WO2017168963A1 - Nickel-hydrogen battery - Google Patents

Abstract

This nickel-hydrogen battery is provided with: an electrode group obtained by winding a girdle-like positive electrode, a girdle-like negative electrode, and a girdle-like separator interposed between the positive electrode and the negative electrode; and an electrolyte that is included in the electrode group. The positive electrode contains a nickel compound as a positive electrode active material, and the negative electrode contains a hydrogen storing alloy as a negative electrode active material. The negative electrode has a fluorine resin attached to the surface thereof, and the negative electrode has a first portion which is disposed at the outermost periphery of the electrode group, and a second portion which represents the portion other than the first portion. The mass M₁ of the fluorine resin attached to a unit mass of the first portion is greater than the mass M₂ of the fluorine resin attached to a unit mass of the second portion.

Description

Nickel metal hydride storage battery

The present invention relates to a nickel-metal hydride storage battery provided with a wound electrode group.

The nickel metal hydride storage battery includes a strip-shaped positive electrode, a strip-shaped negative electrode, an electrode group around which a strip-shaped separator interposed therebetween is wound, and an electrolyte included in the electrode group. The positive electrode includes a nickel compound as a positive electrode active material, and the negative electrode includes a hydrogen storage alloy as a negative electrode active material.

In nickel-metal hydride storage batteries, the capacity of the negative electrode is usually larger than the capacity of the positive electrode in order to suppress the generation of hydrogen gas at the negative electrode during overcharge.

During overcharge, oxygen gas is generated in the positive electrode due to oxidation of hydroxide ions. Oxygen gas generated at the positive electrode is absorbed by the negative electrode. Specifically, in the negative electrode, oxygen gas reacts with hydrogen in the hydrogen storage alloy and is reduced to water. Thus, in a nickel metal hydride storage battery, the capacity of the negative electrode is made larger than the capacity of the positive electrode, and oxygen gas generated at the positive electrode is reduced and consumed at the negative electrode while suppressing the generation of hydrogen gas at the negative electrode during overcharge. This suppresses an increase in battery internal pressure during overcharge.

On the other hand, during overdischarge, hydrogen gas is generated at the positive electrode due to the reduction of water. Hydrogen gas generated at the positive electrode is absorbed by the negative electrode. Specifically, in the negative electrode, hydrogen gas reacts with the hydrogen storage alloy, and the alloy is hydrogenated. Thus, in a nickel metal hydride storage battery, the hydrogen gas generated at the positive electrode during overdischarge is absorbed by the negative electrode, thereby suppressing an increase in battery internal pressure during overdischarge.

In Patent Document 1, in order to enhance the oxygen gas consumption reaction of the negative electrode during overcharge, a monoparticulate fluororesin having a particle size of 0.05 to 1.0 μm is applied to the surface of the negative electrode containing a hydrogen storage alloy. It has been proposed that 0.0005 to 0.005 g be present per ^two . Patent Document 2 proposes that 0.02 to 0.11 mg / cm ^{2 of} polytetrafluoroethylene (PTFE) is adhered to the surface of a negative electrode containing a hydrogen storage alloy. This PTFE is used to prevent the active material from peeling off when a conductive core material having a low porosity is used, but it adheres to the surface of the negative electrode, so that the gas absorbability of the negative electrode is improved.

Gas absorption of the negative electrode (hydrogenation of the alloy or reduction reaction of oxygen gas) is the interface between the location where the electrolyte layer is formed on the surface of the hydrogen storage alloy and the location where the electrolyte layer is not formed, that is, the gas phase (Gas), a liquid phase (electrolyte), and a solid phase (hydrogen storage alloy). Therefore, the degree of formation of the three-phase interface in the negative electrode affects the gas absorbability of the negative electrode. As described in Patent Documents 1 and 2, it is considered that by providing a fluororesin having water repellency on the surface of the negative electrode, a three-phase interface is easily formed in the negative electrode, so that the gas absorbency of the negative electrode is improved.

JP 2004-327387 A JP 2010-161014 A

Incidentally, in order to further increase the capacity of the nickel-metal hydride storage battery, it is necessary to fill the space in the battery with the positive electrode active material and the negative electrode active material as much as possible to reduce the volume of the remaining space. When the volume of the remaining space in the battery (in the electrode group) becomes small, the amount of gas that can stay in the electrode group decreases, so the internal pressure of the battery tends to increase rapidly with gas generation during overcharge and overdischarge. .

In the methods described in Patent Documents 1 and 2, the gas absorbability of the negative electrode can be improved to some extent, but it is difficult to sufficiently suppress the increase in battery internal pressure when the battery is further increased in capacity. If the battery internal pressure rises excessively, the electrolyte may leak out of the battery.

An object of the present disclosure is to provide a nickel-metal hydride storage battery that can achieve both high capacity and suppression of increase in battery internal pressure during overcharge and overdischarge.

A nickel metal hydride storage battery according to one aspect of the present disclosure includes a strip-shaped positive electrode, a strip-shaped negative electrode, an electrode group in which a strip-shaped separator interposed between the positive electrode and the negative electrode is wound, and an electrolyte included in the electrode group. Prepare. And
The positive electrode includes a nickel compound as a positive electrode active material,
The negative electrode includes a hydrogen storage alloy as a negative electrode active material,
Fluorine resin is attached to the surface of the negative electrode,
The negative electrode has a first portion disposed on the outermost periphery of the electrode group and a second portion other than the first portion.

The mass M ₁ of the fluororesin adhering per unit mass of the first part is larger than the mass M _{2 of the} fluororesin adhering per unit mass of the second part.

According to the present disclosure, it is possible to provide a nickel-metal hydride storage battery that can achieve both high capacity and suppression of increase in battery internal pressure during overcharge and overdischarge.

FIG. 1 is a cross-sectional view schematically showing a nickel metal hydride storage battery according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing the cylindrical battery of FIG. FIG. 3 is an enlarged view of a portion surrounded by a circle indicated by III in FIG. FIG. 4 is a schematic perspective view schematically showing an example of a negative electrode used in the electrode group of FIG. FIG. 5 is a schematic side view of the negative electrode of FIG. FIG. 6 is a schematic perspective view schematically showing another example of the negative electrode used in the electrode group in FIG. 2. FIG. 7 is a schematic side view of the negative electrode of FIG. FIG. 8 is a schematic perspective view schematically showing still another example of the negative electrode used in the electrode group in FIG. 2. FIG. 9 is a schematic side view of the negative electrode of FIG.

The present invention includes a strip-like positive electrode containing a nickel compound as a positive electrode active material, a strip-like negative electrode containing a hydrogen storage alloy as a negative electrode active material, and an electrode group in which a strip-like separator interposed between the positive electrode and the negative electrode is wound. And an electrolyte contained in an electrode group, and a nickel-metal hydride storage battery in which a fluororesin is attached to the surface of a negative electrode.

In order to further increase the capacity of the nickel-metal hydride storage battery, it is necessary to fill the space in the battery with the positive electrode active material and the negative electrode active material as much as possible to reduce the volume of the remaining space. If the volume of the remaining space in the battery (in the electrode group) decreases, the amount of gas that can stay in the battery (in the electrode group) decreases, so the internal pressure of the battery suddenly increases due to gas generation during overcharge and overdischarge. It becomes easy to rise. For this, it is conceivable that the amount of fluororesin adhering to the surface of the negative electrode is further increased to further increase the gas absorbability of the negative electrode. However, simply increasing the amount of the fluororesin adhering to the negative electrode surface increases the volume occupied by the fluororesin in the entire negative electrode, reducing the area where the negative electrode active material is in contact with the electrolyte, resulting in a decrease in battery capacity. Will be invited.

Therefore, the present invention increases the amount of the fluororesin attached to a specific part of the negative electrode. That is, a negative electrode having a first portion (hereinafter simply referred to as a first portion) disposed on the outermost periphery of the electrode group and a second portion other than the first portion (hereinafter simply referred to as a second portion). , The mass M ₁ of the fluororesin adhering per unit mass of the first part is made larger than the mass M _{2 of the} fluororesin adhering per unit mass of the second part. In this case, the mass of the fluororesin adhering per unit capacity of the first part is larger than the mass of the fluororesin adhering per unit capacity of the second part. That is, the mass M _1n of the fluororesin adhering per unit mass of the negative electrode active material of the first part is larger than the mass M _{2n of the} fluororesin adhering per unit mass of the negative electrode active material of the second part. . The first portion may be disposed on the entire outermost periphery of the electrode group, or may be disposed on a portion of the outermost periphery of the electrode group.

By setting M ₂ <M ₁ , the gas absorbency of the first portion can be further increased, the gas absorption of the negative electrode can be efficiently performed in the battery, and the effect of suppressing the increase in the battery internal pressure is more remarkable. Is obtained. Therefore, even when the amount of positive and negative electrode active materials filled in the battery is increased and the volume of the remaining space in the battery is reduced, the internal pressure of the battery is sufficiently increased due to gas generation from the positive electrode during overcharge and overdischarge. Can be suppressed. As a result, it is possible to prevent the electrolyte from leaking out of the battery due to excessive increase in the battery internal pressure.

Since the outer peripheral side of the first portion faces the battery case that also serves as the negative electrode terminal portion and does not face the positive electrode, the amount of the negative electrode active material used for the reaction with the positive electrode in the first portion compared to the second portion There are few. For this reason, in the 1st part, in order to raise gas absorptivity compared with the 2nd part, you may increase the amount of fluororesins with respect to the amount of negative electrode active materials. This is because, even if the area where the negative electrode active material is in contact with the electrolyte in the first portion is reduced and the utilization factor of the negative electrode active material in the first portion is reduced to some extent, a reduction in battery capacity can be avoided. That is, the amount of the fluororesin can be increased with respect to the amount of the negative electrode active material in the first portion, without reducing the battery capacity, as compared with the second portion. Further, in order to satisfy M ₂ <M ₁ without reducing the battery capacity, the amount of the negative electrode active material per unit area in the first portion is reduced compared to the amount of the negative electrode active material per unit area in the second portion. Can do.

Examples of the fluororesin include polytetrafluoroethylene (PTFE), polychlorofluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), a copolymer of tetrafluoroethylene-hexafluoropropylene (FEP), and ethylene-tetrafluoroethylene. Copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).

As a method of attaching the fluororesin to the surface of the negative electrode, for example, a method of drying after applying a fluororesin dispersion on the surface of the negative electrode (negative electrode active material layer) is used. As the dispersion medium, for example, an organic medium such as ethanol, toluene, methanol, or isopropanol is used.

The mass of the fluororesin attached to the surface of the negative electrode can be adjusted by appropriately changing the amount of the fluororesin dispersion applied to the surface of the negative electrode. When a fluororesin dispersion obtained by mixing fluororesin particles and a dispersion medium in a mass ratio of 1: 5 to 1:20 is applied to the negative electrode surface, the fluororesin per unit area of the negative electrode The coating amount of the dispersion is, for example, 0.3 to 0.6 mg / cm ² .

The mass M ₁ of the fluororesin adhering per unit mass of the first part is preferably 5.3 to 12.5 mg / g. When the mass M _{1 of the} fluororesin adhering per unit mass of the first part is 12.5 mg / g or less, it is easy to increase the capacity. When the mass M _{1 of the} fluororesin adhering per unit mass of the first portion is 5.3 mg / g or more, it is possible to more reliably suppress an increase in the internal pressure of the battery during overcharge and overdischarge.

The mass M _{1 of the} fluororesin adhering per unit mass of the first part and the mass M _{2 of the} fluororesin adhering per unit mass of the second part are expressed by the relational expression:
1.05 ≦ M ₁ / M ₂ ≦ 2.5
It is preferable to satisfy.

When M ₁ / M ₂ is 1.05 or more, an increase in battery internal pressure during overcharge and overdischarge can be more reliably suppressed. When M ₁ / M ₂ is 2.5 or less, it is easy to increase the capacity.

M ₁ / M ₂ is more preferably 1.1 to 2.2, and even more preferably 1.3 to 2.0, since the effect of improving the discharge characteristics of the battery and the effect of suppressing the increase in the internal pressure of the battery can be obtained in a balanced manner. Particularly preferred is 1.5 to 1.9.

From the viewpoint of increasing the capacity, the negative electrode preferably has a negative electrode current collector and a negative electrode active material layer formed on both surfaces of the negative electrode current collector. The fluororesin is formed on the outer peripheral surface of the negative electrode (surface of the negative electrode active material layer located on the outer peripheral side of the negative electrode) and on the inner peripheral surface of the negative electrode (surface of the negative electrode active material layer located on the inner peripheral side of the negative electrode). Adhering to both. For the negative electrode current collector, a porous or non-porous substrate may be used.

As the non-porous substrate used for the negative electrode current collector, for example, a metal foil is used. As the porous substrate used for the negative electrode current collector, for example, an expanded metal, a punching metal, or a metal net is used. Examples of the material of the negative electrode current collector include nickel, nickel-plated iron, and the like.

When the negative electrode current collector is made of a porous substrate, the negative electrode is coated with a negative electrode active material covering the outer surface of the porous substrate, and the negative electrode active material is filled in the pores of the porous substrate. Including layers. The coating layer corresponds to the negative electrode active material layer. The thickness of the negative electrode active material layer formed on the surface of the negative electrode current collector refers to the thickness of the coating layer.

The porosity of the porous substrate is, for example, 30 to 45%.

As the negative electrode active material, a known hydrogen storage alloy may be used. For example, A ₂ B ₇ type (or Ce ₂ Ni ₇ type), AB ₅ type (CaCu ₅ type or MmNi ₅ type (Mm represents Misch metal). )), AB ₃ type (or CeNi ₃ type), and / or AB ₂ type (MgCu ₂ type or the like).

The negative electrode active material layer and the negative electrode active material filling layer may be a negative electrode mixture layer containing a binder, a conductive agent, and / or a thickener in addition to the negative electrode active material. Examples of the binder include a resin material, for example, a rubber-like material such as styrene-butadiene copolymer rubber (SBR), a polyolefin resin, and / or an acrylic resin (including its Na ion crosslinked product). Examples of the thickener include carboxymethyl cellulose (CMC) and a salt thereof, polyvinyl alcohol, and / or polyethylene oxide. Examples of the conductive agent include carbon black, conductive fibers, and / or organic conductive materials.

The negative electrode may be produced using a known method.

As a method of setting M ₂ <M ₁ , for example, the thickness of the whole negative electrode (negative electrode active material layer) is made constant, and the mass M _1A of the fluororesin adhering per unit area of the first part is changed to that of the second part. than the mass M _2A of the fluororesin to adhere to the per unit area include the first method to increase.

Further, as a second method, the thickness of the negative electrode (negative electrode active material layer) of the first part is made smaller than the thickness of the negative electrode (negative electrode active material layer) of the second part, and further, per unit area of the negative electrode The mass of the fluororesin adhering to the surface is made constant (M _1A = M _2A ) or the mass M _1A of the fluororesin adhering per unit area of the first part per unit area of the second part And a method of increasing the mass of the fluororesin adhering to the mass M _2A .

As the negative electrode used in the second method, the difference (T _1n −T _1c ) between the negative electrode thickness T _1n and the negative electrode current collector thickness T _1c in the first part, and the negative electrode in the second part The difference between the thickness T _2n of the negative electrode current collector and the thickness T _2c of the negative electrode current collector (T _2n −T _2c ) is:
0.4 ≦ (T _1n −T _1c ) / (T _2n −T _2c ) ≦ 1.0
It is preferable to satisfy.

When (T _1n −T _1c ) / (T _2n −T _2c ) is 0.4 or more, the negative electrode capacity necessary for gas absorption in the first portion can be secured. The increase in battery internal pressure can be more reliably suppressed. When (T _1n −T _1c ) / (T _2n −T _2c ) is 1.0 or less, it is easy to increase the capacity, and by arranging a sufficient negative electrode in the second portion facing the positive electrode, good discharge Characteristics are easy to obtain.

Note that (T _1n −T _1c ) corresponds to the total thickness T _1na of the negative electrode active material layer formed on both surfaces of the negative electrode current collector in the first portion. (T _2n −T _2c ) corresponds to the total thickness T _2na of the negative electrode active material layer formed on both surfaces of the negative electrode current collector in the second portion.

When the negative electrode current collector is a porous substrate, the thickness of the negative electrode current collector refers to the thickness of the portion of the substrate that does not have holes.

(T _1n −T _1c ) / (T _2n −T _2c ) is more preferably 0.4 to 0.95. When it is within the above range, the amount of the fluororesin adhering per unit area of the negative electrode is made constant, that is, M ₁ / M ₂ is within the range of 1.05 to 2.5, with M _1A = M _2A. It can be adjusted easily.

The negative electrode used in the second method has a main body portion positioned on the inner peripheral side of the electrode group, a thin portion positioned on the outermost periphery of the electrode group, and a tapered portion positioned therebetween. Is preferred. When configuring the electrode group, the tapered portion is disposed so that the outer end of the positive electrode overlaps. The length of the thin portion in the longitudinal direction is, for example, 50 to 115%, preferably 70 to 110%, or 80 to 105% of the length in the longitudinal direction of the outermost periphery of the electrode group.

In this case, the thin part located in the outermost periphery of the electrode group in a negative electrode corresponds to said 1st part. The part other than the first part in the negative electrode corresponds to the second part. However, the thickness of the second portion refers to the thickness of the main body. The region satisfying M ₂ <M ₁ is provided over, for example, 85% or more of the length of the first portion from the end portion on the winding end side of the negative electrode.

By using the negative electrode, the mass of the fluororesin adhering per unit area of the negative electrode (the mass of the dispersion of the fluororesin applied per unit area of the negative electrode) is made constant, and M ₂ <M ₁ is easily obtained. This makes it easier to attach the fluororesin to the negative electrode.

Further, by using the negative electrode, it is possible to suppress the diameter of the electrode group measured at the position of the outer end of the positive electrode from becoming excessively large, so that the electrode group can be easily inserted into the battery case. In addition, since the thickness of the negative electrode active material layer is larger in the tapered portion than in the thin portion, the quantitative balance (N / P ratio balance) between the negative electrode active material and the positive electrode active material in the vicinity of the outer end of the positive electrode may be lost. It is suppressed. Therefore, it is possible to suppress a decrease in capacity and output.

Since the outer peripheral side of the first part does not face the positive electrode, the negative electrode active material used for the reaction with the positive electrode in the first part (particularly, the negative electrode active material layer on the outer peripheral side of the first part) compared to the second part. The amount of is small. Therefore, the amount of the negative electrode active material per unit area in the first portion is reduced compared with the amount of the negative electrode active material per unit area in the second portion without reducing the battery capacity, that is, the thin portion is reduced in the first portion. Can be provided.

In the thin part, it is sufficient that at least the thickness of the negative electrode active material layer on the outer peripheral side is smaller than the thickness of the negative electrode active material layer on the outer peripheral side of the main body part. The thickness of the layer may be smaller than the thickness on the inner peripheral side of the main body. In addition, the taper portion may be such that at least the thickness of the negative electrode active material layer on the outer peripheral side is gradually reduced from the main body portion side toward the thin wall portion side. In addition to the outer peripheral side, on the inner peripheral side, the thickness of the negative electrode active material layer of the taper portion may be gradually decreased from the main body portion side toward the thin wall portion side.

At least the mass M _{1O of the} fluororesin adhering per unit mass of the negative electrode active material on the outer peripheral side of the first portion is equal to the mass M _{2O of the} fluororesin adhering per unit mass of the negative electrode active material on the outer peripheral side of the second portion It only has to be more. The mass M _1i of the fluororesin adhering per unit mass of the negative electrode active material on the inner peripheral side of the first portion is larger than the mass M _{2i of the} fluororesin adhering per unit mass of the negative electrode active material in the second part. It may be the same as the mass M _2i .

The positive electrode only needs to contain at least a positive electrode active material, and a positive electrode mixture described later may be formed on a sintered positive electrode current collector. Further, the positive electrode may include a porous or non-porous positive electrode current collector and a positive electrode active material attached to the positive electrode current collector. More specifically, the positive electrode is formed on at least one of the positive electrode current collector made of a porous or non-porous substrate and the surface of the positive electrode current collector, or the positive electrode filled in the gap of the positive electrode current collector You may have a mixture.

As the non-porous substrate used for the positive electrode current collector, for example, a metal foil is used. As the porous substrate used for the positive electrode current collector, for example, a sheet-like foam or sintered body is used. Examples of the material of the positive electrode current collector include nickel or a nickel alloy.

As the positive electrode active material, a nickel compound such as nickel hydroxide or nickel oxyhydroxide is used.

The positive electrode active material layer and the positive electrode active material filling layer may be a positive electrode mixture layer containing a binder, a conductive agent, and / or a thickener in addition to the positive electrode active material. As the conductive agent, the binder, and the thickener, known materials may be used, and may be appropriately selected from those exemplified for the negative electrode. Further, as the conductive agent, conductive cobalt oxide such as cobalt hydroxide and / or γ-type cobalt oxyhydroxide may be used.

The positive electrode may be produced using a known method.

As the separator, a known separator may be used, for example, a resin microporous film or a non-woven fabric is used. Examples of the resin include polyolefin resins such as polyethylene and polypropylene, vinyl resins such as polyvinyl oxide, polyamide resins, and acrylic resins, and these may be used alone or in combination of two or more. Good. The thickness of each separator can be appropriately selected from the range of 10 to 300 μm, for example, and may be 15 to 200 μm, for example.

As the electrolyte, an aqueous solution containing an alkali (alkaline electrolyte) is used. Examples of the alkali include alkali metal hydroxides such as lithium hydroxide, potassium hydroxide, and / or sodium hydroxide. The specific gravity of the alkaline electrolyte is, for example, 1.03 to 1.55.

Examples of batteries include cylindrical batteries and square batteries. In the case of a cylindrical battery, an electrode group having a substantially circular cross section is accommodated in a bottomed cylindrical battery case. In the case of a prismatic battery, a substantially flat electrode group is accommodated in a bottomed rectangular cylindrical battery case.

(Embodiment 1)
Hereinafter, a nickel metal hydride storage battery according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view schematically showing the structure of a nickel metal hydride storage battery according to an embodiment of the present invention.

A cylindrical nickel-metal hydride storage battery includes an electrode group in which a strip-shaped positive electrode 2, a strip-shaped negative electrode 1, and a strip-shaped separator 3 (first separator) interposed therebetween are spirally wound, and the electrode group. An electrolyte. The electrode group including the electrolyte is accommodated in a bottomed cylindrical battery case 4. The negative electrode 1 of the electrode group is in contact with the battery case 4 at the outermost periphery. Thereby, since the battery case 4 is electrically connected with the negative electrode 1, it can serve also as a negative electrode terminal. A sealing plate 7 including a safety valve 6 is disposed in the opening of the battery case 4 via an insulating gasket 8, and the cylindrical battery is sealed by caulking the opening end of the battery case 4 inward. . The sealing plate 7 also serves as a positive electrode terminal, and is electrically connected to the positive electrode 2 via the positive electrode current collector plate 9.

FIG. 2 is a cross-sectional view schematically showing the nickel-metal hydride storage battery of FIG. FIG. 3 shows an enlarged view of the vicinity of the outer end of the positive electrode (that is, a portion surrounded by a circle indicated by III in FIG. 2). FIG. 4 is a schematic perspective view schematically showing an example of a negative electrode used in the electrode group of FIG. FIG. 5 is a schematic side view of the negative electrode of FIG.

In the electrode group shown in FIG. 2, the positive electrode 2 and the negative electrode 1 are wound via a separator (first separator) 3. The negative electrode 1 includes a main body portion 1a located on the inner peripheral side of the electrode group, a thin portion 1c located on the outermost periphery of the electrode group, and a tapered portion 1b located therebetween. Thin portion 1c corresponds to a first portion _{P 1.} Portions were combined and the main body 1a, and a tapered portion 1b corresponds to a second portion P _2. Here, the second portion P ₂ of the thickness refers to the thickness of the main body portion 1a.

Thin portion 1c is an area of a length L ₃ from the outer end of the negative electrode 1, the taper portion 1b is a region of length L ₂ adjacent to the thin portion 1c. Body portion 1a, of the negative electrode 1, a region other than the thin portion 1c and the tapered portion 1b, has a length L _1. The outermost periphery of the positive electrode 2 is covered with a thin portion 1 c of the negative electrode 1 through the first separator 3, and the thin portion 1 c is in contact with the inner wall of the battery case 4.

The negative electrode 1 includes a negative electrode current collector 11 made of a porous or non-porous substrate, and a negative electrode active material layer 12 formed on the surface of the negative electrode current collector 11. When the negative electrode current collector 11 is made of a porous substrate, the negative electrode current collector 11 has a large number of holes (not shown). The negative electrode active material layer 12 includes a negative electrode active material layer 12 a formed on the outer peripheral surface of the negative electrode current collector 11 and a negative electrode active material layer 12 b formed on the inner peripheral surface of the negative electrode current collector 11. Including. The thickness t _3o of the negative electrode active material layer 12a on the outer peripheral side in the thin-walled portion 1c of the negative electrode 1 is smaller than the thickness t _1o of the negative electrode active material layer 12a on the outer peripheral side in the main body 1a (t _1o > t _3o ). . The thickness t _2o of the negative electrode active material layer 12a on the outer peripheral side of the taper portion 1b is _{gradually reduced} from the main body portion 1a toward the thin portion 1c. That is, the thickness t _2o varies in an inclined manner within a range of t _3o ≦ t _2o ≦ t _1o .

A fluororesin (not shown) is attached to the surface of the negative electrode 1 (negative electrode active material layers 12a and 12b). At this time, the mass M ₁ of the fluororesin adhering per unit mass of the first portion P ₁ (thin portion 1c) adheres per unit mass of the second portion P ₂ (main body portion 1a and taper portion 1b). More than the mass M _{2 of the} fluororesin.

By setting M ₂ <M ₁ , the gas absorbability of the first portion P ₁ can be further increased, the gas absorption of the negative electrode can be efficiently performed in the battery, and the effect of suppressing an increase in the battery internal pressure is obtained. More noticeable. Therefore, even when the amount of positive and negative electrode active materials filled in the battery is increased and the volume of the remaining space in the battery is reduced, the internal pressure of the battery is sufficiently increased due to gas generation from the positive electrode during overcharge and overdischarge. Can be suppressed.

Negative electrode active material layer 12a of the first portion P ₁ of the outer peripheral side, the positive electrode and not opposed, in the negative electrode active material layer 12a of the first outer peripheral side of the portion P _1, the negative electrode active material of the second portion P ₂ of the outer peripheral side Compared to the layer 12a, the amount of the negative electrode active material used for the reaction with the positive electrode is small. Therefore, without lowering the battery capacity, it is possible to reduce the thickness _{t 3o} of the first partial negative electrode active material layer 12a of the _{P 1} than the thickness _{t 1o} of the second negative electrode active material layer 12a of portion _{P 2.} Therefore, it is possible to further increase the capacity of the battery while further improving the gas absorbability of the negative electrode.

The thickness of the main body 1a of the negative electrode 1 is, for example, 0.1 to 0.6 mm, and preferably 0.2 to 0.4 mm.

The thickness t _1o of the negative electrode active material layer 12a on the outer peripheral side and the thickness t _i of the negative electrode active material layer 12b on the inner peripheral side are, for example, 0.03 to 0.3 mm, preferably 0.08. ~ 0.2 mm. The thicknesses t _1o and t _i may be appropriately determined in consideration of the balance with the positive electrode active material amount.

The negative electrode active formed on both surfaces of the negative electrode current collector 11 in the second portion P ₂ of the total thickness T _1na of the negative electrode active material layer 12 formed on both surfaces of the negative electrode current collector 11 in the first portion P ₁ . The ratio of the total thickness T _2na of the material layer 12: T _1na / T _2na is preferably 0.4 to 0.95. When T _1na / T _2na is within the above range, the amount of fluororesin adhering per unit area of the negative electrode is made constant, and M ₁ / M ₂ is easily within the range of 1.05 to 2.5. Can be adjusted. The total thickness T _1na is a _{value obtained by adding} the thickness t _3o of the negative electrode active material layer 12a on the outer peripheral side of the thin portion 1c and the thickness t _i of the negative electrode active material layer 12b on the inner peripheral side. The total thickness T _2na is a _{value obtained by adding} the thickness t _1o of the negative electrode active material layer 12a on the outer peripheral side of the main body 1a and the thickness t _i of the negative electrode active material layer 12b on the inner peripheral side.

For the negative electrode current collector 11, for example, a porous substrate (for example, a thickness of 20.0 to 50.0 μm and an aperture ratio of 30 to 45%) such as punching metal or expanded metal is used.

Using the negative electrode 1 in which the negative electrode active material layer 12 is formed on the surface of the porous substrate having the thickness and the porosity in the above range, the mass M of the fluororesin adhering per unit mass of the first portion P _{1 When 1} is 5.3 to 12.5 mg / g, the mass M _1n of the fluororesin adhering per unit mass of the negative electrode active material of the first portion P ₁ is, for example, in the range of 6 to 17 mg / g. .

When the negative electrode 1 is used and M ₁ / M ₂ is in the range of 1.05 to 2.5, the mass of the fluororesin adhering per unit mass of the negative electrode active material of the first portion P ₁ of M _1n, the ratio by weight _{M 2n} of the fluororesin to adhere to the per unit mass of the negative electrode active material of the second part _{P 2: M} 1n _/ M _2n, for example, in the range of 1.05 to 2.94.

In the case of the negative electrode 1, as a method of satisfying M ₂ <M ₁ , for example, the mass of the fluororesin adhering per unit area of the negative electrode 1 is made constant, that is, fluorine adhering per unit area of the first portion P _1. A method in which the mass M _1A of the resin is the same as the mass M _{2A of the} fluororesin attached per unit area of the second portion P ₂ can be mentioned. As another method, for example, the mass M _1A of the fluororesin adhering per unit area of the first portion P ₁ is more than the mass M _{2A of the} fluororesin adhering per unit area of the second portion P _2. There are many ways to do this.

From the viewpoint of work efficiency for attaching the fluororesin to the negative electrode, it is preferable to make the mass of the fluororesin per unit area of the negative electrode 1 constant (M _1A = M _2A ). In this case, the mass M _1O fluororesin to adhere to the per unit mass of the first portion P ₁ of the outer peripheral side of the negative electrode active material layer 12a is, per unit mass of the negative electrode active material layer 12a of the second outer peripheral side of the portion P _{2 More} than the mass M _{2 O of the} fluororesin adhering to the substrate. The mass M _1i of the fluororesin to adhere to the per unit mass of the first portion P ₁ of the inner circumferential side of the negative electrode active material layer 12b, the unit weight of the negative electrode active material layer 12b of the inner periphery of the second part P ₂ It is the same as the mass M _{2i of the} fluororesin adhering to the _hit .

Mass M ₁ of the fluororesin to adhere to the per unit mass of the first part P ₁ is, for example, in the region of up to winding end length from the end portion of the side L _3/2 of the thin portion 1c having a length L ₃ It is obtained by punching into a circular shape of a predetermined size, and measuring the mass of the punched portion and the mass of the fluororesin adhering to the portion.

The mass M ₂ of the fluororesin adhering per unit mass of the second part P ₂ is, for example, punched into a circular shape of a predetermined size near the center in the longitudinal direction of the main body 1a, It is calculated | required by measuring the mass of the fluororesin adhering to the said part.

The thickness t _i of the negative electrode active material layer 12b on the inner peripheral side is the same in the main body portion 1a, the tapered portion 1b, and the thin portion 1c. The thickness t _i may be the same as or different from the thickness t _1o .

In the present embodiment, the thickness t _i was a constant, in consideration of the balance between the positive electrode active material of opposite positive electrode 2, it may be changed by site if necessary.

In the electrode group, the outer end of the positive electrode 2 is arranged so as to overlap the tapered portion 1 b of the negative electrode 1 with the first separator 3 interposed therebetween. When forming the wound electrode group, the negative electrode 1 including the tapered portion 1b and the thin portion 1c is used, thereby suppressing the diameter of the electrode group measured at the position of the outer end of the positive electrode 2 from becoming excessively large. Therefore, the ease of inserting the electrode group into the battery case 4 can be ensured. Further, since the thickness of the negative electrode active material layer 12a is larger in the taper portion 1b than in the thin portion 1c, the quantitative balance between the negative electrode active material and the positive electrode active material in the vicinity of the outer end of the positive electrode 2 (balance of N / P ratio). Is prevented from collapsing. Therefore, it is possible to suppress a decrease in capacity and output.

In the electrode group, the positive electrode 2 and the negative electrode 1 may be disposed so that the outer end of the positive electrode 2 overlaps at least the taper portion 1b. It is preferable to arrange the positive electrode 2 and the negative electrode 1 so as to be near the center. For example, the end surface of the outer end of the positive electrode 2 is located in a region of ± 0.2 × L ₂ (preferably a region of ± 0.1 × L ₂ ) with the center in the length direction of the taper portion 1b interposed therebetween. Moreover, it is preferable to overlap the outer end of the positive electrode 2 with the tapered portion 1b.

In the outer end of the positive electrode 2 and its periphery, the length of the region facing the taper portion 1b (the length from the end surface of the outer end of the positive electrode 2) is, for example, 1 to 15% of the length of the positive electrode 2 It is preferably 1 to 5%.

The length L ₂ of the tapered portion 1b is shorter becomes steep slope of the tapered portion, it becomes easy to stress is applied to the outer end and its vicinity of the positive electrode disposed in the tapered portion 1b, to some extent reduce the gradient of the taper portion 1b , that is, it is preferable that length L ₂ is to have a certain size. From this point of view, the length L ₂ of the tapered portion, the length of the outermost periphery of the negative electrode, longer is favored over 1/6, may be 1/5 or more or 1/4 or more. The length L ₂ of the tapered portion is preferably equal to or less than half of the length of the outermost periphery of the negative electrode.

The second separator 3 a is disposed between the tapered portion 1 b of the negative electrode 1 and the first separator 3 in contact with the outer end of the positive electrode 2. Thereby, it can suppress that an internal short circuit occurs in the outer end of the positive electrode 2 and its periphery, or that internal resistance increases and generates heat. The second separator 3a may be disposed so as to overlap at least the outer end of the positive electrode 2 and its periphery so as to support the outer end of the positive electrode 2.

In addition to the above, the second separator 3 a may be disposed between the outer end of the positive electrode 2 and the tapered portion 1 b of the negative electrode 1. At this time, it is preferable to arrange the second separator 3 a so as to overlap the outer end of the positive electrode 2 so as to protect the outer end of the positive electrode 2. In addition to the above, it may be disposed between the outer end of the positive electrode 2 and the first separator 3 in contact with the tapered portion 1 b of the negative electrode 1.

Since the stress applied to the outer end of the positive electrode 2 can be reduced by the tapered portion 1b and the second separator 3a, the outer end of the positive electrode 2 and its surroundings can be obtained even if the number of turns of the negative electrode 1 is increased or the thickness is increased. The occurrence of an internal short circuit can be suppressed. The number of turns of the negative electrode 1 can be selected according to the size of the cylindrical battery. For example, when the outer diameter of the cylindrical battery is 6 to 24 mm, it can be 2 to 10 mm, or 3 to 6 mm. .

The main body 1a is a region that is located on the center side (or inner peripheral side) of the electrode group, both surfaces are opposed to the positive electrode 2, and mainly performs the electrode reaction. In this specification, for the sake of convenience, the entire region of the negative electrode 1 on the center side excluding the thin-walled portion 1c and the tapered portion 1b on the outer peripheral side is referred to as a main body portion 1a. In the region not facing 2, the thickness of the negative electrode active material layer 12 may be partially reduced as necessary.

The length of the second separator. 3a, the _{L 2,} for example, 50 to 200% may be 80-100%. The second separator 3a only needs to protect the outer end of the positive electrode 2 and its periphery. Therefore, the length of the second separator 3a is sufficient effect can be obtained even shorter than the length L ₂ of the tapered portion 1b. In this case, the length of the second separator. 3a, the _{L 2,} for example, less than 50% to 100%, and preferably less than 80% or more 100%.

Since the first separator 3 has a function of electrically insulating the positive electrode 2 and the negative electrode 1, the width of the second separator 3 a may be smaller than the width of the positive electrode 2 and / or the negative electrode 1. However, from the viewpoint of more effectively suppressing the occurrence of an internal short circuit at the outer end and the periphery of the positive electrode 2, the width of the second separator 3 a is preferably larger than the width of the positive electrode 2, and the width of the negative electrode 1. May be larger. Further, the width of the second separator 3 a may be approximately the same as the width of the first separator 3.

The length of the second separator 3a is the length of the second separator 3a in a direction parallel to the length direction of the electrode, and the width of the second separator 3a is a direction perpendicular to the length direction of the electrode. Is the length of the second separator 3a.

(Embodiment 2)
The nickel metal hydride storage battery of the present embodiment will be described with reference to FIGS. FIG. 6 is a schematic perspective view schematically showing another example of the negative electrode used in the electrode group in FIG. 2. FIG. 7 is a schematic side view of the negative electrode of FIG. The configuration is the same as that of the first embodiment except that the negative electrode 21 is used instead of the negative electrode 1.

The negative electrode 21 has a main body portion 21a positioned on the inner peripheral side of the electrode group, a thin-walled portion 21c positioned on the outermost periphery, and a tapered portion 21b positioned therebetween. Thin portion 21c corresponds to the first part _{P 1.} Part of the combined main body portion 21a and the tapered portion 21b corresponds to a second portion _{P 2.} Here, the second portion _{P 2} of the thickness refers to the thickness of the body portion 21a. The negative electrode 21 includes a negative electrode current collector 31 made of a porous or non-porous substrate, and a negative electrode active material layer 32 formed on the surface of the negative electrode current collector 31. When the negative electrode current collector 31 is made of a porous substrate, the negative electrode current collector 31 has a large number of holes (not shown). The negative electrode active material layer 32 includes a negative electrode active material layer 32 a formed on the outer peripheral surface of the negative electrode current collector 31 and a negative electrode active material layer 32 b formed on the inner peripheral surface. The negative electrode active material layer 32a is the same as the negative electrode active material layer 12a shown in FIGS.

As in the case of the negative electrode active material layer 32a on the outer peripheral side, the thickness t _3i of the negative electrode active material layer 32b on the inner peripheral side in the thin portion 21c of the negative electrode 21 is the same as that of the negative electrode active material layer 32b on the inner peripheral side in the main body portion 21a. It is smaller than the thickness t _1i (t _1i > t _3i ). The thickness t _2i of the negative electrode active material layer 32b on the inner peripheral side in the taper portion 21b is gradually reduced from the main body portion 31a toward the thin portion 31c. That is, the thickness t _2i varies in an inclined manner within a range of t _3i ≦ t _2i ≦ t _1i .

Since the negative electrode 21 has the taper part 21b and the thin part 21c, the effect similar to the case where the negative electrode 1 is used in Embodiment 1 is acquired.

In the thin portion 21c, since both the outer peripheral negative electrode active material layer 32a and the inner peripheral negative electrode active material layer 32b are thin, only the thickness of the outer peripheral negative electrode active material layer 12a in the thin portion 1c. It is easier to provide a thickness change between the main body portion and the thin portion (between the first portion and the second portion) than in the first embodiment in which the thickness is reduced.

A fluororesin (not shown) is attached to the surface of the negative electrode 21 (negative electrode active material layers 32a and 32b). The mass M ₁ of the fluororesin adhering per unit mass of the first portion P ₁ (thin portion 21c) adheres per unit mass of the second portion P ₂ (portion combining the main body portion 21a and the tapered portion 21b). More than the mass M _{2 of the} fluororesin. The masses M ₁ and M ₂ may be obtained by the same method as in the first embodiment.

By setting M ₂ <M ₁ , the gas absorbability of the first portion P ₁ can be further increased, the gas absorption of the negative electrode can be efficiently performed in the battery, and the effect of suppressing an increase in the battery internal pressure is obtained. More noticeable. Therefore, even when the amount of positive and negative electrode active materials filled in the battery is increased and the volume of the remaining space in the battery is reduced, the internal pressure of the battery is sufficiently increased due to gas generation from the positive electrode during overcharge and overdischarge. Can be suppressed.

The outer peripheral side of the first part P _1, since the positive electrode and not opposed, the first part P _1, as compared with the second part P _2, the amount of the negative electrode active material utilized in the cell reaction between the positive electrode is small. For this reason, the first part is more than the total thickness (t _1o + t _1i ) of the negative electrode active material layer 32 of the second part P ₂ with t _1o > t _3o and t _1i > t _3i without reducing the battery capacity. The total thickness (t _3o + t _3i ) of the P ₁ negative electrode active material layer 32 can be reduced. Therefore, it is possible to further increase the capacity of the battery while further improving the gas absorbability of the negative electrode.

The thickness of the main body 21a of the negative electrode 21 is, for example, 0.1 to 0.6 mm, and preferably 0.2 to 0.4 mm.

The thickness t _1o of the negative electrode active material layer 32a on the outer peripheral side and the thickness t _1i of the negative electrode active material layer 32b on the inner peripheral side are, for example, 0.01 to 0.3 mm, preferably 0.08. ~ 0.2 mm. The thicknesses t _1o and t _1i may be appropriately determined in consideration of the balance with the positive electrode active material amount.

The negative electrode active material formed on both surfaces of the negative electrode current collector 31 in the second portion P ₂ of the total thickness T _1na of the negative electrode active material layer 32 formed on both surfaces of the negative electrode current collector 31 in the first portion P ₁ . The ratio of the total thickness T _2na of the material layer 32: T _1na / T _2na is preferably 0.4 to 0.95. When T _1na / T _2na is within the above range, the amount of fluororesin adhering per unit area of the negative electrode is made constant, and M ₁ / M ₂ is easily within the range of 1.05 to 2.5. Can be adjusted. The total thickness T _1na is a _{value obtained by adding} the thickness t _3o of the negative electrode active material layer 32a on the outer peripheral side of the thin portion 21c and the thickness t _3i of the negative electrode active material layer 32b on the inner peripheral side. The total thickness T _2na is a _{value obtained by adding} the thickness t _1o of the negative electrode active material layer 32a on the outer peripheral side of the main body 21a and the thickness t _1i of the negative electrode active material layer 32b on the inner peripheral side.

For the negative electrode current collector 31, for example, a porous substrate (for example, a thickness of 20.0 to 50.0 μm, an opening ratio of 30 to 45%) such as punching metal or expanded metal is used.

Using the negative electrode 21 in which the negative electrode active material layer 32 is formed on the surface of the porous substrate having the thickness and the open area ratio in the above ranges, the mass M of the fluororesin adhering per unit mass of the first portion P _{1 When 1} is 5.3 to 12.5 mg / g, the mass M _1n of the fluororesin adhering per unit mass of the negative electrode active material of the first portion P ₁ is, for example, in the range of 6 to 17 mg / g. .

Further, when the negative electrode 21 is used and M ₁ / M ₂ is in the range of 1.05 to 2.5, the mass of the fluororesin adhering per unit mass of the negative electrode active material of the first portion P ₁ of M _1n, the ratio by weight _{M 2n} of the fluororesin to adhere to the per unit mass of the negative electrode active material of the second part _{P 2: M} 1n _/ M _2n, for example, in the range of 1.05 to 2.94.

In the case of the negative electrode 21, as a method of satisfying M ₂ <M ₁ , for example, the mass of the fluororesin adhering per unit area of the negative electrode 21 is made constant, that is, fluorine adhering per unit area of the first portion P _1. A method in which the mass M _1A of the resin is the same as the mass M _{2A of the} fluororesin attached per unit area of the second portion P ₂ can be mentioned. As another method, for example, the mass M _1A of the fluororesin adhering per unit area of the first portion P ₁ is more than the mass M _{2A of the} fluororesin adhering per unit area of the second portion P _2. There are many ways to do this.

From the viewpoint of work efficiency for attaching the fluororesin to the negative electrode 21, it is preferable to make the mass of the fluororesin per unit area of the negative electrode 21 constant (M _1A = M _2A ). In this case, the mass M _1o fluororesin to adhere to the per unit mass of the first portion P ₁ of the outer peripheral side of the negative electrode active material layer 32a is, per unit mass of the negative electrode active material layer 32a of the second outer peripheral side of the portion P _{2 More} than the mass M _{2o of the} fluororesin adhering to the substrate. Further, fluorine resin mass M _1i adhering per unit mass of the first portion P ₁ of the inner circumferential side of the negative electrode active material layer 32b is, unit mass of the negative electrode active material layer 32b of the second inner peripheral side of the portion P ₂ More than the mass M _{2i of the} fluororesin adhering to the _hit .

In the present embodiment, the thickness of the negative electrode active material layer 32b on the inner peripheral side is changed in the same manner as the thickness of the negative electrode active material layer 32a on the outer peripheral side. The outer peripheral side and the inner peripheral side are not necessarily the same, and may be different. The position where the thickness of the negative electrode active material layer on the inner peripheral side starts to decrease from the main body side toward the thin wall side is not necessarily between the main body portion and the tapered portion (that is, the thickness of the negative electrode active material layer on the outer peripheral side is the main body). It does not need to coincide with the position where the portion starts to decrease from the portion side toward the thin portion side, and may overlap with either the main body portion or the tapered portion. Similarly, the position at which the decrease in the thickness of the negative electrode active material layer on the inner peripheral side converges does not necessarily coincide with the end point of the tapered portion (between the tapered portion and the thin portion), and the tapered portion and the thin portion. It may overlap with any of the above.

(Embodiment 3)
Hereinafter, the nickel metal hydride storage battery of the present embodiment will be described with reference to FIGS. FIG. 8 is a schematic perspective view schematically showing still another example of the negative electrode used in the electrode group in FIG. 2. FIG. 9 is a schematic side view of the negative electrode of FIG. The configuration is the same as that of the first embodiment except that the negative electrode 41 is used instead of the negative electrode 1.

The negative electrode 41 includes a negative electrode current collector 51 made of a porous or non-porous substrate and a negative electrode active material layer 52 formed on the surface of the negative electrode current collector 51. When the negative electrode current collector 51 is made of a porous substrate, the negative electrode current collector 51 has a large number of holes (not shown). The negative electrode active material layer 52 includes a negative electrode active material layer 52 a formed on the outer peripheral surface of the negative electrode current collector 51 and a negative electrode active material layer 52 b formed on the inner peripheral surface.

In this case, the whole part located in the outermost periphery of the electrode group in the negative electrode corresponds to the first part. A portion other than the first portion (outermost circumference) in the negative electrode corresponds to the second portion. The region satisfying M ₂ <M ₁ is provided over, for example, 85% or more of the length of the first portion from the end portion on the winding end side of the negative electrode.

In any of the first part _{P 1} and second part _{P 2} of the negative electrode 41, negative electrode active material layer 52a has a constant thickness _{t o,} the anode active material layer 52b has a constant thickness _{t i.} The negative electrode active material layer 52b has a configuration similar to that of the negative electrode active material layer 12b.

A fluororesin (not shown) is attached to the surface of the negative electrode 41 (negative electrode active material layers 52a and 52b). The mass M ₁ of the fluororesin adhering per unit mass of the first part P ₁ is larger than the mass M _{2 of the} fluororesin adhering per unit mass of the second part P ₂ .

By setting M ₂ <M ₁ , the gas absorbability of the first portion P ₁ can be further increased, the gas absorption of the negative electrode can be efficiently performed in the battery, and the effect of suppressing an increase in the battery internal pressure is obtained. More noticeable. Therefore, even when the amount of positive and negative electrode active materials filled in the battery is increased and the volume of the remaining space in the battery is reduced, the internal pressure of the battery is sufficiently increased due to gas generation from the positive electrode during overcharge and overdischarge. Can be suppressed.

Since the outer peripheral side of the first part P ₁ does not face the positive electrode, the first part P ₁ (particularly the negative electrode active material layer 52 a) has a negative electrode active used for reaction with the positive electrode compared to the second part P _2. The amount of substance is small. Therefore, without lowering the battery capacity, it is possible to increase the fluorine resin amount be attached to the first portion P ₁ of the surface. Therefore, it is possible to further increase the capacity of the battery while further improving the gas absorbability of the negative electrode.

The thickness of the negative electrode 41 is, for example, 0.1 to 0.6 mm, and preferably 0.2 to 0.4 mm.

The thickness t _1o of the negative electrode active material layer 52a on the outer peripheral side of the negative electrode 41 and the thickness t _1i of the negative electrode active material layer 52b on the inner peripheral side are, for example, 0.01 to 0.3 mm, preferably 0.1 to 0.3 mm, respectively. 0.2 mm. The thicknesses t _1o and t _1i may be appropriately determined in consideration of the balance with the positive electrode active material amount.

For the negative electrode current collector 51, for example, a porous substrate (for example, a thickness of 2.0 to 5.0 μm and an aperture ratio of 30 to 45%) such as punching metal or expanded metal is used.

Using the negative electrode 41 in which the negative electrode active material layer 52 is formed on the surface of the porous substrate having the thickness and the open area ratio in the above ranges, the mass M of the fluororesin adhering per unit mass of the first portion P _{1 When 1} is 5.3 to 12.5 mg / g, the mass M _1n of the fluororesin adhering per unit mass of the negative electrode active material of the first portion P ₁ is, for example, in the range of 6 to 17 mg / g. .

Further, when the negative electrode 41 is used and M ₁ / M ₂ is in the range of 1.05 to 2.5, the mass of the fluororesin adhering per unit mass of the negative electrode active material of the first portion P ₁ of M _1n, the ratio by weight _{M 2n} of the fluororesin to adhere to the per unit mass of the negative electrode active material of the second part _{P 2: M} 1n _/ M _2n, for example, in the range of 1.05 to 2.94.

In the case of the negative electrode 41, as a method of setting M ₂ <M ₁ , for example, the fluororesin mass M _1A attached per unit area of the first part P ₁ is attached per unit area of the second part P _2. An example is a method in which the amount is larger than the mass M _{2A of the} fluorine resin.

More specifically, at least, the mass M _1o fluororesin to adhere to the per unit mass of the first portion P ₁ of the outer peripheral side of the negative electrode active material layer 52a, the negative electrode active material layer of the second portion P ₂ of the outer peripheral side What is necessary is _just to _increase more than mass _{M2o of the} fluororesin adhering per unit mass of 52a. Mass M _1i of the fluororesin to adhere to the per unit mass of the first portion P ₁ of the inner circumferential side of the negative electrode active material layer 52b is per unit mass of the second portion P ₂ of the inner circumferential side of the negative electrode active material layer 52b It may be the same as the mass M _2i of the adhering fluororesin or may be larger than the mass M _2i .

In the present embodiment, the mass M ₁ of the fluororesin adhering per unit mass of the first portion P ₁ is, for example, from the end portion on the winding end side of the first portion P ₁ to ½ of the length in the longitudinal direction. In this area, it is obtained by punching into a circular shape of a predetermined size, and measuring the mass of the punched portion and the mass of the fluororesin adhering to the portion.

The mass M ₂ of the fluororesin adhering per unit mass of the second portion P ₂ is, for example, punched into a circular shape of a predetermined size near the center in the longitudinal direction of the second portion P ₂ , and the mass of the punched portion And the mass of the fluororesin adhering to the part.

Hereinafter, the present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.

Example 1
An AA cylindrical nickel-metal hydride storage battery having a capacity of 2300 mAh was produced by the following procedure.

(1) Production of Negative Electrode The negative electrode shown in FIGS. 6 and 7 was produced by the following method.

100 parts by mass of hydrogen storage alloy powder (La _0.40 Ce _0.60 Ni _3.63 Co _0.76 Mn _0.42 Al _0.29 , average particle size = about 45 μm), 0.7 parts by mass of SBR as a binder, CMC 0. 15 parts by mass, 0.3 parts by mass of ketjen black as a conductive agent, 0.7 parts by mass of yttrium oxide as an oxidation inhibitor, and further adding and mixing an appropriate amount of water, the negative electrode mixture slurry Prepared. SBR was used in the form of an aqueous dispersion.

In addition, the thing which performed the alkali treatment by the well-known method was used for the hydrogen storage alloy powder. The alkali treatment can be performed, for example, by bringing the hydrogen storage alloy particles into contact with an alkaline aqueous solution (for example, by contact), and drying as necessary. As the alkaline aqueous solution, an aqueous solution of an alkali metal hydroxide such as NaOH or KOH is used.

The obtained negative electrode mixture slurry was applied to both surfaces (outer surface) and pores of a porous substrate as a negative electrode current collector so that the positive electrode capacity was 1.25 times. As the porous substrate, an iron punching metal (thickness 60 μm, hole diameter 1 mm, hole area ratio 42%) whose surface was plated with nickel was used. At this time, the coating amount of the negative electrode mixture slurry is set to the length of the negative electrode current collector so that the thickness of the negative electrode active material layer formed on both surfaces of the negative electrode current collector is different between the main body part, the taper part, and the thin part. Changed in direction. The coating film of the negative electrode mixture slurry was dried at 95 ° C. for 10 minutes, and then the negative electrode was formed by pressing the coating film together with the negative electrode current collector with a roller.

The main body 21 a of the obtained negative electrode 21 was formed in a region having a length L ₁ = 100 mm from one end in the length direction of the negative electrode current collector 31. The thickness t _1o of the negative electrode active material layer 32a of the main body 21a and the thickness t _1i of the negative electrode active material layer 32b were each 0.14 mm.

The taper portion 21b is formed in a region between the main body portion and the thin portion, and the length L ₂ of the taper portion is 10 mm.

The thin portion 21 c was formed in a region having a length L ₃ = 45 mm from the other end portion in the length direction of the negative electrode current collector 31.

(2) Adhesion of fluororesin to the negative electrode surface Using an ultrasonic homogenizer (amplitude 80 μm, frequency 20 kHz), PTFE particles as fluororesin and ethanol are mixed at a mass ratio of 1:15. A PTFE dispersion was prepared. The PTFE particles used had a BET specific surface area of 3 m ² / g as determined by a nitrogen gas adsorption method, a maximum particle size of 20 μm, and an average particle size of 12 μm.

The PTFE dispersion obtained above was applied to the surface of the negative electrode obtained above (surface of the negative electrode active material layer). At this time, the mass of the PTFE dispersion applied per unit area of the negative electrode was about 0.50 mg / cm ² . The obtained negative electrode having a coating film was dried at 120 ° C. for 1 minute to produce a negative electrode in which PTFE was adhered to the surface of the negative electrode active material layer. At this time, the thickness of the PTFE layer formed on the surface of the negative electrode active material layer was 9 to 20 μm.

(3) Production of positive electrode A non-sintered nickel positive electrode was produced by the following procedure.

First, nickel hydroxide powder containing 2.5% by mass of zinc and 1.0% by mass of cobalt as a coprecipitation component was added to an aqueous cobalt sulfate solution. While stirring the resulting mixture, an aqueous sodium hydroxide solution (sodium hydroxide concentration: 1 mol / L) was gradually added dropwise to adjust the pH to 11, followed by further stirring for a predetermined time. The precipitate was filtered off from the resulting mixture. The precipitate separated by filtration was washed with water and vacuum-dried to obtain a powder in which the surface of nickel hydroxide particles was coated with 5% by mass of cobalt hydroxide.

10 parts by mass of an aqueous sodium hydroxide solution (sodium hydroxide concentration: 48% by mass) was added to 1 part by mass of the powder obtained above. The resulting mixture was heat-treated at 85 ° C. for 8 hours with stirring, then washed with water and dried at 65 ° C. By this heat treatment, in the layer containing cobalt hydroxide on the surface of the nickel hydroxide particles, a part of cobalt hydroxide is made higher-order and converted into cobalt oxyhydroxide, and sodium is introduced. Composite particles in which a coating layer containing cobalt oxyhydroxide and 1% by mass of sodium was formed on the surface of the nickel hydroxide particles were obtained.

By adding and mixing 25 parts by mass of an aqueous solution (CMC concentration: 0.2% by mass) containing CMC as a binder to 100 parts by mass of the obtained composite particles and zinc oxide mixed powder, A positive electrode mixture slurry was prepared. The mass ratio of the composite particles and zinc oxide in the mixed powder was 100: 2.

The obtained positive electrode mixture slurry was applied to both surfaces (outer surface) and pores of a nickel foam (surface density (unit weight) of about 325 g / m ² , thickness of about 1.2 mm) as a positive electrode current collector, Dried. The dried product was rolled to a thickness of 0.66 mm to obtain a positive electrode (length 118 mm, width 44.7 mm, thickness 0.66 μm).

In addition, an exposed portion of a core material that does not hold an active material was provided at one end portion in the length direction of the positive electrode current collector, and a positive electrode lead was connected to the exposed portion.

(4) Production of nickel-metal hydride storage battery A first separator (length 330 mm, width 47 mm, thickness 0.090 mm) is arranged between the negative electrode obtained above and the positive electrode obtained above. The electrode group was produced by winding in a spiral. At this time, it wound so that the main-body part of a negative electrode might become an inner peripheral side, a thin part might become an outer peripheral side, and the outer end of a positive electrode might overlap with the taper part of a negative electrode. At this time, a second separator (length 10 mm, width 47 mm, thickness 0.090 mm) was disposed between the outer end of the positive electrode and the tapered portion, and between the tapered portion and the first separator. The second separator was arranged so that the end face on the outer peripheral side of the positive electrode came near the center in the length direction. As the first separator and the second separator, a sulfonated polypropylene nonwoven fabric (thickness 90 μm, basis weight 50 g / m ² , and sulfonation degree 1.90 × 10 ⁻³ ) was used. The number of turns of the negative electrode in the electrode group was 5.

The obtained electrode group was inserted into an AA bottomed cylindrical metal battery case (outer diameter 14.60 mm) having a ring-shaped groove on the opening side, and the outermost negative electrode (thin wall portion) was inserted. The battery case was brought into contact with the inner surface. Moreover, the positive electrode lead connected to the positive electrode was welded to the inner bottom surface of the cover plate of the sealing body. The sealing body is arranged so as to close the gas vent hole at the center of the top plate of the lid plate having a circular vent hole at the center, the insulating packing attached to the periphery of the lid plate, and the lid plate. And a cap-like positive electrode terminal having a protrusion that covers the valve body.

Next, an alkaline electrolyte was poured into the battery case, the opening of the battery case was covered with a sealing body, and sealed by insulating caulking. The diameter was reduced by pressing the peripheral surface of the battery case from the outside. And the groove part formed in the opening part side of the battery case was crimped | bonded so that a battery total height might be set to 50.25 mm by pressing a battery case in a height direction. As the alkaline electrolyte, an aqueous solution containing sodium hydroxide at a concentration of 7.5 mol / L was used.

The donut-shaped insulating member was arranged on the upper part of the sealing body with the protruding portion of the positive electrode terminal protruding from the central hole of the insulating member. Next, by attaching an exterior label so as to cover the peripheral part of the sealing body (peripheral part of the insulating member disposed on the sealing body), the peripheral surface of the battery case, and the peripheral part of the bottom surface of the battery case A battery was obtained.

In the production of the negative electrode, the thickness t _3o of the negative electrode active material layer 32a and the thickness t _3i of the negative electrode active material layer 32b of the thin-walled portion 21c were changed to the values shown in Table 1, and negative electrodes (a-1) to (a- 7) was produced. Batteries (A-1) to (A-7) were produced using the negative electrodes (a-1) to (a-7).

Table 1 shows values of M ₁ , M ₂ , M ₁ / M ₂ , M _1n / M _2n , and T _1na / T _{2na for} the negative electrodes (a-1) to (a-7).

T _1na / T _2na was formed on both sides of the negative electrode current collector in the second part of the total thickness T _1na of the negative electrode active material layer formed on both sides of the negative electrode current collector in the first part. It is a ratio to the total thickness T _2na of the negative electrode active material layer. T _2na was determined from the difference between the thickness of the main body 21a of the negative electrode 21 and the thickness of the negative electrode current collector 31 (portion having no holes). T _1na was determined from the difference between the thickness of the thin portion 21c of the negative electrode 21 and the thickness of the negative electrode current collector 31 (portion having no holes).

M ₁ represents the mass (mg / g) of PTFE deposited per unit mass of the first portion.

In Example 1, M _1, in the length region from the winding end side of the end portion of the thin portion 21c to a length L _3/2 with L _3, punched into a predetermined size circular, punched It calculated | required by measuring the mass of a part and the mass of PTFE adhering to the said part. The said measurement was performed about three places and calculated | required from the average value.

In Example 2 and Comparative Example 1 to be described later, M ₁ is a circular shape having a predetermined size in a region from the end of the first portion P _{1 on} the winding end side to ½ of the length in the longitudinal direction. This was determined by measuring the mass of the punched part and the mass of the fluororesin adhering to the part. The said measurement was performed about three places and calculated | required from the average value.

M ₁ / M ₂ represents the ratio of the mass M ₁ of PTFE deposited per unit mass of the first portion to the mass M ₂ of PTFE deposited per unit mass of the second portion.

In Example 1, M ₂ may be in the longitudinal direction near the center of the main body portion 21a, punched into a predetermined size circular, measuring the mass of stamped parts, and the mass of PTFE to adhere to the portion Determined by The said measurement was performed about three places and calculated | required from the average value.

In Example 2 and Comparative Example 1 described later, M ₂ is punched into a circular shape of a predetermined size in the vicinity of the center in the longitudinal direction of the second portion P ₂ , and the mass of the punched portion and adheres to the portion. It calculated | required by measuring the mass of a fluororesin. The said measurement was performed about three places and calculated | required from the average value.

M _1n / M _2n is the ratio of the mass M _1n of PTFE adhering per unit mass of the negative electrode active material of the first part to the mass M _2n of PTFE adhering per unit mass of the negative electrode active material of the second part. To express.

M _1n was determined by the following procedure. First, it determined by measurement of the M _1, based on the weight of the value of the PTFE to adhere to the portion punched in a predetermined size, to determine the mass of PTFE adhering per unit area of the punched part. Next, in Example 1, the mass of the negative electrode active material per unit area of the punched portion was determined based on the size of the thin portion 21c and the mass of the negative electrode active material filled in the thin portion 21c. In Example 2 and Comparative Example 1 described later, based on the weight of the negative electrode active material filled in size and the first portion P ₁ of the first part P _1, the negative electrode active material per unit area of the punched portion The mass was determined. And M1n was _{calculated |} required based on the mass of the PTFE adhering per unit area of the obtained said punched-out part, and the mass of the negative electrode active material filled per unit area of the said punched-out part.

M _2n was determined by the following procedure. First, it determined by measurement of the M _2, based on the weight of the value of the PTFE to adhere to the portion punched in a predetermined size, to determine the mass of PTFE adhering per unit area of the punched part. Next, in Example 1, the mass of the negative electrode active material per unit area of the punched portion was determined based on the size of the main body portion 21a and the mass of the negative electrode active material filled in the main body portion 21a. In Example 2 and Comparative Example 1 described later, based on the weight of the negative electrode active material filled in size and a second portion P ₂ of the second part P _2, the negative electrode active material per unit area of the punched portion The mass was determined. And M1n was _{calculated |} required based on the mass of the PTFE adhering per unit area of the obtained said punched-out part, and the mass of the negative electrode active material filled per unit area of the said punched-out part.

Example 2
The negative electrode 41 shown in FIGS. 8 and 9 was produced by the following method.

The thickness of the negative electrode active material layer formed on both sides of the negative electrode current collector of the first part was the same as the thickness of the negative electrode active material layer formed on both sides of the negative electrode current collector of the second part. Specifically, in both the first part and the second part of the negative electrode, the thickness of the negative electrode active material layer formed on both surfaces of the negative electrode current collector was 0.14 mm.

The mass of the PTFE dispersion applied per unit area of the first part was larger than the mass of the PTFE dispersion applied per unit area of the second part (about 0.50 mg / cm ² ). Specifically, M ₁ was changed to the values shown in Table 2 by changing the mass of the PTFE dispersion applied per unit area of the first part.

Except for the above, negative electrodes (b-1) to (b-7) were produced in the same manner as in Example 1.

Table 2 shows values of M ₁ , M ₂ , and M ₁ / M _{2 for} the negative electrodes (b-1) to (b-7).

Batteries (B-1) to (B-7) were produced in the same manner as in Example 1, except that the negative electrodes (b-1) to (b-7) were used instead of the negative electrode of Example 1.

<< Comparative Example 1 >>
The mass of the PTFE dispersion applied per unit area of the first part was the same as the mass of the PTFE dispersion applied per unit area of the second part. Specifically, in both the first part and the second part of the negative electrode, the mass of the PTFE dispersion applied per unit area of the negative electrode was about 0.50 mg / cm ² .

Except for the above, a negative electrode (c) was produced in the same manner as in Example 2.

A battery (C) was produced in the same manner as in Example 1 except that the negative electrode (c) was used instead of the negative electrode in Example 1.

The following evaluation was performed on the battery produced above. For each of the following evaluation tests (i) and (ii), 50 batteries of Examples 1 and 2 and Comparative Example 1 were prepared.

[Evaluation]
(I) Measurement of discharge capacity In an environment of 20 ° C., after charging under the following conditions, the battery was rested for 60 minutes and then discharged under the following conditions, and the discharge capacity at this time was measured. The average value of the measured values of 50 batteries was determined.

(Charging conditions)
Charging current: 0.5 CA, charging time: 2 hours 24 minutes, charging control: -dV control (= 5 mV)
(Discharge conditions)
Discharge current: 1.0 CA, end voltage: 1.0 V
(Ii) Overcharge test A hole with a diameter of 1.0 mm was made in the bottom of the battery obtained above, and a pressure sensor was attached. The battery was charged to a charge state (SOC) of 110% of full charge at a current value of 1.0 CA under an environment of 20 ° C., and the internal pressure of the battery was measured. The average value of the measured values of 50 batteries was determined.

The evaluation results of each battery are shown in Tables 1 and 2. In addition, the discharge capacity in Tables 1 and 2 and the value of the battery internal pressure at the time of overcharge are the indexes where the value of the discharge capacity of the battery (C) of Comparative Example 1 and the battery internal pressure at the time of overcharge are 100, respectively. Show.

In the battery (C) of Comparative Example 1, a good discharge capacity was obtained, but the battery internal pressure significantly increased during overcharge.

In contrast, in the batteries (A-1) to (A-7) and the batteries (B-1) to (B-7) of Examples 1 and 2 of the present invention, high capacity is obtained and overcharge is performed. At that time, the increase in the internal pressure of the battery was sufficiently suppressed. In particular, in the batteries (A-2) to (A-6) and (B-2) to (B-6) in which M ₁ / M ₂ is 1.1 to 2.2, The effect of improving the discharge characteristics of the battery was obtained with a good balance.

The nickel-metal hydride storage battery according to the present invention can be suitably used as a power source for various devices in addition to an alternative to a dry battery because it can suppress an increase in battery internal pressure even when the capacity is increased.

1, 21, 41 Negative electrode 1a, 21a Body portion 1b, 21b Tapered portion 1c, 21c Thin portion 2 Positive electrode 3 First separator 3a Second separator 4 Battery case 6 Safety valve 7 Sealing plate 8 Insulating gasket 9 Positive electrode current collector plate 11, 31 , 51 Negative electrode current collector 12, 12a, 12b, 32a, 32b, 32c, 52a, 52b Negative electrode active material layer

Claims (4)

A strip-shaped positive electrode, a strip-shaped negative electrode, and an electrode group wound with a strip-shaped separator interposed between the positive electrode and the negative electrode, and an electrolyte included in the electrode group,
The positive electrode includes a nickel compound as a positive electrode active material,
The negative electrode includes a hydrogen storage alloy as a negative electrode active material,
A fluororesin is attached to the surface of the negative electrode,
The negative electrode has a first part disposed on the outermost periphery of the electrode group, and a second part other than the first part,
The nickel metal hydride storage battery, wherein the mass M _{1 of the} fluororesin adhering per unit mass of the first part is larger than the mass M _{2 of the} fluororesin adhering per unit mass of the second part. The nickel-metal hydride storage battery according to claim 1, wherein a mass M _{1 of the} fluororesin adhering per unit mass of the first portion is 5.3 to 12.5 mg / g. The mass M _{1 of the} fluororesin adhering per unit mass of the first part and the mass M _{2 of the} fluororesin adhering per unit mass of the second part are expressed by the relational expression:
1.05 ≦ M ₁ / M ₂ ≦ 2.5
The nickel hydride storage battery of Claim 1 or 2 satisfy | filling. The negative electrode has a negative electrode current collector and a negative electrode active material layer formed on both surfaces of the negative electrode current collector,
The difference (T _1n -T _1c ) between the thickness T _1n of the negative electrode and the thickness T _1c of the negative electrode current collector in the first portion, the thickness T _{2n of the} negative electrode in the second portion, The difference (T _2n −T _2c ) from the thickness T _2c of the negative electrode current collector is a relational expression:
0.4 ≦ (T _1n −T _1c ) / (T _2n −T _2c ) ≦ 1.0
The nickel-metal hydride storage battery according to any one of claims 1 to 3, wherein

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