Electrode assembly and method of manufacturing electrode assembly

A positive electrode plate includes a front positive electrode active material layer on a front surface of a positive electrode metal foil, and having a positive electrode large tapered portion that extends at an incline from one edge of the front surface of the positive electrode metal foil at a positive electrode large inclination angle. A negative electrode plate includes a front negative electrode active material layer on a front surface of a negative electrode metal foil, and having a negative electrode large tapered portion that extends at an incline from one edge of the front surface of the negative electrode metal foil at a negative electrode large inclination angle. The positive and negative electrode plates are alternately laminated with a separator interposed therebetween such that each of their front surfaces is oriented in the same direction in the rear-to-front directional axis along the thickness of the plates.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a National Phase entry of, and claims priority to, PCT Application No. PCT/JP2015/080492, filed Oct. 29, 2015, which is incorporated by reference herein in its entirety for all purposes.

BACKGROUND

This disclosure relates to an electrode assembly and a method for manufacturing said assembly.

According to Japanese Laid-Open Patent Publication No. 9-120836, describing a secondary battery, an electrode assembly and electrolyte solution are sealed in an inside of a case. The electrode assembly includes positive electrode plates and negative electrode plates that are stacked in an alternating manner wherein each of the positive electrode plates is enveloped by a separator. The electrolyte solution is filled in the case when a secondary battery is new. Accordingly, the electrolyte solution is filled around active material layers of the positive electrode plates and the negative electrode plates. Over time, the electrolyte solution is reduced with the use of the secondary battery due to electrolysis or evaporation. As a result, the active material layers of the positive electrode plates and the negative electrode plates are exposed from the electrolyte solution as the electrolyte solution is reduced. An electrolyte solution is built up around the exposed active material layers. The electrolyte solution immersed in the active material layers stays around the active material layers due to surface tension so as to form the built up electrolyte solution. The electrolyte solution immersed in the active material layers stays around the active material layers due to surface tension so as to form this electrolyte sump. The active material layers expand and contract while the secondary battery is charged and discharged. In accordance with this expansion and contraction, the electrolyte solution flows out and back between the active material layers and the built up electrolyte solution. The electrolyte solution is supplied to the active material layers as the electrolyte solution returned to the active material layers. The active material layers are impregnated with the electrolyte solution so as not to dry.

The Japanese Laid-Open Patent Publication No. 9-120836 does not disclose a specific structure for promoting the electrolyte solution to be supplied into each active material layer. It does not disclose a specific structure for suppressing uneven impregnation of electrolyte solution in a laminating direction of positive electrode plates and negative electrode plates. It does not disclose a specific structure for ensuring sufficient capacity for the active materials of each of the positive and negative electrode plates.

BRIEF SUMMARY

Exemplary embodiments of the present disclosure provide a structure for promoting electrolyte solution to be supplied to each active material layer in an electrode assembly in which positive electrode plates and negative electrode plates are stacked. Additionally, the present disclosure may provide a structure that suppresses uneven impregnation of electrolyte solution in a laminating direction of the positive electrode plates and negative electrode plates. Still further, the present disclosure may provide a structure for ensuring sufficient capacity for the active materials of each of the positive and negative electrode plates.

According to one aspect of the present disclosure, the electrode assembly includes positive electrode plates, negative electrode plates and separators. Each of the positive electrode plates includes a positive electrode metal foil, where a front positive electrode active material layer is provided on the front surface of the positive electrode metal foil and a rear positive electrode active material layer is provided on a rear surface of the positive electrode metal foil. Each of the negative electrode plates includes a negative electrode metal foil, where the front negative electrode active material layer is provided on a front surface of the negative electrode metal foil and a rear negative electrode active material layer provided on a rear surface of the negative electrode metal foil. Each of the separators is interposed between each of the positive electrode plates and each of the negative electrode plates. The front positive electrode active material layer of each positive electrode plate has a positive electrode large tapered portion that is inclined from one edge of the front surface of the positive electrode metal foil to an inner side of the positive electrode plate at a positive electrode large inclination angle. The rear positive electrode active material layer has a positive electrode small tapered portion that is inclined from one edge of the rear surface of the positive electrode metal foil to the inner side of the positive electrode plate at a positive electrode small inclination angle, where said angle is smaller than the positive electrode large inclination angle. The front negative electrode active material layer has a negative electrode large tapered portion that is inclined from one edge of the front surface of the negative electrode metal foil to the inner side of the negative electrode plate at a negative electrode large inclination angle. The rear negative electrode active material layer has a negative electrode small tapered portion that is inclined from one edge of the rear surface of the negative electrode metal foil to the inner side of the negative electrode plate at a negative electrode small inclination angle, where said angle is smaller than the negative electrode large inclination angle. Furthermore, in the electrode assembly, the positive electrode plates and the negative electrode plates are alternately laminated with the separator or separators interposed therebetween such that the front surface of the positive electrode plates having the positive electrode large tapered portion and the front surface of the negative electrode plates having the negative electrode large tapered portion are both oriented in the same direction on the rear-to-front directional axis along the thickness of the positive electrode plates and the negative electrode plates.

According to the above-described electrode assembly, the positive electrode large tapered portion and the negative electrode large tapered portion inclined to each inner side of the positive electrode plates and the negative electrode plates, respectively, are provided at each outer edge of the front positive electrode active material layer and the front negative electrode active material layer. Therefore, built up electrolyte is formed along each of the large tapered portions of the electrode assembly so as to be directed to the inner side of each of the respective positive electrode plates and negative electrode plates. Accordingly, in the electrode assembly, supply of the electrolyte solution to each inner side of the positive electrode plates and the negative electrode plates is promoted so that the impregnation efficiency of the electrolyte solution in the front positive electrode active material layer and the front negative electrode active material layer may be improved. As a result, with this electrode assembly, the supply of the electrolyte solution to the rear positive electrode active material layer and the rear negative electrode active material layer, which are opposed to each other with the separator between the front negative electrode active material layer and the front positive electrode active material layer, is also promoted such that the impregnation efficiency of the electrolyte solution to the rear positive electrode active material layer and the rear negative electrode active material layer may also be improved.

According to the electrode assembly described above, the positive electrode plates and the negative electrode plates are laminated with their front surfaces having the positive electrode large tapered portion or the negative electrode large tapered portion, respectively, oriented in the same direction. In the electrode assembly, such an orientation evenly distribute clearances into which the electrolyte solution enters as compared with the case where, for example, the positive electrode plates and the negative electrode plates are laminated such that their front surfaces and rear surfaces are laminated in random directions. As a result, with this electrode assembly, the uneven impregnation of the electrolyte solution in the laminating direction of the positive electrode plates and negative electrode plates may be prevented, whereas the evenly distributed supply of the electrolyte solution in each of the active material layers is promoted as described above. Further, with this structural configuration, the positive electrode plates and the negative electrode plates can also ensure sufficient capacity for the active materials by fixing the inclination angle of both the positive electrode small tapered portion and the negative electrode small tapered portion to be small.

According to another aspect of the present disclosure, one of the positive electrode plates or the negative electrode plates constitutes an electrode plate unit enveloped in a bag shape with the separator having a larger surface area than that of the one of the positive electrodes or negative electrode plates. The positive electrode large inclination angle is set to be smaller than the negative electrode large inclination angle when one of the positive electrode plates constitutes the electrode plate unit. Conversely, the negative electrode large inclination angle is set to be smaller than the positive electrode large inclination angle when one of the negative electrode plates constitutes the electrode plate unit.

In the above-described electrode plate unit, the separator covers the built-up electrolyte formed around the outer edge of the electrode plates from the outside in order to become a part of a plane which may retain the built-up electrolyte. In other words, the separator helps the formation of the built-up electrolyte. Therefore, with the structure of the electrode plate unit, the built-up electrolyte formed along the large tapered portion is stably retained as compared to the electrode plates in an exposed state (exposed electrode plates). Thus, with the retained built-up electrolyte it is possible to equalize an amount of the built-up electrolyte, which is formed at the respective large tapered portions of the electrode plate unit as well as the exposed electrode plates, by setting the inclination angle of the large tapered portion of the electrode plate of the electrode plate unit smaller than the inclination angle of the large tapered portion of the exposed electrode plates. Since these electrode units and exposed electrode plates are alternately laminated, the uneven impregnation of the electrolyte solution in the laminating direction can be prevented in the electrode assembly.

According to another aspect of the present disclosure, the separator is made as a one-piece construction. The surface area of the positive electrode metal foil is smaller than the surface area of the negative electrode metal foil. The positive electrode large inclination angle is set to be smaller than the negative electrode large inclination angle.

In the above-described electrode assembly, since the surface area of the positive electrode plate is smaller than the surface area of the negative electrode plate, the negative electrode plate projects from and is stacked on top of the positive electrode plate. This projecting part of the negative electrode plate becomes a part of a plane, which retains the built-up electrolyte formed around the outer edge of the positive electrode plate, to help the formation of the built-up electrolyte. Therefore, the built-up electrolyte formed along the large tapered portion of the positive electrode plate tends to be stably retained as compared with that of the negative electrode plate. Thus, it is possible to equalize an amount of the built-up electrolyte, which is formed at respective large tapered portions of the positive electrode plate and the negative electrode plate by setting the inclination angle of the large tapered portion of the positive electrode plate smaller than the inclination angle of the large tapered portion of the negative electrode plate. Since these positive electrode plates and negative electrode plates are alternately laminated, the uneven impregnation of the electrolyte solution in the laminating direction can be prevented in the electrode assembly.

According to another aspect of the present disclosure, each of the front negative electrode active material layer and the rear negative electrode active material layer is covered with a heat-resistant layer. The negative electrode large tapered portion extends from the front negative electrode active material layer to the heat-resistant layer. The front negative electrode active material layer is exposed at the negative electrode large tapered portion.

In the above electrode assembly, as described, both active material layers on the negative electrode plate are covered with a heat-resistant layer. In this configuration, the heat-resistant layer may effectively prevent short-circuiting between the positive electrode plate and negative electrode plate caused by, for example, high heat. With the negative electrode plate described above, the negative electrode large tapered portion extends up to the heat-resistant layer while the negative electrode large tapered portion exposes a part of the front negative electrode active material layer. This may promote the supply of the electrolyte solution from the built-up electrolyte, which is formed along the negative electrode large tapered portion, to the front negative electrode active material layer. Consequently, the impregnation speed of the electrolyte solution into the front negative electrode active material layer is accelerated.

Another aspect of the present disclosure relates to a method for manufacturing electrode assemblies including positive electrode plates, negative electrode plates and separators interposed between the positive electrode plates and negative electrode plates. According to this method for manufacturing the electrode assemblies, a positive electrode base sheet, having a front positive electrode active material layer and a rear positive electrode active material layer on each of the front and rear surfaces of a strip-shaped positive electrode metal foil, is prepared. Further, a negative electrode base sheet, having a front negative electrode active material layer and a rear negative electrode active material layer on each of the front and rear surfaces of a strip-shaped negative electrode metal foil, is prepared. Subsequently, a laser beam irradiates the positive electrode base sheet from the front positive electrode active material layer to the rear positive electrode active material layer in order to cut out the positive electrode plate from the positive electrode base sheet and in order to form a positive electrode large tapered portion which is inclined from one edge of a front surface of the positive electrode metal foil of the positive electrode plate to an inner side of the positive electrode plate at a positive electrode large inclination angle. The rear positive electrode active material layer is formed with a positive electrode small tapered portion that is inclined from one edge of a rear surface of the positive electrode metal foil of the positive electrode plate to an inner side of the positive electrode plate at a positive electrode small inclination angle smaller than the positive electrode large inclination angle. A laser beam irradiates the negative electrode base sheet from the front negative electrode active material layer to the rear negative electrode active material layer in order to cut out the negative electrode plate from the negative electrode base sheet and in order to form a negative electrode large tapered portion which is inclined from one edge of a front surface of the negative electrode metal foil of the negative electrode plate to an inner side of the negative electrode plate at a negative electrode large inclination angle. The rear negative electrode active material layer is formed with a negative electrode small tapered portion that is inclined from one edge of a rear surface of the negative electrode metal foil of the negative electrode plate to the inner side of the negative electrode plate at a negative electrode small inclination angle smaller than the negative electrode large inclination angle. After being cut out, the positive electrode plates and the negative electrode plates are laminated while the front surfaces of the positive electrode plates provided with the positive electrode large tapered portion and the front surfaces of the negative electrode plates provided with the negative electrode large tapered portion, respectively, are oriented in the same direction on the rear-to-front directional axis along the thickness of the positive electrode plate and negative electrode plate.

In the above method for manufacturing the electrode assemblies, the positive electrode large tapered portions and the negative electrode large tapered portions inclined to the inner side of the positive electrode plate and/or the negative electrode plate respectively are provided at each respective outer edge of the front positive electrode active material layer and the front negative electrode active material layer. Consequently, built-up electrolyte is formed in the electrode assembly as a final product along these large tapered portions to be directed to each inner side of the positive electrode plate and the negative electrode plate. This promotes supply of the electrolyte solution to each of the respective inner sides of the positive electrode plate and the negative electrode plate in the electrode assembly, to collectively improve the impregnation efficiency as a whole of the electrolyte solution in the front positive electrode active material layer and the front negative electrode active material layer. As a result, this electrode assembly also promotes the supply of the electrolyte solution to the rear negative electrode active material layer and the rear positive electrode active material layer, each of which respectively opposes the front positive electrode active material layer or the front negative electrode active material layer, with the separator interposed therebetween.

According to the above method for manufacturing the electrode assemblies, the positive electrode plate and the negative electrode plate are laminated with each of the front surfaces having the positive electrode large tapered portion and/or the negative electrode large tapered portion oriented in the same direction. In the electrode assembly, this evenly distributes clearances into which the electrolyte solution can enter as compared to the case where, for example, each of the front surfaces and rear surfaces of the positive electrode plates and the negative electrode plates, respectively, is laminated facing in random directions. As a result, uneven impregnation of the electrolyte solution in the laminating direction of the positive electrode plates and negative electrode plates may be prevented in the electrode assembly, while the evenly distributed supply of the electrolyte solution in each of the active material layers is promoted as described above. Furthermore, sufficient capacity of the active material can be ensured by setting the respective inclination angle of the positive electrode small tapered portion of the positive electrode plate and the negative electrode small tapered portion of the negative electrode plate to be small.

According to another aspect of the present disclosure, the laser beam is focused on a focal point at a predetermined position on the positive electrode base sheet or the negative electrode base sheet, and irradiates the respective base sheets such that an optical axis of the laser beam is perpendicular to the base sheet.

In the above method for manufacturing the electrode assemblies, the laser beam irradiates the base sheets such that it is perpendicular to each base sheet. In this way, large tapered portions having a symmetrical shape are formed on both sides of each base sheet across a cutting line formed by the laser beam. For example, when cutting out rectangular positive electrode plates in a continuously adjacent manner along a longitudinal direction of the positive electrode base sheet (see dotted lines inFIG. 10), the positive electrode large tapered portions each having a symmetrical shape can be formed on two sides of the cut-out positive electrode plates opposed to the longitudinal direction of the positive electrode base sheet such that the anisotropic arrangement of the positive electrode plates can be suppressed. In a similar manner, the anisotropic arrangement of the negative electrode plates may also be suppressed.

DETAILED DESCRIPTION

One exemplary embodiment according to the present invention will be described with reference to the drawings. An electric storage device1shown inFIG. 1is, for example, a lithium ion secondary battery. A case10of the electric storage device1includes a rectangular parallelepiped case main body12with a bottom and a flat lid11which covers a rectangular opening at the top of the case main body12. The lid11includes external connection terminals14and16. The external connection terminals14and16penetrate through the lid11, and intersect with the lid11to form two circular planes, respectively. The circular planes formed by the intersection of the lid11with external connection terminals14and16, respectively, are parallel to the directional axis along the thickness of the positive electrode plates and the negative electrode plates at the positive and negative electrode tabs32band42b, respectively.

As shown inFIG. 1, the electric storage device1includes an electrode assembly20and electrolyte solution18, both of which are stored inside of the case10. The electrode assembly20is connected with the external connection terminals14and16via a positive electrode tab32band a negative electrode tab42b, respectively, as described below. The electrode assembly20supplies electricity to the outside of the electric storage device1via the external connection terminals14and16(discharge) and is supplied with electricity from the outside of the electric storage device (recharge). As will be described below, the electrolyte solution18is filled in the case10when the electric storage device1is new. The electric storage device1as shown inFIG. 1is not new, but in a used state in which recharging and discharging have been repeated, therefore, the electrolyte solution18is reduced from a fully charged state due to electrolysis or evaporation. Consequently, a part of the electrode assembly20not submerged in electrolyte solution18may be exposed. A submersion level of a liquid surface of the electrolyte18shall not be limited to the exemplary level shown inFIG. 1and may be above or below the level shown inFIG. 1.

The electrode assembly20is configured such that positive electrode plate units50(electrode plate units) and negative electrode plates40are stacked in an alternating manner. As shown inFIG. 2andFIG. 3, the positive electrode plate unit50includes a positive electrode plate30and an enveloping separator54. The positive electrode plate30is configured in a rectangular shape. The separator54is a thin film made of porous resin which is folded approximately in half lengthwise. Opposite lateral faces of the positive electrode plate30are enveloped by the separator54in a saclike manner. As shown inFIG. 3, the portion of positive electrode plate30including the opposing lateral faces and their shared contiguous lengthwise edge at the top of the plate is collectively interposed between the separator54that is folded in half. The separator54includes a first separator part54aconfigured to cover a front surface30aof the positive electrode plate30and a second separator part54bconfigured to cover a rear surface30b, the opposite lateral face of front surface30a, of the positive electrode plate30. Both separator parts54aand54bhave a surface area larger than that of the lateral faces of the positive electrode plate30. After the interposition of positive electrode plate30, both separator parts54aand54bare welded together along their respective outer peripheries of three edges, outward of the corresponding outer peripheries of the positive electrode plate30, excluding the shared contiguous lengthwise positive electrode tab edge38aat the top of the positive electrode plate30, where the edge of separator54marking the folding between54aand54bfits over edge38a. In particular, the positive electrode tab32bprotrudes upward out of the separator54through a complementary sized opening hole54cof the separator54. Instead of being folded in half in this manner, the positive electrode unit50may also instead include separators that cover individually a front or rear opposing lateral surface of the positive electrode plate30, where the outer peripheries of the separators may be welded to each other outward of the corresponding outer peripheries of all four edges of the positive electrode plate30.

As shown inFIGS. 3, 4 and 6, the positive electrode plate30includes a positive electrode metal foil32, a front positive electrode active material layer34and a rear positive electrode active material layer36. The positive electrode metal foil32may be, for example, an aluminum foil. The positive electrode metal foil32includes a flat (two-dimensional) rectangular shaped positive electrode main body32aand a positive electrode tab32b, which extends from one side of the positive electrode main body32a. The front positive electrode active material layer34is provided on the front surface32cof the positive electrode metal foil32and may cover substantially the entire area of one of two lateral faces of the rectangular positive electrode main body32a. The rear positive electrode active material layer36is provided on the rear surface32dof the positive electrode metal foil32and may cover substantially the entire area of the other, opposing lateral face of the rectangular positive electrode main body32a. Both positive electrode active material layers34and36are made of, for example, a lithium-containing metal oxide. The electrolyte solution18(seeFIG. 1) impregnates both positive electrode active material layers34and36after the positive electrode plate30is accommodated in the case10together with the electrolyte solution18in which the plate is submerged. Referring toFIG. 4, the positive electrode main body32atogether with both positive electrode active material layers34and36collectively constitute a positive electrode base38.

The front positive electrode active material layer34and the rear positive electrode active material layer36are intentionally provided so as to not cover the positive electrode tab32b, so that the positive electrode metal foil32may be exposed at the positive electrode tab32b. The positive electrode tabs32bof each positive electrode plate30are laminated in combination with each other and may collectively, for example, be welded to one external connection terminal14(seeFIG. 1). In this specification, an edge of the positive electrode plate30provided along with the positive electrode tab32b, comprising the shared contiguous edge of the opposite lateral faces of the positive electrode plate30at the top of the plate, perpendicular to positive electrode tab32b, is referred to as a positive electrode tab edge38a. An edge vertically opposed to the positive electrode tab edge38ais referred to as a positive electrode tab opposing edge38b. Two edges parallel to positive electrode tab32band orthogonal to the positive electrode tab edge38aand the positive electrode tab opposing edge38bon both the left and right sides of tab32bare referred to as a first positive electrode edge38cand a second positive electrode edge38d.

As shown inFIGS. 3, 4 and 6, the front positive electrode active material layer34includes positive electrode large tapered portions34a. The positive electrode large tapered portions34aare respectively provided along the positive electrode tab opposing edge38b, first positive electrode edge38cand second positive electrode edge38d. Each positive electrode large tapered portion34ais linearly inclined from each corresponding edge38b,38cand38drearward and outward toward the interior of the positive electrode plate30, on the front surface32cof the positive electrode metal foil32, with respect to the rear-to-front direction along the thickness of the positive electrode plate30. Each of the positive electrode large tapered portions34ais configured to have a positive electrode large inclination angle θ1A (seeFIG. 6) relative to the rear-to-front directional axis along the thickness of the positive electrode plate30.

As shown inFIGS. 4 and 6, the rear positive electrode active material layer36includes positive electrode small tapered portions36a. The positive electrode small tapered portions36aare respectively provided along the positive electrode tab opposing edge38b, the first positive electrode edge38cand the second positive electrode edge38d. Each of the positive electrode small tapered portions36ais linearly inclined frontward from each corresponding edge38b,38cand38dtoward the interior of the positive electrode plate30, on the rear surface32dof the positive electrode metal foil32, with respect to the rear-to-front direction along the thickness of positive electrode plate30. Each of the positive electrode small tapered portions36ais configured to have a positive electrode small inclination angle θ1B (seeFIG. 6) relative to the rear-to-front directional axis along the thickness of the positive electrode plate30. The positive electrode small inclination angle θ1B is smaller than the positive electrode large inclination angle θ1A. The positive electrode small inclination angle θ1B may be 0 degrees, in which case, the positive electrode small tapered portions36aare not formed.

As shown inFIGS. 2, 5 and 6, the negative electrode plate40includes a negative electrode metal foil42, a front negative electrode active material layer44and a rear negative electrode active material layer46. The negative electrode metal foil42may be, for example, a copper foil. The negative electrode metal foil42includes a rectangular negative electrode main body42aand a negative electrode tab42bwhich extends from an upper edge of the negative electrode main body42a. The surface area of the negative electrode main body42ais larger than the above-described area of the positive electrode main body32a. The front negative electrode active material layer44is provided on the front surface42cof the negative electrode metal foil42and may substantially cover the entire surface area of the front surface of the negative electrode main body42a. The rear negative electrode active material layer46is provided on the rear surface42dof the negative electrode metal foil42and may substantially cover the entire surface area of the rear surface of the negative electrode main body42a. Both negative electrode active material layers44and46may include, for example, carbon. The electrolyte solution18(seeFIG. 1) is impregnated in both positive electrode active material layers44and46after the negative electrode plate40is accommodated in the case10and submerged in the electrolyte solution18. As referring toFIG. 5, the negative electrode main body42aand both negative electrode active material layers44and46collectively constitute a negative electrode base48.

The front negative electrode active material layer44and rear negative electrode active material layer46do not cover the area where the negative electrode tab42bprojects outward so that the negative electrode metal foil42at the negative electrode tab42bis exposed. The negative electrode tabs42bof each negative electrode plate40are laminated in combination with each other and may, for example, be collectively welded to one external connection terminal16(seeFIG. 1). In this specification, an edge of the negative electrode plate40provided with the negative electrode tab42bat the top of the negative electrode plate40is referred to as negative electrode tab edge48a. An edge vertically opposed to the negative electrode tab edge48ais referred to as a negative electrode tab opposing edge48b. Two edges orthogonal to the negative electrode tab edge48aand the negative electrode tab opposing edge48b, and parallel to the negative electrode tab42b, located at the left and ride sides of said electrode tab42b, are respectively referred to as a first negative electrode edge48cand a second negative electrode edge48d.

As shown inFIGS. 2, 5 and 6, the front negative electrode active material layer44includes negative electrode large tapered portions44a. The negative electrode large tapered portions44aare respectively provided along the negative electrode tab opposing edge48b, the first negative electrode edge48c, and the second negative electrode edge48d. Each of the provided negative electrode large tapered portions44ais linearly inclined frontward from each corresponding edge48b,48cand48d, toward the interior of the negative electrode plate40, on the front surface42cof the negative electrode metal foil42. Each of the negative electrode large tapered portions44ais configured to have a negative electrode large inclination angle θ2A relative to the rear-to-front axis along the thickness of the negative electrode plate40(seeFIG. 6). The negative electrode large inclination angle θ2A is larger than the above described positive electrode large inclination angle θ1A.

As shown inFIGS. 5 and 6, the rear negative electrode active material layer46includes negative electrode small tapered portions46a. The negative electrode small tapered portions46aare respectively provided along the negative electrode tab opposing edge48b, the first negative electrode edge48c, and the second negative electrode edge48d. Each of the negative electrode small tapered portions46ais linearly inclined frontward from each corresponding edge48b,48cand48dtoward the interior of the negative electrode plate40, on the rear surface42dof the negative electrode metal foil42. Each of the negative electrode small tapered portions46ais configured to have a negative electrode small inclination angle θ2B (seeFIG. 6). The negative electrode small inclination angle θ2B is smaller than the negative electrode large inclination angle θ2A. The negative electrode small inclination angle θ2B may be 0 degrees. In this case, the negative electrode small tapered portions46aare not formed.

FIG. 6illustrates the inside of the electric storage device1from a top view, above the liquid surface interface of the electrolyte solution18(seeFIG. 1). The electrolyte solution18impregnates each pair of active material layers34and36, as well as44and46for the positive electrode plate30and negative electrode plate40, respectively. The electrolyte solution18stays around each electrode plate30and40and the separator54due to surface tension to form the built up electrolyte E. Each pair of the active material layers34and36,44and46expands and contracts while the electric storage device1is charged and discharged. In accordance with this expansion and contraction, the surrounding electrolyte solution18flows out and back between the built up electrolyte E and each of the active material layers34and36,44and46. The electrolyte solution18is supplied to each of the active material layers34and36,44and46as the electrolyte solution18returns to each of the active material layers34and36,44and46. Each of the active material layers34and36,44and46is impregnated with the electrolyte solution18so as not to dry. InFIG. 6, the built up electrolyte E is shown in dotted areas.

As shown inFIG. 6, the built up electrolyte E is formed along the positive electrode large tapered portion34ato be directed toward the interior of the positive electrode plate30. This formation promotes the supply of the electrolyte solution18toward the inside of the positive electrode plate30in the electrolyte solution18. As a result of this formation, the impregnation efficiency of the electrolyte solution18in the front positive electrode active material layer34may be improved, and consequently the supply of the electrolyte solution18to the rear negative electrode active material layer46, vertically opposed to the front positive active material layer34with the separator54interposed therebetween, is promoted as well. Therefore, due to the formation of the built up electrolyte E along34a, the impregnation efficiency of the electrode solution18is improved in front positive electrode active material layer34, and also in the rear negative electrode active material layer46.

As shown inFIG. 6, the built up electrolyte E is formed along the negative electrode large tapered portion44ato be directed toward the interior of the negative electrode plate40. This formation promotes the supply of the electrolyte solution18toward the inside of the negative electrode plate40in the front negative electrode active material layer44. As a result, the impregnation efficiency of the electrolyte solution18in the rear negative electrode active material layer44may be improved, and consequently the supply of the electrolyte solution18to the rear positive electrode active material layer36, vertically opposed to the front negative active material layer44with the separator54interposed therebetween, is promoted as well. Therefore, due to the formation of the built up electrolyte E along44a, the impregnation efficiency of the electrode solution18is improved in front negative electrode active material layer44, and also in the rear positive electrode active material layer36.

As shown inFIG. 6, the positive electrode plate30and the negative electrode plate40are laminated with the respective front surface30aand40aof each plate having the positive electrode large tapered portion34aand the negative electrode large tapered portion44aoriented in the same general direction, inclined at a positive angle with respect to the rear-to-front directional axis along the thickness of the plates. Therefore, in the electrode assembly20, clearances into which the electrolyte solution18can enter may be disposed in a distributed manner as compared with the case where, for example, the positive electrode plates30and the negative electrode plates40are laminated with their front surfaces30aand40aopposed to each other as, for example, in an electrode assembly20shown inFIG. 7. As a result of the distributed manner of the clearances, with this electrode assembly20, the uneven impregnation of the electrolyte solution18in the laminating direction of the positive electrode plates30and negative electrode plates40may be suppressed while the evenly distributed supply of the electrolyte solution18in each pair of the active material layers34and36, as well as44and46, is promoted as described above. The inclination angles θ1B and θ2B of the positive electrode small tapered portion36aand the negative electrode small tapered portion46ain the positive electrode plate30and the negative electrode plate40, respectively, are set to be small. In this way, with a smaller angle resulting in a larger material area, sufficient capacity for the respective active material at the positive electrode plate30and the negative electrode plate40can be ensured.

As shown inFIG. 6, the positive electrode large tapered portion34ais surrounded by the separator54. The separator54provides a barrier to the built up electrolyte E formed along the positive electrode large tapered portion34afrom the outside to be a part of a plane which retains the built up electrolyte E. In this way, the separator54facilitates the formation of the built up electrolyte E. The negative electrode large tapered portion44ais exposed outside of the separator54. Therefore, the built up electrolyte E formed along the negative electrode large tapered portion44ais retained minimally compared to the built up electrolyte E formed along the positive electrode large tapered portion34a. Accordingly, it is possible to equalize an amount of the built up electrolyte E, formed at the positive electrode large tapered portion34aand the negative electrode large tapered portion44a, respectively, by setting the positive electrode large inclination angle θ1A to be smaller than the negative electrode large inclination angle θ2A. As a result of the equalization of built up electrolyte E, the uneven impregnation of the electrolyte solution18among the positive electrode plate30and the negative electrode plate40in the laminating direction can be suppressed in the electrode assembly20.

Typically, in the electrode assembly20, force may mostly be applied at the respective outer edge of the positive electrode plate30and the outer edge of the negative electrode plate40. Consequently, the positive electrode plate30and the negative electrode plate40may touch each other (internal short circuit) if the separator54is torn between each of the outer edges. For this reason, in the electrode assembly20shown inFIG. 6, the positive electrode large tapered portion34aand the negative electrode large tapered portion44aare provided at the respective outer edges of the positive electrode plate30and the negative electrode plate40at an inclined angle as described. As a result, a clearance corresponding to the space between the inclined large tapered portions34aand44ais formed between each of the outer edges of the positive electrode plate30and the negative electrode plate40such that an internal short circuit can be prevented even if the separator at the outer edge of the positive electrode plate30and the negative electrode plate40is torn due to applied force, etc.

Further, a method for manufacturing the electrode assembly20will be described. As shown inFIG. 8, the method for manufacturing the electrode assembly20includes a positive electrode plate manufacturing step S1, a negative electrode plate manufacturing step S2, and a lamination step S3. The positive electrode plate manufacturing step S1includes a positive electrode base sheet preparation step S1a, a positive electrode laser processing step S1b, and a positive electrode separator enveloping step S1c. The negative electrode plate manufacturing step S2includes a negative electrode base sheet preparation step S2aand a negative electrode laser processing step S2b. The positive electrode plate producing step S1and the negative electrode plate preparing step S2may be performed in parallel, or sequentially. The lamination step S3may be performed after the positive electrode plate manufacturing step S1and the negative electrode plate manufacturing step S2.

As shown inFIG. 9, a coating-and-drying apparatus70is used in the positive electrode base sheet preparation step S1a. The coating-and-drying apparatus70comprises a supply roller71, a coating apparatus72, a dryer73, a press roller74and a take-up roller76. As shown inFIG. 9, the positive electrode metal foil32is rolled out from the supply roller71and passes through the coating apparatus72, the dryer73and the press roller74in succession. The positive electrode metal foil32is coated with an active material on both sides of the positive electrode metal foil32by the coating apparatus72. This coating results in the formation of the front positive electrode active material layer34on the front surface32cof the positive electrode metal foil32and the rear positive electrode active material layer36on the rear surface32d. Both positive electrode active material layers34and36are dried by the dryer73and pressed by the press roller74in a rear-to-front directional axis along the thickness of the positive electrode plates and the negative electrode plates. In this way, a positive electrode base sheet61having each of the positive electrode active material layers34and36formed on the front and rear surfaces of the positive electrode metal foil32, respectively, is manufactured. The manufactured positive electrode base sheet61is then rolled up by the take-up roller76while being tensioned with each of the rollers77.

The positive electrode base sheet61includes the strip-shaped positive electrode metal foil32, the front positive electrode active material layer34, and the rear positive electrode active material layer36, formed collectively as described above. Both positive electrode active materials34and36are formed in the active material layer formation regions61a(seeFIG. 10) corresponding to each other at the same position on the front surface32cand the rear surface32dof the positive electrode metal foil32, respectively. InFIG. 10, lines to be cut by a laser beam LS (seeFIG. 13), which will be described later, are shown as dotted lines. The width of the active material layer formation region61a(height inFIG. 10) corresponds to substantially double of the length from the positive electrode tab opposing edge38bto the positive electrode tab edge38a. Both the uppermost and lowermost sides of the positive electrode base sheet61in a widthwise direction are configured as metal foil exposed regions61band61cas shown inFIG. 10where in these regions front positive electrode active material layer34and the rear positive electrode active material layer36are not provided so as to expose the negative electrode metal foil32. The width of each metal foil exposed region,61band61c, respectively, corresponds to the length of the positive electrode tab32bin an extending direction as shown, e.g., inFIG. 2. The active material layer formation region61aand both metal foil exposed regions61band61care continuous over the entire length of the positive electrode base sheet61in the longitudinal direction. InFIG. 10, the active material layer formation region61ais indicated by the pattern of diagonal lines. The positive electrode base sheet61will then be transferred to the positive electrode laser processing step S1bas will be described next.

In the positive electrode laser processing step S1b, a laser processing apparatus80may be used. As shown inFIG. 11, the laser processing apparatus80includes a supply roller81, a conveying device82, a laser apparatus88, a controller86and a collector84. The conveying device82is a conveyor that includes a belt82cstretched around a pair of rollers82aand82b. The conveying device82conveys the positive electrode base sheet61on an upper surface of the belt82cin one direction. The positive electrode base sheet61is rolled out from the supply roller81and conveyed under predetermined tension. The motion of the conveyor82is controller by the controller86. The conveying device82moves the positive electrode base sheet61by a predetermined distance, wherein the belt82cwraps around the rollers and the conveyance is repeated over the same distance conveyance, and the conveying device82periodically suspends the conveyance of the positive electrode base sheet61.

As shown inFIG. 12, the laser apparatus88includes a first laser apparatus90and a second laser apparatus190. The first laser apparatus90irradiates the active material layer formation region61awith the first laser beam LS1. The second laser apparatus190irradiates both of the metal foil exposed regions61band61cwith second laser beam LS2. Hereinafter, both lasers LS1and LS2are individually referred to the first laser beam LS1and the second laser beam LS2, respectively, to distinguish between them, while are collectively referred to as the laser beam LS. Two second laser apparatuses190bmay be provided for corresponding to both the metal foil exposed regions61band61c.FIG. 12illustrates an example in which only one second laser apparatus190is provided.

As shown inFIG. 12, the first laser apparatus90includes a laser head92, an XY-axis robot94, an assist gas feeder96, and a laser beam oscillator98. The laser head92is attached to the XY-axis robot94. The XY-axis robot94moves the laser head92in the X and Y axial directions. The XY-axis robot94includes, for example, an X axis member94amovably supporting the laser head62in an X direction, which corresponds to a widthwise direction of the positive electrode base sheet61as described above, and a Y axis member94bmovably supporting the X axis member with attached laser head62in a Y direction, which corresponds to a longitudinal direction of the positive electrode base sheet6. The XY-axis robot94is connected to the controller86, and moves the laser head92in accordance with programs stored in the controller86.

As shown inFIG. 12, the assist gas feeder96is connected to the laser head92. The assist gas feeder96serves to feed assist gas. The laser beam oscillator98is connected to the laser head92, for example, via a fiber cable. The laser beam oscillator98serves to supply the laser beam itself to the laser head92. The laser beam oscillator98is connected to the controller86, for example, via a cable for control signals (not shown). The controller86serves to control the supply of the laser beam from the laser beam oscillator98to the laser head92. The controller89may supply the laser beam to the laser head92while the laser head92is moved by the XY-axis robot94, for example, when the positive electrode base sheet61has had conveying movement periodically suspended by the conveying device82.

As shown inFIG. 13, the laser head92irradiates the active material layer formation region61aof the positive electrode base sheet61with the first laser beam LS1. The laser head92includes a lens92a. This lens92afocuses the first laser beam LS1toward the focal point P that is set at a predetermined position from the bottom of the head92, lying on the positive electrode base sheet61. In particular, this focal point P is located in the vicinity of the center of the thickness (widthwise) direction of the positive electrode metal foil32and is located, for this reason, within the thickness of the positive electrode metal foil32. Alternatively, the focal point P may instead be located within the front positive electrode active material layer34at its bottom region in the vicinity of the positive electrode metal foil32or within the rear positive electrode active material layer36at its top region in the vicinity of the positive electrode metal foil32.

As shown inFIG. 13, the first laser beam LS1irradiates the positive electrode base sheet61such that its optical axis J extends perpendicular to the base sheet61. Therefore, with this orientation of J, the linear distance of the first laser beam LS1from the laser head92, passing through both positive electrode active material layers34and36and the positive electrode metal foil32, will be the shortest. In contrast, when the first laser beam LS1is obliquely irradiated with respect to the positive electrode base sheet61, then the linear distance is longer. Therefore, because of the orientation of J and the short linear distance, it is possible to set the output of the first laser beam LS1to be weak. The optical axis J is a straight line passing through the radial center of the lens92aand the focal point P. The first laser beam LS1irradiates in the direction from the front positive electrode active material layer34toward the rear positive electrode active material layer36. In so irradiating, the first laser beam LS1melts and cuts both positive electrode active material layers34and36and the positive electrode metal foil32. The above-described assist gas blows away the residual portions of both positive electrode active material layers34and36as well as the positive electrode metal foil32that are melted by the first laser beam LS1.

The first laser beam LS1is a continuous wave laser. The wave length of the first laser beam LS1is preferably set within the range of 300 to 1100 nm. The spot diameter of the first laser beam LS1is preferably set within the range of 10 to 100 μm (micrometer). The cutting speed by the first laser beam LS1is preferably set within the range of 0.5 to 3 m/s. The output of the first laser beam LS1is preferably set within the range of 0.01 to 2.0 kW.

As shown inFIG. 12, the second laser apparatus190includes a laser head192, an XY-axis robot194, an assist gas feeder196, and a laser beam oscillator198. Since each of the apparatuses192,194,196and198of the second laser apparatus190functions in the same manner as each of the analogous apparatuses92,94,96and98of the first laser device90, the repeated descriptions shall be omitted. The laser head92irradiates both metal foil exposed regions61band61cof the positive electrode base sheet61with the second laser beam LS2. Like laser head92, the laser head192also has a lens (not shown). This lens focuses the second laser beam LS2toward the focal point that is set at a predetermined position from the bottom of the head192, lying on the positive electrode base sheet61. The focal point is located in the vicinity of the center of the thickness direction of positive electrode metal foil32and is located, for that reason, within the thickness of the positive electrode metal foil32. The second laser beam LS2irradiates such that its optical axis extends perpendicular to the positive electrode base sheet61.

The second laser beam LS2is a pulse wave laser. The wave length of the second laser beam LS2is preferably set within the range of 500 to 1100 nm. The spot diameter of the second laser beam LS2is preferably set within the range of 25 to 100 μm (micrometer). The cutting speed by the second laser beam LS2is preferably set within the range of 1 to 3 m/s. The output of the second laser beam LS2is preferably set within the range of 10 to 100 W. The pulse width of the second laser beam LS2is preferably set narrower than 20 ps (picoseconds). The repetition frequency of the second laser beam LS2is preferably set within the range of 0.1 to 1 MHz.

As shown inFIG. 12, the laser beam LS cuts the positive electrode plate30out of the positive electrode base sheet61in a periodic repeating pattern. InFIGS. 10 and 12, lines to be cut by the laser beam LS (not shown inFIG. 10) are indicated by dotted lines. The laser beam LS cuts out positive electrode base portions38in a rectangular shape in the active material layer formation region61aand cuts out positive electrode tabs32bin both metal foil exposed regions61band61c. The laser beam LS cuts out two positive electrode plates30aligned vertically in the widthwise direction of the positive electrode base sheet61. The first laser beam LS1cuts out the positive electrode tab opposing edge38bat the widthwise center of the active material layer formation region61aalong the longitudinal direction of the positive electrode base sheet61. Further, the first laser beam LS1also cuts out the first positive electrode edge38cand second positive electrode edge38dalong the widthwise direction of the positive electrode base sheet61. The first positive electrode edge38cand the second positive electrode edge38dof the positive electrode plates30have the same width, are parallel to each other, and are spaced apart by a predetermined distance in the longitudinal direction of the positive electrode base sheet61. The second laser beam LS2cuts out the positive electrode tab edge38aalong the longitudinal direction of the positive electrode base sheet61at each respective border at the widthwise ends of the sheet, between both metal foil exposed regions61band61cand the active material layer formation region61a. Further, the second laser beam LS2cuts out the positive electrode tabs32bin both of the metal foil exposed regions61band61c, respectively. InFIGS. 10 and 12, the active material layer formation region61ais indicated by the pattern of diagonal lines.

As shown inFIG. 13, the irradiation of the first laser beam LS1forms a positive electrode large tapered portion34aon the front positive electrode active material layer34. Further, the irradiation of the first laser beam LS1also forms a positive electrode small tapered portion36aon the rear positive electrode active material layer36. The configuration of both tapered portions34aand36ais as described above with reference toFIG. 6. Both tapered portions34aand36aare formed on opposite sides of each of the positive electrode tab opposing edge38b, the first positive electrode edge38cand the second positive electrode edge38d, respectively. Both tapered portions34aand36aare simultaneously formed by irradiation of the first laser beam LS1.

The first laser beam LS1irradiates the positive electrode base sheet61from the laser head92in a perpendicular direction to said sheet, as shown inFIG. 13. Consequently, the positive electrode large tapered portions34aare formed symmetrically on both sides of the widthwise direction of the positive electrode base sheet61about the cutting line cut by the first laser beam LS1. Namely, the mutually symmetrical positive electrode large tapered portions34aabout the widthwise directional axis at the cutting axis J are formed at the first positive electrode edge38cand the second positive electrode edge38d. Similarly, the mutually symmetrical positive electrode small tapered portions36aare formed in an analogous manner at the first positive electrode edge38cand the second positive electrode edge38d. The two positive electrode plates30(see dotted lines extending in the longitudinal direction of the base sheet61inFIG. 10) that are cut out in the middle area of the positive electrode base sheet61at the widthwise center, extending in the longitudinal direction, have the positive electrode large tapered portions34aformed at each positive electrode tab opposing edge38b, wherein the shapes of the positive electrode large tapered portions34aare also symmetrical, about the longitudinally extending dotted line at the widthwise center of sheet61. This also applies by extension to the positive electrode small tapered portions36aformed at each positive electrode tab opposing edge38bon the opposite side of the base sheet61.

Each positive electrode plate30that is cut out by the laser beam LS may be collected by the collection device84shown inFIG. 11. The collection device84may include, for example, a suction hand84aand a collection box84b. The suction hand84asuctions each positive electrode plate30upward from the conveyor belt82c, and then drops each respective plate30in the collection box84b. In this manner, each of the positive electrode plates30may be stacked in the collection box84b. Each of the stacked positive electrode plate30will then be transferred to the positive electrode separator enveloping step S1c, which will be described below.

As shown inFIG. 3, in the positive electrode separator enveloping step S1c, the positive electrode plate30is inserted between the separator54folded in half, in the direction on the rear-to-front directional axis along the thickness of said separator. Subsequently, by being enveloped in between the separator54in this manner, the front surface30aof the positive electrode plate30is covered by the first separator part54awhile the rear surface30bof the positive electrode plate30is covered by the second separator part54b. The positive electrode tab32bis exposed and projects vertically upward through the opening hole54c. Thereafter, both separator parts54aand54bare welded together at the collective outer periphery of the positive electrode tab opposing edge38b, the first positive electrode edge38c, and the second positive electrode edge38d. As a result, a positive electrode plate unit50is produced in which the positive electrode plates30are enveloped with the separators54having a bag shape. The completed positive electrode plate unit50will then be transferred to a lamination step S3, which will be described later.

In the negative electrode sheet preparation step S2a, the negative electrode base sheet63is prepared in a similar manner to the positive electrode base sheet preparation step S1a. Namely, as shown inFIG. 9, the negative electrode metal foil42is rolled out from the supply roller71and passes through the coating apparatus72, the dryer73, and the press roller74in succession. As a result, a negative electrode base sheet63having the front negative electrode active material layer44and the rear negative electrode active material layer46formed on both the front and rear surfaces of the negative electrode metal foil42, respectively, is prepared. The negative electrode base sheet63is rolled up by the take-up roller76.

The negative electrode base sheet63includes a strip-shaped negative electrode metal foil42, the front negative electrode active material layer44, and the rear negative electrode active material layer46as described above. The negative electrode active material layers44and46are formed at the active material layer formation regions63a(seeFIG. 10) on the front surface42cand the rear surface42dof the negative electrode metal foil42wherein the front surface42cand the rear surface42dcorrespond each other at the same position on opposite sides of foil42. The width of the active material layer formation region63a(height inFIG. 10) corresponds to substantially double the length from the negative electrode tab opposing edge48bto the negative electrode tab edge48a. Both the uppermost and lowermost areas of the negative electrode base sheet63in a widthwise direction are configured as metal foil exposed regions63band63cas shown inFIG. 10where in these regions front negative electrode active material layer44and the rear negative electrode active material layer46are not provided so as to expose the negative electrode metal foil42. The width of each metal foil exposed region,63band63c, respectively, corresponds to the length of the negative electrode tab42bin an extending direction, as shown, e.g., inFIG. 5. The active material layer formation region63aand both metal foil exposed regions63band63care continuous over the entire length of the negative electrode base sheet63in the longitudinal direction. InFIG. 10, the active material layer formation region63ais indicated by the pattern of diagonal lines. The negative electrode base sheet63will then be transferred to the negative electrode laser processing step S2bas will be described next.

In the negative electrode laser processing step S2b, the negative electrode plates40are cut out of the negative electrode base sheet63in a similar procedure to that of the positive electrode laser processing step S1b. The laser processing apparatus80(seeFIG. 11) also operates in the negative electrode laser processing step S2bsimilarly to the positive electrode laser processing step S1b. The negative electrode laser processing step S2bwill be briefly described.

As shown inFIG. 13, the first laser beam LS1irradiates the active material layer formation region63aof the negative electrode base sheet63from the laser head92. The first laser beam LS1is focused with the lens92aon the focal point P that is set at a predetermined position from the bottom of the head92, lying on the negative electrode base sheet63. In particular, this focal point P is located in the vicinity of the center of the thickness (widthwise) direction of the negative electrode metal foil42and is located, for this reason, within the thickness of the negative electrode metal foil42. Alternatively, the focal point P may instead be located within the front negative electrode active material layer44at its bottom region in the vicinity of the negative electrode metal foil42or within the rear negative electrode active material layer46at its top region in the vicinity of the negative electrode metal foil42. The first laser beam LS1irradiates the negative electrode base sheet63such that its optical axis J extends perpendicular to the base sheet63. The first laser beam LS1irradiates the base sheet63through the front negative electrode active material layer44to the rear negative electrode active material layer46.

As shown inFIG. 12, the second laser beam LS2irradiates the negative electrode base sheet63from the laser head192to both metal foil exposed regions63band63cof the base sheet63. The second laser beam LS2is focused with the lens of the laser head192on the focal point that is set at a predetermined position on the negative electrode base sheet63. The focal point is located in the vicinity of the center of the thickness (widthwise) of the negative electrode metal foil42and may be located, for example, within the thickness of the negative electrode metal foil42. The second laser beam LS2may be, for example, irradiate the negative electrode base sheet63such that its optical axis extends perpendicular to the base sheet63.

As shown inFIG. 12, the laser beam LS cuts the negative electrode plates40out of the negative electrode base sheet63. InFIGS. 10 and 12, the lines to be cut by the laser beam LS (not shown inFIG. 10) are indicated by dotted lines. The laser beam LS cuts the negative electrode base portions48in a rectangular shape out from the active material layer formation region63a, and cuts the negative electrode tabs42bout from both metal foil exposed regions63band63c. The laser beam LS cuts out two negative electrode plates40aligned vertically in the widthwise direction of the negative electrode base sheet63. The first laser beam LS1cuts the negative electrode tab opposing edge48bout from the widthwise center of the active material layer formation region63aalong the longitudinal direction of the negative electrode base sheet63. Further, the first laser beam LS1also cuts out the first negative electrode edge48cand second negative electrode edge48dalong the width direction of the negative electrode base sheet63. The first negative electrode edge48cand the second negative electrode edge48dof the negative electrode plates40have the same width, are parallel to each other, and are spaced apart by a predetermined distance in the longitudinal direction of the negative electrode base sheet63. The second laser beam LS2cuts the negative electrode tab edges48aalong the longitudinal direction of the negative electrode base sheet63out from each respective border at the widthwise ends of the sheet, between both metal foil exposed regions63band63cand the active material layer formation region63a. Further, the second laser beam LS2cuts the negative electrode tabs42bout from both of the metal foil exposed regions63band63c, respectively. InFIGS. 10 and 12, the active material layer formation region63ais indicated by the pattern of diagonal lines.

As shown inFIG. 13, the irradiation of the first laser beam LS1forms a negative electrode large tapered portion44aon the front negative electrode active material layer44. In addition, the irradiation of the first laser beam LS1also forms a negative electrode small tapered portion46aon the rear negative electrode active material layer46. The configuration of both tapered portions44aand46ais as described above with reference toFIG. 6. Both tapered portions44aand46aare formed on opposite sides of the negative electrode tab opposing edge48b, the first negative electrode edge48cand the second negative electrode edge48d, respectively. Both tapered portions44aand46aare simultaneously formed by irradiation of the first laser beam LS1.

As shown inFIG. 13, the first laser beam LS1irradiates the negative electrode base sheet63in a perpendicular direction to the base sheet63. Consequently, the negative electrode large tapered portions44aare formed symmetrically on both sides of the widthwise direction of the negative electrode base sheet63about the cutting line cut by the first laser beam LS1. In other words, the mutually symmetrical negative electrode large tapered portions44aabout the widthwise directional axis at the cutting axis J are formed at the first negative electrode edge48cand the second negative electrode edge48d. Similarly, the mutually symmetrical negative electrode small tapered portions46aare formed in an analogous manner at the first negative electrode edge48cand the second negative electrode edge48d. In the two negative electrode plates40(see dotted lines extending in the longitudinal direction of the base sheet63inFIG. 10) cut out from both sides at the widthwise center of the negative electrode base sheet63, the shapes of the negative electrode large tapered portions44aformed at each negative electrode tab opposing edge48bare also symmetrical with each other about the longitudinally extending dotted line at the widthwise center of sheet63. This also applies to the negative electrode small tapered portions46aformed at each negative electrode tab opposing edge48bon the opposite side of the base sheet63.

Each negative electrode plate40cut out by the laser beam LS may be stacked in a collection box84bby the collection device84shown inFIG. 11. Each negative electrode plate40will then be transferred to the lamination step S3, which will be described below.

As shown inFIG. 14, in the lamination step S3, the positive electrode plate units50and the negative electrode plates40are alternately stacked. In the lamination step S3, a lamination device100may be used. The lamination device100includes, for example, a slide surface102and a lamination box104. The positive electrode plate units50and the negative electrode plates40are alternately transported from a conveyer (not shown) in succession onto the slide surface102. Once transported onto the slide surface102, the positive electrode plate units50and the negative electrode plates40fall from the slide surface102into the lamination box104. The lamination box104is inclined at a predetermined angle W with respect to the horizontal surface. In this way, due to the gravitational force resulting from the incline, the positive electrode units50and the negative electrode plates40are deposited into the lamination box104move to a front surface104aside of the lamination box104so that they can be successively laminated from the front surface104aside. As a result, an electrode assembly20(seeFIG. 6) is produced in which the positive electrode plate units50and the negative electrode plates40are alternately laminated in succession in the rear-to-front direction along the thickness of the plates. The positive electrode plate units50and the negative electrode plates40are laminated with their respective front surfaces30aand40aoriented in the same direction in said rear-to-front direction of the positive electrode plates30and the negative electrode plates40. Therefore, in the electrode assembly20, the front positive electrode active material layers34provided with the positive electrode large tapered portion34aand the front negative electrode active material layers44provided with the negative electrode large tapered portion44aare also consequently oriented in the same direction.

Subsequently, the electrode assembly20is transferred to an in-case sealing step. As shown inFIG. 15, in the in-case sealing step, the electrode assembly20is sealed in the case10. Further, the case10communicates with a tank110through an injection port K (not shown inFIG. 1). The tank110includes a tank main body110afilled with electrolyte solution18and a communication passage110bconfigured to facilitate communication between the tank main body110aand the case10. The electrolyte solution18flows through the communication passage110bfrom the tank main body110ainto the case10as indicated by an arrow Y shown inFIG. 15. The electrolyte solution18is then filled in the case10. Subsequently, this configuration is held until the electrolyte solution18impregnates each of the active material layers34and36,44and46(seeFIG. 6). After the electrolyte solution18has impregnated each of the material layers34and36,44and46, the injection port K is then sealed, thereby completing the construction of the electric storage device1(seeFIG. 1).

In the in-case sealing step described above, conventionally, a very long time was required until the electrolyte solution is impregnated each of the active material layers. On the contrary, as shown inFIG. 6, due to the positive electrode large tapered portions34a, which are inclined toward the inner side of the positive electrode plate30, such a long time is not required. The large tapered portions34a, provided at the outer edge of the front positive electrode active material layer34of the electrode assembly20, promotes the supply of the electrode solution18toward the inner side of the positive electrode plate30in the front positive electrode active material layer34, due to their inclination. As a result, the impregnation efficiency of the electrolyte solution18is enhanced in the front positive electrode active material layer34. Similarly, the supply of the electrolyte solution18in the rear negative electrode active material layer46opposing to the front positive electrode active material layer34with the separator54interposed therebetween is also enhanced. This may also improve the impregnation efficiency of the electrolyte solution18in the rear negative electrode active material layer46.

As shown inFIG. 6, the negative electrode large tapered portions44a, which are inclined toward the inner side of the negative electrode plate40, are provided at an incline at the outer edge of the front negative electrode active material layer44of the electrode assembly20. This promotes the supply of the electrolyte solution18toward the inner side of the negative electrode plate40in the front negative electrode active material layer44due to said incline. As a result, the impregnation efficiency of the electrolyte solution18is enhanced in the front negative electrode active material layer44. Similarly, the supply of the electrolyte solution18in the rear positive electrode active material layer36opposing to the front negative electrode active material layer44with the separator54interposed therebetween is also enhanced. This may also improve the impregnation efficiency of the electrolyte solution18in the rear positive electrode active material layer36.

As shown inFIG. 6, the positive electrode plate30and the negative electrode plate40are laminated with each of the front surfaces30aand40ahaving the positive electrode large tapered portion34aand the negative electrode large tapered portion44aoriented in the same direction, respectively. This may position clearances, into which the electrolyte solution18can enter, in an evenly distributed manner as compared to the case where, for example, the positive electrode plate30and the negative electrode plate40are laminated with each of the front surfaces30aand40afacing towards each other. Therefore, because of said even distribution of clearances, the uneven impregnation of the electrolyte solution18in the laminating direction of the positive electrode plates30and negative electrode plates40, may be prevented in the electrode assembly20while the supply of the electrolyte solution18in each of the active material layers34and36,44and46is promoted as described above.

The exemplary embodiments of the present invention have been described above, however, it would be obvious for one skilled in the art that these are susceptible of some replacement, improvement and/or modification without departing from the object of the present invention. Therefore, the exemplary embodiments of the present invention may include any replacement, improvement and/or modification without departing from the gist and object of the attached claims. For example, the exemplary embodiments of the present invention are not limited to the above specific structure, and can be modified as follows.

The positive electrode large tapered portions34a(seeFIG. 4) may be provided at all four edges38a,38b,38cand38dof the positive electrode plate30or may instead be provided at least one side of these four edges38a,38b,38cand38d. Similarly, the negative electrode large tapered portions44a(seeFIG. 5) may be provided at all four edges48a,48b,48cand48dof the negative electrode plate40or may instead be provided at at least one side of these four edges48a,48b,48cand48d.

The positive electrode large inclination angle θ1A and the positive electrode small inclination angle θ1B (seeFIG. 6) may be set individually for each edge at each of the edges38a,38b,38c, and38dof the positive electrode plate30. In this case, the positive electrode large inclination angle θ1A is set larger than the corresponding positive electrode small inclination angle θ1B at each of the corresponding edges38a,38b,38cand38dof the positive electrode plate30. Similarly, the negative electrode large inclination angle θ2A and the negative electrode small inclination angle θ2B (seeFIG. 6) may be set individually at each of the edges48a,48b,48cand48dof the negative electrode plate40. In this case, the negative electrode large inclination angle θ2A is set larger than the corresponding negative electrode small inclination angle θ2B at each of the corresponding edges48a,48b,48cand48dof the negative electrode plate40. The magnitude relation (θ1A<θ2A) as described above between the positive electrode large inclination angle θ1A and the negative electrode large inclination angle θ2A is fulfilled at each edge of the positive electrode plate30and each corresponding edge of the negative electrode plate40. Specifically, this magnitude relation is fulfilled at the positive electrode tab edge38aand the negative electrode tab edge48a, the positive electrode tab opposing edge38band the negative electrode tab opposing edge48b, the first positive electrode edge38cand the first negative electrode edge48d, and at the second positive electrode edge38dand the second negative electrode edge48d.

As shown inFIG. 20, instead of the positive electrode large tapered portion34aand the positive electrode small tapered portion36aof the embodiment described above, the positive electrode large tapered portion34band the positive electrode small tapered portion36bmay be curved or inclined in a mountain-shaped concave upward and downward curve, respectively. Further alternatively, as shown inFIG. 21, the positive electrode large tapered portion34cand the positive electrode small tapered portion36cmay be curved or inclined in a valley-shaped upward or downward convex curve, respectively. Similarly, the negative electrode large tapered portion and the negative electrode small tapered portion may also be analogously curved or inclined in a concave or convex curve shape. The repeated description shall be omitted by assigning the same reference numerals as inFIGS. 1 to 15to the parts inFIGS. 16 to 21that have the same or substantially the same construction and function as those parts inFIGS. 1 to 15.

The electrode assembly21shown inFIG. 16may be adopted as the electrode assembly. In the electrode assembly21, the positive electrode plate30and the negative electrode plate40are both respectively exposed without being enveloped with the separator. The separator56as a one sheet shape is placed between the positive electrode plate30and the negative electrode plate40. Due to the lack of being enveloped by a separator, the positive electrode large inclination angle θ1A is smaller than the negative electrode large inclination angle θ2A.

As shown inFIG. 16, the surface area of the positive electrode plate30is smaller than that of the negative electrode plate40. Therefore, the differential is manifested as a projecting part49of the negative electrode plate40that projects from outward from the outer edge of positive electrode plate30. A separator projecting part56acovering the projecting part49becomes a part of a plane, which due to the projecting part56aretains the built up electrolyte E formed around the outer edge of the positive electrode plate30, to encourage the formation of the built-up electrolyte. Therefore, with a greater length of projecting portion56arelative to positive electrode plate30as compared to negative electrode plate40, the built up electrolyte E formed along the positive electrode large tapered portion34atends to be more stably retained compared to the built up electrolyte E formed along the negative electrode large tapered portion44a. It is however possible to equalize an amount of the built up electrolyte E, which is formed at respective positive electrode large tapered portion34aand the negative electrode large tapered portion44a, by setting the inclination angle of the positive electrode large tapered portion34asmaller than the inclination angle of the negative electrode large tapered portion44a. Uneven impregnation of the electrolyte solution18in the laminating direction can also be suppressed in the electrode assembly21when the positive electrode plate30and the negative electrode plate40are laminated while the front surface30aof the positive electrode plate30provided with the positive electrode large tapered portion34aand the front surface40aof the negative electrode plate40provided with the negative electrode large tapered portion44aare oriented in the same direction in the rear-to-front directional axis along the thickness of the positive electrode plate30and negative electrode plate40.

The electrode assembly22shown inFIG. 17may be adopted as the electrode assembly. According to the electrode assembly22, the front negative electrode active material layer44and the rear negative electrode active material layer46are respectively covered with a heat-resistant layer58. The heat-resistant layer58is formed over the entire contiguous surface area at the top of negative electrode active material layer44, and at the bottom of negative electrode active material layer46, as shown inFIG. 17. The heat-resistant layer58may be made of ceramic. The heat-resistant layer58may effectively prevent short-circuiting between the positive electrode plate30and negative electrode plate40caused by, for example, high heat. The negative electrode large tapered portion44ais provided to extend linearly from the negative electrode metal foil42to the heat-resistant layer58at the top of the front negative electrode active material layer44at an incline. Further, the front negative electrode active material layer44is exposed at the negative electrode large tapered portion44a(i.e. it is not covered by the heat-resistant layer at44a). Therefore, since the supply of the electrolyte solution18from the built up electrolyte E, which is formed along the negative electrode large tapered portion44a, to the front negative electrode active material layer44is promoted, the impregnation speed of the electrolyte solution18into the front negative electrode active material layer44is accelerated. The negative electrode small tapered portion46ais provided to extend linearly from the negative electrode metal foil42to the heat-resistant layer58at the bottom of the rear negative electrode active material layer46. Further, the rear negative electrode active material layer46is exposed at the negative electrode small tapered portion46a.

The electrode assembly may include the positive electrode plate unit50(seeFIG. 2) and the negative electrode plate40(seeFIG. 17) having the heat-resistant layer58on both front (at the top) and rear sides (at the bottom), and may be configured such that these positive electrode plate units50and the negative electrode plates40are alternately laminated.

The heat-resistant layer(s)58may be formed on the separator(s) as the electrode assembly23shown inFIG. 18. The heat-resistant layer58is formed over the entire contiguous surface area of the plane of the separator56on the side oppositely facing the negative electrode plate40. With this configuration, similar to the electrode assembly22shown inFIG. 17, the heat-resistant layer58may effectively prevent short-circuiting between the positive electrode plate30and negative electrode plate40caused by, for example, high heat. Further, the built up electrolyte E may be formed along the positive electrode large tapered portion34aand the negative electrode large tapered portion44a. The built up electrolyte E may promote the supply of the electrolyte solution18to the front positive electrode active material layer34and the front negative electrode active material layer44. This promotion of built up electrolyte E may accelerate the impregnation speed of the built-up electrolyte18to the front positive electrode active material layer34and the front negative electrode active material layer44.

Instead of the configuration described above, the electrolyte assembly may instead include the positive electrode plate30not enveloped with the separator, and where the negative electrode plate40is enveloped with the separator. The negative electrode plate40may be, for example, enveloped with the separator having a larger area than that of the negative electrode plate40thereby comprising the negative electrode plate unit (electrode plate unit). The positive electrode plate30and the negative electrode plate unit are alternately laminated. In this case, the negative electrode large inclination angle is set to be smaller than the positive electrode large inclination angle.

As shown inFIG. 19, the positive electrode base sheet61may be configured such that the width (height as shown inFIG. 19) of the positive electrode base sheet61substantially coincides with the length from the positive electrode tab opposing edge38bto the positive electrode tab edge38a. In this case, only one positive electrode plate30is cut out in the width direction of the positive electrode base sheet61as indicated by the dotted lines inFIG. 19. Similarly, the negative electrode base sheet63may be configured such that the width in the active material layer formation region63asubstantially coincides the length from the negative electrode tab opposing edge48bto the negative electrode tab edge48a. Only one negative electrode plate40is cut out in the width direction of the negative electrode base sheet63.

The coating-and-drying apparatus70and the laser processing apparatus80shall not be limited to those with the configuration described in the above exemplary embodiments but may be any of those with the configuration that may similarly function as those of the above exemplary embodiments. The laser apparatus may be, for example, a scanner-type that can change the three dimensional irradiation position of the laser beam with a mirror. The laser beam need not be irradiated in a direction such that its optical axis extends perpendicular to the positive electrode base sheet61and the negative electrode base sheet63. In addition, instead of cutting when stopped, the laser apparatus may irradiate the positive electrode base sheet61and the negative electrode base sheet63with the laser beam so as to cut the positive electrode base sheet61and the negative electrode base sheet63during conveying movement of the positive electrode base sheet61and the negative electrode base sheet63.