Sheet-like lithium primary battery

Abstract

To provide a sheet-like lithium primary battery having an excellent storage characteristic, and a manufacturing method for the same.SOLUTION: A sheet-like lithium primary battery of the present invention, is formed by housing a negative electrode, a positive electrode, a separator, and a non-aqueous electrolyte that contain a lithium or a lithium alloy in an outer casing constructed by a laminate film having a heat deposition resin layer. A volume of a gas increased in a battery when it is stored for 30 days under an atmosphere of 70°C and 90% of a relative humidity, and is 20% of a content volume in the battery before the storage. A manufacturing method of the sheet-like lithium primary battery of the present invention, includes: a temporal sealing step of sealing a power generation element in an outer housing; a preparation discharge step of discharging one part of a capacitance provided in a temporal assembly; a storage step of holding the temporal assembly in a heating state; a degasification step of opening a part of the outer casing after that, and removing a gas in an inner part; and a main sealing step of sealing the outer casing after the degasification step.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a sheet-shaped lithium primary battery having excellent storage characteristics and a method for producing the same. [Background technology]

[0002] Lithium primary batteries used as power sources for various devices are generally of a type in which a wound electrode body, in which a positive electrode and a negative electrode are stacked with a separator between them and wound in a spiral shape, is housed in a cylindrical metal container, or of a flat type known as a coin shape or button shape, in which a laminated electrode body, in which a positive electrode and a negative electrode are stacked with a separator between them, is housed in a flat metal container.

[0003] However, in recent years, there has been a need for applications that are difficult to apply the above-mentioned metal containers, such as thin electronic devices, and in order to meet such demands, sheet-type lithium primary batteries using laminate film exterior bodies have also been developed. In the case of sheet-type batteries using laminate film exterior bodies, in addition to the fact that they can be easily made into a thin shape, unlike metal containers, the exterior body is flexible and the shape can be changed to a certain extent as needed, so there is an advantage that the range of applicable devices is wider than that of batteries using metal containers as described above.

[0004] In addition, while sheet-type lithium primary batteries can have a larger capacity than coin-type lithium primary batteries, the amount of active material in the negative and positive electrodes is greater and the area of ​​the electrodes is also larger, making it easier for gas to be generated due to a reaction between the moisture in the battery and the electrodes. Furthermore, since the exterior body made of a laminate film is easily deformed, battery swelling can easily become a problem when stored at high temperatures, for example.

[0005] Technological developments are also being conducted to solve the problem of gas generation in such sheet-type batteries. For example, Patent Document 1 proposes a method in which a power generating element is housed in a laminate film exterior body, sealed, and then subjected to an aging treatment, and the exterior body is opened to vent the gas generated during the aging treatment, and then resealed to assemble the battery. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2009-187711 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, according to the study by the present inventors, it was found that even in the method of Patent Document 1, deformation of the exterior body due to gas generation during storage of the battery is observed. Therefore, in terms of improving the storage stability of the sheet-shaped lithium primary battery, there is still room for improvement in the technology described in Patent Document 1.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sheet-shaped lithium primary battery having excellent storage characteristics and a method for producing the same. [Means for solving the problem]

[0009] The sheet-form lithium primary battery of the present invention contains a negative electrode containing lithium or a lithium alloy, a positive electrode, a separator, and a nonaqueous electrolyte solution in an exterior body made of a laminate film having a heat-sealable resin layer, and is characterized in that the volume of gas increased within the battery when stored for 30 days in an atmosphere of 70°C and a relative humidity of 90% is 20% or less of the internal volume of the battery before storage.

[0010] In addition, the manufacturing method of the sheet-type lithium primary battery of the present invention is a method for manufacturing a sheet-type lithium primary battery comprising an outer casing made of a laminate film having a heat-sealable resin layer and a power generating element consisting of a negative electrode containing lithium or a lithium alloy, a positive electrode, a separator, and a non-aqueous electrolyte, and is characterized in having a temporary sealing process for enclosing the power generating element in the outer casing and preparing a temporary assembly, a preliminary discharge process for discharging a portion of the capacity of the temporary assembly, a storage process for maintaining the temporary assembly in a heated state, a degassing process for opening a portion of the outer casing after the preliminary discharge process and the storage process and removing internal gas, and a main sealing process for sealing the outer casing after the degassing process. Effect of the Invention

[0011] According to the present invention, it is possible to provide a sheet-shaped lithium primary battery having excellent storage characteristics and a method for producing the same. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic diagram of an example of an electrode body for a sheet-shaped lithium primary battery of the present invention. [Diagram 2] FIG. 2 is a plan view showing a schematic diagram of an example of a positive electrode of the sheet-shaped lithium primary battery of the present invention. [Diagram 3] FIG. 2 is a plan view illustrating another example of a positive electrode of the sheet-shaped lithium primary battery of the present invention. [Figure 4] FIG. 1 is a plan view illustrating a sheet-shaped lithium primary battery according to an embodiment of the present invention. [Diagram 5] 5 is a cross-sectional view taken along line II in FIG. 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The sheet-form lithium primary battery of the present invention contains a negative electrode containing lithium or a lithium alloy, a positive electrode, a separator, and a nonaqueous electrolyte solution in an exterior body made of a laminate film having a heat-sealable resin layer, and when stored for 30 days in an atmosphere of 70°C and a relative humidity of 90%, the volume of gas increased within the battery is 20% or less of the internal volume of the battery before storage.

[0014] That is, in the sheet-shaped lithium primary battery of the present invention, internal gas generation during storage is highly suppressed, and even if stored under relatively severe conditions, the degree of deformation of the exterior body caused by internal gas generation is small. Thus, the sheet-shaped lithium primary battery of the present invention has excellent storage characteristics.

[0015] Furthermore, by the manufacturing method of the present invention described below, a sheet-shaped lithium primary battery having excellent storage characteristics can be manufactured. For example, the volume of gas that increases in the battery when stored for 30 days in an atmosphere of 70°C and 90% relative humidity can be suppressed to 20% or less, preferably 10% or less, of the internal volume of the battery before storage.

[0016] (1) Temporary sealing process In the temporary sealing step, power generating elements such as the negative electrode, positive electrode, separator, and non-aqueous electrolyte are enclosed in an exterior body made of a laminate film having a heat-welding resin layer to prepare a temporary assembly.

[0017] The exterior body is sealed by heat welding of the heat-sealable resin associated with the heat-sealable resin layer of the laminate film constituting the exterior body, but in the temporary assembly, it is preferable to make the exterior body larger than the size required for the sheet-shaped lithium primary battery. As described below, the temporary assembly is partially opened in a process described below, but if the exterior body is made larger, a sheet-shaped lithium primary battery of the desired size can be manufactured even if the temporary assembly is opened by cutting a part of the exterior body.

[0018] (2) Pre-discharge process In the preliminary discharge step, a part of the capacity of the temporary assembly obtained in the temporary sealing step is discharged. This preliminary discharge reduces the voltage of the temporary assembly to a level at which the moisture present inside the battery is not electrolyzed, thereby suppressing gas generation due to the decomposition of moisture in the sheet-shaped lithium primary battery.

[0019] The amount of electricity pre-discharged in the pre-discharge step is preferably 1 to 10% of the capacity of the temporary assembly (i.e., the design capacity of the sheet-shaped lithium primary battery), which allows the voltage of the temporary assembly to be reduced to a level at which the moisture present therein is not electrolyzed.

[0020] In the preliminary discharge, the entire amount of electricity to be discharged may be discharged in one step, or may be discharged in multiple steps (two, three, four, etc.).

[0021] (3) Storage process In the storage process, the temporary assembly is stored in a heated state. This storage stabilizes the voltage of the temporary assembly (sheet-shaped lithium primary battery), and also gasifies the moisture inside the battery by reacting with the active material, etc., thereby minimizing the amount of moisture remaining in the battery.

[0022] The storage conditions of the temporary assembly in the storage step may be, for example, 40 to 80° C. and 6 to 96 hours.

[0023] The order of the preliminary discharge step and the storage step may be reversed, with the storage step being carried out first, but carrying out the preliminary discharge step first can provide a greater effect.

[0024] (4) Gas removal process In the degassing step, a part of the exterior body of the temporary assembly that has been through the preliminary discharge step and the storage step is opened to remove the internal gas.

[0025] In this case, as described above, if the size of the exterior body of the temporary assembly is made larger than the size required for a sheet-type lithium primary battery, even if the assembly is opened by cutting a portion of the welded portion of the exterior body, a sheet-type lithium primary battery of the specified size can be obtained thereafter.

[0026] There are no particular limitations on the method of degassing, but since simply opening the outer packaging may not be enough to fully remove the internal gas, it is preferable to employ a method of forcibly degassing the packaging, such as by reducing the pressure inside the packaging.

[0027] (5) Main sealing process In the main sealing step, the opened portion of the temporary assembly that has been subjected to the degassing step is resealed to obtain a sheet-shaped lithium primary battery.

[0028] According to the manufacturing method of the present invention, by going through the preliminary discharge step, storage step, and degassing step, the moisture in the exterior body is gasified and removed, and not only the amount of moisture remaining in the battery is significantly reduced (storage step and degassing step), but also the remaining moisture can be made difficult to gasify by electrolysis (predischarge step). Therefore, according to the manufacturing method of the present invention, it is possible to obtain a sheet-shaped lithium primary battery of the present invention in which the volume of gas increased in the battery when stored for 30 days in an atmosphere of 70°C and relative humidity of 90% satisfies the above value, and deformation of the exterior body due to the internal gas during storage is highly suppressed.

[0029] In the sheet-shaped lithium primary battery thus produced, for example, the positive electrode active material contains lithium equivalent to the amount of electricity pre-discharged, ie, 1 to 10% of the total discharge capacity of the battery.

[0030] The fact that the positive electrode active material contained in the battery already contains lithium equivalent to 1 to 10% of the total discharge capacity of the battery can be determined as follows.

[0031] The amount of lithium in the positive electrode active material can be measured by an analytical method such as ICP (inductively coupled plasma) emission spectrometry.

[0032] The total discharge capacity of the battery is calculated by determining the discharge capacity of the battery by the method employed in the examples described later, and adding thereto a capacity estimated from the amount of lithium in the positive electrode active material (corresponding to the capacity consumed in the preliminary discharge carried out in the preliminary discharge step in the production method of the present invention).

[0033] For the positive electrode of a sheet-shaped lithium primary battery, for example, a structure in which a positive electrode mixture layer composed of a positive electrode mixture containing a positive electrode active material, a conductive assistant, a binder, etc. is formed on one or both sides of a current collector can be used.

[0034] Examples of the positive electrode active material include manganese dioxide, vanadium oxide, niobium oxide, titanium oxide, sulfides such as iron disulfide, graphite fluoride, etc. Among these, manganese dioxide is preferred because of its high capacity and high voltage.

[0035] Examples of the conductive assistant for the positive electrode include flake graphite, acetylene black, ketjen black, and carbon black. Only one of these may be used, or two or more of them may be used in combination.

[0036] Furthermore, examples of the binder for the positive electrode include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polymers of propylene hexafluoride. Only one of these may be used, or two or more of them may be used in combination.

[0037] The positive electrode can be manufactured, for example, as follows. First, a conductive auxiliary and a binder are mixed with a positive electrode active material, and water or the like is added as necessary to form a positive electrode mixture (slurry). This is rolled using a roll or the like to form a preliminary sheet, which is then dried and pulverized and formed into a sheet shape again by roll rolling or the like to form a positive electrode mixture sheet for constituting the positive electrode mixture layer.

[0038] Such a positive electrode mixture sheet is joined to a positive electrode current collector by pressing or the like to produce a positive electrode.

[0039] Examples of the positive electrode current collector include those made of stainless steel such as SUS316, SUS430, and SUS444, or aluminum, and examples of the form of the positive electrode current collector include plain woven wire mesh, expanded metal, lath mesh, punched metal, and foil (plate).

[0040] The thickness of the positive electrode current collector is preferably 0.05 to 0.15 mm.

[0041] A paste-like conductive material can be applied to the surface of the positive electrode current collector. When a net-like positive electrode current collector having a three-dimensional structure is used, the current collecting effect is significantly improved by applying the conductive material, as in the case of using a material essentially consisting of a flat plate such as a metal foil or punched metal. This is presumably due to the effective use of not only the path in which the metal part of the net-like current collector directly contacts the positive electrode mixture layer, but also the path via the conductive material filled in the mesh.

[0042] As the conductive material, for example, silver paste or carbon paste can be used. In particular, carbon paste is less expensive than silver paste and has a contact effect substantially equal to that of silver paste, so it is suitable for reducing the manufacturing cost of sheet-shaped lithium primary batteries. As the binder for the conductive material, it is preferable to use a heat-resistant material such as water glass or an imide-based binder. This is because the moisture in the positive electrode mixture layer is removed by drying at a high temperature exceeding 200°C.

[0043] From the viewpoint of increasing the capacity and energy density of the battery, the thickness of the positive electrode mixture layer is preferably 0.3 mm or more, more preferably 0.4 mm or more, and even more preferably 0.6 mm or more. However, if the positive electrode mixture layer is too thick, the internal resistance of the positive electrode mixture layer increases, and the capacity of the positive electrode may not be fully utilized. In addition, the flexibility of the positive electrode is likely to decrease, and cracks and chips are likely to occur in the positive electrode mixture layer. Therefore, from the viewpoint of improving the characteristics of the battery and ensuring the flexibility, the thickness of the positive electrode mixture layer is preferably 1 mm or less, and more preferably 0.9 mm or less.

[0044] In addition, a sheet-type battery having an exterior body made of a laminate film is relatively flexible, unlike a battery having an exterior body such as a metal can, and may be deformed slightly as necessary for installation in an applicable device. However, if the positive electrode (positive electrode mixture layer) is made thicker to increase capacity, cracks and chips are likely to occur in the positive electrode mixture layer when the exterior body is deformed.

[0045] Therefore, when the positive electrode mixture layer is thickened as described above, it is preferable that a part of the positive electrode mixture layer (positive electrode mixture sheet) is joined to the positive electrode current collector to be integrated, and the other part is a non-jointed part that is not joined to the positive electrode current collector. In this case, even if the positive electrode is bent slightly, the positive electrode mixture layer may be displaced from the positive electrode current collector at the non-jointed part, so that it is possible to suppress excessive stress from being applied to the positive electrode mixture layer and to suppress cracking or chipping of the positive electrode mixture layer. This makes it possible to obtain a sheet-shaped lithium primary battery that can effectively suppress capacity reduction even when applied to a device that requires some deformation of the battery when installed.

[0046] FIG. 1 shows a cross-sectional view that typically illustrates an electrode assembly (an electrode assembly having a positive electrode, a negative electrode, and a separator) of a sheet-form lithium primary battery of the present invention.

[0047] The electrode body 100 shown in FIG. 1 is a laminated electrode body formed by stacking a positive electrode 10 and a negative electrode 20 with a separator 30 interposed therebetween. The positive electrode 10 is configured by arranging positive electrode mixture layers (positive electrode mixture sheets) 11, 11 on both sides of a positive electrode collector 12. The negative electrode 20 is configured by arranging a negative electrode active material layer 21 on one side (the side on the separator 30 side) of a negative electrode collector 22. Furthermore, in the electrode body 100, the separator 30 is arranged on both sides of the positive electrode 10 by folding back a single sheet-like piece and sandwiching the positive electrode 10, and the negative electrode 20 is arranged so as to face the positive electrode 10 on the outside of the separator 30 by folding back a single sheet-like piece and sandwiching the separator 30 arranged on the outside of the positive electrode 10.

[0048] In the positive electrode 10, the positive electrode mixture layers (positive electrode mixture sheets) 11, 11 are joined at their portions (positive electrode mixture layer joints 11a) to the adjacent positive electrode current collector 12, and only the positive electrode mixture layer joints are integrated. In the electrode body 100 in Fig. 1, the positive electrode mixture layer joints 11a are the contact portions between the positive electrode mixture layers 11, 11 and the positive electrode current collector 12 at the shaded areas to the left of the dotted line in the figure.

[0049] When the positive electrode has a positive electrode mixture layer (positive electrode mixture sheet) on both sides of the positive electrode current collector, it is preferable that a portion of each of the positive electrode mixture layers is bonded to the positive electrode current collector and another portion is not bonded, as shown in FIG.

[0050] The location where the positive electrode mixture layer is joined to the positive electrode current collector is not particularly limited as long as flexibility can be imparted to the positive electrode. As shown in FIG. 1, the joint may be provided on the peripheral edge of the positive electrode mixture layer, or may be provided at a location other than the end of the positive electrode mixture layer (such as the center).

[0051] In order to reliably fix the positive electrode mixture layer to the positive electrode current collector, the area of ​​the joint between the positive electrode mixture layer and the positive electrode current collector is preferably 0.5% or more, and more preferably 1% or more, of the area of ​​the positive electrode current collector (however, the area excluding the tab portion described below).

[0052] On the other hand, in order to increase the proportion of the non-jointed portion of the positive electrode mixture layer that is not joined to the positive electrode current collector and thereby increase the flexibility of the positive electrode, the area of ​​the joint portion of the positive electrode mixture layer with the positive electrode current collector is preferably 30% or less, and more preferably 10% or less, of the area of ​​the positive electrode current collector.

[0053] If the positive electrode mixture layer (positive electrode mixture sheet) is provided with only a portion of the joint with the adjacent positive electrode current collector, the positive electrode mixture layer and the positive electrode current collector may come apart during battery manufacture or inside the battery. In such a case, the portion of the electrode body where the non-jointed portion of the positive electrode is located may be fixed using a clip, strap, ring, or the like to an extent that does not impair the positional shift caused by deformation of the battery at the non-jointed portion of the positive electrode.

[0054] Fig. 2 shows a plan view that shows a schematic example of a positive electrode of the sheet-shaped lithium primary battery of the present invention. In Fig. 2, the dashed line indicates the position of a portion of the positive electrode current collector 12 that is disposed on the rear side of the positive electrode mixture layer (positive electrode mixture sheet) 11 in the figure (the same applies to Fig. 3 described later). In the positive electrode 10 shown in Fig. 2, the end of the positive electrode current collector 12 is disposed on the inner side of the end of the positive electrode mixture layer in plan view, except for the tab portion 12 described later.

[0055] In a sheet-shaped lithium primary battery, it is preferable to arrange at least a part of the end of the positive electrode current collector inside the end of the positive electrode mixture layer (positive electrode mixture sheet) in a plan view. In this case, even if a positional deviation occurs between the positive electrode mixture layer and the positive electrode current collector due to deformation of the battery, the part of the end of the positive electrode current collector arranged inside the end of the positive electrode mixture layer is unlikely to be exposed to the surface, and contact between the end of the positive electrode current collector and the separator is suppressed by the positive electrode mixture layer, so that it is possible to suppress the occurrence of a short circuit caused by the separator being scratched by the positive electrode current collector.

[0056] It should be noted that it is difficult to remove burrs from stainless steel mesh, particularly from the edges, and when such a mesh is used as a positive electrode current collector, the separator is likely to be scratched if misalignment occurs with the positive electrode mixture layer. However, by positioning at least a part of the edge of the positive electrode current collector more inward than the edge of the positive electrode mixture layer (positive electrode mixture sheet) in a plan view, the occurrence of short circuits due to scratches on the separator can be effectively suppressed even in the case of using such a positive electrode current collector.

[0057] When the positive electrode has a positive electrode mixture layer (positive electrode mixture sheet) on both sides of the positive electrode current collector, it is preferable that at least a part of the end of the positive electrode current collector is disposed inside the ends of both positive electrode mixture layers (positive electrode mixture sheets) in a plan view.

[0058] If at least a portion of the end of the positive electrode current collector is disposed inward in plan view from the end of the positive electrode mixture layer, the effect of suppressing a short circuit in the battery can be obtained; however, for example, as shown in FIG. 2, when the positive electrode current collector 12 has a rectangular (including a rectangle and a square; the same applies hereinafter in this specification) main body portion 12a and a tab portion 12b, and the positive electrode mixture layer 11 is rectangular, it is preferable to dispose the end of the main body portion of the positive electrode current collector in plan view more inward than the end of the positive electrode mixture layer 11 (the positive electrode mixture layer 11 disposed on the front side of the positive electrode current collector 12 in FIG. 2, and the positive electrode mixture layer disposed on the rear side of the positive electrode current collector 12 in FIG. 2) in at least one peripheral portion in the longitudinal direction of the positive electrode mixture layer (in the case of a square, a direction parallel to one of the sides).

[0059] When the battery is bent in the longitudinal direction of the positive electrode mixture layer, the positional deviation between the positive electrode mixture layer and the positive electrode current collector becomes larger than when the battery is bent in the direction perpendicular to the longitudinal direction, and a short circuit is more likely to occur. In particular, when one of the longitudinal peripheral portions of the positive electrode mixture layer is joined to the peripheral portion of the main body of the positive electrode current collector to form a positive electrode mixture layer joint 11a (in FIG. 2, the joint 11a with the positive electrode current collector 11 is formed on the surface of the positive electrode mixture layer 11 at the back side in the figure (the shaded portion in FIG. 2)), no positional deviation occurs between the positive electrode mixture layer and the positive electrode current collector at that portion, but a large positional deviation occurs at the other longitudinal peripheral portion of the positive electrode mixture layer. For this reason, it is more preferable to arrange the end of the main body of the positive electrode current collector on the side to which the positive electrode mixture layer is not joined inside the two positive electrode mixture layers in a plan view.

[0060] Furthermore, in order to further enhance the short-circuit prevention effect, it is particularly preferable that, in a portion of the positive electrode current collector to which the positive electrode mixture layer is not joined, the entire end of the main body portion is positioned more inward than the end of the positive electrode mixture layer in a planar view.

[0061] In this specification, the term "rectangle" representing the shape of the positive electrode mixture layer or the positive electrode current collector also includes shapes in which at least one of the four corners is cut out and shapes in which each side representing the end is gently curved.

[0062] FIG. 3 shows a plan view that shows a schematic representation of another example of a positive electrode for a sheet-shaped lithium primary battery. In the positive electrode 10 shown in FIG. 3, the main body 12a of the positive electrode collector 12 is substantially circular, and the end of the positive electrode collector 12, excluding the tab portion 12b protruding from the main body 12a, is disposed inside the end of the positive electrode mixture layer (positive electrode mixture sheet) (the positive electrode mixture layer 11 disposed on the front side of the positive electrode collector 12 in the figure shown in FIG. 3, and the positive electrode mixture layer disposed on the back side of the positive electrode collector 12 in the figure not shown). Even when the sheet-shaped battery of the present invention has a positive electrode in the form shown in FIG. 3, it is possible to effectively suppress the damage of the separator caused by the end of the positive electrode collector when a positional deviation occurs between the positive electrode collector and the positive electrode mixture layer.

[0063] In this specification, the term "circular" representing the shape of the positive electrode mixture layer or the positive electrode current collector includes positive electrode current collector 12 shown in FIG. 3 in which a part of the main body deviates from the circumference, and this is expressed as being approximately circular.

[0064] In the positive electrode, in a portion where the end of the positive electrode collector is disposed inside the end of the positive electrode mixture layer, the distance between the end of the positive electrode collector and the end of the positive electrode mixture layer in a plan view is preferably 1 mm or more, more preferably 2 mm or more, from the viewpoint of better suppressing the occurrence of short circuit of the battery due to scratches on the separator. However, if the distance between the end of the positive electrode collector and the end of the positive electrode mixture layer becomes large, it becomes difficult to collect current at the peripheral portion of the positive electrode mixture layer. Therefore, in a portion where the end of the positive electrode collector is disposed inside the end of the positive electrode mixture layer, the distance between the end of the positive electrode collector and the end of the positive electrode mixture layer in a plan view is preferably 5 mm or less, more preferably 4 mm or less.

[0065] Regarding the composition of each component in the positive electrode mixture layer, the amount of the positive electrode active material is preferably 80 to 90 mass %, the content of the conductive assistant is preferably 1.5 to 10 mass %, and the content of the binder is preferably 0.3 to 10 mass %.

[0066] From the viewpoint of flexibility, the thickness of the entire positive electrode is preferably 2.5 mm or less, and more preferably 2.0 mm or less.

[0067] The negative electrode of the sheet-form lithium primary battery contains lithium or a lithium alloy as a negative electrode active material, and for example, a structure in which a negative electrode active material layer containing the negative electrode active material is formed on one or both sides of a current collector can be used.

[0068] The negative electrode active material layer of the sheet-shaped lithium primary battery can be composed of, for example, a lithium sheet (lithium metal foil or lithium alloy foil). When the negative electrode active material layer is composed of a lithium alloy foil, the lithium alloy can be lithium-aluminum or the like. In particular, it is preferable to use a laminate made by bonding a lithium metal foil and a thin aluminum foil together for the negative electrode active material layer, and to place the thin aluminum foil side at least on the positive electrode mixture sheet side. The laminate of the lithium metal foil and the aluminum foil produces a lithium-aluminum alloy at the interface by contacting with a non-aqueous electrolyte described later in the battery. Therefore, when the laminate of the lithium metal foil and the thin aluminum foil is used, a lithium-aluminum alloy is produced on the surface of the lithium sheet constituting the negative electrode active material layer in the battery, but at this time, the lithium-aluminum alloy is pulverized, so that the specific surface area of ​​the alloy-containing surface of the lithium sheet is increased. Therefore, by making this alloy-containing surface the surface facing the positive electrode mixture layer, the battery can be discharged more efficiently.

[0069] The lithium sheet constituting the negative electrode active material layer preferably has a thickness of 0.1 to 1 mm. When the laminate of the lithium metal foil and the thin aluminum foil is used, the lithium metal foil preferably has a thickness of 0.1 to 1 mm, and the thin aluminum foil preferably has a thickness of 0.005 to 0.05 mm.

[0070] The negative electrode current collector can be made of foil such as copper, nickel, iron, or stainless steel. Since the internal volume of the battery container (external can) is reduced by the thickness of the negative electrode current collector, it is preferable that the thickness of the negative electrode current collector is as small as possible, and specifically, for example, it is recommended that the thickness is 0.1 mm or less. That is, if the negative electrode current collector is too thick, the amount of lithium sheet constituting the negative electrode active material layer must be reduced, and there is a risk that the effect of improving the battery capacity by making the positive electrode thick as described above will be reduced. In addition, if the negative electrode current collector is too thin, it will be easily torn, so the thickness of the negative electrode current collector is preferably 0.005 mm or more. In addition, the width of the negative electrode current collector is preferably the same as or wider than the width of the lithium sheet constituting the negative electrode active material layer, and the area of ​​the negative electrode current collector is preferably 100 to 130% of the area of ​​the lithium sheet. By setting the area of ​​the negative electrode current collector as described above, the width of the negative electrode current collector is the same as or wider than the width of the lithium sheet, and the length is long, so that it is possible to prevent the lithium sheet from being cut along the periphery of the negative electrode current collector, thereby preventing electrical connection from being cut.

[0071] In the sheet-shaped lithium primary battery, the separator interposed between the positive electrode and the negative electrode can be a separator used in non-aqueous primary batteries such as conventional lithium primary batteries, i.e., a separator made of a microporous resin film or a separator made of a resin nonwoven fabric. Examples of the material include polyolefins such as polyethylene (PE), polypropylene (PP), and polymethylpentene, as well as fluororesins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymers (PFA) for heat resistance, polyphenylene sulfide (PPS), polyether ether ketone (PEEK), and polybutylene terephthalate (PBT). In addition, by using a separator with a multilayer structure formed by laminating a plurality of microporous films and nonwoven fabrics of the above materials, or laminating a plurality of microporous films or nonwoven fabrics, the reliability when used in a high-temperature environment can be improved.

[0072] The thickness of the separator is preferably, for example, 10 to 500 μm. The porosity of the separator is preferably 20% or more, more preferably 30% or more, and preferably 90% or less, more preferably 70% or less. The porosity of the separator referred to here is a value obtained by cutting out a sample of a certain area, measuring its mass and thickness, and calculating from these measured values.

[0073] In the case of an electrode body in which a negative electrode is disposed on both sides of a positive electrode via a separator, two separators may be used and each may be disposed on the surface of the positive electrode facing the negative electrode, or one separator may be folded back and disposed so as to sandwich the positive electrode, as shown in FIG. 1. In addition, two negative electrodes may also be used and each may be disposed so as to face the positive electrode with a separator sandwiched therebetween, or one negative electrode may be folded back and disposed so as to sandwich the separator disposed on the outside of the positive electrode, as shown in FIG. 1. In this way, the productivity of the battery can be improved.

[0074] For the non-aqueous electrolyte of the sheet-shaped lithium primary battery, a non-aqueous electrolyte solution in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; and ethers such as 1,2-dimethoxyethane, diglyme (diethylene glycol dimethyl ether), triglyme (triethylene glycol dimethyl ether), tetraglyme (tetraethylene glycol dimethyl ether), methoxyethoxyethane, 1,2-diethoxyethane, and tetrahydrofuran. In particular, it is preferable to use the carbonates and ethers in combination.

[0075] When a carbonate ester and an ether are used in combination as a nonaqueous electrolyte solvent, the ratio (mixing ratio) of the carbonate ester to the ether in the total solvent is preferably carbonate ester:ether=30:70 to 70:30 by volume.

[0076] Examples of electrolytes that can be dissolved in the non-aqueous electrolyte include LiBF4, LiPF6, LiAsF6, LiSbF6, LiClO4, and LiC n F 2n+1 SO3(n≧1) [LiCF3SO3, LiC4F9SO3, etc.], lithium imide salts [LiN(CF3SO2)2, LiN(C2F5SO2)2, etc.], LiC(CF3SO2)3, LiCF3CO2, LiB 10 Cl 10 , lithium lower fatty acid carboxylate, LiAlCl4, LiCl, LiBr, LiI, lithium chloroborane, lithium tetraphenylborate, etc., and at least one of them is used.

[0077] The concentration of the electrolyte in the non-aqueous electrolyte is not particularly limited, but is preferably 0.2 to 2 mol / l, and more preferably 0.3 to 1.5 mol / l.

[0078] The non-aqueous electrolyte is usually used as it is in liquid form, but it may be gelled with a polymer or the like (gelled electrolyte) and used.

[0079] In a sheet-type lithium primary battery, a positive electrode and a negative electrode are stacked with a separator interposed therebetween to form an electrode assembly (laminated electrode assembly), which is housed in an exterior body.

[0080] 4 and 5 are drawings that show a schematic diagram of an example of the sheet-shaped lithium primary battery of the present invention. Fig. 4 is a plan view of the sheet-shaped lithium primary battery, and Fig. 5 is a cross-sectional view taken along line II in Fig. 4.

[0081] The sheet-shaped lithium primary battery 1 contains an electrode assembly 100 and a nonaqueous electrolyte (not shown) in an exterior body 2 made of two laminate films, and the exterior body 2 is sealed at its outer periphery by heat-welding the upper and lower laminate films (their heat-welding resin layers). In order to avoid complicating the drawing, each layer constituting the exterior body 2 and the positive electrode, negative electrode, and separator constituting the electrode assembly are not shown separately in Fig. 5.

[0082] The positive electrode of the electrode body 100 is connected to a positive electrode external terminal 3 within the battery 1, and although not shown, the negative electrode of the electrode body 100 is also connected to a negative electrode external terminal 4 within the battery 1. One end of the positive electrode external terminal 3 and the negative electrode external terminal 4 is drawn out to the outside of the exterior body 2 so that they can be connected to an external device or the like. In other words, the positive electrode external terminal 3 and the negative electrode external terminal 4 are drawn out to the outside of the exterior body 2 while being fixed at a sealing portion of the exterior body 2.

[0083] The positive electrode external terminal may be formed of a tab portion of a positive electrode current collector, or may be provided by welding a metal plate, metal wire, etc. to the tab portion of the positive electrode current collector. The negative electrode external terminal may be formed of a tab portion of a negative electrode current collector, or may be provided by welding a metal plate, metal wire, etc. to the tab portion of the negative electrode current collector.

[0084] The laminate film constituting the exterior body of the sheet-shaped lithium primary battery has a heat-sealable resin layer. The exterior body is sealed by heat welding between an end of the heat-sealable resin layer of one laminate film (e.g., the positive electrode side) and an end of the heat-sealable resin layer of the other laminate film (e.g., the negative electrode side). The resin constituting the heat-sealable resin layer is preferably one that melts at a temperature of 200°C or less. The resin that melts at 200°C or less that constitutes the heat-sealable resin is a resin that has a melting temperature of 200°C or less measured according to the JIS K 7121 standard if it has a melting point, and a resin that has a glass transition temperature of 200°C or less measured according to the JIS K 7121 standard if it does not have a melting point. Specific examples of the resin include modified polyolefin films (e.g., modified polyolefin ionomer films), polyethylene, polypropylene, and copolymers thereof. The thickness of the heat-sealable resin layer is preferably 20 to 100 μm.

[0085] In the laminate film, a resin film as a base material is usually laminated on a heat-sealable resin layer. Examples of such resin films include nylon films (such as nylon 66 film) and polyester films (such as polyethylene terephthalate (PET) film). The thickness of the resin film as a base material is preferably 20 to 100 μm.

[0086] A metal layer may be laminated on the surface of the resin film, which is the base material of the laminate film, opposite to the surface on the heat-fusible resin layer side. The metal layer may be composed of a vapor-deposited film of aluminum (including aluminum alloys), an aluminum film (aluminum foil, including aluminum alloy foil), a stainless steel film (stainless steel foil), etc. The thickness of the metal layer is preferably 10 to 150 μm.

[0087] The laminate film may be a film having a structure in which a heat-fusible resin layer and the above-mentioned metal layer are laminated together.

[0088] Furthermore, the laminate film constituting the exterior body may be one in which a water vapor barrier layer for preventing the permeation of water vapor is laminated onto a heat-sealable resin layer or the resin film serving as a base material.

[0089] The water vapor barrier layer can be made of an electrically insulating oxide. Examples of oxides constituting the water vapor barrier layer include inorganic oxides such as aluminum oxide and silicon oxide. A layer made of silicon oxide tends to have a higher function of suppressing the permeation of moisture in the electrolyte in the battery than a layer made of aluminum oxide. Therefore, it is more preferable that the water vapor barrier layer is a layer made of silicon oxide.

[0090] The water vapor barrier layer can be formed on the surface of the heat-fusible resin layer or the resin film serving as the base material by, for example, a vapor deposition method. The thickness of the water vapor barrier layer is preferably 10 to 300 nm.

[0091] In the case of a laminate film having a water vapor barrier layer, a protective layer for protecting the water vapor barrier layer may be formed on the surface of the oxide layer (the surface opposite to the base resin film or heat-weldable resin layer).

[0092] As the resin film having a water vapor barrier layer, for example, a laminate film that is commercially available under the name of barrier film or the like for applications such as medical and pharmaceutical use, electronic devices, and food can be used.

[0093] Examples of commercially available laminate films include "GL FILM" and "PRIME BARRIER" (both product names) manufactured by Toppan Printing Co., Ltd., "MAX BARRIER" and "TL" (both product names) manufactured by Mitsui Chemicals Tocello Inc., "TECH BARRIER" (product name) manufactured by Mitsubishi Chemical Corporation, "IB-Film" (product name) manufactured by Dai Nippon Printing Co., Ltd., and "Ecosyar" (product name) manufactured by Toyobo Co., Ltd.

[0094] The shape of the exterior body may be polygonal (triangle, quadrangle, pentagon, hexagon, heptagon, octagon) in plan view, or may be circular or elliptical in plan view. In the case of an exterior body that is polygonal in plan view, the positive electrode external terminal and the negative electrode external terminal may be led out from the same side or may be led out from different sides.

[0095] Alternatively, an exterior body can be constructed by folding a large-sized laminate film so as to sandwich the electrode body, and then heat-sealing the outer peripheral portions of the laminate films above and below the electrode body other than the folded portions.

[0096] The sheet-form lithium primary battery of the present invention can be thinned to a thickness of 1.5 to 5 mm, making it possible to produce a battery with high energy density.

[0097] The sheet-type lithium primary battery of the present invention can be applied to the same applications as conventionally known lithium primary batteries, but can also be preferably applied to applications where batteries using metal containers of cylindrical or flat shapes are difficult to apply due to problems with their shapes. In particular, a general feature of sheet-type batteries is that they can be easily made into a thin shape, so the sheet-type lithium primary battery of the present invention is useful as a power source for thin electrical devices and the like. EXAMPLES

[0098] The present invention will be described in detail below with reference to examples, although the present invention is not limited to the following examples.

[0099] Example 1 (Preparation of positive electrode) First, a positive electrode mixture (mass ratio of solid content: water content = 100:30) was prepared by the following procedure. 2 3% by mass of carbon black and 92% by mass of manganese dioxide were mixed in a planetary mixer for 5 minutes in a dry state, and then water was added to the mixture to make the solid content 20% (mass ratio) of the solid content, and mixed for 5 minutes. A PTFE dispersion was prepared in an amount such that the solid content was 5% (mass ratio) of the solid content of the positive electrode mixture, and this was diluted with the remaining water, added to the mixture, and mixed for 5 minutes to obtain a positive electrode mixture.

[0100] The positive electrode mixture was rolled into a sheet using two rolls with a diameter of 250 mm, the roll temperature was adjusted to 125±5°C, and the conditions were a press pressure of 7 tons / cm, a roll gap of 0.4 mm, and a rotation speed of 10 rpm. The positive electrode mixture (preliminary sheet) that passed through the rolls was dried at 105±5°C until the residual moisture was 2% or less. The dried preliminary sheet was then crushed using a crusher. At this time, the preliminary sheet was crushed until it was more than twice the original apparent volume. Most of the particle diameter after crushing was 1 mm or less, and the PTFE added as a binder was also cut into fibers with a length of 1 mm or less. The crushed material was again sheeted using rolls. The roll gap was adjusted to 0.6±0.05 mm, and the roll temperature was adjusted to 125±10°C, the press pressure was 7 tons / cm, and the rotation speed was adjusted to 10 rpm to obtain a positive electrode mixture sheet. The obtained positive electrode mixture sheet had a thickness of 0.65 mm. The density of the positive electrode mixture sheet is 2.5 g / cm 3 The porosity was 42%. This positive electrode mixture sheet was cut to obtain two positive electrode mixture sheets with a width (length of a in FIG. 2): 26 mm and a length (length of b in FIG. 2): 65 mm.

[0101] A stainless steel (SUS304) net with a thickness of 0.1 mm was used for the positive electrode current collector. This net was cut into a shape having a rectangular main body with a width (length of c in FIG. 2): 23.5 mm and a length (length of d in FIG. 2): 60 mm, and a tab with a width (length of e in FIG. 2): 10 mm and a length (length of f in FIG. 2): 5 mm. Furthermore, carbon paste was applied to this net in an amount that did not crush the mesh, and then it was dried at a temperature of 105±5°C to obtain a positive electrode current collector. The amount of carbon paste applied after drying was 5 mg / cm. 2 It was made so that:

[0102] Next, a positive electrode current collector was sandwiched between the two positive electrode mixture sheets, and each positive electrode mixture sheet and the positive electrode current collector were joined only at the lower peripheral portion (end and vicinity) in FIG. 2 to integrate the three, thereby obtaining a positive electrode. When integrating the three, the ends of the two left and right sides in FIG. 2 of the positive electrode current collector were set 1.25 mm inside the ends of the two left and right sides in FIG. 2 of the two positive electrode mixture sheets, respectively, and the ends of the two top and bottom (longitudinal) sides in FIG. 2 of the positive electrode current collector were set 2.5 mm inside the ends of the two top and bottom (longitudinal) sides in FIG. 2 of the two positive electrode mixture sheets, respectively. In addition, the width of the positive electrode mixture sheet joint 11a was set to 5 mm.

[0103] (Preparation of negative electrode) A metallic lithium foil with a thickness of 0.27 mm was cut to a width of 25.5 mm and a length of 130 mm. A copper foil with a thickness of 10 μm was cut to a shape having a main body with a width of 26.5 mm and a length of 130 mm and a tab with a width of 10 mm and a length of 3 mm for use as a negative electrode current collector. The metallic lithium foil was placed and attached to the center of the width direction of the main body of the copper foil to obtain a negative electrode having a negative electrode agent layer made of metallic lithium on one side of the negative electrode current collector.

[0104] (Preparation of electrode body) A microporous polyethylene film with a width of 31 mm, a length of 138 mm, and a thickness of 16 μm and a polyethylene nonwoven fabric with a width of 31 mm, a length of 138 mm, and a thickness of 40 μm were used as a separator, which was folded back so as to sandwich the positive electrode from both sides. The negative electrode was then folded back so as to sandwich the outside of the separator that had been folded back to sandwich the positive electrode, forming an electrode body with a cross-sectional structure as shown in FIG. 1. Nickel external terminals (positive electrode external terminal and negative electrode external terminal) with a width of 6 mm, a length of 11 mm, and a thickness of 0.1 mm were welded to the tab portion of the positive electrode and the tab portion of the negative electrode of the electrode body, respectively.

[0105] (Assembly of sheet-type lithium primary batteries) An aluminum laminate film having a heat-weldable resin layer and a thickness of 0.085 mm, a width of 37 mm, and a length of 156 mm was folded back so as to sandwich the electrode body, and two sides of the aluminum laminate film on the top and bottom of the electrode body were heat-welded. Then, a nonaqueous electrolyte (a solution in which lithium trifluoromethanesulfonate was dissolved at a concentration of 0.45 mol / L in a mixed solvent of ethylene carbonate, propylene carbonate, and dimethoxyethane in a volume ratio of 15:25:60) was injected from the remaining side of both aluminum laminate films. Thereafter, while reducing the pressure inside both aluminum laminate films, the openings were heat-sealed to temporarily seal the exterior body, thereby obtaining a temporary assembly.

[0106] Next, the temporary assembly was pre-discharged to a capacity equivalent to 2% of the design capacity of the battery (capacity before pre-discharge), and then stored for 12 hours at 60° C. After storage, the temporary assembly was opened by cutting out a part of the welded portion, and the inside was depressurized to remove gas, and the exterior body was heat sealed while depressurizing the inside again, to obtain a sheet-shaped lithium primary battery with the appearance shown in Fig. 4 and the same cross-sectional structure as that shown in Fig. 5 except for the configuration of the folded part of the exterior body.

[0107] Example 2 A sheet-shaped lithium primary battery was produced in the same manner as in Example 1, except that the discharge capacity during preliminary discharge was set to 4% of the design capacity of the battery.

[0108] Example 3 A sheet-shaped lithium primary battery was produced in the same manner as in Example 1, except that the discharge capacity during preliminary discharge was set to 8% of the design capacity of the battery.

[0109] Example 4 A sheet-shaped lithium primary battery was fabricated in the same manner as in Example 1, except that the storage conditions after the preliminary discharge were set to 60° C. for 24 hours.

[0110] Comparative Example 1 A sheet-shaped lithium primary battery was produced in the same manner as in Example 1, except that storage after preliminary discharge was not carried out.

[0111] Comparative Example 2 A sheet-shaped lithium primary battery was produced in the same manner as in Example 1, except that the preliminary discharge was not carried out.

[0112] The sheet-shaped lithium primary batteries of the Examples and Comparative Examples were stored in an environment of 70° C. and 90% relative humidity for 30 days, and then the following evaluations were carried out.

[0113] <Gas generation rate measurement> The batteries were decomposed in liquid paraffin before and after storage, and the gas inside the exterior was sampled. The increase in gas was calculated from the change in volume, and the ratio of this to the internal volume of the battery (internal volume before storage) was calculated.

[0114] <Capacity reduction rate> The battery was discharged before and after storage at a current value of 1 / 500C (mA), assuming that the design capacity of the positive electrode is C (mAh), and the discharge capacity until the battery voltage dropped to 2V was measured. The capacity drop rate was calculated using the following formula.

[0115] Capacity reduction rate (%) = 100 × (discharge capacity before storage - discharge capacity after storage) ÷ discharge capacity before storage

[0116] These results are shown in Table 1 along with the conditions for each step in the production of each battery.

[0117] [Table 1]

[0118] As shown in Table 1, the sheet-type lithium primary batteries of Examples 1 to 4, which were fabricated through the preliminary discharge process, storage process, and degassing process in a temporary assembly, showed little capacity loss after storage and also suppressed internal gas generation after storage, and had excellent storage characteristics.

[0119] In contrast, the battery of Comparative Example 1 was produced without a storage step after the preliminary discharge step, and therefore had a large amount of water remaining in the battery when it was assembled, and a large amount of gas was generated due to a reaction with the active material during storage at 70° C. Furthermore, the discharge capacity of the battery was significantly reduced due to the reaction.

[0120] In addition, although the amount of water remaining in the battery of Comparative Example 2 was less than that of Comparative Example 1 due to the storage process, since the battery was produced without undergoing a preliminary discharge process, the remaining water was decomposed to generate a large amount of gas, and the discharge capacity of the battery was significantly reduced due to the reaction. [Explanation of symbols]

[0121] 1. Sheet-type lithium primary battery 2 Exterior body 3 Positive external terminal 4 Negative external terminal 10 positive electrode 11 Positive electrode mixture layer (positive electrode mixture sheet) 12 Positive electrode current collector 12a Main body of positive electrode current collector 12b Tab portion of positive electrode current collector 20 negative electrode 21 Negative electrode active material layer 22 Negative electrode current collector 30 Separator 100 electrode body

Claims

1. A sheet-shaped lithium primary battery comprising an exterior body made of a laminate film having a heat-sealable resin layer, and housing a negative electrode containing lithium or a lithium alloy, a positive electrode, a separator, and a non-aqueous electrolyte, 1. A sheet-shaped lithium primary battery, characterized in that when stored for 30 days in an atmosphere at 70° C. and 90% relative humidity, the volume of gas increased within the battery is 20% or less of the internal volume of the battery before storage.

2. 2. The sheet-shaped lithium primary battery according to claim 1, wherein the positive electrode contains manganese dioxide as a positive electrode active material.

3. 3. The sheet-shaped lithium primary battery according to claim 1, wherein the positive electrode active material contained in the positive electrode contains lithium in advance in an amount equivalent to 1 to 10% of the total discharge capacity of the battery.

4. 4. The sheet-shaped lithium primary battery according to claim 1, wherein the laminate film has a water vapor barrier layer.

5. A method for producing a sheet-shaped lithium primary battery having a power generating element including a negative electrode containing lithium or a lithium alloy, a positive electrode, a separator, and a non-aqueous electrolyte, in an exterior body made of a laminate film having a heat-sealable resin layer, comprising: a temporary sealing step of enclosing the power generating element in the exterior housing to prepare a temporary assembly; a preliminary discharge step of discharging a part of the capacity of the temporary assembly; a storage step of maintaining the temporary assembly in a warm state; a degassing step of removing gas from the battery by opening a part of the exterior body after the preliminary discharge step and the storage step; and a final sealing step of sealing the exterior body after the degassing step.

6. 6. The method for producing a sheet-shaped lithium primary battery according to claim 5, wherein the amount of electricity discharged in the preliminary discharge step is 1 to 10% of the capacity of the temporary assembly.

7. 7. The method for producing a sheet-shaped lithium primary battery according to claim 5, wherein the temporary assembly is kept at 40 to 80° C. in the storage step.

8. The method for producing a sheet-shaped lithium primary battery according to any one of claims 5 to 7, wherein manganese dioxide is used as a positive electrode active material for the positive electrode.

9. The method for producing a sheet-shaped lithium primary battery according to any one of claims 5 to 8, wherein the laminate film has a water vapor barrier layer.

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