JP4670258B2 - Electrode material for electrochemical device and electrochemical device provided with the same - Google Patents

Description

  The present invention relates to an electrode material for an electrochemical device comprising an organic sulfur compound and an electrochemical device using the same.

In recent years, the market for lithium ion batteries, which are one of electrochemical devices, has expanded rapidly. In lithium ion batteries currently on the market, LiCoO ₂ is used as a positive electrode active material and a carbonaceous material is used as a negative electrode active material. However, the energy density of such a lithium ion secondary battery is reaching a limit value.

Therefore, research and development of alternative active materials is being conducted. For example, a battery using an organic sulfur compound as an electrode material using a reversible oxidation-reduction reaction of an organic sulfur compound has been proposed. Patent Document 1 discloses a disulfide compound that is an organic sulfur compound. This organic sulfur compound is represented most simply by R—S—S—R (R is a hydrocarbon and S is sulfur), and the S—S bond is cleaved by an electroreduction reaction, and the metal ion M in the electrolyte ⁺ and in association 2R-S ^- generating a · M metal salt represented by ^+. This metal salt returns to the original R—S—S—R by the electrolytic oxidation reaction. This document proposes a metal-disulfide secondary battery in which a metal M that supplies and captures metal ions M ⁺ and a disulfide compound are combined. This battery is expected to have a high energy density of 150 Wh / kg or more.

  On the other hand, high-density integrated circuits (LSIs) used in electronic devices are moving toward a constant voltage, and the battery that is the power source is starting to be demanded from 4V type to 2V type. . Also in this respect, it can be said that the secondary battery using the disulfide compound exhibiting an operating voltage of about 2.0 V is a battery that meets the market demand.

  However, a battery using a disulfide compound as an electrode material has a problem in that the capacity is significantly reduced due to a charge / discharge cycle. This is because the oxidation-reduction reaction of the disulfide compound is a reaction involving the cleavage and polymerization of the S—S bond as described above. Therefore, the disulfide compound is reduced in molecular weight at the time of the cleavage, and the disulfide compound is eluted out of the electrode. It was caused by.

In order to solve this problem, Patent Document 2 proposes that a high-molecular component having a thiol group introduced into an electrode to efficiently react as a disulfide compound during electrode reaction. However, as described in this document, the method of obtaining an electrode material by introducing a thiol group into a polymer is not easy to process into an electrode for an electrochemical device that can obtain sufficient characteristics, so the production method is greatly limited. It was to be done.
US Pat. No. 4,833,048 JP-A-6-163049

  An object of the present invention is to solve the above-mentioned problems. An organic sulfur-based electrode material for an electrochemical device in which elution of the electrode material is suppressed even when charging / discharging is performed, and an electrode for an electrochemical device and an electrochemical device including the same Is to provide.

(1) electrode for an electrochemical device material consisting of the obtained Ru, an organic sulfur compound containing no SS bond by crosslinking.
(2) The electrode material for an electrochemical device according to ( 1 ) , wherein an organic sulfur compound having a thiomethacrylate group is crosslinked.
(3) The electrode material for an electrochemical device according to ( 1 ) or ( 2 ), which has a molecular structure represented by the following (Chemical Formula 1 ).
(4) An electrochemical device comprising the electrode material for an electrochemical device according to ( 1 ), ( 2 ), or ( 3 ) .

  The electrode material for an electrochemical device of the present invention does not mainly have an S—S bond portion, and an organic sulfur compound contributes to a redox reaction in the form of a cation radical or an anion radical. In the electrode for electrochemical devices using this, the SS bond is not cleaved as in the case of the disulfide compound described in 1. The elution of the electrode material accompanying charging / discharging is suppressed.

  In addition, the organic sulfur compound having a thiomethacrylate group can be easily cross-linked by a radical obtained from a radical polymerization initiator or actinic light from a thiomethacrylate group present in the molecule.

  It is possible to provide an electrode material for an electrochemical device with little risk of elution even when oxidation-reduction is performed. Moreover, the electrode for electrochemical devices and electrochemical device using the same can be provided.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following description.

  As a method for synthesizing an organic sulfur compound that is a raw material for an electrode material for an electrochemical device of the present invention, for example, as shown below, an organic sulfur compound is easily reacted with a thiol derivative that is an organic sulfur compound and methacryloyl chloride in the presence of an alkali. It is possible to synthesize.

  Examples of thiol derivatives include thiocresol, 2-mercaptoethyl acetate, methyl 2-mercaptoacetate, 2-thiazolinethiol, 2-mercaptopyridine, 4-mercaptopyridine, 2-mercapto-5-methyl-1,3,4-thiadiazole 2,5-dimercapto-1,3,4-thiadiazole, 2-benzothiazolethiol, 2-benzimidazolethiol, and the like, but are not limited thereto.

  The reaction between the thiol derivative and methacryloyl chloride is preferably carried out at a low temperature by diluting the raw material with an ether solvent such as tetrahydrofuran for the purpose of suppressing runaway reaction. In order to further increase the yield of the reaction, the reaction system is preferably performed in a non-aqueous environment.

  When producing the electrode material for electrochemical devices of the present invention using the organic sulfur compound thus obtained, sufficient ion conductivity and electron conductivity are ensured while suppressing elution of the electrode material into the electrolyte. In order to achieve this, it is preferable to carry out crosslinking after being supported on the surface of a carbon material having a large specific surface area. For example, 2-Methyl-thioacrylic acid S- [5- (2-methyl-acryloylsulfanyl)-[1,2,5] thiadiazol-2-yl] ester and the radical initiator azobisisobutyronitrile are diluted with a solvent. Then, after immersing activated carbon fiber in the solution, the solvent is removed by heating to about 80 ° C., followed by thermal crosslinking at about 120 ° C. to use as an electrode. As a crosslinking method, in addition to thermal crosslinking and ultraviolet crosslinking using a radical initiator, a method using ionizing radiation is also preferable.

  Since the electrode material for an electrochemical device of the present invention takes a cation radical structure or an anion radical structure in an electrochemical reaction system, it may be used for any of a pair of electrodes constituting the electrochemical device. For example, when the electrode material of the present invention is applied to a lithium ion battery as an electrochemical device, it may be used for a positive electrode or a negative electrode. Furthermore, you may use for both poles.

  When the electrode material for electrochemical devices of the present invention is used for a positive electrode, a material generally used for a lithium battery electrode or a capacitor electrode can be used for the negative electrode. For example, lithium-containing alloys such as lithium metal, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and wood alloy, and the following carbon materials are exemplified. For example, natural graphite, artificial graphite, amorphous carbon, fibrous carbon, powdered carbon, petroleum pitch-based carbon, coal coke-based carbon, activated carbon, activated carbon fiber, and the like are preferably used. These carbon materials are preferably particles or fibers having a diameter or fiber diameter of 0.01 to 10 μm and a fiber length of several μm to several mm. However, it is not limited to these.

  Furthermore, the carbon material can be modified by adding a metal oxide such as tin oxide or silicon oxide, or by adding phosphorus or boron. Moreover, when using a carbon material as a negative electrode active material, it is preferable to use a carbon material and lithium metal, a lithium containing alloy together, or to reduce electrochemically beforehand.

When the electrode material for electrochemical devices of the present invention is used for a negative electrode, a material generally used for a lithium battery electrode or a capacitor electrode can be used for the positive electrode. However, since the electrode material for a lithium battery of the present invention has a relatively noble potential, when it is used for a negative electrode, it is necessary to use a positive electrode active material that operates at a noble potential. For example, materials such as lithium-containing transition metal oxides, phosphates, activated carbons, and activated carbon fibers that exhibit a discharge voltage of 3 V or more with respect to lithium are preferably used. In particular, a material capable of obtaining a discharge potential of 4 V or more is more preferable because a high battery voltage can be obtained and the energy density is improved. Examples of the lithium-containing transition metal oxide include Li _y Co _1-x M _x O ₂ , Li _y Mn _{2 -x} M _x O ₄ {M is a group I to VIII metal (for example, Li, Ca , Cr, Ni, Fe, Co, Mn, etc.), and the x value indicating the amount of substitution of different elements is effective up to the maximum amount that can be replaced, but preferably 0 ≦ from the point of discharge capacity x ≦ 1. In addition, as the y value indicating the amount of lithium, the maximum amount capable of reversibly utilizing lithium is effective, but preferably 0 <y ≦ 2 from the viewpoint of discharge capacity. }, But is not limited thereto.

Other active materials can be further mixed with the positive electrode active material. For example, Group I metal compounds such as CuO, Cu ₂ O, Ag ₂ O, CuS, CuSO ₄ , Group IV metal compounds such as TiS ₂ , SiO ₂ , SnO, V ₂ O ₅ , V ₆ O ₁₂ , VO _x , Group V metal compounds such as Nb ₂ O ₅ , Bi ₂ O ₃ , Sb ₂ O ₃ , Group VI metal compounds such as CrO ₃ , Cr ₂ O ₃ , MoO ₃ , MoS ₂ , WO ₃ , SeO ₂ , MnO ₂ , Examples include Group VII metal compounds such as Mn ₂ O ₃ and Group VIII metal compounds such as Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , FePO ₄ , Ni ₂ O ₃ , NiO, CoO ₃ , and CoO. Furthermore, conductive polymer compounds such as polypyrrole, polyaniline, polyparaphenylene, polyacetylene, and polyacene materials, pseudographite structure carbonaceous materials, and the like may be used, but are not limited thereto.

  Examples of the method for forming the electrode material of the present invention include a roller coating such as an applicator roll, a screen coating, a doctor blade method, a spin coating, a bar coater, and a dip coating. Although it is preferable to apply to a desired shape, the present invention is not limited to this. In addition, when these means are used, it is possible to increase the actual surface area of the electrochemically active substance in contact with the electrolyte layer and the current collector.

  In the electrode material of the present invention, a conductive agent, a binder, a solid electrolyte, a filler and the like can be added to the electrode mixture as necessary.

  As the conductive agent, any electronic conductive material that does not adversely affect battery performance may be used. Usually, natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, acetylene black, ketjen black, carbon whisker, carbon fiber and metal (copper, nickel, aluminum, silver, gold, etc.) Conductive materials such as powders, metal fibers, and conductive ceramic materials can be included as one type or a mixture thereof. Among these, acetylene black is preferable from the viewpoints of conductivity and coatability. The addition amount is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight. These mixing methods are physical mixing, and the ideal is uniform mixing. Therefore, powder mixers such as V-type mixers, S-type mixers, crackers, ball mills, and planetary ball mills can be mixed dry or wet.

Examples of the binder include heat such as tetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene-propylene diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber, carboxymethyl cellulose, and the like. A plastic resin, a polymer having rubber elasticity, a polysaccharide, or the like can be used as one kind or a mixture of two or more kinds. Moreover, it is preferable that the binder which has a functional group which reacts with lithium like a polysaccharide deactivates the functional group, for example by methylating. The addition amount is preferably 1 to 50% by weight, particularly preferably 2 to 30% by weight.

  In order to ensure sufficient ion conductivity while suppressing elution of the electrode material into the electrolyte, it is preferably used in combination with a solid electrolyte. As the solid electrolyte, a lithium ion conductive polymer electrolyte or an inorganic solid electrolyte which is solid or solid at a temperature of -20 to 60 ° C. can be used. Among these, a lithium ion conductive polymer electrolyte is preferable. Examples of such a polymer electrolyte include a polyethylene oxide derivative in which an ionic compound is dissolved or at least a polymer containing the derivative, a polypropylene oxide derivative or a polymer containing at least the derivative, polyphosphazene, the derivative, and an ion dissociation group. Ion conduction of polymer matrix materials (gel electrolytes) containing non-aqueous electrolytes in polymers, phosphate ester polymer derivatives, polyvinyl pyridine derivatives, bisphenol A derivatives, polyacrylonitrile, polyvinylidene fluoride, fluororubber, etc. What consists of a property compound can be used.

  The filler may be any material as long as it does not adversely affect battery performance. Usually, olefin polymers such as polypropylene and polyethylene, aerosil, zeolite, glass, carbon and the like are used. The amount of filler added is preferably 0 to 30% by weight.

  As a material that can be used for the positive electrode current collector and the negative electrode current collector, any material can be used as long as it is an electronic conductor that does not have an adverse effect on the constituted battery. For example, as the positive electrode current collector, aluminum, titanium, stainless steel, nickel, carbon, conductive polymer, conductive glass, etc., as well as the surface of aluminum or the like for the purpose of improving adhesion, conductivity, and oxidation resistance. Can be used which has been treated with carbon, nickel, titanium, silver or the like. In addition to copper, nickel, iron, stainless steel, titanium, aluminum, carbon, conductive polymer, conductive glass, Al-Cd alloy, etc., negative electrode current collector improves adhesion, conductivity, and oxidation resistance For this purpose, a material obtained by treating the surface of copper or the like with carbon, nickel, titanium, silver or the like can be used. The surface of these materials can be oxidized or etched. As for these shapes, in addition to the foil shape, a film shape, a sheet shape, a net shape, a punched or expanded product, a lath body, a porous body, a foamed body, a formed body of a fiber group, and the like are used. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used. Among these current collectors, aluminum foil or nickel foil is used for the positive electrode, and copper foil, nickel foil, iron foil, and one of them are stable for the negative electrode in a reduction field and have excellent conductivity. An alloy foil containing a part is preferred. Further, it is preferable that the foil has a rough surface roughness of 0.2 μmRa or more, which is excellent in adhesion between the electrochemically active material layer and the current collector. Electrolytic foil and etching foil are excellent for the purpose of obtaining such a rough surface.

  As a battery exterior material using the electrode material of the present invention, a metal can such as iron, stainless steel, and aluminum can be used. From the viewpoint of weight energy density, a metal laminated with a metal foil and a resin film. A resin composite film is preferred. As an example of the metal foil used for the metal resin composite film, aluminum, iron, nickel, copper, stainless steel, titanium, gold, silver, and the like may be anything as long as the foil does not have a pinhole, but a lightweight and inexpensive aluminum foil is preferable. . In addition, a resin film having an excellent piercing strength such as a polyethylene terephthalate film or a nylon film on the outer surface and a thermoplastic and fusible film such as a polyethylene film or a nylon film on the inner surface is also suitably used. . From the viewpoint of solvent resistance, the opening of such a resin film is preferably sealed with a thermoplastic resin.

  As separators for batteries using the electrode material of the present invention, polyolefin-based, polyester-based, polyacrylonitrile-based, polyphenylene sulfide-based, polyimide-based, and fluororesin-based microporous membranes and nonwoven fabrics can be used. Among them, it is preferable to treat the microporous membrane with poor wettability with a surfactant or the like. The solid electrolyte can be used as a separator.

The porosity of the separator is preferably 98% by volume or less from the viewpoint of strength. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

Examples of the ionic compound used for the electrolyte in the battery using the electrode material of the present invention include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiSCN, LiBr, LiI, Li Inorganic ion salts containing one of Li, Na, or K, such as ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO ₄ , KSCN, LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n-C ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-maleate, (C ₂ H ₅ ) ₄ N-benzoate, _{(C 2 H 5) 4 N} -phta Quaternary ammonium salts such as ate, lithium stearyl sulfonate, lithium octyl sulfonate, organic ion salts such as dodecylbenzene lithium sulfonate are exemplified.

  The ionic compound can be used by dissolving in an organic solvent or the like. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and the like. Chain esters such as methyl acetate and methyl butyrate; ethers such as tetrahydrofuran or derivatives thereof, 1,3-dioxane, 1,2-dimethoxyethane, methyl diglyme; nitriles such as acetonitrile and benzonitrile Dioxalane or a derivative thereof; sulfolane, sultone or a derivative thereof alone or a mixture of two or more thereof may be added. However, it is not limited to these. By adding such an organic solvent, battery characteristics such as cycle characteristics and stability can be improved.

  The electrolytic solution may be injected after the separator of the present invention is sandwiched between electrodes or stacked or wound. As the injection method, it is possible to inject at normal pressure, but a vacuum impregnation method or a pressure impregnation method may be used.

  The following examples illustrate the present invention in more detail.

  Synthesis of 2-methyl-thioacrylic acid S- [5- (2-methyl-acryloylsulfanyl)-[1,2,5] thiadiazol-2-yl] ester (hereinafter referred to as “MDM”) was performed as follows. did.

As shown in the following chemical reaction formula, 600 mg (4 mmol) of 2,5-dimercapto-1,3,4-thiadiazole was placed in a reaction tank A, and 100 ml of dry tetrahydrofuran was added and dissolved. This solution was cooled to −78 ° C. using a cooling bath, and 5.57 ml (8.8 mmol) of a 1.58M hexane solution of n-butyllithium was added dropwise thereto, followed by further stirring for 1 hour.

  To the reaction vessel B, 0.86 ml (8.8 mmol) of methacryloyl chloride was added, and 70 ml of dry tetrahydrofuran was added and dissolved. This solution was cooled to −78 ° C. using a cooling bath and dropped into the reaction vessel B using a transfer tube. The mixture was stirred for 1 hour while maintaining the temperature at −78 ° C., the cooling bath was removed, and stirring was continued for 1 hour at room temperature. The reaction was stopped by adding water thereto and extracted with diethyl ether. The obtained diethyl ether layer was washed with water, a saturated aqueous sodium hydrogen carbonate solution, and a saturated saline solution in this order. MDM was obtained by filtering off organic substances not dissolved in diethyl ether and removing diethyl ether from the filtrate under reduced pressure.

(Production of electrode material for electrochemical device and electrode for electrochemical device)
0.0509 g of MDM, 0.2 g of carbon material (manufactured by Lion Corporation, trade name: Ketjen Black, product number: EC600JD) and 0.0111 g of α, α′-azobisisobutyronitrile were weighed out, 0 0.5 ml of tetrahydrofuran was added and mixed. Tetrahydrofuran was removed by heating at 60 ° C., and MDM was crosslinked by heating at 130 ° C. for 2 hours under an argon atmosphere. The resulting MDM- by kneading a Ketjen chain down black composite powder 0.2583g polytetrafluoroethylene 0.0506G, was molded into a sheet having a thickness of 150 [mu] m. The obtained sheet was punched into a size of 15 mm × 15 mm and pressed onto an aluminum expanded current collector to obtain a working electrode. On the other hand, 20 mm × 20 mm metal lithium was crimped to a nickel mesh to make a counter electrode. A power generating element was constructed by laminating in order of working electrode / polyethylene microporous membrane (thickness 25 μm) / counter electrode, and the power generating element was covered with a metal resin composite film as an exterior material. As the nonaqueous electrolyte, an electrolytic solution in which LiPF ₆ was dissolved at a concentration of 1 mol in a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 was used. The peripheral part of the exterior material was sealed by heat sealing. Thus, the battery of the present invention was produced.

Cyclic voltammetry (CV) measurement was performed using the battery of the present invention. The lower limit on the scanning potential + 2 and ~ + 4 V, was subjected to linear scan of a few cycles, redox peaks were observed. The results are shown in FIG.

  Since the electrode material for electrochemical devices of the present invention is characterized by being obtained by crosslinking, it can be very easily processed into an electrode for electrochemical devices in order to obtain sufficient characteristics. That is, in the electrode material of the present invention, the organic sulfur compound having a thiomethacrylate group that is in a state before crosslinking can be dissolved in a general solvent. Therefore, the organic sulfur compound having a thiomethacrylate group can be thinly applied in a state where it is dissolved in a solvent. After application, the electrode material for an electrochemical device of the present invention insoluble in a solvent is obtained by crosslinking. In this way, the electrode material for an electrochemical device of the present invention in which the electrode material for an electrochemical device of the present invention is processed into a thin film state can be produced very easily. Such characteristics cannot be realized with electrode materials such as oxide-based active materials and carbon materials. This has the potential to be immeasurable as an electrode material for electrochemical devices that require high rate discharge characteristics.

It is a current-voltage characteristic view of the battery of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode collector 2 Positive electrode 3 Electrolyte and separator 4 Negative electrode 5 Negative electrode collector 6 Exterior material 7 Terminal

Claims (4)

Obtained by crosslinking, electrode for an electrochemical device material comprising an organic sulfur compound containing no SS bond. The electrode material for an electrochemical device according to claim 1, wherein an organic sulfur compound having a thiomethacrylate group is crosslinked. The electrode material for electrochemical devices according to claim 1 or 2, which has a molecular structure represented by the following (Chemical formula 1).
An electrochemical device comprising the electrode material for an electrochemical device according to claim 1 , 2 or 3.