Method and apparatus for manufacturing wound electrode assembly for battery

The present invention aims to provide a method for bonding protective tapes to the cut edges of an electrode plate within a short period to prevent short circuit in an electrode assembly. An electrode plate cutting & tape bonding process includes (1) cutting an electrode plate into pieces 100a and 100b, (2) forming a gap W between edges 106 and 107 of the pieces 100a and 100b, (3) bonding protective tapes 51 and 52 to both sides of the pieces 100a and 100b, covering the edges and the gap, and (4) conveying the pieces 100a and 100b connected together. Next, the tapes 51 and 52 are cut into pieces 51a & 52a and 51b & 52b. Then, the electrode plate piece 100a with the tape pieces 51a & 52a and 51b & 52b is wound together with a negative electrode plate, with a separator sandwiched therebetween.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a method for manufacturing electrode assemblies for batteries and an apparatus for manufacturing wound electrodes, and in particular to a method for manufacturing wound electrode assemblies by cutting and winding pieces of an electrode plate pulled out from an electrode plate roll.

(2) Description of the Related Art

As a method for manufacturing wound electrode assemblies for batteries, it is common to pull out an electrode plate bit by bit from an electrode plate roll, cut off one-cell-long pieces from the electrode plate with a cutter, and wind the electrode plate pieces.

Here, degradation of the cutter increases the occurrence of burrs at the cut edges, and increases burrs in size as well. Such burrs can be a cause of short circuit in a wound electrode assembly (Japanese Patent Application Publication No. 10-241737).

In view of this, a conventional method to control burrs is required to beforehand determine an acceptable level of burrs, regularly check the burrs by sampling, and change the cutter with a new one when the acceptable level is reached.

Also, as disclosed in Japanese Patent Application Publication No. 2001-85066, there is a well-known technique to prevent short circuit in an electrode assembly even if burrs occur at the cut edge. According to this method, protective tapes are bonded to the cut edges so as to sandwich them and cover the both sides of the electrode plate pieces.

SUMMARY OF THE INVENTION

However, since each one-cell-long electrode plate piece has two cut edges namely the downstream-side edge and the upstream-side edge, two processing steps are required to bond protective tapes to the downstream-side and upstream-side edges. This takes a considerable time. As the time required for these tape bonding steps increases, the takt time (i.e. the time interval between winding up of a one-cell-long piece and winding up of the next one-cell-long piece) of the winding process increases as well. This can be a cause of degradation of the productive efficiency.

Here, it is possible to bond protective tapes to a position to be cut, before cutting an electrode plate, and cut the protective tapes and the electrode plate together. This requires only a single step to bond the protective tapes per one-cell-long electrode plate piece, and reduces the time for bonding the tapes. However, if a burr that is larger than the thickness of the protective tapes occurs in the cutting of the electrode plate, the protective tapes can not cover the whole burr. In such cases, the protective tapes do not have a sufficient effect of preventing the occurrence of short circuit in the electrode assembly.

The present invention is made in view of the above problem. An object of the present invention is to provide a method for achieving a sufficient effect of preventing the occurrence of short circuit in an electrode assembly by bonding protective tapes to cut edges of an electrode plate, without taking a considerable time for the bonding the protective tapes.

To fulfill this object, the present invention provides a method for manufacturing a wound electrode assembly, comprising: an electrode plate cutting step of cutting off an electrode plate piece having a length of one cell from a strip of electrode plate; a gap forming step of forming a gap between cut edges of the electrode plate piece and the electrode plate; a tape bonding step of bonding protective tapes to both sides of the electrode plate piece and the electrode plate to cover the gap and the cut edges; a tape cutting step of cutting the protective tapes at a position within the gap; and a winding step of winding the electrode plate piece having the cut protective tapes bonded thereto. Here, the “protective tape” means a tape for covering the surface of the electrode plate.

With the stated method for manufacturing a wound electrode assembly pertaining to the present invention, a strip of electrode plate is cut in the electrode plate cutting step, into electrode plate pieces each having a length of one cell.

Then, in the gap forming step and the tape bonding step, the cut edges of each electrode plate piece are covered with protective tapes, which are bonded to both sides of the electrode plate piece, and thus adjacent electrode plate pieces are connected together by protective tapes. Also, as protective tapes are bonded to the cut edges after the cutting of the electrode plate, the cut edges are covered with protective tapes in a favorable manner.

After that, the protective tapes are cut in the tape cutting step, at a position within the gap between the adjacent electrode plate pieces, and the electrode plate pieces are separated. Even after the separation, the cut edges are covered with the protective tapes bonded to both sides of the electrode plate pieces. Each of the electrode plate pieces with the protective tapes is wound up in the winding step, and thus a wound electrode assembly is manufactured. In an electrode assembly thus manufactured, the edges of the electrode plate piece are covered with the protective tapes which sandwich the edges. The tapes therefore have an effect of preventing the occurrence of short circuit in an electrode assembly even if burrs that are larger than the thickness of the protective tapes have occurred at the cut edges.

Also, according to the stated method for manufacturing a wound electrode assembly, protective tapes are bonded in the tape bonding step to both sides of the electrode plate piece and the electrode plate, to cover the gap and the cut edges. Thus, protective tapes are bonded to both cut edges by a single operation. That is, only a single operation is required to bond protective tapes to a one-cell-long electrode plate piece, which reduces the time for bonding the tapes.

As a result, the method pertaining to the present invention prevents the increase in takt time in the winding process which might be caused due to the time required for the bonding of the protective tapes.

Another aspect of the present invention is a wound electrode assembly manufacturing apparatus for manufacturing a wound electrode assembly by pulling out a strip of electrode plate bit by bit, cutting off an electrode plate piece having a length of one cell from the electrode plate, and winding the electrode plate piece, the apparatus comprising: an electrode plate cutter operable to cut off the electrode plate piece;

a gap forming unit operable to form a gap between cut edges of the electrode plate piece and the electrode plate; a tape bonding unit operable to bond protective tapes to both sides of the electrode plate piece and the electrode plate to cover the gap and the cut edges; a tape cutter operable to cut the protective tapes at a position within the gap; and a winding unit operable to wind the electrode plate piece having the cut protective tapes bonded thereto. This apparatus for manufacturing wound electrode assembly achieves the same effect as the manufacturing method described above.

As explained above, the method and the apparatus pertaining to the present invention realize manufacturing of a wound electrode assembly that does not easily cause short circuit, without degrading the productive efficiency.

In the above-described method and apparatus for manufacturing the wound electrode assembly, the electrode plate may be pulled out bit by bit to a first stage in which the electrode plate cutting step, the gap forming step and the tape bonding step are performed, and the electrode plate piece with the protective tapes may be conveyed from the first stage to a second stage in which the tape cutting step is performed. With this structure, the processes can be performed in parallel in the first stage and the second stage.

This structure further reduces the total time required for the electrode plate cutting, the gap forming, the tape bonding and the tape cutting, and more efficiently prevents the increase in takt time in the winding process.

Moreover, the second stage immediately before the electrode plate winding process includes only the protective tape cutting, and it is unnecessary to perform the electrode plate cutting in this stage. This prevents powder dust and small fragments, generated in the electrode plate cutting, from being mixed into the electrode assembly in the electrode plate winding process.

The present invention realizes the manufacture of a wound electrode assembly that does not easily cause short circuit, without degrading the productive efficiency. Thus, the present invention is suitable for the manufacture of wound electrode assemblies for various kinds of batteries such as nonaqueous electrolyte batteries.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1is a process chart showing manufacturing processes for an electrode assembly pertaining to an embodiment of the present invention.

AsFIG. 1shows, the manufacturing processes for an electrode assembly include an electrode plate roll manufacturing process, a tab attaching process, an electrode plate cutting & tape bonding process, a protective tape cutting process, and an electrode plate winding process.

An electrode plate roll manufactured through the electrode plate roll manufacturing process is set up in an electrode assembly winding apparatus.

The electrode assembly winding apparatus includes a stage for the tab attaching process, a stage for the electrode plate cutting & tape bonding process, a stage for the protective tape cutting process, and a stage for the electrode plate winding process.

The electrode plate pulled out from the electrode plate roll passes through the stages (i.e. stations) in the electrode assembly winding apparatus one by one, and each of the processes are performed in the corresponding stage. Specifically, while a portion of the electrode plate pulled out beforehand in the electrode assembly winding apparatus is going through the electrode plate winding process, the subsequent portion of the electrode plate piece goes through the protective tape cutting process, and another portion of the electrode plate, following the subsequent electrode plate, goes through the electrode plate cutting & tape bonding process and the tab attaching process, respectively in the corresponding stages.

The following explains each of the processes, based on an example case of manufacturing an electrode assembly for a nonaqueous electrolyte battery and bonding protective tapes to the positive electrode plate of the electrode assembly.

1. Electrode Plate Roll Manufacturing Process

A positive-mixture slurry is firstly manufactured by mixing lithium cobalt oxide as a positive-electrode active material, a carbon powder as an electrical conducting material, polyvinylidene fluoride as a binding agent, and N-methylpyrrolidone.

The slurry is applied on both sides of an aluminum foil (having the thickness of 15 μm, for example) pulled out from an aluminum foil roll. Here, the slurry is not applied on cutting areas102near cutting lines A, and tab areas103to each of which a collector tab is to be attached (SeeFIG. 2).

The applied slurry is dried with a dryer and pressed with a roller, and thus a positive-mixture layer104is formed. These steps produce a positive electrode plate, which is an aluminum foil as a core material, having the positive-mixture layer104formed thereon.

The electrode plate thus manufactured is cut with a slitter into strips each having a predetermined width. Also, each of the strips is wound up to be in the form of a roll. Thus, an electrode roll in the roll shape is manufactured.

2. Tab Attaching Process

The electrode roll is set up in the electrode assembly winding apparatus, and a tab105is welded to each of the tab areas103of the electrode plate pulled out from the electrode roll.

FIG. 2shows an electrode plate100pulled out from the electrode roll, to which tabs105have been attached.

The electrode plate100is conveyed to the subsequent stage for the electrode plate cutting & tape bonding process.

3. Electrode Plate Cutting & Tape Bonding Process

FIGS. 3A to 3Dillustrate the electrode plate cutting & tape bonding process. As shown in this drawing, the electrode plate cutting & tape bonding process includes the steps of electrode plate cutting (FIG. 3A), pitch widening (FIG. 3B), tape bonding (FIG. 3C) and electrode plate conveying (FIG. 3D), which are to be performed in the stated order.

For performing these steps, a pair of rollers10a&10band a roller11, which are for conveying the electrode plate100, are provided downstream (i.e. the left side onFIGS. 3A to 3D) and upstream (i.e. the right side onFIGS. 3A to 3D), respectively.

The electrode assembly winding apparatus is also provided with a pair of cutters20a&20bfor cutting the electrode plate100, two pairs of chucks21a&21band22a&22bfor grasping the electrode plate100, and a pair of tape bonding jigs23&24for bonding protective tapes to the electrode plate100.

The cutters20a&20bare arranged at a cutting position B between the roller11and the rollers10a&10b. The positions of the tape bonding jigs23&24are also adjusted according to the cutting position B.

The chucks21a&21band22a&22bare provided downstream and upstream from the cutting position B, respectively. Note that the chucks22a&22bare configured to be able to move upstream while grasping the electrode plate100.

The tape bonding jigs23&24are jigs each for sucking protective tapes one by one and bonding each tape to the surface of the electrode plate by pressing it against the plate. Specifically, a vacuum suction pad may be used for this purpose.

The following explains the steps one by one.

The electrode plate100is conveyed by operation of the rollers10a&10b, and is stopped when a cutting line A reaches the cutting position B.

Then, the electrode plate is grasped with the chucks21a&21band the chucks22aand22b, and is cut off with the cutters20a&20b. Thus the electrode plate100is cut along the cutting line A into a preceding electrode plate piece100aand a succeeding electrode plate piece100b. The electrode plate piece100ahas the length required for manufacturing a single cell.

FIG. 4illustrates a control mechanism for stopping the cutting line A at the cutting position B.

A plurality of reflectance sensors25ato25care arranged near the cutting position B along the conveyance direction. Each of the reflectance sensors25ato25cirradiates the part of the electrode plate100that passes immediately below the sensor with light, and receives the reflected light to sequentially obtain the reflectances. The reflectances are input to a roller drive controller26.

The reflectance of the surface of the electrode plate100is large on the cutting area102to which the positive mixture is not applied, whereas it is small on the positive-mixture layer104. That is, the reflectance to be measured by the reflectance sensors25ato25cgreatly changes at the border (i.e. edge) between the cutting area102and the positive-mixture layer104. Thus, the roller drive controller26is capable of predicting when the edge passes immediately below the reflectance sensors25ato25c, based on the reflectances sequentially received from the reflectance sensors25ato25c. The roller drive controller26predicts when the cutting line A reaches the cutting position B, and stops the rollers10a&10baccording to the obtained timing. Here, note that the present embodiment is provided with the cutting areas102and the tab areas103, to which the positive mixture is not applied. Alternatively, the cutting areas102may be configured to be longer than the tab areas103, and the distance between the reflectance sensor25aand the reflectance sensor25cmay be configured to be longer than the tab areas103(e.g. no less than 10 mm) so that the cutting areas102can be detected. Another method to stop the cutting lines A at the cutting position B is detecting the tabs105attached to the electrode plate100.

The chucks22a&22bare moved upstream under the condition that the electrode plate pieces100aand100bare both grasped with the chucks21a&21band the chucks22a&22brespectively, so that a gap W having a constant length is formed between the upstream-side edge106of the electrode plate piece100aand the downstream-side edge107of the electrode plate piece100b.

Then, protective tapes51and52are attached to the electrode plate pieces100aand100bwith the tape bonding jigs23&24so as to cover the gap W kept between the upstream-side edge106and the downstream-side edge107. Specifically, the protective tapes are attached such that the electrode plate pieces100aand100bare sandwiched between the protective tapes51and52, and the upstream-side edge106, the downstream-side edge107and the gap W therebetween are covered with the protective tapes51and52.

Here, it is preferable that the protective tapes51and52are adhesive insulating tapes. Usable base material of the tapes is, for example, resin of polyolefin such as polyethylene and polypropylene, polyester, polyimide, polyamide, polyphenylene sulfide, or the like. Glass cloth tapes are also usable. A preferable thickness of the base material of the protective tapes51and52is 10 to 100 μm.

AsFIG. 5Ashows, the upstream-side edge106of the preceding electrode plate piece100aand the downstream-side edge107of the succeeding electrode plate piece100bare connected by the bonded protective tapes51and52, and the upstream-side edge106and the downstream-side edge107are covered with the protective tapes51and52.

Even if large burrs occur at the edges106and107in the electrode plate cutting process described above, the burrs are pressed with the tape bonding jigs23&24and are reduced in size in this tape bonding process.

The chucks21a&21band the chucks22a&22bare released and the rollers10a&10bare driven, so that the connected electrode plate pieces100aand100bare conveyed to the next stage for the protective tape cutting process.

4. Protective Tape Cutting Process

FIGS. 6A and 6Billustrate the process for cutting the protective tapes.

The protective tape cutting process includes the steps of protective tape cutting (FIG. 6A) and electrode plate conveying (FIG. 6B), which are to be performed in the stated order.

In the stage for the protective tape cutting process, two pairs of rollers60a&60band61a&61bfor conveying the electrode plate100are provided downstream and upstream respectively, in the similar manner as in the stage for the electrode plate cutting & tape bonding process described above. The stage is also provided with a pair of cutters70a&70bfor cutting the protective tapes and two pairs of chucks71a&71band72a&72bfor grasping the protective tapes.

The cutters70a&70bare provided at the cutting position D between the pair of rollers60a&60band the pair of rollers61a&61b. The pair of chucks71a&71band the pair of72a&72bare provided downstream and upstream from the cutting position D, respectively.

The rollers60a&60bare driven so as to convey the connected electrode plate pieces100aand100b. The electrode plate pieces100aand100bare stopped when the cutting line C (SeeFIG. 5AandFIG. 7) of the protective tapes51and52reach the cutting position D. The mechanism for stopping the cutting line C at the cutting position D is the same as explained above for the electrode plate cutting process. The cutting line C positioned within the gap between the upstream-side edge106and the downstream-side edge107(e.g. in the middle of the gap), namely in an area where only the protective tapes51and52exist and the electrode plate does not.

Then, the protective tapes51and52are grasped with the chucks71a&71band the chucks72aand72b, and are cut off with the cutters70a&70b.

AsFIG. 5Bshows, the protective tapes51and52are cut along the cutting line C and divided into protective tape pieces51aand52aand protective tape pieces51band52b, respectively. The electrode plate pieces100aand100bare separated, but the upstream-side edge106of the electrode plate piece100aand the downstream-side edge107of the electrode plate piece100bare kept covered with the protective tape pieces51aand52aand the protective tape pieces51band52b, respectively.

FIG. 7shows that the protective tapes are cut and the electrode plate pieces100aand100bthat have been connected are separated from each other. The electrode plate piece100band the electrode plate piece100cfollowing it are connected by the protective tapes51and52.

The chucks71a&71band the chucks72a&72bare released and the rollers60a&60bare driven, so that the electrode plate piece100athat has been separated is conveyed to the next stage for the electrode plate winding process.

5. Electrode Plate Winding Process

This stage is for manufacturing a wound electrode assembly as shown inFIG. 8by winding, from the downstream-side edge107, the electrode plate100aconveyed from the previous stage, to which the pairs of protective tape pieces51a&52aand51b&52bhad been bonded, together with an negative electrode plate200manufactured separately, such that a separator300is sandwiched therebetween.

The negative electrode plate200is manufactured in the following manner. A negative-mixture slurry is firstly manufactured by mixing graphite as a negative-electrode active material and carboxymethyl cellulose and styrene-butadiene rubber as a binding agent with water. Then, this slurry is applied to a copper foil (having the thickness of 8 μm, for example). The applied slurry is dried and thus a negative-mixture layer is formed. Finally, the foil is cut into pieces each having a predetermine size. As the separator, a microporous polyethylene film may be used, for example.

In the wound electrode assembly thus manufactured, the downstream-side edge107(i.e. the starting position of the winding) of the positive electrode plate piece100ais kept covered with the protective tape pieces51band52b, and the ending position of the winding (i.e. the upstream-side edge106) is kept covered with the protective tape pieces51aand52a. Hence, even if burrs occur at the downstream-side edge107and the upstream-side edge106, short circuit to the negative electrode plate200is prevented.

Advantageous Effects of the Manufacturing Method Pertaining to the Embodiment

According to the wound electrode assembly manufacturing method pertaining to the embodiment described above, the protective tapes are attached to the cut edges of the electrode plate after the electrode plate is cut into pieces. Thus, the cut edges are covered with protective tapes in a preferable manner. As a result, even if burrs occur at the cut edges, the protective tapes achieve a sufficient effect of preventing the occurrence of short circuit in the electrode assembly.

According to the wound electrode assembly manufacturing method pertaining to the embodiment described above, in the tape bonding process, the protective tapes51and52are integrally bonded to so as to cover the upstream-side edge106of the electrode plate piece100aand the downstream-side edge107of the electrode plate piece100b. Thus, only a single taping operation is required to bond the protective tapes51and52to both the upstream-side edge106and the downstream-side edge107. In other words, only a single taping operation is required to manufacture the electrode plate piece for each single cell. Thus, the method pertaining to the embodiment does not require a long time for the bonding of the protective tapes.

Accordingly, the time required for the electrode plate cutting & tape bonding process and the protective tape cutting process is reduced, which prevents the increase in takt time in the winding process.

Moreover, according to the wound electrode assembly manufacturing method pertaining to the embodiment described above, the electrode plate cutting & tape bonding process and the protective tape cutting process are performed in different stages. Thus, the method allows the processes to be performed in parallel. This further reduces the time required for the electrode plate cutting & tape bonding process and the protective tape cutting process.

Furthermore, the stage immediately before the stage for the electrode plate winding process includes only cutting of the protective tapes is, and does not include cutting of the electrode plate. This prevents powder dust and small fragments, generated in the electrode plate cutting, from being mixed into the electrode assembly in the electrode plate winding process.

As described above, the wound electrode assembly manufacturing method pertaining to the embodiment reduces the time required for the electrode plate cutting & tape bonding process and the protective tape cutting process. Thus, it is easy to complete these processes in a shorter period than the winding of a one-cell-long electrode plate. This prevents an undesired increase in takt time of the winding process.

EXAMPLES

The following shows example sizes of electrode plates to be manufactured according to the embodiment above, protective tapes to be bonded to the electrode plates, and so on.

InFIG. 2, example sizes of the electrode plate100are depicted.

The width of the electrode plate100is 56.8 mm, and the length corresponding to one cell is 683 mm. The width of each cutting area102is 57.5 mm. The width of each tab area103is 10 mm. The length between the cutting area102and the tab area103is 201 mm.

InFIGS. 9A to 9C, examples sizes of the part of the protective tapes51and52where is bonded to the electrode plate are depicted.

In the example depicted inFIG. 9A, the width of each of the protective tapes51and52is 16 mm. The length of the gap W between the upstream-side edge106and the downstream-side edge107is 6 mm. The margin for bonding of each electrode plate is 5 mm.

On the side of the upstream-side edge106, the protective tapes51and52are bonded to the cutting area102to which the positive mixture is not applied. However, on the side of the downstream-side edge107, the width of the cutting area102to which the positive mixture is not applied is only 3 mm, and thus the upstream edges of the protective tapes51and52are bonded to the positive-mixture layer104.

Part of the protective tapes51and52lies off the electrode plate for 1 mm from each side of the electrode plate.

In the example depicted inFIG. 9B, the protective tapes51and52mentioned above are cut in the middle. The widths of the protective tape pieces51aand51band the protective tape pieces51band52bare each 8 mm.

FIG. 9Cshows an example case of discarding the protective tape pieces51band52b, and a part of the electrode plate piece100bafter completing the protective tape cutting process. The length of the part from the downstream-side edge107is 5 mm. In such a case, the electrode plate winding process is performed on the electrode plate100awith a protective tape piece attached only to the downstream-side edge.

Modifications

According to the embodiment described above, the protective tapes are bonded only to the positive electrode plate. However, it is possible to bond the protective tapes to the negative electrode plate in a similar manner. The protective tapes may be bonded only to the negative electrode plate, or to both the positive electrode plate and the negative electrode plate.

According to the embodiment described above, the electrode plate winding process is performed on the electrode plate100awithout removing the protective tape pieces51aand52abonded to the upstream-side edge106and the protective tape pieces51band52bbonded to the downstream-side edge107. However, in the cases where the protective tape at the starting part of the winding of the electrode plate piece100a, the protective tape pieces51aband52band a downstream-side part (i.e. the vicinity of the downstream-side edge107) may be cut off after the completion of the protective tape cutting process, and then the winding process may be performed (SeeFIG. 9C).

Although the embodiment above is explained based on an example case of manufacturing an electrode assembly for a nonaqueous electrolyte battery, the present invention has no limitation on battery type. The present invention is applicable to manufacturing of any type of wound electrode assembly.