JPH09293513A - Electrode material and secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sulfide family electrode material capable of substantially increasing the charging/discharging capacity of a secondary battery by containing a simple substance of sulfur and an organic material having an S-S bond. SOLUTION: An electrode material of a secondary battery is obtained by containing a simple substance of sulfur and an organic material having an S-S bond. The organic material represented by the formula of R-(S)n -R' (2<=n<=7, R and R' are a group comprising an organic material) or R-(S)n -M (1<=n<=6, R is a group comprising an organic material, M is a metal element or H) is preferable. The electrolyte of a secondary battery using this electrode material is preferable to contain a metal sulfide. The adding amount of the simple substance of sulfur is preferable to be 1-7 times the organic material in the molar ratio.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a battery electrode material. More specifically, it relates to a sulfide-based electrode material.

[0002]

2. Description of the Related Art In recent years, communication equipment and office automation equipment have become portable, and competition for weight reduction and miniaturization of these equipment has been promoted. Higher efficiency is also required for such various devices and secondary batteries used as power sources for electric vehicles and the like. In response to this demand, batteries using new electrode materials are being developed, but among them, since the energy density is relatively high, electrode materials using disulfide compounds (US Pat. No. 4833048 and the like) have attracted attention. ing. This compound has a disulfide bond consisting of two sulfurs between two organic groups (R
-S-S-R ') is used as an electrode material.

The SS bond is cleaved by the supply of two electrons by electrolytic reduction, and the cation or proton (M
⁺⁾ Combine with ^{2 (R-S - · M} +) next, during electrolytic oxidation back to the original R-S-S-R, to release the 2 electrons.
In this secondary battery, 15 times that of other ordinary secondary batteries
It is said that an energy density of 0 Wh / kg or more can be expected. However, the inventors of the above-mentioned US patent
From the content reported in m.Soc.ol.136.No.9, p.2570-2575 (1989), the electron transfer rate of the electrode reaction of this disulfide-based secondary battery is extremely slow, and therefore, near room temperature. It is difficult to take out a large current suitable for practical use, and it is 60 ° C.
A problem was pointed out that it was limited to the above use.

Then, as a technique for improving this disulfide-based secondary battery to cope with a large current, Japanese Patent Application Laid-Open No. H5-74
As disclosed in Japanese Patent No. 459, etc., an electrode material has been proposed in which an organic compound having a disulfide group is combined with a conductive polymer such as polyaniline. However, although this technique can be expected to increase the reaction rate, it does not attempt to increase the energy density.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a sulfide-based electrode material capable of remarkably improving a charge / discharge capacity when applied to an electrode material of a secondary battery, and a rechargeable battery having a remarkably high charge / discharge capacity. The purpose is to provide a secondary battery.

[0006]

In order to solve the above-mentioned problems, the electrode material of the present invention has a structure containing elemental sulfur and an organic compound having an S--S bond as described in claim 1. Have. Sulfur as a simple substance (hereinafter referred to as "sulfur") is used in high temperature such as sodium-sulfur battery,
For example, an organic solvent-based secondary battery normally does not work as an effective active material, but the presence of sulfur in an organic solvent-based secondary battery using an organic material having an S—S bond as an active material causes a specific expansion of the electric capacity. be able to. Although the details of the reason are unknown, it is considered as follows.

The organic substance having an S--S bond functions as a positive electrode active material of a secondary battery. That is, at the time of discharging, the bond (S—S bond) between the sulfur atom and the sulfur atom is cleaved by electrolytic reduction, and an ionic bond is formed between the sulfur atom and the metal.
During charging, the S—S bond is formed again by electrolytic oxidation. It is considered that the elemental sulfur acts at this time as if it were a disulfide compound.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the S—S bond may be a single bond or may be a continuous bond (hereinafter referred to as S—S—S).
It is called "continuous S-S bond". ) May be provided (hereinafter, both are referred to as “S—S bond”). These S-
The S bond includes 2,5-dimercapto-1,3,4-thiadiazole (hereinafter referred to as "DMcT"), trithiocyanuric acid (hereinafter referred to as "TTCA"), and N, N ,.
N ', N'-tetra-mercapto ethane ((HS) ₂ NC
H ₂ CH ₂ N (SH) ₂ ), 2-mercapto-5-methyl-1,3,4-thiadiazole, and other compounds having a small mass and having a plurality of S—H (thiol groups). It is desirable for the group to be bonded by substituting it with hydrogen because the energy density will be high.

Other examples of the above compounds include those represented by the chemical formulas (I) to (XIV).

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[Chemical 6]

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[Chemical 12]

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In these chemical formulas (I) to (XIV), X is O, S, Se, NH, NR, CH ₂ , CH.
R, CRR ', C = O , C = NH, C = NR, a group such as C = S, _{also, Y 1, Y 2, Y} 3 and Y ₄ are each, -CH _3, -C ₂ Aliphatic group represented by H ₅ and its derivative, aromatic group represented by —C ₆ H ₅ and its derivative, halogen group such as —F, —Cl, —Br, and —I, —
COOR, -NRR ', - OR, -COR, -SO 3
R, -CONRR ', -N RR'R ", -SR, -O
COR, -NHCOR, -N = CRR ' , - SO 2 R,
-SOR, -SSR, -P (= O) RR ', -P (=
S) RR ', -ONO, -N = C = O, -N = C = S,
_{-OCN, -SCN, -CN, -NO 2} , -H, -PR
R ', -P ⁺ F, -P ⁺ Cl, -P ⁺ Br, -P ⁺ I, wherein R, R'and R "represent hydrogen, an aliphatic or aromatic hydrocarbon group. , In these organics,
It may be a polymer, but its degree of polymerization is theoretically independent of the energy density.

Among the organic substances having an S—S bond used in the present invention, a method for synthesizing an organic substance having a single S—S bond is as follows:
It is widely known such as US Pat. No. 4,833,048. On the other hand, an organic substance having a continuous SS bond can be synthesized, for example, as follows. A substance having one or more thiol groups in the molecule is dissolved in an organic solvent such as methylene chloride, and to this, an amount of disulfur dichloride or sulfur dichloride corresponding to the amount of the thiol groups is added, React for about an hour. Then, this system is poured into methanol, and unreacted disulfur dichloride or sulfur dichloride is reacted with methanol to obtain a precipitate when decomposed.

Similarly, a substance having one or more thiol groups is used as a raw material, and this is dissolved in diethyl ether, and an amount of disulfur dichloride or sulfur dichloride corresponding to the amount of the thiol groups and pyridine are obtained. It is obtained by adding and reacting at around -80 ° C, and then neutralizing the system with an aqueous sodium hydroxide solution. When disulfur dichloride is used in the above, an even number of S-bonds is formed, and when monosulfur dichloride is used, an odd-numbered S-bond is formed.

In the present invention, the amount of sulfur added is the amount of S existing when fully charged in the sulfide secondary battery.
An organic substance having a —S bond is represented by R— (S) _n —R ′ (2 ≦ n ≦ 7, R and R ′ are groups made of an organic substance.
And R'may be the same), this S
The molar ratio is preferably 1 to 7 times that of the organic substance having a —S bond. If the added amount is small, the effect is low, and if the added amount is too large, the amount of sulfur that does not contribute to the capacity increase increases, which is wasteful and the energy density per weight decreases.

As the conductive material used together with the electrode molding, those which are usually used as conductivity imparting materials such as furnace black can be used. Here, what is marketed as Ketjen black has a high conductivity and is excellent in handleability. From the viewpoint of workability during mixing, it is desirable that these conductive materials be in powder form.

An electrolyte used for assembling a secondary battery is prepared by combining an organic solvent and an electrolyte. That is, as the organic solvent or the electrolyte, any one can be used as long as it is one that is used in a normal non-aqueous solvent battery.
That is, as the organic solvent, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,
2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-
Dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, sulfolane, acetonitrile, propionitrile, anisole and the like can be used alone or in combination.

Further, as the electrolyte, LiPF ₆ , Li
ClO ₄ , LiAsF ₆ , LiBF ₄ , LiCF ₃ SO ₃ or the like can be used. These are dissolved in the organic solvent so as to have an appropriate concentration to form an electrolyte. As the negative electrode, an electrode usually used in secondary batteries can be used. That is, examples thereof include metallic lithium, a lithium-aluminum alloy, and an interlayer compound of lithium and graphite or carbon. A battery is formed by combining the positive electrode, the electrolytic solution, and the negative electrode, and the battery can be applied regardless of the shape of the battery at that time, that is, a flat type, a cylindrical type, a prismatic type, or the like.

[0017]

[Examples] Examples and comparative examples of the present invention will be described below. All processes that cause troubles when performed in an atmosphere with air or moisture are performed under an argon atmosphere, and unless otherwise specified. Performed at room temperature.

[2,2′-dithiobis (5-methyl-
Synthesis of 1,3,4-thiadiazole) 2,2′-dithiobis (5-methyl-1,3,4-thiadiazole) used as an organic compound having an S—S bond was obtained as follows. Under an argon atmosphere, add 5 ml to 30 ml of methanol.
mmol of iodine was dissolved, and 2-mercapto-5-methyl-1,3,4-thiadiazole 10 mmo was previously dissolved therein.
1, a solution of 5 mmol of sodium methoxide in 30 ml of methanol was slowly added dropwise, and then the mixture was stirred for 3 hours and then cooled to -60 ° C. The formed precipitate was separated by filtration, dried under reduced pressure, and then dried with ethanol. Three
Recrystallization was performed twice to obtain 2,2′-dithiobis (5-methyl-1,3,4-thiadiazole).

[Example 1: Investigation with cyclic voltammogram] The above 2,2'-dithiobis (5-methyl-)
Cyclic voltammograms of 1,3,4-thiadiazole) with sulfur, without sulfur, and with sulfur alone were examined. That is, lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) was dissolved in γ-butyrolactone so as to be 0.2 mol / l to prepare an electrolytic solution. In addition to the above, 2 '
-Dithiobis (5-methyl-1,3,4-thiadiazole) and sulfur were added so as to each be 5 mmol / l, a platinum wire was used as a counter electrode, a silver / silver ion electrode was used as a reference electrode, and glassy carbon was used as a sample electrode. A cyclic voltammogram when the potential was changed at a scanning speed of 50 mV / sec (Example 1) and a cyclic voltammogram (Comparative Example 1) when the same as in Example 1 except that sulfur was not added were obtained. It was These cyclic voltammograms are shown in FIG. Further, FIG. 2 shows a cyclic voltammogram (Comparative Example 2) in the same manner as in Example 1 except that 2,2′-dithiobis (5-methyl-1,3,4-thiadiazole) was not added. .

From FIG. 1, the addition of sulfur does not change both the oxidation potential showing the peak of the oxidation current and the reduction potential showing the peak of the reduction current, but the peak current value increases. This shows that the addition of sulfur increases the charge / discharge capacity. Therefore, the system to which sulfur is added can cope with the discharge at a large current. Similarly, when the charge / discharge electric quantity is calculated from FIG.
By adding sulfur, the charge / discharge capacity is increased 1.6 times, and as a result, the charge / discharge energy amount (product of charge / discharge electricity amount and potential difference) is also 1.6 times. In addition, the increase in mass at this time was 2,2′-dithiobis (5-methyl-1,3,4-
(Thiadiazole) has a molecular weight of 262.40, while sulfur as a simple substance has a molecular weight of 32.07.
2%, and therefore the energy density (charge / discharge energy amount per unit weight of active material) due to the addition of sulfur
It can be seen that is significantly increased. Further, it can be seen from FIG. 2 that only a very small peak current value can be obtained with sulfur alone. This shows that it is practically impossible to use sulfur alone as an active material.

[Example 2: Investigation in coin-type battery] [0021] According to the above cyclic voltammogram study, a system in which sulfur is used in combination with an organic compound having an S-S bond can be used as an electrode material of a secondary battery. Although it was suggested that this was possible, next, in order to carry out a test under more practical conditions, a coin-type battery was examined. As in Example 1,
The following studies were carried out using 2,2′-dithiobis (5-methyl-1,3,4-thiadiazole) as an organic substance having an S—S bond.

(Preparation of positive electrode) 2,2'-dithiobis (5-methyl-1,3,4-thiadiazole) and 2,2'-trithiobis (5-methyl-1,3,3) which are active materials.
4-thiadiazole), sulfur, lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), a conductive agent, Ketjen Black, and polyethylene oxide (molecular weight 2,000,000) were mixed in four weight ratios as shown in Table 1. , And these were dispersed in acetonitrile to obtain a dispersion liquid. These dispersions were spread on a petri dish and acetonitrile was volatilized to form a sheet having a thickness of 500 μm.
Each of these was punched into a diameter of 14 mm and used as a positive electrode hereinafter. (Note that the weights of these positive electrodes were almost the same.)

[0023]

[Table 1]

As a battery D having a material having a continuous S—S bond as an active material, a positive electrode was prepared with the composition shown in Table 1. The 2,2′-trithiobis (5-methyl-1,3,4-thiadiazole) used here is
It is obtained as follows. That is, 2-mercapto-5-methyl-1,3,4-thiadiazole 100 m
mol is dissolved in 200 ml of tetrahydrofuran, and 125 mmol of sulfur dichloride is slowly added dropwise thereto (a precipitate is formed by the addition). After the dropping, 5 at room temperature
Stir for 10 minutes. Then, after filtration and washing with tetrahydrofuran, the precipitate was dried under reduced pressure to obtain 2,2′-trithiobis (5-methyl-1,3,4-thiadiazole).

(Analysis of Active Material) 2,2′-used above
Dithiobis (5-methyl-1,3,4-thiadiazole) (hereinafter also referred to as “active material α”) and 2,2′-trithiobis (5-methyl-1,3,4-thiadiazole)
(Hereinafter also referred to as “active material β”) was analyzed.
That is, CHNS analysis and O analysis (Perkin Elmer 2
400II, CHNS / O analyzer), FAB-MS
Analysis (JEOL JMS AX505H, primary particles: xenon 2 kV, 20 mA, scan range (m / z):
20-2000, scan rate: 2 seconds, matrix: glycerin, ion multi: 1.5 kV), ¹ H-
NMR (EX-270 manufactured by JEOL, pulse width 45 °, chemical shift reference ¹ H: 0.00 ppm), heavy solvent: chloroform-d ₁ ) and ¹³ C-NMR spectrum analysis (EX-270 manufactured by JEOL, pulse width) 45 ° C., chemical shift standard ¹³ C 0.00 ppm), and heavy solvent: chloroform-d ₁ ) were performed. The molecular weight confirmed by CHNS analysis and 0 analysis result (mass ratio of carbon, hydrogen, nitrogen, sulfur and oxygen in integer ratio based on nitrogen) and FAB-MS analysis are shown in Table 2, ¹ H-NMR and ¹³ The results of the C-NMR spectrum analysis are shown in Table 3. In addition, the active material α
The ¹ H-NMR spectrum, ¹³ C-NMR spectrum and FAB-MS spectrum of are shown in FIG. 3, FIG. 4 and FIG. 5, respectively, and the ¹ H-NMR spectrum and ¹³ C-NM spectrum of the active material β are shown in FIG.
The R spectrum and FAB-MS spectrum are shown in FIGS. 6, 7 and 8, respectively.

[0026]

[Table 2]

[0027]

[Table 3]

(Preparation of Solid Electrolyte) Copolymer of acrylonitrile and methyl acrylate (molar ratio 9: 1)
1.5 g of lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) was mixed in advance with a solution of γ-butyrolactone to a concentration of 1 mol / l and uniformly dispersed, and then spread on a Petri dish heated to 120 ° C. After that, it was allowed to cool to obtain a solid electrolyte having a thickness of 1500 μm, which was punched into a diameter of 16 mm and used. Note that this solid electrolyte also serves as a separator between the positive electrode and the negative electrode when the battery is manufactured. (Production of Negative Electrode) A lithium metal foil having a thickness of 400 μm was punched out to a diameter of 15 mm to obtain a negative electrode.

(Production of Battery) Using the above four types of positive electrode, separator (solid electrolyte) and negative electrode, a flat type battery whose exploded perspective view is shown in FIG. 9 (respectively battery A (Example 3), Battery B (Comparative Example 3), Battery C (Comparative Example 4) and Battery D (Example 4)) were produced. Reference numerals 1 to 6 in FIG. 9 indicate a positive electrode can, a packing, a positive electrode, a separator (solid electrolyte), a negative electrode and a negative electrode can, respectively. The packing 2 is provided between the positive electrode can 1 and the negative electrode can 6 and functions to shield the inside formed by these from the outside air and at the same time to insulate them.

(Evaluation of Battery) The discharge capacities of these batteries A, B, C and D were examined. In addition, in the following, the theoretical charge electricity quantity means 2,2-dithiobis (5-methyl-1,3,4) contained in the case of the battery A.
-Thiadiazole) and equimolar 2,2-trithiobis (5-methyl-1,3,4-thiadiazole) S-S
Assuming that the bonds are all cleaved by the discharge, the S-
In the case of the battery B, 2,2′-dithiobis (5-) containing the theoretical amount of electricity required to restore all the S bonds.
When all the S-S bonds of (methyl-1,3,4-thiadiazole) are cleaved by the discharge, the S-S
In the case of Battery D, 2,2-trithiobis (5-) containing the theoretical amount of electricity required to restore all the bonds.
Methyl-1,3,4-thiadiazole) and equimolar 2,
Assuming that all the S-S bonds of 2-tetrathiobis (5-methyl-1,3,4-thiadiazole) were cleaved by the discharge, the theoretical amount of electricity required to restore all the S-S bonds was calculated as Point to each.

Further, the full charge means 0.
Whichever comes first, until the voltage between the electrodes becomes 4.5 V at a current of ² mA / cm ² or the charged quantity of electricity reaches the theoretical charged quantity of electricity (only in case of battery A, battery B and battery D) And the complete discharge means discharging with a current of 0.2 mA / cm ² with respect to the positive electrode area until the inter-electrode voltage becomes 2.0 V. These batteries A to D were completely discharged and fully charged twice in advance, and then completely discharged. The discharge condition at this time is shown in FIG. From FIG. 10, the discharge capacities of the battery A and the battery D, which are the batteries according to the present invention, are significantly higher than the discharge capacities of the battery B according to the related art containing no sulfur and the discharge capacity of the battery C containing no sulfide compound. The effect of the present invention is obvious.

[0032]

EFFECTS OF THE INVENTION By using an organic substance having an S—S bond in combination with sulfur, the discharge capacity is remarkably expanded, and the charge / discharge energy value of a battery using such an electrode material according to the present invention is the same as that of a conventional sulfide. It is much higher than the theoretical energy value of the battery using the compound polymer. In addition, such a battery can simultaneously discharge a large amount of current.

[Brief description of drawings]

FIG. 1 is a cyclic voltammogram of Example 1 of the present invention and Comparative Example 1.

2 is a cyclic voltammogram of Comparative Example 2. FIG.

FIG. 3: 2,2′-dithiobis (5-methyl-1,3,
It is a figure which shows the < ¹ > H-NMR spectrum of 4-thiadiazole).

FIG. 4: 2,2′-dithiobis (5-methyl-1,3,
It is a figure which shows the < ¹³ > C-NMR spectrum of 4-thiadiazole).

FIG. 5 shows 2,2′-dithiobis (5-methyl-1,3,
It is a figure which shows the FAB-MS spectrum of 4-thiadiazole).

FIG. 6: 2,2′-trithiobis (5-methyl-1,
It is a diagram showing ¹ H-NMR spectrum of 3,4-thiadiazole).

FIG. 7 shows 2,2′-trithiobis (5-methyl-1,
It is a figure which shows the < ¹³ > C-NMR spectrum of 3,4-thiadiazole.

FIG. 8 shows 2,2′-trithiobis (5-methyl-1,
It is a figure which shows the FAB-MS spectrum of 3,4-thiadiazole).

FIG. 9 is an exploded perspective view of a flat battery model.

FIG. 10 is a diagram showing discharge states of batteries A and D of examples of the present invention and batteries B and C of comparative examples.

[Explanation of symbols]

 1 Positive electrode can 2 Packing 3 Positive electrode 4 Separator 5 Negative electrode 6 Negative electrode can

Claims (7)

[Claims] 1. An electrode material containing elemental sulfur and an organic substance having an S—S bond. 2. The organic substance having an S—S bond is represented by the following formula R— (S) _n —R ′ (2 ≦ n ≦ 7, R and R ′ are groups consisting of an organic substance). The electrode material according to claim 1, which is characterized. 3. The organic substance having an S—S bond is represented by the following formula R— (S) _n —M (1 ≦ n ≦ 6, R is a group consisting of an organic substance, and M is a metal or hydrogen). Claim 1 characterized by the above.
The electrode material according to. 4. A secondary battery containing elemental sulfur and an organic substance having an S—S bond. 5. The organic substance having an S—S bond is represented by the following formula: R— (S) _n —R ′ (2 ≦ n ≦ 7, R and R ′ are groups consisting of an organic substance). The secondary battery according to claim 4, which is characterized in that. 6. The organic substance having an S—S bond is represented by the following formula R— (S) _n —M (1 ≦ n ≦ 6, R is a group consisting of an organic substance, and M is a metal or hydrogen). 5. The method according to claim 4, wherein
2. The secondary battery according to 1. 7. An electrolytic solution containing elemental sulfur, an organic substance represented by the following formula R—S—M (R is a group consisting of an organic substance, M is a metal or hydrogen), and a metal sulfide. Characteristic secondary battery.