JP2006012703A - Secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a secondary battery enabling both high output and high capacity. <P>SOLUTION: A positive electrode plate 5 and a negative electrode plate 6 are rolled in an electrode group 18. In the positive electrode plate 5, the thickness of a mix layer is set by changing from 44 μm to 88 μm generally at a constant gradient, and the density thereof is set to 2.7 g/cm<SP>3</SP>regardless of the thickness. In the negative electrode plate 6, the thickness of a mix layer is set by being changed from 35 μm to 77 μm generally at a constant gradient, and the density thereof is set to 1 g/cm<SP>3</SP>. In each of the positive electrode plate 5 and the negative electrode plate 6, a part having a small thickness of the mix layer is rolled on the side of shaft center 10. In the positive electrode plate 5 and the negative electrode plate 6, a plurality of current collection tabs are formed one-by-one at every certain length of a collector. Resistance of charge transfer is reduced on the shaft center 10 side having a small thickness of the mix layer, and the quantity of an active material is increased on the peripheral side having a large thickness. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a secondary battery, and in particular, a separator layer is provided between a positive electrode plate and a negative electrode plate in which a mixture layer containing an active material is applied to a current collector, and a plurality of current collector tabs are respectively led out from the current collector. The present invention relates to a secondary battery having an intervening electrode group.

  Secondary batteries are widely used as power sources for various portable devices and information devices such as VTR cameras, laptop computers, and mobile phones, and recently, they are also expected as power sources for electric vehicles and the like. Generally, in a secondary battery, an electrode group is accommodated in a battery container, and the battery container is sealed after injecting an electrolytic solution. The electrode group is formed by being wound or laminated so that the positive and negative electrode plates do not directly contact each other with the separator interposed therebetween. On the positive and negative electrode plates, a mixture containing an active material is applied almost evenly to a metal foil (current collector) to form a mixture layer.

  In the various devices described above, a large current is required at the start (power-on), and after that, a continuous output with a relatively small load is often required. It is required to achieve both high capacity. In order to increase the capacity of the secondary battery, it is necessary to increase the volume of the active material in the battery as much as possible, and it is effective to increase the thickness of the mixture layer. On the other hand, in order to obtain a high output, it is preferable to reduce the thickness of the mixture layer from the viewpoint of mass transfer and charge transfer. At this time, in order to obtain a high output, the thickness of the mixture layer is made to be substantially uniform, and when the number of positive or negative electrode plates is increased or the number of laminated layers is increased to increase the capacity, the mixture is sandwiched between the positive and negative electrode plates. Since the volume for the separator increases, the increase in the occupied volume of the active material becomes insufficient. As a technology for increasing the capacity of a secondary battery, for example, in a secondary battery having a single current collecting tab, the thickness of the mixture layer applied to at least the positive electrode plate is reduced as the distance from the current collecting tab decreases. A technique for making charge transfer in the agent layer uniform is disclosed (see Patent Document 1).

JP 2000-21453 A

  However, in the technique of Patent Document 1, although the charge transfer is made uniform and the capacity is improved, the resistance increases because the thickness of the mixture layer in the vicinity of the current collecting tab is increased because there is only one current collecting tab. It is difficult to obtain high output. Further, when the thickness of the mixture layer of the positive electrode plate is changed in one battery, the ratio of the discharge capacity of the positive electrode plate to the discharge capacity of the negative electrode plate is different per unit volume of the opposing positive and negative electrode plates Therefore, a load may be applied to only one of the positive and negative electrode plates during charging and discharging. For this reason, a technology that achieves both high capacity and high output, which are contradictory characteristics, is currently under development even though there are many demands.

  In view of the above case, an object of the present invention is to provide a secondary battery that can achieve both high output and high capacity.

  In order to solve the above-described problem, a first aspect of the present invention is a positive mode in which a current collector is coated with a mixture layer containing an active material, and a plurality of current collecting tabs are respectively derived from the current collector. In the secondary battery having an electrode group in which a separator is interposed between the negative electrode plates, the positive electrode plate and the negative electrode plate both have a thickness of the mixture layer larger than the inside of the electrode group, and the mixture The bulk densities of the layers are substantially uniform, and the current collecting tabs are led out one by one from the end face of the electrode group for a certain length of the current collector.

  In the first aspect, both the positive and negative electrode plates have a thickness of the mixture layer that is greater on the outside than the inside of the electrode group, and the bulk density of the mixture layer is substantially uniform, so that charge transfer is performed on the inside of the electrode group. Therefore, when a high output is required, the output from the inside of the electrode group having a small resistance mainly contributes, one by one from the end face of the electrode group to a certain length of the current collector. Since the amount of active material is increased outside the electrode group while being discharged through the derived current collecting tab, when the amount of electricity is required continuously, the electrode group is rich from the active material amount. The main output contributes to the discharge through the current collecting tab, so that both high output and high capacity can be achieved.

  Further, according to the second aspect of the present invention, a separator layer is provided between a positive electrode and a negative electrode plate in which a mixture layer containing an active material is applied to a current collector, and a plurality of current collector tabs are respectively led out from the current collector. In the secondary battery having the electrode group interposing the electrode group, each of the positive and negative electrode plates has a weight per unit area of the mixture layer larger than the inside of the electrode group and whether the mixture layer is The thickness density is substantially uniform, and the current collecting tab is led out from the end face of the electrode group one by one for a certain length of the current collector.

  In the second aspect, both the positive and negative electrode plates have a weight per unit area of the mixture layer that is greater on the outside than the inside of the electrode group, and the bulk density of the mixture layer is substantially uniform. Since the resistance to charge transfer is reduced on the inside, when high output is required, the output from the inside of the electrode group with low resistance mainly contributes to the fixed length of the current collector from the end face of the electrode group. In addition to being discharged through current collecting tabs that are led out one by one, the amount of active material increases outside the electrode group. Since the output from the outside of the group mainly contributes and is discharged through the current collecting tab, both high output and high capacity can be achieved.

  In the first and second embodiments, the electrode group may have at least two sets of positive and negative electrode plates having different thicknesses or weights per unit area of the mixture layer. At this time, it is preferable that an insulating thin plate is interposed between the electrode groups having at least two pairs of positive and negative plates. Alternatively, the mixture layer may be applied to both sides of the current collector of the positive and negative electrode plates so that the thickness or weight per unit area of the mixture layer is different on both sides of the current collector. In this case, the secondary battery may be a lithium ion secondary battery.

  According to the present invention, both the positive and negative electrode plates have a thickness of the mixture layer or a weight per unit area that is larger on the outside than the inside of the electrode group, and the bulk density of the mixture layer is substantially uniform. When the output is required, the output from the inside of the electrode group having a small resistance mainly contributes, and through the current collecting tab derived one by one for the fixed length of the current collector from the end face of the electrode group. In addition to being discharged, when the amount of electricity is required continuously, the output from the outside of the electrode group rich in the amount of active material contributes mainly and is discharged through the current collecting tab, so it has high output and high capacity. Can be achieved.

  Embodiments in which the present invention is applied to a cylindrical lithium ion secondary battery will be described below with reference to the drawings.

(Constitution)
As shown in FIG. 1, the cylindrical lithium ion secondary battery 20 of the present embodiment is made of nickel-plated steel battery can 19 having a bottomed cylindrical shape and an electrically insulating hollow cylindrical shape. Around the shaft core 10, there is an electrode group 18 in which a belt-like positive electrode plate and a negative electrode plate are wound in a spiral shape with a separator interposed therebetween.

  On the upper side of the electrode group 18, an aluminum disc-shaped positive electrode current collector 13 for collecting the electric potential from the positive electrode plate is disposed. The positive electrode current collecting member 13 is fixed to the upper end portion of the shaft core 10. Ends of the plurality of positive electrode tabs 11 led out from the upper end surface of the electrode group 18 are ultrasonically welded to the periphery of the positive electrode current collecting member 13. A disc-shaped battery lid 17 serving as a positive electrode external terminal is disposed above the positive electrode current collecting member 13. One end of a ribbon-like positive electrode lead plate made of aluminum is fixed to a substantially central portion of the upper surface of the positive electrode current collecting member 13, and the other end of the positive electrode lead plate is joined to the lower surface of the battery lid 17.

  On the other hand, a copper disc-shaped negative electrode current collecting member 14 for collecting the electric potential from the negative electrode plate is disposed below the electrode group 18, and the negative electrode current collecting member 14 is disposed at the lower end portion of the shaft core 10. It is fixed. The ends of the plurality of negative electrode tabs 12 led out from the lower end surface of the electrode group 18 are welded to the periphery of the negative electrode current collecting member 14. A negative electrode lead plate is welded to the lower portion of the negative electrode current collecting member 14, and the negative electrode lead plate is resistance welded to the inner bottom portion of the battery can 19.

The battery lid 17 is fixed by being crimped to the upper part of the battery can 19 via an insulating resin gasket. For this reason, the inside of the lithium ion secondary battery 20 is sealed. A predetermined amount of non-aqueous electrolyte is injected into the battery can 19. For the non-aqueous electrolyte, for example, 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) can be used by dissolving in a carbonate-based mixed solvent such as ethylene carbonate or diethyl carbonate. In addition, the electrode group 18 in the battery can 19 is water-removed by vacuum drying at 60 ° C. for 20 hours before injecting the non-aqueous electrolyte.

  As shown in FIG. 2, the electrode group 18 includes a positive electrode plate 1 and a negative electrode plate 2 around a shaft core 10 and a microporous polyethylene separator 7 having a thickness of 30 μm so that the two electrode plates do not directly contact each other. Has been wound through. The positive electrode plate 1 and the negative electrode plate 2 are wound to have a diameter that is approximately half the outer diameter of the electrode group 18. A polypropylene insulating sheet 9 having a thickness of 100 μm is wound around the wound periphery of the positive electrode plate 1 and the negative electrode plate 2 for one turn. Around the insulating sheet 9, the positive electrode plate 3 and the negative electrode plate 4, whose weight per unit area of the mixture layer is larger than that of the positive electrode plate 1 and the negative electrode plate 2, respectively, are the same as the positive electrode plate 1 and the negative electrode plate 2. Has been wounded. Therefore, the electrode group 18 has two types of positive electrode plates 1 and 3 and negative electrode plates 2 and 4 having different weights per unit area of the mixture layer. The electrode group 18 includes a positive electrode plate 1 and a negative electrode plate 2 having a small weight per unit area on the axial core 10 (winding center) side, and a positive electrode plate 3 and a negative electrode having a large weight per unit area on the outer peripheral side. A plate 4 is arranged. An insulating sheet 9 is interposed between the electrode group of the positive electrode plate 1 and the negative electrode plate 2 and the electrode group of the positive electrode plate 3 and the negative electrode plate 4.

  The width of the mixture layer of the positive plates 1 and 3 (vertical direction in FIG. 2) is arranged so as to be within the width of the mixture layer of the negative plates 2 and 4. The entire surface is wound with the mixture layers of the negative electrode plates 2 and 4 facing each other. The positive electrode tab 11 and the negative electrode tab 12 are led out to opposite sides of both end faces of the electrode group 18, respectively. An insulation coating (not shown) is applied to the entire outer peripheral surface of the electrode group 18 and the positive electrode current collector 13.

The positive plates 1 and 3 constituting the electrode group 18 have an aluminum foil having a thickness of 20 μm as a positive electrode current collector. On both surfaces of the aluminum foil, a positive electrode mixture containing lithium manganese composite oxide powder as a positive electrode active material is applied substantially evenly to form a mixture layer. In the positive electrode mixture, 10 parts by weight of carbon powder as a conductive agent and 5 parts by weight of polyvinylidene fluoride (hereinafter abbreviated as PVDF) as a binder (binder) with respect to 85 parts by weight of the positive electrode active material. Is blended. The positive electrode mixture uses N-methylpyrrolidone (hereinafter abbreviated as NMP) as a viscosity adjusting solvent, and is kneaded substantially uniformly by a planetary mixer and vacuum defoamed. When the positive electrode mixture is applied to the aluminum foil, a coating machine capable of adjusting the weight per unit area of the mixture layer (hereinafter referred to as the positive electrode coating amount) is used. The positive electrode coating amount is set to 120 g / m ² per one side of the aluminum foil in the positive electrode plate 1 and 240 g / m ² in the positive electrode plate 3. The positive plates 1 and 3 are all pressed by a roll press so that the bulk density of the positive electrode mixture is 2.7 g / cm ³ . For this reason, in the positive electrode plate 1 whose positive electrode coating amount is smaller than the positive electrode plate 3, the thickness of the mixture layer is also reduced. An uncoated portion of the positive electrode mixture is formed on the side edge on one side in the longitudinal direction of the aluminum foil. The uncoated portion is cut into a comb shape at substantially equal intervals, and a plurality of positive electrode tabs 11 are formed. For this reason, the positive electrode tabs 11 are formed one by one for a certain length of the aluminum foil.

On the other hand, the negative plates 2 and 4 have a copper foil having a thickness of 10 μm as a negative electrode current collector. On both surfaces of the copper foil, a negative electrode mixture containing amorphous carbon powder as a negative electrode active material is applied to form a mixture layer. The negative electrode mixture contains 5 parts by weight of acetylene black as a conductive agent and 5 parts by weight of PVDF as a binder with respect to 90 parts by weight of the negative electrode active material. The negative electrode mixture is the same as the positive electrode mixture. Have been prepared. When coating the negative electrode mixture on the copper foil, a coating machine similar to the coating of the positive electrode mixture is used. The weight per unit area of the mixture layer (hereinafter referred to as negative electrode coating amount) is set to 35 g / m ² per one side of the copper foil in the negative electrode plate 2 and is set to 70 g / m ² in the negative electrode plate 4. ing. The negative electrode plates 2 and 4 are both pressed by a roll press so that the bulk density of the negative electrode mixture is 1 g / cm ³ . For this reason, in the negative electrode plate 2 whose negative electrode coating amount is smaller than the negative electrode plate 4, the thickness of the mixture layer is also reduced. An uncoated portion of the negative electrode mixture is formed on the side edge on one side in the longitudinal direction of the copper foil, and a plurality of negative electrode tabs 12 are formed in the same manner as the positive electrode plates 1 and 3. For this reason, the negative electrode tabs 12 are formed one by one for a certain length of the copper foil. Note that the width of the coating portion of the negative electrode mixture is set to be about 2% larger than the width of the coating portion of the positive electrode mixture.

(Action etc.)
Next, the operation and the like of the lithium ion secondary battery 20 of the present embodiment will be described.

  In the lithium ion secondary battery 20 of the present embodiment, the electrode group 18 has the positive electrode plate 1 with a small positive electrode coating amount and the negative electrode plate 2 with a small negative electrode coating amount wound on the axial core 10 side. A positive electrode plate 3 having a large positive electrode coating amount and a negative electrode plate 4 having a large negative electrode coating amount are wound on the outer peripheral side. That is, the electrode group 18 has two sets of positive and negative electrode plates having different positive and negative electrode coating amounts. For this reason, on the shaft core 10 side where the positive electrode plate 1 and the negative electrode plate 2 are opposed to each other via the separator 7, the resistance of charge transfer during charge / discharge is reduced, and the positive electrode plate 3 and the negative electrode plate 4 are opposed to each other via the separator 7. On the outer peripheral side, the amount of the active material becomes large for both the positive and negative electrode plates. Thereby, when a high output is required, discharge from the positive electrode plate 1 and the negative electrode plate 2 having a small charge transfer resistance mainly contributes to discharge, and subsequently a large amount of electricity is required continuously. In some cases, the output from the positive electrode plate 3 and the negative electrode plate 4 having a large amount of active material mainly contributes to discharge. The positive electrode plates 1 and 3 are formed with a plurality of current collecting tabs 11 led out one by one with respect to the predetermined length of the aluminum foil, and the negative electrode plates 2 and 4 have a predetermined length of the copper foil. A plurality of current collecting tabs 12 led out one by one are formed. Therefore, even when high output is required or when the amount of electricity is required continuously, two sets of positive and negative electrode plates having different positive and negative electrode coating amounts constituting the electrode group 18 in response to the request from the load side Since the amount of electricity is collected according to the resistance difference between the mass transfer and the charge transfer, both high output and high capacity can be achieved.

  Further, in the lithium ion secondary battery 20 of the present embodiment, the positive electrode plate 1 and the negative electrode plate 2 having a small positive / negative electrode coating amount are opposed to the positive electrode plate 3 and the negative electrode plate 4 having a large positive / negative electrode coating amount, respectively. The positive electrode plates 1 and 3 and the negative electrode plates 2 and 4 have the same bulk density of the positive and negative electrode mixtures. For this reason, the ratio of the discharge capacity per unit volume of the positive plates 1 and 3 to the discharge capacity per unit volume of the negative plates 2 and 4 is the axis 10 side of the electrode group 18 regardless of the positive and negative electrode coating amount. And it becomes almost constant on the outer peripheral side. Thereby, it can prevent that a load is applied only to either one of the positive / negative electrode plates at the time of charging / discharging. Further, an insulating sheet 9 is wound around the outer periphery of the positive electrode plate 1 and the negative electrode plate 2 that are wound. For this reason, for example, it is possible to prevent the positive and negative electrode plates from facing each other due to the different thicknesses such that the positive electrode plate 1 having a large positive electrode coating amount and the negative electrode plate 4 having a large negative electrode coating amount are opposed to each other. be able to.

  Furthermore, in the lithium ion secondary battery 20 of this embodiment, the positive electrode plate 1 and the negative electrode plate 2 are wound on the axial core 10 side of the electrode group 18, and the positive electrode plate 3 and the negative electrode plate 4 are wound on the outer peripheral side. For this reason, the positive electrode plate 1 and the negative electrode plate 2 having a small positive / negative electrode coating amount are wound with a small winding diameter, and the positive electrode plate 3 and the negative electrode plate 4 having a large positive / negative electrode coating amount are wound with a large winding diameter. Since it rotates, it can prevent that damage, such as a crack, arises in a mixture layer at the time of winding of a positive / negative electrode plate.

  Furthermore, since the positive and negative electrode coating amounts are increased in the positive electrode plate 3 and the negative electrode plate 4, the usage amount of the separator 7 is reduced, so that the number of times of one set of the positive electrode plate 1 and the negative electrode plate 2 is increased. Thus, the volume of the positive and negative electrode active materials can be increased by the volume of the separator 7, and the capacity can be increased. Furthermore, there is an advantage that a control circuit and a battery configuration are not complicated as compared with a case where a battery having a positive and negative electrode plate having a large positive and negative electrode coating amount and a battery having a small positive and negative electrode plate are connected in parallel.

  On the other hand, in a conventional lithium ion secondary battery, since a set of positive and negative electrode plates having substantially uniform positive and negative electrode coating amounts are wound, it is difficult to achieve both high output and high capacity. In addition, reducing the thickness of the mixture layer to obtain a high output, and increasing the number of times to increase the capacity, the amount of active material decreases due to the volume of the separator interposed between the positive and negative electrodes. High capacity is insufficient. Furthermore, even if it has a large part and a small part of the positive and negative electrode coating amount, if the ratio of the discharge capacity per unit volume of the opposing positive and negative electrode plates is different, only one of the positive and negative electrode plates is loaded during charging and discharging. May take. Instead, a battery having a positive / negative electrode plate with a large positive / negative electrode coating amount and a battery having a positive / negative electrode plate with a small positive / negative electrode coating amount are connected in parallel to achieve both high output and high capacity. To do so, the control circuit and battery configuration become complicated. In the lithium ion secondary battery 20 of this embodiment, these problems can be solved.

  In addition, in the lithium ion secondary battery 20 of this embodiment, although the electrode group 18 was formed using two sets of positive / negative electrode plates from which the amount of positive / negative electrode coating differs, this invention is not limited to this. For example, three or more sets of positive and negative electrode plates having different positive and negative electrode coating amounts may be used, and the thickness of the mixture layer may be different from the positive and negative electrode coating amounts. Alternatively, a pair of positive and negative electrode plates formed by changing the thickness of the mixture layer with a substantially constant gradient (thickness increase rate) may be used. For example, as shown in FIG. 3, the electrode group 18 of the lithium ion secondary battery 20 is arranged around the shaft core 10, and the thickness of the mixture layer has a substantially constant gradient in the longitudinal direction of the positive and negative electrode plates. The positive electrode plate 5 and the negative electrode plate 6 formed as described above are wound through a separator 7, and the positive electrode plate 5 and the negative electrode plate 6 are both disposed on the shaft core 10 side with the smaller thickness of the mixture layer. Can do.

In the production of the positive electrode plate 5, when the positive electrode mixture is applied to the aluminum foil, the thickness of the coating start portion is 44 μm (the coating amount per one side) using a coating machine capable of controlling the thickness of the mixture layer. 120 g / m ² ), and the thickness is gradually increased so that the thickness of the coating end portion is 88 μm (the coating amount is 240 g / m ² per side). At this time, the gradient of the thickness of the mixture layer is made substantially constant from the coating start part to the coating end part. At the time of press working after coating the positive electrode mixture, a bulk density of the positive electrode mixture is 2.7 g regardless of the thickness of the mixture layer by using a machine that can change the clearance of the roll press machine during the press by sequence control or the like. / Cm ³ to press. On the other hand, in the production of the negative electrode plate 6, as in the production of the positive electrode plate 5, the thickness of the mixture layer at the beginning of coating is set to 35 μm (coating amount 35 g / m ² per side), and the thickness is gradually increased. Then, the coating is applied so that the thickness of the coating end portion is 70 μm (the coating amount is 70 g / m ² per side). At the time of pressing, the negative electrode mixture is pressed to a bulk density of 1 g / cm ³ in the same manner as the positive electrode plate 5. The prepared positive electrode plate 5 and negative electrode plate 6 are wound with the portion having a small thickness (beginning of coating) facing the axial core 10 side, so that the thickness of the mixture layer in the electrode group 18 gradually increases from the axial core 10 side. Positive and negative electrode plates are arranged. Thereby, both high output and high capacity can be achieved.

  Thus, when a positive / negative electrode plate with a large mixture layer thickness and a positive / negative electrode plate with a small thickness are mixed in one battery, if the ratio of the discharge capacities of the opposing positive and negative electrode plates is different, the positive and negative electrodes are charged and discharged. Since only one of the plates is loaded, it is desirable that the ratio of the discharge capacity per unit volume of the opposing positive and negative electrode plates is substantially constant. For this reason, when winding one set of positive and negative electrode plates, it is necessary to gradually reduce or gradually increase the thickness of the mixture layer, but it is not easy to accurately control the gradient of the mixture layer thickness. . Taking into account the complexity of using a coating machine capable of sequence control at the time of coating the positive and negative electrode mixture, at least two pairs of positive and negative electrode plates having different thickness of the mixture layer or different positive and negative electrode coating amounts are wound. It is preferable. At this time, in order to avoid that the ratio of the discharge capacity of the opposing positive and negative electrode plates is different, the winding of the positive and negative electrode plates is once terminated at the boundary of changing the thickness of the mixture layer or the coating amount of the positive and negative electrodes. It is preferable that the positive and negative electrode plates having different thicknesses are wound after the thin plate or the like is disposed.

  Moreover, in the lithium ion secondary battery 20 of this embodiment, although the example which winds a positive / negative electrode plate and produces the electrode group 18 was shown, this invention is not limited to this, A positive / negative electrode plate is strip-shaped. It may be cut into a shape and laminated. For example, as shown in FIG. 4, in the electrode group 18 of the prismatic lithium ion secondary battery, the positive electrode plates 1 and the negative electrode plates 2 are alternately stacked, and the insulating sheets 9 are formed on both sides of the stacked positive and negative electrode plates. Can be realized by alternately laminating the positive electrode plate 3 and the negative electrode plate 4 on both outer sides of the insulating sheet 9. The positive plates 1 and 3 are covered with a separator 7 processed into a bag shape. The thickness of the stacked positive electrode plate 1 and negative electrode plate 2 is approximately half of the total thickness of the electrode group 18 in the stacking direction. Each positive electrode plate is formed with one positive electrode tab on one side of each side, and each negative electrode plate is formed with one negative electrode tab on the other side of one side. For this reason, one positive / negative electrode tab is derived for each side length. When the positive and negative electrode plates are stacked, the positive electrode tab and the negative electrode tab are arranged so as not to overlap each other.

  The battery can of the rectangular lithium ion secondary battery has a rectangular parallelepiped shape, and one surface of the rectangular parallelepiped is made of stainless steel so as to be fitted to a plate-shaped battery lid. The electrode group 18 is inserted into a battery can after being inserted into a polypropylene inner box in order to insulate it from the battery can. The positive electrode tab is made of aluminum and ultrasonically welded to a prismatic strap 15, and the negative electrode tab is made of copper and ultrasonically welded to a prismatic strap not shown. Each strap is fastened with a bolt to positive and negative external terminals fixed to the battery lid via an electrical insulating member. Aluminum and copper materials are used for the positive and negative external terminals, respectively. Further, the battery lid is formed with a liquid injection port through which a taper screw can be screwed to inject a non-aqueous electrolyte. The outer periphery of the battery lid and the opening of the battery can are sealed by laser welding. The electrode group 18 is vacuum-dried at 60 ° C. for 20 hours before the non-aqueous electrolyte injection to remove moisture. A non-aqueous electrolyte is injected into the battery can from an injection port, and a taper screw wound with a sealing tape is screwed into the injection port.

  When the electrode group 18 is produced by laminating the positive and negative electrode plates in this way, the thickness of the mixture layer may be adjusted (controlled) so that the discharge capacity ratio of the opposed positive and negative electrode plates is substantially constant. Compared with adjusting the amount of positive / negative electrode coating, the electrode group 18 having at least two sets of positive / negative electrode plates having different thicknesses of the mixture layer can be easily realized.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, an example in which the thickness of the mixture layer or the coating amount of the positive and negative electrodes is the same on both sides of the current collector is shown on both the positive and negative electrode plates. However, the thickness of the mixture layer or the coating amount of the positive and negative electrodes may be changed on both sides of the current collector. In this case, in order to make the discharge capacity per unit volume of the positive and negative electrode plates facing each other substantially constant, the surfaces where the thickness of the mixture layer or the positive and negative electrode coating amount is increased and the surfaces which are reduced are made to face each other. Is preferred. Also, if the thickness of the mixture layer or the amount of positive and negative electrode coating is changed on both sides of the current collector, the positive and negative electrode plates will bend and warp during pressing, so a certain amount of tension will be applied when winding the positive and negative electrode plates. It is preferable to wind. When such warpage occurs, it is difficult to stack the positive and negative electrode plates. Therefore, in a stacked battery in which positive and negative electrode plates are stacked, the thickness of the mixture layer or the positive and negative electrode coating amount may be the same on both current collector surfaces. preferable.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, the insulating sheet interposed between the electrode group of the positive electrode plate 1 and the negative electrode plate 2 and the electrode group of the positive electrode plate 3 and the negative electrode plate 4 has a thickness of 100 μm. Although the example which uses the insulating sheet 9 made from a polypropylene was shown, this invention is not limited to this. As the insulating sheet, it is only necessary to be able to insulate a plurality of sets of positive and negative electrode plates having different thicknesses or positive and negative electrode coating amounts, for example, a material such as polyolefin such as polyethylene may be used, There is no particular limitation on the thickness.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, specific numerical values such as the thickness of the mixture layer, the coating amount of the positive and negative electrodes, the bulk density of the positive and negative electrode mixtures are exemplified, but the present invention includes them. It is not limited and may be selected as appropriate within the range that is usually used. Moreover, although the lithium ion secondary battery 20 was illustrated in this embodiment, it cannot be overemphasized that this invention is applicable to a secondary battery generally.

  Hereinafter, examples of the lithium ion secondary battery 20 manufactured according to the present embodiment will be described. In addition, it describes together about the lithium ion secondary battery of the comparative example produced for the comparison. Moreover, in the batteries of the examples and comparative examples, the battery capacities were set to be the same.

Example 1
In Example 1, two sets of positive and negative electrode plates having different positive and negative electrode coating amounts were wound around the shaft core 10 to produce a lithium ion secondary battery 20 (hereinafter referred to as battery 1) (see FIG. 2). .

(Example 2)
In Example 2, a lithium ion secondary battery (hereinafter referred to as battery 2) was produced using positive and negative electrode plates in which the thickness of the mixture layer was gradually increased from the axial core 10 side toward the outer peripheral side (FIG. 3). reference).

Example 3
In Example 3, a square lithium ion secondary battery (hereinafter referred to as battery 3) in which two sets of positive and negative electrode plates having different positive and negative electrode coating amounts were laminated was produced (see FIG. 4).

(Comparative Example 1)
In Comparative Example 1, the positive electrode coating amount was 180 g / m ² (the average coating amount of the positive electrode plates 1 and 3), and the negative electrode coating amount was 52.5 g / m ² (the average coating amount of the negative electrode plates ^{2 and} 4). A lithium ion secondary battery (hereinafter referred to as the battery 4) was produced in the same manner as in Example 1 except that the amount was changed to (Amount). That is, the battery 4 of Comparative Example 1 is a battery using a set of positive and negative electrode plates in which the positive and negative electrode coating amounts are made substantially uniform.

(test)
About each battery of an Example and a comparative example, it discharged with the electric current value of 0.5C (2 hour rate) and 3C (1/3 hour rate), measured the change of the battery voltage with respect to discharge capacity, and created the discharge curve. . The discharge curves of 0.5C and 3C are shown in FIGS. 4 and 5, respectively. 4 and 5, the discharge capacity indicates a percentage (unit%) with respect to the battery capacity.

  As shown in FIGS. 4 and 5, in the battery 4 using a set of positive and negative electrode plates in which the positive and negative electrode coating amounts are made substantially uniform, the voltage drop at the initial stage of discharge becomes large, and the battery voltage accompanying the increase in the discharge capacity. The decline in the price also increased. On the other hand, in the batteries 1 to 3 in which the positive and negative electrode plates having different thicknesses or positive and negative electrode coating amounts were wound or laminated, the voltage drop at the initial stage of discharge was small and averaged at any discharge rate. The discharge voltage could be improved. Therefore, it was found that the batteries 1 to 3 can output higher power than the battery 4 having the same discharge capacity (unit Ah) and can supply a larger amount of power (unit Wh).

  The present invention provides a secondary battery capable of achieving both high output and high capacity, contributes to manufacturing and sales, and can be used industrially.

It is sectional drawing which shows the cylindrical lithium ion secondary battery of embodiment to which this invention is applied. It is sectional drawing which shows the electrode group of the cylindrical lithium ion secondary battery of embodiment. Sectional drawing which shows the electrode group which wound the positive / negative electrode board which increased the thickness of the mixture layer gradually from the start part to the end part by the substantially constant gradient in the cylindrical lithium ion secondary battery which can apply this invention It is. It is sectional drawing which shows the electrode group which laminated | stacked two sets of positive / negative electrode plates from which the coating amount of positive / negative electrode mixture differs in the square lithium ion secondary battery which can apply this invention. It is a graph which shows the relationship between the discharge capacity and discharge voltage of a lithium ion secondary battery in 2 hour rate discharge. It is a graph which shows the relationship between the discharge capacity and discharge voltage of a lithium ion secondary battery in 1/3 time rate discharge.

Explanation of symbols

1, 3, 5 Positive electrode plate 2, 4, 6 Negative electrode plate 9 Insulating sheet (insulating thin plate)
11 Positive electrode tab (current collection tab)
12 Negative electrode tab (current collection tab)
18 Electrode group 20 Cylindrical lithium ion secondary battery (secondary battery)

Claims (8)

  A secondary battery having an electrode group in which a mixture layer containing an active material is applied to a current collector, and a plurality of current collecting tabs are led out from the current collector, and a separator is interposed between positive and negative electrode plates In each of the positive and negative electrode plates, the thickness of the mixture layer is larger on the outside than the inside of the electrode group, and the bulk density of the mixture layer is substantially uniform, and the current collecting tab is A secondary battery, wherein the secondary battery is led out from the end face of the electrode group one by one for a certain length of the current collector.   A secondary battery having an electrode group in which a mixture layer containing an active material is applied to a current collector, and a plurality of current collecting tabs are led out from the current collector, and a separator is interposed between positive and negative electrode plates In each of the positive and negative electrode plates, the weight per unit area of the mixture layer is larger on the outside than the inside of the electrode group, and the bulk density of the mixture layer is substantially uniform, respectively. The secondary battery is characterized in that one electric tab is led out from the end face of the electrode group one by one for a certain length of the current collector.   The secondary battery according to claim 1, wherein the electrode group includes at least two pairs of positive and negative electrode plates having different thicknesses of the mixture layer.   The secondary battery according to claim 2, wherein the electrode group includes at least two pairs of positive and negative electrodes having different weights per unit area of the mixture layer.   5. The secondary battery according to claim 3, wherein an insulating thin plate is interposed between the electrode group having the at least two sets of positive and negative electrode plates.   2. The mixture layer according to claim 1, wherein the mixture layer is applied to both surfaces of the current collector of the positive and negative electrode plates, and the thickness of the mixture layer is different on both surfaces of the current collector. Secondary battery.   The mixture layer is coated on both surfaces of the current collector of the positive and negative electrode plates, and the weight per unit area of the mixture layer is different on both surfaces of the current collector. 2. The secondary battery according to 2.   The secondary battery according to claim 1, wherein the secondary battery is a lithium ion secondary battery.