JP4892174B2 - Organic / inorganic hybrid electrode and secondary battery using the same - Google Patents

Description

  The present invention relates to an organic / inorganic hybrid electrode and a secondary battery using the same.

  The conventional nonaqueous solvent type lithium (ion) secondary battery uses lithium cobaltate, lithium manganate or lithium nickelate as the positive electrode material, but the capacity is theoretically 137 mAh / g, 148 mAh, respectively. / G, 193 mAh / g, not exceeding 200 mAh / g. Currently, iron olivicate-based materials and vanadium oxide-based materials are also being developed as positive electrode materials. Since these materials are originally insulating, a large amount of conductive material (for example, carbon black) is added. In addition, there is a problem in cycle characteristics due to phase transformation generated by charging and discharging.

  As a positive electrode material aiming at high capacity, Non-Patent Document 1 describes an organic / inorganic hybrid positive electrode in which poly (3,4-ethylenedioxythiophene) (PEDOT) is inserted between layers of vanadium pentoxide which is a layered compound. Has been. This positive electrode exhibits a positive electrode capacity of 240 mAh / g. Non-Patent Document 2 describes a positive electrode having a capacity of 329 mAh / g by optimizing the amount of PEDOT in a positive electrode material made of vanadium pentoxide and PEDOT. However, all of these positive electrodes exhibit such a high capacity only in the first charge / discharge cycle, and the discharge potential range is as narrow as 2V.

  Some positive electrode materials in which a non-conductive organic sulfur compound is inserted between vanadium pentoxide layers are also known. Non-Patent Document 3 describes a positive electrode material in which 2,5-dimercapto-1,3,4-thiadiazole (DMcT) having a high energy density is inserted between vanadium pentoxide layers. Non-Patent Document 4 describes a positive electrode material in which polyaniline (PANI), which is a conductive polymer material, is inserted together with DMcT. However, each of the positive electrodes has a capacity of about 200 mAh / g and a discharge lower limit potential of up to 2 V at most, and has not yet reached such a large capacity and discharge potential.

  Further, Patent Document 1 proposes a technique for achieving a high capacity by mixing three materials of a conductive polymer, a nonconductive organic sulfur compound, and a metal. However, the positive electrode disclosed in Patent Document 1 uses copper as a current collector, and it is clear that the capacity of the high capacity is dominated by the Cu-Li battery rather than by the positive electrode active material.

In addition, a battery using DMcT as a positive electrode material is eluted when DMcT itself becomes a monomer, and is released from the positive electrode and reaches the negative electrode, and the proton of the mercapto group of DMcT is reduced to generate hydrogen gas. is there. In order to suppress gas generation, Patent Document 2 discloses using a lithium salt instead of DMcT. However, the initial capacity of the positive electrode was 140 mAh / g, and after 200 cycles of charge / discharge, the capacity had dropped to 80 mAh / g.
J. Mater. Chem. 2001, 11, 2470-2475 Electrochemistry Communication 4 (2002) 384-387 Langmuir 1999, 15, 669-973 Journal of Power Sources 103 (2002) 273-279 Japanese Patent Laid-Open No. 10-32217 JP 2000-82468 A

  Accordingly, an object of the present invention is to provide an organic / inorganic hybrid electrode that can simultaneously achieve high capacity and high cycle characteristics, and a secondary battery using the same.

As a result of diligent research, the present inventors have found that a layered compound having an oxidizing property such as vanadium pentoxide (V ₂ O ₅ ) and a sulfur-containing conductive polymer having a redox activity such as PEDOT together with DMcT. It was found that by inserting a non-conductive organic sulfur compound, a high capacity and a high cycle characteristic that could not be achieved at the same time can be achieved at the same time. The present invention is based on such knowledge.

  That is, according to one aspect of the present invention, a conductive substrate and an electrode material layer formed on the surface of the conductive substrate are provided, and the electrode material includes Group V elements and Group VI elements of the periodic table. A layered compound of at least one element selected from the group consisting of: at least one non-conductive organic sulfur compound having redox activity; and at least one sulfur-containing conductive polymer having redox activity. An organic-inorganic hybrid electrode is provided in which the polymer and the organic sulfur compound are inserted between layers of the layered compound.

  According to another aspect of the present invention, a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode are provided, and the positive electrode is constituted by the hybrid electrode of the present invention. A secondary battery is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the organic-inorganic hybrid electrode which can achieve a high capacity | capacitance and a high cycle characteristic simultaneously, and a secondary battery using the same are provided.

Hereinafter, the present invention will be described in more detail.
The organic / inorganic hybrid electrode of the present invention has a layer of an electrode material on the surface of a conductive substrate. The electrode material comprises at least one layered compound of Group V elements and / or Group VI elements of the periodic table, at least one non-conductive organic sulfur compound having redox activity, and at least one type having redox activity. An organic-inorganic hybrid (composite) material containing a sulfur-containing conductive polymer. The sulfur-containing conductive polymer and the organic sulfur compound are inserted between layers of the layered compound.

  In the present invention, the substrate (current collector) that supports the electrode material layer is a conductive substrate that exhibits conductivity at least on the surface in contact with the electrode material layer of the present invention. The substrate can be formed of a conductive material such as metal, conductive metal oxide, or conductive carbon, but is preferably formed of copper, gold, aluminum, an alloy thereof, or conductive carbon. Alternatively, the substrate can also be formed by coating a substrate body formed of a nonconductive material with these conductive materials.

  In the present invention, at least one layered compound of Group V element and / or Group VI element in the periodic table is selected from the group consisting of oxides and sulfides of Group V element and Group VI element. Can do. The layered compound is preferably an oxide or sulfide of vanadium, niobium or tantalum, and particularly preferably vanadium pentoxide. The layered compounds can be used alone or in combination. An oxidizable layered compound such as an oxide or sulfide is a monomer that forms a sulfur-containing conductive polymer when it is formed by polymerization of a sulfur-containing conductive polymer between layers of the layered compound described in detail below. As a result, the monomer undergoes oxidative polymerization to form a sulfur-containing conductive polymer.

The at least one non-conductive organic sulfur compound having redox activity used in the present invention is an organic compound containing sulfur and includes an organic compound having a thiolate group or a thiol group. In the present invention, for example, 2-mercaptoethyl ether, 2-mercaptoethyl sulfide, 1,2-ethanediol, tetrathioethylenediamine, N, N′-dithio-N, N′-dimethylethylenediamine, trithiocyanuric acid, 2,4 -Dithiopyridine, 4,5-diamino-2,6-dimethylmercaptopyrimidine, N, N'-dimercaptopiperazine, 2,5-dimercapto-1,3,4-thiadiazole (DMcT), etc. can be used. Furthermore, the following formulas (1) to (5):

The compound shown by can also be used. These organic sulfur compounds may be in the form of oligomers or polymers. Among these organic sulfur compounds, secondary batteries having an electrode formed using DMcT as a positive electrode, particularly lithium secondary batteries, exhibit particularly excellent charge / discharge characteristics.

The sulfur-containing conductive polymer used in the present invention has redox activity and contains sulfur. A polythiophene compound can be used as such a sulfur-containing conductive polymer. The polythiophene compound has the following formula (I):

(Here, R ¹ and R ² are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms, or bonded to each other and optionally substituted alkylene group or 1 , 2-cyclohexyne group may be formed), and a polythiophene compound having a repeating unit represented by Among these, poly (3,4-ethylenedioxythiophene) (PEDOT) is particularly preferable. These polythiophene compounds have the following formula (II):

(Here, R ¹ and R ² have the same meaning as R ¹ and R ² in formula (I)), and can be obtained by polymerization of a thiophene compound (monomer). As the thiophene compound represented by the formula (II), 3,4-ethylenedioxythiophene (EDOT) is particularly preferable.

  The electrode material of the present invention preferably contains an organic sulfur compound in a proportion of 0.5 to 20 parts by weight and a sulfur-containing conductive polymer in a proportion of 1 to 30 parts by weight per 100 parts by weight of the layered compound. When the amount of the organic sulfur compound is less than 0.5 parts by weight, the capacity improvement effect is hardly obtained, and when it exceeds 20 parts by weight, the conductivity is lowered and the organic sulfur compound is taken in between the layers of the layered compound. Elution is not complete, and there is a possibility that gas is generated by the reaction and cycle characteristics are deteriorated. Further, if the amount of the sulfur-containing conductive polymer is less than 1 part by weight, the conductivity cannot be maintained, and if it exceeds 30 parts by weight, the sulfur-containing conductive polymer cannot be taken in between the layers of the layered compound and the capacity is increased. Shows a downward trend. More preferably, the electrode material of the present invention contains 1 to 10 parts by weight of the organic sulfur compound and 5 to 20 parts by weight of the sulfur-containing conductive polymer per 100 parts by weight of the layered compound.

  The electrode material of the present invention preferably contains conductive particles in addition to the layered compound, organic sulfur compound and sulfur-containing conductive polymer. The conductive particles improve the conductivity of the electrode material of the present invention. Examples of conductive particles include conductive carbon (conductive carbon black such as ketjen black), copper, iron, silver, nickel, palladium, gold, platinum, indium, tungsten and other metals, indium oxide, oxidation Conductive metal oxides such as tin. These conductive particles are preferably contained in a proportion of 1 to 30% by weight of the total amount of the layered compound, organic sulfur compound and sulfur-containing conductive polymer.

  The electrode material of the present invention suspends a layered compound, a monomer corresponding to a sulfur-containing conductive polymer, and an organic sulfur compound in water, a mixed solvent of water and alcohol (methanol, ethanol, etc.), and the suspension It is preferable that the monomer is produced by subjecting it to conditions under which the monomer is polymerized. Usually, the polymerization can be carried out by heating the suspension under reflux for about 12 hours or more. When the layered compound is an oxide, oxygen gas can be supplied to the suspension during the polymerization in order to prevent oxygen from escaping from the layered compound. The monomer corresponding to the sulfur-containing conductive polymer polymerizes between the layers of the layered compound, and thus exists between the layers of the layered compound. Moreover, an organic sulfur compound can also be inserted between the layered compounds and polymerized between the layered compounds to form a polymer.

  The electrode material thus obtained is dried, mixed with a binder such as polyvinylidene fluoride, preferably with conductive particles, and coated on the electrode substrate (current collector), whereby the organic / inorganic hybrid of the present invention. An electrode can be produced.

  In the present invention, the electrode material layer preferably has a thickness of 10 to 100 μm.

In the electrode material of the present invention, since the sulfur-containing conductive polymer is inserted between the layers of the layered compound, the capacity of the insulating layered compound can be maximized by the sulfur-containing conductive polymer, The phase transformation of the crystal structure of the layered compound can be controlled. The suppression of the phase transformation of this crystal structure is due to the fact that the sulfur-containing conductive polymer has a part extending from the layer of the layered compound to the outside, and the extended part fixes the crystal structure of the sulfur-containing conductive polymer to some extent. It can be said that. Furthermore, in the electrode material of the present invention, the discharge potential range can be expanded by utilizing the redox capacity of an insulating (non-conductive) organic sulfur compound. In addition, since the organic sulfur compound is also inserted between the layers of the layered compound, the elution of the organic sulfur compound itself can be controlled, and even if the organic sulfur compound contains a mercapto group, it is a non-conductive material that has become a polymer. Even if the organic sulfur compound is made into a monomer, elution of the monomer can be suppressed, and H ₂ gas generated by reduction of the proton of the mercapto group on the negative electrode can be reduced. Thus, the electrode material of the present invention can simultaneously achieve a high capacity and a high cycle characteristic, and the discharge lower limit voltage is 2 V or less. The electrode material of the present invention has at least one peak at a diffraction angle (2θ) of 10 ° or less in the X-ray diffraction pattern.

  The hybrid electrode of the present invention is preferably used as a positive electrode of a secondary battery, particularly as a positive electrode of a lithium secondary battery. The secondary battery includes a positive electrode and a negative electrode, and an electrolyte layer is disposed between them. In the lithium secondary battery, the negative electrode is preferably formed of a lithium-based material. Examples of such lithium-based materials include lithium-based metal materials such as metallic lithium and lithium alloys (for example, Li-Al alloys), intermetallic compound materials of metals such as tin and silicon, and lithium nitride. Examples of the lithium compound or lithium intercalation carbon material can be given. The lithium-based metal material is preferably used in the form of a foil in terms of reducing the weight of the battery.

In the lithium secondary battery, as electrolyte, CF ₃ SO ₃ Li, C ₄ F ₉ SO ₈ Li, (CF ₃ SO ₂ ) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, LiBF ₄ , LiPF ₆ , LiClO _{4 are used.} Lithium salts such as can be used. The solvent for dissolving these electrolytes is preferably a non-aqueous solvent. Non-aqueous solvents include chain carbonates, cyclic carbonates, cyclic esters, nitrile compounds, acid anhydrides, amide compounds, phosphate compounds, amine compounds, and the like. Specific examples of the non-aqueous solvent include ethylene carbonate, diethyl carbonate (DEC), propylene carbonate, dimethoxyethane, γ-butyrolactone, n-methylpyrrolidinone, N, N′-dimethylacetamide, acetonitrile, or propylene carbonate and dimethoxyethane. And a mixture of sulfolane and tetrahydrofuran. The electrolyte layer interposed between the positive electrode and the negative electrode may be a solution of the above electrolyte in a non-aqueous solvent or a polymer gel (polymer gel electrolyte) containing this electrolyte solution.

  Hereinafter, the present invention will be further described by examples.

Example 1
Mixing 2 g of vanadium pentoxide, 1 g of 3,4-ethylenedioxythiophene (EDOT) and 0.3 g of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) in a 1: 1 volume ratio of water and ethanol The desired organic / inorganic hybrid electrode material was synthesized by suspending in a solvent and heating with stirring for 12 hours under reflux. After drying this hybrid electrode material, it is mixed with conductive carbon black in an amount corresponding to 25% by weight and polyvinylidene fluoride (PVDF) (binder) in an amount corresponding to 5% by weight, and N-methylpyrrolidone as a solvent. After slurrying using (NMP), a positive electrode was produced by coating on an aluminum foil by a doctor blade method. Using this positive electrode, as the electrolytic solution, a solution containing LiBF ₄ at a concentration of 1M in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1: 3 was used, and metallic lithium was used for the negative electrode. A lithium secondary battery was assembled, charge / discharge evaluation was performed with 0.1 C discharge, and the amount of gas generated after 100 cycles was also measured.

  The results are shown in FIG. 1 and FIG. FIG. 1 shows the relationship between the discharge capacity per gram of electrode active material (vanadium pentoxide, PEDOT and DMcT) and voltage, and FIG. 2 shows the relationship between the discharge capacity per gram of electrode active material and the number of cycles. Show. As can be seen from the results shown in FIG. 1 and FIG. 2, the capacity per active material exceeded 400 mAh / g at a potential of 1 V cut at 0.1 C discharge, and this capacity decrease was hardly seen even after 100 cycles. In the subsequent 0.05 C and 1 V, a capacity of 600 mAh / g per active material was shown. Further, there was no hydrogen generation after 100 cycles. The total gas generation amount was 0.8 mL.

Conventional Example 1
The positive electrode material of Conventional Example 1 was synthesized by suspending 2 g of vanadium pentoxide and 1 g of EDOT in water and heating them under reflux for 12 hours while stirring. Using this positive electrode material, a secondary battery was assembled in the same manner as in Example 1, and charge / discharge evaluation was performed. The results are shown in FIG.

  As can be seen from the results shown in FIG. 3, the initial characteristics were good at about 500 mAh / g per active material (vanadium pentoxide and PEDOT) at 0.1 C discharge and 1 V cut, but the cycle characteristics were significantly reduced. It has been shown.

Conventional example 2
The positive electrode material of Conventional Example 2 was synthesized by suspending 2 g of vanadium pentoxide and 0.3 g of DMcT in water, and heating under reflux for 12 hours with stirring. Using this positive electrode material, a secondary battery was assembled in the same manner as in Example 1, and charge / discharge evaluation was performed. The results are shown in FIG. Here, the active materials are vanadium pentoxide and DMcT.

  As can be seen from the results shown in FIG. 4, the initial characteristics were only about 350 mAh / g with 0.1 C discharge and potential 1 V cut, and the cycle characteristics were also significantly reduced.

  The X-ray diffraction (XRD) patterns of the positive electrode materials of Example 1 and Conventional Examples 1 and 2 are shown in FIG. In these XRD patterns, in addition to the vanadium pentoxide pattern, there is a peak on the low-angle side, and there is a portion where the organic substance is inserted and the layer of vanadium pentoxide is 10 mm or more. It was done.

  In addition, vanadium was removed from the positive electrode materials of Example 1 and Conventional Examples 1 and 2, and only the organic matter was taken out and the IR spectrum was measured. The results are shown in FIG. As can be seen from the results, the organic substances inserted between the layers were PEDOT (Conventional Example 1), poly DMcT (Conventional Example 2), and their composite polymers (Example 1).

Conventional example 3
DMcT and PANI were mixed with conductive carbon black in an amount corresponding to 25% by weight thereof, and polyvinylidene fluoride (PVDF) in an amount corresponding to 5% by weight, and a slurry using N-methylpyrrolidone (NMP) as a solvent. Then, coating was performed on the Al foil by the doctor blade method to produce a positive electrode. Using this positive electrode, a lithium secondary battery was assembled in the same manner as in Example 1, charge / discharge evaluation was performed with 0.1 C discharge, and the amount of gas generated after 100 cycles was also measured. As a result, the generation amount of hydrogen gas was 1.7 mL, the total generation amount of gas was 7.8 mL, and it was shown that 10 times as much gas was generated as compared with Example 1.

Conventional example 4
According to JP 2000-82468, a dilithium salt of DMcT and PANI are mixed with conductive carbon black in an amount corresponding to 25% by weight and polyvinylidene fluoride (PVDF) in an amount corresponding to 5% by weight, and a solvent. As a slurry using NMP, a positive electrode was prepared by coating on an Al foil by the doctor blade method. Using this positive electrode, a lithium secondary battery was assembled in the same manner as in Example 1, charge / discharge evaluation was performed with 0.1 C discharge, and the amount of gas generated after 100 cycles was also measured. As a result, as described in JP-A-2000-82468, the gas generation amount was small (hydrogen gas generation amount 0.2 mL; total gas generation amount 1.0 mL), but the initial characteristics were JP-A 2000-82468. It was about 140 mAh / g described in the publication.

The graph which shows the relationship between the discharge capacity per gram of electrode active materials of the electrode material of Example 1, and a voltage. The graph which shows the relationship between the discharge capacity per gram of electrode active materials of the electrode material of Example 1, and the number of cycles. The graph which shows the relationship between the discharge capacity per gram of electrode active materials of the electrode material of the prior art example 1, and the number of cycles. The graph which shows the relationship between the discharge capacity per gram of electrode active materials of the electrode material of the prior art example 2, and a cycle number. The figure which shows the X-ray-diffraction pattern of the electrode material of Example 1 with that of the prior art example 1 and the prior art example 2. FIG. The figure which shows IR spectrum of the electrode material of Example 1 with that of the prior art example 1 and the prior art example 2. FIG.

Claims (8)

A conductive substrate and an electrode material layer formed on the surface of the conductive substrate, wherein the electrode material is at least one layer selected from the group consisting of oxides and sulfides of vanadium, niobium and tantalum A non-conductive organic sulfur compound comprising a compound, 2,5-dimercapto-1,3,4-thiadiazole, and at least one sulfur-containing conductive polymer having redox activity, per 100 parts by weight of the layered compound, Including 0.5 to 20 parts by weight of the non-conductive organic sulfur compound and 1 to 30 parts by weight of the sulfur-containing conductive polymer, the sulfur-containing conductive polymer and the organic sulfur compound are provided between the layered compounds. An organic-inorganic hybrid electrode for a positive electrode of a lithium secondary battery, wherein the organic-inorganic hybrid electrode is inserted into a lithium secondary battery .   The hybrid electrode according to claim 1, wherein the layered compound contains vanadium pentoxide.   3. The hybrid electrode according to claim 1, wherein the sulfur-containing conductive polymer is polymerized from a corresponding monomer between layers of the layered compound in the presence of the organic sulfur compound. .   The hybrid electrode according to claim 1, wherein the sulfur-containing conductive polymer contains a polythiophene compound. The polythiophene compound is represented by the following formula (I):

(Here, R ¹ and R ² are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms, or bonded to each other and optionally substituted alkylene group or 1 , 2-cyclohexyne group may be formed), and the hybrid electrode according to claim 4. The polythiophene compound is represented by the following formula (II):

(Here, R ¹ and R ² are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms, or bonded to each other and optionally substituted alkylene group or 1 The hybrid electrode according to claim 4, wherein the hybrid electrode is obtained by polymerization of a thiophene compound represented by (2), which may form a 2-cyclohexyne group).   The hybrid electrode according to claim 1, wherein the electrode material further includes conductive particles. A positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode are provided, and the positive electrode is constituted by the hybrid electrode according to any one of claims 1 to 7. Lithium secondary battery.

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