JP2012142099A - Secondary battery and manufacturing method thereof - Google Patents

Abstract

Disclosed is a secondary battery capable of reliably infiltrating an electrolyte into an electrode group even in a large electrode group in which several tens of layers of a positive electrode plate, a negative electrode plate, and a separator are laminated, and a method for manufacturing the same To do.
An expansion member that is flat at normal pressure and expands at vacuum between at least one of an electrode group and a bottom surface of an outer case on which the electrode group is placed or between an electrode group and a lid member. A secondary battery in which the expansion member is inflated at the time of evacuation, presses the central part of the electrode group, sufficiently discharges air in the central part of the electrode group that is difficult to escape, and then injects the electrolyte And its manufacturing method.
[Selection] Figure 1A

Description

  The present invention relates to a secondary battery, and in particular, in a secondary battery having a stacked electrode group, an electrolyte can be efficiently and surely permeated even in a secondary battery having a large electrode group. The present invention relates to a secondary battery and a manufacturing method thereof.

  In recent years, lithium secondary batteries have been used as power source batteries for portable electronic devices such as mobile phones and notebook computers because they have a high energy density and can be reduced in size and weight. Further, since the capacity can be increased, it has been attracting attention as a motor drive power source for electric vehicles (EV) and hybrid electric vehicles (HEV), and a storage battery for power storage.

  In the lithium secondary battery, an electrode group in which a positive electrode plate and a negative electrode plate are arranged opposite to each other with a separator interposed therebetween is housed in an outer case constituting a battery can, filled with an electrolyte, and positive electrode current collectors of a plurality of positive electrode plates A positive current collecting terminal coupled to the tab; a positive external terminal electrically connected to the positive current collecting terminal; a negative current collecting terminal coupled to the negative current collecting tabs of the plurality of negative electrode plates; and the negative current collecting terminal. It is set as the structure provided with the negative electrode external terminal electrically connected with an electrical terminal.

  As the electrode group, a wound type and a laminated type are known. The wound electrode group has a configuration in which a separator is interposed between a positive electrode plate and a negative electrode plate, and is integrally wound. The laminated electrode group has a positive electrode plate and a negative electrode plate interposed via a separator. It is the structure which laminated | stacked multiple layers.

  In a lithium secondary battery including a stacked electrode group, an electrode group in which a plurality of layers of a positive electrode plate and a negative electrode plate are stacked via a separator is housed in an outer case and filled with a non-aqueous electrolyte, respectively. A positive current collecting terminal coupled to the positive current collecting tab of the positive electrode plate, an external terminal electrically connected to the positive current collecting terminal, and a negative current collecting terminal coupled to the negative current collecting tab of the negative electrode plate And an external terminal electrically connected to the negative electrode current collecting terminal.

  In order to produce a secondary battery with a large capacity in the case of this stacked type, it is necessary to increase the areas of the positive electrode plate and the negative electrode plate, increase the number of stacked layers, and increase the amount of electrolyte to be filled. Therefore, it is important to ensure that the electrolytic solution penetrates into the electrode group having a large surface area and a large thickness.

  Conventionally, in order to infiltrate the electrolyte solution into the wound electrode group and the stacked electrode group, a vacuum injection method in which the inside of the battery can is evacuated and the electrolyte solution is injected is employed. To increase the density of the active material and increase the tightness of the positive electrode plate, the negative electrode plate, and the separator as the capacity increases, to improve the productivity of the non-aqueous electrolyte injection process that decreases, and to improve the battery quality A first step of evacuating the inside of the can, a second step of injecting a gas that can be dissolved in the electrolytic solution, a third step of injecting the electrolytic solution, and a fourth step of reducing the pressure for a certain time. In addition, a method for manufacturing a secondary battery has already been disclosed (for example, see Patent Document 1).

JP 2007-335181 A

  In order to increase the capacity of the secondary battery having the positive electrode plate, the negative electrode plate, and the electrolyte and to extend the battery life, it is preferable to increase the power generation area and increase the amount of the electrolyte to be filled. The area of the electrode plate is increased, the number of layers to be stacked is increased, and the amount of electrolyte solution to be filled tends to be increased. If it does so, time until electrolyte solution osmose | permeates inside the laminated | stacked electrode plate (center part of an electrode group) will become long, and productivity of an electrolyte solution injection process will fall.

  It is possible to infiltrate the electrolyte into the electrode group by evacuating the battery can and injecting the electrolyte. However, when the size of the electrode group is increased, it is difficult to completely exhaust the air inside the electrode group, and residual air is generated, which causes a problem that the electrolyte cannot be sufficiently permeated.

  Further, in the method described in Patent Document 1, even if the battery quality can be improved, the gas to be dissolved in the electrolytic solution is injected, so that the process becomes complicated and an extra device is required. This is not preferable because the injection cost increases.

  Therefore, it is preferable that the electrolytic solution is reliably infiltrated into the electrode group by a simpler method, the battery structure is capable of infiltrating the electrolytic solution in a shorter time, and is a method for manufacturing a battery. preferable.

  Moreover, in order to improve battery quality, it is important to sufficiently infiltrate the electrolyte into the electrode group. In particular, a large number (for example, several tens of layers) of positive electrode plates, negative electrode plates, and separators are laminated. In a large-capacity stacked secondary battery including the electrode group, it is preferable to reliably infiltrate the electrolyte into the electrode group in order to maintain stable battery capacity and battery quality.

  Therefore, even in a large electrode group in which several tens of layers of a positive electrode plate, a negative electrode plate, and a separator are stacked, a secondary battery having a battery structure that can permeate the electrolyte into the electrode group in a relatively short time It is preferable that the method is a method for manufacturing a secondary battery in which the electrolytic solution can penetrate into the electrode group in a relatively short time.

  Therefore, in view of the above problems, the present invention can reliably infiltrate the electrolyte into the electrode group even in a large electrode group in which several tens of layers of a positive electrode plate, a negative electrode plate, and a separator are laminated. It is an object of the present invention to provide a secondary battery and a manufacturing method thereof.

  To achieve the above object, the present invention provides an electrode group obtained by laminating a plurality of layers of a positive electrode plate and a negative electrode plate with a separator interposed therebetween, an exterior case that accommodates the electrode group, and a lid member that seals the exterior case. A secondary battery in which an electrolyte is injected into a battery can constituted by the outer case and the lid member and penetrates and fills the inside of the electrode group, the stacking direction of the electrode group An expansion member that is flat during normal pressure and expands during vacuum is interposed between at least one of the bottom surface of the outer case and the electrode group, or between the electrode group and the lid member. It is said.

  According to this structure, since the expansion member which swells at the time of vacuum is interposed, when the electrolyte solution is injected into the vacuum, the electrode group can be pressed by the expansion member and the air remaining inside can be pushed out. Therefore, it is possible to obtain a secondary battery in which air does not remain in the center portion of the electrode group and the electrolyte solution can reliably penetrate into the electrode group.

  According to the present invention, in the secondary battery configured as described above, the expansion member has a circular bag shape in plan view, and expands into a convex lens shape in a vacuum. According to this configuration, the expansion member swells in a convex lens shape in a vacuum state and presses the central portion of the electrode group, and exerts an action of pushing out air in the central portion that is difficult to be exhausted. Can penetrate.

  According to the present invention, in the secondary battery having the above-described configuration, the expansion member has an oval bag shape in plan view, and expands into a convex lens shape in a vacuum. According to this configuration, even when the electrode group has a rectangular shape having a long side portion and a short side portion, the electrolyte solution can be permeated to the central portion of the electrode group through the expansion member whose central portion swells elliptically. it can.

  In the secondary battery having the above-described configuration, the present invention is characterized in that a curved plate that curves in a convex lens shape with a predetermined curvature is interposed between the expansion member and the electrode group. According to this configuration, when the expansion member expands during the vacuum, the electrode group can be pressed according to the curved shape of the curved plate, and air in a predetermined area at the center of the electrode group can be discharged.

  According to the present invention, in the secondary battery having the above-described configuration, a pressing plate composed of two plates connected to be displaceable at a central portion of the expansion member is interposed between the expansion member and the electrode group. It is characterized by. According to this configuration, since the connecting portion of the pressing plate composed of the two plates is pushed up by the expansion member that swells in a convex lens shape in a vacuum, the central portion of the electrode group can be reliably pressed and air can be discharged without remaining. it can.

  Further, the present invention includes an electrode group in which a plurality of layers of a positive electrode plate and a negative electrode plate are laminated via a separator, an exterior case that accommodates the electrode group, and a lid member that seals the exterior case. And a lid member. A method of manufacturing a secondary battery in which an electrolyte is injected into a battery can constituted by infiltrating and filling the inside of the electrode group, and the exterior in the stacking direction of the electrode group At least one of the bottom surface of the case and the electrode group or between the electrode group and the lid member is provided with an expansion member that is flat at normal pressure and swells when vacuumed. The electrolytic solution is injected after the expansion member is expanded by a predetermined amount by vacuuming.

  According to this structure, since it swells at the time of a vacuum, it can press out an electrode group and can push out all the air remaining inside. Therefore, it becomes the structure which injects electrolyte solution after fully exhausting the air inside an electrode group, and becomes a manufacturing method of the secondary battery which can infiltrate electrolyte solution to the inside of an electrode group reliably.

  Further, the present invention provides a method for manufacturing a secondary battery having the above-described structure, wherein the electrode can be accommodated in the outer case and the lid member is attached to produce a sealed battery can; And a third step of injecting an electrolyte into the battery can. According to this configuration, since the second step of expanding the expansion body by decompressing the inside of the battery can is provided, it is possible to effectively push out the air inside by pressing the center part of the electrode group during vacuum. It is possible to reliably execute the preparation for penetrating the electrode group into the electrode group.

  According to the present invention, in the method of manufacturing a secondary battery having the above-described configuration, the expansion member is formed into a bag shape having a circular shape in plan view or an elliptical shape in plan view, and is expanded into a convex lens shape in a vacuum. According to this configuration, it becomes a configuration that swells in a convex lens shape in a vacuum and presses the central part of the electrode group, exerts an action of pushing out the air of the central part that is difficult to be exhausted, and ensures the electrolyte solution to the central part of the electrode group Can penetrate.

  According to the present invention, in the method for manufacturing a secondary battery having the above-described configuration, a curved plate that is curved in a convex lens shape with a predetermined curvature is interposed between the expansion member and the electrode group. According to this configuration, the expansion member is inflated at the time of vacuum, and the curved plate is bent to press the predetermined region of the electrode group, so that the air in the central portion of the electrode group that is difficult to remove air can be sufficiently discharged.

  According to the present invention, in the method for manufacturing a secondary battery having the above-described configuration, a pressing plate including two plates movably connected at a central portion of the expansion member is provided between the expansion member and the electrode group. It is characterized by wearing. According to this configuration, since the connecting portion of the pressing plate composed of the two plates is pushed up by the expansion member that swells in a convex lens shape in a vacuum, the central portion of the electrode group can be reliably pressed and air can be discharged without remaining. Thus, the electrolyte can be sufficiently penetrated into the electrode group.

  According to the present invention, an expansion member that is flat at normal pressure and expands during vacuum is interposed between at least one of the electrode group and the bottom surface of the outer case or between the electrode group and the lid member. The electrode can be pressed by the member to push out the air remaining inside. Therefore, even in a large electrode group in which several tens of layers of a positive electrode plate, a negative electrode plate, and a separator are stacked, a secondary battery that can reliably infiltrate the electrolyte into the electrode group and a method for manufacturing the same are obtained. be able to.

It is a cross-sectional schematic diagram which shows 1st embodiment of the secondary battery which concerns on this invention. It is a cross-sectional schematic diagram which shows the modification of 1st embodiment. It is a cross-sectional schematic diagram which shows 2nd embodiment of the secondary battery which concerns on this invention. It is a cross-sectional schematic diagram which shows 3rd embodiment of the secondary battery which concerns on this invention. It is a principal part enlarged view of the secondary battery of 3rd embodiment. It is a principal part enlarged view which shows the state which the expansion member expanded. It is a schematic explanatory drawing which shows the osmosis | permeation state of the electrolyte solution inside an electrode group. It is a measurement figure which shows the effect | action of the expansion member which concerns on this invention. It is a disassembled perspective view of a secondary battery. It is a disassembled perspective view of the electrode group with which a secondary battery is provided. It is a perspective view which shows the completed product of a secondary battery. It is a schematic sectional drawing of an electrode group.

  Embodiments of the present invention will be described below with reference to the drawings. Moreover, the same code | symbol is used about the same structural member, and detailed description is abbreviate | omitted suitably.

  A lithium secondary battery will be described as the secondary battery according to the present invention. For example, the secondary battery RB1 according to this embodiment shown in FIG. 1A is a stacked lithium secondary battery, and includes a stacked electrode group 1 in which a plurality of positive electrode plates and negative electrode plates are stacked via a separator. I have. Further, by increasing the area of the electrode plate and increasing the number of stacked layers, it becomes a secondary battery having a relatively large capacity, and can be applied to a storage battery for electric vehicles or a storage battery for power storage.

  Next, specific configurations of the stacked lithium secondary battery RB and the electrode group 1 will be described with reference to FIGS.

  As shown in FIG. 6, the stacked lithium secondary battery RB has a rectangular shape in plan view, and includes an electrode group 1 in which a positive electrode plate, a negative electrode plate, and a separator, each of which is rectangular, are stacked. Moreover, it accommodates in the battery can 10 comprised from the exterior case 11 and the cover member 12 which are provided with the bottom part 11a and the side parts 11b-11e, and is made into a box shape, and the side surface (for example, side part 11b, The charging / discharging is performed from an external terminal 11f provided on two opposing side surfaces of 11c.

  The electrode group 1 has a configuration in which a plurality of layers of a positive electrode plate and a negative electrode plate are laminated via a separator. As shown in FIG. 7, the positive electrode current collector 2b (for example, an aluminum foil) is coated with a positive electrode active material on both surfaces. The positive electrode plate 2 having the positive electrode active material layer 2a formed thereon and the negative electrode plate 3 having the negative electrode active material layer 3a formed of the negative electrode active material formed on both surfaces of the negative electrode current collector 3b (for example, copper foil) It is laminated through.

  Although the separator 4 insulates the positive electrode plate 2 and the negative electrode plate 3 from each other, lithium ions can be transferred between the positive electrode plate 2 and the negative electrode plate 3 through the electrolyte filled in the outer case 11. It has become.

Here, as the positive electrode active material of the positive electrode plate 2, oxides of lithium is contained (such as _{LiCoO 2, LiNiO 2, LiFeO 2} , LiMnO 2, LiMn 2 O 4) or a part of the transition metal in the oxide And a compound in which is substituted with other metal elements. Among these, in a normal use, if a material that can use 80% or more of lithium held in the positive electrode plate 2 for the battery reaction is used as the positive electrode active material, safety against accidents such as overcharge can be improved.

  Further, as the negative electrode active material of the negative electrode plate 3, a material containing lithium or a material capable of inserting / removing lithium is used. In particular, in order to have a high energy density, it is preferable to use a lithium insertion / extraction potential close to the deposition / dissolution potential of metallic lithium. A typical example is natural graphite or artificial graphite in the form of particles (scale-like, lump-like, fibrous, whisker-like, spherical and pulverized particles).

  In addition to the positive electrode active material of the positive electrode plate 2, and in addition to the negative electrode active material of the negative electrode plate 3, a conductive material, a thickener, a binder, and the like may be contained. The conductive material is not particularly limited as long as it is an electron conductive material that does not adversely affect the battery performance of the positive electrode plate 2 or the negative electrode plate 3. For example, carbon black, acetylene black, ketjen black, graphite (natural graphite, artificial graphite) ), Carbonaceous materials such as carbon fibers, conductive metal oxides, and the like can be used.

  As the thickener, for example, polyethylene glycols, celluloses, polyacrylamides, poly N-vinyl amides, poly N-vinyl pyrrolidones and the like can be used. The binder serves to hold the active material particles and the conductive material particles together, and includes a fluorine-based polymer such as polyvinylidene fluoride, polyvinyl pyridine and polytetrafluoroethylene, a polyolefin polymer such as polyethylene and polypropylene, Styrene butadiene rubber or the like can be used.

  Moreover, as the separator 4, it is preferable to use a microporous polymer film. Specifically, films made of a polyolefin polymer such as nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, polybutene can be used.

  Moreover, it is preferable to use an organic electrolytic solution as the electrolytic solution. Specifically, as an organic solvent of the organic electrolyte, esters such as ethylene carbonate, propylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, dioxolane , Diethyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, and other ethers, dimethyl sulfoxide, sulfolane, methyl sulfolane, acetonitrile, methyl formate, and methyl acetate can be used. These organic solvents may be used alone or in combination of two or more.

Further, the organic solvent may contain an electrolyte salt. Examples of the electrolyte salt include lithium perchlorate (LiClO ₄ ), lithium borofluoride, lithium hexafluorophosphate, trifluoromethanesulfonic acid (LiCF ₃ SO ₃ ), lithium fluoride, lithium chloride, lithium bromide, and iodide. And lithium salts such as lithium and lithium tetrachloroaluminate. In addition, these electrolyte salts may be used independently and may be used in mixture of 2 or more types.

  The concentration of the electrolyte salt is not particularly limited, but is preferably about 0.5 to about 2.5 mol / L, and more preferably about 1.0 to 2.2 mol / L. When the concentration of the electrolyte salt is less than about 0.5 mol / L, the carrier concentration in the electrolytic solution is lowered, and the resistance of the electrolytic solution may be increased. On the other hand, when the concentration of the electrolyte salt is higher than about 2.5 mol / L, the dissociation degree of the salt itself is lowered, and there is a possibility that the carrier concentration in the electrolytic solution does not increase.

  The battery can 10 includes an outer case 11 and a lid member 12, and is made of iron, nickel-plated iron, stainless steel, aluminum, or the like. Further, in the present embodiment, as shown in FIG. 8, the battery can 10 is formed so that the outer shape is substantially a flat rectangular shape when the outer case 11 and the lid member 12 are combined. ing.

  The outer case 11 is a box shape having a bottom portion 11a having a substantially rectangular bottom surface and four side portions 11b to 11e erected from the bottom portion 11a, and the electrode group 1 is accommodated inside the box shape. To do. The electrode group 1 includes a positive electrode current collecting terminal connected to a current collecting tab of the positive electrode plate and a negative electrode current collecting terminal connected to the current collecting tab of the negative electrode plate, and is electrically connected to these current collecting tabs. External terminals 11 f are provided on the sides of the outer case 11. The external terminal 11f is provided, for example, at two locations on the opposite two side portions 11b and 11c. Reference numeral 10a denotes a liquid injection port from which an electrolytic solution is injected.

  After the electrode group 1 is accommodated in the outer case 11 and each current collecting terminal is connected to an external terminal, or each external terminal is connected to the current collecting terminal of the electrode group 1 and accommodated in the hand outer case 11, After fixing the terminal to a predetermined portion of the outer case, the lid member 12 is fixed to the opening edge of the outer case 11. Then, the electrode group 1 is sandwiched between the bottom portion 11 a of the outer case 11 and the lid member 12, and the electrode group 1 is held inside the battery can 10. The lid member 12 is fixed to the exterior case 11 by, for example, laser welding. Further, the connection between the current collecting terminal and the external terminal can be performed using a conductive adhesive or the like in addition to welding such as ultrasonic welding, laser welding, and resistance welding.

  As described above, the stacked secondary battery according to the present embodiment includes an electrode group 1 in which a plurality of positive electrode plates 2 and negative electrode plates 3 are stacked via a separator 4, and the electrode group 1 is accommodated in an electrolyte solution. , An external terminal 11f provided on the external case 11, a positive / negative current collecting terminal for electrically connecting the positive / negative electrode plate and the external terminal 11f, and a lid member attached to the external case 11 12.

  For example, as shown in FIG. 9, the electrode group 1 accommodated in the outer case 11 includes a positive electrode plate 2 in which a positive electrode active material layer 2a is formed on both surfaces of a positive electrode current collector 2b, and both surfaces of a negative electrode current collector 3b. The negative electrode plate 3 on which the negative electrode active material layer 3a is formed is laminated via the separator 4, and the separator 4 is disposed on both end faces. Moreover, it is good also as a structure which replaces with the separator 4 of both end surfaces, and winds the resin film of the same material as this separator 4, and coat | covers the electrode group 1 with the resin film which has insulation. In any case, the upper surface of the laminated electrode group 1 has a configuration in which members having electrolyte permeability and insulating properties are laminated. Therefore, the lid member 12 can be brought into direct contact with this surface, and can be pressed with a predetermined pressure via the lid member.

  Further, in order to exert a predetermined battery capacity, it is important that the electrolyte solution penetrates sufficiently into the inside of the electrode group 1. Therefore, when the electrode group 1 becomes large and thick, At the time of manufacture, it is required to sufficiently evacuate the air so that no air remains in the electrode group 1.

  It is possible to discharge the air inside the electrode group 1 by housing the electrode group 1 in the outer case 11 and evacuating the sealed battery can 10 with the lid member 12 attached. However, when the size of the electrode group 1 is increased, it becomes difficult to completely exhaust the air remaining in the electrode group 1 even if the degree of vacuum is increased and the time for vacuuming is increased.

  Therefore, in the present embodiment, even in a large electrode group in which several tens of layers of a positive electrode plate, a negative electrode plate, and a separator are stacked, an expansion member that positively pushes out air inside the electrode group is interposed and stacked. It is a secondary battery that efficiently extrudes air that is difficult to escape from the center of the body, improves the penetration of the electrolyte, and allows the electrolyte to penetrate into the inside of the electrode group, and its manufacturing method. is there. Next, specific embodiments of the secondary battery will be described with reference to FIGS.

  The secondary battery RB1 of the first embodiment shown in the schematic cross-sectional view of FIG. 1A is always between the electrode group 1 housed in the outer case 11 and the bottom surface of the outer case 11 on which the electrode group 1 is placed. It has a configuration in which an expansion member 13 that is flat at the time of pressure and expands at the time of vacuum is interposed. Further, a state in which the expansion member 13 is inflated when evacuated is schematically shown.

  Further, the battery can 10 is configured by attaching the lid member 12 to the outer case 11. The lid member 12 may have a flat plate shape as shown in the figure, or may have a dish shape in which a portion contacting the upper surface of the electrode group 1 protrudes in a convex shape and fits into the outer case 11. The shape is appropriately selected depending on the size of the battery can 10 and the thickness of the electrode group 1. In any case, the positive electrode plate and the negative electrode plate included in the electrode group 1 can be configured to be in close contact with each other via the lid member 12.

  Moreover, it is good also as a structure which interposes the expansion member 13 between the electrode group 1 and the cover member 12 like secondary battery RB1a of the modification shown to FIG. 1B. In any case, at least one of the bottom surface of the outer case 11 and the electrode group 1 in the stacking direction of the electrode group 1 or between the electrode group 1 and the lid member 12 is flat and vacuum at normal pressure. It is preferable to interpose an expansion member 13 that sometimes expands.

  As described above, in the present embodiment, since the expansion member 13 that swells during vacuum is interposed, the electrode group 1 is pressed by the expansion member 13 and remains in the interior when the electrolyte is vacuum-injected. Air can be pushed out. Therefore, air does not remain in the electrode group 1, so that the electrolyte penetration can be improved, and the electrolyte can be reliably infiltrated into the central portion of the thick electrode group 1.

  The expansion member 13 is a hollow bag made of a resin material having heat resistance, chemical resistance, and insulation, and is sealed so as not to allow air or electrolyte to pass through. The expansion member 13 has a flat shape at normal pressure. . Moreover, the shape of the plan view is a circular shape or an elliptical shape, as will be described later, and the center portion is expanded into a convex lens shape in accordance with the degree of vacuum to be evacuated.

  The battery can 10 is manufactured in a state in which the expansion member 13 is laid in a substantially central portion of the electrode group 1. Then, after the inside of the battery can is evacuated and the air is evacuated, the electrolytic solution is injected to produce the secondary battery RB1. At this time, the expansion member 13 expands according to the degree of vacuum for evacuating the inside of the battery can, and exerts an action of pressing the electrode group 1 against the lid member 12.

  That is, the expansion member 13 that expands in accordance with the degree of vacuum at the time of vacuuming expands into a convex lens shape and strongly presses the central portion of the electrode group 1, and has the effect of pushing out the air remaining in the central region. Demonstrate.

  Therefore, if it is secondary battery RB1 of the said structure, RB1a, the center part of the electrode group 1 can be pressed reliably and it can discharge | emit without leaving air, and electrolyte solution penetration property can be improved. Therefore, even in the large-sized electrode group 1 in which several tens of layers of the positive electrode plate 2, the negative electrode plate 3, and the separator 4 are stacked, the electrolyte can be reliably infiltrated into the electrode group 1.

  When the shape of the electrode group 1 is substantially square in plan view, the expansion member 13 preferably has a circular outer shape in plan view. If it is this structure, it will become a structure which a center part swells in the shape of a convex lens at the time of a vacuum, and presses the center part of the electrode group 1 of planar view square, exhibits the effect | action which extrudes the air of the center part which is hard to exhaust, and an electrode group The electrolyte can be sufficiently permeated to the central portion of 1.

  Moreover, when the shape of the electrode group 1 is a rectangular shape in plan view, the expansion member 13 preferably has an elliptical shape in plan view. With this configuration, even if the electrode group 1 has a rectangular shape having a long side portion and a short side portion, the central portion of the electrode group 1 having a rectangular shape in plan view is interposed through an expansion body in which the central portion swells elliptically. It becomes the structure which presses, exhibits the effect | action which extrudes the air of the center part which is hard to be exhausted, and can fully infiltrate electrolyte solution to the center part of the electrode group 1. FIG.

  The secondary battery RB2 of the second embodiment shown in FIG. 2 is an example in which a curved plate 14 is interposed between the expansion member 13 and the electrode group 1. In addition, a state is schematically shown in which the expansion member 13 expands and presses the central portion of the electrode group 1 through the curved plate 14 when evacuated. The curved plate 14 is preferably curved into a shape that presses a predetermined central portion of the electrode group 1. In particular, when the central portion is pressed evenly, a curved plate 14 that curves in a convex lens shape with a predetermined curvature may be used.

  The curved plate 14 may be a plate that is previously curved with a predetermined curvature, or may be a plate that is curved into a predetermined shape when pressed. The curved plate 14 may be a plate material made of a material having heat resistance and chemical resistance and not deteriorated by an electrolyte. For example, a hard resin plate made of polyethylene or polypropylene material can be used. A sheet metal plate on which an insulating film is formed can also be used.

  If it is said structure, it will press the predetermined area | region of the electrode group 1 by inflating the expansion | swelling member 13 at the time of a vacuum and curving the bending plate 14 through the bending plate which curves so that a predetermined range may be pressed. The air in the central portion of the electrode group 1 where it is difficult for air to escape can be sufficiently discharged, and the electrolyte can be sufficiently permeated to this portion.

  In the electrode group 1 in which several tens of layers of electrode plates and separators having a large area are stacked, air is likely to remain in a predetermined region in the central portion and is difficult to be discharged. For this purpose, it is only necessary to press a predetermined region where air easily remains, and it is preferable to interpose a curved plate that curves with a predetermined curvature. That is, by using the curved plate 14 that is curved with a predetermined curvature in accordance with the size and thickness of the electrode group 1 to be constructed, it is possible to effectively exhaust the air at the center of the electrode group 1.

  When only the central portion of the electrode group 1 needs to be strongly pressed, a plate whose portion corresponding to the central portion is greatly displaced can be used. For this purpose, an embodiment in which two plates are connected so as to be displaceable and this connecting portion is arranged so as to match the central portion of the electrode group 1 will be described with reference to FIGS. 3A to 3C.

  The secondary battery RB3 of the third embodiment shown in FIG. 3A includes a pressing plate 15 composed of two plates that are movably connected at the center of the expansion member 13 between the expansion member 13 and the electrode group 1. This is an example of intervention. Moreover, when the evacuation is performed, the state in which the expansion member 13 is expanded and the pressing plate 15 is bent at the connecting portion to press the central portion of the electrode group 1 is schematically shown.

  As shown in FIG. 3B, the pressing plate 15 is configured such that a flat plate-like first plate 15 a and a second plate 15 b are movably connected via a connecting portion 15 c. At this time, as a configuration of the connecting portion 15c, for example, a method of connecting two plates with a flexible resin, rubber material, stretchable tape, or the like is employed. Moreover, the structure which connected two plates in hinge shape may be sufficient, and it does not specifically limit.

  When the expansion member 13 expands during vacuum, the connecting portion 15c is pushed up as shown in FIG. 3C. In this way, by interposing the pressing plate 15 that connects at least two plates so as to be displaceable, the expansion member 13 swells like a convex lens and pushes up the connecting portion 15c at the time of vacuum, thereby pressing the central portion of the electrode group 1 In addition, the air inside the electrode group 1 can be exhausted. Therefore, even with this configuration, the electrolyte can be sufficiently permeated to the center of the electrode group.

  In addition, the pressing plate 15 having a configuration in which two flat plates are movably connected is flat at normal pressure, so that the dimension in the thickness direction can be suppressed, and excessive thickening of the secondary battery can be suppressed. Can do.

  The expansion member 13 that swells at the time of decompression and presses the electrode group 1 to push out the internal air may be in the form of a sealed bag, and is a resin material having heat resistance, chemical resistance, and insulation, such as polyethylene or polypropylene. A bag made of a material can be used.

  In addition, an experiment for confirming the bulge in a state where a predetermined load was applied was performed using the polyethylene expansion member 13. The result is shown in FIG.

  The expansion line L1 shown in the figure is in a state where a load (1 weight) corresponding to the electrode group 1 is applied. Indicates the amount of swelling when the pressure is reduced. Further, an expansion line L2 indicates a bulge amount in a state where a load (2 weight) twice as large as the 1 weight is applied.

  For example, in the expansion line L1, the degree of expansion is 0 at a vacuum level of 50 kPa, the amount of expansion is 10 mm when the degree of vacuum is 3 kPa, the amount of expansion is 15 mm when the degree of vacuum is 2 kPa, and the amount of expansion when the degree of vacuum is 1.5 kPa. Shows an experimental example in which becomes 20 mm.

  Further, in the expansion line L2 in which the load is doubled, the bulge amount is 0 when the degree of vacuum is 50 kPa, the bulge amount is 4 mm when the degree of vacuum is 3 kPa, the bulge amount is 6 mm when the degree of vacuum is 2 kPa, and the degree of vacuum is The result that the bulge amount was 9 mm at 1.5 kPa was obtained.

  As can be seen from this experiment, it is possible to press the central portion of the electrode group 1 with a predetermined pressing force via the expansion member 13 by evacuating to a predetermined degree of vacuum. Therefore, according to this embodiment which interposes the expansion member 13, the air of the center part of the electrode group which is hard to exhaust can be pushed out, and electrolyte solution can fully infiltrate to the center part of an electrode group.

  Therefore, as shown in FIG. 4, in the state where the expansion member 13 is not interposed, a permeation portion DA in which the electrolyte solution permeates and an unpermeation portion DB in which the electrolyte solution does not permeate exist in the electrode group 1 </ b> A. However, in the electrode group 1 with the expansion member 13 interposed, there is no non-permeated portion DB through which the electrolytic solution does not permeate, and the permeated portion DA is uniformly permeated with the electrolytic solution.

  Next, the actually produced lithium secondary battery will be described.

(Example)
[Preparation of positive electrode plate]
LiFePO4 (90 parts by weight) as a positive electrode active material, acetylene black (5 parts by weight) as a conductive material, and polyvinylidene fluoride (5 parts by weight) as a binder are mixed, and N- A slurry is prepared by appropriately adding methyl-2-pyrrolidone to disperse each material, and the slurry is uniformly applied on both sides of an aluminum foil (thickness 20 μm) as a positive electrode current collector and dried, and then rolled. It compressed with the press and cut | disconnected by predetermined size, and produced the plate-shaped positive electrode plate 2. As shown in FIG.

  Moreover, the size of the produced positive electrode plate was 140 mm × 250 mm, the thickness was 230 μm, and 32 positive electrode plates 2 were used.

[Preparation of negative electrode plate]
Natural graphite (90 parts by weight) as a negative electrode active material and polyvinylidene fluoride (10 parts by weight) as a binder are mixed, and N-methyl-2-pyrrolidone as a solvent is appropriately added to each material. A slurry is prepared by dispersing, and the slurry is uniformly applied on both sides of a copper foil (thickness 16 μm) as a negative electrode current collector and dried, then compressed by a roll press, and cut into a predetermined size. A plate-like negative electrode plate 3 was produced.

  Further, the size of the prepared negative electrode plate was 142 mm × 255 mm, the thickness was 146 μm, and 33 negative electrode plates 2 were used.

  In addition, as a separator, 64 polyethylene films having a size of 145 mm × 255 mm and a thickness of 25 μm were prepared.

[Preparation of non-aqueous electrolyte]
A non-aqueous electrolyte was prepared by dissolving 1 mol / L of LiPF ₆ in a mixed solution (solvent) in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70.

[Production of battery cans]
As materials for the outer case and the lid member constituting the battery can, nickel-plated iron plates were used, respectively. In addition, each of them has a thickness of 0.8 mm, a longitudinal direction × a lateral direction × a depth, and each internal size, 320 mm × 150 mm × 40 mm battery can size, and can be opened and closed with a rectangular lithium with an inlet plug A secondary battery was produced. Moreover, in order to make a lid member closely_contact | adhere to the upper surface of an electrode group, it was set as the structure which uses the plate-shaped lid member which fits in the inside of a can instead of flat form. When the dish-shaped lid member is used, it is possible to prevent the lid member from moving when welding the lid member, and the welding operation is facilitated. Moreover, it can respond easily to the change of the thickness of the electrode group to accommodate by changing the amount of depressions of a dish shape. Furthermore, a dish shape is preferable because the strength of the lid member and the strength of the battery can can be improved.

[Assembly of secondary battery]
A positive electrode plate and a negative electrode plate are alternately laminated via a separator. At that time, 32 positive electrode plates, 33 negative electrode plates, and 64 separators were laminated so that the negative electrode plate was located outside the positive electrode plate, and this laminate was used a polyethylene film having the same thickness of 25 μm as the separator. An electrode group (laminated body) was constructed as a structure to be wound.

  As described above, the size of the separator interposed between the positive and negative electrode plates is 145 mm × 255 mm, which is slightly larger than the positive electrode plate (140 × 250) and the negative electrode plate (142 × 255). Thereby, the active material layer formed on the positive electrode plate and the negative electrode plate can be reliably coated. Moreover, the connection piece of the current collection member (current collection terminal) was connected to the current collector exposed portion of the positive electrode and the current collector exposed portion of the negative electrode.

  The electrode group to which the current collector terminal was connected was housed in an outer case, the current collector terminal and the external terminal were connected, a lid member was attached and sealed, and the nonaqueous electrolyte was injected under reduced pressure from the liquid injection hole. After the liquid injection, the liquid injection holes were sealed, and 10 secondary batteries of each embodiment were produced.

  Example 1 is a secondary battery corresponding to the secondary battery RB1 of the first embodiment, in which an expansion member having a film thickness of 0.1 mm and a flat thickness of 0.5 mm is interposed. Further, the shape is an ellipse in a plan view when flat, and the short diameter is 70 mm and the long diameter is 120 mm with respect to the separator size of 145 mm × 255 mm.

  Example 2 is a secondary battery corresponding to the secondary battery RB2 of the second embodiment, in which a curved plate made of hard resin having a plate thickness of 1 mm is interposed in addition to the same expansion member. In addition, the curved plate has a shape curved in a convex lens shape with a predetermined curvature. Example 3 is a secondary battery corresponding to the secondary battery RB3 of the third embodiment, and is an example in which two hard resin press plates having a plate thickness of 1 mm are interposed in addition to the expansion member. The width of the curved plate and the pressing plate is preferably a width shorter than the width of the laminated surface in order to efficiently press the central portion of the laminated surface that comes into contact, and here the expansion member is 100 mm with respect to the separator width of 145 mm. It is about the width. The length is about 255 mm of the separator.

[Production of Comparative Example]
As the secondary battery of the comparative example, the electrode group (laminated body) used in the above-described examples was used in the same manner, and assembled into a battery can of the same size to produce a secondary battery without using an expansion member. Even in this case, the convex portion provided on the lid member is in close contact with the upper surface of the electrode group. That is, the step depth of the protrusion provided on the lid member is increased by the flat thickness of the expansion member.

  The charge capacity was confirmed using 10 each of Examples 1 to 3 and 10 comparative batteries. Moreover, the sample with the low charge capacity confirmed was decomposed | disassembled, and the electrolyte solution penetration | infiltration state inside an electrode group was confirmed. The experimental results are shown in Table 1.

  As shown in Table 1, in Examples 1 to 3, one sample with the lowest charge capacity was disassembled and the penetration of the electrolyte inside the electrode group was confirmed. All were normal. In addition, it can be understood that these charge capacities are all 93% or more of the design capacity.

  In Comparative Example 1 in which the expansion member 13 is not interposed, two samples having a low charge capacity were selected and disassembled for investigation. As a result, an unpermeated portion in which the electrolyte solution did not permeate was generated in the two electrode groups. I found out. This can also be understood as a matter of course because the charging capacity is only about 60% of the designed capacity.

  As described above, if the secondary battery includes the expansion member 13 according to this embodiment, even a large electrode group in which several tens of layers of a positive electrode plate, a negative electrode plate, and a separator are stacked, It is possible to reliably infiltrate the electrolyte into the inside. In addition, since the electrolyte solution penetration into the electrode group is improved, the time until the electrolyte solution penetrates does not increase, and the productivity of the electrolyte solution injection process does not decrease.

  Next, a method for manufacturing a secondary battery capable of reliably infiltrating the electrolyte into the electrode group will be further described.

  The method for manufacturing a secondary battery according to the present embodiment includes an electrode group in which a plurality of layers of a positive electrode plate and a negative electrode plate are stacked via a separator, an outer case that houses the electrode group, and a lid member that seals the outer case The electrolyte solution is injected into a battery can constituted by the outer case and the lid member from a liquid inlet provided in the outer case, and penetrates into the electrode group to be filled. This is a method for manufacturing a secondary battery. Further, at least one of the electrode group and the bottom surface of the outer case on which the electrode group is placed or between the electrode group and the lid member is provided with an expansion member that is flat during normal pressure and expands during vacuum. And the inside of the battery can is evacuated to inflate the expansion member by a predetermined amount, and then the electrolyte is injected.

  In this manufacturing method, since it swells in a vacuum, the electrode group can be pressed to push out air remaining inside. Therefore, after the air inside the electrode group is sufficiently exhausted, the electrolyte solution is injected to improve the penetration of the electrolyte solution into the electrode group and to ensure that the electrolyte solution penetrates into the electrode group. The manufacturing method of the secondary battery which can be made to become.

  As described above, the manufacturing method of the secondary battery according to the present embodiment includes the first step of manufacturing the sealed battery can by housing the electrode group in the outer case and attaching the lid member, and the inside of the battery can. A second step of expanding the expansion body by reducing the pressure and a third step of injecting an electrolyte into the battery can are provided. With such a configuration, since the second step of expanding the expansion body by decompressing the inside of the battery can is provided, it is possible to positively push out the internal air by pressing the central part of the electrode group during vacuum. The electrolyte solution can be sufficiently penetrated into the electrode group. That is, it is possible to reliably execute preparation for allowing the electrolytic solution to penetrate into the electrode group.

  Further, the inflating member is preferably a bag shape having a circular shape in plan view or an elliptical shape in plan view, and is preferably inflated into a convex lens shape in a vacuum. If it is this configuration, it becomes a configuration that swells like a convex lens during vacuum and presses the central part of the electrode group, exerts the action of pushing out the air of the central part that is difficult to be exhausted, exhausts all the air, and discharges the electrode group Electrolyte can be penetrated to the central part.

  Further, a manufacturing method in which a curved plate that curves in a convex lens shape with a predetermined curvature is interposed between the expansion member and the electrode group is preferable. With this configuration, the expansion member is inflated at the time of vacuum, and the curved plate is bent to press the predetermined region of the electrode group, so that the air at the center of the electrode group that is difficult to remove air can be sufficiently discharged.

  Moreover, the manufacturing method which interposed the press plate which consists of two plates displaceably connected by the center part of the expansion member between the expansion member and the electrode group may be sufficient. With this configuration, the connecting portion of the pressing plate composed of two plates is pushed up by the expansion member that swells in the shape of a convex lens at the time of vacuum, so that the central portion of the electrode group can be reliably pressed and exhausted, The electrolyte can be sufficiently penetrated into the electrode group.

  As described above, according to the present invention, at least one of the electrode group and the bottom surface of the outer case on which the electrode group is placed, or between the electrode group and the lid member, is under normal pressure. Because it is flat and has an expansion member that swells in a vacuum, the electrolyte solution can be reliably infiltrated into the electrode group even in the case of a large electrode group in which several tens of layers of a positive electrode plate, a negative electrode plate, and a separator are laminated. A secondary battery that can be manufactured and a method for manufacturing the same can be obtained.

  In addition, an electrode group is interposed between the expansion member and the electrode group with a curved plate curved in a convex lens shape with a predetermined curvature, or a pressing plate composed of two plates movably connected at the center. By pressing the predetermined area, the air in the center of the electrode group that is difficult to remove air can be sufficiently discharged.

  In addition, since air does not remain inside the electrode group, the design capacity can be satisfied even with a large capacity secondary battery using a large-sized electrode group, and a stable battery capacity can be maintained. A secondary battery and a method for manufacturing the same are possible.

  Therefore, the secondary battery according to the present invention can be suitably used for a large-capacity storage battery that is required to be increased in size and stabilized in performance.

DESCRIPTION OF SYMBOLS 1 Electrode group 2 Positive electrode plate 3 Negative electrode plate 4 Separator 10 Battery can 11 Exterior case 12 Lid member 13 Expansion member 14 Curved plate 15 Press plate RB, RB1-RB3 Secondary battery

Claims (10)

An electrode group in which a plurality of layers of a positive electrode plate and a negative electrode plate are laminated via a separator, an exterior case that accommodates the electrode group, and a lid member that seals the exterior case, and the exterior case and the lid member A secondary battery in which an electrolytic solution is injected into a configured battery can and penetrates and fills the inside of the electrode group,
An expansion member that is flat at normal pressure and expands at vacuum is provided between at least one of the bottom surface of the outer case and the electrode group in the stacking direction of the electrode group, or between the electrode group and the lid member. A secondary battery characterized by being interposed. The secondary battery according to claim 1, wherein the expansion member has a circular bag shape in plan view, and expands into a convex lens shape in a vacuum. 2. The secondary battery according to claim 1, wherein the expansion member is formed in a bag shape having an elliptical shape in plan view and expands into a convex lens shape in a vacuum. 4. The secondary battery according to claim 1, wherein a curved plate that is curved in a convex lens shape with a predetermined curvature is interposed between the expansion member and the electrode group. 5. 4. The pressing plate comprising two plates movably connected at the central portion of the expansion member is interposed between the expansion member and the electrode group. 5. Secondary battery described in 1. An electrode group in which a plurality of layers of a positive electrode plate and a negative electrode plate are laminated via a separator, an exterior case that accommodates the electrode group, and a lid member that seals the exterior case, and the exterior case and the lid member A method of manufacturing a secondary battery in which an electrolyte is injected into a battery can configured and penetrates and fills the inside of the electrode group,
An expansion member that is flat at normal pressure and expands at vacuum is provided between at least one of the bottom surface of the outer case and the electrode group in the stacking direction of the electrode group, or between the electrode group and the lid member. A method for producing a secondary battery, comprising interposing, inflating the expansion member by a predetermined amount by evacuating the inside of the battery can, and then injecting the electrolytic solution. A first step of producing a sealed battery can by housing the electrode group in the outer case and mounting the lid member; a second step of expanding the expansion body by decompressing the inside of the battery can; The method for producing a secondary battery according to claim 6, further comprising a third step of injecting an electrolytic solution into the battery can. The method of manufacturing a secondary battery according to claim 6, wherein the expansion member is formed into a bag shape having a circular shape in plan view or an elliptical shape in plan view, and expands into a convex lens shape in a vacuum. The method for manufacturing a secondary battery according to claim 6, wherein a curved plate that is curved in a convex lens shape with a predetermined curvature is interposed between the expansion member and the electrode group. 9. A pressing plate comprising two plates that are connected to each other so as to be displaceable at a central portion of the expansion member, is interposed between the expansion member and the electrode group. The manufacturing method of the secondary battery as described in any one of.

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