Hydrogen storage alloy negative electrode and nickel-metal hydride secondary battery including the same

Abstract

The present invention provides a hydrogen storage alloy negative electrode capable of improving cycle life characteristics and low-temperature charging characteristics. The hydrogen storage alloy negative electrode contains a hydrogen storage alloy and yttrium fluoride as an additive. The mass of yttrium fluoride is 0.1 part by mass or more and 0.2 part by mass or less with respect to 100 parts by mass of the hydrogen storage alloy powder.

Description

Technical Field

[0001] The present invention relates to a hydrogen storage alloy negative electrode and a nickel-metal hydride secondary battery including the hydrogen storage alloy negative electrode. Background Art

[0002] Compared with nickel-cadmium secondary batteries, nickel-metal hydride secondary batteries have a high capacity and excellent environmental safety, and thus are used in various devices such as portable electronic devices, power tools, and hybrid electric vehicles, and their uses are expanding. Along with the expansion of these uses, higher performance of nickel-metal hydride secondary batteries is desired. Japanese Patent Laid-Open No. 8-329934 discloses that improvement of cycle life characteristics is an important technical problem. That is, a large amount of research has been conducted to improve cycle life characteristics in a manner that can increase the number of charge and discharge cycles of the battery.

[0003] In Japanese Patent Laid-Open No. 2016-149299, in order to extend the cycle life, for example, rare earth fluorides are proposed as additives to the negative electrode active material mixture. By using these materials, corrosion of the hydrogen-containing hydrogen storage alloy as the negative electrode active material by the high-concentration alkali as the electrolyte can be suppressed. Therefore, the cycle life of the battery can be improved.

[0004] However, when rare earth fluorides are added at a concentration above a certain level, for example, when charging in a low-temperature environment at the freezing point of -10°C, there is a problem that the discharge capacity decreases. That is, the low-temperature charging characteristics deteriorate. In the present disclosure, the "low-temperature charging characteristics" means that the normal charging characteristics usually represent the maximum charging capacity when charging at room temperature (25°C), and here it represents, for example, the maximum capacity that can be discharged in a room-temperature environment after charging at a temperature below room temperature such as -10°C or below the freezing point.

[0005] Therefore, an object of the present invention is to provide a hydrogen storage alloy negative electrode that can simultaneously achieve cycle life characteristics and low-temperature charging characteristics, and a nickel-metal hydride secondary battery including the hydrogen storage alloy negative electrode. Summary of the Invention

[0006] The hydrogen storage alloy negative electrode of the present invention is characterized by including a hydrogen storage alloy and yttrium fluoride as an additive, and the mass of the yttrium fluoride is 0.1 part by mass or more and 0.2 part by mass or less relative to 100 parts by mass of the hydrogen storage alloy powder. Brief Description of the Drawings

[0007] Figure 1 It is a perspective view showing a partial cutaway of a nickel-metal hydride secondary battery of one embodiment.

[0008] Figure 2 It is a table showing low-temperature charging characteristics and cycle life characteristics.

[0009] Figure 3It is a graph showing the changes in low-temperature charging characteristics and cycle life characteristics with respect to the addition amount of yttrium fluoride. Detailed implementation mode

[0010] 1. Composition and manufacturing of nickel-metal hydride secondary battery

[0011] Hereinafter, the nickel-metal hydride secondary battery (hereinafter referred to as the battery) 2 of the present disclosure will be described with reference to the accompanying drawings.

[0012] For example, Figure 1 A cylindrical battery 2 of AA size is shown, but the size of the battery 2 to which the present disclosure can be applied is not limited to AA size.

[0013] As Figure 1 Shown, the battery 2 includes an outer can 10, which has a bottomed cylindrical shape with an open upper end. The bottom wall 35 of the outer can 10 has conductivity and functions as a negative terminal. A sealing body 11 is fixed at the opening of the outer can 10. The sealing body 11 includes a cover plate 14 and a positive terminal 20, which seals the outer can 10 and also constitutes the positive terminal 20. A circular plate-shaped cover plate 14 having conductivity and an annular insulating gasket 12 surrounding the cover plate 14 are arranged inside the opening of the outer can 10. The insulating gasket 12 is fixed to the opening edge of the outer can 10 by riveting the opening edge 37 of the outer can 10. That is, the cover plate 14 and the insulating gasket 12 cooperate with each other to airtightly seal the opening of the outer can 10.

[0014] The cover plate 14 has an exhaust hole 16 in the center, and a rubber valve body 18 blocking the exhaust hole 16 is arranged on the outer surface of the cover plate 14. In addition, a flanged cylindrical positive terminal 20 is fixed to the outer surface of the cover plate 14 so as to cover the valve body 18. The positive terminal 20 presses the valve body 18 against the cover plate 14. Among them, a vent hole (not shown) is provided in the positive terminal 20. Usually, the exhaust hole 16 is airtightly blocked by the valve body 18. However, when gas is generated inside the outer can 10 and its internal pressure rises, the valve body 18 is compressed by the internal pressure and the exhaust hole 16 is opened. Thereby, the gas is discharged from the inside of the outer can 10 through the exhaust hole 16 and the vent hole of the positive terminal 20. That is, the exhaust hole 16, the valve body 18 and the positive terminal 20 form the safety valve of the battery.

[0015] An electrode group 22 is housed in the outer can 10. The electrode group 22 includes a strip-shaped positive electrode 24, a negative electrode 26 and a separator 28 respectively. The separator 28 is wound in a spiral shape while being sandwiched between the positive electrode 24 and the negative electrode 26. That is, the positive electrode 24 and the negative electrode 26 face each other with the separator 28 interposed therebetween and overlap in the radial direction of the outer can 10.

[0016] Inside the outer can 10, a positive electrode lead 30 is disposed between one end of the electrode group 22 and the cover plate 14, and each end portion of the positive electrode lead 30 is connected to the positive electrode 24 and the cover plate 14 respectively. That is, the positive terminal 20 of the cover plate 14 and the positive electrode 24 are electrically connected to each other through the positive electrode lead 30 and the cover plate 14. In addition, a circular insulating member 32 is disposed between the cover plate 14 and the electrode group 22, and the positive electrode lead 30 extends through a slit 39 provided in the insulating member 32. A circular insulating member 34 is also disposed between the electrode group 22 and the bottom of the outer can 10.

[0017] A predetermined amount of alkaline electrolyte (not shown) is injected into the outer can 10. The alkaline electrolyte is impregnated in the positive electrode 24, the negative electrode 26, and the separator 28, and participates in the charge and discharge reaction between the positive electrode 24 and the negative electrode 26. As this alkaline electrolyte, there is no particular limitation, and an alkaline electrolyte containing NaOH as the main solute can be used. As the alkaline electrolyte in this embodiment, ideally, as the solute, in addition to NaOH, it also contains at least one of KOH and LiOH. For example, an electrolyte composed of an NaOH solution and an LiOH solution in a ratio of 8.0:0.7 is used. Thus, it is ideal to use an electrolyte with a high sodium content, whereby the overvoltage required for the water decomposition reaction can be increased, and the charging efficiency can be further improved.

[0018] In the electrode group 22, the separator 28 is not wound around the outer periphery, and the outermost peripheral portion 22 of the negative electrode 26 forms the outer periphery of the electrode group 22. By contacting the peripheral wall of the outer can through its outer surface, the negative electrode 26 and the outer can 10 are electrically connected to each other.

[0019] The separator 28 is preferably made of, for example, a non-woven fabric composed of polypropylene fibers subjected to sulfonation treatment. Among them, the sulfonic acid group captures metal ions dissolved in the electrolyte and prevents the dissolved metal ions from depositing on the surfaces of the positive electrode active material and the negative electrode active material respectively. When the separator 28 is subjected to sulfonation treatment in this way, not only hydrophilicity can be imparted, but also the deposition of dissolved metal ions on the active material surface can be prevented, which is the main factor for reducing the charging temperature characteristics and the cycle life characteristics. Therefore, it also helps to suppress the self-discharge of the battery 2.

[0020] The positive electrode 24 is composed of a conductive positive electrode substrate having a porous structure and a positive electrode mixture held in the pores of the positive electrode substrate and on the surface of the positive electrode substrate. As the positive electrode substrate, for example, a nickel-plated mesh, sponge-like, or fibrous metal body or foamed nickel can be used.

[0021] The positive electrode mixture contains positive electrode active material particles, a conductive material, a positive electrode additive, and a binder. The positive electrode active material particles are nickel hydroxide particles or higher-order nickel hydroxide particles. In addition, it is preferable that at least one of zinc, magnesium, and cobalt is also solid-solved in these nickel hydroxide particles.

[0022] Positive electrode additives are appropriately selected as needed to improve the characteristics of the positive electrode. As main positive electrode additives, for example, yttrium oxide and zinc oxide can be cited.

[0023] As the conductive material, one or more selected from cobalt compounds such as cobalt oxide (CoO) and cobalt hydroxide (Co(OH)2) and cobalt (Co) can be used. The conductive material is added to the positive electrode mixture as needed, and in addition to the powder form, it can also be included in the positive electrode mixture in a coating form that covers the surface of the positive electrode active material.

[0024] The binder serves to bond the positive electrode active material particles, the conductive material, and the positive electrode additive, and also to bond the positive electrode mixture to the positive electrode substrate. Here, as the binder, for example, carboxymethyl cellulose, methyl cellulose, polytetrafluoroethylene (PTFE) dispersion, hydroxypropyl cellulose (HPC) dispersion, etc. can be used.

[0025] These positive electrode active material particles, conductive material, positive electrode additive, binder, and water are mixed to prepare a positive electrode active material slurry.

[0026] For example, under the conditions of 3 wt% of zinc, 0.4 wt% of magnesium, and 1 wt% of cobalt with respect to metallic nickel, while stirring a mixed aqueous solution of nickel sulfate, zinc sulfate, magnesium sulfate, and cobalt sulfate, an aqueous sodium hydroxide solution is slowly added to keep the pH in the reaction stable at 13 - 14 and dissolve nickel hydroxide. After washing it three times with 10 times the amount of pure water, a nickel hydroxide active material is prepared through a dehydration and drying process.

[0027] Next, 10 wt% of cobalt hydroxide, 0.5 wt% of yttrium oxide, 40 wt% of hydroxypropyl cellulose (HPC) dispersion, and 0.3 wt% of zinc oxide are mixed in the nickel hydroxide active material to prepare a positive electrode active material slurry. The positive electrode active material slurry is filled into the positive electrode substrate, dried, rolled, and cut to a specified size to prepare a nickel positive electrode plate.

[0028] The negative electrode 26 has a strip-shaped conductive negative electrode core body, and a negative electrode mixture is loaded in the negative electrode core body. The negative electrode core body is composed of a sheet metal material with through holes distributed, and for example, an iron punching plate with nickel plating on the surface is used. When the negative electrode mixture is held in the negative electrode core body, a negative electrode mixture layer is formed.

[0029] The negative electrode mixture includes hydrogen storage alloy particles, negative electrode additives, conductive materials, and binders.

[0030] A hydrogen storage alloy is an alloy that can store and release hydrogen as a negative electrode active material. As the hydrogen storage alloy, a general hydrogen storage alloy can be used. Here, in the present disclosure, a rare earth-Mg-Ni-based hydrogen storage alloy containing rare earth elements, Mg, and Ni can be used as the hydrogen storage alloy.

[0031] The hydrogen storage alloy particles can be obtained, for example, as follows.

[0032] Weigh and mix La, Mg, Ni, and Al under conditions to form a specified composition, melt the mixture in a high-frequency induction melting furnace in an argon atmosphere, pour it into a mold, cool it to room temperature to obtain an alloy ingot. Fill the alloy ingot in a metal container, replace the inside of the container with argon and then seal it. Then, put the container into a heat treatment furnace and perform heat treatment at a temperature of 900 °C or higher and 1000 °C or lower for 10 hours. After cooling, crush the alloy ingot and classify it by screening to obtain hydrogen storage alloy particles with the required particle size.

[0033] Here, there is no particular limitation on the particle size of the hydrogen storage alloy particles. Preferably, hydrogen storage alloy particles with a volume average particle size (MV) of 65.0 μm are used. In the present disclosure, the volume average particle size (MV) refers to the volume average particle size obtained by the laser diffraction scattering method using a particle size distribution measuring device.

[0034] As the negative electrode additive, powders of fluorides of rare earth elements (Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) can be used. In the present embodiment, yttrium fluoride (YF3) can be used as the fluoride of rare earth elements. In terms of weight ratio, when the weight of the hydrogen storage alloy powder is recorded as 100%, the amount of yttrium fluoride is more preferably 0.1% by weight or more and 0.2% by weight or less. In addition, calcium fluoride can also be added as the negative electrode additive.

[0035] The binder not only bonds the hydrogen storage alloy particles, the negative electrode additive, and the conductive material to each other but also plays a role in bonding the negative electrode mixture to the negative electrode core. As the binder, hydrophilic or hydrophobic polymers, etc. can be used. In addition, as the conductive material, carbon black, graphite, nickel powder, etc. can be used.

[0036] When the powder of the obtained hydrogen storage alloy is regarded as 100%, 0.4% by weight of sodium polyacrylate, 0.1% by weight of carboxymethyl cellulose (CMC), 1.0% by weight of a dispersion of styrene-butadiene rubber (SBR) with a solid content of 50%, 0.5% by weight of Ketjen black, 0.5% by weight of calcium fluoride, 30% by weight of ion-exchanged water, and a specified weight percentage of yttrium fluoride were added and kneaded to prepare a paste of the negative electrode mixture. The paste was uniformly coated on both sides of the negative electrode core. After the paste was dried, the negative electrode core with the hydrogen storage alloy powder attached was further roll-pressed to increase the alloy amount per unit volume, cut to a specified size, and a hydrogen storage alloy negative electrode was prepared. The negative electrode mixture was not only filled in the through-holes of the negative electrode core but also layered and held on both sides of the negative electrode core respectively.

[0037] The positive electrode 24 and the negative electrode 26 prepared in the above process were opposed to each other with the separator 28 interposed therebetween, and wound into a spiral shape and housed in the outer can 10. In addition, a specified amount of an electrolytic solution composed of a weight ratio of NaOH solution:LiOH solution of 8.0:0.7 was injected into the outer can 10 and the opening of the outer can 10 was sealed. Thus, a battery 2 with a nominal capacity of 2000 mAh was manufactured.

[0038] The manufactured battery 2 was charged at 0.20 A for 16 hours, then discharged at 0.4 A until the battery voltage dropped to 1.0 V, and the initial activation treatment was completed by repeating the charge-discharge operation 5 times. In this way, the battery 2 was brought to a usable state.

[0039] 2. Example

[0040] In order to examine the cycle characteristics and low-temperature charging characteristics of the battery having the above configuration, the weight of the hydrogen storage alloy powder was set to 100% by weight, and batteries 2 were manufactured by changing the weight percentages of yttrium fluoride and calcium fluoride as negative electrode additives respectively. In addition, the preparation conditions of the battery 2 other than the addition amounts of yttrium fluoride and calcium fluoride as negative electrode additives were the same.

[0041] (Example 1)

[0042] A battery was prepared that contained 0.2% by weight of yttrium fluoride as a negative electrode additive and did not contain calcium fluoride.

[0043] (Example 2)

[0044] A battery was prepared that contained 0.2% by weight of yttrium fluoride and 0.5% by weight of calcium fluoride as negative electrode additives.

[0045] (Example 3)

[0046] A battery was prepared that contained 0.1% by weight of yttrium fluoride and 0.5% by weight of calcium fluoride as negative electrode additives.

[0047] (Comparative Example 1)

[0048] A battery was prepared in which neither yttrium fluoride nor calcium fluoride was contained as a negative electrode additive.

[0049] (Comparative Example 2)

[0050] A battery was prepared in which yttrium fluoride was not contained as a negative electrode additive and 0.5% by weight of calcium fluoride was contained.

[0051] (Comparative Example 3)

[0052] A battery was prepared in which 0.3% by weight of yttrium fluoride and 0.5% by weight of calcium fluoride were contained as negative electrode additives.

[0053] (Comparative Example 4)

[0054] A battery was prepared in which 0.05% by weight of yttrium fluoride and 0.5% by weight of calcium fluoride were contained as negative electrode additives.

[0055] 3. Evaluation of nickel-metal hydride secondary battery (1) Low-temperature charging characteristics

[0056] For each of the batteries of Examples 1 to 3 and Comparative Examples 1 to 4 that had completed the initial activation treatment, charging was performed at 2.0 A in an environment of (a) 25°C. At this time, after the battery voltage reached the maximum value, charging was terminated when the voltage decreased by 10 mV from the maximum value, that is, charging under so-called -ΔV control (hereinafter simply referred to as -ΔV charging) was performed. After the -ΔV charging was completed, (b) the battery was left for 1 hour and then discharged at 2.0 A until the battery voltage dropped to 1.0 V. The discharge capacity of Battery 2 at this time was measured as the initial capacity [A] mAh. Then, (c) Battery 2 was left in an environment of 25°C for 1 hour. Steps (a) to (c) were taken as 1 cycle, and charge-discharge was performed for 3 cycles.

[0057] Next, after Battery 2 was left in an environment of 0°C for 3 hours, it was fully charged at 2.0 A in an environment of 0°C and -ΔV charging was performed. After the -ΔV charging in an environment of 0°C, Battery 2 was left in an environment of 25°C for 3 hours again, and then discharged at 2.0 A until the battery voltage dropped to 1.0 V. The discharge capacity of Battery 2 at this time was measured as the capacity [B] mAh. Based on the capacity obtained by the above steps, the charging characteristic ratio was calculated by the following formula (I).

[0058] Low-temperature charging characteristic ratio (%) = B / A = (Capacity B) / (Initial capacity A) … (I)

[0059] Therefore, the higher the low-temperature charging characteristic ratio, the smaller the influence of the reduction in charging capacity caused by low temperature (0°C) during the charging of Battery 2 in an environment of 0°C. Figure 2 The low-temperature charging characteristics of Examples 1 to 3 and Comparative Examples 1 to 3 are shown.

[0060] Regarding the low-temperature charging characteristics, it is 89.8% in Example 1, 92.2% in Example 2, and 92.7% in Example 3. In contrast, it is 88.5% in Comparative Example 1, 86.3% in Comparative Example 2, and 85.4% in Comparative Example 3.

[0061] When comparing the above results, it can be seen that the batteries of Examples 1 to 3 containing 0.1% by weight to 0.2% by weight of yttrium fluoride have a larger discharge capacity after low-temperature charging than the batteries of Comparative Examples 1 to 3. That is, this indicates that in a low-temperature environment such as at 0°C, the battery can be charged with a larger capacity. In addition, it can be seen that when the amount of yttrium fluoride is 0.05% by weight, less than 0.1% by weight, the low-temperature charging characteristics deteriorate. On the other hand, even when the amount of yttrium fluoride is 0.3% by weight, more than 0.2% by weight, the low-temperature charging characteristics also deteriorate. Therefore, as the amount of yttrium fluoride, the batteries containing 0.1% by weight to 0.2% by weight have excellent low-temperature charging characteristics.

[0062] (2) Cycle life characteristics

[0063] For each of the batteries of Examples 1 to 3 and Comparative Examples 1 to 4, in an environment of 25°C, charging was performed at 1.0C, and charging was terminated when the battery voltage decreased by 10 mV from the maximum value, and the battery was left standing for 1 hour. Then, in the same environment, discharging was performed at 1.0C until the battery voltage reached 1.0V, and the battery was left standing for 1 hour. The above charge-discharge cycle was regarded as 1 cycle, and the charge-discharge was repeated, and the discharge capacity of each cycle was measured. Here, the discharge capacity of the first cycle was used as the initial capacity, and the capacity initial ratio of each cycle was calculated according to the following formula (II).

[0064] Capacity initial ratio (%) = (Discharge capacity in each cycle / Initial capacity) × 100... (II)

[0065] The charge-discharge was repeated for each of the batteries of the examples and comparative examples, and the number of cycles until the capacity initial ratio reached 60% was calculated. For the measured number of cycles, the battery of Comparative Example 1 that did not add either yttrium fluoride or calcium fluoride was used as a standard. The ratio of the number of cycles of the batteries of Examples 1 to 3 and Comparative Examples 2 to 4 was calculated when the number of cycles of this standard was regarded as 100. The more the number of cycles until the capacity initial ratio reaches 60%, the longer the cycle life of the battery. This ratio is shown in Figure 2 Table 1 shown below.

[0066] The cycle life characteristics are 100 in Example 1, 122 in Example 2, and 116 in Example 3. In contrast, they are 103 in Comparative Example 2, 128 in Comparative Example 3, and 100 in Comparative Example 4.

[0067] As can be seen from the above, from Examples 1, 2, 3 and Comparative Example 3, by including yttrium fluoride of 0.1% by weight or more, compared with the batteries of Comparative Example 1 or Comparative Example 4 with yttrium fluoride below 0.1% by weight, the cycle life of the battery is extended.

[0068] In addition, it can be seen that when comparing Examples 1, 2, and 3 containing yttrium fluoride of 0.1% by weight or more, the batteries of Example 2 or 3 containing calcium fluoride as an additive have a longer cycle life than the batteries of Example 1 without calcium fluoride. This tendency can also be seen between the batteries of Comparative Example 1 without either yttrium fluoride or calcium fluoride and the batteries of Comparative Example 2 without yttrium fluoride but containing calcium fluoride. From this, it can be known that the batteries added with calcium fluoride have a longer cycle life.

[0069] 4. Investigation

[0070] From the results in Table 1, it can be seen that compared with the batteries without yttrium fluoride added, the low-temperature charging characteristics such as at 0 °C of the batteries added with 0.1 - 0.2% by weight of yttrium fluoride are improved. Specifically, even in a low-temperature environment, the batteries added with 0.1 - 0.2% by weight of yttrium fluoride can be charged with a capacity close to the charging capacity in a room-temperature environment. It is considered that this is because by adding 0.1 - 0.2% by weight of yttrium fluoride to the negative electrode mixture, the factors that hinder the charging of the battery 2 in a low-temperature environment are reduced, and the inhibitory effect of yttrium fluoride on the corrosion of the hydrogen storage alloy can be exerted more greatly.

[0071] When the addition amount of yttrium fluoride is greater than 0.2% by weight, although the cycle life is extended, the low-temperature charging characteristics are reduced. In addition, when the addition amount of yttrium fluoride is below 0.1% by weight, it is considered that the absolute amount is not sufficient to improve the low-temperature charging characteristics.

[0072] In addition, for the cycle life, by comparing Example 1 with Example 2, or Comparative Example 1 with Comparative Example 2, it can be seen that compared with the batteries without calcium fluoride added, the batteries added with calcium fluoride have an extended cycle life.

[0073] Figure 3 The low-temperature charging characteristics and cycle life characteristics with respect to the addition amount of yttrium fluoride in the results shown in Table 1 are shown in a graph. When increasing the addition amount of yttrium fluoride relative to the hydrogen storage alloy powder, it can be seen that the cycle life is extended as it increases. On the other hand, the low-temperature charging characteristics reach a peak between 0.1% and 0.2% by weight of yttrium fluoride, and the low-temperature charging characteristics decrease when yttrium fluoride increases.

[0074] As can be seen from the above, while adding 0.1% by weight or more and 0.2% by weight or less of yttrium fluoride relative to the hydrogen storage alloy powder, by adding 0.5% by weight of calcium fluoride, the extension of the cycle life and the improvement of the low-temperature charging characteristics of the nickel-metal hydride secondary battery can be achieved simultaneously.

[0075] The hydrogen storage alloy negative electrode according to the present invention can improve the charge-discharge cycle life in a nickel-metal hydride secondary battery including the hydrogen storage alloy negative electrode, and can achieve an improvement in low-temperature charging characteristics.

[0076] In addition, the present invention is not limited to the above-described embodiments and examples, and various modifications can be made. For example, as the negative electrode additive, in addition to yttrium fluoride and calcium fluoride, fluorides of other rare earth elements can also be added. Further, the shape of the nickel-metal hydride secondary battery can also be square, and the shape of the battery is not particularly limited.

Claims

1. A hydrogen storage alloy negative electrode, characterized in that, It contains a hydrogen storage alloy and yttrium fluoride as an additive, and the mass of the yttrium fluoride is 0.1 part by mass or more and 0.2 part by mass or less relative to 100 parts by mass of the hydrogen storage alloy powder. The additive further contains calcium fluoride, and the mass of the calcium fluoride is more than 0 part by mass and 0.5 part by mass or less relative to 100 parts by mass of the hydrogen storage alloy powder. The hydrogen storage alloy contains La, Mg, Ni and Al.

2. A nickel-metal hydride secondary battery, which includes the hydrogen storage alloy negative electrode according to claim 1, and a positive electrode that faces the hydrogen storage alloy negative electrode across a separator and contains nickel hydroxide. The hydrogen storage alloy negative electrode and the positive electrode are housed together with an electrolytic solution in an outer can.

Images