Flat non-aqueous electrolyte battery and manufacturing method thereof

Abstract

To provide a flat non-aqueous electrolyte battery having excellent discharge characteristics and a method for manufacturing the flat non-aqueous electrolyte battery with high productivity.SOLUTION: A flat non-aqueous electrolyte battery according to the present invention includes a battery container formed by sealing the opening of an outer can with a sealable can via a gasket, the negative electrode has a lithium layer, a lithium-aluminum alloy layer having an area larger than that of the lithium layer is formed on the separator side of the lithium layer, the lithium layer is contained in the sealable can, and the positive electrode is contained in the outer can. The gasket includes a base portion whose bottom surface is located on the inner bottom surface side of the outer can, and inner and outer walls rising from the base portion toward the sealable can, with a gap provided between the inner and outer walls. The peripheral wall of the sealable can, the outer periphery of the separator, and the outer periphery of the lithium-aluminum alloy layer are inserted into the gap.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a flat nonaqueous electrolyte battery having excellent discharge characteristics and a method for manufacturing the flat nonaqueous electrolyte battery with high productivity. [Background technology]

[0002] In flat nonaqueous electrolyte batteries such as coin-type and button-type batteries, for example, when lithium is used as the negative electrode, a lithium layer may be disposed on the inner surface of a sealing can that constitutes the battery container to form the negative electrode. In this case, if lithium pieces that match the shape of the inner surface of the sealing can are punched out of a lithium sheet and attached to the inner surface of the sealing can, for example, if the inner surface of the sealing can is circular or elliptical, it is difficult to punch out the lithium pieces from the lithium sheet without loss.

[0003] Therefore, in Patent Document 1, polygonal lithium pieces are punched out from a lithium sheet so that at least one side of adjacent lithium pieces is common, and then the pieces are placed on the inner surface of a sealed can and pressure-molded to produce a lithium negative electrode that matches the inner surface shape of the sealed can. In Patent Document 1, the above-mentioned method makes it possible to punch out the lithium pieces without loss.

[0004] On the other hand, in order to improve the storage and discharge characteristics of batteries, aluminum foil has also been attached to the surface of the positive electrode side of lithium metal to form a lithium-aluminum alloy layer. Patent Document 2 proposes that, in order to eliminate aluminum foil punching loss, a sheet-like laminate formed by layering aluminum foil on a lithium sheet is punched into a polygonal shape, the resulting polygonal laminate is placed on the inner surface of a sealed can, and then pressure-molded to deform the lithium in the laminate to a shape that matches the inner surface shape of the sealed can. In this process, the aluminum foil remains on the lithium without deformation, so a laminate with a polygonal aluminum foil of smaller area is formed on the lithium layer. Assembling a battery using this laminate results in a flat battery having a negative electrode in which a lithium-aluminum alloy of smaller area is formed on the positive electrode side surface of the lithium layer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 6-30250 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-246014 Summary of the Invention [Problem to be solved by the invention]

[0006] When the area of ​​the aluminum foil placed on the lithium layer is smaller than the area of ​​the lithium layer, a lithium-aluminum alloy is formed on the lithium layer where the lithium layer is in contact with the aluminum foil, but it is difficult to form a lithium-aluminum alloy in areas where there is no aluminum foil on the lithium layer and the lithium layer is exposed. Therefore, the effect of improving the storage characteristics and discharge characteristics by forming a lithium-aluminum alloy layer is limited compared to when a lithium-aluminum alloy is formed over the entire lithium layer.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a flat nonaqueous electrolyte battery with excellent discharge characteristics and a method for manufacturing the flat nonaqueous electrolyte battery with high productivity. [Means for solving the problem]

[0008] The flat nonaqueous electrolyte battery of the present invention comprises a battery container formed by sealing the opening of an outer can with a sealable can via a gasket, and filled with a positive electrode and a negative electrode stacked together with a separator interposed therebetween, and a nonaqueous electrolyte; the negative electrode has a lithium layer, and a lithium-aluminum alloy layer having an area larger than that of the lithium layer is formed on the separator side of the lithium layer; the lithium layer is contained within the sealable can; and the positive electrode is contained within the outer can; the gasket has a base portion whose bottom surface is located on the inner bottom surface side of the outer can, and inner and outer walls rising from the base portion toward the sealable can, with a gap provided between the inner wall and the outer wall, and the peripheral wall of the sealable can, the outer periphery of the separator, and the outer periphery of the lithium-aluminum alloy layer being inserted into the gap.

[0009] The flat nonaqueous electrolyte battery of the present invention comprises: a step (A) of forming a lithium layer by molding a lithium piece; and a step (B) of using aluminum foil and a separator punched to have an area larger than the lithium layer, arranging the lithium layer so that it is in contact with the inner surface of a sealed can; overlapping the aluminum foil and the separator on the lithium layer so that the aluminum foil is in contact with the lithium layer and the separator is in contact with the surface of the aluminum foil opposite to the surface of the aluminum foil facing the lithium layer; placing a positive electrode between the surface of the separator opposite to the surface facing the aluminum foil and the inner surface of an outer can; and sealing the battery together with a nonaqueous electrolyte in a battery container; and the battery can be produced by the manufacturing method of the present invention, in which in step (B), the peripheral wall of the sealed can, the outer periphery of the aluminum foil, and the outer periphery of the separator are inserted into gaps between the inner and outer walls of a gasket. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a flat nonaqueous electrolyte battery having excellent discharge characteristics and a method for manufacturing the flat nonaqueous electrolyte battery with high productivity. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of a flat nonaqueous electrolyte battery of the present invention. [Figure 2] FIG. 2 is an enlarged view of a main part of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] Fig. 1 shows a cross-sectional view schematically illustrating one example of a flat nonaqueous electrolyte battery of the present invention, and Fig. 2 shows an enlarged view of a main portion of Fig. 1. In the flat nonaqueous electrolyte battery 1 shown in Fig. 1 and Fig. 2, a positive electrode 2, a negative electrode 3, a separator 4 interposed between the positive electrode 2 and the negative electrode 3, and a nonaqueous electrolyte (not shown) are enclosed in a battery container formed by an outer can 5, a sealing can 6, and a resin gasket 7 interposed between them.

[0013] The sealing can 6 is fitted into the opening of the outer can 5 via a gasket 7, and the open end of the outer can 5 is tightened inward, causing the gasket 7 to abut against the sealing can 6, thereby sealing the opening of the outer can 5 and creating an airtight structure inside the battery.

[0014] The gasket 7 has a base portion 71 arranged on the inner bottom surface side of the outer can 5, and an inner wall 72 (a wall portion located more inward of the battery container) and an outer wall 73 (a wall portion located more outward of the battery container) that rise from the base portion 71 toward the sealing can 6 side, and a gap is provided between the inner wall 72 and the outer wall 73, and the peripheral wall of the sealing can 6 is inserted into this gap.

[0015] The negative electrode 3 has a lithium layer 31, and a lithium-aluminum alloy layer 32 having an area larger than that of the lithium layer 31 is formed on the separator 4 side of the lithium layer 31. In addition, the separator 4 having an area larger than that of the lithium layer 31 of the negative electrode 3 is disposed between the negative electrode 3 (lithium-aluminum alloy layer 32) and the positive electrode 2.

[0016] The positive electrode 2 is accommodated in an outer can 5 of the battery container and is in contact with the inner surface of the outer can 5, and the lithium layer 31 of the negative electrode 3 is accommodated in a sealing can 6 of the battery container and is in contact with the inner surface of the sealing can 6. Therefore, the outer can 5 also serves as a positive electrode terminal when electrically connecting the flat nonaqueous electrolyte battery 1 to an external device. The sealing can 6 also serves as a negative electrode terminal when electrically connecting the flat nonaqueous electrolyte battery 1 to an external device.

[0017] In the flat nonaqueous electrolyte battery 1 shown in FIGS. 1 and 2, the outer periphery of the lithium-aluminum alloy layer 32 and the outer periphery of the separator 4 are inserted into the gap between the inner wall 72 and the outer wall 73, and neither is in a flat state. However, in the case where they are not flat, the areas of the lithium-aluminum alloy layer 32 and the separator 4 mentioned above refer to the areas when they are in a flat state.

[0018] The lithium-aluminum alloy layer of the negative electrode is formed by combining a lithium layer and an aluminum foil in a battery container and bringing them into contact with a nonaqueous electrolyte, but if an aluminum foil with a larger area than the lithium layer is used, lithium diffuses not only to the areas of the aluminum foil that contact the lithium layer but also to areas that protrude outward from the lithium layer, so that the introduced aluminum foil itself becomes a lithium-aluminum alloy layer. As a result, the area of ​​the lithium-aluminum alloy layer becomes larger than the area of ​​the lithium layer, and the lithium-aluminum alloy layer is present on the entire surface of the lithium layer (the surface on the lithium-aluminum alloy layer side), making it possible to improve the discharge characteristics and storage characteristics of a flat nonaqueous electrolyte battery.

[0019] Furthermore, since the area of ​​the lithium-aluminum alloy layer is larger than the area of ​​the lithium layer, even if some misalignment occurs when placing the aluminum foil on the lithium layer, the entire surface of the lithium layer can be in contact with the aluminum foil, and therefore the lithium-aluminum alloy layer can be present on the entire surface of the lithium layer.

[0020] Therefore, a flat nonaqueous electrolyte battery manufactured by the manufacturing method of the present invention, i.e., a flat nonaqueous electrolyte battery of the present invention having a negative electrode in which a lithium-aluminum alloy layer having an area larger than that of the lithium layer is formed on the separator side of the lithium layer, has excellent discharge characteristics (and also excellent storage characteristics).The manufacturing method of the present invention makes it possible to manufacture flat nonaqueous electrolyte batteries having such excellent characteristics with high productivity.

[0021] For example, when an aluminum foil having a larger area than the lithium layer is used during the manufacture of a flat nonaqueous electrolyte battery, if the aluminum foil is misaligned when being superimposed on the lithium layer, the outer periphery of the aluminum foil or the lithium-aluminum alloy layer formed by the reaction may bend toward the positive electrode along the inner surface of the gasket wall facing the battery, possibly resulting in contact with the positive electrode or the outer can that also serves as the positive electrode terminal, resulting in a short circuit.

[0022] 1 and 2, in the flat nonaqueous electrolyte battery, the outer periphery of the lithium-aluminum alloy layer 32 is inserted into the gap between the inner wall 72 and the outer wall 73 of the gasket. This makes it possible to prevent the lithium-aluminum alloy layer 32 from coming into contact with the positive electrode 2 or the outer can 5, thereby improving the safety and reliability of the flat nonaqueous electrolyte battery.

[0023] In order to prevent contact between the lithium-aluminum alloy layer of the negative electrode and the positive electrode, the area of ​​the separator is usually set to be equal to or larger than that of the lithium-aluminum alloy layer. Therefore, as shown in Figures 1 and 2, when the outer periphery of the lithium-aluminum alloy layer 32 is inserted into the gap between the inner wall 72 and the outer wall 73 of the gasket, the outer periphery of the separator 4 is also inserted into the gap between the inner wall 72 and the outer wall 73 of the gasket.

[0024] For the lithium layer of the negative electrode, a lithium sheet (lithium foil or lithium alloy foil) made of lithium or a lithium alloy can be used.

[0025] Examples include a foil (lithium foil) made of Li (and unavoidable impurities) to form a lithium layer, and a foil (lithium alloy foil) made of a Li alloy containing alloy components such as Fe, Ni, Co, Mn, Cr, V, Ti, Zr, Nb, and Mo in a total amount of 40 mass% or less, preferably 10 mass% or less, and more preferably 5 mass% or less, with the remainder being Li and unavoidable impurities.

[0026] The thickness of the lithium foil or lithium alloy foil for forming the lithium layer is preferably 0.1 to 1.5 mm.

[0027] The aluminum foil for forming the lithium-aluminum alloy layer of the negative electrode may be a foil made of Al (and unavoidable impurities), or a foil (aluminum alloy foil) made of an Al alloy containing alloy components such as Fe, Ni, Co, Mn, Cr, V, Ti, Zr, Nb, and Mo, with the balance being Al and unavoidable impurities (the content of the alloy components is, for example, 50 mass % or less in total, preferably 10 mass % or less, and more preferably 5 mass % or less).

[0028] The thickness of the aluminum foil used in the negative electrode may be within a range that can satisfactorily ensure the effects of forming a lithium-aluminum alloy layer, and is, for example, preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more.

[0029] The thicker the aluminum foil used, the lower the capacity per volume of the negative electrode. Furthermore, if the aluminum foil is too thick, cracks in the lithium-aluminum alloy layer formed will become deeper, and there is a risk that the lithium-aluminum alloy will fall off from the negative electrode when subjected to large vibrations. Therefore, the thickness of the aluminum foil used is preferably 20 μm or less, more preferably 15 μm or less.

[0030] The aluminum foil in contact with the lithium layer electrochemically reacts with lithium during or after the process of sealing the battery container together with a nonaqueous electrolyte, forming a lithium-aluminum alloy layer on the surface of the lithium layer. The lithium from the lithium layer also diffuses to a certain extent in the portion of the aluminum foil located outside the lithium layer, forming a lithium-aluminum alloy layer.

[0031] The area of ​​the aluminum foil used in the negative electrode is preferably 105% or more of the area of ​​the lithium layer, more preferably 110% or more, and even more preferably 115% or more. By setting the area of ​​the aluminum foil as described above, even if there is some misalignment in the placement position of the aluminum foil, the entire surface of the lithium layer can be covered with the aluminum foil, and therefore the entire surface of the lithium layer on the lithium-aluminum alloy layer side can be covered with the lithium-aluminum alloy layer. In this case, the aluminum foil existing outside the lithium layer is converted to a lithium-aluminum alloy to the extent that lithium can diffuse, so the area of ​​the lithium-aluminum alloy layer is larger than the area of ​​the lithium layer. Therefore, the area of ​​the lithium-aluminum alloy layer in the negative electrode is also preferably 105% or more of the area of ​​the lithium layer, more preferably 110% or more, and even more preferably 115% or more.

[0032] Even if the area of ​​the lithium-aluminum alloy layer is increased, its outer periphery can be inserted into the gap between the inner and outer walls of the gasket as shown in Figures 1 and 2 to prevent short circuits due to contact with the positive electrode or the outer can. However, if the area is increased too much, the inner wall of the gasket will be interposed between the lithium-aluminum alloy layer and the positive electrode, resulting in a large area that is less likely to participate in the battery reaction. Therefore, the area of ​​the lithium-aluminum alloy layer is preferably 170% or less, more preferably 150% or less, of the area of ​​the lithium layer. Furthermore, the area of ​​the aluminum foil for forming the lithium-aluminum alloy layer is preferably 170% or less, more preferably 150% or less, of the area of ​​the lithium layer.

[0033] The negative electrode may be composed of a lithium layer and a lithium-aluminum alloy layer, and may further include a current collector as necessary.

[0034] Examples of negative electrode current collectors include those made of copper, nickel, iron, and stainless steel, and examples of their forms include plain woven wire mesh, expanded metal, lath mesh, punched metal, metal foam, and foil (plate). The thickness of the current collector is preferably, for example, 5 to 100 μm. It is also desirable to apply a paste-like conductive material such as carbon paste or silver paste to the surface of such a current collector.

[0035] The positive electrode of a flat nonaqueous electrolyte battery can be, for example, a compact obtained by molding a mixture (positive electrode mixture) containing a positive electrode active material, a conductive additive, a binder, etc. into a pellet shape, or a structure having a layer (positive electrode mixture layer) made of the positive electrode mixture on one or both sides of a current collector.

[0036] Positive electrode active materials include manganese dioxide, lithium-containing manganese oxides (e.g., LiMn3O6, and composite oxides having the same crystal structure as manganese dioxide (e.g., β-type, γ-type, or a mixed structure of β-type and γ-type) and containing 3.5% by mass or less, preferably 2% by mass or less, more preferably 1.5% by mass or less, and particularly preferably 1% by mass or less), Li aTi 5 / 3 Examples include lithium-containing composite oxides such as O4 (4 / 3≦a<7 / 3); vanadium oxide; niobium oxide; titanium oxide; sulfides such as iron disulfide; and graphite fluoride.

[0037] Examples of conductive additives for the positive electrode mixture 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.

[0038] Furthermore, examples of binders for the positive electrode mixture 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.

[0039] In the case of a molded body of a positive electrode mixture, the positive electrode can be manufactured, for example, by press-molding a positive electrode mixture prepared by mixing a positive electrode active material, a conductive additive, a binder, etc. into a predetermined shape.

[0040] Furthermore, in the case of a positive electrode having a positive electrode mixture layer and a current collector, for example, a positive electrode active material, a conductive additive, a binder, and the like are dispersed in water or an organic solvent such as N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture-containing composition (slurry, paste, etc.) (the binder may be dissolved in the solvent), which is then applied to a current collector, dried, and, if necessary, subjected to a pressing process such as a calendaring process, thereby producing the positive electrode.

[0041] However, the positive electrode is not limited to those produced by the above methods, and may be produced by other methods.

[0042] The composition of the positive electrode mixture for the positive electrode is preferably such that the amount of positive electrode active material is 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 %.

[0043] In the case of a positive electrode mixture molded body, its thickness is preferably 0.15 to 4 mm. On the other hand, in the case of a positive electrode having a positive electrode mixture layer and a current collector, the thickness of the positive electrode mixture layer (thickness per surface of the current collector) is preferably 30 to 300 μm.

[0044] When a current collector is used for the positive electrode, the current collector may be made of stainless steel such as SUS316, SUS430, or SUS444, and may be in the form of plain woven wire mesh, expanded metal, lath mesh, punched metal, metal foam, or foil (plate). The thickness of the current collector is preferably 0.05 to 0.2 mm, for example. It is also desirable to apply a paste-like conductive material such as carbon paste or silver paste to the surface of such a current collector.

[0045] The separator between the positive and negative electrodes is typically a nonwoven fabric or a microporous membrane (microporous film). Examples of suitable materials include polyolefins such as polyethylene (PE), polypropylene (PP), and ethylene-propylene copolymers. In addition, if heat resistance is required for the battery's intended use, other suitable materials include fluororesins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymers (PFA), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polybutylene terephthalate (PBT), polymethylpentene, polyamides, polyimides, aramids, and cellulose. The nonwoven fabric or microporous membrane may be made of one or more of the materials listed above. The separator may be made of a single layer of the materials listed above, or a laminated structure, for example, consisting of multiple nonwoven fabrics or microporous membranes made of different materials.

[0046] From the viewpoint of suppressing a decrease in the energy density of the battery, the thickness of the separator may be, for example, 500 μm or less, preferably 450 μm or less, and more preferably 300 μm or less. However, if the separator is too thin, the function of preventing short circuits may be reduced, so when a nonwoven fabric is used, the thickness may be, for example, 30 μm or more, preferably 100 μm or more, and more preferably 150 μm or more. Furthermore, when a microporous membrane is used, the thickness is preferably 10 μm or more, and more preferably 15 μm or more.

[0047] The area of ​​the separator is appropriately set to match the areas of the negative electrode and positive electrode from the viewpoint of reliably insulating them. For example, in relation to the area of ​​the lithium layer, the area is preferably 105% or more of the area of ​​the lithium layer, more preferably 110% or more, even more preferably 115% or more, and preferably 170% or less, and more preferably 150% or less. In relation to the area of ​​the positive electrode, the area of ​​the separator is preferably 105% or more of the area of ​​the positive electrode, more preferably 120% or more, and preferably 170% or less, and more preferably 160% or less. As will be described later, when a flat nonaqueous electrolyte battery is manufactured using a laminate of aluminum foil and a separator, the area of ​​the separator is approximately equal to the area of ​​the aluminum foil. In this case, if a lithium-aluminum alloy is formed on the entire surface of the aluminum foil to be introduced into the battery, the area of ​​the separator will be approximately equal to the area of ​​the lithium-aluminum alloy layer.

[0048] Non-aqueous electrolytes for flat non-aqueous electrolyte batteries include those prepared by dissolving electrolytes such as LiPF, LiBF, LiClO, and LiCFSO in an organic solvent. Examples of such organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; linear carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; 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; cyclic esters such as γ-butyrolactone; and mononitriles such as acetonitrile and propionitrile. One or more of these organic solvents can be used. Combinations of the carbonates and ethers are particularly preferred.

[0049] When a carbonate and an ether are used in combination as the non-aqueous electrolyte solvent, the ratio (mixing ratio) of the carbonate to the ether in the total solvent is preferably carbonate:ether=30:70 to 70:30 by volume.

[0050] The concentration of the electrolyte in the non-aqueous electrolyte is preferably 0.3 to 1.5 mol / l.

[0051] Furthermore, additives can be added to the non-aqueous electrolyte as needed to improve storage characteristics at high temperatures, etc. Usable additives include saturated sultone compounds such as 1,3-propane sultone and 1,4-butane sultone; unsaturated sultone compounds such as 1,3-propene sultone; acid anhydrides such as maleic anhydride and phthalic anhydride; organoboron lithium salts such as LiB(C2O4)2; and dinitriles such as malononitrile, succinonitrile, glutaronitrile, and adiponitrile; and one or more of these can be used.

[0052] The content of the additive in the non-aqueous electrolyte is, for example, preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and particularly preferably 0.5% by mass or more. On the other hand, if the content of the additive is too high, the internal resistance of the battery may increase and the effect of improving the discharge characteristics may be reduced, so the content of the additive in the non-aqueous electrolyte is preferably 3% by mass or less, more preferably 2% by mass or less, and particularly preferably 1.5% by mass or less.

[0053] As shown in Figures 1 and 2, flat-type nonaqueous electrolyte batteries use battery containers (including those called button-shaped and coin-shaped) that combine a metal can (external can) with an opening and a lid (sealing can) and then crimp-seal them with a gasket.

[0054] The outer can and sealing can can be made of stainless steel, etc. The gasket can be made of polypropylene, nylon, etc., or, if heat resistance is required for the flat non-aqueous electrolyte battery's intended use, heat-resistant resins with melting points above 240°C, such as fluororesin (e.g., tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA)), polyphenylene ether (PPE), polysulfone (PSF), polyarylate (PAR), polyethersulfone (PES), polyphenylene sulfide (PPS), and polyetheretherketone (PEEK), can also be used.

[0055] The shortest distance between the sealing can and the upper end of the inner wall of the gasket (in the case of the flat nonaqueous electrolyte battery 1 shown in FIG. 2, the length a indicated by the arrow in the figure) is preferably 0.15 mm or more, from the viewpoint of enabling the peripheral wall of the sealing can, the outer periphery of the separator, and the outer periphery of the lithium-aluminum alloy layer to be more reliably inserted into the gap between the inner and outer walls of the gasket. There is no particular upper limit to the shortest distance between the sealing can and the upper end of the inner wall of the gasket, but if it is too long, the proportion of the area occupied by the electrodes, which are the power generating elements, in the internal volume of the battery container will decrease, which may result in a decrease in the energy density of the battery. Therefore, the upper limit is usually 1.0 mm or less.

[0056] The flat non-aqueous electrolyte battery can be produced, for example, by the following production method including the steps of (A) forming a lithium layer and (B) assembling the battery.

[0057] In step (A), lithium pieces cut from a lithium sheet are shaped to form a lithium layer. When cutting lithium pieces from a lithium sheet, for example, if lithium pieces that are circular in plan view are cut, waste portions that cannot be used as lithium pieces will be generated between adjacent lithium pieces. However, if the lithium pieces are cut into a polygonal shape (such as a square or hexagon), it is possible to eliminate most of the waste portions between adjacent lithium pieces. Therefore, by adopting this step, battery productivity can be further improved. Then, the lithium pieces cut into a polygonal shape are shaped to fit the shape of a battery container by applying pressure or the like to form a lithium layer. For example, when a battery container having an outer can and a sealed can is used, the lithium pieces can be placed inside the sealed can and pressed to shape the lithium pieces to fit the shape of the inner bottom surface of the sealed can, thereby forming a lithium layer.

[0058] In step (B), aluminum foil and a separator punched to have an area larger than the lithium layer are used, and the lithium layer is arranged so as to be in contact with the inner surface of a sealed can. The aluminum foil and the separator are then placed on top of the lithium layer so that the aluminum foil is in contact with the lithium layer and the separator is in contact with the surface of the aluminum foil opposite to the surface of the aluminum foil facing the lithium layer. A positive electrode is placed between the surface of the separator opposite to the aluminum foil side and the inner surface of the outer can, and the resultant is sealed in a battery container together with a nonaqueous electrolyte to obtain a flat nonaqueous electrolyte battery.

[0059] When punching out the aluminum foil and the separator, they may be punched out individually, but the aluminum foil required to form the lithium-aluminum alloy layer is usually very thin, and it is not easy to cut the aluminum foil alone into a shape corresponding to the lithium layer after molding, or to accurately align and place the cut aluminum foil on the lithium layer, due to its insufficient strength.

[0060] Therefore, when manufacturing a flat non-aqueous electrolyte battery, it is preferable to cut the aluminum foil to be overlaid on the lithium layer in the state of a laminate overlaid with a separator. This allows the aluminum foil, which has low strength, to be cut while being reinforced by the separator, making it easier to cut the aluminum foil into a desired shape, thereby further improving the productivity of the aluminum foil used in the negative electrode and, ultimately, the productivity of flat non-aqueous electrolyte batteries.

[0061] When forming a laminate of aluminum foil and a separator, the aluminum foil and the separator may be simply stacked on top of each other, or may be integrated by pressure bonding or the like.

[0062] By punching out the aluminum foil and the separator so that their areas are larger than the area of ​​the lithium layer, the surface of the lithium layer can be completely covered with the aluminum foil, and the area of ​​the lithium-aluminum alloy layer can be maximized after the flat nonaqueous electrolyte battery is formed.

[0063] When a laminate of aluminum foil and a separator is punched for use, the area of ​​the aluminum foil and the area of ​​the separator in the punched laminate are approximately equal. Therefore, in a flat nonaqueous electrolyte battery obtained using this laminate, if the range in which lithium can diffuse extends over the entire aluminum foil, the area of ​​the lithium-aluminum alloy layer derived from the aluminum foil and the area of ​​the separator will be approximately equal, even if some change in area during alloying is taken into account.

[0064] The punched aluminum foil and separator, positive electrode, and lithium layer are then arranged in this order: lithium layer, aluminum foil, separator, positive electrode, and then sealed in a battery container together with a nonaqueous electrolyte to obtain a flat nonaqueous electrolyte battery. At this time, the aluminum foil electrochemically reacts with the lithium in the lithium layer in the presence of the nonaqueous electrolyte to form a lithium-aluminum alloy layer.

[0065] When each component is enclosed in the battery container, the outer periphery of the aluminum foil and the outer periphery of the separator are inserted into the gap between the inner and outer walls of the gasket together with the peripheral wall of the sealing can, as described above. In a battery having such a configuration, the lithium-aluminum alloy layer will have an uneven portion, but the area comparison with the lithium layer is performed using the area when the lithium-aluminum alloy layer is made in a flat state as a whole, as described above.

[0066] The flat nonaqueous electrolyte battery of the present invention is primarily in the form of a primary battery, but can also be in the form of a secondary battery, and can be used in a variety of applications in which conventionally known nonaqueous electrolyte primary batteries and nonaqueous electrolyte secondary batteries are used. [Example]

[0067] The present invention will be described in detail below based on examples, but the following examples do not limit the present invention.

[0068] Example 1 <Preparation of positive electrode> A positive electrode mixture was prepared by mixing manganese dioxide, which is a positive electrode active material, carbon black, which is a conductive additive, and PTFE, which is a binder, in a mass ratio of 90:5:5. The positive electrode mixture was then molded to obtain a positive electrode (positive electrode mixture molded body) with a diameter of 15.4 mm and a thickness of 1.8 mm.

[0069] <Lithium layer formation> The lithium pieces punched into square shapes were placed inside a circular stainless steel sealed can and pressed to form a roughly circular shape in plan view, forming a lithium layer with a diameter of 15.5 mm and a thickness of 1.2 mm.

[0070] <Formation of a laminate of aluminum foil and separator> A laminate obtained by laminating an aluminum foil having a thickness of 9 μm and a separator (nonwoven fabric made of polymethylpentene) having a thickness of 320 μm was punched into a circle having a diameter of 19.2 mm. The ratio of the area of ​​the aluminum foil and the separator to the area of ​​the lithium layer was 153%.

[0071] <Assembly of flat non-aqueous electrolyte primary batteries> A nonaqueous electrolyte solution was prepared by dissolving LiClO4 at a concentration of 0.5 mol / L in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 1:1, and then adding 2% by mass of 1,3-propane sultone. A lithium layer was inserted into the sealed can, which had the laminate placed on top of the lithium layer. A PPS gasket was attached to the sealed can, and the nonaqueous electrolyte solution and the positive electrode were sealed inside a battery container formed by fitting the sealed can and a stainless steel outer can together, to obtain a flat nonaqueous electrolyte primary battery with a structure similar to that shown in Figures 1 and 2. 1 and 2, the gasket used had a base portion located on the inner bottom surface side of the outer can, and inner and outer walls rising from the base portion toward the sealed can side, and when assembling the flat nonaqueous electrolyte primary battery, the outer periphery of the aluminum foil and the outer periphery of the separator were inserted into the gap between the inner and outer walls of the gasket together with the peripheral wall of the sealed can. The laminate was positioned so that the aluminum foil side faced the lithium layer side.

[0072] In the resulting flat-type non-aqueous electrolyte primary battery, the area of ​​the formed lithium-aluminum alloy layer was approximately the same as the area of ​​the original aluminum foil, and the shortest distance between the sealing can and the inner wall of the gasket was 0.20 mm.

[0073] Comparative Example 1 A flat nonaqueous electrolyte primary battery was fabricated in the same manner as in Example 1, except that, instead of a laminate of aluminum foil and a separator, a piece of aluminum foil with a thickness of 9 mm punched out into a circle with a diameter of 10 mm was placed on the lithium layer placed in the sealed can, and a separator (nonwoven fabric made of polymethylpentene) punched out into a circle with a diameter of 19.2 mm was placed on top of this aluminum foil, and the outer periphery of the separator was not inserted into the gap between the inner wall and outer wall of the gasket.

[0074] The ratio of the area of ​​the lithium-aluminum alloy layer to the area of ​​the lithium layer was 42%, which was almost the same as the area of ​​the original aluminum foil. Thus, in the battery of Comparative Example 1, the aluminum foil was made smaller in size, so its outer periphery could not be inserted into the gap between the inner and outer walls of the gasket.

[0075] Comparative Example 2 A flat non-aqueous electrolyte primary battery was fabricated in the same manner as in Example 1, except that the outer periphery of the aluminum foil and the outer periphery of the separator were not inserted into the gap between the inner and outer walls of the gasket.

[0076] The flat nonaqueous electrolyte primary batteries of the Examples and Comparative Examples were evaluated as follows.

[0077] (Discharge characteristic evaluation) The flat nonaqueous electrolyte primary batteries of the Examples and Comparative Examples were discharged at room temperature to an electrical capacity of 120 mAh, and then the batteries were placed in a thermostatic chamber at −40° C. After the battery temperature had dropped, the batteries were discharged at a current value of 10 mA, and the discharge voltage [closed circuit voltage (CCV)] of the batteries 10 ms after the start of discharge was measured to evaluate the discharge characteristics at low temperatures.

[0078] (Short circuit resistance evaluation) For 100 flat non-aqueous electrolyte primary batteries of each Example and Comparative Example, after fabrication, they were stored at room temperature for 3 days, and then the open circuit voltage (OCV) was measured. Batteries with an OCV of less than 3.0 V were considered to have short-circuited, and the number of such batteries was counted.

[0079] These results are shown in Table 1.

[0080] [Table 1]

[0081] As shown in Table 1, the flat nonaqueous electrolyte primary battery of Example 1, which had a negative electrode with a lithium-aluminum alloy layer having an area larger than that of the lithium layer, and in which the outer periphery of the lithium-aluminum alloy layer and the outer periphery of the separator were inserted into the gap between the inner and outer walls of the gasket together with the peripheral wall of the sealing can, had a high CCV at low temperatures and excellent discharge characteristics. Furthermore, in Example 1, no short circuits were observed in any of the 100 batteries produced, demonstrating that highly reliable batteries could be produced with excellent productivity.

[0082] In contrast, in the battery of Comparative Example 1, in which the area of ​​the lithium-aluminum alloy layer was reduced by reducing the size of the aluminum foil overlapping the lithium layer, no short circuits were observed in 100 batteries produced, but the CCV at low temperatures was low and the discharge characteristics were poor. Also, in the battery of Comparative Example 2, in which the outer periphery of the lithium-aluminum alloy layer and the outer periphery of the separator were not inserted into the gap between the inner and outer walls of the gasket, the discharge characteristics were equivalent to those of the battery of Example 1, but short circuits were observed in 45 of the 100 batteries produced, indicating poor productivity. [Explanation of symbols]

[0083] 1 Flat nonaqueous electrolyte battery 2 Positive electrode 3 negative electrode 4 Separator 5 Outer can 6 Sealed cans 7 Gasket 71 Base 72 Inner wall 73 Exterior Wall

Claims

1. A flat nonaqueous electrolyte battery is formed by sealing the opening of an outer can with a sealing can via a gasket, and the battery container is filled with a positive electrode and a negative electrode stacked with a separator interposed therebetween, and a nonaqueous electrolyte, the negative electrode has a lithium layer, a lithium-aluminum alloy layer having an area larger than that of the lithium layer is formed on the separator side of the lithium layer; the lithium layer is accommodated in the sealed can, and the positive electrode is accommodated in the outer can; the gasket has a base portion whose bottom surface is located on the inner bottom surface side of the outer can, and an inner wall and an outer wall rising from the base portion toward the sealed can side, a gap is provided between the inner wall and the outer wall, and the peripheral wall of the sealed can, the outer periphery of the separator, and the outer periphery of the lithium-aluminum alloy layer are inserted into the gap.

2. 2. The flat nonaqueous electrolyte battery according to claim 1, wherein the shortest distance between the sealing can and the upper end of the inner wall of the gasket is 0.15 mm or more.

3. 2. The flat nonaqueous electrolyte battery according to claim 1, wherein the area of ​​said lithium-aluminum alloy layer is 105% or more of the area of ​​said lithium layer.

4. 2. The flat nonaqueous electrolyte battery in accordance with claim 1, wherein the area of ​​said lithium-aluminum alloy layer is approximately equal to the area of ​​said separator.

5. 2. The flat nonaqueous electrolyte battery according to claim 1, wherein the area of ​​said separator is 105 to 170% of the area of ​​said lithium layer.

6. 2. The flat nonaqueous electrolyte battery according to claim 1, wherein the area of ​​the separator is 105 to 170% of the area of ​​the positive electrode.

7. A method for manufacturing the flat nonaqueous electrolyte battery according to any one of claims 1 to 6, comprising: Step (A) of forming a lithium layer by molding lithium pieces; and (B) using an aluminum foil and a separator punched to have an area larger than that of the lithium layer, and arranging the lithium layer so that it is in contact with the inner surface of a sealed can, and arranging the aluminum foil and the separator on the lithium layer so that the aluminum foil is in contact with the lithium layer and the separator is in contact with the surface of the aluminum foil opposite to the surface of the aluminum foil on which the lithium layer is located, and disposing a positive electrode between the surface of the separator opposite to the surface on which the aluminum foil is located and the inner surface of an outer can, and sealing the positive electrode together with a nonaqueous electrolyte in a battery container, a method for manufacturing a flat nonaqueous electrolyte battery, wherein in the step (B), the peripheral wall of the sealing can, the outer periphery of the aluminum foil, and the outer periphery of the separator are inserted into a gap between the inner wall and the outer wall of a gasket.

8. 8. The method for producing a flat nonaqueous electrolyte battery according to claim 7, wherein the aluminum foil and the separator used in step (B) are prepared by laminating the aluminum foil and the separator together, and then punching the laminate into a piece having an area larger than that of the lithium layer.

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