JP5130718B2 - Negative electrode for nickel-hydrogen storage battery and nickel-hydrogen storage battery - Google Patents

Description

  The present invention relates to a nickel-hydrogen storage battery, and more particularly to improvement of a negative electrode mainly composed of a hydrogen storage alloy.

  Nickel-hydrogen storage batteries using negative electrodes containing hydrogen storage alloys are characterized by being environmentally friendly and high in energy density compared to conventional nickel-cadmium storage batteries. Various cordless and electronic devices such as communication devices and personal computers It is used as a power source for electric tools and electric vehicles, which are indispensable for charging and discharging with a large current. Corresponding to such expansion of applications, further improvement of charge / discharge characteristics is desired.

  Conventional negative electrodes for nickel-metal hydride storage batteries add fine binders such as polytetrafluoroethylene and styrene butadiene rubber, thickeners such as methylcellulose, carboxymethylcellulose, and polyvinyl alcohol to finely divided hydrogen storage alloy powders. The paste is kneaded with water to form a paste, and the paste is applied to a punching metal as a core material, dried and pressed to form an active material layer.

  Since the surface of the hydrogen storage alloy powder of the negative electrode for nickel-hydrogen storage battery manufactured in this way is coated with a binder, the conductivity between the alloy powders is likely to decrease. When the conductivity is lowered, there is a problem that the ratio of the alloy powder not involved in charging / discharging increases, leading to an increase in internal pressure during battery overcharge and a decrease in large current discharge characteristics.

In order to solve the above problem, a method of increasing the conductivity between the hydrogen storage alloy powders by a technique (for example, Patent Document 1) in which carbon powder is added to the negative electrode as a conductive agent has been reported. However, simply increasing the conductivity is not sufficient to suppress an increase in internal pressure during overcharge, and a technique for covering at least a part of the surface of the carbon powder with a metal film (for example, Patent Document 2) or a conductive agent It is considered effective to promote the gas absorption reaction by using a technique (for example, Patent Document 3) using nickel powder containing 0.2 to 3% by weight of carbon.
JP 11-185745 A Japanese Patent Laid-Open No. 11-111298 Japanese Patent Laid-Open No. 07-0665826

  However, when the nickel-hydrogen storage battery is rapidly charged, there is a problem that the internal pressure of the battery cannot be sufficiently suppressed even if the technique of Patent Document 2 is used. Moreover, although patent document 3 has a high effect of suppressing the internal pressure of the battery in rapid charging, there is a problem that the large current discharge characteristics cannot be sufficiently improved.

  The present invention solves the above-described problems, and an object of the present invention is to provide a large-capacity nickel-hydrogen storage battery that suppresses an increase in internal pressure of the battery and is excellent in large current discharge characteristics.

  In order to solve the above problems, the negative electrode for nickel-hydrogen storage battery according to the present invention has a structure in which an active material layer containing a hydrogen storage alloy powder and a carbon powder is provided on a conductive support, and at least a part of the carbon powder. And at least one nonmetallic element selected from sulfur and phosphorus.

  By including a nonmetallic element in the carbon powder, which is a conductive agent, both the affinity with the oxygen gas generated in the battery and the conductivity are increased for unknown reasons. By increasing the conductivity, not only the large current discharge characteristics are improved, but also a loss reaction (gas generation reaction) during rapid charging can be suppressed. In addition, since the oxygen gas generated at the time of rapid charging is reduced to water by the gas affinity of the carbon material of the present invention, the increase in battery internal pressure can be greatly reduced).

  According to the above-described configuration of the present invention, since good conductivity and gas affinity can be imparted to the carbon powder, the increase in internal pressure can be suppressed even when rapid charging is performed, and nickel- A hydrogen storage battery can be provided.

  Embodiments of the present invention will be described below.

  1st invention is the structure which provided the active material layer containing hydrogen storage alloy powder and carbon powder on the electroconductive support body, At least 1 nonmetal chosen from sulfur and phosphorus in at least one part of the said carbon powder The present invention relates to a negative electrode for a nickel-hydrogen storage battery characterized by containing an element. By including a nonmetallic element in the carbon powder, which is a conductive agent, both the affinity with the oxygen gas generated in the battery and the conductivity are increased for unknown reasons. By increasing the conductivity, not only the large current discharge characteristics are improved, but also a loss reaction (gas generation reaction) during rapid charging can be suppressed. In addition, oxygen gas generated during rapid charging is led to the negative electrode by the gas affinity of the carbon material of the present invention, and then reacts with hydrogen stored in the hydrogen storage alloy to be reduced to water, thus increasing the internal pressure of the battery. It can be greatly reduced.

  In the first invention, it is not necessary for all of the carbon powder to contain a nonmetallic element, and if at least a part of the powder contains a nonmetallic element, the effect of the first invention is exhibited. Moreover, only 1 type may be contained in a carbon powder among the said nonmetallic elements, and both nonmetallic elements may be contained in a carbon powder.

The specific surface area of the carbon powder is not particularly limited, but is preferably in the range of 1000 to 5000 m ² / g. In the present invention, since the gas affinity is proportional to the specific surface area of the carbon powder, when the specific surface area is less than 1000 m ² / g, the gas affinity becomes insufficient and the increase in internal pressure during overcharge increases. On the other hand, when the specific surface area exceeds 5000 m ² / g, the binder that plays the role of maintaining the shape of the active material layer is excessively absorbed by the carbon powder, so that the strength is impaired, and the active material layer from the conductive substrate. It becomes easy to produce peeling. The preferred range of the specific surface area is calculated as an average value for all the carbon powders, and it is not necessary for all the carbon powders to be within this preferred range.

The bulk density of the carbon powder is not particularly limited, but is preferably in the range of 0.05 to 0.09 g / cm ³ . When the bulk density is less than 0.05 g / cm ³ , the paste viscosity becomes too high when preparing a paste containing carbon powder that is a precursor of the active material layer, making it difficult to produce the active material layer. On the other hand, when the bulk density exceeds 0.09 g / cm ³ , the carbon powder tends to aggregate and the dispersion in the negative electrode becomes non-uniform, resulting in a slight decrease in conductivity. The preferable range of the bulk density is calculated as an average value for all the carbon powders, and it is not necessary that all the carbon powders are within this preferable range.

Furthermore, although the addition amount of carbon powder is not specifically limited, It is preferable that it is the range of 0.1-1.0 weight part with respect to 100 weight part of hydrogen storage alloys. If the addition amount is less than 0.1 parts by weight, the carbon powder is not uniformly arranged between the hydrogen storage alloy powders, and therefore the conductivity and gas affinity cannot be sufficiently improved. On the other hand, when the addition amount exceeds 1.0 part by weight, not only the amount of hydrogen storage alloy per unit volume of the negative electrode is reduced, but also the binder that plays the role of maintaining the shape of the active material layer is excessively absorbed by the carbon powder. Therefore, the strength is impaired, and the active material layer is easily peeled off from the conductive substrate.

  The second invention is characterized in that, in the first invention, the content of the nonmetallic element in the carbon powder is 0.001 to 1.50% by weight. When the content is less than 0.001% by weight, the gas affinity is lowered, which is not preferable. When the content exceeds 1.50 parts by weight, it is difficult to add these nonmetallic elements to the carbon powder. Note that the preferable range of the content is calculated as an average value for all the carbon powders, and it is not necessary that all the carbon powders are within this preferable range.

  According to a third invention, in the first invention, at least a part of the carbon powder further contains at least one metal element selected from the group consisting of Ni, Co, Ca, Fe, Mg, Mn, Ti and V. It is characterized by that. Since the conductivity of the carbon powder can be increased by adding the above-described metal element, it is possible to further improve the large current discharge characteristics. Note that it is not necessary for all of the carbon powder to contain a metal element, and if at least a part of the powder contains a metal element, the effect of the third invention is manifested.

  In the third invention, the content of the metal element in the carbon powder is not particularly limited, but is preferably in the range of 0.001 to 1.50% by weight. When the content is less than 0.001% by weight, the conductivity of the carbon powder is not improved so much, which is not preferable. When the content exceeds 1.50 parts by weight, the carbon powder is hardly contained. Note that the preferable range of the content is calculated as an average value for all the carbon powders, and it is not necessary that all the carbon powders are within this preferable range.

  According to a fourth invention, in the first invention, the carbon powder has a dibutyl phthalate absorption amount (hereinafter referred to as DBP oil absorption amount) of 400 ml / 100 g or more. The DBP oil absorption is a measure of the conductivity of the carbon powder. By using a carbon powder having this value of 400 ml / 100 g, a negative electrode for a nickel-hydrogen storage battery having high conductivity can be produced. There is no particular upper limit on the DBP oil absorption amount for the carbon powder of the present invention, but in consideration of handling during production, carbon powder of 450 ml / 100 g or less is generally practical. Moreover, the suitable range of DBP oil absorption is calculated as an average value with respect to all the carbon powders, and all the carbon powders do not need to be in this suitable range.

  A fifth invention is characterized in that, in the first invention, the carbon powder is a secondary agglomerate in which primary particles are agglomerated. Such carbon powder has an advantage that it is easy to manufacture an electrode plate because of its moderate size. Although it does not specifically limit here, it is preferable that the average particle diameter of a primary particle is 5-30 nm, and the average particle diameter of a secondary aggregate is 5-20 micrometers. When the average particle diameter of the primary particles exceeds 30 nm, the formation of a chain for ensuring conductivity is insufficient, and the conductivity of the carbon powder is slightly lowered. On the other hand, if the average particle size of the primary particles is less than 5 nm, it is not practical because the carbon powder has sufficient conductivity and gas absorption, but it becomes difficult to produce the carbon powder. On the other hand, when the average particle diameter of the aggregated particles exceeds 20 μm, the dispersibility is lowered, and the contact with the hydrogen storage alloy powder is not uniform in the negative electrode, and the conductivity becomes slightly insufficient. Conversely, if the average particle size of the aggregated particles is less than 5 μm, the carbon powder has sufficient conductivity and gas absorbability, but the viscosity of the paste becomes excessive and it becomes difficult to produce the negative electrode, which is not practical.

The carbon powder in the fifth invention can be produced by spraying aromatic hydrocarbons at a high temperature. A typical example of such a method is an oil furnace method which is an incomplete combustion method. Hereinafter, this production method will be described in detail. First, the temperature of a furnace having a heat resistance of 2000 ° C. or higher is raised to around 1800 ° C. Next, an aromatic hydrocarbon oil to which a predetermined amount of a nonmetallic element is added as a raw material oil is continuously sprayed on a high-temperature reaction section in the furnace and reacted with air. After collecting the obtained carbon powder, the carbon powder of the fifth invention is obtained by pulverization and classification. The particle size of the carbon powder can be controlled by controlling the temperature, time, and pulverization conditions.

  The produced carbon powder has a chain shape in which individual particles are fused. Individual spherical particles characterize the irregularities on the surface of the agglomeration unit, and the particle diameter of the carbon powder is expressed by regarding these as single particles (primary particles). Such a chain aggregate consisting of several to several hundred particles is expressed as a secondary aggregate.

  The negative electrode for nickel-hydrogen storage batteries of the present invention can be produced, for example, by the following method. First, the carbon powder of the present invention was kneaded with a hydrogen storage alloy powder, a binder and pure water to prepare a paste, and the prepared paste was applied to a conductive support to form an active material layer and dried. Then, it is a method of rolling and forming.

The composition of the hydrogen storage alloy powder is not particularly limited. For example AB ₅ type alloy having a CaCu ₅ type structure, A ₂ having AB ₂ type alloy having a Laves phase structure (MgCu ₂ type or MgZn ₂ type), AB-based alloy having a CsCl type structure, or a Mg ₂ Ni structure It is preferable to use a B alloy or the like. The average particle diameter of these hydrogen storage alloy powders is preferably 10 to 50 μm in view of the filling properties in the active material layer.

  As the binder, styrene-butadiene copolymer (SBR), polytetrafluoroethylene (PTFE), or the like can be used. It is also preferable to add a thickener such as carboxymethylcellulose derivative (CMC) or polyvinyl alcohol (PVA) in order to make the above-mentioned paste easy to apply.

  A conductive support having an electrochemically stable structure under the negative electrode potential of a nickel-hydrogen battery can be used. Specific examples include a foil, a perforated plate, a three-dimensional porous body made of nickel, and a nickel-plated surface.

  6th invention is related with the nickel-hydrogen storage battery characterized by using the negative electrode for nickel-hydrogen storage batteries of the invention in any one of 1-5 mentioned above. Specifically, the negative electrode for a nickel-hydrogen storage battery according to any one of the first to fifth inventions is opposed to a positive electrode using nickel hydroxide as an active material and a separator (such as a polypropylene nonwoven fabric having a hydrophilic group), The nickel-hydrogen storage battery of the present invention is configured by injecting an alkaline aqueous solution (KOH, NaOH, LiOH, etc.).

  Hereinafter, the present invention will be described in more detail on the basis of examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications without departing from the scope of the present invention. It is.

(Battery A1)
(I) Preparation of carbon powder Based on the oil furnace method mentioned above, it produced as follows. First, a furnace having a heat resistance of 2000 ° C. was heated to 1800 ° C. Next, pseudocumene (aromatic hydrocarbon oil C ₆ H ₃ (CH ₃ ) ₃ ) added with 0.045% by weight of white phosphorus as a raw material oil was continuously sprayed to a high-temperature reaction section in the furnace. The obtained carbon powder was collected, ground in a mortar, and classified with a 325 mesh sieve to produce carbon powder containing phosphorus as a nonmetallic element.

Elemental analysis of this carbon powder revealed that phosphorus equivalent to 0.05% by weight was present in the carbon powder. In order to examine this phosphorus distribution, the cross section of the carbon powder was analyzed using an electron beam microanalyzer (EPMA), and phosphorus was detected from the inside of the carbon powder. From this result, it is presumed that phosphorus penetrates between layers of carbon powder. Subsequently, in a method according to JIS-K-6217, C.I. W. The measurement result of DBP oil absorption using an Absorpmeter-E type manufactured by Brabender was 410 ml / 100 g. Moreover, the measurement result of the specific surface area by the gas absorption method using the Shimadzu ASAP2000 specific surface area measuring apparatus was 2100 m ² . In addition, the measurement result of the bulk density using a bulk density measuring machine (Shimadzu dry density meter Accupic 1330) was 0.065 g / cm ³ . Furthermore, the measurement result of the average particle diameter using a Shimadzu SALD-2001 laser particle size distribution measuring apparatus (laser diffraction method) was 11.5 μm. When this carbon powder was observed using a JEOL JSM-5900LV electron microscope manufactured by JEOL, it was a secondary agglomerated particle in which primary particles were agglomerated. Met.

(Ii) Production of Negative Electrode A hydrogen storage alloy having a composition represented by MmNi _3.55 Co _0.75 Mn _0.4 Al _0.3 was pulverized with a ball mill to obtain a powder having an average particle size of 24 μm. 100 parts by weight of this hydrogen storage alloy powder, 0.3 parts by weight of the carbon powder described above, 0.15 parts by weight of CMC as a thickener, and 0.8 parts by weight of SBR as a binder Was mixed with water as a dispersion medium to prepare a paste. This paste is applied to a punching metal (perforated steel plate with nickel plating) as a conductive support to form an active material layer, dried and rolled to have a thickness of 0.33 mm, a width of 3.5 cm, A negative electrode was produced by cutting to a length of 31 cm.

(Iii) Production of Nickel-Hydrogen Storage Battery The above-described negative electrode was replaced with a known paste-type nickel positive electrode (width 3.5 cm, length 26 cm, thickness 0.57 mm) via a separator (nonwoven polypropylene fabric provided with a hydrophilic group). The electrode group was formed by winding in combination and spirally housed in an SC size battery case. After injecting an electrolytic solution in which lithium hydroxide was dissolved at a rate of 40 g / L into a potassium hydroxide aqueous solution with a specific gravity of 1.30, the upper part of the case was sealed with a sealing plate to produce a nickel-hydrogen storage battery with a nominal capacity of 3000 mAh. . This is designated as battery A1.

(Battery A2)
Nickel having the same structure as that of the battery A1 except that the phosphorus contained in the carbon powder is replaced with sulfur with respect to the battery A1 (the physical properties of the carbon powder and the addition amount of nonmetallic elements are all the same as those of the battery A1). -Let the hydrogen storage battery be battery A2.

(Battery A3)
The battery A3 is a nickel-hydrogen storage battery configured in the same manner as the battery A1 except that the non-metallic element is not contained in the carbon powder with respect to the battery A1 (all the physical properties of the carbon powder are the same as those of the battery A1). .

After the above-mentioned battery is left in a 25 ° C. environment for one day, the battery is charged at 300 mA for 15 hours at 20 ° C., and then charged and discharged at 600 mA until the battery terminal voltage reaches 1.0 V. Made. Thereafter, the battery was charged with a current of 3000 mA at 20 ° C. for 1.2 hours, and the internal pressure of each battery was measured. The results are shown in (Table 1). Further, after charging and discharging at 3000 mA for 1.2 hours at 20 ° C. and discharging at 3000 mA until the battery terminal voltage reaches 1.0 V, charging at 3000 mA for 1.2 hours at 20 ° C. The battery was discharged at 30 A until the terminal voltage of the battery reached 0.8V. The average discharge voltage during this 30 A discharge is shown in (Table 1). Further, the battery was charged at 3000 mA for 1.2 hours at 20 ° C., and discharged at 600 mA until the battery voltage reached 1.0V. The discharge capacity at the time of 600 mA discharge is assumed to be 100%, and the discharge capacity ratio at the time of 30 A discharge is shown in (Table 1).

The batteries A1 and A2 of the present invention were not only excellent in large current discharge characteristics as compared with the battery A3 as a comparative example, but also suppressed an increase in the internal pressure of the battery during overcharging. The reason is considered as follows. That is, since the carbon powder containing a nonmetallic element has high conductivity and gas absorbability, it is considered that the internal pressure of the battery can be prevented from increasing when the battery is overcharged or charged with a large current. On the other hand, it is considered that the effect described above was not obtained in the battery A3 because the thermal conductivity of the carbon material was not sufficient.

(Batteries B1 to B8)
In comparison with the battery A1, the amount of white phosphorus added to pseudocumene, which is an aromatic hydrocarbon oil in the production of carbon powder, is changed proportionally, and the amount of phosphorus with respect to the carbon powder is 0.0005% by weight (battery B1), 0 0.001 wt% (Battery B2), 0.005 wt% (Battery B3), 0.10 wt% (Battery B4), 0.50 wt% (Battery B5), 1.0 wt% (Battery B6), 1 Batteries B1 to B8 are nickel-hydrogen storage batteries configured in the same manner as the battery A1, except that the content is 0.5 wt% (battery B7) and 1.65 wt% (battery B8).

  The battery described above was initially activated in the same manner as in Example 1, and the battery internal pressure was measured and the large current discharge characteristics were evaluated. The results are shown in Table 2 together with the battery A1.

As shown in (Table 2), as the content of the nonmetallic element increases, the gas affinity of the negative electrode increases and the internal pressure of the battery decreases. However, since the battery B1 having a nonmetallic element content of less than 0.001% by weight cannot sufficiently exhibit the effects of the present invention, the effect of suppressing the internal pressure is insufficient. On the other hand, the battery B8 in which the content of the nonmetallic element exceeds 1.5% by weight shows a good battery internal pressure characteristic, but it is difficult to add the nonmetallic element to the carbon powder, so that the production yield decreases. Occurred. This tendency was the same when the nonmetallic element was changed from phosphorus to sulfur. Therefore, the content of the nonmetallic element in the carbon powder is preferably 0.001 to 1.50% by weight.

(Batteries C1 to C5)
For the battery A1, the DBP oil absorption of the carbon powder was changed to 377 ml / 100 g (battery C1), 389 ml / 100 g (battery C2), 400 ml / 100 g (battery C3) by changing the furnace temperature and pulverization conditions in the production of the carbon powder. ), 420 ml / 100 g (battery C4), except that it is 433 ml / 100 g (battery C5), nickel-hydrogen storage batteries configured similarly to battery A1 are designated as batteries C1 to C5.

  The battery described above was initially activated in the same manner as in Example 1, and the battery internal pressure was measured and the large current discharge characteristics were evaluated. The results are shown in Table 3 together with the battery A1.

As shown in (Table 3), as the DBP oil absorption increases, the conductivity of the negative electrode increases, and the effect increases for improving the large current discharge characteristics and reducing the battery internal pressure. The reason for this is that the electrode reaction is activated by reducing the contact resistance between the hydrogen storage alloy powders, and hydrogen is easily stored in the hydrogen storage alloy near the negative electrode surface during charging. This is thought to be a result of the improvement in battery internal pressure due to hydrogen gas leakage. However, the effects described above are not sufficient for the batteries C1 and C2 whose DBP oil absorption is smaller than 400 ml / 100 g. From this result, it can be seen that the DBP oil absorption is in a preferable range of 400 ml / 100 g or more.

(Batteries D1 to D8)
With respect to the battery A1, 0.03 wt% of Ni (battery D1), Co (battery D2), Ca (battery D3), Fe (battery D4), Mg (battery D5) in addition to the carbon powder. , Mn (battery D6), Ti (battery D7), and V (battery D8) are added, and nickel-hydrogen storage batteries configured similarly to battery A1 are designated as batteries D1 to D8.

  The battery described above was initially activated in the same manner as in Example 1, and the battery internal pressure was measured and the large current discharge characteristics were evaluated. The results are shown in Table 4 together with the battery A1.

As shown in Table 4, the use of carbon powder containing metal in addition to non-metallic elements increases the conductivity, so that the electrode reaction is activated by reducing the contact resistance between the hydrogen storage alloy powders. This is thought to be due to the fact that, during charging, hydrogen is easily stored in the hydrogen storage alloy near the negative electrode surface, so that the large current charge / discharge characteristics of the battery are improved and the increase in the internal pressure of the battery due to leakage of hydrogen gas is prevented. .

  The effect of the present invention can be used for all nickel-hydrogen storage batteries, but can exhibit a remarkable effect particularly when the capacity is large. Therefore, a great effect can be expected when the technology of the present invention is developed as a power source for electric tools and electric vehicles.

Claims (6)

A negative electrode for a nickel-hydrogen storage battery in which an active material layer containing a hydrogen storage alloy powder and a carbon powder is provided on a conductive support,
A negative electrode for a nickel-hydrogen storage battery, wherein at least a part of the carbon powder contains at least one nonmetallic element selected from sulfur and phosphorus. 2. The negative electrode for a nickel-hydrogen storage battery according to claim 1, wherein a content of the nonmetallic element in the carbon powder is 0.001 to 1.50 wt%. 2. The carbon powder further contains at least one metal element selected from the group consisting of Ni, Co, Ca, Fe, Mg, Mn, Ti and V in at least a part of the carbon powder. Negative electrode for nickel-hydrogen storage battery. The negative electrode for a nickel-hydrogen storage battery according to claim 1, wherein the carbon powder has a dibutyl phthalate absorption of 400 ml / 100 g or more. The negative electrode for a nickel-hydrogen storage battery according to claim 1, wherein the carbon powder is a secondary agglomerate in which primary particles are agglomerated. A nickel-hydrogen storage battery using the nickel-hydrogen storage battery negative electrode according to claim 1.