Sheet-type 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, which are 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 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 to 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 therefore the shape can be changed to some extent as needed, which has the advantage that they can be used in a wider range of devices than batteries using the above-mentioned metal containers.

[0004] Furthermore, 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 more likely that gas will be generated due to a reaction between moisture in the battery and the electrodes.Furthermore, because the exterior body made of laminate film is easily deformed, swelling of the battery can easily become a problem when stored at high temperatures, for example.

[0005] Technological developments are also being made 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 the battery is resealed and assembled. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-187711 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 with the method of Patent Document 1, deformation of the exterior body due to gas generation during storage of the battery was observed. Therefore, there is room for improvement in the technology described in Patent Document 1 in terms of improving the storage properties of sheet-shaped lithium primary batteries.

[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-shaped lithium primary battery of the present invention contains a negative electrode containing lithium or a lithium alloy, a positive electrode, a separator, and a non-aqueous electrolyte solution in an exterior body made of a laminate film having a heat-sealable resin layer, and is characterized in that 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.

[0010] The method for manufacturing a sheet-shaped lithium primary battery of the present invention is a method for manufacturing a sheet-shaped lithium primary battery comprising an outer casing made of a laminate film having a heat-sealable resin layer, and a power generating element comprising a negative electrode containing lithium or a lithium alloy, a positive electrode, a separator, and a non-aqueous electrolyte, and is characterized by comprising the following steps: a temporary sealing step of enclosing the power generating element in the outer casing to prepare a temporary assembly; a pre-discharge step of discharging part of the capacity of the temporary assembly; a storage step of maintaining the temporary assembly in a heated state; a degassing step of opening part of the outer casing after the pre-discharge step and the storage step and removing internal gas; and a final sealing step of sealing the outer casing after the degassing step. [Effects 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 explanation of the drawings]

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

[0013] The sheet-shaped 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 that increases 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 when stored under relatively harsh conditions, the degree of deformation of the exterior body due to 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, and for example, the volume of gas that increases inside 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 sealed in an exterior body made of a laminate film having a heat-sealable 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 that constitutes the exterior body, and 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 will be described later, the temporary assembly will be partially opened in a process that will be described later, 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 portion of the exterior body.

[0018] (2) Pre-discharge process In the preliminary discharge step, a portion 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 that does not electrolyze the water present inside the battery, thereby suppressing gas generation due to decomposition of water inside 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 that does not electrolyze the water present inside.

[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-type lithium primary battery), and also gasifies the moisture inside the battery by reacting it with the active material, etc., thereby minimizing the amount of moisture remaining inside the battery.

[0022] The storage conditions for 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 of the temporary assembly that has been through the preliminary discharge step and the storage step is opened to remove the gas inside.

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

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

[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 pre-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 is made less likely to be gasified by electrolysis (pre-discharge 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 90% relative humidity satisfies the above-mentioned 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 produced in this manner, 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 the capacity estimated from the amount of lithium in the positive electrode active material (corresponding to the capacity consumed in the pre-discharge carried out in the pre-discharge step in the production method of the present invention).

[0033] The positive electrode of the sheet-shaped lithium primary battery can have a structure in which a positive electrode mixture layer made of a positive electrode mixture containing a positive electrode active material, a conductive additive, a binder, etc. is formed on one or both sides of a current collector.

[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 conductive additives 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 binders for the positive electrode include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polymers of propylene hexafluoride, and only one of these may be used, or two or more may be used in combination.

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

[0038] Such a positive electrode mixture sheet is joined to a positive electrode current collector by pressing or the like, thereby producing 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 its form 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 three-dimensional mesh-like positive electrode current collector is used, the application of the conductive material significantly improves the current collection effect, as in the case of using essentially flat materials such as metal foil or punched metal. This is presumably due to the effective use of not only the path where the metal part of the mesh-like current collector comes into direct contact with the positive electrode mixture layer, but also the path via the conductive material filled in the mesh.

[0042] Examples of conductive materials that can be used include silver paste and carbon paste. Carbon paste, in particular, is less expensive than silver paste and provides contact effects similar to those of silver paste, making it suitable for reducing the manufacturing costs of sheet-shaped lithium primary batteries. Heat-resistant materials such as water glass and imide-based binders are preferably used as binders for conductive materials. This is because the positive electrode mixture layer is dried at high temperatures exceeding 200°C to remove moisture.

[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 there is a risk that the capacity of the positive electrode will not be fully utilized. In addition, the flexibility of the positive electrode is likely to decrease, and cracks and chips will easily occur in the positive electrode mixture layer. Therefore, from the viewpoint of improving the battery characteristics and ensuring better flexibility, the thickness of the positive electrode mixture layer is preferably 1 mm or less, and more preferably 0.9 mm or less.

[0044] Unlike batteries with exterior bodies such as metal cans, sheet-type batteries with exterior bodies made of laminated films are relatively flexible, and may therefore be slightly deformed as necessary for installation in applicable devices. However, if the positive electrode (positive electrode mixture layer) is made thicker to achieve higher capacity, cracks and chips are more 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 to bond a portion of the positive electrode mixture layer (positive electrode mixture sheet) to the positive electrode current collector and integrate it, while leaving the remaining portion unbonded. 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 unbonded portion. This prevents excessive stress from being applied to the positive electrode mixture layer, making it possible to prevent cracking or chipping of the positive electrode mixture layer. This allows for a sheet-type lithium primary battery that can effectively suppress capacity loss even when used in equipment that requires some deformation of the battery during installation.

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

[0047] The electrode assembly 100 shown in FIG. 1 is a laminated electrode assembly 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 current collector 12. The negative electrode 20 is configured by arranging a negative electrode active material layer 21 on one side (the side facing the separator 30) of a negative electrode current collector 22. Furthermore, in the electrode assembly 100, the separators 30 are arranged on both sides of the positive electrode 10 by folding back a single sheet and sandwiching the positive electrode 10 therebetween. 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 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 a portion (positive electrode mixture layer joint 11a) to the adjacent positive electrode current collector 12, and only the positive electrode mixture layer joint 11a is integrated. In the electrode body 100 of Fig. 1, the positive electrode mixture layer joint 11a is the contact portion between the positive electrode mixture layers 11, 11 and the positive electrode current collector 12 at the shaded area to the left of the dotted line in the figure.

[0049] When the positive electrode has positive electrode mixture layers (positive electrode mixture sheets) on both sides of the positive electrode current collector, it is preferable that, as shown in FIG. 1, a portion of each positive electrode mixture layer is bonded to the positive electrode current collector, and the other portion is not bonded.

[0050] The location where the positive electrode mixture layer and the positive electrode current collector are joined is not particularly limited as long as flexibility can be imparted to the positive electrode. As shown in FIG. 1, the joint may be formed on the peripheral edge of the positive electrode mixture layer, or may be formed in 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 (excluding the area of ​​the tab portion described below).

[0052] On the other hand, in order to increase the proportion of the non-bonded portion of the positive electrode mixture layer that is not bonded to the positive electrode current collector and thereby increase the flexibility of the positive electrode, the area of ​​the bonded 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 only partially joined to the adjacent positive electrode current collector, there is a risk that the positive electrode mixture layer and the positive electrode current collector may come apart during battery manufacturing or inside the battery. Therefore, in such a case, the location of the electrode assembly where the non-joined 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 positional displacement due to deformation of the battery at the non-joined portion of the positive electrode.

[0054] Fig. 2 is a plan view schematically illustrating an example of a positive electrode of a sheet-shaped lithium primary battery of the present invention. In Fig. 2, the dashed line indicates the position of a portion of a positive electrode current collector 12 that is disposed on the rear side of a 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 inward of the end of the positive electrode mixture layer in plan view, excluding a tab portion 12 described later.

[0055] In a sheet-shaped lithium primary battery, it is preferable that at least a part of the edge of the positive electrode current collector is located more inward than the edge of the positive electrode mixture layer (positive electrode mixture sheet) in plan view. In this case, even if misalignment occurs between the positive electrode mixture layer and the positive electrode current collector due to deformation of the battery or the like, the part of the edge of the positive electrode current collector that is located more inward than the edge of the positive electrode mixture layer is less likely to be exposed to the surface, and contact between the edge of the positive electrode current collector and the separator is suppressed by the positive electrode mixture layer, thereby suppressing the occurrence of a short circuit due to the separator being damaged 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 it is misaligned with the positive electrode mixture layer. However, by positioning at least a portion 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, it is possible to effectively prevent short circuits caused by scratches on the separator, even when such a positive electrode current collector is used.

[0057] When the positive electrode has positive electrode mixture layers (positive electrode mixture sheets) 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 located more inward than the ends of both positive electrode mixture layers (positive electrode mixture sheets) in plan view.

[0058] If at least a portion of the end of the positive electrode current collector is disposed inward in plan view relative to the end of the positive electrode mixture layer, the effect of suppressing short circuits 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 more inward in plan view relative to 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 not shown disposed on the back side of the positive electrode current collector 12 in the figure) at least on one peripheral edge in the longitudinal direction of the positive electrode mixture layer (the direction parallel to one of the sides in the case of a square).

[0059] When a battery is bent in the longitudinal direction of the positive electrode mixture layer, the misalignment 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, making a short circuit more likely to occur. In particular, when one longitudinal peripheral edge of the positive electrode mixture layer is joined to the peripheral edge 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 rear surface of the positive electrode mixture layer 11 (the shaded area in FIG. 2)), no misalignment occurs between the positive electrode mixture layer and the positive electrode current collector at that portion, but a large misalignment occurs at the other longitudinal peripheral edge of the positive electrode mixture layer. For this reason, it is more preferable to position the end of the main body of the positive electrode current collector on the side not joined to the positive electrode mixture layer 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 plan 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 is a plan view schematically illustrating another example of a positive electrode for a sheet-type lithium primary battery. In the positive electrode 10 shown in FIG. 3, the main body 12a of the positive electrode current collector 12 is substantially circular, and the end of the positive electrode current 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 current collector 12 in FIG. 3, and the positive electrode mixture layer (not shown) disposed on the back side of the positive electrode current collector 12 in FIG. 3). Even when the sheet-type battery of the present invention has a positive electrode having the configuration shown in FIG. 3, scratches on the separator caused by the end of the positive electrode current collector when misalignment occurs between the positive electrode current collector and the positive electrode mixture layer can be effectively prevented.

[0063] In this specification, the term "circular" representing the shape of the positive electrode mixture layer or the positive electrode current collector includes a 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 a positive electrode, in a portion where the end of the positive electrode current collector is located inside the end of the positive electrode mixture layer, the distance between the end of the positive electrode current 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 a short circuit in the battery due to scratches on the separator. However, if the distance between the end of the positive electrode current 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 current collector is located inside the end of the positive electrode mixture layer, the distance between the end of the positive electrode current 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] As for the composition of each component in the positive electrode mixture layer, the amount of positive electrode active material is preferably 80 to 90 mass %, the content of conductive additive is preferably 1.5 to 10 mass %, and the content of 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 a 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, examples of the lithium alloy include lithium-aluminum. In particular, it is preferable to use a laminate formed by bonding lithium metal foil and thin aluminum foil together for the negative electrode active material layer, with the thin aluminum foil side being disposed at least on the positive electrode mixture sheet side. The laminate of lithium metal foil and aluminum foil generates a lithium-aluminum alloy at the interface when it comes into contact with the nonaqueous electrolyte described below in the battery. Therefore, when a laminate of lithium metal foil and thin aluminum foil is used, a lithium-aluminum alloy is generated on the surface of the lithium sheet constituting the negative electrode active material layer in the battery. At this time, the lithium-aluminum alloy is pulverized, thereby increasing the specific surface area of ​​the alloy-containing surface of the lithium sheet. Therefore, by making this alloy-containing surface the surface facing the positive electrode mixture layer, the battery can be discharged more efficiently.

[0069] The thickness of the lithium sheet constituting the negative electrode active material layer is preferably 0.1 to 1 mm. When the laminate of the lithium metal foil and thin aluminum foil is used, the thickness of the lithium metal foil is preferably 0.1 to 1 mm, and the thickness of the thin aluminum foil is preferably 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. Because the internal volume of the battery container (external can) is reduced by the thickness of the negative electrode current collector, the thickness of the negative electrode current collector is preferably as small as possible; specifically, a thickness of 0.1 mm or less is recommended. That is, if the negative electrode current collector is too thick, the amount of lithium sheet or the like that constitutes the negative electrode active material layer must be reduced, which may reduce the effect of improving battery capacity achieved by thickening the positive electrode. Furthermore, if the negative electrode current collector is too thin, it becomes prone to tearing, so the thickness of the negative electrode current collector is preferably 0.005 mm or more. Furthermore, the width of the negative electrode current collector is preferably the same as or wider than the width of the lithium sheet that constitutes the negative electrode active material layer, and its area 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, which makes it possible to prevent the lithium sheet from being torn along the periphery of the negative electrode current collector, thereby preventing electrical connection from being cut.

[0071] In sheet-type lithium primary batteries, the separator interposed between the positive electrode and the negative electrode can be a separator used in conventional nonaqueous primary batteries such as lithium primary batteries, i.e., a separator made of a microporous resin film or a separator made of a resin nonwoven fabric. Examples of materials include polyolefins such as polyethylene (PE), polypropylene (PP), and polymethylpentene, as well as heat-resistant fluororesins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), and polybutylene terephthalate (PBT). Furthermore, the use of a multilayer separator, constructed by laminating multiple microporous films and nonwoven fabrics made of the above materials, or by laminating multiple microporous films or nonwoven fabrics, can improve reliability when used in high-temperature environments.

[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 measurements.

[0073] In the case of an electrode assembly in which a negative electrode is disposed on both sides of a positive electrode via a separator, two separators may be used, each disposed on the side of the positive electrode facing the negative electrode, or a single separator may be folded over and disposed so as to sandwich the positive electrode, as shown in FIG. 1. Similarly, two negative electrodes may be used, each disposed so as to face the positive electrode with a separator sandwiched between them, or a single negative electrode may be folded over and disposed so as to sandwich the separator disposed on the outside of the positive electrode, as shown in FIG. 1. This can increase the productivity of batteries.

[0074] The non-aqueous electrolyte for sheet-type lithium primary batteries can be a non-aqueous electrolyte solution prepared by dissolving an electrolyte in an organic solvent. 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. It is particularly preferable to use the carbonates and ethers in combination.

[0075] When a carbonate ester and an ether are used in combination as the 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 the electrolyte to 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 electrolytic solution is not particularly limited, but is preferably 0.2 to 2 mol / l, more preferably 0.3 to 1.5 mol / l.

[0078] The non-aqueous electrolyte is usually used in its liquid state, but may be gelled with a polymer or the like (gel electrolyte).

[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 diagrams showing a schematic view of an example of the sheet-type lithium primary battery of the present invention. Fig. 4 is a plan view of the sheet-type 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 non-aqueous electrolyte (not shown) in an exterior housing 2 made of two laminate films, and the exterior housing 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 cluttering the drawing, Fig. 5 does not distinguish between the layers that make up the exterior housing 2 and the positive electrode, negative electrode, and separator that make up the electrode assembly.

[0082] The positive electrode of the electrode assembly 100 is connected to a positive electrode external terminal 3 within the battery 1, and although not shown, the negative electrode of the electrode assembly 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 external devices, etc. 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 by a tab portion of the 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 by a tab portion of the 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 an end of the heat-sealable resin layer of one laminate film (e.g., the positive electrode side) to 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. If the heat-sealable resin constituting the heat-sealable resin has a melting point, it is a resin whose melting temperature measured in accordance with JIS K 7121 is 200°C or less. If the heat-sealable resin does not have a melting point, it is a resin whose glass transition temperature measured in accordance with JIS K 7121 is 200°C or less. Specific examples of such resins 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 a laminate film, a resin film serving as a substrate 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 serving as a substrate is preferably 20 to 100 μm.

[0086] A metal layer may be laminated on the surface opposite to the heat-sealable resin layer side of the resin film that serves as the base material in the laminate film. 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), or the like. The thickness of the metal layer is preferably 10 to 150 μm.

[0087] The laminate film may also 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 a heat-sealable resin layer or a resin film serving as a base material, on which a water vapor barrier layer for preventing water vapor permeation is laminated.

[0089] The water vapor barrier layer can be made of an electrically insulating oxide. Examples of oxides that make up the water vapor barrier layer include inorganic oxides such as aluminum oxide and silicon oxide. Note that a layer made of silicon oxide tends to have a higher function of suppressing the permeation of moisture in the electrolyte solution in the battery than a layer made of aluminum oxide. Therefore, it is more preferable that the water vapor barrier layer be 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 substrate 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] The resin film having a water vapor barrier layer may be, for example, a laminated film commercially available under the name of barrier film for medical and pharmaceutical use, electronic device use, food use, or the like.

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

[0094] The shape of the exterior body may be polygonal in plan view (triangle, quadrangle, pentagon, hexagon, heptagon, or octagon), 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 outer casing can be constructed by folding a large laminate film so as to sandwich the electrode body, and then heat-sealing the outer peripheral portions of the laminate film above and below the electrode body, excluding the folded portions.

[0096] The sheet-shaped lithium primary battery of the present invention can be thinned to 1.5 to 5 mm, and can be made into 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 such as cylindrical or flat containers are difficult to apply due to their shape. In particular, since a general feature of sheet-type batteries is that they can be easily made into a thin shape, the sheet-type lithium primary battery of the present invention is useful as a power source for thin electrical equipment and the like. [Example]

[0098] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples.

[0099] Example 1 (Preparation of positive electrode) First, a positive electrode mixture (mass ratio of solid content to 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 dry for 5 minutes using a planetary mixer, and then water was added to the mixture so that the solid content was 20% (by mass) of the solid content, followed by mixing for 5 minutes. PTFE dispersion was prepared in an amount corresponding to 5% (by mass) of the solid content of the positive electrode mixture, 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 ton / cm, a roll gap of 0.4 mm, and a rotation speed of 10 rpm. The positive electrode mixture (preparatory sheet) that had passed through the rolls was dried at 105±5°C until the residual moisture content was 2% or less. The dried preliminary sheet was then crushed using a crusher. The preliminary sheet was crushed until it was at least twice its original apparent volume. Most of the crushed particles had a particle diameter of 1 mm or less, and the PTFE added as a binder was also cut into fibers with lengths of 1 mm or less. The crushed material was then again crushed into a sheet using rolls. The roll gap was adjusted to 0.6±0.05 mm, and the roll temperature was adjusted to 125±10°C, a press pressure of 7 ton / cm, and a rotation speed of 10 rpm to obtain a positive electrode mixture sheet. The resulting 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 positive electrode mixture sheet was cut to obtain two positive electrode mixture sheets each having a width (length of a in FIG. 2): 26 mm and a length (length of b in FIG. 2): 65 mm.

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

[0102] Next, a positive electrode current collector was sandwiched between the two positive electrode mixture sheets, and the positive electrode mixture sheets and the positive electrode current collector were joined only at the lower peripheral portions (edges and their vicinity) in FIG. 2 to integrate the three components, thereby obtaining a positive electrode. When the three components were integrated, the two left and right edges of the positive electrode current collector in FIG. 2 were positioned 1.25 mm inward from the two left and right edges of the two positive electrode mixture sheets in FIG. 2, respectively, and the two top and bottom (longitudinal) edges of the positive electrode current collector in FIG. 2 were positioned 2.5 mm inward from the two top and bottom (longitudinal) edges of the two positive electrode mixture sheets in FIG. 2, respectively. The width of the positive electrode mixture sheet joint 11a was 5 mm.

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

[0104] (Preparation of electrode body) A microporous polyethylene film measuring 31 mm in width, 138 mm in length, and 16 μm in thickness was used as a separator, and a polyethylene nonwoven fabric measuring 31 mm in width, 138 mm in length, and 40 μm in thickness was stacked on top of each other. This was folded over to sandwich the positive electrode from both sides. The negative electrode was then folded over to sandwich the outside of the separator that had been folded over to sandwich the positive electrode, forming an electrode assembly with the cross-sectional structure shown in FIG. 1. Nickel external terminals (positive electrode external terminal and negative electrode external terminal) measuring 6 mm in width, 11 mm in length, and 0.1 mm in thickness were welded to the tab portions of the positive electrode and negative electrode of the electrode assembly, 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 the two sides of the aluminum laminate film on the top and bottom of the electrode body were heat-welded. A nonaqueous electrolyte (a solution of lithium trifluoromethanesulfonate 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 then injected into the remaining sides of both aluminum laminate films. The openings were then heat-sealed while the pressure inside both aluminum laminate films was reduced, thereby temporarily sealing the exterior body and 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 portion of the welded portion, and the interior was depressurized to remove gas.The exterior body was then heat-sealed while again depressurizing the interior, yielding a sheet-shaped lithium primary battery with the appearance shown in Figure 4 and the same cross-sectional structure as that shown in Figure 5, except for the configuration of the folded portion of the exterior body.

[0107] Example 2 A sheet-shaped lithium primary battery was fabricated 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 fabricated 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 pre-discharge were set to 60° C. for 24 hours.

[0110] Comparative Example 1 A sheet-shaped lithium primary battery was fabricated 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 fabricated in the same manner as in Example 1, except that pre-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 volume was determined from the change in volume, and the ratio 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 (mAh) when the design capacity of the positive electrode was C (mAh), and the discharge capacity until the battery voltage dropped to 2V was measured, and 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-shaped 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 suppressed internal gas generation after storage, and had excellent storage characteristics.

[0119] In contrast, the battery of Comparative Example 1 was fabricated without a storage step after the preliminary discharge step, and therefore a large amount of water remained 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] Furthermore, 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, because it was produced without undergoing a pre-discharge process, the remaining water decomposed to generate a large amount of gas, and the discharge capacity of the battery was significantly reduced due to this 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 a negative electrode containing lithium or a lithium alloy, a positive electrode, a separator, and a non-aqueous electrolyte solution accommodated therein, the positive electrode has a positive electrode mixture layer and a current collector, the positive electrode mixture layer having a thickness of 0.3 mm or more, the positive electrode active material contained in the positive electrode contains lithium in advance in an amount corresponding to 1 to 10% of the total discharge capacity of the battery, A sheet-type lithium primary battery characterized in that the volume of gas increased within the battery when stored for 30 days in an atmosphere at 70°C and 90% relative humidity 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 laminate film has a water vapor barrier layer.

3. A sheet-shaped lithium primary battery comprising an exterior body made of a laminate film having a heat-sealable resin layer, and a negative electrode containing lithium or a lithium alloy, a positive electrode, a separator, and a non-aqueous electrolyte solution accommodated therein, the laminate film has a water vapor barrier layer made of an electrically insulating oxide; the positive electrode active material contained in the positive electrode contains lithium in advance in an amount corresponding to 1 to 10% of the total discharge capacity of the battery, A sheet-type lithium primary battery characterized in that the volume of gas increased within the battery when stored for 30 days in an atmosphere at 70°C and 90% relative humidity is 20% or less of the internal volume of the battery before storage.

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

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