JP2007258132A - Secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery made to have enough tracking ability to a lower current collector connected through a welding point to a metal case with a bottom, and having excellent a large-current discharge property hardly deteriorating a connection state in an operating environment such as an electric tool or an electric vehicle, in which excessive vibrations or shocks are added. <P>SOLUTION: The secondary battery is provided with slits 34 extended in a plurality of radiation directions and coupled with a lower part current collector 31 at a center part, and a welding point 32 with a metal case with a bottom 27 is provided at a tongue piece 35 with rich flexibility surrounded by slits 34. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a secondary battery, and more particularly to a current collecting structure thereof.

  There are various types of secondary batteries, but nickel-metal hydride storage batteries and lithium ion secondary batteries are typical. Since these secondary batteries are highly reliable and easy to maintain, they are widely used in various applications such as power supplies for mobile phones and notebook computers. In recent years, there has been a demand for the development of a secondary battery having excellent vibration resistance and suitable for large current discharge as a power source for electric tools, electric assist bicycles, electric motorcycles, and electric vehicles.

  A secondary battery suitable for such a large current discharge has a positive electrode plate made of a strip-like positive electrode core material and a positive electrode active material, and a negative electrode plate made of a negative electrode core material and a negative electrode active material with a separator for separation interposed therebetween. The electrode plate group is formed by overlapping and winding the whole in a spiral shape, and this electrode plate group is housed in a metal bottomed case together with the electrolytic solution.

  In addition, as a current collecting structure suitable for large current discharge, the upper current collector is welded to the exposed portion of the positive electrode core material protruding from the upper end surface of the electrode plate group at a plurality of locations, and protrudes from the lower end surface of the electrode plate group. The lower current collector is welded at a plurality of locations to the exposed portion of the negative electrode core member.

  FIG. 5 is a partially cutaway perspective view showing a configuration example of a conventional cylindrical secondary battery, and FIG. 6 is a plan view of a conventional lower current collector.

  As shown in the figure, the strip-shaped positive electrode plate 1 and the negative electrode plate 2 are spirally wound via a separator 6 to constitute an electrode plate group 5. An exposed portion of the negative electrode core member 4 protruding from the lower end surface of the electrode plate group 5 and a burring portion 13 bent above the lower current collector 11 are welded at a plurality of locations. The lower current collector 11 is connected to the electrode plate group 5. In addition, it is housed in a metal bottomed case 7.

  The exposed portion of the positive electrode core member 3 protruding from the upper end surface of the electrode plate group 5 and the upper current collector 10 welded at a plurality of locations are electrically connected to the sealing member 9 via the connection leads 8, and the lower current collector 10. The electric body 11 and the metal bottomed case 7 are formed by inserting a welding electrode rod into the hole 10a formed in the central portion of the upper current collector 10 and the hollow portion 5a on the winding start side of the electrode plate group 5, It is resistance welded to the bottom surface of the bottomed case 7 made of metal through a projection (welding point 12) of the current collector 11. This resistance welding is performed with the lower current collector 11 and the bottom surface of the metal bottomed case 7 sandwiched between the welding electrode rod and the welding electrode disposed on the bottom surface of the metal bottomed case 7.

  However, in such a connected state of the lower current collector 11 and the metal bottomed case 7, the power source for electric tools, electric assist bicycles, electric motorcycles, electric vehicles and the like that are particularly required to have vibration resistance and large current discharge characteristics. When used, there is a concern that the welding point 12 between the lower current collector 11 and the metal bottomed case 7 is peeled off due to the excessive vibration and the current collecting property is lowered.

  As a means for solving such a problem, the rigidity of the central portion of the lower current collector 11 is made lower than that of other portions to give elasticity, and the vibration applied to the welding point 12 by this elastic deformation is buffered. A method for preventing the welding point 12 from peeling is proposed.

FIG. 7 shows a plan view of another conventional lower current collector. As a function of following the swelling of the bottom surface of the metallic bottomed case 7, a plurality of slits 14 are formed radially in the lower current collector 11, and a portion 15 is provided with elasticity by making the rigidity lower than other portions. The central portion is welded to the metal bottomed case 7 via the welding point 12 (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2001-256594

  However, in such a method in which a plurality of slits 14 are radially formed in the lower current collector 11 and the rigidity in the vicinity of the slits 14 is made lower than that in other portions, an environment in which excessive vibration and impact are continuously applied. In this case, the followability of the portion where the rigidity is lowered is insufficient, and the connection portion between the lower current collector 11 and the metal bottomed case 7 connected via the welding point 12 is peeled off and connected. May become unstable, resulting in a decrease in current collecting performance and a decrease in the large current discharge characteristics of the secondary battery.

  The present invention solves the above-described conventional problems, and sufficiently follows a lower current collector connected to a metal bottomed case through a welding point even in an environment where excessive vibration and impact are continuously applied. It is an object of the present invention to provide a secondary battery excellent in high-current discharge characteristics that has a high conductivity and does not deteriorate the connection state.

  In order to solve the above-described problems, the present invention provides a positive electrode plate and a negative electrode plate which are provided with an active material layer while leaving one end face in the width direction of the belt-like core material so that the protruding sides of the core material face each other. An electrode plate group wound through a separator, a lower current collector made of a flat plate connected to one of the electrode plate groups, a metal bottom case housing an electrolyte, and the metal A secondary battery comprising a sealing body that seals an upper portion of a bottom case, wherein the lower current collector is provided with a plurality of slits extending in a radial direction and connected at a central portion, and is surrounded by the slits. Further, the present invention is characterized in that a welding point with the metal bottomed case is provided on a highly flexible tongue piece.

  With this configuration, the lower current collector can have sufficient followability, so that the welding point between the lower current collector and the bottom of the metal bottomed case is not affected by continuous excessive vibration or shock. An effect of suppressing a decrease in connection state such as peeling can be achieved.

  According to the present invention, the positive electrode plate and the negative electrode plate, which are provided with the active material layer while leaving one end face in the width direction of the belt-like core material, are wound via the separator so that the protruding sides of the core material face each other. An electrode plate group, a lower current collector made of a flat plate connected to one of the electrode plate groups, an upper current collector made of a flat plate connected to the other electrode plate group, and an electrolyte A secondary battery comprising a metal bottomed case and a sealing body that seals an upper portion of the metal bottomed case, wherein a plurality of the lower current collectors extend in a radial direction and are connected at a central portion. By providing a structure having a welded point with the metal bottomed case on a flexible tongue piece surrounded by each slit, continuous excessive use such as a power source for an electric vehicle is provided. Low connection between the lower current collector and the bottom of the metal bottom case against vibration and shock Suppressed, the secondary battery current collecting property and excellent large current discharge characteristic does not decrease is obtained.

In the present invention, the positive electrode plate and the negative electrode plate provided with the active material layer while leaving one end face in the width direction of the belt-like core material are wound through the separator so that the protruding side of the core material faces each other. An electrode plate group, a lower current collector made of a flat plate connected to one of the electrode plate groups, an upper current collector made of a flat plate connected to the other electrode plate group, and an electrolyte A secondary battery comprising a metal bottomed case and a sealing body that seals an upper portion of the metal bottomed case, wherein a plurality of the lower current collectors extend in the radial direction and are connected at the center. A slit is provided, and a flexible tongue piece surrounded by the slits is provided with a welding point with the metal bottomed case.

According to this configuration, the flexible tongue surrounded by the slits absorbs vibration and shock against continuous excessive vibration and shock, and the lower current collector and the metal bottom case As a result, the secondary battery excellent in the high-current discharge characteristics in which the current collecting property does not deteriorate can be obtained without the weld point with the bottom of the metal layer being peeled off.
In addition, even when the internal pressure of the battery rises, such as when the battery is overcharged, and the bottom surface of the metal bottomed case swells, the lower current collector is flexible when connected to the metal bottomed case via a welding point. Since the rich tongue piece can follow the deformation of the bottom surface of the metal bottomed case, the stress applied to the welding point is relaxed, and the effect of improving the problem that the welding point peels off and the contact resistance value increases can be obtained. .

  Moreover, it is preferable to provide a welding point near the part where the slits of the lower current collector are connected.

  Thus, if a welding point is provided near the portion where the slits of the lower current collector are connected, the flexible tongue can further absorb vibrations and shocks, and the presence of metal Even in a state where the bottom surface of the bottom case swells, the effect of further increasing the allowable stress at the welding point can be obtained. In addition, by bringing the welding point closer to the center of the lower current collector, the space of the hole formed in the central portion of the upper current collector and the hollow portion on the winding start side of the electrode plate group can be reduced. Since more active material can be stored in the bottomed case, the battery capacity is increased.

  Moreover, it is preferable to provide three or more slits.

  As described above, by providing three or more slits, the distortion and twist of the slit with respect to vibration and impact are facilitated, so that the effect of greatly improving the flexibility of the tongue piece can be obtained. As the number of slits is increased, the interval between the slits is reduced, so that an effect of increasing the flexibility of the tongue piece surrounded by the slits can be obtained.

  Moreover, it is preferable to provide a projection at a position to be a welding point.

  Thus, the effect of further increasing the welding strength can be obtained by welding the lower current collector and the bottom surface of the metal bottomed case through the projection.

  FIG. 1 is a partially cutaway perspective view showing a configuration example of a cylindrical secondary battery of the present invention, FIG. 2 is a perspective view of a lower current collector showing an embodiment of the present invention, and FIG. 3 is a plan view thereof. FIG. 4 is a plan view showing another embodiment of the present invention.

  The strip-shaped positive electrode core material 23 forms the positive electrode plate 21 provided with the positive electrode active material layer while leaving one end face in the width direction. Similarly, the strip-shaped negative electrode core material 24 leaves the one end face in the width direction. The negative electrode plate 22 provided with is formed. The positive electrode plate 21 and the negative electrode plate 22 are wound in a spiral shape via a separator 26 so that the positive electrode core material 23 and the negative electrode core material 24 are opposed to each other, thereby forming an electrode plate group 25.

  The exposed portion of the negative electrode core member 24 protruding from the lower end surface of the electrode plate group 25 and the burring portion 33 bent above the lower current collector 31 are welded at a plurality of locations. In addition, it is housed in a metal bottomed case 27.

As shown in FIG. 2, FIG. 3 or FIG. 4, the lower current collector 31 is formed with a plurality of slits 34 extending in the radial direction and connected at the central portion, so that the lower current collector 31 is flexible at the central portion. It is characterized in that three or four rich tongue pieces 35 are provided. The lower current collector 31 shown in FIGS.
Each of the three slits 34 extending in the radial direction and connected at the center is formed so that each angle is about 120 °, and three flexible tongue pieces 35 surrounded by the slits 34 are provided. Yes. The lower current collector 31 shown in FIG. 4 is formed such that each angle of the four slits 34 extending in the radial direction and connected at the center is about 90 °, and is surrounded by the slits 34. Four tongue pieces 35 rich in nature are provided.

  The lower current collector 31 is provided with a plurality of notch portions 33a having a predetermined width in a radial manner, and burring portions 33 that protrude upward are provided at both side edges of the notch portion 33a. The burring portion 33 is welded in a state where the burring portion 33 is bitten into the negative electrode core member 24 of the negative electrode plate 22 protruding below the electrode plate group 25, thereby connecting the negative electrode plate 22 and the lower current collector 31 with a low resistance value. be able to.

  On the other hand, the exposed portion of the positive electrode core member 23 protruding from the upper end surface of the electrode plate group 25 and the upper current collector 30 welded at a plurality of locations are connected to the sealing member 29 via the connection lead 28.

  The lower current collector 31 and the metal bottomed case 27 are formed by inserting a welding electrode rod into the hole 30a formed in the central portion of the upper current collector 30 and the hollow portion 25a on the winding start side of the electrode plate group 25. Resistance welding is performed via a welding point 32 in a state where the lower current collector 31 and the bottom surface of the metal bottomed case 27 are clamped between welding electrodes arranged to receive the bottom surface of the bottomed case 27 made of metal. .

  A ring-shaped insulating plate 36 is placed on the periphery of the upper surface of the upper current collector 30 to prevent an internal short circuit with the metal bottomed case 27, and a groove is formed on the upper side surface of the metal bottomed case 27. Then, the electrode plate group 25 is held in the metal bottomed case 27.

  Next, a predetermined amount of alkaline electrolyte is injected into the metal bottomed case 27 using the holes 30a of the upper current collector 30, the connection leads 28 are bent, and the sealing body 29 is placed on the groove. And the opening part of the upper end of the metal bottomed case 27 is crimped inward, and a cylindrical alkaline storage battery is produced.

  Further, the secondary battery configured in this manner is also suitable for use as a battery pack containing a plurality of these.

  In the battery pack, a plurality of secondary batteries are connected in series or in parallel and used as a power source for electric tools, electric assist bicycles, electric motorcycles, electric vehicles and the like. In this case, particularly, the secondary batteries connected in series transmit stronger vibrations and impacts to the vertical vibrations. Even under such conditions, the flexible tongue piece 35 formed by the slit 34 of the lower current collector 31 absorbs vibration and shock, and the bottom of the lower current collector 31 and the metal bottomed case 27 Thus, an effect of providing a battery pack excellent in the large current discharge characteristics in which the current collecting property does not deteriorate can be obtained.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the figure shown here is an example, Comprising: If it has the structure represented to the claim of this invention, the same effect can be acquired.

Example 1
The positive electrode core material 23 of the positive electrode plate 21 made of sintered nickel having a thickness of 1.0 mm protrudes upward 1.5 mm, and the negative electrode core material 24 of the negative electrode plate 22 made of paste type cadmium having a thickness of 0.70 mm downward. An electrode plate group 25 having a height of 50.8 mm was formed by projecting 1.5 mm and spirally wound through a separator 26.

  A connection lead 28 made of low carbon steel having a width of 13.0 mm and a plate thickness of 0.4 mm was welded to the upper surface of the upper current collector 30 made of low carbon steel having a plate thickness of 0.30 mm and an outer diameter of 30.0 mm. .

  A burring portion (not shown) projecting downward is formed on the lower surface of the upper current collector 30, and the burring portion and the tip of the positive electrode core member 23 projecting upward from the electrode plate group 25 are welded. . Similarly, the burring portion 33 of the lower current collector 31 having a plate thickness of 0.30 mm and an outer diameter of 30.0 mm was welded to the tip portion of the negative electrode core member 24 protruding downward from the electrode plate group 25.

  The electrode plate group 25 in which the upper current collector 30 and the lower current collector 31 are welded is inserted into a metal bottomed case 27 having an outer diameter of 32.5 mm and a plate thickness of 0.48 mm. The lower current collector 31 was resistance welded. A sealing body 29 having an outer diameter of 31.0 mm and a plate thickness of 0.50 mm was resistance-welded to one of the connection leads 28 welded to the upper current collector 30.

  A ring-shaped insulating plate 36 made of resin and having an outer diameter of 30.8 mm is placed on the periphery of the upper surface of the upper current collector 30 to prevent an internal short circuit with the metal bottomed case 27, and the metal bottomed Grooves were formed on the upper side surface of the case 27 to hold the electrode plate group 25 in the metal bottomed case 27.

  Next, a predetermined amount of alkaline electrolyte is injected into the metal bottomed case 27 using the holes 30a of the upper current collector 30, the connection leads 28 are bent, and the sealing body 29 is placed on the groove. And the opening part of the upper end of the metal bottomed case 27 was crimped inward, and the cylindrical alkaline storage battery was produced. This cylindrical alkaline storage battery has a diameter of 32.5 mm, a height of 60.3 mm, and a nominal capacity of 5000 mAh.

  As shown in FIGS. 2 and 3, the lower current collector 31 was formed by connecting three slits 34 extending in the radial direction at the center. The slit 34 has a length from the connected central part of 4.0 mm and a width dimension of 0.4 mm, and is provided with three flexible tongue pieces 35 arranged radially at substantially equal intervals. A welding point 32 was provided on the tongue 35 at a position about 1 mm from the center of the lower current collector 31.

(Example 2)
A cylindrical alkaline storage battery produced in the same manner as in Example 1 except that a projection was provided on the lower current collector 31 and a welding point 32 was provided via this projection was designated as Example 2. The diameter of the projection was 0.6 mm.

(Example 3)
As shown in FIG. 4, a cylindrical alkaline storage battery produced in the same manner as in Example 1 except that four slits 34 extending in the radial direction were provided and a flexible tongue 35 was provided at four locations. Was taken as Example 3.

Example 4
A cylindrical alkaline storage battery produced in the same manner as in Example 3 except that a projection was provided on the lower current collector 31 and a welding point 32 was provided via this projection was designated as Example 4. The diameter of the projection was 0.6 mm.

(Comparative Example 1)
As shown in FIG. 6, it was produced in the same manner as in Example 1 except that a slit was not provided, a projection having a diameter of 1.2 mm was provided at the center, and a welding point 12 was provided via this projection. A cylindrical alkaline storage battery was used as Comparative Example 1.

(Comparative Example 2)
As shown in FIG. 7, six slits 14 having a length of 3.0 mm and a width dimension of 0.4 mm from the central portion of the lower current collector 11 are arranged radially at substantially equal intervals. A cylindrical alkaline storage battery produced in the same manner as in Comparative Example 1 was used as Comparative Example 2 except for the above.

  The cylindrical alkaline storage battery produced as described above was subjected to an elastic test and a vibration / drop impact test of the lower current collector.

<Elasticity test of lower current collector>
In order to confirm the followability of the lower current collector resistance-welded to the inner bottom surface of the metal bottomed case, in Examples 1 to 4 and Comparative Examples 1 and 2, a dummy sealed with a sealing body without injecting an alkaline electrolyte 30 batteries were produced.

(1) Confirmation of fracture of welding point A hole having a diameter of about 3 mm was formed near the center of the sealing body of the dummy battery, and a metal pipe for sending atmospheric pressure was connected to this hole. The connection of the metal pipe was secured by soldering the periphery of the connection part so that the atmospheric pressure did not leak. Through this metal pipe, an internal pressure of 3 MPa is applied to the metal bottomed case to forcibly deform the bottom surface of the metal bottomed case, and the bottom surface of the metal bottomed case and the welding point of the lower current collector are visually observed. The presence or absence of fracture (disconnection) of the weld point was evaluated.

(2) Contact resistance variation measurement The contact resistance variation before and after the elastic test of the dummy battery was measured. The contact resistance before the elastic test was measured by welding the lower current collector to the metal bottomed case before sealing with the sealing body, and then inserting the measuring terminal of the resistance measuring instrument into the hollow part of the electrode plate group. The contact resistance of the welding point was measured by pressing against the upper surface of the metal plate and pressing the other measurement terminal so as to be sandwiched from the bottom surface of the metal bottomed case. The contact resistance after the elasticity test was measured in the same manner after the sealing body was removed, but those whose resistance could not be measured because the weld point was broken by the elasticity test were omitted from the data. For the measurement of the contact resistance, a micro-resistance meter (milliohm meter, manufactured by Hewlett Packard) was used to calculate an average value of 20 pieces before and after the elastic test, and comparatively evaluated the variation rate.

<Vibration / drop impact test>
In order to confirm the large current discharge characteristics when assuming a use environment in which excessive vibration and impact are continuously applied, 400 cylindrical alkaline storage batteries of Examples 1 to 4 and Comparative Examples 1 and 2 were produced, and the circuit was opened. 200 pieces each were used for voltage fluctuation measurement and for large current discharge capacity fluctuation measurement.

  The conditions of the vibration / drop impact test are as follows. After each cylindrical alkaline storage battery is fully charged, a vibration test with a frequency of 10 to 110 Hz and a total amplitude of 3.2 mm is continuously performed in the vertical direction of the battery for a total of 96 hours. Was dropped from the height of 1.0 m onto the surface of the hard concrete 30 times in the vertical direction of the cylindrical alkaline storage battery.

(3) Fluctuation measurement of open circuit voltage 200 open circuit voltages of each cylindrical alkaline storage battery before and after the vibration / drop impact test were measured, and a battery whose drop in open circuit voltage after the vibration / drop impact test was 25 mV or more was reduced in voltage. Judged as.

(4) Fluctuation measurement of large current discharge capacity Measure the discharge capacity of each cylindrical alkaline storage battery before and after the vibration / drop impact test 200 times and measure the change in the average discharge capacity before and after the vibration / drop impact test. Comparative evaluation was made.

This variation in the discharge capacity is the same as the discharge capacity when the battery before the vibration / drop impact test is fully charged and continuously discharged to a discharge end voltage of 0.3 V at a constant current of 100 A, and then fully charged in the same manner. After the vibration / drop impact test, the battery was measured for fluctuations with the discharge capacity when continuously discharged to the final discharge voltage under the same conditions. These charging / discharging was performed in a normal temperature atmosphere (23 ± 2 ° C.).

  The results of the elasticity test of the lower current collector and the vibration / drop impact test are shown in Table 1.

As shown in (Table 1), a plurality of slits 34 extending in the radial direction and connected at the central portion are provided in the lower current collector 31, and a flexible tongue piece 35 surrounded by the slits 34. The first to fourth examples in which the welding point 12 with the metal bottomed case 27 is provided on the bottom are clearly compared with the comparative examples 1 and 2 in which such tongue pieces are not provided. It was also confirmed that the vibration / drop impact test results were good.

  There were no breaks in the weld points after the elastic test in Examples 1 to 4, whereas Comparative Example 1 had 8 breaks in 30 and Comparative Example 2 had 4 breaks in 30. There was.

  It is considered that this is because the lower current collector 11 of Comparative Example 1 cannot follow the deformation of the bottom of the metal bottomed case 7 and the welding point 12 was easily broken. Further, since the lower current collector 11 of the comparative example 2 has the slits 14 radially, the slits 14 follow the deformation of the bottom of the metal bottomed case 7, and as a result, the welding point 12 is not broken. It seems that it has decreased. However, since there were four breaks, it was found that the followability to the deformation of the bottom portion of the metal bottomed case 7 was insufficient. On the other hand, in each of Examples 1 to 4, since each slit 34 is connected at the substantially central portion of the lower current collector 31, it is considered that the followability to the deformation of the bottom portion of the metal bottomed case 27 is excellent. It is done.

  The variation rate of the contact resistance before and after the elasticity test was 1% to 4% in the increase rate of the contact resistance in Examples 1 to 4, whereas that in Comparative Example 1 was increased by 26%. Rose 11%.

  Thus, it is thought that the reason why the increase rate of the contact resistance in Comparative Examples 1 and 2 is large is the same as that in the above-described weld fracture. Even if it is not completely broken, it is considered that the electrical connection state has decreased.

  Moreover, according to Examples 1-4, it turns out that the increase rate of the contact resistance of Example 2 and Example 4 which provided the projection tends to be small compared with Example 1 and Example 3 which did not provide the projection. It was. This is presumably because resistance welding through the projection suppresses the invalid current shunting and stabilizes the welding strength.

As for open circuit voltage fluctuation before and after the vibration / drop impact test, Examples 1 to 4 had no voltage fluctuation of 25 mV or more, whereas Comparative Example 1 was 12 out of 200, and Comparative Example 2 was 3 out of 200. Individual voltage fluctuations were confirmed. When this voltage drop product was disassembled, the welding point 12 between the lower current collector 11 and the metal bottomed case 7 was slightly broken, and it was confirmed that the connection was clearly unstable. Therefore, it is considered that the contact resistance between the lower current collector 11 and the metal bottomed case 7 became unstable and a large voltage fluctuation occurred.

  The fluctuation of the large current discharge capacity before and after the vibration / drop impact test was 13 to 30 mAh in Examples 1 to 4, whereas that in Comparative Example 1 was 247 mAh, and that in Comparative Example 2 was 331 mAh. . According to Examples 1 to 4, it is considered that the fluctuation of the large current discharge capacity is small because the fluctuation of the contact resistance is small. In particular, in Example 2 and Example 4, since the lower current collector 31 is provided with a projection, it is considered that the fluctuation of the large current discharge capacity is further reduced.

  On the other hand, the reason why the large current discharge capacity of Comparative Example 1 is reduced may be the fluctuation of the contact resistance of the welded part 12 due to the vibration / drop impact test.

  The reason why the large current discharge capacity of Comparative Example 2 is greatly reduced is that the radial slits 14 formed around the welding point 12 of the lower current collector 11 are gathered by the lower current collector 11 in addition to the influence due to the fluctuation of the contact resistance. This is thought to be due to a reduction in the current area and current collection path. Since the electrode plate group 5 and the metal case 7 are electrically connected via the lower current collector 11, the current collection area and the current collection path of the lower current collector 11 are reduced in this way. It is considered that the efficiency is lowered, and the reduction of the discharge capacity is increased particularly in the case of large current discharge.

  Moreover, when the battery with a large decrease in the large current discharge capacity of Comparative Example 2 was disassembled, it was found that the vicinity of the welding point 12 of the lower current collector 11 was partially melted. It is considered that this is because the part resistance value of the lower current collector 11 is partially concentrated and increased during a large current discharge, and excessive heat generation is generated in this resistance increasing portion, so that it is blown out.

  According to the first to fourth embodiments, the lower current collector 31 is provided with a plurality of slits 34 extending in the radial direction and connected at the center, and the flexible tongue piece 35 surrounded by the slits 34 is made of metal. Since the welding point 32 with the bottomed case 27 is provided, the energization path between the lower current collector 31 and the metal bottomed case 27 is dispersed even in a large current discharge test after an excessive vibration / drop test, and the lower current collection is performed. It is considered that the component resistance value of the electric body 31 does not increase due to partial concentration.

  In addition, even if the tongue piece 35 rich in flexibility was provided at 5 to 8 places, the same or better effect was obtained. However, it is difficult to provide a large number of slits 34 in the lower current collector 31, and if a large number of slits 34 are provided, the space between the slits 34 becomes small, so that welding becomes difficult and the efficiency of the welding process is improved. Because of the reduction, up to about eight tongue pieces 35 are considered appropriate for battery sizes currently in practical use.

  The secondary battery of the present invention is useful as a power source for electric tools, electric assisted bicycles, electric motorcycles, electric vehicles, and the like that require excellent vibration resistance and large current discharge characteristics.

Partially cutaway perspective view showing a configuration example of a cylindrical secondary battery of the present invention The perspective view of the lower collector which showed one example of the present invention The top view of the lower collector which showed one example of the present invention The top view of the lower electrical power collector which showed other examples of the present invention Partially cutaway perspective view showing a configuration example of a conventional cylindrical secondary battery Plan view of conventional lower current collector Plan view of another conventional lower current collector

Explanation of symbols

DESCRIPTION OF SYMBOLS 21 Positive electrode plate 22 Negative electrode plate 23 Positive electrode core material 24 Negative electrode core material 25 Electrode plate group 25a Hollow part 26 Separator 27 Metal bottomed case 28 Connection lead 29 Sealing body 30 Upper collector 30a Hole 31 Lower collector 32 Welding Point 33 Burling part 33a Notch part 34 Slit 35 Tongue piece 36 Insulating plate

Claims (4)

An electrode plate group in which a positive electrode plate provided with an active material layer leaving one end face in the width direction of the belt-shaped core material and a negative electrode plate are wound through a separator so that the protruding sides of the core material face each other; A bottomed current collector made of a flat plate connected to one of the electrode plate group, an upper current collector made of a flat plate connected to the other of the electrode plate group, and a metal bottomed case containing an electrolyte therein And a sealing battery that seals the upper part of the metal bottomed case,
The lower current collector is provided with a plurality of slits extending in the radial direction and connected at the center, and a flexible tongue piece surrounded by the slits is provided with a welding point with the metal bottomed case. Secondary battery provided.   The secondary battery according to claim 1, wherein a welding point is provided near a portion where the slit of the lower current collector is connected.   The secondary battery according to claim 1, wherein the number of slits is three or more. The secondary battery of Claim 1 which provided the projection in the position used as the said welding point.