JP2002008662A - Organic sulfur secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reliable non-aqueous secondary battery having high capacity and small capacity fall in a charge/discharge cycle, by making an organic sulfur compound having a portion expressed with a basic skeleton structure (CxSyNz)n (where, x>=2, y>=1.8, z>0, n>=2) and an excellent reversibility in a charge/discharge, a positive electrode active material of the non-aqueous secondary battery. SOLUTION: The organic sulfur compound having a portion expressed with a basic skeleton structure (CxSyNz)n (where, x>=2, y>=1.8, z>0, n>=2) is manufactured by heating poly-carbon sulfide with a vulcanization agent or a vulcanization accelerator agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an organic sulfur secondary battery using, as a positive electrode active material, an organic sulfur compound having a basic skeleton structure composed of carbon, sulfur and nitrogen in a molecule.

[0002]

2. Description of the Related Art With the rapid growth of portable devices, there is a demand for batteries that are power sources for the devices to be lighter, smaller, and capable of being used for a longer time. On the other hand, a battery that achieves this is accepted by the market, and the market can be rapidly expanded.
In line with this demand, Ni / M as a new type battery in the 1990s
H batteries and lithium ion secondary batteries have appeared, and the market has been rapidly expanding.

[0003] However, even in a lithium ion secondary battery (cathode active material: LiCoO ₂ , anode active material: carbonaceous material), the market size of which has been rapidly expanded in response to market demands, the cathode active Since the energy density of LiCoO ₂ , which is a substance, is a low value of about 140 mAh / g, it is considered that the improvement of the energy density as a battery eventually reaches a limit value.

[0004] Therefore, as an alternative material, sulfur source
Elemental or organic sulfur compounds (CS _a)_bSuch as the positive electrode active material
There is a growing movement to use it as quality. That
The reason is that sulfur element or its compound is energy
-High theoretical value of density, 1675 mAh for single sulfur
/ G, organic sulfur compound (CS_a)_bEven 600-1
It has an energy density of 200 mAh / g and is currently
LiCoO used for lithium ion secondary batteries, etc.
_TwoIs much larger than 137mAh / g
It is.

On the other hand, LS used for electronic equipment
The voltage of I is proceeding in the direction of lowering the voltage, and the battery serving as the power source is starting to be required from a 4V system to a 2V system. Also in this regard, a secondary battery using the above-mentioned sulfur element or organic sulfur exhibiting an operating voltage of around 2.0 V can be said to be a battery that meets market requirements.

However, sulfur is originally an insulator at room temperature (resistivity at 20 ° C .: 1.9 × 10 ¹⁷ Ω · cm).
And the reactivity is extremely low. So, as a countermeasure,
High temperature region where resistivity decreases (for example, 8 × 10 at 440 ° C.)
^{6 Ω} · cm) battery is used in the configuration (Li / CuS, Li
/ FeS battery, etc.), it has been attempted to facilitate ring opening of sulfur S ₈ , generate radicals, and use it as a battery.

However, the use of a battery at a high temperature involves problems such as a part of energy being taken away for heating the battery and a need to control the temperature of the battery. There is a serious problem in practicality such as a problem of corrosion due to sulfur, which limits the materials constituting the battery.

[0008] In view of this point, Moltec USA
h Corporation) has proposed a secondary battery using an organic sulfur compound in which a negative electrode is lithium and a positive active material is a -C = C- structure and a polysulfur component is incorporated (US Patent Nos. 5,441,831 and 5,460,905). No. 5,601,947
No. 11-506799). That is, although sulfur alone is an insulator as described above, a compound of sulfur and a substance having a structure of -C = C- has relatively high conductivity (resistivity: about 10 ⁷ to 10 ¹² Ω · cm). Thus, it can be used as a positive electrode active material at room temperature. That is, it is considered that when sulfur is bonded to carbon having a -C = C- structure, conductivity and reactivity are improved by the contribution of the resonance effect of π electrons. Here, a higher ratio of -C = C- in the molecule is preferable for improving the conductivity, but a lowering of the sulfur ratio leads to a lowering of the battery capacity.
In the organic sulfur compound represented by S _a ) _b , it is considered practically preferable that a ≧ 0.9.

[0009]

However, according to the study of the present inventors, it has been found that a compound having this structure still has insufficient conductivity and can be used only for charging and discharging at a small current value. It has been found that further contrivance is required to make full use of such organic sulfur compounds.

In other words, as a countermeasure against the above-mentioned problem, it has been studied to reduce the current density on the surface of the active material to suppress polarization by pulverizing the active material and making the area of the positive electrode extremely large. Technology, such as pulverization of powder, and a coating technology to apply the positive electrode mixture thinly and uniformly on the current collector are required.
Even with these technologies, the problem was not fundamentally solved. In addition, the increase in the electrode area increases the volume ratio of the current collector, the separator, and the like, thereby causing another problem that the energy density of the battery is significantly reduced.

[0011]

SUMMARY OF THE INVENTION The present invention aims at solving the above-mentioned problems, and has a basic skeleton structure (C _x S _y N _z ) _n (where x ≧
2, y ≧ 1.8, z> 0, n ≧ 2), by using an organic sulfur compound having excellent reversibility to charge and discharge as a positive electrode active material of an organic sulfur secondary battery, It is intended to provide a highly reliable organic sulfur secondary battery.

That is, the basic skeleton structure (C _x S _y N _z )
An organic sulfur compound having a portion represented by _n (where x ≧ 2, y ≧ 1.8, z> 0, n ≧ 2) has a resonance effect of the π electrons promoted by a nitrogen atom present in the molecule. It is considered that the radical generation is facilitated, so that the reversibility of the compound in the oxidation-reduction reaction is improved, and the charge and discharge are facilitated and the cycle characteristics are improved.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION As a method for synthesizing an organic sulfur compound used in the present invention, for example, a method using a vulcanizing agent or a vulcanization accelerator can be considered as shown below. That is, a conventionally known organic sulfur compound such as polycarbon sulfide and (R ₂ NCSS) ₂ (R is an alkyl group) generally known as a vulcanizing agent or a vulcanization accelerator.
A compound such as mixed, by heating, to obtain an organic sulfur compound having a basic skeleton structure _{(C x S y N z)} n in the molecule. Here, examples of the vulcanizing agent or vulcanization accelerator include compounds such as tetramethylthiuram disulfide, tetramethylthiuram sulfide, tetrabutylthiuram disulfide, and zinc dibutyldithiocarbamate. The heating temperature is 100 to 3
A temperature of about 00 ° C is appropriate, and a range of 140 to 200 ° C is more preferable. The heating time is suitably several minutes to several tens of minutes, and the atmosphere is preferably an inert atmosphere to prevent oxidation of the compound.

The organic sulfur compound used for the synthesis is not particularly limited, but any compound represented by the general formula (CS _m ) _t (where m ≧ 0.9, t ≧ 2) This is desirable because not only is the reversibility excellent, but a higher capacity battery can be realized.

A positive electrode is composed of a composite of the obtained organic sulfur compound and, if necessary, a conductor and a binder. As the conductor, for example, a carbon material such as graphite and carbon black, a metal powder such as nickel, and a conductive polymer are preferably used. As the conductive polymer, for example, polymers having a conjugated structure such as polyacene, polyacetylene, and polyaniline polypyrrole, and derivatives thereof having side chains such as methyl, butyl, and benzyl can be preferably used.

Examples of the binder include a positive electrode active material such as polyvinylidene fluoride, amorphous polyether, polyacrylamide, polyaniline or polypyrrole soluble in a solvent, or a copolymer of these compounds or a compound formed by crosslinking. It is desirable that the polymer compound is chemically stable to a substance and has a strong adhesive force.

The negative electrode active material includes alkali metals such as lithium and sodium, alkaline earth metals such as calcium and magnesium, alloys of these metal elements with aluminum, carbonaceous materials such as graphite, and tin or silicon. It is possible to use an oxide, a nitrogen cobalt compound, a polymer having a conjugated structure such as polyacene, polyacetylene, polyaniline, polythiophene, or polypyrrole, or a conductive polymer including a derivative having a side chain such as methyl or butylbenzyl thereof. it can. Similarly to the positive electrode, the negative electrode is composed of a composite of the negative electrode active material and, if necessary, a conductor and a binder.

Examples of the electrolyte include an inorganic electrolyte and an organic electrolyte.
Electrolytes or their solutions in organic solvents,
A non-aqueous electrolyte such as a limer gel electrolyte is used. Special
In addition, LiF, LiCl, LiClO_Four, LiPF₆, Li
BF_Four, LiAsF₆, LiSbF₆, LiCF_ThreeSO_Three,
LiC_FourF₉SO_Three, LiCF_ThreeCO_Two, Li_TwoC_TwoF_Four(SO
_Three)_Two, LiN (RfSO_Two) (Rf'SO_Two), LiC
(RfSO_Two)_Three, LiC_nF _{2n + 1}SO_Three(N ≧ 2), Li
N (RfOSO_Two)_Two[Where R_fAnd Rf 'are fluoroa
Alkyl group] or ethylene carbonate
Non-aqueous electrolyte dissolved in solvents such as propylene carbonate
Decomposition or the above lithium salt is
Contained in polymer gels such as sulfides and polyvinylidene fluoride
Preferably, a polymer gel electrolyte is used.

[0019]

The present invention will be described in more detail with reference to the following examples.

(Example 1) General formula (CS) _n (n ≧ 4)
Is mixed with 10 parts by weight of ((CH ₃ ) ₂ NCSS) ₂ as a vulcanizing agent, and reacted at 170 ° C. for 10 minutes in an argon gas atmosphere to obtain (C ₂ An organic sulfur compound represented by S _1.92 N _0.08 ) _n (n ≧ 2) was synthesized. Next, 50 parts by weight of the synthesized organic sulfur compound, 4 parts by weight of acetylene black,
21 parts by weight of graphite (trade name: KS-6) and 25 parts by weight of polyvinylidene fluoride were mixed and stirred with 125 parts by weight of N-methylpyrrolidone to prepare a positive electrode mixture. This is 20
It was applied to an aluminum foil having a thickness of μm and vacuum-dried at 70 ° C. all day and night to obtain a positive electrode. This positive electrode was further vacuum-dried at 120 ° C. for 2 hours before producing the battery and used.

The negative electrode was prepared by placing a metallic lithium foil on a nickel foil in an argon gas atmosphere and pressing with a roller.

The electrolytic solution is prepared by adding Li to a mixed solvent of propylene carbonate and ethylene carbonate having a weight ratio of 1: 1.
The PF ₆ using a solution dissolved at a concentration of 1.2 mol / l. The water concentration in this electrolytic solution was 8 ppm.

The positive electrode and the negative electrode were laminated in an argon gas atmosphere via a polyethylene separator, placed in an aluminum laminate package, and injected with an electrolytic solution to obtain an organic sulfur secondary battery. This battery has a capacity of 60 m per 1 g of the positive electrode active material.
Charge / discharge was performed at a current value corresponding to A (discharge end voltage was 1.5 V), and this was repeated 10 cycles, and the change in discharge capacity per unit weight of the positive electrode active material was examined. The results are shown in Table 1.

(Example 2) An organic sulfur secondary battery was prepared in the same manner as in Example 1 except that the addition amount of the polycarbon sulfide was changed to 50 parts by weight, and the discharge capacity was measured. The synthesized organic sulfur compound is (C ₂ S _0.9 N
_0.1 ) _n (n ≧ 2).

Comparative Example An organic sulfur secondary battery was prepared in the same manner as in Example 1 except that a polycarbon sulfide represented by the general formula (CS) _n (n ≧ 4) was used as a positive electrode active material. The discharge capacity was measured.

[0026]

[Table 1]

As is clear from the table, the organic sulfur secondary battery using the organic sulfur compound of the present invention has a basic skeleton structure (C _x S _y N _z ) _n (where x ≧ 2, y ≧ 0.9, z> 0,
Since it has a portion represented by (n ≧ 2), it can be seen that the capacity is less reduced in charge / discharge cycles and the cycle characteristics are significantly improved as compared with the battery of the comparative example using the conventional polycarbon sulfide. .

[0028]

As described above, according to the present invention, an organic sulfur compound having high utility as a cathode active material particularly for a non-aqueous secondary battery can be provided. That is, the basic skeleton structure of the present invention _{(C x S y N z)} n ( provided that x ≧ 2, y ≧ 1.
8, z> 0, n ≧ 2) By using an organic sulfur compound having a portion represented by the following formula as a positive electrode active material of a non-aqueous secondary battery, high capacity and little reduction in capacity during charge / discharge cycles are reliable. A non-aqueous secondary battery having a high power can be provided.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Ryu Nagai 1-88 Ushitora, Ibaraki-shi, Osaka F-term in Hitachi Maxell, Ltd. (Reference) 5H029 AJ02 AK05 AL12 AM03 AM05 AM07 CJ11 HJ02 HJ11 5H050 AA02 BA17 CA19 CB12 GA11 HA02 HA11

Claims (2)

[Claims] 1. The basic skeleton structure (C _x S _y N _z ) _n (where x
≧ 2, y ≧ 1.8, z> 0, n ≧ 2) An organic sulfur secondary battery using a positive electrode, a negative electrode, and a non-aqueous electrolyte using an organic sulfur compound having a portion represented by the following formula: 2. The compound obtained by reacting a compound represented by the general formula (CS _m ) _t (where m ≧ 0.9, t ≧ 2) with a vulcanizing agent or a vulcanization accelerator. The organic sulfur secondary battery according to claim 1, wherein: