Patent ID: 12211973

DETAILED DESCRIPTION

Embodiments of the present disclosure will be explained below. Any features other than the matter specifically set forth in the present specification and that may be necessary for carrying out the present disclosure can be regarded as design matter for a person skilled in the art based on conventional techniques in the relevant technical field. That is, the present disclosure can be realized on the basis of the disclosure of the present specification and common technical knowledge in the relevant technical field. In the drawings that accompany the explanation below, members and portions that elicit identical effects are explained while denoted by identical reference numerals. The dimensional relationships (length, width, thickness and so forth) in the figures do not necessarily reflect actual dimensional relationships. The reference symbol X in the figures denotes a “width direction”, the reference symbol Y denotes a “depth direction”, and the reference symbol Z denotes a “height direction”. These directions are defined however for convenience of explanation, and are not intended to limit the manner in which a secondary battery is arranged, during use or manufacture.

The term “secondary battery” in the present specification signifies a power storage device in general in which charge and discharge reactions occur as a result of movement of charge carriers across a pair of electrodes (positive electrode and negative electrode) via an electrolyte. Such secondary batteries include so-called storage batteries such as lithium ion secondary batteries, nickel-metal hydride batteries and nickel cadmium batteries, as well as capacitors such as electric double layer capacitors. The technology disclosed herein is not limited to a specific type of secondary battery, and can be widely used in secondary batteries in general that are provided with a wound electrode body and with a collector terminal.

1. Structure of the Secondary Battery

The structure of a secondary battery according to the present embodiment will be explained hereafter with reference toFIG.1toFIG.5.FIG.1is a front-view diagram illustrating schematically the internal structure of a secondary battery according to the present embodiment.FIG.2is a perspective-view diagram illustrating schematically a wound electrode body in the present embodiment.FIG.3is a side-view diagram illustrating schematically a connection portion of a wound electrode body and a collector terminal of the secondary battery according to the present embodiment.FIG.4is a front-view diagram illustrating schematically a connection portion of the wound electrode body and the collector terminals of the secondary battery according to the present embodiment.FIG.5is cross-sectional diagram as viewed from arrow V-V inFIG.4.

As illustrated inFIG.1, in a secondary battery1according to the present embodiment a wound electrode body20and an electrolyte (not shown) are accommodated inside a case10. Further, external terminals40connected to an external device such as a vehicle motor are attached to the outer surface of the case10. In the secondary battery1according to the present embodiment the wound electrode body20and each external terminal40are electrically connected via a respective collector terminal30. The secondary battery1having such a configuration will be specifically explained next.

(1) Case

The structure of the case10is not particularly limited as long as the case10can accommodate the wound electrode body20and an electrolyte (not shown). For instance a flat square case10is used in the secondary battery1having the structure illustrated inFIG.1. The case10includes a box-shaped case body12having an open top face and a lid body14that plugs the top face opening of the case body12. The material of the case10is not particularly limited, and a material having a predetermined strength can be used herein, without limitations. Examples of the material of the case10include aluminum (typically an aluminum alloy).

(2) Terminal Structure

As described above, the external terminals40which are connection members for connecting the secondary battery1and an external device are attached to the outer surface of the case10(lid body14). The external terminals40are electrically connected to the wound electrode body20inside the case10via the collector terminals30. Specifically, each collector terminal30is an elongated plate-like member extending in a height direction Z. A lower end portion30aof the collector terminal30is connected to the wound electrode body20. Meanwhile, an upper end portion30bof each collector terminal30runs through the case10(lid body14) and is exposed outside the case10. The upper end portion30bof the collector terminal30is connected to the external terminal40via an external connection member42. A width dimension (length in a width direction X) of the collector terminals30is preferably about 5 mm to 10 mm A sufficient connection surface area with the wound electrode body20can be ensured as a result.

(3) Wound Electrode Body

As illustrated inFIG.2, the wound electrode body20includes a pair of electrode sheets50each made up of a positive electrode sheet and a negative electrode sheet. Each electrode sheet50of the pair thereof includes a collector52, an electrode mix layer54, and an uncoated portion56. The collector52is an elongated foil-shaped conductive member. The thickness of the collector52can be set to 10 μm to 150 μm (for instance about 100 μm). Next, the electrode mix layer54is applied onto the surface of the collector52. The electrode mix layer54contains an active material being a particulate material that stores and releases charge carriers (for instance Li ions). In addition to the active material, the electrode mix layer54may contain additives such as a binder and a conductive material. Next, the uncoated portion56is a region at which the electrode mix layer54is not applied and the collector52is thus exposed. The uncoated portion56is formed on one side edge portion, in the width direction X, of the electrode sheet50. The material of each member (collector52and electrode mix layer54) that makes up the electrode sheet50is not particularly limited, and a conventionally known material can be selected, without particular limitations, in accordance with the polarity. As an example, to construct a lithium ion secondary battery there can be used an aluminum foil as the collector on the positive electrode side, and a lithium-transition metal complex oxide (for instance a lithium-nickel-cobalt-manganese complex oxide) as an active material on the positive electrode side. Meanwhile, a copper foil can be used as the collector on the negative electrode side of the lithium ion secondary battery, and a carbon-based material (for instance carbon black) can be used as an active material on the negative electrode side.

The wound electrode body20in the present embodiment is produced by forming a stack in which the pair of electrode sheets50is laid up across a separator70which is an insulating sheet, followed by winding of the resulting stack. A core portion22resulting from winding so that the electrode mix layers54of the pair of electrode sheets50face each other becomes thus formed, as a result, at the central portion of the wound electrode body20in the width direction X. In the wound electrode body20, moreover, each electrode sheet50is laid up so that the uncoated portion56of one electrode sheet50protrudes beyond the other electrode sheet50, at each side edge portion in the width direction X. As a result, a respective collector wound portion24becomes formed in that the uncoated portion56of one electrode sheet50is wound in a state of protruding from the other electrode sheet50, at both side edge portions of the wound electrode body20. In the secondary battery1provided with the wound electrode body20having such a configuration, the core portion22at which the electrode mix layers54face each other constitutes a main site for charge and discharge reactions, and the collector wound portion24resulting from winding of the uncoated portions56(collectors52) constitutes sites for connection to the respective collector terminal30(seeFIG.1). Although not meant to limit the technology disclosed herein, the overall width W1of the wound electrode body20illustrated inFIG.1is preferably from 290 mm to 300 mm, and a height dimension Z1of the wound electrode body20is from 90 mm to 100 mm. The maximum thickness of the wound electrode body20illustrated inFIG.3(thickness T1of the core portion22) is preferably from 36 mm to 39 mm

(4) Connection Structure of the Wound Electrode Body and the Collector Terminals

As illustrated inFIG.3, in the wound electrode body20of the present embodiment collector bundles26are formed in at least a partial region of respective collector wound portions24. Each collector terminal30is connected to a respective collector bundle26. Specifically, each collector bundle26is formed through pressing of part of the respective collector wound portion24(typically upper end portion of the collector wound portion24) so as to be pinched in a depth direction Y, and through squashing part of the collector wound portion24. The wound layers of the uncoated portions56(collectors52) in the collector bundle26are thus bundled and brought into close contact with each other. In the secondary battery1according to the present embodiment each collector bundle26and the lower end portion30aof the respective collector terminal30are connected in a state of surface contact therebetween. Thus a conductive path of superior conductivity (little electric resistance) can be formed through connection of the collector terminal30to the collector bundle26in which multiple layers of the collectors52are brought into close contact with each other. The means for connecting the collector bundle26and the collector terminal30to each other is not particularly limited, and a conventionally known connection means can be resorted to herein without particular limitations. Examples of such connecting means include ultrasonic bonding, laser welding and resistance welding.

As illustrated inFIG.4, an elongated slit28running through the respective collector wound portion24becomes formed, in the secondary battery1according to the present embodiment, between each collector bundle26and the core portion22, in the width direction X. Each slit28is formed continuously so as to conform to a respective collector bundle26, in the height direction Z. For instance, the slit28illustrated inFIG.4extends in the height direction Z so as to be substantially parallel to a respective collector bundle26. In the wound electrode body20having such a configuration, regions of the collector wound portions24positioned outward of the slits28are separated from the core portion22, as illustrated inFIG.4andFIG.5. As a result, strong tension that may occur at the time of the formation of a conventional convergence section125(seeFIG.9) does not arise in a case where the collector bundles26are formed through squashing of a region, of the collector wound portions24, separated from the core portion22, as illustrated inFIG.5. Therefore, the secondary battery1according to the present embodiment allows preventing detachment of the collector bundles26or the collector terminals30derived from breakage of the uncoated portions56(collectors52) present between the core portion22and the collector bundles26, and accordingly allows contributing to improving the yield of the secondary battery in the production process.

A length L2(seeFIG.4) of each slit28in the height direction Z is not particularly limited, and can be appropriately modified in accordance with the dimensions of the wound electrode body20and of the collector terminals30. For instance a ratio (L2/L1) of the length L2of the slit28relative to the length L1of the collector bundle26is preferably 1/4 or higher. By forming such a slit28of sufficient length it becomes possible to suitably prevent strong tension from acting on the collectors52between the collector bundle26and the core portion22. In the collector wound portions24of the secondary battery1according to the present embodiment, on the other hand, battery resistance may increase if the length L2of the slit28is made longer than necessary, since current flows so as to wrap around the slits28. From this point of view, the above ratio L2/L1is preferably 1 or lower, more preferably 1/2 or lower. A concrete length L2of the slit28is preferably from 50 mm to 100 mm. As illustrated inFIG.4, the term “length L1of the collector bundle26” in the present specification denotes a height dimension from an upper end24aof each collector wound portion24to the lower end30cof the respective collector terminal30.

As illustrated inFIG.4, each slit28in the present embodiment is formed at a region that includes the upper end24aof a respective collector wound portion24. As a result, all collector bundles26at the upper end portion in the height direction Z are separated from the core portion22, and accordingly it becomes possible to reliably prevent a large tension from acting on the collectors52that are present between each collector bundle26and the core portion22. Further, the distance from a side edge22aof the core portion22up to the slit28is preferably from about 1 mm to 2 mm Damage to the electrode mix layers54at the time of formation of the slit28can be properly prevented by providing thus a certain spacing between the side edge22aof the core portion22and the slit28.

A circular opening (termination hole28a) having a diameter larger than the width of the slits28is formed at an end of each slit28in the present embodiment. For instance the collectors52may break, so that the slit28accordingly extends, in a case where stress concentrates at the end of the slit28when an external force such as vibration acts on the collector wound portion24. When by contrast the termination hole28asuch as that described above is formed, stress acting on the end portion of the slit28can be dispersed, and accordingly the collectors52can be prevented from breaking so that the slit28extends. In a case specifically where the width of the slit28is from 1 mm to 2.5 mm, the diameter of the termination hole28ais preferably from about 2 mm to 5 mm, and more preferably from about 3 mm to 5 mm

(5) Volume of a Charge/Discharge Region

The secondary battery1according to the present embodiment is also advantageous in that the volume of the electrode mix layers54can be easily increased. Specifically, increasing the volume of the electrode mix layers included in the wound electrode body allows increasing the space efficiency of the secondary battery (i.e. the volume ratio of the charge/discharge region relative to the space in the case), and in consequence allows improving battery performance for instance in terms of battery capacity. When a wound electrode body having an increased volume of the electrode mix layers is used, however, a problem arises in that detachment of the collector bundle or the collector terminal is likely to occur due to the collector breakage. In the secondary battery1according to the present embodiment, by contrast, detachment of the collector bundles26or of the collector terminals30can be suitably prevented even when using a wound electrode body20having large-volume electrode mix layers54. The above will be explained specifically below.

Means for increasing the space efficiency of the secondary battery include means that involve increasing the width of the core portion (coated region of the electrode mix layer), which is the charge/discharge region, and reducing the width of the collector wound portions (uncoated portions). When using however such a wound electrode body having narrow collector wound portions, it is necessary to gather the collectors under very strong tension in order to form collector bundles of sufficient width so as to allow for connection of the collector terminals. As a result, the collectors break readily, and hence the collector bundles and the collector terminals may detach frequently, giving rise to a significant drop in yield. In the secondary battery1according to the present embodiment, by contrast, the core portion22and the collector bundles26are separated by the slits28, and hence collector bundles26of sufficient width can be formed, without strong tension acting on the collectors52between the core portion22and the collector bundle26, even if the width W2of the collector wound portions24is reduced. As an example, it is deemed that the collector bundles or the collector terminals detach frequently when the ratio of the width of the collector wound portions relative to the overall width of the wound electrode body is lower than 0.1. In the secondary battery1according to the present embodiment, by contrast, the collector bundles26and the collector terminals30can be suitably prevented from coming off even when a ratio (W2/W1) of the width W2of the collector wound portions24relative to the overall width W1of the wound electrode body20is 0.04 or lower. That is, the present embodiment allows producing a secondary battery1of high space efficiency and superior battery performance, without incurring drops in yield. A concrete dimension of the of the width W2of the collector wound portions24in the present embodiment is appropriately from about 5 mm to 10 mm.

Other means for increasing the space efficiency of the secondary battery include means that involve increasing the thickness of the electrode mix layers and means that involve increasing the number of times that the electrode sheets are wound. Also in cases where the thickness of the core portion is increased by relying on these means, however, strong tension acts readily on the collectors between the core portion and the collector bundles, and accordingly a drop in yield is likely to occur on account of detachment of the collector bundle or the collector terminal. In the secondary battery1according to the present embodiment, by contrast, the core portion22and the collector bundles26are separated by the slits28. As a result, it is possible to prevent strong tension from acting on the collectors52between the core portion22and each collector bundle26, even when the thickness T1of the core portion22is large. As an example, it is deemed that when in conventional secondary batteries a ratio of the thickness of the collector bundles relative to the thickness of the core portion is lower than 1/5, the collector bundles and the collector terminal start to detach, and that the frequency of detachment of the collector bundle or of the collector terminal increases significantly when the above ratio is below 1/10. In the secondary battery1according to the present embodiment, by contrast, the collector bundles26or the collector terminals30can be suitably prevented from detaching even when a ratio (T2/T1) of the thickness T2of the collector bundles26relative to the thickness T1of the core portion22is 1/5 or less (preferably 1/10 or less).

2. Method for Producing the Secondary Battery

The structure of the secondary battery1according to the present embodiment has been explained above. An example of a method for producing the secondary battery1having such a structure will be described next with reference to accompanying drawings.FIG.6is a plan-view diagram schematically illustrating an electrode sheet used in the production of a wound electrode body of the present embodiment.FIG.7is a side-view diagram for explaining the production of a wound electrode body in the present embodiment.FIG.8is a cross-sectional diagram for explaining connecting of a wound electrode body and a collector terminal in the present embodiment. The secondary battery disclosed herein is not limited to a secondary battery produced in accordance with the below-described production method.

As illustrated inFIG.6, in the production method according to the present embodiment firstly each electrode sheet50, which is a constituent member of the wound electrode body, is prepared, and then there are formed a plurality of elongated openings59extending in the longitudinal direction of the electrode sheet50, at each uncoated portion56of the electrode sheet50. In the present embodiment circular holes59aare created at this time at both ends of the elongated openings59. In the winding of the electrode sheet50described below, the intervals between the plurality of openings59are appropriately adjusted so that the openings59are stacked at a respective same position. The means for forming the openings59is not particularly limited, and means such as punching, cutting or laser melting can be resorted to without particular limitations.

In the production method according to the present embodiment, a pair of electrode sheets50is next laid up and wound, as illustrated inFIG.7. As a concrete procedure of that step, firstly there are prepared electrode supply units50A around which only a respective electrode sheet50is wound, and separator supply units70A around which only a respective separator70is wound. Then each electrode sheet50is paid out from the respective electrode supply unit50A, each separator70is paid out from the respective separator supply unit70A, and the tips of the electrode sheets50and of the separators70are attached to a cylindrical winding shaft WL. When the winding shaft WL is caused to rotate in this state, the electrode sheets50of the pair thereof become wound while being laid up on each other via the separators70. A cylindrical wound body20A is formed as a result on the outer periphery of the winding shaft WL. At this time the slits28running through respective collector wound portions24become formed (seeFIG.2) by virtue of the fact that the openings59of the respective electrode sheets50are stacked at a respective same position. The cylindrical wound body20A is then squashed in such a manner that the slits28are folded back at the upper ends24aof the collector wound portions24, to produce a flat wound electrode body20. As a result, respective elongated slits28extending in the height direction Z are formed in a region that includes the upper ends24aof the collector wound portions24, such that respective collector wound portion24A positioned outward of the slits28are separated from the core portion22. In the present embodiment the circular holes59aformed at both ends of the openings59are stacked at a respective same position, and as a result the termination holes28aare formed at both end regions of the slit28.

In the production method according to the present embodiment each collector wound portion24A separated from the core portion22is then squashed to thereby form a respective collector bundle26, as illustrated inFIG.8, whereupon the respective collector terminal30is connected to the collector bundle26. As a concrete procedure, firstly a region24A1adjacent to the slit28, in the collector wound portion24A separated from core portion22, is clamped between and fixed by a pair of foil pressing jigs P1. Next, the collector terminal30is arranged so as to be adjacent to the foil pressing jigs P1, and the collector wound portion24A and the collector terminal30are brought into surface contact with each other. The collector terminal30and the collector wound portion24A are then clamped between a pair of pressing jigs P2, and the collector wound portion24A separated from the core portion22is squashed. As a result, there is formed a collector bundle26in which multiple layers of collectors52are bundled together. The collector terminal30is then connected to the collector bundle26, to thereby elicit electrical connection between the wound electrode body20and the collector terminal30. In a case where the collector bundle26and the collector terminal30are to be ultrasonically bonded, preferably a horn is built into one jig of the pair of pressing jigs P2, with the other pressing jig P2serving as an anvil (receiving jig). The collector terminal30can be connected as a result while the collector bundle26is shaped by pressing.

As described above, in the production method according to the present embodiment the collector wound portions24A separated from the core portion22are squashed to thereby form the collector bundles26. As a result, it becomes possible to prevent strong tension from acting on the collectors52(uncoated portions56) that are present between the core portion22and the collector bundles26. Therefore, the production method according to the present embodiment allows preventing detachment of the collector bundles26or the collector terminals30derived from large breakage in the collectors52, and allows contributing to increasing the production yield of the secondary battery1.

3. Other Embodiments

One embodiment of the technology disclosed herein has been explained above. However, the above embodiment is not meant to limit the technology disclosed herein in any way. That is, the secondary battery disclosed herein can encompass various modifications to the secondary battery1according to the embodiment described above.

For instance, the slits28of the secondary battery1according to the embodiment described above extend in the height direction Z so as to be substantially parallel to the collector bundles26(seeFIG.4). However, it suffices that each slit be formed between the core portion and the respective collector bundle so as to conform to the collector bundle, and thus the slit need not be substantially parallel to the collector bundle. By setting for instance a range from 0° (parallel) about to 45° for the angle of intersection between a linear slit and a respective collector bundle, the collector bundle and the core portion can be properly separated, and large tension can be prevented from acting on the collector between the collector bundle and the core portion. Further, the slit need not extend linearly, and may extend in a curved manner, as viewed from the front, so long as the collector bundle and the core portion can be separated.

Further, each slit28in the embodiment described above is formed in a region that includes the upper end24aof the respective collector wound portion24. As a result, tension can be suitably prevented from acting on the collectors52that are present between each collector bundle26and the core portion22, and breakage of the collectors52can be reliably prevented. However, the slit28need not be formed at the upper end24aof the collector wound portion24. In other words, the collector bundle26and the core portion22may be linked via the collectors52, at the upper end24aof the collector wound portion24. The collectors52that are present at the upper end24aof the collector wound portion24may break when such a configuration is adopted. Even if the collectors52at the upper end24abreak, however, that break does not grow into a large enough break such that the collector terminal30or the collector bundle26comes off, and hence the manufacturing yield of the secondary battery1is unaffected.

In the embodiment described above, moreover slits28are formed in respective collector wound portions24at both side edges of the wound electrode body20, as illustrated inFIG.2. However, the slit28may be formed in just one of the collector wound portions24. In the embodiment described above, the termination hole28ais formed at an end portion of each slit28. However, such a termination hole28ais not an essential structure. The technology disclosed herein prevents the action itself of strong tension on the collector between the collector bundle and the core portion, and accordingly breakage such that the slit extends can be sufficiently suppressed even if no termination hole is formed at an end portion of the slit. Also in a case where no termination hole is formed at an end portion of the slit, breakage such that the slit extends can be reliably prevented by attaching a protective tape or the like to the end portion of the slit.

In the production method according to the embodiment described above there are used electrode sheets50in which a plurality of elongated openings59are formed in the uncoated portion56, such that each slit28is formed through stacking of the plurality of openings59at a same respective position (seeFIG.2andFIG.6). However, the means for forming the slit28, such as that illustrated inFIG.4, is not limited to the production method described above. For instance, each slit28may be formed between the core portion22and the respective collector bundle26also when the collector wound portions24are cut along the side edges22aof the core portion22after production of the wound electrode body20.

Concrete examples of the present disclosure have been explained in detail above, but the examples are merely illustrative in nature, and are not meant to limit the scope of the claims in any way. The art set forth in the claims encompasses various alterations and modifications of the concrete examples illustrated above.