Method of producing hydrogen absorbing alloy powder, and electrode using hydrogen absorbing alloy powder produced by said method

FIELD OF THE INVENTION
The present invention relates to a hydrogen absorbing alloy powder having excellent keeping quality and, particularly to, a method of producing a hydrogen absorbing alloy powder which is used for the negative electrode of a nickel-hydrogen secondary battery to ensure satisfactory initial activity therein. Further, the invention concerns an electrode using the hydrogen absorbing alloy powder produced by the aforesaid method.
BACKGROUND OF THE INVENTION
Since the alloys capable of absorbing and absorbing hydrogen (which are abbreviated as "hydrogen absorbing alloys" hereinafter) were discovered, they have been applied to not only a hydrogen absorbing means but also a battery and the like. In particular, alkaline secondary batteries utilizing such alloys were already used practically, and the hydrogen absorbing alloys used therein have undergone successive improvements with the intention of heightening the battery capacity and lengthening the battery life.
More specifically, in the initially studied LaNi.sub.5 hydrogen absorbing alloy having a CaCu.sub.5 type crystal structure, it has been tried to partially replace the La by other rare earth elements, such as Ce, Pr and Nd, and the Ni by other metal elements, such as Al, Co and Mn, thereby enabling the secondary battery to have a higher capacity and a longer life.
However, such a replacement in the hydrogen absorbing alloy caused a drop in the initial activity of a secondary battery when the resultant alloy was used for a negative electrode of the battery although it was successful in heightening the battery capacity and lengthening the battery life.
The initial activity of a secondary battery is, in general, expressed in terms of the number of charge-discharge cycles repeated until the battery reaches the maximum capacity, so that the initial activity is considered to be higher the smaller such a number is. Usually, the initial activity is evaluated by the capacity in the first cycle and the number of charge-discharge cycles repeated until the battery reaches the maximum capacity.
When a secondary battery having a low initial activity is sealed hermetically, the balance between positive and negative electrodes is lost decreasing the battery capacity and the battery life.
In order to solve the aforementioned problem, it has so far been known to treat hydrogen absorbing alloys with acids or alkalis. However, these treatments have defects that not only the alloy is subject to surface oxidation during treatment but also the treated alloy is liable to oxidation upon drying and storage, so that they are insufficient in the ease of the handling and cannot ensure sufficient stability in the treated alloy.
SUMMARY OF THE INVENTION
As a result of our intensive studies of hydrogen absorbing alloy powders for the negative electrode of a secondary battery and methods of producing such alloy powders for the purpose of solving the foregoing problems, it has been found that the treatment of a pulverized hydrogen absorbing alloy with a solution comprising a condensed phosphoric acid, phytic acid or a mixture thereof enabled simple preparation of a hydrogen absorbing alloy powder having excellent keeping quality and easiness of handling. When the hydrogen absorbing alloy powder which has undergone the aforesaid treatment was applied to the negative electrode of a nickel-hydrogen secondary battery, the initial activity of the battery was elevated without attendant lowering of the battery capacity and life, thereby achieving the present invention.
Therefore, a first object of the present invention is to provide a method of producing a hydrogen absorbing alloy powder having excellent keeping quality and easiness of handling.
A second object of the present invention is to provide a negative electrode used for a nickel-hydrogen secondary battery having an excellent initial activity.
The aforementioned objects of the present invention are attained by a method of producing a hydrogen absorbing alloy powder, which comprises a step of treating a pulverized hydrogen absorbing alloy with a solution comprising a condensed phosphoric acid having 2 to 20 phosphorus atoms, phytic acid or a mixture thereof.
DETAILED DESCRIPTION OF THE INVENTION
The hydrogen absorbing alloy used in the present invention has no particular restriction, but it can be selected properly from hydrogen absorbing alloys known to be usable for negative electrodes, including hydrogen absorbing Ti alloys of AB.sub.n (n=1 or 2) type, hydrogen absorbing Zr alloys of AB.sub.2 type and hydrogen absorbing rare earth alloys of AB.sub.5 type. In particular, the use of a hydrogen absorbing alloy basically having a composition of MmNi.sub.5 is appropriate from the viewpoint of ensuring a satisfactory cycle life in the secondary battery. The symbol Mm in the foregoing composition is referred to as "a Mish metal", or a mixture of rare earth elements including La, Ce, Pr, Nd and the like. In view of further improvement in cycle life, it is desirable for the hydrogen absorbing alloy of MmNi.sub.5 type that the nickel thereof is partially replaced by not only Mn but also Al, and further by Co.
The hydrogen absorbing alloys especially preferred in the present invention are alloys represented by the compositional formula (La).sub.x R.sub.1-x (Ni.sub.a M.sub.b), wherein R is Ce, Pr, Nd or a mixture of two or more thereof, M is at least one metallic element selected from a group consisting of Mn, Al, Co, Ti, Fe, Cu and Zr, x is from 0.2 to 1, a+b is from 4.0 to 6.0, and 0<b.ltoreq.2.0.
Those metals are mixed so as to have the foregoing composition, fused together, and then cooled to prepare an ingot. Further, the ingot is ground into a powder by means of a grinder such as a ball mill, a jet mill or a pulverizer. The thus obtained powder is used in the treatment according to the present invention.
In the present invention, a pulverized hydrogen absorbing alloy is treated with a solution comprising a condensed phosphoric acid and/or phytic acid, and further washed with water, if needed, for the purpose of producing a hydrogen absorbing alloy powder which has a high keeping quality and easiness of handling and further ensures a satisfactory initial activity in a secondary battery when the alloy is used for the negative electrode of the battery. In the step of washing the treated alloy powder, the use of alkali for neutralization is effective in many cases to produce an improvement on the characteristics of the treated alloy powder.
The present treatment is generally carried out at a temperature ranging from room temperature to 130.degree. C., preferably from room temperature to 100.degree. C. And it may be performed under a pressure of 10 kgf/cm.sup.2 or below in an airtight vessel, if desired. The treatment performed under a high temperature or while cooling is undesirable in view of economy, because it entails too high a cost of equipment and facilities for production on an industrial scale. In particular, the treatment carried out while cooling is impractical, because the treatment time becomes too long.
The treatment time is preferably chosen from the range of 10 minutes to 10 hours, and adjusted properly depending on the treatment temperature. In other words, the treatment time is shortened when the treatment temperature is high; while it is lengthened when the treatment temperature is low.
Further, it is desirable that the concentration of a condensed phosphoric acid, phytic acid or a mixture of these acids in the treating bath be from about 0.01 to 10 weight %, preferably from 0.1 to 1 weight %, based on the hydrogen absorbing alloy treated therein. When the concentration is lower than 0.01 weight %, the keeping quality improving effect produced by the treatment becomes insufficient; while, when the concentration is higher than 10 weight %, the hydrogen absorbing-desorbing reaction is suppressed by the acid used to result in a decrease of hydrogen storage capacity.
The condensed phosphoric acids which can be used in the solution for the present treatment include polyphosphoric acids which are produced by linear condensation of orthophosphoric acid and represented by formula, H.sub.n+2 P.sub.n O.sub.3n+1, and polymetaphosphoric acids which are produced by cyclic condensation of orthophosphoric acid and represented by formula, (HPO.sub.3).sub.n. Of these poly-acids, the condensed phosphoric acids having 2 to 20 phosphorus atoms per molecule are used to advantage in the present invention. In particular, those having 2 to 10 phosphorus atoms can produce better results. When the alloy powder is treated with a solution of orthophosphoric acid (H.sub.3 PO.sub.4), the initial activity can be somewhat improved, but the treated alloy becomes liable to be oxidized to result in deterioration of storage characteristics and difficulty in handling, and further a drop in the capacity achieved. When the number of phosphorus atoms in a poly-acid used is greater than 20, on the other hand, the hydrogen absorbing-desorbing reaction is suppressed by the poly-acid used to result in a decrease of hydrogen storage capacity.
In the present invention, such condensed phosphoric acids can be used alone or as a mixture of two or more thereof, or phytic acid can be used together with those condensed phosphoric acids or in place of them.
As for the solvent used for dissolving phytic acid, water, an alcohol (preferably having 1 to 5 carbon atoms), an aromatic hydrocarbon (e.g., toluene) and a ketone (e.g., acetone) are examples thereof. Also, mixed solvents (such as a water-alcohol mixture and an acetone-toluene mixture) may be used.
Further, it is preferable in the present invention that a pretreatment with a solution of mineral acid or alkali be performed prior to the treatment with a solution comprising the aforementioned condensed phosphoric acid(s) and/or phytic acid.
The concentration of a mineral acid used for the pretreatment can be chosen properly. More specifically, it is desirable that the mineral acid concentration be adjusted to 0.05-1.0 N, preferably 0.1-0.5 N. When the acid concentration is lower than 0.05 N, the alloy particle surface cannot experience sufficient pretreatment effect; as a result, the activation effect of the acid cannot be produced. When the acid concentration is higher than 1.0 N, on the other hand, the pretreatment proceeds to the interior of the alloy particles, and thereby the hydrogen storage capacity of the treated alloy tends to be decreased.
The mineral acid used in the present invention is not limited to any particular ones, but it can be selected properly from known mineral acids. Preferably, the mineral acid comprising at least hydrochloric acid, sulfuric acid or nitric acid is used.
After the pretreatment with a mineral acid, the alloy powder is washed with water, if needed, and then subjected to the treatment with a solution comprising a condensed phosphoric acid and/or phytic acid.
The suitable temperature in the pretreatment with a mineral acid is from room temperature to 130.degree.. The pretreatment under heating or cooling is undesirable in view of economy, because it causes a decrease of productivity and entails a high cost for the production in an industrial scale. In particular, the pretreatment carried out while cooling is impractical, because the pretreatment time becomes too long. Also, the pretreatment at a temperature higher than 130.degree. C. is undesirable, because the pretreatment proceeds to the interior of the alloy powder, thereby decreasing the hydrogen storage capacity.
When the pretreatment is carried out with an alkali in the present invention, the alkali has no particular restriction, but it can be selected properly from known alkalis. Specifically, the alkali comprising at least lithium hydroxide, sodium hydroxide or potassium hydroxide is used to advantage. In particular, lithium hydroxide is preferred over the others.
After the pretreatment with an alkali, it is desirable that the alkali-treated alloy be neutralized prior to the present treatment with a condensed phosphoric acid and/or phytic acid.
For neutralizing the alkali-treated alloy, any of conventional mineral acids can be used. Preferably, hydrochloric acid, sulfuric acid, nitric acid or a mixture of two or more thereof is employed.
The alkali concentration in the pretreatment can be chosen properly. More specifically, it is desirable that the alkali concentration be adjusted to 1.0-10.0 N, preferably 3.0-6.0 N. When the concentration is lower than 1.0 N. the alloy particle surface cannot experience sufficient pretreatment effect; as a result, the activation effect of the alkali cannot be produced. When the concentration is higher than 10.0 N, on the other hand, the pretreatment proceeds to the interior of the alloy particles, and thereby the hydrogen storage capacity of the treated alloy is decreased.
The suitable temperature in the pretreatment with an alkali is from room temperature to 150.degree. C. The pretreatment performed under a high temperature or while cooling is undesirable in view of economy because it lowers industrial productivity. More specifically, the pretreatment carried out while cooling requires too long a time, and the pretreatment at a temperature higher than 150.degree. C. is also undesirable because the pretreatment proceeds to the interior of the alloy powder, thereby decreasing the hydrogen storage capacity.
As for the pretreatment time, the range of 0.1 to 10 hours is appropriate in the case of using a mineral acid as well as the case of using an alkali. The time for the pretreatment can be adjusted properly depending on the pretreatment temperature. In other words, the pretreatment time is shortened when the temperature is high; while it is lengthened when the temperature is low. Also, the pretreatment may be carried out under a pressure of 10 kgf/cm.sup.2 or below in an airtight vessel, if needed.
The present invention has no particular restriction as to the way of the treating a hydrogen absorbing alloy, but any of known ways, e.g., immersing a hydrogen absorbing alloy in a treating solution, can be adopted. For effectively achieving the treatment, it is desirable that, prior to the immersion, the hydrogen absorbing alloy be ground to a powder. Preferably, the agitation is carried out during the immersion, and thereby the initial activity of the electrode using the thus treated alloy powder can be further elevated.
When the hydrogen absorbing alloy powder treated in accordance with the present method is applied to the negative electrode of a nickel-hydrogen secondary battery, the initial activity of the secondary battery undergoes a significant improvement. As a reason for this improvement, it can be presumed that the hydrogen alloy surface is covered by phosphorus compounds adsorbed thereon by undergoing the treatment with a condensed phosphoric acid and/or phytic acid after the pretreatment with a mineral acid or alkali.
The hydrogen absorbing alloy powder according to the present invention can be easily prepared in the following manner; A hydrogen absorbing alloy produced by fusing a metallic mixture having the composition as mentioned hereinbefore by means of, e.g., a known high frequency induction furnace is ground to a powder, and this powder is treated with a mineral acid or alkali, if desired, washed or neutralized, if needed, and immersed in a solution comprising a condensed phosphoric acid and/or phytic acid, and further washed, if desired, and dried.
In the present invention, the thus obtained alloy powder is kneaded with a binder, such as PVA, a cellulose derivative, PTFE or polyethylene oxide, to make a paste, and this paste is filled into a three-dimensional conductive support, such as textile Ni or foamed Ni, or a two-dimensional conductive support such as a punching metal, and then pressed, thereby preparing a negative electrode.
In accordance with the present method, a hydrogen absorbing alloy powder having not only high activity but also excellent keeping quality and easiness of handling can be obtained with great ease. Further, the use of the hydrogen absorbing alloy powder obtained in accordance with the present method can ensure excellent initial activity in the negative electrode of a nickel-hydrogen secondary battery.

The present invention will now be illustrated in greater detail by reference to the following examples. However, the invention should not be construed as being limited to these examples.
EXAMPLES AND COMPARATIVE EXAMPLES
The metallic elements Mm, Al, Co Mn and Ni were weighed out in the atomic ratio of 1.00:0.30:0.75:0.20:3.75. The metallic element Mm used herein was a Mish metal constituted of 61 weight % of La, 7 weight % of Ce, 23 weight % of Pr and 9 weight % of Nd. These elements were fused under an atmosphere of argon by means of a high frequency induction furnace to give a hydrogen absorbing alloy ingot. This ingot was subjected to a heat treatment at 1020.degree. C., and then ground to a fine powder having an average particle size of 32 .mu.m.
Various treating solutions were prepared using the condensed phosphoric acids set forth in Table 1 or phytic acid respectively. Herein, the concentration of each treating solution was chosen from the range of 0.01 to 30 weight %.
The alloy powder obtained in the foregoing manner and each of those treating solutions were mixed in a proportion of 2 kg to 1 liter with stirring. The resulting mixture was filtered off, and then dried. Each of the thus treated powders was used for an electrode of the secondary battery described below. The characteristics of these secondary batteries were examined using the method mentioned below, and thereby the electrode performance and the treated alloy powder quality were evaluated. The evaluation results are shown in Tables 1 and 2.
In addition to the foregoing experiments, other experiments were carried out, wherein the alloy powder was pretreated with a mineral acid solution having its concentration in the range of 0.01 to 1.5 N, and then treated with the aforementioned treating solutions respectively. The thus treated alloy powders were evaluated in the same way as described above. These evaluation results are shown in Tables 3 and 6. Further, the same experiments as the above, except that the alloy powder was pretreated with an alkali solution having its concentration in the range of 0.1 to 12 N in place of an mineral acid solution, were carried out, and the alloy powders thus treated were evaluated in the same way as described above. The evaluation results obtained are shown in Tables 7 to 10.
Making Secondary Battery
The treated powder in an amount of 2 g was mixed with 0.5 g of a 3 weight % solution of polyvinyl alcohol (average polymerization degree: 2,000) to prepare a paste. This paste was applied to a textile Ni support, dried, and then subjected to pressure molding to form into a negative electrode having a thickness of 0.5 mm. Further, a sintered nickel prepared by a conventional method was used as a nickel oxide positive electrode, a nonwoven fabric of polypropylene was used as a separator, and a 6N aqueous solution of KOH was used as an electrolytic solution. These were combined with the foregoing negative electrode to make an negative electrode-regulated open-type nickel-hydrogen secondary battery.
Evaluation of Initial Activity and Initial Capacity
The thus made battery was charged for 5 hours by sending thereto an electric current of 180 mA at a temperature regulated at 20.degree. C., and then made to discharge an electric current of 120 mA until the battery voltage was dropped to 1.0 V. This charge-discharge cycle operation was repeated for 10 times. The initial activity was evaluated by the capacity measured at the first cycle, and the initial capacity was evaluated by the capacity measured at the tenth cycle. These results are shown in Tables 1, 3, 4, 7 and 8 together with the conditions employed in each treatment.
Evaluation of Storage Characteristics
Secondary batteries were made in the same manner as described above, except that the alloy powders treated as shown in Tables 1, 3, 4, 7 and 8 were used respectively after two months' storage, and their initial activities and initial capacities were evaluated by the same procedures as described above. The evaluation results are shown in Tables 2, 5, 6, 9 and 10.
In Tables 1 to 10, Experiment No. to which the mark * is attached corresponds to Comparative Example. The symbols used therein stand for the following compounds respectively:
Pn: Condensed phosphoric acid of formula H.sub.n+2 P.sub.n O.sub.3n+1 (which is symbolized by the number of phosphorus atoms therein).
F: Methanol solution of phytic acid
C: Hydrochloric acid
N: Nitric acid
S: Sulfuric acid
K: KOH
N: NaOH
L: LiOH
K/L: KOH/LiOH=9/1
TABLE 1__________________________________________________________________________ Treating Treating agent Treatment Treatment 1st-cycle 10th-cycleExperiment agent concentration temperature time capacity capacityNo. (P.sub.n) (wt %) (.degree. C.) (min) (mAh/g) (mAh/g)__________________________________________________________________________ 0* none 0 -- -- 204 291 1* P1 0.5 60 60 210 2942 P2 0.5 20 60 228 3143 P2 0.5 60 60 230 3184 P2 0.5 100 60 222 3125 P2 0.5 120 60 208 2926 P4 0.005 60 60 209 2917 P4 0.01 60 60 221 3138 P4 0.5 60 60 236 3209 P4 10 60 60 225 31810 P4 15 60 60 207 29311 P4 0.5 60 3 210 29412 P4 0.5 60 10 226 31713 P4 0.5 60 300 232 31614 P4 0.5 60 600 229 31515 P4 0.5 60 900 208 29616 P10 0.5 60 60 227 31517 P20 0.5 60 60 224 31418 F 0.5 60 60 232 31919* P25 0.5 60 60 206 295__________________________________________________________________________ *: Comparative Examples Treating Agent: Condensed phosphoric acid (H.sub.n+2 P.sub.n O.sub.3n+1)
TABLE 2__________________________________________________________________________ Treating Treating agent Treatment Treatment 1st-cycle 10th-cycleExperiment agent concentration temperature time capacity capacityNo. (P.sub.n) (wt %) (.degree. C.) (min) (mAh/g) (mAh/g)__________________________________________________________________________ 100* none 0 -- -- 161 282 101* P1 0.5 60 60 191 284102 P2 0.5 20 60 228 316103 P2 0.5 60 60 229 319104 P2 0.5 100 60 219 314105 P2 0.5 120 60 198 284106 P4 0.005 60 60 167 282107 P4 0.01 60 60 216 311108 P4 0.5 60 60 235 320109 P4 10 60 60 224 316110 P4 15 60 60 202 281111 P4 0.5 60 3 178 281112 P4 0.5 60 10 222 315113 P4 0.5 60 300 230 316114 P4 0.5 60 600 230 314115 P4 0.5 60 900 204 278116 P10 0.5 60 60 228 315117 P20 0.5 60 60 218 313118 F 0.5 60 60 233 320 119* P25 0.5 60 60 201 280__________________________________________________________________________ *: Comparative Examples Treating Agent: Condensed phosphoric acid (H.sub.n+2 P.sub.n O.sub.3n+1)
TABLE 3__________________________________________________________________________Acid Treatment Treatment with Treating Agent Mineral Treating acid Treating agent Treatment Treatment 1st-cycle 10th-cycleExperiment Mineral concentration Temperature Time agent concentration temperature time capacity capacityNo. acid (N) (.degree. C.) (hr) (P.sub.n) (wt %) (.degree. C.) (min) (mAh/g) (mAh/g)__________________________________________________________________________0* -- none -- -- none 0 -- -- 204 291 A-1-1 -- none -- -- P2 0.5 60 60 230 318 A-1-2* C 0.15 60 0.5 none 0 -- -- 219 290A-2* C 0.15 60 0.5 P1 0.5 60 60 219 289A-3 C 0.15 20 0.5 P2 0.5 60 60 251 305A-4 C 0.15 60 0.5 P2 0.5 60 60 267 307A-5 C 0.15 130 0.5 P2 0.5 60 60 261 309A-6 C 0.15 150 0.5 P2 0.5 60 60 220 281A-7 C 0.15 60 0.5 P4 0.5 20 60 264 308A-8 C 0.15 60 0.5 P4 0.5 60 60 269 310A-9 C 0.15 60 0.5 P4 0.5 130 60 254 306A-10 C 0.15 60 0.5 P4 0.5 150 60 219 285A-11 C 0.01 60 0.5 P4 0.5 60 60 207 280A-12 C 0.05 60 0.5 P4 0.5 60 60 252 301A-13 C 0.5 60 0.5 P4 0.5 60 60 268 307A-14 C 1 60 0.5 P4 0.5 60 60 262 300A-15 C 1.5 60 0.5 P4 0.5 60 60 218 268A-16 N 0.15 60 0.5 P4 0.5 60 60 255 301A-17 S 0.15 60 0.5 P4 0.5 60 60 262 307__________________________________________________________________________ *: Comparative Examples Treating Agent: Condensed phosphoric acid (H.sub.n+2 P.sub.n O.sub.3n+1)
TABLE 4__________________________________________________________________________Acid Treatment Treatment with Treating Agent Mineral Treating acid Treating agent Treatment Treatment 1st-cycle 10th-cycleExperiment Mineral concentration Temperature Time agent concentration temperature time capacity capacityNo. acid (N) (.degree. C.) (hr) (P.sub.n) (wt %) (.degree. C.) (min) (mAh/g) (mAh/g)__________________________________________________________________________A-18 C 0.15 60 0.05 P10 0.5 60 60 218 279A-19 C 0.15 60 0.1 P10 0.5 60 60 257 306A-20 C 0.15 60 0.5 P10 0.5 60 60 260 308A-21 C 0.15 60 1 P10 0.5 60 60 258 307A-22 C 0.15 60 5 P10 0.5 60 60 256 305A-23 C 0.15 60 10 P10 0.5 60 60 253 304A-24 C 0.15 60 15 P10 0.5 60 60 219 268A-25 C 0.15 60 0.5 P20 0.005 60 60 214 291A-26 C 0.15 60 0.5 P20 0.01 20 60 255 303A-27 C 0.15 60 0.5 P20 0.5 60 60 258 310A-28 C 0.15 60 0.5 P20 10 60 60 252 304A-29 C 0.15 60 0.5 P20 15 60 60 217 283A-30 C 0.15 60 0.5 P20 0.5 60 3 217 280A-31 C 0.15 60 0.5 P20 0.5 60 10 256 306A-32 C 0.15 60 0.5 P20 0.5 60 300 255 309A-33 C 0.15 60 0.5 P20 0.5 60 600 250 308A-34 C 0.15 60 0.5 P20 0.5 60 900 215 289 A-35* C 0.15 60 0.5 P25 0.5 60 60 211 282A-36 C 0.15 60 0.5 F 0.5 60 60 264 311__________________________________________________________________________ *: Comparative Example Treating Agent: Condensed phosphoric acid (H.sub.n+2 P.sub.n O.sub.3n+1)
TABLE 5__________________________________________________________________________Acid Treatment Treatment with Treating Agent Mineral Treating acid Treating agent Treatment Treatment 1st-cycle 10th-cycleExperiment Mineral concentration Temperature Time agent concentration temperature time capacity capacityNo. acid (N) (.degree. C.) (hr) (P.sub.n) (wt %) (.degree. C.) (min) (mAh/g) (mAh/g)__________________________________________________________________________ A-100* -- none -- -- none 0 -- -- 161 282 A-101-1 -- none -- -- P2 0.5 60 60 229 319 A-101-2* C 0.15 60 0.5 none 0 -- -- 145 281 A-102* C 0.15 60 0.5 P1 0.5 60 60 152 279A-103 C 0.15 20 0.5 P2 0.5 60 60 250 305A-104 C 0.15 60 0.5 P2 0.5 60 60 267 308A-105 C 0.15 130 0.5 P2 0.5 60 60 259 307A-106 C 0.15 150 0.5 P2 0.5 60 60 170 269A-107 C 0.15 60 0.5 P4 0.5 20 60 262 306A-108 C 0.15 60 0.5 P4 0.5 60 60 268 310A-109 C 0.15 60 0.5 P4 0.5 130 60 254 305A-110 C 0.15 60 0.5 P4 0.5 150 60 201 280A-111 C 0.01 60 0.5 P4 0.5 60 60 205 275A-112 C 0.05 60 0.5 P4 0.5 60 60 253 302A-113 C 0.5 60 0.5 P4 0.5 60 60 265 305A-114 C 1 60 0.5 P4 0.5 60 60 258 300A-115 C 1.5 60 0.5 P4 0.5 60 60 177 259A-116 N 0.15 60 0.5 P4 0.5 60 60 254 300A-117 S 0.15 60 0.5 P4 0.5 60 60 260 305__________________________________________________________________________ *: Comparative Examples Treating Agent: Condensed phosphoric acid (H.sub.n+2 P.sub.n O.sub.3n+1)
TABLE 6__________________________________________________________________________Acid Treatment Treatment with Treating Agent Mineral Treating acid Treating agent Treatment Treatment 1st-cycle 10th-cycleExperiment Mineral concentration Temperature Time agent concentration temperature time capacity capacityNo. acid (N) (.degree. C.) (hr) (P.sub.n) (wt %) (.degree. C.) (min) (mAh/g) (mAh/g)__________________________________________________________________________A-118 C 0.15 60 0.05 P10 0.5 60 60 200 270A-119 C 0.15 60 0.1 P10 0.5 60 60 257 305A-120 C 0.15 60 0.5 P10 0.5 60 60 261 308A-121 C 0.15 60 1 P10 0.5 60 60 256 306A-122 C 0.15 60 5 P10 0.5 60 60 256 304A-123 C 0.15 60 10 P10 0.5 60 60 251 302A-124 C 0.15 60 15 P10 0.5 60 60 209 267A-125 C 0.15 60 0.5 P20 0.005 60 60 192 279A-126 C 0.15 60 0.5 P20 0.01 60 60 252 301A-127 C 0.15 60 0.5 P20 0.5 60 60 259 310A-128 C 0.15 60 0.5 P20 10 60 60 253 303A-129 C 0.15 60 0.5 P20 15 60 60 215 273A-130 C 0.15 60 0.5 P20 0.5 60 3 199 273A-131 C 0.15 60 0.5 P20 0.5 60 10 253 304A-132 C 0.15 60 0.5 P20 0.5 60 300 255 306A-133 C 0.15 60 0.5 P20 0.5 60 600 250 306A-134 C 0.15 60 0.5 P20 0.5 60 900 214 285 A-135* C 0.15 60 0.5 P25 0.5 60 60 211 263A-136 C 0.15 60 0.5 F 0.5 60 60 263 310__________________________________________________________________________ *: Comparative Example Treating Agent: Condensed phosphoric acid (H.sub.n+2 P.sub.n O.sub.3n+1)
TABLE 7__________________________________________________________________________ Treatment with Treating AgentAlkali Treatment Treating Alkali Treating agent Treatment Treatment 1st-cycle 10th-cycleExperiment concentration Temperature Time agent concentration temperature time capacity capacityNo. Alkali (N) (.degree. C.) (hr) (P.sub.n) (wt %) (.degree. C.) (min) (mAh/g) (mAh/g)__________________________________________________________________________0* -- none -- -- none 0 -- -- 204 291 B-1-1 -- none -- -- P2 0.5 60 60 230 318 B-1-2* K 6 110 5 none 0 -- -- 218 289B-2* K 6 110 5 P1 0.5 60 60 217 288B-3 K 6 20 5 P2 0.5 60 60 252 300B-4 K 6 60 5 P2 0.5 60 60 260 302B-5 K 6 110 5 P2 0.5 60 60 263 305B-6 K 6 150 5 P2 0.5 60 60 264 306B-7 K 6 180 5 P2 0.5 60 60 211 285B-8 K 6 110 5 P4 0.5 20 60 259 305B-9 K 6 110 5 P4 0.5 130 60 260 303B-10 K 6 110 5 P4 0.5 150 60 218 284B-11 K 0.1 110 5 P4 0.5 60 60 207 279B-12 K 1 110 5 P4 0.5 60 60 251 303B-13 K 3 110 5 P4 0.5 60 60 256 306B-14 K 6 110 5 P4 0.5 60 60 261 308B-15 K 10 110 5 P4 0.5 60 60 264 308B-16 K 12 110 5 P4 0.5 60 60 221 279B-17 N 6 110 5 P4 0.5 60 60 258 301B-18 L 6 110 5 P4 0.5 60 60 250 300B-19 K/L 6 110 5 P4 0.5 60 60 266 308__________________________________________________________________________ *: Comparative Examples Treating Agent: Condensed phosphoric acid (H.sub.n+2 P.sub.n O.sub.3n+1)
TABLE 8__________________________________________________________________________ Treatment with Treating AgentAlkali Treatment Treating Alkali Treating agent Treatment Treatment 1st-cycle 10th-cycleExperiment concentration Temperature Time agent concentration temperature time capacity capacityNo. Alkali (N) (.degree. C.) (min) (P.sub.n) (wt %) (.degree. C.) (min) (mAh/g) (mAh/g)__________________________________________________________________________B-20 K 6 110 3 P10 0.5 60 60 200 277B-21 K 6 110 10 P10 0.5 60 60 250 301B-22 K 6 110 60 P10 0.5 60 60 252 303B-23 K 6 110 300 P10 0.5 60 60 258 305B-24 K 6 110 600 P10 0.5 60 60 260 306B-25 K 6 110 900 P10 0.5 60 60 212 286B-26 K 6 110 300 P20 0.005 60 60 218 288B-27 K 6 110 300 P20 0.01 60 60 252 300B-28 K 6 110 300 P20 0.5 60 60 260 302B-29 K 6 110 300 P20 10 60 60 261 304B-30 K 6 110 300 P20 15 60 60 221 284B-31 K 6 110 300 P20 0.5 60 3 218 281B-32 K 6 110 300 P20 0.5 60 10 259 301B-33 K 6 110 300 P20 0.5 60 300 261 304B-34 K 6 110 300 P20 0.5 60 600 258 305B-35 K 6 110 300 P20 0.5 60 900 220 288 B-36* K 6 110 300 P25 0.5 60 60 218 278B-37 K 6 110 300 F 0.5 60 60 268 307__________________________________________________________________________ *: Comparative Examples Treating Agent: Condensed phosphoric acid (H.sub.n+2 P.sub.n O.sub.3n+1)
TABLE 9__________________________________________________________________________ Treatment with Treating AgentAlkali Treatment Treating Alkali Treating agent Treatment Treatment 1st-cycle 10th-cycleExperiment concentration Temperature Time agent concentration temperature time capacity capacityNo. Alkali (N) (.degree. C.) (hr) (P.sub.n) (wt %) (.degree. C.) (min) (mAh/g) (mAh/g)__________________________________________________________________________ B-100* -- none -- -- none 0 -- -- 161 282 B-101-1 -- none -- -- P2 0.5 60 60 229 319 B-101-2* K 6 110 5 none 0 -- -- 143 279 B-102* K 6 110 5 P1 0.5 60 60 207 276B-103 K 6 20 5 P2 0.5 60 60 252 300B-104 K 6 60 5 P2 0.5 60 60 259 301B-105 K 6 110 5 P2 0.5 60 60 262 305B-106 K 6 150 5 P2 0.5 60 60 260 303B-107 K 6 180 5 P2 0.5 60 60 209 278B-108 K 6 110 5 P4 0.5 20 60 256 303B-109 K 6 110 5 P4 0.5 130 60 260 302B-110 K 6 110 5 P4 0.5 150 60 211 279B-111 K 0.1 110 5 P4 0.5 60 60 207 277B-112 K 1 110 5 P4 0.5 60 60 251 303B-113 K 3 110 5 P4 0.5 60 60 255 305B-114 K 6 110 5 P4 0.5 60 60 261 307B-115 K 10 110 5 P4 0.5 60 60 263 305B-116 K 12 110 5 P4 0.5 60 60 217 276B-117 N 6 110 5 P4 0.5 60 60 254 301B-118 L 6 110 5 P4 0.5 60 60 250 301B-119 K/L 6 110 5 P4 0.5 60 60 266 309__________________________________________________________________________ *: Comparative Examples Treating Agent: Condensed phosphoric acid (H.sub.n+2 P.sub.n O.sub.3n+1)
TABLE 10__________________________________________________________________________ Treatment with Treating AgentAlkali Treatment Treating Alkali Treating agent Treatment Treatment 1st-cycle 10th-cycleExperiment concentration Temperature Time agent concentration temperature time capacity capacityNo. Alkali (N) (.degree. C.) (min) (P.sub.n) (wt %) (.degree. C.) (min) (mAh/g) (mAh/g)__________________________________________________________________________B-120 K 6 110 3 P10 0.5 60 60 198 270B-121 K 6 110 10 P10 0.5 60 60 250 301B-122 K 6 110 60 P10 0.5 60 60 252 303B-123 K 6 110 300 P10 0.5 60 60 259 305B-124 K 6 110 600 P10 0.5 60 60 258 304B-125 K 6 110 900 P10 0.5 60 60 212 283B-126 K 6 110 300 P20 0.005 60 60 178 273B-127 K 6 110 300 P20 0.01 60 60 251 300B-128 K 6 110 300 P20 0.5 60 60 260 302B-129 K 6 110 300 P20 10 60 60 261 304B-130 K 6 110 300 P20 15 60 60 220 282B-131 K 6 110 300 P20 0.5 60 3 185 281B-132 K 6 110 300 P20 0.5 60 10 257 301B-133 K 6 110 300 P20 0.5 60 300 261 305B-134 K 6 110 300 P20 0.5 60 600 258 306B-135 K 6 110 300 P20 0.5 60 900 218 282 B-136* K 6 110 300 P25 0.5 60 60 218 271B-137 K 6 110 300 F 0.5 60 60 269 308__________________________________________________________________________ *: Comparative Example Treating Agent: Condensed phosphoric acid (H.sub.n+2 P.sub.n O.sub.3n+1)
As is apparent from the results shown in Table 1 (specifically, by making comparisons between Comparative Examples (e.g., Experiment No. 0) and the present Examples e.g., Experiment Nos. 2, 8, 17 and 18), the initial activity of the secondary battery was elevated by the treatment according to the present invention. Further, the results of Experimental Nos. 1 to 19 demonstrate that the expected effects were fully achieved by using as a treating agent a condensed phosphoric acid having 2 to 20 phosphorus atoms or phytic acid. Furthermore, it was confirmed by the results of Experiment Nos. 6 to 10 that the condensed phosphoric acid had a beneficial effect when the concentration thereof was in the range of about 0.01 to 10 weight % and the effect produced thereby was maximal in the concentration range of about 0.1 to 1 weight %.
As for the treatment temperature, it was confirmed by the results of Experiment Nos. 2 to 5 that the treatment effect was lessened when the treatment was carried out at a temperature higher than 100.degree. C. As a cause thereof, it is assumed that the alloy surface is oxidized during the treatment at such a high temperature.
Moreover, the comparisons between the data set forth in Table 1 and those set forth in Table 2 prove that the drops in initial activity and initial capacity due to the use of the stored alloy powders were decidedly small in the experiments according to the present invention, compared with those in the comparative experiments. These results indicate that the alloy powder treated in accordance with the present invention had excellent storage stability.
From the results shown in Tables 3 and 4 (specifically, by making comparisons between Comparative Examples (Experiment Nos. 0, A-2 and A-35) and the present Examples (e.g., Experiment Nos., A-4, A-8, A-20, A-27 and A-36), it is also apparent that not only the initial activity but also the initial capacity were elevated by the treatment according to the present invention. In particular, the results of Experiment Nos. A-11 to A-15 indicate that the expected effects were fully achieved in the case where the pulverized alloy was treated in advance with a 0.05-1 N mineral acid and then with a solution of condensed phosphoric acid or phytic acid. Further, it was confirmed by the results of Experiments No. A-3 to A-6 that the discharge capacity was lowered when the pretreatment with a mineral acid was carried out at a temperature higher than 130.degree. C. In addition, it was confirmed by the results of Experiment Nos. A-8, A-16 and A-17 that similar elevation effects were produced by using as the mineral acid not only hydrochloric acid but also nitric acid or sulfuric acid.
Furthermore, it is seen from the results of Experimental Nos. A-25 to A-29 that the present condensed phosphoric acid or phytic acid had satisfactory effects when it was used in a proportion of 0.01 to 10 weight %, and the optimum effects were accomplished when the proportion was in the range of 0.1 to 1 weight %. As for the treatment temperature, it was confirmed by the results of Experiment Nos. A-7 to A-10 that the treatment effects were lessened when the treatment was carried out at a temperature higher than 130.degree. C.
With respect to the keeping quality of the hydrogen absorbing powder, it was confirmed by the comparisons between the data set forth in Tables 3 and 4 and the data set forth in Tables 5 and 6 that, in contrast to the hydrogen alloy powder untreated or undergone a treatment other than those according to the present invention, the hydrogen alloy powder undergone the pretreatment with an acid and the treatment with a condensed phosphoric acid or phytic acid caused only a slight or no decrease in the initial activity and the initial capacity even when it was used after a long-range storage. These results indicate that the alloy powder treated in accordance with the present invention had excellent storage stability.
From the results shown in Tables 7 and 8 (specifically, by making comparisons between Comparative Examples (Experiment Nos. 0, B-1-2, B-2 and B-36) and the present Examples (e.g., Experiment Nos. B-5, B-14, B-23, B-28 and B-33), it is also apparent that the treatment according to the present invention was successful in elevating not only the initial activity but also the initial capacity. In particular, the results of Experiment Nos. B-11 to B-16 indicate that the expected effects were fully achieved in the case where the pulverized alloy was treated in advance with a 1-10 N alkali and then with a solution of condensed phosphoric acid or phytic acid. Further, it was confirmed by the results of Experiments No. B-3 to B-7 that the discharge capacity was lowered when the pretreatment with an alkali was carried out at a temperature higher than 150.degree. C. In addition, it was confirmed by the results of Experiment Nos. B-14, B-17 and B-19 that potassium hydroxide, sodium hydroxide, lithium hydroxide and mixtures thereof were effectively used in the pretreatment.
Furthermore, it is seen from the results of Experimental Nos. B-26 to B-30 that the present condensed phosphoric acid or phytic acid had satisfactory effects when it was used in a proportion of 0.01 to 10 weight %, and the optimum effects were accomplished when the proportion was in the range of 0.1 to 1 weight %. As for the treatment temperature, it was confirmed by the results of Experiment Nos. B-8 to B-10 and B-14 that the treatment effects were lessened when the treatment was carried out at a temperature higher than 130.degree. C.
With respect to the keeping quality of the hydrogen absorbing powder, it was confirmed by the comparisons between the data set forth in Tables 7 and 8 and the data set forth in Tables 9 and 10 that, in contrast to the hydrogen alloy powder untreated or undergone a treatment other than those according to the present invention, the hydrogen alloy powder undergone the pretreatment with an alkali and the treatment with a condensed phosphoric acid or phytic acid caused only a slight or no decrease in the initial activity and the initial capacity even when it was used after a long-range storage. These results indicate that the alloy powder treated in accordance with the present invention had excellent storage stability.
As demonstrated above, the treatment according to the present invention enables a hydrogen absorbing alloy powder to have high activity and satisfactory storage characteristics, and the negative electrode using the thus treated alloy powder can ensure high initial activity in the nickel-hydrogen secondary battery.

Number	Date	Country
8-294473	Oct 1996	JPX
8-297121	Oct 1996	JPX
8-297122	Oct 1996	JPX

Number	Name	Date	Kind
5605585	Yamamoto et al.	Feb 1997
5695530	Hong et al.	Dec 1997

Method of producing hydrogen absorbing alloy powder, and electrode using hydrogen absorbing alloy powder produced by said method

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Patent Abstracts of Japan, vol. 096, No. 002, Feb. 29, 1996 & JP 07 2881929 (Shin Etsu Chem Co Ltd), Oct. 31, 1995.
Patent Abstracts of Japan, vol. 017, No. 152 (E-1340), Mar. 25, 1993 & JP 04 319258, (Furukawa Battery Co Ltd: The), Nov. 10, 1992.
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Patent Abstracts of Japan, vol. 097, No. 007, Jul. 31, 1997 & JP 09 063581 (Furukawa Electric Co Ltd: The; Furukawa Battery Co Ltd: The), Mar. 7, 1997.
Patent Abstracts of Japan, vol. 017, No. 628 (M-1512), Nov. 19, 1993 & JP 05 195008 (Matsushita Electric Ind Co Ltd), Aug. 3, 1993.