate was subtracted from the electrode weight and the positive electrode capacity was estimated, it was 580 mAh.

(3. Preparation of cobalt-coated nickel hydroxide positive electrode)
Add cobalt hydroxide, CMC, and PTFE to 3%, 0.2%, and 2% by weight of commercially available cobalt-coated nickel hydroxide (CZ manufactured by Tanaka Chemical Research Laboratory), and add water to add 20% water. % Slurry was prepared. In the same manner as in the method for producing a cobalt-free positive electrode, a foamed nickel base material was filled with this slurry and pressed to obtain a cobalt-coated nickel hydroxide positive electrode. The capacity of this positive electrode was 600 mAh.

[Example of negative electrode production]
(1. Production of cobalt-free negative electrode 1)

The obtained negative electrode alloy powder, SBR binder, polyacrylic acid soda, CMC thickener, and carbon powder (Ketjen Black) are mixed at a mass ratio of 100: 1.5: 0.5: 0.2: 0.5 did. Ion exchange water was added to the mixture to prepare a slurry having a water content of 22% by mass. This slurry was applied to a punching metal substrate having a thickness of 0.05 mm and dried. Then, it was set as the cobalt free negative electrode 1 by pressing to thickness 0.35mm using a roller press. The weight of the base material was subtracted from the electrode weight, and the negative electrode weight was estimated to be 1750 g / m ² .

  (2. Preparation of cobalt-free negative electrode 2)

  (3. Production of cobalt-free negative electrode 1)

  (4. Preparation of cobalt-containing negative electrode)

  The cobalt-free positive electrode and the cobalt-free negative electrode 1 were arranged via a sulfonated polypropylene nonwoven fabric having a thickness of 120 μm as a separator and wound to obtain an electrode group. This electrode group was disposed in a Sub-C size cylindrical battery case (diameter: 23 mmφ × height: 43 mm). At this time, a polypropylene spacer was inserted into the gap between the cylindrical battery case and the electrode group, and the electrode group was fixed. A sealed battery of Example 1 was obtained by injecting 3.5 g of an electrolyte solution of 6.5M-KOH / 1.5M-LiOH and further sealing the can. The battery capacity of the sealed battery of Example 1 was 760 mAh.

  A sealed battery of Example 2 was obtained in the same manner as in Example 1 except that the cobalt-free negative electrode 2 was used instead of the cobalt-free negative electrode 1. The battery capacity of the sealed battery of Example 2 was 760 mAh.

  A sealed battery of Example 3 was obtained in the same manner as in Example 1 except that the cobalt-free negative electrode 3 was used instead of the cobalt-free negative electrode 1. The battery capacity of the sealed battery of Example 3 was 760 mAh.

  A sealed battery of Comparative Example 1 was obtained in the same manner as in Example 1 except that a cobalt-containing negative electrode was used instead of the cobalt-free negative electrode 1. The battery capacity of the sealed battery of Comparative Example 1 was 760 mAh.

  A sealed battery of Comparative Example 2 was obtained in the same manner as in Example 1 except that a cobalt-coated nickel hydroxide positive electrode was used instead of the cobalt-free positive electrode. The battery capacity of the sealed battery of Comparative Example 2 was 760 mAh.

(Sealed battery test 1 / Charge / discharge test)
A charge / discharge test was performed on the sealed batteries of Examples 1 to 3 and Comparative Example 1. The charge / discharge test was performed in two ways: (a) charge: 1C, 110% / discharge: 1C, final voltage 0.8V; and (b) charge 1C, 110% / discharge: 10C, final voltage 0.6V. The test environment temperature was 25 ° C.

  FIG. 5 shows a graph relating to the charge / discharge cycle test results of the sealed batteries of Examples 1 to 3 and Comparative Example 1. FIG. 5A shows the case of 1C during discharge / end voltage 0.8V, and FIG. 5B shows the case of 10C during discharge / end voltage 0.6V. In both 1C and 10C discharges, the cobalt-free sealed batteries of Examples 1 to 3 (sealed alkaline secondary batteries) exhibited a higher discharge voltage than the sealed battery of Comparative Example 1. The difference was 20 to 40 mV in 1C discharge and reached 0.2V in 10C discharge.

  As shown in FIGS. 5 (a) and 5 (b), a sealed battery using a cobalt-free negative electrode has a substantially equal high discharge voltage when the value of “y + z” of the negative electrode alloy is in the range of 3.9 to 4.7. As shown, there was a tendency for the discharge voltage to increase as the value of “y + z” increases.

(Sealed battery test 2 / cycle characteristic test)
6 shows a graph regarding the cycle characteristics of the sealed batteries of Examples 1 to 3 and Comparative Example 1. FIG. In the sealed battery of Example 1, a decrease in discharge capacity was observed after about 500 cycles. The value of “y + z” of the negative electrode alloy is Example 1 <Example 2 <Example 3, but as the value of “y + z” increases, the number of cycles at which the discharge capacity begins to decrease is observed to decrease. It was.

(Crystal structure analysis of negative electrode alloy)
For the negative electrode alloys used in Examples 1 to 3 and Comparative Example 1, powder X-ray diffraction was performed using X-rays having a wavelength of λ = 0.512 mm using the beam line BL19B2 of the high-intensity synchrotron radiation facility Spring-8. The pattern was measured. The alloy powder for measurement was enclosed in a Lindeman glass capillary (0.2 mmφ).

When the crystal structure analysis by the Rietveld method was performed, Examples 1 to 3 showed the intensity of the diffraction peak by assuming three types of CaCu ₅ type phase, Ce ₅ Co ₁₉ type phase and Pr ₅ Co ₁₉ type phase. It was confirmed that the shape could be accurately reproduced. Similarly, the alloy of Comparative Example 1 could be reproduced with a single phase of CaCu ₅ type phase. The weight fraction of each phase was derived by crystal structure analysis.

FIG. 7 shows the type and amount (mass%) of the laminated phase and the conventional alloy phase contained in each negative electrode alloy. From FIG. 7, it was confirmed that the ratio of the CaCu ₅ type crystal phase which is a conventional alloy phase increases as the value of “y + z” of the cobalt-free negative electrode alloy used in the example increases. For this reason, as the value of “y + z” increases, the properties of the cobalt-free negative electrode alloy approach those of a conventional CaCu ₅ type crystal phase, and since it does not contain Co, pulverization proceeds by charge / discharge. And it was inferred that the cycle life tends to be reduced.

(Sealed battery test 3 / self-discharge test)
For the sealed batteries of Example 1 and Comparative Example 1, the charge / discharge cycle was repeated 50 times. The charging conditions were 1C and 110%, the discharging conditions were 1C and the final voltage was 0.8V. The test environment temperature was 25 ° C. After that, (1) Charging at 1C, 110% at an environmental temperature of 25 ° C; (2) Removing the terminal and storing it for one week at an environmental temperature of 45 ° C; (3) 1C at an environmental temperature of 25 ° C, final voltage 0.6V The self-discharge amount of the sealed battery was confirmed.

FIG. 8 shows the discharge curves of the sealed batteries of Example 1 and Comparative Example 1 at the time point (3). For Example 1, the discharge curve after 10 minutes from the charging of (1) is also shown in FIG. As shown in FIG. 8, the sealed battery of Example 1 showed a higher discharge capacity. Since both the sealed batteries of Example 1 and Comparative Example 1 were placed in a high temperature of 45 ° C., a part of the positive electrode active material was changed from nickel oxyhydroxide (NiOOH) in a charged state to nickel hydroxide (NiOOH) in a discharged state ( It was speculated that the return to Ni (OH) ₂ ) was the main cause of the decrease in discharge. In the sealed battery of Comparative Example 1, since the cobalt eluted from the negative electrode alloy re-deposited on the separator during the charge / discharge of 50 times and during storage at 45 ° C., a micro short circuit path was formed. It was assumed that the self-discharge amount was larger than that of the sealed battery.

(Sealed battery test 4 / cycle endurance test during overcharge)
Next, using the sealed batteries of Example 1 and Comparative Example 2, a cycle durability test during overcharge was performed. The charging conditions were 0.9 hour at 1C and 2 hours at 0.3C, and a total of 150% was charged. The discharge conditions were 1C, a final voltage of 1V, 0.2C every 50 cycles, and a final voltage of 1.0V. The test environment temperature was 25 ° C.

  FIG. 9 shows a graph relating to the cycle durability characteristics of the sealed batteries of Example 1 and Comparative Example 2. Conventionally, it is known that if overcharge is performed when carbon is used as a conductive additive, the carbon is oxidized and changed to a gas such as carbon dioxide, and the performance of the positive electrode is significantly reduced. However, from FIG. 9, the sealed battery of Example 1 using nickel hydroxide with oxidation-resistant carbon as a conductive additive as the positive electrode material is Comparative Example 2 using conventional cobalt-coated nickel hydroxide as the positive electrode material. Compared with the closed type battery, the capacity retention rate was almost the same.

(Sealed battery test 5 / High rate discharge test)
The sealed batteries of Example 1 and Comparative Example 2 were subjected to a high rate discharge test. The high rate discharge test was performed under the conditions of charge: 1C, 110% / discharge: 10C, final voltage: 0.6V. The test environment temperature was 25 ° C.

  FIG. 10 shows a graph relating to the high rate discharge test of the sealed batteries of Example 1 and Comparative Example 2. As shown in FIG. 10, the sealed battery of Example 1 using a cobalt-free positive electrode exhibits a higher voltage than the sealed battery of Comparative Example 2 using a cobalt-coated nickel hydroxide positive electrode. Was confirmed.

[Example 4]
An open type battery of Example 4 was obtained using the cobalt-free positive electrode, the cobalt-free negative electrode 1, the same separator as in Example 1, and the same electrolyte as in Example 1. The battery capacity of the open type battery of Example 4 was 120 mAh.

[Comparative Example 3]
An open-type battery of Comparative Example 3 was obtained using the cobalt-coated nickel hydroxide positive electrode, the cobalt-free negative electrode 1, the same separator as in Example 1, and the same electrolytic solution as in Example 1. The battery capacity of the open type battery of Comparative Example 3 was 120 mAh.

(Open battery test 1 / Forced short circuit test)
Using the open type batteries of Example 4 and Comparative Example 3, a forced short circuit test was performed. First, (1) charging was performed under the conditions of 0.25C and 120%; and (2) discharging was performed under the conditions of 0.25C and a final voltage of 1.0V. The environmental temperature during charging and discharging was 25 ° C. Thereafter, (3) the positive electrode terminal and the negative electrode terminal were short-circuited and stored in a constant temperature bath at 45 ° C. for a certain number of days.

  FIG. 11 shows a graph plotting the relationship between the short circuit days ((3) storage days) and the capacity retention rate after 45 ° C. storage for the open batteries of Example 4 and Comparative Example 3. As shown in FIG. 11, the open type battery of Comparative Example 3 using the cobalt-coated nickel hydroxide positive electrode has a capacity retention rate that decreases as the number of short-circuit days increases, and the capacity maintenance rate after storage for 6 weeks is initial. Of 83%. On the other hand, the open-type battery of Example 4 using a cobalt-free positive electrode had little decrease in capacity, and the capacity retention rate after storage for 6 weeks was 96% of the initial stage.

(Open battery test 2 / Forced overdischarge test)
For the open batteries of Example 4 and Comparative Example 3, a forced overdischarge test was performed. First, (1) the battery was charged at 0.25C, 120%; and (2) the battery was discharged at 0.25C, 10 hours. The steps (1) and (2) were repeated, and discharging corresponding to 200% of the battery capacity was performed. The environmental temperature during charging and discharging was 25 ° C.

  FIG. 12 shows the charge / discharge curves of the open batteries of Example 4 and Comparative Example 3 in the next charge / discharge cycle in which discharge corresponding to 200% of the battery capacity was performed. As shown in FIG. 12, the discharge capacity of the open type battery of Comparative Example 3 was significantly reduced to the initial 39%. On the other hand, the open type battery of Example 4 had an initial discharge capacity of 82% even in the next cycle after forced overdischarge.

  When the positive electrode and the negative electrode are short-circuited and kept at a high temperature, or when forced overdischarge is performed, the cobalt oxyhydroxide that has formed the conductive network is reduced to cobalt hydroxide. Cobalt hydroxide has low conductivity and does not function sufficiently as a conductive network, and part of it is eluted into the electrolyte. When charging again, a part of cobalt reprecipitates to reconstitute the conductive network. However, some cobalt does not completely return to the original state but reprecipitates on the separator. For this reason, it is guessed that deterioration of battery performance, such as a reduction in battery capacity, is caused.

  As shown in FIGS. 8, 11, and 12, when cobalt is contained in either the positive electrode or the negative electrode, cobalt elution into the electrolytic solution and cobalt reprecipitation during charging Is repeated, the capacity is deteriorated and the self-discharge amount is increased. Large industrial batteries used for public transportation such as buses or trains, driving large machinery such as gantry cranes and using regenerative energy, or for peak cuts in natural energy generation such as wind power or solar power, Compared with small consumer batteries, it is assumed that it will be used for a long time in harsh conditions, such as high output characteristics, high capacity characteristics, cycle life characteristics, low self-discharge characteristics, overdischarge resistance and overcharge resistance, We have to meet more demands.

  As a conductive aid for improving the utilization rate of the positive electrode and an anti-dusting agent for the negative electrode alloy, cobalt is conventionally essential for the active material, but the cobalt-free alkaline secondary battery of the present invention includes a cobalt-free positive electrode and a cobalt-free positive electrode. By combining with a cobalt-free negative electrode, not only can the active material of the positive electrode and negative electrode be replaced with a cobalt-free alternative material, but also the elution of electrode constituent elements is suppressed, and the self-discharge suppression function and overdischarge resistance are greatly improved. It is possible.

  The cobalt-free alkaline secondary battery of the present invention is useful as a secondary battery for large industries in various technical fields.

21: Powder for positive electrode (carbon coated positive electrode active material)
31: Core particles 33: Conductive material particles made of carbon 37: Reaction section 41: Fluidized bed coating device 43: Fluidized tank 45: Air exhauster 47: Fluidized bed 49: Sprayer 51: Disk rotor 53: Air dispersion plate 55: Impeller 57 : Nozzle 59: Gas supply port 61: Liquid supply port 65: Filter 67: Removal mechanism A: Air flow CL: Coating liquid

Claims (5)

A positive electrode having a positive electrode material containing no cobalt as a conductive additive;
A negative electrode having a negative electrode active material not containing cobalt;
An electrolyte solution comprising an alkaline aqueous solution;
A separator;
An alkaline secondary battery comprising:   The alkaline secondary battery according to claim 1, wherein the positive electrode material is a positive electrode active material having a surface coated with carbon.   The alkaline secondary battery according to claim 1 or 2, wherein the positive electrode material is nickel hydroxide having a surface coated with carbon. The negative electrode active material is represented by chemical formula 1: RE _1-x Mg _x Ni _y Al _z.
The alkaline secondary battery according to any one of claims 1 to 3, which is a hydrogen storage alloy represented by:
Where RE is a rare earth element;
0.05 ≦ x ≦ 0.3, 2.9 ≦ y ≦ 4.4, and 0.1 ≦ z ≦ 0.3.   The alkaline secondary battery according to claim 1, wherein the electrolytic solution is an aqueous solution containing potassium hydroxide and lithium hydroxide.