JP5623073B2 - Secondary battery - Google Patents

Description

  The present invention relates to a secondary battery suitable for use in, for example, an automobile driving power source, and more particularly to a technique for improving the durability and heat dissipation of the battery.

  In an in-vehicle lithium ion secondary battery, a plurality of single cells (cells) each having a positive electrode, a negative electrode, and an electrolyte are arranged in series to form an assembled battery, and a cell controller for charge / discharge control is connected. Then, the battery module is formed so as to obtain a necessary voltage.

  In such a secondary battery unit cell, an electrode sheet and a separator are stacked, and after being wound into a flat type or a cylindrical type as shown in FIGS. 2 (a) and 3 (a), FIG. As shown in FIG. 3 (b), there are two types: a crushed wound type storage element, or a laminated type storage element in which electrodes and separators cut out in a flat plate shape are stacked, and these are stored in a cylindrical case. Some are housed in a rectangular or flat case (for example, see Patent Document 1).

  When the storage element is housed in a square case, the current collector foils on the positive electrode side and the negative electrode side, which are led out from both ends of the power storage element, are overlapped and ultrasonically welded to the current collectors (leads) on the positive electrode side and the negative electrode side, respectively And stored in a case.

  Among the above, the stacked power storage element has a constant surface pressure to each electrode, has no bent portion, and has less problems such as dropping off of the active material than the wound power storage element. However, the process for cutting out the electrodes and stacking and accumulating the power storage elements is complicated, and the manufacturing cost increases because the productivity decreases.

  On the other hand, since the winding type power storage element is manufactured by winding a long sheet, the process can be simplified and the cost can be reduced. However, in the flat type, there is a problem that when the winding core portion becomes space, the filling density of the case is less likely to increase than the stacked type storage element, and in order to improve the packing density, the storage element is inserted when loading the case. Crush and load.

  In order to increase the energy density of the power storage element, it is necessary to increase the electrode active material ratio of the power storage element. To this end, it is necessary to make the electrode foil thinner and the active material layer thicker. As a result of investigations by the inventors, when a particulate active material is formed using a resin binder made of PVDF or SBR, the thicker the active material mixture layer is, the more the active material mixture layer becomes, as examined in the graph of FIG. It was found that cracking occurred in the material and the active material dropped out from the metal current collector foil. In an electrode made of a carbonaceous material, particularly graphite particles, as shown in FIGS. 2 and 3, when the space of the center portion 30 or 31 after the winding core is removed after winding of the electricity storage element 24 or 25, the curvature becomes It was found that electrode cracks are likely to occur in the corner regions A at both ends where R is small. In the crack portion, the adhesion between the active material layer and the electrode foil is lowered, the active material is dropped, and the resistance of the electrode is increased. In general, there is a method of strengthening electrode cracking with a fibrous filler such as VGCF. However, if the amount of VGCF or the like is increased, the time of the dispersion and mixing process becomes longer, and the viscosity of the slurry is increased. Productivity decreases as speed decreases. Moreover, since the material cost of VGCF itself is high, there existed a problem of an increase in cost.

  As a result, the corner regions A at both ends of the electricity storage device 24 (25) cannot be crushed to a certain degree or more, so the device has an elliptical shape having the hollow portion 30 (31), and the packing density of the electrodes cannot be improved. There arises a problem that the capacity cannot be improved. In particular, this dead space becomes large when a large element used in an electric vehicle or the like is used.

  Furthermore, since the longitudinal region B existing between the corner regions A at both ends of the elliptical shape is not constrained, it is recessed inward with respect to the hollow portion 30 (31), and an array type as shown in FIG. It becomes a shape. Thus, since there is no binding force from the case at the center of the element, (1) the heat transfer area from the center of the element to the case is reduced and the heat dissipation is reduced, so that the temperature is likely to rise. The temperature variation inside the device increases, and the active material deteriorates. Further, (2) the gas generated by the decomposition of the electrolytic solution is likely to accumulate between the electrodes, and if bubbles remain, the effective electrode area decreases and the resistance increases. Further, (3) due to expansion / contraction of the negative electrode, the adhesion due to the load between the negative electrode active material and the electrode foil is lowered, and the contact resistance is increased. For these reasons (1) to (3), there has been a problem that the durability and life of the battery are reduced as a result.

JP 2009-032670 A

  The present invention has been made in order to solve the above-described problems of the prior art, and has a structure in which heat dissipation and durability are improved in a secondary battery structure for an automobile loaded with a winding type storage element. The object is to provide a secondary battery.

  A secondary battery according to the present invention is a secondary battery including a first power storage element having an electrolyte solution in which a positive electrode sheet, a separator, and a negative electrode sheet are stacked and wound, and a battery case that houses the first power storage element. The first power storage element has a flat shape and forms a longitudinal region and a corner region, and a central portion of the longitudinal region is pressed against the battery case by a surface pressure generating member.

  In the secondary battery having the above configuration, since the surface pressure generating member is accommodated in the battery and presses the first power storage element, the central portion of the longitudinal region where the first power storage element is likely to be bent and the battery Since the case is in contact, heat generated from the power storage element is easily transmitted to the battery case, and heat dissipation is improved. Further, durability against vibration applied to the battery and durability against expansion / contraction of the power storage element itself due to repeated charge / discharge are improved.

In the secondary battery of the present invention, the first storage element is wound around the surface pressure generating member, the surface pressure generating member is composed of a second storage element which turned positive electrode sheet, a separator and a negative electrode sheet winding, the The active material layer of the two electricity storage elements is further characterized by being formed thinner than the active material layer of the first electricity storage element.

In the secondary battery of the present invention, the first power storage element is wound around a surface pressure generating member, and the surface pressure generating member is formed from a second power storage element in which a positive electrode sheet, a separator, and a negative electrode sheet are wound or stacked. The positive electrode sheet is composed of a positive electrode active material and a positive electrode current collector foil on which the positive electrode active material is formed, and the negative electrode sheet is composed of a negative electrode current collector foil on which the negative electrode active material and the negative electrode active material are formed. As a further feature , the ratio of the thickness of the positive electrode or negative electrode current collector foil to the positive electrode or negative electrode active material in the element is larger than the ratio of the thickness of the positive electrode or negative electrode current collector foil to the positive electrode or negative electrode active material in the first power storage element. Yes.

  In the secondary battery having the above configuration, since the second power storage element exists as a surface pressure generating member inside the first power storage element, the longitudinal region of the power storage element is prevented from being bent and is in close contact with the case. This can not only improve the heat dissipation and durability of the electricity storage device, but also suppress the collapse of the corner area of the electricity storage device and maintain a large curvature, thereby preventing the active material from falling off. In addition, since the contact area between the battery case and the power storage element is increased, a binding force is evenly applied to the power storage element, and the distance between the electrodes is constant, so that an increase in internal resistance can be prevented. In the following description of the present application, the terms “thin”, “thin film”, “thick”, and “thick film” mean “relatively thin” and “relatively thick”. Moreover, the thickness of an electrode compound-material layer and an active material layer shows the thickness formed in the single side | surface of current collection foil.

  Further, in the secondary battery having the above configuration, since the surface pressure generating member also serves as the second power storage element, the amount of the power storage element, that is, the total amount of the active material is increased, thereby improving the capacity of the secondary battery. Can do.

  Further, in the secondary battery having the above configuration, the active material layer of the second power storage element is thinner than the active material layer of the first power storage element, or the positive electrode with respect to the positive electrode or the negative electrode active material layer in the second power storage element Alternatively, since the ratio of the thickness of the negative electrode current collector foil is larger than the ratio of the thickness of the positive electrode or negative electrode current collector foil to the positive electrode or negative electrode active material layer in the first power storage element, Is easily transmitted, and the heat at the center of the power storage element is easily radiated to the outside through the current collector foil. In addition, since the active material layer is thinner than the first power storage element, cracks are less likely to occur, so that the element can be crushed and densely filled so as to reduce the curvature.

The secondary battery of the present invention is further characterized in that a plurality of first power storage elements are provided, and a surface pressure generating member is provided between the plurality of first power storage elements.

  In the secondary battery having the above configuration, the surface pressure generating member between the plurality of first power storage elements crushes and fixes the adjacent first power storage elements, so that the first power storage elements are pressed and the first power storage elements are pressed. The battery case is in contact with the central portion of the longitudinal region where the element is likely to be bent, and heat dissipation and durability are improved. In addition, since the curvature of the corner area of the power storage element can be suppressed and maintained with a large curvature, the active material can be prevented from falling off, and the contact area between the battery case and the power storage element can be increased. Since the restraining force is evenly applied to the elements and the distance between the electrodes is constant, an increase in internal resistance can be prevented.

In the secondary battery of the present invention, the surface pressure generating member is further characterized in that the surface pressure generating member is composed of a second power storage element in which a positive electrode sheet, a separator, and a negative electrode sheet are wound .

  In the secondary battery having the above configuration, since the surface pressure generating member also serves as the second power storage element, the amount of the power storage element, that is, the total active material amount can be increased, and the capacity of the secondary battery can be improved. .

In the secondary battery of the present invention, the second storage element is wound, the active material layer of the second power storage device, as a further feature that it is thinner than the active material layer of the first storage element Yes.

  In the secondary battery having the above configuration, since the active material layer of the second power storage element is thinner than the active material layer of the first power storage element, the ratio of the current collector foil is relatively large, and heat is easily transmitted. The heat at the center of the storage element is easily radiated to the outside through the current collector foil. In addition, since it is thinner than the first power storage element, cracks are less likely to occur, so that the element can be crushed and densely filled so that the curvature is reduced.

  In the secondary battery of the present invention, the second power storage element has a wound flat shape, and forms a longitudinal region and a corner region. The thickness of the active material layer in the corner region is the active material layer in the longitudinal region. It is a preferred embodiment that the thickness is less than the thickness.

  In the secondary battery having the above-described configuration, the curvature becomes smaller toward the center, but the active material layer is thin and the proportion of the electrode foil is large in the central corner region where the active material layer is likely to crack. Generation | occurrence | production can be suppressed and an electrical storage element can be filled more densely.

  According to the present invention, the surface pressure generating member can press the power storage element against the battery case and reliably restrain the battery element, thereby improving the durability and heat dissipation of the electrode elements and improving the battery life. Can do. Further, if the surface pressure generating member is an additional power storage element, the energy density can be improved.

It is a see-through | perspective perspective view which shows the structure of the cell common to each embodiment of this invention. It is sectional drawing which shows the electrical storage element of the conventional cell. It is sectional drawing which shows the electrical storage element of the conventional cell. It is a graph which shows the thickness of the electrode layer in the conventional cell, and the relationship between the curvature in which a crack arises. 1 shows a power storage element and a single battery according to an embodiment of the present invention, wherein (a) is a cross-sectional view of a single power storage element, (b) is a side cross-sectional view of the single battery, and (c) is a current collector portion of the single battery. It is the side view which saw through the case. The electrical storage element and unit cell which concern on other embodiment of this invention are shown, (a) is sectional drawing of an electrical storage element single-piece | unit, (b) is a sectional side view of a unit cell, (c) is the collector part of a unit cell It is the side view which saw through the case. The electrical storage element and unit cell which concern on other embodiment of this invention are shown, (a) is sectional drawing of an electrical storage element single-piece | unit, (b) is a sectional side view of a unit cell, (c) is the collector part of a unit cell It is the side view which saw through the case. The electrical storage element and unit cell which concern on other embodiment of this invention are shown, (a) is sectional drawing of an electrical storage element single-piece | unit, (b) is a sectional side view of a unit cell, (c) is the collector part of a unit cell It is the side view which saw through the case. FIG. 5 shows a unit cell according to another embodiment of the present invention, in which (a) is a side sectional view of the unit cell, and (b) is a side view seen through a case of a current collector portion of the unit cell. A conventional cell is shown, (a) is a sectional side view of the cell, and (b) is a side view of a case of a current collector portion of the cell. It is sectional drawing which shows each layer which comprises the electrical storage element which concerns on one Embodiment of this invention. It is sectional drawing which shows each layer which comprises the electrical storage element which concerns on other embodiment of this invention. It is sectional drawing which shows each layer which comprises the electrical storage element which concerns on other embodiment of this invention. It is a schematic diagram which shows the manufacturing method of the cell of this invention. It is a schematic diagram which shows the manufacturing method of the cell of this invention. It is a graph which shows the relationship between the frequency | count of charging / discharging and the capacity | capacitance fall rate in the Example and comparative example of this invention. It is a graph which shows the relationship between the frequency | count of charging / discharging and a resistance increase rate in the Example and comparative example of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a perspective view showing a general cell to which the present invention can be applied. The unit cell is a known lithium ion secondary battery or the like, and includes a battery case 10 and a battery lid 11. In the battery case 10, a positive electrode sheet coated with a positive electrode active material, a separator, and a negative electrode sheet coated with a negative electrode active material are stacked and wound, and a storage element 24 of a wound body impregnated with an electrolyte solution The positive electrode lead plate 21 and the negative electrode lead plate 23 connected to positive and negative current collector foils led out from both ends of the electric storage element 24 are accommodated. In each of the positive electrode lead plate 21 and the negative electrode lead plate 23, a positive electrode terminal 20 and a negative electrode terminal 22 are provided outside the battery through the battery lid 11.

  In such a conventional unit cell, when the thickness of the electrode layer is increased, as shown in the cross-sectional view of the power storage element in FIG. 10, the power storage element 24 has a hollow portion 30, and Since the power storage element 24 is not restrained in the longitudinal region existing between the corner regions, there is a problem that the longitudinal region is recessed with respect to the hollow portion 30 as described above.

First embodiment (coaxial type)
FIG. 5A is a cross-sectional view illustrating a power storage element in the unit cell according to the first embodiment of the present invention, which solves such a conventional problem. The power storage element 24 has a second power storage element 40 that is a coaxial surface pressure generating member in a hollow portion. Similar to the first power storage element 24, the second power storage element 40 has a structure in which a positive electrode sheet, a separator, and a negative electrode sheet are stacked and wound. The first and second power storage elements thus formed are housed in the case 10 as shown in the cross-sectional view of FIG. 5B and the perspective side view of FIG.

  According to the single battery of the first embodiment configured as described above, since the second power storage element presses the first power storage element, the central portion of the longitudinal region where the first power storage element is likely to bend is in contact with the battery case. Therefore, heat generated from the power storage element is easily transmitted to the battery case, and heat dissipation is improved. Further, durability against vibration applied to the battery and durability against expansion / contraction of the power storage element itself due to repeated charge / discharge are improved.

  In addition, the corner area of the power storage element can be prevented from being crushed and the curvature can be kept large, so that the active material can be prevented from falling off, and the contact area between the battery case and the power storage element can be increased. Since the restraining force is evenly applied to the elements and the distance between the electrodes becomes constant, an increase in internal resistance can be prevented even during long-term use.

  Furthermore, since the surface pressure generating member also serves as the second power storage element, the amount of the power storage element, that is, the total active material amount can be increased, and the capacity of the secondary battery can be improved.

  Here, in 1st Embodiment, it is preferable that the active material layer of a 2nd electrical storage element is thinner than the active material layer of a 1st electrical storage element. The advantages of such a structure will be described below. FIG. 11A shows a relatively thin active material layer of such a second power storage element of the present invention, and FIG. 11B shows a relatively thick active material layer of the first power storage element. Show. FIGS. 12A and 12B show a second power storage element and a first power storage element in which the thickness of the active material layer does not change, respectively. As shown in FIG. 11A, when the active material layer of the second power storage element, that is, the positive electrode material 51 and the negative electrode material 53 is thin, the ratio of the current collector foil, that is, the positive electrode foil 50 and the negative electrode foil 54 whose thickness remains unchanged. It becomes relatively large, heat is easily transmitted, and heat at the center of the power storage element is easily radiated to the outside through the current collector foil. For this reason, the thermal variation between the central portion and the outer peripheral portion of the power storage element is reduced, and deterioration due to an extreme temperature rise in the central portion can be prevented. In addition, since it is thinner than the first power storage element, it is difficult to crack even if it is bent. Therefore, the element can be crushed and densely filled so as to reduce the curvature.

  FIG. 6 shows a modification of the first embodiment. As illustrated in FIG. 6, the wound second power storage element 40 may be changed to a stacked second power storage element 41. Similarly, in the case of the stacked second power storage element 41, ultrasonic welding is performed in parallel with the first power storage element 24 by current collecting foils at both ends to which no active material is applied.

  In the first embodiment, the thickness of the active material layer of the first power storage element is preferably set in the range of 50 to 500 μm. In this case, the thickness of the active material layer of the second power storage element is 10 to 50 μm. It is preferable to set the range.

  In the first embodiment, the preferred electrode thicknesses at the center and the outer periphery vary depending on the crack toughness of the electrode mixture layer. For example, the adhesion between the current collector foil and the electrode mixture layer, the type of active material constituting the electrode mixture layer, the particle size, the density of the electrode mixture layer, and the amount of the binder forming the electrode mixture layer can be mentioned. The ratio of the 2nd electrical storage element which can be loaded in a 1st electrical storage element can be optimized with the following method. First, the curvature at which corner electrode cracks occur can be experimentally determined according to the electrode thickness of the outer first power storage element. What is necessary is just to load the 2nd electrical storage element of the size which can be loaded in the said hollow part which consists of a thinner electrode layer in the hollow part which has a curvature which does not exceed this "crack limit". For example, in FIG. 7, when the electrode thickness of the first power storage element 24 is 100 μm and the crack limit polarity of this electrode layer is 8 mm, the second power storage element is loaded into the hollow portion of 8 mm inside. 42 is created. For example, the thickness of the electrode active material layer is set to 50 μm.

  In the first embodiment, a third power storage element 43 may be further loaded in the second power storage element 42 as shown in FIG. In this case, considering the curvature and crack limit of each power storage element, for example, the electrode thickness of the first power storage element 24 is 120 μm, the electrode thickness of the second power storage element 42 is 80 μm, and the third power storage element 43 The electrode thickness is set to 50 μm.

  As a method of loading a plurality of power storage elements, a method of winding a power storage element consisting of a thin active material layer, which will be described later, and winding a power storage element consisting of a thick active material layer on the outside thereof, or a stacked type power storage element And a method of winding an electricity storage element around the outside, and a method of producing an outside electricity storage element and inserting an electricity storage element made of a thin active material layer into the hollow portion inside.

  As shown in FIGS. 7 and 8, there may be a slight hollow portion in the center of the innermost power storage element. In that case, in order to maintain the close contact between the power storage element and the battery case, With respect to the curvature diameter R of the corner portion of the hollow portion, the length of depression of the longitudinal region of the power storage element must be maintained at R / 2 or less.

  In the first embodiment, two power storage elements are accommodated in the case, but the number of power storage elements is not limited to this aspect, and may be one or three or more.

Second embodiment (adjacent type)
FIG. 9 is a cross-sectional view showing a power storage element in a cell according to the second embodiment of the present invention. The two power storage elements 24 having the hollow portion 30 have the adjacent surface pressure generating member 44 between them. The power storage element 24 and the surface pressure generating member 44 are accommodated in the case 10 in a state where the hollow portion 30 of the power storage element 24 is crushed by the surface pressure generating member 44.

  According to the unit cell of the second embodiment configured as described above, the surface pressure generating member between the two power storage elements crushes and fixes the adjacent power storage element, so that the power storage element is pressed and the power storage element is bent. The central portion of the longitudinal region that is likely to be in contact with the battery case improves heat dissipation and durability. In addition, since the curvature of the corner area of the power storage element can be suppressed and maintained with a large curvature, the active material can be prevented from falling off, and the contact area between the battery case and the power storage element can be increased. Since the restraining force is evenly applied to the elements and the distance between the electrodes is constant, an increase in internal resistance can be prevented.

  As long as the surface pressure generating member 44 is a flat member as shown in FIG. 9, the material is not limited, such as a highly rigid material or an elastic material, but the surface pressure generating member 44 includes a positive electrode sheet, a separator, and a negative electrode sheet. It is preferable that the second power storage element 44 is wound or stacked.

  According to the unit cell configured as described above, since the surface pressure generating member also serves as the second power storage element, the amount of the power storage element, that is, the total amount of the active material is increased, and the capacity of the secondary battery can be improved.

  Here, also in the second embodiment, it is preferable that the second power storage element 44 is a winding type, and the active material layer of the second power storage element 44 is thinner than the active material layer of the first power storage element 24. When the active material layer of the second power storage element 44 is thin, the ratio of the current collector foil is relatively increased and heat is easily transmitted, and the heat at the center of the power storage element is easily radiated to the outside through the current collector foil. Moreover, since it is thin compared with the 1st electrical storage element 24, it is hard to produce a crack, Therefore An element can be crushed and filled densely so that a curvature may become small.

  Also in the second embodiment, two power storage elements 24 are accommodated in the case in FIG. 9, but the number of power storage elements is not limited to this mode, and is assumed to be three or more and adjacent to each other. A second power storage element 44 may be provided. In that case, the 1st electrical storage element located inside compared with the 1st electrical storage element located in the both ends which contact | connects a case side surface is pinched by the 2nd electrical storage element from both sides, and is crushed more. Therefore, in consideration of this, the thickness of the second power storage element is thick in the second power storage elements at both ends and thin in the other second power storage elements, and may be appropriately adjusted.

  In both forms of the first embodiment and the second embodiment, the second power storage element is a wound flat shape, constituting a longitudinal region and a corner region, and the thickness of the active material layer in the corner region is It is preferably formed thinner than the thickness of the active material layer in the longitudinal region. FIG. 13 is a schematic diagram showing the second power storage element in which the corner region has a relatively small thickness. FIG. 13A shows a positive electrode sheet (both surfaces of the positive foil 50 before winding). Fig. 13 (b) shows a case where the positive electrode material 51 is applied) or a negative electrode sheet (which is formed by applying the negative electrode material 53 on both sides of the negative electrode foil 54). The corner area | region of the 2nd electrical storage element at the time of being wound is shown.

As shown in FIG. 13 (a), the positive electrode (negative electrode) sheets at a predetermined interval _C 1 -C _4, it is formed so as cathode material 51 (negative electrode material 53) is thinned. When the positive electrode (negative electrode) sheet is formed in this manner and wound so that the thinly formed portion comes to the corner region, a second power storage element as shown in FIG. 13B can be manufactured. .

In the second energy storage device having the above-described configuration, since the active material layer is thin and the proportion of the electrode foil is large in the corner region where the active material layer is likely to generate cracks, the generation of cracks can be suppressed, and the curvature can be reduced. Can be crushed so as to be smaller, so that the case can be filled with the power storage element more densely. In the winding process, since the electrode sheet circumferential length increases from the center to the outer periphery, the appearance interval of the portion corresponding to the corner region, that is, the portion to be thinly formed, increases. Therefore, in the electrode sheet application step, the electrode material may be applied at intervals C ₁ <C ₂ <C ₃ <C ₄ so that the thinly formed portion is adapted to the change in circumference.

2. Manufacturing Method of Secondary Battery There are two methods for manufacturing the secondary battery of the present invention. In the first method, a positive electrode sheet, a separator, and a negative electrode sheet constituting the second power storage element are overlapped and wound, and the second power storage element is set in another winding device in the next process, so that the second power storage In this method, the electrode body of the first power storage element and the separator are wound around the element as a winding axis. Specifically, the positive electrode sheet, the separator, and the negative electrode sheet that constitute the second electricity storage element are overlapped and wound, the separator that constitutes the first electricity storage element is wound on the outer periphery of the second electricity storage element, and the first electricity storage element A positive electrode sheet and a negative electrode sheet constituting the battery are inserted between separators and wound around the outer periphery of the second power storage element. At this time, different separators such as thickness and porosity may be used for the separators of the second power storage element and the first power storage element.

  According to the manufacturing method having the above configuration, the winding process of the first power storage element is continuously performed following the winding process of the second power storage element while realizing high productivity and low cost by using the existing winding equipment. The secondary battery with improved element filling rate of the present invention can be suitably manufactured.

  Further, the second method is a method shown in FIGS. 14 and 15 described later. In this method of manufacturing a secondary battery, after winding a positive electrode sheet, a separator, and a negative electrode sheet constituting the second electricity storage element, the first electricity storage element is constituted at the rear end portion of each sheet using the same device. It is preferable that the positive electrode sheet and the front end of the negative electrode sheet are continuously formed or connected, and the first power storage element is wound.

  According to the manufacturing method having the above-described configuration, the separators of the second power storage element and the first power storage element are the same continuous separator, and the rear end portion of each sheet constituting the second power storage element and the first power storage element are configured. Since the front end portion of each sheet can be wound continuously as a single sheet formed continuously, it can be created with a single device and productivity can be improved. Is possible. Further, when the active material layer for forming the second power storage element and the first power storage element is formed on a continuous sheet, since the electrodes are electrically connected, there is no switching of the electrode sheet, and productivity is increased. It can be improved.

  In the second embodiment of the present invention, the first power storage element and the second power storage element can be independently produced by a known method, and these can be stacked and accommodated in the battery case. The manufacturing method of the electrical storage element in 1st Embodiment is demonstrated. 14 and 15 are schematic views showing a manufacturing apparatus according to such a manufacturing method.

  First, a positive electrode material is applied to both surfaces of the positive electrode foil by a known method (not shown) to produce a positive electrode sheet. At this time, two types of positive electrode sheets in which the thickness of the applied positive electrode material is changed, that is, a thin film positive electrode sheet 80 and a thick film positive electrode sheet 81 are produced. Similarly, a thin film negative electrode sheet 84 and a thick film negative electrode sheet 83 are produced. In each of these sheets, electrode rolls 70, 71, 73, and 74 are set, and separator sheet rolls 72 and 75 are set in the state shown in FIG.

  The thin film positive electrode sheet 80, the separator sheet 82, the thin film negative electrode sheet 84, and the separator sheet 85 are stacked in this order through a plurality of guide rolls indicated by white circles in FIG. 14, and the front end of the sheet is fixed to a winding core (not shown). It is wound around the core. Thus, when the second power storage element 60 is manufactured and the second power storage element 60 reaches a predetermined thickness, each of the sheets is cut, and the rear end of the sheet is the surface of the second power storage element 60. It is fixed at a predetermined switching position. In order to prevent the occurrence of a step at the boundary between the rear end portion and the front end portion of the sheet, the switching position between the rear end portion and the front end portion is formed above the case and the unit cell having a large clearance.

  Subsequently, as shown in FIG. 15, the thick film positive electrode sheet 81, the separator sheet 82, the thick film negative electrode sheet 83, and the separator sheet 85 are stacked in this order through a plurality of guide rolls. The front end portion of the sheet is fixed at a predetermined position and wound around the second power storage element 60. Thus, when the first power storage element 61 is manufactured and the first power storage element 61 reaches a predetermined thickness, each of the sheets is cut, and the rear end portion of the sheet is the surface of the first power storage element 61. It is fixed at a predetermined position.

  According to the manufacturing method having the above-described configuration, the separators of the second power storage element and the first power storage element are the same continuous separator, and the rear end portion of each sheet constituting the second power storage element and the first power storage element are configured. Since the front end portion of each sheet can be wound continuously as a single sheet formed continuously, it can be created with a single device and productivity can be improved. Is possible. Further, when the active material layer for forming the second power storage element and the first power storage element is formed on a continuous sheet, since the electrodes are electrically connected, there is no switching of the electrode sheet, and productivity is increased. It can be improved.

  According to the manufacturing method having the above configuration, the winding process of the first power storage element is continuously performed following the winding process of the second power storage element while realizing high productivity and low cost by using the existing winding equipment. The secondary battery with improved element filling rate of the present invention can be suitably manufactured.

Hereinafter, each component of the present invention will be described in detail.
The positive electrode sheet constituting the positive electrode sheet power storage element has a structure in which a positive electrode material is bound on both surfaces of a positive electrode current collector made of aluminum. As the positive electrode material of this example, Li oxide powder is used, and as the conductive filler, acetylene black, ketjen black, VGCF, and the like can be given. The positive electrode and negative electrode active materials of the central storage element and the outer peripheral storage element may be the same or different.

The negative electrode sheet constituting the negative electrode sheet storage element has a structure in which a negative electrode material is bound on both surfaces of a negative electrode current collector made of copper or the like. As the negative electrode material of this embodiment, a carbon material that occludes and releases lithium ions, and an alloy or oxide containing Sn, Si, Pb, and Co can be used. Examples of the carbon material include natural graphite, artificial graphite, activated carbon, a low-temperature carbon body calcined at 600 to 1200 ° C. (for example, pitch, mesophase pitch as an easily graphitizable carbon precursor, or phenol as a non-graphitizable carbon precursor). Resin, xylene resin, PPS, cellulose, etc.) synthesized by heat treatment in an inert atmosphere. The electrode active materials of the central element and the peripheral element may be the same or different. For example, the element in the central part is likely to deteriorate because the temperature is high, so that hard carbon with high deterioration toughness and small expansion is used for the negative electrode in the central part, and soft carbon and graphite materials are used for the outer electrode. You can also.

As the separator sheet constituting the separator sheet power storage element, a polyolefin microporous separator such as polyethylene, polypropylene or a nonwoven fabric separator such as polyester fiber or aramid fiber can be used.

Examples of the electrolyte solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (γ- BL), sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran and the like. A solvent may be used independently or may be used in mixture of 2 or more types. Examples of the electrolyte include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium boron tetrafluoride (LiBF ₄ ), lithium hexafluoroarsenide (LiAsF ₆ ), and lithium trifluoromethanesulfonate. Examples include lithium salts such as (LiCF ₃ SO ₃ ) and bistrifluoromethylsulfonylimide lithium [LiN (CF ₃ SO ₃ ) ₂ ]. The electrolyte may be used alone or in combination of two or more. The amount of electrolyte dissolved in the solvent is usually about 0.2 mol / L to 2 mol / L. Various ionic liquids may be mixed. In addition, it may be a gel electrolyte retained by the electrolytic solution, and the retaining material may be polyethylene oxide, polypropylene oxide, vinylidene fluoride (VdF), hexafluoropropylene (HFP) or a derivative thereof, or a copolymer. Can do.

The element at the center of the storage element production can be either a wound type or a laminated type. However, the outer peripheral element is preferably a wound type. In particular, it is suitable for a flat wound type. Eventually, the current collector foil of each element in the central part and the outer peripheral part is connected in parallel to form an integrated element. Therefore, when producing an electricity storage element, the electrode rolls forming each element have different thicknesses continuously. The center part and the outer peripheral part may be formed from separate electrode rolls. Further, by loading a plurality of flat wound elements into the case, the ratio of the R portion outside the elements is reduced, so that the volume filling efficiency of the rectangular case can be improved.

As the electrode terminal of the electrode terminal positive electrode terminal and the negative electrode terminal, a metal such as copper, nickel, aluminum, stainless steel, an alloy containing these, or a metal plated with these metals as a base material can be used.

To process the shape of the battery case bottom surface, aluminum, stainless alloy, or resin can be used, but an aluminum alloy produced by impact molding or transfer press processing is preferable. The case preferably has a structure that is in close contact with the power storage element. This reduces the space between the case and the power storage element, and the liquid level rises when the electrolyte is injected. There is an effect that can be shortened.

  As described above, the present invention is a technique for improving the cell life and energy density in the structure of a high energy density battery. INDUSTRIAL APPLICABILITY The present invention is effective not only for secondary batteries but also for power storage devices using electrode bodies composed of aggregates of particulate or fibrous microparticles such as capacitors and hybrid capacitors, and in particular, Si that has expansion and contraction. It is effective for a power storage device comprising a lithium ion battery electrode containing Sn or graphite.

Hereinafter, specific production examples of the present invention will be described.
[Example 1]
A wound type power storage element having a two-layer structure of a central portion and an outer peripheral portion was produced. An electrode body having a positive electrode coating width of 120 mm, a negative electrode coating width of 122 mm, and an uncoated portion of 7 mm was used as the central electrode. A separator having a thickness of 25 μm was used. As the negative electrode current collector foil, a Cu foil was used with a thickness of 10 μm, and as the positive electrode current collector foil, an Al foil was used with a 20 μm foil. LiNi _0.33 Mn _0.33 Co _0.33 O ₂ having a particle diameter D ₅₀ = 12 μm was used as the positive electrode active material, and artificial graphite particles having a particle diameter of 22 μm were used as the negative electrode active material. An electrode was prepared using PVDF as a binder, and the thickness of the active material layer after pressing the electrode body was 40 μm. The electrode density of the negative electrode was 1.5 g / cm ² , and the electrode density of the positive electrode was 3.85 g / cm ³ .

As the outer peripheral electrode, an electrode body having a positive electrode coating width of 120 mm, a negative electrode coating width of 122 mm, and an uncoated portion of 9 mm was used. A separator having a thickness of 25 μm was used. As the negative electrode current collector foil, a Cu foil was used with a thickness of 10 μm, and as the positive electrode current collector foil, an Al foil was used with a 15 μm foil. LiNi _0.33 Mn _0.33 Co _0.33 O ₂ having a particle diameter D ₅₀ = 12 μm was used as the positive electrode active material, and artificial graphite particles having a particle diameter of 22 μm were used as the negative electrode active material. An electrode was produced using PVDF as a binder, and the thickness of the active material layer after pressing the electrode body was 100 μm. The electrode density of the negative electrode was 1.5 g / cm ² , and the electrode density of the positive electrode was 3.85 g / cm ³ .

1) Production of electricity storage element A separator is wound up by a biaxial winding core of Φ2 mm, and the center electrode is wound by inserting a positive electrode and a negative electrode between the separators to produce a flat electricity storage element having an element thickness of 8 mm. did. Further, this element was set, and the electrodes on the outer peripheral portion were wound in the same manner from the outside of the element, and a flat electricity storage element having an element thickness of 19 mm was produced. The uncoated portions of the positive electrode and the negative electrode were left and right to form a current collecting portion. Two power storage elements were prepared.

2) Welding of electricity storage elements Two electricity storage elements are arranged side by side so that they are connected in parallel, and a lead tab made of a Cu plate having a width of 4 mm and a thickness of 0.3 mm is applied to the current collector foil formed at both ends. Ultrasonic welding was performed from above, and this was performed at two locations on the front and back. Similarly, the positive electrode was welded with an Al plate having a thickness of 4 mm and a thickness of 0.5 mm. In order to insulate the case from the power storage element, the entire power storage element including the welded portion of the terminal was covered with a polyester resin sheet.

3) The connecting lid portion of the lead and lid is a 2 mm thick plate having positive and negative terminals. A hole for an electrolyte injection hole is formed in the lid. The positive and negative lead plates coming out of the power storage element were welded and joined to the terminal portion of the case lid.

4) Production of Case A case was produced by impact molding using the aluminum alloy of A3003. The case thickness was 0.5 mm, the case outer dimensions were 40 mm thickness, 120 mm height, and 150 mm width.

5) Sealing of elastic member and power storage element The structure in which the power storage element and the lid produced in 3) were integrated was inserted into the case. The lid and case were sealed by YAG welding and then vacuum-dried at 80 ° C. for 24 hours. In this way, the single cell of Example 1 shown in FIG. 7 was produced.

6) After the impregnation vacuum drying, the inside of the unit cell is depressurized in the glove box, and then the electrolyte solution 1.0M LiPF ₆ / (EC + DMC + EMC) is injected, and the depressurization, normal pressure, and depressurization are repeated twice. It was. CCCV charging was performed for 8 hours at a current of 0.2 C up to 4.2 V with a charging / discharging device. Thereafter, the battery was discharged at 1C up to 2.7 V with a charge / discharge device, and this charge / discharge cycle was performed 5 times. Charging was performed up to SOC50. As described above, the initial battery capacity and the initial resistance were measured. Table 1 below shows the measurement results of the initial battery capacity and the initial resistance.

[Example 2]
Using a biaxial winding core of φ8 mm, using only the electrodes on the outer periphery in Example 1, positive and negative electrodes were inserted between the separators, and an electricity storage device was produced so that the device thickness was 21 mm. Two of these were prepared. Next, the central storage element 44 shown in FIG. 9 was prepared in the same manner as the first storage element of Example 1. However, the element thickness was 6 mm. The power storage element 44 was sandwiched between two power storage elements, and the current collector foil of the power storage element 44 was ultrasonically welded to 38 mm and loaded into the case. In this way, the unit cell of Example 2 shown in FIG. 9 was produced, and the initial battery capacity and the initial resistance were measured.

[Comparative example]
Using a biaxial winding core of φ8 mm, using only the electrodes on the outer periphery in Example 1, inserting positive and negative electrodes between separators, producing a storage element so that the element thickness is 21 mm, crushing 2 mm, and 19 mm did. A single cell of the comparative example shown in FIG. 10 was prepared and the initial battery capacity and the initial resistance were measured in the same manner as in the example except that two were prepared and loaded in the connection case in parallel.

  Then, about the cell of Example 1 and the comparative example, 4000 times charge / discharge was repeated by test temperature 55 degreeC, voltage range upper limit 4.2V-lower limit 3.0V, and charging / discharging electric current 2C. In this charge / discharge cycle test, the capacity decrease rate is shown in FIG. 16, and the resistance increase rate is shown in FIG. In addition, resistance calculated the internal resistance at 25 degreeC by the 4-point method in the electric current value of 10, 20, 30, 40A.

  As described above, according to the present invention, the filling rate of the electricity storage elements into the square elements is improved, and thus the electrode length can be increased. Therefore, the initial capacity was improved and the internal resistance was suppressed. Furthermore, as a result of the charge / discharge cycle test, as shown in FIGS. 16 and 17, in the comparative example, the capacity decreases and the resistance increases with charge / discharge.

  The reason for this is that, in the comparative example, the internal resistance is high and thermal variation easily occurs inside the rectangular cell, so that there are a low resistance region and a high resistance region in the device. It is thought that capacity reduction is likely to occur because of the difference in the number of times of charge / discharge of the material layer. In the comparative example, the increase in internal resistance is large from the beginning. This is because the constraining force of the element is reduced, so that the conductivity is reduced in the electrode surface due to the expansion and contraction of the graphite particles due to charge and discharge, and the adhesion to the current collector foil is reduced, so that the resistance is increased. Conceivable.

  According to the present invention, the energy density can be improved, and the life of the battery is improved by improving the durability and heat dissipation of the storage element. Therefore, the present invention is applied to an in-vehicle lithium ion secondary battery system. Very promising.

A ... Corner area,
B ... Longitudinal region,
10 ... Battery case,
11 ... Battery cover,
12 ... electrolyte inlet,
20: Positive terminal,
21 ... Positive electrode lead plate,
22: negative terminal,
23 ... negative electrode lead plate,
24, 25 ... 1st electrical storage element,
30, 31 ... hollow part,
40, 41, 42 ... 2nd electrical storage element (coaxial surface pressure generating member),
43 ... 3rd electrical storage element (coaxial type surface pressure generating member),
44 ... 2nd electrical storage element (adjacent type surface pressure generating member),
50 ... positive foil,
51 ... Positive electrode material,
52 ... separator,
53. Negative electrode material,
54 ... negative electrode foil,
60 ... 2nd electrical storage element (coaxial type surface pressure generating member),
61 ... 1st electrical storage element,
70: Thin film positive electrode sheet take-up roller,
71 ... Thick film positive electrode sheet take-up roller,
72 ... Separator sheet take-up roller,
73 ... Thick film negative electrode sheet take-up roller,
74: Thin film negative electrode sheet take-up roller,
75 ... Separator sheet take-up roller,
80 ... thin film positive electrode,
81 ... thick film positive electrode,
82, 85 ... separator,
83 ... thick film negative electrode,
84: Thin film negative electrode.

Claims (6)

A first power storage element having an electrolyte solution in which a positive electrode sheet, a separator, and a negative electrode sheet are stacked and wound;
A secondary battery including a battery case that houses the first power storage element,
The first power storage element has a flat shape and constitutes a longitudinal region and a corner region,
The central portion of the longitudinal region is pressed against the battery case by a surface pressure generating member ,
The first power storage element is wound around the surface pressure generating member,
The surface pressure generating member is composed of a second power storage element in which a positive electrode sheet, a separator, and a negative electrode sheet are wound,
The active material layer of the second power storage element is formed thinner than the active material layer of the first power storage element. A first power storage element having an electrolyte solution in which a positive electrode sheet, a separator, and a negative electrode sheet are stacked and wound;
A secondary battery including a battery case that houses the first power storage element,
The first power storage element has a flat shape and constitutes a longitudinal region and a corner region,
The central portion of the longitudinal region is pressed against the battery case by a surface pressure generating member,
The first power storage element is wound around the surface pressure generating member,
The surface pressure generating member is composed of a second power storage element in which a positive electrode sheet, a separator, and a negative electrode sheet are wound or laminated,
The positive electrode sheet comprises a positive electrode active material and a positive electrode current collector foil on which the positive electrode active material is formed,
The negative electrode sheet comprises a negative electrode active material and a negative electrode current collector foil on which the negative electrode active material is formed,
The ratio of the thickness of the positive electrode or negative electrode current collector foil to the positive electrode or negative electrode active material in the second power storage element is larger than the ratio of the thickness of the positive electrode or negative electrode current collector foil to the positive electrode or negative electrode active material in the first power storage element. A secondary battery characterized by that. A first power storage element having an electrolyte solution in which a positive electrode sheet, a separator, and a negative electrode sheet are stacked and wound;
A secondary battery including a battery case that houses the first power storage element,
The first power storage element has a flat shape and constitutes a longitudinal region and a corner region,
The central portion of the longitudinal region is pressed against the battery case by a surface pressure generating member, A plurality of the first power storage elements are provided,
The surface pressure generating member is provided between the plurality of first power storage elements,
The surface pressure generating member is composed of a second power storage element in which a positive electrode sheet, a separator, and a negative electrode sheet are wound,
The active material layer of the second power storage element is formed thinner than the active material layer of the first power storage element. The second power storage element is a wound flat shape, and constitutes a longitudinal region and a corner region,
The secondary battery according to claim 1 , wherein a thickness of the active material layer in the corner region is formed thinner than a thickness of the active material layer in the longitudinal region. A method of manufacturing a secondary battery according to claim 1 or 2 ,
Winding the positive electrode sheet, the separator and the negative electrode sheet constituting the second power storage element,
Fixing the ends of the positive electrode sheet, the separator and the negative electrode sheet constituting the first energy storage element on the outer periphery of the second energy storage element;
A method for manufacturing a secondary battery, wherein a positive electrode sheet, a separator, and a negative electrode sheet constituting the first power storage element are overlapped and wound around an outer periphery of the second power storage element. After winding the positive electrode sheet, the separator, and the negative electrode sheet constituting the second power storage element, the positive end sheet, the separator, and the negative electrode sheet constituting the first power storage element are respectively attached to the rear end portions of the respective sheets. The method for manufacturing a secondary battery according to claim 5 , wherein the first power storage element is connected and wound.

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