WO2021210653A1

WO2021210653A1 - Secondary cell and method for manufacturing same

Info

Publication number: WO2021210653A1
Application number: PCT/JP2021/015622
Authority: WO
Inventors: 弥生勝; 真人藤岡; 隆幸山平; 高木　良介
Original assignee: 株式会社村田製作所
Priority date: 2020-04-16
Filing date: 2021-04-15
Publication date: 2021-10-21

Abstract

According to an embodiment of the present invention, there is provided a secondary cell including an electrode provided with a current collector (11), an electrode material layer (12), and an electroconductive adhesive layer (13) provided between the current collector and the electrode material layer, these elements being provided along the lamination direction, the current collector being configured from a thin metal and/or a resin, and the electrode material layer having a porosity of 25% or less.

Description

Secondary battery and its manufacturing method

The present invention relates to a secondary battery and a method for manufacturing the secondary battery.

Secondary batteries that can be repeatedly charged and discharged have been used for various purposes. For example, a secondary battery is used as a power source for electronic devices such as smartphones and notebook computers.

The secondary battery has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator arranged between the positive electrode and the negative electrode, and an electrolyte are housed in an exterior body. The positive electrode includes a positive electrode current collector and a positive electrode material layer provided on at least one main surface of the positive electrode current collector. The negative electrode includes a negative electrode material layer provided on at least one main surface of the negative electrode current collector and the negative electrode current collector.

Japanese Unexamined Patent Publication No. 2000-200610 Japanese Patent No. 6190980

In recent years, there has been an increasing demand for miniaturization and weight reduction of secondary batteries, and in order to meet such demand, a thin layer of the current collector, that is, a current collector composed of a thin metal or the like is required. In addition to this, from the viewpoint of improving the energy density of the secondary battery, there is an increasing demand for increasing the density of the electrode material layer.

As a conventional method for manufacturing an electrode, an electrode material layer slurry is applied onto a foil to be a current collector, and the obtained laminate is subjected to a drying treatment to include a foil 11'and an electrode material layer 12'. The laminate 10'was subjected to a step of pressurizing with, for example, a roll press machine 400'(see FIG. 6). However, when the laminated body 10'is pressurized, the foil 11'which becomes a current collector composed of a thin metal or the like stretches, and it may be difficult to increase the density of the electrode material layer 12'. As a result, it may be difficult to improve the energy density of the secondary battery.

The present invention was devised in view of such circumstances. Specifically, an object of the present invention is to provide a secondary battery capable of increasing the density of the electrode material layer even by using a current collector composed of a thin metal or the like, and a method for manufacturing the secondary battery.

In order to achieve the above object, in one embodiment of the present invention,
The electrode includes a current collector, an electrode material layer, and a conductive adhesive layer provided between the current collector and the electrode material layer along the stacking direction.
A secondary battery is provided in which the current collector is composed of at least one of a thin metal and a resin and the porosity of the electrode material layer is 25% or less.

In order to achieve the above object, in one embodiment of the present invention,
A method for manufacturing a secondary battery including an electrode forming process.
The electrode forming process
A step of forming a laminate by sequentially coating a conductive adhesive layer slurry and an electrode material layer slurry on a temporary support sheet, and
A step of drying the laminate to form a conductive adhesive layer and an electrode material layer on the temporary support sheet, and
A step of pressurizing the laminated body along the laminating direction of the laminated body so as to sandwich the upper surface and the lower surface of the laminated body.
The step of peeling off the temporary support sheet after the pressurization and
A method for manufacturing a secondary battery is provided, which comprises a step of laminating a current collector composed of at least one of a metal and a resin on the conductive adhesive layer after the peeling.

According to one embodiment of the present invention, it is possible to increase the density of the electrode material layer even by using a current collector such as a thin metal or a resin.

It is sectional drawing which shows typically the secondary battery which concerns on one Embodiment of this invention. It is an enlarged cross-sectional view which shows typically the electrode of the secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the manufacturing method (preparation step of the temporary support sheet) of the electrode of the secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the manufacturing method (coating process of the conductive adhesive layer slurry) of the electrode of the secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the manufacturing method (coating process of electrode material layer slurry) of the electrode of the secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the manufacturing method (drying step of a laminated body) of the electrode of the secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the manufacturing method (pressurizing process of a laminated body) of the electrode of the secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the manufacturing method (peeling step of the temporary support sheet) of the electrode of the secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the manufacturing method of the electrode of the secondary battery (the process of laminating and crimping a current collector) which concerns on one Embodiment of this invention. It is an enlarged cross-sectional view which shows typically the manufacturing method (pressurizing process of a laminated body) of the electrode of the secondary battery which concerns on one Embodiment of this invention. It is sectional drawing which shows typically the basic structure of the electrode constituent layer. It is a schematic perspective view which concerns on the technical subject of this application.

Hereinafter, the secondary battery according to the embodiment of the present invention will be described in detail with reference to the drawings. The various elements in the drawings are merely schematically and exemplified for the understanding of the present invention, and the appearance, dimensional ratio, etc. may differ from the actual ones.

Before explaining the method for manufacturing a secondary battery according to an embodiment of the present invention, the basic configuration of the secondary battery will be described. The term "secondary battery" as used herein refers to a battery that can be repeatedly charged and discharged. The "secondary battery" is not overly bound by its name and may include, for example, a "storage device". The term "planar view" as used herein refers to a state in which an object is viewed from above or below along a thickness direction based on a stacking direction of electrode materials constituting a secondary battery. Further, the "cross-sectional view" referred to in the present specification is a state when viewed from a direction substantially perpendicular to the thickness direction based on the stacking direction of the electrode materials constituting the secondary battery. The "vertical direction" and "horizontal direction" used directly or indirectly in the present specification correspond to the vertical direction and the horizontal direction in the drawings, respectively. Unless otherwise specified, the same reference numerals or symbols shall indicate the same members / parts or the same meanings. In one preferred embodiment, it can be considered that the vertical downward direction (that is, the direction in which gravity acts) corresponds to the "downward direction" and the opposite direction corresponds to the "upward direction".

The various numerical ranges referred to herein are intended to include the lower and upper limits themselves. That is, taking a numerical range such as 1 to 10 as an example, it can be interpreted as including the lower limit value "1" and the upper limit value "10".

[Basic configuration of secondary battery]
The present invention provides a secondary battery. The secondary battery has a structure in which the electrode assembly and the electrolyte are housed and sealed inside the exterior body. The electrode assembly may include a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The electrode assembly may be a laminated electrode assembly or a wound (jelly roll) electrode assembly. The laminated electrode assembly is a stack of a plurality of electrode constituent layers including a positive electrode, a negative electrode, and a separator. The wound electrode assembly is a wound electrode constituent layer including a positive electrode, a negative electrode, and a separator. Further, for example, the electrode assembly may have a so-called stack-and-folding structure in which a positive electrode, a separator, and a negative electrode are laminated on a long film and then folded.

The positive electrode 10A is composed of at least a positive electrode current collector 11A and a positive electrode material layer 12A (see FIG. 5), and the positive electrode material layer 12A is provided on at least one side of the positive electrode current collector 11A. A drawer tab on the positive electrode side is positioned at a portion of the positive electrode current collector 11A where the positive electrode material layer 12A is not provided, that is, at the end of the positive electrode current collector 11A. The positive electrode material layer 12A contains a positive electrode active material as an electrode active material. The negative electrode 10B is composed of at least a negative electrode current collector 11B and a negative electrode material layer 12B (see FIG. 5), and a negative electrode material layer 12B is provided on at least one surface of the negative electrode current collector 11B. The negative electrode side drawer tab is positioned at a portion of the negative electrode current collector 11B where the negative electrode material layer 12B is not provided, that is, at the end of the negative electrode current collector 11B. The negative electrode material layer 12B contains a negative electrode active material as an electrode active material.

The positive electrode active material contained in the positive electrode material layer 12A and the negative electrode active material contained in the negative electrode material layer 12B are substances directly involved in the transfer of electrons in the secondary battery, and are mainly responsible for charge / discharge, that is, the battery reaction. It is a substance. More specifically, ions are brought to the electrolyte due to the "positive electrode active material contained in the positive electrode material layer 12A" and the "negative electrode active material contained in the negative electrode material layer 12B", and such ions are brought to the electrolyte with the positive electrode 10A and the negative electrode. It moves to and from 10B, and electrons are transferred to charge and discharge. The positive electrode material layer 12A and the negative electrode material layer 12B are particularly preferably layers capable of occluding and releasing lithium ions. That is, a secondary battery in which lithium ions move between the positive electrode 10A and the negative electrode 10B via an electrolyte to charge and discharge the battery is preferable. When lithium ions are involved in charging and discharging, the secondary battery corresponds to a so-called "lithium ion battery".

Since the positive electrode active material of the positive electrode material layer 12A is made of, for example, granules, it is preferable that the positive electrode material layer 12A contains a binder for more sufficient contact between the particles and shape retention. Further, a conductive auxiliary agent may be contained in the positive electrode material layer 12A in order to facilitate the transfer of electrons that promote the battery reaction. Similarly, when the negative electrode active material of the negative electrode material layer 12B is composed of particles, for example, it is preferable that the negative electrode active material contains a binder for more sufficient contact between particles and shape retention, and facilitates the transfer of electrons that promote the battery reaction. The conductive auxiliary agent may be contained in the negative electrode material layer 12B. As described above, the positive electrode material layer 12A and the negative electrode material layer 12B can also be referred to as a "positive electrode mixture layer" and a "negative electrode mixture layer", respectively, because of the form in which a plurality of components are contained.

The positive electrode active material is preferably a substance that contributes to the occlusion and release of lithium ions. From this point of view, 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. That is, in the positive electrode material layer 12A of the secondary battery, 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 part of the transition metal thereof replaced with another metal. Such a positive electrode active material may be contained as a single species, but may be contained in combination of two or more species. In a more preferred embodiment, the positive electrode active material contained in the positive electrode material layer 12A is lithium cobalt oxide.

The binder that can be contained in the positive electrode material layer 12A is not particularly limited, but is limited to polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluorotyrene copolymer and polytetrafluoro. At least one species selected from the group consisting of Tylene and the like can be mentioned. The conductive auxiliary agent that can be contained in the positive electrode material layer 12A is not particularly limited, but is carbon black such as thermal black, furnace black, channel black, ketjen black and acetylene black, graphite, carbon nanotubes and vapor phase. At least one selected from carbon fibers such as grown carbon fibers, metal powders such as copper, nickel, aluminum and silver, and polyphenylene derivatives can be mentioned. For example, the binder of the positive electrode material layer 12A may be polyvinylidene fluoride. Although it is merely an example, the conductive auxiliary agent of the positive electrode material layer 12A is carbon black. Further, the binder and the conductive auxiliary agent of the positive electrode material layer 12A may be a combination of polyvinylidene fluoride and carbon black.

The negative electrode active material is preferably a substance that contributes to the occlusion and release of lithium ions. From this point of view, the negative electrode active material is preferably, for example, various carbon materials, oxides, lithium alloys, and the like.

Examples of various carbon materials for the negative electrode active material include graphite (natural graphite, artificial graphite), soft carbon, hard carbon, and diamond-like carbon. In particular, graphite is preferable because it has high electron conductivity and excellent adhesion to the negative electrode current collector 11B. Examples of the oxide of the negative electrode active material include at least one selected from the group consisting of silicon oxide, tin oxide, indium oxide, zinc oxide, lithium oxide and the like. The lithium alloy of the negative electrode active material may be any metal that can be alloyed with lithium, for example, Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, It may be a binary, ternary or higher alloy of a metal such as La and lithium. It is preferable that such an oxide is amorphous as its structural form. This is because deterioration due to non-uniformity such as grain boundaries or defects is less likely to occur. Although it is merely an example, the negative electrode active material of the negative electrode material layer 12B may be artificial graphite.

The binder that can be contained in the negative electrode material layer 12B is not particularly limited, but is at least one selected from the group consisting of styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyimide-based resin, and polyamide-imide-based resin. Seeds can be mentioned. For example, the binder contained in the negative electrode material layer 12B may be styrene-butadiene rubber. The conductive auxiliary agent that can be contained in the negative electrode material layer 12B is not particularly limited, but is carbon black such as thermal black, furnace black, channel black, ketjen black and acetylene black, graphite, carbon nanotubes and vapor phase. At least one selected from carbon fibers such as grown carbon fibers, metal powders such as copper, nickel, aluminum and silver, and polyphenylene derivatives can be mentioned. The negative electrode material layer 12B may contain a component derived from a thickener component (for example, carboxylmethyl cellulose) used at the time of manufacturing the battery.

Although it is merely an example, the negative electrode active material and the binder in the negative electrode material layer 12B may be a combination of artificial graphite and styrene-butadiene rubber.

The positive electrode current collector 11A and the negative electrode current collector 11B used for the positive electrode 10A and the negative electrode 10B are members that contribute to collecting and supplying electrons generated by the active material due to the battery reaction. Such a current collector may be a sheet-shaped metal member and may have a perforated or perforated form. For example, the current collector may be a metal leaf, a punching metal, a net, an expanded metal, or the like. The positive electrode current collector 11A used for the positive electrode 10A is preferably made of a metal foil containing at least one selected from the group consisting of aluminum, stainless steel, nickel and the like, and may be, for example, an aluminum foil. On the other hand, the negative electrode current collector 11B used for the negative electrode 10B is preferably made of a metal foil containing at least one selected from the group consisting of copper, stainless steel, nickel and the like, and may be, for example, a copper foil.

The separator 50 is a member provided from the viewpoint of preventing a short circuit due to contact between the positive and negative electrodes and retaining the electrolyte. In other words, it can be said that the separator 50 is a member through which ions pass while preventing electronic contact between the positive electrode 10A and the negative electrode 10B. Preferably, the separator 50 is a porous or microporous insulating member and has a film morphology due to its small thickness. Although only an example, a microporous polyolefin membrane may be used as the separator. In this regard, the microporous membrane used as the separator 50 may contain, for example, only polyethylene (PE) or polypropylene (PP) as the polyolefin. Furthermore, the separator 50 may be a laminate composed of a "microporous membrane made of PE" and a "microporous membrane made of PP". The surface of the separator 50 may be covered with an inorganic particle coat layer and / or an adhesive layer or the like. The surface of the separator may have adhesiveness.

The separator 50 should not be particularly bound by its name, and may be a solid electrolyte, a gel-like electrolyte, an insulating inorganic particle, or the like having the same function. From the viewpoint of further improving the handling of the electrodes, it is preferable that the separator 50 and the electrodes (positive electrode 10A / negative electrode 10B) are adhered to each other. The separator 50 and the electrode are bonded by using an adhesive separator as the separator 50, applying an adhesive binder on the electrode material layer (positive electrode material layer 12A / negative electrode material layer 12B), and / or thermocompression bonding. Can be done. Examples of the material of the adhesive binder that provides adhesiveness to the separator 50 or the electrode material layer include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene polymer, and acrylic resin. The thickness of the adhesive layer obtained by applying an adhesive binder or the like may be 0.5 μm or more and 5 μm or less.

When the positive electrode 10A and the negative electrode 10B have a layer capable of occluding and releasing lithium ions, the electrolyte is preferably an "non-aqueous" electrolyte such as an organic electrolyte and / or an organic solvent (ie, the electrolyte is a non-aqueous electrolyte). Is preferable). In the electrolyte, metal ions released from the electrodes (positive electrode 10A and negative electrode 10B) are present, and therefore the electrolyte assists the movement of the metal ions in the battery reaction.

A non-aqueous electrolyte is an electrolyte containing a solvent and a solute. As a specific solvent for the non-aqueous electrolyte, a solvent containing at least carbonate is preferable. Such carbonates may be cyclic carbonates and / or chain carbonates. Although not particularly limited, the cyclic carbonates include at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC) and vinylene carbonate (VC). be able to. Examples of the chain carbonates include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC). Although only an example, a combination of cyclic carbonates and chain carbonates may be used as the non-aqueous electrolyte, and for example, a mixture of ethylene carbonate and diethyl carbonate may be used. Further, as a specific non-aqueous electrolyte solute, for example, Li salts such as _{LiPF 6} and LiBF _{4 are used.} Further, as a specific non-aqueous electrolyte solute, a Li salt such as _{LiPF 6} and / or LiBF _{4 is preferably used.}

As the positive electrode current collector lead and the negative electrode current collector lead, any current collector lead used in the field of secondary batteries can be used. Such a current collecting lead may be composed of a material in which electron transfer can be achieved, and is composed of a conductive material such as aluminum, nickel, iron, copper, or stainless steel. The positive electrode current collecting lead is preferably made of aluminum, and the negative electrode current collecting lead is preferably made of nickel. The form of the positive electrode current collecting lead and the negative electrode current collecting lead is not particularly limited, and may be, for example, a wire or a plate.

As the external terminal, any external terminal used in the field of secondary batteries can be used. Such external terminals may be made of a material in which electron transfer can be achieved, and are usually made of a conductive material such as aluminum, nickel, iron, copper, stainless steel. The external terminal 5 may be electrically and directly connected to the substrate, or may be electrically and indirectly connected to the substrate via another device. Not limited to this, the positive electrode current collector lead connected to each of the plurality of positive electrodes may have the function of the positive electrode external terminal, and the negative electrode current collector connected to each of the plurality of negative electrodes. The lead may have the function of an external terminal for a negative electrode.

The exterior body may take the form of a conductive hard case or a flexible case (pouch, etc.). When the outer body is in the form of a flexible case (pouch or the like), each of the plurality of positive electrodes is connected to the external terminal for the positive electrode via the current collecting lead for the positive electrode. The external terminal for the positive electrode is fixed to the exterior body by the seal portion, and the seal portion prevents the electrolyte from leaking. Similarly, each of the plurality of negative electrodes is connected to the external terminal for the negative electrode via the current collecting lead for the negative electrode. The external terminal for the negative electrode is fixed to the exterior body by the seal portion, and the seal portion prevents the electrolyte from leaking. The current collector lead for the positive electrode connected to each of the plurality of positive electrodes may have the function of an external terminal for the positive electrode, and the current collector for the negative electrode connected to each of the plurality of negative electrodes may be provided. The lead may have the function of an external terminal for a negative electrode. When the outer body is in the form of a conductive hard case, each of the plurality of positive electrodes is connected to an external terminal for the positive electrode via a current collecting lead for the positive electrode. The external terminal for the positive electrode is fixed to the exterior body by the seal portion, and the seal portion prevents the electrolyte from leaking.

The conductive hard case consists of a main body and a lid. The main body portion is composed of a bottom portion and a side surface portion constituting the bottom surface of the exterior body. The body and lid are sealed after accommodating the electrode assembly, electrolyte, current collector leads and external terminals. The sealing method is not particularly limited, and examples thereof include a laser irradiation method. As the material for forming the main body and the lid, any material that can form a hard case type exterior body can be used in the field of the secondary battery. Such a material may be any material in which electron transfer can be achieved, including conductive materials such as aluminum, nickel, iron, copper and stainless steel. The dimensions of the main body and the lid are mainly determined according to the dimensions of the electrode assembly. For example, when the electrode assembly is housed, the dimensions are such that the movement (displacement) of the electrode assembly inside the exterior body is prevented. It is preferable to have. By preventing the electrode assembly from moving, the electrode assembly is prevented from being destroyed, and the safety of the secondary battery is improved.

The flexible case is composed of a soft sheet. The soft sheet may have enough softness to achieve bending of the seal portion, and is preferably a plastic sheet. The plastic sheet is a sheet having a property of maintaining deformation due to an external force when it is removed after applying an external force. For example, a so-called laminated film can be used. A flexible pouch made of a laminated film can be manufactured, for example, by laminating two laminated films and heat-sealing the peripheral portion thereof. The laminated film is generally a film in which a metal foil and a polymer film are laminated, and specifically, a three-layer structure composed of an outer layer polymer film / metal foil / inner layer polymer film is exemplified. The outer layer polymer film is for preventing damage to the metal foil due to permeation of moisture and the like and contact, and polymers such as polyamide and polyester can be preferably used. The metal foil is for preventing the permeation of moisture and gas, and a foil of copper, aluminum, stainless steel or the like can be preferably used. The inner layer polymer film protects the metal foil from the electrolyte stored inside and melts and seals the metal foil at the time of heat sealing, and polyolefin or acid-modified polyolefin can be preferably used.

[Method for manufacturing the secondary battery of the present invention]
The method for manufacturing the secondary battery according to the embodiment of the present invention will be described below in consideration of the basic configuration of the secondary battery.

The inventors of the present application have diligently studied a solution for making it possible to increase the density of the electrode material layer even by using a current collector composed of a thin metal or the like. As a result, a method for manufacturing the secondary battery of the present invention having the following characteristics has been devised.

Specifically, the method for manufacturing a secondary battery according to an embodiment of the present invention includes a step of forming the electrode 10. The step of forming the electrode 10 is
Along the stacking direction, the conductive adhesive layer slurry 13a and the electrode material layer slurry 12a are sequentially coated on the temporary support sheet 200 to form the laminated body 300.
The laminate 300 is dried to form the conductive adhesive layer 13 and the electrode material layer 12 on the temporary support sheet 200.
Pressurizing the laminate 300 along the stacking direction so as to sandwich the upper surface 301 and the lower surface 302 of the laminate 300,
Peeling the temporary support sheet 200 after pressurization and
It includes laminating and crimping a current collector 11 composed of at least one of metal and resin on the conductive adhesive layer 13.

Specifically, first, as shown in FIG. 3A, a temporary support sheet 200 such as a PET film is prepared. The "temporary support sheet" referred to in the present specification does not function as a component of the obtained secondary battery of the present invention, but is a component of the secondary battery (specifically, a conductive adhesive layer) during manufacturing. ) Temporarily supports the member. Therefore, specifically, a material other than the PET film may be used as long as it can support the member to be the conductive adhesive layer. After preparing the temporary support sheet 200, as shown in FIG. 3B, the conductive adhesive layer slurry 13a is applied onto the temporary support sheet 200. Next, as shown in FIG. 3C, the electrode material layer slurry 12a is coated on the coated conductive adhesive layer slurry 13a to form a predetermined laminated body 300. Next, as shown in FIG. 3D, the laminate 300 is dried to form the conductive adhesive layer 13 and the electrode material layer 12 located on the conductive adhesive layer 13 on the temporary support sheet 200.

After that, as shown in FIG. 3E, the laminated body 300 is pressurized along the laminating direction so as to sandwich the upper surface 301 and the lower surface 302 of the laminated body 300. The pressurizing method is not particularly limited, but specifically, as shown in FIG. 4, a roll press machine composed of two rolls 400 facing each other is used to hold the laminate 300 between the two rolls 400. You may let it pass and press the laminated body 300 at that time.

The surface free energy of the temporary support sheet 200 used in the present embodiment ^{is preferably 20 mJ / m 2} or more. When the value is equal to or higher than the surface free energy, it is possible to preferably suppress the transfer of the conductive adhesive layer 13 which is a component of the laminated body 300 to the roll 400 side during the roll press.

Next, as shown in FIG. 3F, the temporary support sheet 200 is peeled off. Finally, as shown in FIG. 3G, a current collector 11 composed of at least one of metal and resin is laminated and pressure-bonded on the conductive adhesive layer 13. The surface free energy of the surface of the conductive adhesive layer 13 exposed after the temporary support sheet 200 is peeled off ^{is preferably 8.0 mJ / m 2} or more. When the value is equal to or higher than the surface free energy, the binding property of the current collector 11 to the conductive adhesive layer 13 can be suitably ensured at the time of crimping the current collector 11 during roll pressing.

From the above, a predetermined electrode 10 can be obtained.

After forming the electrodes 10 (positive electrode and negative electrode), the electrode constituent layer is formed by laminating the positive electrode and the negative electrode along the stacking direction via the separator. By laminating at least two electrode constituent layers along the laminating direction, a laminated electrode assembly can be finally formed. Further, by winding a single electrode constituent layer, a wound electrode assembly can be finally formed.

After forming a predetermined electrode assembly (winding type / laminated type), the current collecting tab is welded while accommodating the electrode assembly in the exterior body. Then, the electrolytic solution is injected into the exterior body based on the decompression method.

By mainly going through the above steps, the secondary battery according to the embodiment of the present invention can be manufactured.

From the above, one embodiment of the present invention does not adopt a method of pressurizing a laminate having a foil as a current collector and an electrode material layer as in the past, but laminates at the time of pressurization. It is characterized in that a temporary support sheet 200 is applied instead of the current collector as a component of the body 300. According to such a feature, in the step of pressurizing the laminated body 300 so as to sandwich the laminated body 300, the laminated body 300 does not include a current collector. That is, when the laminated body 300 is pressurized, the current collector, which is a component of the electrode, is not pressurized. Therefore, the elongation of the foil that becomes the current collector due to the pressurization of the current collector is avoided. As a result, the electrode material layer, which is a component of the electrode, does not exist on the current collector, which tends to generate elongation when the laminated body 300 is pressurized, but on the temporary support sheet 200, which does not easily generate elongation. There will be an electrode material layer. Therefore, when the laminated body 300 is pressurized, it is possible to suitably realize a high density of the electrode material layer. Specifically, the porosity of the electrode material layer can be reduced to 25% or less, and the density of the electrode material layer can be increased. From the above, according to one embodiment of the present invention, the density of the electrode material layer 12, which is a component of the secondary battery, can be increased even if a current collector having a property of easily causing elongation is used. Can be done. As a result, it becomes possible to improve the energy density of the secondary battery.

Furthermore, as described above, in the present invention, when the laminated body 300 is pressurized, the current collector which is finally a component of the electrode is not pressurized. Therefore, even if a current collector having a property of easily generating elongation or a thin-layered current collector is used in order to meet the demand for miniaturization and weight reduction of the secondary battery, when the laminated body 300 is pressurized, It is possible to avoid the problem that the foil that becomes the current collector stretches. As a result, the strength of the current collector can be maintained even if a current collector having a property of easily causing elongation or a thinned current collector is used.

Specifically, it is possible to use a thin current collector (specifically, a metal current collector) having a thickness of 10 μm or less. It is also possible to use a current collector (specifically, a resin current collector) having a Young's modulus of 5 GPa or less and having a relatively easily stretchable property. On the other hand, in the present invention, when the laminate 300 is pressurized, the electrode material layer which is a component of the electrode is pressurized. Therefore, it is possible to suitably realize a high density of the electrode material layer. Specifically, the porosity of the electrode material layer is 25% or less. From the above, according to one embodiment of the present invention, even if a thin current collector or a current collector having a property of being easily stretched is used, the density of the electrode material layer can be increased and the strength of the current collector 11 can be maintained. It becomes compatible.

[Secondary battery of the present invention]
Hereinafter, the characteristic portion of the secondary battery according to the embodiment of the present invention obtained through the above steps will be described.

FIG. 1 is a cross-sectional view schematically showing a secondary battery according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view schematically showing an electrode of a secondary battery according to an embodiment of the present invention.

The present invention has a configuration characteristic of electrodes, which are components of a secondary battery. Specifically, the electrode 10 has a current collector 11, an electrode material layer 12, and a conductive adhesive layer 13 provided between the current collector 11 and the electrode material layer 12 along the stacking direction. Become. Further, the current collector 11 is a current collector composed of at least one of a thin metal and a resin, and the porosity of the electrode material layer 12 is 25% or less. As an example, as shown in FIG. 2, as the current collector 11, a thin metal current collector 11I can be adopted. As another example, as shown in FIG. 2, a resin current collector 11II can be used as the current collector 11.

By having such a feature, when the current collector 11 is a current collector composed of at least one of a thin metal and a resin, that is, when the current collector 11 is relatively thin and / or relatively elongated. Even when it has an easy property, the porosity of the electrode material layer 12 is 25% or less, that is, the porosity at which the density of the electrode material layer can be increased is achieved. From the above, according to one embodiment of the present invention, even when a current collector using a thin metal, a resin, or the like or a current collector in which elongation is likely to occur is used, the secondary battery It is possible to increase the density of the electrode material layer 12, which is a component of the above. As a result, it becomes possible to improve the energy density of the secondary battery. As used herein, the term "current collector composed of at least one of a thin metal and a resin" refers to a current collector having a thickness relatively smaller than the thickness of a normally used current collector of 50 μm or more and 500 μm or less. A body, specifically, a current collector having a thickness of 10 μm or less, and / or a current collector having a Young ratio of 5 GPa or less.

Further, from the viewpoint of the structure of the object itself, since the current collector 11 and the electrode material layer 12 are joined to each other via the conductive adhesive layer 13, the current collector 11 is separated from the electrode material layer 12. Is suppressed. Therefore, it is possible to prevent the current collector 11 from being partially curved or the like. As a result, not only is it accompanied by "avoidance of stretching of the foil serving as the current collector when the laminated body 300 is pressurized" described in the above-mentioned manufacturing method column, but also by suppressing partial bending of the current collector 11 itself. , It becomes possible to maintain the strength of the current collector 11.
From the above, according to one embodiment of the present invention, it is possible to increase the density of the electrode material layer 12, which is a component of the secondary battery, while maintaining the strength of the current collector 11.

Although one embodiment of the present invention has been described above, it merely exemplifies a typical example of the scope of application of the present invention. Therefore, those skilled in the art will easily understand that the present invention is not limited to this, and various modifications can be made.

Hereinafter, examples will be described.

Example 1:
<Implementation process>
An electrode was formed through the following steps.

First, a temporary support sheet was prepared. Specifically, a PET film having a surface free energy of 32.6 mJ / m ^{2 was prepared.} A conductive adhesive layer was applied onto the temporary support sheet so as to have a predetermined thickness. Then, it was vacuum dried at 80 degrees for 10 minutes or more. Modified PP-A is used as a binder to be included in the conductive adhesive layer, and AB (acetylene black) is used as a filler.
AB and the binder were weighed in predetermined amounts so that the volume of AB was 12 vol%. Then, while applying ultrasonic dispersion, the mixture was prepared by mixing with a fill mix at 4000 rpm for 10 minutes.

The positive electrode slurry was coated on the dried conductive adhesive layer to a predetermined thickness, and vacuum dried at 120 ° C. for 10 minutes or more after the coating. _{LiCoO 2} was used as the positive electrode active material, and a slurry was prepared using a solvent-based binder and an organic solvent.

The conductive adhesive layer was applied onto a current collector (a resin current collector with a Young's modulus of 1.6 GPa) in the same manner so as to have a predetermined thickness.

The obtained laminate was pressed so as to have a density of 3.65 g / cc. A roll press was used for the press, and the temperature of the roll surface was set to 100 ° C. Then, it was cut out to a size of 14 mmΦ for evaluation of battery characteristics, and the surface on the active material side and the separator cut out to 14 mmΦ were thermocompression bonded. Then, the PET film was peeled off. A current collector with a conductive adhesive layer was cut out to 15 mmΦ, laminated so that the conductive adhesive layer was positioned on the side where the PET film was peeled off, and thermocompression bonded again to integrate them.

A coin cell secondary battery was assembled using an integrated electrode and separator, metallic lithium cut into 15 mmΦ and attached to a spacer made of SUS with the same diameter, and an electrolytic solution. The coating thickness of the electrode was adjusted so that the battery capacity was about 1.7 mAh.

From the above, the secondary battery of the present invention was obtained. The obtained secondary battery was measured under the following conditions.

<Measurement conditions>
After the secondary battery was manufactured, after a pause of 10 hours, the battery was charged with a current of 0.2 C to a constant current and constant voltage up to an upper limit voltage of 4.2 V. The condition after the step at the time of constant voltage charging was 0.01 C current. At the time of discharge, a constant current was discharged to a final voltage of 2.5 V with a current of 0.2 C. This "0.2C" is a current value at which the theoretical capacity can be completely discharged in 5 hours. The above conditions were repeated for 3 cycles. The capacity of the third cycle was defined as the battery capacity.

When investigating the cycle characteristics, first, the discharge capacity was measured by charging and discharging for 2 cycles in an atmosphere of 25 ° C. Subsequently, the discharge capacity was measured by repeatedly charging and discharging until the total number of cycles reached 100 cycles in the same atmosphere. Finally, the cycle maintenance rate (%) = (discharge capacity in the 100th cycle / discharge capacity in the second cycle) × 100 was calculated. At the time of charging, the battery was charged with a constant current and constant voltage up to an upper limit voltage of 4.2 V with a current of 0.2 C. The condition after the step at the time of constant voltage charging was 0.01 C current. At the time of discharge, a constant current was discharged to a final voltage of 2.5 V with a current of 0.2 C.

AC resistance measurement (HIOKI3560ACmΩ) is performed before the cycle characteristic survey, and AC resistance measurement (HIOKI3560ACmΩ) is performed after the cycle characteristic survey, and the ratio (AC resistance value before the cycle / AC resistance value after the cycle) is calculated to calculate the AC resistance increase rate. And said. Table 2 shows the respective resistance values and the rate of increase.

The pressed electrode was cut out to a predetermined size, attached to a measuring jig, the PET film was peeled off, and the surface free energy of the peeled surface was measured. For the obtained electrode, the porosity of the active material layer was determined with a mercury porosimeter (micromeritics AutoPole IV / SHIMADZU). Each measured value is shown in Table 1.

At the stage where only the conductive adhesive layer was applied on the temporary support sheet, it was confirmed whether or not there was transfer to the roll during roll-to-roll.

<Result>
From Example 1, it was confirmed that even when a resin current collector having a Young's modulus of 1.6 GPa was used, a high density of 3.65 g / cc could be achieved and that the battery could be charged and discharged. .. It was also confirmed that the rate of increase in AC resistance before and after the cycle was 10%, and that the increase in resistance due to the cycle was suppressed. Furthermore, it was also confirmed that the conductive adhesive layer coated on the temporary support sheet did not transfer to the roll during roll-to-roll.

Example 2:
<Implementation process>
An electrode was formed through the following steps.

As the temporary support sheet, a PET film having a surface free energy of 22.8 mJ / m ^{2 was used.} After that, the conductive adhesive layer was applied onto the temporary support sheet in the same manner as in Example 1. The negative electrode slurry was similarly coated on the dried conductive adhesive layer to a predetermined thickness, and vacuum dried at 120 ° C. for 10 minutes or more after the coating. Gr was used as the negative electrode active material, and a slurry was prepared using a solvent-based binder and an organic solvent.

The conductive adhesive layer was applied onto a current collector (resin current collector having a Young's modulus of 1.6 GPa) similar to that in Example 1 in the same manner so as to have a predetermined thickness. The obtained laminate was pressed so as to have a density of 1.65 g / cc. The press was pressed at room temperature using a roll press machine. After that, the PET film was peeled off and thermocompression bonded to a current collector (a resin current collector having a Young's modulus of 1.6 GPa) in the same procedure as in Example 1. The coin cell evaluation, the surface free energy measurement, the porosity measurement, and the AC resistance measurement before and after the cycle test were also carried out under the same conditions as in Example 1.

Also, at the stage where only the conductive adhesive layer was applied on the temporary support sheet, it was confirmed whether or not there was transfer to the roll during roll-to-roll.

<Result>
From Example 2, it was confirmed that even when a resin current collector having a Young's modulus of 1.6 GPa was used, a high density of 1.65 g / cc could be achieved and that the battery could be charged and discharged. .. In addition, the rate of increase in AC resistance before and after the cycle was 14%, confirming that the increase in resistance due to the cycle could be suppressed. Furthermore, it was confirmed that the conductive adhesive layer coated on the temporary support sheet did not transfer to the roll during roll-to-roll.

Example 3:
<Implementation process>
An electrode was formed through the following steps.

As the temporary support sheet, a PET film having a surface free energy of 24.7 mJ / m ^{2 was used.} After that, the conductive adhesive layer was applied onto the temporary support sheet and dried in the same manner as in Example 1. The same negative electrode slurry as in Example 2 was applied onto the dried conductive adhesive layer using the same jig so as to have a predetermined thickness, and after the application, it was vacuum dried at 120 ° C. for 10 minutes or more. The conductive adhesive layer was applied onto a current collector (copper foil having a thickness of 10 μm) in the same manner so as to have a predetermined thickness.

The obtained laminate was pressed so as to have a density of 1.65 g / cc. The press was pressed at room temperature using a roll press machine. After that, the PET film was peeled off and thermocompression bonded to a current collector (10 μm copper foil) in the same procedure as in Example 1. The coin cell evaluation, the surface free energy measurement, the porosity measurement, and the AC resistance measurement before and after the cycle test were also carried out under the same conditions as in Example 1.

Separately, at the stage where only the conductive adhesive layer was applied on the temporary support sheet, it was confirmed whether or not there was transfer to the roll during roll-to-roll.

<Result>
It was confirmed that even with a thinned electrode having a thickness of 10 μm, a high density of 1.65 g / cc could be achieved and that the battery could be charged and discharged. The rate of increase in AC resistance before and after the cycle was 6%, confirming that the increase in resistance due to the cycle could be suppressed. Furthermore, it was confirmed that the conductive adhesive layer coated on the temporary support sheet did not transfer to the roll during roll-to-roll.

Example 4:
<Implementation process>
An electrode was formed through the following steps.

As the temporary support sheet, a PET film having a surface free energy of 24.7 mJ / m ^{2 was used.} After that, the conductive adhesive layer was applied onto the temporary support sheet and dried in the same manner as in Example 1. On the dried conductive adhesive layer, the same negative electrode slurry as in Example 2 was applied to a predetermined thickness using the same jig, and vacuum dried at 120 ° C. for 10 minutes or more after the application. The conductive adhesive layer was applied onto a current collector (copper foil having a thickness of 6 μm) in the same manner so as to have a desired thickness.

The obtained laminate was pressed so as to have a density of 1.65 g / cc. The press was pressed at room temperature using a roll press machine. After that, the PET film was peeled off and thermocompression bonded to the current collector (6 μm copper foil) in the same procedure as in Example 1. The coin cell evaluation, the surface free energy measurement, the porosity measurement, and the AC resistance measurement before and after the cycle test were also carried out under the same conditions as in Example 1. Separately, at the stage where only the conductive adhesive layer was applied on the temporary support sheet, the presence or absence of transfer to the roll during roll-to-roll was confirmed.

<Result>
It was confirmed that even with a thinned electrode having a thickness of 6 μm, a high density of 1.65 g / cc could be achieved and that the battery could be charged and discharged. The rate of increase in AC resistance before and after the cycle was 8%, confirming that the increase in resistance due to the cycle could be suppressed. Furthermore, it was confirmed that the conductive adhesive layer coated on the temporary support sheet did not transfer to the roll during roll-to-roll.

Comparative Example 1:
<Implementation process>
An electrode was formed through the following steps.

A conductive adhesive layer similar to that in Example 1 was adjusted to have a predetermined thickness on a resin current collector having a Young's modulus of 1.6 GPa, and coated using a jig. On the dried conductive adhesive layer, the same negative electrode slurry as in Example 2 was applied to a predetermined thickness using the same jig and dried.

The obtained electrode was pressed so as to have a density of 1.65 g / cc. The press was pressed at room temperature using a roll press machine.

<Result>
It was confirmed that the electrode after pressing had wrinkles, the density did not rise to the target, and the density varied within the same electrode. Since the degree of wrinkles was severe, it was impossible to evaluate the subsequent process and battery characteristics.

Comparative Example 2:
<Implementation process>
An electrode was formed through the following steps.

A conductive adhesive layer similar to that in Example 1 was adjusted to have the desired thickness on a copper foil having a thickness of 10 μm, and was coated using a jig. On the dried conductive adhesive layer, the same negative electrode slurry as in Example 2 was applied to a predetermined thickness using the same jig and dried.

The obtained electrode was pressed so that the target density was 1.65 g / cc, but it became clear that the electrode had wrinkles. As a result of pressing in a range where wrinkles did not occur, it was found that the density of the electrodes could only be increased to 1.57 g / cc. The press was pressed at room temperature using a roll press machine. After that, a coin cell having a metallic lithium counter electrode was prepared in the same manner as in Example 1, and the coin cell was evaluated, the surface free energy was measured, the porosity was measured, and the AC resistance was measured before and after the cycle test.

<Result>
It was found that the electrode density can only be increased to 1.57 g / cc in order to produce a high-quality electrode that does not generate wrinkles after pressing. It was confirmed that the battery can be charged and discharged using this electrode, but the AC resistance increase rate before and after the cycle was about 150%, and it was confirmed that the resistance increased remarkably with the cycle. ..

Comparative Example 3:
<Implementation process>
An electrode was formed through the following steps.

A conductive adhesive layer similar to that in Example 1 was adjusted to have a predetermined thickness on a Cu foil having a thickness of 6 μm, and coated using a jig. On the dried conductive adhesive layer, the same negative electrode slurry as in Example 2 was applied to a predetermined thickness using the same jig and dried.

The obtained electrode was pressed so that the target density was 1.65 g / cc, but the electrode after pressing had wrinkles, and it was confirmed that some of the electrodes and the copper foil were peeled off. Therefore, as a result of performing electrode pressing within a range where wrinkles and tears did not occur, it was found that the density could only be increased to 1.50 g / cc. A roll press was used for the press, and the press was performed at room temperature. After that, a coin cell having a metallic lithium counter electrode was prepared in the same manner as in Example 1, and the coin cell was evaluated, the surface free energy was measured, the porosity was measured, and the AC resistance was measured before and after the cycle test.

<Result>
It was found that the electrode density can only be increased to 1.50 g / cc in order to produce a high-quality electrode that does not cause wrinkles or tears after pressing. It was confirmed that the battery can be charged and discharged using this electrode, but the AC resistance increase rate before and after the cycle was about 300%, and it was confirmed that the resistance increased remarkably with the cycle. ..

Comparative Example 4:
<Implementation process>
An electrode was formed through the following steps.

As the temporary support sheet, a PET film having a surface free energy of 32.6 mJ / m ^{2 was used.} The conductive adhesive layer is not coated on the temporary support sheet, and the same positive electrode slurry as in Example 1 is coated with a jig so as to have a predetermined thickness, and after coating, 120 degrees for 10 minutes. The above was vacuum dried. _{LiCoO 2} was used as the positive electrode active material, and a slurry was prepared using a solvent-based binder and an organic solvent.

The obtained temporary support sheet electrode was pressed so as to have a density of 3.65 g / cc. A roll press was used for the press, and the temperature of the roll surface was set to 100 ° C. Then, it was cut out to a predetermined size for evaluation of battery characteristics, and the active material side and the separator were thermocompression-bonded, and then the PET film was peeled off. A current collector (resin current collector with a Young's modulus of 1.6 GPa) without a conductive adhesive layer was laminated on the PET film peeling side of the positive electrode active material layer, and thermocompression bonded again to integrate them.

<Result>
It became clear that the active material and the current collector (resin current collector with Young's modulus of 1.6 GPa) did not crimp even if the thermocompression bonding pressure and temperature conditions were changed, making it impossible to evaluate battery characteristics. There was found.

Comparative Example 5:
<Implementation process>
An electrode was formed through the following steps.

As the temporary support sheet, a PET film having a surface free energy of 17.7 mJ / m ^{2 was used.} The same conductive adhesive layer as in Example 1 was adjusted to have the desired thickness, and the coating was applied using a jig. After drying, the presence or absence of transfer to the roll during roll-to-roll was confirmed by the same procedure as in Example 2.

<Result>
It was confirmed that the conductive adhesive layer adhered to the roll and transferred.

Table 1. Electrode fabrication conditions

Table 2. Battery characteristics evaluation results

The secondary battery according to the embodiment of the present invention can be used in various fields where storage is expected. Although only an example, the secondary battery according to the embodiment of the present invention, particularly the non-aqueous electrolyte secondary battery, is used in the fields of electricity, information, and communication (for example, mobile phones, smartphones, notebooks, etc.) in which mobile devices and the like are used. Mobile device fields such as personal computers and digital cameras, activity meters, arm computers, electronic paper), home / small industrial applications (for example, power tools, golf carts, home / nursing / industrial robot fields), large industries Applications (eg, forklifts, elevators, bay port cranes), transportation systems (eg, hybrid vehicles, electric vehicles, buses, trains, electrically assisted bicycles, electric motorcycles, etc.), power system applications (eg, various power generation) , Road conditioner, smart grid, general household installation type power storage system, etc.), medical use (medical equipment field such as earphone hearing aid), medical use (field such as dose management system), IoT field, space / deep sea It can be used for various purposes (for example, in the fields of space explorers, submersible research vessels, etc.).

10, 10'Electrode 10A Positive electrode 10B Negative electrode 11, 11' Electrode collector 11A Positive electrode current collector 11B Negative electrode current collector 11I Metal current collector 11II Resin current collector 12, 12' Electrode material layer 12A Positive electrode material layer 12B Negative electrode material Layer 13 Conductive adhesive layer 13a Conductive adhesive slurry 20 Electrolyte 30 Exterior 30B, 30B'Negative electrode side external terminal 50 Separator 100 Secondary battery 200 Temporary support sheet 300 Laminated body 301 Upper surface of laminated body 302 Lower surface of laminated body 400, 400'roller

Claims

The electrode includes a current collector, an electrode material layer, and a conductive adhesive layer provided between the current collector and the electrode material layer along the stacking direction.
A secondary battery in which the current collector is composed of at least one of a thin metal and a resin, and the porosity of the electrode material layer is 25% or less.
The secondary battery according to claim 1, wherein the current collector has a thickness of 10 μm or less.
The secondary battery according to claim 1 or 2, wherein the current collector has a Young's modulus of 5 GPa or less.
The secondary battery according to any one of claims 1 to 3, wherein the electrode can occlude and release lithium ions.
A method for manufacturing a secondary battery including an electrode forming process.
The electrode forming process
A step of forming a laminate by sequentially coating a conductive adhesive layer slurry and an electrode material layer slurry on a temporary support sheet, and
A step of drying the laminate to form a conductive adhesive layer and an electrode material layer on the temporary support sheet, and
A step of pressurizing the laminated body along the laminating direction of the laminated body so as to sandwich the upper surface and the lower surface of the laminated body.
The step of peeling off the temporary support sheet after the pressurization and
A method for manufacturing a secondary battery, which comprises a step of laminating a current collector composed of at least one of a metal and a resin on the conductive adhesive layer after the peeling.
The method for manufacturing a secondary battery according to claim 5, wherein in the step of pressurizing the laminate, the laminate does not include the current collector.
The method for manufacturing a secondary battery according to claim 5 or 6, wherein the thickness of the current collector is 10 μm or less.
The method for manufacturing a secondary battery according to any one of claims 5 to 7, wherein the Young's modulus of the current collector is 5 GPa or less.
The method for manufacturing a secondary battery according to any one of claims 5 to 8, wherein the porosity of the electrode material layer is 25% or less.
The method for manufacturing a secondary battery according to any one of claims 5 to 9, wherein the surface free energy of the temporary support sheet is 20 mJ / m 2 or more.
The method for manufacturing a secondary battery according to any one of claims 5 to 10, wherein the surface free energy of the surface of the conductive adhesive layer is 8.0 mJ / m 2 or more.