JP3352205B2 - 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 hydrogen secondary battery having an improved separator.

[0002]

2. Description of the Related Art A nickel-hydrogen secondary battery is composed of a paste-type positive electrode containing nickel hydroxide and a paste-type negative electrode containing a hydrogen-absorbing alloy, each of which is made up of an electrode group and a container together with an alkaline electrolyte. Has a structure housed inside. The secondary battery has excellent voltage compatibility with a nickel cadmium secondary battery including a negative electrode including a cadmium compound instead of the hydrogen storage alloy, and has a higher capacity than the nickel cadmium secondary battery. Has characteristics.

Conventionally, the separator of the nickel-metal hydride secondary battery is formed of amide resin fiber having high hydrophilicity. The separator has excellent liquid retention due to its high hydrophilicity. However, when the secondary battery including the separator is stored at a high temperature in a charged state, the separator is oxidized and decomposed due to poor oxidation resistance to generate nitrate ions, nitrite ions, and ammonia.
These impurities are NiOO which is a charge product of the positive electrode.
H is reduced, that is, self-discharge occurs. Accordingly, there has been a problem that the degree of progress of self-discharge during storage of the secondary battery at a high temperature increases.

[0004] For this reason, a non-woven fabric made of an olefin resin fiber having a hydrophilic group provided on an olefin resin fiber which is hydrophobic but has excellent oxidation resistance, such as an olefin resin fiber having a surface-adsorbed surfactant, is used as the separator. And
It has been practiced to prevent oxidative decomposition during storage at high temperature by using a nonwoven fabric made of a composite fiber in which the surface of an olefin resin core material is coated with an ethylene-vinyl alcohol copolymer resin.

[0005] However, secondary batteries provided with these separators have the following problems. A separator made of an olefin resin fiber nonwoven fabric having a surfactant adsorbed on the surface thereof, the surfactant is eluted into the electrolytic solution immediately after being incorporated into the secondary battery, so that hydrophilicity is impaired. The liquid retention decreases.

On the other hand, a separator composed of a nonwoven fabric made of a conjugate fiber in which the surface of the olefin resin core material is coated with an ethylene-vinyl alcohol copolymer resin is provided by a hydroxyl group of the ethylene-vinyl alcohol copolymer resin present on the surface of the composite fiber. Holds the electrolytic solution. However,
In the separator, a part of the hydroxyl groups is present inside the composite fiber because the arrangement of the copolymer of the copolymer resin is random. Further, the electrolyte does not easily penetrate into the interior of the composite fiber. For this reason, the hydroxyl group present inside the composite fiber does not contribute to holding the electrolytic solution. Further, the hydroxyl group is eliminated from the separator by repeating a charge / discharge cycle. As a result, the separator does not always have a sufficient liquid retaining property.

If the nickel-hydrogen secondary battery provided with each of the above-mentioned separators is stored at a high temperature in a charged state, there has been a problem that the degree of progress of self-discharge increases in relation to a negative electrode containing a hydrogen storage alloy. That is, the hydrogen storage alloy of the negative electrode has an equilibrium pressure and a hydrogen storage amount at each temperature determined, and the hydrogen storage alloy stores and releases hydrogen gas by changing the equilibrium pressure and the hydrogen storage amount according to the change in the temperature. . When the temperature of the hydrogen storage alloy increases, the equilibrium pressure increases with the temperature, and the hydrogen storage amount decreases. Therefore, when the secondary battery is stored at a high temperature, the hydrogen storage alloy has a higher equilibrium pressure, and the hydrogen storage amount at this temperature is smaller than the hydrogen storage amount at room temperature. Release outside the alloy. On the other hand, when a nonwoven fabric is used as the separator, there is a gap between the fibers of the nonwoven fabric, so that the hydrogen gas released from the hydrogen storage alloy reduces the NiOOH of the positive electrode through the gap between the fibers of the separator. That is, self-discharge occurs. When a sufficient amount of electrolyte is held in the separator, the entire surface including the gaps between the fibers of the separator is covered with an electrolyte film, so that the hydrogen gas cannot pass through the separator, and self-discharge occurs. Can be suppressed. However, the separator made of each of the nonwoven fabrics described above has a low liquid retention property, so that the amount of retained electrolyte is small. Therefore, the electrolyte film is less on the surface of the separator, and the hydrogen gas released from the hydrogen storage alloy passes through the gap between the fibers of the separator, and self-discharge occurs.

Further, since the separator made of the nonwoven fabric described above has a low liquid retaining property, the electrolyte is depleted as the charge / discharge cycle proceeds, and the internal resistance increases. As a result, the discharge voltage and the discharge capacity of the secondary battery are reduced, so that the charge / discharge cycle life is shortened.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the conventional problems, and has a separator having improved liquid retaining properties, thereby suppressing self-discharge during storage at high temperatures and achieving a longer life. It is an object of the present invention to provide a nickel-metal hydride secondary battery.

[0010]

SUMMARY OF THE INVENTION The present invention provides a paste-type positive electrode containing nickel oxide, a paste-type negative electrode containing a hydrogen storage alloy, a separator interposed between the positive electrode and the negative electrode, In a nickel-metal hydride secondary battery including an electrolytic solution, the separator has a plurality of fine continuous pores from the surface to the inside, and a surfactant is filled in at least the continuous pores , and the surface area is 20 to 90
Ri Do a nonwoven fabric comprising a polyolefin resin fiber m ² / g,
The content of the surfactant in the separator is 0.3 to
A nickel hydrogen secondary battery characterized by being in the range of 1% by weight .

A nickel-hydrogen secondary battery according to the present invention will be described with reference to FIG. Paste type nickel positive electrode 1
It is spirally wound with a separator 3 interposed between the negative electrode 2 and the hydrogen storage alloy negative electrode 2 and housed in a bottomed cylindrical container 4. The negative electrode 2 is arranged at the outermost periphery of the manufactured electrode group and is in electrical contact with the container 4. The alkaline electrolyte is contained in the container 4. Hole 5 in the center
Is disposed in the upper opening of the container 4. The ring-shaped insulating gasket 7 is disposed between the peripheral edge of the sealing plate 6 and the inner surface of the upper opening of the container 4, and the sealing plate is formed on the container 4 by caulking to reduce the diameter of the upper opening inward. 6 is hermetically fixed via the gasket 7. One end of the positive electrode lead 8 is connected to the positive electrode 1, and the other end is connected to the lower surface of the sealing plate 6. A positive electrode terminal 9 having a hat shape is mounted on the sealing plate 6 so as to cover the hole 5. A rubber safety valve 10 is disposed in a space surrounded by the sealing plate 6 and the positive electrode terminal 9 so as to close the hole 5.

The positive electrode 1 is prepared by adding a conductive material to nickel hydroxide powder as an active material, kneading the mixture with a polymer binder and water to prepare a paste, filling the paste into a conductive substrate, and drying the paste. After that, it is manufactured by molding.

The negative electrode 2 is prepared by adding a conductive material to a hydrogen storage alloy powder, kneading the mixture with a polymer binder and water to prepare a paste, filling the paste into a conductive substrate, drying the paste, and forming the paste. It is manufactured by doing.

The hydrogen storage alloy is not particularly limited, and may be any alloy that can store hydrogen electrochemically generated in an electrolyte and can easily release the stored hydrogen during discharge. . For example, LaNi ₅ , MmNi
₅ (Mm; misch metal), LmNi ₅ (Lm; lanthanum-enriched misch metal), and a part of these Nis are represented by Al, Mn, Co, Ti, Cu, Zn, Zr, C
multi-elements substituted by elements such as r and B, or T
iNi-based and TiFe-based ones can be used. Among them, the formula LmNi _x Mn _y A _z (However, A is A
At least one metal selected from l and Co, and their atomic ratios x, y and z have a total value of 4.8 ≦ x + y + z ≦ 5.4.
It is desirable to use a hydrogen storage alloy represented by the following formula:

Examples of the polymer binder include those having water repellency such as polytetrafluoroethylene and water-soluble ones such as carboxymethylcellulose, methylcellulose and sodium polyacrylate.

The conductive material includes carbon black. Examples of the conductive substrate include punched metal, expanded metal, a perforated rigid plate, a two-dimensional substrate such as a nickel net, a felt-like metal porous body, and a three-dimensional substrate such as a sponge-like metal substrate. .

The separator 3 has a plurality of fine continuous pores from the surface to the inside, and is made of a nonwoven fabric containing an olefin resin fiber filled with a surfactant at least in the continuous pores.

The weight ratio of the olefin resin fibers contained in the separator 3 is desirably 10 wt% or more. This is for the following reason.
If the weight ratio is less than 10 wt%, the liquid retention of the separator 3 may be reduced.

The separator 3 may be a nonwoven fabric formed from a single olefin resin fiber, or a nonwoven fabric formed from two or more types of fibers composed of the olefin resin fiber and other fibers. The other fibers contained in the separator 3 are preferably fibers composed of an olefin resin, and specifically, a single fiber composed of an olefin resin, and an olefin different from the olefin resin on the surface of a core material composed of the olefin resin. Resin-coated conjugate fibers, olefin resin core material whose surface is coated with an ethylene-vinyl alcohol copolymer resin, and the like can be mentioned. Examples of the olefin resin include polyethylene and polypropylene.

It is desirable that the thickness of the olefin resin fiber is in the range of 2 to 6 denier. The diameter of the continuous pores is desirably in the range of 2 μm or less.

The surface area of the olefin resin fiber is 20 m
It is desirable to be in the range of ² / g or more. This is due to the following reasons. The surface area is 20 m ² / g
If it is less than 3, the liquid retaining property of the separator 3 may be reduced. More preferred surface area is 20 m ² / g to 90 m
² / g. This means that the surface area is 90 m ² /
When the value exceeds g, it may be difficult to produce the fiber due to technical problems in fiber production.

Examples of the surfactant include fatty acid esters of glycerol, fatty acid esters of pentaerythritol, fatty acid esters of sorbitol and sorbitan, fatty acid esters of sucrose, alkyl ethers of polyhydric alcohols, fatty acid amides of alkanolamines, and higher fatty acid esters. Alcohol ethylene oxide adducts, such as ethylene
Ethylene oxide adducts of alkylphenols such as oxide nonyl phenyl ether , fatty acid ethylene oxide adducts, polyhydric alcohol fatty acid ester ethylene oxide adducts, higher alkylamine ethylene oxide adducts, fatty acid amide ethylene oxide adducts, and fats and oils ethylene oxide adducts And polypropylene glycol ethylene oxide adducts.

The amount of the surfactant contained in the separator 3 is preferably in the range of 0.3% by weight to 1.0% by weight. This is due to the following reasons. When the amount of the surfactant is less than 0.3% by weight, the liquid retention of the separator may be reduced. On the other hand, when the amount of the surfactant exceeds 1.0% by weight, the performance of the secondary battery may be deteriorated.

Examples of the alkaline electrolyte include sodium hydroxide (NaOH) and lithium hydroxide (LiO
H), a mixed solution of potassium hydroxide (KOH) and LiOH, a mixed solution of KOH, LiOH and NaOH, and the like.

[0025]

The olefin resin fiber having a plurality of fine continuous pores extending from the surface to the inside used in the separator of the present invention is filled with a surfactant through the continuous pores. Moreover, the olefin resin fiber has a large surface area, for example for polypropylene fiber 20m ² / g~90m ² / g 100 to 500 times greater than the surface area of the conventional polyolefin fibers (0.18m ² / g) high surface area, A large amount of surfactant can be filled inside.
Therefore, a separator having a plurality of fine continuous pores from the surface to the inside and comprising a nonwoven fabric containing an olefin resin fiber in which the surfactant is filled in at least the continuous pores has a high hydrophilicity over a long period of time. Therefore, the charge-discharge cycle life of the nickel-hydrogen secondary battery incorporating the separator can be improved.

Since the separator can hold a sufficient amount of electrolyte for a long period of time, the entire surface including the gap between the fibers is covered with the electrolyte membrane. Therefore, when the secondary battery is stored at a high temperature in a charged state, the hydrogen gas generated from the hydrogen storage alloy of the negative electrode can be cut off by the electrolyte film, so that self-discharge during high temperature storage can be suppressed. Can be.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings. Example 1 Commercially available lanthanum-enriched misch metals Lm and Ni,
LmNi using Co, Mn, Al by high frequency furnace
_A hydrogen storage alloy having a composition of _4.0 Co _0.4 Mn _0.3 Al _0.3 was produced. The hydrogen storage alloy was mechanically pulverized and passed through a 200-mesh sieve. 0.5 parts by weight of sodium polyacrylate and 100 parts by weight of the obtained alloy powder, carboxymethyl cellulose (CMC)
0.125 parts by weight, polytetrafluoroethylene dispersion (specific gravity 1.5, solid content 60 wt%) 2.5
A paste was prepared by mixing 1.0 part by weight of carbon powder as a conductive material with 50 parts by weight of water. This paste was applied to punched metal, dried, and then molded under pressure to produce a hydrogen storage alloy negative electrode.

On the other hand, a mixed powder consisting of 90% by weight of nickel hydroxide powder and 10% by weight of cobalt oxide powder was added to 0.3% by weight of carboxymethyl cellulose and 0.5% by weight of polytetrafluoroethylene based on the nickel hydroxide powder. %, Followed by adding 45% by weight of pure water thereto and kneading the mixture to prepare a paste. After filling this paste into a sintered fiber substrate, the paste was further applied to both surfaces thereof, dried, and rolled by a roller press to produce a paste-type nickel positive electrode.

Next, the thickness is 2 denier, the surface area is 60 m ² / g, and a plurality of diameters are 2 μm from the surface to the inside.
A nonwoven fabric having a basis weight of 60 g / m ² and a thickness of 0.20 mm was prepared from polyethylene fibers having continuous pores of m or less. The nonwoven fabric is made of ethylene oxide nonylphenyl
A separator was prepared by immersing the surfactant in the ether to fill the continuous pores with the surfactant. The amount of the surfactant in the obtained separator was 0.5% by weight.

Next, the separator was interposed between the negative electrode and the positive electrode and spirally wound to form an electrode group. Such an electrode group and 7N KOH and 1N LiO
The electrolytic solution composed of H was housed in a cylindrical container having a bottom to assemble an AA-size cylindrical nickel-metal hydride secondary battery having the structure shown in FIG. 1 described above. Example 2 Core-sheath type composite fiber in which polypropylene was coated with polyethylene, 2 denier in thickness and 60 m ² / g in surface area
And a polyethylene fiber having a plurality of continuous pores having a diameter of 2 μm or less from the surface to the inside in a weight ratio of 50: 5
By mixing at a ratio of 0, a nonwoven fabric having a basis weight of 60 g / m ² and a thickness of 0.20 mm was produced. Etch the non-woven fabric
By immersing the surfactant in oxide nonylphenyl ether and filling the continuous pores with the surfactant, a separator was produced. The amount of the surfactant in the obtained separator was 0.5% by weight.

Next, the separator was interposed between the negative electrode and the positive electrode in the same manner as in Example 1, and spirally wound to form an electrode group. Such an electrode group was housed in a bottomed cylindrical container together with an electrolytic solution having the same composition as that of Example 1 and FIG.
An AA-size cylindrical nickel-metal hydride secondary battery having the structure shown in FIG. Example 3 A core-sheath composite fiber obtained by coating polypropylene with polyethylene, a core-sheath composite fiber obtained by coating polypropylene with an ethylene-vinyl alcohol copolymer resin, a denier of 2 weight, a surface area of 60 m ² / g, and a surface And a plurality of polyethylene fibers having continuous pores having a diameter of 2 μm or less throughout the inside thereof, mixed at a weight ratio of 20:40:40 to have a basis weight of 60 g / m ² and a thickness of 0.20 mm. A non-woven fabric was produced. The nonwoven fabric is ethylene oxide nonyl
A separator was produced by immersing in phenyl ether and filling the continuous pores with the surfactant.
The amount of the surfactant in the obtained separator is 0.5% by weight.
Met.

Next, the separator was interposed between the negative electrode and the positive electrode as in Example 1, and spirally wound to form an electrode group. Such an electrode group was housed in a bottomed cylindrical container together with an electrolytic solution having the same composition as that of Example 1 and FIG.
An AA-size cylindrical nickel-metal hydride secondary battery having the structure shown in FIG. Comparative Example 1 A core-sheath composite fiber obtained by coating polypropylene with polyethylene and a core-sheath composite fiber obtained by coating polypropylene with an ethylene-vinyl alcohol copolymer resin, having a basis weight of 60 g / m ² and a thickness of 60 g / m ² A secondary battery similar to that of Example 1 was assembled except that a 0.20 mm nonwoven fabric separator was used. Comparative Example 2 Example 1 was repeated except that a separator made of a nonwoven fabric having a surface weight of 60 g / m ² and a thickness of 0.20 mm was formed from polyethylene fibers having ethylene oxide nonylphenyl ether adsorbed on the surface. A secondary battery similar to the above was assembled.

After the obtained secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 were charged at 1 CmA to 150%,
The charge / discharge cycle of discharging until the battery voltage reached 1.0 V at CmA was repeated, and the discharge capacity was calculated from the time until the battery voltage reached 1.0 V at 1 CmA for each cycle. From the obtained discharge capacity, the discharge capacity ratio (1 in Example 1)
The discharge capacity at the cycle was set to 100). Further, a cycle number ratio (the number of cycles when the discharge capacity ratio of Example 1 reaches 80 was taken as 100) was determined from the obtained number of cycles. FIG. 2 shows the relationship between the cycle number ratio and the discharge capacity ratio in each of such secondary batteries.

As is apparent from FIG. 2, a separator comprising a plurality of fine continuous pores extending from the surface to the inside and comprising a nonwoven fabric containing polyethylene fibers filled with at least a surfactant in the continuous pores is provided. Examples 1-3
It can be seen that the secondary battery can maintain a high discharge capacity ratio over a long period of time. On the other hand, the secondary battery of Comparative Example 1 provided with a separator made of a nonwoven fabric containing a core-sheath type composite fiber obtained by coating polypropylene with an ethylene vinyl alcohol copolymer resin, and a polyethylene fiber nonwoven fabric having a surface-adsorbed surfactant. It can be seen that the discharge capacity ratio of the secondary battery of Comparative Example 2 including the separator composed of

Further, the obtained secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 were left in a thermostat at 45 ° C. for 14 days while being charged at 1 CmA at 150%, and then charged at 1 Cm.
At A, the battery was discharged until the battery voltage reached 1.0 V, and the discharge capacity was measured. From the measured discharge capacity, the remaining capacity ratio (45
150C at 1 CmA before storing in a thermostat at 14 ° C for 14 days.
% And discharged at 1 CmA until the battery voltage reaches 1.0 V). The result is shown in FIG.

As is apparent from FIG. 3, a separator comprising a plurality of fine continuous pores extending from the surface to the inside and comprising a nonwoven fabric containing polyethylene fibers filled with at least a surfactant in the continuous pores is provided. Examples 1-3
Has a residual capacity of 70% after storage at high temperature.
As described above, it is clear that self-discharge can be suppressed. On the other hand, the secondary battery of Comparative Example 1 provided with a separator made of a nonwoven fabric containing a core-sheath type composite fiber obtained by coating polypropylene with an ethylene vinyl alcohol copolymer resin, and a polyethylene fiber nonwoven fabric having a surface-adsorbed surfactant. It can be seen that the secondary battery of Comparative Example 2 provided with a separator made of was low in the residual capacity ratio after storage at a high temperature of 60% and had a high degree of progress of self-discharge.

[0037]

As described above in detail, according to the nickel-metal hydride secondary battery of the present invention, self-discharge during storage at a high temperature can be suppressed, and the charge / discharge cycle life can be improved. Has a remarkable effect.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a nickel-metal hydride secondary battery of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a cycle number ratio and a discharge capacity ratio in the nickel-hydrogen secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 of the present invention.

FIG. 3 is a characteristic diagram showing the remaining capacity ratio of the nickel-hydrogen secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 of the present invention after storage at a high temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator, 4 ... Container.

(56) References JP-A-2-304862 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 2/16 H01M 10/30

Claims (1)

(57) [Claims] 1. A nickel-metal hydride comprising a paste-type positive electrode containing nickel oxide, a paste-type negative electrode containing a hydrogen storage alloy, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte. In the secondary battery, the separator has a plurality of fine continuous pores extending from the surface to the inside, and a surfactant is filled in at least the continuous pores , and the olefin resin fiber has a surface area of 20 to 90 m ² / g. Ri Do a nonwoven fabric containing said in the separator
A nickel-metal hydride secondary battery, wherein the content of the surfactant is in the range of 0.3 to 1% by weight .