Secondary battery and method for manufacturing the same

Abstract

The present invention provides a secondary battery with high energy density and capacity, excellent cycle characteristics, and high productivity. The present invention relates to a secondary battery comprising: a laminate formed by alternately bending a sheet comprising a negative electrode without a negative electrode active material and a separator or solid electrolyte disposed on both sides of the negative electrode multiple times at acute angles; and a plurality of positive electrodes disposed in gaps formed between the separators or solid electrolytes, which are disposed opposite each other by bending the sheet.

Description

Technical Field

[0001] The present invention relates to a secondary battery and a method for manufacturing the same. Background Art

[0002] In recent years, technologies that convert natural energy such as sunlight and wind into electrical energy have attracted much attention. Consequently, various batteries have been developed as safe and energy-storage devices capable of storing large amounts of electrical energy.

[0003] Among them, secondary batteries that are known to be charged and discharged by moving metal ions between the positive electrode and the negative electrode exhibit high voltage and high energy density. Typically, lithium-ion secondary batteries are known. As a typical lithium-ion secondary battery, an active material capable of retaining lithium is introduced into the positive electrode and the negative electrode, and charging and discharging are performed by giving and accepting lithium ions between the positive electrode active material and the negative electrode active material. In addition, as a secondary battery that does not use an active material at the negative electrode, a lithium metal secondary battery has been developed that retains lithium by precipitating lithium metal on the negative electrode surface.

[0004] For example, Patent Document 1 discloses a high-energy-density, high-output lithium metal anode secondary battery having a volumetric energy density exceeding 1000 Wh / L and / or a mass energy density exceeding 350 Wh / kg when discharged at a rate of at least 1 C at room temperature. Patent Document 1 discloses that an extremely thin lithium metal anode is used to realize such a lithium metal anode secondary battery.

[0005] Patent Document 2 also discloses a lithium secondary battery comprising a positive electrode, a negative electrode, a separator sandwiched between them, and an electrolyte. The negative electrode comprises metal particles formed on a negative electrode current collector. During charging, these particles migrate from the positive electrode to form lithium metal on the negative electrode current collector within the negative electrode. Patent Document 2 discloses a lithium secondary battery that addresses issues arising from the reactivity of lithium metal and problems encountered during assembly, while also improving performance and lifespan.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application No. 2019-517722

[0009] Patent Document 2: Japanese Patent Application No. 2019-537226 Summary of the Invention

[0010] However, when the present inventors conducted detailed studies on conventional secondary batteries including those described in the above-mentioned documents, they found that there were deficiencies in at least one of energy density, capacity, cycle characteristics, and productivity.

[0011] For example, since the negative electrode of the lithium metal secondary battery described in the above patent document, which retains lithium by precipitating lithium metal on the negative electrode surface, does not have a negative electrode active material, although the energy density is high, the negative electrode of such a lithium metal secondary battery is very thin and difficult to handle, so mass production technology has not yet been established. For example, in order to increase the capacity or output voltage of the battery, when using the automatic lamination device used in the past to stack multiple positive electrodes, negative electrodes, and separators arranged between the positive and negative electrodes, due to the very thin negative electrode, fine wrinkles are generated on the negative electrode, and the cycle characteristics of the resulting secondary battery are reduced. Therefore, the lithium metal secondary battery described in the above patent document must be produced manually, which reduces productivity.

[0012] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a secondary battery having high energy density and capacity, excellent cycle characteristics, and high productivity, and a method for producing the same.

[0013] A secondary battery according to one embodiment of the present invention comprises: a laminate formed by alternately bending a sheet having a negative electrode without a negative electrode active material and separators arranged on both sides of the negative electrode at acute angles multiple times; and a plurality of positive electrodes, each arranged in each gap formed between the separators facing each other by bending the above-mentioned sheet.

[0014] Since such a secondary battery has a negative electrode without a negative electrode active material, charging and discharging are performed by precipitation of metal on the surface of the negative electrode and dissolution of the precipitated metal. In addition, the above-mentioned secondary battery has a laminated structure of multiple positive electrodes, negative electrodes, and separators arranged between the positive and negative electrodes. As a result, the above-mentioned secondary battery has high energy density and capacity. In addition, compared with the negative electrode without a negative electrode active material, which is very thin and difficult to handle, the above-mentioned sheet having a negative electrode and separators arranged on both sides of the negative electrode has a thickness and mechanical strength that makes it easy to handle. As a result, the above-mentioned secondary battery can be automatically manufactured using an automatic lamination device without causing breakage or distortion in the negative electrode, and has excellent cycle characteristics and productivity.

[0015] A secondary battery according to one embodiment of the present invention comprises: a laminate formed by alternately bending a sheet having a negative electrode without a negative electrode active material and a solid electrolyte arranged on both sides of the negative electrode at acute angles multiple times; and a plurality of positive electrodes, each arranged in each gap formed between the solid electrolytes facing each other by bending the above-mentioned sheet.

[0016] Since such a secondary battery has a negative electrode without a negative electrode active material, charging and discharging are performed by precipitation of metal on the surface of the negative electrode and dissolution of the precipitated metal. In addition, the above-mentioned secondary battery has a laminated structure of multiple positive electrodes, negative electrodes and a solid electrolyte disposed between the positive electrode and the negative electrode. As a result, the energy density and capacity of the above-mentioned secondary battery are high. In addition, compared with the negative electrode without a negative electrode active material, which is very thin and difficult to handle, the above-mentioned sheet having a negative electrode and a solid electrolyte disposed on both sides of the negative electrode has a thickness and mechanical strength that is easy to handle. As a result, the above-mentioned secondary battery can be automatically manufactured using an automatic lamination device without causing breakage or distortion in the negative electrode, and has excellent cycle characteristics and productivity.

[0017] The secondary battery is preferably a lithium secondary battery that is charged and discharged by the deposition of lithium metal on the surface of the negative electrode and the dissolution of the deposited lithium. This embodiment further increases the energy density.

[0018] The negative electrode is preferably an electrode consisting of at least one selected from the group consisting of Cu, Ni, Ti, Fe, other metals that do not react with Li, their alloys, and stainless steel (SUS). According to this method, since highly flammable lithium metal can be omitted during manufacturing, safety and productivity are further improved. In addition, since such a negative electrode is stable, the cycle characteristics of the secondary battery are further improved.

[0019] The secondary battery preferably has no lithium foil formed on the surface of the negative electrode before initial charging. This configuration eliminates the need for using highly flammable lithium metal during manufacturing, resulting in improved safety and productivity.

[0020] The positive electrode is preferably positioned at a distance of 0.01 mm to 5.00 mm from the end of the bent portion of the sheet. This configuration allows the positive and negative electrodes to face each other with a suitable area via a separator or solid electrolyte, thereby further increasing energy density and capacity.

[0021] The average thickness of the negative electrode is preferably 4 μm or more and 20 μm or less. According to this embodiment, since the volume occupied by the negative electrode in the secondary battery is reduced, the energy density of the secondary battery is further improved.

[0022] The secondary battery preferably has an energy density of 350 Wh / kg or more.

[0023] The positive electrode may include a positive electrode active material.

[0024] A method for manufacturing a secondary battery according to one embodiment of the present invention includes: a process of preparing a sheet having a negative electrode without a negative electrode active material and separators arranged on both sides of the negative electrode; and a process of forming a formed body, wherein the formed body includes a laminate formed by alternately bending the above-mentioned sheet at acute angles multiple times and a plurality of positive electrodes respectively arranged in each gap formed between the separators opposite to each other by bending the above-mentioned sheet.

[0025] According to such a manufacturing method, since a negative electrode without a negative electrode active material is used, it is possible to manufacture a secondary battery that is charged and discharged by the precipitation of metal on the surface of the negative electrode and the dissolution of the precipitated metal. In addition, the secondary battery obtained by the above-mentioned manufacturing method has a laminated structure of multiple positive electrodes, negative electrodes and separators arranged between the positive and negative electrodes. As a result, the secondary battery obtained by the above-mentioned manufacturing method has high energy density and capacity. In addition, compared to the negative electrode without a negative electrode active material, which is very thin and difficult to handle, the sheet having a negative electrode and separators arranged on both sides of the negative electrode has a thickness and mechanical strength that makes it easy to handle. As a result, since the above-mentioned manufacturing method can automatically manufacture a secondary battery without forming wrinkles on the negative electrode, a secondary battery with high cycle characteristics can be manufactured with high productivity.

[0026] A method for manufacturing a secondary battery according to one embodiment of the present invention includes: a process of preparing a sheet, wherein the sheet has a negative electrode without a negative electrode active material and a solid electrolyte arranged on both sides of the negative electrode; and a process of forming a formed body, wherein the formed body includes a laminate formed by alternately bending the above-mentioned sheet at acute angles multiple times and a plurality of positive electrodes respectively arranged in each gap formed between the solid electrolytes facing each other by bending the above-mentioned sheet.

[0027] According to such a manufacturing method, since a negative electrode without a negative electrode active material is used, it is possible to manufacture a secondary battery that is charged and discharged by the precipitation of metal on the surface of the negative electrode and the dissolution of the precipitated metal. In addition, the secondary battery obtained by the above-mentioned manufacturing method is a laminated structure having multiple positive electrodes, negative electrodes, and a solid electrolyte disposed between the positive electrode and the negative electrode. As a result, the secondary battery obtained by the above-mentioned manufacturing method has high energy density and capacity. In addition, compared to the negative electrode without a negative electrode active material, which is very thin and difficult to handle, the sheet having a negative electrode and a solid electrolyte disposed on both sides of the negative electrode has a thickness and mechanical strength that makes it easy to handle. As a result, the above-mentioned manufacturing method can automatically manufacture a secondary battery with high cycle characteristics because it can do so without forming wrinkles on the negative electrode.

[0028] The above-mentioned forming process may also include a bending process, which bends the above-mentioned sheet by pressing the first flat plate toward the above-mentioned sheet from a first direction perpendicular to the stacking direction of the above-mentioned stack, pressing the second flat plate toward the above-mentioned sheet from a second direction opposite to the above-mentioned first direction, and pressing the above-mentioned stack from the direction opposite to the stacking direction of the above-mentioned stack.

[0029] The first and second flat plates include the positive electrode and a substrate integral with the positive electrode. During the bending step, the positive electrode can be inserted into each gap formed by bending the sheet simultaneously with the sheet. This configuration makes it easier to form a laminated structure comprising the positive electrode, the negative electrode, and a separator or solid electrolyte disposed therebetween, thereby further improving productivity.

[0030] The forming step may include, after the bending step, a step of inserting the positive electrodes into the gaps formed by bending the sheet.

[0031] Effects of the Invention

[0032] According to the present invention, a secondary battery having high energy density and capacity, excellent cycle characteristics, and high productivity, and a method for producing the same can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic cross-sectional view of a secondary battery according to the first embodiment.

[0034] Figure 2 This is a schematic cross-sectional view of a conventional secondary battery.

[0035] Figure 3 It is a schematic perspective view of a secondary battery according to the first embodiment.

[0036] Figure 4 This is a flowchart showing the manufacturing process of the secondary battery according to the first embodiment.

[0037] Figure 5 This is a schematic cross-sectional view of one step of the manufacturing process of the secondary battery according to the first embodiment.

[0038] Figure 6 This is a flowchart showing another method for manufacturing the secondary battery according to the first embodiment.

[0039] Figure 7 It is a schematic perspective view of a secondary battery according to the second embodiment.

[0040] Figure 8 It is a schematic cross-sectional view of a secondary battery according to the third embodiment. DETAILED DESCRIPTION

[0041] Below, with reference to the accompanying drawings as needed, an embodiment of the present invention (hereinafter referred to as the "present embodiment") will be described in detail. In the accompanying drawings, identical elements are denoted by the same reference numerals, and duplicate descriptions are omitted. Positional relationships, such as up and down, left and right, are based on those shown in the accompanying drawings unless otherwise specified. The dimensional ratios in the accompanying drawings are not limited to those shown.

[0042] [First embodiment]

[0043] (Secondary Battery)

[0044] Figure 1 1 is a schematic cross-sectional view of a secondary battery according to the first embodiment. Figure 1 As shown, the secondary battery 100 involved in the first embodiment includes: a laminate 150, which is formed by alternately bending a sheet 130 having a negative electrode 120 without a negative electrode active material and a first separator 110a and a second separator 110b arranged on both sides of the negative electrode 120 at acute angles multiple times; and a plurality of positive electrodes 140, respectively arranged in each gap formed between the separators facing each other by bending the sheet.

[0045] (Sheet)

[0046] The sheet 130 includes a negative electrode 120 having no negative electrode active material, and a first separator 110 a and a second separator 110 b disposed on both surfaces of the negative electrode 120 .

[0047] (negative electrode)

[0048] Negative electrode 120 does not contain a negative electrode active material. Secondary batteries with negative electrodes containing a negative electrode active material have difficulty increasing their energy density due to the presence of this negative electrode active material. On the other hand, since the secondary battery 100 of this embodiment includes a negative electrode 120 without a negative electrode active material, this problem does not arise. Specifically, the secondary battery 100 of this embodiment achieves high energy density because charging and discharging are performed by metal deposition on the surface of the negative electrode 120 and dissolution of this deposited metal.

[0049] In this specification, the term "negative electrode active material" refers to a substance that is used to hold metal ions, or metals corresponding to these metal ions (hereinafter referred to as "carrier metals"), which serve as charge carriers, in the negative electrode 120 in the battery. Alternatively, it can be referred to as a host material for the carrier metal. The mechanism for such holding is not particularly limited, and examples include intercalation, alloying, and absorption of metal clusters. In this specification, the term "negative electrode active material" typically refers to a substance used to hold lithium metal or lithium ions in the negative electrode 120.

[0050] There is no particular limitation on such negative electrode active materials, and examples thereof include carbon-based materials, metal oxides, and metals or alloys. There is no particular limitation on the carbon-based materials, and examples thereof include graphene, graphite, hard carbon, mesoporous carbon, carbon nanotubes, and carbon nanohorns. There is no particular limitation on the metal oxides, and examples thereof include titanium oxide compounds, tin oxide compounds, and cobalt oxide compounds. There is no particular limitation on the metals or alloys as long as they are capable of alloying with the carrier metal, and examples thereof include silicon, germanium, tin, lead, aluminum, gallium, and alloys thereof.

[0051] As the negative electrode 120, if it does not have a negative electrode active material but can be used as a current collector, there is no particular limitation, and for example, at least one composition selected from the group consisting of Cu, Ni, Ti, Fe and other metals that do not react with Li and their alloys, and stainless steel (SUS) is listed. In addition, when SUS is used in the negative electrode 12, various types of SUS that are conventionally known can be used. The above-mentioned negative electrode materials are used alone or in combination of two or more. In addition, in this specification, "metal that does not react with Li" refers to a metal that does not react with lithium ions or lithium metal to form an alloy under the operating conditions of the secondary battery 100.

[0052] The negative electrode 120 is preferably an electrode that does not contain lithium. According to this method, since highly flammable lithium metal can be omitted during manufacturing, the safety and productivity of the secondary battery 100 are further improved. From the same point of view and from the perspective of improving the stability of the negative electrode 120, the negative electrode 120 is more preferably composed of at least one selected from the group consisting of Cu, Ni, their alloys, and stainless steel (SUS). From the same point of view, the negative electrode 120 is more preferably composed of Cu, Ni, or an alloy composed of them, and is particularly preferably composed of Cu or Ni.

[0053] In this specification, "the negative electrode does not contain a negative electrode active material" means that the content of the negative electrode active material in the negative electrode is 10% by mass or less relative to the total negative electrode. The content of the negative electrode active material in the negative electrode is preferably 5.0% by mass or less, more preferably 1.0% by mass or less, even more preferably 0.1% by mass or less, and particularly preferably 0.0% by mass or less relative to the total negative electrode. In addition, the secondary battery 100 having a negative electrode without a negative electrode active material means that the secondary battery 100 is an anode-free secondary battery, a zero-anode secondary battery, or an anode-free secondary battery in the generally used sense.

[0054] The negative electrode 120 preferably has an adhesive layer formed on its surface to enhance the adhesion between the deposited carrier metal and the negative electrode. This method further enhances the adhesion between the negative electrode 120 and the deposited metal when the carrier metal, particularly lithium metal, is deposited on the negative electrode 120. As a result, the separation of the deposited metal from the negative electrode 120 is further suppressed, further improving the cycle characteristics of the secondary battery 100.

[0055] As the bonding layer, for example, metals other than the negative electrode, their alloys, and carbon-based substances are listed. Although not intended to be limiting, examples of the bonding layer include Au, Ag, Pt, Sb, Pb, In, Sn, Zn, Bi, Al, Sb, Pb, Ni, Cu, graphene, graphite, hard carbon, mesoporous carbon, carbon nanotubes, and carbon nanohorns. The thickness of the bonding layer is not particularly limited, but is preferably between 1 nm and 300 nm, more preferably between 50 nm and 150 nm. When the bonding layer is in the above-mentioned manner, the adhesion between the negative electrode 120 and the precipitated metal can be further improved. In addition, when the bonding layer is equivalent to the above-mentioned negative electrode active material, the bonding layer is less than 10% by mass relative to the negative electrode, preferably less than 5.0% by mass, more preferably less than 1.0% by mass, and more preferably less than 0.1% by mass.

[0056] The average thickness of the negative electrode 120 is preferably 4 μm to 20 μm, more preferably 5 μm to 18 μm, and even more preferably 6 μm to 15 μm. In this manner, the volume occupied by the negative electrode 120 in the secondary battery 100 is reduced, thereby further improving the energy density of the secondary battery 100.

[0057] (Separator)

[0058] The first separator 110a is a component that prevents battery short circuits by isolating the positive electrode 140 from the negative electrode 120 and ensures ionic conductivity for metal ions, which serve as charge carriers between the positive and negative electrodes 140 and 120. It is composed of a non-conductive material that does not react with metal ions. Furthermore, when an electrolyte is used, the first separator 110a also serves to retain the electrolyte. The first separator 110a is not limited as long as it fulfills the aforementioned functions and may be composed, for example, of porous polyethylene (PE), polypropylene (PP), or a laminated structure thereof.

[0059] The first separator 110a may also be covered by a separator covering layer. The separator covering layer may cover both sides of the first separator 110a or only one side. The separator covering layer has ion conductivity and is not particularly limited as long as it is a component that does not react with metal ions that become charge carriers. It is preferably capable of firmly bonding the first separator 110a and the layer adjacent to the first separator 110a. Such a separator covering layer is not particularly limited, and examples thereof include objects containing adhesives such as polyvinylidene fluoride (PVDF), styrene-butadiene rubber-carboxymethyl cellulose composite material (SBR-CMC), polyacrylic acid (PAA), lithium polyacrylate (Li-PAA), polyimide (PI), polyamide-imide (PAI) and aramid. The separator covering layer may also add inorganic particles such as silicon, aluminum oxide, titanium dioxide, zirconium dioxide, magnesium oxide, magnesium hydroxide, etc. to the above-mentioned adhesive.

[0060] The average thickness of the first separator 110a is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less. This reduces the volume occupied by the first separator 110a in the secondary battery 100, further improving the energy density of the secondary battery 100. Furthermore, the average thickness of the first separator 110a is preferably 3 μm or greater, more preferably 5 μm or greater. This allows for more reliable isolation of the positive electrode 140 and the negative electrode 120, further minimizing battery short circuits.

[0061] The second separator 110b may be the same as or different from the first separator 110a as long as it has the above-mentioned structure as the first separator 110a. Preferred embodiments of the second separator 110b are the same as those of the first separator 110a.

[0062] (laminated body)

[0063] In the secondary battery 100, the laminate 150 has a zigzag structure (or also called a "snake-shaped folding structure") in which the sheet 130 is bent into an acute angle in a plurality of bends 160, and the bends 160 and the plane portions 170 are alternately connected toward the stacking direction Z. Here, "bending into an acute angle in the bend 160" means that the angle formed by the two plane portions 170 connected to the bend 160 is an acute angle. The laminate 150 preferably has a bend 160 in which the angle formed by the two plane portions 170 connected to the bend 160 is approximately 0 degrees. That is, the laminate 150 is preferably bent in a manner so that the adjacent plane portions 170 become approximately parallel to each other. According to this method, the number of stacking layers in the laminate 150 can be further increased.

[0064] The number of layers of the laminate 150 refers to the number of times the sheet 130 is bent, and corresponds to the number of bent portions 160. For example, a laminate 150 formed by bending the sheet 130 three times has four flat portions 170 and three bent portions 160, and the number of layers is three.

[0065] In the bent portion 160 of the laminate 150, the angle formed by the two flat portions 170 connected to the bent portion 160 may be 0 degrees or greater, 1 degree or greater, 3 degrees or greater, 5 degrees or greater, 10 degrees or greater, or 15 degrees or greater. In the bent portion 160 of the laminate 150, the angle formed by the two flat portions 170 connected to the bent portion 160 may be 40 degrees or less, 30 degrees or less, 20 degrees or less, or 18 degrees or less.

[0066] In the secondary battery 100, the number of layers is 2 or more, that is, it has a laminate having three flat portions 170 and two bent portions 160. The number of layers of the secondary battery 100 is preferably 3 or more, more preferably 5 or more, and even more preferably 10 or more. When the number of layers of the secondary battery 100 is within the above range, the capacity of the secondary battery 100 is further improved. The upper limit of the number of layers of the secondary battery 100 is not particularly limited, and the number of layers may be 50 or less, 40 or less, or 30 or less. When the number of layers of the secondary battery 100 is within the above range, productivity is further improved.

[0067] Figure 2 This is a schematic cross-sectional view of a conventional secondary battery. Figure 2 As shown, conventional secondary battery 200 has a multi-layered structure comprising a positive electrode 210, a separator 220, and a negative electrode 230 containing a negative electrode active material. Although conventional secondary battery 200 can be automatically laminated using an automatic lamination device as described below, the energy density is low due to the presence of the negative electrode active material in negative electrode 230.

[0068] The process of automatically stacking the existing secondary battery 200 by the automatic stacking device is as follows. First, prepare a plurality of positive electrodes 210, separators 220 and negative electrodes 230, and set them in the specified positions of the automatic stacking device according to their types. Then, the automatic stacking device takes out one of the positive electrodes 210 set at the specified position. Similarly, the automatic stacking device takes out one separator 220 and negative electrode 230 set at the specified position each time, and stacks them in the above order to obtain a structure in which the positive electrode 210, separator 220 and negative electrode 230 are stacked. By repeating the above stacking sequence, a structure as shown in FIG. Figure 2 The structure shown is a stacked structure of a plurality of positive electrodes 210, separators 220, and negative electrodes 230.

[0069] On the other hand, in order to increase energy density, when a negative electrode without a negative electrode active material is used instead of the negative electrode 230 with a negative electrode active material to manufacture a secondary battery, when the stacked structure of the positive electrode, separator, and negative electrode is formed by automatic lamination in the same way as described above, there is a tendency for wrinkles to form on the stacked negative electrode because the negative electrode without a negative electrode active material is very thin and difficult to handle. When wrinkles form on the negative electrode like this, the carrier metal deposited on the negative electrode has insufficient adhesion to the negative electrode, and the carrier metal deposited on the negative electrode easily peels off from the negative electrode during use of the secondary battery. As a result, the cycle characteristics of such a secondary battery are poor.

[0070] Figure 1 The secondary battery 100 involved in the first embodiment includes a laminate 150 formed by laminating sheets 130. The sheet 130 is not laminated as a single body with the negative electrode 120, which is very thin and difficult to handle, but is formed into a whole with the first separator 110a and the second separator 110b arranged on both sides of the negative electrode 120. Since the sheet 130 includes the negative electrode 120, the first separator 110a and the second separator 110b, its average thickness is thicker than the average thickness of the negative electrode 120, making it easy to handle. In addition, since the negative electrode 120 is clamped between the first separator 110a and the second separator 110b, physical pressure is applied from both sides, making it difficult to wrinkle. As a result, since the secondary battery 100 can suppress the generation of wrinkles on the negative electrode 120 and is formed by an automatic lamination device, it has excellent cycle characteristics and high productivity.

[0071] (positive electrode)

[0072] like Figure 1 As shown, in the secondary battery 100, the positive electrodes 140 are arranged in each gap formed by the folding of the sheet 130. More specifically, the positive electrodes 140 are arranged between adjacent planar portions 170. A positive electrode 140 arranged between a planar portion 170 (a first planar portion 170) and a planar portion 170 adjacent to the first planar portion 170 in the stacking direction Z (a second planar portion 170) has one side facing the first separator 110a belonging to the first planar portion 170 and the other side facing the first separator 110a belonging to the second planar portion 170. A positive electrode 140 arranged between the first planar portion 170 and a planar portion 170 adjacent to the stacking direction Z opposite to the first planar portion 170 (a third planar portion 170) has one side facing the second separator 110b belonging to the first planar portion 170 and the other side facing the second separator 110b belonging to the third planar portion 170.

[0073] Since the positive electrodes 140 are disposed between adjacent planar portions 170 as described above, both sides of the positive electrodes 140 face the negative electrodes 120 via the first separator 110a or the second separator 110b. Furthermore, the secondary battery 100 can include multiple positive electrodes 140. Consequently, the capacity of the secondary battery 100 is increased.

[0074] exist Figure 1 In the embodiment, the positive electrode 140 is configured to be at a distance from the end (bent end) 180 of the bent portion 160 in the laminate 150 preferably within a range of 0.01 mm to 5.00 mm. That is, the distance d between the positive electrode 140 and the bent end 180 is preferably 0.01 mm to 5.00 mm. By having a distance d of 0.01 mm or more, the time required for positioning the positive electrode 140 is shortened, so the productivity of the secondary battery 100 is further improved. In addition, since the distance d is 5.00 mm or less, the relative area between the positive electrode 140 and the negative electrode 120 is further increased, so the energy density and capacity of the secondary battery 100 are further improved. From the same point of view, the distance d is more preferably 0.05 mm to 4.00 mm, and more preferably 0.10 mm to 3.00 mm.

[0075] In addition, the distance d between the positive electrode 140 and the bent end 180 can be measured as follows. First, the secondary battery 100 is cut parallel to the stacking direction Z and perpendicular to at least one bent portion 160. The obtained cross-section is observed using a method such as the naked eye, an optical microscope, or an electron microscope, and the distance d between the positive electrode 140 and the bent end 180 is measured for at least two or more positive electrodes 140. By calculating the average of the measurement results, the distance d between the positive electrode 140 and the bent end 180 can be calculated. The bent end 180 is the point in the bent portion 160 in the cross-section of the secondary battery 100 that is the longest in distance from the positive electrode 140. In other words, in the cross-section of the secondary battery 100, when the distance between the positive electrode 140 and any point on the bent portion 160 is d', the point on the bent portion 160 where d' is the largest is the bent end 180.

[0076] Generally, the positive electrode 140 is not particularly limited as long as it is used in a secondary battery, and a known material can be appropriately selected according to the application of the secondary battery and the type of carrier metal. From the perspective of improving the stability and output voltage of the secondary battery, the positive electrode 140 preferably contains a positive electrode active material.

[0077] In this specification, the term "positive electrode active material" refers to a substance for retaining a support metal in the positive electrode 140 , or in other words, a host material for the support metal. In this specification, the positive electrode active material is typically a substance for retaining lithium ions in the positive electrode 140 .

[0078] There are no particular limitations on such positive electrode active materials, and examples thereof include metal oxides and metal phosphates. There are no particular limitations on the above-mentioned metal oxides, and examples thereof include cobalt oxide compounds, manganese oxide compounds, and nickel oxide compounds. There are no particular limitations on the above-mentioned metal phosphates, and examples thereof include iron phosphate compounds and cobalt phosphate compounds. In the case where the carrier metal is lithium ion, typical positive electrode active materials include LiCoO2, LiNi x Co y Mn Z O2(x+y+z=1), LiNi x Mn y O2 (x+y=1), LiNiO2, LiMn2O4, LiFePO4, LiCoPO4, LiFeOF, LiFeOF, LiNiOF, and TiS2. The positive electrode active materials described above are used alone or in combination of two or more.

[0079] The positive electrode 140 may also contain components other than the above-mentioned positive electrode active material. Such components are not particularly limited, and examples thereof include known conductive additives, binders, solid polymer electrolytes, and inorganic solid electrolytes.

[0080] The conductive additive in the positive electrode 140 is not particularly limited, and examples thereof include carbon black, single-walled carbon nanotubes (SW-CNTs), multi-walled carbon nanotubes (MW-CNTs), carbon nanofibers, and acetylene black. Furthermore, the binder is not particularly limited, and examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, acrylic resin, and polyimide resin.

[0081] The content of the positive electrode active material in the positive electrode 140 may be, for example, 50% by mass or more and 100% by mass or less relative to the total positive electrode 140. The content of the conductive additive may be, for example, 0.5% by mass or more and 30% by mass or less relative to the total positive electrode 140. The content of the binder may be, for example, 0.5% by mass or more and 30% by mass or less relative to the total positive electrode 140. The total content of the solid polymer electrolyte and the inorganic solid electrolyte may be, for example, 0.5% by mass or more and 30% by mass or less relative to the total positive electrode 140.

[0082] (Electrolyte)

[0083] The secondary battery 100 may also include an electrolyte. The electrolyte may be impregnated in the first separator 110a and / or the second separator 110b, or may be enclosed together with the laminate 150 to form the secondary battery 100. The electrolyte, containing an electrolyte and a solvent, is an ionically conductive solution that serves as a conductive path for lithium ions. Therefore, the internal resistance of the secondary battery 100 containing the electrolyte is further reduced, and the energy density, capacity, and cycle characteristics are further improved.

[0084] If the electrolyte is a salt, there is no particular limitation, and examples include salts of Li, Na, K, Ca, and Mg. As the electrolyte, a lithium salt is preferably used. As the lithium salt, there is no particular limitation, and examples include LiI, LiCl, LiBr, LiF, LiBF4, LiPF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2CF3CF3)2, LiB(O2C2H4)2, LiB(O2C2H4)F2, LiB(OCOCF3)4, LiNO3, and Li2SO4. From the perspective of better energy density, capacity, and cycle characteristics of the secondary battery 100, the lithium salt is preferably LiN(SO2F)2. In addition, the above-mentioned lithium salts are used alone or in combination of two or more.

[0085] The solvent is not particularly limited, and examples thereof include dimethyl ether, diglyme, triglyme, acetonitrile, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, chlorinated ethylene carbonate, fluorinated ethylene carbonate, difluoroethylene carbonate, trifluoromethylpropylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, nonafluorobutyl methyl ether, nonafluorobutyl ethyl ether, tetrafluoroethyl tetrafluoropropyl ether, trimethyl phosphate, and triethyl phosphate. These solvents may be used alone or in combination of two or more.

[0086] (Positive terminal and negative terminal)

[0087] Figure 3 1 is a schematic perspective view of a secondary battery according to the first embodiment. Figure 3 As shown, the secondary battery 100 according to the first embodiment includes at least one negative electrode terminal 310 on the planar portion 170 of the laminate 150. Furthermore, the secondary battery 100 includes a positive electrode terminal 320 at each positive electrode. Negative and positive terminals 310 and 320 are each connected to an external circuit. The materials for negative and positive terminals 310 and 320 are not particularly limited as long as they are conductive; examples include Al and Ni.

[0088] (Use of secondary batteries)

[0089] The secondary battery 100 is charged and discharged by connecting the negative terminal 310 to one end of the external circuit and the positive terminal 320 to the other end of the external circuit. If there are multiple negative terminals 310, all of them are connected to the external circuit so that they have the same potential. Similarly, all of the positive terminals 320 are connected to the external circuit so that they have the same potential.

[0090] The secondary battery 100 is charged by applying a voltage between the positive terminal 320 and the negative terminal 310 so that a current flows from the negative terminal 310 to the positive terminal 320 through an external circuit. By charging the secondary battery 100, the carrier metal is precipitated at the interface between the negative electrode 120 and the first separator 110a and the interface between the negative electrode 120 and the second separator 110b. The precipitated carrier metal is typically lithium metal. Since the negative electrode 120 in the secondary battery 100 is suppressed from wrinkling, the precipitated carrier metal has excellent adhesion to the negative electrode 120. As a result, the carrier metal precipitated on the negative electrode 120 is difficult to peel off from the negative electrode, and the secondary battery 100 has excellent cycle characteristics.

[0091] The secondary battery 100 may also form a solid electrolyte interface layer (SEI layer) at the interface between the negative electrode 120 and the first separator 110a and / or the interface between the negative electrode 120 and the second separator 110b through initial charging. The SEI layer formed is not particularly limited, and for example, it may also include inorganic substances of the carrier metal and organic substances of the carrier metal. Typically, it may also include lithium-containing inorganic compounds and lithium-containing organic compounds. The typical average thickness of the SEI layer is not less than 1 nm and not more than 10 μm.

[0092] When an SEI layer is formed on the secondary battery 100, the carrier metal deposited when the secondary battery 100 is charged can be deposited at the interface between the negative electrode 120 and the SEI layer, at the interface between the SEI layer and the first separator 110a, or at the interface between the SEI layer and the second separator 110b.

[0093] After charging, the secondary battery 100 is discharged by connecting the positive terminal 320 and the negative terminal 310. The carrier metal formed at least at one of the interface between the negative electrode 120 and the SEI layer, the interface between the SEI layer and the first separator 110a, and the interface between the SEI layer and the second separator 110b dissolves.

[0094] (Method for Manufacturing Secondary Battery)

[0095] The manufacturing method of the secondary battery of this embodiment includes: a process of preparing a sheet, wherein the sheet has a negative electrode without a negative electrode active material and a separator arranged on both sides of the negative electrode; a forming process of forming a formed body, wherein the formed body includes a laminate formed by alternately bending the sheet at an acute angle multiple times and a plurality of positive electrodes respectively arranged in each gap formed between the separators opposite to each other by bending the sheet. Figure 4 As shown in Figure 1 1 is a flowchart of a method for manufacturing the secondary battery 100 according to the first embodiment. Each step will be described below.

[0096] (Sheet preparation process)

[0097] In the secondary battery manufacturing method of this embodiment, first, a sheet having a negative electrode without a negative electrode active material and separators disposed on both sides of the negative electrode is prepared (sheet preparation step, step 1). The sheet preparation step is not particularly limited as long as the separators are disposed on both sides of the negative electrode in a manner that does not cause wrinkles on the negative electrode, and a roll-to-roll method can be used, for example.

[0098] The roll-to-roll method can be performed as follows, for example. That is, a roll is prepared by rolling up a sheet containing the material constituting the negative electrode 120 (hereinafter referred to as the "negative electrode sheet"), a roll is prepared by rolling up a sheet containing the material constituting the first separator 110a (hereinafter referred to as the "first separator sheet"), and a roll is prepared by rolling up a sheet containing the material constituting the second separator 110b (hereinafter referred to as the "second separator sheet"). By placing these rolls in a prescribed device, each roll is restored to a sheet shape and the negative electrode sheet is clamped with the first separator sheet and the second separator sheet, and pressed in the thickness direction of the sheet, a sheet is formed in which the first separator sheet and the second separator sheet are arranged on both sides of the negative electrode sheet. The obtained sheet can be rolled up into a roll and supplied to the next process.

[0099] When the roll-to-roll method is used in the sheet preparation process, the negative electrode sheet is stretched in the surface direction and the first and second separator sheets are placed on both sides of the negative electrode sheet. This reduces the risk of wrinkles in the negative electrode sheet. Furthermore, since the resulting sheet is rolled into a roll, it is easily supplied to subsequent processes, resulting in superior productivity.

[0100] The negative electrode sheet may be the same thickness as the negative electrode 120 or thicker than the negative electrode 120. If the negative electrode sheet is thicker than the negative electrode 120, it may be thinned by rolling the negative electrode sheet before sandwiching the negative electrode sheet between the first and second separator sheets.

[0101] The sheet preparation process may include a cleaning step and a drying step before and / or after forming a sheet having a negative electrode and separators disposed on both sides of the negative electrode. Examples of the cleaning step include cleaning the negative electrode sheet with a solvent containing aminosulfonic acid and then ultrasonically cleaning it with ethanol.

[0102] (Positive electrode preparation process)

[0103] Then, if Figure 4 Prepare the positive electrode 140 as shown (positive electrode preparation process, step 2). The method for manufacturing the positive electrode 140 is not particularly limited as long as it is a method for obtaining the above-mentioned positive electrode 140. For example, a positive electrode mixture obtained by mixing a positive electrode active material, a known conductive additive, and a known binder can be applied to one side of a metal foil (e.g., Al foil) with a thickness of 5 μm to 1 mm and then stamped. Alternatively, a commercially available positive electrode for a secondary battery can be used.

[0104] (Forming process)

[0105] Then, if Figure 4 As shown, a formed body is formed, which includes: a laminate formed by alternately bending the obtained sheet multiple times at acute angles; and a plurality of positive electrodes respectively arranged in each gap formed between separators facing each other by bending the sheet (forming process, step 3).

[0106] In this way, because the forming process forms a formed body comprising a laminate formed using sheets of appropriate thickness and mechanical strength, and the positive electrode disposed in each gap within the laminate, wrinkles are unlikely to form on the negative electrode, even when an automated lamination device is used. In other words, the formed body can be automatically formed without wrinkling on the negative electrode. Therefore, the secondary battery manufacturing method of this embodiment can produce secondary batteries with excellent cycle characteristics with high productivity.

[0107] Figure 5 A method of representing a forming process. In a forming process of a certain embodiment, first, the sheet 130 is bent by pressing the first flat plate 500 toward the sheet 130 from a first direction X1 perpendicular to the stacking direction Z of the stack, pressing the second flat plate 510 toward the sheet 130 from a second direction X2 opposite to the first direction, and pressing the sheet 130 from a direction opposite to the stacking direction Z of the stack. Here, the first flat plate 500 includes the positive electrode 140 and a first substrate 520 integrated with the positive electrode 140, and the second flat plate 510 includes the positive electrode 140 and a second substrate 530 integrated with the positive electrode 140. Thereafter, the first substrate 520 and the second substrate 530 are removed. According to this method, since it is possible to simultaneously perform Figure 1The formation of the laminate 150 and the insertion of the positive electrode 140 are simplified, so the productivity is further improved.

[0108] Furthermore, when bending the sheet 130 as described above, it is preferable to fix one end of the sheet 130 in the longitudinal direction and stretch the other end, thereby applying tension in the longitudinal direction of the sheet 130. This prevents the sheet 130 from loosening, thereby further suppressing the formation of wrinkles in the negative electrode 120. The tension applied in the longitudinal direction of the sheet 130 can be appropriately adjusted based on the thickness of the sheet 130, and can be, for example, not less than 0.1 kgf and not more than 10.0 kgf.

[0109] In the first flat plate 500, the method for integrating the positive electrode 140 with the first substrate 520 is not particularly limited. For example, the positive electrode 140 may be placed on the first substrate 520, or the positive electrode 140 may be attracted to the first substrate 520 connected to a suction device. When the positive electrode 140 is attracted to the first substrate 520 connected to a suction device, the attraction of the positive electrode 140 must be released before removing the first substrate 520.

[0110] like Figure 6 As shown, in other embodiments, the forming process may also include bending Figure 1 The sheet 130 is formed Figure 1 The bending process of the laminate 150 and the Figure 1 The sheet 130 is bent so that the gaps formed are inserted into Figure 1 Insertion step of the positive electrode 140.

[0111] The bending process is a process of pressing the first flat plate toward the sheet 130 from a first direction perpendicular to the stacking direction of the stack, pressing the second flat plate toward the sheet 130 from a second direction opposite to the first direction, and pressing the sheet 130 from a direction opposite to the stacking direction of the stack, bending the sheet 130, and then removing the first flat plate and the second flat plate. Figure 1 The laminate 150 is shown.

[0112] The inserting process is obtained through the bending process Figure 1 The process of inserting the positive electrode 140 into each gap of the laminate 150. That is, in the inserting process, the positive electrode 140 is inserted between the adjacent flat portions 170.

[0113] (Enclosure process)

[0114] Then, if Figure 4 as well as Figure 6As shown, a molded body with multiple positive electrodes 140 arranged in the gaps between the stack 150 is sealed in a sealed container to obtain an enclosed body, which is used as the secondary battery 100 (sealing process, step 4). During the sealing process, an electrolyte can also be sealed in the sealed container. In this way, since the internal impedance of the secondary battery 100 is further reduced by sealing the electrolyte, the energy density, capacity, and cycle characteristics of the secondary battery 100 are further improved.

[0115] The sealed container in the sealing step is not particularly limited, and an example thereof is a laminate film.

[0116] [Second embodiment]

[0117] (Secondary Battery)

[0118] Figure 7 : is a schematic perspective view of a secondary battery according to the second embodiment. Figure 7 As shown, the secondary battery 700 according to the second embodiment includes a negative electrode terminal 310 on each flat surface portion 170 of the laminate 150. Furthermore, each positive electrode of the secondary battery 700 includes a positive electrode terminal 320. In the secondary battery 700, the plurality of negative electrode terminals 310 are connected to an external circuit so that all negative electrode terminals 310 have the same potential.

[0119] According to this embodiment, since the negative electrode 120 includes multiple negative terminals 310 and is connected so that the negative terminals 310 have the same potential, the negative electrode 120 is more easily maintained at the same potential, and the internal impedance of the secondary battery 700 is further reduced. As a result, the energy density, capacity, and cycle characteristics of the secondary battery 700 are further improved.

[0120] The secondary battery 700 has the same configuration as the secondary battery 100 according to the first embodiment except for the above, and exhibits the same effects.

[0121] [Third embodiment]

[0122] (Secondary Battery)

[0123] Figure 8 : is a schematic cross-sectional view of a secondary battery according to the third embodiment. Figure 8As shown, the secondary battery 800 according to the third embodiment includes a laminate 830 formed by alternately bending a sheet 820 having a negative electrode 120 without a negative electrode active material and a first solid electrolyte 810a and a second solid electrolyte 810b disposed on opposite sides of the negative electrode 120 multiple times at acute angles; and a plurality of positive electrodes 140 disposed in gaps formed between separators facing each other by the bent sheet. In other words, the secondary battery 800 is the secondary battery 100 according to the first embodiment, with the first separator 110a and the second separator 110b replaced with the first solid electrolyte 810a and the second solid electrolyte 810b, respectively.

[0124] (Solid Electrolyte)

[0125] Generally speaking, batteries with liquid electrolytes experience different physical pressures on the negative electrode surface due to the oscillation of the liquid. However, because the secondary battery 800 includes the first solid electrolyte 810a and the second solid electrolyte 810b, the pressure applied to the surface of the negative electrode 120 by the first and second solid electrolytes 810a, 810b becomes more uniform, which can further uniformize the shape of the carrier metal deposited on the surface of the negative electrode 120. This further suppresses the growth of the carrier metal deposited on the surface of the negative electrode 120 into a dendritic shape, resulting in improved cycle characteristics for the secondary battery 800.

[0126] The first solid electrolyte 810a is not particularly limited as long as it is generally used in solid batteries. A known material can be appropriately selected according to the purpose of the secondary battery 800 and the type of carrier metal. The first solid electrolyte 810a preferably has ion conductivity but not electron conductivity. By having ion conductivity but not electron conductivity, the internal impedance of the secondary battery 800 is further reduced, and internal short circuits in the secondary battery 800 can be further suppressed. As a result, the energy density, capacity, and cycle characteristics of the secondary battery 800 are further improved.

[0127] The first solid electrolyte 810a is not particularly limited, and examples thereof include resins and salts. Examples of such resins are not particularly limited, and examples thereof include resins having ethylene oxide units in the main chain and / or side chain, acrylic resins, vinyl resins, ester resins, nylon resins, polysiloxanes, polyphosphonitriles, polyvinylidene fluoride, polymethyl methacrylate, polyamides, polyimides, aramids, polylactic acid, polyethylene, polystyrene, polyurethane, polypropylene, polybutene, polyacetal, polysulfone, and polytetrafluoroethylene. These resins may be used alone or in combination of two or more.

[0128] The salt contained in the first solid electrolyte 810a is not particularly limited, and examples thereof include salts of Li, Na, K, Ca, and Mg. Examples of lithium salts include LiI, LiCl, LiBr, LiF, LiBF4, LiPF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2CF3CF3)2, LiB(O2C2H4)2, LiB(O2C2H4)F2, LiB(OCOCF3)4, LiNO3, and Li2SO4. The above lithium salts may be used alone or in combination of two or more.

[0129] Generally speaking, the ratio of the resin to the lithium salt content in the solid electrolyte layer is determined by the ratio of oxygen atoms in the resin to lithium atoms in the lithium salt ("Li" / "O"). In the first solid electrolyte 810a, the resin to lithium salt content ratio ("Li" / "O") is adjusted so that the ratio is preferably 0.02 to 0.20, more preferably 0.03 to 0.15, and even more preferably 0.04 to 0.12.

[0130] The first solid electrolyte 810a may contain components other than the above-mentioned resin and salt. Such components are not particularly limited, and examples thereof include solvents.

[0131] The solvent is not particularly limited, and examples thereof include those exemplified in the electrolyte solution that can be contained in the secondary battery 100 .

[0132] The average thickness of the first solid electrolyte 810a is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less. In this manner, the energy density of the secondary battery 800 is further improved due to the reduction in the volume occupied by the first solid electrolyte 810a. Furthermore, the average thickness of the first solid electrolyte 810a is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 10 μm or more. In this manner, the positive electrode 140 and the negative electrode 120 can be more reliably isolated, and battery short circuits can be further suppressed.

[0133] The second solid electrolyte 810b may be the same as or different from the first solid electrolyte 810a as long as it has the above-mentioned configuration as the first solid electrolyte 810a. Preferred embodiments of the second solid electrolyte 810b are the same as those of the first solid electrolyte 810a.

[0134] In this specification, "solid electrolyte" refers to a substance including a gel electrolyte. The gel electrolyte is not particularly limited, and examples thereof include substances containing a polymer, an organic solvent, and a lithium salt. The polymer in the gel electrolyte is not particularly limited, and examples thereof include copolymers of polyethylene and / or polyethylene oxide, polyvinylidene fluoride, and copolymers of polyvinylidene fluoride and hexafluoropropylene.

[0135] (Method for Manufacturing Secondary Battery)

[0136] The secondary battery 800 can be manufactured in the same manner as the method for manufacturing the secondary battery 100 according to the first embodiment, except that a solid electrolyte is used instead of a separator.

[0137] The manufacturing method of the first solid electrolyte 810a and the second solid electrolyte 810b is not particularly limited as long as it is a method for obtaining the above-mentioned solid electrolyte 810a. For example, it can be as follows. The resin and salt previously used in the solid electrolyte (for example, the resin that can be included in the solid electrolyte 810a is the above-mentioned resin and salt) are dissolved in an organic solvent. The obtained solution is cast on a forming substrate in a manner to a predetermined thickness to obtain the first solid electrolyte 810a and the second solid electrolyte 810b. Here, the mixing ratio of the resin and the lithium salt can also be determined by the ratio of oxygen atoms contained in the resin to lithium atoms contained in the lithium salt ("Li" / "O") as described above. The above-mentioned ratio ("Li" / "O") is, for example, not less than 0.02 and not more than 0.20. In addition, the organic solvent is not particularly limited, and for example, acetonitrile can also be used. The forming substrate is not particularly limited, and for example, a PET film or a glass substrate can also be used.

[0138] The above-described embodiment is an example for explaining the present invention, and the present invention is not limited to the embodiment, but can be modified in various forms without departing from the spirit of the present invention.

[0139] For example, the secondary battery of this embodiment may also be a solid secondary battery. Furthermore, the secondary battery of this embodiment may also be a lithium secondary battery in which lithium metal is deposited on the surface of the negative electrode and the deposited lithium dissolves to perform charging and discharging. From the perspective of effectively and reliably achieving the effects of this embodiment, the secondary battery of this embodiment is preferably a lithium secondary battery in which lithium metal is deposited on the surface of the negative electrode and the deposited lithium dissolves to perform charging and discharging.

[0140] The secondary battery of this embodiment may also not have a lithium foil formed between the separator or solid electrolyte and the negative electrode before initial charging. When the secondary battery of this embodiment does not have a lithium foil formed between the separator or solid electrolyte and the negative electrode before initial charging, the highly flammable lithium metal can be avoided during manufacturing, resulting in a secondary battery with improved safety and productivity.

[0141] The secondary battery of this embodiment may also include a current collector configured to contact the negative electrode or the positive electrode. Such a current collector is not particularly limited, and examples thereof include current collectors that can be used in negative electrode materials. In addition, when the secondary battery does not include a current collector, the negative electrode and the positive electrode themselves function as the current collector.

[0142] In addition, in this specification, "high energy density" or "high energy density" means high capacity per unit total volume or total mass, preferably 800Wh / L or 350Wh / kg or more, more preferably 900Wh / L or 400Wh / kg or more, and further preferably 1000Wh / L or 450Wh / kg or more.

[0143] In addition, in this specification, "excellent cycle characteristics" means that the battery capacity has a low rate of reduction before and after the number of charge and discharge cycles that can be imagined in normal use. That is, it means that when comparing the initial capacity with the capacity after the number of charge and discharge cycles that can be imagined in normal use, the capacity after the charge and discharge cycle has hardly decreased relative to the initial capacity. Here, the "number of times that can be imagined in normal use" varies based on the purpose of using the secondary battery, for example, 50 times, 100 times, 500 times, 1000 times, 5000 times, or 10000 times. In addition, "the capacity after the charge and discharge cycle has hardly decreased relative to the initial capacity" means that the capacity after the charge and discharge cycle is 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more relative to the initial capacity, depending on the purpose of using the secondary battery.

[0144] Example

[0145] The present invention will be described in more detail below using Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[0146] [Example 1]

[0147] As the negative electrode sheet, a sheet with 100nm of Sn foil coated on both sides of an 8μm thick Cu substrate was prepared. The negative terminal was installed by pre-joining a Ni terminal to the negative electrode sheet via ultrasonic welding. As the first and second separator sheets, separators (thickness: 15μm) coated with a mixture of polyvinylidene fluoride (PVDF) and Al2O3 were prepared. The negative electrode sheet was sandwiched between the first and second separator sheets and pressed along the thickness direction of the sheet to obtain a sheet with separators configured on both sides of the negative electrode.

[0148] In N-methylpyrrolidone (NMP) as a solvent, 96 parts by mass of LiNi 0.8 Co 0.15 Al 0.05 O2, 2 parts by mass of carbon black as a conductive aid, and 2 parts by mass of polyvinylidene fluoride (PVDF) as a binder are coated on both sides of 12μm Al foil and stamped. The obtained molded body is punched into a specified size by punching to obtain a positive electrode. In addition, in the above-mentioned Al foil, the positive terminal is pre-installed by joining the Al terminal by ultrasonic welding. After the obtained positive electrode is charged to 4.2V (relative to the lithium metal counter electrode) with a current equivalent to 0.1C, it is discharged to 3.0V (relative to the lithium metal counter electrode), and the discharge capacity of the positive electrode is obtained to be 4.8mAh / cm 2 .

[0149] Next, a sheet with separators arranged on both sides of the negative electrode is placed in an automatic lamination device, and the sheet is automatically bent multiple times at an acute angle to form a laminate. In addition, in this process, the automatic lamination device repeatedly presses the first flat plate against the sheet from a first direction perpendicular to the stacking direction of the laminate, presses the second flat plate against the sheet from a second direction opposite to the first direction, and presses the sheet from the opposite direction of the stacking direction of the laminate to bend the sheet, and then removes the first and second flat plates, thereby automatically bending the sheet multiple times at an acute angle. In addition, in this process, tension is applied to the long axis direction of the sheet and the sheet is bent. In addition, the number of stacking layers of the laminate is adjusted so that the initial capacity of the secondary battery obtained becomes 10Ah.

[0150] Next, the positive electrodes prepared above are inserted into the gaps of the laminate obtained as above. At this time, the positive electrodes are inserted in such a way that the distance between the positive electrodes and the bent end of the laminate becomes 0.01 mm or more and 5.00 mm or less. Figure 1 As shown, the positive electrode 140 is arranged in each gap of the laminate 150. Then, it is inserted into the outer packaging body of the laminate.

[0151] Furthermore, a 4M LiN(SO2F)2 (hereinafter also referred to as "LFSI") dimethoxyethane (hereinafter also referred to as "DME") solution was injected into the outer package as an electrolyte, and the outer package was sealed to obtain a secondary battery.

[0152] [Comparative Example 1]

[0153] An electrode coated with 100 nm of Sn foil on both sides of an 8 μm thick Cu substrate was washed in a solvent containing sulfamic acid and then punched into a specified size. The negative electrode was ultrasonically cleaned with ethanol and then dried to obtain a negative electrode. The Ni terminal was joined to the obtained negative electrode by ultrasonic welding to install the negative terminal. In addition, a positive electrode with a positive terminal installed was prepared in the same manner as in Example 1. In addition, as a separator, a separator (thickness: 15 μm) with a surface coated with a mixture of polyvinylidene fluoride (PVDF) and Al2O3 was prepared.

[0154] Next, the positive electrode, separator, and negative electrode were manually stacked one by one in this order. The resulting stack was inserted into the outer packaging of the laminate, and a secondary battery was obtained in the same manner as in Example 1. The number of stacks was adjusted so that the initial capacity of the resulting secondary battery reached 10 Ah.

[0155] [Comparative Example 2]

[0156] In the same manner as in Comparative Example 1, a negative electrode, a positive electrode, and a separator were prepared.

[0157] Next, using an automated lamination device different from that used in Example 1, multiple sheets of the positive electrode, separator, and negative electrode were automatically stacked in the order described above. Furthermore, during this step, the automated lamination device automatically stacked the positive electrodes, separators, and negative electrodes, one by one, each placed in a predetermined position according to their type. The resulting stack was inserted into the outer packaging of the laminate, and a secondary battery was obtained in the same manner as in Example 1. The number of stacks was adjusted so that the initial capacity of the resulting secondary battery reached 10 Ah.

[0158] Furthermore, in the obtained laminate, when the laminated negative electrodes were observed with the naked eye, it was thought that fine wrinkles were generated.

[0159] [Productivity Evaluation]

[0160] The secondary battery of each example was produced in 10 minutes. Table 1 shows the number of secondary batteries produced per 10 minutes.

[0161] [Evaluation of Cycle Characteristics]

[0162] As follows, the cycle characteristics of the secondary batteries produced in each embodiment and comparative example were evaluated. After the 10Ah secondary battery produced was charged to a voltage of 4.2V at 0.5A, it was discharged to a voltage of 3.0V at 0.5A (hereinafter referred to as "initial discharge"). Next, the cycle of charging to a voltage of 4.2V at 1.0A and then discharging to a voltage of 3.0V at 1.0A was repeated 100 times under an environment with a temperature of 25°C. For each example, the ratio of the capacity obtained from the discharge after the above 100 cycles (hereinafter referred to as "capacity after use") to the capacity obtained from the initial discharge (hereinafter referred to as "initial capacity") was calculated (capacity after use / initial capacity) (hereinafter referred to as "capacity maintenance rate"). The cycle characteristics of each example were evaluated based on the following benchmarks. In addition, the closer the capacity maintenance rate is to 100%, the better the cycle characteristics.

[0163] A: Capacity retention rate is above 80%

[0164] B: Capacity retention rate is 50% or more and 80% or less

[0165] C: Capacity retention rate is less than 50%

[0166] The evaluation of the cycle characteristics in each example is shown in Table 1. In addition, the initial capacity was 10 Ah in all examples. In addition, the energy density calculated from the initial capacity of Example 1 was 450 Wh / kg.

[0167] [Table 1]

[0168]

[0169] Industrial Applicability

[0170] The secondary battery of the present invention has high energy density and capacity and excellent cycle characteristics, and therefore has industrial applicability as a power storage device used in various applications.

[0171] Description of Reference Numerals

[0172] 100, 200, 700, 800 secondary batteries

[0173] 110a, 110b separators

[0174] 120 negative electrode

[0175] 130, 820 sheets

[0176] 140 positive electrode

[0177] 150, 830 layered body

[0178] 160 Bending section

[0179] 170 plane part

[0180] 180 bend end

[0181] 210 positive electrode

[0182] 220 separator

[0183] 230 negative electrode

[0184] 310 Negative terminal

[0185] 320 positive terminal

[0186] 500 First Flatbed

[0187] 510 Second Tablet

[0188] 520 first substrate

[0189] 530 Second Substrate

[0190] 810a, 810b solid electrolyte.

Claims

1. A secondary battery comprising: A laminate formed by alternately bending a sheet having a negative electrode and separators disposed on both sides of the negative electrode multiple times at acute angles, the negative electrode having no negative electrode active material before initial charge; and A plurality of positive electrodes are respectively arranged in gaps formed between separators facing each other by bending the sheet, The average thickness of the negative electrode is not less than 4 μm and not more than 20 μm. The average thickness of the separator is 5 μm or more and 20 μm or less.

2. A secondary battery comprising: A laminate formed by alternately bending a sheet having a negative electrode and a solid electrolyte disposed on both sides of the negative electrode multiple times at acute angles, the negative electrode having no negative electrode active material before initial charge; and A plurality of positive electrodes are respectively arranged in each gap formed between the solid electrolytes facing each other by bending the sheet, The average thickness of the negative electrode is not less than 4 μm and not more than 20 μm. The average thickness of the solid electrolyte is 5 μm or more and 20 μm or less.

3. The secondary battery according to claim 1 or 2, wherein The secondary battery is a lithium secondary battery that is charged and discharged by the deposition of lithium metal on the surface of the negative electrode and the dissolution of the deposited lithium.

4. The secondary battery according to claim 1 or 2, wherein The negative electrode is an electrode composed of at least one selected from the group consisting of Cu, Ni, Ti, Fe, other metals that do not react with Li, alloys thereof, and stainless steel (SUS).

5. The secondary battery according to claim 1 or 2, wherein Before initial charge, no lithium foil is formed on the surface of the negative electrode.

6. The secondary battery according to claim 1 or 2, wherein The positive electrode is disposed at a distance from the end of the bent portion of the sheet within a range of 0.01 mm to 5.00 mm.

7. The secondary battery according to claim 1 or 2, wherein The average thickness of the negative electrode is 5 μm or more and 18 μm or less.

8. The secondary battery according to claim 1 or 2, wherein The energy density is above 350Wh / kg.

9. The secondary battery according to claim 1 or 2, wherein The positive electrode has a positive electrode active material.

10. A method for manufacturing a secondary battery, comprising: a step of preparing a sheet comprising a negative electrode and separators disposed on both sides of the negative electrode, wherein the negative electrode does not have a negative electrode active material before initial charge; and a step of forming a formed body comprising a laminate formed by alternately bending the sheet multiple times at acute angles, and a plurality of positive electrodes disposed in respective gaps formed between separators opposed to each other by bending the sheet; The average thickness of the negative electrode is not less than 4 μm and not more than 20 μm. The average thickness of the separator is 5 μm or more and 20 μm or less.

11. A method for manufacturing a secondary battery, comprising: a step of preparing a sheet comprising a negative electrode and a solid electrolyte disposed on both surfaces of the negative electrode, wherein the negative electrode does not have a negative electrode active material before initial charge; and a step of forming a formed body comprising a laminate formed by alternately bending the sheet multiple times at acute angles, and a plurality of positive electrodes disposed in respective gaps formed between solid electrolytes opposed to each other by bending the sheet; The average thickness of the negative electrode is not less than 4 μm and not more than 20 μm. The average thickness of the solid electrolyte is 5 μm or more and 20 μm or less.

12. The method for manufacturing a secondary battery according to claim 10 or 11, wherein: The forming process includes a bending process, which bends the sheet by pressing a first flat plate toward the sheet from a first direction perpendicular to the stacking direction of the stack, pressing a second flat plate toward the sheet from a second direction opposite to the first direction, and pressing the sheet from a direction opposite to the stacking direction of the stack.

13. The method for manufacturing a secondary battery according to claim 12, wherein: The first plate and the second plate include the positive electrode and a substrate integrated with the positive electrode. In the bending step, the positive electrodes are inserted into the gaps formed by bending the sheet simultaneously with the bending of the sheet.

14. The method for manufacturing a secondary battery according to claim 12, wherein: The forming step includes, after the bending step, a step of inserting the positive electrodes into the gaps formed by bending the sheet.

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