JP5820704B2 - Stacked battery - Google Patents

Description

  The present invention relates to a stacked battery in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween.

  In recent years, lithium-ion secondary batteries have attracted attention as secondary batteries with high energy density, and their research, development, and commercialization have been promoted rapidly. Lithium ion secondary batteries are widely used. Furthermore, large secondary batteries with higher capacity and higher output than conventional batteries are demanded as storage batteries for home use, industrial use, and in-vehicle use due to problems such as global warming, depleted fuel, and nuclear power plants.

  The electrode group put in the battery outer can and the outer bag is mainly divided into a wound type and a laminated type. The wound electrode group has a limited battery shape, and it is difficult to make a battery other than a cube, a rectangular parallelepiped, or a cylinder. In addition, the innermost circumference of the wound electrode group tends to cause cracks in the electrode, which causes a reduction in capacity and a short circuit.

  On the other hand, the stacked electrode group has a relatively high battery shape, it can be thickened because it does not wind, and there is no risk of winding misalignment caused by bending due to high-density electrodes. Energy density is possible.

  In a stacked electrode group, it is difficult to short-circuit and is excellent in productivity. For example, a positive electrode or a negative electrode is inserted alternately into a separator bag body in which two separators are stacked and thermally welded in a bag shape. Some have a configuration in which they are laminated (Patent Documents 1 and 2).

  In the case of a rectangular electrode group in plan view, a rectangular separator bag is used. For example, in order to create a rectangular separator bag by overlapping two separators, three of the four sides of the rectangular separator or two sides that are orthogonal to each other are thermally welded into a U-shape or L-shape. Welded. When a separator separator is folded at the center to form a rectangular separator bag, at least one of the two sides orthogonal to the bent portion or any of the two sides orthogonal to the bent portion The one side and the tip side extending parallel to the bent portion are heat-welded.

  The separator is generally made by stretching a resin base material. The conventional separator has a structure in which the heat shrinkage is larger in the stretching direction than in the transverse direction perpendicular to the stretching direction when heat-sealing. Therefore, when creating a separator bag body, in order to prevent distortion of the separator due to thermal shrinkage, the welding length in the direction along the stretching direction (MD direction) of the separator is shortened (welding area is small), The welding length in the direction along the lateral width direction (TD direction) was long (the welding area was large).

JP2003-017112A JP2008-130370

EVS24 HEV FCEV Symposium 2009 Asahi Kasei E-materials takada et

  In the case of power tools such as hybrid cars and power tools, and UPS high-power batteries for backup power supplies during power outages, the separator has a lower air permeability (the time it takes for the separator to pass through 100 cc of air, that is, the value) The lower the is, the easier it is for air to pass through and the easier it is for ions to pass through), and higher porosity is required. As a result, the separator has been extended further than before. In recent years, development of an inorganic filler-containing separator that can be further stretched by mixing an inorganic filler with a polyolefin resin to increase the strength has been in progress (Non-patent Document 1).

  However, as the stretching of the separator increases, the resin of the separator exhibits anisotropy remarkably, and the fiber lines of the resin are generated in parallel along the stretching direction (MD direction) by stretching. As described above, it was found that when a separator bag body was produced in the conventional manner using a highly stretched separator, welding was uneven and wrinkles were generated.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a stacked battery capable of improving productivity by suppressing generation of wrinkles due to welding of a separator. is there.

  A laminated battery of the present invention that solves the above problems is a laminated battery having an electrode group in which a separator formed by stretching in a uniaxial direction is thermally welded, and the separator extends along the extending direction of the separator. The extending direction welded portion has a widthwise welded portion extending along the widthwise direction orthogonal to the extending direction of the separator, and the extending length of the stretched direction welded portion is the widthwise welded portion. It is characterized in that it is longer than the extension length.

  According to the present invention, since the extension length of the stretch-direction welded portion is longer than the extension length of the width-direction weld portion, when a highly stretched separator is used, wrinkles are generated due to thermal welding. Thus, productivity of the stacked battery can be improved. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

The exploded perspective view of a lamination cell. The external appearance top view of a lamination cell. FIG. 3 is a cross-sectional view taken along line AA in FIG. 2. The exploded view of an electrode group. The schematic diagram of a comparative example. The schematic diagram of an Example. The schematic diagram of a separator.

  Next, the present embodiment will be described below with reference to the drawings. In the present embodiment, a lithium ion secondary battery will be described as a specific example of a stacked battery, but other batteries such as a capacitor can be applied and are not limited to the following configurations. . Furthermore, in the present embodiment, the case of a laminated cell will be described as an example of the cell shape of the laminated battery, but the present invention is not limited to this, and may be a square cell, for example.

  1 is an exploded perspective view of a laminate cell in the present embodiment, FIG. 2 is a plan view of the laminate cell, FIG. 3 is a cross-sectional view taken along line AA in FIG. 2, and FIG. FIG. 5 is a schematic diagram of a separator, FIG. 6 is a schematic diagram of a comparative example, and FIG. 7 is a schematic diagram of an example.

  The laminate cell 1 is a lithium ion secondary battery, and has a configuration in which a laminated electrode group 2 is sealed with laminate films 3 and 4. The laminate cell 1 is filled with an electrolyte solution (not shown). The electrode group 2 has a rectangular flat plate shape having a predetermined thickness. A positive terminal 12 and a negative terminal 22 protrude from one short side of the electrode group 2.

  The electrode group 2 has a configuration in which a plurality of positive electrodes 11 and negative electrodes 21 are alternately stacked with separators 31 therebetween. The number of the positive electrode 11 and the negative electrode 21 stacked may be any number, and any number may be used. The electrode group 2 was formed by laminating a plurality of sets each including a positive electrode 11 inserted into a separator bag body constituted by the separator 31 and a negative electrode 21 superimposed on the outer surface of one separator 31. It has a laminated structure.

  The separator 31 has a rectangular shape, and has a configuration formed in a bag shape by heat welding along two or three sides of the two separators 31 in order to suppress a short circuit and improve productivity. Yes. For example, a separator bag body may be configured by stacking two separators 31 and 31 on each other and welding them in an L shape along one long side and one short side. The separator bag body may be configured by welding in a U shape along the side and one short side. In addition, the separator 31 is good also as a structure formed by bend | folding in the center part of the separator 31, and heat-welding at least one part of the one side or two sides which mutually overlap, and was formed in the bag shape.

  The separator 31 is formed by stretching a strip-shaped resin base material in a uniaxial direction, and is more highly stretched than before. As shown in FIG. 5, the separator 31 has resin fiber stripes 32 parallel to the stretching direction (MD direction). The fiber streak 32 is considered to cause unevenness in welding and cause wrinkles. And it is considered that the larger the stretching, that is, the lower the air permeability and the higher the porosity, the higher the anisotropy, and the more likely wrinkles occur during heat welding.

The separator 31 has an air permeability of 10 (sec / 100 cc) to 400 (sec / 100 cc), preferably 10 (sec / 100 cc) to 200 (sec / 100 cc). Have a degree. The separator 31 has a porosity of 30% or more and 80% or less, and preferably has a porosity of 60% or more and 80% or less. When the air permeability is lower than 10 (sec / 100 cc) and when the porosity is higher than 80%, the separator is too sparse and the voltage drop is large, so that it cannot be used. The effect is particularly large when the air permeability is 200 (sec / 100 cc) or less, and the effect is particularly large when the porosity is between 60 and 80%. The air permeability is measured according to JIS P8117, and the porosity is measured according to the specific gravity (g / cm ³ ) of the separator material and the actual weight per separator volume (g / cm ³ ). ^It was calculated from the ratio with ³ ).

  Thus, using the separator 31 in which the fiber streak 32 is generated by high stretching, the welding length in the direction along the stretching direction (MD direction) of the separator 31 is shortened as usual (the welding area is small). If the welding length in the direction along the horizontal width direction (TD direction) of the separator 31 is increased (the welding area is increased), unevenness is generated in the welding, resulting in wrinkles.

  Therefore, in the present embodiment, the welding length in the direction along the stretching direction (MD direction) of the separator is increased (the welding area is large), and the welding length in the direction along the lateral width direction (TD direction) of the separator. Was made short (welding area was small).

  The separator 31 includes a stretching direction weld portion 31a extending along the stretching direction (MD direction) of the separator 31, and a width direction welding portion extending along a width direction (TD direction) orthogonal to the stretching direction of the separator 31. 31b, and the extending length of the extending direction weld portion 31a is longer than the extending length of the width direction welding portion 31b.

  Specifically, for example, as shown in FIG. 4, the separator 31 has a length in the Y direction that is longer than a length in the X direction, so that the long side extends in the extending direction and the length in the width direction is short. The extending direction of the separator 31 is the Y direction so that the sides extend, the extending direction welded portion 31a is formed along the Y direction, and the width direction welded portion 31b is formed along the X direction.

  Therefore, it is possible to increase the welding length of the stretching direction weld portion 31a in the stretching direction (MD direction) with a small thermal shrinkage, and shorten the welding length of the width direction welding portion 31b in the width direction with a large heat shrinkage, Generation | occurrence | production of a wrinkle by welding can be suppressed. In the configuration of the present embodiment, the separator 31 has a lower air permeability and a higher porosity, and the effect is greater.

  In addition, in FIG. 4, although the extending | stretching direction welding part 31a is provided along a pair of long sides, and the width direction welding part 31b is provided along one short side, the structure welded in the U shape is shown. It is good also as a structure which provided the extending | stretching direction weld part 31a along one long side, and provided the width direction weld part 31b along one short side, and welded it in the L-shape.

  Moreover, in the above-described example, the case where both the stretching direction welded portion 31a and the width direction welded portion 31b are provided has been described, but when the separator bag body can be configured by welding only the stretching direction with less thermal shrinkage, The width direction weld portion 31b can be omitted. For example, a single separator 31 may be folded and overlapped at the center in the stretching direction, and may be linearly welded along a side extending in a direction orthogonal to the folded portion to provide a stretching direction weld. According to such a configuration, since the widthwise welded portion 31b in the widthwise direction with large thermal shrinkage can be omitted, generation of wrinkles can be further suppressed.

  The present invention can also be applied to inorganic filler-containing separators and inorganic filler-coated separators. However, the inorganic filler-coated separator may not be heat-welded when the inorganic filler layer is thick. In that case, it is necessary to weld the part which does not have an inorganic filler layer. Therefore, it is good also as a structure which has an inorganic filler layer in the part (non-thermal welding part except the part welded) except the extending | stretching direction welding part 31a and the width direction welding part 31b among the surfaces of the separator 31.

These inorganic fillers _are those containing SiO 2, _Al 2 _{O 3,} montmorillonite, mica, _ZnO, and TiO 2, BaTiO _3, at least one such ZrO _2.

The positive electrode 11 has an aluminum foil as a positive electrode current collector foil. On both surfaces of the aluminum foil, lithium-containing transition metal double oxide LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was used as the positive electrode active material. In addition, various lithium transition metal composite oxides can be used for the positive electrode active material of the lithium ion secondary battery. For example, a part of the positive electrode active material such as lithium nickelate, lithium cobaltate, and lithium manganate, such as Ni, Co, and Mn, can be substituted with one or more transition metals. In addition to the positive electrode active material, a carbon material conductive material and a binder of polyvinylidene fluoride (hereinafter abbreviated as PVDF) were used as the positive electrode active material mixture. When the positive electrode active material mixture is applied to the aluminum foil, the viscosity is adjusted with a dispersion solvent such as N-methylpyrrolidone (hereinafter abbreviated as NMP). At this time, a positive electrode uncoated portion where the positive electrode active material mixture is not applied is formed on a part of the aluminum foil. That is, the aluminum foil is exposed in the positive electrode uncoated portion. The density of the positive electrode 11 is adjusted by a roll press after drying.

  On the other hand, the negative electrode 21 has a copper foil as a negative electrode current collector foil. Amorphous carbon was used as the negative electrode active material on both sides of the copper foil. In addition, a material capable of reversibly occluding and releasing lithium ions, such as carbon-based materials such as natural graphite and artificial graphite, oxide-based materials, and alloy-based materials can be used as the negative electrode active material. As the negative electrode active material mixture, acetylene black or graphite was used as a conductive material in addition to the negative electrode active material, and a PVDF binder was further used. When the negative electrode active material mixture is applied to the copper foil, the viscosity is adjusted with a dispersion solvent such as NMP. At this time, a negative electrode uncoated portion where the negative electrode active material mixture is not applied is formed on a part of the copper foil. That is, the copper foil is exposed in the negative electrode uncoated portion. The density of the negative electrode 21 is adjusted by a roll press after drying. The positive electrode uncoated portion and the negative electrode uncoated portion are bundled and ultrasonically welded to the positive electrode terminal 12 and the negative electrode terminal 22 that electrically connect the inside and outside of the battery. The welding method may be other welding methods such as resistance welding. The positive terminal 12 and the negative terminal 22 may be preliminarily coated with or attached to a sealing portion of the terminal in order to further seal the inside and outside of the battery.

  In the laminate cell 1, the edges of the laminate films 3 and 4 sandwiching the electrode group 2 are thermally welded and sealed, and the positive electrode terminal 12 and the negative electrode terminal 22 are passed through in an electrically insulated state. In order to provide a liquid injection port, the sealing was performed by heat-welding first except for one side and injecting the electrolytic solution, and then heat-welding and sealing the other side while applying vacuum. The number of weldings may be any number.

As the electrolytic solution, an electrolyte of 1M LiPF ₆ was used, which was dissolved in a solvent of EC: EMC = 1: 3 (vol%). Other electrolytes include, for example, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, γ-valerolactone, methyl acetate, ethyl acetate, methyl propionate, tetrahydrofuran, 2 -Methyltetrahydrofuran, 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 3-methyltetrahydrofuran, 1,2-dioxane, 1,3-dioxane, 1,4-dioxane, 1,3-dioxolane, 2 -Non-aqueous solvent selected from at least one selected from methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane and the like include, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (C ₂ F ₅ SO ₂ ) A known electrolyte used in a battery such as an organic electrolytic solution in which at least one lithium salt selected from ₂ or the like is dissolved, a solid electrolyte having a lithium ion conductivity, a gel electrolyte, or a molten salt can be used. .

<Example>
There are two types of separators 31 used in this example, separator A and separator B. The separator A has a three-layer structure in which a polyethylene layer is sandwiched between polypropylene layers, and has a configuration with a thickness of 20 μm, an air permeability of 350 sec / 100 cc, and a porosity of 40%. The separator B is an inorganic-containing separator in which an inorganic filler (silica) is contained in polyethylene, and has a thickness of 20 μm, an air permeability of 80 sec / 100 cc, and a porosity of 60%. Separator bags using separator 31 using separator A and separator 31 using separator B were produced.

  As a comparative example, for each of the separator A and the separator B, the long side is welded in parallel with the width direction (TD direction) of the separator bag, and the short side is heated in parallel with the extending direction (MD direction) of the separator 31. Welded.

  As an example, for each of the separator A and the separator B, the long side is welded in parallel with the extending direction (MD direction) of the separator 31 and the short side is heat welded in parallel with the width direction (TD direction) of the separator 31. I let you.

  The stretching direction (MD direction) of the separator A and the separator B has a larger thermal shrinkage rate than the width direction (TD direction). In addition, the separator A and the separator B have a feature that, when pierced and penetrated with a nail having a diameter of about several millimeters, the separator A and the separator B are easily torn in the extending direction (MD direction) and hardly torn in the width direction (TD direction).

  As a welding result of the separator A and the separator B, FIG. 6 shows a schematic diagram of a comparative example, and FIG. 7 shows a schematic diagram of this example.

  As shown in FIG. 6, when the long sides of the separator 31 are welded in parallel along the lateral width direction (TD direction) and the short sides are heat welded in parallel along the stretching direction (MD direction), welding can be performed successfully. In both separator A and separator B, wrinkles were generated, and in the worse case, the positive electrode 11 did not enter the separator bag and became defective. In particular, with respect to the separator B, a result that wrinkles are large was obtained.

  On the other hand, as shown in FIG. 7, the long side of the separator 31 is welded along the drawing direction (MD direction) in parallel, and the short side is heat-welded in parallel along the width direction (TD direction). The separator 11 and the separator B were not wrinkled, and the positive electrode 11 could be easily sandwiched in the separator bag.

  The laminate cell 1 described above was formed into a bag shape by thermally welding two or three sides of the two separators 31 or by bending the center of the separator 31 and thermally welding the other one or two sides. The rectangular separator bag body has a structure in which the long side is welded parallel to the MD direction of the separator 31 and the short side is heat welded parallel to the TD direction. Therefore, generation | occurrence | production of the wrinkle resulting from heat welding can be suppressed, the defect of the separator 31 can be suppressed, and the productivity of a laminated battery can be improved. Particularly, a large stacked battery having a high output and a high capacity is very effective because the area of the separator is large.

DESCRIPTION OF SYMBOLS 1 Laminate cell 2 Electrode group 3, 4 Laminate film 11 Positive electrode 12 Positive electrode terminal
21 Negative electrode 22 Negative electrode terminal
31 Separator
31a Stretch direction welded portion 31b Width direction welded portion 32 Fiber streak

Claims (5)

A laminated battery having an electrode group in which a separator formed by stretching in a uniaxial direction is thermally welded,
The separator has a stretch direction welded portion that is folded at the center portion in the stretch direction and overlapped with each other and extends in a direction perpendicular to the bend portion. The stacked battery according to claim 1, wherein the separator has an inorganic filler layer in a non-thermally welded portion of the surface of the separator excluding a thermally welded portion. _3. The stacked battery according to claim 2, wherein the inorganic filler layer includes at least one kind such as SiO ₂ , Al ₂ O ₃ , montmorillonite, mica, ZnO, TiO ₂ , BaTiO ₃ , and ZrO ₂ . 4. The stacked battery according to claim 1 , wherein the separator has an air permeability of 10 (sec / 100 cc) or more and 400 (sec / 100 cc) or less. 5. The stacked battery according to any one of claims 1 to 4 , wherein the separator has a porosity of 30% or more and 80% or less.

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