JP7582333B2 - Secondary battery and method for manufacturing the same - Google Patents

Description

The present invention relates to a secondary battery and a method for manufacturing the secondary battery. In particular, the present invention relates to a secondary battery having an electrode assembly composed of electrode constituent layers including a positive electrode, a negative electrode, and a separator, and a method for manufacturing the secondary battery.

Secondary batteries are storage batteries, which means they can be repeatedly charged and discharged, and are used for a variety of purposes. For example, secondary batteries are used in mobile devices such as mobile phones, smartphones, and laptops. In recent years, there has been a demand for the development of secondary batteries with even higher energy density in order to further increase the capacity of batteries.

As a secondary battery that improves energy density, Patent Document 1 describes an energy storage element that includes an electrode body formed by stacking a positive electrode plate, a negative electrode plate, and a separator, in which the positive electrode plate does not protrude from the edge of the separator, and the negative electrode plate has a protruding portion that protrudes from the separator. According to this energy storage element, the energy density is improved by making the negative electrode plate protrude from the edge of the separator and increasing the size of the negative electrode plate.

JP 2020-64723 A

The inventors of the present application realized that there were problems to be overcome with conventional secondary batteries and found it necessary to take measures to address these problems. Specifically, the inventors of the present application found the following problems:

In order to improve the capacity and energy density of a battery, it is important to increase not only the area of the negative electrode, but also the opposing area where the positive and negative electrodes face each other, thereby increasing the area in which an electrochemical reaction can occur.

The invention described in Patent Document 1 has a structure in which the electrode area is increased by having the negative electrode plate protrude from the edge of the separator, but because the current collectors of the positive and negative electrodes are indirectly electrically connected via a current collector and a gasket, there is room to increase the areas of the positive and negative electrodes by the size of the current collector and gasket. In other words, there is room to increase the opposing area by making the positive and negative electrode areas larger.

The present invention has been made in view of these problems. That is, the main object of the present invention is to provide a technology relating to a secondary battery and a method for manufacturing a secondary battery that increases the opposing area of the positive electrode and the negative electrode and improves the battery capacity and energy density.

The inventors of the present application attempted to solve the above problems by approaching them in a new direction, rather than by simply extending the conventional technology. As a result, they came up with the invention of a secondary battery that achieves the above-mentioned main objective.

The secondary battery according to the present invention includes an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode;
and an exterior body that houses the electrode assembly,
One of the positive electrodes and the negative electrodes is bundled together in a plurality of electrodes to collect current, while the other electrode is separated from the other and directly collects current.

In addition, a method for producing a secondary battery according to the present invention includes the steps of:
an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode;
and an exterior body that houses the electrode assembly,
an electrode formation step of forming a positive electrode and a negative electrode;
and a current collecting step of bundling a plurality of one of the positive electrodes and the negative electrodes together to collect current, and directly collecting current from the other electrode while keeping them spaced apart.

In the secondary battery according to the present invention, one of the positive and negative electrodes is bundled together to collect current, and the other electrode is separated from the other and directly collects current, so the positive and negative electrode areas can be made larger. In other words, there is no need for a current collector and gasket as in the conventional technology, and the opposing areas of the positive and negative electrodes can be increased accordingly. This makes it possible to improve the battery capacity and energy density of the secondary battery.

FIG. 1 shows a schematic diagram of an electrode assembly, in which FIG. 1(a) is a cross-sectional view showing a planar laminated structure, and FIG. 1(b) is a cross-sectional view showing a wound structure. FIG. 2( a ) is a plan view of a positive electrode of the secondary battery of the first embodiment, and FIG. 2( b ) is a cross-sectional view of the positive electrode of the secondary battery of the first embodiment. FIG. 3( a ) is a plan view of the negative electrode of the secondary battery of the first embodiment, and FIG. 3( b ) is a cross-sectional view of the negative electrode of the secondary battery of the first embodiment. FIG. 4 is a plan view of the secondary battery according to the first embodiment of the present invention. FIG. 5 is a cross-sectional view taken along line VI-VI of FIG. FIG. 6 is a plan view of a secondary battery according to a modified example of the first embodiment of the present invention. FIG. 7 is an explanatory diagram for explaining the projected area in the present invention. FIG. 8 is a graph showing the relationship between the area ratio (A/S) and the exterior body projected area S. 9A and 9B are schematic diagrams showing exemplary forms of secondary batteries, where FIG. 9A is a perspective view of a square secondary battery, and FIG. 9B is a perspective view of a button or coin secondary battery. FIG. 10 is a plan view of a secondary battery according to a second embodiment of the present invention. FIG. 11A is a plan view of the negative electrode of the secondary battery of the third embodiment, and FIG. 11B is a cross-sectional view of the negative electrode of the secondary battery of the third embodiment. FIG. 12 is a plan view of a secondary battery according to a third embodiment of the present invention. FIG. 13 is a cross-sectional view taken along line XI-XI of FIG. FIG. 14 is a plan view of a secondary battery according to a fourth embodiment of the present invention. FIG. 15 is a plan view of a secondary battery according to a modified example of the fourth embodiment of the present invention.

In the following, a secondary battery according to one embodiment of the present invention will be described in more detail. Although the description will be given with reference to the drawings as necessary, the various elements in the drawings are merely shown as schematic and illustrative examples for understanding the present invention, and the appearance or dimensional ratios may differ from the actual ones. Note that the "plan view" used in this specification is based on a sketch of an object viewed from above or below along the direction in which the positive and negative electrodes in the electrode assembly constituting the secondary battery face each other.

[Description of the Secondary Battery of the Present Invention]
In this specification, the term "secondary battery" refers to a battery that can be repeatedly charged and discharged. Therefore, the secondary battery according to the present invention is not limited to the name, and may also include, for example, a power storage device.

-First embodiment of secondary battery-
A secondary battery according to a first embodiment of the present invention will be described with reference to FIGS. 1 to 9. FIG. FIG. 1 is a schematic diagram of an electrode assembly, FIG. 1(a) is a cross-sectional view showing a planar laminated structure, FIG. 1(b) is a cross-sectional view showing a wound structure, FIG. 2(a) is a plan view of a positive electrode of a secondary battery of a first embodiment, FIG. 2(b) is a cross-sectional view of a positive electrode of a secondary battery of a first embodiment, FIG. 3(a) is a plan view of a negative electrode of a secondary battery of a first embodiment, FIG. 3(b) is a cross-sectional view of a negative electrode of a secondary battery of a first embodiment, FIG. 4 is a plan view of a secondary battery according to a first embodiment of the present invention, FIG. 5 is a cross-sectional view taken along line VI-VI of FIG. 4, FIG. 6 is a plan view of a secondary battery according to a modified example of the first embodiment of the present invention, FIG. 7 is an explanatory diagram for explaining a projected area in the present invention, FIG. 8 is a graph showing the relationship between the area ratio (A/S) and the projected area S of an exterior body, and FIG. 9 is a schematic diagram showing an example form of a secondary battery, (a) is a perspective view of a prismatic secondary battery, and (b) is a perspective view of a button-type or coin-type secondary battery.

The secondary battery according to the present invention has an electrode assembly including an electrode configuration layer 5 including a positive electrode 1, a negative electrode 2, and a separator 3. FIG. 1(a) and FIG. 1(b) show an example of an electrode assembly 10. As shown in the figure, the positive electrode 1 and the negative electrode 2 are stacked with the separator 3 interposed therebetween to form an electrode configuration layer 5, and the electrode assembly 10 is constructed by stacking at least one or more of such electrode configuration layers 5. In FIG. 1(a), the electrode configuration layer 5 may have a planar laminated structure in which the electrode configuration layer 5 is not wound but is laminated in a planar manner. In other words, the electrode assembly 10 may have a configuration in which the electrode configuration layers 5 are stacked on top of each other. On the other hand, in FIG. 1(b), the electrode configuration layer 5 extending relatively long in a strip shape may have a wound structure wound in a roll shape. In other words, in FIG. 1(b), the electrode configuration layer 5 extending relatively long in a strip shape including the positive electrode 1, the negative electrode 2, and the separator 3 arranged between the positive electrode 1 and the negative electrode 2 may have a wound structure wound in a roll shape. In a secondary battery, such an electrode assembly 10 may be enclosed in an exterior body 50 together with an electrolyte (e.g., a non-aqueous electrolyte). The structure of the electrode assembly 10 is not necessarily limited to a planar laminated structure or a wound structure, and for example, the electrode assembly 10 may have a so-called stack-and-folding type structure in which the positive electrode 1, the separator 3, and the negative electrode 2 are laminated on a long film and then folded.

The positive electrode 1 may have a positive electrode body 1a formed by cutting out a substantially rectangular metal foil, and a positive electrode active material layer 1b in which the positive electrode body 1a is coated with an electrode active material (see FIG. 2). In addition, as shown in the plan view of FIG. 2, for example, the positive electrode 1 may have a positive electrode current collector 1c in which a portion of the positive electrode body 1a is exposed from the positive electrode active material layer 1b.

The negative electrode 2 may have a negative electrode body 2a and a negative electrode active material layer 2b in which the negative electrode body 2a is coated with an electrode active material (see FIG. 3). In FIG. 3, which shows an example, the negative electrode body 2a may have a substantially L-shaped shape in a plan view, and may have a shape in which a position corresponding to the positive electrode current collector 1c is cut out when the negative electrode 2 is opposed to the positive electrode 1 (see FIG. 11). The outer periphery of the negative electrode 2 may have a negative electrode exposed portion 2c where the negative electrode body 2a is exposed. In addition, the area of the negative electrode 2 is preferably larger than the area of the positive electrode 1 to prevent electrolytic deposition.

The electrode active materials provided in the positive electrode 1 and the negative electrode 2, i.e., the positive electrode active material and the negative electrode active material, are materials directly involved in the transfer of electrons in the secondary battery, and are the main materials of the positive and negative electrodes that are responsible for charging and discharging, i.e., the battery reaction. More specifically, ions are brought to the electrolyte due to the positive electrode active material and the negative electrode active material, and these ions move between the positive electrode and the negative electrode to transfer electrons and charge and discharge. The positive electrode 1 and the negative electrode 2 may be layers that can absorb and release lithium ions in particular. In other words, it is preferable that the secondary battery according to the present invention is a non-aqueous electrolyte secondary battery in which lithium ions move between the positive electrode and the negative electrode via the non-aqueous electrolyte to charge and discharge the battery. When lithium ions are involved in charging and discharging, the secondary battery according to the present invention corresponds to a so-called "lithium ion battery", and the positive electrode and the negative electrode may have layers that can absorb and release lithium ions.

The positive electrode active material layer 1b is, for example, made of granular material, and may contain a binder for better contact between particles and shape retention. Furthermore, a conductive assistant may be included to facilitate the transfer of electrons that promote the battery reaction. Similarly, the negative electrode active material layer 2b is, for example, made of granular material, and may contain a binder for better contact between particles and shape retention, and may contain a conductive assistant to facilitate the transfer of electrons that promote the battery reaction. Thus, because of the form in which multiple components are contained, the positive electrode active material layer 1b and the negative electrode active material layer 2b can also be referred to as a "positive electrode composite layer" and a "negative electrode composite layer", respectively.

The positive electrode active material in the positive electrode active material layer 1b may be a material that contributes to the absorption and release of lithium ions. From this perspective, the positive electrode active material is preferably, for example, a lithium-containing composite oxide. More specifically, the positive electrode active material is preferably a lithium transition metal composite oxide containing lithium and at least one transition metal selected from the group consisting of cobalt, nickel, manganese, and iron. In other words, in the positive electrode 1 of the secondary battery according to the present invention, such a lithium transition metal composite oxide is preferably contained as the positive electrode active material. For example, the positive electrode active material may be lithium cobalt oxide, lithium nickel oxide, lithium manganate, lithium iron phosphate, or a material in which a part of the transition metal is replaced with another metal. Such a positive electrode active material may be contained as a single type, or may be contained in a combination of two or more types.

The binder that may be included in the positive electrode active material layer 1b is not particularly limited, but may be at least one selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, etc. The conductive assistant that may be included in the positive electrode active material layer 1b is not particularly limited, but may be at least one selected from the group consisting of carbon black such as thermal black, furnace black, channel black, ketjen black, and acetylene black, carbon fibers such as graphite, carbon nanotubes, and vapor-grown carbon fibers, metal powders such as copper, nickel, aluminum, and silver, and polyphenylene derivatives.

The thickness dimension of the positive electrode active material layer 1b is not particularly limited, but may be 1 μm or more and 300 μm or less, for example, 5 μm or more and 200 μm or less. The thickness dimension of the positive electrode material layer is the thickness inside the secondary battery, and the average value of the measured values at any 10 points may be used.

The negative electrode active material in the negative electrode active material layer 2b may be a material that contributes to the absorption and release of lithium ions. From this perspective, it is preferable that the negative electrode active material is, for example, various carbon materials, oxides and/or lithium alloys.

Examples of various carbon materials for the negative electrode active material include graphite (natural graphite, artificial graphite), hard carbon, soft carbon, diamond-like carbon, etc. In particular, graphite has high electronic conductivity and excellent adhesion to metal foil. Examples of oxides for the negative electrode active material include at least one selected from the group consisting of silicon oxide, tin oxide, indium oxide, zinc oxide, and lithium oxide. The lithium alloy for the negative electrode active material may be any metal that can form an alloy with lithium, and may be, for example, a binary, ternary, or higher alloy of lithium and a metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, or La. It is preferable that such oxides have an amorphous structure. This is because deterioration caused by non-uniformity such as grain boundaries or defects is less likely to occur.

The binder that may be included in the negative electrode active material layer 2b is not particularly limited, but may be at least one selected from the group consisting of styrene butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyimide resin, and polyamideimide resin. The conductive assistant that may be included in the negative electrode active material layer 2b is not particularly limited, but may be at least one selected from carbon black such as thermal black, furnace black, channel black, ketjen black, and acetylene black, carbon fibers such as graphite, carbon nanotubes, and vapor-grown carbon fibers, metal powders such as copper, nickel, aluminum, and silver, and polyphenylene derivatives. The negative electrode active material layer 2b may contain a component resulting from a thickener component (e.g., carboxymethyl cellulose) used during battery production.

The thickness dimension of the negative electrode active material layer 2b is not particularly limited, but may be 1 μm or more and 300 μm or less, for example, 5 μm or more and 200 μm or less. The thickness dimension of the negative electrode material layer is the thickness inside the secondary battery, and the average value of the measured values at any 10 points may be used.

The metal foil used for the positive electrode body 1a and the negative electrode body 2a is a member that contributes to collecting and supplying electrons generated in the electrode active material due to the battery reaction. The metal foil may be a sheet-shaped metal member and may have a porous or perforated form. For example, a punched metal, a mesh, an expanded metal, etc. may be used instead of the metal foil. The metal foil used for the positive electrode 1 is preferably made of a metal foil containing at least one selected from the group consisting of aluminum, stainless steel, nickel, etc., and may be, for example, aluminum foil. On the other hand, the metal foil used for the negative electrode 2 may be made of a metal foil containing at least one selected from the group consisting of nickel, copper, nickel-plated copper, stainless steel, etc., and may be, for example, copper foil.

The separator 3 is a member provided from the viewpoint of preventing short circuits due to contact between the positive and negative electrodes and retaining the electrolyte. In other words, the separator 3 is a member that allows ions to pass through while preventing electronic contact between the positive electrode 1 and the negative electrode 2. Preferably, the separator 3 is a porous or microporous insulating member, and has a membrane form due to its small thickness.

The separator 3 may be designed to be larger than the area of either the positive electrode 1 or the negative electrode 2 in order to prevent short circuits due to contact between the positive and negative electrodes. For example, referring to FIG. 4, the separator 3 may be made larger than the area of the positive electrode active material layer 1b in a plan view. Furthermore, as a preferred separator 3, in order to further prevent short circuits between the positive and negative electrodes, for example, a protrusion 3a protruding beyond the ends of either the positive electrode 1 or the negative electrode 2 may be provided on the terminal member 60 side (i.e., the side where the negative electrode 2 does not contact the exterior body 50) of the separator 3 shown in FIG. 5.

The microporous film used as the separator 3 may be, for example, a film containing only polyethylene (PE) or only polypropylene (PP) as a polyolefin, or a laminate consisting of a "PE microporous film" and a "PP microporous film." The surface of the separator may be covered with an inorganic particle coating layer and/or an adhesive layer, etc. The surface of the separator may have adhesive properties.

Furthermore, if an abnormality occurs during the operation of the secondary battery and heat is generated, the separator 3 may thermally shrink, narrowing the gap between the positive electrode 1 and the negative electrode 2 arranged above and below the separator 3, which may cause a short circuit. In order to prevent a short circuit between the positive electrode and the negative electrode caused by the thermal shrinkage of the separator, the separator 3 may be made of a material that is difficult to thermally shrink. As merely an example, oxide-based ceramics such as alumina, carbide-based ceramics such as silicon carbide, and nitride-based ceramics such as silicon nitride may be used. In the present invention, the separator should not be particularly limited by its name, and may be a solid electrolyte, a gel electrolyte, and/or insulating inorganic particles having similar functions.

The thickness dimension of the separator is not particularly limited, but may be 1 μm or more and 100 μm or less, for example, 2 μm or more and 20 μm or less. The thickness dimension of the separator is the thickness inside the secondary battery (particularly the thickness between the positive electrode and the negative electrode), and the average value of the measured values at any 10 points may be used.

In the secondary battery of the present invention, an electrode assembly 10 consisting of an electrode constituent layer 5 including a positive electrode 1, a negative electrode 2, and a separator 3 may be enclosed in an exterior body 50 together with an electrolyte. The electrolyte can assist the movement of metal ions released from the electrodes (positive electrode 1 and/or negative electrode 2). The electrolyte may be a "non-aqueous" electrolyte such as an organic electrolyte and an organic solvent, or may be an "aqueous" electrolyte containing water. When the positive electrode 1 and the negative electrode 2 have a layer capable of absorbing and releasing lithium ions, it is preferable that the electrolyte is a "non-aqueous" electrolyte containing an organic electrolyte or an organic solvent. In other words, it is preferable that the electrolyte is a non-aqueous electrolyte. In the electrolyte, metal ions released from the electrodes (positive electrode and/or negative electrode) are present, and therefore the electrolyte assists the movement of metal ions in the battery reaction. The electrolyte may be in the form of a liquid or gel.

The non-aqueous electrolyte is an electrolyte containing a solvent and a solute. A specific solvent for the non-aqueous electrolyte may contain at least a carbonate. Such a carbonate may be a cyclic carbonate and/or a chain carbonate. Although not particularly limited, the cyclic carbonate may be at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC) and vinylene carbonate (VC). The chain carbonate may be at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC). Although merely illustrative, a combination of a cyclic carbonate and a chain carbonate may be used as the non-aqueous electrolyte, for example, a mixture of ethylene carbonate and diethyl carbonate may be used. As a specific example of the solute of the non-aqueous electrolyte, a Li salt such as _LiPF6 and/or _LiBF4 may be used.

The exterior body 50 of the secondary battery may be a member capable of housing or encasing the electrode assembly 10 having the electrode configuration layer 5 including the positive electrode 1, the negative electrode 2, and the separator 3. The exterior body 50 is preferably a metal exterior body having a non-laminated structure. The metal exterior body may be a single member made of metal such as stainless steel (SUS) and/or aluminum. In a broad sense, the "single metal member" means that the exterior body 50 does not have a so-called laminated structure, and in a narrow sense, the exterior body 50 is a member made substantially of metal only. Therefore, if it is a member made substantially of metal only, the surface of the metal exterior body may be subjected to an appropriate surface treatment. For example, in a cut surface obtained by cutting such a metal exterior body in the thickness direction, a single metal layer can be confirmed except for the part that has been subjected to the surface treatment. In addition, "stainless steel" in this specification refers to stainless steel as defined in "JIS G 0203 Steel Terminology", for example, and may be an alloy steel containing chromium or chromium and nickel.

From the viewpoint of easily storing the electrode assembly 10, the exterior body 50 may have a lid-shaped member and a cup-shaped member, and the lid-shaped member and the cup-shaped member may be joined by welding. In the present embodiment, a terminal member 60 is provided on the cup-shaped member, and an insulating material 70 may be disposed between the terminal member 60 and the cup-shaped member (see Figs. 4 and 5). In this specification, the "cup-shaped member" refers to a member having a side portion corresponding to a body portion and a main surface portion (for example, a bottom portion in a typical embodiment) continuous therewith, and a hollow portion is formed inside. In this specification, the "lid-shaped member" refers to a member provided to cover such a cup-shaped member. The lid-shaped member may be, for example, a single member (typically a flat member) extending in the same plane. In the exterior body, the lid-shaped member and the cup-shaped member may be combined so that the outer edge portion of the lid-shaped member and the upper end portion of the outer periphery of the cup-shaped member are aligned with each other.

The insulating material 70 is provided so as to fill the gap between the cup-shaped member and the terminal member 60, and can be understood as contributing to "sealing". For example, as shown in Figs. 4 and 5, the insulating material 70 may be shaped to extend to the outer region of the terminal member 60. In other words, the insulating material 70 may be provided on the exterior body 50 so as to protrude from the terminal member 60 to the outside. There is no particular limit to the type of insulating material 70 as long as it exhibits "insulating properties". It is preferable that the insulating material has not only "insulating properties" but also "adhesive properties". For example, the insulating material 70 may be made of a thermoplastic resin. Although this is merely one specific example, the insulating material 70 may be made of a polyolefin such as polyethylene and/or polypropylene. In this specification, "insulating properties" refers to a property that makes it difficult for electric current to flow, and means a resistivity range of 10 ⁶ Ω·m or more.

The terminal member 60 means an output terminal in the secondary battery that is used to connect to an external device. The terminal member 60 may have, for example, a flat plate shape. The flat terminal member 60 may be, for example, a metal plate. The material of the terminal member 60 is not particularly limited, and may include at least one metal selected from the group consisting of aluminum, nickel, and copper, and may have multiple layers made of different metal materials. The shape of the terminal member 60 as viewed from the side (as viewed from the X direction in Figures 4 and 5) is not particularly limited, and may be, for example, a circle, or a rectangle including a square.

The terminal member 60 may be electrically connected to one of the positive electrode 1 or the negative electrode 2 of the electrode assembly 10. Meanwhile, the other of the positive electrode 1 or the negative electrode 2 of the electrode assembly 10 may be electrically connected to the metallic exterior body 50. In this embodiment, the terminal member 60 is electrically connected to the positive electrode 1 of the electrode assembly 10, and the negative electrode 2 of the electrode assembly 10 is electrically connected to the metallic exterior body 50.

In the example shown in Fig. 4, the terminal member 60 is offset in the Y direction from the center of the exterior body 50 to correspond to the position of the positive electrode current collector 1c. The position of the terminal member 60 is not limited to the form shown in Fig. 4, and it may be formed without offset, for example, as in the form shown in Fig. 6, to correspond to the position of the positive electrode current collector 1c. In other words, the terminal member 60 can be formed at any position.

The positive electrodes 1 are bundled together to collect current and are electrically connected to the terminal member 60. On the other hand, the negative electrodes 2 are electrically connected to the terminal member 60 by directly collecting current while being spaced apart from each other. As an embodiment, for example, in FIGS. 4 and 5, a plurality of positive electrode current collectors 1c may be bundled together and electrically connected to the terminal member 60, and the negative electrode main body 2a and the negative electrode active material layer 2b may be protruding from the separator 3 and electrically connected to the metal exterior body 50 while being spaced apart from each other.

Here, "separated state" in this specification means a state in which the negative electrode bodies 2a are stretched while maintaining the separated state of each other, more specifically, a state in which the negative electrode bodies 2a are not physically in contact with each other, that is, a state in which the negative electrode bodies 2a are not bundled together like the positive electrode current collector 1c. In addition, "direct current collection" in this specification means a state in which the negative electrode body 2a is directly in contact with the outside and current collection is performed, which is different from the conventional technology (for example, JP 2020-064723 A) in which current collection is performed indirectly via a current collector and a gasket. In addition, the difference between the current collection mode of the positive electrode (current collection in a bundled state) and the current collection mode of the negative electrode (direct current collection in a separated state) is also different from the conventional technology. 4 and 5, the positive electrodes are not bundled together and current is collected, and the negative electrodes are separated from each other and directly collected, but the present invention is not limited to this embodiment, and the current collection mode of the negative electrodes and the current collection mode of the positive electrodes may be reversed. In other words, the negative electrodes may be not bundled together and current is collected, and the positive electrodes may be separated from each other and directly collected.

According to this embodiment, one of the positive and negative electrodes is bundled together to collect current, and the other electrode is directly collected while being separated from the other. Therefore, compared to the "indirect current collection method" using a current collector and gasket as in the conventional technology, no components such as a current collector and gasket are required, and the opposing area of the positive and negative electrodes can be increased by the size of the current collector and gasket. Therefore, the battery capacity and energy density of the secondary battery can be improved.

Next, a more specific current collection mode for the electrical connection of the electrodes of this embodiment will be described. In a preferred embodiment, the state in which the negative electrodes are separated from each other may be a state in which the negative electrodes are not bundled together. In other words, the negative electrodes may be in a state in which they are not in physical contact with each other. In this way, when the negative electrodes are directly collected without being bundled together, the process of bundling the electrodes can be omitted, and the manufacturing process can be simplified.

In a preferred embodiment, the electrodes may be configured to collect current by contacting their ends. In other words, in FIG. 4 and FIG. 5, the ends of the negative electrode body 2a and the negative electrode active material layer 2b constituting the negative electrode may be electrically connected by contacting an output member that outputs to the outside. Since electrical connection is obtained by contacting the ends of the electrodes, electrical connection can be made by a simple method.

4 and 5, as a specific embodiment of the output member when electrically connecting with the negative electrode, the negative electrode may be brought into contact with a metallic exterior body 50 to collect current. By electrically connecting the electrode by directly contacting the metallic exterior body 50 in this way, the electrode area can be increased without the need for any conductive member.

In a preferred embodiment, the electrical connection between the electrode and the exterior body may be formed by contacting at least two sides of the outer periphery of the electrode in a plan view. That is, referring to FIG. 4, the four sides of the outer periphery of the negative electrode 2 may be directly contacted with the exterior body 50 and electrically connected. According to such a connection method, it is possible to increase the number of contact positions between the electrode and the exterior body 50, and the transfer of electrons that promote the battery reaction can be performed more smoothly. In addition, since the electrodes are electrically connected at multiple sides, the reliability of the electrical connection can be improved. Note that, instead of the form shown in FIG. 4, three sides of the outer periphery of the negative electrode 2 (for example, three sides of the outer periphery of the negative electrode 2 excluding the side on the terminal member 60 side) may be directly contacted with the exterior body 50, or any two sides of the outer periphery may be directly contacted with the exterior body.

In addition, in FIG. 4 and FIG. 7, the maximum projected area of the overlapping region where the positive electrode 1 and the negative electrode 2 overlap when viewed from the overlapping direction (Z direction in FIG. 7) may be 75% or more of the maximum projected area of the exterior body 50 when viewed from the overlapping direction of the exterior body 50. In this specification, the "projected area" means an area that is a shadow when light is projected perpendicularly onto a projected object. Specifically, in the embodiment of FIG. 4 and FIG. 7, the maximum projected area of the overlapping region indicates the maximum area A when the overlapping region where the positive electrode 1 and the negative electrode 2 overlap is projected, and the maximum projected area S of the exterior body 50 indicates the maximum planar area S when the exterior body 50 is projected. Note that the maximum planar area S of the exterior body 50 depends on the size of the electronic device in which the secondary battery is mounted, and is, for example, 200 mm ² or more and 650 mm ² or less. In terms of the maximum planar area S of such an outer casing 50, for example, when comparing a conventional configuration in which both the positive and negative electrodes are bundled together to collect current, with this embodiment, the A/S of the overlapping region in the conventional configuration is less than 75%, whereas the A/S of the overlapping region in this embodiment can be 75% or more. With such a configuration, the opposing area over which the positive and negative electrodes face each other is increased, making it possible to increase the area in which an electrochemical reaction occurs (see FIG. 8).

In a preferred embodiment, the battery may further include a conductive adhesive that keeps the other electrodes separated from each other and allows current to be collected. That is, in the embodiment shown in FIG. 4 and FIG. 5, a conductive adhesive may be used to firmly contact the negative electrode 2 with the outer casing 50 when directly collecting current between the outer casing 50 and the negative electrode 2. By using a conductive adhesive, the electrodes can be kept separated from each other and allow current to be collected.

In this embodiment, the secondary battery has a substantially rectangular shape when viewed from the terminal member side. That is, the secondary battery 100 has a square shape in terms of its external shape (see FIG. 9(a)). However, the present invention is not necessarily limited to this. For example, the secondary battery may be a button-type or coin-type secondary battery (see FIG. 9(b)). That is, the secondary battery 100 is not limited to a rectangular shape when viewed from the terminal member side, and may have a circular or elliptical shape, etc.

--Second embodiment of secondary battery--
Next, a secondary battery according to a second embodiment of the present invention will be described with reference to Fig. 10. Fig. 10 is a plan view of the secondary battery according to the second embodiment of the present invention. Note that the description of the same configuration as the first embodiment will be omitted.

In the secondary battery according to this embodiment, the positive electrodes 1 are bundled together to collect current, and the negative electrodes 2 are separated from each other and directly collected by a conductive member 80 different from the exterior body 50. This embodiment is not limited to this, and the current collection mode of the negative electrodes and the current collection mode of the positive electrodes may be reversed. In other words, the negative electrodes 2 may be bundled together to collect current, and the positive electrodes 1 may be separated from each other and directly collected by the conductive member 80.

In this embodiment, the conductive member 80 collects the negative electrode 2, and therefore may be made of at least one material selected from the group consisting of nickel, copper, nickel-plated copper, and SUS, which are materials for the negative electrode 2. By using the material for the negative electrode 2 as the conductive member 80 for collecting the negative electrode in this way, it is possible to collect the current without affecting the non-aqueous electrolyte in the exterior body 50. In addition, the thickness of the conductive member 80 is preferably relatively thin from the viewpoint of widening the electrode area of the negative electrode 2. For example, a foil-like member is preferable. In addition, as a modified example, when collecting the current directly to the conductive member 80 while separating the positive electrodes 1 from each other, the conductive member 80 may be selected from the group consisting of aluminum, stainless steel, nickel, and the like, which are materials for the positive electrode 1.

According to the second embodiment, the negative electrodes 2 are separated from each other and directly collected by the conductive member 80, and the positive electrodes 1 are bundled together to collect current. This increases the opposing area between the positive and negative electrodes by the amount that the positive electrodes 1 are bundled together to collect current, thereby increasing the area in which an electrochemical reaction occurs. In particular, if the conductive member 80 is in the form of a foil, the electrode area can be made larger.

--Third embodiment of secondary battery--
Next, a secondary battery 100 according to a third embodiment of the present invention will be described with reference to Fig. 11 to Fig. 13. Fig. 11(a) is a plan view of the negative electrode of the secondary battery according to the third embodiment, Fig. 11(b) is a cross-sectional view of the negative electrode of the secondary battery according to the third embodiment, Fig. 12 is a plan view of the secondary battery according to the third embodiment of the present invention, and Fig. 13 is a cross-sectional view taken along line XI-XI of Fig. 12. Note that a description of the same configuration as in the first embodiment will be omitted.

11, the negative electrode 2 of the secondary battery according to the third embodiment includes a negative electrode active material layer 2b in which the negative electrode body 2a is covered with a negative electrode active material, and a negative electrode exposed portion 2c in which the negative electrode body 2a is exposed. The negative electrode exposed portion 2c may be located on the outer peripheral edge of the negative electrode 2 and may protrude beyond the negative electrode active material layer 2b. An electrode assembly 10 including this negative electrode 2 may be housed in an exterior body 50.

In the secondary battery according to the third embodiment, the negative electrode exposed portions 2c protruding from the negative electrode active material layer 2b may directly collect current without contacting each other (see Figs. 12 and 13). In other words, the negative electrode exposed portions 2c can transmit electrons more smoothly than the negative electrode active material layer 2b, so only the negative electrode exposed portions 2c may be in contact with the exterior body 50.

13, the negative electrode exposed portion 2c contacts the exterior body 50 by extending along the X and Y directions, but the contact with the exterior body 50 may be firm surface contact rather than point contact. In other words, the protruding negative electrode exposed portion 2c may be folded or rounded.

According to the third embodiment, current is collected directly while the exposed portions are spaced apart from each other, increasing the opposing area between the positive and negative electrodes and increasing the area in which an electrochemical reaction can occur.

--Fourth embodiment of secondary battery--
Next, a secondary battery according to a fourth embodiment of the present invention will be described with reference to Fig. 14 and Fig. 15. Fig. 14 is a plan view of the secondary battery according to the fourth embodiment of the present invention, and Fig. 15 is a plan view of a secondary battery according to a modified example of the fourth embodiment of the present invention. Note that a description of the same configuration as the first embodiment will be omitted.

In the secondary battery according to the fourth embodiment, the exterior body 50 is provided with a positioning portion for positioning the electrode assembly 10. Because the positioning portion is provided, the position of the electrode assembly 10 housed in the exterior body 50 is fixed. This makes it possible to prevent the electrical connection of the electrodes from being lost due to impact and/or vibration.

14, the positioning portion may be a convex portion 51 protruding from the inner wall surface of the exterior body 50. The position of the electrode assembly 10 can be fixed by contacting the convex portion 51 with the electrode assembly 10. Note that in this embodiment, the convex portion 51 extends from the bottom surface of the exterior body 50, but this is not limiting and the convex portion 51 may extend from the side surface of the exterior body 50 or from a lid-like member of the exterior body 50.

As a modification of the positioning portion of this embodiment, as shown in Fig. 15, a recessed portion 52 formed by recessing the exterior body 50 toward the inside may be used as the positioning portion. The position of the electrode assembly 10 can be fixed by contacting the electrode assembly 10 with the recessed portion.

[Description of the method for producing the secondary battery of the present invention]
Next, a method for producing a secondary battery of the present invention will be described. The method for producing a secondary battery of the present invention includes an electrode forming step of forming a positive electrode 1 and a negative electrode 2, and a current collecting step of bundling one of the positive electrode 1 and the negative electrode 2 together to collect current, and directly collecting current from the other electrode in a state of being spaced apart from each other. The steps will be described below.

- Electrode formation process -
The electrode formation step is a step of forming the positive electrode 1 and the negative electrode 2 constituting the electrode assembly 10. First, a positive electrode body 1a constituting the positive electrode 1 is prepared. The positive electrode body 1a is preferably a metal foil containing at least one selected from the group consisting of aluminum, stainless steel, nickel, etc., and is formed into a shape shown in FIG. 2, for example, by using a die for punching the metal foil. Next, a positive electrode active material layer 1b may be formed on both sides of the positive electrode body 1a. The positive electrode active material layer 1b is formed by coating a mixture of a positive electrode active material with a binder, a solvent, etc.

Here, the positive electrode current collector 1c shown in Figure 2 is not coated with a positive electrode active material. In this way, the method of forming the uncoated portion where the active material is not coated may be, for example, a method of printing a pattern on the metal foil, a method of masking the uncoated portion, or a method of forming an active material layer on the entire surface of the metal foil and then laser processing the portion corresponding to the positive electrode current collector 1c.

The above-mentioned electrode formation method can also be adopted as a method for forming the negative electrode 2. For example, a negative electrode having a negative electrode exposed portion 2c in which the electrode is exposed on the outer periphery as shown in FIG. 11 can be formed. After the positive electrode 1 and the negative electrode 2 are formed, the positive electrode 1, the negative electrode 2, and the separator 3 are stacked to form the electrode assembly 10. In this embodiment, the positive electrode 1, the negative electrode 2, and the separator 3 may be stacked in the stacking direction. In other words, the electrode assembly 10 may have a planar stacking structure. With such a stacking structure, it is possible to adjust the battery capacity by the number of stacks of the positive electrode, the negative electrode, and the separator. Instead of the stacking structure, a winding structure in which the electrode configuration layer including the positive electrode 1, the negative electrode 2, and the separator 3 is wound into a roll may be used. With the winding structure, the electrode assembly can be manufactured by winding the electrode configuration layer with a winding machine or the like, and the manufacturing process can be simplified.

- Current collection process -
After the electrode assembly 10 is formed, the electrode assembly 10 is housed in an exterior body 50, and the positive electrodes 1 and the negative electrodes 2 are electrically connected so as to output electricity to the outside. As an example, in this embodiment, the positive electrodes 1 are bundled by the positive electrode current collecting portion 1c and electrically connected to the terminal member 60. Any method may be used for current collection of the positive electrodes as long as the positive electrodes 1 can be brought into contact with each other, and an example of the method is ultrasonic welding.

On the other hand, the negative electrode 2 is directly collected by the metallic exterior body 50 with the electrodes spaced apart. In this embodiment, the negative electrodes 2 are electrically connected to the exterior body 50 by directly contacting the metallic exterior body 50 with the electrodes spaced apart. As described above, in order to firmly contact the negative electrodes 2 with the exterior body 50, a conductive adhesive may be used and/or the electrode assembly 10 may be fixed by contacting it with a positioning portion.

As described above, according to the method for manufacturing a secondary battery of the present invention, one of the positive and negative electrodes is bundled together and current is collected, and the other electrode is separated and directly collected, so that the opposing area of the positive and negative electrodes can be increased, and a secondary battery with improved battery capacity and energy density can be manufactured.

It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to be a basis for a restrictive interpretation. Therefore, the technical scope of the present invention should not be interpreted solely by the above-described embodiments, but should be defined based on the claims. Furthermore, the technical scope of the present invention includes all modifications that are equivalent in meaning to and within the scope of the claims.

The secondary battery of the present invention can be used in various fields where battery use or electricity storage is expected. Although merely illustrative, the secondary battery of the present invention can be used in the electrical, information and communication fields in which mobile devices and the like are used (for example, mobile phones, smartphones, notebook computers and digital cameras, activity meters, arm computers, electronic paper, wearable devices, or small electronic devices such as RFID tags, card-type electronic money, and smart watches, or the electrical and electronic device fields or mobile device fields), household and small industrial applications (for example, power tools, golf carts, household, nursing care and industrial robots), large industrial applications (for example, forklifts, elevators, and port cranes), transportation systems (for example, hybrid cars, electric cars, buses, trains, electrically assisted bicycles, and electric motorcycles), power system applications (for example, various power generation, road conditioners, smart grids, and general household installation type power storage systems), as well as medical applications (medical equipment fields such as earphone hearing aids), pharmaceutical applications (medical management systems, etc.), IoT fields, and space and deep sea applications (for example, space probes, submersible research vessels, etc.).

REFERENCE SIGNS LIST 1 Positive electrode 1a Positive electrode body 1b Positive electrode active material layer 1c Positive electrode current collector 2 Negative electrode 2a Negative electrode body 2b Negative electrode active material layer 2c Negative electrode exposed portion 3 Separator 3a Protruding portion 5 Electrode constituent layer 10 Electrode assembly 50 Exterior body 51 Convex portion 52 Concave portion 60 Terminal member 70 Insulating material 80 Conductive member 100 Secondary battery

Claims (20)

an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode;
and an exterior body that houses the electrode assembly,
A secondary battery, in which one of the positive electrodes and the negative electrodes is bundled together in multiples to collect current, and the other electrode is extended and current is collected directly at the ends of the extended electrodes while being spaced apart from each other. The secondary battery according to claim 1, wherein the state in which the other electrodes are separated from each other is a state in which the electrodes are not bundled together. The secondary battery according to claim 1 or 2, wherein the positive electrode, the negative electrode, and the separator are stacked in a stacking direction. The secondary battery according to any one of claims 1 to 3, further comprising an output member that contacts the ends of the other electrodes to collect current. The secondary battery according to claim 4, wherein at least two sides of the outer periphery of the other electrode are in contact with the output member in a plan view. The secondary battery according to claim 4 or 5, wherein the output member is a metal exterior body. The secondary battery according to claim 4 , wherein the output member is a foil-like conductive member different from the exterior body. The secondary battery according to any one of claims 1 to 7, wherein the other electrode has a protrusion, at least a part of which protrudes from the separator to collect current from each other. the other electrode includes an active material portion covered with an active material and an exposed portion where the electrode is exposed,
9. The secondary battery according to claim 1, wherein the exposed portions are provided on the outer periphery of the electrodes, and current is collected directly without being in contact with each other. The secondary battery according to any one of claims 1 to 9, wherein the material of one electrode comprises at least one selected from the group consisting of aluminum, stainless steel, and nickel, and the material of the other electrode comprises at least one selected from the group consisting of nickel, copper, nickel-plated copper, and stainless steel. The secondary battery according to any one of claims 1 to 10, wherein the one electrode is a positive electrode and the other electrode is a negative electrode. The secondary battery according to any one of claims 1 to 11, wherein the ratio A/S of the maximum projected area A when viewed from the overlapping direction of the positive electrode and the negative electrode and the maximum projected area S when viewed from the overlapping direction of the exterior body is 75% or more in a range of S = 200 ^mm2 or more and 650 ^mm2 or less. The secondary battery according to any one of claims 1 to 12, wherein the exterior body has a positioning portion for positioning the electrode assembly. The secondary battery according to claim 13, wherein the positioning portion protrudes from the inner wall surface of the exterior body. The secondary battery according to claim 13, wherein the positioning portion is a recess recessed inward from the outer periphery of the exterior body. The secondary battery according to any one of claims 1 to 15, further comprising a conductive adhesive that keeps the other electrodes separated from each other and in a state where current is collected. The secondary battery according to any one of claims 1 to 16, wherein the separator comprises ceramic. The secondary battery according to any one of claims 1 to 17, wherein the positive electrode or the negative electrode is capable of absorbing and releasing lithium ions. A method for producing a secondary battery according to any one of claims 1 to 18, comprising the steps of :
an electrode formation step of forming the positive electrode and the negative electrode;
a current collecting step of bundling a plurality of one of the positive electrodes and the negative electrodes together to collect current, and directly collecting current from the other electrode while keeping them spaced apart. The method for manufacturing a secondary battery according to claim 19, wherein the electrode formation process includes a step of applying an active material to the electrode and a step of forming an exposed portion at the outer periphery where the electrode is exposed.

Images