JP2005158654A - Cylinder-shaped alkali storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylinder-shaped alkali storage battery prevented from increase of inner pressure at charging, suitable for increasing its capacity, having a good high-rate discharge property. <P>SOLUTION: The cylinder-shaped alkali storage battery comprises a cylinder-shaped conductive outer case and an electrode group housed in the outer case together with alkaline electrolyte. The electrode group is formed by winding a negative electrode 26 and a positive electrode through a separator in a swirl-shape so as to locate the negative electrode 26 at an outermost periphery, and the outermost periphery composed of the negative electrode 26 is made to contact the inner wall of the outer case. The negative electrode includes a belt-shaped negative electrode core body 46 and activator layers 48, 50 held on the negative electrode core body 46. Further, the negative electrode 26 is composed of a main body part 52 wound at the inside of the electrode group and a thin thickness part 56 wound as an outermost part of the electrode group, of which the thickness of the activator layer 50 is thinner than that of the main body part 52. The activator layer 48, 50 of the main body part 52 has water repellent layers 58 on its surface. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a cylindrical alkaline storage battery.

  Examples of the alkaline storage battery include a nickel cadmium secondary battery and a nickel hydride secondary battery, depending on the type of active material included. There is a cylindrical type in which a group of electrodes wound in a spiral shape is housed in a cylindrical outer can that also serves as a negative electrode terminal. Usually, the negative electrode is longer than the positive electrode, and the negative electrode is positioned on the outermost periphery of the electrode group. This is to ensure a large negative electrode capacity compared to the positive electrode capacity in order to prevent the increase in internal pressure by reducing the oxygen gas generated at the positive electrode at the time of overcharge (Neumann principle), therefore, the battery The capacity is defined by the positive electrode capacity.

Since this type of cylindrical alkaline storage battery is suitable for a wide range of applications, various technical developments have been made to improve various performances (for example, Patent Document 1 and Patent Document 2).
In the alkaline storage battery disclosed in Patent Document 1, a water-repellent resin is applied to the surface of the negative electrode. The water-repellent resin enhances the gas permeability of the negative electrode surface to facilitate the diffusion of oxygen gas into the negative electrode, thereby suppressing the increase in battery internal pressure during rapid charging and the voltage drop during discharging. Conceivable.

The cylindrical alkaline storage battery disclosed in Patent Document 2 is positioned on the outermost periphery of the electrode group, and the volume efficiency is increased by reducing the thickness of the negative electrode part that contributes less to the battery reaction than the other parts. It is thought that high capacity will be achieved.
Japanese Patent No. 334589 JP-A-4-206474

  By the way, in the alkaline storage battery of patent document 1, the water-repellent resin provided to the negative electrode surface becomes an electric resistance layer, and increases the reaction resistance between the positive electrode and the negative electrode. In addition, in the battery in which the electrical connection between the negative electrode and the negative electrode terminal (external can) is realized by direct contact between the negative electrode positioned on the outermost peripheral portion of the electrode group and the inner peripheral wall of the external can. Since the electrical resistance increases between the negative electrode and the outer can due to the interposition of the electrical resistance layer, there is a problem that the high-rate discharge characteristics are deteriorated.

In addition, in the cylindrical alkaline storage battery of Patent Document 1, in order to establish the Neumann principle, the decrease in the amount of the negative electrode active material in the thinned negative electrode portion is reduced, and the negative electrode active material amount in the other portion of the negative electrode is reduced. It is necessary to compensate by increasing.
However, in the portion of the negative electrode where the amount of the negative electrode active material has increased due to such compensation, there is a problem that the density of the negative electrode active material becomes high and gas diffusion is hindered, resulting in a reduction in oxygen reduction performance.

  And, in order to improve the oxygen reduction performance that has been lowered due to the increase in the density of the active material, when a water repellent resin is applied to the surface of the other part of the negative electrode, the water repellent action increases the density of the active material. The alkaline electrolyte that is unevenly distributed on the negative electrode surface moves to the outermost peripheral portion of the electrode group, and exists as a free electrolyte. Since the free electrolyte occupies an excessive space in the battery that temporarily receives oxygen gas generated at the positive electrode, there arises a problem that the internal pressure of the battery tends to increase during charging.

  An object of the present invention is to solve the above-mentioned problems and to provide a cylindrical alkaline storage battery that prevents an increase in internal pressure during charging, is suitable for increasing the capacity, and has good high-rate discharge characteristics.

  In order to achieve the above object, according to the first aspect of the present invention, the conductive cylindrical outer can and the outer can are housed together with the alkaline electrolyte, and are held by the strip-shaped negative electrode core and the negative electrode core. A negative electrode including an active material layer and a positive electrode are wound in a spiral shape so that the negative electrode is positioned on the outermost periphery via a separator, and an outermost part composed of the negative electrode is in contact with an inner peripheral wall of the outer can In the cylindrical alkaline storage battery, the negative electrode is wound as a main body wound inside the electrode group and an outermost peripheral part of the electrode group, and the active material layer is compared with the main body part. A thin-walled portion, and the active material layer of the main body portion has a water-repellent layer on the surface.

  In the above configuration, since the negative electrode has a thin portion, the cylindrical alkaline storage battery is suitable for increasing the capacity. Further, since the main body portion of the negative electrode has a water-repellent layer on the surface, the main body portion of the negative electrode has improved gas permeability and exhibits good oxygen reduction performance, thereby preventing an increase in battery internal pressure during charging. On the other hand, the thin-walled part of the negative electrode is not provided with a water-repellent layer serving as an electric resistance layer on the surface, preventing an increase in electric resistance between the negative electrode and the inner peripheral wall of the outer can and preventing a decrease in high-rate discharge characteristics Is done.

The invention according to claim 2 is characterized in that the active material layer of the main body part contains more active material per unit volume than the active material layer of the thin-walled part.
According to the above configuration, the active material layer in the main body portion of the negative electrode contains more negative electrode active material per unit volume than the active material layer in the thin wall portion, thereby reducing the thickness of the active material layer in the thin wall portion. A decrease in the amount of the negative electrode active material can be compensated. Therefore, according to this configuration, a sufficient negative electrode capacity with respect to the positive electrode capacity is ensured, and oxygen gas generated at the positive electrode during overcharge can be reduced at the negative electrode to prevent an increase in internal pressure.

According to a third aspect of the present invention, the length of the thin wall portion is in the range of 85% to 115% with respect to the peripheral length of the inner peripheral wall of the outer can.
According to the above-described configuration, it is possible to contact the thin portion over the entire circumferential direction of the inner peripheral wall of the outer can, preventing an increase in electrical resistance between the negative electrode and the outer can, and good high-rate discharge characteristics Can be secured. In addition, since the thin-walled portion and the outer can can be contacted over the entire circumferential direction, local current concentration on the thin-walled portion is prevented, and early deterioration of the negative-electrode active material in the thin-walled portion is prevented. A good cycle life can be ensured.

The invention according to claim 4 is characterized by having a length substantially equal to the peripheral length of the inner peripheral wall of the outer can.
According to the above configuration, the thin portion can be reliably brought into contact with the entire circumferential direction of the inner peripheral wall of the outer can. Therefore, good high rate characteristics and cycle life can be ensured.

The cylindrical alkaline storage battery of the present invention is suitable for high capacity and has good high-rate discharge characteristics (claim 1).
In addition, the cylindrical alkaline storage battery of the present invention is suitable for higher capacity because it prevents an increase in internal pressure during charging (claim 2).
Furthermore, the cylindrical alkaline storage battery according to the present invention ensures good high-rate discharge characteristics and cycle life (claims 3 and 4).

A cylindrical nickel-hydrogen secondary battery (hereinafter referred to as battery A) according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings.
As shown in FIG. 1, the battery A includes an outer can 10 having a bottomed cylindrical shape with an open upper end, and the outer can 10 has conductivity and functions as a negative electrode terminal. In the opening of the outer can 10, a conductive cover plate 14 is disposed via a ring-shaped insulating packing 12, and the insulating packing 12 and the cover plate 14 are fixed in the opening by caulking the opening edge. Yes.

  The cover plate 14 has a gas vent hole 16 in the center, and a rubber valve element 18 is disposed on the outer surface of the cover plate 14 so as to close the gas vent hole 16. Further, a cap-shaped positive terminal 20 covering the valve body 18 is fixed on the outer surface of the cover plate 14, and the positive terminal 20 presses the valve body 18 against the cover plate 14. Accordingly, the outer can 10 is normally airtightly closed by the lid plate 14 together with the insulating packing 12 and the valve body 18. On the other hand, when gas is generated in the outer can 10 and its internal pressure increases, the valve body 18 is compressed and the gas is released from the outer can 10 through the gas vent hole 16. That is, the cover plate 14, the valve body 18, and the positive electrode terminal 20 form a safety valve.

  A substantially cylindrical electrode group 22 is accommodated in the outer can 10 together with an alkaline electrolyte (not shown), and the outermost peripheral portion of the electrode group 22 is in direct contact with the inner peripheral wall of the outer can 10. The electrode group 22 includes a positive electrode 24, a negative electrode 26, and a separator 28. Examples of the alkaline electrolyte include a sodium hydroxide aqueous solution, a lithium hydroxide aqueous solution, a potassium hydroxide aqueous solution, and an aqueous solution obtained by mixing two or more of these. Etc.

  Further, in the outer can, a positive electrode lead 30 is disposed between one end of the electrode group 22 and the lid plate 14, and both ends of the positive electrode lead 30 are connected to the positive electrode 24 and the lid plate 14. Therefore, the positive electrode terminal 20 and the positive electrode 24 are electrically connected via the positive electrode lead 30 and the lid plate 14. A circular insulating member 32 is disposed between the cover plate 14 and the electrode group 22, and the positive electrode lead 30 extends through a slit provided in the insulating member 32. A circular insulating member 34 is also disposed between the electrode group 22 and the bottom of the outer can 10.

Referring to FIG. 2, in the electrode group 22, the positive electrode 24 and the negative electrode 26 are alternately overlapped when viewed in the radial direction of the electrode group 22 with the separator 28 interposed therebetween.
More specifically, each of the electrode groups 22 includes a strip-like positive electrode 24, a negative electrode 26, and a separator 28. It is formed by winding. Therefore, one end (inner end) 36, 38 of the positive electrode 24 and the negative electrode 26 is positioned on the center side of the electrode group 22, while the other end (outer end) 40, 42 of the positive electrode 24 and the negative electrode 26 is the outer periphery of the electrode group 22. Is located on the side. The negative electrode 26 is longer than the positive electrode 24, extends in a spiral shape from the inside of the positive electrode inner end 36 to the outer side of the positive electrode outer end 40, and sandwiches the positive electrode 24 from both sides across the entire longitudinal direction via the separator 28. Yes. The separator 28 is not wound around the outermost periphery of the electrode group 22, and the negative electrode 26 forms the outermost periphery of the electrode group 22. In the outermost peripheral portion of the electrode group 22, the negative electrode 26 and the outer can 10 are electrically connected to each other, and the negative electrode outer end 42 is sufficient for the negative electrode 26 to cover the outside of the positive electrode outer end 40 through the separator 28. It is positioned in the vicinity of the positive electrode outer end 40, separated by a length. Since the core is pulled out after winding, a space 44 corresponding to the shape of the core exists in the center of the electrode group 22.

Examples of the material of the separator 28 include polyamide fiber nonwoven fabrics, and polyolefin fiber nonwoven fabrics such as polyethylene and polypropylene that are provided with hydrophilic functional groups.
Although not shown, the positive electrode 24 has a conductive positive electrode core having a strip shape, and a positive electrode mixture is held in the core. Examples of the positive electrode core include a foamed nickel base material having a porous structure. In the case of a foamed nickel base material, the positive electrode mixture is held in the communication hole of the foamed nickel base material.

  The positive electrode mixture includes, for example, a positive electrode active material, an additive, and a binder. The positive electrode active material is not particularly limited, and examples thereof include nickel hydroxide particles or nickel hydroxide particles in which cobalt, zinc, cadmium or the like is dissolved. Examples of the additive include a conductive agent made of a cobalt compound, and examples of the binder include a hydrophilic or hydrophobic polymer.

  As shown in FIG. 3 and FIG. 4, the negative electrode 26 has a conductive negative electrode core 46 having a strip shape, and the negative electrode mixture 46 holds a negative electrode mixture. The negative electrode core 46 is made of a sheet-like metal material having a plurality of through holes (not shown) in the thickness direction, and examples thereof include a punching metal, a metal powder sintered body substrate, and an expanded metal. And nickel nets. In particular, a punched metal or a metal powder sintered body substrate obtained by molding and sintering a metal powder is suitable for the negative electrode core 46. In FIG. 1 and FIG. 2, the negative electrode core 46 is omitted for convenience of drawing.

Since the battery A is a nickel metal hydride secondary battery, the negative electrode mixture is composed of hydrogen storage alloy particles capable of storing and releasing hydrogen as a negative electrode active material and a binder. In the present specification, the hydrogen storage alloy is also referred to as a negative electrode active material for convenience of explanation.
The hydrogen storage alloy particles may be any particles that can store hydrogen generated electrochemically in an alkaline electrolyte when the battery A is charged and can easily release the stored hydrogen during discharge. Such a hydrogen storage alloy is not particularly limited, and examples thereof include AB ₅ type alloys such as LaNi ₅ and MmNi ₅ (Mm is a misch metal). In addition, examples of the binder include hydrophilic or hydrophobic polymers. Further, a conductive agent such as carbon black or Ni powder may be added as necessary. If a cadmium compound is used instead of the hydrogen storage alloy, the battery A can be a nickel cadmium secondary battery, but a nickel hydride secondary battery is suitable for improving the battery capacity.

  The negative electrode mixture described above is filled in the through hole of the negative electrode core body 46, and the negative electrode core body 46 is in the form of a sheet. Therefore, as shown in FIGS. An active material layer (mixture layer) is formed by being layered on the top. Hereinafter, the layer of the negative electrode mixture that covers the inner surface of the negative electrode core 46 and faces the central axis side of the electrode group 22 is referred to as the inner hydrogen storage alloy layer 48 or the inner alloy layer 48, and the outer surface of the negative electrode core 46 is The layer of the negative electrode mixture that is covered and faces the outside of the electrode group 22 is referred to as an outer hydrogen storage alloy layer 50 or an outer alloy layer 50.

  In the negative electrode 26, the thickness T 2 of the inner alloy layer 48 is substantially constant from the negative electrode inner end 38 to the negative electrode outer end 42. On the other hand, the thickness of the outer alloy layer 50 varies between the negative electrode inner end 38 and the negative electrode outer end 42, and the negative electrode 26 has three regions with respect to the thickness of the outer alloy layer 50 as viewed in the longitudinal direction of the negative electrode core 46. In other words, the main body 52, the boundary 54, and the thin portion 56 are sequentially divided from the negative inner end 38 toward the negative outer end 42.

The main body 52 is wound inside the electrode group 22, and the positive electrode 24 is disposed on both sides with the separator 28 interposed therebetween. The thickness of the outer alloy layer 50 in the main body 52 is approximately equal to the thickness T2 of the inner alloy layer 48.
The boundary portion 54 is formed between the main body portion 52 and a thin-walled portion 56 to be described later, the thickness changes in the longitudinal direction of the negative electrode core 46, and the electrode group 22 when wound as the electrode group 22. When viewed in the circumferential direction, the positive electrode outer end 40 is positioned at a different position. In the present embodiment, the boundary portion 54 has a length L, and the thickness of the outer alloy layer 50 at the boundary portion 54 gradually decreases from the main body portion 52 toward the thin portion 56 at a substantially constant change rate, It changes from thickness T2 to thickness T1.

When the negative electrode 26 is developed on a flat reference surface, the inclination angle of the surface of the outer alloy layer 50 in the boundary portion 54 with respect to the surface of the outer alloy layer 50 in the reference surface or the thin portion 56 is θ, The inclination angle θ is within a range of 0 ° <θ <10 ° as a preferred embodiment.
The thin-walled portion 56 is wound around the outer side of the electrode group 22 as the outermost peripheral portion of the negative electrode 26 to form the outermost peripheral portion of the electrode group 22, and covers the outer side of the positive electrode outer end 40 via the separator 28. Close contact with the inner peripheral wall of the can 10. The thickness T1 of the outer alloy layer 50 in the thin portion 56 is constant in the longitudinal direction of the negative electrode core 46, and is thinner than the thickness of the outer alloy layer 50 in the main body portion 52, that is, the thickness T2 of the inner alloy layer 48. . Therefore, in the thin portion 56, the inner alloy layer 48 is thicker than the outer alloy layer 50.

In addition, the length Xd of the thin part 56 is in the range of 85% to 115% of the circumferential length of the inner peripheral wall of the outer can 10, that is, the circumference, as a preferable mode, and more preferably, the outer can 10. Is set to be approximately equal to the circumference of the inner peripheral wall. The circumference of the inner peripheral wall can be obtained based on the inner diameter d (see FIG. 2).
Thus, in the negative electrode 26, the thin portion 56 is thinner than the main body portion 52.

  In the battery A, a water repellent layer 58 is formed on the surface of the main body 52 of the negative electrode 26, that is, on the surfaces of the inner alloy layer 48 and the outer alloy layer 50 in the main body 52. Although the water repellent layer 58 is made of, for example, PTFE (polytetrafluoroethylene), as a suitable material for the water repellent layer 58, in addition to PTFE, FEP (fluorinated ethylene propylene), PFA (tetrafluoroethylene perfluoro) Examples thereof include fluororesins such as kilovinyl ether), PCTFE (polychlorotrifluoroethylene), and PVDF (polyvinylidene fluoride). For convenience of drawing, these water repellent layers 58 are omitted in FIGS.

If the water repellent layer 58 is too thin, the water repellency will be poor, and if it is too thick, the electrical resistance will be large. Therefore, the water repellent layer 58 is preferably in the range of approximately 10.0 μm to 25.0 μm. 3 and 4, the water-repellent layer 58 is clearly shown on the inner and outer alloy layers 48 and 50, but the boundary between the water-repellent layer 58 and the inner and outer alloy layers 48 and 50 is clear. Need not be.
In addition, the amount of hydrogen storage alloy particles contained in the main body portion 52 per unit volume of the inner and outer alloy layers 48, 50 is included in the thin portion 56 per unit volume of the inner and outer alloy layers 48, 50. In other words, the main body 52 has a higher density of hydrogen storage alloys in the inner and outer alloy layers 48 and 50 than the thin portion 56.

In the negative electrode 26, as a preferred embodiment, the amount of hydrogen storage alloy contained per unit area of the thin portion 56 is in the range of 40% to 75% of the amount of hydrogen storage alloy contained per unit area of the main body portion 52. In.
Although the battery A described above can be manufactured by applying a normal method, an example of a method for manufacturing the negative electrode 26 will be described below.

  First, a paste of, for example, punching metal and negative electrode mixture to be the negative electrode core 46 is prepared, and the paste is applied to the punching metal so that the thin portion 56 is thin and the main portion 52 is thick. Wear and dry. After drying, it is compressed from both sides in the thickness direction through a gap between a pair of rolling rolls. During this rolling, the pressing force of the roll is variably controlled so as to be larger in the portion serving as the main body portion 52 than in the portion serving as the thin portion 56, and in the negative electrode 26 obtained, the unit volume of the inner and outer alloy layers 48 and 50 is controlled. The amount of the hydrogen storage alloy contained per hit is set so that the main body portion 52 is larger than the thin portion 56. Then, the rolled product is cut into a predetermined size, and the strip-shaped negative electrode 26 is manufactured. Next, a solution containing, for example, 60% by weight of a water repellent resin such as PTFE or FEP is applied to the surface of the portion to be the main body 52 and dried. In addition, the inclination angle θ of the boundary portion 54 can be adjusted by controlling the thickness of the applied paste, the pressing force, or the like.

According to the battery A having the above-described configuration, the volume of the positive electrode 24 can be increased corresponding to the volume of the negative electrode 26 that is reduced by making the thin portion 56 thinner than the main body portion 52. By increasing the volume of the positive electrode 24, the amount of the positive electrode active material contained in the battery A can be increased, and thus the capacity of the battery A can be increased.
In the battery A, the main body 52 of the negative electrode 26 has a water-repellent layer 58 formed on the surface thereof, and gas permeability is improved. Accordingly, the oxygen gas generated in the positive electrode 24 during charging can easily diffuse inside the main body portion 52 and inside the outer alloy layers 48 and 50, so that the oxygen reduction reaction proceeds rapidly in the main body portion 52, and the battery A is charged. The increase in internal pressure is prevented. On the other hand, since the water repellent layer is not formed on the surface of the thin portion 56 of the negative electrode 26, the outer alloy layer 50 of the thin portion 56 is in direct contact with the inner peripheral wall of the outer can 10. Therefore, the battery A is prevented from increasing the electric resistance between the negative electrode 26 and the outer can 10 due to the interposition of the water repellent layer, and has good high-rate discharge characteristics.

  In addition, the battery A compensates for the decrease in the amount of the negative electrode active material due to the thinning of the thin portion 56 by increasing the amount of the hydrogen storage alloy contained per unit volume of the inner and outer alloy layers 48 and 50 in the main body portion 52. doing. Therefore, the battery A has a sufficient negative electrode capacity with respect to the positive electrode capacity, can reduce the oxygen gas generated at the positive electrode 24 at the time of overcharge by the negative electrode 26 and prevent an increase in internal pressure, and is more suitable for higher capacity. To do. Here, in the battery A, even if the hydrogen storage alloy density of the inner and outer alloy layers 48 and 50 in the main body 52 is high, the water repellent layer 58 is formed on the surface of the main body 52, and the inner and outer alloy layers 48, Since the amount of the alkaline electrolyte contained in 50 is reduced, the oxygen gas can easily diffuse inside the body portion 52 and inside the outer alloy layers 48 and 50. Therefore, all the hydrogen storage alloys contained in the main body 52 can contribute effectively to the oxygen reduction reaction, and the oxygen gas is reliably reduced to prevent an increase in internal pressure.

  In the battery A, the thin portion 56 has a length Xd within the range of 85% to 115% of the circumference of the inner peripheral wall of the outer can 10 and is in contact with substantially the entire circumferential direction of the inner peripheral wall. It is possible. Here, the preferable value of the lower limit was set to 85% because the thin-walled portion having high conductivity while limiting the contact area between the main body 52 having the water-repellent layer 58 having high electrical resistance and the inner peripheral wall of the outer can 10. This is to maximize the contact area between the inner wall 56 and the inner peripheral wall of the outer can 10. Thereby, in the battery A, an increase in electrical resistance between the negative electrode 26 and the outer can 10 is prevented, and good high-rate discharge characteristics are ensured. Further, by restricting the contact area between the main body 52 and the inner peripheral wall of the outer can 10, local current concentration on the thin portion 56 having high conductivity is prevented, and the negative electrode active material contained in the thin portion 56. Is prevented from premature deterioration. Therefore, the battery A also ensures a good cycle life.

On the other hand, the preferable value of the upper limit is set to 115% because when the length Xd of the thin portion 56 becomes too long, the alkaline electrolyte moves from the main body portion 52 toward the thin portion 56 due to the water repellency of the water repellent layer 58. That is, the amount of free electrolyte increases, the excess space in the battery A decreases, and the internal pressure easily rises.
For these reasons, the length Xd of the thin portion 56 is more preferably substantially equal to the circumference of the inner peripheral wall of the outer can 10.

The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, if the boundary portion 54 does not contact the inner peripheral wall of the outer can 10, the surface of the boundary portion 54 is repelled. An aqueous layer may be formed. Furthermore, a water repellent layer may be formed on the surface of the inner alloy layer 48 also in the thin portion 56.
Further, in the thin portion 56, not only the outer alloy layer 50 is made thinner than the main body portion 52, but both the inner and outer alloy layers 48, 50 may be made thinner.

  Then, instead of the sheet-like negative electrode core body 46 having through holes, a substrate having a porous structure, for example, a foamed nickel base material, may be used for the negative electrode core body as in the case of the positive electrode 24. In this case, the hydrogen storage alloy layer is held by the negative electrode core in a state in which the skeleton of the foamed nickel base material extends in a network shape in the hydrogen storage alloy layer.

Examples 1-4, Comparative Examples 1-9
1. Assembling of batteries As Examples 1 to 4, 100 AA-sized cylindrical nickel-hydrogen secondary batteries having the configurations shown in FIGS. 1 to 4 were assembled.
In Examples 1, 3 and 4, the water repellent layer 58 is made of PTFE, and in Example 2, the water repellent layer 58 is made of FEP. And in Examples 1-4, in the main-body part 52 of the negative electrode 26, the hydrogen storage alloy density is high compared with the thin part 56, and the peripheral length (inside the outer can) of the outer peripheral wall of the outer can 10 The length Xd of the thin portion 56 is set so that the ratio of the length Xd of the thin portion to the (circumferential length) becomes the value shown in Table 1, respectively.

As Comparative Examples 1 and 2, 100 AA-size cylindrical nickel-metal hydride secondary batteries were respectively provided in the same manner as in Example 1 except that the water-repellent layer was not formed on the surface of the negative electrode body. Assembled.
As Comparative Examples 2 and 3, the water repellent layer was not formed on the surface of the main body of the negative electrode, and the ratio of the length of the thin portion to the inner peripheral length of the outer can was 85% or less or 115% or more. Except for this, in the same manner as in Example 1, 100 AA-sized cylindrical nickel-metal hydride secondary batteries were assembled.

As Comparative Example 4, an AA size cylindrical nickel-metal hydride secondary battery was prepared in the same manner as in Examples 1 and 2, except that the thickness of the negative electrode was constant and a water repellent layer was not formed on the surface. 100 pieces were assembled.
As Comparative Example 5, 100 AA-sized cylindrical nickel metal hydride secondary batteries were assembled in the same manner as in Example 1 except that a water-repellent layer was also formed on the surface of the boundary and the thin part of the negative electrode. .

As Comparative Example 6, an AA size cylindrical nickel metal hydride secondary battery was prepared in the same manner as Comparative Example 4 except that a water repellent layer made of PTFE was formed on the surface of the portion corresponding to the main body of the negative electrode. 100 pieces were assembled.
As Comparative Example 7, 100 AA-sized cylindrical nickel-metal hydride secondary batteries were assembled in the same manner as Comparative Example 4 except that a water-repellent layer made of PTFE was formed on the entire surface of the negative electrode.

As Comparative Example 8, 100 AA-sized cylindrical nickel-hydrogen secondary batteries were assembled one by one in the same manner as Comparative Example 7 except that a water-repellent layer made of FEP was formed.
2. Battery Characteristic Evaluation Test The following evaluation tests were performed on the batteries of the obtained Examples and Comparative Examples.
(1) Measurement of internal pressure during charging For each of the batteries of the example and comparative example, after attaching a pressure sensor capable of measuring the internal pressure of the battery, charging was performed for 1.5 hours at a current value of 1 ItA, and the maximum during charging The internal pressure was measured. The results are shown in Table 1, normalized with the result of Comparative Example 5 being 100. In addition, the result of each battery is an average value of 100 pieces.

(2) Measurement of high-rate discharge characteristics For each battery of the example and comparative example, after charging for 1.5 hours at a current value of 1 ItA, the discharge capacity when discharged to a final voltage of 1.0 V at a current value of 3 ItA It was measured. The results are shown in Table 1, normalized with the result of Comparative Example 5 being 100. In addition, the result of each battery is an average value of 100 pieces.

(3) Measurement of cycle life For each battery of the example and comparative example, after charging for 1.5 hours at a current value of 1 ItA, charging to discharge to a final voltage of 1.0 V at a current value of 1 ItA while measuring the discharge capacity. The discharge cycle was repeated until the discharge capacity became 80% or less of the initial discharge capacity, and the number of cycles was counted. The results are shown in Table 1, normalized with the result of Comparative Example 5 being 100. In addition, the result of each battery is an average value of 100 pieces.

From Table 1, the following is clear.
From the comparison between Examples 1 and 2 and Comparative Example 1, it can be seen that if the water-repellent layer 58 is formed on the surface of the main body 52 of the negative electrode 26, an increase in internal pressure during charging can be effectively prevented.
From comparison between Examples 1 and 2 and Comparative Example 5, it can be seen that when a water repellent layer is formed on the thin portion 56, the high-rate discharge characteristics are lowered and the internal pressure during charging is increased. This is because the electrical resistance increased between the negative electrode and the outer can due to the interposition of the water repellent layer in the thin wall portion, the alkaline electrolyte moved from the surface of the thin wall portion to the excess space of the battery, and the free electrolyte solution This is thought to be because the excess space decreased due to the increase.

  From a comparison between Examples 1 and 2 and Comparative Examples 6 and 7, it can be seen that the high rate discharge characteristics and the cycle life are reduced when the outermost peripheral portion of the negative electrode is not thinned. This is presumably because there were many hydrogen storage alloys that were included in the outermost peripheral portion of the negative electrode not facing the positive electrode and did not contribute to the charge / discharge reaction. In particular, in Comparative Example 7 in which the water-repellent layer is also formed on the surface of the outermost peripheral portion of the negative electrode, the deterioration of the high rate discharge characteristics is significant. This is presumably because the water-repellent layer acted as an electric resistance layer in addition to the fact that the conductivity of the outermost periphery of the negative electrode was low due to the fact that it was not originally thinned.

  From comparison between Examples 1 and 2 and Example 3, when the length of the thin portion 56 of the negative electrode 26 is 50% with respect to the circumference of the inner peripheral wall of the outer can 10, high rate discharge characteristics and cycle life characteristics It turns out that falls. This is because the thin-walled portion 56 is shortened, so that the main body portion 52 comes into contact with the inner peripheral wall of the outer can 10 through the water-repellent layer 58, and the electrical resistance increases between the negative electrode 26 and the outer can 10. This is probably because the current is concentrated on the thin portion 56 having high conductivity, and the hydrogen storage alloy contained in the thin portion 56 has deteriorated early.

From comparison between Examples 1 and 2 and Example 4, when the length of the thin portion 56 of the negative electrode 26 is 150% of the circumference of the inner peripheral wall of the outer can 10, the internal pressure increases during charging. I understand. This is considered to be because the free electrolytic solution around the thin portion 56 increased due to the length of the thin portion 56, and the surplus space for temporarily storing the gas generated at the positive electrode decreased.
From these results, it can be seen that the length of the thin portion 56 of the negative electrode 26 is preferably in the range of 50% or more and 150% or less with respect to the circumference of the inner peripheral wall of the outer can 10. % Is more preferable, and it is most preferable that they are substantially the same.

1 is a partially cutaway perspective view of a cylindrical nickel-metal hydride secondary battery according to an embodiment of the present invention. It is a cross-sectional view of the battery of FIG. It is the perspective view which expanded and showed the negative electrode used for the battery of FIG. It is a side view of the negative electrode of FIG.

Explanation of symbols

26 Negative electrode 46 Negative electrode core 48 Inner hydrogen storage alloy layer (inner alloy layer)
50 Outer hydrogen storage alloy layer (outer alloy layer)
52 Body 54 Boundary 56 Thin-walled 58 Water-repellent layer

Claims (4)

A conductive cylindrical outer can;
The outer can is housed together with an alkaline electrolyte, and a negative electrode including a strip-shaped negative electrode core, an active material layer held on the negative electrode core, and a positive electrode are swirled so that the negative electrode is positioned on the outermost periphery through a separator. In a cylindrical alkaline storage battery comprising an electrode group that is wound in a shape and the outermost peripheral portion made of the negative electrode is in contact with the inner peripheral wall of the outer can.
The negative electrode is
A main body wound inside the electrode group;
Wound as the outermost peripheral portion of the electrode group, including a thin portion where the thickness of the active material layer is thin compared to the main body portion,
The cylindrical alkaline storage battery, wherein the active material layer of the main body has a water repellent layer on the surface.   2. The cylindrical alkaline storage battery according to claim 1, wherein the active material layer of the main body includes more active material per unit volume than the active material layer of the thin-walled portion.   3. The cylindrical alkaline storage battery according to claim 2, wherein a length of the thin wall portion is in a range of 85% to 115% with respect to a peripheral length of an inner peripheral wall of the outer can.   4. The cylindrical alkaline storage battery according to claim 3, wherein the thin portion has a length substantially equal to a peripheral length of an inner peripheral wall of the outer can. 5.

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