JP7197250B2 - secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a secondary battery, and more particularly to a secondary battery including an iron battery can.

A secondary battery is known as one type of battery that is used as a power source for various devices. A secondary battery is a convenient battery that can be used repeatedly by repeating charging. One type of such secondary batteries is a cylindrical secondary battery.

In a cylindrical secondary battery, an electrode group formed by spirally winding a positive electrode and a negative electrode, which are superimposed with a separator sandwiched between them, is placed in a bottomed cylindrical battery can that also serves as a negative electrode terminal. It is housed together with the electrolyte, and is formed by sealing the upper end opening of this battery can with a cover plate having a positive electrode terminal.

By the way, since the electrolytic solution described above is generally highly corrosive, it is ideal to use nickel, which is excellent in corrosion resistance, as a material for a battery can used in a secondary battery.

However, the price of nickel is soaring along with the increase in demand. Considering the production cost of the battery, it is desirable to use as little nickel as possible.

Therefore, it is common practice to use iron, which is cheaper than nickel, as a base material, and use a nickel-plated material such as a nickel-plated steel sheet to manufacture a bottomed cylindrical battery can. (See Patent Document 1, for example).

JP-A-08-055613

By the way, when manufacturing a secondary battery, the outermost peripheral portion of the electrode group and the inner peripheral surface of the battery can rub against each other during the process of inserting the electrode group into the battery can. As a result, the inner peripheral surface of the battery can may be damaged, exposing the iron of the substrate. When the iron is exposed in this way, the iron may be eluted into the electrolyte when the battery is left for a long period of time. A part of the iron dissolved in the electrolyte is deposited on the surface of the positive electrode. The iron deposited on the positive electrode causes a decrease in the charging voltage at the positive electrode, lowers the charging efficiency, and reduces the capacity of the battery. The capacity drop caused by this elution of iron is different from the capacity drop caused by deactivation, and the capacity does not recover even after repeated charging and discharging. In other words, the elution of iron causes a decrease in the capacity recovery rate of the secondary battery.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a secondary battery capable of suppressing a decrease in capacity recovery rate due to elution of iron.

In order to achieve the above object, according to the present invention, a bottomed cylindrical battery which is formed of a plate material having an iron substrate and a coating layer covering the surface of the substrate and which also serves as a terminal of one pole. A battery can, a sealing body electrically connected to a terminal of the other electrode and sealing the upper end opening of the battery can, and the one electrode and the other electrode are laminated with a separator interposed therebetween to form a spiral shape. a wound columnar electrode group, the electrode group being housed together with an electrolytic solution in the battery can, wherein the electrode group has a fluororesin layer on the outermost periphery. and the amount of the fluororesin is 0.3 g/cm ² or more.

In addition, it is preferable that the fluororesin layer is formed at least on a portion of the electrode group having the maximum diameter.

In the secondary battery according to the present invention, since the electrode group has a fluororesin layer on the outermost peripheral portion, even if the outermost peripheral portion of the electrode group rubs against the inner peripheral surface of the battery can, the battery can remains intact. It is possible to sufficiently prevent the coating layer from being scratched, and to prevent the substrate of the battery can from being exposed. Therefore, even if the battery is left for a long period of time, the elution of iron from the substrate of the battery can into the electrolyte can be suppressed. Therefore, according to the present invention, it is possible to provide a secondary battery capable of suppressing a decrease in capacity recovery rate due to elution of iron.

1 is a partially broken perspective view of a nickel-metal hydride secondary battery according to an embodiment of the present invention; FIG. 1 is a cross-sectional view showing a cross section of a nickel-hydrogen secondary battery according to an embodiment of the present invention; FIG. 1 is a perspective view showing the configuration of an intermediate product of a negative electrode according to an embodiment of the present invention; FIG. 1 is a side view showing the configuration of a negative electrode according to one embodiment of the present invention; FIG.

Hereinafter, as a secondary battery according to the present invention, an AA size cylindrical nickel-metal hydride secondary battery (hereinafter referred to as a battery) 2 will be taken as an example and described with reference to the drawings.

As shown in FIG. 1, the battery 2 has a cylindrical battery can 10 with an open top and a bottom. The battery can 10 is electrically conductive and its bottom wall 35 functions as a negative terminal.

Here, the battery can 10 is formed by processing a plate material having an iron substrate and a coating layer covering the surface of the substrate into a cylindrical shape with a bottom. A steel plate is generally used as the iron substrate. A nickel plating layer is preferably used as the coating layer covering the surface of the steel sheet. That is, it is preferable to use a nickel-plated steel sheet as the material of the battery can 10 .

A sealing member 11 is fixed to the opening of the battery can 10 . The sealing member 11 includes a cover plate 14 and a positive electrode terminal 20 and seals the battery can 10 . The cover plate 14 is a disc-shaped member having electrical conductivity. A cover plate 14 and a ring-shaped insulating packing 12 surrounding the cover plate 14 are arranged in the opening of the battery can 10 . It is fixed to the opening edge 37 of the can 10 . That is, the cover plate 14 and the insulating packing 12 cooperate with each other to seal the opening of the battery can 10 .

Here, the lid plate 14 has a central through hole 16 in the center. A rubber valve body 18 is arranged on the outer surface of the cover plate 14 to close the central through hole 16 . Furthermore, on the outer surface of the cover plate 14, a metal positive electrode terminal 20 having a cylindrical shape with a flange is electrically connected so as to cover the valve body 18. As shown in FIG. The positive electrode terminal 20 presses the valve body 18 toward the cover plate 14 . The positive electrode terminal 20 is provided with a gas vent hole (not shown).

Nickel-plated steel sheets are also preferably used as materials for the cover plate 14 and the positive terminal 20 described above.

The above-described central through-hole 16 is normally airtightly closed by a valve body 18 . On the other hand, when gas is generated in the battery can 10 and the pressure of the gas increases, the valve body 18 is compressed by the pressure of the gas and opens the central through-hole 16 , so that the central through-hole 16 is penetrated from the battery can 10 . Gas is released to the outside through the hole 16 and the gas vent hole (not shown) of the positive electrode terminal 20 . In other words, the central through-hole 16 , the valve body 18 and the positive terminal 20 form a safety valve for the battery 2 .

An electrode group 22 is accommodated in the battery can 10 . The electrode group 22 includes strip-shaped positive electrodes 24, negative electrodes 26, and separators 28, respectively.

Specifically, referring to FIG. 2 , in the electrode group 22 , positive electrodes 24 and negative electrodes 26 are alternately stacked with separators 28 interposed therebetween when viewed in the radial direction of the electrode group 22 .

Here, the manufacturing procedure of the electrode group 22 is as follows.
First, strip-shaped positive electrode 24, negative electrode 26 and separator 28 are prepared. Then, a laminate is formed by stacking the positive electrode 24 and the negative electrode 26 with the separator 28 interposed therebetween. The laminate thus obtained is spirally wound from one end thereof using a winding core. Thus, a columnar electrode group 22 is obtained.

Since the electrode group 22 is manufactured as described above, one ends (winding start ends) 36 and 38 of the positive electrode 24 and the negative electrode 26 are positioned on the center side of the electrode group 22, and the other ends of the positive electrode 24 and the negative electrode 26 ( Winding end ends 40 and 42 are positioned on the outer peripheral side of the electrode group 22 . The separator 28 is not wound around the outer periphery of the electrode group 22 , and the outermost peripheral portion 50 of the negative electrode 26 forms the outermost peripheral portion of the electrode group 22 . That is, the radially outer surface (outer surface) 52 of the electrode group 22 in the outermost peripheral portion 50 of the negative electrode 26 is not covered with the separator 28 . A radially inner surface (inner surface) 54 of the electrode group 22 in the outermost peripheral portion 50 of the negative electrode 26 faces the positive electrode 24 with the separator 28 interposed therebetween. That is, the outermost peripheral portion 50 of the negative electrode 26 faces the positive electrode 24 only at the inner surface 54 .

Furthermore, in the negative electrode 26, an inner peripheral portion 56 is continuous inside the outermost peripheral portion 50, and near the winding center of the electrode group 22 further inside the inner peripheral portion 56, the innermost peripheral portion 58 are consecutive.

The inner peripheral portion 56 described above is a portion in which both the outer surface 52 and the inner surface 54 of the negative electrode 26 face the positive electrode 24 with the separator 28 interposed therebetween. It extends to near the center of rotation.

The innermost peripheral portion 58 described above is positioned at the center of the electrode group 22 , and its outer surface 52 faces the positive electrode 24 with the separator 28 interposed therebetween. In the electrode group 22, the core is removed after the winding work using the core is completed, so a through hole 44 is formed in the portion where the core is removed.

As described above, the outermost periphery of the electrode group 22 is formed by a portion of the negative electrode 26 (outermost peripheral portion 50), and the electrode group 22 housed in the battery can 10 is such that the outermost peripheral portion 50 of the negative electrode 26 is It is in contact with the inner peripheral surface of the battery can 10 . Thereby, the negative electrode 26 and the battery can 10 are electrically connected to each other.

Inside the battery can 10 , a positive electrode lead 30 is arranged between a part of the electrode group 22 and the cover plate 14 . Specifically, as shown in FIG. 1 , the positive electrode lead 30 has one end connected to the positive electrode 24 and the other end connected to the cover plate 14 . Therefore, the positive electrode terminal 20 and the positive electrode 24 are electrically connected to each other via the positive electrode lead 30 and the cover plate 14 . A circular upper insulating member 32 is arranged between the cover plate 14 and the electrode group 22 , and the positive electrode lead 30 extends through a slit 39 provided in the upper insulating member 32 . A circular lower insulating member 34 is also arranged between the electrode group 22 and the bottom wall 35 of the battery can 10 .

Furthermore, a predetermined amount of alkaline electrolyte (not shown) is injected into the battery can 10 . The electrode group 22 is impregnated with this alkaline electrolyte, and an electrochemical reaction (charging/discharging reaction) between the positive electrode 24 and the negative electrode 26 during charging/discharging proceeds. As the alkaline electrolyte, it is preferable to use an aqueous solution containing at least one of KOH, NaOH and LiOH as a solute.

As a material for the separator 28, for example, a nonwoven fabric made of polyamide fiber to which a hydrophilic functional group is added, or a nonwoven fabric made of polyolefin fiber such as polyethylene or polypropylene to which a hydrophilic functional group is added can be used.

The positive electrode 24 includes a conductive positive electrode base material having a porous structure, and a positive electrode material mixture retained within the pores of the positive electrode base material.

As such a positive electrode substrate, for example, a nickel-plated foam metal sheet, a foam nickel sheet, or the like can be used.

The positive electrode mixture contains positive electrode active material particles, a binder, and a conductive agent. Moreover, a positive electrode additive is added to the positive electrode mixture as necessary.

The binder described above functions to bind the positive electrode active material particles to each other and to bind the positive electrode active material particles to the positive electrode substrate. Here, as the binder, for example, carboxymethyl cellulose, methyl cellulose, PTFE (polytetrafluoroethylene) dispersion, HPC (hydroxypropyl cellulose) dispersion, or the like can be used.

Examples of conductive agents include cobalt monoxide.
Examples of positive electrode additives include zinc oxide and cobalt hydroxide.

As the positive electrode active material particles, nickel hydroxide particles generally used for nickel-hydrogen secondary batteries are used. As the nickel hydroxide particles, it is preferable to employ nickel hydroxide particles having a higher order.

The positive electrode active material particles as described above are produced by a production method generally used for nickel-hydrogen secondary batteries.

Then, the positive electrode 24 can be manufactured, for example, as follows.
First, a positive electrode mixture slurry containing positive electrode active material particles, water and a binder is prepared. The prepared positive electrode mixture slurry is filled into, for example, a nickel-plated metal foam sheet and dried. After drying, the sheet of foamed metal filled with nickel hydroxide particles or the like is rolled and then cut. Thus, the positive electrode 24 is manufactured.

Next, the negative electrode 26 will be described.
The negative electrode 26 includes a strip-shaped conductive negative electrode core 62 , a negative electrode mixture layer 68 formed of a negative electrode mixture carried on the negative electrode core 62 , and a top layer of the negative electrode 26 in the negative electrode mixture layer 68 . It is provided with a fluororesin layer 90 formed of a fluororesin 85 disposed on the surface of a portion corresponding to the outer peripheral portion 50, and has a strip shape as a whole. Here, the fluororesin layer 90 is formed by disposing the fluororesin 85 on at least part of the surface of the portion of the negative electrode mixture layer 68 corresponding to the outermost peripheral portion 50 of the negative electrode 26 .

The negative electrode core 62 is a strip-shaped metal material with a large number of through holes, and for example, a punching metal sheet can be used.

The negative electrode mixture is not only filled in the through-holes of the negative electrode core 62 , but also carried in layers on the first surface 64 and the second surface 66 of the negative electrode core 62 to form the negative electrode mixture layer 68 . ing.

The negative electrode mixture contains hydrogen-absorbing alloy particles capable of absorbing and releasing hydrogen as a negative electrode active material, a conductive agent, a binder, and a negative electrode auxiliary agent.

The above-described binder functions to bind the hydrogen-absorbing alloy particles, the conductive agent, etc. to each other and to bind the hydrogen-absorbing alloy particles, the conductive agent, etc. to the negative electrode substrate. Here, the binder is not particularly limited. For example, binders commonly used for nickel-metal hydride secondary batteries, such as hydrophilic or hydrophobic polymers and carboxymethyl cellulose, can be used. can be used.

Styrene-butadiene rubber, sodium polyacrylate, and the like can be used as the negative electrode auxiliary agent.

The hydrogen-absorbing alloy constituting the hydrogen-absorbing alloy particles is not particularly limited, and it is preferable to use a hydrogen-absorbing alloy for general nickel-metal hydride secondary batteries. More preferably, a hydrogen storage alloy having a composition represented by general formula (I) shown below is used.
Ln _1-x Mg _x Ni _yab Al _a M _b (I)

However, in general formula (I), Ln is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y, Ti and Zr represents at least one selected element, and M is at least one selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P and B and the subscripts a, b, x, and y are respectively 0.05 ≤ a ≤ 0.30, 0 ≤ b ≤ 0.50, 0 ≤ x < 0.05, 2.8 ≤ y ≤ 3 .9 satisfies the relationship.

Particles of the hydrogen-absorbing alloy are obtained, for example, as follows.
First, metal raw materials are weighed and mixed so as to have a predetermined composition, and the mixture is melted in, for example, a high-frequency induction melting furnace, and then cooled to form an ingot. The obtained ingot is subjected to heat treatment at 900 to 1200° C. in an inert gas atmosphere for 5 to 24 hours. Thereafter, the ingot is pulverized and sieved to obtain hydrogen-absorbing alloy particles having a desired particle size.

Here, the particle size of the hydrogen-absorbing alloy particles is not particularly limited, but those having an average particle size of 55.0 to 80.0 μm are preferably used. Here, the average particle size means the volume average particle size (MV) determined by a laser diffraction/scattering method using a particle size distribution analyzer.

As the conductive agent, a conductive agent commonly used for negative electrodes of nickel-hydrogen secondary batteries is used. For example, carbon black or the like is used.

Next, a fluororesin layer 90 formed of the fluororesin 85 is provided at a predetermined position of a portion of the negative electrode mixture layer 68 corresponding to the outermost peripheral portion 50 of the negative electrode 26 . Therefore, even if the outermost peripheral portion 50 of the negative electrode 26, which is the outermost peripheral portion of the electrode group 22, abuts against the inner peripheral surface of the battery can 10, the coating layer, that is, the nickel-plated layer on the inner peripheral surface of the battery can 10 does not adhere to the nickel plating layer. Work without hurting.

Examples of the fluororesin 85 include polytetrafluoroethylene (hereinafter referred to as PTFE), ethylene tetrafluoride-propylene hexafluoride copolymer (hereinafter referred to as FEP), perfluoroalkoxyalkane (hereinafter referred to as PFA), and the like. is preferably used.

Here, the shape of the negative electrode intermediate product 60 before the fluororesin layer 90 is formed will be described with reference to FIG. In addition, in FIG. 3, the thickness of the negative electrode mixture layer 68 and the like are exaggerated in order to facilitate understanding of the configuration of the intermediate product 60 . 3, illustration of the innermost peripheral portion 58 positioned near the winding center of the electrode group 22 is omitted.

The negative electrode intermediate product 60 has a strip shape, and as shown in FIG. and a negative electrode mixture layer 68 formed of the negative electrode mixture carried on the substrate 66 . The first surface 64 is positioned on the outer surface 52 side of the negative electrode 26 , and the second surface 66 is positioned on the inner surface 54 side of the negative electrode 26 .

The negative electrode mixture layer 68 includes a first negative electrode mixture layer 70 positioned on the first surface 64 side and a second negative electrode mixture layer 72 positioned on the second surface 66 side.

The first negative electrode mixture layer 70 includes an outermost peripheral first region 74 positioned at a position corresponding to the outermost peripheral portion 50 of the negative electrode 26 and an inner peripheral first region 76 that is continuous with the outermost peripheral first region 74 . contains.

The second negative electrode mixture layer 72 includes an outermost second region 78 located on the opposite side of the outermost first region 74 and in a range corresponding to the outermost first region 74 , and the inner first region 76 described above. on the opposite side to the inner peripheral first region 76 and the inner peripheral second region 80 located in the corresponding range.

The thickness t1 of the outermost first region 74 is thinner than the thicknesses t2, t3, t4 of the other portions, that is, the outermost second region 78, the inner first region 76, and the inner second region 80. FIG. In addition, it is preferable that each thickness of t2, t3, and t4 be the same dimension.

Further, the amount of the negative electrode mixture per unit area in the outermost peripheral portion 50 of the negative electrode 26 is set to a range of 50% or more and 80% or less of the amount of the negative electrode mixture per unit area in the inner peripheral portion 56 of the negative electrode 26. preferably.

The outermost peripheral portion 50 of the negative electrode 26 is a portion that faces the inner peripheral surface of the battery can 10 and does not face the positive electrode 24 (see FIG. 2). For this reason, since the outermost peripheral portion 50 of the negative electrode 26 does not contribute much to the battery reaction, the amount of the negative electrode mixture is smaller than the other portions, and the outermost portion 50 is formed thinner than the other portions.

In the present invention, as shown in FIG. 4, a fluororesin layer 90 is formed in the outermost peripheral first region 74 portion. In addition, in FIG. 4, the thickness of the negative electrode mixture layer 68 and the like are exaggerated in order to facilitate understanding of the configuration of the negative electrode 26 .

Here, let A be the amount of the fluororesin 85 forming the fluororesin layer 90 in the outermost first region 74 . A is preferably 0.3 g/cm ² or more in terms of mass per unit area of the portion where the fluororesin layer 90 is formed. That is, when the fluororesin layer 90 is formed in the outermost first region 74 , the fluororesin layer 90 is formed using the amount of the fluororesin 85 that is 0.3 g or more per unit area of the outermost first region 74 . do.

When the fluororesin layer 90 is formed by applying the fluororesin 85 in such an amount that A becomes 0.3 g/cm ² or more, the thickness of the obtained fluororesin layer 90 is the same as the inner peripheral surface of the battery can 10. It is thick enough not to damage the coating layer (nickel plating layer). In addition, since the fluororesin has a low coefficient of friction and excellent lubricity, it contributes to ease of insertion when inserting the electrode group 22 into the battery can 10 .

If the above A is less than 0.3 g/cm ² , the fluororesin layer 90 having a sufficient thickness cannot be obtained, and when the electrode group 22 rubs against the inner peripheral surface of the battery can 10, the battery can 10 There is a risk of scratching the coating layer (nickel plating layer) on the inner peripheral surface of the.

On the other hand, if the above-described A exceeds 4.0 g/cm ² , the thickness of the resulting fluororesin layer 90 may become too thick, and discharge characteristics may deteriorate.

Therefore, the value of A is preferably 0.3 g/cm ² or more and 4.0 g/cm ² or less. By setting the value of A within the above range, the effect of suppressing damage to the coating layer (nickel plating layer) on the inner peripheral surface of the battery can 10 at the outermost peripheral portion of the electrode group 22 and the deterioration of the discharge characteristics can be suppressed. A suppressing effect is obtained.

The negative electrode 26 can be manufactured, for example, as follows.
First, a hydrogen-absorbing alloy powder, which is an aggregate of hydrogen-absorbing alloy particles as described above, a conductive agent, a binder, and water are prepared and kneaded to prepare a negative electrode mixture paste. Next, the obtained paste is applied to both surfaces of the negative electrode core. At this time, as shown in FIG. also thin. After that, the paste is dried. After drying, the negative electrode mixture carried on the negative electrode core 62 is subjected to rolling treatment. Thus, an intermediate product 60 of a negative electrode is obtained.

Next, a predetermined amount of a fluororesin dispersion is applied to the outermost peripheral first region 74 of the negative electrode intermediate product 60 . The method of applying the fluororesin dispersion to the negative electrode intermediate product 60 is not particularly limited, but it is preferable to use, for example, a method of applying with a brush, a sponge roller, a doctor blade, or the like.

Then, after the coating step described above, a drying step for performing a drying treatment is provided to evaporate the water content of the dispersion. As a result, as shown in FIG. 4, the fluororesin layer 90 is formed by leaving the fluororesin 85 on the negative electrode mixture layer 68 .

In the step of applying the fluororesin dispersion described above, it is preferable to apply the fluororesin dispersion to the negative electrode intermediate product 60 in an environment of 20° C. or more and 25° C. or less.

Furthermore, in the drying process after the coating process, the negative electrode intermediate product 60 that has undergone the coating process is held in a temperature environment of 40° C. or more and 80° C. or less for 5 minutes or more and 15 minutes or less. is preferably evaporated. If the drying temperature is less than 40° C., evaporation of the water content of the fluororesin dispersion does not proceed well, making it difficult to maintain the designed amount of the fluororesin. On the other hand, if the temperature exceeds 80°C, the fluororesin and other constituent materials may deteriorate. Therefore, it is preferable to set the drying temperature in the drying process within the range described above. Further, if the holding time in the drying process is less than 5 minutes, the fluororesin dispersion will not be sufficiently dried. On the other hand, the drying of the dispersion is completed by holding for at least 15 minutes. Therefore, it is preferable to set the holding time of the drying step within the range described above.

As described above, the negative electrode intermediate product 60 that has undergone the process of applying the fluororesin dispersion and the process of drying is cut into a predetermined shape. As a result, the negative electrode 26 having the fluororesin layer 90 formed at a predetermined position on the negative electrode mixture layer 68 is obtained.

Here, the overall thickness of the negative electrode 26 used in the present invention is preferably 0.100 mm or more and 0.550 mm or less. If the total thickness is less than 0.100 mm, the amount of hydrogen-absorbing alloy filled in one electrode plate is small, making it difficult to obtain the required battery capacity. On the other hand, if the total thickness is thicker than 0.550 mm, the volume of the negative electrode in the constituent members of the battery increases, making it difficult to accommodate the electrode group 22 in the battery can 10 .

The positive electrode 24 and the negative electrode 26 manufactured as described above are spirally wound with the separator 28 interposed therebetween, thereby forming the electrode group 22 . The outermost peripheral portion 50 of the negative electrode 26 is positioned at the outermost peripheral portion of the obtained electrode group 22 , and the fluororesin layer 90 exists at a predetermined position of the outermost peripheral portion 50 of the negative electrode 26 .

The electrode group 22 thus obtained is housed in the battery can 10 . Subsequently, a predetermined amount of alkaline electrolyte is injected into the battery can 10 . After that, the battery can 10 containing the electrode group 22 and the alkaline electrolyte is sealed with a sealing member 11 having a positive electrode terminal 20 to obtain the battery 2 according to the present invention. The obtained battery 2 is subjected to an initial activation process to be ready for use.

In the battery 2 according to the present invention, the negative electrode 26 included therein has the fluororesin layer 90 in the outermost peripheral first region 74 corresponding to the outermost peripheral portion of the electrode group 22. Therefore, the electrode group 22 is used for batteries. Even if the electrode group 22 comes into contact with the inner peripheral surface of the battery can 10 when being inserted into the can 10 , the nickel plating layer on the inner peripheral surface of the battery can 10 can be prevented from being damaged. Therefore, the substrate of the battery can 10 is prevented from being exposed, and iron can be prevented from eluting from the substrate of the battery can 10 into the electrolytic solution even if the battery can 10 is left for a long period of time. Therefore, the battery 2 according to the present invention is an excellent battery capable of suppressing a decrease in capacity recovery rate due to elution of iron.

Here, the fluororesin layer 90 exists in the outermost peripheral first region 74 of the negative electrode 26 corresponding to the outermost peripheral portion of the electrode group 22, but the amount of the fluororesin 85 constituting this fluororesin layer 90 is 0. .3 g/cm ² or more and 4.0 g/cm ² or less. With such a coating amount of the fluororesin 85, the outermost peripheral first region 74 of the negative electrode 26 has a covered portion and an uncovered portion when viewed microscopically. After the electrode group 22 is inserted into the battery can 10, the diameter of the electrode group 22 increases as it attempts to return in the direction opposite to the direction in which it was wound. Therefore, the electrode group 22 applies pressure to the inner peripheral surface of the battery can 10 . As a result, the portion of the outermost peripheral first region 74 of the negative electrode 26 that is not covered with the fluororesin 85 is pressed against the inner peripheral surface of the battery can 10 and comes into contact, thereby electrically connecting the negative electrode 26 and the battery can 10 . is planned.

In the above-described embodiment, the fluororesin layer 90 is formed on the negative electrode intermediate product 60, but the present invention is not limited to this embodiment. Alternatively, the fluororesin layer 90 may be formed by applying a fluororesin dispersion to the outermost periphery of the .

In the above-described embodiment, the fluororesin layer 90 is provided over the entire outermost peripheral first region 74 of the negative electrode 26, but the present invention is not limited to this aspect. It suffices if it is formed at least in the portion where the

Moreover, the same effect can be obtained even if the fluororesin layer 90 is provided on the inner surface side of the battery can 10 .

[Example]
1. Manufacture of battery (Example 1)
(1) Production of positive electrode

A predetermined amount of nickel sulfate was added to a 1N sodium hydroxide aqueous solution containing ammonium ions to prepare a mixed aqueous solution. While stirring the obtained mixed aqueous solution, a 10N sodium hydroxide aqueous solution was gradually added to the mixed aqueous solution to cause a reaction. The pH during the reaction here was stabilized at 13-14. This produced nickel hydroxide particles (positive electrode active material particles).

The obtained nickel hydroxide particles were washed three times with ten times the amount of pure water, and then dehydrated and dried. As a result, nickel hydroxide powder, which is an aggregate of nickel hydroxide particles, was obtained. As a result of measuring the particle size of the obtained nickel hydroxide particles using a laser diffraction/scattering particle size distribution analyzer, the volume average particle size (MV) of the nickel hydroxide particles was found to be 8 μm. .

Next, 0.01 parts by mass of cobalt monoxide powder, 0.003 parts by mass of carboxymethylcellulose powder, and 5 parts by mass of water are added to 10 parts by mass of the nickel hydroxide powder obtained as described above. and kneaded to prepare a positive electrode mixture slurry.

Next, a sheet-shaped metal foam as a positive electrode substrate was filled with this positive electrode mixture slurry. Here, as the foamed metal, one having a surface density (basis weight) of about 300 g/m ² , a porosity of 95%, and a thickness of about 2 mm was used. The foam metal is plated with nickel.

After drying the positive electrode material mixture slurry filled in the foamed metal, it was rolled and then cut into a predetermined size. Thus, a positive electrode 24 for AA size was obtained.

(2) Production of Negative Electrode Metal materials of La, Sm, Mg, Ni, and Al were mixed at a predetermined molar ratio to obtain a mixture. This mixture was melted in a high-frequency induction melting furnace in an inert gas (argon gas) atmosphere, and the resulting molten metal was poured into a mold and cooled to room temperature to obtain an alloy ingot. Then, the alloy ingot is homogenized by heat treatment held at 1000 ° C. for 10 hours in an argon gas atmosphere, and then mechanically pulverized in an argon gas atmosphere to produce a rare earth-Mg-Ni hydrogen storage alloy. A powder was obtained. The particle size distribution of the obtained rare earth-Mg—Ni hydrogen storage alloy powder was measured by a laser diffraction/scattering particle size distribution analyzer. As a result, the volume average particle diameter (MV) was 65 μm.

Further, when the obtained hydrogen storage alloy was subjected to composition analysis using an inductively coupled plasma (ICP) emission spectrometer, the composition of the hydrogen storage alloy was La _0.194 Sm _0.776 Mg _0.03 Ni. _3.30 Al _0.20 .

Next, 0.005 parts by mass of carboxymethyl cellulose powder, 0.05 parts by mass of carbon black powder and 2.5 parts by mass of water were added to 10 parts by mass of the obtained hydrogen-absorbing alloy powder. The mixture was kneaded to prepare a negative electrode mixture paste.

This negative electrode mixture paste was applied to the first surface (surface on the front side) and the second surface (surface on the back side) of a punching metal sheet as a negative electrode core. This perforated metal sheet is a belt-like body made of cold-rolled steel plate (SPCC steel plate) having a large number of through holes with a diameter of 1 mm. The negative electrode mixture paste is also filled in the through-holes of the punched metal sheet.

Here, the thickness of the negative electrode mixture paste is such that the thickness of the outermost peripheral first region 74 is 0.14 mm, the outermost peripheral second region 78 , the inner peripheral first region 76 and the inner peripheral second region 80 are 0.14 mm thick. The thickness of each portion was 0.25 mm.

Next, after drying the negative electrode mixture paste, the negative electrode mixture supported on the punching metal sheet was roll-rolled, and then cut into a predetermined size. Thus, a negative electrode intermediate product 60 was obtained.

Next, after a coating step of applying a dispersion liquid containing PTFE as a fluororesin to the outermost peripheral first region 74 of the negative electrode intermediate product 60 with a brush under a temperature environment of 25° C., the water content of the dispersion liquid is removed. Evaporation drying was applied. The drying treatment was performed by holding the intermediate product of the negative electrode in an environment of 60° C. for 15 minutes. Thus, a negative electrode 26 was obtained.

Here, in the coating step described above, a predetermined amount of the fluororesin-containing dispersion was applied to the outermost peripheral first region 74 . Details are as follows.

Assuming that the amount of the dispersion liquid applied to the outermost first region 74 is a predetermined amount B, the predetermined amount B of the dispersion liquid contains 0 mass per unit area of the outermost first region 74. The fluorine resin was contained in an amount of .3 g/cm ² . Therefore, after the drying process, the fluororesin layer 90 was formed in an amount of 0.3 g/cm ² in terms of mass per unit area of the outermost peripheral first region 74 .

Here, when the fluororesin layer 90 is formed using the predetermined amount B of the dispersion liquid in the outermost peripheral first region 74, the amount A of the fluororesin in the obtained fluororesin layer 90 is 0.3 g/cm ² . In order to confirm whether or not this is the case, the following confirmation work was performed.

First, the mass of the negative electrode intermediate product 60 (hereinafter referred to as basic mass) was measured. Then, after applying a predetermined amount B of a fluororesin dispersion liquid to the outermost peripheral first region 74, the intermediate product 60 was subjected to a drying process of being held in an environment of 60° C. for 15 minutes. The mass of the intermediate product 60 after drying (hereinafter referred to as mass after B application) was measured. Then, the total mass of the fluororesin layer 90 was obtained by subtracting the basic mass from the mass after B coating. Then, from the total mass of the fluororesin layer 90 and the area of the outermost first region 74, the amount A of the fluororesin in terms of mass per unit area of the outermost first region 74 was calculated. As a result, it was confirmed that the amount A of the fluororesin was 0.3 g/cm ² .

(3) Assembly of Nickel Metal Hydride Secondary Battery Two separators 28 were prepared, and the positive electrode 24 and negative electrode 26 obtained as described above were prepared. Then, the separator 28, the positive electrode 24, the separator 28, and the negative electrode 26 were laminated in this order to form a laminate. Next, a winding core was placed on one end of the bottom layer separator 28 , and the laminate was spirally wound with the negative electrode 26 facing outward, thereby manufacturing the electrode group 22 . The separator 28 used in the manufacture of the electrode group 22 here was a sulfonated polypropylene fiber non-woven fabric, and had a thickness of 0.15 mm (basis weight: 53 g/m ² ). Next, the obtained spiral electrode group 22 was housed in a bottomed cylindrical battery can made of nickel-plated SPCC steel plate (housing step).

After that, the positive electrode lead previously joined to a predetermined position of the positive electrode was joined to the sealing body.

On the other hand, an alkaline electrolyte, which is an aqueous solution containing KOH, NaOH and LiOH as solutes, was prepared. This alkaline electrolyte has a mass mixing ratio of KOH, NaOH and LiOH of KOH:NaOH:LiOH=11.0:2.6:1.0. The normality of this alkaline electrolyte is 8N.

Then, through the housing step, 2 g of the prepared alkaline electrolyte was poured into the bottomed cylindrical battery can 10 housing the electrode group 22 . After that, the opening of the battery can 10 was closed with the sealing member 11, and an AA size battery 2 with a nominal capacity of 1000 mAh was assembled.

(Example 2)
A nickel-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that a dispersion containing PFA was used instead of PTFE.

(Comparative example 1)
A nickel-hydrogen secondary battery was manufactured in the same manner as in Example 1, except that the fluororesin dispersion liquid was not applied to the outermost peripheral first region 74 of the negative electrode intermediate product 60 and the fluororesin layer was not provided. manufactured.

2. Evaluation of batteries (1) Measurement of capacity recovery rate For the batteries of Example 1 and Comparative Example 1 that had undergone initial activation, the battery voltage reached the maximum value at a charging current of 1000 mA in an environment of 25°C. After that, the battery was charged under the so-called -ΔV control, in which the battery was charged until the battery dropped by 10 mV. This charging/discharging operation is called a first charging/discharging operation.

After the first charge/discharge operation was completed, each battery was charged under an environment of 25° C. with a charging current of 100 mA for 16 hours and then rested for 1 hour. It was discharged to 1.0V. This charge/discharge operation is called a second charge/discharge operation.

Each battery after completion of the second charging/discharging operation was left in an environment of 25° C. for 3 months.
Each battery after being left for 3 months was charged under a so-called -ΔV control in an environment of 25° C. with a charging current of 1000 mA until the battery voltage reached the maximum value and then dropped by 10 mV. After that, the battery was rested for 1 hour, and then discharged at a discharge current of 200 mA until the battery voltage reached 1.0 V. The charging/discharging cycle was repeated three times. This charge/discharge operation is called a third charge/discharge operation.

After the third charge/discharge operation, each battery was charged under an environment of 25°C with a charging current of 100 mA for 16 hours, and then rested for 1 hour. It was discharged to 1.0V. This charge/discharge operation is called a fourth charge/discharge operation.

The discharge capacity was measured during the second charge/discharge operation described above. The result was taken as the discharge capacity before standing.
Also, the discharge capacity was measured during the fourth charge/discharge operation described above. The result was taken as the discharge capacity after standing.

Then, the capacity recovery rate was determined by the following formula (II), and the results are shown in Table 1.
Capacity recovery rate [%] = (discharge capacity after standing/discharge capacity before standing) x 100 (II)

(2) Analysis of Amount of Deposited Iron Each battery for which capacity recovery rate measurement was completed was disassembled, and the positive electrode was taken out from the inside of the battery. The positive electrode thus taken out was cut into a square shape of 2 cm long and 2 cm wide without washing to obtain a sample.
The obtained sample was set in a fluorescent X-ray analyzer, fluorescent X-rays of iron were detected, and the amount of iron was measured from the intensity thereof. At this time, when the amount of iron within the measurement field of the fluorescent X-ray spectrometer is f, and the mass of the positive electrode within the measurement field is p, the amount of iron deposited was determined by the following formula (III). The obtained results are shown in Table 1 as the amount of iron deposited on the positive electrode.
Amount of iron deposited on the positive electrode [%] = (f / p) × 100 (III)

(3) Consideration In the battery of Comparative Example 1, which does not have a fluororesin layer on the outermost periphery of the electrode group 22, the amount of iron deposited on the positive electrode was 0.256%.

In contrast, in the batteries of Examples 1 and 2 having the fluororesin layer on the outermost periphery of the electrode group 22, the amounts of iron deposited on the positive electrode were 0.128% and 0.136%, respectively. It can be seen that the amount of iron deposited is less than in Example 1.

From this, if a layer of fluororesin is present in the outermost peripheral portion of the electrode group 22 (negative outermost peripheral first region 74) in contact with the inner peripheral surface of the battery can 10, the inner peripheral surface of the battery can 10 It can be said that the coating layer (nickel plating layer) on the surface is not damaged, and the elution of iron from the substrate of the battery can can be suppressed to a minimum even after being left for a long period of time.

Also, regarding the capacity recovery rate after standing for 3 months, the capacity recovery rate of the battery of Comparative Example 1, which does not have a fluororesin layer, is 95.2%, whereas the battery of the battery having a fluororesin layer has a capacity recovery rate of 95.2%. The capacity recovery rates of the batteries of Examples 1 and 2 were 96.4% and 96.3%, indicating that the batteries of Examples 1 and 2 had improved capacity recovery rates over the battery of Comparative Example 1. .

Therefore, by providing the fluororesin layer on the outermost periphery of the electrode group 22, the elution of iron from the substrate of the battery can is suppressed, and as a result, the decrease in the capacity recovery rate due to the elution of iron is suppressed. It can be said that

The present invention is not limited to the above-described embodiments and examples, and various modifications are possible. For example, in the above examples, a nickel-metal hydride secondary battery was described, but the present invention is not limited to this embodiment, and is a secondary battery including a battery can using iron as a base material, which is a nickel-cadmium secondary battery. Similar effects can be obtained by applying the present invention to other secondary batteries such as lithium ion secondary batteries.

In the above-described embodiments and examples, the electrode on the side connected to the battery can is the negative electrode, and the electrode on the side connected to the sealing body is the positive electrode, but the present invention is limited to this aspect. Alternatively, the electrode connected to the battery can may be the positive electrode, and the electrode connected to the sealing body may be the negative electrode.

In addition, in the above-described embodiments and examples, the outermost peripheral portion of the negative electrode is made thinner than the other portions, but the present invention is not limited to this aspect, and the thickness of the outermost peripheral portion of the negative electrode may have the same thickness as the other portions.

<Aspect of the present invention>
A first aspect of the present invention is a bottomed cylindrical battery can which is formed of a plate material having an iron substrate and a coating layer covering the surface of the substrate, and which also serves as a terminal for one electrode, and the other electrode. A sealing body to which the terminals of the electrodes are electrically connected and which seals the upper end opening of the battery can; a columnar electrode group, the electrode group being housed together with an electrolytic solution in the battery can, wherein the electrode group has a fluororesin layer on the outermost periphery thereof; The secondary battery, wherein the amount of resin is 0.3 g/cm ² or more.

Thus, according to the first aspect of the present invention, even if the outermost peripheral portion of the electrode group rubs against the inner peripheral surface of the battery can, it is possible to sufficiently suppress damage to the coating layer of the battery can, It is possible to prevent the substrate of the battery can from being exposed. Therefore, it is possible to suppress the elution of iron from the substrate of the battery can, and it is possible to obtain the effect of suppressing the decrease in the capacity recovery rate due to the elution of iron.

A second aspect of the present invention is the secondary battery according to the first aspect of the present invention, wherein the fluororesin layer is formed at least on a portion of the electrode group having the maximum diameter.

Thus, according to the second aspect of the present invention, since the fluororesin layer is present in the portion of the electrode group that is particularly likely to come into contact with the inner peripheral surface of the battery can, the covering layer of the battery can is not damaged. It is possible to obtain the effect of being able to more reliably suppress wearing.

2 Nickel metal hydride secondary battery (battery)
22 Electrode Group 24 Positive Electrode 26 Negative Electrode 28 Separator 62 Negative Core 68 Negative Mixture Layer 70 First Negative Mixture Layer 72 Second Negative Mixture Layer 74 Outermost First Region 76 Inner First Region 78 Outermost Second Region 80 inner peripheral second region 85 fluororesin 90 fluororesin layer

Claims (2)

a bottomed cylindrical battery can that is formed of a plate material having an iron substrate and a coating layer that covers the surface of the substrate, and that also serves as a terminal for one electrode;
a sealing body to which the terminal of the other electrode is electrically connected and which seals the upper end opening of the battery can;
a columnar electrode group in which the one electrode and the other electrode are laminated with a separator interposed therebetween and wound in a spiral shape, the electrode group being accommodated in the battery can together with an electrolytic solution;
with
The outermost peripheral portion of the one electrode is positioned on the outermost periphery of the electrode group, and includes an outermost peripheral first region located radially outside the electrode group and an outermost peripheral portion located radially inside the electrode group. and a second region,
The outermost peripheral first region of the one electrode has a fluororesin layer,
The secondary battery, wherein the amount of the fluororesin is 0.3 g/cm ² or more. 2. The secondary battery according to claim 1, wherein said fluororesin layer is formed at least on a portion of said electrode group having a maximum diameter.

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