JP3444463B2 - Electrode containing organic disulfide compound and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite electrode containing an organic disulfide compound used for electrochemical devices such as batteries, electrochromic display devices, sensors, and memories, and a method for producing the same.

[0002]

2. Description of the Related Art Since conductive polyacetylene was discovered in 1971, when a conductive polymer was used as an electrode material,
Conductive polymer electrodes are being actively studied because electrochemical devices such as lightweight, high-energy density batteries, large-area electrochromic devices, and biochemical sensors using microelectrodes can be expected. Since polyacetylene is unstable and impractical as an electrode, other π-electron conjugated conductive polymers have been studied, and relatively stable polymers such as polyaniline, polypyrrole, polyacene, and polythiophene have been developed. Lithium secondary batteries used for the positive electrode have been developed. The energy density of these batteries is said to be 40-80 Wh / kg.

Recently, an organic disulfide compound has been proposed in US Pat. No. 4,833,048 as an organic material which can be expected to have a higher energy density. The compound is most easily is M ⁺ - ^over S-R-S ^{chromatography} -M ⁺ and represented (R is an aliphatic or aromatic organic group, S is sulfur, M ⁺
Is a proton or metal cation). The compounds bind to each other via an S-S bond by the electrolytic oxidation, M ⁺ - ^over S-R-S-S- R-S-S-R-S ^{chromatography} -M ⁺ polymer shaped like a Become The polymer thus formed returns to the original monomer by electrolytic reduction. A metal-sulfur secondary battery combining a metal M for supplying and trapping cations (M ⁺ ) and an organic disulfide compound has been proposed in the aforementioned U.S. Patent. At 150 Wh / kg or more, an energy density comparable to or higher than that of a normal secondary battery can be expected.

[0004]

Such an organic disulfide compound has a problem that the electrode capacity gradually decreases when oxidation-reduction (charge / discharge) is repeated. When the organic disulfide compound is oxidized (charged), a polydisulfide compound having electrical insulation and poor ion conductivity is generated. Polydisulfide compounds have poor solubility in electrolytes. On the other hand, an organic disulfide monomer generated when the polydisulfide compound is monomerized by reduction (discharge) has high solubility in an electrolyte. Therefore, when oxidation and reduction are repeated, a part of the monomerized disulfide is dissolved in the electrolyte, and the dissolved monomer is polymerized in a place different from the place originally located in the electrode. The polydisulfide compound polymerized and separated from the conductive agent such as carbon is isolated from the electron / ion conduction network in the electrode and does not participate in the electrode reaction.

[0005] When oxidation and reduction are repeated, the number of isolated polydisulfide compounds increases, and the capacity of the battery gradually decreases. In addition, highly soluble organic disulfide monomers are
It is easy to move and dissipates from the positive electrode into the separator or electrolyte, and further to the negative electrode side. For this reason, a battery using an electrode containing an organic disulfide compound as a positive electrode has a drawback that the charge / discharge efficiency is reduced or the charge / discharge cycle life is shortened. An object of the present invention is to solve such a problem and to provide an electrode that does not impair the feature of the high energy density of the organic disulfide compound, and that maintains high charge-discharge efficiency and obtains good charge-discharge cycle characteristics. And

[0006]

In the electrode of the present invention, a sulfur-sulfur bond is cleaved by electrolytic reduction to form a sulfur-metal ion (including proton) bond, and a sulfur-metal ion bond is formed by electrolytic oxidation. Characterized by containing a complex of an organic disulfide compound that regenerates a sulfur-sulfur bond and a nickel ion. The method for producing an electrode containing an organic disulfide compound according to the present invention comprises a step of dissolving the organic disulfide compound in NR-2-pyrrolidone (R is a hydrogen atom or an alkyl group), and adding polyaniline to the obtained solution to form a solution. A, a step of dissolving a nickel salt in NR-2-pyrrolidone to obtain a solution B,
And a solution B, and a step of heating the obtained mixture in an inert gas atmosphere or in a vacuum.
A lithium secondary battery according to the present invention includes the above electrode as a positive electrode, a nonaqueous electrolyte, and a negative electrode. As the negative electrode, an electrode using lithium as an active material, such as lithium metal, an alloy containing lithium, and a lithium-containing composite oxide through which lithium can enter and exit reversibly, is used.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The electrode of the present invention contains at least a complex of an organic disulfide compound and a nickel ion. In this complex, an organic disulfide compound is coordinated to a nickel ion as a ligand. The organic disulfide compound forming a complex includes a compound represented by the general formula (R
(S) _y ) The compound represented by _n can be used. R
Is an aliphatic group or an aromatic group, S is sulfur, y is an integer of 1 or more, and n is an integer of 2 or more. HSCH ₂ CH ₂ S
H, dithioglycol (hereinafter referred to as DTG), C ₂ N ₂ S (SH) ₂ , 2,5-dimercapto-1,3,4-thiadiazole (hereinafter referred to as DMcT), C S-Triazine-2 represented by ₃ H ₃ N ₃ S ₃
4,6-trithiol (hereinafter referred to as TTA), C ₆ H ₆
7-methyl-2,6,8-trimercaptopurine (hereinafter referred to as MTMP) represented by N ₄ S ₃ or C ₄ H ₆
For example, 4,5 diamino-2,6-dimercaptopyrimidine (hereinafter, referred to as DDPy) represented by N ₄ S ₂ is used. In each case, commercially available products can be used as they are. Further, a polymer containing a dimer or a tetramer of an organic disulfide compound obtained by polymerizing these organic disulfide compounds by a chemical polymerization method using an oxidizing agent such as iodine, potassium ferricyanide, or hydrogen peroxide, or by an electrolytic oxidation method is used. Can be.

[0008] Nickel ions forming a complex include:
A complex (hereinafter, referred to as SSNi) of an organic disulfide compound and a nickel ion that can use a divalent nickel ion can be synthesized, for example, as follows. DMc as an organic disulfide compound
Although the case where T is used will be described, it goes without saying that an organic disulfide compound other than DMcT can be synthesized by the same method.

0.76 g (6 mmol) of iodine in 50 m
The solution obtained by dissolving in 1
1.43 g (6 mmol) of water salt (NiCl ₂ .6H ₂ O)
Is added to a solution obtained by dissolving in 25 ml of ethanol.
The obtained mixed solution is added to a solution obtained by dissolving 1.8 g (12 mmol) of DMcT in 50 ml of ethanol. Immediately, a red-orange complex is formed as a solid. The solid matter of the formed complex is separated by centrifugation, and the solid matter obtained by filtration is washed several times with hot alcohol, finally washed with ethyl ether, and dried under vacuum to distribute two molecules of DMcT to nickel ions. Complex, Ni
(C ₂ HN ₂ S ₃ ) ₂ is obtained. Ni (C ₂ H ₂ S ₂ ) ₂ when the organic disulfide compound is DTG, Ni ₃ (C ₃ N ₃ S ₃ ) ₂ when TTA, and Ni when MTMP
(C ₆ H ₄ N ₄ S ₃ ) ₂ , Ni (C ₄ H ₄
N ₄ S ₂ ) ₂ is obtained.

[0010] SSNi of an organic disulfide compound and monovalent nickel ions can be synthesized by mixing an ethanol solution of nickel chloride reduced with SO ₂ and an ethanol solution of an organic disulfide compound.

[0011] SSNi can be used as an electrode by pressing powder as it is. A conductive material such as a conductive polymer powder such as polyaniline, acetylene black, metal nickel powder or the like can be mixed with the complex and used as an electrode. In particular, in a positive electrode containing a complex and polyaniline, polyaniline not only acts as a conductive material, but also acts as a ligand for nickel ions, and furthermore, an organic disulfide compound acts as a dopant for polyaniline to form a complex, Higher-order metal-polymer complexes (hereinafter, SSNiPAn) in which organic disulfide compound molecules, polyaniline molecules, and nickel ions interact three-dimensionally.
) Is formed. The metal polymer complex holds the organic disulfide compound in the electrode more strongly than the complex of the organic disulfide compound and the nickel ion, so that high reversibility is obtained. The compounding ratio of SSNi to polyaniline is preferably 0.1 to 10 polyaniline molecules per 1 molecule of the organic disulfide compound.

As the polyaniline used for SSNiPAN, those obtained by polymerizing aniline or a derivative thereof by a chemical polymerization method or an electrolytic polymerization method are used. In particular, undoped reducible polyaniline is preferred because it effectively captures organic disulfide monomers.
The degree of reduction (RDI) of polyaniline is determined by converting polyaniline to N
In the electronic absorption spectrum of a solution in which a trace amount is dissolved in -methyl-2-pyrrolidone, the intensity of the absorption peak due to the para-substituted benzene structure appearing on the short wavelength side near 340 nm (I
₃₄₀ ) and the intensity (I ₆₄₀ ) of the absorption peak due to the quinone diimine structure appearing on the long wavelength side near 640 nm, which is represented by RDI = I ₆₄₀ / I ₃₄₀ . RDI is 0.5
The following polyaniline is preferably used. The degree of undoping of polyaniline is represented by conductivity. Conductivity, 10 ^@ 5 S / cm or less of the polyaniline is preferably used.

An electrode containing SSNiPAn can be obtained by mixing SSNi powder and polyaniline powder. In particular, when NR-2-pyrrolidone (hereinafter, referred to as NAP) is used as a solvent, an organic disulfide compound,
An electrode in which nickel ions and polyaniline are uniformly blended at the molecular level can be obtained. First, an organic disulfide compound is dissolved in NR-2-pyrrolidone to obtain a solution. A polyaniline powder is added to this solution to obtain a solution A. On the other hand, a nickel salt is dissolved in NR-2-pyrrolidone to obtain a solution B. These solution A and solution B are mixed,
The mixture is preferably applied to a suitable conductive support, and heated in an inert gas atmosphere or in vacuum to obtain an electrode containing SSNiPAn.

As the NAP used for the production of an electrode containing SSNiPAn, a commercially available reagent can be used as it is, or a NAP having a water content reduced to 20 ppm or less by a zeolite adsorbent can be used. For example, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-butyl-2-pyrrolidone, and the like in which R is a hydrogen atom, a methyl group, an ethyl group, or a butyl group can be used.

An organic polymer binder such as polyvinylpyrrolidone, polyvinyl alcohol and polyvinylpyridine may be added to the electrode of the present invention. Further, LiBF ₄ , LiPF ₆ , LiAsF ₆ ,
Lithium salts such as LiClO ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ are dissolved, and this organic electrolyte is gelled with a polymer compound such as polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride, or polyacrylic acid. The gel electrolyte obtained by the above can be added to and mixed with the electrode material.

[0016]

【Example】

Example 1 1 g of Ni (C ₂ HN ₂ S ₃ ) ₂ powder, a complex synthesized from nickel chloride hexahydrate and DMcT, and 0.05 g of acetylene black powder were mixed. On the other hand, a mixed solvent of propylene carbonate and ethylene carbonate is L
The electrolyte solution in which iBF ₄ was dissolved was gelled with polyacrylonitrile, and the gel electrolyte was diluted with acetonitrile.
1 g of this diluted gel electrolyte solution was added to the above mixture, and the resulting slurry was applied on a porous carbon sheet having a thickness of 5 μm and a size of 5 × 10 cm made of fluororesin and acetylene black. By heating, an electrode A having a thickness of 75 μm including the carbon sheet was obtained. The gel electrolyte solution was composed of 10.5 g of propylene carbonate and 7.9 g of ethylene carbonate.
2.3 g of LiBF ₄ was dissolved in a mixed solvent obtained by mixing the above, 3 g of polyacrylonitrile powder was added to the obtained organic electrolyte, and the mixture was heated to 100 ° C. to dissolve the polyacrylonitrile powder, and then 20 g of acetonitrile was added. It is diluted.

Comparative Example 1 1 g of DMcT powder, 0.05 g of acetylene black powder, and 1 g of gel electrolyte solution
Was mixed, and the resulting slurry was applied on a porous carbon film and heated at 60 ° C. in vacuum to obtain an electrode A ′ having a thickness of 82 μm including a carbon sheet.

Example 2 Nickel chloride hexahydrate and TTA
1 g of Ni ₃ (C ₃ N ₃ S ₃ ) ₂ powder synthesized from
0.05 g of acetylene black powder and 1 g of the gel electrolyte solution used in Example 1 were mixed. The obtained slurry is made of a fluororesin and acetylene black having a thickness of 50.
After coating on a porous carbon sheet having a size of 5 μm and a size of 5 × 10 cm, an electrode B having a thickness of 80 μm including the carbon sheet was obtained by vacuum heating at 60 ° C.

Comparative Example 2 1 g of DMcT powder, 0.05 g of acetylene black powder, and 1 g of gel electrolyte solution
Was mixed, and the obtained slurry was applied on a porous carbon film and heated at 60 ° C. in vacuum to obtain an electrode B ′ having a thickness of 88 μm including a carbon sheet.

Example 3 1.5 g of DMcT was dissolved in 10 g of N-methyl-2-pyrrolidone (hereinafter referred to as NMP). Nitto Denko polyaniline (trade name Anilead)
Is dedoped in an alkaline solution and reduced by hydrazine, and 1.0 g of undoped reduced polyaniline powder having a conductivity of 10 ⁻⁸ S / cm and an RDI value of 0.26 is added to the above solution, and blue is added. A green viscous DMcT-PAn-NMP solution was obtained. Next, 0.57 g of anhydrous nickel chloride was added to NM.
Dissolved in 5 g of P. This solution was added to DMcT-PAn-NM.
In addition to the P solution, a viscous ink was obtained. This ink was applied on a titanium foil current collector having a thickness of 30 μm and a size of 5 × 8 cm, and vacuum-dried at 80 ° C. for 2 hours to obtain an electrode C having a thickness of 52 μm including the titanium foil.

Comparative Example 3 A DMcT-PAn-NMP solution was applied on a titanium foil current collector and vacuum-dried at 80 ° C. for 2 hours to obtain an electrode C ′ having a thickness of 50 μm including the titanium foil. .

Example 4 1.8 g of TTA was added to NMP10
g. Nitto Denko polyaniline (trade name Anirido) dedoped in an alkaline solution, the conductivity obtained by reduction with hydrazine is 10 ^{@ 8} S / cm, RDI value 0.
28 g of the undoped reduced polyaniline powder of No. 28 was added to the solution, and a blue-green viscous TTA-PAn-NM was added.
A P solution was obtained. Next, 0.87 g of anhydrous nickel chloride was dissolved in 5 g of NMP. This solution was added to TTA-PAn-N
In addition to the MP solution, a viscous ink was obtained. This ink was applied on a titanium foil current collector having a thickness of 30 μm and a size of 5 × 8 cm, and vacuum dried at 80 ° C. for 2 hours to obtain an electrode D having a thickness of 56 μm including the titanium foil.

Comparative Example 4 A TTA-PAn-NMP solution was applied on a titanium foil current collector and vacuum dried at 80 ° C. for 2 hours to obtain an electrode D ′ having a thickness of 58 μm including the titanium foil. .

Electrode Performance Evaluation Electrodes A, B, C, D and A ', B', C ', D' obtained in Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3, 4
A positive electrode, a 0.3 mm thick metal lithium as a negative electrode, and a 0.6 mm thick gel electrolyte as a separator layer, 2 × 2
cm square batteries A, B, C, D and A ', B',
C 'and D' were constructed. The gel electrolyte is LiBF
_This was obtained by gelling 3.0 g of polyacrylonitrile with 20.7 g of a propylene carbonate / ethylene carbonate (1: 1 volume ratio) solution in which 4M was dissolved in 1M. Battery A
~ D and A '~ D' at 20 ° C at 0.2 mA
At a constant current of 4.65 to 2.0 V, and discharge capacity (unit: mA) in each charge / discharge cycle
h) was measured to evaluate the charge / discharge cycle characteristics. Table 1 shows the results. The discharge voltage of the fifth cycle of charge and discharge for the batteries A and A ', the batteries B and B', the batteries C and C ', and the batteries D and D' is shown in FIG. 1, FIG. 2, FIG. 4 and FIG.

[0025]

[Table 1]

As is clear from the above results, the batteries using the electrodes of Examples 1 to 4 according to the present invention have lower discharge capacities during the charge / discharge cycle than the batteries using the corresponding electrodes of Comparative Examples. The drop is small. Further, the battery using the electrode of the example gives a relatively flat voltage of 3.5 to 2.5 V as compared with the battery using the electrode of the comparative example.

[0027]

As described above, according to the present invention, it is possible to reduce the dissipation of the active material from the inside of the electrode during charge and discharge, and to provide a high energy density secondary battery with a small decrease in discharge capacity during charge and discharge. Can be provided. In addition, an electrode that gives a flat discharge voltage can be obtained. Although only the battery is shown in the embodiment, in addition to the battery, a biochemical sensor such as an electrochromic device having a high color development / fading speed and a glucose sensor having a fast response speed can be obtained by using the electrode of the present invention as a counter electrode. be able to. Further, an electrochemical analog memory having a high writing / reading speed can be configured.

[Brief description of the drawings]

FIG. 1 is a view showing a discharge voltage of a lithium secondary battery using an electrode A of Example 1 and an electrode A ′ of a comparative example as positive electrodes.

FIG. 2 is a view showing a discharge voltage of a lithium secondary battery using an electrode B of Example 2 and an electrode B ′ of Comparative Example as positive electrodes.

FIG. 3 is a diagram showing a discharge voltage of a lithium secondary battery using an electrode C of Example 3 and an electrode C ′ of a comparative example as positive electrodes.

FIG. 4 is a view showing a discharge voltage of a lithium secondary battery using an electrode D of Example 4 and an electrode D ′ of Comparative Example as positive electrodes.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/36-4/62 H01M 10/36-10/40 G01N 27 / 333 G02F 1/155

Claims (3)

(57) [Claims] 1. A sulfur-sulfur bond is cleaved by electrolytic reduction to produce a sulfur-metal ion (including proton) bond,
An electrode containing an organic disulfide compound, comprising a complex of nickel ion and an organic disulfide compound in which a sulfur-metal ion bond regenerates the original sulfur-sulfur bond by electrolytic oxidation. 2. A sulfur-sulfur bond is cleaved by electrolytic reduction to produce a sulfur-metal ion (including proton) bond,
An electrode containing a complex of an organic disulfide compound in which a sulfur-metal ion bond regenerates the original sulfur-sulfur bond by electrolytic oxidation and a nickel ion, and an organic disulfide compound containing polyaniline. 3. A sulfur-sulfur bond is cleaved by electrolytic reduction to form a sulfur-metal ion (including proton) bond,
A step of dissolving an organic disulfide compound in which a sulfur-metal ion bond regenerates the original sulfur-sulfur bond by electrolytic oxidation in NR-2-pyrrolidone (R is a hydrogen atom or an alkyl group), and adding polyaniline to the obtained solution Solution A
, A step of dissolving a nickel salt in NR-2-pyrrolidone to obtain a solution B, a step of mixing the solution A and the solution B, and heating the resulting mixture in an inert gas atmosphere or vacuum. A method for producing an electrode containing an organic disulfide compound, comprising the step of: