WO2025229751A1 - Lithium secondary battery - Google Patents

Abstract

The present disclosure provides a lithium secondary battery excellent in safety and cycle characteristics. The present disclosure relates to a bipolar lithium secondary battery comprising a laminate in which a plurality of bipolar electrodes are stacked, wherein: each bipolar electrode is formed by laminating a positive electrode current collector, a resin layer, and a negative electrode current collector in the stated order; the laminate has a separator and an electrolyte sealed in a predetermined region between bipolar electrodes facing each other; and in each of the plurality of bipolar electrodes, the positive electrode current collector and the negative electrode current collector are electrically connected to each other outside the predetermined region.

Description

Lithium secondary battery

The present invention relates to a lithium secondary battery.

In recent years, technology that converts natural energy such as solar or wind power into electrical energy has been attracting attention. Accordingly, a variety of secondary batteries have been developed as highly safe energy storage devices capable of storing large amounts of electrical energy.

Among these, lithium secondary batteries, which charge and discharge by transferring lithium ions between the positive and negative electrodes, are known to exhibit high voltage and high energy density. A typical lithium secondary battery is the lithium-ion secondary battery (LIB), which has active materials capable of retaining lithium elements in the positive and negative electrodes and charges and discharges by transferring lithium ions between the positive and negative electrode active materials.

Bipolar batteries are known as one type of lithium-ion secondary battery. Bipolar batteries are batteries equipped with bipolar electrodes, one side of which acts as a positive electrode and the other as a negative electrode. They are attracting attention because it is relatively easy to increase voltage, reduce the number of parts, reduce electrical resistance between unit cells, and increase energy density by eliminating unnecessary space.

Patent Document 1 discloses a bipolar lithium-ion battery with excellent stackability between unit cells and excellent electrical contact between the unit cells. The bipolar secondary battery comprises a first current collector, an adhesive resin layer with through holes, and a second current collector stacked in this order, with the first current collector and second current collector bonded together via the adhesive resin layer.

Patent Document 2 discloses a resin current collector containing a polyolefin resin and a conductive carbon filler as a means for improving the cycle characteristics of a lithium ion battery, in which the total surface area of the conductive carbon filler contained in 1 g of the resin current collector is 7.0 ^m2 or more and 10.5 ^m2 or less.

Patent Document 3 discloses a non-aqueous electrolyte secondary battery with excellent cycle characteristics and safety, which uses a resin film as a support and a laminated body formed on one side of the support with a laminated structure of a conductive layer and a contact resistance-reducing layer as a current collector.

JP 2017-73374 A International Publication No. 2019/078160 International Publication No. 2021/145344

As mentioned above, various bipolar batteries have been proposed, but bipolar secondary batteries that are both highly safe and exhibit reduced degradation during charge/discharge cycles (hereinafter, this characteristic will be referred to as "cycle characteristics") are still in the development stage.

The present invention was made in consideration of the above circumstances, and aims to provide a lithium secondary battery with excellent safety and cycle characteristics.

One aspect of the present disclosure provides a bipolar lithium secondary battery comprising a laminate of multiple bipolar electrodes, each of which has a positive electrode current collector, a resin layer, and a negative electrode current collector stacked in this order, the laminate containing an electrolyte sealed in a predetermined region between each of the opposing bipolar electrodes, and in each of the bipolar electrodes, the positive electrode current collector and the negative electrode current collector are electrically connected outside the predetermined region.

The bipolar lithium secondary battery described above has multiple cells sandwiched between two bipolar electrodes and sealed with an electrolyte. In the bipolar lithium secondary battery described above, the bipolar electrodes isolating each cell have a resin layer, and the positive electrode current collector and negative electrode current collector are electrically connected outside the area where the cells are formed, ensuring the isolation of adjacent cells. As will be described later, this gives the bipolar lithium secondary battery described above excellent safety and cycle characteristics.

The present invention can provide a lithium secondary battery with excellent safety and cycle characteristics.

1 is a schematic cross-sectional view showing an example of a bipolar lithium secondary battery according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of a bipolar electrode according to the present embodiment. FIG. 4 is an enlarged schematic cross-sectional view showing another example of the bipolar electrode of the present embodiment. FIG. 10 is an enlarged schematic cross-sectional view showing yet another example of the bipolar electrode of the present embodiment. 3A to 3C are enlarged schematic cross-sectional views showing an example of a method for manufacturing the bipolar lithium secondary battery of the present embodiment.

The following provides a detailed description of an embodiment of the present invention (hereinafter simply referred to as "the present embodiment"); however, the present invention is not limited to the present embodiment. Various modifications of the present invention are possible without departing from the spirit of the invention. In the drawings, identical elements are designated by the same reference numerals, and redundant explanations will be omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to those shown.

1. Bipolar Lithium Secondary Battery The basic configuration of a bipolar lithium secondary battery according to this embodiment (hereinafter also simply referred to as "lithium secondary battery according to this embodiment" or "lithium secondary battery 1") will be described with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view showing an example of a bipolar lithium secondary battery according to this embodiment. As shown in Fig. 1, the lithium secondary battery according to this embodiment includes a stack of multiple bipolar electrodes 100, and multiple cells C sandwiched between two bipolar electrodes.

The bipolar electrode 100 is composed of a positive electrode current collector 110, a resin layer 120, and a negative electrode current collector 130 stacked in this order. A positive electrode 112 is formed on the positive electrode current collector 110, and a negative electrode 132 is formed on the negative electrode current collector 130. Cell C is sandwiched between two bipolar electrodes 100 and sealed together with a sealing member 150. In cell C, the positive electrode current collector 110 on which the positive electrode 112 is formed faces the negative electrode current collector 130 on which the negative electrode 132 is formed, and the positive electrode 112 and negative electrode 132 are separated by a separator 140. Cell C is filled with electrolyte 160.

As described above, the lithium secondary battery 1 shown in FIG. 1 has multiple bipolar electrodes 100 and multiple cells C formed between two bipolar electrodes. Each cell C has a laminated structure of a positive electrode 112, a separator 140, and a negative electrode 132, as well as an electrolyte 160, sealed by a sealing member 150.

In the lithium secondary battery 1, the number of bipolar electrodes 100 may be, for example, 2 to 100, 2 to 50, or 3 to 30. Each configuration is described in detail below.

1.1 Bipolar Electrode The bipolar electrode 100 includes a positive electrode current collector 110, a resin layer 120, and a negative electrode current collector 130 stacked in this order, and the positive electrode current collector 110 and the negative electrode current collector 130 are electrically connected outside the predetermined region where the electrolyte solution 160 is sealed, i.e., outside the region where the cell C is formed.

In this specification, when two components are "electrically connected," it means that the two components are electrically connected by being in physical contact with each other, or that the two components are electrically connected by being connected via an electrically conductive material.

In the lithium secondary battery according to this embodiment, the bipolar electrode 100 has a resin layer 120, and the positive electrode current collector 110 and negative electrode current collector 130 are electrically connected outside the area where the cell C is formed, resulting in excellent safety and cycle characteristics.

In other words, because the bipolar electrode 100 has a resin layer 120, if abnormal heat is generated due to overcharging or high temperature, the resin layer 120 melts, damaging the bipolar electrode 100 and interrupting the short-circuit current inside the battery. This prevents a sudden rise in temperature inside the lithium secondary battery 1 and prevents the battery from catching fire.

Furthermore, when the bipolar electrode includes a resin layer, it is necessary to electrically connect the positive electrode current collector formed on one side of the resin layer and the negative electrode current collector formed on the other side. In this embodiment, the positive electrode current collector 110 and the negative electrode current collector 130 are electrically connected outside the region where cell C is formed, thereby suppressing irreversible reactions between the current collectors as described below. That is, when the positive electrode current collector and the negative electrode current collector are electrically connected in the region where cell C is formed, if even a small pinhole is present in the positive electrode current collector or the negative electrode current collector, for example, the negative electrode active material formed on the negative electrode current collector will come into contact with the positive electrode current collector together with the electrolyte through the pinhole, causing an alloying reaction with lithium in the positive electrode current collector and reducing the charge/discharge capacity. Therefore, in this embodiment, the positive electrode current collector 110 and the negative electrode current collector 130 are electrically connected outside the region where cell C is formed, suppressing such irreversible reactions between the current collectors, resulting in lithium secondary battery 1 having excellent cycle characteristics.

The positive electrode current collector 110 is a current collector made of a conductive material on which the positive electrode 112 is formed. The positive electrode current collector 110 is in physical and/or electrical contact with the positive electrode 112 and functions to donate and receive electrons to and from the positive electrode 112. The positive electrode current collector 110 is made of a conductor such as a metal that does not react with lithium in a lithium secondary battery.

The material that constitutes the positive electrode current collector 110 is not particularly limited, but examples include gold, aluminum, titanium, stainless steel, nickel, and alloys thereof. Among these, gold, aluminum, or aluminum alloys are preferred, with aluminum being particularly preferred. These materials may be used alone or in combination of two or more. In this specification, "metal that does not react with lithium" means a metal that does not react with lithium ions or lithium metal to form an alloy under the operating conditions of a lithium secondary battery.

The positive electrode current collector 110 may be, for example, a metal foil formed on the resin layer 120, or may be a metal foil attached to the resin layer 120 via an adhesive layer. The method for forming the metal foil on the resin layer 120 is not particularly limited, and examples include vapor deposition, sputtering, and electrolytic plating.

The thickness of the positive electrode current collector 110 is not particularly limited, but may be, for example, 0.05 μm or more and 30 μm or less.
In one embodiment, the thickness of the positive electrode current collector 110 is, for example, 0.05 μm to 5.0 μm, preferably 0.1 μm to 4.0 μm, 0.3 μm to 2.5 μm, 0.4 μm to 2.0 μm, or 0.4 μm to 1.5 μm. In this case, for example, the positive electrode current collector 110 may be an electrically conductive layer, such as a metal foil, formed on the resin layer 120.
In one embodiment, the thickness of the positive electrode current collector 110 is, for example, 3.0 μm or more and 30 μm or less, preferably 4.0 μm or more and 25 μm or less, or 5.0 μm or more and 20 μm or less. In this case, for example, the positive electrode current collector 110 may be an electrically conductive layer, such as a metal foil, attached onto the resin layer 120 via an adhesive layer.

1.1.2. Resin Layer The resin layer 120 is an insulating layer containing resin, and prevents electrical conduction between the metal layers provided on both sides of the resin layer. The resin layer 120 is not particularly limited, but may be composed of, for example, a sheet-like (film-like) resin. Examples of resins that constitute the resin layer 120 include polyethylene terephthalate (PET), polypropylene, polyethylene, polyamide, acrylic resin, polycarbonate, polyvinyl chloride, and polystyrene. Among these, it is preferable to include at least one selected from the group consisting of polyolefins and polyesters. The above resins may be used alone or in combination of two or more.

In addition to the resins described above, the resin layer 120 may contain other additives as appropriate depending on the desired physical properties. Additives are not particularly limited, but examples include colorants, flame retardants, surfactants, etc.

The thickness of the resin layer 120 is not particularly limited, but is, for example, 1.0 μm or more and 15 μm or less, preferably 1.0 μm or more and 8.0 μm or less, 2.0 μm or more and 8.0 μm or less, or 3.0 μm or more and 7.0 μm or less.

The negative electrode current collector 130 is a current collector made of a conductive material on which the negative electrode 132 is formed. The negative electrode current collector 130 is in physical and/or electrical contact with the negative electrode 132 and functions to donate and receive electrons to and from the negative electrode 132.

The material that constitutes the negative electrode current collector 130 is not particularly limited, but examples include conductors that do not alloy with lithium in lithium secondary batteries. The negative electrode current collector 130 is preferably made of a material different from the material that constitutes the positive electrode current collector 110. It is more preferable that the positive electrode current collector 110 and the negative electrode current collector 130 are made of different metals.

Examples of materials that can be used to form the negative electrode current collector 130 include gold, copper, nickel, titanium, iron, other metals that do not react with lithium, and alloys of these, as well as stainless steel. Among these, gold, copper, nickel, and alloys of these are preferred, with copper being particularly preferred. Note that a "metal that does not react with lithium" may be a metal that does not react with lithium ions or lithium metal to form an alloy when the lithium secondary battery 1 is in operation. These materials may be used alone or in combination of two or more.

The negative electrode current collector 130 may be, for example, a metal foil formed on the resin layer 120, or may be a metal foil attached to the resin layer 120 via an adhesive layer. The method for forming the metal foil on the resin layer 120 is not particularly limited, and examples include vapor deposition, sputtering, and electrolytic plating.

The thickness of the negative electrode current collector 130 is not particularly limited, but may be, for example, 0.05 μm or more and 30 μm or less.
In one embodiment, the thickness of the negative electrode current collector 130 is, for example, 0.05 μm to 5.0 μm, preferably 0.1 μm to 4.0 μm, 0.3 μm to 2.5 μm, 0.4 μm to 2.0 μm, or 0.4 μm to 1.5 μm. In this case, for example, the negative electrode current collector 130 may be an electrically conductive layer, such as a metal foil, formed on the resin layer 120.
In one embodiment, the thickness of the negative electrode current collector 130 is, for example, 3.0 μm to 30 μm, preferably 4.0 μm to 20 μm, and more preferably 5.0 μm to 15 μm. In this case, for example, the negative electrode current collector 130 may be an electrically conductive layer, such as a metal foil, attached onto the resin layer 120 via an adhesive layer.

1.1.4. Configuration In the bipolar electrode 100, the positive electrode current collector 110 and the negative electrode current collector 130 are electrically connected outside the predetermined region where the electrolyte solution 160 is sealed, i.e., outside the region where the cell C is formed.

FIG. 2 is a schematic cross-sectional view showing an example of a bipolar electrode 100. In the embodiment shown in FIG. 2, the bipolar electrode 100 includes a conductive part 200 that electrically connects the positive electrode current collector 110 and the negative electrode current collector 130 outside the area where the cell C is formed. The conductive part 200 is disposed outside the sealed area of the cell C and is a conductive member that physically and electrically connects the positive electrode current collector 110 and the negative electrode current collector 130.

In one embodiment, the conductive portion 200 is a cured product of a conductive adhesive that is applied across the positive electrode current collector 110 and the negative electrode current collector 130. A conductive adhesive is an adhesive in which conductive filler such as metal particles is dispersed in a binder resin such as epoxy or urethane, and after curing, the filler forms a conductive path, thereby exhibiting conductivity. Examples of conductive adhesives include conductive pastes such as silver paste and anisotropic conductive paste, and anisotropic conductive film.

In this embodiment, the conductive portion 200 is formed on at least a portion of the end of the bipolar electrode 100 so as to straddle the positive electrode current collector 110 and the negative electrode current collector 130. From the perspective of increasing the conductive path between the positive electrode current collector 110 and the negative electrode current collector 130 and providing a battery that suppresses deterioration even during large current charging and discharging (hereinafter, this characteristic will be referred to as "rate characteristics"), it is preferable that the conductive portion 200 be formed on at least 10%, 20%, 30%, 40%, 50%, 60%, or 70% of the perimeter of the end of the bipolar electrode 100. If the bipolar electrode 100 is polygonal in plan view, it is preferable that the conductive portion 200 be provided on each side. For example, if the bipolar electrode 100 is rectangular in plan view, it is preferable that the conductive portion 200 be provided on all four sides. This embodiment tends to make the reactivity within the battery uniform and further improve the cycle characteristics.

In one embodiment, the conductive portion 200 is a metal sheet bonded to each of the positive electrode current collector 110 and the negative electrode current collector 130. There are no particular limitations on the metal that constitutes the metal sheet, but examples include aluminum, titanium, stainless steel, nickel, copper, iron, and alloys thereof, as well as stainless steel.

In one embodiment, the metal sheet may be a sheet formed by joining a first metal sheet joined to the positive electrode current collector 110 and a second metal sheet joined to the negative electrode current collector 130.
In one embodiment, the metal sheet may be a sheet having one end joined to the positive electrode current collector 110 and the other end joined to the negative electrode current collector 130 .

Methods for joining the metal sheet and the current collector are not particularly limited, but include, for example, welding such as ultrasonic welding, laser welding, resistance welding, and spot welding, as well as joining with a conductive adhesive.

FIG. 3 is a schematic enlarged cross-sectional view showing another example of a bipolar electrode 100. In the embodiment shown in FIG. 3, the bipolar electrode 100 forms a bonding region where the positive electrode current collector 110 and the negative electrode current collector 130 are in direct physical contact without the resin layer 120 interposed therebetween outside the region where the cell C is formed, thereby electrically connecting the positive electrode current collector 110 and the negative electrode current collector 130. Note that FIG. 3 is an enlarged view showing the bonding region.

As shown in FIG. 3, the cross section of the bonding region includes a first region R1 and a second region R2. In the first region R1, the positive electrode current collector 110 and the negative electrode current collector 130 are integrally bonded. That is, in the first region R1, the positive electrode current collector 110 and the negative electrode current collector 130 are electrically connected by being in direct physical contact without the resin layer 120 interposed therebetween. The first region R1 may be substantially free of the resin layer 120 along the stacking direction. The first region R1 provides a physical path for electrically connecting the positive electrode current collector 110 and the negative electrode current collector 130.

In one embodiment, the first region R1 may be located between two second regions R2. In the second region R2, the positive electrode current collector 110 and the negative electrode current collector 130 are stacked with the resin layer 120 sandwiched between them. In other words, the second region R2 is a region that includes the resin layer 120 along the thickness direction.

In one embodiment, the first region R1 may be formed by welding. In this case, during welding, the positive electrode current collector 110 and the negative electrode current collector 130 may be pressed together in the thickness direction. This softens the resin layer 120 at the welded location and pushes it outward in the width direction (left and right direction in Figure 3) from the welded location. Furthermore, the positive electrode current collector 110 and the negative electrode current collector 130 are thermally fused and integrated at the welded location. This allows the first region R1 and the second region R2 to be formed. The welding may be, for example, ultrasonic welding, laser welding, resistance welding, or spot welding. One example of the welding is ultrasonic welding.

In the embodiment shown in FIG. 3, the bonding region may be formed in one or more locations outside the region where the cell C is formed. The number of bonding regions formed may be one or more, and may be 1 to 100, 2 to 80, 3 to 70, 4 to 60, 5 to 50, 6 to 40, 7 to 30, or 8 to 25.

Each bonding region may be formed with an area of 0.1 mm ² to 10 cm ² , 1 mm ² to 1 cm ² , 3 mm ² to 50 mm ² , 5 mm ² to 30 mm ² , or 8 mm ² to 20 mm ² .

The total area of the bonded regions may be 1 mm ² to 100 cm ² , 10 mm ² to 10 cm ² , 30 mm ² to 5 cm ² , 50 mm ² to 3 cm ² , or 80 mm ² to 2 cm ² .

FIG. 4 is a schematic enlarged cross-sectional view showing yet another example of a bipolar electrode 100. In the embodiment shown in FIG. 4, the bipolar electrode 100 has a bonding region where the positive electrode current collector 110 and the negative electrode current collector 130 form a bonding region together with a metal sheet 400 disposed on the surface of the positive electrode current collector 110. In the embodiment shown in FIG. 4, the metal sheet 400 is disposed on the surface of the positive electrode current collector 110, but the metal sheet 400 may also be disposed on the surface of the negative electrode current collector 130. Furthermore, the metal sheet 400 may also be disposed on the surfaces of both the positive electrode current collector 110 and the negative electrode current collector 130.

As shown in FIG. 4, the cross section of the bonding region includes a first region R1 and a second region R2. In the first region R1, the positive electrode current collector 110, the negative electrode current collector 130, and the metal sheet 400 are integrally bonded together. In the first region R1, the positive electrode current collector 110 and the negative electrode current collector 130 are electrically connected to each other by direct physical contact without the resin layer 120 in between. However, in the embodiment shown in FIG. 4, unlike the embodiment shown in FIG. 3, the metal sheet 400 is bonded in the bonding region. By using the metal sheet 400 to form the bonding region, the electrical resistance in the bonding region is further reduced, which tends to further improve the rate characteristics and cycle characteristics.

The material constituting the metal sheet 400 is not particularly limited, and any metal can be used. When the metal sheet 400 is disposed and bonded to the surface of the positive electrode current collector 110, examples include aluminum, titanium, stainless steel, nickel, and alloys thereof. Among these, aluminum or aluminum alloys are preferred, and aluminum is particularly preferred. The metal sheet 400 may be the same metal as the metal constituting the positive electrode current collector 110.

When the metal sheet 400 is disposed and bonded to the surface of the negative electrode current collector 130, examples of materials that can be used include aluminum, copper, nickel, titanium, iron, other metals that do not react with lithium, and alloys of these, as well as stainless steel. Among these, aluminum, copper, nickel, and alloys of these are preferred, with aluminum and copper being particularly preferred. The metal sheet 400 may be the same metal as the metal that constitutes the negative electrode current collector 130.

Other than having the metal sheet 400, the embodiment shown in Figure 4 may be similar to the embodiment shown in Figure 3.

1.1.5 Adhesive Layer The bipolar electrode 100 may further include an adhesive layer between the positive electrode current collector 110 and the resin layer 120, or between the resin layer 120 and the negative electrode current collector 130. The bipolar electrode 100 including the adhesive layer can be easily fabricated by attaching a metal foil positive electrode current collector or negative electrode current collector to a resin layer having a positive electrode current collector or negative electrode current collector formed on one side thereof.

The adhesive layer can be an adhesive or adhesive sheet commonly used in the field of batteries. The adhesive material contained in the adhesive layer is not particularly limited, but examples of adhesive polymers that can be used include isocyanate-based, polyvinyl alcohol-based, gelatin-based, vinyl latex-based, aqueous polyester-based, natural rubber-based, synthetic rubber-based, acrylic resin-based, silicone-based, urethane-based, vinyl alkyl ether-based, polyvinyl alcohol-based, polyvinylpyrrolidone-based, polyacrylamide-based, and cellulose-based adhesive polymers.

The thickness of the adhesive layer is not particularly limited, but is, for example, 0.1 μm or more and 10 μm or less, or 1.0 μm or more and 8.0 μm or less.

The positive electrode 112 is a layer containing a positive electrode active material formed on the positive electrode current collector 110. The positive electrode active material is a material for retaining lithium elements in the positive electrode 112, and can also be called a host material for lithium elements (lithium ions). Lithium ions are charged into and released from the positive electrode active material as the battery is charged and discharged.

In one embodiment, the positive electrode active material is a metal oxide or a metal phosphate. The metal oxide may be, for example, a cobalt oxide-based compound, a manganese oxide-based compound, or a nickel oxide-based compound. The metal phosphate may be, for example, an iron phosphate-based compound or a cobalt _phosphate -based compound. In one embodiment, the positive electrode active material may be at least one selected from the group consisting of _LiCoO2 , _LiNixCoyMnzO (x+ _y + _{z =} 1), _LiNixCoyAlzO (x+y+ _z =1), LiNixMnyO(x+y=1) _{, LiNiO2 , LiMn2O4} , _LiFePO4 , _LiCoPO4 , LiFeOF, LiNiOF, and _LiTiS2 . The positive electrode active material may be used alone or in combination of two or more. In one embodiment, the content of the positive electrode active material in the positive electrode 112 may be 50% by mass or more and 100% by mass or less with respect to the entire positive electrode 112.

In one embodiment, the positive electrode 112 may contain one or more components other than the positive electrode active material. Such components include a sacrificial positive electrode agent, a polymer electrolyte, a conductive additive, and a binder.

The sacrificial positive electrode agent is a lithium-containing compound that undergoes an oxidation reaction and does not substantially undergo a reduction reaction in the charge/discharge potential range of the positive electrode active material. In one embodiment, the total content of the sacrificial positive electrode agent may be 0% by mass or more and 10% by mass or less with respect to the entire positive electrode 112.

The polymer electrolyte may be, for example, a solid polymer electrolyte containing primarily a polymer and an electrolyte, or a semi-solid polymer electrolyte containing primarily a polymer, an electrolyte, and a plasticizer. The polymer electrolyte may be a gel electrolyte containing a polymer, an organic solvent, and a lithium salt. The polymer in the gel electrolyte may be, for example, a copolymer of polyethylene and/or polyethylene oxide, polyvinylidene fluoride, or a copolymer of polyvinylidene fluoride and hexafluoropropylene. In one embodiment, the total content of the polymer electrolyte may be 0% by mass or more and 30% by mass or less with respect to the entire positive electrode 112.

The conductive additive may be, for example, carbon black, single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), carbon nanofibers (CF), or the like.
The binder may be, for example, polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, acrylic resin, polyimide resin, or the like.
The content of the conductive additive and the content of the binder may be independently 0% by mass or more and 30% by mass or less with respect to the total mass of the positive electrode 112 .

The positive electrode 112 may be made of a known material selected appropriately depending on the application. The thickness of the positive electrode 112 may be adjusted appropriately depending on the desired battery capacity and rate characteristics. In one embodiment, the thickness of each positive electrode 112 is, for example, 20 μm or more and 150 μm or less.

1.3. Negative Electrode The negative electrode 132 is a layer containing a negative electrode active material formed on the negative electrode current collector 130. The negative electrode active material is a material that causes an electrode reaction, i.e., an oxidation reaction and a reduction reaction, in the negative electrode 132. Specifically, the negative electrode active material in this embodiment includes lithium metal and a host material of lithium element (lithium ion or lithium metal). The host material of lithium element refers to a material provided to hold lithium ion or lithium metal in the negative electrode 132. Examples of such a holding mechanism include intercalation, alloying, and occlusion of metal clusters, and intercalation is typically used.

Anode active materials are not particularly limited, but examples include lithium metal and alloys containing lithium metal, carbon-based materials, metal oxides, metals that alloy with lithium, and alloys containing such metals. The carbon-based materials are not particularly limited, but examples include graphene, graphite, hard carbon, and carbon nanotubes. The metal oxides are not particularly limited, but examples include titanium oxide-based compounds and cobalt oxide-based compounds. The metals that alloy with lithium are not particularly limited, but examples include silicon, germanium, tin, lead, aluminum, and gallium.

In the lithium secondary battery of this embodiment, the negative electrode active material may be lithium metal. In this case, lithium metal is deposited on the negative electrode current collector 130 after the initial charge of the lithium secondary battery 1, and the deposited lithium metal is then electrolytically dissolved, thereby charging and discharging. In other words, in this case, the negative electrode 132 is lithium metal. Therefore, such a battery has the advantage of, in principle, having a high energy density because the volume and mass occupied by the negative electrode active material are reduced, resulting in a smaller overall battery volume and mass.

1.4. Separator The separator 140 is not particularly limited as long as it has the function of physically and/or electrically isolating the positive electrode 112 and the negative electrode 132 and the function of ensuring ionic conductivity of lithium ions. Examples of such a separator include an insulating porous material, a polymer electrolyte, and a gel electrolyte. The separator 140 may be made of one material alone or a combination of two or more materials.

The separator 140 is preferably made of an insulating porous material, a polymer electrolyte, or a gel electrolyte, either singly or in combination.
The polymer electrolyte is not particularly limited, but examples thereof include solid polymer electrolytes mainly containing a polymer and an electrolyte, and semi-solid polymer electrolytes mainly containing a polymer, an electrolyte, and a plasticizer.
The gel electrolyte is not particularly limited, but examples thereof include those that mainly contain a polymer and a liquid electrolyte (i.e., a solvent and an electrolyte).

Polymers that can be contained in polymer electrolytes and gel electrolytes include, but are not limited to, polymers containing functional groups containing oxygen atoms such as ethers and esters, halogen groups, and polar groups such as cyano groups. Specific examples include resins having ethylene oxide units in the main chain and/or side chains such as polyethylene oxide (PEO), resins having propylene oxide units in the main chain and/or side chains such as polypropylene oxide (PPO), acrylic resins, vinyl resins, ester resins, nylon resins, polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polysiloxane, polyphosphazene, polymethyl methacrylate, polyamide, polyimide, aramid, and polytetrafluoroethylene. The above resins may be used alone or in combination of two or more.

Examples of electrolytes contained in the polymer electrolyte and gel electrolyte include salts of Li, Na, K, Ca, and Mg. Typically, in this embodiment, the polymer electrolyte and gel electrolyte contain a lithium salt. The lithium salt is not particularly limited, but may be, for example, any salt that can be contained in the electrolyte solution described below. Such salts or lithium salts may be used alone or in combination of two or more.

The compounding ratio of the polymer to the lithium salt in the polymer electrolyte and gel electrolyte may be determined by the ratio of the polar groups in the polymer to the lithium atoms in the lithium salt. For example, if the polymer contains oxygen atoms, it may be determined by the ratio ([Li]/[O]) of the number of oxygen atoms in the polymer to the number of lithium atoms in the lithium salt. In the polymer electrolyte and gel electrolyte, the compounding ratio of the polymer to the lithium salt can be adjusted so that the ratio ([Li]/[O]) is, for example, 0.02 or more and 0.20 or less, 0.03 or more and 0.15 or less, or 0.04 or more and 0.12 or less.

The solvent contained in the gel electrolyte is not particularly limited, but for example, the solvents that can be contained in the electrolyte solution described later can be used alone or in combination of two or more. Preferred examples of the solvent are also the same as those for the electrolyte solution described later.
The plasticizer contained in the semi-solid polymer electrolyte is not particularly limited, but examples thereof include components similar to the solvent that can be contained in the gel electrolyte, and various oligomers.

When separator 140 includes an insulating porous member, the pores of the member are filled with an ionically conductive substance, causing the member to exhibit ion conductivity. The material that constitutes the insulating porous member is not particularly limited, and examples include insulating polymer materials, specifically polyethylene (PE) and polypropylene (PP). In other words, separator 140 may be a porous polyethylene (PE) film, a porous polypropylene (PP) film, or a laminated structure of these.

1.5. Electrolyte The electrolyte 160 is a liquid containing a solvent and an electrolyte, and has ion conductivity. The electrolyte may also be referred to as a liquid electrolyte, and acts as a conductive path for lithium ions. The electrolyte is a solution that fills each cell C.

The electrolyte contained in the electrolytic solution may be a lithium salt, and the lithium salt _may be, for example, one or _a combination _of two or _more selected from the group consisting of _LiI , LiCl, LiBr, LiF, _LiBF4 , _LiPF6 , _{LiAsF6 , LiSO3CF3} , _LiN ( _SO2F ) ₂ , LiN( _SO2CF3 ) ₂ , LiN( _SO2CF3CF3 ) _{2 ,} LiB( _O2C2H4 ) ₂ , _LiB (C2O4) ₂ , _LiB (O2C2H4 _{) F2} , LiB( _OCOCF3 ) ₄ , LiNO3, _{and Li2SO4 .}

Solvents contained in the electrolyte solution include, for example, non-aqueous solvents containing fluorine atoms (hereinafter referred to as "fluorinated solvents") and non-aqueous solvents not containing fluorine atoms (hereinafter referred to as "non-fluorinated solvents").

Examples of fluorinated solvents include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

Examples of non-fluorinated solvents include triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,2-dimethoxyethane, dimethoxyethane, dimethoxypropane, dimethoxybutane, diethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, chloroethylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, trimethyl phosphate, triethyl phosphate, and 12-crown-4.

The solvent in the electrolyte may be used alone, or two or more may be used in any desired combination in any desired ratio. The contents of the above-mentioned fluorinated solvent and non-fluorinated solvent are not particularly limited, and the ratio of the fluorinated solvent to the total solvent may be 0 to 100% by volume, and the ratio of the non-fluorinated solvent to the total solvent may be 0 to 100% by volume.

1, the lithium secondary battery 1 includes a sealing member 150 that seals the electrolyte 160 in a predetermined region. The sealing member 150 may have any configuration as long as it serves to define a region including the positive electrode 112, the separator 140, the negative electrode 132, and the electrolyte 160. A cell C is formed by defining the region with the sealing member 150, the positive electrode current collector 110, and the negative electrode current collector 130.

The sealing member 150 is, for example, a member that is impermeable to the electrolyte 160 and can accommodate the positive electrode 112, separator 140, and negative electrode 132. Specifically, it may be, for example, a member with a through-hole that can be adhered to the positive electrode current collector 110 and negative electrode current collector 130. With such a member, cell C can be easily formed by accommodating the positive electrode 112, separator 140, negative electrode 132, and electrolyte 160 in the through-hole and sealing the two openings of the through-hole with the positive electrode current collector 110 and negative electrode current collector 130.

The sealing member 150 may be, for example, a frame made of a resin sheet. The planar shape (external shape) of the frame may be any shape. The frame can be made by forming through holes in the resin sheet. The planar shape of the through holes may be the same as the planar shapes of the positive electrode 112, separator 140, and negative electrode 132. The through holes are preferably sized to accommodate the positive electrode 112, separator 140, and negative electrode 132 with almost no gaps.

The thickness of the sealing member 150 is not particularly limited, but is preferably thicker than the combined thickness of the positive electrode 112, separator 140, and negative electrode 132. The thickness of the sealing member 150 is, for example, 30 μm or more and 5 mm or less, preferably 50 μm or more and 1 mm or less, and 100 μm or more and 500 μm or less.

The material that constitutes the sealing member 150 is not particularly limited, but it can be made of a film such as polyethylene terephthalate (PET) or polyvinyl chloride. To facilitate adhesion to the positive electrode current collector 110 and the negative electrode current collector 130, the sealing member 150 is preferably a heat-welded resin film.

1.7. Other Configurations The lithium secondary battery 1 preferably has current collectors at the top and bottom of the bipolar electrode 100 stack (the top and bottom layers in FIG. 1 ). A positive electrode current collector 110 is provided at either the top or bottom, and a negative electrode current collector 130 is provided at the other. Whether the positive electrode current collector 110 or the negative electrode current collector 130 is provided at the top or bottom may be determined depending on the stacking orientation of the bipolar electrode 100. For example, in the embodiment shown in FIG. 1 , the bipolar electrode 100 is stacked so that the positive electrode current collector 110 faces upward, so the negative electrode current collector 130 is disposed at the top and the positive electrode current collector 110 is disposed at the bottom. Therefore, by disposing current collectors at both ends of the stacking direction of the stack (the top and bottom in FIG. 1 ), cells C are formed at both ends.

In the lithium secondary battery 1, the current collectors at both ends of the stacking direction of the laminate may be provided with positive and negative electrode tabs, respectively. Providing such tabs makes it easier to connect the lithium secondary battery 1 to an external circuit.

The negative electrode tab may be made of, for example, at least one material selected from the group consisting of copper, titanium, stainless steel, nickel, and alloys thereof.
The positive electrode tab may be made of, for example, aluminum or an aluminum alloy.
The negative electrode tab and the positive electrode tab may be joined to the current collector by welding, for example, ultrasonic welding, laser welding, resistance welding, or spot welding.

2. Method for Producing Lithium Secondary Battery The method for producing the lithium secondary battery according to this embodiment is not particularly limited, but it can be produced, for example, by the following method.

The lithium secondary battery according to this embodiment can generally be manufactured by forming a positive electrode and a negative electrode on a bipolar electrode and then stacking them. Each step will be explained below with reference to the figures.

First, a bipolar electrode such as that described above is prepared. For example, a positive electrode current collector and/or a negative electrode current collector is formed by depositing metal foil on a resin film, which is a resin layer, using methods such as vapor deposition, sputtering, and electrolytic plating. Alternatively, a positive electrode current collector and/or a negative electrode current collector may be formed on the resin layer by attaching metal foil to the resin film via an adhesive layer. In this process, the thickness of the positive electrode current collector and a negative electrode current collector can be adjusted by appropriately changing the deposition conditions and the thickness of the attached metal foil.

Next, a positive electrode is formed on the positive electrode current collector, and a negative electrode is formed on the negative electrode current collector.
The positive electrode can be formed, for example, as follows. First, a positive electrode active material and, if necessary, one or more of a conductive additive, a binder, and a polymer electrolyte are mixed to obtain a positive electrode mixture. The blending ratios thereof may be, for example, 50% by mass or more and 99% by mass or less of the positive electrode active material, 0% by mass or more and 30% by mass or less of the conductive additive, 0% by mass or more and 30% by mass or less of the binder, and 0% by mass or more and 30% by mass or less of the polymer electrolyte, relative to the total positive electrode mixture. The obtained positive electrode mixture is applied to one side of a positive electrode current collector and dried to obtain a positive electrode formed on the positive electrode current collector.

The negative electrode can be formed, for example, as follows. First, a negative electrode active material and, if necessary, one or more conductive additives and binders are mixed to obtain a negative electrode mixture. The blending ratios may be, for example, 50% to 99% by mass of the negative electrode active material, 0% to 30% by mass of the conductive additive, and 0% to 30% by mass of the binder relative to the total negative electrode mixture. The resulting negative electrode mixture is applied to one side of a negative electrode current collector and dried to obtain a negative electrode formed on the negative electrode current collector. Note that when lithium metal is used as the negative electrode active material, the negative electrode may not be formed during the battery manufacturing process, but may be formed by depositing lithium metal on the negative electrode current collector when the battery is assembled and initially charged.

In this manner, a bipolar electrode 100 having a positive electrode 112 and a negative electrode 132 formed thereon is prepared, as shown in FIG. 5(A). Next, as shown in FIG. 5(A), separators of similar size and shape to the positive electrode 112 and a negative electrode 132 are arranged, and sealing members 150 having through holes of similar size and shape to the positive electrode 112 and a negative electrode 132 are arranged on the positive electrode current collector 110 and the negative electrode current collector 130, respectively. The sealing members 150 may be, for example, heat-sealed resin films, and are adhered to the positive electrode current collector 110 and the negative electrode current collector 130, respectively.

Next, as shown in FIG. 5(B), electrolyte solution 160 is poured into the frame of the sealing member 150, and the opening is sealed with a bipolar electrode 100 formed with a positive electrode 112 and a negative electrode 132. The bipolar electrodes 100 are stacked so that the positive electrode 112 and the negative electrode 132 face each other with the separator 140 interposed between them. By bringing the sealing member 150 into close contact with the bipolar electrode 100, a cell C is formed in which the electrolyte solution 160 is sealed.

By repeating the process of placing separators 140, injecting electrolyte 160, and stacking bipolar electrodes 100 in this manner, a stacked structure of bipolar electrodes 100 can be formed. Then, by placing a positive electrode current collector 110 with a positive electrode 112 and a negative electrode current collector 130 with a negative electrode 132 at both ends of the stacking direction of the stack (the top and bottom of Figure 5(B)), cells C are formed at both ends, and the lithium secondary battery 1 shown in Figure 1 can be produced.

The shape of the lithium secondary battery according to this embodiment is not particularly limited, and may be, for example, a sheet type, a laminated sheet type, a thin type, a cylindrical type with a bottom, a prismatic type with a bottom, etc.

3. Applications The lithium secondary battery according to this embodiment may be used in machines, electronic devices, appliances, devices, systems (assemblies of multiple devices, etc.) that can use a secondary battery as a driving power source or a power storage source for storing power, etc. For example, the lithium secondary battery according to this embodiment may be used as a battery pack that includes the lithium secondary battery according to this embodiment and a housing.

The housing houses the lithium secondary battery according to this embodiment and serves to protect it from external impacts. The housing may be made of plastic, rubber, metal, or a combination of these.

The battery pack may include one or more lithium secondary batteries according to this embodiment, and may include multiple lithium secondary batteries according to this embodiment. In one embodiment, the battery pack may include a battery pack including multiple lithium secondary batteries according to this embodiment. The battery pack may include lithium secondary batteries according to this embodiment electrically connected in series, parallel, or a combination of series and parallel.

The battery pack may include external current-carrying terminals connected to the lithium secondary battery of this embodiment. The external current-carrying terminals are for outputting current from the lithium secondary battery of this embodiment to the outside and/or for inputting current from the outside to the lithium secondary battery of this embodiment. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external current-carrying terminals. Furthermore, when charging the battery pack, charging current (including regenerative energy from the power of an automobile, etc.) is supplied to the battery pack through the external current-carrying terminals.

The battery pack may be equipped with a protection circuit that controls the functions of the lithium secondary battery according to this embodiment. The protection circuit controls the charging and discharging of the lithium secondary battery according to this embodiment. Note that a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobiles, etc.) may also be used as the protection circuit for the battery pack.

The lithium secondary battery and battery pack according to this embodiment may be included in electronic devices. Examples of electronic devices include, but are not limited to, cameras, mobile phones, laptop computers, radios, portable televisions, and portable information terminals.

The lithium secondary battery and battery pack according to this embodiment may be provided in a vehicle. The vehicle is preferably an electric vehicle or a hybrid vehicle. The vehicle is preferably equipped with a regenerative mechanism that converts the vehicle's kinetic energy into regenerative energy and stores it in the lithium secondary battery and/or battery pack according to this embodiment.

A vehicle may be equipped with multiple battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, electrically connected in parallel, or electrically connected using a combination of series and parallel connections. For example, if each battery pack includes a battery pack, the battery packs may be electrically connected in series, electrically connected in parallel, or electrically connected using a combination of series and parallel connections. If each battery pack includes a single battery, the batteries may be electrically connected in series, electrically connected in parallel, or electrically connected using a combination of series and parallel connections.

<Additional Notes>
Embodiments of the present disclosure include the following aspects.
[1]
a laminate including a plurality of bipolar electrodes, each of which has a positive electrode current collector, a resin layer, and a negative electrode current collector stacked in this order;
the stack includes an electrolyte sealed in a predetermined region between each of the opposing bipolar electrodes;
In each of the bipolar electrodes, the positive electrode current collector and the negative electrode current collector are electrically connected outside the predetermined region.
Bipolar lithium secondary battery.
[2]
The thickness of the positive electrode current collector or the negative electrode current collector is 0.05 μm or more and 5.0 μm or less.
The bipolar lithium secondary battery according to [1].
[3]
the positive electrode current collector and the negative electrode current collector are made of different metals;
The bipolar lithium secondary battery according to [1] or [2].
[4]
The thickness of the resin layer is 1.0 μm or more and 8.0 μm or less.
The bipolar lithium secondary battery according to any one of [1] to [3].
[5]
The resin layer contains at least one selected from the group consisting of polyolefins and polyesters.
The bipolar lithium secondary battery according to any one of [1] to [4].
[6]
the bipolar electrode further includes an adhesive layer at least one between the positive electrode current collector and the resin layer and between the resin layer and the negative electrode current collector;
[1] The bipolar lithium secondary battery according to any one of [1] to [5].
[7]
the bipolar electrode further includes a conductive portion that electrically connects the positive electrode current collector and the negative electrode current collector outside the predetermined region;
The bipolar lithium secondary battery according to any one of [1] to [6].
[8]
the conductive portion is a cured product of a conductive adhesive applied to straddle the positive electrode current collector and the negative electrode current collector;
The bipolar lithium secondary battery according to [7].
[9]
the conductive portion is a metal sheet joined to each of the positive electrode current collector and the negative electrode current collector,
The bipolar lithium secondary battery according to [7].
[10]
the metal sheet is formed by joining a first metal sheet joined to the positive electrode current collector and a second metal sheet joined to the negative electrode current collector outside the predetermined region;
The bipolar lithium secondary battery according to [9].
[11]
the positive electrode current collector and the negative electrode current collector form a joining region in which they are in direct physical contact with each other outside the predetermined region without the resin layer therebetween, thereby electrically connecting the positive electrode current collector and the negative electrode current collector;
The bipolar lithium secondary battery according to any one of [1] to [6].
[12]
In the bonding region, the positive electrode current collector and the negative electrode current collector form the bonding region together with a metal sheet disposed on a surface of the positive electrode current collector or the negative electrode current collector.
The bipolar lithium secondary battery according to [11].
[13]
A battery pack comprising the bipolar lithium secondary battery according to any one of [1] to [12] and a housing.
[14]
The battery pack according to [13], further comprising an external terminal for current supply connected to the bipolar lithium secondary battery, and a protection circuit.
[15]
A battery pack includes a plurality of the bipolar lithium secondary batteries,
The battery pack according to [13] or [14], wherein the bipolar lithium secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.
[16]
An electronic device comprising the battery pack according to any one of [13] to [15].
[17]
A vehicle equipped with the battery pack according to any one of [13] to [15].
[18]
The vehicle according to [17], further comprising a mechanism for converting kinetic energy of the vehicle into regenerative energy and storing the energy in the battery pack.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples.

1. Fabrication of a Lithium Secondary Battery (Example 1)
A 0.5 μm thick aluminum layer was vapor-deposited on one side of a 6 μm thick polyethylene terephthalate (PET) resin layer to form a positive electrode current collector. A 0.5 μm thick copper layer was vapor-deposited on the opposite side of the resin layer to form a negative electrode current collector. This sheet was cut into a size of 6.0 cm × 7.0 cm to form an electrode in which a positive electrode current collector, a resin layer, and a negative electrode current collector were formed in this order.

Next, to form the negative electrode, 97 parts by mass of graphite as the negative electrode active material, 0.5 parts by mass of carbon black as a conductive additive, and 1.5 parts by mass of carboxymethyl cellulose (CMC) and 1.0 part by mass of styrene-butadiene rubber (SBR) as binders were added to water as a solvent to prepare a negative electrode mixture material.

To form the positive electrode, 96 _parts by mass of _{LiNi0.8Co0.15Al0.05O2} as _the positive electrode active material, 2 parts by mass of carbon black as a conductive additive, and 2 parts by mass of polyvinylidene fluoride (PVDF) as a binder were added to N-methyl _- pyrrolidone (NMP) as a solvent to prepare a positive electrode mixture material.

The negative electrode mixed material was applied to an area of 5.0 cm x 5.0 cm using a screen printer on the surface of the electrode prepared above where copper was formed as the negative electrode current collector. The negative electrode mixed material was applied so that the basis weight was 15 mg/ ^cm2 . Next, the positive electrode mixed material was applied to an area of 4.0 cm x 4.0 cm using a screen printer on the surface of the electrode prepared above where aluminum was formed as the positive electrode current collector. The positive electrode mixed material was applied so that the basis weight was 23 mg/ ^cm2 . The negative electrode mixed material and the positive electrode mixed material were applied so that the center of the negative electrode and the center of the positive electrode coincided.

Next, silver paste was applied to the sides (all four peripheral surfaces) of the electrode, which had the positive electrode current collector, resin layer, and negative electrode current collector formed in that order, and then dried to electrically connect the positive electrode current collector and negative electrode current collector. In this way, a bipolar electrode was produced.

Next, a sheet of polyethylene microporous membrane (thickness: 15 μm, 5.2 cm×5.2 cm) whose surface was coated with a mixture of polyvinylidene fluoride (PVDF) and Al ₂ O ₃ was prepared as a separator.

In addition, an electrolyte solution was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at 1 M in a solvent containing a 30:35:35 mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a ratio of 30:35:35 parts by mass, and adding 2 parts by mass of vinylene carbonate (VC) to the solution.

Next, a heat-sealing film (manufactured by DNP, heat-sealing film) serving as a sealing member was cut to a size of 6.0 cm x 8.0 cm, and a through-hole was formed by punching out an area of 5.2 cm x 5.2 cm.

The heat-sealed film was placed on the negative electrode current collector so that the center of the through-hole in the heat-sealed film was aligned with the center of the negative electrode. The heat-sealed film was then heated with a heat sealer to bond the heat-sealed film to the negative electrode current collector.

A separator was placed in the through-hole in the heat-sealed film, and another bipolar electrode that had been treated for conductivity was placed over it. After injecting the electrolyte, the positive electrode current collector of the newly installed bipolar electrode was sealed to the heat-sealed film with a heat sealer. This resulted in the positive electrode, separator, and negative electrode being stacked in that order between the two bipolar electrodes, forming a sealed cell together with the electrolyte.

The above process was repeated to stack four bipolar electrodes and form three cells. Next, in order to seal both ends of this stack in the stacking direction, a negative electrode with a negative electrode formed on one side and a positive electrode with a positive electrode formed on the other side were fabricated as follows.

First, a 6.0 cm × 9.0 cm sheet of 8 μm copper foil was prepared as a negative electrode current collector. Using a screen printer, the negative electrode mixture was applied to the copper foil in an area of 5.0 cm × 5.0 cm. The negative electrode mixture was applied to a basis weight of 15 mg/ ^cm² .

Additionally, a 6.0 cm × 9.0 cm aluminum foil with a thickness of 12 μm was prepared as a positive electrode current collector. Using a screen printer, the positive electrode mixture material was applied to an area of 4.0 cm × 4.0 cm on the aluminum foil. The positive electrode mixture material was applied so that the basis weight was 23 mg/ ^cm² .

Four bipolar electrodes were stacked to form three cells. A negative electrode with a negative electrode formed on one side and a positive electrode with a positive electrode formed on the other side were attached to both ends of the stacking direction of the laminate. The attachment was performed by heating the heat-sealing film with a heat sealer.

Furthermore, a 0.2 mm thick piece of nickel-plated copper was ultrasonically welded to the portion of the negative electrode current collector where the negative electrode was not formed, to form an electrode tab for the negative electrode. Similarly, a 0.2 mm thick piece of aluminum was ultrasonically welded to the portion of the positive electrode current collector where the positive electrode was not formed, to form an electrode tab for the positive electrode. In this way, the bipolar lithium secondary battery of Example 1 was fabricated.

Example 2
The bipolar lithium secondary battery of Example 2 was fabricated in the same manner as Example 1, except that in forming the bipolar electrode, instead of electrically connecting the positive electrode current collector and the negative electrode current collector with silver paste, the laminated structure of the positive electrode current collector, resin layer, and negative electrode current collector was welded with an ultrasonic welder to physically contact the positive electrode current collector and the negative electrode current collector, thereby electrically connecting the positive electrode current collector and the negative electrode current collector. Welding was performed in three places on each side (12 places in total) within an area of 2 mm x 5 mm.

Example 3
A bipolar lithium secondary battery of Example 3 was produced in the same manner as in Example 2, except that in forming the bipolar electrode, when the laminated structure of the positive electrode current collector, resin layer, and negative electrode current collector was welded by an ultrasonic welding machine, a 7.0 μm thick aluminum foil was placed on the negative electrode current collector side as a metal sheet before welding, thereby electrically connecting the positive electrode current collector and the negative electrode current collector.

Example 4
The bipolar lithium secondary battery of Example 4 was produced in the same manner as in Example 1, except that in forming the bipolar electrode, instead of electrically connecting the positive electrode source current body and the negative electrode current collector with silver paste, a 12 μm thick aluminum foil was ultrasonically welded to the positive electrode current collector as a first metal sheet, a 12 μm thick aluminum foil was ultrasonically welded to the negative electrode current collector as a second metal sheet, and the first metal sheet and the second metal sheet were further ultrasonically welded together to electrically connect the positive electrode source current body and the negative electrode current collector.

Examples 5 and 6
Bipolar lithium secondary batteries of Examples 5 and 6 were fabricated in the same manner as in Example 3, except that in forming the bipolar electrode, a 6 μm thick polyethylene (PE) or polypropylene (PP) was used instead of a 6 μm thick polyethylene terephthalate (PET) resin layer.

Example 7
A bipolar lithium secondary battery of Example 7 was fabricated in the same manner as in Example 2, except that the bipolar electrode was formed as follows.
First, 0.5 μm of aluminum was vapor-deposited onto one side of a 6 μm-thick polyethylene terephthalate (PET) resin layer as a positive electrode current collector. A 12 μm-thick copper foil was attached to the opposite side of the resin layer as a negative electrode current collector using an acrylic resin adhesive. This sheet was cut into a size of 6.0 cm x 7.0 cm to form an electrode consisting of a positive electrode current collector, a resin layer, an adhesive layer, and a negative electrode current collector formed in this order. The adhesive layer was 3 μm thick.

(Example 8)
A bipolar lithium secondary battery of Example 8 was fabricated in the same manner as in Example 2, except that the bipolar electrode was formed as follows.
First, 0.5 μm of copper was vapor-deposited onto one side of a 6 μm-thick polyethylene terephthalate (PET) resin layer as a negative electrode current collector. A 20 μm-thick aluminum foil was attached to the opposite side of the resin layer using an acrylic resin adhesive. This sheet was cut into a size of 6.0 cm x 7.0 cm to form an electrode consisting of a positive electrode current collector, an adhesive layer, a resin layer, and a negative electrode current collector, in that order. The thickness of the adhesive layer was 3 μm.

Examples 9 and 10
A bipolar lithium secondary battery of Example 9 was fabricated in the same manner as in Example 3, except that in forming the bipolar electrode, copper was vapor-deposited to a thickness of 0.05 μm as the negative electrode current collector.
Furthermore, a bipolar lithium secondary battery of Example 9 was fabricated in the same manner as in Example 3, except that in forming the bipolar electrodes, aluminum of 1.0 μm was vapor-deposited as the positive electrode current collector and copper of 3.0 μm was vapor-deposited as the negative electrode current collector.

Examples 11 and 12
Bipolar lithium secondary batteries of Examples 11 and 12 were fabricated in the same manner as in Example 2, except that in forming the bipolar electrode, the thickness of the polyethylene terephthalate (PET) resin layer was changed from 6 μm to 8 μm or 2 μm.

Example 13
A bipolar lithium secondary battery of Example 13 was fabricated in the same manner as in Example 3, except that in forming the bipolar electrode, gold was vapor-deposited to a thickness of 0.05 μm as the positive electrode current collector.

Example 14
A bipolar lithium secondary battery of Example 14 was fabricated in the same manner as in Example 2, except that in forming the bipolar electrode, the thickness of the polyethylene terephthalate (PET) resin layer was changed from 6 μm to 12 μm.

Example 15
A bipolar lithium secondary battery of Example 15 was fabricated in the same manner as in Example 1, except that in forming the bipolar electrode, the thickness of the polyethylene terephthalate (PET) resin layer was changed from 6 μm to 12 μm.

(Comparative Example 1)
A bipolar lithium secondary battery of Comparative Example 1 was fabricated in the same manner as in Example 1, except that the bipolar electrodes were formed as follows.
A 20 μm aluminum foil as a positive electrode current collector and a 12 μm copper foil as a negative electrode current collector were bonded together using an acrylic resin adhesive. This sheet was cut into a size of 6.0 cm x 7.0 cm to form an electrode in which a positive electrode current collector, an adhesive layer, and a negative electrode current collector were formed in this order. Next, a negative electrode and a positive electrode were formed in the same manner as in Example 1 to produce a bipolar electrode. The adhesive layer had a thickness of 3 μm.

(Comparative Example 2)
A bipolar lithium secondary battery of Comparative Example 2 was fabricated in the same manner as in Example 1, except that the bipolar electrodes were formed as follows.
A 20 μm thick aluminum foil was used as a positive electrode current collector, and a 0.5 μm thick copper film was vapor-deposited as a negative electrode current collector. This sheet was cut into a size of 6.0 cm × 7.0 cm to form an electrode including a positive electrode current collector and a negative electrode current collector. Next, a negative electrode and a positive electrode were formed in the same manner as in Example 1 to prepare a bipolar electrode.

(Comparative Example 3)
A bipolar lithium secondary battery of Comparative Example 3 was fabricated in the same manner as in Comparative Example 2, except that in forming the bipolar electrode, the thickness of the copper serving as the negative electrode current collector was changed from 0.5 μm to 3.0 μm.

2. Evaluation of Lithium Secondary Battery 2.1. Cycle Characteristics In a thermostatic chamber at 25°C, while applying an external pressure of 50 kPa, the battery was CC charged at a current of 9 mA until the voltage reached 21.0 V, and then CC discharged at a current of 9 mA until the voltage reached 15.0 V. CC charging refers to charging at a constant current value, and CC discharging refers to discharging at a constant current value. Charging and discharging were repeated under the same conditions. The discharge capacity at the 100th cycle was calculated based on the discharge capacity at the first cycle, and the cycle capacity retention rate was calculated. A higher cycle capacity retention rate indicates better cycle characteristics. The results are shown in Table 1 as "cycle characteristics."

2.2. Rate Characteristics The fabricated lithium secondary batteries were charged in a thermostatic chamber at 25°C under an external pressure of 50 kPa at a current of 3 mA (0.05 C rate) until the voltage reached 21.0 V, and then discharged at a current of 6 mA (0.1 C rate) until the voltage reached 15.0 V (first cycle). Following the first cycle, the batteries were charged at a current of 3 mA (0.05 C rate) until the voltage reached 21.0 V, and then discharged at a current of 180 mA (3 C rate) until the voltage reached 15.0 V (second cycle). The ratio of the discharge capacity at the second cycle to the discharge capacity at the first cycle was calculated to calculate the discharge rate characteristics. A higher discharge rate characteristic indicates better rate characteristics. The results are shown in Table 1 as "Rate Characteristics."

2.3 Safety The battery was charged in a constant temperature bath at 25°C with an external pressure of 50 kPa and a current of 3 mA until the voltage reached 21.0 V. The battery was then removed from the jig and subjected to a nail penetration test. The nail penetration test involves penetrating a nail into the battery to forcibly cause an internal short circuit. Table 1 shows the changes in appearance during the nail penetration test.

1...Bipolar lithium secondary battery (lithium secondary battery), 100...Bipolar electrode, 110...Positive electrode current collector, 112...Positive electrode, 120...Resin layer, 130...Negative electrode current collector, 132...Negative electrode, 140...Separator, 150...Sealing member, 160...Electrolyte, 200...Conductive part, 400...Metal sheet, C...Cell, R1...First region, R2...Second region.

Claims (18)

a laminate including a plurality of bipolar electrodes, each of which has a positive electrode current collector, a resin layer, and a negative electrode current collector stacked in this order;
the stack includes an electrolyte sealed in a predetermined region between each of the opposing bipolar electrodes;
In each of the bipolar electrodes, the positive electrode current collector and the negative electrode current collector are electrically connected outside the predetermined region.
Bipolar lithium secondary battery. The thickness of the positive electrode current collector or the negative electrode current collector is 0.05 μm or more and 5.0 μm or less.
2. The bipolar lithium secondary battery according to claim 1. the positive electrode current collector and the negative electrode current collector are made of different metals;
2. The bipolar lithium secondary battery according to claim 1. The thickness of the resin layer is 1.0 μm or more and 8.0 μm or less.
2. The bipolar lithium secondary battery according to claim 1. The resin layer contains at least one selected from the group consisting of polyolefins and polyesters.
2. The bipolar lithium secondary battery according to claim 1. the bipolar electrode further includes an adhesive layer at least one between the positive electrode current collector and the resin layer and between the resin layer and the negative electrode current collector;
2. The bipolar lithium secondary battery according to claim 1. the bipolar electrode further includes a conductive portion that electrically connects the positive electrode current collector and the negative electrode current collector outside the predetermined region;
7. The bipolar lithium secondary battery according to claim 1. the conductive portion is a cured product of a conductive adhesive applied across the positive electrode current collector and the negative electrode current collector;
8. The bipolar lithium secondary battery according to claim 7. the conductive portion is a metal sheet joined to each of the positive electrode current collector and the negative electrode current collector,
8. The bipolar lithium secondary battery according to claim 7. the metal sheet is formed by joining a first metal sheet joined to the positive electrode current collector and a second metal sheet joined to the negative electrode current collector outside the predetermined region;
10. The bipolar lithium secondary battery according to claim 9. the positive electrode current collector and the negative electrode current collector form a joining region in which they are in direct physical contact with each other outside the predetermined region without the resin layer therebetween, thereby electrically connecting the positive electrode current collector and the negative electrode current collector;
7. The bipolar lithium secondary battery according to claim 1. In the bonding region, the positive electrode current collector and the negative electrode current collector form the bonding region together with a metal sheet disposed on a surface of the positive electrode current collector or the negative electrode current collector.
12. The bipolar lithium secondary battery according to claim 11. A battery pack comprising the bipolar lithium secondary battery according to any one of claims 1 to 6 and a housing. The battery pack of claim 13, further comprising an external terminal for current flow connected to the bipolar lithium secondary battery, and a protection circuit. A battery pack includes a plurality of the bipolar lithium secondary batteries,
14. The battery pack according to claim 13, wherein the bipolar lithium secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. An electronic device comprising the battery pack described in claim 13. A vehicle equipped with the battery pack described in claim 13. 18. The vehicle according to claim 17, further comprising a mechanism for converting kinetic energy of the vehicle into regenerative energy and storing the energy in the battery pack.