JP3297375B2 - Nickel hydride rechargeable battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-metal hydride secondary battery, and more particularly to a nickel-metal hydride secondary battery containing a hydrogen storage alloy as a main component and having a proper capacity ratio between a cathode and an anode.

[0002]

2. Description of the Related Art At present, a nickel hydride using a hydrogen storage alloy capable of reversibly absorbing and releasing hydrogen as a cathode and a nickel hydroxide used as a known nickel cadmium secondary battery as an anode. Secondary batteries are attracting attention because they allow for higher capacities.

[0003] The hydrogen storage alloys include titanium-based alloys, manganese-based alloys, rare-earth-based alloys, and the like, and are alloys that can rapidly store and release hydrogen electrochemically in an electrolyte. As such, a LaNi ₅ -based alloy is known. However, LaNi ₅ cannot provide the results satisfying both the electric capacity and the charge / discharge cycle life as it is, and takes into account the change in lattice spacing when hydrogen is occluded in the alloy, which is directly related to those characteristics. Therefore, it is necessary to design a hydrogen storage alloy having optimum characteristics when it is applied to the cathode of a secondary battery by adding another metal element.

[0004] The study of conventional hydrogen storage alloy, by substituting a part of Ni Mn, Al, in Co, LmNi _a Mn _{b A}
l _C Co _d (where Lm is a lanthanum-enriched misch metal), wherein a> 3.6, d ≦ 1,
It has been found that the hydrogen storage alloy specified in 4.8 ≦ a + b + c + d ≦ 5.2 has almost satisfactory characteristics as the cathode of the aforementioned secondary battery. However, when a secondary battery is configured by combining a cathode made of such a hydrogen storage alloy and an anode made of a nickel electrode, if the composition of the hydrogen storage alloy changes, the characteristics of the alloy change, and as a result, the cathode characteristics Changes. For this reason, the optimum capacity ratio between the cathode and the anode changes, and there is a problem that the above-mentioned optimum capacity ratio obtained with LaNi ₅ cannot be applied as it is.

[0005] In a nickel-metal hydride secondary battery using a hydrogen storage alloy, it is necessary to find the optimum capacity ratio between the cathode and the anode every time the alloy composition is changed. As the capacity of the cathode is larger,
Although the cycle life becomes longer, the capacity of the battery is regulated by the nickel electrode, which is the anode. For this reason, when the volume of the cathode increases with an increase in the capacity of the cathode, the volume of the anode, which is the counter electrode, must be reduced because the power generation element group is housed in a metal can of a fixed volume. The capacity is reduced, and thus the battery capacity is reduced. Conversely, if the capacity of the cathode is reduced, the capacity of the battery can be increased.However, the rate of deterioration of the electrode capacity is higher for the hydrogen storage alloy, which is the cathode, than for the nickel electrode, which is the anode. As a result, the capacity of the cathode becomes smaller than the capacity of the anode, and thereafter the capacity of the battery rapidly decreases, and at the time of charging, hydrogen is generated from the cathode to increase the internal pressure of the battery.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned conventional problems, and has been made to optimize the capacity ratio between a cathode and an anode mainly composed of a hydrogen storage alloy, and to reduce the electrode capacity and charge / discharge. An object of the present invention is to provide a nickel-hydrogen secondary battery that can satisfy both cycle life.

[0007]

A nickel-hydrogen secondary battery according to the present invention comprises: a cathode mainly composed of a hydrogen storage alloy;
An anode mainly composed of a nickel compound and a power generation element group including a separator interposed between the cathode and the anode are housed in a metal can, an alkaline electrolyte is injected, and an opening of the can is opened with a lid. in nickel-hydrogen secondary battery of sealed structure, the hydrogen storage _{alloy, LnNi a Mn b Al c Co} d
(However, Ln is lanthanum alone or rare earth containing lanthanum
A mixture of class elements, a> 3.6, d ≦ 1, 4.8 ≦ a + b
+ C + d ≦ 5.2), and a value obtained by converting the hydrogen storage amount of the hydrogen storage alloy at normal pressure into an electric capacity is represented by S (mAh / g). When the amount of the hydrogen storage alloy contained is M (g / cm ² ) and the capacity per unit area of the anode is C (mAh / cm ² ), C = x ₁ · S · M (1) the value of x _1, shown is 0.3 or more, setting the M such that 0.8 or less, and the separator is characterized in that comprising a nonwoven fabric including polyolefin fibers.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A nickel-hydrogen secondary battery according to the present invention has a cathode mainly composed of a hydrogen storage alloy, an anode mainly composed of a nickel compound, and a cathode interposed between the cathode and the anode. In a nickel-metal hydride secondary battery having a structure in which a power generation element group including a separator is housed in a metal can, an alkaline electrolyte is injected, and the opening of the can is sealed with a lid, the maximum hydrogen storage capacity of the hydrogen storage alloy is Is converted to electric capacity, S (mAh / g), the amount of hydrogen storage alloy contained per unit area of the cathode is M (g / cm ² ), and the capacity per unit area of the anode is C (mAh / g). cm ² ), M is set so that the value of x _{1 represented} by the relationship of C = x ₁ · S · M (1) becomes 0.3 or more and 0.8 or less. is there.

As the hydrogen storage alloy, for example, Ln
_{Ni a Mn b Al c Co d} ( provided that a mixture of rare earth elements Ln may include lanthanum alone or lanthanum, a> 3.6, d
≦ 1, 4.8 ≦ a + b + c + d ≦ 5.2). As the Ln,
Lm in which the amount of cerium (Ce) among the rare earth elements is reduced to 15% or less and the amount of La is relatively increased (enriched)
Is preferred. Ni, M
The total amount (a + b + c + d) of n, Al, and Co is 4.8 to
The reason for setting the range to 5.2 is that if the composition is less than 4.8 or more than 5.2, the hydrogen storage amount per 1 g of the hydrogen storage alloy is significantly reduced. The reason for limiting the amount a of Ni and the amount d of Co is that when a is 3.6 or less and d exceeds 1, the battery voltage is reduced. A more preferable composition ratio represented by the above formula is when the contents of Mn, Al, and Co are each 0.1 to 0.7. Hydrogen storage alloy having such a composition is the hydrogen storage amount of the normal pressure is 360mAh approximately per 1g in terms of electric capacity, the amount of hydrogen that can electrochemically reversibly absorbing and desorbing is when charged at 1C It reaches 300 mAh in terms of electric capacity.

Examples of the anode mainly composed of the above nickel compound include a paste type electrode formed by filling a three-dimensional mesh core such as sponge nickel and sintered nickel short fiber with nickel oxide and press-molding the same. Can be.

The reason for limiting the value of x ₁ in the above relational expression (1) is that when x ₁ exceeds 0.8, the charge / discharge cycle life is reduced, while when x ₁ is less than 0.3, a large capacity secondary battery can be obtained. It will be difficult. More preferable value of x ₁ is 0.4
It is in the range of 0.6.

[0012] Another nickel-hydrogen secondary battery according to the present _{invention, LnNi a Mn b Al c Co} d ( provided that a mixture of rare earth elements Ln may include lanthanum alone or lanthanum, a>
3.6, d ≦ 1, 4.8 ≦ a + b + c + d ≦ 5.2), a cathode mainly composed of a hydrogen storage alloy, an anode mainly composed of a nickel compound, and a cathode interposed between the cathode and the anode. In a nickel-metal hydride secondary battery having a structure in which a power generation element group including a separator is housed in a metal can, an alkaline electrolyte is injected, and an opening of the can is sealed with a lid, the unit is included per unit area of the cathode. Hydrogen storage alloy amount is M
(G / cm ² ), and the capacity per unit area of the anode is C
When (mAh / cm ² ), M is set so that the value of x _{2 represented} by the relationship of C = x ₂ · M (2) becomes 100 or more and 300 or less. It is.

The reason for limiting the value of x ₂ in the above relational expression (2) is that when x ₂ exceeds 300, the charge / discharge cycle life is reduced, while when x ₂ is less than 100, a large capacity secondary battery can be obtained. It will be difficult. More preferable value of x ₂ is 140 to
The range is 220.

[0014] Inside the nickel-metal hydride secondary battery, a cathode and an anode are closely arranged via a separator. When the distance between the cathode and the anode is very small, an electrode reaction occurs between the opposed cathode and the anode. For this reason,
Designing a battery based on the ratio of the total capacity of the electrodes incorporated in a metal can, including the capacity of the electrode part where the cathode and anode are not opposed to each other, is only possible when the battery sizes are different or the same. If the electrode size changes even in the size, the optimum capacity ratio between the cathode and the anode must be found again, which is not a universal and theoretical design method.

Therefore, when determining the optimum capacitance ratio between the cathode and the anode, it is necessary to determine the capacitance ratio of the surfaces facing the electrodes. Specifically, it is appropriate to determine the capacity per unit area of the cathode and the anode. It is assumed that the capacity reversibly obtained from the hydrogen storage alloy by the electrochemical method is equal to the capacity calculated from the maximum hydrogen storage capacity of the hydrogen storage alloy, and that the capacity of the hydrogen storage alloy electrode is not deteriorated in the alkaline electrolyte without any deterioration. When the decrease does not occur, the capacity of the hydrogen storage alloy electrode per unit area may be equal to the capacity per unit area of the nickel electrode as the counter electrode. That is, the value of x ₁ in the equation (1) is 1, the value of x ₂ in the equation (2) is 360, but good. However, the capacity actually reversibly obtained from the hydrogen storage alloy electrode by the electrochemical method is smaller than the capacity calculated from the maximum storage alloy amount of the hydrogen storage alloy, and is gradually oxidized in the alkaline electrolyte. In addition, the capacity decreases.

In the present invention, a value obtained by converting the maximum hydrogen storage amount of the hydrogen storage alloy used for the cathode into an electric capacity in consideration of the above two matters is included in S (mAh / g) per unit area of the cathode. M (g / cm ² )
When the capacity per unit area of the anode containing the nickel compound as a main component is C (mAh / cm ² ), the upper limit of x _{1 represented} by C = x ₁ · S · M (1) is charged / discharged. By setting the M to 0.8 in relation to the cycle life and 0.3 to the lower limit in relation to the capacity, the capacity ratio between the cathode and the anode mainly composed of a hydrogen storage alloy is optimized, and the electrode capacity is adjusted. And a nickel-hydrogen secondary battery satisfying both the charge-discharge cycle life.

In the present invention, in consideration of the above two points, the amount of the hydrogen storage alloy contained per unit area of the cathode mainly containing the hydrogen storage alloy having a specific composition is M (g / cm).
² ) When the capacity per unit area of the anode mainly composed of a nickel compound is C (mAh / cm ² ), the upper limit of x _{2 represented} by C = x ₂ · M (2) is charged and discharged. By setting the M to 300 in relation to the cycle life and the lower limit to 100 in relation to the capacity, the capacity ratio between the cathode and the anode mainly composed of a hydrogen storage alloy is optimized, and the electrode capacity is adjusted. And a nickel-hydrogen secondary battery satisfying both the charge-discharge cycle life.

[0018]

Embodiments of the present invention will be described below in detail.

Example 1 A battery element group was wound by using a cathode, a nickel electrode as an anode, and a separator, each of which will be described later, with the separator interposed between the cathode and the anode to form a battery element group. After being housed in a can, the lead of the anode was connected to a lid, an alkaline electrolyte was injected into the can, and the lid was attached to the upper opening of the can to be sealed. Assembled. The lid is provided with a valve that operates when the inside of the can becomes 15 kg / cm ² or more, for example, and allows gas to escape to the outside. The outermost periphery of the cathode side is connected to the inner surface of the can at the time of winding without interposing a lead.

The nickel electrode is a paste-type electrode produced by filling a three-dimensional mesh core made of nickel sintered fiber with nickel oxide as an active material and press-molding the same, and has a capacity per unit area. C is 35mAh / c
Three kinds of electrodes of m ² , 40 mAh / cm ² , and 45 mAh / cm ² were used.

The cathode has an LmNi _4.2 having a value S obtained by converting a hydrogen storage amount at normal pressure into an electric capacity of 360 mAh / g.
Before use, a hydrogen storage alloy made of Mn _0.3 Al _0.3 Co _0.3 (Lm; lanthanum-enriched misch metal) is absorbed and released before use to make gaseous hydrogen fine, and this powder is mixed with carbon and polytetrafluoroethylene powder. After kneading to form a sheet, the sheet was press-bonded to a nickel mesh. Incidentally, the values of x ₁ to determine the hydrogen storage alloy amount M contained per unit area from the equation (1) as a cathode 0.2 for each nickel electrode, 0.
Fifteen types set to be 4, 0.6, 0.8, and 1.0 were used.

The separator used was a nonwoven fabric whose main fiber was made of polyolefin and had a thickness of 0.2 mm.

The electrolyte solution has a KOH of 7N, a LiOH
Use the battery adjusted so that
2.2 ml was injected.

After the above-described secondary battery was allowed to stand at room temperature for one day, the battery was charged at 0.3 C for 5 hours and charged and discharged at 1 C to 1 V. However, a one-hour rest period was provided between charging and discharging, and between discharging and charging. The cycle life of each battery was determined from the number of cycles until the battery capacity reached 90% of the capacity of the initial cycle (third cycle). In addition, the valve operated during the charge / discharge cycle was checked, and for the valve operated, the charge / discharge cycle was stopped at that time, and the number of times was determined as the cycle life. The relationship between x ₁ and cycle life of the hydrogen absorbing alloy constituting the cathode shown in Figure 1. Also shown in Figure 2 the relationship between the volume ratio of x ₁ of the hydrogen storage alloy constituting the cathode initial cycle of each battery (third cycle). Volume ratio, the value of x ₁ is 0.6
Is expressed as a relative value when the capacity is 100. 1 and 2 indicate that the capacity per unit area is 35 mAh.
/ Cm ² nickel electrode, □ indicates the same capacity of 40 mAh / cm
² of nickel electrode, △ marks are those same capacity were used nickel electrode of 45 mAh / cm ^2. In FIG. 2, x
_If the value of ₁ is 1.0, it is not listed because the valve was activated and the capacity could not be measured in the third cycle or more.

As is apparent from FIG. ₁ , the value of x ₁ is 0.6
In the following cases, the cycle life is all 300 cycles. However, the cycle life does not mean 300 cycles, but only 300 cycles were performed at the maximum.
cycle life when the value of x ₁ is 0.8 becomes approximately 280 cycles, the value of x ₁ becomes a mere 2 cycle when it comes to 1. The value of this x ₁ becomes 2 cycles when one is expected battery internal pressure rises, because the valve operating is made. Therefore, it is understood from the results of the cycle life in FIG. ₁ that the content of the hydrogen storage alloy in the cathode needs to be set so that the value of x1 is 0.8 or less.

Further, the value of x ₁ As is clear from Figure 2 that the battery capacity is also reduced with the smaller, as the capacitance per unit area of the nickel electrode is small, that the battery capacity decreases decreases Understand. This is for the following reason. decreasing the value of x ₁ is equivalent to increasing the content of the hydrogen storage alloy. In order to store the power generation element group in a metal can with a fixed volume, it is necessary to reduce the volume of the nickel electrode by increasing the content of the hydrogen storage alloy, but the capacity of the nickel electrode is originally small and the volume is small In this case, the volume of the nickel electrode to be reduced can be reduced. Nickel electrode capacity per unit area
In the case of 45 mAh / cm ² , if the value of x ₁ is 0.2, the relative capacity ratio decreases to about 60. When the relative capacity ratio is 60, it is insufficient in terms of increasing the capacity, and it is necessary that the relative capacity ratio be 70 or more. For this purpose, it can be seen that it is necessary to set the content of the cathode of the hydrogen storage alloy as the value of x ₁ is 0.3 or more.

[0027] Example _{2 LmNi 3.9 Mn 0.3 Al 0.3 Co} 0.5; with gaseous hydrogen was absorbed and released prior to use a hydrogen storage alloy consisting of (Lm lanthanum enriched misch metal a) finely divided carbon to the powder After mixing and kneading with a polytetrafluoroethylene powder to form a sheet, the sheet is press-bonded to a nickel net, and the amount of hydrogen storage alloy M contained per unit area is determined by the above-mentioned relational formula ( 2) capacitance C 35 mAh / cm ² values per each nickel electrode (unit area x ₂ determined from, 40mAh / cm ^2, 45mAh /
An AA-size secondary battery similar to that of Example 1 was assembled except that 15 kinds of cathodes set to 80, 130, 220, 300, and 400 with respect to cm ² ) were used.

After the above-mentioned secondary battery was allowed to stand at room temperature for one day, the battery was charged at 0.3 C for 5 hours and charged and discharged at 1 C to 1 V. However, a one-hour rest period was provided between charging and discharging, and between discharging and charging. The cycle life of each battery was determined from the number of cycles until the battery capacity reached 90% of the capacity of the initial cycle (third cycle). In addition, the valve operated during the charge / discharge cycle was checked, and for the valve operated, the charge / discharge cycle was stopped at that time, and the number of times was determined as the cycle life. The relationship between x ₂ and cycle life of the hydrogen absorbing alloy constituting the cathode shown in Figure 3. Also, it is shown in FIG. 4 the relationship between volume ratio between x ₂ of the hydrogen storage alloy constituting the cathode initial cycle of each battery (third cycle). Volume ratio, the value of x ₂ is 220
Is expressed as a relative value when the capacity is 100. The circles in FIGS. 3 and 4 indicate that the capacity per unit area is 35 mAh.
/ Cm ² nickel electrode, □ indicates the same capacity of 40 mAh / cm
² of nickel electrode, △ marks are those same capacity were used nickel electrode of 45 mAh / cm ^2. In FIG. 4, x
_If the value of ₂ is 400, it is not listed because the valve was activated and the capacity could not be measured in the third cycle or more.

As is apparent from FIG. 3, the value of x ₂ is 220
In the following cases, the cycle life is all 300 cycles. However, the cycle life does not mean 300 cycles, but only 300 cycles were performed at the maximum.
becomes the cycle life value of x ₂ is 300 becomes approximately 280 cycles, the value of x ₂ becomes when it comes to a mere 2-cycle 400. The value of the x ₂ becomes 2 cycle when the 400 is expected battery internal pressure rises, because the valve operating is made. Therefore, it can be seen that the value of x ₂ hydrogen storage alloy content of the specific composition of the cathode from the results of the cycle life of the Figure 3 it is necessary to set to be 300 or less.

As is clear from FIG. 4, the battery capacity decreases as the value of x ₂ decreases. However, the smaller the capacity per unit area of the nickel electrode, the smaller the battery capacity decrease. Understand. This is for the following reason. decreasing the value of x ₂ is equivalent to increasing the content of the hydrogen storage alloy. In order to store the power generation element group in a metal can with a fixed volume, it is necessary to reduce the volume of the nickel electrode by increasing the content of the hydrogen storage alloy, but the capacity of the nickel electrode is originally small and the volume is small In this case, the volume of the nickel electrode to be reduced can be reduced. Nickel electrode capacity per unit area
In the case of 45 mAh / cm ² , when the value of x ₂ is 80, the relative capacity ratio decreases to about 60. With a relative capacity ratio of 60,
It is insufficient in terms of increasing the capacity, and it is necessary that the capacity be 70 or more. For this purpose, the content of the hydrogen storage alloy having a specific composition of the cathode value of x ₂ it can be seen that it is necessary to set so that 100 or more.

[0031]

As described above in detail, according to the present invention, a nickel-hydrogen battery capable of optimizing a capacity ratio between a cathode and an anode mainly composed of a hydrogen storage alloy and satisfying both an electrode capacity and a charge / discharge cycle life. A secondary battery can be provided.

[Brief description of the drawings]

[1] characteristic diagram showing the relationship between x ₁ values and cycle life.

[Figure 2] characteristic diagram showing the relationship between the value of x ₁ and the capacitance ratio.

[Figure 3] characteristic diagram showing the relationship between the x ₂ values and cycle life.

[4] characteristic diagram showing the relationship between the value of x ₂ and the capacitance ratio.

Claims (2)

(57) [Claims] 1. A power generation element group including a cathode mainly composed of a hydrogen storage alloy, an anode mainly composed of a nickel compound, and a separator interposed between the cathode and the anode is housed in a metal can. and, injecting the alkaline electrolyte in the nickel-hydrogen secondary battery having the structure sealing the opening of the can with a lid, the hydrogen storage _{alloy, LnNi a Mn b Al c Co} d ( however
And Ln is lanthanum alone or a rare earth element containing lanthanum
Element mixture, a> 3.6, d ≦ 1, 4.8 ≦ a + b + c
+ D ≦ 5.2), and a value obtained by converting the hydrogen storage amount of the hydrogen storage alloy at normal pressure into an electric capacity is represented by S (mAh / g), per unit area of the cathode. When the amount of the hydrogen storage alloy contained is M (g / cm ² ) and the capacity per unit area of the anode is C (mAh / cm ² ), C = x ₁ · S · M (1) the value of x _1, shown is 0.3 or more, setting the M such that 0.8 or less, and the separator are nickel-hydrogen secondary battery, characterized by comprising a nonwoven fabric including polyolefin fibers. 2. The hydrogen storage alloy according to claim 1 , wherein said Ln is a lantern.
Of rare earth elements containing up to 15% Ce
2. The nickel-metal hydride secondary battery according to claim 1, wherein: