Method and apparatus for manufacturing expanded mesh sheet and battery using this expanded mesh sheet

Abstract: Fine slits are formed in the metal sheet (B) at the slit forming section (11) by plate cutters (15), excluding portions in the center and on both sides in a widthwise direction of the metal sheet (B), after which the areas where the slits have been formed are drawn out at the expanding section (12) thereby opening the slits and obtaining a mesh sheet (C) which has solid portions in the central portion and on both sides. This mesh sheet (C) is flattened at the rolling section (14) to obtain an expanded mesh sheet (D). An electrode sheet is prepared by applying an active material onto the portions of the expanded mesh sheet (D) where the mesh has been formed, and collectors (1a, 2a) for a battery are cut out from this electrode sheet such that lead connecting portions (1c, 2c) thereof are located at the solid portion of the mesh sheet where there is no openings, with which a positive and negative electrode plates (1, 2) for the battery are manufactured.

Description: The present invention relates to an expanded mesh sheet that is preferable for use as a battery collector, and more particularly to a method and apparatus for manufacturing an expanded mesh sheet with which a fine reticulated configuration can be formed in a thin metal sheet for realizing smaller, thinner, and higher capacity batteries, and to a battery using this expanded mesh sheet. As portable instruments such as portable telephones have become smaller, thinner, and lighter in weight, the batteries used as a source of power by such instruments have been required to have higher capacities, as well as to be smaller and lighter. Figs. 13 and 14 show the constitution of a polymer electrolyte secondary cell, a type of battery developed in response to these requirements. This battery comprises a laminated electrode 4, of positive electrode plates 1 and a negative electrode plate 2 laminated together with separators 3 therebetween, held within an outer case 7 comprising a laminated sheet. As shown in Fig. 14, which shows a cross sectional view of Fig. 13 at line XIV-XIV, the above-mentioned positive electrode plate 1 is formed of positive electrode active material 1b coated on a positive electrode collector 1a; the above-mentioned negative electrode plate 2 is formed of negative electrode active material 2b coated on a negative electrode collector 2a. These positive electrode plate 1 and negative electrode place 2 are layered together with separators 3 consisting of solid electrolyte material therebetween and sealed along with liquid electrolyte within an outer case 7, comprising a pair of laminated sheets heat fused along their perimeters at seal portions P 1 , P 2 , P 3 . The positive electrode lead 8 is connected with the lead connecting portions 1c, 1c each formed on the two positive electrode collectors 1a, 1a; and the negative electrode lead 9 is connected to the lead connecting portion 2c formed on the negative electrode collector 2a. These positive electrode lead 8 and negative electrode lead 9 are insulated from each other with an insulating sheet 6 and drawn out to the outside of the outer case 7 so as to be used as battery connection terminals for the positive and negative electrodes of the battery. The above-mentioned positive electrode plate 1 and negative electrode plate 2 are manufactured as follows. The positive electrode active material, prepared as a paste, is applied on an expanded mesh sheet of aluminum that will constitute the positive electrode collector 1a, which is then dried and rolled to form a positive electrode sheet. The positive electrode plate is cut to a prescribed form and size from this positive electrode sheet thus obtained wherein the positive electrode active material 1b is adhered to a prescribed thickness on the positive electrode collector 1a. Also, the negative electrode active material, prepared as a paste, is applied on both surfaces of an expanded mesh sheet of copper that will constitute the negative electrode collector 2a, which is then dried and rolled to form a negative electrode sheet. The negative electrode plate is cut to a prescribed form and size from this negative electrode sheet thus obtained wherein the negative electrode active material 2b is adhered to a prescribed thickness on both surfaces of the negative electrode collector 2a. As shown in Fig. 13, these positive electrode plate 1 and negative electrode plate 2 are cut from the positive electrode sheet and negative electrode sheet respectively, such that the lead connecting portion 1c protrudes from the positive electrode collector 1a at a position offset from the center line, and such that the lead connecting porcion 2c protrudes from the negative electrode collector 2a at a position offset from the center line opposite from the lead connecting portion 1c of the positive electrode collector 1a. The aluminum positive electrode lead 8 is joined to the lead connecting portion 1c of the positive electrode collector 1a, and the copper negative electrode lead 9 is joined to the lead connecting portion 2c of the negative electrode collector 2a, respectively, at welding points S using resistance welding or ultrasonic welding. In order to satisfy the requirement that a battery be small, light, and have higher capacity, the expanded mesh sheet used as a collector must be thin, with a fine mesh grid, and yet have the strength to withstand the tensile force applied during manufacture. Moreover, the mesh sheet must be superior in binding properties to the active material and collecting properties. In the collector, the electrodes of same polarity are connected to each other at the lead connecting portions, and the lead is further connected thereto. Therefore, the lead connecting portions are required to have better welding properties as the number of laminated positive and negative electrodes increases. However, in collectors wherein an expanded mesh sheet with a high rate of openings is used, the lead connecting portions tend to have poor welding properties, and low bonding strength and conductivity between collectors and leads. The above-mentioned expanded mesh sheet is manufactured by pulling a metal sheet, wherein slits have been formed in a zigzag pattern, in a direction perpendicular to the orientation of the slits, thereby opening the slits to form a lozenge-shaped reticulated configuration. In other words, as shown in Fig. 15A, a multiplicity of slits a are formed intermittently and parallel to each other in the direction in which the metal sheet A extends. The slits a are arranged in a zigzag pattern, with the parallel and adjacent positions being offset in the direction in which the metal sheet A extends; nodes b are formed between intermittent slits a, a. Furthermore, as shown in Fig. 15B, bulges c are formed by plastic deformation at positions sandwiched between slits a, a juxtaposed in a widthwise direction, protruding from both surfaces of the metal sheet alternately in opposite directions. Such a metal sheet, wherein slits a, nodes b, and bulges c have been formed, is pulled widthwise as shown in Fig. 16 to attain an expanded mesh sheet having a mesh grid structure, wherein the slits a, a are opened thus forming lozenge-shaped openings surrounded by linear lattice bars d connected by nodes b. Current methods for manufacturing this type of mesh sheet include those using a rotary system and those using a reciprocating system. Fig. 17 shows an example of a rotary-type apparatus for manufacturing expanded mesh sheets. This apparatus includes a pair of rolls 100, 100 which is constructed such that a plurality of disk-shaped cutters 31, that are provided with raised portions 32 for forming the above-mentioned bulges c on the periphery, are superposed coaxially at intervals approximately equal to the thickness of the disk-shaped cutters 31. The rolls 100, 100 are disposed opposite to each other with their axes being parallel and their positions in the axial direction being offset by the thickness of the disk-shaped cutters 31. Blades for forming the slits a in the direction in which the metal sheet A is supplied and in an area between the disk-shaped cutters 31 of one roll 100 and the disk-shaped cutters 31 of the other roll 100, are formed on both edges of each disk-shaped cutter 31. Recessed portions 33 for interrupting the formation of the slits a and for forming the nodes b are formed at a prescribed pitch on the blades in the direction of the circumference of the disk-shaped cutters 31. By supplying the metal sheet A between these rolls 100, 100 and rotating the rolls 100, 100 around their respective axes, the slits a connected with the nodes b are formed in the metal sheer A, as well as the bulges c protruding in mutually opposite directions are formed at positions where slits a, a, are juxtaposed with each other, as shown in Figs. 15A and 15B. An example of such a rotary system is described in detail in US-A-4291443. One disadvantage of such rotary system is that the disk-shaped cutters 31 need to have at least a certain minimum thickness in order to ensure the strength of the disks, wherefore there are limits to the thinness and fineness of the cutters. For this reason, the above-mentioned reciprocating system is more appropriate for manufacturing expanded mesh sheets with a fine mesh grid. In the method of manufacturing expanded mesh sheets with a reciprocating system, slits j are formed intermittently and widthwise in an elongated sheet 55 in such a manner that the slits j are arranged in a zigzag pattern offset in the direction of the orientation of the slits as shown in Fig. 19 by a pair of upper and lower plate cutters 53, 54 as shown in Fig. 18, one row at a time. The cutters 53, 54 include raised portions as part of slit forming blades, with which bulges k are formed at the same time that the slits j are formed. The elongated sheet 55, in which the slits j and bulges k have been formed in a zigzag pattern, is pulled in a direction lengthwise to the elongated sheet as shown in Fig. 19, whereupon the slits j and bulges k are spread out and an expanded mesh sheet having a lozenge-shaped mesh is attained. An example of such a reciprocating system is described in GB-A-2071530 where, instead of plain cutters firtree shaped cutters are used to cut a chevron-shaped arrangement of slits in each cut. Even in this example only one set of slits are cut with each reciprocation. The above-described method for manufacturing expanded mesh sheets with a reciprocating system has the problems of high costs, low productivity, and slow working speed because the slits j are made one row at a time. Also, it is preferable that the ends of the expanded mesh sheet include solid portions where a mesh is not formed in order to ensure the strength to withstand processes of applying active material to and rolling the thin expanded mesh sheet and in order to form lead connecting portions for connecting leads to the collectors. However, with the reciprocating system as shown in Fig. 18, a mesh structure has to be formed on the entire surface of the mesh sheet because of the specific expanding method, wherefore it was impossible to manufacture an expanded mesh sheet provided with solid portions which has no reticulated configuration. It is an object of the present invention to provide a method and apparatus for manufacturing an expanded mesh sheet wherein a fine mesh grid structure is formed in a thin metal sheet by a reciprocating system efficiently The method of manufacturing an expanded mesh sheet according to the present invention comprises the steps of: supplying an elongated sheet (B) between an upper mold and lower mold, comprising a plurality of plate cutters that have a plurality of blades for forming slits and are superposed at prescribed intervals; intermittently forming a plurality of slits in a zigzag arrangement lengthwise to the elongated sheet (B) throughout an area defined by the length and width of the superposed plate cutters by a reciprocating movement of said upper mold and lower mold in opposite directions; moving the elongated sheet (B) intermittently by the length of the plate cutters; and, pulling the elongated sheet (B) in a direction so as to expand widthwise dimensions of the elongated sheet (B), whereby a mesh grid is formed in the elongated sheet (B). According to this manufacturing method, slits are formed in a plurality of rows at once in the elongated sheet by plastic working using an upper mold and lower mold comprising a plurality of superposed plate cutters in an area defined by the length of the plate cutters and the width of the superposed plate cutters, whereby the mesh can be formed efficiently even with the reciprocating system. Also, the thickness of the plate cutters can be made thinner without losing their strength and rigidity, wherefore formation of a fine mesh grid structure is possible. Furthermore, by adding a process of rolling the mesh sheet following expansion thereof, an expanded mesh sheet is formed to be further thinner, from which a thin collector with the fine mesh grid structure reguired for the manufacture of small, thin, high capacity batteries can be obtained. Also, by manufacturing the expanded mesh sheet such that when forming slits, a band of solid portion lengthwise to the elongated sheet at prescribed locations is provided so that the elongated sheet, after being expanded, has a portion where there is no mesh grid, the tensile strength of the elongated sheet increases thanks to this solid portion, by which the elongated sheet will have enough strength to withstand the tension during transportation or rolling process even with a thin thickness. Also, when used in battery collectors, thesesolid portions can be used to form lead connecting portions for the electrode plates. This can improve the welding properties of electrode plates to leads. An apparatus for manufacturing an expanded mesh sheet according to the present invention comprises: slit forming means including an upper mold and a lower mold, each of the upper mold and lower mold comprising a plurality of plate cutters superposed at intervals roughly equal to the thickness thereof, the plate cutters having blades formed on both faces thereof, a plurality of protrusions projected at prescribed intervals, and recessed portions provided between said protrusions by cutting away one surface and the other surface of said blades at an angle alternately, wherein said upper mold and lower mold are positioned opposite to each other and offset by the thickness in the direction in which the plate cutters are superposed, said upper mold and lower mold being driven to reciprocate in opposite directions, thereby in each reciprocation, forming a plurality of slits in a lengthwise direction and in a zigzag arrangement throughout an area defined by the length and the width of the plate cutters in an elongated sheet (B) fed intermittently between said upper mold and lower mold in a lengthwise direction of said plate cutters; means for intermittently conveying said elongated sheet (B) by the length of the plate cutters lengthwise to the plate cutters in the slit forming means; expanding means for pulling the elongated sheet (B) in a direction so as to expand widthwise dimensions of the elongated sheet (B) and opening said slits thereby producing a mesh sheet (C) having a reticulated configuration; and, rolling means (14) for flattening said mesh sheet (C) fron both upper and lower surfaces. According to this construction, slits can be formed at once in a prescribed area even with the reciprocating system, whereby processing speed can be remarkably increased as compared with a conventional construction wherein slits are formed one row at a time. Also, since plate cutters are used for forming slits, machining precision of the cutters can be readily attained thereby reducing cost for molds. Also, by making the thickness of the plate cutters thinner, a fine mesh can be formed, and the thin collectors having the fine mesh grid structure required for the manufacture of small, thin, high capacity batteries can be obtained from this expanded mesh sheet. In the above construction, the thickness of the plate cutters may gradually increase toward the sides of the upper mold and lower mold, by which the width of the linear lattice bars forming the lozenge-shaped cells constituting the mesh grid structure gradually increases towards the edges of the sheet, and the strength of the side portions of the sheet to which particularly strong tension is applied can be improved. Furthermore, by providing a configuration such that the blades between the recessed portions of the plate cutters are formed such that corner parts are chamfered away towards the recessed portions on both sides, the nodes connecting the cells in the mesh grid are widened and both corners formed by the ends of the long diagonals of the cells are formed with an obtuse angle, by which the strength of the mesh structure is further increased. Furthermore, the upper mold and lower mold are constructed such that the plate cutters are not disposed at positions corresponding to prescribed areas in a widthwise direction of the elongated sheet, so that solid portions where slits are not formed are provided lengthwise to the elongated sheet. The strength of the mesh sheet to the tension exerted thereto during transportation or rolling process is thereby enhanced. Also, when using the mesh sheet as a battery collector, connecting portions for drawing out leads are cut out from this solid portions, whereby the welding properties between the electrodes and leads can be improved. Furthermore, bending means for forming indentations or bosses in the solid portions of the elongated sheet before rolling the elongated sheet is provided, by which indentations or bosses are formed in the solid portions of the elongated sheet, which provide a play when the solid portions are expanded, thereby adjusting elongation of the meshed portion and the solid portions when the mesh sheet is rolled, thereby producing an expanded mesh sheet with less deformation caused by rolling. In the above construction, the solid portions provided in the expanded mesh sheet are formed lengthwise to the elongated sheet in the widthwise central portion and on both sides. As a result, the tensile strength is equalized in a widthwise direction and deformation during transport and rolling is suppressed. Moreover, collectors can be cut away without waste of material since the solid portion in the central area can be used for a lead connecting portion. By manufacturing the expanded mesh sheet using an aluminum or copper sheet, a mesh sheet of aluminum is used as the collector for a positive electrode of a battery and a mesh sheet of copper is used as a collector for a negative electrode Also, the reticulated configuration formed in the expanded mesh sheet comprises lozenge-shaped cells of which length of shorter direction is within a range 0.5 to 2.0 ram. Manufacture of an expanded mesh sheet with a fine reticulated configuration for constituting a smaller battery of a higher performance is thereby possible. Furthermore, since the distance between the active material to the mesh sheet is equalized, a collector which helps exhibit good discharging characteristics and collecting properties can be obtained. Preferred embodiments of the present invention will be described with reference to the accompanying drawings, in which: Fig. 1 is a perspective view showing a process of manufacturing an expanded mesh sheet according to the present invention; Fig. 2 is a partial perspective view showing the metal sheet wherein slits have been formed in the slit forming section; Fig. 3 is a partial perspective view showing the constitution of plate cutters in the slit forming section; Fig. 4A is a plan view showing the state in the slit forming section where the upper mold and lower mold are engaged; Fig. 4B is a plan view showing the state where slits are formed in the metal sheet; Fig. 5A is a plan view showing the state of the metal sheet wherein slits are formed before expanding; Fig. 5B is a plan view showing the state wherein the metal sheet is expanded to become a mesh sheet having a lozenge-shaped reticulated configuration; Fig. 6A is a plan view showing the state wherein indentations are formed in the solid portions of the mesh sheet; Fig. 6B is a side view of the same; Fig. 7 is a perspective view showing a modification of the plate cutters in the slit forming section; Fig. 8 is a plan view showing the reticulated configuration formed by those cutters; Fig. 9 is a plan view showing the way how collectors are cut from the expanded mesh sheet; Fig. 10 is a perspective view showing a process of manufacturing a plurality of expanded mesh sheets at the same time; Fig. 11 is a perspective view showing a process of separating the plurality of expanded mesh sheets produced as shown in Fig. 10; Fig. 12 is a plan view showing a state wherein a metal sheet is folded in half; Fig. 13 is a plan view showing the construction of a polymer electrolyte battery; Fig. 14 is a cross sectional view of Fig. 13 at line XIV-XIV; Fig. 15A is a plan view showing the state wherein slits are formed in the metal sheet; Fig. 15B is a side view of the same; Fig. 16 is a plan view showing the state where the reticulated configuration is being formed in the metal sheet by expanding; Fig. 17 is a side view showing the method of forming slits with a rotary system; Fig. 18 is a perspective view showing the method of forming slits with a reciprocating system; and Fig. 19 is a perspective view showing the state where the slits formed by the reciprocating system are expanded. Fig. 1 shows a manufacturing process according to the method for manufacturing an expanded mesh sheet of the present invention. The expanded mesh sheet in this embodiment is manufactured by forming a fine mesh grid in a thin, elongated metal sheet such as a copper sheet or aluminum sheet, with the provision of solid portions wherein this mesh grid is not formed in the central portion and on both side edges of the sheet. This expanded mesh sheet is used, for example, as a collector for constituting electrode plates of a non-aqueous electrolyte battery. In Fig. 1, a long metal sheet B, wound in a roll in the coil section 10, is reeled out from the end and delivered to the slit forming section 11. An upper mold and lower mold, comprising the superposed plate cutters discussed below, are positioned opposite to each other in the slit forming section 11. By driving these molds in opposite directions, slits e are formed, and bulges g are also formed by plastic deformation, as shown in Fig. 2 in a prescribed region of the metal sheet B fed between the upper mold and lower mold. In the upper mold and lower mold disposed in the slit forming section 11, the above-mentioned plate cutters are not located at positions corresponding to the widthwise central portion and edge portions of the metal sheet B. As a result, the slits e are not formed in the widthwise central portion and at both side edges of the metal sheet B. The metal sheet B, wherein slits e have been formed, is delivered to an expanding section 12 by conveyor means (not shown), where the metal sheet B is drawn out in the widthwise direction so that the bulges g are spread out in the widthwise direction and the slits e are opened, whereby the areas where the slits are joined in a zigzag fashion with nodes f are expanded to become the mesh sheet C, wherein lozenge-shaped cells are disposed in a zigzag arrangement. In the subsequent bending section 13, groove-like indentations 19, or alternatively, bosses, are formed widthwise to the mesh sheet C in the central solid portion Nc and side solid portions Ns of this mesh sheet C, where there are no lozenge-shaped openings. These indentations 19 are discussed below with reference to Figs. 6A and 6B. The mesh sheet C that has been provided with the indentations 19 is rolled by compression rollers 18, 18 in the rolling section 14 to become the expanded mesh sheet D, and is wound into a roll. The constitution of the slit forming section 11 for the expanded mesh sheet D, manufactured with the above-mentioned processes, is explained below. Fig. 3 is a partial view of the upper mold 21 and lower mold 22 disposed in the slit forming section 11. A plurality of plate cutters 15 superposed at prescribed space thereby constituting a shearing cutter are formed with blades 24 of the shearing cutter on both sides thereof, and semicircular protrusions 23 are projected at prescribed intervals on the plate cutters 15. Furthermore, skip portions (or recessed portions) 25 are formed in the straight areas between the above-mentioned protrusions 23 such that the blades 24 are cut away at an angle on one face of the plate cutter 15 and on the other face thereof alternately. The plate cutters 15 of such configuration are superposed at intervals which are approximately the same as the thickness of the plates, thereby forming each of the upper mold 21 and lower mold 22. These upper mold 21 and lower mold 22 are positioned so as to be opposed to each other and offset by the thickness of the plate cutters 15 in the direction in which the plate cutters are superposed. By driving this upper mold 21 and lower mold 22 in mutually opposite directions, the plate cutters 15 of the upper mold 21 and plate cutters 15 of the lower mold 22 are meshed together, by which slits e are formed, with bulges g due to the above-mentioned protrusions 23, as shown in Fig. 2, in the metal sheet B fed therebetween. Fig. 4A shows a plan view of the state where the above-mentioned upper mold 21 and lower mold 22 are engaged, and corresponding thereto, Fig. 4B shows the state of the metal sheet B that is fed between the upper and lower molds in the position shown in Fig. 4A and formed with slits e. As shown, the slits e are intermitcently formed in a zigzag arrangement at positions where the upper and lower blades 24, 24 meet, whereas no slits e are formed at positions where the upper and lower skip portions 25, 25 meet, since the blades 24 are cut away as described above. In other words, nodes f are formed between the intermittent slits e. Also, bulges g, protruding alternately from both surfaces of the metal sheet B, are formed by the protrusions 23 at positions where the slits e, e are juxtaposed in parallel. As discussed above, the upper mold 21 and lower mold 22, of superimposed plate cutters 15, are moved upwards and downwards in the slit forming section 11, whereby rows of slits e are formed at the same time. It is therefore possible to form a plurality of slits at once in a prescribed area with a reciprocating system. The number of blades of the plate cutters 15 need to be only a fraction of the number of the blades formed on the edges of disk-shaped cutters 31 as shown in Fig. 14, and since these are laid out in a plane, each cutter can be made small in size and thickness, whereby fine slits can be formed that was unattainable with a rotary system. With these plate cutters 15, it is possible to form fine slits down to a minimum thickness of 100 µm. Consequently, manufacture of collectors with a fine mesh structure that is indispensable for the production of small, high capacity batteries becomes possible. Once the metal sheet B that has been provided with slits e, bulges g, and nodes f in the slit forming section 11 as shown in Fig. 5A is pulled and expanded widthwise in the expanding section 12, the mesh sheet C having a reticulated configuration is achieved, wherein the slits e have been opened and the bulges g have been expanded to form lozenge-shaped cells i surrounded by linear portions h, each cell i being joined by nodes f as shown in Fig. 5B. The amount of elongation of the area wherein the slits e are formed varies depending on the widthwise expansion of the metal sheet B. In this embodiment, the areas with slits e are expanded with the amount such that the ratio of the long diagonal LW to the short diagonal SW of the lozenge-shaped cells that have been formed by the opening of the slits e is approximately 2:1. This mesh sheet C is then conveyed to the bending section 13, where the above-mentioned indentations 19 are formed in the central solid portion Nc and side solid portions Ns on either side of the mesh sheet. At the bending section 13, a male roller formed with protrusions in a widthwise direction at locations corresponding to the central solid portion Nc and side solid portions Ns, and a female roller formed with recesses corresponding thereto, are located opposite to each other (not shown). The mesh sheet C is passed and thus pressed between the male roller and female roller, whereby groove-like indentations 19 are formed in the widthwise direction as shown in Figs. 6A and 6B, in the central solid portion Nc and side solid portions Ns on both sides. It is to be noted that the indentations 19 may also be formed as bosses which project from the top face of the sheet. The mesh sheet C that has been provided with the indentations 19 is then delivered to the rolling section 14. The mesh sheet C is pressed between a pair of compression rollers 13, 18 having flat surfaces in the rolling section 14 so as to flatten out any irregularities in the meshed portion M and the indentations 19 in the solid portions Nc, Ns, and to make the thickness of the entire mesh sheet uniform. At this time, the elongation of the meshed portion M having the reticulated configuration is greater than that of the solid portions Nc, Ns, but the irregularity of the elongation is adjusted by the indentations 19 or bosses formed in the solid portions Nc, Ns. This can prevent deformation of the expanded mesh sheet D issued from the rolling section 14 and deformation or breakage of the meshed portion M. Consequently, the dimensions and number of the indentations 19 or bosses formed in said bending section 13 may be set so that the elongation of the meshed portion M when rolled out corresponds with that of the solid portions Nc, Ns, and the above-mentioned male roller and female roller may be formed on this basis. The expanded mesh sheet D thus manufactured as described above has a much greater tensile strength thanks to the solid portions Nc and Ns than the case where there is no such solid portions. Manufacture of an expanded mesh sheet D, optimal for use as a collector in a thin, small battery, which has a strength to withstand the tension when transported through the processes, while having a fine reticulated configuration and being thin, is thereby possible. Fig. 7 shows a modified example of the plate cutters 15 in the above-mentioned slit forming section 11. In this arrangement, the skip portions 25 of the plate cutters 15 that are formed by cutting away the blades 24 are provided with chamfers 36 on the corners thereof on both sides next to the blades 24, that are formed by cutting the corners away in a direction from the blades side towards the skip portions 25. This configuration further improves strength of the mesh grid. Specifically, the provision of the chamfers 36 increases the width of the part where slit formation by the blades 24 is interrupted by the skip portions 25. As a result, the slits e become slightly shorter and, in the lozenge-shaped cells i formed by the opening of the slits e when the metal sheet is spread out, the angle made at inner corners on both ends of a cell i in a lengthwise direction becomes not acute but obtuse which is rounded as shown in Fig. 8. The width of the nodes f connecting the lozenge-shaped cells i is thereby broadened, and the tensile strength of the mesh sheet is further increased as each of the cells i is connected by obtuse angles. The lozenge-shaped cells i of the expanded mesh sheet D explained above basically have a uniform size. It is also possible for the size of the cells to gradually decrease towards the side edges of the mesh sheet or to vary at different locations. For example, if the widths of the panels forming the plate cutters 15 constituting the upper mold 21 and lower mold 22 gradually increase towards the side edges of the metal sheet B, the width of the linear lattice bars h surrounding the cells i gradually increases towards the side edges of the metal sheet B. This can further improve the strength of the side portions to which great force is applied when the sheet is expanded. The dimensions of the protrusions 23, blades 24, and skip pertions 25 may be varied corresponding to changes in the thickness of the plate cutters 15, whereby the ratio of the long diagonal to the short diagonal of the lozenge-shaped cell i can remain the same, even if the size of the cells i changes. Next, the process for producing a polymer-electrolyte secondary cell using the expanded mesh sheet, manufactured as above, as a collector for the positive and negative electrode plates, will be explained with reference to Figs. 9, 13, and 14. The expanded mesh sheets are manufactured using metal sheets, aluminum for the positive electrode collector and copper for the negative electrode collector of the battery. Especially in the case of constituting a small, lightweight battery such as a polymer-electrolyte secondary cell, the collector is required to be as thin as possible. In this embodiment, a metal sheet of 0.06 mm thickness is used. The expanded mesh sheet D prepared of an aluminum sheet is coated with a binding agent. Then the positive electrode active material 1b, prepared as a paste, is applied on the meshed portion M of the expanded mesh sheet D. After drying, this is rolled to form a positive electrode sheet with the prescribed thickness (0.15 mm in this embodiment). Similarly, the expanded mesh sheet D prepared of a copper sheet is coated with a binding agent, after which the negative electrode active material 2b, prepared as a paste, is applied on the meshed portion M of the expanded mesh sheet D. After drying, this is rolled to form a negative electrode sheet with the prescribed thickness (0.32 mm in this embodiment). The positive electrode collector 1a and negative electrode collector 2a are cut out from the positive electrode sheet and negative electrode sheet obtained as above respectively to form the positive electrode plate 1 and negative electrode plate 2. At this time, the positive electrode collector 1a and negative electrode collector 2a are cut therefrom such that their respective lead connecting portions 1c, 2c are positioned on the central solid portion Nc formed in the expanded mesh sheet D as shown in Fig. 9, by which material is not wasted and the lead connecting portions 1c, 2c can be cut out from areas without openings. The positive electrode plate 1 and negative electrode plate 2 that are thus obtained are layered with separators 3 interposed therebetween, heated between heated rollers, and compressed, thereby joining opposed surfaces by thermal fusion and forming a laminated electrode 4. Each of the lead connecting portions 1c of two sheets of the positive electrode collector 1a, 1a in this laminated electrode 4 are connected to the positive electrode lead 8 and with each other by welding. Similarly, the negative electrode lead 9 is connected to the lead connecting portion 2c of the negative electrode collector 2a by welding. As noted above, since each lead connecting portion 1c, 2c is cut out from the central solid portions Nc without the mesh grid of the expanded mesh sheet D, the welding is securely effected when resistance welding or ultrasonic welding is performed. Also, the connective properties of the lead connecting portions 1c, 2c with each lead 8, 9 are improved and the output of a high current becomes possible because the conductive surface area is large. The laminated electrode 4, to which the leads 8, 9 are connected, is inserted into an outer case 7 formed in an envelope-like shape that is obtained by folding a laminate sheet folded at the fold line T and bonding seal portions P 1 , P 3 by heat fusion as shown in Fig. 13. After injecting a prescribed quantity of liquid electrolyte into this outer case 7, the seal portion P 2 is bonded by heat fusion thereby sealing the laminated electrode 4 within the outer case 7 and completing a polymer electrolyte secondary battery. Next, the relation between battery performance and the construction of the expanded mesh sheets D used as the collectors 1a, 2a for the polymer-electrolyte secondary cell constituted as explained above, is described. The thickness of the expanded mesh sheets D, used as the collectors 1a, 2a for the small, lightweight non-aqueous electrolyte battery described above directly influences the thickness and weight of the battery, and thus is required to be as thin as possible, within a range wherein the battery performance and manufacturing process are not affected. Also, the thinner the thickness of the collectors 1a, 2a is, the more that of the active material 1b, 2b constituting the electrode plates can be increased, whereby the battery capacity can be made large even with the same electrode plate thickness. Consequently, although it is desirable to use a thinner expanded mesh sheet D, it was heretofore impossible to use sheets of less than 0.1 mm thick because of their limited mechanical strength. As noted above, however, the structure including solid portions Nc, Ns in the expanded mesh sheet D makes it possible to use sheets of less than 0.1 mm thick (0.06 mm in this embodiment). Also, a minute reticulated configuration in the expanded mesh sheet D results in improved discharge characteristics of the battery since the distance between the collectors 1a, 2a and the active material 1b, 2b is equalized. However, there are machining limits of the cutters for forming slits in the metal sheet. Also, if the lozenge-shaped cells in the mesh grid are formed so that the ratio of the long diagonal LW in the lozenge shape to the short diagonal SW is 2:1, as shown in Fig. 5B, the bonding properties with the active materials and the discharge characteristics of the battery can be enhanced. Further, narrowing the widths of the linear lattice bars h forming the cells i improves the collection properties. However, in order for the mesh to have the strength to withstand the rolling process, and also in view of the above-mentioned limits to the cutters, the width of the linear lattice bars h should not be made narrower than 0. 1mm. In this regard as well, providing the solid portions Nc, Ns, as noted above, is effective in accomplishing the object to form a fine reticulated configuration in the expanded mesh sheet D thereby improving battery performance and yet maintaining the strength to withstand the manufacturing process. As set forth above, according to the apparatus and method for manufacturing an expanded mesh sheet of the present invention, it is possible to form fine slits with the use of plate cutters, wherefore the manufacture of an expanded mesh sheet with a minute reticulated configuration is possible. As a result, it is possible to produce collectors having a fine mesh grid that is necessary for producing small, high capacity batteries. Also, when forming slits in the metal sheet, solid portions, where slits are not formed, are provided in the widthwise central portion and on both sides of the metal sheet, and an expanded mesh sheet which is provided with solid portions is obtained by expanding this metal sheet. These solid portions improve the tensile strength of the metal sheet and therefore helps prevent the occurrence of breakage during transportation or rolling process in the manufacturing processes of the expanded mesh sheet and in the manufacturing processes of the battery electrodes using this sheet. Furthermore, the above-mentioned solid portions can also be used as areas for welding leads or the like when manufacturing the battery collectors. Since the welding is made at an area without openings, the connection of the electrode to the leads is superior, making possible the output of a high current and contributing to improvements in battery capacity. Figs. 10 to 12 show a method of manufacturing an expanded mesh sheet by which a plurality of expanded mesh sheets D1, D2 can be produced at the same time from the same number cf elongated metal sheets B1, B2. More specifically, two strips of elongated metal sheets B1, B2, one being superposed on the other, are fed from the coil section 10 to the slit forming section 11. Successively, the metal sheets B1, B2 are delivered to the expanding section 12 where they are formed into mesh sheets C1, C2, which are further fed to the bending section 13 and the rolling section 14, thereby obtaining two strips of superposed expanded mesh sheets D1, D2, that are then wound in a roll. The descriptions of the coil section 10, slit forming section 11, expanding section 12, bending section 13, and rolling section 14 are omitted, as they are substantially the same as those explained with reference to Fig. 1 through Fig. 8. Two superposed strips of expanded mesh sheets D1, D2 are separated as shown in Fig. 11. It is of course possible to superpose more than three strips of elongated metal sheets and to produce the same number of expanded mesh sheets therefrom at the same time, using the above method. It is also possible to fold one wide and long metal sheet B' along a fold line F in a lengthwise direction to form a sheet B" comprising a plurality of elongated metal sheets superposed upon one another, as shown in Fig. 12. A plurality of expanded mesh sheets may be also manufactured at the same time using such folded metal sheet in accordance with the method as shown in Figs. 10 and 11.

Claims: A method of manufacturing an expanded mesh sheet comprising the steps of: supplying an elongated sheet (B) between an upper mold (21) and lower mold (22), comprising a plurality of plate cutters (15) that have a plurality of blades (24) for forming slits and are superposed at prescribed intervals; intermittently forming a plurality of slits in a zigzag arrangement lengthwise to the elongated sheet (B) throughout an area defined by the length and width of the superposed plate cutters (15) by a reciprocating movement of said upper mold (21) and lower mold (22) in opposite directions; moving the elongated sheet (B) intermittently by the length of the plate cutters (15); and, pulling the elongated sheet (B) in a direction so as to expand widthwise dimensions of the elongated sheet (B), whereby a mesh grid is formed in the elongated sheet (B). The method of manufacturing an expanded mesh sheet according to Claim 1, wherein in the step of forming the slits in the elongated sheet (B), a band of solid portion in a lengthwise direction is provided at a prescribed location in the elongated sheet (B), so that the elongated sheet (B), after being expanded, has a portion where there is no mesh configuration. A method of manufacturing an expanded mesh sheet according to claim 1 or 2, wherein a plurality of elongated sheets (B1, B2) superposed on one another are supplied between the upper mold (21) and lower mold (22), so that slits are formed in the superposed sheets; and the superposed elongated sheets (B1, B2) are then pulled in a direction so as to expand widthwise dimensions of the elongated sheets (B1, B2), whereby a mesh grid is formed in the elongated sheets (B1, B2). An apparatus for manufacturing an expanded mesh sheet comprising: slit forming means (11) including an upper mold (21) and a lower mold (22), each of the upper mold (21) and lower mold (22) comprising a plurality of plate cutters (15) superposed at intervals roughly equal to the thickness thereof, the plate cutters (15) having blades (24) formed on both faces thereof, a plurality of protrusions (23) projected at prescribed intervals, and recessed portions (25) provided between said protrusions (23) by cutting away one surface and the other surface of said blades (24) at an angle alternately, wherein said upper mold (21) and lower mold 22 are positioned opposite to each other and offset by the thickness in the direction in which the plate cutters (15) are superposed, said upper mold (21) and lower mold (22) being driven to reciprocate in opposite directions, thereby in each reciprocation, forming a plurality of slits in a lengthwise direction and in a zigzag arrangement throughout an area defined by the length and the width of the plate cutters (15) in an elongated sheet (B) fed intermittently between said upper mold (21) and lower mold (22) in a lengthwise direction of said plate cutters (15); means for intermittently conveying said elongated sheet (B) by the length of the plate cutters (15) lengthwise to the plate cutters (15) in the slit forming means (11); expanding means (12) for pulling the elongated sheet (B) in a direction so as to expand widthwise dimensions of the elongated sheet (B) and opening said slits thereby producing a mesh sheet (C) having a reticulated configuration; and, rolling means (14) for flattening said mesh sheet (C) from both upper and lower surfaces. The apparatus for manufacturing an expanded mesh sheet according to Claim 4, wherein the thickness of the plate cutters (15) gradually increases toward the sides of the upper mold (21) and lower mold (22). The apparatus for manufacturing an expanded mesh sheer according to Claim 4 or 5, wherein the blades (24) between the recessed portions (25) of the plate cutters (15) are configured such that corner parts are chamfered away towards the recessed portions (25) on both sides. The apparatus for manufacturing an expanded mesh sheet according to Claim 4, 5 or 6, wherein the upper mold (21) and lower mold (22) are constructed such hat the plate cutters (15) are not disposed at positions corresponding to prescribed areas in a widthwise direction of the elongated sheet (B), so that solid portions where slits are not formed are provided lengthwise to the elongated sheet (B) The apparatus for manufacturing an expanded mesh sheet according to Claim 6, further comprising bending means (13) for forming indentations (19) or bosses in the solid portions of the elongated sheet (B) before rolling the elongated sheet (B).

Inventors: GODA YOSHIO, KOBAYASHI HIROYUKI, NAKATSUKA SABURO, OGAWA MASAHIKO, GODA, YOSHIO, KOBAYASHI, HIROYUKI, NAKATSUKA, SABURO, OGAWA, MASAHIKO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1999
Main classification: B21D31
IPC codes: B21D31