JP2000311684A - Lithium secondary battery and manufacture of its positive electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-energy density battery by forming the battery with a positive electrode, a negative electrode and a nonaqueoous electrolyte including lithium salt, and containing at least one kind of compound selected from a group of a lithium thiolic compound and a thiol compound and lithium sulfide in the positive electrode. SOLUTION: A thiol compound or a lithium thiolic compound and lithium sulfide are fixed at the molecular level to the positive electrode of a lithium secondary battery having an inorganic-organic hybrid structure made of at least one kind selected from a group of the lithium thiolic compound and the thiol compound as an active material, therefore the dissipation of the thiol compound or the lithium thiolic compound from the electrode and the isolation of simple substance sulfur can be suppressed. The battery is operated at the voltage of the thiol compound or the lithium thiolic compound while keeping a gravimetric and volumetric high capacity of the lithium sulfide. The battery preventing the reduction of its electric capacity after repeated charges/discharges and having a good charge/discharge cycle is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery containing lithium and sulfur in a positive electrode 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 have been actively studied because electrochemical devices such as light-weight, high-energy-density batteries, large-area electrochromic devices, and biochemical sensors using microelectrodes can be expected. Besides polyacetylene,
As other π-electron conjugated conductive polymers, polyaniline,
Relatively stable polymers such as polypyrrole, polyacene, and polythiophene have been developed, and lithium secondary batteries using such polymers for the positive electrode have been developed. The energy density of these batteries is said to be 40 to 80 Wh / kg.

Recently, US Pat. No. 4,833,048 has been proposed as an organic material which can be expected to have a higher energy density.
Organic disulfides have been proposed in the article. This compound, the ^{easiest, M + - - S-R} -S - represented as ^{-M +} (R is an aliphatic or aromatic organic group, S is sulfur, M ⁺
Is a proton or metal cation). This compound is bonded to each other via an SS bond by electrolytic oxidation, and is polymerized in a form such as M ^{+ --} S-R-S-S-S-R-S-S-R-S ^-- M ⁺ . I do. The polymer thus formed returns to the original monomer by electrolytic reduction. A metal-sulfur secondary battery combining a metal M that supplies and traps cations (M ⁺ ) and an organic disulfide compound has been proposed in the aforementioned U.S. Patent.

[0004] These batteries use a lithium metal negative electrode, the operating voltage of the battery is 3 to 4 V, and the energy density is 150 Wh / kg or more, so that the energy is equal to or higher than that of a normal secondary battery. Density can be expected. On the other hand, with the aim of further increasing the energy density, studies have been made to use elemental sulfur itself for the positive electrode by taking advantage of the high capacity of sulfur, and US Pat.
No. 179. This battery has an operating voltage of 2 V using a metal lithium anode, and 100 to 800 W
It is said that a high energy density of h / kg can be expected.

However, when the organic disulfide compound as described above repeatedly undergoes polymerization by electrolytic oxidation (charge) and oxidation-reduction (charge / discharge) of monomerization by electrolytic reduction (discharge), the electrode capacity is gradually reduced. There's a problem. This is thought to be due to the following. 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. For this reason, a part of the disulfide monomerized by reduction (discharge) is dissolved in the electrolyte, and the dissolved monomer is polymerized by oxidation (charging) in a place different from the place where the electrode was originally located. 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. Therefore, when redox is repeated, the number of isolated polydisulfide compounds increases, and as a result, the capacity of the battery gradually decreases. Further, the organic disulfide monomer having high solubility is easy to move and is dissipated from the positive electrode into the separator or the electrolyte and further to the negative electrode side.

As described above, a battery using an electrode containing an organic disulfide compound as a positive electrode has disadvantages such as a decrease in charge / discharge efficiency and a shortened charge / discharge cycle life. Furthermore, when lithium metal is used for the negative electrode to improve the volume energy density, dendrites are generated on the surface of the lithium metal during the charge / discharge cycle, and there is a danger of ignition due to a short circuit, etc. Or decrease.

On the other hand, when elemental sulfur is used for the positive electrode in order to increase the capacity, the operating voltage is as low as 2 V, and the charge / discharge cycle characteristics are poor. The phenomenon of charge / discharge cycle deterioration when using elemental sulfur for the positive electrode is as follows:
It is considered as follows. As for elementary sulfur, many allotropes are known. Cyclooctasulfur (S ₈ ) is known to have three types of structures, α-type (orthogonal), β-type (monoclinic), and γ-type (monoclinic). Cyclohexasulfur (S ₆ ) has a rhombohedral structure, and in addition, larger cyclic, chain-like and amorphous structures have been reported. That is, it is understood that the energy difference between these structures is small, and that the sulfur element takes various forms unstable while forming chains. When the sulfur powder in such a situation is used as a starting material for charging and discharging, and discharging (lithium insertion) and charging (lithium desorption) are repeated, the sulfur in the initial state cannot be reproduced, and the insulating sulfur is isolated. It is thought that the transfer of electrons and the insertion of lithium ions will not be performed.

[0008]

SUMMARY OF THE INVENTION The present invention reduces the dissipation and isolation of a positive electrode active material from inside a positive electrode during charge and discharge,
Maintains the voltage characteristics of lithium thiolate compounds and the high capacity characteristics of lithium sulfide, and has a flat discharge voltage of 3V class.
An object is to provide a high energy density lithium secondary battery. An object of the present invention is to provide a method for manufacturing a positive electrode that provides such a lithium secondary battery.

[0009]

The lithium secondary battery of the present invention comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte containing a lithium salt, wherein the positive electrode is selected from the group consisting of a lithium thiolate compound and a thiol compound. Or at least one compound and lithium sulfide.
Here, the lithium thiolate compound is a compound having a sulfur-lithium ion bond that generates a sulfur-sulfur bond by charging and regenerates the sulfur-lithium ion bond by discharging. In addition, the thiol compound is converted to sulfur-
A compound in which a sulfur bond is cleaved to generate a sulfur-metal ion (including proton) bond, and the sulfur-sulfur bond is regenerated by charging. The positive electrode further comprises a conductive polymer and / or
Or it is preferable to contain elemental sulfur.

[0010] The present invention provides at least one compound selected from the group consisting of a lithium thiolate compound and a thiol compound.
Disclosed is a method for producing a positive electrode for a lithium secondary battery, which comprises a step of uniformly mixing a species compound, a solvent for dissolving the compound, and lithium sulfide.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The positive electrode of a lithium secondary battery of the present invention has an inorganic-organic hybrid structure comprising lithium sulfide and at least one selected from the group consisting of a lithium thiolate compound and a thiol compound as active materials. ing. In this inorganic-organic hybrid structure, it is preferable that both active materials are uniformly mixed at a molecular level. The method for producing the positive electrode having such an inorganic-organic hybrid structure will be described in detail below. In a positive electrode having an inorganic-organic hybrid structure, a thiol compound (monomer) or a lithium thiolate compound (monomer) is fixed to lithium sulfide at the molecular level with an electrode, so that a thiol compound (monomer) or a lithium thiolate compound (monomer) is used. ) Can be suppressed from dissipating from the electrode and isolation of elemental sulfur. In addition, it can operate at the voltage of a thiol or lithium thiolate compound, while maintaining the high weight and volume capacity of lithium sulfide. Therefore, when a battery is formed using an active material uniformly mixed at the molecular level as the positive electrode, a high capacity is maintained while maintaining a voltage of 3 V class, and the electric capacity does not decrease even if charge and discharge are repeated. That is, a battery having a good charge / discharge cycle can be obtained.
In addition, when this positive electrode is used, lithium is not required for the negative electrode when the battery is constructed, so that another negative electrode can be used without using lithium metal, and there is also a problem of danger and capacity deterioration due to the use of metallic lithium. You can avoid it.

[0012] The starting material of the lithium thiolate compound
Some thiol compounds include organic disulfide compounds
Substance, organic trisulfide compound, organic tetrasulfide
And the like. These are contained in the monomer molecule.
Are different in the number of sulfur atoms
The reaction that changes between the yellow-sulfur bond and the sulfur-lithium bond
The response mechanisms are all the same. Organic disulfide compounds and
The compound represented by the general formula (R (S) y) n
Can be. R is an aliphatic group or an aromatic group, and S is
Sulfur and y are integers of 1 or more, and n is an integer of 2 or more. H
SCH_TwoCH_TwoDithioglycol represented by SH, C_TwoN_Two
S (SH)_Two2,5-dimercapto-1, represented by
3,4-thiadiazole, C_ThreeH_ThreeN_FourS_TwoS- represented by
Triazine-2,4,6-trithiol, C₆H₆N_FourS_Three
7-methyl-2,6,8-trimercaptop represented by
Lynn, C _FourH₆N_FourS_Two4,5-diamino-2,
6-dimercaptopyrimidine and the like are used. Any
Commercial products can be used as they are. Also, these
Organic disulfide compounds are converted to iodine and potassium ferricyanide.
Organic polymerized using an oxidizing agent such as aluminum or hydrogen peroxide
Compounds containing dimers and dimers of disulfide compounds are also used
Can be. Oxidizing agent for organic disulfide compound
Electrolytic oxidation without using oxidizing agent
It can also be polymerized by a method.

When these starting materials are treated with R · Li (R is an aliphatic group or an aromatic group) such as butyllithium or phenyllithium to be lithiated, a sulfur-sulfur bond is generated by a charging reaction and a discharging reaction is performed. Thus, a lithium thiolate compound that regenerates a sulfur-lithium ion bond can be obtained. In addition, even if an electrode is composed of a thiol compound and lithium sulfide, and a sulfur-lithium bond is formed at the time of the first discharge or chemical conversion treatment, the thiol compound and lithium sulfide are uniformly mixed at the molecular level. The above properties can likewise be obtained if they have an organic hybrid structure.

As lithium sulfide, Li ₂ S, Li ₂ S
_{2, Li 2 S 4, Li} 2 S 5, Li 2 S 6, Li 2 S 8, Li 2 S
There are _{12 and the} like, which can be obtained by a method such as reduction of lithium sulfate, oxidation of lithium hydrogen sulfide, and chemical conversion treatment of sulfur. Among them, Li ₂ S and Li ₂ S ₂ are known as substances which are stably obtained in a solid state. Others are generated as ions in the liquid. Also in this case, it is possible to use lithium sulfide from the starting point or a method of performing lithiation after mixing with elemental sulfur, etc., and it is possible to have an inorganic-organic hybrid structure that is uniformly mixed at the molecular level. If so, the above properties can be obtained similarly. By mixing such a thiol compound or lithium thiolate compound with lithium sulfide at a molecular level in a liquid, an inorganic-organic hybrid structure is formed. Alternatively, lithiation treatment may be performed after elemental sulfur is mixed with a thiol compound or a lithium thiolate compound in a liquid at a molecular level. When charging and discharging are performed while maintaining such a structure, dissipation and isolation of each active material can be avoided, and good charge and discharge cycle characteristics can be obtained while maintaining the respective characteristics.

The positive electrode may be mixed with a conductive polymer material. Examples of the conductive polymer material include polyaniline, polypyrrole, polyacene, polythiophene, and polyacetylene. When these conductive polymer materials are mixed with a thiol compound or a lithium thiolate compound and lithium sulfide at the molecular level, they are mixed three-dimensionally, so that higher-order inorganic materials that are more entangled with each other than before are mixed. A polymeric hybrid structure is formed. This inorganic-polymer hybrid structure is
The lithium thiolate compound and lithium sulfide are more strongly held in the electrode. Therefore, the charge / discharge cycle becomes better for both the lithium thiolate compound and lithium sulfide. In particular, polyaniline not only acts as a conductive material, but also a thiol compound or a lithium thiolate compound acts as a dopant for polyaniline to form a complex, so that a thiol compound or a lithium thiolate compound, a polyaniline molecule, and lithium sulfide are used. They can interact three-dimensionally.
As the polyaniline, 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 shown by an electronic absorption spectrum of a solution in which a small amount of polyaniline is dissolved in n-methyl-2-pyrrolidone. That is, 64
The ratio (RDI) between the intensity (I ₆₄₀ ) of the absorption peak due to the quinone diimine structure appearing on the long wavelength side near 0 nm and the intensity (I ₃₄₀ ) of the absorption peak due to the para-substituted benzene structure appearing on the short wavelength side near 340 nm = _I640 /
I ₃₄₀ ). Polyaniline having an RDI of 0.5 or less is preferably used.

To produce the positive electrode of the present invention, a lithium thiolate compound and / or a thiol compound, a solvent for dissolving the compound, and lithium sulfide are uniformly mixed. The solvent used here is preferably one that also dissolves lithium sulfide. Such solvents include tetrahydrofuran, (the R represents hydrogen or CH _3, C ₂ H _5, alkyl groups such as C ₃ H ₇₎ dimethylformamide and N-R-2-pyrrolidone is. In a preferred embodiment of the method for producing a positive electrode according to the present invention, (a) a step of dissolving at least one compound selected from the group consisting of a lithium thiolate compound and a thiol compound in NR-2-pyrrolidone; b) a step of mixing lithium sulfide with the obtained solution, and (c) a step of applying the obtained mixture on a conductive substrate and heating in an inert gas or vacuum.

In another preferred embodiment of the method for producing a positive electrode according to the present invention, (a) at least one compound selected from the group consisting of a lithium thiolate compound and a thiol compound is converted to NR-2-pyrrolidone. Dissolving, (b) mixing elemental sulfur with the obtained solution,
(C) a step of applying the obtained mixture on a conductive substrate and heating it in an inert gas or in a vacuum to produce an electrode;
And (d) lithiation of the elemental sulfur in the electrode. In still another preferred embodiment of the method for producing a positive electrode according to the present invention, (a) the thiol compound is
-Dissolving in R-2-pyrrolidone, (b) mixing lithium sulfide with the obtained solution, (c) applying the obtained mixture on a conductive substrate, and applying the mixture in an inert gas or vacuum. A step of preparing an electrode by heating; and (d) a step of subjecting the thiol compound in the obtained electrode to lithiation. In still another preferred embodiment of the method for producing a positive electrode according to the present invention, in the above embodiment, a step of adding a conductive polymer to the solution obtained in the step (a) prior to the step (b). including.

When NR-2-pyrrolidone is used as a solvent as described above, a thiol compound, a lithium thiolate compound, lithium sulfide, and polyaniline can be uniformly mixed at a molecular level. Therefore,
An electrode having a uniform composition in the form of a thin film or a large area can be easily obtained. As the NR-2-pyrrolidone, a commercially available reagent can be used as it is, or a reagent whose water content has been reduced to 20 ppm or less by a zeolite adsorbent can be used.

The positive electrode of the lithium secondary battery according to the present invention contains, in addition to the lithium thiolate compound, lithium sulfide and a conductive polymer material, an organic polymer binder such as polyvinylpyrrolidone, polyvinyl alcohol, polyvinylpyridine, and polyvinylidene fluoride. You may make it contain.
Further, a conductive material such as acetylene black or carbon black may be mixed with these materials. Further, a gel electrolyte may be contained in the electrode. This gel electrolyte is
LiBF ₄ , LiPF ₆ , LiAs are added to aprotic solvents such as propylene carbonate and ethylene carbonate.
F ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ S
An organic electrolyte solution in which a lithium salt such as O ₂ ) ₂ is dissolved is gelled with a polymer compound such as polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride, or polyacrylic acid. Further, a polymer electrolyte may be used as the non-aqueous electrolyte of the lithium secondary battery according to the present invention. As the polymer electrolyte, the above-described gel electrolyte may be used.

[0020]

Embodiments of the present invention will be described below. Example 1 2,5-dimercapto-1,3,4-thiadiazole (hereinafter abbreviated as DMcT) was lithiated by a chemical conversion treatment to obtain a lithium thiolate compound (hereinafter abbreviated as L-DMcT). This chemical conversion treatment was performed by immersing DMcT in an n-hexane solution of n-butyllithium (1.53 mol / L) for 1 hour. After this treatment, it was thoroughly washed with n-hexane. L-DMcT1.3 obtained
g, DMcT 0.2 g, and lithium sulfide (Li ₂ S)
2 g was dissolved in 5 g of tetrahydrofuran. Next, 2.3 g of LiBF ₄ was added to a mixed solvent obtained by mixing 10.5 g of propylene carbonate and 7.9 g of ethylene carbonate.
Was dissolved to prepare an organic electrolytic solution. 3 g of polyacrylonitrile powder was added to the organic electrolyte solution, heated to 100 ° C. to dissolve and gel the polyacrylonitrile, and then diluted with 20 g of acetonitrile to prepare a gel electrolyte solution. 1 g of this gel electrolyte solution, 2 g of the previously prepared tetrahydrofuran solution, and 0.05 g of acetylene black powder were mixed to obtain a mixed slurry. A 50 μm thick porous carbon sheet made of a fluororesin and acetylene black was cut into a size of 5 × 10 cm. The mixed slurry was applied to the porous carbon sheet, and then dried by heating at 60 ° C. in a vacuum. The thickness of the electrode A thus produced was 75 μm including the carbon sheet.

Comparative Example 1 1 g of the gel electrolyte solution prepared in Example 1, 1 g of DMcT powder, and 0.05 g of acetylene black powder were mixed to obtain a mixed slurry. This mixed slurry was used in Example 1
Was applied to a porous carbon sheet in the same manner as described above, and dried. The thickness of the electrode A ′ thus produced was 80 μm including the carbon sheet.

EXAMPLE 2 Lithium sulfide (Li) was added to 5 g of dimethylformamide.
Was dissolved ₂ S) 1 g of sulfur 0.7 g, further L-DMc
1.5 g of T was dissolved. Next, 2 g of this solution was mixed with 1 g of the gel electrolyte solution prepared in Example 1 together with 0.05 g of acetylene black to obtain a mixed slurry. This mixed slurry was applied to a porous carbon sheet in the same manner as in Example 1 and dried. The thickness of the electrode B thus produced was 85 μm including the carbon sheet.

Comparative Example 2 1 g of sulfur powder was dissolved in 5 g of tetrahydrofuran, and this was dissolved in 0.05 g of acetylene black powder in Example 1
Was mixed with 1 g of the gel electrolyte solution prepared in the above to obtain a mixed slurry. This mixed slurry was applied to a porous carbon sheet and dried in the same manner as in Example 1. The thickness of the electrode B ′ thus produced was 77 μm including the carbon sheet.

Example 3 1.5 g of L-DMcT used in Example 1 was
It was dissolved in 10 g of 2-pyrrolidone (hereinafter abbreviated as NMP). On the other hand, polyaniline (manufactured by Nitto Denko Corporation; trade name: Anilead, hereinafter abbreviated as PAn) was undoped in an alkaline solution, and then reduced with hydrazine to obtain undoped reduced PAn. This undoped and reduced PAn had a conductivity of 10 ^-8 S / cm and an RDI value of 0.28. 1.0 g of the undoped and reduced PAn powder was added to the solution prepared above, and a blue-green viscous (L-DMc) was added.
T) -PAn-NMP solution was obtained. Next, 2 g of lithium sulfide (Li ₂ S) was mixed with this solution to obtain a viscous ink. 30μm thick titanium foil current collector 5 × 8cm
The titanium foil current collector was coated with the previously prepared ink, and dried at 80 ° C. in vacuum for two hours. The thickness of the electrode C thus manufactured was 53 μm including the titanium foil.

Comparative Example 3 DMcT-PAn-N prepared in the same manner as in Example 3
The MP solution was applied on a titanium foil and dried. The thickness of the electrode C ′ thus produced was 5
It was 1 μm.

Example 4 Blue-green viscous DMcT prepared in the same manner as in Example 3.
-2 g of elemental sulfur was mixed with the -PAn-NMP solution to obtain a viscous ink. This ink was applied on the same titanium foil current collector as in Example 3, and dried at 80 ° C. in vacuum for two hours. After that, in order to lithiate the dried electrode, n-
Butyllithium n-hexane solution (1.53 mol /
L) for 30 minutes. After that, it was thoroughly washed with n-hexane. The thickness of the electrode D thus produced was 61 μm including the titanium foil.

Comparative Example 4 DMcT-PAn-N prepared in the same manner as in Example 3
The MP solution was applied on a titanium foil and dried, and then treated with the same n-butyl lithium n-hexane solution as in Example 4. The thickness of the electrode D ′ thus produced was 59 μm including the titanium foil.

The electrodes A to D of Examples 1 to 4 and the electrodes A 'to D' of Comparative Examples 1 to 4 were each 0.3 m thick.
The batteries A to D and A ′ to D ′ each having a size of 2 × 2 cm were formed in combination with the metallic lithium negative electrode of m and the separator layer. For the separator layer, a gel electrolyte having a thickness of 0.6 mm was used. The gel electrolyte was obtained by gelling 20.7 g of a mixed solution of propylene carbonate and ethylene carbonate in which LiBF ₄ was dissolved in 1 M at a volume ratio of 1: 1 with 3.0 g of polyacrylonitrile. These batteries were charged at a constant current of 0.2 mA at 20 ° C.
The battery was repeatedly charged and discharged in a range of 2.0 V. The discharge capacity in each charge / discharge cycle was measured, and the charge / discharge cycle characteristics were evaluated based on the degree of decrease in the discharge capacity with the progress of the charge / discharge cycle. Table 1 shows the results.

[0029]

[Table 1]

Table 1 shows that the lithium secondary battery of the example according to the present invention has a larger discharge capacity and a smaller decrease in the discharge capacity as the charge / discharge cycle progresses, as compared with the lithium secondary battery of the comparative example. Understand. FIG.
And batteries A, B, A ′ using the electrodes of Comparative Examples 1 and 2,
The discharge voltage with respect to the discharge capacity of the fifth cycle of charge and discharge of B ′ is shown. The horizontal axis represents the discharge capacity (unit: mAh), and the vertical axis represents the battery voltage (unit: V). From FIG. 1, it can be seen that the batteries A and B using the electrodes according to the present invention exhibited a relatively flat discharge voltage even when the discharge capacity was increased, and showed a gentle voltage from around 3.5 V to around 2.5 V. Is descending. On the other hand, in the battery A 'of the comparative example, the discharge voltage sharply drops as the discharge capacity increases. Battery B 'has a large discharge capacity, but shows a flat behavior at a discharge voltage around 2V. FIG. 2 shows the discharge voltage of the fifth cycle of charging and discharging of batteries C, D, C ′, and D ′ using the electrodes of Examples 3 and 4 and Comparative Examples 3 and 4. As is apparent from the figure, the lithium secondary battery according to the present invention has a relatively flat voltage between 3.5 and 2.5 V, and has a good result of high capacity. As is clear from the above Table 1 and FIGS. 1 and 2, the lithium secondary battery according to the present invention maintains a high capacity while maintaining a voltage of 3 V class, and does not decrease in electric capacity even after repeated charging and discharging. It can be seen that a battery having a good charge / discharge cycle can be obtained.

In the above embodiment, lithium metal was used for the negative electrode. However, since the lithium secondary battery of the present invention contains lithium in the positive electrode active material from the beginning, it contains lithium such as carbon. The above characteristics are not lost even if a battery is formed using a negative electrode which is not used. Further, in the examples, as the lithium thiolate compound, DM
Although cT was used as a starting material, similar effects can be obtained by using other organic disulfide compounds, organic trisulfide compounds, organic tetrasulfide compounds, other thiol compounds, and mixtures thereof as starting materials.
Furthermore, in the examples, polyaniline was used as the conductive polymer, but other polypyrrole, polyacene, polythiophene, polyacetylene, and mixtures thereof can also be used. Further, even if an electron conductive material or an organic polymer binder is mixed with the positive electrode active material, the effect of the present invention is not impaired. In addition, butyllithium is used for the lithiation treatment of the thiol compound and elemental sulfur, but the same effect can be obtained by using phenyllithium instead, or by a treatment using another method.

[0032]

As described above, according to the present invention, dissipation and isolation of the positive electrode active material from the inside of the positive electrode during charging and discharging are reduced, and the voltage characteristics of the lithium thiolate compound and the high capacity characteristics of lithium sulfide are improved. A high-energy-density lithium secondary battery that retains and has a 3V-class flat discharge voltage can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the discharge characteristics of the fifth cycle of charge / discharge of a battery using the electrodes of Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention.

FIG. 2 is a diagram showing the discharge characteristics of the fifth cycle of charging and discharging of batteries using the electrodes of Examples 3 and 4 and Comparative Examples 3 and 4 of the present invention.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hiromu Matsuda 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Toyoguchi ▲ Yoshi ▼ Toku 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.F-term (reference) EE03 EE05 EE10 5H029 AJ02 AJ03 AK11 AK16 AK18 AM03 AM05 AM07 AM16 CJ02 CJ08 CJ22 DJ09 EJ12

Claims (12)

[Claims] 1. A positive electrode, a negative electrode, and a nonaqueous electrolyte containing a lithium salt, wherein the positive electrode contains at least one compound selected from the group consisting of a lithium thiolate compound and a thiol compound, and lithium sulfide. A lithium secondary battery. 2. The lithium secondary battery according to claim 1, wherein the positive electrode further contains a conductive polymer. 3. The lithium secondary battery according to claim 1, wherein the positive electrode further contains sulfur. 4. The lithium secondary battery according to claim 1, wherein the lithium thiolate compound is selected from the group consisting of a lithiated disulfide compound, a lithiated trisulfide compound, and a lithiated tetrasulfide compound. . 5. The lithium secondary battery according to claim 1, wherein the thiol compound is selected from the group consisting of a disulfide compound, a trisulfide compound, and a tetrasulfide compound. 6. The lithium secondary battery according to claim 1, wherein the negative electrode active material does not contain lithium when the battery is configured. 7. A positive electrode for a lithium secondary battery, comprising a step of uniformly mixing at least one compound selected from the group consisting of a lithium thiolate compound and a thiol compound, a solvent for dissolving the compound, and lithium sulfide. Production method. 8. The positive electrode for a lithium secondary battery according to claim 7, wherein the solvent is selected from the group consisting of tetrahydrofuran, dimethylformamide, and NR-2-pyrrolidone (R represents hydrogen or an alkyl group). Production method. 9. At least one member selected from the group consisting of (a) a lithium thiolate compound and a thiol compound
Dissolving a species compound in NR-2-pyrrolidone (R represents hydrogen or an alkyl group), (b) mixing lithium sulfide with the obtained solution, and (c) mixing the obtained mixture. A method for producing a positive electrode for a lithium secondary battery, comprising a step of coating on a conductive substrate and heating in an inert gas or vacuum. 10. (a) dissolving at least one compound selected from the group consisting of a lithium thiolate compound and a thiol compound in NR-2-pyrrolidone (R represents hydrogen or an alkyl group); (B) a step of mixing elemental sulfur with the obtained solution, (c) a step of applying the obtained mixture on a conductive substrate and preparing an electrode to be heated in an inert gas or in a vacuum, and (d) A) a method for producing a positive electrode for a lithium secondary battery, comprising a step of lithiating a thiol compound and elemental sulfur in the obtained electrode. 11. The method according to claim 11, wherein (a) the thiol compound is NR-2-
Dissolving in pyrrolidone (R represents hydrogen or an alkyl group), (b) mixing lithium sulfide with the obtained solution, (c) applying the obtained mixture on a conductive substrate, and applying an inert gas A method for producing a positive electrode for a lithium secondary battery, comprising: a step of preparing an electrode by heating in a medium or a vacuum; and (d) a step of lithiating a thiol compound in the obtained electrode. 12. The method for producing a positive electrode for a lithium secondary battery according to claim 9, further comprising a step of adding a conductive polymer to the solution obtained in the step (a) prior to the step (b). Method.