JP7382549B2 - electrochemical device - Google Patents

Description

The present disclosure relates to an electrochemical device that includes a positive electrode that includes a conductive polymer.

In recent years, electrochemical devices with performance intermediate between lithium ion secondary batteries and electric double layer capacitors have attracted attention, and the use of conductive polymers as positive electrode materials is being considered (for example, patent literature 1). Electrochemical devices containing conductive polymers as positive electrode materials charge and discharge by adsorbing (doping) and dedoping (dedoping) anions, so their reaction resistance is low, and compared to typical lithium-ion secondary batteries, Has high output. In Patent Document 1, a carbonaceous material capable of intercalating and deintercalating ions is used as the negative electrode material.

Japanese Patent Application Publication No. 2014-35836

In the electrochemical device as described above, during charging, anions contained in the electrolyte are adsorbed to the positive electrode, and cations are occluded to the negative electrode. Due to such adsorption and occlusion of ions, both the positive electrode and the negative electrode expand during charging. In an electrochemical device including a wound element, when silicon oxide is used as the negative electrode material, peeling of the conductive polymer at the positive electrode becomes noticeable and cycle characteristics deteriorate.

One aspect of the present disclosure includes a wound element in which a positive electrode including a positive electrode material, a negative electrode including a negative electrode material, and a separator interposed between the positive electrode and the negative electrode are wound, and an electrolytic solution; The electrolytic solution includes cations and anions, the positive electrode material includes a conductive polymer that dopes and dedopes the anions by charging and discharging, and the negative electrode material includes a negative electrode that occludes and releases the cations by charging and discharging. The negative electrode active material contains SiOx (0<x<2), and at least one of the innermost electrode and the outermost electrode of the wound element is the negative electrode. Concerning chemical devices.

According to the above aspect of the present disclosure, deterioration in cycle characteristics can be suppressed in an electrochemical device including a wound element having a positive electrode containing a conductive polymer and a negative electrode containing silicon oxide.

FIG. 1 is a vertical cross-sectional view schematically showing an electrochemical device according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram for explaining the configuration of the winding element in FIG. 1. FIG. 3 is a cross-sectional view schematically showing the winding element in FIG. 1. FIG. FIG. 4 is a cross-sectional view schematically showing the configuration of the positive electrode, separator, and negative electrode of the wound element of FIG. 3 before winding.

An electrochemical device according to one aspect of the present disclosure includes a wound element including a positive electrode including a positive electrode material, a negative electrode including a negative electrode material, and a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Be prepared. The electrolyte contains cations and anions. The positive electrode material includes a conductive polymer that is doped and dedoped with anions by charging and discharging. The negative electrode material includes a negative electrode active material that occludes and releases cations by charging and discharging. This negative electrode active material contains SiOx (0<x<2). At least one of the innermost electrode and the outermost electrode of the wound element is a negative electrode. Hereinafter, SiOx may be referred to as the first material.

In an electrochemical device using a positive electrode material containing a conductive polymer, the conductive polymer is doped with anions in an electrolytic solution during charging and expands, and dedoped and contracts during discharge. Further, the conductive polymer absorbs the electrolyte and swells. Therefore, the expansion of the positive electrode during charging is large. Silicon oxide SiOx can reversibly occlude and release many cations, so it can have a high capacity, but it expands significantly when charged. That is, in an electrochemical device using such an electrode material, both the positive electrode and the negative electrode expand significantly during charging. As the expansion of the electrode increases, large compressive stresses will be applied to the electrode in the wound element.

In addition, in an electrochemical device using the above electrode material, from the viewpoint of balancing the capacity of the positive electrode and the capacity of the negative electrode, the negative electrode has a high SOC (state of charge) (for example, SOC of 70% or more). Charging and discharging will take place within this range. On the other hand, the positive electrode is charged and discharged over a wide range (for example, an SOC of 0 to 100%). Therefore, while the negative electrode expands and its volume increases, the positive electrode expands and contracts significantly due to charging and discharging. Therefore, large compressive stress is likely to be applied to the electrode. On the innermost circumferential side of the wound element, the curvature of the electrode is large and stress is difficult to escape, so large compressive stress is likely to be applied to the electrode. Further, on the outermost circumferential side of the wound element, a large compressive stress is applied to the electrode due to the expansion of the electrode located on the inner circumferential side and the pressure caused by the case. Furthermore, since the outermost end of the wound element is fixed with adhesive tape, there is little space around the electrode, making it difficult to relieve the large compressive stress applied to the electrode. In particular, when such a large compressive stress is applied to the positive electrode, peeling of the conductive polymer becomes noticeable, leading to a decrease in cycle characteristics.

In the present disclosure, in an electrochemical device using the above electrode material, at least one of the innermost electrode and the outermost electrode of the wound element is a negative electrode. This prevents large stress from being applied to the positive electrode at the innermost circumferential side and/or the outermost circumferential side, so that peeling of the conductive polymer at the positive electrode can be suppressed. By suppressing peeling of the conductive polymer, high capacity can be ensured even after repeated charging and discharging. Therefore, deterioration of cycle characteristics can be suppressed. Further, by using the above electrode material, high capacity can be ensured.

In the wound element, at least the innermost electrode is preferably a negative electrode. By using the innermost electrode to which a large compressive stress is applied as the negative electrode, peeling of the conductive polymer at the positive electrode can be effectively suppressed.

On the innermost circumferential side of the wound element, a length L1 of a region of the negative electrode that does not face the positive electrode (hereinafter referred to as a first region) is preferably 5 mm or more and 20 mm or less. By setting the length of the first region within such a range, it is possible to further enhance the effect of suppressing peeling of the conductive polymer in the positive electrode while ensuring high capacity.

When the outermost electrode of the wound element is a negative electrode, the length L2 of the area of the negative electrode that does not face the positive electrode (hereinafter referred to as the second area) on the outermost side is 5 mm or more and 20 mm or less. It is preferable. By setting the length of the second region within such a range, the effect of suppressing peeling of the conductive polymer at the positive electrode can be further enhanced while ensuring high capacity.

Note that in a wound element, a pair of strip-shaped (or band-shaped) electrodes with different polarities (specifically, a positive electrode and a negative electrode) is usually inserted between the pair of electrodes from one end in the length direction of each electrode. It is formed by winding with a separator interposed. In this specification, the term "innermost electrode" refers to an electrode of a pair of electrodes in which one end in the length direction of the electrode is located closer to the inner circumference. The outermost electrode refers to an electrode of a pair of electrodes whose other end in the length direction is located closer to the outer circumference.

The length direction of the electrode is perpendicular to the winding axis of the winding element. The region of the negative electrode that does not face the positive electrode refers to the region where the negative electrode material of the negative electrode exists and does not face the region where the positive electrode material of the positive electrode exists. However, the first region is a continuous region that includes one end located on the inner peripheral side of the wound element among both ends of the negative electrode in the length direction. Further, the second region is a continuous region including the other end in the length direction of the negative electrode (that is, the end located on the outer peripheral side of the wound element). The length L1 of the first region is the length of the first region from the inner peripheral end of the negative electrode in a direction parallel to the length direction of the negative electrode. The length L2 of the second region is the length of the second region from the outer peripheral end of the negative electrode in a direction parallel to the length direction of the negative electrode.

The length L1 of the first region and the length L2 of the second region may be obtained from a cross-sectional photograph of the wound element in the direction perpendicular to the winding axis, and the wound element taken out from the electrochemical device is expanded. You can also find it in the same state. Further, L1 and L2 may be determined for the laminate of the positive electrode, negative electrode, and separator before winding.

Below, an electrochemical device according to an embodiment of the present disclosure will be described in more detail with reference to the drawings as appropriate.
[Electrochemical device]
The electrochemical device according to this embodiment includes a wound element in which a positive electrode, a negative electrode, and a separator interposed therebetween are wound, and an electrolyte.

FIG. 1 is a schematic cross-sectional view of an electrochemical device 100 according to the present embodiment, and FIG. 2 is a schematic diagram of a part of the wound element 10 included in the electrochemical device 100.

The electrochemical device 100 includes a wound element 10, a container 101 containing the wound element 10 and an electrolytic solution (not shown), a sealing body 102 that closes an opening of the container 101, a lead wire 104A led out from the sealing body 102, 104B, and lead tabs 105A and 105B that connect each lead wire and each electrode of the winding element 10. The vicinity of the open end of the container 101 is drawn inward, and the open end is curled so as to be caulked to the sealing body 102.

FIG. 3 is a cross-sectional view schematically showing the configuration of the wound element 10. FIG. 3 shows a cross section of the wound element 10 taken in a direction perpendicular to the winding axis. FIG. 4 is a cross-sectional view schematically showing the configuration of the positive electrode, separator, and negative electrode of the wound element 10 of FIG. 3 before winding. FIG. 4 shows a cross section taken in a direction perpendicular to the winding axis (that is, a cross section parallel to the length direction of the positive electrode and the negative electrode). In FIGS. 3 and 4, the positive current collector lead 60 and the negative current collector lead 70 are omitted for convenience. Further, FIG. 3 shows the states of the positive electrode 11, negative electrode 12, and separator 13 on the innermost and outermost sides of the wound element 10, and the states of the positive electrode 11, negative electrode 12, and separator 13 in the part between them. The state is omitted.

The total length of the negative electrode 12 is longer than the total length of the positive electrode 11 (that is, the total length in the direction parallel to the length direction of the positive electrode 11). In the illustrated example, the negative electrode 12 includes a first region A1 and a second region A2 that do not face the positive electrode 11 on the innermost and outermost sides of the wound element 10, respectively. The length of the first region A1 from the innermost end 12a of the negative electrode 12 is indicated by L1, and the length of the second region A2 from the outermost end 12b is indicated by L2. In FIG. 4, the positive electrode 11 is placed between a pair of separators 13. The laminate of the separator 13, the positive electrode 11, the separator 13, and the negative electrode 12 shown in FIG. By winding the positive electrode 11 from the portion 12a, a wound element 10 as shown in FIG. 3 is formed. Note that the winding core is removed after winding.

The positive electrode material contained in the positive electrode 11 includes a conductive polymer that dopes and dedopes anions contained in the electrolytic solution through charging and discharging. The negative electrode material included in the negative electrode 12 includes a negative electrode active material that occludes and releases cations contained in the electrolytic solution by charging and discharging. Here, the negative electrode active material includes a first material, that is, SiOx (0<x<2). In this embodiment, the compressive stress applied to the positive electrode 11 can be reduced by using the innermost electrode and the outermost electrode of the wound element 10 as the negative electrodes 12 as described above. Therefore, peeling of the conductive polymer in the positive electrode 11 can be suppressed. Although FIGS. 3 and 4 show an example in which both the innermost electrode and the outermost electrode are negative electrodes 12, this is not limited to these cases. Either one of the side electrodes may be used as the negative electrode 12.

Hereinafter, the constituent elements of the electrochemical device will be explained in more detail.
(positive electrode)
Positive electrode 11 includes positive electrode material. The positive electrode 11 typically includes a positive electrode material and a positive electrode current collector supporting the positive electrode material.

For example, a sheet-shaped metal material is used for the positive electrode current collector. As the sheet-shaped metal material, for example, metal foil, metal porous body, punched metal, expanded metal, etched metal, etc. are used.

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

The thickness of the positive electrode current collector is, for example, 10 μm to 100 μm.

The positive electrode material includes a conductive polymer that dopes and dedopes anions contained in the electrolyte through charging and discharging. As the conductive polymer, a π-conjugated polymer is preferable. Examples of the π-conjugated polymer include polymers having a basic skeleton of polypyrrole, polythiophene, polyfuran, polyaniline, polythiophene vinylene, or polypyridine. Such polymers include not only polypyrrole, polythiophene, polyfuran, polyaniline, polythiophene vinylene, and polypyridine, but also polymers having substituents on their skeletons (also referred to as substituted products). Note that the substituents include not only monovalent groups but also polyvalent groups that form a bridged ring together with a ring included in the basic skeleton. For example, polythiophenes include polythiophene and substituted products thereof, and substituted products include poly(3,4-ethylenedioxythiophene) (PEDOT).

The conductive polymers may be used singly or in combination of two or more. Polyanilines may be used from the viewpoint of easily achieving high adhesion between the positive electrode material and the positive electrode current collector. Since polyanilines can be directly produced on the positive electrode current collector by an electrolytic polymerization process, they are advantageous in increasing the adhesion between the positive electrode material and the positive electrode current collector. Polyanilines include polyaniline and substituted products thereof.

Note that polyanilines include polymers containing aniline (Bz-NH ₂ ) and/or substituted products thereof as monomers. The polyanilines have an amine structural unit of -Bz-NH-Bz-NH- and/or an imine structural unit of -Bz-N=Bz=N-. Bz represents a benzene ring. Each benzene ring may have one or more substituents. Examples of the substituent include, but are not limited to, an alkyl group such as a methyl group, a halogen atom, and the like.

The weight average molecular weight of the conductive polymer is not particularly limited, but is, for example, 1,000 to 100,000. Note that the weight average molecular weight is a polystyrene equivalent weight average molecular weight measured by gel permeation chromatography.

A dopant may be introduced into the conductive polymer. Dopants include 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 ^- ), fluorosulfate ion (FSO ₃ ^- ), bis(fluorosulfonyl)imide ion (N(FSO ₂ ) ₂ ^- ), bis( Examples 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. Polymer ions include polyvinylsulfonic acid, polystyrenesulfonic acid, polyallylsulfonic acid, polyacrylsulfonic acid, polymethacrylsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyacrylic Examples include ions such as acids. These may be homopolymers or copolymers of two or more types of monomers. These may be used alone or in combination of two or more.

In the positive electrode 11, the positive electrode material may be formed in a layered manner on at least one main surface of the positive electrode current collector. The thickness of such a layered positive electrode material (hereinafter also referred to as a positive electrode material layer) is, for example, 10 μm to 300 μm on one side of the positive electrode current collector.

Note that a carbon layer may be formed between the positive electrode current collector and the positive electrode material, if necessary. By providing the carbon layer, the resistance between the positive electrode current collector and the positive electrode material can be kept low. Further, when forming the positive electrode material on the positive electrode current collector by electrolytic polymerization or chemical polymerization, the formation of the positive electrode material becomes easy.

The carbon layer includes a conductive carbon material. The carbon layer may include a polymer material in addition to the conductive carbon material. Graphite, hard carbon, soft carbon, carbon black, etc. can be used as the conductive carbon material. The material of the polymer material is not particularly limited, but it is electrochemically stable and has excellent acid resistance. Polymer) etc. are preferably used.
(Negative electrode)
Negative electrode 12 includes negative electrode material. The negative electrode 12 typically includes a negative electrode material and a negative electrode current collector supporting the negative electrode material.

For example, a sheet-shaped metal material is used for the negative electrode current collector. As the sheet-shaped metal material, for example, metal foil, metal porous body, punched metal, expanded metal, etched metal, etc. are used. As the material of the negative electrode current collector, for example, copper, copper alloy, nickel, stainless steel, etc. can be used.

The thickness of the negative electrode current collector is, for example, 10 μm to 100 μm.

The negative electrode material includes a negative electrode active material that occludes and releases cations by charging and discharging. That is, occlusion and release of cations by the negative electrode active material are performed reversibly. The negative electrode active material includes SiOx (0<x<2), which is a first material. Note that the cation preferably contains at least lithium ion. The first material is capable of electrochemically occluding and releasing cations such as lithium ions. By using the first material, high capacity can be ensured.

In SiOx, x preferably satisfies 0.5≦x≦1.5, and may also satisfy 0.5<x<1.5. When x is within such a range, a high amount of lithium ions can be stored, which is advantageous from the viewpoint of increasing capacity. When x is in such a range, the amount of expansion of SiOx during charging is also large. However, according to the present disclosure, the compressive stress applied to the positive electrode 11 can be reduced by using the outermost circumferential side and/or the outermost circumferential side electrode as a negative electrode. Therefore, even though the first material having x in such a range is used, deterioration in cycle characteristics can be suppressed.

In addition to the first material, the negative electrode active material can include a second material that inserts and releases cations such as lithium ions. Examples of the second material include carbon materials, metal compounds, alloys, and ceramic materials. As the carbon material, graphite, non-graphitizable carbon (hard carbon), and easily graphitizable carbon (soft carbon) are preferable, and graphite and hard carbon are particularly preferable. Examples of the metal compound include compounds other than the first material, such as tin oxide. Examples of alloys include silicon alloys and tin alloys. Examples of the ceramic material include lithium titanate and lithium manganate. These may be used alone or in combination of two or more. Among these, carbon materials (particularly graphite) are preferable because they have a high capacity to store cations such as lithium ions and can lower the potential of the negative electrode 12. Note that graphite includes a carbon material having a graphite-type crystal structure. Examples of graphite include natural graphite and/or artificial graphite.

The ratio of the first material in the negative electrode material is, for example, 0.5% by mass or more, may be 1% by mass or more, may be 3% by mass or more, 4% by mass or more, or 5% by mass. It may be more than that. When the ratio of the first material is within such a range, the effect of using the innermost and/or outermost electrode as the negative electrode 12 is likely to be exhibited. Moreover, it is easy to ensure high capacity. The ratio of the first material is, for example, 15% by mass or less, may be 12% by mass or less, or may be 10% by mass or less. Even when the ratio of the first material is in this range, a high capacity can be ensured, and it is easy to balance the capacity with the capacity of the positive electrode 11. Furthermore, the effect of suppressing peeling of the conductive polymer in the positive electrode 11 can be further enhanced. These lower limit values and upper limit values can be arbitrarily combined.

Note that the qualitative analysis of the first material in the negative electrode material can be performed by, for example, X-ray absorption spectroscopy such as X-ray absorption near edge (XANES) spectrum. For example, when the negative electrode material includes the first material, both the peak of simple Si and the peak of SiO ₂ are detected in the XANES spectrum of the negative electrode material. By detecting these peaks, the presence of the first material in the negative electrode material can be confirmed. Note that when qualitative analysis of the first material is performed on the negative electrode taken out from the electrochemical device, the taken out negative electrode is washed with water and dried before use.

The ratio of the first material in the negative electrode material may be calculated from the total amount of the constituent components (solid content) of the negative electrode material and the mass of the first material. For example, the ratio of the first material may be calculated using such a calculation method for the negative electrode mixture paste used for producing the negative electrode. Furthermore, the ratio of the first material may be determined for the negative electrode taken out from the electrochemical device. In this case, the negative electrode is taken out from the electrochemical device, washed with a nonaqueous solvent of the electrolytic solution (for example, an organic solvent such as dimethyl carbonate), and thoroughly dried before use. More specifically, after drying the negative electrode, a predetermined amount of negative electrode material is taken out and heated at 800°C for 1 hour in an oxygen atmosphere.The change in mass is determined, and this mass change is subtracted from the mass before heating. The ratio (mass %) of the difference in time to the mass before heating can be determined as the ratio of the first material in the negative electrode material.

In addition to the negative electrode active material, the negative electrode material can contain a conductive agent, a binder, and the like. Examples of the conductive agent include carbon black and/or carbon fiber. Examples of the binder include fluororesins, acrylic resins, rubber materials, and/or cellulose derivatives (cellulose ether, cellulose ether, etc.). Examples of the fluororesin include polyvinylidene fluoride, polytetrafluoroethylene, and tetrafluoroethylene-hexafluoropropylene copolymer. Examples of the acrylic resin include polyacrylic acid, acrylic acid-methacrylic acid copolymer, or salts thereof (sodium salt, ammonium salt, etc.). Examples of rubber materials include styrene-butadiene rubber, and examples of cellulose derivatives include cellulose ethers, such as carboxymethyl cellulose or salts thereof (sodium salts, ammonium salts, etc.).

The ratio of the conductive agent in the negative electrode material is, for example, 5% by mass or less. The proportion of the conductive agent may be 0.1% by mass or more. The ratio of the binder in the negative electrode material is, for example, 5% by mass or less, and may be 0.1% by mass or more.

According to the present embodiment, by using the negative electrode 12 as at least one of the innermost electrode and the outermost electrode of the wound element 10, excessive compressive stress is suppressed from being applied to the positive electrode 11. . Therefore, peeling of the conductive polymer in the positive electrode 11 can be suppressed, and as a result, high cycle characteristics can be ensured. In particular, it is preferable that at least the innermost electrode be the negative electrode 12 . Since a particularly large compressive stress is likely to be applied to the electrode on the innermost circumferential side, by making the electrode at this portion serve as the negative electrode 12, it becomes easier to ensure higher cycle characteristics.

On the innermost circumferential side of the wound element 10, the length L1 of the first region of the negative electrode 12 that does not face the positive electrode 11 may be 3 mm or more, 5 mm or more, or 10 mm or more. When the length L1 of the first region is within such a range, the effect of suppressing peeling of the conductive polymer in the positive electrode 11 can be further enhanced. The length L1 of the first region may be 25 mm or less, 23 mm or less, or 20 mm or less. When the length of the first region is within such a range, higher capacity can be ensured while suppressing peeling of the conductive polymer in the positive electrode 11. These lower limit values and upper limit values can be arbitrarily combined.

On the outermost circumferential side of the wound element 10, the length L2 of the second region of the negative electrode 12 that does not face the positive electrode 11 may be 3 mm or more, 5 mm or more, or 10 mm or more. When the length L2 of the second region is within such a range, the effect of suppressing peeling of the conductive polymer in the positive electrode 11 can be further enhanced. The length L2 of the second region may be 25 mm or less, 23 mm or less, or 20 mm or less. When the length of the second region is within such a range, higher capacity can be ensured while suppressing peeling of the conductive polymer in the positive electrode 11. These lower limit values and upper limit values can be arbitrarily combined.

In addition, from the viewpoint of easily reducing the compressive stress applied to the positive electrode 11, when one of L1 and L2 is 3 mm or more (for example, 3 mm or more and 5 mm or less), the other is set to, for example, 5 mm or more or 10 mm or more. Good too.

It is desirable that the negative electrode 12 be pre-doped with lithium ions. Pre-doping with lithium ions lowers the potential of the negative electrode 12, thereby increasing the potential difference (ie, voltage) between the positive electrode 11 and the negative electrode 12, and improving the energy density of the electrochemical device 100.

For example, the pre-doping of the negative electrode 12 with lithium ions can be carried out by forming a metal lithium film, which serves as a lithium ion supply source, on the surface of the negative electrode material layer, and then applying the negative electrode 12 having the metal lithium film to an electrolytic solution having lithium ion conductivity. Proceed by impregnating with. At this time, lithium ions are eluted from the metal lithium film into the electrolytic solution, and the eluted lithium ions are occluded in the negative electrode active material. The amount of lithium ions to be pre-doped can be controlled by the mass of the metal lithium film.

The step of pre-doping the negative electrode 12 with lithium ions may be performed before assembling the wound element 10. Alternatively, the pre-doping may proceed after the wound element 10 and the electrolyte are housed in the container 101 of the electrochemical device 100.
(Separator)
As the separator 13, a microporous membrane, woven fabric, nonwoven fabric, etc. are preferable. Examples of materials constituting the separator include organic materials (polyolefin, polymeric materials such as cellulose, etc.), inorganic materials (glass, etc.), and the like. Examples of fibers constituting woven fabrics and nonwoven 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 300 μm. The thickness of the separator 13 is, for example, 10 μm to 40 μm in the case of a microporous membrane, and 100 μm to 300 μm in the case of a woven fabric or nonwoven fabric.
(electrolyte)
Electrochemical device 100 includes an electrolyte. The electrolyte contains cations and anions. Preferably, the cation includes at least lithium ion. An electrolytic solution containing lithium ions has lithium ion conductivity. As such an electrolytic solution, for example, a non-aqueous electrolytic solution containing a lithium salt and a non-aqueous solvent in which the lithium salt is dissolved is preferable. At this time, the anion of the lithium salt can reversibly repeat doping and dedoping into the positive electrode 11. On the other hand, cations (preferably lithium ions derived from lithium salt) are reversibly inserted into and released from the negative electrode 12.

Examples of lithium salts 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, and L. iBr, LiI , LiBCl ₄ , LiN(FSO ₂ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ and the like. These may be used alone or in combination of two or more. Among these, 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 and a lithium salt having an imide anion.

The cations preferably include at least lithium ions (first cations), and may include lithium ions and cations other than lithium ions (second cations). Examples of the second cation include inorganic cations other than lithium ions, such as sodium ions, potassium ions, calcium ions, and magnesium ions, as well as organic cations. The electrolytic solution may contain one kind of second cation, or may contain two or more kinds of second cations.

The concentration of lithium salt in the electrolyte in a charged state (SOC 90 to 100%) is, for example, 0.2 mol/L to 5 mol/L.

Examples of nonaqueous 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, 1,2-diethoxyethane, and ethoxymethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, etc. Cyclic ether, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propionitrile, nitromethane, ethyl monoglyme, trimethoxymethane, sulfolane, methylsulfolane, 1,3-propanesultone, etc. can be used. These may be used alone or in combination of two or more.

The electrolytic solution may contain additives as necessary. Examples of additives include unsaturated carbonates. Examples of the unsaturated carbonate include vinylene carbonate, vinylethylene carbonate, divinylethylene carbonate, and the like.
[Method for manufacturing electrochemical device]
An example of a method for manufacturing the electrochemical device 100 according to the present disclosure will be described below with reference to FIGS. 2 to 4. However, the method for manufacturing the electrochemical device 100 according to the present disclosure is not limited to this.

The electrochemical device 100 described above includes, for example, a step of winding a positive electrode 11, a negative electrode 12, and a separator 13 to form a wound element 10, and a step of sealing the wound element 10 and an electrolytic solution. It can be manufactured by any manufacturing method. The positive electrode 11, the negative electrode 12, and the separator 13 are each prepared, for example, prior to the step of forming the wound element 10. The electrolyte, for example, is prepared prior to the sealing step. Sealing can be performed by accommodating the wound element 10 and the electrolyte in a container 101 and closing the opening of the container 101 with a sealing body 102.

The positive electrode 11 can be prepared, for example, by supporting a positive electrode material on a positive electrode current collector. As described above, a sheet-like metal material is used for the positive electrode current collector, but if necessary, surface treatment such as hydrophilic treatment may be performed. When the positive electrode 11 includes a carbon layer, the carbon layer is formed on the positive electrode current collector, and the positive electrode material is supported on the positive electrode current collector via the carbon layer. The carbon layer may be formed using a known procedure. The carbon layer may be formed, for example, by depositing a conductive carbon material onto the positive electrode current collector, and by applying a carbon paste containing the conductive carbon material onto the positive electrode current collector and drying the coating film. It may also be formed by The carbon paste includes, for example, a conductive carbon material, a polymer material, and a liquid medium.

For the positive electrode material, for example, a positive electrode current collector (or a laminate of a positive electrode current collector and a carbon layer) is immersed in a reaction solution containing a raw material monomer of a conductive polymer, and the raw material monomer is electrolytically polymerized or chemically polymerized. As a result, it is supported on the positive electrode current collector. In electrolytic polymerization, polymerization is performed using a positive electrode current collector as an anode. In this way, the positive electrode material containing the conductive polymer is formed so as to cover the surfaces of the positive electrode current collector and the carbon layer. The positive electrode material may be formed by a method other than electrolytic polymerization or chemical polymerization. For example, the positive electrode material can be supported on the positive electrode current collector by bringing a solution in which a conductive polymer is dissolved or a dispersion in which the conductive polymer is dispersed into contact with the positive electrode current collector or a carbon layer. Good too.

The raw material monomer used in electrolytic polymerization or chemical polymerization may be any polymerizable compound that can produce a conductive polymer through polymerization. The raw material monomer may include an oligomer. As the raw material monomer, for example, aniline, pyrrole, thiophene, furan, thiophene vinylene, pyridine, or substituted products thereof are used. These may be used alone or in combination of two or more. The raw material monomer is preferably aniline, since the positive electrode material is easily supported on the surface of the positive electrode current collector or carbon layer.

Electrolytic polymerization or chemical polymerization is preferably performed using a reaction solution containing an anion (dopant). It is desirable that the conductive polymer dispersion or solution also contains a dopant. By doping a π-electron conjugated polymer with a dopant, it exhibits excellent conductivity. For example, in chemical polymerization, a positive electrode current collector (or a laminate of a positive electrode current collector and a carbon layer) is immersed in a reaction solution containing a dopant, an oxidizing agent, and a raw material monomer, and then removed from the reaction solution and dried. Just let it happen. In addition, in electrolytic polymerization, a positive electrode current collector (or a laminate of a positive electrode current collector and a carbon layer) is immersed in a reaction solution containing a dopant and a raw material monomer, and the positive electrode current collector is used as an anode, and a counter electrode is is used as a cathode, and a current can be passed between the two.

Although water may be used as the solvent for the reaction solution, a non-aqueous solvent may be used in consideration of the solubility of the monomer. As the nonaqueous solvent, it is desirable to use alcohols such as ethyl alcohol, methyl alcohol, isopropyl alcohol, ethylene glycol, and polypropylene glycol. Water and the above-mentioned non-aqueous solvents can also be used as a dispersion medium or solvent for the conductive polymer.

Note that supporting the positive electrode material on the positive electrode current collector is usually carried out in an acidic atmosphere depending on the oxidizing agent and dopant used.

The thickness of the formed positive electrode material layer can be controlled, for example, by adjusting the polymerization time. In electrolytic polymerization, the layer thickness can also be controlled by adjusting the electrolytic current density. When using solutions or dispersions containing conductive polymers, it is necessary to adjust the concentration of the conductive polymer in these liquids and the number of times the liquid is brought into contact with the positive electrode current collector or carbon layer. By this, the thickness of the positive electrode material layer can be controlled.

For example, the negative electrode 12 is prepared by preparing a negative electrode mixture paste by mixing a first material (and a second material if necessary), a conductive agent, a binder, etc. together with a dispersion medium, and then preparing the negative electrode mixture paste. It is formed by applying it to a negative electrode current collector and then drying it.

In the step of preparing the positive electrode 11, a lead member (a lead tab 105A having a lead wire 104A) is connected to the positive electrode 11. In the preparation step for the negative electrode 12, another lead member (lead tab 105B provided with the lead wire 104B) is connected to the negative electrode 12.

In the step of forming the wound element 10, the lead member is wound from one end surface as shown in FIG. An exposed wound element 10 is obtained. The outermost circumference of the winding element 10 is fixed with a winding tape 14.

In the sealing step, first, as shown in FIG. 1, the wound element 10 is housed together with an electrolyte (not shown) in a cylindrical container 101 with an opening and a bottom. Lead wires 104A and 104B are led out from the sealing body 102. A sealing body 102 is placed at the opening of the container 101 to seal the container 101. Specifically, the vicinity of the open end of the container 101 is drawn inward, and the open end is curled so as to be caulked to the sealing body 102 . The sealing body 102 is made of, for example, an elastic material containing a rubber component.

In the above embodiment, a cylindrical wound electrochemical device has been described, but the scope of application of the present disclosure is not limited to the above, and can also be applied to a rectangular wound electrochemical device. .
[Example]
Hereinafter, the present disclosure will be specifically described based on Examples and Comparative Examples, but the present disclosure is not limited to the following Examples.
(Examples 1 to 8 and Comparative Example 1)
(1) Preparation of positive electrode An aluminum foil with 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 of 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 surface 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.

The positive electrode current collector on which the carbon layer was formed and the counter electrode were immersed in an aniline aqueous solution, and electrolytically polymerized at a current density of 10 mA/cm ² for 20 minutes to dope sulfate ions (SO ₄ ^2- ). A conductive polymer (polyaniline) film was deposited on the carbon layer on the front and back sides of the positive electrode current collector.

The conductive polymer doped with sulfate ions was reduced to dedope the sulfate ions. In this way, a positive electrode material layer containing a conductive polymer dedoped with sulfate ions was formed. Next, the positive electrode material layer was thoroughly washed, and then dried. The thickness of the positive electrode material layer was 35 μm per side.
(2) Preparation of negative electrode A copper foil with a thickness of 20 μm was prepared as a negative electrode current collector. On the other hand, a mixed powder of 97 parts by mass of negative electrode active material (total amount of SiO (first material) and artificial graphite), 1 part by mass of carboxycellulose, and 2 parts by mass of styrene-butadiene rubber, and a predetermined amount of water were mixed. A kneaded negative electrode mixture paste was prepared. The mass ratio of SiO and artificial graphite was adjusted so that the ratio (mass %) of the first material in the negative electrode material (solid content) was the value shown in Table 1.

The negative electrode mixture paste was applied to both sides of the negative electrode current collector and dried to obtain a negative electrode having 35 μm thick negative electrode material layers on both sides. Next, metallic lithium foil was attached to the negative electrode material layer in an amount calculated such that the negative electrode potential in the electrolytic solution after pre-doping was 0.2 V or less relative to metallic lithium.
(3) Preparation of wound element After connecting lead tabs to the positive and negative electrodes, as shown in FIGS. 2 and 4, a cellulose nonwoven fabric separator (thickness 35 μm), a positive electrode, and a cellulose nonwoven fabric separator ( A laminate in which a negative electrode (with a thickness of 35 μm) and a negative electrode were stacked in this order was wound to form a wound element. When laminating the positive electrode, negative electrode, and separator, the length of the negative electrode was adjusted so that the length L1 of the first region and the length L2 of the second region became the values shown in Table 1. However, when the innermost and/or outermost electrodes are positive electrodes, the lengths of the regions of the positive electrodes that do not face the negative electrodes are listed in the L1 and/or L2 columns of Table 1.
(4) Preparation of electrolyte solution A solvent was prepared by adding 0.2% by mass of vinylene carbonate to a mixture of propylene carbonate and dimethyl carbonate at 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 nonaqueous electrolyte containing lithium ions as cations and hexafluorophosphate ions (PF ₆ ⁻ ) as anions.
(5) Fabrication of electrochemical device A wound element and an electrolytic solution were placed in a bottomed container having an opening, and an electrochemical device as shown in FIG. 1 was assembled. Thereafter, aging was performed at 25° C. for 24 hours while applying a charging voltage of 3.8 V between the positive electrode and negative electrode terminals to advance pre-doping of lithium ions into the negative electrode.
(evaluation)
The obtained electrochemical device was evaluated as follows.

The electrochemical device was charged with a voltage of 3.8V and then discharged to 2.5V with a current of 5.0A. The amount of discharged charge (A·s) that flowed during the drop from 3.3V to 3.0V on the way was divided by the voltage change ΔV (=0.3V) to obtain the initial capacity C ₀ (F).

The above cycle of charging and discharging was repeated 100,000 times. The capacity C ₁ at the 100,000th cycle was determined in the same manner as the initial capacity C ₀ , and the ratio (%) of the capacity C ₁ at the 100,000th cycle to the initial capacity C ₀ was determined as the capacity retention rate and used as an index of cycle characteristics. . The capacity retention rate R was calculated by R=C ₁ /C ₀ ×100.
(Reference example 1)
A negative electrode and an electrochemical device were produced and evaluated in the same manner as in Example 1, except that only artificial graphite was used as the negative electrode active material.

The evaluation results are shown in Table 1. Examples 1 to 8 are A1 to A8, Comparative Example 1 is B1, and Reference Example 1 is R1.

As shown in Table 1, R1, in which the negative electrode does not contain SiO, has a high cycle characteristic of 88%. On the other hand, when the negative electrode contains SiO and the outermost and innermost electrodes are used as positive electrodes, the cycle characteristics are significantly reduced to 40% (B1). On the other hand, when the negative electrode contains SiO, high cycle characteristics of 60 to 90% can be ensured in A1 to A8 by using the outermost and/or innermost electrodes as negative electrodes. Further, in A1 to A8, a high capacity of 1200F or more can be obtained.
(Examples 9 to 11)
The ratio of the first material in the negative electrode material was changed to 11% by mass. In Examples 10 to 11, the length of the negative electrode was further adjusted so that L1 and L2 had the values shown in Table 2. Except for these, a negative electrode and an electrochemical device were produced and evaluated in the same manner as in Example 1.

The evaluation results are shown in Table 2. Examples 9 to 11 are A9 to A11. Table 2 also shows the results of A1 to A3, B1, and R1.

As shown in Table 2, A9 to A11 also ensured high capacity and had higher cycle characteristics than B1. From the viewpoint of ensuring higher cycle characteristics, the ratio of the first material in the negative electrode material is preferably 10% by mass or less.
(Example 12 and 13)
A negative electrode and an electrochemical device were produced and evaluated in the same manner as in Example 2, except that the length of the negative electrode was adjusted so that L1 and L2 became the values shown in Table 3.

The evaluation results are shown in Table 3. Examples 12 and 13 are A12 and A13. Table 3 also shows the results of A2, A4 to A6, B1, and R1.

As shown in Table 3, A12 and A13 also ensured high capacity and had higher cycle characteristics than B1. From the viewpoint of ensuring higher cycle characteristics, it is preferable that L1 and/or L2 be 5 mm or more. Note that even if one of L1 and L2 is 3 mm, if the other is made larger (for example, 5 mm or more or 10 mm or more), higher cycle characteristics than A13 can be ensured.

From the viewpoint of easily ensuring high capacity, it is preferable that L1 and/or L2 be 20 mm or less.

The electrochemical device according to the present disclosure provides excellent cycle characteristics. Therefore, it is suitable for various electrochemical devices that require high cycle characteristics, especially as a backup power source.

10: Winding element 11: Positive electrode 12: Negative electrode 12a: Innermost end of negative electrode 12b: Outermost end of negative electrode 13: Separator 14: Winding tape 100: Electrochemical device 101: Container 102: Sealing body 104A, 104B: Lead wire 105A, 105B: Lead tab A1: First area A2: Second area L1: Length of first area L2: Length of second area

Claims (5)

A wound element in which a positive electrode containing a positive electrode material, a negative electrode containing a negative electrode material, and a separator interposed between the positive electrode and the negative electrode are wound, and an electrolyte,
The electrolyte includes cations and anions,
The positive electrode material includes a conductive polymer that dopes and dedopes the anion by charging and discharging,
The negative electrode material includes a negative electrode active material that occludes and releases the cations by charging and discharging,
The negative electrode active material includes SiOx (0<x<2),
The ratio of the SiOx in the negative electrode material is 0.5% by mass or more and 10% by mass or less,
The innermost electrode and the outermost electrode of the wound element are the negative electrodes,
On the innermost circumferential side, a length L1 of a region of the negative electrode that does not face the positive electrode is 5 mm or more and 20 mm or less,
In the electrochemical device, a length L2 of a region of the negative electrode that does not face the positive electrode on the outermost circumferential side is 5 mm or more and 20 mm or less. The electrochemical device according to claim 1, wherein the conductive polymer is formed by electrolytic polymerization . The electrochemical device according to claim 1 or 2, wherein the x satisfies 0.5≦x≦1.5. The electrochemical device according to claim 1, wherein the negative electrode material further contains graphite. The electrochemical device according to any one of claims 1 to 4, wherein the conductive polymer contains polyanilines.

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