JPWO2019188758A1 - Electrochemical devices and their manufacturing methods - Google Patents

Abstract

In the present invention, the electrochemical device includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The positive electrode includes a positive electrode current collector and an active layer on the positive electrode current collector. The active layer contains a conductive polymer. A silane compound is present between the positive electrode current collector and the active layer.

Description

The present invention relates to an electrochemical device including an active layer containing a conductive polymer and a method for producing the same.

In recent years, electrochemical devices having intermediate performance between a lithium ion secondary battery and an electric double layer capacitor have been attracting attention, and for example, the use of a conductive polymer as a positive electrode material has been studied (for example, patent documents). 1). An electrochemical device containing a conductive polymer as a positive electrode material is charged and discharged by adsorption (doping) and desorption (dedoping) of anions, so that the reaction resistance is small and compared with a general lithium ion secondary battery. It has a high output.

Japanese Unexamined Patent Publication No. 2014-35836

Impurities may be mixed in the active layer in the process of manufacturing the positive electrode of the electrochemical device. Impurities can interfere with anion doping during charging, reducing capacity.

One aspect of the present invention includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the positive electrode includes a positive electrode current collector and an active layer on the positive electrode current collector. The present invention relates to an electrochemical device, wherein the active layer contains a conductive polymer, and a silane compound is present between the positive electrode current collector and the active layer.

Another aspect of the present invention is a method for manufacturing an electrochemical device including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the step of obtaining the positive electrode, the positive electrode, and the positive electrode are used. The step of laminating the separator and the negative electrode is provided, and the step of obtaining the positive electrode includes a step of forming an active layer containing a conductive polymer on the positive electrode current collector and the positive electrode current collector. The present invention relates to a method for producing an electrochemical device, comprising a step of imparting a silane compound between the active layer and the active layer.

According to the above aspect of the present invention, in the electrochemical device, the mixing of impurities into the active layer of the positive electrode can be suppressed, and the decrease in capacity can be suppressed.

FIG. 1 is a schematic cross-sectional view of a positive electrode of an electrochemical device according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of the electrochemical device according to the embodiment. FIG. 3 is a schematic diagram for explaining the configuration of the element included in the electrochemical device of FIG.

An electrochemical device according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode. The positive electrode includes a positive electrode current collector and an active layer on the positive electrode current collector. The active layer contains a conductive polymer. A silane compound is present between the positive electrode current collector and the active layer.

Reaction solutions and treatment solutions used in the process of producing positive electrodes for electrochemical devices may contain anionic components. Therefore, impurities such as anionic components may be mixed in the active layer containing the conductive polymer. When the anionic component, which is an impurity, is irreversibly doped into the conductive polymer, the reversible doping of the anion into the conductive polymer during charging is hindered. As a result, the capacity of the electrochemical device is reduced. For example, if an anionic component remains in a component of a positive electrode (hereinafter, also referred to as a base layer) that is a base of an active layer, such as a positive electrode current collector, the active layer is formed as an impurity when the active layer is formed. It will be mixed and irreversibly doped into the conductive polymer. The anionic component is contained as a sulfate ion in, for example, a reaction solution (electrolytic solution) for electrolytic polymerization used when forming an active layer. In addition, the reaction solution for chemical polymerization and other treatment solutions may contain anionic components such as sulfate ions as neutralizing agents and oxidizing agents. When these reaction liquids and treatment liquids come into contact with the base layer such as the positive electrode current collector, the anionic component adheres to and is retained in the base layer, and becomes the active layer during or after the active layer is formed. It becomes easy to mix.

According to the above embodiment of the present invention, a silane compound is present between the positive electrode current collector and the active layer. Since the underlying layer of the active layer is hydrophobized by the silane compound, even if impurities such as anionic components (hydrophilic impurities, etc.) adhere to the underlying layer in the process of producing the positive electrode, the underlying layer and its vicinity are present. Hard to stay (that is, hard to survive). Therefore, impurities are suppressed from being mixed into the active layer during or after the active layer is formed. By suppressing the mixing of impurities into the active layer, it is possible to suppress the inhibition of doping and dedoping of the anions responsible for the charge / discharge reaction, so that it is possible to suppress a decrease in the capacity of the electrochemical device.

The surface of the positive electrode current collector is often hydrophilized, and hydrophilic impurities such as anionic components tend to remain. Therefore, when the silane compound is present on the surface of the positive electrode current collector, the residual impurities can be suppressed more effectively, and the effect of suppressing the mixing of impurities into the active layer is enhanced.

Since the positive electrode current collector is generally made of a metal material, an oxide film is likely to be formed on the surface of the positive electrode current collector, and this oxide film serves as a resistance component. Therefore, in the positive electrode, if a carbon layer is interposed between the positive electrode current collector and the active layer, the resistance on the surface of the positive electrode current collector and the resistance between the positive electrode current collector and the active layer are suppressed from increasing. it can. Further, in electrolytic polymerization or chemical polymerization, by providing the carbon layer, it becomes easy to form an active layer containing a conductive polymer. In the above embodiment of the present invention, when the positive electrode has a carbon layer, the silane compound is selected from the group consisting of between the carbon layer and the positive electrode current collector, between the carbon layer and the active layer, and within the carbon layer. It is preferable that it exists in at least one place. When the silane compound is present at such a position, the underlying layer of the active layer can be made hydrophobic, so that the residual impurities in the underlying layer can be suppressed. In the carbon layer, the carbon layer itself is often non-uniform, and pinholes may be formed. Even in such a case, by allowing the silane compound to exist at the above position, impurities are added to the underlying layer. It can be suppressed from remaining. Therefore, it is possible to suppress the mixing of impurities into the active layer. Since the silane compound can be attached to the surface of fine irregularities, the silane compound can also be present on the inner wall of the pinhole when the pinhole is formed in the carbon layer.

In addition, in this specification, an expression such as a base layer of an active layer or a portion serving as a base may be used. When the positive electrode does not contain a carbon layer, examples of the base layer of the active layer include a positive electrode current collector. In this case, for example, the surface of the positive electrode current collector (including between the positive electrode current collector and the active layer) is a portion that serves as a base for the active layer. When the positive electrode contains a carbon layer, examples of the base layer of the active layer include a positive electrode current collector and a carbon layer. In this case, for example, the surface of the positive electrode current collector (including between the positive electrode current collector and the carbon layer), the surface of the carbon layer (the surface of the carbon layer on the positive electrode current collector side, the inner wall of the pinhole of the carbon layer, carbon). (Including between the layer and the active layer) and the inside of the carbon layer are the base parts of the active layer.

The electrochemical device according to the present embodiment can be manufactured by a manufacturing method including a step of obtaining a positive electrode and a step of laminating a positive electrode, a separator, and a negative electrode. Here, the step of obtaining the positive electrode includes a step of forming an active layer containing a conductive polymer on the positive electrode current collector and a step of applying a silane compound between the positive electrode current collector and the active layer. ing. By adding a silane compound, the underlying layer of the active layer is made hydrophobic. As a result, the residual impurities in the base layer and its vicinity can be suppressed, and the mixing of impurities in the active layer can be suppressed. Therefore, it is possible to obtain an electrochemical device in which a decrease in capacity is suppressed. The step of applying the silane compound is performed before forming the active layer. In the step of applying the silane compound, after the active layer is formed, the silane compound is applied so that the silane compound is located between the active layer and the positive electrode current collector.

In the step of applying the silane compound, the silane compound can be applied to the surface of the positive electrode current collector, for example. In this case, since the surface of the positive electrode current collector, in which hydrophilic impurities such as anionic components tend to remain, can be made hydrophobic, the residual impurities in the underlying layer can be suppressed more effectively. The silane compound can be applied, for example, by contacting the surface of the positive electrode current collector.

The step of obtaining the positive electrode may include a step of forming a carbon layer on the positive electrode current collector and a step of forming an active layer on the carbon layer. In this case, in the step of applying the silane compound, the silane compound is applied to at least one place selected from the group consisting of the carbon layer and the positive electrode current collector, the carbon layer and the active layer, and the inside of the carbon layer. It is preferably given. In this case, when the positive electrode has a carbon layer, the underlying layer of the active layer can be made hydrophobic, and the residual impurities in the underlying layer can be suppressed. Even when pinholes are formed in the carbon layer, the residual impurities in the underlying layer can be suppressed.

In the step of applying the silane compound, the silane compound can be applied by bringing the silane compound into contact with at least one of the surface of the positive electrode current collector and the surface of the carbon layer. The underlying layer can be made hydrophobic by a simple operation of bringing the silane compound into contact with each other, and the residual impurities in the underlying layer can be suppressed.

The step of applying the silane compound may be carried out at least in the step of forming the carbon layer. In this case, the carbon layer can be formed by applying a carbon paste containing a silane compound to the surface of the positive electrode current collector to form a coating film, and then drying the coating film. By making the carbon layer itself hydrophobic, the residual impurities can be suppressed. Further, when the carbon layer is formed, it can be made hydrophobic, so that it is possible to suppress an increase in the number of steps.

Hereinafter, the configurations of the electrochemical device and the manufacturing method thereof according to the present embodiment will be described more specifically with reference to the drawings as appropriate.

[Electrochemical device]
The electrochemical device according to the present embodiment includes a positive electrode, a negative electrode, and a separator interposed between them. As shown in FIG. 1, the positive electrode includes, for example, a positive electrode current collector 111 and an active layer 113 formed on the positive electrode current collector 111 via a carbon layer 112. That is, in the illustrated example, the positive electrode (positive electrode 11) includes a positive electrode current collector 111, a carbon layer 112 formed on the positive electrode current collector 111, and an active layer 113 formed on the carbon layer 112. The carbon layer 112 contains a conductive carbon material, and the active layer 113 contains a conductive polymer. In this embodiment, the positive electrode 11 further contains a silane compound 114. In the illustrated example, the silane compound 114 exists between the positive electrode current collector 111 and the carbon layer 112 (more specifically, the surface of the positive electrode current collector 111). In FIG. 1, it is shown that the silane compound 114 exists in a layered manner, but not limited to such a case, if the silane compound 114 exists between the positive electrode current collector 111 and the active layer 113, It may exist in any form and may exist in any position. By allowing the silane compound 114 to exist between the positive electrode current collector 111 and the active layer 113, the positive electrode current collector 111 and the carbon layer 112 in which impurities such as anionic components serve as the base layer of the active layer 113, and these. It is suppressed that it remains in the vicinity of. Therefore, it is possible to prevent impurities from being mixed into the active layer 113.

FIG. 2 is a schematic cross-sectional view of the electrochemical device 100 according to the present embodiment, and FIG. 3 is a schematic view of a part of the element 10 included in the electrochemical device 100.

The electrochemical device 100 includes an element 10, a container 101 that houses the element 10, a sealing body 102 that closes the opening of the container 101, leads 104A and 104B that are led out from the sealing body 102, and each lead wire and the element 10. Lead tabs 105A and 105B for connecting the electrodes of the above are provided. The vicinity of the opening end of the container 101 is drawn inward, and the opening end is curled so as to be crimped to the sealing body 102.
(Positive current collector)
For the positive electrode current collector 111, for example, a sheet-shaped metal material is used. As the sheet-shaped metal material, for example, a metal foil, a metal porous body, a punching metal, an expanded metal, an etching metal, or the like is used.

As the material of the positive electrode current collector 111, for example, aluminum, aluminum alloy, nickel, titanium and the like can be used, and aluminum and aluminum alloy are preferably used.

The thickness of the positive electrode current collector 111 is, for example, 10 μm to 100 μm.
(Silane compound)
The silane compound may be present in the base portion of the active layer 113. That is, the silane compound may be present at any position as long as it is between the positive electrode current collector 111 and the active layer 113. The silane compound can be arranged on the surface of the positive electrode current collector 111, for example. In this case, in the positive electrode having no carbon layer, the silane compound is arranged between the positive electrode current collector and the active layer formed on the positive electrode current collector, and when it has a carbon layer, it is shown in the illustrated example. As described above, it is arranged between the positive electrode current collector 111 and the active layer 113. Further, not limited to these cases, when the positive electrode has a carbon layer, the silane compound 114 may be arranged between the carbon layer 112 and the active layer 113, or may be contained in the carbon layer 112, for example. Good. Moreover, you may combine these as appropriate. For example, the silane compound may be arranged both between the positive electrode current collector and the carbon layer and between the carbon layer and the active layer, and may be arranged both between the positive electrode current collector and the carbon layer and in the carbon layer. A silane compound may be arranged. In this way, by allowing the silane compound to be present in the base portion when forming the active layer 113, impurities are suppressed from remaining in the base portion, so that the remaining impurities are mixed in the active layer 113. Is suppressed.

The arrangement state of the silane compound is not particularly limited. The silane compound may be present in a layered state (or a film form) in the positive electrode, for example. As shown in the illustrated example, the layered silane compound is not limited to between the positive electrode current collector and the carbon layer, but may be between the carbon layer and the active layer, or both of them. The silane compound does not necessarily have to be distributed in layers, and may be present in a dispersed or interspersed state. For example, the silane compounds may be interspersed on the surface of the positive electrode current collector and / or the surface of the carbon layer, and may be interspersed or dispersed in the carbon layer. Alternatively, it may be a combination of these.

The silane compound is not particularly limited as long as it can hydrophobize the underlying layer of the active layer 113 and is hard to fall off. As the silane compound, a compound having a hydrophobic group can be used. Further, the silane compound preferably has a functional group that causes a reaction or interaction with the positive electrode current collector 111 or the carbon layer 112 so as not to cause shedding. As such a functional group, a hydrolyzable group or the like is preferable.

Examples of the hydrophobic group contained in the silane compound include a hydrophobic hydrocarbon group. Of these, an aliphatic hydrocarbon group is preferable as the hydrophobic group. The aliphatic hydrocarbon group may be saturated or unsaturated. Of these, a hydrophobic alkyl group is preferable. Examples of the hydrophobic alkyl group include alkyl groups having 6 or more carbon atoms, such as hexyl, 2-ethylhexyl, octyl, decyl, dodecyl, tetradecyl, hexadecyl, octadecyl, and behenyl groups. These silane compounds having an alkyl group are advantageous because they are easy to secure hydrophobicity, are relatively inexpensive, and are easily available. The alkyl has, for example, 6 to 26 carbon atoms and may be 6 to 20 or 6 to 16. The silane compound may have one hydrophobic group or two or more hydrophobic groups. When the silane compound has two or more hydrophobic groups, the types of the hydrophobic groups may be the same, or at least a part thereof may be different. The number of hydrophobic groups of the silane compound is preferably 1 to 2, and even one can sufficiently exert the effect.

The hydrolyzable group contained in the silane compound causes a hydrolysis reaction and a condensation reaction on the surface of the positive electrode current collector 111 and the inorganic component (for example, a conductive carbon material) in the carbon layer 112, so that the positive electrode has a positive electrode. The silane compound can be retained in the current collector 111 or the carbon layer 112. The hydrolyzable group is sometimes called a hydrolyzable condensable group. As the hydrolyzable group, an alkoxy group is preferable. As the alkoxy group, methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, s-butoxy, t-butoxy group and the like are preferable. The silane compound may have one hydrolyzable group or two or more hydrolyzable groups. When the silane compound has two or more hydrolyzable groups, the types of hydrolyzable groups may be the same, or at least a part thereof may be different. The number of hydrolyzable groups of the silane compound may be one or more, preferably a plurality.

As the silane compound, one type may be used alone, or two or more types may be used in combination. The silane compound has a hydrophobic group and a hydrolyzable group depending on the number of Si bonds, and may further have a functional group other than these groups. The total number of hydrophobic groups, hydrolyzable groups, and other functional groups is the number of Si bonds, or 4. When such a silane compound is used, the reaction or interaction between the hydrolyzable group and the surface of the positive electrode current collector 111 or the inorganic component of the carbon layer 112 is utilized to form a silane compound on the base portion of the active layer 113. Can be easily introduced, so that it can be easily hydrolyzed.

In this way, when the silane compound is introduced into the base portion of the active layer by a reaction or interaction, the silane compound reacts (or mutually) with the positive electrode current collector or the inorganic component of the carbon layer in the positive electrode. It contains a component (which may be referred to as a component derived from a silane compound) that has acted). As described above, even when the component derived from the silane compound is present between the positive electrode current collector and the active layer, it is assumed that the silane compound is contained between the positive electrode current collector and the active layer. ..
(Carbon layer)
The carbon layer 112 does not have to be formed, but if the carbon layer 112 is provided, the resistance between the positive electrode current collector 111 and the active layer 113 can be suppressed to a low level. Further, when the active layer 113 is formed by electrolytic polymerization or chemical polymerization, the formation of the active layer 113 becomes easy.

The carbon layer 112 contains a conductive carbon material. The carbon layer 112 may contain a polymer material in addition to the conductive carbon material, and may contain a silane compound 114 in addition to these components.

The carbon layer 112 may be formed on the surface of the positive electrode current collector 111, or may be formed on the positive electrode current collector 111 to which the silane compound 114 is added. For example, when the silane compound 114 is formed in layers as shown in the illustrated example, the carbon layer 112 is formed on the layer of the silane compound 114.

As the conductive carbon material, graphite, hard carbon, soft carbon, carbon black or the like can be used. Of these, carbon black is preferable because it is easy to form a thin carbon layer 112 having excellent conductivity. The average particle size D1 of the conductive carbon material is not particularly limited, but is, for example, 3 nm to 500 nm, preferably 10 nm to 100 nm. The average particle size is the median diameter (D50) in the volume particle size distribution obtained by a laser diffraction type particle size distribution measuring device (hereinafter, the same applies). The average particle size D1 of carbon black may be calculated by observing with a scanning electron microscope.

The material of the polymer material is not particularly limited, but it is electrochemically stable and has excellent acid resistance. Therefore, fluororesin, acrylic resin, polyvinyl chloride, styrene-butadiene rubber (SBR), and water glass (sodium silicate) are used. Polymer) and the like are preferably used.

Examples of the silane compound 114 contained in the carbon layer 112 include those described above. A component derived from the above-mentioned compound may be contained in the carbon layer 112 as the silane compound 114.

When the silane compound is contained in the carbon layer, the amount of the silane compound in the carbon layer is, for example, 0.01% by mass or more, preferably 0.5% by mass or more. When the amount of the silane compound is in such a range, it is easy to secure the hydrophobicity of the carbon layer. The amount of the silane compound in the carbon layer is, for example, 5% by mass or less, and preferably 2% by mass or less. When the amount of the silane compound is in such a range, the high conductivity of the carbon layer can be maintained, so that the active layer can be easily formed by electrolytic polymerization or the like, and the distance between the positive electrode current collector and the active layer is high. It is easy to secure adhesion. These lower limit values and upper limit values can be arbitrarily combined.

The amount of the silane compound in the carbon layer can be determined, for example, by measuring the amount of Si in the cross section of the carbon layer with an X-ray photoelectron spectroscopy analyzer (XPS).

The thickness of the carbon layer 112 is, for example, 1 μm to 20 μm.

The presence or absence of the silane compound in the positive electrode can be confirmed, for example, by analyzing Si present on the surface of the positive electrode with XPS.

For the quantification and analysis of Si, a positive electrode taken out from an electrochemical device is washed with water and dried.
(Active layer)
The active layer 113 contains a conductive polymer.

As the conductive polymer, a π-conjugated polymer is preferable. As the π-conjugated polymer, for example, polypyrrole, polythiophene, polyfuran, polyaniline, polythiophene vinylene, polypyridine, or derivatives thereof can be used. These may be used alone or in combination of two or more.

The weight average molecular weight of the conductive polymer is not particularly limited, but is, for example, 1000 to 100,000. The weight average molecular weight is a polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography.

The derivatives of polypyrrole, polythiophene, polyfuran, polyaniline, polythiophene vinylene, and polypyridine mean polymers having polypyrrole, polythiophene, polyfuran, polyaniline, polythiophene vinylene, and polypyridine as basic skeletons, respectively. For example, polythiophene derivatives include poly (3,4-ethylenedioxythiophene) (PEDOT) and the like.

Dopants may be introduced into the conductive polymer. The dopant, sulfate ion, nitrate ion, phosphate ion, borate ion, benzenesulfonate ion, naphthalenesulfonate ion, toluenesulfonate ion, methanesulfonate ion (CF ₃ SO ₃ ^-), perchlorate ion (ClO ₄ ^-), tetrafluoroborate ion (BF ₄ ^-), hexafluorophosphate ion (PF ₆ ^-), fluorosulfonic acid ion (FSO ₃ ^-), bis (fluorosulfonyl) imide ion (N (FSO _{2) 2} ^-), bis ( Examples thereof include trifluoromethanesulfonyl) imide ion (N (CF ₃ SO ₂ ) ₂ ⁻ ). These may be used alone or in combination of two or more.

The dopant may be a polymer ion. Examples of high molecular weight ions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylsulfonic acid, poly (2-acrylamide-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, and polyacrylic. Examples include ions such as acid. These may be homopolymers or copolymers of two or more kinds of monomers. These may be used alone or in combination of two or more.

The thickness of the active layer 113 is, for example, 10 μm to 300 μm per one side of the positive electrode current collector 111.
(Negative electrode)
The negative electrode 12 has, for example, a negative electrode current collector and a negative electrode material layer.

For the negative electrode current collector, for example, a sheet-shaped metal material is used. As the sheet-shaped metal material, for example, a metal foil, a metal porous body, a punching metal, an expanded metal, an etching metal, or the like is used. As the material of the negative electrode current collector, for example, copper, copper alloy, nickel, stainless steel or the like can be used.

The thickness of the negative electrode current collector is, for example, 5 μm to 100 μm.

The negative electrode material layer preferably includes, as the negative electrode active material, a material that electrochemically occludes and releases lithium ions. Examples of such materials include carbon materials, metal compounds, alloys, ceramic materials and the like. As the carbon material, graphite, non-graphitized carbon (hard carbon), and easily graphitized carbon (soft carbon) are preferable, and graphite and hard carbon are particularly preferable. Examples of the metal compound include silicon oxide and tin oxide. Examples of the alloy include a silicon alloy and a tin alloy. Examples of the ceramic material include lithium titanate and lithium manganate. These may be used alone or in combination of two or more. Among them, the carbon material is preferable in that the potential of the negative electrode 12 can be lowered.

It is desirable that the negative electrode material layer contains a conductive agent, a binder, or the like in addition to the negative electrode active material. Examples of the conductive agent include carbon black and carbon fiber. Examples of the binder include fluororesin, acrylic resin, rubber material, cellulose derivative and the like. Examples of the fluororesin include polyvinylidene fluoride, polytetrafluoroethylene, and tetrafluoroethylene-hexafluoropropylene copolymer. Examples of the acrylic resin include polyacrylic acid and acrylic acid-methacrylic acid copolymers. Examples of the rubber material include styrene-butadiene rubber, and examples of the cellulose derivative include carboxymethyl cellulose.

For the negative electrode material layer, for example, a negative electrode active material, a conductive agent, a binder, and the like are mixed together with a dispersion medium to prepare a negative electrode mixture paste, and the negative electrode mixture paste is applied to the negative electrode current collector. It is formed by drying.

It is desirable that the negative electrode 12 is pre-doped with lithium ions. As a result, the potential of the negative electrode 12 decreases, so that the potential difference (that is, voltage) between the positive electrode 11 and the negative electrode 12 increases, and the energy density of the electrochemical device 100 improves.

For pre-doping the negative electrode 12 of lithium ions, for example, a metallic lithium film serving as a lithium ion supply source is formed on the surface of the negative electrode material layer, and the negative electrode 12 having the metallic lithium film is subjected to an electrolytic solution having lithium ion conductivity (for example,). , Non-aqueous electrolyte solution) to proceed. At this time, lithium ions are eluted from the metallic lithium film into the non-aqueous electrolytic solution, and the eluted lithium ions are occluded in the negative electrode active material. For example, when graphite or hard carbon is used as the negative electrode active material, lithium ions are inserted between the graphite layers and the pores of the hard carbon. The amount of lithium ions to be pre-doped can be controlled by the mass of the metallic lithium film.

The step of pre-doping the negative electrode 12 with lithium ions may be performed before assembling the element 10, or the element 10 may be housed in the container 101 of the electrochemical device 100 together with the non-aqueous electrolytic solution, and then the pre-doping may proceed.
(Separator)
As the separator 13, a microporous film, a woven fabric, a non-woven fabric, or the like is preferable. Examples of the material constituting the separator include organic materials (polymer materials such as polyolefin and cellulose) and inorganic materials (glass and the like). Examples of fibers constituting woven fabrics and non-woven fabrics include polymer fibers such as polyolefin, cellulose fibers, and glass fibers. These materials may be used in combination.

The thickness of the separator 13 is, for example, 10 μm to 100 μm.
(Non-aqueous electrolyte)
The electrochemical device 100 preferably contains a non-aqueous electrolyte solution.

The non-aqueous electrolyte solution preferably has lithium ion conductivity. Such a non-aqueous electrolyte solution contains, for example, a lithium salt and a non-aqueous solvent for dissolving the lithium salt. At this time, the lithium salt anion can reversibly repeat doping and dedoping of the positive electrode 11. On the other hand, lithium ions derived from the lithium salt are reversibly stored and released into the negative electrode 12.

Examples of the lithium salt include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiFSO ₃ , LiCF ₃ CO ₂ , LiAsF _{6 , LiB 10} Cl ₁₀ , LiCl, LiBr, LiI. , LiBCl ₄ , LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) _{2, and the} like. These may be used individually by 1 type, or may be used in combination of 2 or more type. Among them, it is desirable to use at least one selected from the group consisting of a lithium salt having an oxoacid anion containing a halogen atom suitable as an anion and a lithium salt having an imide anion.

The concentration of the lithium salt in the non-aqueous electrolytic solution in the charged state (charging rate (SOC) 90 to 100%) is, for example, 0.2 mol / L to 5 mol / L.

Non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, and fats such as methyl formate, methyl acetate, methyl propionate and ethyl propionate. Group carboxylic acid esters, lactones such as γ-butyrolactone and γ-valerolactone, chain ethers such as 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE) and ethoxymethoxyethane (EME). , Cyclic ethers such as tetrahydrofuran, 2-methyltetraoxide, dimethylsulfoxide, 1,3-dioxolane, formamide, acetamido, dimethylformamide, dioxolane, acetonitrile, propionitrile, nitromethane, ethylmonoglyme, trimethoxymethane, sulfolane, methylsulfolane. , 1,3-Propane salton and the like can be used. These may be used alone or in combination of two or more.

The non-aqueous electrolyte solution may contain additives, if necessary. Examples of the additive include unsaturated carbonates. As the unsaturated carbonate, vinylene carbonate, vinylethylene carbonate, divinylethylene carbonate and the like are preferable.

[Manufacturing method of electrochemical device]
The above-mentioned electrochemical device can be manufactured by a manufacturing method including a step of obtaining a positive electrode, a step of laminating a positive electrode, a separator, and a negative electrode. Here, the step of obtaining the positive electrode includes a step of forming an active layer containing a conductive polymer on the positive electrode current collector and a step of applying a silane compound between the positive electrode current collector and the active layer. .. When the positive electrode contains a carbon layer, the step of obtaining the positive electrode includes a step of forming a carbon layer on the positive electrode current collector and a step of forming an active layer on the carbon layer.

Hereinafter, an example of the method for manufacturing the electrochemical device 100 of the present invention will be described with reference to FIGS. 2 and 3. However, the method for manufacturing the electrochemical device 100 of the present invention is not limited to this.

The electrochemical device 100 has, for example, a step of obtaining a positive electrode 11, a step of stacking the obtained positive electrode 11, a separator 13 and a negative electrode 12 in this order to obtain an element 10, and a non-aqueous electrolytic solution of the obtained element 10. It is manufactured by a method including a step of accommodating in a container 101 together with.

A lead member (lead tab 105A including the lead wire 104A) is connected to the positive electrode 11 obtained as described above, and another lead member (lead tab 105B including the lead wire 104B) is connected to the negative electrode 12. Subsequently, a separator 13 is interposed between the positive electrode 11 and the negative electrode 12 to which these lead members are connected and wound to obtain a winding element 10 in which the lead member is exposed from one end surface as shown in FIG. The outermost circumference of the element 10 is fixed with the winding stop tape 14.

Next, as shown in FIG. 2, the element 10 is housed in a bottomed cylindrical container 101 having an opening together with a non-aqueous electrolytic solution (not shown). Lead wires 104A and 104B are derived from the sealing body 102. The sealing body 102 is arranged in the opening of the container 101, and the container 101 is sealed. Specifically, the vicinity of the opening end of the container 101 is drawn inward, and the opening end is curled so as to be crimped to the sealing body 102. The sealing body 102 is made of, for example, an elastic material containing a rubber component.
(Step to obtain positive electrode)
The step of obtaining the positive electrode 11 includes a step of forming the active layer 113 on the positive electrode current collector 111 and a step of applying the silane compound 114 between the positive electrode current collector and the active layer. When the positive electrode 11 includes the carbon layer 112, the step of obtaining the positive electrode 11 also includes a step of forming the carbon layer 112. The positive electrode current collector 111 is prepared prior to the application of the silane compound 114 or the formation of the carbon layer 112. As described above, a sheet-shaped metal material is used for the positive electrode current collector 111, but if necessary, surface treatment such as hydrophilic treatment may be performed.

(Step to add silane compound)
The silane compound 114 may be applied to a portion to be a base of the active layer 113 at an appropriate stage before forming the active layer 113. The silane compound 114 may be applied as long as the silane compound 114 can be brought into contact with the underlying portion of the active layer 113. For example, the silane compound 114 can be imparted by applying the silane compound 114 to the base portion of the active layer 113, or by immersing the silane compound 114 at least in the base portion of the active layer 113. it can.

For example, by applying the silane compound 114 to the surface of the positive electrode current collector 111, a positive electrode in which the silane compound 114 exists can be formed on the surface of the positive electrode current collector 111. When the positive electrode 11 includes the carbon layer 112, the silane compound 114 is composed of a group consisting of the carbon layer 112 and the positive electrode current collector 111, the carbon layer 112 and the active layer 113, and the inside of the carbon layer 112. It may be given to at least one selected place. In this case, the silane compound 114 may be applied by contacting with at least one of the surface of the positive electrode current collector 111 and the surface of the carbon layer 112. When the silane compound 114 is added to the carbon layer 112, the carbon layer 112 containing the silane compound 114 is provided by using a carbon paste containing the silane compound 114 in the step of forming the carbon layer 112, as described later. It may be formed.

When the above-mentioned compound having a hydrophobic group and a hydrolyzable group is used as the silane compound 114, the hydrolyzable group is reacted with the surface of the positive electrode current collector 111 and the inorganic component of the carbon layer 112. Therefore, it is preferable to introduce the hydrophobic group into the base portion of these active layers 113.

The silane compound 114 may be applied to the base portion of the active layer 113 by using the silane compound 114 itself or by using a solution obtained by diluting the silane compound 114 with a solvent. The concentration of the silane compound 114 contained in the solution is, for example, 0.1 to 5% by mass, preferably 0.5 to 2% by mass. When a solution having such a concentration is used, an appropriate amount of the silane compound can be attached to the base portion of the active layer 113, so that the mixing of impurities into the active layer can be further suppressed. The solvent is not particularly limited, and examples thereof include alcohols, esters, and / or ethers.

(Step to form carbon layer)
The carbon layer 112 is formed by depositing a conductive carbon material on the surface of the base layer of the carbon layer 112 (for example, the surface of the positive electrode current collector 111 or the positive electrode current collector 111 to which the silane compound 114 is applied). It is formed by doing. Alternatively, the carbon layer 112 is formed by applying a carbon paste containing a conductive carbon material on a layer underlying the carbon layer 112 (for example, on the surface of the positive electrode current collector 111 or on the positive electrode current collector 111 to which the silane compound 114 is applied. ) To form a coating film, and then the coating film is dried to form a coating film. The carbon paste includes, for example, a conductive carbon material, a polymer material, and water or an organic solvent. When the silane compound 114 is contained in the carbon layer 112, a carbon paste containing the silane compound 114 in addition to the above components may be used.

When the carbon layer 112 is formed by using the carbon paste containing the silane compound 114, the silane compound 114 can be added in the step of forming the carbon layer 112. Therefore, it is not necessary to provide a step of applying the silane compound 114 separately from the step of forming the carbon layer 112. Therefore, it is advantageous in suppressing the increase in the number of steps.

The amount of the silane compound in the solid content of the carbon paste is, for example, 0.1% by mass or more, preferably 0.5% by mass or more. When the amount of the silane compound is in such a range, it is easy to secure the hydrophobicity of the carbon layer. The amount of the silane compound in the solid content of the carbon paste is, for example, 5% by mass or less, and preferably 2% by mass or less. When the amount of the silane compound is in such a range, the effect of suppressing the mixing of impurities into the active layer can be further enhanced while maintaining the high conductivity of the carbon layer 112. These lower limit values and upper limit values can be arbitrarily combined.

(Step to form active layer)
The active layer 113 is formed on the positive electrode current collector 111. The active layer 113 may be formed directly on the positive electrode current collector 111, or may be formed on the carbon layer 112 formed on the positive electrode current collector 111. Further, the active layer 113 may be formed on the positive electrode current collector 111 to which the silane compound 114 is applied or on the carbon layer 112 to which the silane compound 114 is applied.

The active layer 113 is made of, for example, a positive electrode current collector 111 to which the silane compound 114 is added (or a laminate of the positive electrode current collector 111 and the carbon layer 112 to which the silane compound 114 is added) and is made of a conductive polymer. It is formed by immersing in a reaction solution containing the raw material monomer of No. 1 and electrolytically polymerizing or chemically polymerizing the raw material monomer in the presence of the positive electrode current collector 111. In electrolytic polymerization, polymerization is carried out using the positive electrode current collector 111 as an anode. In this way, the active layer 113 containing the conductive polymer is formed so as to cover the surface of the underlying layer (for example, positive electrode current collector 111, carbon layer 112, etc.) of the active layer 113. At this time, the active layer 113 may be formed on the base layer to which the silane compound 114 is applied. The active layer 113 may be formed by a method other than electrolytic polymerization or chemical polymerization. For example, the active layer 113 is provided with a solution in which a conductive polymer is dissolved or a dispersion in which a conductive polymer is dispersed, and a positive electrode current collector 111 and / or a silane compound 114 to which a silane compound 114 is added. It may be formed by contacting the carbon layer 112.

From the viewpoint that the dense active layer 113 is easily formed, it is preferable to form the active layer 113 by electrolytic polymerization or chemical polymerization. The reaction solution of electrolytic polymerization or chemical polymerization contains impurities such as anionic components (sulfate ions, etc.), and impurities are likely to remain on the surface of the positive electrode current collector 111, the carbon layer 112, and the vicinity thereof. .. Therefore, by allowing the silane compound 114 to be present in these portions, it is possible to suppress the remaining impurities and effectively suppress the mixing of impurities into the active layer 113.

The raw material monomer used in electrolytic polymerization or chemical polymerization may be any polymerizable compound capable of producing a conductive polymer by polymerization. The raw material monomer may contain an oligomer. As the raw material monomer, for example, aniline, pyrrole, thiophene, furan, thiophene vinylene, pyridine or derivatives thereof are used. These may be used alone or in combination of two or more. The raw material monomer is preferably aniline because the active layer 113 is likely to be formed on the surfaces of the positive electrode current collector 111 and the carbon layer 112.

It is desirable that electrolytic polymerization or chemical polymerization be carried out using a reaction solution containing an anion (dopant). It is desirable that the dispersion liquid or solution of the conductive polymer also contains a dopant. The π-electron conjugated polymer exhibits excellent conductivity by doping with a dopant. For example, in chemical polymerization, the base layer to which the silane compound 114 is applied may be immersed in a reaction solution containing a dopant, an oxidizing agent, and a raw material monomer, and then the base layer may be withdrawn from the reaction solution and dried. Further, in electrolytic polymerization, the base layer to which the silane compound 114 is applied and the counter electrode are immersed in a reaction solution containing a dopant and a raw material monomer, and the positive electrode current collector 111 is used as an anode and the counter electrode is used as a cathode. A current should be passed between them.

Water may be used as the solvent of the reaction solution, but a non-aqueous solvent may be used in consideration of the solubility of the monomer. As the non-aqueous solvent, it is desirable to use alcohols such as ethyl alcohol, methyl alcohol, isopropyl alcohol, ethylene glycol and propylene glycol. Examples of the dispersion medium or solvent of the conductive polymer include water and the above-mentioned non-aqueous solvent.

The active layer 113 is usually formed in an acidic atmosphere due to the influence of the oxidizing agent and the dopant used.

The thickness of the active layer 113 can be controlled, for example, by adjusting the polymerization time. In electrolytic polymerization, the thickness of the active layer 113 can also be controlled by adjusting the current density of electrolysis. When a solution or dispersion containing a conductive polymer is used, the concentration of the conductive polymer in these liquids is adjusted, or the number of times the liquid is brought into contact with the underlying layer is adjusted to adjust the active layer 113. The thickness of the can be controlled.

In the above embodiment, the electrochemical device including the cylindrical winding element has been described, but the scope of application of the present invention is not limited to the above, and the angular electrochemical device including the winding element and the laminated element is described. It can also be applied to.

[Example]
Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.
(Example 1)
(1) Preparation of Positive Electrode An aluminum foil having a thickness of 30 μm was prepared as a positive electrode current collector. On the other hand, an aniline aqueous solution containing aniline and sulfuric acid was prepared.

A mixed powder obtained by mixing 11 parts by mass of carbon black and 7 parts by mass of polypropylene resin particles was kneaded with water to prepare a carbon paste. The obtained carbon paste was applied to the entire front and back surfaces of the positive electrode current collector and then dried by heating to form a carbon layer. The thickness of the carbon layer was 2 μm per side.

A water / ethanol solution (mass ratio of water / ethanol = 1/1) containing hexyltrimethoxysilane as a silane compound at a concentration of 1% by mass is applied to the surface of the carbon layer and heat-treated at 110 ° C. for 30 minutes. A silane compound was introduced on the surface of the carbon layer.

After introduction of the silane compound, and a carbon layer formed positive electrode current collector and the counter electrode, was immersed in aniline solution, 10 mA / cm 20 min at ^second current density, subjected to electrolytic polymerization, sulfate ion (SO ₄ ^{2 A film of a conductive polymer (polyaniline) doped with −} ) was attached onto the carbon layers on the front and back of the positive electrode current collector.

The sulfate ion-doped conductive polymer was reduced, and the doped sulfate ion was de-doped. In this way, an active layer containing a conductive polymer dedoped with sulfate ions was formed. The active layer was then thoroughly washed and then dried. The thickness of the active layer was 30 μm per side.
(2) Preparation of Negative Electrode A copper foil having a thickness of 10 μm was prepared as a negative electrode current collector. On the other hand, a negative mixture paste obtained by kneading 97 parts by mass of hard carbon, 1 part by mass of carboxycellulose, 2 parts by mass of styrene-butadiene rubber, and water at a mass ratio of 40:60. Was prepared. The negative electrode mixture paste was applied to both sides of the negative electrode current collector and dried to obtain a negative electrode having a negative electrode material layer having a thickness of 52 μm on both sides. Next, a metallic lithium foil in an amount calculated so that the negative electrode potential in the electrolytic solution after the completion of pre-doping was 0.2 V or less with respect to metallic lithium was attached to the negative electrode material layer.
(3) Preparation of winding element After connecting the lead tabs to the positive electrode and the negative electrode respectively, as shown in FIG. 3, the separator (thickness 35 μm) made of cellulose non-woven fabric and the positive electrode and the negative electrode are alternately superposed. The laminated body was wound to form a winding element.
(4) Preparation of non-aqueous electrolytic solution A solvent was prepared by adding 0.2% by mass of vinylene carbonate to a mixture of propylene carbonate and dimethyl carbonate in a volume ratio of 1: 1. _{LiPF 6} as a lithium salt was dissolved in the obtained solvent at a predetermined concentration to prepare a non-aqueous electrolytic solution having _{hexafluorophosphate ion (PF 6} ^{−) as an anion.}
(5) Preparation of Electrochemical Device An electrochemical device as shown in FIG. 2 was assembled by accommodating a winding element and a non-aqueous electrolytic solution in a bottomed container having an opening. Then, while applying a charging voltage of 3.6 V between the terminals of the positive electrode and the negative electrode, aging was performed at 25 ° C. for 24 hours to allow pre-doping of lithium ions into the negative electrode.
(Evaluation)
The initial capacity of the obtained electrochemical device was determined by the following procedure.

The electrochemical device was charged with a voltage of 3.6 V and then discharged to 2.5 V with a current of 1 mA. The value obtained by dividing the amount of discharge charge (A · s) that flowed while the voltage dropped from 3.3 V to 3.0 V on the way by the voltage change ΔV (= 0.3 V) was obtained as the initial capacitance (F). It was.
(Example 2)
The introduction of the silane compound was carried out not on the surface of the carbon layer but on the surface of the positive electrode current collector. Except for this, an electrochemical device was prepared and evaluated in the same manner as in Example 1.
(Example 3)
A carbon paste was prepared by kneading a mixed powder obtained by mixing 11 parts by mass of carbon black and 7 parts by mass of polypropylene resin particles, 2 parts by mass of hexyltrimethoxysilane, and water to form a carbon layer. No silane compound was introduced on the surface of the carbon layer. Except for these, an electrochemical device was prepared and evaluated in the same manner as in Example 1.
(Comparative Example 1)
An electrochemical device was prepared and evaluated in the same manner as in Example 1 except that the silane compound was not introduced on the surface of the carbon layer.

The evaluation results are shown in Table 1. Examples 1 to 3 are A1 to A3, and Comparative Example 1 is B1.

As shown in Table 1, in the examples, a higher initial capacity can be secured as compared with the comparative examples. It is considered that this is because the introduction of the silane compound into the base portion of the active layer suppresses the residual impurities such as sulfate ions in the base portion. It is considered that this suppressed the mixing of impurities into the active layer and suppressed the adsorption of anions during charging.

In the electrochemical device according to the present invention, the decrease in capacity is suppressed. Therefore, it is suitable as a backup power source for various electrochemical devices that require high capacity.

10: Element 11: Positive electrode 111: Positive electrode current collector 112: Carbon layer 113: Active layer 114: Silane compound 12: Negative electrode 13: Separator 14: Winding tape 100: Electrochemical device 101: Container 102: Sealing body 104A, 104B : Lead wire 105A, 105B: Lead tab

Claims (9)

A positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode are provided.
The positive electrode includes a positive electrode current collector and an active layer on the positive electrode current collector.
The active layer contains a conductive polymer and contains
An electrochemical device in which a silane compound is present between the positive electrode current collector and the active layer. The electrochemical device according to claim 1, wherein the silane compound has an alkyl group having 6 or more carbon atoms. The electrochemical device according to claim 1 or 2, wherein the silane compound is present on the surface of the positive electrode current collector. The positive electrode further includes a carbon layer interposed between the positive electrode current collector and the active layer.
The silane compound is present at least one selected from the group consisting of the carbon layer and the positive electrode current collector, between the carbon layer and the active layer, and within the carbon layer. The electrochemical device according to claim 1 or 2. A method for manufacturing an electrochemical device including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.
The step of obtaining the positive electrode and
A step of laminating the positive electrode, the separator, and the negative electrode is provided.
The step of obtaining the positive electrode includes a step of forming an active layer containing a conductive polymer on the positive electrode current collector and a step of applying a silane compound between the positive electrode current collector and the active layer. How to make an electrochemical device. The method for producing an electrochemical device according to claim 5, wherein the silane compound is applied to the surface of the positive electrode current collector in the step of applying the silane compound. The step of obtaining the positive electrode includes a step of forming a carbon layer on the positive electrode current collector and a step of forming the active layer on the carbon layer.
In the step of applying the silane compound, the silane compound is selected from the group consisting of the carbon layer and the positive electrode current collector, the carbon layer and the active layer, and the inside of the carbon layer. The method for manufacturing an electrochemical device according to claim 5, which is applied to at least one place. The method for producing an electrochemical device according to claim 7, wherein in the step of applying the silane compound, the silane compound is brought into contact with at least one of the surface of the positive electrode current collector and the surface of the carbon layer. The step of applying the silane compound is carried out at least in the step of forming the carbon layer.
The carbon layer according to claim 7 or 8, wherein the carbon layer is formed by applying a carbon paste containing the silane compound to the surface of the positive electrode current collector to form a coating film, and then drying the coating film. How to make electrochemical devices.

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