Negative electrode material for nickel-hydrogen battery and negative electrode composition containing the same

Abstract

To provide an anode material for nickel metal hydride batteries and the like, which is abundant as a resource, lightweight, and has a large charge-discharge capacity per unit volume.SOLUTION: There is provided an anode material for nickel metal hydride batteries that is a carbon material, in which BET specific surface area per unit volume expressed as BET specific surface area [m2 / g]×bulk density [g / cm3] is 700 m2 / cm3 or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The technology disclosed in this specification relates to a negative electrode material for a nickel - hydrogen battery, a composition for a negative electrode, and the like.

Background Art

[0002] A nickel - hydrogen secondary battery (hereinafter, also simply referred to as a nickel - hydrogen battery) is a secondary battery that uses a nickel oxide compound such as nickel hydroxide for the positive electrode and a hydrogen storage alloy for the negative electrode. The nickel - hydrogen battery uses a highly safe alkaline aqueous solution as an electrolyte. Therefore, the nickel - hydrogen battery is widely used as an alternative to batteries for hybrid vehicles and dry batteries from the viewpoints of environmental performance, high - speed charge and discharge, cycle life, and the like.

[0003] The hydrogen storage alloy used as the negative electrode material of a nickel - hydrogen battery takes in protons and electrons in water as hydrogen atoms during charging and stores them, and releases protons and electrons during discharging. As the hydrogen storage alloy, rare - earth metal - based alloys typified by LaNi5 - based alloys are used. However, rare - earth metals are difficult to secure resources and are costly. There is also a problem of high equilibrium hydrogen pressure.

[0004] On the other hand, as a material for the negative electrode of a capacitor that exhibits the same power storage function as a nickel - hydrogen battery, activated carbon that is rich in resources, lightweight, and has a large specific surface area is known. For example, a hybrid capacitor using nickel hydroxide for the positive electrode and activated carbon for the negative electrode is disclosed (Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, carbon materials typified by activated carbon generally have a low bulk density, and when the carbon material is filled and used in a battery container, the charge and discharge capacity per unit volume was not sufficient.

[0007] The technology disclosed in this specification provides a negative electrode material for a nickel-hydrogen battery, etc., which is rich as a resource, lightweight, and has a large charge and discharge capacity per unit volume.

Means for Solving the Problems

[0008] This specification discloses a negative electrode material for a nickel-hydrogen battery, a method for manufacturing the negative electrode material, a composition for a negative electrode of a nickel-hydrogen battery, a negative electrode of a nickel-hydrogen battery, a nickel-hydrogen battery, etc.

[0009] The negative electrode material is a carbon material having a BET specific surface area per unit volume [m 2 / g] × bulk density [g / cm 3 of 700 m 2 / cm 3 or more, and a bulk density of 0.4 g / cm 3 or more and 1.0 g / cm 3 or less. By using a carbon material having a BET specific surface area per unit volume within the above range and a bulk density within the above range as the negative electrode material of a nickel-hydrogen battery, a nickel-hydrogen battery having a large charge and discharge capacity per unit volume can be provided. In addition, since the carbon material is rich as a resource, lightweight, and easily available, a compact nickel-hydrogen battery can be provided continuously and at low cost.

[0010] This specification discloses a composition for a negative electrode of a nickel-hydrogen battery. The composition for a negative electrode contains the above carbon material. According to the composition for a negative electrode, a lightweight and compact nickel-hydrogen battery having a large charge and discharge capacity per unit volume can be provided continuously and at low cost.

[0011] This specification discloses a method for manufacturing a negative electrode material for a nickel-hydrogen battery. The manufacturing method uses, as a raw material, a BET specific surface area per unit mass of 700 m 2A raw material preparation step of preparing a carbon material having a specific surface area of 700 m2 / g or more, and a pressing step of pressing the carbon material to make the BET specific surface area per unit volume represented by [BET specific surface area [m2 / g]] × [bulk density [g / cm3]] 700 m2 / cm3 or more. By providing these steps, it is possible to continuously and inexpensively provide a negative electrode material that can contribute to a nickel-hydrogen battery having a large charge / discharge capacity per unit volume, being lightweight and compact. 2 / g] × bulk density [g / cm 3 so that the BET specific surface area per unit volume is 700 m 2 / cm 3 or more. By providing these steps, it is possible to continuously and inexpensively provide a negative electrode material that can contribute to a nickel-hydrogen battery having a large charge / discharge capacity per unit volume, being lightweight and compact.

[0012] This specification discloses a negative electrode of a nickel-hydrogen battery. The negative electrode contains the above-described composition for a negative electrode. Further, this specification discloses a nickel-hydrogen battery. The nickel-hydrogen battery includes a positive electrode, an electrolytic solution, a negative electrode, and a separator. The negative electrode contains the above-described composition for a negative electrode. According to the nickel-hydrogen battery including such a negative electrode, it is lightweight and compact, and it is possible to continuously increase the charge / discharge capacity per unit volume at low cost.

[0013] This specification provides a vehicle including the above-described nickel-hydrogen battery. According to such a vehicle, it is possible to provide a vehicle including a battery that is low-cost, lightweight, and compact.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0015] The negative electrode material of the nickel-hydrogen battery disclosed in this specification is, as described above, a carbon material, with a BET specific surface area of 700 m 2 / cm 3 or more per unit volume, and a bulk density of 0.4 g / cm 3 or more and 1.0 g / cm 3 or less. By having such characteristics, when used as a negative electrode material to form the negative electrode of a nickel-hydrogen battery, the charge-discharge capacity per unit volume of the nickel-hydrogen battery can be increased.

[0016] Although not restricting the disclosure of this specification, the following inferences can be made about the effects of the negative electrode material disclosed in this specification. In FIG. 1, as an example of the negative electrode material disclosed in this specification, activated carbon is exemplified to show the structural model of the negative electrode material disclosed in this specification. As shown in FIG. 1(a), it is considered that conventional activated carbon has graphene alone or stacked in a small number, for example, 10 layers or less, with individual graphene separated from each other. As a result, it is considered that relatively large gaps are formed between individual graphene. For this reason, the bulk density [g / cm 3 is low. In contrast, the activated carbon as the negative electrode material disclosed in this specification is considered to have a structure in which the gaps existing between individual graphene of conventional activated carbon are compressed, as shown in FIG. 1(b). By adopting such a structure with compressed gaps, the graphene existing per unit volume becomes densified. As a result, it is considered that the bulk density increases and the BET specific surface area per unit volume increases. Also, due to the proximity of graphene, the interaction between molecules (for example, hydrogen molecules and proton ions) adsorbed between them also increases, and it is considered that the electrochemical characteristics related to charge and discharge are also improved.

[0017] Hereinafter, the negative electrode material of the nickel-hydrogen battery disclosed in this specification, the manufacturing method of the negative electrode material, the composition for the negative electrode of the nickel-hydrogen battery containing the negative electrode material, the negative electrode containing the composition for the negative electrode, the nickel-hydrogen battery provided with the negative electrode, and vehicles provided with the nickel-hydrogen battery will be described.

[0018] In addition, in this specification, descriptions of "above" and "below" with respect to numerical values include the meanings of "more than" and "less than", respectively. Therefore, for example, in this specification, when it is described as 0.4 g / cm 3 or more and 1.0 g / cm 3 or less, in addition to the literal meaning, it includes aspects of more than 0.4 g / cm 3 and less than 1.0 g / cm, more than 0.4 g / cm 3 and less than 1.0 g / cm, more than 0.4 g / cm 3 and less than 1.0 g / cm, and more than 0.4 g / cm 3 and less than 1.0 g / cm. 3 3 3 is included.

[0019] <Negative electrode material of nickel-metal hydride battery> The negative electrode material disclosed in this specification is a carbon material. The carbon material is not particularly limited. For example, it may include a material having a graphene with a sheet structure of SP 2 bonded carbon atoms at least in part. Such carbon materials include, for example, activated carbon which is a porous material having various forms such as powder form, graphite having single-layer or multiple-layer graphene, graphene fiber such as graphene nanofiber having a fiber structure of the above graphene, carbon nanotube having a tube structure of the above graphene, carbon nanohorn having a conical structure of the above graphene, graphene porous material such as graphene mesoporous having a pore wall of the above graphene, carbon nanorod having graphene, graphene nanoribbon, and the like. From the viewpoint of a large BET specific surface area, activated carbon can be used.

[0020] The carbon material may be one in which some of the carbon atoms are substituted with other atoms than carbon atoms, or one in which other atoms or molecules are intercalated between the lattice spaces or layers. In addition, the carbon atoms of the carbon material may be those in which functional groups are introduced by known treatments.

[0021] In order to promote the adsorption of hydrogen molecules, etc. by bringing the graphene layers or the distance between the walls closer by pressurizing the carbon material described above, for example, a binder for maintaining and ensuring the proximity effect by pressurization may be effective. Such a binder may be added in the manufacturing process of the negative electrode material. In that case, the negative electrode material can contain in advance, for example, compounds such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-diene copolymer, styrene-butadiene rubber, carboxymethyl cellulose, and acrylic resin as binders for the carbon material.

[0022] The binder can be, for example, 0.01% by mass or more based on the total mass of the carbon material and the binder. The lower limit can also be, for example, 0.05% by mass or more, and also, for example, 0.1% by mass or more, and also, for example, 0.5% by mass or more, and also, for example, 1% by mass or more, and also, for example, 2% by mass or more, and also, for example, 3% by mass or more. The upper limit is, for example, 10% by mass or less based on the above total mass. This is because the binder has no charge-discharge ability, and if the content ratio of the binder exceeds 10% by weight, the charge-discharge amount of the negative electrode material decreases. The upper limit can also be, for example, 8% by mass or less, and also, for example, 6% by mass or less, and also, for example, 5% by mass or less. The content range of the binder can be set by appropriately combining the above-described lower limit and upper limit. For example, it is 0.2% by mass or more and 10% by mass or less, and also, for example, 2% by mass or more and 8% by mass or less, and also, for example, 2% by mass or more and 6% by mass or less, and also, for example, 2% by mass or more and 5% by mass or less, and also, for example, 2% by mass or more and 4% by mass or less.

[0023] The negative electrode material has a BET specific surface area per unit volume of 700 m 2 / cm 3 or more. In this specification, the BET specific surface area per unit volume is represented by the product of the BET specific surface area of the material [m 2 / g] and the bulk density of the material [g / cm 3 .

[0024] In this specification, the BET specific surface area (hereinafter, also simply referred to as the specific surface area) is the specific surface area measured by the BET adsorption method. The BET adsorption method used in this specification is a method of obtaining the amount of nitrogen adsorbed on a material using the equation of state of a gas from the change in the pressure of nitrogen introduced into the measurement cell of BELSORP-max manufactured by MicrotracBEL Corporation, and calculating the specific surface area of the material from the adsorption isotherm assumed by the BET theory.

[0025] The specific surface area of the negative electrode material is, for example, 700 m 2 / g or more, and for example, 800 m 2 / g or more, and for example, 900 m 2 / g or more, and for example, 1000 m 2 / g or more, and for example, 1100 m 2 / g or more, and 1200 m 2 / g or more, and for example, 1300 m 2 / g or more, and for example, 1400 m 2 / g or more, and for example, 1500 m 2 / g or more, and for example, 1600 m 2 / g or more, and for example, 1700 m 2 / g or more, and for example, 1800 m 2 / g or more, and for example, 1900 m 2 / g or more, and for example, 2000 m 2 / g or more, and for example, 2200 m 2 / g or more, and for example, 2400 m 2 / g or more, and for example, 2600 m 2 / g or more, and for example, 2800 m 2 / g or more. The specific surface area is not particularly limited, but for example, it is 4000 m 2 / g or less, and for example, 3600 m 2 / g or less, and for example, 3400 m 2 / g or less, and for example, 3200 m 2 / g or less, and for example, 3000 m 2is below / g. The suitable specific surface area range can be set by combining the above-mentioned lower limit and upper limit. For example, it can be 700 m 2 / g or more and 3600 m 2 / g or less, etc.

[0026] The negative electrode material preferably has a predetermined bulk density. The bulk density in this specification is a value calculated by forming the material into a disk with a predetermined diameter under a pressure of 0.1 MPa, measuring the height and diameter of the formed carbon material to obtain the volume, and dividing the mass of the used material by the volume.

[0027] The bulk density of the negative electrode material is, for example, 0.40 g / cm 3 or more, and also, for example, 0.50 g / cm 3 or more, and also, for example, 0.60 g / cm 3 or more, and also, for example, 0.70 g / cm 3 or more, and also, for example, 0.80 g / cm 3 or more, and also, for example, 0.90 g / cm 3 or more. Also, because it becomes difficult for hydrogen molecules to penetrate when the interlayer distance of graphene becomes short, the bulk density is, for example, 1.00 g / cm 3 or less, and also, for example, 0.95 g / cm 3 or less, and also, for example, 0.90 g / cm 3 or less, and also, for example, 0.85 g / cm 3 or less, and also, for example, 0.80 g / cm 3 or less, and also, for example, 0.75 g / cm 3 or less, and also, for example, 0.70 g / cm 3 or less, and also, for example, 0.65 g / cm 3 or less, and also, for example, 0.60 g / cm 3 or less, and also, for example, 0.65 g / cm 3 or less, and also, for example, 0.60 g / cm 3 or less, and also, for example, 0.55 g / cm 3The following is true. The range of the suitable bulk density can be set by combining the above-described lower limit value and upper limit value. For example, it can be 0.40 g / cm 3 or more and 1.00 g / cm 3 or less. Also, for example, it can be 0.40 g / cm 3 or more and 0.95 g / cm 3 or less, etc.

[0028] The specific surface area per unit volume of the negative electrode material is 700 m 2 / cm 3 or more. Also, for example, it is 800 m 2 / cm 3 or more. Also, for example, it is 900 m 2 / cm 3 or more. Also, for example, it is 1000 m 2 / cm 3 or more. Also, for example, it is 1100 m 2 / cm 3 or more. The upper limit is not particularly limited. However, due to the relationship between the specific surface area and the bulk density, for example, it is 3000 m 2 / cm 3 or less. Also, for example, it is 2800 m 2 / cm 3 or less. For example, it is 2600 m 2 / cm 3 or less. Also, for example, it is 2400 m 2 / cm 3 or less. Also, for example, it is 2200 m 2 / cm 3 or less. Also, for example, it is 2000 m 2 / cm 3 or less. Also, for example, it is 1800 m 2 / cm 3 or less.

[0029] <Method for manufacturing negative electrode material> The negative electrode material disclosed in this specification is not particularly limited. For example, it can be manufactured by the following method.

[0030] (Raw material preparation step) The method for manufacturing the negative electrode material has a specific surface area per unit mass of 700 m2 The carbon material used as the raw material may be any of various known carbon materials such as the activated carbon constituting the negative electrode material described above.

[0031] The carbon material used as the raw material is not particularly limited, but a carbon material having a larger specific surface area than the specific surface area of ​​the negative electrode material to be obtained can be selected because the specific surface area will decrease due to the subsequent pressurizing step. The specific surface area per unit mass of the carbon material used as the raw material is, for example, 700 m 2 / g or more, and for example, 750m 2 / g or more, and for example, 800m 2 / g or more, and for example, 900m 2 / g or more, and for example, 1000m 2 / g or more, and for example, 1100m 2 / g or more, 1200m 2 / g or more, and for example, 1300m 2 / g or more, and for example, 1400m 2 / g or more, and for example, 1500m 2 / g or more, and for example, 1600m 2 / g or more, and for example, 1700m 2 / g or more, and for example, 1800m 2 / g or more, and for example, 1900m 2 / g or more, and for example, 2000m 2 / g or more, and for example, 2200m 2 / g or more, and for example, 2400m 2 / g or more, and for example, 2600m 2 / g or more, and for example, 2800m 2 The specific surface area per unit mass of the carbon material as the raw material is not particularly limited, but is, for example, 4000 m 2 / g or less, and for example, 3600m 2 / g or less, and for example, 3400m 2It is 3200 m / g or less, and for example, 3200 m / g 2 It is 3000 m / g or less, and for example, 3000 m / g 2 It is 3600 m / g or less. The suitable specific surface area range of the carbon material as the raw material can be set by combining the above-mentioned lower limit value and upper limit value. For example, it can be 750 m / g 2 or more and 3600 m / g 2 or less, etc.

[0032] The carbon material used as the raw material is not particularly limited, but a carbon material with a bulk density smaller than that of the negative electrode material to be obtained, that is, a bulky carbon material, can be selected. This is to improve the bulk density in the subsequent pressing process. The bulk density of the carbon material as the raw material is, for example, 0.10 g / cm 3 or more, and for example, 0.20 g / cm 3 or more, and for example, 0.30 g / cm 3 or more, and for example, 0.40 g / cm 3 or more, and for example, 0.50 g / cm 3 or more, and for example, 0.60 g / cm 3 or more. Also, the bulk density is, for example, 0.90 g / cm 3 or less, 0.80 g / cm 3 or less, and for example, 0.70 g / cm 3 or less, and for example, 0.65 g / cm 3 or less, and for example, 0.60 g / cm 3 or less, and for example, 0.50 g / cm 3 or less. The suitable bulk density range of the carbon material as the raw material can be set by combining the above-mentioned lower limit value and upper limit value. For example, it can be 0.20 g / cm 3 or more and 0.70 g / cm 3 or less, or for example, 0.20 g / cm 3 or more and 0.65 g / cm 3 or less, etc.

[0033] The specific surface area per unit volume of the carbon material as the raw material is not particularly limited. For example, it is 400 m2 / cm 3 and above, and for example, 450 m 2 / cm 3 and above, and for example, 500 m 2 / cm 3 and above, and for example, 600 m 2 / cm 3 and above, and for example, 650 m 2 / cm 3 and above, and for example, 700 m 2 / cm 3 and above. The upper limit is not particularly limited, but from the relationship between the specific surface area and the bulk density, for example, 800 m 2 / cm 3 and below, and for example, 750 m 2 / cm 3 and below, for example, 700 m 2 / cm 3 and below, and for example, 650 m 2 / cm 3 and below, and for example, 600 m 2 / cm 3 and below. The suitable specific surface area per unit volume of the carbon material as the raw material can be set by combining the above-mentioned lower limit value and upper limit value. For example, it can be 450 m 2 / cm 3 or more and 800 m 2 / cm 3 or less, etc.

[0034] Carbon materials such as activated carbon as such raw materials can be appropriately obtained commercially.

[0035] As raw materials, in addition to carbon materials, a binder can be used. The binder is considered to be able to uniformly press the carbon material to increase its density and contribute to maintaining the densified state of structures such as graphene in the carbon material due to pressing. The binder is not particularly limited as long as it can bind the carbon materials, and the aforementioned binders described in the negative electrode material can be used. From the perspective that the pressed carbon material can be remolded as it is even after being pulverized after the pressing step described later, polytetrafluoroethylene (PTFE) can be used as the binder.

[0036] Also, the content ratio of the binder is not particularly limited as long as it can act as a binder. For example, it can be 0.01% by mass or more based on the total mass of the carbon material and the binder. In addition, the content in the form already described in the description of the negative electrode material can be adopted.

[0037] (Pressing step) The pressing step is a step of pressing the carbon material as a raw material so that the specific surface area per unit volume represented by [m 2 / g] × bulk density [g / cm 3 is 700 m 2 / cm 3 or more. By the pressing step, when the carbon material as a raw material is pressed, the distance between graphene layers or walls is approximated. As a result, it is considered that the carbon material is densified by densification and the bulk density of the raw material is improved. At the same time, it is considered that the specific surface area of the raw material decreases.

[0038] In the pressing process, although not particularly limited, for example, a known compression molding machine such as a hydraulic press can be used. The pressing process may be carried out once, but it can also be repeated a plurality of times with respect to the carbon material as the raw material. By performing it a plurality of times, sufficient densification can be achieved even with a small pressure. The number of times of the pressing process is not particularly limited and is appropriately set according to the carbon material used, the pressure during pressing, and the intended degree of densification. For example, it is 1 or more and several tens or less, and for example, 1 or more and 50 or less, and for example, 1 or more and 20 or less, and for example, 1 or more and 10 or less, and for example, 1 or more and 6 or less, and for example, 1 or more and 5 or less.

[0039] When the pressing process is carried out a plurality of times, although not particularly limited, for example, pressure may be continuously applied to the raw material after pressing. Also, for example, the once-pressed raw material may be crushed, pulverized or ground, and the crushed material or the like as the raw material may be pressed again. When the pressing process is repeated a plurality of times, in addition to the carbon material as the raw material, the above-described binder is used, and by performing the pressing process in the presence of the binder, densification can be more effectively achieved by the plurality of pressing processes.

[0040] Regarding the crushing, pulverizing or grinding of the pressed raw material, although not particularly limited, a device for performing known crushing, pulverizing or grinding can be used. For example, various mills such as a planetary ball mill, a vibration ball mill, a jet mill, a hammer mill, grinders, blenders, etc. can be appropriately used. The crushing or the like can be carried out under an air atmosphere, at normal temperature and normal pressure.

[0041] The conditions of the pressurization process are not particularly limited. The pressure in the pressurization process is not particularly limited and is set so that the charge-discharge capacity per volume of the carbon material used as the raw material can be increased. Such pressure depends on the number of times of the pressurization process, but the carbon material as the raw material can be pressurized, for example, at 50 MPa or more, or for example, at 100 MPa or more, or for example, at 120 MPa or more, or for example, at 140 MPa or more, or for example, at 200 MPa or more, or for example, at 500 MPa or more, or for example, at 600 MPa or more, or for example, at 700 MPa or more, or for example, at 800 MPa or more. If it is less than 50 MPa, the compressing force is small, and it is difficult to obtain the target bulk density. Also, when using activated carbon as the raw material, a pressure of 100 MPa or more can be used from the viewpoint of fully exhibiting the compression effect.

[0042] Also, the pressure in the pressurization process depends on the number of times of the pressurization process, but for example, it can be pressurized at 1200 MPa or less, or for example, at 1000 MPa or less, or for example, at 900 MPa or less, or for example, at 800 MPa or less, or for example, at 750 MPa or less. Also, if the pressure exceeds 1200 MPa, it is not practical because problems such as the durability of the equipment used for the treatment will occur. Also, considering the durability of the molding die, it is desirable to perform the high-pressure compression treatment at a pressure of 500 MPa or less.

[0043] The pressurization range in the pressurization process can be set by appropriately combining the above-mentioned lower limit and upper limit. For example, it is 50 MPa or more and 1200 MPa or less, or for example, 100 MPa or more and 1200 MPa or less, or for example, 700 MPa or more and 1200 MPa or less.

[0044] The temperature in the pressurization process is not particularly limited either. For example, it can be carried out at a temperature from room temperature to 200 °C. Also, the pressurization time in the pressurization process is not particularly limited. For example, the pressurization time can be about several seconds to 10 minutes as the time for maintaining the pressure. The gas atmosphere in the pressurization process is not particularly limited, and it can be carried out under normal pressure in an air atmosphere.

[0045] The carbon material obtained through the pressurization process and the mixed material of the carbon material and the binder are provided with graphene in which the carbon material is densified or consolidated by pressurization. Such a mixed material is supplied as a negative electrode material for a nickel-metal hydride battery as a molded body or after the molded body is crushed, pulverized or ground into a powder form or the like. When supplied as a molded body, it is crushed or the like before the preparation of the negative electrode composition.

[0046] <Composition for negative electrode of nickel-metal hydride battery> The composition for negative electrode of nickel-metal hydride battery disclosed in this specification contains the above-mentioned negative electrode material. According to the composition for negative electrode, a negative electrode of a nickel-metal hydride battery with an effectively increased charge capacity per unit volume can be obtained.

[0047] The composition for negative electrode can contain a binder for the carbon material as the negative electrode material. As the binder, various known binders such as polytetrafluoroethylene can be used as described above in relation to the negative electrode material. The binder contained in the composition for negative electrode may be only the binder used in the production of the negative electrode material, or may be only the binder newly added to the negative electrode material during the preparation of the composition for negative electrode, or may include both of these binders. Any form of binder can contribute to the increase in the charge capacity per unit volume due to the densified carbon material.

[0048] The content of the binder in the composition for negative electrode is not particularly limited, but for example, the same form as that in the above-mentioned negative electrode material can be adopted, such as in the range of 0.01% by mass or more and 10% by mass or less based on the total mass of the carbon material and the binder.

[0049] The composition for the negative electrode can similarly contain components included in the composition for the negative electrode of a known nickel-hydrogen battery, such as, in addition to the negative electrode material, conductive aids such as metal powders like Ni powder, oxides such as cobalt oxide, and carbon materials such as graphite and carbon nanotubes. The addition amount of the conductive aid is not particularly limited. For example, a range of 0.1 part by mass or more and 50 parts by mass or less, or for example, a range of 0.1 part by mass or more and 30 parts by mass or less, is preferable with respect to 100 parts by mass of the negative electrode material. Such a composition for the negative electrode can also be used, for example, as a negative electrode paste. A person skilled in the art can appropriately mix these known components in addition to the negative electrode material to prepare a composition for the negative electrode.

[0050] <Nickel-Hydrogen Battery and Its Negative Electrode> The nickel-hydrogen battery disclosed in this specification includes a positive electrode, a negative electrode, an electrolytic solution, and a separator, and the negative electrode contains the above-described composition for the negative electrode. These battery elements of the nickel-hydrogen battery are housed in a housing (battery case). The battery elements of the positive electrode, negative electrode, electrolytic solution, and separator can adopt known forms such as a wound type or a laminated type, for example. Also, examples of the shape of the battery include a coin type, a laminate type, a cylindrical type, and a rectangular type.

[0051] (Positive Electrode) The positive electrode generally consists of a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material layer may further contain at least one of a conductive aid, a binder, and a thickener. The positive electrode active material is not particularly limited as long as it is a substance that functions as a battery when combined with the negative electrode material, and examples thereof include a simple metal, an alloy, and a hydroxide. As the positive electrode active material, one containing nickel oxide and mainly composed of nickel oxyhydroxide and / or nickel hydroxide can be used. The amount of nickel oxide in the positive electrode active material is, for example, 90% by mass or more and 100% by mass or less, and 95% by mass or more and 100% by mass or less.

[0052] The conductive additive is not particularly limited as long as it is a material capable of imparting electronic conductivity, and examples thereof include metal powders such as Ni powder, oxides such as cobalt oxide, carbon materials such as graphite and carbon nanotubes. The addition amount of the conductive additive is not particularly limited, but for example, it is 0.1 part by mass or more and 50 parts by mass or less, and for example, 0.1 part by mass or more and 30 parts by mass or less, based on 100 parts by mass of the positive electrode active material. As the binder, for example, synthetic rubbers such as styrene-butadiene rubber (SBR), celluloses such as carboxymethyl cellulose (CMC), polyols such as polyvinyl alcohol (PVA), fluororesins such as polyvinylidene fluoride (PVDF), acrylic resins, etc. can be mentioned. The amount of the binder may be, for example, 7 parts by mass or less, 0.01 part by mass or more and 5 parts by mass or less, and for example, 0.05 part by mass or more and 2 parts by mass or less, based on 100 parts by mass of the positive electrode active material.

[0053] Examples of the thickener include carboxymethyl cellulose and its modified products (including salts such as Na salt), cellulose derivatives such as methyl cellulose, saponified products of polymers having vinyl acetate units such as polyvinyl alcohol, polyalkylene oxides such as polyethylene oxide, etc. These thickeners can be used alone or in combination of two or more. The amount of the thickener is, for example, 5 parts by mass or less, and for example, 0.01 part by mass or more and 3 parts by mass or less, and for example, 0.05 part by mass or more and 1.5 parts by mass or less, based on 100 parts by mass of the positive electrode active material.

[0054] Examples of the material of the positive electrode current collector include stainless steel, aluminum, nickel, iron, titanium, etc. In addition, examples of the shape of the positive electrode current collector include foil shape, mesh shape, porous shape, etc.

[0055] The positive electrode can be formed by attaching a positive electrode composition containing a positive electrode active material to a support (positive electrode current collector). The positive electrode composition is usually prepared by pasting together, in addition to the positive electrode active material described above, a conductive assistant and a binder. As the dispersion medium, water, an organic medium, or a mixed medium obtained by mixing two or more media selected from these can be used.

[0056] The positive electrode may be formed by applying the positive electrode mixture paste to the support according to the shape of the support or the like, or by filling the pores of the support. The positive electrode can be formed by applying or filling the support, drying to remove the dispersion medium, and compressing the obtained dried product in the thickness direction (for example, rolling between a pair of rolls).

[0057] (Negative electrode) The negative electrode usually consists of a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer contains, as the negative electrode active material, a negative electrode composition containing at least the negative electrode material described above.

[0058] Examples of the material of the negative electrode current collector include steel, stainless steel, aluminum, nickel, iron, titanium, carbon, etc. Examples of the shape of the negative electrode current collector include foil shape, mesh shape, porous shape, etc.

[0059] The negative electrode can be obtained by applying a paste-like negative electrode composition onto the negative electrode current collector and drying to form a negative electrode active material layer on the negative electrode current collector. It can also be obtained by molding the negative electrode composition into a predetermined shape and supporting the molded negative electrode paste with the negative electrode current collector.

[0060] (Electrolyte layer: electrolyte solution and separator) The electrolyte layer is a layer containing an electrolyte solution formed between the positive electrode and the negative electrode. In this specification, the electrolyte solution is an electrolyte solution mainly using water as a solvent, and the solvent may contain substances other than water. The ratio of water to the total solvent of the electrolyte solution is, for example, 50 mol% or more, and for example, 70 mol% or more, and for example, 90 mol% or more, and for example, 100 mol%.

[0061] The electrolyte is preferably an alkaline aqueous solution. Examples of the solute of the alkaline aqueous solution include potassium hydroxide (KOH), sodium hydroxide (NaOH), etc., and LiOH may be included therein. The higher the concentration of the solute in the electrolyte, the more preferable it is. For example, it is 3 mol / l or more, and for another example, it is 5 mol / l or more.

[0062] The electrolyte layer has a separator. Examples of the separator include non-woven fabrics and porous membranes containing resins such as sulfonated polyethylene and polypropylene.

[0063] (Housing) The housing is a battery case (cell container) for housing the positive electrode, negative electrode and separator and filling with an electrolyte. The housing only needs to be stable without being corroded by the electrolyte and capable of holding the gas (oxygen or hydrogen) and electrolyte that are temporarily generated during charging without leaking to the outside. For example, metal cases, resin cases, etc. are generally used.

[0064] The nickel-hydrogen battery and its negative electrode disclosed in this specification are suitable, for example, for in-vehicle secondary batteries. As an in-vehicle battery, in addition to a hybrid vehicle battery that supplies power to a motor for vehicle driving, it may also be a battery that supplies power to a starter motor. Note that the secondary battery includes the primary battery use of the secondary battery (use for the purpose of only one discharge after charging).

[0065] (Vehicle) The vehicle disclosed in this specification is equipped with a nickel-hydrogen battery such as a nickel-hydrogen battery using the above negative electrode material composition as a negative electrode as a power supply source for a motor, etc. Since it is a lightweight, low-cost and compact nickel-hydrogen battery, it can contribute to the fuel consumption of the vehicle, etc.

[0066] This specification includes aspects of the following items. [1] BET specific surface area [m2 / g] × bulk density [g / cm 3 and the BET specific surface area per unit volume represented by is 700 m 2 / cm 3 or more, and the bulk density is 0.4 g / cm 3 or more and 1.0 g / cm 3 or less, which is a negative electrode material for a nickel - hydrogen battery. [2] The negative electrode material according to [1], wherein the BET specific surface area per unit volume is 900 m 2 / cm 3 or more. [3] The negative electrode material according to [1], wherein the BET specific surface area per unit volume is 1000 m 2 / cm 3 or more. [4] A negative electrode composition for a nickel - hydrogen battery containing the negative electrode material according to any one of [1] to [3]. [5] The negative electrode composition according to [4], further containing a binder for the carbon material. [6] The negative electrode composition according to [5], containing 10 mass% or less of the binder. [7] The negative electrode composition according to [5] or [6], wherein the binder is polytetrafluoroethylene. [8] A method for manufacturing a negative electrode material for a nickel - hydrogen battery, comprising: a raw material preparation step of preparing, as a raw material, a carbon material having a BET specific surface area per unit mass of 700 m 2 / g or more; and a pressing step of pressing the carbon material so that the BET specific surface area per unit volume represented by BET specific surface area [m 2 / g] × bulk density [g / cm 3 is 700 m 2 / cm 3 or more. The manufacturing method comprising the above steps. [9] The manufacturing method according to [8], wherein the carbon material is activated carbon.

[10] The manufacturing method according to [8] or [9], wherein the pressing step is a step of pressing the carbon material at a pressure of 50 MPa or more and 1200 MPa or less.

[11] The pressing step is the manufacturing method according to any one of [8] to

[10] , which presses the carbon material in the presence of a binder.

[12] A nickel-metal hydride battery, comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode contains the negative electrode composition according to any one of [4] to [7].

[13] A vehicle,

[12] A vehicle equipped with the nickel-metal hydride battery according to

[12] .

Example

[0067] Hereinafter, specific examples embodying the disclosure of this specification will be described, but the disclosure of this specification is not limited to the following specific examples.

Example

[0068] (Manufacture of negative electrode material) In this example, carbon materials with various specific surface areas and a binder were mixed to form a mixed raw material, and then the mixed raw material was pressed at various pressures to obtain a densified carbon material, which was used as the negative electrode material.

[0069] As the carbon materials, commercially available activated carbons (activated carbons 1 to 5) with the specific surface areas and bulk densities shown in Table 1 were obtained, and the negative electrode materials of Production Examples 1 to 5 were manufactured. In Production Examples 1 to 5, PTFE was used as the binder. Further, as Comparative Production Examples (hereinafter simply referred to as Comparative Examples), in addition to activated carbons 1 to 5, activated carbon 6 shown in Table 1 was also used. The specific surface area and bulk density per unit mass of activated carbons 1 to 6 shown in Table 1 were measured by the following method. In the following description, the specific surface area and bulk density were measured by the following method.

[0070] <Specific surface area> The activated carbon to be measured was placed in the measurement cell of BELSORP-max manufactured by MicrotracBEL Corporation. The amount of nitrogen adsorbed on the activated carbon was determined from the change in the pressure of nitrogen introduced into the measurement cell using the equation of state of the gas, and the specific surface area of the activated carbon was calculated from the adsorption isotherm assumed by the BET theory.

[0071] <Bulk density> The material was formed into a disk with a predetermined diameter under a pressure of 0.1 MPa. The height and diameter of the formed carbon material were measured to obtain the volume, and the bulk density was calculated by dividing the mass of the used material by the volume.

[0072] Hereinafter, the negative electrode materials of Production Examples 1 to 5 will be described with reference to Table 2, and the negative electrode materials of Comparative Examples 1 to 6 will be described with reference to Table 3.

[0073]

Table 1

[0074] <Production Example 1> 0.485 g of activated carbon 1 and 0.015 g of PTFE were mixed to prepare a mixture (PTFE content: 3% by mass). This mixture was put into a mold with a diameter of 16 mm of a hydraulic compression molding machine and pressed at the pressure shown in Table 2 at room temperature to form a columnar molded body. The molded body was pulverized using an agate mortar and pestle, and the pulverized material was again pressed at the pressure shown in Table 2. Such pressing operations were repeated until the total number reached 4 times. Finally, the obtained molded body was pulverized with an agate mortar and pestle, and its specific surface area and bulk density were measured. Also, the specific surface area per unit volume was calculated. These results are shown in Table 2.

[0075] <Production Example 2> Using activated carbon 2, the negative electrode material of Production Example 2 was produced in the same manner as in Production Example 1 except that the pressure and number of times shown in Table 2 were used for pressing. The specific surface area and bulk density were measured, and the specific surface area per unit volume was calculated. These results are shown in Table 2.

[0076] <Production Examples 3 to 5> 0.294 g of activated carbon 3 - 5 and 0.016 g of PTFE were mixed to prepare each mixture (PTFE content: 2% by mass). The negative electrode materials of Production Examples 3 - 5 were produced in the same manner as in Production Example 1, except that they were put into a mold with a diameter of 10 mm of a hydraulic compression molding machine and pressed at the pressure and number of times shown in Table 2. The specific surface area and bulk density were measured, and the specific surface area per unit volume was calculated. The results are shown in Table 2.

[0077] <Comparative Examples 1 - 7> As shown in Table 3, for the negative electrode materials of Comparative Examples 1 - 6, the obtained activated carbons 1 - 6 were used as they were. Further, for Comparative Example 7, 0.294 g of activated carbon 6 and 0.016 g of PTFE 0.016 g were mixed to prepare a mixture (PTFE content: 2% by mass). The negative electrode material of Comparative Example 7 was produced in the same manner as in Production Example 1, except that it was put into a mold with a diameter of 10 mm of a hydraulic compression molding machine and pressed at the pressure and number of times shown in Table 3. The specific surface area and bulk density were measured, and the specific surface area per unit volume was calculated. The results are shown in Table 3.

[0078]

Table 2

[0079]

Table 3

[0080] As shown in Tables 2 and 3, the untreated activated carbons 1 - 5 of Comparative Examples 1 - 5 had a bulk density of 0.20 - 0.62 g / cm 3 The negative electrode materials of Production Examples 1 - 5 obtained by pressing activated carbons 1 - 5 all had a bulk density greater than that of the respective raw material activated carbons, and became 0.40 - 1.0 g / cm 3 That is, the bulk density increased by about 1.5 to 2.2 times due to pressing. The untreated activated carbons 1 - 5 of Comparative Examples 1 - 5 had a specific surface area per unit mass of 750 - 3250 m 2 / g, but for the negative electrode materials of Production Examples 1 - 5 that were pressed, it was 750 - 2840 m 2 / g, and the specific surface area of each activated carbon was equal to or less than that. That is, the specific surface area tended to be about the same or slightly smaller under pressure.

Example

[0081] (Manufacture of nickel-hydrogen battery and evaluation of charge-discharge capacity) In this example, using the negative electrode materials of Production Examples 1 to 5 and Comparative Examples 1 to 7 manufactured in Example 1, a negative electrode was produced, and further, a nickel-hydrogen battery was produced and the charge-discharge capacity was evaluated.

[0082] 6% by mass of SBR latex was added to 84% by mass of the negative electrode material of the production example and 10% by mass of carbon black to prepare a paste as a negative electrode composition. This paste was applied to one side of a Ni porous body punched into a disk shape with a diameter of 20 mm, dried, and then pressed at a pressure of 27 MPa to produce a negative electrode. Similarly, negative electrodes were produced using Comparative Examples 1 to 7. The amount of the negative electrode material contained in this negative electrode was 0.06 to 0.09 g.

[0083] The produced negative electrode was combined with a separator and a positive electrode and set in a commercially available battery container (Takumi Giken, flat cell (with pressure sensor)). As the positive electrode, a nickel hydroxide electrode (a nickel porous body filled with nickel hydroxide, disk shape with a diameter of 20 mm) was used. As the separator, a sulfonated polypropylene nonwoven fabric (circular, diameter 23 mm) was used. 0.3 ml of an alkaline electrolyte (7N potassium hydroxide aqueous solution) was injected into the battery container.

[0084] Note that the positive electrode capacity of the battery was about 80 mAh, and the positive electrode capacity was made excessive compared to the negative electrode capacity. In a practical battery, the positive electrode capacity is made less than the negative electrode capacity to be dominated by the positive electrode capacity, but in this example, since attention is paid to the performance of the negative electrode, the positive electrode capacity was made excessive with respect to the negative electrode capacity to be dominated by the negative electrode capacity. The charge-discharge evaluation was performed by the following method.

[0085] <Charge-discharge evaluation method> The fabricated battery was subjected to constant current charge and discharge at a current of 60 mA per 1 g of the mass of the negative electrode material in a constant temperature bath at 25°C. The charge cut-off voltage was 1.6 V, and the discharge cut-off voltage was 1.0 V or 0.8 V, and charge and discharge evaluation was performed.

[0086] The results of the charge and discharge evaluation are shown in Tables 2 and 3 together. Also, Fig. 2 shows the relationship between the weight charge and discharge capacity and the specific surface area per unit mass when the charge cut-off voltage is 1.6 V and the discharge cut-off voltage is 1.0 V, and Fig. 3 shows the relationship between the volume charge and discharge capacity and the specific surface area per unit volume under the same conditions.

[0087] Regarding the generation of hydrogen gas, when the charge voltage reached 1.6 V during charging, the internal pressure of the battery was measured by a pressure sensor to evaluate the presence or absence of hydrogen gas generation. When the measured value of the pressure by the pressure sensor was less than 0.005 MPa, it was evaluated as "no hydrogen gas generation", and when the measured value was 0.005 MPa or more, it was evaluated as "hydrogen gas generation". The results are shown in Tables 2 and 3 together.

[0088] As shown in Table 3 and Figs. 2 to 3, the activated carbons without pressure application in Comparative Examples 1 to 6 (258 to 780 m 2 / g, 0.20 to 0.63 g / cm 3 ), and the activated carbon with pressure application but a small specific surface area and a large bulk density (400 m 2 / g, 1.2 g / cm 3 ) had a volume charge and discharge capacity of 6 to 16 mAh / cm 3 . Also, the specific surface area per unit volume in Comparative Examples 1 to 7 was 258 to 700 m 2 / cm 3 , and none of the comparative examples satisfied a specific surface area per unit volume of 700 m 2 / cm 3 or more and a bulk density of 0.40 to 1.00 g / cm 3 or less.

[0089] On the other hand, as shown in Table 2 and Figs. 2 to 3, the volume charge and discharge capacity of the negative electrode materials in Production Examples 1 to 5 was 17 to 35 mAh / cm 3As a result, compared with the volume charge-discharge capacities of the corresponding Comparative Examples 1 to 5, it was 1.4 to 2.2 times. From these facts, it was considered that the interaction between protons and carbon increased due to the high density during charging. Also, the specific surface area per unit volume of Production Examples 1 to 5 was 700 m 2 / cm 3 ~1136 m 2 / cm 3 and the bulk density was in the range of 0.40 to 1.0 g / cm 3 or less.

[0090] From the above, by pressing a carbon material such as activated carbon having a specific surface area per unit mass of a certain level or more to increase the density and increase the bulk density, the interaction between protons and the like and carbon during charging was increased, and it was considered that the charge-discharge capacity per unit volume of the nickel-metal hydride battery could be increased.

[0091] Also, as shown in Tables 2 and 3, it was found that hydrogen gas was not generated by using a carbon material as the negative electrode material. That is, it was considered that hydrogen gas was sufficiently adsorbed on the negative electrode material.

[0092] From the above, it was found that the negative electrode material produced in the production example was useful as a negative electrode material for a nickel-metal hydride battery.

Claims

1. A negative electrode material for a nickel-hydrogen battery, having a BET specific surface area [m² / g] of 2600 [m² / g] or more and 2840 [m² / g] or less, The bulk density is 0.40 g / cm 3 or more and 0.43 g / cm 3 or less, and the BET specific surface area [m ２ / g] × bulk density [g / cm ３ The BET specific surface area per unit volume represented by the formula ] is 1100 m ２ / cm ３ The carbon material, and containing

2. A negative electrode composition for a nickel-hydrogen battery, containing the negative electrode material according to Claim 1.

3. The negative electrode composition according to Claim 2, further containing a binder for the carbon material.

4. The negative electrode composition according to Claim 3, wherein the binder is polytetrafluoroethylene.

5. A method for manufacturing a negative electrode material for a nickel-hydrogen battery, As a raw material, a raw material preparation step of preparing a carbon material having a BET specific surface area of 3000 m ２ / g or more is performed; Pressurize the mixture containing the carbon material so that the BET specific surface area [m² / g] is 2,600 [m² / g] or more and 2,840 or less [m² / g], the bulk density is 0.40 g / cm³ or more and 0.43 g / cm³ or less, and the BET specific surface area per unit volume represented by [m ２ / g] × bulk density [g / cm ３ is 1,100 m ２ / cm ３ or more; a pressurization step to make it so; comprising

6. In the raw material preparation step, the carbon material is activated carbon having a BET specific surface area [m² / g] of 3000 [m² / g] or more and 3250 [m² / g] or less, and a bulk density of 0.20 g / cm³ or more and 0.26 g / cm³ or less. The manufacturing method according to Claim 5.

7. The pressing step is a step of pressing the carbon material in the presence of a binder. The manufacturing method according to Claim 5 or 6.

8. A nickel-hydrogen battery, comprising a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein the negative electrode contains the negative electrode composition according to any one of Claims 2 to 4. A nickel-hydrogen battery.

9. A vehicle equipped with the nickel-hydrogen battery according to Claim 8.

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