JP4826245B2 - Winding type secondary battery - Google Patents

Description

  The present invention relates to a wound secondary battery, and more particularly, to a wound secondary battery having an electrode group in which positive and negative electrode plates each coated with a mixture are wound on the outside of a shaft core.

  2. Description of the Related Art Conventionally, a wound secondary battery having an electrode group in which positive and negative electrode plates each having a mixture coated on a current collector are wound has been used in various applications. Among these, wound lithium secondary batteries are mainly used in portable devices such as VTR cameras, notebook computers, and mobile phones, taking advantage of the high energy density. On the other hand, research and development of large wound lithium secondary batteries for high capacity, high output, and high output density for electric vehicles and power storage are being actively conducted. In particular, in the automobile industry, development of electric vehicles using only a motor as a power source and hybrid electric vehicles using both an internal combustion engine and a motor is underway in order to deal with environmental problems. Some have already been put to practical use.

  In general, in a small wound lithium secondary battery, an axis is not used at the winding center of an electrode group. However, in a large-sized wound lithium secondary battery, since the electrode area is increased, the electrode group becomes larger, and a safety mechanism or the like is arranged to ensure safety. Becomes very heavy. As a result, the influence of vibration, impact, etc. on the battery on the electrode group increases, so it is important to fix the electrode group. For example, a technique using a hollow shaft core is disclosed for fixing the electrode group (see, for example, Patent Document 1). In this technique, since the shaft core is hollow, the weight of the electrode group can be reduced. Moreover, when the electrode group is manufactured, the positive and negative electrode plates can be wound while applying torque to the outside of the shaft core by inserting the winding shaft of the winding device into the hollow portion of the shaft core. Dispersion can be suppressed. Furthermore, by injecting the electrolytic solution from the hollow portion of the shaft core, the electrode group can be easily infiltrated into the electrolytic solution.

JP 2001-126769 A.

  However, when a wound lithium secondary battery using a hollow shaft core is deformed by a certain amount or more by external pressure, the electrode group and the shaft core are deformed in parallel. For this reason, the shaft core is crushed along with the deformation of the electrode group, so that the edge of the crushed shaft core cuts the separator and the positive and negative electrode plates to cause a short circuit. At this short-circuited location, the positive and negative electrode plates penetrate the separator and stab into the counter electrode in a folded or cut state, so that the mixture at the stabbed portion slides down and the current collectors come into contact with each other. For this reason, the resistance of the short-circuited portion is reduced, and since the wound lithium secondary battery has a high capacity and a high output, a large current flows through the short-circuited portion to generate heat and the temperature rises. As a result, there is a problem that the internal pressure rises at an accelerated rate because the vaporization (vaporization) of the battery constituent material and gasification due to thermal decomposition occur in a chained manner.

  An object of the present invention is to provide a wound type secondary battery that can moderate the behavior at the time of battery abnormality in which the battery deforms due to external pressure.

In order to solve the above problems, the present invention provides a wound secondary battery having an electrode group in which positive and negative electrode plates each coated with a mixture are wound on the outside of the shaft core. Is a circular tube formed with a circular or non-circular hollow portion, and the hollow portion of the shaft core has a cross-sectional area smaller than the cross-sectional area of the hollow portion and is equal to the rigidity of the shaft core. Or a support member having a rigidity larger than that of the shaft core is inserted over the entire length of the shaft core .

In the wound secondary battery of the present invention, since the cross-sectional area of the support member is smaller than the cross-sectional area of the hollow portion of the shaft core, the support member can be easily inserted into the shaft core. In addition, since the support member having rigidity equal to or greater than the rigidity of the shaft core is inserted over the entire length of the shaft core, almost the entire length of the shaft core is occupied by the support member. Therefore, even if it is deformed by pressure from the outside, the shaft core is supported by the support member and the shaft core is prevented from being damaged, so that the short circuit due to the contact between the current collectors is suppressed along with the shaft core being damaged. Therefore, the behavior when the battery is abnormal can be made gentle.

In this case, the support member may be a synthetic resin or a metal. Further, if the support member is a solid rod, no space is formed inside the support member, so that the shaft core can be supported even when the pressure from the outside increases. Furthermore, if the outer peripheral surface of the support member has a shape along the inner peripheral surface of the shaft core, the support member is disposed on almost the entire hollow portion of the shaft core. Ru can be used to support the axis also for.

According to the present invention, since the cross-sectional area of the support member is smaller than the cross-sectional area of the hollow portion of the shaft core, the support member can be easily inserted into the shaft core. Since the support member having a rigidity equal to or greater than the rigidity is inserted so as to extend over the entire length of the shaft core, almost the entire length of the shaft core is occupied by the support member . Even if it is deformed by pressure, the shaft core is supported by the support member and damage to the shaft core is suppressed, so short-circuiting due to contact between current collectors is suppressed, so the behavior during battery abnormalities is moderated The effect of being able to be obtained can be obtained.

  Embodiments of a cylindrical lithium ion secondary battery to which the present invention is applied will be described below with reference to the drawings.

(Constitution)
As shown in FIG. 1, a cylindrical lithium ion secondary battery 20 of this embodiment is made of steel with nickel plating and has a bottomed cylindrical shape, and has a cleavage groove (safety mechanism) that operates when the internal pressure rises at the bottom. The battery case 7 in which is formed and the belt-like positive and negative electrode plates have an electrode group 6 wound in a spiral shape in cross section via a separator.

  A hollow cylindrical shaft core 1 made of polypropylene resin is used at the winding center of the electrode group 6. A rod-like member 21 as a solid (substantially cylindrical) support member made of polypropylene resin is inserted into the hollow portion of the shaft core 1. In this example, the dimensions of the shaft core 1 are set to an outer diameter of 9 mm, an inner diameter of 7 mm, and a height of 114.3 mm, and the bar-shaped member 21 is set to a diameter of 6.5 mm and a height of 114 mm. As shown in FIG. 2, the outer peripheral surface of the rod-shaped member 21 is disposed along the inner peripheral surface of the shaft core 1, and a gap is formed between the outer peripheral surface of the rod-shaped member 21 and the inner peripheral surface of the shaft core 1. Has been. For this reason, the cross-sectional area S1 of the rod-shaped member 21 is smaller than the cross-sectional area S2 of the hollow portion of the shaft core 1. Even if the same material is used for the rod-shaped member 21 and the shaft core 1, since the diameter of the rod-shaped member 21 is smaller than the inner diameter of the shaft core 1, the rigidity of the rod-shaped member 21 is larger than the rigidity of the shaft core 1.

  As shown in FIG. 1, on the upper side of the electrode group 6, an aluminum positive electrode current collecting ring 4 for collecting the electric potential from the positive electrode plate is disposed on a substantially extension line of the shaft core 1. The positive electrode current collecting ring 4 is fixed to the upper end portion of the shaft core 1. The edge part of the positive electrode lead piece 2 led out from the positive electrode plate is joined by ultrasonic welding to the peripheral edge of the flange part integrally protruding from the periphery of the positive electrode current collecting ring 4. A disc-shaped battery lid serving as a positive electrode external terminal is disposed above the positive electrode current collecting ring 4. The battery lid includes a lid case 12, a lid cap 13, a valve retainer 14 that keeps airtightness, and a cleavage valve 11 that is cleaved by an increase in internal pressure, and these are laminated to fix the periphery of the lid case 12 by caulking. It is assembled by doing. One end of two positive electrode leads 9 formed by superposing a plurality of aluminum ribbons is fixed to the upper portion of the positive electrode current collecting ring 4, and another one is fixed to the lower surface of the lid case 12. One end is welded. The other ends of the two positive electrode leads 9 are joined by welding.

  On the other hand, a copper negative electrode current collecting ring 5 for collecting a potential from the negative electrode plate is disposed below the electrode group 6. The outer peripheral surface of the lower end portion of the shaft core 1 is fixed to the inner peripheral surface of the negative electrode current collecting ring 5. The end of the negative electrode lead piece 3 led out from the negative electrode plate is joined to the outer peripheral edge of the negative electrode current collecting ring 5 by welding. A negative electrode lead plate 8 made of copper for electrical conduction is welded to the lower part of the negative electrode current collecting ring 5, and the negative electrode lead plate 8 is joined to the inner bottom portion of the battery container 7 by welding. In this example, the dimensions of the battery container 7 are set to an outer diameter of 40 mm and an inner diameter of 39 mm.

The battery lid is caulked and fixed to the upper part of the battery container 7 via an insulating and heat resistant EPDM resin gasket 10. For this reason, the inside of the lithium ion secondary battery 20 is sealed. In addition, a non-aqueous electrolyte is injected into the battery container 7. As the non-aqueous electrolyte, a solution obtained by dissolving 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) as a lithium salt in a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1 is used. .

  In the electrode group 6, the positive electrode plate and the negative electrode plate are wound around the outer periphery (outside) of the shaft core 1 through a separator so that the two electrode plates do not directly contact each other. In this example, a porous polyethylene film having a width of 107.5 mm and a thickness of 40 μm is used as the separator. The positive electrode lead piece 2 and the negative electrode lead piece 3 are disposed on both end surfaces of the electrode group 6 opposite to each other. Insulation coating is applied to the entire circumference of the collar surface of the electrode group 6 and the positive electrode current collector ring 4. For the insulation coating, an adhesive tape in which a hexamethacrylate adhesive is applied to one side of a polyimide base material is used. The pressure-sensitive adhesive tape is wound one or more times from the peripheral surface of the collar portion to the outer peripheral surface of the electrode group 6. By adjusting the lengths of the positive electrode plate, the negative electrode plate, and the separator, the diameter of the electrode group 6 is set to 38 ± 0.1 mm.

  The negative electrode plate constituting the electrode group 6 has a rolled copper foil having a thickness of 10 μm as a negative electrode current collector. A negative electrode mixture containing amorphous carbon powder capable of occluding and releasing lithium ions as a negative electrode active material is coated on both surfaces of the rolled copper foil. In the negative electrode mixture, for example, 10 parts by weight of polyvinylidene fluoride (hereinafter abbreviated as PVDF) as a binder (binder) is blended with 90 parts by weight of amorphous carbon powder. When applying the negative electrode mixture to the rolled copper foil, a dispersion solvent N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) is used. An uncoated portion of a negative electrode mixture having a width of 30 mm is formed on the side edge on one side in the longitudinal direction of the rolled copper foil. The uncoated part is notched in a comb shape, and the negative electrode lead piece 3 is formed in the notch remaining part. The interval between the adjacent negative electrode lead pieces 3 is set to 50 mm, and the width of the negative electrode lead piece 3 is set to 5 mm. The negative electrode plate is pressed with a heatable roll press so as to have a thickness of 70 μm after being dried, and is cut into a width of 105 mm.

  On the other hand, the positive electrode plate has an aluminum foil having a thickness of 20 μm as a positive electrode current collector. A positive electrode mixture containing a lithium transition metal double oxide as a positive electrode active material is applied to both surfaces of the aluminum foil. In the positive electrode mixture, for example, 10 parts by weight of flaky graphite as a conductive material and 5 parts by weight of PVDF as a binder are blended with 100 parts by weight of lithium transition metal double oxide. When applying the positive electrode mixture to the aluminum foil, a dispersion solvent NMP is used. An uncoated portion of a positive electrode mixture with a width of 30 mm is formed on the side edge on one side in the longitudinal direction of the aluminum foil, and a positive electrode lead piece 2 is formed. The interval between the adjacent positive electrode lead pieces 2 is set to 50 mm, and the width of the positive electrode lead piece 2 is set to 5 mm. The positive electrode plate, after drying, is pressed in the same manner as the negative electrode plate so as to have a thickness of 90 μm, and is cut into a width of 99 mm.

(Battery assembly)
The lithium ion secondary battery 20 is assembled in the following procedure. First, the positive and negative electrode plates are wound around the shaft core 1 with a winding device through a separator to produce the electrode group 6. At this time, the winding shaft of the winding device is inserted into the hollow portion of the shaft core 1 and wound while applying torque to the shaft core 1. After the positive electrode lead piece 2 and the negative electrode lead piece 3 respectively led out from both end faces of the electrode group 6 are welded to the positive electrode current collecting ring 4 and the negative electrode current collecting ring 5, the electrode group 6 is inserted into the battery container 7. . A negative electrode lead plate 8 pre-welded to the negative electrode current collecting ring 5 is welded to the inner bottom portion of the battery container 7, and the positive electrode current collecting ring 4 and the battery lid are connected by the positive electrode lead 9. After pouring a non-aqueous electrolyte into the battery container 7 from the hollow portion of the shaft core 1 to infiltrate the electrode group 6 into the non-aqueous electrolyte solution, the rod-shaped member 21 is inserted into the hollow portion of the shaft core 1. The injection amount of the non-aqueous electrolyte is set in consideration of the volume of the rod-shaped member 21. Thereafter, the battery lid is caulked and fixed to the upper part of the battery container 7 to complete the assembly of the lithium ion secondary battery 20.

(Action etc.)
Next, the operation and the like of the lithium ion secondary battery 20 of the present embodiment will be described.

  In the conventional lithium ion secondary battery, a hollow shaft core is used at the center of winding of the electrode group, and the hollow portion of the shaft core is filled with a nonaqueous electrolyte. When the battery is deformed by a certain amount or more by an external force from the side surface, the deformation of the electrode group and the deformation of the shaft core occur in parallel within the battery. As shown in FIG. 3, the hollow shaft core 31 is deformed and crushed along with the deformation of the electrode group 36, and the edge of the crushed shaft core 31 presses and cuts the separator and the positive and negative electrode plates to cause a short circuit. . That is, when the direction in which the external force is applied is vertical (the direction of arrow A in FIG. 3), a short circuit occurs at the short circuit points P1 on both sides of the shaft core 31 in the horizontal direction. In the short circuit location P1, the positive and negative electrode plates are bent or cut and penetrate the separator and pierce the counter electrode. In the pierced positive and negative electrode plates, the positive and negative electrode mixture slides when piercing the separator and the counter electrode, so that the positive and negative electrode current collectors come into contact with each other. For this reason, the resistance at the short-circuited portion P1 is reduced, a large current flows, and the temperature of the short-circuited portion P1 rapidly increases. As the temperature rises, evaporation (vaporization) of the battery constituent material and gasification due to thermal decomposition occur in a chain, so that the battery reaches a thermal runaway state and the internal pressure of the battery rapidly increases. A lithium ion secondary battery is usually provided with a safety valve for releasing the internal pressure. However, if the gas generation speed inside the battery exceeds the capacity of the safety valve, the battery contents are violently released.

  In contrast, in the lithium ion secondary battery 20 of the present embodiment, the rod-shaped member 21 is inserted into the hollow shaft core 1, and the same material polypropylene resin is used for the rod-shaped member 21 and the shaft core 1. Yes. Since the diameter of the rod-shaped member 21 is smaller than the inner diameter of the shaft core 1, even if the rod-shaped member 21 and the shaft core 1 are the same material, the rigidity of the rod-shaped member 21 is larger than the rigidity of the shaft core 1. For this reason, even if the lithium ion secondary battery 20 is deformed by an external force from the side surface, the shaft core 1 is supported by the rod-shaped member 21, so that the deformation of the shaft core 1 is suppressed. Thereby, since a short circuit due to contact between the positive and negative electrode current collectors is suppressed, the battery behavior can be gently suppressed even when the battery is deformed by an external force.

  As shown in FIG. 4, in the lithium ion secondary battery 20 of the present embodiment, even if the electrode group 6 is deformed, the deformation of the shaft core 1 is suppressed, so that an external force is applied before the shaft core 1 is crushed. When the separators located above and below the shaft core 1 in the direction (direction of arrow A in FIG. 4) are deformed and become thin and insulation cannot be maintained, a short circuit occurs. That is, a short circuit occurs at the upper and lower short circuit locations P2 of the shaft core 1. Since a short circuit occurs due to breakage of the separator, only the positive and negative electrode mixtures are in contact with each other and the positive and negative electrode current collectors are not in contact with each other at the short circuit point P2. For this reason, the resistance at the short-circuited portion P2 is increased and the flowing current is reduced, so that the rate of increase in temperature and internal pressure is reduced as compared with the case where the rod-shaped member 21 is not inserted. Accordingly, since the gas generation speed inside the battery can be suppressed below the capacity of the safety valve, the internal pressure is gently released by the operation of the safety valve, and the safety of the battery can be ensured.

  Further, in the lithium ion secondary battery 20 of the present embodiment, one solid member is used in which the cross-sectional area S1 of the rod-shaped member 21 is smaller than the cross-sectional area S2 of the hollow portion of the shaft core 1. Are arranged along the inner peripheral surface of the shaft core 1. For this reason, since almost the entire hollow portion of the shaft core 1 is occupied by the rod-shaped member, the deformation of the shaft core 1 can be suppressed even when pressure is applied from any external direction. Moreover, since the cross-sectional area S1 is one smaller than the cross-sectional area S2, the rod-shaped member 21 can be easily inserted into the shaft core 1.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, the rod-shaped member 21 is inserted into the hollow portion of the shaft core 1 after the nonaqueous electrolytic solution is injected. For this reason, the usage-amount of nonaqueous electrolyte can be reduced by the volume of the rod-shaped member 21. FIG. Since the non-aqueous electrolyte solution is expensive, the cost can be reduced by reducing the amount used. Moreover, since the nonaqueous electrolyte solution is pushed out from the hollow portion of the shaft core 1 by inserting the rod-shaped member 21 after the nonaqueous electrolyte solution is injected, the nonaqueous electrolyte solution is infiltrated into the electrode group 6 substantially evenly. be able to.

  In the lithium ion secondary battery 20 of the present embodiment, the rod-shaped member 21 inserted into the hollow portion of the shaft core 1 is made of a polypropylene resin made of the same material as that of the shaft core 1. It is not limited to. The material of the shaft core 1 may be a polyolefin resin or the like having a rigidity equal to or larger than that of the shaft core 1, and a metal having a rigidity higher than that of the shaft core 1 may be used. For example, as shown in FIG. 5, a metal member 25 may be used instead of the rod-shaped member 21. The metal member 25 has an aluminum bar 22. The dimensions of the bar 22 are set to a diameter of 6.5 mm and a height of 112 mm. A polypropylene plate 23 having a thickness of 1 mm is attached to both ends of the bar 22 with an adhesive. For this reason, the metal member 25 has a diameter of 6.5 mm and a height of 114 mm. Since the metal member 25 has higher rigidity than the shaft core 1, even if the pressure applied from the outside of the battery increases, the deformation of the shaft core 1 can be surely suppressed. Further, since the specific gravity is increased by increasing the rigidity, it is possible to prevent the metal member 25 from floating (in the non-aqueous electrolyte) when the metal member 25 is inserted into the hollow portion of the shaft core 1. It does not take time and effort. Furthermore, since the polypropylene plates 23 are attached to both ends of the metal member 25, electrical insulation can be ensured even if they are in contact with the positive electrode lead 9 and the negative electrode lead plate 8.

  Moreover, in the lithium ion secondary battery 20 of this embodiment, although the cylindrical axial core 1 was illustrated, this invention is not limited to this, For example, the axial core 1 is non-circular, such as a flat shape. It is good also as a shape. In this case, a member that is flat and has an outer peripheral surface that follows the inner peripheral surface of the hollow portion may be used as the rod-shaped member 21. Furthermore, the rod-shaped member 21 and the metal member 25 may be formed in a cylindrical shape in which a hollow portion is formed. If the outer peripheral surfaces of the rod-shaped member 21 and the metal member 25 are along the inner peripheral surface of the hollow portion of the shaft core 1, even if the rod-shaped member 21 and the metal member 25 are cylindrical, the rigidity is greater than that of the shaft core 1. The shaft core 1 can be supported and deformation due to external force can be suppressed.

Furthermore, in this embodiment, the rod-shaped member 21 and the metal member 25 which are inserted into the hollow portion of the shaft core 1 have an outer peripheral surface that is shaped along the inner peripheral surface of the shaft core 1, and an example in which one is inserted is shown. but the invention is not name limited thereto. To prevent damage such as the positive electrode lead 9, for example, bar-shaped member 21, after inserting the metal member 25 in the hollow portion of the shaft 1, it is arranged a closure member such as the ends of the shaft 1 Good. Furthermore, it is good also considering the rod-shaped member 21 inserted in the hollow part of the shaft core 1, and the metal member 25 as two or more, for example, two.

Furthermore, in the lithium ion secondary battery 20 of the present embodiment, a lithium transition metal double oxide as a positive electrode active material, amorphous carbon as a negative electrode active material, scaly graphite as a conductive material, ethylene carbonate as a non-aqueous electrolyte, and While a mixed solvent of dimethyl carbonate obtained by dissolving a LiPF ₆ in the illustrated respectively, the invention is not intended to be limited to, materials may be used that are ordinarily used in a lithium ion secondary battery.

  Furthermore, in the present embodiment, the cylindrical lithium ion secondary battery 20 is exemplified, but the present invention is not limited to this, and is generally applied to a wound secondary battery in which the positive and negative electrode plates are wound. Is possible. Examples of such a wound secondary battery include a nickel hydride battery, a lead storage battery, and a nickel cadmium battery. Further, the shape of the battery is not particularly limited. For example, the battery may have a square shape in addition to the cylindrical shape.

  Next, examples of the lithium ion secondary battery 20 manufactured according to the present embodiment will be described. In addition, it describes together about the lithium ion secondary battery of the comparative example produced for the comparison.

Example 1
In Example 1, a solid rod-shaped member 21 made of polypropylene was used. The dimensions of the rod-shaped member 21 were 6.5 mm in diameter and 114 mm in height, and the shape of the cross-section of the rod-shaped member 21 was similar to the shape of the cross-section of the shaft 1 (see FIG. 2). The cross-sectional area of the rod-shaped member 21 corresponds to 86% of the cross-sectional area of the hollow portion of the shaft core 1.

(Example 2)
In Example 2, it carried out similarly to Example 1 except using the metal member 25 which affixed the polypropylene board 23 of thickness 1mm to the both ends of the rods 22 made from aluminum. The dimensions of the bar 22 were 6.5 mm in diameter and 112 mm in height, and the shape of the cross section of the metal member 25 was similar to the shape of the cross section of the shaft core 1 (see FIG. 5). The cross-sectional area of the metal member 25 corresponds to 86% of the cross-sectional area of the hollow portion of the shaft core 1.

(Comparative Example 1)
Comparative Example 1 was the same as Example 1 except that nothing was inserted into the shaft core. Therefore, the lithium ion secondary battery of Comparative Example 1 is a conventional battery in which the hollow portion of the shaft core is filled with the nonaqueous electrolytic solution.

<Test and evaluation>
Each battery of the produced example and comparative example was evaluated by performing the following Test 1 and Test 2.

(Test 1)
Each battery of the example and the comparative example was deformed without being charged, and the deformed portion was investigated. In the deformation, an uncharged battery is laid horizontally and fixed, and a stainless steel semi-cylindrical crushing jig having a diameter equal to the diameter of the battery container 7 is pressed against the battery container 7 by a hydraulic press machine. A crushing test was conducted by crushing until crushing. After measuring the resistance (short circuit resistance) at the short circuit point of the deformed battery, the electrode group 6 was taken out, the electrode group 6 was unrolled while measuring the resistance, and the short circuit location was investigated. The measurement results of the resistance at the short-circuit point are shown in Table 1 below.

  In the lithium ion secondary battery of Comparative Example 1, a short-circuited portion after the crush test was found near the axis in the horizontal direction when the crushing direction was vertical (see FIG. 3). The cause of the short circuit at this time is that the shaft core is greatly deformed due to the collapse of the hollow portion of the shaft core, the edge of the deformed shaft core breaks through the positive and negative electrode plates and the separator, and the positive and negative electrode current collectors are in contact. It was. On the other hand, in the lithium ion secondary battery 20 of Example 1 and Example 2, the short circuit location was recognized by the axial center vicinity on the extension line | wire of the crushing direction (refer FIG. 4). The cause of the short circuit at this time was that the separator was deformed and broken, and the positive and negative electrode mixture contacted. Since the rod-shaped member 21 and the metal member 25 are inserted in the hollow portion of the shaft core 1, the deformation of the shaft core 1 is small, and no short circuit is observed in the vicinity of the horizontal axis when the crushing direction is vertical. It was.

  As shown in Table 1, in the lithium ion secondary battery of Comparative Example 1, the short circuit resistance was 1Ω or less. On the other hand, in the lithium ion secondary battery 20 of Example 1 and Example 2, short circuit resistance became 10-100 ohms, and it was confirmed that it is larger than the battery of the comparative example 1. From this result, in the battery of Comparative Example 1, the aluminum foil of the positive electrode current collector and the rolled copper foil of the negative electrode current collector were in direct contact, whereas in the batteries of Example 1 and Example 2, the positive and negative electrode current collectors were in contact. It is considered that the electrical conductors were not in direct contact with each other, and a short circuit occurred due to contact between the positive electrode mixture and the negative electrode mixture. From these things, it turned out that a short circuit location (range which a short circuit generate | occur | produces) can be controlled by inserting the rod-shaped member 21 and the metal member 25 in the hollow part of the axial core 1. FIG. It has also been found that by inserting the rod-like member 21 and the metal member 25 into the hollow portion of the shaft core 1, the short-circuit resistance is increased and the current flowing through the short-circuit point can be reduced.

(Test 2)
About each battery of an Example and a comparative example, after charging to 4.1V, the safety when deform | transforming was evaluated. For deformation, the battery after charging is horizontally laid and fixed, a stainless steel semi-cylindrical crushing jig having a diameter equal to the diameter of the battery container 7 is pressed, and the diameter of the battery container 7 is reduced by a hydraulic press. A crushing test was conducted by crushing until crushing. The test was carried out five times for each battery. When only the cleavage valve (safety valve) 11 and the cleavage groove at the bottom were operated, “no rupture”, the caulking part of the battery lid was detached or the battery container 7 was opened. The number of batteries was counted as “ruptured” when it was torn at a portion other than the cleavage groove. The measurement results of Test 2 are shown in Table 2 below.

  As shown in Table 2, in the lithium ion secondary battery of Comparative Example 1, bursting occurred in the total number of batteries tested, whereas in the lithium ion secondary battery 20 of Example 1 and Example 2, bursting occurred. No ignition was confirmed. From this result, it has been found that inserting the rod-like member 21 and the metal member 25 into the hollow portion of the shaft core 1 improves the safety when the battery is abnormally deformed by an external pressure.

  The present invention contributes to the manufacture and sale of wound secondary batteries in order to provide a wound secondary battery that can moderate the behavior of abnormal battery deformation due to external pressure. Has industrial applicability.

It is sectional drawing which shows the cylindrical lithium ion secondary battery of embodiment to which this invention is applied. It is sectional drawing which shows the state by which the rod-shaped member was inserted in the hollow part of the axial center of the cylindrical lithium ion secondary battery of embodiment. It is sectional drawing which shows a short circuit location when the conventional cylindrical lithium ion secondary battery is crushed. It is sectional drawing which shows a short circuit location when the cylindrical lithium ion secondary battery of embodiment is crushed. It is sectional drawing of the metal member which can be inserted in the hollow part of an axial center.

Explanation of symbols

1 Shaft core 6 Electrode group 20 Cylindrical lithium ion secondary battery (winding type secondary battery)
21 Bar-shaped member (support member)
25 Metal member (support member)

Claims (4)

In a wound secondary battery having a group of electrodes in which positive and negative electrode plates each coated with a mixture are wound on the outside of the shaft core, the shaft core is formed with a circular or non-circular hollow portion And a support member having a cross-sectional area smaller than a cross-sectional area of the hollow portion and having a rigidity equal to or greater than a rigidity of the shaft core. Is inserted so as to extend over the entire length of the shaft core .   The wound secondary battery according to claim 1, wherein the support member is a synthetic resin or a metal.   The wound secondary battery according to claim 1 or 2, wherein the support member has a solid rod shape. Wound type secondary battery according to any one of claims 1 to 3, characterized in that the outer peripheral surface of the support member has a shape along the inner peripheral surface of the axis.

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